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...

Selection of Coal for inclusion in Coal Blend in Coke Making Sep26

Selection of Coal for inclusion in Coal Blend in Coke Making...

Selection of Coal for inclusion in Coal Blend in Coke Making Blending of coals is necessary from economical point of view by reducing the percentage of high cost, prime or hard coking coals and replacing it with medium or soft coking coals. In some coke oven plants even a small percentage of non-coking or steam coals have also been used in the blend. Selection of a proper coal blend for use in by product coke ovens is always a big challenge for the coke producer since the blend has to meet the following requirements. It is to meet the requirement of crushing during coal preparation. All the components of the coals are neither be over crushed or under crushed. The sized coal blend for charging the coke ovens is to meet the requirements of density, flow, and the size fractions. It is to have necessary coking and caking properties for producing coke of quality which meets the quality requirements of blast furnace (BF) coke. The three basic quality requirements of BF coke are (i) to provide heat for the endothermic reactions taking place in the blast furnace, (ii) to act as a reducing agent by producing the necessary reduction gases, and (iii) to provide a permeable support in the BF for the iron bearing burden. It is to provide safe pushing performance in coke ovens. It must not put excessive pressure on coke oven walls during the process of coking and damage them. It should meet the yield requirements not only of BF coke but also of coke oven gas. A proper coal blend will not produce excessive nut coke and coke breeze. It is to be economical. In view of the above varied types of requirements, the decisions regarding coal blends are not...

Non recovery coke ovens battery May12

Non recovery coke ovens battery...

Non recovery coke ovens battery The manufacture of coke by heating coal in absence of air has its origins at the start of industrial revolution when Abraham Darby used in the smelting of iron ores in 1709 in England. The method of coke production was initially the same as for the production of charcoal, stockpiling coal in round heaps, igniting the piles, and then covering sides with clay. This laid the foundation for beehive coke making. Gradual advances led to the development of beehive, reverberatory and byproducts ovens, culminating into regenerative coke ovens with recovery of the byproducts around a century ago. There are three proven processes for the manufacture of metallurgical coke. These are Beehive coke ovens Byproduct coke ovens Non recovery coke ovens. When the heat energy of flue gases is recovered in the form of steam then these ovens are known as heat recovery coke ovens or energy recovery coke ovens. The first non recovery oven was built in Jewell in 1960s and the first non recovery coke plant with heat recovery was commissioned at Indiana USA in March 1998. The plant had 268 ovens with a capacity of 1.3 Mtpa and a heat recovery power plant rated at 100 MW. Coke making process in non recovery ovens In the process of coke making in the non recovery ovens (Fig 1), volatiles evolved during coal carbonization are not recovered as byproducts but are combusted in the oven itself in the presence of controlled quantity of air and the heat of the volatiles of evolving gases is utilized for coking of the coal mass into coke and thus no external heating is required. The higher level of heat importantly is used to break up the potentially polluting hydrocarbons into the constituent combustible...