Method for heat recovery in urea synthesis process

Claim 1

IN A UREA SYNTHESIS PROCESS COMPRISING REACTING AMMONIA AND CARBON DIOXIDE AT ELEVATED PRESSURE, REDUCING THE PRESSURE AND HEATING THE SYNTHESIS EFFLUENT STREAM TO DECOMPOSE A PORTION OF THE CONTAINED AMMONIUM CARBAMATE AND PRODUCE OF A FIRST OFF-GAS CONTAINING AMMONIA AND CARBON DIOXIDE AT A PRESSURE OF ABOUT 275 P.S.I.G. AND TEMPERATURE OF ABOUT 305*F. AND RESIDUAL LIQUID EFFLUENT STREAM CONTAINING PRODUCT UREA, HEATING SAID RESIDUAL LIQUID EFFLUENT STREAM AT REDUCED PRESSURE TO DECOMPOSE RESIDUAL AMMONIUM CARBAMATE AND PRODUCE A SECOND OFF-GAS CONTAINING AMMONIA AND CARBON DIOXIDE AT A PRESSURE OF ABOUT 15 P.S.I.G. AND A FINAL LIQUID PRCESS STREAM CONSISTING OF PRODUCT AQUEOUS UREA SOLUTION, THE IMPROVE METHOD OF HEATING SAID RESIDUAL LIQUID EFFLUENT STREAM AND RECOVERING HEAT BY ABSORPTION OF SAID FIRST OFF-GAS IN AQUEOUS ABSORBENT SOLUTION WHICH COMPRISES ASPIRATING SAID AQUEOUS ABSORBENT SOLUTION INTO SAID FIRST OFF-GAS TO PROVIDE INITIAL GAS-LIQUID MIXING, PASSING THE RESULTING MIXED GAS-LIQUID SOLUTION CONTAINED AT A TEMPERATURE OF ABOUT 295*F. IN HEAT EXCHANGE MEANS, RECYCLING A STREAM OF AQUEOUS SOLUTION FROM SAID HEAT EXCHANGE MEANS TO SAID ASPIRATION STEP, SAID RECYCLE STREAM OF AQUEOUS SOLUTION CONSTITUTING ABOUT 80% OF THE TOTAL AQUEOUS ABSORBENT SOLUTION, RECOVERING A FINAL MIXED GAS-LIQUID STREAM OF REDUCED HEAT CONTENT FROM SAID HEAT EXCHANGE MEANS AT A PRESSURE OF ABOUT 225 P.S.I.G. AND A TEMPERATURE OF ABOUT 260*F., HEATING SAID RESIDUAL LIQUID EFLUENT STREAM IN SAID HEAT EXCHANGE MEANS FROM AN INITIAL TEMPERATURE OF ABOUT 194*F. TO A FINAL TEMPERATURE OF ABOUT 235*F. AT SAID REDUCED PRESSURE OF ABOUT 15 P.S.I.G. BY HEAT EXCHANGE WITH SAID AQUEOUS SOLUTION, WHEREBY AMMONIUM CARBOMATE IN SAID RESIDUAL LIQUID EFFLUENT STREAM IS DECOMPOSED BY ABSORPTION OF HEAT FROM SAID AQUEOUS SOLUTION AND SAID SECOND OFF-GAS IS PRODUCED.