scholarly journals CFD Hydrodynamics Investigations for Optimum Biomass Gasifier Design

Processes ◽  
2020 ◽  
Vol 8 (10) ◽  
pp. 1323
Author(s):  
Emanuele Fanelli
Keyword(s):  
Fluid Dynamic ◽  
Clean Energy ◽  
Reaction Chamber ◽  
Solid Particles ◽  
Multiphase Model ◽  
Full Time ◽  
Momentum Exchange ◽  
Plant Availability ◽  
Bubbling Fluidized Bed ◽  
Fuel Particles

Biomass gasification is nowadays considered a viable option for clean energy production. Furthermore, still more efforts need to be spent to make this technology fully available at commercial scale. Drawbacks that greatly limit the full-time plant availability—and so its economically feasibility—mainly concerns syngas purification by contaminants such as tars. Different technological approaches were investigated over last two decades with the aim to increase both the plant availability and the overall efficiency by keeping, at the same time, CAPEX and OPEX low. Among technologies, fluidized beds are surely the most promising architectures for power production at thermal scale above 1 MWth. Gasifier can be surely considered the key component of the whole power plant and its proper design, the main engineering effort. This process involves different engineering aspects: thermo-structural, heat, and mass transfer, and chemical and fluid-dynamic concerns being the most important. In this study, with the aim to reach an optimal reaction chamber design, the hydrodynamics of a bubbling fluidized bed reactor was investigated by using a CFD approach. A Eulerian–Eulerian multiphase model, supported by experimental data, was implemented to describe the interactions between the solid and fluid phases inside the reactor while a discrete dense phase model (DDPM) model was considered to investigate momentum exchange among continuous phases and solid particles simulating char. Different process parameters, such as the bed recirculation rate and the particles circulation time inside the bed, were at least analyzed to characterize the hydrodynamics of the reactor. Results indicate that the recirculation time of bed material is in the order of 6–7 s at bench scale and, respectively, of 15–20 s at full scale. Information about solid particles inside the bed that should be used to avoid elutriation and agglomeration phenomenon, suggest that the dimension of the mother fuel particles should not exceed the value of 5–10 mm.

Fluidization Characteristic of Sewage Sludge Particles

2015 ◽  
Vol 776 ◽  
pp. 294-299
Author(s):  
I. Nyoman Suprapta Winaya ◽  
Rukmi Sari Hartati ◽  
I. Nyoman Gde Sujana
Keyword(s):  
Sewage Sludge ◽  
Fluid Dynamic ◽  
Solid Particles ◽  
Cfd Modeling ◽  
Multiphase Model ◽  
Particle Sizes ◽  
Eulerian Model ◽  
Visual Phenomena ◽  
Basic Characteristics ◽  
Sludge Particle

The main objective of this study is to determine the basic characteristics of fluidization using sewage sludge particle as non-visual phenomena which can then be modeled physically and numerically with the program of Computational Fluid Dynamic (CFD). CFD modeling using Eulerian model incorporating the kinetic theory for solid particles was applied to the gas-solid flow at various superficial velocities for different particle sizes. The transfer momentum was calculated using Syamlal-O'Brien drag function and Eulerian multiphase model was used for analysis. Two-Dimensional computational domains discretized using rectangular cells (Quad), made within the 20 iteration steps of 0,001s. The gas velocity is found to be the ​​the most important factors that influence the formation process of fluidization; by increasing the rate of fluidization the bed expanse occurs higher as well the time of onset fluidization is shorter. The phenomenon can be explained well by modeling and simulation.

scholarly journals CFD Modeling and Simulation of Hydrodynamics in a Fluidized Bed Dryer with Experimental Validation

2011 ◽  
Vol 2011 ◽  
pp. 1-9 ◽  
Author(s):  
Mahdi Hamzehei
Keyword(s):  
Fluidized Bed ◽  
Fluid Dynamic ◽  
Expansion Ratio ◽  
Industrial Applications ◽  
Solid Particles ◽  
Cfd Modeling ◽  
Momentum Exchange ◽  
Fluidized Bed Dryer ◽  
Wide Range ◽  
Simulation Results

Gas-solid fluidized bed dryers are used in a wide range of industrial applications. With applying computational fluid dynamic (CFD) techniques, hydrodynamics of a two-dimensional nonreactive gas-solid fluidized bed dryer was investigated. A multifluid Eulerian model incorporating the kinetic theory for solid particles was applied to simulate the unsteady state behavior of this dryer and momentum exchange coefficients were calculated by using the Syamlal-O'Brien drag functions. A suitable numerical method that employed finite volume method was used to discretize the equations. Simulation results also indicated that small bubbles were produced at the bottom of the bed. These bubbles collided with each other as they moved upwards forming larger bubbles. Also, solid particles diameter and superficial gas velocity effect on hydrodynamics were studied. Simulation results were compared with the experimental data in order to validate the CFD model. Pressure drops and bed expansion ratio as well as the qualitative gas-solid flow patterns predicted by the simulations were in good agreement with experimental measurements at superficial gas velocities higher than the minimum fluidization velocity. Furthermore, this comparison showed that the model can predict hydrodynamic behavior of gas solid fluidized bed reasonably well.

scholarly journals Particle Accumulation Structures in a 5 cSt Silicone Oil Liquid Bridge: New Data for the Preparation of the JEREMI Experiment

2021 ◽  
Vol 33 (2) ◽  
Author(s):  
Paolo Capobianchi ◽  
Marcello Lappa
Keyword(s):  
Liquid Bridge ◽  
Silicone Oil ◽  
Fluid Dynamic ◽  
Solid Particles ◽  
Critical Threshold ◽  
Marangoni Flow ◽  
Disk Radius ◽  
Carrier Fluid ◽  
Aspect Ratios ◽  
Time Periodic

AbstractSystems of solid particles in suspension driven by a time-periodic flow tend to create structures in the carrier fluid that are reminiscent of highly regular geometrical items. Within such a line of inquiry, the present study provides numerical results in support of the space experiments JEREMI (Japanese and European Research Experiment on Marangoni flow Instabilities) planned for execution onboard the International Space Station. The problem is tackled by solving the unsteady non-linear governing equations for the same conditions that will be established in space (microgravity, 5 cSt silicone oil and different aspect ratios of the liquid bridge). The results reveal that for a fixed supporting disk radius, the dynamics are deeply influenced by the height of the liquid column. In addition to its expected link with the critical threshold for the onset of instability (which makes Marangoni flow time-periodic), this geometrical parameter can have a significant impact on the emerging waveform and therefore the topology of particle structures. While for shallow liquid bridges, pulsating flows are the preferred mode of convection, for tall floating columns the dominant outcome is represented by rotating fluid-dynamic disturbance. In the former situation, particles self-organize in circular sectors bounded internally by regions of particle depletion, whereas in the latter case, particles are forced to accumulate in a spiral-like structure. The properties of some of these particle attractors have rarely been observed in earlier studies concerned with fluids characterized by smaller values of the Prandtl number.

scholarly journals Numerical simulation of gas-solid flow in an interconnected fluidized bed

2015 ◽  
Vol 19 (1) ◽  
pp. 317-328 ◽  
Author(s):  
Giuseppe Canneto ◽  
Cesare Freda ◽  
Giacobbe Braccio
Keyword(s):  
Numerical Simulation ◽  
Fluidized Bed ◽  
Experimental Tests ◽  
Solid Particles ◽  
Multiphase Model ◽  
Cold Model ◽  
Conservation Equations ◽  
Solid Flow

The gas-particles flow in an interconnected bubbling fluidized cold model is simulated using a commercial CFD package by Ansys. Conservation equations of mass and momentum are solved using the Eulerian granular multiphase model. Bubbles formation and their paths are analyzed to investigate the behaviour of the bed at different gas velocities. Experimental tests, carried out by the cold model, are compared with simulation runs to study the fluidization quality and to estimate the circulation of solid particles in the bed.

scholarly journals A 2D Multiphase Model of Drop Behavior during Electroslag Remelting

Metals ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 490
Author(s):  
Jérémy Chaulet ◽  
Abdellah Kharicha ◽  
Sylvain Charmond ◽  
Bernard Dussoubs ◽  
Stéphane Hans ◽  
...  
Keyword(s):  
Small Volume ◽  
Slag Phase ◽  
Volume Fraction ◽  
Liquid Pool ◽  
Electroslag Remelting ◽  
Multiphase Model ◽  
Momentum Exchange ◽  
Small Volume Fraction ◽  
Drag Law ◽  
Two Fluid

Electroslag remelting is a process extensively used to produce metallic ingots with high quality standards. During the remelting operation, liquid metal droplets fall from the electrode through the liquid slag before entering the liquid pool of the secondary ingot. To better understand the process and help to optimize the operating condition choice, a 2D axisymmetric multiphase model of the slag domain has been developed using a two fluid Eulerian approach. During their fall, droplets hydrodynamic interactions are calculated thanks to an appropriate drag law. Influence of droplets on the electromagnetic field and on the slag hydrodynamics is discussed, as well as their heat exchange with the slag. Even with a small volume fraction, the droplets influence is noticeable. The present investigation shows that small droplets have a large influence on the slag hydrodynamics, due to a great momentum exchange. However heat transfer is more influenced by large drops, which are found to be relatively far from the thermal equilibrium with the slag phase.

Experimental and Computational Investigation of an Air Core Inside a Milling Circuit Hydroclone

2017 ◽  
Author(s):  
J. R. Kadambi ◽  
C. Shingote ◽  
R. Ke ◽  
Z. Tian ◽  
J. Furlan ◽  
...  
Keyword(s):  
Flow Field ◽  
Flow System ◽  
Industrial Applications ◽  
Solid Particles ◽  
Test Fluid ◽  
Multiphase Model ◽  
Phase Flow ◽  
Computational Results ◽  
Number Range ◽  
Air Core

Hydrocyclone separators are widely used in various industrial applications in the oil and mining industries to sort, classify and separate solid particles or liquid droplets within liquid suspensions. Often, studies in the literature have investigated idealized and simplified geometries, which are also typically scaled down to very small sizes. In this study, the two phase flow system inside a transparent acyclic model with actual milling circuit cyclone hydraulics was investigated computationally and experimentally. The diameter and height of the hydrocyclone are 12.7 cm and 94 cm, respectively. In many industrial applications, a single phase flow system in a hydrocyclone is a rarity, since nearly all cyclones have an underflow which is open to atmosphere, and therefore an air core is present along the central axis. In this study, the flow field with an air core present has been investigated. The computational modelling was conducted using Star CCM+, a commercial Computational Fluid Dynamics (CFD) software package. Large Eddy Simulation (LES) and the Volume of Fluid multiphase model was used. Additionally, the computational studies also focused on the prediction of the dimensions of the air core, which were measured experimentally. The tests were conducted in the Reynolds number range of 20,000–150,000 and 9000–67,800 for the water and NaI solution respectively. The model hydrocyclone was made of optically transparent acrylic plastic with flat, smooth outer surfaces so that there were no reflections, distortions, or obstructions. Refractive index matching, to minimize refraction effects, between the test fluid and acrylic test piece was achieved using a test liquid of sodium iodide aqueous solution (63.3% NaI by weight). Images of the flow field with the air core were taken using a Canon DSLR camera. A comparison between the experimental data and the computational results were made in the r-z plane. The experimental results and the computational results will be discussed in this paper.

CFD Based Ash Deposition Prediction in a BFB Firing Mixtures of Peat and Forest Residue

2003 ◽  
Author(s):  
Christian Mueller ◽  
Dan Lundmark ◽  
Bengt-Johan Skrifvars ◽  
Rainer Backman ◽  
Maria Zevenhoven ◽  
...  
Keyword(s):  
Combustion Chamber ◽  
Computational Fluid Dynamic ◽  
Power Plants ◽  
Fossil Fuels ◽  
Fluid Dynamic ◽  
Thermal Power ◽  
Biomass Combustion ◽  
Mineral Matter ◽  
Forest Residue ◽  
Bubbling Fluidized Bed

Fuels currently used for energy production in thermal power plants are characterized by their huge variety ranging from fossil fuels to biomass and waste. This multitude of fuels offers opportunities to the energy industry and nowadays many power plants do not fire either of these fuels but mixtures of them are burnt. While this procedure may lead to overall economic and environmental advantages it is very demanding for the boiler operators to still meet expectations concerning boiler performance, boiler availability and emission regulations. In the course of this latest trend in boiler operation, ash related operational problems such as slagging, fouling and corrosion are ranking very high on the list of reasons leading to significant reduction of boiler availability. Ash related problems strongly dependent on fuel specific aspects, such as the mineral matter distribution in the fuel, aspects specific to the used combustion technique as well as design aspects unique for the combustion chamber of any operating power plant. The overall goal in combustion related research is therefore the prediction of potential operational problems originating from fuel streams entering the combustion chamber as well as those originating from the design of individual furnaces. In our earlier work we have strongly focused on developing an advanced ash behavior prediction tool for biomass combustion combining computational fluid dynamic calculations (CFD) and advanced fuel analysis. In this paper the tool is applied to analyze the slagging and fouling tendency in a 295 MW bubbling fluidized bed boiler fired with mixtures of peat and forest residue. In addition to the overall deposition prediction this work focuses on details of the models used in the computational fluid dynamic calculations. These include a study on the importance of the accurate description of the fuel feeding system and related to this aspect the advanced description of the bubbling bed with regard to release of primary gas and ash particles from its surface to the freeboard. Evaluation of the predictions comparing simulation results with deposits on the furnace walls show good agreement.

Fluid-dynamic assessment of sugarcane bagasse to use as feedstock in bubbling fluidized bed gasifiers

2014 ◽  
Vol 73 (1) ◽  
pp. 238-244 ◽  
Author(s):  
Nestor Proenza Pérez ◽  
Einara Blanco Machin ◽  
Daniel Travieso Pedroso ◽  
Julio Santana Antunes ◽  
Jose Luz Silveira
Keyword(s):  
Fluidized Bed ◽  
Sugarcane Bagasse ◽  
Fluid Dynamic ◽  
Dynamic Assessment ◽  
Bubbling Fluidized Bed

Fluid dynamic simulation of O3 decomposition in a bubbling fluidized bed

AIChE Journal ◽  
2003 ◽  
Vol 49 (11) ◽  
pp. 2793-2801 ◽  
Author(s):  
Madhava Syamlal ◽  
Thomas J. O'Brien
Keyword(s):  
Fluidized Bed ◽  
Dynamic Simulation ◽  
Fluid Dynamic ◽  
Bubbling Fluidized Bed

scholarly journals Validation of a thermal non-equilibrium Eulerian-Eulerian multiphase model of a 620 MWe pulverized fuel power boiler

2021 ◽  
Vol 347 ◽  
pp. 00004
Author(s):  
Brad Rawlins ◽  
Ryno Laubscher ◽  
Pieter Rousseau
Keyword(s):  
Heat Fluxes ◽  
Multiphase Model ◽  
Eulerian Model ◽  
Combustion Dynamics ◽  
Pulverized Fuel ◽  
Fuel Particles ◽  
Flexible Operation ◽  
Power Boiler ◽  
Modelling Approach ◽  
Non Equilibrium

The use of a thermal non-equilibrium Eulerian-Eulerian model for the simulation of a 620 MWe power boiler is proposed for capturing the combustion and radiative heat transfer found in the pulverized fuel systems. The models eliminates the use of a Lagrangian reference frame in tracking solid fuel particles thereby reducing the computational expense and time. The model solves the scalar transport for the particle mass, energy and radiation interactions between the pseudo-particle and continuous phases. The goal is to apply the modelling approach to generate a simulation database for different load cases and firing conditions which in turn will be used to study flexible operation. The model is validated against both numerical and applicable site data measurements. It is shown that the model is able to adequately resolve the furnace and superheater wall heat fluxes. Additionally the resolution of the flow field, combustion dynamics and wall fluxes are demonstrated for both an 80% and 60% operational loads. Moreover, it is shown that the Eulerian-Eulerian model results in approximately a 30% computational resource reduction when compared to traditional modelling approaches.

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