Thermal Oxidizer

The most basic type of thermal oxidizer is a direct-fired thermal oxidizer, also known as an afterburner. As the simplest type of thermal oxidizer, it does not include any heat recovery, heat exchanger, scrubber, adsorbent, or catalyst material. It offers the lowest upfront capital investment cost, but is thermally inefficient, so it requires the most energy to operate. Other thermal oxidizer designs implement a heat recovery mechanism or catalyst to reduce the required reaction temperature.

Due to the lack of heat recovery, this design is best suited for applications with a very high concentration of VOCs or applications that only need to run for a small percentage of time. If the exhaust stream has a high concentration of VOCs and can run nearly steady-state with little to no supplemental natural gas required, then a direct-fired thermal oxidizer is a good choice. Often times, the direct-fired thermal oxidizer is used in combination with a VOC concentrator to provide the highly-concentrated solvents. The direct-fired type oxidizer offers a destruction efficiency of 99%.

A more complex design, the catalytic oxidizer uses a precious metal catalyst, such as Platinum, Palladium, and Rhodium, within the combustion chamber to lower the required reaction temperature. Whereas a direct-fired oxidizer would require temperatures near 1400°F - 1450°F, in the presence of a catalyst, the same reaction can complete at a much lower temperature: 600°F - 650°F. The lower firing temperature requires less natural gas than both a direct-fired and recuperative oxidizer. It also comes in a regenerative catalytic oxidizer design (RCO).

The downside of catalytic oxidizers and RCOs is a higher capital cost and potentially high maintenance costs. The precious metal catalysts are often very expensive and prone to fouling. Once the catalyst is sufficiently fouled, it must be replaced or the reaction temperature must be increased. When selecting an oxidizer, an analysis of VOCs and pollutants must be completed to determine likelihood of fouling.

Best suited for large air volumes with high concentrations of VOCs, the the Regenerative Thermal Oxidizer, aka "RTO", boasts the best thermal efficiency of all oxidizers. Using two or three beds of ceramic media, the RTO design captures waste heat and stores it in the ceramic media. It then uses the captured waste heat to heat the incoming air to temperatures of 1350+°F, very near to the oxidation temperature. At reaction temperatures of 1400°F, the RTO burner will only need to heat the air ~50°F. Using the ceramic media to capture waste heat, the RTO is 95% thermally efficient.

The standard three-tower RTO design allows for one tower to be exothermic, giving off heat to the incoming air, while another tower will be endothermic, absorbing waste heat from the exiting air, and the third tower to be purging air at any time. Purge air is sent through the combustion chamber to ensure all VOCs are captured and destroyed before being released to atmosphere. The RTO is the most popular type of industrial air pollution control equipment.

Currently being installed in 2017, this new paint manufacturing facility will feature a new regenerative thermal oxidizer (RTO) provided by CPI. The RTOs will be used for control of the paint oven's hazardous air pollutant (HAP) emissions, while the recuperative oxidizer will control VOC emissions from the vehicle body paint booths. This customer plans to operate their thermal oxidizers in parallel for 24 hours a day, six days a week. Slated to start production in early 2018, these new oxidizers will net energy savings over their older VOC control equipment.

This Motor Manufacturer selected a large regenerative oxidizer (RTO) to control both their paint booth and cure oven VOC emissions. A three-tower 50,000 CFM unit is one of the largest RTOs that TKS has ever installed. The customer elected to save money by combining the paint booth and oven emissions into the same VOC control equipment. The RTO is well suited for this application with low concentration VOCs coming from their industrial paint ovens, and running three shifts daily, and six-to-seven days per week, near continuous operation.

The downside from a maintenance perspective is tar. When the hot oven air meets the cool booth air, the gaseous tar products in the oven exhaust condense and stick to the ductwork, the fans, and the RTO's ceramic media bed. As a result, this customer achieves lower air volume throughput as it become clogged with tar and the ceramic media requires replacing every 3-4 years instead of every 5-6 years as is typical.

This Automaker selected a recuperative thermal oxidizer with VOC concentrator to treat their VOC emissions from both paint spray booths and heated flash-off tunnels. A pair of heat exchangers use the post-oxidation waste heat to preheat the VOC-laden air before it enters the thermal oxidizer's combustion chamber and heats the air for the carbon desorption loop.

This Automotive OEM has chosen for Taikisha USA formerly TKS to install a total of five (5) oxidizers at its Kentucky manufacturing facilities since 2014. While the first oxidizer installed was a simple direct-fired oxidizer, the customer has since progressed to a thermally recuperative oxidizer with not one, but two heat exchangers (HEXs). They have drastically reduced their emissions and carbon footprint, with goals for the entire campus to be carbon neutral by 2025.

During construction of their new manufacturing plant in 2012, this OEM selected two 30,000 CFM regenerative thermal oxidizers (RTOs). One RTO services the combined oven exhaust while the second RTO services the VOC exhausts from two clear coat paint booths. Regenerative oxidizers are ideal for their low VOC concentrations and long, continuous operation.

This dual-RTO approach comes with slightly increased upfront capital investment, but avoids the tar issues that some are experiencing with their single RTO implementation. As today’s most widely accepted air pollution control technology across nearly every industry, the Regenerative Thermal Oxidizer, commonly referred to as an RTO, is robust, versatile, and extremely thermally efficient – with heat recovery efficiency reaching up to 97%. This is achieved through the storage of waste heat via structured ceramic blocks.