here was developed using equilibrium data provided by the W.R Grace &. Company. (8). Nitrogen adsorption was represented with the Langmuir expression:.
Experimental
and Numerical
Adsorption/Desorption
Investigation
in Packed
under Ideal and Non-Ideal
of
Sorption
Beds
Flows
H. Mohamadinejad Boeing Aerospace Huntsville,
Company
AL
J. C. Knox Marshall
Space Flight Center
National
Aeronautics
Huntsville,
James.
and Space Administration
AL
E. Smith,
Department
Ph.D
of Chemical
University
of Alabama
Huntsville,
Engineering in Huntsville
AL ABSTRACT
The importance nitrogen,
and water on molecular
dimensional diameter partial
of the wall effect
computer
cylindrical differential
equations
column
(submitted
are solved
to Separatuin
breakthrough
information
Science
results
are presented
measurements
linear driving
and Tchnology) Additional
effects of carrier
and desorption
cm in radius is examined
using finite differences
non-isothermal,
concentration.
on the interactive
Experimental
with concentration
data with the axial-dispersed, model
beds in the adsorption
sieve 5A of 0.127
simulations.
column
on packed
gas coadsorption
experimentally
for a 22.5-cm
taken at various
radial
and Newmans's
method.
force model
is required
comparisons
of carbon
of
suggests
for accurate test
data
and with onelong
by
locations.
4.5-cm
The set of
Comparison
of test
that a two-dimensional
simulation with
dioxide,
the
of the average model
with CO2, as well as CO2-H:O
provided
interactions.
Introduction
In a packed and therefore increase
bed, the presence
heat and mass transfer
in porosity
particle
diameter
infinite porous governing
of the confining
walls can have a significant
in the packed
near the wall can have opposing
ratio, R, less than about
medium
influence.
(1,2,3).
Between
bed. The viscous
shear
effects
permeability.
for an R value greater
force
has been shown
of 7 and 30, variations
For R values above 30, the influence
it was found to be important
on overall
7, the permeability R values
influence
is generally
on the axial flow
along
For values
to increase
in bed packing
considered
than 100 in an adsorption
the wall and the of tube to
above that of an may determine
insignificant
the
(3), although
study by Tobis and Vortmeyer
(4). Wall effects on packed
bed processes
the value of R is frequently a heater packed
matrix
results
within this sensitivity
in small rectangular
range.
columns
in heat and mass transfer
Examples (CDRA
are thermal
refs),
driven
processes,
swing adsorption
wall-cooled
catalytic
since
beds where
reactors
(5) and
bed energy storage units (6).
In this work, we examine desorption nitrogen
in a packed carder
thermal
model
balances
adsorption
The experimental
information
results
for carbon
on the sensitivity
diameter
was developed
(radial
for the pellet, and axial)
and desorption
dioxide
of the adsorption
ratio, R, of 15. Adsorption
during
and water
adsorption
and
adsorption
to wall effects
breakthrough
in a
in a column
data is presented
of permeability
gas
Station
on the finite-differencing
in a flow-through
and canister,
model
was also
and is described
The test flow rate was scaled Space
based
and desorption
Experimental
International
on mass and heat transfer
at the bed exit, which can be used as a measure
gas adsorption
dimensional
of wall effects
or channeling
for
along
wall.
A computer simulates
column.
tube to particle
radial locations
the column
the influence
gas provides
with an intermediate various
can be significant
and
the momentum
developed
to predict
technique.
and multicomponent equation the effect
The model adsorption;
are included. of flow
A two-
channeling
on
in a later paper (7).
Apparatus
and Results Adsorption
to give gas velocities
Carbon
bed. Single
numerical
Dioxide
Removal
Test System
similar to that in the proposed Assembly.
Instrumentation
flight beds for the
of the packed
column
includes temperature probesandsampling tubesformeasurements atsorbent material endpoints andone intermediate point.To attainapproximately adiabatic bedconditions, thecolumnwasfirstcovered with Mansfield Q-fiberfeltinsulation, thenwrapped witha thermal blanketof Mansfield Min-Kmaterial.For adsorption runs,anadditional jacketfabricated of STSExternal Tankinsulating foamwasattached. The insulation, approximately 3 inches thickinall,wasusedwithsatisfactory results. Instrumentation wasprovidedfor continuous measurement of packedcolumnoutletCO2 andH20 concentration. Thelocationofsensors andotherequipment comprising theadsorbing apparatus areshown inFigure1.Thecolumnbypass isused priortotheteststarttoensure stable columninletconditions. Thegaschromatograph, a Shimadzu GC-14AwithCR601integrator, wasusedto sampleat three sample portlocations to determine gasconstituent volumetric fractionsduringtheadsorption runs.The probedepthof thesampling tubeat thecolumnexit wasadjusted to obtaina radialprofileof theexit concentration duringaseries ofidentical CO2adsorption tests. Column A small packed column 2) located sorbent.
at Marshall A 10-inch
with approximate
Space Flight Center
packing
was used
Dynamics
Test Bed
dimensions
of 2 inches
was used. The column
in this study for quicker
Placing 4.75 inches of glass beads at the two ends of the column
in diameter and 20 inches long (Figure may be packed
results
with up to 20 inches of
and reduced
eliminated
thermal
end effects.
the end effects.
Procedure Experiments Nitrogen bypass
were performed
on the insulated
is the carrier gas. Experiments
as it proceeded
Figure
The sorbent
is a 5A zeolite.
begin with the column at ambient room temperature.
was switched
before exposure
during the test to follow
The column
of the column to the
the sorbate mass transfer
wave
down the bed.
Results 3 shows
the water breakthrough
of gas mixed
gas breaks through process
rig at MSFC.
shown in Figure 1 was used to obtain intended inlet conditions
inlet gas. The GC sampling location
pressure
fixed-bed
efficiency
by passing
before
through
and Discussion
at the column
glass beads downstream
the gas at the centerline,
for the two-inch
diameter
midpoint
column.
indicating
and outlet. Also shown is the HzO partial of the sorbent
that channeling
material.
Note the mixed
has a significant
effect on the
To providea measure of theradialvariationin axialflow, adsorption testsof CO2andN2were conducted repeatedly withtheexitsampling tubein differentradialpositions. Thetestresults, shownin Figure4, showa clearrelationship between concentration andradialposition.As observed for H20 breakthrough results, these resultsindicate greater permeability nearthecolumn wall.Sincetheheater core of the4BMS(FourBedMolecularSievs)sorbent bedconsists of channels roughlyone-halfinchin diameter, thechanneling effecton CO2removalwill likelybe significant.Theresultsof thetwodimensional modelpresented in partII alsoconfirmthatchanneling hasa significant effecton this adsorption process. Mathematical
Gas/Solid
The Company
model
discussed
here
(8). Nitrogen
was developed
adsorption
*
Equilibrium
using
was represented
Model
equilibrium
with the Langmuir
data
provided
by the W.R
Grace
&
expression:
qmiBiPi
(1)
qi = l+BiPi Carbon dioxide
and water adsorptions
•
qmiBiPi
qi -
Two approaches
Prasusnitz,
by an iterative
for multiple
procedure
PY i
i=1
t 7rAni
(RTqmiJ
(9):
(2)
1-11 n--_
]
of gases adsorbed
components.
with the ideal
(10). For the case of the Langmuir-Freundlich
exp(
equation
ni
were used to solve for the amounts
i=n
by the Langmuir-Freundlich
l+BiPini
with the gas phase concentrations was obtained
were correlated
in the solid phase in equilibrium
For simulations
adsorption
solution
single component
with
and CO 2, the solution
N 2
theory isotherm,
(IAST)
of Myers
one gets:
1=0
(3)
and
Knowing estimated H20,
the total pressure
and solution
will be obtained
and CO2 the approach
based
found to give a more accurate process
for submision
towards
in details
correlations
predicts
adsorption
is under predicted,
systems
was
of co2/h2o, a paper is in the
the use of IAST and Langmuir-Freundlich
and test results
for components
multicomponent
equilibrium adsorption
as discussed
model.
equilibria
on the adsorption
of
OuC i
Ox 2
_x
For
adsorptivities. example,
indicates
low sensitivity
However,
at low
work
humidity
continues
levels,
for CO 2 and H20. At higher humidity
to
levels,
IAST CO z
by Finn (11).
In the bulk stream of the gas within the bed, the material
_2C i
using these correlations
with differing
Mass Balance
Boundary
with N 2,
(4)
gas/solid
accurately
- Dl
for multicomponent
rc is
ni
of simulation
a comprehensive
Ot
equation
pressure
For the simulations
l+_Bjpjnj J
agreement
_C i
for the spreading
until Eq. 3 is satisfied.
on the Langmuir-Freundlich
qmiBiPi
qi
of these
by iteration
a value
on the 5a :
•
limitations
temperature,
results than lAST model based on the non-ideality
to discuss
CO2/Nz and H20/CO2/N2
The favorable
and the solid
1-e
Equation
balance
for the adsorbate
concentration
d _"
is
(5)
e
and initial conditions: att O,
%._=O
x< L (9)
forx=O for x= L
OX
Note that Tw is calculated
in Eq 12.
Solid Phase The energy
equation for the solid phase includes
phase plus heat generation
Energy
Equation
the term for heat flux from the solid phase to the gas
due to adsorption.
m
aT s
a2Ts
p sC ps -'_-t = k s 7
Boundary
n
d qi
+ hsa s (Tg - Ts ) - i=1 ]_ AHi _
(10)
and initial conditions:
att O,
Ts=T
att>-O,--_-=O
i
x
