A process and a related plant layout for producing urea are disclosed, wherein the high-pressure loop (1) comprises a synthesis reactor (2), a thermal stripper (3), a condenser (4), and an adiabatic CO2 stripper (10) disposed upstream said thermal stripper, separating a vapour phase (13) containing ammonia from the urea solution (9) discharged from the reactor, and recycling said vapour phase to the reactor. The adiabatic stripper (10) can be incorporated in a reactor (200) having a top reaction zone and a bottom adiabatic stripping zone. A revamping method for a conventional urea plant in accordance with the inventive process is also disclosed.