Gas holdup and overall volumetric oxygen transfer coefficient in airlift contactors

Abstract

The two major types of airlift contactors, concentric-tube and external-loop, were investigated for their gas holdup (riser and downcomer) and overall mass transfer characteristics. Results obtained in batch charges of tap water and 0.15 kmol/m(3) NaCl solution are reported for external-loop airlift contactors having downcomer-to-riser cross-sectional area ratios, A(d)/A(r), ranging from 0.11 <or= A(d)/A(r) <or= 0.69 and for concentric-tube types in the range 0.13 <or= A(d)/A(r) <or= 0.56.The results are compared and contrasted for the two types of airlift contactors and also with corresponding results obtained in a bubble column (A(d)/A(r) = 0). Both the riser gas holdup, (epsilon(G))(r), and the overall volumetric mass transfer coefficient, (K(L)a(D))(T), were found to increase with increasing gas superficial velocity and the corresponding specific gassing power input, (P(G)/V(D))(T). However, at a specified power input both (epsilon(G))(r) and (K(L)a(D))(T) decreased with increasing A(d)/A(r) due to a resultant increase in circulating liquid velocity. Unifying generalized correlations for both types of airlift contactors are given for both (epsilon(G))(r) and (K(L)a(D))(T). These correlations are expected to be applicable as well to continuous-liquid flow bubble columns at comparable liquid velocities.

Airlift Bioreactor Fluid-Dynamic Characterizationfor the Cultivation of Shear Stress Sensitivemicroorganisms

“…Consequently, the differences observed between the experimental values from this study and the values obtained from different theoretical correlations proposed by others [5,20,28] (Fig. 3b), are due to the fact that not all the parameters included in the current bioreactor design have their values within the range of the parameters for those proposed correlations (Ug, for example).…”

“…A correlation for the kLa can be obtained as a function of the superficial gas velocity {kLa=α[1+Ad/Ar] -2 (Ug) ß } [20], such as the one presented in Fig. 6b, where the parameters α and β were adjusted using the experimental data, producing the following equation:…”

Characterization of gas transfer and mixing in a bubble column equipped with a rubber membrane diffuser

“…This number is twice the increase reported by Bello et al (1985) (using a perforated plate) reflecting the formation of small bubbles by the membrane sparger-a characteristic which is less obvious in the coalescent liquid. In spite of this, our values for the coalescent liquid (coarse bubbles) are high compared with other systems (Bello et al, 1985;Heijnen and van't Riet, 1984). In the homogeneous flow regime gas holdup depends linearly on gas velocity (Deckwer and Schumpe, 1993) and can be estimated from Eq.…”

“…Burckhart and Deckwer (1976) found a power law correlation, k L a ‫ס‬ 1.5v s 0.78 (method: gassing-in/out N 2 , 78-L liquid volume), for a sintered plate sparger in NaCl solutions Table I). Bello et al (1985) found k L a values for a perforated plate (conventional rigid sparger) in a ''bubble coalescence-inhibiting system'' of 0.15 M NaCl (method: gassing-in/out N 2 , 30-L liquid volume) of only 40% to 50% of the values obtained in this report.…”

Hydrodynamics and mass transfer in a novel multi-airlifting membrane bioreactor

“…One Is based on empirical correlation (Bello et al 1985;Chlstl et al 1987;Gavrllescu and Tudose 1998;Popovic and Robinson 1984;Popovic and Robinson 1988) Zuber and Findlay (1965), which Is Independent of geometrical restrictions, but more efforts are needed on experimentally determining parameters. can reduca the gas holdup In the riser of airlift reactor.…”