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Concentration Measurement

Tips for the Process Measurement of Sulfuric Acid from 0 to 110 Percent

| Author / Editor: Gerald Schwarz, Kornelia Fröch* / Dr. Jörg Kempf

Sulfuric acid, a color- and odorless oily liquid that is soluble in water in any ratio, is a central substance in the chemical industry.
Sulfuric acid, a color- and odorless oily liquid that is soluble in water in any ratio, is a central substance in the chemical industry. (Source: / Zoefkris / CC BY-SA 4.0)

For the production of sulfuric acid and oleum, fertilizers, batteries and detergents as well as oil refining, chemical synthesis, and wastewater processing an accurate and reliable measurement of sulfuric acid is important.

Sulfuric acid (H2SO4), a color- and odorless oily liquid that is soluble in water in any ratio, is a central substance in the chemical industry. To guarantee highest accurate H2SO4 concentration measurement in the process, the physical property which shows the biggest change upon change in acid concentration should be employed. Depending on the measuring range, different measuring methods (density and sound velocity) are available to achieve highly accurate measurement results. Anton Paar sensors are suitable wherever H2SO4 measurement is required and cover the entire concentration range of H2SO4 (0 to 100 %) as well as in the oleum range (0 to 45 % free SO3).

Depending on the application Anton Paar offers different setups for the online concentration measurement of H2SO4 solutions and oleum.
Depending on the application Anton Paar offers different setups for the online concentration measurement of H2SO4 solutions and oleum. (Source: Anton Paar)

The acidic nature and the specific behavior of H2SO4 at different concentrations require special materials and instruments. Depending on the application Anton Paar offers different setups for the online concentration measurement of H2SO4 solutions and oleum (see table). All sensors can be equipped with the transmitter Pico 3000. This transmitter can be integrated into the electronics housing of the sensor or into a remote control housing. Different interfaces are offered for direct communication with your plant. A human-machine interface (HMI) is also available as an option.

H2SO4 Concentration Monitoring 0 to 90 %

The highly accurate density sensor L-Dens 7400 Version TAN with the wetted parts made of Tantalum is the perfect solution for H2SO4 concentration measurement from 0 to 90 % w/w. Density has a steep and almost linear dependence and ensures continuous and highly accurate monitoring of the H2SO4 concentration. The modular design of the density sensor allows different possibilities for an easy installation into the process. The sensor can be installed inline (see Gallery: Fig. 1a) or in a bypass system (Fig. 1b).

H2SO4 Concentration Monitoring 90 to 100 %

The L-Sonic 5100 Version HAS sound velocity sensor was specially designed to measure sulfuric acid from 90 to 100 % w/w with very high accuracy as the sound velocity is strongly influenced by a concentration change. Using Hastelloy Hybrid-BC1, the newest generation of corrosion resistance material, no plastic coating is required which would negatively influence the concentration measurement. In Fig. 1c an inline installation of the sound velocity sensor is shown.

Continuous H2SO4 Monitoring from 90 to 110 %

The L-Com 5500 Version HAS, the combined density and sound velocity sensor, masters the challenge of measuring in the transition zone between sulfuric acid and oleum. Only Anton Paar is able to measure continuously from 90 to 110 % w/w H2SO4 with just one sensor. A specially developed concentration formula combines both measuring values to a continuous measurement (Fig. 2). Using only one measurand it can not be determined secured whether the concentration is below or above 100 % H2SO4.

The installation of the L-Com 5500 is equal to the L-Dens 7400 installation.

Oleum Monitoring 0 to 45 %

The concentration of oleum (H2S2O7) is expressed as the amount of “free SO3” in 100 % sulfuric acid. Thus 45 % oleum contains 45 % of free SO3 in 100 % sulfuric acid and corresponds to a concentration of 110 % H2SO4. In the oleum range of 0 to 45 % free SO3, the density sensor L-Dens 7400 Version HAS is best suited. Sound velocity would also be possible in a reduced range (0 to 30 % oleum) and with a lower accuracy.

Additional Information
 
Benefits of the Sensors

* G. Schwarz, Product Competence, and K. Fröch, Product Management, Anton Paar, Graz/Austria.

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