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Real-time monitoring of dissolution processes

What fixed time intervals can only estimate, LiquiSonic measures® - continuously, inline, and in real time.

The challenge

Zum Beispiel in Rühreaktoren, Ansatzbehältern oder Chargengefäßen lässt sich ein Auflösungsfortschritt von außen nicht beobachten. Daher laufen die meisten Anlagen standardmäßig nach festen Timern, weil sich nicht mit Sicherheit sagen lässt, wann die Auflösung vollständig und die Charge tatsächlich fertig ist. Dieser konservative Puffer kostet bares Geld – jede überschüssige Minute bindet Reaktorkapazität, verbraucht Energie und verzögert den nächsten Batch. Wird die Charge hingegen zu früh gestoppt, bleiben ungelöste Feststoffe zurück. Auch das hat direkte Folgen für die Produktqualität und nachgelagerte Prozesse. Die einzige Alternative, die manuelle Laborprobe, ist arbeitsintensiv und liefert das Ergebnis viel zu spät.

Our solution

The LiquiSonic® measurement system is installed directly in the vessel and continuously measures the speed of sound in the liquid in the tank. This changes with concentration: the more solid dissolves, the higher the measured value. As long as dissolution continues, the measured speed of sound rises steadily. The process temperature measured at the same time is used for compensation so that the measured value remains meaningful at all times. As soon as all solids are completely dissolved, it stabilizes at a constant plateau at the target value.

In addition, the attenuation of the ultrasonic signal is monitored. It provides further indications of undissolved components, particles, or gas bubbles in the medium and thus supports the assessment of whether the process is homogeneous and stable.

The process step by step

The LiquiSonic® measurement system accompanies the batch throughout the entire process. As soon as the solid is added and the stirring process starts, measurement begins without delay.  In this initial phase, the speed of sound is still unstable because undissolved particles or gas bubbles can affect the measurement. The simultaneously performed attenuation measurement makes these visible and thus supports the evaluation of the dissolution progress.  As dissolution progresses, the speed of sound in the liquid increases steadily. The sensor continuously records this increase and responds immediately to every change in the process. The more solid goes into solution, the more evenly and precisely the measured value shifts toward the target value.

Shortly before the target value, the curve flattens. This is a clear sign that most of the solid has now dissolved and the dissolution process is approaching its end. The sensor detects this slowdown and prepares endpoint detection. As soon as the speed of sound remains stable at the target value, the endpoint has been objectively reached. The solution is completely homogeneous, and all solids are dissolved. The system can automatically release the batch so that no intervention, no laboratory sample, and no safety buffer are required.

Advantages

The use of LiquiSonic® makes every dissolution process measurable, efficient, and reliable:

  • Shorter cycle times: Batches end exactly when they are finished, not when a predefined timer expires
  • More capacity: Vessels are released earlier for the next batch
  • Lower energy consumption: No unnecessary continued stirring or heating after the endpoint
  • Assured product quality: Complete dissolution is objectively confirmed
  • No manual sampling: Process and release can be fully automated


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Frequently asked questions

How can dissolution processes be monitored?

LiquiSonic® continuously measures the speed of sound in the process liquid. Since the speed of sound changes directly with the concentration of dissolved substances, the progress of dissolution can be tracked in real time. At the same time, signal attenuation and process temperature are recorded and used for compensation so that the measured value remains reliable even with a high proportion of gas bubbles or fluctuating temperatures.

For which solids and media is the system suitable?

The measurement principle is material-independent and works wherever the speed of sound in the liquid changes with the progress of dissolution. Typical applications include salts such as potassium sulfate and sodium chloride, sugar, polymers, alkali and acid preparations, as well as CIP and tank rinsing processes. For certain media, SensoTech recommends an application-specific calibration.

How reliable is the measurement system in practice?

The endpoint is identified based on a stable plateau of the speed of sound at the defined target value. It is an objective, reproducible signal that is independent of operator judgment or laboratory results. SensoTech adapts the detection parameters to the specific application and process to ensure the earliest possible reliable endpoint signal and tight, repeatable batch cycles.

Does the measurement also work with slowly dissolving solids?

LiquiSonic® continuously tracks the course of dissolution and responds immediately to changes in the process. Even with slowly dissolving solids, the system reliably detects the endpoint of the dissolution process because it does not wait for a fixed target value but instead uses stabilization of the measured value as the criterion. Application-specific adjustments to the detection logic are possible.

What happens with fluctuating input quantities?

LiquiSonic® captures the progress of dissolution in real time and reflects process changes without delay. Even with poorly soluble solids or fluctuating input quantities, the system reliably determines the completion of the dissolution process. The basis for this is not solely reaching a rigid setpoint, but the stabilization of the measured value. The endpoint detection logic can be adapted to the respective application.

Can LiquiSonic be used simultaneously in multiple vessels?

Yes, multiple sensors can be connected to a central evaluation unit via a common sensor bus with a cable length of up to 1000 m. This enables parallel monitoring of multiple reactors or vessels from a single system.

How can the measurement system be integrated into an existing plant control system?

The LiquiSonic® measurement system supports common industrial standards for signal output and can

How high is the maintenance effort during ongoing operation?

LiquiSonic® works without moving parts, without consumables and without regular calibration in normal operation. The sensor is designed for continuous operation and requires no routine intervention, which can significantly reduce unplanned downtime and operating costs.

What are the disadvantages of a timer-based process in resolution processes?

Timer-based process control is based on conservative estimates, not on the actual process status. This systematically leads to excessively long batch times, unnecessary energy consumption and tied up reactor capacity. If the timer is set too short, incomplete resolution will have negative quality consequences. Continuous measurement of the speed of sound replaces the timer with an objective, real-time endpoint signal, allowing each batch to end exactly when dissolution is actually complete.

What alternatives are there to manual sampling in dissolution processes?

Manual laboratory samples always provide a delayed picture of the process status. The sample is taken, analyzed and evaluated while the process continues. In addition, manual sampling is labor-intensive, error-prone and associated with safety risks when using aggressive or temperature-sensitive media. LiquiSonic® measures the dissolution state directly in the container several times per second and completely eliminates the need for manual intervention for endpoint control.

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