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INTRODUCTION TO BOILER
A boiler is a closed vessel in which water or other fluid is heated. The heated or
vaporized fluid of the boiler for use in various processes or heating applications
Types of Boilers:
Based on Principle of Working:
1. Fire tube boilers
2. Water tube boilers
1. Fire tube boilers:
Fire-tube boiler is a type of boiler in which hot gases from a fire pass
through one or more tubes running through a sealed container of water.
The heat of the gases is transferred through the walls of the tubes by thermal
conduction, heating the water and ultimately creating steam. There are Several
Types of Fire tube Boilers, they are
� Cornish Boiler: This boiler has a long horizontal cylinder with a single
large flue consisting the fire
Figure 1: Cornish Boiler
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� Lancashire boiler: Same as Cornish boiler, this has two large flues
compressing the fires. It has three major constituents, double walled
firebox, horizontal and cylindrical boiler barrel consists with small flue
tubes and smoke box provided with chimney for exhaust gases. They are
used in traction engines, portable engines and some other steam road
vehicles
Figure 2: Lancashire Boiler
� Scotch marine boiler: This form of boiler uses large number of small
diameter tubes. It provides greater heating surface area for both weight
and volume
Figure 3: Scotch Marine Boiler
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2. Water tube boilers:
Water tube boiler is a type of boiler in which water passes through the
boiler where the tubes are placed in combustion chamber. They are
� Babcock & Wilcox boiler: Babcock and Wilcox, this type has a single drum,
with feed water drawn from the bottom of the drum into a header that
supplies inclined water-tubes. The water tubes supply steam back into the
top of the drum. Furnaces are located below the tubes and drum
Figure 4: Babcock & Wilcox Boiler
� Yarrow: this type has three drums in a delta formation connected by water
tubes. The drums are linked by straight water tubes, allowing easy tube-
cleaning. This does however mean that the tubes enter the drums at
varying angles, a more difficult joint to caulk. Outside the firebox, a pair of
'cold-leg' pipes between each drum act as 'down comers'
Figure 5: Yarrow Boiler
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� Thorny croft: Thorny croft type features a single steam drum with two sets
of water tubes either side of the furnace. These tubes, especially the
central set, have sharp curves. Apart from obvious difficulties in cleaning
them, this may also give rise to bending forces as the tubes warm up,
tending to pull them loose from the tube plate and creating a leak.
Figure 6: Thorny croft Boiler
Based on Design:
1. Packaged boiler
2. Fluidized Bed Combustion Boiler
3. Stoker Fired Boiler
4. Pulverized Fuel Boiler
5. Waste Heat Boiler
6. Thermic Fluid Heater
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1. Packaged boiler:-
The packaged boiler is so called because it comes as a complete package.
Once delivered to site, it requires only the steam, water pipe work, fuel supply
and electrical connections to be made for it to become operational. Package
boilers are generally of shell type with fire tube design so as to achieve high
heat transfer rates by both radiation and convection
Figure 7: Packaged Boiler
2. Fluidized Bed Combustion Boiler
Fluidized bed combustion (FBC) has emerged as a viable alternative and
has significant advantages over conventional firing system and offers multiple
benefits – compact boiler design, fuel flexibility, higher combustion efficiency
and reduced emission of noxious pollutants such as SOx and NOx. The fuels
burnt in these boilers include coal, washery rejects, rice husk, bagasse & other
agricultural wastes. The fluidized bed boilers have a wide capacity range- 0.5
T/hr to over 100 T/hr
� Atmospheric Fluidized Bed Combustion (AFBC) Boiler: Most operational
boiler of this type is of the Atmospheric Fluidized Bed Combustion. (AFBC).
This involves little more than adding a fluidized bed combustor to a
conventional shell boiler. Such systems have similarly being installed in
conjunction with conventional water tube boiler
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� Pressurized Fluidized Bed Combustion (PFBC) Boiler: In Pressurized
Fluidized Bed Combustion (PFBC) type, a compressor supplies the Forced
Draft (FD) air and the combustor is a pressure vessel. The heat release
rate in the bed is proportional to the bed pressure and hence a deep bed is
used to extract large amount of heat. This will improve the combustion
efficiency and sulphur dioxide absorption in the bed. The steam is
generated in the two tube bundles, one in the bed and one above it. Hot
flue gases drive a power generating gas turbine. The PFBC system can be
used for cogeneration (steam and electricity) or combined cycle power
generation. The combined cycle operation (gas turbine & steam turbine)
improves the overall conversion efficiency by 5 to 8%
� Atmospheric Circulating Fluidized Bed Combustion Boilers (CFBC): In a
circulating system the bed parameters are so maintained as to promote
solids elutriation from the bed. They are lifted in a relatively dilute phase
in a solids riser, and a down-comer with a cyclone provides a return path
for the solids. There are no steam generation tubes immersed in the bed.
Generation and super heating of steam takes place in the convection
section, water walls, at the exit of the riser
Figure 8: Fluidized Bed Combustion Boiler
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3. Stoker Fired Boiler
Stokers are classified according to the method of feeding fuel to the
furnace and by the type of grate. The main classifications are spreader stoker
and chain-gate or traveling-gate stoker
� Spreader Stokers: Spreader stokers utilize a combination of suspension
burning and grate burning. The coal is continually fed into the furnace
above a burning bed of coal. The coal fines are burned in suspension; the
larger particles fall to the grate, where they are burned in a thin, fast-
burning coal bed. This method of firing provides good flexibility to meet
load fluctuations, since ignition is almost instantaneous when firing rate is
increased. Due to this, the spreader stoker is favored over other types of
stokers in many industrial applications
� Chain-grate or Traveling-grate Stoker: Coal is fed onto one end of a
moving steel grate. As grate moves along the length of the furnace, the
coal burns before dropping off at the end as ash. Some degree of skill is
required, particularly when setting up the grate, air dampers and baffles,
to ensure clean combustion leaving the minimum un-burnt carbon in ash
Figure 9: Stoker Fired Boiler
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4. Pulverized Fuel Boiler
Most coal-fired power station boilers use pulverized coal, and many of the
larger industrial water-tube boilers also use this pulverized fuel. This technology
is well developed, and there are thousands of units around the world,
accounting for well over 90% of coal-fired capacity
Figure 10: Pulverized Fuel Boiler
5. Waste Heat Boiler
Wherever the waste heat is available at medium or high temperatures, a
waste heat boiler can be installed economically. Wherever the steam demand is
more than the steam generated during waste heat, auxiliary fuel burners are
also used. If there is no direct use of steam, the steam may be let down in a
steam turbine-generator set and power produced from it. It is widely used in
the heat recovery from exhaust gases from gas turbines and diesel engines
Figure 11: Waste Heat Boiler
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6. Thermic Fluid Heater
In recent times, Thermic fluid heaters have found wide application for
indirect process heating. Employing petroleum - based fluids as the heat
transfer medium, these heaters provide constantly maintainable temperatures
for the user equipment. The combustion system comprises of a fixed grate with
mechanical draft arrangements The modern oil fired Thermic fluid heater
consists of a double coil, three pass construction and fitted with modulated
pressure jet system. The Thermic fluid, which acts as a heat carrier, is heated
up in the heater and circulated through the user equipment. There it transfers
heat for the process through a heat exchanger and the fluid is then returned to
the heater. The flow of Thermic fluid at the user end is controlled by a
pneumatically operated control valve, based on the operating temperature. The
heater operates on low or high fire depending on the return oil temperature,
which varies with the system load
Figure 12: Thermic Fluid Heater
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Fluidized Bed Combustion Boiler:
The Project work is now coming to the main part i.e., Fluidized Bed Combustion Boiler,
where the Fluidized beds suspend the solid fuels on upward-blowing jets of air during
the combustion process. These Boilers are more flexible than conventional plants in
that they can be fired on coal and other fuels. Some of the Major Components of the
Fluidized Bed Combustion Boiler are:
1. Induced Draft Fan
2. Forced Draft Fan
3. Booster Fan
4. Coal Feeder
5. Mobrey
6. Chimney
7. Coal Crusher
8. Safety Valves
9. Stop Valve
10. Air Vent Valve
11. Blow down Valve
12. Feed Check Valve
13. Refractory
14. Level Indicators
1. Induced Draft Fan: - The Induced Fan is used to feed the hot products of
the combustion extracted from the Furnace when the fuel has burnt and
feed to the chimney.
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2. Forced Draft Fan: - The heat used for generating the steam is obtained
by burning fuel in a furnace, or combustion chamber, but to do this
Process, it requires the provision of air which is provided by a forced-
draught.
3. Booster Fan: - In Additional to the above two fans, one more fan is also
available to overcome the draught losses if the resistance was not
anticipated when the plant was originally designed. These are called as
Booster Fan.
4. Coal Feeder: - The Coal feeder is used to feed the Fuel Continuously
without any speed variations to avoid the disturbances to the Boiler.
These are equipped with dust collection system to ensure pollution to
remain under control.
5. Mobrey: - Mobrey Controls are a comprehensive range of magnetically
operated water isolating and sequential controls. They are designed to
meet the requirements for automatic on/off control of boiler feed pump,
burner cut-out, high and/or low level alarm or any combination. It also
provides the Positive Purging of the Water Connection, float chamber and
Steam Connection.
6. Chimney: - A chimney is a structure for venting hot flue gases or smoke
from a boiler, stove, furnace or fireplace to the outside atmosphere.
Chimneys are typically vertical, or as near as possible to vertical, to
ensure that the gases flow smoothly, drawing air into the combustion in
what is known as the stack, or chimney, effect. The space inside a
chimney is called a flue. The height of chimneys plays a role in their
ability to transfer flue gases using stack effect, the dispersion of
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pollutants at higher altitude helps to ease down its influence on
surroundings. In the case of aggressive output, the tall chimney allows
particles to self-neutralization in the air before they reach the ground.
7. Coal Crusher: - Most of ‘boilers’ fuel is coal, so coal crusher is the main
part for crushing coal. We should make optimal design of a coal crushing
system. In order to promote the concept of coal particles and
prefabricated. We use prefabricated, dry coal shed stacked, two broken
and three screening can be a fundamental solution to block coal bunker
coal, the furnace bed material quality degradation trends and improve
coal preparation of system reliability. So, the Coal Crusher relies on its
unique advantages in a wide range of applications in the boiler system.
8. Safety Valves: - A safety valve is a valve mechanism for the automatic
release of a substance from a boiler, pressure vessel, or other system
when the pressure or temperature exceeds its preset limits.
9. Stop Valve: - A non-return stop valve in the Steam line is used to control
the flow of Steam to the desired output wherever required.
10. Air Vent Valve: - To remove the Air from the inner vessel of the boiler to
feed the water through feed check valve.
11. Blow down Valve: - This Valve is used to remove suspended solids
present in the system which are caused by feed water contamination, by
internal chemical treatment precipitates, or by exceeding the solubility
limits of otherwise soluble salts.
12. Feed Check Valve: - A non-return stop valve in the feed water line. This
may be fitted to the side of the boiler, just below the water level, or to
the top of the boiler.
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13. Refractory: - The main purpose of refractory material is used inside a
boiler is to contain the heat generated by burning of the fuel in the
furnace. It is important that these materials have insulating properties
and are able to withstand high temperatures. Refractory material should
have sufficient mechanical strength and are able to expand and contract
uniformly with temperature change without cracking.
14. Level Indicators: - These Indicators are used to show the operator the
level of fluid available in the boiler, also known as a sight glass, water
gauge or water column.
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OPERATION OF BOILER
General Procedures:-
1. Check the levels of Feed Water Tank and it should be ¾ % and the feed
water softness to be checked every 4 hours of Operation, if exceed below
mentioned parameters, regenerate the water softener.
a. TDS should maintain below 100 PPM
b. Hardness should maintain below 5 PPM
c. pH should maintain between 8.5 to 9.5
2. Make sure no Excessive sound is coming from motors of fans or any
other moving parts.
3. Make sure all the valves and joints are leak-proof.
4. Induced Draft Fan should maintain at 60 mm Wc, Furnace Draft should
maintain within -2 to -5 mm Wc to avoid the Back Fire
5. Forced Draft should maintain minimum of 300mm Wc to avoid No Firing
and it can be up to 600mm Wc
6. Maintain the Feed Pump back Pressure 15 Kg/cm2
7. Blow down the boiler at regular intervals to maintain the below
mentioned parameters
a. TDS should maintain between 3500 to 4500 PPM
b. Hardness should maintain below 5 PPM
c. pH should maintain between 11 to 12
8. Blow down the Mobrey level Switch and the gauge glasses once in a shift
9. Drain the feed water pre-heating tank once in a shift to remove any
particles that may have settled down.
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10. Ensure that fuel is properly sized. There should be no metal pieces,
stones, etc in the fuel
11. Check that the bed height is at pre-set level. Operate the ash drain and
adjust to set levels, if level rises
12. Check whether the stack temperature is within desired range of given
load. If higher check for fouling o heat transfer surface or blockings of
flue gas passages.
Start-up Procedure:-
1. Test the Boiler Feed Water for its suitability as per standard parameters.
2. Check that the soft water service tank is full.
3. Boiler Inner Vessel Water Level should be ½ to ¾%.
4. Ensure that the water filters and strainers are clean.
5. Air Vent Value should be Open.
6. Blown down Valve and Stop Valve should be Closed.
7. Charge the normal sand of particle size 0.5 to 1.5mm for husk, and
prepare a sand bed just touching the bottom point of tubes in the bed to
make 8 inch deep bed of uniform level.
8. Close the main steam stop valve.
9. Close the ID damper (Manually) and FD fan dampers to minimum.
10. Open the fuel dampers (under the bunker) required for fuel firing.
11. Check and ensure that all other safeties are within acceptable limits and
the water level is enough.
12. Feed the Charcoal on the Bed manually and start Firing.
13. Sprinkle diesel or kerosene over the bed and ignite the charcoal.
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14. After the Charcoal catches full fire then ON the ID & FD Fans and run
them as per the requirement.
15. After the Temperature is raised up to 5500C, the bed looks like bubbling
lava and is ready for charging fuel
16. Then Switch on the Coal Feed Conveyor to feed the fuel automatically.
17. After the Pressure reached 3 Kg/cm2, close the Air Vent Valve.
18. Adjust the Stop Valve as per the required by the User.
Shut-down Procedure:-
1. Stop Coal Feeding to the boiler.
2. Wait until the furnace temperature falls below 4000C
3. Switch off FD and ID Fan
4. Keep ash doors and ID fan damper full open to facilitate cooling by
natural draught
5. Close the main steam stop valve and crank open the air vent valve. It is
important to keep the air vent open to prevent vacuum in steam drum.
6. Allow fuel to burn off.
7. Blow down the boiler, membrane panel header, inbed header, Mobrey
level switch and gauge glasses under pressure.
8. The Blow down should be such as to maintain a TDS in a boiler to less
than 3500 ppm.
9. Make sure that boiler is filled with water. Put off the main electric switch
and close the valves
10. Clean the boiler and its surroundings.
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Safety & Necessary Precautions while Operation of Boiler:-
1. Boiler House should have proper ventilation and lighting arrangement.
2. All electrical supply should be switched off and maintenance staff should
ensure no supply is available in the equipment.
3. Make sure the “UNDER MAINTENANCE” board and work permit system
should be introduced when entering into the furnace for maintenance.
4. Ensure proper earthing of all the electrical equipment.
5. Do not use nylon/Polyester clothing, during the operation and
maintenance of Boilers/Heaters.
6. None of the safeties and controls should be bypassed during the
operation of boiler.
7. The fuel storage formalities and safety precaution need to be taken.
8. The Boiler house should be kept free from spillage of water/Oil.
9. All Hot Surfaces should be insulated properly.
10. Before opening the Pressure parts of the boiler, make sure the pressure
is released completely and the air vent valve is fully open and no
discharge of vapour through the air vent line.
11. Blow down pit should be made of concrete/MS and should be covered
properly with adequate venting arrangement.
12. Use leather hand gloves while working on hot surfaces.
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MAINTENANCE OF BOILER
General and Preventive Maintenance:- The Performance of a Boiler
depends on maintenance carried out. The boiler, water pipelines, strainers, etc
should be kept clean to maintain water flow to boiler. The types of maintenance
are General, Daily, Weekly, Monthly, Quarterly, Half-yearly and Yearly.
General Maintenance:-
1. Refractory Maintenance:-
a. Check the condition of refractory after every 6 months. If any fallen
bricks found, replace immediately by proper shaped bricks.
b. Avoid door bangs to prevent refractory from breakage.
c. Avoid cold blast for cooling the furnace to avoid thermal shocks.
d. The mortar and pointing on hot surface of the furnace get damaged
with use and need frequent mending well in time.
2. Care of Idle Boilers:- During the Idle periods leads to onset of corrosion in
the steam and water spaces from which serious attack may develop
during subsequent working periods. Corrosion can start as a boiler is
emptied and the attack will be high if pools of water are left in boiler.
a. The Tube Surfaces should be properly cleaned.
b. Air should be blown to dry out the tubes and remove loose soot.
c. The Chimney stack should be either disconnected or the damper
should be closed. A tray of unsalted lime should be places in the
furnace to keep fireside dry.
3. De-Scaling of Boiler:- To avoid scaling, ensure that always soft and
properly dosed and softened water is feed to boiler. De-scaling is not a
routine maintenance, as de-scaling shortens the life of boiler and tubes.
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4. Blow down:- The object of Blow down is to maintain the level of TDS to
Pre-determined value. Blow down for this type of boiler should be given
when concentration of total dissolved solids (TDS) rises to 3000 ppm.
Blowing down helps in removing sludge, loose scale and other fine
material that might accumulate in the boiler shell.
5. Economizer:- Cleaning the Economizer fire tube & remove Fly ash from
tubes bottom for Every 24 hours of Boiler running.
Daily Maintenance:-
1. Check the Softness of the water by carrying out the tests.
2. Make Blow down at regular intervals depending on feed water analysis.
3. Blow down the Mobrey level switch.
4. Blow down the gauge glasses.
5. Check fly ash and ensure timely ash removal.
Weekly Maintenance:-
1. Make sure the Panels are cleaned from outside and inside, free from dust
2. Regenerate the water softener, if the hardness is more than regeneration
is required more than once
3. Check the working of feed water pre-heater/de-aerator tank
4. Ensure that the gauge glasses are clean from inside and outside so that
the water level is clearly visible.
5. Check the working of Mobrey level switch. Ensure that the minimum and
maximum water levels are properly controlled.
6. Check the working of Safety valves by closing the main steam stop valve
and other valves of boiler and allow the steam to increase and the valve
should open at set pressure and pressure should drop on opening of it.
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Monthly Maintenance: -
1. Repeat all the Maintenance Steps carried out in Daily Maintenance.
2. Drain the soft water tank. Clean it from inside and refill it with soft water.
3. Tighten the stuffing box of the pump, if necessary.
4. Clean silver contacts of relays with carbon tetra chloride or with paper, if
required. (Emery paper should not be used)
5. Tighten the screws connected wires to terminals strips, various relays,
motors, controls, etc.
6. Ease the steam safety valves and reset.
7. Check and replace oil in gear boxes.
8. Check the condition of grate bars and replace damaged ones, if any.
9. Open the smoke chamber doors, take out the spirals and clean the tubes
with brush (The Brush must not be loose when inserted in tubes)
10. Check tension and alignment of ID and FD fan belts and bolts.
Quarterly Maintenance: -
1. Repeat all the Maintenance Steps carried out in Monthly Maintenance.
2. Drain and clean the feed water storage tank.
3. Clean the ID and FD Fan blades.
4. Lubricate the bearings of water pump, ID and FD fans.
Half-Yearly Maintenance: -
1. Repeat all the Maintenance Steps carried out in Quarterly Maintenance.
2. Check the condition of refractory wall of the combustion chamber.
3. Check all valves for leakages and lap them with lapping paste, if required.
4. Check the ducts and other joints for infiltration of fresh air.
5. Check the quantity of resin inside the water softener and top it up.
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Yearly Maintenance: -
1. Repeat all the Maintenance Steps carried out in Yearly Maintenance
2. Check and repair the insulation lining of boiler.
3. Clean various tanks and paint them.
4. Clean inside of the flue gas outlet.
5. Grease electric motors.
6. Check the membrane panel, its headers and tubes from outside for
cleanliness and clean if necessary.
7. Check the boiler tubes for cleanliness from inside and de-scale if required.
8. Check the condition of impellers and replace them, if necessary.
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IMPROVING THE EFFECIENCY OF BOILER
Efficiency of Boiler:- Thermal efficiency of boiler is defined as the
percentage of heat input that is effectively utilized to generate steam. There
are two methods of assessing boiler efficiency.
1. The Direct Method:- Where the energy gain of the working fluid
(water and steam) is compared with the energy content of the boiler fuel.
This is also known as ‘input-output method’ due to the fact that it needs
only the useful output (steam) and the heat input (i.e. fuel) for evaluating
the efficiency. This efficiency can be evaluated using the formula
Boiler Efficiency = (Heat Output / Heat Input) X 100
Boiler Efficiency = {(Q X hg – hf) / (q X GCV)} X 100
Where:
Q – Quantity of steam generated per hour in kg/hr.
hg – Enthalpy of saturated steam in kCal/kg of steam.
hf – Enthalpy of feed water in kCal/kg of water.
q – Quantity of fuel used per hour (q) in kg/hr.
GCV – Gross Calorific Value of the fuel in kCal/kg of fuel
2. The Indirect Method:- Where the efficiency is the difference between
the losses and the energy input. Indirect method is also called as heat
loss method. The efficiency can be arrived at, by subtracting the heat loss
fractions from 100. The standards do not include blow down loss in the
efficiency determination process. A detailed procedure for calculating
boiler efficiency by indirect method is given below.
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The principle losses that occur in a boiler are:
� Loss of heat due to dry flue gas
� Loss of heat due to moisture in fuel and combustion air
� Loss of heat due to combustion of hydrogen
� Loss of heat due to radiation
� Loss of heat due to un-burnt Fuel
I. Heat loss due to dry flue gas
= (m×Cp×(Tf –Ta) × 100) / GCV of Fuel
II. Heat loss due to evaporation of water to H2 in fuel
= [9 H2 {584 + C p (Tf-Ta)} x 100] / GCV of Fuel
III. Heat loss due to evaporation of moisture present in fuel
= [M x {584 + C p (Tf -Ta)} x 100] / GCV of Fuel
IV. Heat loss due to moisture present in air
= [AAS × humidity factor ×Cp x (Tf -Ta) x 100] / GCV of Fuel
V. Heat loss due to un-burnt fuel in fly ash
= Total ash collected/kg of fuel burnt xGCV of fly ash x 100 / GCV of coal
VI. Heat loss due to un-burnt fuel in bottom ash
= Total ash collected/kg of fuel burnt xGCV of bottom ash x100 /GCV of coal
Boiler Efficiency = 100 - (I + II + III + IV + V + VI)
Where,
m – Mass of dry flue gas in kg/kg of fuel
Cp – Specific heat of flue gas
Tf – Flue gas temperature
Ta – Ambient temperature
H2 - kg of Hydrogen in 1 kg of fuel
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M – kg of moisture in 1kg of fuel
GCV – Gross Calorific Value
AAS – Actual mass of air supplied
The Efficiency of Boiler by Direct Method is
Type of boiler : Coal fired Boiler 10 TPH
Quantity of steam (dry) generated : 6000 Kgs/hr
Steam pressure (gauge) / temp : 10 kg/cm2(g)/ 180°C
Quantity of coal consumed : 1230 Kgs/hr
Feed water temperature : 85°C
GCV of coal : 4100 kCal/kg
Enthalpy of steam at 10 kg/cm2 pressure : 665 kCal/kg (saturated)
Enthalpy of feed water : 85 kCal/kg
Efficiency of Boiler = (6000 x (665-85) / 1230 x 4100) x 100
= (6000 x 580 / 1230 x 4100) x 100
= (3480000 / 5043000) x 100
= 69.01%
The Efficiency of Boiler by Indirect Method is
m – 10.38 Kg
Cp –0.23 kCal/kg °C)
Tf – 200 °C
Ta – 30 °C
H2 – 0.03 Kg
M – 0.31 Kg
GCV – 4100 kCal/kg
AAS – 10.07 Kg
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I. Heat loss due to dry flue gas
= (m×Cp×(Tf –Ta) × 100) / GCV of Fuel
= (10.38 x 0.23 x {200-30} x 100) / 4100
= (10.38 x 0.23 x 170 x 100) / 4100
= 9.89%
II. Heat loss due to evaporation of water to H2 in fuel
= [9 H2 {584 + C p (Tf-Ta)} x 100] / GCV of Fuel
= [9 x 0.03 {584 + 0.23(200-30)} x 100] / 4100
= [0.27 {584+39.1} x 100] / 4100
= 16823.7 / 4100
= 4.1%
III. Heat loss due to evaporation of moisture present in fuel
= [M x {584 + C p (Tf -Ta)} x 100] / GCV of Fuel
= [0.31 x {584 + 0.23(200-30)} x 100] / 4100
= [0.31 x 623.1 x 100] / 4100
= 4.71%
IV. Heat loss due to moisture present in air
= [AAS × humidity factor ×Cp x (Tf -Ta) x 100] / GCV of Fuel
= [10.07 x 0.204 x 0.23 x (200-30) x 100] / 4100
= [10.07 x 0.204 x 0.23 x 170 x 100] / 4100
= 1.95%
V. Heat loss due to un-burnt fuel in fly ash
= Total ash collected/kg of fuel burnt xGCV of fly ash x 100 / GCV of coal
= 0.1x0.0863 x 452.5 x 100 / 4100
= 0.09%
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VI. Heat loss due to un-burnt fuel in fly ash
= Total ash collected/kg of fuel burnt xGCV of bottom ash x100/GCV of coal
= 0.9x0.0863 x 800 x 100 / 4100
= 1.51%
Efficiency of Boiler = 100 - (I + II + III + IV + V + VI)
= 100 – (9.89+4.1+4.71+1.95+0.09+1.51)
= 100 – 22.25
= 77.75%
How to Increase the Efficiency of Boiler:- The Efficiency of the Boiler
can be improve by using the below mentioned Technique’s
1. Condensate Recovery System
2. Economizer
3. Pre-Heater
4. Coal Intensifier
5. Good Maintenance Practices
6. Minimizing of Losses
� Dry Flue Gas Loss
� Fuel Moisture Loss
� Blow Down Losses
1. Condensate Recovery System: It is an attractive method of improving your
Boiler plant’s energy efficiency by Collecting the Heat and Condensate Recovery
from Steam Traps and return to the boiler. Condensate steam traps will be located
within the Plant, inside Process Units as well as in interconnecting Pipe lines to
provide opportunities for recovering sensible heat as well as de-mineralized grade
Boiler make-up water. Recovery schemes can be engineered in-house. Pumping of
flashed steam condensate can be achieved through commercially available steam
pressured pumps, which offer energy benefits as compared with motor driven
pumps
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Returning hot condensate to the boiler makes sense for several reasons. As more
condensate is returned, less make-up water is required, saving fuel, makeup
water, and chemicals and treatment costs. Less condensate discharged into a
sewer system reduces disposal costs. Return of high purity condensate also
reduces energy losses due to boiler blow down. Significant fuel savings occur as
most returned condensate is relatively hot, reducing the amount of cold makeup
water that must be heated
A simple calculation indicates that energy in the condensate can be more than
10% of the total steam energy content of a typical system. The heat remaining in
the condensate at various condensate temperatures, for a steam system
operating, with makeup water
Let:
hc= enthalpy of condensate at 180°F = 150 Btu/lb
hm= enthalpy of makeup water at 90°F = 60 Btu/lb
hs= enthalpy of steam at 10 Kg/Cm2 = 665 Btu/lb
Heat remaining in condensate (%): = (hc – hm)/ (hs – hm) x 100
= (150 – 60)/ (665 – 60) x 100
= 14.87%
Quantity of Make-up water through condensate Recovery System = 9000 Liters
Annual Water, Sewage savings
= (Rate of Makeup Water/Liter x Quantity of Makeup Water + Rate of Effluent
treatment/Liter x Quantity of Makeup water) x Boiler Running Days/year
= (0.08 X 9000 + 1.98 X 9000) x 355
= Rs 65, 81,700.
Figure 13: Condensate Recovery System
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2. Economizer: A feed water economizer reduces steam boiler fuel requirements by
transferring heat from the flue gas to incoming feed water. Boiler flue gases are
often rejected to the stack at temperatures more than 200°F to 160°F higher than
the temperature of the generated steam. Generally, boiler efficiency can be
increased by 1% for every 6°C reduction in flue gas temperature. By recovering
waste heat, an economizer can often reduce fuel requirements by 5% to 10% and
pay for itself in less than 2 years. The waste heat in the flue gas was recovered by
installing an economizer, which transfers waste heat from the flue gases to the
boiler feed water. This resulted in a rise in feed water temperature by about 26ºC
3. Pre-Heater: The Air Pre-Heater reduces steam boiler fuel requirements by
sending the Hot air to the Furnace which leads to completely burning of fuel and
stabilize the temperature. The air heater design using either rotating heat transfer
surface or rotating air distribution hoods predominates for utility air heating
applications. The air heater arrangement may consist of one, two, three, or four air
heaters, depending on the size of the unit and the degree of fuel flexibility desired
Figure 14: Economizer and Pre-Heater System
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Quantity of fuel gases = Fuel supply rate x Flue gas quantity
Quantity of recovered heat in the flue gases
= Quantity of fuel gases x Cp x (Tf -Ta)
Where,
Average quantity of steam generated : 6000
Average flue gas temperature : 2000C
Average steam generation/kg of fuel : 4.87 kg
Feed water inlet temperature : 90ºC
Fuel supply rate : 20.5 kg/hr
Flue gas quantity : 10.38 kg/kg of fuel
Annual Operating Hours : 8520 hr
Quantity of fuel gases = 20.5 x 10.38
= 212.79 kg/hr.
Quantity of recovered heat in the flue gases
=Quantity of fuel gases x Cp x (Tf -Ta)
= 212.79 x 0.23 x (200-30)
= 212.79 x 0.23 x 170
= 8320.08 kCal/hr.
Annual savings = 8520 x 30
= Rs 255600
4. Coal Intensifier: Coal Intensifier is used for burning of Coal completely. The
Coal Intensifier is added with the fuel while entering into the bunker for burning of
fuel up to 99%. By adding the Intensifier the black smoke will also be controlled.
By using the Intensifier the Fuel can be saved up to 1%
Quantity of fuel saved by hr = Rs 12
Annual Savings = 8520 x 12
= Rs 102240.
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5. Good Maintenance Practices: The Maintenance of the Boiler play very keen
role on the efficiency.
I. Steam Traps: By maintaining the steam traps we can The key functions of
steam traps are increase the economy of fuel in all steam-use systems and is
one of the major efficiency opportunities which can yield surprising results
� Traps that are open, meaning those draining steam and condensate, result
in loss of energy and direct loss of condensate (the purest form of water)
and significant economic loss as boiler operating costs increase.
� Traps that are closed, or become blocked, result in reduced heating capacity
of steam heating equipment, and direct loss of production, which is
undesirable
II. De-Scaling: Scale formation inside the boiler is an important problem. It leads
to several other problems such as corrosion and pitting, decrease in overall heat
transfer efficiency and choking inside the tubes. All these results in
� The Decrease in the efficiency of the boiler
� Increased fuel consumption
� Decreased steam generation
� Risks of boiler accidents and unexpected shutdowns
To avoid the above mentioned activities we are using the de-scaling compound
mixed in the feed water. By doing this we will get the following benefits
� Peak heat transfer efficiency is obtained
� Minimized fuel consumption through peak heat transfer
� Peak steam output
� No corrosion or pitting
� Reduces coil/tube failures and unscheduled shutdowns
� Protective oxide film is formed over bare metal surfaces
� Brings down the overall risks of boiler accidents
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III. Softening of Feed Water : To avoid the unwanted breakdowns of the boiler
the chemicals will be used for the softening of the feed water
� Oxygen Scavenger: It removes last traces of the dissolved oxygen from the
boiler feed water to help preventing oxygen pitting inside the Boiler
� De-foamer: It helps in reducing the carryover and foaming in Boiler
� Scale Inhibitor: It protects from corrosion & pitting inside the boiler and
condenser by decomposing O2 & CO2. It is highly effective anti-scalant that
prevents scale formation, which improves heat transfer efficiency.
� pH Booster: It acts as an alkalinity builder and maintains pH 9.0 – 12.0 in
the blow down water.
By using the above mentioned we can get the peak heat transfer efficiency and
can reduce the energy losses.
IV. Thermal Losses: The Thermal losses of the Boiler can be reduced by good
maintenance of Insulation over the pipelines and other accessories of Boiler.
� To Reduce Heat Losses
� To Provide Weather Proofing
� Heat Losses from Un-Insulated surface is given in Table.2
� Heat Losses from Insulated surface is given in Table.3
6. Minimizing of Losses: There are several losses on the boiler that can be
minimized using the below mentioned
I. Dry Flue Gas Loss: Flue gas is the gas exiting to the atmosphere via a flue,
which is a pipe or channel for conveying exhaust gases from the Furnace
and are exhausted to the outside air. Flue gases are produced when fuel
is combusted in an industrial furnace. The Flue gas can be utilized by converting
the hot flue gas to the inlet of the Economizer and the Air Pre-Heater to attain
Efficiency and to minimize the losses.
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II. Fuel Moisture Loss: Fuels are constantly exchanging moisture with the
surrounding air. During periods of high humidity and precipitation there is a net
gain in fuel moisture. However, when the air is dry, with low humidity, fuels are
giving up more moisture to the air than they receive. Several factors influence
the rate of moisture exchange between fuels and the air. If the moisture content
in the atmosphere remained constant for a period of time, the fuels and the air
would eventually achieve equal vapor pressures. This we call equilibrium
moisture content, which occurs when there is no net gain or loss of moisture
between fuels and the surrounding air. This can occur in small, fine fuels, but
rarely occurs in larger fuels, as the time required to reach equilibrium in larger
fuels is much longer.
� The fuel loss can be minimized by storing the fuel at place where moisture
content is low
� The latent heat loss due to boiling of water in the fuel can be reduced by
using the condensate recovery system
III. Blow down Losses: Blow down is a necessary task in boiler operation
intermittently reducing the concentration of solids in the boiler. How much blow
down is necessary depends on the quality of the feed water, the use of the life
steam, and the quality of the make-up water. In practice we see a blow down of
0 % to 15 % of feed water. The consequence of too much blow down is
increased fuel consumption. Too little blow down also increases fuel
consumption.
� By Using the Condensate Recovery water the make up water the blow down
can be minimized as it’s hardness is almost 0 ppm.
� By Using the Softening of Feed Water Techniques also the Blow down can be
minimized
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Table:1 – Steam Calculation Table
Absolute
pressure
Boiling
point
Specific volume
(steam)
Density
(steam)
Specific enthalpy of liquid water
(sensible heat)
Specific enthalpy of steam
(total heat)
Latent heat of
vaporization
Specific
heat
(bar) (oC) (m3/kg) (kg/m3) (kcal/kg) (kcal/kg) (kcal/kg) (kJ/kg)
0.02 17.51 67.006 0.015 17.54 605.15 587.61 1.8644
0.03 24.1 45.667 0.022 24.12 608.02 583.89 1.8694
0.04 28.98 34.802 0.029 29 610.13 581.14 1.8736
0.05 32.9 28.194 0.035 32.91 611.83 578.92 1.8774
0.06 36.18 23.741 0.042 36.19 613.24 577.05 1.8808
0.07 39.02 20.531 0.049 39.02 614.46 575.44 1.884
0.08 41.53 18.105 0.055 41.53 615.53 574.01 1.8871
0.09 43.79 16.204 0.062 43.78 616.49 572.72 1.8899
0.1 45.83 14.675 0.068 45.82 617.36 571.54 1.8927
0.2 60.09 7.65 0.131 60.06 623.35 563.3 1.9156
0.3 69.13 5.229 0.191 69.1 627.07 557.97 1.9343
0.4 75.89 3.993 0.25 75.87 629.81 553.94 1.9506
0.5 81.35 3.24 0.309 81.34 631.98 550.64 1.9654
0.6 85.95 2.732 0.366 85.97 633.79 547.83 1.979
0.7 89.96 2.365 0.423 89.99 635.35 545.36 1.9919
0.8 93.51 2.087 0.479 93.56 636.71 543.15 2.004
0.9 96.71 1.869 0.535 96.78 637.92 541.14 2.0156
1 99.63 1.694 0.59 99.72 639.02 539.3 2.0267
1.1 102.32 1.549 0.645 102.43 640.01 537.59 2.0373
1.2 104.81 1.428 0.7 104.94 640.93 535.99 2.0476
1.3 107.13 1.325 0.755 107.29 641.77 534.49 2.0576
1.4 109.32 1.236 0.809 109.49 642.56 533.07 2.0673
1.5 111.37 1.159 0.863 111.57 643.3 531.73 2.0768
1.5 111.37 1.159 0.863 111.57 643.3 531.73 2.0768
1.6 113.32 1.091 0.916 113.54 643.99 530.45 2.086
1.7 115.17 1.031 0.97 115.42 644.64 529.22 2.095
1.8 116.93 0.977 1.023 117.2 645.25 528.05 2.1037
1.9 118.62 0.929 1.076 118.91 645.83 526.92 2.1124
2 120.23 0.885 1.129 120.55 646.39 525.84 2.1208
2.2 123.27 0.81 1.235 123.63 647.42 523.78 2.1372
2.4 126.09 0.746 1.34 126.5 648.36 521.86 2.1531
2.6 128.73 0.693 1.444 129.19 649.22 520.04 2.1685
2.8 131.2 0.646 1.548 131.71 650.03 518.32 2.1835
3 133.54 0.606 1.651 134.1 650.77 516.68 2.1981
3.5 138.87 0.524 1.908 139.55 652.44 512.89 2.2331
4 143.63 0.462 2.163 144.43 653.87 509.45 2.2664
4.5 147.92 0.414 2.417 148.84 655.13 506.29 2.2983
5 151.85 0.375 2.669 152.89 656.24 503.35 2.3289
5.5 155.47 0.342 2.92 156.64 657.23 500.6 2.3585
6 158.84 0.315 3.17 160.13 658.13 498 2.3873
6.5 161.99 0.292 3.419 163.4 658.94 495.54 2.4152
7 164.96 0.273 3.667 166.49 659.69 493.2 2.4424
7.5 167.76 0.255 3.915 169.41 660.37 490.96 2.469
8 170.42 0.24 4.162 172.19 661 488.8 2.4951
8.5 172.94 0.227 4.409 174.84 661.58 486.73 2.5206
9 175.36 0.215 4.655 177.38 662.11 484.74 2.5456
9.5 177.67 0.204 4.901 179.81 662.61 482.8 2.5702
10 179.88 0.194 5.147 182.14 663.07 480.93 2.5944
11 184.06 0.177 5.638 186.57 663.38 477.35 2.6418
12 187.96 0.163 6.127 190.7 663.67 473.94 2.6878
13 191.6 0.151 6.617 194.58 664.02 470.7 2.7327
14 195.04 0.141 7.106 198.26 664.25 467.6 2.7767
15 198.28 0.132 7.596 201.74 664.52 464.61 2.8197
16 201.37 0.124 8.085 205.06 665.79 461.74 2.862
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Table 2: Heat Loss from Un-Insulated Surfaces
Internal Temp in Deg.C Heat Loss in kCal/hr for M2
50 291
100 894
200 3065
300 6690
400 12114
Table 3: Heat Loss from Insulated Surfaces
Note: Thickness in mm and Heat Loss in kCal/hr for M2
Temp in Deg.C 25 thk 40 thk 50 thk 65 thk 85 thk 100 thk
50 47 36 -- -- -- --
100 135 95 73 -- -- --
200 338 244 190 150 122 --
300 -- 420 310 255 220 170
400 -- -- 455 370 320 244