Deionisation apparatus and processes are well known.

They generally involve the exchange of unwanted cations and anions in water with hydrogen and hydroxide ions using ion-exchange substances such as resins. The resins can be in packed beds'.

Some resins are designed to be regenerated in order for the resins to continue to provide their deionisation action. One common method of regeneration is to provide a regenerant flow across the resins. For cationic resins, this generally involves the use of an acid, such as hydrochloric acid, designed to replace the cations held by the resins with hydrogen ions. For anionic resins, this generally involves the use of a strong alkali, such

as caustic soda, to replace the cations on the resins with hydroxide ions.

After the chemical regenerant flow, the resins are usually rinsed with water, and the resins re-renter deionisation service.

Naturally, it is desired to achieve best possible regeneration for maximum efficiency of the deionisation apparatus. For this, there should be minimal resin"fluidisation"during the resin regeneration i. e. the resin bed should as fixed as possible. This is especially for counter-current regeneration.

Whilst the resins can be held in position at the beginning of the regeneration step by using a fast air or water flow to compact'them together, in packed bed systems some room (generally termed"free board") in the resin holding vessel is still required to allow space for the expansion and contraction of the resins. This is because ion- exchange resins shrink or contract when in contact with solutions of high concentrations due to osmosis. Ion exchange resins generally comprise about 50% water, and the resin surface acts as a semi-permeable membrane, such that water is transported across the resin surface depending upon the concentration therearound, thereby contracting and expanding the size of the resin.

Also, fully converting a strong acid cation resin from a heavily laden sodium'form to the regenerated hydrogen form, will cause about a 7% swelling due to the change in ionic form.

Similarly, a strong base resin may swell by more than 20% when fully converting from a chloride' form to the regenerated hydroxide form.

In practice, swelling and contraction changes are not usually as large as this, as the full capacity of resins is not usually used.

It is generally desired to keep the amount of free board in a packed bed ion-exchange apparatus to below 5% for cation units, and below 10% for anion units. However, this is commonly difficult to achieve as variations in swelling occur, both because different ionic forms of ion-exchange resins have differing volumes, and because resin substances such as beads tend to repack or rearrange themselves during use, thereby altering their original loaded' depth in the deionisation apparatus.

Thus, during conventional regeneration, the ion- exchange materials expand and contract, due to being in contact with regenerant chemicals due to osmosis, and also due to the changes in volume going from one ionic form to another.

It is an object of the present invention to improve the regeneration of deionisation substances.

Thus, according to one aspect of the present invention, there is provided a process for the regeneration of a deionisation substance comprising the steps of: providing a regenerant flow across the substance; providing a water rinse across the substance; providing at least one further regenerant flow across the substance; and providing at least one further water rinse across the substance.

By introducing the regenerant in a number of steps, the present invention reduces the fluidisation of the deionisation substance, thus improving the regeneration efficiency. This can also lead to an improved deionisation capacity, and hence treated water quality.

The deionisation substance may be any substance known in the art. One particular substance is ion- exchange resins. The substance can be provided in any suitable form known in the art. One suitable form is in the form of beads.

The present invention is useable with co-or counter-flow regeneration processes, i. e. where the regenerant flows either the same way or opposite to the feed water flow. Preferably, the invention is used with counter-flow regeneration, in which freeboard is more important.

The regenerant may be any suitable regenerant well known in the art for the deionisation substance.

The regenerant will generally be a strong acid for cationic deionisation substances, and a strong alkali for anionic deionisation substances.

Generally, the same amount of regenerant is used as with or in prior art process.

In deionisation systems having more than one deionisation substance, the process of the present invention in preferably carried out on each substance, possibly wholly or substantially simultaneously.

In one embodiment of the present invention, the process comprises two regenerant flows. The second flow could be at any stage in terms of time, regenerant volume or other measurement, after the first regenerant flow and rinse. For example, the first regenerant flow could involve a percentage, e. g. 10-90% (without limitation) of the total usable regenerant. A different second regenerant flow could be after approximate 50% regenerant use by volume in the first regenerant flow.

In another embodiment of the present invention, the regenerant could be used in a series of small amounts or volumes, e. g. 5-10%, possibly followed each time by a rinse step. One possibility is to have a set time for each step, e. g. one minute regenerate flow followed by one minute water rinse.

The time periods need not be the same either for each flow, or each type of flow.

Presently the concentration of regenerants for regeneration processes in electrodeionisation units is generally in the range 2-5% for chemicals such as hydrochloric acid and sodium hydroxide, usually 2- 4%, and generally 0. 8-2% for sulfuric acid.

However, the involvement of multiple rinse steps provides a further advantage to the invention, in that the concentration of the or each regenerant can be increased, possibly substantially increased, possibly by 100% or more, beyond prior art levels or expected levels. Thus each regenerant could be at a concentration level of 2-8%. This increase in concentration gradient acting on the substance between each regenerant flow and each rinse flow provides a greater driving force'of regeneration action. This leads to better regeneration of the deionisation substance, and hence better quality of deionisation thereafter, as more unwanted cations and anions are driven off the deionisation substances.

An additional feature to the above is that the time required for regeneration could be shortened, if higher concentrations of regenerant can be used (for the same overall amount of regenerant), reducing the down time'of the deionisation system or apparatus.

Further additionally, the multiple flow steps of the process of the present invention can lead to increased compaction of the deionisation substance in a packed bed system, further improving their deionisation effectiveness thereafter.

The above is based on the flow rates for each step being the same, or generally the same, as prior art flow rates. However, variation in all the flow rates is also possible.

Thus, using a 20 minute regeneration cycle as an example, a prior art process would introduce a 2% concentration of regenerant for 10-15 minutes, followed by a water rinse step. By the present invention using for instance four regenerant flow steps and four water rinse steps sequentially over 20 minutes, the regenerant concentration, for the same flow rates, could be increased to say 4% because of the increased number of rinse steps.

According to a further embodiment of the present invention, a water rinse step follows each regenerant flow step.

The process of the present invention can still involve a prior compaction step, i. e. a higher velocity flow to compact the substances such as resins, generally in the form of beads, together. Regenerant could be included in this flow. This can save time in the regeneration of the resins by having the regeneration start earlier than normal.

It also provides an earlier start to any required dilution of the regenerant. The present invention extends to the possible use of regenerant in the compaction flow being the first regenerant flow step of the regeneration process.

The present invention provides a further benefit to the regeneration of deionisation substances.

"Organic species"as referred to water treatments are naturally occurring substances which have large carbon chains, and typically can be fulvic or humic acids derived from decaying matters such as leaves, etc. These enter the anion resins and are difficult to remove. If not removed, they reduce the efficiency of the resin, leading to low capacity in pure treated water quality.

Presently, a brine wash is often used with the anion resin. One of the effects of this is to'squeeze' the resin osmotically, in an attempt to drive out fixed or reluctant'organic species.

As the present invention involves at least two regenerant flows across the substance, leading to at least two contractions/expansions of the substance, the accentuated shrinking and swelling helps drive out the organic species (and other difficult to remove species). Using higher concentrations of regenerant in the flows also accentuates the shrinking and swelling effect, providing better physical cleaning and better compaction of the substance.

The repeated, and if desired regular, change in resin bead volume provided by the present invention also assists in the dissociation of any physical debris on the surface of the resin, keeping the resin cleaner, and hence more efficient. A repeated for example 10% change in volume will significantly help in cracking off'physical debris.

According to a second aspect of the present invention, there is provided an apparatus for the deionisation of water, the apparatus including one or more deionisation substances, and means to regenerate the or each deionisation substance, wherein the means to regenerate the or each deionisation substance is adapted to provide at least two flows of a regenerant across the or each deionisation substance, and at least two water rinses across the or each deionisation substance.

More particularly, the apparatus of the present invention includes means to provide a process for the regeneration of the or each deionisation substance therein, said process being as hereinbefore defined.

An embodiment of the present invention will now be described by way of example only, and with reference to the accompanying drawing, Figure 1, showing a schematic diagram for a deionisation apparatus and processes therewithin.

In figure 1; EJ1 : acid ejector EJ2 : caustic soda ejector FI1 : acid flow indicator FI2 : caustic soda flow indicator FIM : flow indicator and totalising meter with volume switch FL : flow limiter FR : flow restrictor FT : flow transducer PI : pressure indicator PU1 pump RI : resistivity indicator and switch V1 TO V13 INCL & V26 : automatic valves V14 & V15 : flow metering valves V16 & V17 : drain/sample valves V18 TO V22 and V24, V25 : non return valves V23 : Actuated valve Referring to Figure 1, a complete deionisation system generally involves two resins, a cation resin to remove cationic impurities such as calcium, magnesium, sodium and potassium, and an anion resin to remove anions, which are mainly by carbonates, chlorides, sulphates and nitrates. Figure 1 shows a 3-bed deionisor apparatus 2; the resins are housed in three separate cylinders 4,6, 8, thereby forming three"beds".

The resins used in the apparatus 2 are synthetic organic copolymers of styrene and divinyl-benzene.

These are in the physical form of small spherical beads of about 1/2 mm average diameter.

The cation resin is used in the hydrogen form, and when impure water containing cations other than hydrogen is passed through the cation bed 4, the cationic impurities react chemically with the resin, and the equivalent amount of hydrogen ion is released into the water. The strong base anion resin is used in the hydroxyl form, wherein the chemical equivalent of hydroxyl ions are released into the water when the anionic impurities in the impure water flow react with the resin. The hydrogen ions released from cation resin combine with the hydroxyl ions from the anion resin to form water, which has replaced the impurities that were originally present in the water.

The second cation resin bed 8 removes trace quanties of sodium hydroxide present in the outlet water from the preceding anion resin bed 6.

The apparatus 2 is designed to treat potable towns mains or borehole water, free from suspended solids.

The apparatus 2 can also be used to deionise permeate water produced by reverse osmosis.

In use, a water supply e. g. from an adjacent storage tank, is fed to the connection labelled"feed water inlet". It passes through a first automatic valve Vl, and then a multi-stage centrifugal pump PU1.

From there, it passes through the next valve V3 into

a composite GRP polyethylene lined or vinylester tank 4 containing the cation ion-exchange resin beads. The water flows through the cation resin in a downward direction, thereby exchanging the positively charged metal cation components of the salts in the feed water, such as calcium, magnesium and sodium for hydrogen ions, producing inter alia mineral acids.

The decationised water flows from the bottom connection of the cation vessel 4 via valve V8, to the top connection of the second vessel 6, a similar tank containing strong base anion exchange resin beads. The water flows through the anion resin in a downward direction, exchanging the negatively charged anion components of the mineral acids, etc, such as chlorides, sulphites and carbonates, for hydroxyl ions. The salts in the feed water are thus removed, and remain on the resin. The remaining hydrogen and hydroxyl ions combined to form water molecules.

The deionised water flows from the bottom of the anion vessel 6, through a valve V26, to the top connection of the third vessel 8, a similar tank, containing cation exchange resin beads. Any trace quantities of for example sodium ions from sodium hydroxide will be exchanged onto the cation resin.

The hydrogen ions exchanging off the cation resin will be combined with the hydroxyl ions to form further water molecules.

The deionised water flows from the bottom of the second cation vessel 8 is also continuously monitored by an in-line automatically temperature compensated resistivity indicator RI. The resistivity of the deionised water can be continuously displayed on a control panel situated at the front of the unit (not shown).

Providing the resistivity of the deionised water is within the resistivity specification, it will pass through the automatic flow control valve V13 and leave the apparatus 2 via the connection marked "Deionised Water Outlet".

After a pre-set volume of water has been deionised by the apparatus 2, the apparatus sets or is set to regenerate the cation and anion exchange resins.

The regeneration process is as follows:- The automatic deionsed water outlet valve V13 is closed to prevent water or regeneration chemicals passing to service during the regeneration process.

The feed pump PU1 is stopped for a short time to allow the valve changeover to be completed. The feed water automatic inlet valve V1 is closed and the regeneration water automatic inlet valve V2 is opened. With the automatic valves V3, V8 and V26 closed and automatic valves V4, V6, V7, V10 and V12 open, deionised water is pumped upwards through both ion exchange vessels to drain at a sufficient velocity to compact the resins against the upper

distributor of each vessel 4,6 and simultaneously remove any dirt particles which may have collected on the top of the resin bed during the service cycle.

After a short time, the automatic valves V6 and V12 are closed. Deionised water continues to be pumped through the automatic valve V4, the acid ejector EJ1 and the caustic soda ejector EJ2. The automatic valves V5 and V9 open; and about half the concentrated regenerants, usually 32% Hydrochloric acid and 32% Sodium hydroxide, are drawn into the ejectors and are diluted to the required concentration with deionised water before being fed into the bottom connection of the second cation and the anion vessels 8,6 respectively.

The required flow rate for the concentrated regenerant chemicals is set during commissioning of the apparatus 2 by adjusting the manual metering valves V14 and V15 in conjunction with meters FI1 and FI2 situated upstream of the ejectors.

The regenerant chemicals flow upward through the resin beds removing salts exchanged onto the resins during the service cycle. The hydrochloric acid flows from the top of the second cation vessel 8 to the bottom connection of the first cation vessel 4.

The salts flow out of the top of each resin vessel 4,6, 8, through automatic valves V7 and V10, and are mixed together producing an initial degree of neutralisation before flowing to a drain connection.

At the end of the chemical injection time period, automatic valves V5 and V9 close. Deionised water continues to be pumped through automatic valves V4 and the ejectors EJ1 and EJ2 in order to provide a primary rinse to the resins to remove the regenerant chemicals.

In accordance with the present invention, the valve arrangement then returns to provide a further regenerant flow, i. e. with the remaining half of the concentrated reagents. Valves V6 and V12 are closed; valves V5 and V9 opened, and the diluted regenerant flows are fed into the bottom connections of the second cation vessel 8 (and so onto the first cation vessel 4) and the anion vessel 6 as before.

Thereafter, there is a second rinse step in the same manner as described above for the primary rinse flow.

At the end of the final rinse period the process pump PU1 is stopped allowing the ion exchange resins to settle. The automatic drain valves V7 and V10 are closed and the automatic valves V3, V8, V26 and Vll opened. The process pump PU1 is started ; the final stage of the regeneration is a recycle in the service direction in order to produce a satisfactory deionised water resistivity (conductivity) before the unit re-enters the service cycle.

The multi-regenerant and rinse flows or pulses'of the process of the present invention cause multiple swelling and shrinking of the resin beads, reducing the fluidisation of the beads due to at least two factors. Firstly, because there is less overall osmotic effect in each bed each time. Secondly, because a proportion of the resin near the bottom of the bed has already swollen'due to ionic change, this reduces the free board in the next regenerant flow pluse. Thus, the amount of free board needed is less, or can be kept well within desired limits.

The resin beds can thus remain as fixed as possible during regeneration.

The number, concentration, timing, etc. of the regenerant flows, and indeed number and timing of the rinse flows, can be varied to suit particular circumstances and designs of apparatus and resins, etc.

The invention is not limited in this way. Different regenerants could also be used for different regenerant flows.

The multi-pulse regeneration process of the present invention need not take any further, or any significantly further, time for regenerating the resins.

Table 1 hereinafter indicates the improved capacity and quality between using the previous one- regenerant flow process, and the new multi-

regenerant flow process. In Table 1, Tests 1-3 relate to the prior art process involving a single regenerant injection step. Tests 4-9 involve the use of the process of the present invention. The megohm figures in Table 1 relate to the level of contamination of the water; megohm is the reciprocal of conductivity. 18.2 megohm is virtually absolutely pure water from an ionic point of view and is equivalent to 0.055 microsiemens per cm.

Water quality better than 10 megohm is considered to be very'pure water.

In Tests 1-3, the acid and caustic regenerants were added in one input'. The program for Tests 4-6 was "Pl"-shown in Table 2 hereinafter, and for Tests 7-9, it was"P3"shown in Table 3 hereinafter.

The first service'rows show the volume of water needed for the plant to achieve that level of water purity.

The results in Table 1 show that although the ultimate water quality is similar, the capacity is better, and the rinse volumes required to reach various quality points are lower in Tests 4-9 compared with Tests 1-3.

The final service rows confirm the volume of purified water that the regenerated plant can provide prior to that level of water quality or contamination being reached. The lower the level of water quality (ie the lower the Megaohm figure), the

greater volume of purified water can be produced.

Different plant operators use different cut-off' contamination levels, prior to the need for regeneration of the deionisation substances.

Thus, in general it can be seen that the average production capacity to say 10 megohm, i. e. very pure water, over Tests 1-3 is 11. 52m3, whereas the average over Tests 4-6 is 12. 67m3, a 10% increase.

Even at 5 megohms, the average increase is from 12. Om3 to 13. 37m3, still an 11% increase.

The average production capacity to 10 megohm over tests 7-9 is 13. 65m3, some 18% improvement over Tests 1-3 (the conventional regeneration technique).

Similarly the capacity to 5 megohm shows an 18% improvement.

Taking into account the volumes of water going through such water treatment plants, being able to provide a 10%, 11% or even 18% improvement in production is a significant extra'capacity, and hence saving on running costs.

Total organic carbon content from the apparatus has been less than lOOppb.

The present invention provides a simple but effective method of minimising fluidisation of deionisation substances during their regeneration.

This provides improved regeneration and improved

resin capacity, without requiring any new apparatus or equipment. TABLE 1 TEST 1 2 3 4 5 6 7 8 9 Regen (litre Acid 32% litres 15 10 15 15 15 20 20 20 Caustic 28% litres 19 10 19 19 19 25 25 25 Flow (m3/hr) Service 10 10 10 10 10 10 10 10 10 Recycle 11 11 11 11 11 11 11 11 11 Service 4 Megohm 0.73 0.13 0.02 0.48 (m3) 5 Megohm 0.94 0.86 0.54 0. 28 0.68 6 Megohm 1.12 1.13 0.67 0. 52 0.87 rinse 7 Megohm 1.29 0.79 0.73 1.06 8 Megohm 1. 44 1.54 0. 87 0. 88 1.24 9 Megohm 1.60 1. 74 1.05 1. 06 1.41 10 Megohm 1.76 1.94 1.16 1. 21 1.59 11 Megohm 1.93 2.16 1.27 1.40 1.76 12 Megohm 2.10 2.39 1.41 1.58 1.94 13 Megohm 2.31 2. 65 1.56 1.79 2.16 14 Megohm 2.51 2.98 1.74 2.02 2.40 15 Megohm 2.84 3.36 2.01 2.35 2. 72 16 Megohm 3. 30 3. 94 2.44 2.95 3.16 17 Megohm production 10 Megohm 11.68 11. 19 11. 69 13.32 12. 30 12.39 13.95 13.65 13. 36 5 Megohm 12.23 11.79 12.21 14.02 13. 02 13.08 14. 54 14.35 14. 02 1 Megohm 13.39 12. 90 13.24 15.33 14.36 14.40 15. 58 ANION 0.50 Megohm n/a n/a nla n/a nua nla Best quality Megohm 17. 5 17. 5 17. 3 16. 8 17.4 17.5 Comments Original Original Original P1 P1 P1 P3 P3 P3 TABLE 2 t ; t i lgerrtECn ( : utsj= x Compaction 1min 20s V2, V4, V6, V7, V10, V12, V23 Regeneration Pulse 1 (chemical inject) 5 V2, V4, V5, V7, V9, V10, V23 Regeneration Rinse 1 1 V2, V4, V7, V10, V23,--- Regeneration Pulse 2 (chemical inject) 5 V2, V4, V5, V7, V9, V10, V23--- Regeneration Rinse 2 12 V2, V4, V7, V10, V23 Regen Rinse 3 (Fast) 3 V2, V4, V6, V7, V10, V12, V23 Settle 1 V2, V3, V8, V11, V23, V26 Recirculation to Water Good 38 max. V2, V3, V8, V11, V23, V26 Unit Flow Recirculation on Water Good 1 V2, V3, V8, V11, V26 Unit Flow TABLE 3 n ; r. it$Pulsë} , s J C ga >. @ it 0 t, » Pulse 1 & Compaction (chemical inject) 1min 20s V2, V4, V5, V6, V7, V9, V10, V12, V23 Regeneration Pulse 2 (chemical inject) 2 V2, V4, V5, V7, V9, V10, V23 Regeneration Rinse 1 1 V2, V4, V7, V10, V23 Regeneration Pulse 3 (chemical inject) 2 V2, V4, V5, V7, V9, V10, V23 Regeneration Rinse 2 1 V2, V4, V7, V10, V23 Regeneration Pulse 4 (chemical inject) 2 V2, V4, V5, V7, V9, V10, V23 Regeneration Rinse 3 12 V2, V4, V7, V10, V23--- Regen Rinse 4 (Fast) 3 V2, \ ? 4, V6, V7, V10, V12, V23 Settle 1 V2, V3, V8, V11, V23, V26 Recirculation to Water Good 38 max. V2, V3, V8, V11, V23, V26 Unit Flow Recirculation on Water Good 1 V2, V3, V8, V11, V26 Unit Flow