Elie:
You provide the needed process information, but nothing on the heat exchanger except that it is a sheel and tube. I can make assumptions as to design, materials, tube size and pitch, thicknesses, etc., but the results are not terribly representative. You could probably get a smaller flow if you can go to a plate exchanger, but you might have a larger pressure drop (but no indication of the pressure of the water, or on the pump). In general, you will have a lot of water use, as your LMTD is pretty small, assuming an approach of 10 deg F. Typically the water is reused (using a cooling tower), abnd especially effective at that altitude (rarely at that elevation is there a high relative humidity or absolute dew point - you can probably count on getting a 70 deg or cooler water out of the tower, as the dew point is probably less than 50 - 55 deg F at any time).
The answer is, yeah, you'll be using a lot of water. You can do some engineering design to minimize it, and add a CT to minimize operating cost (you might have to reuse water anyway, because getting a permit to use and discharge that much water is either costly or impossible, or somewhere in bewteen).
... Bruce D. Bullough ...
Sebesta Blomberg & Associates, Inc.
2381 Rosegate
Roseville, MN 55113 USA
desk: 651-634-7344 fax: 651-634-7400
www.sebesta.com
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Subject: [PipingDesign] Water volume require to cool natural gas
[bcc][faked-from][mx][spf]
The problem:
I need to cool natural gas from 130 deg F to 110 deg F using a shell & tube heat exchanger with 70 deg F water.
Question: How much water do I need?
Design conditions:
Ambient Temp: 100 deg. F .
Altitude: 6700 ft, atmospheric pressure 11.6 psia
Process Gas: Natural gas, sweet, 95 % methane, 2% CO2, specific gravity 0.55-0.60, 46 ,000,000 scf/day ( 90,000 lb/hr) , 130 deg F, operating 350 -545 psi, Relief valve set at 500 psig .
Cooling Medium: Produced water,80-90 psig, 70 deg F, specific gravity 1.04.
I am piping/pipeline facilities engineer (not a process engineer).
I have requested information from a heat exchanger vendor. The flow rate of water required per vendor calculation is very high. I have ran hand calculations and compared my answer with the online calculation available at http://www.freecalc.com/hxfram.htm. The vendor reported flow rate is 3 times higher than what I came up with (hand calc & freecalc).
Supported formulas with your reply are very much appreciated.
Cheers,
[Non-text portions of this message have been removed]
Yahoo! Groups Links Received on Mon Sep 12 14:49:00 2005
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