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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 5 more authors.
Engineering Failure Analysis | Year: 2016

High pressure letdown valve in direct coal liquefaction is used to adjust the flow rate of coal-oil slurry that enters into the downstream separator. Severe erosion-cavitation wear is found on the valve spool, seriously affecting the safety and reliability of unit. The majority of this paper investigates the failure process of valve spool and proposes a corresponding structural optimization via computational fluid dynamics (CFD) methodology. Three geometries of different failure states are selected as the computational domains in the numerical simulation. The Schneer-Sauer model, particle rebound-velocity model and erosion model are employed to calculate the cavitation phenomenon and erosion rates distribution. Experiments of flow rates and cavitation on valve model under different pressure drops are conducted to validate the accuracy of numerical approach. Results showed that the damage development of valve spool aggravates the erosion-cavitation wear. The maximum erosion rates are located on the top of spool head in all the three states. The erosion rates on spool arc surface are two orders of magnitude higher than that on parabolic surface. The decrease in radius of spool head reduces the intensities of erosion-cavitation wear. The numerical results are in agreement with actual failure morphologies of valve spool in different states. © 2016 Elsevier Inc.

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.

Jin H.,Zhejiang Sci-Tech University | Zheng Z.,Zhejiang Sci-Tech University | Ou G.,Zhejiang Sci-Tech University | Ou G.,Hangzhou Fluid Technology Co. | And 4 more authors.
Engineering Failure Analysis | Year: 2015

Under harsh working conditions-high pressure differential, solid concentration and high velocity of a regulating valve in coal liquefaction, the valve plug damages easily. Its longest service life is less than 2000. h, which seriously affects the running safety. Failure analysis of valve plug is conducted via computational fluid dynamics (CFD) by using the actual physical parameters. The results show that the damage of valve plug results from a synergistic effect of cavitation erosion and abrasion. Two cavitation regions exist on the wall of valve bushing and plug, and a high-speed reflux appears on the plug head where the pressure is higher than the saturation pressure. Driven by the reflux, the cavitation bubbles and solid particles move toward the plug head, thus the most severe cavitation erosion and abrasion occur on the plug head because of the bubbles collapse and particle impacts. The decrease of valve opening tends to aggravate the valve plug damage caused by the combined effects of cavitation erosion and abrasion. Compare with the actual corrosion morphology, the accuracy of failure analysis is verified. © 2015 Elsevier Ltd.

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.

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.

Ou G.,Zhejiang Sci-Tech University | Ou G.,Hangzhou Fluid Technology Co. | Wang K.,Zhejiang Sci-Tech University | Zhan J.,Zhejiang Sci-Tech University | And 4 more authors.
Engineering Failure Analysis | Year: 2013

In the present research, root causes of the tube explosion of a refinery hydrocracking reactor effluent air cooler (REAC) were studied. For this purpose, anatomical analysis was firstly used and ammonium salt crystals were found. Based on the actual operating conditions, ionic equilibrium model was established by Aspen software to calculate the crystal temperature of the NH4Cl and NH4HS. The results indicate that NH4Cl crystal temperature ranged from 175°C to 210°C with different chlorine and nitrogen content of the feedstock, which is higher than the operating temperature of REAC. To analyze the impact of the air cooler structure on the ammonium salt deposition location, numerical simulation including the air cooler header box and bundles was conducted by the Fluent software. The results show that a bias flow regime exists because of the large vortex formed in both sides of the header box inlet. The velocity and aqueous phase fraction of the multiphase were low in the tubes of the header box inlet both sides, which result in the NH4Cl deposition and under-deposit corrosion. In order to verify the failure analysis results, other in service air coolers were inspected using the infrared camera, and the results show that other air coolers had the plugging features at the same position. Finally, some recommendations were given to mitigate the NH4Cl deposition. © 2013 Elsevier Ltd.

Ou G.-F.,Zhejiang Sci-Tech University | Ou G.-F.,Hangzhou Fluid Technology Co. | Zheng Z.-J.,Zhejiang Sci-Tech University | Jin H.-Z.,Zhejiang Sci-Tech University
Gao Xiao Hua Xue Gong Cheng Xue Bao/Journal of Chemical Engineering of Chinese Universities | Year: 2016

Based on three-phase physical properties including oil, gas and water in an air cooler (REAC) system of the hydrogenation reactor effluent, a physical model of static blade mixer is established. The numerical analysis on the multiphase flow characteristics inside the blade mixer is conducted via CFD software by utilizing Mixture multiphase model and Realizable k-ɛ turbulent model. The pressure drops between the inlet and outlet of mixer obtained from simulation agree well with experiment data, it verifies the reliability of the simulation calculation. The results show that: The multiphase flow velocity increases and turbulence intensity enhances obviously in the mixing region. There is also a large scale eddy occurs at the bottom of the lowest vortex blade. By analyzing water phase fraction and non-uniformity coefficient in different pipeline cross sections, it shows that the uniformity of water phase fraction is improved through mixing. Within the velocity range of 2 to 6 m·s-1, the mixing effect is not affected by the change of the flow velocity. The dimensionless parameter λ was used to define the ratio between the flowing distance from the mixer outlet L and the mixer length l, it can be observed when the λ ≥ 3, the non-uniformity coefficient will not change obviously. A large wall shear stress region is formed on the wall of export pipeline, which is close to the critical erosion value of carbon steel. Therefore, stainless steel liners should be considered to be added in the mixer outlet to prevent wall thinning induced by corrosion-erosion. © 2016, Zhejiang University. All right reserved.

Jin H.,Zhejiang Sci-Tech University | Wang K.,Zhejiang Sci-Tech University | Ou G.,Zhejiang Sci-Tech University | Ou G.,Hangzhou Fluid Technology Co. | Ren H.,Zhejiang Sci-Tech University
Shiyou Xuebao, Shiyou Jiagong/Acta Petrolei Sinica (Petroleum Processing Section) | Year: 2015

Based on the analysis of ammonium salt crystalline process in hydrogenation effluent, the model for calculating ammonium salt crystallization rate was established. The prediction of ammonium salt crystal deposition from hydrogenation reaction effluent was realized by developing the calculation model as a user module on Aspen Plus platform. The crystallization rates of NH4Cl and NH4HS in hydrogenation effluent of different feedstocks under different operation conditions were analyzed. The results showed that the ammonium salt crystallization did not occur at higher effluent temperatures, but began to appear with the decrease of effluent temperature after the effluent entering the heat exchangers. The initial crystallization temperature of ammonium salt increased with the increase of nitrogen, chlorine or sulfur mass fractions in feedstock. The initial crystallization temperature of NH4Cl increased but its maximum crystallization rate decreased with the increase of process pressure. The crystallization temperature of NH4Cl was in the range of 160-210℃, while that of NH4HS was in the range of 30-60℃ with the maximum crystallization rate 4 to 5 orders of magnitude higher than that of NH4Cl. Typical case application indicated the method being accurate and reliable. © 2015, Editorial Office of Acta Petrolei Sinica. All right reserved.

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.

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.

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