Refining of Indian coals to obtain super clean coals having insignificant amounts of deleterious elements under milder conditions

ABSTRACT

Indian coals have difficult to formidable washability characteristics. Presently, five Indian coals were subjected to solvent extraction under ambient pressure conditions using N-methylpyrrolidone (NMP) containing a small amount of Ethylenediammine (EDA) (termed as e,N solvent system). The coals and their solvent refined super clean coal (SCC) products obtained after solvent extraction have been extensively characterised for calorific value, ATR-FTIR spectral analysis, XRD measurements and ICP-MS analysis. The organo-refining of coals through the use of e,N extraction resulted in the production of Super clean coals (SCCs) having 0.2–1.5% ash. Studies have been carried out for the first time to analyse the concentration of minor elements in super clean coal. However, the ATR-FTIR analysis, XRD measurements and ICP-MS analysis also revealed the reduction of major elements such as Na, K, Al, Mg, Ca and Fe. The ATR-FTIR and XRD studies of SCC clearly demonstrated deashing of coals. As high as 94% improvement in calorific value in one of the high ash coals, Pandra coal could also be achieved on extraction with e,N solvent system.

KEYWORDS:

• Coal
• e,N solvent system
• super clean coal
• ICP-MS

Acknowledgements

The authors would like to thank Ministry of coal, Govt. Of India and NTPC Badarpur, New Delhi, India for providing coals for research, Dr. Sreedevi Upadhyayaula for helping in ATR-FTIR spectral analysis and CPCB, New Delhi for carrying out ICP-MS analysis to identify some of the trace elements in raw coals and SCCs.

Disclosure statement

No potential conflict of interest was reported by the authors.