Discussion on flow rate issues when chemical process pumps start at variable frequency or at line frequency
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Aromatic extraction station: Two backwash pump units, one in use and one as a spare; one of the pumps is controlled at power frequency while the other is controlled via frequency conversion. During the switch-over this month, after the variable-frequency pump was started, even though the frequency was set to 100%, the flow rate was still much lower than that of the constant-frequency pump; currently, this does not meet the process requirements. I checked the inlet filter, as well as the pipelines, the outlet check valve, and the outlet pipeline, and everything was in order. An attempt was made to start the variable-frequency pump at its mains frequency, and it was found that the flow rate met the requirements. It can be confirmed at present that for the same pump, the flow rate is much lower when started using variable frequency, while it operates normally when started at normal frequency. It’s not clear at the moment whether there is a problem with the inverter or something else. I’m reaching out to various equipment enthusiasts for their help in analyzing this, and I thank them in advance. The data for the mechanical pump are as follows:
Under the same operating conditions, the flow rate in centrifugal pumps is proportional to the rotational speed, and it has nothing to do with whether the pump is variable-frequency or not. Measure the actual speed of the variable-frequency pump on-site to determine where the problem lies.
Considering inlet throttling, the equipment fails to reach the output specified on its nameplate when calculated based on the medium {:9028:}
Measure the actual speed of the pump when the down-conversion is at 100%. If the speed does not reach the pump’s rated speed, it is either a problem with the frequency converter or with the DCS program
With many frequency converters, a 100% setting can only achieve 80% of the rated speed at line frequency
It’s possible to measure the actual rotation speed; it might be due to the frequency converter.