SMARTREC: The Molten Salt Plant for High-Temperature Heat Recovery
In the European SMARTREC project, Spike designed and built a laboratory plant dedicated to the study of molten salts as heat transfer fluids (HTFs) for high-temperature industrial heat recovery. Recovering heat above 600 °C represents one of the most complex challenges for industry, as exhaust gases are often corrosive, intermittent, and contain particulate matter. SMARTREC proposes a modular solution based on Heat Pipe Heat Exchangers (HPHE), Dual Media Thermocline (DMT) thermal storage, and a molten salt circuit as HTF. To develop and validate this technology, a dedicated experimental facility, the Molten Salt Test Plant (MSTP), was realized by Spike.
The Molten Salt Test Plant: A Platform for High-Temperature Testing
The MSTP was designed to test different molten salt mixtures under realistic operating conditions, evaluating thermal stability, material compatibility, and fluid dynamic performance. The plant’s technical specifications indicate a maximum operating temperature of 600 °C, a design temperature of 650 °C, an operating pressure of 1 bar, and a salt flow rate up to 4 m³/h, with a total mass of about 500 kg of molten salts. The system aims to simulate conditions analogous to industrial applications, where heat must be transferred from dirty and cyclic processes to storage systems or thermal users.
Plant Configuration and Materials
The MSTP includes a drainage tank with electric heaters for initial salt melting, a preheating section of the piping, a test section for measuring thermal and fluid dynamic properties, and a cooling system with radiant heat exchange. All piping is electrically traced to prevent solidification and thermal shock. Material selection was guided by corrosion considerations: the system is primarily made of SS316 stainless steel, widely used in nitrate salt applications and chosen to ensure chemical resistance at high temperatures. SMARTREC technical documents note that many alternative mixtures (fluorides, chlorides, mixed salts) offer superior performance but require expensive materials such as Hastelloy B/N, Incoloy 800H, or Haynes 556, making installation less competitive. Thus, the MSTP becomes an essential test bench to evaluate these mixtures under controlled conditions and verify compatibility with more economical materials like SS304 and SS316.
Testing with Nitrate Salts and New HTF Mixtures
The plant was initially tested with the nitrate mixture NaNO₃–KNO₃ (65%–35%), traditionally used in concentrated solar plants. These tests validated the system’s correct functionality, PLC control logic, and start/stop procedures. The results demonstrated full operational stability and laid the groundwork for experimenting with more innovative HTFs, such as fluorides and chlorides, which could enable heat recovery above 650–700 °C, increasing the efficiency of thermal storage and transfer systems.
The Role of MSTP in the SMARTREC Project
SMARTREC aims to convert cyclic thermal sources, such as ceramic or aluminum furnaces, into continuously usable heat via thermal storage. The MSTP is the experimental core required to test HTFs, define viscosity, density, conductivity, and thermal stability curves, and provide data for CFD and thermo-fluid dynamic models developed by the project. Technical reports indicate that the MSTP allows testing salts up to 630 °C, enabling validation of simulations and design of the industrial demonstrator circuit based on Dual Media Thermocline and HPHE.
A Platform for the Next Generation of Industrial HTFs
Thanks to the MSTP, Spike has created a unique platform to study new molten salt mixtures, investigate corrosion phenomena, measure pressure drops, and test components such as pumps, valves, and heat exchangers before installation in real plants. This activity is essential to overcome the economic and technical barriers that currently limit high-temperature heat recovery and represents one of Spike’s most significant contributions to the development of SMARTREC technology.