Fuels for Biomass Cofiring
AUTHOR: Rohan Fernando
DATE: December 2005
There is considerable current interest in the use of biomass for power generation. This is due to several reasons, the principal one being that, if the biomass is grown in a regenerative manner, its combustion will not produce any net CO2 emissions. Many countries have initiated various incentives in recent years to encourage the utilisation of biomass for electricity production. However, there are some disadvantages of the use of biomass which relate to its supply, transportation and composition but these can be reduced if the biomass is cofired with coal. Direct cofiring involves firing the coal and biomass in the same boiler. This is the simplest and most widely applied technology for cofiring biomass. As all the constituents of the biomass enter the coal boiler, several technical issues arise depending on the type of boiler and the kind of biomass. Biomass cofiring has been successfully demonstrated in over 150 installations worldwide for most combinations of fuels and boiler types. About a hundred of these have been in Europe. In the US there have been over 40 commercial demonstrations and the remainder have been mainly in Australia.
A broad combination of fuels, such as residues, energy crops, herbaceous and woody biomasses have been cofired in PCC, stoker and cyclone boilers. The proportion of biomass has ranged from 1% to 20%. The experience of biomass cofiring in PCC boilers has demonstrated that, cofiring woody biomass resulted in a modest decrease in boiler efficiency but no loss of boiler capacity. There was, however, a considerable reduction of SO2, NOx and mercury emissions. Though herbaceous biomass have cofired in several plant worldwide, their higher inorganic matter content results in higher chance of slagging and fouling. Cofiring herbaceous fuels tend to be more difficult and costly than other fuels but it is possible to cofire these fuels if there is a regulatory incentive to do so.