What is a Regenerative Thermal Oxidizer?
- A regenerative thermal oxidizer (also known as a RTO) is a type of industrial control equipment that destroys various types of air pollutants, volatile organic compounds (VOCs) and odorous emissions. RTOs are commonly used in industry to control and reduce emissions of potentially toxic materials and byproducts of industrial processes. While RTOs are common, the RTO at Saint-Gobain is a first-of-its-kind application of this technology to destroy PFAS emissions.
What is the Goal of the Regenerative Thermal Oxidizer?
- The primary goal of a regenerative thermal oxidizer is to destroy and otherwise reduce PFAS in the facility’s emissions to levels that are within prescribed limits before the emissions are released to the ambient air.
How does a Regenerative Thermal Oxidizer Work?
- Oxidizers work by mixing various types of air pollutants with sufficient heat and oxygen to trigger chemical reactions that break them down (i.e., oxidation reactions). A regenerative oxidizer includes heat exchanging media to recapture heat energy from one step in the process and reuse the heat energy to preheat the next cycle.
- The process begins when gas or untreated air from an industrial process is transferred to the RTO inlet by a booster fan. Once the gas enters the RTO inlet, a series of valves direct the air flow through a series of chambers. In the first chamber, the incoming air is preheated by heat energy from a previous combustion cycle. In the second chamber, there are active combustion burners to further raise the temperature of the gas (to the point where oxidation occurs). Following combustion, the oxidized gases move through a heat exchanger media to capture heat energy to be used to preheat a future treatment cycle.
- This absorption lowers the temperature of the gas to a point where it is only slightly warmer than when it first entered the system. This “cleaned and cooled air” is then released into the atmosphere.
- Many RTOs work by using two chambers and switching the direction of air flow every few minutes. However, with a two chamber system there is a brief period of time each cycle (while the flow direction shifts) that untreated air may potentially vent directly to atmosphere. To eliminate this at our Merrimack facility, we installed a three-chamber RTO. With the third chamber, untreated gas instead makes its way to the additional chamber when air flow direction changes and the air is reintroduced for treatment.
What makes the system regenerative?
- The system is regenerative because the heat that is transferred back into the ceramic material after oxidation occurs can then be reused in the process when new gas enters the system. This thermal efficiency also makes the system more energy efficient and cost-effective.
At what temperature does the Merrimack RTO operate to destroy PFAS?
- The temporary air permit issued by The New Hampshire Department of Environmental Services requires the system to operate at an hourly block average of 1832°F, and to maintain a minimum residence time of 1 second.
Does the RTO run at all times?
- Our air permit requires operation of the RTO at all times when fabric coating operations are being performed in the plant.