燃煤锅炉烟气深冷过程积灰与低温腐蚀的耦合作用机理研究

The coupling effect between ash deposition and low temperature corrosion is the key factor during flue gas deep cooling to acid dew point. It is essential to investigate the coupling effect mechanism for energy saving and pollution reduction. In the present project, firstly, on the basis of the theoretical analysis and the results of ash deposition corrosion test, the condensation characteristic of acidic gases and the influence of ash to the acid dew point，the change law of ash deposit and heat transfer characteristics for the tube will be acquired. Then，the condensation and deposition law of the acid gaseous will be revealed. Secondly, based on the microanalysis results of ash and corrosion product by ICP\XRF\XRD\SEM, the physicochemical property of ash particles changed by the condensed acid will be acquired. A deposition model for ash particles containing acid will be proposed. According to chemical kinetics theory and elements of migration theory, the mass transfer of the acid in the ash layer and the detailed reaction mechanism between ash deposition and low temperature corrosion will be revealed. Finally, the detailed reaction mechanism will be verified by field test. Combined the condensation and deposition law of the acid gaseous with the deposition characteristic for ash particles containing acid，the coupling effect between ash deposition and low temperature corrosion will be revealed. Also it will be coupled in CFD calculation to predict the dew point corrosion rate of the tube. The present project will enrich the theory system on energy saving and pollution reduction，and it has a vital significance for engineering applications of this energy saving technology.

积灰与低温腐蚀的耦合作用是影响燃煤烟气冷却至露点温度以下的关键因素，研究其耦合作用机理对实现燃煤烟气深冷增效减排具有重要意义。本项目通过理论分析、积灰腐蚀实验研究，获得酸性气体的冷凝特性，获得飞灰对烟气露点的影响规律，获得换热管壁的积灰和传热特性变化规律，揭示积灰对酸性气体冷凝沉积的影响规律。其次，基于积灰和腐蚀产物的ICP、XRF、XRD、SEM等分析结果，获得酸液对灰颗粒理化特性的改变规律，建立含酸灰颗粒的沉积模型。综合化学反应动力学理论、元素迁移扩散理论，揭示冷凝酸液在灰层内的传质机理，揭示积灰与低温腐蚀耦合过程的详细反应机理。最后，通过实炉实验验证上述详细反应机理，结合酸性气体冷凝沉积特性、含酸灰颗粒沉积特性，揭示积灰与低温腐蚀的耦合作用机理，并耦合CFD计算预测管材低温腐蚀速率。本项目对丰富燃煤烟气深度冷却增效减排理论体系，促进燃煤烟气深冷增效减排技术应用和推广具有重要意义。

燃煤锅炉的排烟温度普遍偏高，电站锅炉排烟温度通常为120~150℃，工业锅炉更是高达160~300℃，排烟余热利用潜力十分巨大。但是在烟气深度冷却的过程中，露点腐蚀和粘性积灰可能造成管束泄露和受热面堵塞，严重影响了机组安全性和经济性。因此，有必要深入研究燃煤锅炉烟气深度冷却过程中的露点腐蚀和粘性积灰特性并揭示其耦合机理。.首先，基于理论分析提出了露点腐蚀和粘性积灰的主要影响因素，探讨了避免或减轻露点腐蚀和粘性积灰的理论方法。其次，通过低温腐蚀性能实验装置分别对燃煤电站锅炉和工业锅炉的露点腐蚀和粘性积灰特性进行实验研究。利用XRF、XRD和SEM-EDS对处理后的灰样和金属试样进行系统理化分析，得到了露点腐蚀和粘性积灰随壁面温度变化的规律，建立了酸冷凝、灰酸吸附反应、露点腐蚀和粘性积灰的耦合模型，揭示了露点腐蚀和粘性积灰的共生耦合机理。对比了静电除尘器前后以及燃煤电站锅炉和工业锅炉在露点腐蚀和粘性积灰特性上的差异，系统地总结了燃煤锅炉露点腐蚀和粘性积灰的耦合机理以及形成过程中酸冷凝的吸收凝并作用机制。最后，考察长周期运行后发生腐蚀堵灰的空预器和烟气深度冷却器的性能参数和腐蚀积灰情况，并实地静态提取灰样和金属试样，然后对处理后的试样进行XRF、XRD、SEM-EDS以及激光粒度等分析，发现了空气预热器和烟气深度冷却器上不同区域发生腐蚀和积灰的原因，建立了真实条件下长周期露点腐蚀和粘性积灰的耦合生长模型，揭示了实际低温受热面露点腐蚀和粘性积灰的形成机理，并验证了理论分析和现场实验的研究结果。.本项目在低温受热面露点腐蚀和粘性积灰理论分析的基础上，经过现场实验和工业实验的多尺度综合研究分析和交叉验证，建立了完整的露点腐蚀和粘性积灰理论体系，提出了与酸冷凝、露点腐蚀和粘性积灰相关的关键温度预测方法，形成了燃煤锅炉露点腐蚀和粘性积灰的防护准则，为烟气余热利用技术在燃煤锅炉上的应用提供了重要的理论和技术指导。