The goals of a research program recently completed at the University of California, Irvine were to develop analysis strategy for solid oxide fuel cell (SOFC) based systems, to apply the analysis strategy to tubular SOFC hybrid systems and to identify promising hybrid configurations. A pressurized tubular SOFC combined with an intercooled-reheat gas turbine (SureCell™ cycle) is chosen as the base cycle over which improvements are sought. The humid air turbine (HAT) cycle features are incorporated to the base cycle resulting in the SOFC-HAT hybrid cycle which shows an efficiency of 69.05 percent while the base cycle has an efficiency of 66.23 percent. Exergy analysis identified the superior efficiency performance of the SOFC component. Therefore, an additional cycle variation added a second SOFC component followed by a low pressure combustor in place of the reheat combustor of the gas turbine of the SOFC-HAT hybrid. The resulting dual SOFC-HAT hybrid has a thermal efficiency of 75.98 percent. The single SOFC-HAT hybrid gives the lowest cost of electricity (3.54¢/kW-hr) while the dual SOFC-HAT hybrid has the highest cost of electricity (4.02¢ /kW-hr) among the three cycles with natural gas priced at $3/GJ. The dual SOFC-HAT hybrid plant cost is calculated to be significantly higher because the fraction of power produced by the SOFC(s) is significantly higher than that in the other cases on the basis of $1100/kw initial cost for the SOFC. The dual SOFC-HAT hybrid can only be justified in favor of the single SOFC-HAT hybrid when the price of natural gas is greater than $14/GJ or if a severe carbon tax on the order of $180/ton of CO2 is imposed while natural gas price remains at $3/GJ. Copyright © 2003 by ASME.

The emergence of fuel cell systems and hybrid fuel cell systems requires the evolution of analysis strategies for evaluating thermodynamic performance and directing design and development. A description and application of the recently developed tool for analyzing tubular SOFC based systems is presented. The capabilities of this tool include an analytical model for the tubular SOFC derived from first principles and the secondary equipment required to analyze hybrid power plants. Examples of such secondary equipment are gas turbine, reformer, partial oxidation reactor, shift reactor, humidifier, steam turbines, compressor, gas expander, heat exchanger, and pump. A "controller" is included which is essential for modeling systems to automatically iterate in order to meet the desired process or system design criteria. Another important capability that is included is to be able to arrange the various components or modules as defined by the user in order to configure different hybrid systems. Analysis of the hybrid cycle as originally proposed by Westinghouse (SureCellm) indicates that the thermal efficiency of the cycle is quite insensitive to the pressure ratio, increasing from 65.5 percent to 66.6 percent on a lower calorific value of the fuel as the pressure ratio decreases from 15 to 6.5.

The goals of a research program recently completed at the University of California, Irvine were to develop analysis strategy for Solid Oxide Fuel Cell (SOFC) based systems, to apply the analysis strategy to tubular SOFC hybrid systems and to identify promising hybrid configurations. A pressurized tubular SOFC combined with an intercooled-reheat gas turbine (SureCell ™ cycle) is chosen as the Base Cycle over which improvements are sought. The humid air turbine (HAT) cycle features are incorporated to the Base Cycle resulting in the SOFC-HAT hybrid cycle which shows an efficiency of 69.05% while the Base Cycle has an efficiency of 66.23%. Exergy analysis identified the superior efficiency performance of the SOFC component. Therefore, an additional cycle variation added a second SOFC component followed by a low pressure combustor in place of the reheat combustor of the gas turbine of the SOFC-HAT hybrid. The resulting Dual SOFC-HAT hybrid has a thermal efficiency of 75.98%. The Single SOFC-HAT hybrid gives the lowest cost of electricity (3.54¢/kW-hr) while the Dual SOFC-HAT hybrid has the highest cost of electricity (4.02¢/kW-hr) among the three cycles with natural gas priced at $3/GJ. The Dual SOFC-HAT hybrid plant cost is calculated to be significantly higher because the fraction of power produced by the SOFC(s) is significantly higher than that in the other cases on the basis of $1100/kw initial cost for the SOFC. The Dual SOFC-HAT hybrid can only be justified in favor of the Single SOFC-HAT hybrid when price of natural gas is greater than $14/GJ or ffa severe carbon tax on the order of $180/ton of CO2 is imposed while natural gas price remains at $3/GJ. Copyright © 2001 by ASME.

The goal of the U.S. Department of Energy's (DOE's) FutureGen project initiative is to develop and demonstrate technology for ultra clean 21st century energy plants that effectively remove environmental concerns associated with the use of fossil fuels for producing electricity, and simultaneously develop highly efficient and cost-effective power plants. The design optimization of an advanced FutureGen plant consisting of an advanced transport reactor (ATR) for coal gasification to generate syngas to fuel an integrated solid oxide fuel cell (SOFC) combined cycle is presented. The overall plant analysis of a baseline system design is performed by identifying the major factors effecting plant performance; these major factors being identified by a strategy consisting of the application of design of experiments (DOEx). A steady state simulation tool is used to perform sensitivity analysis to verify the factors identified through DOEx, and then to perform parametric analysis to identify optimum values for maximum system efficiency. Modifications to baseline system design are made to attain higher system efficiency and to lower the negative impact of reducing the SOFC operating pressure on system efficiency. © 2006.

An advanced coal based power plant system that has an electrical efficiency of 60% on an HHV basis is defined. The solid oxide fuel cell (SOFC) hybrid has been shown to be an essential requirement in order to achieve such a high efficiency. The coal is gasified utilizing a high pressure air-blown advanced transport reactor (ATR). A thermo-economic analysis of this integrated gasification fuel cell (IGFC) plant is performed by comparing it to an integrated gasification combined cycle (IGCC) plant that utilizes a gas turbine combined cycle for power generation. Results of this thermo-economic analysis indicate that the required "break even" cost of the SOFC system is $400/kW on an installed cost basis such that the cost of electricity of IGFC plant is the same as that of the IGCC plant. Coproduction of H2 and capture of carbon emissions may be incorporated in the design without causing a major thermal penalty on the system performance when high temperature separation membranes are employed. An O2-blown gasifier is required for such applications. The technology development needs are addressed. Copyright © 2005 by ASME.

A novel process configuration consisting of integrating the air separation unit with a H2 separation membrane reactor (HSMR) in a coal gasification based coproduction facility with near zero emissions is described. The plant utilizes an air separation unit operating at elevated pressure to produce an Intermediate Pressure (IP) N2 stream in addition to the O2 required by the coal gasifier. The syngas produced by the gasifier after cleanup is supplied to the membrane reactor which produces H2 by shifting the carbon monoxide while simultaneously separating the fy. The IP N2 is used as sweep gas to assist in the separation of the H 2 diffusing across the membrane walls by decreasing the partial pressure of the H2 on the permeate side. The total pressure of gases on the permeate side may thus be increased such that the H2 / N 2 mixture may be fed directly to the gas turbines at the required pressure without requiring cooling and compression of the HT. An added advantage is that the total pressure differential across the membrane wall is reduced. The N2 in the fuel gas functions both as a thermal diluent for reducing the formation of nitrogen oxides and as additional motive fluid for expansion in the turbine. The carbon dioxide rich gas (non-permeate) leaving the membrane reactor after catalytic oxidation of the residual combustibles constitutes the carbon capture stream which may be further compressed and pipelined for CO2 sequestration. High purity H2 may be coproduced for export from a portion of the H2-N2 stream leaving the HSMR utilizing a Pressure Swing Adsorption (PSA) unit. The techno-economic advantages of such a coproduction facility are addressed. Copyright © 2006 by ASME.

Under the sponsorship of the U.S. Department of Energy/National Energy Technology Laboratory, a multi-disciplinary team led by the Advanced Power and Energy Program of the University of California at Irvine is defining the system engineering issues associated with the integration of key components and subsystems into power plant systems that meet performance and emission goals of the Vision 21 program. Earlier tasks of the program have narrowed down the myriad of fuel processing, power generation, and emission control technologies to selected scenarios that identify those combinations having the potential to achieve the Vision 21 program goals of high efficiency and minimized environmental impact while using fossil fuels. These analyses have been extended to consider coal gasification processes combined with the advanced power cycles previously identified. 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 solid oxide fuel cells, advanced cycle gas turbines, membrane separation of gases and oxygen-enhanced combustion.