Eulerian-Eulerian Computational Fluid Dynamics Model Research Articles

CFD simulation of hydrodynamics and heat transfer characteristics in gas–solid circulating fluidized bed riser under fast pyrolysis flow condition

• Proper heat is needed for Circulating fluidized bed riser for fast pyrolysis. • A 3D EE-TFM model was developed and validated with experiment. • Hydrodynamics and heat transfer characteristics were examined for CFB riser. • Demonstrate the gas–solid heat transfer affected under different hydrodynamics. Pyrolysis process through circulating fluidized bed (CFB) is a promising technology to produce synthetic fuel and other products from biomass feedstocks. Computational fluid dynamics (CFD) computing means provide valuable insights to better understand gas–solid flow hydrodynamics, troubleshoot performance issues and optimize reactor operations. In this study, gas–solid flow hydrodynamics and heat transfer characteristics of a CFB riser for fast pyrolysis are investigated using a three-dimensional (3D) Eulerian-Eulerian CFD model. The main observations are discussed to provide insights on the factors affecting CFB riser performance. The model parameters, specularity and particle–particle restitution coefficients, were considered and tuned to accurately predict of gas–solid flow hydrodynamics and heat distribution with respect to different gas velocities and solid circulation rates. The results have shown that the CFD model predicted well the flow hydrodynamics and both specularity and particle–particle restitution coefficients are critical parameters as they affect particle behavior and temperature distribution fields. The lower specularity coefficient (Φ − 0.00001) was fairly able to predict the axial solid holdup profile into CFB riser. However, the lower value for particle–particle restitution coefficient ( e s s - 0.8) significantly overpredict the bottom dense region. The results shows that the increase of operating velocity promotes the mixing behaviors and heat transfer performance. In this work the suitable gas and solid circulation flow rates are U g = 4.5 m/s and G s = 81.23 kg/m 2 s.

Detailed simulations of fast pyrolysis of biomass in a fluidized bed reactor

In the present work, an Eulerian-Eulerian computational fluid dynamics model with an advanced kinetic scheme is used to simulate the fast pyrolysis of biomass in a fluidized bed reactor. The focus of this work is to investigate the influence of pyrolysis temperature and biomass components on the fast pyrolysis of biomass. Initially, the simulations were carried out to validate the model. The results showed that the model could make a good prediction about the fast pyrolysis of biomass. Further simulations were conducted to investigate the fast pyrolysis at different temperatures. The results indicated that the pyrolysis temperature considerably influenced the product yields and reaction rates of fast pyrolysis reactions of biomass and bio-oil compositions. In addition, the ability of different components of biomass to produce pyrolysis products was also studied. The results showed that cellulose had the strongest ability to produce bio-oil, while lignin had the strongest ability to produce char. The energy recovery coefficient of bio-oil obtained at different pyrolysis temperatures was also calculated and analyzed in this paper.

Modeling multiple gas jet interactions during fluidization in a pseudo-2D bed

The hydrodynamics of fluidized beds involving gas and particle interactions are very complex, and must be carefully considered when modeling such a system using computational fluid dynamics (CFD). One of the issues is the interaction of multiple jets developing above the distributor plate, which affects the uniformity of fluidization. To model the distributor plate, one approach is to use a uniform velocity at the inlet and the other is to model the distributor holes and specify the jet velocity. To predict and examine the hydrodynamics of interacting jets, a multi-fluid Eulerian-Eulerian CFD model was employed. In the present work, simulations of a pseudo-two-dimensional (2D) fluidized bed were compared to a corresponding experiment designed to examine multiple jet interactions for two distributor plate configurations with 9 and 5 holes. Two-dimensional and three-dimensional simulations of the pseudo-2D bed were used to investigate fluidization characteristics, volume fractions and solids velocity distributions. The deadzones formed due to multiple jet configurations of the distributor were quantified and their distributions over the plate were analyzed. It was found that three-dimensional simulations captured the effect of multiple jets and provided more accurate predictions of pressure, particle velocity and particle distribution. It was shown that increasing the number of holes along the gas inlet plane changed the fluidization characteristics, whereby fewer holes restricted the amount of particles that fluidized, irrespective of inlet velocity. When the number of holes increased, more material fluidized with increasing velocity. It was also found that although the reactor geometry is effectively two-dimensional, using two-dimensional simulations did not always capture all aspects of the flow, especially, the particle velocity.

An Experimental and Numerical Study of Two-phase Flow in Horizontal Eccentric Annuli

The aerated fluids have a potential to increase rate of penetration, minimize formation damage, minimize lost circulation, reduce drill pipe sticking, and, therefore, assist in improving the productivity. The technology of drilling using aerated fluids in the area of offshore drilling is very common. The use of compressible drilling fluids in offshore technology has found applications in old depleted reservoirs and in the new fields with special drilling problems. However, the drilling performed with gas-liquid mixture, calculating the pressure losses and the performance of cutting transportation is more difficult than single-phase fluid due to the characteristics of multi-phase fluid flow. In case configured drilling is directional or horizontal, these types of calculations are becoming more difficult depending on the slope of the wells. Both hydraulic behavior and mechanism of cutting transportation of the drilling fluids formed by gas-liquid mixture are not fully understood yet, especially there is a large uncertainty in selection of most appropriate flow regarding two phases. In this study, gas-liquid flow inside horizontal eccentric annulus is simulated using an Eulerian-Eulerian computational fluid dynamics model for two-phase flow patterns in an annulus, i.e., dispersed bubble, dispersed annular, plug, slug, wavy annular. A flow loop was constructed in order to conduct experiments using air-water mixtures for various in-situ air and water flow velocities. A digital high speed camera is used for recording each test dynamically for identification of the liquid holdup and flow patterns.

An Eulerian-Eulerian Model for the Dispersion of a Suspension of Microscopic Particles Injected Into a Quiescent Liquid

The convective dispersion of a suspension of microscopic particles injected into an initially quiescent liquid is examined using a finite volume, Eulerian-Eulerian computational fluid dynamics model. The motion of the phases is coupled with particle-particle interactions represented using a solids pressure formulation. The solids are of greater density than the liquid and settle after injection, creating a liquid flow field that eventually results in a toroidal plume of solids descending through the liquid phase. Excellent qualitative agreement between predicted plume shapes and published experimental shapes are obtained for 50 μm particles. For particle diameters less than 50 μm, the solids plume exhibits a toroidal recirculation in the liquid and particle phases relative to the downward motion of the plume. However, for particle diameters greater than 375 μm, a toroidal liquid recirculation is not predicted within the solids plume. The initial shape of the plume immediately after injection is affected by all parameters: density ratio, liquid viscosity, particle diameter, and injection parameters. It is concluded that it is this initial shape that determines the subsequent plume shape at a particular depth of penetration for varying solids density and liquid viscosity.