Environmental Engineering Reference
In-Depth Information
exposed to steam and carefully controlled amounts of air or oxygen under high
temperatures and pressures. Sulphur is converted to hydrogen sulphide (clean-up
reactor in
Fig. 5.3
) and can be captured by processes presently used in the
chemical industry.
The exhaust heat from the combustion turbine is recovered in the heat recovery
steam generator to produce steam. The waste heat is passed to a steam turbine
system, while heat is recovered from both the gasification process and the gas
turbine exhaust in advanced boilers producing steam. The steam is then used in
steam turbines to produce additional electrical power, while the syngas mixture
could also feed a fuel cell plant (IGFC).
A potential advantage of this technology is that carbon dioxide can be easily
separated from the syngas and then captured, instead of being released into the
atmosphere [
56
-
58
]. If oxygen is used in a coal gasifier instead of air, carbon
dioxide is emitted as a concentrated gas stream in syngas at high pressure. In this
form, it can be captured and sequestered more easily and at lower costs. Finally,
plasma technology added to gasification plant has been recently proposed to
improve energy performance and quality of product mixtures [
59
].
Hydrogen could be produced from coal gasification with near-zero greenhouse
gas emissions only if CCS technology, in particular the crucial sequestration stage,
will be successfully developed in the next decades. In this view, the coal gasifi-
cation technology appears most appropriate for large-scale, centralized hydrogen
production plants, where handling of large amounts of coal and CCS technologies
could be more functionally managed. Significant technological efforts towards the
development of an advanced apparatus capable to enhance efficiency, environ-
mental performance and reliability appear necessary.
2.1.1.5 Biomass Gasification
The choice of a carbon neutral source class as feedstock for hydrogen production,
such as biomass substances, could permit the problem of carbon dioxide emissions
to be overcome.
In recent years, several methods for hydrogen production starting from biomass
materials have been investigated [
60
-
62
], and great efforts have been addressed in
particular in selecting advanced solutions for optimization of the previously ana-
lysed thermal processes, such as SR or gasification, by substituting the fossil fuel
feedstocks (coal or petroleum-derived fuels) with different types of biomass-
derived fuels.
In particular, biomass-derived materials could be converted in gasifiers, to
obtain a gaseous mixture of hydrogen, carbon monoxide, carbon dioxide and other
compounds, by applying heat under pressure in the presence of steam and a
controlled amount of oxygen, very similar to coal gasification process. On the
other hand, the produced syngas could be reformed to maximize hydrogen pro-
duction but it may also feed an electrical power plant coupled to an electrolysis
unit [
63
].
