65
Steam Gasification and Reforming Technologies
wood and leaves, paper, textile, and plastics. The syngas composition was measured
as functions of temperature, steam-to-MSW ratio, and catalyst-to-MSW ratio at
an atmospheric pressure. The results showed >99% tar removal at 800°C with a
significant production of hydrogen. The catalyst significantly improved hydrogen
production. Higher temperature gave higher gas and hydrogen yields. While higher
steam-to-MSW ratio gave better results, an excessive steam-to-MSW ratio lowered the gasification temperature and degraded the product quality. The optimum
value of Steam/MSW ratio was found to be 1.33 under the operating conditions.
The optimum value of the catalyst-to-MSW ratio was found to be about 0.5. A twostage (pyrolysis followed by catalytic steam gasification) process for olive waste was
studied by Encinar et al. (2010, pers. comm.). The catalyst used was dolomite. The
two-stage process produced gas, liquid, and solid, the yields of which were strongly
dependent on the temperature and the amount of catalyst. Higher temperature and
catalyst amount gave higher amount of gases and the presence of steam gave higher
amount of hydrogen and carbon dioxide.
Hofbauer et al. [75–79] used a fast internally circulating fluidized bed (CFB; at
a pilot scale) to gasify biomass with steam. Using a natural catalyst as bed material,
and at a temperature of 750°C, tar content was significantly reduced and gas with
high hydrogen content was obtained. The internal circulating bed allowed the flexibility in varying residence times needed to lower tar concentration. Herguido et al.
[80] studied gasification of pine sawdust, pinewood chips, cereal straw, and thistles
from energy crops in the presence of steam in a fluidized bed reactor. The product
gases were hydrogen, CO, and CO 2 , and their amount and composition varied with
the nature of biomass in the temperature range of 650°C–780°C.
A novel two-stage fluidized bed approach was used by Pfeifer et al. [81] in which
the first stage carried out steam gasification of solid biomass to generate heat and
power as well as provide raw materials for downstream chemical synthesis. The
residual biochar from the first stage is combusted in the second stage and the hot
bed materials from the second stage provide the heat needed for the first stage. This
concept was also analyzed by Gopalakrishnan [82] and Matsuoka et al. [83]. The
latter study showed that separating the combustion zone from the gasification zone
resulted in high-efficiency gasification. They used γ-alumina as particles for bed
materials and tested two different types of sawdusts. Since the residence time of the
bed material can be controlled in the gasifier of the circulating dual bubbling fluidized bed system, the tars captured by the porous alumina particles (coke) as well as
chars were effectively gasified. Since coke was preferentially gasified compared with
char, higher carbon conversion and hydrogen yield can be achieved in this type of
dual bed system than in the conventional CFB.
In the studies described earlier, the process generated gases with about 40 vol%
hydrogen. Furthermore, an addition of carbonate adsorbed carbon dioxide and
moved carbon dioxide from the gasification to the combustion zone (they called it
adsorption-enhanced reforming [AER]). This concept has been successfully adapted
by an 8 MW combined heat and power (CHP) plant in Güssing, Austria, since 2002.
A new pilot plant of 100 kW has also been built to see the effect of the AER concept in improving hydrogen concentration to 75 vol% in the product gases. The
possibilities of getting high hydrogen concentration, operating the reactors at low
Steam Gasification and Reforming Technologies
wood and leaves, paper, textile, and plastics. The syngas composition was measured
as functions of temperature, steam-to-MSW ratio, and catalyst-to-MSW ratio at
an atmospheric pressure. The results showed >99% tar removal at 800°C with a
significant production of hydrogen. The catalyst significantly improved hydrogen
production. Higher temperature gave higher gas and hydrogen yields. While higher
steam-to-MSW ratio gave better results, an excessive steam-to-MSW ratio lowered the gasification temperature and degraded the product quality. The optimum
value of Steam/MSW ratio was found to be 1.33 under the operating conditions.
The optimum value of the catalyst-to-MSW ratio was found to be about 0.5. A twostage (pyrolysis followed by catalytic steam gasification) process for olive waste was
studied by Encinar et al. (2010, pers. comm.). The catalyst used was dolomite. The
two-stage process produced gas, liquid, and solid, the yields of which were strongly
dependent on the temperature and the amount of catalyst. Higher temperature and
catalyst amount gave higher amount of gases and the presence of steam gave higher
amount of hydrogen and carbon dioxide.
Hofbauer et al. [75–79] used a fast internally circulating fluidized bed (CFB; at
a pilot scale) to gasify biomass with steam. Using a natural catalyst as bed material,
and at a temperature of 750°C, tar content was significantly reduced and gas with
high hydrogen content was obtained. The internal circulating bed allowed the flexibility in varying residence times needed to lower tar concentration. Herguido et al.
[80] studied gasification of pine sawdust, pinewood chips, cereal straw, and thistles
from energy crops in the presence of steam in a fluidized bed reactor. The product
gases were hydrogen, CO, and CO 2 , and their amount and composition varied with
the nature of biomass in the temperature range of 650°C–780°C.
A novel two-stage fluidized bed approach was used by Pfeifer et al. [81] in which
the first stage carried out steam gasification of solid biomass to generate heat and
power as well as provide raw materials for downstream chemical synthesis. The
residual biochar from the first stage is combusted in the second stage and the hot
bed materials from the second stage provide the heat needed for the first stage. This
concept was also analyzed by Gopalakrishnan [82] and Matsuoka et al. [83]. The
latter study showed that separating the combustion zone from the gasification zone
resulted in high-efficiency gasification. They used γ-alumina as particles for bed
materials and tested two different types of sawdusts. Since the residence time of the
bed material can be controlled in the gasifier of the circulating dual bubbling fluidized bed system, the tars captured by the porous alumina particles (coke) as well as
chars were effectively gasified. Since coke was preferentially gasified compared with
char, higher carbon conversion and hydrogen yield can be achieved in this type of
dual bed system than in the conventional CFB.
In the studies described earlier, the process generated gases with about 40 vol%
hydrogen. Furthermore, an addition of carbonate adsorbed carbon dioxide and
moved carbon dioxide from the gasification to the combustion zone (they called it
adsorption-enhanced reforming [AER]). This concept has been successfully adapted
by an 8 MW combined heat and power (CHP) plant in Güssing, Austria, since 2002.
A new pilot plant of 100 kW has also been built to see the effect of the AER concept in improving hydrogen concentration to 75 vol% in the product gases. The
possibilities of getting high hydrogen concentration, operating the reactors at low