Fluidization gasifier

The means by which synthetic gaseous fuels could be produced from a variety of biomass sources are variable and many of the known gasification technologies can be appHed to the problem (70,71,76—82). For example, the Lurgi circulatory fluidized-bed gasifier is available for the production of gaseous products from biomass feedstocks as well as from coal (83,84). 

The heavy vacuum bottoms stream is fed to a Flexicoking unit. This is a commercial (125,126) petroleum process that employs circulating fluidized beds at low (0.3 MPa (50 psi)) pressures and intermediate temperatures, ie, 480—650°C in the coker and 815—980°C in the gasifier, to produce high yields of hquids or gases from organic material present in the feed. Residual carbon is rejected with the ash from the gasifier fluidized bed. The total Hquid product is a blend of streams from Hquefaction and the Flexicoker. 

The first coimneicial fluidized-bed systems used WinMei units in which lignite and its chat are gasified at atmospheric pressure with ait or oxygen... 

A medium heat (11.2 MJ/m (300 Btu/ft )) gas for iadustrial appHcation has been produced at Westiaghouse Electric s pilot plant ia Waltz Mill, Pennsylvania (50), where lignite is gasified ia a pressurized fluidized bed which uses oxygen and steam. 

The CO2 Acceptor process, also developed under AGA/DOE sponsorship, by the ConsoHdation Coal Co., uses steam to gasify lignitic coal. Heat is supphed by the exothermic reaction between CO2 and calciaed dolomite [17069-72-6]. The dolomite is calciaed ia a separate fluidized bed. This process operates ia a 40 t/d pilot plant, but there are no plans for commercialization as of this writing. 

There are essentially three types of coal gasifiers moving-bed or countercurrent reactors fluidized-bed or back-mixed reactors and entrained-flow or plug-flow reactors. The three types are shown schematically in Eigure 2. 

Dried coal is pneumatically conveyed to feed bins, pressurized through lockhoppers, and fed to the refractory-lined fluidized-bed gasifier vessel by variable-speed screws. The gasifying agent, mixed oxygen and steam, is fed near the bottom of the gasifier. The bed operates at 2.5 MPa (25 bar) and... 

Physical Properties The free-swelling index (FSl) measures the tendency of a coal to swell when burned or gasified in fixed or fluidized beds. Coals with a high FSl (greater than 4) can usually be expected to cause difficulties in such beds. Detads of the test are given by the ASTM D 720 (American Society for Testing and Materials, op. cit.) and U.S. Bureau of Mines Report of Investigations 3989. 

The subjeet of fluidization and researeh and development in this field, probably reaehed its peak in the early 1980 s with extensive work being applied by the petroleum industry in synthetie fuels development sueh as shale oil, eoal gasifieation, pyrolysis applications. Prior to this, significant development work was done in the petroleum industry for flexieraeking and flexieoking operations. Fluidization still remains an area of aetive researeh and industry development, and the teehnology is well established in a variety of industry seetors. 

Beyond the ATS program, the DOE is looking at several new initiatives to work on -with industry. One, Vision 21, aims to virtually eliminate environmental concerns associated with coal and fossil systems while achieving 60 percent efficiency for coal-based plants, 75 percent efficiency for gas-based plants, and 85 percent for coproduction facilities. Two additional fossil cycles have been proposed that can achieve 60 percent efficiency. One incorporates a gasifier and solid oxide fuel into a combined cycle the other adds a pyrolyzer with a pressurized fluidized bed combustor. Also under consideration is the development of a flexible midsize gas turbine. This initiative would reduce the gap between the utility-size turbines and industrial turbines that occurred during the DOE ATS program. 

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