Salt heater

Salt mixtures as heat transfer fluid

“Thermal salts” are used as heat transfer media in salt heaters.

Heat transfer systems that use thermal oils can work almost without pressure up to approx. 340 °C. For temperatures up to 400 °C, synthetic heat transfer oils with an overpressure of approx. 16 bar are used. Even higher operating temperatures - up to 550 °C - can be achieved with melted salt mixtures.

Salt heaters are used in Industry sectors where high heat flux densities [> 300 kW/m²] are required.

Salt plants are designed to be self-draining (gravity return). They form circuits via a floor tank into which all the salt flows after the system is switched off in order to avoid solidification in the system. All consumer return lines flow into the salt tank at the bottom at a constant gradient.

The heater itself has two coils connected in parallel as heating surfaces and is designed as a two- or three-pass heater. A standing design is absolutely necessary because the heater must also be self-draining.

The salt melts are usually mixtures of different metal salts (eutectic 2 to 3 component mixtures) and are selected based on their specific thermophysical properties. A commonly used thermal salt in such applications is a mixture of nitrates, such as: sodium nitrate (NaNO₃).

In many cases, the composition of the salt mixtures is selected to have synergistic effects to reduce the melting temperature or to achieve other desired thermal properties such as low viscosity, high heat capacity and very good heat transfer properties in unpressurized operation.

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