Valve Sizing Alumina Refinery

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Thread Starter

Richard King

Hi all, I want to place a Mag Flow and Keystone-Valves Butterfly control valve into a 200mm line. (Process fluid is Dilution - weak Liquor-NaCO-Caustic, 70 GPL of solids, slightly scaling) The Cv calculated ( 694 ) for the valve indicates I need a 100mm (CV = 681) valve for Maximum flow. (Flow 405 m3/hr, Inlet Pressure 133 kpa, dp 50, temp 90 Deg C, Sg 1.1, Viscosity 1.2 kPa.S) A 100mm Mag Flow will have a 14 m/s Max flow velocity, 200mm Mag flow Max flow velocity would be 3.58, 150mm mag flow will have a more reasonable Max flow velocity of 6.37 m/s. Should I 1. over-size the control valve and make the mag flow and control valve 150mm (Cv = 2310) to reduce the flow velocities? 2. Or use a 100mm Magflow and except the 14m/s flow velocity (This will look strange 200mm line to 100mmline back to 200mm) 3. Or have 3 different pipe sizes (200mm To 150mm To 100mm back to 200mm) I am not sure which is the lesser of the three evils. Option 2 and 3 will be an unpopular choice with maintenance and production for different reasons, and I don't think option 1 will control effectively. Have I picked the wrong type of valve ? (Butterfly Valves historically have been used for this process at this refinery, and I thought it was a good choice) This is not a big issue, but I am interested in your opinions. regards, Richard King Alesa Alusuisse Engineering Australia Pty Limited. Phone: +61 7 3218 3555 Fax : +61 7 3236 0155 Email: [email protected] Web : http://www.alesa.com.au
 
You may be incorrect in the valve Cv. You don't mention Min/Max flow. and the upstream presure @ min/max. You may need single reduction for all. It might be wise considering V-Ball connected reverse (for cleaning: like in the paper industry). [email protected]
 
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David Corking

Here are the sketchy opinions your Q triggered in me: - find out if your line is a little oversized for a reason, perhaps the solids plug up the line when you throttle it. Similar reasoning may influence plants preference for butterfly type. - I guess you should recalculate flow and dps for each of your proposed configurations - it will only take a few minutes. See if they are in your acceptable ranges - if you must oversize your control valve, consider throttling the flow somewhere else in your line (save money with a small magflow, or use an orifice plate or piece of narrow diameter pipe). This lowers the dp needed across the valve and may bring it back to acceptable parameters. I have done this successfully with small needle valves; I would be interested to know how the numbers work out with your butterfly, and to hear other opinions. David in a personal capacity DE, USA
 
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David Corking

I wrote: > - if you must oversize your control valve, consider throttling the flow somewhere else in your line (save money with a small magflow, > or use an orifice plate or piece of narrow diameter pipe). It went without saying - if you throttle, do it downstream of your valve, to reduce your chance of cavitation at the control valve. I agree with jmgiraud that you should calculate the overall desired pressure reduction at max+min flows. Let us know how you get on.
 
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