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Commentator

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Transfer Gas Requirement

01/04/2012 12:19 AM

Dear sir,

We would like to transfer liquid by nitrogen pressure. The liquid transfer rate is 20 m3/hr so nitrogen required is 20 Nm3/hr.

If the pressure required for transferring is 2.5 barg (3.5 bara).

Then by using gas law

P1V1 / T1 = P2V2 / T2

the nitrogen required is coming 6.45 m3/hr.

Please confirm whether my calaculations are correct.

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#1

Re: Transfer gas requirement

01/04/2012 1:15 AM

What is the temp range ?

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#3
In reply to #1

Re: Transfer gas requirement

01/04/2012 1:46 AM

How can your gas flow be less than the liquid flow ? You know it has to be more, and at nearly 2 atm nearly double...rearrange your equation

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#2

Re: Transfer gas requirement

01/04/2012 1:42 AM

You've got it back-to-front. The quantity of gas required will be 20m3/hr at 2.5barg (since the gas will be at more-or-less the same pressure as the liquid when it's actually moving the liquid). So you need about 50Nm3/hr of N2.

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#4
In reply to #2

Re: Transfer gas requirement

01/04/2012 4:33 AM

sir,

It is okay gas reqt. 20 m3/hr @ 2.5 barg.

one more thing when we are pressurising liquid from tanker of 20 m3 with gas of 2.5 barg. Does the liquid surface is at same pressure as gas while transferring.

If liquid is transferred from tanker to storage tank, liquid entry to storage tank is from bottom side.

After complete liquid transfer does the gas reaches upto storage tank since liquid hold up is around 0.5 m3 of liquid in the pipeline (liquid is explosive). Does this liquid hold up remains in the line.

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#5
In reply to #4

Re: Transfer gas requirement

01/04/2012 4:47 AM

"Does the liquid surface is at same pressure as gas while transferring" ... yes - the rules of physics would have to change to make it otherwise.

"Does this liquid hold up remains in the line" .... think this depends on your physical arrangement (about which we know little). Why is there a "liquid hold up"?

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#6
In reply to #5

Re: Transfer gas requirement

01/04/2012 5:05 AM

sir,

for first, when 2.5 barg gas enters into free board of tanker it will expand. so sir on liquid surface pressure would be eventually increase so flow will start once pressure starts building inside tanker free space.

if bernoli eqn is used for this case which pressure should be considered?

for second, transferring will stop once the tanker pressure is reached 2.5 barg. Please confirm. but how to know about transferring lines upto storage tank.

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#7
In reply to #6

Re: Transfer gas requirement

01/04/2012 5:21 AM

bhalchandra, I think you're out of your depth here.

You have the head (height difference between the liquid level in the supply tanker and the storage tank) plus a number of other factors.

As you're dealing with an explosive liquid, I strongly suggest you consult an experienced and trusted engineer in this field (and don't take the word of an unknown, unaccountable person on an open internet forum).

I shall say no more, as I may be wrong, I may misinterpret your statements or you may misinterpret my answers, and the results could be tragic. Good luck and stay safe.

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#8
In reply to #6

Re: Transfer gas requirement

01/04/2012 11:09 PM

Dear Bala

If the piping system has lowest point i.e. outlet is elevated, there is good chance that the liquid accumulates at the lowest point.

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#9
In reply to #8

Re: Transfer gas requirement

01/05/2012 1:10 AM

dear sir,

piping system -1. line goes up from tanker to piperack 2. line goes down from piperack to tank bottom entry.

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#11
In reply to #9

Re: Transfer gas requirement

01/05/2012 1:28 AM

Dear Bala,

Are you using Labview for this automation work ???

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Commentator

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#15
In reply to #9

Re: Transfer gas requirement

01/05/2012 2:49 AM

Then you should worry about the pipe from tamker to the pipe rack. The second portion of pipe, I do not think any liquid accumulation.

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#10
In reply to #2

Re: Transfer gas requirement

01/05/2012 1:22 AM

Don't we need to consider the compressibility of gas here ????

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#12
In reply to #10

Re: Transfer gas requirement

01/05/2012 1:43 AM

sir pardon, but im not getting please clarify.

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#13
In reply to #12

Re: Transfer gas requirement

01/05/2012 1:56 AM

Hope you are trying to automate the system, if I understood correct from the early messages. where you want to transfer the the explosive fluids from one tank to another and the second tank pressure limit is 2.5 psig . Correct!!! As pre my understanding, these kind of automation works are so effectively done using commercial software called LabView from offered by National Instruments. May be you might be using an adiquate and confrotable system as per the requirements .. anyway wanted to share a small piece of info.. thanks.and i m sorry if its of No use to this work.

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#14
In reply to #13

Re: Transfer gas requirement

01/05/2012 2:23 AM

slight misunderstanding from ur side.

It is transfer of liquid from tanker to storage tank by using n2 pressure of 2.5 barg .

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#16
In reply to #14

Re: Transfer gas requirement

01/05/2012 3:01 AM

Dear Bala.

1. There were incidents in the past where the tanker/container exploded due to overpressure. If the N2 supply pressure is higher than the tanker design pressure, then you need some overpressure protection device e.g. PSV

2. The volume you mentioned is only in theory, in reality you will need much more to flush the system.

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#17
In reply to #16

Re: Transfer gas requirement

01/05/2012 4:59 AM

sir,

would like to know how to ensure these lines are flushed completely with N2.

Do we need to provide separate N2 line for flushing these lines or does N2 supplied to tanker will do this.

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#18
In reply to #17

Re: Transfer gas requirement

01/05/2012 7:49 PM

Dear Bhala

For flushing the N2 velocity must be high enough to carry liquid droplet over to the storage.

You can estimate the minimum velocity required by following correlation

Velocity in m/s = 0.15 x SQRT((density of liquid - density of N2)/density of N2).

Then apply pressure drop equation to determine the upstream pressure that will give the right N2 pressure.

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#19
In reply to #18

Re: Transfer gas requirement

01/05/2012 7:57 PM

Dear Bhala

As a safety precaution, transfer the liqid at a very slow rate to avoid static electricity accumulation that could be the source of ignition.

Apply earthing correctly to the piping system to dissipate any static build-up

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