Determine Centifugal Compressor Torque

[JamesDUK]

Hello,
If I have a compressor with known speed and gas power required, can I simply use those two parameters to calculate the torque required. I.e. Torque = power/angular velocity.
Can I further use the fan laws to calculate the power and therefore the torque at lower speeds which would give me an (inaccurate) estimation of the start-up torque of the compressor?
Query relates to a problem motor starting torque with a 7.9MW motor driven compressor, my electrical mates have worked out the motor available torque. There is also a 10:1 gearbox in the string.

Thanks

 

[JamesDUK]

In answer to my own question (i've been swotting up).
Calculating the torque by this method is correct but cannot be used to give an accurate start-up curve because it is based on rated conditions. However during start-up the system may have been partially or fully blown down, regardless the compressor will be started on recycle so the 100% speed power will be the recycle power.

If anyone has got anything else to add or knows any programs avaiable to verify vendor produced curves I'd much appreciate it.

 

[milltir]

Assuming this is a centrifugal machine, the theoretical torque demand is proportional to the square of the speed (rpm). However, theory doesn't apply from say 0 to 25% speed - there is a "stiction" effect to overcome - you need to get the rotor moving. The vendor torque-speed curve should look something like a tick mark.