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

摘要

Significant ecological concerns and attractive financial opportunities are raised by growing deposits of waste coal fines in the United States. Roughly 2 billion tons of waste coal fines are stored in impoundments in the United States and approximately 50 million additional tons are generated annually. These fines can be utilized by extrusion or roller press briquetting along with a binder to impart mechanical strength and water resistance to the briquettes. In this study, a variety of binder materials were considered 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 the primary focus in this study due to their excellent performance in all areas. The goal of this study was to characterize a briquetted coal product, using waste plastics, which may be an economically and ecologically viable substitute for conventional stoker coal. High density polyethylene (HDPE) and low density polyethylene (LDPE) provide water resistance to the coal briquettes, and since they do not contain chlorine will not promote dioxin or furan formation when combusted. In addition, the heating value of LDPE is 46.4 MJ/kg—over double that of the 21.9 MJ/kg waste coal fines used in this study. A 10 wt% LDPE-90 wt% coal mixture was found to have an 11% higher heating value over the neat waste coal fines. A number of coal/LDPE mixtures were briquetted with varying coal particle size distributions, moisture content, and LDPE concentrations using a laboratory-scale roller press briquetter. To examine mechanical robustness, briquettes were subjected to compressive testing and tumbler testing according to ASTM D 441-07. Thermal analysis of the briquetted fuels using thermogravimetric analysis/simultaneous differential scanning calorimetry (TGA/DSC) in air revealed a significant interaction between coal and LDPE. Laboratory-scale combustion tests revealed a dependence of combustion efficiency on LDPE concentration in the briquetted fuel. Gas chromatography of effluent gas at 3 minutes validated this trend. The results of this work indicate that HDPE and LDPE can serve as excellent waste coal binders due to their high energy density, water resistance, binding ability, and relatively low cost.