Page 74 - MODERN ASPECTS OF ELECTROCHEMISTRY

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Direct MethanolAFuel Cells
provide electricityand heat for apartment buildings, hospitals, shopping
centers, etc. Overall efficiencies higher than 85% for fuel consumption
(natural gas → electricityplus heat) have been demonstrated in these
power plants.= In the U.S.= Department of Energy -sponsored fuel cell
program, PAFC systems are also being considered as power plants for fleet
vehicles (buses, trucks, delivery vehicles) and 100-kW units have been
installed and tested in buses; the performance of these buses is quite
promising. Apart from the ONSI program, the most active PAFC devel-
opment and commercialization programs are in Japan and conducted by
Fuji, Toshiba, and Mitsubishi.=
Molten carbonate fuel cells have the advantages of (1) not requiring
noble metal electrocatalysts, (2) efficient heat transfer from the exother-
mic fuel cell reaction to the endothermic fuel-processing reaction (internal
reforming), (3) CO being a reactant and not a poison, and (4) the rejected
heat from the MCFC power plant being of high enough quality to produce
electricity in a gas turbine or steam in a steam turbine (for cogeneration).
The active MCFC developers are (1) Energy Research Corporation and
M-C Power Corporation in the United States: (2) ECN and Ansaldo in
Europe; and (3) IHI, Toshiba, Mitsubishi, Hitachi, and Sanyo in Japan.=
Power plants with power ratings of 100 kW to 2 MW have been con-
structed and tested.
The solid oxide fuel cells have practically the same advantages as the
MCFCs for applications in electric utility companies and chemical indus-
tries.= An additional advantage is that because the SOFC power plant is a
two-phase system (gas, solid) whereas all other types of fuel cells are
three-phase systems (gas, liquid, and solid), the complex problems asso-
ciated with liquid electrolytes are eliminated and mass transport problems
are thus greatly minimized. The world leader in this technology is West-
inghouse Electric Corporation in the United States.= The materials used in
the electrochemical cell stack are relatively inexpensive, but the costs of
fabrication of thin-film structures are prohibitive.= The Westinghouse
power plants (100 kW) with a tubular structure have reached the perform-
ance goals and shown promise of reaching the lifetime goals.= Flatplate
-
designs are more desirable than a tubular one for the SOFCs from the
points of view of scale up to megawatt sizes and maÀed lowering of the
capital cost.= Siemens in Germany is at the most advanced state in devel -
oping the flat-plate design.= Other companies woÀing in this area are IHI
in Japan and ZTEK, Allied Signal, SOFCO, and MTI in the United States.=