Re: [Fwd: queries on compressor]

Paul (assume you are forwarding this one) This is a common problem in plant air (or process) compressors. The unit is sized for design flow and pressures, then when plant is operating at less than maximum throughput, the compressor is moving too much product. There are several procedures to compensate:

Speed Control: Effective and saves energy input, but probably has limited range (usually maximum 40% turndown). Good if you have an engine driver, can be very expensive if you have to go to a VFD for electric motors.

Bypass/Regulation: Gas is returned from the discharge side to the suction through a regulator. Probably lowest initial cost, but very wasteful of energy input to the driver.

Load Control (Displacement): Throughput can be controlled by deactivating ends of compressor cylinders. Can achieve large variations of throughput, but can cause vibration or machine damage. Load Control (Clearance): If the machine was designed with adjustable clearance, can provide close control with no wasted horsepower. Probably best option, but is difficult to add after the unit is manufactured. Requires calculatlion of operating conditions in cylinders to avoid possible mechanical problems.

Active Valve Control (Hoerbiger Hydro-Com or Dresser-Rand Infinite Step): Suction valves are held open through part of the compression stroke, effectively reducing displacement of the cylinders. Can provide infinitely variable throughput, form zero to full displacement. Expensive ($150,000-$500,000 per machine) to install, and can cause high discharge temperatures due to pre-heating of suction gas.

So, there are many ways to handle this problem - how much change do you want and how much do you want to pay? Typically you would define the required/desired turn down, evaluate cost of energy input, amount of time operating at reduced throughput, and decide what is economic.

George McKinney
Sr. Compression Engineer
Augusta Engineering & Design
<a href="/group/PipingDesign/post?postID=wy2CY35VZ0ddJhauUehtRJHVPF6z1aN-mXhCk9UTWTjPj5gwhH0gNwxvc_DRFh6el8guNx95Sni1ZeCkYmsBsg">gmckinney@augustaeng.com</a> ----- Original Message -----
From: "Paul Bowers" <pbowers@pipingdesign.com> To: <PipingDesign@yahoogroups.com> Sent: Saturday, November 12, 2005 10:56 AM Subject: [PipingDesign] [Fwd: queries on compressor]

> Sir,
> I had a question :
> when we operate Reciprocating compressors we are either operating at
a
> certain fixed motor RPM. This allows for the rated capacity of Compressor.
> But if the demand flow rate is required in less quantity i.e. under
> part-load conditions it doesn't change the RPM accordingly so as to adjust
> to the desired flow rate. Hence it actually consumes the same power under
> low-load conditions as the peak-load conditions.
>
> So, can we apply some VFD's for such systems which can adjust accordigly
> as the desired flow rate so that automatically RPM's vary and power
> consumed is comparatively less under part-load conditions.
>
> Regards,
> Anindya Mazumdar
> Maxpro Department
> United Phosphorus Limited
> Unit-1,GIDC ,Ankleshwar
>
>
>
>
>
>
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Received on Mon Nov 14 10:22:00 2005