Control Air Pollution with a Low-Temperature Catalytic Oxidizer
How Does a Catalytic Oxidizer Control Air Pollution?
A catalytic oxidizer heats a suitable VOC- or hazardous-air-pollutant-containing gas stream and passes it through a catalyst that promotes oxidation. For many hydrocarbon compounds, the principal products are carbon dioxide (CO2), water vapour (H2O) and heat. The required destruction efficiency and operating limits must be established for the specific process and applicable permit.
Catalytic oxidizers can be used for industrial exhaust streams containing compatible volatile organic compounds (VOCs), volatile hazardous air pollutants (HAPs) and some odorous compounds. They are related to thermal oxidizers, but the catalyst allows the oxidation reaction to proceed at a lower temperature than a comparable non-catalytic system.
Why Can Catalytic Oxidation Use a Lower Temperature?
A catalyst provides a reaction pathway that promotes oxidation without being consumed in normal operation. The gas stream is heated to the required catalyst inlet temperature, mixed with oxygen and directed through the catalyst bed. Performance depends on:
- the VOC and HAP species and concentrations;
- catalyst formulation and available active surface area;
- gas temperature, oxygen content and residence time;
- flow distribution through the catalyst bed;
- particulate, aerosol and condensable loading; and
- the presence of catalyst poisons or masking agents.
There is no single operating-temperature range suitable for every catalytic oxidizer. The required setpoint is determined by the waste-stream chemistry, catalyst supplier data, equipment design and demonstrated operating conditions.
Does a Catalytic Oxidizer Always Reduce Fuel Use?
Lower reaction temperature can reduce auxiliary fuel demand, but a fixed percentage saving should not be assumed. Actual fuel use depends on inlet VOC concentration, airflow, operating schedule, heat recovery, pressure drop, burner efficiency and process variability.
A recuperative catalytic oxidizer uses a heat exchanger to preheat incoming gas with energy recovered from the treated exhaust. Regenerative catalytic systems instead alternate airflow through heat-storage media. The appropriate configuration depends on the application and lifecycle economics.
When Is a Catalytic Oxidizer Appropriate?
Catalytic oxidation is most suitable when the contaminants can be oxidized effectively and the stream is compatible with the selected catalyst. Particulates and compounds containing silicon, phosphorus, sulfur, halogens or certain metals may foul, mask or deactivate some catalyst formulations. Pretreatment, filtration or a different control technology may therefore be required.
System selection should consider normal and maximum airflow, contaminant composition and variability, oxygen and moisture, required destruction efficiency, turndown, startup frequency, monitoring requirements and maintenance access. Final performance must be supported by project-specific engineering and testing.
Catalytic Oxidizer Questions
Is a Catalytic Oxidizer the Same as a Thermal Oxidizer?
Both technologies oxidize suitable gaseous contaminants, but a catalytic oxidizer uses a catalyst to promote the reaction at a lower temperature. A conventional thermal oxidizer relies on higher gas temperature, adequate residence time and mixing without a catalyst bed.
What Information Is Needed to Evaluate a Catalytic Oxidizer?
Useful starting information includes airflow, VOC and HAP species, concentration range, oxygen, moisture, particulate and aerosol content, potential catalyst poisons, required outlet limits, operating schedule and available utilities.
For system configurations, visit HiTemp catalytic oxidizer systems. To discuss a specific exhaust stream, contact HiTemp Tech Corporation.
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