Anti-freezing Measures for Cooling Towers in Winter

Guide Reading
In the cold winter, the temperature in the northern region is usually below 0°C.

According to different technological characteristics, some closed cooling towers operate throughout the day in winter, some operate during certain periods, and some are hardly used. However, in any case, the anti-freezing problem of the cooling towers needs to be considered. Therefore, taking effective anti-freezing measures has become the focus of people's attention.
This article will elaborate on the freezing locations and causes of cooling towers, as well as the anti-freezing measures taken.
1 Reasons for Freezing of Cooling Towers in Winter and Prone-to-freezing Parts
1.1 Reasons for Freezing
① Freezing may occur when the wet bulb temperature around the cooling tower is minus 10 degrees.
② Due to the uneven distribution of the water load on the tower packing, ice will form at the periphery of the tower packing, at the blocked water spraying holes, and on the inner wall of the tower and the small water flows along the supporting beams and columns.
③ The walls, beams, columns, packing, etc. where there are small water flows are the attachments for ice formation.
1.2 Prone-to-freezing Parts
1.2.1 Inlet of the Cooling Tower
The inlet of the cooling tower is the most common and easiest part to freeze.
(1) For the inlet of a natural draft cooling tower, ice usually forms at the lower edge of the inner wall of the tower cylinder, or ice hangs on the edge of the water baffle inside the tower. In mild cases, a thin ice curtain is formed, and in severe cases, it freezes together with the herringbone columns of the tower cylinder to form a thick ice wall. On the leeward side of the tower, ice forms because part of the water droplets are blown onto the inner side of the herringbone columns by the through wind in the tower.
(2) Ice hangs on the inner edge of the louver at the inlet of the cross-flow cooling tower, and the leakage of the top water inlet tank causes large-area ice formation on the support columns of the inlet and the outer side of the louver.
The main reason for the ice formation at the inlet is that the water volume around the cooling tower's water spraying packing is too small, causing the small water flow flowing down along the inner wall of the tower to freeze at the upper edge of the inlet or the edge of the water baffle due to the intrusion of the cold air entering the tower.
1.2.2 Local Water Spraying Packing and Packing Support Beams and Columns
If the heat load and water volume of the whole tower are small, or due to uneven water volume distribution, ice will form at the lower part of the local or even all the tower packing; at the periphery of the tower packing, when the water spraying density is small, the cold air will first invade from here, and it is most likely to cause freezing damage; in other areas with a small water spraying density, such as blocked or damaged water tanks, blocked nozzles, fallen and misaligned water splashing dishes, etc., local freezing damage is also likely to occur; because the local water volume of the water spraying packing is too small, it flows down along the peripheral support beams and columns, and it is also easy to freeze when it encounters the intrusion of the cold air entering the tower. For example, in a cooling tower of a certain factory in Daqing, large ice columns 2 to 4 meters long formed at the lower part of the local packing, and even crashed the tower packing.
1.2.3 Top of the Cooling Tower
Inside and outside the rigid ring at the top of the natural draft cooling tower, due to the accumulation of water vapor, ice cones are formed, and in severe cases, large ice blocks are formed.
1.2 Hazards of Freezing
The freezing of the cooling tower poses a serious threat to the safe and economical operation of the tower.
(1) The water spraying device bears a large overload, resulting in the collapse of the water spraying packing and its supporting beams and columns, and even causing serious accidents such as local or overall collapse.
(2) The concrete components of the water spraying device, herringbone columns, ventilation cylinder and other parts are damaged by the freeze-thaw cycle many times, greatly reducing the service life of the components.
(3) The frost heaving force generated by the expansion of water after it freezes may directly burst facilities such as pipelines, ditches, and valves; the frost heaving force of the soil may also directly burst the bottom plate of the collecting tank, the walls and bottom plate of the circulating water ditch, etc.
(4) Due to the freezing of the inlet and the water spraying packing, the cooling effect is directly affected, which will cause the temperature of the circulating water to rise throughout the year, thus affecting the economic benefits of the device. The freezing on the ground around the tower and at the top of the tower may also cause accidental casualties or other accidents.
2 Anti-freezing Measures for Cooling Towers
2.1 Install a Bypass Water Pipe
The bypass water volume accounts for most or all of the water volume during winter operation.

A bypass water pipe is connected to the inlet pipe of the cooling tower and leads to the collecting tank, so that the bypass return water is mixed with the original cold water in the collecting tank, thereby adjusting the water temperature of the pool, raising the water temperature of the pool, and achieving the purpose of anti-freezing. When introducing the bypass water pipe, it is required to turn on the circulating water pump first when starting the unit, and slightly open the valve of the out-of-service pipeline a few turns, so that a small amount of circulating water flows in the pipeline, directly enters the collecting tank without heat dissipation through the packing, and heats the water in the pipeline and the collecting tank. The advantage of this is to prevent the circulating water with no heat load or a very small heat load from freezing after passing through the packing, thus protecting the out-of-service cooling tower and the corresponding pipeline from freezing damage. Similarly, when stopping the unit, stop the steam turbine first and then the circulating water pump to avoid the same freezing problem as described above. In addition, adjusting the opening degree of the valve directly affects the circulating water volume entering the operating cooling tower, which belongs to the "disguised hot water bypass adjustment method".
2.2 Steam Trace Heating
Since steam is convenient to obtain, has a large latent heat of condensation, and its temperature is easy to adjust, steam trace heating is also an effective measure for thermal insulation and anti-freezing and ice melting, and is widely used in various engineering constructions. Its working principle is to use the heat emitted by the trace heating medium to supplement the heat loss of the traced object through direct or indirect steam-water heat exchange, so as to meet the requirements of heating up, thermal insulation or anti-freezing.

For the steam trace heating used for the anti-freezing of the cooling tower, a steam pipe is led from the steam pipeline to the collecting tank of the cooling tower, and a coil is made at the bottom of the collecting tank. The steam enters the steam coil in the collecting tank through the pipeline, and the water temperature of the pool is raised through steam-water heat exchange to achieve the purpose of anti-freezing.
2.3 Use Electric Heating Treatment
When the ambient temperature is only around 0°C, an electric heater or other heat sources can be considered to be added to the pipeline or the circulating water tank to increase the surface temperature of the closed cooling tower, so as to achieve the purpose of anti-freezing.
2.4 Install a Water Baffle at the Inlet of the Cooling Tower
On the tower wall on one side of the inlet of the cooling tower, a considerable part of the water flows down along the tower wall and freezes at the inlet. To prevent this situation, a water baffle is installed on the inner side of the tower wall at an angle of 30 to 45 degrees with the tower wall, so that the water flowing down along the tower wall jumps into the pool to prevent the tower wall on one side of the inlet from freezing.
2.5 Hang a Windshield at the Inlet of the Cooling Tower
During winter operation, a windshield is hung at the inlet of the cooling tower to prevent the cold air from intruding into the tower, avoid the water flow in this area from being invaded by the external cold air, maintain the temperature at the inlet, and thus eliminate the ice hanging phenomenon at the inlet. The installation and disassembly of the windshield should be adjusted in a timely manner according to the local climatic conditions, wind force and wind direction, as well as the internal ice formation situation of the cooling tower. It can be installed in a semi-circle on the windward side, or only installed in the upper part or installed throughout the tower. The air temperature at the water spraying device should be controlled above 0°C, the water temperature of the pool should be above 10 to 15°C, and there should be no large amount of ice formation. According to the production process of the windshield, the height of the windshield generally does not exceed 3m, and the width is not more than 0.88m. The structure of the windshield should be convenient for mechanical and manual installation and disassembly.
2.6 Adopt an "Anti-icing Ring"
The so-called "anti-icing ring" is to install a circular anti-freezing spray pipe on the periphery of the water distribution system of the cooling tower and on the upper side inside the inlet. Several branch pipes are evenly connected to the lower part of the pipe to spray hot water into the tower. In this way, a hot water curtain is formed at the inlet of the cooling tower to block the cold air from entering, and at the same time, cut the ice curtain and ice columns at the inlet to prevent them from increasing. The hot water of the "anti-icing ring" comes from the circulating water supply pipe. The specific method is: two anti-freezing pipes are led out from the circulating water supply pipe, and ring pipes are made along the inner wall of the tower in opposite directions respectively, each bearing half of the spray water volume of the tower, and the pipes are blocked at the joint. At the same time, several branch pipes are led out from the lower end of the "anti-icing ring" and evenly distributed around the tower to form spray pipes. The spray pipes are generally segmented arc pipes, and each pipe section is not connected. The water flow in the "anti-icing ring" is controlled by a temperature control valve installed on the pipe. The anti-freezing principle of the "anti-icing ring" is that the hot water sprayed by the "anti-icing ring" preheats the air entering the cooling tower, thus changing the atmospheric environment of the water spraying packing. The hot water curtain formed by the hot water sprayed by the "anti-icing ring" at the inlet of the tower increases the resistance of the air flowing from the outside to the inside of the tower, thus limiting the air intake of the tower, preventing the intrusion of cold air, improving the thermal insulation conditions at the inlet, and avoiding the ice formation at the inlet.
2.7 When There are Several Cooling Towers, Some of the Towers Can be Out of Service
Concentrate the heat load on a few towers, increase the heat load of these towers, or stop the fans to raise the water temperature after cooling to prevent freezing.
2.8 Reverse Rotation of the Fan
For mechanical draft cooling towers, in addition to using the above methods to prevent the tower from freezing, the method of reverse rotation of the fan can also be used. Regularly discharge the hot air from the inlet of the tower to the outside of the tower to prevent the inlet of the tower from freezing, which is also an effective method. The reverse rotation time of the fan generally should not be too long, and it should not exceed half an hour at a time to prevent damage to the fan and affect the cooling.
2.9 Adjust the Operation Mode of the Anti-icing System in a Timely Manner
According to the winter temperature, the heat load of the unit, and the ice formation situation of the cooling tower, adjust the operation mode of the anti-freezing system of the cooling tower in a timely manner, and adjust the water volume distribution of each anti-icing system, so as to ensure that the water temperature of the pool and the water temperature of the packing are higher than the "freezing point", and make the circulating water system operate under the best economic conditions.