Gasifier design

Improved gasifier designs would be more durable and capable of handling a variety of carbon-based feedstocks. Advanced gas cleaning technologies would capture virtually all of the ash particles, sulfur, nitrogen, alkali, chlorine and hazardous air pollutants. 

The three principal reactor types employed in coal gasifier design are the moving packed bed, the entrained flow, and the fluidized bed reactor. In the discussion of gasification principles the moving packed bed (Fig. 3) was used to illustrate steam-oxygen or steam-air gasification of coal. 

Coal gasifier designs are almost as numerous as the many different types and ranks of coal. The basic configurations, hardware, and operations that have been considered are described here because several of them are applicable to biomass gasification (c/. National Academy of Engineering, 1973, and accompanying references). 

A few representative biomass gasification processes that have been commercialized or that are near commercialization are described here to illustrate some of the details of gasifier designs and the operating results. The biomass pyrolysis plants described in Chapter 8 are not discussed here because the major products are liquids and charcoals, and the by-product gases are used for plant fuel. 

Compositions of combustion deposits from probes in the disengagement zone and horizontal pass show that virtually all of the potassium in the deposits can be accounted for as chloride (30%) and sulfate (70%). Although the probe locations employed are not representative of commercial gasifier designs, the collected deposits show K to be present primarily in other forms, either as bed particles or soil minerals adhering to these organic material rich deposits. 

Flow direction. This must be examined from two points of view. First we consider the flow direction of the reactants in relation to one another. In an entrained-bed process the reactants flow by definition in co-current flow, but in a moving-bed reactor one has a choice. The most well-known moving-bed reactor, the Lurgi-Sasol dry bottom gasifier, operates in counter-current flow, but there are a number of smaller gasifier designs that use cocurrent flow to reduce the tar make. 

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