Introduction

In industrial production, there is often a large amount of heat generated, which increases the temperature of production operating conditions. In order to avoid affecting the safety and normal operation of production, cooling must be carried out in time.Discharge of waste heat can also be seen everywhere in daily life, such as the air conditioning system in buildings and the cold storage system.Therefore, the production and improvement of living standards must be accompanied by the discharge of a large number of waste heat, which is generally carried to the environmental waters or scattered to the atmosphere through the cooling water.

In industrial enterprises, the proportion of cooling water is very large, basically accounting for more than 90% to 95% of the total water consumption. The earliest industrial cooling water in China mostly uses direct-current cooling water, which wastes a lot of water resources. With the increasing use of cooling water and the depletion of cooling water resources, people gradually realize that the cooling water must be recycled and the heat in the cooling water must be released in a short time. Cooling towers, such devices that fully or indirectly contact the air with cooling water, so that the heat of water in a short period of time to send to the atmosphere, have emerged as the times require.

Our company has been developing and producing various specifications of FRP cooling towers since the early 1970s. It is one of the earliest manufacturers of cooling towers in China. After more than 40 years of hard work and development, our cooling tower products have a certain scale, by the majority of users trust and praise. Especially the FRP cooling tower produced by our company, through continuous improvement and optimization, in the same industry to create excellent evaluation, thermal, energy consumption, noise three major assessment indicators are all leading, has won the provincial, ministerial and national excellent title, won a good reputation and reputation in various industries in China.

In recent years, the water saving effect brought by the circulating cooling water system is obvious: the supplementary water rate of general cooling water can be reduced to less than 5% of the circulating water amount.At present, the use of recirculated cooling water instead of dc cooling water has become the consensus and action of all industries, and the problem of corrosion and scaling of heat exchangers in the system has been paid more and more attention.The company designs a variety of models according to the tower structure, ventilation mode, cooling medium, direction of water vapor flow and other requirements of customers, and sets up a variety of side filters and automatic dosing devices, so as to guarantee the good operation of the circulating cooling water system.

二、Working principle and classification of cooling towers

When the cooling tower is running, hot water in the tower is sprayed uniformly downward from the top of the tower by the water distribution system through the sprinkler nozzle, forming a water film on the filling. Air flows in the reverse direction from the bottom up to the water droplets or water film, or flows vertically in the horizontal direction. Heat and mass transfer is carried out during the process of air and water contact, so as to reduce the water temperature.

The heat transfer type of cooling tower is divided into two categories: natural ventilation and mechanical draft according to the situation of air entering the tower. Natural ventilation tower is easy to maintain and save power, but capital investment is large. The ventilation rate of mechanical ventilation tower is controlled and adjusted by machinery, the effect is stable, the distribution of gas and water is uniform, the cooling efficiency is high, but the energy consumption is large.

According to the location of fan installation, it can be divided into blast type and mechanical draft type. The air blower is installed on the side of the bottom of the tower, and the fresh air is blown into the tower. The exhaust fan is installed on the top of the tower. Blowing type can be used for cooling water system containing oil corrosive substances in cooling water (a way to avoid damage to the fan), generally commonly used for the mechanical draft type.

Most of the tower is equipped with splashing device or filling, called sprinkler device, is the key part of the cooling tower, water cooling mainly in this part.

According to the direction of air flow can be divided into cross-flow type and counter-flow type, my company cooling towers are more mechanical ventilation counter-flow type, processing capacity can be from a few tons per hour to 5000 or 6,000 tons, small towers are mostly FRP structure or steel structure, large towers are mostly reinforced concrete structure or steel structure, with the continuous breakthrough of technology. In the past year, our company has developed a large FRP cooling tower with large capacity to accommodate more project.

Mechanical draft counter-flow cooling tower mainly includes five parts: fan system, water distribution system, sprinkler filling, drift eliminator and tower body. Hot water is sprayed on the top of the packing through a hot water pipe or trough, and the attached splashing device sprays the hot water on the top of the packing. In the filling area, the hot water contacts the air sufficiently to transmit the heat of the water to the air, and then the air is pumped out of the tower through a fan located on the top of the tower.

三、Blast Type and Mechanical Draft Type

In the wind tube natural ventilation cooling tower of the open circulating cooling system, the air needed for water cooling is provided by the air flow around the cooling tower. In the mechanical ventilation cooling tower, the air flow needed for water cooling is supplied by axial flow fans. This axial-flow fan is characterized by large air volume, low static pressure head, high efficiency, low cost, can be reversed and can be adjusted by adjusting the number of blades or blade installed angle to change air volume and pressure, widely used in mechanical draft cooling tower.

Mechanical draft cooling tower is divided into exhaust cooling tower and blast cooling tower according to mechanical draft mode, compared with blast cooling tower.The outlet hot air velocity is higher.Therefore, the fan of cooling tower generally adopts the installation method of ventilation.

Comparison of mechanical draft type cooling tower and blast type cooling tower：

① The air distribution of the draught filling section is uniform and the cooling effect is good.

②The air velocity at the draft type outlet is relatively high, and the humid and hot air can still keep up 10-12 m after leaving the cooling tower outlet, which greatly reduces the possibility of hot air reflux.

③The velocity of hot air at the outlet of the blast type is low, and the air velocity at the inlet of the fan is high. In case of weak natural wind, it is possible to blow hot air to the inlet at the bottom, forming hot air reflux to reduce the cooling efficiency.

④The height of the blast inlet is high, and the lift of the circulating water pump is large. It is easy to freeze on the blades of air blower in winter, and the blades of mechanical draft type are not easy to freeze because of the hot air.

Despite the shortcomings of the installation method of the blower, the blower cooling tower can show greater advantages than the mechanical draft cooling tower in the case of corrosive circulating water quality, anti-seismic and anti-flying projectiles and other special requirements of the application conditions：

When the circulating water is corrosive, the chance of the blower contacting the circulating water is much less than that of the mechanical draft cooling tower, so the possibility of corrosion of the blower is less. For the important water system of the nuclear power plant, the circulating water flow is not large but the safety of the cooling tower is highly demanded. The aseismic protection of the blower is easier than that of the mechanical draft cooling tower. Much more, and it can also be well protected when flying objects are encountered.