Cocurrent packed columns, mass-transfer coefficients

The reported study on gas-liquid interphase mass transfer for upward cocurrent gas-liquid flow is fairly extensive. Mashelkar and Sharma19 examined the gas-liquid mass-transfer coefficient (both gas side and liquid side) and effective interfacial area for cocurrent upflow through 6.6-, 10-, and 20-cm columns packed with a variety of packings. The absorption of carbon dioxide in a variety of electrolytic and ronelectrolytic solutions was measured. The results showed that the introduction of gas at high nozzle velocities (>20,000 cm s ) resulted in a substantial increase in the overall mass-transfer coefficient. Packed bubble-columns gave some improvement in the mass-transfer characteristics over those in an unpacked bubble-column, particularly at lower superficial gas velocities. The value of the effective interfacial area decreased very significantly when there was a substantial decrease in the superficial gas velocity as the gas traversed the column. The volumetric gas-liquid mass-transfer coefficient increased with the superficial gas velocity. 

Most recently. Kirillov and Nasamanyan15 carried out a very interesting unsteady-state analysis of liquid-solid mass transfer for cocurrent upflow in a fixed-bed reactor. The analysis was compared and verified by the steady-state measurements of liquid-solid mass-transfer coefficients in a 10-cm x 10-cm square column with a height of 50 cm. Three types of packings, 30-mm and 8-mm... 

Oshima, S, T, Takemasu, Y, Kuriki, K, Shimada, M, Suzuki, and J, Kato, "Liquid Phase Mass Transfer Coefficient and Gas Holdup in a Packed Bed Cocurrent Upflow Column", Kagaku Kogaku 3, (1977) 400-404,... 

It shoiild be pointed out that in most liquefaction processes, the flow of the reactants is cocurrent i q)ward. In cocurrent operation, there is no flooding limit, and greater throu put is attained compared with co mterc irrent column of similar size. Moreover, for the same values of gas and liquid flow rates, interfacial area, liqiaid mass transfer coefficient and pressure drop values in a cocurrent upward packed column are always higher than those obtained in downflow towers (l 3). Upflow operations also give a better performance due to larger liqioid holdup and better liq iid distribution throu out the catalyst bed jlkk). 

In packed columns, it is conceptually incorrect to use the staged model even though it works if the correct height equivalent to a theoretical plate (HETP) is used. In this chapter we will develop a physically more realistic model for packed columns that is based on mass transfer between the phases. After developing the model for distillation, we will discuss mass transfer correlations that allow us to predict the required coefficients for common packings. Next, we will repeat the analysis for both dilute and concentrated absorbers and strippers and analyze cocurrent absorbers. A simple model for mass transfer on a stage will be developed for distillation, and the estimation of stage efficiency will be considered. After a mass transfer analysis of mixer-setder extractors. Section 16.8 and the appendix to Chapter 16 will develop the rate model for distillation. 

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