1 Overview

a power plantHow to reduce the water content of chamber filter press cakePhase I of the 2×630 MW unit project adopts limestone-gypsum wet full flue gas desulphurisation (FGD) with one furnace and one tower desulphurisation device, and the design desulphurisation efficiency is not less than 95 %. The desulphurisation wastewater treatment system adopts XAZ140/1250-U chamber filter press, and the specific technical parameters are as shown in Table 1.

The filter plate of chamber filter press is quadrangular, the filter cloth is in the concave filter plate on the projecting part, from 2 quadrangular filter plate to form a closed filter chamber. The main advantages of chamber filter press are low loss of feed, fast filtration speed, high temperature and pressure resistance, good sealing performance, uniform cake, low water content, basically applicable to all solid-liquid separation industries.

2 Working Principle of Chamber Filter Press When the chamber filter press is working, the hydraulic cylinder will press all the filter plates between the movable head plate and the fixed tail plate, so that the adjacent filter plates form a sealed filter chamber, and the slurry will be fed from the feeding holes of the fixed tail plate with a certain pressure. After all the chambers are filled with slurry, the filtration process begins, and the slurry is separated from the solids and liquids by the pressure of the feed pump. Solid particles remain in the filter chamber due to the blockage of the filter cloth, and the filtrate is discharged through the filter cloth along the drain on the filter plate. After a period of time, the filtrate no longer outflow, that is, the completion of the dewatering process. At this time, you can stop feeding, through the hydraulic manipulation system adjustment, the head plate back to the original position; by the filter plate moving device will be pulled open one after another; the filter cake rely on self-weight fall off, and is located in the lower part of the belt to transport away. In order to prevent the filter cloth eyelets from clogging, affecting the filtering effect, the filter cloth needs to be cleaned after unloading the cake. So far, the whole filtering process is completed.

3 Problems and Improvement of Vane Filter Presses

3.1 Problems in the actual application, affected by a variety of factors, the water content of the filter cake of the chamber filter press is relatively large, and the effect of filtration is not ideal. The large water content of the cake causes the cake to become sludge-like, attached to the filter cloth. Even if you use a shovel to poke, you can't drop the whole piece, and some of them even need to rinse the filter cloth before the next cycle, resulting in high labour intensity of the staff and long unloading time.

3.2 Problem analysis The lower the feed concentration, the higher the moisture of the filter cake. When the concentration of feed material is low, fine particles are very easy to enter the eyelets of the filter cloth, pass through, block or cover them, so that the eyelets of the filter cloth will be blocked soon. With the increase of feed concentration, there will be more particles close to or to the filter cloth eyelets, due to mutual interference, the vast majority of particles can not enter the eyelets and the formation of arches and bridges on the eyelets, which can make the filter holes in a longer period of time is not seriously blocked. With the filtration process, the average particle size of the filter cake formed on the surface of the filter cloth along the feeding direction from the outside to the inside gradually increases, and the cake resistance gradually decreases, so that the dewatering of the inner side of the cake (close to the side of the filter cloth) is affected, and this effect is gradually strengthened with the decrease in the concentration of the feeding material. After the study of the field conditions and a lot of tests, it was found that under the existing equipment, by adjusting the feed pressure, feed time, press [Abstract] A power plant chamber filter press in the application of the problem of large moisture content of the cake, the effect of filtration is not ideal. The problem was analysed, and it was confirmed that under the existing equipment and operating parameters, the filter press did not have the conditions to further reduce the water content of the cake. By increasing compressed air, the water content of the filter cake was reduced from 60 % to 10 %, which improved the sludge discharge efficiency. Parameters such as pressure and feed concentration can no longer effectively reduce the water content of the filter cake in the filter press, so it is necessary to propose an improvement programme.

3.3 Improvement programme In order to effectively reduce the water content of the filter cake in the chamber filter press, compressed air can be fed through the feed pipe after the feed of the filter press (unlike the diaphragm filter press). Compressed air automatic control device is added, and it can be switched directly through the DCS screen. The air and feed use the same inlet, when the feed is finished, close the feed valve and flush the feed pipe. After flushing, start conveying compressed air until no filtrate is discharged from the feed pipe to reach the state of equipment sludge discharge.

4 Conclusion

(1) Before using compressed air to reduce the water content of the filter cake, the filter cake in the filter press must be filled. If the cake is too thin, it will result in low water content of the cake at the inlet of compressed air, and the farther away it is, the higher the water content will be, and it will not even be able to play a role in reducing the water content.

(2) The time to pass into the compressed air needs to be determined according to the situation. Different materials, through the compressed air time is different. If the time is short, the water content of the cake is large; if the time is too long, it will cause the cake to dry out in contact with the filter cloth and attach to the filter cloth, increasing the workload.

(3) After adding compressed air, the material conveying pipeline needs to add a way of flushing water. Due to the influence of compressed air, the water content of the residual slurry in the feed pipe will also decrease, and further air-dry. After many times, the air-dried slurry will clog the pipe.

(4) After the transformation, after the actual operation verification, the effect of desliming has obvious improvement, the filter cake forming is more complete, the water content is as low as 10 %. the whole operation process can realise the continuous automatic cycle of mud, not only to improve the efficiency of the system mud, but also to reduce the frequency of manual on-site operation.