Optimizing performance of the heskett station

摘要

The overall conclusion from this work is that a switch from river sand bed211u001ematerial to limestone at the R.M. Heskett Station would provide substantial 211u001ebenefits to MDU. A switch to limestone would increase the fuel flexibility of the 211u001eunit, allowing fuels higher in both sodium and sulfur to be burned. The limestone 211u001ebed can tolerate a much higher buildup of sodium in the bed without 211u001eagglomeration, allowing either the bed turnover rate to be reduced to half the 211u001ecurrent sand feed rate for a fuel with equivalent sodium or allow a higher sodium 211u001efuel to be burned with limestone feed rates equivalent to the current sand feed 211u001erate. Both stack and ambient SO(sub 2) emissions can be controlled. A small 211u001eimprovement in boiler efficiency should be achievable by operating at lower 211u001eexcess oxygen levels at low load. This reduction in oxygen will also lower NO(sub 211u001ex) emissions, providing a margin of safety for meeting emission standards. No 211u001edetrimental effects of using limestone at the Heskett Station were uncovered as a 211u001eresult of the test burn. Some specific conclusions from this work include the 211u001efollowing: The bed material feed rate can be reduced from the current rate of 211u001e5.4% of the coal feed rate (57.4 tons of sand/day) to 2.5% of the coal feed rate 211u001e(27 tons of limestone/day). This will result in an annual savings of 211u001eapproximately $200,000. (1) SO(sub 2) emissions at the recommended feed rate 211u001ewould be approximately 250 ppm (0.82 lb/MMBtu) using a similar lignite. Based on 211u001ethe cost of the limestones, SO(sub 2) allowances could be generated at a cost of 211u001e$60/ton SO(sub 2) , leaving a large profit margin for the sale of allowances. The 211u001eaddition of limestone at the same rate currently used for sand feed could 211u001egenerate $455,000 net income if allowances are sold at $200/ton SO2 . (2) At full-211u001eload operation, unburned carbon losses increase significantly at excess oxygen 211u001elevels below 2.8%. No efficiency gains are expected at high-load operation by 211u001eswitching from sand to limestone. By reducing the oxygen level at low load to 211u001e8.5%, an efficiency gain of approximately 1.2% could be realized, equating to 211u001e$25,000 to $30,000 in annual savings. (3) A reduction of 25 tons/day total ash 211u001e(bed material plus fly ash) will be realized by using limestone at the 211u001erecommended feed rate compared to the current sand feed rate. No measurable 211u001echange in volume would be realized because of the lower bulk density of the 211u001elimestone-derived material.