INDUSTRY 08

Pulp & Paper

08 / PULP & PAPER

Inline consistency across LC / MC / HC pulp stages plus black-liquor density and white-liquor caustic concentration — non-nuclear alternative to Cs-137 gauges.

3 applicable products 1 application cases
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Overview

Pulp & paper is a heritage industry for density / consistency measurement. From wood preparation, digesting, washing, bleaching to the paper machine, pulp consistency drives fibre dispersion, chemical efficiency and machine stability. Three regimes coexist — LC (1-6%), MC (10-15%) and HC (>20%) — each demanding its own measurement principle. Kraft mills also monitor black-liquor density at evaporator inlets, white-liquor caustic concentration in recovery, and green-liquor concentration.

Process challenges

  • Fibres clog and wrap around intrusive sensors
  • Black liquor is hot (>100°C), alkaline and scale-prone — demands rugged wetted parts
  • Dilution water on the paper machine must respond in milliseconds to hold basis weight
  • Cs-137 gauge retirement is accelerating under tightening environmental rules

Recommended solutions

Measurement pointPrincipleModels
LC pulp (1-6%)Microwave / ultrasonic sound velocityPS7600 / PS7020
MC pulp (10-15%)Ultrasonic acoustic impedancePS7000
Black liquor (evaporator inlet)Ultrasonic + T/P compensationPS7000
White liquor caustic concentrationUltrasonic sound velocityPS7020
Digester caustic feedUltrasonic / differential pressurePS7000 / PS7300
RECOMMENDED PRODUCTS

Products that fit this industry

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PS7000

Slurry density meter

The PS7000 series ultrasonic acoustic‑impedance slurry density meter completely eliminates the radiation safety risks and cumbersome environmental‑approval maintenance costs associated with conventional gamma‑ray density meters. By employing an innovative chirp acoustic‑impedance analysis algorithm, it overcomes measurement blind spots in complex operating conditions, enabling high‑precision continuous measurement.
PS7400

Online tuning fork density meter

The PS7400 series online tuning fork density meter monitors liquid density in real time by leveraging piezoelectric excitation and changes in the tuning fork’s resonant frequency, requiring no maintenance while delivering highly accurate, repeatable measurements. Its built-in PT1000 temperature compensation eliminates drift due to temperature variations, making it suitable for diverse industrial applications such as pipelines and storage tanks, and widely used in the petrochemical, chemical, and pharmaceutical industries.
PS7600

Microwave concentration/density meter

The PS7600 series online microwave density meter accurately captures the phase shift and amplitude attenuation of microwaves in the medium, thereby providing real-time measurements of slurry concentration, density, and moisture content. Employing a non‑nuclear, zero‑radiation microwave phase‑shift method coupled with Pt‑100 temperature compensation, it is ideally suited for challenging applications such as flue‑gas desulfurization in thermal power plants and coal‑washing slurries.
APPLICATION CASES

Cases in this industry

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Slurry density meter · PS7000

Online concentration monitoring for low-concentration LC / medium-concentration MC / black liquor / white liquor

In the alkali recovery section of a paper mill, the measurement of black liquor and white liquor concentrations has long been plagued by severe corrosion, high viscosity, and radiation safety constraints. Conventional gamma-ray and differential pressure instruments are prone to failure and incur high maintenance costs. The Pisonics PS7000 ultrasonic acoustic impedance density meter, featuring a non-contact probe, a corrosion-resistant PTFE/Hastelloy construction, and an anti-bubble algorithm, enables continuous online concentration monitoring across the entire process—on key points such as the black liquor evaporation outlet and the white liquor causticization outlet—supporting DCS closed-loop control. As a result, black liquor concentration fluctuations have been reduced from ±2.5% to ±0.5%, and white liquor alkali consumption has decreased by approximately 3%.

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Industry FAQ

Which density meter for paper-mill black / white liquor?

The core measurement requirements for paper‑making black liquor (digestion waste liquor, containing lignin and alkali) and white liquor (a mixture of NaOH and Na2S) are as follows:

concentration monitoring, recovery efficiency, and energy‑saving control.

Black liquor conditions: high viscosity (500–3,000 cP), dark color (optical methods are not applicable), temperature 70–150°C, and presence of fine particles.

We recommend the PS7600 microwave density meter (dielectric sensitivity to water allows measurement of solids content and concentration) or the PS7020 sound velocity method (immune to color interference).

White liquor conditions: strong alkaline corrosion, temperature 80–120°C.

We recommend the PS7110 refractometer (with a sapphire prism resistant to NaOH) or the PS7400 tuning fork (with PTFE coating). For green liquor (the precursor to recovered white liquor), refer to the black liquor solution.

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