Stephen E. Veyo

Status of Pressurized SOFC/Gas Turbine Power System Development at Siemens Westinghouse

Pressurized solid oxide fuel cell (PSOFC)/micro gas turbine generator (MTG) hybrid power systems have the potential to generate electric power at high efficiency [circa 60% (net AC/LHV)] at multi-hundred kWe and multi-MWe capacities. Thus, good fuel economy and low CO2 emissions are positive system attributes, as are low NOx and SOx emissions due to the propensity of the SOFC for low NOx generation, the need for no firing of the gas turbine combustor during normal hybrid system power operations, and the use of desulfurized fuel. Exhaust temperatures are sufficiently high to enable the recovery of heat for steam/hot-water production, and system energy efficiencies of at least 80% are feasible. Work is ongoing at Siemens Westinghouse on three PSOFC/MTG power systems. Two, with 220 kWe and 300 kWe capacities, are proof-of-concept demonstration units. The 220 kWe PSOFC/MTG power system is in test at the National Fuel Cell Research Center, University of California-Irvine, and the 300 kWe system, which is currently being designed, will be demonstrated in two tests to be performed in Europe. The status of work on the 220 kWe and 300 kWe power systems is reviewed. The third system is to have capacity of at least 500 kWe. This system, which will be demonstrated also, is viewed as a prototype commercial product. The 500 kWe-class PSOFC/MTG concept is described and performance estimates are presented.Copyright

Solid Oxide Fuel Cell Power System Cycles

Reviewed are power system concepts employing the solid oxide fuel cell (SOFC) at atmospheric pressure in simple cycle; in an atmospheric pressure hybrid cycle with a gas turbine (SOFC/GT); and in a pressurized SOFC/GT hybrid (PSOFC/GT). Estimates of power system performance are presented and discussed. Simple atmospheric pressure SOFC systems designed for combined heat and power (CHP) application can approach 50% electric generation efficiency (net AC/LHV) and 80% fuel effectiveness [(net AC + useful heat)/LHV]. Pressurized SOFC systems with intercooled, recuperated, and SOFC-reheated GT cycles can approach 70% electric generation efficiency, while the atmospheric pressure SOFC/GT hybrid cycle and a simple pressurized SOFC/GT cycle can approach 55% and 60% generation efficiency, respectively. These high levels of efficiency are extraordinary in that they are achievable at the MW capacity level.Copyright

Tubular SOFC Hybrid Power System Status

Power generation systems of exemplary efficiency can be configured through the synergistic thermal-hydraulic coupling of a solid oxide fuel cell (SOFC) generator module with a gas turbine engine electric generator. Analysis indicates that hybrid cycle power systems have the potential to achieve electrical generation efficiencies ranging from over 50% for 300 kWe atmospheric pressure hybrid systems to near 70% for pressurized fuel cell reheat gas turbine hybrid systems. Analysis results are reviewed. Siemens Westinghouse has fabricated two simple-cycle proof-of-concept designs for pressurized SOFC/micro gas turbine generator (PSOFC/MTG) hybrid systems. The efficiency horizon for simple-cycle PSOFC/MTG systems is 60%. The world’s first SOFC Pressurized Hybrid of 200 kWe capacity [PH200] was built for Southern California Edison (SCE) and is installed at the National Fuel Cell Research Center at the University of California – Irvine. The unit has operated for over 2000 hours with an indicated efficiency of 53%. Although operation has been troubled by SOFC stack nonconformance problems, this unit has demonstrated the technical feasibility of the PSOFC/MTG hybrid technology. Following the most recent stack repair, the unit was restarted in November, 2002. System operation and performance information is reviewed. A second proof-of-concept unit, a PH300 built for a consortium led by RWE, a German utility, is nearing completion and is scheduled for initial operation in early 2003, and another PH300 will be installed at an Edison S.p.A site in Italy later in 2003. PH300 project status information is presented.Copyright

Comparative Evaluation of SOFC/Gas Turbine Hybrid System Options

Solid Oxide Fuel Cell [SOFC]/Gas Turbine [GT] hybrid power systems can synergistically exploit the high operating temperature and high electrical generation efficiency of the solid oxide fuel cell and the high power density and simplicity of the gas turbine engine generator. Continued studies at Siemens Westinghouse seek practical system configurations with commercialization potential. Pressurized SOFC [PSOFC]/GT system concepts [directly heated Brayton cycles] can yield electrical power generation at the highest efficiency [circa 70%] {net ac/LHV} with concomitant complexity in configuration, operation and installation. Indirectly heated Brayton cycles utilizing an atmospheric pressure SOFC [ASOFC] can achieve a more modest electrical power generation efficiency [circa 55%] with considerably less complexity. Co-firing of the GT combustor to yield state-of-the-art [SOA] turbine inlet temperature [TIT] can most fully exploit the capability of SOA turbine technology yielding a hybrid system of lesser efficiency, but also of lesser cost (

A High-Efficiency SOFC Hybrid Power System Using the Mercury 50 ATS Gas Turbine

/kWe). The ideal gas turbine and/or system configuration remains elusive however. Recent studies have focused on the indirectly heated cycle wherein the gas turbine exhaust serves directly as the SOFC oxidant. Consequently, the GT exhaust flow rate and temperature must be compatible with SOFC generator inlet requirements. This compatibility can be difficult to achieve with a state-of-the-art micro gas turbine generator [MTG] that typically operates with relatively low pressure ratio [3 to 4]. Alternatives ranging from the ideal GT to system level feature additions allowing SOA GTs have been analyzed. These alternatives are identified and discussed, and results of a comparative performance and cost evaluation are reviewed.Copyright

Tubular Solid Oxide Fuel Cell/Gas Turbine Hybrid Cycle Power Systems — Status

The conceptual design of a 20 MWe-class hybrid power generating system that integrates a Siemens Westinghouse pressurized solid oxide fuel cell generator with a Mercury 50 gas turbine is discussed. The Mercury 50 was designed and developed by Caterpillar/Solar Turbines during the U.S. Department of Energy (DOE) Advanced Turbine Systems (ATS) program, and the hybrid system design concept was evaluated during a recently completed project that was part of the DOE High Efficiency Fossil Power Plant (HEFPP) program. While achieving a high power system efficiency by the hybrid cycle approach was important, the focus of the design study was to select the SOFC generator capacity such that the low specific cost of the ATS gas turbine and the high efficiency of the more expensive PSOFC generator would combine optimally to produce an attractively-low cost of electricity (COE) for the overall power system. The system cycle and physical characteristics are described; power, efficiency, and emissions estimates are presented; and estimates of system cost and COE are provided. In addition, two bottoming cycle options (steam turbine and ammonia turbine) are described, and performance and cost projections for each are reviewed.© 2001 ASME

Single module pressurized fuel cell turbine generator system

The solid oxide fuel cell (SOFC) is a simple electrochemical device that operates at 1000°C, and is capable of converting the chemical energy in natural gas fuel to AC electric power at approximately 45% efficiency (net AC/LHV) when operating in a system at atmospheric pressure. Since the SOFC exhaust gas has a temperature of approximately 850°C, the SOFC generator can be synergistically integrated with a gas turbine (GT) engine-generator by supplanting the turbine combustor and pressurizing the SOFC, thereby enabling the generation of electricity at efficiencies approaching 60% or more. Conceptual design studies have been performed for SOFC/GT power systems employing a number of the small recuperated gas turbine engines that are now entering the marketplace. The first hardware embodiment of a pressurized SOFC/GT power system has been built for Southern California Edison and is scheduled for factory acceptance tests beginning in Fall, 1999 at the Siemens Westinghouse facilities in Pittsburgh, Pennsylvania. The hybrid power cycle, the physical attributes of the hybrid systems, and their performance are presented and discussed.Copyright