Transcript No Slide Title

ENGINEERING 536
MASS TRANSFER
OPERATIONS
FALL 1997
TEAM MEMBERS:
Dr. Jim Henry, P.E.
Sean Cunningham
Mark Koss, P.E.
Sandy Koss
Tara Ostrander, E.I.
Nittaya Pittayataree
Beth Ruta
Nitipol Suksathaporn
Introduction
Study of mass transfer operations
using the distillation column
Approach to the study of the
distillation column included
- Literature search
- Operating the column
- Computer modeling
+ Ponchon-Savarit
+ PROII
This report will cover
- column calibrations
- experimental results
- computer modeling
DISTILLATION COLUMN
TI
Cooling Water Supply
Condenser
TI
TI
Cooling Water Return
Electromagnetic Reflux Control
TI
TI
TI
Product Cooler
1
2
3
LI
TI
TI
TI
TI
TI
TI
TI
TI
TI
Reboiler
TI
Distillate
Pump
4
5
TI
6
Feed Tank
7
(Product Tank)
Feed Pump
8
9
10
11
PI
12
LI
Reboiler Pump
COLUMN DESCRIPTIONS
Condenser
Reflux valve
Trays
RTDs
Pumps
-
Feed pump
Reboiler pump
Distillate pump
Auxiliary pump
Reboiler
Level Control
- Condenser
- Reboiler
FEED LOCATIONS
Column Calibrations
Heat loss study
RTD calibration
Pump and cooling water
calibration
Heat Loss Study
Previous heat loss calculations
seemed excessive
Parameters of the study are
- selected reboiler amperage
- 100% reflux
- no condensate produced
Column losses are equal to the
energy input into the column
Minimum amperage to maintain the
temperature on tray 1 is between 6
and 7 amps
Estimated column heat loss is
between 1230 Watts and 1435 Watts
Temperature of tray 1 at 7 amps
Temperature (C)
Reboiler Amps = 7
66.0
65.8
65.6
65.4
65.2
65.0
70
72
74
76
78
80
Time
Temperature of tray 1 at 6 amps
Temperature (C)
Reboiler Amps = 6
65.5
65.0
64.5
64.0
63.5
63.0
78
79
80
81
82
Time
83
84
85
RTD Calibration
Temperature is calculated by
multiplying the voltage by the
scale and then adding the offset
Steps to calibrate RTDs
- fill reboiler with pure
methanol
- allow steady state
- set offset to zero
- set scale to one
- collect voltage readings
- repeat with water
Voltage is taken at 100oC (pure
water) and 64.5oC (pure
methanol)
Straight line was fit between
the two points
Slope of the line is the scale
y intercept is the offset
Pump and Cooling Water
Calibration
Pump and cooling water
calibrations seem to be reliable
Pump calibration
- by measuring the outflow
of the pump for a timed
period
Cooling water calibration
- by measuring the flow at
the cooling water system
drain at various valve
openings
Pump Calibration Curve
Flowrate (ml/min)
Feed Pump Calibration Curve
600
500
400
300
200
100
0
2
F = -2.3996M + 98.326M - 81.102
2
R = 0.9942
0
Pump : 7017-21 Pattern No. 3.358.609
2
4
6
Pump S etting
8
10
Conclusions
(calibrations)
Pump and cooling water
calibrations seem to be reliable
Calibrations performed on the
glass RTDs were unsuccessful (
repeated several times)
Replacement of the glass RTDs
with stainless steel improved the
calibrations
- three RTDs do not give
reliable temperature
indication
Recommendation
(calibrations)
Perform calibrations
- after a period of inactivity
- whenever equipment is changed
or modified
Reduce time spent on
calibrations
- Calibrate the RTDs individually
with ice and boiling water
- UTC engineering/maintenance
personnel should complete
calibrations
Experimental Results
Energy and mass balance
Capacity test
Feed location impact
Reflux ratio impact
Energy and Mass
Balance
Excel spreadsheet was developed to
facilitate mass and energy
calculations
Calculations showed an increase in
water and a decrease in methanol
Column had not reached steadystate conditions
Flowrate (gms/min)
Mixture Methanol Water
Feed
321
315
12
Bottoms 205
168
12
Distillate 116
147
0
DISTILLATION COLUMN EXPERIMENT (10/15/97)
MASS BALANCE
Inputs
Reflux Ratio=
Distillate:
Pump Setting:
RTD Reading:
Density:
1.78
1.20
64.57
0.79
Tank Temp=
Reboiler:
Pump Setting:
RTD Reading:
Density:
30.00
Distillate
%MeOH (Molar)
Frac (Wt)
Flow Rate (ml/min)
Mass flow rate (g/min)
Mass MeOH (g/min)
Mass H2O(g/min)
99.55
1.00
15.05
11.91
11.88
0.03
Reboiler:
%MeOH (Molar)
Frac (Wt)
Flow Rate (ml/min)
Mass flow rate (g/min)
Mass MeOH (g/min)
Mass H2O(g/min)
water balance
MeOH balance
31.48 gm/min
-25.39 gm/min
2.10
75.67
0.94
39.15
0.53
336.57
315.13
168.14
147.00
Feed:
Pump Setting:
%MeOH(Molar):
Density
Feed Pump:
%MeOH (Molar)
Frac (Wt)
Flow Rate (ml/min)
Mass flow rate (g/min)
Mass MeOH (g/min)
Mass H2O(g/min)
ENERGY BALANCE
ENERGY IN AT REBOILER
Reboiler (Amps)
15.43
Energy In(watts)
3394.60
CONDENSER
Cool Water Temp-in(°C)
Cool Water Temp-out (°C)
Cool Water Flow (ml/min)
Water Cp (KJ/KgoK)
Energy Out Cond(watts)
Latent Heat(watts)
19.74
20.63
9000.00
4.18
557.94 Qcond
615.07 Qlatent
RE BOILER
Delta T
MeOH Cp
Reboiler Energy
45.67
2.55
794.47 Qr
5.00
0.50
0.92
50.00
0.64
350.54
320.95
205.41
115.54
Capacity Test
Performed to determine the
maximum capacity of the
column to produce distillate
Parameters for the test are
- reboiler was filled with a mixture
of methanol and water
- reboiler current set at 20 amps
(maximum)
- reflux set 95 % Methanol distillate
- steady-state conditions were
established
- Set various feed pump settings
- Set various reflux ratios
- Determine distillate and reboiler
flowrate
- Column did not produce distillate at
pump setting of 7
Capacity Test Comparison
Feed Pump Feed Flowrate Percent Distillate Reboiler
Setting
(ml/min) Reflux Flowrate Flowrate
(ml/min) (ml/min)
3
192
76
25
180
5
350
75
32
332
6
420
76
21
390
7
490
-
Feed Location Impact
Parameter
- Pump setting of 3
- Reboiler amps at 20
- 70% reflux
Results
- Tray 4 - 89%
- Tray 5 - 93%
- Tray 6 - 97%
Reflux Impact
Parameter
- Feed location tray 4
- Pump setting of 3
- Reboiler amps at 20
Results
- Reflux 50% - 78% at 43
ml/min
- Reflux 70% - 89% at 23
ml/min
Conclusions
(Experimental Results)
Design and execution of
experiments
- useful way of gaining experience
- found column performed in a
predictable manner
- increased the students’ level of
confidence
energy and mass balance
calculations demonstrated
- purity of the product was surpassed
with a reduction in the quantity of
the product
Based on observations from the
capacity test
- maximum output of the reboiler heaters
could not maintain boiling conditions
above a feedwater flowrate of 420ml/min
Based on observations from the
feed location experiment
- optimum feed tray location - tray 6
- due to the higher methanol composition
in the distillate
Based on observations from the
percent reflux experiment
- between 50- and 70-percent reflux
* two times the distillate flowrate
* 1.6 times the amount of methanol
Recommendation
(Experimental Results)
Review the RTD calibrations to
account for the discrepancies
in the mass balance
Perform additional feed
location impact experiments
Take physical measurement of
the distillate flow (not pump
flowrates)
Computer Modeling
Pro II
Ponchon-Savarit
PRO II
Steady-state heat and material
balance simulator
Simulates any number of
components, streams, units,
and recycle loops
Requirement
- Feed stream
- composition
- temperature
- flowrate
- pressure
- Tray efficiency
Specify two of the following
parameters
- Any specific tray temperature
-
Heat duty of the condenser
Temperature of the distillate
Composition of the distillate
Flowrate of the distillate
Reflux ratio
Temperature of the bottoms
Composition of the bottoms
Flowrate of the bottoms
Heat duty of the reboiler
PROII will calculate remaining
parameters
PRO II - Optimizing Distillation Column
Stream Name
Stream Description
Phase
Temperature
Pressure
Flowrate
Composition
MEOH
H2O
Total Stream
Rate
Std. Liq. Rate
Temperature
Pressure
Molecular Weight
Enthalpy
1
C
ATM
G-MOL/MIN
2
Liquid
Liquid
Liquid
25 65.53888 99.82745
0.994603 0.994603 0.994603
12.00385 6.488153 5.515693
0.5
0.5
G-MOL/MIN
G/MIN
CM3/MIN
C
ATM
M*J/MIN
J/G
3
12.00385
300.4381
350
25
0.994603
25.0285
0.023033
76.66611
1
0.514083
0.006671
0.45835
9.962891
0.858395
0.859242
33.18008
Mole Fraction Liquid
Reduced Temperature
Reduced Pressure
Acentric Factor
UOP K-Value
Std. Liquid Density
G/CM3
Sp. Gravity
API Gravity
Vapor
Rate
G-MOL/MIN n/a
G/MIN
n/a
CM3/MIN
n/a
Molecular Weight
n/a
Z (from Density)
n/a
Enthalpy
J/G
n/a
CP
J/G-C
n/a
Density
G/CM3
n/a
Th. Conductivity
KCAL/HR-M-C
n/a
Viscosity
CP
n/a
Liquid
Rate
G-MOL/MIN 12.00385
G/MIN
300.4381
CM3/MIN
352.8752
Molecular Weight
25.0285
Z (from Density)
0.001195
Enthalpy
J/G
76.66611
CP
J/G-C
3.115483
Density
G/CM3
0.851401
Surface Tension
DYNE/CM
n/a
0.925 6.91E-05
0.075 0.999931
6.488153
201.0676
250.4837
65.53888
0.994603
30.98997
0.034942
173.7827
1
0.647976
0.011017
0.552148
10.55651
0.802717
0.803509
44.60248
5.515693
99.37048
99.51627
99.82745
0.994603
18.01597
0.041537
417.998
1
0.576169
0.004556
0.348015
8.76176
0.998535
0.999521
10.06786
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
n/a
6.488153
201.0676
265.9261
30.98997
0.001467
173.7827
2.895487
0.756103
n/a
5.515693
99.37048
103.6818
18.01597
0.000611
417.998
4.21597
0.958418
n/a
Ponchon-Savarit Theory
Graphical Method
• Plots Enthalpy Against
Composition
Provides Exact Solutions
Incorporates Effects of Heat
Losses
• Inputs of Individual Tray Losses
• Inherent Material and Energy
Balances
Ponchon-Savarit
Diagram on Excel
Inputs Needed (highlighted in
yellow)
• Distillate and Bottoms
Compositions Desired
• Distillate and Bottoms Flowrates
• Heat Losses on Each Tray
Works For Up To 13 Stages
Tested For Bottoms
Concentrations down to 0.01%
and Distillate Concentrations up
to 97.9%
Conclusion
(Computer Modeling)
PROII
- user friendly
- fast
- not accurate
- limited by constraints
Ponchon-Savarit
- heat loss on individual trays
must be known
- only valid for methanol-water
mixtures
Recommendations
(Computer Modeling)
Modify the PROII model to more
closely approximate the UTC
distillation column
Conduct training for students
on the use of modeling tools
Determine the heat losses on
the individual trays (PonchonSavarit)
Conclusions
(Final)
Technical
- Study of mass transfer operations
using the distillation column
- Approach to the study of the
distillation column included
- Literature search
- Operating the column
- Computer modeling
* Ponchon-Savarit
* PROII
- Each student had the opportunity
to participate in
- operation
- calibration
- repair
- Provided a better understanding
through
- research
- classroom discussion
- design of experiments
Accomplishments
- Ponchon-Savarit spreadsheet
developed
- PROII model developed
- Energy and mass balance
spreadsheet developed
- Determination of the column
capacity
- Determination of heat lost to the
environment
- Performed feed input experiments
Recommendations
(Final)
Allow for more continuous
laboratory time
- Modify class schedule
- Maintain the distillation column
components
- Establish course objectives,
perform calibrations, research
literature, and familiarize
students with modeling programs
within the first month of the
semester