There are several main reasons for filter cloth blockage:
First, the reason of the filter cloth itself
1. The quality of filter cloth is determined by many factors such as its material, compilation process and interface process.
2. Polyester material: This material is an ideal choice under acidic conditions. It is resistant to high temperature (the temperature is less than 150 degrees when the PH value is 1-9), strong in tensile strength and stable in vertical and horizontal directions, and its wear resistance is second only to nylon.
3. Polypropylene has good acid and alkali resistance, (ph 1-13) its service temperature is less than 90℃, but its tensile strength is not high. Most foreign filter cloth manufacturers do not choose this material. Since the ph value of slurry from absorption tower is generally between 4-7, and the temperature of gypsum is 70-80℃, the filter cloth is woven with 100% polyester silk yarn with high temperature resistance and good alkali resistance.
4. Weaving technology: The weaving technology of monofilament, silk yarn and satin weave is generally adopted in the world. The advantages of this weaving method are smooth surface, rough back, different opening sizes before and after, large surface holes and small back holes, which make it easy to intercept solids and drain water. Smooth surface makes the removal of solids on the surface more efficient. Polyester silk yarn of many filter cloth manufacturers contains polypropylene, not 100% polyester material, and filter cloth is affected by gypsum slurry temperature in absorption tower.
Second, due to the filter itself:
1. Main machine flushing system: Because filter cloth flushing water uses process water, it is generally not blocked, while filter cake flushing water generally uses process water+filter cloth flushing water backwater+vacuum pump circulating water backwater (water ring vacuum pump is adopted), mainly vacuum pump circulating water+filter cloth flushing water backwater, and the process water is only supplemented occasionally. The gypsum content in filter cloth flushing water backwater is relatively high, so it is easy to cause clogging of filter cake flushing water nozzle. Generally, the pressure of the nozzle of the flushing system of the main engine is more than 3 kg. When it is less than this value, the flushing effect of the filter cloth cannot be achieved. If the filter cloth is not cleaned for a long time, gypsum will be deposited on the surface of the filter cloth, and the surface of the filter cloth will be blocked.
2. The distance between the scraper and the filter cloth surface is too large, and a large amount of gypsum is deposited on the filter cloth surface, which makes it difficult to clean. It is easy to scale on the filter cloth surface for a long time, and the occurrence rate is not blocked on the surface.
3. Sealing property of main engine: If the water content of secondary dehydrated gypsum is more than 10%, the sealing property of main engine should also be considered. Poor sealing property will lead to low vacuum degree of the whole system, and the water content of dehydrated gypsum filter cake is obviously high, which affects the filtering effect. The main reasons for this problem are:
A, vacuum chamber butt joint degumming, vacuum chamber is generally made of high molecular polymer, this kind of material has strong expansion deformation, if it is not fixed in time or fixed badly, it may cause vacuum chamber degumming, in this case, only after stopping, put down the vacuum chamber to replenish glue and fix each vacuum chamber.
B, the flange joint under the vacuum chamber leaks. There is usually a whistle. To solve this problem, it is necessary to put down the vacuum chamber after parking, check the gasket, and replace the gasket if there is any problem; If it's not the gasket problem, just tighten the flange bolts at the leak.
C. If the filtrate main pipe leaks, just tighten the bolts at the leaking place. If there is a gasket problem, replace the gasket after parking. To prevent vacuum leakage, it is necessary to test the vacuum degree after the system is installed and before the filter cloth is installed. This can control the problem before driving and avoid the trouble after driving.
How to clean filter cloth blockage:
1. For the filter cloth used for alkaline filter materials, when cleaning, it needs to be soaked in weak acid solution;
2. When cleaning the filter cloth used for acidic filter materials, it needs to be soaked in weak alkali solution.
The soaking time is 1 day to 2 days. And then clean.
Or:
1. high pressure water gun cleaning;
2. Cleaning by cloth washer, adding cleaning agent;
3. Cleaning with hydrochloric acid or citric acid;
4. Cleaning with caustic soda or hydrogen peroxide;
5. The cloth washing cycle should be established according to the actual situation, generally not more than 2 months.
