Semi-dry treatment method and system for flue gas desulfurization and denitrification

The invention relates to a semi-dry treatment method and system for flue gas desulfurization and denitrification, and belongs to the technical field of flue gas purification, and the method comprises the following steps: step 1, sulfur oxides in low-temperature flue gas react with a urea solution to generate a generation solution containing ammonium sulfite; step 2, reacting the generation liquid containing ammonium sulfite in the step 1 with medium-temperature flue gas to form a supersaturated solution of ammonium sulfite, and converting the medium-temperature flue gas into low-temperature flue gas; 3, the supersaturated solution of ammonium sulfite in the step 2 and the high-temperature flue gas are in parallel flow and make contact with each other, the supersaturated solution of ammonium sulfite is evaporated into solid particles, ammonium sulfite in the solid particles reacts with nitric oxide in the high-temperature flue gas to generate ammonium sulfate solid particles, and the high-temperature flue gas