硝酸熔融盐蓄热过程中NOx的排放研究

发布时间：2018-03-20 05:13

  本文选题：硝酸熔融盐　切入点：NOx　出处：《华南理工大学》2014年硕士论文　论文类型：学位论文

【摘要】：太阳能热发电技术以其能够缓解能源危机和提供高品质电能等优势成为世界各国争相发展的技术。高温蓄热技术是太阳能热发电的关键技术,高温蓄热材料又是高温蓄热技术的核心。硝酸熔融盐高温蓄热材料以其熔点低、价格便宜、使用温度范围广和粘度小等优点成为太阳能热发电的首选材料之一,NaNO3-KNO3二元熔盐已应用于完全商业化的太阳能热发电站中。 但硝酸熔盐在高温下不稳定,热分解可能会产生NOx,因此本文参照空气中监测NOx的国家标准对常见硝酸熔盐在蓄热过程中是否排放NOx进行系统地研究,并探究温度和容器材质(碳钢和不锈钢)对硝酸熔盐排放NOx的影响,通过热力学计算从理论上对硝酸熔盐排放NOx的原因进行解释。 实验对石英舟中的硝酸熔盐在蓄热过程中排放的气体进行监测,改变温度和加入不同材质钢重复实验。结果表明,本实验条件下硝酸熔盐会放出NOx,且排放NOx的1h平均浓度随温度的升高逐渐增大。相同条件下,三、四元硝酸熔盐排放NOx的1h平均浓度比二元熔盐大。硝酸熔盐接触45#碳钢或不锈钢后,确实会放出更多的NOx。蓄热后,二元熔盐样品中NO2-的浓度随温度的升高而增大,三、四元熔盐样品中NO3-和NO2-的含量随温度变化不规律。 热力学计算表明,K/NaNO3分解为K/NaNO2和O2是二元熔盐热力学上能发生的反应；三、四元熔盐含NaNO3较少,KNO3和NaNO2较多,KNO3分解为KNO2和O2以及NaNO2被空气氧化为NaNO3和NaNO2分解为Na2O、N2和NaNO3的反应在热力学上都可以发生,但不产生NOx气体。考虑容器材质发现,在热力学上硝酸盐能与SiO2反应生成NO和NO2,这是实验监测到NOx的真正原因。金属(Fe、Cr、Ni、Mn)会与K/NaNO3反应生成NO; Fe/Cr/Ni分别或其中任意两个与K/NaNO3反应生成NO2或与NaNO2反应生成NO的反应在热力学上都可以发生,这些反应使硝酸熔盐接触碳钢或不锈钢后排放的NOx增多。K/NaNO3除热分解产生NO2-外,也会与金属反应产生K/NaNO2,使二元硝酸熔盐接触钢材后样品中的NO2-增多；而三、四元熔盐除这两种反应外,本身的NaNO2也会氧化或参与反应,几种反应的结果使熔盐中NO3-和NO2-的含量变化不规律。 上述研究表明硝酸熔融盐在由金属材料制成的蓄热系统中运行时会排放NOx,接触水蒸汽后会腐蚀管路；用在开式系统应增加尾气吸收装置,否则会对环境造成污染。
[Abstract]:Solar thermal power generation technology, with its advantages of alleviating the energy crisis and providing high quality electric energy, has become a competitive technology all over the world. High temperature thermal storage technology is the key technology of solar thermal power generation. High temperature storage material is the core of high temperature heat storage technology. High temperature storage material of molten nitrate salt is cheap because of its low melting point. The advantages of wide temperature range and low viscosity have become one of the preferred materials for solar thermal power generation. Nano _ 3-KNO _ 3 binary molten salt has been used in fully commercial solar thermal power plants. However, the nitric acid molten salt is unstable at high temperature, and the thermal decomposition may produce no _ x. Therefore, according to the national standard for monitoring NOx in air, this paper makes a systematic study on whether the common nitric acid molten salt releases NOx during the process of heat storage. The effect of temperature and container material (carbon steel and stainless steel) on the NOx emission of nitric acid molten salt was investigated. The reason of NOx emission from nitric acid molten salt was explained theoretically by thermodynamic calculation. The experiment was carried out to monitor the gas emitted by molten nitrate in quartz boat during the process of heat storage, to change the temperature and to add steel of different materials repeatedly. The results show that, In this experiment, nitric acid molten salt will release no _ x, and the 1h average concentration of NOx emission increases with the increase of temperature. The 1h average concentration of NOx discharged by the quaternary nitric acid molten salt is higher than that of the binary molten salt. When the nitrate molten salt contacts with 4carbon steel or stainless steel, it does release more no _ x.After heat storage, the concentration of no _ 2- in the binary molten salt increases with the increase of temperature. The contents of no 3-and no 2-in the quaternary molten salt samples vary irregularly with temperature. The thermodynamic calculation shows that the decomposition of K / nano _ 3 into K / no _ 2 and O _ 2 is the thermodynamic reaction of binary molten salt. The reactions of quaternary molten salt containing less NaNO3, less KNO3 and more NaNO2, decomposed into KNO2 and O2, and NaNO2 oxidized by air to NaNO3 and NaNO2 into Na _ 2O _ 2, N _ 2 and NaNO3 can occur thermodynamically, but no NOx gas is produced. In thermodynamics, nitrate can react with SiO2 to produce no and no _ 2, which is the real reason for the experimental monitoring of NOx. The metal Fe _ (C) / Nno _ 3 reacts with K / nano _ 3 to produce no, and Fe/Cr/Ni reacts with K / no _ 3 or any two of them to produce NO2 or NaNO2 to produce no. Should be thermodynamically possible, These reactions increase the amount of NOx emitted by nitric acid molten salt after contact with carbon steel or stainless steel. In addition to thermal decomposition, K- / nano _ 3 also reacts with metal to produce K / nano _ 2, which increases the amount of no _ 2- in the sample after binary nitric acid molten salt contact with steel; and third, In addition to these two reactions, the NaNO2 of the quaternary salt also oxidizes or participates in the reaction. The results of several reactions make the contents of no _ 3- and no _ 2- in the molten salt irregular. The results show that nitric acid molten salt will discharge no _ x when it is operated in a regenerative system made of metal materials and corrode the pipeline after contact with water vapor. The exhaust gas absorber should be added to the open system otherwise the environment will be polluted.
【学位授予单位】：华南理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TQ126.25;TM615

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