Page 296 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory
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272                          Biomass Gasification, Pyrolysis and Torrefaction


               The Koppers-Totzek atmospheric pressure gasifier also uses side feeding.
            It consists of two side-mounted burners where a mixture of coal and oxygen
            is injected. The gas leaves from the top of the gasifier at temperatures around
            1500 C and is quenched with water downstream. The reactor has a steam

            jacket to protect its shell from high temperatures (Higman and van der
            Burgt, 2008, p. 129).
               The E-gas gasifier is a side-fed two-stage entrained-flow slagging gasifier
            with a coal water slurry feed. It is designed to use sub-bituminous coal
            (Figure 8.17). The coal slurry is fed at the nonslagging stage, where the
            upflowing gas heats it. Thus, the gas exits at a lower temperature and then
            passes through a fire-tube boiler and is filtered in a hot candle filter. The
            char, separated out by the filter, is taken back to the slagging zone. The slag
            is quenched in a water bath at the bottom of the slagging reactor.

            8.4.3 Advantages of Entrained-Flow Gasifiers
            Entrained-flow gasifiers have several advantages over other types:

              Low tar production
              A range of acceptable feed
              Ash produced as slag
              High-pressure, high-temperature operation
              Very high conversion of carbon
              Low methane content well suited for synthetic gas production.

            8.4.4 Entrained-Flow Gasification of Biomass

            For thermal gasification of the refractory components of biomass (those diffi-
            cult to gasify) such as lignin, the minimum temperature requirement is simi-
            lar to that for coal (B900 C) (Higman and van de Burgt, 2008, p. 147).

            Entrained-flow gasification of biomass is therefore rather limited and has not
            been seen on a commercial scale for the following reasons:
              The residence time in the reactor is very short. For the reactions to com-
               plete, the biomass particles must be finely ground. Being fibrous, biomass
               cannot be pulverized easily.
              Molten ash from biomass is highly aggressive because of its alkali com-
               pounds and can corrode the gasifier’s refractory or metal lining.
               Given these shortcomings, entrained-flow gasifiers are not popular for
            biomass. However, there is at least one successful entrained-flow biomass
            gasifier known as the Choren process.

            8.4.4.1 Choren Process
            The Choren entrained-flow biomass gasifier is comprised of three stages
            (Figure 8.18). The first stage receives biomass in a horizontal stirred-type
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