Gas-liquid columns

Now, from its essential notion, we have the feedback interconnection implies that a portion of the information from a given system returns back into the system. In this chapter, two processes are discussed in context of the feedback interconnection. The former is a typical feedback control systems, and consists in a bioreactor for waste water treatment. The bioreactor is controlled by robust asymptotic approach [33], [34]. The first study case in this chapter is focused in the bioreactor temperature. A heat exchanger is interconnected with the bioreactor in order to lead temperature into the digester around a constant value for avoiding stress in bacteria. The latter process is a fluid mechanics one, and has feedforward control structure. The process was constructed to study kinetics and dynamics of the gas-liquid flow in vertical column. In this second system, the interconnection is related to recycling liquid flow. The experiment comprises several superficial gas velocity. Thus, the control acting on the gas-liquid column can be seen as an open-loop system where the control variable is the velocity of the gas entering into the column. There is no measurements of the gas velocity to compute a fluid dynamics... 

A set of experiments on gas-liquid motion in a vertical column has been carried out to study its d3mamical behavior. Fluctuations volume fraction of the fluid were indirectly measured as time series. Similar techniques that previous section were used to study the system. Time-delay coordinates were used to reconstruct the underl3ung attractor. The characterization of such attractor was carried out via Lyapunov exponents, Poincare map and spectral analysis. The d3mamical behavior of gas-liquid bubbling flow was interpreted in terms of the interactions between bubbles. An important difference between this study case and former is that gas-liquid column is controlled in open-loop by manipulating the superficial velocity. The gas-liquid has been traditionally studied in the chaos (turbulence) context [24]. 

There are numerous applications for bubble columns, for example, gas-liquid columns include the absorption of isobutylene in sulfuric acid, and liquid-liquid columns are used for nitration of aromatic hydrocarbons. 

A detailed model for a gas-liquid column with external recirculation loop has been published by Orejas [11]. The model takes into account the axial dispersion and mass transfer from bubbles. An important conclusion is that the mass-transfer rate is fast compared with the chemical reaction. As a result, a pseudohomoge-neous model for liquid-phase reaction may be applied for design purposes. 

The effects of liquid velocity (at least at low velocities), direction of flow and liquid properties are only minor for Newtonian fluids. Correlations on gas-liquid columns are given by Joshi [63], Field and Davidson [64] measured the dispersion in a large industrial column (de - 3.2 m, H — 19 m) and found agreement with the correlations of Dcckwer et al. [65] and Joshi [63] (Tabic 3). The influence of particles can be expected to be small, at least for low concentrations and small particles. This is confirmed by the early experiments of Kato et al. [15, 69], For particle sizes ranging from 63... 

GSC is based on adsorption of gaseous substances on solid surfaces. Distribution constants are generally much larger than those for GLC. As a result, GSC is useful for the separation of species that are not retained by gas-liquid columns, such as the components of air, hydrogen sulfide, carbon disulfide, nitrogen oxides, carbon monoxide, carbon dioxide, and the rare gases. 

If we wished to perform the same liquid-lifting task as shown in Example 14.1, we could use the apparatus sketched in Fig. 14.5. For such an apparatus, with the flow rates given in Example 14.1, calculate the necessary pressures at the inlets to the turbine and to the pump (assume that these pressures are the same). Compare these with the necessary pressure at the base of the gas-liquid column in Example 14.1. Assume that the overall vertical elevation change is 20 ft for both gas and liquid in both cases. 

Gagnon, H., Lounes, M., and Thibault, J. (1998), Power consumption and mass transfer in agitated gas-liquid columns A comparative study, Canadian Journal of Chemical Engineering, 76(3) 379-389. 

Bennett MA, West RM, Luke SP, Jia X, Williams RA. (1999) Measurement and analysis of flows in gas-liquid column reactor. Chem. Eng. Sci., 54 5003-5012. 

PHYSICAL MODELING OF AXIAL MIXING IN SLUGGING GAS-LIQUID COLUMNS... 

Physical Modeling of Axial Mixing in Slugging Gas-Liquid Columns 51... 

Here, we will discuss the mass balances for a PER with three phases. A volume element in a gas-liquid column reactor is shown in Figure 6.16. The liquid flow direction is set in the... 

FIGURE 6.16 A volume element in a gas-liquid column reactor. 

The Crawford-Wilke flooding correlation for liquid-liquid contactors is shown as Figure 11-7. The values for surface area and void fraction for commonly used random dumped packings are given in Tables 11-4, 11-5, and 11-6. The correlations to predict maximum capacity of liquid-liquid contactors do not provide the same degree of reliability as offered by correlations for gas-liquid columns. 

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