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

Abstract

The invention discloses a low-viscosity liquid sulfur working medium and a preparation method and application thereof.The low-viscosity liquid sulfur working medium comprises liquid sulfur and at least one doping substance, the doping substance contains sodium sulfide or copper chloride, and the doping substance is preferably sodium sulfide nonahydrate or copper chloride dehydrate; wherein the weight percentage of the sodium sulfide or the copper chloride to the liquid sulfur is preferably 2-10%. The liquid sulfur is doped with metal salts such as sodium sulfide or copper chloride, so that free hydrogen atoms or chlorine atoms occupy the tail end position of chain-shaped sulfur, and the chain segment of long-chain sulfur is broken, thereby reducing the viscosity of the liquid sulfur working medium. Compared with hydrogen sulfide, halogen, organic substances and other dopants with high volatility, the modified sulfur obtained by doping the metal salts has more stable viscosity change and better high-temperature resistance after multiple heat storage and release cycles, the dopant decomposition caused by high temperature is avoided, the doping process is simple, the cost is low, and the method is suitable for industrial production. The large-scale application of the liquid sulfur working medium is favorably realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-temperature heat storage, and in particular relates to a low-viscosity liquid sulfur working fluid and a preparation method and application thereof. Background Art

[0002] Compared with sensible heat materials such as molten salt or phase change heat storage materials, elemental sulfur has many advantages as a heat storage material: first, elemental sulfur is abundant in global reserves, and its production cost is extremely low (about 1 / 5 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°C. At the same time, the low melting point of elemental sulfur (~114°C) also helps to keep elemental sulfur at a relatively low temperature for liquid heat storage, 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 heat charging and discharging rate of its heat storage system is 3 to 14 times higher than that of the phase change heat storage system (PCM-TES). Therefore, 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 λ-transition zone at 160°C, and the maximum viscosity appears at about 186-188°C. This special viscosity-temperature relationship may be caused by the polymerization behavior of sulfur. In liquid sulfur, there are cyclic sulfur (S8) and chain sulfur (S x , x>8), as the temperature rises, the S8 ring breaks to form longer chain sulfur, and the entanglement and interweaving of these long chains lead to an increase in viscosity. After exceeding the critical temperature of 188°C, the chain sulfur begins to break, and the viscosity of liquid sulfur gradually decreases with increasing temperature. Such a drastic change in viscosity will significantly affect the flow and heat transfer characteristics of liquid sulfur.

[0004] Previous research literature has screened out several doping substances that can reduce the viscosity of elemental sulfur: including hydrogen sulfide, halogens and organic substances. Different dopants not only have different degrees of influence on the viscosity of sulfur, but also change the temperature zone where the viscosity peak of sulfur is located. The mechanism of reducing viscosity is that impurity atoms occupy the terminal position of chain sulfur and interrupt the chain segments of long-chain sulfur, thereby reducing viscosity. However, halogens and hydrogen sulfide are volatile and toxic at high temperatures, and hydrogen sulfide needs to be doped under high pressure. These factors increase the technical difficulty in its industrial application, so it is still difficult to promote such doped modified sulfur on a large scale. Summary of the invention

[0005] Purpose of the invention: The present invention provides a low-viscosity liquid sulfur working fluid and a preparation method and application thereof, so as to solve the problem that the existing doped modified sulfur is difficult to achieve industrial application due to factors such as safety, manufacturing difficulty and production cost, and to provide a new approach for the modification of liquid sulfur with simple process, low cost, safety and stability.

[0006] Invention content: To achieve the above objectives, the present invention provides a low-viscosity liquid sulfur working fluid, including liquid sulfur and at least one doping substance, wherein the doping substance contains sodium sulfide or copper chloride.

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

[0008] The modified sulfur obtained by doping with sodium sulfide nonahydrate can stably perform heat storage and release cycles. Sodium sulfide nonahydrate is cheap and easy to obtain, the doping process is simple, does not require complex equipment or process improvements, and the viscosity reduction effect is more significant than that of sodium sulfide. At the same time, the reason for limiting the doping ratio is that if the ratio of sodium sulfide is too low, it is difficult to ensure the viscosity reduction effect, and if the ratio is too high, it will affect the heat storage and release efficiency of the liquid sulfur working fluid.

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

[0010] The modified sulfur obtained by doping with copper chloride dihydrate can also stably perform heat storage and release cycles. Copper chloride dihydrate is stable at room temperature and does not release toxic gases such as hydrogen sulfide during heating. The doping process is simple and does not require complex equipment or process improvements. The viscosity reduction effect is more significant than that of copper chloride. At the same time, the reason for limiting the doping ratio is that if the proportion of copper chloride is too low, it is difficult to ensure the viscosity reduction effect, and if the proportion is too high, it will affect the heat storage and release efficiency of the liquid sulfur working fluid.

[0011] Furthermore, the present invention also includes a method for preparing the above-mentioned low-viscosity liquid sulfur working fluid, comprising:

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

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

[0014] In addition, the present invention also includes 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] Beneficial effects:

[0016] The present invention dopes liquid sulfur with metal salts such as sodium sulfide or copper chloride, so that free hydrogen atoms or chlorine atoms can occupy the terminal position of chain sulfur, interrupt the chain segments of long-chain sulfur, and thus reduce the viscosity of liquid sulfur working fluid. Compared with highly volatile dopants such as hydrogen sulfide, halogens, and organic substances, the modified sulfur doped with the above metal salts has a more stable viscosity change after multiple heat storage and release cycles, and has better high temperature tolerance, and will not cause dopant decomposition due to high temperature. At the same time, the doping process is simple and low-cost, which is conducive to the large-scale application of liquid sulfur working fluid. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0018] Figure 2 This is a graph showing the viscosity changes of three liquid sulfur working fluids at high temperatures in Example 1 of the present invention;

[0019] Figure 3 This is a graph showing the viscosity changes of three liquid sulfur working fluids at high temperatures in Example 2 of the present invention. DETAILED DESCRIPTION

[0020] To make the technical solution of the present invention clearer, the technical solution in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is a part of the embodiment of the present invention, not all the embodiments. Based on the embodiment of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0021] like Figure 1 The present invention provides a low-viscosity liquid sulfur working medium, which includes liquid sulfur and at least one doping substance, wherein the doping substance contains sodium sulfide or copper chloride. The low-viscosity liquid sulfur working medium can be used for reversible energy storage, and can be specifically used in the field of high-temperature heat storage technology.

[0022] Embodiment 1:

[0023] Sodium sulfide nonahydrate was selected as the doping substance, and 2%, 5% and 10% by weight of sodium sulfide were added to liquid sulfur, respectively, and the viscosity test at high temperature was carried out. Figure 2 It can be seen that these three modified sulfurs achieve significant viscosity reduction effects, reducing the peak viscosity of liquid sulfur working fluid from 90,000 mPa·s to 1,700 mPa·s, 740 mPa·s and 250 mPa·s.

[0024] Embodiment 2:

[0025] Copper chloride dihydrate was selected as the doping material, and the doping material was ground and pre-treated to react more fully with liquid sulfur. 2%, 5% and 10% by weight of copper chloride were added to liquid sulfur, and the viscosity test at high temperature was carried out. Figure 3 It can be seen that these three modified sulfurs can also achieve significant viscosity reduction effects, reducing the peak viscosity of liquid sulfur working fluid from 90,000 mPa·s to 350 mPa·s, 230 mPa·s and 140 mPa·s.

[0026] The high-temperature viscometer in the above experiment uses the rotation method to test the high-temperature melt viscosity. The viscosity of the fluid is determined mainly by measuring the viscous torque of the fluid acting on the rotor. Effective calibration was performed before the test to ensure the accuracy of the test results. At the same time, in order to verify the stability of the above-mentioned modified sulfur, each liquid sulfur working fluid has undergone more than 3 heat storage and release cycles. For the same liquid sulfur working fluid, the obtained viscosity test curves are basically the same, which shows that the dopant will not decompose due to high temperature, and the high temperature tolerance is better than that of volatile dopants.

[0027] After a large number of experimental studies, it was found that not all metal salts can effectively improve the viscosity of liquid sulfur working fluid, such as NaCl, ZnCl2, etc., but doping substances containing sodium sulfide or copper chloride can achieve effective viscosity reduction effects, such as sodium sulfide or copper chloride, but the effect is weaker than that of metal salts containing hydrates. The modification principles of these two metal salts are: sodium sulfide is hygroscopic during the doping process, which will produce some hydrogen sulfide, so that hydrogen atoms occupy the end position of chain sulfur and interrupt the long-chain sulfur segments, thereby effectively reducing the viscosity of liquid sulfur working fluid; while the chlorine atoms in copper chloride can directly occupy the end position of chain sulfur and interrupt the long-chain sulfur segments, thereby effectively reducing the viscosity of liquid sulfur working fluid.

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

Claims

1. A low-viscosity liquid sulfur working fluid, characterized in that: The invention comprises liquid sulfur and at least one doping substance, wherein the doping substance contains sodium sulfide or copper chloride.

2. The low-viscosity liquid sulfur working fluid according to claim 1, characterized in that: The doping material is sodium sulfide nonahydrate, wherein the weight percentage of sodium sulfide to liquid sulfur is 2-10%.

3. The low-viscosity liquid sulfur working fluid according to claim 1, characterized in that: The doping material is copper chloride dihydrate, wherein the weight percentage of copper chloride to liquid sulfur is 2-10%.

4. A method for preparing the low-viscosity liquid sulfur working fluid according to any one of claims 1 to 3, characterized in that: include: The doping material is dissolved in liquid sulfur to form a low-viscosity liquid sulfur working fluid.

5. The preparation method according to claim 4, characterized in that: The doping material is ground and dissolved in liquid sulfur.

6. An application of the low-viscosity liquid sulfur working fluid as claimed in claim 1, characterized in that: The low-viscosity liquid sulfur working medium is used for reversible energy storage.

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