Causes of oil running of chillers and their solutions

Causes of oil running of chillers and their solutions

During the commissioning of the chiller, I encountered the oil running of the unit many times. Most of the units with this problem used a flooded evaporator. Today, the editor of okmarts.com will share with you the reasons for the “oil running" of the chiller. And specific solutions, I hope it can be helpful to everyone!

　　 There are many chillers on the market that are constructed according to the following idea: mixing refrigerating oil and refrigerant, using an oil separator to separate the refrigerated oil from the refrigerant, and then returning the refrigerant to the compressor through a flooded evaporator. This type of model has good cooling effect and has a high degree of promotion, but there is a question in its operation, that is, it is easy to "run off", that is, when the cooling water temperature is low, the exhaust gas superheat is not high, and then the oil and refrigerant The separation is not complete. After the mixture enters the heat exchanger, the low pressure of the unit is low, and even worse, the expansion valve is blocked and the unit cannot be started.

1. No trace of oil can be seen in the oil separator. At this moment, the oil does not accumulate in the condenser, but enters the evaporator through the expansion valve. The oil will stick to the heat exchange copper tube of the evaporator, causing it to evaporate. The evaporation effect of the compressor is not good, resulting in a low pressure in the evaporator, which together causes the compressor's suction superheat to be very low or even directly sucks the refrigerant liquid, and the compressor discharge temperature is very low, and the oil and the refrigerant are still inseparable , Such a vicious cycle will cause all the oil to gather in the evaporator, the compressor will shut down due to the lack of oil supply and announce infinite noise, and even the oil level of the oil separator of the unit will alarm.

2. No trace of oil can be seen in the oil separator. All the oil will follow the exhaust to the condenser. If the water temperature continues to be low, all the oil will gather in the condenser and cause the expansion valve to generate oil. Blockage, due to the lack of liquid supply in the evaporator, the pressure starts to decrease until the low pressure alarms and stops.

　　 The above is the so-called runaway phenomenon. The main reason is that the chilled water temperature is low and the exhaust temperature is low.

　　The solutions to this type of question during the boot process are as follows:

　　1. When it is found that the oil level in the oil is lowering, the University of Marathon will adjust the unit to manual control mode to restrict the compressor load, for example, restrict its energy to 50%.

　　2. Reduce the low-pressure alarm value and low-pressure shutdown value of the chiller unit to the allowable range, and try to ensure that the unit can be in operation.

　　3. If the oil level is still low at the moment and the pressure in the evaporator is also very low, it is necessary to consider whether the oil has run into the evaporator. See if there is a lot of white foam tumbling in the evaporator sight glass. If so, it means that the oil is in the evaporator, otherwise, it may be in the condenser.

　　4. With the above several processes, after half an hour or so, the temperature of the cooling water and the exhaust temperature should increase to normal, and start to collect the oil below: the oil is in the evaporator. At this moment, pay close attention to the temperature of the chilled water. You can first properly reduce its flow rate to lower the outlet water temperature, and then quickly increase the flow rate to make the evaporator outlet water temperature quickly increase. At this time, the water temperature will exceed the full temperature of the refrigerant by a lot, and then make The refrigerant is fiercely jubilant, and the refrigerant oil will be sucked into the compressor with the tumbling refrigerant foam. At this time, the exhaust temperature should be lowered, but it should also far exceed the separation temperature of the oil and the refrigerant, and then the oil will be brought back to the oil. Separator and make them separate. After several times, the oil will be fully recovered into the oil separator. Here pay attention to the time distance of each adjustment of the water volume, it is best to make the exhaust temperature rise back to before the adjustment after each adjustment.

　　 The oil is in the condenser. At this time, there is no need to pay too much attention to the water temperature, as long as the unit can operate normally, there will be no big doubts. At this moment, the expansion valve should be gradually opened to the maximum (the opening process should not be too fast to prevent too much liquid supply from damaging the copper pipes in the evaporator), and wait for a few minutes until the high and low pressure of the unit is balanced. I saw a lot of white foam in the mirror, which means that the oil has entered the transpirator from the condenser. Just repeat the process A, and the oil will be quickly recovered.