Calculation of cooling tower make-up water. Cooling tower

EMERGENCY SITUATION AT ROSTOV NPP IS HIDING FROM THE PRESS Oleg Pakholkov spoke about the emergency situation at the third power unit of the Rostov Nuclear Power Plant

State Duma Deputy Oleg Pakholkov: Good afternoon! My parliamentary reception office received a letter from a person who wished to remain anonymous. I know this person very well, he is a competent specialist and a reliable source. A letter was received from him with a request to immediately publish information about the purpose of Sergei Kiriyenko’s visit to the Rostov NPP. I will read this letter: “About Kiriyenko’s visit! Unit 3 is undergoing scheduled maintenance! A problem has emerged: the cooling tower is faulty and it will take more than six months and several hundred million rubles to fix it (the money, of course, will not be from the budget - the cooling tower is under warranty), but it is not able to cool the water properly! But... here's the thing! The cooling tower partially collapsed from the inside, possibly due to the fact that the products were replaced from metal, as in the German project, to fiberglass. And also, possibly counterfeit, supplied from Latvia! So there you go! The situation at the nuclear power plant is hidden from the press. If the cooling tower is not started up, the damage to the Russian economy will be colossal – billions! They want to coordinate and launch without internal products - the rationale “kills” me: “it won’t be hot now, winter is coming.” The cooling tower of the 4th block is the same. There were prerequisites for this - the temperature of the cooling tower from the moment of commissioning was always higher than the design one - the water coked and collapsed the structures!” https://www.youtube.com/watch?v=eUxrdV2TNQY

I appeal to the leadership of Minatom and the management of the Rostov NPP! Immediately remove this issue from the information blockade. We, residents of Volgodonsk and surrounding areas, have the right to know what is happening with the third power unit. Will you start it now or repair it along the way. This is indirectly confirmed by the fact that today all vacations at the Rostov NPP were canceled. And everyone who can repair the cooling tower has been recalled from vacation and is at the nuclear power plant on a daily basis. What decision will you make? Start it with an insufficient cooling system and repair it as you go. Or will you still shut down the power unit for half a year? I understand the difficulty of making this decision. I understand that in winter the country needs a lot of electricity and with this decision we can undermine the country’s energy system. In any case, we must know what is going on there! For my part, I want to reassure the population. There is no danger of a major accident at the Rostov NPP, which could lead to an environmental disaster! Because, firstly, the third power unit is “shut down” today. Secondly, the system of a modern nuclear reactor, which is in the third power unit, has all the protection systems and, again, it can simply be shut down. Today the main problem is economic. Who will restore the cooling tower. This is a problem for the Russian Federation, because the prestige of nuclear energy is very much in question. How will we build nuclear power plants for export if we cannot build them in our own country? This is a problem, how will the 4th power unit be cooled. Will the organization that issued the warranty for this cooling tower be able to repair it at its own expense? Who will pay off the losses if the unit has to be stopped for half a year? While all the problems, thank God, are not in the field of ecology, they do not pose a threat to the life and health of the population. For now, all the issues lie in the field of economics. And as I understand, Kiriyenko’s visit today is connected primarily with the meeting at which a decision on this issue should be made. Either the block is started up and repaired along the way, or they will still stop this block.

Open type wet cooling tower.

More often wet cooling tower associated with cooling towers, which can be seen next to thermal power plants or giant enterprises. But for most enterprises the capacity of cooling towers is not required.

Open wet cooling tower or open type cooling towers- the principle of its operation is the same as that of a tower, only unlike the first, an open wet cooling tower is completely transportable and its performance range is quite wide, because in most cases, such a design is a module and by connecting several modules the required performance is achieved.

The principle of operation of the cooling tower is based on the spraying of hot water through nozzles, from which it is actually cooled. Very often this process is supplemented with air flow using axial fans.
Tower cooling towers are used to cool large volumes of water, several times greater than the volume of water in industrial enterprises. This equipment is used primarily in thermal and nuclear power plants.

Closed type wet cooling tower.

A cooling tower in which the main water circuit does not come into contact with the environment, but which still uses the principle of reducing temperature due to evaporation, is called closed type wet cooling tower. Its operation is based on a heat exchanger (or a bundle of pipes), located in a housing which is washed with water and blown with ambient air. As a result of this combination, it is possible to obtain a water temperature at the outlet of the cooling tower approximately equal to the wet-bulb temperature, and it is also safe to use in winter, since non-freezing liquid can be used in the main circuit.

Cooling tower use cases - in cooling systems

One of the important points for the most efficient use of cooling towers in a water circulation system is the optimal choice of the hydraulic connection circuit diagram. Hydraulic circuit designs may vary depending on the number of cooling towers used in a single circuit, as well as the nature of the customer. The range of regulation of water cooler performance is determined by the nature of the consumer. The simplest hydraulic circuit for a single cooling tower, used for one service area, is shown in Fig. 1.


Fig.1 Diagram of the hydraulic cooling circuit for one consumer	Fig.2 Cooling system with cooling towers having separate preparation and consumption circuits

Water from cooling towers and enters the tank, from where it is supplied to the consumer by a circulation pump and further.

In the field of industrial construction, especially when the water flow circulating through the consumer cooler is noticeably less than the water flow circulating through cooling towers, the scheme shown in Fig. 2.Here, return water coming from consumers is settled in storage tanks (the volume of which is calculated for approximately 5-10 minutes of operation of the installation). From it, the pump(s) of the working fluid preparation circuit pumps out water to the evaporative cooling towers. From the equipment, cooled water flows into a similar bath. The main distinguishing feature of such a scheme is the hydraulic independence of the working water preparation and consumption circuits, ensured by the presence of a compensation pipe between the containers (one container can also be used with a partition that provides overflow between its parts). ConsequentlyIt is not at all necessary to constantly adjust the power of cooling towers in accordance with user requirements. Cooling tower fans can operate in a simple On/Off mode. In addition, each such cooling tower always operates at full load and provides the maximum possible cooling of water for given weather conditions. Both schemes are not sensitive to frost, since this equipment is completely drained into storage tanks installed indoors or located underground.

Placement and operation of cooling tower (with axial fans)

To ensure convenience and safety of maintenance, cooling towers must have platforms arranged in accordance with the requirements of the relevant SNiP. Before starting to operate the fan cooling tower, you need to check the hydraulic tightness of pipelines, tanks, as well as the condition of the installed fittings.
The best option is when each water cooler is installed separately on the roof. If this is not possible, then the choice of installation location should be such that recirculation does not occur (Fig. 3). In this case, it is necessary to take into account possible gusts of wind (leeward side) and the nearest location of buildings, which can change the flow of forced air back into the air intake.

Fig.3 Effect of wind and obstacles

Before the first start-up, it is necessary to flush the water lines to remove debris and scale that could have formed there during the welding process, and then visually check the uniform operation of all nozzles. All detected defects must be eliminated before use. Periodic inspections of cooling towers are recommended to be performed at least once a month. Routine repairs of cooling towers should be carried out as needed, but at least once a year, and, if possible, coincide with summer time. The scope of routine repairs includes work that does not require shutting down the cooling tower for a long period of time, for example, cleaning and repairing the water distribution device, pipelines and nozzles, water traps, putting adjustment and shut-off devices in order. During a major overhaul, all work that requires a long shutdown of equipment is performed: eliminating damage to the sprinkler, water distribution system, repairing or replacing the fan unit, etc.

Operating a cooling tower in winter

In winter, operation may become more difficult due to freezing of their structures, especially for cooling towers located in harsh climatic conditions. Freezing of cooling towers can lead to an emergency condition, causing deformation and collapse of the sprinkler due to additional loads from the ice formed on it. Freezing of a cooling tower usually begins at outside temperatures below -10°C and occurs in places where the cold air entering the cooling tower comes into contact with a relatively small amount of warm water. Internal icing is dangerous because, due to intense fog formation, it can only be detected after the sprinkler has been destroyed. Therefore, in winter, fluctuations in thermal and hydraulic loads should not be allowed; it is necessary to ensure uniform distribution of cooled water over the sprinkler area and not allow a decrease in irrigation density in certain areas. Due to the high speeds of incoming air, the irrigation density in fan cooling towers in winter is advisable to maintain at least 10 m 3 / m 2 (not lower than 40% of the full load). The temperature of the chilled water can be used as a criterion for determining the required air flow. If the flow of incoming air is controlled so that the temperature of the chilled water is not below +12 o C ... +15 ° C, then icing of cooling towers usually does not exceed acceptable limits. Reducing the flow of cold air into the cooling tower can be achieved by turning off the fan or switching it to operate at a reduced speed. It is possible to prevent icing of cooling towers by supplying all the water to only part of the cooling towers and completely shutting off the rest, sometimes with a reduction in the flow of circulating water. Blower fans are susceptible to freezing. This can be caused by two things: water droplets hitting the fan from inside the equipment and recirculation of the cooling tower exhaust air containing small droplets of water and steam that condenses when mixed with cold outside air. In such cases, you can avoid icing of the fan blades in the following ways: - reduce the fan rotation speed, - check the pressure in front of the nozzles and, if necessary, clean them, - use fiberglass impellers, - use autonomous heating of the fan shells using flexible electric heaters. It should be noted that uneven ice formation on the blades can lead to imbalance and vibration of the fan. If during the winter period, for any reason, cooling tower fans were turned off, then before starting them up, it is necessary to check the condition of the shells for the presence of ice on them. If ice is detected, it must be removed to avoid damage to the fan impellers.

Methodology for selecting a cooling tower

Initially, it is necessary to determine the following initial data:
Q Г, kW - heat flow (amount of heat) that must be released into the environment,
Tmt, °C - wet thermometer temperature at the hottest time, characteristic of a given region,
Tout, °C - water temperature that should be obtained at the end of the cooling process.

It should be noted that the heat flow for air compressors usually does not exceed the electrical power of the compressor drive; the heat flow for a refrigeration machine is the sum of the refrigeration capacity and the electrical power of the compressor unit drive; the heat flow for technological installations where no fuel is burned usually does not exceed the electrical power of the drives, etc. The temperature of the wet thermometer is determined according to SNiP 23.01-99 "Building climatology", or preliminary according to data from Table 1.

Calculated parameters of atmospheric air. Table 1.

Locality	Dry bulb temperature, T, °C	Relative humidity, F, %	Temperature according to wet thermometer, T, °С
Arkhangelsk	23,3	58	18
Astrakhan	30,4	52	23,2
Volgograd	31	33	20
Vologda	24,5	56	18,8
Grozny	29,8	43	21
Dudinka	22,9	59	17,9
Ekaterinburg	25,8	49	18,8
Irkutsk	22	63	17,6
Kazan	26,8	43	18,7
Krasnodar	28	55	21,6
Krasnoyarsk	24,4	55	18,6
Lugansk	30,1	30	18,8
Magadan	19,5	61	15,2
Monchegorsk	24,6	53	18,5
Moscow	27	55	20,8
Murmansk	22	58	17
Nizhny Novgorod	26,8	48	19,6
Novosibirsk	25,4	54	19,3
Omsk	27,4	44	19,4
Petrozavodsk	24,5	58	19,1
Rostov-on-Don	29,2	37	19,5
Sagwhard	23,7	57	18,3
Samara	28,5	44	20,2
Saint Petersburg	26	56	20,1
Syktyvkar	25,1	49	18,3
Tobolsk	26,5	53	20
Tomsk	24,3	60	19,2
Tula	25,5	56	19,6
Ufa	27,6	44	19,5
Khanty - Mansiysk	26,5	55	20,3
Chelyabinsk	26	51	19,4
Chita	25	48	18
Yakutsk	26,3	40	17,8
Yaroslavl	24,8	53	18,7

The water temperature that must be obtained at the end of the cooling process is determined by the technical parameters of the equipment being cooled and, as a rule, is indicated in the equipment data sheet. Having determined the necessary parameters, you can make a preliminary selection of a cooling tower using cooling curves for various values of tmt.
Example.
It is necessary to select cooling towers for cooling the compressor station in Petrozavodsk. The station includes 3 4VM10-63/9 compressors with a drive Me = 380 kW each, and two compressors are constantly in operation.

Solution .

We determine the total heat flow removed:

Using the table of calculated parameters of atmospheric air, we determine the temperature of the wet thermometer:

In the compressor data sheet we find the temperature at the inlet to the compressor cooling system equal to the outlet temperature:
tOUT=25 °C
Using the cooling curves for the wet bulb temperature, we find the intersection points of the lines corresponding to the total heat flux removed and the temperature at the outlet of the cooling tower with the cooling curves. From the construction we determine which equipment will provide the necessary heat flow.

Dry Coolers (Drycooler)

This type of equipment is much simpler in design than a chiller, since it does not have a refrigeration circuit. The water in dry cooling towers is cooled in plate heat exchangers, onto which several fans circulate outdoor air. Thus, dry cooling towers are located outside the production premises. On average, the thermodynamic limit of dry cooling towers is about 5 degrees. This means that if the air temperature outside is +35°C, then the cooling tower is capable of cooling water to a temperature of +40°C - for cooling the hydraulic fluid or the chiller condenser - a completely acceptable temperature. If the street is below +10°C, then a cooling tower can simply replace a chiller (more precisely, temporarily replace it), supplying water not only to the heat exchanger of the hydraulic circuit of the injection molding machine, but also cooling the mold, which requires water at a temperature of +5°C up to +15°С. Taking into account the fact that in cooling towers cooling is carried out by atmospheric air using fans that do not require much power, they allow energy savings to be achieved in comparison with chillers. Obviously, it is impossible to manage with a cooling tower all year round, since in our country, in addition to winter, there are also very warm summers - it is absolutely impossible to do without a chiller. On the other hand, truly warm weather lasts no more than 4-5 months in a row. What's the point of running the chiller for the remaining 7-8 months when the temperature outside the window ranges from -10°C up to +10°С. But despite this, dry cooling towers are still unclaimed equipment. Even though using a combination of chiller and dry cooler, it is possible to achieve annual energy savings of up to 40%.

There are cooling towers that are directly connected to the hydraulic circuit. It is not a glycol solution that circulates in them, but directly hydraulic fluid. As a result, the intermediary in the form of an intermediate coolant is eliminated from the circuit, which only increases the cooling efficiency. As a result, the hydraulics are cooled by an economical dry cooling tower, and the chiller serves exclusively the mold and injection unit. This allows for a very economical two-temperature energy saving scheme to be implemented. However, on the basis of a chiller and cooling tower, it is possible to implement energy saving schemes in a more familiar form.
Dry coolers are designed for outdoor installation, so glycol must be added to prevent freezing during the cold season.

The use of dry coolers has the following advantages:

Operation of cooling towers in winter - our specialists will give you recommendations.

Recall again the operation of the psychrometer described in the previous chapter, since the cooling tower is a kind of giant psychrometer.
OPERATING PRINCIPLE OF THE COOLING TOWER

At the top of the cooling tower is a device called a spray nozzle. It is a set of tubes with holes in the bottom into which warm water is supplied with high pressure. This water flows out of the holes in the tubes, splashes and flows down. On their way, the water jets meet a powerful upward flow of dry air supplied inside the cooling tower body using a fan. Thus, water and air move in opposite directions.
Dry air absorbs water vapor, leading to intense evaporation of the water flowing downwards, and consequently to its strong cooling. The higher the cooling tower, the longer the water will be in contact with the air and the more it will cool. In order to improve heat transfer, a device called a sprinkler is installed inside the cooling tower, which is usually a honeycomb structure with a developed irrigation surface (see Fig. 73.1). Sprayable in
At the top of the cooling tower, water falls on the irrigated surface, its fall slows down, the time and area of contact with air increases, as a result of which the degree of cooling of the flowing water significantly increases.
To replenish the amount of water that is carried away with the air in the form of water vapor, the cooling tower provides for replenishment of the water circuit with water. To do this, a receiving water tank equipped with a float valve is installed in the lower part of the cooling tower. This valve maintains a constant water level in the tank, hence the cooling tower draws water from the mains. However, how big is this consumption? The water consumption of a cooling tower is negligible compared to a water-cooled condenser cooled by running water. For example, to discharge heat of about 100 kW, you need about 4.5 m3/hour of flowing water for a water-cooling condenser and only 0.15 m3/hour for a cooling tower. That is, the cooling tower consumes 30 times less water than a water-cooled condenser cooled by running water. Thus, water savings amount to 95%."
Note: Do not confuse the huge flow of water circulating in the cooling tower cooling circuit with the negligible flow of water through the make-up float valve: the flow of water circulating in the cooling circuit is approximately 50 times the amount of water that evaporates!

One of the main parameters that determine the efficiency of a cooling tower is the wet-bulb temperature, which in this case is 21°C. Even in an ideal cooling tower, it is impossible to cool the water to a temperature lower than the outside wet-bulb temperature.
If the outside wet bulb temperature is 21°C, it is impossible to cool the water below 21°C.
However, it is very expensive to build cooling towers that are too tall. In practice, most cooling towers have a so-called cooling zone height*, equivalent to 6...7 K. The concept of “cooling zone height” is decisive for assessing the perfection of a cooling tower. It shows how close the cooling water temperature leaving the cooling tower is to the outside air wet-bulb temperature, while demonstrating that in practice the chilled water temperature will never be equal to the outside air wet-bulb temperature.
In our example (see Fig. 73.2), the height of the cooling zone is assumed to be equivalent to 6 K. In this case, the temperature of the water leaving the cooling tower will be equal to the outside air wet-bulb temperature (21 ° C) plus the height of the cooling zone (6 K), then there is 21°C + 6 K = 27°C (and this is not bad at all, if you take into account that the outside air temperature according to the dry bulb is 34°C!).

OPERATING PARAMETERS OF REFRIGERATION UNIT WITH COOLING TOWER
In Fig. Figure 73.3 shows the average typical operating parameters of a refrigeration unit equipped with a cooling tower with forced air circulation at a wet-bulb temperature of Th = 21°C and a dry-bulb temperature of 34°C.

* The height of the cooling zone is a characteristic of cooling towers with forced air circulation, defined as the difference between the average temperature of the cooled water at the outlet of the cooling tower and the wet-bulb temperature of the outside air (see, for example, the New International Dictionary of Refrigeration Science and Technology. Publishing house MIKh. : Paris - 1995). Rarely used in Russian literature (editor's note).

At Th = 21°C, the temperature of the water leaving the cooling tower is: 21°C + 6 K (approximately), which gives a value of 27°C.
If the water temperature at the condenser inlet is 27°C, the condensation temperature will be about 40°C (bearing in mind that the temperature difference for a water-cooled condenser is in the range from 12 to 15 K), that is, the value of the HP will be quite acceptable, despite the fact that that the outside dry bulb temperature is 34°C!
In this case, an air-cooled condenser would give us a condensing temperature of about 50°C, and a dry cooler would give us about 60°C (see Section 70.1).

73.1. EXERCISE. TEMPERATURE RELAY

For normal operation of cooling towers with forced air circulation, a fan is required. The fan provides the required air flow, which allows the water flowing over the irrigated surface to evaporate (and therefore cool).
If the fan does not work, the warm water entering the cooling tower ceases to come into contact with the amount of air necessary for its intensive evaporation and cooling, the cooling of the water deteriorates and the performance of the cooling tower decreases sharply.
On the other hand, if the outside wet bulb temperature becomes very
low, the water will begin to cool very strongly and the productivity of the cooling tower will increase greatly. However, at low condenser inlet water temperatures, the condensing temperature, and therefore the HP, can drop to unacceptably low values (see section 33).
Therefore, to control the operation of the fan, it is necessary to include a temperature relay in the cooling tower, which should operate as follows:
Is the water leaving the cooling tower too cold? The relay turns off the fan, the cooling tower's performance drops and the water temperature begins to rise.
Is the water too warm? The relay turns on the fan, the cooling tower's performance increases and the water temperature drops.
1) Where should the relay thermal bulb be installed?
At point A (see Fig. 73.4): at the water inlet to the cooling tower?
At point B: at the air outlet of the cooling tower?
At point C: at the water outlet of the cooling tower?
At point D: to measure the outside temperature?
2) At what temperature should the relay stop the fan?
Solution on next page...

Option A. When stopping the pump supplying water from the cooling tower to the condenser, some of the water from the pipe pos. 1 in Fig. 73.5 flows into the tank (passing through the stopped pump) in accordance with the law of communicating vessels and the pipe through which water is supplied to the cooling tower is emptied. The water level in the tank and in the pipe is set in accordance with pos. 2. Excess water is drained through the pipe pos. 3.
From this point on, the temperature measured by the thermal bulb will correspond to the ambient temperature. Let's imagine a situation where both the pump and the compressor are stopped. There is no water in pipe pos. 1 and if the outside temperature is high or pipe 1 is heated by the sun, the relay contact will be closed and the fan will work, although neither the pump nor the refrigeration machine is running.

In other words, in this case the fan operates in conditions where there is no irrigation to the cooling tower. Not only does this result in unnecessary energy consumption, but it also increases the air flow through the fan, since there is no resistance to the air flow from the falling water.

As a result, as air flow increases, the current consumed by the fan motor begins to increase very quickly (see section 20.5), and eventually the fan's current protection may trip and turn it off!

By the way, this is why the fan contactor (VT) is connected to the power circuit in series with the power supply contact for the NG cooling tower pump (see Fig. 73.6).
Rice. 73.6.

Options B and D (see Fig. 73.7).

The cooling tower is designed to cool water: therefore, when it operates, it is necessary to measure the temperature of the water, not the air.
Indeed, in options B and D, the relay bulb will measure either the ambient air temperature entering the cooling tower or the air temperature leaving it. However, some installations must operate in the off-season, and even in winter, often at outside temperatures below 15°C.

If the relay bulb is exposed to a very low temperature, the fan will never be able to turn on, even if the compressor is running: as a result, the circulating water will not be properly cooled and the compressor will most likely be turned off by the HP protection!

Option C (see Fig. 73.8). The thermal bulb relay actually controls the "efficiency of the cooling tower." If the water temperature in the tank is high, the fan turns on. If this temperature drops, the fan turns off.
Note. When installing a fan relay thermal bulb on the pipeline leaving the cooling tower, it would seem that one should be wary of the so-called “cycling” of the fan operation. Indeed, when the temperature of the water leaving the cooling tower drops, for example, below 27°C, the fan should turn off. But at the same time, water with a temperature of 32°C continues to flow into the upper part of the cooling tower. Without cooling, it drains into the tank, the water in the tank heats up and the fan must turn on again.
In fact, the amount of water in the tank is significantly greater than the amount of warm water that comes from above. Therefore, the cooling tower has a high thermal inertia, which avoids fan “cycling” mode. At the same time, the relay differential should not be less than 2...3 K. Today, most cooling towers are equipped with fans with two-speed motors (see section 65), which are controlled by two-stage relays, which makes it possible to completely eliminate the “cycling” mode.
What should be the setting of the relay regulator?
Let's imagine that in the summer we configured the relay to turn off the fan when the water temperature at the outlet of the cooling tower is 20°C. A priori, this value seems reasonable, doesn’t it?
Let's think a little: in order to get water with a temperature of 20°C at the outlet of the cooling tower (and stop the fan), you need to have air with a wet bulb temperature below 20°C - 6 K (height of the cooling zone) = 14°C!
The relay should never be set to turn off the fan at a temperature lower than the average outdoor wet bulb temperature at the location of the tower plus the temperature equivalent of the cooling zone height (6 to 7 K).
For example, if a cooling tower is installed in a city where the average wet bulb temperature is 20°C according to meteorological tables, the fan should stop when the water temperature leaving the tower drops to approximately 26°C (20°C + 6 K = 26°C). The fan should turn on when the water temperature rises to 28...29°C (see Fig. 73.9).
On the other hand, it would be undesirable to cool the water too much: the condensation temperature will begin to fall and the low HP value in most installations will not allow for a normal pressure drop across the expansion valve.

PROBLEM OF SALT DEPOSITION

When you frequently boil water in the same pan, after some time you notice that a whitish coating appears on the bottom of the pan.
The water you boil is drinking water. Like any tap water, it contains dissolved mineral salts.
When boiling, water vapor (which is a gas) is absorbed by the surrounding air (which is also a gas), and the mineral salts, being solid compounds, remain at the bottom of the pan (see Fig. 73.10).
As the water boils, the concentration of salts increases and over time they transform into
into a hard scum, firmly bound to the bottom of the vessel in which the water was boiled. In this regard, from time to time the dishes must be cleaned of scale, otherwise the water in it will heat up for a very long time, since scale is a good heat insulator and prevents the transfer of heat from the heating source to the water.

Unfortunately, we will encounter this same problem in the cooling tower return water circuit. We have already understood that the cooling of water passing through a cooling tower occurs due to its partial evaporation. But if part of the water in the cooling tower turns into steam, then the concentration of mineral salts contained in it in the remaining part of the water increases!
In the example in Fig. 73.11 The recirculating water circuit is recharged using ordinary tap water with a hardness of 10CF (see section 68), which is quite acceptable.
However, it should be firmly understood that the salts that entered the circuit along with this water will never be able to leave the circuit unless provision is made for their removal, that is, periodic partial drainage of the water circulating in the circuit.
Even with a low initial hardness of the make-up water, over time, as the cooling tower operates, the water hardness begins to increase and, in some cases, can exceed 200CF!

Water with such hardness will inevitably lead to failure of most of the circuit elements (pump, condenser, pipes, the cooling tower itself), since with increasing concentration, some of the salts fall out of solution in the form of solid particles, acting on the circuit elements as an abrasive powder. With such rigidity, scale forms very quickly in the condenser and cooling tower pipes. If the circuit operates continuously, then in less than 2 months scale can completely block the flow sections of the pipes.
Therefore, you should constantly drain some of the water from the circuit to remove salts. This operation (removal of salts) is recommended to be performed while the cooling tower pump is running, as shown in Fig. 73.12.

The flow rate of water drained during the salt removal operation (desalting) is determined by the hardness of the makeup water.
In order to maintain the water hardness in the circuit at an acceptable level (maximum 40°p), it is recommended to provide the following values of water flow through the desalination line:
If the hardness of the make-up water is 10°р, the flow rate through the desalination line should be equal to a single flow rate of water for evaporation in the cooling tower.
If the hardness of the make-up water is 20°р, then the flow through the desalination line should be equal to twice the water flow for evaporation in the cooling tower.
If the hardness of the make-up water is 30°р, the flow through the desalination line should be equal to four times the water flow for evaporation in the cooling tower.
Let's give an example. With a cooling capacity of 100 kW, the cooling tower evaporates from 180 to 200 liters of water per hour. If the make-up water hardness is 10°F, the flow rate in the desalination line should be approximately 200 l/h. If the make-up water hardness is 30°F, the flow rate in the desalination line will be 4 x 200 l/h = 800 l/h.

Exercise
A unit with a cooling capacity of 50 kW uses make-up water with a hardness of 15°F to operate the cooling tower. Determine the water flow through the desalination line.

Solution
With a cooling capacity of 100 kW, about 200 liters of water per hour evaporate, then with a cooling capacity of 50 kW, 100 liters of water will evaporate per hour. If the make-up water hardness is 10°F, the flow rate in the desalination line is equal to one time the water flow rate for evaporation. At a hardness of 20°F, the flow rate in the desalination line is equal to twice the water flow rate for evaporation. We have make-up water with a hardness of 15°F, which means the water flow in the desalination line should be equal to one and a half times
water consumption for evaporation, that is, 150 liters per hour.
There are several technical solutions for desalting water in a cooling tower circuit. The simplest one is shown in Fig. 73.12: The water supply pipeline to the cooling tower has a drain pipe connecting this pipeline to the sewer. A manual valve is installed on the drain pipe. With this scheme, desalination occurs only when the pump is running, that is, only when there is water supply to the cooling tower (as a rule, the pump runs only when the compressor is running). When the pump stops, the pipe supplying water to the cooling tower is emptied and the flow of water through the desalination line automatically stops.

Another solution involves the use of an electric valve (item 1 in Fig. 73.13) installed on the desalting line, which is cut into the pipe at the outlet of the cooling tower. In addition, two manual valves are installed on this line. Valve pos. 2 allows you to isolate the solenoid valve from the outlet of the cooling tower for its maintenance, repair and, if necessary, replacement. Valve pos. 3 provides regulation of water flow for desalting.
Attention! The handle? valve pos. 3 after setting it, as a rule, is removed so that no one can accidentally or intentionally change its setting. Therefore, if you find that the valve pos. 3 without handle or handwheel, do not touch it unless you are convinced that the setting needs to be changed.
In this scheme, the solenoid valve should be open only when the cooling tower pump (item 4) is running, and even better, when the fan is running (item 5).
Then desalting will be carried out only when the system as a whole is operating, that is, if the process of evaporation of water in the cooling tower is in progress. However, there is one drawback to this solution: if the solenoid valve becomes clogged or jammed, desalting stops. Conversely, if after removing the voltage the valve does not close or has a leak, water loss increases significantly.

DESCALING WATER-COOLED CONDENSERS
Any natural water contains many mineral salts: calcium, magnesium, sodium, and silicon. Under the influence of temperature, calcium and magnesium salts fall out of solution and are deposited on the walls of pipelines in the form of a mineral crust, the so-called scale. This scale worsens heat transfer, reduces the flow area of pipelines, and sometimes completely blocks it: in cooling circuits of condensers with circulating water, this leads to numerous malfunctions and, above all, to an unacceptable increase in HP.
For cleaning pipelines from scale, the most widely used method is based on the use of a solution of hydrochloric acid with a concentration of approximately 10% (1 liter of concentrated hydrochloric acid per 10 liters of water). In addition, commercially available cleaning solutions usually also contain corrosion inhibitor additives (corrosion inhibitor substances). These are chemical compounds that are added to a hydrochloric acid solution to minimize corrosion of copper pipes when cleaning condensers.
For each metal you need to use a different cleaning solution with a special inhibitor. For example, a cleaner used for copper is not suitable for steels, including stainless steel, zinc, etc. Therefore, in no case should you descale the cooling tower return water circuit by simply pouring the cleaner into the cooling tower tank and pumping it along the contour. With such an operation, you risk causing irreparable damage to the cooling tower equipment (the walls of the pipelines may be corroded until many small holes appear in them).

The condenser cleaning operation requires strict adherence to the recommendations of the cleaning agent manufacturer!

How to clean the capacitor? If the cleaning procedure was provided for when designing the installation, then it is relatively simple to carry out (see Fig. 73.14).

The condenser is cut off from the water cooling circuit using two manual valves, then the water is drained from it.
After this, using a special pump, a cleaning solution is pumped into the water circuit of the condenser, organizing its movement in the circuit according to the countercurrent principle, that is, in the direction opposite to the movement of water when the condenser is operating. The solution is poured into the same container, from where it is pumped into the condenser.
ATTENTION! Cleaning solutions produce acidic fumes.
Therefore, when carrying out the cleaning operation, it is necessary to strictly follow the recommendations of the cleaning agent manufacturer and, in particular, be sure to wear protective gloves and glasses to protect yourself from possible burns if the acid comes into contact with the skin and eyes. If you prepare the cleaning solution yourself, remember: you need to pour the acid into the water, and not vice versa - splashes of pure acid are very dangerous.
Acid, entering into a chemical reaction with scale, leads to the formation of abundant foam. Therefore, during cleaning, make sure that the cleaner drain container does not overfill!
NOTE. Using warm water reduces the time required to descale. To heat the cleaning solution, it is allowed to start the compressor for a short time, but remember: in this case, under no circumstances should the HP safety relay be turned off!
How to determine that the scale has been completely removed? During cleaning, a lot of foam appears in the container for draining the cleaning solution. Let's say that, for example, an hour after the start of cleaning, the foam disappears. This can be due to two reasons: either the scale has been completely removed, or the cleaning solution has run out of acid as the scale gradually neutralizes the acid.
Then you should refresh the cleaning solution by adding a little acid and again observe whether foam forms. If it forms, then the scale has not yet been removed.
ATTENTION! The cleaning solution containing acid circulates not only in scale-covered pipes. Moreover, it is easiest for it to pass through clean pipes, since their flow area is larger: therefore, the acid can also affect clean pipes. For this reason, it is necessary to carefully monitor the cleaning process and be sure to use cleaning solutions containing corrosion inhibitors for copper pipes.
When the condenser is completely cleaned, the descaling operation is stopped. However, the cleaning solution remaining in the waste container may still contain some acid. Therefore, it is strictly forbidden to pour this solution into the sewer. It is necessary to neutralize it by adding a special neutralizer (a strong alkali solution).

Before connecting the condenser circuit to the refrigeration system after descaling it, it is recommended to pump a neutralized cleaning solution through it and then rinse it with clean water.
Note 1. Cooling towers are usually made of galvanized steel with an anti-corrosion coating. To descale such curtains, special cleaning solutions recommended by the manufacturers are used. Mechanical cleaning can also be used. It is carried out with special brushes after removing the spray nozzles. Then they take a plastic mallet and, gently tapping the pipes and sheets, beat off the scale from their surface.
Note 2: There may be another problem in some regions. The fact is that the cooling tower creates a warm and very humid environment in which algae can multiply: the author has often seen trash cans filled to the brim with algae, which had to be raked out of cooling towers during their maintenance!

We should not forget about such a problem associated with the operation of cooling towers as the so-called “Legionnaires' disease” *. At one time, this problem was widely covered in the media and caused great public outcry. Cooling towers are a potential source of this disease, therefore, in a number of countries and regions, there are regulations that prescribe preventive measures to prevent it and, first of all, periodic laboratory tests of water to identify the causative agents of Legionnaires' disease.
Note 3: If a tower pump is being replaced or the tower's hydraulic circuit is being reconstructed, sealed pumps such as those used in ice water circuits or heating systems should not be installed in the hydraulic circuit of an open tower (see Figure 73.15).

In canned pumps, the drive motor is located in the liquid being pumped. The rotor of such an engine will very quickly become covered with scale, especially since the engine heats up during operation. After a few months of operation, the engine may seize and fail.
This is why open cooling tower water supply circuits use only gland pumps with shaft seals (stuffing box packing or slotted mechanical seals) whose drive motors are not exposed to the fluid being pumped (see Section 90, “A Little About Pump Design”).
* Legionnaires' disease (legionnaires' disease) was first described in 1976 in Philadelphia (USA) and was named so because American war veterans (legionnaires) gathered in one of the hotels suddenly fell ill with pneumonia (of the 240 people who fell ill, 36 died). It turned out that special microorganisms (called Legionella) live in the hotel's air conditioning system and cause pneumonia. The optimal temperature for their reproduction is from 20 to 50С. They reproduce in humid and warm environments (air conditioners, humidifiers, swimming pools, water parks, etc.) (ed.).

WHAT IS A COOLING TOWER. WHAT IS IT DESIGNED FOR?

A cooling tower is a heat exchanger used in circulating water supply systems. They serve to cool circulating water used to remove heat from industrial process equipment.

Thus, cooling towers protect installations and assemblies from overheating and destruction under the influence of high temperatures, and also provide stable conditions for reactions or product production.

Water circulation systems with cooling towers are widely used in metallurgy, energy, engineering, aviation and chemical industries, and at military-industrial complex enterprises.

The word gradieren itself, meaning evaporation, perfectly describes the principle of operation: water evaporates and, according to the laws of physics, cools down.

The first cooling tower of the familiar form was built in the Netherlands in 1918. Before this there was no specific type.

History of appearance and other interesting facts

Domestic scientists made a significant contribution to the development of the theory and practice of city building - Farvorsky B.S., Yampolsky T.S., Berman L.D., Averkiev A.G., Arefiev Yu.I., Ponomarenko V.S. and others.

Improving the design of cooling towers is associated with the desire to maximize the heat exchange area, both due to the area of the cooling tower and the volume of the sprinkler, and by increasing the complexity of the design and increasing the efficiency of the units. This process has been going on for many years and no further increase in the heat exchange area using a sprinkler is expected due to the achievement of the theoretical limit of the surface of the irrigation device.

There are other types and types of cooling towers with their own pros and cons.

CLASSIFICATION OF COOLING TOWERS

Taking into account the specifics of technological processes of various industries, two main types have been developed - the so-called dry and evaporative (wet) cooling towers.

The main difference between dry cooling towers and wet ones is the closed circuit through which the coolant circulates. Moreover, not only water can be used as a coolant.

FAN COOLING TOWERS

A fan cooling tower is the most common and most effective type for enterprises in various industries.

Sectional (block) fan cooling towers are independent sections that are mounted into a single cooling unit.

Each individual section is a rectangular reinforced concrete, metal, or, less commonly, fiberglass frame. At the top of this structure there is a fan group, and inside there is a set of technological elements. The entire frame of the cooling tower, with the exception of the air inlet windows, is covered with casing.

Interactive cooling tower diagram

Hover over image to view description

Thanks to the wide variability of section sizes, you can easily select a cooling tower that best suits the needs of the technological process, and the ability to operate autonomously section by section makes it easy to adapt to changes in the volume of cooled water and seasonal load fluctuations.

Due to the fact that sectional fan cooling towers are much more compact than tower and free-standing SK-400 and SK-1200, they are easier to place on the territory of the enterprise, easier to maintain and repair. Because of their versatility, they are currently the most effective for factories.

Dry cooling towers

They are heat exchange structures in which radiators serve as the heat transfer surface; they are equipped with fans to remove heated air.

Heat is transferred from the heated liquid flowing inside the radiator tubes to atmospheric air without direct contact with it, through a large surface area of the fins of the radiator tubes. The lack of direct contact limits cooling to a heat transfer process; there is no mass transfer (evaporation). This fact reduces work efficiency.

However, dry cooling towers are used in cases where, due to the technological features of production, a closed circuit of circulating water is necessary, when there is no possibility of replenishing losses from evaporation, or when the temperature of the circulating water is so high that its cooling in evaporative cooling towers is impossible.

The advantages of this equipment include:

no loss of cooled liquid volume
Various contaminants do not enter the coolant
There is virtually no corrosion of supporting structures
possibility of cooling high temperature liquids

They have significant disadvantages, which often outweigh all the advantages:

with the same productivity, the cost of a dry cooling tower will be 3-5 times higher than the cost of an evaporative one
big sizes
low cooling efficiency
expensive components
possibility of liquid freezing in the radiator tubes and its damage
difficulty increasing productivity

EVAPORATORY (WET) COOLING TOWERS

Their work is based on the transfer of heat from liquid to atmospheric air through surface evaporation and direct contact of media.

There are different types of evaporative cooling towers, but they all rely on cooling water as it evaporates.

Below we will look at the main types and their scope.

There are 4 main types of evaporative cooling towers:

tower
free-standing fans
sectional fans
small-sized

All other types of cooling towers are variations of these types.

Cooling towers

This is the largest variety, which is used to cool large volumes of water with a small temperature difference.

They are often used at thermal power plants and nuclear power plants, less often at large industrial enterprises, where the total thermal power is more important than the cooling depth.

A cooling tower is a structure in which natural air draft is created due to the pressure difference at the bottom and top of the tower.

This type of cooling tower contains all the classic technological elements: sprinkler, water distribution with nozzles, water trap, shutters.

Cooling towers may differ from each other in shape, size, and individual technological solutions, but they are based on the same operating principle.

Hot water from the water distribution system is sprayed over the entire irrigation area using nozzles. Water that gets onto the irrigation device forms a thin film on its surface or is crushed into very small drops. The entire resulting surface undergoes an evaporation process, due to which the temperature of the remaining circulating water decreases. And thanks to the draft created by the difference in height, the droplet-air mixture saturated with warm vapor is removed from the cooling tower.

Fan cooling towers work in a similar way. The main difference is that the draft in the hailstone is created artificially due to the operation of a fan.

Cooling towers type SK-400 or SK-1200

Free-standing cooling towers are a reinforced concrete or metal frame of a cylindrical shape more than 10 meters high, with a base diameter of 24 meters for SK-400 and 36 meters for SK-1200.

At the top of the structure there is a powerful fan placed in a special housing - a diffuser. It is the fan installation that creates the necessary draft inside the cooling tower. The remaining technological elements repeat the “filling” of the cooling tower. The processes occurring in SK-400 are also similar.

Cooling towers SK-400 and SK-1200 are widely used in the Soviet Union at chemical and petrochemical enterprises. Their main advantages are high performance, resistance to freezing, the ability to regulate draft by changing the fan operating mode, and ease of maintenance and repair work.

However, there are also disadvantages of this design - an expensive fan group, the complexity of its design and high energy costs to ensure the operation of the fan.

Most of these shortcomings are eliminated in the design of sectional fan cooling towers.

Small cooling towers

Another type that should be highlighted separately is small-sized cooling towers. They are similar to conventional sectional ones, but differ in the type of fan. The fan is a pressure fan and is installed from below.

Small-sized cooling towers solve the problem of water cooling in enterprises with a small circulation cycle. All their advantages and disadvantages are due to their design.

Due to their compact size, they are delivered assembled and ready for use, are easily transported from place to place and do not require a special pool.

However, due to their size, they cannot provide deep cooling of circulating water (usually no more than 5-7 0 C), and an increase in the volume of the circulating cycle requires the supply of new units, because it is impossible to change the configuration and number of technological elements of an existing cooling tower.

The main problem of “small-sized” is freezing in the cold season, which appears due to the lower location of the fan and drops of water falling on it.

Hybrid cooling towers

Hybrid cooling towers are complex technical structures that combine the processes inherent in evaporative and dry cooling towers. Air draft can be created by an exhaust tower, a fan, or jointly by a tower and several fans located around the perimeter of the tower in its lower part.

The technological and technical-economic indicators of a hybrid cooling tower are better than dry ones, but inferior to evaporative ones.

They have less expensive heat exchange equipment and their cooling capacity is less dependent on changes in air temperature. The advantages of a hybrid cooling tower include a noticeable reduction in irretrievable water losses in comparison with evaporative cooling towers and the ability to operate without a visible steam torch.

In terms of cooling capacity, they are superior to dry ones, but inferior to evaporative cooling towers.

Hybrid cooling towers are more complex in design and construction and require increased attention and maintenance during operation of not only the cooling tower itself, but also the water circulation system as a whole. If the circulating water is of insufficient quality, salt deposits form on the walls inside the radiator pipes, and the fins of the pipes become contaminated with dust from the incoming air, which leads to a sharp increase in thermal resistance.

All this causes a violation of the design operating modes of the dry and evaporation parts, as well as emergency situations in winter.

In our country, they have not become widespread due to increased operating requirements and higher cost compared to conventional evaporative cooling towers.

Each of the described types solves specific problems of cooling the water cycle of an enterprise. The correct choice of cooling tower allows you to achieve your goals at the lowest cost, and in the future to avoid difficulties during their operation.

FAN COOLING TOWER DESIGN

MAIN ELEMENTS OF A COOLING TOWER

Sprinkler blocks

Sprinkler blocks, or simply sprinkler, are the main element of the cooling tower, determining its cooling capacity.

Its task is to provide maximum surface area for cooling water when it comes into contact with the oncoming air flow.

Sprinklers are divided into film, drip-film, combined and spray.

Combined and spray types have not received proper distribution, so their detailed consideration does not make sense.

The sprinkler must have the following properties:

provide high cooling capacity
have a reliable and durable structure
have increased chemical resistance
ensure uniformity when filling the internal volume of the cooling tower
have high wettability and low weight
be resistant to deformation
maintain their properties at temperatures from -50 0 C to +60 0 C degrees

Sprinklers can have different shapes and be made of different materials.

Currently, various polymer materials are used as raw materials for the manufacture of sprinklers, for example: polypropylene, polyethylene, polyvinyl chloride, etc.

The most common type that provides a high cooling effect is film, but it has a significant drawback: clogging of the gaps between individual elements in the block with suspended substances and impurities present in the cooled water.

The task of a film-type sprinkler is to retain a thin film of water on its surface, which provides a large irrigation area for effective heat and mass transfer.

For the most productive operation of the film sprinkler, various changes are made to its design, namely:

use of porous materials
increase in surface roughness
use of corrugated materials
creating a complex shape of heat and mass transfer surface per unit area

One type of such sprinkler is the tubular type. It is a group of polymer tubes soldered together. Such a block, like its counterpart made from corrugated sheets, requires uniform distribution of water over the surface, since the possibility of water redistribution occurs only in the space between the tubes and sheets. In this case, pipes occupy up to 50% of the volume, which reduces its efficiency. In order to avoid the through flow of water without crushing, the sprinkler blocks are made of low height using gaps between the blocks to mix the water.

When the concentration of various substances in the water is high, it is necessary to use drip-film sprinklers, as they are more resistant to clogging.

The mesh structure of such blocks is increasingly used in various types of cooling towers due to the optimal combination of material consumption and increased cooling effect.

Thanks to the mesh structure, breaks occur as water and air move, which leads to alternating drip and film operating modes. Due to this redistribution and additional turbulization of interacting flows, heat and mass transfer sharply increases, that is, the cooling capacity of the sprinkler increases by approximately 70% compared to sheets and corrugated pipes. This structure significantly reduces the aerodynamic drag coefficient, which has a positive effect on energy savings.

The drip-film type sprinkler comes in various shapes and designs. The most common blocks consist of:

mesh prisms
mesh rolls
mesh gratings

Water catcher

During operation of the cooling tower, air saturated with water vapor and water droplets is released into the atmosphere, resulting in dropwise entrainment of circulating water. In winter, this can lead to icing of surrounding buildings, structures, etc. To eliminate this problem, cooling towers use an element such as a water trap.

A water trap for a cooling tower minimizes droplet entrainment with minimal aerodynamic drag. The water trap is a wave-shaped structure. It serves to condense moisture and deposit water droplets flying upward in the air flow on its surface, as well as to uniformly distribute air at the outlet of the cooling tower.

Water traps are made mainly from various polymers, which results in a relatively low weight and reliable design. Their ability to capture droplets depends on the size of the droplets themselves and the air flow rate in the cooling tower. It follows from this that different types of cooling towers can use water traps of different shapes. The efficiency of droplet collection in fan cooling towers is maximum at an air speed of 2-3 m/s, in tower cooling towers - 0.7-1.5 m/s, in small-sized ones - 4 m/s.

Water traps come in various shapes:

half wave
cellular
lattice
cell phone

In a cellular drop separator, the working elements have the shape of a half-wave in a vertical section, and along the length of the block they have depressions and peaks.

The honeycomb water trap is a monolithic block with fiberglass channels. It received this name because the top view resembles a honeycomb. Its ability to collect water is quite high, however, the aerodynamic drag is 2-3 times higher than that of the “half-wave”.

The aerodynamic resistance of water catchers can vary significantly depending on their shape. The most optimal and common design of a water trap today is considered to be half-wave. This shape ensures effective droplet collection of up to 99.98%, eliminating the need to use multi-tiered droplet eliminators with high aerodynamic resistance.

When placing droplet eliminator blocks on the cooling tower site, it is necessary to eliminate through gaps between the blocks and the walls of the cooling tower. This is done so that the air flow in these places at increased speed does not carry moisture with it.

Requirements for water traps:

highly efficient droplet collection up to 99.9%
low aerodynamic drag
low specific gravity
chemical resistance to impurities in circulating water
exclusion of fouling by biologically active substances

Water distribution system

The water distribution system of the cooling tower is designed to uniformly distribute cooled water over the surface area of the sprinkler.

It should not interfere with the free passage of air masses in the cooling tower.

The water distribution device of the cooling tower can be divided into 3 groups:

spray
no splashing
movable

Currently, the main water distribution system is the spray pressure water distribution device.

A pressure spray water distribution system is a structure consisting of a system of pipelines with water spray nozzles connected to them. To manufacture this system, both steel pipelines and pipelines made of composite materials (for example, fiberglass or low-density polyethylene) can be used. Plastic nozzles (or nozzles) of various types and designs are mainly used as water-spraying devices. When there are aggressive substances or suspensions in the circulating water, stainless steel nozzles can be used.

The nozzles of the water distribution system should create optimal droplet sizes of 2-3 mm when spraying circulating water and hitting them on the surface of the sprinkler.

To achieve uniform distribution of water, the nozzles are installed at a distance determined by calculation, based on the characteristics of the nozzle and the change in the cross-sectional diameter of the pipe along the direction of water movement.

Basic requirements for nozzles:

providing a torch with a radius of 1.5-2 m
no clogging with suspended solids

Nozzles are divided into:

centrifugal
jet-screw
drums

When installed on a pipeline of a water distribution system, the nozzles can be mounted with the torch direction either up or down. This depends on the design of the cooling tower and the shape of the nozzle itself. The speed of water movement in collectors should be 1.5-2 m/s, in distribution systems no more than 1.5 m/s. At a flow speed of 0.8-1 m/s, sedimentation of suspension occurs, which leads to clogging of pipes and nozzles.

Fan units

Depending on the irrigation area, fan cooling towers are equipped with exhaust and injection fan units. For small irrigation areas (up to 16 m2), injection fans can be used, however, their efficiency is 15-20% lower than that of exhaust fans.

The cooling tower fan unit is designed to create sufficient air flow and consists of:

diffuser (fan housing)
impeller

In modern conditions, the diffuser is made of composite materials with stiffening ribs placed inside and consists of several sectors. The diffuser is used to reduce the pressure loss that occurs at high speeds of air flow at the outlet of the cooling tower, to direct the air flow, and to increase the productivity of the fan installation.

The impeller is designed to create a constant flow of air in the cooling tower and consists of blades and a hub. Impeller blades are usually made of fiberglass or metal. The hub is used to fasten the blades and attach the impeller to the electric drive shaft.

The diameters of impellers in fan cooling towers can be from 2.5 m to 20 m.

ALTERNATIVE TO COOLING TOWER

Cooling ponds and splash pools are used as alternatives.

The first are natural water reservoirs of gigantic size. At the Magnitogorsk Iron and Steel Works it stretches across the entire city.

Cooling occurs due to the contact of water droplets with air, and occurs more intensely in the presence of wind, reaching a difference of 5-7 °. But at the same time, droplet entrainment increases.

A big problem in maintaining these structures is water bloom. To avoid strong heating in the sun, the depth is made more than 1.5 meters.

Advantages of splash pools:

construction cost is 2-3 times lower than the cost of a cooling tower
easy to use
durable

Flaws:

low temperature difference
low cooling effect on the leeward side
The area of the pool is significantly larger than the area of the cooling tower
the appearance of fogs, which in winter leads to icing of nearby buildings

ADVANTAGES AND DISADVANTAGES OF ONE TYPE OF COOLING TOWER

As already mentioned, there are three types - dry, wet and combined (hybrid) cooling towers. Any of these types has significant design differences, which are described in detail above, and these types of cooling towers have certain advantages and disadvantages.

For example, in dry cooling towers, the coolant circulates in a closed circuit and the advantages of such a cooling system are:

no loss of cooled liquid volume due to the elimination of the evaporation process
in specially prepared coolant, hardness salts are not formed and various contaminants from the external and industrial environment do not enter
there is virtually no corrosion of supporting structures that do not have direct contact with the coolant
the ability to cool high-temperature liquids using heat-resistant radiators, which are usually made of metals with high thermal conductivity

Considering the fact that in dry cooling towers the cooled liquid does not have direct contact with air, i.e. There is no mass transfer during the cooling process, making it difficult to increase productivity.

Here the water passes inside the radiator tubes, through the walls of which only its heat is transferred to the air. Consequently, increasing the cooling capacity of a dry cooling tower requires increasing air exchange by increasing the area of quite expensive radiators with a large number of powerful fan equipment.

For example, to lower the water temperature from 40° to 30° C at an air temperature of 25° C, about 1000 m³ of air must be supplied per 1 m³ of cooled water in evaporative cooling towers, and in dry cooling towers, in which the air is only heated, but not humidified ,—about 5000 m³ of air.

In addition, the use of closed liquid cooling circuits at subzero ambient temperatures does not prevent the liquid from freezing in the radiator tubes, and in the summer, radiator units are susceptible to clogging with dust.

Taking into account the high-tech production of components for dry cooling towers, the cost and maintenance of such cooling towers increases by 3-5 times compared to fan cooling towers.

Wet (or evaporative) cooling towers have the largest application today. In such cooling towers, the cooling process is carried out due to the evaporation of water - mass transfer, as well as due to heat exchange between hot water and cold atmospheric air.

Heated water is sprayed onto a special irrigation nozzle (irrigation layer), through which cooling atmospheric air passes in countercurrent.

In tower cooling towers, air flows naturally, due to pressure differences at different heights - according to the principle of draft in a pipe.

Such cooling towers are used, as a rule, to cool a very large amount of water - up to 30,000 m³/hour and do not require large energy costs, but are difficult to operate.

We must not forget that one of the most important indicators of a cooling tower is its cooling capacity. In tower cooling towers it is impossible to cool water to a temperature close to the wet-bulb temperature during the hot season, and the cooling depth in such cooling towers is 8-10°C. In addition, during transitional climatic periods, problems arise with regulating the cooling process.

It should be added that the construction of a cooling tower has a complex design, which requires large construction costs with the use of expensive lifting equipment and additional equipment.

Open-type fan cooling towers are by far the most common and cost-effective solution in the field of circulating water cooling and justify their use in all industries.

The main advantage of such a cooling tower is its cooling capacity. The difference in circulating water can reach 30°C. This indicator is achieved through the use of fan units, which create a powerful air flow in the irrigation space against the flow of cooled water and, thereby, increased heat and mass transfer.

To cool large volumes of water, fan cooling towers are installed in blocks, each of which has several sections. This arrangement of cooling towers allows cooling of several circuits of the circulating water system at once.

The design features of a fan cooling tower, compared to tower ones, are much simpler and cheaper. They are structures made of metal structures, which are manufactured in detail at the manufacturer’s procurement site, delivered to the customer and mounted on pre-prepared foundations in the drainage basin.

Technological elements of a cooling tower, such as a fan casing, impeller, cladding of external walls and wind partitions, a water trap, and a water distribution system are currently presented in a wide range, and in combination from one manufacturer, these components create an optimal solution for cooling the circulating water of enterprises.

Automation of energy consumers of a fan cooling tower allows you to regulate the cooling process with maximum accuracy according to the specified parameters of circulating water and effectively use energy resources both in summer and winter, which increases their service life.

The use of high-tech materials in the manufacture of efficient technological elements of fan cooling towers makes it possible to provide cooling of circulating water at enterprises of all industries with a long overhaul interval. It should be added that the materials from which they are made are resistant to aggressive environments, biological deposits and have high strength characteristics.

So, we hope that from this article you received a lot of interesting and useful information about cooling towers. And if you are faced with the task of choosing a cooling tower for production, then call us without hesitation!

evaporative, in which heat transfer from water to air occurs mainly through evaporation;

radiator, or dry, in which heat is transferred from water to air through the wall of radiators due to thermal conductivity and convection;

mixed, which use heat transfer through evaporation, conduction and convection.

The theoretical limit for water cooling in evaporative cooling towers is the ambient wet-bulb temperature, which can be several degrees lower than the dry-bulb temperature.

In combined radiator-evaporative cooling towers, as well as in dry ones, water is cooled through the walls of radiators, irrigated from the outside with water. The transfer of heat by water flowing through radiators to the air is carried out due to thermal conductivity through the walls and evaporation of irrigating water. These cooling towers are less widespread than evaporative and radiator ones due to inconvenience during operation.

According to the method of creating air draft, cooling towers are divided into:

ventilator, through which air is pumped by injection or suction fans;

tower, in which air draft is created by a high exhaust tower;

open, or atmospheric, in which natural air currents - wind and partly natural convection - are used to move air through them.

Depending on the design of the irrigation device and the method by which an increase in the surface of contact of water with air is achieved, cooling towers are divided into film, drip And splashing.

Each of these types of cooling towers can have various designs of individual elements of the irrigation device, differ in their sizes, distances between them and can be made of different materials.

The choice of the type of cooling tower should be made according to technological calculations, taking into account the water flow rates specified in the project and the amount of heat removed from the products, apparatus and cooled equipment, the temperatures of the cooled water and the requirements for the stability of the cooling effect, meteorological parameters, engineering-geological and hydrological conditions of the cooling tower construction site , conditions for placing the cooler on the enterprise site, the nature of the development of the surrounding territory and transport routes, the chemical composition of additional and recycled water and sanitary and hygienic requirements for it, technical and economic indicators of the construction process of these structures.

3. Main types of cooling towers

The type and dimensions of the cooler should be taken into account:

estimated water consumption;

the design temperature of the chilled water, the temperature difference of the water in the system and the requirements of the technological process for the stability of the cooling effect;

cooler operating mode (constant or periodic);

calculated meteorological parameters;

the conditions for placing the cooler on the enterprise site, the nature of the development of the surrounding area, the permissible noise level, the impact of the wind carrying away drops of water from the coolers on the environment;

chemical composition of additional and circulating water, etc.

Cooling towers should be used in circulating water supply systems that require stable and deep cooling of water at high specific hydraulic and thermal loads.

If it is necessary to reduce the volume of construction work, maneuver the temperature of chilled water, or automate, fan cooling towers should be used to maintain a given temperature of chilled water or cooled product.

In areas with limited water resources, as well as to prevent contamination of circulating water with toxic substances and protect the environment from their effects, the possibility of using radiator (dry) cooling towers or mixed (dry and fan) cooling towers should be considered.

3.1 Fan cooling towers

Fan cooling towers should be used in circulating water supply systems that require stable and deep cooling of water, at high specific hydraulic and thermal loads, when it is necessary to reduce the volume of construction work, and maneuverable control of the temperature of chilled water by means of automation.

The technological diagram of a fan cooling tower includes the following main elements: a shell (body), consisting of a frame covered with sheet material, a water distribution device, a sprinkler, a water trap, a drainage basin and a fan unit.

Crap. 1. Diagram of a fan counterflow cooling tower

1 - diffuser;
2 - fan;
3 - water catcher;
4
5 - irrigation device;
6 - air guide visor;
7 - air inlet windows;
8 - air distribution space;
9 - overflow conduit;
10 - mud conduit;
11 - drainage basin;
12 - wind barrier;
13 - outlet water pipeline;
14 - supply water pipeline

3.2 Cooling towers

Tower cooling towers should be used in circulating water supply systems that require stable and deep cooling of water under high specific hydraulic and thermal loads.

Tower cooling towers can be evaporative, radiator, or dry and mixed - evaporative-dry. Evaporative-dry cooling towers include dry cooling towers, in which water (usually demineralized) is sprayed onto radiators to increase the cooling depth.

Tower cooling towers are designed, as a rule, to be evaporative and with a countercurrent flow pattern of water and air.

The main technological elements - water distribution device, sprinkler, drainage basin, water trap and air control device - in tower cooling towers perform the same functions as in fan cooling towers, and can often be similar in design.

Crap. 2. Tower counterflow cooling tower

1 - exhaust tower;
2 - water catcher;;
3 - water distribution system;
4 - irrigation device;
5 - air control device;
6 - drainage basin

3.3 Open cooling towers

Open cooling towers - drip and spray - are intended primarily for systems with a flow rate of circulating water from 10 to 500 m 3 / h, serving water consumers II and III categories according to SNiP 2.04.02-84. Fuck it. Figure 3 shows a diagram of an open drip cooling tower with a plan area of 2´ 4 m.

Cooling towers are characterized by a high cooling effect without the consumption of electricity for air supply, simplicity of building structures, operating conditions and repairs. However, their use is limited by the possibility of placement on an undeveloped site, strongly blown by the wind, as well as by the permissibility of a short-term increase in the temperature of the cooled water during a calm period.

Diagram of an open drip cooling tower

1 - water distribution system;
2 - irrigation device;
3 - air guide blinds;
4 - overflow conduit;
5 - mud conduit;
6 - outlet conduit

3.4 Radiator cooling towers

Radiator cooling towers or air-cooled water cooling units (AWCs), sometimes called dry cooling towers, consist of elements: radiators made of finned copper, aluminum, carbon, stainless or brass pipes through which cooled water flows; axial fans pumping atmospheric air through radiators; air supply pipes ensuring smooth air supply to the fan, and supporting structures.

Radiator cooling towers should be used:

if necessary, have a closed water circulation circuit in the circulating water supply system, isolated from atmospheric air;
at high temperatures of heating circulating water in heat exchange technological devices, which do not allow its cooling in evaporative cooling towers;
in the absence or serious difficulties in obtaining fresh water to replenish losses in the circulation cycles.

Crap. 4. Diagram of a radiator cooling tower

1 - sections of finned pipes; 2 - fan 2VG 70

To prevent water from freezing in radiator tubes and damaging them, it is necessary to install containers to drain water from the system in emergency situations in winter or fill the system with low-freezing liquids (antifreeze).

In circulation systems with radiator cooling towers, there are practically no irrecoverable losses due to evaporation and carryover.

4. Maintenance and operation of cooling towers

The placement of coolers on enterprise sites must be provided to ensure free access to air, as well as the shortest length of pipelines and channels. In this case, it is necessary to take into account the directions of winter winds to prevent freezing of buildings and structures (for cooling towers and spray ponds).

When locating cooling towers on an enterprise site, it is necessary to ensure unimpeded access of atmospheric air to them and favorable conditions for the removal of humidified air discharged from the cooling towers. For these reasons, it is not recommended to locate a group of cooling towers surrounded by tall buildings or at a close distance from them. The distance must be more than one and a half times the height of the buildings. In this case, it is necessary to take into account the wind rose and the direction of winter winds to prevent moisture and freezing of buildings and structures near cooling towers.

To prevent icing of cooling towers in winter, it is necessary to provide for the possibility of increasing thermal and hydraulic loads by turning off part of the sections or cooling towers and reducing the supply of cold air to the sprinkler.

To prevent the destruction of structural materials (concrete and wood), the temperature of the water entering the cooling towers should, as a rule, not exceed 60 °C. When the incoming water temperature is above 60 °C, protective coatings of structures or heat-resistant materials should be used.

In terms of reliability, convenience and economical operation, it is recommended from 2 to 12 sections or cooling towers in one water supply circulation cycle. If, according to technological calculations, the number of sections or cooling towers is more than 12 or less than 2, you should select a different standard size of cooling towers.

For high-quality operation of the cooling tower, it is necessary to carry out a number of measures related to water preparation. In particular, recycled water should not cause corrosion of pipes, equipment and heat exchangers, biological fouling, precipitation of suspended matter and salt deposits on heat exchange surfaces.

To meet these requirements, it is necessary to provide for appropriate purification and treatment of make-up and return water.

4.1 Water losses

For recycling water supply systems, a water balance must be drawn up, taking into account losses, necessary discharges and additions of water to the system to compensate for the loss from it.

Table 4.1.1

4.2 Prevention of mechanical deposits

The possibility and intensity of the formation of mechanical deposits in cooling tower reservoirs and in heat exchangers should be determined on the basis of operating experience of circulating water supply systems located in a given area, operating on water from a given source, or based on data on the concentration, particle size distribution (hydraulic fineness) of mechanical water contaminants and air.

To prevent and remove mechanical deposits in heat exchangers, periodic hydropulse or hydropneumatic cleaning should be provided during operation, as well as partial clarification of the circulating water.

Water from surface sources used as additional water in the recycling water supply system must be clarified.

4.3 Control of algae and biological fouling.

To prevent the development of bacterial biological fouling in heat exchangers and pipelines, chlorination of circulating water should be used. The dose of chlorine should be determined based on experience in operating water supply systems using water from a given source or based on the chlorine absorption capacity of the additional water.

With high chlorine absorption of water and a long length of pipelines of the recycling water supply system, dispersed input of chlorine water is allowed at several points in the system.

In order to prevent algae fouling of cooling towers, spray pools and irrigation heat exchangers, periodic treatment of cooling water with a solution of copper sulfate should be used. The concentration of copper sulfate solution in the solution tank should be 2-4%. Additional treatment of water with chlorine should be carried out simultaneously or after treating it with a solution of copper sulfate.

Tanks, trays, pipelines, equipment and shut-off valves in contact with copper sulfate solution must be made of corrosion-resistant materials.

4.4 Prevention of carbonate deposits

Water treatment to prevent carbonate deposits should be provided under the condition Shdob·Ku≥3, Shdob - alkalinity of additional water, mEq/l, Ku - coefficient of concentration (evaporation) of salts that do not precipitate. In this case, the following water treatment methods should be adopted: acidification, recarbonization, phosphating with polyphosphates and combined phosphate-acid treatment. The use of organophosphorus compounds is allowed.

Water treatment methods to prevent carbonate deposits should be:

Acidification - at any values of alkalinity and general hardness of natural waters and coefficients of water evaporation in systems;

Phosphating - when the alkalinity of the additional water Shdob is up to 5.5 mEq/l;

Combined phosphate-acid water treatment - in cases where phosphating does not prevent carbonate deposits or the amount of purging is not economically feasible;

Recarbonization with flue gases or gaseous carbon dioxide - with the alkalinity of the additional water up to 3.5 mEq/l and evaporation coefficients not exceeding 1.5.

4.5 Prevention of sulphate deposits

To prevent calcium sulfate deposits, the product of active ion concentrations in circulating water should not exceed the product of calcium sulfate solubility.

To maintain the values of the product of active ion concentrations within the specified limits, an appropriate coefficient of evaporation of circulating water should be taken by changing the amount of system purging or partially reducing the ion concentrations in the additional water.

To combat sulfate deposits in circulating water supply systems, water should be treated with sodium tripolyphosphate at a dose of 10 mg/l or carboxymethylcellulose at a dose of 5 mg/l.

4.6 Corrosion prevention

If there are impurities in the circulating water that are aggressive to the materials of the cooling tower and spray pond structures, water treatment or protective coatings for the structures must be provided.

To prevent corrosion of pipelines and heat exchangers, water treatment with inhibitors, protective coatings and electrochemical protection should be used.

When using inhibitors and protective coatings in circulating water supply systems, careful cleaning of heat exchangers and pipelines from deposits and fouling should be provided. As inhibitors, sodium tripolyphosphate, sodium hexametaphosphate, a three-component composition (sodium hexametaphosphate or tripolyphosphate, zinc sulfate and potassium bichromate), sodium silicate, etc. should be used. The most effective type of corrosion inhibitor should be determined experimentally in each specific case.

5. Main disadvantages of cooling towers, environmental protection

A cooling system built on the basis of an evaporative cooling tower has a number of disadvantages:

1. Low quality of water, its contamination due to contact with dust of the air surrounding the cooling tower;

2. Contamination of the system with salts, which constantly accumulate due to the continuous evaporation of water. For every cubic meter of evaporated tap water, at least 100 grams accumulate in the system. salt deposits. This leads to a sharp decrease in the heat transfer coefficient on the heat transfer surfaces and, consequently, the efficiency of heat transfer;

3. Development of algae and microorganisms in the system, including dangerous bacteria due to active aeration;

4. Continuous oxidation and corrosion of metal;

5. Icing of cooling towers in the winter season;

6. Lack of flexibility and accuracy of temperature control;

7. Fixed costs for water and chemicals for cleaning;

8. Large pressure losses in the system.

Regarding environmental protection, the main harmful factors produced by cooling towers are noise and the impact of aerosols emitted from cooling towers into the environment

The harmful effects occur as a result of the release of drops of recycled water into the atmosphere, the deposition of drops on the soil and on the surface of surrounding objects.

The drops may contain corrosion inhibitors, scale inhibitors, and chemicals to prevent biological fouling that are added to the circulating water.

In addition, droplets may contain pathogenic microorganisms, bacteria, viruses, and fungi. Some microorganisms in cooling towers, under favorable conditions for their life activity, can multiply.

Drops of water spread in the atmosphere in the area of cooling towers and moisten the surface of the earth and nearby structures, and in winter they cause icing, therefore SNiP II-89-80 provides the permissible minimum distances from cooling towers to the nearest structures.

The zone of droplet moisture precipitation on the ground surface has the shape of an ellipse with a major axis passing through the center of the cooling tower in the direction of the wind. The highest intensity of droplets falling onto the ground surface in this zone is on the major axis of the ellipse at a distance of approximately two heights of the cooling tower. The size of the zone depends on the height of the cooling tower, wind speed, the degree of air turbulence in the surface layer, the concentration and size of droplets, as well as the temperature and humidity of the atmospheric air.

If there are gaseous impurities in the atmospheric air, the moisture coming out of cooling towers can interact with them and form compounds harmful to the environment. For example, when moisture interacts with sulfur oxides, sulfur dioxide is oxidized into sulfates that are more harmful to humans.

6. List of references:

1. SNiP 2.04.02-84. Water supply. External networks and structures/Gosstroy of the USSR. M.: Stroyizdat, 1985.

2. A manual on the design of cooling towers (to SNiP 2.04.02-84. Water supply. External networks and structures) / VNII VODGEO of the USSR State Construction Committee. M.: CITP Gosstroy USSR, 1989.

3. Ponomarenko V.S., Arefiev Yu.I. Cooling towers of industrial and energy enterprises: Reference manual/ Pod. total ed. V.S. Ponomarenko. - M.: Energoatomizdat: 1998. - 376 p.: ill.

Calculation of cooling tower make-up water. Cooling tower - what is it, types and types