FUNDED BY THE EUROPEAN UNION … Technical Training ... • It is a shell-and-tube heat exchanger in...

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EUROPEAN UNION

High Pressure Cogeneration for Sugar Sector in Pakistan

Comprehensive Technical

Training

For Sugar Mills Staff on Operation & Maintenance of

Baggase Based HP Cogeneration System

Schedule: 10th July to 13th July, 2017

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EUROPEAN UNION


Thermal Power Plant

Training Lecture

Steam Turbine

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Contents

• Basics of Turbine

• Condenser

• Condenser Air Extraction

• Circulating Water System

• Lube and Control Oil System

• Steam Turbine Gland Steam Sealing System and drains

• Extraction System

• Turning Gear

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What is Steam

Turbine

• A Turbine is a device whichconverts the heat energy ofsteam into the kineticenergy & then to rotationalenergy

• The Motive Power in asteam turbine is obtainedby the rate of change inmomentum of a highvelocity jet of steamimpinging on a curved bladewhich is free to rotate

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Principle of Steam

Turbine

• Steam turbine depends completely upon the dynamic

action of the steam.

• According to Newton’s second law of motion, the force is

proportional to the rate of change of momentum (mass x

velocity).

• If the rate of change of momentum is caused in the steam

by allowing a high velocity jet of steam to pass over

curved blade, the steam will impart a force to the blade.

If the blade is free, it will free off (rotate) in the direction

of force.

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PROCESS A-B: ISENTROPIC/ADIABATIC COMPRESSION PROCESSFEED WATER TO BOILER IS PRESSURIED TO BOILER

FEED WATER HEATED UPTO SATURATION TEMP T1 CALLEDCONSTANT PRESSURE PROCESSPROCESS B-C:

SENSIBLE HEATING POINT C IS INTERMEDIATE POINT OF

VAPOURISATION POINT D IS STEAM IS DRY & SATURATED.FEED WATER IS VAPOURISED CALLED LANTENT HEAT OFCONSTANT PRESSURE & TEMPERATURE PROCESSPROCESS C-D:

ISENTROPIC/ADIABATIC EXPANSION PROCESSEXPANSION OF STEAM TO VACCUM

PROCESS D-E:

AT POINT D, STEAM IS DRY & SATURATED.REJECTION OF HEAT TO CONDENSOR TO CONDENSE THE STEAM.CONSTANT PRESSURE & TEMPERATURE PROCESSPROCESS E-A:

STEAM GENERATION

A

B

C D

E

D'

E'

WORK DONE

HEAT REJECTED

ENTROPY, S

TEM

PERATU

RE,

T

RANKINE CYCLE

RANKINE CYCLE

HEAT REJECTED

TEM

PERATU

RE,

T

A

B WORK DONE

C

G

D

F

RANKINE CYCLE

(Reheat Cycle)

E

ENTROPY, S

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Types of Turbines

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Turbines Classification

Based on Inlet & Outlet Steam Condition

Condensing: • The steam is exhausted to a

condenser

• Low exhaust pressureallows the turbine to makemaximum use of thethermal energy in thesteam and makes the powerplant more efficient

• Nearly all large utilitysteam turbines are of thistype

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Non-Condensing

(Backpressure turbine)

• The exhaust is notcondensed

• The steam is typicallyused for some usefulpurpose such asheating a building.

• Used in processplants such as steelmills, refineries, andpaper mills

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Extraction turbines

• Medium or lowpressure steamrequired by theprocess plant isextracted fromthe intermediatestage of acondensing orback pressureturbine

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Condenser

• Heat transfer device in whichthe exhaust steam of a turbineor an engine is condensed bymeans of cooling water atpressure below atmospheric

• The condenser shell is anairtight casing that encloses thesteam compartment and hasthe cooling water tubes runningthrough it

• The cooling water flows throughhundreds (sometimesthousands) of tubes and theexhaust steam from the turbineis condensed on the outside ofthe tubes

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Components Of

Surface Condenser

• Circulating water inlet and outlet water boxes

• Condenser tubes and tube sheets

• Hot Well

• Condensate or Hot Well pump

• Air removal section

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Advantage of

Condenser

• It increases the work output per kg of steam

supplied to the power plant

• Reduces the specific steam consumption

• Reduces the size of power plant of given

capacity

• Improves the thermal efficiency of power plant

• Saves the cost of water to be supplied to boiler

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Types of

Condensers

Depending upon condensation techniques, there are mainly two types of steam condensers

Jet Steam Condenser• cooling water is sprayed on the exhaust steam

• This is very fast process of condensing steam. But here cooling water and condensed steam are mixed up which can not be separated

Surface Steam Condenser• It is a shell-and-tube heat exchanger in which steam is condensed

on the shell-side while cooling water flows through the tubes

• The condensate and cooling water leave the system separately

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Jet Condensers Vs Surface

Condensers

Jet Condenser Surface Condenser

Process is Faster, Simpler and cheaper. Process is Slow, Complex and Costly.

The process is used where sufficient boiler feed water is available.

The process is used where sufficient boiler feed water is not available and the condensed steamis reused as boiler feed water.

The process is installed where cooling water is easily and cheaply made suitable for boiler feed.

The process is suitable where cooling water can not be easily made suitable for boiler feeding

In Jet condenser, the condensed steam, air, cooling water and uncondensed vapour and other gases are mixed up and can not be easily separated.

In surface condenser, the condensed steam is totally free from cooling water hence can be reused easily as boiler feed water.

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Air Ejector

• It consists of convergent-divergent nozzle and adiffuser.

• Steam from boiler entersfrom ‘a’ nozzle where its K.Eincreases and pressuredecreases

• Pipe ‘c’ is connected tocondenser form where theair mixes with low pressuresteam at ‘b’

• The mixture of steam andair moves to diffuser ‘d’where its velocity decreasesand pressure increases atthe time of leaving

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Why Vacuum is

Maintained?

• Efficiency of steam power plant Increases due to high vacuum and greater enthalpy drop

• More work will be available per kg of steam condensing.

• To remove non condense gas's in steam

• To avoid back pressure on steam turbine

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Turbine Operational

Procedure

• Steam stream meets all the conditions aboutpressure and temperature before to be taken toturbine

• All the systems including: electrical, control,pneumatic system, closed cooling watersystem, condensate system, feed water system,boiler) in normal operation condition

• No more failure on the devices

• The steps for starting turbine as following:-

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Continued

• Placing the turbine lubrication oil system in service:-

• Start one duty pump and place the remain in spare test changeover

• Check parameter: pressure, temperature, condition of cooler,filter.

• Running turning gear system: -

• Turning gear is done before start up and after shutdown turbine.

• The turning gear times depend on the outage duration of turbine(start up) or metal temperature (shutdown), may be from severehours to one day in case of start up. Less than one day: 2 hoursUp to7 days: 6 hours Up to 30 days: 12 hours Over 30 days: 24hours normally, a motor is used for turning gear.

• The turning speed varies from above ten rpm to hundred rpm

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Continued

• Placing the turbine governing system (or EHC) in service:-

• Start the hydraulic pump, check header pressure

• Check condition of valve and pipe is not abnormal

• Trip test (by push Emergency stop button)

• Setting initial loading (for generator driven) or no-load speed (compressor orpump driven) and loading limiter (gradient)

• Pre-run up checks of turbine valves:-

• In order to detect valve malfunction before steam admitted to the turbine ifhaving any problem in valve operation.it must be repaired before turbine startup

• The valves are tested including stop valves and control valves

• During the valve checks, the turbine isolating valves close to prevent steam flowthrough the turbine. once valve completely checked, these valve open to allowsteam flow to the emergency stop valve

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Continued

• Place the condensate cooling water (ccw) system in service:-

• Start ccw pump, check the parameters

• Place the condensate cleaning system in service

• Place vacuum the primary system (for water box) in service (ifinstalled)

• Place the gland sealing steam system in service:-

• To sealing turbine before pulling condensate vacuum

• Before start up, gland sealing steam is extracted from the livesteam system ( or auxiliary steam system) and decreased bothpressure and temperature (pressure: slighter than atmosphericabout 30-40 mbar, temperature: different from metal temperatureabout 50oC)

• Check the gland steam condenser in normal condition

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Continued

• Pulling condenser vacuum:-

• To reduce the tendency of the LP turbine exhaust tooverheat

• To prevent excessive flow induced vibration ofmoving blades in the turbine last stage

• Placing the LP turbine exhaust cooling system inservice:-

• Supply the cooling spray water to protect the LPturbine last stages, condensate tubes fromoverheating when turbine exhaust temperature ishigh

• The control valve will open and closing base onexhaust temperature

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Continued

• Turbine warm-up:• To reduce thermal stress caused by temperature different

between live steam and turbine metal

• Normally, a control valve is used to extract steam from live steamand taken to the turbine

• The temperature rising of turbine metal is limited and depend onthe initial turbine metal temperature, may from 30-100o C/hour.

• After temperature different between live steam and turbinemetal below 50o C, can finish warm-up step

Start - up turbine:• Cold start: Turbine metal temperature < 150o C

• Warm start: Turbine metal temperature :150o C - 410o C

• Hot start: Turbine metal temperature > 410o C

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Check Point Before

Start up

• Before start up, operators must carefully checkperformance of all the system concerned are normal andready, example: vacuum pressure, lube oil pressure andtemperature, position of drain valve

• Setting the speed target, run up rate, initial loading,holding speed, warm up time.. base on mismatch diagram.carefully check in case of auto-setting

• Press start button to run up turbine

• The control valve will slowly open and steam flow to theturbine for rotary -Turning gear disengaged and turbinerun up base on start up curve

• Start up curve

• Start up on DCS

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Monitoring in

operation

• Critical speed

• Shaft eccentricity

• Thermal stress

• Shaft vibration

• Differential Expansion

• Temperature: lube oil temperature, bearing metal

temperature, Turbine exhaust hood

• Vacuum temperature

• Steam qualities: Silica, conductivity, pH

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Circulating Water

System

• The circulating water system removes the latent heat of

vaporization from the steam in the main condenser

• Removing the latent heat of vaporization in the

condenser is the largest single loss of energy in

the power plant's steam-water cycle

• Large heat removal requirement of the condenser

requires a large cooling source, such as cooling towers,

or a large volume of cooling water, such as a lake or

river

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Lube Oil System

Purpose of Lube Oil System:

• To lubricate the bearings of turbo-generator unit,

• Supply sealing oil to generator hydrogen seal and

• Supply oil to Jacking oil pump

• The oil supply of turbine lubricating oil system is in MOP-BOP mode. MOP is directly driven by turbine main shaft & discharge HP oil to drive BOP to run

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Basic Functions of

Lubricating Oil System

• It reduces friction between rotating and fixedelements of the turbine and generator such as occurin the journal bearings and thrust bearings

• This reduces wear, reduces heat and improvesefficiency

• It removes heat from the bearings. This heat mayeither be generated by friction within the bearing orby conduction along the shaft from the turbines

• In mechanical hydraulic governing systems, it is usedas a hydraulic pressure fluid. In these governingsystems, lubricating oil is used for both the pilot oiland power oil systems

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Quality Requirements for

Turbine Oil

• Excellent thermal and oxidation

stability

• Good Viscosity-temperature

characteristics and proper viscosity

• Good low temperature operating

performance

• Excellent demulsibility

• Excellent defoaming performance

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Components of Lube

Oil System

• Lube Oil Reservoir

• Motor (AC and DC) Driven Pumps

• Vapor Extractor

• Lube Oil Coolers

• Lube Oil Filters

• Supply and Return Piping

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Gland Sealing System

• To prevent or reduce steam leakage between the

rotating and stationary components of the turbines if

the steam pressure is higher than atmospheric.

• To prevent or reduce air ingress between the rotating

and stationary components of the turbines if the steam

pressure is less than atmospheric.

• A power loss is associated with steam leakage or air

ingress. Thus, the design of glands and seals is

optimized to reduce any leakage.

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Working Principal

• The seal steam supply valve provides sealing steam from

the main steam system during startup, low loads, and

shutdown

• Upon low header pressure (typically below 3 psig, or 1.2

bar), the main steam supply valve opens, supplying high-

pressure steam to the steam seal header, which directs the

steam to the individual labyrinth seals on the turbine shaft

• As turbine load increases, leakage from the pressurized

sections of the turbine meets or exceeds the requirements of

the seal system for the LP section seals. At this time the

turbine is said to be "self-sealing

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Working Principal

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Extraction System

• An extraction line (sometimes called a bleeder line)on a turbine is nothing more than an openingbetween the turbine stages that allows a portion ofthe steam to bleed off of the turbine.

• This steam can be used for a variety of purposes.Forexample:-

• Steam can be provided to feed water heaters forfeed water heating

• Steam can be used to drive turbine drivenequipment such as boiler feed pumps

• Steam can be sold as process steam to customers

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Turning Gear

• Turning gears are used to slowly rotate the turbine rotor during shutdown, prior to startup, and when the turbine rotor is hot

• Normally turning gears rotate the turbine shaft at 3 to 5 RPM

• Turning gear may be operated locally, remotely, manually, and/or automatically

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Working Principal

• A typical turning gear consists ofan electric motor driving a speedreducing gear train

• The gear train drives a piniongear or "clash pinion" as it isoften called, that can swing intowards and out away from the"bull gear" mounted on theturbine rotor

• The "bull gear" is normallymounted between the turbineand generator couplings

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Thank You for Your Kind Attention

FUNDED BY THE EUROPEAN UNION … Technical Training ... • It is a shell-and-tube heat exchanger in...

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