A gas–liquid Eulerian computational fluid dynamics (CFD) model coupled with a population balance equation (PBE) was presented to investigate hydrodynamics of an air–water bubble column (1.8 m in ...height and 0.1 m in inner diameter) under elevated pressure in terms of pressure drop, gas holdup, mean bubble size, and bubble surface area. The CFD‐PBE model was modified with three pressure correction factors to predict both the total gas holdup and the mean bubble size in the homogeneous bubbly flow regime. The three correction factors were optimized compared to experimental data. Increasing the pressure led to increasing the density, reducing the bubble size, and increasing the gas holdup. The bubble size distribution moved toward a smaller bubble size, as the pressure increased. The modified CFD‐PBE model validated with experimental data and empirical models represented well hydrodynamics of the bubble column at P = 0.1, 1.5, and 3.5 MPa.
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•The effects of gas density, surface tension, and viscosity on gas holdup and flow regime transition were studied.•The dual effect of viscosity was observed and analyzed.•Transition ...gas holdup was correlated as a function of the gas density, surface tension, and liquid viscosity.
The homogeneous-to-heterogeneous flow regime transition point dependence on gas and liquid properties was investigated in a semi-cylindrical bubble column of 1.8m height and 0.21m inner diameter operating as a semi-batch system. He, air, and CO2 gases were injected at superficial gas velocities of up to 239mm/s. The batch liquids included water, aqueous ethanol solutions, and aqueous glycerol solutions, all with a gas-free liquid height settled at 1m. When the gas density increased, the gas holdup increased at all superficial gas velocities, delaying the flow regime transition. The gas holdups in the liquid mixtures were higher than those for tap water. The transition gas holdup for the ethanol solutions increased to a sharp maximum and then decreased as the surface tension increased. Also, the glycerol solutions showed similar behavior with respect to increasing liquid viscosity, but with a shallower maximum. The transition gas holdup was empirically correlated as a function of the gas density, surface tension, and liquid viscosity, employing dimensional constants. The measured transition gas holdups for liquid mixtures, as well as some data from the literature, were fitted by the correlation.
The effect of reaction temperature and time on the products and the asphaltene dispersion according to the residue conversion was investigated in a slurry-phase hydrocracking reaction. The ...experiments were carried out with two different approaches to control the hydrocracking reaction, which the reaction time was changed from 4 h to 20 h (at 410 °C) and the reaction temperature from 430 °C to 453 °C (for 1 h) at 100 bar (at 80 °C) of initial hydrogen pressure and 500 wt.ppm of molybdenum concentration. As a result, it was found that the control of the reaction time and reaction temperature may give different effect to the stability of the asphaltene in the liquid phase in spite of the same VR conversion. In order to understand this, the dipole moments of the liquid product and structural change of the asphaltene was compared. And it was found that enhancing hydrogenation reaction by increasing reaction time at low temperature delayed the time of decreasing point for dipole moments of the liquid phase and increased the length of alkyl chain of remaining asphaltene. Therefore, it is considered that the dispersibility of asphaltene with high polarity is increased. Additionally, it was found that enhancing hydrogenation can also improve the catalyst dispersion in the liquid phase below 80% of residue conversion.
Pyrolysis is a relatively simple upgrading process that can produce light oil from unconventional oil and heavy residue. For effective utilization of pyrolysis processes, it is important to ...understand its kinetic parameters. In this study, the nonisothermal pyrolysis of vacuum residue (VR) was analyzed using a thermogravimetric analyzer and the activation energy of the VR pyrolysis reaction was estimated by several theoretical methods. It was found that isoconversional methods were more suitable than nonisoconversional methods for analyzing complex pyrolysis reaction of VR. The Friedman method, a differential isoconversional method, is thought to be the most appropriate among the various methods tested because it can describe the complexity of the pyrolysis reaction of VR and there is no need for information of exact reaction model and mathematical assumptions for temperature integral, which can raise systematic errors in the kinetic analysis. Finally, the kinetic parameters of VR pyrolysis were determined based on the results of Friedman analysis and distributed activation energy model (DAEM), and VR pyrolysis behavior was well expressed with the kinetic parameters obtained from DAEM analysis.
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•Hydrocracking of vacuum residue (VR) was performed in a slurry bubble column reactor.•Physical properties estimated during hydrocracking were experimentally compared.•A CFD model ...with a new drag coefficient was developed for the bubble column.•Gas holdup at 425 °C and 160 bar (6.2%) was in agreement with empirical value (6.6%).•Axial and radial hydrodynamics of the bubble column were examined via the CFD model.
Vacuum residue (VR) was subjected to catalytic hydrocracking with H2 in a pilot-scale slurry bubble column reactor (SBCR) with 0.05 m diameter and 2 m height at 425 °C and 160 bar in the homogeneous regime. The gas holdup (αG) and composition of the product classified into five pseudo-components were measured in the SBCR. The physical properties such as density, viscosity, and surface tension of VR (feed) were analyzed prior to a three-dimensional Eulerian computational fluid dynamics (CFD) simulation to predict axial and radial hydrodynamics in the SBCR. Rather than considering the hydrocracking reactions in the CFD model, a reaction-mixture model was used to predict the variation of the axial physical properties as the reaction progresses. A customized drag coefficient based on experimental data was applied to the CFD model. The value of αG predicted by the CFD model at a superficial gas velocity of 6.4 mm/s was 6.2% which is comparable to the experimental value (6.6%). The Sauter mean diameter and specific surface area were estimated to be 1.2 mm and 304 m2/m3, respectively. The proposed CFD model, which was integrated with the axial physical properties but decoupled from chemical reaction, successfully predicted the hydrodynamics of the H2-VR SBCR.
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A multiphase computational fluid dynamics (CFD) model coupled with the population balance equation (PBE) was developed in a homogeneous air–kerosene bubble column under elevated ...pressure (P). The specific pressure drop (ΔP/L), gas holdup (αG), and Sauter mean diameter (d32) were experimentally measured in the bubble column with 1.8 m height and 0.1 m inner diameter, which was operated at a superficial gas velocity of 12.3 mm·s−1, and P = 1–35 bar (1 bar = 105 Pa). A modified drag coefficient model was proposed to consider the effect of bubble swarm and pressure on hydrodynamics of the bubble column. The Luo breakage model was modified to account for liquid density, viscosity, surface tension and gas density. The ΔP/L, αG, and d32 obtained from the CFD model were compared with experimental data, and the gas density-dependent parameters of the CFD model were identified. With increasing P from 1 to 35 bar, the αG varied from 5.4% to 7.2% and the d32 decreased from 2.3 to 1.5 mm. The CFD-PBE model is applicable to predict hydrodynamics of pressurized bubble columns for gas–organic liquid in the homogeneous regime.
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•Kinetic model for thermal and catalytic hydrocracking of asphaltene was developed.•A linear relationship between coke yields and liquid yields was found.•A critical gas mass fraction ...was proposed as a coke formation determining criterion.•The kinetic model can predict well the moment when coke begins to form.
In this study, a five-lump model was proposed for kinetic modeling of asphaltene placed in a batch reactor with a commercial slurry-phase catalyst (Mo-octoate). Asphaltene was separated from vacuum residue using normal pentane. The kinetic experiments were carried out at 380∼430℃ for 1∼20 h together with a 1000 ppm concentration of Molybdenum in thermal and catalytic hydrocracking reaction modes. The results showed that the coke induction period and maximum maltene yield are changed with reaction temperature and time at thermal and catalytic hydrocracking. In addition, a linear relationship between coke and liquid (maltene + asphaltene remains) yields was shown so that the critical gas amount could be found as a criterion for determining the end of the coke induction period. Significantly, the kinetic model fit the experimental data well and, moreover, was found to be able to predict the moment when coke begins to form as well as maximum maltene yields.
The bubble breakage rate in gas-liquid bubble columns increases for organic liquid and at high pressure. This study developed a breakage model that accounts for different liquid properties in ...gas-liquid pressurized bubble columns in the homogeneous regime. The Luo (1996), Lehr (2002), and Wang (2003) breakage models, which are widely used for the population balance equation (PBE) of bubble columns, were compared in terms of the total breakage rate, daughter size distribution, and computational time. The model with two empirical equations, modified from Luo’s breakage kernel, was proposed. One represented bubble deformation behavior in different liquid properties in terms of buoyancy, surface tension, and viscosity. The other considered the effect of operating pressure (or gas density) on the breakage rate. The modified model was compared with experimental data and a rigorous breakage model from the literature. The proposed breakage model shows good agreement with experimental data and computational efficiency. This breakage model is applicable for computational fluid dynamics with PBE in pressurized bubble columns with organic liquids.
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•Reduction of Mo-Fe/MgO catalyst leads to high-yield carbon production.•Increasing reduction temperature leads to larger CNT diameter and higher crystallinity.•Increasing reduction ...hydrogen partial pressure (pH2) leads to larger CNT diameter.•Optimum reduction conditions (Temp, pH2, Time) of Mo-Fe/MgO catalyst for high quality CNT were found.
The effects of temperature, hydrogen partial pressure, and time in catalytic reduction step on carbon nanotube growth in a catalytic methane decomposition have been investigated for Mo-Fe/MgO catalysts. The results show that the reduction conditions of the catalyst affect the crystal structure of the metal formed on the catalyst surface and the growth mechanism of the generated carbon nanotubes. Both diameter distribution and crystallinity of the CNTs increased with the increase of reduction temperature in the range of 400 to 800 °C. The optimal reduction temperature with the maximum carbon yield was found to be 500 °C. The increase of hydrogen partial pressure and reduction time increased the CNT diameter distribution, and the optimal hydrogen partial pressure and reduction time with maximum carbon yield were found to be 0.1 atm, 60 min and 0.3 atm, 5 min, respectively. In the different combination of hydrogen partial pressure and reduction time for maximizing carbon yield, the CNT average diameter did not have a significant change, while the CNT crystallinity showed opposite trends depending on the methane decomposition reaction time. Ultimately, it was confirmed that the Mo-Fe/MgO catalyst can change the properties of CNTs produced through control of reduction conditions.
•SDA extraction was conducted using vacuum residue and bunker C oil as feedstocks.•HSPs were measured for saturate, aromatic, resin, and asphaltene fractions.•Properties of DAO produced under ...different operating conditions were compared.•DAO yield was highly correlated with the HSP of the feedstock and extraction solvent.
Solvent deasphalting (SDA) is a heavy oil upgrading process that selectively extracts deasphalted oil (DAO) and rejects asphaltenes. In this study, a quantitative analysis was conducted to predict DAO yields in the SDA process using relative energy difference (RED); the RED was calculated from Hansen solubility parameters (HSPs) of the feedstock and extraction solvent along with the extraction conditions, such as temperature and solvent-to-oil ratio (SOR). SDA extraction experiments were performed in a continuous bench-scale unit using vacuum residue (VR) and a mixture of bunker C fuel oil (BC) and VR as feedstocks. The HSPs of saturate, aromatic, resin, and asphaltene fractions derived from the VR and BC were measured using solubility tests, wherein the fractions were dissolved in 37 different solvents. Finally, simple and accurate correlations between the DAO yield and corresponding modified RED were acquired and used to explain the effects of temperature and SOR on the DAO yield.
