CONTROL SYSTEM AND METHOD FOR SUPPRESSING BIOLOGICAL GROWTH, SCALE FORMATION AND/OR CORROSION IN A RECIRCULATING EVAPORATIVE COOLING FACILITY.

Abstract

A control system suppresses biological growth, scale formation and/or corrosion in a recirculating evaporative cooling facility (1). The control system is configured to: monitor a value (C) from at least one sensor (19a-l). The value is indicative of an ion concentration in a cooling liquid of the recirculating evaporative cooling facility (1). The control system controls at least one flow regulation device (21, 23) for regulating the hydraulic operation of at least one de-ionising unit (13) of the recirculating evaporative cooling facility (1). The control system is configured to control at least one parameter of hydraulic operation of the at least one de-ionising unit (13) based on an adaptive target water saving as long as the monitored value (C) does not pass a pre-determined threshold.

Claims

1. A control system for suppressing biological growth, scale formation and/or corrosion in a recirculating evaporative cooling facility, wherein the control system is configured to: monitor a value from at least one sensor, wherein the value is indicative of an ion concentration in a cooling liquid of the recirculating evaporative cooling facility; and control at least one flow regulation device for regulating the hydraulic operation of at least one de-ionizing unit of the recirculating evaporative cooling facility, wherein the control system is configured to control at least one parameter of hydraulic operation of the at least one de-ionizing unit based on an adaptive target water saving as long as the monitored value does not pass a pre-determined threshold.

2. The control system according to claim 1, wherein the at least one parameter of hydraulic operation of the at least one de-ionizing unit is: a frequency of de-ionizing cycles or a flow through the at least one de-ionizing unit; or a de-ionizing duration per de-ionizing cycle; or a frequency of de-ionizing cycles or a flow through the at least one de-ionizing unit and a de-ionizing duration per de-ionizing cycle.

3. The control system according to claim 2, wherein the control system is configured to increase the flow through the at least one de-ionizing unit only if: the frequency of de-ionizing cycles has reached a maximum; or the de-ionizing duration per de-ionizing cycle has reached a maximum; or the frequency of de-ionizing cycles has reached a maximum and the de-ionizing duration per de-ionizing cycle has reached a maximum.

4. The control system according to claim 1, wherein: the control system is configured to recursively control the at least one parameter of hydraulic operation of the at least one de-ionizing unit; the at least one parameter of hydraulic operation of the at least one de-ionizing unit is increased at least if the monitored value is changing towards the pre-determined threshold at a rate exceeding a pre-determined rate limit; and the adaptive target water saving is increased at least if the monitored value is outside a pre-determined range about the pre-determined threshold and is not changing towards the pre-determined threshold at a rate exceeding the pre-determined rate limit and the at least one parameter of hydraulic operation of the at least one de-ionizing unit is at a respective initial parameter.

5. The control system according to claim 1, wherein: the control system is configured to recursively control the at least one parameter of hydraulic operation of the at least one de-ionizing unit; the at least one parameter of hydraulic operation of the at least one de-ionizing unit and the adaptive target water saving are maintained at least if the monitored value is within a pre-determined range about the pre-determined threshold and changing towards the pre-determined threshold at rate not exceeding a pre-determined rate limit.

6. The control system according to claim 1, wherein: the control system is configured to recursively control the at least one parameter of hydraulic operation of the at least one de-ionizing unit; the adaptive target water saving is decreased at least if the monitored value is changing towards the pre-determined threshold at a rate exceeding a pre-determined rate limit and the at least one parameter of hydraulic operation of the at least one de-ionizing unit is at a respective parameter maximum; and the at least one parameter of hydraulic operation of the at least one de-ionizing unit is decreased at least if the monitored value is changing away from the pre-determined threshold and the adaptive target water saving is at or above an initial target water saving.

7. The control system according to claim 1, wherein: the control system is configured to monitor a performance value of the at least one de-ionizing unit and trigger a regeneration cycle of the at least one de-ionizing unit or trigger a cleaning cycle of the at least one de-ionizing unit or trigger both a regeneration cycle and a cleaning cycle of the at least one de-ionizing unit if the performance value crosses a pre-determined performance threshold.

8. The control system according to claim 1, wherein the control system is configured to recursively adapt the adaptive target water saving, wherein the adaptive target water saving is increased at least if the adaptive target water saving is below an initial target water saving and the monitored value is changing away from the pre-determined threshold or the monitored value is outside a pre-determined range about the pre-determined threshold and is not changing towards the pre-determined threshold at a rate exceeding the pre-determined rate limit.

9. A recirculating evaporative cooling facility comprising a control system for suppressing biological growth, scale formation and/or corrosion in a recirculating evaporative cooling facility, wherein the control system is configured to: monitor a value from at least one sensor, wherein the value is indicative of an ion concentration in a cooling liquid of the recirculating evaporative cooling facility; and control at least one flow regulation device for regulating the hydraulic operation of at least one de-ionizing unit of the recirculating evaporative cooling facility, wherein the control system is configured to control at least one parameter of hydraulic operation of the at least one de-ionizing unit based on an adaptive target water saving as long as the monitored value does not pass a pre-determined threshold.

10. A method for suppressing biological growth, scale formation and/or corrosion in a recirculating evaporative cooling facility, the method comprising the steps of: monitoring a value that is indicative of an ion concentration in a cooling liquid of the recirculating evaporative cooling facility; and controlling at least one flow regulation device for regulating a hydraulic operation of at least one de-ionizing unit of the recirculating evaporative cooling facility, wherein at least one parameter of hydraulic operation of the at least one de-ionizing unit is controlled based on an adaptive target water saving as long as the monitored value does not pass a pre-determined threshold.

11. The method according to claim 10, wherein the at least one parameter of hydraulic operation of the at least one de-ionizing unit is a frequency of de-ionizing cycles or a flow through the at least one de-ionizing unit or a de-ionizing duration per de-ionizing cycle or any combination of a frequency of de-ionizing cycles, and a flow through the at least one de-ionizing unit and a de-ionizing duration per de-ionizing cycle.

12. The method according to claim 11, wherein the flow through the at least one de-ionizing unit is only increased if the frequency of de-ionizing cycles and/or de-ionizing duration per de-ionizing cycle has reached a maximum.

13. The method according to claim 10, wherein: the at least one parameter of hydraulic operation of the at least one de-ionizing unit is controlled recursively; the at least one parameter of hydraulic operation of the at least one de-ionizing unit is increased at least if the monitored value is changing towards the pre-determined threshold at a rate exceeding a pre-determined rate limit; and the adaptive target water saving is increased at least if the monitored value is outside a pre-determined range about the pre-determined threshold and is not changing towards the pre-determined threshold at a rate exceeding the pre-determined rate limit and the at least one parameter of hydraulic operation of the at least one de-ionizing unit is at a respective initial parameter.

14. The method according to claim 10, wherein: the at least one parameter of hydraulic operation of the at least one de-ionizing unit is controlled recursively; and the at least one parameter of hydraulic operation of the at least one de-ionizing unit and the adaptive target water saving are maintained at least if the monitored value is within a pre-determined range about the pre-determined threshold and changing towards the pre-determined threshold at rate not exceeding a pre-determined rate limit.

15. The method according to claim 10, wherein: the at least one parameter of hydraulic operation of the at least one de-ionizing unit is controlled recursively; the adaptive target water saving is decreased at least if the monitored value is changing towards the pre-determined threshold at a rate exceeding a pre-determined rate limit and the at least one parameter of hydraulic operation of the at least one de-ionizing unit is at a respective parameter maximum; and the at least one parameter of hydraulic operation of the at least one de-ionizing unit is decreased at least if the monitored value is changing away from the pre-determined threshold and the adaptive target water saving is at or above an initial target water saving.

16. The method according to claim 10, further comprising monitoring a performance value of the at least one de-ionizing unit and triggering a regeneration cycle of the at least one de-ionizing unit or a cleaning cycle of the at least one de-ionizing unit or both regeneration cycle and a cleaning cycle of the at least one de-ionizing unit if the performance value crosses a pre-determined performance threshold.

17. The method according to claim 10, wherein: the adaptive target water saving is adapted recursively; the adaptive target water saving is increased at least if the adaptive target water saving is below an initial target water saving and the monitored value is changing away from the pre-determined threshold or the monitored value is outside a pre-determined range about the pre-determined threshold and is not changing towards the pre-determined threshold at a rate exceeding the pre-determined rate limit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Embodiments of the present disclosure will now be described by way of example with reference to the following figures of which:

[0065] FIG. 1 is a schematic representation of an example of a recirculating evaporative cooling facility as disclosed herein;

[0066] FIG. 2 is a schematic representation showing more detail of a filtration side-stream of the recirculating evaporative cooling facility as shown in FIG. 1;

[0067] FIG. 3 is a schematic flow diagram of an example of a method disclosed herein; and

[0068] FIG. 4 is a view of several diagrams of the development of parameters and values over time when an example of a method disclosed herein is applied.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0069] FIG. 1 shows a recirculating evaporative cooling facility 1 comprising a heat exchanger 3, a cooling tower 5 and a cooling water reservoir 7. Cooling water from the reservoir 7 flows through the heat exchanger 3 for receiving thermal energy. The heated-up cooling water leaves the heat exchanger and cools down in the cooling tower 5, where it loses thermal energy, especially by a certain amount of evaporation. Apart from further losses in the cooling tower 5, the remaining cooling water is fed back into the reservoir 7 to close the cooling circuit 9. The remaining cooling water entering the reservoir 7, however, has a higher ion concentration than the cooling water leaving the reservoir 7. Therefore, the ion concentration increases over time within the total cooling water in the cooling circuit 9. A high ion concentration may, however, be a problem for the recirculating evaporative cooling facility 1, because it facilitates biological growth, scale formation and/or corrosion.

[0070] In order to supress biological growth, scale formation and/or corrosion, the ion concentration must be kept below a pre-determined threshold, typically defined by the operator of the recirculating evaporative cooling facility 1. Therefore, the recirculating evaporative cooling facility 1 comprises a filtration side-stream 11 with a de-ionising unit 13, here in form of a nanofiltration or reverse-osmosis filter. The cooling water in the reservoir 7 is pumped via the filtration side-stream 11 through the de-ionising unit 13. The permeate (also referred to as product) of the de-ionising unit 13 has a low ion concentration and is fed back into the reservoir 7 to reduce the ion concentration therein. The retentate (also referred to as brine or concentrate) of the de-ionising unit 13 has a high ion concentration.

[0071] Depending on the operation mode of the de-ionising unit 13, the retentate may be discharged directly as blowdown (BD) water (continuous mode) or fed into a feed tank 15 (batch or continuous-batch mode). The feed tank 15 is here used to recirculate at least a certain fraction of retentate through the de-ionising unit 13 again. In a batch mode, a batch of cooling water from the cooling circuit 9 is transferred directly, or via the de-ionising unit 13 without de-ionising the cooling liquid, to the feed tank 15, which is then feeding the de-ionising unit for de-ionisation. The retentate is led back to the feed tank 15 from where at least a portion of the retentate is recirculated through the de-ionising unit 13 until the end of the de-ionizing cycle when the remaining retentate in the feed tank 15 is discarded. In a continuous-batch mode, which is a modified batch mode, the de-ionizing operation is implemented in two steps. The first step involves feeding the de-ionizing unit 13 with cooling water directly from the cooling circuit 9 just as in continuous mode, but the retentate is not discarded. It is collected in the feed tank 15. The second step involves feeding the de-ionizing unit 13 with retentate collected in the feed tank 15 during the previous step, wherein the resulting retentate is again led back to the feed tank 15 from where at least a portion of the retentate is, while producing permeate, recirculated through the de-ionizing unit 13 until the end of the de-ionizing cycle when the remaining retentate in the feed tank 15 is discarded. When the feed tank 15 is full or reached a certain filling level, the operation is switched to batch mode.

[0072] FIG. 2 shows the filtration side-stream 11 of the recirculating evaporative cooling facility 1 in more detail with a control system for suppressing biological growth, scale formation and/or corrosion. The control system comprises a control module 17 implemented as hardware or software on a computer or cloud-based computing system. The control system further comprises a plurality of sensors 19a-l and flow regulation de-vices in form of a pump 21 and several valves 23. The control module has a wired or wireless signal connection 25 (dashed lines) to each sensor 19, the pump 21 and each valve 23 for receiving values and/or setting parameters of hydraulic operation of the de-ionising unit 13. The control module 17 controls the hydraulic operation of the of the de-ionising unit 13 by controlling the pump 21 and the valves 23 on the basis of the received values measured by the sensors 19. The pump 21 is installed upstream of the de-ionising unit 13 to provide an input pressure measured by a pressure sensor 19a upstream of the de-ionising unit 13. In order to measure the de-ionising performance, a flow sensor 19b, an ion concentration sensor 19c and a temperature sensor 19d are also installed upstream of the de-ionising unit 13. The output pressure at the retentate line is measured downstream of the de-ionising unit 13 by a pressure sensor 19e. The flow, pressure, and ion concentration of the permeate is measured downstream of the de-ionising unit 13 by sensors 19f, 19g, 19h.

[0073] An ion concentration sensor 19i installed at the reservoir 7 measures the ion concentration of the cooling water within the reservoir 7. A level sensor 19j installed at the reservoir 7 measures the filling level of the reservoir 7. The control module 17 controls a valve 23 in the MU water line to fill the reservoir to keep the level above a set minimum. A flow sensor 19k measures the flow of MU water. A level sensor 19l in the feed tank 15 indicates when to switch operation modes or a blowdown of the feed tank 15.

[0074] The three valves 23 in the retentate line may be particularly important to control the hydraulic operation of the de-ionising unit 13. The valve 23 directly downstream the pressure sensor 19e in the retentate line is a regulating valve which can be opened and closed to a degree controlled by the control module 17. It can be used to control the pressure in the de-ionising unit 13 and thereby indirectly the permeate flow and/or the retentate flow. The valve 23 further downstream in the retentate line towards a blowdown water drain can be opened to switch to continuous mode, whereas the third valve 23 in the retentate line towards the feed tank 15 is opened for operating in batch mode or continuous-batch mode.

[0075] FIG. 3 shows a flow diagram that shows how the control system is used to save as much water as possible while suppressing successfully biological growth, scale formation and/or corrosion in the recirculating evaporative cooling facility 1. The control module 17 may comprise a user interface for an operator to define reference settings, initial parameters, target water savings, thresholds, ranges and limits in step 301. Alternatively, or in addition, the control system may be pre-configured with default reference settings, initial parameters, target water savings, thresholds, ranges and limits. In particular, the parameters and target water savings are adapted recursively by the applied algorithm.

[0076] Due to evaporation in the cooling tower 5, a certain amount of makeup (MU) water and blowdown (BD) water is inevitable. However, the amount of evaporation may vary with different weather conditions and thus the need for de-ionisation may vary. A typical measure in this regard is cycle-of-concentration (CoC) that specifies the number of times water parameters (hydraulic or ionic) in the reservoir are concentrated relative to the make-up water. CoC can be calculated as the ratio

[00001]$CoC=\frac{C_{\mathrm{CC}}}{C_{MU}}$

between me ion concentration in the cooling circuit C.sub.cc and the ion concentration in the makeup water C.sub.MU. The suitable measure

[00002]$X_a=\frac{V_{MU}}{V_{BD}},$

for the water consumption is wherein V.sub.MU is the makeup water volume and V.sub.BD is the blowdown water volume. A reference recirculating evaporative cooling facility may have a reference CoCr and a reference water consumption X.sub.r. An initial target water saving WS, e.g. in percent, may be defined as a makeup water saving

[00003]$W{S}_{MU}=1-\frac{\left(1-\frac{1}{X_r}\right)}{\left(1-\frac{1}{X_a}\right)}$

or a blowdown water saving

[00004]$W{S}_{BD}=1-\frac{\left(X_r-1\right)}{\left(X_a-1\right)}.$

For instance, it WS.sub.MU is set to 10% initially, it means that the initial goal is to use 10% less makeup water compared to a reference recirculating evaporative cooling facility, which is preferably based on common knowledge about, experience with or a fictive model of essentially the same recirculating evaporative cooling facility without the control system disclosed herein.

[0077] The initial cycle frequency may be set by the number N of de-ionising cycles per day, preferably to a minimum cycle frequency. A maximum cycle frequency, e.g. a maximum number of cycles per day

[00005]$N_{\max }=\frac{24}{T_d},$

may be limited by the de-ionisation duration T.sub.d per cycle, i.e. de-ionisation is not stopped between cycles at maximum cycle frequency. A cycle frequency below the maximum cycle frequency means that there is a time T.sub.i available between the de-ionisation durations T.sub.d. The cycle period is T.sub.i+T.sub.d.

[0078] The initial flow through the de-ionising unit 13 is also initially set, preferably to a minimum flow within a flow range recommended by the manufacturer of the de-ionising unit. As the performance of the de-ionising unit 13 degrades quicker at higher flows, the flow through the de-ionising unit 13 is preferably kept as low as possible for as long as possible.

[0079] After the initial definitions and settings in step 301, the cycle starts at step 303 and in following step 305, the water level in the reservoir as indicated by level sensor 19j is monitored and MU water added if needed to keep the water level above a defined minimum level. The MU water flow is measured by flow sensor 19k and used to record the cumulative make water volume V.sub.MU in step 307. The ion concentration C is monitored in step 309 by means of the ion concentration sensor 19i. If the ion concentration has exceeded a pre-determined threshold, an extraordinary de-ionising cycle is started immediately (step 311). Otherwise, the water level and the ion concentration are monitored until time T.sub.i has lapsed (step 313). If the de-ionising unit 13 is ready for starting de-ionisation (step 314), e.g. not currently being cleaned or regenerated, de-ionising in side-stream 11 is started in step 319 after or while the blowdown volume V.sub.BD (step 315), water recovery WR and the de-ionising duration T.sub.d (step 317) are calculated. The blowdown volume V.sub.BD is based on the target water saving. The water recovery WR is determined as

[00006]$\mathrm{WR}=1-\frac{V_{BD}}{V_F},$

wherein V.sub.F is an initially set feed volume per de-ionising cycle. In batch mode or continuous-batch mode, V.sub.F is limited by the volume of the feed tank 15. In continuous mode, V.sub.F is limited by the maximum flow and the maximum cycle duration. The de-ionising duration T.sub.d per cycle can then be determined to be

[00007]$T_d=\mathrm{WR}.Math.\frac{V_F}{Q_p},$

wherein Q.sub.p is the permeate flow, i.e. the flow through the de-ionising unit 13. So, the de-ionising duration T.sub.d per cycle is adapted inversely to the permeate flow Q.sub.p. The maximum cycle frequency, e.g. a maximum number of cycles per day

[00008]$N_{\max }=\frac{24}{T_d},$

may thus be higher for higher permeate flow Q.sub.p.

[0080] In step 321, the permeability as a performance value of the de-ionising unit 13 is monitored. If the permeability or any other pre-defined performance indicator crosses a pre-determined performance threshold, de-ionising is stopped and the de-ionising unit 13 is cleaned and/or regenerated in step 323. Otherwise, de-ionising is continued until the de-ionising duration T.sub.d per cycle has lapsed (step 325) and the cycle end in step 327.

[0081] After the cycle has ended in step 327, the cycle frequency, the permeate flow Q.sub.p and the target water saving are adapted based on how the ion concentration in the reservoir 7 has developed during the cycle. An average rate of change, i.e. slope, of the ion concentration in the reservoir 7 is determined in step 329 as

[00009]$\frac{C_2-C_1}{T_i+T_d},$

wherein C.sub.1 is the ion concentration at the start of the cycle and C.sub.2 is the ion concentration at the end of the cycle.

[0082] If the slope is negative (step 331), it means that there is room for water saving. If the current target water saving is below the initial value (step 337), the target water saving is increased in step 339 by a certain amount or directly set to the initial target water saving. If the current target water saving is at or above the initial value (step 337), the permeate flow for the next cycle is reduced in step 341 and, if the permeate flow is already at the initially set minimum flow, the cycle frequency is reduced for the next cycle. If also the cycle frequency is at the initially set minimum frequency, there is even more room for water savings and the target water saving is increased. Thereby, the water saving is recursively maximised.

[0083] If the slope is positive in step 331, it is checked in step 333 if the slope exceeds a pre-determined rate limit, which may be a fixed value set in step 301 or an adaptive value, e.g. the slope of the previous cycle or an average slope over more than one previous cycle. If the slope exceeds the rate limit, it means that the ion concentration approaches the threshold too quickly and the de-ionising intensity must be increased. In step 343, the cycle frequency is recursively increased from cycle to cycle until it reaches a maximum, i.e. when T.sub.i=0. If the cycle frequency is at a maximum, the permeate flow is recursively increased from cycle to cycle until it reaches a maximum. If the permeate flow is also at a maximum, the target water saving is decreased.

[0084] However, there may be room for water savings even if the slope is positive, but within the pre-determined rate limit, i.e. the ion concentration approaches the threshold at an acceptable low rate. If the ion concentration is within a range about the threshold (step 335), all settings may be maintained for the next cycle in step 345. If the ion concentration is, however, outside the range about the threshold (step 335), there is room for water saving as described for steps 337, 339 and 341. The table below summarises the logic for adapting the parameters and the target water saving.

TABLE-US-00001 Step Step Step Step 331 333 335 337 C slope C slope C Target water nega- within within saving ≥ tive? limit? range? initial? Action Step yes n/a n/a yes decrease param- 341 no yes no yes eters, then increase target water saving yes n/a n/a no increase target 339 no yes no no water saving no no n/a n/a increase param- 343 eters, then decrease target water saving no yes yes n/a maintain settings 345

[0085] Based on the cycle frequency and the de-ionising duration T.sub.d per cycle, the next non-de-ionising time T.sub.i per cycle is determined in step 347 before the next cycle starts with step 303.

[0086] FIG. 4 shows an example how some parameters and values develop over time if the control algorithm as shown in FIG. 3 is applied. At the beginning, the cycle frequency and the permeate flow are initially set to be minimal. The ion concentration C is relatively far below the threshold and an initial target water saving is achieved. After the first cycle (a), all settings are maintained for the second cycle (b). After each cycle (a-u), the slope of C is determined as shown in cycle (b) as an average rate of change over a cycle period T.sub.i+T.sub.d. As the positive slope of C exceeds the limit in the second cycle (b) (see steps 331 and 333), the cycle frequency is increased for the third cycle (c). This means, T.sub.i is reduced in step 343 for the third cycle (c). As the ion concentration continues rising quickly towards the threshold in the following cycles (d) and (e), the cycle frequency reaches a maximum in cycle (e), so that the flow is increased for cycle (f). This is still not sufficient to bring down the slope of C, so that the flow is increased further in cycle (g), where it reached a maximum flow. So, the target water saving is decreased in cycle (h) according to step 343. This means that the blowdown water is increased in cycle (h), which brings here the ion concentration C down before it reaches the threshold. For the next cycle (i), the target water saving is set back to the initial target water saving (see step 339). The negative slope of C continues for cycles (j) and (k), so that the permeate flow is recursively reduced to the initial minimum in cycle (k) according to step 341. In the following cycles (l) and (m), the cycle frequency is reduced according to step 341.

[0087] As can be seen in the bottom diagram of FIG. 4, the permeability is monitored (step 321) during the de-ionising duration T.sub.d. The permeability reduces with each cycle, i.e. the de-ionising performance degrades with each cycle. In cycle (m), the permeability falls below a lower performance threshold, which triggers a cleaning and/or regeneration cycle of the de-ionising unit 13, e.g. a cleaning-in place (CIP). The de-ionising unit 13 is not ready to use during the cleaning and/or regeneration cycle. As the ion concentration is always monitored in step 309, a blowdown at reference settings is triggered if the ion concentration exceeds the threshold during the cleaning and/or regeneration cycle as shown in FIG. 4.

[0088] Once the de-ionising unit 13 is cleaned and/or regenerated, the cycles continue with the latest setting in cycle (n). The positive slope of C is quite flat in cycle (N), so that the settings are maintained for cycle (o). In cycle (o), the slope of C towards the threshold is below the rate limit, but the ion concentration is close to the threshold, so that all setting are maintained for cycle (q). During T.sub.i of cycle (q), however, the ion concentration exceeds the threshold (step 311), which immediately triggers a start of de-ionising duration T.sub.d, which successfully brings the ion concentration below the threshold. The settings are maintained for cycle (r). As the ion concentration is falling in (r), the cycle frequency is reduced for cycle (s) to the initial minimal cycle frequency. In cycle (s), the slope of C is found to be negative and both the permeate flow and the cycle frequency are at a minimum, so that the target water saving is increased for cycle (t) above the initially set target water saving. This results in a steep rise of the ion concentration in cycle (t), which triggers an increase in the cycle frequency for cycle (u). The water saving is thereby maximised while keeping the ion concentration below the threshold.

[0089] Where, in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present disclosure, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the disclosure that are described as optional, preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims.

[0090] The above embodiments are to be understood as illustrative examples of the disclosure. It is to be understood that any feature described in relation to any one aspect or embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the aspects or embodiments, or any combination of any other of the aspects or embodiments. While at least one exemplary aspect or embodiment has been shown and described, it should be understood that other modifications, substitutions and alternatives are apparent to one of ordinary skill in the art and may be changed without departing from the scope of the subject matter described herein, and this application is intended to cover any adaptations or variations of the specific embodiments dis-cussed herein.

[0091] In addition, “comprising” does not exclude other elements or steps, and “a” or one does not exclude a plural number. Furthermore, characteristics or steps which have been described with reference to one of the above exemplary aspects or embodiments may also be used in combination with other characteristics or steps of other exemplary embodiments described above. Method steps may be applied in any order or in parallel or may constitute a part or a more detailed version of another method step. It should be understood that there should be embodied within the scope of the patent warranted hereon all such modifications as reasonably and properly come within the scope of the contribution to the art. Such modifications, substitutions and alternatives can be made without departing from the spirit and scope of the disclosure, which should be determined from the appended claims and their legal equivalents.

[0092] While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

LIST OF REFERENCE NUMERALS

[0093] 1 recirculating evaporative cooling facility [0094] 3 heat exchanger [0095] 5 cooling tower [0096] 7 reservoir [0097] 9 cooling circuit [0098] 11 filtration side-stream [0099] 13 de-ionising unit [0100] 15 feed tank [0101] 17 control module [0102] 19a-l sensors [0103] 21 pump [0104] 23 valves [0105] 25 signal connection [0106] 301 define initial parameters, references and thresholds [0107] 303 start cycle [0108] 305 add make-up water [0109] 307 record cumulative make-up water volume [0110] 309 monitor ion concentration [0111] 311 check if ion concentration exceeds threshold [0112] 313 check if non-de-ionising time per cycle has lapsed [0113] 314 check if de-ionisation unit is ready to use [0114] 315 calculate blowdown volume per cycle [0115] 317 calculate water recovery and de-ionising duration [0116] 319 operate de-ionising unit [0117] 321 check if performance crosses threshold [0118] 323 clean/regenerate de-ionising unit [0119] 325 check if de-ionising duration per cycle has lapsed [0120] 327 end cycle [0121] 329 calculate slope of ion concentration C [0122] 331 check if slope of C is negative [0123] 333 check if slope is within limit [0124] 335 check if C is within range about threshold [0125] 337 check if target water saving is at or above initial value [0126] 339 increase target water saving [0127] 341 decrease parameters, then increase target water saving [0128] 343 increase parameters, then decrease target water saving [0129] 345 maintain settings [0130] 347 calculate non-de-ionising time per cycle