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


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
TI
Cooling Water Return
Electromagnetic Reflux Control
TI
TI
TI
TI
TI
TI
TI
TI
TI
TI
TI
TI
Reboiler
TI
4
5
6
1
2
3
7
8
9
10
11
12
Condenser
TI
PI
TI
LI
Distillate
Pump
Feed Pump
LI
Product Cooler
Feed Tank
(Product Tank)
Reboiler Pump





Condenser
Reflux valve
Trays
RTDs
Pumps




- Feed pump
- Reboiler pump
- Distillate pump
- Auxiliary pump
Reboiler
Level Control
- Condenser
- Reboiler
FEED LOCATIONS


Heat loss study

RTD calibration

Pump and cooling water calibration


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

66.0
65.8
65.6
65.4
65.2
65.0
70
Temperature of tray 1 at 7 amps
Reboiler Amps = 7
72 74
Time
76 78 80
Temperature of tray 1 at 6 amps
Reboiler Amps = 6
65.5
65.0
64.5
64.0
63.5
63.0
78 79 80 81
Time
82 83 84 85


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 100 o C (pure water) and 64.5
o C (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 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

Feed Pump Calibration Curve
600
500
400
300
200
100
0
0
Pump : 7017-21 Pattern No. 3.358.609
2
F = -2.3996M
2
+ 98.326M - 81.102
R
2
= 0.9942
4 6
Pump Setting
8 10


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


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







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
Bottoms 205 168
Distillate 116 147
12
12
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
Feed:
2.10
Pump Setting:
75.67
%MeOH(Molar):
0.94
Density
Distillate
%MeOH (Molar)
Frac (Wt)
99.55
1.00
Flow Rate (ml/min) 15.05
Mass flow rate (g/min) 11.91
Mass MeOH (g/min) 11.88
Mass H2O(g/min) 0.03
water balance
MeOH balance
31.48 gm/min
-25.39 gm/min
Reboiler:
%MeOH (Molar)
Frac (Wt)
Feed Pump:
39.15
%MeOH (Molar)
0.53
Frac (Wt)
50.00
0.64
Flow Rate (ml/min) 336.57
Flow Rate (ml/min) 350.54
Mass flow rate (g/min) 315.13
Mass flow rate (g/min) 320.95
Mass MeOH (g/min) 168.14
Mass H2O(g/min) 147.00
Mass MeOH (g/min) 205.41
Mass H2O(g/min) 115.54
ENERGY BALANCE
5.00
0.50
0.92
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


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
5
3 192
350
(ml/min) (ml/min)
76 25 180
6
7
420
490
75 32 332
-
76 21 390
-


Parameter
- Pump setting of 3
- Reboiler amps at 20
- 70% reflux

Results
- Tray 4 - 89%
- Tray 5 - 93%
- Tray 6 - 97%


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


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


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)





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
Mole Fraction Liquid
Reduced Temperature
Reduced Pressure
Acentric Factor
UOP K-Value
Std. Liquid Density
Sp. Gravity
API Gravity
Vapor
Rate
Molecular Weight
Z (from Density)
Enthalpy
CP
Density
Th. Conductivity
Viscosity
Liquid
Rate
C
ATM
1
Liquid
25
0.994603
0.5
0.5
2
Liquid
65.53888
0.994603
0.925
0.075
Liquid
99.82745
0.994603
G-MOL/MIN 12.00385
6.488153
5.515693
n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a
3
6.91E-05
0.999931
G-MOL/MIN 12.00385
6.488153
5.515693
G/MIN 300.4381
201.0676
99.37048
CM3/MIN
C
ATM
350 250.4837
99.51627
25 65.53888
99.82745
0.994603
0.994603
0.994603
M*J/MIN
J/G
G/CM3
25.0285
30.98997
18.01597
0.023033
0.034942
0.041537
76.66611
173.7827
417.998
1 1 1
0.514083
0.647976
0.576169
0.006671
0.011017
0.004556
0.45835
0.552148
0.348015
9.962891
10.55651
8.76176
0.858395
0.802717
0.998535
0.859242
0.803509
0.999521
33.18008
44.60248
10.06786
G-MOL/MIN n/a
G/MIN n/a
CM3/MIN n/a n/a
J/G
J/G-C
G/CM3 n/a n/a n/a n/a
CP n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a n/a
Molecular Weight
Z (from Density)
Enthalpy
CP
Density
Surface Tension
G-MOL/MIN 12.00385
6.488153
5.515693
G/MIN
CM3/MIN
300.4381
352.8752
201.0676
265.9261
99.37048
103.6818
25.0285
30.98997
18.01597
0.001195
0.001467
0.000611
J/G
J/G-C
G/CM3
76.66611
3.115483
0.851401
DYNE/CM n/a
173.7827
2.895487
0.756103
n/a
417.998
4.21597
0.958418
n/a


Graphical Method
• Plots Enthalpy Against
Composition

Provides Exact Solutions

Incorporates Effects of Heat
Losses
• Inputs of Individual Tray Losses
• Inherent Material and Energy
Balances


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%


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


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 (Ponchon-
Savarit)


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

- E ach student had the opportunity to participate in
- operation
- calibration
- repair
- P rovided 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


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