Process for the modernization of existing urea plants and a modernized urea plant

A process for modernizing an existing urea plant to increase urea yield of the plant, reduce energy consumption by the plant and inhibit corrosion within the plant, the plant including a reactor for synthesizing urea from ammonia and carbon dioxide, a stripper for stripping product leaving the reactor with a reagent, a condenser for condensing carbamate out of an ammonia feed stream for the reactor, a scrubber for treating vapors leaving the reactor, means for introducing an amount of passivating air into the stripper, scrubber and condenser, a decomposer for decomposing products of the stripper, and an evaporator, the modernization process comprising the steps of:

• introducing an oxidizing agent into the plant at a location in the plant upstream of the stripper and condenser, the oxidizing agent being in a liquid phase;
• increasing the molar ratio of ammonia to carbon dioxide within the reactor to produce an excess of ammonia in the reactor of between 2.8 and 3.4 mol while reducing the amount of passivating air in the stripper, scrubber and condenser by about 1/3;
• distilling products from the stripper at medium pressure between 6 and 50 bar in a medium pressure distillation means located between the stripper and the decomposer, and condensing vapors produced by the distillation in a pre-evaporator at low pressure, said pre-evaporator being located downstream of the medium pressure distillation means and in series with a first vacuum stage of the evaporator.