Design insights on a new type of belt-driven elevator-type dust removal and coking stopper machine

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Design experiences of a new belt-driven car-type dust removal and coke stopper machine ———— Keywords: design, dust removal, environment. Overview: Coke oven machinery is important equipment in coke production, mainly including coal charging cars, coke pushers, coke stoppers, coke quenching cars, locomotives, switchers, and other devices. They operate respectively at the top of the coke oven, on both sides of the machine and coke, and at the bottom layer of the coal tower’s furnace surface platform; their function is to carry out tasks such as coal loading, coke removal, coke quenching, and heating/cooling adjustments of the coke oven. This coke catcher is a 4.3m dust removal coke catcher with a lifting car, designed for the new No. 4 coke oven at Laigang. To improve labor productivity, further enhance the operating environment of coke ovens, and keep up with the trend toward larger-scale coke ovens, there are now demands for mechanization, automation, and a pollution-free environment in coke oven machinery. In particular, as environmental protection standards become stricter, the requirements for pollution-free coke production have become even more stringent. Therefore, taking all relevant factors into account, I designed it as a dust removal and coking stopper machine. In addition to being used, just like traditional quenching machines, to open and close the furnace doors on the coke side and to guide the coke into the quenching car through a coke guide grid during coke pushing, it also enables the dust generated during the coke guiding process to be captured by a dust collection hood. This dust is then directed through smoke guidance devices into the dust collection main pipe and sent to an on-ground dust treatment station for purification, thereby significantly improving the working environment in the production area. The dust removal coke stopper is also equipped with devices for handling the coke at the beginning and end of the process, which reduces the workload on workers and enhances the level of mechanization and automation of the equipment; therefore, this new type of coke stopper represents the trend in the development of coke stopper equipment for blast furnaces in the future. The rationale for setting this goal: China is a major producer of coke. In terms of coke production, there are over 170 coking enterprises across the country, which produce 80 Mt of machine-made coke per year, ranking first in the world. However, at present, the vast majority of coke ovens across the country are operating without any environmental protection measures, causing severe pollution to the environment. In developed countries abroad, coking production has reached a highly advanced level in terms of pollution control; however, it remains subject to strict environmental regulations. As a result, its production scale is decreasing, and there is an increasing reliance on importing coke instead. This has also led to a significant increase in coke production in our country. However, in recent years our country has also been raising environmental protection standards and establishing strict environmental regulations in accordance with the law, in order to ensure bluer skies and greener waters as well as to improve the health of the population. Therefore, addressing coking pollution has become an urgent task for metallurgical enterprises and the coking industry at present. Coke oven production generates large amounts of dust during the processes of coal charging and coke extraction. In particular, the dust produced in the processes of coal charging, coke extraction, and coke quenching during coke production is considered one of the three major sources of pollution in this process. Its main pollutants include solid suspended particles (TSP), benzene-soluble substances (BSO), benzo[a]pyrene (BAP) and other harmful substances that severely pollute the environment and endanger human health. In uncontrolled conditions, the emission level is around 2.37 kg per ton of coal. BAP and BAO are serious carcinogens that are directly related to the incidence of lung cancer; as early as November 1987, Document No. (87) Wei Zi Liu Shi, jointly issued by the Ministry of Health, the Ministry of Labor and Personnel, the Ministry of Finance, and the National Trade Unions, listed lung cancer as an occupational disease among coke oven workers. According to statistics, the average lifespan of workers in coking plants is shorter than the average lifespan in society. There is no doubt that this is related to working in a heavily polluted environment for a long time. In recent years, there have been repeated calls to strengthen environmental protection measures in chemical and coking plants, and some progress has indeed been made in pollution control. Model factories such as Baosteel have also been established in China, but overall, the environmental pollution problem caused by coking remains severe. Over the past few years, large coking enterprises across the country have been actively conducting research and working to address the pollution problems caused by coke ovens. To address the pollution caused by coke pushing in coke production management, various types of dust removal-equipped coke stopping cars have been introduced. In China, there are dust and coking stoppers that use the flap valve interface method based on technology imported from Japan, represented by Baosteel’s coking plant, as well as those that use a belt conveyor system based on technology from the German company Otto, represented by Shougang’s coking plant. Both of these mainstream models can meet the requirements for coke pushing and dust removal effectively. It is possible to achieve no dust leakage at the time of coke discharge, with a dust capture rate of 97%. Current standard: dust emission concentration below 50 mg/m3. The following provides a brief introduction to the working principle of pusher-type dust removal machines for coke removal. The dust removal process for both models is generally as follows: The coke stopper operates on fixed tracks on the coke side of the coke oven; it is used to open the oven door on the coke-side, and during coke pushing, the coke is guided into the coke quenching vehicle by a coke guide grid. As the coke is guided, dust and smoke are captured by dust collection covers and sent through smoke guidance devices into the main dust collection ducts, from where they are sent to the ground-based dust treatment station for purification. The advantages and disadvantages of the coke car for the two dust removal methods are detailed in Part 2 below. The new belt-driven quenching machine I have designed and described consists of several main components. Taking the quenching machine for Laiyang Iron and Steel Plant’s No. 4 coke oven as an example, it mainly includes a door-opening vehicle, a sealed coke guiding vehicle, a dust collection device, a belt-driven lifting vehicle, devices for handling coke at the beginning and end of the process, an electrical control system, and a hydraulic system. The newly built No. 4 coke oven at Laigang is a 4.3m coke oven. The main unit of the quenching machine is designed with a two-stage alignment method. The dust removal device operates on the third rail and is hinged to the coke guide car. When the coke picker discharges coke, the main sources of dust are as follows: 1. Dust that leaks out from the furnace tip when the door is opened. 2. Dust leaking from the furnace head during focus adjustment. 3. The large amount of dust generated when coke falls from the coke guide grid onto the coke quenching vehicle during coke guiding. Among them, the dust generated when it falls from the focus guide grid onto the quenching vehicle is the greatest, with a dust concentration of generally 7–9 g/m3. For these aspects, I took into account the following dust removal device configurations and design calculations in my design. I. Determination of the dust collection hood’s shape: Since this coke oven uses a low-moisture coke quenching method, the length of its coke quenching vehicle is 7.2 m. Based on the dimensions of the coke quenching car, the upper dimensions of the dust removal hood are determined to be length × width = 7.2m × 4.2m. To ensure effective dust removal, the lower dimension of the dust collection hood is designed to be 7.6m × 4.45m, allowing it to fully cover the cross-sectional area of the coke quenching vehicle; a gap of approximately 200 mm is left above the upper edge of the vehicle’s cross-section (see Figure 1 for details). The temperature of the flue gas generated during coke receiving can reach around 1000°C. It may cause damage to the dust removal system. Based on the empirical data from several design attempts and on-site adjustments, it has been proven that maintaining a gap of 200 mm between the lower edge of the dust collection hood and the upper edge of the coke quenching car carriage is the most suitable approach. It ensures that dust does not escape during coke extraction, while also allowing some cold air to be drawn in in order to lower the temperature of the flue gas. II. Determination of flue gas exhaust systems At present, there are mainly two types of flue gas exhaust systems used in China: one is the interface flap valve type adopted by Baosteel, and the other is the belt conveyor type that makes use of technology from the German company Otto, as used by Shougang. Since the 4.3m quenching machine features secondary alignment, if flap valves are used, the dust generated at the furnace head when the door is opened cannot be collected. This is the drawback of the flap valve-type dust removal coke stopper. By using a belt conveyor, the exhaust gas can be led outside, enabling continuous connection with the dust removal main duct. All the dust generated when opening the door can be collected, drawn into a large dust collection hood, and then fed into the main dust removal pipeline. From the perspective of quench box operation, the use of a belt-driven lifting trolley functions as a movable interface. It also has advantages such as easy maintenance and good dust removal performance. Therefore, the belt conveyor system is the best solution for the dust and smoke removal device at Laiwu Iron and Steel Plant. III. Improved design of the dust removal hood at the furnace head near the focus guide grid. During coke extraction, some dust remains at the junction between the top of the focus guide grid and the furnace door frame; relying solely on the seal between the focus guide grid and the furnace door frame is far from sufficient to prevent this dust from escaping. Many attempts have been made to solve this problem. During the dust removal renovation of the coke stopper machines in the 4.3m coke ovens at Beijing Coking Plant, a small smoke hood fixed to the head of the coke guide grid structure was used, along with an axial flow fan with a power of 4KW and an air volume of 22,500 m3/h; this approach resulted in a significant improvement in the removal of dust from the furnace area compared to before. However, since the small smoke hood is fixed to the quenching machine and operates together with it, it must maintain a certain safety distance from the furnace frame. Still, a small amount of smoke and dust leaks out from here. To further improve the dust removal efficiency, significant modifications were made to the previous small smoke hood this time. In addition to using the existing fans, the original fixed small smoke hood has been replaced with one fixed smoke hood and one telescopic smoke hood that can move together with the flame guide grid inside the fixed smoke hood. In this way, when guiding the coke, as the coke guide grid moves toward the furnace door frame, it also pulls the movable smoke hood along with it toward the furnace door frame, thereby reducing the distance between it and the furnace door. Coupled with the smoke baffle installed at the upper part of the coke oven, this approach effectively solves the problem of dust leakage from the furnace head during coke guidance. IV. Design and calculation of the driving transmission mechanism: The new type of dust removal coke stopper machine incorporates a belt lift vehicle, which results in a larger and wider overall structure; its weight amounts to 100 tons. Therefore, the driving mechanism needs to have increased power, and considering changing from one machine to drive it to three machines for driving. Since one frequency converter is used to drive three motors, it is necessary to ensure even power distribution in order for operation to be smooth, thereby preventing any situation where one motor becomes overloaded while another has insufficient output. Therefore, it is necessary to conduct design calculations for the transmission mechanism, which is key to ensuring the proper operation of the new dust removal and coke stopper machine (a schematic diagram of the transmission mechanism is shown in Figure 2). The design weight of the quenching machine is 100,000 Kg, with a traveling speed of 6~60 m/min. Reducer model XBY200-25-5T. Wheel diameter φ600mm. It is planned to use three 15KW motors for driving, with the motor model being YZR200L-8. Operating resistance P_static = P_friction + P_slope + P_wind. 1. P_friction = k – rolling friction coefficient, where k = 0.08; u – bearing friction coefficient, where u = 0.015; d – inner diameter of the bearing, which is 10 cm; D – diameter of the wheel, which is 60 cm. 2. P_slope = k_slope × G, where G = 0.001 × 100000 = 100 Kg. k_slope – the slope coefficient, 0.01. 3. P_wind = Cq × F_wind = 1.4 × 15 × 80 = 1680 Kg. C – coefficient related to wind as a carrier; q – standard wind pressure of 15 Kg/cm2. F_wind – wind-facing area of 80 m2. 4. P_static = P_friction + P_slope + P_wind = 775 + 100 + 1688 = 2555 Kg. N_static = N = K_electric × N_static = 1.3 × 9.39 = 12.2 KW. n – Mechanical transmission efficiency: 0.8; m – Number of motors. Under normal operating conditions, the output power of each motor does not exceed 12.2 KW. Considering that the motors have a certain overload capacity, the quenching machine can also be pulled away from its working position when one of the motors fails. V. Design Insights Over the years, I have designed multiple dust removal and coke catching devices, including those for the 4.3m coke ovens at Beijing Coking Plant, the 4.3m coke ovens at Anyang Iron and Steel Plant, the 4# and 5# 4.3m coke ovens at Shougang Coking Plant, the 4.3m coke ovens at Laigang Coking Plant, and the 5.5m coke oven at Tangsteel Coking Plant. Through the design of quenching machines for several projects, particularly the improved design of the new 4.3m belt-conveyor type quenching machine used at Laigang, China has reached an advanced level in terms of solving the problems related to coke discharge and dust removal. Projects such as the renovation of the coke dust removal and coke catching machines at Beijing Coking Plant, the dust removal renovation of such machines at Shougang’s No. 4 and No. 5 coke ovens, and the design of a new type of dust removal and coke catching machine for Laigang’s No. 4 coke oven have all achieved the expected results. The first two of these projects have passed the inspection by Beijing’s environmental protection authorities. The new dust removal and coke stopping machine for Laiyuan Iron and Steel’s No. 4 coke oven has now passed the company-level acceptance. Through the design of dust removal coke stoppers for several completed projects and observations of their on-site operation, I have drawn the following conclusions regarding such dust removal coke stoppers: 1. For coke stoppers that require multiple alignments, I believe it is best to use a smoke guiding device of the belt elevator type. This enables continuous dust removal, allowing the smoke dust from the door-mounted burners as well as that from the burner areas at the coke guide grids to be collected. The smoke guidance device functions as a moving interface that operates simultaneously with the quenching machine. Thus, it does not add driver operation steps, saving operational time. Low operating costs and low failure rate. The disadvantage is that when the levelness of the track on the dust removal main pipe is not high, the belt tends to deviate from its path. But effective solutions have now been found. For disposable alignment coke stoppers, both solutions can meet the process requirements, but the operating cost of the belt cart is lower. 2. The design of the smoke hood that moves at the top of the focus guide grid should take full account of the dimensions of the struts and gaskets in the coke oven structure; otherwise, interference may occur. Additionally, the design of the movable smoke hood is also constrained by the coke oven safety guide rails and slide rail supports. The above aspects should be designed in conjunction with the coke oven process, allowing the flue hood to be made as large as possible. 3. The sealing between the focusing grid and the dust removal cover needs further improvement. A high-temperature resistant labyrinth design is proposed to be used. References: Li Zhehao, *New Technologies in Coking*, Metallurgical Industry Press; Yao Zhaozhang, *Coking Science*, Metallurgical Industry Press; Hong Zhiyu and Lin Liangming, *Continuous Conveyors*, Machinery Industry Press; Liu Yuncai, *Ironmaking Processes and Energy-Saving Technologies*, China Metal Society; Anshan Coking and Refractory Research Institute, *Introduction to General Design for Small and Medium-Sized Coking Plants*, Metallurgical Industry Press; Wuhan Iron and Steel Institute, *Questions and Answers on Coking Production*, Metallurgical Industry Press; Anshan Coking and Refractory Research Institute, *Fuel and Chemical Engineering*. Last edited by ryn on 2009-2-16 10:14