ENERGY CONVERSION Lab FILE - Er. Sachin Chaturvedi · PDF fileDEPARTMENT OF MECHANICAL...

DPC & Lecturer SACHIN CHATURVEDI

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OF

ENERGY CONVERSION Lab FILE

By: MR. SACHIN CHATURVEDI

DPC & LECTURER (B.H.C.E.T.) DEPARTMENT OF MECHANICAL ENGINEERING


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INDEX

S.

No.

Experiment Date Page No. Signature

1. To study about various types of

mountings & accessories of boiler.

2. To study about low pressure boiler

( Lancashire Boiler ).

3. To study about high pressure boiler

(La-Mont Boiler & Loeffler Boiler).

4. To study the working principle and

working construction of the Impulse

and Reaction steam turbines.

5. To prepare heat balance sheet for

given boiler data.

6. To study about the different

components of Bomb Calorimeter.

7. To study about the throttling

calorimeter.

8. To study the different types of steam

condenser.

9. To study Cooling Tower and find it’s

Efficiency.


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EXPERIMENT NO. 1

OBJECTIVE: To study about various types of mountings & accessories of boiler.

INTRODUCTION:

BOILER: It is a closed vessel in which steam is produced from water by combustion of fuel.

CLASSIFICATION OF BOILERS:

1. According to there Axis (Horizontal, Vertical or Inclined).

If the axis of the boiler is horizontal, the boiler is called as horizontal.

If the axis is vertical, it is called vertical boiler.

If the axis is inclined it is known as inclined boiler.

2. Fire Tube and Water Tube.

In the fire tube boilers, the hot gases are inside the tubes and the water surrounds the tubes.

Examples: Cochran, Lancashire and Locomotive boilers.

In the water tube boilers, the water is inside the tubes and hot gases surround them.

Examples: Babcock and Wilcox boiler.

3. Externally Fired and Internally Fired.

The boiler is known as externally fired if the fire is outside the shell.

Examples: Babcock and Wilcox boiler.

The furnace is located inside the boiler shell.

Examples: Cochran, Lancashire boiler etc.

4. Forced Circulation and Natural Circulation.

In forced circulation type of boilers, the circulation of water is done by a forced pump.

In natural circulation type of boilers, circulation of water in the boiler takes place due to natural

convention currents produced by the application of heat.

Examples: Lancashire, Babcock and Wilcox boiler etc.


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5. High Pressure and Low Pressure Boilers.

The boilers which produce steam at pressures of 80 bar and above are called high pressure boilers.

Examples: Babcock and' Wilcox boilers.

The boilers which produce steam at pressure below 80 bar are called low pressure boilers.

Examples: Cochran, Lancashire and Locomotive boilers.

6. Stationary and Portable.

Primarily, the boilers are classified as either stationary (land) or mobile (marine and locomotive).

Stationary boilers are used for power plant-steam, for central station utility power plants, for plant

process steam etc.

Mobile boilers or portable boilers include locomotive type, and other small units for temporary use

at sites (Large Ships).

7. Single Tube and Multi-tube Boilers.

The fire tube boilers are classified as single tube and multi-tube boilers, depending upon whether

the fire tube is one or more than one.

MOUNTINGS:

These are the fitting and devices which are necessary for the operation and safety of a boiler.

TYPES OF MOUNTINGS:

Safety valves

Water level indicator

A pressure gauge

A steam stop valve

A feed check valve

A Fusible plug

A blow-off cock

SAFETY VALVES:

It is use for release the excess steam when the pressure of steam inside the boiler

exceeds the rated pressure.

Types of safety valve are the following:

Dead weight safety valve

Lever safety valve

Spring loaded safety valve

Gravity safety valve


5 WATER LEVEL INDICATOR:

It is use to indicate the level of water in the boiler constantly.

WATER LEVEL INDICATOR

PRESSURE GAUGE:

It is use to measure the pressure exerted inside the vessel.

PRESSURE GUAGE


6 STEAM STOP VALVE:

It is use to regulate the flow of steam from the boiler to the steam pipe.

STEAM STOP VALVE

FEED CHECK VALVE:

It is use to control the supply the water to the boiler and to prevent the

escaping of water from the boiler when the pump is stopped.

FUSIBLE PLUG:

It is use to protect the boiler against damage due to overheating for low water level.

BLOW-OFF COCK:

It is use to discharge a portion of water when the boiler is empty when necessary

for cleaning, inspection, repair, mud, scale and sludge.


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BLOW-OFF COCK

ACCESSORIES:

These are auxiliary plants required for steam boilers for the proper operation and for the

increase of their efficiency.

TYPES OF ACCESSORIES:

Feed pumps

Injector

Economiser

Air preheater

Superheater

Steam separator

FEED PUMPS:

It is used to deliver feed water to the boiler by the pump.


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FEED PUMP

INJECTOR:

The water is delivered to the boiler by steam pressure; The Kinetic energy of steam is

used to increase the pressure and velocity of feed water.

ECONOMISER:

It is a device in which the waste heat of flue gases is utilized for heating the feed

water.

ECONOMISER

AIR PREHEATER:

It is use to increase the temperature of air before it enters the furnace.


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SUPERHEATER:

It is use to increase the temperature of steam above it saturation point.

SUPERHEATER

STEAM SEPARATOR:

It is use to separate the water particles from the steam to the steam engine or

steam turbine.


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EXPERIMENT NO. 2

OBJECTIVE: To study about low pressure boiler ( Lancashire Boiler ).

INTRODUCTION

It is a stationary, fire tube, internally fired, horizontal and natural circulation boiler. It is

used where working pressure and power required are moderate.

CONSTRUCTION:

These boilers have a cylindrical shell of 1.75m to 2.75m diameter. Its length varies from 7.25m to

9m. It has two internal flue tubes having diameter about 0.4 times that of shell. This type of boiler is set in brick

work forming external flue so that part of the heating surface is on the external shell.

WORKING:

This boiler consist of a long cylindrical external shell(1) built of steel plates, in sections riveted

together. It has two large internal flue tubes(2). These are reduced in diameter at the back end to provide access to

the lower part of the boiler. A fire grate(3) also called furnace, is provided at one end of the flue tubes on which

solid fuel is burnt. At the end of the fire grate, there is a brick arch(5) to deflect the flue gases upwards. The hot

flue gases, after leaving the internal flue tubes pass down to the bottom tube(6). These flue gases move to the

front of the boiler where they divide and flow into the side flue(7). The flue gases then enter to the main flue(9),

which leads them to chimney.


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The damper(8) is fitted at the end of sides flues to control the draught and thus regulate the rate of

generation of steam. These dampers are operated by chain passing over a pulley on the front of the boiler.

A spring loaded safety valve(10) and a stop valve(11) is mounted as shown in fig. The stop valve

supplies steam to the engine as required. A high steam and low water safety valve(12) is also provided.

A perforated feed pipe(14) controlled by a feed valve is used for feeding water uniformly. When

the boiler is strongly heated, the steam generated carries a large quantity of water in the steam space, known as

priming. An anti-priming pipe(15) is provided to separate out water as far as possible. The stop valve thus

receives dry steam.

A blow-off cock(16) removes mud, etc., that settles down at the bottom of the boiler, by forcing

out some of the water. It is also used to empty water in the boiler, whenever required for inspection. Manholes are

provided at the top and bottom of the boiler for cleaning and repair purpose.

SPECIFICATION:

Cylindrical shell – 1.75m to 2.75m diameter.

Length – 7.25m to 9m.

Flue tubes diameter – 0.4 times that of shell.


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EXPERIMENT NO. 3

OBJECTIVE: To study about high pressure boiler (La-Mont Boiler & Loeffler Boiler).

LA-MONT BOILER

INTRODUCTION:

This is a modern high pressure water tube steam boiler working on a forced circulation.

CONSTRUCTION & WORKING:

The circulation is maintained by a centrifugal pump, driven by a steam turbine, using steam from

the boiler. The forced circulation causes the feed water to circulate through the water walls and drums equal to ten

times the mass of steam evaporated. This prevents the turbines from being over-heated.

The feed water passes through the economizer to an evaporating drum. It is then drawn to the

circulating pump delivers the feed to the headers, at a pressure above the drum pressure. The header distributes

water through nozzles into the generating tubes acting in parallel. The water and steam from these tubes passes

into the frum. The steam in the drum is then drawn through the superheater.


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LOEFFLER BOILER

INTRODUCTION:

This is a water tube boiler using a forced circulation. Its main principle of working is to

evaporate the feed water by means of superheated steam from the superheater. The hot gases from the

furnace are used for superheating.

CONSTRUCTION & WORKING:

A diagrammatic sketch of a Loeffler steam boiler. The feed water from the economizer

tubes is forced to mix with the superheated steam in the evaporating drum. The saturated steam, thus

formed is drawn from the evaporating drum by a steam circulating pump.

This steam passes through the tubes of the combination chamber walls and then enters the

superheater. From the superheater, about one-third of the superheated steam passes to the turbine and the

remaining two-third is used to evaporate the feed water in the evaporating drum.


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EXPERIMENT NO. 4

OBJECTIVE: To study the working principle and working construction of the Impulse

and Reaction steam turbines.

INTRODUCTION:

STEAM TURBINE: A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and

converts it into rotary motion.

CLASSIFICATION OF STEAM TURBINES:

1. According to the mode of steam action.

Impulse turbine

Reaction turbine

2. According to the direction of steam flow.

Axial flows turbine

Radial flows turbine

3. According to the exhaust condition of steam.

Condensing turbine

Non-condensing turbine

4. According to the of pressure stages.

Single stage turbines

Multistage impulse and reaction turbines

5. According to the number of cylinders.

Single cylinder turbines

Double cylinder turbines

Three cylinder turbines

Four cylinder turbines

http://en.wikipedia.org/wiki/Thermal_energy

http://en.wikipedia.org/wiki/Steam


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6. According to pressure of steam.

Low pressure turbines, using steam at a pressure of 1.2 to 2 atm

Medium pressure turbines, using steam at pressures of upto 40 atm

High pressure turbines, utilising pressures above 40 atm

IMPULSE TURBINE: A Impulse Turbine is a prime mover in which fluid under pressure enters a stationary nozzle

where its pressure (potential) energy is converted to velocity (kinetic) energy and absorbed by

the rotor.

DE-LEVEL IMPULSE TURBINE:

A De-Level turbine is the simplest type of impulse steam turbine, and is

commonly used in which steam impinges upon revolving blades from a flared nozzle. The flare of the nozzle causes

expansion of the steam, and hence changes its pressure energy into kinetic energy. It has the following main

components:

1. Nozzle. It is a circular guide mechanism, which guides the steam to flow at the designed direction and

velocity. It also regulates the flow of the steam. The nozzle is kept very close to the blades, in

order to minimize the losses due to windage.


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2. Runner and blades. The runner of the De-Laval impulse turbine essentially consists of a circular disc

fixed to a horizontal shaft. On the periphery of the runner, a number of blades are fixed

uniformaly. The steam jet impinges on the buckets, which moves in the direction of the jet. The

movement of the blades makes the runner to rotate.

The surface of the blades is made very smooth to minimize the frictional losses.

The blades are generally made of special steel alloys.

3. Casing. It is an air tight metallic case, which contains the turbine runner and blades. It controls the

movement of steam from the blades to the condenser, and does not permit it to move into the

space. Moreover, it is essential to safeguard the runner against any accident.

REACTION TURBINE: A Reaction Turbines are those turbines in which the energy of the fluid is partly

transformed into kinetic energy before it enters the runner of the turbine.


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PARSON’S REACTION TURBINE: A Parson’s turbine is the simplest type of reaction steam turbine, and is

commonly used in which power is obtained mainly by an impulse force of the incoming steam and small reactive force of

the outgoing steam. It has the following main components:

1. Casting. It is an air-tight metallic case, in which the steam from the boiler turbine, under a high pressure

and temperature, is distributed around the fixed blades (guide mechanism) in the casting. The

casting is designed in such a way that the steam enters the fixed blades with a uniform velocity.

2. Guide mechanism. It is a mechanism, made up with the help of guide blades, in the form of a wheel.

This wheel is, generally, fixed to the casting; that is why these guide blades are also called

fixed blades. The guide blades are properly designed in order to:

a) Allow the steam to enter the runner without shock. This is done by keeping the relative velocity at

inlet of the runner tangential to the blade angle.

b) Allow the required quantity of steam to enter the turbine. This is done by adjusting the openings

of the blades.

The guide blades may be opened or closed by rotating the regulating shaft, thus allowing the

steam to flow according to the need. The regulating shaft is operated by means of a governor whose

function is to govern the turbine ( i.e. to keep speed constant at varying loads).

3. Turbine runner. The turbine runner of a Parson’s reaction turbine essentially consists of runner

blades fixed to a shaft or rings, depending upon the type of the turbine. The blades,

fixed to the runner, are propely designed in order to allow the steam to enter and leave

the runner without shock. The surface of the turbine is made very smooth to minimize

the frictional losses.

4. Drafting tube. The steam, after passing through the runner, flow into the condenser through a tube

called draft tube. It may be noted that if this tube is not provided in the turbine, then the steam

will move freely and will cause steam eddies.


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EXPERIMENT NO. 5

OBJECTIVE: To prepare heat balance sheet for given boiler data.

Pressure of steam = 10 bar

Steam condenser = 540 kg/h

Fuel used = 65 kg/h

Moisture in fuel = 2% by mass

Mass of dry flue gases = 9 kg/kg of fuel

Lower calorific value of fuel = 32,000 kJ/kg

Temperature of the flue gases = 325° C

Temperature of boiler house = 28° C

Feed water temperature = 50° C

Mean specific heat of flue gases = 1 kJ/kg K

Dryness fraction of steam = 0.95

SOLUTION:

Given:

p = 10 bar

ms = 540 kg/h

mf = 65 kg/h mm = 0.02 kg/kg of fuel

mg = kg/kg of fuel

C = 32,000 kJ/kg

tg = 325° C

t = 28° C

t1 = 50° C

cpg = 1 kJ/kg K

x = 0.95

First of all, let us find the heat supplied by 1kg of fuel. Since the moisture in fuel is 0.02kg, therefore

heat supplied by 1kg of fuel

= ( 1- 0.02 ) 32,000 = 31 360 kJ

7. Heat utilized in raising steam per kg of fuel.

We know that the mass of water actually evaporated per kg of fuel,

me = ms / mf = 540 / 65 = 8.31 kg

From steam tables, corresponding to a feed water temperature of 50° C, we find that

hf1 = 209.3 kJ/kg

and corresponding to a steam pressure of 10 bar,we find that

hf = 762.6 kJ/kg ; hfg = 2013.6 kJ/kg

∴ Heat utilized in raising steam per kg of fuel


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= me ( h – hf1 )

= me ( hf + hfg – hf1 )

= 8.31( 762.6 + 0.95 x 2013.6 – 209.3 )

= 20,495 kJ

8. Heat carried away by dry flue gas.

We know that heat carried away by dry flue gas

= mg cpg ( tg – tb )

=9 x 1 (325 – 28 )

=2673 kJ

9. Heat carried away by moisture in fuel per kg of fuel.

From steam tables, corresponding to a temperature of 28° C, we find that

hb = 117.3 kJ/kg

We know that heat carried away by moisture in fuel

= mm [ 2676 + cp ( tg – 100 ) – hb ]

= 0.02 [ 2676 + 2.1 ( 325 – 100 ) – 117.3 ]

= 60.6 kJ

…( Taking cp for superheated steam = 2.1 kJ/kg K )

10. Heat lost by radiation etc.

We know that heat lost by radiation etc. ( by difference )

= 31,360 – ( 20,495 + 2673 + 60.6 )

= 8131.4 kJ

Now complete heat balance sheet per kg of fuel is given below:

Heat supplied kJ Heat expenditure kJ %

Heat supplied by

1kg of fuel 31 360 1. Heat utilized in raising steam

2. Heat carried away by dry flue gases

3. Heat carried away by moisture in fuel

4. Heat lost by radiation etc. ( by difference ).

20 495

2673

60.6

8131.4

65.35

8.53

0.19

25.93

Total 31 360 Total 31 360 100


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EXPERIMENT NO. 6

OBJECTIVE: To study about the different components of Bomb Calorimeter.

INTRODUCTION:

It is used to finding the higher calorific value of solid and liquid fuels. In this calorimeter,

as shown in fig., the fuel is burnt at a constant volume and under a high pressure in a closed vessel

called bomb.

CONSTRUCTION:

The bomb is made mainly of acid-resisting stainless steel, machined from the solid metal, which

is capable of with standing high pressure, heat and corrosion. The cover or head of the bomb carries the oxygen

valve for admitting oxygen and a release valve for exhaust gases. A cradle or carrier ring, carried by the ignition

rods, supports the silica crucible, which in turn holds the sample of fuel under test. There is an ignition wire of

platinum or nichrome which dips into the crucible. It is connected to a battery, kept outside, and can be

sufficiently heated by passing current through it so as to ignite the fuel.

The bomb is completely immersed in a measured quantity of water. The heat, liberated by the combination of fuel, is

absorbed by this water, the bomb and copper vessel. Therise in the temperature of water is measured by a precise

thermometer, known as Beckmann thermometer which reads upto 0.01°C.


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WORKING:

A carefully weighted sample of the fuel is placed in the crucible. Pure oxygen is then admitted

through the oxygen valve, till pressure inside the bomb rises to 30 atm.The bomb is then completely submerged in

a known quantity of water contained in a large copper vessel. This vessel is placed within a large insulated copper

vessel to reduce loss of heat by radiation. When the bomb and its contents have reached steady temperature, fuse

wire is heated up electrically. The fuel ignites, and continues to burn till whole of it is burnt. The heat released

during combustion is absorbed by the surrounding water and the apparatus itself. The rise in temperature of water

is noted.

mf = Mass of fuel sample burnt in the bomb in kg.

H.C.V.= Higher calorific value of the fuel sample in kg/kg.

mw = Mass of water filled in the calorimeter in kg.

me = Water equivalent of apparatus in kg.

t1 = Initial temperature of water and apparatus in °C.

t2 = Final temerature of water and apparatus in °C.

We know that heat liberated by fuel

= mf X H.C.V … (i)

And heat absorbed by water and apparatu

= (mw +me ) cw (t2- t1) ….(ii)

Since the heat liberated is equal to the heat absorbed, therefore equating equation (i) & (ii)

mf X H.C.V. =(mw +me ) cw (t2- t1)

H.C.V.= (mw +me ) cw (t2- t1) kJ/kg

mf

NOTE: To complete for the loss of heat by relation a cooling correct is added observed temp rise is used in the above

expression

H.C.V.= (mw + me ) cw [(t2 – t1) + tc]

mf

tc = Cooling correction.


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EXPERIMENT NO. 7

OBJECTIVE: To study about the throttling calorimeter.

INTRODUCTION:

FUELS:

A substance ( containing mostly carbon and hydrogen ) which, on burning with oxygen in the

atmospheric air, produces a large amount of heat.

Principle Constituents of a Fuel:

Carbon and hydrogen, therefore , it is also known as hydrocarbon fuel. Sometimes, a few traces

of sulphur are also presented in it.

CLASSIFICATION OF FUELS:

The fuel may be classified into the following three general forms:

1. Solid Fuels

2. Liquid Fuels

3. Gaseous Fuels

Each of these fuels may be sub-divided into the following two types:

a) Natural Fuels

b) Prepared Fuels

1. SOLID FUELS:

Natural Solid Fuel : Wood, peat, lignite or brown coal, bituminous coal & anthracite coal.

Prepared Solid Fuel: Wood charcoal, coke, briquetted coal & pulverized coal.

a) WOOD:

It consist of mainly carbon & hydrogen. The wood is converted into coal when burnt in the

absence of air. It is not considered as a commercial fuel, except, in industries, where a large

amount of waste wood is available. The calorific value of wood is 19700kJ/kg.

b) PEAT:

It is a spongy humid substance found in boggy land. It has a large amount of water contents &

therefore has to be dried before use. Its average calorific value is 23000kJ/kg.


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c) LIGNITE OR BROWN COAL:

It contains nearly 40% moisture & 60% of carbon. When dried, it crumbles & hence does not

store well. Due to its brittleness, it is converted into briquettes which can be handled easily. Its

average calorific value is 25000kJ/kg.

d) BITUMINOUS COAL:

It contains very little amount of moisture ( 4 to 6%) & 75 to 90% of carbon. It is aweather-

resistant & burns with a yellow flame. Th average calorific value of bituminous coal is

33500kJ/kg.

e) ANTHRACITE COAL:

It consist 90% or more carbon with a very little volatile matter. It is comparatively smokeless, &

has very little flame. It possesses a high calorific value of about 36000kJ/kg.

f) WOOD CHARCOAL:

It is made by heating wood with a limited supply of air to a temperature not less than 280°C.

g) COKE:

It is produced when coal is strongly heated continuously for 42 to 48 hours in the absence of air

in a closed vessel. This process is known as carbonization of coal. Coke is dull black in colour,

porous & smokeless. It has a high carbon contant ( 85 to 90% ) & has a higher calorific value

than coal.

1. LIQUID FUEL:

Almost all the commercial liquid fuels are derived from natural petroleum. The liquid fuels

consists of hydrocarbons. The following liquid fuels are:

a) PETROL OR GASOLINE:

It is the lightest & the most volatile liquid fuel, mainly used for light petrol engines. It is distilled

at a temperature from 65°C to 220°C.

b) KEROSENE OR PARAFFIN OIL:

It is heavier & less voletile fuel than the petrol, & is used as heating & lighting fuel. It is distilled

at a temperature from 220°C to 345°C.

c) HEAVY FUEL OIL:

The liquid fuels distilled after petrol & kerosene are known as heavy fuel oils. These oils are used

in diesel engines & in oil-fired boilers. These are distilled at a temperature from 345°C to

470°C.


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2. GASEOUS FUELS:

It essentially, consist of marsh gas or methane (CH4) together with small amounts of other gases

such as ethane (C2H6), carbon dioxide (CO2) & carbon monoxide (CO).

The following prepared gases are:

a) COAL GAS:

It is also known as town gas. It is obtained by the carbonization of coal and consists of mainly of

hydrogen, carbon monoxide & various hydrocarbons. It is very rich among combustible gases, &

is largely used in towns for calorific value is about 21000 to 25000kJ/m3.

b) PRODUCER GAS:

It is obtained by the partial combustion of coal, coke,anthracite coal or charcoal in a mixed air

steam blast. Its manufacturing cost is low, & has a calorific value of about 5000 to 6700kJ/m3.

c) WATER GAS:

It is a mixture of hydrogen & carbon monoxide & is made by passing stream over incandescent

coke. As it burns with a blue flame, it is also known as blue water gas.

d) MOND GAS:

It is produced by passing air & large amount of steam over waste coal at about 650°C. It is also

suitable for use in gas engines. Its calorific value is about 5850kJ/m3.

CALORIFIC VALUE OF FUEL:

The calorific value (briefly written as C.V.) or heat value of a solid or heat fuel may be define as

the amount of heat given out bye the complete combustion of 1 kg of fuel. It is expressed in terms of kJ/kg of

fuel. The calorific value of gaseous fuels is, however, expressed in terms of kJ/m3 at a specified temperature

and pressure.

Following are the two types of the calorific value of fuels:

1. Gross or higher calorific value.

2. Net or lower calorific value.

1. GROSS OR HIGHER CALORIFIC VALUE:

The amount of heat obtained by the complete combustion of 1 kg of fuel, when the

products of its combustion are cooled down to the temperature of supplied air, is called the gross

or higher calorific value of fuel. It is briefly written as H.C.V.

If the chemical analysis of a fuel is available, then the higher calorific value of the fuel is

determined by the following formula known Dulong’s formula.

H.C.V.=33800 C + 144000 H2 + 9270S kJ/kg

Where C, H2 and S represent the mass of carbon, hydrogen and sulphur in 1 kg of fuel and the

numerical value indicate their calorific values.


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If the fuel contains oxygen(O2), then it is assumed that the whole amount is combined

with hydrogen having mass equal to 1/8th

of that of oxygen. Therefore, while finding the calorific

value of fuel this amount of hydrogen should be subtracted.

∴ H.C.V.=33800C +144000[H2- (O2/8)] + 9270S kJ/kg

2. NET OR LOWER CALORIFIC VALUE:

When the heat absorbed or carried away by the products of combustion is not recovered

and the steam formed during combustion is not condensed, then the amount of heat obtained per

kg of fuel is known as net or lower calorific value. It is briefly written as L.C.V.

If the higher calorific value is known, then the lower calorific value may be obtained

by subtracting the amount of heat carried away by the products of combustion from H.C.V.

∴ L.C.V.= H.C.V. – heat of steam formed during combustion

Let ms = mass of steam formed in per kg of fuel = 9H2

Since the amount of heat per kg of steam is the latent heat of vaporization of water

corresponding to standard temperature of 15°C, is 2466 kJ/kg,

∴ L.C.V. = H.C.V.- ms X 2466 kJ/kg

= H.C.V. - 9H2X 2466 kJ/kg …(∵ ms = 9H2)


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EXPERIMENT NO. 8

OBJECTIVE: To study the different types of steam condenser.

INTRODUCTION

STEAM CONDENSER:

A steam condenser is a closed vessel into which the steam is exhausted, and condensed after

doing work in an engine cylinder or turbine. A steam condenser has the following two objects:

1. The primary object is to maintain a low pressure ( below atmospheric pressure ) so as to obtain the

maximum possible energy from steam and thus to secure a high efficiency.

2. The secondary object is to supply pure feed water to the hot well, from where it is pumped back to the

boiler.

CLASSIFICATION OF STEAM CONDENSER:

The steam condensers may be broadly classified into the following two types, depending upon

the way in which the steam is condensed:

11. Jet condensers or mixing type condensers, and

12. Surface condensers or non-mixing type condensers.

1. JET CONDENSERS These days, the jet condensers are seldom used because there is some loss of condensate

during the process of condensation and high power requirements for the pumps used. Moreover,

the condensate can not be used as feed water to the boiler as it is not free from salt. However, jet

condensers may be used at places where water of good quality is easily available in sufficient

quantity.

Types of Jet Condensers

The jet condensers may be further classified, on the basis of the direction of flow of the

condensate and the arrangement of the tubing system, into the following four types:

Parallel flow jet condenser

Counter flow or low level jet condenser

Barometric or high level jet condenser

Ejector condenser.

Parallel Flow Jet Condensers

In parallel flow jet condensers, both the steam and water enter at the top, and the mixture

is removed from the bottom.


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The principle of this condenser is shown in fig. The exhaust steam is condensed when it

mixes up with water. The condensate, cooling water and air flow downwards and are removed by

two separate pumps known as air pump and condensate pump. Sometimes, a single pump known

as wet air pump, is also used to remove both air and condensate. But the former gives a greater

vacuum . The condensate pump delivers the condensate to the hot well, from where surplus water

flows to the cooling water tank through an overflow pipe.

Counterflow or Low Level Jet Condensers In counterflow or low level jet condensers, the exhaust steam enters the bottom, flows upwards

and meets the downcoming cooling water.

The vacuum is created by the air pump, placed at the top of the condenser shell. This draws the

supply of cooling water, which falls in a large number of the jets, through perforated conical plate as

shown in fig. The falling water is caught in the trays, from which it escapes in a second series of jets and

meets the exhaust steam entering at the bottom. The rapid condensation occurs, and the condensate and

cooling water descends through a vertical pipe to the condensate pump, which delivers it to hot well.


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Barometric or High Level Jet Condensers

These condensers are provided at a high level with a long vertical discharge pipe as

shown in fig. In high level jet condensers, exhaust steam enters at the bottom, flows upwards and

meets the downcoming cooling water in the same way as that of level jet condenser. The vacuum

is created by the air pump, placed at the top of the condenser shell. The condensate and cooling

water descends through a vertical pipe to the hot well without the aid of any pump. The surplus

water from the hot well flows to the cooling water tank through an overflow pipe.


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Ejector Condensers In ejector condensers, the steam and water mix up while passing through a series of metal cones.

Water enters at the top through a number of guide cones. The exhaust steam enters the condenser through

non-return valve arrangement. The steam and air then passes through the hollow truncated cones. After

that it is dragged into the diverging cones where its kinetic energy is partly transformed to pressure energy.

The condensate and cooling water is then discharge to the hot well as shown in fig.

2. SURFACE CONDENSER

A surface condenser has a great advantage over the jet condensers, as the condensate does not

mix up with the cooling water. As a result of this, whole condensate can be reused in the boiler. This type

of condenser is essential in ships which can carry only a limited quantity of fresh water for the boilers. It is

also widely used in land installations, where inferior water is available of the better quality of water for

feed is to be used economically.


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Figure shows a longitudinal section of a two pass surface condenser. It consist of a horizontal cast

cylindrical vessel packed with tubes, through which the cooling water flows. The ends of the condenser are

cut off by vertical perforated type plates into which water tubes are fixed. This is done in such a manner

that the leakage of water into the centre condensing space is prevented. The water tubes pass horizontally

through the main condensing space for the steam. The steam enters at the top and is forced to flow

downwards over the tubes due to thesuction of the extraction pump at the bottom. The cooling water flows

in one direction through the lower half of the tubes and returns in opposite direction through the upper

half.

Types of Surface Condensers

The surface condensers may be further classified on the basis of the direction of flow of

the condensate, the arrangement of tubing system and the position of the extraction pump, into the

following four types:

Down flow surface condenser.

Central flow surface condenser.

Regenerative surface condenser.

Evaporative condenser.

Down Flow Surface Condensers

In down flow surface condensers, the exhaust steam enters at the top and flow

downwards over the tubes due to force of gravity as well as suction of the extraction pump fitted

at the bottom. The condensate is collected at the bottom and then pumped by the extraction pump.

The dry air pump suction pipe, which is provided near the bottom, is covered by a baffle so as to

prevent the entry of condensed steam into it, as shown in fig.

As the steam flows perpendicular to the direction of flow of cooling water ( inside the

tubes ), this is also called a cross-surface condenser.

Central Flow Surface Condensers

In central flow surface condensers, the exhaust steam enters at the top and flow

downwards. The suction pipe of the air extraction pump is placed in the centre of the tube nest as

shown in fig. This causes the steam to flow radially inwards over the tubes towards the suction


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pipe. The condensate is collected at the bottom and then pumped by the extraction pump as shown

in fig.

The central flow surface condenser is an improvement over the down flow type as the

steam is directed radially inward by a volut casing around the tube nest. It, thus, gives an access to

the whole periphery of the tubes.

Regenerative Surface Condensers

In regenerative surface condensers, the condensate is heated by a regenerative method.

The condensate is falling. At the same time, a current of air circulates over the water film, causing

rapid evaporation of some of the cooling water. As a result of this, the steam circulating inside the

pipe is condensed. The remaining cooling water is collected at an increased temperature and is

reused. Its original temperature is restored by the addition of the requisite quantity of cold water.

Evaporative Condenser

The steam to be condensed enters at the top of a series of the pipes outside of which a

film of cold water is falling. At the same time, a current of air circulates over the water film,

causing rapid evaporation of some of the cooling water. As a result of this, the steam circulating

inside the pipe is condensed. The remaining cooling water is collected at an increased temperature

and is reused. Its original temperature is restored by the addition of the requisite quantity of cold

water.


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The evaporative condensers are provided when the circulating water is to be used again

and again. These condensers consist of gilled piping. Which is bent backwards and forwards and

placed in a vertical plane, as shown in fig.


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EXPERIMENT NO. 9

OBJECTIVE: To study Cooling Tower and find it’s Efficiency.

INTRODUCTION:

This section briefly describes the main features of cooling towers.

COOLING TOWER:

Cooled water is needed for, for example, air conditioners, manufacturing processes or power

generation. A cooling tower is an equipment used to reduce the temperature of a water stream by extracting

heat from water and emitting it to the atmosphere. Cooling towers make use of evaporation whereby some of

the water is evaporated into a moving air stream and subsequently discharged into the atmosphere. As a

result, the remainder of the water is cooled down significantly. Cooling towers are able to lower the water

temperatures more than devices that use only air to reject heat, like the radiator in a car, and are therefore

more cost-effective and energy efficient.

Components of a cooling tower The basic components of a cooling tower include the frame and casing, fill, cold-water basin,

drift eliminators, air inlet, louvers, nozzles and fans. These are described below.1

Frame and casin:

Most towers have structural frames that support the exterior enclosures (casings), motors, fans, and

other components. With some smaller designs, such as some glass fiber units, the casing may essentially be

the frame.

Fill:

Most towers employ fills (made of plastic or wood) to facilitate heat transfer by maximizing water

and air contact. There are two types of fill:

o Splash fill:

water falls over successive layers of horizontal splash bars, continuously breaking into smaller

droplets, while also wetting the fill surface. Plastic splash fills promote better heat transfer than wood splash

fills.

o Film fill:

consists of thin, closely spaced plastic surfaces over which the water spreads, forming a thin film in

contact with the air. These surfaces may be flat, corrugated, honeycombed, or other patterns. The film type of

fill is the more efficient and provides same heat transfer in a smaller volume than the splash fill.

Cold-water basin:

The cold-water basin is located at or near the bottom of the tower, and it receives the cooled water

that flows down through the tower and fill. The basin usually has a sump or low point for the cold-water

discharge connection. In many tower designs, the coldwater basin is beneath the entire fill. In some forced

draft counter flow design, however, the water at the bottom of the fill is channeled to a perimeter trough that

functions as the coldwater basin. Propeller fans are mounted beneath the fill to blow the air up through the

tower. With this design, the tower is mounted on legs, providing easy access to the fans and their motors.

Drift eliminators:


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These capture water droplets entrapped in the air stream that otherwise would be lost to the

atmosphere.

Air inlet:

This is the point of entry for the air entering a tower. The inlet may take up an entire side of a tower

(cross-flow design) or be located low on the side or the bottom of the tower (counter-flow design).

Louvers:

Generally, cross-flow towers have inlet louvers. The purpose of louvers is to equalize air flow into

the fill and retain the water within the tower. Many counter flow tower designs do not require louvers.

Nozzles:

These spray water to wet the fill. Uniform water distribution at the top of the fill is essential to

achieve proper wetting of the entire fill surface. Nozzles can either be fixed and spray in a round or square

patterns, or they can be part of a rotating assembly as found in some circular cross-section towers.

Fans:

Both axial (propeller type) and centrifugal fans are used in towers. Generally, propeller fans are used

in induced draft towers and both propeller and centrifugal fans are found in forced draft towers. Depending

upon their size, the type of propeller fans used is either fixed or variable pitch. A fan with non-automatic

adjustable pitch blades can be used over a wide kW range because the fan can be adjusted to deliver the

desired air flow at the lowest power consumption. Automatic variable pitch blades can vary air flow in

response to changing load conditions.

Tower materials Originally, cooling towers were constructed primarily with wood, including the frame, casing,

louvers, fill and cold-water basin. Sometimes the cold-water basin was made of concrete. Today,

manufacturers use a variety of materials to construct cooling towers. Materials are chosen to enhance

corrosion resistance, reduce maintenance, and promote reliability and long service life. Galvanized steel,

various grades of stainless steel, glass fiber, and concrete are widely used in tower construction, as well as

aluminum and plastics for some components.

Frame and casing.

Wooden towers are still available, but many components are made of different materials, such as the

casing around the wooden framework of glass fiber, the inlet air louvers of glass fiber, the fill of plastic and

the cold-water basin of steel. Many towers (casings and basins) are constructed of galvanized steel or, where

a corrosive atmosphere is a problem, the tower and/or the basis are made of stainless steel. Larger towers

sometimes are made of concrete. Glass fiber is also widely used for cooling tower casings and basins,

because they extend the life of the cooling tower and provide protection against harmful chemicals.

Fill.

Plastics are widely used for fill, including PVC, polypropylene, and other polymers. When water

conditions require the use of splash fill, treated wood splash fill is still used in wooden towers, but plastic

splash fill is also widely used. Because of greater heat transfer efficiency, film fill is chosen for applications

where the circulating water is generally free of debris that could block the fill passageways.

Nozzles.

Plastics are also widely used for nozzles. Many nozzles are made of PVC, ABS, polypropylene, and

glass-filled nylon.

Fans.

Aluminum, glass fiber and hot-dipped galvanized steel are commonly used fan materials. Centrifugal

fans are often fabricated from galvanized steel. Propeller fans are made from galvanized steel, aluminum, or

molded glass fiber reinforced plastic.

TYPES OF COOLING TOWERS


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This section describes the two main types of cooling towers: the natural draft and mechanical draft

cooling towers.

Natural draft cooling tower The natural draft or hyperbolic cooling tower makes use of the difference in temperature between the

ambient air and the hotter air inside the tower. As hot air moves upwards through the tower (because hot air

rises), fresh cool air is drawn into the tower through an air inlet at the bottom. Due to the layout of the tower,

no fan is required and there is almost no circulation of hot air that could affect the performance. Concrete is

used for the tower shell with a height of up to 200 m. These cooling towers are mostly only for large heat

duties because large concrete structures are expensive.

There are two main types of natural draft towers:

o Cross flow tower : air is drawn across the falling water and the fill is located outside the tower

o Counter flow tower : air is drawn up through the falling water and the fill is therefore located inside the

tower, although design depends on specific site conditions

Cross flow natural draft cooling tower Counter flow natural draft cooling tower

Forced draft cooling tower Air is blown through the tower by a fan located in the air inlet. Forced draft cooling towers are very similar to

induced draft cooling towers. The primarydifference is that the air is blown in at the bottom of the tower and exits at

the top. Forced draftcooling towers are the forerunner to induced draft cooling towers. Water distribution problemsand

recirculation difficulties discourage the use of forced draft cooling towers.


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Forced Draft Cooling Tower

Induced draft cooling towers

Induced draft cooling towers are constructed such that the incomingcirculating water is dispersed

throughout the cooling tower via a spray header. The spray isdirected down over baffles that are designed to

maximize the contact between water and air. The air is drawn through the baffled area by large circulating fans

and causes the evaporation andthe cooling of the water.

Induced draft cross flow cooling tower:

o water enters at top and passes over fill

o air enters on one side (single-flow tower) or opposite sides (double-flow tower)

o an induced draft fan draws air across fill towards exit at top of tower

Induced draft cross flow cooling tower


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Induced draft counter flow cooling tower

o hot water enters at the top

o air enters bottom and exits at the top

o uses forced and induced draft fans

Induced draft counter flow cooling tower

Cooling towers are rated in terms of approach and range, where

the approach is the difference in temperature between the cooled-water temperature and the entering-airwet bulb

- twb - temperature

the range is the temperature difference between the water inlet and exit states

Since a cooling tower is based on evaporative cooling the maximum cooling tower efficiency is limited by the wet bulb

temperature - twb - of the cooling air.

Cooling Tower Efficiency

The cooling tower efficiency can be expressed as

μ = (ti - to) 100 / (ti - twb) (1)

where

μ = cooling tower efficiency - common range between 70 - 75%

ti = inlet temperature of water to the tower (oC,

oF)

to = outlet temperature of water from the tower (oC,

oF)

twb = wet bulb temperature of air (oC,

oF)

The temperature difference between inlet and outlet water (ti - to) is normally in the range 10 - 15 oF.

ENERGY CONVERSION Lab FILE - Er. Sachin Chaturvedi · PDF fileDEPARTMENT OF MECHANICAL...

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