This PPT explains detailed calculations in Boiler Efficiency calculations through direct and indirect method. It also explains pros and cons of boiler efficiency calculation through direct and indirect method. For further clarifications you can reach out to me at tahoorkhn03@gmail.com or connect with me on my linkedin profile by clicking at www.linkedin.com/in/tahoorkhan
5. 5
Direct Method
Boiler efficiency by Direct Method is the ratio of Heat Supplied by Boiler to the
amount of heat given to boiler through fuel combustion.
It is given by:
Boiler Efficiency
where,
m = mass of Main Steam (t/hr)
hms = Enthalpy of Main Steam (kcal/kg)
hfw = Enthalpy of Feed Water (kcal/kg)
GCV = Gross Calorific Value of Coal
=
π β (βππ β βππ€)
πΉπππ πππ‘π β πΊπΆπ
β 100
6. 6
Direct Method
For higher capacity boilers with Re-heat:
Boiler Efficiency is given by:
πΉπ
β βππ
β βππ€ + πΉβπβ β ββπβ
β βππβ + πΉπβπ β (ββπβ β βππ€)
πΉπππ π ππ‘π β πΊπΆπ
where,
Fm = mass of Main Steam (t/hr) Fhrh = HRH Flow (t/hr)
hms = Enthalpy of Main Steam (kcal/kg) Fcrh = CRH Flow (t/hr)
hfw = Enthalpy of Feed Water (kcal/kg) Frhs = Reheat Spray Flow (t/hr)
GCV = Gross Calorific Value of Coal
9. 9
Indirect Method
For calculating efficiency through Indirect Method, Boiler losses are calculated
first and then subtracted from 100.
Boiler efficiency through Indirect Method = 100 β Boiler Losses.
This method is also known as Loss Method as boiler losses are to be calculated
first.
11. 11
Dry Flue Gas Loss
Dry Flue Gas Loss is the result of heat being carried away by the hot flue gases
from the furnace.
Dry Flue Gas Loss is given by: π β πΆππ β (ππ β ππ)
πΊπΆπ
β 100
where,
m= mass of flue gases (kg/kg of coal)
Cpf = Specific heat of Flue gases (kcal/kg deg. C)
Tf = Temperature of Flue gases exiting boiler (deg. C)
Ta = Ambient air temperature (deg. C)
12. 12
Dry Flue Gas Loss
Relation of Residual Oxygen with Excess Air
13. 13
Excess Air and Residual Oxygen as per BHEL recommendation:
Dry Flue Gas Loss
14. 14
Hydrogen in Fuel Loss
It is the loss arising due to heat being carried away by the water formed due to
oxidation of hydrogen in fuel.
H2 in Fuel Loss is given by: 9 β π» β {584 + πΆππ β ππ β ππ }
πΊπΆπ
β 100
where,
H = % of hydrogen in fuel
Cps = Specific heat of steam (kcal/kg deg. C)
Tf = Temperature of Flue gases exiting boiler (deg. C)
Ta = Ambient air temperature (deg. C)
15. 15
Moisture in Fuel Loss
It is the loss arising due to heat being carried away by the moisture present in
fuel at the time of firing.
Moisture in Fuel Loss is given
by:
π β {584 + πΆππ β ππ β ππ }
πΊπΆπ
β 100
where,
M = % of moisture in fuel
Cps = Specific heat of steam (kcal/kg deg. C)
Tf = Temperature of Flue gases exiting boiler (deg. C)
Ta = Ambient air temperature (deg. C)
16. 16
Moisture in Air Loss
It is the loss arising due to heat being carried away by the moisture present in
air supplied for combustion and transportation of fuel.
Moisture in Air Loss is given by: π΄ππ β βπ’πππ‘πππ‘π¦ β {πΆππ β ππ β ππ }
πΊπΆπ
β 100
where,
ASS = Total air supplied for combustion (kg /kg of fuel)
humidity = Ambient air humidity (kg/kg of air)
Tf = Temperature of Flue gases exiting boiler (deg. C)
Ta = Ambient air temperature (deg. C)
17. 17
Unburnt Carbon Loss
This loss is the result of incomplete combustion of fuel in boiler. It also includes
loss due to carry over of unburnt fuel along with flue gases.
Unburnt
Carbon
Loss
Incomplete
combustion loss
Unburnt in
Bottom Ash
Unburnt in Fly
Ash
18. 18
Incomplete Combustion Loss
This loss is the result of incomplete combustion of coal in boiler. This loss is
evident from increased CO2 in stack.
This loss is given by:
%πΆπ β πΆ β 5654 β 100
%πΆπ+πΆπ2 β πΊπΆπ
where:
%CO = CO percentage as shown in DCS
C = Carbon content in coal
CO2 = CO2 percentage as shown in DCS
22. 22
Unburnt in Bottom Ash
This loss is due to the presence of unburnt carbon content in bottom ash.
It is given by :
%π΄ β%π΅π β %ππ β 8084
πΊπΆπ ππ πΆπππ
where:
%A = Ash content in coal
%Ba = Bottom ash percentage in total ash generation
%Ub = Percentage of unburnt in Bottom Ash
23. 23
Unburnt in Fly Ash
This loss is due to the presence of unburnt carbon content in fly ash.
It is given by :
%π΄ β %πΉπ β %ππ β 8084
πΊπΆπ ππ πΆπππ
where:
%A = Ash content in coal
%Fa = Fly ash percentage in total ash generation
%Uf = Percentage of unburnt in Fly Ash
24. Other Boiler Losses
24
Radiation Loss:
Heat Leakage from boiler
surfaces.
Ensuring proper insulation
help reduce this loss.
Blow down Losses
This are the losses arising due
to loss of heat through hot
water through blow down.
This are the losses which go
unaccounted while unit
operation.
Unaccountable Loss
Tolerance by manufacturer
for efficiency calculation.
Manufacturerβs Margin
26. Boiler Losses In Brief
26
Unburnt Carbon
Others
Dry Flue Gas
Moisture in Air
Hydrogen in Fuel
Moisture in Fuel
Heat carried away by flue gases
Heat carried by water formed due to hydrogen
in fuel
Heat carried by moisture in fuel
Incomplete combustion loss, Unburnt in Bottom
Ash and Fly Ash
Radiation, Unaccounted, Manufacturer
Margin
Heat carried by moisture in air
27. 27
Efficiency by Indirect Method
Total Boiler Losses = Dry Flue Gas + Moisture in Air + Moisture in Fuel + H2 in Fuel
+ Incomplete Combustion + Unburnt in BA + Unburnt in FA
+ Others
Boiler Efficiency by Indirect Method = 100 β Total Boiler Losses
28. 28
Methods of Boiler Efficiency Calculations
Pros and Cons of each Method
Improving Boiler Efficiency
CONTENTS
30. 30
Optimizing Dry Flue Gas Loss
οΆ Optimization of excess air keeping unburnt carbon content under
control.
οΆ Soot blowing of heat transfer surfaces like water walls, super heater
coils and APH baskets.
οΆ Avoiding air infiltration/ingress by ensuring proper sealing of man holes
and inspection doors.
οΆ Optimization of excess air also helps to reduce fan power.
οΆ Scheduled sampling of flue gas from field and verifying the same with
DCS data.
31. 31
Excess Air and Boiler Efficiency Relation
Dry Flue Gas Loss
USEFUL
FACT
β’ Every 22 deg. C
rise in exit gas
temperature
reduces Boiler
Efficiency by
1%.
33. 33
Optimizing Hydrogen in
Fuel Loss
This loss is beyond the control of
Operator and it depends solely
upon Hydrogen contents in coal
derived from ultimate analysis.
34. 34
Optimizing Moisture in Fuel Loss
Ensuring proper stacking of coal in coal yard as per the recommendation.
35. 35
Optimizing Moisture in Fuel Loss
Maintaining recommended primary air and mill outlet temperature for
drying coal before it enters furnace
37. 37
Optimizing Moisture in Air Loss
οΆ Avoid air ingress in furnace through loose manholes and inspection
windows.
οΆ Restricted use of cold air for tempering of mixed air for maintaining
mill outlet temperature.
οΆ Maintaining recommended secondary air temperature at APH outlet
by APH soot blowing as per schedule.
39. 39
Optimizing Incomplete Combustion Loss
οΆ Ensuring air rich mixture by supplying excess air for adequate
turbulence inside furnace.
οΆ Coal to PA ratio too high or too low.
οΆ Checking of SADC damper for their opening as per the command from
DCS.
οΆ Ensuring equal burner tilt position at all corners.
οΆ Ensuring equal velocity of coal in all four coal pipes.
40. 40
Optimizing Unburnt in BA and FA
οΆ Mill fineness to be checked at scheduled intervals. Classifier
adjustment, roller setting and roller replacement to be considered
when deterioration is observed in mill fineness.
οΆ Restrict pulverized coal particle size of 50 mesh to <2% at mill outlet
and ensure more than 70% coal pass through 200mesh.
οΆ AA dampers to be opened if unburnt in BA increases.
οΆ Retention time of coal particles inside furnace to be ensured by
maintaining draught as per recommendation.
41. 41
Methods of Boiler Efficiency Calculations
Pros and Cons of each Method
Improving Boiler Efficiency
CONTENTS
42. Pros
οΆ Less parameters are
required.
οΆ Less instrumentation
required.
οΆ Rapid Calculations
οΆ THR can be calculated
with minor changes
Pros and Cons of Direct Method
Cons
οΆ Doesnβt furnish a
detailed report as to
why the efficiency is
lagging or leading.
οΆ Cannot be used for
efficiency
improvement projects.
42
43. Pros
οΆ Detailed report is
generated.
οΆ Highlights the area for
improvement.
οΆ Ideal for using in
efficiency
improvement projects
Pros and Cons of Indirect Method
Cons
οΆ Wide variety of
parameters and
instruments are
required
οΆ Huge calculations
οΆ Ultimate analysis of
coal required
43
44. β
Great things are not done by
one person. They are done by
a team of people.
44
-Steve
Jobs
You can find me at:
tahoor.khan@rattanindia.com
www.linkedin.com/in/tahoorkhan
Editor's Notes
Enthalpy definition
Gcv
Why excess air is provided
Cold end corosion
Nitrogen
EA calculation
How much O2 in infinite air
2H2 + O2 = 2H2O
4 + 32 = 36
Percentage of CO2 is decreasing with increase in excess air
This shape reduces surface area and hence less exposure to atm. Rainfall water do not accumulate