The efficiency of a combination reformer/fuel cell system is significantly improved
by recapturing the energy value of heat generated in the fuel cell and producing
additional power. The cooling water from the fuel cell is mixed, entirely or in
part, with sufficient or excess compressed air, and at least partially evaporates
in the compressed air. The air is at least sufficient to support the oxidative
reactions in the fuel cell and also to serve as oxidant in a burner that provides
heat to reform fuel/steam mixtures into hydrogen-containing reformate. This air/steam
mixture, after leaving the fuel cell, is further heated by heat exchange with the
reformate stream and reformate-producing modules, and with the exhaust stream of
the burner. The steam/air mixture is injected into the burner, optionally after
superheating in the burner exhaust, and is reacted with fuel in the burner. The
burner exhaust may be used to provide heat to a fuel reforming reaction. The high-temperature
burner exhaust may also be used to drive an expander, preferably a turbine, at
a location in the system which is downstream of the burner, but in which the exhaust
is at a high temperature so as to run the turbine efficiently. The turbine recovers
heat energy from the fuel cell as mechanical energy, typically in excess of the
energy required to run a compressor, because of the addition of steam to the compressed
air. Moreover, system heat removal elements, such as radiators, as well as overall
system size and cost, can be markedly reduced for a given level of output.
