Page 295 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory
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Chapter | 8  Design of Biomass Gasifiers                     271


                                                               Syngas to
                                                                treating



                                                                Hot candle
                                                                  filter
                                               Fire tube
                                                boiler
                                   Second
                                    stage
                  Coal
                 slurry
                                                       Char
                                                      recycle
                                  First stage


                       Oxygen
                                       Slag/water
                       Refractory
                                         slurry
                                     Slag
                                  by-product

             FIGURE 8.17 A schematic of a side-fed entrained-flow gasifier.

                The fuel gasifier process of Siemens uses a top-fired reactor design, in
             which the reactants are introduced through the single centrally mounted
             burner. This has several advantages. First, it is of an axisymmetric construc-
             tion, reducing equipment costs; second, the flow of reactant occurs from a sin-
             gle burner, reducing the number of burners to be controlled; finally, the prod-
             uct gas and the slag flow in the same direction, which reduces any potential
             blockage in a slag trap (Higman and van der Burgt, 2008, p. 132).

             8.4.2 Side-Fed Gasifier

             In side-fed gasifiers, powdered fuel is injected through horizontal nozzles set
             opposite each other in the reactor’s lower section (Figure 8.17). Jets of fuel
             and gasifying agents form a stirred-tank reactor characterized by a high
             degree of mixing. The product gas moves upward and exits through the top.
             Because of the high oxygen availability in this mixing zone, rapid exother-
             mic reactions take place, raising the gas temperature to well above the

             ash-melting point (.1400 C). Thus, the ash, instead of traveling up, is sepa-
             rated in this zone as slag from the fuel and drained. Some gasifier designs
             (e.g., E-gas, MHI, and Eagle) inject additional fuel further downstream from
             the main reaction zone.
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