Mechanical, pyrolysis, and combustion characterization of briquetted coal fines with municipal solid waste plastic (MSW) binders

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Significant ecological concerns and attractive financial opportunities are raised by growing deposits of waste coal fines in the United States. These fines can potentially be utilized by extrusion or roller press briquetting along with a binder to impart mechanical strength and water resistance to the briquettes. This research focuses on low density polyethylene (LDPE) as a binder, which is abundant in waste streams and possesses desirable energy, waterproofing, and binding characteristics. The goal of this study was to characterize a briquetted fuel made from waste coal and LDPE that may be an economic and ecologic viable substitute for conventional stoker coal. Thermal and mechanical analyses of the fuel were conducted using standard techniques including compression and attrition testing, bomb calorimetry, thermogravimetric analysis/differential scanning calorimetry (TGA/DSC), and lab-scale combustion testing. The results of this work indicate that LDPE is an effective binding agent when incorporated at suitable concentrations and particle sizes. Addition of 10% LDPE increases the measured higher heating value of the coal from 21.9MJ/kg to 24.3MJ/kg and imparts water resistance to the compacted fuel. Differential scanning calorimetry of coal/LDPE mixtures indicates a significant interaction, consistent with prior research. Addition of LDPE in concentrations as low as 5% eases ignition of the fuel by significantly lowering the onset temperature of exothermic decomposition. Lab-scale combustion experimentation confirms that ignition characteristics of the parent coal are positively influenced by the addition of LDPE.