Process for preparing urea

Claim 1

IN PROCESSES FOR THE SYNTHESIS OF UREA BY REACTING AMMONIA AND CARBON DIOXIDE IN A SYNTHESIS ZONE, AT ELEVATED TEMPERATURE AND PRESSURE AND WHEREIN THE AMMONIUM CARBAMATE. CONTAINED IN THE EFFLUENT SYNTHESIS SOLUTION WHICH IS WITHDRAWN FROM SAID SYNTHESIS ZONE, IS DECOMPOSED AT HIGH PRESSURE AND THE AMMONIA AND CARBON DIOXIDE CONTENT OF SAID SOLUTION IS THEREAFTER EXPELLED THEREFROM FIRSTLY IN A HIGH PRESSURE ZONE TO GENERATE A HIGH PRESSURE AMMONIA-CARBON DIOXIDE-WATER VAPOR MIXTURE AND SECONDLY IN A LOW PRESSURE ZONE TO GENERATE A LOW PRESSURE AMMONIA-CARBON DIOXIDE-WATER VAPOR MIXTURE, FRESH CARBON DIOXIDE IS SUPPLIED TO SAID HIGH PRESSURE ZONE AND AN AQUEOUS UREA SOLUTION SUBSTANTIALLY FREE OF AMMONIUM CARBAMATE IS DISCHARGE FROM SAID LOW PRESSURE ZONE, AND WHEREIN SAID HIGH PRESSURE MIXTURE, TOGETHER WITH FRESH AMMONIA FEED, IS CONDENSED IN A HIGH PRESSURE CONDENSATION ZONE AND THEN RECIRCULATED TO SAID SYNTHESIS ZONE, AND SAID LOW PRESSURE MIXTURE IS PROCESSED INTO A LOW PRESSURE AMMONIUM CARBAMATE SOLUTION FOR RECIRCULATION, THE IMAN INERT-CONTAINING OVERHEAD GAS MIXTURE IS ALSO DISCHARGED FROM SAID SYNTHESIS ZONE AND PROCESSED THROUGH A WASHING ZONE FOR RECOVERY OF AMMONIA AND CARBON DIOXIDE COMPONENTS THEREFROM INTO A HIGH PRESSURE AMMONIUM CARBAMATE SOLUTION, FOR RECIRCULATION, THE IMPROVEMENT CONSISTING ESSENTIALLY IN: A. COMPRESSING AND DELIVERING SAID LOW PRESSURE AMMONIUM CARBAMATE SOLUTION TO SAID WASHING ZONE FOR EFFECTING SAID RECOVERY OF AMMONIA AND CARBON DIXIDE COMPONENTS FROM SAID OVERHEAD GAS AND TO GENERATED A WASH SOLUTION, B. WITHDRAWING A QUANTITY OF UREA-CONTAINING SOLUTION FROM SAID SYNTHESIS ZONE, AND C. UTILIZING A JET PUMP, DRIVENT BY SAID FRESH AMMONIA FEED, TO DELIVER SAID WASH SOLUTION AND SAID UREA-CONTAINING SOLUTION TO SAID HIGH PRESSURE CONDENSATION ZONE, WHEREBY, INTRODUCTION OF ADDITIONAL WATER IN SAID WASHING ZONE IS SUBSTANTIALLY AVOIDED AND THE HEAT REQUIRED TO RAISE THE WASH SOLUTION TO THE TEMPERATURE OF THE SAID HIGH PRESSURE CONDENSATION ZONE IS OBTAINED IN SAID WASHING ZONE AND THEREBY EXCESS HEAT UTILIZABLE AT A HIGHER TEMPERATURE IS AVAILABLE FROM SAID HIGH PRESSURE CONDENSATION ZONE.