Evaluation of the Fuel Properties and Pollution Potentials of Lignite Coal and Pellets of its Blends with Different Biowastes

Abstract

The fuel properties and pollution potentials of lignite coal, wood chippings, cashew leaf litter, yam peels and rice husks were improved by blending, carbonisation and pelletization. Four blends of lignite coal with the biomass samples were prepared in 20:80 ratio and made into pellets using vegetable oil as binder. The lignite coal, biomass and their blends were carbonised at 623 K. Proximate and ultimate analyses were carried out while the calorific values, lignocellulosic content of each biomass and their blends were determined. Also the pollution potentials of each fuel in a hypothetical pulverised fuel combustion plant were derived using a metallurgical and thermochemical data base (MTDATA). The quantities of CO2, NO2 and SO2 that would be emitted per hour from the plant were calculated. The results of the proximate analysis for the raw samples showed that lignite coal had the highest fixed carbon (26.10%) and moisture content (31.50%). Except for lignite, the carbonised samples had an improved fixed carbon and volatile matter contents, relative to the uncarbonised blends. The ultimate analysis of carbonised blends showed an increase in hydrogen and oxygen content with a decrease in sulphur and nitrogen contents. However, the calorific values of the pelletised blends almost doubled, showing clearly the improvement in energy content of the blends. For the simulated pulverised fuel combustion power plant analysis using MTDATA, each fuel showed that blending and carbonisation can improve lignite coal, thereby reducing the high moisture content, high ash and also the SO2, CO2 and NO2 emissions to an extent. It also proves that most of the NOX gases are generally thermal in nature. Therefore, blending of lignite coal with different biomass and waste materials should be encouraged in coal fired power plants to reduce environmental pollution, increase energy and power output.