MINIMAL FLOW-RATE RATIO OF SLURRY AND GAS IN LIME LIMESTONE FLUE-GAS SCRUBBING TECHNOLOGY

The lime/limestone scrubbing process is the most commonly used method for reduction of the SO2 concentration in flue gases. The process requires a large amount of energy for slurry recycling in the scrubber and therefore careful control of the ratio between slurry and gas flow rate is required. Calculation of the minimum ratio of slurry to gas flow rate (L/V)m under equilibrium conditions, in spite of its complexity, ought to be included at the design stage in order to avoid errors connected with the chemistry of the process. This is particularly important if there is a high chloride ion concentration in the slurry liquor. The appropriate calculation method has been developed applying the Bechtel Radian Equilibrium Program, in which more than 40 chemical components are taken into consideration. It has been proved by calculation that it is possible to reduce the (L/V)m value and therefore the energy requirement for slurry circulation by adding adipic acid to the slurry and by increasing the concentration of the appropriate cations (Mg++ or Na+) in the slurry liquor. Increased SO2 concentrations in the flue gas and higher chloride ion concentrations in the liquid produce the opposite effect.