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Cooling tower "past life"


Release time:

2019-06-14

Cooling tower is not only a kind of equipment, but also a subject. As a device, it directly or indirectly contacts the cooling water with the atmosphere and transfers the heat of the water to the atmosphere. It is an interdisciplinary subject involving fluid mechanics, hydraulics, heat and mass transfer, mechanical transmission and materials science. In recent decades, with the continuous development of my country's economy and the continuous improvement of people's living standards, the cooling tower industry has developed faster and faster, especially small and medium cooling towers, which are almost everywhere. Cooling tower as a scientific research began in the early 20th century, has been nearly a hundred years of development history. In the development history of this century, we must not forget the past 1

Cooling towerIt is not only a device, but also a subject. As a device, it directly or indirectly contacts the cooling water with the atmosphere and transfers the heat of the water to the atmosphere. It is an interdisciplinary subject involving fluid mechanics, hydraulics, heat and mass transfer, mechanical transmission and materials science. In recent decades, with the continuous development of my country's economy and the continuous improvement of people's living standards, the cooling tower industry has developed faster and faster, especially small and medium cooling towers, which are almost everywhere.

Cooling tower as a scientific research began in the early 20th century, has been nearly a hundred years of development history. In the development history of this century, we must not forget some special people, special stages and special events in the past 100 years, which have promoted the progress and development of the cooling tower discipline.

Of course,Cooling towerThe emergence of is by no means accidental. Cooling tower as a product of modern industry, its origin can be traced back to the industrial era, or even earlier. In the past, rivers, oceans, lakes and ponds were used to supply water. Due to limited industrial activities and abundant water sources in the past, cooling water was used once more and then discharged to nearby waters to obtain cold water. Gradually, when selecting the industrial plant site, the available rivers, rivers, lakes and oceans should be used as the water source and drainage site for cooling water, or the available cooling water storage, cooling, circulation or discharge ditches. Gradually, people found that hot water can be quickly cooled by spraying in a fixed space, which gradually formed the fountain technology. The development of technology has sprayed cooling towers, which are the prototype of today's spray cooling towers. After gradual improvement, the airflow mechanical equipment was added, and the spray cooling tower with fan appeared. Later, in order to solve the problem of the settling velocity of water droplets in the tower, filler was added to the tower, which was the beginning of the modern cooling tower. At present, the main systems of the cooling tower are fan system (mechanical ventilation cooling tower), water collector (device), water distribution system, spray filler, water collection tank (device), water pump and tower body.

After nearly a hundred years of development, cooling towers have formed various forms according to their operating conditions and heat transfer methods. For example, according to the ventilation mode, it can be divided into natural/mechanical ventilation cooling tower, wet/dry/wet/closed cooling tower, seawater/fresh water/other medium cooling tower, civil/industrial cooling tower, countercurrent/cross flow cooling tower, etc.

Throughout the history of modern industrial development, the largest and most concentrated users of cooling water are power plants, and most of the cooling towers of power plants are natural ventilation cooling towers. Natural draft cooling tower is a cooling device that relies on the difference of air density inside and outside the tower to make air flow and heat transfer. Because of its large and eye-catching air duct, it is also known as the air duct natural ventilation cooling tower. As early as 1912, the world's first simple natural ventilation cooling tower was built and put into use in a mine in the Netherlands, and the modern industrialization process of the cooling tower was officially launched. Since then, the Netherlands has built the world's first hyperbolic natural draft cooling tower. In 1919, there was a cross-flow cooling tower with a wooden closed steel structure in the world. In 1920, a reinforced concrete conical shell cooling tower was built in Dunkirk, France. The first hyperbolic natural ventilation cooling tower was built in Berlin, Germany in 1954, the first hyperbolic natural ventilation cooling tower in the United States in 1955, the first natural ventilation cooling tower over 100 meters high in the United States in 1958, and the first hyperbolic natural ventilation dry cooling tower in the United Kingdom. In 1960, the height of cooling towers in U.S. power plants reached 150 meters in 1971. At present, the height of the large cooling tower in Cologne, Germany has reached 200 meters, and the nozzle area has reached 14000 square meters. In the foreseeable future, natural draft cooling towers will be developed on a large scale.

Due to China's industrial level and other reasons, the cooling tower construction started late. The earliest natural draft cooling tower was built in Japan in 1938 for the self-owned power plant of a cement plant in Huludao City, Liaoning Province. In the 1950 s, China could only build cooling towers with a water spray area of 1250-1500 square meters and a height of 60 meters. In the 1960 s and 1970 s, the technical level developed greatly. Shandong Yantai Power Plant built a cooling tower with a water spray area of 3000 square meters and a height of 75 meters. The first experimental cross-flow cooling tower. The aluminum ventilation cooling tower was built in Henan Changge Power Plant, and the first large-scale cross-flow cooling tower was built in Henan Kaifeng Power Plant. Natural draft cooling tower nozzle area 1750m2In 1986, Huainan Luohe Power Plant built a natural ventilation cooling tower with a nozzle area of 7000 m for 300MW units.2The tower is 96m high. In 2000, Shanghai Wujing Power Plant completed a cooling tower for 600MW units. It was put into operation with a sprinkling area of 10000 square meters and a height of 160 meters. By the end of 2006, the cooling tower of 1000 MW units in Phase IV of Shandong Zouxian Power Plant had been put into operation with a sprinkling area of 1000 MW. In 2009, the 13800-square-meter seawater cooling tower of Zhejiang Ninghai Power Plant was put into operation with a height of 177 meters, which once maintained the largest scale and height of natural towers in China and Asia. In October 2017, the third phase of cooling tower in Ezhou City, Hubei Province was completed, with a total height of 181m and a spray area of 15000m.2.

The mechanical ventilation cooling tower does not have a high air duct, and the air flow in the tower is not generated by the air density difference between the inside and outside of the tower, but by the fan, which has the characteristics of high cooling efficiency and good stability. In recent years, the development of mechanical ventilation cooling towers has become more and more rapid, from traditional air conditioning and cold storage systems to petrochemical, metallurgy, light industry and even some small and medium-sized thermal power plants. In addition to the advantages of the mechanical ventilation cooling tower, small footprint, less capital investment, short construction period and other factors are also prominent in the people. Note. In addition, small-scale manufacturers of civil cooling towers have spread all over the provinces of China, or up to 1000, and the cooling towers are made into standard series, and each manufacturer has its own unique design style, which is not described in detail.

Mechanical ventilation cooling towers can be divided into counterflow and cross-flow according to the ventilation mode. Regardless of the form, it includes fans, air guides, air intake, fillers, water distribution systems, water collectors and other components. Reverse flow, that is, water and air flow in opposite directions. Before the 1970 s, the main tower type of mechanical ventilation cooling tower was reinforced concrete cooling tower, with a fan diameter of 4.7 meters and a treatment water volume of 600-800 t/h. The filler was cement net, the water collector was louvered, the water distribution was mostly trough type, and the nozzle was spray water and air. The pipes are made of reinforced concrete. In the 1970 s, Anqing Petrochemical Company introduced several countercurrent towers from France. The diameter of the fan is 9.14m, the plane size is 16.5m × 16.5m, and the height of the air inlet is 5.4m. In 1972, a 500 square meter mechanical ventilation countercurrent cooling tower was built in Qinling Power Plant in Huayin City, Shaanxi Province. Subsequently, Chaoyang Power Plant in Liaoning Province built a circulating countercurrent mechanical ventilation cooling tower with a spray area of 1962 square meters, a diameter of 50 meters, and a fan diameter of 20 meters, which can meet the cooling requirements of circulating water for 200MW units. In the 1980 s, mechanical ventilation cooling towers were greatly developed. The Ministry of Chemical Industry has standardized the design of fan diameters of 8.53m and 9.14m, and has been widely used in various industries. At present, the water treatment capacity of the countercurrent cooling tower has reached 5000 t/h.

With cross-flow, that is, the air is perpendicular to the flow direction. It is widely used in China, especially in petroleum and chemical systems. The main reason is that China introduced more than 10 large-scale fertilizer projects from abroad in the 1970 s, and most of the cooling towers supporting these projects are mechanical ventilation cross-flow cooling towers. With the introduction of these projects, domestic professional designers have more understanding and preferences for mechanical ventilation cross-flow cooling towers. Therefore, cross-flow cooling towers are mostly used in new projects. This situation continued until the mid-1990s, such as Yanshan Petrochemical's 450000-ton ethylene renovation and expansion project. Most of these imported mechanical ventilation cross-flow cooling towers are filled with U-plates and M-plates from Mali in the United States and plastic sine wave fillers and asbestos panels from Japan. Because these drop-by-drop fillers are easy to freeze in winter, or rinse off the sprinkler fillers with concentrated circulating water in the north. To this end, the domestic development of the packing mixing technology, that is, the installation of film packing on the outside of the cross-flow tower, the inner side of the drop-by-drop packing, a better solution to this problem.

Overall, our countryCooling towerTechnology development has gone through three stages: 80 years before the independent research stage, China's cooling tower technology development lags behind Europe and the United States, the Soviet Union and other developed countries; digestion and absorption stage. Introduced in the 1980 s and 1990 s, the flow between China and foreign countries increased, and the cooling tower of the Belgian Harmon cooling tower company was also introduced. Technically, the design technology of the cooling tower has reached the foreign level; the third stage is the transcendence stage, which began with the rapid development of China's economy after 2000. At the same time, the technical demand for cooling towers has grown rapidly, and cooling tower technology has also been greatly developed, so that my country's research on cooling towers has surpassed other countries. After nearly a hundred years of development, cooling tower has formed a complete set of theoretical discipline system, China has also been among the world's leading technology ranks, but the future is still a long way, we need to move towards more efficient, more environmentally friendly, more innovative direction.