脱C_4塔塔顶压力分程调节系统的调试

脱C_4塔是石家庄炼油厂选择性叠合工号中的一个装置,由叠合反应塔出来的物料经降压后进入该塔,在塔内将叠合物和未反应物C_4馏分进行分离。如图1所示。

压力分程控制系统在顺丁橡胶装置的灵活应用

通过把传统压力分程控制系统的PID调节方式改为逻辑调节,根据实际工艺控制参数范围制定合理的分程控制点,杜绝传统压力分程控制系统中调节阀的频繁开关现象,减少氮气和仪表风消耗,同时降低物料排放次数及其导致的环境污染。经实际运行过程中的数据统计,以验证该措施在顺丁橡胶装置降耗减排的实施效果。鉴于该项技术改造措施的零成本、高收益的特点,适合在其他石油化工装置物料储罐的压力分程控制系统中推广应用。

带有空冷器的分程控制系统分析

本文所介绍的是一个由一台阀门和一个空冷器组所组成的压力分程控制系统在分馏塔中的应用实例。由于空冷器的特点和工艺要求,在控制系统实施中与一般分程控制存在差异,为此对该回路的控制过程、回路构成和仪表调试等方面进行了定性、定量分析。

重整装置反应压力控制方案分析与投用

通过对连续重整装置的反应原理和工艺流程的简单介绍,说明了反应压力与目标产品的关联性以及压力控制的必要性和重要性。设计上反应压力控制采用压力-转速串级分程控制方案,通过压缩机的转速实时调节反应压力。由于认知不足,此控制方案自开工以来一直没有投用,反应压力采用压缩机定转速控制,且压缩机防喘阀一直保持一定的开度,导致反应压力波动大、影响产品质量且压缩机能耗大,因此优化反应压力的控制效果显得异常重要。通过论证、解析该控制方案,优化了PID控制参数和投用方法,成功地将控制方案投入实际生产,投用后重整反应压力非常稳定,提高了产品的收率和质量;同时由于防喘阀的关闭降低了压缩机能耗,提高了压缩机的工作效率,为企业带来了较高的经济效益。

己二酸装置冷凝液回收系统的设计与优化

分析研究了公司己二酸生产装置冷凝液回收利用系统的使用现状,系统地分析了装置能耗及伴热管网的整体耗能情况,优化了其工艺流程,解决了冷凝液回收过程中高压和中压蒸汽冷凝液气相系统的剩余热量耗损及冷凝液回收气相管排放口带液抛洒、伴热管网压力波动大及冷凝液品质异常时回收系统的中断与切换等问题。实现了节能降耗以及高温物料全自动化检测、切换与控制的目的,降低了现场劳动强度,改善了周边工作环境,保障了装置的长周期安全稳定运行,提高了己二酸的市场竞争力,具有良好的市场效益与社会效益。

氨压缩机的控制与应用

介绍氨压缩机入口导叶和防喘回流阀在防喘振与压力分程控制下的动作方式,给出机组的启/停和导叶加载控制方法。

连续重整装置专有控制技术的实现和应用

针对炼油企业连续重整装置的专有控制技术,通过对汽轮机转速,压缩机高、低压缸防喘振阀,超压放空阀,入口分液罐,重整产物分离罐以及再生接触罐等设备的压力、流量多变量解耦控制,保证压缩机在不同工况下达到最优、最节能和最安全的工作状态。

Improved finite difference method for pressure distribution of aerostatic bearing

An improved finite difference method （FDM）is described to solve existing problems such as low efficiency and poor convergence performance in the traditional method adopted to derive the pressure distribution of aerostatic bearings. A detailed theoretical analysis of the pressure distribution of the orifice-compensated aerostatic journal bearing is presented. The nonlinear dimensionless Reynolds equation of the aerostatic journal bearing is solved by the finite difference method. Based on the principle of flow equilibrium, a new iterative algorithm named the variable step size successive approximation method is presented to adjust the pressure at the orifice in the iterative process and enhance the efficiency and convergence performance of the algorithm. A general program is developed to analyze the pressure distribution of the aerostatic journal bearing by Matlab tool. The results show that the improved finite difference method is highly effective, reliable, stable, and convergent. Even when very thin gas film thicknesses （less than 2 Win）are considered, the improved calculation method still yields a result and converges fast.

Numerical simulation of residual stress field in green power metallurgy compacts by modified Drucker-Prager Cap model

Compaction process simulation and residual stress prediction of green PM compact were carried out with elasto-plastic 3D FEA based on the modified Drueker-Prager Cap model in Abaqus. The model parameters of the investigated powder Distaloy AE were determined as functions of relative density through typical mechanical property tests of powder. The model was implemented as a user subroutine USDFLD. Single sided compaction of a d20 ram^5 mm disk green compact of Distaloy AE was simulated, and the residual stress of the disk after ejection was predicted with FEA. The FEA results of the compaction process and the residual stress of the disk show good agreement with compaction experiments and X-ray diffraction measurements, which validates the model and its parameters. The results indicate that the compressive residual stresses exist mainly in a thin layer on the side surface, but the residual stresses are very small on the top and bottom surfaces.

Effect of pre-tensioned rock bolts on stress redistribution around a roadway—insight from numerical modeling

The importance of the pre-tensioned force of rock bolts has been recognized by more and more researchers. To investi- gate the effect of pre-tensioned rock bolts on stress redistribution around roadways, a numerical analysis was carried out using FLAC3D and a special post-process methodology, using surfer, is proposed to process the numerical simulation results. The results indicate that pre-tensioned rock bolts have a significant effect on stress redistribution around a roadway. In the roof, pre-tensioned rock bolts greatly increase vertical stress; as a result, the strength of the rock mass increased significantly which results in a greater capacity of bearing a large horizontal stress. The horizontal stress decreases in the upper section of the roof, indicating that pre-tensioned rock bolts significantly reduce the coefficient and the size of the region concentration of horizontal stress. At the lat- eral side, pre-tensioned rock bolts greatly increase the horizontal stress; therefore, the rock mass strength significantly increases which results also in a greater capacity of bearing a large vertical stress. The greater the size of pre-tensioned force, the larger the region of stress redistribution around a roadway is affected and the higher the size of the stress on the roadway surface the more the rock mass strength increases.

Study of vehicle accident reconstruction based on the information of the tire marks

The tire mark is the important legacy information left at the accident scene. Based on the vehicle collision dynamics model, this study provided an optimized algorithm with vehicle final location and other related information for the tire marks. When the tire marks simulation results fit the real one well, the state of vehicle can be understood as the real state in the accident. Based on above, the vehicle velocity and direction are decided. According to the velocity and direction of the vehicle, the complete accident process can be simulated. With the help of the Pc-Crash software, the method has been applied in typical collision accident cases analysis. The reconstruction results will provide the scientific and numerical references for vehicle collision accidents analyzing and appraising.

Non-complete relief method for measuring surface stresses in surrounding rocks

The measurement of surface stresses in surrounding rocks with the use of a relief method of annular hole-drilling was studied by numerical analysis. The stress relief process by hole-drilling was then simulated with the use of finite element method. The influences of the borehole diameter(d), the initial stresses and the ratio of the initial principle stresses on the variations of the remained stress and the released stress in function of the relief depth(h) were discussed. The relation between the non-dimensional ratio of the released principle strains and that of the initial principle stresses, and the effect of the elastic modulus and the Poisson ratio of the rock mass on the stress relief curves were studied. The results show that the stress relief behavior formulated with the non-dimensional ratio of the released stress and the ratio of h/d is only sensitive to the ratio of the initial principle stresses and the Poisson ratio. The stresses are completely released when h equals 1.6d, and the tensile stresses take place on the bore core surface in the relief measurement process. Finally, a non-complete relief method of annular hole-drilling for measuring surface stress in surrounding rocks is proposed and the procedure is presented.

Progress in Pressure Swing Adsorption Models During the Recent 30 Years

The pressure swing adsorption (PSA) models discussed here are divided into three categories: partialdifferential equation model, electrical analogue model and neural network model. The partial differential equationmodel, including equilibrium and kinetic models, has provided an elementary viewpoint for PSA processes. Usingthe simplest equilibrium models, some influential factors, such as pressurization with product, incomplete purge,beds with dead volume and heat effects, are discussed respectively. With several approximate assumptions i.e.,concentration profile in adsorbent, 'frozen' column, symmetry and heat effects of bed wall, the more complexkinetic models can be simplified to a certain degree at the expense of a limited application. It has also been foundthat the electrical analogue model has great flexibility to handle more realistic PSA processes without any additionalhypothesis.

Scattering wave field around a cavity with circular cross-section embedded in saturated soil using boundary element method

Based on Biot’s theory and considering the properties of a cavity,the boundary integral equations for the numerical simulation of wave scattering around a cavity with a circular cross-section embedded in saturated soil are obtained using integral transform methods.The Cauchy type singularity of the boundary integral equation is discussed.The effectiveness of the properties of soil mass and incident field on the dynamic stress concentration and pore pressure concentration around a cavity is analyzed.Our results are in good agreement with the existing solution.The numerical results of this work show that the dynamic stress concentration and pore pressure concentration are influenced by the degree of fluid–solid coupling as well as the pore compressibility and water permeability of saturated soil.With increased degree of fluid–solid coupling,the dynamic stress concentration improves from 1.87 to 3.42 and the scattering becomes more significant.With decreased index of soil mass compressibility,the dynamic stress concentration increases and its maximum reaches 3.67.The dynamic stress concentration increases from 1.64 to 3.49 and pore pressure concentration improves from 0.18 to 0.46 with decreased water permeability of saturated soil.

Parametric analysis of mixed lubrication characteristics in work zone of strip rolling

A theoretical model for mixed lubrication with more accurate contact length has been developed based on the average volume flow model and asperity flattening model,and the lubricant volume flow rate and outlet speed ratio are determined by integrating differential equations based on rolling parameters.The lubrication characteristics at the roll-strip interface with different surface roughness,rolling speed,reduction and lubricant viscosity are analyzed respectively.Additionally,the average volume flow rates of lubricant under different rolling conditions are calculated and used to explain the change rule of lubrication characteristics.The developed scheme is able to determine the total pressure,lubricant pressure,film thickness and real contact area at any point within the work zone.The prediction and analysis of mixed lubrication characteristics at the interface is meaningful to better control the surface quality and optimize the rolling process.

Outlining a stepwise,multi-parameter debris flow monitoring and warning system:an example of application in Aizi Valley,China

In recent years, the increasing frequency of debris flow demands enhanced effectiveness and efficiency of warning systems. Effective warning systems are essential not only from an economic point of view but are also considered as a frontline approach to alleviate hazards. Currently, the key issues are the imbalance between the limited lifespan of equipment, the relatively long period between the recurrences of such hazards, and the wide range of critical rainfall that trigger these disasters. This paper attempts to provide a stepwise multi-parameter debris flow warning system after taking into account the shortcomings observed in other warning systems. The whole system is divided into five stages. Differentwarning levels can be issued based on the critical rainfall thresholds. Monitoring starts when early warning is issued and it continues with debris flow near warning, triggering warning, movement warning and hazard warning stages. For early warning, historical archives of earthquake and drought are used to choose a debris flow-susceptible site for further monitoring. Secondly, weather forecasts provide an alert of possible near warning. Hazardous precipitation, model calculation and debris flow initiation tests, pore pressure sensors and water content sensors are combined to check the critical rainfall and to publically announce a triggering warning. In the final two stages, equipment such as rainfall gauges, flow stage sensors, vibration sensors, low sound sensors and infrasound meters are used to assess movement processes and issue hazardwarnings. In addition to these warnings, communitybased knowledge and information is also obtained and discussed in detail. The proposed stepwise, multiparameter debris flow monitoring and warning system has been applied in Aizi valley China which continuously monitors the debris flow activities.

Hydrodynamics numerical investigation of hoistable masts for underwater vehicles

Using the unsteady incompressible Navier-Stokes equation as the governing equation, the large eddy simulation (LES) model is implemented to investigate the shedding of vortices, the flow pattern of turbulence, the unsteady pressure fluctuation and the time history of the lift coefficient and drag coefficient of hoistable masts with various mast shapes and various arrangements in this paper. Combining the FFT, combined time-frequency transform and wavelet power spectrum analysis, the characteristics of unsteady pressure can be obtained in both time and frequency domain. It shows that the main frequency of pressure fluctuation is near the frequency of vortex shedding in time domain using the FFT method. It can be inferred from the combined time-frequency transform that the unsteady pressure fluctuation has obviously the peak value and the second peak value in time domain. It could indicate that the fluctuation power varies from the fluctuation frequency through the power spectrum analysis. By the data analysis, it shows that the vortex shedding is the dominant cause of the periodically pressure fluctuation. And the interaction pattern of wake and interplay between wake and the walls of masts under different arrangements are also discussed in this paper.

Computer simulation of flow and mixing at the duodenal stump after gastric resection

AIM： To investigate the flow and mixing at the duodenal stump after gastric resection, a computer simulation was implemented. METHODS： Using the finite element method, two different Billroth fl procedure cases （A and B） were modeled. Case A was defined with a shorter and almost straight duodenal section, while case B has a much longer and curved duodenal section. Velocity, pressure and food concentration distribution were determined and the numerical results were compared with experimental observations. RESULTS： The pressure distribution obtained by numerical simulation was in the range of the recorded experimental results. Case A had a more favorable pressure distribution in comparison with case B. However, case B had better performance in terms of food transport because of more continual food distribution, as well as better emptying of the duodena section. CONCLUSION： This study offers insight into the transport process within the duodenal stump section after surgical intervention, which can be useful for future patient-specific predictions of a surgical outcome.

Control of Vortex Shedding and Drag Reduction through Dual Splitter Plates Attached to a Square Cylinder

In this paper we have made a numerical study on the control of vortex shedding and drag reduction of a cylinder by attaching thin splitter plates. The wake structure of the cylinder of square cross-section with attached splitter plates is analyzed for a range of Reynolds number, based on the incident stream and height of the cylinder, in the laminar range. The Navier-Stokes equations governing the flow are solved by the control volume method over a staggered grid arrangement. We have used the semi-implicit method for pressure-linked equation （SIMPLE） algorithm for computation. Our results show that the presence of a splitter plate upstream of the cylinder reduces the drag, but it has a small impact on the vortex shedding frequency when the plate length is beyond 1.5 time the height of the cylinder. The presence of a downstream splitter plate dampens the vortex shedding frequency. The entrainment of fluid into the inner side of the separated shear layers is obstructed by the downstream splitter plate. Our results suggest that by attaching in-line splitter plates both upstream and downstream of the cylinder, the vortex shedding can be suppressed, as well as a reduction in drag be obtained. We made a parametric study to determine the optimal length of these splitter plates so as to achieve low drag and low vortex shedding frequency.

Coupled effects of stress damage and drilling fluid on strength of hard brittle shale

During well drilling process,original stress state of hard brittle shale will be changed due to stress redistribution and concentration,which leads to stress damage phenomenon around the borehole.Consequently,drilling fluid will invade into formation along the tiny cracks induced by stress damage,and then weaken the strength of hard brittle shale.Based on this problem,a theoretical model was set up to discuss damage level of shale under uniaxial compression tests using acoustic velocity data.And specifically,considering the coupled effect of stress damage and drilling fluid,the relationship between hard brittle shale strength and elapsed time was analyzed.