Efficient Nitric Acid Scrubber: Design, Applications, Principle of Operation, and Selection Guidelines

HNO₃ is a corrosive liquid that can form in gas streams, condensing into acidic droplets or aerosols. The most common method of producing nitric acid is the Ostwald process, wherein ammonia is oxidized using oxygen in the presence of a catalyst. The reaction occurs in two steps:
1. 4NH3 + 5O2 → 4NO + 6H2O
2. 2NO + O2 → 2NO2, which then reacts with water to produce HNO₃.
Wet scrubbers, such as packed towers, are often employed to remove it, where the acid can be absorbed by water or an alkaline solution.
To ensure a safe and environmentally compliant atmosphere, it's essential to employ a nitric acid fume scrubber when dealing with air contaminants containing nitric acid.

The principle of operation for a nitric acid scrubber involves:

1. Gas Introduction: Contaminated gas with nitric acid fumes is introduced into the scrubber.
2. Contact with Scrubbing Liquid: As the gas flows through, it comes into direct contact with a scrubbing liquid, commonly water or an alkaline solution.
3. Absorption: The acid fumes are absorbed into the liquid, neutralizing the acid and forming a less harmful solution.
4. Separation: The cleaned gas is then separated from the scrubbing liquid and discharged, while the spent liquid is treated or disposed of.
5. Cleaned Gas Release: The now-cleaned gas is released into the atmosphere or directed to further treatment processes if necessary.

The nitric acid scrubber design process requires careful attention to the specific requirements of the application, safety measures, and environmental regulations. The goal is to efficiently remove or neutralize the acid vapors from exhaust gases.

Here's a more detailed approach to design a nitric acid scrubber.

Design Specifications

• Packing Material: If using a packed bed scrubber, choose an appropriate packing material that is chemically resistant to HNO₃.
• Gas Velocity: Maintain an optimal gas velocity to ensure maximum contact without flooding the system.
• Liquid Rate: Ensure adequate liquid-to-gas ratio for effective absorption.
• Nozzle Design: For spray towers, proper nozzle design ensures efficient distribution of the scrubbing liquid.

Safety Protocols and Measures

• When designing a nitric acid gas scrubber, it's essential to account for overpressure scenarios.
• Ensure corrosion-resistant materials are used.
• Design appropriate safety relief systems.

Scrubbing Liquid

• Water can be used as a scrubbing liquid for HNO₃.
• Depending on the specific application, you might also consider alkali solutions to neutralize the acid.

Instrumentation, Control, and Performance Monitoring

• Implement pH meters to monitor the acidity of the scrubbing liquid.
• Use flow meters to monitor and control gas and liquid flow rates.
• Implement temperature and pressure monitors as needed.
• After the nitric acid scrubber is in operation, routinely evaluate its performance.
• Collect samples of the treated gas to ensure acid is being effectively removed or neutralized.

Operational Optimization and Environmental Considerations

• Based on the performance evaluations, adjust operating parameters like liquid-to-gas ratio, liquid circulation rate, and gas flow rate for better efficiency.
• Manage the wastewater. Depending on the scrubbing liquid, the effluent will contain HNO₃ or nitrate salts. Ensure proper treatment or disposal.
• Monitor the exhaust gas for compliance with environmental regulations.

Maintenance Considerations

• Design with easy access for routine maintenance tasks like cleaning or replacing packing material.
• Monitor for signs of corrosion or material degradation.

Remember that this is a general guideline. The specific details and requirements may vary based on your application, local regulations, and the specific characteristics of your gas stream. We recommend consulting with our Torch-Air engineering specialists who have experience in scrubber design. We will select the necessary equipment and install it at your facility. Reach out, we'll help.