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.

1 Problems of moisture control in refined coal products

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∶0.25∶0.12∶0.08. 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.

2 Main dewatering equipment and parameters for refined coal products

Fine coal product processing equipment of the Coal Processing Plant Headquarters includes 4 kinds of coarse fine coal centrifuge dewatering machines, fine coal mud centrifuge dewatering machines, fine coal mud sedimentation centrifuge dewatering machines and fine coal filter presses, and the dewatering requirements and process parameters of each dewatering equipment are different from each other, and the specific equipment models and technical parameters.

3 Specific measures to reduce the moisture of refined coal products

3.1 Enhanced cleaning of equipment

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.

3.2 Enhanced maintenance of equipment

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.

The parameters meet the requirements for coal selection.

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.

3.3 Strengthening production process control

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].

3.4 Enhancing technological transformation

After thorough investigation and demonstration, the coal preparation plant has implemented targeted technical modifications to further improve the reliability of the equipment and strengthen the foundation of reducing the moisture content of the refined coal products. Replace the coarse and fine coal arc sieve with a high aperture rate sieve plate with a slit of 0.4 mm and a back width of 0.8 mm, increase the coarse cut-off volume of the arc sieve, reduce the flotation feed volume of 20%, and improve the proportion of fine coal sub-products. Increase the arc screen exciter and striker to improve the working effect of the arc screen and reduce the moisture of the centrifuge feed. Compare withFilter Press ManufacturersIn cooperation with the company, we installed edge-feeding type filter press for secondary flotation concentrate dewatering, after the transformation, the press pressure of the filter press was increased from 13 MPa to 20 MPa, and the filtration area was increased from 490 m2 to 550 m2, so as to solve the problem of high moisture of the cake of KZG-type concentrate filter press while increasing the processing capacity. Open holes in the outer wall of the centrifuge, and draw high-pressure wind from the high-pressure air package all the way to the inside of the centrifuge, forming five air outlets facing the screen; install an electromagnetic blowing valve on the air package pipeline, and realise the function of blowing automatically for 30 s immediately after stopping the car through a relay and a time-delay controller, so as to blow off the debris adhering to the screen, and improve the working performance of the centrifuge. The research and development of the "unattended" system in the coal receiving pit realises that the coal feeder automatically allocates and adds coal according to the storage condition in the coal receiving pit, so as to supply coal of uniform quality and quantity to the maximum extent possible, and to reduce the influence of the change of coal quality and quantity on the production system.

3.5 Enhanced experimental analyses

Product quality inspection is the "eyes" of coal preparation plant, and experimental analysis is necessary to promote the "health" of coal preparation production system, which can provide the basis for guiding the production and optimising the production plan. Coal processing workshop, together with quality inspection workshop, carries out experimental comparative analysis of process adjustment, such as whether the materials in three or four rooms of primary flotation enter the secondary flotation machine, whether the materials in one or two rooms of primary flotation are doped with coarse or not, whether the heavy media slurry bucket is replenished with water or not during the large diversion, etc, in order to search for the best control scheme of moisture of refined coal products. The quality inspection workshop carries out "key moisture point" test, strengthens the statistical analysis, weekly, monthly, every ten days statistics of heavy medium, coarse and fine, primary and secondary flotation moisture changes, and guides the operation of dewatering operation of the coal processing workshop with the phased rule. According to the raw coal quality and incoming material quality concentration, particle size, viscosity, optimise the operating parameters of sedimentation centrifuge and filter press to ensure that the product moisture meets the standard. Carry out "comparative" test for dewatering equipment. Follow up the single and double dewatering equipments, compare the moisture, and provide timely feedback. We benchmark the advanced value of similar equipments in the industry, carry out targeted benchmarking management and promotion work, continuously track the dewatering situation after adjusting and maintaining the dewatering equipments, and then optimise and adjust the equipments again, so as to make the equipments reach the best working efficiency. Carry out experiments on parameters such as press pressure and press time of the filter press, and finally conclude that under the conditions of feed pressure of 0.6 MPa, feed time of 420 s, press pressure of 1.0 MPa, press time of 300 s, and side blowing pressure of 0.7 MPa, extending the side blowing time to 900 s can achieve better moisture index of secondary flotation coal products. Carry out experiments on the effect of overflow weir height of sedimentation centrifuge on products, and finally conclude that with the increase of overflow weir height, the diameter of gas-liquid interface decreases, the length of settling zone increases, the separation strength decreases, the average particle size of solid products decreases, the moisture of products increases, and the solids content in filtrate decreases. Reasonable selection of the optimal overflow weir height can reduce the moisture of the primary flotation coal product to a certain extent.

3.6 Strengthening education and training

The coal industry has been transformed from the past kind of rough and labour-intensive to knowledge-based technology, and in order to survive in the wave of reform, the enterprise must educate and train the workers, enhance their sense of belonging to the enterprise and sense of ownership, and consciously think about what the enterprise thinks and urgently need the enterprise's urgency. Carry out staff education and training, explain the importance of moisture index of fine coal, form a good atmosphere that everyone pays attention to the moisture index and participates in the control of the moisture index, and promote the maximisation of the enterprise's benefit. Systematically collate the factors affecting refined coal products, decompose them in a targeted way, and form operation points, so that the workers understand what to do, how to do it, and to what extent to do it; organise the relevant units to carry out the "Reducing the moisture of refined coal products" discussion activities by workshop, team and post, so as to collect ideas and promote the reduction of the moisture of refined coal products. According to on-site practice, carry out the abnormal treatment method of fine coal product moisture.

Summarise, combined with the post operation points, post common problems, post standardized operating procedures, etc. to do a good job in reducing the water content of fine coal products micro-course development, evaluation, hanging on the Internet, convenient for workers to consult and learn; organise knowledge and experience dissemination meetings, increase the strength of the post to pass on the efforts of the technical inheritance, and promote the skills of workers as a whole team to improve. Organize the revision of post operation process, promote work standardization, normalization, institutionalization, scientification; vigorously carry out technical competitions, "master and apprentice" activities, to create a "compare, learn, catch up, help and surpass" a good learning and competitive environment, to create a theoretical, technical and high-quality talent team. High-quality talent team.

3.7 Increased appraisal

Appraisal is the baton of behaviour, Huaibei Coal Preparation Plant clarifies the moisture control index of fine coal products and the moisture control index of fine coal sub-products, and increases the appraisal, so as to make the system become a strong backing to promote the reduction of the moisture of fine coal products. The leading group of the project to reduce the moisture of refined coal was set up to determine the moisture control target according to the current status of the process and the performance of the equipment: the moisture of the shipped refined coal is less than or equal to 9.5%, the moisture of the heavy-medium refined coal is less than or equal to 3.5%, the moisture of the coarse refined coal is less than or equal to 10.0%, the moisture of the primary flotation refined coal is less than or equal to 20.0%, and the moisture of the secondary flotation refined coal is less than or equal to 15.0%. Implementing the "double equal" assessment system, i.e., equal assessment of refined coal moisture and ash content, equal assessment of coal processing workshop, quality inspection workshop and installation and maintenance centre, to promote the coal processing workshop, quality inspection workshop and installation and maintenance centre to strengthen the communication and liaison, and to analyse and find out the reasons from the aspects of coal quality, equipment and operation, so as to make the moisture of refined coal products reach the assessment level and to ensure the quality of coal products meet the requirements. To make the moisture of fine coal products meet the assessment requirements. Scheduling coordinator does a good job in coordinating the work, and makes it clear that all relevant departments will sort out the details of materials needed to reduce the moisture content of refined coal products before the 20th of each month and report the material plan, and the material management department will contact the material branch of the group company to make purchases in a timely manner, track the arrival situation and issue the materials in a timely manner. The quality analysis meeting is held every month, in which the chief engineer of the plant, the relevant functional departments and the main leaders of the coal selecting workshop, quality inspection workshop, installation and maintenance centre and other workshops participate to analyse the coal quality situation, systematically find out the existing problems and improve them, and carry out rewards and punishments according to the completion situation, so as to promote the moisture control to meet the target requirements.

4 Conclusion

Product quality is the cornerstone of enterprise development. As an important indicator of product quality, especially for coking coal products, the moisture of fine coal will affect the coke yield and comprehensive energy consumption of downstream coking enterprises, increase the amount of ineffective transportation, increase the cost of transportation, and pollute the environment around the transportation line. This is contrary to the national carbon peak carbon neutral target and must be taken seriously. Through a series of measures, the headquarter of Huaibei Coal Preparation Plant has reduced the moisture of refined coal products from 10.2% to less than 9.5%, which is a very significant result and provides a useful reference for the control of moisture of refined coal products in the industry.

Sudong or Sodong (name)filter press 18851718517