What are Regenerative Thermal Oxidizers?
Regenerative Thermal Oxidizers destroy Volatile Organic Compounds (VOCs) and Hazardous Air Pollutants (HAPs), that are created through chemical processes, and industrial exhaust steams. This type of oxidizer uses extremely high heat, about 1500°F, to clean the exhaust of dangerous pollutants and compounds. Developed for large volumes, and low VOC concentration air pollution applications, Regenerative Thermal Oxidizer technology is based on using ceramic media as heat exchangers, and switching values. This design contrasts with Recuperative Thermal Oxidizers which use metallic shell and tube heat exchanger technology, with primary and/or secondary heat. In this configuration, among other distinctions, the outgoing clean process stream of the secondary heat exchanger process is routed to another part of the plant for its use or back to the process itself.
RTO technology delivers low operating costs for high air flow, low volatile organic compound (VOC) fume streams. Rather than allowing the clean hot air to exhaust to atmosphere, the RTO unit captures up to 95% of the heat prior to exhausting it to atmosphere.
How Does the RTO Process Work?
Step 1: The RTO unit is brought up to combustion temperature using supplemental fuel such as natural gas, propane, diesel or bio-fuel. During this start up period, the RTO unit initially purges itself with fresh air and continues to process fresh air until it reaches combustion temperature equilibrium. The RTO unit is now ready to switch over to process air and begin the thermal oxidation of VOC with destruction efficiency up to 99%.
Step 2: The RTO switches from start-up mode running on clean air to operating on VOC process air from the source. To maximize heat recovery, the RTO will automatically cycle or alternate the inlet and outlet (see diagrams below) via a series of pneumatic valves.
Because the RTO is so efficient at reclaiming effluent heat, the units often times are capable of sustaining combustion temperatures without any supplemental fuel, utilizing the VOC as the only source of fuel.
Two of the most common sizing configurations for Regenerative Thermal Oxidizers are two-canister and three-canister.
Two-canister Regenerative Thermal Oxidizers have a low CAPEX and more efficient maintenance, while generating a DRE up to 98-99%. In a two-can RTO, the exhaust stream, laden with VOCs, is fed into the first heat exchange bed, using a high-pressure fan system. There, it passes directly through the media, where it begins the heating process. It then enters the combustion chamber, where burners heat the stream to the optimal temperature for combustion, to complete the oxidization process. Once this step is completed, the now clean stream filters into the second heat exchange bed, to be cooled. This clean stream passes through another bed of media, which brings the temperature of the stream down, and the temperature of the media up. The clean and cooled stream is then released into the atmosphere.
Three-can RTO systems are the best solution for vapor-tolerant and aqueous applications. The high DRE, in excess of 99%, ensures the odor and organic material is nearly completely destroyed. Through this process, the RTO converts the pollutants in the stream into carbon dioxide, and water vapor, all while recovering thermal energy that could be used to reduce the cost of operating the equipment. The process in which this is accomplished is very similar to that of a two-canister RTO. The exhaust stream, laden with VOCs, enters the heat exchange bed using a high-pressure fan system. Here, the stream passes directly through the media, heating it in preparation for the combustion chamber. The combustion chamber then heats the stream further, using burners, to the optimal temperature for combustion, to complete the oxidization process. After that, the clean stream is lead to the heat recovery chamber, where it passes through the media bed, which cools the air, and heats the media. The final step, which makes the 3-can regenerative thermal oxidizer more efficient, occurs in the final chamber, which traps any remaining VOC’s in the “clean” stream, by purging the stream with clean air. This final step is not available in a 2-can RTO, which is why a 3-can RTO can achieve a slightly higher DRE.
Two-canister Regenerative Thermal Oxidizers have a lower CAPEX and more efficient maintenance, while generating a DRE up to 98-99%. Three-canister RTOs are better suited to bake-out processes, have a high DRE of 99% or higher, but have a larger physical footprint.
The following potential disadvantages of a Regenerative Thermal Oxidizer may outweigh the advantages. These drawbacks include:
- High electrical costs
- Larger real estate footprint
- Weight spec that can be up to three times that of a recuperative oxidizer
Gulf Coast Environmental Systems offers additional, though less common sizing options. A 5-can system is generally the maximum sizing, before we recommend other solutions. However, we have manufactured equipment larger than 5-canisters. A 5-canister regenerative thermal oxidizer works in the same way smaller Regenerative Thermal Oxidizers work. As the dirty exhaust stream travels through the first bed of ceramic media, the exhaust stream adsorbs the heat energy stored in the ceramic media mass, which pre-heats the exhaust stream. The exhaust stream then enters the burner reactor chamber, where heat energy is added from the burner to reach the system operating temperature. After the temperature has been elevated and retained, the clean exhaust stream then passes through the second energy recovery canister. As the exhaust stream passes through the canister, the cold ceramic media mass absorbs the heat energy of the exhaust stream, and stores the heat energy for the reverse flow of the system. Once the heat energy of the first two canisters has been depleted through the absorption of the incoming air stream, the flow through the system is rotated, so the incoming dirty air stream is then directed through the second set of energy recovery canisters, with the clean waste gas now going through the third set of recovery canisters. As soon as the heat energy is absorbed by the air stream in the second energy recovery canister set and then absorbed by the ceramic media in the third energy recovery canister set, the cycle again rotates with the third canister set becoming the passage way for the dirty exhaust stream entering the RTO and the fourth canister set ceramic media absorbs the heat energy as the clean air exits the system. This completes the 4th cycle and rotates to the 5th and final cycle before the process starts over again at cycle 1.
How does a RTO compare to a Thermal Recuperative Oxidizer?
- Compared to other emission control technologies, Regenerative Thermal Oxidizers (RTO) are particularly reliable and carry a low operating cost
- This high energy efficiency comes in at around 95% and even, in some circumstances, up to 99%, greatly reducing fuel consumption
- Preferred method of oxidation, because of its variety of uses and applications
- Design simplicity
- No metal expansion issues
- High thermal efficiency
- Achieve high levels of VOC destruction, to keep processes well below required DRE emission levels
- Low NOx operation
- Perfect solution for continuous operation
- Several customizable options, based on specific output and applications, often allowing for a reduction in cost.
- Eliminates as much as 99% of VOCs, which meets all EPA requirements for MACT, RACT, BACT, and LAER
- Adjustable stack heights
- Reactor has ceramic lining, which reduces cracks and spallings, allowing for a longer product life
- Easy installation
- Ceramic media beds absorb heat, and recycle up to 95% for powering the equipment, reducing fuel costs.
- A digital controller, allowing proper maintained temperature control
- Weatherproof, high-density steel enclosure, allowing the processing of highly concentrated exhaust streams
- Modulating burner
- Typical sizing from 300 to 60,000 SCFM
- Custom built, turnkey systems
- Adjustable stacks, and multi-bed configurations
- Option of force, or induced, draft fan arrangements
- Designs available, for smaller or restricted spaces
- A variety of material options, to withstand corrosive and high temperature exhaust streams
- Primary and secondary heat recovery systems
- Control panels, that are built in-house
- Aqueous RTO – Patent pending proprietary technology
- Carbon Absorbers
- Rotor Concentrator
GCES has performed dozens of products tests over the years comparing everything from media to wire to ensure our pollution control equipment operates with consistency, efficiency and accuracy. When selecting media we have chosen the most efficient heat-recovery media for regenerative thermal oxidizers (RTO). Available in three configurations, 160 square feet, 180 square feet or 200 square feet of heat transfer surface per cubic foot, our engineers are unlimited in the options for RTO customization for any given customer specification.
The parallel-plate structure of our media packs more ceramic material into each cubic foot, up to 80% more than saddles with less resistance to air flow. Our results are a unique combination of:
- High heat capacity
- Rapid heat transfer
- Low pressure drop
- Great resistance to plugging by particles
Replacing/Retrofitting RTO Media:
When 1 inch saddles are replaced with our multi layer media for 200 square foot of heat transfer surface, bed depths can be reduced by more than 50%. Benefits of a retrofit include:
- Reduced Operating Costs: Replacing media can raise thermal efficiency and reduce RTO fuel consumption providing a potentially rapid payback.
- Boost Capacity: Replacing media allows RTOs to operate at gas velocities of 400 scfm/square foot or higher. In many cases a client can replace media and upgrade their fan to improve RTO capacities instead of buying an entire second RTO unit.
- Improve VOC Destruction Efficiency: when shorter bed depths provide an effectively enlarged combustion chamber back pressure decreases result in less leakage through switch valves.
- Reduce Maintenance Costs: Particulates are able to more easily pass through canisters and be burned up resulting in less frequent shut downs for media cleaning and replacement.
Whether replacing media to improve the performance of an existing unit or selecting an original equipment manufacturing partner for your new regenerative thermal oxidizer it is important to consider every aspect of the units components. Substandard media could result in a very large long term cost difference when factoring elements such as fuel consumption and maintenance costs.
Regenerative Thermal Oxidizers – A New Application: The Aqueous RTO
Regenerative thermal oxidizers can be also applied to destroy wastewater onsite; to learn about the Aqueous Regenerative Thermal Oxidizer, Click Here.
Gulf Coast Environmental Systems continues to be one of the most trusted customized pollution control equipment providers in the world. Please reach out to one of our experts today, to discuss your abatement options! Call us at 1.832.476.9024, or email us at email@example.com