Integrated process and plant for production of urea and UAS (urea-ammonium sulphate) mixtures

An integrated urea and urea-ammonium sulphate production process comprising:

• a urea synthesis step carried out in a urea synthesis reactor;
• a recovery and concentration step in which a urea solution produced in the urea synthesis step is progressively concentrated in at least one recovery section comprising at least a medium pressure recovery section and a low pressure recovery section, and in a concentration section located downstream of said at least one recovery section to recover unreacted ammonia and carbon dioxide and water from said urea solution;
• an ammonium sulphate production step carried out in a plurality of stages in series and that occurs by reaction of sulphuric acid and ammonia in an ammonium sulphate production apparatus, wherein:
• at least a part of the ammonia is from at least one off-gas containing unreacted ammonia from the urea solution produced in the urea synthesis step that is recovered from the recovery and concentration step,
• the at least one off-gas is a medium pressure off-gas from a head outlet of a condenser of the medium pressure recovery section and is supplied to a first stage of the ammonium sulphate production step,
• a first low pressure off-gas is supplied from a gas head outlet of a low pressure decomposer of the low pressure recovery section and is supplied to a second stage of the ammonium sulphate production step, and
• a second low pressure off-gas is supplied from a head outlet of an absorption tower of the low pressure recovery section and is supplied to a third stage of the ammonium sulphate production step;
• a mixing step of mixing said ammonium sulphate with concentrated urea from the concentration section to produce a urea-ammonium sulphate mixture;
• and
• a urea finishing step in which the mixture of ammonium sulphate and urea is granulated or prilled.