Factors Influencing Tar Yield Under Industrial Conditions

摘要

The requirements on coke quality and cost consciousness have changed the cokemaking practice at Tata Steel significantly. The changes are on two fronts. One, the very technology itself and second, the coal blend for cokemaking. On technological front various pre-carbonisation techniques with their specific pros and cons are available. On the front of change in blend, use of inferior blends having higher volatile matter, coals with non-coking and semi-soft and semi-hard characteristics having relatively lower VM are being used yielding similar coke characteristics. This may be looked at as the outcome of advancement in cokemaking technology ― the precarbonisation techniques. However, the influence of such changes in coke making on recovery of by-products is not very well established―particularly the most valuable one―the coal tar. The coal tar yield is governed by the content of volatile matter, their characteristics, the extent of their cracking during carbonisation inside oven and its transport from oven to tar collector. The cracking of volatiles is guided by the thermal regime inside the oven, the free space and the gas carrying main, the space between the coal cake and the oven wall. Stamped charging technology, which charges the coal in the form of a cake into ovens at higher bulk density, provides greater opportunity for cracking of volatiles resulting in lower tar yield. Present paper outlines the theoretical considerations for tar yield and validates it with some significant parameters under operating condition of an industrial set-up having both stamp charged as well as conventional top charged ovens.