Cogeneration system for a fuel cell
A fuel cell system and process using an organic Rankine cycle to produce shaft work to operate a fuel cell system component such as an air compressor. The air compressor delivers compressed air to a fuel cell stack. The steps of the Rankine cycle include pumping a liquid working fluid to an elevated pressure, heating the fluid to a gas, expanding the high temperature and high-pressure gas through an expander to produce shaft work used to drive a fuel cell system component such as an air compressor, and then removing energy from the cooling fluid to change the gas back to a liquid, and repeating the cycle. The liquid fluid can be heated by an external boiler, or one of the components of the fuel cell system such as the combustor and/or the fuel cell stack.
1. A process comprising:
circulating a working fluid through a first flow path, wherein the working fluid comprises molecules comprising carbon;
pumping the working fluid in liquid form to an elevated pressure;
flowing the working fluid through the center of a bipolar plate in a fuel cell stack;
heating the working fluid to a high temperature and high-pressure gas;
expanding the high temperature and high-pressure gas through an expander to produce shaft work;
using the shaft work to drive an air compressor for compressing air and delivering compressed air to a fuel cell subcomponent;
and removing energy from the gas to change the gas to the working fluid in liquid form;
and flowing hydrogen through a second flow path including the fuel cell stack to generate electricity using the hydrogen, and wherein the first flow path does not include a steam reforming reactor to reform the working fluid.
2. A process as set forth in claim 1 further comprising using the shaft work to drive a pump for pressuring and delivering cooling fluid to a fuel cell component.
3. A process as set forth in claim 1 wherein the working fluid comprises CClF 2 CClF 2 .
4. A process as set forth in claim 1 wherein the molecules further comprise a halide.
5. A process as set forth in claim 1 wherein the first flow path and the second flow path do not share a common portion.
6. A process of heating a fuel cell stack during relatively cold startup conditions comprising:
(a) pumping a fuel cell stack liquid cooling fluid to an elevated pressure, and wherein the liquid cooling fluid comprises molecules comprising carbon;
(b) flowing the liquid cooling fluid through the center of a bipolar plate in a fuel cell stack thereby transferring thermal energy between the fuel cell stack liquid cooling fluid and a fuel cell stack;
(c) heating the liquid cooling fluid;
(d) immediately thereafter expanding the heated cooling fluid in an expander to produce shaft work;
(e) using the shaft work to drive an air compressor for compressing air and delivering compressed air to the fuel cell stack;
(f) directing the cooling fluid through a condenser comprising fans and wherein the condenser fans are turned off, and
(g) repeating steps (a–f) until the temperature of a fuel cell stack has reached a predetermined temperature suitable for operating the fuel cell stack under cross-startup operating conditions.
7. A process as set forth in claim 6 further comprising using the shaft work to drive a pump for pressurizing and delivering cooling fluid to a fuel cell system component.
8. A process as set forth in claim 6 wherein the liquid cooling fluid comprises CClF 2 CClF 2 .
9. A process as set forth in claim 6 wherein the molecules further comprise a halide.