Ikelic - Alliance Digital Repository

COAL
be maintained on a sustainable basis and to Im
prove the eco-acceptabllity of coal-fired power
production. In part this will be achieved through
improvements to cycle efficiency, as this con
tributes to both the environmental and security-
of-supply constraints. A complementary solution
is to replace some coal by fuels which reduce
C02
phere.
and other pollutants released into the atmos
An example of this approach is the initiative that
has been established by the European Commis
sion within the APAS Program. A short duration
multipartner collaborative program has been set
up, to determine and evaluate the impact on
gasification processes of utilizing biomass,
sewage sludge and other wastes as co-
feedstocks with coal. The intention is to provide
a link between the application of regenerative
energy sources and the utilization of coal, so of
fering improvements in the economical use of fos
sil fuels with a reduction in environmental impact
and the utilization of associated waste materials.
The co-gasification applied research and develop
ment project was undertaken by industry, in
dustrial research organizations and appropriate
universities. CRE Group Ltd., is the overall coor
dinator for the project.
Several types of gasification technology have
been evaluated, namely fluidized-bed, moving-
bed and entrained-flow. In terms of capacity, the
test equipment ranges from small laboratory
scale rigs to a large scale (150 megawatt) unit.
The use of sewage sludge in combination with
both brown and hard coals is being examined by
Rheinbraun and British Coal Corporation respec
tively. Trials have been undertaken by
Rheinbraun on a process demonstration unit
(PDU) at the Technical University of Aachen and
on the High Temperature Winkler demonstration
plant. Apart from sewage sludge, other waste
materials such as loaded brown coal cokes, have
been processed at Rheinbraun. At British Coal,
preliminary
test work with hard coal and pei-
letized sludge in an atmospheric fluidized-bed
gasifier rig has been followed by more extensive
4-26
trials in a pressurized unit. This has a thermal in
put of 2 megawatts and comprises a spouted
bed gasifier, a cyclone, hot gas filtration unit and
fuel gas combustor.
The use of biomass-derived fuel sources such as
straw, wood and miscanthus, and the impact of
the different feedstocks with coal on gasifier per
formance and operability are being investigated
several partners. The Technical Research
by
Center of Finland (VTT) has carried out tests on
their pressurized fluidized-bed gasifier, using
Polish coal and Finnish pine sawdust and various
woody biofuels. They have also undertaken
some preliminary trials for Elkraft using Danish
wheat straw. Elkraft has also subcontracted test
work on the entrained flow gasifier at Noell-DBI.
Their studies have shown that pulverized straw
can be gasified in an entrained-flow gasifier,
either alone or in mixtures with coal, to give a
high carbon conversion. The gas, after purifica
tion, can be fired in a gas turbine. In contrast,
gasification of straw alone in a fluidized-bed
gasifier is extremely
difficult due to ash sintering.
Co-gasification of straw and coal appears to be a
promising possibility in the immediate future.
A program to examine the feasibility of using
fluidized-bed gasification technology to utilize
low grade Spanish coal/wastes and biomass
blends, has been established by CIEMAT in con
junction with Union Fenosa, CENET, Lurgi and
TPS. Test work at the University of Cataluna will
be followed by pilot plant studies at Lurgi and
TPS, and modeling activities. Preliminary results
from the Lurgi circulating fluidized-bed gasifier tri
als suggest that the addition of high volatile
biomass enhances the gasification of low reac
tivity coal processing wastes.
Fuel Gas Contaminants
A key issue for co-gasification is the release and
control of fuel gas contaminants such as tars, sul
fur and nitrogen species, halldes and alkali met
als. At VTT the emphasis of the work was on the
formation of different gas impurities in the
gasification of wood, coal and straw. Their work
showed that the gasification and hot gas clean-
THE SYNTHETIC FUELS REPORT, JANUARY 1995