As heat transfer fluids and heat storage mediums, the molten nitrates have been widely used in the solar thermal power generation system in latest years, among which Solar salt system (60% NaNO3?40% KNO3, mass ratio) is the most optimized one. However, there still exists lots of problems in large-scale industrial application, for example, the high temperature stability of Solar salt system is not clear enough. Thus this work aims to investigate the thermal stability of Solar salt system under the conditions of thermal storage and constant high temperatures. The thermal decomposition temperature of Solar salt system was detected by thermo-gravimetric (TG). Meanwhile, constant high temperature experiment of NaNO3, KNO3 and Solar salt were studied in an open system at different temperatures. The constant thermal stability values of Solar salt system and the roles of NaNO3 and KNO3 played in its high-temperature instability were obtained. The high temperature instability of Solar salt system was manifested as mass loss, which was mainly caused by thermal decomposition and volatilization of components. The TG result showed that the thermal decomposition temperature of Solar salt system was 590.6℃ in nitrogen atmosphere. The constant high-temperature experiment showed that Solar salt system was unstable above 500℃ in air, and the higher temperature was, the more unstable of it. The degree of instability was NaNO3>Solar salt system>KNO3 under the same temperature. The content of the decomposed product NO2? eventually reached an equilibrium at some time, and the equilibrium content of NO2? increased while equilibrium time of the reaction decreased as the rising of temperature. However, another decomposed product metal oxides was low. Besides, the mass loss of Solar salt caused by thermal decomposition and volatilization was close to 1:1. In the Solar salt system, NaNO3 was the main cause of thermal decomposition, and KNO3 played the role of anti-volatilization.
Chongjing HU Ze SUN Long HUANG Haijun ZHANG Xingfu SONG Jianguo YU
. Analysis on thermal stability of molten nitrates at high temperatures[J]. The Chinese Journal of Process Engineering, 2018
, 18(6)
: 1315
-1322
.
DOI: 10.12034/j.issn.1009-606X.218143
[1]Serrano-López R, Fradera J, Cuesta-López S.Molten salts database for energy applications[J].Chemical Engineering & Processing, 2013, 73(73):87-102
[2] Mathur A.Heat Transfer and Latent Heat Storage in Inorganic Molten Salts for Concentrating Solar Power Plants[J]., 2013, :-
[3] Laing D.Solar Thermal Energy Storage Technologies [J]., 2008, :-
[4]Kearney D, Herrmann U, Nava P, et al.Assessment of a Molten Salt Heat Transfer Fluid in a Parabolic Trough Solar Field[J].Journal of Solar Energy Engineering, 2003, 125(2):293-299
[5]Cordaro J G, Rubin N C, Bradshaw R W.Multicomponent Molten Salt Mixtures Based on NitrateNitrite Anions[J].Journal of Solar Energy Engineering, 2011, 133(1):169-175
[6] Bradshaw R W, Brosseau D A.Low-melting point inorganic nitrate salt heat transfer fluid.[J]., 2009, :1-12
[7] Bradshaw R W, Cordaro J G, Siegel N P.Molten Nitrate Salt Development for Thermal Energy Storage in Parabolic Trough Solar Power Systems [C] //ASME 2009 International Conference on Energy Sustainability Collocated with the Heat Transfer and Interpack09 Conferences, USA, 2008, 631-637.
[8] Bradshaw R W, Siegel N P.Development of molten nitrate salt mixtures for concentrating solar power systems
[9] Wu Y T, Ren N, Li Y, et al.Improving the Thermal Properties of NaNO3-KNO3 for Concentrating Solar Power by Adding Additives [J].Solar Energy Materials & Solar Cells, 2017, 160:263-268
[10]王超，任楠，吴玉庭，等.新型低熔点混合熔盐的开发和热物性测定[J].太阳能学报, 2012, 36(11):2601-2609
[11]Wang C, Ren N, Wu Y T, et al.Exploitation and Experimental Study on New Mixed Molten Salt with Low Melting Point[J].Acta Energiae Solaris Sinica, 2012, 36(11):2601-2609
[12]任楠, 吴玉庭, 马重芳.新型低熔点熔盐黏度的实验研究[J] [J].工程热物理学报, 2012, 33(3):497-500
[13]Ren N, Wu Y T, Ma C F.Experimental Study of Viscosity of New Kind of Molten Salt with Low Melting Point[J].Journal of Engineering Thermophysics, 2012, 33(3):497-500
[14]Peng Q, Yang X, Ding J, et al.Thermodynamic performance of the NaNO3–NaCl–NaNO2 ternary system[J].Journal of Thermal Analysis & Calorimetry, 2014, 115(2):1753-1758
[15]彭强, 杨晓西, 丁静, et al.三元硝酸熔盐高温热稳定性实验研究与机理分析[J].化工学报, 2013, 64(5):1507-1512
[16]Peng Q, Yang X X, Ding J, et al.Experimental Study and Mechanism Analysis for High-temperature Thermal Stability of Ternary Nitrate Salt[J].CIESC Journal, 2013, 64(5):1507-1512
[17]Peng Q, Ding J, Wei X, et al.The preparation and properties of multi-component molten salts[J].Applied Energy, 2010, 87(9):2812-2817
[18]彭强, 魏小兰, 丁静, 等.多元混合熔融盐的制备及其性能研究[J].太阳能学报, 2009, 30(12): 1621-1626
[19]Peng Q, Wei X L, Ding J, et al.Research on the Preparation and properties of Multi-component Molten Salts[J].Acta Energiae Solaris Sinica, 2009, 30(12):1621-1626
[20]Fernández A G, Ushak S, Galleguillos H, et al.Development of new molten salts with LiNO3 and Ca(NO3)2 for energy storage in CSP plants[J].Applied Energy, 2014, 119(15):131-140
[21]Concentrating Solar Power Projects [EB/OL].https://www.nrel.gov/csp/solarpaces/by_project.cfm
[22]Gomez J C, Calve t N, Starace A K, et al.Ca(NO3)2-NaNO3-KNO3 Molten Salt Mixtures for Direct Thermal Energy Storage Systems in Parabolic Trough Plants[J].Journal of Solar Energy Engineering, 2013, 135(135):420-431
[23]Raade J W, Padowitz D.Development of Molten Salt Heat Transfer Fluid with Low Melting Point and High Thermal Stability[J].Journal of Solar Energy Engineering, 2011, 133(3):91-96
[24][20[GB]2367-2006, 工业亚硝酸钠.
[25]2367-2006, Sodium Nitrite for Industrial Use.
[26]Bradshaw R W, Dawson D B, Wilfredo D L R, et al.Final Test and Evaluation Results from the Solar Two Project [J].Energy Storage, 2002, :-
[27]柯以侃.分析化学手册-光谱分析[M]. 北京: 化学工业出版社, 1998: 1161-1164.
[28]Ke Y.Analytical Chemistry Handbook-Spectrum analysis [M]. Beijing: Chemical Industry Press, 1998: 1120-1167.
[29]喻宗鑫.KNO3-NaNO2-NaNO3体系熔盐结构的Raman光谱研究 [D]. 秦黄岛: 东北大学, 2014: 21-27.
[30]Yu Z.Raman Spectra Study on Structure of KNO3-NaNO2-NaNO3 Molten Salts System [D]. Qin Huangdao: Northeastern University, 2014: 21-27.
[31]Bartholomew R F.A Study of the Equilibrium KNO3(l) ? KNO2(l)+12O2(g) over the Temperature Range 550-750°[J].Journal of Physical Chemistry, 1966, 70(11):3442-3446
[32]Cordaro J G.Chemical Perspectives on Alkali and Earth Alkaline Nitrate and Nitrite Salts for Concentrated Solar Power Applications[J].Green, 2013, 3(1):9-18
[33] Stern K H.High temperature properties and thermal decomposition of inorganic salts with oxyanions [M]. CRC Press, 2001, 145-157.
