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With the rapid development of the steel industry, particularly the increase in the size of blast furnaces, there are rising demands both for the quality and quantity of coke, which has led to an increasing shortage of coking coal supply. Traditionally, bituminous coal is used for coking, but statistics show that bituminous coal used for coking in China accounts for only about 37%. Although the variety of such coal is relatively complete, its distribution in terms of structure and location is highly uneven. Weakly caking bituminous coal accounts for a large proportion, at 55.9%, and is easy to process into coal ； The reserves of coking coal and fat coal with good cohesiveness and caking properties are only 14.6% and 17.1% respectively; most of these coals are difficult to process, and they are primarily concentrated in the North China region. This resource situation of bituminous coal determines the long-term shortage of high-quality coking coal in our country, and it also severely hinders the sustainable development of the coking industry. China is extremely rich in anthracite resources, which are also distributed fairly evenly; anthracite can be found in most regions. There is also anthracite available near most domestic coking enterprises, and the transportation distances are generally short. Incorporating a certain amount of anthracite into the coking process is an effective way to address the current shortage of coking coal resources and to diversify the sources of such coal. Lianyungang Iron and Steel is located in central Hunan, where there are abundant reserves of anthracite, providing favorable conditions for using anthracite in coke production. For the future development of Lianyungang Iron and Steel, its Technology Center and coking plant collaborated with Wuhan University of Science and Technology in 2004 to conduct experimental studies on coking using anthracite. 1 The impact of using anthracite in coking on coke quality. Anthracite is a type of coal with high degree of coalification and high carbon content; it does not melt during the coking process. During this process, the surface of anthracite can adsorb some of the liquid products resulting from the pyrolysis of active components through interfacial interactions and reactions. This reduces the amount of liquid phase within the plastic mass, adjusts the fluidity and expansion properties of the coaling coal, fills the cracks and voids in its structure, reduces the shrinkage of semi-coke, improves its porosity and pore wall structure, enhances the strength of both semi-coke and coke, and also improves the size of the coke particles, thereby serving a role in strengthening the material. 2 Basic conditions for using anthracite in coke production To improve the quality of coke, it is necessary to make full use of the weakening and strengthening effects of anthracite, while also achieving good economic benefits. The following basic conditions must be met when using anthracite in coke production: (1) The cohesiveness of the active components in the bituminous coal fed into the furnace should be sufficient to maintain a favorable balance ； (2) The proportion of anthracite used is moderate to maintain appropriate fluidity and expansion ； (3) Bituminous coal with good grindability and thermal stability, as well as an appropriate particle size, is used to achieve the lowest power consumption and the best coke quality. 3 Experimental studies on coking with anthracite 3.1 Study of the coal currently used for coking at Lianyungang Steel Through sampling from freight cars, a comprehensive analysis was conducted on a total of 27 different types of coking coal supplied to Lianyungang Steel, including industrial analysis, elemental analysis, caking index, maximum thickness of the vitrinite layer, Oya expansion degree, and reflectance distribution charts of the coal. Based on laboratory analyses, the basic characteristics of the coking coal currently used by Lianyungang Iron and Steel Group, as well as the composition of the blended coals, were examined. The coal types were reclassified according to their actual grades. An optimized blending scheme for coking using anthracite was determined by taking into account the properties of the coal and the available resources, as shown in Table 1. http://www.nmtech.com.cn/jishuwang/upload1/070710925297852.jpg 3.2 Study of the properties of anthracite and selection of coal types 3.2.1 Study of the general properties of anthracite The anthracite used in these experiments was sampled from the freight cars carrying anthracite intended for injection into the blast furnaces at Lianyungang Iron and Steel Company. Through industrial analysis of all 11 types of bituminous coal available for blast furnace injection, it was found that 7 samples had an ash content greater than 10%, while 4 samples had an ash content less than 10%. These 4 types of coal were designated as A, B, C, and D respectively. To prevent an increase or a decrease in the ash content of coke produced in the coking process using bituminous coal blends, it is necessary to select bituminous coal with low ash content; this is a fundamental requirement when choosing bituminous coal. Based on this, the aforementioned 4 types of bituminous coal were first selected as the bituminous coal for this study. Elemental analysis was performed on these four types of coal; their V daf value was below 6%, and their hydrogen volume fraction (H daf%) was around 2.5%. Therefore, all of them belong to bituminous coal type 2. 3.2.2 Study on the Physical Properties of Bituminous Coal 3.2.2.1 Thermal Stability When bituminous coal is used in coke production, its thermal stability is poor; at certain temperatures during the coking process, cracking occurs, resulting in the formation of new cracks or crack centers, which increases the number of cracks in the coke and reduces its strength. Through thermal stability analysis of all anthracite samples, it was found that the aforementioned four types of coal with lower ash content also exhibited good thermal stability. The TS +6 values for these coals were 54.81%, 47.85%, 30.15%, and 62.25% respectively. The sums of their TS +6 and TS 3-6 values were 73.2%, 66.25%, 51.99%, and 79.05% respectively. It is generally considered that when the values of TS +6 and TS 3-6 are above 60%, the thermal stability of anthracite is good. For coal types other than these 4, the TS +6 value is only around 20%, and the sum of TS +6 and TS 3-6 is also low; such anthracites are not suitable for use in coal blending for coking. 3.2.2.2 Grindability The grindability of coal refers to the ease with which coal can be crushed. Compared to bituminous coal, anthracite has relatively higher hardness and a lower grindability index (HGI); it needs to be crushed separately before it can be used in coal blending for coke production. Therefore, it is extremely important to select the grindability of anthracite. Because the grindability affects particle size and particle size distribution, which in turn influences coke strength ； On the other hand, the grindability directly affects the power consumption cost associated with the grinding of anthracite. The general range of the grindability index for thermal coal in our country is 25–129. Coal with an HGI greater than 86 is considered easy to grind, while coal with an HGI less than 62 is considered difficult to grind. For the four types of bituminous coal that have been identified earlier, their grindability indices are 131, 191, 82, and 127 respectively, indicating that all four types of coal have relatively good grindability. The grindability of other coals is determined; some coals can be ground, but some have poor grindability. Through the aforementioned analytical studies on all the anthracites used in Lianyungang Iron and Steel Company’s blast furnaces, types A, B, C, and D were ultimately selected as the appropriate anthracite varieties for coking using in Lianyungang Iron and Steel Company’s coal blending processes. 3.3 Study on the inerting capacity of bituminous coal: The inerting rate refers to the ability of the reactive components in bituminous coal to accommodate the inert substances inherent in the coal itself or those added externally. It can generally be characterized by values such as the bonding index C and the Oya swelling degree. By studying the inerting rate when bituminous coal is mixed with anthracite, it is possible to understand the patterns of change in the C value after the addition of anthracite, as well as the amount of anthracite that can be added. This helps to determine the optimal balance between active and inert components in the coal mixture used for coking, thereby achieving the best active-inert ratio and predicting the quality of the coke produced. This is also a key focus in research related to coking using anthracite. The measurement study was carried out in two parts. One part involves using a basic coal blending scheme prepared for research purposes and producing blended coals to determine the caking index CR.I; the other part is the focus of the study. The research method consists of adding different proportions of anthracite, ranging from 3% to 7%, to both the basic coal blending scheme used for research and the blended coals used in production, in order to determine the swelling index CR.D. The inertness rate tests led to the following conclusions: (1) With the same ratio of bituminous coal and anthracite, the addition of the four different types of anthracite, A, B, C, and D, resulted in CR.D values that did not change by more than 2 units, remaining within the acceptable error range. This indicates that the physicochemical properties of these four types of bituminous coal are very similar, and they can be used together in future research. (2) The CR.D of the bituminous coal scheme used for research in combination with anthracite is better than that of the produced blended coal combined with anthracite. (3) Based on the CR.D results, an appropriate amount of anthracite to be added is 3% to 5%. When the amount of anthracite increased to 7%, its CR.D values were all low, indicating that an increase in the amount of anthracite led to this effect. 3.4 Tests on 40kg small coke ovens: Bituminous coal and anthracite differ greatly in terms of degree of metamorphism as well as other process-related factors; using anthracite for coking is generally more complex than using bituminous coal. To determine the optimal particle size of bituminous coal for use in coking, as well as the amount of bituminous coal that can be used or the optimal amount to be used ； After adding anthracite, the variation patterns of the compatibility and coking properties of the blended coal, as well as the trends in coke quality changes ； A series of issues, such as the impact on the quality of chemical products and on the level of process operation after coking with bituminous coal, need to be resolved step by step through pilot coke oven tests and industrial-scale trials. The purpose of this experimental study on Lianyungang’s 40kg small coke ovens is to provide technical support for industrial trials and future applications. 3.4.1 Test plan for blending with anthracite In addition to the originally planned coal blending scheme using bituminous coal, in order to determine whether the coking coal blend currently used by Lianyungang Iron and Steel Company can be directly supplemented with a certain proportion of anthracite, samples of this production blend were also taken to be used in the tests on coking with anthracite. The basic coal blending scheme for the bituminous coal test and the coal quality analysis results are shown in Table 1, while the test scheme is shown in Table 2. http://www.nmtech.com.cn/jishuwang/upload1/070710926536697.jpg The bituminous coal used in this coking process is actually of low degree of metamorphism, high volatility, and poor quality; it is one of the three types of coal that Lianyungang Iron and Steel Company purchases and uses as 1/3 coking coal. The coking experiment using bituminous coal this time did not take the inclusion of lean coal into consideration. 3.4.2 Test Procedure (1) Test Steps First, Scheme No. 1 for the basic coal blend is selected to form new coal blends with bituminous coals of different particle sizes, in order to conduct coking tests and better study the impact of bituminous coal particle size on coal blending for coking. Then, different basic coal blending schemes were altered, along with various particle sizes and ratios were tested; the particle size of anthracite varied mainly between <1mm and <2mm, while the ratio was adjusted between 4% and 5%. (2) Coking conditions: To maintain the consistency, comparability, and reliability of the test results from small coke ovens at the same level, the process conditions used in the tests were basically modeled after or similar to those of industrial furnaces; for each corresponding test scheme, two parallel tests were conducted. The coking parameters are: heating time of 12 hours, holding time of 6.5 hours, and coking time of 18.5 hours ； Coal loading temperature: 700℃ ； Final temperature at the center of the coke cake: 1,030℃ ； The moisture content of the coal fed into the furnace is uniformly set at 10.0% ； Fineness of coal fed into the furnace: 80±1% ； Coke quenching method and water usage: Wet coke quenching, with uniform water injection for 10 seconds ； Treatment and sampling of coke: The entire coke is sampled at the same level after being dropped twice from a height of 1,840 mm. 3.4.3 Test Data From early September to November 20, 2004, over a period of more than two months, Lianyungang Iron and Steel carried out numerous tests and analytical examinations. A total of 38 valid coking tests were conducted, along with analyses of the coaling materials and coke used in these tests. For each testing scheme, two parallel tests were performed, and the arithmetic average of the results from these two tests was taken as the final test result, as shown in Table 3. http://www.nmtech.com.cn/jishuwang/upload1/070710927309957.jpg 3.5 Test Results Conclusions can be drawn through a comprehensive analysis of all the test results. 3.5.1 The tests conducted as part of this research on using anthracite for coking have little impact on the conventional indicators of coke quality. 3.5.2 For coking with anthracite, it is preferable that the particle size be less than 1 mm. 3.5.3 When the proportion of anthracite does not exceed 5%, the crushing strength index M40 of coke remains relatively stable, with little to no decrease, except in a few cases. However, the wear resistance strength of M10 decreased in all groups, with some approaches showing a decrease of nearly 2%. This indicates that the caking property of the blended coal remains low; therefore, in future expanded tests, the caking property of this blended coal should be further improved to enhance its wear resistance. 3.5.4 After the addition of anthracite, the coke thermal strength CSR value showed an improvement in terms of trend; aside from a few abnormal research results, most of the findings were favorable, with some even increasing by more than 2%. It can be seen that when using anthracite for coking, the thermal strength of the coke does indeed improve. However, according to the test results, the reactivity CRI of most of the coals increased, and the reasons for this need to be further analyzed and investigated in subsequent research experiments. 3.5.5 Based on previous studies on the coking properties of bituminous coal and numerous experiments conducted using 40 kg small coke ovens, it can be concluded that it is feasible to use the existing bituminous coal supply at Lianyungang Iron and Steel Company, to enhance the caking property of this coal slightly, and to incorporate 3%–5% anthracite in the coal mixture for coking. 4 Economic benefit assessment of coking with anthracite: Using anthracite as a component in coal for coking allows for significant improvements in a company’s economic performance, as anthracite is cheaper than coking coal and usually comes from closer sources. For Lianyungang Iron and Steel, the current average prices at the plant are as follows: anthracite at 580 yuan per ton, lean coal at 780 yuan per ton. The annual production of coke is 1.3 million tons, with approximately 1.82 million tons of bituminous coal required for coke production. The ratio of anthracite used to replace lean coal in coke production is 4%. The average processing cost of anthracite in China (including operational expenses, wages, depreciation, etc.) is roughly 30 yuan per ton. Thus, Lianyungang Iron and Steel’s cost of coal used for coking when using anthracite can be reduced by: 182×4.0%×(780—580)—182×4.0%×30 = 12.38 million yuan. 5 Conclusion Coaling bituminous coal for coking is a new technology that has attracted considerable attention among those working in the coke industry. By using bituminous coal in combination with other coals for coking, it not only expands the available resources for coking but also helps to alleviate the current shortage in the coking coal market, thereby enabling more rational use of resources ； At the same time, when there is an excess of cohesion in the blending coal, it can also serve to thin out the mixture and enhance its strength, thereby improving the quality of the coke. Since the price of anthracite is much lower than that of coking coal, using anthracite in coke production offers good economic benefits.