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This paper was submitted by the faculty of FAU’s Harbor Branch Oceanographic Institute.
Notice: ©1986 American Society of Mechanical Engineers. This manuscript is an author version with
the final publication available and may be cited as: Wang, T., & Lenahan, R. (1986). Gasometric device
for measuring CO2 scrubber performance efficiency. In T. McGuinness & H. H. Shih (Eds.), Current
practices and new technology in ocean engineering: [symposium] OED-Vol. 11 (pp. 363-370). New
York, NY: American Society of Mechanical Engineers.
GASOMETRIC DEVICE FOR MEASURING C02 SCRUBBER PERFORMANCE EFFICIENCY
T. Wang and A. Lenahan
Harbor Branch Foundation
Fort Pierce , Florida
INTRODUCTION
Carbon dioxide absorbent materials and canister
configurations in submersibles and other diving
equipment have been studied for many years (1, 2, 3).
The scrubber performance varies with absorbent granule
size, porosity, carbon dioxide concentration, gas flow
rate and canister configuration (1, 4, 5, 6). A
scrubber is normally required to undergo a performance
test prior to its use to determine expected life span
at various environmental conditions (7, 8, 9). The
test based on the scrubber breakthrough time does not
provide either the actual absorbent conversion
efficiencies nor the gas flow pathways inside the
canister. This test is also very time consuming and
requires sophisticated equipment. This paper
' describes a gasometric device which acidifies the
carbonate from exhausted absorbents and measures the
amount of co 2 released from absorbing agents.
Lithium hydroxide and Sodasorb (sodalime) are the
most widely used absorbents in co 2 scrubbing systems.
The reaction between lithium hydroxide and co 2 can be
expressed as follows: (10)
+
2 LiOH • H20 + C0 2
2 Li OH • H20
+
Li 2co3 + 3 H20
(A)
+
Li 2co 3 + H20
+
(D)
H2co 3
2 H2co3 + 2 NaOH + 2 KOH
+
Na 2co 3 + K2co 3 + 2 Ca(OH) 2
+
Na 2co 3 + K2co 3
+
2 Caco 3 + 2 NaOH
2 KOH
(F)
The overall reactions can be combined as:
(G)
APPARATUS AND PROCEDURES
The apparatus in this study is similar to that
used for carbonate content determination in a sediment
sample (12, 13). The apparatus consists of a bomb, a
pressure gauge, a thermocquple wire and an acid vial
as shown in Figure 1. The bomb is made by welding a
plexiglass tube segment to a plexiglass bottom. An
aluminum base attached to the plexiglass bottom
supports the side rods. The plexiglass top has two
holes. One hole holds an "o-ring" pipe-to-tube
fitting with a gas chromatograph septum which seals
the pipe hole when the fitting is hand tightened and
relieves the pressure when the fitting is loosened.
(B)
combining Eq. (A) and (B):
2 .LiOH + C0 2
C0 2 + H20
The end products of either absorbent are
carbonates and water as shown in equations (C) and
(G). After co 2 absorption, the exhausted absorbents
can be placed in a confined bomb and reacted with acid
to evolve carbon dioxide. The gas produced from the
acidification can be measured with a pressure gauge.
CARBON DIOXIDE REACTION KINETICS
2 Li OH + 2 H20
14 to 19% water moisture. The chemical reactions of
co 2 with Sodasorb are as follows: (11)
(C)
Sodasorb normally consists of hydrated lime Ca(OH) 2 ,
sodium hydroxide (NaOH), potassium hydroxide (KOH) and
363
The other hole in the top of the bomb is fitted with a
quick connect which is attached to a pipe of
polyethylene tubing adjoined to a pressure gauge.
in Eq. C and G, the co 2 absorption capacity can be
calculated as:
The operating procedures are as follows:
Absorption capacity g co 2/g absorbent
=
(no. of mole of co 2 absorbed) x (C0 2 molecular weight)
initial we.ight of fresh absorbent
1. Before co 2 absorption, five grams of fresh
absorbents is packed in a 202 ~m screen Nitex
capsule. The capsules are then placed in various
locations inside the co 2 scrubber.
RESULTS AND DISCUSSION
2. After scrubbing, collect the capsules and dry the
sample content in a vacuum oven at 2oo•c
overnight. Accurately weigh 1 g of dried exhausted co 2 absorbent ~nd place this sample in the
bomb.
A comparison of breakthrough duration test and
gasometric device tests was made. Figure 4 shows the
laboratory duration testing apparatus. Five grams of
LiOH or 10 g of Sodasorb were placed in the sample
tube for the co 2 absorption capacity test in each
experimental run. The experimental conditions were
carried out isothermally at 80°F in the water bath and
the humidity was 90-95~ in the gas stream. The
experiments were terminated at various concentrations.
The calculated co 2 absorption capacity expressed as
grams of co 2 absorbed/gram of absorbent was obtained
by knowing the total amount of co 2 passing through the
sample tube, breakthrough times and the amount of
fresh absorbents packed in the tubes (14, 15). After
termination of each duration test, one gram of dried
exhausted absorbent from the sample tub~ was placed in
the bomb for the gasometric determination. Tables 1
and 2 show the co 2 absorption efficiency of lithium
hydroxide and Sodasorb determined by both methods at
various breakthrough concentrations. The results show
that the deviation of both methods was less than 4~.
This demonstrates that the gasometrfc device is an
effective and expedient method for measuring the C0 2
absorption capacity.
3. Place 10 mt of 6N hydrochloric acid (HCl) into a
small plastic vial. then set the acid-filled vial
into the bomb.
4. Place the top on the bomb without spilling the HCl
and tighten the wing nuts. Open the pressure
relief valve and let the air inside the bomb
escape.
5. Connect the pressure gauge tubing. Hand-tighten
the relief valve and record the initial pressure.
Tilt the bomb to spill the HCl and shake the bomb
gently until the sample has completely reacted
with the acid.
6. Read and record the pressure after sample
acidification, subtracting the initial value to
obtain the net pressure gained. There may be some
temperature rise due to the reaction. If so, wait
until the temperature returns to its initial value
before reading pressure. A thermal wire can be
attached to the bomb for measuring the
temperature.
Since this device only requires a small amount of
sample for the measurement, the different portions of
absorbent packed in the canister can undergo
gasometric determinations to obtain the actual amount
of carbonate formed at different locations inside the
scrubber . The results can be used to define the gas
flow path and packing uniformity. A field study was
performed to measure scrubber performance efficiencies
inside the pilot sphere and diving chamber of the
JOHNSON-SEA-LINK I submersible. Approximately 5.9 kg
of Sodasorb was packed in each scrubber . After five
hours of scrubber operation in the submersible, the
absorbents from different portions of scrubbers were
analyzed using the gasometric method. The co 2
scrubber consists of two semi-circular halves which
clamp together around the power unit forming a
doughnut-shaped ring with an inner and outer wall of
perforated stainless steel lined with filter material.
The dimensions of the canister are 33 em O.D. x 20.3
em I.D. x 14.6 em thickness. Two boxer fans in series
powered with 28-31 volt DC at 2 amps draws the air
stream through the canister bed and exits through the
fans in the pilot sphere. The air stream scrubbing
rate at atmospheric pressure is 2. 52 m3/min. In the
diving compartment, a Lindberg-Hammer motor and blower
adapted to fit the canister scrubber is powered with
24-60 volt AC or DC at 3-4 amps. Air streams are
pulled by the motor and pushed through the canister
bed. The air scrubbing rate for this scrubber is 1.33
m3/min. Tables 3 and 4 show the results of absorbing
7. Prepare a calibration curve with 0.25 g, 0.5 g,
0.75 g and 1.00 g of carbonate (either Li 2co 3 or
Caco3 ) and follow procedures 1-5. The purity of
Li 2 co 3 and caco 3 are 99.3~ and 99.8~.
respectively. Plot the pressure values versus the
weight of carbonate. A linear equation can be
obtained. Figures 2 and 3 show the caco 3 and
Li 2co 3 calibration curves, respectively. From the
standard curve, the carbonate content of exhausted
absorbents can be obtained.
8. Run a blank of 1.00 g of fresh absorbent (either
lithium hydroxide or Sodasorb), using the standard
curves to obtain the carbonate impurities present
in the initial fresh absorbents.
9. Subtract the initial carbonate content in the
fresh absorbent from the total carbonate content
in the exhausted sample. The dffference is the
actual carbonate formed due to the co 2 absorption
process of the absorbents.
10. By knowing the amount of carbonate formed and that
the number of moles of carbonate formed is equal
to the number of moles of co 2 absorbed, as shown
364
capacity of chemicals inside the scrubbers. The
absorption capacity in the pilot chamber scrubber
ranged between 0.1081 g/g to 0.2290 g/g and the mean
absorption was 0.175 g/g or 36~ absorption efficiency.
In the diving compartment, the absorption capacity
ranged from 0.1557 g/g to 0.27 g/g and the overall
absorption capacity and efficiency were 0.213 g/g and
44~. respectively.
4.
Lower, B.R. Removal of co 2 from Closed-Circuit
Breathing Apparatus. In: Proceedings, Equipment
for the Working Diver, February 1970. pp. 261282. Office of the Supervisor of Diving.
5.
Nuckols, M.L., Purer, A., Deason, G.A., The
Design of Axial Flow Canisters for Carbon Dioxide
Absorption, In: Proceedings, OCEANS '83, 1983.
pp. 450-455.
CONCLUSION
6. Boryta, D.A., Mass, A.J., Carbon Dioxide
Absorption Dynamics of Lithium Hydroxide, In:
Proceedings, The Characteristics of Carbon
Dioxide Absorbing Agents for Life Support
Equipment, OED Vol. 10, The American Society of
Mechanical Engineers, November 1982. pp. 83-102.
The gasometric device proved to be a quick, easy,
and effective method to assess the co 2 scrubber
performance. The method does not only provide the co 2
absorption capacity but defines gas flow paths and
packing uniformity. This information can aid
engineers and operation personnel in designing or
improving other scrubbing equipment.
7. Wang, T.C., 1975. Temperature Effects in
Baralyme, Sodasorb and Lithium Hydroxide, Ind.
Eng. Chern. Process. Des. Dev. 1975, Vol 14, pp.
191-193.
ACKNOWLEDGMENTS
8. MacGregor, t.D., Fraser, M.G., The effect of
Pressure on the Efficiency of Carbon Dioxide
Absorbents, In:
Proceedings, The
Characterization of Carbon Dioxide Absorbing
Agents for Life Support Equipment, OED Vol. 10,
The American Society of Mechanical Engineers,
November 1982, pp. 75-82.
The authors wish to thank Ms. Debbie Farb for
typing the manuscript and Ms. Wendy Lin for collecting
data. This paper is Harbor Branch Foundation
Contribution Number 474.
REFERENCES
9. Riegel, P.S., Candy, D.W., Airflow and Pressure
Drop in Hyperbaric Beds, In: Proceedings, The
Characterization of Carbon Dioxide Absorbing
Agents for Life Support Equipment, OED Vol. 10,
The American Society of Mechanical Engineers,
November 1982, pp. 103-110.
1. Wang, T.C., Carbon Dioxide Scrubbing Materials in
Life Support Equipment, In: Proceedings, The
Characterization of Carbon Dioxide Absorbing
Agents for Life Support Equipment, OED Vol. 10,
November 1982, pp. 1-22.
10. William, D.O., R.R. Miller, The Effect of Water
Vapor on the LiOH-co 2 Reaction, Part I. Dynamic
Isothermal System, NRL Report 6939, 1966. Naval
Research Laboratory, Washington, D.C.
2. Bentz, R.L. Some Design Considerations for
Hyperbaric co 2 Scrubbers. In: Proceedings,
Divers Gas Purity Symposium, November 1976.
pp . 9.1-9.10. U.S. Navy Supervisor of Diving,
Naval Sea Systems Command.
3.
11. Data Sheet- Sodasorb and Sodasorb H.P. Dewey and
Almy Chemical Division, W.R. Grace~ Co.,
Cambridge, MA.
Purer, A., Deason, G.A., and Nuckols, M.L.,
Carbon Dioxide Absorption Characteristics of
Hydrated Calcium Hydroxide with Metal Hydroxide
Activators.
In:
Proceedings, The
Characterization of Carbon Dioxide Absorbing
Agents for Life Support Equipment, OED Vol 10,
The American Society of Mechanical Engineers,
November 1982, pp. 57-74.
12. Schink, J.C., Stockwell, J.H., Ellis, R.A., An
Improved Device for Gasometric Determination of
Carbonate In Sediment. J. of Sed. Petrology,
1979. Vol. 49, pp. 651-653.
13. Presley, B.J., A Simple Method for Determining
Calcium Carbonate in Sediment Samples . Jour.
Sed. Petrology, 1975, Vol. 45, pp. 745-746.
365
9
1~
T
14 . 6 em
Perforated Stainless Steel Screen
Stainless Steel Plate
4--~
T~ble
co 2
S~mple
Loc~t ion
1
2
3
4
5
6
7
8
3.
co 2 Scrubber
in the Pilot Sphere
absorption
C~pacity
(g C0 2/g Absorbent)
0.2140
0.2051
0.1415
0.1719
0.2257
0.2060
0.1081
0.0779
s~mple
Location
9
10
11
12
13
14
15
i6
C0 2 Absorption
Capacity
(g C0 /g Absorbent)
2
0.2126
0.1375
0.1719
0.1871
0.1511
0.1628
0.2044
0.2290
33
em
T
15
16
14 . 6 em
~1
Perforated Stainless Steel Screen
Stainless -Steel Plate
.--6
Table 4.
co 2
Scrubber in the Oive Compartment
Scrubbing Time:
4 hr. 49 min.
co 2
Sample
Location
--1
2
3
4
5
6
7
8
Absorption
Capacity
(g co 2/g Absorbent)
co 2
Sample
Location
0.2140
0.1962
0 .2079
0.2700
0 . 1768
0 . 1723
0.2265
0.2423
9
10
11
12
13
14
15
16
367
Absorption
Capacity
(g C0 2/g Absorbent)
0.2271
0 .2075
0 . 2144
0 .2454
0.2314
0.1998
0.1953
0.1557
PRESSURE
GAUGE
WING NUT
SUPPORT ROO
BASE
FIGURE 1.
GASOMETRIC O[YICE
100
80
,.......
0
a...
.::L
.......-
60
<ll
I...
:l
Ill
Ill
<ll
40
I...
a...
20
0 .4
0 .6
0 .8
1.0
1.2
Calcium Carbonate Weight ( gm)
Figure 2.
Calcium Carbonate Calibration Curve
368
A- Inlet Atr Stre1111
G - Mtdget Bubbler
B - Flow Meter
H - Te.penture lnd H•tdtty Sf!nsor
C-
Taper•tu~
0-
Cop~er
Controlled W.ter Bath
I - Absorbent Tube
Co tl. 6.10 • x 0.3175 c•
J - Dr:rtng Tube
[ - Atr-Wlter Mtxer
l - C0 2 Detector
L - Strt p Chut Reco!"'d.
F - Syrtnge PIMI!p
M - Wet Test Meter
Ftgure '·
Dynutc Gu now SystN
100
80
.......
0
a..
~
'-"
60
Q)
.....
~
(/)
en
Q)
40
.....
a..
20
0
0 .0
0.2
0 .4
0.6
0 .8
1.0
1.2
Lithium Carbonate Weight (gm)
,.
I
Figure 3.
Lithium Carbonate Calibration Curve
•II
\1
369
Diving
Compartment
Figure 5.
JOHNSON-SEA-LINK Submersible
reprinted from
Current Practices and New Technology in Ocean Engineering - OEO.Vol. 11
Editors : T . McGuinness and H . H . Shih
(Book No. 100206)
published by
THE AMERICAN SOCIETY OF MECHANICAL ENGINEERS
345 East 47th Street, New York , N . Y . 10017
Printed in U.S.A.