中文摘要：

炼油厂常减压装置塔顶低温部位的腐蚀和铵盐沉积是影响装置长周期安全运行的主要因素，腐蚀薄弱环节发生在露点区域，而影响露点腐蚀的关键N素是pH值。选用Aspen软件中的电解质模型，根据塔顶的组分及腐蚀气体的含量，对此低温系统的pH值进行了模拟计算，确定了露点区域溶液中的pH值，并对工艺防腐措施中的注氨和注水进行模拟计算，研究其变化对PH值的影响。利用氯化铵盐的结晶曲线分析塔顶系统的氯化铵结晶趋势，得到了沉积温度，同时探讨塔顶系统的操作压力、注氨量和注水量等变化对氯化铵盐沉积温度的影响，得到了沉积规律。

英文摘要：

Atmospheric and vacuum distillation unit is an important processing equipment of crude oil. In the whole unit, corrosion at low temperature region and ammonium salt deposition are always the main factors that effect on long period and safe operation for the unit. The compo- sitions of the product from atmospheric and vacuum distillation are usually so complicated that ac- tual proportions of compositions are unavailable; thus the light hydrocarbons and fictitious com- ponents are only estimated by simulation method. Based on flow rate of the atmospheric and vac- uum distillation unit, chemical process of the primary tower, atmospheric tower and vacuum are simulated by using software Aspen, to obtain the component and flow rate of overhead. Serious corrosion at low-temperature part of column top system usually occurs in the dew point region, in which pH value is a key impact factor. Based on contents of components and corrosive gas in top i of tower, electrolyte model of Aspen is used to determine the pH value in solution of dew i~oint region. And the processes of ammonia and water injection are simulated to investigate the influ-