Effect of Pretreatment on Pyritic Sulphur Reduction from Coal

A. Malik1, M.G. Dastidar2*, P.K. Roychoudhury3

1 Department of Applied Chemistry, Faculty of Engineering, Utsunomiya University, Utsunomiya, Tochigi 321 - 8585, Japan
2 Centre for Energy Studies, Indian Institute of Technology Delhi, New Delhi - 110 016, India
3 Department of Biochemical Engineering and Biotechnology, Indian Institute of Technology Delhi, New Delhi - 110 016, India

Received 17 June 2002; accepted 1 November 2002


Biological attack of pyrite is a potential method of reducing pyritic sulphur in coal. Integration of such attacks with microwave pretreatment can enhance the efficiency of the process. Alternatively, processes such as oil-agglomeration can be coupled with the biological attack to obtain higher rates of pyritic sulphur removal. In this study desulphurization of Indian (Assam) coal was carried out under two contrasting modes of operation, i.e. physical (microwave) pretreatment of coal followed by biological desulphurization using Thiobacillus ferrooxidans (method 1) and bacterial pretreatment of coal followed by physical technique of oil agglomeration (method 2). Microwave pretreatment of coal did not show any improvement in pyritic sulphur reduction (PSR) during subsequent biodesulphurization. On the other hand, significant PSR in short period was observed using method 2 and the PSR increased further by increasing the cell concentration in bacterial pretreatment liquor. To examine the effect of bacterial metabolites, Thiobacillus ferrooxidans membrane-filtered bacterial liquor (TMFBL) which contained no bacterial cells, was used for pretreatment for various time periods. Even in absence of cells using TMFBL, significant PSR (96.2%) could be achieved by 120min pretreatment. However, pretreatment of coal with mixed bacterial liquor (MBL) did not produce substantial PSR, thus indicating specificity of Thiobacillus ferrooxidans for pyrite removal. This study indicates that the method 2 is a much better process for pyrite removal as compared to the method 1. High PSR (82.7-99.1%) and cleaner coal product with increased calorific value were obtained in short period (2.5 -120 minutes) using method 2 as compared to 76.2% PSR in 20-day period by method 1.

Keywords: Coal; Desulphurization; Pretreatment; Mixed culture; Thiobacillus ferrooxidans

* Corresponding Author
   E-mail : dastidar@ces.iitd.ernet.in