PROCEDURE AND MEANS FOR FILTERING AND HOMOGENIZING LIQUID SUBSTANCES

Abstract: A procedure and means for filtering and homog­ enizing liquid substances and for automatic cleaning of the filters. In the procedure are utilized an ultrasonic generator (4) connected in conjunction with the filter unit (1; 2) and ultrasonic oscillators (1.11; 2.11) thereto connected, their power and frequency being controlled on the basis of the differential pressure present across the filter units (1; 2), the liquid pressure acting in the fil­ ter unit, the liquid flow rate, signals from liquid temper­ ature pick-ups. In order to enhance the cleaning event of the filter elements (1.2; 2.2) taking place with ultra­ sonics, the filter unit (1; 2) is emptied during the clean­ ing phase, making use of compressed air conducted into the filter. In order to facilitate the liquid filtering event and to reduce the need of cleaning action with ultrason­ ics, during normal filtering an ultrasonic power is main­ tained which is sufficient for homogenizing the liquid. The filter unit (1; 2) furthermore contains one or several cylindrical filter elements (1.2; 2.2).

Description: The present invention concerns to a procedure and a filter according to the preamble of claims 1 and 9. Such a procedure and such a filter is disclosed in WO-A-79/00884. The known procedure and filter are based on using filter elements and ultrasonic oscillators and generators. In a liquid filtering event in which the liquid is passed through filter elements, the elements are soiled down and have to be replaced or cleaned. Since filter element replacing entails many detriments, e.g. the need to keep such elements in stock, the work involved in the replacement operation and possibly interruption of the filtering process, endeavours are generally aimed at performing doing the cleaning during operation if possible. In the case of oils, for instance, cleaning during operation is usually implemented by conducting part of the flow which is being filtered back in reversed direction in an endeavour to achieve that the woven mesh, which is the type most often employed, will be flushed clean by the filtered liquid itself. In the foregoing those natural drawbacks have already been described which arise from filter element replacing. The above-mentioned cleaning method during operation, based on reverse flow, also entails a number of drawbacks: the filter mesh fails to be completely cleaned in such a procedure. Secondly, the mesh may suffer damage from the pressure peaks induced by fuel supply pumps. Thirdly, when the liquid quantity required for reverse flushing is large, loss of time is incurred, and unnecessary twice-over purifying of the respective liquid quantity. With the aid of the procedure and the filter of the invention quite significant improvement is achieved regarding the drawbacks mentioned, among others. In order to implement this, the procedure and the filter of the invention are respectively characterized by that which has been stated in the characterising portions of claim 1 and claim 8. The most important advantages of the invention over other cleaning processes which take place during operation are to be seen in that by the procedure of the invention the filter elements will be more completely cleaned, the risk of damaging the filter mesh is prevented and reciprocating running of liquid is avoided. The advantages gained as regards replacement of filter elements are obviously the same as those of cleaning during operation, which have already been discussed. The invention is described in the following, referring in detail to the drawing attached, presenting an embodiment example of the invention. The invention is in no way narrowly confined to the details of said example. As depicted in Fig. 1, the means comprises two identical filter units 1 and 2, these units being alternately one in use and the other in its cleaning cycle, or on conclusion of the cycle in readiness for use, and a switch-over valve assembly 3 with actuating mechanism, and an ultrasonic generator 4. A filter unit is composed of a filter body 1.1, a filter element 1.2 which is exchangeable according to operating need, a filtering residue removal valve 1.3, a single-action pneumatic actuator 1.4, a pilot valve 1.5, a float chamber 1.6 for air venting, a float-operated switch 1.7, a valve 1.8, a filling valve 1.9, a restriction 1.10, an ultrasonic oscillator 1.11, a compressed air flushing valve 1.12, a differential pressure switch or differential,pressure pick-up 1.13 and a control unit 5. Equivalent components of filter unit 2 can be similarly identified as identical components, using reference numerals 2.1 to 2.13, component 2.1 being the equivalent of component 1.1 in filter unit 1, and so on. The switch-over valve assembly consists of a switch-over valve 3.1 for pure liquid, a switch-over valve 3.2 for impure liquid, a pneumatic actuating means 3.3 common to the foregoing components 3.1 and 3.2, and a pilot valve 3.4 for governing the component 3.3. It is assumed in the example illustrating the operation of the means that filter unit 1 is operating, while unit 2 is standing by. The degree of cleanness of the filter elements is monitored with a differential pressure switch, or pick-up, 1.13 installed across the incoming and outgoing pipelines, and to which may also be connected a differential pressure indicator means. When the differential pressure has reached a given, pre-set limit value, the valve 3.4 causes with the aid of the actuating means 3.3 the switch-over valves 3.1 and 3.2 to be positioned so that the liquid to be filtered will pass through the filter unit 2, which was in stand-by state heretofore. During normal filtering, the ultrasonic head 1.11 (2.11) is operated on low power in order to produce a slight cavitation phenomenon within the liquid to homogenize the liquid that is being filtered. When the limit switch on the actuator of the switch-over valve actuator indicates that the liquid is passing through unit 2, unit 1 is switched to the cleaning cycle, the ultrasonic head 1.11 being now switched to receive power at a rate higher than the homogenizing power. The compressed air valve 1.12 opens and the pilot valve 1.5 causes the filtering residue elimination valve 1.3 to open, the size of which valve is selectable with a view to obtaining sufficient throttling, as a result of which the filter chamber will be drained within desired time. When the chamber is filled to capacity, and when it is being emptied, the internal cavitation caused in the liquid by the ultrasonics causes efficient cleaning of the filter elements 1.2. After a pre-set, adjustable time, the ultrasonic generator is switched to lower power and the filter residue elimination valve 1.3 and the compressed air valve 1.12 are closed, whereafter valve 1.9 and valve 1.8 open. Liquid replenishment from the main liquid flow line flows through the restriction 1.10 into filter unit 1. Abrupt disturbances caused by lowered main flow pressure can be eliminated with the restricted flow. Filling to capacity of the filter chamber is observed by automatics, which close the valves 1.9 and 1.8 with the aid of the float-operated switch in the float chambers 1.6. On conclusion of the sequence just described, filter unit 1 remains at stand-by. When the differential pressure in filter unit 2 rises (due to soiling down) to the pre-set value, the above sequence is repeated, now in this latter unit. The liquid filtering and homogenizing procedure is mainly characterized in that the power output of the ultrasonic generator is controlled with a signal from the differential pressure switch or pick-up 1.13 connected across the filter units. This signal may be a limit value-actuated switch-on signal starting the above-described filter cleaning function, or it may be a continuous differential pressure signal from the differential pressure switch 1.13. Since, as is well known, ultrasonics due to the cavitation which they cause have an attritive effect on materials, its power has to be optimized in relation to the interaction of ultrasonics promoting the filtering and liquid homogenizing action. The efficiency of ultrasonics in aiding liquid filtering and homogenizing is furthermore dependent on a number of factors, e.g the pressure, temperature, viscosity and flow velocity of the liquid, the filter mesh size, and the frequency/frequency spectrum of the ultrasonics. Therefore the procedure of the invention for filtering and homogenizing liquids is also mainly characterized in that not only the power but also the frequency of the ultrasonics is controlled not only by said differential pressure switch or pick-up 1.13 but also by a liquid pressure pick-up 1.14, a temperature pick-up 1.15 or a liquid flow rate meter or pick-up 1.16 determining the flow going through the filter units. The procedure for filtering and homogenizing liquids is further characterized in that endeavours are made to maximize the filter area e.g. as shown in the section A-B in Fig. 1, i.e., by disposing cylindrical filter cartridges in concentric circular configuration in the filter body 1.1, and on the outer circle so that ultrasonic cleaning applied in the filtering process might be needed at intervals as infrequent as possible. If needed, various ancillaries promoting the action of the invention just described may be added, for instance a heating system to be connected to the jackets of the filter chambers, when implied by the particular liquids to be filtered and by the filtering conditions.

Claims: A procedure for cleaning filter units automatically when filtering liquid substances and for filtering liquid substances by using ultrasonic oscillators (1.11;2.11) and an ultrasonic generator (4) in which each of said filter units comprises an associated ultrasonic oscillator, the ultrasonic oscillators being driven by an ultrasonic generator (4), said ultrasonic oscillator (1.11;2.11) and generator (4) are being operated upon receiving a signal at a preselected high power level required in cleaning the filter unit (1;2) and a draining valve (1.3;2.3) associated to the filter unit to be cleaned is opened, characterized in that during filtration said ultrasonic oscillator (1.11;2.11) is operated at a lower power level to homogenize the liquid which is being filtered, that a compressed air flushing valve (1.12;2.12) associated to the filter unit is opened at the same time as the ultrasonic oscillator and generator are operated at the high power level, that the draining valve (1.3;2.3) is opened by a pilot valve (1.5;2.5), that the size and degree of throttling of the draining valve (1.3;2.3) are adjusted to regulate a filter unit emptying time so that a desired cleaning time for the ultrasonic cleaning procedure may be effected, that after an adjustable predetermined time, the ultrasonic generator is switched to a lower power level required for homogenizing the substance which is being filtered and the draining valve (1.3;2.3) and the compressed air flushing valve (1.12;2.12) are closed whereafter a h valve (1.8;2.8) which connects the filter unit (1;2) to the atmosphere and a filling valve (1.9;2.9) are opened to refill the filter unit (1;2) with the liquid substance which derives from a main liquid flow line through a restriction (1.10;2.10), and that automatics observe filling to capacity of the filter chamber (1;2) and close the filling valve (1.9;2.9) and the valve (1.8;2.8) which connects the filter unit (1,2) with the atmosphere by means of a float operated switch in a float chamber (1.6;2.6). Procedure according to claim 1, characterized in that the power of the ultrasonic oscillator (1.11;2.11) is controlled on the basis of the differential pressure present across the filter unit (1;2). Procedure according to claim 1, characterized in that the power of the ultrasonic oscillator (1.11;2.11) is controlled on the basis of the flow rate of the substance flowing through the filter unit (1;2). Procedure according to claim 1, characterized in that the power of the ultrasonic oscillator (1.11;2.11) is controlled on the basis of the liquid pressure acting in the filter unit (1;2). Procedure according to claim 1, characterized in that the power of the ultrasonic oscillator (1.11;2.11) is controlled on the basis of the temperature of the liquid flowing through the filter unit (1;2). Procedure according to one of claims 1 to 5, characterized in that the power of ultrasonic cleaning is increased by varying the pressure acting in the filter unit (1;2). Procedure according to one of claims 1 to 6, characterized in that the cleaning effect of the filter and homogenizing effect of the liquid flowing throught the filter unit (1;2) are increased by varying the frequency and the frequency spectrum of the ultrasonic oscillator (1.11;2.11). Filter suitable to be cleaned by the procedure according to claims 1 to 7, comprising filter units (1;2), each filter unit comprising an operatively-connected ultrasonic oscillator (1.11;2.11), an ultrasonic generator (4) for driving said ultrasonic oscillators (1.11;2.11), means which, upon receiving a signal, switches the oscillator (1.11;2.11) to a higher power level required for cleaning the associated filter unit (1;2), a draining valve (1.3;2.3) and a filling valve (1.9) associated to each filter unit, characterized by the ultrasonic generator (4) being arranged to operate the oscillator (1.11;2.11) at a lower power level during filtration, compressed air flushing valves (1.12;2.12) associated to each filter unit and being openable at the same time as the means switches the oscillator (1.11;2.11) to said high power level, a pilot valve (1.5;2.5) for opening the draining valve (1.3;2.3), the size and degree of throttling of the draining valve (1.3;2.3) being adjustable to regulate a filter unit emptying time so that a desired cleaning time for the ultrasonic cleaning procedure may be effected, by said means being arranged to switch the oscillator after an adjustable predetermined time to a lower power level required in homogenizing the substance which is being filtered, by a restriction (1.10;2.10) associated to a main liquid flow line for restricting the liquid flow when refilling the filter unit (1;2) after the cleaning procedure, and by automatics for closing the filling valve (1.9) and a valve (1.8;2.8) which connects the filter unit (1;2) to the atmosphere by means of a float-operated switch arranged in a flow chamber (1.6;2.6) when the capacity of the filter unit (1;2) is reached. Filter according to claim 8, characterized in that the power of the ultrasonic oscillator (1.11;2.11) is controlled on the basis of the differential pressure present across the filter unit (1;2). Filter according to claim 8, characterized in that the power of the ultrasonic oscillator (1.11;2.11) is controlled on the basis of the flow rate of the substance flowing through the filter unit. Filter according to claim 8, characterized in that the power of the ultrasonic oscillator (1.11;2.11) is controlled on the basis of the liquid pressure acting in the filter unit (1;2). Filter according to claim 8, characterized in that the power of the ultrasonic oscillator (1.11;2.11) is controlled on the basis of the temperature of the liquid flowing through the filter unit (1;2). Filter according to one of claims 8 to 12, characterized by one or several ultrasonic elements with different frequencies or power. Filter according to one of claims 8 to 13, characterized in that within the filter unit (1;2) one or several cylindrical filter elements (1.2;2.2) are installed parallel to the longitudinal axis of the filter unit (1;2).

Inventors: LAIHO KARI, LAIHO, KARI
Applicants: LAIHO KARI, LAIHO, KARI
Application year: 1989
Main classification: B01D35
IPC codes: B01D35, B01D29