Ammonia in the Petrochemicals Steam Cracking Plant
Prepared for the AIChE Spring Nation Meeting, EPC Conference
April 23-27, 2006
Ammonia is a common contaminant in ethylene plants throughout the world. It can enter the plant in refinery gases, gas feeds or as nitrogen compounds that crack to ammonia in the steam cracking furnaces. Ammonia is a serious contaminant in ethylene and propylene because it is a poison to polyethylene and polypropylene catalysts.
This paper is a case study on some causes of ammonia contamination in our plant, how it proceeds through the plant and some mitigation techniques.
In late 2003 and early 2004, several customers began to notice small amounts of ammonia in the pipeline ethylene coming from the An investigation began even though the on-line Gas Chromatograph/Mass Spectrometer for ammonia analysis did not detect ammonia in the ethylene product. Other techniques (including the MDA tape analyzer from C.I. Analytics, Drager Tubes, scrubbing the ethylene through water and then using wet chemical methods for detecting the ammonia in water, and later Ion Mobility) confirmed that ammonia was in the ethylene product. Subsequent investigation revealed the drier upstream of the C2 splitter was saturated with ammonia.
As moisture adsorbed on to the drier containing 3A molecular sieve, ammonia was desorbed into the ethylene stream. The drier was taken off-line for regeneration and the Ion Mobility Ammonia Analyzer (as well as the scrubbed samples and the MDA Tape Analyzer) clearly showed the drop in ammonia in the ethylene product. From April through September of 2004, no off-spec incidents took place but monitoring of ammonia was done using the on-line Ion Mobility technology. However, during October, while the ethylene drier was being regenerated, ammonia again went off-spec in the ethylene product and a flaring event occurred. Since October of 2004, ammonia has been monitored but no off-spec events have occurred.