TM-114073Heat Rate Improvement Reference Manual

Heat Rate Improvement Reference Manual

Training Guidelines

Heat Rate Improvement Reference Manual

Training Guidelines

TM-114073

Training Manual, December 1999

EPRI Project Manager

P. Ruestman

EPRI • 3412 Hillview Avenue, Palo Alto, California 94304 • PO Box 10412, Palo Alto, California 94303 • USA800.313.3774 • 650.855.2121 • [email protected] • www.epri.com

DISCLAIMER OF WARRANTIES AND LIMITATION OF LIABILITIES

THIS DOCUMENT WAS PREPARED BY THE ORGANIZATION(S) NAMED BELOW AS AN ACCOUNT OFWORK SPONSORED OR COSPONSORED BY THE ELECTRIC POWER RESEARCH INSTITUTE, INC.(EPRI). NEITHER EPRI, ANY MEMBER OF EPRI, ANY COSPONSOR, THE ORGANIZATION(S) BELOW,NOR ANY PERSON ACTING ON BEHALF OF ANY OF THEM:

(A) MAKES ANY WARRANTY OR REPRESENTATION WHATSOEVER, EXPRESS OR IMPLIED, (I) WITHRESPECT TO THE USE OF ANY INFORMATION, APPARATUS, METHOD, PROCESS, OR SIMILAR ITEMDISCLOSED IN THIS DOCUMENT, INCLUDING MERCHANTABILITY AND FITNESS FOR A PARTICULARPURPOSE, OR (II) THAT SUCH USE DOES NOT INFRINGE ON OR INTERFERE WITH PRIVATELY OWNEDRIGHTS, INCLUDING ANY PARTY'S INTELLECTUAL PROPERTY, OR (III) THAT THIS DOCUMENT ISSUITABLE TO ANY PARTICULAR USER'S CIRCUMSTANCE; OR

(B) ASSUMES RESPONSIBILITY FOR ANY DAMAGES OR OTHER LIABILITY WHATSOEVER (INCLUDINGANY CONSEQUENTIAL DAMAGES, EVEN IF EPRI OR ANY EPRI REPRESENTATIVE HAS BEEN ADVISEDOF THE POSSIBILITY OF SUCH DAMAGES) RESULTING FROM YOUR SELECTION OR USE OF THISDOCUMENT OR ANY INFORMATION, APPARATUS, METHOD, PROCESS, OR SIMILAR ITEM DISCLOSEDIN THIS DOCUMENT.

ORGANIZATION(S) THAT PREPARED THIS DOCUMENT

EPRI

Duke/Fluor Daniel

ORDERING INFORMATION

Requests for copies of this report should be directed to the EPRI Distribution Center, 207 Coggins Drive,P.O. Box 23205, Pleasant Hill, CA 94523, (925) 934-4212.

Electric Power Research Institute and EPRI are registered service marks of the Electric Power ResearchInstitute, Inc. EPRI. POWERING PROGRESS is a service mark of the Electric Power Research Institute, Inc.

Copyright © 1999 Electric Power Research Institute, Inc. All rights reserved.

i

CITATIONS

This document was prepared by

Duke/Fluor DanielDFo1A2300 Yorkmont RoadCharlotte, North Carolina 28217-4522

Principal InvestigatorR. Snyder

EPRI3412 Hillview AvenuePalo Alto, CA 94304

Principal Investigator or AuthorJ. Tsou

This document describes research sponsored by EPRI.

The publication is a corporate document that should be cited in the literature in thefollowing manner:

Heat Rate Improvement Reference Manual, Training Guideline, EPRI, Palo Alto, CA,1999. TM-114073.

iii

ACKNOWLEDGEMENT

EPRI wishes to acknowledge members of the Heat Rate Interest Group for providingguidance in development of this manual and training guide. EPRI also wishes toacknowledge the following people for reviewing and providing comments to the draftmanual and training guideline.

Duane Hill, Dairyland Power CooperativeWes Hull, Central and South West ServicesSam Korellis, Illinois Power Company"

v

ABSTRACT

Performance optimization of fossil power plants has always been a high priority within theelectric power industry. However, it has become of paramount importance in meeting thechallenges mandated by operating within a competitive environment. Recently, manypower producers have downsized and currently lack experienced staff required to maintainoptimal performance. Thus, a resource was needed to capture the lost experience to aid inthe retraining of less experienced personnel.

The objective of this project was to produce a manual to be used by power producers as atraining tool and reference source for the development of heat rate and performanceengineers. This document provides required information to understand thermodynamicproperties and precepts, guidance on how to use them and methods of determination toassess their impact on system performance.

This training guide, a compliment to the reference manual, used EPRI CS-4554 Heat RateImprovement Guidelines as a basis for development of the program. Specifically, thismanual includes:

• A description of the properties of water, its phases, and the determination of each. Adiscussion of the Steam Tables and Mollier diagram and how each is used to find theproperties of water/steam. A brief discussion of the Ideal Gas Law.

• A definition and application of the concepts of the first law of thermodynamics andrequired energy conversion calculations to power plant components. The relationship isused to develop an understanding of how plant parameters are affected by the operationof the components.

• A review of the principles and applications of fluid flow. Discussion includes pumpsand pump operation for forced fluid flow.

• A discussion of the concept of thermal efficiency and the methods employed tomaximize efficiency.

• An explanation of the various modes of heat transfer and the equations used with eachmode. It gives an introduction to nucleate boiling and the factors affecting DNB.A discussion of natural circulation and a brief discussion on heat exchangers are alsocovered.

• An explanation and review of power plant systems, which include the water/steamcycle, boiler fuel, air and flue gas systems, as well as, balance of plant systems.

• An introduction to the ‘Heat Rate Improvement Reference Manual’, the purpose,organization and use of the manual.

REVIEW OF THERMODYNAMIC

PROPERTIES (1)

2

1. OVERVIEW:This Lesson Plan describes the properties of water, its phases, and the determinationof each. It also includes a discussion of the Steam Tables and Mollier diagram andhow each is used to find the properties of water/steam. A brief discussion of the IdealGas Law is also included.

3

TERMINAL OBJECTIVE:

At the end of this class the student should have a working knowledge ofThermodynamic principles that can be used by those involved in the Heat RateImprovement Program. This will be accomplished by meeting the requirements of thefollowing enabling objectives.

ENABLING OBJECTIVES:

1. Define each of the following terms:

1.1 Temperature

1.2 Pressure

1.3 Density and Specific Volume

1.4 Enthalpy

1.5 Entropy

1.6 Specific Heat Capacity

1.7 BTU

2. Convert a known temperature from one scale to another.

3. Convert a known pressure from one scale to another.

4. State and define the different phases of water.

5. Explain each of the following

5.1 Saturation Temperature

5.2 Latent heat

5.3 Quality

5.4 Sensible Heat

6. Given a set of conditions and using the steam tables, determine thethermodynamic properties and phases of water.

7. Given a set of conditions using the Mollier diagram determine theproperties and phases of water.

4

8. Using the ideal gas law, solve problems relating to pressure, temperatureand volume of an ideal gas.

5

LESSON OUTLINE

1. INTRODUCTION

2. PRESENTATION

2.1 Fluid Properties

2.2 Temperature

2.3 Pressure

2.4 Specific Volume

2.5 Enthalpy

2.6 Entropy

3. DETERMINING THE PROPERTIES OF WATER

3.1 Steam Tables

3.2 Phase of Water

3.3 Mollier Diagram

4. GAS RELATIONSHIP

4.1 Ideal Gases

6

1. INTRODUCTION

1.1 Overview

This lesson covers the properties of water/steam and the phases of water. Italso covers the steam tables and Mollier diagram and their use in the powerplant.

1.2 Objectives

2. PRESENTATION

2.1 Fluid Properties

The thermodynamic properties of a fluid are measurable or quantifiablecharacteristics of the fluid and include the following:

Temperature Internal Energy

Pressure Enthalpy

Specific Volume Entropy

2.2 Temperature

A. Definition: A measure of the average molecular kinetic energy:

(Thermal Driving Head)

B. Temperature Scales

1. Absolute °R and °K:

• R = °F + 460(459.69°)

• K = °C + 273

2. Relative °F = (1.8 x C) + 32

oF is used most often, but oR is used when absolute temperatures arerequired.

2.3 Pressure

A. Definition: Force per unit area (P=F/A)

B. Scales

1. PSIA = (Absolute Pressure)

a) Pressure above a perfect vacuum

b) Atmospheric pressure + gauge pressure

2. PSIV = Pressure measured below a reference (atmospheric pressure)

7

a) PSIG = Gage pressure = pressure measured from atmospheric

b) (PSIG = PSIA - ATMOS)

3. Inches of Hg Pressure (1 PSIA~- 2" Mercury Hg)

4. Inches of Hg Vacuum = PSIV x 2

2.4 Specific Volume (V) and Density (ρ)

A. Definition of Specific Volume: Volume per unit mass.

v = Volume = ft3

Mass lbm

B. Definition of Density (ρ): The inverse of Specific Volume

1 = lbm

v ft3

C. Specific Volume and Density are affected by temperature and pressure.

Pressure: as pressure Temperature: astemperature

↑ ↓ ↑ ↓

v ↓ ↑ ↑ ↓

ρ ↑ ↓ ↓ ↑

1. Example:Using the Steam Tables find the density of a saturated liquid at

200oF.

v = 0.016637 ft3/lbm

ρ = 1/v = 1/0.016637 = 60.1 lbm/ft3

2. Now raise its temperature to 300oF. v = 0.01745 - ft3/lbm

ρ = 1/v = 1/0.01745 = 57.3 lbm/ft3

2.5 Internal Energy

A. Definition: Thermal energy stored within a substance itself. This is due to theposition and movement of the molecules or atoms which make up asubstance in relation to each other.

B. Enthalpy (h)

1. Definition

a) Sum of the internal energy and pv (pressure x specific volume)(flow) energy.

8

b) Energy content of one pound mass of a fluid at a given temperatureand pressure. Units of heat energy are in BTU’s which stands forBritish Thermal Units.

C. h = specific enthalpy; h = u + pv, where u = Specific Internal Energy inBTU/lbm

1. h = BTU/lbm

To convert pv to BTU/lbm divided by Joules Constant = 778 ft- 1bf/BTU

pv = Flow energy due to pressure and volume.

pv = BTU J lbm

2. Example: Find the internal specific energy of saturated steam at 1000psia.h = u + pv = h - pv

J J

u = 1192.9 BTU - (1000 lb) (144 in2) (0.44596 ft3/lbm)

lbm in2 ft2 778 ft - 1bf BTU

u = 1110.4 BTU lbm

3. Notice that nearly all the enthalpy was internal energy.

Generally a change in internal energy results in a change intemperature, but not always.

PROOF: For a saturated liquid at 1000 psia, find the internal energy.

U = H - pv = 542.6 BTU - (1000)(144)0.02159

j lbm 778ft_-_1bf

BTU

U = 538.6 BTU

lbm

At 1000 psia, the change in internal energy is from 538.6 to 1110.4BTU/lbm, but the temperature remained constant. The only changewas a change from a saturated liquid to a saturated vapor.

D. Total Enthalpy (H)

1. Total energy of a given mass (H = U + pv)

2. To find total enthalpy, simply multiply specific enthalpy times the amountof mass present.

H = (h)(m)

9

2.6 Entropy (S)

A. Definition: A measure of the unavailable energy in a fluid @ a giventemperature and pressure.

Units: BTU on an absolute scale

lbm-oROR:

BTU

lbm - oF on a relative scale

We are more interested in Entropy changes (Delta S = Sfinal - Sinitial) than

specific values of Entropy.

1. Example:Find Delta S when energy is added to a saturated liquid @ 100oF and changes the saturated liquid to a saturated vapor @ 300oF

Delta S = Sfinal - Sinitial

Delta S = Sg - Sf Sf@ 100oF = 0.1295 BTU/lbmoF

Sg@ 300oF = 1.6351 BTU/lbmoF

Delta S = 1.6351 - 0.1295

Delta S = 1.5056 BTU/lbmoF

2. The point is, as heat is added to this example, more of the energy of theliquid-vapor is unavailable. Also the reverse is true for removing energywhich results in a decrease in entropy.

3. The change in entropy (Delta S) is used to account for the energy thathas been made unavailable for work.

4. For example: Use the main condenser.

a) When steam is condensed, the temperature remains constant, butthe entropy decreases.

b) If condenser pressure is 1 psia, saturated steam exhausts from theturbine into the condenser and condenses with no subcooling. Findthe heat rejected

.(qrej)

10

qrej = T (Delta S) at 1 psia Sf = 0.1325 BTU/lbmoF

Sg = 1.9781 BTU/lbmoF

T = oF + 460

= 101.74 + 460 =

561.74oR

1) qrej = (561.74)(0.1326 - 1.9781)

2) qrej = 1036.12 BTU's Rejected

5. Notice the qrej is equal to hfg which is the Latent Heat of Condensation.

The BTU's are the BTU's or heat given to the Condenser CirculatingWater (CCW) System.

6. Qualitatively: We can say that S of condensate decreased when heatwas removed and S of CCW increased as heat was added.

7. Summary: The energy that is available in the condensate to do work

(useful) per lbmoF has increased. This is mainly due to theinadequacies of the working fluid and the process. Also, the value of hfgindicates that amount of energy that has become unavailable in ourwork process is S .

B. Discussion of T-S Diagram

43

1000

900

ENTROPY ( BTU/lbm - RENTROPY ( BTU/lbm - RENTROPY ( BTU/lbm - R

TEM

PER

ATU

RE

( F

)TE

MPE

RA

TUR

E (

F )

TEM

PER

ATU

RE

( F

)

800

700

600

500

400

300

200

100

00 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4

CRITICALPOINTCRITICALPOINTCRITICALPOINT

2200 PSIA2200 PSIA2200 PSIA 1000 PSIA1000 PSIA1000 PSIA

2 PSIA2 PSIA2 PSIA

WET VAPORSfg

WET VAPORSfg

WET VAPORSfg

SUBC. LIQUIDSf

SUBC. LIQUIDSf

SUBC. LIQUIDSf

SUPER HEATEDVAPOR

Sg

SUPER HEATEDVAPOR

Sg

SUPER HEATEDVAPOR

Sg

11

1. We assume that at 32oF, S = 0 (Even though S = 0 at O oR).

2. Saturation Line: Every single point on the line, to the left of the criticalpoint is where a saturated liquid exists.

3. Critical Point: At these conditions of temperature (705.47oF) andpressure (3208.2 psia), the following is true.

a) There is no difference in specific volume between a saturated liquidand a saturated vapor.

b) There is no difference in enthalpy between a saturated liquid and asaturated vapor.

c) There is no difference in entropy between a saturated liquid and asaturated vapor.

OR

vf = vg vfg = 0 hf = Hg hfg = 0 Sf = sg sfg = 0

At the critical point, the liquid/vapor acts like a perfect gas.

4. Subcooled Region: Region left of critical point and left of saturatedliquid line.

5. Wet Vapor Region: Area under saturation line.

6. Constant Pressure Lines: From the point where it touches the saturatedliquid line, it is horizontal until it touches the saturated vapor line.

7. Enthalpy Lines: Range from 100-1800 (bottom-top) and extendhorizontally across the entire diagram.

8. In order to locate a point on the diagram for any condition except atsaturated conditions, you must know two properties of the liquid, wetvapor, or superheated steam.

9. If you are a saturated liquid at 212oF.

a) Pressure is found by noting where constant pressure line touches

sat. liquid curve for 212oF.

b) Enthalpy is the horizontal line crossing through the sat. liquid line for

212oF.

c) Entropy is the vertical line crossing through the sat. liquid line for

212oF.

d) Ex. a saturated liquid at 212oF. P = 15 psia

h = 1150 BTU/lbm

Ss = 1.75

BTU/lbmoR

12

10. Go back to condenser example

a) 1 psia, saturated liquid = 100oF by T-s diagram.

b) The saturated steam changed to saturated liquid.

Note that enthalpy and entropy decreased.

Sinitial = 1.98 Sfinal = 0.12

c) Heat rejected from condenser was heat added to CondenserCirculating water.

3. DETERMINING THE PROPERTIES OF WATER

3.1 Steam Tables

A. The Steam Table consist of 3 separate tables

1. Table 1. Saturated Steam: Temperature Table

a) Consists of columns for:

1) Temperature

2) Pressure - corresponds to temperature for saturation conditions.

3) Specify Volume

4) Enthalpy

5) Entropy

b) The v, h, and s columns each have values for saturated liquid (vf)

saturated vapor (vg), and the change (vfg) from liquid to vapor.

2. Table 2. Saturated steam: Pressure Table

a) This table is set up the same as table except the temperature andpressure columns are reversed.

3. Table 3. Superheated steam

a) This table is set up differently. It consists of:

1) Abs pressure column with sat. temperature in parentheses.

2) Across the top is temperature - degrees Fahrenheit. Thisrepresents the actual temp of the steam.

3) Sh column represents the degrees super heat.

4) It then has columns for v, h, and s.

4. The last part of the steam tables is a conversion factors chart used forconverting from one parameter to another.

13

3.2 Specific Heat

A. Definition: Specific heat capacity (c)

1. Heat required to cause 1 lbm of any substance to change by 1oF.

2. Sensible heat - heat added that raises the temperature of water.

c = BTU

lbm oF

3.3 Phases of Water

There are 5 exact phases of water that we consider in the power industry.

A. Subcooled Liquid (Compressed Liquid)

1. Liquid below the boiling point.

2. Enthalpy (h) of a subcooled liquid is determined by one of the followingmethods.

a) Definition: Heat required to cause 1 lbm of any substance to

change by 1oF. Heat added that raises the temperature of water is"sensible heat".

c = BTU

lbm oF

b) Subtract 32oF from the temperature and use the units of enthalpy(BTU/lbm).

NOTE: Below~- 300oF, this is a fairly accurate method. But > 300o

F, the accuracy drops due to changes in the Specific HeatCapacity of the fluid, i.e., it takes more and more heat to

cause the temperature to change by 1oF as its temperatureincreases.

c = Specific Heat Capacity (Assume 1.4 BTU/lbmoF for ReactorCoolant)

c) The most desirable (most accurate) method to find h is to look uptemperature of liquid in the steam tables and assume hsc = hf

T-32 STM Table Method Actual hf hf

Assume at 400psi

(Example on two methods)

hsc @ 100oF => 68 68

14

69.5

hsc @ 200oF => 168 168 169

hsc @ 300oF => 269.7 268 270.3

hsc @ 400oF => 375.1 368 375.3

Conclusions

1) Note the increasing error.

2) Use steam table method

B. Saturated Liquid

1. Water at the boiling point

2. The properties of Hf, sf, vf, Tsat, Psat are found in the Saturated Steam

Tables.

3. Example: find hf @ 100 psia

100 oF

300 psia

300oF

100 psia

C. Wet Vapor

1. A combination of saturated liquid and saturated steam at the boilingpoint.

2. Enthalpy is determined by:

hwv = hf + x(hfg) Where hwv = Enthalpy Wet Vapor

hf = Enthalpy Liquid

x = Quality of Vapor

hfg = Latent Heat of Vaporization

(hfg = The latent heat of vaporization or condensation)

Numerically, hfg is the amount of heat which must be added to 1 lbm of

a saturated liquid to change it to 1 lbm of steam or the amount of heatwhich must be removed to change 1 lbm of saturated steam to 1 lbm ofsaturated liquid.

15

3. x = Quality = amount of vapor in a wet vapor.

x = 100%-m (m = % moisture in a wet vapor)

4. Example: Find hfg @ 1 psia

100 psia

300 oF

1000 psia

5. Example: Find enthalpy of wet vapor @ 500 psia if m = 15%.

a) hwv = hf + (xhfg)

D. Saturated Steam

1. Steam at the boiling point (no moisture, 100% vapor).

2. The properties of hg, sg, vg, Tsat, Psat are found on the saturated

steam tables.

3. Example:

Find: hg vg sg for the following

460oF

180oF

400 psia

1000 psia

E. Superheated Steam

1. Steam above the boiling point

2. The properties of h, s, v, P, and T are found in the superheated steamtables.

3. Superheat term refers to # of degrees above Tsat.

4. Example: Find Tsh @ 400, 450, 500oF when @ 100 psia.

3.4 Mollier Diagram

16

45 P

SIA

15 P

SIA

280

240

MOLLIERMOLLIER

SAT

. LIN

E

SAT

. LIN

E

MOISTUREMOISTURE

1172 BTUs1172 BTUs

A. A pictorial representation of steam tables (does not contain specific volume)called a H-S diagram.

1. Find h of steam at saturation with x = 100% and 900 psia.

a) From Mollier on saturated steam line h =

b) From steam tables h=

2. Find the temperature and h of a system at 500 psia and 20o superheat.

a) T = h =

3. Find the enthalpy and temperature of a system at 300 psia for thefollowing.

a) Saturated:

b) m = 4% :

Note that since we are under saturation line;

c) m = 12%: temperature is constant.

4. GAS RELATIONSHIP

4.1 Ideal Gases

17

A. Ideal gases are described as gases comprised of molecules that do notinteract with one another. The pressure exerted by an ideal gas is the forceexerted on the surface by the collision of these molecules. The forcesexerted by the molecules increase with the absolute KE as measured bytemperature. Similarly, the pressure exerted by the molecules increases asthe density of the molecules increases. So we can say that,

P α PT Since ρ = m/v, we can substitute and rearrange as follows:

P α m/v T, or

P v = T for 1 lbm.

If we compare initial and final conditions on a particular system of ideal gaswe can write the equation.

(P1 V1)/T1 = P2V2 /T2

This is the ideal gas law.

B. The Ideal Gas Law is actually a combination, of 2 laws; Charles Law andBoyles law.

1. Charles Law states: The volume of a given mass of gas, maintained atconstant pressure, varies linearly with temperature or,

V1 T1 = V2 T2

2. Boyles Law states: For a fixed mass of gas at a constant temperature,the volume of gas is inversely proportional to its pressure or,

P1V1 = P2V2

C. All pressures and temperatures must be in absolute scales.

D. Examples:

If 20 cu ft of Nitrogen at 15 psia is heated from 73oF to 150oF, what will bethe pressure if the volume remains constant?

P1V1 P2V2 = T1 T2

15 1b/in2 (20 ft3) P(20 ft3) =

(73 + 460) oR (150 + 460) oR

17 psia = P2

1


PROPERTIES (2)

2

1. OVERVIEWThis Lesson Plan defines and applies the concept of the first law of Thermodynamicsand Energy conversions to power plant components. This relationship is used todevelop an understanding of how plant parameters are affected by the operation ofthe components.

3

TERMINAL OBJECTIVE:

At the end of this lesson the students will have a working knowledge of the First Lawof Thermodynamics and Energy Conversions.

ENABLING OBJECTIVES:

1. List and define the six energy forms considered in the study ofThermodynamics.

2. Identify the properties which indicate a change in each of the six energyforms.

3. State the First Law of Thermodynamics

4. State the Continuity Equation and apply it in determining mass flow rate,volume flow rate and velocity changes in power plant components.

5. Describe the energy conversions which occur in a moving fluid and relatethem to changes in observable parameters and fluid properties for:

5.1 Constant diameter pipe

5.2 Nozzle and venturi

5.3 Throttling device

5.4 Pump

5.5 Turbine

6. Plot the throttling process on a Mollier Diagram and determine fluidproperties upstream and downstream, given appropriate information.

7. Define pump efficiency.

8. Determine turbine work and power given appropriate information.

9. Define turbine efficiency.

4

LESSON OUTLINE

1. INTRODUCTION

1.1 Purpose of this lesson

1.2 Overview

2. THE ENERGY FORMS ASSOCIATED WITH THERMODYNAMICS

2.1 Energy

2.2 Forms of Energy

3. THE FIRST LAW OF THERMODYNAMICS APPLIED

3.1 First law of Thermodynamics

3.2 The Steady Flow Energy Equation

3.3 Power

4. APPLICATIONS OF THE GENERAL EQUATION

4.1 Constant Diameter Pipe

4.2 Nozzle and Venturi

4.3 Throttling Device

4.4 Pump

4.5 Turbine

5. ATTACHMENT 1

5

1. INTRODUCTION


A. Develop concepts of energy conversion within power plant components.

B. Apply the concepts in order to enable the student to predict the effects onsystem parameters.

C. Predict the effects of changing operational conditions on plant parameters.

D. Develop the building blocks which will be used in the power plant cycleslesson.

1.2 Overview of the lesson - Review objectives.

2. ENERGY AND THE ENERGY FORMS ASSOCIATED WITHTHERMODYNAMICS

2.1 Energy

A. Energy is defined as the capacity for producing an effect

1. The effect produced is frequently mechanical work thus the commondefinition is "the capacity for doing work."

2. Energy in some forms is intangible but the effects produced can usuallybe evaluated

B. General Methods of Classifying Energy

1. Stored energy and energy in transition

a) Energy in Transition

1) Momentary energy form; in an intermediate state between twoor more stored forms

2) Begins and ends as stored energy

3) Heat and work are the forms of energy in transition

b) Stored Energy

1) Energy associated with or contained in systems or bodies suchas the working fluid

2) The stored energy forms we will be dealing with are:

(a) Kinetic

(b) Potential

(c) Flow or Pv

(d) Internal

6

2. Mechanical and Thermal Energy

a) Mechanical Energy

1) Energy which stems from the position or motion of relativelylarge bodies

2) Forms of Mechanical Energy

(a) Kinetic

(b) Flow or Pv

(c) Potential

(d) Mechanical Work

3) Transfer of mechanical energy is by physical contact betweenlarge masses either directly or through a machine such as amoving shaft or piston

4) Unit of mechanical energy is the foot pound force (ft-lbf)

b) Thermal Energy

1) Energy associated with the configuration and motion ofmolecules

2) Characterized by its ability to be transferred from one body toanother by temperature difference alone

3) The mechanism of thermal energy transfer is through thecollision of molecules or electromagnetic waves

4) Forms of thermal energy

(a) Internal energy

(b) Heat

5) Unit of thermal energy is the British Thermal Unit (BTU)

c) Relating mechanical and thermal energy

1) Joules equivalent, the mechanical equivalent of heat is themathematical relationship between units used to expressmechanical energy and thermal energy. Symbol J

2) 778 ft lbf = 1 BTU

or J = 778 ft lbf / BTU

7

C. Kinetic Energy - Stored mechanical energy due to the mass and velocity thatthe mass has or the work to bring mass up to observed velocity

→1. KE = MV2 gc = 32 lbm ft

2gc lbf sec2

2. The parameter that is an indication of the KE of a fluid is the velocity

→KE α V2

D. Potential Energy (PE) - Stored mechanical energy associated with theelevation relative to a reference elevation or work done in bringing a massfrom Ref to Height Z.

1. PE = mgz / gcor PE per unit mass = gz / gc

2. Height is an indication of PE

E. Flow work or displacement energy(Wf) - stored mechanical

1. The Energy necessary to maintain a continuous steady flow of a streamof fluid

2. Flow work is not present unless there is flow

3. Wf is the product of the force acting on any cross-section of the stream

and the distance through which the force must act to cause any selectedmass to pass that cross section

4. Thus Wf = Pv

P = Pressure

v = Specific volume of the fluid

5. Derivation - optional

Wk = Force (F) x L

F = P(press) A(area)

Volume (V) = A(area) L(length)

V also equals Mass(M) v (specific volume)

Therefore AL = Mv

PAL = PMv therefore Wk = PMv

and the work per unit mass is Wf = pv

8

F. Internal Energy (u) - Stored thermal energy associated with the moleculesand atoms of a substance

1. Majority is contained as vibrational KE of the molecules and atoms of asubstance

a) Temperature is a measure of this energy

b) Also energy associated with the spin of molecules

c) And the spacing between molecules

2. The energy distribution between these various forms of internal energyis what causes the heat capacity of a substance to vary

Example: At low temp Cp of H20 ≅ 1 BTU/ lbm °F

In this condition, almost all of a BTU added goes into the vibrational KEand therefore will show up as a temperature change.

At high temperatures and pressures Cp H20 ≅ 1.4 BTU / lb-°F

In this case, a portion of the BTU added is going into increasing the spinand spacing of the molecules => show up as an increase in Cp because

since all the BTU is not directly related to the increase in vibrationalKE.(thus temperature change)

Example Problem:

1) Find the h, Pv, u for a saturated liquid at 500°F

2) hstm table = 487.9 BTU/lbm

3) Pv = PSAT x v =

↑ from stm tables

(680.86 lbf/in2)(144 in2/ft2)(.02043 ft3/lbm)

__________________________________ =

778 ft-lbf/BTU

Pv = 2.57 BTU/lbm

4) U = h-Pv = 487.9 BTU/lbm - 2.57 BTU/lbm

U = 485.33 BTU/lbm

3. During a phase change all the energy goes to increasing distancebetween molecules (internal potential energy), therefore there will be noincrease in temperature of the substance.

9

G. Work - Force applied in moving something through a distance

1. W = F x D

2. Units - ft-lbf

3. Work as such cannot be stored, but work done on a system will show upas an increase of one or more of the stored energy forms.

4. Work done on system is evidenced by a mechanical device passingthrough the boundary and is moved by some external source

5. Work is done by a system if the mechanical device is passing throughthe boundary and the force which causes movement of this device isdeveloped from within the system. (Mechanical output such as turbine)

6. Heat - Transient Thermal Energy - Energy transferred from one regionto another due to a temperature difference.

a) Methods of heat transfer

1) Conduction - Heat transfer through a medium

2) Radiation - Heat transfer without a medium via electromagneticradiation

3) Convection - Heat transfer by the combined action ofconduction, storage, and mixing of a fluid between regions ofhigh and low temperature.

3. THE FIRST LAW OF THERMODYNAMICS APPLIED

3.1 First law of Thermodynamics

A. Energy can neither be created nor destroyed but only transformed

B. When applied to a system - Net energy entering the system will equal thenet energy leaving the system plus the energy accumulated within thesystem

or

Energy in = Energy out + Energy Accumulated

3.2 The Steady Flow Energy Equation

A. Statement of the first law considering all energy forms assuming steady flow

Energy accumulated = 0 in steady flow.

B. Energy in = Energy out

KE1 + PE1 + Pv1 + u1 + qin + Won = KE2 + PE2 +

Pv2 + u2 + qout + (Wby)

Divide the mechanical terms by J to get all in BTU's

10

3.3 Power

A. Power is defined as the rate of doing work

B. The General Energy Equation becomes a power equation

when multiplied by M the mass flow rate in lbm/hrC. Some equivalents

1hp = 2545 BTU/hr = 42.42 BTU/min

= 33000 ft lbf/min = 550 ft lbf/sec

1kw = 3.4 x 103 BTU/hr = 1.34 hp

D. This will be applied to the turbine, pump, and heat exchanger later

4. APPLICATION OF GENERAL ENERGY EQUATIONS

4.1 Energy balance on fluid flowing through a pipe

A. Assumptions:

-Water is incompressible

-Water temperature is ambient

-Area1 = Area2

-No change in height

-Steady flow conditions

B. KE1 + PE1 + u1 +Pv1 + Qin +Won = KE2 + PE2 + u2 + Pv2 +

Qout +Wby

C. Since no change in area => KE1 = KE2

D. No change in height => PE1 = PE2

E. No heat in or out and no work done on or by the system

=> Qin & Qout = 0

Wby & Won = 0

F. Therefore, we are left with:

U1 + Pv1 = U2 + Pv2

U1 - U2 = v(P2 - P1)

∆U = v∆P

11

G. Recall that: h = u + Pv J

1. (u1 + Pv)-(u2 + Pv) = ∆h

J J2

2. u2 > u1 due to friction

3. Pv2 < Pv1 due to drop in fluid energy due to friction

H. The conversion of flow energy (Pv) to internal energy (u) due to friction iscalled "Head Loss".

The effects of head loss will be discussed further in the fluid flow lesson.

4.2 Energy Balance on a Nozzle/Venturi

A. Assumptions:

1. Mass flow in = mass flow out

2. Fluid is water = > incompressible

3. No friction

4. Area1 > Area2

5. Area1 = Area3

B. Converging section - nozzle

1. PE1 + KE1 + Pv1 +U1 + Qin + Won =

PE2 + KE2 + Pv2 + U2 + Qout + Wby

a) ∆PE = 0 - no change in height

b) ∆U = 0 - no friction

c) Qin & Qout = 0

d) No work done by the system => Wby = 0

e) No work done on the system => Won = 0

2. This leaves: KE1 + Pv1 = KE2 + Pv2

Pv1 - Pv2 = KE2 - KE1

∆Pv = ∆KE

3. The continuity equation can be applied to determine which of the energyterms increased.

a) Since we know that in a steady flow condition o othe M M

12

into a = out of , we can say that

system the system

→ →ρin Ain Vin = ρout Aout Vout

→ →ρAV1 = ρAV2 - Since the fluid is water and relatively incompressible

then ρ1 = ρ2.

→ →Since A2 < A1 then V2 > V1

4. Parameter property changes

• Velocity increases

• Pressure decreases

• Enthalpy decreases

• Temperature Increases - not noticeable

• Entropy Increases - slightly

5. Application

a) Steam turbine nozzles to convert pressure to velocity

b) Air ejector nozzle to create low pressure area

c) Flow measurement

→1) ∆P α ∆V2

2) Recall ∆Pv = ∆KE

→and KE = 1/2mv2

gc oalso V α velocity

oV = Volume Flow Rate (GPM)

3) then o ∆P α V2

To make an equality use Venturi constant K givingo

V = K (∆P)1/2

13

K varies based on friction and geometry and will be affected byfouling of the Venturi

4) For mass flow rateo oM = V x density oro

M = k (∆P)1/2 (ρ)

d) Diverging section 2 to 3

1) The Reverse Process Occurs

2) Since A3 = A1

(a) Velocity decreases from point 2 to point 3

(b) Pressure will increase

(c) Neglecting friction

Pressure will return to the value at point1 and velocity will

drop to the initial value

3) Effect of friction will result in some pressure drop across thedevice

(a) This effect is minimized by the smooth transition

(b) The orifice is not smooth and significant pressure dropwill occur.

4) Application

(a) Inc. NPSH on pump suction

(b) Steam Jet

(c) Pump Volute

(d) Accommodate expansion

14

4.3 Energy Balance on a Pump

NOTE: Sketch pump on board with suction as Point 1 and Discharge Point 2.

A. Assumptions:

1. No heat transferred in or out

2. No friction o o

3. Steady flow conditions => Min = Mout

4. The fluid is water => ρin = ρout

5. Suction diameter = Discharge diameter

B. Evaluation using General Energy Equation

1. Pv1 + U1 + KE1 + PE1 + Qin + Won =

Pv2 + U2 + KE2 + PE2 + Qout + Wby

a) ∆KE = 0 - at point 2 as compared to point 1

Since A1 = A2

b) ∆pe = 0 - no noticeable difference in height

c) ∆u = 0 - no friction assumption

d) Qin & Qout = 0 - no heat in or out

15

e) No work by the system => Wby = 0

f) Wpump = Pv2 - Pv1

Wpump = v (∆P)

2. ∆P is called Pump Head and is expressed as:

a) PSID

b) Feet of water (2.31 ft of water = 1 psi) or43 psi = 1 ft.

c) Sometimes ft-lbf

C. Pump power o o

1. Wpump = M x Wpump o

Power = M x v∆P

2. If all the power supplied by the prime mover was imported as flow workthe pump would be 100% efficient

3. Pump Efficiency oηpump = output = M V∆P (power into head)

input Brake HP (input by prime mover)

a) Pump efficiency ≅ 85 - 99%

Due to friction and other losses in the pump

D. Parameter & property changes across pump

1. Pessure Increases

2. Velocity constant (assume same disch & suct diameter)

3. Enthralpy increases

4. Entropy increases due to friction and other losses

5. Temperature increases not noticeable

6. U↑

4.4 Energy Balance on a Turbine

NOTE: Sketch Turbine on board with inlet as point 1 and exhaust as point 2

A. Assumptions:

1. No friction => constant entropy o o

2. Qin and Qout = 0

o o

16

3. Min = Mout => no extraction flows

4. Inlet pressure is 1000 psia

5. Condenser pressure is 1 psia

NOTE: In the turbine steam is expanded through the stages so specificvolume increases.

B. Energy Balance

1. KE1 + PE1 + Pv1 + U1 +Qin + Won =

KE2 + PE2 + Pv2 + Q2 +U2 + Wby

a) Qin and Qout = 0 No heat transfer

b) No work done on => Won = 0

c) ∆KE ≅ 0

Since the steam expands through the turbine and v↑ , the area ofthe exhaust is made larger to accommodate the expansion. Theresult is that there is little difference in velocity between inlet andoutlet.

d) PE - overall height being looked at is 10 to 15 feet.

Any change in PE in this case would be very small compared to theother changes.

2. U1 + Pv1 = U2 + Pv2 + Wby

rearranged to:

Wby = (U1 + Pv1) - (U2 + Pv2)

and since h = U + Pv then: J

Wby = Wturb = ∆h

C. Turbine Power o

Turbine power = Mstm ∆h

oTurbine power = Mstm (hstm - hexh)

D. Property and Parameter Changes

1. Enthalpy decreases

2. Velocity unchanged

17

3. Pressure decreases

4. Temperature decreases

5. Specific volume increases

6. Entropy increases for real turbine; constant for ideal

E. Plot turbine on Mollier Diagram Real and Ideal

NOTE: For Real turb. must know h or % M to get work, Ideal assume const.entropy

F. Turbine efficiency

1. In Ideal Turbine there will be a larger ∆h for a given pressure drop

2. The ∆h for the real turbine working between the same two pressures willbe smaller. Due to losses in the turbine Entropy increases indicatingsome of the steam energy has become unavailable for conversion towork.

3. Turbine efficiency

a) ηturb = Wturb real = ∆h real

Wturb Ideal ∆h ideal

b) Typically the turbine is designed to be most efficient at full load 85%- 92%

G. Example:

Given: Inlet conditions; 900 psiao

Msteam = 5 x 105 lbm/hr

Outlet conditions; 1 psia, 28% moisture

18

Find: Real Turbine power in HP and KW

Ideal turbine power in HP

Turbine efficiency0

P turb Real = Mstm (hstm - hexh)

5 x 105 lbm/hr (1195 BTU - 815 BTU) = 74.8 x 103 hp

2.54 x 103 BTU/hr-hp

or = 55.9 x 103 KW

or = 3.4 x 103 BTU/hr-KW

P turb Ideal = 5 x 105 lbm/hr (1195BTU-781 BTU)= 81.5 x 103 hp

2.54 x 103

ηturb = 74.8/81.5 = 91.7%

19

ATTACHMENT 1

1. What happens to each one of the following parameters as the diameter ofa pipe gets smaller (increase, decrease or stay the same)?

1.1 Enthalpy

1.2 Entropy

1.3 KE

1.4 PE

1.5 Work

2. A pump takes suction on the hotwell at 28" vac. & 107o F and dischargesat a pressure of 350 psia. Pump flow rate is 1 x 107 lbm/hr. What is thepump work? (In HP) Assume suction is a Saturated liquid.

3. Given the following:Psm: 1000 psiao

M - 14 x 106 lbm/Hr

Pcond - 28" Hg Vac

Turb. Exit Quality = 83%

What is ideal Turb. work, real turb work and turbine efficiency?

4. EXTRA:

A pump has a ∆h = 3 btu/lbm. If the pump head is 500 psi, how much of the ∆h isdue to ∆u? (Inlet temp. = 370°F)

20

5. Given the following conditions:

• NC press = 2235 psig

• PRT press = 0 psig

• NC-32 (PORV) Leaking by.

Find the following for the downstream fluid:

5.1 Phase

5.2 Temp.

5.3 Quality

5.4 Entropy

5.5 Enthalpy

6. A 'C' HTR DRN Pump takes suction on the 'C' HTR DRN tank at 5 x 106lbm/Hr. SUCT pressure is 1 psig and discharge pressure is 650 psia. The suction temp. is 210o F. What is pump horsepower?

21

ANSWERS

1.

1.1 ↓

1.2 ↑

1.3 ↑

1.4 →

1.5 →

2. 28" = 1 psia

107°F v = .016155 ft3/lbm

o

m = 10 x 106 lbm/Hr

Wk = 10 x 106 lbm/Hr (.016155 ft3/lbm) (349 lb/in2) (144 in2/ft2)

= 8.11 x 109 ft-lbf/hr (1 hr/3600 sec.)(.0018182 ft - lbf sec)

HP

•••••••••••

= • 4100 HP •

•••••••••••

o o

3. WkI = M (∆h) WkR = M ∆h

= 14 x 106 lbm/Hr (1192.9 - 775) = 14 x 106 lbm/Hr(1192.9 - 930)

= 5.85 x 109 BTU/Hr = 3.67 x 109 BTU/Hr

η = WkR/WkI

= 3.67 x 109 = 62.9%

5.85 x 109

4. ∆h = ∆u + ∆Pv

3 BTU/lbm = ∆u + (500 lbf/in2) (144 in2/ft2)(.01824 ft3/lbm)

778 Ft-lbf

BTU

22

3 BTU/lbm = ∆u + 1.688 BTU/lbm

1.31 = ∆u

5. h = ~1118 BTU’sphase = Wet Vapor

Temp = 212°F

X = 97%

S = 1.71

6. Wk = 5 x 106 lbm/Hr (634 lb/in2)( 144 in2/ft2 ) (.0167 ft3/lbm) = 7.6 x 109ft-lb/Hr (1 Hr/3600 sec.) (.0018182 ft - lbf sec)

HP

= 3850 Horsepower

1


PROPERTIES (3)

2

OVERVIEW

This lesson is a review of the principles and applications of fluid flow. Discussion willinclude pumps and pump operation for forced fluid flow.

1. REFERENCES:

1.1 Introduction to Thermodynamics; Kurt C. Rolle

1.2 Pump Handbook; Karassik, Krutzsch, Frasser, Messina

3

TERMINAL OBJECTIVE

At the end of this lesson the student will have a working knowledge of the principlesand applications of fluid flow. He will also understand pumps and pump operation forforced fluid flow.

ENABLING OBJECTIVES

1. Define the following:

1.1 Head Loss

1.2 Friction

2. Explain how a change in each of the following will affect friction HeadLoss.

2.1 Friction Factor

2.2 Pipe Length

2.3 Pipe Diameter

2.4 Fluid Velocity

3. Describe the two types of flow that can occur in a system:

3.1 Laminar

3.2 Turbulent

4. Explain the purpose of a pump.

5. Explain the theory of operation for a centrifugal pump.

5.1 Define pump head.

5.2 Explain how flowrate, head, and power vary with pump speed.

6. Define NPSH available and NPSH required.

7. Define Cavitation.

7.1 List the conditions and parameters that affect cavitation.

7.2 Explain how cavitation is detected.

7.3 Explain how cavitation is prevented or stopped.

4

8. Define pump runout.

8.1 Explain the problems associated with runout.

8.2 Explain plant design features that limit runout.

9. Define pump shutoff head.

10. Explain the theory of operation of a positive displacement pump.

10.1 Explain how to vary the capacity of a positive displacement pump.

10.2 Explain how a Pd pump is affected by cavitation and runout.

11. Define "water Hammer"

5

LESSON OUTLINE

1. INTRODUCTION

1.1 Overview

1.2 Objectives

2. PRESENTATION

2.1 Fluid Flow

2.2 Headloss

3. PUMPS AND PUMP OPERATIONS

3.1 Centrifugal Pumps

3.2 Series and Parallel pump operations.

3.3 Closed System pump Operation

3.4 Open System Pump Operation

3.5 Positive Displacement Pumps

4. PLANT PROBLEMS

4.1 Water Hammer

6

1. INTRODUCTION

1.1 This lesson will discuss: Fluid flow, factors affecting fluid flow, pumps and pumpoperation.

1.2 Cover appropriate objectives.

2. PRESENTATION

2.1 Fluid Flow

A. Definition: Fluid flow is the movement of a fluid from one point to another ina system.

B. Development of Fluid Flow.

1. No flow can be developed within a system until a driving force isestablished.

2. This difference in pressure (the driving force) can be created by twomethods:

a) By a pump

b) By a difference in density of a fluid.

3. Recall that the energy balance performed on the straight pipe showedthat energy conversions took place between points one and two.

4. Remember that P1V1 > P2V2 and U2 > U1V, where V is the specific

volume. The change in pressure between the two points (Delta P), ordifferential pressure, resulted due to the flow of fluid within the pipe.

5. The pressure loss in the pipe was a conversion of flow energy (Pv) to

internal energy (U) caused by the friction between the fluid and the pipewall. This conversion is called Headloss.

6. Friction is the resistance to movement.

2.2 Headloss

A. Definition: Headloss is the conversion of flow energy to internal energy dueto friction.

B. Headloss (HL) is dependent on any factor in a piping system which will

change or vary the amount of friction in that system.

7

C. The factors that affect headloss are:

1. Pipe length: as the length of pipe increases, headloss will increase.

2. Friction factor: as the roughness of the pipe increases or the viscosity ofthe fluid increases; the friction, headloss and pressure drop willincrease.

3. Fluid velocity: as the fluid velocity (squared) increases, the friction,headloss and pressure drop will increase.

4. Pipe diameter: as the pipe diameter increases, the friction, headlossand pressure drop will decrease.

D. An equation is used to illustrate the terms affecting headloss and is knownas Darcey's equation:

1. hL = FLV2 where: F is the friction factor

D 2 gc L is the length of pipe

V2 is the fluid velocity squared

D is the pipe diameter

2. When a system is designed, built and then operated, the hL equation

becomes:

hL = KV2

2gcBecause F, L, D are constant, the constant k is substituted and HL is

proportional to the V2. The velocity of the fluid will have a direct effecton the type of flow in the pipe.

E. Operators have some control over system headloss in the following ways.

1. Valve position changes will change the friction felt by the fluid and thevelocity of the fluid.

2. Changing the system lineup by adding more components or removingcomponents also changes the friction factor.

3. Varying the speed of a single pump or the configuration of severalpumps within the system will vary the velocity term.

8

F. There are two categories that flow will fall into. One type results in lowheadloss and another type causes high amounts of headloss.

1. Laminar flow - this is fluid flowing in layers and occurs in low flowsystems (v < 10 ft/sec.)

a) In this type of flow, layers of fluid near the pipe wall covers theroughness of the pipe wall. As far as headloss is concerned, this willreduce friction, headloss and the pressure drop.

b) One problem with laminar flow is that the layers of fluid act likeinsulation and reduce the heat transferred into or out of the fluid.

2. Turbulent flow - this is fluid flowing with random motion in the system. (v >12 ft/sec)

a) This type of flow creates more friction between the moleculesthemselves and between the water molecules and pipe wall. Because of increased friction, the headloss and pressure dropincrease.

b) One advantage to turbulent flow is that the random mixing action ofthe fluid will enhance the heat transfer process.

c) Friction is related to the type of flow in a pipe through Reynolds

number (R#). R# is related to velocity: as v ↑ --> R#↑

R# = Vav D R# is unitless v Vav = average velocity v = viscosity

D = pipe diameter

For R# < 2000 the flow is Laminar. From 2000-3000 the flow is in

Transition. For R# > 3000 the flow is turbulent.

3. PUMPS AND PUMP OPERATIONS

3.1 Centrifugal Pumps

A. Principle of Operation - As Fluid enters the suction of the pump, it undergoesa pressure drop. The impeller then increases the velocity of the fluid as thefluid moves along the impeller vanes. The fluid also sees an increase inarea which will convert some of the velocity to pressure (A↑ → v↓ → p↑ ). The fluid then passes into the volute where the rest of the velocity increasefrom the impeller is converted to pressure by another area increase.

B. Characteristics

1. For a given speed the pump head will decrease as volume flow rateincreases. (Where pump head = discharge press - suction pressure)

9

2. Centrifugal Pump Laws

•a) The change in V α the change in speed. ( ∆V α ∆N)

• •V1 / V2 = N1 / N2

where: N = speed or RPM

•V = ft3/time

b) The change in pump head α the change in pump speed, squared.

( ∆Hd α ∆N2)

Delta P1 / Delta P2 = (N1)2 / (N2)

2

where Delta P = pump head (psid or ft of water)Pump head = Disch press - Suction Press.

c) The change in pump power is α the change in pump speed, cubed.

( ∆P α ∆N3)

P1 / P2 = (N1)3 / (N2)

3

where: P = power d) Example: Given; variable speed pump at 2000 RPM

Delta P = 250 psid, V = 3000 gpm, P= 5000 HP

Find V, Delta P, and P at a speed of 4000 RPM

1) V α N;

V1/V2 = N1/N2

V2 = (N2/N1) V1 = (4000/2000) 3000 gpm = 6000 gpm

2) Delta P α N2

Delta P1 / Delta P2 = (N1)2 / (N2)

2

Delta P2 = [(N2)2 / (N1)

2] Delta P1

Delta P2 = [40002 / 2000

2] 250 psid

Delta P2 = 1000psid

3) ∆PWR α N3

P1 / P2 = (N1)3 / (N2)

3

P2 = [(N2)3 / (N1)

3] P1

10

P2 = [40003 / 2000

3] 5000 HP

P2 = 40000 HP

3. Series and Parallel Pump Operation

a) Series Configuration

Consider a condensate and feed system. Imagine a single pumpthat takes a suction on the hotwell and pumps it to the boiler. Thepump must create enough Delta P to overcome the headlossassociated with the components in the system plus the difference inpressure from the condenser to the boiler. This job would require apump with many stages. The option is to design a system withmore pumps in series. Each pump will create a Delta P toovercome headlosses and provide suction pressure for the nextpump in the system.

1) Each pump has its own characteristic curve, each producessome head for a given volume flow rate.

2) When placed in series, the first pump increases the pressure inthe system. The discharge of pump #1 is now the suction lineto #2 pump which will also create its own Delta P. Since thepumps add their pressures independently, the total or combinedhead curve is merely the addition of pumps 1 and 2.

3) In series pump operation, the capacity for flow is no greaterthan the capacity of one pump.

4) In an operating system, the characteristic curve for that systemhas not changed but the operating point (the intersection of thepump and system curves) has. The increased pump headcreates higher volume flow rate. Higher volumetric flow rate (V)in turn creates more headloss and shifts the operating point upthe system characteristic curve.

5) The above explanation is the same as describing the operationof one multistage pump where each stage is an individualpump.

b) Parallel Configuration

In order to increase the flow capacity of any system, additionalpumps are added in parallel. This is done instead of using one

variable speed pump to reduce power consumption. ( ∆P α ∆N3)

1) Each pump has its own characteristic curve, each producessome head for a given volume flow rate.

11

2) When placed in parallel, each pump draws suction from thesame point and discharges to another common point. Sinceeach pump sees the headloss of the system the Delta P of eachpump is not additive as it is in series configurations.

3) The total capacity of both pumps will be the addition of bothpumps flow rate.

4) Adding the second pump in parallel causes the fluid toaccelerate thus the headloss increases. We see an increase involume flow rate and a small increase in head of the pumps atthe new operating point.

5) Note the increased pump head for the second pump addition. Generally the increase in pump head is limited by the maximumhead of the largest of the two pumps.

6) This design is desirable for high volume flow requirement wherethe Delta P is less of a concern.

C. Problems

1. Cavitation

a) Definition - cavitation is the formation of vapor voids in the lowpressure area of the pump followed by their collapse in the highpressure region.

b) Cavitation is caused by insufficient pressure available at the suctionof the pump.

2. Net Positive Suction Head

a) Net positive suction head available is the absolute pressure at thesuction of the pump minus the vapor pressure of the fluid at thesame point.

b) Required NPSH - required amount of pressure above the vaporpressure necessary to prevent cavitation for some given volumeflow rate (V). This pressure will be equal to the pressure drop in thepump from the inlet flange to the eye of the impeller. It isdetermined at the factory and will be plotted on the pump curves.

c) Example: Instructor make up example for NPSH-Available

d) Results of cavitation

1) Pitting and subsequent erosion of impeller

2) Flow oscillations

3) Pump vibration

4) Overheating

12

e) Indications

1) Vibration and noise

2) Motor current fluctuations

3) Fluctuations in discharge pressure and/or flow rates.

f) Prevention Methods

1) Head tank to create a static pressure at pump suction.

2) Booster pump to increase pressure to suction of next pump.

3) Large suction pipe to convert KE to pressure increase.

4) Subcooled liquid to raise NPSHA (lower vapor pressure).

5) Pressurize entire system.

6) Close down on discharge valve - this will decrease fluid velocityand reduce the pressure drop in the pump and thus reduce therequired NPSH.

3. Other centrifugal pump problems

a) Pump Runout - the maximum flow rate at the lowest anticipatedsystem head for a given system design and pump selection. Pumpswhich operate in an oversized system can reach their maximum flowrates because of not enough system headloss.

Correctly sized pumps can reach runout due to ruptures in thesystem which drastically reduces or eliminates headloss. Pumpsrunning in parallel may runout if one pump trips.

1) Results

(a) Pump efficiency decreases

(b) Eventual flow loss (possible cavitation problems)

(c) Overheat motor and/or pump

2) Prevention methods

(a) System design - choose correct pump for system.

(b) Throttle discharge to prevent high flow rates.

(c) Create some minimum static head the pump mustalways discharge against.

b) Pump Deadhead - pump is running with little or no flow.

1) Results

(a) Overheat pump and/or motor.

(b) Efficiency is very low

13

(c) So much heat put into water (Wp) that temperature will

increase; therefore, a greater pressure is required toprevent cavitation.

2) Prevention Methods

(a) Supply a flow path which will produce the manufacturedsuggested minimum safe flow rate. (i.e. recirc line)

3.2 Positive Displacement Pumps

A. Principle of Operations - the pump is usually a reciprocating piston devicewhich draws the fluid into a chamber on one stroke and then compressesthe trapped fluid before releasing it into the system.

B. Types of Positive Displacement Pumps

1. Reciprocating

2. Rotary

3. Screw

C. Characteristics

1. For a given speed, the volumetric flow rate is constant. Ideally, thevolume flow rate will not vary (for that speed) until the mechanicalleakage increases when the pump operates at extremely high dischargepressures.

2. The head (discharge pressure minus suction pressure) is dependent onthe system the pump discharges into.

D. Problems

1. Cavitation

a) A positive displacement pump will cavitate and the results,indications, and prevention are basically the same as for acentrifugal pump.

2. Runout

a) A PD Pump will not suffer runout.

4. PLANT PROBLEMS

4.1 Water Hammer

A. Defined as a force wave of fluid striking an obstruction in a pipe (e.g. closedvalve, abrupt turn)

B. Causes

1. Starting a pump with the discharge valve open.

14

2. Initiating flow in an unvented system.

3. Rapidly closing a valve with flow in the line.

C. Effects

1. Causes rattling in pipes.

2. Loud Noise.

3. Damage to piping, hangers, components.

D. Prevention

1. Always initiate flow in an unvented, unfilled system slowly.

2. Use good sense and judgement when starting pumps andopening/closing valves.

1


PROPERTIES (4)

2

OVERVIEW:

This lesson plan discusses the concept of Thermal Efficiency and the methodsemployed to maximize efficiency..

1. REFERENCES:

1.1 Elements of Applied Thermodynamics: Johnson, Brocket,

1.2 Brock, Keating: Naval Institute Press.

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TERMINAL OBJECTIVE

At the end of this lesson the student will understand the concept of Thermal Efficiencyand the methods employed to maximize efficiency..

ENABLING OBJECTIVES

1. Define Thermal Efficiency and discuss its relationship to the heat andwork in a Thermodynamic Cycle.

2. Discuss the Rankine Cycle in terms of the processes involved, and thecomponent corresponding to each process.

3. Discuss the effects of the following on Thermal Efficiency:

3.1 Feedwater Heater Operation

3.2 Condenser Pressure

3.3 Condensate Depression

3.4 Turbine Load

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LESSON OUTLINE

1. INTRODUCTION TO POWER PLANT CYCLES

1.1 Purpose of the lesson

2. PRESENTATION

2.1 Power Cycles

2.2 Thermal Efficiency and the Second Law

2.3 Rankine Cycle

A. Elements of the Cycle

B. Cycle Efficiency

2.4 Design Improvements In Efficiency

A. Feedwater heating

2.5 Operational Effects on Efficiency

A. Condenser Pressure

B. Condensate Subcooling

C. Throttling

D. Operating Power Level

E. Other Considerations

F. Indications of Changing Efficiency

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1. INTRODUCTION TO POWER PLANT CYCLES


A. Define Power Cycles

B. Tie individual components discussed previously into the plant

C. Develop the concept of Thermal Efficiency, discuss the conditions whicheffect it.

1. Design

2. Operational

2. PRESENTATION

2.1 Power Cycles

A. Definition

1. A Thermodynamic Cycle is a recurring series of thermodynamicprocesses used for transforming energy into a useful effect.

2. For a power cycle the energy is in the form of heat and the useful effectis mechanical work.

B. Elements of the Thermodynamics Cycle

1. A working substance

a) Acts as the medium for transport of energy through the cycle.

b) Steam/water is the working substance in power cycles.

2. An engine

a) The device where thermal energy of the working substance isconverted to mechanical work.

b) The steam turbine is the engine for power cycles we will bediscussing.

3. A source or high temperature energy reservoir

a) Supplies energy as heat to the working substance

b) The boiler furnace and the fuel supplied provides the heat source.

4. A sink or low temperature energy reservoir

a) Absorbs energy as heat from the working substance either directlyor through an intermediate heat transfer device known as a receiver.

b) The lake, river, ocean, cooling towers, etc will be the sink.

c) The Condenser is a receiver.

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5. A pump - moves the working substance from the low pressure region ofthe cycle to the high pressure region.

C. More elements or components may be introduced into the cycle in order toimprove performance, as we will see later.

2.2 Thermal efficiency and the second law of thermodynamics

A. For a work producing cycle the thermal efficiency (η) equals the outputdivided by the input.

1. η =OUTPUTINPUT

2. For a cycle where heat is converted to work.

η =Net work outHeat Input

B. Applying the first law of thermo to the basic cycle.

1. Energy Balance

a) Energy into cycle = Energy out of the cycle.

b) Qadded = Work out + Qrejected

rearranging; Work out = Qadded - Qrejected

2. Thermal efficiency can be expressed as:

η = work out

Q added

substituting for Work out:

η = Qadded - Qrejected

Qadded

3. The first law does not restrict how the energy conversion takes place norto what extent.

C. The Second law of Thermodynamics

1. Early efforts to increase the cyclic work produced from a given heatinput by reducing the heat rejected suggested the possibility of reducingthis waste. This led to the Second Law.

2. No engine, actual or ideal, when operating in a cycle can convert all theheat supplied it into mechanical work.

D. The Carnot Cycle

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CARNOT CYCLECARNOT CYCLE

ENTROPY

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S1 S2

A B

CD

1. Used here to illustrate the basic relationships which effect cycleefficiency.

a) Most efficient cycle conceivable though not practical.

b) Serves as a standard of comparison for all heat cycles in use today.

2. Composed of four reversible thus ideal processes.

a) Constant temperature heat addition.

1) Heat is added to the working fluid at the source temperaturefrom a to b.

2) The heat added is the area under the a-b Process line on the T-S Plot. (T∆S1-2)

b) Isentropic expansion from b to c gives the work output

c) Constant temperature heat rejection from c to d.

1) Heat is transferred from the working fluid at the sinktemperature

2) The heat rejected in the area under the c to d process line onthe T-S Plot. (Tsink∆ S2-1)

d) Isentropic compression from d to a.

3. The work produced by the cycle is the difference between the heatadded and the heat rejected. Area a b c d on the T-S plot.

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4. Cycle efficiency

a) Efficiency Relationship

1) η = work

Qadded! =

! !

!Q Q

Q

added rejected

added

−

2) Recall that !Q added = Tsource ∆S1-2

!Q rejected = Tsink ∆S2-1

3) Substituting and dividing out ∆S

η = T T

Tsource sink

source

−

η = 1−

TT

sink

source

b) Means of increasing Carnot Efficiency

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INCREASE CARNOTCYCLE EFFICIENCY ?

• INCREASE TEMP FORHEAT ADDITION.

INCR. WORK w/oINCREASING Qrej.

• APPLICATION:HIGHER TaveSUPER HEATMSRsFW HEATINGLIMITS ON MATERIALS

• DECREASE TEMP FORHEAT REJECTION.LIMITED BY SINK TEMP

ENTROPY

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1) Increase the temperature at which heat is added

(a) Increases the work out without increasing Q rejected.

(b) This concept has application in the real world

• Raising Temperature

• Using superheat

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• Feedwater heating

(c) Constant temperature heat addition is not possible withreal working fluids resulting in a sacrifice of work.Example is preheat to sat. temp. of feedwater.

2) Reduce the temperature at which the heat is rejected

(a) Lowers Qrejected for a given Qadded with acorresponding improvement in workout.

(b) This principle is limited by the available heat sink such aslake temperature.

2.3 The Rankine Cycle

A. Elements of the Cycle

1. Represents the simplest steam cycle. Serves as the starting point forfurther refinements.

2. Working fluid - Water in the vapor and liquid phases.

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RANKINE CYCLE

a

a1 b

cd

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ENTROPY

3. Heat addition in the Steam Generator.

a) Subcooled liquid from the pump discharge enters the boiler at boilerpressure. (Point a)

b) A portion of the heat added to the feedwater goes to raising thetemperature to saturation (point a1)

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c) The majority of the heat added goes to vaporizing the liquid(constant temperature) from Point a1 to b.

d) The heat added per lbm. in the boiler is:

q h hsteam feed= −

e) The average temperature at which the heat is added during the pre-heat portion is lower than during vaporization which results in alower efficiency than the carnot cycle.

4. Expansion in the Turbine

a) Ideal turbine b to c

1) Constant entropy expansion to condenser pressure

2) Enthalpy is converted to work

work per lbm h hsteam feed= −

3) Wet vapor is exhausted to the condenser.

b) Real turbine b to c.

1) Losses due to throttling, moisture, friction etc. result in less ofthe energy being converted to work

2) Entropy increases from inlet to outlet

3) Exhaust enthalpy for the real turbine at the same pressure ishigher than the ideal turbine indicating:

(a) Less work per lbm

(b) More heat rejected per lbm

(c) Lower cycle efficiency

5. Heat Rejection in the Condenser

a) Wet vapor at condenser pressure enters the condenser.

b) The heat is rejected to the cooling water, condensing the steam, c tod.

c) The heat rejected per lbm. is:

q h hexh condensate= −

6. Pump-d to a

a) Constant entropy compression

b) Raises the pressure from condenser pressure to boiler pressure.

7. Superheat/reheat brings the energy of the fluidback to a high level for use in the turbines.

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REHEAT CYCLE

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ENTROPY

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Superheat

2.4 Cycle Efficiency

A. Feedwater Heating

1. Principle of Feedwater heating

a) A portion of the steam flow is extracted from the turbine afterexpanding through several stages.

b) The extracted Steam Condenses in the feedwater heater

c) The heat of condensation is transferred into the feedwater returningto the Steam Generator.

d) The drains from the feed heaters are returned to the feedwatersystem by the drain pumps.

2. Effect of Feedwater heating is improvement of the cycle efficiency

a) Raises the average temperature of heat addition in the steamgenerator.

1) Feed heating raises the temperature from a to a1

2) Heat from the reactor is added from a1 to b.

3) A larger portion of the heat is added at a higher temperature,improving efficiency.

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b) Less heat rejected

1) Some of the energy in the steam is recirculated into thefeedwater rather than being rejected in the condenser.

2) This results in less total steam flow through the turbine but theeffect improves efficiency.

2.5 Operational Effects On Efficiency

A. Condenser Pressure

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OPERATIONAL EFFECTS:OPERATIONAL EFFECTS:CONDENSER PRESSURECONDENSER PRESSURE

!LOWER ABSOLUTE PRESSURE!LOWER AVERAGE TEMPERATURE FOR

HEAT REJECTION!LARGER DELTA h PER lbm STEAM

TE

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ENTROPYENTROPY

1. Lower condenser pressure (higher vacuum) in general yields improvedefficiency.

a) Lower pressure means lower temperature at which the heat isrejected. (The condenser is at saturation conditions)

b) A larger portion of the steam enthalpy is converted to work.

c) Less heat rejected.

2. Condenser Pressure is affected by:

a) Condenser Cooling Water flow rate - lower flow rate yields highercondenser temperature and pressure

b) Condenser Cooling Water inlet temperature - higher temperatureyields higher condenser temperature and pressure.

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c) Condenser heat load - higher steam flow rate into the condenser fora given Condenser Cooling Water inlet temperature and flow ratecauses higher Condenser Cooling Water average temperature andcondenser to Condenser Cooling Water ∆T. Condensertemperature and pressure will be higher.

B. Condensate subcooling (condensate depression)

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OPERATIONAL EFFECTS:OPERATIONAL EFFECTS:CONDENSATE SUBCOOLINGCONDENSATE SUBCOOLING

"EXTRA HEAT ADDITION REQ’d"EFFICIENCY REDUCED"REQ’d FOR PUMP NPSH

!CNS DESIGN MINIMIZES

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ENTROPYENTROPY

1. Condensate depression occurs when the heat rejected exceeds heatwhich is required to condense the exhaust steam from the turbineresulting in subcooling of the condensate.

2. The extra heat rejected must be replaced by the heat source.

3. Efficiency is reduced.

4. Some subcooling may be desirable in order to provide NPSH for theHotwell pumps.

C. Throttling

1. Throttling the steam flow prior to admission to the turbine reducesefficiency.

a) Throttling is constant Enthalpy.

b) Turbine inlet pressure is lower

c) Less of the enthalpy is converted to work in the turbine inexhausting to the same condenser pressure

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d) The throttling loss eventually shows up as increased heat rejected.

2. Operational Considerations

a) Sequential operation of governor valves

b) Operation with governor valves fully open at full power if possible.

D. Superheat and Reheat

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RANKINE CYCLE

a

a1 b

cd

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e

f

1. Superheat and reheat adds temperature and energy to the cycle.

2. It also has the effect of increasing the quality of the fluid.

E. Operating Power Level

1. In general, the plant is more efficient at full load then at lower powerlevels.

a) Turbine is designed to be most efficient at full load.

b) Less throttling losses.

2. Increasing power level thus total steam flow can cause reducedefficiency if corrective action is not taken.

F. Other methods of maintaining maximum efficiency.

1. Minimize auxiliaries

2. Fix steam leaks

3. Fix air leaks into condenser

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4. Operation of SJAE condenser.

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PROPERTIES (5)

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1. OVERVIEWThis lesson covers the various modes of heat transfer and the equations used witheach mode. It gives an introduction to nucleate boiling and the factors affecting DNB.A discussion of natural circulation and a brief discussion on heat exchangers is alsocovered.

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OBJECTIVES

1. Define 'Heat Transfer'.

1.1 State the three ways heat is transferred in a power plant.

2. Define 'Conduction' heat transfer.

2.1 Explain the variables that effect the rate of conduction heat transfer.

2.2 List the formulas used for conduction heat transfer.

2.3 Give an example of where conduction heat transfer occurs in the power plant.

2.4 Given a set of parameters, be able to work conduction problems.

3. Define 'Convection' heat transfer.

3.1 Explain the variables that effect the rate of convection heat transfer.

3.2 List the formulas used for convection heat transfer.

3.3 Give an example of convection heat transfer in the power plant.

3.4 Given a set of parameters, be able to work convection problems.

4. Define 'Radiation' heat transfer.

4.1 Explain the variables that effect the rate of radiation heat transfer.

4.2 Give an example of radiation heat transfer in power plant.

5. Explain why a counter flow heat exchanger is the most efficient type ofheat exchanger.

5.1 Using the appropriate heat transfer formulas and given information, be able towork heat exchanger heat transfer problems.

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OUTLINE

1. INTRODUCTION

2. PRESENTATION

2.1 Heat

2.2 Conduction

2.3 Convection

2.4 Natural Circulation

2.5 Radiation Heat Transfer

3. HEAT EXCHANGERS

3.1 Heat Transfer in Heat Exchangers

3.2 Types of Heat Exchangers

3.3 Applications

4. SUMMARY

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1. INTRODUCTIONThis lesson will present the topic of heat transfer including the 3 modes of heattransfer, natural circulation, and heat exchangers.

2. PRESENTATION

2.1 Heat- Energy transferred between two substances due to a temperaturedifference.

A. Rate of Heat Transfer (Q) - Energy/unit time (BTU/hr)

B. Heat is transferred by three methods

1. Conduction

2. Convection

3. Radiation

2.2 Conduction - transfer of heat thru a material due to a Delta T across the material. It involves no motion of the material itself, but is a result of collisions betweenthe molecules of the material.

A. Thermal Conductivity (k) - the rate of heat transfer between opposite facesof a unit cube of material with a Delta T = 1°F. (BTU/hr - °F- ft.) "k" varieswith the type of material and temperature range. The larger the value of k,the better a material will conduct heat

B. As the feedwater enters the lower boiler drum it is delivered up the inside ofthe boiler wall tubes. In these tubes the water conducts the heat trough theboiler tube walls from the heat input from the boiler furnace. The water, as itturns to steam, goes to the steam drum..

C. Conduction through a material can be calculated by:

Q = K A Delta T Delta X

Where K = thermal conductivity

A = Area

Delta T = Temperature difference

Delta X = Material thickness

D. If there are several materials together, such as through a heat exchangertube, the rate of heat transfer is a result of all the k's, A's, Delta T's, andDelta X's for the materials.

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E. To simplify working with conduction problems, the terms k and Delta X havebeen combined to give the term "overall heat transfer coefficient"

(U = BTU/hr- oF - ft2) and results in the formula:

Q = UA Delta T

(U also includes another variable to be discussed in convection heattransfer.) Used anytime heat is transferred across a material and the 'U' and'A' terms are known. In the power plant it is used in problems relating to theboiler tubes, condenser tubes, Hx tubes, etc.

2.3 Convection - transfer of heat energy by the combined action of conduction,energy storage, and mixing motion of a fluid between regions of high and lowtemperatures (i.e. the energy transfer between a surface and a flowingsubstance).

If the fluid is being pumped, we have forced convection. If flow is due to achange in the fluid density, we have natural convection.

A. The rate of heat transfer (Q) due to convection will be dependent on severalproperties of the fluid, such as; temperature, velocity, specific heat, viscosity,etc. These variables have been combined into one factor called the NusseltNumber (Nu). Also affecting Q are the thermal conductivity and the length offluid being observed. To further simplify this, another factor has been usedto combine all of these variables; Convection Heat Transfer Coefficient.

hc = Nu K L

This term is also included in the U term of Q = UA Delta T.

Looking back at this formula for a moment, we see that we can increase theQ by doing three things:

1. Increase the Delta T (not desirable)

2. Increase the A (set by design)

3. Increase U (done by increasing hc)

Looking further, "U" can be increased by two methods: (1) decreaselaminar layer or (2) break up the laminar layer

B. Reheat and superheat sections of the boiler use convection heat transfer.The superheat section take the saturated steam from the boiler steam drumand raises its temperature to the desired level. In this process any smalldroplets of water carried out of the drum are also evaporated. The reheatsection takes steam exiting the HP turbine. This steam is piped back to theboiler to the reheat section so that the energy of the steam and the quality ofthe steam can be increased back to a superheat condition for use in the IPand LP turbines.

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C. The formulas used for convective heat transfer are:

1. Q = MC Delta T and,

2. Q = M Delta h

D. Uses

1. Q = M C Delta T

a) Used for heat transfer in medium with no phase changes and noboundary is crossed.

2. Q = M Delta h

a) Used for heat transfer where there is a phase change, but noboundary is crossed.

Example:

1) Feedwater to steam in the boiler

2) Steam to condensate in the condenser

2.4 Natural Circulation

A. Mechanism

1. Natural Circulation occurs due to density difference between fluids ortwo points in the same fluid system. As a fluid is heated up its densitydecreases. Fluids of higher temperature, lower density have a naturaltendency to rise to a higher elevation. Conversely, fluids with lowertemperature, higher density have a tendency to fall to a lower elevation.

a) Example

---------------Levels equal-------------

70 F 180 F

Tank 'A' water has a higher density than tank 'B' because of thelower temp. Static pressure felt on either side of the valve will bedue to the difference in density between the tanks since there is noheight difference.

Flow will occur from tank 'A' to Tank 'B' until levels changesufficiently to cause the Delta P = 0.

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b) In the above example we could place a heater in tank 'B' and a heatexchanger in tank 'A' to remove heat and we would still only get flowuntil the levels changed to make Delta P = 0. To have continuousflow between the tanks, a complete path from tank 'B' to tank 'A' anda completely filled loop is needed. With the heat source (heater),heat sink (heat exchanger), and return flow path, we can establish asmall natural circulation flow.

A B HEATER(SOURCE)

COOLING FLOW (SINK)

2. The amount of flow we can get from the above system can be aidedfurther by elevating the heat sink (tank 'A') above the source (tank 'B'). The difference in height will cause a greater Delta P, increasing flow.

A

B

HEIGHT

2.5 Radiation Heat Transfer - the emission of heat energy in the form ofelectromagnetic radiation from a body by virtue of its temperature. Unlikeconduction and convection, radiation heat transfer is independent of anymedium and depends entirely on the absolute temperature of the radiating body. The rate of heat transfer is still dependent on the Delta T between two bodies. When conduction and convection cease due to loss of transfer medium radiationtransfer will be the only means of heat removal.

2.6 Types of Heat Exchangers

A. Counter Flow heat exchangers - In a counter flow heat exchanger the twofluids flow in opposite directions. Because of this, the average Delta T is atits maximum all along the tubes. This gives the maximum heat transfer of allthe heat exchangers.

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B. Parallel flow - In parallel flow exchangers the two fluids flow in the samedirection. This results in a large Delta T at the inlet, with a small delta T atthe outlet. The heat transfer rate for a parallel heat exchanger is less thanfor a counter flow heat exchanger of the same size.

C. Cross-Flow

1. In a cross flow heat exchanger, one fluid flows across the tubes. Theseheat exchangers are of two types.

a) Single pass- fluid makes one pass at right angles

b) Multi-pass - fluid makes several passes back and forth across thetubes to set up an approximation of counter flow.

2. The Main Condenser is a cross flow heat exchanger.

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3. SUMMARY

3.1 Three methods of Heat Transfer

A. Conduction

B. Convection

C. Radiation

3.2 Cover Objectives

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HEAT RATE IMPROVEMENT

REFERENCE MANUAL:

INTRODUCTION AND USE

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1. OVERVIEW

1.1 This lesson will provide the student with an introduction to the ‘Heat RateImprovement Reference Manual’, the purpose, organization and use of themanual.

2. REFERENCES

2.1 Heat Rate Improvement Reference Manual, Duke/Fluor Daniel

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LESSON OUTLINE

1. Purpose

2. The Heat Rate Improvement Reference Manual

2.1 Heat Rate Primer

2.2 Heat Rate Logic Trees

3. Fossil Steam Station Components

3.1 Thermal Kits

3.2 Boilers

3.3 Turbine

3.4 Plant Auxiliaries

3.5 Condenser

3.6 Cooling Towers

3.7 Feedwater Heaters

4. Elements of a Thermal Performance Monitoring Program

4.1 Goals

4.2 Initial Steps for Establishing a Heat Rate Monitoring Program

4.3 Performance Tutorial

4.4 Performance Loss Monitoring and Trending of Key Parameters

4.5 Unit Performance Survey

5. Instrumentation and Testing Requirements for Heat Rate Monitoring

5.1 Instruments and Performance

5.2 Testing Program

6. Cycle Isolation

7. Heat Rate Improvement Program

8. Appendix A and B

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TERMINAL OBJECTIVE

At the end of this class the students will have a working knowledge of the Heat RateImprovement Reference Manual.

ENABLING OBJECTIVES

1. At the end of this class the student will be able to:

1.1 State the purpose of the Heat Rate Improvement Reference Manual.

1.2 Define HEAT RATE.

1.3 Discuss the following in detail:

A. Design Heat Rate

B. Best Achievable Heat Rate

C. Actual Heat Rate

D. Factors Affecting Plant Efficiency

E. Controllable Losses

F. Accounted for Losses

G. Unaccounted for Losses

2. Read and interpret the logic trees, how to modify them for a particularplant/facility and how to use them to develop decision criteria.

3. Discuss Thermal Kits.

4. Perform the following:

4.1 Loss calculations for various plant components including turbines, boilers,condensers, cooling towers and feedwater heaters.

4.2 Set up thermal monitoring performance programs including:

A. Deciding upon which plant parameters to monitor

B. Determining deviations from expected values

C. Use of logic trees to identify possible causes of the deviations

D. Plan an appropriate course of action to resolve performance deviations.

5. Discuss short vs long term performance activities as follows:

5.1 Cycle Isolation Techniques

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5.2 Improved Operation Practices

5.3 Preventive Maintenance Programs

5.4 Upgrades of Plant Instrumentation

5.5 Repair/Replacement of Components

5.6 Cost-Benefit.

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1. PURPOSE - To define the performance standards necessary tosuccessfully manage a heat rate improvement plan. The informationcontained in the manual can enable management , staff and technicalindividuals to make their company more competitive and successful in thefuture production of electricity.

1.1 The value of this is to measure how well the unit is doing its job in producingelectricity. Decisions should not necessarily be made only to improvethermodynamic efficiency but rather to improve a company’s overallperformance.

1.2 A thermal performance program is actually the development of performanceparameters which characterize a unit’s operation.

2. The Heat Rate Improvement Reference Manual - (NOTE: all referencesto figure numbers indicate figures located in the manual)

2.1 Heat Rate Primer

A. This chapter provides the user with definitions of heat rate

1. Heat rate - the amount of heat input into a system divided by theamount of power generated by a system.

2. As-designed heat rate - a tool that provides a definable benchmark forcomparison and trending purposes. It is simply a curve generated fromturbine heat balance curves, unit expected auxiliary consumption anddesign boiler efficiency.

3. Best achievable heat rate - the same as the net heat rate obtainedfrom unit acceptance test when the equipment was new and the unitwas operated at optimum. This heat rate value is realistic and attainablefor it has been achieved before.

4. Operating heat rate - calculated from the heat energy consumed by aunit or station for a specified time period regardless of the operatingstatus of the unit or station.

5. Incremental heat rate - units within a utility system and within a powerpool are dispatched (loaded upon the grid) based on their incrementalheat rate and resulting cost curve. It is also used in productionsimulation for maintenance planning and projecting fuel procurementneeds and for pricing of power for sale or resale.

B. A summary of heat rate measurement methods is also provided

1. Actual heat rate

2. Input/Output method

3. Output/Loss Method

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C. Efficiency Factor - a quick reference of unit performance in relation to what itwas designed to be.

2.2 Heat Rate Logic Trees - a systematic approach to aid station engineering inidentifying the root cause(s) of declining unit performance

A. Heat Rate Losses Tree - used to identify areas in the plant where heat ratedegradation may be occurring without conducting expensive tests.

1. Structured to provide a process by which decisions can be determinedthat narrow down the cause of the problem based on the availableinformation.

2. A statement of the problem starts the tree.

B. Major Cycle Component Tree - identifies major areas in the plant cycle thathave the potential for contributing to the overall problem.

1. Components such as boiler and turbine

2. Systems such as condensate/feedwater, cooling water,auxiliary systemsand fuel handling.

C. Logic Model Symbols.

1. “OR” gate - output occurs if one or more of the input events occur.

‘OR’ Gate

2. “AND” gate - output occurs if all of the input events occur.

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‘AND’ Gate

3. “TRANSFER IN” - indicates that the logic model is developed further atthe occurrence of the corresponding transfer out. Transfers can be usedto simplify logic model construction by eliminating the need to developduplicate branches.

“TRANSFER IN”

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4. “TRANSFER OUT” - denotes a transfer of a portion of the logic model tocorresponding transfer in. Transfer out symbol can correspond withmultiple transfer in symbols.

“TRANSFEROUT”

D. Logic Tree Application The engineer must first obtain data from varioussources at the station including routine monitoring of selected plantperformance parameters, special tests, outage reports, initial designdocuments and interviews with plant personnel. He must then convert thedata into decision criteria and associate these with the appropriate areas ofthe plant. (use figures 2-4 through 2-22 of the Heat Rate ImprovementReference Manual to explain how the logic trees are used).

3. Fossil Steam Station Components

3.1 Thermal Kits - a collection of manufacturer turbine generator data in the form ofsecondary cycle diagrams, curves, equations and constants. This data issupplied to the purchaser in order to best describe the expected performancecharacteristics of the turbine generator. (A sample thermal kit is supplied, butspecific plant data and thermal kits should be used if possible)

A. Purpose - the thermal kits are used primarily for the following functions:

1. Standards for monitoring

2. Data for cycle model verifications and studies

3. Unit net capability calculations

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4. Turbine testing calculations

5. Corrected unit cycle heat rate or output computation

B. Details - the following covers the definition, explanation and applications ofthe various items in thermal kits.

1. Heat Balance - a diagram of the unit’s secondary cycle describing theexpected conditions at a specific unit power level or at a valve point. Thecycle conditions described in a heat balance include:

a) enthalpies

b) absolute pressures

c) fluid temperatures

d) main steam quality

e) simplified normal cycle flow paths and flow rates

f) feedwater and condensate booster pumps enthalpy rises

g) gross generatoin

h) turbine heat rate

i) cycle expansion end points

j) fixed mechanical and electrical turbine generator losses

k) electrical generator conditions

l) calculation assumptions, units, steam tables used.

2. Turbine Heat Rate Curve - the heat rates and loads from the heatbalances are used to form the turbine heat rate curve. This expectedheat rate curve has been drawn through the locus of valve points.

3. Expansion Lines/Mollier Diagrams - the steam conditions duringexpansion through the turbine are illustrated by a plot on a Mollierdiagram. The thermal kit expansion lines may be used as a basis forcomparison for test results and cycle model verification. If a test dataexpansion line shifts to the right, there has been a decrease in eficiencyof that specific section.

4. Extraction Pressure vs. Flow - the extraction zone pressure isdetermined by the turbine flow to the downstream stages. Either a graphor equation is supplied that defines the expected Extraction pressure asa function of turbine downstream flow for each extraction and for the firststage shell pressure.

5. Enthalpies and End Points - expected stage, extraction and expansionline end point enthalpies are plotted against flow by some venders.These reflect the design at the turbine and its accessories.

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6. Leakoffs - this data may be used for cycle models when no test data isavailable. These may also be used as the baseline for comparison tomonitoring/trend results.

a) Control, Stop or throttle valve stems and packings

b) Turbine and gland steam seals

7. Exhaust Loss Curve - unrecoverable losses occur in the exhaust hoodof each LP turbine. The total exhaust loss is plotted as a function ofexhaust volumetric flow. The components are:

a) Leaving loss - the wasted kinetic energy of the steam leaving thelast stage.

b) Hood loss - results from the pressure drop of the steam passingthrough the exhaust hood.

c) Turnup loss - occurs due to flow instabilities and recirculation foundat very low exhaust flows.

d) Shock wave pressure drop loss - due to the shock eaves formed atthe turbine exhaust when the pressure drop across the last stage isgreater than that required for sonic flow.

8. Choked (Limited) Condenser Pressure - each turbine generator unit hasa specific LP turbine exhaust pressure below which unit performance starts to deteriorate, assuming steady flow and heat cycle conditions.Choke limited pressure is nearly a linear function of turbine exhaust endsteam flow. Operation at a condenser pressure lower that the chokelimited pressure results in loss of net output and a higher heat rate.

9. Turbine Section Efficiency and Effectiveness - vender supplied curvesas a function of flow. These reflect expected performance. Turbine testresults are compared to these curves to determine which sections orcomponents have performance levels that deviate from the norm.

10. Electrical Generator Losses - the total generator loss is a function ofpower factor, load, hydrogen purity and hydrogen pressure. This lossinformation is used for calculating the turbine used energy endpoint inorder to calculate gross generation from cycle parameters.

3.2 Boilers -

A. Dry Gas Loss - high excess air and lower heat absorption in the boilersystem can cause exit gas temperatures higher than expected resulting inDry Gas Loss. A 40o F rise in exit gas temperatures can raise the Heat Rateby one percent. High exit gas temperatures can be caused by:

1. Plugging or fouling of preheaters, hot or cold side where moisture hasformed due to reaching the dewpoint.

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a) Ensure proper soot blowing for preheater.

b) Periodic high pressure washing may be necessary if the pressuredrop across the preheater starts to limit fan capablity.

2. Corroded or eroded Preheater. During the process of combustion, sulferin the fuel is converted to SO2 and, dpending on the excess airavailable, part of the SO2 is converted to SO3. The SO3 reacts with anywater vapor to form sulfuric acid (H2SO4).

a) Ensure proper operation of steam coils or preheater bypass damperto keep the preheater above the cold end minimum metaltemperature (Figure 3-2).

b) If steam coils are used, perform periodic inspections for leaks whichwould increase water vapor to the preheater.

c) Open or close plant windows and doors to circulate outside airthrough the plant and around the boiler to the Forced Draft fansuction to minimize steam coil usage.

3. Inadequate boiler soot blowing can cause slag to build on heatabsorbing surfaces and proper heat transfer cannot occur.

4. Air Preheater average air in-gas out temperature too high abovedewpoint.

5. Incorrect number of pulverizer mills in service at a given load - causesan increase in tempering air. This decreases the percentage of total airflow which goes through the preheater, raising exit gas tempertures.

6. Excess pulverizer mill tempering air - causes low mill temperature.

7. Fuel/air control system - maintain O2 as low as possible withoutadversely affecting combustion

8. Improper O2 monitoring system

a) Calibrate or repair monitors

b) Ensure location and quantity of monitors gives a representativeindication.

9. Air inleakage in boiler, preheater or ducts.

a) Run O2 rise test on boiler to locate air inleakage and make repairs.

b) O2 readings should be taken at several locations simultaneously toisolate cause of air inleakage.

B. Dry Gas Loss Calculations (use Heat Rate Improvement Reference Manual’section 3 along with actual plant data to perform calculations)

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C. Unburned Carbon Loss - A flyash sample should be collected and analyzedfor unburned carbon. The percent unburned carbon is also called Loss OnIgnition (LOI). This can usually be traced to the following.

1. Improper excess air in the furnace

2. Poor mixing of the fuel and air in the furnace

3. Pulverized coal fineness is incorrect

4. High surface moisture in the coal can lead to agglomeration and havethe same effect as coarse coal during the combustion process.

D. Carbon Loss Calculations - (use Heat Rate Improvement ReferenceManual’ section 3 along with actual plant data to perform calculations)

E. Moisture Loss - Boiler efficiency calculations use the Higher Heating Value(HHV) as the amount of heat generated in complete combustion of the fuel.Since these losses are related to the percent moisture and hydrogen in thefuel, improvements can only be made by minimizing the exit gastemperatures discussed earlier.

F. Moisture Loss Calculations - (use Heat Rate Improvement ReferenceManual’ section 3 along with actual plant data to perform calculations)

G. Radiation and Unaccounted for Losses (RUMA)

1. Radiation losses account for heat losses to the air through conduction,radiation and convection. The heat emanates from the boiler, ductworkand pulverizers. If the unit is equipped with hot side precipitators, theycan be a source of significant gas temperature drop.

2. Unaccounted for losses include difficult to measure losses that areincluded in a heat balance to arrive at a guaranteed efficiency. Theseinclude heat lost in the ash leaving the furnace through the bottom ashhoppers and economizer hoppers and any apparent losses due toinstrumentation errors.

H. RUMA Loss Calculations - (use Heat Rate Improvement Reference Manual’section 3 along with actual plant data to perform calculations)

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3.3 Turbine Steam is admitted through control valves to the turbine where thethermal energy is converted to kinetic energy and then to mechanical energy byexpansion through the turbine sections. For maximum efficiency the turbinestages contain a combination of impulse bucket and reaction blade designs. Themethod used to control the steam flow to the turbine at various loads affects theplant performance. Partial arc admission can be used where the control valvesare throttled successively which adjusts the active nozzle area and the throttlepressure remains constant through the load range. In Full arc admission thecontrol valves remain fully open and the load is changed by varying the boilerpressure or the boiler pressure can remain constant and all the control valvesare operated together until the desired load is reached. Usually the bestoperation is a combination of fixed and variable pressure operation where thecontrol valves are throttled to a valve point and reduced pressure operation isused in a particular load range. There are a number of factors dealing with theturbine which can affect the unit heat rate.

A. Main Steam Temperature - A throttle temperature change can affect theturbine load and heat rate. Curves supplied with the unit thermal kit are usedto estimate the effects of temperature deviations on the unit heat rate.

B. Main Steam Pressure - as with main steam temperature a change inpressure can affect the unit load in several ways. The curve for calculatingheat rate improvements due to increased throttle pressure should beincluded in the unit thermal kit.

1. A 5% increase in initial pressure will result in a 5% increase in steamflow which in turn will cause a 5% unit load increase.

2. The increase in flow will cause an increase in steam velocity leaving thelast stage, increasing the total exhaust loss. An increase in exhaust lossresults in poorer low pressure turbine efficiency.

3. The throttle available energy increases as the pressure increases.

C. Design Features - Design considerations affecting turbine efficiency includecomponent design to minimize pressure drops, stationary and rotating bladedesign to obtain optimum steam velocity, and section design to minimizefriction and leakage losses.

D. Maintenance Items - during maintenance outages all packing seals shouldbe inspected for wear and turbine blades and nozzles should be inspectedfor corrosion or erosion.

1. Solid particle erosion (SPE) of turbine buckets and blades, nozzles andcontrol valves has been a problem of concern for many years. Thisdamage can be minimized by water chemistry, thermal cycling, materilchanges and elimination of air inleakage. Damage to turbine seals,nozzles or blades can normally be detected from performing enthalpydrop tests on the turbine quarterly.

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2. Enthalpy drop test - (use ‘Heat Rate Improvement Reference Manual’section 3 for discussion of this test, instrumentation required, Unitoperating setup, calculation and corrections)

3.4 Plant Auxiliaries - Overall unit heat rate is calculated by dividing total Btu inputby total net generation. Since gross generation is not used, the electricalauxiliaries used to operate the plant can affect the heat rate significantly.

A. Each unit should have a curve of expected auxiliaries for a given load and itshould be updated whenever equipment is added or removed.

B. An effect on the heat rate due to high plant electrical auxiliaries can becaused by the following:

1. Operating plant equipment when it is not needed for the plant status.

2. Operate equipment such as service water pumps and air compressorsonly as needed.

3. Maintain equipment whose power usage increases with deterioratingperformance such as pulverizers and pumps.

4. Maintain boiler ducts and expansion joints to prevent air inleakage toconserve FD and ID fan power.

5. Investigate possible installation of variable speed drives for fans insteadof using dampers for air flow control.

6. Outdoor lighting should be controlled by automatic sensors.

7. Maintain heating and air conditioning controls for proper operation.

8. Turn off personal computers when not in use, especially overnight.

3.5 Condenser

A. The condenser receives exhaust steam from the low pressure turbine andcondenses it to liquid for reuse.

B. The water cooled surface condenser is the most common type of condenserused in modern power plants. Efficiency increases as condenser absolutepressure decreases. With condenser pressure as low as possible theamount of heat rejected is lower and the amount of work of the turbineincreases. This is accomplished by optimizing the heat transfer rate betweenthe condensing steam and the cooling water, effectively allowing no leakageof air into the condensing space and minimizing any cycle leakage to thecondenser which would add heat load.

C. Things that affect the heat transfer are:

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1. Tube fouling or restriction - detected by monitoring absolute backpressure and the terminal temperature terminal difference between theturbine exhaust and cooling water outlet temperature. Possiblecorrective or preventative measures:

a) Backwashing arrangements may be provided

b) Sponge balls or brushes may be automatically circulated throughthe condenser.

c) Periodic condenser tube cleaning

d) Chemical cleaning

e) Install condenser pressure differential transmitters to monitor tuberestrictions

2. Cooling water flow rate inadequate

a) Place additional pumps in service

b) Monitor flow rate

c) Determine if cooling water blowdown is installed on CCW inlet. Itshould be installed on the outlet.

d) Test circulating cooling water pumps for proper flow and rebuild asnecessary

e) Maintain clean racks or screens and waterboxes.

3. Cooling water temperature too high

a) Place additional cooling tower cells in service

b) Perform cooling tower maintenance

4. Condenser backpressure too high with proper cooling water

a) Perform helium leak test for condenser inleakage

b) Inspect steam jet air ejectors for proper operation

c) Check incoming drain lines, feedwater heater high level dumps,minimum flow valves and steam traps for leakage or improperoperation

d) Isolate pressure sensing lines at condenser to check for instrumentline leaks.

3.6 Cooling Towers Condenser cooling water systems are either once through orclosed systems. A once through system is where water is pumped from a river orlake through the condenser and the warmer water is returned to the source. Aclosed loop system rejects the heat to the atmosphere through the use of eithera cooling tower or a body of water such as a cooling lake. Most newer plants usecooling towers because of the environmental restraints.

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A. Cooling tower performance is affected by the ambient wet bulb temperature,deterioration of the fill material, fill silt buildup, icing on tower structure, lowwater loading and high water loading.

B. Wet Bulb temperature - Using the range and the tower outlet temperature,the corresponding calculated wet bulb temperature can be found from thevender’s design curves using either the design or measured value forcirculating water flow.

1. If the actual wet bulb temperature is higher than the calculated the toweris performing at or better that expected.

2. If the actual wet bulb temperature is consistently lower that thecalculated then further testing or inspections are necessary to determinecaused of the deficiency

C. Deterioration of fill material - routine inspections are necessary to surveydamage or deteriorated fill material or to remove any debris

D. Fill silt or algae buildup - Purpose of the fill material is to increase the contactarea between the air and water and to increase the water residence time. Tomaintain its maximum effectiveness buildup must be prevented byblowdown and proper water treatment.

E. Low water loading can cause poor water distribution and high water loadingcan cause excessive air pressure losses.

1. Inspect distribution nozzles

2. Clogged distribution nozzles

3. Fan blade deterioration

4. Motor problems

3.7 Feedwater Heaters - Provide three purposes in the power plant.

A. Provide efficiency gains in the steam cycle by increasing the initial watertemperature to the boiler, reducing the amount of heat input required by theboiler’

B. Provide efficiency by reducing the heat rejected in the condenser.

C. Minimize thermal effects in the boiler.

D. Items that can affect performance:

1. Improper heater level can cause flashing in the drain cooler section andtube damage

a) Check operation of automatic controls and level instrumentation.

b) Check for possible tube leaks in feedwater heater.

c) Vent valves may not be set up properly.

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2. Improper extraction line pressure drops. Possible problem withextraction line check valve.

3. Tube fouling due to corrosion affects the heat transfer in the heater andalso increases the problem of deposition of oxides on heat transfersurfaces.

a) Reduce the level of dissolved gases such as oxygen and carbondioxide in feedwater and adjust pH of the feedwater.

b) Clean tube bundles

4. Continuous vent orifice plugging

5. Channel pass partition/gasket leak

E. Feedwater Heater Calculations (use Heat Rate Improvement ReferenceManual’ section 3 along with actual plant data to perform calculations)

4. Elements of a Thermal Performance Monitoring Program (the studentsshould refer to section 4 of the manual throughout this section of study)

4.1 Goals -

A. The goal of a performance monitoring program is to improve unit efficiency.These are needed because of increased fuel cost, increasing age of theunits and their equipment, increased cost of capitol improvements andincreased competition in the utility industry.

B. Improvements should initially concentrate on activities that can beaccomplished with little capitol investment in a relatively short time.

1. Cycle isolation

2. evaluating selected parameters to improve operations control

3. Identify preventive maintenance that can easily be conducted on selectequipment

4.2 Initial steps for establishing a heat rate monitoring program:

A. Evaluate cycle isolation for leaks or improperly positioned valves (UseSection 6 of the manual for details on cycle isolation)

B. Determine which performance parameters are being monitored at the unitwith existing instrumentation (use Table 4-1 for a list of parameters that canbe monitored at a typical fossil station).

C. Obtain readings of the selected parameters from Table 4-1 and compare thereadings with expected values. If no historical readings are available useTable 2-2 as a starting point.

D. Determine the magnitude of the parameters deviation from expected. An aidin this is to review Table 2-1 for utility experienced deviations.

E. Determine the heat rate deviation as shown in Table 4-4.

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F. List the parameters deviating from expected in descending order of effect onheat rate.

G. Select a parameter to be investigated from the list. Discuss the parametersand their deviation with unit operators and other plant personnel to ensureits validity.

H. Review logic trees or parameter diagnostic tables to identify componentseffected and potential caused for the deviation. Modify the logic trees fromone of the demonstration reports to suit the unit being evaluated.

I. Refer to performance parameter accounting manual such as found inAppendix B of the manual, or the Performance Tutorial in section 4. Preparea list of possible corrections to the deviation.

J. Review with operations and maintenance to determine the appropriateaction for correction.

4.3 Performance Tutorial - This section of the manual is designed to be ofassistance in identifying losses while operating the plant . Use this section as aguide to addressing various plant problems that have an effect on plantefficiency.

4.4 Performance Loss Monitoring and Trending of Key Parameters - This section ofthe manual describes how the units performance can be surveyed for losses andtrended to follow the effects of operation .

A. Loss Monitoring - required for determining how well a unit is beingmaintained and operated. A successful program consists of:

1. Gathering accurate operating data from adequate sources to provide acomplete status of unit operating parameters.

2. The data must then be incorporated into the proper calculations fordetermining actual performance losses for cost/benefit analysis.

3. If a source of degradation is identified the plant staff can then pursuedetermining the root cause for the degradation.

4. From the root causes plant staff can optimize their preventivemaintenance program, their instrumentation requirements, operatingpractices and their performance parameter monitoring needs.

B. Classification - It is helpful to classify performance losses so responsibilitiesfor loss reduction can be more effectively delegated

1. Controllable losses - are performance losses that can be minimized bythe plant operating personnel, such as:

a) throttle pressure

b) throttle temperature

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c) hot reheat temperature

d) condenser pressure

e) make-up flow

f) feedwater heater terminal temperature difference

g) feedwater heater drain cooler approach temperature

h) main steam desuperheater spray flow

i) reheat desuperheater spray flow

j) auxiliary electrical loads

k) dry gas loss

l) carbon loss

m) coal weighing error

2. Accounted-for losses - those remaining performance losses for which aneffect on heat rate can be determined. These are usually correctable bymaintenance

a) reheater pressure drop

b) extraction line pressure drop

c) hydrogen loss

d) moisture in fuel loss

e) RUMA loss

f) turbine efficiency

g) miscellaneous

h) light-off fuel

3. Unaccounted-for losses - performance losses for which an effect onheat rate cannot easily be established. These may or may not be knownto exist.

a) heat loss to the condenser

b) soot blowing

c) steam coils usage

d) plant auxiliary steam heating

e) condensate/feedwater recirculation

f) improper valve alignment

g) excessive turbine shaft seal leakages

h) LP turbine efficiency

i) others

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C. Quantification - to achieve total benefit from monitoring performance losses,the effect on unit efficiency must be correctly quantified (use the example insection 4)

4.5 Unit Performance Survey - not since the initial acceptance tests on many fossilunits has an overall level of performance been established, Since that time unitoperating modes have changed, modifications have been made, coal quality haschanged and equipment has aged. With this in mind it is the primary goal of theUnit Performance Survey program to determine the present level of overallperformance and to improve it by identifying and minimizing losses. The mainobjectives are: (Use section 4 to identify particular items in each of the followingto aide in presenting this section)

A. To stress the importance of performance and to provide a means for ‘on-the-job’ performance training for station and results personnel.

B. To establish a present level of performance for each fossil unit.

C. To identify cycle and equipment problems and obtain information for use inproblem resolution.

D. To improve the present level of performance of each fossil unit by identifyingand minimizing losses.

5. Instrumentation and Testing Requirements for Heat Rate Monitoring

5.1 Instruments and Performance - A problem with the objective of efficient unitoperation is one which provides the operators with the tools they require tomaintain all important parameters at an optimal value. The operators should alsobe motivated to utilize this information to strive for efficient unit operation. TheThermal Performance program is jeopardized severely when instrument errorexists. This is an unaccounted-for loss undetectable until a calibration isperformed.

A. ASME Performance test codes - if a plant component performance issuspect, based on on-line testing with normal instrumentation an ASMECode test can be performed to verify, identify and quantify the problems.

B. Instrumentation - Once it has been decided which performance parametersshould be monitored, and the effect of each of these parameters on unitheat rate has been determined, the type if instrumentation to be used andthe frequency of monitoring must be decided

5.2 Testing Program - (use section 5 of the manual for a list of periodic and specialtesting that may be performed)

6. Cycle Isolation

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6.1 Each steam plant has a normal path for the flow of liquid or steam. These can bedifferent at various loads. These paths are usually well represented on the heatbalance diagrams provided by the vendors. What is not shown are the numerouspaths which are available for liquid or steam to escape from the normal flowpaths.

6.2 When flow is diverted from the normal steam path is either lost from the cyclecompletely or returned to a section of the cycle where energy is removed fromthe fluid without providing any useful work.

6.3 The only way to appropriately deal with cycle isolation problems is to performperiodic cycle walkdowns. This will allow a utility to identify the particular lossesthat are occurring in a unit and schedule maintenance activities to correct theseproblems as required.

6.4 Cycle isolation method

A. Prepare a detailed cycle configuration checklist. This should contain all thelines not used during normal operation and they should be isolated. Thisshould also contain all lines which have steam traps to ensure steam trapoperability.

B. The walkdown consists of determining if there is any leakage through theisolation valve by checking either the downstream pipe wall temperature orby listening for flow

C. Lines which terminate at the base slab drain or are vented to theatmosphere can be checked visually.

D. Attention to the deaerator and feedwater vents can be important

E. A list of valves will be produced from the walkdown. This list may need to bereduced. The reduced list should be used on a frequency bases to checkcycle condition. A number of these valves may need repair.

7. Heat Rate Improvement Program

7.1 The financial success of electric utilities in an increasingly competitiveenvironment depends largely on improving plant performance to maintain orlower the cost of producing electricity while meeting ever more stringentenvironmental regulations. A heat rate improvement program can include cyclemodifications, component modifications, improved maintenance practices orincreased use of microprocessor based controls and instrumentation.

7.2 Cycle Modifications - examples of cycle modifications include retrofitting a unitfor variable pressure operation, installing variable speed drives on plantequipment and modification or addition of equipment for improved heat recovery.

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A. Variable Pressure Operation - EPRI report GS-6772 presents a discussionof variable pressure operation for efficiency improvements, a portion of thisreport is highlighted in the manual.

B. Variable Speed Drives - an option increasingly being considered in both newplant designs and life extension projects. Increasing fuel costs andimprovements in technology and reliable have caused a decisive shifttoward the use of this equipment.

1. There are three basic ways a motor’s speed can be changed:

a) change the number of poles on the motor

b) change the slip of the motor

c) change the frequency of the energy supply to the motor

2. Two speed motors - a good example of changing the poses the make aspeed change. These machines do not have the flexibility to meet morethan two plant conditions.

3. Wound rotor motor drives are a form of variable speed drive that hasbeen found in generating stations throughout the years.

4. The most efficient and most commonly used type of variable speedequipment is the adjustable frequency synchronous motor. The benefitsare reduced electrical auxiliary usage at reduced loads.

C. Heat Recovery Modifications - a power plant Rankine thermal cycle sufferstremendous energy losses, therefore it is important to recover even smallheat losses.

1. Circulating water heat recovery - more than half of the fuel burned is lostto the condenser cooling system. These are considered unavoidable,but it is possible to recover some of this waste energy for a secondaryuse such as air preheating.

2. Air preheating evaluation results are shown in table 7-1, Coil designoperating results in table 7-2

3. Heat pipe air heater technology - are high performance heat transferdevices that are simple, inexpensive and reliable over a long service life.There are no moving parts and positive seal connections reduceleakage to effectively zero while high heat transfer rates permit a low-weight, low-volume, low-cost package. (use section 7 for a detaileddiscussion)

D. Component Modifications - there are many areas in the plant where smallinvestments can improve unit heat rate and provide cost savings.

1. Boiler duct expansion joint leaks

24

2. Boiler oxygen measurement is extremely important to proper boileroperation. The proper number of analyzers and the proper location isimportant

3. Windbox damper operation is critical for proper fuel and air mixing.

4. Accurate feedwater heater level controls should be installed andmaintained.

E. Maintenance Practices - if proper unit maintenance is not carefully plannedand executed then unit thermal performance will suffer greatly. A goodperformance program should help drive the maintenance plan.

7.3 Cost Benefit Analysis -EPRI report TR-101249 describes the efforts of SouthernCalifornia Edison Company to improve heat rate at Ormond Beach GeneratingStation Unit 2. A brief of this report is in section 7 of the manual.

8. Appendix A and B

8.1 Appendix A - Procedure for calculating expected unit net heat rate.

A. Purpose - to provide a standard for comparison with actual unit net heatrate.

B. Use section 8 to guide discussion of net heat rate calculations.

8.2 Appendix B - Performance Parameter Accounting Manual.

1

POWER PLANTSYSTEMS

2

1. OVERVIEW: This lesson will provide the student with a review of power plantsystems which will include the following:

1.1 The Water/Steam cycle

1.2 Boiler fuel, air and flue gas systems

1.3 Balance of plant systems

2. References:

2.1 Electric Generation Steam Stations, Skrotzki, Bernhardt

3

TERMINAL OBJECTIVE

At the end of this lesson the student will understand power plantsystems which will include the following: The Water/Steam cycle, Boilerfuel, Air and flue gas systems and Balance of plant systems

ENABLING OBJECTIVES

1. Describe the Water/Steam cycle.

2. List the boiler fuels most commonly used.

3. Describe the air and flue gas systems

4. Describe other major plant systems used to produce electrical power.

4

LESSON OUTLINE

1. PLANT CYCLES

4.1 1.1 STEAM/WATER CYCLE

4.2 1.2 BASIC CYCLE

5. BOILER FUEL, AIR AND FLUE GAS SYSTEMS

6. BALANCE OF PLANT SYSTEMS

5

1. PLANT CYCLES (Water and Steam)

1.1 The steam-water cycle is the heart of the steam-electric power plant. This maincycle uses two primary types of equipment.

A. Shell and tube type heat exchangers (boilers, superheaters, economizers,condensers, heaters)

1. Bring two fluids close to each other, one hot and the other cold,separated by a thin metal wall.

2. The Hot fluid transmits its heat to the cold fluid.

3. Typical problems:

a) Boiler tubes must contain water and steam at very high pressureswhile the outer side of the tube can be at very high temperatures(3500 degrees)

b) Condensers must handle tremendous volumes of exhaust steamand transmit heat between steam and cooling water whosetemperatures differ by only 20 degrees. Occasionally air leaks bythe sealing mechanisms into the condenser. This air can plate outon the surfaces of the condenser tubes increasing the heat transfermedium in which heat must be transferred. The exhaust pressurewill increase and reduce the efficiency of the cycle.

B. Rotating shaft equipment (pumps, fans, turbines)

1. Pumps are used through out the steam-electric plant. Areas where theyare used are:

a) Condensate/Feedwater pumps

b) Chemical addition pumps

c) Fuel oil pumps (oil fired plants)

d) Boiler feed pumps

e) Circulating water pumps

2. Fans are used to provide air to the boiler as:

a) Forced draft fans

b) Induced draft fans

c) Pulverizer fans, primary air fans(Coal fired plants)

3. Turbines are used to provide the rotating motive force for the generatorand for the moving of fluids (turbine driven feedwater pumps)

6

1.2 The basic water-steam cycle is the same for all steam-electric power plants.

9

THE CYCLE:

BOILERS

PUMP TURBINE

CONDENSER

A. Condenser hotwell

1. The condenser hotwell provides a large quantity of boiler quality water tobe circulated through the system to the boiler.

2. This hotwell condensate pumps take a suction on the hotwell andprovide enough discharge pressure to send this water through a numberof condensate heaters

a) The hotwell condensate pumps are usually relatively low pressurepumps and operates with a low suction head (hotwell is under avacuum)

b) These pumps provide suction pressure to a higher head pump.

B. Condensate heaters

1. Condensate heaters provide preheating of the condensate prior toproviding this water to the boiler.

7

2. By preheating the water, less energy has to be added to the water in theboiler to provide the quality of steam required by the turbine/generatorthereby making the cycle more efficient.

3. Heating steam for the condensate heaters is provided to the heatersfrom extraction (bleed) steam from different stages of the turbine. Thesteam provided to the heaters is compatible (temperature) to provide agradual increase in the feedwater temperature.

4. The number of stages of feedwater heating is dependent on the heatingrequirements to make the cycle as efficient as is possible. Too few ortoo many heaters can make a marked difference in cycle efficiency. Thenumber of heaters is a function of plant design.

5. Taking heaters out of service will effect cycle efficiency.

C. Condensate/Feedwater is delivered to the boiler at the required pressure bythe boiler feedwater pump. This pump can be a constant speed motordriven centifugal or variable speed turbine driven centrifugal pump. It canalso be a positive displacement pump.

1. If a constant speed motor driven feedwater pump is used, varying theamount of feedwater to the boiler must be performed by boiler feedwatercontrol valves.

2. If a variable speed turbine driven pump is used, a combination offeedwater pump speed and feedwater control valve position is used tocontrol boiler water level.

3. This water delivered to the boiler will have energy applied such that thewater will be turned into steam.

WATER/STEAM CYCLE

Steam

Un

hea

ted

Do

wn

com

er

Hea

ted

Ris

er

8

D. Boiler

1. Types of boilers used:

a) Natural draft (circulation) - air is allowed to enter the furnace area ofthe boiler to feed the combustion process and the natural flowthrough the boiler to the stack is allowed to occur.

b) Forced draft - air is supplied to the furnace area with forced draftfans and forced though the boiler sections to the stack. This typeboiler produces better heat transfer to all areas of the boiler.

2. Heat left in the combustion gases leaving the boiler is the largest singleloss in a steam generating unit. Economizers are used to recover someof that heat. The economizer is used to preheat feedwater going to thelower boiler drum. The hotter the water entering the boiler, the lessenergy is required to produce the steam required by the unit.

3. Water that is supplied is heated as it flows up the boiler inside boilertubes

4. Heat produced in the boiler through the ignition and burning of fuelsmust be transferred through the boiler tube wall to the water flowinginside. Anything that will reduce the heat transfer of this heat to thewater will reduce cycle efficiency.

5. Steam is produced when the water is heated to the vaporization phase.

6. Superheaters take the saturated steam leaving the steam drum andraises it’s temperature to the desired level.

7. Steam leaves the boiler through main steam lines to the high pressureturbine

8. Reheaters provide for greater efficiency of the IP and LP turbines byincreasing the energy of the steam prior to it reaching the IP and LPturbines. Reheaters also increase the cycle efficiency by using thecombustion gases leaving the furnace.

E. Turbine

1. The turbine is the prime mover of the generator to produce the requiredelectrical power output.

2. There are numerous arrangements of the high pressure and lowpressure turbines that are used to produce the desired electrical output,

a) single casing, single flow

b) single casing, double flow

c) tandem compound, single or single/double flow

d) tandem compound, triple exhaust

9

e) cross compound, double flow

f) cross compound, quadruple exhaust

g) triple cross compound

3. There is usually a single high pressure turbine, possibly an intermediatepressure turbine and one to three low pressure turbines.

4. The high pressure turbine receives the high pressure steam from theboiler and produces the highest amount of torque on the turbine shaft. Alarge amount of the energy is removed from the steam by this turbine.

5. The steam is then piped to the reheater section of the boiler whereadditional temperature and energy is added and then it is directed to theIP and LP turbine(s). The blades on the IP and LP turbines are muchlarger than those on the high pressure turbine. These larger bladesallow the turbine to use more of the steams remaining energy.

9

THE CYCLE:

BOILER

PUMP TURBINE

CONDENSER

F. Condenser

10

1. The steam from the low pressure turbine is exhausted to the condenserwhere it is condensed back to a subcooled liquid to begin thewater/steam cycle over again.

2. Circulating cooling water is supplied to the condenser throughcondenser tubes to condense the steam. The circulating water can besupplied from a lake, river, ocean, cooling towers or any other largesupply of cooling water.

2. BOILER FUEL, AIR and FLUE GAS SYSTEMS

2.1 Boilers use various fuels to provide the necessary heat required to producesteam. These fuels are classified as solid, liquid and gas.

A. Solid fuels are coal (various types of coal are used), wood, coke and eventrash.

1. Coal is ranked by percent moisture, fixed carbon, oxygen and sulfurcontent. All of these are determining characteristics which define howmuch heat (BTUs) and ash content can be expected to be producedwhen burned.

a) The higher the BTU content the less fuel is required to produce thesteam requirements of the plant.

b) The lower the ash and sulfur content the fewer emissions releasedfrom the plant and the less flyash that has to be removed.

c) Flyash plates out on the boiler tubes, especially in the superheatsections of the boiler. This reduces the heat transfer of the hotgases to the water/steam and, therefore, reduces cycle efficiency.

d) Sulfur dioxide is a byproduct of the firing process of coal. The higherthe sulfur content the more Sulfer dioxide is produced. This , whencombined with water, produces sulfuric acid.

2. Coke is a byproduct of oil refineries that may be burned in pulverized-coal-fired boilers.

3. Wood is used usually in the form of waste from lumbering ormanufacturing processes. Special furnaces are required for this fuel.

B. Liquid fuels are oil and coal tars

1. Fuel oils such as diesel fuels to number 6 crude oils are used. Btucontent, water, specific gravity, sulfur and flash point are the test thatoils must undergo prior to use in boilers.

C. Gas used is natural gas

2.2 Air and Flue Gas Systems

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A. Inorder for the fuel supplied to the boiler to burn and burn properly air mustbe added to the fuel mixture. This is usually provided by forced draftfans/primary air fans.

1. Forced draft fans are controlled either from the control room.

2. Induced-draft fans are used to “suck” the gases out of the boiler anddeposit them to the stack at a slightly higher than atmospheric pressure.

B. Flue gas temperature leaving the economizer is still quite high. Some of thisenergy can be removed and transferred to the inlet air through the use of air-heaters. Flue gas outlet temperature must be watched closely to ensureinlet air temperature doesn’t drop too low. If temperature gets too low waterdroplets can form in the air. This mixed with the sulfur products producessulfuric acid.

C. It has already been stated that when burning fuels byproducts of the fuelburning process are produced and must be removed from the boiler and thestack emissions.

1. In the burning of coal slag is produced which falls to the bottom of theboiler. Systems are provided to crush this slag into particles that aresized such that they can be sluiced to a holding tank where trucks canremove them from the plant or sluiced to an area outside of the plant.

2. Flyash is also produced when coal is burned. High efficiencyprecipitators have been installed in the flue gas flow path to catch andfunnel flyash to areas where it can be removed from the plant.

3. BALANCE OF PLANT SYSTEMS

3.1 Coal handing equipment or fuel oil handing equipment as well as coal or fuel oilstorage facilities must be provided. There needs to be enough fuel stored tooperate the plant for an extended period of time.

A. Coal must be moved to conveyor belts, then crushed and moved to otherconveyor belts to move it to the top of the plant where it is stored again fordaily use in the plant. This plant storage or ‘hoppers’ must be refilled daily.The coal is further crushed as necessary to be used in the furnaces in theboilers.

B. Fuel oil must be stored in large tanks and must be kept at a temperaturesuch that the oil will flow easily through the piping but not to hot to where ismay ignite prematurely.

3.2 The circulating water system will have some sort of intake screening system toprevent large objects from entering the condenser waterboxes and possiblyblocking condenser tubes. This will cause a reduction in cycle efficiency.

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3.3 Demineralized water must be either produced in the plant or delivered to theplant by some means. The boilers require clean demineralized water for use inthe boilers. This reduces the amount of deposits and boiler downtime.

3.4 Various oil systems must be provided to lubricate turbine and pump bearings toprevent component failures. This will also require oil purification systems.

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TM-114073Heat Rate Improvement Reference Manual

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Transcript of TM-114073Heat Rate Improvement Reference Manual