Showing posts with label pulp & paper. Show all posts
Showing posts with label pulp & paper. Show all posts

A Free Technical Paper Explaining Refractive Index

Refractive Index

Refractive index measurement is a measurement of the speed of light in a medium. The speed of light (usually denoted by c) is 299 792 458 m/s in a vacuum. In other media, the speed of light is lower, and the refractive index (R.I.) of a medium is how much slower the light's speed is in the medium.

The detection of liquid concentrations by optical means is not new. The law of refraction was mathematically formulated first by Ibn Sahl in 984 but not known in Europe. Instead, its discovery misattribution goes to the Dutch astronomer and mathematician Willebrord Snellius (Snell), who rediscovered the law and published it in 1621. The first laboratory instrument to accurately measure liquids' refractive index was developed by Ernst Abbe in 1874.

This technical paper, courtesy of Vaisala K-Patents, is a technical explanation and understanding of the refractive index.

For more information about industrial refractometers, contact Piping Specialties / PSI Controls by calling 800-223-1468 or by visiting their web site at

Thermal Flow Meters for Pulp & Paper Applications

Thermal Flow Meters for Pulp & Paper Applications
Trees used in paper-making go through processing in a de-barker and a chipper, where they reduce to approximately one-inch wood chips. The wood chips are pressure cooked in a digester and become pulp, refined, turned into slush, and screened. Screening drains away liquid, and the resulting pulp is then pressed and dried into the paper. Several steps within the pulp and paper-making process create emissions that must be monitored and reported.

Creating paper pulp relies on a careful balance of low-velocity air flows among the various processes. For example, the recovery boiler following the digester modulates to follow the digester load changes. Additionally, a recovery boiler uses the black liquor's chemical reaction to generate heat for the boiler. It has three airflow systems requiring tight control to create stable air flows.

Kurz Instruments provides a good application note explaining the areas where thermal flow meter uses appear in the pulp and paper production process. You can download the application note below.


For more information on instrumentation for pulp and paper mills in New England, contact PSI Controls (Piping Specialties, Inc.). Call them at 800-223-1468 or visit their website at

Process Refractometers Used in Black Liquor Recovery Boilers

recovery boiler
The recovery boiler plays a central role in the chemical cycle of a modern pulp mill. The recovery boiler is a chemical reactor, which is used for recovering chemicals from spent kraft liquor and generating energy at the same time.

In the recovery boiler, the organic matter is burned. The dry solids liquor content required for firing is at least 60 %, but preferably more than 65 %. Black liquor is concentrated by evaporating water from the liquor. When the concentration of black liquor is maximized, so is the energy production. Before entering the burners, sodium sulfate decahydrate, or glauber salt, is added to cover chemical losses.

Black liquor
Chemical curve: R.I. per Black
liquor Conc% at Ref. Temp. of 20 ̊C

The liquor should have a high content of combustible dry solids in order to minimize flue gas emissions and maximize boiler efficiency.

Too low concentration of dry solids fed to the burners may result in a steam explosion with consequent damage or destruction to the boiler. Therefore, it is essential to utilize a refractometer to monitor the black liquor feed to the recovery boiler to ensure a safe operation.

Instrumentation and installation

The K-Patents Digital Divert Control System DD-23 complies strictly with all recommendations of the Black Liquor Recovery Boiler Advisory Committee (BLRBAC).

The DD-23 system includes two SAFE-DRIVE Process Refractometer sensors in the main black liquor line, two indicating transmitters and a divert control unit in an integrated panel.

The sensors are installed using K-Patents patented SAFE-DRIVE Isolation valve. This allows for safe and easy insertion and retraction of the refractometers under full operating pressure, without having to valve off the liquor piping or having to shut down the process. The SAFE-DRIVE Isolation valve contains a steam wash system for automatic prism cleaning. The system contains a SAFE-DRIVE Retractor Tool SDR-23 for safe sensor insertion and retraction.

For more information about refractometers used on blacl liquor recovery boilers, contact Piping Specialties by calling 800-223-1468 or visit

Instructional Video: Inserting K-Patents Generation 2.1 SAFE-DRIVE™ Process Refractometer PR-23-SD

This video is intended for individuals installing, commissioning, operating, and/ or servicing the K-Patents Safe-DriveTM Process Refractometer PR-23-SD, generation 2 model. The purpose of this video is to provide a quick guide for the above mentioned tasks in the form of K-Patents recommended best practices.

K-Patents SAFE-DRIVE™ design allows for safe and easy insertion and retraction of the sensor under full operating pressure without having to shut down the process.

Below the video is the document "Best Practices for the Safe-DriveTM Process Refractometer PR-23-SD Generation 2" for your convenience.

For more information, visit or call 800-223-1468.