Stefan-Boltzmann Fire for Depressurization

[ProcessAche]

I have been using the Aveva PRO/II simulator to calculate BDV valve relief rates considering adiabatic processes. Recently, considering API 521, I wanted to consider the heat transfer rate according to the Stefan-Boltzmann fire equation, but my simulations do not converge for small volumes. Have you performed similar simulations with this software?

thread798-45368

 

[Sawsan311]

Hi, can you confirm that your blowdown rate estimation is for the fire scenario and not the warm adiabatic case since the thread you are referring to is discussing a totally different objective like MDMT check which we perform using ischoric adiabatic modelling and falls with different assumptions.

The referred Stefan Boltzman fire equation is the analytical method explained by API 521 Annex A and which is recommended for a more rigorous estimation of the fire heat flux for pool and jet fires. This method is evidently not applicable for the adiabatic process you mentioned. In case of pool fire, why don't you use the API empirical equation which involves the wetted area estimation, I think this would be pretty simple for small systems and a fair approximation for pool fires with heat flux within ~ 100 kw/m2 but NOT Jet or confined fires. I never used Pro II but from my experience in ASPEN HYSYS, you can try tune/reduce your time step size increment to allow the model to converge. Just give it a try.