The energy consumption of distillation columns can be reduced by dividing the vapor phase inside the column in different partitions. This technique is known as parastillation.
In parastillation, the vapor flow is divided into at least two upward and parallel streams in the bottom of the column. These streams make contact alternatively with a single downward liquid flow. This arrangement allows to increase the number of theoretical stages per unit of column height. According to BIASI et al. (2020), it is possible to allocate more stages of parastillation (including the condenser and the reboiler) in a column shell of the same height when compared to conventional distillation.
BIASI et al. (2020) proposed a mathematical model for simulating parastillation columns with any number of vapor phase partitions. This model was implemented in iiSE and the parastillation columns can be simulated by specifying the number of partitions of the vapor phase.
To exemplify the effect of phase division on energy consumption, the alcoholic distillation reported by BIASI et al. (2020) is considered. A stream of saturated liquid at 94 °C and 518.04 kgmol water/h and 14.35 kgmol ethanol/h is fed to the columns. The distillate flow rate is fixed at 17 kgmol/h and the column pressure at 1 atm. In this example, a parastillation column with 2 vapor streams is compared to another of conventional distillation of the same height. The conventional and parastillation columns have, respectively, 20 and 37 stages, including the condenser and reboiler. Fixing the mass percentage of ethanol in the distillate at 93.0%, the parastillation column demanded a reflux ratio approximately 20% lower than that of conventional distillation.
Post by Dr. Lilian Caroline Kramer Biasi, also the author of the original work “A new unified model to simulate columns with multiple phase divisions and their impact on energy savings”, Computers & Chemical Engineering, v. 140, p. 106937, 2020.