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Emergency Vent Scrubber

Typical applications of emergency vent scrubbers in chemical processes are to absorb emissions, such  as chlorine, bromine, phosgene, sulfur dioxide, NOx, HF and ammonia. For the neutralization of these gases, caustic soda and caustic potash solutions are used. The gas flow passes the scrubbing liquid and in case of emergency, the release of toxic or critical gases is prevented. SensoTech inline analyzers are often used to monitor the scrubbing liquid, which improves the system stability and quality.

Sonic velocity measurement with LiquiSonic® 40


The scrubbing liquid of an emergency vent scrubber circulates and is continually in contact with the gas stream to be cleaned. If toxic or environmentally  hazardous chemicals are included in this stream, they will be absorbed. Even during standard operation (without emergency), certain components, e.g. CO2, are chemically bound and the NaOH concentration decreases. In order to ensure an effective absorption in the event of an emergency and a sufficient volume of scrubbing liquid, the concentration of NaOH and salts (NaCl and Na2CO3) must be monitored.

If the NaOH content is under limit, it must be redosed. In case of too high salt content, the salt must be removed from the circulation stream, to prevent crystallization in the system and blocked nozzles. The LiquiSonic® 40 analyzer allows the concentration measurement of 3-components-liquids, due to the parallel detection of two physical quantities such as sonic velocity and conductivity. 


The LiquiSonic® immersion sensor is easily installed directly into pipelines. A typical installation point, combined with a conductivity meter, are DN 80 pipelines from the scrubber to the regeneration tank.
The robust sensor construction and the optional special materials, like HC2000, promote long process life. 

The LiquiSonic® controller 40 is connected to the LiquiSonic® ultrasonic sensor and the device for the second physical value (conductivity meter). The controller displays NaOH concentration and salt content. 

Typical measuring range:
NaOH concentration range: 5 to 20 wt%,
Na2CO3/NaCl concentration range: 5 to 30 wt%
temperature range: 30 to 60 °C

Customer value

The LiquiSonic® analyzer provides a precise inline concentration measurement with real-time monitoring.  Due to automatic control, a sufficient level of scrubbing liquid is maintained, thus keeping the scrubber at its optimal absorption efficiency. 

LiquiSonic® enables a reduction of labor cost through the elimination of manual process steps:

  • time saving: 1 h per day

The prevention of an over- and underdosing leads to the reduction of material input for the scrubbing liquid.

The LiquiSonic® system ensures consistent plant and system safety, even in emergency case.