Thermal and Mechanical Analysis of Briquetted Coal Fines Using Municipal Solid Waste (MSW) Plastics

摘要

Significant ecological concerns and attractive financial opportunities are raised by growing deposits ofwaste coal fines in the United States. Roughly two billion tons of waste coal fines are stored inimpoundments in the United States and approximately 50 million additional tons are generated annually[1]. These fines can be utilized by extrusion or roller press briquetting along with a binder to impartmechanical strength and water resistance to the briquettes. In this study, a variety of materials wereconsidered for use as a binder and were evaluated on seven criteria: cost, availability, binding ability,processability, water resistance, heating value, and toxicity/environmental impact. Municipal solid waste(MSW) plastic binders are our primary focus in this study due to their superior performance in all areas.The goal of this study was to characterize a briquetted coal product, using waste plastics, which may bean economically and ecologically viable substitute for conventional stoker coal. High densitypolyethylene (HDPE) and low density polyethylene (LDPE) provide water resistance to the coalbriquettes, and since they do not contain chlorine will not yield dioxin or furan formation whencombusted. In addition, the heating value of LDPE is 46.4 MJ/kg - over double that of the 21.9 MJ/kgwaste coal fines used in this study. For example, a 10 wt% LDPE-90 wt% coal mixture was found tohave an 11% higher heating value over the neat waste coal fines. A number of coal/LDPE mixtures werebriquetted with varying coal particle size distributions, moisture content, and LDPE concentrations usinga laboratory-scale roller press. To examine mechanical robustness, briquettes were exposed to simulatedrain and then subjected to compressive testing and tumbler testing according to ASTM D 441-07.Thermal analysis of the briquetted fuels using thermogravimetric analysis/simultaneous differentialscanning calorimetry (TGA/DSC) in air revealed a significant interaction between coal and LDPE.Laboratory-scale combustion tests revealed a dependence of combustion efficiency on LDPEconcentration in the briquetted fuel. The results of this work indicate that HDPE and LDPE can serve asexcellent waste coal binders due to their high energy density, water resistance, binding ability, andrelatively low cost.