ELECTRICITY GENERATION FROM FUEL CELL WASTE HEAT USING AN ORGANIC RANKINE CYCLE

Fuel cells produce exhaust waste heat that can be harnessed to either meet local heating needs or produce additional electricity via an appropriately chosen bottoming cycle. Power production can often be more economically attractive than heating due to the much higher value of electricity than heat on an equivalent energy basis, especially given fuel cell incentives and subsidies that are based on the net electrical output of the (combined cycle) fuel cell power plant. In this paper we review the application of the Organic Rankin Cycle (ORC) for power production from fuel cell waste heat, with emphasis on the resulting improvements in overall power plant power output, efficiency, economics (e.g., cents/kWh maintenance costs), and emissions levels (e.g., lb/MWh emissions). We also highlight a much less obvious advantage of ORC bottoming of fuel cells; namely, its ability to partially compensate for fuel cell stack degradation over time, and corresponding potential to extend the time required between fuel cell stack overhauls. We will also review the relative difficulty of several well established commercial applications of the ORC for power production from waste heat such as power production from gas turbine exhaust, etc. in comparison to fuel cell applications. We conclude that not only is the ORC ideal for fuel cell bottoming, but also that fuel cells are a nearly ideal commercial application area for the ORC. In closing, we summarize a recently completed project believed to be the world's first commercial application of ORC technology to a fuel cell power plant. This project was completed in less than a year after its initiation, and utilizes a single ORC in conjunction with five fuel cells, all located within a fuel cell park that produces nearly 15 MW of electricity.