Gasification

Hie Winkler Process

The Winkler atmospheric fluid-bed process was the first modern continuous gasifi­cation process using oxygen rather than air as blast. The process was patented in 1922 and the first plant built in 1925. Since then some 70 reactors have been built and brought into commercial service with a total capacity of about 20 million Nm3/d (Bogner and Wintrup 1984). This process is now, however, only of historic interest, since all but one of these plants has been shut down almost entirely for economic reasons. (See Figure 5-8.)

The Winkler process is operable with practically any fuel. Commercial plants have operated on browncoal coke, as well as on sub-bituminous and bituminous coals. Coal preparation requires milling to a particle size below 10 mm but does not require drying if the moisture content is below 10%. The feed is conveyed into the gasifier or generator by a screw conveyor. The fluid bed is maintained by the blast, which enters the reactor via a conical grate area at the base. An additional amount of blast is fed in above the bed to assist gasification of small, entrained coal particles. This also raises the temperature above that of the bed itself, thus reducing the tar content of the syngas. The reactor itself is refractory lined. Operation temperature is maintained below the ash melting point. Most commercial plants have operated between 950 and 1050°C. At maximum load the gas velocity in a Winkler generator is about 5 m/s. The flow sheet incorporates a radiant waste heat boiler and a cyclone

to remove the ash. The ash contains a considerable amount of unreacted carbon— over 20% loss on feed (Kunii and Levenspiel 1991)—which can be burnt in an auxiliary boiler. Final solids removal is effected with a water wash (not shown in Figure 5-8).