How many does the turn down of a centrifugal compressor vary if its fixed speed driver be substituted by the variable speed(VFD, Hydrocoupling,or ...)?
Please think about the question carefully. i know what you said about the advantage of varaiable speed with respect to fixed speed in view of energy saving.
But, my question isnot about a case study or specific compressor, to review its map.
My question is to open a general discussion. As you know turn down is defined as the stability range, the allowable operating range between the design point and the surge line, at any given speed for a fixed compressor head.
Generally, how will flow variation range inlet the compressor be if the variable speed driver be used instead of fixed speed one.? And at this condition, will the turn down remain constant, or may change neglegiblly?
With Respect
Pro409, Better advice still. Read your own question carefully. See if it really makes any sense to you, then you'll appreciate the difficulty you're having getting answers to it.
"I am sure it can be done. I've seen it on the internet."
Pro409, review any variable speed centrifugal compressor curve and the link provided by BigInch. you MAY then be able to rephrase the question or have a better understanding of the situation/operation of these machines.
lastly, before changing any fixed speed compressor with a variable speed, i highly recommend you consult with the compressor mfg and review the process conditions. perhaps there are better economical alternatives to achieve the solution . . .
good luck and please take heed in the responses provided . . .
-pmover
The only other thing I can say with the information you've given is that it depends.
It depends on how you presently control your machine; hold your inlet pressure, outlet pressure, flowrate and power draw. Too little actual flow for a particular rpm will stall the blades, too much and it will stonewall or run short of power. Actual flow of course depends on your inlet pressure, power draw, the actual flowrate at inlet conditions and the differential pressure. A typical maximum compression range for such a general question as you pose, typical for many centrifugal compressors is probably about 2.5:1, which doesn't exactly describe a turndown ratio, since turndown implies a range of exact flowrate ratios, which could vary infinitely within the also essentially infinite number of possible inlet and outlet conditions that you might be able to develop at your paraticular installation.
"I am sure it can be done. I've seen it on the internet." BigInch's favorite client.
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