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Ou G.F.,Zhejiang Sci-Tech University | Ou G.F.,Hangzhou Fluid Technology Co. | Sun L.,Zhejiang Sci-Tech University | Zhu M.,Zhejiang Sci-Tech University | And 2 more authors.
Procedia Engineering | Year: 2015

In order to confirm the source of fouling and corrosion type, the process analysis is conducted based on the bending tubes of hydro-cracking reactor effluent air coolers (REAC) in a refinery. The process of sediment deposition was analyzed by using the CFD technology, and the critical condition of bending deformation and instability of tubes was determined via stress analysis. On this base, reasons of bending deformation in air cooler system and the targeted control measures were determined. The results showed that corrosion system of H2S-NH3-H2O existing in the cooling and separation process of hydrogenation reactor effluent stream, which would result in high temperature corrosion of H2S/H2 and erosion-corrosion of NH4HS solution. A large amount of corrosion products located at the end of tubes, which could block the air coolers when at a low flow velocity. In the air-cooler system, the temperature and force distribution were uneven when some part of pipes were blocked. Once the number of blocked pipes exceeds 9, the pipe bundles were diastrophic. The failure risk of bending deformation in reactor effluent air coolers (REAC) system could reduce, when the generation and deposition of corrosion products should be retarded, amount of water injection should be increased, desulfidation in recycle hydrogen should be strengthened and the design of REAC should be optimized. © 2015 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license. Source

Zheng Z.,Zhejiang Sci-Tech University | Ou G.,Zhejiang Sci-Tech University | Ou G.,Hangzhou Fluid Technology Co. | Ye H.,Zhejiang Sci-Tech University | And 4 more authors.
Engineering Failure Analysis | Year: 2016

The deposition failure of a reactor effluent air cooler (REAC) is investigated by the technical analysis and multiphase flow simulation. The blockages of REAC tubes are mainly induced by the corrosion products come from the upstream heat exchangers, a result of the high temperature H2S-H2 corrosion. Meanwhile, NH4Cl salts crystallize upstream the air coolers and enter into the REAC tubes, flowing along with the corrosion products. Through analyzing the residence times and deposition rates of salts, it is found that the corrosion products tend to deposit on two sides of the header box, the third row of tubes and the regions of low velocities. The temperatures inside the REAC tubes significantly decrease once the tubes are blocked. Fouling of NH4HS salts occurs when the temperature falls below 30 °C. The expansion and contraction of carbon steel with large difference in temperature lead to the bucking of tubes. The regions with high risk deposition are obtained from simulation, which agree well with the actual failure phenomenon. © 2016 Elsevier Inc. Source

Ou G.,Zhejiang Sci-Tech University | Qiu J.,Zhejiang Sci-Tech University | Qiu J.,Hangzhou Fluid Technology Co. | Zhu Z.,Zhejiang Sci-Tech University | And 2 more authors.
Lixue Xuebao/Chinese Journal of Theoretical and Applied Mechanics | Year: 2010

In order to research the failure of reducer, we focused on the protective corrosion product film formed on the wall of reducer and investigated the mechanism of erosion-corrosion damage caused by interaction of corrosion and fluid. The mathematical model of fluid-structure interaction was established. N-S equation of viscosity liquid and control equation of solid area of corrosion products are postulated with Arbitrary Lagrange-Euler (ALE). The interaction between multiphase liquid in boundary layer within pipe wall and the damage of protective erodent products film is analyzed. Applying with the Femlab software, the deformation of protective erodent products film in three different ways were analyzed, including different flows in reducer, different structures of reducer and different specifications of reducer. The numerical simulation result indicated that the deformation of protective erodent products film is relatively small, when the following conditions are satisfied, such as the fluid flows from the small inlet to large outlet, the concentric reducer and the relatively small difference of two end calibers of reducer. The obtained results can be used in erosion protecting and technical modification for the reducer. Source

Ou G.,Zhejiang Sci-Tech University | Ou G.,Hangzhou Fluid Technology Co. | Jin H.,Zhejiang Sci-Tech University | Xie H.,Zhejiang Sci-Tech University | And 2 more authors.
Engineering Failure Analysis | Year: 2011

Corrosion by wet ammonium salt is one of the main causes to the failure of reactor effluent air cooler (REAC) tubes. Based on a failure case, this paper presents the dynamic process of ammonium chloride (NH 4Cl) deposition. A finite element method was used for the numerical simulation of the flow field, temperature field and concentration field to analysis this deposition process. The effect of velocity on ammonium salt deposition was also analyzed by the simulation. Based on the study, we suggest that the process of ammonium salt deposition may be affected by multi-physical field coupling. Higher temperature gradient exists between the fluid and the wall surface. As velocity increases, the amount of deposited salt reduces while the distance of the position with max amount to REAC inlet increases. Compared with actual failure instances, this method can be used effectively in predicting the relative severity of ammonium salt corrosion in REAC tubes. © 2011 Elsevier Ltd. Source

Guofu O.,Zhejiang Sci-Tech University | Guofu O.,Hangzhou Fluid Technology Co. | Li S.,Zhejiang Sci-Tech University | Min Z.,Zhejiang Sci-Tech University | And 2 more authors.
Petroleum Refinery Engineering | Year: 2015

The corrosion failure mechanisms of air cooler system are analyzed based upon process of hy-drogenation reaction effluent. The pH value variations of solution medium in air cooler system are obtained for different feedstocks with different sulfur, nitrogen and chlorine contents at the conditions of 105 t/h feedstock flowrate and 13 MPa operating pressure of air cooler by the establishment of pH value computational model of multinphase flow system for reactor effluents. The results show that: ( 1 ) the pH value of solution medium in high-temperature region (higher than 145 °C) is 5. 5 lower than that of low-temperature region (lower than 140 °C ) ; The corrosion failure risk of the air cooler is high; (2) the different sulfur, nitrogen and chlorine contents have impacts on pH value of solution medium. At the 152°C inlet temperature of air cooler reactor's effluent, the pH value of solution medium is 4.4 ∼5.4, which imposes a higher corrosion failure risk; (3) The 13 t/h water injection rate can effectively reduce the risk of corrosion failure of air cooler. It is suggested that, when the feedstock with high sulfur, nitrogen and chlorine is processed, proper amount of ammonia liquor or organic ammonia can be injected to minimize the corrosion failure risk of air cooler caused by pH value. Source

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