2 replies to this topic

[Bruce]

I am absorbing benzene on a carbon bed and need some thoughts on how to develop the relieving rate for sizing the PSV under fire exposure.

Container is 50 psig design bare carbon steel vessel with about half the total internal volume filled with carbon. Benzene can be adsorbed up to about 40% of weight of carbon. Normal internal atmosphere is nitrogen. Normal operating pressure is 2 psig. PSV set is 50 psig.

Under unwetted vessel fire sizing without adsorbed benzene, there is no relief (at internal temperature equal to wall temperature, pressure does not exceed set point.)

When carbon is partially or fully loaded, benzene will desorb when internal temperature exceeds about 300 F. I need to develop a heat input rate to determine a benzene evolution rate.

Wetted wall fire calculations are straight-forward but I don't have wetted walls. Is there a way to use the Environmental (insulation) Factor to simulate metal to gas rather than metal to liquid heat transfer?

Is there a better approach to estimate the heat input?

Thanks for your help.

[Bruce]

Thanks.

I ended up using your second suggestion, equivalent wetted area. After talking with several collegues, it seemed adequately conservative and easiest to defend.