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

Ignition temperature and surface emissivity of heterogeneous loosely packed materials from pyrometric measurements

This paper reports the ignition temperature and emissivity of heterogeneous materials characterised by high void fraction of between 0.92 and 0.94 and composed of loose particles of shredded grass and paper, planed wood, shredded plastic bags, as well as sugar and bread, with about 95 % of the particles (by mass) of less than 50 mm in size. These materials reflect a typical composition and void fraction of so-called refuse- derived fuels (RDF), which are obtained from municipal solid waste, then densified and combusted for energy recovery. An infrared pyrometer, with a spectral response range of 8 to 14 μm, recorded the surface temperature of the surrogate RDF, prior to the onset of the flaming combustion, in a stand alone mass loss calorimeter operated at 20 and 45 kW m-2. The overlapping spectral ranges of the pyrometer and the radiator heater necessitated the development of a practical methodology to obtain the actual surface temperature from the apparent measurements, which included the effect of the reflected radiation. In addition to surface temperatures (292 – 325 °C for 20 kW m-2 and 250 – 294 °C for 45 kW m-2), in this contribution, we estimate the actual emissivities (0.95 – 0.98) of the materials from the intensity of the reflected radiation

Prediction of heat release rate of shredded paper tapes based on profile burning surface

A series of shredded paper fire experiments were conducted by means of a calorimeter. The mass loss rate and heat release rate were measured. The flame spread process was recorded, which shows that the flame spread process can be divided into four typical stages, and the mean spread rates along different directions were obtained from the observed combustion process. Based on the mean flame spread rate, a mathematical model for predicting the burning surface as a function of time during the four stages is established. Combining this model with the effective heat of combustion calculated from measured mass loss rate and heat release rate, an improved model to predict the heat release rate as a function of time was developed. In this model, the linear relationship between heat release rate and burning surface is found, and the predicted result agrees well with the measured heat release rate