Fluidized-bed steam generator

FIG. 17-30 Fluidized-bed steam generator at Georgetown University 12.6-kg/s (100,000-lb/h) steam at 4.75-MPa (675-pslg) pressure. (From. Georgetown Univ. () Tech. Frog. Rep. METC/DOE/10381/135, July-September 1980.)... 

Another hydrogenation process utilizes internally generated hydrogen for hydroconversion in a single-stage, noncatalytic, fluidized-bed reactor (41). Biomass is converted in the reactor, which is operated at about 2.1 kPa, 800°C, and residence times of a few minutes with steam-oxygen injection. About 95% carbon conversion is anticipated to produce a medium heat value (MHV) gas which is subjected to the shift reaction, scmbbing, and methanation to form SNG. The cold gas thermal efficiencies are estimated to be about 60%. 

Fig. 11. Typical circulating fluidized-bed (CFB) steam generator. FBHE = Fluidized bed, high efficiency...

This process (usually with addition of steam) can also be used to generate gas mixtures from partial oxidation of coal for synthetic gasoline production (see (4), above). Fluidized beds offer convenience for continuous handling of the feed solids. 

Fluidized bed reactors typrcally are vertical cylindrical vessels equipped with a support grid and feed sparger system for adequate fluidization and feed distribution, internal cooling coils for heat removal, and either external or internal cyclones to minimize catalyst carryover. Fluidizauon of the catalyst assures intimate contact between feed and product vapors, catalyst, and heat-transfer surfaces, and results in a uniform temperature within the reactor. Reaction heat can be removed by generating steam within the cooling coils or by some oilier heat-transfer medium. 

Fluidized-bed combustors are complex chemical reactors, a fact often overlooked because their primary purpose is to generate steam and electricity. The reactions of importance in fluidized beds include those relating to coal combustion,... 

A further example of using chemical fluidized-bed processes is that of plants where fluidizable solids are used as a heat transfer medium. Willing [98] describes the use of this process for the cracking of oil arrears, but fluidized-bed plants are also suitable for catalytic or gas-solid reactions. The easy controllability of the reactor temperature is emphasized by Baranek et al. [7], wherein the heat of reaction can be used by immersed coolers to generate steam. The isothermal behavior, and the possibility of both supplying and removing heat, are further advantages. 

Analysis of Industrial Processes Application to Pressurized Fluidized Bed Combustor with Steam and Gas Turbine Generators," Paper 10, Intern. Conference on Cogeneration, Washington, D.C., Oct. (1981). 

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