Blast Furnace Coke Requirements and Methods of Improving Its Quality: A Review

The effectiveness of coke functions in the blast furnace process largely depends on its reactivity. The reactivity of coke affects the course of blast furnace smelting, especially the profile of temperature distribution and gas flows in the furnace, and the degree of gas utilization and the specific consumption of reducing agent. It is shown that the reactivity of coke depends not only on its ash content, but also on its qualitative characteristics, that is, on the total content of oxides of various types, which affect the rate of reaction of carbon with carbon dioxide. The basic equations for calculating the ash basicity index of the batch are given, which are used to quantitatively assess the influence of ash components on the thermochemical properties of coke. It has been established that by calculating the basicity index, it is possible to provide a reasonable comparative assessment and characterize the technological value of coal concentrates and batches, as well as to quickly adjust the composition of production batches. Forecasting the quality of coke based on the properties and composition of coal batches is important for the long-term planning of supplying coke plants with coal for coking and for optimizing the composition of coal batches in the production process. The various mathematical models for predicting reactivity (CRI) and coke post-reaction strength (CSR), including using the genetic characteristics of coal, the chemical composition of their mineral substance was analyzed in the article. An equation is proposed for calculating the predictive indicators of CSR and CRI based on the basicity index of the batch ash for the raw material conditions of coke plant "ArcelorMittal Kryvyi Rih". The dependences of the CSR and CRI indicators of coke on the ash basicity index Iо of the batch and on the ash basicity index of the Иo batch were constructed, taking into account the ash content and yield of volatile substances of the batch. The use of the proposed equations will allow to optimize the composition of the production coal batch and achieve an increase in the quality of coke according to the post-reaction strength (CSR) indicator by 3-3.5%.

How to implement a quality program in a coking plant — The AHMSA experience

The production of hot metal through the blast furnace route is stilled the most cost-effective and highly productive process and probably remains the coming decades besides developed many alternative ironmaking technologies. In the recent past, the working volume of the blast furnace has been increased drastically to increase the blast furnace productivity. This means the blast furnace performance is more correlated to specific productivity which measures the efficiency in terms of ton hot metal. These modern blast furnaces favour high quality of coke, i.e. high coke CSR and M40 value, high iron content sinter and pellets. These high quality of input raw materials increased blast furnace efficiency and productivity. Generally, cokemakers increases the ratio of prime hard coking coal in the coal blend to achieve the high quality of coke. This increase in prime hard coking coal is not desirable for coke oven batteries because it creates high oven wall pressure and high coke cost and also not suitable for raw material security. The present investigation highlights few cases which clearly show that the high quality of coke (coke CSR: 69–71) may be easily produced with the optimal proportion of prime hard coking coal in the blend if the selection of coals is proper. Results confirmed that upto 30% primary hard coking coal with 15% non-coking coal in the coal blend produce an excellent quality of coke which naturally requires a careful selection on the blend component. The optimum composite coking potential (CCP) value of 4.6–4.9 is the ideal value for producing coke CSR in the range of 69–71 in recovery stamp charge cokemaking process in the real-time plant operation. Therefore, it is necessary to select the right coals for the coal blend based on the adopted cokemaking technologies to conserve the reserve of prime hard coking coal, oven health and cost-effectiveness.

Microalgae blending for sustainable metallurgical coke production – Impacts on coking behaviour and coke quality

An actual direction in the development of blast-furnace smelting technology is the implementation of stable operating modes of blast furnaces in terms of the parameters of the used charge materials and hot combined blast. For this purpose, complex indicators characterizing the thermal and reduction modes of blast furnace smelting, and integral indicators of iron ore raw materials (IORM) quality are being studied. The object of the study is the blast furnace process under the conditions of PJSC NLMK. The database of the main indicators of the operation of blast furnaces No. 4, 6 and 7 for the period 2013–2018 was analyzed. The furnaces operate under raw material conditions, with similar combined blast parameters and coke consumption. When the consumption of natural gas, pulverized coal and process oxygen changes, the values of the degree of compensation (the ratio of the consumption of reducing additives to the consumption of process oxygen) are in the range of 0.9–1.1. This provides a constant level of hearth heating, stability of the gas-dynamic mode of melting and coke consumption. At the same time, the different level of development of the processes of indirect (Ri) and direct (rd) reduction in blast furnaces No. 4, 6 and 7 makes it possible to perform correct studies of the features of blast furnace smelting in a wide range of Ri and rd values. It has been established that under the conditions of stable operation of blast furnaces on raw materials from sinter and pellets using combined blast, the type of dependence of the sulfur and silicon content in pig iron on the values of the integrated iron ore raw materials quality index is determined by degree development level of direct reduction processes rd. It has been established that the mode of blast furnace smelting with natural gas, pulverized coal and process oxygen, characterized by the level of rd values less than 20–25 %, is distinguished by the presence of a pronounced extreme dependence of coke consumption and productivity on the parameters of the combined blast.

Modern integrated steel mills that use coal-based ironmaking processes face the significant challenge of reducing greenhouse gases and pollutants such as CO2, SOx, and NOx. This article investigates using oxygen in steelmaking to improve process efficiency and drastically reduce carbon emissions. Compared to the conventional ironmaking process that uses hot air, the ironmaking process using oxygen can further reduce overall carbon consumption. Additionally, this process captures and utilises emitted carbon dioxide, making it a low-carbon ironmaking process until a fossil fuel-free ironmaking process is developed. The FINEX® process, while smaller than conventional Blast Furnace (BF) ironmaking in terms of commercial production scale, plays a critical role in reducing greenhouse gas emissions by using oxygen instead of air. Although the oxygen blast furnace is currently under development. FINEX® employs preheated hot compacted iron (13.7%) and dust burners (19.8%) to address the upper heat deficiency issue encountered with high levels of oxygen enrichment in blast furnaces. Furthermore, designing and implementing optimised Tuyeres to facilitate the injection of pulverised coal injection and natural gas can enhance the performance and operation of oxygen blast furnaces in the future. Using oxygen has the advantage of being able to respond to the environment better than air using conventional ironmaking processes and can quickly switch to a hydrogen-reduced process. Similar to the development of the basic oxygen furnace (BOF) process, which converted cheap air into oxygen to increase productivity and cleanliness of the steel in the steelmaking process, the alternative bridge technology to the realisation of complete carbon neutrality will be an oxygen-based ironmaking process. After all, in the current decarbonisation environment, oxygen should be viewed not as a luxury or cost burden, but as an essential requirement.

This article examines the preparation of coke for blast-furnace smelting by a method that most fully meets the requirements of blast-furnace technology: screening of the −36 mm fraction, the separation of nut coke of the 15‐36 mm fraction, and its charging into the furnace in a mixture with the iron-ore-bearing charge components. An analysis is made of trial use of coke of the Premium class on blast furnace No. 5 at the Enakievo Metallurgical Plant. Use of this coke makes it possible to reduce the consumption of skip coke by 3.2‐4.1%. Recent decades have seen significant progress in blast-furnace technology, advances made in this area having increased furnace productivity to 2.5‐3.5 tons/(m 3 ·day), reduced coke consumption to 250‐300 kg/ton pig iron, and lowered the pig’s sulfur content to 0.011‐0.015% [1]. The main reasons for these changes have been the wide-scale use of additional types of fuel and improvements in all of the original components of the technology: the quality of the charge materials, the slag and blast regimes, and the design of the furnace and other equipment. The most important factor in allowing these changes was an improvement in the quality of the coke, which has experienced an increase in the mechanical, thermal, chemical, abrasive, and other types of loads. Data from German researchers show that the strength properties of German coke has more than doubled in the last 20‐30 years. Abroad, the quality of skip coke is being improved while continuing to satisfy the other requirements of the smelting operation by improving the quality of the coke-bearing component of the charge, the coking regime, and the coke’s preparation for the blast furnace. In accordance with the requirements of modern blast-furnace technology, in most of the developed nations the minimum value of the index that characterizes the hot strength of coke (CSR) is 60‐65% or more, while the index that characterizes its reactivity is lower than 25‐30% [2].

Currently, the most promising blast-furnace technology involves pulverized-coal injection, and the most promising blast-furnace technology for coke production involves ramming the coal batch before delivery to the coke ovens, so as to ensure high packing density. In classic bed coking, the packing density of the coal batch is also of great importance. In the absence of mechanical methods (such as ramming or partial briquetting), the packing density mainly depends on the ash and moisture content and the degree of crushing of the batch. It follows from industrial tests in the coke plant at PAO ArcelorMittal Krivoy Rog and analysis of the multifactorial correlation of the strength M25 and wear resistance M10 with the packing density of the batch that, with decrease in packing density, the coke strength and wear resistance decline. That increases coke consumption and considerably complicates blast-furnace operation. Since improvement in coke quality entails decreasing the moisture content of the coal batch, a method has been developed for decreasing the moisture content directly in the silo, on the basis of osmosis and vacuum, that permits decrease in the coal’s moisture content to the optimal value, thereby boosting coke quality and improving blast-furnace performance. For example, it has been established that, in the blast-furnace shops at PAO ArcelorMittal Krivoy Rog, 1% decrease in M10 lowers the mean coke consumption by 5.5%. With increase in M25 by 1%, the mean coke consumption falls by 2.1%, on average.

Coal preparation has become a very important technique for preparation of high-quality metallurgical coke, the quality characteristics of which play a major role in the performance and economics of blast furnaces. Since availability of good quality metallurgical coals are meager in India, coal charge blends for carbonization in slot-type coke ovens are prepared from blending of various indigenous and imported sources of diverse characteristics. Preparation of coal blends for carbonization assumes paramount importance in terms of cost, quality, and resource utilization. Judicious coal-blending techniques based on intrinsic quality parameters coupled with various precarbonization steps to maintain blend homogeneity, granulometry, caking and coking properties of the blend are practiced under Indian conditions. The quality of metallurgical coke depends on type of coal, its physico-chemical properties including its granulometry, and its thermochemical behavior. Quality parameters of coke produced from a particular coal blend can be significantly influenced by the coal preparation technique adopted particularly when the blend comprises several sources of diverse quality parameters. Groupwise crushing of coal was developed with the aim to reduce the heterogeneity of different size fractions in terms of distribution of inerts and reactive contents. The groupings were based on their grindability indices, caking/coking properties, and dilation properties of individual size fractions. This article discusses in detail new coal preparation methodologies for improvement in coal charge blend granulometry and flowability, reduction in microfines content, and improvement in blast furnace coke quality.

The effectiveness of blast furnace (BF) operation is closely linked with the coke quality. Coke is the only solid material in the furnace that supports the iron-bearing burden and provides a permeable bed necessary for slag and metal to pass down into the hearth and for hot gases to pass upwards in BF. Therefore hot strength of coke i.e. coke strength after reaction (CSR) is one of the key parameters for efficient operation of BF. In this paper effect of ash chemistry (basic to acid ratio), plastic range (PR) and mean max reflectance of coal blend on the coke quality at Bhilai Steel Plant discussed. Two different regions were identified, in the first region BAR is the controlling factor while in the other region PR was a dominating factor for CSR. A new prediction model for CSR was also developed using plant data.

In the steel industry, the blast furnace (BF) is a core piece of equipment along the route from iron ore to steel, with the largest energy consumption and CO2 emissions. The stable, efficient, and economically viable thermal control of blast furnaces is still a challenging task, and fully automatic solutions are not applied industrially. The process exhibits multi-phase and multi-scale physio-chemical phenomena, in the presence of fast and very slow dynamics with latency periods of 6-8 h. Direct online measurements of key inner variables are missing, and unknown disturbances are strongly influencing the process; in particular, the quality of solid raw materials that are fed at the top of the furnace. Partial automation is the state-of-the-art strategy in the operation and control of industrial blast furnaces, and the experience and the dedication of the operators have a direct impact on the stability and efficiency of the operation. Model-based optimizing control schemes, which can be deployed either in closed-loop or as a guidance system to achieve a smooth, efficient, and reliable operation of blast furnaces, are promising. In this work, we propose a hybrid dynamic model based optimizing control scheme for the stable, energetically efficient, and economically optimal thermal control of blast furnaces. The underlying optimization problem is formulated as a combined tracking and performance optimizing control problem, where the goal is the tight control of the hot metal silicon content ([Si]) and the slag basicity (SB), while simultaneously maximizing the CO-efficiency of the furnace. These two variables are key product quality indices, and [Si] is an indicator of the internal thermal state of the BF process. Simulation results using real operational data of a large-scale industrial blast furnace are presented to demonstrate the potential of the approach for an improved operation of blast furnaces.

Coke production is a strategic branch of the Polish, European and global economy. Economic growth is linked to the demand for high steel products, which is also connected to higher coke production. A sustainable supply of raw materials – like metallurgical coal – requires balanced, cost effective and environmentally friendly mining, to provide the best quality of coal and coke. There are various types of steelmaking coals mined in Poland (in the Upper Silesia Coal Basin), thus laboratory tests on extracted coals need to be undertaken in order to create safe mixtures of coals (coal blends) which will be processed in the blast furnace. With this mind a new tool – the safety calculation model – has been developed and implemented by the CLP-B Laboratory. This new approach taken by the laboratory is a multi-component analysis which assesses the possible risk associated with the transformation of coal blends during the coking process in the furnace. The new calculation model allows for the sustainable management of raw materials such as coking (steelmaking) coals – to produce the best quality of coke in safe conditions. In the new proposed formula, the parameters identified as critical ones for assessing the safety of the furnace feed, are moisture, ash and sulphur content, volatile matter, pressure expansion, dilatation, shrinkage, volume, CRI and CSR.

The coke plant/blast furnace will remain dominant for the production route from iron ores to crude steel.There exists a community of fate for the coke plant and the blast furnace as blast furnaces cannot be operated without coke for physical reasons. For cost optimization, it was and is important to minimize the coke rate in the blast furnace and to utilize the by-products of the blast furnace and of the coking plant. The paper discusses, for an interconnecting network of an integrated iron and steelworks, the potentials of the use of coke oven gas and blast furnace gas. The coke oven gas can be utilized for electric power and heat production, for conversion into hydrogen and methanol as well as reducing gas in the blast furnace or in a DRI plant. Blast furnace gas can be used conventionally for blast heating, coke plant underfiring and power production, or it can be recycled to the blast furnace in the nitrogen-free blast furnace process and in the plasma heated blast furnace process. A critical comprehensive assessment is also given for these potentials with respect to CO2 emissions.

The steel industry is an important foundation of the national economy and the livelihood of the people, producing a large amount of carbon dioxide gas, accounting for about 70% of the carbon dioxide gas generated in the steel industry, which occurs during the ironmaking process. Therefore, the key technology to reduce the pollution and improve competitiveness is to increase the stability of blast furnace production and the quality of hot metal. Since the operation requirements for temperature control in the vanadium-titanium blast furnace are dramatically different compared to the traditional ones due to the low fluidity of vanadium-titanium slag, maintaining the required hot metal temperature within a narrow range with smaller fluctuations is essential. In addition, the adjustment parameters of the lower part have a significant influence on the tuyere combustion flame temperature during the daily operation of blast furnaces. At present, there is no relevant research on the online detection and analysis of vanadium-titanium blast furnace tuyere combustion flame temperature. In this study, the temperature of four tuyeres in a 500 m3 vanadium and titanium blast furnace at Jianlong Steel was detected by an online detection system. The tuyere combustion flame temperature was then calculated using colorimetric temperature measuring methodology at various times and at four distinct locations. After that, the calibration analyses, imaging parameter and the temperature tendencies in different directions of the blast furnace were investigated. This study not only offers new methods for understanding the regularity of operation and increasing the degree of visualization in vanadium and titanium smelting blast furnaces but also provides technical support for intelligent and low-carbon operation in blast furnaces.

Iron in the United States is largely produced from iron ore mined in the United States or imported from Canada or South America. The iron ore is typically smelted in Blast Furnaces that use primarily iron ore, iron concentrate pellets metallurgical coke, limestone and lime as the raw materials. Under current operating scenarios, the iron produced from these Blast Furnaces is relatively inexpensive as compared to current alternative iron sources, e.g. direct iron reduction, imported pig iron, etc. The primary problem the Blast Furnace Ironmaking approach is that many of these Blast furnaces are relatively small, as compared to the newer, larger Blast Furnaces; thus are relatively costly and inefficient to operate. An additional problem is also that supplies of high-grade metallurgical grade coke are becoming increasingly in short supply and costs are also increasing. In part this is due to the short supply and costs of high-grade metallurgical coals, but also this is due to the increasing necessity for environmental controls for coke production. After year 2003 new regulations for coke product environmental requirement will likely be promulgated. It is likely that this also will either increase the cost of high-quality coke production or will reduce the available domestic U.S. supply. Therefore, iron production in the United States utilizing the current, predominant Blast Furnace process will be more costly and would likely be curtailed due to a coke shortage. Therefore, there is a significant need to develop or extend the economic viability of Alternate Ironmaking Processes to at least partially replace current and declining blast furnace iron sources and to provide incentives for new capacity expansion. The primary conclusions of this comparative Study of Alternative Ironmaking Process scenarios are: (1) The processes with the best combined economics (CAPEX and OPEX impacts in the I.R.R. calculation) can be grouped into those Fine Ore based processes with no scrap charge and those producing Hot Metal for charge to the EAF. (2) A pronounced sensitivity to Steel Scrap Cost was felt less by the Hot Metal Processes and the Fine Ore Processes that typically do not utilize much purchased scrap. (3) In terms of evolving processes, the Tecnored Process (and in particular, the lower-operating cost process with integral co-generation of electrical power) was in the most favorable groupings at all scrap cost sensitivities. (4) It should be noted also that the Conventional Blast Furnace process utilizing Non-Recovery coke (from a continuous coking process with integral co-generation of electrical power) and the lower-capital cost Mini Blast Furnace also showed favorable Relative Economics for the low and median Scrap Cost sensitivities. (5) The lower-cost, more efficient MauMee Rotary Hearth Process that uses a Briquetted Iron Unit Feed (instead of a dried or indurated iron ore pellet) also was in the most favorable process groupings. Those processes with lower-cost raw materials (i.e. fine ore and/or nonmetallurgical coal as the reductant) had favorable combined economics. In addition, the hot metal processes (in part due to the sensible heat impacts in the EAF and due to their inherently lower costs) also had favorable combined economics.