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Case Study - Packed Tower Scrubber System for NH3 and H2S Removal

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Customer’s Problem

The off-gases originate from a large paddle dryer that processes egg waste, along with other miscellaneous equipment such as material conveyors, two vessels, and two dumpsters.

During the dehydration process, the egg waste releases odorous compounds—specifically ammonia (NH3) and hydrogen sulfide (H2S)—along with water vapor. Most of the water vapor is condensed before the remaining air streams combine and enter the scrubber system.

Inlet Gas Conditions and Required Removal Efficiency

  • Contaminants: NH3 and H2S

  • Minimum Overall Removal Efficiency: 99%

  • Desired Outlet Composition:

    • H2S: <= 1 ppm

    • NH3: <= 3 ppm

  • Normal Gas Flow Rate: 5,000 ACFM (Air, H2O, H2S, and NH3)

  • Normal Inlet Temperature: 84°F

  • Inlet Pressure: –2.0 inches H2O

Solution Provided

To address the customer’s requirements, two packed tower scrubbers were supplied. The first stage uses sulfuric acid as a chemical reagent to remove NH3, while the second stage uses caustic and bleach to remove H2S. The relevant chemical reactions are as follows:

H2SO4(aq)+2NH3→(NH4)2SO4(aq)

H2S+2NaOH(aq)+NaOCl→Na2SO4(aq)+NaCl(aq)+H2O

Both scrubbers were installed indoors as part of the egg waste system. To conserve space, two tubular fans were mounted on a single skid—one operational and one on standby. Pick-up branches from each off-gas point vent into a main trunk line that feeds the vent gas into the scrubber system.

The system is equipped with sensors for pH, ORP, conductivity, differential pressure, and pressure, as well as level switches, level detectors, leak detectors, pneumatically controlled valves, and solenoid valves. Both on/off and PID loop controls are integrated with a PLC, allowing the system to operate automatically. In the event of any abnormality, the PLC triggers an alarm and/or automatically shuts down the system.

Packed Towers installed


Results

During startup and commissioning, the NH3 and H2S concentrations in the incoming vent gas varied. However, the Continuous Emission Monitoring System (CEMS) on the exhaust duct never triggered any alarms. Outlet NH3 levels remained consistently below 3 ppm, and H2S levels below 1 ppm, meeting the desired performance targets.
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