Patent EA-005090-B1 (EA)
Title: Process for size classifying ammonium sulfate crystals which are present in a suspension
Inventor: LOOMANS-V D ANKER NATASJA ANOU
IPC: B01D29/11
Filed: 2002-04-05
Abstract: 1. Process for size classifying ammonium sulfate crystals using a screen, said process comprising: feeding a feed suspension to the screen, said feed suspension comprising said ammonium sulfate crystals in an ammonium sulfate solution, size classifying the ammonium sulfate crystals, and keeping both sides of the screen immersed in liquid during said size classifying. 2. Process according to claim 1, wherein the process comprises withdrawing a permeate suspension from the screen, said permeate suspension comprising ammonium sulfate crystals and ammonium sulfate solution which have been transported through the openings of the screen, and withdrawing a product suspension from the screen, said product suspension comprising ammonium sulfate crystals and ammonium sulfate solution which have not been transported through the openings of the screen. 3. Process according to claim 2, wherein a screening apparatus is used, said screening apparatus comprising a first chamber, a second chamber and the screen, the screen forming a partition between the first chamber and the second chamber, and wherein the process comprises: introducing the feed suspension into the first chamber, withdrawing the permeate suspension from the second chamber, and withdrawing the product suspension from the first chamber. 4. Process according to any one of claims 1 to 3, wherein the process comprises controlling the flow rate of the feed suspension entering the first chamber, the flow rate of the permeate suspension exiting the second chamber and/or the flow rate of the product suspension exiting the first chamber, such as to keep both sides of the screen immersed in liquid. 5. Process according to any one of claims 1 to 4, wherein the feed suspension which is fed to the screen comprises less than 25 vol. % ammonium sulfate crystals. 6. Process according to any one of claims 2 to 5, wherein the product suspension which is withdrawn from the screen comprises less than 50 vol. % ammonium sulfate crystals. 7. Process according to any one of claims 1 to 6, wherein transport of the suspension at the side of the screen to which the feed suspension is fed, takes place in a direction essentially parallel to the screen. 8. Process according to claim 7, wherein transport of the suspension at the side of the screen to which the feed suspension is fed, takes place at a rate of at least 0.01 m/s in a direction parallel to the screen. 9. Process according to any one of claims 1 to 8, wherein the process comprises wiping off ammonium sulfate crystals from the screen with mechanical means. 10. Process according to claim 9, wherein the screening apparatus as defined in claim 3 is used, and wherein the mechanical means are inside the first chamber. 11. Process according to claim 10, wherein at least part of the wall of the first chamber forms a cylinder, said cylindrical part of the wall including at least part of the screen, wherein the mechanical means are inside the first chamber and wherein said mechanical means can be rotated around an axis parallel to the length axis of the cylinder. 12. Process according to any of claims 1 to 11, wherein the feed suspension comprises fine crystals to which the openings of the screen are permeable, and coarse crystals to which the openings of the screen are not permeable, and wherein the process comprises at least partially separating said fine crystals from said coarse crystals. 13. Process according to any one of claims 1 to 12, wherein contact of the openings of the screen with air is prevented.