OCR Text |
Show Values of the equilibrium constants for S02 and C02 are given in Table 2. The partitioning of pollutant between gas and liquid phases in the absorber may be described by: PI = P2 + P3 (ix) where PI is the partial pressure in the flue gas prior to gas/liquid equilibration (i.e. upstream of the absorber), P2 is the partial pressure of the pollutant remaining in the gas phase after equilibration in the absorber, and P3 is the partial pressure which would result if the specIes dissolved at equilibrium were transferred to the gas phase. The total activity of dissolved species at equilibrium is : PI (x) L.R.T + I/H* L is the volumetric ratio of liquid to gas in the absorber (e.g. m3liquid/m3gas), R is the gas constant (0.082 I atm mol-1K-l) and T is the absolute temperature in K. P3 may be estimated from: P3 = L.R.T. aT (xii) The efficiency of absorption may be defined as: (xiii) From equations (x), (xii) and (xiii): L.R.T E(%) = . 100 L.R.T + I/H* (xiv) The efficiency of absorption increases with increasing pH and liquid to gas ratio as shown in Figures 1 and 2 for S02 and C02 respectively. At equilibrium virtually all of the S02 could be absorbed in sea-water (PH -8) for L/G ratios typical of scrubbers (L/G = 10-3 - 10-2). Carbon dioxide is absorbed less efficiently. At a L/G ratio of 10-2 up to 25 % of the CO2 could be absorbed. These absorption efficiencies assume complete equilibration between gaseous and aqueous J?hases in the scrubber, a conditIon not met in practice. The extent of equilibratIon depends on the mass transfer characteristics of the system. The residence time in conventional scrubbers is of the order of seconds, too short for complete equilibration to take place. Nevertheless a very high S02 absorption efficiency of 99.9% has been determined at a L/G ratio of 0.01 in a laboratory scrubber (3). 3 |