RTOs: Fact vs. Fiction

RTOs (Regenerative Thermal Oxidizers) are used to treat waste gas in a variety of applications, from paint and coatings to pharmaceuticals, food processing, and wastewater treatment. RTOs are popular due to their high energy efficiencies, but are they as reliable as manufacturers claim?

The unfortunate reality is that RTOs are often misapplied and misunderstood. Across the board, Regenerative Thermal Oxidizers are best suited to applications with low VOC concentrations and high waste stream flow rates. The process stream should be very clean and dry with few – if any – particulates and condensables. If your application varies from this description, your RTO will likely experience performance and/or reliability issues. (Learn how RTOs work.)

When compared to other emission control technologies, RTOs offer some well-publicized advantages… and lesser-publicized drawbacks.

It’s True:

1. “RTOs allow for high thermal efficiencies and lower fuel costs.” RTOs are known for achieving thermal efficiencies of 95% or higher, resulting in lower energy costs than most thermal oxidizers of equal size. Because RTOs are so efficient at reclaiming heat, in some situations the units are capable of sustaining acceptable combustion temperatures without supplemental fuel (natural gas) by using hydrocarbon contribution (VOCs) from the waste stream as the only source of fuel.
2. “RTOs provide high destruction efficiencies.” Regenerative Thermal Oxidizers can provide consistent destruction removal efficiencies (DRE) of 95% – 99%. When an RTO is well designed for the application, properly serviced, repaired, and maintained, high DRE performance can be maintained for many years.
3. “RTOs offer good range of air volumes.” RTOs can be designed for very high air volumes – virtually any volume of air above 5,000 SCFM can be accommodated. Some individual systems can be 50,000 SCFM or greater.

It’s Questionable:

1. “RTOs offer the highest reliability/uptime.” Not always. Certainly, a poorly designed or constructed RTO with lower quality instruments/components will result in lower reliability. However, reliability issues can affect even a well-designed/constructed RTO due to its use of so many moving parts and their associated hardware (e.g., valves/dampers, solenoids/cylinders, gaskets, actuators, etc.). These parts require proper and timely monitoring, preventative maintenance, and servicing. For example, burners must be accurately tuned, and diverter valves must seal tightly. Furthermore, there are limitations with media in any RTO. Regardless of media type (e.g., saddles or structured), bed obstruction can quickly hinder performance. Once a media bed becomes obstructed due to process particulates or condensables, a costly media replacement may be the only solution to restore long-term performance and efficiency.
2. “RTOs offer the least expensive cost of ownership.” True “cost of ownership” must account for utility usage, repairs and maintenance, and reliability. After all, a system that has failed can cause potentially extensive shut-downs of your processes and have significant impact on profitability. Variables that affect reliability on an RTO are quality of construction, quality of components, quality of maintenance, and process conditions. If a well designed and constructed RTO is misapplied to a process (e.g., processes heavy in particulates, one which includes contributions which easily condense, or a stream containing vapor form of silicone), cost of system ownership can quickly escalate. Additionally, even if an RTO is operating in a suitable application, it will require general maintenance to help maintain peak system efficiency and reduce unnecessary costs. This is one reason many of our customers choose annual Service Agreements for their systems.
3. “RTOs offer the lowest energy costs.” Usually, but not always. For high airflows and light VOC concentrations, it’s true that an RTO can provide much lower energy costs than most other types of thermal oxidizer systems. However, many common variables can adversely affect the energy efficiency of an RTO – including poorly tuned burners, inappropriate operating conditions, and plugged media. Also, if the application’s airflow is intermittent, the RTO has to be shut down when waste gas isn’t flowing, which causes the system to cool down. It can take many hours (and dollars) to reheat an RTO to operating temperature.