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Show efficiencies. In this case the gas effluent from a catalyst regenerator passes through a dust separator and a gas expander, a crude form of gas turbine, to recover the mechanical energy from the flue gas effluent. This was the precursor of pressurized fluidized-bed combustion (PFBC). The fluidization technology was developed under the sponsorship of several oil companies; Exxon, then Esso, was the major sponsor. After the war, Exxon sold or leased some of its fluidization technology to Dorr-Oliver, a company which had a long history in solid-liquid handling. This transition was made under the agreement that Dorr-Oliver would concentrate its fluidization effort in roasting of ores, calcining of limestone, and waste incineration. Further developments in FBC came about as result of England's energy famine. An efficient means of extracting heat energy had to be found. English coal seams are often less than 3 feet thick, and there is no easy way to get rid of the inert rock which is inadvertantly mined with the coal. FBC was found to be one means to burn coal with such high inert-solid content, and fluidized-bed combustion has worked well in England. The British researchers found that the heat transfer coefficients achieved in FBC were roughly five to 10 times higher than in a conventional boiler. The British are currently conducting research in pressurized fluidized-bed combustion (PFBC) for development of more compact FBC boilers and better application to combined cycle power generation. At this same time two U.S. boiler makers, Babcock & Wilcox and Combustion Engineering, were also conducting in-house FBC research. The U.S. FBC research, however, was not as actively pursued until the late sixties, when a retired mechanical engineer, John Bishop, was employed by Pope, Evans and Robbins, an architecture and engineering firm, to develop new types of, or variations on, coal-fired boilers. Mr. Bishop selected FBC as a good potential alternative to conventional coal-fired boilers. Fluidized-bed combustion is not a novel technology, but an evolving one. It has technical continuity in this country as a result of Government and private research. Today, one can buy a fluidized-bed incinerator off-the-shelf from companies like Dorr-Oliver, Copeland, Fuller, and many others. The quality of these units and further realization of potential applications for FBC is constantly improving and expanding as data from continuing research is applied to the technology as a whole. Basic Components of a Fluidized-Bed Combustion Boiler In figure 3, a schematic diagram is shown describing basic components of a typical fluidized-bed combustion boiler. Air from a compressor is preheated (exhaust flue gas from the fluidized-bed combustor can be used for this purpose). The preheated air enters the plenum, an air chamber under the air distributor. The plenum serves as a surge tank which tempers any pressure pulses from the piping system and the air mover. The air distributor's main function is the even distribution of air across the bottom of the fluidized bed. 11-5 |