FIELD: chemistry.
SUBSTANCE: invention relates to a method of modernising a urea production plant (1). The plant includes: a reactor (2) for urea synthesis, means (7, 8) for feeding ammonia and carbon dioxide into said reactor (2) for urea synthesis, an apparatus (3) for desorption with carbon dioxide for treating the reaction mixture from the reactor (2) and containing urea, carbamate and free ammonia in aqueous solution, with partial decomposition of carbamate and partial separation of free ammonia, thus obtaining a stream containing ammonia and carbon dioxide in vapour phase and a stream containing urea and residual carbamate in aqueous solution, a urea extraction section for treating the stream coming out of the desorption apparatus (3) and containing urea and residual carbamate in aqueous solution for separating urea from residual carbamate in aqueous solution, at least one at least one vertical film condensation apparatus (4) for partial condensation of the stream coming out of the desorption apparatus (3) and containing ammonia and carbon dioxide in vapour phase, thus obtaining a liquid stream containing carbamate in aqueous solution and a gaseous stream containing ammonia and carbon dioxide in vapour phase, means (15, 14) for respectively feeding the stream containing carbamate in aqueous solution and the gaseous stream containing ammonia and carbon dioxide in vapour phase into said reactor (2) for urea synthesis. Said at least one condensation apparatus (4) is provided with means for essentially full condensation of at least a portion of the stream coming out of the desorption apparatus (3) and containing ammonia and carbon dioxide in vapour phase to obtain a stream containing urea and carbamate in aqueous solution. The method involves the following stages: providing second desorption apparatus (47), providing means (9) for feeding a first portion of the stream of reaction mixture coming out of the reactor (2) and containing urea, carbamate and free ammonia in aqueous solution into said desorption apparatus (3), providing means (48) for feeding a second portion of the stream of reaction mixture coming out the reactor (2) and containing urea, carbamate and free ammonia in aqueous solution into said second desorption apparatus (47), and providing means (49) for feeding at least a portion of the stream coming out of said second desorption apparatus (47) and containing ammonia and carbon dioxide in vapour phase directly into the synthesis reactor (2). A method of producing urea and a urea production plant are also disclosed.
EFFECT: invention ensures high output of the product with low power consumption.
12 cl, 2 ex, 2 dwg
