29-jan-2011 Thanks for posted questions on bird cage inisulation. We are in the process of advancing a project with bird cage design and removable panels. Your concern on build up of hydrocarbon in the air gap between the coke drums and panels due to a leak is something we have not considered. The insulation panel system is not air tight, so gas will dissipate. However, it ultimately comes down to (A) the size of the leak and (B) the rate gas can escape. If A is greater than B, it will accumulate in the air gap, possibly creating an LEL risk. Mitigations that come to my mind are to provide a way (I have no exact idea at this point) for leaks to pass through the insulation system (tell tale vents), eliminating the risk; have a rigorous inspection program for the circ welds that allows cracks to be found and monitored (expensive solution). We are going to do further analysis of this risk and get back to the forum.
1-feb-2011 We have determined that the installation of “chimney stop” baffles (every 8 – 12 ft in elevation) within the bird cage will prevent the accumulation of hydrocarbon gas within the air gap volume. Leaks will then be detectable through seams in the insulation system. Ignition of leaks, and damage to the insulation, is always a possibility with all insulation systems, but we view this as a low, manageable risk. Prevention of large coke drum cracks and leaks requires an effective inspection/maintenance/repair strategy. Every owner/operator will need to make their own risk-based analysis of the scenario. Best regards – Mitch