Title: Time optimal control operation of bulk lyophilisation of materials on trays reduces the exergy losses and increases the efficiency of energy utilisation

Authors: Athanasios I. Liapis; Roberto Bruttini; Jee-Ching Wang

Addresses: Department of Chemical and Biochemical Engineering, Missouri University of Science and Technology, 100 Bertelsmeyer Hall, 1101 North State Street, Rolla, Missouri 65409-1230, USA ' Criofarma, Strada del Francese 97/2L, 10156 Turin, Italy ' Department of Chemical and Biochemical Engineering, Missouri University of Science and Technology, 100 Bertelsmeyer Hall, 1101 North State Street, Rolla, Missouri 65409-1230, USA

Abstract: Exergy represents a measure of quality of energy and because exergy is destroyed due to process irreversibilities within a system to produce entropy, the exergy expressions and analysis developed in this work could be used to operate the intrinsically unsteady-state lyophilisation processes more efficiently. It is shown that the time optimal control operation of a freeze dryer with respect to heat input to the trays and total pressure in the drying chamber, reduces the duration times of the primary and secondary drying stages by 42.43% and 41.17%, respectively, and this leads to a reduction of 38.19% in the magnitude of the total exergy losses of the lyophilisation system studied in this work. Also, the potential for reducing further the exergy losses when organic co-solvents and water forming non-ideal mixtures of solvents with positive deviations from Raoult's law are used in a lyophilisation system operated under time optimal control, is discussed.

Keywords: drying cycle time; exergy inputs; exergy losses; freeze drying; heat inputs; lyophilisation; primary drying stage; secondary drying stage; time optimal control operation; drying chamber pressure.

DOI: 10.1504/IJEX.2020.108945

International Journal of Exergy, 2020 Vol.32 No.4, pp.329 - 355

Received: 10 Oct 2019
Accepted: 15 Jan 2020
Published online: 10 Aug 2020 *

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