Enhancement of coking potential of coals with improvised crushing mechanism

ABSTRACT

Crushing mechanism plays a vital role in liberation of coal macerals (organic constituents), which aid in coke making. Due to the use of impact mills, vitrinite maceral grains shatter and participation in coke making is reduced. To address this issue, a new crushing machine based on a shear fracture mechanism has been developed and termed as coal shear crusher (CSC). It is shown that by using CSC one can take advantage of the viscoelastic property of vitrinite maceral. When compared to hammer mill, CSC processed coal showed improvement in plastic layer thickness (PLT), crucible swelling number (CSN), rank and coke strength after reaction (CSR) of the coal blends. Coals with vitrinite reflectance (Ro) greater than 1%, when processed using CSC showed greater improvement in coke properties as compared to coals with less than 1% Ro. Coal blend cost reduction can be effectively obtained if CSC technology is used, by increasing the portion of poor coking coal by replacing good coking coals. Present study scopes the utilization of up to 10% of CSC processed component in the coal blend, which is currently limited due to concerns related to coal cake stability which if overcome can increase the fraction of poor-coking coal in blends even further.

KEYWORDS:

• Maceral liberation
• coal shear crusher
• non-coking coal
• carbonization
• stamp charging
• plastic layer thickness¹

Highlight

• Coal crushing by new in-house developed coal shear crusher (CSC) for coke making application;

• Increase in coking activity of the coal after comminution due to shear forces applied by CSC;

• Higher fraction of non-coking coal can be used in blend without compromising the coke properties.

Acknowledgments

The authors would like to thank the Tata Steel management and Dr Sanjay Chandra, Chief R&D (Tata Steel Limited) for his encouragement during the project and permission to publish the paper. The authors are thankful to Dr. Atanu Ranjan Pal, Chief Product Research and Dr. Saurabh Kundu, Chief Process Research (Tata Steel Limited) for the trust and constant support during the studies. The authors are also thankful to the professionals of the Grinding Lab and CCT Lab, RD&SS (Tata Steel Limited) for their help in carrying out all studies.

Disclosure Statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Notes

1. . Abbreviations: CSC, Coal Shear Crusher; PLT, plastic layer thickness; CSN, crucible swelling number; CSR, coke strength after reaction; CRI, coke reactivity index; VM, volatile matter; Ro, vitrinite reflectance; HM, hammer mill; ASTM, American society for testing materials; IS, Bureau of Indian Standards; m, meter; mm, millimeter; s, second; kg, kilogram; hr, hour.