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Ribbed heat exchange tubes in which the aspect ratio of the ribs is less than 5, provide greater indirect heat exchange than conventional heat exchange tubes with or without fins, when used in a slurry comprising a liquid phase, in which is dispersed flowing gas bubbles or particulate solids and flo

Ribbed heat exchange tubes in which the aspect ratio of the ribs is less than 5, provide greater indirect heat exchange than conventional heat exchange tubes with or without fins, when used in a slurry comprising a liquid phase, in which is dispersed flowing gas bubbles or particulate solids and flowing gas bubbles. The ribs, and typically also the longitudinal axis of the heat exchange tubes, are aligned in a direction parallel to, or spirally along the gas bubble flow direction. This is useful to increase either (i) the productivity of a slurry Fischer-Tropsch hydrocarbon synthesis reactor without an increase in the temperature in the reactor or (ii) increasing the production of higher molecular weight hydrocarbons by reducing the reaction temperature at a given feed conversion.

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What is claimed is: 1. A process for adding or removing heat to or from a slurry comprising a liquid phase and at least one of (i) flowing gas bubbles and (ii) a flowing gas bubbles and particulate solids, by indirect heat exchange with means located in the slurry, wherein said means comprises one

What is claimed is: 1. A process for adding or removing heat to or from a slurry comprising a liquid phase and at least one of (i) flowing gas bubbles and (ii) a flowing gas bubbles and particulate solids, by indirect heat exchange with means located in the slurry, wherein said means comprises one or more hollow conduits containing a heat exchange fluid flowing within, in indirect heat exchange relationship with said surrounding slurry, with each of said one or more conduits having a plurality of ribs attached to and extending outward from its exterior and wherein said ribs have an aspect ration of less than five. 2. A process according to claim 1 wherein said one or more conduits and said ribs are heat conductive. 3. A process according to claim 2 wherein the ratio of the base O.D. of said one or more tubes or conduits to the height of said ribs is greater than 10. 4. A process according to claim 3 wherein each of said conduits has a longitudinal axis aligned parallel to the flow direction of said gas bubbles. 5. A process according to claim 4 wherein said aspect ratio is less than 3. 6. A process according to claim 5 wherein the ratio of said base O.D. to the width of the channel or spacing between said ribs is greater than 10. 7. A process according to claim 6 wherein the thickness of said ribs divided by the width of the channel or spacing between them is greater than 1. 8. A process according to claim 7 wherein said aspect ratio is less than 2. 9. A process for increasing the production of higher molecular weight hydrocarbon products from a hydrocarbon synthesis reaction in a slurry hydrocarbon synthesis reactor in which said slurry comprises a particulate catalyst and flowing gas bubbles in a slurry hydrocarbon liquid, said process comprising reducing the reaction temperature without reducing the conversion of the CO feed passed into said reactor, by increasing indirect heat exchange in said slurry using heat conductive heat exchange means in said slurry, said means comprising one or more hollow conduits containing a heat exchange fluid flowing within, in indirect heat exchange relationship with said surrounding slurry, with each of said one or more conduits having a plurality of ribs attached to and extending outward from its exterior surface wherein said ribs have an aspect ration of less than five, and wherein at least a portion of said synthesized hydrocarbons are upgraded by one or more upgrading operations. 10. A process according to claim 9 wherein said conduits have a longitudinal axis aligned substantially vertically in said slurry and wherein said ribs are aligned substantially parallel to or spirally along said longitudinal conduit axes. 11. A process according to claim 10 wherein the ratio of the base O.D. of said one or more tubes or conduits to the height of said ribs is greater than 10. 12. A process according to claim 11 wherein the ratio of said base O.D. to the width of the channel or spacing between said ribs is greater than 10. 13. A process according to claim 12 wherein said aspect ratio is less than 3. 14. A process according to claim 13 wherein the thickness of said ribs divided by said width of said channel or spacing between them at their bottom is greater than 1. 15. A process for increasing theproduction of hydrocarbon products from a hydrocarbon synthesis reaction in a slurry hydrocarbon synthesis reactor, in which said slurry comprises a particulate catalyst and flowing gas bubbles in a slurry hydrocarbon liquid, said process comprising increasing the conversion of the CO feed passed into said reactor at a given temperature, by increasing indirect heat exchange in said slurry which comprises one or more vertical, hollow conduits containing a heat exchange fluid flowing within, in indirect heat exchange relationship with said surrounding slurry, with each of said one or more conduits having a plurality of ribs attached to and extending outward from its exterior wherein said ribs have an aspect ration of less than five, and wherein at least a portion of said synthesized hydrocarbons are upgraded by one or more upgrading operations. 16. A process according to claim 15 wherein the ratio of the base O.D. of said one or more tubes or conduits to the height of said ribs is greater than 10. 17. A process according to claim 16 wherein the ratio of said base O.D. to the width of the channel or spacing between said ribs is greater than 10. 18. A process according to claim 17 wherein said aspect ratio is less than 3 and the thickness of said ribs divided by said width of said channel or spacing between them at their bottom is greater than 1. 19. A slurry hydrocarbon synthesis process comprises the steps of: (a) contacting a synthesis gas comprising a mixture of H2 and CO with a particulate hydrocarbon synthesis catalyst, in a slurry body comprising said particles of said catalyst and gas bubbles in a continuous phase hydrocarbon slurry liquid in a hydrocarbon synthesis reactor, in which said H2 and CO react under reaction conditions effective to form hydrocarbons from said synthesis gas, along with heat produced by the exothermic synthesis reaction, wherein at least a portion of said synthesized hydrocarbons are liquid at the reaction conditions and form said slurry liquid and wherein said catalyst comprises at least one Group VIII catalytic metal component; (b) removing at least a portion of said synthesized hydrocarbons from said reactor and then upgrading at least a portion thereof by one or more upgrading operations; and (c) removing a least a portion of said reaction heat from said reactor by heat exchange means immersed in said slurry therein, said heat exchange means comprising one or more vertical, elongated, hollow conduits containing a heat exchange fluid flowing within, in indirect heat exchange relationship with said surrounding slurry, with each of said one or more conduits having a plurality of ribs attached to and extending outward from its exterior wherein said ribs have an aspect ratio of less than five. 20. A process according to claim 19 wherein said catalyst comprises a catalytic cobalt component and a support component. 21. A process according to claim 20 wherein the ratio of the base O.D. of said one or more conduits to the height of said ribs is greater than 10. 22. The process of claims 1, 9, 15, or 19 wherein said ribs are aligned longitudinally along the flow direction of said gas bubbles. 23. The process of claims 1, 9, 15, or 19 wherein said ribs are aligned spirally along the flow direction of said gas bubbles. 24. A process according to claim 19 where said synthesized hydrocarbons comprise C5+ hydrocarbons. 25. A process according to claim 24 wherein at least a portion of said C5+ hydrocarbons are subjected to conversion. 26. A process according to claim 25 wherein said C5+ hydrocarbons are subjected to a non-catalytic conversion in which the molecular structure of at least a portion of said hydrocarbon is changed. 27. A process according to claim 25 wherein said C5+ hydrocarbons are subjected to a catalytic conversion in which the molecular structure of at least a portion of said hydrocarbon is changed. 28. A process according to claim 25 wherein a liquid fuel is the product of said conversion. 29. A process according to claim 25 wherein a lubricating oil is the product of said conversion. 30. A process according to claim 28 wherein said liquid fuel includes motor gasoline, diesel fuel, kerosene and jet fuel. 31. A process according to claim 29 wherein said lubricating oil includes automotive, jet, turbine and metal working oils.