Investigation and large-scale application of co-gasification and co-pyrolysis of biomass and coal are becoming more common recently. In addition to the reduction of CO2 emission, cogasification of biomass provides several advantages over biomass or coal gasification (Kumabe et al., 2007). One of the advantages is the reduction of sulfur and ash that cause equipment corrosion and environmental problems in coal gasification (Chmielniak and Sciazko, 2003; McLendon et al., 2004). It can also reduce the high cost of the feedstock and high tar generation in biomass gasification.

Likewise, co-pyrolysis has advantages over sole biomass or coal pyrolysis. Although pyrolysis of coal is a good method for producing liquid fuels, the yields of these products are limited because of the low H/C ratio in coal. The high H/C ratio in biomass renders bio­mass to act as a hydrogen donor in co-pyrolysis of biomass/coal blends. Moreover, the high thermochemical reactivity and high content of volatiles of biomass facilitate the conversion and the upgrading of the fuel. Therefore, it’s considered promising to co-fire the two fuels as a step toward valid, sustainable utilization of coal and biomass and to minimize the impact on the environment.

Pyrolysis gas has a high heating value, 17 MJ/kg (http://www. nh. gov/oep/programs/ energy/documents/biooil-nrel. pdf), and both pyrolysis oil and char can be gasified to pro­duce syngas; it is a promising technique to further process the pyrolysis products through gasification to produce syngas more efficiently. Here, the process consists of the pyrolysis and subsequent gasification sections. In the first reactor, biomass is pyrolyzed with coal at 500-700 °C. The pyrolysis gas is quenched to produce liquid oil, and the char is flowed to the gasifier where steam and limited air are supplied to produce syngas.