Blow case design and control vs liquid handling capacity 1

[Bobolink]

We are using the horizontal blowcase system for liquid handling at suction compressor. The problem which we're facing is it take so long time to dump the liquid out.

The operating philosophy is when the level in blowcase reach setting level, the dump sequence will start by means of using the discharge compressor gas to dump the liquid out. This is required some differential pressure of 5-10 psig approx between where I take the power gas from my compressor discharge piping, and where I inject the condensate out of the blowcase back into it. As I said, this sequence is taking long time.

My question are,

1. How can we minimize this time? From my initial thought, if I reduce the liquid volume per dump by decreasing the level setting, the dump time should be reduced but I'm sure it will be significant.

2. Do you have the program for calculation of the time for dump at difference value of drive gas pressure and liquid volume in the blowcase?

 

[zdas04]

Horizontal blowcases are inherently slow because of the volume you have to pressurize before you get fluid flow.

You didn't say how much liquid you are trying to move per day or the dump capacity of your blowcase. I looked at this problem in the early '90's and decided that I had to design my own vertical blowcase since there were no commercial designs available. The ones I used were 8-inch pipe, 6 ft long with a dump capacity of 3.5 gallons/dump (using two-stage floats). With the very small dead volume at the top I had no problem handling 500 bbl/day which is less than 4 seconds from full to empty and back to full. The "trick" was to use a 2-inch pipe for both the vent and the power gas so that I could cycle the process with minimal friction losses.

For your horizontal application you might want to look at your pipe sizes before you tinker with dump span--you can get the thing to stop working altogether with a small change in dump span.

The arithmetic was all mass balances, I don't think there was anything special.

David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

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[dcasto]

Get bigger valves (trim).