Thermal and Catalytic Oxidizers (RTO): How They Work
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Thermal and Catalytic Oxidizers (RTO): How They Work
By the BM Process Management engineering team · Reviewed by our oxidation and emission control engineers · Last reviewed: September 2026
A regenerative thermal oxidizer (RTO) is an air pollution control device that destroys volatile organic compounds and other combustible pollutants by heating the gas stream until they oxidise into carbon dioxide and water, while recovering most of its own heat to stay energy-efficient. Alongside catalytic oxidisers, RTOs are among the most reliable ways to meet strict VOC destruction requirements.
This page explains how thermal and catalytic oxidisers work, how an RTO and a recuperative unit differ, where each is used across industries, how electric RTOs fit into decarbonisation, and how the same catalytic oxidation principle appears in ammonia oxidation and the Ostwald process. BM Process helps match the right oxidation technology to an emission stream.
Thermal and Catalytic Oxidizers (RTO): Frequently Asked Questions
Thermal oxidiser and RTO basics
What is a thermal oxidizer and what does it do?
A thermal oxidizer is an air pollution control device that destroys volatile organic compounds and other combustible pollutants by heating the gas stream to a high enough temperature for them to oxidise into carbon dioxide and water. Its job is to meet the destruction efficiency required by the plant’s permit, turning a stream that would otherwise emit pollutants into a compliant one. It is a key part of a wider emission control strategy.
How does a thermal oxidizer work, and what is the thermal oxidizer process?
A thermal oxidizer works by bringing the polluted gas to a high enough temperature, for long enough and with enough mixing, that the VOCs and other combustibles oxidise fully to carbon dioxide and water. The three factors of temperature, residence time and turbulence together determine how completely the pollutants are destroyed. Different designs mainly differ in how efficiently they reach and hold that temperature.
What is a regenerative thermal oxidizer (RTO)?
A regenerative thermal oxidizer is a thermal oxidizer that recovers most of its own heat using ceramic media beds, which preheat the incoming gas with heat from the outgoing clean gas. This regeneration makes RTOs highly energy-efficient, so they are the usual choice for large, continuous VOC streams where running cost matters.
How does a regenerative thermal oxidizer work?
In an RTO, the polluted gas passes through a hot ceramic bed that preheats it, then into a combustion chamber where VOCs are destroyed, and out through a second ceramic bed that captures the heat from the clean gas. Valves periodically switch the flow direction so the beds alternate between absorbing and releasing heat. This cycling is what gives an RTO its high thermal efficiency.
What are the main parts of an RTO, including the burner, chamber and heat recovery system?
An RTO combines ceramic media beds for heat recovery, a combustion chamber with a burner that raises the gas to oxidation temperature, and flow-switching valves that cycle the beds. Together the burner, chamber and ceramic heat recovery system deliver both high destruction efficiency and low fuel use.
Catalytic oxidisers and thermal vs catalytic
What is a catalytic oxidizer?
A catalytic oxidizer destroys VOCs at a much lower temperature than a purely thermal unit by passing the gas over a catalyst that speeds up oxidation. Because it runs cooler it uses less fuel, though the catalyst must be protected from poisons and masking agents. It suits streams with the right composition and moderate concentrations.
What is the difference between a catalytic and a thermal oxidizer?
A thermal oxidizer relies purely on high temperature to destroy pollutants, while a catalytic oxidizer uses a catalyst to achieve destruction at lower temperature and lower fuel use. Thermal, especially regenerative, units handle a wider range of streams and contaminants; catalytic units save energy but need compatible, catalyst-safe gas. The best choice depends on flow, concentration and contaminants.
What is a recuperative oxidizer and how does it differ from a regenerative one?
A recuperative oxidizer recovers heat through a heat exchanger that transfers warmth from the clean outgoing gas to the incoming dirty gas, whereas a regenerative oxidizer stores and releases heat using ceramic beds. Regenerative units generally recover more heat and suit large continuous flows, while recuperative units can be simpler and well suited to smaller or lower-flow applications.
What is a catalytic recuperative oxidizer?
A catalytic recuperative oxidizer combines two fuel-saving ideas: a catalyst that lowers the required oxidation temperature, and a recuperative heat exchanger that preheats the incoming gas with heat from the clean outgoing gas. Together these can substantially reduce fuel use on suitable streams, provided the gas is compatible with the catalyst.
Ammonia oxidation and catalysis
What is catalytic oxidation, in general terms?
Catalytic oxidation is the use of a catalyst to make an oxidation reaction proceed faster and at a lower temperature than it otherwise would. In pollution control it is used to destroy VOCs efficiently; in chemical synthesis it is used to make products such as nitric acid from ammonia. In both cases the catalyst lowers the energy needed for the reaction without being consumed by it.
What is catalytic oxidation of ammonia (NH3 oxidation)?
Catalytic oxidation of ammonia is a reaction in which ammonia is oxidised over a catalyst, most famously in the Ostwald process where a platinum-based catalyst converts ammonia to nitric oxide as the first step in making nitric acid. The same principle of catalyst-assisted oxidation underlies both this industrial synthesis and catalytic pollution-control devices.
What catalyst is used in the Ostwald process for ammonia oxidation?
The Ostwald process uses a platinum, or platinum-rhodium, gauze catalyst to oxidise ammonia to nitric oxide at high temperature. The precious-metal catalyst allows the reaction to proceed quickly and selectively, which is why catalyst selection and condition are so important to yield in ammonia oxidation.
What happens in an ammonia oxidation reactor?
In an ammonia oxidation reactor, a mixture of ammonia and air is passed over a platinum or platinum-rhodium catalyst at high temperature, where the ammonia is oxidised to nitric oxide as the first step in nitric acid production. The reaction is fast, and catalyst condition, temperature and gas mixture strongly influence how selectively the desired product forms.
Electric options, applications and servicing
What is an electric RTO or electric thermal oxidizer?
An electric regenerative thermal oxidizer uses electrical heating instead of, or alongside, fuel firing to reach oxidation temperature. As industries decarbonise, electric and electric-heated oxidisers are increasingly attractive because they can cut or eliminate direct combustion emissions, particularly where low-carbon electricity is available.
Where are electric and hybrid oxidisers most useful, including tank terminals?
Electric and electric-heated RTOs are most useful where a site wants to cut or remove the direct combustion emissions of a fuel-fired unit, and where reasonably clean or low-carbon electricity is available. They are of growing interest at tank terminals and in sectors under pressure to decarbonise. The best fit depends on the electricity supply, the VOC load and the site’s wider energy and emissions goals.
Which industries use regenerative thermal oxidizers?
RTOs are used across the chemical and petrochemical industries, at oil and gas facilities and tank terminals, in pharmaceuticals and coatings, and in emerging areas such as renewable natural gas (RNG), green hydrogen, solar manufacturing and other sectors. Wherever a large, continuous VOC stream must be destroyed efficiently, an RTO is a common choice because its heat recovery keeps running costs down. The unit is engineered to each application.
What is industrial RTO software and control?
RTO control software manages the burner, the flow-switching valves and the temperature profile so the unit maintains its destruction efficiency and heat recovery safely and automatically. Sound control is central to reliable, efficient operation and to demonstrating performance.
What does oxidiser maintenance and servicing involve?
Oxidiser maintenance focuses on the parts that determine destruction efficiency and heat recovery: the burner or heating system, the ceramic media in an RTO, the catalyst in a catalytic unit, the flow-switching valves, and the instrumentation and controls. Catalytic units also need the catalyst checked for poisoning or masking. Keeping these in good condition maintains both compliance and energy efficiency over the unit’s life.
Selecting and specifying an oxidiser
How do I choose the right oxidizer for VOC control?
Selection depends on the gas flow rate, VOC concentration and variability, the presence of catalyst poisons, energy costs and the destruction efficiency you must reach. A regenerative thermal oxidizer suits large continuous streams; a catalytic unit can cut energy where the gas allows it. Where vapours are valuable, a vapour recovery unit may be preferred over destruction, and VOC monitoring verifies whichever route is chosen. BM Process helps match the right oxidation technology to your emission stream; outline your requirements at https://bmprocess.nl/.
Can BM Process design, specify or service a thermal or catalytic oxidiser?
Yes. BM Process helps select, specify and integrate thermal, regenerative and catalytic oxidisers as part of an emission control train, matched to the flow, concentration and contaminants of the stream and to the plant’s permit obligations. Because we combine process engineering with emission control, the oxidiser is designed to fit the process and the wider abatement strategy rather than in isolation.
About BM Process Management
Written and reviewed by the BM Process Management engineering team. BM Process Management is an industrial process and emission control engineering consultancy based in the Netherlands, selecting, specifying and integrating thermal and catalytic oxidisers for industrial clients across Europe, in partnership with Krantz Clean Air Solutions. The answers on this page reflect field experience in oxidation and VOC abatement.
