The main part of the plant was built in 1972, with the original design capacity of 240 Mt\/year, adopting single and double independent jigging main re-washing, coal slurry flotation, tailing coal pressing and filtering joint process, it is a large-scale centralised coking coal beneficiation plant, which is mainly used to wash the coal from Huaibei mining area, and has many types of washed raw coal and big changes in coal quality, and its leading products are Jiushen brand 12-grade metallurgical coke coal and Qinglongshan brand 9-12-grade lean fine coal used in metallurgical coking. In 2012, in order to adapt to the changes in coal quality and market requirements, the company commissioned the Tangshan Guohua Design Institute to carry out a technological transformation, adopting two 1.3 m non-pressurised, three-product, heavy-duty cyclones and the \"2+2\" coal slurry and slurry water treatment process, with a processing capacity of 4.0 Mt\/year. With the fluctuation of the coal market, users are more and more strict on the moisture requirements, especially for coking coal used for coking, high moisture, will extend the coking time, increase the energy consumption of coking as well as reduce the service life of the coke oven, will increase the cost of transport, affecting the efficiency of the enterprise, but also cause environmental pollution along the transport route [1], it must be paid attention to.<\/p>\n
1 Problems of moisture control in refined coal products<\/p>\n
The refined coal of the plant consists of four sub-products, namely, heavy medium refined coal, final refined coal, primary flotation refined coal and secondary flotation refined coal, with the ratio of 0.55\u22360.25\u22360.12\u22360.08. The four sub-products are produced by different equipments, and then uniformly enter into the refined coal belt, which is transferred to the refined coal silo to become the final refined coal product. The moisture fluctuation of any one of the sub-products will affect the moisture of the final refined coal product. In the case of fixed production process and equipment, the moisture of each sub-product depends on the process performance of the equipment. However, when the moisture fluctuates slightly within a production shift during the production process, the equipment is generally not overhauled, adjusted or replaced for the sake of continuous production. In the production process, every hour to do the ash check, but the moisture is not a candidate for \"shipping moisture\" as a guide, back to check the coal quality and equipment, moisture control lags behind. There are a lot of debris in the raw coal, cotton yarn, small pieces of wood and other items clogging the fine coal desorption sieve, centrifuge screen basket, affecting the effect of product dewatering; fine coal slime content in the raw coal is large, the coarse and fine coal centrifuge screen basket sticky slime, the effect of dewatering is poor. There is the phenomenon that the equipment is running and leaking, and there is the phenomenon that foreign water enters into the fine coal products, and at the same time, there is the phenomenon that the workers' sense of responsibility is not strong, and the belt machine and scraper machine bring the water directly into the fine coal products.<\/p>\n
2 Main dewatering equipment and parameters for refined coal products<\/p>\n
The fine coal product handling equipment in the Coal Processing Plant Headquarters includes a coarse fine coal centrifuge dewaterer, fine coal mud centrifuge dewaterer, and fine coal mud settling centrifuge dewaterer,Fine Coal Filter Press<\/a> There are 4 kinds of dewatering equipment, the dewatering requirements, process parameters are different, specific equipment models and technical parameters.<\/p>\n 3 Specific measures to reduce the moisture of refined coal products<\/p>\n 3.1 Enhanced cleaning of equipment<\/p>\n The coal preparation workshop refines the internal market implementation programme, formulates detailed equipment cleaning standards, rewards and penalties to the team, to the individual, and clarifies the acceptance signature process to ensure the effect of equipment cleaning. Enhance the cleaning of de-balling screen grading section during the stopping period to reduce the clogging of screen plate and ensure the normal grading of heavy fine; check the centrifuge screen basket and feel the centrifuge centrifugal liquid to ensure that the screen basket is intact; flush and clean the fine coal settling centrifuge screen basket and filter press cloth to ensure that the centrifuge screen basket, filter press cloth and filtrate nozzle are intact. During the production process, clean the debris on the screen grate every 1 h to ensure that the screen surface is free of debris and the screen holes are not blocked. Every 2 h on the coarse and fine coal centrifuge, arc sieve striker operation (striking interval time adjustment) and arc sieve dewatering effect of the inspection, and make relevant records, and found that the problem is timely reported to deal with. Observe the working condition of the arc sieve in the middle of the shift, and when there are phenomena such as water running away and material piling up on the surface of the sieve, according to the actual situation, take measures such as turning around, cleaning the surface of the sieve and replacing the surface of the sieve, so as to ensure the working effect of the arc sieve.<\/p>\n 3.2 Enhanced maintenance of equipment<\/p>\n The installation and maintenance centre pays attention to the working condition of each dewatering equipment every day, analyses and finds out the reasons from the aspect of equipment when abnormal moisture occurs, and improves the performance of equipment by adjusting, replacing the accessories or transforming the equipment, so as to reach or exceed the dewatering performance of the equipment at the time of leaving the factory, and ensure that the moisture of the product meets the standard.The LLL-type centrifuges are measured once a shift, and the screen slits of the screen basket of the roughness and fineness centrifuges are maintained in the range of 0.35 to 0.4 mm. Replace the sieve basket when the sieve gap exceeds 0.4 mm after wear and tear. The screen basket gap is maintained at 1-3 mm, and once the gap changes, it will be adjusted in time by various methods to ensure the equipment process.<\/p>\n The parameters meet the requirements for coal selection.<\/p>\n The feeding pressure of the sedimentation centrifuge is around 0.3 MPa, if the pressure fluctuates, the feeding equipment will be overhauled immediately, the overflow parts will be replaced, and when the opening rate of the sieve slit decreases, it will be cleaned in coordination with the coal selecting workshop, so as to ensure the performance of the equipment. Filter press head feed pressure is between 0.7 and 0.8 MPa, feed pressure is between 0.5 MPa, and press pressure is around 0.6 MPa. The installation and maintenance centre always pays attention to the moisture of refined coal and the operation of the equipment, and if the pressure fails to meet the requirements, it will find out the reasons for the equipment at the first time, and if it is necessary to change the pump, it will be changed under the arrangement of production scheduling, so as to reduce the moisture of refined coal. Make two-dimensional code for each dewatering equipment and install it in the appropriate position of the equipment. When the chartered personnel of the installation and maintenance centre inspect the equipment, they can scan the code to fill in the basic information of the equipment and the inspection and maintenance records, which will form the equipment history file and the maintenance record file. According to the equipment files, a dynamic maintenance schedule can be formed to remind the team of the maintenance deadline in real time, helping the team to arrange preventive maintenance measures in advance, and improving the planning and reliability of equipment maintenance.<\/p>\n 3.3 Strengthening production process control<\/p>\n There are many factors affecting the product moisture, Huaibei Coal Preparation Plant adopts QC total quality management, systematically analyses the factors affecting the moisture of each sub-product of refined coal, takes targeted measures, strengthens the control of the production process, and reduces the influence of the influencing factors on the sub-products of refined coal. Coal processing workshop coal every 10 min record of raw coal into the wash, to ensure that the supply of raw coal as far as possible uniform and stable, the processing speed control in the range of 310 ~ 330 t \/ h; reasonable adjustment of the vibrating screen de-mediation of circulating water dosage, to maintain a stable level of coarse coal slurry barrels, fine coal slurry drums, to ensure that the head of the arc screen material supply is stable; to maintain flotation into the quality of the concentration of material in the 80 ~ 90 g \/ L, to ensure that the quality concentration of flotation material stable [2]. Maintain the quality concentration of flotation feed at 80~90 g\/L, ensure the flotation feed quality concentration is stable [2]; keep the liquid level of the material in the second flotation drum not less than 200 cm, ensure the feed of the second flotation filter press is sufficient; strictly control the use of anti-foaming water in the concentrate tank of the flotation machine, reduce the viscosity of the flotation foam, and improve the processing effect of the fine coal filter press. Strengthen the raw coal removal in the coal processing workshop to reduce the debris in the system and prevent the debris from clogging the sieve plate and screen mesh; increase the heavy-medium diversion to reduce the amount of coal sludge in the system and reduce the output of flotation coal; check whether the belt machine and scraper are stocked with water before starting the operation; and strictly manage the operation of centrifugal machines and filter presses to prevent the centrifugal liquid, filter press filtrate and other external water from entering the refined coal products. The quality inspection workshop carries out the moisture inspection of the primary flotation and secondary flotation of heavy-medium lump fine coal and coarse fine coal within 1 hour after adding coal in each shift. During the production process, when the moisture of heavy-medium lump coal is more than 5% and the moisture of rough coal is more than 13%, the chemist will report to the dispatching in time, and the dispatching will notify the coal selecting workshop and the safety and maintenance centre to investigate and deal with the problems on the spot, and reduce the moisture as soon as possible; when the moisture of heavy-medium lump coal is more than 6% and the moisture of rough coal is more than 15%, the dispatching will arrange to stop the car to deal with the problem, and only when the problem is solved can it start to add coal to production. Only after the problem is solved can the company start to add coal for production. During the production process, the final product moisture is weighted according to the output and moisture of each sub-product to guide the production control, changing the previous practice of passively controlling the moisture of fine coal products by \"shipping water\". The company has established a big data analysis library of coal production, including the production date of heavy media parameters, washing programme, raw coal information, production process and abnormalities, and analysed and recorded the production situation of the current shift after each shift, so as to provide references for the future production. At the same time, we firmly implement the \"large diversion and water replenishment operation method, and systematically carry out mud removal to reduce the impact of high ash and fine mud on the dewatering process of fine coal products [3].<\/p>\n 3.4 Enhancing technological transformation<\/p>\n