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United States

Boiler MACT Compliance Testing Identifies Operational Malfunction Risk

40 CFR 63 Subpart DDDDD, known as the Process Heater and Boiler MACT, requires facilities that are major emission sources of hazardous air pollutants (HAPs) to perform regularly scheduled tune-ups on industrial boilers and process heaters. The objective of this regulation is to ensure a facility is operating these combustion units at optimal performance and to reduce HAPs emissions. TRC’s Process Heater and Boiler MACT Team routinely assist many of our clients nationwide with evaluating performance and compliance with the applicable standards.



During an annual compliance tune-up at a client’s refinery, TRC identified a significant operational malfunction with one of the facility’s process heaters. As part of the tune-up process, TRC noted a discrepancy between the output readings on a process heater’s O2 Continuous Emission Monitoring System (CEMS) and the readings on TRC’s portable combustion analyzer, which indicated O2 levels in the process heater were dangerously low.

Coincidentally, the process heater controls were causing the heater to shut down when the operators increased the firing rate of the heater to typical operating loads. Because the CEMS O2 readings were erroneously reading significantly higher than the unit controls, operations staff were unable to identify and troubleshoot the recurring shutdown issue.



After learning of the inaccurate O2 CEMS readings, it was identified that a sensor probe in the convection box of the process heater was damaged during a routine maintenance inspection earlier in the day. Instrumentation and electrical maintenance staff were able to replace the damaged probe with a new one and calibrate it to provide accurate readings, so the process heater could reach the necessary firing rates without triggering the safety shutdown system. The challenge was quickly resolved due to the competency and experience of TRC’s Process Heater and Boiler MACT Team.



TRC’s Process Heater and Boiler MACT Team was recognized at the refinery operation’s morning safety meeting the next day for identifying the discrepancy in the O2 readings, thus allowing operations to identify and correct the problem on the same day. TRC’s assistance helped to mitigate potentially dangerous conditions that could have caused harm to individuals and/or damage to process equipment.

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