Flow Measurement of Gaseous Hydrochloric Acid during MDI Production

During the production process of the intermediate product MDI, which is important for the plastics industry, gaseous hydrochloric is produced as a byproduct.
It is reprocessed and transferred to the chlorine division at the customers chemical site in a concentration of approx. 32%. The desired concentration is set by adding diluted acid to the HCI absorbers. In order to load them evenly and add the correct amount of diluted acid, the quantity of HCI gas must be measured at the inlet of the absorber.

The facility cannot be operated without flow measurement at this point. Due to the specific requirements regarding the reliability of the measurement, this was, until now, conventionally done using a differential pressure meter. However, even this apparently sound measuring equipment did not reach satisfactory service lives. In particular, the small tubes of the pressure transducer proved to be extremely susceptible to wear. The result were frequent leakages. Necessary maintenance work meant the process to be shutdown and involving an enormous amount of work, where the pipelines have to be emptied and cleaned under compressed air conditions.

Since the installation of the non-invasive FLUXUS clamp-on ultrasonic gas flow meter, these nuisances are finally a thing of the past. Even the slight negative pressure of -20 mbar at the measuring point is not a challenge to the FLUXUS flow meter. The measured flow rates are fed into the process control system and used to control the addition of the diluted acid.

Advantages

  • Accurate and reliable flow measurement without media contact
  • No pressure loss, No wear and tear by the aggressive medium, No risk of leakages
  • Installation, set-up and any necessary modifications or maintenance of the measuring system without pipe work
  • No process interruption
  • Reliable, continuous regulation of concentration

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