(727e) Modeling A Scaled 300 kWth Circulating Fluidized Bed Reactor With Barracuda

MODELING A SCALED 300 kW_th
CIRCULATING FLUIDIZED BED REACTOR WITH BARRACUDA

CHEMICAL LOOPING COMBUSTION WITH OXYGEN UNCOUPLING

ABSTRACT

As
global warming is continuing to gain recognition as a problem, new technologies
for capturing greenhouse gasses such as CO₂ are being
introduced.  The aim of these techniques
is to capture CO₂ before it enters the atmosphere thus ameliorating
its deleterious effects on global temperature and climate.  Chemical looping combustion with oxygen
uncoupling (CLOU), a subset of chemical looping combustion (CLC), allows for
isolation of carbon dioxide (CO₂) as an almost pure gaseous stream,
suitable for compression and storage.  This
is done by using two interconnected fluidized beds (CFB) with a metal oxygen
carry capable of transferring oxygen from an air reactor to a fuel
reactor.  The flue gas of the fuel
reactor contains a highly concentrated stream of CO₂ and H₂O.  After condensing H₂O the CO₂
can be easily captured.  This eliminates
any direct efficiency loss from the combustion process.  The goal of this study was to study fluid
dynamics of a 300 kW_th CFB using computation particle fluid dynamic
software Barracuda VR, then scaling this reactor to a cold flow model and
demonstrating with Barracuda that similar fluid dynamics could be obtained.

The
scaling was performed similar to Chalmers University of Technologies which was adapted
from Levenspiel's text Fluidization Engineering.  This method uses dimensionless π-groups
to determine the similarities of the beds. 
Then from these an overall scaling value is determined and used to
adjust the geometric dimensions of the CFB. 
The time scale dimension is determined from raising the overall scaling
value to the ½ power.  The particle
density and fluid density ratio must be maintained for the cold and hot set
up.  The hot system has a gas density of 0.236
kg/m³ and a particle density of 2140 kg/m³.  From these scaling parameters it was
determined that helium (0.167 kg/m³) was
the required fluidization gas and that a particle with density of 1450 kg/m³
would be required.  The particle of the
hot system will fall within the Geldart A group and
the particle in the cold system will fall in the Geldart
A group.  Due to the price and difficulty
of obtaining helium it was also determined that the scaled reactor would be run
using air at 20 ^oC as the fluidizing
gas.  The models to be meshed in
Barracuda were created using Solidworks 2012.

Using
Barracuda the following transient data was obtained and analyzed: oxygen
carrier volume fraction (at points in the air reactor, at points in the air
reactor riser, at point in the fuel reactor, and loop seals); the gas pressure
at different points of the reactors.  The
oxygen carrier mass was monitored at the outlet of the air reactor riser and
the cyclone outlet.  The average
residence time of the oxygen carrier was determined in the air reactor and fuel
reactor.  The reactors were visual inspected
using movies created in Barracuda.  These
were compared for the hot reactor, cold reactor with helium as the fluidizing
gas, and the cold reactor with air as the fluidizing gas.

From
the Barracuda simulations it was determined that the hot and both cold reactor
systems function with similar fluidization patterns.  It is recommended that the cold flow model
should be constructed to study the effects of static electricity and other
unknown inputs.  Then kinetics can be
added to Barracuda to fully study the hot system.