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...

Carbonization of Coal for Metallurgical Coke Production Nov15

Carbonization of Coal for Metallurgical Coke Production...

Carbonization of Coal for Metallurgical Coke Production Carbonization of coal is also known as coking of coal. The process consists of thermal decomposition of coals either in the absence of air or in controlled atmosphere to produce a carbonaceous residue known as coke. Carbonization of coal can be carried out at the following three temperature ranges. Low temperature carbonization is normally carried out in the temperature range of 500 deg C to 700 deg C. In this type of carbonization, the yields of liquid products are higher and there is lower gaseous product yield. The coke produced is having higher volatile matter and is free burning. Medium temperature carbonization is done at temperature range of around 800 deg C. This carbonization produces smokeless soft coke. By products produced are similar in characteristics to high temperature carbonization. Medium temperature carbonization is rarely practiced these days. High temperature carbonization is carried out at a temperature which is above 900 deg C. This carbonization gives higher yield of gaseous products and lower yield of liquid products. This carbonization produces hard coke and is normally employed for the production of metallurgical coke from coking coals. Process of carbonization of coal The coal to coke transformation takes place as the coal is heated. When the state of fusing is reached, the layer of heated coal softens and fuses. From about 375 deg C to 475 deg C, the coal decomposes to form plastic layer.  Destructive distillation reactions proceed rapidly in the plastic layer with evolution of volatile products. At about 475 deg C to 600 deg C, there is a marked evolution of tar, and aromatic hydrocarbon compounds. The gas and condensable vapour are entrapped in the plastic mass and, as they expand tend to swell it. As the...

Technologies for improvement in Coking process in Byproduct Coke Ovens Jul31

Technologies for improvement in Coking process in Byproduct Coke Ovens...

Technologies for improvement in Coking process in Byproduct Coke Ovens Coking coals are converted to coke in large byproduct coke oven batteries. The coking process consists of heating blend of crushed coking coals in the absence of air to drive off the volatile compounds. The resulting coke is a hard, but porous carbon material which is used for the reduction of iron bearing materials in a blast furnace. The byproduct coke oven also recovers volatile chemicals in the form of coke oven gas, ammonium sulphate, tars, and oils. In last three to four decades several technologies have been developed which have not only resulted into vast improvements in the process of coking in the byproduct coke oven batteries but also have improved the quality of produced metallurgical coke. Majors of these technologies are given below. Selective crushing of coals This technology is a theoretically sound technology and aims at controlling the degree of crushing of the different constituents of coal.  It aims to improve homogeneity of reactive and inert components in coal. The reactive components of coals are primarily vitrinites and are the softest constituents while the mineral matters of coals are the hardest components. In conventional coal crushing units, the vitrinites get crushed to a relatively finer size compared to mineral matter constituents when the entire coal is crushed together. For producing coke of higher quality, it is desirable to crush the mineral matter finer than the vitrinite component of the coal so that during the process of coking, when the coal charge softens, the mineral matter is assimilated better, leading to the improved strength. This is usually carried out by crushing of coals in two stages. This technology is helpful when coals are petrographically heterogeneous. Coal moisture control Coal moisture control uses...