Experimental study on the removal of SO_3 from coal-fired flue gas by alkaline sorbent

摘要

Selective Catalytic Reduction (SCR) system can efficiently remove NOx in coal-fired power plant, while raise SO3 concentration in the flue gas. Alkaline sorbent injection is a major approach to remove SO3. Experiments were conducted to study the SO3 absorption performance of alkaline sorbent. The SO3 absorption performance of the three alkaline sorbents was Na2CO3 > Ca(OH)(2) approximate to Mg(OH)(2). The ratio of SO3 absorption rate to SO2 absorption rate for Na2CO3 increased with the increasing temperature. The key parameters on the SO3 absorption performance of Na2CO3 were studied. The SO3 absorption by Na2CO3 was increased by 72.7% with increasing temperature from 150 degrees C to 300 degrees C, and the temperature had little influence on SO3 absorption above 300 degrees C. The increasing SO3 concentration and decreasing particle size of Na2CO3 enhanced SO(3 )absorption. However, when the average particle diameter was less than 50 the SO3 absorption was no longer significantly increased. The increasing CO2 concentration slightly reduced the SO3 absorption. After adding vapor into the flue gas, the SO3 absorption was obviously increased below 300 degrees C. The SO3 absorption variation above 300 degrees C was similar to the condition without vapor. When reaction temperature was 300 degrees C or above and reaction time was less than 20 min, external diffusion became the control step for SO3 absorption. On the basis of external diffusion control model, the mass transfer coefficient slightly increased from 1.68 x 10(-3)m/s to 1.75 x 10(-3) m/s when the reaction temperature increased from 300 degrees C to 400 degrees C.