Solid-Liquid Separation：固液分离

1、Solid-Liquid SeparationBasant AhmedRichard RodriguezJennifer GilmerDavid QuirozSteven HeringChina high speed decanter centrifuge. 2010. Photograph. GN Solid ControlsWeb. 24 Nov 2013. .1IntroductionSolid-liquid separation is a necessary step in obtaining the desired product from a precipitation or cr

2、ystallization reaction Centrifugation is the way to achieve the required solid-liquid separationThere are two types of centrifugationSedimentingFilteringMost popular in chemical and pharmaceutical applications and the main focus of this selection processCrystallization. 2013. Photograph. WikipediaWe

3、b. 24 Nov 2013. .2Steps to Centrifuge SelectionThe best process for choosing the proper centrifuge is the following detailed three step process1. Process and Application Determine sedimenting or filteringBased on reaction type and process specificationsi.e. crystallization vs. precipitation Temperat

4、ure, pH, flow rate, batch size2.Product PropertiesDetermine required centrifuge properties based on the product propertiesFilterability for filtering centrifuges based product properties i.e. particle size, shape , rigidity3. Centrifuge DesignChose specific centrifuge based on prior selection criter

5、ia that is process and product requirementsChoose vertical, horizontal, or inverted for filterDecanter is on option for sedimenting centrifuge selectionPatnaik, Tom.Solid-liquid Separation: A guide to Centrifuge Selection. 2012. Graphic. .3Selection by Process & ApplicationFirst step is to choose fi

6、ltering or sedimenting centrifugation This will be chosen based particle size, washing required, concentration of solid in slurry, and throughput Filtering a batch-operated machine that uses a filter media to capture and collect a filter cake inside a rotating basket. Suitable for slurries with larg

7、e particles due ease of filtration of large particlesDry solid products require filtering due to extending spinning helping dry the product which is not possible in continuous sedimentationPreferable when the solid(the cake) is the required product and it allows for a long wash liquid residence time

8、 inside the solid cake Sedeminting a machine that is continuous and uses high rotational velocities to create high magnitude g-forces inside a solid bowl to separate the liquid from the solidPreferable for when solid particle size and concentration are small and the volume of the liquid is low becau

9、se the filter needed increases with liquid volumeUsually preferred when the liquid the valuable and desired product of the specific reaction and products being purified Patnaik, Tom.Solid-liquid Separation: A guide to Centrifuge Selection. 2012. Graphic. .Clarke, Peter.Theory of sedimentation and ce

10、ntrifugation. 2009. Infographic. n.p. Web. 24 Nov 2013. .4Selection by Product PropertiesAn analysis of the particle size, shape and distribution is the main determinant of filterability which is an important factor when dealing with filtering centrifuges. Particle shape is the main factor that infl

11、uences filterabilitySpherical particles are the ideal for filtration and are easiest to filter followed by roundedFibrous particles are the most difficult to filter due to formation of dense cakesThe shape factor determined to compare actual shape to ideal sphereNormalized from 0 to 1Particle size i

12、s the factor affecting cake porosity, residual cake moisture and throughput ratesBigger particles form cakes with large capillaries and thus have a higher porosity and higher thought rateSystem pressure also effects filterability. At high pressure cake compact causing filterability to decreaseSlurry

13、 filterability is expressed in flux fate gpm/ft2 Function of particle size, shape and structureTo filter slurry flux rate can be between 1gpm/ft2 to 6gpm/ft2 to filter wellPatnaik, Tom.Solid-liquid Separation: A guide to Centrifuge Selection. 2012. Graphic. .5Selection By Centrifuge DesignSelection

14、of the specific centrifuge base on the preceding factorsFiltering centrifuge specificsUse a perforate bowl lined with a filter cloth to retain the desired solid cake and the liquid passes through and is discardedUsually operated as batchThree types of Filter centrifugesVertical BasketHorizontal Peel

15、erInverting Filter DecantersA type of sedimenting centrifuge which is used in bio-pharmaceutical process that need high g forcesSeparate solid and liquid by the basic process of sedimentation filtration lined out in previous and proceeding slidesPatnaik, Tom.Solid-liquid Separation: A guide to Centr

16、ifuge Selection. 2012. Graphic. .6Types of Filtrating CentrifugesVertical Basket Used for slow/medium filtering slurries. Even distribution of cake across vertical face is ideal and is the result in slow and medium filteringProne to high process vibrationThree typesVertical basket manual discharge c

17、ake discharge is manualVertical basket peeler automatic plow used to discharge cake to avoid safety risks for toxic cakesVertical basket cGPM designed for sanitary operation and have a clean in place system Horizontal PeelerHave a high volume capacityProcess components can be separated from mechanic

18、al componentsLimitation could be formation of heelInverting FilterUseable on a vide range of filtering systems from easy to poorDo not form a heel which is suitable for a thin-cake operationPatnaik, Tom.Solid-liquid Separation: A guide to Centrifuge Selection. 2012. Graphic. .7Centrifuge Examples8Ve

19、rtical Centrifuge Horizontal Centrifuge Inverting Filter Centrifuge Centrifuge TheoryThe separation of solids from liquids via settling and filtration rely on many factors:Flow ratesParticle sizeParticle geometry9Centrifuge TheoryThe driving forces for settling and filtration is gravity and pressure

20、 gradients. These forces are usually not enough on there own to create rapid separation.Rate = Driving Force / Resistance This relationship shows that in order to increase the rate of separation via settling and filtration is to either:Decrease resistanceIncrease driving forceCentrifuges perform #21

21、0Centrifuge TheoryCentrifuges are able to speed up separation by dramatically increasing the force of gravity by several thousand times. Centrifuges do this by spinning at very high angular velocities creating very strong centripetal and centrifugal forces which are the same in magnitude by differ i

22、n directio11Centrifuge TheoryCentrifugal force varies from gravitational forces in terms of magnitude onlyRCF : relative centrifugal force (g-force): angular velocityg: gravitational force12Centrifugal SettlingWhen the density of particles suspended in a solution is greater than the density of the l

23、iquid then settling will occur.This does not always happen in a practical length of time, making centrifuges necessary.Several forces are important when settling occurs:Gravitational forcesBuoyancyCentrifugal forceParticle drag13Centrifugal SettlingAll of these forces are important when determining

24、the velocity at which the particle will settle: viscosity of liquidDp: particle diameterV: settling velocityp: particle density: liquid densityac: centrifugal accelerationfunction v = settlingv( ac,Dp,pp,p,u )% function settlingv calculates settling velocity of particle in centrifuge% input:% ac = c

25、entrifugal acceleration (m/s2) % Dp = particle diameter (m)% pp = particle density (kg/m3) % p = liquid density (kg/m3)% u = liquid viscosity (Pa s)% output:% v = settling velocity (m/s) v = Dp.2*(pp-p)/18/u*ac; end14Centrifugal Settling ac = 250; pp = 1250; p = 1000; u = 0.001002; Dp = linspace(0.0

26、0001,0.00010); v = settlingv(ac,Dp,pp,p,u); plot(Dp,v); xlabel(particle diameter (m); ylabel(settling velocity (m/s); title(v vs. Dp); Dp = 0.00004; pp = 1250; p = 1000; u = 0.001002; ac = linspace(100,500); v = settlingv(ac,Dp,pp,p,u); plot(ac,v); xlabel(centrifugal acceleration (m/s2); ylabel(sett

27、ling velocity (m/s); title(v vs. ac);15Centrifugal SettlingFor a continuous centrifuge, the flow rate that the solution is moving through the bowl will determine whether a particle will be filtered or if it will flow out.Qc: volumetric flow rate through bowl: viscosity of liquidDp: particle diameter

28、p: particle density: liquid densityac: centrifugal accelerationV: volume of liquid held in the bowls: thickness of a thin liquid layerfunction Qc = VflowBowl( ac,u,Dp,pp,p,V,s )% function VflowBowl calculates the volumetric flow through bowl in centrifuge% input: % ac = centrifugal acceleration (m/s

29、2) % u = liquid viscosity (Pa s)% Dp = particle diameter (m)% pp = particle density (kg/m3) % p = liquid density (kg/m3)% output:% Qc = Volumetric flow through bowl (m3/s) if nargin7|isempty(s), s = 0.001; endif nargin u = 0.001002; Dp = 0.00004; pp = 1250; p = 1000; ac = linspace(100,500); Qc = Vfl

30、owBowl(ac,u,Dp,pp,p); plot(ac,Qc); xlabel(centrifugal acceleration (m/s2); ylabel(volumetric flow (m3/s); title(Qc vs. ac); u = 0.001002; pp = 1250; p = 1000; ac = 250; Dp = linspace(0.00001,0.00010); Qc = VflowBowl(ac,u,Dp,pp,p); plot(Dp,Qc); xlabel(particle diameter (m); ylabel(volumetric flow (m3

31、/s); title(Qc vs. Dp);17Centrifugal FiltrationFiltration is achieved by creating a pressure difference across a filter cloth.The pressure difference forces the liquid through the cloth while leaving behind a cake (the solid) behind.This force is usually done using gravity or a vacuum on the other si

32、de of the cloth but centrifugal force can be used as an alternative to creating a pressure difference across the cloth.18Centrifugal FiltrationVolumetric Flow rate through the filterQ: volumetric flow rate through filter: density of filtrate: angular velocityr1: distance from the center to the cake

33、surfacer2: distance from the center to the centrifuge wall: viscosity of the solutionmc: mass of cake deposited on filter: specific cake resistanceA: area of cakeRm: resistance of the filter medium to filtrate flow19Centrifugal Filtration w = linspace(100,500); Q = VflowFilter(w); plot(w,Q); xlabel(

34、angular velocity (m/s); ylabel(volumetric flow (m3/s); title(Q vs. w);function Q = VflowFilter( w,p,r1,r2,u,mc,a,A,Rm )% function VflowBowl calculates the volumetric flow through bowl in% centrifuge% input: % w = angular velocity (m/s) % p = filtrate density (kg/m3), default = 900% a = specific cake

35、 resistance (m/kg), default = 100% Rm = resistance of filter medium to filtrate flow (1/m), default = 0.000001 % output:% Q = Volumetric flow through filter (m3/s) if nargin9|isempty(Rm), Rm = 0.000001; endif nargin8|isempty(A), A = 0.00001; endif nargin7|isempty(a), a = 100; endif nargin6|isempty(mc), mc = 0.01; endif nargin5|isempty(u), u = 0.001; endif nargin4|isempty(r2), r2 = 0.1; endif nargin3|