Countercurrent packed column

The efficiencies which may be obtained can consequently be calculated by simple stoichiometry from the equilibrium data. In the ease of countercurrent-packed columns, the solute can theoretically be completely extracted, but equilibrium is not always reached because of the poorer contact between the phases. The rate of solute transfer between phases governs the operation, and the analytical treatment of the performance of such equipment follows closely the methods employed for gas absorption. In the ease of two immiscible liquids, the equilibrium concentrations of a third component in each of the two phases are ordinarily related as follows ... 

FigHre 2.6 Schematic diagiam of a countercurrent packed column. 

Packed columns are used for the continuous contact between liquid and gas. The countercurrent packed column is the most common type of unit encountered in gaseous pollutant control for the removal of the undesirable gas. 

In a countercurrent packed column, n-butanol flows down at a rate of 0.25 kg/m2 s and is cooled from 330 to 295 K. Air at 290 K, initially free of n-butanol vapour, is passed up the column at the rate of 0.7 m /m2 s. Calculate the required height of tower and the condition of the exit air. 

Laboratory reactor for studying three-phase processes can be divided in reactors with mobile and immobile catalyst particles. Bubble (suspension) column reactors, mechanically stirred tank reactors, ebullated-bed reactors and gas-lift reactors belong the class of reactors with mobile catalyst particles. Fixed-bed reactors with cocurrent (trickle-bed reactor and bubble columns, see Figs. 5.4-7 and 5.4-8 in Section 5.4.1) or countercurrent (packed column, see Fig. 5.4-8) flow of phases are reactors with immobile catalyst particles. A mobile catalyst is usually of the form of finely powdered particles, while coarser catalysts are studied when placing them in a fixed place (possibly moving as in mechanically agitated basket-type reactors). 

Ammonia is recovered from an air-ammonia gas mixture by absorption into water, using a countercurrent packed column. The absorption of ammonia in water is accompanied by the evolution of heat which causes a rise in the liquid water temperature and hence a change in the equilibrium relationship. The problem and data values are taken from Backhurst and Harker (1990). 

The influence of pressure on the mass transfer in a countercurrent packed column has been scarcely investigated to date. The only systematic experimental work has been made by the Research Group of the INSA Lyon (F) with Professor M. Otterbein el al. These authors [8, 9] studied the influence of the total pressure (up to 15 bar) on the gas-liquid interfacial area, a, and on the volumetric mass-transfer coefficient in the liquid phase, kia, in a countercurrent packed column. The method of gas-liquid absorption with chemical reaction was applied with different chemical systems. The results showed the increase of the interfacial area with increasing pressure, at constant gas-and liquid velocities. The same trend was observed for the variation of the volumetric liquid mass-transfer coefficient. The effect of pressure on kia was probably due to the influence of pressure on the interfacial area, a. In fact, by observing the ratio, kia/a, it can be seen that the liquid-side mass-transfer coefficient, kL, is independent of pressure. 

P.C. Simoes, MJ. Cebola, R. Ruivo and M. Nunes da Ponte, Hydrodynamics in countercurrent packed columns at high pressure conditions, 259-262, GVC-Fachausschuss High Pressure Chemical Engineering, Karlsruhe, March 3-5 (1999). 

B. Benadda, M. Otterbein, K. Kafoufi and M. Prost, Influence of pressure on the gas-liquid interfacial area a and the coefficient ki.a in a countercurrent packed column, Chem. Engng. Processing, 35 (1996) 247-253. 

B. Benadda, K. Kafoufi, P. Monkam and M. Otterbein, Hydrodynamics and mass transfer phenomena in countercurrent packed column at elevated pressures, Chem. Engng. Science, in press. 

Roberts, RV., Hopkins, G.D., Munz, C., Riojas, A.H. (1985) Evaluating two-resistance models for air stripping of volatile organic contaminants in countercurrent, packed column. Environ. Sci. Technol. 19, 164—173. 

In a countercurrent packed column, n-butanol flows down at the rate of 0.25 kg/m2 s and is cooled from 330 to 295 K. Air at 290 K, initially free of n-butanol vapour, is passed up the column at the rate of 0.7 m3/m2 s. Calculate the required height of tower and the condition of the exit air. Data Mass transfer coefficient per unit volume, hDa = 0.1 s 1. Psychrometric ratio, (h/hDpAs) = 2.34. Heat transfer coefficients, hL = 3hG. Latent heat of vaporisation of n-butanol, A = 590 kJ/kg. Specific heat capacity of liquid n-butanol, Cl = 2.5 kJ/kg K. Humid heat of gas , s = 1.05 kJ/kg K. 

First, we measured thermodynamic and mass transfer data of the multicomponent system olive 0U/CO2 (3,4). The phase equilibria was modulated by correlating the partition coefficients (Kj = y /x ) of each component present in the mixture as a function of the mole fraction of the FFA fraction in the liquid phase (3). Mass transfer studies were performed in a lab-scale countercurrent packed column. The experimental measured mass transfer coefficients were... 

A waste-air stream containing 2 mol % of impurity A is purified to 0.02% by scrubbing with pure water in a countercurrent packed-column. The column provides 7 overall gas-phase transfer units in a height of 1.75 m. The equilibrium mole fractions of A in the vapor and liquid are related according to ... 

Fig. 13. Interfacial areas (a) and true liquid-side mass-transfer coefficients (b) in countercurrent packed columns. (See tabulation on p. 71.)...

The sulfur dioxide content of a gas stream is lowered by 90% by scrubbing with water in a countercurrent packed column. The column is 1.25 m in diameter and 5 m in height. The gas rate is 500 kmol/h, and the inlet sulfur dioxide concentration is 2% mole. The column was designed such that the sulfur dioxide concentration in the bottoms does not exceed 0.04% mole. Determine the required water rate, the number of gas-phase transfer units, the height of the gas-phase transfer unit, and the mass transfer coefficient KyU. The equilibrium relationship for sulfur dioxide is given as Y = 38X. 

Countercurrent packed column target species Henry s law constant <10 kPa/mol fraction feed gas concentration <1 vol%. Efficiencies 95+%. Vulnerable to plugging. OK for foaming and corrosive. 

There are no effective interfacial area correlations in the literature for the specific cases discussed here. The correlation that conies closest to that required for trickle bed operation is that of Puranik and Vogelpohl [29], which is for a continuous gas phase and a dispersed liquid phase, but in a countercurrent packed column, well below the loading point. They derived the following correlation (for piLfQ, = 1.5 kg/m s) ... 

Spray chamber Economic NTU = 4 gas energy consumption 2.5 kj/m with liquid to gas ratio about 1.5 L/m design on gas phase controlling, superficial gas velocity 0.9 to 1.2 m/s. Power usage 0.03 to 0.5 kW s/m. Ap gas = 0.5 kPa. Countercurrent packed column Economic NTU usually < 5 critical energy consuming phase is the gas at about 3 kj/m with liquid to gas ratio about 0.7 to... 

---