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Pulp & Paper

Optimized quality control

One of the most important processes in the pulp & paper industry is the alkaline sulfate process where lignin is separated from the fibrous material. Due to economic and environmental reasons, the chemicals used in this process need to be recycled. 

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Application report green liquor

Application report green liquor | 2 MB

In the recycling process the black liquor will be concentrated and burned to remove organic materials like lignin. This recovery process generates - in addition to energy - a smelt with high salt content, the base material for green liquor. Through causticizing with lime, the sodium carbonate in green liquor is converted to sodium hydroxide, re-used in white liquor for the next pulping process. 

By using LiquiSonic® analyzers, each process step can be inline monitored and set in an optimal way. The LiquiSonic® system provides an optimized quality control and productivity increase, especially through fast process monitoring while liquor recycling.

The analyzer LiquiSonic® has a lot of applications in the industry of pulp & paper:

  • real time concentration monitoring of green liquor
  • phase detection and separation in different process steps
  • black liquor evaporation monitoring
  • incoming goods control
  • recycled white liquor control


The LiquiSonic® technology offers customers in the pulp & paper industry, numerous advantages:

  • robust and maintenance free even for hot (up to 200°C) and high coating liquors
  • layer-free, no steam wash system necessary
  • no frequent mounting and dismounting for maintenance and cleaning
  • reduced laboratory costs
  • highly accurate inline concentration measurement of green, black and white liquor (up to ± 0.1 wt%)
  • ideal lime dosage in causticizing
  • enhancement of operational safety

Possible measuring points in the production process

Unbeatable utilization rates
The industry of pulp & paper sets high demands on housing, electronics and sensor technology. Our application specialists fit our systems into process requirements, because all components can be adapted to the existing process conditions. A rugged housing is crucial for protection and high mechanical stability. Depending on the sensor type our housings are able to withstand temperatures up to 200 °C or 392 °F.

Well connected 
SensoTech sensors may be equipped with all common process adapters and fittings and can be used under the most complex application conditions. By changing immersion lengths or the process adapters, sensors fit into tanks and vessels of almost every design, as well as directly in every size tube. Because the measuring technology is not dependent on color, turbidity or other optical attributes, the user will have no limitations, even under the most difficult application conditions.

Product and process may change
LiquiSonic® systems can easily be adapted to accommodate various modified process conditions. The Controller software manages up to 256 various product characteristics. Depending on the user access rights, these characteristics may be activated after the sensor replacement or when process conditions change. This concept ensures the return on investment, and decrease the response time on changing boundary conditions. For new applications, a completely new calculation model can be created by using process reference values.

Individual interfaces
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SensoTech is able to offer all current and emerging standards of signal processing. For continuous concentration and density measurement, 4 … 20 mA in 2-wire loop powered or 4-wire technology, Profibus PA, Foundation Fieldbus, Modbus or Ethernet are available. For alarm level detection and switching a non-contact output or a digital output can be configured. SensoTech analyzers can always match installation needs.