Heat recovery in urea synthesis

Claim 2

The process of claim 1 wherein steam generated in step (a) is at a temperature from about 160*F. to about 190*F. and the compressed steam in step (b) is at a temperature from about 200*F. to about 350*F.

Claim 3

In a urea synthesis wherein carbon dioxide and ammonia are reacted to produce urea, the reaction product is passed to a first decomposition zone wherein gases are removed and an aqueous urea solution is recovered, the gases removed are contacted with an absorption medium and the aqueous urea solution from the first decomposition zone is passed to a second decomposition zone to effect further removal of gases and the aqueous urea solution from the second decomposition zone is passed to a flash zone to effect still further removal of gases, and the aqueous urea solution from the flash zone is passed to a recovery zone for recovering urea by converting the water to steam, a method for recovering heat comprising: introducing the steam produced in the recovery zone into the flash zone to contact the aqueous urea solution and strip gases therefrom.

Claim 4

The process of claim 4 wherein the recovEry zone comprises first and second concentration zones and the steam produced in the second concentration zone is passed to the flash zone.

Claim 5

The process of claim 5 wherein the absorption medium withdrawn from the absorption zone containing absorbed gas is passed in heat transfer relationship with the aqueous urea solution in the first concentration zone to provide heat requirements for concentration.

Claim 6

The process of claim 6 wherein the steam introduced into the flash zone is at a temperature from about 245* to about 265*F. and a pressure from about 5.0 to about 6.5 psia.

Claim 7

In a urea synthesis wherein carbon dioxide and ammonia are reacted to produce urea, the reaction product is passed to a first decomposition zone wherein gases are removed and a urea solution is recovered, the gases removed are contacted with an absorption medium in an absorption zone, and the urea solution from the first decomposition zone is passed to a second decomposition zone to effect further removal of gases, and an aqueous urea solution is passed from the second decomposition zone to a recovery zone for recovering urea, a process for recovering heat comprising: a. passing the absorption medium containing absorbed gas from the absorption zone in heat transfer relationship with said aqueous urea solution in a first concentration zone in the recovery zone to provide heat requirements for partial concentration of the aqueous urea solution; introducing the resulting partially concentrated urea solution into a second concentration zone in the product recovery zone to produce steam and, effect further concentration of the urea solution; recovering said steam from the second concentration zone; and introducing the recovered steam into the second decomposition zone to contact the urea solution and strip gases therefrom.

Claim 8

The process as defined in claim 8 wherein the second decomposition zone is operated at close to atmospheric pressure and the steam introduced therein is at a temperature from about 245* to about 265*F. and a pressure from about 5.0 to about 6.5 psia.