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Methods for producing clean liquid/wax products from a slurry used in a Fischer-Tropsch reactor are disclosed. In general, one embodiment of the present invention comprises a solid/liquid filtration system having a filter medium comprising a substrate and a filter cake deposited on the substrate, wh

Methods for producing clean liquid/wax products from a slurry used in a Fischer-Tropsch reactor are disclosed. In general, one embodiment of the present invention comprises a solid/liquid filtration system having a filter medium comprising a substrate and a filter cake deposited on the substrate, wherein the filter cake is generated by deposition of solids from the slurry. The thickness of the filter cake can be maintained within a desired range by controlling the slurry velocity and/or the pressure differential across the filter medium. This invention relates to a method of operation of such filtration system which increases filtration cycle time and improved filtrate quality resulting in very low solid content in filtrate.

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1. A method for producing a filtrate of low solid content from a slurry stream from a Fischer-Tropsch slurry bed reactor, the method comprising:a) providing a filter housing comprising a slurry chamber and a filtrate chamber separated by a filter medium comprising a filter cake disposed on a substra

1. A method for producing a filtrate of low solid content from a slurry stream from a Fischer-Tropsch slurry bed reactor, the method comprising:a) providing a filter housing comprising a slurry chamber and a filtrate chamber separated by a filter medium comprising a filter cake disposed on a substrate, wherein the filter cake has a thickness and provides a substantial majority of the filtration activity; removing a slurry, comprising a liquid phase and a solid phase, from the linear velocity; c) applying a pressure differential between the slurry chamber and the filtrate chamber so as to form a filter cake comprising a portion of the slurry solid phase disposed on the substrate; d) permeating a portion of the slurry liquid phase through the filter cake and the substrate to generate a filtrate flux; and e) periodically performing a cake thickness reduction step. 2. The method according to claim 1 wherein at least a portion of the filter cake comprises particles from the slurry solid phase.3. The method according to claim 1 wherein the substrate has a nominal rating and a fraction of slurry solid phase comprises particles having a size smaller than the substrate's nominal rating.4. The method according to claim 1 wherein at least 95 weight percent of the particles fall within the range 10-200 um.5. The method according to claim 1 wherein the slurry solid phase has a number average particle size between 20 and 50 um.6. The method according to claim 1 wherein the slurry solid phase comprises from 5 to 25 vol % of the slurry.7. The method according to claim 1 wherein the substrate comprises a medium selected from the group consisting of sintered woven wire-mesh media, sintered powered metal media, porous metal fiber, metal supported membranes, and wedged wire media.8. The method according to claim 1 wherein the filtrate medium's filtrate flux is independent of substrate morphology.9. The method according to claim 1 wherein the substrate has a cylindrical body with a longitudinal axis parallel to the direction of the slurry flow through the slurry chamber.10. The method according to claim 1 wherein the slurry linear velocity is less than 5.0 ft/sec.11. The method according to claim 1 wherein the slurry linear velocity is between 0.1 and 5.0 ft/sec.12. The method according to claim 1 wherein the filtration system has a filtration flux of at least 0.2 gal/min/ft2.13. The method according to claim 1 wherein the liquid phase comprises hydrocarbons produced from Fischer-Tropsch synthesis and the solid phase comprises a catalyst active for Fischer-Tropsch synthesis.14. The method according to claim 13 wherein the catalyst comprises at least one of cobalt, ruthenium, or iron.15. The method according to claim 13 wherein the catalyst comprises a support selected from the group consisting of alumina, silica, titania, zirconia, and combinations thereof.16. The method according to claim 1 wherein the pressure differential between the slurry chamber and the filtrate chamber is less than 30 psi.17. The method according to claim 1 wherein the filtrate comprises less than 25 ppm by weight of solids after the cake is formed.18. The method according to claim 1 wherein the filtrate comprises less than 10 ppm by weight of solids after the cake is formed.19. The method according to claim 1 wherein the filtrate comprises less than 5 ppm by weight of solids after the cake is formed.20. The method according to claim 1 wherein the thickness of the cake is partially reduced by stopping the filtrate flow and maintaining the slurry flow through the slurry chamber for at least 2 minutes.21. The method according to claim 1 wherein the thickness of the cake is partially reduced by increasing the linear velocity of the slurry for a period of at least 2 minutes.22. The method according to claim 1 wherein step (d) lasts at least 2 hours.23. The method according to claim 1 wherein step (d) lasts at least 4 hours.24. A method for operating a filtration system of a Fischer-Tropsch slurry bed reactor system with a long cycle time comprising:a) providing a filtration housing comprising a slurry chamber and a filtrate chamber separated by a filter medium comprising a filter cake disposed on a substrate, wherein the filter cake has a thickness and provides a substantial majority of the filtration activity; b) removing a slurry, comprising a liquid phase and a solid phase, from a reactor, degassing the slurry, and passing at a slurry linear velocity through the slurry chamber; c) applying a pressure differential between the slurry chamber and the filtrate chamber so as to form a filter cake comprising a portion of the slurry solid phase disposed on the substrate; d) permeating a portion of the slurry liquid phase through the filter cake and the substrate to generate a filtrate flux; e) periodically performing a cake thickness reduction step; f) removing the filter cake after performing several cake thickness reduction steps (e); and g) repeating steps b through f. 25. The method according to claim 24 wherein step g is performed by at least one technique selected from the group consisting of reversing the filtrate flow across the substrate, stopping filtrate flow while continuing slurry flow through the slurry chamber, and passing a gas stream from the filtrate chamber to the slurry chamber.26. The method according to claim 24 wherein the thickness of the cake is partially reduced by stopping the filtrate flow and maintaining the slurry flow through the slurry chamber for at least 2 minutes.27. The method according to claim 24 wherein the thickness of the cake is partially reduced by increasing the linear velocity of the slurry for a period of at least 2 minutes.28. The method according to claim 24 wherein at least a portion of the filter cake comprises particles from the slurry solid phase.29. The method according to claim 24 wherein the substrate has a nominal rating and a fraction of slurry solid phase comprises particles having a size smaller than the substrate's nominal rating.30. The method according to claim 24 wherein at least 95 weight percent of the particles fall within the range 10-200 um.31. The method according to claim 24 wherein the slurry solid phase has a number average particle size between 20 and 50 um.32. The method according to claim 24 wherein the slurry solid phase comprises from 5 to 25 vol % of the slurry.33. The method according to claim 24 wherein the substrate comprises a medium selected from the group consisting of sintered woven wire-mesh media, sintered powered metal media, porous metal fiber, metal supported membranes, and wedged wire media.34. The method according to claim 24 wherein the filtrate medium's filtrate flux is independent of substrate morphology.35. The method according to claim 24 wherein the substrate has a cylindrical body with a longitudinal axis parallel to the direction of the slurry flow through the slurry chamber.36. The method according to claim 24 wherein the slurry linear velocity is less than 5.0 ft/sec.37. The method according to claim 24 wherein the slurry linear velocity is between 0.1 and 5.0 ft/sec.38. The method according to claim 24 wherein the filtration system has a filtration flux of at least 0.2 gal/min/ft2.39. The method according to claim 24 wherein the liquid phase comprises hydrocarbons produced from Fischer-Tropsch synthesis and the solid phase comprises a catalyst active for Fischer-Tropsch synthesis.40. The method according to claim 39 wherein the catalyst comprises at least one of cobalt, ruthenium, or iron.41. The method according to claim 39 wherein the catalyst comprises a support selected from the group consisting of alumina, silica, titania, zirconia, and combinations thereof.42. The method according to claim 24 wherein the pressure differential between the slurry chamber and the filtrate chamber is less than 30 psi.43. The method according to claim 24 wherein the filtrate comprises less than 25 ppm by weight of solids after the cake is formed.44. The method according to claim 24 wherein the filtrate comprises less than 10 ppm by weight of solids after the cake is formed.45. The method according to claim 24 wherein the filtrate comprises less than 5 ppm by weight of solids after the cake is formed.46. The method according to claim 24 wherein step (d) lasts at least 2 hours.47. The method according to claim 24 wherein step (d) lasts at least 4 hours.48. A method for operating a filtration system comprising:flowing a slurry to a settler, wherein the slurry comprises a liquid phase and a solid phase, wherein the solid phase further comprises large diameter particles and small diameter particles; extracting from the settler a first portion of the slurry containing a high concentration of large diameter particles; passing the first portion of the slurry through a filter housing comprising a slurry chamber and a filtrate chamber separated by a filter medium comprising a substrate; applying a pressure differential between the slurry chamber and the filtrate chamber so as to form a filter cake comprising primarily large diameter particles disposed on the substrate, wherein the filter cake has a thickness and provides a substantial majority of the filtration activity; passing the slurry having both large and small diameter particles through the filter housing so as to permeate a portion of the slurry liquid phase through the filter cake and the substrate to generate a filtrate flux. 49. The method of claim 48 further comprising performing a cake thickness reduction operation to remove only a portion of the cake from the substrate.50. The method according to claim 49 wherein the cake thickness reduction operation is performed by at least one technique selected from the group consisting of reversing the filtrate flow across the substrate, stopping filtrate flow while continuing slurry flow through the slurry chamber, and passing a gas stream from the filtrate chamber to the slurry chamber.51. The method according to claim 49 wherein the cake thickness reduction operation includes stopping the filtrate flow and maintaining the slurry flow through the slurry chamber for at least 2 minutes.52. The method according to claim 49 wherein the thickness of the cake is partially reduced by increasing the linear velocity of the slurry for a period of at least 2 minutes.53. The method according to claim 49 further comprising removing the filter cake after performing several cake thickness reduction operations.54. The method according to claim 48 wherein the substrate has a nominal rating and a fraction of slurry solid phase comprises particles having a size smaller than the substrate's nominal rating.55. The method according to claim 48 wherein at least 95 weight percent of the particles fall within the range 10-200 um.56. The method according to claim 48 wherein the slurry solid phase has a number average particle size between 20 and 50 um.57. The method according to claim 48 wherein the slurry solid phase comprises from 5 to 25 vol % of the slurry.58. The method according to claim 48 wherein the substrate comprises a medium selected from the group consisting of sintered woven wire-mesh media, sintered powered metal media, porous metal fiber, metal supported membranes, and wedged wire media.59. The method according to claim 48 wherein the filtrate medium's filtrate flux is independent of substrate morphology.60. The method according to claim 48 wherein the substrate has a cylindrical body with a longitudinal axis parallel to the direction of the slurry flow through the slurry chamber.61. The method according to claim 48 wherein the slurry linear velocity is less than 5.0 ft/sec.62. The method according to claim 48 wherein the slurry linear velocity is between 0.1 and 5.0 ft/sec.63. The method according to claim 48 wherein the filtration system has a filtration flux of at least 0.2 gal/min/ft2.64. The method according to claim 48 wherein the liquid phase comprises hydrocarbons produced from Fischer-Tropsch synthesis and the solid phase comprises a catalyst active for Fischer-Tropsch synthesis.65. The method according to claim 64 wherein the catalyst comprises at least one of cobalt, ruthenium, or iron.66. The method according to claim 64 wherein the catalyst comprises a support selected from the group consisting of alumina, silica, titania, zirconia, and combinations thereof.67. The method according to claim 48 wherein the pressure differential between the slurry chamber and the filtrate chamber is less than 30 psi.68. The method according to claim 48 wherein the filtrate comprises less than 25 ppm by weight of solids after the cake is formed.69. The method according to claim 48 wherein the filtrate comprises less than 10 ppm by weight of solids after the cake is formed.70. The method according to claim 48 wherein the filtrate comprises less than 5 ppm by weight of solids after the cake is formed.