Evaluating the potential of waste plastics as fuel in cement kilns using bench-scale emissions analysis

In an effort to reduce emissions and lower fuel costs, cement plants have explored the use of waste materials to displace coal and petroleum coke. A potential candidate is non-recyclable waste plastics. Knowledge of potential changes in cement kiln parameters with a change in the composition of operating fuel prior to full-scale application is necessary for obtaining permits and for plant preparedness. Most bench-scale performance studies have targeted the prediction of full-scale stack emissions with variable degrees of success. In this work, a bench-scale tube furnace and a heated grid reactor (HGR) have been used to compare combustion and emission changes when waste plastics displace an equivalent amount of heat from the coal/coke blend. Trends in the results from bench-scale experiments on residual volatile organic compound (VOC) emissions matched full-scale observations on kiln thermal performance. Bench-scale particulate matter (PM) emissions indicated that no significant changes were likely in full-scale stack PM emissions when using waste-derived fuel (WDF). This bench-scale fuel characterization approach has been used to study the potential impact of waste plastics on the performance of a local cement kiln.