Packed-Bed Absorber

Henry s law, which depends on total pressure, can be used to predict solubility only when the equilibrium line is straight, the case when the solute concentration is very dilute. Another form of Henry s law is 

Calculate Henry s law constant (/-/) from thesolublllty of SOj in pure water at 30°C and 1 atm. The data are given in Table 7.1. 

Source Data from Peytavy, J. L. et al. 1990. Chemical Engineering and Processing, 27(3), 155-163. 

The mole fraction of SOj in the gas phase, y, is calculated by dividing the partial 

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By far the major portion of the available gas-absorption data have been obtained for countercurrent flow, which is the normal mode of operation for packed-bed absorbers. Special mention may be made of the results of Dodds et al. (D6), who examined mass transfer by the absorption of gas in liquid under cocurrent downward flow at flow rates higher than those corresponding to the flooding point for countercurrent operation. 

This paper presents the experimental results, with a focus on studies of the regeneration of the hexamine cobalt complex additive by using the activated carbon in a laboratory packed-bed absorber. 

Absorption is another gas-liquid process with two phases. Packed bed absorbers have three phases when also taking the solid packing of the column into consideration. Both continuous, i.e., packed bed, and multistage absorption are common in the chemical and biological industry. 

Show that the steady- state and dynamic models for a double-pipe, counter-current heat exchanger can have the same form as the model of a packed bed absorber. Discuss the assumptions inherent in both the heat exchanger and the absorber models which might lead to significant differences in the kinds of model equations used to describe each system. 

The high capital investment cost of the Asahi process is due to the necessity for large absorbers, evaporators, crystallizers, dryers, rotary kiln crackers and screw decanter separators. The major operating and maintenance costs are electricity, fuel oil, steam and chemicals such as soda ash, EDTA and limestone. The requirement for consumption of large amounts of utilities is associated with the operation principle and design of the Asahi process. According to the economic evaluation, equipment required for N0X and SO2 absorption (such as packed-bed absorbers) accounts for 20% of total direct capital investment for treatment of dithionate ion (such as evaporator, crystallizer, dryer, and cracker) it accounts for about 40% and for treatment of nitrogen-sulfur compounds (such as screw decanter and cracker) it accounts for only 2%. 

To conclude, the desired reaction (12.1) is favored by a large gas/liquid interfacial area and a small liquid fraction. This can be obtained in a spray column. Another consideration favoring spray-tower over packed-bed absorbers is the large gas flow to be processed. 

Usually, flow in a packed-bed absorber is countercurrent. Gravity causes the liquid to flow down through the packing, whereas a small pressure drop drives the gas flow upward. This pressure drop plays an important role in packed beds. Without liquid present, the pressure-drop across dry packing increases approximately with the square of the gas flowrate (see Fig. 8). 

Combine material and energy balances with mass-transfer considerations to determine the height required by a packed-bed absorber or stripper when heat effects are important. 

Caustic solution (typically 10-20 wt% caustic soda in water) is also commonly nsed in packed-bed absorbers to control HCl, CI2, and HF emissions. Because these compoimds react with caitstic, the driving force for mass transfer is increased and more efficient removal is achieved at the same liqirid-to-gas ratio and packing depth. 

Deleye and Froment (1986) have reported the data on absorption of CO2 in aqueous solution of monoethanol amine (MEA) in a packed bed absorber. Gas containing CO2 at a partial pressure of 2 atm is to be purified by absorption into an aqueous solution of MEA in a packed bed filled with 5 cm diameter steel pal rings. Assuming excess concentration of MEA in the solution, the reaction between CO2 and MEA is treated as pseudo-first order reaction with rate constant k = 7.194 x 1(P s L A quantity of 6500 rcF/h of gas is treated with 1000 m /h of MEA solution. Partial pressure of CO2 is to be reduced to 0.02 bar. Column diameter is 2 m and it is operating at a pressure of 14.3 bar and a temperature of 315 K. Calculate the height of the bed. The following data are reported. 

Design of a packed bed absorber for the absorption of ammonia in sulfuric acid. After Ramm [1953]. 

The first troubleshooting problem involves a packed-bed absorber. The absorber has been designed to remove a contaminant from an air purge stream and has been operating for some time as designed. Then it is observed that the oudet air contains more contaminant than it should. A similar problem involving a tray absorber is given at the end of chapter. 

The knowledge of packed-bed absorber performance illustrated on the Colburn graph is a good starting point. Any or all of these parameters could be different from design conditions. 

The following are used to simulate packed-bed absorber in Aspen Plus ... 

The column diameter and the height of the packed-bed absorber estimated by PRO/II are shown in Figure 7.70. 

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