While perfect energy efficiency cannot be achieved, in real-world applications we are only concerned with economic efficiency such that the cost calculus can make thermal storage a viable option. Thermal storage stores energy in the form of heat that is either "sensible" or "latent".
Sensible heat corresponds to thermal storage in a single phase where the temperature of the material varies with the amount of stored energy. Both liquid water, oil, molten salt and solid rock, metal media can be used. Molten salts have high boiling points, low viscosity, low vapor pressure, and high volumetric heat capacities. In choosing the chemical mixture, it is advantageous to have the lowest possible melting point and highest boiling point to maximize the available temperature range for the molten salt.
If the melting point is too high, additional heating may be required to prevent freezing. The salts are heated and stored in an insulating container during off-peak hours. When energy is needed, the salt is pumped into a steam generator that boils water, spins a turbine, and generates electricity. The conversion of thermal energy to electricity can proceed by different cycles such as the Rankine, Brayton, and Air-Brayton cycles.
Other applications include using the stored heat directly for high temperature processes such H 2 production and coal-to-liquid conversion , which avoids the thermodynamic cost incurred from converting to electricity. There are two different configurations for the molten salt energy storage system: two-tank direct and thermocline. The two-tank direct system, using molten salt as both the heat transfer fluid absorbing heat from the reactor or heat exchanger and the heat storage fluid, consists of a hot and cold storage tank.
To charge, salt flows out of the cold side, is heated by the heat exchanger reactor , and flows into the tank's hot side. To discharge, salt flow out of the hot side, transfers heat to generate power turbine , and flows into the tank's cold side. Thermal energy storage is currently being used in concentrated solar plants consisting of parabolic mirrors troughs or sun-tracking mirrors heliostats that direct sunlight at a focal point receiver tube in the trough or a single "power tower" shown in Fig.
In , the "AndaSol-1" solar thermal plant in Spain became the first commercial parabolic trough plant in Europe. A wide range of salt blends can help achieve specific operating temperatures required in certain applications. Compared to hydrocarbon fluids, molten salts experience minimal vapor pressure, regardless of how close operating temperatures are to their limits.
As a result, high-pressure equipment and piping are almost entirely unneeded. Molten salts are also usable at higher temperatures compared to other fluids such as silicone fluids and synthetic oils. They also have thermal stability and good heat transfer properties. Their high efficiency makes them suitable for use as heat transfer and molten salt energy storage media, as they are eco-friendly and can reduce operating costs. These include circulated molten salt, salt bath heaters, and direct heating for applications such as metal assembly heat treating.
We have the resources and experience needed to design fully automated custom systems. We can help you meet all of your process needs with our innovative solutions. With these concerns in mind, as long as the system is designed with proper heat trace, molten salts will provide excellent heat transfer and minimal degradation throughout the lifetime of your system. Nitrate salts usually are manufactured in prill form small beads and may arrive in 2,lb super sacks or smaller packages.
For smaller systems, the salt can be added directly after opening the container, ensuring the salt is spread out uniformly for better heat distribution. As the salt melts, its volume from crystalline prill form to liquid form will reduce by about 50 percent due to the air spaces between the prills.
If the melting tank is large enough, the salt can be added all at once. If there are some space restrictions, the salt can be melted and added in several increments. For much larger systems, the salt may be emptied and loaded onto conveyor systems, where it is deposited inside the large tank as the salt melts. Nitrate molten salts are stable and have low toxicity, but they are oxidizers. In the presence of fire or open flames, they can break down and liberate oxygen, providing a fuel source for the flame.
Molten nitrate salts should be kept away from open flame, sparks and other sources of ignition. If proper precautions are taken, the salts should not pose any hazards. Molten salts are used in applications ranging from high temperature circulating systems to thermal storage and phase-change systems. Molten salts often are used in concentrated solar power plants CSP , where the salt can store heat obtained from sunlight for long periods of time.
Some of these CSP systems flow the salt directly through the receiver tubing, where sunlight hits a parabolic mirror and concentrates the sunlight to a tube in which the salt flows. Other systems use a combination of a high temperature synthetic fluid with the salt storage. The synthetic fluid flows through the receiver tubing and transfers the heat into the molten salt storage tanks.
Other systems may use molten salts for preheating natural gas lines or keeping reactors hot by using the molten salt in the jacket around a tank.
Salts also have relatively high latent heat capacity — similar to many of the phase-change waxes that are used today — and are sometimes used in phase-change applications. When salts melt, they absorb large amounts of heat, and when they freeze, they release large amounts of heat.
By utilizing this phenomenon, it is possible to create advanced thermal storage or temperature-regulating systems, depending on the process. Patrick McMullen is business development manager at Dynalene Inc. As a physicist who has analyzed different nuclear reactor designs , including small modular reactors , I believe that molten salt reactors are unlikely to be successfully deployed anytime soon. MSRs face difficult technical problems, and cannot be counted on to produce electricity consistently.
Molten salt reactors use melted chemicals like lithium fluoride or magnesium chloride to remove the heat produced within the reactor. In many MSRs, the fuel is also dissolved in a molten salt. Slower neutrons are more effective in triggering fission reactions as compared to highly energetic, or fast, neutrons.
The enriched uranium is dissolved in a fluoride salt in the IMSR. It does not use any material to slow down neutrons. Because of the different kinds of fuel used, these MSR designs need special facilities — not present in Canada currently — to fabricate their fuel. The enriched uranium for the IMSR must be produced using centrifuges , while the Moltex design proposes to use a special chemical process called pyroprocessing to produce the plutonium required to fuel it.
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