ABSTRACT
The experiment is conducted to investigate the air pressure drop in an absorption column as a function of the air flow for varying water flow rates and to determine the flooding characteristics of the column at different water and gas flow rates. In this experiment, the model that was used is (BP7!"B #bsorption $olumn% which is intended to ma&e students familiar with the basis of wor&in wor&ing g princi principle ple of gas absorp absorptio tion n by mean mean li'uid li'uidss (solv (solvent ent absorp absorpti tion% on%.. This This absorp absorptio tion n column consists of receiving vessels, circulation pump and more. The e'uipment is usually used to conduct experiments on gas absorption of carbon dioxide into water. ifferent values of air flow rate and water flow rate will be used by regulating the valves, and finally, the pressure drop across across the column column will be record recorded. ed. )rom )rom the experim experiment ent data, it can be seen seen that that as the air flowrate increases with constant water flowrate the more the pressure will drop. It too& !*+ -min air to achieve flooding point when the water flowrate used is !. -min. /eanwhile for . -min and run 0 for 0. -min, the flooding point decreases at air flowrate of !+ and !++ -min respectively. )rom the experiment, it can be concluded that each water flowrate has its own flooding point. This is because as the water flowrate increases, the lower the flooding point in the gas absorption column. The flooding point is important to be determined so that the process could be operated efficiently because the process will be no longer feasible even before it reaches the flooding point. This experiment was done successfully.
1
1.1
INTRODUCTION
Pac&ed columns are efficient e'uipment used for contact processes between gases and li'uids. It consists of a column filled with pac&ing material that is either dumped or organi1ed. Pac&ing materials are considered based on their surface to volume ratio, good wettability, and sufficient stability among others. The li'uid enters from the inlet located above the column and exits at the bottom while gasses enter from the inlet located at the bottom and exits through the top. The contact between the two phases are aided by the pac&ing material. The pressure inside a column is high at the bottom and decreases with height of column to allow gas flow to the top. 2ith increasing gas flow the pressure drop will also increase until some li'uid will retain inside the pac&ing. This phenomenon is called the loading point. )looding is the term used when pressure drop rises drastically and the li'uid starts accumulating from the bottom of the column. The gas velocity at this point is called the flooding velocity. In the industry pac&ed columns are operated well below the flooding velocity. This is to ensure the pac&ings and e'uipment are not damaged.
1.2
OBJECTIVES
To investigate the air pressure drop in an absorption column as a function of the air flow for varying water flow rates. To determine the flooding characteristics of the column at different water and gas flow rates.
1.3
THEORY
2hen a $3"air mixture flows up a pac&ed column, it comes into contact with the water flowing down. #s the air flow rate increases, the resistance against water flowing down will also increase.
2
)igure !.! 4 Pac&ed $olumn
If the air flow rate is high enough, it will cause the li'uid to start accumulating inside the pac&ing material.This is called the loading point. If the gas flow continues to increase, the whole column
1.4
will
be
filled
with
water
and
this
is
called
flooding.
APPARATUS AND CHEMICALS
5'uipment (BP7!"B #bsorption $olumn% !
#bsorption $olumn (6!%
eceiving 8essels (B!, B%
0
$irculation Pump (P!%
9
Basic Instrumentations and $ontrol
)ramewor& (stainless steel tubes and clamps%
3
/aterials !
2ater (laboratory mains supply%
$ompressed air (laboratory mains supply%
0
:as ($3 gas supply%
1.5
PROCEDURE
general start up procedure
use different values of air flow rate and water flow rate
record the pressure drop across the column
)igure !. 4 /ethodology of ;ydrodynamics Pac&ed $olumn (2et $olumn Pressure rop% !
The general start"up procedure is performed. The receiving vessel B is filed with + of water through the charge port by opening
0 9
vessel 80 and 8. The valve 80 and 8 is opened. The valve 80 is closed. The valves 8!+ #< 8= are opened slightly. The flow from the vessel B! is observed
>
through pump P!. The pump P! is switched on and the valve 8!! is slowly opened and ad?usted in order to give the water flow rate around !. -min. The water is allowed to enter the top of the column 6!, flowed down the column and accumulated at the bottom until it overflows
bac& into vessel B!. 7 The valve 8!! is opened and ad?usted to give a water flow rate of !. -min into the *
column 6!. The valve 8! is opened and ad?usted to give an air flow rate of 9+ -min into column 6!.
4
=
The li'uid and gas flow in the column 6! is observed in the column 6! and the pressure
drop across the column at dPT"+!. !+ @teps > to 7 are repeated with different values of air flow rate, each time increasing by 9+ -min while maintaining the same water flow rate. !! @teps to * are repeated with different values of water flow rate, each time increasing by !.+ -min by ad?usting the valve 8!!.
1.6
RESULTS
)lowrat e (-min% #ir 2ater + !. . 0.
Pressure rop (mm;3%
+
9+
>+
*+
!++
!+
!9+
!>+
!*+
!= 0 0
! 0=
= 99
= 09 >!
00 9 7=
07 >*
99
9=
*0
Table !.! 4 Pressure rop for 2et $olumn
Pressure Drop vs Air Flow Rate 100 80 60
Pressure Drop (mbar)
40 20 0 0
20 40 60 80 100120140160180200
Air Flow Rate (L/min)
)igure ! 4 Pressure rop vs #ir )low ate 1.7
CALCULATIONS 5
SAMPLE CALCULATION
ata ensity of air A !.!7 &g-m0 ensity of water A ==> &g-m0 $olumn diameter A *+ mm #rea of pac&ed column diameter A +.+++7 m Pac&ing )actor A =++ m 2ater viscosity A +.++!
Theoe!"#$% &%oo'"() Po"(! *
::, gas flow rate (&g-m s% :: A :y p-# 20 L
A
min
x
1 min 60 sec
x
1.175 kg
m
3
x
1m
3
1000 L
0.005027
A+.+77= &g-m s
6
C$+$#"!, +$$-e!e ,/$0"
13.1
μ L
0.1
( GG ) F P ( P ) 2
L
PG ( P L − P G)
(
13.1 0.0779
)
2
900
(
(
0.001 996
0.1
) =0.01542
−1.175 )
1.175 996
L %""' %o$!e +e ("! #o%-( #o/e#!"o($% $e$
G L X P A
1.2 L
min
x
1 min 60 sec
x
1.175 kg 3
m
x
1m
3
1000 L
0.005027
A 9.>79* x !+"0 &g-m
&%o +$$-e!e 0/$0"
ρG ρ L
x"axis A
√ ¿
G L GG
¿
7
: (&g-ms% 9.>79* x !+"0 *.7+9 x !+"0 +.+!97
2ater )low ate (-min% !. . 0.
#ir )low ate (-min% + 9+ >+ *+ !++ !+ !9+ !>+ !*+
#ir )low ate (-min% + 9+ >+ *+ !++ !+ !9+ !>+ !*+
:: (&g-ms% +.+77= +.!* +.007 +.0!!7 +.0*=> +.9>7 +.99 +.>00 +.7+!
$apacity Parameter (y"axis% +.+!0* +.+>! +.!0*90 +.9> +.0*97 +.0=9 +.70=0 +.=*9>= !.9>!=
)low Parameter (x"axis% !.+0+> x !+"0 >.*7+> x !+"9 .!!0 x !+"9 9.!!0 x !+"9 0.909> x !+"9 .=99+ x !+"9 .7>! x !+"9 .*== x !+"9
!.**=9 x !+"0 !.=> x !+"0 =.999+ x !+"9 7.> x !+"9 >.=>> x !+"9 .0=70 x !+"9 9.77 x !+"9 9.!=*+ x !+"9
.79=! x !+"0 !.*07 x !+"0 !.079! x !+"0 !.+==9 x !+"0 =.!>!> x !+"9 7.*0! x !+"9 >.*7!> x !+"9 >.!+* x !+"9
8
1.
DISCUSSION
The main ob?ective in this experiment is to investigate the pressure drop across the absorption column by ad?usting the air flow with constant water flow rate. )irstly, water is pumped up onto the absorption column. The water will flow down the pac&et filled column into the receiving tan&. * and 7= mm; 3 according to the run respectively. This shows that each water flowrate has its own flooding point. #s the water flowrate increases, the lower the flooding point in the gas absorption column. This phenomenon can be understand easily, for instance, people can easily lift up a light weightbar but if the weightbar is heavy it will become difficult for a person to lift it and too& more energy to lift it. In this case the weightbar can represent water flowrate, the person as airflowrate and the CenergyD as pressure drop. 2hich means at low airflowrate the pressure drop is too low to lift up the water that flows down and at high flowrate the pressure drop is high enough to lift up the water and eventually if airflowrate is increased, the water will be blown up. The experiment shows that, the gas absorption cannot be done at high pressure drop and high gas flowrate. 5ven before reaching flooding point the process is no longer feasible. )or 9
example at run ! of experiment at air flowrate of !9+ -min, accumulation of water or pools can be seen at - of the column height. #s it goes up to !>+ -min the pools already reaches at about 0.- of column height and eventually at !*+ -min the pools already at about 9.- of the column height. The same pattern also shown for the last run albeit at lower air flowrate. The pool of water happened because the air hinders the li'uid downflow, as it hinders the li'uid the pressure drop increases. #t this point it is called the loading point. ;owever, only at flooding point the li'uid could no longer flow down through the pac&ing. #lthough, the li'uid still flows down at flooding point, it is still not wise to set it up as operating process. In reality, operating tower, the gas velocity and flowrate is below flooding point. The optimum economic gas velocity and flowrate is about half or more of flooding point (:ean&oplis, Transpot Processes E @eperation Processes Principles, +!9%.
1.8
CONCLUSION
:as li'uid contacting devices are used widely in the chemical industry for absorbing gases into li'uids and solvents. These devices varied from stirred vessels to pac&ed beds and bubble columns and are employed for a variety of different industrial applications. )rom this experiment, it can be concluded that as the air flowrate increases with constant water flowrate the more the pressure will drop. This can be proven from the data recorded, when the water flowrate was about !. -min, it too& !*+ -min air to achieve flooding point. #s for . -min and 0. -min, the flooding point decreases at air flowrate of !+ and !++ -min respectively. It also can be seen that the pressure drop was very large, *0, >* and 7= mm;3 respectively as the process reached its flooding point. The aim of this experimentF to study the air pressure drop in an absorption column as a function of the air flow for varying water flow rates and to determine the flooding characteristics of the column at different water and gas flow rates was successfully achieved.
10
1.19
RECOMMENDATION
The experiment is conducted to determine the air pressure drop across the column as a function of air flow rate for different water flow rates through the column. The experiment is highly recommended in improving the safety measures as fre'uently chec& and rectify any lea& that might be exist through the system. Besides that, all the operating instructions supplied must be clearly understood before performing the experiment. In terms of handling the ha1ardous chemicals in the system especially the carbon dioxide $3 which is flammable, the chemicals need to be ensure to operate under ventilated and atmospheric pressure wor&ing condition.
1.11
RE&ERENCES:APPENDICES
!.
/c$abe, ., @mith G.$. and ;arriot, P. (++!% Hnit 3perations of $hemical 5ngineering,
> th 5dition,
:ean&oplis, $.G. (++0%. Transport Processes and @eparation Process Principle, 9 th
5dition.
iitb.vlab.co.in,. (+!%. ;ydrodynamics of pac&ed column. etrieved 0 /arch +!>,
from iitb.vlab.co.in-KsubA*EbrchA!!>EsimA=+EcntA9
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