Steam Gasification and Reforming Technologies
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In the ITM technology (being developed by a consortium of industries and
universities headed by Air Product), one side of the membrane separates oxygen
from air at around the room temperature and 0.03–0.20 atm pressure; on the other
side, methane and steam react at high pressure (3–20 atm) to produce syngas. The
membrane is made up of nonporous multicomponent oxides that operate at a temperature higher than 725°C and has high permeability and selectivity for oxygen
transfer. Partial oxidation provides the heat for reforming reaction. The syngas can
either be reformed to produce hydrogen or converted to produce fuels and chemicals.
The ITM technology generally uses flat plate system.
In the sorbent-enhanced reforming (SER) technology, the steam reforming is
accompanied by simultaneous removal of carbon dioxide and carbon monoxide by
calcium oxide. The removal of carbon dioxide allows the reforming reaction to occur
at 400°C–500°C as opposed to the normal reforming temperature of 800°C–1000°C.
The reaction also produces reasonably pure hydrogen (90% H 2 , 9.5% CH 4 , 0.5% CO 2 ,
and <50 ppm CO), and this alleviates the downstream expensive purification processes
such as water–gas shift reaction, preferential oxidation, and membrane separation.
Thermal plasma technology is a high-temperature (2,700°C to about 10,000°C)
process to generate hydrogen and hydrogen-rich gas from a variety of feedstock.
High temperature accelerates the rate of reforming process. The products generally
contain ethylene and acetylene along with hydrogen, carbon monoxide, and carbon
dioxide. The process can handle various reaction volumes, interelectrode gap, sulfur
impurities, and carbon deposit. The process can be operated in auto-thermal mode.
The process can generate a large range of fuel power (10–40 kW) and can give up to
90% conversion of methane.
One attractive method to improve the transport limitations in the reforming reactor is to use micro-channel reactor that can operate at 10 ms or lower residence
time compared to conventional reactor that operates at the residence time of 1 s.
Since intrinsic reforming reaction is very fast, at a high residence time, a significant
portion of the catalyst volume in the steam reformer is wasted. The micro-channel
reactor allows a reduction of plant volume by about a factor of 30, and thereby
reducing both capital and operating costs for steam reforming of methane. Also,
the micro-channel reactors allow high reaction rates by increasing the heat transfer
rates. For highly active catalyst, equilibrium can be reached in less than 0.5–1 ms
residence time. This indicates that further lowering of transport resistances can
further reduce residence time to reach the desired equilibrium.
Besides the eight different types of reforming reactors that are being developed
(particularly for small-scale applications), solar reforming reactors that use solar
energy to carry out steam reforming reactions are gaining more popularity. These
reactors are described in the following sections.
4.7 nOVel steam GasiFiCatiOn and reFOrminG PrOCesses
4.7.1 SolAr gASiFiCATion TeChnology
Solar thermochemistry refers to a number of process technologies such as thermal or thermochemical splitting of water, solar electrolysis, solar gasification, and