Update of the Activities of the NOx Safety Task Group

The initial AIChE Task Group for NOx Safety was set up following a disclosure of significant accumulations of the NOx compound, N₂O_3, in an ethylene cold box located at a plant on the Gulf Coast.  Twenty-five years ago they issued their report describing the potential risks from the accumulation of NOx compounds in ethylene plant cold boxes.  The report included recommendations on how to handle these accumulations.  A few years later in 1990 there was a catastrophic explosion in the cold box at the Shell plant in Berre, France.  In late 1991 a second task group, which is still in place, was organized to perform an in depth study of the safety issues associated with NOx compound accumulations in ethylene plant cold boxes.  Over the last twenty years this task group has presented numerous updates on their findings and has presented several tutorials on this subject.  Although industry awareness has increased, there are still plant incidents associated with NOx accumulation and new findings to report.

This paper will update the latest activities of the Task Group with focus on the proceedings of a meeting held in September 2012 which included 28 participants.  The meeting included presentations by Eastman Chemicals, Shell Chemicals, ExxonMobil Chemicals and BASF Port Arthur.  Key findings from these presentations will be discussed.  These papers highlighted issues regarding NOx accumulation in plants where the traditional feedstocks are not expected to contain NOx precursors, unexpected sources of NOx precursors and accumulation of NOx compounds in sections of the cold box previously thought to be too warm for NOx compound formation.  The meeting concluded with a discussion on the future path for the Task Group.  The main follow-up objective set forth from this meeting was to update the 2007 Tutorial on NOx Safety in Ethylene Plant Cold Boxes with the latest findings and understandings of NOx accumulation in cold boxes.