Study on characteristics of self-desulfurization and self-denitrification in biobriquette combustion

Abstract

The characteristics of self-desulfurization and self-denitrification in biobriquettes were studied experimentally and numerically in this paper. The biobriquette was produced by mixing coal, biomass, desulfurizer, and/or denitrificater under a high-compression pressure condition. The combustion process of biobriquette appears in two stages, namely the volatile combustion stage and the char combustion stage. It was proved that limestone, wasted scallop shell, and calcium hydroxide have effective self-desulfurization capability in biobriquette combustion and that desulfurization mainly happens in the char combustion stage. Comparatively among the three desulfurizers used, calcium hydroxide has the highest desulfurization capability because of its lower calcination temperature, and scallop shell the second because of the larger porosity after calcination. A desulfurization efficiency as high as about 80% can be reached for some kinds of coals using scallop shell as desulfurizer with Ca/S over 3.A modified shrinking-core model was developed to predict the desulfurization efficiency in the char combustion stage, and an approximate agreement was obtained between the predictions and the experiments. It was also found that pulp black liquid, an industrial waste to roll as binder in the biobriquetting process, has both self-denitrification and self-desulfurization capabilities in biobriquette combustion. A denitrification efficiency of about 40% can be obtained by adding the pulp black liquid into biobriquette with about 15% in mass.