Absorption of gas

Partial pressure of solute in gas phase (kN/m2) Concentration of solute in water kg/1000 kg water  

Whilst the solubility of a gas is not substantially affected by the total pressure in the system for pressures up to about 500 kN/m2, it is important to note that the solubility falls with a rise of temperature. Thus, for a concentration of 25 per cent by mass of ammonia in water, the equilibrium partial pressure of the ammonia is 30.3 kN/m2 at 293 K and 46.9 kN/m2 at 303 K. 

In many instances the absorption is accompanied by the evolution of heat, and it is therefore necessary to fit coolers to the equipment to keep the temperature sufficiently low for an adequate degree of absorption to be obtained. 

For dilute concentrations of most gases, and over a wide range for some gases, the equilibrium relationship is given by Henry s law. This law, as used in Chapter 11, can be written as  

Tests are made on the absorption of carbon dioxide from a carbon dioxide-air mixture in a solution containing 100 kg/m3 of caustic soda, using a 250 mm diameter tower packed to a height of 3 m with 19 mm Raschig rings. 

The carbon dioxide in the inlet gas was 315 parts per million and the carbon dioxide in the exit gas was 31 parts per million. 

What is the value of the overall gas transfer coefficient KGal 

The NaOH, solution contains 100 kg/m3 NaOH. The mean molecular mass of liquid is  

For dilute gases, y = Y and a mass balance over the tower gives G m(yi - y2)A = KGaP(y - ye)ta ZA 

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Fig. 9. Genesis of acid tain (13). From the oxidation of C, S, and N during the combustion of fossil fuels, there is a buildup in the atmosphere (gas phase, aerosol particles, raindrops, snowflakes, and fog) of CO2 and the oxides of S and N, which leads to acid—base interaction. The importance of absorption of gases into the various phases of gas, aerosol, and atmospheric water depends on a number of factors. The genesis of acid rain is shown on the upper right as an acid—base titration. The data given are representative of the environment in the vicinity of Zurich, Switzedand.

Enabhng the use of hard or even sea water for heat rejection e,g, for absorption of gases (CO9, SO9, CIO9, , , ) in chilled water (desorption is provided simultaniously with chilling) when a direct contact barometric condenser is used. 

Mass-transfer theory indicates that for trays of a given design the factors most hkely to inflnence E in absorption and stripping towers are the physical properties of the flnids and the dimensionless ratio Systems in which the mass transfer is gas-film-controlled may be expected to have plate efficiencies as high as 50 to 100 percent, whereas plate efficiencies as low as 1 percent have been reported for the absorption of gases of low sohibility (large m) into solvents of relatively high viscosity. 

FIG. 14-78 Liqnid-film resistance in absorption of gases in wetted-wall columns. Theoretical lines are calculated for oxygen absorption in water at 55 F. To convert feet to meters, multiply by 0.3048 C = /9 ( F — 32). (Sheixuood and Vigfoid, Absorption and Extraction, 2d ed., McGraw-Hill, New York, 1952. )... 

Cbarcoal usually is ground in hammer mills with screen or air classification. For absorption of gases it is usuahy crushed and graded to about No. 16 sieve size. Care should be taken to prevent it from igniting during grinding. 

Propeller mixers are unsuitable for suspending rapid settling substances and for the absorption of gases. Propellers are designed on the basis of data obtained from properly executed modeling experiments. 

Gas absorption The process of absorption of gases that takes place in certain solids or liquids. 

The adsorption of gases on solid surfaces proceeds to such an extent that approximately 10 7 gr. is present per cm.2 in the equilibrium state. This is of the same order of magnitude as the strength of the limiting capillary layer of a liquid ( 184), hence it is not improbable, as suggested by Faraday (9) (1884), that the adsorbed gas is sometimes present in the liquid state. The adsorbed amount increases with the pressure and diminishes with rise of temperature. The first effect does not follow a law of simple proportionality, as in the case of the absorption of gases by liquids, rather the adsorbed amount does not increase so rapidly, and the equation ... 

H.W. Webb, Absorption of Nitrous Gases , Longmans, Green Co, London (1923) (Absorption of gases by nitric acid description of various absorption towers, etc) 16) F.A. Ernst, Fixation of Atmospheric Nitrogen , Van Nostrand, NY (1928) 17) Anon, IEC 22, 433 (1930)... 

Lj + G —> L2 Absorption of gases in water Dissolution of gases like hydrogen chloride, ammonia and carbon dioxide in water... 

Absorption of gases and vapour by drops has been studied by Garner and Kendrick(15) and Garner and Lane(16) who developed a vertical wind tunnel in which drops could be suspended for considerable periods of time in the rising gas stream. During the formation of each drop the rate of mass transfer was very high because of the high initial turbulence. After the initial turbulence had subsided, the mass transfer rate approached the rate for molecular diffusion provided that the circulation had stopped completely. In a drop with stable natural circulation the rate was found to approach 2.5 times the rate for molecular diffusion. 

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