1. Process for urea production of the type comprising the steps of:
performing a reaction between ammonia and carbon dioxide in a reaction space to obtain a reaction mixture comprising urea, carbamate and free ammonia in aqueous solution;
subjecting said mixture to a treatment of partial decomposition of the carbamate and partial separation of said free ammonia in aqueous solution to obtain a first flow comprising ammonia and carbon dioxide in vapor phase and a flow comprising urea and residual carbamate in aqueous solution;
subjecting said first flow comprising ammonia and carbon dioxide in vapor phase to at least partial condensation to obtain a first portion of carbamate in aqueous solution;
recycling said first portion of carbamate to said reaction space;
feeding said flow comprising urea and residual carbamate in aqueous solution to a urea recovery section;
separating in said recovery section said residual carbamate from the urea to obtain a second portion of carbamate in aqueous solution;
characterized in that it comprises the additional steps of:
subjecting at least part of said second portion of carbamate in aqueous solution obtained in said recovery section to a treatment of partial decomposition to obtain a second flow comprising ammonia and carbon dioxide in vapor phase and a flow comprising residual carbamate in aqueous solution;
subjecting said second flow comprising ammonia and carbon dioxide in vapor phase to at least partial condensation to obtain a third portion of carbamate in aqueous solution;
recycling said third portion of carbamate to said reaction space.
2. Process according to claim 1, characterized in that the treatment of partial decomposition of the said at least part of the second portion of carbamate in aqueous solution is carried out at a pressure substantially corresponding to the pressure in the reaction space.
3. Process according to claim 1, characterized in that it further comprises the step of:
feeding the flow comprising residual carbamate in aqueous solution resulting from the treatment of partial decomposition of the second portion of carbamate to said urea recovery section.
4. Process according to claim 1, characterized in that it comprises the steps of:
feeding the reaction mixture comprising urea, carbamate and free ammonia in aqueous solution to a decomposition unit;
feeding said at least part of the second portion of carbamate in aqueous solution to said decomposition unit,
wherein the treatment of partial decomposition of the reaction mixture and of the second portion of carbamate is carried out in the same decomposition unit to obtain said first and second flow comprising ammonia and carbon dioxide in vapor phase and a flow comprising urea and residual carbamate in aqueous solution.
5. Process according to claim 1, characterized in that at least 50% of said second portion of carbamate in aqueous solution is subjected to the treatment of partial decomposition.
6. Process according to claim 5, characterized in that at least 65% of said second portion of carbamate in aqueous solution is subjected to the treatment of partial decomposition.
7. Plant for urea production comprising:
a urea synthesis reactor (1);
a first stripping unit (2) for subjecting a reaction mixture leaving said reactor (1) to a treatment of partial decomposition of the carbamate and partial separation of the free ammonia in aqueous solution present in said mixture;
means (6) for condensing at least partially the vapors leaving said first stripping unit (2) and of recycling (24) a first portion of carbamate in aqueous solution to said reactor (1);
a recovery section (3, 4, 7, 8) of a flow comprising urea and residual carbamate in aqueous solution leaving said first stripping unit (2) for separating the urea produced in the reactor (1) from a second portion of carbamate in aqueous solution;
characterized in that it comprises:
a second stripping unit (9) for subjecting at least part of said second portion of carbamate in aqueous solution to a treatment of partial decomposition;
means for condensing at least Partially the vapors leaving said second stripping unit (9) and of recycling a third portion of carbamate in aqueous solution to said reactor (1).
8. Plant according to claim 7, characterized in that said means for condensing the vapors leaving said second stripping unit (9) comprises said means (6) for condensing the vapors leaving said first stripping unit (2).
9. Plant according to claim 7, characterized in that it further comprises:
means (33) for feeding a flow comprising residual carbamate in aqueous solution from said second stripping unit (9) to said recovery section (3, 4, 7, 8).
10. Plant for urea production comprising:
a urea synthesis reactor (1);
a stripping unit (2) for subjecting a reaction mixture leaving said first reactor (1) to a treatment of partial decomposition of the carbamate and partial separation of the free ammonia in aqueous solution present in said mixture;
means (6) for condensing at least partially the vapors leaving said stripping unit (2) and of recycling a first portion of carbamate in aqueous solution to said first reactor (1);
a recovery section (3, 4, 7, 8) of a flow comprising urea and residual carbamate in aqueous solution leaving said stripping unit (2) for separating the urea produced in the reactor (1) from a second portion of carbamate in aqueous solution;
characterized in that it comprises:
means for feeding (26) at least part of said second portion of carbamate in aqueous solution to the stripping unit (2).
11. Method for modernizing a plant for urea production of the type comprising:
a urea synthesis reactor (1);
a first stripping unit (2) for subjecting a reaction mixture leaving said reactor (1) to a treatment of partial decomposition of the carbamate and partial separation of the free ammonia in aqueous solution present in said mixture;
means (6) for condensing at least partially the vapors leaving said first stripping unit (2) and of recycling a first portion of carbamate in aqueous solution to said reactor (1);
a recovery section (3, 4, 7, 8) of a flow comprising urea and residual carbamate in aqueous solution leaving said first stripping unit (2) for separating the urea produced in the reactor (1) from a second portion of carbamate in aqueous solution;
characterized in that it comprises the steps of:
providing a second stripping unit (9) for subjecting at least part of said second portion of carbamate in aqueous solution to a treatment of partial decomposition;
providing means for condensing at least partially the vapors leaving said second stripping unit (9) and of recycling a third portion of carbamate in aqueous solution to said reactor (1).
12. Method for modernizing a plant for urea production of the type comprising:
a urea synthesis reactor (1);
a first stripping unit (2) for subjecting a reaction mixture leaving said reactor (1) to a treatment of partial decomposition of the carbamate and partial separation of the free ammonia in aqueous solution present in said mixture;
means (6) for condensing at least partially the vapors leaving said first stripping unit (2) and of recycling a first portion of carbamate in aqueous solution to said reactor (1);
a recovery section (3, 4, 7, 8) of a flow comprising urea and residual carbamate in aqueous solution leaving said first stripping unit (2) for separating the urea produced in the reactor (1) from a second portion of carbamate in aqueous solution;
characterized in that it comprises the steps of:
providing a second stripping unit (9) for subjecting at least part of said second portion of carbamate in aqueous solution to a treatment of partial decomposition;
providing means for feeding (32) the vapors leaving said second stripping unit (9) to said means for condensing (6) the vapors leaving said first stripping unit (2).
13. Method according to claim 11 or 12, characterized in that it further comprises the step of:
providing means for feeding (33) a flow comprising residual carbamate in aqueous solution from said second stripping unit (9) to said recovery section (3, 4, 7, 8).
14. Method for modernizing a plant for urea production of the type comprising:
a urea synthesis reactor (1);
a stripping unit (2) for subjecting a reaction mixture leaving said first reactor (1) to a treatment of partial decomposition of the carbamate and partial separation of the free ammonia in aqueous solution present in said mixture;
means (6) for condensing at least partially the vapors leaving said stripping unit (2) and of recycling a first portion of carbamate in aqueous solution to said first reactor (1);
a recovery section (3, 4, 7, 8) of a flow comprising urea and residual carbamate in aqueous solution leaving said stripping unit (2) for separating the urea produced in the reactor (1) from a second portion of carbamate in aqueous solution;
characterized in that it comprises the step of:
providing means for feeding (26) at least part of said second portion of carbamate in aqueous solution to the stripping unit (2).
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A flat panel display device comprising in order a first waveguide, a transition waveguide and a second waveguide and display panel, wherein said second waveguide and display panel has a display surface and a substantially wedged shape and wherein the surface profile of said second waveguide and display panel compensates the distortions in the displayed image generated by the light path of incident image rays in said first waveguide and said transition waveguide.
2. The flat panel display device according to claim 1, wherein said incident image rays within a selected range of angles exit said second waveguide and display panel at substantially the same angle, after they have travelled through said first waveguide and said second waveguide.
3. The flat panel display device according to claim 1, wherein said exit angle is smaller than the critical angle of said second waveguide and display panel, whereby the exit rays do not intercept the display surfaces at an angle equal to or shallower than the critical angle.
4. The flat panel display device according to claim 1, wherein said transition waveguide has a surface profile that restricts said light rays from the first waveguide to bounce not more than once in said transition waveguide.
5. The flat panel display device according to claim 1, wherein said display surface of said second waveguide and display panel includes a plurality of sections, wherein surface profile of a first section of said display surface most adjacent to said transition waveguide is determined by calculating the optical path of image rays from a light source positioned at the entrance side of said first waveguide with a first incident angle passing through said first waveguide and said transition waveguide to produce a selected range of exit angles and surface profile of an nth (n is a natural number equal or greater than 2) section of said display surface is determined by calculating optical path of image rays of said light source with an nth incident angle passing through said first waveguide, said transition waveguide and the first to n\u22121th sections of said second waveguide and display panel to produce said selected range of exit angles.
6. The flat panel display device according to claim 5, wherein said selected range of exit angles comprise an angle smaller than the critical angle of said second waveguide and display panel, whereby the exit rays do not intercept the display surfaces at an angle equal to or shallower than the critical angle.
7. The flat panel display device according to claim 1, wherein said transition waveguide forms a U shape.
8. The flat panel display device according to claim 5, wherein said transition waveguide forms a U shape.
9. The flat panel display device according to claim 1, further comprising a prism positioned at an entrance end of said first waveguide.
10. The flat panel display device according to claim 1, wherein a surface of said transition waveguide forms a circular curve.
11. The flat panel display device according to claim 1, wherein a surface of said transition waveguide forms a parabolic curve.
12. The flat panel display device according to claim 1, further comprising an anti-reflection coating on said display surface.
13. The flat panel display device according to claim 12, wherein said anti-reflection coating comprises a gradient index coating (GRIN).
14. The flat panel display device according to claim 12, wherein said anti-reflection coating comprises an antireflection structured (ARS) surface.
15. A method to determine the optical profile of a flat panel display device comprising in order a first waveguide, a transition waveguide and a second waveguide and display panel, wherein said second waveguide and display panel has a display surface and a substantially edged shape, said method comprising the steps of:
determining optical profile of said first waveguide and said transition waveguide;
selecting major incident angles of lights, and
calculating to obtain surface profile of sections in said second waveguide and display panel corresponding respectively to said selected light angles, to compensate distortions in displayed image generated by said selected lights’ paths in said first waveguide.
16. The method according to claim 15, wherein said calculation in surface profile of said second waveguide and display panel comprises the steps of:
selecting a first light angle to calculate and obtain surface profile of a first section in said second waveguide and display panel most adjacent to said transition waveguide, to compensates distortion in said displayed image generated by said light of said first angle in said first waveguide and said transition waveguide:
selecting an nth (n is a natural number equal to or greater than 2) light angle to calculate and obtain surface profile of an nth section in said second waveguide and display panel following said first section, to compensates distortion in said displayed image generated by lights of said nth angle in said first waveguide, said transition waveguide and the first to n\u22121th section of said second waveguide and display panel; and
repeating the previous step until all selected light angles are calculated.
17. The method according to claim 15, wherein said transition waveguide has a surface profile that restricts the light rays from said first waveguide to a maximum number of bounces in said transition waveguide.
18. The method according to claim 17, wherein said maximum number is 1.
19. The method according to claim 15, wherein said determination in surface profile of said second waveguide and display panel comprises the steps of:
calculating to obtain surface profile of a first section of said second waveguide and display panel’s display surface according to optical path of image rays from a light source positioned at entrance side of said first waveguide with a first incident angle passing through said first waveguide and said transition waveguide to produce a selected range of exit angles; and
calculating to obtain the surface profile of an nth (n is a natural number equal or greater than 2) section of said display surface according optical path of image rays from said light source with an nth incident angle passing through said first waveguide, said transition waveguide and the first to n\u22121th sections of said second waveguide and display panel to produce said selected range of exit angles.
20. The method according to claim 19, wherein said selected range of exit angles comprise an angle smaller than the critical angle of said second waveguide and display panel, whereby the exit rays do not intercept the display surfaces at an angle equal to or shallower than the critical angle.
21. A method for determination of the surface profile of a flat panel display device comprising a first waveguide, a transition waveguide and a second waveguide and display panel, comprising the steps of:
determining optical profile of said first waveguide and said transition waveguide;
determining a desired range of exit angles for said image rays;
selecting a first incident light angle and calculating optical paths of incoming image rays with said first incident angles in said first waveguide and said transition waveguide to obtain surface profile of a first section of said second waveguide and display panel most adjacent to said transition waveguide, such that image rays of said first incident angle exit said display surface with said desired range of exit angles;
selecting a second incident light angle for said incoming image rays and calculating to obtain surface profile of a second section of said second waveguide and display panel following said first section;
repeating previous step until said selected incident light angles are all calculated; and
determining surface profile of said fist waveguide, said transition waveguide and said second waveguide and display panel according to results so obtained.
22. The method according to claim 21, wherein said selected range of exit angles comprise an angle smaller than the critical angle of said second waveguide and display panel, whereby the exit rays do not intercept the display surfaces at an angle equal to or shallower than the critical angle.
23. The method according to claim 21, wherein said transition waveguide is designed to have a shortest possible curve length, counting from junction of said first waveguide and said transition waveguide to junction of said transition waveguide and said second waveguide and display panel, while maintaining the smoothest possible curve of said surface of said transition waveguide that connects surface of said first waveguide and said second waveguide and display panel.
24. The method according to claim 21, wherein said transition waveguide is designed to allow incoming image rays to bounce not more than once in said transition waveguide.
25. The method according to claim 21, wherein said optical paths are calculated using the basic trigonometric relationship of said incident image rays and surfaces profile of said first waveguide and said transition waveguide.
26. The method according to claim 21, wherein said second and following incident angles are respectively greater than the incident angle selected in a previous step.
27. The method according to claim 21, wherein said steps stop when the shallowest angle of said incident image rays is calculated.
28. A method to prepare a flat panel display device comprising in order a first waveguide, a transition waveguide and a second waveguide and display panel, wherein said second waveguide and display panel has a display surface and a substantially edged shape, said method comprising the steps of:
determining optical profile of said flat panel display device comprising the substeps of:
determining optical profile of said first waveguide and said transition waveguide;
selecting major incident angles of lights, and
calculating to obtain surface profile of sections in said second waveguide and display panel corresponding respectively to said selected light angles, to compensate distortions in displayed image generated by said selected lights’ paths in said first waveguide; and
preparing said flat panel display device using optical profile information so determined.
29. The method according to claim 28, wherein said transition waveguide has a surface profile that restricts light rays from said first waveguide to a maximum number of bounces in said transition waveguide.
30. The method according to claim 29, wherein said maximum number is 1.
31. The method according to claim 29, wherein said determination in surface profile of said second waveguide and display panel comprises the steps of:
calculating to obtain surface profile of a first section of said second waveguide and display panel’s display surface according to optical path of image rays from a light source positioned at entrance side of said first waveguide with a first incident angle passing through said first waveguide and said transition waveguide to produce a selected range of exit angles; and
calculating to obtain the surface profile of an nth (n is a natural number equal or greater than 2) section of said display surface according optical path of image rays from said light source with an nth incident angle passing through said first waveguide, said transition waveguide and the first to n\u22121th sections of said second waveguide and display panel to produce said selected range of exit angles.
32. The method according to claim 31, wherein said selected range of exit angles comprise an angle smaller than the critical angle of said second waveguide and display panel, whereby the exit rays do not intercept the display surfaces at an angle equal to or shallower than the critical angle.
33. A method for the preparation of a flat panel display device comprising a first waveguide, a transition waveguide and a second waveguide and display panel, comprising the steps of:
determining optical profile of said flat panel display device using the substeps of:
determining optical profile of said first waveguide and said transition waveguide;
determining a desired range of exit angles for incoming image rays;
selecting a first incident light angle for said incoming image rays and calculating optical paths of said incoming image rays with said first incident angles in said first waveguide and said transition waveguide to obtain surface profile of a first section of said second waveguide and display panel most adjacent to said transition waveguide, such that said image rays of said first incident angle exit said display surface with said desired exit angles;
selecting a second incident light angle for said incoming image rays and calculating to obtain surface profile of a next section of said second waveguide and display panel following said first section;
repeating previous step until all said selected incident light angles are calculated; and
determining surface profile of said fist waveguide, said transition waveguide and said second waveguide and display panel according to results so obtained; and
preparing said flat panel display device using optical profile information so obtained.
34. The method according to claim 33, wherein said transition waveguide is designed to allow said incoming image rays to bounce not more than once in said transition waveguide.
35. The method according to claim 33, wherein said selected range of exit angles comprise an angle smaller than the critical angle of said second waveguide and display panel, whereby the exit rays do not intercept the display surfaces at an angle equal to or shallower than the critical angle.