Rotary drum screen method for thin stillage filtration

Abstract

A rotating drum screen method for separating solids from thin stillage obtained from ethanol fermentation, the thin stillage comprising one or more of solids and suspended solids. Thin stillage is chemically treated with an anionic polymer to form stable particles of one or more of solids and suspended solids. Introducing the treated thin stillage into a rotating drum screen system. The drum screen includes a filter screen that retains at least a portion of the solids within a hollow portion of the drum screen and which produces a liquid effluent that is discharged from an outer surface of the drum screen. The retained solids are removable from the drum screen via a solid discharge end. A head box is disposed within the hollow portion of the drum screen and has a plurality of fluid flow channel dividers dividing and directing an influent stream outwardly against the drum screen.

The invention claimed is: 
     
       1. A rotating drum screen method for separating solids from thin stillage obtained from ethanol fermentation, the thin stillage comprising one or more of solids and suspended solids, the rotating drum screen method comprising:
 chemically treating the thin stillage with an anionic polymer to form stable particles of one or more of solids and suspended solids; 
 introducing the treated thin stillage into a rotating drum screen system comprising:
 a housing having an influent inlet at an influent inlet end, a solid discharge end, and an area between the influent inlet end and the solid discharge end, the influent inlet permitting a flow of treated thin stillage into a hollow portion of a drum screen positioned lengthwise in the area between the influent inlet end and the solid discharge end, the drum screen comprising a filter screen that retains at least a portion of the stable particles within the hollow portion of the drum screen and which produces a liquid effluent that is discharged from an outer surface of the drum screen, the retained portion of stable particles being removed from the drum screen via the solid discharge end; and 
 a head box disposed within the hollow portion of the drum screen proximate the influent inlet end and in fluid communication with the influent inlet, the head box being configured to direct the treated thin stillage outwardly against the drum screen; and 
 
 directing the treated thin stillage against the drum screen wherein the filter screen retains at least a portion of the stable particles and produces the liquid effluent that is discharged from the outer surface of the drum screen. 
 
     
     
       2. The rotating drum screen method as recited in  claim 1 , wherein the head box is disposed at an elevated position within the drum screen, such that the treated thin stillage initially contacts the drum screen at a position between a top-to-bottom centerline of the drum screen and approximately 30° below the top-to-bottom centerline of the drum screen. 
     
     
       3. The rotating drum screen method as recited in  claim 2 , wherein the elevated position of the head box causes the treated thin stillage to initially contact the drum screen at a position between 5° to 20° below the top-to-bottom centerline of the drum screen. 
     
     
       4. The rotating drum screen method as recited in  claim 1 , wherein the influent inlet and a portion of the head box in contact with the influent inlet has a rectangular cross-section. 
     
     
       5. The rotating drum screen method as recited in  claim 1 , wherein the drum screen comprises a flight or series of flights extending from an inner surface of the drum screen along a spiral path, the flight or series of flights having a variable height along the drum screen, with a first, lower, height proximate the influent inlet end and permitting a discharge of the head box to be placed proximate the filter screen, and with a second, higher, height proximate the solid discharge end. 
     
     
       6. The rotating drum screen method as recited in  claim 5 , wherein the first, lower, height of the flight or series of flights proximate the influent end is a height less than or equal to approximately 2.5 cm. 
     
     
       7. The rotating drum screen method as recited in  claim 5 , wherein the second, higher, height of the flight or series of flights proximate the solid discharge end has a height between 2.5 cm and 25% to 50% of a filter-screen-to-filter-screen diameter of the drum screen. 
     
     
       8. The rotating drum screen method as recited in  claim 1 , further comprising spraying a fluid through the filter screen in an exterior-to-interior direction, wherein the fluid is selected from the group consisting of:
 air; 
 a mixture of air and an aqueous solution; and 
 an aqueous solution. 
 
     
     
       9. The rotating drum screen method as recited in  claim 1 , wherein the drum screen comprises a non-stick perfluorocarbon coating disposed on the filter screen. 
     
     
       10. The rotating drum screen method as recited in  claim 9 , wherein the non-stick perfluorocarbon coating comprises a material selected from the group consisting of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluorinated ethylene propylene (FEP), perfluoroalkoxy alkane (PFA), and ethylene tetrafluoroethylene (ETFE). 
     
     
       11. The rotating drum screen method as recited in  claim 1 , wherein the drum screen rotates in a direction opposite a direction in which the treated thin stillage contacts the drum screen. 
     
     
       12. The rotating drum screen method as recited in  claim 1 , wherein the drum screen rotates at a rate between approximately 4 revolutions per minute (rpm) and approximately 25 rpm. 
     
     
       13. The rotating drum screen method as recited in  claim 1 , wherein the anionic polymer has a molecular weight greater than 10,000,000 Da. 
     
     
       14. A rotating drum screen method for separating solids from thin stillage obtained from ethanol fermentation, the thin stillage comprising one or more of solids and suspended solids, the rotating drum screen method comprising:
 chemically treating the thin stillage with an anionic polymer a molecular weight greater than 10,000,000 Da to form stable particles of one or more of solids and suspended solids; 
 introducing the treated thin stillage into a rotating drum screen system comprising:
 a housing having an influent inlet at an influent inlet end, a solid discharge end and an area between the influent inlet end and the solid discharge end, the influent inlet permitting a flow of treated thin stillage into a hollow portion of a drum screen positioned lengthwise in the area between the influent inlet end and the solid discharge end, the drum screen comprising a filter screen that retains at least a portion of the stable particles within the hollow portion of the drum screen and which produces a liquid effluent that is discharged from an outer surface of the drum screen, the retained stable particles being removable from the drum screen via the solid discharge end, wherein the filter screen has a size in the range of 25 μm and 150 μm; and 
 a head box disposed within the hollow portion of the drum screen proximate the influent inlet end and in fluid communication with the influent inlet, the head box comprising a plurality of parallel fluid flow channel dividers dividing the flow of treated thin stillage received at the influent inlet into a plurality of parallel ongoing streams; and 
 
 directing the plurality of ongoing streams outwardly against the drum screen wherein the filter screen retains at least a portion of the stable particles and produces the liquid effluent that is discharged from the outer surface of the drum screen. 
 
     
     
       15. The rotating drum screen method as recited in  claim 14 , wherein the head box is disposed at an elevated position within the drum screen, such that the treated thin stillage initially contacts the drum screen at a position between a top-to-bottom centerline of the drum screen and approximately 30° below the top-to-bottom centerline of the drum screen. 
     
     
       16. The rotating drum screen method as recited in  claim 14  wherein the drum screen comprises a flight or series of flights extending from an inner surface of the drum screen along a spiral path, the flight or series of flights having a variable height along the drum screen, with a first, lower, height proximate the influent inlet end and permitting a discharge of the head box to be placed proximate the filter screen, and with a second, higher, height proximate the solid discharge end. 
     
     
       17. The rotating drum screen method as recited in  claim 14 , further comprising spraying a fluid through the filter screen in an exterior-to-interior direction, wherein the fluid is selected from the group consisting of:
 air; 
 a mixture of air and an aqueous solution; and 
 an aqueous solution. 
 
     
     
       18. The rotating drum screen method as recited in  claim 14 , wherein the drum screen comprises a non-stick coating disposed on the filter screen. 
     
     
       19. The rotating drum screen method as recited in  claim 18 , wherein the non-stick coating comprises a material selected from the group consisting of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluorinated ethylene propylene (FEP), perfluoroalkoxy alkane (PFA), and ethylene tetrafluoroethylene (ETFE). 
     
     
       20. The rotating drum screen method as recited in  claim 14 , wherein the drum screen rotates at a rate between approximately 4 revolutions per minute (rpm) and approximately 25 rpm. 
     
     
       21. A rotating drum screen method for separating solids from thin stillage obtained from ethanol fermentation, the thin stillage comprising one or more of solids and suspended solids, the rotating drum screen method comprising:
 chemically treating the thin stillage with a cationic polymer to form stable particles of one or more of solids and suspended solids;   introducing the treated thin stillage into a rotating drum screen system comprising:
 a housing having an influent inlet at an influent inlet end, a solid discharge end, and an area between the influent inlet end and the solid discharge end, the influent inlet permitting a flow of treated thin stillage into a hollow portion of a drum screen positioned lengthwise in the area between the influent inlet end and the solid discharge end, the drum screen comprising a filter screen that retains at least a portion of the stable particles within the hollow portion of the drum screen and which produces a liquid effluent that is discharged from an outer surface of the drum screen, the retained portion of stable particles being removed from the drum screen via the solid discharge end; and 
 a head box disposed within the hollow portion of the drum screen proximate the influent inlet end and in fluid communication with the influent inlet, the head box being configured to direct the treated thin stillage outwardly against the drum screen; and 
   directing the treated thin stillage against the drum screen wherein the filter screen retains at least a portion of the stable particles and produces the liquid effluent that is discharged from the outer surface of the drum screen.    
     
     
       22. The rotating drum screen method as recited in claim 21, wherein the head box is disposed at an elevated position within the drum screen, such that the treated thin stillage initially contacts the drum screen at a position between a top-to-bottom centerline of the drum screen and approximately 30° below the top-to-bottom centerline of the drum screen.  
     
     
       23. The rotating drum screen method as recited in claim 22, wherein the elevated position of the head box causes the treated thin stillage to initially contact the drum screen at a position between 5° to 20° below the top-to-bottom centerline of the drum screen.  
     
     
       24. The rotating drum screen method as recited in claim 21, wherein the influent inlet and a portion of the head box in contact with the influent inlet has a rectangular cross-section.  
     
     
       25. The rotating drum screen method as recited in claim 21, wherein the drum screen comprises a flight or series of flights extending from an inner surface of the drum screen along a spiral path, the flight or series of flights having a variable height along the drum screen, with a first, lower, height proximate the influent inlet end and permitting a discharge of the head box to be placed proximate the filter screen, and with a second, higher, height proximate the solid discharge end.  
     
     
       26. The rotating drum screen method as recited in claim 21, further comprising spraying a fluid through the filter screen in an exterior-to-interior direction, wherein the fluid is selected from the group consisting of:
 air;   a mixture of air and an aqueous solution; and   an aqueous solution.    
     
     
       27. The rotating drum screen method as recited in claim 21, wherein the drum screen comprises a non-stick perfluorocarbon coating disposed on the filter screen.  
     
     
       28. The rotating drum screen method as recited in claim 27, wherein the non-stick perfluorocarbon coating comprises a material selected from the group consisting of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluorinated ethylene propylene (FEP), perfluoroalkoxy alkane (PFA), and ethylene tetrafluoroethylene (ETFE).  
     
     
       29. The rotating drum screen method as recited in claim 21, wherein the drum screen rotates in a direction opposite a direction in which the treated thin stillage contacts the drum screen.  
     
     
       30. The rotating drum screen method as recited in claim 21, wherein the drum screen rotates at a rate between approximately 4 revolutions per minute (rpm) and approximately 25 rpm.  
     
     
       31. A rotating drum screen method for separating solids from thick and/or thin stillage obtained from ethanol fermentation, the thick and/or thin stillage comprising one or more of solids and suspended solids, the rotating drum screen method comprising:
 chemically treating the thick and/or thin stillage with a polymer to form stable particles of one or more of solids and suspended solids;   introducing the treated thick and/or thin stillage into a rotating drum screen system comprising:
 a housing having an influent inlet at an influent inlet end, a solid discharge end, and an area between the influent inlet end and the solid discharge end, the influent inlet permitting a flow of treated thick and/or thin stillage into a hollow portion of a drum screen positioned lengthwise in the area between the influent inlet end and the solid discharge end, the drum screen comprising a filter screen that retains at least a portion of the stable particles within the hollow portion of the drum screen and which produces a liquid effluent that is discharged from an outer surface of the drum screen, the retained portion of stable particles being removed from the drum screen via the solid discharge end; and 
 a head box disposed within the hollow portion of the drum screen proximate the influent inlet end and in fluid communication with the influent inlet, the head box being configured to direct the treated thick and/or thin stillage outwardly against the drum screen; and 
   directing the treated thick and/or thin stillage against the drum screen wherein the filter screen retains at least a portion of the stable particles and produces the liquid effluent that is discharged from the outer surface of the drum screen.    
     
     
       32. The rotating drum screen method as recited in claim 31, wherein the head box is disposed at an elevated position within the drum screen, such that the treated thin stillage initially contacts the drum screen at a position between a top-to-bottom centerline of the drum screen and approximately 30° below the top-to-bottom centerline of the drum screen.  
     
     
       33. The rotating drum screen method as recited in claim 32, wherein the elevated position of the head box causes the treated thin stillage to initially contact the drum screen at a position between 5° to 20° below the top-to-bottom centerline of the drum screen.  
     
     
       34. The rotating drum screen method as recited in claim 31, wherein the influent inlet and a portion of the head box in contact with the influent inlet has a rectangular cross-section.  
     
     
       35. The rotating drum screen method as recited in claim 31, wherein the drum screen comprises a flight or series of flights extending from an inner surface of the drum screen along a spiral path, the flight or series of flights having a variable height along the drum screen, with a first, lower, height proximate the influent inlet end and permitting a discharge of the head box to be placed proximate the filter screen, and with a second, higher, height proximate the solid discharge end.  
     
     
       36. The rotating drum screen method as recited in claim 31, further comprising spraying a fluid through the filter screen in an exterior-to-interior direction, wherein the fluid is selected from the group consisting of:
 air;   a mixture of air and an aqueous solution; and   an aqueous solution.    
     
     
       37. The rotating drum screen method as recited in claim 31, wherein the drum screen comprises a non-stick perfluorocarbon coating disposed on the filter screen.  
     
     
       38. The rotating drum screen method as recited in claim 37, wherein the non-stick perfluorocarbon coating comprises a material selected from the group consisting of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), fluorinated ethylene propylene (FEP), perfluoroalkoxy alkane (PFA), and ethylene tetrafluoroethylene (ETFE).  
     
     
       39. The rotating drum screen method as recited in claim 31, wherein the drum screen rotates in a direction opposite a direction in which the treated thin stillage contacts the drum screen.  
     
     
       40. The rotating drum screen method as recited in claim 31, wherein the drum screen rotates at a rate between approximately 4 revolutions per minute (rpm) and approximately 25 rpm.