EP0687878B1 - Evaporative cooling tower - Google Patents

Abstract

The cooling tower has an OD (DA) of the tubes forming the tube coil of less than 25 mm. The straight line tube sections (3a,3b) of the immediately adjacent tubes (2a,2b) have a mean vertical tube distribution (S2) and are formed from tube centre to tube centre with between one and two times the OD. The vertical distance from tube centre to tube centre of the tube sections (3a,3b) corresponds to double the vertical tube distribution (S2). <IMAGE>

Description

The invention relates to an evaporative cooling tower for cooling or condensation of fluids using cooling air with at least one additional with water acted pipe coil heat exchanger, the straight of which Pipe sections and pipe bends connecting these pipe sections existing coils in such a way with their beginning at a distributor and with their end are connected to a collector that the straight, in essentially horizontal and lying in the same plane Pipe sections of adjacent coils with a division between the input and Are arranged three times their hydraulic outer diameter, wherein the directly adjacent, straight pipe sections in Flow direction of the water acting on the coils offset to each other and with an average vertical pipe pitch from the center of the pipe Pipe center between one and two times the outer hydraulic Diameter are arranged.

Evaporative cooling towers of this type are known from DE-U-89 07 113. At used this for cooling or condensation of fluids by means of cooling air An evaporative cooling tower replaces a coil coil heat exchanger other types of known cooling or trickle internals to one closed circuit for the fluid to be cooled or condensed receive. Such a cooling tower design is also called a fluid cooling tower, Evaporative condenser or closed evaporative cooling tower.

In such an evaporative cooling tower, the respective fluid is generated by means of air cooled or condensed. In addition, the outer surface of the Pipe coil heat exchanger is sprayed or wetted with water, by using evaporative cooling to improve the heat transfer performance to increase this heat exchanger significantly. Accordingly stand in such an evaporative cooling tower three material flows in thermodynamically Contact, depending on the embodiment in the same and / or counter and / or Cross current to each other.

A key target when designing such evaporative cooling towers is the lowest possible outlet temperature of the fluid the temperature of the coolant used, i.e. the air, is physically limited is. This limit value is also used when evaporative cooling is used due to the wet air temperature, which is significantly lower than the dry air temperature is determined. Especially at higher air temperatures in the summer Fluid outlet temperature reduced with relatively simple technical means by injecting additional water into the cooling air flow. The fine Distributed water drops evaporate for the most part and lead to one Cooling of the air and thus an improved cooling of the fluid in the Heat exchanger.

In the embodiment known from DE-U-89 07 113, a larger one Water quantity above the heat exchanger using spray nozzles if possible equally distributed. The water trickles over the pipes of the heat exchanger below and is collected in the cooling tower trough. Then this sprayed or secondary water is pumped up again for water distribution promoted. It forms on the surface of the heat exchanger tubes Water film and in the interstices water droplets and strands of them Surfaces a small amount of water evaporates into the cooling air flow. The Evaporation loss must be constantly supplemented with make-up water. The in the Evaporative cooling tower inflowing cooling air experiences a change in temperature, is enriched with water vapor and finally back into the environment dissipated. It removes the water film on the heat exchanger tubes Heat so that the fluid flowing inside the pipes is cooled or is condensed. With such an evaporative cooling in one Evaporative cooling tower is therefore a combined heat and Mass transfer process, which due to its very complex nature a safe Performance determination only after extensive investigations have been carried out allows.

The sprinkled heat exchanger is preferably made of smooth, non-finned Pipes that are resistant to external pollution and high have area-specific transmission power. The pipes become inexpensive processed into snakes and on distribution and collecting pipes for the inner fluid connected. The straight lines next to each other Pipe sections of the coils become more thermodynamically advantageous Way vertically offset from each other, with larger with smaller Alternate distances. These are called vertical divisions.

In order to achieve a higher area-specific in such evaporative cooling towers To achieve heat transfer rate, neighboring coils of endure EP-B1-0 007 829 known evaporative cooling tower a certain distance in Horizontal direction to each other. The coils not touching each other have a preferred tube geometry with an outer tube diameter of 26.7 mm and an inner bending radius of 53.2 mm. This results in an average, vertical division from tube center to tube center of the neighboring Tubes of 66.5 mm (inner bending radius plus half the outer tube diameter). The corresponds to approximately 2.5 times the outer pipe diameter.

According to the prior art are used for the coil coil heat exchangers described prefers pipes with a relatively large outside diameter of selected about 25 to 30 mm. This can reduce the manufacturing effort, because compared to smaller pipe diameters with the same heat exchanger surface a smaller number of tubes per cooling tower cross-section and coils is needed.

In the coil coil heat exchanger both according to DE-U-89 07 113 Even according to EP-B1-0 272 766, elliptical tubes are used for straight Pipe sections used, which are also a preferred distance from each other in Have horizontal direction.

Finally, EP-A-0 119 934 is a coil coil heat exchanger for one Evaporative cooling tower can be seen, the pipes in the horizontal Pipe sections are provided with ribs in order to enlarge them Surface to increase performance.

It can thus be seen from the prior art that a high area-specific Heat transfer rate of the coil-shaped heat exchangers then is achieved when the adjacent coils have a certain, but not too great distance from each other, namely regardless of which pipe shape or which pipe diameter is used and whether these pipes are finned. Furthermore, in the known state of the art Technology selected the largest possible vertical division of the tubes. this happens on the one hand from a manufacturing perspective, since the bending radii chosen are too small for the Buckling or other undesirable deformation of the pipe bends. On the other hand, the water drops between the pipes are not insignificant Dimensions of the already described heat and mass transfer process and thus of the Performance of the heat exchanger involved, it being obvious that with larger horizontal and vertical divisions, larger spaces for education created by drops and thus the entire surface of all drops is enlarged. So has an enlarged surface of the trickle water to the air the current doctrine - an increased heat transfer capacity of the Evaporation cooling tower result.

The invention has for its object to increase the area-specific transmission power in an evaporative cooling tower of the type described above or to achieve a reduction in the required surface of the heat exchanger and thus the material used, without having to accept a higher air-side pressure loss and thus an increased fan performance must become.

The solution to this problem by the invention is characterized in that the outer hydraulic diameter of the straight pipe sections of the coils is so much smaller than 25 mm that a significant increase in the area-specific transmission capacity of the coil heat exchanger is achieved.

The trickle water dripping at the lowest point of the pipe cross-section has in Pipe coil heat exchanger according to the invention a much shorter Distance until it hits the same vertical plane immediately put the pipe underneath. Reduced with the vertical division significantly the number of trickle water drops, so that the entire heat and mass transfer surface of the trickle water as well decreases. Of course, in accordance with the usual Doctrine also the reduction of the total trickle water surface Reduction of the heat transfer capacity of the evaporative cooling tower Episode.

The performance contribution of the drops located between the rows of pipes has been greatly overestimated so far. A row of pipes holds the straight ones Pipe sections together, which are in the same horizontal plane. It it was found that a drop reduction in these tube-free spaces only a small reduction in the total heat transfer performance has the consequence. But this is due to the rapidly increasing evaporation flow, from the trickle film surfaces of the individual pipes to the air flowing around them is more than compensated. The narrower in the vertical direction tubes that are moved together create a more uniform and intense tube Flow around the pipes, leading to an increase in the rate of evaporation Evaporation current per transmission area is defined leads. It got in In this regard, the vertical division has also been shown to be advantageous train evenly. The evaporation rate becomes smaller by choosing smaller ones Pipe outside diameter reinforced in a previously unknown order of magnitude, so that the desired increase in the area-specific transmission power of the Pipe coil heat exchanger is reached.

Furthermore, due to the reduced number of drops between the tubes air pressure loss is reduced, so that the air throughput can be increased. This leads to a further increase in the total transmission power.

According to a further feature of the invention, the vertical distance corresponds from pipe center to pipe center of the straight line belonging to the same coil Pipe sections twice the vertical pipe pitch. This results in on the cross-sectional area perpendicular to the longitudinal direction of the straight one Pipe sections covered a uniform pipe arrangement of all pipes of the Heat exchanger with the result of a compact design and an increased Performance.

In preferred embodiments of the invention, the vertical pipe division corresponds of pipes the simple of the outer hydraulic diameter. The pipes can also have an oval cross-sectional shape according to the invention. Finally the tubes can be finned.

Fig. 1

eine schematische, teilweise geschnittene Seitenansicht eines mit einem Rohrschlangen-Wärmetauscher ausgestatteten Verdunstungskühlturms;

Fig. 2

einen Schnitt durch den Verdunstungskühlturm gemäß der Schnittlinie II - II in Fig. 1;

Fig. 3

einige mit Luft und Rieselwasser beaufschlagte, gerade Rohrabschnitte gemäß einem teilweisen Querschnitt durch den Rohrschlangen-Wärmetauscher in Fig. 1;

Fig. 4

eine vergrößerte Darstellung des Rohrschlangen-Wärmetauschers gemäß Fig. 2;

Fig. 5

einen modifizierten Rohrschlangen-Wärmetauscher gemäß Fig. 4;

Fig. 6

eine weiter modifizierte Rohrschlangenanordnung des erfindungsgemäßen Rohrschlangen-Wärmetauschers gemäß Fig. 4;

Fig. 7

einen vergrößert dargestellten Teilschnitt durch einige Schlangen des Rohrschlangen-Wärmetauschers gemäß der Schnittlinie VII - VII in Fig. 4 bzw. Fig. 5;

Fig. 8

einen der Fig. 7 entsprechenden Teilschnitt einer Rohrgeometrie nach dem Stand der Technik und

Fig. 9

ein Diagramm mit dem Flächenbedarf des erfindungsgemäßen Rohrschlangen-Wärmetauschers als Funktion des äußeren hydraulischen Durchmessers und der vertikalen Rohrteilung.

An exemplary embodiment of the evaporative cooling tower according to the invention is shown in the drawing, namely:

Fig. 1

is a schematic, partially sectioned side view of an evaporative cooling tower equipped with a coil coil;

Fig. 2

a section through the evaporative cooling tower along the section line II - II in Fig. 1;

Fig. 3

some straight pipe sections to which air and trickle water have been applied according to a partial cross section through the coil heat exchanger in FIG. 1;

Fig. 4

an enlarged view of the coil heat exchanger according to FIG. 2;

Fig. 5

a modified coil heat exchanger according to FIG. 4;

Fig. 6

a further modified pipe coil arrangement of the pipe coil heat exchanger according to the invention according to FIG. 4;

Fig. 7

an enlarged partial section through some coils of the coil heat exchanger according to the section line VII - VII in Fig. 4 and Fig. 5;

Fig. 8

7 corresponding partial section of a tube geometry according to the prior art and

Fig. 9

a diagram with the area requirement of the coil coil heat exchanger according to the invention as a function of the outer hydraulic diameter and the vertical pipe pitch.

The evaporative cooling tower shown schematically in FIGS. 1 and 2 is used for Cooling or condensing fluids and is for this purpose with a Pipe coil heat exchanger 1 equipped. This essentially exists of a plurality of coils 2a and 2b, which are in vertical planes lying close to each other without a gap. The coils 2b are in an alternating sequence to the pipe coils 2a in the vertical direction transferred. Each coil 2 a and 2 b is in the embodiment by six straight lines parallel to each other and at the same distance above each other Pipe sections 3a and 3b and pipe elbows 4a and 4 connecting them to one another 4b formed, cf. Fig. 2. This results in twelve vertically one above the other arranged rows of pipes, one row of pipes each in a horizontal Flat, straight pipe sections 3a and 3b lying side by side summarizes.

All coils 2a and 2b are connected to a box-shaped distributor 5 and a collector 6 connected. The fluid to be cooled or encoded is fed through an inlet nozzle 7 to the distributor 5 and through this the individual coils 2a and 2b distributed. The individual sub-streams are then merged again by the collector 6. On this is a Outlet port 8 connected through which the cooled or condensed fluid drains away.

The cooling of the fluid in the individual coils 2a and 2b of the coil heat exchanger 1 is done by air. For this purpose, a motor 9 drives over a V-belt 10 to a radial fan 11, which according to the environment the arrows drawn in FIGS. 1 and 2 suck the cooling air. This will through the outlet opening 12 of the radial fan 11 into the distribution space 13 pressed to feed them to the individual coils 2a and 2b from below. For this purpose, the evaporative cooling tower faces outwards Housing walls 14 on.

The coils 2a and 2b of the coil heat exchanger 1 are additionally applied with water to the cooling effect of the air by application evaporative cooling. The water is from the Reservoir of a cooling tower trough 15 sucked in with a pump 16 and via a Riser 17 of the nozzle water distribution 18 supplied. This consists of several pipes and nozzles not shown, um to distribute the water over the coil heat exchanger 1.

The water is sprayed into a multitude of drops, which after impact on the outer surfaces of the straight, horizontal Pipe sections 3a and 3b according to FIG. 3, thin, downward flowing films 19 train. This flows at the lowest point 20 of the respective pipe cross section Trickle water in the form of drops and falls through one between the pipes horizontal plane 21 formed, the drops from the counter-flowing Air is further divided and distributed in the intermediate spaces. The drops then hit the pipes immediately below, where others Trickle films 19 are formed. This continues from tube to tube.

The drops from the bottom tubes of the coil heat exchanger 1 1 and 2 fall into the distribution space 13 and are finally in the Cooling tower trough 15 collected. On the way from distribution to Collection evaporates from the surfaces of the trickle drops and films of water in the counter-flowing air flow. The strong with steam enriched air then flows through a droplet separator 22, which entrained water drops, and then leaves the evaporative cooling tower. The resulting loss of evaporation is shown in FIG. 2 by additional water constantly added via line 23.

4, the coil coil heat exchanger 1 according to FIGS. 1 and 2 is shown enlarged in order to be able to better recognize essential structural details. The straight pipe sections 3a and 3b are connected to prefabricated pipe bends 4a and 4b, for example by welding, in order to obtain pipe coils 2a and 2b which have a uniform vertical division s ₂ between the straight pipe sections 3a and 3b (see FIG. 7). In the exemplary embodiment, this value corresponds to 1.5 times the outer hydraulic diameter d _A and is equal to the radius of the pipe bends 4a and 4b up to the center of the pipe. The coils 2a and 2b are supported several times by horizontal, strip-shaped support elements 24, which in turn are attached to an outer, solid support frame 25, and are positioned in their spatial position.

In Fig. 5 is a modified coil design of the coil heat exchanger 1 shown in FIGS. 1,2 and 4. Here the straight ones Pipe sections 3a and 3b not with pipe bends, but with short, straight ones Pipe pieces 26a and 26b connected. The pipe ends are used for this purpose cut at a 45 ° angle. The straight pipe sections 26a and 26b are particularly easy to manufacture and therefore cheaper than prefabricated pipe bends 4a and 4b according to Fig. 4. They also allow the Average vertical division of the straight pipe sections 3a and 3b to each other easily to the even cheaper 1.0 times the value of the external hydraulic Reduce diameter.

The goal of maximum heat transfer performance of the evaporative cooling tower requires the selection of an outer hydraulic diameter that is less than 25 mm is. This can cause the fluid velocity in the pipes to increase gets big. A further exemplary embodiment according to FIG. 6 shows one for these cases Arrangement of coils that are nested in the vertical direction are. On the box-shaped distributor 28 and on the similar collector 29 the coils are connected with four rows of pipes. The corresponds to the previous exemplary embodiments according to FIGS. 2.4 and 5 a doubling so that the internal fluid velocity is halved.

In FIG. 7, an enlargement of the pipe coil heat exchanger 1 according to FIGS. 4 and 5 shows some pipe coil sections with the preferred geometric relationships in cross section. In this embodiment, the outer diameter of the round tube corresponding to the hydraulic diameter d _A is 18 mm; the inner tube diameter d _I is 15 mm; the average horizontal pitch s ₁ is 37 mm and the average vertical pitch s ₂ , which here is equal to the bending radius r _B , is 27 mm. The vertical division s ₂ is uniform and corresponds here to 1.5 times the outer tube diameter d _A.

This representation in FIG. 7 is compared with FIG. 8, an arrangement corresponding to the prior art, which has an outer tube diameter d _A of 26 mm and a vertical division s ₂ as the mean of the two vertical offsets s _2a and s _2b of 65 mm having. This corresponds to 2.5 times the outer pipe diameter d _A.

The diagram of FIG. 9 shows the curves for constant cooling capacity the required surface of an air and water sprinkled coil coil heat exchanger 1 according to FIGS. 1 to 6 depending from its geometric data. The starting point of the consideration is the known prior art corresponding geometric arrangement Fig. 8 represents by an outer tube diameter of 26 mm and a vertical Line ratio of 2.5 is characterized. To manage the cooling capacity becomes a defined surface of the coil heat exchanger with this pipe geometry required by 100%.

If you follow the upper curves that show the performance behavior of the represent known vertical division ratios of 2.0 to 3.0, is a Reduction of the heat exchanger surface required only with relatively small Determine pipe diameters. However, the material savings that can be achieved in this way are in Considering the larger number of pipes required, an increased Manufacturing effort means not enough.

It can also be clearly seen in this diagram that, with the pipe diameters of more than 25 mm previously used, the vertical pipe division ratio according to the invention only brings about a marginal reduction in the heat exchanger surface required. _A significant effect is only achieved with external hydraulic diameters d _A smaller than 25 mm. The required surface area drops particularly sharply when the vertical pitch is smaller than 2.0 times the pipe diameter as the external hydraulic diameter becomes smaller. However, the curves are flatter again with diameters smaller than 16 mm. Furthermore, it was found that an even smaller vertical division than 1.0 times the outer hydraulic diameter again leads to a reduction in the performance of the heat exchanger, since, due to the pipes which are then moved very close together, there is a steep increase in the air-side pressure loss.

These basic results also apply to finned tubes and Pipe shapes that deviate from the circular shape, e.g. the oval tube. In these In each case, the hydraulic diameter should be used as the standard of assessment.

Claims (5)

1. Evaporation cooling tower for the cooling or condensation of fluids by means of cooling air, with at least one tube-coil heat exchanger (1) which is additionally loaded by water and of which tube coils (2a,2b) consisting of straight tube portions (3a,3b) and of tube bends (4a, 4b) connecting these tube portions (3a, 3b) are connected at their start to a distributor (5) and at their end to a collector (6), in such a way that the straight tube coils (2a, 2b) running essentially horizontally and adjacent to tube portions (3, 3b) lying in the same plane are arranged with a division (s₁) of between once and three times their hydraulic outside diameter (d_A), the straight tube portions (3a, 3b) located directly next to one another being arranged so as to be offset to one another in the direction of flow of the water loading the tube coils (2a, 2b) and with an average vertical tube division (s₂) from tube centre to tube centre of between once and twice the hydraulic outside diameter (d_A) characterized in that the hydraulic outside diameter (d_A) of the straight tube portions (3a, 3b) of the tube coils (2a, 2b) is designed to be smaller than 25 mm by an amount such that a significant increase in the area-specific transmission capacity of the tube-coil heat exchanger (1) is achieved.
2. Evaporation cooling tower according to Claim 1, characterized in that the vertical distance from tube centre to tube centre of the straight tube portions (3a and 3b) belonging to the same tube coil (2a and 2b respectively) corresponds to double the vertical tube division (s₂).
3. Evaporation cooling tower according to Claim 1 or 2, characterized in that vertical tube division (s₂) of the tubes corresponds to once the hydraulic outside diameter (d_A).
4. Evaporation cooling tower according to at least one of Claims 1 to 3, characterized in that the tubes have an oval cross-sectional shape.
5. Evaporation cooling tower according to at least one of claims 1 to 4, characterized in that the tubes are ribbed.

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