Blending control method with determination of untreated water hardness via the conductivity of the soft water and blended water

Abstract

A method for operating a water softening plant includes an automatic blending device, an incoming flow of untreated water being divided into a first partial flow which is softened and a second partial flow which is not softened and then combined into a flow of blended water. The proportions of the two partial flows are adjusted by the automatic blending device such that a desired hardness DV results in the flow of blended water. The conductivity of the softened water and blended water are measured by conductivity sensors in their respective flows. The conductivity of the untreated water is calculated from the measured conductivity of the soft water, from the measured conductivity of the blended water and from the determined proportions of the partial flows. It is possible for the hardness of the blended water to be adjusted very reliably and with improved accuracy.

Claims

1. A method for operating a water softening plant comprising the steps of: providing the water softening plant comprising an automatic blending device, an incoming flow of untreated water V.sub.untreated being divided into a first partial flow V.sub.part1 which is softened, and a second partial flow V.sub.part2 which is not softened, and the two partial flows V.sub.part1, V.sub.part2 being combined into a flow of blended water V.sub.blended; adjusting by the automatic blending device the proportions of the two partial flows Prop.sub.part1, Prop.sub.part2 in the flow of blended water V.sub.blended such that a desired hardness results in the flow of blended water V.sub.blended; calculating the proportions to be adjusted of the two partial flows Prop.sub.part1, Prop.sub.part2 from a hardness of the untreated water H.sub.untreated and from a hardness of the softened water H.sub.soft; deriving the hardness of the untreated water H.sub.untreated from the conductivity of the untreated water Cond.sub.untreated; measuring the conductivity of the softened water Cond.sub.soft by a conductivity sensor in the first partial flow V.sub.part1; measuring the conductivity of the blended water Cond.sub.blended by a conductivity sensor in the flow of blended water V.sub.blended; determining the proportions of the partial flows Prop.sub.part1, Prop.sub.part2 in the flow of blended water V.sub.blended; and calculating the conductivity of the untreated water Cond.sub.untreated from the measured conductivity of the soft water Cond.sub.soft, from the measured conductivity of the blended water Cond.sub.blended and from the determined proportions of the partial flows Prop.sub.part1, Prop.sub.part2.

2. The method according to claim 1, wherein the conductivity of the untreated water Cond.sub.untreated is calculated using the formula: ${\mathrm{Cond}}_{\mathrm{untreated}}=\frac{{\mathrm{Cond}}_{\mathrm{blended}}-{\mathrm{Prop}}_{\mathrm{part}1}.Math.{\mathrm{Cond}}_{\mathrm{soft}}}{{\mathrm{Prop}}_{\mathrm{part}2}}.$

3. The method according to claim 2, wherein the proportions of the partial flows Prop.sub.part1, Prop.sub.part2 in the flow of blended water V.sub.blended are determined by two flowmeters.

4. The method according to claim 1, wherein in order to determine the proportions of the partial flows Prop.sub.part1, Prop.sub.part2, including a step of arranging a first flowmeter in the first partial flow V.sub.part1 and arranging a second flowmeter in the flow of blended water V.sub.blended.

5. The method according to claim 1, wherein the proportions of the partial flows Prop.sub.part1, Prop.sub.part2 are determined from an adjustment position of the automatic blending device, the automatic blending device comprising a sensor for determining the adjustment position.

6. The method according to claim 1, including the step of averaging over an averaging period T or across a number N of single measurements the conductivity Cond.sub.soft measured by the conductivity sensor in the first partial flow V.sub.part1 and the conductivity Cond.sub.blended measured by the conductivity sensor in the flow of blended water V.sub.blended, wherein the averaged values of Cond.sub.soft and Cond.sub.blended are used in calculating the conductivity of the untreated water Cond.sub.untreated.

7. The method according to claim 6, wherein the proportions of the partial flows Prop.sub.part1, Prop.sub.part2 are not changed by the automatic blending device during the averaging period T or across the number N of single measurements.

8. The method according to claim 6, wherein the proportions of the two partial flows Prop.sub.part1, Prop.sub.part2 are also averaged over the averaging period T or across a number N of single determinations, and the averaged values of Prop.sub.part1 and Prop.sub.part2 are used to calculate Cond.sub.untreated.

9. The method according to claim 6, wherein the step of averaging is over the averaging period T, wherein the averaging period T is at least 2 minutes.

10. The method according to claim 6, wherein the step of averaging is over the averaging period T, wherein the averaging period T is at least 10 minutes.

11. The method according to claim 6, wherein the step of averaging is across the number N of single measurements, wherein the number N of single measurements or of single determinations is at least 100.

12. The method according to claim 6, wherein the step of averaging is across the number N of single measurements, wherein the number N of single measurements or of single determinations is at least 1000.

13. The method according to claim 6, wherein some of the values which fall within the averaging period T or which belong to the number N of single measurements or a single determination are disregarded for the determination of the averaged value of Cond.sub.soft and/or Cond.sub.blended and/or of the proportions of Prop.sub.part1, Prop.sub.part2.

14. The method according to claim 13, wherein the disregarded values are outside a predetermined value interval, or in that the disregarded values belong to a predetermined relative proportion of highest or lowest values in the averaging period T or within the N single measurements or single determinations.

15. The method according to claim 1, wherein at regular intervals at least every 10 minutes in an automatic manner the conductivity of the untreated water Cond.sub.untreated is recalculated from current values of Cond.sub.soft, Cond.sub.blended, Prop.sub.part1 and Prop.sub.part2, the hardness of the untreated water H.sub.untreated is derived again therefrom, the proportions, to be adjusted, of the partial flows Prop.sub.part1, Prop.sub.part2 are recalculated therefrom, and an adjustment position of the automatic blending device is readjusted accordingly.

16. The method according to claim 15, wherein the regular intervals are at least every 2 minutes.

17. The method according to claim 1, wherein the hardness H.sub.soft of the first partial flow V.sub.part1 is assumed to be H.sub.soft=0 dH.

18. The method according to claim 1, wherein a hardness of the untreated water H.sub.untreated which is used to control a regeneration procedure of a softening device of the water softening plant is derived from the calculated conductivity Cond.sub.untreated of the untreated water by a first calibration characteristic curve K1, and in that the hardness of the untreated water H.sub.untreated which is used to control the automatic blending device is derived from the calculated conductivity Cond.sub.untreated of the untreated water by a second calibration characteristic curve K2, wherein the first calibration characteristic curve K1 is based on a conversion factor of 30 S/cm per dH, and wherein the second calibration characteristic curve K2 is based on a conversion factor of 38 S/ dH.

19. The water softening plant comprising the automatic blending device, having the conductivity sensor in the soft water region and the conductivity sensor in the blended water region, designed to implement the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is illustrated in the drawings and will be described in more detail on the basis of embodiments. In the drawings:

(2) FIG. 1 shows the schematic construction of an embodiment of a water softening plant according to the invention, comprising two conductivity sensors and two flowmeters;

(3) FIG. 2 shows the schematic construction of a further embodiment of a water softening plant according to the invention, comprising two conductivity sensors and one flowmeter as well as a sensor for determining the adjustment position of the automatic blending device; and

(4) FIG. 3 is a schematic flow chart of the method according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) FIG. 1 shows, by way of example, a water softening plant 1 according to the invention for implementing the method according to the invention.

(6) The water softening plant 1 is connected to a local water supply system, for example to the drinking water network, by an inlet 2. The entire flow of untreated water V.sub.untreated flowing in the inlet 2 is divided into two partial flows at a branch point 20.

(7) A first partial flow V.sub.part1 of the (entire) untreated water flow V.sub.untreated flows into a softening device 4 which has in particular a control head 5 and two tanks 6a, 6b containing ion exchange resin 7. A second partial flow V.sub.part2 flows into a bypass line 8.

(8) The untreated water of the first partial flow V.sub.part1 flowing into the softening device 4 flows through at least one of the two tanks 6a, 6b containing ion exchange resin 7, the water being completely softened. In the process, the hardeners, i.e. calcium ions and magnesium ions, are stoichiometrically exchanged for sodium ions. The softened water then flows through a conductivity sensor 9a, which determines the conductivity Cond.sub.soft in the softened first partial flow V.sub.part1, and through a flowmeter 3a.

(9) The second partial flow V.sub.part2 in the bypass line 8 passes through an automatically actuatable blending device 19, here comprising a blending valve 11 which can be adjusted by a servomotor 10.

(10) The first partial flow V.sub.part1 and the second partial flow V.sub.part2 are finally combined at a combining point 21 to produce a blended water flow V.sub.blended which flows to an outlet 12. The outlet 12 is connected to a downstream water installation, for example to the freshwater pipes of a building. The blended water flow V.sub.blended is measured by a flowmeter 3b. Furthermore, the conductivity of the blended water Cond.sub.blended is measured by the conductivity sensor 9b.

(11) The measurement results of the conductivity sensors 9a, 9b and of the flowmeters 3a, 3b are transmitted to an electronic control device 13. In turn, the electronic control device 13 can actuate the servomotor 10 of the blending valve 11 and can thereby adjust the second partial flow V.sub.part2. The ratio of the second partial flow V.sub.part2 to the first partial flow V.sub.part1, the flow cross section of which is not variable here, can thus be changed. The electronic control device 13 can be considered as belonging to the automatic blending device 19.

(12) A desired value DV for a blended water hardness is stored in the electronic control device 13. The following procedure is carried out in order to provide the desired water hardness H.sub.blended in the blended water at the outlet 12.

(13) The control device 13 firstly reads out a current soft water conductivity Cond.sub.soft at the conductivity sensor 9a and a current blended water conductivity Cond.sub.blended at the conductivity sensor 9b. At the same time the current partial flow V.sub.part1 is determined by flowmeter 3a and the current blended water flow V.sub.blended is determined.

(14) The conductivity of the untreated water Cond.sub.untreated is then calculated using formula:

(15) ${\mathrm{Cond}}_{\mathrm{untreated}}=\frac{{\mathrm{Cond}}_{\mathrm{blended}}-{\mathrm{Prop}}_{\mathrm{part}1}.Math.{\mathrm{Cond}}_{\mathrm{soft}}}{{\mathrm{Prop}}_{\mathrm{part}2}}.$
where Prop.sub.part1=V.sub.part1/V.sub.blended and Prop.sub.part2=V.sub.part2/V.sub.blended. Using the correlation V.sub.part1+V.sub.part2=V.sub.blended, the variable V.sub.part2 can be eliminated, and the following formula results:

(16) ${\mathrm{Cond}}_{\mathrm{untreated}}=\frac{V_{\mathrm{blended}}.Math.{\mathrm{Cond}}_{\mathrm{blended}}-V_{\mathrm{part}1}.Math.{\mathrm{Cond}}_{\mathrm{soft}}}{V_{\mathrm{blended}}-V_{\mathrm{part}1}}.$

(17) This formula is stored in a memory 18 of the control device 13, as is all the other information required for the control functions of the water softening plant 1.

(18) For example, if Cond.sub.soft=660 S/cm, Cond.sub.blended=645 S/cm, V.sub.part1=5,000 cm.sup.3/min and V.sub.blended=15,000 cm.sup.3/min, then Cond.sub.untreated=638 S/cm.

(19) The untreated water hardness can then be determined from this conductivity of the untreated water Cond.sub.untreated. It is noted that in this situation, assuming that the untreated water conductivity is 95% of the soft water conductivity, then an untreated water conductivity of 627 S/cm would be produced, which corresponds to a difference of almost 2%.

(20) In the embodiment shown, the untreated water hardness is calculated twice in different ways by the control device 13 from the untreated water conductivity Cond.sub.untreated. Firstly, an untreated water hardness H.sub.untreated which is used for the regeneration control of the softening device 4 is determined using a first calibration characteristic curve K1. Here, the first calibration characteristic curve K1 is based on a conversion factor of 30 S/cm per dH in this case, which is stored in the memory 18 of the control device 13. In the above example where Cond.sub.untreated=638 S/cm, this thus produces an untreated water hardness H.sub.untreated of 21.3 dH for the purpose of the regeneration control.

(21) Secondly, using a second calibration characteristic curve K2, an untreated water hardness H.sub.untreated is determined which is used for the blending control. Here, the second calibration characteristic curve K2 is based on a conversion factor of 38 S/ dH. When Cond.sub.untreated=638 S/cm, an untreated water hardness H.sub.untreated of 16.8 dH for the purpose of the blending control is then produced.

(22) Using the untreated water hardness H.sub.untreated, the required proportions Prop.sub.part1, Prop.sub.part2 of the two partial flows V.sub.part1, V.sub.part2 in the blended water flow V.sub.blended can then be calculated by the control device 13 in order to achieve a particular desired value DV of the blended water hardness H.sub.blended.

(23) The correlation between the hardness in the soft water H.sub.soft, the hardness in the untreated water H.sub.untreated and the hardness H.sub.blended in the blended water is:
H.sub.blended=Prop.sub.part1.Math.H.sub.soft+Prop.sub.part2.Math.H.sub.untreated.
When Prop.sub.part2=1Prop.sub.part1 and solved for Prop.sub.part1, there results:

(24) ${\mathrm{Prop}}_{\mathrm{part}1}=\frac{H_{\mathrm{untreated}}-H_{\mathrm{blended}}}{H_{\mathrm{untreated}}-H_{\mathrm{soft}}}.$

(25) When H.sub.blended=DV, a desired proportion Prop.sub.part1(DV) then results for the first partial flow V.sub.part1, to which the blending valve can then be adjusted. If the current proportion Prop.sub.part1=V.sub.part1/V.sub.blended is less than Prop.sub.part1(DV), the soft water proportion is then increased during blending by adjusting the blending valve 11. If the current proportion Prop.sub.part1=V.sub.part1/V.sub.blended is greater than Prop.sub.part1(DV), the soft water proportion is then decreased by adjusting the blending valve.

(26) H.sub.soft in the above formula can usually be assumed to be 0 dH in a good approximation, thereby further simplifying the calculation.

(27) If, for example, when H.sub.untreated=16.8 dH from the above example, the blended water hardness is to be adjusted to 5.0 dH, i.e. DV=5.0 dH, then at an assumed soft water hardness H.sub.soft of 0 dH, a desired proportion for the first partial flow is Prop.sub.part1(DV)=0.70 or 70%. The electronic control device 13 then adjusts this proportion at the blending valve 11 by means of the servomotor 10.

(28) The electronic control device 13 also monitors the state of exhaustion of the ion exchange resin 7 in the two tanks 6a, 6b. When water is removed, the removed quantity of soft water (cf. the first partial flow V.sub.part1 and the water meter 3a) is in each case weighted with the associated current untreated current water hardness H.sub.untreated calculated for the regeneration control, and is subtracted from the current residual capacity. If a tank 6a, 6b is exhausted, the electronic control device 13 takes the exhausted tank 6a, 6b from the network and subjects it to regeneration, and the other tank 6a, 6b can take over the provision of soft water for this time. For regeneration, a regeneration valve 14 comprising a servomotor 15 is automatically actuated by the electronic control device 13, as a result of which regenerating agent solution (preferably brine) 16 flows out of a storage vessel 17 through the exhausted tank 6a, 6b.

(29) In a variant of the described method, it can be provided to resort to averaged values of Cond.sub.soft and Cond.sub.blended for the determination of the untreated water conductivity Cond.sub.untreated. For this purpose, a relatively large number of single measurements, for example N=8, is typically carried out and the average is formed in each case, cf. the following Table 1 (values in S/cm in each case):

(30) TABLE-US-00001 TABLE 1 N.sub.i 1 2 3 4 5 6 7 8 Average Cond.sub.soft 660 665 690 655 660 640 610 665 656 Cond.sub.blended 645 635 655 640 580 640 650 650 637

(31) The averaging above all prevents pointless single readjustments, here for example for measurements no. 5 (where Cond.sub.blended is obviously too low) and no. 7 (where Cond.sub.blended was measured as being greater than Cond.sub.soft which is physically implausible). The adjustment position of the blending device 19 is readjusted here in each case, after (here) N=8 single measurements were made and the averaging was carried out using these single measurements, on the basis of the averages obtained. It is noted that the single measurements can be distributed evenly over the period of time between two readjustments, or they can also be bundled together, in particular all shortly before the end of the period of time between two readjustments.

(32) It is also possible to discard single values of a group of values for the averaging, for example in the above example in each case the highest and lowest measured value from each group of N=8 single measurements, cf. Table 2 showing corresponding deletions (values again in S/cm). As a result, the averaging quality can generally be further improved.

(33) TABLE-US-00002 TABLE 2 N.sub.i 1 2 3 4 5 6 7 8 Average Cond.sub.soft 660 665 655 660 640 665 658 Cond.sub.blended 645 635 640 640 650 650 643

(34) FIG. 2 shows an alternative construction of a water softening plant 1 according to the invention. Only the essential differences compared with the previous construction are described.

(35) In this water softening plant 1, there is only one flowmeter 3 in the still undivided inflowing untreated water flow V.sub.untreated. Here, the blending valve 11 is provided with an additional sensor 11a, by means of which the adjustment position of the blending valve 11, measured here as the extended length of a locking pin, can be read out. For example the following Table 3 is stored in the control device 13 for this purpose:

(36) TABLE-US-00003 TABLE 3 Extended length Prop.sub.part1 Prop.sub.part2 0 mm 0.25 0.75 1 mm 0.30 0.70 2 mm 0.40 0.60 3 mm 0.55 0.45 4 mm 0.75 0.25 5 mm 1 0

(37) Here, the locking pin can be extended by between 0 mm and 5 mm. When the locking pin is fully retracted (position 0 mm), the greatest possible second partial flow V.sub.part2 of 75% is established at the blended water flow V.sub.blended. The second partial flow V.sub.part2 can be completely blocked by fully extending the locking pin (position 5 mm); in this case, soft water is provided at the outlet 12.

(38) The division of the proportions Prop.sub.part1, Prop.sub.part2 can then be determined at any time from the position of the locking pin. Proportions Prop.sub.part1, Prop.sub.part2 in explicitly tabled positions can be read off directly from Table 3, and the proportions Prop.sub.part1, Prop.sub.part2 are determined by linear interpolation at positions of the locking pin between the indicated table points. Thus, for example, an extended length of 1.5 mm corresponds to a proportion Prop.sub.part1 of 35%, or a proportion Prop.sub.part1 of 60% corresponds to an extended length of 3.25 mm.

(39) In this embodiment, a flowmeter is not required for the blending control. Using the flowmeter 3 (together with the current proportion Prop.sub.part1 that accounts for the first partial flow V.sub.part1 during a respective water removal and with the current untreated water hardness H.sub.untreated), only the absolute quantity of water which has been treated since the last regeneration of the softening device 4 is followed here in order to be able to promptly initiate the next regeneration.

(40) FIG. 3 is a flow chart of the method according to the invention, for example as implemented in the water softening plant of FIG. 1.

(41) During normal operation, the water softening plant continuously provides blended water 100, the proportions Prop.sub.part1 of softened water (first partial flow) and Prop.sub.part2 of non-softened water (second partial flow) in the blended water, to which the automatic blending device is adjusted, being predetermined, for example by a previous calculation (see step 112) or by standard programming for the start of the method according to the invention. Using these proportions, a predetermined desired value DV is at least approximately obtained as the hardness of the blended water H.sub.blended.

(42) Typically, at the end of a particular period of time since the start of the method or since the last recalculation of the proportions Prop.sub.part1, Prop.sub.part2 (see step 112), for example after 10 minutes, the current soft water conductivity Cond.sub.soft, the current blended water conductivity Cond.sub.blended and here also the current proportions Prop.sub.part1, Prop.sub.part2 are measured 102. Alternatively, a plurality of measurements of these values can also be made 104, in particular spread over the mentioned particular time period, and subsequently averaging 106 is carried out. It is noted that the proportions Prop.sub.part1, Prop.sub.part2 can also be determined without throughflow measurements, from the adjustment position of the automatic blending device.

(43) Using these values or averaged values, while evaluating both Cond.sub.soft and Cond.sub.blended which were measured by sensors in the soft water region and in the blended water region, the current untreated water conductivity Cond.sub.untreated is calculated 108. The untreated water hardness H.sub.untreated is then determined 110 from this untreated water conductivity Cond.sub.untreated for the purposes of the blending control. In addition, an untreated water hardness H.sub.untreated can now also be calculated for the purposes of the regeneration control.

(44) Using the untreated water hardness H.sub.untreated, the desired proportions of the partial flows in the blended water are re-determined 112 in order to obtain a blended water hardness H.sub.blended corresponding to the predetermined desired value DV. The provision of blended water 100 is then continued, the proportions Prop.sub.part1, Prop.sub.part2 of the partial flows now being adjusted to the desired values which have just been obtained. The measurements 102, 104 are repeated at the end of the mentioned particular time period, and so on.