BROWN INDUSTRIES, INC.
GGBL Building
Ann Arbor, MI 48109-2136
DATE: September 7, 2005
TO: Michael Senra, Plant Supervisor
FROM: Scott Fogler, Engineering Manager
SUBJECT: Methanol Recovery Optimization via Distillation
Brown Industries wants to determine the feasibility of recovering methanol from waste aqueous steams for sale to outside vendors. The available aqueous methanol feed streams have concentrations ranging from 5 to 10% (by volume). In order for the methanol to be sellable, the final concentration should be at least 97% (by volume).
I request that your engineers conduct this feasibility study using the available packed-bed distillation column. This feasibility study should include pilot-scale experiments that characterize the methanol-water distillation process and identify the operational limits of the column, as well as the development of a working model for the packed-bed distillation that incorporates an economic analysis of the distillation process. The model must allow an operator to set the feed flow rate, the reflux ratio (or reflux flow rate), and the reboiler power to produce methanol of a desired purity given the feed composition.
The following objectives should be attained in each of the rotations to meet the overall campaign goal. Note that all experimental studies should be performed for distillate concentrations of 85% (by volume) and greater.
Rotation 1:
1. Download from the web and verify the T-x-y diagram for the methanol-water system provided. This diagram will allow you to estimate concentrations from temperatures measured throughout the column, reducing the number of GC measurements. (Please note that you are being asked to verify, not develop your own T-x-y diagram.)
2. Download from the web and verify with a few standard samples the GC calibration curve provided for you. (Please note that you are being asked to verify, not develop your own calibration.)
3. Using the TECHNOVATE packed-bed distillation column, quantify the effect of changing the reflux ratio and reboiler power on the product concentration and the mass transfer coefficient. All measurements should be taken after the column has reached steady-state, which must be confirmed by a mass balance, temperature profiles, and/or any other relevant measurable quantities. Explain and outline in the report the procedure you used for sampling so that the same method can be used for future users of the distillation column.
4. Determine if a constant molar overflow assumption or an enthalpy-concentration method should be used to simulate this distillation column.
5. Compare the calculated mass transfer coefficients with the data from Scientific Development Co. The data can be found in appendix to section 3 of the equipment manual.
6. Prepare (in advance, whenever possible) McCabe-Thiele diagrams for each of your runs, and evaluate the placement (or misplacement) of the feed.
Rotation 2:
1. Quantify the effect of feed flow rate, feed temperature and feed location on the product concentration and/or mass transfer coefficient.
2. Determine the operating conditions for which the column will flood. Determine if a generalized flooding correlation can be applied to this column so flooding can be predicted and prevented. To achieve the greatest throughput, it is suggested to operate the column at vapor flow rates just below flooding.
3. Develop a model that can be used to predict the performance of the column. Inputs to the model should include the feed flow rate, the reflux ratio (or reflux flow rate), and the reboiler power; make sure that the number of inputs is equal to the degrees of freedom of the column. One potential approach to modeling the column is to adapt the packed absorption column formulation discussed in the seventh edition of Perry et al. (section 14, Packed-tower design) to distillation and converting the mass-transfer data from Scientific Development Co. to data needed for this system. If necessary, the model should account, for any variations in the mass transfer coefficient due to changes in column conditions, such as changes in the liquid and vapor streams as discussed in Perry et al (section 5, Interphase mass transfer). In addition, this model should also account for the effect of liquid and vapor flows on the flooding of the column, so that flooding can be prevented.
Rotation 3:
A new plant technician was just hired last month. The new plant technician thinks the equipment is operating poorly. He recently took a number of measurements and repeated them several times and believes his data are accurate. His data as well as the reports of the previous two rotations (which do not agree with the technician’s data) will be provided for you. We feel that the data of the previous two rotations should be correct.
1. Brainstorm all the things that could explain the new plant technician’s data.
2. Use K.T. analysis (either PA or PPA in modified form) and other troubleshooting strategies to help you deduce the disparity. Present your analysis in the form of a table or chart.
3. Choose the most likely cause or set of conditions that you think produced the new technician’s data and run the equipment at these conditions to try to reproduce the new technician’s data to verify your reasons for the poor equipment operation.
Distillation_memo.doc