A framework methodology for the simulation and sizing of diaphragm filter presses

Transcription

1 Loughborough University Institutionl Repository A frmework methodology for the simultion nd sizing of diphrgm filter presses This item ws submitted to Loughborough University's Institutionl Repository by the/n uthor. Cittion: WAKEMAN, R.J. nd TARLETON, E.S., A frmework methodology for the simultion nd sizing of diphrgm filter presses. Minerls Engineering, 7 (11), pp Additionl Informtion: This rtile ws published in the journl, Minerls Engineering [ Elsevier] nd the definitive version is vilble t: Metdt Reord: Version: Aepted for publition Publisher: Elsevier Plese ite the published version.

2 This item ws submitted to Loughborough s Institutionl Repository ( by the uthor nd is mde vilble under the following Cretive Commons Liene onditions. For the full text of this liene, plese go to:

3 1 A FRAMEWORK METHODOLOGY FOR THE SIMULATION AND SIZING OF DIAPHRAGM FILTER PRESSES R.J. Wkemn nd E.S. Trleton (e.s.trleton@lboro..uk) Seprtion Proesses Centre, University of Exeter, Devon, UK. Dept. of Chemil Engineering, Loughborough University, Loughborough, Leis., UK. ABSTRACT A frmework for simulting filter yles is presented, bsed on blend of tested theoretil models nd epted design proedures. Output from the simultor predits orretly the generl effets of proess vribles. Some smple results re used to illustrte these when it is pplied in generl sense to diphrgm (vrible volume) filter press. INTRODUCTION Of the mny unit opertions vilble to the proess engineer, those ssoited with solid/liquid seprtion re perhps the most diffiult to speify. For these systems it would be rre prtie to use fundmentl theoretil reltionships for either the seletion, design or optimiztion of equipment with the result tht the speifition of hemil plnt is rrely performed without reourse to extensive lbortory nd pilot sle tests. Whilst the tsk of eleting solid/liquid seprtor for given duty hs been onsiderbly simplified by the reent introdution of the omputer softwre p C -SELECT 1,2, softwre for filter design is generlly not vilble. When prtiulr type of seprtor hs been identified, the seprtions tehnologist is still fed with the prospet of undertking n extensive test progrmme to enble sle-up nd optimistion of seprtor size nd onfigurtion. These problems re ompounded by the derth of literture relting to suh mtters nd the pprent lk of stndrd proedures. Solid/liquid seprtion tehnology, whether it be in the res of seletion, design or optimistion, is best delt with by intertive omputer softwre. To be most effetive the softwre must inorporte well hosen mix of lgorithms, expert system nd input informtion from the user, be bsed on sound ides nd proven dt from experimentl nd theoretil reserh projets, nd mintin the bility to give dvie nd edution in ongenil fshion so tht ny psyhologil brriers to omputer use re voided. This pper desribes some preliminry results from softwre pkge designed to simulte the opertion of pressure filters, using dt bsed on the work reported previously 3-7, with the im of demonstrting the generl usefulness of the pprohes tken in tht work. The softwre lso lys the foundtion for design proedures whih my inorporte more omplex models for ke formtion 8-10, whih re bsed on more rigorous models of suspension flows nd prtile deposition. The softwre utilises industrilly proven methodologies whih re ombined with omputer ode to produe modulr routines pble of modelling ke formtion, ompression dewtering nd wshing. The tehniques used to desribe the opertion of the diphrgm filter press re shown nd informtion regrding typil filter yle is presented. FILTER CYCLE DESCRIPTION

4 2 The verstility of the diphrgm filter press llows the rnge of operting onfigurtions shown in Figure 1. Slurry is fed into the hmbers of the press through suitble porting with either entrifugl, diphrgm, single srew or reiproting pump 11 suh tht filtrtion n our t onstnt rte/vrible pressure or vrible rte/vrible pressure, depending on the type of pump used. Cke is formed simultneously on the two opposing sides of the filter hmber, with the ke surfes growing towrds eh other. If the hmbers re not ompletely filled by ke during this primry filtrtion stge then seondry filtrtion stge my follow where the suspension remining between the kes is filtered t onstnt pressure by movement of the flexible diphrgm loted on one filtering surfe. During this stge (ii) proess, filtrte is olleted from only one dringe surfe whilst further ke lso forms on the sme surfe. When suffiient movement of the diphrgm hs ourred nd suspension hs been filtered for the surfes of the two kes to meet s result of the primry nd/or seondry filtrtion stges, further ke onsolidtion by the diphrgm (t onstnt pressure), ke dewtering by ir blowing, nd/or ke wshing n be undertken to omplete the filter yle prior to ke dishrge. In ny single filter yle, seletion of the stges shown on Figure 1 my be utilised; some stges my be repeted within yle, nd the order of utilistion n differ between pplitions. Any simultion methodology must be flexible enough to llow ny ombintion of stges (i) to (v). Stges (i) nd (ii): Cke Formtion It is most ommon to desribe filtrtion proesses by the generl filtrtion eqution for the reiprol volume flow rte of filtrte: dtf dv f = αvμ μrm V 2 f A Δp + AΔp (1) where α v is the speifi resistne of the ke verged over pressure to the pplied pressure differene Δp, μ is the filtrte visosity, A is the filter re, R m is the resistne of the filter medium, nd the effetive onentrtion of solids in the feed,, is given by ρms = 1 mm s (2) ρ is the density of the filtrte, M s is the mss frtion of solids in the feed suspension, nd m is the rtio of the mss of the wet ke to the mss of the dry ke. In the most generl sense, both the pressure nd rte n vry nd it is neessry to impose the pump hrteristis on the governing equtions. Hene eqution (1) n be rrnged to: V f 2 1 A Δp = AR αv μq m (3) where α v is funtion of the pressure pplied to the solid/liquid mixture by the pump. To ount for the potentil ompressibility of the ke, it is ommon prtie to relte the speifi resistne (α) nd porosity (ε) or voids rtio (e) of the filter ke (evluted t prtiulr pressure) to the solids ompressive pressure through so-lled onstitutive equtions 12,13 similr to: n 0 s 0 ( ) n α = α p or α = α 1+ p (4) s

5 3 ( ) ε = ε p or ε = ε + p (5) 1 0 s 0 s ( ) e = e0 blog 1+ ps (6) Although reent work 5-7 hs found eqution (6) to be better representtion of vilble dt thn one of the forms of eqution (5), the ltter will be used here for illustrtive purposes. Combining the integrted form of eqution (4) (to give n verge ke resistne) with eqution (3) nd performing mss blne on the solids in the ke yields the two equtions governing ke formtion during the primry filtrtion phse (Stge (i)). The filtrte volume produed is V f 2 1 A Δp = n ARm α0 ( 1 n) Δp μq (7) nd the totl thikness of ke in the hmber is ρs VM f s ( m 1) + 1 ρ h = 2 ρs A ( 1 mms ) ρ (8) When unfiltered suspension remins in the filter hmber(s) seondry filtrtion phse my follow the initil primry filtrtion. If the seondry phse ours, then further filtrtion tkes ple t onstnt pressure (with the pressure pplied by the diphrgm rther thn the pump), with filtrte drining through one filtrtion surfe in eh hmber. Modifying eqution (1), to ount for the effetive inrese in resistne to filtrtion due to the presene of filter ke on the filter medium t the strt of the filtrtion, gives the governing eqution: tf ttr αvμ μ αvv p p = 2 ( Vf + Vtr ) + + Rm Vf Vtr ( A 2) Δp ( A 2) Δp ( A 2) (9) Thus, if the pump hrteristis relting Δp nd Q, nd the onstitutive equtions relting α nd ε (nd hene m) to Δp, re known from lbortory sle tests, ke formtion rtes n be lulted. Stge (iii): Cke Consolidtion Cke onsolidtion is performed t onstnt pressure through use of filter diphrgm nd is nlysed vi n empiril reltionship relting the onsolidtion rtio U ho h = h o h (10) to dimensionless onsolidtion time defined by 2 nct 1 T = (11) ω 2 0

6 4 suh tht U = 4T ν ( 1+ ( 4T ) ) 12 π π ν (12) where C is the onsolidtion oeffiient nd ν the onsolidtion behviour index. Vlues for ν nd the other sle-up onstnts in the onstitutive equtions for the onsolidtion phse n be obtined through lbortory tests with, for instne, lef filter or piston press (s previously desribed 3-7 nd relted through equtions (10)-(12) to give expressions for ke height nd filtrte volume during the onsolidtion period(s). Consolidtion is ssumed to end when the flow rte of liquid from the filter flls below predetermined, usully uneonomi, level. (iv) Cke Dewtering: (by Air Blowing) The dewtering phse is nlysed through ombintion of empiril nd theoretil reltions. These filitte the lultion of the time required to hieve given filter ke moisture ontent nd the ir flow rte through the ke during the dewtering period, nd hve been desribed in detil Two prmeters of prime importne in dewtering re the pressure required to initite dewtering (p b ) nd the irreduible sturtion of the filter ke (S ). Although these should be mesured experimentlly, the former n be determined with suffiient ury from p b ( ε ) v σ = (14) ε x v v Correltions exist (for reltively lrge, grnulr mterils) whih llow estimtion of S, for exmple N p ( + Δ ) 2 ( 1 ε ) hσ ε x ρgh p = 3 2 v v d v (15) ( N 0.49 ) S = (16) p Similr orreltions re not vilble for fine prtile kes, nd the bove should not be used if lterntive dt re vilble. With dt for p b nd S vilble, nd ssuming tht no dewtering of the ke ours through evportion of the mother liquor nd tht the displing fluid is sturted instntly s it enters the ke, dimensionless sturtion (S R, termed the redued sturtion) n be relted empirilly to dimensionless time (θ) by S R S S = 1 S (17)

7 5 1 1 θ = 1 b2 S R 1 b3 (18) where b 2 nd b 3 re onstnts determined by fitting eqution (18) to numeril solutions of the differentil equtions desribing simultneous gs nd liquid flow through the filter ke 14,15. The dewtering time (t d ) is then estimted from t d ( ) θε 2 v μh 1 S = (19) Δpk d v Allowing for losses in the feed pipes to the filter nd the effets of plnt elevtion, the ir flow rte required to hieve the desired moisture ontent n be lulted 15-17, nd the gs or ir blower sized ordingly. (v) Cke Wshing: (by Displement) The tehnique used in the nlysis of wshing phse(s) employs the dispersion model to interpret the rtes of solute mss trnsfer from the voids in the filter ke. Use of the model requires superfiil wsh veloity, whih is estimted from the modified Dry eqution u o Δpw = μ α ρ h ε R ( ( 1 ) + ) w v s v m (20) nd the produt of the Reynolds nd Shmidt numbers, lulted from ux o v Re.S = (21) ε D v The dispersion oeffiient vries with the filter ke thikness 20, nd is lulted from D L ( ) Re.S 0 h 0.1 m D = + (22) D L ( ) Re.S h 0.1 m D = + > (23) The dispersion number is then given by D n ( Re.S) h = (24) DL xv D If the degree of wshing is speified in terms of the required removl of solute, the number of wsh rtios used in the wshing n be lulted using design hrts derived from solutions of the differentil equtions desribing solute dispersion in filter kes With knowledge of the number of wsh rtios to be pplied the wshing time (t w ), effluent solute onentrtion () nd frtionl

8 6 solute reovery (F) n be estimted. Allownes re mde for ke sturtion t the strt of wshing, nd for the sle nd type of filter being used for the seprtion 17,18. AN EXAMPLE OF FILTER SIMULATION The bove methodologies enble flexible simultions to be developed. When suitbly pplied these n model most ombintions of ke formtion, onsolidtion, dewtering nd wshing to llow preliminry sizing nd sle-up of equipment to be performed. Although the exmple of diphrgm press hs been hosen, the proedures n be redily dpted to model the performne of other filtrtion devies suh s tube presses nd rotry vuum filters. The dt shown below illustrte how informtion ssoited with the entire filter yle n be produed for set of typil operting onditions through softwre simultion tehniques. Exmple Problem A diphrgm filter press hs been identified s suitble for produing nominl 5 te of dry prtiulte solids from n 8% w/w slurry. Following the formtion stge(s), the homogeneity of the ke is to be improved through onsolidtion with the diphrgm. The resultnt ompt is then to be dewtered by ir blowing until moisture ontent of 20% is hieved, nd subsequently wshed until the solute onentrtion in the ke is redued from 30 to 2.5 kg m -3. The feed is delivered to the filter press vi entrifugl pump (see Tble 1 for the hrteristi urve of the pump), nd the feed suspension hrteristis hve been determined experimentlly. Filter nd septum hrteristis: Filter hmber thikness 80 mm Filter medium resistne 3x10 11 m -1 Operting onditions: Seondry filtrtion pressure (if needed) 600 kp Consolidtion nd wshing pressure 600 kp Dewtering pressure 400 kp Brometri pressure 100 kp Solids onentrtion in feed 8% w/w Solute onentrtion in feed 30 kg m -3 Solute onentrtion in wsh 0.5 kg m -3 Cke properties: Mx. ke thikness on eh filter surfe 20 mm Constitutive equtions during filtrtion α = 6x10 9 Δp 0.6 e = 3 0.1logΔp Constitutive equtions during onsolidtion C = 1x10-8 Δp 0.1 e = logΔp 0.1 Consolidtion behviour index 3 Prtile nd fluid properties: Density of solids 2500 kg m -3 Men size of solids in feed 10 μm Density of filtrte nd wsh 988 kg m -3 Visosity of filtrte nd wsh P s Surfe tension of filtrte nd wsh 0.07 N m -1

9 7 Irreduible ke sturtion 0.26 Visosity of ir 1.8x10-5 P s Solute diffusivity 10 9 m 2 s -1 The problem is to determine if the seprtion n be hieved, the filter yle time, the filter re, nd other performne inditors. Solution vi Simultion When the omputer simultion pkge is used to model the bove problem welth of dt relted to both the individul phses nd the totl filter yle is produed. Figures 2 to 7 give exmples, where the simultions for the bove dt re given by the open irles (o) on eh plot. The dt suggest tht the required objetives of the seprtion n be redily hieved with the diphrgm press nd pump speified. The filter re nd totl yle time re estimted to be 380 m 2 nd 6311 s, with the filtrtion, onsolidtion, dewtering nd wshing phses projeted to end fter 2028 s (0.56 h), 4056 s (1.13 h), 4707 s (1.31 h) nd 6311 s (1.75 h) respetively. During the period of the primry filtrtion the kes in eh of the filter hmbers progressively grow to ombined thikness (noting tht ke formtion ours on two surfes in eh hmber) of 34 mm (Figure 4), whilst the pressure in the hmbers inreses from 49.7 to 94 kp (Figures 2 nd 3) s the kes form. At the end of the primry filtrtion period (t f = 1140 s) unfiltered suspension remins in the hmbers nd seondry filtrtion t onstnt pressure is required. Within this period the kes in eh hmber ontinue to form nd eventully join to hieve the mximum llowble thikness of 40 mm (i.e. 2x20 mm) (Figure 4) fter 2028 s. At the end of the ke formtion stges the hmber nd ke moisture ontents re identil nd equl to 52.1% with the totl solids, liquid nd solute msses in the filter estimted t 5092, 5534 nd 166 kg respetively. The filtrte flow rte dereses progressively s ke is formed (Figure 5), with very rpid deline orresponding to the seondry filtrtion used by the diphrgm. Following the ke formtion phses the onsolidtion, dewtering nd wshing stges re sequentilly initited. During the period of onsolidtion the ke moisture nd solute mss re redued to 27% nd 57 kg respetively, whilst the ke thikness is redued to 21 mm (Figure 4) nd is ssumed to remin t tht vlue for the subsequent dewtering nd wshing phses. The solute mss nd moisture ontent of the ke re further lowered to 38 kg nd the desired 20% (Figure 7) respetively t the end of the dewtering period, using n overll ir rte of 1.8x10-5 m 3 m -2 s -1. In the wshing period, bout two wsh rtios (bsed on the unsturted ke) re used to produe the required solute onentrtion of 2.5 kg m -3 ; the frtionl reovery for the wshing period lone is 88%. This finl wsh inreses the moisture ontent of the ke to over 27% (Figure 7), tht is, to its vlue t the end of the onsolidtion (stge (iii)) in the yle when the ke ws lst fully sturted. The filtrte nd wsh liquor rtes for the whole yle re shown on Figure 6. The wsh liquor rte shown on Figure 6 is greter thn the filtrte rte t the end of onsolidtion (stge (iii)) due to the different methods of pressure pplition nd trnsmission through the filter hmber. During onsolidtion, the 600 kp is pplied by the diphrgm nd the stress is trnsmitted minly through the solid phse in the ke; s onsolidtion proeeds, n inresing proportion of the pplied stress is trnsmitted in this wy. During wshing, the 600 kp is pplied in the liquid phse, nd the only stress trnsmitted to the solids is tht whih results from drg t the prtile surfes. Hene, during wshing the flow of liquid is higher thn it is t the end of onsolidtion (stge (iii)) but lower thn t the end of filtrtion (stges (i) nd (ii)). At the end of the filter yle it is estimted tht 5092 kg of solids, 1891 kg of liquid, nd 4.7 kg of solute remin in the filter press.

10 8 EFFECTS OF THICKER CAKE FORMATION It is well known in prtie tht greter produtivity is obtined from filters if thinner kes re formed, nd if the simultor funtions properly it should predit suh behviour. To do this the dt shown erlier is used, but the mximum ke thikness t the end of either stge (i) or (ii) on eh filter surfe is hnged to 30 mm nd 40 mm (obviously 40 mm thikness ompletely fills the hmber, hene no seondry filtrtion (stge (ii)) ours in this instne). The lulted dt re ompred with the 20 mm ke se on Figures 2 to 7. Some effets of the thikness of ke formed during stges (i) nd (ii) re summrised on Tble 2. Effets of llowing further ke growth in the filter re not obvious priori beuse of the intertions between so mny of the vribles. Ckes re formed t slower rtes s they beome thiker, dependent on the shpe of the pump hrteristi urve. The pressure differene ross thiker ke is greter. This ould potentilly use more omption of the ke if it is ompressible, but the time tken to ompt thiker ke is onsiderbly greter thn tht needed to ompt thinner one, nd hene the filtrte flux from thiker ke tends to be rther lower. An uneonomi flux is therefore rehed when the ke is in less onsolidted stte, leving the thiker ke with more open struture. Hene, even though the men speifi resistne will tend to inrese t higher pressures, whilst the voids rtio will derese, the net effet of these hnges will be to redue filtrte rtes (s indited on Figure 5) during ke formtion (stges (i) nd (ii)). (In this exmple, during onsolidtion (stge (iii)) the thikness of the 40 mm ke (per filter surfe) is redued by 22% to 31 mm nd tht of the 20 mm ke by 47% to 10.5 mm.) The more open struture of the finl ke is refleted in the higher wsh liquor rtes (Figure 6) nd higher finl ke moisture ontents (Figure 7) ssoited with the thiker ke. Inresing the ke thikness uses number of hnges in the yle whih impt on the eonomis of the seprtion. The min ftors to onsider re: i. the extension of the yle time, with the gretest extension ourring during stge (iv) (ke dewtering) in the yle simulted in this exmple ii. higher energy onsumption per unit mss of produt n be ssoited with longer yle times iii. redution in the overll solids (or filtrte) produtivity rte iv. n inrese in the wsh rtio (or the totl volume of wsh liquor used) in stge (v) (this is prtiulrly importnt if wsh liquor is to be regenerted thermlly for re-use, s would be the se when solvent wsh is used) v. redution in the filtrtion re required for the seprtion. Of these ftors, (i) to (iv) tend to inrese seprtor operting osts (or derese revenues in the se of (iii)), whilst (v) redues pitl (nd to lesser extent mintenne) osts. Hene, for ny prtiulr yle onfigurtion there my exist n optimum eonomi ke thikness whih should be formed during the filtrtion stges of the yle. In prtie, it my lso be possible to investigte different yle onfigurtions to minimise the osts. CONCLUSIONS

11 9 This pper outlines the brod methodology behind the simultion of filter yles, using the diphrgm filter press s n exmple. It indites how omputer simultions n signifintly improve the understnding of the opertions whih n our during the filter yle. Eh of the theories used to model the ke formtion, onsolidtion, dewtering nd wshing phses hs been proven in pilot sle nd industril tests, but re pble of onsiderble improvement from fundmentl point of view. It is pprent tht the modelling proedures dopted for the simultion of the diphrgm filter press n be redily dpted to inlude optimistion routines nd extended to enompss other types of seprtion equipment. When fully developed, suh omputer softwre should provide suite of progrms whih re suffiiently powerful to minimise the number of ostly nd time onsuming experiments whih need to be performed to ssess the suitbility of equipment for prtiulr duty. NOMENCLATURE A totl re of filter medium (m) index in eqn. (5) (-) b 2, b 3 oeffiients used in eqn. (18) (-) C modified onsolidtion oeffiient (m 2 s -1 ) instntneous solute onentrtion in wsh effluent (kg m -3 ) effetive feed suspension onentrtion (kg m -3 ) D moleulr diffusivity of solute (m 2 s -1 ) D L dispersion oeffiient (m 2 s -1 ) D n dispersion number (-) e voids rtio (-) F frtion of reoverble solute removed from filter ke (-) g elertion due to grvity (m s -2 ) h totl thikness of filter ke (m) k filter ke permebility (m 2 ) M s solids mss frtion in feed suspension (-) m rtio mss wet ke to mss dry ke (-) N p pillry number (-) N index in eqn. (4) (-) n 1 number of dringe surfes per filter hmber (-) p b brekthrough pressure (P) Q flow rte of liquid from filter (m 3 s -1 ) Re Reynolds number (-) R m filter medium resistne (m -1 ) S filter ke sturtion (-) S R redued sturtion (-) S irreduible sturtion (-) S Shmidt number (-) T dimensionless onsolidtion time (-) t time (s) U onsolidtion rtio (-) u o superfiil wsh veloity (m s -1 ) V umultive volume of liquid produed from filter (m 3 ) x v men prtile size in feed suspension (μm) Greek symbols

12 10 α lol speifi ke resistne (m kg -1 ) α v verge speifi ke resistne (m kg -1 ) α 0 speifi ke resistne t Δp = 1 kp (m kg -1 ) Δp pressure pplied to solid/liquid mixture (P or kp) Δp pressure drop over filter ke (P) ε lol filter ke porosity (-) ε v verge porosity of filter ke (-) ε 0 filter ke porosity t Δp = 1 kp (-) θ dimensionless time (-) μ liquid visosity (P s) ν onsolidtion behviour index (-) ρ liquid density (kg m -3 ) ρ s solids density (kg m -3 ) σ liquid surfe tension (N m -1 ) ω o volume of solids produed per unit re of dringe surfe (m 3 m -2 ) Subsripts d f o p tr w onsolidtion phse dewtering phse filtrtion phse strt of phse end of previous phse trnsition from primry to seondry filtrtion phse wshing phse t equilibrium REFERENCES 1. Trleton E.S. nd Wkemn R.J., Solid/Liquid Seprtion Equipment Simultion nd Design: p C - SELECT Personl Computer Softwre for the Anlysis of Filtrtion nd Sedimenttion Test Dt nd the Seletion of Solid/Liquid Seprtion Equipment, Seprtions Tehnology Assoites, (1991). 2. Wkemn R.J. nd Trleton E.S., Solid/liquid seprtion equipment simultion nd design n expert systems pproh, Filtrtion nd Seprtion, 28(4), (1991). 3. Wkemn R.J., Sbri M.N. nd Trleton E.S., Ftors ffeting the formtion nd properties of wet ompts, Powder Tehnology, 65(1-3), (1991). 4. Wkemn R.J., Sle-up proedures nd test methods in solid/liquid seprtion: 1. Test methods nd lultion proedures for pressure filtrtion, Pro. 13 th Annul Meeting of Interntionl Fine Prtile Reserh Institute, Hrrogte, 24 (My/June 1992). 5. Wkemn R.J. nd Sbri M.N., Sle-up proedures nd test methods in solid/liquid seprtion: Test methods nd effets of the prinipl vribles in pressure filtrtion, IFPRI Reserh Report ARR 25-01, Seprtion Proesses Centre Report No. 7/92, 24 (Nov. 1992).

13 11 6. Wkemn R.J. nd Sbri M.N., Sle-up proedures nd test methods in solid/liquid seprtion: 1. Filtrtion of binry prtile mixtures nd floulted suspensions, Pro. 14 th Annul Meeting of Interntionl Fine Prtile Reserh Institute, Psden, 18 (June/July 1993). 7. Wkemn R.J., Sle-up proedures nd test methods in solid/liquid seprtion: Filtrtion of binry prtile mixtures nd floulted suspensions, IFPRI Reserh Report ARR 25-02, Seprtion Proesses Centre Report No. 13/93, 24 (Nov. 1993). 8. Busll R. nd White L.R., The onsolidtion of onentrted suspensions, J. Chem. So. Frdy Trns. 1, 83, (1987). 9. Lndmn K.A., Sirkoff C. nd White L.R., Dewtering of floulted suspensions by pressure filtrtion, Phys Fluids A, 3(6), (1991). 10. Koenders M.A. nd Wkemn R.J., A mthemtil model for the initil stges of the ompt formtion proess, (to be submitted). 11. Young I.M., in Solid/Liquid Seprtion Equipment Sle-up, 2 nd Edn., D.B. Purhs nd R.J. Wkemn (Eds.), pp , Uplnds Press nd Filtrtion Speilists, London, (1986). 12. Tiller F.M. nd Leu W.F., Bsi dt fitting in filtrtion, J. Chinese Institute Engineers, 11, (1980). 13. Shirto M., Murse T., Iritni E., Tiller F.M. nd Alitore A.F., Filtrtion in the Chemil Proess Industry, in Filtrtion, M.J. Mtteson nd C. Orr (Eds.), Mrel Dekker, New York, (1987). 14. Wkemn R.J., Vuum dewtering nd residul sturtion of inompressible filter kes, Interntionl J. Minerl Proessing, 3, (1976). 15. Wkemn R.J., An improved nlysis for the fored gs deliquoring of filter kes nd porous medi, J. Seprtion Proess Tehnology, 3, (1982). 16. Wkemn R.J., The performne of filtrtion post-tretment proesses: 1. The predition nd lultion of ke dewtering hrteristis, Filtrtion nd Seprtion, 16(6), (1979). 17. Wkemn R.J. nd Trleton, E.S., Modelling, simultion nd proess design of the filter yle, Filtrtion nd Seprtion, 27(6), (1990). 18. Wkemn R.J., The performne of filtrtion post-tretment proesses: 2. The estimtion of ke wshing hrteristis, Filtrtion nd Seprtion, 17(4), (1980). 19. Wkemn R.J., Trnsport equtions for filter ke wshing, Chemil Engineering Reserh nd Design, 64, (1986). 20. Wkemn R.J. nd Attwood G.A., Developments in the pplitions of ke wshing theory, Filtrtion nd Seprtion, 25, (1988). 21. Wkemn R.J. nd Attwood G.A., Simultions of dispersion phenomen in filter ke wshing, Chemil Engineering Reserh nd Design, 68, (1990).

14 12 FIGURES AND TABLES Figure 1: Opertions whih n be rried out during diphrgm filter press yle.

15 Pressure in filter hmber (kp) Cke thikness/surfe: 20 mm 30 mm mm end of primry filtrtion Filter yle time (s) Figure 2: Vrition of pressure in the filter hmber during ke formtion nd onsolidtion for different ke thiknesses formed on eh filtering surfe during the primry nd seondry filtrtion stges. 700 Pressure in filter hmber (kp) Cke thikness/surfe: 20 mm mm 40 mm Filter yle time (s) Figure 3: Vrition of pressure in the filter hmber over the totl operting yle for different ke thiknesses formed on eh filtering surfe during the primry nd seondry filtrtion stges.

16 14 Totl ke thikness in hmber (m) b b b d d Filter yle time (s) d end of filtrtion b end of onsolidtion end of dewtering d end of wshing Figure 4: Vrition of the totl ke thikness in the filter hmber during the operting yle of the filter Filtrte flow rte (m 3 s -1 ) Cke thikness/surfe: 20 mm 30 mm 40 mm end of filtrtion b end of onsolidtion Filter yle time (s) Figure 5: Deline in filtrte flow rte during the ke formtion stges for different ke thiknesses formed on eh filter surfe during the primry nd seondry filtrtion stges.

17 15 Filtrte or wsh liquor flow rte (m 3 s -1 ) Cke thikness/surfe: 20 mm 30 mm 40 mm end of filtrtion b end of onsolidtion end of dewtering d end of wshing d d Filter yle time (s) d Figure 6: Vrition in liquid flow rte oming from the filter press throughout the operting yle. Moisture ontent in hmber (%) Filter yle time (s) Cke thikness/surfe: 20 mm 30 mm 40 mm Figure 7: Vrition of moisture ontent in the filter hmber during the operting yle for different ke thiknesses formed on eh filter surfe.

18 16 Flow rte (m 3 s -1 ) Pressure (kp) Tble 1: Pump hrteristis. Filtrtion re (m 2 ) Totl yle time (h) Cke thikness per hmber (mm) Solids prodution rte (kg h -1 ) Tble 2: Effet of ke thikness on filter size nd produtivity.