CN1136839A - Moist air cooling tower with antifreeze - Google Patents

Abstract

Wet cooling tower comprising an exchange body (20), a water dispensing network above the exchange body provided with valves (16) supplying each of the water nozzles located above a section of the exchange body to form cooling cells which can be isolated, and a manifold for water which has flowed through the water exchange and pumping body directing the water collected towards the dispensing network. The cooling tower comprises static means for automatic limitation. The increase in the hydrostatic pressure applied to the nozzles beyond a given value, above the value attained when all the cells are operational, is automatically static limited. Part of the water flow which is brought to the distribution level, is therefore bypassed upon exceeding a given value.

Description

Wet Air Cooling Tower with Freeze Protection

The invention relates to an air cooling tower comprising an exchange body (consisting of a water flow structure), a water distribution network installed above the exchange body and equipped with water supply nozzles for each water spray, and water collecting and pumping devices The valves, water spray nozzles are installed above the different parts of the exchange body to form cooling compartments, and the water collecting and pumping device collects the water flowing through the exchange body and pumps the water to the water distribution network.

In industry, this type of cooling tower is used when heat needs to be removed and there is not enough water to directly exchange it with it. The cooling tower is used in particular in a thermoelectric central station to cool the main condenser and/or the auxiliary lines of the central station.

As far as air cooling towers are concerned, some air cooling towers are naturally ventilated, with channels around the exchange body allowing air to circulate either against or perpendicular to the water flow. Some other air cooling towers are forced draft, with blowers or extractors circulating the air.

There are several problems in the use of wet air cooling towers, one of which is that when the air temperature is lower than 0°C, there is a danger of freezing of the flowing water. Water freezes in the exchange body and can damage the exchange body due to mechanical overload caused by the weight of the ice. In addition, the presence of ice hinders the passage of air, thus affecting the cooling effect.

This problem is particularly serious when, as is often the case, there is communication with very low air temperatures, the heating power is reduced to well below the rated power of the cooling tower. This situation is particularly likely to occur when the auxiliary lines of the central station cool down. Over a longer period of time, the power consumed in operation may be less than 10% of the maximum power determined by the air cooling tower.

To solve this problem, various solutions have been proposed. In particular it has been proposed to deactivate parts of the exchange body and only supply water to certain compartments. In the case of forced draft cooling towers, one can simultaneously stop the fans that are moving air through the corresponding compartments. There are major flaws in this approach. If the water that does not enter certain compartments is sent directly to the water collection device, then the temperature of the collected water increases rapidly, which is usually not acceptable. However, if the entire water flow is sent to some compartments, the head loss will be greatly increased, which will change the working state of the pump and increase the hydrostatic pressure on the nozzle. If the increase is too large, the mechanical properties of the nozzle may be affected. damage. According to this reason, in practice, this method can only reduce the exchange surface by at most 50%. In this case, if the air temperature is -20°C, the minimum thermal power at which the danger of freezing can be avoided is not less than a few tenths of the rated power.

The present invention aims to provide an air cooling tower of the type identified above which is more practical in reducing the risk of icing than known prior cooling towers. To this end, the invention inter alia proposes to reduce the increase in hydrostatic pressure on the nozzles due to the supply of water to said nozzles with a nominal flow rate, without adding active devices, ie devices requiring remote control and/or electrical power for operation.

In particular, the present invention proposes an air cooling tower of the type identified above, characterized in that it comprises a hydrostatic head (or pressure height) applied to the nozzle once it exceeds a certain value, greater than all compartments when working A static device that automatically limits the increased hydrostatic pressure at a value of , and is used to divert a portion of the water flow directed to the distribution height starting from exceeding a determined value.

In the first embodiment, the static device includes an overflow outlet interposed between the water tower and several return pipes, the water tower is supplied with water by the pumping device, and the water is supplied to the water distribution network through the water collection device, and the return pipe surrounds the water supply in the working state. Nozzles, overflows are at heights corresponding to the specified values.

This kind of cooling tower can also include a diversion pipe that diverts flow towards the water collection device, and its high point can be located at a height higher than the height of the water distribution network inlet water collection device and lower than the height of the overflow outlet, so that the diversion flow can be reached even after reaching Intervention begins before the value is determined. Such ducts can have a very small cross-section, since the purpose of said ducts is only to avoid dead spots of the catchment.

In another embodiment, the cooling tower includes at least one auxiliary distribution network in at least some of the compartments, arranged in sections, each connected to auxiliary nozzles, each connected to a respective compartment, each connected to the main distribution network The corresponding part of the auxiliary net is used to supply water to the auxiliary nozzles only when the hydraulic pressure head reaches the height fixed by the high point of the auxiliary net.

The two above embodiments can be combined, the first being supplemented by an auxiliary network.

The invention will be better understood with the aid of the drawings and the description of a non-limiting embodiment.

The accompanying drawings are as follows:

Fig. 1 is the schematic diagram of the possible structure of air cooling tower exchanging device in the first embodiment of the present invention;

Fig. 2 is the front view of the forced-air exchange device that the present invention can implement;

Fig. 3 is a front view similar to Fig. 2, especially for a naturally ventilated exchange device;

Figure 4 is a front view of another embodiment similar to Figure 3;

Fig. 5 is the view of another natural ventilation exchange device that can be implemented in the present invention;

Fig. 6 is a top view of the distribution network and the air cooling tower exchange body in Fig. 5 .

The heat exchange device and hydraulic system shown in Fig. 1 can especially be equipped with natural draft air cooling towers, including passages not shown, although said heat exchange device and hydraulic system are also suitable for forced draft cooling towers. The heat exchange device and hydraulic system include a water tower 10 into which the water to be cooled is sent by one or several pumps 12 . The water tower supplies water to at least one water collector 14, and the water collector is connected with as many shunt pipes as the compartments, and the compartments can stop working independently. Each manifold is provided with an inlet valve 16 which is generally remotely controlled. The inlet valve feeds water to the nozzles 18 arranged above the exchange body 20 where the diverted water flows and cools in contact with the circulating air rising along the arrow f. The cooling water is collected in the water collection tank 22, and the water is accelerated in the water collection tank by the circulation pump 24, and the circulation pump sends the water to the exchange device, and the water is preheated in the exchange device before returning to the water tower. Pumps 12 and 24 in series could be replaced by an identical pump.

In the embodiment of the invention shown in Figure 1 , the static means comprising the overflow 26 reduce the hydrostatic pressure exerted on the remaining nozzles when certain valves are closed. Once the height of the water in the water tower exceeds the value h ₀ , part of the hot water delivered by the pump 12 is diverted to the channel 28 from where the conduit 30 directs the water into the sump 22 . The discharge of an overflow wave increases in proportion to the square root of its thickness Δh. Therefore, under the condition that the overflow has sufficient length, the water head can be limited to a value slightly larger than _h0 .

In addition, the static components may also include one or several drain pipes 32 . Drain 32 sends water from sump 14 directly into sump 22 when the hydrostatic head is above height _h'1 , below _h0 , but above that given by pump 12 when all compartments are in operation (indicated by a solid line) or channel 28 (indicated by a dotted line). Accordingly, the conduit has a bend 34 forming a high point of height _h'1 .

In order to avoid that the drain pipe 32 forms a siphon which, once connected, permanently supplies water, the vent pipe 36 is placed at a high point. The ventilation pipe opens to a height higher than h ₀ to avoid water overflowing from the ventilation pipe. In some cases, an elbow may also prevent channel 28 from supplying water to the catchment.

Compartments 20 may be configured at an angle. Generally speaking, this case is a natural draft large-scale cooling tower. Compartments may also be arranged along the sump 14 . In this case, the conduit 32 extends the sump so as to protect the sump. Such a compartment may supply water to a channel leading into a sump from which a pump 24 draws water. The conduit 32 advantageously leads to the end of the channel remote from the sump.

In another embodiment, the sump 14 is fed directly by the pump 12 . The overflow port 26 is located at the opposite end from the sump.

The air cooling tower in the embodiment shown according to FIG. 2 is of the forced draft type, and the figure shows two compartments in its entirety, the air cooling tower comprising an extractor fan 40 for each compartment. The air enters the compartment between the deflectors 42 , circulates against the water flow in the exchange body 20 , and is sent to the outside by the ventilator 40 . The water inlet valve 16 of each compartment supplies water to the main network of water distribution pipes equipped with nozzles 18 , which are generally located at the same level and installed above the exchange body 20 . The water flowing out from the exchange body is collected in the sump 44, and the channel 46 communicates with the general sump. However, the exchange bodies of all compartments can be configured directly above the same sump.

In the embodiment shown in FIG. 2 , the static components comprise a secondary network of conduits fed by water distribution means 48 supplied by an ascending manifold 50 on the main network downstream of valve 16 . The water distribution device includes a high point at the height of _h1 , and after the position of the high point is determined, it communicates with the atmosphere through the ventilation channel 36 leading to the height of _h2 .

In the embodiment shown in FIG. 2, the nozzle 52 of the auxiliary network is installed above the nozzle 18, and the water distribution device 48 is installed above the height of the main network water distribution device. This arrangement (and the arrangement of the nozzle 52 below the nozzle 18) can reduce head loss through the air. It is also possible to install two water distribution networks at the same height.

FIG. 3 shows only the water distribution network of the compartments, and the embodiment shown in FIG. 3 differs from the embodiment shown in FIG. 2 . Components in FIG. 3 corresponding to those in FIG. 2 are designated with the same reference numerals, and the exchange body of the compartment is divided vertically into two superimposed water flow areas 20a and 20b. The auxiliary water distribution network is installed so that it only sprays water to the lower water flow area 20b. This arrangement increases the efficiency of the antifreeze device.

In another embodiment shown in FIG. 4 , the water tower supplies water to channels 54 each acting on a compartment through a respective valve 16 . The main water distribution starts at the bottom 54 of the channel. The auxiliary water distribution device 42 is supplied with water from the channel when the water level in the channel exceeds the height _h3 . In this case, it is not necessary to provide high points and ventilation channels on the water distribution device 48, but instead the channels 54 communicate with free air.

Finally, Figures 5 and 6 show a possible embodiment of a natural draft cooling tower having a channel 56 of general construction using the present invention. This channel is provided on the ground through an annular duct with free access to the air. The channel comprises an exchange body formed, for example, from a grid of slats. This exchange body is divided by partitions 60 into several compartments. In the case shown in Figure 6, the partition 60 defines a central compartment and six peripheral compartments. The partitions 60 are almost hermetic and they extend vertically from the bottom of the exchange body to the upper part of the distribution network duct. A central water tower 10 feeds a partial network dedicated to each compartment through nozzles or conduits equipped with water inlet valves 16 . These conduits supply water to the water distribution unit, which has a structure as previously described.

In the embodiment shown in Figures 5 and 6, the central compartment comprises only the main water distribution network. On the contrary, each peripheral compartment comprises on the one hand the main water distribution means and on the other hand the auxiliary water distribution means 48 with a high point, the general structure may be that shown in FIG. 2 .

As shown in Figures 5 and 6, when only some compartments have auxiliary nets, if antifreeze is required, the unequipped compartments should be separated from the former.

The invention is capable of several other embodiments. For example, an auxiliary net of this type shown in FIGS. 2 to 5 can be arranged on an air cooling tower with a general structure as shown in FIG. 1 . In this case, an ascending manifold is provided downstream of at least some of the valves 16, supplying water to the auxiliary nozzles. The high point of the manifold must be below h ₀ . On the contrary, said high point should be above the level reached by the water in the water tower 10 when all the compartments are working simultaneously by the opening of the valve 16 .

It is also possible to arrange several manifolds with high points of different heights downstream of the water inlet valve.

It is also possible to equip only the most sensitive parts of the exchange body with auxiliary nets for frost protection, that is to say in the parts of the exchange body through which the cold air first passes. The invention is applicable to any type of known air exchange device, in particular to both cross-draft and counter-draft air cooling towers. In addition, the invention may be combined with means for preventing icing at inlets, for example, at the inlet of an air cooling tower, where a curtain of uncooled water is directed towards the air channel.

Claims (12)

1. A kind of air cooling tower, it comprises exchange main body (20), water distribution network and water collecting and water pumping device (22,24,12,10), and described water distribution network is installed on the top of exchange main body and is equipped with each A valve (16) for supplying water from a water spray nozzle mounted above the different parts of the exchange body to form a cooling compartment, the water collecting and pumping means collecting the water flowing through the exchange body and transferring it to pumping to the water distribution network, characterized in that it comprises static means for automatically limiting the increased hydrostatic head as soon as the hydrostatic head applied to said nozzles exceeds a determined value, greater than the value reached when all compartments are in operation, The static device is used to divert a part of the water flow directed to the water distribution height starting from exceeding a certain value. 2. The cooling tower according to claim 1, characterized in that, said static device comprises an overflow outlet (26) interposed between a water tower (10) and some return pipes (30), and said water tower is supplied by a pump The water supply device (12) supplies water to the water distribution network, the return pipe surrounds the nozzle in operation, and the overflow port is at a height corresponding to the determined value (h ₀ ). 3. cooling tower according to claim 2, it is characterized in that, it also comprises the shunt pipe (32) towards water collection device diversion, the height of its high point is higher than the height of water distribution network inlet water collection device, lower at the height of the overflow. 4. Cooling tower according to claim 3, characterized in that the high point is provided with a ventilation pipe (36) which leads to a height above the overflow. 5. Cooling tower according to claim 1, characterized in that said static device comprises at least one auxiliary water distribution network in at least some compartments, arranged in several parts, each part is connected with auxiliary nozzles, all with The respective compartments are connected, each fed parallel to the corresponding part of the main distribution network, said auxiliary network for supplying water to the auxiliary nozzles only when the hydraulic head reaches a height fixed by the high point of said auxiliary network. 6. A cooling tower according to claim 5, characterized in that it is provided with several auxiliary water distribution networks with high points of different heights. 7. Cooling tower according to claim 5 or 6, characterized in that said nozzles of the auxiliary water distribution network are installed on the middle height of the exchange body so as to spray water only to the lower part (20b) of the exchange body. 8. The cooling tower according to claim 5 or 6, characterized in that the auxiliary water distribution network is installed at a height lower than the main water distribution network, and water is supplied through a high point. 9. The cooling tower according to claim 5 or 6, characterized in that the auxiliary water distribution network is installed at a height higher than the main water distribution network. 10. An air cooling tower comprising a flowing water structure, at least one main water distribution network, and water collecting and pumping devices (22a, 24, 12, 10), said main water distribution network being installed above the exchange main body, equipped with valves (16) each supplying water to the water spray nozzles mounted above the corresponding part of the exchange body to form a cooling compartment, the water collecting and pumping means collecting the water flowing through the exchange body and Collected water is pumped to a distribution network, characterized in that it has at least one auxiliary distribution network in at least some compartments, arranged in sections, each section connected to the auxiliary nozzles of the corresponding compartment, all connected to the main distribution network The corresponding part of the net feeds water in parallel, and said auxiliary net supplies water to the auxiliary nozzles only when the hydraulic head applied to the compartment reaches a value such as that the water level reaches the high point of the auxiliary net. 11. Cooling tower according to claim 10, characterized in that the high point is provided with a vent pipe (36) opening to a height above the overflow opening which limits the water head. 12. A cooling tower according to claim 5, 10 or 11, characterized in that the nozzles of the auxiliary water distribution network are arranged to spray water only to a part of the lower part of the exchange body.

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