Under sponsorship of the Morgantown Energy Technology Center of the Department of Energy, the Westinghouse Electric Corporation and Avco Research Laboratory/Textron (ARL) are developing a direct coal-fired 80-MW combustion turbine. This is to be an element in a 207-MW direct coal-fired combustion turbine combined cycle, comprising another combustion turbine, a heat-recovery steam generator, and a steam turbine. Following conceptual and economic studies, the first experimental task has been to develop a direct coal-fired slagging combustor in small scale. A year’s testing with this unit has now been accomplished. It is thus possible to discuss experimental results in the areas of slag management, general combustor operability, coal fuel feed, heat loss, pressure loss, combustion efficiency, and emissions.
Westinghouse and ARL selected the slagging combustor for use in this program because of its unique ability to accept inexpensive standard utility-type coal without sending excessive pollutants and particulates to the expander-turbine. It accomplishes this by burning the coal at a temperature high enough to melt the ash, and then removing the molten slag with an impact separator. This combustor is also of the rich-lean type, which allows it to emit very low levels of NOx. Sulfur oxides are controlled through injection of a sorbent which combines with gaseous forms of sulfur in the rich zone, and then takes them out with the slag.
The plan in this program is to develop the slagging combustor in small scale at 12 million Btu/h (12.66 million kJ/h) heat input, 6 atmospheres pressure, and then move to design and verification testing of a full-scale 70 million Btu/h (73.85 million kJ/h), 14-atmosphere unit. It is with the smaller burner that this paper is concerned. During this period, coals have been fed into the 6-atm combustor exclusively in the dry-pulverized form with air as the carrier gas. To date, high- and low-sulfur eastern bituminous, and low-sulfur western subbituminous coals have been evaluated, with, and without sorbents, which have included various calcium and iron containing minerals. Coal samples have been of the 200 mesh size, and have not been beneficiated.
Combustor operation has been efficient and repeatable and slag flow has been symmetrical and manageable. Slag removal has been greater than 90 percent and carbon burnout has been greater than 99 percent. Nitrogen oxide emissions meet the goals of EPA’s NSPS for coal-fired plants. Current tests are focused on the goal of 90 percent sulfur removal. Although some results are available, various sorbents and injection techniques continue under test.