CIRCULATING WATER PREPARATION SYSTEM, COOLING SYSTEM AND METHOD FOR OPERATING A COOLING SYSTEM

Abstract

A circulating water preparation system for cooling plants, a cooling system, in particular a recooling system, and a method for operating such a cooling system. In such a cooling system a surface of a heat exchanger is cooled by wetting with water, the water is collected in a collecting tank and returned by means of a water circuit for the renewed wetting of the surface of the heat exchanger. The method is characterised in that the water is purified by means of a filter, in particular a membrane filter. As a result considerably less biocide is needed to keep the water free of germs, in particular legionella, compared to conventional cooling systems or methods for operating such cooling systems.

Claims

1. Circulating water preparation system for cooling plants, comprising: a circulating water reservoir and a filter device, which are placed in a circuit, and a filtration pump for circulating recooling water in the circuit.

2. Circulating water preparation system according to claim 1, wherein the filter device has a membrane filter.

3. Circulating water preparation system according to claim 1, wherein the filter device has a filter with a maximum pore size of 1 μm.

4. Circulating water preparation system according to claim 1, further comprising a flushing device, which can flush the filter device with water and/or air in and/or against a flow direction of the water and/or air.

5. Circulating water preparation system according to claim 1, further comprising a chemical dosing device for feeding a cleaning chemical to the filter device.

6. Cooling system comprising: a heat exchanger, wherein a surface of the heat exchanger is cooled with an air flow to which water is added, a collecting tank for collecting the water, and a water circuit for returning the water into the airflow, wherein the water circuit is connected to the circulating water preparation system according to claim 1.

7. Method for operating the cooling system according to claim 6, comprising: cooling the surface of the heat exchanger by wetting the surface of the heat exchanger with water; collecting the water in the collecting tank and returned returning the water with a water circuit for the renewed wetting of the surface of the heat exchanger; and using a filter to purify the water.

8. Method according to claim 7, comprising purifying the water with a membrane filter.

9. Method according to claim 7, comprising flushing the filter device regularly with water or air or a water/air mixture.

10. Method according to claim 9, comprising carrying out the flushing operation against or in a flow direction of the water or air or water/air mixture during the filter operation.

11. Method according to claim 9, comprising adding a cleaning chemical during the flushing operation.

12. Method according to claim 7, comprising temporarily storing the water in the circulating reservoir and circulating the water in a purifying circuit in which the filter device is located for purifying the water.

13. Method according to claim 7, comprising adding a biocide to the water.

14. Method according to claim 13, wherein the biocide is chlorine dioxide with an active agent concentration of 3000 ppm or sodium hypochlorite with an active agent concentration of 1600 ppm, added to the water in a quantity of no more than 0.3 mg/l water an hour.

15. Method according to claim 12, wherein the water in the purifying circuit is circulated cyclically or permanently.

16. Method according to claim 12, wherein the water circuit of the cooling system and the purifying circuit are operated simultaneously or alternately.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The invention is explained in greater detail below by way of example with reference to the drawings. The drawings show diagrammatically:

[0029] FIG. 1 is a purification circuit in a block diagram, and

[0030] FIG. 2 is a heat exchanger of a recooling system with a water circuit in a block diagram.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] The recooling system 20 according to the invention has a heat exchanger 21 with an inlet 22 for feeding in a tempering medium and an outlet 23 for discharging the tempering medium. The heat exchanger 21 is provided with several fins 24, through which the tempering medium flows.

[0032] A fan device 25 generates an air flow 26 directed onto the fins 24 for the cooling thereof. With a nozzle 27 cooling water wetting the fins 24 is injected into the air flow 26. The fins 24 are cooled by the water. A part of the water evaporates, thereby generating an additional cooling effect. The remaining water drips off and is collected in a collecting tank 28. From the collecting tank 28 the water is carried by means of a line 29 to a circulating water preparation system 30, which is shown more precisely in FIG. 1 and described in greater detail below In the circulating water preparation system 30 the water is purified and then delivered via the line 31 to the nozzle 27 by means of a pump 32 and again added to the air flow 26. In this way the water is circulated in a purification circuit.

[0033] As explained above, the water collected in the collecting tank 28 is contaminated by germs or other particles because of the intensive air contact. This contaminated water 8 is fed to a circulating water reservoir 6 and there stored temporarily. The water in the circulating water reservoir 6 can be purified as explained below and again fed to the purification circuit in the form of purified cooling water 9.

[0034] With a filtration pump 7, water can be drawn from the circulating water reservoir 6 and delivered to a filter device 2. The filter device 2 is designed as a membrane filter. One or more filter cartridges with a hollow fibre membrane arrangement as described in DE 102 20 916 A1 are preferably provided.

[0035] The purified water 1 (permeate) is returned to the circulating water reservoir 6 via a line. The water of the circulating water reservoir 6 can be circulated several times before being returned to the water circuit of the recooling system 20.

[0036] The filter device 2 is connected to a fan gas flushing unit 4, with which gas can be supplied for cleaning the filter device. In the present embodiment the fan gas flushing unit 4 is located on the inlet side of the filter device 2, so that the cleaning gas, which is air as a rule, is fed to the filter device on the same side as the water (filtrate). Within the scope of the invention it is obviously also possible to provide the fan gas flushing unit 4 at the outlet of the filter device or to provide an additional fan gas flushing unit there.

[0037] On the outlet side of the filter device 2 there is located a water backflushing unit 3, which is a connection to a fresh water line as a rule. With the fresh water the filter device can be backflushed against the flow direction during the filter operation. A chemical dosing unit 5, with which cleaning chemicals can be supplied to the fresh water for backflushing the filter device 2, can be coupled to the water backflushing unit 3.

[0038] The following experiments were carried out with such a recooling system:

[0039] Experiment 1

[0040] Sodium hypochlorite (active agent concentration in the product 1600 ppm corresponds to 1600 mg/l) was used as a biocide. Using a standardised measuring method, it was determined at regular intervals whether the mandatory limit values for legionella were adhered to. As filter devices four C-MEM cartridges each, available from SFC of Umwelttechnik GmbH, Salzburg, Austria, with an overall filter area of 24 square metres, were used. The maximum pore size was 0.02 μm.

[0041] Without filtration a dosing of at least 1 mg/l circulating water an hour was necessary. This corresponds to 0.625 l biocide per 1000 l an hour or 15 l per 1000 l circulating water a day.

[0042] With the filtration a dosing of no more than 0.1 mg/l circulating water an hour was sufficient to adhere to the limit values permanently. This is less than 10% of the quantity required without filtration or less than 1.5 l per 1000 l a day.

[0043] Experiment 2

[0044] Chlorine dioxide (active agent concentration in the product 3000 ppm corresponds to 3000 mg/l) was used as a biocide. Apart from this, the same experiment was carried out.

[0045] Without filtration a dosing of more than 1 mg/l circulating water an hour was necessary. This corresponds to 0.333 l biocide per 1000 l an hour or 8 l per 1000 l circulating water a day.

[0046] With the filtration a dosing of no more than 0.1 mg/l circulating water an hour was sufficient to adhere to the limit values permanently. This is less than 10% of the quantity required without filtration or less than 0.8 l per 1000 l a day.

[0047] By providing the circulating water reservoir 6, the operation of the water circuit of the recooling system 20 is decoupled from the filter operation of the circulating water preparation system. In both circuits water can be circulated independently of each other. These two circuits can be operated simultaneously or alternately.

[0048] During operation the water circuit is often activated initially. From a certain operating time, it has then to be assumed that the water contains a certain degree of contamination. This based on empirical values and greatly depends on the germ and particle loading of the ambient air and on ambient temperature. Verified empirical values are available for this. No later than the presence of a predetermined germ or particle loading, the circulating water preparation system 30 is activated and water is circulated across the filter device 2 and purified. This cleaning operation can be continued even if the cooling system is no longer in operation and its water circuit stands idle.

[0049] This decoupling makes it possible to keep a large quantity of cooling water substantially contamination-free in the long run even with a relatively small, compact filter device and to reduce the need for biocides considerably compared to conventional systems.

[0050] Within the scope of the invention, it is also possible to provide, instead of a circulating water reservoir 6, two water reservoirs for the contaminated water entering the circulating water preparation system and for the non-contaminated water emerging from the circulating water preparation system 30. These two reservoirs can be designed separately from each other. They are preferably connected to each other by a line, however, in which at least one control valve and in particular a feed pump are provided, so that a multiple recirculation is possible here as well and can be activated in a targeted manner.

[0051] Examples of the invention are specified below:

[0052] 1.sup.st example: Circulating water preparation system of hybrid recooling plants or other cooling plants, characterised in that the circulating water preparation system is designed such that there is a cyclical or permanent circulation of contaminated recooling water through the circulating water preparation system and thus a partial or complete removal of microorganisms and other particulate contaminants from the circulating water.

[0053] 2.sup.nd example: Circulating water preparation system according to the 1.sup.st example, characterised in that the circulating water preparation system is designed such that the purification of the circulating water is performed physically by a filtration according to the principle of size exclusion for particulate substances >0.1 μm.

[0054] 3.sup.rd example: Circulating water preparation system according to the 1.sup.st or 2.sup.nd example,

characterised in that
the filtration power can be held constant optionally by a cyclical water flushing of the filter and/or optionally by a cyclical gas flushing of the filter and/or optionally by a cyclical chemical cleaning of the filter by introducing oxidative and/or optionally alkaline and/or optionally acidic cleaning chemicals by way of backflushing.

[0055] 4.sup.th example: Circulating water preparation system according to any of the 1.sup.st to 3.sup.rd examples,

characterised in that
the circulating water preparation system has a circulating water reservoir (6) and a filter device (2), which are placed in a circuit, and a filtration pump (7) for circulating recooling water in the circuit.

[0056] 5.sup.th example: Circulating water preparation system according to the 4.sup.th example,

characterised in that
the circulating water preparation system further comprises

[0057] a water backflushing unit (3) for the filter device (2) and/or

[0058] a fan gas flushing unit (4) for the filter device (2) and/or

a chemical dosing unit (5) for a chemical cleaning of the filter device (2).