Intensification of an Irreversible Process Using Reactive Distillation – Simulation Studies

In this study, a steady state simulation of the process for the production of xylene isomers by reactive distillation was performed using Aspen Plus software. The simulations were aimed studying the parameters like number of stages in the different sections of the RD column, reflux ratio, and the boil-up ratio, which maximize the conversion of Toluene and improves the selectivity and yield of the p- Xylene. Keywords: Reactive Distillation, Process Intensification, Toluene Methylation, Aspen Plus, Simulation Studies,

Modeling of Melt Flow and Heat Transfer in Stationary Gas Tungsten Arc Welding with Vertical and Tilted Torches

A 3D numerical simulation was conducted to study the transient development of temperature distribution in stationary gas tungsten arc welding with filler wire. Heat transfer to the filler wire and the workpiece was investigated with vertical (90°) and titled (70°) torches. Heat flux, current flux, and gas drag force were calculated from the steady-state simulation of the arc. The temperature in the filler wire was determined at three different time intervals: 0.12 s, 0.24 s, and 0.36 s. The filler wire was assumed not to deform during this short time, and was therefore simulated as solid. The temperature in the workpiece was calculated at the same intervals using heat flux, current flux, gas drag force, Marangoni convection, and buoyancy. It should be noted that heat transfer to the filler wire was faster with the titled torch compared to the vertical torch. Heat flux to the workpiece was asymmetrical with both the vertical and tilted torches when the filler wire was fully inserted into the arc. It was found that the overall trends of temperature contours for both the arc and the workpiece were in good agreement. It was also observed that more heat was transferred to the filler wire with the 70° torch compared with the 90° torch. The melted volume of the filler wire (volume above 1750 °K) was 12 mm3 with the 70° torch, compared to 9.2 mm3 with the 90° torch.

The use of flow diagnostics to rank model ensembles

Ensembles of geomodels provide an opportunity to investigate a range of parameters and possible operational outcomes for a reservoir. Full-featured dynamic modelling of all ensemble members is often computationally unfeasible, however some form of modelling, allowing us to discriminate between ensemble members based on their flow characteristics, is required. Flow diagnostics (based on a single-phase, steady-state simulation) can provide tools for analysing flow patterns in reservoir models but can be calculated in a much shorter time than a full-physics simulation. Heterogeneity measures derived from flow diagnostics can be used as proxies for oil recovery. More advanced flow diagnostic techniques can also be used to estimate recovery. With these tools we can rank ensemble members and choose a subset of models, representing a range of possible outcomes, which can then be simulated further. We demonstrate two types of flow diagnostics. The first are based on volume-averaged travel times, calculated on a cell by cell basis from a given flow field. The second use residence time distributions, which take longer to calculate but are more accurate and allow for direct estimation of recovery volumes. Additionally we have developed new metrics which work better for situations where we have a non-uniform initial saturation, e.g., a reservoir with an oil cap. Three different ensembles are analysed: Egg, Norne, and Brugge. Very good correlation, in terms of model ranking and recovery estimates, is found between flow diagnostics and full simulations for all three ensembles using both the cell-averaged and residence time based diagnostics.

Simulation of Subsea and Platform Production Schemes to Quantify Flow Assurance Risks under Transient and Steady State Conditions in Offshore Kuwait

In offshore production, the type of field development scheme is crucial aspect due to its associated flow assurance risks, which affect project economic, safety, and sustainability. The objective of this study is to simulate and evaluate two offshore field development schemes, namely subsea and platform in offshore Kuwait. Further objective is to carry out detailed transient simulation study on the subsea scheme to investigate flow assurance risks related to terrain slugging, and hydrates formation during shut-in and re-start transient events. The evaluation of the two schemes is based on the associated flow assurance risks, and project economics. Steady state simulations are used to identify the feasible production scheme, which is further simulated under transient shut-in/restart events to investigate flow assurance risks related to terrain slugging and hydrates formation. The steady state simulation results of this study showed that flow assurance risks such as hydrates and pipeline corrosion are significant in both production schemes. To mitigate these risks, sixteen different field development designs of both production schemes were simulated and economically evaluated. Results revealed that the subsea multiphase development scheme with 10-in. ID carbon steel multiphase flowline and 0.3-in. thick polypropylene thermal insulation is the optimum design. Consequently, the optimum design is further analyzed under transient conditions, resulting in appreciable risk of terrain slugging due to hilly-terrain pipeline configuration, especially for the low production rate cases. The transient shut-in/restart simulation results revealed a risk of hydrates formation due to cooling effect during shut-in, which is mitigated by MEG injection. In conclusion, the subsea multiphase flow scheme is selected over platform scheme due to manageable flow assurance risks, low capital investment cost, and minimum environmental impact. This study would enable Kuwait Oil Company to evaluate different offshore development schemes to ensure sustainable production with safe operation and protected environment.

Wind Environment Simulation Accuracy in Traditional Villages with Complex Layouts Based on CFD

Using wind speed, wind direction, and turbulence intensity values as evaluation indicators, the ventilation performance of villages with complex building layouts was studied. We used the SKE, RNG, and RKE solvers in CFD-3D steady-state Reynolds-averaged Navier–Stokes (RANS) to simulate the wind environment of a village. The findings show that for the simulation of rural wind environments with complex building layouts, steady-state simulation solvers need to be evaluated in detail to verify their accuracy. In this study, a village with a complex architectural layout in Southern Shaanxi, China, was taken as the research object, and three steady-state simulation solvers were used to evaluate the ventilation performance of the village. The simulated data were compared with the measured data to find the most suitable solver for this kind of village wind environment simulation. The results show that for the simulation of the village wind environment with a complex building layout, the RNG simulation results have the lowest reliability among the three steady-state solvers. The reliability of wind speed distribution and turbulence intensity distribution are 0.7881 and 0.2473, respectively. However, the wind speed and turbulence intensity values obtained by the SKE solver are the closest to the measured values, which are 0.8625 and 0.9088, respectively. Therefore, for villages with complex building layouts, the SKE solver should be the first choice for simulating wind environment distribution. When using the RNG solver, the overall turbulence intensity value obtained is higher than the measured value. The average deviation between the simulated data and SKE and RKE at a height of 1.7 m is 42.61%. The main reason for this is that RNG overestimates the vortices and underestimates the airflow rate in the building intervals.

Features of processes in a microwave discharge in water vapor

A zero-dimensional steady-state simulation of microwave discharge in water vapor at atmos-pheric and reduced pressures and a constant gas temperature has been carried out. A model of a continuous stirring reactor is used. A joint solution of the balance equations for neutral and charged plasma components, the Boltzmann equation for plasma electrons, and the equation for the stationary distribution of the microwave field in a volume filled with plasma is carried out. The dependences of various parameters of thedischarge (the magnitude of the microwave field, the concentrations of all components) on the input specific power WVare obtained. It is shown that at reduced pressure the magnitude of the microwave field in the plasma is signifi-cantly lower, and the electron concentration is higher than at atmospheric pressure at the same applied specific power. At atmospheric pressure the water plasma is electronegative, and quasi-neutrality is maintained by the negative OH-ion in the range of the considered WV values. Transition from electronegative to electropositive plasma occurs at pressure of 30 Torr and ap-plied specific power of 60–70 kW/cm3

Effects of Blade Pressure Side Modification On Unsteady Pressure Pulsation and Flow Structures in a Centrifugal Pump

In this paper, the effects of modifying the blade pressure side on unsteady pressure pulsation and flow structures in a low specific speed centrifugal pump are carried out by experimental and CFD. Seven monitor points are arranged in the circumferential direction of the impeller outlet to capture the pressure signals in the volute at the flow rate of 0.2-1.6Qd. Results show that blade PS modification introduced here can significantly alleviate the amplitude of pressure pulsation at blade passing frequency in all concerned operation conditions. The volute domain is replaced by an even outlet region for CFD analysis to study the effects on internal flow field. The SST turbulence model is adopted for steady-state simulation while the DDES based on the SST approach is adopted for transient simulation. Results show that local velocity fluctuation is the dominant reason for pressure pulsation in the volute. After PS modification, the relative velocity distribution at impeller outlet is more uniform and the intensity of shedding vortex at the blade trailing edge decreases significantly. The change of internal flow structure improves the uniformity of circumferential velocity distribution at downstream of impeller outlet, which leads to the decrease of pressure fluctuation amplitude in the volute. Meanwhile, the Local Euler Head distribution and the blade loading of PS are presented and compared. Results show that the reduction of pressure pulsation attributes to the more uniform energy distribution at impeller outlet which is achieved by actively unloading the PS of the modified blades.