Fire properties of surrogate refuse-derived fuels

This paper investigates the fundamental fire properties of surrogate refuse-derived fuels (RDF), a class of multicomponent materials characterized by high void fraction, with particles of polydisperse sizes and significant internal porosity. A surrogate RDF was developed to improve the reproducibility of experimental measurements. This surrogate RDF reflects typical municipal solid waste collected in the city of Newcastle, in the state of New South Wales in Australia. The material consists of shredded newspaper, wood, grass and plastic bags, with small amounts of sugar and bread. About 95% of the material passes through 50mm square screens, as required by ASTM E828 standard for RDF-3 specification. The experiments presented in this paper were performed with the components of the RDF dried in a forced-air oven at 103° C, except for grass which was dried under nitrogen. The material was found to be very hygroscopic, requiring special care in handling. The experiments performed in the cone calorimeter were designed to measure the heat release rate, total heat release, time to ignition, time to extinction, effective heat of combustion and formation of CO during the combustion process, as a function of sample thickness, sample density and the magnitude of the imposed radiative heat flux. The thermophysical properties of the surrogate material were either measured (solid density, void space, particle density, particle porosity) or extracted from the published data (heat capacity). The present surrogate RDF material was found to ignite easily, within a few seconds of the imposition of the incident heat flux of 40 kW m -2, and then to reach rapidly the peak heat release rate of 110-165 kW m -2. The deduced values of the critical heat flux, pyrolysis temperature and effective thermal conductivity are 9-10 (±2) kW m -2, 280-310 (±30)° C, and 0.4-0.7 (±0.3)Wm -1 K -1, respectively, depending on the material density. The effective heat of combustion of the RDF was estimated as 15.3 MJ kg -1. The material produced 1 kg of CO per 18 kg of dried RDF, mostly during smouldering phase after the extinguishment of the flaming combustion. These results indicate that dried RDF pose significant fire risks, requiring that fire safety systems be implemented in facilities handling RDF