Abstract A process for the production of urea from ammonia and carbon dioxide, combined with the preparation of ammonia, is disclosed wherein ammonium carbamate in the urea solution produced is removed from said urea solution by subjecting the urea solution to two stripping stages. The first stripping stage uses the urea synthesis starting gas, which contains hydrogen, nitrogen and carbon dioxide. The second stripping stage, which is at substantially the same pressure as the first stripping stage, uses a gas containing at least one of the components needed in the ammonia synthesis. This second stripping gas is substantially free of ammonia and carbon dioxide. The disclosed process has the advantage, compared to prior processes, that the stripping gases need not be compressed at relatively high temperatures.
a secondary stripping stage operated at substantially the same pressure level as said primary stripping stage wherein said first urea solution is stripped with a secondary stripping gas, said secondary stripping gas being substantially free of ammonia and carbon dioxide and selected from the group consisting of hydrogen, nitrogen,, or combinations thereof, yielding a second urea solution of further reduced ammonium carbamate and free ammonia content and a second stripping off-gas containing carbon dioxide and ammonia, and delivering said second stripping off-gas to said carbamate condensing stage, wherein ammonia and carbon dioxide are removed from said first and said second stripping off-gases and recycled to said urea synthesis reactor.
Claim 2
Dependent Claim
32 words
The process of claim 1 wherein said secondary stripping gas is at least a portion of said synthesis gas substantially free of ammonia and carbon dioxide obtained from said carbamate condensing stage.
Claim 3
Dependent Claim
17 words
The process of claim 1 wherein said synthesis gas containing hydrogen and carbon dioxide additionally contains nitrogen.
Claim 4
Dependent Claim
15 words
The process of claim 1 wherein said secondary stripping gas comprises essentially hydrogen and nitrogen.
Claim 5
Dependent Claim
23 words
The process of claim 1 wherein said primary stripping stage and said secondary stripping stage are carried out at substantially the urea-synthesis pressure.
Claim 6
Dependent Claim
14 words
The process of claim 5 wherein said urea-synthesis pressure is at least 300 atmospheres.