Slurry density meter · PS7000

Online Density Measurement for Limestone Slurry Preparation

Flue-gas desulfurization in power plants

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.

Applicable industries
Power Emission Control
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Online Density Measurement for Limestone Slurry Preparation

I. Process Background

Limestone slurry is the “ammunition” that the WFGD system uses to consume SO2. Powdered limestone (CaCO3) is conveyed by belt or pneumatic means into a powder silo, then fed by a dosing valve at a set rate into the slurry preparation tank, where it is mixed with process water under agitation to produce a limestone slurry with a mass concentration of approximately 20%–30%. This slurry is subsequently pumped through long pipelines to the absorption tower to participate in the desulfurization reaction.

The slurry concentration directly determines the calcium-to-sulfur ratio (Ca/S) within the absorption tower—too high a concentration results in an excess of CaCO3 being fed per unit time, with unreacted particles leading to waste and exacerbating scaling inside the tower; too low a concentration, on the other hand, compromises desulfurization efficiency, causes SO2 emissions to exceed limits, and sharply increases environmental compliance risks. Therefore, online density measurement of the slurry at the outlet of the preparation tank or on the feed line to the absorption tower is a “critical” parameter for optimizing energy consumption and ensuring environmental compliance in the flue-gas desulfurization system.

II. Pain Points of Traditional Density Measurement Solutions

• Limestone slurry is highly abrasive (the fine limestone particles are very hard). Conventional insertion-type tuning fork, Coriolis, rotor, or diaphragm differential pressure instruments exhibit significant wear after just 6 to 12 months of operation, resulting in zero‑point drift and reduced measurement range.

• The slurry preparation system experiences frequent start‑stops, and prolonged residence times in the pipelines promote settling and scaling. Contact-style instruments are particularly sensitive to fouling, requiring shutdowns for cleaning one to two times per month.

• Although mass flow meter‑based density meters offer reliable accuracy, their use in limestone slurry applications—where processes are well‑established and safety and compliance requirements are increasingly stringent—is gradually being phased out.

• Lagging or unstable measurement data prevent the PLC/DCS from implementing precise “water addition/powder addition” closed‑loop control, leaving operations dependent on manual adjustments by巡检工s and resulting in large fluctuations in slurry concentration.

III. PS7000 Solution

The PS7000 is installed via flange at the outlet of the slurry preparation tank (or on the main discharge line of the transfer pump), using ultrasonic acoustic impedance technology to measure slurry density in a non‑contact manner. It transmits real‑time data to the PLC/DCS system, enabling automatic closed‑loop regulation of powder feed rates and make‑up water volumes to maintain slurry concentration within the process‑set target range.

Online Density Measurement for Limestone Slurry Preparation

Figure 2: Schematic diagram of online density measurement and closed‑loop control in the limestone slurry preparation section

Key Technical Advantages of the PS7000 in This Process Condition

▸ Customized wear-resistant probe: 316L / 2205 duplex stainless steel combined with special ceramics, surface roughness Ra ≤ 0.4μm, smooth and anti-scaling;

▸ Non-contact ultrasonic measurement principle, unaffected by limestone powder abrasion, probe service life ≥ 5 years;

▸ 0–80% mass concentration, full-scale linear measurement, accuracy ±1% FS, resolution 0.001 g/cm³, meeting fine-control requirements;

▸ Supports 4G remote transmission (optional), enabling the central control room and operations & maintenance center to view historical curves and operating status in real time;

▸ Built-in 20,000-cycle data storage and 400 log entries; no data loss upon power failure, ensuring traceability for fault analysis.

IV. Customer Value

Comparison Dimensions

Original differential pressure / tuning fork solution

PS7000 Solution

Concentration Control Accuracy

± 3%–5% variation

± 1%FS stable output

Instrument service life

6–12 months of wear

≥ 5 years of maintenance-free operation

Shutdown Cleaning Frequency

1–2 times per month

No shutdown required

Closed-loop control response

Data drift · Difficult to achieve closed-loop control

Second-level response · Automatic closed loop

Overall SO2 removal rate

High fluctuation

Stable ≥ 95%

Limestone powder consumption rate

Slightly high

Decreased by approximately 3%–8%

In a limestone slurry preparation system serving a 2×600 MW generating unit, after three months of PS7000 commissioning, slurry concentration variability decreased from ±5% to within ±1%. Operators reported, “Powder addition is now largely determined automatically by the system, eliminating reliance on empirical adjustments.” The unit achieved substantial annual savings in limestone powder and water consumption while significantly reducing the risk of scaling in the desulfurization tower.

More applications for Slurry density meter

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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 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.

Online Measurement of Slurry Density in Non-ferrous Metallurgical Beneficiation Plants

In nonferrous metal concentrators, fluctuations in slurry density directly affect metal recovery rates and energy consumption. The PS7000 concentration meter employs ultrasonic non-contact measurement technology and features a flanged direct‑insertion installation, eliminating the wear and fouling issues common to conventional instruments, ensuring long‑term stable operation, and operating entirely without radiation, thus obviating the need to obtain a Radiation Safety License.

Selection support

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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.