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...

Coking coals

Coking coals  Coking coals because of their special characteristics are suitable for carbonizing to produce blast furnace (BF) coke. Coking coal is also known as metallurgical coal. Fig 1 shows coking coal.  Fig 1 Coking or Metallurgical coal  Important properties required technically to produce good coke are Good coking and caking properties such as fluidity, dilatation and crucible swelling number etc. Appropriate rank indicated by reflectance value (MMR) Properties important for commercial as well as BF operation such as total moisture, ash etc. Properties which affects the properties of hot metal and steel such as percentage of sulphur and phosphorus. Modern coke making practice involves carbonization of a blend of coking coals. Coking coals in blended form are carbonized in a coke oven battery to produce metallurgical grade coke which is suitable for the operation of a blast furnace. Each plant uses its own blend based on the facilities available. In some of the Japanese plants coal blends consists of up to 20 different coals ranging in quality from coals with very high coking properties to coals with almost zero coking properties. The blended coking coal should have desirable coking properties for producing coke of required properties for BF operation. Quality requirement of coking coals Total moisture – It is limited to 10% maximum in as received condition. High moisture creates handling problem and lowers available carbon. Ash – It is limited to 10% maximum in air dried condition. High ash content reduces BF productivity and increases coke rate in the furnace. Volatile matter (VM) – The volatile matter in coking coals ranges from 20% to 35% in air dried sample. High volatile matter reduces the yield of metallurgical coke in coke oven battery but improves the coke oven gas generation. Sulphur – In coking coals sulphur is...