How to consider relief case exceeding column vapour flood.

[mrtangent]

Dear All,

I have uncovered some relief case designs on some installations which the vapour rate exceeds the packing flood rate for the column. The relief valves are located on the vapour overhead line.

I've been on the Kister distillation course (a long time ago mind) he recommends that you design this out becuase in this instant the relief valve will not only need to handle vapour but entained liquid as flood point is exceeded. So, I am seeking advice here which would you suggest is the most approprate pratical option.

1. Ignore it - kister is conservative and the column flood will not overly exceed the design case for the valve. (liquid orfice size for the valve is much less than vapour)
2. Relocate the RV to the column sump (this means new valve, and new Materials of construction but allowable)
3. Perform detail calculations on what the exepected reliefing rate is needed and what the expected column pressure rise would be. Determine if that is acceptable.

The actual calculations were not completed in house a 3rd party design house completed these.

Thanks in advance

James