ABSTRACT
The technology for reacting suspended coal particles with a gas fl owing through them dates back to the 1920s when the Winkler gas generator was developed in Germany. The petroleum industry was responsible for the commercial expansion of fl uidization techniques in the U.S. (1940s), particularly in the use of solids which catalytically crack vaporized heavy oils to produce gasoline and other petroleum fuels. The application of fl uidized bed combustion (FBC) technology (to various solid fuels) is widespread in the U.S. and in other countries for all types of industrial processes. More than 350 atmospheric fl uidized bed units are operating in North America, Europe and Asia. FBC is part of the answer to the question-how do we control our major emissions from coal sources? Briefl y an FBC boiler is a fi nely divided bed of solid fuel particles in admixture with limestone particles which are suspended or conveyed by primary combustion air moving in the vertical upward direction. The limestone reacts with sulfur dioxide to remove it from the fl ue gas. The low uniform temperature (ca 1550F) has a benefi cial effect on nitrogen oxide suppression. The emission from coal combustion schemes of nitrogen oxides (NO
2 ), together with carbon oxides (CO and CO 2 ), particulate matter and solid wastes must
always be compared when evaluating various alternative schemes. The potential consequences of gaseous emissions, include the greenhouse effect and acid rain, which have received much publicity in recent years. The practical FBC limit of SO
2 removal is currently about 95%. Nitrogen oxide formation is lower than with conventional pulverized coal (PC) boiler NO
TYPES OF FLUIDIZED BED COMBUSTORS (FBCS)
FBCs are generally referred to as either circulating (CFB) or bubbling beds. However, the bubbling type may be classifi ed according to whether reaction takes place at atmospheric (AFB) or under pressurized conditions (PFB).
