9846

Operation of a Dividing Wall Column and a Petlyuk Column

Consider a ternary mixture composed of 20 mole% benzene, 60 mole% toluene and 20 mole% -xylene. This mixture can be separated by the usual direct or indirect sequences using two distillation columns. A more efficient method is to use the dividing wall column [1, 2] (DWC) or the Petlyuk column [3]. Both methods are thermodynamically equivalent. DWC allows up to 30% saving in capital investment and energy cost. Here, we feed the DWC, operating at atmospheric pressure, with the ternary mixture. The feed, a saturated liquid, has a flow rate equal to 100 kmol/hr and a temperature equal to 104.87 °C. This Demonstration computes the composition profiles in both the main column and the fractionator. The steady-state compositions of benzene, toluene, and -xylene are indicated in red, blue, and green, respectively. You can change the values of the reflux and reboil ratios, the liquid and vapor split ratios, and the sidestream draw rate. In addition, both the DWC and Petlyuk column setups are given. Finally, a comparison with Aspen HYSYS simulation results shows excellent agreement. The DWC snapshot indicates that it is possible to separate the pure benzene, pure toluene, and pure -xylene that exit as distillate, intermediate, and bottom products, respectively.

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DETAILS

Expressions for pure component molar vapor and liquid enthalpies were adapted from Aspen HYSYS.
The mixture is assumed to obey Raoult's law since it is composed of only aromatic compounds with Antoine constants taken from Aspen HYSYS.
References
[1] R. O. Wright, Fractionation Apparatus, US Patent 2,471,134, filed July 17, 1946, and issued May 24, 1949. www.google.com/patents/US2471134.
[2] M. A. Schultz , D. G. Stewart, J. M. Harris, S. P. Rosenblum, M. S. Shakur, and D. E. O'Brien, "Reduce Costs with Dividing-Wall Columns," Chemical Engineering Progress, May 2002, pp. 64–71.
[3] F. B. Petlyuk, V. M. Platonov, and D. M. Slavinskii, "Thermodynamically Optimal Method for Separating Multicomponent Mixtures," International Journal of Chemical Engineering, 5(3), 1965 pp. 555–561.
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