4. Gasification
Gasification processes involve heterogeneous gas-solid chemical reactions, which require
substantial amounts of heat and mass transfer, and the problems posed in the design and
development of plant to carry out these processes have led to a variety of type of gasifiers [7].
Gasifiers are used to produce fuel gas from coal, or other feedstocks such as wood,
biomass or refuse. Industrial implementation of gasifiers depends upon the economics of each
application and this is affected considerably by the cost of the feedstocks and the efficiency of
conversion [7, 8].
Fluidized bed gasifiers are one type of gasifier and have advantages of uniform
temperature distribution throughout the gasifier and the adaptability to varying load demand
without serious loss of efficiency. These gasifiers can be used to produce low sulphur gas
content, sufficient to meet environmental requirements, either by addition of limestone or
dolomite with the coal feed to absorb the sulphur, or by post-gasification purification
techniques.
Figure 1 shows the flow sheet for the fluidized bed gasification plant. It is used for
gasifying coal with the presence of limestone [9].