1. Experimental Data
⊙
Theoretical background
At steady state, the transfer of absorbing gas from the gas stream should equal
that transferred to the liquid.
Let: L1 and L0 be the volume flow of liquid entering and leaving the column
respectively.
Let: Gi and Go be the total gas molal flow entering and leaving the column
respectively.
Let: Yi and Yo be the mole fractions of CO2 entering and leaving the column in
the gas stream.
Amount of CO2 removed from the gas stream:
[Gi – Go(g.moles/sec)] as no air dissolved in the solution.
And, the amount of CO2 removed from the liquid stream equals the amout of
carbonate ions produced:
H2O+CO2--->H2CO3
Lo·CNo - Li·CNi
(g.moles/sec)
Above two equations are equals, and Go can be calculated from a molar balance on the air stream, none of
which is absorbed:
Go(1-Yo) = Gi(1-Yi)
G can be calculated from the fact that one gram mole occupies 22.42 L at 273K and 760mmHg pressure:
Carbon dioxide content of gas samples:
From use of Hempl apparatus, volume fraction of CO2 =
V2
V1
For ideal gases, volume fraction = mole fraction = Y. Check that the sample taken from the inlet to the absorption
column should give the same value of CO2 = fraction as that indicated by the inlet flow meters.
Calculation of amount of absorbed CO2 in column from analysis of samples at inlet and oulet.
From analysis with Hempl apparatus, volume fraction of CO2 in gas stream at inlet:
V
V
and at outlet, Y0 = ( 2)
( 2) = Yi
V1 i
V1 0
If Fa is liters/second of CO2 absorbed between top and bottom, then:
Note: Liters/second can be converted to gmoles/second as follows:
※The assumption implicitly made here is that the volume flow is not affected by the pressure drop through the
column as this drop should be small in comparison with atmospheric pressure.
⊙Experiment Processes
a.
Turn on the main water supply to fill the column with flowing water.
b.
Put caustic soda solution into measuring part of apparatus.
c.
Open the valves that flow control of water and gas flow, and carbon dioxide cylinder, and set the
flow rate approximately air
d.
After 5 minutes or so of steady operation, take samples of gas from the middle sample point.
e.
Operate valve suitable to put extracted water into prepared caustic soda, and measure the rise up
of volume from caustic soda + water, and calculate the absorption of carbon dioxide into water
flowing down the tower with above theoretical equation.
2. Results
•The setting value and measured volume are
Readings at inlet
F3 (CO2 )
6 L/s
Calculations
F2 (Air)
V1
V2
F3
F3 + F2
V2
( ) = Yi
V1 i
20 L/s
20ml
0.75ml
0.231
0.0375
From flow meters
From Hempl apparatus and
sample point S3
•The pressure (mmH2O) of column
Middle
Middle
395
280
After the extract the sample
The absorb of CaCO3 from the calculation:
Made H2O(V2) =0.75ml=0.75g=0.0417mol. But we don’t get the asorbed CO2 amount. Because lack
of the information that for Y0.
So I want to calculate in my way,
Inlet Gas
Amount of Gas ( ℓ / min )
Air
20
CO2
6
Total
26
In case of inlet gas, CO2 mole fraction, we assume that ideal gas then it is same with volume fraction.
Take the gas by piston
20 ㎖
CO2 amount in NaOH
0.75 ㎖
,
Inlet- Outlet = Absorption amount,
So we calculate absorption amount x. We assume that the CO2 only absorbed except air.
The x is
Absorption Ratio is
=5.227
That is 87.12%
3. Discussion
-There a little error in result, but ion exchange was almost end.
We can get the result of Ga (g.mol/sec) from measure of absorption of CO2 in outlet (middle sample)
flow, and relation with water flow rate (steady state).
But can’t use the equations of theoretical background and manual, because the equation supposed to
measure the absorption of CO2 in 2 points ; Top or bottom with middle point that we checked. So, I
thought that there was something wrong about processes. To use the equations and theory in manual,
we need measure 2 points in column.
4. Referneces
-UOP7 Manual – Issue 19_gas absorption column.pdf