Introduction

Molten salt technology has become increasingly important in thermal energy storage systems, concentrated solar power (CSP) plants, and other high-temperature industrial applications.

Accurate level measurement is essential for maintaining safe and efficient operation of molten salt storage tanks. However, measuring molten salt levels is challenging due to extreme temperatures, corrosive properties, vapor generation, and potential crystallization.

A reliable measurement system must provide stable performance under harsh operating conditions while ensuring accurate monitoring of storage capacity and process status.

This article introduces key considerations for selecting suitable instrumentation for molten salt level measurement, including level measurement technologies, pressure monitoring, flow measurement, material selection, and installation requirements.

Challenges of Molten Salt Level Measurement

Molten salt applications typically operate at temperatures ranging from 290°C to 600°C.

For example:

• Cold salt tanks usually operate around 290°C
• Hot salt tanks in thermal storage systems may reach temperatures above 500°C

Under these conditions, conventional level instruments may experience performance limitations.

The main challenges include:

High Temperature

Continuous exposure to high temperatures can affect:

• Sensor performance
• Electronic components
• Mechanical structures

Therefore, instruments used for molten salt applications require high-temperature-resistant designs and proper thermal protection.

Corrosion Risk

Common molten salt materials include:

Solar Salt

A mixture of:

• Sodium nitrate (NaNO₃)
• Potassium nitrate (KNO₃)

Hitec Salt

Containing:

• Sodium nitrite (NaNO₂)
• Sodium nitrate (NaNO₃)
• Potassium nitrate (KNO₃)

These molten salts may cause corrosion when incompatible materials are used.

Material selection is therefore a critical factor for long-term reliability.

Common corrosion-resistant materials include:

• Hastelloy alloys
• 316L stainless steel
• Ceramic materials

Salt Vapor and Crystallization

During operation, molten salt may produce vapor.

When vapor contacts cooler surfaces, salt deposits and crystallization may occur.

This can lead to:

• Reduced measurement stability
• Signal interference
• Increased maintenance requirements

Proper instrument selection and installation design can significantly reduce these problems.

Selecting the Right Level Measurement Technology

For high-temperature molten salt applications, different measurement technologies can be considered depending on operating conditions.

Radar Level Measurement

Radar level measurement is widely used in molten salt storage applications because it provides non-contact measurement.

Since the sensor does not directly contact the molten salt, it reduces the risk of corrosion and mechanical damage.

Main advantages include:

• Non-contact operation
• High measurement stability
• Low maintenance requirements
• Suitable for large storage tanks

For high-temperature applications, the installation design should consider:

• Suitable antenna selection
• Temperature isolation
• Protection against salt vapor accumulation

In practical applications, radar-based measurement is often integrated into a complete molten level tracking solution to provide continuous information about tank level changes and operating conditions.

Pressure Measurement for Molten Salt Systems

Pressure-based level measurement is another commonly used method.

However, standard pressure instruments are usually unsuitable for direct exposure to high-temperature molten salt.

A remote diaphragm seal system is often applied to isolate the measuring element from the process medium.

The system typically consists of:

• Process diaphragm
• Capillary connection
• Pressure transmitter

Advantages:

• Suitable for closed tanks
• Continuous level monitoring capability
• Improved protection of measuring components

Recommended diaphragm materials include:

• Hastelloy
• Stainless steel alloys

Flow Measurement in Molten Salt Systems

Level monitoring is often combined with flow measurement to improve overall process control.

Monitoring the circulation flow helps operators understand:

• Material balance
• Heat transfer efficiency
• System operating conditions

Common flow measurement technologies include:

Electromagnetic Flow Measurement

Advantages:

• No moving parts
• Low pressure loss
• Suitable for continuous operation

Coriolis Mass Flow Measurement

Advantages:

• Direct mass flow measurement
• High accuracy
• Density measurement capability

Material Selection Considerations

Material compatibility is one of the most important factors when selecting instruments for molten salt applications.

Hastelloy Alloy

Features:

• Excellent corrosion resistance
• Good high-temperature performance

Applications:

• Wetted components
• Diaphragm systems
• High-temperature sections

316L Stainless Steel

Features:

• Good corrosion resistance
• Cost-effective solution

Applications:

• Lower temperature areas
• General industrial conditions

Ceramic Materials

Features:

• Excellent chemical resistance
• High temperature stability

Applications:

• Special flow measurement applications

Installation Recommendations

Proper installation plays an important role in measurement reliability.

Hot Salt Storage Tanks

For high-temperature tanks:

Recommended practices:

• Install instruments with suitable thermal protection
• Avoid direct exposure to excessive heat
• Reduce the influence of salt vapor
• Consider purge systems when required

Cold Salt Storage Tanks

Recommended practices:

• Select corrosion-resistant components
• Ensure stable signal transmission
• Perform regular inspection and maintenance

Common Problems and Solutions

Measurement Signal Instability

Possible causes:

• Salt deposits
• Improper installation
• Temperature fluctuations

Solutions:

• Optimize installation conditions
• Select suitable measurement technology
• Maintain stable operating conditions

Instrument Corrosion

Possible causes:

• Incorrect material selection
• Long-term exposure to molten salt

Solutions:

• Verify material compatibility
• Use corrosion-resistant materials

Increased Maintenance Requirements

Possible causes:

• Unsuitable instrument design
• Difficult installation location

Solutions:

• Select reliable measurement technologies
• Consider maintenance accessibility during system design

How to Choose the Right Instrumentation for Molten Salt Applications

Before selecting measurement equipment, consider:

Process Conditions

• Molten salt type
• Operating temperature
• Pressure conditions
• Tank dimensions
• Measurement range

Instrument Requirements

• Accuracy requirements
• Communication interface
• Installation method
• Environmental protection rating

Long-Term Reliability

• Material compatibility
• Maintenance requirements
• Technical support availability

Conclusion

Reliable level measurement is essential for the safe and efficient operation of high-temperature molten salt systems.

Due to extreme temperatures, corrosion risks, and crystallization challenges, selecting appropriate instrumentation requires careful consideration of process conditions, material compatibility, and installation requirements.

A well-designed measurement system combining level measurement, pressure monitoring, and flow measurement technologies can provide accurate process information and improve system reliability.

As thermal energy storage and high-temperature industrial applications continue to develop, advanced monitoring technologies will play an increasingly important role in ensuring stable and efficient operation.