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Fenton/Coughlin/Fall 01
CHEMICAL ENGINEERING LABORATORYCHEG 237
Bubble-Cap Distillation Column
Objective: The objective of this experiment is to gain
experience in operation of largeequipment, to practice sampling and
analysis techniques, to review the
principles and hardware of distillation, and to compare
experimentalresults to theoretical predictions.
Theory: Information on the theory of distillation is given in
References 1-5.Theoretical prediction of compositions throughout
the column can byobtained by solving simultaneous material and
energy balances usingASPEN or other means. The references provide
equations for estimatinglimiting conditions in the column such as
minimum reflux and minimumnumber of stages at total reflux.
SAFETY PRECAUTIONS:1. The reagents used in this lab may be
flammable. Smoking in the
laboratory is reason for immediate ejection and safety glasses
must be worn at all times. Hard hats are required in the bay
area.
2. Make sure the condenser vent is open and that all other
valves are properly positioned before turning on steam. There are
many drainlines, etc., which may be open to the atmosphere.
3. During shut-down, do not turn the condenser water off until
thereboiler temperature has dropped to 140 oF. This is to
preventescape of uncondensed distillate out the vent. On shut-down,
turn
off two valves in series on the reboiler system.4. Concentration
analysis will be performed using a gas
chromatograph. Make a group inspection of the apparatus.5. THINK
BEFORE YOU ACT !!!!!
Preliminary Preparations:1. Review the necessary theory.2.
Examine the spare column sections. Note the details of the sample
piping
and the plate construction.3. Plan your experiments. Note that
steady state operation is required to give
meaningful results and determine an efficient procedure for
getting to
steady state. Plan a technique for sampling from the trays to
avoidcompositional changes and include a trial to evaluate the
reproducibility ofyour experimental runs and the precision of your
sampling and analyticaltechniques. Run at total reflux until the
group is familiar with all aspectsof the operation.
4. Develop a specific plan for converting the gas chromatograph
output intothe concentrations you desire. Review the information in
the instructionmanuals.
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Procedure: Review continuous operation of distillation columns
before operating theequipment. The column is to be run continuously
using various refluxratios (making sure the column is operating
above the predicted minimumreflux). Students should include a run
at total reflux. Students may alsochoose to investigate the effect
of feed plate location at constant reflux on
component distribution or experimentally determine the minimum
refluxratio. The instructor will specify the mixture to be
separated.
Rich Kozel will review start-up and shut-down procedures for
thedistillation column with students prior to operation.
Determine the precision of your measurements and the
reproducibility ofyour runs by making repeat measurements and
performing repeat trials.
Analysis: For all runs check mass and energy balances. Determine
the effect thatvarious controllable variables have on the
distribution of components
throughout the column (including the tops and bottoms products).
Using published correlations or ASPEN, estimate the minimum reflux
ratio,minimum number of trays at total reflux, and optimal feed
plate locationfor this process.
Report: Describe the design of your experiments and the results
obtained,including an error analysis. Provide thoughtful and
quantitative discussionof results, explain trends using physical
principles and relate yourexperimental observations to predicted
results (optimal feed plate location,minimum number of trays,
minimum reflux ratio, etc). Express anydiscrepancies between
observed and predicted results in terms ofquantified experimental
uncertainties or limitations of the correlations orcomputational
software used.
References:
1. Bennett, C. O. and Myers, J. E., Momentum, Heat, and Mass
Transfer , 3 rd Ed, McGraw-Hill, New York, NY (1982), Chapters 4
and 6.
2. Geankoplis, C.J., Transprot Processes and Unit Operations ,
3rd Ed.,Prentice Hall, New Jersey, (1993).
3. Hengsteback, R. J., Distillation Principles and Design
Procedures ,Reinhold Publishing Corp., New York, (1961).
4. McCabe, W. L. and Smith, J. C., and Harriott, P., Unit
Operations ofChemical Engineering, 6th Ed ., McGraw-Hill Publishing
Co., New York,
NY, (2001).5. Perry, J. H, Ed., Chemical Engineers Handbook , 7
th Ed., McGraw-Hill,
New York, NY (1997).
