Solid-Liquid Separation

1. Solid-Liquid Separation • Basant Ahmed • Richard Rodriguez • Jennifer Gilmer • David Quiroz • Steven Hering China high speed decanter centrifuge. 2010. Photograph. GN Solid ControlsWeb. 24 Nov 2013. <http://oilfield.gnsolidscontrol.com/china-high-speed-decanter-centrifuge/>.

2. Introduction • Solid-liquid separation is a necessary step in obtaining the desired product from a precipitation or crystallization reaction • Centrifugation is the way to achieve the required solid-liquid separation • There are two types of centrifugation • Sedimenting • Filtering • Most popular in chemical and pharmaceutical applications and the main focus of this selection process Crystallization. 2013. Photograph. WikipediaWeb. 24 Nov 2013. <http://upload.wikimedia.org/wikipedia/commons/d/d3/Snow_crystallization_in_Akureyri_2005-02-26_19-03-37.jpeg>. http://www.visualphotos.com/photo/1x6037988/precipitation_reaction_giving_iron_ii_hydroxide_a500337.jpg

3. Steps to Centrifuge Selection • The best process for choosing the proper centrifuge is the following detailed three step process • 1. Process and Application • Determine sedimenting or filtering • Based on reaction type and process specifications • i.e. crystallization vs. precipitation Temperature, pH, flow rate, batch size • 2.Product Properties • Determine required centrifuge properties based on the product properties • Filterability for filtering centrifuges based product properties • i.e. particle size, shape , rigidity • 3. Centrifuge Design • Chose specific centrifuge based on prior selection criteria that is process and product requirements • Choose vertical, horizontal, or inverted for filter • Decanter is on option for sedimenting centrifuge selection Patnaik, Tom. Solid-liquid Separation: A guide to Centrifuge Selection. 2012. Graphic. www.aiche.org/cepPrint.

4. Selection by Process & Application • First step is to choose filtering 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 large particles due ease of filtration of large particles • Dry solid products require filtering due to extending spinning helping dry the product which is not possible in continuous sedimentation • Preferable when the solid(the cake) is the required product and it allows for a long wash liquid residence time 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 solid • Preferable for when solid particle size and concentration are small and the volume of the liquid is low because the filter needed increases with liquid volume • Usually 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. www.aiche.org/cepPrint. Clarke, Peter. Theory of sedimentation and centrifugation. 2009. Infographic. n.p. Web. 24 Nov 2013. <http://www.bbka.org.uk/local/iceni/bm~doc/pollensuspension-2.pdf>.

5. Selection by Product Properties • An 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 influences filterability • Spherical particles are the ideal for filtration and are easiest to filter followed by rounded • Fibrous particles are the most difficult to filter due to formation of dense cakes • The shape factor determined to compare actual shape to ideal sphere • Normalized from 0 to 1 • Particle size is the factor affecting cake porosity, residual cake moisture and throughput rates • Bigger particles form cakes with large capillaries and thus have a higher porosity and higher thought rate • System pressure also effects filterability. At high pressure cake compact causing filterability to decrease • Slurry filterability is expressed in flux fate gpm/ft^2 • Function of particle size, shape and structure • To filter slurry flux rate can be between 1gpm/ft^2 to 6gpm/ft^2 to filter well Patnaik, Tom. Solid-liquid Separation: A guide to Centrifuge Selection. 2012. Graphic. www.aiche.org/cepPrint.

6. Selection By Centrifuge Design • Selection of the specific centrifuge base on the preceding factors • Filtering centrifuge specifics • Use a perforate bowl lined with a filter cloth to retain the desired solid cake and the liquid passes through and is discarded • Usually operated as batch • Three types of Filter centrifuges • Vertical Basket • Horizontal Peeler • Inverting Filter • Decanters • A type of sedimenting centrifuge which is used in bio-pharmaceutical process that need high g forces • Separate solid and liquid by the basic process of sedimentation filtration lined out in previous and proceeding slides Patnaik, Tom. Solid-liquid Separation: A guide to Centrifuge Selection. 2012. Graphic. www.aiche.org/cepPrint.

7. Types of Filtrating Centrifuges • Vertical Basket • Used for slow/medium filtering slurries. Even distribution of cake across vertical face is ideal and is the result in slow and medium filtering • Prone to high process vibration • Three types • Vertical basket manual discharge – cake discharge is manual • Vertical basket peeler – automatic plow used to discharge cake to avoid safety risks for toxic cakes • Vertical basket cGPM – designed for sanitary operation and have a clean in place system • Horizontal Peeler • Have a high volume capacity • Process components can be separated from mechanical components • Limitation could be formation of heel • Inverting Filter • Useable on a vide range of filtering systems from easy to poor • Do not form a heel which is suitable for a thin-cake operation Patnaik, Tom. Solid-liquid Separation: A guide to Centrifuge Selection. 2012. Graphic. www.aiche.org/cepPrint.

8. Centrifuge Examples Vertical Centrifuge Horizontal Centrifuge http://www.rousselet-robatel.com/images/products/rental-SLAB-540lg.jpg http://img.directindustry.com/images_di/photo-g/horizontal-peeler-centrifuges-71914-2503229.jpg http://img.directindustry.com/images_di/photo-g/inverting-filter-centrifuges-21373-2367189.jpg http://www.flottweg.de/cms/upload/bildergalerie/Komponenten/Decanter/unter_Druck_engl.jpg Inverting Filter Centrifuge

9. Centrifuge Theory • The separation of solids from liquids via settling and filtration rely on many factors: • Flow rates • Particle size • Particle geometry http://techalive.mtu.edu/meec/module06/images/soil_000.JPG http://homepage.usask.ca/~mjr347/prog/geoe118/images/shape1.gif

10. Centrifuge Theory • The driving forces for settling and filtration is gravity and pressure 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 resistance • Increase driving force • Centrifuges perform #2 http://i01.i.aliimg.com/img/pb/387/707/567/567707387_658.jpg http://www.thenakedscientists.com/HTML/uploads/RTEmagicC_Centrifuge-wheel-cff.png.png

11. Centrifuge Theory • Centrifuges 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 in directio

12. Centrifuge Theory • Centrifugal force varies from gravitational forces in terms of magnitude only • RCF : relative centrifugal force (g-force) • ω: angular velocity • g: gravitational force http://upload.wikimedia.org/wikipedia/commons/9/97/Centripetal_force.PNG http://content.answcdn.com/main/content/img/oxford/Oxford_Sports/0199210896.centrifugal-force.1.jpg

13. Centrifugal Settling • When the density of particles suspended in a solution is greater than the density of the liquid 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 forces • Buoyancy • Centrifugal force • Particle drag

14. Centrifugal Settling • All of these forces are important when determining the velocity at which the particle will settle: • μ: viscosity of liquid • Dp: particle diameter • V: settling velocity • ρp: particle density • ρ: liquid density • ac: centrifugal acceleration function [ v ] = settlingv( ac,Dp,pp,p,u ) % function settlingv calculates settling velocity of particle in centrifuge % % input: % ac = centrifugal 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; end

15. Centrifugal Settling >> ac = 250; >> pp = 1250; >> p = 1000; >> u = 0.001002; >> Dp = linspace(0.00001,0.00010); >> 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('settling velocity (m/s)'); >> title('v vs. ac');

16. Centrifugal Settling • For 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 • μ: viscosity of liquid • Dp: particle diameter • ρp: particle density • ρ: liquid density • ac: centrifugal acceleration • V: volume of liquid held in the bowl • s: thickness of a thin liquid layer function [ Qc ] = VflowBowl( ac,u,Dp,pp,p,V,s ) % function VflowBowl calculates the volumetric flow through bowl in centrifuge % % input: % ac = centrifugal acceleration (m/s2) % u = liquid viscosity (Pa s) % Dp = particle diameter (m) % pp = particle density (kg/m3) % p = liquid density (kg/m3) % V = volume of liquid in bowl (m3), default = 0.001 % s = thickness of thin layer liquid (m), default = 0.001 % % output: % Qc = Volumetric flow through bowl (m3/s) if nargin<7||isempty(s), s = 0.001; end if nargin<6||isempty(V), V = 0.001; end Qc = Dp.^2*(pp-p)*V/9/u/s*ac; end

17. Centrifugal Setting >> u = 0.001002; >> Dp = 0.00004; >> pp = 1250; >> p = 1000; >> ac = linspace(100,500); >> Qc = VflowBowl(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/s)'); >> title('Qc vs. Dp');

18. Centrifugal Filtration • Filtration 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 side of the cloth but centrifugal force can be used as an alternative to creating a pressure difference across the cloth. http://img.medicalexpo.com/images_me/photo-g/laboratory-filtration-centrifuges-84315-6088741.jpg http://www.rousselet-robatel.com/images/products/HP-centrif-filtrationlg.jpg

19. Centrifugal Filtration • Volumetric Flow rate through the filter • Q: volumetric flow rate through filter • ρ: density of filtrate • ω: angular velocity • r1: distance from the center to the cake surface • r2: distance from the center to the centrifuge wall • μ: viscosity of the solution • mc: mass of cake deposited on filter • α: specific cake resistance • A: area of cake • Rm: resistance of the filter medium to filtrate flow http://csmres.co.uk/cs.public.upd/article-images/Fig-9---belt_cake_discharge.JPG http://www.bokela.de/typo3temp/pics/27735eca79.jpg

20. Centrifugal Filtration 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 % r1 = distance from center to cake surface (m), default = 0.05 % r2 = distance from center to centrifuge wall (m), default = 0.1 % u = solution viscosity (Pa s), default = 0.001 % mc = mass of cake deposited on filter (kg), default = 0.01 % a = specific cake resistance (m/kg), default = 100 % A = area of cake (m2), default = 0.00001 % Rm = resistance of filter medium to filtrate flow (1/m), default = 0.000001 % % output: % Q = Volumetric flow through filter (m3/s) if nargin<9||isempty(Rm), Rm = 0.000001; end if nargin<8||isempty(A), A = 0.00001; end if nargin<7||isempty(a), a = 100; end if nargin<6||isempty(mc), mc = 0.01; end if nargin<5||isempty(u), u = 0.001; end if nargin<4||isempty(r2), r2 = 0.1; end if nargin<3||isempty(r1), r1 = 0.05; end if nargin<2||isempty(p), p = 900; end Q = w.^2*p*(r2^2-r1^2)/2/u/(mc*a/(A^2)+Rm/A); end • >> w = linspace(100,500); • >> Q = VflowFilter(w); • >> plot(w,Q); • >> xlabel('angular velocity (m/s)'); • >> ylabel('volumetric flow (m3/s)'); • >> title('Q vs. w');

21. Conclusion • Solid Liquid Separation by centrifugation • Two types: Sedimenting and Filtering • Centrifuge Selection • Three Steps: Process and Application, Product Properties, and Centrifuge Design • Centrifuge Designs • Thee Types: Vertical Basket, Horizontal Peeler, and Inverting Filter http://cmbe.engr.uga.edu/engr4520/Other/Ch%205%20Disc%20Centrifuge%20schematic.jpg http://www.sswm.info/sites/default/files/toolbox/EPA%202000%20Centrifuge%20Thickening%20and%20Dewatering.jpg

22. Conclusion • Centrifuge Theory • Rate of Separation = Driving Forces/Resitance • Centrifuges simply increase the rate by increasing the driving forces • MATlab Programs • Calculate the settling velocity (m/s), and Volumetric flow through bowl (m3/s) in settling • Calculate the Volumetric flow through filter (m3/s) in filtering http://bgsctechclub.files.wordpress.com/2011/08/centrifugal-force-diagram.jpg?w=682

23. Future Work and Research • Further research on the shape and structure for maximizing recovery • Increased Efficiency of Centrifuges • Particularly vital in the area of nuclear energy. • “America's only domestic supplier of nuclear fuel, the United States Enrichment Corporation (USEC), has created an advanced centrifuge that officials say is the world's fastest and largest, able to produce enriched uranium using just 5 percent of the electricity required by the company's previous design” • http://www.popularmechanics.com/science/energy/nuclear/4257042 http://www.world-nuclear.org/uploadedImages/org/info/Nuclear_Fuel_Cycle/Enrichment_and_Conversion/centrfge.jpg