Gas

Abstract
The main results of an experimental work on gasification of Colombian coal in a fluidised bed
are reported in this paper. Experiments were carried out at different steam/coal (F
s
/F
c
) and
air/coal (F
a
/F
c
) ratios and temperatures of gasifying agent. In addition, the influence of bed
temperature on coal conversion was analysed. Results show a maximum value in the curve of
high heating value versus F
a
/F
c
. From the environmental standpoint, low concentrations of
sulphur compounds were obtained but more work should be done in order to decrease particulate
matter.
Abstract
The coal gasification process of a slurry feed type, entrained-flow coal gasifier was numerically
predicted in this paper. By dividing the complicated coal gasification process into several
simplified stages such as slurry evaporation, coal devolatilization and two-phase reactions
coupled with turbulent flow and two-phase heat transfer, a comprehensive numerical model was
constructed to simulate the coal gasification process. The k–ε turbulence model was used for the
gas phase flow while the Random-Trajectory model was applied to describe the behavior of the
coal slurry particles. The unreacted-core shrinking model and modified Eddy break-up (EBU)
model, were used to simulate the heterogeneous and homogeneous reactions, respectively. The
simulation results obtained the detailed information about the flow field, temperature and species
concentration distributions inside the gasifier. Meanwhile, the simulation results were compared
with the experimental data as a function of O
2
/coal ratio. It illustrated that the calculated carbon
conversions agreed with the measured ones and that the measured quality of the syngas was
better than the calculated one when the O
2
/coal ratio increases. This result was related with the
total heat loss through the gasifier and uncertain kinetics for the heterogeneous reactions.

Abstract
Thermodynamic equilibrium calculations using the HSC-Chemistry program were performed to
determine the distribution and mode of occurrence of potentially toxic and corrosive trace
elements in gases from coal gasification processes. The influence of temperature, pressure and
gas atmospheres on equilibrium composition was evaluated. In these reducing conditions, the
behaviour of the trace elements is complex, but some form of organization can be attempted.
Elements


were classified into three groups. Group A includes those elements that, according to
thermodynamic data at equilibrium, could probably be condensed in coal gasification. Mn is
classified in this group. Group B contains those elements that could be totally or partially in gas
phase 888in gas cleaning conditions, and can be divided into two subgroups, depending on
whether the cleaning conditions are hot or cold. Co, Be, Sb, As, Cd, Pb, Zn, Ni, V, Cr are
elements in this gvvvvroup. Group C contains those elements that could be totally in gas phase in
all the possible conditions, including flue gas emissions. Se, Hg and B are the elements that
make up this group.



Coal gasification is the process of producing syngas–a mixture consisting primarily of methane
(CH
4
) carbon monoxide (CO), hydrogen (H
2
), carbon dioxide (CO
2
) and water vapor (H
2
O)–
from coal and water, air and/or oxygen. Historically, coal was gasified using early technology to
produce coal gas (also known as "town gas"), which is a combustible gas traditionally used for
municipal lighting and heating before the advent of industrial-scale production of natural gas. In
current practice, large-scale instances of coal gasification are primarily for electricity generation,
such as in integrated gasification combined cycle power plants, for production of chemical
feedstocks, or for production of synthetic natural gas. The hydrogen obtained from coal
gasification can be used for various purposes such as making ammonia, powering a hydrogen
economy, or upgrading fossil fuels. Alternatively, coal-derived syngas can be converted into
transportation fuels such as gasoline and diesel through additional treatment via the Fischer-
Tropsch process or into methanol which itself can be used as transportation fuel or fuel additive,
or which can be converted into gasoline by the methanol to gasoline process. Methane or natural
gas extracted from coal gasification can be converted in to LNG for direct use as fuel in transport
sector. LNG would fetch good price equivalent to gasoline or diesel as it can replace these fuels
in transport sector.
[1]



Scheme of a Lurgi gasifier
During gasification, the coal is blown through with oxygen and steam (water vapor) while also
being heated (and in some cases