Coal Carbonization for Coke Production Dec08

Coal Carbonization for Coke Production...

Coal Carbonization for Coke Production Coal carbonization is the process by which coal is heated and volatile products (liquid and gaseous) are driven off, leaving a solid residue called coke. Carbonization of coal involves heating coal to high temperatures either in the absence of oxygen (O2) or in control quantity of O2. A gaseous by-product referred to as coke oven gas (COG) along with ammonia (NH3), water, and sulphur compounds are also thermally removed from the coal. The coke which remains after this distillation largely consists of carbon (C), in various crystallographic forms, but also contains the thermally modified remains of various minerals which have been in the original coal. These mineral remains, usually referred to as coke ash, do not burn and are left as a residue after the coke is burned. Until recently, the carbonization of coal was considered as ‘destructive distillation’, but with the increased importance of the products of carbonization, this phrase is falling out of use. Now, the coal carbonization is considered to be a physico-chemical process which depends on the coking rate, operating parameters, coal blend properties and the transport of thermal energy. The heating rate of coal influences the strength and the fissuring properties of coke. In order to arrive at a homogeneous quality, the heating of the coal cake in a coke oven is therefore to be uniform over the total length and height of the oven. In addition to this, the plastic layer migration rate influences the level of thermal stress in the re-solidified mass and therefore, the level of fissuring. The coal carbonization process started at the beginning of the 18th century by carbonizing good quality of coking coal in heaps on the ground, which subsequently led to the development of beehive ovens of...

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...