Coal slurry dewatering for coal preparation plant, permeated in all aspects, which filter press in the process link, is the most important coal slurry dewatering equipment, it will be solid-liquid thorough separation, after separation of filtrate can be recycled again, fast-open typediaphragm filter pressFurther dewatering by diaphragm pressing effectively reduces the moisture of the filter cake.

?Structure and working principle of filter press

Quick-opening diaphragm filter pressesIn terms of its structure, it consists of five parts: filter press plate, hydraulic system, filter press frame, filter plate transfer system and electrical system, and belongs to one kind of separation equipment. As shown in Figure 1, the working principle diagram of the quick-opening filter press is the process of converting coal slurry into filter cake. When the equipment is in operation, the piston rod on the cylinder body pushes the press plate to press the diaphragm plate, the filter plate, and the filter cloth, which are located between the press plate and the thrust plate, so as to ensure that the filter slurry with pressure is filtered under pressure inside the chamber[1] . At the beginning of filtration, the slurry is driven by the feed pump and enters the filter chamber through the inlet of the thrust plate. The slurry is separated from the solids by the pressure generated by the feed pump, and the solids are retained in the filter chamber to form a cake due to the action of the filtering medium (filter cloth), while the filtrate is discharged through the drain valve. This process is the initial dewatering of the filter press, and the second stage of dewatering will be initiated with the end of the feeding process. The second stage of dewatering is to fill the diaphragm with compressed air from an air compressor. The deformation of the diaphragm creates a two-dimensional pressure that destroys the arches formed between the particles, and squeezes out the filtrate that remains in the interstices between the particles. The compressed air often has a high pressure, resulting in a strong air flow will bring out the capillary water in the filter cake, so as to ensure that the moisture content of the filter cake is reduced to a minimum. As a new type of filter press, the degree of automation is high, and the system has a high degree of automation in the process of unloading. When the filter plate is pulled open, it is combined with the chain drive, so that several filter plates are pulled open at the same time, and the closing is automatic at the same time, and it adopts the hydraulic cylinder drive. This design makes the unloading speed fast and timely, ensures the compactness of the press, avoids the shaking of the filter plate during the unloading process, and greatly improves the working efficiency and quality of work.

Filter Press Dewatering Process

Filter press dewatering process, as an important stage of coal processing plant production, changes the traditional slurry pump feeding method, introduces the air compressor into the system, and uses compressed air as feeding method. The action process is achieved by the automatic control system, the use of compressed air as the power source of feeding, saving the feeding time, through the filter press will be obtained by the recycled water reuse process optimisation study In the actual operation of the enterprise, due to the impact of the equipment or technical process, there are deficiencies in the dewatering process of the filter press, according to the operating parameters of the equipment, you can further improve the dewatering effect of the filter press. According to the operating parameters of the equipment, the dewatering effect of the filter press can be further improved. Specifically, in combination with the dewatering process of the filter press, the following technical modifications can be carried out.

Changing the method and frequency of feeding

The filter press is designed for a single feeding, with two side feeds. After one feeding, the overall water permeability of the filter cake is not good due to its own reasons; and the two-side feeding method will cause the residual material to exist in the feeding hole, which will be replaced by the unloading operation at a later stage, and will inevitably affect the moisture content of the refined coal. For this reason, it was decided to increase the number of feeds and to use a single side feed. The two feeds allow for two presses to be performed within the same filter press time period, which creates two permeable layers of coarse particles. And the single-side feeding method can reduce the residual material in the pore to a certain extent, which can improve the water filtration in the filtration process together and reduce the water content of fine coal powder.

Replacement of filter cloth material

As an important medium for solid-liquid separation, filter cloth plays a certain effect on dewatering. At the beginning of the operation of the equipment is a composite filter cloth, the material of the filter cloth is easy to stick to the coal, when the cycle times are more, there will be a filtering pressure is not tight, affecting the discharge of water, which is very much related to the material of the filter cloth. Therefore, by changing the material of the filter cloth, the above situation can be alleviated. Monofilament filter cloths can fulfil all the functions of composite filter cloths. In comparison, monofilament filter cloths are easier to clean and less likely to be clogged, and only need to be rinsed with water in the event of a shutdown.

Reduced wind loss

There is a close relationship between the position of the air duct and the filter plate and the dewatering efficiency. When the filter plate is closer to the air duct, it helps to remove water from the filter plate, but on the contrary, it affects the dewatering effect. In this filter press, the middle filter plate is far away from the air duct, and when the wind is transmitted to the middle position, the wind power is weakened, and the water in the flotation coal cannot be removed effectively. In order to alleviate this phenomenon and equalise the filtration effect of the filter plates, we can reduce the drainage holes of the two ends of the filter plates, so as to reduce the loss of high wind pressure, avoid the influence of wind consumption and equalise the drainage effect of each filter plate. Now, the return valve is opened for 10 s to blow the wet material in the feed pipe back to the feed drum, and then the return valve is closed while blowing, which ensures that a large amount of high-pressure air passes through the filter cake and takes away the cake gap[5] . In addition, if the air blowing and pressing actions are carried out separately, it will not only affect the looseness of the cake, but also have a greater impact on the moisture content. If the two actions are completed at the same time, the phenomenon will be improved, which not only ensures the looseness of the cake, but also effectively improves the permeability of the cake and reduces the moisture content.

Ensure even feeding

If the feed to the plant is not homogeneous and the distribution of coarse and fine particles is not appropriate, then the moisture content of the same quality sample will vary after entering the concentrate pond, resulting in the overall moisture content of the concentrate not being met. In order to make the feed size uniform, the design with stirring function is added. Since there is an air compressor in the whole process, the stirring is carried out by using the high pressure of compressed air to ensure the uniformity of the feed size. Through the adjustment of the above process, and taking the sample data before and after the adjustment as the standard, the water content of the fine coal powder in the sample data obtained from the two filter presses was reduced, which reached the expected goal, and the moisture content of the fine coal was in accordance with the standard. The most significant feature of this feeding method is that cavitation is avoided.

Conclusion

Through the exploration of filter press dewatering process, it is found that changing the feeding method and frequency of filter press, replacing the filter cloth and other ways can effectively improve the dewatering efficiency of the filter press. Fully demonstrates that the fast-opening diaphragm filter press is a kind of dewatering effect is better equipment, in the actual operation process, can also be the kind offilter pressCombined with other different types of filter presses, it improves the dewatering capacity of coal processing and ensures that the production indexes meet the standards.