SCR脱硝过程中ABS挥发动力学及控制方法研究

发布时间：2018-05-10 14:57

  本文选题：ABS + 挥发特性　； 参考：《华北电力大学》2017年硕士论文

【摘要】：以NH3或尿素为还原剂的选择性催化还原法(SCR)是目前火电厂应用最为广泛的脱硝技术,该方法技术成熟、脱硝效率高、运行可靠且便于维护和操作。在烟气脱硝的过程中,SCR催化剂在催化还原NOX的同时,也使烟气中部分SO2(0.5%-2.0%)氧化成SO3,进而与SCR脱硝过程中的逃逸氨生成硫酸氢铵(ABS),液态的ABS具有粘性,易于在催化剂表面及SCR反应器的下游设备和管道上沉积,吸附烟气中的大量飞灰,引起催化剂活性降低、空预器阻力增大,传热元件传热效率下降等,严重时导致停机。因此,研究ABS的挥发特性与调控方法非常有必要。本文利用自行设计的挥发试验台,研究ABS的挥发特性及挥发后的冷凝规律,得出:随温度升高,ABS挥发速率增大,温度达400℃时,挥发速率出现陡增;接触面积增大,ABS的挥发速率明显升高;ABS颗粒越细,其挥发速率越快;随着飞灰中掺杂ABS量的增加,挥发速率呈下降趋势;利用离子色谱法对冷凝产物进行分析,得出当挥发温度低于300℃时,冷凝管中冷凝产物可能为NH4HSO4和少量的H2SO4,高于350℃时,冷凝产物可能是H2SO4和少量的硫酸铵(AS)。热重分析表明,ABS起始挥发温度为206℃左右,297-390℃为快速挥发阶段,在378℃时实现最快挥发速率;ABS的分解过程为:先发生脱氨反应,随后硫酸进一步分解为SO3和H2O;热重数据和等速升温动力学分析表明:ABS的挥发过程分为三个温度段,各段均符合反Jander挥发动力学模型,为三维扩散。高温条件下,ABS和AS对碳钢的腐蚀速率均随温度升高而降低,200℃以上变化不大;低于200℃时,ABS对碳钢的腐蚀速率比AS快;ABS浓度越高,腐蚀速率越快;利用SEM/EDS和XRD分析,确定腐蚀产物可能为铁的氧化物和(NH4)Fe(SO4)2等;机理为碳钢先发生酸性腐蚀和氧腐蚀,生成的Fe2+发生系列次生反应,生成铁的氧化物和(NH4)Fe(SO4)2等。结合实验研究结果表明,采用空预器控温的手段,应使烟气温度在350℃左右,以保证在实现一定的ABS挥发效果的同时,避免后续腐蚀问题。DSI法可以实现较好的SO3脱除效率,对ABS的控制效果好且运行费用较低。本论文研究对企业控制或减轻ABS的不良影响提供了理论基础。
[Abstract]:Selective catalytic reduction method with NH3 or urea as reductant is the most widely used denitrification technology in thermal power plants at present. The technology is mature, the denitrification efficiency is high, the operation is reliable and easy to maintain and operate. In the process of flue gas denitrification, the catalyst catalyzes the reduction of NOX, at the same time, it also oxidizes part of so _ 2 in flue gas to so _ 3, and then forms ammonium bisulfate with the escaping ammonia in the process of SCR denitrification. The liquid ABS is viscous. It is easy to deposit on the surface of catalyst and on the downstream equipment and pipeline of SCR reactor, and adsorb a large amount of fly ash in flue gas, which results in the decrease of catalyst activity, the increase of air preheater resistance and the decrease of heat transfer efficiency of heat transfer elements. Therefore, it is necessary to study the volatilization characteristics and control methods of ABS. In this paper, the volatilization characteristics and condensation law of ABS after volatilization are studied by using the self-designed volatilization test rig. It is concluded that the volatilization rate of ABS increases with the increase of temperature, and the volatilization rate increases steeply when the temperature reaches 400 鈩，

本文编号：1869766