No-load test run of centrifugal compressor

Ensuring no backpressure at the inlet and no pressure increase at the outlet constitutes a no-load test; as mentioned in the second part, having the manhole at the inlet open and the outlet open also counts as a no-load test

Ensuring no backpressure at the inlet and no pressure increase at the outlet constitutes a no-load test; as mentioned in the second part, having the manhole at the inlet open and the outlet open also counts as a no-load test

I noticed that the construction acceptance specifications for natural gas compressor installations do not specify detailed procedures for no-load testing. Are there any regulations or manufacturer requirements regarding testing with the compressor’s inlet and outlet open, without any back pressure? I believe that although there is no pressure applied during this type of testing, the flow rate is high, and the compressor is still under load

The so-called no load mainly refers to the absence of compression ratio

No-load test: even if the inlet and outlet are open, it’s not considered a no-load condition. Your centrifugal compressor can’t possibly be of the first stage, right? Could it be an impeller? If the inlet is the atmosphere, there will also be pressure differences between stages, and since air is denser than natural gas, the exhaust temperature of the compressor will vary for the same volume flow rate. If you use air, you need to calculate the flow rate carefully. With an inverter-driven motor, it’s possible to increase the speed while monitoring the exhaust temperature; there is a maximum limit for this temperature, which is determined based on the compressor’s design. In the case of a motor driven at fixed frequency, you need to control the flow rate by using the inlet valve when starting the unit. There is only one way to achieve the no-load test you mentioned: the inlet and outlet of the compressor must be sealed off, vacuuming should be performed, and there must be no medium inside the unit for it to be considered in no-load condition.

I have used fans that operate with gas as a medium; I’m checking to see if their approach is worth considering. For the operation of such equipment, an opening should be provided behind the compressor inlet valve, along with a filter device to prevent the intake of foreign objects (depending on the capacity of the compressor). Or it is a front-opening type with pre-filter in front), designed specifically for air testing. If it is a compressor with a mechanism for adjusting air volume. If not, it is best to install a baffle or a valve at the opening to control the amount of air drawn in. Then the relief valve must be fully open. Centrifugal compressors require a minimum amount of suction to start operating; therefore, the suction volume must not be too high nor too low, and it should be set according to the instructions. Once the gas pipeline and other auxiliary facilities are ready for testing, operation can be initiated. Once it starts running, it is considered to be in a no-load state; this period should not be too long. After checking that there are no issues with sound and vibration within 3 to 5 minutes, the flow rate can be increased gradually. The reference point is to keep the load at approximately the motor’s rated current, and it must not be exceeded. When increasing this amount of air, it must be done slowly, in stages. It is also necessary to monitor for overpressure after shutdown (the vent settings for some compressors vary). If the vehicle is in good condition during this process, pressure increase operations can be carried out, in stages. For example, start with 10% of the operating pressure; if everything checks out, it’s better to have a trend line. Once all the operating points are parallel, the pressure can be increased further by 20%, 40%, 60%, and so on, up to the design pressure of 100%. It is also best to check the setting pressure of the safety valve to see if it is normal. At the same time, check whether other problems will arise under high pressure. It is best to do this item before ending the test drive. (You can also skip it). As required, the unit shall be operated for 72 hours under working pressure (or as specified otherwise). After that, it should be stopped, and all bearings should be disassembled to check the wear of the bearing bushes. The filters in the oil circuit need to be replaced, the quality of the oil must be checked and analyzed, and a thorough inspection of all instruments and motors is necessary. Oh, and the water circuit also needs to be checked. The air opening in front of the sealing machine has returned to normal operating conditions. After all inspections are completed, trial operations of the production medium are carried out, which represents the preparations for starting production. Is nitrogen purging required for the equipment pipelines? Is it necessary to circulate nitrogen during the startup of the equipment before switching over to natural gas? With all inspections completed, the natural gas trial run of the production medium can proceed. The specific process is the same as that in air testing, with pressure regulation achieved either by venting or by circulation; however, the circulation control should not be carried out for too long, as this could cause the temperature inside the machine to rise and lead to accidents. The above are my views for your reference.

True no-load condition is only achieved by evacuating the chamber; for some manufacturers, high-speed dynamic balancing of the rotor is accomplished through vacuuming

True no-load condition is only achieved by evacuating the chamber; for some manufacturers, high-speed dynamic balancing of the rotor is accomplished through vacuuming

The so-called no-load test mentioned usually takes place without any back pressure. I’ve only seen vacuuming done at the manufacturer’s facility during high-production periods

Thank you to the seniors upstairs. Our unit features an 8-stage impeller, 2-stage compression, and a variable-frequency motor. After the first major overhaul, if testing with air is carried out, should the inlets and outlets of each of the 2 stages be left open? Also, it is necessary to pay attention to the air flow rate to prevent the motor from experiencing overcurrent or excessive exhaust temperature.