Co-current absorbers

This is a straight line with a slope of - L/V, and is plotted in Figure 12-16B. At equilibrium, y = 0, and can be found from the operating equation as shown in Figure 12-16B. When equilibrium is not attained, the system can be designed with the mass transfer analysis discussed in Chapter 16. Co-current absorbers are used commercially for irreversible absorption. 

A schematic of a co-current absorber is shown in Figure 16-9A. The analysis will be done for dilute... 

D13. Repeat Example 16-3 to determine riQQ except use a co-current absorber. 

Figure 11-12. Diagram of verticai SMV co-current absorber with liquid recirculation foliowed by a gas-liquid separator. Pyles and Rader, 1989 ...

The term three-phase fluidization requires some explanation, as it can be used to describe a variety of rather different operations. The three phases are gas, liquid and particulate solids, although other variations such as two immiscible liquids and particulate solids may exist in special applications. As in the case of a fixed-bed operation, both co-current and counter- current gas-liquid flow are permissible and, for each of these, both bubble flow, in which the liquid is the continuous phase and the gas dispersed, and trickle flow, in which the gas forms a continuous phase and the liquid is more or less dispersed, takes place. A well established device for countercurrent trickle flow, in which low-density solid spheres are fluidized by an upward current of gas and irrigated by a downward flow of liquid, is variously known as the turbulent bed, mobile bed and fluidized packing contactor, or the turbulent contact absorber when it is specifically used for gas absorption and/or dust removal. Still another variation is a three-phase spouted bed contactor. 

It is possible to inject glycol in a gas line and have it absorb the water vapor in co-current flow. Such a process is not as efficient as countercurrent flow, since the best that can occur is that the gas reaches near equilibrium with the rich glycol as opposed to reaching near equilibrium with... 

DDIF has been applied to understand two-phase flow (air and water) in a Berea sandstone sample and the relationship to the pore geometry [65], Several different states of saturation were studied full saturation and partial saturation by three methods, i.e., centrifugation, co-current imbibition and counter-current imbibition. Imbibition is a process in which a porous sample absorbs the wetting fluid through capillary force. In the case of co-current imbibition, the bottom of the rock sample was kept in contact with water, so the water is imbibed into the rock and the water and air flowed in the same direction. For counter-current imbibition, the whole sample was immersed and the water was drawn into the center of the rock as, the air was forced out in this case, the water and air flowed in opposite directions. 

Particularly in co-current down-flow operation, very high gas-slurry interfacial areas per cubic meter of reactor volume can be realized [6]. To improve the solids suspension and/or to improve mass or heat transfer, in many cases a stirrer is added to the system. Particularly where pure gases have to be absorbed in the slurry and no gases are produced, the gas may be sparged into the liquid via a hollow shaft stirrer, sucking the gas from the free board above the slurry. 

In both contact processes the sulfur trioxide is, after the final passage through the final tray and cooling to 180 to 200°(3, absorbed in 98.5 to 99% sulfuric acid. This occurs either in a countercurrent absorber tower or in a jet scrubber in which acid is sprayed from the top in co-current with the reaction gas and is accompanied by conversion of sulfur trioxide into sulfuric acid. 

Fluid phase only Countercurrent flow Absorber Countercurrent flow Absorber Countercurrent flow Spray tower Co-current or countercurrent Bubble column Absorber or Reactor Venturi Static mixers Falling film, etc. 

Many workers (51-56) have considered the design of counter-current packed columns. The equipment can effectively be used in co-current operation since there is no disadvantage due to driving force as in the case of physical absorbers (57). Figure 7 shows schematically such a column and Table 3 gives the simplifying assumptions of Juvekar and Sharma (50). 

Forms for systems with three phases where two phases flow co-currently and countercurrent to the third phase were developed by Wankat (1980). Forms of the Kremser equation for columns with multiple sections are developed by Brian (1972, Chap. 31 and by King (1980, pp. 371-376). Forms for reboiled absorbers are given by Hwang et al. (1992a). 

B3. You want to use both co-current and countercurrent absorbers in a process. Sketch as many ways of doing this as you can think of. What are the advantages and disadvantages of each method ... 

In Section 12.9 we noted that co-current operation of absorbers was often enployed when a single equilibrium stage was sufficient. Co-current operation has the advantage that flooding cannot occur. This means that high vapor and liquid flow rates can be used, which automatically leads to small-diameter columns. 

Another convective reformer is shown in Figures 3.11 and 3.12. It was developed for use in low-pressure systems where a diluted fuel is available as off-gas from a fuel cell [475]. The reformer has two parallel catalyst beds. The burner is located in the eentre and the flue gas is added between the two beds where the catalytie reaction can absorb the heat to limit wall temperatures. By use of this mechanical configuration, the flue gas has co-current flow in the second bed and counter-current flow in the first bed to extract as much heat as possible. Results are shown in [114] [502],... 

Mass transfer in a wetted wall column (liquid film flowing down tube walls that absorbs a gas from a counter- or co-current gas flow stream) is given by (4)... 

Computer projections of atmospheric CC2 concentration for the next 200 years predict escalating increases in C02 concentration. Only about half the C02 released by humans is absorbed by Earth s natural systems. The other half increases the C02 concentration in the atmosphere by about 1.5 ppmv per year. Two conclusions can be drawn from the these facts. First, even if C02 emissions were reduced to the amount emitted in 1990 and held constant at that level, the concentration of CO, in the atmosphere would continue to increase at about 1.5 ppmv per year for the next century. Second, to maintain C02 at its current concentration of 360 ppmv, we would have to reduce fossil fuel consumption by about 50% immediately. 

Most Mossbauer experiments are currently performed with commercially available radioactive sources. For some applications, however, a so-called source experiment may be useful, in which the sample is labeled with the radioactive parent-isotope of the Mossbauer nucleus such as Co. The y-radiation of the radioactive sample is then analyzed by moving a single-line absorber for Doppler modulation in front of the detector. 

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