Optimize the Life & Efficiency of Your RTO Ceramic Media BedsJuly 14, 2020
Considering ceramic media replacement in your regenerative thermal oxidizer (RTO)? Wondering about the many options and claims you have heard from peers at other companies? We hope this post provides some clarity to start you on the right path.
RTOs have been a workhorse oxidizer for over 30 years. Many ceramic media types and designs have been developed over that time offer a significant improvement in performance and plugging resistance allowing an RTO to be utilized to treat nearly any airstream.
Designed and installed correctly, ceramic media replacement offers an opportunity to reduce your operating costs and future replacement costs. So where do you start?
Know Your Airstream
- Particulates – organic and inorganic particulates present difficult challenges but depending on the characteristics may still be overcome
- VOC concentration – VOC concentrations can often drive RTO ceramic media selection in some cases
Know Your RTO
- Airflow characteristics in an RTO can expand or limit the available ceramic media options
Know Your Airstream:
Particulates: Particulate (dust/sticky VOCs/silicones) can significantly shorten the life of a ceramic media bed. Particulates not known or not planned for will usually either adhere to or become hung up in the ceramic media bed.This can be a costly surprise for a new RTO owner if it requires a bed replacement in the first few years of ownership. Provided your airstream contains particulate, knowing the volume and characteristics of them is the first crucial step to designing the best ceramic media bed for your application.
A ceramic media bed does a very good job of filtrating the air stream, but that is not its main purpose. With proper understanding of the airstream, a ceramic media bed can be designed to optimize the heat exchange performance (its main purpose), while allowing a majority of particulates to pass through the beds and reduce plugging. This will extend the life of the RTO bed. There are a wide variety of structured ceramic media choices, with various flow path opening sizes to provide passage of some or all particulates.
In situations where particulates can’t be completely mitigated but simply reduced, the RTO may benefit from a design that “captures” particulates in the top layer of the bed. This approach would, limit the scope of future replacement to the top layer only, making future media bed replacements quicker and less costly.
If particulates do not build up in a certain layer of the bed but affect the entire volume, a better bed selection might be one that is easy and less costly to replace in terms of capital and downtime. This can still achieve maximum thermal efficiency. The lowest cost option is usually random packed ceramic media, like saddles. With this bed design, you can plan for the inevitable build-up of particulate and just accept that there will be frequent, but less costly replacement.
VOC Concentration: Volatile organic compound (VOC) concentration can determine the flexibility available for selecting ceramic media. Since fuel cost is typically the largest operating cost contributor for an RTO, the first goal is normally to provide the highest thermal efficiency possible for the lowest capital cost. That would be the simple approach if the airstream is without particulate and the RTO design has good flow characteristics. The media bed design comes down to economics only: optimal thermal efficiency vs. bed replacement cost.
However, if the VOC concentration is high and particulates are present, the media bed can be de-rated in thermal efficiency to accommodate expected plugging, but still have no negative impact on fuel costs. This de-rating can be done by reducing the depth of the ceramic media bed or use structured media with extra-large flow paths.
Know Your RTO
Over the years, we’ve had experience with nearly every RTO design. While some have well-designed airflow mixing, others—by limits of their design—do not properly distribute the airflow before entering the beds. This is a problem if structured ceramic media is being considered. Structured beds have shallow depth, and typically maintain any flow imbalance throughout the entire media bed, with no lateral (side to side) mixing of air volume. This unbalanced flow in the beds reduces the thermal efficiency of the bed by causing cold pockets in the media bed, which can reduce the VOC destruction performance of the RTO. How is unbalanced flow corrected by the design of a ceramic media bed? By creating flow resistance (pressure drop) through the bed we can create better flow distribution before the air enters the bed. We can also use media that encourages mixing in the lower, entering layer. Different styles of ceramic media (saddles or structured) produce differing resistance as air passes through the bed.
By selecting ceramic media mixes that create an optimized pressure drop across the beds we can:
Choosing 100% random saddle media provides the best flow balancing if that were the main goal, but that choice may create an unnecessary pressure drop and an increased fan horsepower draw. Usually, a mixed bed of random media plus structured media or a mix of several structured media types will be the best option.
- Correct the intrinsic flow imbalance of an RTO system.
- Optimize the thermal efficiency and the VOC destruction efficiency for a specific application.
Bonus: Can the Flow Capacity be Increased?
In most cases YES! New structured media design advances can improve older beds originally utilizing random packed (saddle) media, providing as much as 25% capacity increases. However, fan and burner capacity calculations will need to be completed to determine the actual airflow increase possible.
The RTO and your application introduce many variables affecting ceramic media selection and each of those variables are co-dependent upon the other. It is important for your next regenerative thermal oxidizer ceramic media replacement that you make it a point to know your airstream and know your RTO. This will lead to a successful ceramic media bed replacement in your RTO.
Ceramic media replacement does not have to be a mystery. We have seen nearly every media bed design and would appreciate the opportunity to complete a free analysis and provide guidance. Send us your unique application and begin the evaluation process. If you agree with our recommendation, we would be happy to prepare a quote including the removal and replacement of your existing ceramic media bed in a timely fashion.