88
Water for Energy and Fuel Production
While the large commercial reformers are designed as described above, more
compact and economical designs are used in the smaller scale reformers [120–134,
188–190]: (1) annular bed reformers, (2) plate-type reformers, (3) membrane reactors,
(4) auto-thermal reactors, (5) ITM reformers, (6) sorbent-enhanced reformers, (7) plasma
reformers, and (8) micro-channel reformers. These different designs consider the ways
to improve the heat transfer rate, the area and the efficiency since reforming requires a
large supply of heat due to an endothermic nature of the reaction. Improvement of material cost is another important consideration. Finally, a process that carries out simultaneous reaction and separation of hydrogen is important to improve the conditions for
equilibrium and purity of hydrogen product. The following paragraphs briefly summarizes the descriptions of these eight reformers given in References 120–134.
The annular bed reformer is used for FCs and low hydrogen production (on the
order of 2 kW) needs. In the latter case, it is generally operated at a low temperature
of about 700°C and a low pressure of about 3 atm. These mild conditions reduce the
cost of materials and produce an energy efficiency of about 70%–80%. This type
of reformer is used by industries such as Haldor Topsoe, Ballard Power Systems,
Sanyo Electric, and International Fuel Cells. The technology produces more compact reformers at a lower cost than conventional reformers.
Plate-type reformers are more compact than annular or conventional long  tube
reformers and are often used for proton exchange membrane (PEM) FC or residentialtype FC (20 kW) applications. It has the same energy efficiency as that of annular
reformer. The plates are arranged in a stack in which one side of the plate is coated
with the catalyst and on the other side (anode) exhaust gas from FC undergoes catalytic combustion to supply heat for the endothermic steam reforming reaction. The
unit is compact and low cost, and has good heat transfer and small heat-up period. For
PEM FC applications, Osaka Gas Co., Japan, is developing a low cost reformer with
an integrated plate design that carries out sulfur removal, steam reforming, water–gas
shift reaction, and CO removal steps all in one unit making the final device more
compact and economical. GASTEC is applying the technology for residential-type
FCs and minimizing the cost by testing the variables such as combustion catalysts,
coatings, and substrate materials.
In the membrane reactor, reforming, water–gas shift reaction, and further CO cleaning step all occur in the same unit. The reaction and separation functions are thus
combined. The reactor operates under high pressure and uses the Pd membrane on one
side through which H 2 permeates with high selectivity. The constant removal of hydrogen on the downstream side allows equilibrium to be shifted to achieve better conversion
by reforming at a lower temperature. The reactor also produces high-purity hydrogen.
In the auto-thermal reformer, endothermic reforming reaction is accompanied by partial oxidation reaction that generates enough heat to supply the heat needed for reforming reaction. Thus, the reactor does not need any external source for the heat. Arthur D.
Little, Nuvera, Epyx, and a consortium of McDermott Technology/Catalytica, among
others, have developed a 50 kW FC reformer of this type. Small-scale (10–50 kW) autothermal reactors have been developed for PEM FC by Honeywell, DaimlerChrysler,
Analytical Power, and IdaTech, among others [120]. Generally, auto-thermal reactors
use gasoline, diesel, and logistic fuels along with natural gas. The use of diesel and
logistic fuels makes them specially useful for FC applications on ships [120].