Procédé et installation de préparation d'urée, ainsi que les produits conformes à ceux obtenus par le présent procédé ou procédé similaire

摘要

In a process for the synthesis of urea from ammonia and carbon dioxide having a conversion rate of ammonium carbamate to urea of from 40 to 90%, the product stream containing urea, water vapour and ammonium carbamate is passed to a primary ammonium carbamate decomposer maintained at pressure of atmospheric to 320 p.s.i.g. and a temperature of 200 DEG to 320 DEG F., wherein 75 to 95% of the ammonium carbamate is decomposed to ammonia and carbon dioxide, separation into gas and liquid phases is effected and the latter is passed to an evaporator decomposer maintained at such conditions that the remainder of the carbamate is decomposed to ammonia and carbon dioxide and water is evaporated from the product stream in the evaporator decomposer to give a urea concentration of 95 to 99.95% by weight, there being withdrawn from said evaporator decomposer a gas stream containing ammonia, carbon dioxide and water vapour and a separate stream comprising a urea melt containing les than 0.7% biuret. The gas stream withdrawn from the evaporator decomposer may be scrubbed with water to provide an aqueous solution of ammonia and carbon dioxide which is subsequently stripped to give gaseous ammonia and carbon dioxide. The liquid phase withdrawn from the primary decomposer may be contacted in the evaporator decomposer with a counter-currently flowing stream of inert sweep gas (e.g. ammonia, nitrogen or carbon dioxide) which may be separately withdrawn from the said scrubbing and stripping stages and recycled to the evaporator decomposer.ALSO:In a process for the synthesis of urea from ammonia and carbon dioxide having a conversion rate of ammonium carbamate to urea of from 40 to 90%, the product stream containing urea, water vapour and ammonium carbamate is passed to a primary ammonium carbamate decomposer maintained at pressure of atmospheric to 320 p.s.i.g. and a temperature of 200 DEG to 320 DEG F. wherein 75 to 95% of the ammonium carbamate is decomposed to ammonia and carbon dioxide, separation into gas and liquid phases is effected and the latter is passed to an evaporator decomposer maintained at such conditions that the remainder of the carbamate is decomposed to ammonia and carbon dioxide and water is evaporated from the product stream in the evaporator decomposer to give a urea concentration of 95 to 99.95% by weight, there being withdrawn from said evaporator decomposer a gas stream containing ammonia, carbon dioxide and water vapour and a separate stream comprising a urea melt containing less than 0.7% biuret. The gas stream withdrawn from the evaporator decomposer may be scrubbed with water to provide an aqueous solution of ammonia and carbon dioxide which is subsequently stripped to give gaseous ammonia and carbon dioxide. The liquid phase withdrawn from the primary decomposer may be contacted in the evaporator decomposer with a counter-currently flowing stream of inert sweep gas (e.g. ammonia, nitrogen or carbon dioxide) which may be separately withdrawn from the said scrubbing and stripping stages and recycled to the evaporator decomposer.