On the efficiency of centrifugal compressors
Thread Content
I’m a newcomer and work in the field of long-distance natural gas pipelines. I would like to ask a question regarding the efficiency of centrifugal compressors: Our natural gas compressors have been in operation for 3 years, and recently I studied their performance curves and efficiency levels; I noticed that the efficiency of these compressors is increasing continuously, which puzzles me. I would like to ask if anyone else has encountered such a situation. First, I used more than 100 sets of actual production data from 2013 to 2014 to adjust the performance curves provided by the manufacturer (operating flow rate – polytropic head), thereby obtaining what I believe to be a more accurate representation of the compressor’s performance. Then, the performance test data points for the summer of 2013, the summer of 2014, and the winter of 2015 (operating flow rate – polytropic head, i.e., actual head) were plotted on the corrected performance curve. Meanwhile, it was possible to determine the corresponding head value on the performance curve based on the operating flow rate and speed at that time (i.e., curve head). Subtracting the curve energy head from the actual energy head yields an energy head difference of Delta H, which represents the offset in energy head. The larger this value, the greater the actual working capacity of the compressor; it is capable of providing a higher energy head to the gas under the same flow rate and speed conditions, as compared to the performance curve used as a reference ； Conversely, this indicates that the actual working capacity of the compressor is poorer. In the end, I found that the energy head difference Delta H across these three tests kept increasing, which indicates an improvement in the compressor’s efficiency? Is this situation correct, or did I make a mistake in my calculations? Have any of you experienced an increase in the efficiency of a compressor after it was used? Does a centrifugal compressor, as a piece of equipment, also have a running-in period?
This is related to the density of the medium; since the actual natural gas differs from the designed value, the efficiency cannot increase
We have a chromatograph, but we cannot detect any changes in gas density. So I really don’t understand this situation either.
What you are doing here is calculating the difference between the outlet pressure at various operating conditions and the calculated value; although this difference increases, it cannot be said that the efficiency has improved. I am not familiar with gas pipeline transportation; I can only analyze it from the perspective of compressor performance. I hope to receive some guidance if I have the opportunity. Also, since you represent data from three different periods of testing, are you affected by environmental factors? When the flow is unobstructed, an increase in temperature leads to a decrease in efficiency. Furthermore, if the inlet and outlet parameters of the compressor are available, its thermodynamic performance can be estimated.
The efficiency of a compressor is inversely proportional to the temperature of the medium; lower temperatures result in higher efficiency.