【Mechanical Equipment Technology Edition】Daily Question 201801025: Common Faults in Refrigeration Systems (8.2)
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This post was last edited by YORK Industrial Refrigeration on 2018-1-27 at 08:32. Starting from now, in order to enhance communication among users, a \"Question of the Day\" campaign has been launched on the Mechanical Equipment Technology forum. We hope everyone will participate actively to progress and improve together! ! ! Rewards: 3 wealth points for active participation, 10-15 wealth points for correct answers. This question is valid for two days; no score will be assigned if more than two days pass. Oil from the compression unit system leaks into the evaporator, and the evaporator used is a full-liquid-type evaporator! How can oil be returned quickly? Induction oil return involves selecting several oil extraction points on the refrigerant side within the evaporator, based on the refrigerant level; generally, the lowest point (the oil-poor area where oil mixes with the refrigerant) is chosen, while the highest point at the standard liquid level (the oil-rich area) is used. Since there is oil leakage, it is necessary to check whether the liquid level in the evaporator has reached the oil extraction point. Most of the oil in the evaporator is above the refrigerant level; therefore, bringing the oil level to the extraction point will allow the oil to be recovered! When the liquid level is low, it is possible to increase the level by raising the pressure appropriately, thereby bringing the oil-rich area closer to the oil extraction point. How can the liquid level be increased? 1. Increase the exhaust pressure. 2. Change the evaporator load by adjusting the amount of water supplied. 3. Increase the liquid supply volume. ============================== Premium promotions: Mechanical equipment——York screw compressors: Maintenance procedures https://bbs.hcbbs.com/thread-1806833-1-1.html Mechanical equipment——Upgrading York Quinton control centers https://bbs.hcbbs.com/thread-1804837-1-1.html Mechanical equipment——Overhaul of GEA Grasox screw compressors https://bbs.hcbbs.com/thread-1800467-1-1.html Mechanical equipment——Disassembly and maintenance of British HOWDEN screw compressors https://bbs.hcbbs.com/thread-1832529-1-1.html Mechanical equipment——Disassembly and maintenance of Japanese Maekawa MYCOM screw compressors https://bbs.hcbbs.com/forum.php?mod=viewthread&tid=
I only know that there is a process for cutting off the liquid at the bottom of the evaporator to remove the oil. Specifically, how to return the oil and what to do about it
1. When it is detected that the oil level in the oil system is dropping, immediately switch the unit to manual control mode to limit the compressor load, for example by restricting its capacity to 50%. 2. Appropriately reduce the cooling water flow rate to raise the water temperature as much as possible, thereby increasing the condensation pressure (if possible, the temperature of the water can be raised by using bypass cooling water) ； Furthermore, controlling the operation of the cooling tower fan via an inverter or turning it off directly can also increase the temperature of the cooling water). 3. Reduce the low-pressure alarm value and low-pressure shutdown value of the unit to acceptable levels, so as to ensure that the unit can remain in operational condition as much as possible. 4. If the oil level is still very low at this point, and the pressure inside the evaporator is also low, then it is necessary to consider whether all the oil has moved into the evaporator. Check through the evaporator sight glass to see if there is a large amount of white foam swirling; if so, it indicates that the oil is inside the evaporator, whereas if not, it may be inside the condenser. 5. With these steps followed, after about half an hour (the waiting time varies depending on the unit), the temperature of the cooling water and the exhaust gas should rise to normal levels (the superheat for R22 is around 17-22 degrees, while for R134A it is around 9-12 degrees). Now, oil collection can begin: A: The oil is inside the evaporator. At this point, it is important to pay close attention to the temperature of the chilled water; the flow rate of this water can be reduced slightly to lower the temperature of the water exiting the system, after which the flow rate can be increased rapidly to raise the temperature of the water exiting the evaporator. At this stage, the water temperature will be much higher than the saturation temperature of the refrigerant, causing the refrigerant to boil vigorously. The refrigeration oil will then be drawn into the compressor along with the bubbling refrigerant foam. The exhaust temperature should decrease somewhat at this point, but it will still be well above the separation temperature between the oil and the refrigerant, thereby carrying the oil back to the oil separator where they can be separated. After repeating this several times, all the oil will be returned to the oil separator. Pay attention to the time interval between each adjustment of the water volume; it is best to restore the exhaust temperature to its optimal level before each adjustment. B: The oil is in the condenser. At this point, there is no need to pay too much attention to the water temperature; as long as the unit operates properly, there will be no major issues. At this point, the expansion valve should be gradually opened to its maximum setting – the opening process should not be too rapid, in order to prevent excessive liquid supply from damaging the copper tubes inside the evaporator. Wait for a few minutes until the high and low pressures in the unit are balanced; at that time, a large amount of white foam can be seen through the sight glass of the evaporator, indicating that the oil has moved from the condenser into the evaporator. As long as step A is repeated, the oil will be drawn back quickly.
An oil separator is used to separate the unit’s refrigeration oil from the refrigerant, after which the refrigerant returns to the compressor via a full-liquid evaporator.
I am learning about *compressors, specifically screw-type ones, and I hope you can provide more information on them! Thank you!
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I’ve learned it; it’s great. The oil is inside the evaporator. At this point, it is important to pay close attention to the temperature of the chilled water; the flow rate of this water can be reduced slightly to lower the temperature of the water exiting the system, after which the flow rate can be increased rapidly to raise the temperature of the water exiting the evaporator. At this stage, the water temperature will be much higher than the saturation temperature of the refrigerant, causing the refrigerant to boil vigorously. The refrigeration oil will then be drawn into the compressor along with the bubbling refrigerant foam. The exhaust temperature should decrease somewhat at this point, but it will still be well above the separation temperature between the oil and the refrigerant, thereby carrying the oil back to the oil separator where they can be separated. After repeating this several times, all the oil will be returned to the oil separator.
The oil is in the evaporator. At this point, it is important to pay close attention to the temperature of the chilled water; the flow rate of this water can be reduced slightly to lower the temperature of the water exiting the system, after which the flow rate can be increased rapidly to raise the temperature of the water exiting the evaporator. At this stage, the water temperature will be much higher than the saturation temperature of the refrigerant, causing the refrigerant to boil vigorously. The refrigeration oil will then be drawn into the compressor along with the bubbling refrigerant foam. The exhaust temperature should decrease somewhat at this point, but it will still be well above the separation temperature between the oil and the refrigerant, thereby carrying the oil back to the oil separator where they can be separated.
For the R22 working fluid, the oil return measures adopted include: creating several oil return ports horizontally near the evaporator liquid level, and using the high-pressure exhaust gas from the compressor to continuously draw back the liquid with a high oil concentration into the compressor； Several oil return ports are installed horizontally near the evaporator level; by utilizing the pressure changes resulting from the variations in speed of the high-speed airflow in the compressor’s suction pipe, the liquid with a higher oil concentration is continuously drawn back toward the compressor against the flow direction ； Two oil return ports are provided vertically near the evaporator liquid level; by utilizing the height difference, the liquid with a higher oil concentration falls into the oil collection container, and the high-pressure exhaust gas from the compressor is used to push this liquid back into the compressor intermittently. 2. For the R134a refrigerant, the oil return measures adopted include: creating two or more oil return ports in the vertical or horizontal direction near the evaporator liquid level, and using the high-pressure exhaust gas from the compressor to continuously draw the liquid in the evaporator back into the compressor ； An oil return port is provided near the evaporator level; by utilizing the height difference, the liquid inside the evaporator flows into a heat exchanger. The refrigerant liquid absorbs the heat from the high-temperature liquid coming out of the condenser, thereby evaporating. The remaining oil is periodically pushed back into the compressor by the high-pressure exhaust gas from the compressor.