IE46780B1 - Regeneration of ion exchange materials - Google Patents

Description

The invention relates to methods of, and apparatus for, regenerating ion exchange materials.

Modern high pressure boilers require a very high degree of purity in their feed water, particularly boilers of the or.ee5 through type. It is essential to ensure that corrosion products do not enter the boiler system and also to guard against ingress of soluble compounds due to condenser leaks and other faults.

Very high.purity water is.often ret; Fred in other industries also, for example as wash water in tiie electronics industry for washing electronic components which have to be absolutely free from impurities during manufacture.

One of the most important water treatment processes for .. . . achieving such high purity water is the mixed bed deionisation process. The use of a mixed bed of ion exchange material means -'-*. that, in effect, the feedwater is passed through a very large number of cation and anion layers.

The regeneration of such mixed beds requires tha!: the ion exeh-mr.e watt rials are sep.aratcd into discrete layers. This is achieved by b.-ck-wushxng the mi:;:·cl materials to cause the anion material, which has the lover density, te rise to form an upper layer rusting on top of the cation material.

After separation of the materials Into their respect:ve layers, the anion and cation materials can be regenerated using sodium hydroxide and sulphuric or hydrochloric acid, respectively.

It is at this stage where imperfections in the process arise.

For example, at the inlerfaeial region between the layers it is impossible to achieve perfect separation of the materials and consequently each layer is contaminated to some degree by material of the other layer. For the maximum degree of purity of the treated water it is important that mixing of one type of ion exchange materi. with another should be eliminated as far as possible.

The reason for this is that any cation material mixed with anio: material is contacted, on regeneration, by the sodium hydroxide regenerant which causes the cation to be converted to the sodium form. This sodium form ol the cation can subsequently give rise to sodium leakage during service flow through the mixed bed.

In the case of anion material the position is mo're complex.

It is recogniu-d with the types of ani.'ri materials currently available that, during their life, degradation takes place and some of 4· the strong base groups are degraded to weak base groups. Thus, if anion material is left in the cation material, the weak base groups are converted to the sulphate or bisulphate form if sulphuric, acid is used ns a regenerant, which converted form is a strong absorbent for sulphuric acid. The rate at which the absorbed sulphuric acid is released appears to deteriorate with the age of the resin.

This results in the anion material increasingly retaining the acid during the standard rinsing period thus leaving more to be leached cut during service flow. Also during the treatment cycle, hydro10 lysis of the anion material results in the release of tho acid into the water being treated. This latter situation also arises when the hydrtichloride form of the anion material is present after regeneration of the cation material with hydrochloric acid, thus giving release of hydrochloric acid into the water being treated.

The separated layers of ion exchange material may be regenerated in the vessel in which they are separated, the respective regenerants being fed into or taken from the vessel at a distributor /collector means positioned at an intermediate position of the vessel. A typical regeneration method of this type is described Z0 in UK Patent Specification No. 1318102, dated 23rd November, 1970.

In this type of method, it will be clear that even when the iiiterfaci; 1 region between the layers is coincident with the dintrihutor/colieelor means, because of the limitations on the dffiiiltIon of I lie I.TiVirfacial region, some material from each layer will he contacted with the incorrect regenerant. In practice, it will he very difficult to. ensure that the interfacial region is . I coincident with the The separated layers may be isolated from one. another, for example by the anion layer being transferred to another vessel , prior to being regenerate:!. A typical regeneration method of this type is described in US Patent Specification No, 3414503, patented 3rd December 1968, Tills type of method, however, also depends on the definition JO of the jnterfaciai region, whether said region is coincident with an outlet, for the anion layer and whether any turbulence oi the transfer wartr causes mixing of the layers in said region during the trainr step. As the cation contaminating the, anion layer has been regarded us the more serious of the two situations there has been a tendency to ensure that, by suitable positioning of the outlet, the transfer of the anion layer has only taken anion material even at the expense of leaving anion material in the cation layer.

Also, when dealing with boiler feed water, it has been the practice to raise the pH of the feed water to e.g. 9.4 - 9.6 using ammonia to reduce the amount of corrosion in the boiler. Ammonia is preferred because it passes through the vapour cycle and redissolves in the condensate. In this situation, to stop the cation material tripping ammonia from tho. boiler water, the cation material is ancioui.· ti d after being regenerated. This ammoniation step can 678 0 also ho applied to the regi-nt-raled anion layer to convert the sodium form of the con'.iniinant cation material to the required ammoniatod form as described in US Patent Specification No.3385367, patented 28th May 1968.

This practice, however, only provides a solution to the problem and does not prevent it; nor is ir a solution when ammoniation ci the treated water is not required and may even be undesirable.

Alternatively, as that process uses a considerable quantitj1· of ammonia solution it is usual to operate initially with the hydrogen form of the cation material thus allowing the cation material to strip ammonia from the condensate. The process require; ammonia to be ro-introduced downstream of the ion-exchange units to maintain the required pH level.

However, when all the hydrogen sites on the cation material are exhausted by ammonia, the ammonia then displaces any sodium thereon from the cation material and leads to sodium leakage into the holler water.

Clearly, the amount of leakage is dependent on the amount of sodium remaining on the cation material after regeneration which, in turn, depends on the separation achieved during classification and transfer or regeneration and the efficiency of regeneration.

I Tn a similar p inner, chloride leakage may occur due t>· the displace went of chloride Iocs fro·» tl ·· anicn material by hydroxide ions. XI··?. again depends on the separation achieved during classification and transfer or regeneration ard the efficiency cf regenerant .

It is an object or the present 'nvention to reduce or obviate ore or more of the above mentioned disadvantages.

In accordance with the present invention, a method of regenerating ion exchange materials comprises separating the materials into an upper anion material layer, an intermediate inter facial region and a lower cation material layer above a perforate barrier in a separator vessel, removing materials from the separator vessel by flow through an elongate conduit having an outlet outside the separator vessel and an inlet in the separator vessel adjacent said perforate barrier, continuing said flow until at least a major proportion of the cation material has passed through said outlet of the conduit and a major proportion of material from the interfacial region has entered the conduit, detecting an interface in the conduit between materials, isolating said outlet, from said inlet in response to detection of said interface, regenerating the ion exchange materials and re-mixing said regenerating materials.

When considering cation and anion m,.t.erials, the intcrfacial region contains cat.Jo material heavily contaminated with ai’i.ou malarial. and anion pi,,i erial heavily con tin·, tooted with cation, the material'· on either side of the intorfacial regioa being relatively uucontaminated vetion material and relatively uncontaminated anion material.

Tin’, amount of contamination of one material, with the other in the intcrfacial region can be reduced by the introduction of an inert particulate material which has a density intermediate the densities of the cation and anion materials. The inert material has a separating and diluting effect on the crosscontamination of the cation and anion materials. 1!) It is preferred, however, to add sufficient inert material to t.hc ion exchange materials such that, on separation into layers there is a layer of substantially pure inert material formed between the cation material and anion material layers, said layer of substantially pure inert material comprising the interfacial region.

This layer of substantially pure inert material does contain anion and cation particles but in such small quantities time it is impracticle to remove them, even if that is possible, by continued classification of the materials. Once such a layer of substantially pure inert material has been, formed, then the addition of further quantities of the inert material makes little, if any, difference to the numbers of anion and cation particles present in the layer.

The interface lies between substantially uncolamina ted cation and anion materials and is virtually co-extcnsive with the interfacial region where inert material in absent or of a volume itw-vf·'25 icient to give optimum reparation of I nc cation and anion ma t<- iai;·. ΐΊ·» ιι 11»· int '·,’ f.'c! ;ι I ιτ ΐ'.ίοιι comp· 1.· :,a id layer of erb· stantially pure inert material, two intc. fates ,ι·-ο formed. Tha first interface ot.curs between substantially uacoi··-aminated cation material and the interfacial region end the second inl'.er5 face occur.'· Iirtwen the interfacial reg’on end substantially uncont't.ii.nntcd anion material.

Preferably, the cation material, lias a particle size of not less than substantially 0.5 millimetres (nra) diameter, the anior. material has a particle size of not greater than substantially 1.2 mm and the inert material lias a particle size substantially in the range of 0,5 mm to 0.9 mm diameter.

Within the scop.· of the basic method are a number or alternative steps' that can be taken as will be apparent from the more detailed description given below with reference to the accompanying drawings.

Also, in accordance with the invention, rpparatus for regenerating particulate anion and cation materials which apparatus comprises at least first and second vessels each containing in a lower region thereof a respective perforate barrier to retain ion exchange material thereon, said first vessel having supply means by which a classifying flow of liquid can be established to separate materials therein into an upper anion material layer, an interfacial region and a lower cation ·...·. crial layer, said supply means also comprising transfer flow supply means for effecting hydraulic transfer from the first to the second vessel of cation material and material of said interfacial region, an elongate conduit having at a first end an inlet 5 in said lower region of said first vessel and an outlet at a second end of said conduit in said second vessel above said perforate barrier thereof, a detector means intermediate said ends of the conduit and a valve in the conduit arranged to be closed to isolate the outlet from the inlet of the conduit 10 in response to detection by said detector means of an interface between materials in the conduit.

Methods and apparatus will now be described by way of example to illustrate the invention with reference to the accompanying drawings, in which:15 ' Figure 1 is a schematic diagram of one form of apparatus; and Figure 2 is a chart recording of conductivity measured during a test transfer in which all the materials were transferred between two 20 vessels through an elongate conduit. » ϊ Figure 1 shows a regeneration station comprising a separator ί ! I vessel 10 and a cation regenerator vessel 12. The vessels 10 and 12 j 1 I. have inverted frusto-conically shaped bases. The included angles, j 1 i as seen in diametral cross-section, of the bases of the vessels 10 ! o ’ and 12 are 30 . The vessels 10 and 12 have respective perforate ; barriers 14 and 16 in their bases, which barriers 14 and 16 permitting the passage of liquid while retaining ion exchange resins thereon, . I The vessels 10 and 12 have respective lower inlet/outlet pipe- 1 > lines 16 and 20.

The pipelines 18 and 20 are connected to: (a) an air supply pipeline 22 via valves 24 and 26, respectively} (b) a water supply pipeline 32 via flow control valves 34, 36 and 38 and 40 respectively; and i < respective drain pipeline 42 and 44 via valves 46 and 48, respectively.

I Tlie eir supply pipeline 22 is connect' ·Ί to other pipelines via v.’iivt·;· 2f! and 30 .is described below.

Tlio Vvescls 10 and 12 have respective upper inlet/eutlet pipelines 50 and 52.

The pipelines 50 and 52 are connected to: (<·; a furtln-r water inlet pipeline 32^ via flow control valves 54, 56 and 58, 60, respectively; and i (b) respective drain pipelines 66 and 68 via valves 10 70 and 72, respectively.

The pipe!int 50 also has a pipeline 74 connecting it to the drain pipeline 66 via a flow control valve 76.

The vessels 10 and 12 have respective regenerant inlet pipelinos 78 and SO controlled by valves 82 and 84, respectively, in the vessels 10 and 12.

The vessels 10 and 12 have upper pipelines 90 and 92, respectively, controlled by respective, air vent valves 94 and 96, respectively. The pipelines 90 and 92 are also counecved to air supply pipnlinn 22. by the valves 28 and 30, respectively. '3The vessel 10 has an j.nlct 98 contro! ι ;·:1 by valve 100 .-in through v’lich rrgjo.·, rservice unit can he ini reduced into the V. ...'.C.l 10.

The vessel 10 has a further drain pipeline 10.2 centre]led by valve <04, th<· pipeline 102 living connected to the p< online 78.

Tlic vessel 10 also has a (.rangier conduit 106 connecting it to the. vessel 12 and which has a valve 108. The inlet to the transid conduit J06 is adjacent the screen 14 end is centrally located of the vessel 10, As a guide it is proposed to space the inlet of the transfer conduit 106 .from the screen 14 of the vessel 30 hy an amount approximately equal to half the radius of the transfer conduit 106.

A del cting means, for exoTiple, a. conductivity-responsive instrument 110, is located in the transfer conduit 106 to enable an interface between materials to be debuted therein. The instrument responds to the change in the apparent composite conductivity of the transferring liquid and of the materials being tr .usferved as the interface passes the instrument. Λ pipeline 112 controlled by a valve 114 leads from the transfer conduit 106 tack to the service unit. Water for effecting this transfer can he introduced into pipeline 18 via valve 116 which aJlcws a high flow rate into the vessel 10.

A water supply pipeline 112 is connected to the transfer conduit 106 on either side of valve 108 via valves 120 and 122 to enable flushing water to be supplied to Ihe transfer coeduil 106 on oi the·· side of the valve 108.

The vessel 12 is connected to the vessel 10 by· a second transfer conduit 124 controlled by a valve 126.

The flow control valves each permit a flow determined by the step being performed.

The service unit contains, for example, Duolite A161CI (Trade Name), an anion ioit exchange recin having a particle size of not greater than 0.9 rnra diameter Duolite: C26TR (Trade Name), a cation ion exchange resin have a particle size of net less than 0.7 mm diameter; and a polystyrene co> polymer particulate material, an inert-resin having a particle site in the range 0.65 mm tc. 0.85 mm diameter and a density interim diute the densities of the anion and cation resins. These resins are available from Dia15 Proisra 0.K, Limited. Alternative material·: arc avilable from Rohm and Haas (11.R.) Ltd. under the trade names /imhersep 900 (anion), Amberscp 200 (cation) and Ambersep Inert (inert).

In this embodiment sufficient inert resin is present in the admixture, sue’.·, that, upon classification, an iuterfacial region is formed of substantially pure inert resin.

When the resins in the service unit require regeneration, they are transferred Le the »«svl 10 via pJjit-i.1.·.··. open to vent air the v.·:!.;·.’ 10. 78, valve 94 being Valve 24 is opened ''· introduce air and valve 36 is substantially op: -· d to introduc.· backwaah water which goes to drain j.ipcI in,.· 66 v j a valve 70. This is ,-i nreliit iu-iry removal Oi' dirt f'OH! the resins so that a better separation of the resli-j can be achieved. b Valves 24 a::-·' 94 are then closed and an increased flo ι of water into vessel 10 is made by opening valve 34 t-? add to the flow through the piped ii.·· 38 via valve 3’-. The water again leaves the vessel 10 to dr.i.-n pipeline 66 via valve 70.

This controlled flew of water through vessel 10 classifies the resins into an upper anion resin layer, an intcrfacial r ?.ion of substantially pure inert resin and a lover cation resii layer.

The flow of water is then decreased by closity; valve 34 to allow the classified resins to settle to an extent, the valve 36 -still being open, When classification is complete, valve 70 is closed and valves and 96 arc opened. The flow of water through valve 76 estiblishc.·· a alight upwaid flew of water in the vessel 10. Valve 108 is then opened. The surplus of wafer entering the vessel 10 through vab-e 36 over that leaving the vessel 10 through valve 76 causes hydraulic transfer of the cation resin through transfer conduit 106 to the vessel 12. Tie transfer race has to be kept relatively slow in order to maintain the interfacisl region in tbs vessel 10 between the upper and lover resin layers, I.e. the substantially pure inert resin layer, . iilj.-tantial ly horizontal. Too fart a transfer rate causes the inter16 facial region to fall in the contra of the vessel. The uee of a vessel vzilli a cone-shaped base red: -es the area nt the takeoff point for the cation resin.

While the ir.terfacial region can be kept reasonably hc.riz5 onlal without it, the upward flow of water through valve 76 assists in maint lining the intcrfacial region substantially hcrizo ’ta1. It is believed that this happens because t.he upward flow maintains the resins in a slightly fluidised state, thus causing a continuous classification of- the resins to occur during the transfer step which results in the intcrfacial region re,coining sharply defined as it moves down the vessel 10, Without this positive upward flow, an upward flow does still occur to some extent since resin is 'being conveyed down and out of the vessel 10 and sere of the incoming v>tv- has to flow upwardly to occupy the volume previously occupied by the transferred resin.

As the transfer proceeds, the conductivity instrument 110 detects the cation-inert interface. A timer (not shown) is then started and when a suitable timed delay has elapsed the valve 106 is closed in response to the detection of the interface. The timed delay is chosen in accordance with the relative positioning of the instrument 110, and valve 108 and the outlet of the conduit, and the transfer rate to ensure that substantially all of the cation material, and preferably a small amount of the inert material of the intorfaciai region, have left the conduit. Valves 36 and 76 arc closed at the same time as the valve 108. ! --46 78 0 This tcir inaLiou of tin transfer flew thus isolates tlie major proportion of the interfacial legion in the trausfcr conduit 106 ’ .’·ιίο:ι has .in internal volume such as to subs taatial Ay r.-vnodate and isolate that region. A relatively small amount rc tin? inert material -.f the int.rfaeial region may also lrmain in tile vessel 10.

The cat: on resin .not? substantifJ ly wholly in tlie Vessel 1.2, is then g' _'?n -1 air scour by opening vc’ve 26 and this is termin.•L'cti after the necessary length of time by closing valves 26 and 95, The cation renin is then backwashed by opening valves 40 and wl:.i?h a.·.· closed after the u·-.cesser y iii.glh of time tc comp lc tithe h-rekvt·. > The anion resin, in vessel 10, is subject'd to a partial drail.dov. by opening valves 23 and 104 after which they are closed.

Tlie anion resin is then subjected to an air scour and a backwash, similar to the cation resin, by opening and closing valves >4 and ''· end i:btn opening and closing valves 38 nnd 70.

Tht. sl.sailing -.lag· of the resins is the main cleaning step and mo1e vigorous In; a the earlier one as there are less amounts ei real.’ I·· the vessel and a greater force can be used without rr-.’.iu 0--1:.-. Io;,t to drain.

Sodium hydroxide regenerant is introduced into the vessel 10 through pipeline 78 and leaves the vessel 10 to drain 42 via valve 46 and sulphuric asia regenerant is introduced into vessel 12 through pipe]iiu 80 and loaves the vessel ’.2 to drain pipeline 44 hy valve 4«, To counteract the dilution efiect of the water filling the remainder of vessel 10 rbove the anion rosin, relatively stronger solutio. r. of sodium hydi oxide may he used so that they dilute to the required strength in the vessel 10.

After regeneration is complete, valves 82 and 84 are shut and valves 56 and '60 are opened to introduce rinse water to the vessels 10 and 12, respectively.

During the rinsing of the cation resin, the transfer conduit 106, on the vessel 12 side of the valve 108 is subjected to a flushing flow of water by opening and then closing valve 122.

Once the resins are properly rinsed, valves 48, 56 and 60 are shut.

The anion resin is then drained down using air pressure via valve 28. Valve 46 is then closed.

Valves 40, 58, 70 and 126 are opened to hydraulically transfer j k the regenerated cation resin from the vessel 12 back to the vessel 1: . Upon completion of the transfer, valves 40, 58, 70 and 126 ί' are closed. The vessel 10 is then partially drained down by opening / and then closing of valves 2.8 and 104. The resins are then air ; k .. I; rui.'ed by lb·. op-pin... 'mil ; hr..! ci·,sin ,. ·. f v lyes 2.4 and The ::.. d ip in.; ,i· then hydr.-iul it ily ! r.-n··ferred b.p. y to cither .·. · lorn, e v<;i':i·' wi ere It can bt. In Id unti required c, direct to the service unit, 't'br- transfer is achieved by opening valvco V, 3b and r4 to give, a comir'ncd fi o of water into t ransfer coidn't '1 Co and by op-iiin,; live;; 11-. Af.tr the ti. ,;pi -fr.i, lb, a.· foe. valves ;-;e then ebut. Valve 120 ecu tl r be , op.· rated to flush trtiu.icn conduit 106 back tut· vest el 10 to } ensure 'ί resin rcaaininc la the. transfer eu.-duit 106 between t valve jog ?, ·, pipr.Iii c 112 J..·, ί lushed buck into vessel 10 prior to . a tibseqi’ent regencr.U ion cycle. ί If tl·:: reguiiuratcd reaiu-t are returned to the service unit by a pi pel is. other then transfer conduit 106, the transfer conduit I'lfi would η 11 have to be flushed '.o transfer the. remaining portion of the intrrf.-iciai region into the vessel 10 prior to a subsequent rcgcnirafioa cyclo.

I While it is feasible to use parallel-sided vessels, the cone- i ι shaped ba:type of -tssel shot·! in the drawing is preferred. In ; the caw of vessel 10, such a base assists in the transfer of the cation rum therefroiu by restricting the take-off area and in the ; case of vessel 12 reduces if <· awo'.nt of water needed to transfer ' I th.· M-.iva resit, to ves- el 10 again because of the restriction on th·. i-it.'-oft ar<·;,. Tb-.· [.refected inriu'.ed angle of 30° for the; ‘ ί !'· of ·’. I.·,: t tin vi·,:;·ι. 1 Hi ‘:. chosen b,i.·.· one it lias been found , .. , '1 ·.': - ! .η .·, er ;1 .ui '10 , the inl erf.oci.·:! region bec.-me less distinct and that at included angles of less than 30°, the height of the vessel 10 becomes toe great.

Tin barriers 14 and 16 may be wire screens or may be a screen formed by casting sand coated with and bonded by an epoxy re.'in.

It has been found that the wire screen can retain some resin on it. It is thought that this arises when the direction of movement of the resin beads towards the transfer conduit 106 is transverse to the slots in the screen. This results in typically 20 to 30 millilitres per 100 litres of cation resin rem-inine in the vessel 10 to contaminate the anion resin. If this level of contamination can be tolerated then the wire screen is adequate. If it cannot be tolerated, then the bonded-sand screen should he used. The bondedsand screen also has the advantage that it can bi cast to have an inverse conical upper surface having an included angle, as seen in diametral cross-section, of, for example, 160°, the central portion having a flat plate positioned to lie underneath the inlet to the conduit 106. Thus, use of the bonded-sand screen minimises the amount of cation contamination of the anion resin that can arise as a result of the screen.

The invention will how be furthox described in the following example.

EWf’bKJ, Λ test app.iaius war constructed in which the vessel 1.0 had an upper ρ.:;.' Lie!.· sided portio:. nici'niriuj, Ir'C0 mill imetres (mm) in height and 610 ram i.i di-. at·.;, ι od a lewr·;· conical portion having ί l.'igb. r.·;' (ιI.'ί η:π. ;·. l.iwc. <1 ..meter if 3'0 i.. ι ar. jiι·~Itidi.-d angl· or id’, 'fiit, firiiX.fer ¢. .‘d’-it 10G lud .: ί :u;tl in?:!? dinilci?·) of ?0 iif,'. . . i, fa i'oi i . .-. spa' f: oi.i screen lq ί.·ί 5 tin! Tin. vcI 12 v, a pm ..I! rl-tiided v ?. oi bavin,; .?. iie-;;!it cf ! I’·' J «..Ίί a.d :. d’.ii Ler of GIO Iran.

T.-bic i. /pif?l o[ ar. i..'n·: eond 1'..·.·· t uted σ.ι Vim r.g. ΤΛ Gt-,;n Bacla- fa.

Initial flow rave Velocity ini parallcl-rided portion cone base Time Final flow rate Veloei.ly ill; paral.lt I-'. :d pi'v' i\ COli 110..1.: Tiii> lics.'.u Tr.'ii'si'i.r: Inlet fli. ·' vaii; (valve ?f ) Velocity at else of Ciui· Upward ill d d H ow in^A'i ;j/h fiini t as 2.25 1.0 4.0 9.0 1.0 9.0 0.33 TAlil.K T (Cental) .?£&'· 3/, rn n m/h minutes iiic'ii velocity 5n:- pval lel-sidnd portion 1,1 cone base 2.74 Resin transfer £ conveyi.g water 0.78 Time 13 Test» in which the «mount of cation resin, present in the anion 10 resin wore determined were carried oat hy classifying the resins in vessel 10, transferring all of the resins to vessel 5.2 and sampling the resins In the transfer conduit 106. The results are given in Table 11. The volumes of inert resin given are sufficient in the test apparatus to form an interfacial region of substantially pure inert resin.

TABU II Test No. Cation 7,H Anion 711 Volume of inert resin-litres 7cation in in; on Tvo’T/Vol.) 1. 78 Nil 25 0.28 2. 78 Nil 30 0,27 J· 78 Nil 30 0.15 4. 56 4 30 0.075 5. 55 4 30 ^0.1 The.·, e. festa show that the degree of cation contamination is ι a very low level. Fox exai.pi·'. yilh o evn/rtitiot.il ion exchange method, the · ·?ι·ο« r.top/· of cation in anion rosin ·»···υ1(ϊ typically bo 57..

Tlie decrt-ast in. hydroaea ion concentration of the cation rosin i.ncrce :.;f the (leu;-,icy' ci tlie resin and appears to have an apprec5 iable affect m. the level of the coiitarc.in,: ion.. In service the hydrogen ion concentrin'ca of tlie cation r-sin would he typically in tlie η-.,ίνΐι 10% to 30% when the resin is ready for regeneration.

On a typical full size plant, the vessel 10 has an upper parallel-sided portion messuring 2768 ran; in height and 1.800 irm in diameter rad a lower conical portion having a height cf 2426 n.i.i, a lower diameter of 600 tisi and an included angle of 30°. The transfer conduit 106 has a nominal inside diameter of 75 mm snd an int( rn.'il volume sufficient to accommodate. substantially the Intcrfacial region. Typically, the volume·.; of cation and anion. resins to he separated in this vessel are 4.5m (cubic metres) 3 and 2.25in , respectively, there bci·.,; at least 0.1m' of inert resin udmixed therewith to give an intcrfacial region on class- I ificatio·. of some 0.02?m of substantially pure inert material. ) I 1' I Conductivity cells which are available from Electronic ί Instruments Ltd. U.K. arc suitable for detecting the change in ; conductivity at an interface between materials. ;· ί Figure 2 is a chart which chows the changes in response of j, such an instrument corcespoiwina to the changes In apparent if ί 46780 *5 ' 24 conductivity assuming a complete·transfer of all of the classified resins from vessel 10 to vessel 12.

Of course, in carrying oat transfer d«x,-.g actual operation oi tin: method and apparatus, transfer is terminated in response to detection of a change in conductivity. The change in conductivity at the interface between the cation material and the inert resin material of the interfacial region is the west pronounced, a. clearly shown, by the test, trace given in figure 2. However, a fairly ptenounced change also occurs nt the Interfaie b- tv on the inert material of the intorf&cial rcgi.cn and the anion material. Valve operation may occur if preferred in response to that change.

Figure 2 also clearly shews that the anion and cation material can be widely separated by the relatively long interfecial region as the result of passing the material into the relatively long transfer conduit 106, which has an internal diameter which is several times less than the smallest diameter of the lower region of the inverted frusto-conical part of the vessel 10. In other words, the separation achieved in the vessel 10 is enhanced by the effect of the transfer conduit 1.06 and the trace shown in Figure 2 emphasises that differentiation between the materials Is optimised by that increased separation. Thus, the ureserce of the critical interfacial region can be very accurately detected so that an extremely efficient transfer of cation material into the vessel 12 can be readily achieved, 'iso contamination of the cation material is extremely negligible.

Furtii.na.ire, Hie i.sol-lion in l.bc tr.m..ior conduit 100 of a volum·.· . matt rial i.p. sub' tan Li ally the ii.-'vrfacial region means Uiit tic i'.ociliouin? of the detector means 110 along th« transfer conduit. 106 j.k not criticil; nor need the valve 108 be positioned immediately adjacent the detector means 110.

The valv 100 is rtqir’red only to stop flow.

The valve 10- is not. required to c’ose, in every cycle of rcgencT- al precisely the instant when a particular interface OCC’ip'.-.s the vaiv·.·.

Oa tli-r centi.'.>·;»·. the invention requiro? up'roly that the interfacial regt.-n is substantially isolated in the transfer conduit to determine closure of the valve 108. That requirement is easily met on every cycle. Nevertheless, it is always reliable in ensuring complete transfer of cation material but without any contamination beyond at jnnsi: a negligible amount.

Figure 7. also shows that if inert Material is not used, or only a ι la Lively small amount ol inert was used, there, would Still be opprccieb]e eoi’dUJclvity chan, i ample tj indicate that the ii.-rfaci.il rej mi. was in the transfer conduit 100 mid that i’ c.iilou layer Jud passed through the transfe·.· conduit. 106.

Tiu· coalamlnafed untcct.ils of the interfacial region, in this hwtancr arc. pr.-fersl'ly su'icUntially oil isolated in the tr:u f--.r coadn-t 106 so that relatively only very pure, cation and 48780 snici: materials ate regenerated. To ensu'e. t!:..t subs to. fially all of the inCerf.;cial region is isolated, tha ap· :w . tus can be arranged -ach that o.i termination of the traf.ifer flow tome rt iaLxv.iiy uncontaniinateis cation material remains in th: transfer conduit and some relatively uncontai- inafud anion maicri· 1 has entered the iransfer conduit IOC.

When the service units are being operated only cn ill;· hydrogen cycle, tht'.n the contaminated materials of the Interfacial region isolated in the transfer conduit 106 can be returned to the service unit without any appreciable detriment to the quality of the treated water since they have not been contacted with regenerants.

However, it is preferred, and when operation through Into the ammonis cycle Is required it is essential because of the detrimental effects of sodium brcabthrough, to not allow such materials to be returned to the service unit. In this instance, the contaminated materials of the interiacinl region are removed from the transfer conduit 106 before the next regeneration cycle and are preferably returned to the vessel 10 where they would remain until joined by the exhausted mixed realns next transferred from a se rvice, unit.

Thus, the invention provides for complete 1solution of the volume of mixed contaminated resins, which unavoidably form the interfacial region.

Modificaticna. arv ibie as follow : F'.r exwipj».·, οίνο the Hit... iacif.': region has been isolated in !,.e - -{ii.fcr conduit 1(H>. tlie anion mail··-io 1. roy be transferred to -- ι bird vessel for regeneration. j'o! ’ <»g n-en-.-r lion, the mntcrlals may h<- transfer red a i.b'.i i (cr i'lMiriji as IV. cast may he) vessel fo:-. 3\:-iiiirlii-;. /-11 -.: ii,-.. ' vely. they e-.u Io transferred direct, to a &..cvi<-e unit, if sb.c! I 11 ii -c ere :.7.-.1 ϊη’Λι. .fer prosiotin mixing <·. .rein.

Instead of isolating the irtarfacial region in the transfer corJnit ib , pf..'iic>i'.i-ri.y k.»< ,-i inert Bin t·. o'1.-1 is not used co form the kir.if-.:< 1 ϊ'-git-.ii, l’.;: int. if.-ci; 1 rc-.ioi* f.n be. removed from lb- 11 11. - CO'itb’ii ίΟύ ,-.ιιιϊ, far cxr: yh, bi.· held ill 0 sop’raiin hal ; Ϊ.. -.. Ι ϊ during rt :-.:ui-ra:.v:in anJ return--1 to the vessel 10 aftt” the ri.-.iin.; ..h.?i ai.i. i be ι n later,· ΐ to s' ,-,r. or service, '•‘his c.-jr i.e ,·«'.· · ved by .'.'iitiiiuiiig tlie ilo oi tr.-.nsfer water after tlie valve 10-:’- is shut tu tiarsfi”· the. interracial region out of the tra3.-r-.r cer.-init lOf. there being provided further pipelines and C-i-trol vaJvos (neither of which are shown) to enable the ir.ccriacial to be so transferred to, for example, the abeveiX’iitioned hold vcssci and front that vessel back t:o vessel 10. ?0 In tbx.·· in·;Sauce, to e.xsuto that the resins returned to service .ιό a’! i. ralod, the c,a-.uifcr conduit 106 can be flushed out ot .·!.:· - ii'c pr. ιιΙλί Ii·· ρ» ioe to π ?-aeration to flush the n 'Ί'-. 11; ii'i I h- - --,., I i < < Vi . 1-. W ; I?.

In a further variation of this latter modification, the transfer flow can be continued, after the interfacial region has been isolated, to transfer the anion material to a separate regeneration vessel.

In a further modification, when the interfacial region comprises substantially pure inert material, the interfacial region is passed in equal proportions into the regenerator vessels prior to regeneration.

Generally, it has also been found that the anion resin can be 10 contaminated by cation resin fines. Fines are present in the asdelivered resins (owing to limitations of commercial sieving procedures) and they are also created during service.

To remove the fines present in the as-delivered cation resin, the resin is put into vessel 10 and carefully backwashed. This causes the small proportion of fines and other unwanted resin beads, e.g. low density beads, to rise to the top of the cation resin bed.

The cation resin bed is then transferred to the vessel 12, the transfer being terminated when it is estimated that the remaining resin consists predominantly of the fines and the unwanted resin beads.

To remove the cation fines created during service, the resins are separated Into their respective vessels 10 and 12 as described above with reference to Figure 1. Then saturated salt solution is circulated through the vessel containing the anion material to classify the resins, the anion and inert resins floating In the solution above the cation resin.

Once the resins have been classified, the cation fines are discharged through a drain connection (not shown) in conduit 106 by opening valves 36 and 94. After this, the anion resin is rinsed free of salt and regenerated in the manner described above.

Cation resin fines can be removed at, typically, 6 to 9 month intervals. This way of removing the cation resin fines also has the advantage of the saturated salt solution cleaning accumulated organic matter from the anion resin.

Any fines arising from the anion resin are not a problem, since these pass out to drain during backwash via a strainer on the outlet conduit 50 which is not intended to retain fines.

In a modification of the embodiments, inlets of the transfer conduit(s) from the vessels, may be substantially co-planar with the perforate baffle, the transfer conduit(s) extending downwardly out of the vessel(s). In this instance, however, provision would have to be made for ensuring that any materials in the vicinity of the inlet would be properly contacted by classification water, regenerant and rinse water.

In another modification of the embodiments, the conductivity 467 80 cell can be replaced by an Instrument capable of differentiating between the resins by using light transmission or reflection. In another modification, the transfer conduit(s) could have a transparent section so that an operator can view that section and upon visually detecting the interfacial region manually terminating the transfer.

Instead of a conductivity instrument an instrument responsive to the relative apparent pH value of the resin/water mixture may be used. Such an instrument may be of the kind known as a pH cell or glass electrode type; but recently instruments have become commercially available which depend upon the use of dissimilar metals In a probe and which give rise to electro-motive force without the need for an external electric supply. Such a probe may be arranged to protrude into the resin/water mixture in the conduit.

As described above, the use of inert material is advantageous and is preferred but its use is not mandatory. In some cases the use of inert material or of an optimum amount of inert material may be precluded for example because of limitations imposed by preexisting equipment, such as where the invention is applied by way of modification of existing plant which, as originally installed, did not Incorporate the invention. Furthermore, the amount of Inert material, although initially sufficient to ensure adequate separation of the cation and anion materials on classification, may diminish during service and may not be replenished or may be lnad25 equately replenished.

Therefore, in some cases the invention will be practised where the interfacial region is devoid of inert material; or contains Insufficient inert material to ensure optimum separation of the cation and anion materials on classification.

In those instances, detection of the interface is still readily achieved using a conductivity-responsive instrument or other detector even though, as explained above, the interface is then generally coextensive with the interfacial region.

Classification of the ion exchange materials in such cases ί distinctly separate layers with a sharply defined interface is j not necessary since the invention, as explained with reference to the examples described above eliminates, or at least reduces to j a point where they are negligible, the effects of the crosscontamination of the ion exchange materials.

Claims (44)

1. CLAIMS;

1. A method of regenerating ion exchange materials comprising separating the materials into an upper anion material layer, an intermediate interfacial region and a lower cation material layer above a perforate barrier in a separator vessel, removing materials from the separator vessel by flow through an elongate conduit having an outlet outside the separator vessel and an inlet in the separator vessel adjacent said perforate barrier, continuing said flow until at least a major proportion of the cation material has passed through said outlet of the conduit and a major proportion of material from the interfacial region has entered the conduit, detecting an Interface in the conduit between materials, isolating said outlet from said inlet In response to detection of said interface, regenerating the ion exchange materials and re-mixing said regenerated materials.

2. A method according to claim 1, in which said interfacial region comprises cation material contaminated with anion material and anion material contaminated with cation material and in which said interface lies between substantially uncontaminated cation material and substantially uncontaminated anion material.

3. A method according to claim 1, in which the cation and anion materials are in admixture with inert particulate material having a density intermediate the respective densities of the cation and anion materials and in which said interfacial region comprises at least in part inert material, and in which said Interface lies between substantially uncontamlnated cation material and substantially uncontaminated anion material.

4. A method according to claim 1, in which the cation and 5. Anion materials are in admixture with inert particulate material having a density intermediate the respective densities of the cation and anion materials, the inert material being present in such quantity that said interfacial region comprises substantially pure inert material, 10 and in which said interface is an interface between one of said ion exchange materials and said inert material.

5. A method according to claim 3 or claim 4, in which the inert material has a particle size substantially in the range of 0.5-ram to 0.9 mm diameter. 15

6. A method according to claim 5, in which the particle size is in the range 0.65 mm to 0.85 mm.

7. A method according to any preceding claim, in which the cation material has a particle size of not less than substantially 0.5 mm diameter. 20

8. A method according to claim 7, in wiiich the particle size is not less than 0.7 mm.

9. A method according to any preceding claim, in which the I anion material has a particle size of not greater than substantially 1.2 mm diameter.

10. A pethod according to claim 9, in which the particle size 5 is not greater than 0.9 mm.

11. A method according to any preceding claim, in which said J isolation occurs in response to detection of a change in conductivity at said interface. j ι ι I

12. A method according to claim 11, in which said isolation 1 10 occurs in response to detection of a fall in conduct- ' ivity at said interface. ( i

13. A method according to claim 11 as dependent on claim 4, i in which said interface is between cation and inert I I material and in which said isolation occurs in response 15 to detection of a fall in conductivity thereat.

14. A method according to claim 11 as dependent on claim 4, in which said interface is between anion and inert material and in which said isolation occurs in response to detection of a rise in conductivity thereat.

15. A method according to any preceding claim, in which the anion material is regenerated in the separator vessel and the cation material in a cation regenerator vessel.

16. A method according to any claim of claims 1 to 14, in 5 which the anion material is transferred to and regenerated in an anion regenerator vessel and the cation material is regenerated in a cation regenerator vessel.

17. A method according to any claim of claim 15 or 16, in which said isolation is effected so as to isolate at least 10 a major proportion of the interfacial region in the conduit.

18. A method according to claim 16, in which said flow is continued to transfer the anion material to the anion regenerator vessel.

19. A method according to any claim of claims 15, 16 and 18, 15 in which said flow is continued to remove the interfacial region to a container wherein it is isolated from both the cation and anion materials.

20. A method according to claim 17 or claim 19, in which the interfacial region remains isolated from the regenerated 20 materials and is mixed into subsequent unregenerated materials transferred into the separator vessel. .

21. A method according to any preceding claim, in which the regenerated cation and anion materials are re-mixed in the separator vessel.

22. A method according to claim 1, χη which the interface is detected in the conduit hy an instrument capable of differroaterials entiating between the / by using light transmission 5 or reflection. j

23. A method according to any preceding claim, in which after the removal of the cation material, a liquid having a density such that the anion material will float relative to the cation material is circulated in the first vessel ί 10 to separate out cation material fines which are then | J disposted of hy transfer through said conduit to waste.

24. A method according to claim 23, iii which the liquid is saturated sodium chloride solution.

25. Apparatus for regenerating ion exchange materials com15 prising particulate anion and cation materials which apparatus comprises at least first and second vessels each containing in a lower region thereof a respective perforate barrier to retain ion exchange material thereon, said first vessel having supply means by which a class20 ifying flow of liquid can be established to separate materials therein into an upper anion material layer, an j interfacial region and a lower cation material layer, said supply means also comprising transfer flow supply means for effecting hydraulic- transfer from the first to the second ' ' I vessel of cation material and material of said interfacial region, an elongate conduit having at a first end an inlet in said lower region of said first vessel and an outlet at a second end of said conduit in said second vessel above said perforate barrier thereof, a detector means intermediate said ends of the conduit and a valve in the conduit arranged to be closed to Isolate the outlet from the inlet of the conduit in response to detection by said detector means of an interface between materials.

26. Apparatus according to claim 25, iq which said supply means also comprises anion regenerant supply means.

27. Apparatus according to claim 25 or claim 26, in which said conduit has an internal volume such as to substantially accommodate and isolate therein said interfacial region.

28. Apparatus according to claim 25, in which there is provided a third vessel containing in a lower region thereof a perforate barrier to retain ion exchange material thereon, the third vessel being connected above said perforate barrier to the first vessel so that anion material can be transferred thereto for regeneration.

29. Apparatus according to claim 28, in which the connection · between the first and third vessels comprises a branch of said conduit in which a second valve is located to control flow therethrough, the branch of the conduit having an outlet at the end thereof in the third vessel.

30. Apparatus according to any claim of claims 25, 26, 28 and 29, in which a separate container, into which the interfacial region is transferable to be isolated, is connected to the conduit. 5

31. Apparatus according to any claim of claims 25 to 30, in which at least the first vessel is of inverted frusto-conical shape immediately above said barrier.

32. Apparatus according to clain 31, in which the frusto-conical shape has an included angle as seen in diametral cross-section, 10 of 30°.

33. Apparatus according to any claim of claims 25 to 32, in which the barriers are wire screens.

34. Apparatus according to any claim of claims 25 to 32, in which at least the barrier of the first vessel is cast 15 from epoxy resin coated sand.

35. Apparatus according to claim 34, in which the bonded-sand barrier has an inverted conical upper surface.

36. Apparatus according to claim 35, in which the included angle, as seen in diametral cross-section, of said 20 upper surface is 160°.

37. Apparatus according to any claim of claims 25 to 36, in which the inlet of the conduit is spaced from the barrier of the first vessel by an amount substantially equal to half the radius of the conduit, the conduit having a 5 portion extending upwardly from the barrier.

38. Apparatus according to any claim of claims 25 to 37, in which said supply means comprises means such that an upward bleed flow of liquid can be established in the first vessel during transfer flow. I 10

39. Apparatus according to any claim of claims 25 to 38, in I which the detector means comprises a conductivity cell positioned in the conduit.

40. Apparatus according to any claim of claims 25 to 38, in which the detector means comprises an instrument capable 15 of differentiating between the materials by using light transmission or reflection.

41. A method according to claim 1 substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings. . 1 I 20

42. A method according to claim 1 substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings. • I i ί I

43. Apparatus according to claim 25 substantially as hereinbefore described with reference to Figure 1 of the accompanying drawings. · .

44. Apparatus according to claim 25 substantially as herein5 before described with reference to Figures 1 and 2 of the accompanying drawings.