No abstract

In the recent past, it was realised that the gross coke yield was going down as a result of lower oven throughput in the stamp charged batteries of Tata Steel. The basic reason for this being the net reduction in the ash content of the coal blend used due to the incorporation of higher percentage of low ash imported coals and reduction in the ash content of captive coals through washing. The coals having higher ash content improves the bulk density, as the specific gravity of ash is higher than that of pure coal. Moreover, the ash components have affinity for water and pure coal repels water, which in case of pure coal, works against the holding together of the blend. Hence, lower the ash content, less is the bulk density of cake under identical stamping energy and lower the bulk density, less is the oven throughput. In order to maximise the oven throughput and productivity, a study was conducted in the laboratory mainly to assess the effect of various blend constituents and their ash content on the bulk density of coal charge. The effect of ash content on the coal cake stability has also been dealt with. This study, in short, is a useful tool for selecting the right type of coals and designing the optimum blend for stamp charging to achieve maximum throughput and productivity.In addition, studies were also carried out to assess the effect of addition of various binders on coal cake stability at lower moisture level which would also help in achieving higher throughput and productivity.

Disposal of waste plastics is a serious global issue, and hence it is imperative to explore methods to recycle them for efficient utilisation. The coke making process is considered to be a promising area to which the thermal decomposition of waste plastics is applicable, because the process involves coal carbonisation at a high temperature under a reducing atmosphere. As an outcome of the research work carried out on a laboratory scale followed by plant trials at Tata Steel, it was found that waste plastics recycling process using stamp charged coke ovens is feasible to recover coke, tar, light oil and gas from general waste plastics mixed in coal by carbonisation in coke ovens. It has also been established in the laboratory that waste plastics up to 1% can be used in coke making without any deterioration in coke strength. Plant trials have also indicated that co-carbonisation of waste plastics with coal is a possible solution for its disposal.

Stamp charging has been established as a versatile technology which not only improves the coke properties that can be obtained from a given coal blend, but also broadens the coal base for cokemaking, permitting the use of inferior coals without impairing the coke quality. To produce high strength coke at least cost, Tata Steel ventured into stamp charging in combination with 40-45% low ash imported coals. Research carried out by R&D, Tata Steel revealed that stamp charging has the potential power to digest even non-softening carbonaceous inerts, if the coal blend is suitably designed. Addition of such inerts would enhance the carbon content in the resultant coke. However, the use of these inerts calls for judicious selection of other components of the coal blend and optimisation of the blend proportion, or otherwise these inerts may have an adverse impact on the coke quality. Addition of such materials would also contribute to higher coke yield, since the volatile matter contents of these materials are very low. A quantum jump in the coke yield can be envisaged only if the addition of these low ash carbonaceous inerts is substantial (.10%). Therefore, it is imperative to design the base stamp charge coal blend so that it has enough fluidity to assimilate these infusible inerts and still produce coke with high coke strength after reaction. The present paper describes the scope of utilising low ash carbonaceous inerts such as fluid coke and anthracite optimally in the stamp charging blend by replacing the present imported semisoft coal with high fluidity imported coals. The laboratory scale experimentation and the results obtained with respect to improvement in coke properties and yield have been described. The results are also supported by the microscopic investigation of the coke samples.Coke with adequate strength for use in blast furnaces can only be obtained if the coal possesses the required chemical, rheological and petrographical properties. Only a few coals intrinsically possess all the above mentioned properties at optimum level for making good quality coke. Fortunately, a deficiency in one property of a particular coal can be offset by an excess of that property in another coal. As a result, globally coke oven charges are a blend of two or more coals. These optimum levels might also depend on operating parameters and carbonisation technology, which is specific to every cokemaking installation. Once these optimum levels are identified then, suitable blends need to be formulated with proper selection of constituent coals so as to have optimum coal blend properties as mentioned earlier.Worldwide depletion of good quality coking coal and the continued dependence of blast furnace operation on high quality of coke have led to the development of many advanced technologies in the field of cokemaking. Stamp charging is one such technology which has a distinct edge over other technologies, particularly in the Indian context, where the coals have high ash, inferior coking properties, low rank and heterogeneous petr...

The carbonisation mechanism in the coke oven chamber is quite complex and, although much useful information has been generated by empirical studies on both industrial batteries and pilot ovens, attempts to mathematically model the coke oven phenomena met with only limited success. In this study, a mathematical model to simulate volatile matter evolution during the carbonisation process for Indian coals has been developed. This model is a part of the endeavour to develop a rigorous mathematical model to simulate the main physical, chemical changes and transient heat