Fluidity measurement is an important parameter in selection of coals for coal blend optimization to improve coke quality: A case study on Rourkela Steel Plant

摘要

Selection of coal for blending has a high impact on the techno- economics and the desired coke quality. Furthermore, the quality of the blend depends on the quality of individual coals and their interaction making up the blend. Coal, being a highly heterogeneous material, requires special care for determination of its properties and blending of individual coals for coke making. Coal fluidity is one such important coking property which highly influences the coke quality. The hard coking coals having good fluidity, which yield good coke, however are not only very expensive, but also are limited in reserves. To prepare a coal blend with available coals and relating the effect of coal fluidity on coal blending and there by the coke qualities, studies have been conducted using the industrial scale coals and coal blends. The study was carried out for 7m tall battery Coke Oven Battery#6 (COB#6) with state of art technology at RSP. This battery equipped with Coke Dry Quenching (CDQ) facility and is producing coke for newly installed blast furnace (BF#5) of 4060m3 capacity. The quality of coke for BF#5 essentially requires consistency in its quality parameters such as Micum Indices (M10 & M40), Coke Reactivity Index (CRI), Coke Strength after Reaction (CSR), and Coke Ash. Presently COB#6 uses 92.5% of imported coals to produce 1800 Tonne of coke per day with average M10 value to be 6.5. The regular imported coals used for blend preparation are Australian (hard), USA (hard), Australian (soft). The indigenous coal being used in coal blend is Prime Coking Coal (PCC). Sometimes other coals like Low Volatile High Rank coals, Canadian Coal, USA (soft) Coal, Indonesian Coal are also supplied to RSP from time to time and are used in different percentage for blend preparation in COB#6. These coals vary a lot in their properties. In recent period a lot many times the blend has been changed to an extent of 9 to 11 times per month due to non availability of coal and the resulting coke property has shown deterioration and inconsistency in its property. It was observed that the M10 index deteriorated from average of 6.2 to an average value was 6.6. The M10 varied from 5.9 to 6.9. Keeping in view of the present scenario of COB #6, investigation was carried out by RDCIS to find the reasons for deterioration in M10 index and later change of blend, keeping Gieseler Fluidity values as a major input parameter improved M10 Index from average of 6.6 to 6.2 in subsequent generated coke properties.