402
gas mixture may be converted to gasoline range fuels also. It may be pointed out
that the technology of coal gasification is fairly matured. However, coal is slowly
being discarded by many countries because of enormous emission of carbon dioxide, a greenhouse gas (GHG) during electricity production in pulverized coal-fired
thermal power plants. On the other hand, petcoke is a solid residue obtained mainly
from the vacuum distillation tower in a petroleum refinery. With the discovery of
shale oil and new discovery of crude petroleum oil, it is logical to corroborate that
there will be no supply issue of crude oil in the refinery in near future. However,
development of technology for the valorization of petcoke has not matured due to
various reasons. One problem is reluctance from the refiners to further process it at
their location. It has been easy for them to sell it at a cheaper price to local people,
who utilize petcoke for heat requirements during winter seasons and unknowingly
suffer from lung infections due to the presence of sulfur in petcoke. Gasification of
petcoke at an industrial scale offers many solutions like enhanced production of
syngas, waste minimization, and mitigation of atmospheric pollution. Hence, if
implemented, the benefits will outweigh the investment in the field of energy and
environment. Moreover, there will be low emission of SO x , NO x , as well as low solid
residue production during gasification which makes it an attractive technology to
process carbonaceous materials.
2 Gasification of Carbonaceous Materials
Gasification is defined as the reaction between a carbonaceous material and air or
oxygen at elevated temperatures. The amount of air or oxygen should be less than
the stoichiometric amount required for complete combustion. The product is syngas
as already mentioned. In the absence of oxygen, the reaction is known as pyrolysis
or thermal decomposition where the product vapor is condensed and termed as biooil or pyrolysis oil. Other products are biochar and non-condensable gases. This
bio-oil contains water and, hence, needs upgrading by catalytic hydrodeoxygenation, before it may be used as a drop-in fuel. On the other hand, air-fuel ratio more
than the stoichiometric amount will allow combustion where the major product will
be carbon dioxide, a greenhouse gas. Hence, the equivalence ratio, defined as the
ratio of actual air-fuel ratio and stoichiometric air-fuel ratio, should vary between 0
and 1 so that gasification may occur with the formation of syngas. It is to be noted
that the selection of raw material for efficient production of syngas through gasification is a very important step. Hence, the physicochemical characterization of feedstock is of utmost importance. Table 1 presents the proximate analysis of three
potential raw materials for gasification, e.g., coal, biomass, and petcoke.
It is important to discuss the influence of compositions of these important carbonaceous feedstocks on the quantity and quality of products from gasification as well
as the challenges associated with smooth operation of the process. A low moisture
content, preferably below 10 wt% is always preferable for thermochemical operation like pyrolysis and gasification as the energy needed to raise the temperature of
J. P. Chakraborty and R. K. Singh
gas mixture may be converted to gasoline range fuels also. It may be pointed out
that the technology of coal gasification is fairly matured. However, coal is slowly
being discarded by many countries because of enormous emission of carbon dioxide, a greenhouse gas (GHG) during electricity production in pulverized coal-fired
thermal power plants. On the other hand, petcoke is a solid residue obtained mainly
from the vacuum distillation tower in a petroleum refinery. With the discovery of
shale oil and new discovery of crude petroleum oil, it is logical to corroborate that
there will be no supply issue of crude oil in the refinery in near future. However,
development of technology for the valorization of petcoke has not matured due to
various reasons. One problem is reluctance from the refiners to further process it at
their location. It has been easy for them to sell it at a cheaper price to local people,
who utilize petcoke for heat requirements during winter seasons and unknowingly
suffer from lung infections due to the presence of sulfur in petcoke. Gasification of
petcoke at an industrial scale offers many solutions like enhanced production of
syngas, waste minimization, and mitigation of atmospheric pollution. Hence, if
implemented, the benefits will outweigh the investment in the field of energy and
environment. Moreover, there will be low emission of SO x , NO x , as well as low solid
residue production during gasification which makes it an attractive technology to
process carbonaceous materials.
2 Gasification of Carbonaceous Materials
Gasification is defined as the reaction between a carbonaceous material and air or
oxygen at elevated temperatures. The amount of air or oxygen should be less than
the stoichiometric amount required for complete combustion. The product is syngas
as already mentioned. In the absence of oxygen, the reaction is known as pyrolysis
or thermal decomposition where the product vapor is condensed and termed as biooil or pyrolysis oil. Other products are biochar and non-condensable gases. This
bio-oil contains water and, hence, needs upgrading by catalytic hydrodeoxygenation, before it may be used as a drop-in fuel. On the other hand, air-fuel ratio more
than the stoichiometric amount will allow combustion where the major product will
be carbon dioxide, a greenhouse gas. Hence, the equivalence ratio, defined as the
ratio of actual air-fuel ratio and stoichiometric air-fuel ratio, should vary between 0
and 1 so that gasification may occur with the formation of syngas. It is to be noted
that the selection of raw material for efficient production of syngas through gasification is a very important step. Hence, the physicochemical characterization of feedstock is of utmost importance. Table 1 presents the proximate analysis of three
potential raw materials for gasification, e.g., coal, biomass, and petcoke.
It is important to discuss the influence of compositions of these important carbonaceous feedstocks on the quantity and quality of products from gasification as well
as the challenges associated with smooth operation of the process. A low moisture
content, preferably below 10 wt% is always preferable for thermochemical operation like pyrolysis and gasification as the energy needed to raise the temperature of
J. P. Chakraborty and R. K. Singh