Installation of secondary filter screen and precautions
The secondary filter screen system is a device designed and developed to purify the dirt in the water, keep the water chamber of the condenser in a clean state, ensure the normal operation of the rubber ball and improve the recovery rate of the rubber ball.
In China, the environment is more serious, especially in rivers and lakes. Therefore, two kinds of secondary filters, fixed and rotary negative pressure backwash, which are widely used in the open cooling water circulation system, have shown their shortcomings.
In recent years, through the continuous solicitation of the opinions of the majority of users and the repeated trial production and continuous improvement of the secondary filter screen, part of the structure of the old product is retained, the electric device is added, and the strong blowdown device is added, so that the structure and performance of the secondary filter screen are more perfect, and it is widely used in the open cooling water circulation system of 6MW to 300MW Thermal power units.
The inlet of circulating water pump is equipped with trash rack, rotary filter screen and other equipment, but there are still a lot of debris into the condenser. These debris are easy to block the tube sheet, copper tube, and also block the ball collecting net, so secondary filtration is needed.
The secondary filter screen of circulating water not only affects the cleanliness of cooling water, but also affects the flow characteristics of condenser inlet water chamber.
Two kinds of secondary filters, fixed and rotary, are widely used in the circulating water system of condensers in power plants.
It has been proved by practice that there are mainly the following problems
- Features of fixed type
The mesh core can not rotate when it is fixed, the cleaning effect is poor, the mesh hole is easily blocked, and the cleaning has to wait for shutdown.
- Rotary features:
When the mesh core rotates and cleans, it is recoiled by negative pressure. The cleaning capacity of the filter is stronger than that of the fixed type. However, when the cargo water is polluted seriously in the flood peak season, and the water contains plastic film.For example, when the scraper of the sewage chamber is seriously worn, the cleaning effect is worse, and the structure also has some disadvantages.
（1）A pair of big and small gears driving the mesh core run in the water containing sediment and other impurities all the year round, which is very easy to wear and corrosion, seriously affecting the safe and economic operation of the unit.
（2）The transmission control system is more complex, which is generally composed of control solenoid valve, oil pump, oil tank, oil cylinder, oil motor, oil circuit control box, etc.
（3）The workload of maintenance is heavy.
In view of the shortcomings of the above secondary filter screen, we designed the electric rotary recoil secondary filter screen through investigation and trial production.
It is the best secondary filter with the following characteristics:
- It eliminates the shortcomings of the old secondary filter screen, such as complex transmission system, easy to produce faults, safe and reliable operation, convenient maintenance.
- According to the situation that the plastic film is seriously polluted, a strong sewage device is added to overcome the situation that the plastic film cannot be cleaned by other secondary filter devices.
Structure: electric rotary recoil type secondary filter structure, it is mainly composed of: (1) shell, (2) stainless steel mesh core, (3) transmission mechanism, (4) reducer, (5) strong sewage device and other components.
- The circulating water filtered by trashrack and primary filter screen still contains many suspended solids, sediment and other impurities, which are filtered by circulating water pump into secondary filter screen.
- When the suspended solids, plastic film and other impurities in the water attach to a certain amount on the surface of the filter screen, the internal and external water pressure difference of the filter screen increases to the specified value of the control system (generally 500mmh2o column).
- Start up the control system, put the blowdown mechanism into operation, and discharge the attachment from the secondary filter screen. When the internal pressure difference returns to normal (generally ≤ 400mmh2o column), the control mechanism will close and cycle, so as to complete the filtering and blowdown process.
- You can also choose timing sewage according to the user’s situation.
Installation and precautions
- The secondary filter screen can be installed either vertically or horizontally at the inlet of condenser or at the outlet of circulating pump, with the same effect.
- The length of the straight pipe section at the inlet of the filter screen shall be greater than the diameter of the circulating water pipe.
- Do not tilt when installing, the connection should be firm.
- The distance between the filter screen and the inlet of the circulating water pipe of the condenser should be kept at more than 1000mm, and a compensation joint should be installed between the filter screen and the condenser to facilitate the maintenance, assembly, disassembly and compensation.
- After installation, all the sundries in the circulating water pipe in front of the filter screen shall be removed, and the operation test shall be conducted before putting into operation.
- Backwashing water quantity: no more than 5% ~ 10% of the total circulating water quantity
- Backwash interval (setting): 1-24 hours adjustable
- Backwashing time (setting): 0-10 minutes adjustable