Under the background of worldwide climate warming and the depletion of non-renewable energy, the research and development of renewable energy is developing rapidly. The low energy utilization efficiency of traditional industries and the instability of solar and wind energy all require supporting energy storage to solve the mismatch between energy supply and demand in terms of time, space, and intensity.
Molten salt energy storage is an energy storage technology that solves the above problems.
Basic principles of molten salt energy storage
Molten salt refers to liquid salt in a molten state, and molten salt used in engineering usually refers to an inorganic salt melt. Molten salt has the characteristics of high boiling point, low viscosity, low vapor pressure and high volume heat, and is an excellent heat transfer and heat storage medium. Molten salt energy storage technology uses the temperature difference of molten salt during heating and cooling to realize thermal energy storage.
Molten salt energy storage solar thermal power generation field
The world’s first solar thermal power generation project equipped with molten salt heat storage energy storage technology is the Solar Two experimental power station, which laid the foundation for the application of molten salt in the field of solar thermal power generation.
In March 2009, Spain’s Andasol trough solar thermal power station, which was successfully operated, was equipped with a molten salt heat storage system, becoming the world’s first commercial concentrated solar power station.
Qinghai Gonghe 50MW solar thermal power station, which is under the general contract of China Power Construction Group Northwest Survey and Design Research Institute Co., Ltd., adopts the molten salt tower technology route. The load runs for 6 hours.
Binary salt Solar Salt (60% sodium nitrate + 40% potassium nitrate) is currently the heat transfer and storage working fluid selected by most photothermal power plants, with a melting point of 220°C and a maximum working temperature of 600°C. Solar thermal power plants generally use cold/hot molten salt dual storage tanks to store molten salt.
The molten salt in the cold molten salt storage tank is transported to the solar collector through the molten salt pump, and enters the hot molten salt storage tank after absorbing heat energy and heating up. Then the high-temperature molten salt flows into the molten salt steam generator to generate superheated steam, which drives the steam turbine to generate electricity, and the molten salt flows back to the cold molten salt storage tank after the temperature is lowered.
During the actual operation of the solar thermal power station, the intensity of sunlight will continue to change. The heat transfer and storage system needs to adjust the molten salt flow rate in time according to the temperature and pressure of the molten salt in the pipelines of each node, so as to ensure the stable operation of the system and the overall stable output of the power station.
Heating field of molten salt energy storage
Valley electricity thermal storage heating technology is one of the emerging heating technologies in recent years. It utilizes night-time low-valley electric heating to heat the energy storage medium, converts the surplus low-valley power at night into thermal energy for storage.
And it also supplies heat when it is ready for use, effectively solving the problem of the problem of time mismatch between energy supply and demand transfers the surplus low-peak power, improves the comprehensive utilization efficiency of energy, and brings considerable economic benefits. Molten salt energy storage technology can realize off-peak electricity heat storage.
During the valley electricity period at night, the molten salt pump transports the cold molten salt in the low-temperature molten salt storage tank to the molten salt heater, which is heated by the valley electricity and stored in the high-temperature storage tank. During the daytime heating period, the high-temperature molten salt is The molten salt is pumped out and flows into the molten salt-water heat exchanger.
Compared with water heat storage, solid heat storage, and box-type heat storage, the molten salt heat storage heating system has obvious advantages in consideration of factors such as floor area, system safety, service life, and energy storage density.
Molten salt energy storage waste heat recovery field
The energy consumption of China’s iron and steel industry has always been high, and the total energy consumption accounts for about 15% of the national industrial energy consumption. The energy utilization rate is low, only about 30% to 50%. The waste heat generated by the iron and steel industry has a wide range of temperatures, and there is a large amount of recyclable heat in the steel products, steel slag waste, coke, etc. formed in the production process of each process.
Currently widely used converter flue gas waste heat recovery system can only convert high-temperature waste heat into low-grade low-pressure saturated steam for power generation, and the waste heat resources are not fully utilized.
The high-temperature waste heat generated in the molten salt steelmaking process of the iron and steel furnace uses molten salt as the heat exchange and energy storage medium. The flue gas-molten salt heat exchanger is set in the smoke chamber by a plurality of parallel metal tube bundles, and the upper and lower ends are connected to each other.
The flow direction of the molten salt in the tube bundle is opposite to that of the flue gas. The low-temperature molten salt enters the tube bundle from the flue gas outlet, exchanges heat with the flue gas to become a high-temperature molten salt, and is stored in a high-temperature molten salt storage tank.
The high-temperature molten salt passes through the superheater, evaporator, and preheater in sequence through the molten salt pump, exchanges heat with water to become low-temperature molten salt, and returns to the low-temperature molten salt storage tank. The superheated steam generated in the evaporator drives the steam turbine to generate electricity.
In contrast, the steel furnace molten salt waste heat recovery power generation system can convert high-temperature waste heat into high-quality heat energy, generate stable and sustainable high-temperature steam, greatly improve power generation and energy efficiency, and improve the flexibility of the waste heat power generation system.
Thermal power flexibility transformation field
The main goal of thermal power flexibility transformation is to improve the minimum output limit of thermal power units, expand the range of unit output adjustment, and reduce the ratio of power generation to heat generation in the combined heat and power combination, that is, thermoelectric decoupling.
At present, there are many technical routes to realize thermoelectric decoupling of generating units, and molten salt energy storage technology is one of the important methods, which can match the thermal system parameters of thermal power units, and significantly improve the peak-shaving capacity of thermal power units.
The molten salt energy storage thermoelectric decoupling system uses high-temperature steam to heat molten salt energy storage and realize heat supply. When the load of the generating set is high and the heating capacity is excessive, the system switches to the heat storage mode.
That is to say, the low-temperature molten salt is heated by a steam heat exchanger to become high-temperature molten salt, which is transported to the high-temperature molten salt storage tank by the molten salt pump for storage. After heat exchange, the temperature of the high-temperature steam decreases, and enters the heat supply header to supply heat energy users.
When the load of the generator set is so low that the heating parameters cannot be guaranteed (<65%), the system will enter the exothermic mode, that is, the high-temperature molten salt is used as the heating source, and it passes through the superheater, evaporator, and preheater in turn, and the water is heated to generate heat.
Steam, to supply thermal energy users. Through thermoelectric decoupling, the thermal power unit will not be limited by industrial heating, the peak-shaving capability of the generating unit is improved, and the flexibility of unit operation is increased.
Compared with the existing peak-shaving technology of thermal power units, the peak-shaving technology of thermal power units with steam heating molten salt energy storage has the advantages of low energy consumption, more energy-saving and reliable unit operation, and low transformation costs.
Conclusion
Molten salt energy storage technology still needs more in-depth engineering research and mining of wider application scenarios. Scientists are looking for multi-element molten salts with lower melting point, higher working temperature, simpler industrial production and higher energy storage efficiency to meet the ever-growing demand for energy storage.
With the deepening of research, molten salt energy storage technology will release greater potential in reducing environmental pollution and improving energy efficiency. Meanwhile, many companies have made some progress in innovating energy storage technology, and the article top 10 energy storage company in China contains the contents.
Binary salt Solar Salt (60% sodium nitrate + 40% potassium nitrate) is currently the heat transfer and storage working fluid selected by most photothermal power plants, with a melting point of 220°C and a maximum working temperature of 600°C. Solar thermal power plants generally use cold/hot molten salt dual storage tanks to store molten salt.
The molten salt in the cold molten salt storage tank is transported to the solar collector through the molten salt pump, and enters the hot molten salt storage tank after absorbing heat energy and heating up. Then the high-temperature molten salt flows into the molten salt steam generator to generate superheated steam, which drives the steam turbine to generate electricity, and the molten salt flows back to the cold molten salt storage tank after the temperature is lowered.
During the actual operation of the solar thermal power station, the intensity of sunlight will continue to change. The heat transfer and storage system needs to adjust the molten salt flow rate in time according to the temperature and pressure of the molten salt in the pipelines of each node, so as to ensure the stable operation of the system and the overall stable output of the power station.
Valley electricity thermal storage heating technology is one of the emerging heating technologies in recent years. It utilizes night-time low-valley electric heating to heat the energy storage medium, converts the surplus low-valley power at night into thermal energy for storage.
And it also supplies heat when it is ready for use, effectively solving the problem of the problem of time mismatch between energy supply and demand transfers the surplus low-peak power, improves the comprehensive utilization efficiency of energy, and brings considerable economic benefits. Molten salt energy storage technology can realize off-peak electricity heat storage.
During the valley electricity period at night, the molten salt pump transports the cold molten salt in the low-temperature molten salt storage tank to the molten salt heater, which is heated by the valley electricity and stored in the high-temperature storage tank. During the daytime heating period, the high-temperature molten salt is The molten salt is pumped out and flows into the molten salt-water heat exchanger.
Compared with water heat storage, solid heat storage, and box-type heat storage, the molten salt heat storage heating system has obvious advantages in consideration of factors such as floor area, system safety, service life, and energy storage density.
