Data Sheet No. 26 - Effect of Coal and Process Variables on Coke Properties

Abstract

This chapter provides an overview of the effect of coal and process variables on coke properties. The most highly swelling coals within the good coking range may produce weak cokes, because of excessive after-shrinkage, with the formation of cracks, or may create sufficient pressure during the swelling process to damage coke-oven walls. Such adverse effects are overcome by blending with non-swelling coals or coal products such as anthracite, steam coal, coke breeze, or fusain. The four components of banded bituminous coal, vitrain, clarain, durain, and fusain behave differently on carbonization. Fusain is invariably nonswelling. Durains and splint coals are usually non-swelling or less swelling than the associated vitrain and clarain. Clarain is usually the highest swelling component of any given coal. Inherent or equilibrium moisture is a measure of the micro-pore volume of the coal, which is a characteristic of rank and type. There is a fairly well-defined relationship between equilibrium moisture of coal and swelling power. Rate of heating of coal has a profound effect on the coking process. High rates of heating cause maximum swelling, excessive in the case of strongly caking coals, but improving the coke formed from low-swelling coals.