Fluidized bed coal gasifier

In operating a fluidized bed reactor such as a fluidized bed coal gasifier, fine particles tend to be elutriated from the fluidized bed. The elutriated fines, if not recovered, represent a significant carbon loss and thus a significant loss of reactor efficiency. In actual industrial practice, the fines are recycled back to the fluidized bed for further consumption. The location of the fines reinjection point into the fluidized bed reactor is important in order to maximize the consumption of fines in each pass. Otherwise, the fines will build up in the recycle loop and increase the heat load of the reactor operation. The fines reinjection location is selected to maximize the fines residence time in the bed and to provide an conducive environment for consumption, such as high temperature and an oxidizing atmosphere. 

Figure 3. Schematic of fluidized-bed coal gasifier with typical reactor temperature...

The application of large scale computer simulations in modeling fluidized bed coal gasifiers is discussed. In particular, we examine a model wherein multidimensional predictions of the internal gas dynamics, solid particle motion and chemical rate processes are possible. 

The fluidized bed coal gasifier computer model is designed to provide a description of the hydrodynamic mixing and coupled chemistry within the reactor. This model should permit a designer to predict bubble size,... 

The chemistry component of the model is, in most aspects, identical to the chemistry of the classical models of fluidized bed gasification. A major difference between the classical reactor models and the present fluidized bed coal gasifier computer model is that the classical models require specification of the bed hydrodynamics, such as bubble size. The present model can predict bubble size and the associated solids mixing. Again it is expected that the two types of models are complimentary. The present model can be used to define the hydrodynamics in the hot reactive environment and these hydrodynamics (e.g., bubble size) can then be used as... 

Weimer Alan W. and Clough D.H., Modeling a Low Pressure Steam-Oxygen Fluidized Bed Coal Gasifying Reactor , Chemical Engineering Science Vol. 36, pp. 549-567, Pergamon Press Ltd., 1981. 

Tests have been conducted in a laboratory hot cyclone to obtain an estimate of the temperature below which spherical glass particles do not form a firmly attached deposit. A temperature of 800 to 850 C, corresponding to a viscosity between 6.3 X 10 and 2.9 X 10 poises, as calculated from the composition of the glass, was found. We take this viscosity to be approximately that of coal ash above which particles will not deposit in cyclones of fluidized-bed coal gasifiers. 

Mori S, Nomura S, Kurita M, Hiraoka S, Yamada I. Modeling for the fluidized bed coal gasifier. In Kunii D, Toei R, eds. Fluidization IV, Kashikojima, Japan. New York Engineering Foundation, 1983, pp 639-646. 

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 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 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. 

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