Patent ID: 7674933
Filing Date: 2010-03-09
Classification: B01J,C07C,Y02P

Abstract:
1. Method for the modernisation of a plant for urea production of the type comprising: a reactor for urea synthesis; means for feeding ammonia and carbon dioxide to the reactor for urea synthesis; a stripping unit with carbon dioxide for subjecting a reaction mixture comprising urea, carbamate and free ammonia in aqueous solution leaving the reactor to a treatment of partial decomposition of carbamate and partial separation of free ammonia, thus obtaining a flow comprising ammonia and carbon dioxide in vapour phase and a flow comprising urea and residual carbamate in aqueous solution, respectively; a recovery section for the flow comprising urea and residual carbamate in aqueous solution leaving the stripping unit for separating urea from the residual carbamate in aqueous solution; at least one condensation unit of the film type, for subjecting to partial condensation said flow comprising ammonia and carbon dioxide in vapour phase leaving said stripping unit, thus obtaining a liquid flow comprising carbamate in aqueous solution and a gaseous flow comprising ammonia and carbon dioxide in vapour phase; means for respectively feeding the flow comprising carbamate in aqueous solution and the gaseous flow comprising ammonia and carbon dioxide in vapour phase to said reactor for urea synthesis, said modernization method further comprising the step of: providing in said at least one condensation unit means for subjecting to substantially total condensation at least a portion of a flow comprising ammonia and carbon dioxide in vapour phase leaving said stripping unit, obtaining a flow comprising urea and carbamate in aqueous solution, and being characterized by comprising the steps of: providing a second stripping unit, providing means for feeding, a first portion of the flow of reaction mixture comprising urea, carbamate and free ammonia in aqueous solution leaving the reactor to said stripping unit; providing means for feeding a second portion of the flow of reaction mixture comprising urea, carbamate and free ammonia in aqueous solution leaving the reactor to said second stripping unit; and providing means for feeding at least a portion of a flow comprising ammonia and carbon dioxide in vapour phase leaving said second stripping unit directly to the synthesis reactor.