余热利用换热器硫酸和水蒸气耦合凝结数值模拟

Numerical study on coupled condensation of sulfuric acid and steam in heat exchanger for waste heat utilization

为了准确预测烟气换热器表面酸凝结,了解其表面低温腐蚀特性,采用一种预测换热器表面酸蒸气凝结和水蒸气凝结耦合计算方法,通过结合H2SO4-H2O溶液的气液平衡数据和多元组分传输理论,建立了酸蒸气和水蒸气凝结的数值模型,并采用CFD软件对方形翅片管换热器的低温腐蚀特性进行数值分析,重点研究酸蒸气含量和水蒸气含量对酸沉积和腐蚀特性的影响.结果表明:换热器翅片表面酸液质量分数的分布和翅片表面温度的分布趋势一致,酸沉积主要发生在翅片前缘及换热管前方靠近管壁的翅片表面;水蒸气含量升高会导致翅片表面酸液质量分数下降和酸沉积率上升,可能增加换热器低温腐蚀的风险,计算结果可为换热器安全运行提供设计参考.

Low-temperature corrosion characteristics of flue gas heat exchanger surfaces are the key factors affecting the reliability of equipment operation. And an accurate prediction of condensation of sulfuric acid vapor is crucial for investigation into the mechanism of low temperature corrosion characteristics. A coupled numerical model was adopted to predict the condensation of sulfuric acid vapor on the heat exchanger surfaces. By integrating the vapor-liquid equilibrium data of H2SO4-H2O solutions and multi-component diffusion theory,a model for the sulfuric acid pressure on the fin surfaces under the coupled condition was obtained. A rectangular type finned tube heat exchanger was employed to identify the effect of acid vapor content and water vapor content on the sulfuric acid condensation and corrosion by using CFD. The results show that the distribution of acid solution concentration is depen-dent on the fin temperature. The fin regions with higher temperature also are subject to a higher acid solution concentration. An increase in water vapor concentration can result in a sharp reduction in acid solution concentration and an increase in deposition,indicating a severe risk of low-temperature corrosion. The results can be used as a reference for the safety design of heat exchangers.