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Principle of molten salt heat storage and clean energy heating

作者:山西常晟集团时间:2020-01-15

Have you ever heard of "coal to gas" or "coal to electricity", or "salt" for heating? What kind of high-tech thing is "salt"? What kind of ability can it undertake the task of clean heating?

What is "high technology" in "salt"?

When it comes to "salt", we are all very familiar with it. We can hardly live without it. However, the "salt" used for heating is not table salt, but ordinary salt is transformed into molten body after high-temperature treatment to form molten salt.

Figure: molten salt state at different temperatures (source: Sina Technology)

Generally, the molten salt refers to the molten body of inorganic salt, such as the molten body of alkali metal, alkaline earth metal halide, nitrate, sulfate, etc. The generalized molten salt also includes oxide melt and molten organic matter.

Figure: heat storage performance of partial molten salt (source: Network)

Molten salt is an ionic melt composed of cations and anions, which has many unique properties.

For example, molten salt generally has the performance advantages of high heat storage density, low viscosity, low cost, long service life and high efficiency, so it is recognized as a heat transfer and heat storage medium in the world.

In the practice of heat transfer and storage, we can select different types of monomer raw materials according to the performance requirements of the application, and form a mixed eutectic salt with stable performance according to a certain proportion.

Why become the leader of "coal to electricity"?

The application of "molten salt heat storage" in the field of heating is of great significance to reduce coal pollution in winter, improve air quality and reduce the operation cost of "coal to electricity".

"Molten salt heat storage" is essentially a "coal to electricity" technology that uses "low valley electricity" to heat molten salt heat storage central heating. In this technology, molten salt plays a core "role".

So, what is "trough electricity"? To understand the "low power", we first need to understand the "peak valley difference".

The so-called "peak valley difference" refers to the difference between large load and small load in a certain time period (usually in daily units). This is a big problem faced by the traditional power grid.

Figure: implementation of peak valley TOU price

Nowadays, power technology has penetrated into all aspects of social life. However, the traditional power has the particularity of "instant generation and use", which means that the excess "low power" will become "waste energy".

The significance of using "trough electricity" to heat molten salt for heat storage is to absorb the "waste energy" at the trough of power grid.

Of course, the electric energy of abandoning wind and light can also be used to heat molten salt and store heat. In this way, the heating system can replace the coal-fired boiler for heating.

Figure: heat storage heating can "cut peak and fill valley"

The current peak valley electricity price is undoubtedly an incentive measure to absorb "low valley electricity". Using "low valley electricity" to heat molten salt for heat storage central heating can not only achieve the purpose of energy conservation and emission reduction, but also has good economic performance, and is conducive to the optimal allocation of power resources.

How to realize "molten salt" heating?

Maybe you'd like to know how molten salt transfers heat? Don't worry, let's explain it step by step.

In the circulation of molten salt heat storage central heating system, cold and hot molten salt are stored in low-temperature and high-temperature molten salt tanks respectively.

The heating of molten salt is carried out in the molten salt electric heater. The high-temperature molten salt heated by "low valley power", wind power and photovoltaic power enters the high-temperature molten salt tank for storage.

Figure: schematic diagram of electric heating molten salt heat storage heating (source: Jinhe energy)

The high-temperature molten salt enters the heat exchange system through the molten salt pump to heat the feed water into steam. These steam are sent to the hot user side for heating by heating the return water of circulating water. The exothermic molten salt enters the low-temperature molten salt tank for storage and participates in the next heating and exothermic cycle.

The molten salt heat storage central heating system introduced in Beijing adopts a new LMP molten salt heat storage medium, which has the advantages of melting point, specific heat capacity, wide temperature range, small floor area, safe and reliable operation and so on.

Molten salt heat storage central heating has good economic performance and ecological benefits, and will make great contributions to clean heating in the future.

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