Reconstruction of Pore Structures in Petroleum Coke Packed Beds Utilizing CT Scanning and CFD Simulation of Resistance Characteristics

Because of the increasingly deteriorating quality of petroleum coke raw materials, abnormal furnace conditions, such as “firing and blasting”, frequently arise during the calcination of petroleum coke with a high powder/coke ratio in a vertical shaft calciner. This poses an urgent technical challenge that needs to be addressed. In iron and steel metallurgy, the burden distribution system is an important way to regulate blast furnace conditions and improve the permeability of a particle packed bed. In this work, advanced burden distribution concepts were introduced into the calcination process of petroleum coke in a vertical shaft calciner. Experimental devices were established to determine the resistance characteristics of a petroleum coke particle packed bed, along with a cold physical model of a 1/8 scale vertical shaft calciner. The influence of particle size and burden distribution methods on the resistance characteristics and particle motion behavior of the petroleum coke particle packed bed was systematically studied. The research findings indicate that both particle size and burden distribution methods significantly impact the resistance characteristics of petroleum coke particle packed beds. The smaller the particle size, the poorer the permeability of the bed. The layered burden distribution, symmetrical burden distribution, and dual‐particle mixed conventional burden distribution all contribute to improving the permeability of the petroleum coke particle packed bed in the vertical shaft calciner. Furthermore, employing symmetrical burden distribution in Bed‐3, which is packed with petroleum coke particles of diameters −3.2 + 2.5 mm and −1.0 + 0.8 mm, results in the smallest unit pressure drop, at only 1.7% of that of the conventional burden distribution of unscreened raw materials. This is the most effective means of improving the permeability of the bed. During the discharging process, particle size and symmetrical burden distribution have no significant impact on the motion characteristics of petroleum coke particles in the vertical shaft calciner. In general, in the calciner area, particles primarily move in a plug flow pattern and gradually transform into funnel flow in the cooling water jacket area. These research results provide the theoretical basis for addressing the technical challenges associated with powder coke calcination in vertical shaft calciners through reasonable burden distribution methods for fine and coarse particles.

The effects of gas and liquid velocities, liquid viscosity and particle size on the radial dispersion coefficient of liquid phase (Dr) and the bubble properties in three-phase fluidized beds have been determined. A new flow regime map based on the drift flux theory in three-phase fluidized beds has been proposed. In three-phase fluidized beds, D, increases with increasing gas velocity in the bubble coalescing and in the slug flow regimes, but it decreases in the bubble disintegrating regime. The coefficient exhibits a maximum value in the bed of small particles with increasing liquid velocity at lower gas velocities. However, it increases with increasing liquid velocity at higher gas velocities. In two and three-phase fluidized beds of larger particles (6,8 mm), Dr exhibits a maximum value with an increase in liquid viscosity at lower gas velocities, but it increases at higher gas velocities. The mean bubble chord length and its rising velocity increase with increasing gas velocity and liquid viscosity. However, the bubble chord length decreases with an increase in liquid velocity and it exhibits a maximum value with increasing particle size in the bed. The radial dispersion coefficients in the bubble coalescing and disintegrating regimes of three-phase fluidized beds in terms of the Peclet number in the present and previous studies have been well represented by the correlations based on the concept of isotropic turbulence theory.

Efficient transport of sand or cuttings is of great importance in oil and gas industry and the fluid velocity in these processes should be high enough to keep particles continuously moving along the pipe. This minimum fluid velocity below which particles deposit, defined as the critical velocity, depends on various factors including flow regime, particle size, particle concentration, phase velocities and fluid viscosity. The objective of this study is to investigate the effect of parameters such as particle size and liquid viscosity on solid particle transport in horizontal pipelines using Computational Fluid Dynamics (CFD) simulations and validate the numerical model predictions with experimental data. CFD simulations have been conducted with a commercially available software, ANSYS-FLUENT. Eulerian model with k-ω SST turbulence closure model is used to simulate the fluid flow while particles are tracked as the Lagrangian phase. In these simulations eddy interaction model is included to consider the effect of flow turbulence on the particle track. The simulations are created for 0.05 m pipe diameter with 4 m length. The simulations are initialized at relatively high fluid velocity, which is gradually reduced until the particle velocity drops below the acceptable critical velocity. The CFD simulation results are validated with experimental data from literature, Najmi (2015) and Najmi et al. (2016) for two particle sizes and multiple liquid viscosities. It was observed that the critical velocity values for liquid flows are comparable with CFD simulation results. The simulation results show that depending on the flow regimes (laminar or turbulent) and particle size, the critical velocity can demonstrate similar trend with carrier liquid viscosity as that of the experimental data. Also the CFD simulations and experiment results are compared with three models currently used in industry, namely Oroskar and Turian (1980) model, Salama (2000) model and Danielson (2007) model.

Elbows in series are commonly encountered in various piping systems on oil and gas subsea platforms. In numerous oil and gas fields, solid particles are entrained with produced fluid causing solid particle erosion of these elbows. Therefore, solid particle erosion was examined in two standard ID 3-inch (76.2 mm) elbows in series. The distance between the two elbows is twice the pipe diameter (2D). Firstly, paint removal studies were performed to identify the location of the maximum erosion in the second elbow with superficial gas (air) and liquid (water) velocities of 31 m/s and 0.1 m/s, respectively, using 300 and 75 μm particle sizes. Secondly, erosion measurements were conducted in two standard stainless-steel (SS316) elbows with 25, 75, and 300 μm particle sizes. The results of the erosion measurement in the annular flow condition were compared with the gas-solid flow with a gas velocity of 31 m/s and particle sizes of 300 and 75 μm. The paint removal experimental studies showed that the location of the maximum erosion changes with changing the particle sizes in the second elbow. The erosion measurements showed that the erosion ratio (2nd elbow/1st elbow) in gas-solid is higher than in annular flow conditions by a factor of 14.25 and 5.8 with 75 and 300 μm particle sizes, respectively. Also, Computational Fluid Dynamics (CFD) simulations were performed for gas-sand flow conditions with 31 m/s gas velocity to study the effect of particle size on erosion in the investigated elbows. The CFD results over-predicted the erosion ratio (2nd elbow/1st elbow) by a factor of around 2.1 and 2.4 for 75 and 300 μm particle sizes, respectively.

Synergistic impact mechanism of particle size and morphology in superalloy powders for additive manufacturing

Erosion equations are usually obtained from experiments by impacting solid particles entrained in a gas or liquid on a target material. The erosion equations are utilized in CFD (Computational Fluid Dynamics) models to predict erosion damage caused by solid particle impingements. Many erosion equations are provided in terms of an erosion ratio. By definition, the erosion ratio is the mass loss of target material divided by the mass of impacting particles. The mass of impacting particles is the summation of (particle mass × number of impacts) of each particle. In erosion experiments conducted to determine erosion equations, some particles may impact the target wall many times and some other particles may not impact the target at all. Therefore, the experimental data may not reflect the actual erosion ratio because the mass of the sand that is used to run the experiments is assumed to be the mass of the impacting particles. CFD and particle trajectory simulations are applied in the present work to study effects of multiple impacts on developing erosion ratio equations. The erosion equation as well as the CFD-based erosion modeling procedure is validated against a variety of experimental data. The results show that the effect of multiple impacts is negligible in air cases. In water cases, however, this effect needs to be accounted for especially for small particles. This makes it impractical to develop erosion ratio equations from experimental data obtained for tests with sand in water or dense gases. Many factors affecting erosion damage are accounted for in various erosion equations. In addition to some well-studied parameters such as particle impacting speed and impacting angle, particle size also plays a significant role in the erosion process. An average particle size is usually used in analyzing experimental data or estimating erosion damage cases of practical interest. In petroleum production applications, however, the size of sand particles that are entrained in produced fluids can vary over a fairly broad range. CFD simulations are also performed to study the effect of particle size distribution. In CFD simulations, particle sizes are normally distributed with the mean equaling the average size of interest and the standard deviation varying over a wide range. Based on CFD simulations, an equation is developed and can be applied to account for the effect of the particle size distribution on erosion prediction for gases and liquids.

This paper focuses on the modeling of flow and mixing in a bubble column reactor operated at high gas velocities (up to 0.40 m/s). A dual-tip conductivity probe was used to measure local void properties such as local time-averaged gas holdup, chord length distribution, bubble velocity distribution, and interfacial area. Chord length distribution was converted to bubble size distribution, using the backward transformation method. Liquid-phase mixing time measurements were conducted using a conductivity probe. A computational fluid dynamics (CFD) model was developed to simulate the unsteady gas−liquid flow in a bubble column using commercial code FLUENT 6.2. The time-averaged flow properties predicted by CFD simulations were compared with the experimental data. The role of unsteady flow structures in mixing was studied. The “multiple snapshots” approach was used to simulate the mixing time using CFD. The mixing times that were predicted for all superficial gas velocities compared favorably to the measured values. This study of the hydrodynamic behavior of a bubble column at higher gas velocity provides a basis for understanding and simulating solid suspension (or solid mixing) in slurry bubble column reactors.

Improved understanding of flow regime effects on design-influencing engineering quantities is of primary importance. This work is focused on the numerical prediction of pressure gradient and void fraction in a horizontal pipe where gas-liquid stratified flow is present in different operating conditions. The problem was modeled with unsteady, multiphase CFD (computational fluid dynamics) simulations. Volume Of Fluid (VOF) method was used as multiphase model. To define the numerical methodology, this study provides details on the influence of discretization grid and turbulence model on the simulation accuracy. It shows that mesh density on pipe cross-section is the most important grid parameter to focus on. Different turbulence models are required depending on the gas velocity and on its turbulence flow regime. Transition SST is able to model all the operating conditions but Realizable k-ε is adopted to further increase the accuracy of the results. A general underestimation of the pressure gradient is reported with an average error of − 6.43 % and − 16.21 % for a liquid superficial velocity of 0.04 m/s and 0.06 m/s respectively. Comparison with two-fluid 1D models shows that CFD simulations are the most accurate tools for predicting the pressure gradient at gas superficial velocities lower than 1.3 m/s. The implementation of a drift flux model shows a good agreement between experimental results and CFD simulations concerning void fraction estimation. CFD results are also used to underline the physical phenomena limiting the performance of 1D models.

In a downer reactor (0.1 m-I.D.x3.5 m-high), the effects of gas velocity (1.6-4.5 m/s), solids circulation rate (0–40kg/m2s) and particle size (84, 164 Μm) on the gas mixing coefficient have been determined. The radial dispersion coefficient(Dr) decreases and the radial Peclet number (Per) increases as gas velocity increases. At lower gas velocities, Dr in the bed of particles is lower than that of gas flow only, but the reverse trend is observed at higher gas velocities. Gas mixing in the reactor of smaller particle size varies significantly with gas velocity, whereas gas mixing varies smoothly in the reactor of larger particle size. At lower gas velocities, Dr increases with increasing solids circulation rate (Gs), however, Dr decreases with increasing Gs at higher gas velocities. Based on the obtained Dr values, the downer reactor is found to be a good gas-solids contacting reactor having good radial gas mixing.

In the absence of powerful rigorous models, in this research a simple but practical method for calculating the temperature and residence time and carbon black yield in oil-furnace reactors is proposed. For this purpose an empirical formula of the form CxHy is assumed for the carbon black feedstock based on typical feedstock used in this industry. Based on the prevailing reactor conditions, thermodynamic considerations and available outlet tail gas from the reactor, a few representative reactions are considered to describe the entire reaction network. These include complete combustion for the fuel and, incomplete combustion and pyrolysis for the feedstock. Carbon black yield can be estimated from a mass balance. From the combined mass and heat balance, the reactor temperature as well as the residence time is predicted. The reactions can also be used to obtain the composition of the tail gas. Despite the simplicity of the model, in all cases studied, relatively good agreements were observed between the calculated values and the available industrial data as well as those obtained from computational fluid dynamics (CFD) simulation. An exception was the effects of the air/oil ratio on the reactor mean residence time in the CFD approach. The influences of air/oil ratio and inlet air temperature on reactor mean-temperature were studied. In both cases one observes good agreement between our results and CFD simulation data. They both show an increase in reactor mean-temperature as expected. The effects of process air flow rate on reactor residence time also were studied and a good agreement was observed. However, comparison the effects of the air/oil ratio on reactor residence time showed quite different trends. While the results of CFD simulation predicts insignificant change in reactor residence time versus air/oil ratio, our results show a decline in the residence time in this case. To explain this, prediction of carbon black particle size was considered. Utilizing our predicted residence time results for prediction of particle size showed a good agreement with industrial data, while in contrast the CFD simulation data show opposite trend with the industrial data and our work. Therefore, it can be said that one of the most important reasons caused poor prediction in referred CFD simulation in some cases could be considerable error in prediction of the residence time.

Computational fluid dynamics (CFD) simulation for bubbling fluidized bed of fine particles was carried out. The reliability and accuracy of CFD simulation was investigated by comparison with experimental data. The experimental facility of the fluidized bed was 6 cm in diameter and 70 cm in height and an agitator of pitched-blade turbine type was installed to prevent severe agglomeration of fine particles. Phosphor particles were employed as the bed material. Particle size was 22 μm and particle density was 3,938 kg/m3. CFD simulation was carried by two-fluid module which was composed of viscosity input model and fan model. CFD simulation and experiment were carried out by changing the fluidizing gas velocity and agitation velocity. The results showed that CFD simulation results in this study showed good agreement with experimental data. From results of CFD simulation, it was observed that the agitation prevents agglomeration of fine particles in a fluidized bed.

Green petroleum coke (GPC) is an oil refining byproduct that can be used directly as a solid fuel or as a feedstock for the production of calcined petroleum coke. GPC contains a high amount of volatiles and sulfur. During the calcination process, the GPC is heated to remove the volatiles and sulfur to produce purified calcined coke, which is used in the production of graphite, electrodes, metal carburizers, and other carbon products. Currently, more than 80% of calcined coke is produced in rotary kilns or rotary hearth furnaces. These technologies provide partial heat utilization of the calcined coke to increase efficiency of the calcination process, but they also share some operating disadvantages. However, coke calcination in an electrothermal fluidized bed (EFB) opens up a number of potential benefits for the production enhancement, while reducing the capital and operating costs. The increased usage of heavy crude oil in recent years has resulted in higher sulfur content in green coke produced by oil refinery process, which requires a significant increase in the calcinations temperature and in residence time. The calorific value of the process off-gas is quite substantial and can be effectively utilized as an “opportunity fuel” for combined heat and power (CHP) production to complement the energy demand. Heat recovered from the product cooling can also contribute to the overall economics of the calcination process. Preliminary estimates indicated the decrease in energy consumption by 35-50% as well as a proportional decrease in greenhouse gas emissions. As such, the efficiency improvement of the coke calcinations systems is attracting close attention of the researchers and engineers throughout the world. The developed technology is intended to accomplish the following objectives: - Reduce the energy and carbon intensity of the calcined coke production process. - Increase utilization of opportunity fuels such as industrial waste off-gas from the novel petroleum coke calcination process. - Increase the opportunity of heat (chemical and physical) utilization from process off-gases and solid product. - Develop a design of advanced CHP system utilizing off-gases as an “opportunity fuel” for petroleum coke calcinations and sensible heat of calcined coke. A successful accomplishment of the aforementioned objectives will contribute toward the following U.S. DOE programmatic goals: - Drive a 25% reduction in U. S. industrial energy intensity by 2017 in support of EPAct 2005; - Contribute to an 18% reduction in U.S. carbon intensity by 2012 as established by the Administration’s “National Goal to Reduce Emissions Intensity.” 8

The integration of CFD modeling and simulation into plume measurement programs

Gas-Liquid Cylindrical Cyclone (GLCC) separators have been widely accepted as an alternative to conventional vessel-type separator during recent years. The operators are using GLCCs at flow rates higher than the normal recommended operational envelope in applications where the increased liquid carry-over and gas carry-under can be tolerated. Experience gained from production of hydrocarbons with entrained sand has shown that severe degradation of production equipment may occur due to solid particle erosion at high productions rates. However, there are no data and no field feedback on erosion in the inlet region of a GLCC. Thus, the goal of this work is to evaluate the erosion condition in the Gas-Liquid Cylindrical Cyclone (GLCC) separator under gas production and low-liquid loading flow condition.Erosion experiments are conducted with gas-sand and gas-liquid-sand flow conditions in a laboratory scale GLCC with two particle sizes and gas velocities. An ultrasonic thickness measurement system is employed to monitor the erosion rates at the inlet region of the GLCC. Several cases are simulated with commercially available Computational Fluid Dynamics (CFD) software. Based on the experimental data and CFD simulations, a mechanistic one-dimensional model is proposed to calculate maximum thickness loss inside the GLCC.It is observed that the location of maximum erosion is not varying significantly with the flow condition with or without the presence of liquid and particle size, while the liquid entrainment can reduce the value of maximum erosion (in mm/kg) by one order of magnitude. The erosion increases with the flow velocity as expected but not with particle size for the particles used in current experiments. CFD simulation results that are obtained by utilizing the mechanistic erosion equations provided fair agreement with experimental measurements for gas-sand condition, and the simplified model showed consistency with the data in both gas-sand and gas-liquid-sand flow conditions.

The gas−liquid−(solid) three-phase hydrodynamics in an external-loop airlift reactor (EL-ALR) with an upward pipe 0.47 m in diameter and 2.5 m in height, two external loop downward pipes 0.08 m in diameter and 2.5 m in height, were investigated using four different gas sparger designs. The microconductivity probe and the three-dimensional (3-D) laser Doppler anemometry (LDA) techniques were, respectively, implemented to measure the local gas holdup in the riser (αGr) and liquid phase velocity in the downcomer (ULd) using air as the gas phase, water as the liquid phase, and alginate gel beads as the solid phase, over a wide range of operation conditions. The tracer age distribution was measured using the pulse-pursuit response technology. Axial dispersion model (ADM) was used to estimate the model parameter Peclet number (Pe) values as a fitted parameter with the measured data, using the gold partition method for nonlinear programming strategy inequation restrict conditions. The ADM gave better fits to the experimental data at high axial locations and lower superficial gas velocity (UG) for an EL-ALR used with a large L/DR ratio. A synergistic effect of ULd, αGr, Pe, solids loading (SL), and sparger designs on the performance of an EL-ALR was observed in our experiments. The sparger designs were determined to have a noticeable effect on the αGr and Pe in the lower gas velocity and lower solid loading ranges (UG < 0.025 m/s and SL < 2%), but only a slight effect in the high gas velocity and high solid loading ranges (UG > 0.030 m/s and SL > 3%). However, the effect of sparger designs on the ULd is greater in the gas velocity from 0.025 m/s to 0.045 m/s. For the lower solids loading, the increase of orifice diameter leads to a decrease in αGr. This is in accordance with what was presented in the gas−liquid two-phase system. Moreover, the influence of orifice diameters of the spargers is negligible for solids loading of >3%. Although the Pe values decreased with the operating gas velocity, the gas velocity change from 0.03 m/s to 0.04 m/s yielded lower Pe values, as a result of the reduced bubble size. As the gas velocity further increased to 0.06 m/s, the αGr and the ULd values increased, while the Pe values negligibly increased. For a gas−liquid two-phase system, Pe decreases with the orifice diameter and, for 1% of solids, Pe is also lower for sparger P-2 (ϕ 0.6 mm) than for sparger P-1 (ϕ 0.3 mm). For higher amounts of solids (3%), Pe does not have a defined trend. In addition to the gas velocity and sparger design effects, the solids loading had the effect of decreasing the ULd values, while such effect became small and flattened at high solid loadings. The ULd values, especially with VO = 100%, are ~20% lower in three-phase flow than that in two-phase flow. In addition, the ULd profiles in three-phase flow are flatter than that in two-phase flow with VO = 50%−100%, actually showing a parabolic shape rather than the almost linear one encountered in two-phase flow. This is very important for design and optimum operation that are used to systemically investigate the synergistic effect of ULd, αGr, Pe, solid loading (SL), and sparger designs on hydrodynamic performance of an EL-ALR.