Biomedical Engineering Reference
In-Depth Information
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 (
900 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:
B
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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