Fishmeal Odor Treatment with a Regenerative Thermal Oxidizer
Fishmeal production continuously releases trimethylamine and hydrogen sulfide, the two substances that are the main source of the pungent fishy odor around the plant. Treatment methods such as scrubbing and adsorption can only achieve a partial reduction of the odor. Under continuous high-load production, the odor can still escape to the outside, creating the risk of community complaints as well as hidden risks in emission compliance.
An RTO can destroy odor compounds at the molecular level, but whether such a system performs reliably in a fishmeal production scenario depends not so much on the equipment itself as on a complete engineering assessment based on the actual composition of the waste gas, and in particular on the acidic by-products formed after the oxidative conversion of the waste gas. These components not only impose constraints at the emission level, but also cause corrosion damage to the low-temperature sections of the equipment and lead to component failure, so a targeted design is necessary.
1. Two Core Technical Challenges in Fishmeal Waste Gas Treatment
Trimethylamine and hydrogen sulfide have extremely low odor thresholds; even when the residual concentration remains very low, they can still be perceived. Water scrubbing and adsorption merely achieve a phase transfer of the pollutants and can hardly maintain a low residual level stably over the long term. Once the adsorption medium approaches saturation or the scrubbing agent loses its effectiveness, the odor is discharged directly.
When an RTO is used to destroy these odor molecules, simply sending the waste gas into the combustion chamber is not enough. Complete decomposition of the molecules requires not only a matching furnace temperature, but also a sufficiently long residence time of the flue gas in the combustion chamber. If the temperature is insufficient or the residence time is too short, some organic molecules are only partially decomposed and the odor still escapes to the outside. Most fishmeal plants operate in continuous production mode and generate waste gas without interruption, so the treatment system has to be adapted to non-stop operating conditions.
The second challenge is less visible: oxidation is not the end of the problem. Destroying hydrogen sulfide produces acidic by-products (sulfur oxides that form acid on cooling, for example). These by-products raise emission-compliance concerns and corrode the low-temperature sections of the equipment, potentially causing component failure. A design that ignores them removes the odor but creates a new maintenance and compliance burden.
2. Engineering Approach for Fishmeal Operating Conditions
To address the two problems of degrading the native odors in the fishmeal waste gas and of the secondary emission risks brought by RTO combustion, the whole RTO system needs to be engineered from the perspectives of process logic and material selection logic.
2.1 Process Logic: Achieving Complete Decomposition of the Odor Components with the RTO
An RTO relies on a distribution valve to achieve uninterrupted airflow distribution. After the waste gas enters the equipment, it is guided by the distribution valve into the individual regenerative chambers. The waste gas flows through the regenerative ceramic, absorbing the heat stored in the ceramic and heating up in preparation for the subsequent high-temperature oxidation, before it enters the combustion chamber. Inside the combustion chamber, the waste gas is held in a high-temperature environment for the necessary residence time, allowing the trimethylamine and hydrogen sulfide to be oxidatively decomposed.
The purified high-temperature flue gas is then distributed to the remaining regenerative chambers, transferring its heat to the ceramic media; the ceramic completes its heat storage and the temperature of the flue gas drops accordingly. Having released its heat, the flue gas leaves the RTO and travels through the ductwork to the stack. The ceramic media cycle continuously between heat absorption and heat release, giving the RTO a very high heat recovery capacity and thereby reducing auxiliary fuel consumption.
Fig. 1 The process diagram
2.2 Material Selection Logic: Matching the Media Characteristics of the Different RTO Sections
The fan inside the RTO system, the inlet distribution valve and the low-temperature section of the stack come into contact with low-temperature flue gas carrying acidic by-products, and the corrosion risk is concentrated at these locations. During the engineering design stage, all the high-corrosion points along the RTO process must be identified, and the components that come into direct contact with the low-temperature corrosive flue gas must be made of suitable corrosion-resistant materials. The stack likewise needs a sectional protection design based on the conditions under which it comes into contact with the flue gas.
Conclusion
When carrying out a waste gas treatment assessment, it is essential to first map out the complete set of waste gas operating parameters. Simply purchasing a standardized RTO unit does not automatically resolve the various risks arising from corrosion and secondary emissions. Only on the basis of the actual operating conditions can an RTO engineering solution tailored to the site be determined.