Secondary filter screen

Rotating backwash strong sewage secondary filter screen

1、 Overview
The secondary filter system is an indispensable device for purifying pollutants in water, maintaining the cleanliness of the condenser water chamber, ensuring the normal operation of rubber balls, and improving the recovery rate of rubber balls. However, the environment in China is relatively serious, especially the water pollution of rivers and lakes. Therefore, the fixed and rotating negative pressure backwash secondary filters commonly used in open cooling water circulation systems have shown their shortcomings. Our factory is a designated factory for the production of power auxiliary equipment. Through continuous solicitation of opinions from users and repeated trial production and continuous improvement of secondary filters in recent years, we have retained some structures of old products, added electric devices, and added strong discharge devicesBy improving the structure and performance of the secondary filter, it has been widely used in the open cycle cooling water system of 6MW to 300MW thermal power generation units, and has received unanimous praise from both new and old customers.
2、 Product Features
At present, fixed and rotary secondary filters are commonly used in the circulating water system of condensers in various power plants (stations). Through years of operation and practice, it has been proven that there are mainly the following problems:
1. Fixed features:
The mesh core is fixed and cannot rotate, resulting in poor cleaning efficiency for dirt. The mesh holes are prone to blockage, and cleaning requires waiting for the machine to stop.
2. Rotating features:
When the mesh core rotates and is cleaned, it relies on negative pressure backwashing. The cleaning ability of this filter is stronger than that of the fixed type, but when the cargo water pollution is severe during the peak season and the water contains plastic film. When dealing with strong adhesive pollutants such as weeds, the cleaning effect is still not ideal. If the scraper in the sewage chamber is severely worn, the cleaning effect is even worse, and there are also significant structural shortcomings:
(1) The pair of large and small gears that drive the mesh core operate in water containing impurities such as sediment all year round, which is prone to wear and corrosion, seriously affecting the safety and economic operation of the unit.
(2) The transmission control system is relatively complex, generally composed of control solenoid valves, oil pumps, oil tanks, oil cylinders, oil motors, oil circuit control boxes, etc. It is most prone to oil leakage and control failure during operation.
(3) The workload of maintenance and repair is large.
In response to the shortcomings of the secondary filter mentioned above, our factory has designed an electric rotary backwash secondary filter through investigation, research, and repeated trial production. It is currently a high-performance secondary filter with the following characteristics:
1. Eliminating the drawbacks of complex and prone to faults in the transmission system of old-fashioned secondary filters, it operates safely and reliably, and is easy to maintain and repair.
2. In response to the severe pollution caused by plastic film, a strong sewage discharge device has been added to overcome the problem of other secondary filter devices being unable to clean the plastic film.
3、 Structural form and working principle
The structure of the electric rotary recoil type secondary filter screen is shown in Figure 1. It mainly consists of: ⑴ shell ⑵ stainless steel mesh core ⑶ transmission mechanism ⑷ reducer ⑶ strong drainage device and other components.
Working principle: The circulating water filtered through the trash rack and primary filter still contains a lot of suspended solids, sediment and other impurities. It enters the secondary filter through the circulating water pump for further filtration. When the suspended solids, plastic film and other impurities in the water adhere to a certain amount on the surface of the filter, the pressure difference between the inside and outside of the filter increases to the specified value of the control system (usually 500mmH2O column). The control system is activated and the drainage mechanism is put into operation to discharge the attached substances from the secondary filter. When the pressure difference inside returns to normal (usually ≤ 400mmHg column), the control mechanism is closed and the cycle is repeated to complete the filtration and drainage process. Users can also choose to discharge pollutants at regular intervals based on their situation.
4、 Specifications and models (see attached table)
Specification and model
Diameter DN
Shell diameter
Secondary filter height H
Discharge pipe diameter (mm)
Additional notes

① Mesh diameter of 4-8mm, water resistance ≤ 400mmHg, H2O column.
② The installation location is based on user requirements.
③ Design according to user requirements while ensuring the flow rate through the structural dimensions.
④ The rotation speed of the mesh core is designed according to user requirements. Generally controlled below 8 revolutions per minute.
5、 Installation and precautions
(1) The secondary filter can be installed horizontally or vertically on the inlet pipe of the condenser circulating water, or on the outlet of the circulating water pump, with the same effect. It can also be designed separately according to different user situations.
(2) The diameter of the secondary filter inlet expansion section should be larger than the diameter of the circulating water pipeline.
(3) The installation size can be determined according to the user's on-site situation. There must be a solid ground foundation.
(4) The connection between the secondary filter screen and the circulating water pipe of the condenser adopts flange connection, and a compensation joint is installed between the secondary filter screen and the condenser for easy maintenance, disassembly, and compensation.
(5) After installation, all debris in the circulating water pipe in front of the filter screen must be removed, and a running test must be conducted before operation.
6、 Ordering Notice
1. The purchaser shall provide installation plans (vertical installation, horizontal installation, vertical 90 degree installation), and the diameter of the connecting pipe shall be designed according to the installation dimensions or original secondary filter screen drawings provided by the purchaser.
2. The user has a special environment, and our company will send personnel to conduct on-site investigation and design separately.