Slurry density meter · PS7000

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

Paper-making alkali recovery

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%.

Applicable industries
Pulp & Paper
Discuss this application View product PS7000
Online concentration monitoring for low-concentration LC / medium-concentration MC / black liquor / white liquor

PISONICS· Xi’an Pisonics

PS7000 Series

Ultrasonic Acoustic Impedance Slurry Density Meter

Application Case in the Papermaking/Pulping Industry

—— Online Monitoring of Low-Concentration LC/Medium-Concentration MC/Black Liquor/White Liquor Concentrations ——

Non-Nuclear · Replaces Gamma-Ray Concentration Meters · Optimizes Chemical Dosing · Enhances Recovery Rates

Papermaking/Pulping · PS7000 Application Solution

1. Process Background

The pulping and alkali recovery processes in modern paper mills are “hotspots” for density/concentration measurement. In the pulping section, after exiting the digester, the pulp sequentially passes through washing and screening, bleaching, stock tanks, and the paper machine; throughout this entire process, the slurry concentration (classified by industry standards as low-concentration LC ≤ 6%, medium-concentration MC 6–15%, and high-concentration HC ≥ 15%) must be precisely controlled, as even slight deviations can directly affect the basis weight, uniformity, and strength of the paper. In the alkali recovery section, the digested waste liquor (dilute black liquor) is concentrated into thick black liquor (65%–75% solids) via multi-effect evaporators before being sent to the recovery boiler for combustion; the combustion products (green liquor) are then converted into white liquor (NaOH) through reaction with lime in a causticizer, which is returned to the digester, completing a closed-loop cycle for chemical recycling.

Black liquor concentration is a key parameter for ensuring stable operation and energy efficiency of the recovery boiler: too low a concentration leads to unstable combustion and reduced steam production, while too high a concentration can easily clog the burner nozzles. White liquor concentration, on the other hand, determines the effective alkali charge and pulp quality in the digestion process.

2. Pain Points of Traditional Density/Concentration Measurement Solutions

• Black Liquor Section: Black liquor is highly corrosive (pH ≥ 13), highly viscous, and contains organic sulfides. The diaphragms of conventional differential-pressure density meters suffer extremely rapid degradation, showing severe corrosion and drift within 3–6 months.

• Medium- and High-Concentration Pulps: Fibers tend to wrap around and clog the vibrating forks and rotors of insertion-type instruments, requiring shutdowns for cleaning 1–2 times per month on average.

• Gamma-Ray Concentration Meters: Once the industry standard, these have become increasingly difficult to deploy in recent years due to stricter environmental approvals—new paper mill projects struggle to obtain radiation safety permits, and existing installations face retirement pressures.

• In the low-concentration pulp and white liquor sections, though corrosion is less severe, the measurement accuracy of traditional instruments falls short of supporting efficient automated chemical dosing control loops.

3. PS7000 Solution

The PS7000 is deployed at four typical measurement points across the pulping and alkali recovery processes: black liquor concentration (at the evaporator outlet), white liquor caustic soda concentration (at the causticizer outlet), medium-concentration pulp MC (at the high-concentration stock tank outlet), and low-concentration pulp LC (at the paper machine inlet), forming a non-nuclear density-monitoring network covering the entire plant.

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

Figure 1 Schematic Layout of Density Measurements in the Kraft Pulping and Alkali Recovery Process

Core Technical Advantages of the PS7000 in the Papermaking/Pulping Industry

▶ Completely replaces nuclear density meters—serving as a key component in achieving paper mills’ “zero radiation source” goal;

▶ Non-contact probe—pulp fibers do not become entangled or cause blockages, eliminating routine maintenance;

▶ Optional PTFE/Hastelloy probe configurations, resistant to the severe alkaline corrosion of black liquor (pH ≥ 13), with a service life of at least 5 years;

▶ Chirp anti-bubble algorithm—despite the frequent entrainment of large amounts of air in the washing and bleaching sections, the PS7000 delivers consistently stable measurements;

▶ 4–20 mA + MODBUS-RTU connectivity to the paper machine’s DCS/QCS quality control system, enabling closed-loop chemical dosing and adaptive control of pulp consistency;

▶ Wide measurement range, versatile application—one instrument handles everything, from low-concentration LC at 0.5% to black liquor at 75%, with a single model meeting the needs across all paper mill process stages.

4. Customer Value

Comparison Dimensions

Original gamma-ray/differential pressure solution

PS7000 Solution

Radiation Safety

Requires a license · Annual inspection and decommissioning are cumbersome

Completely non-nuclear

Black Liquor Corrosion Resistance

Diaphragm corrodes and fails within 3 to 6 months

PTFE lining ≥ 5 years

Slurry blockage

Fiber winding · Frequent cleaning

Non-contact · Completely maintenance-free

Concentration Feedback

Slow response · Data drift

Second-level response · DCS closed-loop

Reagent Consumption

Estimated dosing · High wastage

Precise dosing · 5%–10% chemical savings

In an alkali recovery retrofit project at a major domestic paper group (annual output of 800,000 tons of cultural paper), three PS7000 units replaced the original nuclear density meters, installed on the thick black liquor feed line to the boiler, the white liquor feed line to the digester, and at the high-concentration stock tank outlet. After 12 months of operation, feedback indicates that black liquor concentration fluctuations narrowed from ±2.5% to ±0.5%, significantly improving steam production stability in the recovery boiler; precise control of white liquor concentration reduced alkali consumption in the digestion process by approximately 3%, saving over ten million yuan annually in white liquor and steam costs.

Conclusion

Based on the four ultrasonic measurement principles of the PS70 series (acoustic impedance/acoustic attenuation/sound velocity/frequency-modulated sonar), Xi’an Pisonics’ PS7000 covers the full range of online density/concentration measurement needs, from two-phase solid-containing slurries to clean, homogeneous liquids. Tailored to the process characteristics of the papermaking/pulping industry, the PS7000 series of ultrasonic acoustic impedance slurry density meters provides end-to-end technical support—from instrument selection and installation/commissioning to long-term maintenance.

For an in-depth discussion of your specific plant conditions, customized selection recommendations, or on-site technical consultation, please feel free to contact the Xi’an Pisonics engineering team at any time.

More applications for Slurry density meter

View all

Online Measurement of Gypsum Slurry Density in Absorption Towers

In the wet flue-gas desulfurization process, real-time monitoring of gypsum slurry concentration is crucial for ensuring the quality of the by-product gypsum and the proper operation of equipment. However, conventional concentration meters—such as mass flow meters, tuning fork sensors, and differential pressure concentration meters—suffer from issues like radiation safety concerns, bubble interference, and scaling. Pisonics’ PS7000 employs ultrasonic technology for non-contact measurement, can penetrate bubble layers to deliver stable and reliable concentration data, and requires no maintenance, with a service life exceeding five years.

Online Density Measurement for Limestone Slurry Preparation

During the preparation of limestone slurry, conventional density-measurement solutions suffer from issues such as wear and scaling, leading to inaccurate data and compromising flue-gas desulfurization efficiency. The PS7000 acoustic impedance concentration meter overcomes these challenges through non-contact ultrasonic measurement, delivering stable, high-precision online density monitoring and ensuring consistent control of slurry concentration.

Online Measurement of Desulfurization Wastewater Density

In the flue-gas desulfurization process at power plants, online monitoring of the slurry density in the underflow from the thickener is critical. Conventional contact-type instruments are prone to scaling and corrosion, making it difficult to meet the demands of long-term, stable operation. Pisonics’ PS7000 acoustic impedance concentration meter employs a non-contact ceramic probe and a corrosion-resistant lining, effectively addressing severe corrosion and fouling while ensuring the accuracy and stability of the measurement data.

Online Density Measurement for the AFT Tower (High-Concentration Desulfurization Slurry Processing Tower)

In the AFT tower, measuring the density of high-concentration, high-viscosity, and easily crystallizing slurries has long been a challenge. The PS7000 acoustic impedance concentration meter, employing non-contact measurement, overcomes the failures of conventional instruments caused by clogging, wear, and crystallization, enabling real-time, continuous monitoring of slurry density and automated control of the discharge process, thereby ensuring stable system operation.

Selection support

Guides

Comparisons

Voices from users of this product

"Our original tuning fork and differential pressure meters on the absorber gypsum discharge main had recurring problems with bubbles and scaling — we had to shut down weekly to clean them. After switching to PS7000, both problems disappeared. Basically maintenance-free now, accuracy is stable, and it fully meets our FGD process control needs."

Thermal Control Foreman Wang
Thermal Control Specialist
A certain thermal power plant in Inner Mongolia

"After switching to the PS7000, our overflow density readings finally stabilized — we stopped tuning reagent dosing by feel. The unexpected win was not having to clean the sensor weekly; our previous radiometric meter needed window-wiping almost daily in the scaling slurry."

Director Li
Mineral Processing Workshop Director
A certain copper mining enterprise

"Our potash blending tank is a harsh environment — KCl near saturation, 30~40% crystal content, temperature swinging 5~20°C. Traditional density meters can't hold up here. After two weeks of PS7000 service, the deviation from manual lab samples stayed in the 0.5~0.8% range, even during concentration peaks. No anomalies."

Director Xie
Process Engineer
A potash fertilizer plant in Qinghai

FAQ

Is the PS7000 ultrasonic density meter a radiometric device? Does it need a radiation license?

The PS7000 is an acoustic-impedance ultrasonic density meter with no radioactive source whatsoever. No radiation license is required. It uses only piezoelectric transducers to send and receive ultrasonic signals — the same physical principle as medical and NDT ultrasound.

If you're currently using a Cs-137 / Co-60 source-based meter and want to remove the regulatory burden, PS7000 is a drop-in alternative. We also offer the PS7500 gamma meter, which uses an exempt-activity Na-22 source (< 1000 KBq) — also requires no radiation license.

Can PS7000 really measure stably in bubbly mining slurries?

Yes.

The PS7000 employs a linear frequency-modulated (Chirp) acoustic impedance algorithm—after transmitting a broadband ultrasonic pulse, the host unit analyzes the echo signal in the frequency domain, and multiple-reflection interference caused by bubbles is identified and eliminated by the algorithm. This is the core difference between the PS7000 and conventional reflective ultrasonic density meters: traditional single-frequency reflection is highly sensitive to bubbles, whereas the PS7000’s Chirp algorithm is virtually immune to them.

At the gypsum discharge line of an absorption tower in a thermal power plant in Inner Mongolia (under conditions of continuous air oxidation that generate dense bubbles), the PS7000 has been operating stably for several years after replacing the original tuning fork concentration meter.

What installation requirements does the PS7000 have?

The installation requirements for the PS7000 flanged direct-insertion type are as follows:

  1. Straight-run pipe sections: ≥5D (upstream) + 2D (downstream), where D is the nominal pipe diameter;
  2. The installation point must operate with a full pipe to avoid stratification of gas and liquid phases;
  3. The applicable pipe sizes range from DN50 to DN1000 (larger sizes can be customized);
  4. The flanges are compatible with ANSI/DIN/JIS standards;
  5. In highly abrasive conditions, it is recommended to use a 316L probe with special ceramics or a 2205 duplex stainless steel probe;
  6. In strongly corrosive environments, a PTFE-lined option is available.

If the pipeline does not allow for tapping, please consider the PS7010 clamp-on type instead.

PS7000 vs nuclear density gauges: which costs less over the life cycle?

On purchase price alone, ultrasonic and nuclear gauges sit in a similar bracket. The gap opens over 5 to 10 years of ownership.

Hidden cost list of a Cs-137 / Co-60 nuclear gauge:

  • Radiation safety licensing and annual reviews, plus operator training and certification;
  • Licensed transport and installation filing for the source;
  • Dose monitoring and record keeping during service;
  • Source replacement as activity decays (purchase, transport, commissioning, return of the old source);
  • End-of-life disposal of the spent source — often the single largest bill.

PS7000 acoustic-impedance ultrasonic gauge: no radioactive source and no permits of any kind; non-contact sensor with zero wear and zero clogging, sensor life of 5 years or more, virtually maintenance free with no consumables. Power plant, potash and iron ore sites have run 2+ years at near zero maintenance.

Bottom line: on a 5-year basis the total cost of ownership of the PS7000 is typically far below a nuclear gauge. Where a nuclear principle is genuinely required (such as dense-medium coal washing), the PS7500 with an exempt-activity Na-22 source needs no license, though the roughly 2.6-year half-life still implies periodic source renewal.