Comparative combustion properties of raw and washed Donkin coals in the CCRL pilot-scale boiler

Abstract

The combustion performance of raw Donkin coal (run of mine) and three levels of cleaned (washed) Donkin 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 (ERL) in Ottawa. The three cleaned coal samples 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 as they were received in Ottawa. Each coal flowed readily through the ERL pilot-scale conveying and coal-handling system. The coals, which ground readily to produce a consistent size product from the pulverizer, ignited easily to produce stable flames at greater than e 96% combustion efficiency. The highest combustion efficiencies were obtained with the more finely ground coal feeds. The washed Donkin coal, containing the lowest ash content, gave the highest combustion efficiency. The ash from each of the Donkin coal samples 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. Without exception, the washed Donkin coal samples burned at a higher combustion efficiency, a lower SO2 level in the flue gas, and a decreased volume of ash and slag on the heat transfer surfaces and the furnace bottom than was obtained with the Donkin raw coal. Washing the Donkin coal did not appear to cause any significant operational difficulties in burning the coal, and as outlined in an earlier report (1) the combustible content of the fly ash can be significantly reduced by increasing the combustion residence time.