НАУЧНИ ТРУДОВЕ НА РУСЕНСКИЯ УНИВЕРСИТЕТ - 2011, том 50, серия 9.1 - 29 - Determination of the Equilibrium Partial Pressure of SO 2 over the Absorption Slurry in Case of Purification of Flue Gas From Sulfur Dioxide using Gypsum Technology Elena Razkazova-Velkova, Ljutzkan Ljutzkanov, Nikolai Kolev, Dimitar Kolev, Daniela Dzhonova-Atanasova Abstract:The most widely used process for purification of flue gases from SO 2 is its absorption with slurry containing CaCO 3 . Up to now there are installations for carrying out of the SO 2 absorption according to this process only for big capacity boilers because of the great height of the existing absorbers for this technology, about 20-30 m. To create new absorbers for small and middle capacity boilers, equilibrium data for the absorption of SO 2 are necessary. Up to now such data are available in the literature only for a temperature of 20 and 25 o C. Key words: SO 2 , purification of flue gas, equilibrium partial pressure, absorption slurry, gypsum, absorption degree, experiment. INTRODUCTION The most widely used process for purification of flue gases from SO 2 is its absorption with slurry containing CaCO 3 [1-14]. Even when Ca(OH) 2 slurry is used as an absorbent, as a result of its circulation in the absorber and saturation in CO 2 from the flue gas (CO 2 concentration about 12%), the absorbent is transformed into CaCO 3 . Up to now there are installations for carrying out of the SO 2 absorption according to this process only for big capacity boilers. It is because the height of the existing absorbers for this technology is too great, about 20-30 m. Building of such installations for small and middle capacity boilers is too expensive and leads to unacceptably long pay back term. Another disadvantage of the existing installations is their low degree of absorption, about 95%. It means that about 5 % of the SO 2 entering the absorber goes out with the flue gases into the atmosphere. Because they are cooled in the installation, their distribution in the atmosphere, with an initial SO 2 concentration of about 150 ppm, requires a great height of the stack. For choosing the technological scheme and type of the absorbers and their calculation, data for the equilibrium partial pressure of SO 2 over the slurry at the temperature in the absorber are necessary. Although a great number of papers are published in the area of the considered technology, data for the equilibrium partial pressure of the SO 2 are found only at a temperature of 20 o C [4] and 25 o C, [12]. There are no data at temperatures at which the industrial apparatuses for absorption of SO 2 from the flue gases operate. The aim of this paper is to obtain the necessary data. Due to the low solubility of the main solid components of the slurry circulating in the absorbers, the concentration of the SO 2 and its partial pressure in the gas phase at a given temperature is practically a function of pH. EXPERIMENTAL At first it was decided the experiment to be carried out by passing gas through a succession of thermostated absorption flasks. The SO 2 partial pressure was calculated from the pressure in the last flask and SO 2 concentration in the out gas, measured by a precise gas-analyzer. For analyzing of the SO 2 in the gas phase an infrared Hartman and Braun analyzer is used. The investigations are carried out at different temperatures and pH values. The equilibrium partial pressure (P SO2 ) in Pa was calculated according to Equation (1): (1), , 2 GSO a O 2 H a a 6 2 SO C P P P P 10 P - = -