Development of coal-like refused derived fuel from hazardous waste / Balasubramaniam Karpan

Balasubramaniam , Karpan (2022) Development of coal-like refused derived fuel from hazardous waste / Balasubramaniam Karpan. PhD thesis, Universiti Malaya.

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Abstract

The quantity of the hazardous waste (HW) generated in Malaysia increased to 7,185 thousand metric tons from 4,013 thousand metric tons in 2019 This was primarily due to power plants and water treatment plants, and the rate of waste generation is likely to continue to rise as these are regarded as essential services. At present only about 30% of these wastes are subjected to recovery activities in Malaysia, where the focus is on material recovery. Many of the HW generated in Malaysia contains more than 8,000 kJ/kg of energy. These wastes can be a potential for energy recovery activities where refused-derived fuel (RDF) can be developed for a specific large volume application and as an alternative to coal. Therefore, RDF has been developed in this work using hazardous wastes and biomass mixtures to obtain solid fuel with coal-like characteristics. For this purpose, the Design of Experiment software was used where more than 500 RDF samples were synthesized using combinations of various wastes to determine the optimum product formulation. In this study, the RDF production process was developed by combining various processes of sorting, weighing, mixing, drying, and fused them together in a process called Thermo-biofusion. The optimum operating conditions of wastes and biomass mixture was identified in this study based on the calorific value (CV), volatile matter , fixed carbon, ash content as well as moisture content. The RDF developed had a CV of approximately 20,000 kJ/kg, moisture content between 15 to 20%, volatile matter, fixed carbon, and ash content of 32 %, 40 %, and 28 %, respectively. A production process was developed, and 1000 tones of RDF was produced and tested for potential utilization as a coal alternative in a cement manufacturing plant with varying RDF ratios, utilising the optimum recipe. This study concluded that every ton of coal with 24,000 kJ/Kg CV could be replaced by approximately 1.5 tones of RDF. The maximum allowable limit of RDF usage was limited to 24% replacement to coal due to limitation on clicker quality and overall emission level. Emission levels of NOx were under the regulatory limit where at 5 ton/hour and 8 ton/hour of RDF feed, the levels of NOX emitted are 356 mg/ Nm3 and 301 mg/ Nm3, respectively, values are lower than the regulatory limits in Malaysia. Heavy metal concentrations were also within the standard limit to prevent any threats to the environment. In terms of the efficiency of clinker and stack gas emission values, the substitution of 15 % of RDF to the coal at a feeding rate of 5 tons per hour in cement production did not cause any processing and quality issues in the existing cement production process. The study concluded that substituting 15 % of RDF with the coal in 1000 ton/day cement plant may reduce 112.8 USD/hour in operating cost. The advantages of co-combustion RDF with coal in the cement plant including reduction in the CO2 emission, cost reduction of clinker production due to the usage of inexpensive fuel, and preservation of resources. This work has proven that by combining pre-selected hazardous wastes, mixture of biomass, and adding appropriate additives, a coal-like RDF can be produced for cement kiln application that meet the energy and emission requirements.

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