Final report on the comparative combustion properties of raw and washed Prince Mine coal

Abstract

The combustion performance of raw Prince mine coal (run of mine) and five levels of cleaned (washed) Prince mine coal was compared with that of a commercially available thermal bituminous coal from Western Canada. Tests were conducted in a pilot-scale pulverized coal-fired research boiler located at the Energy Research Laboratories in Ottawa. Two of the cleaned coal samples were obtained from the Electric Power Research Institute (EPRI) Homer City coal cleaning facility in the USA and the other three were obtained from the CANMET Coal Research Laboratories coal cleaning facility in Devon, Alberta. Chemical, physical, petrographic and thermogravimetric analyses were performed on samples of the coals. Each of the coals flowed readily through the Energy Research Laboratories pilot-scale conveying and coal-handling system. The coals, which ground readily to produce a consistent size product from the pulverizer, all ignited easily to produce stable flames at greater than 96% combustion efficiency. The highest combustion efficiencies (>99%) were obtained with the more finely ground coal feeds. Although the two washed coals with the lowest ash content gave the higher combustion efficiencies, the raw coal, which had the lowest fly ash combustible content, also gave a combustion efficiency greater than 99%. The ash from each of the Prince mine coals was quite fluid and slagged readily in the refractory-lined furnace bottom, whereas the ash deposits on the water-walls and superheater surfaces were light and powdery and did not constitute a fouling problem. The sulphur content of the coal was not significantly lowered until the ash content of the coal was reduced to less than 7%. A reduction to 2.4% ash resulted in a 56% reduction in the sulphur content of the coal. This coal sample (containing 1.8% sulphur) burned in the pilot-scale utility boiler to produce a flue gas containing 0.9 g S02 /MJ of fuel input compared with 3.0 g SO2 for the raw coal, both of which are much higher than the current Canadian national emission guideline.