Airlift internal loop

Cai, J., Nienwstad, T.J., and Kop, J.H. (1992), Flnidization and sedimentation of carrier material in a pilot-scale airlift internal-loop reactor, Water Science <6 Technology, 26(9-11) 2481-2484. 

Trilleros, J., Diaz, R., and Redondo, R (2005), Three-phase airlift internal loop reactor Correlations for predicting the main fluid dynamic parameters, Journal of Chemical Technology <6 Biotechnology, 80(5) 515-522. 

Eig. 23. Airlift reactors (a) spHt cylinder internal loop, (b) draft tube internal loop, and (c) external loop (94). 

The gas is circulated by means of pressurised air. In airlift bioreactors, circulation is caused by die motion of injected gas through a central tube, with fluid recirculation through the annulus between die tube and the tower or vice versa. Figure 6.1 shows an airlift bioreactor widi an internal loop cycle of fluid flow. 

Spatial Profiles of Gas Holdup in a Novel Internal-loop Airlift Reactor... 

Internal-loop airlift reactors (ALRs) are widely used for their self-induced circulation, improved mixing, and excellent heat transfer [1], This work reports on the design of an ALR with a novel gas-liquid separator and novel gas distributor. In this ALR, the gas was sparged into the annulus. The special designed gas-liquid separator, at the head of the reactor, can almost completely separate the gas and liquid even at high gas velocities. 

In this model, energy balances are set up for the reactor and the separator tube separately, and two equations are obtained. The gas holdup can then be obtained from combining these two equations. Details can be found in Zhang et al. [7]. The comparison between the measured and calculated cross-sectional mean gas holdups is shown in Fig. 5. It can be seen that there is a satisfactory agreement between the experimental and calculated gas holdup in the different operating conditions. Therefore, it is reasonable to conclude that the energy balance model used in this work can describe the circulation flow behavior in the novle internal-loop airlift reactor proposed in this work. 

A specially built conductivity probe was used to investigate the gas holdup in a novel internal-loop airlift reactor. The gas holdup generally increases with increasing solid holdup due to increased flow resistance. A model based on energy balance was developed that can be used to predict the average gas holdup in this novel interal-loop airlift reactor. 

Abstract This chapter embodies two sections. In the first section a survey of the state of the art of azo-dye conversion by means of bacteria is presented, with a focus on reactor design and operational issues. The relevance of thorough characterization of reaction kinetics and yields is discussed. The second section is focused on recent results regarding the conversion of an azo-dye by means of bacterial biofilm in an internal loop airlift reactor. Experimental results are analyzed in the light of a comprehensive reactor model. Key issues, research needs and priorities regarding bioprocess development for azo-dye conversion are discussed. 

Figure 5 shows a sketch of the experimental apparatus. It consists of a bench scale internal loop airlift, gas and liquid flow control units and a gas humidifier. 

Geometric details of the reactor are reported by [41], The volume of the liquid phase in the internal loop airlift, hence the reaction volume V, could be changed by varying the level of an overflow duct. 

Fig. 6 Acid orange 7 and phenol concentration in the internal loop airlift reactor operated with Pseudomonas sp. 0X1 biofilm on natural pumice. (A) Aerobic phase. Gas air. Liquid continuous feeding of phenol supplemented synthetic medium. (AN) Anaerobic phase. Gas nitrogen. Liquid batch conditions, dye supplemented medium...

The reactor flow pattern is that of an internal loop airlift with pneumatic mixing of both the liquid and the solid phases [61], the latter consisting in biofilm supported by granular solids. The reactor was assumed uniformly mixed. 

Internal loop airlift bioreactors, 1 742 Internal manifolding method, 12 200 Internal microwave field, 16 513 Internal olefins, sulfonation of, 23 527 Internal-pair formation (IPF),... 

In some respects, airlift reactors (airlifts) can be regarded as modifications ofthe bubble column. Airlift reactors have separate channels for upward and downward fluid flows, whereas the bubble column has no such separate channels. Thus, fluid mixing in bubble columns is more random than in airlift reactors. There are two major types of airlift reactors, namely, the internal loop (IL) and the external loop (EL). 

As this trend levels off with larger columns, it is recommended that values estimated for a 60 cm column are used. If heat transfer is a problem, then heat transfer coils within the column, or even an external heat exchanger, may become necessary when operating a large, industrial bubble column-type fermentor. Scale-up of an internal loop airlift-type fermentor can be achieved in the same way as for bubble column-type fermentors for external loop airhfts see Section 7.7. 

The design of a concentric tube internal loop airlift fermenter for the production of a biocatalysis enzyme at an annual rate of 8000 5%kg/yr is illustrated below. Product recovery efficiency is 80% and the titer... 

Figure 8.1 Internal-loop airlift bioreactor with (a) a baffle separating the riser and downcomer, (b) a continuous draught tube separating the riser and downcomer, and (c) a sectioned draught tube separating the riser and downcomer.

Figure 8.4 Circulation regime progression in a draught tube internal-loop airlift bioreactor (van Benthum et al., 1999b), where is the downcomer liquid velocity and is the gas slip velocity.

The gas separator is an important design feature that is often ignored. The simple reason is that internal-loop airlift bioreactors have only a few options, and the design is essentially the same a vented headspace, which is similar to the tank separator shown in Figure 8.7c. The external-loop airlift bioreactor, however, is presented with additional design options (shown in Figure 8.7a and b), which provides the external-loop airhft bioreactor with some advantages for certain processes. 

The vented tube connector minimizes the problem of gas accumulation, and gas is allowed to separate fairly efficiently. Unfortunately for some processes, the additional separator volume increases the gas separation efficiency relative to an internal-loop airlift bioreactor for the same reasons as for the tank separator ... 

The ELALR can be used for these processes because gas disengagement is very efficient. The bnbbles have a relatively fast rise velocity and slow radial velocity. Hence, bubble-bnbble interactions are diminished in the external-loop variant relative to the bnbble colnmn or stirred-tank bioreactor, which, in turn, leads to higher gas holdnp sensitivity to liquid property variations in bubble columns than in ELALRs (Chisti, 1989 Joshi et al., 1990 Shariati et al., 2007). In other words, the bnbble-bnbble collision frequency is lower in ELALRs, which makes coalescence-adjnsting liqnid properties, such as viscosity, surface tension, or ionic strength, less important. So, while bubble column and internal-loop airlift bioreactor gas holdnp are nsnally similar, the downcomer gas holdup in an external-loop airlift bioreactor is only 0-50% of the riser gas holdup (Bello et al., 1984), which leads to much lower global gas holdup in ELALRs. 

Gas-liquid mass transfer coefficients follow the same gas holdup trends. As shown in Figure 8.9, the gas-Uquid mass transfer coefficient increases monotoni-cally with riser superficial gas velocity. The correlations by Chisti etal. (1988b) (as cited by Murchuk and Gluz (1999) and Popovic and Robinson (1984) were developed using external-loop airlift bioreactors, while the others used the draught tube internal-loop airlift bioreactor. The DT-ILALR has much better performance than the ELALR. It is unfortunate to note that gas-liquid mass transfer correlations are much fewer in number than their gas holdup counterpart. 

Internal loop airlift reactor (ILALR) ILALR has an Internal flow separator creating channels for up- and downflow. + + ++ +++ ++ ++ Limited flow control... 

Blazej, M., Annus, J., andMarkos, J. (2004a), Comparison of gassing-out and pressure-step dynamic methods for kja measurement in an airlift reactor with internal loop, Chemical Engineering Research and Design, 82(10) 1375-1382. 

Blazej, M., Kisa, M., and Markos, J. (2004c), Scale influence on the hydrodynamics of an internal loop airlift reactor, Chemical Engineering and Processing, 43(12) 1519-1527. 

Freitas, C., and Teixeira, J.A. (2001), Oxygen mass transfer in a high solids loading three-phase internal-loop airlift reactor, Chemical Engineering Journal, 84(1) 57-61. 

Lo, C.-S., and Hwang, S.-J. (2003), Local hydrodynamic properties of gas phase in an internal-loop airlift reactor, Chemical Engineering Journal, 91(1) 3-22. 

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