Low-viscosity liquid sulfur working medium, preparation method and application thereof

Abstract

The application discloses a kind of low viscosity liquid sulfur working medium and its preparation method and application, the low viscosity liquid sulfur working medium includes liquid sulfur and at least one doping material, the doping material contains sodium sulfide or copper chloride, the doping material is preferably sodium sulfide nine water or copper chloride dihydrate, wherein the weight percentage of sodium sulfide or copper chloride and liquid sulfur is preferably 2-10%.The application can make free hydrogen atom or chlorine atom occupy the end position of chain sulfur by doping sodium sulfide or copper chloride and other metal salts in liquid sulfur, and break the chain segment of long-chain sulfur, thereby reducing the viscosity of liquid sulfur working medium.Compared with hydrogen sulfide, halogen and volatile organic substances and other strong doping materials, the viscosity of modified sulfur obtained by doping the above metal salt is more stable after several heat storage and release cycles, and has better high temperature resistance.The doping process is simple, and the cost is low, which is conducive to the large-scale application of liquid sulfur working medium.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-temperature heat storage, and particularly relates to a low-viscosity liquid sulfur working medium and a preparation method and application thereof. BACKGROUND

[0002] Compared with sensible heat materials such as molten salts or phase change heat storage materials, elemental sulfur as a heat storage material has many advantages: first, elemental sulfur is abundant in the global range, and its production cost is extremely low (about 1 / 5 of that of commercial molten salt); second, elemental sulfur has excellent thermal stability and can be used as a heat storage fluid at a high temperature of 600 DEG C, and the low melting point (-114 DEG C) of elemental sulfur also helps to maintain liquid heat storage at a relatively low temperature, thereby providing a wider working temperature range; in addition, experimental and numerical simulation results show that elemental sulfur has good heat transfer performance, and the charging and discharging rate of its heat storage system is 3-14 times higher than that of a phase change heat storage system (PCM-TES). Therefore, the liquid sulfur heat storage technology with moderate energy density, high thermal stability and low cost is expected to be applied on a large scale in future new energy systems.

[0003] However, the viscosity of liquid elemental sulfur is an important factor affecting its heat transfer performance. Liquid sulfur enters the lambda-transition zone at 160 DEG C, and the maximum viscosity appears at about 186-188 DEG C. This special viscosity-temperature relationship may be caused by the polymerization behavior of sulfur. In liquid sulfur, there is a balance between cyclic sulfur (S8) and chain sulfur (S x , x>8), and as the temperature rises, S8 rings break to form longer chain sulfur, and the entanglement and interweaving of these long chains cause the increase of viscosity. When the temperature exceeds the critical temperature of 188 DEG C, the chain sulfur begins to break, and the viscosity of liquid sulfur gradually decreases with the increase of temperature. Such a sharp change in viscosity will significantly affect the flow and heat transfer characteristics of liquid sulfur.

[0004] Several doping substances that can reduce the viscosity of elemental sulfur are screened in the previous research literature: including hydrogen sulfide, halogen and organic substances. Different dopants not only have different effects on the viscosity of sulfur, but also change the temperature range of the viscosity peak. The mechanism of reducing viscosity is to occupy the end position of chain sulfur by impurity atoms, thereby breaking the chain segment of long-chain sulfur and reducing the viscosity. However, halogen and hydrogen sulfide have high-temperature volatility and toxicity, and hydrogen sulfide needs to be doped in a high-pressure environment, which increases the technical difficulty of its industrial application, so it is still difficult to promote such doped modified sulfur on a large scale. SUMMARY

[0005] The application provides a low-viscosity liquid sulfur working medium and a preparation method and application thereof, so as to solve the problem that existing doped modified sulfur is difficult to realize industrial application due to safety, manufacturing difficulty, production cost and other factors, and provide a new way for modification of liquid sulfur, which is simple in process, low in cost and safe and stable.

[0006] The application provides a low-viscosity liquid sulfur working medium, which comprises liquid sulfur and at least one doping substance, and the doping substance contains sodium sulfide or copper chloride.

[0007] Specifically, the doping substance is preferably sodium sulfide nonahydrate, and the weight percentage of sodium sulfide to liquid sulfur is preferably 2-10%.

[0008] The modified sulfur obtained by doping sodium sulfide nonahydrate can stably perform heat storage and release cycles, sodium sulfide nonahydrate is low in price and easy to obtain, the doping process is simple, and no complex equipment or process improvement is needed, and the viscosity reduction effect is more significant than that of sodium sulfide. The doping proportion is limited because if the proportion of sodium sulfide is too low, the viscosity reduction effect cannot be guaranteed, and if the proportion is too high, the heat storage and release efficiency of the liquid sulfur working medium is affected.

[0009] Specifically, the doping substance is preferably copper chloride dihydrate, and the weight percentage of copper chloride to liquid sulfur is preferably 2-10%.

[0010] The modified sulfur obtained by doping copper chloride dihydrate can also stably perform heat storage and release cycles, copper chloride dihydrate is stable at room temperature and will not release toxic gases such as hydrogen sulfide during the heating process, the doping process is simple, and no complex equipment or process improvement is needed, and the viscosity reduction effect is more significant than that of copper chloride. The doping proportion is limited because if the proportion of copper chloride is too low, the viscosity reduction effect cannot be guaranteed, and if the proportion is too high, the heat storage and release efficiency of the liquid sulfur working medium is affected.

[0011] Further, the application further comprises a preparation method of the low-viscosity liquid sulfur working medium.

[0012] The doping substance is dissolved in liquid sulfur to form a low-viscosity liquid sulfur working medium.

[0013] Specifically, the doping substance is preferably ground and then dissolved in liquid sulfur.

[0014] In addition, the application further comprises the application of the low-viscosity liquid sulfur working medium, and the low-viscosity liquid sulfur working medium can be used for reversible energy storage.

[0015] Advantages:

[0016] The application can make free hydrogen atoms or chlorine atoms occupy the terminal position of chain sulfur by doping sodium sulfide or metal salts such as copper chloride in liquid sulfur, so as to break the chain segment of long-chain sulfur, thereby reducing the viscosity of the liquid sulfur working medium. Compared with hydrogen sulfide, halogen and other volatile dopants such as organic substances, the modified sulfur obtained by doping the above metal salts has more stable viscosity change and better high-temperature resistance after multiple heat storage and release cycles, and will not decompose due to high temperature, and the doping process is simple and low in cost, which is conducive to the large-scale application of the liquid sulfur working medium. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 It is a schematic diagram of the composition of the liquid sulfur working medium in the application;

[0018] Figure 2 It is a viscosity change graph of three liquid sulfur working mediums at high temperature in Example 1 of the application;

[0019] Figure 3 It is a viscosity change graph of three liquid sulfur working mediums at high temperature in Example 2 of the application. DETAILED DESCRIPTION

[0020] In order to make the technical solutions of the application clearer, the technical solutions in the embodiments of the application will be described clearly and completely below in combination with the drawings in the embodiments of the application. Obviously, the described embodiments are part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor belong to the scope of protection of the application.

[0021] As Figure 1 shown is a low-viscosity liquid sulfur working medium provided by the application, which comprises liquid sulfur and at least one doping substance, and the doping substance contains sodium sulfide or copper chloride. The above low-viscosity liquid sulfur working medium can be applied to the use of reversible energy storage, and can be specifically applied to the field of high-temperature heat storage technology.

[0022] Example 1:

[0023] Nine water sodium sulfide is selected as the doping substance, and 2%, 5% and 10% by weight of sodium sulfide is respectively added to the liquid sulfur, so as to perform viscosity test at high temperature. It can be known from Figure 2 that the three modified sulfurs achieve significant viscosity reduction effect, and can reduce the viscosity peak of the liquid sulfur working medium from 90000 mPa·s to 1700 mPa·s, 740 mPa·s and 250 mPa·s.

[0024] Example 2:

[0025] Copper chloride dihydrate is selected as the doping substance, and the doping substance is ground and pretreated to react with liquid sulfur more fully. 2%, 5% and 10% of copper chloride by weight are respectively added into liquid sulfur, and viscosity tests at high temperature are performed. Figure 3 It can be known that the three modified sulfurs can also achieve significant viscosity reduction effect, and can reduce the viscosity peak of the liquid sulfur working medium from 90000 mPa·s to 350 mPa·s, 230 mPa·s and 140 mPa·s.

[0026] The high-temperature viscometer in the above experiment adopts a rotary method to test the high-temperature melt viscosity, mainly determines the viscosity of the fluid by measuring the viscous torque of the fluid acting on the rotor, and is effectively calibrated before testing to ensure the accuracy of the test results. At the same time, in order to verify the stability of the above modified sulfur, each liquid sulfur working medium has undergone more than 3 times of storage and heat cycle, and the viscosity test curves of the same liquid sulfur working medium are basically the same, which shows that the doping substance will not decompose due to high temperature, and the high temperature resistance is better than the volatile doping substance.

[0027] It is found through a large number of experimental researches that not all metal salts can effectively improve the viscosity of the liquid sulfur working medium, for example, NaCl and ZnCl2, but the doping substances containing sodium sulfide or copper chloride can achieve effective viscosity reduction effect, for example, sodium sulfide or copper chloride, but the effect is weaker than that of the metal salt containing hydrate. The modification principles of the two metal salts are as follows: sodium sulfide has hygroscopicity during the doping process, and part of hydrogen sulfide is generated, so that the hydrogen atom occupies the terminal position of the chain sulfur, breaks the chain segment of the long-chain sulfur, and effectively reduces the viscosity of the liquid sulfur working medium; and the chlorine atom in copper chloride can directly occupy the terminal position of the chain sulfur, break the chain segment of the long-chain sulfur, and effectively reduce the viscosity of the liquid sulfur working medium.

[0028] The above is only a specific embodiment of the present application, which enables those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features applied herein.

Claims

1. A low viscosity liquid sulfur working fluid, characterized by, The liquid sulfur and at least one doping substance containing sodium sulfide or copper chloride; The doping substance is sodium sulfide nine hydrates or copper chloride two hydrates, and the weight percentage of sodium sulfide or copper chloride to the liquid sulfur is 2-10%.

2. A method for producing the low viscosity liquid sulfur working fluid of claim 1, characterized by, The method comprises the following steps: The doping substance is dissolved in the liquid sulfur to form a low-viscosity liquid sulfur working medium.

3. The production method according to claim 2, characterized by, The doping substance is ground and then dissolved in the liquid sulfur.

4. Use of the low viscosity liquid sulfur working fluid of claim 1, wherein, The low-viscosity liquid sulfur working medium is used for reversible energy storage.

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