Mars 90 gas turbine combined cycle project

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1.4 Hybrid Gas Turbine Fuel Cell Systems
In 1999 the turbines program funded a study by Rolls Royce with the goal to produce a turbo-generator, which would cost
approximately $400/kW. When coupled with fuel cells, the turbine would produce approximately 25% of the power for a hybrid in the
1 MW to 5 MW class. The gas turbine would be capable of providing pressurization from 5 pressure ratio (PR), to approximately 15 PR
and higher, all from the same special purpose gas turbine system design. As a stand-alone device, the turbine would produce 1.5 MW of
electric power in a simple cycle mode, without the need of a recuperator (recuperators are not needed in mini-turbines to achieve 30%
efficiency, which reduces costs by 25-30%, reduces space requirements, and contributes to more reliable operation). In the stand-alone
mode, its efficiency would be approximately 33% (comparable to larger 5 MW class gas turbines). The exhaust energy could be used to
operate a combined heat and power cycle.
Detailed and Experimental Studies
After these studies were completed several tests of the hybrid concept were initiated by the U.S. Department of Energy with
industry cost-sharing from FuelCell Energy, General Electric (formerly Honeywell), and Siemens Power Corporation (formerly Siemens
Westinghouse). Each of the projects focused on the sub-1MW class hybrid system.
FuelCell Energy’s hybrid system is comprised of a 250 kW fuel cell stack and a 30 kW Capstone micro-turbine in an indirect
fuel cell bottoming configuration. The sub-MW system tests have provided valuable data that has proven the high efficiency and low
emissions performance of such systems. FuelCell Energy also designed a 40 MW fuel cell turbine hybrid power system in this effort.
The General Electric project includes the sub-MW design and test of a Solid State Energy Conversion Alliance (SECA) solid oxide
fuel cell and a micro-turbine. The project evaluated several turbine cycle configurations, including topping, bottoming, direct and
indirect, and allowed for the evaluation of integration and scale-up issues for SECA-based hybrid systems.
The Siemens Power Corporation hybrid design included a 100 kW tubular SOFC integrated with a 60 kW Ingersoll Rand micro-
turbine generator. This system was built and tested at the National Fuel Cell Research Center, in Irvine, California. In this test the
hybrid direct gas turbine fuel cell topping cycle configuration was demonstrated. This test included pressurization of the fuel cell to
provide a total of 220 kW of power from the hybrid system. Testing proved that high efficiency and ultra-low emissions was achievable
with these types of hybrid cycles, but, that integration and operation is considerably difficult with such complex hybrid systems.
Early optimism regarding the ease of integrating fuel cells with off-the-shelf micro-turbines has been tempered by technical issues
encountered in the test program at the National Fuel Cell Research Center. It is now recognized that integrating fuel cells and turbines is
challenging. Existing gas turbines do not match the pressure ratios, mass flows, and other critical operating and performance parameters
of the small high temperature fuel cells that are currently available. Nonetheless, the early tests have proven the high efficiency and
ultra-low emissions performance characteristics of hybrid gas turbine fuel cell technology so that optimism regarding the potential of
these types of cycles to significantly contribute to future energy demands remains high.
Detailed Paper Studies for Future Hybrid Systems
Additional studies on hybrid systems and the results of recent tests identified significant potential benefits from a combined
fuel cell/turbine power system. These benefits include the ability to achieve net electrical efficiencies in the 70 % + range, to configure
systems in the 20 MW to 40 MW and larger size range, and to significantly surpass emission standards for criteria pollutants while
reducing the emissions of CO2 / kW-hr. Studies also predict lower cost of electricity and lower capital costs than alternative power
generation systems. For example, a market study by Research Dynamics Corporation suggested that such products could compete on
a cost-of-electricity basis with other DG technologies and capture 8.2 GW of market share by 2005.
The historical record of the evolution of hybrid gas turbine fuel cell technology has been documented by White9, and the various
technical elements of the hybrid technology have been presented in a series of sessions sponsored by the American Society of Mechanical
Engineers (ASME) International Gas Turbine Institute (IGTI).10
Under the sponsorship of the U.S. DOE, a multi-disciplinary team led by the Advanced Power and Energy Program (APEP) of
the University of California, Irvine is defining the system engineering issues associated with the integration of key components and
subsystems into central power plant systems that meet stretch performance and emission goals for both natural gas and coal fuel operation.
The myriad of fuel processing, power generation, and emission control technologies are narrowed down to selected scenarios in order
to identify those combinations that have the potential to achieve high efficiency and minimized environmental impact while using fossil
fuels. The technology levels considered are based on projected technical and manufacturing advances being made in industry and on
advances identified in current and future government supported research. Examples of systems included in these advanced cycles are
high-temperature fuel cells, advanced gas turbines, ion transport membrane separation and hydrogen-oxygen combustion.
The overall objectives of DOE study were to (1) produce electricity and transportation fuels at competitive costs, (2) minimize
environmental impacts associated with fossil fuel use, and (3) attain high efficiency. The efficiency target for natural gas fueled plants
was 75% on a LHV basis while that for coal fueled plants was 60% on an HHV basis. All cycles were to include producing electricity
with the potential for CO2 capture and sequestration and co-production of transportation fuels. This study determined that the only
technology that could meet these goals is hybrid gas turbine fuel cell technology.
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