What Are Thermal Oxidisers?
A thermal oxidiser is an air pollution control system that destroys volatile organic compounds (VOCs) and other hazardous gases by heating contaminated air to a high enough temperature that the pollutants oxidise — chemically breaking down into carbon dioxide and water vapour. Unlike scrubbing or filtration technologies, which physically remove pollutants from a gas stream, a thermal oxidiser eliminates them entirely through combustion, making it one of the most complete destruction methods available for organic air pollutants.
“Thermal oxidiser” is really a family name covering several different configurations, each built around the same core combustion principle but optimised differently for efficiency, fuel cost, or the specific process it’s treating.
How Does a Thermal Oxidiser Work?
1. Contaminated air enters the oxidation chamber. VOC-laden process air is drawn into the system, typically pre-mixed or evenly distributed to ensure uniform contact with heat.
2. The air is heated to oxidation temperature. Using a burner (gas- or liquid-fuel-fired) and/or recovered heat, the air is raised to the temperature needed for oxidation — typically in the 750–1,100°C range, depending on the process and target destruction efficiency.
3. Pollutants oxidise. At this temperature, with sufficient oxygen present (typically around 6% excess O₂) and enough residence time, VOCs and other organic pollutants chemically break down into CO₂ and water vapour.
4. Heat is managed and gas is discharged. Depending on the configuration, some or most of the heat generated is recovered for reuse, and the treated gas is cooled as needed before release or further downstream treatment.
Types of Thermal Oxidiser Configuration
Thermal oxidisers are supplied in several configurations, chosen based on the required destruction efficiency, energy costs and process integration.
– After burners / residence chambers — the simplest configuration, providing sufficient time and temperature for oxidation without additional heat recovery
– Direct-fired oxidation — achieves up to 100% destruction removal efficiency (DRE), with no built-in heat recovery, though alternative heat recovery methods can be added
– Recuperative thermal oxidation — uses a continuous heat exchanger to preheat incoming air with heat recovered from the treated gas, typically achieving over 99% DRE and around 75% heat recovery
– Regenerative thermal oxidation (RTO) — uses switching ceramic heat-storage beds to achieve around 98% DRE and up to 95% heat recovery, at the cost of greater mechanical complexity and footprint
– Pyrolysis and pre-combustion chambers — operate above roughly 650°C and 850°C respectively, often as a staged approach for particular waste streams
– Post-combustion NOx abatement systems — added where NOx emissions need to be controlled downstream of oxidation
– Energy recovery – is possible using a waste heat boiler to raise steam or a thermal oil system to recover high-grade heat for use elsewhere in the overall process/system.
What Do Thermal Oxidisers Remove?
– Volatile organic compounds (VOCs) — solvents, hydrocarbons and similar organic emissions
– Hazardous air pollutants (HAPs), including amine-, halogen- and sulphur-containing hydrocarbons
– Odour-causing organic compounds
– Solid, sludge, liquid and gaseous waste streams, depending on system design
Because destruction relies on combustion rather than absorption or adsorption, thermal oxidation works regardless of how soluble or reactive a compound is — but on its own, it isn’t suited to particulate or acid gases, which typically need a scrubbing stage either instead of or alongside oxidation.
Where Are Thermal Oxidisers Used?
– Chemical and pharmaceutical manufacturing — destroying solvent vapours from reactor and process vents
– Coatings, printing and surface finishing — treating solvent-laden exhaust from drying and curing processes
– Waste and wastewater treatment — destroying odour and organic compounds to a very high removal standard
– Any process needing compliance with IED (2010/75/EU) emission limits for VOC, CO and organic compound emissions
Choosing Between Thermal Oxidiser Configurations
The right configuration comes down to balancing destruction efficiency, fuel cost and capital cost against the specific process:
– Direct-fired systems suit lower, intermittent flows where capital cost matters more than ongoing fuel efficiency
– Recuperative systems suit continuous, moderate-flow applications where a simpler heat exchanger design is preferred over the mechanical complexity of ceramic bed switching
– Regenerative (RTO) systems suit large, continuous flows with low-to-moderate VOC concentrations, where the fuel savings from very high heat recovery have the biggest impact on running costs
Thermal Oxidisers vs. Other Air Pollution Control Technologies
– Carbon filters physically adsorb VOCs rather than destroying them, and don’t require combustion — a lower-cost option at lower concentrations, but requiring periodic carbon replacement rather than permanently eliminating the pollutant.
– Chemical scrubbers and bio-trickling filters target acid/basic gases and biodegradable odour compounds respectively, rather than the broad range of organic compounds a thermal oxidiser destroys through combustion.
– Quench vessels are sometimes needed downstream of a thermal oxidiser to cool the hot flue gas before it reaches further treatment stages.
Benefits and Limitations
Benefits:
– Permanently destroys organic pollutants rather than transferring them to another medium
– Multiple configurations available to match flow, concentration and cost requirements
– Process guarantees available covering TOC, CO, dust, dioxin and NOx emissions
– Turndown capability typically up to 5:1 on-ratio, with up to 10:1 overall operating range
Limitations:
– Requires ongoing fuel input unless operating at high, self-sustaining VOC concentrations
– Higher capital cost than simpler adsorption-based technologies for lower-concentration applications
– Not suited to particulate or acid gases on its own
– Higher-efficiency configurations (recuperative, regenerative) add mechanical complexity and footprint
Frequently Asked Questions
What is a thermal oxidiser used for?
A thermal oxidiser is used to destroy volatile organic compounds, hazardous air pollutants and odour-causing organic compounds from industrial exhaust air by heating them to a temperature where they chemically break down into carbon dioxide and water vapour.
What temperature does a thermal oxidiser operate at?
Thermal oxidisers typically operate in the 750–1,100°C range, with the exact temperature depending on the pollutants being treated and the destruction efficiency required.
Does a thermal oxidiser need continuous fuel input?
It depends on VOC concentration and configuration. At sufficiently high pollutant concentrations, a thermal oxidiser can become largely self-sustaining (autothermal), needing little or no auxiliary fuel; at lower concentrations, ongoing fuel input is required to maintain oxidation temperature.
What standards do thermal oxidiser systems need to comply with?
Thermal oxidiser systems are typically designed to comply with standards including EN 746-1 and EN 746-2 (industrial thermoprocessing and combustion safety), EN 298 (automatic gas burner control), and NFPA 82/86 (incinerators, ovens and furnaces), supporting safe operation and burner management.
Explore ERG’s Thermal Oxidiser Technology
For full engineering detail across all configurations, see ERG’s dedicated technical page, which remains the authoritative source on this technology:
– Thermal Oxidisers — full configuration range, design features and compliance standards – What Is a Regenerative Thermal Oxidiser (RTO)? — the deep dive on the highest heat-recovery configuration – Carbon Filters Guide — the physical alternative for lower-concentration VOC removal – Quench Vessels Guide — a common downstream stage for cooling hot flue gas
Talk to our team about a thermal oxidation solution for VOC or hazardous gas destruction at your site.
