Sulfur fixation for raw coal with combined microwave irradiation and ultrafine Ca(OH)2 method

Abstract

Sulfur fixation technology for raw coal can reduce SO2 emission during coal combustion. A method combining microwave irradiation and ultrafine Ca(OH)2 slurry was proposed, where raw coal was pulverized to mix with the slurry, and then treated by microwave irradiation. For anthracite coal (sulfur content = 1.90 wt%) with particle size distributed in the range of 75–180 μm, the treatment fixed 67.98 % of the sulfur in coal ash. Results prove that there is a synergy between microwave irradiation and ultrafine Ca(OH)2 for coal pretreatment, and finer coal particles had higher fixation rate. Under the same treatment condition, the sulfur fixation rate was increased to 74.68 % by adding 1 mol/L NaOH. Applying more NaOH or less Ca(OH)2 both made the fixation rate decrease. The combined treatment was also applied to bituminous coal (sulfur content = 0.79 wt%), and a fixation rate of 87.93 % was obtained. A continuous pretreatment system was developed for practical utilization of the method. Coal treated by the system was made into honeycomb briquette and burnt in a domestic coal stove, where a sulfur fixation rate of 74.97 % was obtained, compared to that of 4.55 % from untreated coal briquette.