Boiler fuel consumption is one of the most critical performance parameters in any steam-generating system. Understanding how to calculate it helps optimize efficiency, reduce operational costs, and improve combustion control. Whether you are operating a coal, oil, gas, or biomass-fired boiler, knowing the actual fuel usage versus theoretical requirements gives you better insight into your plant’s energy balance.
On what factors fuel consumption of the Boiler depends?
Fuel consumption of the Boiler depends on;
- Steam generation
- Boiler efficiency
- Losses in Boiler
- Fuel Moisture
- Fuel calorific value
- Ash content in fuel
- Feed water temperature at economiser inlet
- Combustion air temperature
- Boiler outlet flue gas temperature
What are the different methods employed in measuring/calculating the Boiler fuel consumption?
1-Mass Flow Measurement Method:
In this method a flow meter or belt weigher are installed for directly measuring the fuel consumption. Flow meters are installed for gas and oil flow and Belt weigher are installed for measuring solid fuels consumption
Fuel Consumption=Mass Flow Reading (kg/hr or TPH or Nm³/hr)
No any such theoretical inputs are required for this type of measurement.
2- Time-Based Fuel Consumption (Tank Level Method):
Used for liquid fuels (like Furnace Oil or Diesel) when flow meters are not available.
Procedure:
- Record tank level at start and end of a period (say 1 hour).
- Note steam generation during the same period.
- Calculate the difference in fuel level and convert to volume/mass using fuel density.
Fuel Consumption (L/hr)=Time (hr)Tank Level Drop (litres)
Convert to kg/hr using:
Fuel Consumption (kg/hr)=Fuel Volume (L/hr)×Fuel Density (kg/L)
3-Boiler fuel consumption by assuming Steam to Fuel Ratio (SFR)
Each boiler type has a typical Steam-to-Fuel Ratio (SFR), for various types of fuels. Based on this fuel consumption of the Boiler can directly calculated.
Boiler fuel consumption = Steam Generation or steam flow / SFR
For example:
50 TPH AFBC Boiler has SFR 5 for coal GCV 4800 kcal/kg, then fuel consumption is calculated as,
Boiler fuel consumption = Steam Generation or steam flow / SFR
Boiler fuel consumption = 50 / 5 = 10 TPH
Similarly, Steam to Fuel Ratio (SFR) for various fuels are;
- Bagasse fired Boilers = 2 to 2.6
- Imported coal fired Boilers = 5 to 6.5
- Indian coal fired Boilers = 3 to 4
- Rice husk fired Boilers = 3 to 4
- Oil fired Boiler =13 to 15
- Gas fired Boiler = 14 to 16
Steam to Fuel Ratio (SFR) depends on;
- Boiler efficiency
- Fuel GCV
- Boiler operating parameters
4–Boiler fuel consumption by fuel feeders speed (RPM)
In some Boilers fuel consumption is being calculated based on fuel feeders reference speed.
Various quantity of fuel discharged from the fuel feeders are pre-decided at various reference speed of the fuel feeder.
5-Boiler fuel consumption by direct method:
This is also called as input and output method. Input in this method is Fuel consumption and Output is steam generation.
Inputs required for this are;
- Steam generation
- Feed water consumption
- Steam and feed water heat (Enthalpy)
- Fuel calorific value
- Boiler efficiency
Input in this method is Fuel consumption and Output is steam generation.
Below formula is used for fuel consumption by this method
Fuel consumption in TPH = Steam flow in TPH X (Main steam Enthalpy-Feed water enthalpy at economiser inlet) / (Boiler efficiency X Fuel GCV in kcal/Kg)
Calculation:
Calculate the fuel consumption of 150 TPH capacity boiler operating at pressure 67 Kg/cm2 and temperature 500 deg C. Consider fuel used is imported coal of calorific value 5200 kcal/kg . Consider feed water temperature at economiser inlet is 150 deg C and Boiler efficiency 84%
We have.
Steam flow = 150 TPH
Feed water flow = 150 TPH + Blow down loss = 150 + 150 X 1% = 151.5 TPH
Main steam enthalpy at above parameters = 808 kcal/kg
Feed water enthalpy = 152 kcal/kg
Fuel Calorific value = 5200 kcal/kg
Fuel consumption in TPH = Steam flow in TPH X (Main steam Enthalpy-Feed water enthalpy at economiser inlet) / (Boiler efficiency X Fuel GCV in kcal/Kg)
Fuel consumption in TPH = (150 X 808 -151.5 X 153) / (0.84 X 5200)
Fuel consumption in TPH = 22.44 TPH
TPH = Tons per hour, fuel consumption can be measured in TPH or Kg/hr
6-Boiler fuel consumption by indirect method:
This method is more accurate and diagnostic, as it identifies the sources of heat loss—helping engineers improve overall boiler performance and reduce operating costs.
The indirect method (also called the heat loss method) calculates boiler efficiency and fuel consumption by measuring various losses occurring in the system, such as:
- Dry flue gas loss
- Unburnt fuel loss
- Moisture in fuel and combustion air
- Radiation and convection losses
- Blowdown losses
Once boiler efficiency is known, we can easily determine fuel consumption for a given steam output.
Boiler efficiency (η) by the indirect method is: Boiler Efficiency (%)=100−(L1+L2+L3+L4+L5+L6+L7)
Once efficiency is found, fuel consumption can be calculated as:
Fuel consumption in TPH = Steam flow in TPH X (Main steam Enthalpy-Feed water enthalpy at economiser inlet) / (Boiler efficiency X Fuel GCV in kcal/Kg)
The above listed losses vary based on type of boiler and fuel consumption.
A fuel having high moisture content leads to more losses due to moisture in fuel.
Calculation:
A 200 TPH Boiler operating at 110 Kg/cm2 pressure and temperature and consumes coal as fuel. Various losses calculated are as below;
Consider fuel calorific value and Feed water temperature 4500 kcal/kg and 200 deg C respectively.
Dry flue gas loss: 5%
Unburnt fuel loss: 1.1%
Loss due to hydrogen combustion producing moisture: 2.5%
Moisture in fuel: 3%
Moisture in combustion air:0.1%
Radiation and convection losses: 2%
Then Boiler efficiency = 100-(5+1.1+2.5+3+0.1+2) =86.3%
Then, fuel consumption = Steam flow in TPH X (Main steam Enthalpy-Feed water enthalpy at economiser inlet) / (Boiler efficiency X Fuel GCV in kcal/Kg)
Then, fuel consumption = (200 X 825—202 X 202) / (0.863 X 4500) = 31.98 TPH
Note: Considered Blow down loss 1%
Generally, blow down loss is not being considered for calculating Boiler efficiency by indirect method, however it is used for calculating fuel consumption
