OPTIMIZING PERFORMANCE OF THE HESKETT STATION
The overall conclusion from this work is that a switch from river sand bed material to limestone at the R.M. Heskett Station would provide substantial benefits to MDU. A switch to limestone would increase the fuel flexibility of the unit, allowing fuels higher in both sodium and sulfur to be burned. The limestone bed can tolerate a much higher buildup of sodium in the bed without agglomeration, allowing either the bed turnover rate to be reduced to half the current sand feed rate for a fuel with equivalent sodium or allow a higher sodium fuel to be burned with limestone feed rates equivalent to the current sand feed rate. Both stack and ambient SO{sub 2} emissions can be controlled. A small improvement in boiler efficiency should be achievable by operating at lower excess oxygen levels at low load. This reduction in oxygen will also lower NO{sub x} emissions, providing a margin of safety for meeting emission standards. No detrimental effects of using limestone at the Heskett Station were uncovered as a result of the test burn. Some specific conclusions from this work include the following: The bed material feed rate can be reduced from the current rate of 5.4% of the coal feed rate (57.4 tons of sand/day) to 2.5% of the coal feed rate (27 tons of limestone/day). This will result in an annual savings of approximately $$200,000. (1) SO{sub 2} emissions at the recommended feed rate would be approximately 250 ppm (0.82 lb/MMBtu) using a similar lignite. Based on the cost of the limestones, SO{sub 2} allowances could be generated at a cost of $$60/ton SO{sub 2} , leaving a large profit margin for the sale of allowances. The addition of limestone at the same rate currently used for sand feed could generate $455,000 net income if allowances are sold at $200/ton SO2 . (2) At full-load operation, unburned carbon losses increase significantly at excess oxygen levels below 2.8%. No efficiency gains are expected at high-load operation by switching from sand to limestone. By reducing the oxygen level at low load to 8.5%, an efficiency gain of approximately 1.2% could be realized, equating to $25,000 to $30,000 in annual savings. (3) A reduction of 25 tons/day total ash (bed material plus fly ash) will be realized by using limestone at the recommended feed rate compared to the current sand feed rate. No measurable change in volume would be realized because of the lower bulk density of the limestone-derived material.
- Research Organization:
- Federal Energy Technology Center Morgantown (FETC-MGN), Morgantown, WV (United States); Federal Energy Technology Center Pittsburgh (FETC-PGH), Pittsburgh, PA (United States)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- FC21-93MC30098
- OSTI ID:
- 777110
- Report Number(s):
- DE-FC21-93MC30098-60; TRN: AH200119%%64
- Resource Relation:
- Other Information: PBD: 1 Mar 1999
- Country of Publication:
- United States
- Language:
- English
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