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I. What is a cold oil cooler? The oil cooler is a turbine oil cooling device used in power systems alongside turbines. It is of the plain-tube surface type, and uses circulating water as a medium for heat exchange, thereby ensuring that the oil temperature at the bearing inlet reaches the specified value and guaranteeing the proper operation of the unit. II. What is the function of the oil cooler? The turbine generator set operates normally, and some of the energy is lost due to bearing friction. The cooling oil cooler converts this energy into heat, raising the temperature of the lubricating oil in the bearings. If the oil temperature becomes too high, the bearings may soften, deform, or even be damaged. To ensure the proper operation of the bearings, the temperature of the lubricating oil must be maintained within a certain range. Generally, the temperature of the oil entering the bearings should be between 35–45°C, while the temperature increase of the oil exiting the bearings is usually around 10–15°C. Therefore, the oil that exits the bearings must be cooled before it can be recycled back to lubricate the bearings. The main engine oil cooler is used to cool the lubricating oil of the main engine. The lubricating oil at higher temperature and the cooling water at lower temperature undergo heat exchange in the oil cooler; by adjusting the flow rate of the cooling water, it is possible to control the temperature of the lubricating oil. (Since the rotor temperature is high, especially on the steam inlet side of the high-pressure cylinder, the shaft journals of the oil cooler also transfer heat outward, so the lubricating oil also serves to cool these shaft journals.) III. Where are cold oil coolers mainly used? In places where lubricating oil needs to be circulated and cooled, coolers are required. Taking thermal power plants as an example, the main types of coolers include: coolers for the lubricating oil of the main engines, EH oil coolers, coolers for the lubricating oil of feedwater pumps, coolers for the working oil of hydraulic couplings, coolers for the lubricating oil of small steam turbines, seal oil coolers, coolers for the lubricating oil in coal grinding units, coolers for control oil systems, coolers for induced draft fans, coolers for forced draft fans, and coolers for primary fans. IV. What is the cooling medium for the oil cooler? Under normal circumstances, the medium used in cold oil coolers is circulating water. Since circulating water is divided into startup circulating water and closed-loop circulating water, and as the requirements for operational reliability and safety increase, closed-loop circulating water is mostly used as the cooling medium in cold oil coolers; its water quality is equivalent to that of desalted water and condensed water. V. What are the different types of oil coolers, and what are their characteristics? Based on their structure, oil coolers can be divided into tubular oil coolers and plate-type oil coolers. Tubular oil coolers have poor heat exchange efficiency, but they are inexpensive and require little space, making them suitable for small generator sets. Plate-type cold oil coolers offer good heat exchange efficiency, but they result in high costs and require a large amount of space; they are mainly used in large generator sets. VI. What is the working process of the cold oil cooler in a steam turbine unit? The lubricating oil enters from the lower part of the housing, and flows alternately toward the center or the periphery through the perforated middle partition and the non-perforated small partition; it moves in a zigzag pattern outside the pipes, before finally exiting through the oil outlet at the upper part of the housing. Cooling water enters through the water chamber and exits through the lower water chamber after passing through four processes. When filling the oil cooler with oil, the inlet and outlet valves as well as the air release valve are opened. The oil pressure is controlled using the outlet valve of the low-pressure oil pump to facilitate the filling process; care should be taken to ensure that the filling speed is not too fast. Once all air from the oil side has been removed, the valve is closed, marking the end of the filling process. When filling with oil, be careful to prevent overpressure on the oil side, which could cause equipment damage. Cooling water can be introduced only after the oil cooler is filled with oil. The outlet valve remains fully open, and the inlet cooling water is used to adjust the oil temperature. The two oil coolers operate in parallel, with one serving as a backup. VII. Precautions for switching cold oil coolers: When performing the operation of switching cold oil coolers during unit operation, the principle of engaging them first and then disengaging them should be followed. The operation should be carried out by experienced personnel, with a dedicated person also providing supervision. Monitor the lubricating oil temperature, oil pressure, and bearing temperature to prevent misoperations that could lead to unit tripping and equipment damage. The operation should be carried out slowly; when introducing the oil cooler, gradually increase the inlet throttle to prevent fluctuations in oil pressure, while also removing any air from the system. When stopping, close the outlet throttle and the cooling water inlet valve. (Supervision is required during the switch-over; maintain constant communication with DCS personnel to ensure that the air is completely removed, and proceed slowly to prevent shutdown due to fluctuations in oil pressure.) ) VIII. Brief description of the operation sequence for bringing a single oil cooler into use: 1. Check that the oil drain valve of the oil cooler is closed. 2. Slightly open the oil inlet valve of the oil cooler, open the air valve to release any air present, and then close the air valve on the oil side. 3. During the operation, closely monitor to ensure that the oil pressure, oil temperature, oil quality, and oil flow are all normal. 4. Slowly close the oil outlet valve of the oil cooler; pay attention to adjusting the oil temperature, and ensure that the lubricating oil pressure remains within the allowable range until the valve is fully closed. 5. Close the oil inlet valve once the lubricating oil pressure is stable. IX. Briefly describe the sequence for taking out a single oil cooler. Answer: (1) Ensure that all oil coolers other than the one to be taken out are operating properly. (2) Slowly close the outlet valve of the oil cooler to be removed, and open the inlet valves of the other oil coolers, keeping the oil outlet temperature within the allowable range. (3) Once the oil outlet temperature stabilizes, slowly close the inlet valves until they are fully closed. (4) Slowly close the outlet valve of the oil cooler being removed, paying attention to adjusting the oil temperature and ensuring that the lubricating oil pressure remains above the allowable level, until it is fully closed. (5) After the lubricating oil pressure stabilizes, close the inlet valve. X. Precautions for operating the oil cooler. 1. Monitor the changes in the temperature of the oil and water at the inlet and outlet during operation, and make adjustments as needed to keep the lubricant temperature between 35–45°C; generally, it is recommended to maintain it between 38–42°C. 2. The cooling water pressure during operation should be lower than the oil pressure, to prevent water from entering the oil in case of a leak and thereby affecting the lubrication effect. 3. If oil is detected in the water, the cause should be identified promptly, and the quality of the oil as well as the oil level in the tank should be closely monitored. In the event of a leak, switch immediately to the backup cold oil cooler for operation.