The effect of volume change of coal during carbonization in the direction of coke oven width on the internal gas pressure in the plastic layer

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The coking pressure in a coke oven, which is caused by the internal gas pressure in the coal plastic layer, is determined by the gas permeability of the layer. The gas permeability of the plastic layer depends on its density as well as the physical property of the plastic coal itself. The plastic layer is sandwiched between the coke and the resolidifying layers and the coal layer and the effect of the volume change of these outer layers in the direction of coke oven width, i.e. contraction and compression, on the density of the plastic layer and the internal gas pressure was studied. A sandwich carbonization test, where different kinds of coals were charged in the test coke oven, showed that the internal gas pressure depends not only on the kind of coal in the plastic phase but also on the kind of coal in the resolidifying and the coke phases near the oven walls. The relative volume of coke transformed from the unit volume of coal was measured using an X-ray CT scanner and it varied greatly across the coke oven width depending on the kinds of coals. The volume change of coal during carbonization in the direction of coke oven width affects the density of the plastic layer and the internal gas pressure. The relative volume of semicoke and coke transformed from the unit volume of coal near the oven walls is higher for a high coking pressure coal than that for a low coking pressure coal. This causes the plastic layer to have a high density and the generation of dangerously high internal gas pressure in the oven center.