Overview of the development of dry quenching of coke

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Chapter 1: Dry Quenching of Coke – Section 1: Development of Dry Quenching of Coke I. Development Process of Dry Quenching of Coke Dry quenching of coke originated in Switzerland. In the 1940s, many developed countries began to research and develop this technology; they adopted various approaches, and the scale of these operations was generally small with unstable production levels. Entering the 1960s, the former Soviet Union made breakthrough advances in dry quenching technology, achieving continuous and stable production, obtaining patent rights, and gradually installing this technology in most of its large-scale coking plants. To date, 40% of the coking plants in the former Soviet Union use dry quenching, with a processing capacity of 50–70 t/h per unit. However, the quenching systems in the former Soviet Union did not start at a high level in terms of automatic control and environmental protection measures. The global energy crisis of the 1970s spurred significant progress in dry quenching technology for coke. Japan, which has relatively limited resources, was the first to introduce dry quenching technology from the former Soviet Union, and made effective improvements in terms of larger-scale installations, automatic control, and environmental protection. By the mid-1990s, Japan had built 31 dry quenching units, of which 17 had a processing capacity of over 100 t/h. The dry quenching units constructed by companies such as Nippon Steel and NKK could achieve a processing capacity of over 200 t/h each ； Technologies such as hopper feeding for charging coke, rotary seal valves for continuous coke discharge, and rotary coke drums for coke reception were employed, which reduced the gas-to-material ratio** and significantly lowered the capital investment required for constructing the dry quenching coke unit as well as its operating costs ； Computer control has been implemented for operation, achieving fully automatic, unmanned operation ； In terms of dust removal, a dust removal ground station system is employed to avoid potential secondary pollution from the dry quenching unit. Japan’s dry quenching technology is not only widely used within Japan, but it has also been exported to countries such as Germany, China, and South Korea; its level of development in this area is now at the international leading level. In the 1980s, Germany invented a dry quenching device with water-cooled walls, which optimized the gas circulation system and reduced operating costs. German company TSOA successfully incorporated water-cooled grills and water-cooled walls into the dry quenching furnace, changing its cross-section from circular to square. Fundamental improvements were also made to the methods of coke discharge and gas supply within the furnace; as a result, the coke moved downward while the air flow moved upward, ensuring a uniform distribution. This improved the heat exchange efficiency, reduced the gas-to-coke ratio to below 1000 m3/t of coke, and further lowered the operating costs of the dry quenching system. The TSOA dry quenching technology has been promoted in Germany, and it has also been exported to South Korea and Taipei, China. Over the course of its development, the dry quenching process for coking has taken on various forms, but the basic operational sequence remains largely the same; differences exist only in aspects such as loading cokes, removing cokes, and dust removal from the circulating gas. Representative examples include the dry quenching process designed by the German company TSOA and the one developed by Nippon Steel in Japan. These two typical dry quenching processes have introduced innovations based on the mature dry quenching technologies of the former Soviet Union, developing their own unique features and raising the technology of dry quenching and its applications to a relatively advanced level. Anshan Coking Technology Institute and Shougang Design Institute in China, as well as Wuhan Iron and Steel Group, Baoshan Iron and Steel Group, and Shougang, have carried out some useful work in adopting and adapting Japanese dry quenching technology, and have accumulated considerable experience in this area. Currently, there are approximately 130 dry quenching units in operation around the world, and the construction status of such units in various countries and regions is shown in Table 1-1. II. Current status of dry quenching technology in China: Since the early 1980s, when Baosteel’s first plant introduced dry quenching technology from Japan, six plants in China are now operating with this technology, and there are differences in the way it is utilized across these plants. The construction status of domestic dry quenching units is shown in Table 1–2. (1) Dry quenching status of various plants 1. Baosteel’s dry quenching process: To support its 12×50-hole (6m) coke ovens, Baosteel built 12 sets of dry quenching units with a capacity of 75 t/h each, enabling the annual processing of 5.1 million tons of coke; the construction was carried out in three phases. The first phase of the 4×75t/h dry quenching unit was put into operation in May 1985, while the second and third phases were put into operation in June 1991 and December 1997 respectively. The first phase of the dry quenching unit was entirely imported from Japan ； The second-phase dry quenching unit was developed mainly through domestic design and construction, building on the achievements of the first phase; the proportion of domestically produced equipment accounts for 80% of the total weight of the equipment, with some key components being imported from Japan ； In Phase 3, with the exception of a very small number of key components imported from Japan, the vast majority of the equipment has been domestically produced, achieving a localization rate of over 90%. Baosteel uses only dry quenching for coke, without wet quenching as a backup, and adopts a production mode of \"three in operation and one in standby\". Table 1-1: Overview of the Installation of Dry Quenching Units in Various Countries and Regions Sequence Number Number of Countries/Regions with Designed/Constructed Units 1 New Nippon Steel, Japan: 16; South Korea: 3; China: 9; Germany: 1 2 NKK, Japan: 11 3 Ishikawajima-Harima, Japan: 12; South Korea: 2 4 ThyssenKrupp Otto, Germany: 3; South Korea: 2; Taiwan, China: 1 5 Ukraine (former Soviet Union): 27; China: 6; India: 12; Romania: 5; Poland: 6; Finland: 2 6 Anshan Coking Research Institute, China: 4 7 Italy, Brazil: 5 8 Rodiloki, Finland: 1 Total: 128 2. Dry Quenching Unit at Pudong Gas Plant To support the quenching process of coke ovens that produce 560,000 tons of coke per year, the Pudong Gas Plant introduced a set of dry quenching units with a capacity of 2×70 t/h from the former Soviet Union (Ukraine) in 1984. The core design of these units was carried out by the State Coke Processing Design Institute of the former Soviet Union, while the Anshan Coking Research Institute and the Shanghai Chemical Industry Research Institute were involved in the supplementary design work. The Anshan Coking Research Institute took overall responsibility for the design and construction of these dry quenching units. Construction began in December 1991, and the facility was completed and put into operation in December 1994. The entire set of dry quenching equipment was imported from the former Soviet Union, with wet quenching retained as a backup. 3. Dry quenching of coke at Jigang: To facilitate the quenching of coke produced in quantities of 1.1 million tons per year, Jigang introduced dry quenching equipment with a capacity of 2×70 t/h in 1994 from the former Soviet Union; this equipment was designed jointly by the State Coke Plant Design Institute of the former Soviet Union and Jigang’s own design institute. Regarding the equipment, a combination of partial import and cooperative manufacturing was adopted; the project commenced in 1996 and was completed and put into operation in March 1999. After production began, it was found that Soviet technology was not highly reliable, and it took a long time to reach full capacity. Like the dry quenching unit at the Pudong Gas Plant, this device does not have a high level of automation, and wet quenching is still used as a backup option. 4. Shougang’s dry quenching unit: The first-phase 1×65t/h dry quenching facility at Shougang was built under Japan’s green aid program; the main equipment was supplied by Japan, while the auxiliary equipment was purchased by Shougang itself. The design of this facility was carried out jointly by Nippon Steel and Shougang Design Institute; construction began in 1999, and it came online in January 2001. Since its commissioning, Shougang’s dry quenching unit has operated reliably, with an ideal level of automated control and excellent environmental protection performance. Shougang also retains wet quenching as a backup option. Table 1–2: Status of Dry Quenching Unit Construction in China
Project Details: Baosteel Phase I, Baosteel Phase II, Baosteel Phase III, Jigang Pudong Gas Plant, Shougang, Wugang, Magang
Processing Capacity: 4×75 t/h, 4×75 t/h, 4×75 t/h, 2×70 t/h, 2×70 t/h, 1×65 t/h, 1×140 t/h, 1×125 t/h
Technology Source: Nippon Steel, Nippon Steel, Nippon Steel, Ukraine, Ukraine, Nippon Steel, Nippon Steel, Huatai
Basic Design: Nippon Steel, Nippon Steel, Coking and Refractory Institute, Kharkiv Design Institute, Kharkiv Design Institute, Nippon Steel, Nippon Steel, Huatai
Detailed Design: Nippon Steel Coking and Refractory Institute, Coking and Refractory Institute, Jigang Design Institute; Conversion Design: Coking and Refractory Institute, Conversion Design, Nippon Steel Coking and Refractory Institute, Conversion Design, Huatai
Gas-to-Coal Ratio (m³/t of coal): 1500, 1500, 1500, 2000, 1750, 1500, 1200
Design and Manufacturing of Key Equipment: Elevators – Imported, Imported, Mostly Imported, Purchased; Manufacturing Drawings – Domestic Manufacturing, Imported, Imported, Domestic. Boilers – Imported, Domestic, Joint Domestic and Foreign Design, Domestic Manufacturing; Key Components – Imported, Imported, Imported, Domestic, Domestic. Electric Locomotives – Imported, Imported, Imported, Imported, Imported, Imported, One Domestic, One Domestic. Blowers – Imported, Imported, Imported, Domestic, Imported, Imported, Imported. Loading Devices – Imported, Foreign Design, Detailed Design by Coking and Refractory Institute, Domestic Manufacturing of Key Components, Purchased, Manufacturing Drawings, Domestic Manufacturing, Imported, Imported, Domestic, Domestic. Coke Discharging Devices – Imported, Foreign Design, Detailed Design by Coking and Refractory Institute, Domestic Manufacturing of Key Components, Imported, Imported, Imported, Imported, Imported, Imported. Gas Supply Devices – Designed by Coking and Refractory Institute, Domestic Manufacturing, Designed by Coking and Refractory Institute, Domestic Manufacturing, Imported, Imported, Imported, Domestic, Domestic. Control System for Equipment Level: PLC+DCS, PLC+DCS, Three-Electric Integration, PLC+DCS, PLC+DCS, PLC+DCS, Three-Electric Integration, Three-Electric Integration. Software Development: Foreign, Coking and Refractory Institute, Coking and Refractory Institute, Jigang Design Institute, Foreign, Foreign, Wugang, Huatai. Commissioning Date (Year): 1985, 1991, 1997, 1999, 1994, 2001, 2003, 2004. Investment (100 million yuan): Not calculated separately, Not calculated separately, 4.5, 2.3, 1.0, 2.0, 3. Investment in Wugang’s dry quenching system: Wugang’s No. 7 and No. 8 coke ovens are 2×55-chamber 6m coke ovens, and the design capacity of their dry quenching units is 1×140 t/h. The design of this system was carried out by Japan, with adjustments made by Anshan Coking and Refractory Institute. This project is a digestion and absorption project undertaken by the Economic and Trade Commission; it is currently the dry quenching unit with the largest processing capacity in China. The key equipment for dry quenching of coke was imported from Japan; some of the equipment was designed and supervised by Japanese parties while manufactured by domestic manufacturers. The automatic control system for dry quenching of coke was designed by Wuhan Iron and Steel Group itself. Construction began in October 2002, the facility was completed and put into operation in December 2003, and it reached full capacity by May 2004. The dry quenching of coke in Wugang’s No. 7 and No. 8 coke ovens still retains wet quenching as a backup option. 6. Dry quenching of coke at MaSteel: MaSteel’s No. 5 and No. 6 coke ovens are 2×50-chamber 6m coke ovens, equipped with a dry quenching system with a capacity of 1×125 t/h. This system was constructed under the overall supervision of Anshan Coke and Refractory Research Institute; some of the key equipment was imported from Japan, Germany, and the United States, while the remaining equipment was manufactured domestically. It is the dry quenching system in China that utilizes the most domestically produced equipment. It came online in April 2004, with a wet quenching method also available as a backup. With the continuous improvement of environmental protection regulations and the rising awareness of environmental protection among the general public, it has become essential to develop dry quenching systems for coking. All large steel mills that construct coke ovens with a diameter of over 6 meters must also install corresponding dry quenching systems. (II) Reasons for the difficulty in promoting dry quenching units in the past: It has been nearly 20 years since Baosteel’s first phase introduced Japanese dry quenching units in the 1980s. Yet during this period, dry quenching technology has not been widely adopted in China. The main reasons for this are as follows: 1. The standard specifications were uniform; each enterprise introduced such units according to its own needs, without any organized coordination or integration. This led to repeated introductions, resulting in substantial financial expenditures, yet it failed to address the fundamental issues. As a result, the processing capacity of each dry quenching unit in China remained at a medium level of around 70 t/h or 75 t/h. The uniformity of specifications made it impossible to configure dry quenching units in a way that was economically appropriate based on the production scale of each coking plant. Taking No. 5 and No. 6 coke ovens of Baotou Iron and Steel Company as an example, their production capacity is 1 million tons of dry coke per year, and a dry quenching unit with a capacity of 126 t/h should have been installed. However, due to the limitations imposed by the single processing capacity of existing dry quenching units in China, as well as an inappropriate consideration for thermal standby of the equipment, 3×75 t/h dry quenching units were chosen for design. Their actual processing capacity was nearly 80% higher than what was actually required, resulting in high investment costs and poor efficiency, which led to the failure of the project. 2. The engineering investment was high; in the past, no specialized manufacturing firms were involved in the adaptation of dry quenching equipment, resulting in the failure to localize its production. Equipment such as elevators, circulation fans, motor cars, coking discharge and charging devices, etc., need to be introduced for the construction of a dry quenching system ； Coupled with dry quenching of coke, the control system is complex, requiring the installation of a large number of electrical and automatic control devices, which results in high project costs. 3. Unreasonable energy prices: For a long time, energy prices in China have remained relatively low, which results in limited economic benefits from energy savings in dry quenching of coke, leading to low return on investment and long payback periods. However, at current energy prices, the benefit generated by recovering energy from dry quenching of coke is 10 yuan per ton of coke, which is quite substantial. 4. The additional benefits of dry quenching of coke were not taken into account. In the past, due to internal management issues within steel companies, cost accounting was not carried out rigorously between different stages of production, and the impact of coke quality on the economic efficiency of ironmaking was not evaluated separately. As a result, the improvement in coke quality brought about by dry quenching was not reflected in the economic benefits obtained from ironmaking; this is another reason for the poor economic returns associated with dry quenching projects. In fact, each ton of dry quenched coke brings benefits of about 14 yuan to the ironmaking system. (III) Development trends of dry quenching of coke: With the continuous development of China’s national economy, energy prices have gradually become more reasonable. At the same time, cost accounting and cost-rejection systems are now in use within steel enterprises. Therefore, if the construction costs of dry quenching systems can be effectively reduced, this technology will surely be widely adopted in our country, bringing significant economic and social benefits. As can be seen from the foregoing discussion, the key to reducing the investment in dry quenching of coke is, first, the serialization of dry quenching units to achieve economic rationality in terms of scale. Second is the full localization of dry quenching coke technology and equipment. 1. The serialization of coke dry quenching units makes large-scale deployment economically reasonable. After the coke dry quenching units introduced in Baosteel’s first phase came into operation, China pursued 100% dry quenching in a one-sided manner, meaning that even the backup units for coke dry quenching had to be of this type as well; this resulted in an increase in capital investment, especially as these units became larger in scale, with the increase in investment becoming even more significant. For example, for a coking plant with a capacity of 1 million tons, dry quenching units are required; if 75t/h dry quenching units are used as backup, then 3×75t/h dry quenching units need to be installed, which will increase the capacity by one half ； A 126t/h dry quenching unit will be used as a backup for dry quenching, doubling the capacity. In fact, dry quenching of coke can be fully supplemented by wet quenching, because as new refractory materials for dry quenching are continuously developed, the maintenance intervals for such systems are becoming longer and longer. In Japan, maintenance is carried out every 1.5 to 2.0 years, and each maintenance session lasts only about 20 days; therefore, the necessity of using dry quenching as a backup is diminishing. Economically developed countries such as Japan and Germany have also adopted wet quenching as a backup option when designing dry quenching systems in recent years, in order to reduce capital investment. The Kaiserstuhl coking plant in Germany, which came online at the end of 1992, is the most modern coking plant in the world, as well as one with the highest standards in terms of environmental protection and equipment. It is equipped with the world’s largest dry quenching system with a capacity of 250 t/h; wet quenching is used as a backup method (this method is no longer in use at the plant). Japan, which has the fastest development of dry quenching technology in the world, uses wet quenching as a backup for all dry quenching units built after 1985. The serialization of dry quenching coke units is crucial. With a single scale that does not allow for the creation of a series, it is not possible to reasonably configure dry quenching units based on the different economies of scale associated with coke ovens. Taking a coking plant with a capacity of 1 million tons as another example, if the processing capacity of the dry quenching units is not standardized, only the 75 t/h dry quenching units that were available in China at that time can be used, resulting in a setup of 2×75 t/h dry quenching units. Even if wet quenching is used as a backup option, approximately 20% of the processing capacity will still be wasted. For coking plants with a capacity of 700,000–800,000 tons, a set of 2×75 t/h dry quenching devices is still installed, resulting in a waste of about 60% in processing capacity. Therefore, dry quenching units must be developed in series based on production capacity; the current capacity of 75 t/h is insufficient, and there is a need to move toward larger-scale units. Their processing capacity should at least meet the requirements of coking plants with a capacity of 1.1 million tons, which means developing dry quenching units with a capacity of 140 t/h. It was not until the end of 2003, when the dry quenching systems for Wuhan Iron and Steel Company’s No. 7 and No. 8 coke ovens were put into operation, that China began to have dry quenching units with a capacity ranging from 70 to 140 t/h. Tables 1–3 also reflect the serialization of the configuration of dry quenching units in Japan and the increase in their processing capacity. Table 1–3: Status of Coke Dry Quenching Facilities in Japan
Company Name, Plant Location, Coke Ovens Served, Coke Dry Quenching Capacity (t/h), Year of Commissioning
Nippon Steel: Yawata No. 3, 41×175; 87.2; Muroran No. 5, 61×108; 81.7; Hirotada No. 3, 41×110; 83.11; Nagoya No. 41×129; 82.2; No. 1, 21×106; 85.9; Oita No. 3, 41×180; 85.8; No. 1, 21×190; 88.10
Nippon Steel Chemical: Kunisaki No. 1–3, 33×110; 83.10–84.8; No. 4, 5, 1×170; 88.1
NKK: Keihin No. 1, 5×70; 76.9–12; No. 2, 3×70; 79.7
Fukuyama: No. 4 B.C1, 1×125; 86.4; No. 5, 1×200; 92.4
Kawasaki Steel: Chigyo No. 5–7, 3×56; 77.1; Mizushima No. 3, 4, 2×100; 83.8–9; No. 5, 6, 1×130; 86.1
Sumitomo Metal Industries: Kashima No. 2 C.D1, 1×130; 81.11; No. 2 A.B1, 1×150; 84.1; No. 1 A–D1, 1×195; 86.3
Kansai Thermal Chemistry: Kakogawa No. 1, 2, 1×140; 87.6
Nakayama Iron Works: Funamachi No. 2, 1×60; 93.5

2. Full domestic production of coke dry quenching technology and equipment: In Baosteel’s Phase III project, where a high proportion of the equipment for coke dry quenching is of domestic origin, only some components such as elevators, circulation fans, locomotives, coke discharge devices, as well as electrical and instrumentation components, are imported from abroad. However, this portion accounts for about half of the total investment in equipment. Among these devices, the motor vehicle is a specialized equipment type, characterized by fast startup speed, high traveling speed, and precise alignment requirements ； Currently, there are no available products in China for circulating fans; such fans are required to have good wear resistance and be able to operate continuously and stably at high temperatures ； The elevator is specialized equipment for dry quenching of coke, featuring fast lifting speed, high traveling speed, accurate positioning, and a high degree of automation ； Some components of the coke discharge device had not been used before, so there was uncertainty in choosing domestic equipment. Given the current level of machinery manufacturing in our country, as long as **sufficient human, material, and financial resources are invested, and strong crane manufacturers, fan manufacturers, boiler manufacturers (who will need to further develop their capabilities after the scaling up of coke dry quenching systems), as well as manufacturers of specialized equipment for coke production, are organized effectively, and through the introduction of such technologies followed by adaptation and innovation, it should not be difficult to produce these devices domestically. The construction of the dry quenching systems for Wuhan Iron and Steel Company’s No. 7 and No. 8 coke ovens involved the participation of several capable domestic mechanical and electrical manufacturers; the automatic control system was designed by Wuhan Iron and Steel Company itself. The successful operation of these dry quenching systems has made a significant contribution to the full localization of dry quenching technology and equipment in China. Section 2: Principle of Dry Quenching of Coke Dry quenching of coke is a term used in contrast to wet quenching; it refers to a method of cooling red coke by using inert gases. During the dry quenching process, red coke is fed into the top of the dry quenching furnace. Low-temperature inert gas is blown into the layer of red coke in the cooling section of the furnace by a circulation fan, where it absorbs the sensible heat of the red coke. The cooled coke is then discharged from the bottom of the furnace. The high-temperature inert gas exiting the annular flue of the furnace passes through a dry quenching boiler for heat exchange; this process generates steam. The cooled inert gas is then blown back into the furnace by the circulation fan, allowing it to be reused in a closed system. Dry quenching of coke is superior to wet quenching in terms of energy savings, environmental protection, and improvement of coke quality. I. Characteristics of wet quenching of coke: After coal is converted into coke in the carbonization chamber, it should be removed from there as soon as possible; the temperature of the red coke at the time of removal is approximately 1000°C. To prevent coke from burning and to make it suitable for transportation and storage, it cannot be sent directly to blast furnaces for iron production; the temperature of the red coke must be reduced. One method of quenching coke is to use water spraying to reduce the temperature of the red coke to below 300°C, which is what is commonly referred to as wet coke quenching. The traditional wet quenching system consists of a quenching tower equipped with a water spraying device, a quenching pump room, a quenching water sedimentation tank, and various piping systems; the steam generated during quenching is discharged directly into the atmosphere. The advantages of traditional wet quenching of coke are its relatively simple process, small footprint required for the equipment, lower capital investment, and ease of operation. However, the disadvantages of wet quenching of coke are also very evident. Firstly, wet quenching wastes a large amount of the sensible heat contained in red coke; approximately 3.15–3.36 GJ of energy is required to produce 1 ton of coke, of which 1.49 GJ is wasted due to wet quenching, accounting for about 45% of the total energy consumed ； Secondly, during wet quenching of coke, the rapid cooling of the red coke leads to an increase in cracks in the coke, a decline in its quality, and large fluctuations in its moisture content, which is not conducive to blast furnace iron production ； Thirdly, the steam generated by wet quenching of coke carries corrosive substances such as phenols, cyanides, and sulfides that remain in the coke; these substances erode surrounding objects and cause widespread air pollution. Moreover, as the number of cycles of quenching water increases, this erosion and pollution become more severe ； Fourthly, the steam generated during wet quenching of coke contains a large amount of dust, typically 200–400 g/t of coke, which not only pollutes the environment but also represents a waste. To address the problems associated with wet quenching of coke, coke industry professionals around the world have made relentless efforts to improve the wet quenching equipment and processes. The main improvements in such processes are as follows: (1) Low-water-content coke quenching. A low-water-content coke quenching system consists mainly of process pipelines, water pumps, high-level water tanks, a coke quenching vehicle with precise positioning, and a control system. During the low-moisture coking quenching process, red coke is extinguished by spraying water into the specially designed quenching car at a specific point, using specially designed nozzles and different water pressures. After flowing through the layer of coke solids, the water exits through specially designed grooves or holes; a sufficient water pressure ensures that the water passes rapidly through the coke layer, reaches the bottom plate of the quench car, and flows out of it quickly. When high-pressure water flows through the coke layer, a large amount of steam is generated in a short period of time, instantly filling both the upper and lower parts of the coke layer and suffocating the coke. The low-water quenching process uses low-pressure water during the initial 10–20 seconds of quenching, and high-pressure water during the subsequent 50–80 seconds, to replace the spray-type water distribution used in traditional wet quenching. The quenching water source is provided by a high-level water tank; the quenching water coming out of this tank has its pressure and flow rate automatically controlled by a small PLC that regulates the opening degree of the pneumatic valves. The low-moisture coking quenching process can save 30%–40% of the water used for coking quenching ； It can also reduce and stabilize the moisture content of coke, thereby contributing to the stability of blast furnace operation ； Furthermore, it is also possible to reduce the amount of dust emitted along with steam during the coking process; the dust emission in traditional wet coking is 200–400 g/t of coke, whereas this value can be reduced to around 50 g/t of coke in the case of low-moisture coking. The process flow diagram for low-moisture coking is shown in Figure 1-1.