Method for preparing magnesium hydroxide, magnesium oxide and gypsum from dolomite lime denitration and desulfurization of flue gas

The invention relates to a method for simultaneously preparing magnesium hydroxide, magnesium oxide and gypsum from dolomite lime denitration and desulfurization of flue gas, and belongs to the technical field of flue gas pollution control. The problems of separation of dolomite lime calcium-magnesium separation are ingeniously solved by a low-cost solution of NH4Cl. Ammonia gas (NH3) obtained by ammonia distillation in a calcium-magnesium separation process is heated for denitration. Mg(OH)2 precipitates formed in the calcium-magnesium separation process are used for the desulfurization of the flue gas. A solution of CaCl2 subjected to solid-liquid separation after calcium-magnesium separation is used for precipitating a solution of MgSO4 generated by desulfurization to produce byproducts CaSO4.1/2H2O building gypsum and a solution of MgCl2. Residual Mg(OH)2 is dried or calcinated to form a finished product Mg(OH)2 or MgO. According to the method, the denitration and desulfurization cost is greatly lowered;