Introduction to Energy-Saving and Environmentally Friendly Technologies in Japan’s Coke Oven Processes in Recent Years (Table)

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Introduction to Energy-Saving and Environmentally Friendly Technologies in Japan’s Coke Production Process in Recent Years (Table) According to a report by China Iron and Steel News Network on March 19, 2007, the turn of the century marked a period of transformation in Japan’s coke production; on one hand, weak demand for steel following the collapse in the 1990s led to a reduction in coke production； On the other hand, the coke ovens used for urban gas production have all been shut down as they were replaced by natural gas. In recent years, due to the recovery in steel demand, in addition to increasing the coal injection ratio and extending the lifespan of coke ovens, efforts have been made to restart some coke ovens that had been shut down (such as those at Mitsui Mining) and to build new coke ovens (such as JFE Steel’s No. 5 coke oven). CDQ technology, which is most effective in terms of energy savings, can recover waste heat for power generation and improve the quality of coke, thereby helping blast furnaces to reduce their coke consumption. As a result, it offers good benefits in terms of both energy conservation and CO2 reduction, and its adoption rate has now exceeded 80%. In terms of coal blending, due to the sharp rise in prices of primary coking coal in recent years, and from the perspective of rational resource utilization, efforts have been made to increase the proportion of non-fine coking coal; this proportion rose from 20% in the early 1990s to nearly 40% by 2001, and further increased to 50–60% in recent years. This was achieved mainly through coal preheating techniques to reduce moisture content in the coal, as well as pre-forming techniques for fine coal powder. Currently, such equipment is widely available. In terms of extending the lifespan of the furnace body, thanks to the refinement and improvement of repair techniques, furnace diagnosis methods, and operational management strategies, the average lifespan of coke ovens has reached over 35 years, with some reaching around 40 years. In terms of environmental protection technologies, in addition to strengthening measures to prevent dust emissions and coke oven gas leaks, efforts have also been made to reduce CO2 emissions. Starting in 2000, it was successful to use 1% waste plastic in coking coal, achieving an energy utilization rate of 94%, which is higher than the 75–80% rate achieved through blast furnace injection. In addition to its adoption at the five plants owned by Nippon Steel, this technology was also tried out at the Keihin Plant of JFE Steel in 2006. Subsequently, a technology that allows for an increase in the proportion of waste plastic used to 2% was developed and put into use. In terms of the rational utilization of coke oven gas, technologies for extracting hydrogen from it have been developed over the years; this hydrogen, together with nitrogen – a by-product of oxygen generators – and CO2 – a by-product of lime kilns – is used to produce urea. In recent years, to meet the needs of fuel cell vehicles, Nippon Steel has started to supply the hydrogen extracted from coke oven gas to vehicle hydrogen refueling stations, thereby making greater contributions to energy conservation and environmental protection. To meet the higher demands for energy conservation and environmental protection in the 21st century, the new coke oven project “Scope 21”, developed under the leadership of **, was successfully created through research and development from 1994 to 2003. Based on the results of tests conducted with a furnace operating at a capacity of 50 t/d, its production efficiency is 2.4 to 3 times that of conventional coke ovens. The proportion of coal that is not highly caking-prone also increases, and energy savings amount to around 20%; environmental conditions are further improved as a result. Therefore, Nippon Steel is actively preparing to build practical versions of such furnaces. To save space, we will not repeat the introduction of major energy-saving technologies such as dry quenching of coke, which are already being promoted in China and well-known. Instead, for reference, we will focus on discussing the production of coke ovens and the promotion of energy-saving technologies in Japanese factories in 2001, the technology of using waste plastics in coke ovens, as well as the development process and specific details of the “Scope 21” technology. Brief overview of coke oven production and energy-saving technology promotion in Japan in 2001: In 2001, Japan produced 102.86 million tons of steel, a 3.4% decrease from the previous year; it produced 79.24 million tons of iron and 35.39 million tons of coke, all of which were slightly lower than in the previous year. A total of 45 coke ovens with 4,262 chambers are in operation; the main production indicators and the status of energy-saving technology adoption are shown in Table 1. Table 1: Production indicators of coke ovens and the adoption of energy-saving technologies in various companies
Company and Plant Name, Coke Ovens, Capacity Utilization Rate (%), Heat Consumption kcal/kg, Dry Quenching, Coal Moisture Adjustment, Others, Number of Ovens, Number of Chambers

New Japan Steel, Yawata: 2, 200, 124.5, 510, All, All; Oita: 4, 320, 125.0, 575, All, All; Muroran: 2, 133, 121.7, 632, All; 1 oven with 91 chambers, another with 42 chambers featuring coal preheating; Nagoya: 4, 375, 17.0, 497, All, All; Kunisaki: 5, 469, 116.6, 560, All, All. Total: 17, 1497, 120.9, 554, All.

NKK, Keihin: 2, 198, 119.6, 596, All, None; 124 chambers, with 20.7% using shaped coal; Fushan: 3, 444, 132.3, 599, All; 165 chambers, with 19.8% using shaped coal. Total: 5, 642, 125.0, 598, All, All.

Kawasaki Steel, Chiba: 3, 260, 112.7, 515, All, All; Mizushima: 6, 465, 120.9, 510; 164 chambers without, 301 chambers with. Total: 9, 725, 116.8, 512.

Sumitomo Metal, Wakayama: 3, 274, 97.2, 571; 106 chambers with, 168 chambers without; 22.6% using shaped coal; Kashiwazaki: 4, 333, 101.9, 577, All, All. Total: 7, 607, 99.5, 574.

Kansai Thermochemical (Kagawa): 2, 246, 121.1, 595, All, None; Nakayama Steel (Funamachi): 2, 66, 156.4, 648, All, All; Combined stacking with graded crushing; Mitsubishi Chemical (Sakaide): 3, 323, 129.0, 643; None, None; All have graded crushing; Mitsui Mining (Kitakyushu): 2, 154, 110.7, 608; None, None.

As can be seen from the above, out of 4,262 coke ovens, only 809 do not use dry quenching, indicating that the adoption rate is over 81%. Although the coal moisture adjustment is slightly lower, it is compensated for by coal preheating and shaped coal, resulting in good energy-saving effects as well. Furthermore, by improving management and promoting energy-saving technologies, various factories have not only achieved production levels that exceed their designed capacity but also reached a proportion of non-microbonded materials of around 40% in that same year – all of which are worth learning from. In response to the severe situation of soaring coking coal prices in recent years, Nippon Steel’s Environmental Process Research and Development Center has developed a technology to further increase the proportion of non-fine caking coal through extensive basic research, and this technology is currently being implemented in various factories. Introduction to the application technology of incorporating waste plastics into coking coal. After the 4093 m3 blast furnace at NKK’s Kyobin plant in Japan successfully experimented with using waste plastics as a substitute for coal by following the examples set by NKK’s Bremen plant in Germany in 1995, a voluntary energy-saving and environmental protection plan for the steel industry was introduced in 1996, with the goal of reducing CO2 emissions. This plan set the target of using 1 million tons of waste plastics in the steel industry, thereby achieving a 1.5% energy savings rate. Subsequently, NKK’s Fukuyama plant and Kobe Steel’s Kakogawa plant also began to adopt this approach; the energy utilization efficiency reached 75–80%, provided that the amount of chlorine-containing waste plastics used was no more than 2%. Nippon Steel, building on its previous experience in developing technologies for converting waste plastics into oil, has successfully developed a coking technique that allows 1% waste plastic to be incorporated into coking coal. Of the waste plastic added, 20% turns into coke, while the remaining 40% each becomes gas and chemical by-products, resulting in an energy utilization rate of 94% – higher than the 75–80% achieved through blast furnace injection and the 65% attained through gasification and liquefaction. Additionally, the proportion of chlorine-containing waste plastic can be increased to 5%, giving it a competitive advantage as a latecomer. Thus, Nippon Steel first installed 40,000 t/a pretreatment units at the Kunisaki and Nagoya plants in 2000, and then added 20,000 t/a pretreatment units at the Yawata and Muroran plants in 2001. Under the provisions of the Container and Packaging Recycling Law, the Waste Plastic Processing Association is required to pay processing fees of 20,000 to 40,000 yen per ton to the processing plants. Thanks to this incentive policy, and after Nippon Steel succeeded in developing a technology to increase the proportion of waste materials used to 2%, it doubled the amount of waste processed at its various plants. In 2005, it built a preprocessing facility with an annual capacity of 40,000 tons at its Oita plant; that same year, the five plants together processed over 170,000 tons of waste plastic, exceeding the 150,000 tons used for blast furnace feeding. Not only does Nippon Steel plan to consume a total of 380,000 tons by 2010, but JFE Steel’s Kyobin plant also began testing the use of 6,000 tons in 2005; it intends to increase this amount further once success is achieved. In the future, this will become the standard practice for steel companies when it comes to using waste plastics. The specific preprocessing process is as follows: The recovered mixed plastic waste is unpacked, and obvious foreign materials are removed manually first; it is then crushed by a crusher into pieces about 5 mm in size. If there is an excessive amount of chlorinated plastic waste such as PVC, the excess material can be separated using the specific gravity method. After that, the material is fed into a granulator to be compressed into particles of 2–3 mm in size, which can then be mixed into coking coal in the appropriate proportions. The key to increasing it from 1% to 2% is to ensure that raising the blending ratio does not affect the strength of the coke. After numerous tests, the appropriate granulation size was finally identified, thereby resolving the problem. Technically, more waste plastic can be incorporated, but the downside is that the coke recovery rate will drop from 70% to 20%, meaning the coke production will fall to around 1.5%. Given Japan’s current insufficient coke production capacity, it is appropriate to maintain this level; if this approach is adopted in China, the proportion of waste plastic that can be used could be increased accordingly. (Source: China Science and Technology Information)