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How does a filter bag house work?

Time : 2023-06-26 Hits : 3

The working principle of liquid bag filter is pressure filtration. The complete bag filter consists of three parts: liquid bag filter container, supporting basket and liquid filter bag. The liquid to be filtered is injected from the top or side of the bag filter and directly enters the liquid filter bag to make the liquid filter bag evenly distributed without the negative effect of turbulence; The particles filtered by the bag filter are retained in the liquid filter bag for easy replacement. Liquid bag filter includes single bag filter and multiple bag filter; Or it can be divided into side-entry bag filter, top-entry bag filter and small bag filter.

When the filter is working, the water to be filtered enters from the water inlet, flows through the filter screen, enters the pipeline required by the user through the outlet for process circulation, and the particulate impurities in the water are retained in the filter screen. With such continuous circulation, more and more particles are intercepted and the filtering speed is getting slower and slower, while the imported sewage is still flowing in, and the filter hole will become smaller and smaller, resulting in a pressure difference between the inlet and outlet. When the large difference reaches the set value, the differential pressure transmitter will transmit the electrical signal to the controller, and the control system will start the drive motor to drive the shaft to rotate through the drive component, while the drain outlet will be opened and discharged from the drain outlet, When the filter screen is cleaned, the differential pressure drops to the minimum value, and the system returns to the initial filtering state, and the system operates normally. The filter is composed of shell, multi-element filter element, backwash mechanism, and differential pressure controller. The diaphragm in the shell divides its inner cavity into upper and lower cavities. The upper cavity is equipped with a plurality of filter elements, which makes full use of the filtering space and significantly reduces the volume of the filter. The lower cavity is equipped with backwashing suction cups. During operation, the turbid liquid enters the lower chamber of the filter through the inlet, and then enters the inner chamber of the filter element through the diaphragm hole. Impurities larger than the gap of the filter element are intercepted, and the clean liquid passes through the gap to the upper chamber, and finally is sent out from the outlet. The filter adopts high-strength wedge-shaped filter screen, and automatically cleans the filter element through pressure difference control and timing control. When the impurities in the filter accumulate on the surface of the filter element, causing the differential pressure at the inlet and outlet to increase to the set value, or the timer reaches the preset time, the electric control box sends a signal to drive the backwash mechanism. When the backwash suction cup mouth is aligned with the inlet of the filter element, the blowdown valve opens. At this time, the system depressurizes and drains water. A negative pressure zone with a relative pressure lower than the water pressure outside the filter element appears inside the suction cup and the filter element, forcing part of the clean circulating water to flow into the inside of the filter element from the outside of the filter element, and the impurities and particles adsorbed on the inner wall of the filter element flow into the suction cup with water and are discharged from the blowdown valve. The specially designed filter screen makes the inside of the filter element produce spraying effect, and any impurities will be washed away from the smooth inner wall. When the differential pressure at the inlet and outlet of the filter returns to normal or the timer setting time is over, the material will not be cut off during the whole process, and the backwashing water consumption is low, realizing continuous and automatic production. Filters are widely used in metallurgy, chemical industry, petroleum, paper making, medicine, food, mining, electric power and urban water supply. Such as industrial wastewater, circulating water filtration, emulsion regeneration, waste oil filtration treatment, continuous casting water system, blast furnace water system in metallurgical industry, and high-pressure water descaling system for hot rolling. It is an advanced, efficient and easy to operate full-automatic filtering device.

The water to be treated by the filter enters the body from the water inlet, and the impurities in the water are deposited on the stainless steel filter screen, resulting in pressure difference. The pressure difference at the inlet and outlet is monitored by the pressure difference switch. When the pressure difference reaches the set value, the electric controller sends the hydraulic control valve and drives the motor signal. After the installation of the equipment, the technicians will conduct the commissioning, set the filtering time and cleaning conversion time, and the water to be treated will enter the machine body from the water inlet, and the filter will start to work normally. When the preset cleaning time is reached, the electric controller will send signals to the hydraulic control valve and drive the motor, causing the following actions: the motor will drive the brush to rotate to clean the filter element, and the control valve will be opened to drain. The whole cleaning process will only last for tens of seconds, When the cleaning is finished, close the control valve, the motor stops rotating, the system returns to its initial state, and the next filtering process begins. The interior of the filter housing is mainly composed of coarse filter screen, fine filter screen, sewage suction pipe, stainless steel brush or stainless steel suction nozzle, sealing ring, anti-corrosion coating, rotating shaft, etc.

A simple filter is formed by separating the container into upper and lower cavities with filter media. The suspension is added to the upper chamber and enters the lower chamber through the filter medium under the pressure to become the filtrate. The solid particles are retained on the surface of the filter medium to form a filter residue (or filter cake). During the filtration process, the filter residue layer on the surface of the filter medium is gradually thickened, the resistance of liquid passing through the filter residue layer is increased, and the filtration speed is reduced. When the filter chamber is full of filter residue or the filtering speed is too low, stop filtering, remove the filter residue and regenerate the filter medium to complete a filtering cycle.

The liquid must overcome the resistance when passing through the filter slag layer and the filter medium, so there must be a pressure difference on both sides of the filter medium, which is the driving force to achieve filtration. Increasing the pressure difference can accelerate the filtration, but the deformed particles under pressure are easy to block the pores of the filter medium when the pressure difference is large, and the filtration will slow down.

There are three ways of suspension filtration: slag layer filtration, deep filtration and screen filtration.

① Filter residue layer filtration: at the initial stage of filtration, the filter medium can only retain large solid particles, and small particles pass through the filter medium with the filtrate. After the formation of the initial filter residue layer, the filter residue layer plays a major role in filtration. At this time, large and small particles are intercepted, such as the filtration of the plate and frame filter press.

② Deep filtration: the filter medium is thick, the suspension contains less solid particles, and the particles are smaller than the pore channel of the filter medium. During filtration, particles are adsorbed in the channel after entering, such as porous plastic pipe filter and sand filter.

③ Screen filtration: the solid particles intercepted by filtration are larger than the pores of the filter medium, and the solid particles are not adsorbed inside the filter medium. For example, the coarse impurities in the sewage are filtered by the rotary drum filter screen. In the actual filtering process, the three methods often appear simultaneously or successively.

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