Design and fabrication of arc thermal plasma reactor for petroleum sludge treatment

Abstract

Over 130, 000 metric tonnes of toxic petroleum sludge are generated yearly in Malaysia. The traditional methods of disposing of petroleum sludge are short of providing the much-needed benign treatment. A more robust treatment technique is therefore desirable. The thermal plasma treatment technique is employed to bridge the gap. In this research, a 4.7 kW thermal plasma reactor was designed and fabricated. The output current and the plasma temperature range were 5 – 200 A and 356 – 1694 oC respectively. After the treatment, the morphology of the sludge transformed from jelly-like to crystalline solid. A mass reduction of 36.87 – 91.40% and a total organic compound reduction of 21.47 – 93.76% were achieved in a treatment period of 2 – 5 minutes. The leaching test indicates that the heavy metals were stabilized in the solid, and hence, the solid is safe for secure landfill. The product gas is a mixture of carbon monoxide (CO), carbon dioxide (CO2), hydrogen (H2), water (H2O), methane (CH4), acetylene (C2H2) and ethylene (C2H4). The concentrations of the greenhouse gases, CH4 and CO2, were small. The lower heating value and the cold gas efficiency of the gas were 7.40 – 7.86 MJ/Nm3 and 25.22 – 51.90% respectively. The efficiency is within the range of the efficiency of gasification of petroleum sludge in an updraft gasifier. Based on the operating cost estimation, a profit margin of RM 3.11/kg of sludge was achieved. Two quadratic models, one for cold gas efficiency and the other for CO/CO2 ratio were developed. The developed models, using response surface methodology, showed a good fit with correlation coefficients of 99.32% and 99.66% for cold gas efficiency and CO/CO2 ratio respectively. The optimum operating conditions for the treatment were arc current = 188.15 A, plasma gas flow-rate = 31.54 L/min and treatment time = 1.89 min. The optimum responses obtained from the optimization of the reaction system were 52.59% and 1.80 for cold gas efficiency and CO/CO2 ratio respectively with the desirability of 1. Thermal plasma technique is, therefore, an alternative method for treating petroleum sludge.