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LPG System without a Vapor Return Line

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kabronic

kabronic

Chemical
Apr 3, 2009
5
Dear All

What will be the restriction to load a truck from a set of bullets without a vapor return line? The average ambient temperature is from 95 to 100 F. It is any reason thats this isenthapic process needs to be achive by using a vapor return line?
 
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I can't recall ever seeing a vapor return line in a LPG loading station. The vapor will simply condense as the tank fills. Air in the tank could be a problem, but you don't want that in your bullet tanks either. So I think a vapor line would be useless.
 
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My doubt come because of the temperature at 100F the pressure will rise up to 200 psi.
 
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See this thread which points out that a problem with no vapour return line is that your tanker ends up at about 14 barg and your pump runs out of pressure and the flow rate drops off whilst loading. Whilst the vapour might, over time, condense and the pressure fall as compsosite pro says, the reality is that this takes far longer than the loading process unless you can cool the liquid down a lot pror to loading. An issue is that you need to measure the vapour so that you only charge the customer the net LPG going into the tank and will probably need a cooler to get it to condense, but the key issue then is what is the pressure rating of you tankers and what is the pressure supply from your pumps??

Given that the pump pressure needs to vary from a few barb (3-4) at start of loading to over 14, this either needs multiple series pumps or a big range VSD.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way
 
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Or a suitably sized PD pump... I keep thinking about centrifugals all the time.... It wouldn't work so well with a single one of those. Note the vapour return lines in all those sketches.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way
 
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Ya. Needed them since at least '47.

All the truck and rail car loading facililties I remember had a liquid take off from the bottom of a bullet tank, a separator just before pump, gas going to a compressor going back to the top of the bullet tank, and a vane pump for loading the RC & trucks and another vapor return line from top of the RC & trucks back to the bullet.

Learn from the mistakes of others. You don't have time to make them all yourself.
 
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What is that 47>? It has been taken as a standard?
 
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You asked what will be the restriction? Your restriction will be the pressure rating of your tanker and your filling system if you try to fill a vessel (your truck) with volatile liquid without allowing anywhere for the vapour to go. BI is just pointing out that this issue was "solved" a looooooong time ago.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way
 
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