How does a dto work

A direct thermal oxidizer is a highly effective solution for dealing with waste streams with high calorific value. These are, for example, high VOC concentration inerted streams from production processes, fuel gas streams from reservoir purgiing, and...

Direct thermal oxidizers are a ceramic lined combustion chamber with a burner, usually natural gas or propane. The polluted gas stream is introduced into the hot oxidizer chamber, allowing to burn the pollutants and transform them to CO2 and H2O. this allwos to dispose of these waste gases in a clean and environmentally safe way

How does a direct thermal oxidizer work

The main element of the oxidizer is the combustion chamber: This is a cylindrical chamber, most often horizontal, which is made out of metal and lined with refractory material. The refractory material serves a dual purpose:

Isolates the system, keeping the combustion chamber hot and minimizing heat losses and hence fuel consumption. On the other hand, it keeps the outer chamber shell cold and hence protects personnel in the neighbourhood
Protects the metallic outer shell from abrasion and chemical attach from the pollutants in the air stream

One side of the cylinder has:

a (natural gas or propane) burner, which serves to preheat the chamber to the desired combustion temperature and maintain that temperature
One or multiple injection points for polluted streams. The design of these points differs depending on the stream: an air stream with VOC levels below 25% LEL is treated in a different way than an inert stream with 60% VOC
Entry points for atmospheric air dilution, often needed for supply adequate oxygen for the combustion process, and to avoid the system from overheating

The placement of all elements is carefully considered to ensure even and consistent burning throughout the chamber.

the other side of the cylindrical chamber has an exit, leading to a chimney or a posttreatment unit.

When is a direct thermal oxidizer used

Direct thermal oxidizers are commonly used in two settings:

When there is an ample supply of thermal energy (high VOC content streams), and hence the heat recovery found in regenerative and recuperative oxidizers is not required. This is often the case when the VOC concentration exceeds 40 g/Nm3
When the gas streams are potentially dangerous (e.g. inerted high VOC streams) or aggressive (HCl or HF laden stream) and simplicity and reliability of the system hold a high value.

What after the direct thermal oxidizer?

The exhaust gases from a direct thermal oxidizers have a temperature between 850°C and 1.100°C, depending on the application. A gas stream at this temperature usually has a high energetic value which might be (partially) recovered. To this purpose, it is possible to place heat exchangers (air-air or air-water) after the oxidizer to create hot air, hot water, steam, hot oil.. for your processes and as such improve the energy efficiency of the overall site and lower operating cost.

Sometimes, the exhaust gases from a direct thermal oxidizer still contain harmful compounds. This is e.g. the case when burning halogenated compounds, which results in the formation of HBr, HCl, HF... . In these cases, post-treatment of the exhaust gases is often required to meet emissions limits. This is, for example, a wet scrubbing system, or activated carbon.

Frequently asked questions about direct thermal oxidizers

What happens when halogenated compounds are burned?

Burning halogenated hydrocarbons produces acidic compounds such as HCl, HBr, and HF. Because these substances are highly corrosive, the thermal oxidizer must be designed using appropriate corrosion-resistant materials. In many applications, a downstream treatment system, typically a quench and wet scrubber, is required to remove these acids and comply with emission limits.

What temperature does a direct thermal oxidizer operate at?

Direct thermal oxidizers typically operate between 850°C and 1,100°C, depending on the pollutants to be destroyed and the required destruction efficiency. For readily combustible hydrocarbons, temperatures of 850°C to 900°C are often sufficient. More difficult compounds, such as halogenated hydrocarbons, or applications requiring exceptionally high destruction efficiencies, may require operating temperatures of up to 1,100°C. Higher temperatures generally result in higher fuel consumption and may require upgraded refractory and construction materials.

What is the difference between a direct thermal oxidizer and a recuperative or regenerative oxidizer?

Unlike recuperative and regenerative thermal oxidizers, a direct thermal oxidizer does not rely on a heat recovery system to preheat the incoming gas stream. This simpler design results in a highly robust and reliable system with minimal maintenance requirements. Direct thermal oxidizers are typically selected when the waste gas has sufficient calorific value to sustain combustion efficiently, or when process conditions demand the highest possible operational reliability and simplicity.

What pollutants can be treated in a direct thermal oxidizer?

Direct thermal oxidizers are commonly used to treat VOC-rich gas streams, solvents, hydrocarbons, odorous compounds, fuel gases, and hazardous air pollutants (HAPs). Their robust design also makes them suitable for challenging applications, including corrosive gas streams and inerted waste gases with high VOC concentrations that cannot be safely treated by many other abatement technologies.

How effective is a direct thermal oxidizer?

Most direct thermal oxidizers achieve destruction efficiencies of 95% to 99.99%. The achieved efficiency depends on factors such as the type and concentration of pollutants, combustion temperature, residence time, and mixing conditions. By carefully selecting the operating parameters and system design, a direct thermal oxidizer can be tailored to meet even the most stringent emission requirements.

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