The application of new technologies and equipment in coal preparation design

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The Application of New Technologies and Equipment in Coal Preparation Design Qian Liye, Cai Chengyou (Anshan Jiaonai Design and Research Institute) Since the 1990s, in order to meet the requirements for coke quality imposed by the larger scale of blast furnaces and to improve the mechanization and automation levels in large-scale coking plants, Anshan Jiaonai Design and Research Institute has worked closely with relevant construction and manufacturing units in the design of coal preparation systems for large and medium-sized coking projects. By actively developing and applying new technologies and equipment, the institute has achieved satisfactory results. 1. Reverse “C”-type dump car unloading line: The reverse “C”-type dump car unloading line was used for the first time in the engineering design for the renovation of the coal yard at Shijiazhuang Coking Plant; the factory design for this equipment was completed in 1992. After more than a year of construction, installation, and commissioning, it was officially put into use in May 1993. Over the past few years, the production has operated normally and stably, meeting the design requirements. The Sifang Vehicle Research Institute of the Ministry of Railways conducted on-site tests to evaluate the compatibility between the unloading line of the \"C\" type car dumper at the Shijiazhuang Coking Plant and the vehicles. The various indicators indicate that the car dumper performs well, starts and returns to its position smoothly, and causes little damage to the vehicles. Thanks to the advanced technology of first pressing, then clamping the vehicle, and finally turning it over, the rate of damage to the vehicles has been significantly reduced. It leads among the nearly 200 tipplers currently in use across the country, and represents the future direction for the development of tipplers. 1. 1 Main equipment and process layout of the unloading line. The main equipment includes a car shifter, a \"C\"-type dump car, a car transfer platform, a car pusher, and a check valve. The process layout is shown in Figure 1. Figure 1: Plan view of the unloading line for the fold-back “C”-type car dumper. 1.2 Unloading line operation procedure: For ease of description, the vehicles on the unloading line are first numbered; the empty vehicle that was parked on the car dumper during the previous cycle is assigned number 1 ； The truck that is to be unloaded is Truck No. 2 ； The loaded car coupled to Car 2 is Car 3. “The operation procedure for one cycle of the unloading line using a C-type car dumper is as follows: (1) When the boom of the car shifter lowers, it retracts, and then the train is coupled to Car No. 2 to pull the heavy train forward at a slow speed ； When the coupling between Car 2 and Car 3 is at the uncoupling point in front of the dumper cab, the shunter stops moving forward. (2) After the operator disconnects the hook between Car 2 and Car 3, the boom of the car mover pulls Car 2 onto the tipping platform; once it is in position, the hook is automatically disconnected from Car 2. (3) The boom of the car shifter pushes vehicle No. 1 onto the transfer platform and positions it there; then the boom is raised, and the car shifter returns to its original position at high speed, while the tipper simultaneously unloads vehicle No. 2 before returning as well. (4) The transfer platform sends the empty vehicle No. 1 to the empty vehicle lane for alignment ； The cart pusher pushes the empty cart No. 1 outside the check valve on the empty cart track ； The vehicle transfer platform returns to its original position. With this, one cycle is completed and the next working cycle begins; this process repeats until an entire train has been unloaded. 1. Characteristics of the 3-unloading line: (1) Vehicles are moved using a car handler and positioned at once to enable automatic unloading. The traditional process used in old tipplers, which involved using a hook removal platform or pusher to automatically guide the vehicles into the tipper, has been eliminated; this prevents impact on the vehicles and the equipment itself, and allows for direct control over the operation process. (2) The tipper uses a fixed platform, hydraulic mechanisms for bringing the vehicle into position and holding it in place, ensuring that there is no relative movement of the vehicle during the tipping process. This replaces the mechanical holding mechanisms and moving support systems used in traditional tippers, thereby minimizing damage to the vehicle. (3) The vehicle pressing mechanism is equipped with a unloading device, which eliminates the pressure exerted on the vehicle’s upper beam due to the extension of the vehicle’s bogie springs after unloading, thereby effectively protecting the vehicle. (4) Using a trolley machine to push empty cars out of the car transfer platform and into the empty car line is smoother and more reliable than operating the traditional empty car iron ox system. (5) The unloading line is controlled by PC, enabling fully automatic operation. It also features manual and local operation, along with a complete set of necessary interlock safety systems. 2 New Types of Crushers 2.1 Current Status of Crushing Equipment At present, most coking plants in China use reversible hammer crushers or impact crushers to crush coking coal; the degree of crushing fineness (＜ 3mm) is generally between 75% and 77%. A reversible hammer crusher is mainly composed of components such as a rotor, hammer heads, grates, adjustment devices, and a housing. The product fineness can be controlled by using an adjustment device to modify the distance between the grating and the hammers. Its main drawback is rapid wear of the hammer head and frequent replacement; when the moisture content of the coal is high, the grating tends to get clogged, resulting in a significant drop in output. A counterattack crusher consists of a rotor, hammers (sledge hammers), impact plates, and a housing. Product fineness is controlled by adjusting the distance between the counterplate and the hammers. The main drawback is that the hammer head is disposable and requires high consumption ； Poor adaptability to material moisture levels ； Due to its structure, the equipment has a high exhaust volume, resulting in significant dust dispersion during operation. In recent years, due to the high content of slime and high moisture level in refined coal, crushers tend to get clogged. If cleaning is not carried out promptly, both production capacity and the fineness of the material will decline significantly. Considering the status of coking coal resources in our country, the reserves of high-quality coking coal and fat coal are gradually decreasing, leading to an increasingly tight supply. Bituminous coal, on the other hand, is abundant in reserves and has lower levels of ash and sulfur. To make rational use of coal resources, the proportion of bituminous coal in coking coal blends will gradually increase. In recent years, the technology of ramming coking has developed rapidly; ramming coking requires coal particles to be finer, generally with over 90% at that size. The above two types of crushers are difficult to meet the needs of the development of new coking processes. To this end, we have newly designed a new type of reversible hammer crusher with a counterplate. 2.2 Structural features and performance of the new type of crusher The new type of crusher consists of a rotor, large hammer heads, impact plates, a housing, and a hydraulic opening mechanism. The main features are a small rotor and a large hammer head, providing strong striking power ； Large, uneven counter-impact plates have been added on both sides of the rotor; under the combined action of the high-speed rotating hammers and these counter-impact plates, the material is crushed instantly, thereby improving the degree of pulverization ； The grating under the old-style crusher has been removed, which improves the machine’s adaptability to varying moisture levels in the material and ensures smooth discharge, thereby preventing over-grinding of the material ； The hydraulic box-opening system facilitates equipment maintenance and hammer head replacement, **reducing the labor intensity. At present, the new type of crushers comes in the following series: Model, Processing capacity, t/h – FCK1825: 400; FCK1616: 200–250; FCK1110: 100. 2.3 Use of the new type of crushers: The FCK1825 model (400 t/h) of these new crushers has been used in the second phase of the Panzhihua Iron and Steel Company’s coking plant. Several years of operational experience have shown that it boasts excellent performance, with the grinding fineness of coking coal reaching 80%, which is 4% higher than that achieved in the first phase. The calibration results of the coke quality from the Panzhihua Iron and Steel Company’s coking plant for phases I and II show that, after accounting for other influencing factors, an increase of 4% in the fineness of the coal used in phase II led to a 3.4% rise in the M40 value of the coke, which satisfied the customers greatly. The FCK1616 type crusher has been used in the coal preparation renovation at Jiugang Coking Plant, and the equipment is currently under production. 3 Coking process of blended coal Blended coal coking is an effective way to make more use of weakly caking coals and improve the quality of coke. The first phase of Baosteel’s coking project adopted a coal blending coking process (with a complete set of equipment imported from Japan), achieving the goal of improving coke quality. Baosteel’s Phase III coking project still uses the coal blending process for coking. To further improve this technology, we conducted on-site calibration of the production equipment for type coal of Phase I, as well as necessary experimental research. On this basis, new foreign technologies and processes for coking with blended coals were incorporated, completing the schematic design for the third-phase blended coal coking process. When compared in the same period, the three-stage briquette system has seen significant improvements: it features a simpler process flow, fewer pieces of equipment, less floor space required, and lower investment costs. Apart from key equipment such as horizontal mixers and molding machines, which still need to be imported from Japan, all other equipment is designed by the Anshan Coking and Refractories Research Institute. The plant design was fully completed in August 1996. 3. 1 Problems existing in the briquette production plant (1) The process flow of Baosteel’s first-phase briquette production plant is complex, it involves numerous pieces of equipment, and it requires high levels of investment and energy consumption. To improve the strength of the briquettes, the first-phase plant was equipped with a large cooling system consisting of 8 mesh conveyors and 2 exhaust fans, each with a power output of 550 kW. There is also a 220kW dust removal device on the finished product tank. The equipment for the cooling system and the finished product tank weighs 1,725 tons, with an installed capacity of 1,400 kW. There is also a powder return system with long hold times. (2) The briquette crushing rate is high. Due to the separate transportation and storage of briquettes, they suffer severe fragmentation during transport. The on-site calibration results show that 55% of the crushed coal below the coal tower is less than 10 mm in size ； The proportion of coal that has been re-ground into powder with a particle size of <3 mm reached 36.5%. It reduced the effectiveness of coking with blended coal. (3) High equipment failure rate. Mesh conveyors have the highest failure rate, and they are very difficult to maintain. Briquettes often get clogged while stored in the finished product tank, making discharge quite difficult. Currently, the finished product troughs basically hold no material and are used only as chutes. Due to the large height difference, the briquettes break more severely. The return tank of the powder return system also often gets clogged, leading to frequent accidents that disrupt normal production. 3.2 The process and equipment for briquetting at Baosteel’s Phase III plant (1) The briquetting process at Baosteel’s Phase III plant utilizes a simultaneous (mixed) conveying system. The hot briquettes coming out of the forming machine fall directly onto the pulverized coal, and are then conveyed synchronously to the coal tower via a belt conveyor. Cold pulverized coal can both cool briquettes and protect them, thereby reducing their breakage rate. It is expected that the briquette fragmentation rate below 10 mm at the coal tower can be reduced from 55% in Phase 1 to 40%. (2) The cooling device for briquettes, the finished product tank, and the powder return system were removed, which greatly simplified the process flow. This not only reduced the number of equipment units and the floor space required, but also lowered the project investment and operating costs, with a significant reduction in failure rates as well. (3) Replacing the original mixer and vertical kneader with a \"2-in-1\" horizontal kneader simplifies the structure of the processing plant, enables flexible start-up and shutdown, and creates favorable conditions for synchronized conveying. (4) To prevent segregation in the coal tower feed when synchronously conveying briquetted coal, a segregation prevention device was installed at the feed inlet of the coal tower. Meanwhile, the operating sequence of the coal tower distribution equipment was changed from fixed-point distribution to alternating distribution from two points, which helps to avoid segregation of the briquetted coal within the coal tower. (5) Technical and economic comparison of the two briquette production processes. The technical and economic comparison of transporting briquettes separately and transporting them in mix is shown in Table 1. Table 1: Technical and economic comparison of two coal briquette production processes at Baosteel
| Item | Separate transportation (Phase I) | Mixed transportation (Phase III) | Effects of the new process |
|------|--------------------------------|----------------------------------|--------------------------|
| Land area, m² | 150×200=30,000 | 150×100=15,000 | 50% reduction |
| Equipment weight, t | 3,150 | 1,250 | 60% reduction |
| Estimated investment, 100 million yuan | 2.1 (of which 11.5 million in USD) | 1.3 (of which 8 million in USD) | 38% reduction |
| Electricity consumption, 100 million kWh/year | 6.15 | 2.87 | 60% savings |
| Performance (size of crushed coal briquettes below 10 mm under the coal tower) | 55 | 40 | 4 |
| Coal humidification technology | The coal humidification project at Chongqing Iron and Steel’s coking plant is an energy-saving project funded by Japan; Nippon Steel provided the main equipment and technology, while Anshan Coking and Refractory Research Institute was responsible for the plant design. | | | The moisture control (CMC) device uses heat transfer oil YD-325 as the heat carrier; by recovering the sensible heat from the exhaust gases in the rising pipe and flue, it dries the coal loaded into the furnace, reducing the coal’s moisture content from 10.5% to about 6%. The reduction in the moisture content of the coal used in the furnace increases the production capacity of the coke oven, reduces the heat required for coking, improves the quality of coke, and ensures continuous and stable operation of the coke oven. The coal humidifying device mainly consists of a coal feeding system and a heat transfer oil system. The dried coal for charging is supplied for use in coke ovens No. 3, 4, and 5. Its main process technical parameters are as follows: Coal processing capacity 140 t/h (dry). Coal temperature at the dryer inlet: 20°C. Average moisture content of coal at the dryer inlet: 10.5% (maximum 11%). Coal temperature at the dryer outlet: 80°C. Moisture content of coal at the dryer outlet: 6.5%. Moisture content of coal ready for use in boilers: 6%. 4.1 Dryer The dryer is a key device in the coal humidity control system; it is supplied by Nippon Steel. Its dimensions are Φ3600 × 22000 mm, and it has a long cylindrical structure. It is equipped with fixed heating tubes with diameters of DN65, 80, 90, 100, and 125 mm respectively. The heat transfer oil absorbs heat through the circulation system, reaching a temperature of 210°C. It then enters the heating tubes of the dryer via the rotating interface; after indirect heat exchange with the wet coal, its temperature drops to 107°C. It exits the dryer through the rotating interface and returns to the heat transfer oil circulation system. The dryer housing is rotated by an inverter-driven motor. The wet coal (with a moisture content of 10%–11%) fed in through the quantitative feeding device in the wet coal tank rotates together with the housing inside the dryer; after undergoing indirect heat exchange with the hot oil in the heating tubes, it is discharged from the outlet. By adjusting parameters such as the dryer’s speed, coal feed rate, and the residence time of the material inside the drum, it is ensured that the moisture content of the dried coal remains at around 6.5%. 4.2 Coal Feeding System The original coal preparation workshop at Chonggang Coking Plant (for coal reception, storage, blending, and crushing) was designed to supply coal to the four coke ovens numbered 1 to 4. To support the construction of the new No. 5 coke oven and coal humidification unit, a new coal feeding system has been connected from the third raw coal transfer station. The dryer used for humidifying coal in the new coal supply system operates continuously for 24 hours; it supplies dried coal to furnaces No. 3, 4, and 5, with a processing capacity of 140 t/h (dry). To coordinate the operation of the coke ovens between the old and new systems, a new buffer wet coal tank with a capacity of 650 tons was built for the new coal feeding system. A disc feeder below the trough supplies coal to the dryer in a controlled amount; the dried coal is then conveyed to the new coal tower via screw conveyors and belt conveyors. When the drying system experiences an accident or is under maintenance, wet coal can also be directly fed into the new coal tower. 4.3 Heat transfer oil system: The heat transfer oil system consists of an oil storage tank, a high-level tank, a heat transfer oil circulation pump, a heat transfer oil heater, a heat transfer oil cooler, a flue gas heat exchanger, a rising pipe heat exchanger, heating tubes inside the dryer, and the corresponding piping. The circulation rate of the heat transfer oil is 147 t/h, and the system is controlled by a PC. Under normal operation of the dryer, the heat transfer oil circulation system is as follows: flue gas exchanger → rising pipe exchanger → circulation pump → heat transfer oil heater → dryer → flue gas exchanger. The heat transfer oil circulation system in the dryer’s accident mode is: flue gas exchanger → rising pipe exchanger → circulation pump → heat transfer oil cooler → flue gas exchanger. 4.4 Economic benefits and investment estimates: An increase of 7.7% in coke production; a reduction of 326 MJ/t of coal in the heat required for coking; a decrease of 6.3 t/h in the amount of phenol wastewater generated; a 10% increased use of weakly bindable coal; an improvement of 1% in coke quality (M40). The total investment amounts to 57.5968 million yuan, of which 19 million yuan is for domestic equipment. 5. Wet method for producing coke powder: In the ramming coking process, since a large amount of bituminous coal is used, it is necessary to add an appropriate amount of thinning agents (such as coke powder or low-bonding coal) in order to reduce the volatility of the coking coal, minimize cracks in the coke, and improve the size of the coke pieces. According to relevant information, adding an appropriate amount of fine coke powder can significantly improve the quality of coke, as shown in Table 2. The fineness of coke powder also has a significant impact on the mixing effect, as shown in Table 3. Generally, the fineness of coke powder is preferably between 0.2 and 0.5 mm. The second phase of Qingdao Gas Company’s project utilizes the ramming coking process. The coal blending scheme recommended in the coal blending test report for this project calls for 73%–83% bituminous coal to be used, with 7% fine coke powder (with a particle size of <0.2 mm) to be added as well. To support the design of the Qingdao gas project, we carried out experimental research and scheme design for coke powder preparation. Table 2 Improvement in coke quality after adding thinning agents (%). Coal blending ratio, Serial number: Nantun QM, Tangcun QM, Taozhuang QF, Shanjialin FM, Bucun SM. Coke dust: 150, 101, 520; –5260, –1030, –; 350, 1010, 2010, –. Coal quality: Serial number, Vr, %; Y, mmb, %; Rogowski index; Free expansion order; Fineness, % (<3 mm): 135.8, 414.0, –15685.5, 79.892; 36.97, 17.0, –14.5706.0, 77.393; 36.09, 15.0, –16675.5, 77.48. Coke quality: Serial number, M40, M10, >25 mm; Metallurgical coke rate, Coking rate: 169.7, 10.587.26, 8.452; 60.21, 1.686.16, 7.703; 61.51, 1.186.66, 8.34. Table 3 Effect of coke dust fineness on blending efficiency (%). Serial number, Coal blending ratio, Coke quality: Guanqiao QF, Zaozhuang FM, Fengcheng JS: <0.15 mm coke dust, <1 mm coke dust, M40, M10, >25 mm, >40 mm: 1, 4525, 15 –1582.3, 10.39, 5.79, 5.02; 4525, 1515 –85.5, 10.59, 6.59, 5.23; 4515, 25 –1581.0, 15.39, 6.59, 4.74; 4515, 2515 –84.5, 10.89, 6.19, 4.5. 5.1 Current status of coke dust production at home and abroad. Currently, the dry method is widely used for producing coke dust both domestically and internationally. The process flow is shown in Figure 2. The main equipment includes a combustion furnace, dryer, ball mill, and a large dust removal system. The dry powder production process is well-developed, and it does not increase the moisture content of the coal fed into the furnace after recombination. The main disadvantages are the complex process flow and dust removal system, high energy consumption, severe dust pollution during the powder production process and recombination, which makes it difficult to implement on a wider scale. Figure 3 Flowchart of the wet method for producing coke powder. 5.2 Development and application of the wet method for producing coke powder. In order to simplify the process flow, reduce energy consumption, and improve the operating environment, during the design of the Qingdao gas project, we conducted comparisons among various options and, by drawing on the wet grinding processes used in the mining industry, successfully developed the “wet method for producing coke powder” technology. Since there is no existing technical literature on the wet method for producing coke powder, the process design parameters and the selection of key equipment must be determined through semi-industrial tests. From March to July 1993, we conducted semi-industrial tests on the wet grinding of coke powder and the dehydration of coke powder slurry in collaboration with the Shenzhong Mineral Processing Machinery Research Institute and Kunshan Chemical Machinery Factory. The test results show that the ball mill operates at its best when the slurry concentration is between 40% and 50%, with 85% of the coke powder having a fineness of <0.2 mm ； ＜0.5mm reaches 90%–95% ； Coke dust has good hydrophobic properties; by using a belt vacuum filter to process the coke dust slurry, the moisture content can be reduced to 15%–17%, which fully meets the requirements of coke production. Based on the test results and the actual conditions of the Qingdao project, the parameters for the wet process of producing coke powder as well as the selection of key equipment were determined, and the plant design was completed. Its process flow is shown in Figure 3. The main equipment includes ball mills, belt filters, circulation pumps, and a coke powder recycling system. The coke powder in the raw material tank (<10 mm) is fed into the ball mill by a dosing device, and an appropriate amount of water is added to keep the slurry concentration at 40%–50%. After mixed grinding, the slurry discharged from the ball mill outlet is sent to a belt vacuum filter for dewatering. After dehydration, the moisture content of the coke powder is reduced to 15%–17%. It is then conveyed by a belt conveyor to the product storage area for storage. The coke dust in the product shed is mixed back into the coking coal mixture using a recombination device. The main advantage of this powder-making method is that the production process takes place entirely in a wet state, eliminating dust pollution; it eliminates the need for heating, drying, and dust removal systems, resulting in a simple manufacturing process. Wet grinding wastewater can be reused, with no sewage discharged, thus protecting the environment and saving energy. 5.3 Application Prospects (1) In conventional coke ovens, adding an appropriate amount of fine coke powder to the coal feed to replace part of the lean coal can improve the quality of the coke. (2) Coking plants that produce coking coke also need to add a certain amount of fine coke powder in order to improve the size of the coke pieces. (3) In recent years, in some urban gas plants, powder coke with a particle size of <10mm has faced poor sales, severe inventory buildup, and environmental pollution. If these coked powders are ground into fine powder and reintroduced into the coking coal mixture for coke production, it not only solves the issue of market sales and protects the environment, but also saves a large amount of low-quality coal, resulting in significant economic benefits; some factories have already put this approach into practice. (200806301)