DPC & Lecturer SACHIN CHATURVEDI 1 OF ENERGY CONVERSION Lab FILE By: MR. SACHIN CHATURVEDI DPC & LECTURER (B.H.C.E.T.) DEPARTMENT OF MECHANICAL ENGINEERING
DPC & Lecturer SACHIN CHATURVEDI
1
OF
ENERGY CONVERSION Lab FILE
By: MR. SACHIN CHATURVEDI
DPC & LECTURER (B.H.C.E.T.) DEPARTMENT OF MECHANICAL ENGINEERING
DPC & Lecturer SACHIN CHATURVEDI
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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
DPC & Lecturer SACHIN CHATURVEDI
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
DPC & Lecturer SACHIN CHATURVEDI
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
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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.