C. M. Narayanan
National Institute of Technology
Professor of Chemical Engineering
He received BSc Engg from Banaras Hindu University, M.E. from Indian Institute of Science, Bangalore and PhD from Indian Institute of Technology , Kharagpur. He is actively engaged in Teaching and Research for the last thirty eight years. He has published 85 (eighty five) research papers in Journals of international repute. He is the author of four well known books on Chemical Engineering such as on Computer Aided Design of Chemical Process Equipment, Mechanical Operations for Chemical Engineers, Unit Operations and Unit Processes (in two Volumes) and on Biotechnology and Bioprocess Engineering .
Attempts have been made to perform computer aided analysis and simulation of the performance of a three phase semifluidized bed bioreactor. The bioreactor is of biofilm type and the process considered is the synthesis of Xanthan gum from Cheese Whey (after separating the proteins by Ultrafiltration), which follows Contoise - type kinetic equation. The process is aerobic in nature and both air and substrate solution (Cheese Whey permeate) are admitted from the bottom. The solution forms the continuous phase and air moves up as tiny bubbles (dispersed flow) through the bed of particle – biofilm aggregates (2.5 mm silica granules are used as support particles, each surrounded by a thin film of microbial solution). Being semifluidized, the bioreactor is composed of a fully fluidized bed at the bottom and a packed bed at the top. The performance of the bioreactor is thus analyzed by assuming it to be equivalent to two PFDRs (Plug Flow Dispersion Reactors) in series, each with a different value of dispersion number, Nd (the value of Nd for fluidized section being higher than that for the packed section). The performance equations (assuming dispersed flow) for both sections are written separately and then solved numerically using fourth order Runge – Kutta / line successive over – relaxation method, based on appropriate boundary conditions. The resistance to substrate transfer into the biofilm is accounted for in the analysis by incorporating the effectiveness factor (η) which is a function of substrate concentration at biofilm – solution interface, size of biofilm – particle aggregate and the effective diffusivity of substrate into the biofilm, apart from the Contois kinetic constants. The fractional gas holdup and liquid holdup in both sections, height ratio of fluidized section to that of the packed section and the semifluidization mass velocity are computed at the outset from selected experimental correlations (compiled from available literature). The results obtained from the developed software package are compared with experimental data compiled in the laboratory and satisfactory agreement has been observed between the two (thereby confirming the reliability of the mathematical analysis). The dependence of rate of Xanthan gum production on substrate flow rate, particle size, substrate concentration in feed are studied and illustrated graphically. The developed CAD package can be, therefore, recommended for the design and installation of three phase semifluidised be bioreactors and also for the analysis of existing systems.