Refuse Derived Fuel (RDF) Gasification Using Different Gasifying Agents

Abstract

Wastes represent nowadays, one of the major concerns for modern societies and for the environment, either by the wastage of raw materials and also by the existence of poor management systems that can originate and contaminate the ground water and air, and therefore, change the environment irreversibly. Waste management policies enhance the basic principles of prevention, which are the reduction in origin, followed by its recovery through recycling or energy recovery, in order to reduce the environmental and health impacts of wastes. Refuse Derived Fuel (RDF) is a solid fuel made after basic processing steps or techniques that increase the calorific value of municipal solid waste (MSW), commercial or industrial waste materials. Therefore, energy production from RDF can provide economic and environmental benefits, as reduces the amount of wastes sent to landfill and allows the energy recovery from a renewable source. In this work, it was studied the gasification of RDF collected in a Portuguese company, using steam and air as gasifying agents. This study intended to evaluate the effect of temperature and different molar ratios of both agents in gas production, gas composition and mass conversion of RDF. Physical and chemical composition of RDF was determined according to EN 15359:2011. Results showed that RDF has high quality for thermal valorization being registered high values of Low Heating Value (LHV) (24330 kJ/kg), carbon content (56.2%) and volatile matter content (77.2%). Experiments of RDF gasification were performed in a laboratory scale fixed bed gasifier, under different conditions. The effect of reaction temperature was studied at 750°C and 850°C. Gasification experiments with steam were executed at S/B feeding molar ratios ranging from 0.5 to 1.5 and the ones performed with air ranging from ER 0.2 to 0.6. Results showed that, for the same operational conditions, the rise of gasification temperature improved gas production ratio (Nm3/kg RDF), gas LHV and mass conversion. Results also proved that steam gasification achieved higher LHV values compared with gasification using air in optimal conditions, 9.4 and 9.8 MJ/m3, respectively. The gasification of RDF using steam at S/B ratio of 1.0 enables the production of syngas with 51% of hydrogen (H2), 32% of carbon dioxide (CO2), 11% of carbon monoxide (CO) and 6% of methane (CH4) (in N2 free basis). The increasing of steam to RDF molar ratio, increased the contents of H2 and CO2, while the content of CO, CH4 and heating value decreased. Regarding to gas production ratio the utilization of air, especially at ER of 0.6, induced the formation of 1.5 m3 gas/kg RDF. Instead, steam gasification only allowed the production of 0.5 m3 gas/kg RDF. Mass conversion and carbon conversion achieved almost 100% in air gasification at highest molar ratio.