Design of Biomass Gasifiers - Biomass Gasification, Pyrolysis and Torrefaction - page 271

Syngas to
treating

Hot candle
filter

Fire tube
boiler

Second
stage

Coal
slurry

Char
recycle

First stage

Oxygen

Slag/water
slurry

Refractory

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.

.