Preparation of urea

Claim 1

IN A CONTINUOUS PROCESS FOR THE PREPARATION OF UREA WHEREIN NH3 AND CO2 ARE REACTED AT ELEVATED TEMPERATURE AND PRESSURE TO CONTINUOUSLY PROVIDE AN AMMONIUM CARBAMATE MELT, THEREAFTER IN AN AUTOCLAVE, SAIDMELT BEING CONVERTED INOT A UREA SOLUTION CONTAINING AMMONIUM CARBAMATE AND THE CARBAMATE BEING STRIPPED FROM SAID SOLUTION BY DECOMPOSING SAID CARBAMATE INTO NH3 AND CO2 BYHEAT AND EXPELLING NH3, CO2 AND H2O FROM SAID SOLUTION, THE IMPROVEMENT WHICH COMPRISES CONTINUOUSLY STRIPPING THE UREA SOLUTION WITH CO2 IN A STRIPPING ZONE OUTSIDE SAID AUTOCLAVE AND AT A PRESSURE OF AT LEAST 50 ATMOSPHERES UP TO UREA SYNTHESIS PRESSURE WHEREIN THE UREA SOLUTION FLOWS DOWNWARDLY ALONG THE INSIDE OF EXTERNALLY STEAM HEATED TUBES IN THE STRIPPING ZONE AND CO2 STRIPPING GAS PASSES UPWARDLY IN SAID TUBES IN CONTACT WITH SAID UREA SOLUTION, THE PRESSURE OF THE HEATING STEAM BEING IN THE RANGE OF 15-30 ATM., WHEREBY NH3 AND CO2 ARE EXPELLED FROM SAID SOLUTION, CONDENSING THE RESULTING MIXTURE OF CO2 GAS AND GASES EXPELLED FROM SAID UREA SOLUTION AFTER ADDITION OF FURTHER NH3 AND AT A PRESSURE OF AT LEAST 50 ATMOSPHERE UP TO UREA SYNTHESIS PRESSURE TO FORM A CARBAMATE SOLUTION AMD RETURNING THE THUS FORMED CARBAMATE SOLUTION TO SAID AUTOCLAVE FOR FURTHER UREA SYNTHESIS.