Experimental investigation on NO x emission characteristics of a new solid fuel made from sewage sludge mixed with coal in combustion

Abstract

In this article, a new briquette fuel (SC), which was produced by the mixture of coal fines (25.9%), sewage sludge (60.6%), lignin (4.5%), tannic acid (4.5%) and elemental silicon (4.5%), was provided. Then, in a high temperature electric resistance tubular furnace, the total emissions of NO₂ and NO, effects of combustion temperature, air flow rate and heating rate on NO_x (NO, NO₂) emissions of SC were studied during the combustion of SC; furthermore, effects of additives on hardness were also analysed, and the X-ray photoelectron spectroscopy was applied to investigate the reduced NO_x emission mechanism. The research results showed that, compared with the characteristics of briquette fuel (SC0) produced only by the mixture of coal and sewage sludge (the ratio of coal to sewage sludge was the same as that of SC), the Meyer hardness of SC was 12.6% higher than that of SC0 and the emissions of NO_x were 27.83% less than that of SC0 under the same combustion conditions. The NO_x emissions of SC decreased with the adding of heating rate and increased with the rise of air flow rate. When the temperature was below 1000 °C, the emissions of NO_x increased with the elevated temperature, however, further temperature extension will result in a decreasing in emissions of NO_x. Furthermore, the X-ray photoelectron spectroscopy results proposed that the possible mechanism for the reduction of NO_x emissions was nitrogen and silicon in SC to form the compounds of silicon and nitrogen at high temperatures.