1 FIXED BED GAS ADSORPTION COLUMN OBJECTIVE The overall objective of this experiment is to analyze the behavior of the adsorption breakthrough and desorption elution curves associated with the separation of CO 2 from He using Norit RB2 activated carbon. The equilibrium adsorption capacity of this activated carbon will be determined from this analysis and used to model the experimental breakthrough and elution curves. INTRODUCTION The equipment is designed to demonstrate the gas adsorption phenomenon using a Fixed Bed Adsorption Column. Adsorption and Absorption are easily confused. Adsorption is the attraction between the outer surface of a solid particle and a contaminant, which is held on the surface of the particle by surface forces, whereas Absorption is the uptake of the contaminant into the physical structure of the solid. See Figure 1. Fixed bed adsorption processes are ubiquitous in the chemical process and other industries. Applications include air purification, gas dehydration, solvent or hydrocarbon vapor recovery, water purification, and many others. The fixed bed adsorption processes utilize a solid mass separating agent packed inside a column to effect separation of one or more components from a mixture in a gas or liquid stream as it flows through the packed bed. In this experiment the gas mixture of carbon dioxide and helium is separated. The amount of carbon dioxide adsorbed increases with increasing CO 2 partial pressure, and decreases with increasing temperature. Completely isothermal behavior, in reality, is impossible to achieve unless the feed concentration is extremely dilute (in the ppm range). An overview of the Fixed Bed Adsorption (FBA) Unit, Armfield (UOP15) that you will be using in this experiment is an adsorption column that is jacketed for the purpose of Figure 1. Adsorption and Desorption Courtesy of Armfield Ltd., England
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FIXED BED GAS ADSORPTION COLUMN
OBJECTIVE
The overall objective of this experiment is to analyze the behavior of the adsorption
breakthrough and desorption elution curves associated with the separation of CO2 from He using
Norit RB2 activated carbon. The equilibrium adsorption capacity of this activated carbon will be
determined from this analysis and used to model the experimental breakthrough and elution
curves.
INTRODUCTION
The equipment is designed to demonstrate the gas adsorption phenomenon using a
Fixed Bed Adsorption Column. Adsorption and Absorption are easily confused. Adsorption is
the attraction between the outer surface of a solid
particle and a contaminant, which is held on the
surface of the particle by surface forces, whereas
Absorption is the uptake of the contaminant into the
physical structure of the solid. See Figure 1.
Fixed bed adsorption processes are
ubiquitous in the chemical process and other
industries. Applications include air purification, gas
dehydration, solvent or hydrocarbon vapor
recovery, water purification, and many others.
The fixed bed adsorption processes
utilize a solid mass separating agent packed inside a
column to effect separation of one or more
components from a mixture in a gas or liquid
stream as it flows through the packed bed. In this
experiment the gas mixture of carbon dioxide and
helium is separated.
The amount of carbon dioxide adsorbed increases with increasing CO2 partial
pressure, and decreases with increasing temperature. Completely isothermal behavior, in reality,
is impossible to achieve unless the feed concentration is extremely dilute (in the ppm range).
An overview of the Fixed Bed Adsorption (FBA) Unit, Armfield (UOP15) that you
will be using in this experiment is an adsorption column that is jacketed for the purpose of
Figure 1. Adsorption and Desorption
Courtesy of Armfield Ltd., England
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thermal control. There are six thermocouples sited along the length of the column. The unit
incorporates an Infrared (IR) detector used for the measurement of the concentration of CO2 at
the column outlet. The carbon dioxide IR analyzer operates based on the absorbance of infrared
radiation by carbon dioxide, in a process similar to a spectrophotometer. See Figure 2. for a
picture of the Fixed Bed Adsorption Unit.
Software is included to perform data acquisition and analysis. A USB port is used for
data collection.
Figure 2. Fixed Bed Adsorption Unit (UOP15) Courtesy of Armfield Ltd., England
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REFERENCES
Instruction Manual for UOP15, Fixed Bed Adsorption Column, Armfield Limited, Bridge
Figure 3. Side view of the Fixed Bed Adsorption Unit UOP15 Courtesy of Armfield Ltd., England
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a. Description of Flow
See Figure 5. For a layout of the unit. The unit descriptions that follow will refer to
Figure 5. The gas mixture is fed from compressed gas cylinders to the Column. Two mass flow
meters, helium and carbon dioxide, are incorporated to measure exact flow rates of each gas.
The flow rates are regulated by the inline flow control valves. The exiting CO2 concentration at
the column outlet is measured by the Infra-Red (IR) detector. Part of the gas mixture is
discharged to the surroundings before it enters the IR detector.
Figure 4. Top view of the Fixed Bed Adsorption Unit UOP15 Courtesy of Armfield Ltd., England
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Courtesy of Armfield Ltd., England
Figure 5. UOP15 Layout
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A column bypass is incorporated for system calibration purposes. It includes two 3-
way directional valves, V3 and V4, which divert the gas stream that is between the column and
the bypass. The needle valve incorporated at column outlet, V5, is used to control pressure in the
column. This pressure is measured by the pressure gauge P1.
The experiment is performed at defined temperatures, therefore the FBA Column is
thermally controlled by hot water which is heated and pumped by the Hot Water Circulation
(HWC) System. Water temperature is controlled by the PID temperature controller.
b. Hot Water Circulating (HWC) system.
The HWC is positioned
on the plinth at the rear of the
control console. The maximum
working temperature for the FBA
column is 50°C. The system
consists of a heater element, gear
pump and expansion tank as shown
in Figure 6.
Flexible tubing is used to
connect the pump to the column
jacket. The priming/expansion tank
is used to fill the pump and column
jacket with water and also remove
air from the system.
c. IR detector
The infrared CO2 detector for outlet CO2 concentration measurements is mounted in
the control console. The CO2 concentration is available through the data acquisition system.
The software displays the actual concentration of CO2 in % volume.
d. Gas flow control
There are two flow control valves (needle valves), V1 and V2, which are used to
regulate flow rates of He and CO2 respectively. The flow rates are measured using two mass
flow meters. The CO2 mass flow meter is, F2, and the measurement range is 0 to 1 SLPM. The
He mass flow meter is, F1, and the measurement range is 0 to 5 SLPM. The third mass flow
meter, F3, is located inside the control console and measures the flow that is entering the IR
detector. The measurement range of, F3, is 0 to 1 SLPM. All mass flow rates are available for
data logging. The software displays the actual masses in SLPM.
Figure 6. HWC System Courtesy of Armfield Ltd., England
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e. Control Console
Sensor displays
and controls are mounted on
the control console. See
Figure 7. The control
console incorporates a PID
controller which has two
displays: the upper display
shows the actual value of T7
(hot water circulator) and
the lower display shows the
set point value. The control
console also has an On/Off
switch for the water
circulation pump and for the
water heater. There is also a
low liquid level warning
light for the expansion
vessel on the console.
Below the control
console, on the side of the
Plinth there is a plate
(On/Off USB Plate) that has a USB port for connection to a PC. There are also two lights on this
plate, one indicating the USB power and the other indicating whether the USB is active. The
main power switch for the unit is also on this plate.
f. Fixed Bed Adsorption Column
The fixed bed adsorption column (250 mm effective length) is made of stainless steel
and is jacketed. The maximum operating pressure of the column is approximately 20 psi and is
protected against over pressure with a pressure relief valve. The activated carbon packed in the
column has the form of cylindrical granules (NORIT RB2). The column is shown in Figure 8.
Six temperature sensors, T1 – T6 are located inside the column to measure the
adsorption temperature. They are insulated type K thermocouples. Three of them enter the
column through the top cover plate and three by the bottom cover plate. During operation, the
cool gas entering the bottom of the column may result in thermocouple T6 reading slightly lower
than the thermocouples higher up the column. This does not affect the operation of the column
or the responses obtained.
An additional temperature sensor T7 is located in the expansion tank of the hot water
system. T7 works in conjunction with the PID controller to maintain the desired temperature
inside the column. Thermocouples T1 – T7 are available for data logging.
Figure 7. Control Console Courtesy of Armfield Ltd., England
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Figure 8. Fixed Bed Adsorption Column Courtesy of Armfield Ltd., England
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The two gases are fed from compressed gas cylinders through mass flow meters (F1,
F2) and a cross connector (Figure 5). The cross connector links the two gas streams into the
mixed feed stream to the FBA Column. The pressure gauge, P1, shows system pressure and can
be adjusted with the pressure control valve (V5) at the column outlet.
The column bypass is incorporated for system calibration purposes. A large
proportion of the product stream is discharged to the atmosphere before it reaches the IR
detector. The IR detector works accurately at a concentration up to 5% of CO2 inlet
concentration. The best accuracy of the detector is found when the total flow rate of the gas
through the detector is between 0.5 and 1.0 SLPM. This flow is measured by the third mass flow
meter, F3, and is adjustable with the needle valve located at its inlet, V6.
SYSTEM CONFIGURATION
Make sure the unit is connected to an electrical supply. An electrical cord should be
connected into the mains supply plate found at the rear of the unit. See Figure 9.
A USB data port connector is found on the On/Off USB plate under the control
console. This allows the voltage signals from each of the sensors to be connected to the USB
port of a suitable PC using an Armfield IFD5 interface device.
Two compressed gases are used in this experiment. They are helium and carbon
dioxide gas. There are two stage gas regulators attached to the gas tanks to provide constant gas
pressure to the unit. The regulators are supplied with an outlet control valve that provides a
means to isolate the gas cylinder from downstream equipment.
Figure 9. Mains plate at rear of the unit. Courtesy of Armfield Ltd., England
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The hot water circulator system (HWC) should have water in it and be ready to go. If
not, check to see that all the connections of the HWC system are connected as shown in Figure 6.
Open the priming vessel and fill it up with deionized water. Switch on the pump (Figure 7) and
observe the pump taking the water from the vessel and filling the tubing of the system. Fill up
the vessel before it is empty. Add additional water until the level of water in the vessel remains
constant. The HWC system is now primed.
a. Preparation for Operation
Turn on (up) the circuit breakers at the rear of the unit, See Figure 9 (this should
already be done). Turn on the mains switch (0/1) on the plate below the control console. The
two digital meters on the control console will be illuminated and the level warning light for the
expansion vessel will flash (if the water level is low).
Make sure the small shut off valves on the gas regulator discharge lines are closed.
Open the main valves on the gas cylinders and adjust the discharge pressure of the cylinders with
the regulator valves to 2 bar (29 psi) for the CO2 cylinder and 2.6 bar (38 psi) for the He
cylinder. Do not open the small shut off valves on the regulator discharge line until told to do so.
b. FBA Column Operation
The system includes a hot water circulating system with a 250 W heater to maintain
the FBA column temperature. The thermocouple in the expansion tank (T7) is connected to the
PID controller input. The output of the PID controller is connected to the heater. Additional
controls include no power supplied by the heater when there is a low liquid level in the
expansion tank – indicated by a red light on the control console. The pump must be switched on
for the heater to work to insure there is no boiling around the heater elements.
Set the desired column temperature set point using the PID controller before you
switch on the pump and the heater.
1. Press the Function, F key (bottom left side of PID controller), to change the set point.
2. Use the up and down arrow keys on the PID controller display to change the set point
temperature to the operating temperature.
3. Press the F key when through changing the set point.
4. Press the F and the R key simultaneously to set the temperature and return to the process
function. You can also wait 8 seconds and it will automatically return.
5. The Function, R key (bottom right side of PID controller), changes the setting to its
previous value.
The temperature measured by thermocouple T7 in the expansion tank, which is
displayed on the controller should increase and eventually be controlled to the set point. Check
that the desired temperature in the column (the temperature controller set point) is shown and
maintained by all sensors (T1 – T6) by using the Computer output (diagram screen). It takes a
maximum of 15-20 minutes to raise the temperature in the column by 10C.
Before opening the small valves on the regulator discharge lines direct the 3-way
directional valves of the column, V3 ↑and V4 ↓, to the by-pass path so the gas will flow through
the by-pass allowing for a good adjustment of the flows. Then adjust the flow with the two CO2
and He flow control valves and the pressure gauge with V5.
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The IR detector is used to measure the CO2 concentrations coming out of the FBA
column. The readings are displayed and logged in the PC software.
NOTE: When the process is started, use the flow control valve V6 to regulate the flow rate
needed for the IR detector, between 0.5 and 1.0 SLPM. Do not go over 1.0 SLPM. It is best
to maintain the same flow rate to the IR detector for all trials. A flow rate of 0.5 SLPM is a
good flow rate to use.
c. Maximum system operating conditions
The system pressure is limited by the pressure relief valve to 1.4 bar (20 psi). The
ideal operating pressure of the system is 0.8 to 0.9 bar (11.6 to 13.0 psi) gauge pressure (P1).
The maximum flow rate that can be measured with F1 is 5 SLPM; the recommended flow rate
range is 2-4 SLPM.
The maximum flow rate that can be measured with F2 and F3 is 1 SLPM. It is
recommended to work at a combined CO2/He flow rate in the range of 0 – 5 standard liters per
minute (SLPM). It is best to operate with a CO2 flow rate of 5% of the helium flow rate.
Therefore the recommended operating parameters for the first run are:
• Back Pressure 0.8-0.9 bar (11.6 – 13.0 psi)
• Helium flow rate (F1) 3.0 SLPM
• CO2 flow rate (F2) 0.15 SLPM
• Column temperature 30 C
The maximum operating temperature is restricted to 50°C for this system.
EXPERIMENTAL PROCEDURE
1. Ensure that you have read the operating sections above.
2. Turn on the laptop and log into the student account
3. Start up the computer software data logging program. See Instructions below.
4. Turn on (up) if they are not on, the circuit breakers at the rear of the unit, See Figure 9.
Do not turn them off after running the Lab experiment – they should stay on. Turn on the
mains switch (0/1) on the plate below the control console. The two digital meters on the
control console will be illuminated and the level warning light for the expansion vessel
will flash (if the water level is low).
5. Make sure the small shut off valves on the gas regulator discharge lines are closed. Make
sure the three-way valves just downstream of the small shut off valves are open to the
experimental unit and not venting to the atmosphere. Open the main valves on the gas
cylinders and adjust the discharge pressure of the cylinders with the regulator valves to 2
bar (29 psi) for the CO2 cylinder and 2.6 bar (38 psi) for the helium cylinder. Do not
open the small shut off valves on the regulator discharge line until told to do so.
6. Make sure valve, V6, the flow rate control valve to the IR detector is off and the white
clamp on the plastic tubing is open.
7. The jacket temperature set point should have been set prior to this (see b.FBA Column
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Operation). Switch on the pump and heater to begin bringing the column to the set point
temperature.
8. To begin the experiment, after the column temperatures have stabilized, direct the flow of
helium gas around the column through the bypass. This is done by changing valves, V3
and V4. The arrow on valve V3 should be pointing up (↑) and the arrow on valve V4
should point down (↓) to bypass the column.
9. Open the small shut off valve on the helium regulator discharge line. Regulate the
helium flow using the needle valve, V1, to a flow rate of 3.0 SLPM. Use valve, V5, to
set a back pressure of 0.8-0.9 bar on the pressure gauge, P1. The flow can be monitored
on the computer software diagram screen. NOTE: Setting the back pressure will affect
the flow so you may have to readjust the flow again.
10. Change the position of the valves, V3 and V4, (V3 ↓ and V4 ↑) so the helium flows
through the column. Adjust Valve, V5, so the back pressure through the column is at a
value of 0.8 to 0.9 bar on the pressure gauge, P1 You may have to readjust the He flow
using valve, V1..
11. Wait until the temperature of the column is stabilized around the desired value. The
temperature of thermocouple 7 which measures the temperature in the expansion tank
reaches the set point temperature fairly quickly. The temperature in the column does not
reach the set point temperature quickly. It may take 15 to 20 minutes to reach steady state
temperatures. The column temperatures can be monitored using the software diagram
screen on the computer or you can set up the computer software for data logging to
collect temperature data for a period of time. See the instructions for setting up the
software data logging program below.
12. When the temperatures within the column are at steady state, again switch valves, V3 and
V4 (V3 ↑and V4 ↓) to divert the stream to the bypass. You may have to adjust the back
pressure to 0.8-0.9 bar.
13. Open the small valve on the CO2 regulator discharge line. Adjust the flow of CO2 using
the needle valve, V2, to 0.15 SLPM (5% of the helium flow). The flow can be monitored
on the computer software diagram screen.
14. Adjust the flow of gas to the IR detector to a value of 0.5 SLPM with valve, V6. You
may have to readjust the He flow with valve, V1, and the back pressure to 0.8-0.9 bar
using valve, V5.
15. Start the software data logger (see below for directions on setting up the software for data
logging) to monitor the thermocouple temperatures, gas flows and the CO2 concentration
in the effluent gas stream. Note the percentage of CO2 when it reaches a maximum. This
is the maximum you should see when column breakthrough occurs.
16. Divert the flow mixture to the column by simultaneously switching valves, V3 and V4,
(V3 ↓ and V4 ↑). Note in the Notes section on the data logger table when you
switched the gas streams to the column. You will have to make small adjustments to
the helium flow using valve, V1 (3.0 SLPM), the CO2 flow using valve, V2 (0.15
SLPM), the back pressure to 0.8-0.9 bar using valve,V5, and the gas flow to the IR
analyzer using valve, V6 (0.5 SLPM).
17. Periodically check and adjust if necessary the flows during adsorption and desorption.
18. Wait until the CO2 concentration reaches its maximum concentration (the value you
noted in instruction 15) and the temperature inside the bed is uniform. At this point the
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bed is completely saturated with CO2 and the gas and adsorbed phases are in equilibrium.
This indicates breakthrough has occurred. Let the gases continue flowing through the
column for another five minutes.
19. After breakthrough has occurred you will start the desorption process. Stop the flow of
CO2, by closing valve, V2, so only helium is flowing through the system. Note in the
Notes section on the data logger table the time you stopped CO2 flow to the column. 20. When the IR reading is at zero % the desorption process is complete. Note in the Notes
section on the data logger table the time when it reached zero. At the flow rates given
above the desorption process will take about 30 minutes. Let the desorption process
continue for another five minutes.
21. Stop the data logging and save the data.
22. You might want to see what happens at 35C, 40C and 45C and at smaller percentages of
CO2 gas flow.
23. If you are not going to run any more trials for the day.
24. Make sure that you have desorbed the CO2 gas from the system before you quit for the
day. Plan for enough time before the end of the lab period to do this. Otherwise the next
group will have a problem and will have to desorb the CO2 before they can begin their
experiments. The next group does not know what has been done. In the past there has
been desorption and adsorption occurring at the same time on the first run of the lab
period. You do not want this done to you so you should not do it to someone else.
25. Shut off the flow of Helium at valve, V1.
26. Shut off the hot water circulation system, pump and heater.
27. Shut off the helium and carbon dioxide main tank gas valves before the regulator. Leave
the regulator settings as they are. Open the small shut off valves after the regulator if you
had shut them off. In order to remove the gas from the regulator and the gas lines open
the three-way valves to the vent position so they can vent the compressed gas to the
atmosphere without dumping the gas onto the column. These valves are located after the
small shut off valves
SOFTWARE DATA LOGGING INSTUCTIONS
1. After the computer has booted up and you have logged into the student account, entered
the Password - student, then click on the Fixed Bed Adsorption Icon on the desktop to
open the data logging software.
2. Click on View and on the drop down menu click on Diagram or click on the diagram icon
on the second line. A diagram of the data sensors appears and the actual values are
displayed on the diagram.
3. If you click on View and on the drop down menu click on Table or click on the table icon
on the second line a table appears. If you then click on GO on the second line data
acquisition will start and be placed in the Table.
4. The software should be set up to collect data every 10 seconds continuously.
5. To check if this is correct click on sample, then click on Configure on the drop down
menu to access the configure menu. (You can also access the configure menu by clicking
on the wrench icon on the second menu line).
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6. On the configure menu window the Sampling Operation should be set to Automatic.
7. On the configure menu window the Automatic Sampling Parameters should be set to the
following: Sample Interval = 10 seconds; Duration of Sampling = Continuous (When set
to continuous use GO to start sampling and STOP to stop sampling). You can set it for a
Fixed Duration if you know how long the experiment will take (Click GO to start and it
will stop after the time period has elapsed).
8. After you have collected the data for a run save the data.
9. Create a folder on the desktop for your data.
10. Save the file in your folder with a name that explains the data. It can be saved as an
Excel 5.0 file or a *.vts (formula one 3.x file). The *.vts file can be imported into Excel.
It will normally be easier to save it as an Excel 5.0 file.
11. To collect data for another run click on Sample and on the drop down menu click on Next
Results to get a new table or click on the Table/File icon to the right of the Go Icon.
12. All the runs since you opened the Fixed Bed Adsorption data logging software are
available for viewing by clicking on the RUN No Tab on the bottom of the
spreadsheet/Table.
SAFETY NOTES
1. Safety glasses/goggles should be worn at all times.
2. Water is used in this experiment. Wipe up any spills.
3. Check the safety requirements you need to be aware of when using high pressure gas
cylinders
WASTE DISPOSAL PROCEDURES
There is no waste with this experiment.
05/2012
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SYSTEM DATA
Data about the Adsorption Column
Internal Diameter Di 0.045 m
External Diameter De 0.058 m
Useful Length L 0.25 m
Steel Density ρsteel 749 kg/m3
Standard Temperature Tst 273 K
Standard Pressure Tst 1 atm
Properties of the extrude NORIT RB2 activated carbon
Source Norit RB2
Form Extruded
Mean Dimensions
Length 3.86 mm
Diameter 1.83 mm
Surface Area 27.42 mm2/gm
Volume 10.13 mm3/gm
Equivalent Average Diameter 2.22 mm
Apparent Density 0.82 gm/cm3
Activated Carbon Mass (It depends on the user)
εp, Intraparticular Porosity 0.627
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