(333b) Study on Regional Air Quality Impact from a Chemical Plant Emergency Shutdown

Ground-level ozone is the pervasive air pollutants, which is formed by the reaction between VOC and NOx. Chemical Plant emergency shutdown generates huge amounts of VOC and NOx emissions in a short-time period, which might cause significant impacts to local air quality. Unfortunately, such adverse impacts have not been studied quantitatively. Olefin plant is the backbone of the entire petrochemical industry; however, it is also the largest emission producer of the industry. The cracked gas compressor (CGC) is the most critical unit in an olefin production facility. Once the CGC is tripped, the entire chemical plant will fall into the emergency shutdown procedure. Streams from the cracking furnace have to be sent to flare systems for combustion to secure the safety of chemical plant, which will generate intensive and tremendous flare emissions in a very short time (e.g., 0.5 hr in this study). These flare emissions consisted of VOC and NOx may potentially aggravate the regional ozone pollution and seriously damage the human health. Thus, it is important to know the ozone impact caused by tremendous flare emissions from the CGC emergency shutdown of a typical chemical plant.

In this paper, a systematic methodology has been proposed to study the air quality impact from the CGC emergency shutdown of an olefin plant. Through case studies, it demonstrates that emergency shutdown may cause the ozone hourly increment ranging from 4.7 to 61.6 ppb; meanwhile, it differs due to the different of emergency shutdown starting time and the DRE (Destruction and Removal Efficiency) values. This study will be helpful to understand the ozone impact from CGC emergency shutdown of the olefin plant for decision makers on air quality controls in the future.