These problems ask you to calculate the number of stages in a multi-stage separator. Assume that only the solute transfers between phases, that the separator consists of equilibrium stages, and that the temperature and pressure are constant.
These are some of the same problems as in Chapters 12 and 13. For each problem, generate an XY (solute-free) equilibrium curve, construct the operating lines, and step off the number of stages.
14.1 100 mol/s of CO2 is fed to an absorber operating at 5oC. Pure water is fed at a rate of 100 mol/s. The system pressure is high enough to carbonate the water to 3-4 volumes (soft drink industry speak), or 6-8 g/L, or around 0.003 mol CO2/mol. Determine the flow rate and composition of each stream. If the number of stages does not affect the performance, try to explain.
14.2 100 mol/s of a water stream with 0.1 mol% chloroform is fed to a single-stage stripper operating at 25oC and 1 atm. Enough pure air is fed to remove 99.9 mol% of the chloroform. The two streams mix, equilibrate, and then separate into liquid and gas products. Determine the flow rate and composition of each stream.
14.3 100 mol/s of an air stream with 5 mol% ammonia is fed to an absorber operating at 10oC and 5 atm. Pure water is fed at a rate such that 90 mol% of the ammonia is absorbed. Determine the flow rate and composition of each stream.
Equilibrium data in the form of g NH3/100 g H2O vs PNH3 (mm Hg) is found in Perry's Handbook and on the accompanying spreadsheet Excel "Ammonia Data" that I included for your convenience. I developed polynomial equations to relate liquid phase mole fraction to partial pressure at several temperatures.
14.4 100 mol/s of a water stream with 5 mol% ammonia is fed to a stripper operating at 60oC and 1 atm. Pure air at is fed at a rate such that 90 mol% of the ammonia is stripped. Determine the flow rate and composition of each stream.
14.5 100 mol/s of a water stream with 1 mol% methanol is fed to a stripper operating at 30oC and 760 mm Hg. Enough air is fed to remove 90 mol% of the methanol. Determine the flow rate and composition of each stream.
Equilibrium data for the methanol-water-air system in the form of Pxy diagrams were constructed from ChemCAD and are found on the accompanying spreadsheet Excel "Methanol Data" that I included for your convenience. I fit the curves with polynomial functions to relate liquid phase mole fraction to partial pressure at several temperatures.
14.6 100 mol/s of an air stream with 1 mol% methanol is fed to an absorber operating at 10oC and 3800 mm Hg. Enough water is fed to remove 90 mol% of the methanol. Determine the flow rate and composition of each stream.
Be awesome! For any of these problems, change the flow rates, temperature, pressure, or number of stages and observe the effects. Do the results make sense to you?
Be really awesome! Compare your results to a process simulator like ChemCAD or Aspen. What assumptions have you made that might explain differences? Note that you should use the Sour Water thermodynamics for the ammonia system in ChemCAD - not what the thermo wizard picks.
