Environmental Performance of Coal-Fired FBC
AUTHOR: Mitsuru Takeshita
DATE: November 1994
First introduced in the 1970s, the attraction of coal-fired FBC technology has been its fuel flexibility, in situ SO2 control and inherently low NOx emissions. Over the last decade, AFBC has been rapidly scaled up to relatively large scale co-generation plants and power plants (up to 250 MWe). PFBC and hybrid cycle PFBC have been developed as clean coal technologies with high thermal efficiencies. This report reviews the environmental performance in commercial coal-fired AFBC as well as PFBC and hybrid PFBC. Environmental emissions of concern include SO2, NOx, N2O, particulates, trace elements, organic compounds and residues. Emissions control in FBC is comparable with that of PC-fired plant and IGCC from the viewpoint of efficiency, reliability of operation and economics.
The environmental performance of FBC has been greatly improved through the optimisation of operating parameters and the introduction of advanced designs such as those incorporating fly ash recirculation and SNCR. FBC can meet even the most stringent of current emission limits. Elevated N2O emissions and difficulties with the management of residues are the major disadvantages. N2O is recognised to have a role in ozone depletion in the stratosphere and is a potent greenhouse gas. One promising measure to reduce the N2O emissions by means of afterburning in the cyclone has recently been demonstrated in a pilot plant. Disposal of residues may increase the O&M cost, depending strongly on the coal sulphur content and site-specific conditions.