Prediction of HETP
for randomly packed towers operation: Integration of aqueous and non-aqueous
mass transfer characteristics into one consistent correlation
Simon Piché, Stéphane Lévesque, Bernard P.A. Grandjean and Faïçal Larachi
Department
of Chemical Engineering and CERPIC
Université
Laval, Ste-Foy, Québec, Canada, G1K 7P4
Corresponding
author: flarachi@gch.ulaval.ca
Separation
and Purification Technology, 33, 145-162 (2003)
Abstract :
Height equivalent to a theoretical plate (HETP) calculations, essential
for the design of randomly packed distillation columns were extracted from the
open literature to generate a working database including over 2,350
measurements. The merging of mass transfer characteristics from non-aqueous and
aqueous separation experiments have instigated the generation of a consistent
correlation predicting HETP. Based on results presented
elsewhere for absorption and stripping conditions (Ind.Eng. Chem. Res.
41 (2002) 4911), a set of artificial neural network (ANN) correlations for the
gas-liquid interfacial area (aw) and the pure local mass transfer coefficients
(kx , G or L) was proposed with the following dimensionless
structures: aw/aT = f (ReL, FrL, EoL, I, Xi, K) & Shx = f (Rex,
Frx, Scx, x=G or L).The gas-liquid interfacial area and
the pure local mass transfer coefficients were extracted using a reconciliation
procedure which combined actually measured interfacial areas with pseudo
interfacial areas inferred from the actually measured volumetric mass transfer
coefficients (kLaw, KLaw, kGaw, KGaw – absorption & stripping) and HETP
(distillation). The neural network weights of the two aw and kx correlations
were adjusted using a least-squared composite criterion simultaneously over the
six mass transfer parameters’ databases. The optimized set of ANN correlations
yielded an average absolute relative error (AARE)
of 21.3% for the 2357 HETP measurements available. Likewise, the measured
interfacial area and volumetric mass transfer coefficients (3770 data) were
correlated with an AARE of ca. 26.5%, which
undeniably proves the intimate correspondence of absorption and distillation
mass transfer characteristics in randomly packed towers. HETP predictions
remain as well in accordance with the physical evidence reported in the
literature.
Keywords:
random packed bed, distillation, absorption, stripping, HETP, mass
transfer, neural network, database
You can get the hetp.zip
file that contains an Excel worksheet simulator to compute HETP and more.
You may also download our Excel worksheets simulators for Trickle-bed or Flooded
Bed reactors.
The neural
correlation was developped with the software NNFit