Research Of HCl-H₂O System Dew-point Corrosion Law And Prediction Method

Since the world’s first set of atmospheric and vacuum distillation unit put into use, flow corrosion failure in the overhead of atmospheric and vacuum distillation tower would seriously restrict the stable operation of the device and system. Especially in recent years, along with increasing energy crisis throughout the world, the oil refining industry gradually increase the proportion of high-sulfur, high-acid, processed chlorine and other low-quality crude oil refining unit equipment sparked widespread liquidity corrosion failure accident. Among them, the low-temperature portion of atmospheric tower system caused by the HCl dew point corrosion is one of the most typical and most serious form of failure. Since the dew point corrosion is closely related to corrosion and corrosive media, the process, operating conditions and equipment materials, structure, etc., the failure mechanism is more complex, unpredictable and prevention, it has become a key factor in today’s constrained refining unit safe and stable operation for a long period.In this paper, take atmospheric tower system frequent HCl dew point corrosion in low temperature zone of petrochemical enterprises as the research object, firstly, the calculation method of the dew point temperature is introduced, and then analyzed the mechanism of low temperature HCl dew point corrosion, and clarify the main factors of HCl dew point corrosion. According to the shell and tube heat exchanger failure problem of some refinery atmospheric overhead reflux system, the temperature poine which the aqueous phase start to appear in the heat exchanger operating temperature range is obtained through analyzing tower overhead process, mainly corrosive media, operating conditions and so on. This temperature is called the dew point temperature. Then use heat transfer calculation software HTRI establish shell and tube heat exchanger structure model, combining the resulting data of the tube, shell and tube bundle outer wall temperature distribution calculated by ASPEN, determine the specific location which the dew point temperature occurred in the heat exchanger, to accurately predict the HCl dew point temperature. In the research experiment, the HCl dew point corrosion experiment equipment was built to study the dew point corrosion laws of 10# carbon steel, 15 CrMo steel, duplex steel 2205 and stainless steel 316 L etc. four typical materials in different HCl concentration, different droplet impact velocity and different impact angles, using scanning electron microscope(SEM) to observe the surface corrosion topography of the removal and the retention of corrosion products of the test materials; combined with X-ray diffraction analysis of components dewpoint corrosion products 10# carbon steel and steel 15 CrMo two materials, forming a clear mechanism of corrosion products of both materials and protective properties of the metal matrix material.The innovation of this paper is as follow: Clear the main factors of HCl-H2 O system dew point corrosion by process correlation analysis; experimental device is designed to study HCl dew point corrosion law and corrosive effect on the typical petrochemical materials; establish dew point corrosion calculation model of atmospheric and vacuum tower overhead system and heat transfer calculation model based on process simulation to analysis dew point corrosion mechanism and predict the occurrence of the dew point temperature position precisely. The research results are expected provide foundations for dew point corrosion failure analysis in atmospheric and vacuum tower overhead system, the materials selection of key equipment and preservation and optimization in the petrochemical enterprise.