STEAM BOILER AND WORKING OF BOILER-
boiler is a closed vessel having minimum capacity of 14.5 and working pressure of 3.5 kgF/cm^2
or above they are used to produce steam from water by combustion of fuel . According to IBR
the closed vessel having minimum capacity of 20. 75 letter comes under boiler act such a boiler
are to be registered at boiler Inspector office. every year various types of inspections will be
carried out by boiler inspector .
or above they are used to produce steam from water by combustion of fuel . According to IBR
the closed vessel having minimum capacity of 20. 75 letter comes under boiler act such a boiler
are to be registered at boiler Inspector office. every year various types of inspections will be
carried out by boiler inspector .
classification of boilers-
according to relative position of water and flue gases
- fire tube - flue gases flow through tubes and water surrounds the tubes is called fire tube Ex Cochran boiler , lancashire boiler , locomotive boiler .
- Water tube- water flows through pipes and flue gases flow over the tube is called water tube boiler
backup , wilcox
Strirling , La-mont ,Laeffler
According to method of circulation of water
- Natural circulation type
- forced circulation type
According to major axis of shell
- Horizontal
- Vertical
- Inclined
According to applications
- Stationery
- Mobile
- Marie
according to working pressure of boiler
- low pressure boiler( 3.5 to 10 KGF/ CM^2)
- medium pressure boiler( 11 to 25 KGF/ CM^2)
- high pressure boiler( more than 25 KGF/ CM^2)
characteristics of high pressure boilers -
the high pressure boilers differ in construction and working from low or medium pressure boilers
following are some characteristics and features of high pressure boilers .
following are some characteristics and features of high pressure boilers .
Method of water circulation -
the water circulation in boiler maybe natural circulation due to density difference air force circulation
by using water pump. in all high pressure boilers, the water is always forced circulation , by using
the separate circulation pump . natural circulation cannot be used for high pressure boiler due to
following -
by using water pump. in all high pressure boilers, the water is always forced circulation , by using
the separate circulation pump . natural circulation cannot be used for high pressure boiler due to
following -
figure shows the steam- water drum connected to unheated Unheated riser
the cold water flows down words in town come tubes and it Rises up due to heat supplied by flue
gases in Riser to . the circulation of water is accuring due to density difference . called natural
circulation . the pressure difference causing the natural circulation of water is -
gases in Riser to . the circulation of water is accuring due to density difference . called natural
circulation . the pressure difference causing the natural circulation of water is -
Δৎ = (ৎc )(g)( h1) - ৎh (g)(h2) ৎc = Density of cold water.
= ((ৎc h1)-(ৎh h2))g
But h1=h2=h
Δৎ = (ৎc - ৎh )g
at critical pressure of 221.2 bar, density of water and steam becomes equal so pressure difference
causing natural circulation becomes zero.
causing natural circulation becomes zero.
the use of natural circulation is limited only upto subcritical boiler with working pressure
release then 25 KGF/ centimetre^2 and above pressure Boiler forced circulation becomes essential
release then 25 KGF/ centimetre^2 and above pressure Boiler forced circulation becomes essential
type of tubing -
in all high pressure boilers the water is circulated through tube . hence they are water tube boilers .
however the single tube having very large length is not used because a pressure drop me a cure
which is directly proportional to the length of tube . hence large number of tubes arranged in parallel
with shortage length are always preferred .
however the single tube having very large length is not used because a pressure drop me a cure
which is directly proportional to the length of tube . hence large number of tubes arranged in parallel
with shortage length are always preferred .
improved methods of heating -
in order to increase rate of heat transfer following improved methods are used in high pressure boilers.
- Deceiving of latent heat of evaporation by keeping boiler pressure higher than critical pressure
- the heating of feed water can be carried by using superheated steam. the maximum of
- the heat transfer rate are also increased by keepingvel. of water inside the tube higher and the
these improved methods of heating are used in different high pressure boilers .
Comparison between low and high pressure boiler .-
Low pressure boiler
|
High pressure boiler
|
2.Finance are not water cooled . 3. this Still waters are factory build and are cheaper than water tube boilers . 4. these are natural circulation type 5.these boilers include water drum . 6. these are heavy and large space is required . 7. Example - cochran boiler , simple vertical , lancashire locomotive . | 1. These ar water tube and are suitable for pressure above 30kgf/ cm^2 capacity 50 tonnes /hr . 2. Furnace walls are water cooled and cold wate walls . 3. these are usually builder in parts which are easily transport. 4. These are forced circulation type . 5. Water drume may or may not present . 6. Low weight and compact . 7. Example - hartmannet , velcox , benson etc . |
La Mont boiler -
this is the first high pressure boiler introduced by
the feed water from hot well is pumped into the boiler by feed pump . most of sensible heat required
is supplied to feed water in Equaliser itself . this hot water from drum is force the circulated through
Radiant section of evaporating tube with the help of pump . the water from inlet header is distributed
to different tubes in proportion of heat absorption capacity of each tube .
is supplied to feed water in Equaliser itself . this hot water from drum is force the circulated through
Radiant section of evaporating tube with the help of pump . the water from inlet header is distributed
to different tubes in proportion of heat absorption capacity of each tube .
Usually , the quantity of water circulated in each cube is 3 times the quantity of steam generated
in the tube . so that no overheating results .
in the tube . so that no overheating results .
the mixture of water and steam formed into then comes back to drum where dry skin is separate Taken
from top of drug and faster too conviction superhit placed in the path of two gases and finally steam is
supplied to the turbine .
from top of drug and faster too conviction superhit placed in the path of two gases and finally steam is
supplied to the turbine .
wireless of this design have been mail in capacity up 6,58,000 kg/hr . or 658 tonn/hr and pressure
and temperature upto 180 kgf/cm^2 and 600^o C resp.
and temperature upto 180 kgf/cm^2 and 600^o C resp.
evaluating performance of boiler -
1. evaporation rate or evaporation capacity
evaporation rate is the amount of steam generator by boiler in kg/hr . this evaporation rate is defined
as various basic such as-
as various basic such as-
area grate , furnace value or quantity of fuel burn .
Evaporation rate = mass of steam generated / area of grate
= kg/m^2.hr
= Ms / Af
Evaporation rate = Mass of steam / vol. Of furnace = Kg/m^3.hr
Evaporation rate = mass of steam generated / amt. Of fuel burnt = Ms/Mf = Kg / Kg of fule .
Evaporation rate is not a good factor for comparing performance of boiler because the parameters
like temperature of feedwater, quality of steam generated , type of fuel used , working pressure are
also affect evaporation rate . so when boilers are generating scheme under different working conditions
( temperature, pressure , quality of steam etc.) the capacity comparison can be best done by
comparing amount of heat error in each boiler for steam generation under standard conditions .
the standard conditions are - atmospheric pressure of 1.013 bar and temperature of feedwater at
100°C , temperature of dry saturated steam at 100°C , this is typically called as -
like temperature of feedwater, quality of steam generated , type of fuel used , working pressure are
also affect evaporation rate . so when boilers are generating scheme under different working conditions
( temperature, pressure , quality of steam etc.) the capacity comparison can be best done by
comparing amount of heat error in each boiler for steam generation under standard conditions .
the standard conditions are - atmospheric pressure of 1.013 bar and temperature of feedwater at
100°C , temperature of dry saturated steam at 100°C , this is typically called as -
form 100°C to 100°C
the latent heat only required to add that is hfg = 2256.9 kj/kg .
2. equivalent evaporation -
for comparing the your operating rate of various boilers working under different conditions and
temperature and pressure term used is equivalent evaporation . late MS kg of steam is actually
generator in the boiler and certain amount of heat ( say Q kg . ) Is required to produce this MS kg of
Steam . the same quantity of heat is supplied to the feed water under standard conditions of temperature
and pressure it will be produced Me kg of Steam .
temperature and pressure term used is equivalent evaporation . late MS kg of steam is actually
generator in the boiler and certain amount of heat ( say Q kg . ) Is required to produce this MS kg of
Steam . the same quantity of heat is supplied to the feed water under standard conditions of temperature
and pressure it will be produced Me kg of Steam .
this quantity of steam Me it said to be equivalent to the quantity of steam Ms the specific
enthalpy of evaporation and 1.01 32 bore corresponding to saturation temperature of 100°C is 225 6.9 kj/kg .
or 2257 kj/kg .
enthalpy of evaporation and 1.01 32 bore corresponding to saturation temperature of 100°C is 225 6.9 kj/kg .
or 2257 kj/kg .
factor of evaporation -
it is defined as the ratio of heat absorbed by 1 kg of feed water to convert it into steam under actual
working condition to heat absorbed by 1 kg of water from and at hundred degree Celsius at 1.0132 bar .
working condition to heat absorbed by 1 kg of water from and at hundred degree Celsius at 1.0132 bar .
FACTOR OF EVAPORATION = (h - hf1) / 2257
Where -
h - enthalpy of Steam produces an actual working and temperature .
hf1 - enthalpy of water at given Temperature .
thus , ratio of equivalent evaporation to actually operation is also called factor of operation and it is
always Greater than 1 .
always Greater than 1 .
3. Boiler Efficiency -
it is defined as the ratio of actual heat utilised to produce steam to the total heat supplied by fuel .
= ms(h-hf1) / mf*calorific value of fuel .
Ms - mass of steam produced per hour .
Mf - mass of fuel burnt per hour .
PROBLEMS -
1) Boiler produce which team having x= 0.9 , the working pressure of boiler is 12 bar . it generate
steam at rate of 640 kg/HR and consume the code and rate of 80 kg/hr . if calorific value of coal is
31400 kJ/kg . and water is filled at 20 degree Celsius.
steam at rate of 640 kg/HR and consume the code and rate of 80 kg/hr . if calorific value of coal is
31400 kJ/kg . and water is filled at 20 degree Celsius.
equivalent evaporation from and at 100 degree Celsius .
factor of evaporation
efficiency of boiler
Answer -
Ms = 640 kg/hr .
Me = Ms(h-hf1) / 2257
= 640 ( (hf+xhfg)-hf1)/ 2257
= 640 ((798.4+0.9*1984.3)-83.74) / 2257
= 709.01 Kg/hr
Per kg of fuel burnt = equivalent evaporation / Kg of fuel burns
= Ms(h-hf1) / 2257*Mf
= 709.01 / 80
= 8.86 Kg/Kg of fuel .
Factor of evaporation = Me / Ms = 1.108 (always > 1)
Effysiancy ()=Ms(h-hf1) / Mf*calorific value = 63.7 %
2 ) 6000 Kg of steam is produced per hour at presser of 8 bar . in a boiler feed with water at 36.5^0 C .
dryness fraction of steam generated is 0.98 . the amount of coal burnt is 750 Kg/hr . cal.
Value = 28000Kj/kg .
dryness fraction of steam generated is 0.98 . the amount of coal burnt is 750 Kg/hr . cal.
Value = 28000Kj/kg .
Calculate -
- Equivalent evaporation per kg of coal .
- Boiler Efficiency
- Boiler HP .
Answer-
Ms = 6000 Kg/hr
Me=Ms(h-hf) / 2257
= Ms(( hf+xhfg)-hf1 ) / 2257
= 6841.83 kg/hr .
Eq. evaporation/Kg = Me/Mf
= 9.122Kg/kg of fuel .
= Ms(h-hf1)/Mf*cal.value
= 73.53%
Boiler HP - the amount of water which a boiler can repo rate per hour from and at hundred degrees
known as power of boiler .
known as power of boiler .
Unit = called boiler HP
one boiler HP = evaporation of 15. 3 kg of per hour from and at 100 degree Celsius into dry
saturated steam .
saturated steam .
boiler HP = ( equivalent evaporation / hr )/15.65 = Ms(h-hf1)/15.65*2257=Me/15.65
Boiler HP = 437.17 HP
Evaporation :
the quantity of steam generated Buy a boiler per hour in KG at full load is known as the operative
capacity of boiler .
capacity of boiler .
Evaporative rate evaporative rate = total steam generator / area of grate = Ms/A = kg/m^2/hr .
= Total steam generated/ volume of furnance = Ms/Vf =kg/m3
=Total steam generator/ total fuel burnt=Ms/Mf=kg/kg Of fuel .
= Total steam generated/ volume of furnance = Ms/Vf =kg/m3
=Total steam generator/ total fuel burnt=Ms/Mf=kg/kg Of fuel .
evaporation capacity is the main specification required for the design of grate ., furnace ,
heating surface and other components .
heating surface and other components .
Equivalent evaporation-
if the generating capacity of to boilers is same but if steam is generated at different pressure
and temperature using the same grade of fuel, then some common base is required to compare
the performance of this to boiler.
and temperature using the same grade of fuel, then some common base is required to compare
the performance of this to boiler.
on the basis of equivalent evaporation the boiler performance can be compared. the quantity of
dry saturated steam that Could be generated by the boiler per unit time from water of hundred
degree Celsius( at a pressure corresponding 200 degree Celsius saturated temperature ) is
known as equivalent evaporation. the quality of heat supplied in this saturation by the boiler to
1 kg of steam is 2257 kg .
dry saturated steam that Could be generated by the boiler per unit time from water of hundred
degree Celsius( at a pressure corresponding 200 degree Celsius saturated temperature ) is
known as equivalent evaporation. the quality of heat supplied in this saturation by the boiler to
1 kg of steam is 2257 kg .
Me = Ms(h-hf1) / 2257 Kg/hr
Me = Equalent mass of steam per unit time
Ms = total mass of steam Per unit time
h = enthalpy of steam per kg under given condition .
hf1 = Specific enthalpy of water at Given feed water condition .
Always, Me > Ms .
Boiler thermal efficiency -
it is the ratio of heat absorbed by the steam from the boiler permit time so the heat liberated by the
combustion of fuel during the same time . -
combustion of fuel during the same time . -
=( Ms(h-hf1) / Mf*CV of fuel ) * 100%
Ms = Mass of steam generated per hour
Mf = mass of fuel burnt per hour .
HEAT LOSS IN BOILER PLAINT -
the total heat produced in the boiler due to combustion of fuel is not utilised for reducing Steel. only
certain amount is used and remaining heat may be lost in following ways -
heat loss to few flue gases -
this can be divided into categories as flue gases contain dry products of combustion as well as steam
generated due to combustion of hydrogen present in the fuel-
generated due to combustion of hydrogen present in the fuel-
heat created away by drive flue gases -
Q1 = Mg*Cpg(Tg-Ta)
Mg = mass of flue gases per kg of fuel .
Cpg = Specific heat of flue gases .
Tg = Temperature of flue gases .
Ta = temperature of air entry in boiler furnace .
(Boiler house / room temperature .)
Heat carried away by steam ( water vapour) from due to combustion of H2 in fuel -
Q2 = Ms1(hs1-hf1)
Where -
Ms1 =Mass of water vapour per kg of fuel due to combustion of H2 in fuel .
hf1= enthalpy of water at boiler house temperature
hs1 = Enthalpy of moisture of flue gases .
Heat loss due to incomplete combustion -
if 1 kg of carbon burns to CO Instead of CO2 It releases 10200 kg of heat where as it can release
35000 kg of heat is it burn to CO2 .
35000 kg of heat is it burn to CO2 .
Incomplete combustion of 1 kg of c results in heat losses = 35000-10200=24800Kg ( loss )
the percent of CO in the flue gases indicates incomplete combustion of fuel. if the percentage of CO
and CO2 in the flue gases by volume are known , then carbon burn to CO instead of CO2 per kg
of fuel is given by -
and CO2 in the flue gases by volume are known , then carbon burn to CO instead of CO2 per kg
of fuel is given by -
mass of C 12 CO= CO/CO+CO2 .
Heat loss due to unburnt fuel -
Small particles of fuel fall through fire great ones and are created away with Ash and clinker. this heat
loss due to unburned fuel is ,
loss due to unburned fuel is ,
convention and radiation losses-
hot surfaces of boiler are always exposed to atmosphere so some amount of heat is always lost by
convention and radiation to surrounding. this loss usually measured and calculated by difference .
convention and radiation to surrounding. this loss usually measured and calculated by difference .
Boiler trial and heat balance -
the boiler performance is to be check the periodically . hence trial/ tests on the boilers are conducted
who's objective are -
who's objective are -
- To determine and check specified generative capacity of boiler when working on full load condition.
- to determine Boiler Efficiency.
- to drop heat balance sheet so that suitable corrective action may be taken to improve efficiency .
Following reactions are taken during boiler trials -
- the quantity of fuel supply and its quality
- the pressure and temperature of steam generator as well as quality of steam generated
- feed water temperature
- flue gases volumetric analysis
- the inlet temperature of air and exhaust temperature of gases
- the mass of fuel left unburnt in ash
the observation should be recorded at running boiler under study conditions at an interval of 15 minute
for 6 hour in case of coal fired boiler and for 4 hours in case of oil fired boilers .
for 6 hour in case of coal fired boiler and for 4 hours in case of oil fired boilers .
HEAT BALANCE SHEET -
It is the systematic representation of total heat supplied and heat distributed on per minute
or hour or per kg of fuel burnt basis .
or hour or per kg of fuel burnt basis .
Heat supplied
|
KJ
|
%
|
heat utilised
|
KJ
|
%
|
Heat supplied by combustion of fuel
toatl
|
Qs=Mf *CV
Qs
|
100%
100%
|
|
Q1=Ms(h-hf1)
Q2=MgCpg(Tg-Ta)
Q3=Ms1(hs1-hf1)
Q4=(Co*(C/100)*24800)
/ (Co+Co2)
Q5=Mf*CV
Q =
|
(Q1/Qs)*100
Similar to all
100%
|
boiler thermal efficiency -
it is the ratio of heat absorbed by steam from the boiler per unit time to the heat liberated by
the combustion of fuel during the same time .
THANKS FOR VISIT
the combustion of fuel during the same time .
THANKS FOR VISIT
No comments:
Post a Comment