Environmental Engineering Reference
In-Depth Information
(von Linde) and advances made in the manufacturing of high-pressure vessels set off
the development of high-pressure oxygen-blown gasification. The Lurgi dry ash
(1936) process was the first oxygen-blown moving bed gasifier. Like the Siemens
gasifier, the Lurgi gasifier was operated at temperatures below 1000
C in order to pre-
vent ash melting. This system is, though in slightly modified form, still in operation
(e.g., by Sasol). In 1938, the Koppers-Totzek entrained flow (EF) gasifier came into
commercial use. The Koppers-Totzek gasifier produced synthesis gas (CO and H
2
)
containing no tars and methane on a continuous basis at ca. 1850
C and atmospheric
pressure from oxygen-entrained coal. In relation to these developments, a start was
made in Germany with the production of Fischer
Tropsch (FT) diesel from, a.o.,
wood-derived synthesis gas. This was all done because of the scarcity of liquid fuels
and to become independent of imported oil. After the war, the interest in this technol-
ogy rapidly declined because of the increasing availability of cheap crude oil. At the
end of the 1940s and in the early 1950s, Texaco and Shell developed technologies for
the production of the synthesis gas by oil gasification. These were EF reactors with
top-mounted burners (atomizers) operated in the downflow mode. Operating pres-
sures up to 8.0 MPa and temperatures in the range of 1250
-
1500
C were used. Apart
from Texaco and Shell, also Lurgi developed oil gasification technology, known as
multipurpose gasification.
Nowadays, most oil gasifiers are part of a refinery and are used for polygeneration
of power, H
2
/synthesis gas, and steam. As a result of the oil crisis of the early 1970s,
coal gasification was taken up again. It was again Texaco and Shell (together with
Krupp-Koppers) that developed EF high-pressure (2
-
-
7 MPa) and high-temperature
(>1400
C) coal gasification.
The past decades have shown a gradually increased momentum in the development
of biomass gasification related to the need for green transportation fuels accompanied
with decreased oil dependency, a minimum impact on net CO
2
emissions, and no
competition with food and feed production and land usage.
10.3
(CO)GASIFICATION TECHNOLOGIES FOR DRY BIOMASS
Gasification of biomass, also together with other fuels, e.g., coals, can be carried out
using a variety of chemical reactors, still a number of which are under development at
different commercial companies and research institutes. Since the first (controlled)
attempts regarding thermochemical gasification of biomass, a number of reactor
designs have evolved that are considered as suitable. These reactors can be classified
according to the transport processes occurring (Brown, 2011):
Fixed beds/moving beds: countercurrent updraft, cocurrent downdraft, and
cross-draft
Fluidized beds: bubbling, circulating, and dual connected
EF reactors
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