Sulfuric Acid Production Plants

The process control of a sulfuric acid plant needs good and reliable detection of gas phase sulfur dioxide (SO2). To measure SO2 is a challenge due to the corrosive environment and high concentration of SO2. Several places in the process needs to be monitored and to transport the sample gas is difficult. A large dynamic range is needed as the SO2 concentration can vary between 15% volume and a few mg/m3. Most systems installed need a lot of maintenance, sometimes as often as every day.

The OPSIS DOAS system is different and provides sulfuric acid plants with an accurate analyser that can measure in temperatures up to 1000° C and with a maximum pressure of 1 Bar (G).
The system operates with a minimum of maintenance. The OPSIS DOAS system is a non-contact method, using an optical measurement path that operates across a duct. The optical light is transported in an optical fibre to the analyser and one analyser can operate several paths. 

Besides the measurements of SO2, additional gases such as sulfur trioxide (SO3), water vapour (H2O) and oxygen (O2) can be measured.


  • Combines the benefits of UV/FTIR DOAS and TDL technology
  • Best performance according to QAL 1 certification
  • Longest calibration interval according to QAL 1 certification
  • No sampling required, non-contact measurement system
  • Operates with a minimum of maintenance
  • Low energy consumption
  • Gas calibration only once per year
  • Internationally approved
  • Thousands of systems installed worldwide
  • Serviced by highly skilled service network

    System Overview

    UV and FTIR DOAS and TDL monitoring systems for sulphuric acid plants

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  • Kemira Chemicals

    Demands from the authorities led the Swedish chemical producer Kemira Chemicals to install their first OPSIS system in 1988. Over the years, they have installed another five monitoring paths for measurement of SO2 and NOx.

    “The system just continues to run…”

    Read the full case here »