Practice: Installation and Application of cooling towers

I. Application Fields of Cooling Towers

Cooling towers are widely used in many industrial fields such as power, chemical engineering, metallurgy, and building materials, and also have broad applications in air conditioning refrigeration and waste heat recovery. The main application scenarios are as follows

1. Thermal power plant. Modern thermal power generation mainly relies on steam turbine power generation. 

The exhaust steam of the steam turbine needs to be cooled by a condenser, and the cooling water of the condenser needs to be cooled and recycled in a cooling tower. Therefore, the cooling tower is the core equipment of the power plant's cooling system. Generally, large power plants adopt large counter-flow cooling towers, which can reach a height of over 150 meters, with a designed circulating water volume of tens of thousands or even hundreds of thousands of tons per hour, and are equipped to serve several 1 million kilowatt-level units.

2. Chemical industry. 

Cooling towers are widely used in fields such as petrochemicals and coal chemicals to cool process equipment and products, such as heat exchangers, reactors, and absorption towers. In chemical plant areas, multiple cooling towers of various forms are often arranged, including counter-flow towers and cross-flow towers, with scales ranging from tens to hundreds of square meters. The scale of some large-scale cooling tower clusters for ethylene, MachA and other facilities can be comparable to that of power plants.

3. Steel smelting. 

In the steel production process, large amounts of cooling water are required for procedures such as blast furnace ironmaking, converter steelmaking, and steel rolling. Therefore, from the raw material yard to the finished product wharf, various cooling towers are scattered throughout the steel plant area, which are indispensable supporting facilities for the steel plant. For instance, water used for slag flushing in blast furnaces, cooling water for equipment in front of the furnace, and cooling water for secondary flue gas in converters all need to be cooled by cooling towers before being recycled.

4. Building materials industry. 

Take cement production as an example. From raw material grinding to clinker calcination and then to cement grinding, the equipment in the process flow such as the kiln head and kiln tail, cooler, and roller press all require cooling towers to provide cooling water. Due to the scattered layout of cement plants, cooling towers in cement plants are mostly arranged in a small and scattered manner.

5. Air conditioning system. 

Central air conditioning systems in large public buildings such as shopping malls, airports, stadiums, and subway stations often adopt the form of chiller + cooling tower. The evaporative cooling effect of the cooling tower is utilized to remove the heat from the condenser of the chiller, achieving the recycling of chilled water. Compared with the traditional air-cooled chiller, the system has higher energy efficiency and the operation of the unit is more stable and reliable after adopting the cooling tower.

6. Waste heat utilization. The waste heat generated in industrial production processes, such as flue gas waste heat and steam condensate waste heat, has a relatively high temperature. 

If directly discharged, it will cause energy waste and environmental problems. After being cooled by cooling towers, it can be utilized in a stepwise manner, generating significant energy conservation and emission reduction benefits. For instance, the low-temperature water discharged from the flue gas desulfurization system of thermal power plants can be cooled by cooling towers and then used in dust removal, desulfurization and other processes.

II. Layout Principles of Cooling Towers

The reasonable layout of cooling towers is the prerequisite for giving full play to their cooling performance. Due to the influence of natural ventilation and the distribution of heat load, the operating environment of cooling towers in different areas varies greatly. Improper layout can lead to adverse phenomena such as "short-circuit" wind and "tower crosstalk", reducing the cooling effect. Therefore, when arranging closed circuit cooling tower, factors such as ventilation conditions, heat source distribution, and water source conditions should be comprehensively considered, and the following basic principles should be followed:

1. Good ventilation conditions. 

The evaporative cooling process of a cooling tower relies on air flow to carry away heat and water vapor. Ventilation conditions are the primary factor affecting its cooling effect. Cooling towers should be placed in open and unobstructed areas with fresh air, far away from buildings, structures, large equipment and other obstructions, to ensure that the air intake is adequately supplied with fresh cold air.

2. The air intake side faces the wind. 

When arranging the cooling tower, the air intake side should face the prevailing wind direction throughout the year, which is conducive to forming a good air flow organization inside the tower and promoting heat and moisture exchange. If the prevailing wind direction is changeable, the air intake side should also face the prevailing wind direction in summer as much as possible to cope with the maximum cooling load in summer. The greater the deviation between the air intake surface and the prevailing wind direction, the worse the cooling effect.

3. Avoid crossing towers. 

When multiple towers are arranged, due to the high temperature and humidity of the air at the outlet of the cooling tower, if it enters another tower, it will deteriorate the air intake condition and reduce the cooling effect. Therefore, multiple cooling towers should be arranged in a staggered manner to prevent the hot and humid air on the air outlet side from entering the air inlet of another tower. The distance between the two towers should not be less than 1.5 times the height of each tower.

4. Place the cold and heat sources close to each other.

 Cooling towers should be placed as close as possible to the cold and heat source equipment they serve, such as generator sets and process devices, to shorten the length of the cold and hot water delivery pipelines and reduce heat loss in the pipelines and power consumption of the water pumps. However, factors such as equipment layout and pipeline laying should also be comprehensively considered to avoid excessive investment or construction difficulties.

5. Take water locally. 

The operation of cooling towers requires continuous replenishment of fresh water to make up for evaporation and wind losses. Therefore, they should be placed in areas with abundant water sources and as close to the water source as possible to reduce the length and head of the make-up water pipeline and lower the energy consumption of the water pump. For water-scarce areas, water-saving cooling towers or stepped water usage schemes can be considered.

6. Comprehensive energy conservation. 

Under the premise of meeting the process requirements, when arranging the cooling tower, it is necessary to comprehensively consider reducing the operational energy consumption of the open circuit  cooling water system, such as optimizing the positions of pumps and fans, reducing pipeline resistance, and achieving variable flow operation, etc. When necessary, auxiliary facilities such as the collection pool under the tower and the high-level water tank can be adopted to promote the energy-saving operation of the system,improve the performance of cooling towers.