Effect of some operational parameters on desulphurization of high sulphur Indian coal by KOH leaching

Abstract

This paper presents an experimental study on the effect of potassium hydroxide concentration and reaction time on coal properties during desulphurization of high sulphur Indian coal. Experimental results showed that maximum of 36.79% of total sulphur can be removed from coal by potassium hydroxide leaching with 20% potassium hydroxide concentration and 24 h contact time at atmospheric condition. Total sulphur reduction was contributed by 45.03–49.01% pyritic sulphur, 24.10–33.73% sulphate sulphur and 20.93–30.62% organic sulphur depending on potassium hydroxide concentration of 5–20% and reaction time of 6–24 h. Experimental result shows that ash% of coal increased from 8.33 to 14.09% due to accumulation of insoluble potassium aluminosilicate in the coal. Gross calorific value of coal decreased from 6854 to 6084 kcal/kg due to increase of ash content of coal and loss of some combustible matter in leaching process. Physico-chemical characterizations of raw and treated coal samples were carried out by using field emission scanning electron microscope, Fourier transform infrared, petrographic analysis, thermogravimetric analysis and differential thermogravimetry to appraise the product quality. Field emission scanning electron microscope and coal petrographic image infer the occurrence of pitting and cavitation in the coal structure due to removal of pyrite sulphur (1.51–1.21%) from coal which causes escalation of vitrinite (67.65–70.43%) and few amounts of inertinite (18.03–18.86%) and liptinite (1.24–1.27%) as macerals. Thermogravimetric analysis–differential thermogravimetry analysis infers the improvement in combustion characteristics of treated coal by reduction in peak combustion temperature.