How to improve efficiency of AFBC Boiler

 

How to improve efficiency of AFBC Boiler:

1.      Optimize combustion air supply:  Boiler is designed for particular air and fuel ratio. This ratio also related to excess O2 which is measured after APH . There is minimum excess O2 is to be maintained by tuning the air flow into the furnace. Typically, in AFBC and CFBC boiler excess O2 is maintained 2-3% in optimum operating condition. There are two types of air supplied in this type of boilers, one is primary air (PA) and another is Secondary Air (SA). There is also a ratio between the PA and SA air. PA is basically help to fluidise the bed and secondary air is used to create turbulence at the free board zone for better combustion.

2.      Improve Feed Water Temperature: Raising feed water temperature basically increase the cycle efficiency by reducing the fuel consumption. Every 6deg.C rise in feed water temperature increase the efficiency by 1%.

3.      Reduce flue gas temperature: Reducing the flue gas temperature after APH actually reduces the heat losses to the atmosphere. Every 10Deg.C reduction of the flue gas temperature 1% efficiency of the Boiler increases.

4.      Bed Management: Bed level or bed inventory is to be maintain according to the bed temperature and Bed DP. Sometimes due to impurities in fuel bed bulk density (BD) becomes heavy. So it is to be drained and fresh bed material is to be charged to maintain the bed temperature. Sometimes excessive ash also reduces the bed temperature and increases the bed height.

5.      Control loss on ignition (LOI): LOI can be controlled by increasing the bed temperature, maintaining the proper air /fuel ratio, maintaining fuel sizing, bed material sizing and bed inventory, maintaining proper fluidization across the bed, maintaining the proper nozzle condition, maintaining proper PA/SA air ratio.

6.      Choose proper fuel quality: Each boiler is designed for particular type of fuel to run for optimum efficiency rather it can operate with a fuel having range of GCV (worst, normal and better). Fuel analysis is done in two types one is proximate and another is ultimate analysis. Fuel quality should be within the range it is designed to get the optimum efficiency of the boiler.

7.      Good insulation and soot blower:  Proper insulation outside the boiler reduces the radiation losses of the boiler and soot blowing actually increases the heat transfer of the boiler tube.

8.      Cycle of concentration of the Boiler water: To maintain the Boiler water quality chemical dosing is done in Boiler (HP dosing) and turbine cycle (LP dosing) and make up water is used as DM water with elevated pH by dosing morpholin. All these chemical should have less impurities. Daily and online monitoring system will also optimize the losses in the sytem.

So the blowdown loss will be minimum.

9.      Proper O&M practices: Trained operation and maintenance crew with standard operating procedure will increase the reliability and efficiency of the Boiler.

10. Typically AFBC Boiler efficiency varies from 78-80% to 81-83%