Coking Pressure Phenomena and its Influencing Factors Dec17

Coking Pressure Phenomena and its Influencing Factors...

Coking Pressure Phenomena and its Influencing Factors Coking pressure is a phenomenon which has become important because of the use of the double-heated wall, vertical, slot-type coke ovens. In the round beehive ovens as well in the heat recovery coke ovens, which are also being used for coke production, the coal can freely expand upwards and thus the swelling of the charge is accommodated by this free expansion. On the other hand, in the slot-type coke ovens, the expansion of the coal horizontally to the heated wall is restricted. There are several cases of premature failure of oven walls during the coal carbonization process. The erection of the new, larger and taller coke ovens has been accompanied by undesirable occurrences of distorted walls due to the coking pressure resulting in several studies regarding the expansion behaviour of coal during carbonization. The efforts have been focused on developing a reliable test so that coal blends can be tested for safety prior to their use in the coke ovens. Development of coking pressure During carbonization process, coal passes through the plastic stage and volatile matter (VM) evolves during and, to a lesser extent, after that stage. It is normally accepted that coking pressure arises in the plastic stage. In a coke oven chamber, two vertical plastic layers parallel to the heating walls are formed from the beginning of carbonization. As the carbonization proceeds these layers move towards the centre of the oven. At the same time, similar horizontal layers are formed at the top and bottom of the charge. These are joined with the two vertical layers and the whole forms a continuous region that surrounds the uncarbonized coal and it is usually referred to as the ‘plastic envelope’. The permeability of the plastic layers is...