Distillation Column Troy Hall November 14, 2002 1 November 14, 2002 Troy Hall Red - Yellow Team: Distillation Column College Of Engineering and Computer Science University of Tennessee at Chattanooga 615 McCallie Avenue Chattanooga, TN. 34705 To: Dr. Jim Henry, P.E. Professor of Engineering University of Tennessee at Chattanooga 615 McCallie Avenue Chattanooga, TN. 34705 Dr. Henry: The following report is describing the continuous distillation for constant reflux of 95% but different wattage added to reboiler in the distillation column. This report details the objectives, theory, procedure, equipment analysis, findings, and conclusions obtained. Troy Hall Red – Yellow Team Senior Undergraduate Student Chemical Engineering University of Tennessee at Chattanooga
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Distillation Column
Troy Hall November 14, 2002 1
November 14, 2002
Troy HallRed - Yellow Team: Distillation ColumnCollege Of Engineering and Computer ScienceUniversity of Tennessee at Chattanooga615 McCallie AvenueChattanooga, TN. 34705
To: Dr. Jim Henry, P.E. Professor of Engineering University of Tennessee at Chattanooga 615 McCallie Avenue Chattanooga, TN. 34705
Dr. Henry:
The following report is describing the continuous distillation for constant reflux of 95%but different wattage added to reboiler in the distillation column. This report details theobjectives, theory, procedure, equipment analysis, findings, and conclusions obtained.
Troy HallRed – Yellow TeamSenior Undergraduate StudentChemical EngineeringUniversity of Tennessee at Chattanooga
Distillation Column
Troy Hall November 14, 2002 2
Distillation Column Experiments, Continuous DistillationUniversity of Tennessee at Chattanooga
College of Engineering and Computer ScienceEngineering 435 Chemical Process Laboratory
Author: Troy HallTeam Members: John Mayes
Sidney SpencerAnthony PaolucciTo: Dr. Jim Henry
Cc: Dr. Frank Jones
Distillation Column
Troy Hall November 14, 2002 3
Abstract:
The distillation column at the University of Tennessee at Chattanooga was part of a
study for a continuous distillation with constant reflux of 95% using a binary mixture of
methanol and water. The continuous distillation with constant reflux of 95% but different
wattage added to reboiler in the distillation column. The data was collected from the
continuous distillation at different wattages supplied to the reboiler and the average
temperature was found for the top tray when the system had reached steady state. Perry’s
Handbook for Chemical Engineering provided an X, Y vs. T diagram of methanol and
water. By using the average temperature of the top tray the distillate composition was
found from the graph.
The composition of the column trays was calculated. An energy balance on the condenser
and reboiler was performed. A material balance was performed on the different wattages
being added to the reboiler.
Distillation Column
Troy Hall November 14, 2002 4
Table of Contents: Page
I Introduction………………………………………………………………………5
II Theory………………………………………………………………………...…6
III Equipment……………………………………………………..…………...…10
IV Operation Procedure…………………………………………………………..17
V Experimental Procedure………………………………………………………..19
VI Results………………………………………………………………………...21
VII Discussion of Results…………………………………………………………
VIII Recommendations……………………………………………………………
IX References………………………………………………………………………
X Appendices……………………………………………………………………….
Distillation Column
Troy Hall November 14, 2002 5
Section I -Introduction:
The purpose of this study of the distillation column by the Red – Yellow Team was to
study the continuous distillation for constant reflux but different wattage added to
reboiler in the distillation column. This process was conducted on the system at steady
state conditions.
The University’s distillation column was used to perform this investigation. The
distillation column consists of a liquid storage tank with cal rod for a heating element
called the reboiler, 12 distillation trays aligned in a vertical column. The trays serve to
allow the liquid and vapor phases to come in contact and into equilibrium with each
other. The vapor that is produced from the heating of the liquid in the reboiler is
condensed by cooling water that is located inside the condenser at the top of the
distillation column. This vapor is known as reflux and is collected. The collected reflux is
returned to the reboiler.
A theoretical background describing the distillation column and process is contained
in this report. Equipment section will describe the distillation column. Procedure will
describe the procedure used in the investigation on the system. Results will provide the
data that was recorded. The discussion of the results will follow with recommendations
for future experiments. References and Appendices will conclude this report.
Distillation Column
Troy Hall November 14, 2002 6
Section II-Theory:
Distillation is a process used to separate the substances composing a mixture. It
involves a change of state, as of liquid to gas, and subsequent condensation A simple
distillation apparatus consists essentially of three parts; a flask equipped with a
thermometer and with an outlet tube from which the vapor is emitted; a condenser that
consists of two tubes of different diameters placed one within the other and arranged so
that the smaller tube (in which the vapor is condensed) is held in a stream of coolant in
the larger tube; and last a vessel in which the condensed vapor is collected. The mixture
of substances is placed in the flask and heated. Ideally, the substance with the lowest
boiling point vaporizes first with the temperature remaining constant until that substance
has completely distilled. The vapor is led into the condenser where, on being cooled, it
reverts to the liquid and runs off into a receiving vessel. The product so obtained is
known as the distillate. Those substances having a higher boiling point remain in the
flask and constitute the residue.
With fractional distillation the substance with the lowest boiling point has been
removed, the temperature can be raised and the distillation process repeated with the
substance having the next lowest boiling point. The process of obtaining portions (or
fractions) in this way is one type of fractional distillation. A more efficient method of
fractional distillation involves placing a vertical tube called a fractionating column
between the flask and the condenser. The column is filled with many objects on which
the vapor can repeatedly condense and re-evaporated as it moves toward the top,
effectively distilling the vapor many times. The less volatile substances in the vapor tend
to run back down the column after they condense, concentrating themselves near the
bottom. The more volatile ones tend to re-evaporate and keep moving upward,
concentrating themselves near the top. Because of this the column can be tapped at
various levels to draw off different fractions. Fractional distillation is commonly used in
refining petroleum, some of the fractions thus obtained being gasoline, benzene,
kerosene, fuel oils, lubricating oils, and paraffin.
Distillation Column
Troy Hall November 14, 2002 7
The distillation column at the University of Tennessee at Chattanooga was used to
separate a non-ideal mixture of methanol and water. This is known as a binary system
since it contains only two components.
A vapor - liquid equilibrium diagram, figure 1,was created from tabulated data in
Perry’s Handbook for methanol and water mixture. The diagram was used to determine
the composition of each tray.
Figure 1 represents a diagram of the vapor – liquid equilibrium for methanol and water.
The letter A represents the Dew Point on the liquid equilibrium line and the letter B
represents the Bubble Point on the vapor equilibrium line. In this example a temperature
of 78.0 °C is reached giving a dew point mol fraction of 0.30 for the light composition
methanol. The bubble point mol fraction is 0.67 of methanol.
A constant reflux of 95% was used in the first four experiments and the last
experiment the reflux ratio was switched to 66%The distillate is the product from the top
of the distillate column. At 95% reflux the product is collected in the condenser and the
remaining 5 % of the mixture being distilled. The remaining 95 % is returned to the
distillation column for further distillation. The successive distillation improves the purity
of the product. Therefore, the higher the reflux percentage, the greater amount of liquid is
sent back to the column for further separation.
Vapor Equilibrium line
Liquid Equilibrium Line
AB
Perry's Data for Methanol-Water
60.0
65.0
70.0
75.0
80.0
85.0
90.0
95.0
100.0
0.0 0.2 0.4 0.6 0.8 1.0
x,y
Tem
per
atu
re, o
C
Distillation Column
Troy Hall November 14, 2002 8
The university distillation column contains a rectifying and a stripping section. The
rectifying section is above where the feed is introduced. The stripping section is below
where the feed is introduced.
Energy balance
At steady state the energy added to the distillation column is equal to the energy
removed from the column minus the heat loss to the surrounding environment. Equation
1 was used to find the overall heat loss.
Q reboiler= Q condenser + Q loss (1)
Q reboiler is the energy added to the reboiler, Q condenser is the energy removed from the
condenser, and Q loss is the energy loss by the distillation column to the surrounding
environment.
Q is defined in Equation 2 as:
Q= m Cp ∆T (2)
The above equation was used to perform the energy balance. Q is the energy, in watts,
removed by the condenser. The m is the mass flow rate of cold water entering the
condenser. Cp is the heat capacity of water. ∆T equals the Tout minus Tin and is in °
Celsius.
Material balance
Over all balance was achieved with the following formula.
F=B+D (3)
F is the feed rate entering, B is from the reboiler and D is the distillate.
A balance was performed on the condenser. The following equation was used for the
condenser balance.
RD = L/D (4)
Distillation Column
Troy Hall November 14, 2002 9
RD is the reflux ratio, L is the liquid in the condenser, and D is the distillate.
A balance was also performed on the feed tray. The following equations were used
during the feed tray balance.
L’ L+(1-Xf) F (5)
V’ = V-Xf*F (6)
L is the liquid on solute free bases, L is the liquid in the condenser, Xf is the mole
fraction of methanol in the feed, and F is the feed rate. V’ is the vapor on solute free
bases, V is the vapor in the feed, Xf is the mole fraction of methanol in the feed, and F is
the feed rate.
Distillation Column
Troy Hall November 14, 2002 10
Section III-Equipment:
The distillation column is approximately 15 feet tall and a diameter of 0.5 feet. The
Figure 13 shows the chart that was created from the data supplied from Perry’s Handbook
for Chemical Engineering.
60.0
65.0
70.0
75.0
80.0
85.0
90.0
95.0
100.0
0.000 0.200 0.400 0.600 0.800 1.000
x,y (mol fraction)
Temperature °C
98 mole Percent Methanol
Bubble Point
Liquid
Vapor
Distillation Column
Troy Hall November 14, 2002 28
Figure 14 shows the graph of the methanol composition in the liquid tray. Thesecalculations were performed once the continuous distillation reached steady state. Figure15 illustrates the difference in the liquid composition for the continuous distillation butwith different watts added to the reboiler.
Continuous distillation with Variable Wattage
0
0.5
1
0 5 10
Tray
Mole Fraction Methanol
2250, 2500, 2700,3000 watts @ 95%
3000 watts@ 66%
Distillation Column
Troy Hall November 14, 2002 29
Energy balance
Table 2 shows the energy balance that was performed on the condenser. Reflux and
wattage settings are represented under the continuous distillation column. Cws is the sold
water source and cwr is the cold-water return. Diff t is the difference in the temperature
of the cold-water source and cold water return. Cwf is the cold-water flow is in liters per
minute. A correction factor of 2.8 was need because lab view displays the wrong flow
rate for the system.
ContinuousDistillationReflux % CWS (K) CWR (K) Diff T CWF (L/min) Corr factor Watts absorbed by condenser
Table 4 shows the results of the material balance perfomed on the distillation column.
Watts added Refux Ratio F D B L V L' RD Xf XD XB2250 95% 4 0.53 3.47 10.1 10.62 14.09 19 0.15 1 0.022500 95% 4 0.53 3.5 9.5 10 13.5 19 0.14 0.98 0.022750 95% 4 0.34 3.66 6.4 6.74 10.4 19 0.09 0.96 0.013000 95% 4 0.25 3.75 4.75 5 8.75 19 0.09 0.97 0.013000 66% 4 0.23 3.77 0.45 0.69 4.45 1.94 0.02 0.3 0.003
In the table above F is the feed, D is the distillate, B is the bottom of the column, is the
liquid, L’ is the liquid on solute bases, V is the vapor, RD is the reflux ratio, Xf is the
mole fraction of feed in the feed system, XD is the mole fraction of methanol in the
distillate, and XB is composition at the bottom of the column.
Distillation Column
Troy Hall November 14, 2002 31
Discussion of Results:
The composition of each tray from temperature calculations was shown in Figure 14.
The highest methanol percent was found in tray 1 which was consistent with our theory.
Tray 2 through 12 showed subsequently lower mole fraction of methanol.
Using a constant reflux ratio of 95% and various watts added to the reboiler, it was
shown that the mole fraction of methanol was close to the same in the distillation trays.
The 66% reflux ratio showed a lower mole fraction of methanol in the trays in the
rectifying section of the column. The stripping section of the column showed a more
consistent mole fraction of methanol with either 66% or 95% reflux ratio. This was not at
all what I expected to find when making conclusions about the column.
The material balance showed that the column composition at the bottom of the column is
correct.
The energy balanced showed that as more watts added to the reboiler the Qloss to the
system increased
Distillation Column
Troy Hall November 14, 2002 32
Conclusions:
The methanol concentration in the trays decreases as you move from tray 1 to tray 12.
As the feed is entered in to the column the stripping portion of the column the methanol
is less than it is in the rectifying section.
More energy is loss to the environment around the reboiler as the watts is increased to the
reboiler.
Recommendations:
It would be interesting to see how the column would perform under a different separation
of a binary mixture. Acetone and water or some other compound.
Distillation Column
Troy Hall November 14, 2002 33
References:
Unit Operations of Chemical Engineering, 6th Ed., Warren L McCabe, Julian C. Smith
and Peter Harriott, McGraw-Hill, Boston, 2001.
Cunningham, James R. Dr. Lecture Notes Fall 2002 for ENCH 432 at the University of
Tennessee at Chattanooga.
UTC Engineering Controls Lab Online. University of Tennessee at Chattanooga.
http://distillation.engr.utc.edu/data.htm
Engineering 536 Mass Transfer Operations. University of Tennessee at Chattanooga
http://chem.engr.utc.edu/webres/536f/FINALRPT.htm
Perry, Robert H. and Don W. Green. Perry’s Chemical Engineers Handbook, 7th Edition,
June 1, 1997. McGraw-Hill Professional
Engineering 435 Distillation Column Maintenance. University of Tennessee at
Chattanooga September 24, 2002.
Distillation Column
Troy Hall November 14, 2002 34
Appendices:
Figure 7 shows the tray temperature for 2250 watts added to the reboiler.
Trays Temperature Chart (2250)
606570758085
100 105 110 115 120 125 130
Time (min)
Temperature °C
Tray 1 Temperature Tray 2 Temperature Tray 3 Temperature Tray 4 TemperatureTray 5 Temperature Tray 6 Temperature Tray 7 Temperature Tray 8 Temperature
Tray 9 Temperature Tray 10 Temperature Tray 11 Temperature Tray 12 Temperature
Distillation Column
Troy Hall November 14, 2002 35
Figure 8 shows the tray temperature for 2500 watts added to the reboiler.
Tray Temps 2500 W
65
66
67
68
69
70
50 100 150 200
Time (min)
Temp. ° C
Tray 1 Temperature Tray 2 Temperature Tray 3 Temperature Tray 4 Temperature
Tray 5 Temperature Tray 6 Temperature Tray 7 Temperature Tray 8 Temperature
Tray 9 Temperature Tray 10 Temperature Tray 11 Temperature Tray 12 Temperature
Distillation Column
Troy Hall November 14, 2002 36
Figure 9 shows the tray temperature for 2750 watts added to the reboiler
Tray Temps 2750 W
65
66
67
68
69
70
50 100 150 200Time
Temperature ° C
Tray 1 Temperature Tray 2 Temperature Tray 3 TemperatureTray 4 Temperature Tray 5 Temperature Tray 6 TemperatureTray 7 Temperature Tray 8 Temperature Tray 9 TemperatureTray 10 Temperature Tray 11 Temperature Tray 12 Temperature
Figure 10 shows the tray temperature for 3000 watts added to the reboiler
Tray Temp. 3000 watts
60708090
100110
50 70 90 110
Time (min)
Temperature °C
Tray 1 Temperature Tray 2 Temperature Tray 3 Temperature Tray 4 Temperature
Tray 5 Temperature Tray 6 Temperature Tray 7 Temperature Tray 8 Temperature
Tray 9 Temperature Tray 10 Temperature Tray 11 Temperature Tray 12 Temperature