How to choose the bag filter correctly?

How to choose the correct bag filter?

This article briefly summarizes the development history and technological innovation of bag filters, and points out the advantages and disadvantages of different types of filters. Effective selection of filters can help optimize process operation and reduce maintenance costs.

The bag filter is a relatively common industrial filtration device consisting of a filter housing and a filter bag. In terms of the number of filter bags installed, there are multiple bags and single bags; and from the filter structure, there are door-type filters and quick-open filters. Faced with so many filter manufacturers and models, how to choose the right filter is a difficult problem for industrial users.

In fact, the early form of filtration was simply to tie the filter cloth to the liquid outlet. With the standardization and large-scale production of industrial production, the safety requirements are getting higher and higher, and the leaky filter form does not meet the demand of industrialized large-scale production, so the bag filter of today is gradually formed. Since the filter bag needs to be replaced regularly, the filter opens very frequently. Conventional bag filters have not been considered for ease of operation and safety. It uses multiple bolts to seal the seal. When the filter bag needs to be replaced, the process of opening the filter cover is very time consuming and laborious. After opening the filter cover, field workers often need to stand on the high ladder and take out the filter bag that has been blocked. However, the faceplate (Fig. 1) is at a certain distance from the open face of the filter, and the operation process often requires the use of a tool to take out the filter bag, which is very inconvenient.

The second generation filter is also called the door comparison filter (Fig. 2). In terms of structure, the filter inlet is lower than the design of the disk. After the liquid passes through the elbow, the upper part enters the filter bag. The advantage of this design is that the height of the device is up to the height of the adult, and the faceplate is at the opening. When the filter bag is replaced, the tool bag can be easily removed or installed without the need of tools. Moreover, the way of opening it has also been innovated, from the traditional left and right translation to the upper and lower opening and closing, reducing the space occupied by the equipment. Since the filter cover is too heavy, a booster is often installed. The patented self-balancing device of the company can balance the gravity of the cover at any angle, and the filter can be easily opened by a single person. The door is tighter than the filter with the ring bolt, and the opening is quite cumbersome.

In order to solve the cumbersome problem, the company has designed a patented V-type quick-opening hoop for the new generation of Speedo quick-open filter (Fig. 3). The operator can easily turn on the filter within 10 seconds. In addition, the filter tends to withstand a certain pressure, in order to avoid the safety problems caused by opening the cover, the quick opening mechanism is connected with the pressure relief valve. Before the cover is opened, the pressure relief valve is automatically opened and the safety performance is further improved.

The filter bag style that matches the filter is more complex and varied. In order to meet the chemical and physical properties of the material, the filter bag can be made of various materials, and the commonly used materials are polypropylene, polyester, nylon, and the like. The size of the filter bag is mainly to match the design flow. The main specifications are No. 1 and No. 2 bags. Take the No. 2 bag as an example. The recommended flow rate is usually 20-30m3/h. Of course, the flow rate has a certain relationship with the viscosity and the amount of impurities in the fluid. If the flow is large, a multi-bag filter design is required. At present, the size of filter bags in China is relatively similar, and the matching degree with the filter is high, and each manufacturer can replace each other. Most filter bags have a high filtration accuracy of about 1 um and the filtration efficiency is not high. High-precision or absolute-precision filter bags are designed with multi-layer melt-blown filter media to achieve deep filtration and improve filtration efficiency.

The service life of the filter bag is often proportional to the filter area. When the filter area is increased, the service life will increase exponentially. How to improve the filtration area of the filter bag is an important research direction. For this purpose, the company designed the Rocket filter bag (Fig. 4), which combines the structural advantages of the filter element and the filter bag. It adopts the filter bag seal design, which can directly replace the existing filter bag without modifying the bag filter. . After the folding design, the filter area of the Rocket filter bag is more than 4 times that of the ordinary filter bag, and the dirt consumption and service life are generally higher than the original ordinary filter bag. The increase in the filtration area of a single component allows the filtration of a large flow of liquid, which requires only a small amount of Rocket filter bag to achieve the original process requirements. At the same time, the number of opening covers is also significantly less, which improves the working intensity and working environment of the operator.