In our recent blog, "What's the Best Air Pollution Control Technology for My Process?", we took a look at the many factors that inform the choice of air pollution control equipment. When considering air pollution control needs for a facility, it is important for the plant's engineering staff to discuss the application data with potential suppliers. This data includes details about the process operation such as uptime, maximum VOC loading, maximum air flow, energy usage concerns, permitted emission rates, and other process operation data that may be critical to equipment design. Reviewing this data will help determine the available options that will be able to meet or exceed the facility's environmental goals or outcomes. With this data, the air pollution control equipment supplier will then be able to determine the appropriate Best Available Control Technology (BACT) or Maximum Available Control Technology (MACT).
Here on the CPI blog, we're looking at some example scenarios that can help provide more understanding of how we help our customers determine their BACT or MACT.
Scenario 2: Regenerative Thermal Oxidizer
Your process has an airflow in the range of 2,000 to over 140,000 Standard Cubic Feet per Minute (SCFM) at ambient to medium process temeprature and volatile organic compound (VOC) loadings less than 20% LEL (lower explosive limit). In this case, you may want to consider regenerative thermal oxidation as your preferred technology.
A regenerative thermal oxidizer utilizes a ceramic media as the primary heat exchange medium. A booster fan draws VOC-laden exhaust from your process into the system. From there, VOCs are directed into one of the system's regenerators (an internally insulated vessel containing ceramic media).
The contaminated gases are passed through the first regenerator, where energy is transferred from the ceramic media to the gas to elevate the process gas temperature. This elevated temperature approaches the ignition level for most VOCs. The stream exits the ceramic bed and travels through the internally lined combustion chamber, where minimal heat is added to the oxidized VOC gases. The oxidized gases are then directed to the second regenerator ceramic bed to absorb the heat energy from the hot oxidized gases.
After a fixed amount of time, the gases are reversed through the system, where the regenerator bed that was heating the VOC-laden process air will now accept air from the combustion chamber. This regenerator will now be used to preheat VOC-laden process gas. This continues the energy transfer and oxidation cycle of the process gas before it is released to the atmosphere.
Advantages of this system include:
- The lowest operating costs of all control devices. Because the ceramic media is a better heat sink than metal, a RTO can provide thermal rate efficiencies up to 97%.
- High air flow capacity.
- Competitive capital costs.
- Low NOx and CO emissions.
There are a couple of drawbacks to these systems:
- Plugging – the primary heat exchanger media is susceptible to plugging with high particulate loadings.
- Large footprint/heavy loads – these systems may present some installation challenges.
- More moving parts - valve sealing is critical to operation of the system in the long term, resulting in the potential need for frequent maintenance.
In addition to the oxidizer, there are auxiliary heating systems, such as secondary air to air recovery, air to water recovery, air to oil recovery, or a closed loop direct recirculation process that can be used to further reduce operation costs.
Because of the low capital and operation cost benefits mentioned above, most companies tend to gravitate towards a RTO immediately, but these devices require special scrutinizing of the exhaust stream to be processed. High VOC loadings, the need for process heat recovery, and, more importantly, particulate-laden airstreams may drive educated consumers to different products that may be much more beneficial to the process operation in a long term evaluation.
Please watch for the next blog in this series: “Identifying Your Ideal Air Pollution Control Technology, Scenario 3”
At Catalytic Products International, we work to make sure that our customers are educated about the best solutions to their air pollution control needs and that they have the knowledge to continue to meet these needs as they grow and change. For more examples of how our expertise helps our clients find success, please read our Customer Testimonials.