The installed capacity of new energy will be increased on a large scale, but because new energy sources such as photovoltaics and wind power have shortcomings such as unstable output and mismatches between power generation curves and power consumption curves, it is recommended to use energy storage systems. In the steam sector, the vast majority of traditional fossil fuels are still used.
As the pressure on environmental protection increases, an alternative approach needs to be found. Molten salt energy storage has important advantages such as large heat capacity, strong heat conductivity, stable properties and good economy. It also has broad application prospects in the field of steam supply.
Based on the characteristics of it, this technology has the advantages of environmental protection and low carbon, energy saving and emission reduction, and efficient utilization, and is worthy of large-scale promotion and application. The molten salt energy storage has the advantages of large heat capacity and good economy, and has broad application prospects in the field of steam supply.
1. Characteristics of molten salt energy storage
Molten salt (referred to as molten salt) refers to the molten liquid of salt, and common molten salt refers to the molten body formed when the temperature of inorganic salt rises above its melting point. As an excellent heat transfer and energy storage medium, molten salt has the following advantages:
● Use a wide range of temperature ranges
Molten salt can be mixed with a variety of different elemental salts to form molten salts with different melting points to meet the needs of different working conditions.
● Lower saturation vapor pressure
Due to the good thermal stability of molten salt, its working system is almost an atmospheric system in its working temperature range, and there is no need to operate under pressure.
● High energy storage density
Due to the wide temperature range of molten salt, the use temperature can reach more than 400 °C, which provides a large temperature difference, and the energy storage density has obvious advantages.
● Low viscosity
In the operating temperature range, the fluidity of molten salt is similar to water, reducing pump consumption and saving energy. Good stability and long life In principle, molten salt energy storage uses the sensible heat of the molten salt material itself, and does not undergo chemical changes.
● Cheap and easily acessible
Molten salt is a mixture of one or more types of salt, with extremely rich reserves, a wide range of material sources, and obvious cost advantages.
● High thermal conductivity and heat transfer capacity
Molten salt has a high thermal conductivity at working temperature, and it has more convective heat exchange when used as a medium such as fluid or water. The heat exchange capacity is stronger than that of solid heat storage and phase change heat storage, which can greatly reduce the volume of the heat exchanger.
Based on the excellent characteristics of molten salt, it can be considered that in the field of energy storage technology, this kind of way to store energy has inherent advantages, and molten salt materials and system equipment are the core of molten salt energy storage.
2. Working principle of molten salt system
The molten salt energy storage system is mainly composed of molten salt heating device, molten salt energy storage device, molten salt heat exchange device, water treatment system, pump valve, instrument pipeline system, control system, etc.
Molten salt energy storage technology is an emerging technology gradually developed by using molten salt energy storage materials as the medium to store solar thermal energy, geothermal energy, industrial waste heat, low-grade heat, valley electricity and so on.
In the form of heat energy, and release it when needed, in an effort to solve the problem caused by the mismatch between heat energy supply and demand in time, space or intensity, and maximize the energy utilization rate of the entire system.
3. Benefits of molten salt energy storage
Molten salt energy storage has many important advantages and broad application prospects. The merits lie in:
● Increase equipment utilization
It can effectively solve the contradiction between supply and demand on the energy supply side and the user side, improve energy utilization, and is one of the most valuable energy storage technologies in the field of new energy consumption and steam supply.
● Excellent thermal conductivity
The core of molten salt energy storage technology is composed of molten salt energy storage materials, heating devices, auxiliary supporting equipment, etc. Especially in its operating temperature range, the properties are similar to water, and it is an excellent heat transfer and energy storage medium.
● Paired with solar thermal power generation
New energy sources have a large-scale growth trend, but the intermittent and decentralized nature of technology has led to the lack of mature means to recycle some energy sources. Therefore, it is necessary to increase the value of new energy equipment and improve energy utilization.
The short life of battery energy storage and low energy storage density limit its large-scale development and utilization. Molten salt energy storage has the advantages of high energy storage density, long service life, simple maintenance and high economy, which has attracted widespread attention.
Combining the advantages of the two can get better application. Molten salt energy storage can also enter the household field with the help of batteries. The combination of the energy storage system and the off grid solar batteries can achieve more. Up to now, although there are fewer cases of molten salt energy storage. However, based on the above advantages of molten salt energy storage, this type of project will be promoted on a large scale in the foreseeable future.
4. Application prospect of molten salt energy storage
● New energy consumption
Based on policy factors, China will increase its use of photovoltaic and wind power in the future. However, these new energy sources have the characteristics of discontinuity, a large peak-valley difference, etc., which often limit their development scale.
In the past, in order to cope with the large peak-valley difference of the power grid, the cost of power generation increased and the utilization rate of equipment was low. It is difficult to achieve sustainable and healthy development of energy resources and electricity consumption.
The use of molten salt technology to store energy and to absorb new energy, large-scale recycling of wind energy, solar energy and other energy that cannot be absorbed normally, is conducive to the long-term development of new energy. The application of thermal energy storage is one of the important means to improve the utilization rate of new energy and absorb new energy.
Molten salt energy storage is a sensible heat storage technology that uses the temperature difference of materials in the heating or cooling process to achieve thermal energy storage.
Throughout the entire operating temperature range, the heat storage material remains in a liquid state, and the system has the advantages of a wide range of applications, safety and stability. It is the first choice for large-scale medium and high temperature heat storage technology.
● Industrial steam supply field
In energy storage technology, although chemical energy storage, phase change energy storage and other technologies are research hotspots, their development will be limited by the poor heat transfer performance of the material itself and the low energy storage density.
Electric energy storage density is only equivalent to 1/10 of thermal energy storage density, but the price of electric energy storage is more than 10 times that of thermal energy storage, and it is not suitable for large-scale utilization.
As a kind of sensible heat energy storage, molten salt energy storage is nearing completion in the development stage and is in the stage of large-scale promotion. Due to the excellent characteristics of molten salt, molten salt energy storage has great advantages in the field of medium and high temperature steam supply.
5. Introduction of project application cases
At present, the molten salt energy storage projects that have been completed in China are all used in solar thermal power generation. The use of solar energy heating molten salt for energy storage, the use of low valley electric heating molten salt for energy storage, and the technology is applied to the home energy storage.
The core equipment of the system is molten salt energy storage tank, molten salt heating device, heat exchange equipment. The molten salt is a special mixed molten salt with a low freezing point. Its main workflow is as follows. During the nighttime trough, low-cost electrical energy is converted into heat energy for storage.
When gas is used during the day, the molten salt energy storage system supplies steam through the heat exchanger. To ensure the security of the system, taking into account the economy of the system. The system innovatively adopts the overall lifting method of heat exchange equipment to lift the molten salt pipeline and molten salt related equipment as a whole.
When the system is not working, it can ensure that all molten salt flows back to the molten salt energy storage tank, which can effectively solve the problem of combing salt in the system and reduce the number of combing devices. At the same time, it can also ensure the security of the system and save some costs.
In the context of clean energy targets, emission reduction has become an important target. The application ratio of wind power and photovoltaic will increase on a large scale, resulting in a certain degree of abandonment of wind and light, so energy storage technology will get better development opportunities.
Molten salt energy storage and steam supply technology provide a feasible method to solve the problem and reduce emissions, which is a promising technical route. It can be seen from the project examples that the economic benefits are good. At the same time, it can significantly reduce pollutant emissions.