ISSN:
0178-515X
Source:
Springer Online Journal Archives 1860-2000
Topics:
Process Engineering, Biotechnology, Nutrition Technology
Notes:
Abstract A mixing model is coupled with fermentation kinetics in order to simulate a fermentation as a function of mixing conditions and scale-up. The mixing model for a batch stirred tank with three stirrers consists of three regions, each of them characterized by an ideally mixed compartment around the stirrer and two macromixers, i.e. cascades of tank-in-series, describing the recirculation flow. The model contains four parameters – radial and axial circulation time, volume of the ideally mixed stirrer compartment and the number of tanks in each cascade. These values, determined by Mayr et al. in function of the operational conditions and scale-up, were choosen to simulate the fermentation of glutamic acid to show the pH-fluctuation at different control and scale conditions. By choosing optimal regulation properties, such as input flow rate and/or concentration of the base, regulation span, position of the pH-electrode and base input location, etc., fluctuations of the pH-value in the bio-reactor can be minimized. However, the negative effect of insufficient mixing conditions can be reduced only by an increasing number of the base input places. In large scale fermentors, the axial circulation time is rather high, about 5–10 times larger than the radial one. This might result in a large amplitude of the pH-fluctuation. As it is shown, using an input place for base in each stirrer region, the negative impact of the insufficient axial mixing on the fermentation can be diminished perfectly. In this case ammonia should be fed into the reactor as an aqueous solution. Nomenclature F m3/s liquid flow rate F G m3/s separate gas flow rate F Gax, FGrad m3/s gas flow rate joint with liquid F NH3 mol/s input rate of ammonia as a solution H Pa m3/mol Henry constant k m3/kgs reaction rate constant in Eq. 3 k La 1/s product of mass transfer coefficient and area K kg/m3 Monod constant in Eq. 1, (for oxygen: mol/m3) K P kg/m3 product inhibition constant in Eq. 1 m kg/(m3s) maintenance coefficient M –Mth loop in the physical mixing model (M=1−6) n– number of ideally mixed cascades in a recirculation loop N–Nth element in a loop with the stirrer compartment (N=1−(n+1)) NH3 mol/m3 concentration of ammonia, in liquid – mol/mol in the gas phase O mol/m3 concentration of oxygen, in liquid – mol/mol in the gas phase p Pa pressure P kg/m3 product concentration r kg/(m3s) reaction rate R Pa m3/(mol K) universal gas constant S kg/m3 substrate concentration t s time V m3 liquid volume of reactor V tot m3 volume of liquid+gas phase in reactor V m m3 liquid volume of ideally mixed stirrer compartment V M,N m3 liquid volume of Mth and Nth cascade element V G,M,N m3 gas volume of the Mth and Nth cascade element Y kg/kg yield coefficient, e.g. Ysx yield coeff. of biomass from substrate Greek symbols μ 1/s specific growth rate μmax 1/s maximum value of the growth rate ɛ– gas hold-up in the reactor Subscripts ax axial direction G gas phase in inlet L liquid M Mth loop N Nth element in a loop including the stirrer compartment as well O oxygen P product rad radial
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00369496
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