Removal of Nitrogen Dioxide and Sulfur Dioxide from Air Streams by Absorption in Urea Solution

The study focuses on the absorption rates of NO sub( 2), SO sub( 2) and a mixture of these two acid gases into urea solution in packed bed column. The absorption rate was studied as a function of absorbent temperature, urea concentration and acid gas concentration. The influence of liquid temperature between 10 - 40 degree C, urea concentration between 0.1 - 0.5 M and acid gas concentration NO sub( 2) between 100 - 1000 ppm (191 - 1910 mg/m super( 3)), SO sub( 2) between 500 - 2500 ppm (1310 - 6530 mg/m super( 3)) were investigated. The mass gas flow rate of 20.646 (kg/m super( 2).min) at 25 degree C and the absorption rate were determined by measuring the NO sub( 2) and SO sub( 2) concentrations in the inlet and outlet streams of the absorptioncolumn. The absorption rate of SO sub( 2) increases with the decrease of temperature of absorbent (urea solution) and with the increase of the urea concentration. The presence of NO sub( 2) in the effluent gas stream lowers the absorption rate of SO sub( 2) in urea solution due to the fast reaction of NO sub( 2) with urea as compared with SO sub( 2). The absorption rate of NO sub( 2) decreases as the urea concentration exceeds 0.4 mol/l and for NO sub( 2) gas concentration of 100 ppm due to the decrease the diffusivity of the gas. The experimental data were analyzed using dimensionless analysis to find the correlation of mass transfer coefficient in the packed column Sh (H/dp) super( 1.2) = 4.19*10 super( -2) *(G' dp/ mu sub( g)) super( 0.87) ( mu sub( g)/ rho sub( g) D sub( AB)) super( 0.60) The results confirmed the hypothesis that the absorption is accompanied with chemical reaction. Also it is found the increasing the temperature of absorbent solution the absorption rate of two gases is decreases. The mass transfer coefficient models are in good agreements with the Kramer's equation.