Thermal Protection of Pressure Vessels by Internal Wall Cooling During Pressure Relief

When pressure vessels are exposed to external fire impingement, high wall temperatures can result and these can lead to material degradation and the ultimate failure of the vessel. To protect against this possibility, vessels can be protected by means of pressure relief devices, external thermal barriers or external water spray cooling. This paper deals with a device that cools the walls of fire-impinged vessels carrying pressurized liquids by directing 2-phase fluid along the upper internal surface of the vessel when the vessel pressure relief valve is in action. The device consists of a concentric secondary internal shell that partitions the interior into a core region and an annulus. The bottom of the internal shell is open to allow communication between the two regions. When vapor is vented from the annulus, it results in significant fluid swelling in the annular space. This swelling results in large areas of the wall being wetted and cooled by liquid. Experimental results are presented for the case of a short electrically heated cylindrical vessel with and without the cooling device installed. From the limited tests conducted, it was shown that the device cools areas of the vessel wall that would normally have experienced high wall temperatures and possible material degradation.