Quaternary Nitrate Research Articles

Quaternary nitrate and chloride molten salts for the next concentrating solar power plants: Corrosion considerations for the use of AISI 304L steel

The study addresses the advancement in concentrating solar power (CSP) plants by transitioning from binary nitrate salts to nitrate and chloride quaternary salts, focusing on the corrosivity of four salts as evaluated by immersion testing of AISI 304L stainless steel. Four compositions of salts were evaluated, from solar salt to equimolar NaNO3‐KNO3‐NaCl‐KCl, up to 21 days (500 h) at 500 °C in an open atmosphere, determining the corrosion kinetics using gravimetry. The morphology, chemical composition, and microstructure of the corrosion products were characterized using XRD, FESEM-EDS, and GD-OES. Exposure to the molten salt with 0 mol% Cl‐ (Solar Salt) resulted in negligible corrosion kinetics, consistent with previous studies. The salt with 14 mol% Cl‐ caused a stable corrosion product with a corrosion rate 30 times higher than without chloride. All quaternary salts exhibited a multilayer structure of the top surface with selective chromium (Cr) removal. Specimens exposed to salts with more than 29 mol% Cl‐ displayed a similar structure with Cr and iron (Fe) removal, resulting in more brittle layers and corrosion rates 90 to 250 times higher than the salt without chloride. GD-OES analysis confirmed Cl diffusion into the oxide layer, highlighting the role of pCl2(g) and pO2(g) in driving corrosivity. Based on the results, using in salts with 29 mol% Cl‐ at 500 °C is discouraged, while using 304L with 14 mol% Cl‐ in a cold tank may be considered.

Development and characterization of a quaternary nitrate based molten salt heat transfer fluid for concentrated solar power plant

Over the past few years, there has been growing interest in using inorganic quaternary nitrate-based molten salt mixtures as a highly effective heat transfer fluid (HTF) for concentrated power plants, primarily because they can achieve low melting temperatures. However, the high viscosity of these salt mixtures is still a significant challenge that hinders their widespread adoption. The high viscosity leads to high pumping power requirements, which increases operational costs, and reduces the efficiency of the Rankine cycle. To address this challenge, this study developed and characterized a novel quaternary molten salt, focusing on the effect of LiNO3 additions on the salt's viscosity, thermal conductivity, melting point temperature, heat capacity, and thermal stability. The quaternary mixture comprised KNO3, LiNO3, Ca(NO3)2, and NaNO2, with varying percentages of each salt. The study utilized various standard techniques to examine the characteristics of the developed mixture. Results showed that increasing LiNO3 content led to a decrease in melting temperature, higher heat capacity, improved thermal stability, conductivity, and reduced viscosity at solidification temperature. The lowest endothermic peak for the new mixture emerged at 73.5 °C, which is significantly lower than that of commercial Hitec and Hitec XL, indicating better potential for use as a heat transfer fluid for concentrated solar thermal power plant applications. Furthermore, the thermal stability results showed high stability up to 590 °C for all the samples examined. Overall, the new quaternary molten salt shows promise as a potential replacement for current organic synthetic oil, offering a more efficient solution.

High-temperature corrosion behavior of austenitic stainless steel in quaternary nitrate molten salt nanofluids for concentrated solar power

Molten salt nanofluids have become a hot research topic due to its excellent thermal properties and heat transfer performance. However, there is a few research on the effect of nanofluids on the corrosion of metal materials. In order to know the influence of molten salt nanofluids on the corrosion of stainless steel, a low melting point quaternary nitrate was used as the base salt to analyze the corrosion law of nanofluids. By means of weight loss method, two different stainless steels (304, 316L) were put into the molten salt nanofluids with SiO 2 nanoparticles content of 1 wt% to test the corrosion behavior of stainless steel. The results of 500 h corrosion test revealed that the corrosion rate of mixed molten salt on 304 and 316L stainless steel is reduced by the addition of SiO 2 nanoparticles. The corrosion rates of molten salt nanofluids on 304 and 316L stainless steel were 0.0433 mm/y and 0.0233 mm/y, respectively. The surface morphology analysis by SEM, EDS, XRD and XPS test showed that the reticular silica nanostructures corrosion layer was formed on the surface of stainless steel, such structure can inhibit the corrosion of stainless steel. Therefore, molten salt nanofluids have the good compatibility with metal materials, and adding nanoparticles in molten salt can reduce the corrosion on stainless steel. • Investigating the corrosion behavior of stainless steels (304,316L) in the mixed molten salt and its nanofluids. • Confirming the corrosion reduction of stainless steel in the mixed molten salt nanofluids. • Discovering the nanostructure of reticulated SiO 2 in the corrosion layer of stainless steel. • Revealing the corrosion mechanism of stainless steel in the mixed molten salt containing SiO 2 nanoparticles.

Characterization and Heat Transfer Performance of Quarternary Nitrate Based Molten Salts

The use of molten salts as heat transfer has become the preferable composition. It has excellent properties such as low melting points, high heat capacity, and a wide range of temperatures. This paper focuses on the characterization and heat transfer performance of quaternary nitrate based on molten salts whose composition has been reported by previous researchers. The quaternary molten salts (LiNO3, NaNO3, KNO3, Ca(NO3)2) were characterized to determine the melting point and heat capacity using Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC), respectively. The heat transfer performance was then tested on the test rig of the designated system to determine the heat transfer properties of molten salts. The composition of 10 wt% LiNO3, 10 wt% NaNO3, 40 wt% KNO3, 40 wt% Ca(NO3)2 has a low melting point of 97.7°C, high heat capacity which was 0.46J/g°C, and maximum thermal stability temperature was 439.04°C. The heat transfer performance test showed that this sample can be used as heat transfer fluid and can store energy in the system. In conclusion, quaternary nitrate-based molten salt is a promising candidate for heat transfer and energy storage in heat recovery applications.

Are unexpected chloride ions in molten salt really harmful to stainless steel?

Commercial mixed salt generally contains the impurity chloride ion (Cl−) due to the influence of the preparation process of the single component salt that constitutes the mixed salt. The impurity Cl− can increase the corrosion of molten salt to metal materials. In order to investigate the effect of molten salt with different content of Cl− on the corrosion of metal materials, a low melting point quaternary nitrate and solar salt were selected as the base salt to analyze the corrosion rule of Cl−. Using the weight loss method, the corrosion behaviors of the two molten nitrate salts with and without Cl− to 316L stainless steel were studied. The results of the corrosion test for 1000 h show that the quaternary mixed molten salt with low Cl− content of 0.03 wt% has the lowest corrosion rate on 316L stainless steel than that of the other two salts with Cl− content of 0.01 and 0.05 wt% for the existence of calcium nitrate. Calcium ions (Ca2+) are introduced to solar salt with the same Cl− content of 0.03 wt% to confirm its corrosion effect on stainless steel. The results show that the addition of a small amount of Cl− and Ca2+ can reduce the corrosion rate of solar salt on 316L stainless steel. The corrosion products morphology analysis by SEM, EDS, and XRD test show that the calcium rich oxide layers containing CaFeO4 was found in the corrosion layer of stainless steel, which inhibits the further corrosion of stainless steel in molten salt. This finding has the far-reaching implications for inhibiting corrosion of molten salt with Cl− on stainless steel.

Comprehensive thermal properties of molten salt nanocomposite materials base on mixed nitrate salts with SiO2/TiO2 nanoparticles for thermal energy storage

The purpose of this investigation is to find and prepare novel heat storage materials to meet the requirement of Concentrating Solar Power (CSP) system. This paper focuses on the formulation, fabrication and characterization of a novel molten salt nanocomposite for high-temperature heat energy storage. The molten salt nanocomposite is based on eutectic quaternary salt, and two different concentrations of SiO 2 and TiO 2 nanoparticles are added to improve its specific heat capacity and thermal conductivity by microwave method. Concerning the material characterization, a suite of techniques was used, including simultaneous thermal analysis (STA) and laser flash analysis (LFA). The consequences demonstrate that the melting point and latent heat of molten salt nanocomposites can be reduced by adding two different concentrations of nanoparticles at the same time. The specific heat is 28.1% higher than that of the pure quaternary salt, and 6.3% and 9.8% higher than that of adding SiO 2 and TiO 2 nanoparticles separately when adding 0.1 wt% SiO 2 and 0.9 wt% TiO 2 nanoparticles to the quaternary nitrate. Compared with pure quaternary salt, the thermal conductivity of the molten salt nanocomposites increased by 53.7%, which was 16.8% and 6.3% higher than that of adding SiO 2 and TiO 2 nanoparticles separately. Upon inspection with scanning electron microscopy, a high-density nanostructure and heat transfer channel were observed, which appear to be the reason for the enhancement of specific heat and thermal conductivity of the material. Finally, the molten salt nanocomposite has a broad application prospects in high-temperature thermal storage system. • Novel molten salt nanocomposite is prepared by microwave method for heat storage system. • Two different concentrations of nanoparticles are added to the salt simultaneously. • The specific heat and thermal conductivity of quaternary salt are improved. • The concentration of nanoparticles can affect the thermal properties of molten salt. • The honeycomb structure is the reason for the increase of thermal performance.

Dynamic corrosion behavior of 316L stainless steel in quaternary nitrate-nitrite salts under different flow rates

Nitrate salts have been applied as heat transfer and heat storage medium in the Concentrating Solar Power (CSP) plants. Corrosion is critical to the long-time safe operation of the CSP system. This experimental study was conducted to research the dynamic corrosion behaviors of 316 L stainless steel in high-temperature quaternary nitrate nitrite mixture. The effects of corrosion on 316 L stainless steel were investigated under the varied flow rates of 0.6 m/s, 1.3 m/s and 2 m/s with 565 °C constant temperature for 1000 h. The results showed that oxidation corrosion occurred in 316 L stainless steel at all working conditions. The dynamic corrosion curves were parabolic, and the value corrosion weight loss (mmass) increased with the increase of the flow rate. Meantime, when the products flow rates were 0.6 m/s, 1.3 m/s and 2 m/s, the values of mmass were 3.6 mg cm−2, 3.77 mg cm−2 and 4.36 mg cm−2. The values of corrosion depth (Rdepths) were 0.039 mm/a, 0.041 mm/a and 0.048 mm/a, respectively. Besides, the corrosion products were consisted of hematite (Fe2O3), magnetite (Fe3O4), trace amounts of MgFe2O4 and NaFeO2 with the structure of lamellar. Furthermore, the corrosion products gradually transformed into FeCr2O4 with structures of dense and massive, and the increase of the flow rate deepened the degree of corrosion, but it had little effect on the types of corrosion products.

Experimental study of thermophysical properties and thermal stability of quaternary nitrate molten salts for thermal energy storage

Renewable energy has been rapidly developing because of the increasing severity of pollution and energy crises. In particular, solar thermal power generation technology has been attracting considerable attention globally due to its large scale, low unit cost, and environment-friendliness. Thus, it has been quickly progressing. The intermittence and instability of solar energy can be solved by combination of solar thermal power with heat storage technology. Mixed molten salts stand out as heat transfer and storage materials due to their wide temperature range, low vapor pressure, high heat capacity, low viscosity, and economical environmental protection. In the present study, a new kind of quaternary nitrate molten salt was presented. The salt was Hitec salt with Ca(NO3)2 additive and has a low melting point, high decomposition point, and low cost. The thermophysical properties of the proposed salt, such as melting point, decomposition point, crystallization point, specific heat, density, thermal conductivity, and thermal stability, were measured. Results showed that the melting, crystallization, and decomposition points of the Hitec salt with Ca(NO3)2 additive were 83.1 °C, 163.1 °C, and 628.5 °C, respectively. The proper working temperature range of the new salt was 200–565 °C, which was wider than those of Hitec salt (200–450 °C) and solar salt (290–565 °C). The average specific heat and thermal conductivity of the Hitec salt with Ca(NO3)2 additive were approximately 1.52 J/(g K) and 0.655 W/(m K), respectively, which showed better heat storage and heat transfer performance than did Hitec salt (1.40 J/(g K) specific heat, 0.350 W/(m K) thermal conductivity) and solar salt (1.50 J/(g K) specific heat, 0.520 W/(m K) thermal conductivity). An experimental study was conducted on the stability of mixed molten salts at 565 °C for 1200 h and 120 times for quenching/heating at 200–500 °C, and the Hitec salt with Ca(NO3)2 additive exhibited good thermal stability.

Effect of SiO2 nanoparticles on specific heat capacity of low-melting-point eutectic quaternary nitrate salt

In order to evaluate the effect of nanoparticles on the specific heat capacity of a low-melting-point eutectic quaternary nitrate salt, 1.0 wt% SiO2 nanoparticles with an average size of 20 nm was doped into the mixed salt Ca(NO3)2·4H2O-KNO3-NaNO3-LiNO3. A mechanical dispersion mixer was developed to prepare molten salt nanofluids. The effects of the mixing time (15, 45, 90, 120, and 150 min) and stirring rate (600, 750, and 1000 rpm) on the specific heat capacity of the nanofluids were analyzed using a differential scanning calorimeter. The results showed that the specific heat capacity of the nanofluids varied with the mixing time and stirring rate. It increased by ~ 17.0% at a mixing time of 15 min and stirring rate of 750 rpm. Microstructural characterization of the molten salt nanocomposites was performed using scanning electron microscopy, which showed that special nanostructures, which resemble chain-like nanostructures, were formed on the surface of the solid nanofluids. The special nanostructures with a large specific surface area and high surface energy could increase the specific heat capacity of the molten salt nanofluids.

Characterization and Thermal Properties of Nitrate Based Molten Salt for Heat Recovery System

Molten salt can acts like a storage medium or heat transfer fluid in heat recovery system. Heat transfer fluid is a fluid that has the capability to deliver heat this one side to another while heat recovery system is a system that transfers heat to produce energy. This studies shows about determining the new formulation of different molten nitrate/nitrite salts consisting of LiNO3, KNO2, KNO3 and NaNO2 that give a low temperature of melting point and high average specific heat capacity. Mixed alkaline molten nitrate/nitrite salt can act as a heat transfer fluid due to their advantageous in terms of its properties that feasible in heat recovery system such as high specific heat capacity, low vapour pressure, low cost and wide range of temperature in its application. The mixing of these primary substances will form a new line of quaternary nitrate salt (LiNO3 - KNO2 - KNO3 - NaNO2). The quaternary mixture was heated inside the box furnace at 150°C for four hours and rose up the temperature to 400°C for eight hours to homogenize the mixture. Through heating process, the elements of nitrate/nitrite base were mixed completely. The temperature was then reduced to 115°C for several hours before removing the mixture from the furnace. The melting point of each sample were testified by using thermal gravimetric analysis, TGA/DTA and experiment of determining the specific heat capacity were conducted by using Differential Scanning Calorimeter, DSC. From the result, it is found that the melting point Sample 1 with percentage of weightage (25.4wt% of LiNO3, 33.8wt% of KNO2, 20.7wt% of KNO3 and 20.1wt% of NaNO2) is 94.4°C whereas the average specific heat capacity was 1.0484/g°C while for Sample 3 with percentages of weightage (30.0wt% of LiNO3, 50.2wt% of KNO2, 3.1wt% of KNO3 and 16.7wt% of NaNO2), the melting point is 86.1°C with average specific heat capacity of 0.7274 J/g°C. In the nut shell, the quaternary mixture salts had been a good mixture with good thermal properties that low in melting point and have high specific heat capacity which could be a potential heat transfer fluid in heat recovery application.

Effect of nanoparticle dispersion on enhancing the specific heat capacity of quaternary nitrate for solar thermal energy storage application

Molten salt is considered to be part of the main direction for studying high temperature heat transfer and storage medium in concentrated solar power due to its good thermo physical properties. Specific heat capacity performs a significant role in increasing the overall cycle efficiency and reducing the cost of heat transfer and storage. In this paper, in order to enhance the specific heat capacity, 1wt% SiO2 nanoparticles are added into a quaternary nitrate (Ca(NO3)2-KNO3-NaNO3-LiNO3 with a low melting point called the low melting point salt (LMPS), which are mixed through ultra-sonication. Experimental results show that the specific heat capacity can be enhanced when nanoparticles are evenly distributed in the quaternary nitrate. The optimal ultra-sonication time with a frequency of 45kHz is researched. The average specific heat capacity of nano-LMPS can reach up to 1.87J/(gK) and the average enhancement reaches 19.4%. There is a good linear relationship between the specific heat capacity of nano-LMPS and ultra-sonication time. Scanning electron microgram images reveal that lamellar networks with higher density phase on the solid nano-LMPS surface exist and may cause the specific heat capacity enhancement of nano-LMPS.

Form-stable LiNO3–NaNO3–KNO3–Ca(NO3)2/calcium silicate composite phase change material (PCM) for mid-low temperature thermal energy storage

In this paper, a novel form-stable LiNO3–NaNO3–KNO3–Ca(NO3)2/calcium silicate composite PCM was developed by cold compression and sintering. The eutectic quaternary nitrate is used as PCM, while calcium silicate is used as structural supporting material. X-ray Diffraction (XRD) shows the PCM and the supporting material have good chemical compatibility. This composite PCM has a low melting point (103.5°C) and remain stable without decomposition until 585.5°C. Moreover, this composite shows excellent long term stability after 1000 melting and freezing cycles. Thermal conductivity of the composite was measured to be 1.177Wm−1K−1, and that could be increased by adding thermal conductivity enhancers into the composite. Meanwhile, microstructure of the composite PCM is observed by scanning electron microscopy (SEM). Latent heat and heat capacity of the composite are measured by differential scanning calorimetry (DSC). This composite PCM with low melting temperature, high thermal conductivity and excellent stability could be used as a new PCM for mid-low temperature thermal energy storage (TES) system.

Modular Solar Storage System for Medium Scale Energy Demand Mining in the North of Chile

The current legal framework for the development of renewable energies in Chile offers very favorable conditions for small scale electric generation systems. Incentives range from tariff exemptions on distribution and up to a 5% guaranteed supply rights to regulated customers. Such conditions allow for a viable and fast growing environment for the developments of those generation systems based on the CSP which incorporate optimized storage systems. These systems are likely to play a vital role in meeting the increasing demand for energy from the copper mining sector in the north of Chile as well as that of the smaller electricity networks and local communities. In this direction, the University of Antofagasta, Chile, has developed the implementation and construction of a modular solar storage system, using new ternary and quaternary nitrate mixtures, where in addition to collecting the heat of industrial/mining processes and store them for later use, proposes its implementation in isolated rural systems in the Chilean Norte Grande. The new ternary and quaternary Heat Transfer Fluid (HTF), designed with the addition of Ca(NO3) 2 and LiNO 3 to solar salt, shows a work temperature range of 130 to 600oC. This temperature range, together with the adequate heat capacity of salt and the potential for storage approximately 175 kWh per day to this system, making it suitable to meet the demands of evaluated areas. The economic viability of these new salts has been analyzed taking into account the sources of nitrates in the country, as well as the cost for storage density offered by these new fluids.