The Operation of The Cooling Tower

Section 1: The Significance of Cooling Tower Operation and Maintenance

In power plants, cooling towers are auxiliary equipment. If the cooling tower malfunctions during operation, it will directly affect the operation of the steam turbine, force the unit to shut down, and prevent the power plant from achieving safe production. Power outages or reduced power generation can also cause huge economic losses to other industrial and mining enterprises. This kind of situation has occurred in China before. For instance, in a certain power plant, due to a sudden cold wave, the water distribution packing froze severely, causing a large-scale collapse of the water distribution packing and rendering the cooling tower inoperable. As a result, emergency repairs had to be carried out. It is evident that the operational reliability of cooling towers is closely related to safe power generation, and it is essential to carry out operation and maintenance work with great care.

When the cooling tower operates in its best condition, it can save fuel and generate more electricity. Theoretical analysis conducted by some people holds that the improvement of thermal efficiency in power plants is directly proportional to the reduction of water temperature at the outlet of cooling towers. For every 1℃ reduction in cooling water temperature, the thermal efficiency of medium-pressure units can increase by 0.47%, and that of high-pressure units can increase by 0.35%. For instance, a certain power plant adopts a domestically produced medium-temperature and medium-pressure 50MW condensing steam turbine unit, equipped with a 2,000-square-meter hyperbolic natural ventilation cooling tower. According to the test results in summer, the outlet water temperature of the cooling tower drops by 1℃, and the coal consumption decreases by 1.5g/(kW•h). Based on an annual operation of 7,000 hours, the 50MW unit can save over 500 tons of coal. In addition, in large and medium-sized enterprises, a large amount of circulating water is required, and the power consumption of circulating water pumps is relatively high. Especially in power plants, their power consumption accounts for 1.5% to 3% of the total power generation. If a reasonable operation mode of the cooling tower can be adopted, the potential for electricity saving of the circulating water pump is considerable. Conversely, if the operation and maintenance are improper, the resulting losses will be huge. For instance, after the cooling tower of a certain power plant was put into operation, due to improper operation and maintenance, the cooling tower nozzles became clogged with scale after a short period of operation. Nozzle detachment; The splash dish is misaligned. The sink is clogged with sediment. The sink is full of water and overflows. The water-spraying packing is seriously scaling, etc. The result is a decline in the cooling effect of the cooling tower. In summer, the water temperature at the outlet of the tower rose to 38℃, and the vacuum was less than 80 kPa (600 mmHg), forcing the steam turbine unit to operate at reduced load.

The service life of a cooling tower is closely related to the quality of its operation, maintenance and management. If the operation, management and maintenance of the cooling tower are proper, the major overhaul period can be extended and the service life of the cooling tower can be prolonged. The economic benefits in this regard are also quite considerable. According to relevant data, during the three to four decades of use of cooling towers, the total cost of major overhauls can even exceed the cost of infrastructure construction. In cold regions of our country, the major overhaul period is shorter, generally ranging from 10 to 15 years. It takes longer in non-freezing areas, approximately 15 to 20 years.

Section 2: Operation of the Cooling Tower

After the cooling tower is completed and before it is put into operation, acceptance work must be carried out in order to identify and handle problems in a timely manner. During the acceptance process, in addition to paying special attention to whether the main dimensions of the cooling tower and the elevations of each component are correct, and whether adjustment devices and anti-freezing equipment are installed, it is also necessary to check whether the equipment meets the design and construction technical requirements, as well as the quality of the installation. Such as the tightness of the inlet and outlet water pipes, pipe trenches, water tanks and water collection tanks of the cooling tower, as well as the conditions of installation accessories, stack beam gate plates, etc. When inspecting mechanical ventilation cooling towers, special attention must be paid to the installation quality of the fans, especially whether the centerline and balance are correct, whether the installation Angle of the fan blades meets the requirements, and whether the gap between the blades and the fan casing remains at the value specified by the manufacturer. Before the cooling tower is put into operation, it is necessary to check whether there are any debris left over from construction in the cooling system and whether the overflow sewer has been connected. It is also necessary to check whether the positions of the filter screens and shut-off devices (valves, beam valve plates) on all the main and auxiliary pipelines and channels are correct.

When the cooling tower's water collection pool is first filled with water, its water level should reach the highest elevation. After the circulating water pump is put into operation, water must be continuously supplied from the outside until the entire system is filled with water. At the same time, during the water filling process of the circulation system, it is necessary to pay attention to preventing the interruption of the circulation water pump due to the drop in the water level of the cooling tower's water collection pool. When the cooling tower is shut down in winter and water needs to be drained, measures must be taken to prevent the water in the pipes, ditches, Wells and collection pools from freezing.

The acceptance of cooling towers should be carried out in accordance with the design requirements and the technical specifications for construction and acceptance issued by relevant departments. The acceptance work can be carried out in five steps: acceptance of construction documents, acceptance of the cooling tower shell, acceptance of the water distribution system, acceptance of the water spray device, and acceptance of mechanical ventilation equipment. The relevant contents of the five acceptance steps are not all excerpted. If you are interested, please leave a message to contact the editor.

In the acceptance of cooling towers, emphasis should be placed on inspecting the construction quality of the water distribution system. The quality of construction will directly affect the safe operation and cooling effect of the cooling tower. It is necessary to check whether the water pressure test of the water inlet pipeline is qualified, whether the opening of the water supply valve is flexible, and whether there is any blockage by debris, etc. It is essential to ensure that the water supply system is unobstructed, well-controlled, and free of leakage. It is best to calibrate and measure the relationship between the opening degree of the inlet valve and the rotational speed, and record and file it.

The inspection and acceptance of various sinks are also extremely important. If the pipe connection is not properly handled, a large amount of water leakage will occur, damaging the water distribution packing. Therefore, these interfaces should be carefully inspected and accepted. The dimensional deviations of the installation elevations of each water tank in the entire water distribution system must comply with the design requirements. It is generally required that the water distribution system be horizontal. The horizontal elevation at the bottom of the water distribution trough should comply with the design value, with a deviation of no more than 30mm. All sinks must be cleaned thoroughly before being filled with water. After the cooling tower is filled with water, it is necessary to check that under the rated water load, the minimum water level in the water distribution tank should not be less than 150mm, and under the maximum water load, the water level in the water tank should have a minimum depth margin of 100mm. If the water distribution is uneven and fails to meet the design requirements, adjustments should be made to the outlet pipe diameter of the nozzles or the number of nozzles (it is also allowed to make adjustments after running for a period of time). If a splashing device with ceramic nozzles and ceramic splashing discs is adopted, the alignment rate of the nozzles and splashing discs should reach over 95%. If a plastic splashing device is used, there is no centering problem (as the nozzle is connected to the splashing disc), but it is necessary to pay attention to not tilting the nozzle in the vertical direction. When using trough water distribution, the reserved holes on the water trough must be cleaned, and the burrs should be chiseled off. After all the spatter heads (sleeves), nozzle sleeves, spatter discs, etc. are installed, cement mortar should be used to level and smooth the periphery of the spatter heads (sleeves).

After the prefabricated reinforced concrete frame embedded parts of the cooling tower are welded and fixed, the embedded parts should be covered to prevent the iron parts from corroding. All exposed iron parts should be subject to anti-corrosion measures. The sump should be thoroughly cleaned, and the settlement joints and expansion joints inside the sump should be carefully inspected and accepted. The return water channel, filter screen, drain valve, supplementary water valve, overflow pipe, etc. all need to be inspected and accepted.

Mechanical ventilation cooling towers require the acceptance of ventilators. When inspecting such mechanical and electrical products, they should be inspected item by item in accordance with the product manual provided by the manufacturer. For instance, whether the blade Angle of the ventilator meets the design requirements must be measured and recorded for archiving. Whether the oil level of the gearbox reducer is qualified. Check whether the center of the rotating shaft and the balance of the rotating machinery are appropriate, and whether there is any jamming. Check if all the connecting parts of the rotating components are loose. It is best to inspect all the nuts.

Carry out detailed acceptance work in accordance with the acceptance specifications and design requirements, and keep good records and file them. After the acceptance work of the cooling tower is completed, it can be put into production and use. If significant construction issues are identified during the acceptance process, effective remedial measures must be actively taken to eliminate the defects before the project can be put into operation.