60
Water for Energy and Fuel Production
is hydrogen. While dry reforming converts carbon dioxide and hydrocarbons into
useful syngas, the “tri-reforming” allows the process to produce the syngas with
varying H 2 /CO ratios. The H 2 /CO ratio in syngas is very important for its further use for a variety of chemical products. Syngas can be converted to acetone,
acetic acid, and ethylene by an exothermic reaction [22], while pure CO can be
used for the production of acetic acid, formic acid, polyurethane, polycarbonates,
methyl acrylates, and so on. Both dry reforming and steam reforming reactions
are endothermic. The heat generated from partial oxidation reduces the need for
expensive external heating. Both dry and steam reforming reactions require very
high temperatures (>600°C) to reduce the cooking. While steam reduces carbon
deposition, an addition of oxygen provides necessary heat that can jump start dry
and steam reforming reactions and maintain the catalyst in a clean and carbon-free
state through oxidation of coke on the catalyst surface. The extent to which oxygenates are added to the reforming reactions is strictly determined by the process
conditions and the catalyst employed. Since dry reforming produces water, steam
reforming always accompanies dry reforming, making these studies relevant for
tri-reforming.
Finally, since the real systems where tri-reforming (a combination of steam
reforming, dry reforming, and partial oxidation) will be applied consist of hydrocarbon mixtures, it is important to compare how different types of hydrocarbons
will perform under the same operating conditions. Puolakka [65] made one such
comparison and his results indicate that propane and ethanol give favorable product
distributions compared to toluene and dodecane. Such results may help optimizing
the composition of the mixed streams to get the best syngas (with desired H 2 /CO
ratio) production by tri-reforming. More work on “tri-reforming” is currently being
pursued.
4.5 eFFeCts OF FeedstOCK and OPeratinG
COnditiOns On PrOdUCt d istriBUtiOns
4.5.1 STeAm gASiFiCATion
4.5.1.1 Coal
Corella et al. [66] used the following model for steam gasification of coal at low–
medium (600°C–800°C) temperatures with simultaneous CO 2 capture in a fluidized
bed at an atmospheric pressure. The study also examines the effect of inorganic species on the gasification process.
The gasification of coal with steam follows the following set of reactions [66]:
First, fast pyrolysis of coal follows the reactions:
Coal(C x H y O z ISs) → Tar 1 + Char 1 → Tar 2 (CH 0.85 O 0.17 ) +
Char 2 (CH 0.2 O 0 0.13 ISs) + H 2 + CO + CO 2 +
(4.32)
CH 4 + C 2 H 4 +
Water for Energy and Fuel Production
is hydrogen. While dry reforming converts carbon dioxide and hydrocarbons into
useful syngas, the “tri-reforming” allows the process to produce the syngas with
varying H 2 /CO ratios. The H 2 /CO ratio in syngas is very important for its further use for a variety of chemical products. Syngas can be converted to acetone,
acetic acid, and ethylene by an exothermic reaction [22], while pure CO can be
used for the production of acetic acid, formic acid, polyurethane, polycarbonates,
methyl acrylates, and so on. Both dry reforming and steam reforming reactions
are endothermic. The heat generated from partial oxidation reduces the need for
expensive external heating. Both dry and steam reforming reactions require very
high temperatures (>600°C) to reduce the cooking. While steam reduces carbon
deposition, an addition of oxygen provides necessary heat that can jump start dry
and steam reforming reactions and maintain the catalyst in a clean and carbon-free
state through oxidation of coke on the catalyst surface. The extent to which oxygenates are added to the reforming reactions is strictly determined by the process
conditions and the catalyst employed. Since dry reforming produces water, steam
reforming always accompanies dry reforming, making these studies relevant for
tri-reforming.
Finally, since the real systems where tri-reforming (a combination of steam
reforming, dry reforming, and partial oxidation) will be applied consist of hydrocarbon mixtures, it is important to compare how different types of hydrocarbons
will perform under the same operating conditions. Puolakka [65] made one such
comparison and his results indicate that propane and ethanol give favorable product
distributions compared to toluene and dodecane. Such results may help optimizing
the composition of the mixed streams to get the best syngas (with desired H 2 /CO
ratio) production by tri-reforming. More work on “tri-reforming” is currently being
pursued.
4.5 eFFeCts OF FeedstOCK and OPeratinG
COnditiOns On PrOdUCt d istriBUtiOns
4.5.1 STeAm gASiFiCATion
4.5.1.1 Coal
Corella et al. [66] used the following model for steam gasification of coal at low–
medium (600°C–800°C) temperatures with simultaneous CO 2 capture in a fluidized
bed at an atmospheric pressure. The study also examines the effect of inorganic species on the gasification process.
The gasification of coal with steam follows the following set of reactions [66]:
First, fast pyrolysis of coal follows the reactions:
Coal(C x H y O z ISs) → Tar 1 + Char 1 → Tar 2 (CH 0.85 O 0.17 ) +
Char 2 (CH 0.2 O 0 0.13 ISs) + H 2 + CO + CO 2 +
(4.32)
CH 4 + C 2 H 4 +