Optimising mixture of agricultural, municipal and industrial solid wastes for the production of alternative fuel

Abstract

The valorisation of waste is often represented through the form of energy recovery, nutrient reclamation and other by-products. Solid Recovered Fuel (SRF) or Refuse Derived Fuel (RDF) as a solid alternative fuel has shown promising results for waste management and enhancing the energy security. The energy recovered is dependent on the quality of the solid fuel, which is evaluated by several parameters, including the calorific value, the moisture content, the density, the oxygen content and the gas emissions. The parameters varied following different types of wastes, which increase the complexity in producing high quality of solid fuel from a mixture of solid waste. This study aims to compare different mixtures of alternative fuel composed of municipal solid waste (MSW), non-hazardous industrial waste and agricultural waste. The selected wastes have high calorific value (2,601-8,657 cal/g), low moisture content (0.06 - 9.86 %), various density (63 - 910 kg/m 3 ), high carbon (C) of 45 - 67 %, low nitrogen (N) of 0.15 - 2.22 %, low sulphur (S) of 0.01 - 0.80 %, moderate hydrogen (H) of 4.9 - 8.21 % and high oxygen (O) of 25 - 45.5 %. The high C and O content indicated high energy and combustibility, whereas low N and S concentration can reduce the emissions of unwanted gas. The selection of the optimised mixture is based on technical and economic feasibility assessment. The technical score is calculated over seven criteria, including calorific value, moisture content, density, O and gas emissions (COx, NOx, SOx). Based on the assessment on these parameters, the optimum mixture consists of 23.00 % rice straw, 19.52 % wood, 24.58 % plastics, 18.43 % cotton stalks, and 14.47 % used tires. The optimum mix has a calorific value of 5,272 cal/g, density of 311 kg/m 3 , and moisture content of 1.94 %. The analysis demonstrated that mixture with high proportion of plastics, rice, wood and cotton stalk ranked high as preferable alternative fuel. The analysis also showed that the ranking of the alternative fuel decreases following an increase of sludge and olive pomace in the mixture. The proposed selling price of the alternative fuel produced is 135.47 USD/t covering all capital costs and operational and maintenance costs.