Urea synthesis process

Claim 1

IN A UREA SYNTHESIS PROCESS IN WHICH AMMONIA AND CARBON DIOXIDE FEED STREAMS AND RECYCLED AQUEOUS AMMONIUM CARBAMATE SOLUTION ARE REACTED AT ELEVATED PRESSURE TO FORM UREA, WHEREIN SAID AMMONIA IS PRESENT IN EXCESS OVER THE STOICHIOMETRIC REQUIREMENT AND AT LEAST ONE OF SAID FEED STREAMS CONTAINS INERTS, THE REACTION EFFLUENT STREAM IS HEATED IN A FIRST STAGE AT AN INTERMEDIATE REDUCED PRESSURE TO DECOMPOSE AMMONIUM CARBAMATE AND REMOVE A FIRST MIXED AMMONIA-CARBON DIOXIDE OFF-GAS STREAM CONTAINING INERTS, THE RESIDUAL EFFLUENT STREAM IS FURTHER HEATED IN A SECOND STAGE AT A FURTHER REDUCE LOW PRESSURE TO DECOMPOSE AMMONIUM CARBAMATE AND REMOVE A SECOND MIXED AMMONIA-CARBON DIOXIDE OFF-GAS STREAM CONTAINING INERTS, SAID MIXED OFF-GAS STREAMS ARE COOLED AND PARTIALLY CONDENSED BY SCRUBBING WITH AQUEOUS AMMONIUM CARBAMATE SOLUTIONS AT THEIR RESPRECTIVE PRESSURE LEVELS, THE RESIDUAL OFF-GAS PHASES ARE REFLUXED TO REMOVE RESIDUAL CARBON DIOXIDE AND PRODUCE FINAL OFF-GAS STREAMS OF PURIFIED AMMONIA CONTAINING INERTS, AND PORTIONS OF SAID AQUEOUS AMMONIUM CARBAMATE SOLUTIONS ARE RECYCLED TO UREA SYNTHESIS, THE IMPROVED METHOD OF RECYCLING SAID PURIFIED AMMONIA STREAMS CONTAINING INERTS AND SAID AQUEOUS AMMONIUM CARBAMATE SOLUTIONS TO UREA SYNTHESIS WHICH COMPRISES COMPRESSING SAID LOW PRESSURE SECOND PURIFIED AMMONIA OFF-GAS TO THE PRESSURE LEVEL OF SAID FIRST PURIFIED AMMONIA OFF-GAS, COMBINGING SAID FIRST AND SECOND PURIFIED AMMONIA OFF-GAS STREAMS, COOLING THECOMBINED OFF-GAS STREAM TO CONDENSE A PORTION OF THE CONTAINED AMMONIA AND FORM A LIQUID AMMONIA PHASE, SEPARATING THE RESIDUAL GASEOUS PHASE COMPRISING AMMONIA AND INERTS FROM THE LIQUID AMMONIA PHASE, RECYCLING SAID LIQUID AMMONIA PHASE TO UREA SYNTHESIS, PRESSURIZING A PORTION OF THE LOW PRESSURE AQUEOUS AMMONIUM CARBAMATE SOLUTION TO THE INTERMEDIATE PRESSURE LEVEL OF SAID COMMBINED OFF-GAS STREAM, SCRUBBING SAID RESIDUAL GASEOUS PHASE COMPRISING AMMONIA AND INERTS WITH SAID PRESSURIZED AQUEOUS AMMONIUM CARBAMATE SOLUTION, WHEREBY AMMONIA VAPOR IS ABSORBED FROM SAID RESIDUAL GASEOUS PHASE INTO SAID AQUEOUS AMMONIUM CARBAMATE SOLUTION, DISCHARGING SAID RESIDUAL GASEOUS PHASE ESSENTIALLY COMPRISING INERTS AFTER SAID SCRUBBING STEP, AND RECYCLING SAID AQUEOUS AMMONIUM CARBAMATE SOLUTION CONTAINING DISSOLVED AMMONIA TO UREA SYNTHESIS.