568 Fermentation and Biochemical Engineering Handbook 6.1 Operation The simplest sedimentation centrifuge design is the tube type, con structed of a tube 2 to 5 inches in diameter and spun at 62,000 gs. Slurry enters at the bottom of the tube through a feed nozzle and the effluent discharges over a dam at the top. Solids are deposited along the walls particles intersect the bowl wall and are removed from the fluid. The bowl is suspended from an upper bearing and drive assembly. There is a loose damping assembly at the bottom. By installing two different liquid discharge ports at different radii and elevations, it is feasible to separate two different liquid phases and a solid phase. Solids are unloaded manually when clarity diminishes 7.0 CONTINUOUS DECANTER CENTRIFUGES (WITH CONVEYOR) Typical applications in fermentation are thick fermentation broths with high solids concentrations where a relatively drier cake is required. However, protein precipitate cannot be sedimented and animal cell debris, due to their slimy nature, can render scrolling ineffective Solids and liquids are discharged continuously in this type of design which can process coarse particles that would blind the discharge system and disks of disk bowl machines. The principle of operation is shown in Fig. I This unit, often referred to as a decanter, is constructed with a conical bowl and an internal rotating scroll conveyor to propel solids or beach them along the inclined wall bowl to then be discharged The scroll rotates slower than the bowl at a differential speed of 1/20 to 1/160 of the bowl speed; this differential speed causes translation of the solids along the bowl. Particularly, soft solids can be conveyed with low conveyor differential speeds should higher differential speeds cause resuspensions. Units will have g forces up to 6000 and range in diameter from 6"to 48 ( The solids discharge outlet is usually smaller than the liquid discharge outlet at the opposite end By varying the liquid discharge outlet size the pool level or depth of the pond can be controlled. The lower the level, the greater the length of the dry beach section. These units operate below their critical speeds between fixed bearings attached to a rigid frame. Mechanical seals are available for pressure operation up to 150 psig. Operating temperatures are from-87oC to+260°C
568 Fermentation and Biochemical Engineering Handbook 6.1 Operation The simplest sedimentation centrifuge design is the tube type, constructed of a tube 2 to 5 inches in diameter and spun at 62,000 g's. Slurry enters at the bottom of the tube through a feed nozzle and the effluent discharges over a dam at the top. Solids are deposited along the walls as particles intersect the bowl wall and are removed from the fluid. The bowl is suspended from an upper bearing and drive assembly. There is a loose damping assembly at the bottom. By installing two different liquid discharge ports at different radii and elevations, it is feasible to separate two different liquid phases and a solid phase. Solids are unloaded manually when clarity diminishes. 7.0 CONTINUOUS DECANTER CENTRIFUGES (WITH CONVEYOR) Typical applications in fermentation are thick fermentation broths with high solids concentrations where a relatively drier cake is required. However, protein precipitate cannot be sedimented and animal cell debris, due to their slimy nature, can render scrolling ineffective. Solids and liquids are discharged continuously in this type of design which can process coarse particles that would blind the discharge system and disks of disk bowl machines. The principle of operation is shown in Fig. 1. This unit, often referred to as a decanter, is constructed with a conical bowl and an internal rotating scroll conveyor to propel solids or beach them along the inclined wall bowl to then be discharged. The scroll rotates slower than the bowl at a differential speed of 1/20 to 1/160 of the bowl speed; this differential speed causes translation of the solids along the bowl. Particularly, soft solids can be conveyed with low conveyor differential speeds should higher differential speeds cause resuspensions. Units will haveg forces up to 6000 and range in diameter from 6" to 48".(') The solids discharge outlet is usually smaller than the liquid discharge outlet at the opposite end. By varying the liquid discharge outlet size the pool level or depth of the pond can be controlled. The lower the level, the greater the length of the dry beach section. These units operate below their critical speeds between fixed bearings attached to a rigid frame. Mechanical seals are available for pressure operation up to 150 psig. Operating temperatures are from -87°C to +260°C
iquid Solids Diacharge Slurry Feed Figure 1. Solid Bowl Decanter
Centrifugation 569