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Steam Gasification and Reforming Technologies
to collect and store an amount of solar energy to obtain the maximum conversion
of methane and to produce consistently high-quality synthesis gas. The experiment
used gas-cooled solar tower (GAST) system to produce hot air (up to 0.36 kg/s at
1000°C and 9 bars) to drive separate steam reformer. This air was then fed back
into the GAST cycle. The GAST technology program is described by Becker and
Bohmer [194].
During normal operation, the heating medium, air, is taken from the GAST
circuit (receiver) at a temperature of 1000°C over a suitable bench line and fed
through the electric heater to the reforming reactor inlet. In this solar-only operating mode, air flows through the heater passively without any additional electric
heating. Methane reforming is initiated at the process gas end of the reformer.
A liquid natural gas storage tank directly provides the reforming unit with natural
gas at the required pressure via the Liquid natural gas evaporator. The process gas
mixture is heated by air from 500°C to about 850°C as it passes through the catalyst bed. The endothermic reforming reaction results in the production of hydrogen
and carbon monoxide with a ratio of 3/1. More details of the ASTERIx experiment
are given in References 192–194 and 199.
4.7.3.2 the Weizmann institute tubular reformer/receiver
The WIS (Weizmann Institute of Science) operated a solar central receiver for the
development of high-temperature technology including the storage and transport
of solar energy via methane reforming [192,199,200] (Yeheskel et al., 2012, pers.
comm.). The WIS had a designed facility for testing reformers up to about 480 kW
absorbed energy. The facility was designed for either steam or carbon dioxide
reforming and can accommodate the reformer that operates between 1 and 18 bars.
The reformer systems were operated in coordination with a matching methanator
system that recovered the energy from the reverse reaction [192].
A cavity receiver containing eight vertical reformer tubes (2 inch schedule 80 and
4.5 m long) was designed. The overall dimension of the device was about 5 m high,
4.5 m wide, and 3 m deep. The reactor was designed to produce syngas at 800°C.
It resembled commercial reformers except that a solar cavity receiver had replaced
the conventional gas-fueled radiant furnace [192].
4.7.3.3 soltox Process
In the Soltox process, a parabolic dish is used to concentrate sunlight through a quartz
window into an internally insulated aluminum reactor vessel in which it is absorbed
on a rhodium-coated reticulated ceramic foam absorber [192,199,201,207,210,
212–214]. Concentrated organic waste and steam are mixed and flow through the
hot (>1000°C) catalyst bed, in which they react completely in fractions of a second
to produce hydrogen, carbon dioxide, carbon monoxide, and halogen acids (which
are easily neutralized to simple salts). The extremely good heat and mass transfer
within the reactor result in a compact, highly efficient system [192–194].
When a vaporized organic waste is mixed with steam and passed through the reactor, highly specific, irreversible, endothermic reforming reactions take place on the
catalyst-coated surface of the radiantly heated absorber to quantitatively destroy the
waste. For example, trichloroethylene (TCE) reacts with steam to produce hydrogen,