Process and Reactor Level Simulations of Coal-Direct Chemical-looping Combustion - Novel Combustion Concepts for Sustainable Energy Development - page 338

identi ed to originate from the non-physical closure for the continuum model such

as the frictional solids viscosity or the solids pressure. To address these inaccura-
cies, simulations using Eulerian/Lagrangian modeling approach, which has a
stronger physical foundation, has been introduced in recent literature. In this
approach, the particulate phase is modeled at the individual particle level tracking
their movement using the Lagrangian framework and is coupled with the eld

for interphase mass, momentum, and energy exchange. It should be noted that the
inter-particle collision is described using a deterministic model. Because particles
are treated as discrete elements, this approach is also known as the discrete element
method (DEM). Therefore, a series of transient simulations of quasi-3D spouted
fl

fl uid

fluidized bed apparatus for CD-CLC process are performed using the CFD/DEM
coupled model. Unsteady tracking of individual solid particles and their interactions
with one another as well as the ambient

fluid is enabled to provide the most accurate
and realistic representation of the multiphase

fl

field. The CFD/DEM simulation
approach has been used in various applications which require the modeling of
particle/

fl ow

uid interaction (Chu 2010 ; Feng and Yu 2009 ; Kloss et al. 2009 ; Yang
and Duan 2013 ; Zhu et al. 2008 ); however, its application in the context of close-
loop spouted

fl

fluidized bed system has been quite limited and preliminary. By
establishing the accurate models of CD-CLC con

fl

gurations validated against

laboratory-scale cold flow experimental data, it is expected that this work should

help in gaining deeper insights as well as provide best practices for modeling and
designing an industrial-scale CD-CLC process.
In the coupled CFD/DEM approach to multiphase simulation of CD-CLC pro-
cess, the

fl

fl fluid motion is obtained by solving the incompressible continuity, Navier

-
Stokes, and energy equations. The motion of particulate solids is modeled by the
Newtonian equation of motion. By introducing source terms related to movement
and interaction of solid particles in the fluid dynamics equations and terms due to

forces experienced by the solid particles in the Newtonian equations for the motion
of the solid particles and the mass and heat transfer from the particles to the

fl

fl fluid,

the coupling of solid uid interaction is achieved. On the other hand, the inter-

particle momentum transport is described using soft ball collision model. Detailed
mathematical description of the modeling process can be found in the authors

- fl

other
work (Zhang et al. 2014 ). These simulations employ the commercial simulation
package ANSYS Fluent, release version 14.5 (ANSYS 2012a , b ). All particles are
tracked individually as parcels with the actual particle diameter.

'

4.1 Cold Flow Simulation of Spouted Fluidized Bed
Experiment at TU-Darmstadt

Simulations employing the discrete element method (DEM) coupled with the
hydrodynamics solver are

first conducted for validating the model. The modeling
and simulation is conducted for the laboratory-scale quasi-3D experimental CLC