【作者】 朱恺；

【导师】 周钰明； 谢洪涛；

【作者基本信息】 东南大学 ， 化学工程（专业学位）， 2018， 硕士

【摘要】 苯乙烯精馏分离系统需在真空、添加阻聚剂和较低精馏温度条件下进行,分离塔塔顶馏出物成分复杂、温度较低,容易造成塔顶封头和管线的腐蚀。因此急需研究苯乙烯精馏系统发生腐蚀的原因与机理,进行腐蚀在线监测,提出相应防腐蚀对策。本文针对苯乙烯精馏系统塔顶管线腐蚀泄漏频发,严重影响装置安全稳定运行的问题,开展苯乙烯精馏分离系统腐蚀原因分析及防腐对策研究。分析苯乙烯精馏系统的运行工况,利用气相色谱、等离子发射光谱等手段对精馏塔进料、塔顶馏分的组成和汽液界面上组分进行测定,采用金相显微镜、扫描电子显微镜等手段,对腐蚀垢件进行深度剖析和组成分析。建立实验室苯乙烯精馏分离模拟系统,对苯乙烯精馏系统腐蚀管线材质20#碳钢开展电化学测量,依次探究温度、时间、pH、转速、氧气含量等因素对碳钢管线腐蚀的影响。并模拟管线材质挂片腐蚀试验,研究结果如下:(1)通过对苯乙烯精馏分离系统中成分特征、腐蚀垢件和腐蚀特点进行分析,水样分析呈中性偏弱酸性,HC03-、游离CO2含量较高,碳酸的存在及浓缩导致水样溶液呈酸性,酸性条件下易产生露点腐蚀。Cl-和SO42-含量较高,存在严重的氯腐蚀、硫腐蚀。Cl-浓度4.21mg/L,SO42-浓度13.28mg/L,HCO3-浓度12.80mg/L。三种离子造成腐蚀的严重情况排序是:Cl->S042->HCO3-。回流罐腐蚀垢样主要由Fe203和灼减损失的有机物构成,比例为6:4,垢样分析得到的元素与管路中分离得到的水样中检测到的离子对应一致,包括Mg2+、Na+、Ca2+、SO42-、Cl-等腐蚀性离子,油水比例较低的塔塔顶管线腐蚀最为严重、穿孔最大,会溶解更多的腐蚀介质。苯乙烯精馏系统中流量、pH以及离子浓度都处于一个动态波动的情况下,局部离子浓度较高。穿孔处集中在管路焊接、拐弯以及容易积液位置。(2)通过实验室苯乙烯精馏分离模拟系统,分析与腐蚀塔材一致的20#碳钢的自腐蚀电位、极化曲线、腐蚀速率、交流阻抗的变化。主要控制变量为:介质温度、腐蚀时间、转速、酸度、有无氧气存在等。酸度、有机物、氧、Cl-、sO42-等共同导致20#碳钢表面发生较严重腐蚀,主要是酸腐蚀和离子造成的电化学腐蚀。在模拟体系中,开始时腐蚀迅速发生,随腐蚀反应进行,锈层逐步堆积在表面,电极表面性质逐步达到相对稳定状态,30～95℃时阻抗随温度增加而减小,初始腐蚀速率增长较快,当腐蚀时间达60h后,腐蚀速率逐渐趋于稳定;溶液pH偏碱性时,腐蚀率最低;流速越大,腐蚀愈加严重。(3)建立苯乙烯精馏装置故障树。从结构角度、成分角度、动力学角度、材质角度进行腐蚀原因分析,并提出相应防腐对策。更多还原

【Abstract】 The styrene distillation separation system need to run in the conditions of vacuum,adding polymerization inhibitor and lower distillation temperature.The overhead distillate composition from separation tower is complicated and hypothermal,likely to caused corrosion of the tower head and pipeline.Therefore,it is urgent to study the cause and mechanism of the corrosion in the styrene distillation system,carry out on-line monitoring of corrosion and propose corresponding anti-corrosion measures.This paper aimed at the pressing problem which the overhead pipeline corrosion leaks,seriously affect the safe and stable operation of the device,to carry out the research of styrene distillation separation system corrosion analysis and corrosion prevention measures.Thus,the operating conditions of styrene distillation system were analyzed.The composition and ingredient of distillation column were characterized and analyzed by some professional equipment and methods such as GC-MS,ICP,etc.Besides,the corrosion pieces were dissected by Metallurgical microscopy and Scanning electron microscopy.The simulation system of styrene distillation separation in Lab was set up.The electrochemical measurement of 20#carbon steel in styrene distillation system was carried out.The influencing factor were investigated as follows:temperature,time,pH,rotational speed and oxygen content.And the pipeline material corrosion test piece were simulated。The main research contents are exhibited as follows:(1)By analyzing the components,corrosion scale and corrosion characteristics in styrene distillation separation system,the water samples showed neutral weak acidity,high content of HCO3-and free CO2,the presence and concentration of carbonic acid led to solution become acidic,acidic conditions prone to dew point corrosion.The high content of Cl-and SO42-lead to serious chlorine corrosion and sulfur corrosion.The concentration of Cl-,SO42-and HCO3-is 4.21 mg/L,13.28 mg/L and 12.80 mg/L,respectively.The order of the three ions causing corrosion is Cl->SO42->HCO3-.The corrosion scale of the reflux tank is mainly composed of Fe2O3 and organic matter with loss of ignition loss,the ratio is 6:4.The elements of the scale sample analysis are consistent with the ions detected in the water sample obtained from the pipeline,including Mg2+,Na+,Ca2+,SO42+,Cl-and other corrosive ions.The pipeline with the lower ratio of oil to water has the most serious corrosion and the largest perforation because of more corrosive composition.The flow,pH,and ion concentrations are in a dynamic fluctuations in the styrene distillation system,resulted in the case of higher local ion concentrations.The perforation focused on the pipeline welding,turning and easy fluid accumulation position.(2)Through the simulation system of separation equipment,the corrosion potential,polarization curve,corrosion rate and AC impedance of 20#carbon steel which is consistent with the corrosion tower were analyzed.The main control variables are:medium temperature,corrosion time,rotating speed,acidity,oxygen concentration and so on.The severe corrosion on the surface of 20#carbon steel is due to acidity,organic matter,oxygen,chloride ions,sulfate ions and other factors,mainly caused by acid corrosion and ion-induced electrochemical corrosion.In the simulation system,the corrosion started rapidly.Along with the corrosion reaction continued,the rust layer gradually deposited on the surface,and the surface properties of the electrode gradually reached a relatively stable state.The impedance decreased with the increase of temperature at 30～95℃.The initial corrosion rate increased rapidly and then stabilized when the corrosion time reached 60h.The corrosion rate is the minimum when the solution is alkaline.The greater the flow rate,the corrosion is more severe.(3)The study established the fault tree of styrene rectification plant,analyzed the corrosion reasons from the dimension of structure、composition、dynamics and material quality respectively,and put forward the corresponding anti-corrosion measures.更多还原