۱- Introduction

۲- Problem statement

۳- Methodology

۴- Case studies

۵- Conclusions

References

Abstract

Flare is the last safety measure for daily operations in oil, gas & chemical process industries (OGCPI). However, an excessive flaring releases large quantity of emissions of VOCs and NOx, which may suddenly enhance local ozone as a secondary pollution. Normally, the flare destruction and removal efficiency (DRE) of 98% or 99% is regulated as the national standard and presumed for industrial practices in the U.S. Unfortunately, real DRE values could be much lower than the standard due to impact factors including various meteorological and operating conditions such as the cross-wind speed, flare jet velocity and heating value of combustion. Thus, it is critically important to explore the sensitivity of the regional ozone impact due to low DREs of OGCPI flare combustions. In this paper, a systematic methodology has been developed to examine ozone impacts due to the low flare DREs, which have never been systematically studied before. The DRE formulas were derived from computational fluid dynamic (CFD) modeling and Water Environment Research Foundation (WERF) results and then employed to recompile the point source emission inventory. After that, comprehensive air quality model with extensions (CAMx) was employede to simulate and quantify local ozone changes impacted by flare emissions of OGCPI. Case studies indicate that the maximum hourly ozone increments due to the low DRE through CFD and WERF modeling is 0.18 ppb and 1.3 ppb, respectively. This study could enrich fundamental understandings of industrial point source emissions and provide the quantitative and valuable support for the ozone pollution caused by OGCPI flare emissions under low DRE instead of standard values.

Introduction

Industrial flaring is to safely combust off-spec, unusable, or unwanted process streams, which might otherwise be harmful to local environment if directly vented without destructions. The oil, gas and chemical process industries (OGCPI) in the U.S. daily processes millions of cubic feet of hydrocarbon gases (Baukal and Schwartz, 2001; Aalsalem et al., 2018). Thus, a slight decrease in flaring performance will release millions of cubic feet of gaseous emissions into the atmospheric environment. Note that although flaring is a safety measure for plant safety in OGCPI, excessive flaring will generate large amounts of emissions such as NOx (nitrogen oxides), CO2, CO, VOCs (volatile organic compounds) especially for high reactive VOCs (i.e., HRVOCs such as ethylene, propylene, acetylene). For instance, an olefin plant with a capacity of 1.2 billion pounds of ethylene productivity per year can easily flare about 5.0 million pounds of ethylene during one single start-up 50 operation (Xu and Li, 2008).