90
Water for Energy and Fuel Production
reforming or cracking of water and other carbonaceous materials [192–214]. Many
of these endothermic reactions are carried out by energy harnessed by concentrated
solar beams. Solar gasification generally deals with upgrading and decaronization of
fossil fuels. Such gasification is often carried out in the presence of steam. Successful
solar gasification of carbonaceous materials was first reported in the 1980s in which
coal, activated carbon, coke, and coal/biomass mixtures were employed in a fixedbed windowed reactor. Charcoal, wood, and paper were gasified with steam in a
fixed-bed reactor. More recently, steam gasification of oil shale and coal, biomass,
waste tires and plastics, and coal in a fluidized bed reactor as well as petroleum coke
and vacuum residue in fixed, fluidized, and entrained bed reactors were examined
[192,193,195–199,202–210] (Piatkowski 2012, pers. comm.; Yeheskel et al., 2012,
pers. comm.). In the last type of reactor, dry coke particles, coal–water slurries, and
vacuum residues were tested for the steam gasification.
In a conceptual solar gasification process using steam, biomass is heated rapidly
in a solar furnace to achieve flash pyrolysis at temperatures of about 900°C [192].
Some steam is added to the pyrolyzer to increase the gas yield relative to char. The
char constituting about 10%–20% of the biomass by weight is steam gasified with
external heating at temperatures of 900°C–1000°C; all of the volatile hydrocarbons
are then steam reformed in a solar reformer. Steam for the process is generated from
heat recovered from the product gas. The composition of the syngas is adjusted to the
user’s needs utilizing conventional operation involving the water–gas shift reaction
and CO 2 stripping. This conceptual process can be modified in a number of different
ways depending on the specific needs.
A number of gasification experiments were carried out using small quantities
of biomass, coal, oil shale, and residual oil with external heat supplied by the
Sun [192–207]. These experiments included cellulose gasification and oil shale
gasification with carbon recovery approaching nearly 100% at a temperature of
950°C and short residence times [196,208,209]. While these experiments confirmed the applicability of the flash pyrolysis approach, they did not provide the
data for design and scale-up of a solar gasification process. More work is being
pursued to improve the design and scale-up capabilities of solar gasification process [192–207].
4.7.2 SolAr gASiFiCATion reACTorS And ProCeSSeS
A number of different types of solar steam gasification reactors have also been
examined in the literature [192–206,209]. The reactor configuration examined by
Z’Graggen [202] at Swiss Federal Institute of Technology (ETH) at Zurich consisted
of a cylindrical cavity receiver of 21 cm in length and 12 cm in inside diameter, and
an aperture of 5 cm in diameter for solar beams. The cavity-type geometry was
designed to effectively capture the incident solar radiation and its apparent absorption is estimated to exceed 0.95. The cavity was made of Inconel 601 lined with
Al 2 O 3 and insulated with an Al 2 O 3 /ZrO 2 ceramic foam. The aperture was closed by
0.3-cm-thick clear fused quartz window mounted in a water-cooled aluminum ring
that also served as a shield for spilled radiation. The window was actively cooled and
kept away from particles and condensable gases.
Water for Energy and Fuel Production
reforming or cracking of water and other carbonaceous materials [192–214]. Many
of these endothermic reactions are carried out by energy harnessed by concentrated
solar beams. Solar gasification generally deals with upgrading and decaronization of
fossil fuels. Such gasification is often carried out in the presence of steam. Successful
solar gasification of carbonaceous materials was first reported in the 1980s in which
coal, activated carbon, coke, and coal/biomass mixtures were employed in a fixedbed windowed reactor. Charcoal, wood, and paper were gasified with steam in a
fixed-bed reactor. More recently, steam gasification of oil shale and coal, biomass,
waste tires and plastics, and coal in a fluidized bed reactor as well as petroleum coke
and vacuum residue in fixed, fluidized, and entrained bed reactors were examined
[192,193,195–199,202–210] (Piatkowski 2012, pers. comm.; Yeheskel et al., 2012,
pers. comm.). In the last type of reactor, dry coke particles, coal–water slurries, and
vacuum residues were tested for the steam gasification.
In a conceptual solar gasification process using steam, biomass is heated rapidly
in a solar furnace to achieve flash pyrolysis at temperatures of about 900°C [192].
Some steam is added to the pyrolyzer to increase the gas yield relative to char. The
char constituting about 10%–20% of the biomass by weight is steam gasified with
external heating at temperatures of 900°C–1000°C; all of the volatile hydrocarbons
are then steam reformed in a solar reformer. Steam for the process is generated from
heat recovered from the product gas. The composition of the syngas is adjusted to the
user’s needs utilizing conventional operation involving the water–gas shift reaction
and CO 2 stripping. This conceptual process can be modified in a number of different
ways depending on the specific needs.
A number of gasification experiments were carried out using small quantities
of biomass, coal, oil shale, and residual oil with external heat supplied by the
Sun [192–207]. These experiments included cellulose gasification and oil shale
gasification with carbon recovery approaching nearly 100% at a temperature of
950°C and short residence times [196,208,209]. While these experiments confirmed the applicability of the flash pyrolysis approach, they did not provide the
data for design and scale-up of a solar gasification process. More work is being
pursued to improve the design and scale-up capabilities of solar gasification process [192–207].
4.7.2 SolAr gASiFiCATion reACTorS And ProCeSSeS
A number of different types of solar steam gasification reactors have also been
examined in the literature [192–206,209]. The reactor configuration examined by
Z’Graggen [202] at Swiss Federal Institute of Technology (ETH) at Zurich consisted
of a cylindrical cavity receiver of 21 cm in length and 12 cm in inside diameter, and
an aperture of 5 cm in diameter for solar beams. The cavity-type geometry was
designed to effectively capture the incident solar radiation and its apparent absorption is estimated to exceed 0.95. The cavity was made of Inconel 601 lined with
Al 2 O 3 and insulated with an Al 2 O 3 /ZrO 2 ceramic foam. The aperture was closed by
0.3-cm-thick clear fused quartz window mounted in a water-cooled aluminum ring
that also served as a shield for spilled radiation. The window was actively cooled and
kept away from particles and condensable gases.