Abstract The experiment is based on pressure drop, the air flow
rate , the water flow rate and also the packed column. The pressure
drop is increased when the water flow rate and air flow rate is
increased. This experiment is to examine the air pressure drop
across the column as a function of air flow rate for different
water flow rates through the column. The graph of log pressure drop
against log of air flow rate is plotted. The graph of generalized
theoretical pressure drop correlation chart for random packing is
also plotted. Both of the graph have same principle where high flow
rate parameter is meant for high liquid flowand high pressure drop
while low flow rate parameter is meant for low liquid flow and low
pressure drop.
IntroductionAbsorption is a mass transfer process in which a
vapor solute A in a gas mixture is absorbed by means of a liquid in
which the solute more or less soluble. The gas mixture consists
mainly of an inert gas and the soluble. The liquid also is
primarily in the gas phase; that is, its vaporization into the gas
phase is relatively slight. A typical example is absorption of the
solute ammonia from an air-ammonia mixture by water. Subsequently,
the solute is recovered from the solution by distillation. In the
reverse process desorption or stripping, the same principle and
equations hold.Gas absorption is the unit operation in which one or
more soluble components of a gas mixture are dissolved in a liquid.
The gas phase or gas mixture is inert gas while the liquid phase is
immiscible in the gas phase. Therefore, the liquid phase will
vapourize very slightly in gas phase. Gas absorption(also known
asscrubbing) is an operation in which a gas mixture is contacted
with a liquid for the purpose ofpreferentially dissolving one or
more components of the gas mixture and to provide a solution of
them in the liquid. We can see that there is amass transferof the
component of the gasfrom the gas phase to the liquid phase. The
solute so transferred is said to be absorbed by the liquid.There
are 2 types of absorption processes which are physical
absorptionandchemical absorption, depending on whether there is
anychemical reactionbetween the solute and the solvent
(absorbent).When water and hydrocarbon oils are used as absorbents,
no significant chemical reactions occur between the absorbent and
the solute, and the process is commonly referred to asphysical
absorption.When aqueous sodium hydroxide (a strong base) is used as
the absorbent to dissolve an acid gas, absorption is accompanied by
a rapid and irreversible neutralization reaction in the liquid
phase and the process is referred to aschemical
absorptionorreactive absorption.More complex examples of chemical
absorption are processes for absorbing CO2and H2S with aqueous
solution of monoethanolamine (MEA), diethanolamine (DEA),
diethyleneglycol (DEG) or triethyleneglycol (TEG), where a
reversible chemical reaction takes place in the liquid phase.
Chemical reactions can increase the rate of absorption, increase
the absorption capacity of the solvent, increase selectivity to
preferentially dissolve only certain components of the gas, and
convert a hazardous chemical to a safe compound.
Aim1. To determine the pressure drop across the dry column as a
function of air flowrate.2. To examine the air pressure drop across
the column as a function of air flow rate for different water flow
rates through the column.
TheoryPacked columns are used for efficient gas-liquid contact
processes contact interface into the bulk of the liquid. The
driving force for absorption involves a concentration gradient
across the gas-liquid interface. Figure 1 provides a visual of the
gas-liquid contact interface. Packed columns are used for efficient
gas-liquid contact processes .It is used in processes like gas
absorption, desorption(stripping) , distillation etc. It mainly
consists of a cylindrical column filled with packings , liquid
inlet and distributor at the top, gas inlet at the bottom, liquid
and gas outlets at the bottom and top respectively. Column packings
can be of two types mainly: dumped and structured . A distributor
consists of several perforated pipes used for spreading the liquid
uniformly throughout the cross-section of column.
Figure 1: gas liquid interface
Loading:Amount of liquid accumulate in side packed column that
generate pressure drop.
loadingFigurer 2 : loading in side packed column
Flooding :Amount of the liquid flood in the top of column with
increasing pressure drop due to accumulation of liquid in side
packed column
flooding
Figure 3 :flooding in packed column
Pressure drop is the result of fluid friction between liquid
flow and the packings.
The graph above shows the relationship between pressure drop and
gas flow rate and fordry column, a straight line is plotted and wet
column three curvy lines are plotted. The three curves are parallel
to the straight line. The point where liquid holdup starts to
increase is the point where the slope starts to change. This point
is known as the loadingpoint. Whenthe gas flowrate is
furtherincreased, pressure droprises tremendouslyuntilthe lines
plotted are almost vertical and at this point, liquid is of
continuous
phase.Thispointisknownasthefloodingpointandhappenswhenliquidaccumulatesduetohighgas
flow rate and this accumulation continues until the packed column
is completely filled with liquid.
Material and apparatus
1. Solteq-QVF absorption column (model: BP 751-B)Procedure1. All
valves is ensured are closed except the ventilation valve V13.2.
All the gas connection is checked properly fitted.3. The power for
control panel is on.4. The receiving vessel B2 is filled through
the charge port with 50 L of water by opening valve V3 and V5.5.
Valve V3 is closed.6. Valve V10 and V9 is opened slightly. The flow
of water from vessel B1 through pump P1 is observed.7. Pump P1 is
switch on, valve V11 is open and adjusted slowly to give a water
flow rate of around 1L/min. The water is allowed to enter the top
of the column K1, flow down the column and accumulate at the bottom
until it overflows back into vessel B1.8. Valve V11 is adjusted and
open to give a water flow rate of 1L/min into the column K1.9.
Valve V1 is open and adjusted to give an air flow rate of 20L/min
into column K1.10. The pressure drop is recorded .11. Step 9 is
repeated with the different values of air flow rate, each time
increasing by 20 L/min while maintaining the same flow rate.12.
Step 8 to 9 is repeated with different values of water flow rate,
each time increasing by 1L/min by adjusting valve V11.
Result
Flow rate(L/min)Pressure drop (mm H20)
Air
water20406080100120140160180
101248142851-
20135101773--
3048164858---
Table 1: Flow rate and pressure drop
Flow rate(L/min)Pressure drop (mm H20)
Air
water1.31.61.81.92.02.12.152.22.3
1000.30.60.91.11.41.7-
2000.50.711.21.9--
300.60.91.21.71.8---
Table 2: Log air flow rate and Log pressure drop
CalculationData: Density of air = 1.175 kg/m3density of water =
996 kg/m3Column diameter =80 mmArea of packed column diameter =
0.005027m2Packing Factor = 900 m-1Water viscosity = 0.001Ns/m2
Theoretical flooding point:GG, gas flow rate (kg/m2s)GG = =
=0.0779kg/m2sCapacity parameter, y-axisy-axis = = = 0.0154GL,
liquid flow rate per unit column cross-sectional areaGL = ==3.3002
kg/m2sFlow parameter, x-axisx-axis = = = 1.4551Water flow
rate(L/min)GL (kg/m2s)
1.03.3002
2.06.6004
3.09.9006
Air flow rate(L/min)GG(kg/m2s)Capacity parameter(y-axis)Flow
parameter (x-axis)
1 LPM2 LPM3 LPM
200.07790.01541.45512.91024.3653
400.15570.06140.72801.45602.1840
600.23360.13830.48520.97051.4557
800.31150.24590.36390.72781.0917
1000.38930.38410.29120.58230.8735
1200.46720.55320.24280.48520.7279
1400.62290.75310.20790.41590.6238
1600.62290.98320.18200.36390.5459
DiscussionIn this experiment, we are going to determine the
pressure drop across the dry column as a function of air flow rate
and the air pressure drop across the column as a function of air
flow rate for different flow rates through the column. These two
objectives are achieved by using the same apparatus but different
method. The experiment is bases on the flow rate of liquid and gas
in the packed.Firstly, the water flow rate is kept constant to
1L/min and air flow rate reading is recorded when achieved 1
minute. The air flow rate is kept rising constantly by 20 L/min by
each minute. All reading of pressure drop is recorded until
flooding point is reached. The pressure drop for flow rate of air
are 1, 2, 4, 8 , 14, 28 and 51 mm H20 consequently to 20, 40, 60,
80, 100, 120, 140, and 160 L/min. It cannot reach 180 of air flow
rate, which the water will sprayed out from the column due to the
high flow rate.The the flow rate is adjusted to 2L/min, by using
the same step as recording the 1L/min. the data recorded are 0, 1,
3, 5, 10, 17 and 73 mm H20 consequently to 20, 40, 60, 80, 100,
120, and 140 L/min. Whereby, for flow rate of water 3L/min is 0, 4,
8, 16, 48 and 58 consequently to 20, 40, 60, 80, 100, and 120.With
these data record, the graph of log of pressure drop against the
log of air flow rate is plotted. From the graph plotted, all the
log pressure drop is directly proportional log gas flow rate. We
can conclude that the higher the log of gas flow rate the higher
the log of pressure drop. But the higher the water flow rate, the
lower the log gas flow rate.For correlated value of the pressure
drop is calculated and the graph of capacity parameter against flow
rate parameter is plotted. The capacity parameter is indirectly
proportional to flow rate parameter. Two of the graph is different
as one is directly proportional while the other one is indirectly
proportional.
ConclusionIn conclusion, the aim of experiment which is to
determine the pressure drop across the column as a function of air
flow rate for different water flow rate through the column is
achieved. They are some errors made when the experiment is being
conducted resulting in a slight in accuracy of the experimental
chart plotted.
RecommendationWhen conducting this experiment, there are several
recommendations that will produce better observation which will not
differ much from the theoretical observations.Firstly, safety is
very important when doing experiment. Thus, we need to wear
laboratory coat, helmet and fully cover shoes to avoid any danger
for safety precaution. Titration must take place in fume chamber
and must be stop when the solution turns to light pink. Next, when
taking the reading of volume of sodium hydroxide solution, make
sure that eyes is directly perpendicular with the level of sodium
hydroxide solution inside the burrette to avoid any parallax error.
Before conducting the experiment, we must ensure that all the
apparatus are in good condition and follow all the procedures in
order to get more accurate result.
ReferenceI.
http://en.wikipedia.org/wiki/Liquid%E2%80%93liquid_extractionII.
http://www.academia.edu/3641270/Liquid-Liquid_Extraction_Basic_PrinciplesIII.
http://www.chem.ualberta.ca/~orglabs/Interactive%20Tutorials/separation/Theory/theory1_1.htmIV.
http://courses.chem.psu.edu/chem36/Experiments/PDF's_for_techniques/Liquid_Liquid.pdfV.
Lab Manual