Thermal Oxidizer Types: How to Choose the Right System
Which Thermal Oxidizer Type Is Best?
No single thermal oxidizer configuration is best for every process. The appropriate system depends on exhaust flow, VOC and hazardous air pollutant (HAP) composition and concentration, oxygen and moisture content, particulate or catalyst-poisoning contaminants, required destruction efficiency, operating schedule, heat-recovery goals and permit conditions.
A thermal oxidizer—also called a thermal incinerator—controls suitable volatile organic compound (VOC), carbon monoxide (CO) and volatile HAP emissions through oxidation. For many hydrocarbon compounds, the principal products are carbon dioxide, water vapour and heat. Actual destruction and removal efficiency is system- and stream-specific and must be demonstrated under the applicable testing and regulatory requirements.
What Determines Oxidizer Performance?
Three interrelated combustion conditions are central to thermal oxidizer design:
- Temperature: the chamber must maintain a temperature appropriate for the compounds being treated.
- Residence time: the waste gas must remain at the required temperature long enough for the oxidation reaction.
- Mixing: adequate turbulence must bring the waste gas, oxygen and heat together throughout the chamber.
Compound chemistry, inlet concentration and flow variation also affect performance. Halogenated or otherwise corrosive streams can require additional materials of construction and downstream acid-gas controls. Operating limits should be established through engineering evaluation, permitting and performance testing rather than a universal temperature target.
Direct-Fired Thermal Oxidizers
A direct-fired thermal oxidizer sends the process stream to a combustion chamber without a primary heat-recovery exchanger. Its simpler arrangement can reduce initial complexity, but fuel use may be higher when the incoming stream has a low heating value or the equipment operates for long periods. It can suit intermittent service, smaller flows or streams that make heat recovery impractical.
Recuperative Thermal Oxidizers
A recuperative thermal oxidizer uses a non-contact heat exchanger to transfer energy from treated exhaust to the incoming process stream. This reduces the burner energy required to reach the operating temperature. One or more stages of heat recovery may be used, subject to stream properties, exchanger materials, fouling risk and economics.
Regenerative Thermal Oxidizers
A regenerative thermal oxidizer (RTO) alternates airflow through heat-storage media beds, commonly ceramic, to recover energy from the treated gas and preheat the incoming stream. RTOs can provide high heat recovery for continuous, high-flow applications, but valves, media, pressure drop and potential particulate or condensable loading must be considered.
Catalytic Oxidizers
A catalytic oxidizer uses a catalyst to promote oxidation at a lower operating temperature than a comparable non-catalytic thermal oxidizer. It may use recuperative or regenerative heat recovery. Catalyst compatibility is essential because particulates, silicon, phosphorus, sulfur, halogens and some metals can foul or deactivate certain catalysts.
Terminology note: RCO commonly means regenerative catalytic oxidizer. A recuperative thermal oxidizer should not be labelled RCO without defining a different project-specific abbreviation.
Information Needed to Select a System
- Normal, minimum and maximum airflow
- VOC and HAP species, concentrations and variability
- Oxygen, moisture, particulate and aerosol content
- Potential catalyst poisons or corrosive combustion products
- Required destruction efficiency and outlet limits
- Operating hours, turndown and startup frequency
- Available utilities, footprint and heat-recovery opportunities
- Permit, monitoring and performance-test requirements
Thermal Oxidizer Questions
What Are the Main Types of Thermal Oxidizer Systems?
Common configurations include direct-fired thermal oxidizers, recuperative thermal oxidizers and regenerative thermal oxidizers. Catalytic oxidizers are a related category that uses a catalyst to promote oxidation at a lower temperature.
What Does RCO Mean?
RCO commonly means regenerative catalytic oxidizer. A recuperative thermal oxidizer instead uses a heat exchanger to transfer heat from treated exhaust to the incoming process stream.
For equipment configurations, visit HiTemp thermal oxidizer systems. For a process-specific review, contact HiTemp Tech Corporation with available stream data and emissions requirements.