Introduction

Flare stacks have long been used in industrial applications to control volatile organic compound emissions. However, the accuracy of emission guidelines, particularly the widely used AP-42 guideline, has come into question. This article delves into the findings of the CMA (Combustion and Flare Emissions) testing conducted by the US Environmental Protection Agency (EPA) in 1983, as well as the subsequent emission factors developed by the Texas Natural Resource Conservation Commission (TNRCC). By examining these studies, we aim to shed light on the potential discrepancies between the cited values in the AP-42 guideline and the actual emissions from elevated flares.

Flare Emission Monitoring

During the CMA testing, various gases, including carbon dioxide, carbon monoxide, total hydrocarbons, sulfur dioxide, nitrogen oxides, and oxygen, were continuously monitored above the flare flame using a sample probe. The results indicated that an elevated flare with an open flame had a combustion efficiency of at least 98% when operated correctly (CMA and EPA, 1983, p. 4). However, by following the parameters outlined in 40 CFR 60.18, the combustion efficiency could increase above 99.5% (CMA and EPA, 1983, p. 4).

Discrepancies in Emission Factors

The AP-42 guideline, which serves as a reference for permitting elevated flares, provides average values based on the CMA testing data. However, the wide range of conditions tested in the CMA study suggests that these values may not accurately represent actual flare emissions (CMA and EPA, 1983, p. 2). This discrepancy is particularly important considering the potential impact on air quality.

The TNRCC developed emission factors that accounted for flare type, lower heating value (LHV) of the relief gas, and other variables (CMA and EPA, 1983, p. 5). These factors aimed to estimate actual emissions from elevated flares more accurately. For example, the emission factors for steam-assisted waste gas were derived from multiple tests, resulting in specific values for NOx and CO emissions (CMA and EPA, 1983, p. 6).

Challenges and Supplemental Testing

While the CMA and TNRCC studies provided valuable insights into flare emissions, it is important to note that the results may not apply to all industrial applications due to variations in flare design, tip exit area, and relief gas composition (CMA and EPA, 1983, p. 5). Therefore, supplemental testing considering these variables is necessary to determine emission rates for current industrial applications accurately.

Conclusion

The accuracy of flare emission guidelines, such as the AP-42 guideline, has been called into question due to potential discrepancies between the cited values and actual emissions from elevated flares. The CMA and TNRCC studies shed light on the importance of considering various factors, such as flare type and relief gas composition, to estimate emissions accurately. To ensure the protection of air quality, it is crucial for companies to conduct supplemental testing that reflects the specific conditions of their industrial applications.

By continuously improving emission factors and incorporating real-world data, regulatory bodies and industries can work together to develop more accurate guidelines for flare emissions. This will contribute to better environmental management and the reduction of harmful pollutants in the atmosphere.

References:
CMA and EPA. (1983). Combustion and Flare Emissions Testing. Retrieved from: https://collections.lib.utah.edu/ark:/87278/s6gx4f6r
AP 42, Fifth Edition, Compilation of Air Pollutant Emission Factors.