Understanding the Differences Between Catalytic Oxidizers (CATOX) and Thermal Oxidizers (TOX)
Oxidizer Comparison: Catalytic Oxidizers vs. Thermal Oxidizers
Catalytic Oxidizers (CATOX) and Thermal Oxidizers (TOX) are both effective air pollution control devices used to remove volatile organic compounds (VOCs) and hazardous air pollutants (HAPs) from industrial exhaust streams. However, they operate using different means and are suited for different applications.
Comparing Catalytic Oxidizers (CATOX) to Thermal Oxidizers (TOX)
Thermal Oxidizers (TOX) and Catalytic Oxidizers (CATOX) both aim to control air pollution by oxidizing volatile organic compounds (VOCs) and hazardous air pollutants (HAPs). However, they operate at different temperatures and achieve VOC destruction through different means. TOX units rely on high temperatures, typically between 1400°F and 1500°F, to oxidize pollutants directly. In contrast, CATOX units use a catalyst to promote oxidation at lower temperatures, usually between 600°F and 650°F.
Main Differences
Catalyst presence reduces the fuel energy required
Both TOX and CATOX units achieve high destruction efficiencies by breaking the hydrocarbon bonds of VOCs and HAPs and recombining the freed carbon and hydrogen atoms with oxygen, to create carbon dioxide (CO2) and water vapor (H2O). Passing the airstream over a catalyst in a catalytic system provides an alternative reaction pathway for the breakdown of the hydrocarbon. The reaction happens at a lower temperature resulting in lower activation energy, making the process more energy efficient.
Performance Differences
Catalytic oxidizers have lower average VOC destruction
TOX units often exceed 99% VOC destruction efficiency by maintaining high temperatures for sufficient residence time, ensuring complete combustion of pollutants. CATOX units, on the other hand, achieve efficiencies often exceeding 95% and up to 99%.
Life Expectancy
Catalytic oxidizers have longer life
The high operating temperatures of TOX systems result in shorter life expectancy than CATOX systems. Metal heat exchangers exposed to the high temperatures in TOX systems slowly weaken the metal and the critical seals between clean/dirty air. In systems with metal heat exchangers, the life span of a catalytic unit is 2X that of TOX.
Other Considerations
Catalyst poisons/masking agents
Clean airstreams are well suited for treatment by both TOX and CATOX systems. However, catalyst can suffer degradation in performance when certain chemicals are present in an airstream. Common culprits are silicone, phosphorus, and halogens. These can "poison" the catalyst, or mask it, making it ineffective for VOC destruction. Catalyst can be very expensive to replace; most catalyst contains costly precious metals, such as platinum.
Particulates
Both organic and inorganic particulate can be an issue for CATOX systems, if present in sufficient volume, and specific types. The catalyst beds in CATOX units have narrow airflow paths, making it susceptible to plugging by particulates. TOX systems are also susceptible to plugging but significantly less than CATOX systems.
By comparing the two technologies, industries can make informed decisions based on their specific requirements. Both TOX and CATOX units offer robust solutions for air pollution control, but the best choice will depend on the operational conditions and goals of the facility.
Catalytic Oxidizer Flow Diagram
Thermal Oxidizer Flow Diagram
Choosing the Right Oxidizer
When deciding between purchasing a CATOX and a TOX, consider factors such as the type and concentration of pollutants, exhaust flow rates, energy consumption, and overall cost. Both technologies offer robust solutions for air pollution control, but the best choice depends on your specific application.
The most common alternative to both TOX and CATOX systems are regenerative thermal oxidizers (RTOs). Typically, if an RTO is a good match for an application, it is the best choice due to its long life, lowest total cost compared to TOX and CATOX systems. Another technology to consider pairing with any oxidizer technology is a VOC concentrator. It pre-conditions polluted air prior to passing through any oxidizer system (RTO, TOX, CATOX) for final VOC destruction, resulting in 40%+ fuel and electric savings with an oxidizer alone.
For more information on selecting or maintaining your oxidizer, contact the experts at Kono Kogs. We provide comprehensive solutions tailored to your requirements.
Common Questions related to TOX and CATOX Systems
Get quick answers for some of the most typically asked questions about thermal oxidizers and catalytic oxidizers
Catalyst utilized in a regenerative catalytic oxidizer (RCO) allows chemical reactions to occur at lower temperatures (700-800F) than they occur in a thermal oxidizer (typical 1400-1450F) or an RTO (typical 1600F).
TOXs typically operate at 1400o – 1500o Fahrenheit depending upon the VOC characteristics. Thermocouples inside the chamber monitor temperature and adjust gas burner firing as needed. Adequate temperature is essential to ensure VOC destruction efficiency. In most cases a data log of chamber temperature is required for air quality compliance.
Thermal Oxidizers (TOX) have a heat recovery (efficiency) of 70% typically, but some custom designs will use lower efficiency heat echangers if VOC concentrations are elevated. This technology has higher operating cost than most oxidizer systems.
It depends on numerous factors. See Selecting an Oxidizer for guidance or call us for guidance.
Direct, Regenerative and Recuperative. See Types of Catalytic Oxidizers.
Catalytic Recuperative Oxidizers destroy pollutants discharged in the exhaust air of industrial processes. They achieve high VOC destruction efficiency by heating and maintaining a polluted airstream at temperature (typically 600 to 650F) for a set “dwell” time as it passes through catalyst material. The lower operating temperature of a catalytic oxidizer results in much lower fuel use than thermal recuperative oxidizers. VOC destruction efficiency can reach 99+%. Catalytic oxidizers can operate with an integral heat exchanger for fuel savings, or for a lower capital cost, without a heat exchanger. Learn more here.
Catalytic Oxidizer Treating Foil Coating Emissions
Start-up company needed emission control with low capital & operating costs. We recommended a 12,000 scfm catalytic recuperative oxidizer with bead catalyst.
