A hydrogen fuel cell power system having improved efficiency comprises a fuel
cell,
a source of hydrogen gas, a compressor for creating a pressurized air stream, and
a liquid supply which is heated by waste heat form the power system and evaporates
into the pressurized air stream to produce a pressurized air and steam mixture.
The pressurized air/steam mixture, which is preferably used as the oxidant in the
fuel cell, is combusted with fuel in a burner to produce a high-temperature steam-laden
exhaust stream. The high-temperature steam-laden exhaust stream drives an expander
to produce a power output, and a power take-off from the expander uses the expander
power to, for instance, drive an electrical generator, or drive other system components.
The evaporation of liquid can take place external to the fuel cell, or can take
place directly within the fuel cell, preferably using a cooling liquid that is
directly injected into the fuel cell. The fuel cell power system advantageously
uses the low-temperature waste heat of the fuel cell to evaporate liquid into the
pressurized air, resulting in a steam/air mixture having a relatively large expansion potential.
The systems and related methods of the invention are applicable to a wide range
of fuel cell power systems, including a "pure" or "non-hybrid" fuel cell power
system, powered by hydrogen from either an external source, such as a hydrogen
storage tank, or from "direct" reforming of a fuel at the anode. The invention
is also applicable to integrated or "hybridized" fuel cell power systems which
contain a local fuel reformer. In these systems, the fuel cell is powered by hydrogen-containing
reformate generated by the reformer.
