Use of biomass in electric power generation: the california experience

Abstract

This paper considers the performance and operating characteristics of the 46 power plants in central and northern California presently generating electric power using wood wastes and/or agricultural residues to fire steam turbines. The paper is a synopsis of an assessment of the more than 750 MW of biomass-fueled capacity providing power to the PG&E grid which came on line during the past decade, following the passage of the federal Public Utility Regulatory Policies Act. The plants are fueled by sawdust or pulp process wastes, hog fuel, in-forest thinnings, clean landfilled wood, orchard and vineyard wastes, and other agricultural residues. The challenges associated with combustion of agricultural residues have proved to be much greater than had been anticipated. The smallest plant provides less than 3 MW of power to the utility grid and the largest nearly 50 MW. Overall they consume more than 7 million bone dry tons (BDT) of fuel each year, using about 1 BDT to generate 1 MWh, an overall efficiency of about 20%. Lack of a fuels supply infrastructure resulted in a very tight fuels market and resultant high spot market prices during 1989 and 1990. Nevertheless, most of the plants have had a capacity factor of greater than 80%, though there have been problems associated with design, management and fuels procurement at some others. Some of the plants were constructed from rehabilitated boilers and turbines and have minimal environmental controls; others reflect the best of fluidized bed combustion technologies, with non-catalytic deNO x and “zero-discharge” water treatment capability. Future research should include work on harvesting and collection technologies, better characterization of the fuel resources and integrated programs to produce and use biomass to fuel advanced generation technologies, such as gas turbines and fuel cells.