S. K. Haldar

Use of waste plastics in cokemaking at Tata Steel

Abstract 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.

Prediction of Coke CSR from Ash Chemistry of Coal Blend

Coke reactivity index (CRI) and coke strength after reaction (CSR) are the most important parameters used to assess the blast-furnace coke quality. The present work describes the possibility of estimating CSR for coke from ash chemistry of coal blends. For development and validation of the regression model, data obtained from the Tata Steels coke oven battery numbers 8 and 9 were utilized. It was found that CSR is greatly influenced by coal ash chemistry.

Effect of Indian Medium Coking Coal on Coke Quality in Non-recovery Stamp Charged Coke Oven

The maximum possibility of utilizing the Indian coking coals and inferior grade coking coal for producing metalurgical coke through non Grecovery stamp charging technology was investigated. Indian indigenous coals contained low percent of vitrinite (<50%) and higher content of ash (> 15%) compared to imported coking coal. Therefore, the selection of appropriate proportion of diferent types of coals was a major chalenge for coke makers. Coal blend selection criterion based on a single coeficient, named as composite coking potential (CCP), was develG oped. The use of increased proportion of semisoft coal (crucible sweling number of 2. 5) and high ash (≥15%) indigenous coal in the range of 20%–35% and 20%–65% respectively in the blends resulted in good quality of coke. Plant data of a nonGrecovery coke oven were used for developing and validating the model. The results showed that the coke strength after reaction (CSR) varied in the range of 63.7%–67.7% and the M40 value was between 81.8 and 89.3 in both the cases.

A review of coke making by-products

Existing energy resources are struggling to cope with the current energy requirements. It is therefore, necessary to increase energy efficiency and reduce greenhouse gases emissions in integrated steel industries. The yield of coking by-products is one of the key ways to achieve these goals. This review article is focused on history of the by-products such as coal tar, coal tar pitch, ammonia, hydrogen sulphide, pyridine, hydrogen cynide and carbon based material. Different technology for removal of mentioned by-products are briefly described according to technology development at different stage. Yield and quality of coking byproducts, its impacts on carbonization processes and factors such as volatile matter, rank of coal, reactive macerals, elemental constituents, and temperature were also investigated.

Use of phenolic resin in coke making at Tata Steel

Quality of coke is very much important for blast furnace productivity. Phenol-formaldehyde resin can be used as an additive in small quantity in the coal blend for improvement of coke quality. It enhances the fluidity of coal blend during co-pyrolysis with coal and hence improves the coke quality. After successful lab-scale study, this phenomenon has been demonstrated in top charge battery and heat-recovery oven of Tata Steel through plant trial. It was found that 0.3–0.4% addition of phenolic resin in the coal blend improves coke quality.

Effect of Heating Rate on Coke Quality and Productivity in Nonrecovery Coke Making

The productivity and coke quality of a nonrecovery oven depends on coal blend, operating parameters, and heating rate. A numerical methodology has been proposed for predicting temperatures of the intermediate points with the help of measured temperature in the coke oven. The model was validated with an actual temperature profile of five industrial ovens. The developed model can predict the temperature profile of the oven for a given set of operating conditions. The heating rate under normal operation was found to be in the range of 0.64–1.17°C/min. The effect of temperature variation inside the oven was also correlated with the coke quality and productivity.

A comparative study of by-products yield from coke making processes in a Jenkner apparatus

Physico-chemical characteristics or the industrial behaviour of any coal is directly controlled by its organic micro-components (macerals). The yields of by-products during carbonization of coal are affected by organo micro-components of different coals and operating parameters, such as, charging technologies, carbonization temperature, particle size, bulk density, etc. In the present investigation, the effects of volatile matters (16.61–36.00%), Ro, avg. (0.80–1.36%), exinite (0.5–4.5%), hydrogen (4.34–5.29%) and nitrogen (1.60–2.18%) content of coal on yield of by-products, such as, coke oven gas, coal tar, ammonia, and hydrogen sulphide were studied. The studies revealed that there is a significant difference of the yield of by-products for the two different charging technologies. The coke oven gas, coal tar and ammonia yield was lower in stamp charging process as compared to top charging process, whereas, hydrogen sulphide yield followed a reverse trend.

An approach to maximize the use of non-coking coal in non-recovery coke making

The preservation of metallurgical coal and coke cost reduction are gaining much importance in iron and steel industry. The effort is being made worldwide to increase the use of inferior grade coking coal/non-coking coal in coke making. The objective of this study was to maximize the use of non-coking coal in the coal blend without deteriorating the coke quality in non-recovery coke oven. The selection criterion of coal/coal blend was based on a coefficient, named as composite coking potential model. The study confirms the existence of a relationship between the composite coking potential and the hot strength of coke. The study reveals that upto 35% non-coking coal in coal blend is possible to produce desired quality of coke with coke CSR ≥ 65.

Methodology to Improve the Mean Size of Coke for Stamp Charge Battery

Coke physical properties like mean size and distribution are very important for blast furnace operation. Coke properties mainly depend upon parent coal characteristics and carbonization conditions. Some additives were found to influence the coke properties. This article presents the influence of pyroxenite as an additive and effect on operating parameter on coke size.

Heat recovery stamp charged coke making: An experience in operational excellence

The coal blend quality and process control of coke making technologies is an important lever to produce quality coke with optimal cost. Apart from impacting cost, this improves the CO2 footprint. This is facilitated by proper selection of coke making technologies and coal/coal blend. Each technology has its own advantage and limitation based on its design criteria. Recently, Tata Steel introduced Asia largest single location 1.6 mtpa of heat recovery coke plant for the first time. This paper briefly described the operational philosophy evolved in heat recovery coke plant to produce desired quality coke at comparatively lower cost through operational excellence. The reduction of imported prime hard coking coal in coal blend up to 30% without affecting coke quality adversly and understanding the operational processes and finally mastering heat recovery coke making technology was also part of this paper.