Ammonia scrubbing is one of many process for removing sulfur dioxide from flue gases. The gases are bubbled through an aqueous solution of ammonium sulfite, and the SO2 reacts to form ammonium bisulfite:
(NH4)2SO3 (aq) + SO2 (g) + H2O(l) => 2 NH4HSO3(aq)
Subsequent process steps yield concentrated SO2 and regenerate ammonium sulfite, which is recycled to the scrubber. The sulfur dioxide is either oxidized and absorbed in water to form sulfuric acid or reduced to elemental sulfur. Flue gas from a power plant boiler containing 0.30% SO2 by volume enters a scrubber at a rate of 50000 mol/h at 50°C. The gas is bubbled through
an aqueous solution containing 10.0 mole% ammonium sulfite that enters the scrubber at 25°C. The gas and liquid effluents from the scrubber both emerge at 35°C. The scrubber removes 90% of the SO2 entering with the flue gas.
The effluent liquid is analyzed and is found to contain 1.5 moles (NH4)2SO3 per mole of NH4HSO3. The heat of formation of (NH4)2SO3 (aq) at 25°C is -890.0 kJ/mol, and that of NH4HSO3 (aq) is -760 kJ/mol. The heat capacities of all liquid solutions may be taken to be 4.0 J/(g*°C) and that of the flue gas may be that of nitrogen. Evaporation of water may be neglected. Calculate the required rate of heat transfer to from the scrubber (kW).