Technology Assumptions and Issues

The system described is assumed to be in the contiguous U.S., and to have adequate feedstock supply available within a 80.5 km (50 mile) radius. Other assumptions include adequate highway infrastructure, and ready electricit y transmissio n access. The site for the primary reference study [1] is southwestern Minnesota (FERC Region 5). Thi s technology provides a service similar to base load fossil electric generation and cogeneration plants.

It is expected that biomass gasification systems of the type discussed here will be commercially available in the nex t five years, with the near-term application assumed to be in industrial scale turbines for repowering of pulp/paper an d sugar cane industries. Gasifiers have been developed in the U.S. and Europe to produce low- and medium-heating -value gases from biomass. In Europe, gasifier systems include fixed-bed gasifiers such as the Bioneer gasifier [11] , high pressure gasifiers such as the High Temperature Winkler [12], and circulating fluid bed gasifiers such as th e Studsvik [13], Gotaverken [14], Ahlstrom [15] and Lurgi [16].

In the U.S., gasifiers are being developed by the Institute of Gas Technology(IGT) [17], Battelle Columbus Laboratory (BCL) [18], the University of Missouri at Rolla [19], and Manufacturing and Technology Conversion Internationa l [20]. The IGT system is an air/oxygen-blown fluidized bed gasifier while others are indirectly heated gasifiers, usin g either entrained-flow or fluidized bed reactors. In a jointly funded program, a modified Lurgi-type fixed-bed gasifie r using wood chips has been operated. In addition, commercial-scale gasifiers have been operated in the U.S. to produce low-heating-value gas for use as a plant fuel. The status of these systems range from the level of research an d development to commercially available for generating low calorific gas. A number of advanced systems, such as th e Ahlstrom, TPS/Studsvik, and Institute of Gas Technology and Battelle Columbus Laboratory gasifiers, are considered to be near commercial for generating electricity in combination with commercial gas turbine technology.

The IGT technology is being demonstrated in Hawaii at the 90 Mg/day scale on sugarcane bagasse fuel. The gasifie r has run for over 100 hours and is being prepared for a 1500 hour test during late summer 1997 to verify the readiness of the gasification technology as well as the suitability of hot gas filter material for commercial application wit h biomass fuel. The BCL technology is the subject of a scale-up to 180 Mg/day at the McNeil Generating Station i n Burlington, Vermont. These demonstration tests will be fueled by wood chips and the resulting synthesis gas fired i n the existing McNeil boiler. Subsequent phases of this project call for installation and testing of a gas turbine o f approximately 10 MWe capacity. Successful completion of these tests will provide the final data and technolog y confidence required for scale-up to commercial projects and for obtaining financing for such projects.

The hot gas particulate filter technology used in this characterization was developed by Westinghouse and has bee n demonstrated in numerous applications from pressurized fluidized bed coal combustion at the Tidd demonstratio n project through large scale coal gasification at the Sierra Pacific Pinon Pine Clean Coal demonstration project. Th e filter size used at Tidd has been deemed adequate for biomass gasification applications in the 50-75 MW e range. A number of filter elements were tested at the IGT 9 Mg/day pilot gasifier in Chicago, Illinois [21]. This test established the appropriate filter face velocity for use with biomass derived gases and ability of the filters to be cleaned and recover a stable pressure drop across the filter vessel. The results from this test also indicated that sufficient particulate removal was achieved for subsequent use of the gas in a gas turbine. Alkali levels in the exit gas were acceptably low with the exception of sodium. Subsequent analysis of the filter material indicated that long term durability of the filter was a potential issue. For this reason, long-term (1,500 hour) durability tests are being performed at the Hawaii gasification facility to select a more appropriate filter material from those commercially available and to determine whether th e sodium levels measured in the pilot plant testing are indicative of actual behavior or an anomaly. These tests shoul d settle any final technical issues surrounding use of hot particulate and alkali removal from biomass synthesis gases.

In addition to efficient technology, an abundant and reliable supply of low-cost biomass feedstock is critical fo r significant growth to occur in the biomass power industry. The use of biomass residues, about 35 Tg/yr today, is expected to expand throughout the period, reaching about 50 Tg/yr. A key premise of the U.S. National Biomass Power Program is that a dramatic expansion in future availability of dedicated feedstocks will occur in the 2005-2020 time frame, growing to about 90 Tg/yr by 2020.

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