HW Set No - University of Texas at Austin
Homework Set No. 1 ChE 473K Spring 2024 R.B. Eldridge
Problem No. 1 (Aspen based design, equipment cost estimate, and utility summary)
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It is desired to separate a three component feed stream into two relatively pure product streams and a waste stream
Obtain:
1) The optimized reflux ratio and tray count for each tower.
2) The detailed equipment list including bare equipment cost for the column system (column, reboiler, condenser, overhead accumulator, and reflux pump).
3) The FCI using a delivery factor of 1.08, Lang Factor of 4.74, and a 15 percent contingency.
4) The utility usage based on Aspen default values for low pressure steam and cooling water.
Base the design on a column diameter designed at 80 percent of flood and a tray efficiency of 70 percent. The columns contain single pass sieve trays. The reflux and overhead product streams are subcooled to 49 ˚C. The system is carbon steel. Use the NRTL activity coefficient model to predict the VLE.
Target Stream Data:
| | |FEED |ACETONE |BOTTOMS |AZEO |WATER |
|Mole Flows |kmol/hr |1000.00 |180.50 |819.50 |244.50 |575.00 |
|WATER |kmol/hr |671.29 |4.06 |667.23 |92.23 |575.00 |
|ACETONE |kmol/hr |175.69 |175.66 |0.00 |0.00 |0.00 |
|IPA |kmol/hr |153.02 |0.77 |152.25 |152.25 |0.00 |
Problem No. 2 (FCI and operating cost determination)
A refinery process unit (see figure below) is being operated to recover H2S from a refinery gas by adsorption with a monoethanolamine (MEA) solution. The MEA is recovered in a steam heated stripping tower.
Process data:
MEA rate to absorber 75 GPM
MEA circulation through steam heater 125 GPM
Heater – Steam per lb of MEA circulated 0.045 lbs
Steam at 30 psig, T sat = 275 F
Temperature of MEA leaving stripper 225 ℉
Temperature of MEA entering absorber 195 ℉
Specific heat of MEA 0.52 BTU / lb ℉
Specific gravity of MEA 1.02
Cooling water temperature 110 ℉
Cooling water temperature rise 30 ℉
Design Premises:
Both the absorber and stripper diameter are 4 ft in diameter stainless steel sieve tray towers with 10 trays each on 24 inch tray spacing
Stream time 350 days per year
Heat transfer coefficient (U) for cooler 150 BTU / hr ft2 ℉
Heat flux for reboiler 12,000 BTU/ hr ft2
Pump efficiency 65 percent
Required pump head 50 ft lbf / lbm
Wall thickness of stripper and absorber ¾ in
Density of column steel 3600 lb / ft3
Labor 12 hour shift / 1 operator per shift
Economic data:
Electricity - $ 0.05 / kw hr
Steam - $ 3.00 / 1000 lb
Cooling water - $ 0.08 / 1000 gallon
Labor - $ 100,000 / operator year
Maintenance – 10 percent of FCI
Depreciation - 20 percent of FCI
Indirect costs – 4 percent of FCI + 40 percent of labor
Determine the fixed capital investment for the H2S recovery unit using a Lang factor of 4.74 for a 2024 purchase. Bare equipment costs can be obtained from Table 7.2 (pages 322-324) of the following textbook: (The electronic version is available from the UT Library)
Author: Towler, Gavin
Book: Chemical engineering design: principles, practice, and economics of plant and process design
Publisher: Butterworth-Heinemann
ISBN: 0-08-096659-4, 978-0-08-096659-5
DOI: 10.1016/B978-0-08-096659-5.00007-9
Determine the annual operating cost based on a by-product credit for the H2S of $ 50 / ton.
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Figure P2
Problem No. 3 (Optimization)
In a plastic pipe manufacturing operation, 50,000 lb/hr of air (Cp = 0.24 BTU / lb F) must be cooled form 300 F to 50 F. This can be done in a single heat exchanger using refrigerant. However, in another part of the process, a large quantity of acetone (Cp = 0.50 BTU / lb F) is being heated from 55 F to 105 F using steam. You suggest to your boss a scheme to use the cold acetone in a pre-cooler to save some money. Your proposed process is shown below:
[pic]
Data:
Heat transfer coefficient for each exchanger: U = 15 BTU / hr ft2 F (assume perfect countercurrent flow)
Heat exchanger bare equipment cost = $ 100,000 * (Area / 2000) 0.8 where area = ft2
Refrigeration unit bare equipment cost = $ 2000 * (Q refrigeration in BTU / hr / 12,000) 0.8
Determine the intermediate temperature Ti that will minimize the FCI of the air cooling process.
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