Automatic Bernoulli filters
What is an automatic self-cleaning filter?
Self-cleaning technologies (mechanisms) of liquid filters make it possible to do without periodic cleaning of mud collectors and filter cartridges, which, one way or another, inevitably clog up during operation. Self-cleaning filters today are one of the most innovative technologies in the field of primary water treatment (coarse water purification) for various areas of industry and economy. There is also a significant potential for their use in organizing water intake from open sources in the domestic sphere, as well as in industry and technology, for organizing continuous purification of other highly contaminated liquid media.
In fact, water filters with automatic cleaning are a further development of coarse liquid filters with a manual drive of the backwash mechanism. A water filter with automatic cleaning is a modification of the classic liquid coarse filter, with filtering elements of a disc or mesh type, in which the following are structurally provided:
- Additional mechanism for mechanical cleaning or backwashing of the filter element, operating on a cyclic principle;
- automatic drive system of the cleaning mechanism, the automation of which operates on a time timer, and (or) with command switching on by a signal from sensors that record changes in the pressure of the working medium.
Self-cleaning filters, how they work
At the current level of development of technology, the mechanism of automatic self-cleaning of a liquid (water) filter is implemented according to two main principles:
1) Backwash mechanism. The principle of backwash operation is quite simple and intuitive. By automatic control, the direction of flow of the working medium through the filter element is reversed, as a result of which the accumulated impurities are flushed out of the filter into the waste system in a counterflow. The disadvantage of the backwash mechanism is the impossibility of operating a single liquid filter in the continuous filtration mode, because it must be stopped with switching to the backwash mode. When working with backwash filters, it is necessary to provide for the presence of several duplicate filters, which are cleaned one by one, which significantly complicates and increases the cost of the system.
2) System with a movable cleaning disc. More technically advanced is the self-cleaning mechanism using a movable cleaning disc, which solves the problem of maintaining the process of continuous filtration of the medium within a single apparatus. Such a mechanism is implemented, for example, in the automatic filter of the F450 series manufactured by Georg Schünemann GmbH, presented in the range of products sold by OPEKS Energysystems. The disc, dropping inside the filter mesh, creates the Bernoulli effect, multiplying the speed of water in the area of contamination and cleaning the filter surface.
The design of the automatic filter with a movable scrubbing disc consists of:
- Housings made of composite materials, steel or titanium with inlet and outlet nozzles, which are connected, respectively, to the water intake from an open source and to the consumption system of treated (purified) water, as well as to a discharge system nozzle, where mud sludge is discharged.
- A cylindrical filtering element assembled from compressed disk segments that form a fine-slotted (filtering) through-flow structure.
- A controlled bypass valve installed on the branch pipe of the discharge system.
- Cleaning disc (with a diameter corresponding to the inner diameter of the cylindrical filter element) with a drive rod.
- Cleaning disc rod drive (electric or pneumatic).
- Control automatic switching of the bypass valve and the cleaning disc drive, working with programming according to a time schedule (timer), or by command from signal pressure sensors.
Rice. Appearance of the automatic filter F450 Schünemann with a movable cleaning disc
The operation of the automatic self-cleaning filter type F450 is organized according to the following operating cycles:
1) Filtration in normal mode. The bypass valve of the discharge system is closed, the movable scrubber is raised to the uppermost position. Untreated water from the water intake is pumped into the inner space of the cylindrical filter element through the inlet pipe. Under the action of the discharge pressure, purified water through the slotted gaps of the filter element enters its outer side, into the space between the filter element and the filter housing, and from there, through the outlet pipe, into the water supply system. Solid particles of impurities remaining inside the cylinder of the filter element, accumulating, form a saturated sludge, which gradually clogs the passage slot gaps. As a result, the hydraulic resistance of the filter gradually increases, thereby lowering the pressure of the treated water in its outlet.
2) The first stage of self-cleaning. The signal sensor in the outlet of the filter records a certain level of drop in operating pressure, and gives a command to the controller of the automatic self-cleaning drive (as an option, the automation works according to a time schedule, and the command is given by a timer, at regular intervals). The automation controller opens the bypass valve of the waste system, as a result of which the accumulated mud sludge begins to flow from the inner cavity of the cylindrical filter element into the waste system. In this case, the injection of intake water, and the process of its filtration continues, but with a lower capacity, which is associated with the withdrawal of a part of the pumped medium, together with sludge, into the waste system.
3) The second phase of self-cleaning . The bypass valve of the relief system remains open. The controller gives a command to drive the cleaning disk rod, and the disk, under its influence, begins to move from top to bottom, along the inner space of the filter element cylinder. At the same time, the Bernoulli principle is included in the work, according to which the sum of pressure and flow rate in the pipeline remains unchanged. Accordingly, as the flow area decreases, the flow rate increases in proportion to the pressure drop, and vice versa. When the cleaning disc moves downward, with its lateral edge, it alternately partially overlaps the flow sections of the slotted openings of the filter element, as a result of which the pressure in this area drops sharply, and high-speed counter-current flows arise from the outside of the filter element (from the area of already filtered water) to the inside. These short-lived countercurrents, based on the backwash principle, clean the slotted structure clogged with dirt, with the removal of sludge inside the cylinder of the filter element, and then into the waste system. In this case, the process of water filtration in the areas of the filtering element, remote from the moving cleaning disc, is not interrupted, but continues.
4) The last phase of self-cleaning. The bypass valve of the relief system remains open. The cleaning disc, having reached the bottom dead center, begins to move upward, repeating the process of short-term overlapping of the filter element slots. This re-generates high-speed backwash backwash in the near zone near the scrubber, which further increases the efficiency of the cleaning cycle. Mud sludge continues to flow into the waste system. The process of water filtration in the areas of the filter element, remote from the moving cleaning disc, continues without stopping for a moment. When the top dead center scrubber is reached, the controller sends a command to close the bypass valve and the self-cleaning cycle ends. The filter switches to the standard filtering mode.
Advantages of automatic self-cleaning filters over conventional, manual filters:
- The possibility of organizing a continuous process of primary water treatment (water supply), without interruptions for technological maintenance associated with the need for manual cleaning (flushing), or replacement of filter elements.
- The ability to work with a very dirty environment, with any required frequency (frequency) of cycles of automatic self-cleaning of the filter.
- The possibility of saving on the labor intensity of work on the maintenance of the system, and, accordingly, on the number of maintenance personnel, their wages fund.
- Possibility of installing an automatic filter in hard-to-reach places of the system.
Scope of application of water filters with automatic self-cleaning
Automatic self-cleaning filters can be used in any water supply or water heating systems with appropriate operating parameters, where the stage of primary preparation (purification) of the water used is provided. But the most expedient is their use:
- As a mud cleaner of the "first line" of water treatment at water intakes from open sources (reservoirs) for: industrial enterprises, oil (gas) production plants, municipal water supply systems, irrigation and irrigation systems, remotely located (away from the central water supply systems) houses recreation and sanatoriums, farms and private households.
- In order to protect technological equipment (boilers, heat exchangers, cooling towers, etc.) from pollution, operating in a continuous production cycle.
Parameters for the selection of an automatic self-cleaning filter type F450 Schünemann
When choosing a filter with automatic cleaning, the following parameters should be taken into account:
- appointment in the production cycle;
- aggressiveness of water (sea water with high salinity, fresh water);
- the required degree of water purification, depends on the filter nets used, is determined in microns, microns;
- the required maximum performance of the water purification or water treatment system, in m3 / hour;
- operating and maximum allowable pressure in the system, MPa (bar);
- parameters for connecting the filter to the existing pipeline system (according to the bore diameter of the nozzles DN);
- self-cleaning actuator drive type - electric or pneumatic
The calculation of the performance of the automatic filter is carried out according to special schedules provided by the direct equipment manufacturers. The team of specialists of the OPEKS Power Systems company is ready to professionally select the automatic filters of the F450 Schünemann series available in our implementation for any required operating conditions.