(67d) A Six Sigma Approach to Operational Safety Issues Related with Nitrogen Oxides in the Cold Separation Section of Ethylene Units

During the 2003 turnaround of a Dow naphtha cracker, ammonium nitrite (NH4NO2) was found in the cold separation section. Ammonium nitrite is a thermodynamically unstable component, both thermally and shock sensitive, and is a risk to the safe operation of ethylene plants. Although occurrence of NOx salts in olefin unit cold boxes is a known phenomenon since the early 1980's and several ethylene producing companies have reported finding deposits of these salts, none of Dow units had ever experienced presence of NOx components.

Dow initiated a project using Six Sigma methodology to merge both plant process knowledge and chemistry knowledge to generate hypotheses on the hazard qualification of ammonium nitrite and develop control measures.

This presentation reports the key details regarding the location and form of the deposit. It includes unique photographs of the deposition of the ammonium nitrite inside the equipment. The novel hypotheses will be discussed and participants challenged to test these against historical or company specific knowledge in order to come closer to a solution for this issue.