Open Path UV as an Alternative Method to meet Benzene Fence-line Monitoring Provisions

摘要

The intent of the study was to determine if commercially available open-path UV air monitoring systems have the potential to be used as an alternate method for refinery fence-line monitoring as required in 40 CRT 63.658. The study summarizes data collected along a 450-meter path using an Argos Scientific open-path UV system set up at the fence line of a refinery over an eight-week period. Results indicate that the open-path air monitoring system used in this study has the capability to meet the specific operational characteristics required for an acceptable alternative method. The system's calculated minimum detection limits were below the 0.28 ppb threshold for benzene required in the standard. The presence of significant amounts of target gas (benzene) and/or interfering gases such as aromatics and sulfur dioxide in the sample data skewed the calculated detection limit results when these species were not taken into account. Therefore, real-time analysis of five-minute averages would not consistently achieve detection limits below 0.28 ppm, but post processing of data over longer averaging times while considering the interfering species allows this detection limit to be achieved. The study revealed a significant benefit of using real-time open-path measurements as part of a fence-line measurement program. As seen in Figure 1, during the 14 day interval label Period #1, there were two incidences of benzene detections significantly above background levels. In both cases, the refinery was notified of the presence of elevated benzene in the beam path at the time the event was occurring. This initiated refinery-lead root cause analyses to determine the source of the benzene emissions. In both cases, the source was located and the problem mitigated. The result of the quick action likely resulted in a significant reduction in emissions, a lower 14-day benzene average for that period, and potentially negated the need for additional follow-up root cause analysis that could have resulted if an action level was exceeded. This is a critical benefit of having the ability to measure and report the presence of benzene in the ambient air on a real-time basis. This allows refineries to meet the requirements of the rule in a way that is more simplified and cost effective, while offering a time resolution that facilitates effective root cause analyses.