COOLING SYSTEM AND METHOD FOR OPERATING A COOLING SYSTEM

Description

[0001] The present invention relates to a recooling system and a method for operating a recooling system.

[0002] Cooling systems are used to cool a temperature-controlled medium, which is cooled via a heat exchanger. A stream of air mixed with water is directed onto a surface of the heat exchanger. The water wets the surface of the heat exchanger, removing heat from the surface. Part of the water evaporates, creating a further cooling effect. The remaining water is collected and circulated in a circuit.

[0003] Cooling systems have been known for a long time (e.g. DE 2 322 037 A).

[0004] Further cooling systems are described, for example, in DE 103 16 045 A1 or DE 100 19 528 B4.

[0005] The underlying problem with recooling systems is that the water added from the air stream is heated in the heat exchanger and comes into intensive contact with the air, allowing germs to accumulate and multiply. As the water evaporates, other particles, such as pollen and soot, are also concentrated in the remaining water in the circuit. To kill germs, especially bacteria, biocides are regularly added to the circulating water. The addition of biocides leads to salinization of the water. The water must therefore be changed regularly.

[0006] There was once an accident in which aerosols contaminated with Legionella were released, causing illness to many people in the surrounding area. Since then, strict attention has been paid to ensuring that sufficient biocide is added regularly.

[0007] Membrane filters, for example in the form of hollow fibers, have been known for a long time (e.g. EP 0 554 567 A1 or DE 31 49 423 A1).

[0008] Further membrane filters can be found, for example, in DE 102 20 916 A1 or DE 10 2016 108 202 A1.

[0009] DE 10 2009 040 110 A1 describes a condensate cleaning system for a power plant in which filter elements made of ceramic membranes are used to clean the condenser.

[0010] However, membranes can also be used for other applications, such as the introduction of oxygen into water (see, for example, DE 199 50 457 A1).

[0011] CN 108 253 815 A relates to a cooling tower or recooling system comprising a heat exchanger, a fan, water spray nozzles, and a collection tank. In addition, the recooling system has an external filter system, which, in addition to the filter itself, includes three valves and a water pump.

[0012] US 2013 / 056 413 A1 describes a circulating water treatment system for cooling plants, which includes a cooling system. Water accumulating from the cooling system flows through the pipe via the pump into the filter unit, where it can be cleaned, for example, using ultrafiltration. From there, it then flows back to the cooling area via a reverse osmosis unit.

[0013] US 2015 / 125 212 A1 shows water treatment systems for floating lakes. Water is sucked from the bottom of the lake using a suction device and then pumped through a filter system. Ultrafilters, among other filters, are possible. The filtered water is then pumped back into the lake via a pipe.

[0014] The present invention is based on the object of creating a cooling system and a method for operating such a cooling system, with which the circulating water can be operated with a significantly lower use of biocide and with significantly longer residence times than in conventional cooling systems. Thus, even with small amounts of biocide, excessive microbial contamination, especially Legionella contamination, in the water can be reliably prevented.

[0015] The problem is solved by the subject matter of the independent patent claims. Advantageous embodiments are specified in the respective subclaims.

[0016] According to the invention, a recooling system comprises a heat exchanger whose surface is cooled by an air stream to which water is added. The recooling system further comprises a collection basin for collecting the water, a first line and a second line, and a circulating water treatment system having a circulating water reservoir, a filter device, and a filtration pump connected in a cleaning circuit. The water from the collection basin can be fed to the circulating water reservoir via the first line, wherein the filtration pump is provided for circulating recooling water in the cleaning circuit, so that the water can be cleaned by the filter device and the cleaned water can be fed back to the circulating water reservoir via a line. The water in the circulating water reservoir can be returned to the air stream as cleaned cooling water via the second line.

[0017] The cooling water is thus filtered to reduce the concentration of germs and other particles.

[0018] The inventors of the present invention have discovered that by filtering the water, the need for biocides can be reduced to at least a tenth of the usual requirement. In conventional cooling systems, approximately 5 liters of biocide are added to the water per day. In Germany alone, there are more than 100,000 cooling systems. If all of these cooling systems were equipped with a circulating water treatment system according to the invention, more than 100,000 tons of biocide could be saved per year.

[0019] The filter system of the circulating water treatment system does not kill the germs. However, the inventors recognized that the majority of the germs can be reliably filtered out and, as explained in more detail below, the filter system can be cleaned at regular intervals, allowing the liquid concentrated with germs and particles to be disposed of in an environmentally friendly manner.

[0020] A membrane filter, such as the one described in DE 102 20 916 A1, is particularly suitable as a filter device. Such membrane filters can have a large surface area with small filter volumes.

[0021] The filter device preferably has a filter with a pore size of no more than 1 µm, in particular no more than 0.5 µm, and particularly preferably no more than 0.1 µm. The maximum pore size can also be 0.05 µm or 0.02 µm, or even just 0.01 µm. Such small pores reliably filter germs and other particles from the water.

[0022] A flushing device can be provided, with which water and / or air can be flushed in the direction of flow through the filter device or against the direction of flow. This serves to clean the filter device. Flushing can be performed in the direction of flow or against the direction of flow. Flushing against the direction of flow, known as backflushing with a water / air mixture, is very efficient. Additionally, a cleaning chemical can be added simultaneously or independently of the flushing process. The cleaning chemical can be a biocide or an oxidizing agent, an acid, or a base.

[0023] According to a further aspect of the invention, a method for operating a recooling system is provided, in which a surface of a heat exchanger is cooled by wetting it with water, and the water is collected in a reservoir and recirculated via a water circuit to re-wetting the surface of the heat exchanger. The method is characterized in that the water is purified by a filter. This allows the use of biocides to be significantly reduced compared to conventional recooling systems.

[0024] According to the invention, the method uses a recooling system as explained above.

[0025] The water can be cleaned with a membrane filter.

[0026] The filter system can be regularly flushed with water, air, or a water / air mixture. Flushing can be performed in the opposite direction of or in the direction of flow during filter operation. Preferably, a so-called backwash is used, meaning the flow direction is opposite to the direction of filter operation. This is particularly effective with a water / air mixture in membrane filters.

[0027] A cleaning chemical can be added during rinsing.

[0028] The water can be temporarily stored in a circulating water reservoir and circulated in a purification circuit, in which the filter device is located, to clean the water. This provides a second circuit, the purification circuit, in addition to the water circuit of the cooling system, in which the water can be circulated independently of the operation of the cooling system.

[0029] Chlorine dioxide with an active ingredient concentration of 3000 ppm or sodium hypochlorite with an active ingredient concentration of 1600 ppm may be added to the water as a biocide in an amount of not more than 0.3 mg / l of water per hour, in particular not more than 0.2 mg / l of water per hour or not more than 0.1 mg / l of water per hour.

[0030] The invention is explained in more detail below by way of example with reference to the drawings. The drawings show schematically: Fig. 1 shows a cleaning circuit in a block diagram, and Fig. 2 shows a heat exchanger of a recooling system with a water circuit in a block diagram.

[0031] A cooling system 20 according to the invention comprises a heat exchanger 21 with an inlet 22 for supplying a temperature control medium and an outlet 23 for discharging the temperature control medium. The heat exchanger 21 is provided with a plurality of fins 24 through which the temperature control medium flows.

[0032] A blower device 25 generates an air flow 26, which is directed at the fins 24 to cool them. Cooling water is injected into the air flow 26 through a nozzle 27, which wets the fins 24. The fins 24 are cooled by the water. Part of the water evaporates, thereby creating an additional cooling effect. The remaining water drips off and is collected in a collecting basin 28. From the collecting basin 28, the water is conveyed via a line 29 to a circulating water treatment system 30, which is located in Figure 1 is shown in more detail and described in more detail below. In the circulating water treatment system 30, the water is cleaned and then pumped via line 31 to the nozzle 27 by a pump 32 and fed back into the air stream 26. This circulates the water in a cleaning circuit.

[0033] As explained above, the water collected in the collection basin 28 is contaminated with germs or other particles due to intensive contact with air. This contaminated water 8 is fed to a circulating water reservoir 6 and temporarily stored there. The water in the circulating water reservoir 6 can be purified, as explained below, and returned to the water cycle as purified cooling water 9.

[0034] A filtration pump 7 can draw water from the circulating water reservoir 6 and feed it to a filter device 2. The filter device 2 is designed as a membrane filter. Preferably, one or more filter cartridges with a hollow fiber membrane arrangement are provided, as described in DE 102 20 916 A1.

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

[0036] A blower gas purge 4 is connected to the filter device 2, through which gas can be supplied for cleaning the filter device. In the present embodiment, the blower gas purge 4 is arranged on the inlet side of the filter assembly 2, so that the cleaning gas, which is usually air, is supplied to the filter device on the same side as the water (filtrate). Within the scope of the invention, it is of course also possible to provide the blower gas purge 4 at the outlet of the filter device or to provide an additional blower gas purge here.

[0037] A water backwash device 3, which is typically connected to a fresh water line, is located on the outlet side of the filter device 2. The fresh water can be used to backwash the filter device against the flow direction during filter operation. A chemical dosing device 5 can be coupled to the water backwash device 3, allowing cleaning chemicals to be added to the fresh water to backwash the filter device 2.

[0038] The following tests were carried out using such a cooling system: Attempt 1

[0039] Sodium hypochlorite was used as the biocide (active ingredient concentration in the product: 1600 ppm, corresponding to 1600 mg / l). A standardized measurement method was used at regular intervals to determine whether the prescribed limit values ​​for Legionella were being met.

[0040] Four C-MEM cartridges, available from SFC Umwelttechnik GmbH, Salzburg, Austria, were used as filter units. These cartridges have a total filter area of ​​24 m². The maximum pore size was 0.02 µm.

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

[0042] With filtration, a dosage of no more than 0.1 mg / l of circulating water per hour was sufficient to maintain compliance with the limits over time. This corresponds to less than 10% of what is required without filtration, or less than 1.5 l per 1000 l per day. Attempt 2

[0043] Chlorine dioxide was used as the biocide (active ingredient concentration in the product: 3000 ppm, corresponding to 3000 mg / l). Otherwise, the same test was conducted as above.

[0044] Without filtration, a dosage of more than 1 mg / l of circulating water per hour was required. This corresponds to 0.333 l of biocide per 1000 l per hour, or 8 l per 1000 l of circulating water per day.

[0045] With filtration, a dosage of no more than 0.1 mg / l of circulating water per hour was sufficient to maintain compliance with the limits over time. This corresponds to less than 10% of the amount required without filtration, or 0.8 l per 1000 l per day.

[0046] 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 treatment system. Water can be circulated independently in both circuits. These two circuits can be operated simultaneously or alternately.

[0047] During operation, the water circuit is often activated first. After a certain period of operation, it can be assumed that the water will exhibit a certain degree of contamination. This is based on empirical values ​​and depends heavily on the germ and particle load in the ambient air and the ambient temperature. Reliable empirical values ​​exist for this. At the latest when a predetermined germ or particle load is reached, the circulating water treatment system 30 is activated, and water is circulated and purified through the filter device 2. This purification process can continue even if the cooling system is no longer in operation and its water circuit is at a standstill.

[0048] This decoupling makes it possible to keep a large amount of cooling water essentially free of contamination in the long term, even with a relatively small, compact filter system, and to significantly reduce the need for biocides compared to conventional systems.

[0049] Within the scope of the invention, it is also possible to provide two water reservoirs instead of a single circulating water reservoir 6, one for the contaminated water entering the circulating water treatment system and the other for the uncontaminated water leaving the circulating water treatment system 30. These two reservoirs can be designed separately. However, they are preferably connected to each other via a line in which at least one control valve and, in particular, a feed pump are arranged, so that multiple recirculation of the water is possible and can be controlled in a targeted manner.

[0050] Examples of the invention are given below: 1. Example: Cooling system according to claim 1, characterized in that the circulating water treatment system is designed such that a cyclical or permanent circulation of the contaminated cooling water through the circulating water treatment system and thus a partial or complete removal of microorganisms and other particulate contaminants from the circulating water takes place. 2. Example: Cooling system according to the 1. Example, characterized in that the circulating water treatment system is designed such that the cleaning of the circulating water is carried out physically by filtration according to the principle of size exclusion for particulate substances > 0.1 µm. 3. Example: Cooling system according to the 1. or 2.Example, characterized in that the filtration performance can be kept constant optionally by cyclical water rinsing of the filter and / or optionally by cyclical gas rinsing of the filter and / or optionally by cyclical chemical cleaning of the filter by introducing oxidative and / or optionally alkaline and / or optionally acidic cleaning chemicals via backwashing. 4. Recooling system according to one of the 1st to 3rd examples, characterized in that the circulating water treatment system further comprises a water backwash (3) for the filter device (2), and / or a blower gas rinsing (4) for the filter device (2), and / or a chemical dosing system (5) for chemical cleaning of the filter device (2). Reference symbol list

[0051] 1Purified permeate as recirculation 2Filter device 3Water backwash 4Blower gas purge 5Chemical dosing for chemical cleaning 6Circulation water reservoir 7Filtration pump 8Contaminated cooling water 9Purified cooling water 10Fresh water make-up 11Concentrate discharge 20Recooling system 21Heat exchanger 22Inlet 23Outlet 24Fin 25Blower device 26Air flow 27Nozzle 28Collecting basin 29Line 30Circulating water treatment system 31Line 32Pump

Claims

1. Recooling system, comprising a heat exchanger (21), the surface of which is cooled by a stream of air to which water is added, a collecting basin (28) for collecting the water, a first line (29) and a second line (31), and a circulating water treatment system (30), which has a circulating water reservoir (6), a filter device (2) and a filtration pump (7), which are connected in a cleaning circuit, whereby the water from the collecting basin (28) can be fed to the circulating water reservoir (6) by means of the first pipe (29), wherein the filtration pump (7) is provided for circulating recooling water in the cleaning circuit, so that the water can be cleaned by means of the filter device (2) and the cleaned water (1) can be fed back to the circulating water reservoir (6) via a pipe, whereby the water in the circulating water reservoir (6) can be returned to the air flow as purified cooling water (9) via the second line (31).

2. Recooling system according to claim 1, characterised in that the filter device (2) has a membrane filter.

3. Recooling system according to claim 1 or 2, characterised in that the filter device (2) has a filter with a pore size of maximum 1 µm, preferably maximum 0.5 µm and in particular maximum 0.1 µm or maximum 0.05 µm.

4. Recooling system according to one of claims 1 to 3, characterised in that a flushing device (3, 4) is provided which can flush the filter device (2) with water and / or air in and / or against the direction of flow.

5. Recooling system according to one of claims 1 to 4, characterised in that a chemical dosing unit (5) is provided for supplying a cleaning chemical to the filter device (2).

6. Method for operating a recooling system according to any one of claims 1 to 5, wherein a surface of the heat exchanger (21) is cooled by wetting with water and the water is collected in the collecting basin (28), wherein the water is fed from the collecting basin (28) to the circulating water reservoir (6) by means of the first pipe (29), wherein the filtration pump (7) circulates the recooling water in the cleaning circuit so that the water is cleaned by means of the filter device (2), and the cleaned water (1) is fed back to the recirculating water reservoir (6) via a pipe, whereby the water in the circulating water reservoir (6) is returned to the air flow as purified cooling water (9) via the second line (31) to re-wet the surface of the heat exchanger (21).

7. Method according to claim 6, characterised in that the recooling water is cleaned with a membrane filter.

8. Method according to claim 6 or 7, characterised in that the filter is regularly rinsed with water or air or a water / air mixture.

9. Method according to claim 8, characterised in that the flushing is carried out against or in the direction of flow during filter operation.

10. Method according to claim 8 or 9, characterised in that a cleaning chemical is added during rinsing.

11. The method according to any one of claims 6 to 10, characterised in that the recooling water in the cleaning circuit is circulated cyclically or permanently.

12. The method according to any one of claims 6 to 11, characterised in that the water circuit of the recooling system and the cleaning circuit are operated simultaneously or alternately.

13. A method according to any one of claims 6 to 12, characterised in that a biocide is added to the recooling water, preferably chlorine dioxide with an active substance concentration of 3000 ppm or sodium hypochlorite with an active substance concentration of 1600 ppm being added to the recooling water as biocide in an amount of not more than 0.3 mg / l of water and hour.