molten salt energy storage

Molten salt energy storage application and development trend

Under the background of “dual carbon”, building a new power system is a strategic task to ensure China’s energy security.
 
New energy sources such as photovoltaics, solar heat, wind power and hydraulic power are intermittent and unstable, which can easily cause a mismatch between energy supply and demand, and need to cooperate with energy storage technology.
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Molten salt energy storage is an energy storage method with a high level of safety. It uses molten salt such as nitrate as a heat transfer medium, stores and releases energy through heat storage and heat release cycles of molten salt, and realizes effective energy transfer.

The key core technologies and equipment of molten salt energy storage include molten salt, electric heaters, storage tanks and heat exchangers, etc. It is widely used in the following three directions: solar thermal power generation, peak-shaving and frequency modulation coupling of thermal power units, and coupling of new energy green power heating. For related information, please refer to top 10 thermal power companies.

Comparison of different application scenarios of molten salt energy storage

ApplicationMolten salt use temperature range/℃Heat transfer process
CSP system290~565Molten salt-Steam
Coupling thermal power unit140~650Molten salt-Steam, Steam-Molten salt, Electric-Molten salt
peak shaving FM  
Green power heating140~450Molten salt – steam, electricity – molten salt

For different application scenarios, the use temperature range and heat transfer process of molten salt are quite different. At this stage, the focus is on solving the technical needs of solar thermal power plants, and there is a serious shortage of systematic research on peak and frequency modulation of thermal power units coupled with molten salt energy storage, and green power heating.

Molten salt energy storage key technology

The current selection of molten salt energy storage is mainly high temperature resistant molten salt and low melting point salt. High-temperature-resistant molten salt, such as the mature solar salt, has a maximum working temperature of 565°C, which is suitable for high-parameter solar thermal power generation or heat storage and peak-shaving systems for thermal power units.

Low melting point salts are usually multi-component mixed salts with a melting point lower than 240°C, such as Hitec salts commonly used in engineering, which can reduce the risk of molten salt solidification and are suitable for systems with lower parameters. Molten salt storage tanks mainly include single-tank, double-tank, and multi-tank systems. The single-tank molten salt energy storage system has a simple structure and low cost, and is suitable for small-area civil heating and other fields, but there is a problem that the heat storage efficiency decreases due to the thermocline layer.

The double-tank system consists of a cold tank and a hot tank. The hot and cold molten salt is separated and the heat is circulated in the two tanks, which avoids the problem of the thermocline layer and has relatively low technical risks. On the basis of double tanks, the number of storage tanks can be further increased to form a multi-tank system to increase heat storage. For example, the 50 MW molten salt tower CSP project in Hami pioneered the system configuration of two hot tanks and one cold tank, which improved the reliability and flexibility of the unit.

The key to realizing large-scale molten salt energy storage is the development of low-cost and practical high-voltage molten salt electric heaters. At present, there are three main forms of molten salt electric heaters: resistance type, electrode type, and induction type. The existing technologies are generally 380V or 690V low-voltage resistance heaters, which are mainly used in photothermal power generation scenarios.

If it is used for electric heating of molten salt, such as green power heating, there will be a problem of high power transformation costs due to the mismatch between high-voltage green power input and low-voltage heaters. At present, there is a lack of mature high-voltage molten salt heaters on the market.

Traditional molten salt heat exchangers include shell-and-tube heat exchangers and sleeve-and-tube heat exchangers. Shell-and-tube heat exchangers are the main form of molten salt heat exchangers at present. Many researchers have given recommended tube-side and shell-side heat transfer correlations through experiments and calculations, and described their heat transfer characteristics mathematically.

The casing heat exchanger has the advantages of simple structure and high pressure resistance, and is also used in engineering. Compared with the traditional heat exchangers mentioned above, compact heat exchangers represented by printed circuit board heat exchangers have high efficiency and can withstand high temperature and high pressure conditions. It has great advantages in the coupling of new power systems such as molten salt energy storage and new power cycles.

The comparison and classification of key molten salt technologies are sorted out below, as well as the differences in the selection of molten salt, storage tanks, and heaters in different application scenarios.

Key technologyClassificationAdvantagesApplication range
Molten salt

High temperature

resistant molten salt

Expanded temperature range to support steam operation with higher parametersDevelop high-parameter solar thermal power plants
Low melting point saltExpand the temperature range and increase the operating days of the solar thermal power stationNuclear power and other low-parameter power plants
Storage tankSingle tankSimple structure, low investment costTrough or small solar thermal power generation system
Double tankRelatively low technical riskMost commercial solar thermal power plants
Multiple cansImprove unit reliability and flexibilityPartially applied to intermediate reheating units
HeaterResistance heaterSmall thermal inertia, fast temperature adjustment speed, high temperature control accuracyWidely used
Electrode heaterHigh voltage level (6kV)It is mostly used in conjunction with electrode boilers, and there are few applications at present
Induction Heater

Fast heating speed, avoid resistance heating

The problem of medium resistance wire blown

There are currently few applications
Heat exchangerShell-and-tube heat exchangers are robust and adaptableWidely used

Application of molten salt energy storage in the field of photothermal

Solar thermal power generation is the backbone of the new power system, which has the advantages of barrier-free grid connection and strong continuous power generation and regulation capabilities.

Photothermal power plants store solar energy in the form of heat in molten salt, and then use molten salt to heat feed water to obtain steam. The advantages lie in large energy storage capacity, low requirements on the geographical environment, and a construction scale of more than 10GW. The technical research focus of the solar-thermal molten salt energy storage power station is how to reduce its cost and improve its safety.

Double tank molten salt heat storage system

Double tank molten salt energy storage heat system

The indirect heat storage system requires a heat exchange device to transfer heat, using heat transfer oil or steam as the heat transfer fluid, and storing heat in molten salt. The heat exchange process of the indirect heat storage system is solar energy-molten salt-heat transfer oil-steam. The heat energy stored in the molten salt circulates through the heat transfer oil and reaches the steam generator for heat exchange. The molten salt energy storage system in the indirect heat storage system exists as a relatively independent module, which can be used to transform ordinary solar thermal power plants.

Due to the lack of thermal stability of heat transfer oil, the working temperature of indirect heat storage is generally specified below 400°C. The direct heat storage system uses molten salt as the heat transfer and heat storage medium, and its heat exchange process is solar energy-molten salt-steam, without the need for heat transfer oil circulation, avoiding bad heat exchange, it is suitable for high-temperature working conditions of 400-500°C, and can also improve power station efficiency and Rankine cycle efficiency.

Both forms of photothermal and molten salt coupling are applied in engineering. Molten salt indirect heat storage can generally maintain a high cycle efficiency, and the cost is lower than that of steam energy storage. For example, Andasol trough solar thermal power station in Spain is the first large-scale molten salt indirect heat storage power station with a capacity of about 1000MWh and an energy storage time of 7.5h.

The direct heat storage of molten salt simplifies the composition of power station equipment and facilitates later operation and maintenance. A typical molten salt direct thermal storage power station is the Solar two project in the United States. The nitrate mixed salt used in this project is called Solar salt, and the temperature range is 290~565°C. Since then, most of the tower-type molten salt solar thermal power plants have used the direct heat storage method and this working temperature range, such as the Gemasolar power plant in Spain and the 10MW project of Supcon Delingha in Qinghai.

The future development of CSP mainly lies in high-parameter operation and coupling of new power cycles. The key technology involved in high-parameter operation is high-temperature-resistant molten salt. The selection of carbonate and some chloride salts of the MgCl2-KCl-NaCl mixed system can improve the overall efficiency of the system.

The new power cycle of photothermal coupling mainly involves high-parameter molten salt and molten salt energy storage heat exchanger. Taking the S-CO2 Brayton cycle photothermal power generation system as an example, among them, the maximum working temperature can reach 800°C, and the temperature difference between the hot and cold tank molten salt will reach 100~120°C, which makes energy storage more difficult, and requires the use of stable performance, wide temperature range, and high-parameter molten salt.

The system has high parameters, high efficiency, and compact components, and the molten salt-carbon dioxide heat exchanger involved needs to withstand harsh working conditions. In the field of molten salt-carbon dioxide heat exchange, compact heat exchangers such as printed circuit board heat exchangers can be selected, which have high heat exchange efficiency and can withstand high temperature and high pressure conditions up to 30MPa.

Printed circuit board heat exchangers have been studied for molten salt energy storage and carbon dioxide circulation. He Yaling and others designed and manufactured a wing-shaped fin printed circuit board heat exchanger, which uses fins with better heat transfer performance to strengthen the heat transfer channel in the molten salt system with low working pressure.
Zhang Huzhong and others built a supercritical CO2 heat exchanger test platform with a maximum pressure and temperature of 32MPa and 600°C, respectively, and deeply grasped the flow and heat transfer characteristics of supercritical CO2 in a printed circuit board heat exchanger. In solar thermal power generation, the tower type absorbs the concentrated solar energy through the heat absorbing tower, and transfers heat to the heat tank; the trough type collects solar energy through the heat collecting tube;

The cost of linear Fresnel solar thermal power generation is low, and it has good commercialization prospects in western China; The use of supercritical CO2 in photothermal systems has the advantages of high cycle efficiency and compact structure. Solar thermal power heaters are generally low-voltage resistance type, which can meet the demand at a lower cost. In addition to the heater, the differences in the molten salt energy storage technologies involved in different technical routes can be found in the table below.

Technical routeTemperature/°CCapacity scale/(MWh)Applicable molten saltStorage tankHeat exchanger
Tower type565≥1000Solar saltdouble tankShell-and-tube
Trough type398≥1000

solar salt,

low melting point salt

Single and double tankShell-and-tube
Linear Fresnel type530≥1000solar saltDouble tankShell-and-tube
Supercritical CO2 photothermal system700≥1000high temperature molten saltDouble, Multi tankShell-and-tube、printed circuit board

Application of molten salt energy storage in thermal power peak regulation

The use of energy storage in thermal power units can achieve peak shaving and valley filling. At present, engineering applications can be realized with high-temperature molten salt energy storage heat coupled with thermal power unit peak regulation technology. The advantage of the molten salt-thermal power coupling system is that it can greatly improve the unit’s ability to deep peak regulation and provide high-temperature steam.

There are various forms of molten salt-thermal power coupling, such as extracting part of the main steam and reheated steam into the molten salt energy storage module to realize steam heat storage; Electric heating of molten salt heated by generator outlet electricity; flue gas heat storage through flue gas-molten salt heat exchanger and hybrid heating combined with the above coupling forms. In order to improve the molten salt-steam heat exchange efficiency and increase the energy storage time, the field of thermal power peak regulation mainly involves the selection of molten salt with high parameters and wide temperature range and the safe and stable double-tank molten salt system.

Steam heat storage

Reheat steam heating molten salt

While the thermal power unit is running normally, the high-pressure main steam and reheat steam are extracted to heat the molten salt, the coupling system can improve the peak shaving performance and the cycle efficiency of the whole process, and is mainly suitable for steam heat storage at a level of 500~600 °C in a subcritical primary reheat unit.

Luo Haihua et al. proved the feasibility of the solution of reheating steam to heat molten salt through calculation. This solution uses the heat stored in molten salt to heat feed water and output industrial steam, which can realize thermoelectric decoupling of thermal power units and heat peak regulation.

Molten salt-thermal power coupling can also have multiple steam extraction points. Taking a 600MW unit as an example, Fan Qingwei proposed a multi-tank-multi-heat exchanger heat storage system. The reheat steam is introduced into two heaters respectively, and the exergy efficiency of the heater in the hydrophobic section is the highest.

Reheat and superheated steam heating molten salt

The technical route of simultaneously extracting reheating, superheated steam and molten salt energy storage heat exchange can make full use of the high-temperature steam generated by the boiler, and the applicable main steam temperature is 500-600°C. Wang Hui et al. designed the supercritical 100-megawatt molten salt energy storage process for thermal power units. The specific process is shown in Figure 2.

Among them, the molten salt in the cold tank is divided into two paths after preheating, and enters the overheating heater and the reheating heater respectively, and the two paths are mixed and then enters the hot salt tank to realize the flowing heat storage of the molten salt circuit. Each process module of this scheme is a closed cycle, and the high-temperature working fluid of the boiler and steam turbine is not reduced or wasted in the whole process, which can greatly improve the deep peak-shaving capability and system flexibility.

Molten salt heated by steam in high recooling section

Extracting reheat steam to heat molten salt may cause the reheat temperature to exceed the limit, and the above problems can be avoided by using a double reheat unit with flue gas recirculation. This technical route is suitable for the double reheating unit with the main steam temperature of 600-620°C. In the above-mentioned unit, the steam in the high recooling section is extracted to heat the molten salt, and the stored heat energy can be used to heat the feed water, supply heat or supply industrial steam, improving the flexibility of the unit.

Taking an ultra-supercritical 660MW double-reheat unit as the research object, Zhang Shigang proposed to simultaneously extract high-temperature steam from the primary and secondary high-recooling sections for molten salt energy storage. Pang Liping simulated the load response characteristics of the boiler and steam turbine of the double reheat unit, and the results showed that the steam in the high recooling section is used for heat storage in molten salt, which can improve the response rate of the double reheat unit to the grid load.

Direct steam heat storage technology DSG

For steam heat storage of ultra-supercritical units above 620 °C, direct steam heat storage technology (Direct steam generation, DSG) is required. The DSG power station only produces saturated steam, and the conventional molten salt cold and hot tank switching operation mode cannot be adopted, and it lacks a suitable long-term large-scale heat storage system. In order to solve the bottleneck of DSG technology, high-parameter molten salt technology and multi-tank molten salt system can be used to form the energy storage device of DSG.

For example, Seitz et al. coupled three tanks of molten salt energy storage in the DSG system, cold, hot, and intermediate tanks, to indirectly store the heat of evaporation of feed water for preheating and superheating. The disor project uses sodium nitrate molten salt with a melting point of 306°C as the medium to directly exchange heat with water vapor. Such special cases involve high-parameter molten salts, which have high requirements on the thermal stability of molten salts.

Different situations of steam heating molten salt

In the field of main steam heat storage and reheat steam heat storage, there are differences in the selection of molten salt. The reheat steam pressure parameter is relatively low, generally about 4MPa, corresponding to a saturated steam temperature of about 251°C. Figure shows the heat storage of high-temperature main steam and reheat steam in molten salts with different melting points.

Main steam and reheat steam molten salt thermal storage

a)Reheat steam to heat molten salt       b)Main steam heating molten salt
Main steam and reheat steam molten salt thermal storage

If the melting point is lowered and the molten salt with a melting point of about 100°C is selected, the upper limit of the use temperature can be raised to 450°C. However, the application research of this kind of molten salt is not enough, and it is rarely used in engineering practice. If conventional solar salt is used, its operating temperature is 260~565°C. At this time, the minimum operating temperature of molten salt is close to the saturated steam line, and the space heated by reheated steam is small, so it is not suitable for this scenario.

To sum up, in the case of reheating steam heat storage, molten salt with a lower melting point should be used, and its maximum use temperature does not need to be set too high. On the contrary, the parameters of the main steam are relatively high. Taking the main steam of 14MPa as an example, the corresponding saturated steam temperature is about 335°C, as shown in Figure 3b) point b, its pinch point position is relatively higher, and the restriction on molten salt heating is relatively small .

Fig. 3b) describes the situation where the main steam of the same parameter heats molten salt with different parameters. At this time, the common working temperature range of low melting point molten salt is 140°C~450°C, and the maximum temperature can be further expanded. The working temperature of solar salt is about 260°C~565°C. Under this steam parameter, it can only be heated to about 420°C. If the melting point is lowered, the molten salt can even be heated to above 530°C.

It can be seen that for the main steam heat storage and heat supply scene, conventional molten salt can be applied. However, for the molten salt energy storage scene where steam is generated after the main steam heat storage, it is suitable for wide temperature range molten salt with low melting point but high maximum temperature.

Electric heating molten salt at generator outlet

The technical route of electric heating molten salt at the generator outlet is to use the high-voltage electric heating molten salt at the generator outlet of the power plant, and output the stored heat energy as peak-shaving electric energy, that is, “electricity-heat-electricity” conversion.

The stored thermal energy can also be used to generate heat, i.e. “electricity-heat-heat” conversion. The electric heating molten salt energy storage is easy to start and stop, which can improve the utilization rate of existing heat storage and power generation equipment, reduce the curtailment rate of wind and light, and improve the efficiency of power stations.

Compared with photothermal power generation and electrochemical energy storage, electric heating of molten salt can be realized by adding an electric heating molten salt device at the generator outlet of the power plant, and the cost reduction space is large; Compared with storage batteries such as lithium batteries, its advantage is that it has the function of flexible transformation of thermal power and meets the needs of flexible peak regulation and frequency regulation.

In the scenario of electric heating of molten salt, the electric energy comes directly from the outlet of the generator, and the power scale is large. The use of traditional low-voltage resistance molten salt heaters cannot meet the demand. Therefore, high-voltage heating systems such as high-voltage resistive, induction, and electrode heaters are required. The voltage level of the high-voltage molten salt heater can reach 6-10kV, which can avoid the problem of high transmission line loss in the low-voltage resistance heating scheme, and the cost is low.

“Electric-thermal-electric” molten salt electric thermal storage is a kind of electric thermal energy storage, that is, “Carnot battery” technology. A double-tank molten salt system can be used to generate heat and generate electricity through the circulation of hot and cold tanks. In the case of “electric-thermal-thermal” conversion, molten salt electric heat storage has similarities with solid heat storage and can be combined.

The urban construction community of Chongli District, Zhangjiakou City uses solid heat storage electric boilers. The green electricity enters the 110kV electric boiler to heat the magnesia bricks to 500-550°C. The stored heat energy is then transferred to hot water through the heat exchanger, and the hot water enters the central heating system.

Flue gas heat storage

The high-temperature flue gas in large thermal power units can reach 700-800°C. If heat can be stored in molten salt to form a stable heat source, it can realize sustainable heating with higher parameters or supply civil hot water, and at the same time make the boiler adapt to the heating needs with large changes in heat load, and improve the peak-shaving capability of the unit.

Molten salt flue gas heat storage involves high-parameter molten salt and a special flue gas-molten salt heat exchanger. At present, there are many designs for heat storage and heat exchange equipment for high-temperature flue gas and molten salt, such as guiding the flue gas through the heating rod, a special heat exchange channel for heat storage of high-temperature flue gas molten salt, and a self-cooling panel heater that uses high-temperature flue gas to heat molten salt, etc.

Its advantage is that the heat transfer temperature difference is large and the heat grade is high. The flue gas-molten salt heat exchanger can also collect the high-temperature waste heat generated in the steelmaking process. It is composed of multiple parallel metal tube bundles and arranged in the smoke chamber.

Flue gas waste heat is collected through the flue gas-molten salt heat exchanger, which can be reused through the molten salt double tank system. The cycle of using heat storage in the double-tank molten salt to realize power generation includes: the low-temperature molten salt enters the heat exchanger tube bundle from the flue gas outlet, and exchanges heat with the flue gas to become a high-temperature molten salt;

The feed water is heated through the superheater, evaporator, and preheater in sequence, and the superheated steam is output to drive the steam turbine to generate electricity, and the low-temperature molten salt after heat exchange returns to the storage tank.

The existing high-temperature flue gas molten salt heat exchanger has a small applicable temperature range and cannot utilize the waste heat of low-concentration flue gas, so it still needs to be improved in terms of safety and heat storage and heat transfer capacity. Table shows the selection of molten salt energy storage technology under the scenarios of steam, electric heat storage, and flue gas heat storage.

Applicable molten salt energy storage technologies for different technical routes in thermal power field

Technical routeTemperature/℃Applicable molten saltStorage tankHeat exchangerElectric heaters
Reheat steam heat storage 400~500Low melting point saltDouble tank, multi tankShell-and-tubeLow voltage resistive
Main steam storage400~500Solar salt, low melting point wide temperature range molten saltDouble tank, multi tankShell-and-tubeLow voltage resistive
Electric thermal storage  90~500Solar saltDouble tankShell-and-tubeHigh voltage resistive, inductive, electrode type
Flue gas heat storage 700~800High temperature molten saltSingle tank, double tankShell-and-tube flue gas-molten salt heat exchangerLow voltage resistive

Application of molten salt energy storage in green electric heating

New energy power generation is called green power. Green power heating is a new way of new energy consumption. Through the heat transfer of electricity-molten salt-feed water, it is used for home heating. Generally, a double-tank molten salt system is used to realize green electricity heating, and its principle is shown in the figure.

The molten salt is heated and stored in a high-temperature molten salt tank by using green or off-peak electricity, and the high-temperature molten salt is extracted from the tank during the day, and the feed water is heated through a molten salt heat exchanger to meet various needs.

For example, the supply of 90°C hot water to realize conventional residential heating, the supply of 180-360°C medium-low temperature industrial steam, and the supply of high-temperature steam above 500°C. After heat exchange, the cooled molten salt flows into the low-temperature molten salt tank to complete the cycle.

Principle of molten salt energy storage heating system

Principle of molten salt energy storage heating system

Green electricity heating is an efficient and clean heating method, and pilot projects have been carried out in various places. Hebei Xinji Molten Salt Heat Storage Low-valley Electricity Green Heating Demonstration Project uses low-melting point salt as heat transfer and heat storage working medium, and uses 10-hour low-peak electricity from the power grid to heat molten salt to supply civil hot water, and the heat storage time is 16 hours.

The Beijing Gas Thermal Heating Center converts low-valley green electricity at night into thermal energy and stores it in molten salt at 180-390°C. During the day, it uses molten salt energy storage to heat the Beijing West Railway Station area, and at the same time supplies stable medium and low temperature industrial steam to the outside world.

Compared with gas heating, the operating cost of green electric heating is lower; compared with heat pump heating technology, its initial investment is lower; Compared with water heat storage electric heating, its advantage lies in the small footprint and high energy storage density. Some green power heating units can simultaneously supply civil hot water below 100°C and various types of industrial steam, with high thermal efficiency, providing a new direction for the transformation of thermal power units.

The key technologies involved in green electric heat supply are safe and stable double-tank system, high-efficiency heat exchanger and high-voltage molten salt electric heater. Floating coil elastic tube bundle heat exchangers are often used in ordinary civil hot water supply systems, but in the case of molten salt-water heat exchange, it is necessary to modify and optimize shell-and-tube molten salt heat exchangers.

Since molten salt heaters directly connected to the power grid can save electricity transformation costs, mature and reliable high-voltage molten salt heaters are also required for green electricity heating, such as various types of high-voltage resistance heaters, electrode heaters, and electromagnetic induction heaters.

For some units that only provide civil hot water or medium and low temperature industrial steam, 380V electrode type or resistance type molten salt heating furnace can also be used directly. To summarize the key technologies applicable to different technical routes of green electricity heating, see the table below.

The molten salt energy storage technology applicable to the green electricity heating technology route

Technical routeTemperature/℃Applicable molten saltStorage tankHeat exchangerElectric heaters
High parameter heating, industrial steam360~500Solar saltDouble tankShell-and-tubeHigh voltage resistive, inductive, electrode
Medium and low temperature industrial steam180~360Low melting point saltDouble tankShell-and-tubeHigh voltage or low voltage resistive, inductive, electrode
Civil hot water 90Low melting point saltSingle tank,
double tank
Shell-and-tubeHigh voltage or low voltage resistive, inductive, electrode

In the green electricity heating scenario, molten salt is used to heat steam or supercooled water, and low-parameter or high-parameter molten salt should be selected according to different situations. The heat transfer of molten salt steam in green electricity heating is shown in the figure.

It can be seen from figure a) that the temperature rise of the steam is limited by the pinch point a, to output high-temperature industrial steam exceeding 500°C, it is necessary to increase the heat storage temperature of molten salt to about 600°C, and use high-parameter molten salt to exchange heat with steam.

When supplying medium and low temperature industrial steam, the use of nitrate molten salt with a lower melting point can meet the demand (Figure b). The process of molten salt heating steam is limited by the temperature of pinch point b, and finally in the low-parameter molten salt working range of 150-450 °C, steam at 1.2 MPa and 370 °C can be supplied.

Schematic diagram of molten salt steam heat exchange in green electricity heating

a)High parameter molten salt heating steam   b)Low parameter molten salt heating steam
Molten salt steam heat exchange in green electricity heating

Conclusion

1) At present, there are various technologies related to molten salt energy storage, but all key technologies are lacking, which limits the application and development of molten salt energy storage in new power systems. At present, in the field of multi-component mixed molten salts, low melting point salts are mainly nitrate and nitrite systems of lithium, calcium, potassium and other elements, such as Hitec salt.

The corrosiveness of chloride salts and the easy decomposition of carbonates in high-temperature salts still need to be researched to provide more commercial molten salt materials for the market. In addition, there is insufficient research on the preheating and variable working conditions of molten salt storage tanks, and there is a lack of complete manufacturing standards and specifications for large-scale high-temperature molten salt storage tanks.

The market lacks mature high-voltage grade molten salt electric heaters. Although some electromagnetic induction heaters can be connected to high voltage, the cost is high and it is not universally applicable. At present, the widely used traditional shell-and-tube heat exchangers do not take molten salt as the working fluid into consideration, and there is a lack of experimental research on optimizing the configuration of molten salt heat exchangers.

2) The technological breakthrough of the molten salt energy storage system can improve efficiency and reduce costs, and is also the key to enhancing the competitiveness of solar thermal power plants. At present, in the field of photothermal, China already has the foundation to support the large-scale development of photothermal power generation. The cost control of solar thermal power generation is mainly achieved by improving system efficiency and reducing equipment costs.

molten salt energy storage

There are two main ways to improve system efficiency:

(1) High-parameter solar thermal power generation, with a larger temperature range and heat storage capacity, and higher cycle efficiency;

(2) A new type of power cycle coupled with light and heat, such as a molten salt energy storage coupled with S-CO2 light and heat power generation system, printed circuit board heat exchangers resistant to high temperature and high pressure are required, and the temperature of the heat storage system must exceed 700°C. However, there is no mature commercial molten salt that can meet the demand, and there is a technical bottleneck.

Cost reduction should start with the key technology of molten salt energy storage, such as the selection of molten salt for next-generation solar thermal power plants, which is expected to meet the requirements of low melting point, high temperature resistance, and low cost at the same time. However, regarding the selection of different molten salts, storage tanks, heaters, etc., it is necessary to further refine industry standards, form a standardized evaluation system, and promote the realization of technical support.

3) The combination of thermal power unit and molten salt energy storage is an effective way to increase the flexibility of the unit and improve the cycle efficiency of the whole process. However, at present, there are few studies on the operation conditions of the coupling of thermal power units and molten salt energy storage, and the safety guarantee of the double-tank system still needs further practical research.

The existing research scope of the molten salt-thermal power coupled power generation system is mostly aimed at units with a main steam temperature below 620°C, and there is still a lack of mature solutions for thermal storage of molten salt steam with a main steam temperature above 620°C for ultra-supercritical units.

At present, the feasibility of extracting reheated or superheated steam to heat molten salt has been confirmed, but the standard for the specific steam extraction volume is not yet clear, and the negative impact on the overall thermal power system also needs further comparative research.

To learn more about energy storage, please refer to gravity energy storage, electrochemical energy storage, and the following related articles.

Lucky Li
Lucky Li
My name is Lucky Li, and I have been engaged in the lithium battery industry for more than ten years. It has been 5 years since I started writing about lithium-ion batteries, I have a deep understanding of lithium-ion batteries, not only that, but also analyze and write according to the market in this field, and will continue to learn and research. I hope to provide help to everyone who is interested in the new energy industry.
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