Process for preparing a urea solution from ammonia and carbon dioxide

Claim 2

In a process for the preparation of urea from ammonia and carbon dioxide in a urea synthesis zone at an elevated temperature and pressure, having at least one ammonium carbamate decomposition zone wherein a urea containing liquid process stream, also containing unconverted ammonium carbamate, is expanded to a pressure of between about 1 and 25 kg/cm 2 absolute and heated thereby decomposing at least a portion of said ammonium carbamate and yielding a gas mixture containing ammonia, carbon dioxide and water vapor, the improvement comprising the steps of introducing said gas mixture into a carbon dioxide separation column, along with sufficient diluting water to form, in the bottom of said column, a first residual liquid phase containing ammonia, carbon dioxide and between about 65 and 96 percent by weight water, and separately removing therefrom a first off-gas of carbon dioxide substantially free of ammonia, and said first residual liquid phase, introducing said first residual liquid phase into a desorption column and separately removing therefrom a second off-gas containing ammonia, carbon dioxide and water vapor, and a second residual liquid phase containing water substantially free of ammonia and carbon dioxide, introducing said second off-gas into an ammonia separation column and separately removing therefrom a third off-gas of ammonia substantially free of carbon dioxide and water vapor and a third residual liquid phase containing ammonia, carbon dioxide and water, and recycling said third off-gas to said urea synthesis zone, and introducing said third residual liquid phase into said carbon dioxide separation column, the water content of such third residual liquid phase constituting a portion of said diluting water, wherein said ammonia separation column, desorption column and carbon dioxide separation column are all operated at substantially the same pressure of between about 1 and 25 kg/cm 2 absolute.

Claim 3

The process of claim 1 wherein said ammonia separation column, desorption column and carbon dioxide separation column are all operated at substantially the same pressure of between about 1 and 6 kg/cm 2 absolute.

Claim 4

The process of claim 1 wherein sufficient diluting water is added to said carbon dioxide separation column so as to form a first residual liquid phase containing ammonia, carbon dioxide and between about 80 and 95 percent by weight water.

Claim 5

In a process for the preparation of urea from ammonia and carbon dioxide in a urea synthesis zone at an elevated temperature and pressure, having first and second ammonium carbamate decomposition zones wherein, in said first ammonium carbamate decomposition zone, a urea containing liquid process stream also containing unconverted ammonium carbamate, is heated and stripped by a countercurrent flow of gas selected from the group consisting of ammonia, carbon dioxide or a combination thereof, thereby decomposing a portion of said ammonium carbamate, and resulting in a first gas mixture containing ammonia, carbon dioxide and water vapor, which is thereafter at least partially condensed and recyled to said urea synthesis zone, and a residual urea containing liquid process stream, still containing ammonium carbamate, and in said second ammonium carbamate decomposition zone, said residual process stream is expanded to a pressure of between about 1 and 25 kg/cm 2 absolute and heated thereby further decomposing ammonium carbamate and yielding a second gas mixture containing ammonia, carbon dioxide and water vapor, the improvement comprising the steps of introducing said second gas mixture into a carbon dioxide separation column, along with sufficient diluting water to form, in the bottom of said column, a first residual liquid phase containing ammonia, carbon dioxide and between about 65 and 96 percent by weight water, and separately removing therefrom a first off-gas of carbon dioxide substantially free of ammonia, and said first residual liquid phase introducing said first residual liquid phase into a desorption column and separately removing therefrom a second off-gas containing ammonia, carbon dioxide and water vapor, and a second residual liquid phase containing water substantially free of ammonia and carbon dioxide, introducing said second off-gas into an ammonia separation column and separately removing therefrom a third off-gas of ammonia substantially free of carbon dioxide and water vapor and a third residual liquid phase containing ammonia, carbon dioxide and water, and recycling said third off-gas to said urea synthesis zone, and introducing said third residual liquid phase into said carbon dioxide separation column, the water content of such third residual liquid phase constituting a portion of said diluting water, wherein said ammonia separation column, desorption column and carbon dioxide separation column are all operated at substantially the same pressure of between about 1 and 25 kg/cm 2 absolute.

Claim 6

In a process for the preparation of urea from ammonia and carbon dioxide in a urea synthesis zone at an elevated temperature and pressure, having first and second ammonium carbamate decomposition zones wherein, in said first ammonium carbamate decomposition zone, a urea containing liquid process stream also containing unconverted ammonium carbamate, is heated and stripped by a countercurrent flow of gas selected from the group consisting of ammonia, carbon dioxide or a combination thereof, thereby decomposing a portion of said ammonium carbamate, and resulting in a first gas mixture containing ammonia, carbon dioxide and water vapor, which is thereafter at least partially condensed and recyled to said urea synthesis zone, and a residual urea containing liquid process stream, still containing ammonium carbamate, and in said second ammonium carbamate decomposition zone, said residual process stream is expanded to a pressure of between about 1 and 25 kg/cm 2 absolute and heated thereby further decomposing ammonium carbamate and yielding a second gas mixture containing ammonia, carbon dioxide and water vapor, the improvement comprising the steps of introducing said second gas mixture into a carbon dioxide separation column, along with sufficient diluting water to form, in the bottom of said column, a first residual liquid phase containing ammonia, carbon dioxide and between about 65 and 96 percent by weight water, and separately removing therefrom a first off-gas of carbon dioxide substantially free of ammonia, and said first residual liquid phase introducing said first residual liquid phase into a desorption column and separately removing therefrom a second off-gas containing ammonia, carbon dioxide and water vapor, and a second residual liquid phase containing water substantially free of ammonia and carbon dioxide, introducing said second off-gas into an ammonia separation column and separately removing therefrom a third off-gas of ammonia substantially free of carbon dioxide and water vapor and a third residual liquid phase containing ammonia, carbon dioxide and water, and recycling said third off-gas to said urea synthesis zone, and introducing said third residual liquid phase into said carbon dioxide separation column, the water content of such third residual liquid phase constituting a portion of said diluting water, wherein said ammonia separation column, desorption column and carbon dioxide separation column are all operated at substantially the same pressure of between about 1 and 25 kg/cm 2 absolute.

Claim 7

The process of claim 4 wherein said ammonia separation column, desorption column and carbon dioxide separation column are all operated at substantially the same pressure of between about 1 and 6 kg/cm 2 absolute.

Claim 8

The process of claim 4 wherein sufficient diluting water is added to said carbon dioxide separation column so as to form a first residual liquid phase containing ammonia, carbon dioxide and between about 80 and 95 percent by weight water.