Concerned that your plant may be out of compliance with its air permit? Whether you’re preparing for an upcoming stack test or have just failed one, we have answers…

Tips on How to Inspect & Troubleshoot Your Regenerative Thermal Oxidizer (RTO) for Air Permit Compliance

An RTO is comprised of many moving parts and related hardware, which means there are multiple possible points of failure that can affect its destruction and removal efficiency (DRE). So where should you look if you’re concerned your system is not performing with minimum control efficiency as mandated in your air permit?

#1: Poppet Valves (“Diverter Valves” or “Switching Valves”) 

Based on our extensive experience with and knowledge of RTOs, poppet valves are the most common culprit of a stack test failure. Poppet valves are a key contributor to an RTO’s DRE, yet as high-wear components they often start leaking over time, either by improper sealing or through worn gaskets and cracked discs.

Check for valve leakage by performing an inspection prior to a stack test. First, ensure your RTO’s poppet valves are sealing tightly by visually inspecting them. Listen for any unusual noises when they operate – valve actuation should be smooth and even in both directions.

You can also compare VOC concentration data from the stack if you’re concerned about valve leakage. PPM levels should match closely in both flow directions. If levels vary significantly, your poppet valve actuators or disks may be causing issues.

#2: Burner/Gas Train

If your burner is improperly tuned, or if the air-to-gas mixture is too rich, there may be high methane (or NOx) levels in your RTO’s exhaust – especially if complicated with other issues like media channeling. Visually inspect your burner’s flame for quality (at burner or system peep sight), looking out for telltale signs like a yellowish-orange glow. The flame should normally be “blue” and strong, not “lazy.” Verify this intensity at different firing rates. Also, check the burner for any loose linkages that could be causing slipping of gas and air settings.

#3: Control System

Have any of the oxidizer’s control system inputs, setpoints, parameters, or components been tampered with?  Sometimes operators adjust parameters and setpoints (like valve switching intervals) in response to alarms instead of thoroughly troubleshooting the unit for electrical or mechanical issues first. Inappropriate modifications of things like switch wirings and trip points can cause major issues down the line, even if they seem to provide a workaround in the short-term.

#4: Ceramic Media

Ceramic media issues like channeling of air through the media beds may not directly cause stack test failure, but they affect your RTO’s efficiency and performance by reducing heat exchanging performance characteristics of the ceramic media. Channeling occurs when media is plugged from particulate, or when there’s damage to structured media. In cases like these, the air flowing through the media beds does not achieve the necessary pre-heating temperature for combustion in the chamber, so the RTO must consume more natural gas to perform VOC destruction – sometimes exceeding the amount for which the system was designed.

Ceramic media issues can only be identified by cooling the oxidizer off for an internal inspection of the beds.

#5: RTO Design Flaws and/or Inefficiencies

Unfortunately, some RTOs are not properly designed for their application and were not built with a safety margin at 100% capacity. If you’re operating near 100% capacity during your stack test, know that any performance issue will have an out-sized impact on VOC destruction at that performance level.

RTOs are often chosen because they provide high thermal efficiencies as well as good DRE’s (95+%), but only when they are designed appropriately for the application and properly serviced. Regular inspections and maintenance are necessary to help your oxidizer maintain peak system efficiency and cost-effectiveness.

Consider a Cost-Saving Service Agreement

Of course, the best way to remain in compliance with your air permit – and avoid failing a stack test in the first place – is to perform regular system inspections, preventative maintenance, and timely repairs. When unplanned downtime must be kept to an absolute minimum, save your plant money with a customized Rapid Response Service Agreement.

If you can’t identify the problem, call us for a comprehensive inspection and/or pre-compliance test (nonreportable). Our field service team is specially trained to pinpoint issues – both common and uncommon – that can affect system performance.

Important Note:

This piece is neither intended, nor should it be relied upon, to take the place of professional consultation or services. Information provided for general reference only; it is not intended as a replacement for OEM guidelines or as a substitute for professional inspections, recommendations, and maintenance. It may not apply to all thermal oxidizer systems and/or process conditions.