20 replies to this topic

[Rodscott]

Hello forum members!

I am designing a wet hexane tank. Some streams coming from the process will be connected at the top of the vessel. To avoid problems with development of static electricity inside the vessel, these pipes will be dip pipes, submerged at a certain level inside the liquid. In the HazOp of this system, arose a concern regarding back flow through these dip pipes and my boss asked me to found a solution to it. I was looking for a solution and i found that exist some anti siphon systems to avoid it.

I don´t have experience and i don´t know what is the best practices to design and/or to specified this anti siphon devices.

So, i will aprecciatte if someone help me with experience and knowledge.

Thanks in advance forum members.

Regards,

Rodscott

[breizh]

Just a hole ( a few mm) at the upper part of the dip pipe inside the tank .
Breizh

Edited by breizh, 28 November 2012 - 06:51 AM.

[Rodscott]

Thank you Breizh!

Rodscott

[fallah]

Rodscott,

An open end piece pipe (few inches length) in order to conduct the outgoing fluid through the hole would also be helpful.

Fallah

[Rodscott]

<sup>Fallah,
Are you saying that would be helpful to include an open end piece of pipe on the hole at the upper part of the dip pipe?

Rodscott</sup>

[fallah]

Rodscott,

Yes, exactly...it prvents the fluid splash on the outside of the dip pipe/internal tank surface...

Fallah

[Rodscott]

Ok Fallah.

Thank you very much for your help.

Best Regards,

Rodscott

[sureshrajeshb]

reallly great answer

[sureshrajeshb]

WE had used dip tube in our industry... I don't so that back will occur...any that answer is good

[katmar]

There was a very interesting discussion on exactly this topic over at Eng-Tips a few years ago.

See http://www.eng-tips....d.cfm?qid=91957

[breizh]

thanks Katmar for the attached link.
Breizh

[Dazzler]

I agree with the hole concept, but when there is a hole drilled in the top of the dip pipe I think it is important that it is noted on the tank general arrangement drawing and also perhaps a note on the P&ID so that operations people in future are well aware it is there for considerations of any modificaitons or for maintenance isolation in future. I have seen odd cases where such a hole could actually provide a sneaky vent path from inside the tank back to the upstream process or to atmosphere .

[S.R.Shah]

Hi All

I have come across other similar problem with dip pipe where hole on top of dip pipe can not be used for anti syphon.

Case:
HCl gas is to be passed in reactor through dip pipe for Hydrochlorination.If hole is used gas shall not dissolved or react with reactants of reactor fully.

As gas is to be stopped after completion of reaction;syphoning occurs.As I could not employ Anti syphon dip pipe,simple dip pipe is used.to prevent syphoning one valve is provided at the nozzle entry and dip pipe.Other provisons like vent valve in the system to break negative pressure produced in pipe line after dip pipe.

Operting pressure in this case is atmoshpheric pressure to pass the gas in reactor and overcome other pressure drop.

What shall be other effective ways

for antisyphoning for this case?

SRShah

[Art Montemayor]

SRShah:

I think you have misunderstood the reason for employing a dip pipe (and with a drilled hole at the top, under the vessel’s top wall).

Your example of injecting HCL gas does not apply to the technique because it is a gas injection application. The subject at hand has to do with introducing a LIQUID fluid into a vessel from a top nozzle. The syphoning of the subject LIQUID is what is being discussed, not the seepage of gas through the drilled hole in the dip pipe.

If you have an application where you are trying to “save” costs by using a dip pipe to introduce a liquid feed into a vessel, followed by the injection of a GAS (using the same dip pipe), then you will certainly have problems – but not with syphoning. Your problem is that you are trying to use the dip pipe for two, distinct, and different reasons and, of course, that doesn’t work. If you have to use a dip pipe to introduce a liquid into your reactor, I would certainly use a drilled hole to break a potential vacuum. But I would install a separate, independent sparging mechanism (whether dip pipe or not) for injecting the HCL gas into the vessel and this mechanism would not have a drilled hole.

A further discussion on this application merits a detailed sketch of the subject application in order to have a sound, well-understood explanation of what is proposed.

Thank you.

[S.R.Shah]

Hi All ;

Please find attached sketch showing P and ID for my problem.
Please advise for suitable solution.

Warm Regards
SRShah

Attached Files

•  P AND ID SHOWING DIP PIPE LOCATION IN REACTOR.xlsx   29.16KB   194 downloads

[Dazzler]

G'day S.R.Shah,
With regard to sparge of gas into reactor, so long as there is minimal pressure in the reactor, then the elevated gas pipe loop can prevent liquid being drawn up that far and into the gas supply system. A full vacuum in the gas system for some odd reason (such as syphon liquid or open valve to scrubber) would not be able to lift the reactor liquid high enough before it cavitated (boils). If the reactor had water then 10m height above the reactor would be enough. Its like the concept of a seal leg on the condensate drainage line from a vacuum condenser.
Hope this helps.
Dazzler

[S.R.Shah]

G'day Dazzler

Thanks for you reply.

Actually gas pressure shall be in range of O.4 Bar .Can 4 Meter inverted loop shall be enough to get back syphoned liquid i.e.water

SRShah

[S.R.Shah]

Art

Will you please need more details?

We always like your detailed and to the point advise

SRShah

[breizh]

S.R Shah,

Will it be possible to install a check valve on the line to avoid back flow ?

Breizh

[S.R.Shah]

Breizh;

Thanks.

PP Check valve for HCl gas Line shall be OK.But I have to Check for Pressure Drop and choking possibility if any.Generally I avoid valves and any obstructions to Gas Flow .

it should be just above reactor Nozzle.

I shall give you more feed back after exploring this possibility.

SRShah

[Art Montemayor]

SR Shah:

I'm sorry I haven't responded earlier. I generated a workbook with illustrations on the syphon effect, but I lost the file upon trying to save it. I am in the process of generating it again. Sorry. I will submit as soon as I complete it - again.