Biomass-coal cofiring has been commonly performed by a number of coal power plants in Europe and America with a primary motivation for reducing the environmental impact of emissions. Currently the percentage of cofiring biomass with coal is still small on average below 10%. It can also occur due to a limited supply of wood pellets. But in terms of operational cofiring biomass-coal fly ash will reduce significantly. On the other hand, if the percentage of biomass-coal cofiring is added will cause deposits on boiler pipes that will disrupt the process of heat transfer in the furnace causing inefficient use of fuel with one indicated by the high temperature of the fluegas.
There are three techniques commonly used in biomass-coal cofiring:
1. Mixing of biomass and coal in the fuel handling system (then fed to the boiler).
2. Setting up a separate biomass with coal, and then inject into the boiler.
3. Gasification of biomass to produce a gas which is then burned in the boiler directly or using the integrated gasification combined cycle (IGCC) system.Worldwide reported more than 200 coal power plant that has been tested with biomass (IEA 2010).
Several cofiring options are available on in coal powerplant, among others:
-Cofire with a low percentage of biomass, with a slight modification of the equipment.
-Cofire with a high percentage of biomass, by upgrading equipment.
- Convert/repower individual coal burners to be fired with biomass
- Convert/repower entire coal plants to be fired with biomass
- Cofire with torrefiedwood
Ash content in coal and biomass are generally differ quite large and moreover ash chemistry are also a lot of different. This is factor that causes a lot or at least a deposit in the boiler pipes.Percentage of cofiring biomass-coal up to 10% is generally acceptable. Optimal percentage that causes minimal boiler tube deposits and significant reduction in fly ash can be searched based on the variable characteristics of coal and biomass are used.