Combustion of refuse-derived fuel in a fluidised bed

As a medium to maximise the resources recovery from municipal solid waste, refuse-derived fuel (RDF) is considered as a priority solution in industrialised countries. RDF is a value added material with a higher calorific value and a homogeneous particle size. The main objective of this study was to investigate the RDF combustion characteristics and the associated pollutant emissions in a fluidised bed combustor. A series of combustion tests was carried out using three different RDF samples in two atmospheric fluidised bed combustors (AFBC). The temperature profiles, gas composition and the properties of fly ash residues were investigated for different RDF fuels and operating conditions. Bed temperatures (ranging from 754 to 906 °C) were correlated with different air and RDF feed rates. It was shown that the overall combustion efficiency of the system improved when secondary air jets were introduced into the system. Only between 2.6% and 4.3% of the potential nitrogen in the fuel was converted to NOxNOx. A slight decrease in the NOxNOx concentration was observed upon injection of secondary air. The capture fractions of N, Cl and trace elements in the fly ash were evaluated from the elemental composition of the fuels and fly ashes. The ratios of Ca/(S+0.5Cl)Ca/(S+0.5Cl) between 1.6 and 2.2 proved to be very efficient in capturing Cl in the fly ash. The operating conditions of the AFBC system together with the physical characteristics of the ash allowed a full elutriation of the ash residues.