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.
Highlights
Emission of sulphur dioxide from thermal power plants is a major environmental problem in the 21st century
Pyritic sulphur is present in coal as part of mineral matter whereas the organic sulphur is present as organic compound which is an integral part of the coal matrix
High sulphur coal collected from Makum Coal Field, Assam, India is treated with different KOH concentration (5–20%) and different contact times (6–24 h) have been experimented to verify effects of the sulphur removal efficiency
Summary
Emission of sulphur dioxide from thermal power plants is a major environmental problem in the 21st century. Most of the studies reported in literature are concerned with sulphur removal efficiency as a substitute for treatment on physico-chemical property rather than ash%, GCV, fuel ratio with combustion performance parameters Changes in these physicochemical properties affect the entire utilization capabilities of the treated coal. For commercial implementation of desulphurization of noncooking coal, effects of desulphurization on properties like VM, FC, ASH, C, N, H, S and O are considered mostly as important parameters which were least priority in previous work In this context, the present work reports the effects of KOH concentration (varies from 5 to 20%) and contact time (varies from 6 to 24 h) treatment on different physico-chemical properties of coal like proximate analysis, ultimate analysis, GCV and combustion parameters which have a significant impact on applicability of desulphurized thermal coal. Petrography analysis, Fourier transform infrared (FTIR) and field emission scanning electron microscope (FESEM) were done to observe the effects of KOH treatment on coal structure and changes in its morphological properties
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