Gas absorption/stripping

Fixed-bed desulfuri2ation is impractical and uneconomical if the natural gas contains large amounts of sulfur. In this case, bulk sulfur removal and recovery (qv) in an acid gas absorption—stripping system, followed by fixed-bed residual cleanup is usually employed. 

Spray chamber Cocurrent, cross-flow, countercurrent Differential Gas Absorption, stripping, humidification, dehi i midi ficati o n... 

Line mixer Cocurrent Differential Liquid or gas Absorption, stripping... 

Perfectly isothermal systems are rare in chemical engineering practice and many processes, such as distillation, gas absorption, stripping, condensation, and evaporation, involve the simultaneous transfer of mass and energy across fluid-fluid interfaces. Representative temperature profiles in some nonisothermal processes are shown in Figure 11.1. The temperature profile also has a large influence in chemically reacting systems. For nonisothermal systems it is important to consider simultaneous heat transfer even though we are primarily interested in the mass transfer process. 

In this section we turn our attention to more complex shapes represented by tower packings used in operations such as gas absorption, stripping, and distillation. The operation of such columns is addressed in more detail in Chapter 8. 

Chapter 8 deals with the configuration of bulk flows of two phases/regions (one of which may be solid) perpendicular to the direction of force(s). The directions of motion of the two phases may be parallel to each other in either countercurrent or cocurrent fashion, or they may be in crossflow. Figures 8.1.1-8.1.4 illustrate the counter-current flow vs. force configuration for all three classes of separation systems. Conventional countercurrent devices/ processes of gas absorption/stripping, column distillation... 

Solute diffusion through porous liquid-filled membrane We consider here solute diffusion through a porous liquid-filled membrane under the condition of no convection (Figure 3.4.5(c)). Examples of separation pro-cesses/techniques where such a situation is encountered are isotonic dialysis, membrane based nondispersive gas absorption/stripping or solvent extraction, supported or... 

First we consider gas-liquid equilibrium as in gas absorption/ stripping. 

This equation is being integrated between the two limits of r, namely R,., and the inside radius of the fiber bundle and the outside radius of the fiber bundle in the device, respectively the corresponding limits of species i concentration in the device are C,ro and Cum, where the subscript m indicates the midway point between the first and second halves of the porous membrane based gas absorption/ stripping device ... 

One could also develop an analysis based on individual film coefficients, as we have done in equations (8.1.62(a)-d). Further, if the film coefficient/overall coefficient available is based on equimolar counterdiffusion, then a correction using the bulk flow correction factor has to be used for gas absorption/stripping therefore the expression for NTU will contain additional terms via... 

Countercurrent gas absorption/stripping in a column with axial diffusion/dispersion... 

Figure 8.1.16. Countercurrent gas absorption/stripping column with axial dispersion/diffitsion. (a) Operating lines and equilibrium curve, (b) Concentration profiles of gas and liquid phases along the tower length for gas absorption/stripping with (solid lines) or without...

Gas absorption/stripping in multistage devices having an overall countercurrent flow pattern... 

As practiced in gas absorption/stripping analyses (equations (8.1.54a-c), we may define for the enriching section the height of a transfer unit based on the overall vapor phase, HTUove, and the number of transfer units based on overall vapor performance, NTUove, as follows ... 

Distillation in a packed tower is preferred over a plate tower for small diameter towers having a diameter less than 2 ft. For corrosive liquids, ceramic/plastic packings are preferred along with a packed tower over plate towers. For low pressure drops or vacuum distillation applications, structured packings are preferred. The details provided in Section 8.1.2.1 for gas absorption/stripping processes are equally valid for distillation processes. Calculation methods for flooding based design illustrated there may also be used here. 

T.R. Carey, J.E. Hermes, G.T. Rochelle, A model of add gas absorption/stripping using methyldiethanolamine with added acid. Gas Sep. Purif. 5 (1991) 95-109. 

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