Molten salts are molten minerals that are used in various heating applications. Nitrate salts are the most common, although bromides, chlorides, fluorides and even organic salts are also used for this purpose. They are capable of operating under versatile temperatures and conditions, making them ideal for many heating applications.
This article examines the main advantages and applications of molten salt in heating systems.
Advantages of molten salt
Compared to other heat transfer fluids, molten salts offer a much larger operating temperature range. Salts increase their maximum temperature limits and have lower operating temperatures.
Salts, especially nitrate salts, have low melting points. Lower melting points mean less risk of freezing, as well as allowing use at lower temperatures. To further lower melting points, two salts can be combined.
For example, sodium nitrate has a melting point of 307℃ and potassium nitrate’s melting point is 333℃. But, when the two salts are combined, their mixture of salts has a melting point of 222℃. This allows molten salt to be used at temperatures where natural oil-based transfer fluids begin to break down.
Also, molten salts excel at high temperatures. While even the most expensive synthetic oils can only work at temperatures up to 390℃, molten salts are capable of temperatures in excess of 600℃.
The typical range of operating temperatures for molten salt transfer fluids is 285℃ to 565℃. However, the use of fluoride and chloride salts may allow higher temperature applications.
low vapor pressure
Compared to synthetic oils, molten salt transfer fluids experience minimal vapor pressure, even when operating at high temperatures. As a result, expensive high-pressure piping and equipment are often not needed.
Adding that salts like sodium nitrate create minimal risk of corrosion, molten salts are great for equipment maintenance and longevity.
Molten salts have good thermal stability and demonstrate excellent heat transfer properties. Therefore, they are efficient, environmentally friendly and have low running costs.
Molten Salt Heating Applications
Thermal fluid heating
One of the most common applications of molten salts is the heating of thermal fluids. As discussed in the benefits section, molten salt thermal fluids are ideal for high temperature applications. At temperatures where oil transfer fluids begin to break down, causing inefficiency, equipment damage and fouling, molten salts do not pose that problem.
Considering its efficiency and low vapor pressure, molten salt transfer media are ideal for thermal fluid systems , as long as they operate at least 20℃ to 30℃ above their melting point.
Another common use of molten salts is thermal storage. They have excellent thermal stability and heat transfer capacity. These thermal properties make molten salts ideal for energy storage. For example, they are increasingly used in concentrating solar power plants.
Solar plants have long had energy storage problems. Since they can only work while the sun is out, they cannot produce power 24 hours a day. Storage problems meant that any excess power that could not be used or sold to the grid was lost.
Using immersion water heaters in solar energy systems helps alleviate this challenge by making storage a possibility. By harnessing the thermal properties of molten salts, even greater energy storage is possible. Therefore, they are making solar energy more efficient and increasing its capacity.