WO1996041675A1 - Process and device for controlling a reverse osmosis system for water treatment - Google Patents

Abstract

In the reverse osmosis system for water treatment according to the invention, part of the concentrate is fed back to the raw water side and part is ejected by derivation into the drain. When the load on the capacity of the system changes, the drainage of the concentrate is altered by corresponding measuring and adjusting units (31, 32; 29, 30; 42, 47-49; 14, 50a, b, c, 51-57) to the same extent as the changes in the raw water intake in such a way that the ratio between the two flows remains at least approximately constant. A direct indication of the yield (= permeate outflow/raw water intake) is derived from the ratio between the concentrate outflow and the raw water intake. Devices (27, 32) for automatically adjusting the concentrate outflow/raw water intake ratio (and hence the yield) to variations in the quality of the raw water are also provided.

Description

Method and device for controlling a reverse osmosis system for water treatment

The invention relates to a method for regulating a reverse osmosis system according to the preamble of the main claim. Systems of this type are required, inter alia, in conjunction with hemodialysis machines in order to provide sufficiently pure water which is as germ-free as possible for the production of the dialysis liquid.

The principle of operation of reverse osmosis systems is known to be that the water to be treated is passed in a filter module under high pressure along the surface of a semipermeable membrane, part of the water, the so-called permeate, passing through the membrane and on the other side the membrane is collected and fed to the consumption points. The part of the raw water which does not pass through the membrane and is enriched with retained substances, the so-called concentrate, flows out of the membrane module at the end of the flow path of the primary space.

When operating reverse osmosis systems, the need for treated water can fluctuate greatly, so that the system is often only used to a part of its capacity. Known methods for adapting the output consist of returning the excess permeate to the raw water circuit or reducing the delivery capacity of the pump used to generate pressure, so that the need for raw water to be supplied is correspondingly reduced. The mixed water formed from raw water and recycled permeate has a reduced pollutant concentration, so that the permeate produced from this achieves a correspondingly higher quality.

It is also known to also return part of the outflowing concentrate back into the raw water inflow. Although this measure tends to lead to a deterioration in the quality of the permeate in the sense of an increase in the content of dissolved substances, on the other hand it also leads to an advantageous reduction in the raw water requirement for a certain amount of permeate produced. However, the recycled concentration may be taken into account both with regard to the quality of the permeate produced and with regard to an excessive pollutant concentration on the raw water side of the filter membrane, which may can lead to premature degeneration of the membrane, not be too high.

The invention was based on the object of equipping a reverse osmosis system in such a way that the return of concentrate is automatically adapted even in the event of fluctuating capacity utilization in such a way that the tendentially opposite demands (a) for the highest possible quality of the permeate produced, which corresponds to the intended use, and ( b) after the best possible utilization of the raw water, even with changing capacity utilization of the system. This object is achieved by the features mentioned in the characterizing part of the main claim.

Further features and configurations of the invention result from the subclaims and the following description of exemplary embodiments in conjunction with the figures. It shows

Fig. 1 - the scheme of a urine osmosis system with features according to the invention,

2 shows the diagram of another exemplary embodiment with pressure-controlled concentrate return,

Fig.3 - the schematic of an embodiment with float-controlled concentrate return.

The installation of a reverse osmosis system with design features according to the invention is shown as an example and purely schematically in FIG. 1. The raw water, the inflow of which can be blocked or released by a valve 40, passes via line 10a, b into a container 11 which can be ventilated via a sterile filter 12 and is thus approximately under atmospheric pressure. The level is regulated, for example, by a float 14 which more or less opens or closes an inflow valve 13. From the container, the water passes through the line 15 via the pump 16 into the filter module 17, the primary space 17a of which is separated from the secondary space 17b by a semipermeable membrane 18. The permeate flows from the secondary space into the consumer line 19. Excess permeate can be returned to the container 11 via the line 20a, b, the pressure maintaining valve 21 inserted between the line sections 20a and 20b determining the pressure prevailing in the consumer line 19.

The concentrate flows from the outlet of the primary space of the filter module via line 22a, b to a branching point 23, from which a part of the concentrate returns via line 24a, b to container II and the rest via line 25a, b , c is led into the drain. An between The control valve 26 inserted into the line sections 22a and 22b essentially determines the pressure prevailing in the primary space of the filter module, which is necessary for the filtration.

The flow resistance of the line 24a, b including inserted further components, for example a conductivity measuring cell 27 and / or other parts (not taken into account in FIG. 1), which can be adjusted as required, lies between the branching point 23 and the container. The same applies to the connection via the line sections 25a, b, c to the drain 28. The ratio between the recirculated and the concentrate portion fed into the drain depends on the hydrostatic pressure differences on the lines mentioned and the ratio of the flow resistances.

The invention provides that the concentrate flow in the drain line automatically adjusts to the raw water inflow, at least approximately in such a way that these two flows are brought into a constant relationship to one another. A measuring element, which detects the raw water inflow, and an actuator, which is controlled by the latter and determines the concentrate outflow, serve this purpose. A suitable measure for adjusting the concentrate outflow consists in changing the flow resistance in at least one of the two lines 24a, b and 25a,, c or the pressures acting on them. In Fig. 1, the former possibility is realized by inserting a controllable valve 29 between the line sections 25b and 25c, which valve is actuated via the actuator 30, e.g. in the form of a servo motor.

In the exemplary embodiment according to FIG. 1, the flow sensor inserted into the raw water inflow serves as the measuring element 31, for example in the form of an impeller flow meter, which emits an electrical signal, the frequency of which is proportional to the flow. This signal is converted by an adaptation circuit 32 into a signal suitable for controlling the actuator 30. By properly coordinating the transmission characteristics of the adaptation circuit 32, taking into account the setting characteristics of the controllable valve 29, it can be achieved that changes in the flow in the raw water line caused by changes in the capacity utilization lead to proportional changes in the same direction in the concentrate discharge with sufficient accuracy.

Which accuracy is to be regarded as sufficient with regard to the proportionality depends on the accuracy with which the yield of the system (see below) is to be kept constant in the event of fluctuations in the capacity utilization. High accuracy requirements can be met more reliably, but with greater effort in terms of device technology, by means of a control circuit with feedback, in that a flow meter 33 is also inserted into the line leading to the drain, the signal of which is also fed to the adaptation circuit 32, which in this further embodiment Has the function of an actual controller. By forming the quotient of concentrate discharge and raw water inflow and comparing this quotient with a predetermined target value, the actuator can be influenced on the basis of a determined deviation so that the quotient always reaches the intended value. This arrangement of two flow meters also has the significant advantage that a direct display of the so-called yield can be derived from the measured values of the two flows. Below that is Relationship between the permeate flow used and the raw water flow used for this purpose. The yield e can be calculated from the measured value of the raw water inflow Qw and the concentrate outflow Qa according to the relationship e = 1 - Qa / Qw, since Qa represents the difference between the raw water inflow and the permeate flow directed to the consumers. The technical implementation of such a calculation and its implementation in a corresponding analog or digital display requires no further explanation for the person skilled in the art. The corresponding devices can be part of the adaptation circuit 32, for which purpose this is additionally equipped with a display device 34 for the yield.

When a certain yield is set, which is synonymous with the setting of a certain ratio of the concentration runoff and raw water inflow, certain concentration ratios between raw water, permeate and outflowing concentrate are established for the substances dissolved in the water. These are different for the individual substances and depend on the permeability of the semipermeable membrane of the filter module for the substance under consideration. The setting of the ratio of concentrate discharge and raw water inflow and thus the yield is expediently carried out on the basis of analysis values of the substances, the concentration of which is of particular importance. However, the raw water content of these substances can fluctuate considerably. In view of this, a further embodiment of the invention provides devices for the continuous or periodic determination of analysis values and an automatic adjustment of the set ratio of concentrate outflow and raw water inflow. Suitable sensors for determining analysis values are, for example, in the form of ion-selective electrodes available. For the treatment of tap water, for example for the water supply of hemodialysis machines, a measurement of the electrical conductivity also provides useful information about the total content of dissolved substances, since these are largely present in the form of dissolved salts. For this purpose, a conductivity measuring cell 27 is inserted into the concentrating line leading to the outlet in FIG. 1, which delivers its measuring signal to the adaptation device 32. On the basis of this measurement signal, the ratio of concentrate outflow and raw water inflow is increased according to a pre-programmable function if the measured concentration increases, namely until it reaches a predetermined value again. The control behavior of such a concentration control, in particular the reaction to sudden changes in the concentration of the raw water, can be improved by the adaptation circuit 32 additionally measuring the signal of a conductivity measuring cell built into the raw water line or into the container 11 (in FIG. 1 not shown) is supplied in order to increase the ratio of concentrate outflow and raw water inflow in the event of an increase in concentration in the raw water, even before this is also noticeable at the installation location of the conductivity measuring cell 27.

The diagram in Fig. 2 shows another embodiment of the invention. The measurement of the raw water inflow for automatic adjustment of the concentrate outflow takes place here by means of an adjustable throttle 42, which is inserted between the fill level control valve 13 and the raw water outlet 46, via which the raw water flows freely into the container 11. In line 41, which connects the fill level control valve to throttle 42, a pressure is generated which is dependent on the raw water inflow and is connected to a connected one Manometer 44 can be measured and, in this embodiment, forms the actual measured variable and at the same time the manipulated variable for setting the ratio of raw water inflow and concentrate outflow. This ratio is set here in that the concentrate portion returned to the container 11 is changed in the opposite direction to the raw water inflow, so that the portion discharged into the outflow inevitably changes in the same direction as the raw water inflow. An increase in the raw water inflow has the result that the pressure difference between the branching point 23 and the line 41, into which the returning concentrate line 24a,, c also opens, is reduced. As a result, the flow rate in this line decreases and the flow rate in the line 25a, b, c leading to the outflow increases to the same extent. The quantitative relationship between a change in the raw water inflow and the resultant change in the concentrate outflow can be adjusted by means of the throttle 42 and by means of adjustable flow resistors 47, 48, 49 in the returning and the outflow of the concentrate line so that the yield at fluctuating capacity utilization of the system remains constant with sufficient accuracy.

The flow sensors 31 and 33 are not part of the control device in the exemplary embodiment according to FIG. 2. In conjunction with the display device 34, which is equipped in the manner described above with devices for determining the yield from the two measured flows, they form an advantageous aid for monitoring the yield and for correctly setting the system in the event of fluctuating raw water quality. A particular advantage of the arrangement according to FIG. 2 is that its function is realized with simple hydraulic components which only require low manufacturing costs and which allow a high level of operational safety with simple means.

In the arrangement according to FIG. 3, the level controller for the container 11 also has the function of a measuring element for the raw water inflow. The float 14 and the closure piece of the inlet valve 13 which throttles the raw water inflow are connected to one another by a linkage 50a, b, c which converts a vertical movement of the float into a horizontal movement of the closure piece. At constant pressure in the raw water line 10, the position of the closure piece and thus also the position of the float 14 is a measure of the currently set raw water inflow. The movement of the float is transmitted through the rod 51 and the spring 56 to an actuator which adjusts the portion of the concentrate flow conducted via the line 25 into the drain. A slide 52 is used for this purpose, which increasingly opens an outflow opening 53 leading to the discharge line 25 when the float 14 has a relatively low position when there is a high inflow of raw water. The concentrate line 22b coming from the filter module is connected above the slide to a narrowed part in the lower region of the container in order to ensure that only concentrate actually flows away. The characteristic of the measuring element and the actuator and the resultant relationship between raw water inflow and concentrate outflow can be changed by means of adjusting devices 54 and 55, with which an abutment of the linkage 50a, b, c is displaced or the force of a spring 57 ju¬ acting on the slide 52 bull. The features described in the exemplary embodiments can be combined with one another in various ways, modified and expanded. In particular, other means known per se can also be used for the detection of the raw water inflow and for the generation of the movement for actuating the actuator, for example measuring orifices or flow devices in the manner of the water jet pump in connection with piston-cylinder arrangements or actuating elements with elastic seals such as Bellows or membranes.

Claims

claims 1. A method for controlling a reverse osmosis system with a filter module for separating the raw water supplied into filtered pure water (permeate) and unfiltered waste water (concentrate) enriched with retained substances and devices for returning a variable proportion of the concentrate into the raw water inflow and discharge of the remaining portion of the concentrate into the outflow, characterized in that a manipulated variable derived from the raw water inflow divides the concentrate into the recirculated portion ("concentrate return flow") and the portion led into the outflow ( ⁿ concentrate outflow ") influences the way that a change in the raw water inflow leads to a change in the same direction in the concentrate outflow. 2. The method according to claim 1, characterized in that in the event of changes in the raw water inflow, the ratio of concentrate outflow and raw water inflow is kept approximately constant in accordance with a predetermined setpoint. 3. The method according to claim 2, characterized in that the ratio of concentrate discharge and raw water inflow is measured and the manipulated variable is generated by a controller on the basis of a comparison between the measured ratio and the target value of this ratio. 4. The method according to claim 2 or 3, characterized in that the setpoint as a function of analysis values of Water is automatically adjusted so that the ratio of concentrate runoff and raw water inflow increases with increasing content of dissolved substances. 5. The method according to claim 4, characterized in that a measurement of the electrical conductivity of the concentrate is used to determine the target value. 6. The method according to any one of the preceding claims, characterized in that the raw water inflow Qw and the Konzentra¬ tabflow Qa are measured and the yield e derived from the measured values according to the relationship e = 1 - Qa / Qw and displayed. 7. The method according to at least one of the preceding Ansprü¬ che, characterized in that the manipulated variable for changing the concentrate discharge is derived from the measurement signal of a flow meter inserted in the raw water supply line. 8. The method according to any one of claims 1 to 6, characterized ge indicates that the manipulated variable for changing the concentra flow is derived from the position of a float valve serving to regulate the Rohwas¬ water inflow in a buffer vessel. 9. The method according to any one of claims 1 to 5, characterized ge indicates that the manipulated variable for changing the Konzen¬ trass discharge is derived from the raw water inflow dependent pressure differences. 10. The method according to claim 9, characterized in that a pressure difference dependent on the raw water inflow directly adjusts the counter reflux as a variable and thereby indirectly the concentrate outflow. 11. The device for performing the method according to claim 10, with a reverse osmosis filter (17), the primary space (17a) by a pump (16) from a pressurized, with the raw water inflow (l0a, b) via a fill level controller ( 13, 14) connected buffer vessel (11) is fed, with devices (20a, b, 21) for returning excess permeate produced into the buffer vessel and further devices (24a, b, c, 47, 48) for returning part of the Concentrate in the buffer vessel and devices (25a, b, 49) for discharging the remaining part of the concentrate into the drain, characterized in that between the outlet of the control valve (13) regulating the raw water inflow into the buffer vessel and the free outlet in the line (46) forming the buffer vessel, an adjustable flow resistance (42) is inserted and the concentrate return line (24) into a branch between the control valve (13) and the egg adjustable flow resistance (42) opens.