Practices to Mitigate NOx Risk In Cryogenic Section of Ethylene Plants

In May 2010 the Ethylene Producers Committee NOx Safety Sub-Committee sponsored a discussion on practices to mitigate NOx risk in the cryogenic section of ethylene plants. The meeting was attended by representatives of 10 ethylene producers, 4 ethylene contractors and other contractors, 2 additive vendors, and 4 ethylene industry consultants. This paper is based on that discussion and explores how the meeting participants perceive the process safety risk of NOx and strategies that are deployed to manage the risk. The discussion highlighted two common mitigation techniques. The first technique is to prevent heavy cracked gas components such as butadiene from entering the coldest sections of the cold box and the second technique is to alcohol wash the cold box during warm-ups. The paper compares and contrasts how those techniques are performed.