Preparing pure urea solution, useful as reducing agent for selective catalytic reduction of nitrogen oxides, comprises rinsing urea solution in deaerator, separating urea crystals and re-circulating mother liquor enriched with biuret

摘要

Continuously preparing highly pure urea solution from a conventional urea synthesis, comprises producing a circulation quantity ratio of 10-30 kg solution/kg suspension crystals of concentrated urea solution; rinsing in a deaerator containing a tempered air; degassing with ammonia; separating the crystals from the separating apparatus and provided into dissolving container, to form urea solution, which is free of typical impurities and contains ammonia and biuret; and re-circulating the mother liquor enriched with biuret for biuret decomposition through a reactor. Continuous preparation of highly pure urea solution from a conventional urea synthesis, comprises producing a circulation quantity ratio of 10-30 kg solution/kg suspension crystals of concentrated urea solution in a crystallizer under 0.05-0.2 bar; subsequently concentrating in a separating apparatus to a water content of 5-25%; rinsing in a deaerator containing a tempered air in a quantity ratio of 1-3 kg/kg of crystals; degassing with ammonia; separating the crystals from the separating apparatus and provided into highly turbulent dissolving container, in which the crystals are dissolved with a circulation quantity ratio of 10-30 kg solution/kg crystals in vapor condensate that arises in the urea production, to form urea solution (31.8-33.2%), which is free of typical impurities and contains ammonia (lesser than 30 ppm) and biuret (50 ppm); and re-circulating the mother liquor enriched with biuret for biuret decomposition through a reactor.