HYDRODYNAMICS OF NON-NEWTONIAN LIQUIDS IN EXTERNAL-LOOP AIRLIFT BIOREACTORS - PART 1 - STUDY OF THE GAS HOLDUP

Gas holdup investigation was performed in two external-loop airlift bi oreactors of laboratory (V-L = 1.189 . 10(-3) - 1.880 . 10(-3) m(3); H -R = 1.16 - 1.56 m; H-D = 1.10 m; A(D)/A(R) = 0.111 - 1.000) and pilot scale (V-L = 0.157 - 0.170 m(3); H-R = 4.3 - 4.7 m; H-D = 4.0 - 4.4 m ; A(D)/A(R) = 0.04 - 0.1225), respectively, using as liquid phase non- Newtonian starch solutions of different concentration with K = 0.061 - 3.518 Pa s(n) and n = 0.86 - 0.39 and fermentation broths of P. chlys ogenum, S. griseus, S. erythreus, B. licheniformis and C. acremonium a t different hours since inoculation and from different batches. The in fluence of bioreactor geometry, liquid properties and the amount of in troduced compressed air was investigated. The effect of sparger design on gas holdup was found to be negligible. It was found that gas holdu p depends on the flow media index, epsilon(GR) decreasing with the inc rease of liquid pseudoplasticity, A(D)/A(R) ratio and H-R/H-D ratio. T he experimental data are in agreement with those presented in literatu re by Popovic and Robinson, which take into account liquid properties, geometric parameters and gas superficial velocity, with a maximum err or of +/-30%. It was obtained a correlation for gas holdup estimation taking into account the non-Newtonian behaviour of the fermentation br oths and the dry weight of the solid phase, as well. The concordance b etween the experimental data and those calculated with the proposed co rrelation was good, with a maximum error of +/-17%. Also, a dimensionl ess correlation for gas holdup involving superficial velocities of gas and liquid, cross sectional areas ratio, dispersion height to riser d iameter ratio, as well as Froude and Morton numbers, was obtained.