CENTIFUGES Sedimentation Filtration imperforated basket perforated basket with sieve or cloth as at cake phase with greater density creates layer at bowl filters wall, phase with smaller density is at liqid level near axis. centrifges to separation of emlsions prification, centrifges for separation of small amonts of solids clarification.
Settling in centrifges Settling velocity in centrifges Forces acting on particle settling in rotating liqid Centrifgal force F o Boyant force in centrifgal force field F ov Coriolis force F c Gravitation force G Boyant force in gravitational field F v Drag force F Inertial force de to centrifgal acceleration F s Force balance in radial direction F o F ov F r F sr 0 4 D s r 3 C D F o D 6 3 r s D F ov 6 3 r F r C D D 4
4 D s r 3 C D Settling velocity in centrifgal force field can be determined from eqation for settling velocity in gravitational field replacing acceleration de to gravity of centrifgal acceleration. g rω Stokes region: D s 8 r Transition region: 0,7,4 0, 7,4 D s 0,53 r 0,9 0,43 Newton region:,74 D s r Most of indstrial centrifges (95 %) working in the Stokes region!
Time of sedimentation in bowl centrifges dr dt t 0 dt d r Stokes region: Transition region: t 8 d r 8 t ln D r D s 0,9 0,43 0,9 0,43 dr,5,4 0,7,4 0,7,4 0,7,4 0,53D r s D s Newton region: d r t, 5,74 D r / D s s s 0,9 0,9
Volmetric flow rate in bowl centrifges Batch centrifges coarse sspensions with solid sediment Time of one working period t p : time of sedimentation in centrifge t handling time t m (filling, starting, discharging, braking and stopping) V L V stř L t t m
Mass balance of solid phase: Semi-batch centrifges coarse sspensions with solid sediment m weight of sediment layer at bowl wall m w Lh Weight of sspension from one working period: m s w s liqid discharge liqid srface feed flow m s m w w s Lh w w s particle trajectory Volme of sspension from one working period: slrry feed V s h L s w w s bowl wall
Basic working condition for semi-batch centrifges residence time of sspension mst be eqal to sedimentation time of particle in centrifge t z V V s t liqid discharge Flow rate of sspension: V s V t t L liqid srface feed flow Time of centrifgation: t o V V s s h s w w s t particle trajectory slrry feed Average volmetric capacity: V stř t o V s t m bowl wall
Continos centrifges fine sspensions with flid sediment adis od interface between flid sediment and liqid: pressre balance of interface 3 r p r p o a o a o r 3
Design of centrifges Sedimentation centrifges Test tbe (cell) centrifges boxes for glass cells with volme p to litre laboratory se for determination of clarification velocity or content of sspended particles
Tblar-bowl centrifges small diameter of slender bowl high speed high vales of Frode nmber sfficient residence time small capacities pharmacetical indstry plášť, bben, 3 radiální lopatky, 4 přívod sspenze, 5 otvory, 6 výstp
Bowl centrifges common indstrial se bben, radiální přepážky, 3 přívod sspenze, 4 odsávací trbka, 5 zavírací kžel
Mlti-chamber centrifges concentric vertical compartments accelerated sedimentation increase of residence time from p to 6 chambers classification effect application for removal of fine particles
Disc-bowl centrifges Bowl with cone discs and slrry space Trajectory of sedimentation particle in slrry space a conical disc, b slrry feed inlet
Modern types of disc-bowl centrifges atomatic or continos discharge of sediment (slrry) With atomatic gate discharge With nozzle discharge of slrry pístové šopátko, prostor pro zavírací kapalin, 3 přepadový otvor, 4 přívodní kohot, 5 přívodní kanálek, 6 prostor pro kapalin, 7 otvory pro výstp kal, 8 otvor pro výstp ovládací kapaliny continos discharge angle of cone has to be smaller than angle of friction
Bowl of centrifge for emlsion separation discs, bowl shell discs with holes for inlet of emlsion (sspension) position of holes by densities and contents of both components great density and little heavy component holes toward periphery
Continos horizontal bowl centrifges with screw discharge
EXAMPLE: Semi-batch centrifge Determine volmetric capacity of semi-batch bowl centrifge for separation of sodim crystals greater than 50 m (density 460 kg m -3 ) from liqid detergent (with density 800 kg m -3 and viscosity 0. Pa s). otational speed of bowl is 500 rpm and inside diameter is 300 mm and height is 500 mm. Clear liqid is discharge from overflow with radis 80 mm. Maximal height of particle layer sediment on bowl wall is 35 mm and layer has porosity 0.8. Volmetric concentration of sodim particles greater then 50 m in feed slrry is %. Handling time is approximately 0 min. liqid discharge liqid srface feed flow particle trajectory slrry feed bowl wall
Filtration centrifges Colmn centrifge with pper discharge Working cycle of filtration filling filtration drying cake discharge batch with manal discharge laborios for small capacities frame is hanged on three colmns odstředivka s pohonem, stojan, 3 přívod sspenze
Centrifges with knife discharge horizontal or vertical atomatic cake discharge by hydralic driven knife to inclined partition connected
Top sspended centrifge with lower discharge AO 500 ZVU Hradec Králové stojan, bben 3 závěr bbn 4 závěs ložení hřídele bbn 5 vyhrnovač 6 dělič sirobů 7 čidlo napoštění 8 napoštěcí mechanisms 9 rozdělovací žlab na sspenzi 0 poháněcí stejnosměrný elektromotor ovládací panel Pracovní frekvence otáčení je 00 min nebo 500 min, plnící frekvence otáčení 00 300 min, vyhrnovací frekvence otáčení 30 80 min, počet pracovních cyklů se pohybje od 6 do 4 za hodin. Maximální výkonnost typ AO 500 s vnitřním průměrem bbn 370 mm (s maximální náplní bbn 500 kg) je až 790 t ckroviny za den, štítkový výkon poháněcího elekromotor činí 60 kw. Provoz odstředivky je atomaticky programově řízen, při zkošení cykl je možné rční řízení. easy discharge centrifges for sgar
Continos filtration centrifges eciprocating conveyor centrifge cake is removed by reciprocating psher rotating with basket Helical conveyor filtration centrifge bben odstředivky, šrobové nože, 3 vynášecí bben