In the field of industrial high-temperature heating, the performance of the heat transfer medium directly determines production efficiency, energy consumption, and safety. As industrial technology advances towards higher efficiency and lower carbon emissions, molten salt, as an advanced heat transfer medium with excellent thermal performance, is gradually replacing traditional steam and thermal oil, becoming a new option for demanding heating applications. Compared to steam systems, which must withstand high pressure at high temperatures, thermal oil poses flammability risks, and has limited high-temperature stability, molten salt systems, with their wider temperature range, safer operation, and higher energy efficiency, precisely meet the stringent high-temperature heating requirements of modern industry, driving the upgrading of heating processes across many industries.
By definition, molten salt refers to a medium composed of one or more inorganic salts mixed in specific proportions that can transform from solid to liquid at a certain temperature and stably carry and transfer heat. Its core advantage stems from its scientific compositional formula. Currently, the most widely used salt in industry is eutectic mixed salt, typically a mixture of potassium nitrate, sodium nitrite, and sodium nitrate. This formula effectively lowers the melting point of individual salts while also improving high-temperature stability.
Molten salts exhibit significant advantages in key performance: First, their high heat capacity allows them to store more heat, reducing temperature fluctuations and ensuring a stable heating process. Second, their low viscosity reduces flow resistance within pipelines, reducing energy consumption in the circulation system. Third, their excellent high-temperature stability allows conventional industrial molten salts to operate stably at temperatures up to 500°C for extended periods, without the need for high pressures, achieving efficient heat transfer at atmospheric pressure. Furthermore, molten salts are chemically inert and unlikely to react with equipment materials, extending system life.
However, molten salts also present certain challenges, the most significant of which is their high freezing point (conventional eutectic molten salts have a freezing point of approximately 142°C). If the system temperature drops below this freezing point during operation, the molten salt can solidify and clog the pipelines. Therefore, a comprehensive heating and insulation system is required to prevent the molten salt from solidifying.
A Molten Salt Furnace is an industrial heating device that uses molten salt as a heat transfer medium. It is specifically designed to meet the high-temperature heat source requirements of industrial production. Its applicable temperature range is extremely wide, covering 150°C to 580°C, meeting both medium- and low-temperature heating scenarios and high-temperature process requirements, thus filling the performance gap of traditional heating equipment in the high-temperature range.
In terms of system composition, a molten salt furnace consists of three core components: the molten salt melting tank, which heats the solid molten salt above its melting point, converting it into a liquid state for storage; the thermal oil heater (some models directly use fuel to heat the molten salt), which is the core of heat generation. This heat is converted into heat energy through fuel combustion or electricity and then transferred to the molten salt; and the circulation pump, which provides power for the flow of the molten salt within the system, ensuring continuous and even heat delivery to the heat-consuming equipment. Molten salt furnaces can be categorized by energy source as either fuel-fired (such as coal, oil, gas, or biomass) or electric-fired. These different heating methods are suitable for different energy supply scenarios, meeting the diverse energy needs of enterprises. Modern molten salt furnaces also integrate several advanced features: They utilize a PLC intelligent control system, enabling precise control and automated operation of parameters such as temperature and flow, reducing manual operation. Some models utilize a vertical coil design, optimizing the heating area and spatial layout, improving heat exchange efficiency. Overall thermal efficiency can reach over 92%, significantly exceeding traditional heating equipment and significantly reducing energy consumption.
The heating process of a molten salt furnace follows a closed-loop operation logic and can be divided into the following steps:
Molten Salt Melting Stage: Initially solid, the molten salt is fed into a melting tank. Auxiliary heating devices (such as electric heating tubes or thermal oil exchange) raise the temperature to above its freezing point (typically above 142°C), until it is completely converted into liquid molten salt, ready for subsequent circulation.
Heat Transfer Phase: Driven by a circulation pump, the liquid molten salt enters the heat exchange area of the furnace (such as the coil or furnace), where it undergoes a thorough heat exchange with the high-temperature flue gas generated by the fuel combustion (or heat generated by the electric heating elements). After absorbing heat, the temperature gradually rises to the required process temperature (up to 580°C).
Heat Transport and Utilization Phase: The heated, high-temperature molten salt is transported via pipelines to heat-consuming equipment in industrial production (such as reactors and dryers), transferring heat to the materials or process steps to be heated, thereby meeting production temperature requirements.
Circulation and Reheating Phase: After releasing heat, the low-temperature molten salt is returned to the furnace by the circulation pump, where it participates in the heat exchange process again. This forms a closed-loop cycle of "heating - transport - heat release - reflux," ensuring a continuous supply of heat. Throughout the entire operating process, the circulation pump is the core power source to ensure the flow of molten salt, which directly affects the efficiency and stability of heat transfer. The PLC control system accurately adjusts the heating power and circulation speed by real-time monitoring of molten salt parameters such as temperature, flow, and pressure, ensuring that the system always operates within a safe and efficient range and avoiding failures caused by excessively high or low temperatures.
Based on different classification standards, molten salt furnaces can be divided into various types. Enterprises can choose the appropriate model based on their industry needs and actual conditions.
Coal-fired Molten Salt Furnaces: These use coal as fuel, resulting in lower costs. They are suitable for regions or industries with abundant coal resources and fuel cost sensitivity. However, environmental emission requirements must be met and appropriate dust removal and desulfurization equipment must be installed.
Oil-fired Molten Salt Furnaces: These use diesel, heavy oil, and other fuels, offering rapid ignition and stable heating. They are suitable for applications requiring high heating speeds and convenient fuel supply, but the fuel cost is relatively high.
Gas-fired Molten Salt Furnaces: These use natural gas, liquefied petroleum gas, and other fuels, offering high combustion efficiency and low pollutant emissions (such as nitrogen oxides and particulate matter). They meet environmental requirements and are suitable for regions with ample natural gas supplies, especially for industries with strict environmental standards (such as chemicals and food processing).
Biomass Molten Salt Furnaces: These use renewable energy sources such as straw, wood chips, and biomass pellets as fuel, resulting in low carbon emissions. They are suitable for regions with abundant agricultural and forestry resources and help enterprises achieve green production. Electric-heated molten salt furnaces: Powered by electricity, these furnaces directly heat molten salt through electric heating elements. They offer fast heating speeds, high temperature control precision, and zero pollutant emissions. They are suitable for applications with abundant electricity resources (such as those in regions with off-peak electricity prices) or those with stringent environmental and clean requirements (such as the electronics and pharmaceutical industries). However, operating costs are significantly affected by electricity prices.
Cylindrical Molten Salt Furnaces: Featuring a compact cylindrical furnace body and a small footprint, these furnaces minimize heat loss and facilitate installation and maintenance. They are suitable for small and medium-sized enterprises with limited space or intermittent production.
Box-Type Molten Salt Furnaces: Their box-shaped body offers a large heating area, allowing for the placement of multiple heating elements or burners. This provides high heating efficiency and is suitable for continuous production and high-heating industrial applications (such as metallurgy and large-scale chemical plants).
Frame-Type Molten Salt Furnaces: Supported by a steel frame, these furnaces offer flexible furnace and piping layouts, allowing for customized design based on process requirements. They are suitable for complex heating systems and are ideal for large-scale industrial projects or those with specialized process requirements. When selecting a molten salt furnace, it's important to comprehensively consider the industry's application characteristics (such as required temperature, heating continuity, and environmental requirements) and fuel availability (such as local fuel resource distribution, cost, and supply stability) to ensure the equipment is perfectly aligned with production needs, maximizing economic benefits and operational efficiency.
Compared to traditional heating equipment like steam boilers and thermal oil boilers, molten salt furnaces offer numerous irreplaceable advantages in industrial applications:
Extremely High-Temperature Stability: Conventional molten salt furnaces can operate stably within a temperature range of 150-580°C. Some specialized molten salt furnaces can even withstand higher temperatures, far exceeding the upper temperature limit of thermal oil furnaces (typically up to 320°C). Unlike high-temperature steam boilers, they don't need to withstand the high pressures required, fundamentally reducing the safety risk of high-pressure leaks and meeting the core high-temperature heating requirements of industries like metallurgy and chemicals.
Outstanding Heat Storage Capacity: The high thermal capacity of molten salt provides excellent heat storage capabilities. It can store heat when energy is abundant and release it during energy shortages or peak heat demand, effectively balancing energy supply and demand. Especially when combined with renewable energy sources (such as solar energy), this technology can achieve "peak-shifting" heat utilization, improving energy efficiency.
High Thermal Efficiency and Energy Saving: Molten salt furnaces generally boast a thermal efficiency exceeding 92%, with some advanced models exceeding 95%. The low viscosity of the molten salt reduces energy consumption in the circulation system. Furthermore, precise temperature control and a closed-loop design minimize heat loss, resulting in energy savings of 10%-20% compared to traditional heating equipment. Long-term operation can significantly reduce a company's energy costs.
Greatly Improved Safety: Compared to thermal oil furnaces, molten salt is non-flammable and non-explosive. Even leaks at high temperatures are unlikely to cause fires or other safety hazards. Compared to high-pressure steam boilers, molten salt furnaces operate at atmospheric pressure, eliminating the risk of high-pressure vessel rupture. Furthermore, modern molten salt furnaces are equipped with temperature and pressure monitoring and alarm systems, further enhancing operational safety.
Due to their excellent high-temperature performance and safety features, molten salt heating systems have been widely used in various industrial sectors, providing stable and efficient heat sources for key production processes:
Metallurgy and Foundry
The smelting and casting processes of metals such as aluminum, steel, and copper require a continuous, stable high-temperature environment (e.g., 600-700°C for aluminum alloy smelting and 800-1200°C for billet heating). Molten salt heating systems precisely control temperature, preventing metal defects caused by temperature fluctuations. Their atmospheric pressure operation reduces safety risks in the workshop, improving production efficiency and product quality.
Chemical Industry
Processes such as fertilizer synthesis, melamine production, alumina processing, and pyrolysis recovery of waste plastics and rubber all require high-temperature heat sources to drive chemical reactions or material processing. Molten salt heating systems not only provide temperatures exceeding 500°C, but also ensure uniform chemical reactions through stable heat output, minimizing byproduct formation. Their chemical inertness prevents reactivity with chemical feedstocks, ensuring production safety.
Solar Thermal Power Generation Industry
In solar thermal power generation (CSP) projects, molten salt is the core heat storage and heat transfer medium. During the day, solar collectors heat the molten salt to a high temperature and store it in hot salt tanks. At night or on cloudy days, the high-temperature molten salt releases heat, heating water to generate steam that drives steam turbines for electricity generation, enabling 24-hour continuous power supply. This addresses the intermittent nature of solar power and improves the efficiency and stability of renewable energy utilization.
Natural Gas Processing Industry
During natural gas extraction and transportation, it must be dehydrated and desulfurized. The regeneration of desiccants (such as molecular sieves) requires high-temperature regeneration gas (typically 200-350°C). Molten salt heating systems efficiently heat the regeneration gas, ensuring full desiccant regeneration and ensuring effective dehydration and desulfurization of natural gas processing equipment. Furthermore, their stable temperature control extends the desiccant's service life and reduces operating costs.
Molten salt furnaces, with their wide temperature range, high safety, high thermal efficiency, and robust heat storage capacity, are reshaping the industrial high-temperature heating landscape and becoming an ideal alternative to traditional heating equipment. Its significant advantages in energy efficiency and safety not only help companies reduce energy costs and mitigate safety risks, but also align with the current trend of low-carbon and intelligent industrial development. For companies seeking to upgrade their heating processes, molten salt furnaces are undoubtedly a high-quality option that balances economic, safety, and environmental benefits. They are worthy of exploration and application in more industries, driving the industrial heating sector towards greater efficiency, safety, and sustainability.
