Following are the 16-reasons for increase in Boilers fuel consumption
1. Decreased economiser inlet feed water temperature:
On every 6-8 deg C decrease in Economiser inlet feed water temperature causes the rise in Boiler fuel consumption by 1%.
2. Increased Boiler outlet flue gas temperature:
On every 22 deg C increase in flue gas temperature causes the reduction in Boiler efficiency by 1% & hence boiler fuel consumption increases for generating same steam.
3. Increased moisture content in the fuel
Boilers fuel consumption increases as the moisture in the fuel increases. As it requires more excess air & reduces combustion efficiency leading to unburnt losses
4. Increased excess air
Increase in excess air causes dry flue gas loss & hence more fuel consumption. And also leads to more auxiliary power consumption.
5. Increased unburnt loss
Unburnt fuel or incomplete combustion of fuel leads to increased consumption of fuel. Unburnt is due to improper air fuel mixture or unbalanced draught or variation in the fuel quality
6. Higher blow down
Blow down water carries saturated water/steam through it, so leads into more fuel consumption. Maximum acceptable blow down rate for normal Boiler operation is 0.5 to 1%.
7. Operating the Boiler at lower or partial loads
Operating the Boilers on partial load requires more excess air & leads to incomplete combustion forming unburnts.
8. Operating the boiler at non-standard operating parameters
Operating the Boilers at non standard parameters like pressure, temperatures, flow etc will lead to the higher fuel consumption
9. Leakage into & out of the Boilers
Air & flue gas leakages into the Boiler & out of the Boiler will reduce the working efficiency there by increasing the boiler fuel consumption
10. Steam leakage
It is a direct cause for higher steam consumption. Generally steam leakage is from vent & drains valves, welding & flange joints
11. Boiler heating surfaces internal scaling
Pressure parts namely water wall tubes, economiser tubes & super heater coils internal & external scaling will result into poor heat transfer, which increases fuel input to produce required amount of steam.
Pressure parts internal scaling can damage the pressure parts by over heating
12. Radiation & Convection losses
Radiation & convection losses in the boiler causes increased fuel consumption. These losses may be due to uninsulated or unlagged surfaces of boiler
13. Lower combustion air temperature
On every 20 Deg C decrease in combustion air temperature leads to Boiler efficiency reduction by 1%
14. More ash content in the fuel
More ash content in the fuel takes away heat associated with it during discharging through hoppers. Especially bed ash is having more temperature. Also higher ash fuel are having lower GCV
15. More Volatile matters (VM) in the fuel
Calorific value of the fuel reduces as the VM increases. Boilers using Lower GCV fuel consume more fuel
16. Other potential reasons for increased fuel consumption of a Boiler are;
Boiler design related issuers
Wrong selection of auxiliaries like fans & fuel feeding system
Low quality of Bed materials
Defects in fuel burners & fuel spreaders
Over refractory on internal heating surfaces
Faulty field instrumentsAlso read Why & How these in Boilers???