Conmark Systems Inc.
Continuous Performance Improvements for the Pulp & Paper Industry        

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Dissolving Tank Analyzer

The Dissolving Liquor Analyzer Solution: This solution is reliable and accurate liquor analysis at the dissolving tank and stabilization tank locations for controlling the quality of the green liquor that is pumped to the causticizing process. Stabilizing the green liquor composition as much as possible at these locations ensure that variations in the green liquor are minimized before reaching the recaustizing area.

Stabilization of the green liquor at the dissolving tank is also important for controlling the settling characteristics of the liquor and minimizing scale buildup in piping and process equipment. It is desirable to maintain green liquor TTA in as tight a range as possible; too high a TTA can lead to scaling issues, too low a TTA leads to reactivity issues at the slaker. With an online dissolving/stabilization tank analyzer, the green liquor composition can be controlled in real time to meet target TTA or Na2CO3 levels.

In addition to the green liquor analysis provided by this analyzer, weak wash TTA is also provided allowing for a feed forward-feedback control arrangement. The DURALYZER-NIR dissolving/stabilization tank analyzer provides the required green liquor AA and TTA measurements in a timely, accurate and reliable manner for green liquor composition control. Additionally, green liquor EA, TDS and TDD are also available from the same analyzer as well as the weak wash TTA measurement.

Another important measurement of the Dissolving Tank Analyzer is Reduction Efficiency measurement RE%=Na2S/(Na2S+Na2SO4), which can be used as a feedback signal for controlling air flows of the Recovery Boiler.

Continuous  Digester Analyzer

Application Technology
Reliable and accurate green liquor analysis for the Dissolving tank process is important for optimizing TTA or Na2CO3 levels. The graphic presentation on the front page shows how the DURALYZER-NIR dissolving/stabilization tank analyzer can be implemented for controlling the composition of the green liquor exiting these tanks. The standard analyzer configuration comes with three sample lines. A control signal based on green liquor TTA or Na2CO3 levels can then be used to adjust weak wash flow to maintain target TTA or Na2CO3 levels.

The combination green liquor analysis and weak wash analysis from the analyzer can be used for stabilization tanks to get tight control over the green liquor composition using a feedforward-feedback control system. Dissolving tank analysis is unique among the liquor analysis applications due to the rapid step changes that can occur from smelt rush conditions. In addition, scaling at this location can also be a serious issue, quickly fouling other sensor solutions to a degree that makes them inoperable.

The DURALYZER-NIR analyzer solves both of these issues. Green liquor analysis results can be provided in as short a time as a three minute cycle. Special Teflon lined sample taps ensure that the tap locations do not scale up to a degree that would interfere with collecting a valid process sample.

Manufacturer: R.E. Hodges; Auburn, Alabama

Dissolving Tank Control Application:

Reliable and accurate liquor analysis at the dissolving tank, optionally blending tank locations is the key to controlling the quality of the green liquor that is sent to the causticizing process. This is also important for controlling the settling characteristics of the liquor and minimizing scale buildup in piping and process equipment.

A simple control system is being utilized at existing installations in order to stabilize the green liquor TTA. Smelt sprout cooling water outlet temperature is part of the set-up, so that in case of smelt rush, a rapid TTA compensation can be initiated.

Another important application for this Analyzer is Reduction Efficiency(RE). Optimum conversion of make-up sodium sulfate (Saltcake/Na2SO4) to sodium sulfide (Na2S) is one of the primary reactions in the Recovery Boiler, besides of recovering most of the inorganic chemicals used in the Kraft process. The optimum RE is around 95% and can therefore be increased by a better control of the boiler air flows due to having a continuously available measurement of Reduction Efficiency(RE).

  • Green Liquor variability reduction
  • Reduction Efficiency Improvements
  • Energy savings
  • Reduced emissions
  • Maximized production

Recovery Boiler