Basic knowledge of power plant cooling water

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Thermal power plants have many devices that require cooling, including the condenser for the waste steam discharged from the low-pressure cylinders, the lubrication system for turbine equipment, the bearing shells of various rotating machinery, as well as the stator and rotor components of generators, among others. Different equipment also has varying requirements regarding the quality of cooling water; for some heat exchange components where scaling is not allowed, high-quality deionized water must be used, such as for cooling the stator and rotor of generators. Power plant closed-loop cooling water system: The water used in this cooling system is demineralized water, which helps to prevent scaling on the equipment during heat exchange processes, thereby reducing damage to the equipment that needs to be cooled. Boiler equipment cooled by closed water typically includes: air preheater bearing cooling, forced draft fan lubricating oil cooling, flame detection fan cooling, primary fan bearing cooling, plasma burner cooling, warm air heater drain pump cooling, seal fan bearing cooling, etc. Steam turbine equipment cooled by closed-loop water typically includes: generator stator cooler cooling, generator rotor cooler cooling, seal cooling for feedwater pumps and their pre-pumps, steam and water sampling cooling, fire oil cooling, thrust bearing cooling for condensate pumps, air compressor equipment cooling, and so on. Construction of the closed-circuit cooling water system: The main equipment of the closed-circuit cooling water system includes the closed-circuit cooling water pump, expansion tank for the closed-circuit cooling water, cooling coil for the closed-circuit cooling water, filters, and pipelines. The closed cooling water system is the first system to be commissioned in a power plant; it is also the first system that needs to be commissioned after the unit is energized. Therefore, it must be given top priority during project construction planning, with its installation scheduled to be completed while the plant’s electrical systems remain energized. All pipes should be treated with acid washing or sandblasting; acid washing is recommended as the preferred method. During installation, all welds should be prepared using TIG welding. Connect the device interfaces correctly. The operating pressure on the closed-loop side at the closed-loop cooling water heat exchanger is higher than that on the open-loop water side; therefore, the connections of the heat exchanger must not be reversed. The cooling water return pipe of critical equipment is equipped with sight holes for observing the flow of cooling water. The cleanliness inside the closed cooling water system has a direct impact on the safe operation of rotating machinery; therefore, it is essential to keep the pipes clean. All connections for draining water, releasing air, adding chemicals, and taking samples in the closed cooling water system must have their openings welded in place before formal installation. An opening tool should be used to make these openings, and all metal pins used for such openings must be cleaned thoroughly to prevent them from entering the bearings of the rotating machinery or blocking the cooling water channels, which could lead to overheating and damage to the equipment. Normally, the pressure in the closed cooling water system is higher than that in each cooling system. This means that leaks from the closed cooling water system into the equipment being cooled are permissible, but it is not allowed for the medium in the equipment being cooled to leak into the closed cooling water system. Rinsing of the closed cooling water system: Since closed cooling water is made from deionized water, and the equipment that is cooled by this water constitutes important auxiliary machinery and devices in thermal power plants, internal cleanliness during the installation of the closed cooling water system and rinsing of the system after installation are particularly important. Generally, there are three types of closed-water flushing: closed flushing. It is a water-saving type of flushing, but the flushing time is long. Open flushing. The entire rinsing process requires a large amount of water, but the rinsing time is short. Flushing combined with opening and closing. Start with open flushing, then proceed with flushing while adding water and draining it at the same time, and finally drain all the water from the system. It saves water while meeting the project timeline requirements. When flushing the closed cooling water system, short-circuiting must be performed at a point closest to the interfaces of each piece of equipment. The hydraulic test of the closed cooling water system can be carried out simultaneously with flushing the temporary piping. Power plant cooling water system: Open cooling water system – The cooling water used to start the circulation in wet-cooling units is taken from the circulating cooling water system, while the open-cycle cooling water used for air-cooling units comes from the mechanical ventilation tower system. Equipment cooled by open-circuit circulating cooling water includes the air cooler for the motor of the electric feedwater pump, the air (hydrogen) cooler for the generator, the coolers for the working oil and lubricating oil of the electric feedwater pump, the cooling water for the closed-circuit cooling water system, the coolers for the coal mill lubricating oil station, the vacuum pump cooler, the fixed-discharge cooling water, the cooling water for ash and slag removal, and so on. Construction of open cooling water system: The open cooling water system includes self-cleaning filters, open cooling water pumps, mechanical ventilation fans, trash racks, and their associated pipelines. The open cooling water system is one of the earliest systems to be commissioned in power plants; it is also the first system to be commissioned after the unit is energized. Therefore, it must be given priority during the construction phase of the project. The installation work is planned to be carried out after the commissioning of the closed cooling water system is completed. It is advisable to clean the interior of all pipes, ensuring that there are no rust spots, oxides, or other debris inside. During installation, all welds should be prepared using TIG welding or double-sided welding. Connect the device interfaces correctly. The cooling water return pipes of the important equipment in the open-loop cooling water system are equipped with sight holes for observing the flow of the cooling water. All drain and vent connections on open-loop cooling water systems should have their openings welded in place prior to formal installation; when using flame cutting to create these openings, it is necessary to remove any residual substances such as iron oxide from inside the pipes. Flushing of the open-loop circulating cooling water system: The flushing requirements for the open-loop circulating cooling water system are not as stringent as those for closed-loop cooling systems. In the case of wet-cooling units, flushing of this system can be carried out simultaneously with the trial operation of the circulating water pump. In the case of an air-cooled unit, flushing can be carried out after filling the water in the mechanical ventilation tower tank, during the trial operation of the auxiliary circulation pump. Both flushing methods require the installation of a filter screen in front of the water pump. The hydraulic test for the open cooling water system can be carried out together with the circulating water pipes; if a mechanical ventilation tower is used, the buried pipes outside the plant must undergo a hydraulic test before backfilling is done. Pipes in the plant can be subjected to a hydrostatic test before flushing. Cooling water systems for the stator and rotor of power plants: Cooling water systems for the stator and rotor of generators: The cooling water used for the stator and rotor of generators is the type of water for which the highest quality requirements exist in thermal power plants. Typically, the pH value of the water used for cooling the stator and rotor is between 7 and 9, and the water hardness