Advanced Inline TDS Measurement Technology for Brown Stock Washing Optimization
with Advanced Process Control

Sponsored by Vaisala
Presenters: Keijo Pyörälä , Business Development Manager, Liquid Measurements, Vaisala
                      Rick Van Fleet , Global APC Owner, Andritz

Date: Tuesday, April 04, 2023
Time: 11:00am -12:00pm EST

Advanced digital in-line TDS measurement technology together with advanced process control systems can be used to improve brown stock washing process efficiency. Energy, raw materials, chemicals and water consumption reduction and renewable energy use efficiency is playing important role in pulp mill efficiency now and even more in the future.

Brown stock washing efficiency improvement and evaporation weak black liquor solids% increase yields immediate savings for the mill. Remarkable savings in bleaching chemicals and waste water treatment can be achieved also together with pulp quality and brightness increase. Better washing solids% control can remove some bottlenecks in process and improve bleaching and recovery efficiency also.

Unique digital in-line black liquor TDS analyzer uses advanced fiber optics CCD-camera optical image analysing technology. The measurement is completely digital, there are no trim pots, signal errors, analog communication or calibration drift.  This results in unique accuracy, stability and reliability in measurement signal in difficult process conditions. The digital optical image reflecting from process can be seen from the indicating transmitter large LCD graphics display and is used for measurement multi-diagnostic information.

Air bubbles, fibers, suspended particles, consistency changes, crystals or colour changes do not affect to advanced patented digital optical image analysis. Because of digital measurement principle no drift in measurement and no recalibration or other adjustments needed over the years in use. An automatic prism wash system with steam, condensate or water can be used to clean sensor if any need in process conditions arise. Typically pulp stock in-line solids% measurements are self-clean. 

Black liquor TDS are measured in digester blow line 10-15%ds, digester flush liquor and incoming wash filtrate lines. Another typical in-line TDS measurement locations are in diffuser, pressure or DD-washer feed and outlet 10-15%ds lines in pulp stock consistencies from 5-15%cs. Bleaching plant and oxygen stage feed solids 0-2%ds and filtrates 0-1%ds another common measurement and control optimization location.

Field results and success in several different pulp mills in Scandinavia and North America has proved performance of this unique digital solids% analyser technology in demanding brown stock washing process conditions also. Vaisala K-Patents digital in-line TDS measurement technology have also been successfully used in many other applications in heavy-, strong-, feed- and weak black liquor feed to evaporators, concentrators and recovery boiler firing as well as in dissolving tank green liquor and causticizing control optimisation.

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