Westinghouse fuel cell combined cycle systems

Efficiency (voltage) of the solid oxide fuel cell (SOFC) should increase with operating pressure, and a pressurized SOFC could function as the heat addition process in a Brayton cycle gas turbine (GT) engine. An overall cycle efficiency of 70% should be possible. In cogeneration, half of the waste heat from a PSOFC/GT should be able to be captured in process steam and hot water, leading to a fuel effectiveness of about 85%. In order to make the PSOFC/GT a commercial reality, satisfactory operation of the SOFC at elevated pressure must be verified, a pressurized SOFC generator module must be designed, built, and tested, and the combined cycle and parameters must be optimized. A prototype must also be demonstrated. This paper describes progress toward making the PSOFC/GT a reality

Westinghouse 100 kWe SOFC demonstration status

The world`s first 100 kWe class Solid Oxide Fuel Cell (SOFC) power generation system is being supplied by Westinghouse and is sponsored by EDB/ELSAM, a consortium of Dutch and Danish utilities. This natural gas fueled experimental field unit will be installed near Arnhem, The Netherlands, at an auxiliary district heating plant. The module utilizes tubular Air Electrode Supported SOFCs. The system will achieve an electrical generation efficiency of 49%, and this combined with recovery of heat for district heating can yield an overall fuel effectiveness approaching 80%. Significant progress toward reduction of CO{sub 2}, a greenhouse gas, will be obtained, and the system will be environmentally benign

Tubular solid oxide fuel cell prospect

Driven by technological achievement and rational projection of commercial product cost, expectations for tubular SOFC commercialization are improving. Tubular SOFCs have surpassed 7 yrs operation and have recently demonstrated remarkable toughness in thermal cycling. Customer-owned systems with 25 kW stacks utilizing air electrode supported (AES) cells continue to operate directly on natural gas without degradation after multiple thermal cycles and over 4000 hrs operation. AES cell operation at elevated pressure corroborates theoretical estimates of performance gain without evidence of deleterious effect. Commercial class AES cell of 22 mm dia and 1500 mm length, is now in production for application to 100 kW, 50% efficient (ac/LHV), atmospheric pressure systems. This same cell applied to pressurized systems in combination with conventional turbo machinery (gas turbines) can yield an efficiency approaching 70% for power plants as small as 5 MW. Total installed system cost for commercial 5 MW SOFC/CT units for distributed power generation and on-site cogeneration should approach $1000/kW. A major challenge is formation of funded projects to demonstrate at the turn of the century prototype MW class SOFC/CT combined cycle power plants and to complete the development of commercial fuel cell manufacturing processes

Tubular SOFC and SOFC/gas turbine combined cycle status and prospects

Presently under fabrication at Westinghouse for a consortium of Dutch and Danish utilities is the world`s first 100 kWe Solid Oxide Fuel Cell (SOFC) power generation system. This natural gas fueled experimental field unit will be installed near Arnhem, Netherlands, at an auxiliary district heating plant. Electrical generation efficiency of this simple cycle atmospheric pressure system will approach 50% [net ac/LHV]. For larger capacity systems, the horizon for the efficiency (atmospheric pressure) is about 55%. Pressurization would increase the efficiency. Objectives of the analyses reported were: (1) to document the improved performance potential of the two shaft turbine cycle given access to a better recuperator and lower lead losses, (2) to assess the performance of PSOFC/GT combined cycles in the 3 MW plant application that are based on use of a simple single shaft gas turbine having a design-point turbine inlet temperature that closely matches the temperature of the SOFC exhaust gas (about 850 C), (3) to estimate the performance potential of smaller combined cycle power plants employing a single SOFC submodule, and (4) to evaluate the cogeneration potential of such systems

Tubular solid oxide fuel cell demonstration activities

This reports on a solid oxide fuel cell demonstration program in which utilities are provided fully integrated, automatically controlled, packaged solid oxide fuel cell power generation systems. These field units serve to demonstrate to customers first hand the beneficial attributes of the SOFC, to expose deficiencies through experience in order to guide continued development, and to garner real world feedback and data concerning not only cell and stack parameters, but also transportation, installation, permitting and licensing, start-up and shutdown, system alarming, fault detection, fault response, and operator interaction

Verification test of a 25kW class SOFC cogeneration system

Osaka Gas and Tokyo Gas have high expectations for natural-gas-fueled Solid Oxide Fuel Cell (SOFC) cogeneration systems. SOFC offers many advantages for on-site cogeneration systems, such as high electrical efficiency, high quality by-product heat and low emissions. They are now executing a joint development program with Westinghouse Electric Corporation (hereinafter called as WELCO). This program is aimed to verify a 25kW class SOFC cogeneration system. This system, which was modified by replacing previous zirconia porous support tube cells (PST cells) with newly designed air electrode supported cells (AES cells), commenced operation on March 21, 1995. The system has been successfully operated for 13,100 hours as of February 7, 1997. This paper presents the performance evaluation of the new AES cells and the results of system operation at WELCO

A High Efficiency PSOFC/ATS-Gas Turbine Power System

A study is described in which the conceptual design of a hybrid power system integrating a pressurized Siemens Westinghouse solid oxide fuel cell generator and the Mercury{trademark} 50 gas turbine was developed. The Mercury{trademark} 50 was designed by Solar Turbines as part of the US. Department of Energy Advanced Turbine Systems program. The focus of the study was to develop the hybrid power system concept that principally would exhibit an attractively-low cost of electricity (COE). The inherently-high efficiency of the hybrid cycle contributes directly to achieving this objective, and by employing the efficient, power-intensive Mercury{trademark} 50, with its relatively-low installed cost, the higher-cost SOFC generator can be optimally sized such that the minimum-COE objective is achieved. The system cycle is described, major system components are specified, the system installed cost and COE are estimated, and the physical arrangement of the major system components is discussed. Estimates of system power output, efficiency, and emissions at the system design point are also presented. In addition, two bottoming cycle options are described, and estimates of their effects on overall-system performance, cost, and COE are provided

High-Temperature Tubular Solid Oxide Fuel Cell Generator Development

During the Westinghouse/USDOE Cooperative Agreement period of November 1, 1990 through November 30, 1997, the Westinghouse solid oxide fuel cell has evolved from a 16 mm diameter, 50 cm length cell with a peak power of 1.27 watts/cm to the 22 mm diameter, 150 cm length dimensions of today's commercial prototype cell with a peak power of 1.40 watts/cm. Accompanying the increase in size and power density was the elimination of an expensive EVD step in the manufacturing process. Demonstrated performance of Westinghouse's tubular SOFC includes a lifetime cell test which ran for a period in excess of 69,000 hours, and a fully integrated 25 kWe-class system field test which operated for over 13,000 hours at 90% availability with less than 2% performance degradation over the entire period. Concluding the agreement period, a 100 kW SOFC system successfully passed its factory acceptance test in October 1997 and was delivered in November to its demonstration site in Westervoort, The Netherlands

Solid oxide fuel cell distributed power generation

Fuel cells are electrochemical devices that oxidize fuel without combustion to convert directly the fuel`s chemical energy into electricity. The solid oxide fuel cell (SOFC) is distinguished from other fuel cell types by its all solid state structure and its high operating temperature (1,000 C). The Westinghouse tubular SOFC stack is process air cooled and has integrated thermally and hydraulically within its structure a natural gas reformer that requires no fuel combustion and no externally supplied water. In addition, since the SOFC stack delivers high temperature exhaust gas and can be operated at elevated pressure, it can supplant the combustor in a gas turbine generator set yielding a dry (no steam) combined cycle power system of unprecedented electrical generation efficiency (greater 70% ac/LHV). Most remarkably, analysis indicates that efficiencies of 60 percent can be achieved at power plant capacities as low as 250 kWe, and that the 70 percent efficiency level should be achievable at the two MW capacity level. This paper describes the individual SOFC, the stack, and the power generation system and its suitability for distributed generation