Pressure buildup in solvent pipe

[Dolemite]

I have a 2" solvent pipeline from an outdoor holding tank. The pipe travels on an outdoor pipe rack and eventually makes it way to a building and supplies a batch process. There is a significant elevation change (up) from pump to use point. When solvent is not required for the process, it sits in the line, locked between a check valve at the pump outlet and a valve at the use point. The line picks up heat from direct sunlight on the rack during the times of no flow. When they go to use the solvent, the pressure gets high enough to make it difficult to open the valve at the point of use and the solvent blasts out. Need a simple (and clean) way to relieve the pressure in this section of pipe. Is it acceptable to use a spring loaded psv to relieve pressure and pipe the discharge back to the holding tank? My first post on this forum but have learned much by reading the discussions over the years. Thanks.

 

[EmmanuelTop]

To me this sounds like a textbook example for installing thermal expansion relief valve, with discharge back to the tank.

Since the TRV would be installed between the check valve and the process valve, I would also look at possibilities and associated hazards if anything else (apart from the solvent) starts flowing through the valve (i.e. reverse pressurization from the process side?). This possibility seems very remote but perhaps it is worth investigating.

Dejan IVANOVIC
Process Engineer, MSChE

 

[bimr]

Agree. Thermal relief is necessary. Would depend on the initial temperature, the final temperatures, the fluid properties, the piping materials, etc., none of which you have identified.

The rule of thumb is that if equipment is operating full of liquid, the equipment should be provided with a thermal relief valve if the volume of blocked-in liquid is greater than 0.5 m3.

Review this document:

http://www.chemwork.org/PDF/papers/what you sh...

You might try searching the site as this has been discussed:

http://www.eng-tips.com/viewthread.cfm?qid=393399

 

[LittleInch]

If you don't have a pressure guage on this line you might be unaware just how high pressure can get when you heat a locked in liquid line. This could be design pressure ++. I'm surprised you haven't broken anything yet.

Agree with posters above - this line needs a thermal relief big time. I might help to have some sort of needle valve or other control valve (globe?) at the end to relieve pressure in a more gentle manner.

You could always drill a small hole in the NRV to allow some small expansion back through the pump?

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