Emissions From Direct or Indirect Combustion of Tire-Derived-Fuel

Abstract

This paper reports on partial results of a comprehensive laboratory investigation on the emissions from batch-combustion of tire-derived fuel (TDF) in the form of waste-tire chips placed in fixed beds. TDF is a fuel of technological interest based on its high-energy content, in the range of 30–39 MJ/kg. However, there have been issues with health-hazardous emissions from the combustion of tires. The overall goal of the investigation has been to identify techniques and conditions that minimize toxic emissions. This particular work contrasts emissions from direct combustion of TDF with those from indirect combustion, i.e., staged pyrolysis of TDF followed by combustion of the pyrolyzates. Generation of a pyrolysis gas from TDF allows for effective mixing of this gas with air and, hence, for better control of the subsequent combustion and minimization of pollutant emissions. Emissions CO2, CO, semi-volatile polycyclic aromatic hydrocarbons (PAH) and particulates were monitored herein. Results illustrated that the staged pyrolysis-oxidation approach, albeit more complicated, has the potential for low health-hazardous emissions from waste tire-to-energy plants. It produced drastically less PAH (by up to an order of magnitude) and particulates (by more than an order of magnitude). However, it produced more CO and NOx (by factors of 2–5). The presence of an afterburner (1 s residence time at 1000 °C), curtailed the emissions of CO and, interestingly, it was capable of nearly-equalizing the final emissions of PAH from the two different modes of combustion. However, the afterburner treatment was not as successful in reducing the emissions of particulates and, as a result, the indirect combustion of TDF produced an effluent with a drastically lower particulate loading.