5 replies to this topic

[afd]

We have a solvent storage tank of 60m³. Recently there has been a modification done to prevent vapor venting to atmosphere during offloading of tanker as required by regulations.

 

The modification is the PVRV(pressure vacuum relief valve) outlet(from the positive pressure side) is routed back to the tanker vapor space via a flame arrestor to equalize the pressure and prevent any vapor venting to atmosphere during tanker offloading into the tank.

The PVRV pipe to the tanker has two  manual valves and they remain closed when the tank is in operation. This leads to the tank being isolated and unable to vent(breathe out) if there is a pressure rise. The credible scenario of any pressure increase can be due to a fire, or excessive ambient temperature. The max ambient temperature is 32°C.

 

 

The solvent properties are:

 

IBP=175°C

vapor pressure=0.07kPa @ 20°C

Flash point (TCC)= 51°C

LEL =0.6%V

CAS number=64741-65-7

 

Is there a standard stating there should not be isolation valves downstream of a PVRV?

What if the PVRV malfunctions or flame arrestor gets blocked Can this lead to a undesired high pressure in tank during offloading?

I want to suggest to route the piping upstream of the PVRV back to the tanker as this will make the PVRV independent and also equalize the pressure during tanker offloading.

 

Your expert advice is solicited
AFD
 

[latexman]

"I want to suggest to route the piping upstream of the PVRV back to the tanker as this will make the PVRV independent and also equalize the pressure during tanker offloading."  This is the usual way.  It averts the problems you mentioned.

[proinwv]

afd,

 

What latexman suggests is common practice. It is done in bulk gasoline loading as well as vapor transfer at service stations fueling automobiles.

 

Also, search the previous postings for comments on flame arrestors. There has been postings and you may find their comments interesting.

 

I think that you know what you are doing is not correct. I suggest that you review API 2000 and then send us a sketch of what you have. I just want to be sure that I am seeing the correct picture.

[Art Montemayor]

AFD:

 

I consider any solvent loading/offloading operation a unique and potentially hazardous operation.  I also concur with the comments offered by latexman and especially proinWV.  I have designed and implemented various solvent railcar loading operations in the past and have always incorporated vapor balance lines as you describe – except that I specifically dedicate a nozzle on the tank roof especially for this purpose and run the pipe downwards and parallel to the liquid fill line, with block valves at waist level, besides the tank.  I know of various company practices that prohibit block valves downstream of a PVRV.  I don’t know of anyone who would seriously propose that.

 

I strongly agree with Paul on all he recommends: submit a detailed sketch of what is being proposed and research past threads on flame arrestors for this application.  You will find that the API is strongly against their use – and for some valid technical reasons.

[afd]

I am attaching an excel sheet for the layout. My gratitude to Art M. Who had introduced excel as a drawing tool years back in this forum.

I also observe that the vapor line is a SS 304 line and the studs are of different metal and the gasket is Teflon type. My query is should the flanges have bonding wires to prevent static charge build up I have provided all the data I could gather from the site in the excel sheet.

Just out of curiosity ; if the vapor pressure is 0.07kPa at 20°C what will it be at 35°C?

 

Thanking you

Afd

Attached Files

•  Solvent recovery.xlsx   36.66KB   51 downloads

[breizh]

Afd,

For your last question refer to the attachment ( paragraph 2 ) , VP at 37.8 C

 

http://esis.jrc.ec.e...ts/64741657.pdf

 

Breizh

Edited by breizh, 22 July 2013 - 01:32 AM.