METHOD FOR SYNTHESIZING UREA BY TREATING TRIAZINE COMPOUND-CONTAINING WASTE WATER

PROBLEM TO BE SOLVED: To provide a method for treating triazine compound-containing waste water, also recovering ammonia and carbon dioxide and utilizing them for synthesis of urea. SOLUTION: This method for synthesizing urea by treating the triazine compound-containing water comprises (A) a process of hydrolyzing a waste water having 9-12 pH and 0.5-2% triazine compound concentration under conditions of 150-300 deg.C temperature, 0.5-2 hr mean holding time and 6-10 MPa naturally generated pressure, (B) a process of separating the waste water obtained in the process (A) to a mixed gas of ammonia with carbon dioxide having 15-35 wt.% steam concentration and a bottom liquid not essentially containing the triazine compound and ammonia by a distillation operation, and (C) a process of absorbing the mixed gas of ammonia with carbon dioxide obtained in the process (B) with a process liquid from the urea-producing process for preparing an ammonia excess carbamic acid ammonium solution having 65-75 wt.% water content and feeding it to the urea-producing process.