"Ball Park" Power Requirements
A "first approximation" method to give a rough idea of power requirements for air compression is:
Power = 202 x Volumetric flow rate of air at 'free air conditions' in m3/s x ln (natural logarithm) of the ratio of the delivery pressure to the inlet pressure (in absolute pressure units) and the answer will be in kW.
This is based on isothermal compression with a constant. Actual power will depend upon the type of compressor and the operating point on the characteristics for the particular machine that can be obtained from the manufacturer of the machine.
If this power is mutiplied by the cost of electricity in cents/kW-h and divided by the material flow rate in tonne/hour you will get the cost of conveying the material in cents/tonne. ■
"Natural Gas" & "Air" Compressors
Thank you very much Dr. Mills; ... but is this approximate relation still valid for natural gas compressors? Any modification should be made and how? ■
Natural Gas
The molecular weight and hence both gas constant and density will be different from that of air. Change the constant (202) in the above equation to 165 and work in terms of the mass flow rate of the gas in kg/s instead of free air conditions in m3/s. This should still give a reasonable approximation, as before. ■
Approximate Power Calculation of Compressors
Dear Friends,
There are comprehensive mathematical relations in the literature for calculating the power consumption of compressors (in terms of [kW]). But just as an approximate solution (without considering the parameters such as specific heat ratio, compressibility of gas, and ...), which one of the following is correct?
Power consumption of a compressor is proportional to:
1. (flow rate).(discharge pressure-suction pressure)
2. (flow rate).{ln(discharge presure/suction pressure)}
(ln: natural logarithm)
Any idea about the corresponding coefficient by which I can be able to calculate the power consumption? I mean "k" in the following relation:
P=k.(flow rate) .....
Any comments or sharing any reference in this regard is highly appreciated. Thanks in advance. ■