2 replies to this topic

[fmalik]

Hello,

 

I am assessing various relief scenarios for a system. It involves a closed cooling water (CW) loop where manual flow balancing valves set the CW flow to different users at the outset. Currently, I am sizing the pressure safety valve (PSV) for a heat exchanger on the CW outlet line.

 

Process Side: Hot Gas at approximately 700°C

Cooling Water Requirement: A three-way valve receives 15,000 kg/h, directing 5,000 kg/h to the heat exchanger, with the remaining 10,000 kg/h used elsewhere. The cooling water's exit temperature is roughly 30°C below its boiling point, and the operating pressure is around 4 barg.

 

Considered scenarios include:

- A blocked outlet causing a pressure increase from the pump (Relief Rate = 5,000 kg/h).

- Steam relief due to water boiling from a blocked inlet (Relief Rate calculated based on the heat exchanger duty and the latent heat of vaporization).

 

Should I consider any additional cases? I am contemplating whether water might form a two-phase flow as the PSV opens due to the reduced pressure, necessitating a two-phase relief calculation. Additionally, there's the potential for flash steam when liquid water converts to steam because of the lower pressure in the PSV discharge line.

 

Any feedback and guidance is much appreciated.

[Pilesar]

You don't say whether this is a shell/tube exchanger. Is a tube rupture a reasonable scenario? Or some way for the process side to enter the water side? There is also a possible scenario of pool fire at the exchanger. By asking your questions, I get the impression you are new to relief scenarios. Consider all additional cases! Search on the world wide web for a pressure relief scenario checklist and consider each case to see whether it requires overpressure protection. Document the analysis so it can be audited in the future. Even if you determine 'this case does not apply' then document those scenarios also.

[latexman]

A P&ID would help!