AU2007222890A1

AU2007222890A1 - Heat exchange apparatus

Info

Publication number: AU2007222890A1
Application number: AU2007222890A
Authority: AU
Inventors: Michael Christopher Power; Graham Rowley
Original assignee: AUSTRALIAN WATER CONDITIONERS Pty Ltd
Current assignee: AUSTRALIAN WATER CONDITIONERS Pty Ltd
Priority date: 2006-03-08
Filing date: 2007-03-07
Publication date: 2007-09-13
Also published as: CN101573582A; WO2007101304A1; US20090301114A1

Description

WO 2007/101304 PCT/AU2007/000285 1 HEAT EXCHANGE APPARATUS FIELD OF THE INVENTION 5 The present invention relates to a heat exchange apparatus of the type which transfers heat from a coolant or refrigerant to a fluid. BACKGROUND OF THE INVENTION 10 The principle of using a fluid to remove heat from a coolant or refrigerant to a fluid is well known. Air conditioners and industrial cooling towers operate using this principle. Air conditioning systems have an evaporator that removes heat from the internal air and transfers it to a refrigerant and a condenser that removes heat from the refrigerant and 15 transfers the heat outdoors. Air cooled condensers use air to remove heat from the refrigerant. Water cooled condensers and water towers work on the principle of evaporative cooling. The present invention will be described with particular reference to heat 20 exchange apparatus of the cooling tower type. However it will be appreciated that the invention may apply to suitable type of heat exchange apparatus whereby a fluid is used to lower the temperature of a refrigerant or coolant. Industrial cooling towers are used to recycle cooling water used in an 25 industrial process. Many processes such as refineries, steel mills, petrochemical and manufacturing plants, electric utilities and paper mills use equipment or processes that require temperature control. Cooling water provides this control. Cooling towers were designed to cool heated water such that it could be recycled. Cooling towers are also used in cooling 30 systems in commercial buildings. Cooling towers lower the temperature of water by contacting the water with ambient air resulting in partial evaporation of the water. The evaporation lowers the temperature of the water. The air containing evaporated water is WO 2007/101304 PCT/AU2007/000285 2 exhausted into the atmosphere. The evaporated water leaves behind salts and other chemicals in the water which has not evaporated. This build up may lead to corrosion and scaling. In order to control the concentration of such chemicals, water is drawn or bled off for disposal. Fresh or make up 5 water must be added to compensate for the loss of both evaporated and drawn off water. It is considered desirable to be able to reduce water loss from cooling towers. There have been numerous approaches and suggestions with a view to 10 reducing cooling tower water consumption. It has been proposed to recycle the bleed water back to the make-up water. Contaminants are removed from the bleed water by a series of filters, membranes or the like. Conductivity controllers may be used to automatically control bleed. Automatic bleed devices sense when the conductivity is too high and typically opens a solenoid 15 bleed valve. Other approaches concentrate on water management such as diverting waste water from other areas of an industrial process to provide the make-up water (purifying the make-up water as necessary). Another option is to monitor the 20 heat flow in the system and if the temperature of the water falls below a certain value providing a by pass valve such that some of the water bypasses the cooling tower. Many of these options however increase operational and/or equipment costs. 25 It is therefore an object of the present invention to provide a heat exchange apparatus which may at least partially address the above disadvantages or alternatively provide the public with a useful or commercial choice. 30 DESCRIPTION OF THE INVENTION According to a first broad form of the present invention there is provided an apparatus for transferring heat from a coolant to a fluid in a coolant recycling system, the apparatus including; WO 2007/101304 PCT/AU2007/000285 3 a heat exchange region through which the fluid flows such that heat is transferred from the coolant to the fluid and a recycling loop for recycling the fluid flowing from the heat exchange region, whereby the fluid is cooled in the recycling loop before being returned to the 5 heat exchange region. The fluid may be a gas or a liquid and is typically air or water respectively. Where the coolant is housed in a condenser, the condenser is typically water or air cooled. Where the fluid is air, emission of pollutants into 10 the atmosphere may be decreased or even eliminated. Preferably, the fluid is air and the coolant is water. In the heat exchange region, heat is transferred from coolant to the fluid. Where one of the coolant or fluid is a gas such as air and the other of 15 the coolant or fluid is a liquid such as water, the coolant and fluid are typically in intimate contact. Typically there is a counter current flow of liquid and gas. Alternatively, the fluid and liquid are separated, for example one of the fluid or coolant may be circulated through a cooling coil, fin or the like. 20 The coolant may be any suitable coolant and includes a refrigerant of the type used in air conditioning systems. In this case, the refrigerant is housed in a condenser and heat is removed from the condenser by the fluid. The apparatus includes a recycling loop for recycling the fluid after heat 25 transfer from the coolant. The fluid is cooled in the recycling loop. Cooling may be accomplished by any suitable means. Cooling may be conducted by passive means, such as by the use of heat exchange coils, fins or the like which may vent heat to the atmosphere. Alternatively and preferably, the recycling loop includes a cooling device. A typical cooling device is a 30 condensing coil, supplied by cold water by refrigeration or from other process cold water. When using cold water to cool air, this is typically sprayed into the air so as to establish intimate contact between cold water and the air.

WO 2007/101304 PCT/AU2007/000285 4 The fluid is typically cooled to a temperature below ambient. This may be compared to conventional cooling systems where the fluid is typically at ambient temperature. In those systems where the fluid is air and the coolant is water, contact with ambient air results in evaporative cooling. It will be 5 appreciated that the amount of evaporative cooling that occurs will depend upon the temperature of the air. At lower air temperatures, less evaporative cooling takes place and instead cooling may occur by forced or induction cooling. Thus a preferred apparatus whereby air is cooled to below ambient temperature may include means for optimizing induction and/or forced cooling. 10 Such means may include nozzles designed to optimize water droplet size and/or methods for directing air past the droplets. It will be appreciated that even where the temperature is below ambient, some evaporative cooling will take place. It is preferred that the 15 cooling device is sufficient to condense at least part of the evaporated water in the exhaust air flow. Preferably, substantially all of the water in the exhaust air is condensed and returned as coolant. Conventional evaporative cooling towers trickle water though cooling 20 elements or fill media designed to optimize the evaporative cooling process. It will be appreciated that such elements may not be necessary where the primary cooling mechanism is not evaporative cooling. Avoiding or minimizing the use of such cooling elements or media may enable capital and running costs to be reduced. Still further, the overall size of the system may be 25 reduced when compared to conventional evaporative cooling towers. In this preferred embodiment it is preferred that the cooling means is sufficient to condense at least part of any evaporated water in the exhaust air flow. Preferably, substantially all of the water in the exhaust air is condensed 30 and returned as coolant. According to a further broad form of the invention there is provided an apparatus for transferring heat from heated coolant water to air, the apparatus including; WO 2007/101304 PCT/AU2007/000285 5 a heat exchange region through which air and water flow and heat is transferred from the water to the air; a recycling loop for cooling air flowing from the heat exchange region and returning cooled air to the heat exchange region, the air being cooled 5 sufficiently so as to condense at least some of any water that evaporated into the air in the heat exchange region. The flow of air though the heat exchange region and recycling loop fluid flow may be directed by air induced fans, forced draught fans or both. This is 10 to be compared with some types of conventional air cooled or evaporative cooling devices which are open to the atmosphere such that the fluid, in this case air, is drawn from and vented into the atmosphere. The apparatus of the invention typically has a housing which is closed 15 to the atmosphere and houses both the heat exchange region and the recycling loop. Alternatively, the housing may have a fluid inlet and a fluid outlet, the recycled loop is external to the housing and fluidly connected to the outlet and 20 inlet. It may be appreciated that the inlet and outlets of existing cooling towers or evaporative cooling units may be modified in this manner thereby enabling such units to be retrofitted according to the present invention. According to a further broad form of the invention there is provided a 25 method of modifying a heat transfer apparatus having a fluid inlet, a heat exchange region where heat is transferred from a coolant to the fluid and an outlet for exhausting heated fluid to the atmosphere; the method including providing a recycle loop between the outlet and the inlet, whereby fluid is cooled in the recycling loop before being returned to the heat 30 exchange region through the inlet. According to yet a further broad form of the invention there is provided a method of transferring heat from a coolant to a fluid, the method comprising directing a flow of fluid into a heat exchange region such that heat is WO 2007/101304 PCT/AU2007/000285 6 transferred from_ the coolant to the fluid, cooling the fluid after said heat transfer and recycling the cooled fluid back to the heat exchange region. In the embodiment where the coolant is water, it is preferred that the 5 temperature of the air is cooled to a temperature below that which favours the growth of Legionella pneumophila. Preferably this temperature is below 200C, most preferably about 15 0 C. Legionella pneumophila is a genus of bacteria responsible for a 10 respiratory infection known as Legionnaire's disease. Legionella pneumophila appears in almost every ground and surface water. Cooling towers provide an ideal environment for the growth of Legionella pneumophila. In order to address this potential problem, cooling tower water is periodically dosed with halogens such as chorine or bromine and regular maintenance cleaning of the 15 system. It may be appreciated that by maintaining a low temperature within the tower, the use of such chemicals may be minimized or avoided BRIEF DESCRIPTION OF THE DRAWINGS 20 Figure 1 is a schematic drawing of a first preferred apparatus of the invention; Figure 2 is a schematic drawing of a further preferred apparatus of the present invention and Figure 3 is a schematic drawing of a further preferred apparatus of the 25 present invention DETAILED DESCRIPTION OF THE FIGURES Figure 1 is a schematic view of a preferred apparatus of the present 30 invention. This apparatus has been retrofitted to an existing cooling tower 10 as used to recycle coolant water in an industrial plant. The existing cooling tower 10 is of the conventional type whereby nozzles (not shown) introduce jets of water into the top of the tower. Rising air contacts the water and evaporative cooling of the water takes place in a heat exchange region 9 of WO 2007/101304 PCT/AU2007/000285 7 the tower 10. The heat exchange region 9 includes a fill material for increasing the surface area and maximising water/air contact. Fan 11 draws the air upwards through the water droplets. The cooled water collects in a reservoir 12 at the bottom of the tower 10 and is then recycled to the plant for 5 cooling. Conventionally, the exhaust air and evaporated water are vented to the atmosphere. This conventional cooling tower system has been modified by providing a recycle loop 13. The recycle loop 13 includes a cooling unit 15. The cooling 10 unit 15 has a fin coil radiator 16. The fins 16 are cooled to a temperature of between about 0 to about 100C. A fan 17 draws exhaust air from the upper part of the cooling tower through a diffuser 18 towards fins 16. The exhaust air is typically at a temperature of about 450 and after passing through the cooling unit reaches a temperature of 20 0 C or below. As the air passes 15 though cooling unit 15, evaporated water condenses out of the air and is collected in a second reservoir 19. The collected water is directed to reservoir 12 and the cooled air is returned to the tower through inlet 20. It may be seen that the entire system is sealed from the atmosphere. 20 However the provision of inlet and outlet dampers 21, 22 allows inlet air or exhaust air to be vented if desired. Figure 2 is a schematic view of a further preferred apparatus of the invention in the form of a cooling tower 30. The cooling tower 30 receives 25 coolant water from an industrial plant and disperses this water through nozzles 32. The tower also has a fan 31 for drawing air through water droplets dispersed by nozzles 32 and a reservoir 33 as per conventional cooling towers. Cooled water is pumped from the reservoir 33 back to the industrial plant. However, unlike conventional cooling towers, the apparatus 30 includes an air cooling unit 34 in the form of a water cooled condenser located above water nozzles 32. The condenser typically operates at a temperature of between about 0 to about 60C. Further the cooling tower does not include conventional cooling elements which are used to optimise evaporative cooling.

WO 2007/101304 PCT/AU2007/000285 8 Air is drawn upwards by fan 31 past the cooling unit 34 and redirected in the direction of arrows A through a passageway 35 defined between outer 36 and inner walls 37 of the tower. Cooled air is then available to be redrawn upwards though the water droplets as indicated by arrows B. The air is at a 5 temperature of about 150C. The apparatus includes an air temperature sensor to measure the temperature of the recycled air. The sensor is coupled to an automated control device for controlling the cooling unit 34 such control may increases energy efficiency of the system and to control the level of cooling which may be necessary to accommodate for seasonal temperature 10 variations. The design of the water nozzles, air temperature and air flow is such that the water droplet size and flow optimize induction or forced cooling rather than evaporative cooling. Evaporated water condenses in passageway 35 15 and is received in reservoir 33. Figure 3 shows another embodiment of a cooling tower 50 which has been retrofitted to include a recycling loop 51 according to the present invention. The cooling tower 50 is similar to that as shown in figure 1 and the 20 same reference numbers are used to describe the same features. In this embodiment the cooling tower 50 recycles cooling water from an industrial chiller 52 . The chiller 52 may provide cooling for an air conditioning system. Water from the chiller is introduced into the upper part of the cooling tower through nozzles 53. The fan 11 draws air upwards which meets the 25 downward flowing water and cooling of the water takes place in a heat exchange region 9 of the tower. Cooled water collects in reservoir 12. The reservoir has two outlets 54, 55. Outlet 54 directs water through pump 56 to chiller 52. The other outlet 55 directs water to the recycling loop 51 which will be discussed in further detail below. 30 The rising air flow leaving the heat exchange region 9 is drawn though a drift eliminator 57 which removes air borne water droplets from the air flow. The air is directed through a swirl plate 58 to create a swirling air flow to a first cooling chamber 59. Cooling chamber 59 has a series of spray nozzles 60 WO 2007/101304 PCT/AU2007/000285 9 for spraying chilled water onto the swirling air. The chilled water.is sourced from reservoir 12. Water from outlet 55 is pumped to a refrigeration unit 61 where it is chilled. The chilled water then flows to spray nozzles 60. 5 The chilled water reduces the temperature of the air in chamber 59. Evaporated water in the air flow condenses and is collected in reservoir 62, located at the base of chamber 59. Water from reservoir 62 is recycled to the upper part of the tower 50 at a location above the heat exchange region and is sprayed into the heat exchange region through spray nozzles 63. It may be 10 appreciated that the temperature of water sprayed from nozzles 63 is lower than that sprayed from nozzles 53. This difference in temperature facilitates heat transfer from water introduced from chiller 52. The recycling loop 51 includes a second cooling chamber 64. 15 Air from first cooling chamber 59 flows through to second chamber 64 through drift eliminator 65. A further set of spray nozzles 66 sprays water cooled in refrigeration unit 61 into the second cooling chamber 64. This further cools the air before it is re-introduced into the heat exchange region 9 of the cooling tower 51 through inlet 67. 20 It may be seen that the cooling tower of figures 1,2 and 3 are enclosed systems whereby all water is recycled. No water is lost as the result of bleeding off water to control levels of dissolved impurities, evaporation or drift (the loss of water droplets in the exhaust air). As a result, the addition of 25 make-up water is unnecessary. It will be appreciated that this may lead to considerable water saving. Still further, as no water is lost to evaporation, the level of salts or other impurities in the water is kept at a constant level which ameliorates the need 30 for a bleed and make-up water supply. A further advantage of the sealed system is that the risk of airborne Legionella being lost from the system to the atmosphere is reduced or avoided. Still further, by maintaining the recycled water temperature below WO 2007/101304 PCT/AU2007/000285 10 that required for Legionella growth the use of chemicals or other Legionella control methods is unnecessary. Still further the ingress of dirt, dust, and organisms which may cause biofouling may also be reduced or even eliminated. 5 A still further advantage of the reduced temperature is that the mode of cooling changes from being predominantly evaporative to induced or forced cooling. This may increase cooling efficiency, avoid or reduce the need for cooling elements or media, thereby reducing costs and overall size of the 10 apparatus when compared to conventional evaporative cooling towers. It will be appreciated that various changes and modifications may be made to the invention as described herein without departing form the spirit and scope thereof. 15

Claims

1. An apparatus for transferring heat from a coolant to a fluid in a coolant recycling system, the apparatus including; 5 a heat exchange region through which the fluid flows such that heat is transferred from the coolant to the fluid and a recycling loop for recycling the fluid flowing from the heat exchange region, whereby the fluid is cooled in the recycling loop before being returned to the heat exchange region. 10

2. The apparatus of claim 1 wherein the coolant is water and the fluid is air.

3. The apparatus of claim 2, wherein the air is cooled to a temperature 15 less than ambient.

4. The apparatus of claim 4, wherein the air is cooled to a temperature below about 20 0 C. 20

5. The apparatus of claim 2, wherein any evaporated water in the air condenses as the air is cooled in the recycling loop.

6. The apparatus of claim 1 which includes a housing having a fluid inlet and a fluid outlet, the heat exchange region is located within the housing and 25 the recycling loop is fluidly connected between the outlet and the inlet.

7. The apparatus of claim 1 which includes housing and both the heat exchange region and the recycling loop are located within the housing. 30

8. The apparatus of claim 1 which includes a refrigeration unit in the recycling loop. WO 2007/101304 PCT/AU2007/000285 12

9. A method of modifying a heat transfer apparatus having a fluid inlet, a heat exchange region where heat is transferred from a coolant to the fluid and an outlet for exhausting heated fluid to the atmosphere; the method including providing a recycling loop between the outlet and the 5 inlet, whereby fluid is cooled in the recycling loop before being returned to the heat exchange region through the inlet.

10. A cooling tower for transferring heat from heated coolant water to air, the apparatus including; 10 a heat exchange region through which air and water flow and heat is transferred from the water to the air; a recycling loop for cooling air flowing from the heat exchange region and returning cooled air to the heat exchange region the air being cooled sufficiently so as to condense at least some of any water that evaporated into 15 the air in the heat exchange region.

11. A method of transferring heat from a coolant to a fluid, the method comprising directing a flow of fluid into a heat exchange region such that heat is transferred from the coolant to the fluid, cooling the fluid after said heat 20 transfer and recycling the cooled fluid back to the heat exchange region.