Fluidized bed gasifiers

The application of fluidized-bed reactors in gasification processes started in the 1920s. The atmospheric fluidized-bed process was patented in 1922. The first gasification plant was built by Winkler in 1925. Since then, fluidized beds have been widely used in gasification processes. 

In the last several decades, many gasification processes have been developed using all three regimes of fluidization bubbling fluidized bed, circulating fluidized bed, and transport reactor. Each gasification process exploits the particular characteristics of a fluidization regime. 

The Winkler gasification process has many advantages such as low operating temperature, high reliability, and low tar in the gas product. However, due to the low operating pressure and temperature, the carbon conversion is also low (20%-30% carbon in ash). Most plants using the Winkler process have been shut down for almost entirely economic reasons. 

To improve the gas yield and increase the carbon conversion, many gasification processes (HTW, Kellogg Brown and Root [KBR], Kellogg-Rust-Westinghouse [KRW], U-Gas, etc.) have been developed with increased operating temperatures and pressures, and modified gas distributors. 

The HTW technique, developed by Rheinbraun, utilizes increased pressure (up to 3.0MPa) and operating temperature. In this process, a lock hopper and screw feeder are used to feed the coal particles into the reactor from a high-pressure charge bin. Due to the increases in both temperature and pressure, coal conversion in the HTW process is much higher than in the Winkler process. 

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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). 

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... 

Kojima, T., Yoshitake, H., Kimura, T., Matsukata, M., and Uemiya, S., Contribution of Local Reactions in the Grid Zone to the Performance of a Jetting Fluidized Bed Gasifier of Coal Char, Energy Fuels, 9 379 (1995)... 

KRW Figure 2.5 illustrates key features of this gasifier. Coal and limestone, crushed to below 1/4," are transferred from feed storage to the KRW fluidized-bed gasifier via a lock hopper system. Gasification takes place by mixing steam and... 

In the fluidized bed gasifier, crushed coal is introduced into a fluidized bed of char together with oxygen or air and steam. Coal undergoes drying, devolatilization, gasification and combustion at essentially constant temperature of about 1000 C because of the rapid mixing characteristics of fluidized beds. 

Warnecke, R. 2000. Gasification of biomass comparison of fixed bed and fluidized bed gasifier. Biomass Bioenergy 18 489-497. 

Figure 2. Differentiation between liquefaction and gasification by-product waters by pH and redox potential characteristics 1 and 2, waste water PETC coal liquefaction development unit, disposable catalyst, runs DCD 13B and DCD 12 3, waste water, SRC-1 plant 4, scrubber water, light oil, Blacksville No. 2 coal 5, waste water, fixed-bed gasifier, METC 6, waste water, fluidized-bed gasifier, Rosebud coal, PETC 7, gasifier condensate, 40 atm Nt, catalyst-impregnated Illinois 6 coal 8, gasifier condensate, 40 atm He, Montana Rosebud coal.

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