PROCESS FOR THE MODERNIZATION OF EXISTING UREA PLANTS, AND PLANTS SO OBTAINED WITH INCREASED YIELDS AND FLEXIBILITY, AND REDUCED ENERGY CONSUMPTION AND CORROSION

摘要

The process to modernize existing urea plants which use astripping with carbon dioxide, and to increase urea yieldsand flexibility under overload conditions while at the sametime reducing energy consumption, corrosion phenomena andpossible risks of explosive mixtures, comprises substantiallya passivation stage with the introduction of an oxidisingagent and reduction of the air fed to the system; a mediumpressure distillation stage of the products leaving thestripping section, and a condensation of the products of saiddistillation, effected in a pre-evaporation phase toconcentrate at low pressure the urea solution.The modernized plant, comprising at the start at least areactor, a scrubber, a condenser, a stripper and theevaporators, now includes also a passivation section, amedium pressure distillation section, and a distillationsection with double-effect technique.