66
Water for Energy and Fuel Production
temperature, and thereby improving energy conversion efficiency make this concept
very attractive. As mentioned earlier, Salaices et al. [74] presented a very workable
kinetic model for catalytic steam gasification of cellulose surrogate with Ni/alphaalumina catalyst in a CFB with a riser. The model successfully predicted the production of various gases such as hydrogen, carbon dioxide, carbon monoxide, water, and
methane.
While a significant number of studies have investigated steam gasification in the
presence of air (or oxygen) to improve carbon conversion and energy efficiency of
the steam gasification process, Barrio et al. (2012, pers. comm.) examined the effect
of hydrogen on the steam gasification process. They found that hydrogen inhibits the
steam gasification reaction. They also concluded that the nature of char coming from
beech or birch wood did not significantly affect the final results.
While a major effort on steam gasification is focused at a low temperature using
a catalyst, Donaj et al. [84] and Gupta and Cichonski [85] examined the effectiveness of high-temperature steam gasification. Donaj et al. [84] examined the steam
gasification of straw pellets at temperatures between 750°C and 950°C. The effect
of the steam-to-feed ratio on carbon conversion was marginal (below 850°C), and
in general, higher steam-to-feed ratio gave higher hydrogen production. Gupta and
Cichonski [85] examined the steam gasification of paper, cardboard, and wood pellets in the temperature range of 700°C–1100°C. Once again in all cases, hydrogen
production increased with the temperature and the steam-to-biomass ratio.
Lucas et al. [25] examined the high-temperature air and steam gasification
(HTAG) of densified biofuels. The experiments were carried out in a fixed-bed
updraft gasifier. The results showed that an increase in the feed temperature reduced
the production of tars and soot and char residues, and also increased the heating
value of the dry fuel gas produced. Butterman and Castaldi [86] showed that an
increase in CO 2 feed rate enhanced the char conversion and the production of CO.
The experiments produced a low concentration of methane and a high concentration of hydrogen (above 500°C for the herbaceous and nonwood samples and above
650°C for the wood biomass). The experiments also showed similarities between
the gaseous products from biomass and MSW. The mass decomposition rates and
the gas evolution profiles showed two distinct regions with transition around 400°C.
Large pyrolysis char volumes correlated well with higher lignin compositions. The
biomass fuels examined included woods, grasses, and other lignocellulosic samples.
These included oak, sugar maple, poplar, spruce, white pine, Douglas fir, alfalfa,
cordgrass, beachgrass, maple bark, pine needles, blue noble fir needles, pecan shells,
almond shells, walnut shells, wheat straw, and green olive pit. The complete gasification occurred around 900°C–1000°C.
Aznar et al. [87] examined biomass gasification with steam–O 2 mixtures followed
by a catalytic steam reformer and a CO-shift system. The use of two CO-shift converters downstream from a fluidized bed biomass gasifier, using steam–O 2 mixtures
and a catalytic steam reformer, generated an exit gas with 73% hydrogen (by volume)
on a dry basis and only 2.6% CO. The remaining gas contained CO 2 , O 2 , and CH 4 .
The results showed that the H 2 O/CO ratio in the gas phase at the inlet of the hightemperature shift (HTS) reactor is a very important parameter in the system. CO
conversion up to 90% was obtained, but to get this conversion, the steam/CO ratio
Water for Energy and Fuel Production
temperature, and thereby improving energy conversion efficiency make this concept
very attractive. As mentioned earlier, Salaices et al. [74] presented a very workable
kinetic model for catalytic steam gasification of cellulose surrogate with Ni/alphaalumina catalyst in a CFB with a riser. The model successfully predicted the production of various gases such as hydrogen, carbon dioxide, carbon monoxide, water, and
methane.
While a significant number of studies have investigated steam gasification in the
presence of air (or oxygen) to improve carbon conversion and energy efficiency of
the steam gasification process, Barrio et al. (2012, pers. comm.) examined the effect
of hydrogen on the steam gasification process. They found that hydrogen inhibits the
steam gasification reaction. They also concluded that the nature of char coming from
beech or birch wood did not significantly affect the final results.
While a major effort on steam gasification is focused at a low temperature using
a catalyst, Donaj et al. [84] and Gupta and Cichonski [85] examined the effectiveness of high-temperature steam gasification. Donaj et al. [84] examined the steam
gasification of straw pellets at temperatures between 750°C and 950°C. The effect
of the steam-to-feed ratio on carbon conversion was marginal (below 850°C), and
in general, higher steam-to-feed ratio gave higher hydrogen production. Gupta and
Cichonski [85] examined the steam gasification of paper, cardboard, and wood pellets in the temperature range of 700°C–1100°C. Once again in all cases, hydrogen
production increased with the temperature and the steam-to-biomass ratio.
Lucas et al. [25] examined the high-temperature air and steam gasification
(HTAG) of densified biofuels. The experiments were carried out in a fixed-bed
updraft gasifier. The results showed that an increase in the feed temperature reduced
the production of tars and soot and char residues, and also increased the heating
value of the dry fuel gas produced. Butterman and Castaldi [86] showed that an
increase in CO 2 feed rate enhanced the char conversion and the production of CO.
The experiments produced a low concentration of methane and a high concentration of hydrogen (above 500°C for the herbaceous and nonwood samples and above
650°C for the wood biomass). The experiments also showed similarities between
the gaseous products from biomass and MSW. The mass decomposition rates and
the gas evolution profiles showed two distinct regions with transition around 400°C.
Large pyrolysis char volumes correlated well with higher lignin compositions. The
biomass fuels examined included woods, grasses, and other lignocellulosic samples.
These included oak, sugar maple, poplar, spruce, white pine, Douglas fir, alfalfa,
cordgrass, beachgrass, maple bark, pine needles, blue noble fir needles, pecan shells,
almond shells, walnut shells, wheat straw, and green olive pit. The complete gasification occurred around 900°C–1000°C.
Aznar et al. [87] examined biomass gasification with steam–O 2 mixtures followed
by a catalytic steam reformer and a CO-shift system. The use of two CO-shift converters downstream from a fluidized bed biomass gasifier, using steam–O 2 mixtures
and a catalytic steam reformer, generated an exit gas with 73% hydrogen (by volume)
on a dry basis and only 2.6% CO. The remaining gas contained CO 2 , O 2 , and CH 4 .
The results showed that the H 2 O/CO ratio in the gas phase at the inlet of the hightemperature shift (HTS) reactor is a very important parameter in the system. CO
conversion up to 90% was obtained, but to get this conversion, the steam/CO ratio