Thermal stability of potassium and sodium nitrate molten salt mixtures above 500°C
Nitrate based salts have application as a heat transfer fluid for solar field applications and are normally used up to maximum temperatures of 500°C. There is improved thermodynamic efficiency if the upper operating temperature of these working fluids can be increased. This paper explores the high temperature stability of binary KNO3-NaNO3salt mixtures, the effect of atmosphere on the NOx evolution and the effect of additives to the melt. Several experimental techniques were used including combined thermo-gravimetric and evolved gas analysis; at the milligram and larger twenty gram scale, where the melt stability was examined at temperatures as high as 1000°C. The general findings are that the binary KNO3-NaNO3 molten salt mixture is stable up to temperatures of 500°C, with very little weight change of the melt, although there was some evolved NOx gases over this temperature range. The use of pure dry nitrogen or air as a protective atmosphere was more effective, reducing NOx evolution over the entire temperature range than pure argon gas. At temperatures above 500°C, there is significant evolution of NOx species in the gas and a large weight change observed for the melt. However the weight change far exceeds that expected for nitrate salt decomposition and there is clear evidence that nitrate salt evaporation may be the dominant factor in decreasing melt stability. The thermo-gravimetic studies where the molten salt was progressively heated to 1000°C indicated that carbonate addition to the melt (as a mixture of K2CO3-Na2CO3) may have increased the thermal stability of the melt. This was explored further in a series of experiments where the molten salt mixtures were heated to between 500 and 700°C and held at temperature for two hours to examine weight loss rates of the salt mixtures. The experimental results are also compared with thermodynamic predictions from a general molten salt thermodynamic solution model based on the Cell model being developed by CSIRO. The main purpose of this modeling is to aid in finding and determining the potential operating window of a complex molten salt mixture where the melt is chemically stable.
molten salt potassium nitrate sodium nitrate sodium carbonate potassium carbonate heat transfer
Steven Wright Ty Tran Chunlin Chen Rene Olivares Shouyi Sun
CSIRO Process Science and Engineering, Bayview Ave, Clayton, Vic 3169, Australia CSIRO Energy Technology, 10 Murray Dwyer Circuit, Mayfield West, NSW 2304, Australia
国际会议
Ninth International Conference on Molten Slags,Fluxes and Salts(第九届国际熔渣、溶剂与熔盐学术会议 MOLTEN12)
北京
英文
1-14
2012-05-27（万方平台首次上网日期，不代表论文的发表时间）