Industrial Water Filters for Power Stations in Hydropower Plants

One.Overview
   In general filtration devices, as the filtration process continues, the solid phase impurities in the liquid are retained on the surface of the filter element, causing an increase in pressure drop, an increase in filtration resistance and a decrease in filtration efficiency. At this time, it is generally necessary to interrupt the filtration operation, replace the filter element or take it out for cleaning, which is time-consuming and laborious, affecting the treatment efficiency.The new JSLS automatic backwashing water filter is a good solution to this problem, as it has the advantages of continuous filtration, automatic backwashing and drainage, compact structure, smooth and reliable operation, large capacity, low running costs and long service life.
   The cleaning and draining process of JSLS type automatic water filter is carried out automatically during the operation of the equipment, and the filtering operation can still be carried out while backwashing and draining, without affecting the normal water supply. This filter is mainly used for coarse and fine filtration of power station auxiliary cooling water, industrial circulating water, fire-fighting water, washing liquid and other similar suspended liquids.


Two.Machine construction and working principle
1. Machine structure
 The sketch of the water filter structure is as follows:

     The drive device is composed of motor and reducer, which drives the transmission shaft to rotate at a low speed, and has the characteristics of large torque, high reliability etc.
     If an accidental blockage occurs and the torque exceeds the maximum design value, the electrical protection system will automatically stop and send an alarm signal.

     The differential pressure controller introduces a double contact differential pressure controller with a bellows type sensor for neutral gases such as air, gas and water vapour and liquid media such as water, oil and refrigerant. The controller has an adjustable set value and an adjustable range of 0.02 to 1.6 MPa and a working pressure range of 0.05 to 2.5 MPa.
    The blowdown valve technology of connecting the electric blowdown valve with the blowdown pipe mouth and the electric ball valve produced by key parts are especially suitable for the filter residue with large silt content, which will not be leaked due to torque overload or lax closure, and at the same time, it has the advantages of reliable use and long service life.


2.Working principle
   Both the filtering and backwashing propulsion of the machine are provided by the raw water pressure head or pump lift. The pressure in the filter chamber of the system remains basically constant, the liquid flows outwards from the inner chamber of the filter element and the entrained solid impurities are intercepted on the inner surface of the filter medium, causing the pressure difference between the inner and outer chamber to rise and the filtering resistance to increase gradually.

     The backwashing action is controlled by a differential pressure signal generator (the size of the differential pressure reflects the degree of blockage of the cartridge) and the backwashing time is regulated by a time relay. During the cleaning process, the cleaning area takes up a very small part of the total filtering area and the flushing pressure difference is large, so that the amount of backwashing liquid is small, the filtering process remains continuous, fluctuations are small and the flushing efficiency is high. The only rotating part in the machine is the backwash arm, which has a low speed and smooth operation, as well as an automatic compensation function for wear and tear, good sealing performance and low maintenance costs.


Three, performance characteristics
 3.1 Automatic cleaning:
   The machine uses the clear liquid from its own filtration to automatically backwash the cartridge, without removing the cartridge for cleaning and without the need for a separate cleaning system.
 3.2 Continuous water supply:
   The machine is equipped with several cylindrical cartridges working simultaneously in the tank, and each cartridge is cleaned one by one when backwashing, while the other cartridges are still filtering continuously, which can ensure the continuous supply of filtrate.
 3.3 Low water consumption for backwashing:
   The machine only cleans one or two cartridges at the same time when backflushing, accounting for a tenth to a twentieth of the entire number of cartridges, so the water consumption of the discharge is less than 5% of the design flow, which is more than double that of the traditional structure.
 3.4 Large filtering area:
   As the tank is arranged with multiple cylindrical cartridges, the space of the container is fully utilized, and the effective filtration area can reach 3-5 times of the inlet area, which is about twice as much as the traditional structure.
 3.5 Good backwashing effect:
 As the cartridge gap adopts a wedge-shaped structure, solid impurities are retained on the surface without blocking the gap, while the flared mouth forms a jet, which has a good backwashing effect.
 3.6 High strength of the cartridge:
    As the cartridge is welded with stainless steel wire strips, and there are also multiple ring hoops welded in the length direction to strengthen it, the cartridge has sufficient rigidity and strength against deformation under the premise of ensuring the precision of filtration.
 3.7 Reliable sealing mechanism:
    This machine has changed the traditional design, the cartridge is fixed and the drainage fork tube is used to rotate, and the upper end of the fork tube is equipped with a specially designed mechanical seal, and the contact part with the fixed partition is made of high alloy material, which is resistant to wear and tear, and at the same time, it ensures proper specific pressure and reliable seal.
3.8 High degree of automation:
   In order to meet the increasing requirements of power station automation, the control system of this machine adopts imported electrical components and programmable controller (PLC) control, backwashing can be switched automatically (timing, differential pressure) and manually, and it is easy to realize remote monitoring and convenient to connect with the upper computer



IV. Installation, operation and maintenance of the machine
 1,Installation:
 The following points should be noted when the machine is installed:
 (1) Before installation, the machine should be cleaned and decontaminated.
 (2) The sealing parts must ensure that there is no leakage.
 (3) All transmission parts are required to run flexibly, and the supporting bearings should be filled with calcium and sodium grease.
 (4) The coupling should be solid and reliable.

 2,Operation
   When the machine is running with water, check the tightness of the joints, the lubrication of the lubrication points, the leakage of the seals and the operation of the transmission mechanism. If loose, poor lubrication and leakage are found, the machine must be re-fastened, re-lubricated and the seal ring replaced; if vibration and noise are found in the transmission mechanism, the transmission mechanism must be re-adjusted until all abnormalities are removed.
     This machine adopts programmable control (PLC), backwashing action can have manual and automatic state, these two working states can be switched by the following methods;

     Automatic backwashing, the machine is equipped with differential pressure controller, when the switch is in the automatic position, the machine is in the automatic working state, the differential pressure value of the differential pressure controller and the switching difference can be set by the user.The specific setting method is: the user sets a differential pressure value according to the allowable pressure drop in the pipeline, and then sets the switching difference according to the backwashing time requirement. When the differential pressure reaches the set value, the main motor starts and the drain valve opens to start backflushing.
   To regularly open the manual drain valve at the bottom of the machine to discharge the impurities accumulated in the tank.
 
3. Maintenance:
(1). Regularly check if there are any abnormalities in the work of the transmission parts and lubricate the bearings with calcium and sodium based grease.
(2). Regularly check the sealing parts, if leakage is found, the sealing components must be replaced.
(3). Regularly check the clear liquid, found that the solid phase particles exceed the standard, must stop to check whether the filter element is damaged.