The chemical fundamentals of one variant of the chelate method of combined removal of sulfur and nitrogen oxides from flue gases were described. Special attention was paid for chemical reactions responsible for production of solid wastes. A flow sheet of the technology was presented and the operation of industrial installation of SO2, NOx and dust from combustion gases of two 29 MW, grate boilers each was described. The material balance of the process was made and the quantity of solid wastes produced during 3 weeks test of the technology was presented.