Re: [Fwd: queries on compressor]

Morning, Jack:
You hit a couple of subjects there - only one question per post! Anyhoo: Sizing compressors: you hit right dead center of my area there. I have sized these things for many years, first as engineer for a major gas transmission company, now as a hired gun. My basic approach is: Define suction and discharge pressure RANGE - a design point is typically not where you end up running. Ditto for flow range. Then, with above, start selecting, positive displacement (recip, screw or ?) or dynamic/centrifugal. Define driver requirement, engine or motor. The pressure/flow range can be really a major decision item - obviously you design for full capability at design point, but you try for full load at as low differential as possible, plus operation at maximum differential and maximum load points. I have compressor modeling programs supplied by most of the major equipment manufacturers - they are fantastic for exploring the possibilities that salesmen may miss. Then, knowing the approximate hardware that will do the job, find several potential compressors, evaluate total operating cost (unit, installation, operation and maintenance). From there, go to packagers, and select, based on price, their competence (completeness of skid drawings, P&ID's, experience).

On piping systems, typically we are designing for major flow systems, with a guideline of approximately 40 ft/second for maximum gas velocities in piping. Plant air systems would be a different approach - first problem being defining the maximum flow requirement and associated pressure (at the equipment). Then you can determine allowable pressure drops - although I still would not let velocities go more than 75 ft/second, or you will have a lot of pipe noise, and potential erosion, if you have water/crud in the lines.

Hope this is adequately confusing - it took me 30+ years to get here!

George McKinney
Sr. Compression Engineer
Augusta Engineering & Design, Inc.
----- Original Message -----
From: "Jack Osborn" <jhosborn@yahoo.com> To: <PipingDesign@yahoogroups.com> Sent: Tuesday, November 15, 2005 12:10 PM Subject: Re: [PipingDesign] [Fwd: queries on compressor]

> Hi George.....
>
> I was interested to read your posts, thanks for providing such good
> commentary and advice. I am always curious as to how engineers size
> equipment and piping.....some use software, others charts and tables
> (me)...and still others use standard equations and spreadsheets. For
> Air piping, I am interested to find out how you size the plant air
> piping....do you use air piping friction loss tables or....?
> Something else. I have not had much experience with designing air
> piping for plant air systems and would be interested in your approach.....
>
> thank you!
>
> Jack
>
>
> At 07:22 AM 11/14/2005, you wrote:
> >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:
> >
> >S
>
>
> [Non-text portions of this message have been removed]
>
>
>
>
> =========================================
> PipingOffice - Excel Spreadsheets for Piping Calculations
> <a href="http://www.pipingoffice.us/">http://www.pipingoffice.us/</a>
> =========================================
> Main site: <a href="http://www.pipingdesign.com">http://www.pipingdesign.com</a>
>
> Yahoo! Groups Links
>
>
>
>
>
Received on Tue Nov 15 13:19:00 2005