Numerical study on flow characteristics of hydrate slurry liquid-solid two-phase flow considering the adhesion between particles

A pressure drop prediction model for hydrate slurry based on energy dissipation under turbulent flow condition

This work investigates the flow properties of CO2 hydrate slurry in dynamic loop in the presence of additives (surfactants, antiagglomerants) for use as two-phase secondary refrigerant. To be considered as suitable for refrigeration systems, the use of hydrate slurries must overcome instability phenomena such as hydrate particle agglomeration. The additives were employed in the present work to prevent this phenomena, and thus to improve the stability and the homogeneity of the fluid. A multicriterion approach was used to select additive and to define the optimal operating conditions for its use. The selected additive was an EO/PO block copolymer. The flow properties of CO2 hydrate slurry in aqueous media in the presence of this additive were then measured in an experimental loop. It was possible to model the rheological behavior of the CO2 hydrate slurry in the presence of EO/PO block copolymer by an Newtonian-type equation. The present results were compared to previous results obtained without additive. This article provides new information on CO2-hydrate slurry rheology, which is important not only in the development of hydrate-based refrigeration systems, but also in the field of flow assurance in oil and gas pipelines or for other applications such as gas purification and storage processes using clathrate hydrates.

Investigation into methane hydrate reformation in water-dominated bubbly flow

Modification of kinetic theory of granular flow for frictional spheres, part II: Model validation

Multiphase flows and in particular dispersed flows are frequently encountered in a variety of important process facilities in the chemical industry; herein, the fluidized bed reactors. Whereas the internal and external solid fluxes in the fluidized bed reactors are generally determined by empirical correlations or prescribed in the Kunii–Levenspiel type of models, the two-fluid models serve as highly relevant in the progress of commercial reactors for processes such as the novel sorption-enhanced steam methane reforming (SE-SMR) technology because the solid flux incorporated in the two-fluid model allows for dynamic modeling of interconnected fluidized bed reactors. Nevertheless, the two- and three-dimensional two-fluid models are yet too computationally demanding for chemical process evaluation studies due to the complexity of the gas–solid flow in the bed. Hence, these models are not efficient for studies of the processes such as the SE-SMR technology where the solid particles are transported between reactor units for utilization and recovery of the characteristic solid property, i.e. CO2-capture and CO2-release. Thus, the aim of the present study is to derive a model that allows for a more complex description of the fluidized bed reactors relative to the frequently used Kunii–Levenspiel type of models. On the other hand, the model should not predict details in the flow, as the two- and three-dimensional two-fluid models, in order to ensure reasonable simulation costs. Hence, in this study, the classical SIMPLE algorithm is extended to compressible two-phase reactive flows. The governing equations are cross-sectional averaged to smooth out the details in the flow. The suggested dynamic one-dimensional Eulerian–Eulerian two-fluid model is applied to investigate the reactive gas–solid flows of the SMR and SE-SMR processes; and moreover, the simulation results are compared with the results of the more complex two-dimensional model with a solid stress closure based on kinetic theory of granular flow. The one-dimensional model predictions of the chemical process performance are in good agreement with the corresponding profiles predicted with the two-dimensional model. The deviations are larger comparing the internal flow details but these do not owe significant impact on the chemical process which to a large extent is determined by the imposed temperature in the reactor.

Ocean floor mining : Pearson,J.S. Noyes Data Corporation, Publicity Department, Mill Road at Grand Avenue, Park Ridge, New Jersey 07656, USA (March 1975) 201 pp, $24

In this paper, a mathematical model based on the two-fluid (Euler–Euler) frame model for wet dedusting process is proposed. The model considers in detail the aggregation of particles and droplets caused by turbulence and Brownian diffusion as well as the gravitational deposition process. The population balance model (PBM) is used to describe the spatiotemporal evolution of particle size distribution (PSD) for the dust particle and the water droplet. The wet dedusting process under different conditions is simulated and compared with the detailed experimental data. The results show that the experimental data and simulation results are within the allowable range of error (about 32.3–61.2% in dedusting efficiency for respirable dust by experimental data and about 47.3–57.9% in it by simulation results). This model can be used to predict the effect of PSD of the dust particle, spray flow, and ventilation rate on dedusting efficiency of wet dedusting. The parameter analysis shows that dedusting efficiency decreases as particle size decreases. In order to ensure high capture efficiency of respirable dust, the diameter of droplets should be controlled to between 15 μm and 70 μm. The ratio of droplet volume flow to dust volume flow increases from 2.0 to 12.0, while dedusting efficiency only increases from 39.2% to 54.7%, so it is clear that for spray quantity to dedusting efficiency, larger is not necessarily better. Besides this, the speeds of both spray droplets and ventilation also have great influence on dedusting efficiency, and the related formulas are given.

Numerical simulations using Euler-Euler model (also known as two-fluid model) were used to predict pressure drop in pneumatic conveying (i.e., gas-solid flows) in vertical pipes. Standard \(k - \varepsilon\) turbulence model has been used for gas phase, and kinetic theory of granular flows (KTGF) was used to close solid phase stresses and solid pressure aroused due to inter-particle collisions. The model was validated by comparison with the available experimental data and good agreement was found for pressure drop prediction. The effect of important flow parameters like gas phase Reynolds number, solid loading ratio and particle density on pressure drop was investigated. It was observed that pressured drop increased with gas velocity and solid loading ratio. Finally, computed results for pressure drop are compared with the existing correlations. Present predictions showed good agreement with the correlations of (Reddy and Pei in Ind Eng Chem Fundam 8:490–497, 1969 [1], Capes and Nakamura in Can J Chem Eng 51:31–38, 1973 [2]) data.

Modeling of air and particles flow with revolving rotor hovering over the particles layer

Organic fluid migration in low permeability reservoirs restricted by pore structure parameters

Chemical looping reforming (CLR) is a novel hydrogen production technology, which has attracted great attention, owing to the benefits of lower cost and better concept of environmental protection. To investigate the CLR performance in the fuel reactor (FR), this study develops a multiphase computational fluid dynamics (CFD) reactive model to obtain a better understanding of complex gas–solid flow behavior and reactive characteristic during the CLR process. A bubble-based energy minimization multiscale (EMMS) approach is applied to account for the bubble effect on the gas–solid interaction. A two-fluid model is adopted with a kinetic theory of granular flow for closure. The distributions of concentrations of particles and gas species are obtained in the FR with Ni-based oxygen carriers by means of numerical simulation. This bubble-based EMMS model gives a more reasonable agreement with experimental results by a comparison of gas compositions at the outlet of the reactor.

CFD studies of dual circulating fluidized bed reactors for chemical looping combustion processes

Based on the two-fluid model, a three-zone drag model was developed, and the kinetic theory of granular flows and the Schneiderbauer solids wall boundary model were modified to establish a new three-dimensional (3D) unsteady mathematical model for high-pressure dense-phase pneumatic conveying in horizontal pipe. With this mathematical model, the influence of the three frictional stress models, namely Dartevelle frictional stress model, Srivastava and Sundaresan frictional stress model, and the modified Berzi frictional stress model, on the simulation result was explored. The simulation results showed that the three frictional stress models accurately predicted the pressure drop and its variations with supplementary gas in the horizontal pipe, with relative errors ranging from −4.91% to +7.60%. Moreover, the predicted solids volume fraction distribution in the cross-section of the horizontal pipe using these frictional stress models exhibited good agreement with the electrical capacitance tomography (ECT) images. Notably, the influence of the three frictional stress models on the simulation results was predominantly observed in the transition region and deposited region. In the deposited region, stronger frictional stress resulting in lower solids volume fraction and a higher pressure drop in the horizontal pipe were observed. Among the three frictional stress models, the simulation results with the modified Berzi frictional stress model aligned better with the experimental data. Therefore, the modified Berzi frictional stress model is deemed more suitable for simulating high-pressure dense-phase pneumatic conveying in horizontal pipe.

A numerical study was carried out to investigate the performance of a two-layer model for predicting turbulent gas-particle flows in rough pipes. An Eulerian–Eulerian two-fluid formulation was used to model both the gas and solid phases for turbulent gas-particle flow in a vertical tube. The stresses developed in the particle phase were calculated using the kinetic theory of granular flows while the gas-phase stresses were described using an eddy viscosity model. The two-fluid model typically uses a two-equation k-ɛ model to describe the gas phase turbulence, which includes the suppression and enhancement effects due to the presence of particles. For comparison, a two-layer model was also implemented since it has the capability to include surface roughness. The current study examines the predictions of the two-layer model for both clear gas and gas-solid flows in comparison to the results of a conventional low Reynolds number model. The paper specifically documents the effects of surface roughness on the turbulence kinetic energy and granular temperature for gas-particle flow in both smooth and rough pipes.

Numerical simulation of gas–solid flow with two fluid model in a spouted-fluid bed