GB2027610A - Regeneration of Ion Exchange Materials - Google Patents

Abstract

In the regeneration of mixed resins, separation and transfer of the separated resins is achieved by classifying into an upper anion layer, an intermediate interfacial region and a lower cation layer, transferring the latter from the bottom of the separator vessel and controlling the transfer by detecting an interface between materials. In an illustrative embodiment, the interfacial region comprises inert material and cation material is transferred through elongate conduit 106 from separator/anion regenerator vessel 10 to cation regenerator vessel 12. Transfer is terminated in response to a change in conductivity at an interface between materials being detected by the instrument 110. This allows the interfacial region to be substantially isolated in conduit 106 during regeneration, thereby decreasing the contamination of the regenerated resins. <IMAGE>

Description

SPECIFICATION Regeneration of lon Exchange Materials 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 once-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 required in other industries also, for example as wash water in the 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 that the ion exchange materials are separated into discrete layers. This is achieved by back-washing the mixed materials to cause the anion material, which has the lower density, to rise to form an upper layer resting on top of the cation material.

After separation of the materials into their respective 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 interfacial 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 material with another should be eliminated as far as possible.

The reason for this is that any cation material mixed with anion material is contacted, on regeneration, by the sodium hydroxide regenerant which causes the cation to be converted to the sodium form. This sodium form of 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 more complex. It is recognised with the types of anion materials currently available that, during their life, degradation takes place and some of 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 as 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 out during service flow. Also during the treatment cycle, hydrolysis of the anion material results in the release of the acid into the water being treated.This latter situation also arises when the hydrochloride 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 teing 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 in UK Patent Specification No. 1318102, dated 23rd November, 1970.

In this type of method, it will be clear that even when the interfacial region between the layers is coincident with the distributor/collector means, because of the limitations on the definition of the interfacial region, some material from each layer will be contacted with the incorrect regenerant. In practice, it will be very difficult to ensure that the interfacial region is coincident with the distributor/collector means and consequently relatively large amounts of one or other of the layers may contact the incorrect regenerant.

The separated layers may be isolated from one another, for example by the anion layer being transferred to another vessel, prior to being regenerated. A typical regeneration method of this type is described in US Patent Specification No.3414508, patented 3rd December 1968.

This type of method, however, also depends on the definition of the interfacial region, whether said region is coincident with an outlet for the anion layer and whether any turbulence of the transfer water causes mixing of the layers in said region during the transfer step. As the cation contaminating the anion layer has been regarded as 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 stripping ammonia from the boiler water, the cation material is ammoniated after being regenerated. This ammoniation step can also be applied to the regenerated anion layer to convert the sodium form of the contaminant cation material to the required ammoniated form as described in US Patent Specification No. 3385887, patented 28th May 1968.

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

Alternatively, as that process uses a considerable quantity 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 requires ammonia to be re-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 boiler 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.

In a similar manner, chloride leakage may occur due to the displacement of chloride ions from the anion material by hydroxide ions. This again depends on the separation achieved during classification and transfer or regeneration and the efficiency of regenerant.

It is an object of the present invention to reduce or obviate one 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 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 regenerating materials.

When considering cation and anion materials, the interfacial region contains cation material heavily contaminated with anion material and anion material heavily contaminated with cation, the materials on either side of the interfacial region being relatively uncontaminated cation material and relatively uncontaminated anion material.

The amount of contamination of one material with the other in the interfacial 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 cross-contamination of the cation and anion materials.

It is preferred, however, to add sufficient inert material to the 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 that 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 uncontaminated cation and anion materials and is virtually co-extensive with the interfacial region where inert material is absent or of a volume insufficient to give optimum separation of the cation and anion materials.

When the interfacial region comprises said layer of substantially pure inert material, two interfaces are formed. The first interface occurs between substantially uncontaminated cation material and the interfacial region and the second interface occurs between the interfacial region and substantially uncontaminated anion material.

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

Within the scope of the basic method are a number of 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, apparatus 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 material 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 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 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: 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 vessels through an elongate conduit.

Figure 1 shows a regeneration station comprising a separator vessel 10 and a cation regenerator vessel 12. The vessels 10 and 12 have inverted frusto-conically shaped bases. The included angles, as seen in diametral cross-section, of the bases of the vessels 10 and 1 2 are 300. The vessels 10 and 12 have respective perforate barriers 14 and 1 6 in their bases, which barriers 14 and 1 6 permitting the passage of liquid while retaining ion exchange resins thereon.

The vessels 10 and 12 have respective lower inlet/outlet pipelines 1 8 and 20.

The pipelines 1 8 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 (c) respective drain pipeline 42 and 44 via valves 46 and 48, respectively.

The air supply pipeline 22 is connected to other pipelines via valves 28 and 30 as described below.

The vessels 10 and 12 have respective upper inlet/outlet pipelines 50 and 52.

The pipelines 50 and 52 are connected to: (a) a further water inlet pipeline 32a via flow control valves 54, 66 and 58, 60, respectively; and (b) respective drain pipelines 66 and 68 via valves 70 and 72, respectively.

The pipelines 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 pipelines 78 and 80 controlled by valves 82 and 84, respectively, in the vessels 10 and 1 2.

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 connected to air supply pipeline 22 by the valves 28 and 30, respectively.

The vessel 10 has an inlet 98 controlled by valve 100 and through which resins from a service unit can be introduced into the vessel 10.

The vessel 10 has a further drain pipeline 102 controlled by valve 104, the pipeline 102 being connected to the pipeline 78.

The vessel 10 also has a transfer conduit 106 connecting it to the vessel 12 and which has a valve 108. The inlet to the transfer conduit 106 is adjacent the screen 14 and 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 1 4 of the vessel 10 by an amount approximately equal to half the radius of the transfer conduit 106.

A detecting means, for example, a conductivity-responsive instrument 110, is located in the transfer conduit 106 to enable an interface between materials to be detected therein. The instrument responds to the change in the apparent composite conductivity of the transferring liquid and of the materials being transferred as the interface passes the instrument.

A pipeline 112 controlled by a valve 114 leads from the transfer conduit 106 back to the service unit. Water for effecting this transfer can be introduced into pipeline 1 8 via valve 11 6 which allows a high flow rate into the vessel 10.

A water supply pipeline 11 8 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 the transfer conduit 106 on either 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 Al 61 Cl (Trade Name), an anion ion exchange resin having a particle size of not greater than 0.9 mm diameter Duolite; C26TR (Trade Name), a cation ion exchange resin have a particle size of not less than 0.7 mm diameter; and a polystyrene co-polymer particulate material, an inert resin having a particle size in the range 0.65 mm to 0.85 mm diameter and a density intermediate the densities of the anion and cation resins. These resins are available from Dia-Proism U.K. Limited. Alternative materials are available from Rohm and Haas (U.K.) Ltd. under the trade names Ambersep 900 (anion), Ambersep 200 (cation) and Ambersep Inert (inert).

In this embodiment sufficient inert resin is present in the admixture such that, upon classification, an interfacial region is formed of substantially pure inert resin.

When the resins in the service unit require regeneration, they are transferred to the vessel 10 via pipeline 98, valve 94 being open to vent air from the vessel 10.

Valve 24 is opened to introduce air and valve 36 is substantially opened to introduce backwash water which goes to drain pipeline 66 via valve 70. This is a preliminary removal of dirt from the resins so that a better separation of the resins can be achieved.

Valves 24 and 94 are then closed and an increased flow of water into vessel 10 is made by opening valve 34 to add to the flow through the pipeline 18 via valve 36. The water again leaves the vessel 10 to drain pipeline 66 via valve 70.

This controlled flow of water through vessel 10 classifies the resins into an upper anion resin layer, an interfacial region of substantial pure inert resin and a lower cation resin layer.

The flow of water is then decreased by closing 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 76 and 96 are opened. The flow of water through valve 76 establishes a slight upward flow of water in the vessel 10. Valve 108 is then opened. The surplus of water entering the vessel 10 through valve 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. The transfer rate has to be kept relatively slow in order to maintain the interfacial region in the vessel 10 between the upper and lower resin layers, i.e. the substantially pure inert resin layer, substantially horizontal. Too fast a transfer rate causes the interfacial region to fall in the centre of the vessel. The use of a vessel with a cone-shaped base reduces the area at the take-off point for the cation resin.

While the interfacial region can be kept reasonably horizontal without it, the upward flow of water through valve 76 assists in maintaining the interfacial region substantially horizontal. It is believed that this happens because the 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 interfacial region remaining 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 some of the incoming water 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 surface. A timer (not shown) is then started and when a suitable timed delay has elapsed the valve 108 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 interfacial region, have left the conduit. Valves 36 and 76 are closed at the same time as the valve 108.

This termination of the transfer flow thus isolates the major proportion of the interfacial region in the transfer conduit 106 which has an internal volume such as to substantially accommodate and isolate that region. A relatively small amount of the inert material of the interfacial region may also remain in the vessel 10.

The cation resin, now substantially wholly in the vessel 12, is then given an air scour by opening valve 26 and this is terminated after the necessary length of time by closing valves 26 and 96.

The cation resin is then backwashed by opening valves 40 and 72 which are closed after the necessary length of time to complete the backwash.

The anion resin, in vessel 10, is subjected to a partial draindown by opening valves 28 and 104 after which they are closed.

The anion resin is then subjected to an air scour and a backwash, similar to the cation resin, by opening and closing valves 24 and 94 and then opening and closing valves 38 and 70.

This cleaning stage of the resins is the main cleaning step and more vigorous than the earlier one as there are less amounts of resin in the vessel and a greater force can be used without resin being lost to lirain.

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 acid regenerant is introduced into vessel 12 through pipeline 80 and leaves the vessel 12 to drain pipeline 44 by valve 48. To counteract the dilution effect of the water filling the remainder of vessel 10 above the anion resin, relatively stronger solutions of sodium hydroxide may be 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 the regenerated cation resin from the vessel 12 back to the vessel 10. Upon completion of the transfer, valves 40, 58, 70 and 126 are closed. The vessel 10 is then partially drained down by opening and then closing of valves 28 and 104.

The resins are then air mixed by the opening, and then closing, of valves 24 and 94.

The mixed resins are then hydraulically transferred back to either a storage vessel where it can be held until required or direct to the service unit. The transfer is achieved by opening valves 36, 38 and 54 to give a combined flow of water into transfer conduit 106 and by opening valves 114. After the transfer is completed, these four valves are then shut. Valve 120 can then be operated to flush transfer conduit 106 back into vessel 10 to ensure any resin remaining in the transfer conduit 106 between valve 108 and pipeline 112 is flushed back into vessel 10 prior to a subsequent regeneration cycle.

If the regenerated resins are returned to the service unit by a pipeline other than transfer conduit 106, the transfer conduit 106 would still have to be flushed to transfer the remaining portion of the interfacial region into the vessel 10 prior to a subsequent regeneration cycle.

While it is feasible to use parallel-sided vessels, the cone-shaped base type of vessel shown in the drawing is preferred. In the case of vessel 1 0, such a base assists in the transfer of the cation resin therefrom by restricting the take-off area and in the case of vessel 1 2 reduces the amount of water needed to transfer the cation resin to the vessel 1 0 again because of the restriction on the take-off area. The preferred included angle of 300 for the base of at least the vessel 10 is chosen because it has been found that, at included angles of greater than 300, the interfacial region became less distinct and that at included angles of less than 300, the height of the vessel 10 becomes too great.

The barriers 14 and 1 6 may be wire screens or may be a screen formed by casting sand coated with and bonded by an epoxy resin. 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 miliilitres per 100 litres of cation resin remaining 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 be used.The bonded-sand screen also has the advantage that it can be cast to have an inverse conical upper surface having an included angle, as seen in diametral cross-section, of, for example, 1 600, 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 now be further described in the following example.

Example I A test apparatus was constructed in which the vessel 10 had an upper parallel-sided portion measuring 1000 millimetres (mm) in height and 610 mm in diameter and a lower conical portion having a height of 618 mm, a lower diameter of 390 mm and an included angle of 30 . The transfer conduit 106 had a nominal inside diameter of 20 mm and, therefore, a spacing from the screen 14 of 5 mm.

The vessel 12 was a parallel-sided vessel having a height of 1300 mm and a diameter of 610 mm.

Table I gives typical operating conditions used on the test rig.

Table I Stage m31h m/h minutes Backwash: Initial flow rate 2.25 Velocity in: parallel-sided portion 8 cone base 19 Time 30 Final flow rate 1.0 Velocity in: parallel-sided portion 4.0 cone base 9.0 Time 5 Resin Transfer: Inlet flow rate (valve 36) 1.0 Veiocity at base of cone 9.0 Upward bleed flow 0.33 Bleed velocity in: parallel-sided portion 1.1 cone base 2.74 Resin transfer 8 conveying water 0.78 Time 13 Tests in which the amount of cation resin present in the anion resin were determined were carried out by classifying the resins in vessel 10, transferring all of the resins to vessel 12 and sampling the resins in the transfer conduit 106.The results are given in Table il. The volumes of inert resin given are sufficient in the test apparatus to form an interfacial region of substantially pure inert resin.

Table II % cation in Volume ofinert anion Test No. Cation %H Anion %H resin-litres (Vol./Vol.J 1. 78 Nil 25 0.28 2. 78 Nil 30 0.27 3. 78 Nil 30 0.15 4. 56 4 30 0.075 5. 56 4 30 < 0.1 These tests show that the degree of cation contamination is at a very low level. For example, with a conventional ion exchange method, the percentage of cation in anion resin would typically be 5%.

The decrease in hydrogen ion concentration of the cation resin increases the density of the resin and appears to have an appreciable affect on the level of the contamination. In service the hydrogen ion concentration of the cation resin would be typically in the region 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 measuring 2768 mm in height and 1800 mm in diameter and a lower conical portion having a height of 2426 mm, a lower diameter of 600 mm and an included angle of 300. The transfer conduit 106 has a nominal inside diameter of 75 mm and an internal volume sufficient to accommodate substantially the interfacial region. Typically, the volumes of cation and anion resins to be separated in this vessel are 4.5 m3 (cubic metres) and 2.25 m3, respectively, there being at least 0.1 m3 of inert resin admixed therewith to give an interfacial region on classification of some 0.022 m3 of substantially pure inert material.

Conductivity cells which are available from Electronic Instruments Ltd. U.K. are suitable for detecting the change in conductivity at an interface between materials.

Figure 2 is a chart which shows the changes in response of such an instrument corresponding to the changes in apparent conductivity assuming a complete transfer of all of the classified resins from vessel 10 to vessel 12.

Of course, in carrying out transfer during actual operation of the 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 most pronounced, as clearly shown by the test trace given in Figure 2. However, a fairly pronounced change also occurs at the interface between the inert material of the interfacial region and the anion material.

Valve operation may occur if preferred in response to that change.

Figure 2 also clearly shows that the anion and cation material can be widely separated by the relatively long interfacial 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 1 0. In other words, the separation achieved in the vessel 10 is enhanced by the effect of the transfer conduit 106 and the trace shown in Figure 2 emphasises that differentiation between the materials is optimised by that increased separation. Thus, the presence 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. The contamination of the cation material is extremely negligible.

Furthermore, the isolation in the transfer conduit 106 of a volume of material i.e. substantially the interfacial region means that the positioning of the detector means 110 along the transfer conduit 106 is not critical; nor need the valve 108 be positioned immediately adjacent the detector means 11 0.

The valve 108 is required only to stop flow.

The valve 108 is not required to close, in every cycle of regeneration, at precisely the instant when a particular interface occupies the valve.

On the contrary, the invention requires merely that the interfacial region 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 most a negligible amount.

Figure 2 also shows that if inert material is not used, or only a relatively small amount of inert was used, there would still be an appreciable conductivity change ample to indicate that the interfacial region was in the transfer conduit 106 and that the cation layer had passed through the transfer conduit 106.

The contaminated materials of the interfacial region, in this instance are preferably substantially all isolated in the transfer conduit 106 so that relatively only very pure cation and anion materials are regenerated. To ensure that substantially all of the interfacial region is isolated, the apparatus can be arranged such that on termination of the transfer flow some relatively uncontaminated cation material remains in the transfer conduit and some relatively uncontaminated anion material has entered the transfer conduit 106.

When the service units are being operated only on the hydrogen cycle, then 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 ammonia cycle is required it is essential because of the dentrimental effects of sodium breakthrough, to not allow such materials to be returned to the service unit. In this instance, the contaminated materials of the interfacial 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 resins next transferred from a service unit.

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

Modifications are possible as follows: For example, once the interfacial region has been isolated in the transfer conduit 106, the anion material may be transferred to a third vessel for regeneration.

Following regeneration, the materials may be transferred to a third (or fourth as the case may be) vessel for re-mixing. Alternatively, they can be transferred direct to a service unit if facilities are available for promoting mixing therein.

Instead of isolating the interfacial region in the transfer conduit 106, particularly when inert material is not used to form the interfacial region, the interfacial region can be removed from the transfer conduit 106 and, for example, be held in a separate hold vessel during regeneration and returned to the vessel 10 after the resins therein had been returned to storage or service. This can be achieved by continuing the flow of transfer water after the valve 108 is shut to transfer the interfacial region out of the transfer conduit 106, there being provided further pipelines and control valves (neither of which are shown) to enable the interfacial region to be so transferred to, for example, the above-mentioned hold vessel and from that vessel back to vessel 10.

In this instance, to ensure that the resins returned to service are all regenerated, the transfer conduit 106 can be flushed out on either side of valve 108 prior to regeneration to flush the resins remaining therein into vessels 10 and 12.

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 contaminated by cation resin fines.

Fines are present in the as-delivered 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 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 pre-existing 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 inadequately 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 conductivityresponsive instrument or other detector even though, as explained above, the interface is then generally co-extensive with the interfacial region.

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

Claims (44)

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 uncontaminated cation material and substantially uncontaminated anion material.

4. 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, the inert material being present in such quantity that said interfacial region comprises substantially pure inert material, 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 mm to 0.9 mm diameter.

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.

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

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

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

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

12. A method according to claim 11, in which said isolation occurs in response to detection of a fall in conductivity at said interface.

13. A method according to claim 11 as dependent on claim 4, in which said interface is between cation and inert material and in which said isolation occurs in response 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.

1 5. 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.

1 6. A method according to any claim of claims 1 to 14, in 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.

1 7. A method according to any claim of claim 1 5 or 16, in which said isolation is effected so as to isolate at least a major proportion of the interfacial region in the conduit.

1 8. 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 1 5, 1 6 and 18, 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 1 7 or claim 19, in which the interfacial region remains isolated from the regenerated 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, in which the interface is detected in the conduit by an instrument capable of differentiating between the resins by using light transmission or reflection.

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 to separate out cation material fines which are then disposted of by transfer through said conduit to waste.

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

25. Apparatus for generating ion exchange materials comprising 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 material 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 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, in 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.

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, of 300.

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 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 crosssection, of said upper surface is 1 600.

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 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.

39. Apparatus according to any claim of claims 25 to 38, in 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 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.

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

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 hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.