Integrated Microbial and γ-radiolytic process for Desulphurisation of High Sulphur Coals: Proof of the Concept and A case study on Polish & Indian Coals

Abstract

Coal will continue to be used in thermal power plants to produce electricity to meet the ever increasing demand of energy for several coming decades in the developing nations, particularly India. During thermal generation of electricity, coal is combusted, in the course of which several serious environmental problems are created. To mitigate these problems, lot of emphasis is being put on "clean coal technologies", which, <i>inter alia, </i>include environmental control equipment as also coal cleaning for obtaining clean fuel, especially coal beneficiation before combustion. Precombustion cleaning of coal comprises principally coal washing and desulphurisation. In this context, desulphurisation of high sulphur coals (such coals having 1% or more sulphur content), the total reserves of which is ca. 2840 million tonnes., assumes much greater importance, because the presence of sulphur in coal gives rise to several environmental problems such as environmental pollution causing ecological imbalance, depletion of ozone layer, acid rain etc. The processes in vogue for the precombustion desulphurisation of coal include physical, chemical biological and radiation methods. Of late, extensive research is being carried out on biological desulphurisation of coal. At CFRI Dhanhad a new and effective γ- radiolytic process of desulphurisation has also been developed.<br> The present paper reports the results of desulphurisation of high sulphur bituminous Polish (Janina coal mines of Lybiaz coal field ) and Indian (N-E coal fields, Tinsukia coal, Assam) coals (sulphur content 2-6%) by firstly individual microbial and γ- radiolytic methods, and then in succession (microbial followed by γ- radiolytic method). While the microbial desulphurisation entails the use of isolated cultures o f <i>Thiobacillous ferrooxidans, </i>the γ- radiolytic method comprises irradiation of acidic/ aqueous slurries of the coals at different γ- doses. It was found that the microbial method is more effective for the removal of pyritic sulphur, whilst the γ- radiolytic method is effective to remove both the pyritic and organic sulphur. A comparison between desulphurisation experiments by individual microbial and γ- radiolytic methods and the integrated method (microbial plus γ- radiolytic in succession) evinces that the combined method is much more effective for the removal of sulphur, including organic sulphur, from these coals. It is found that along with removal of sulphur from the coals, mineral matter is also removed simultaneously. The attractive feature of the process is that the caking property of the coal after desulphurisation is either increased slightly or remains unchanged. Another import ant feature is that the coal structure is not affected/ degraded to any appreciable extent after desulphurisation. As such the integrated mi crobial and γ- radiolytic process seems to be a better alternative for the deep desulphurisation of high sulphur coals and this could be a step forward in the direction of environment- friendly" clean coal technology".