Counter-current process for the rapid regeneration of ion exchange materials in an unrestrained bed

A method of regenerating an ion exchanger which is used to treat a solution introduced to the ion exchanger in a downward changing direction. The ion exchanger contains a non-constrained bed of ion exchange material in the form of ion exchange granules and has a concentration profile through the ion exchange material after solution has been introduced to the ion exchanger in the charging direction. The method of regenerating comprises passing a regenerating solution upwardly through the non-constrained bed of ion exchange material in an intermittent flow manner comprising an alternating up flow of regenerating solution followed by a down flow of liquid in a direction opposite to the up flow. The duration and velocity of the up flow of regenerating solution is sufficient to lift and generate a perceptible mixing of ion exchange materials in approximately the bottom portion of the ion exchange bed, with the down flow being sufficient to seat the bed very rapidly and terminate mixing.

FIELD OF INVENTION 
The present invention relates to an improved process for regenerating ion 
exchange materials, and more specifically, for the regeneration of an ion 
exchanger following processes such as water softening or deionization, 
wherein a chemical solution is passed through the ion exchanger for 
regeneration and the exchanger is rinsed free of regenerating chemical, 
after which the exchanger is returned to service for further softening or 
other ion exchange. 
BACKGROUND OF THE INVENTION 
Ion exchange processes such as softening or demineralization are generally 
known, where fixed charged sites present on ion exchange materials, such 
as bead like ion exchange resins, provide sites to bind or store 
oppositely charged ions and/or particles. These ions and or particles may 
be exchanged for others existing in solution in a reversible equilibrium 
process which modifies the ionic composition of the liquid flowing through 
said ion exchange materials. After the exchange process is completed the 
process can be reversed by passing a concentrated solution of the original 
stored ions through the ion exchange medium, eluting the ions or particles 
exchanged from the solution during exhaustion by replacing them with the 
original stored ions, and rinsing both the eluted ions and any residual 
regenerating solution from the ion exchange medium. Once rinsed, the ion 
exchanger can be placed back into service, again releasing the stored ions 
in exchange for other ions or charged particles in solution. The 
exhaustion flow is typically downward, through the ion exchanger, from the 
top of the ion exchanger and out through the bottom. 
To conduct regeneration following exhaustion in the downward direction: it 
is known to introduce the regenerating solution in the same direction as 
the exhausting flow, from top to bottom, i.e., in a co-current direction, 
through the ion exchanger. The regeneration of the ion exchange bed in a 
co-current direction has considerable drawbacks, as illustrated by the 
example of the softening of hard water. In this case, hard water flows 
through layers of ion exchanger material (such as ion exchange resins or 
zeolite) contained in a vessel (ion exchanger), and the ion exchanger 
becomes exhausted, or loaded in the flow direction, i.e., from top to 
bottom, with hardness (principally calcium and magnesium ions). The ion 
exchange process is equilibrium driven and the final reduction of hardness 
in the processed water is dependent upon the concentration of hardness 
ions in the lowermost ion exchange layer (polishing layer), which is the 
last one through which the water to be treated flows. The lower the 
residual hardness in the product water, the better the product water 
quality. During the subsequent regeneration in a co-current system, the 
hardness ions which are highly enriched in the upper layers of the ion 
exchanger are eluted from the resin by the regenerating solution and 
washed downward into the lower layers. In order to generate a good state 
of regeneration in these lower layers, an excess of regenerating chemical 
must be employed. This excess is frequently as much as 2 to 3 times the 
stoichiometric amount required to regenerate the resin depending on the 
level of hardness required in the product water. This excess amount of 
regenerating chemical is not utilized and represents a major economic loss 
both in terms of the cost of the excess regenerating chemical as well as 
the cost associated with its subsequent disposal. 
Introduction of the regenerating solution in an upward direction, opposite 
to that of the exhausting flow, i.e., in a countercurrent direction, 
through the ion exchanger is also known. The disadvantage of this process 
is that the entire bed of ion exchange material, unless fixed or 
restrained in place by some mechanism, is turned over and mixed together. 
In particular, the upper layers of ion exchange resins which are most 
highly charged with hardness are also more dense and are forced from the 
upper layers to the lower layers as mixing occurs, while the less dense 
ion exchange material that is still largely uncharged is forced upward 
from the lower layers to the upper layers. Thus, because of this 
rearrangement, the situation is similar to the cocurrent operation in that 
the entire ion exchange bed must be treated with a large excess of 
regenerating chemical in order to achieve good product quality. The 
drawbacks in using large excesses of regenerating chemical are the same. 
The most efficient use of regenerant and, at the same time, the best 
product quality is obtained when the ion exchange materials are not mixed 
or rearranged during counter current regeneration. As a result, the lower 
most layers of ion exchange materials (or polishing layers) which 
determine the quality of the product during the charging operation are 
treated first with fresh regenerating solution and are thus optimally 
regenerated. Several known systems control this mixing or rearrangement by 
fixing the bed through the use of either physical restraints or a 
combination of physical restraints and blocking liquid and or air flows. 
In each of these methods, the underlying commonality is the need to 
physically fix or otherwise restrain the ion exchange bed during the 
regeneration process in order to solve the known difficulties which arise 
from bed mixing during counter-current regeneration. Each of these known 
processes has its own known drawbacks and operational problems due to 
their bed fixing mechanisms. 
Another method allows an efficient, counter current regeneration of a 
non-constrained (not fixed) layered bed without many of the aforementioned 
problems and is described in allowed U.S. patent application Ser. No. 
07/369,238 to Gerhard K. Kurtz filed Jun. 22, 1989 entitled PROCESS AND 
APATUS FOR ION EXCHANGERS, TICULARLY FOR REGENERATION AFTER 
SOFTENING AND DEMINERALIZATION OF AQUEOUS SOLUTIONS, which is incorporated 
herein by reference. A Kunz counterpart application has issued in the 
Republic of South Africa as Patent 89/4669 and is also incorporated herein 
by reference. In this process, as described by Kunz, an ion exchange 
filter which has been exhausted in a downflow direction is first treated 
with a regenerating chemical solution and then with a rinse solution, 
introducing both in a counter current direction, i.e., upflow. This is 
accomplished by using a series of upward flowing pulses of defined 
velocity and duration which lift the bed some prescribed distance and are 
separated by a settle or rest time during which the ion exchange bed 
returns to substantially its original position without mixing. The 
essential focus of the Kurtz process is its successful approach to 
introducing the regenerant chemical without causing significant mixing 
between the layers of a non-constrained ion exchange bed. This process 
leads to very efficient utilization of regenerating chemical, and provides 
the high quality product characteristic of a countercurrent process, since 
the bed concentration profile is maintained and the lower or polishing 
layers of the ion exchange bed are always treated with fresh regeneration 
solution. However, while eliminating the need for various complicated and 
expensive mechanical apparatus utilized to fix or restrain the ion 
exchange bed, this regeneration process takes significantly longer than 
typical operations, thereby limiting its commercial viability. 
Accordingly, it is the object of the present invention to overcome the long 
regeneration time associated with the Kurtz process while maintaining the 
inherent efficiencies of this process and without re-introducing any of 
the mechanical design difficulties associated with other previous fixed 
bed processes. 
Specifically, it is the object of the present invention to achieve the 
rapid, efficient countercurrent regeneration of an unconstrained ion 
exchange bed in an upward direction with substantially the same amount of 
regenerating chemical as the Kunz process thereby obtaining a significant 
savings in both regenerating chemical cost and subsequent associated waste 
disposal costs without requiring an extended regeneration time. 
SUMMARY OF THE INVENTION 
The present invention is directed to an improved ion exchange regeneration 
process which allows a rapid, efficient counter-current regeneration of a 
non-constrained ion exchange bed in an upward direction. Layered ion 
exchange material in a vessel exhausted by downward flow is first treated 
with a regenerating chemical and then with a rinse solution by feeding 
these solutions in an upward direction through the ion exchange materials, 
a direction opposite to, or countercurrent to, the exhausting flow 
direction. The flow of both regenerating and rinsing solutions are 
conducted in such a manner that mixing or rearrangement between the layers 
of the exchange material is limited to the lower portion or polishing 
layer of the ion exchange bed. The bed lifting and perceptible mixing at 
the bottom of the bed according to this invention allows the highest 
possible flow of regenerating and rinse solutions to be introduced into 
the bed while restricting mixing to the polishing layers of the bed where 
the effect of such mixing on overall performance is minor. This permits 
rapid and efficient regeneration. 
Mixing of polishing layers of the exchange materials in a non-constrained 
bed is controlled in accordance with the present invention by a process in 
which the regenerant chemical and rinse solutions are introduced into the 
exchanger in an upward direction, opposite the exhaustion direction, at a 
velocity and time sufficient to lift the bed and cause perceptible mixing 
within the lower layers of the ion exchange bed, followed by a downward 
flow sufficient to re-settle the bed very rapidly thus terminating the 
preceding perceptible mixing. During the up flow, a flow of regenerant 
chemical or rinse solution passes through the bed. As the up flow is 
allowed to proceed, the bed lifts and perceptible mixing begins to occur 
at the bottom of the ion exchanger. When the perceptible mixing has 
reached a predetermined level, a downward flow of liquid, of volume less 
than the up flow volume, is introduced above the ion exchange bed. This 
down flow seats the bed very rapidly and ends bed mixing. Regenerant 
expelled from the bottom of the bed by this downflow is re-introduced 
along with fresh regenerant in the next up flow mixing interval. This 
sequence is continued until the required quantity of regenerating chemical 
has been passed through the bed. The same process is carried out with a 
rinse solution until the ion exchanger has been rinsed sufficiently free 
of regeneration chemical and displaced ions. The ion exchanger can then be 
placed back in service. 
A variety of up and downward flow velocities and times can be successfully 
used in this process. However, the most rapid regeneration occurs with the 
largest net volume difference between the up and down flows in the 
shortest cycle time between the up flow and down flow periods. This 
relationship can be experimentally determined for a variety of ion 
exchange materials and regenerating chemicals. As an example, in the case 
of a water softening operation within a nominal 1 inch I.D. column 
containing 1 meter of cation resin sold by Rohm and Haas under the 
tradename IR 120 being regenerated with a 4% NaCl brine solution, the 
fastest regeneration times are typically obtained with up flow velocities 
of 0.5 to 1 cm/sec with bed lifting times from 4 to 20 seconds. Down flow 
velocities are typically 3 to 10 cm/sec at times from 0.4 to 1.5 seconds. 
Practice of the current invention by (a) feeding the regenerating chemical 
and rinse streams into the exhausted ion exchanger in an upward direction 
opposite to that of the exhausting flow direction portion of the ion, (b) 
passing this stream through the ion exchanger in the form of up and down 
flows consisting of alternate up flow regenerant chemical or rinse liquid 
introduction and down flow bed re-settling, (c) designing of the up flow 
and down flow intervals and velocities so that the lifting of the bed and 
the degree of perceptible mixing is hydrodynamically controlled provides 
significant advantages over prior art. 
The present invention allows operation of a counter current ion exchange 
unit in a non-fixed unconstrained bed where the time required for 
regeneration is similar to that found in other known systems, including 
typical co-current operations, while maintaining efficient regeneration 
chemical utilization. Other systems which are known to operate at 
regeneration times similar to the present invention must employ regenerant 
chemical flow rates which, without some mechanism of bed restraint, lead 
to mixing of the ion exchange bed and therefore poor regeneration chemical 
utilization. Regeneration according to Kunz provides the efficient 
regeneration chemical utilization typical of counter current operation and 
avoids the problems associated with known restraint mechanisms but at the 
cost of intermittent flows with long pauses, or settle times which lead to 
long regeneration times. Control of the un-constrained bed according to 
the present invention permits rapid introduction of regenerating chemical 
and rinse solutions while localizing the small degree of mixing of the ion 
exchange bed to the polishing layers; thus, the present invention achieves 
the best features of the prior art and provides excellent regeneration 
chemical utilization and short regeneration time through the selection of 
appropriate combinations of controlled bed lifting and perceptible mixing 
level and net regenerant or rinse flows through the bed. 
In the present invention, only the lower or polishing layers of the column 
are allowed to mix so that no significant physical exchange of material 
between the highly exhausted layers at the top of the ion exchange bed and 
the less exhausted layers at the bottom is allowed to occur. The ion 
exchange materials in the upper 65% to 95% of the bed height remain 
substantially in the same relative layers during the regeneration process. 
As a result the concentration profile produced in the ion exchanger during 
the prior charging or exhaustion cycle remains essentially intact. As is 
known in the art, this leads to optimum utilization of regenerating 
chemical. 
The present invention maintains many of the advantages taught by Kurtz. In 
addition, like Kurtz, the ability of the present invention to operate with 
an unconstrained or non-fixed bed obviates the need for mechanical 
installations for restraining the beds such as nozzle plate systems, 
drainage systems, and the like previously required for such countercurrent 
processes. Thus, like systems using the Kurtz process, ion exchange 
systems manufactured in accordance with the present invention can be 
produced at a lower overall cost than other previously known systems.

DETAILED DESCRIPTION OF THE DRAWINGS 
FIG. 1 illustrates an ion exchange vessel 10 with hardware suitable for 
carrying out the present invention. The vessel contains an upper 
distribution system which consists of piping 12 having a distributor 14 
which contains a plurality of openings or ports (not shown) for providing 
a flow of fluid to a resin bed 16. The distributor 14 is operably 
connected via piping 12 to valves 18, 19 and 20 at the top of vessel 10. 
Vessel 10 further contains a lower distribution system which consists of 
piping 22 and a distributor 24 equivalent to that of the upper 
distribution system, with piping 22 being operably connected to valves 26 
and 25, respectively. An unconstrained ion exchange resin bed 16 is 
contained within vessel 10. 
In operation, vessel 10 operates as follows for a typical water softening 
process. 
During the exhaustion cycle, water containing hardness passes through valve 
20 into the vessel 10 through piping 12, through distributor 14, through 
the resin bed 16, down through the lower distributor 24 and out the vessel 
through piping 22 and through valve 28. When exhaustion is complete, 
valves 20 and 28 are closed. A flow of regenerating brine is introduced 
through valve 26, through the distributor 24, upwardly through the bed 16, 
through distributor 14, and out through piping 12 and valve 18 at 
velocities which cause bed lifting and perceptible mixing within the bed. 
The up flow of regenerant is continued until bed lifting and perceptible 
mixing has preceded some predetermined distance up the bed. At that point, 
a flow of water in the opposite or downward direction is introduced into 
vessel 10, through valve 19, through piping 12, through distributor 14, 
down through the resin bed 16 and out of the vessel 10 through distributor 
24, piping 22 and valve 26. This downward flow forces the bed to settle to 
essentially its original position prior to the start of the next up flow 
of regenerant. The chemical displaced from the bottom of vessel 10 during 
the down flow step is then re-introduced along with fresh regenerant 
chemical in the next up flow cycle. This above sequence is repeated until 
enough regeneration chemical has passed through the bed. The process is 
then continued with rinse water being used instead of regenerant chemical 
until enough regenerating chemical has been displaced from the bed. 
The flow of water or other solution through the device of FIG. 1 is 
controlled and monitored by any conventional means available in the art. 
In the case of FIG. 1, a conventional centrifugal pump (not shown) was 
used, but any other means may be employed, such as for example, line 
pressure. Similarly, the timing and sequencing for the up flow and down 
flow may be monitored by a conventional programmable logic controller 
(PLC) which is not shown. 
Although the down flow has been described as being generated using certain 
apparatus described above, it should be understood that any technique or 
process available to the art may be used. For example, in an alternative 
embodiment, as the initial up flow pulse exits the vessel, it enters and 
pressurizes a container called an accumulator which in turn produces the 
pressure and flow which may be used to generate the subsequent down flow 
or counterpulse. It should also be understood that down flows through only 
a portion of the bed would also be effective in creating the bed settling 
requirements of the present invention. 
FIG. 2A shows the up flow period when regenerant chemical or rinse water is 
introduced into the bed and FIG. 2B shows the down flow period used to 
resettle the bed after the bed lifting and perceptible mixing created 
during the up flow period. The arrow and arrow heads indicate the flow 
path in each figure. 
In carrying out the process of the present invention it should be 
understood that any conventional apparatus, hardware and/or control 
mechanisms which are available in the art may be used. For example, 
suitable plumbing, discharge devices, distributors, collectors, and 
related valves and control mechanisms which may be used to run and monitor 
the process of this invention, are taught by the allowed Kunz U.S. 
application and Kunz counterpart South African patent, U.S. Pat. Nos. 
4,181,605, 4,184,893 and 4,202,737, German Patent 1,352,176 to Degremont; 
and German Patent Publication DE 35 28 800 A1 published Feb. 12, 1987 to 
Eumann, all of which are exemplary of the prior art, and all of which are 
incorporated herein by reference. 
For the data presented herein, regeneration performance was described by 
the percent of stoichiometric utilization of regenerating chemical which 
is defined in the case of softening as: 
##EQU1## 
These equations describe regeneration chemical utilization as the ratio of 
chemical equivalents of regenerating chemical introduced into the ion 
exchanger during regeneration to the chemical equivalents of all ions 
displaced from the ion exchanger materials during regeneration. Therefore, 
as the percent of stoichiometric regeneration chemical utilization 
increases, the greater the excess chemical used in the regeneration 
process, with the stoichiometric (theoretical minimum) amount of 
regenerant chemical being used when the percent of stoichiometric 
regeneration chemical utilization equals 100%. 
During the regeneration and slow rinse process, the spent regenerating 
chemical and rinse solutions were accumulated and analyzed to determine 
the amount of regenerating chemical introduced and the amount of hardness 
ions displaced. For example, the spent regenerating solution would be 
tested to determine the amount of NaCl used and the amount of hardness (Mg 
and Ca ions) removed during the regeneration process. 
For a given ion exchange bed, the rate at which regeneration will proceed 
with the present invention is at an optimum when the difference between 
the up flow and the down flow volumes is at a maximum while the time for 
the cycle between the up flow and down flow periods is at a minimum. Also 
for a given ion exchange bed the percent of stoichiometric regeneration 
chemical utilization is a function of the degree of bed lifting and 
perceptible mixing allowed during the up flow portion of the process. The 
relationships for both regeneration rate and percent of stoichiometric 
regeneration chemical utilization have been determined for a vessel, as 
illustrated in FIG. 1, employing a nominal one inch column containing one 
meter of Rohm and Haas IR 120 cation resin and are presented in the 
following graphical manner: 
The data presented in the FIGS. 3, 4 and 5 was obtained using a cation 
exchange resin available from Rohm and Haas under the tradename IR 120. It 
should be understood that any suitable cation or anion exchange resin may 
be used with the present invention. For example; specific reductions to 
practice were also made with IRA 402, a Rohm and Haas anion resin. 
FIG. 3 comprises a series of curves which illustrate the relationship of 
time and velocity required to lift the bed and cause a given bed lifting 
and perceptible mixing height as a percent of total bed height. Each curve 
represents the relationship between the time and velocity required to 
obtain a specified level of bed lifting and perceptible mixing as a 
percent of total bed height. This data was obtained in the following 
manner. An up flow of 4% NaCl was introduced through valve 26 upwardly 
through the bed 16 and out through valve 18 at a given velocity between 
0.2 cm/sec and 2.0 cm/sec. This flow was maintained for a period required 
to lift and perceptibly mix the bottom of the bed to a pre-determined 
height (5 cm, 10 cm, 20 cm, 30 cm) from the bottom of the bed and the time 
required for this degree of bed lifting and perceptible mixing was 
recorded. Mixing to the height of 5 cm, 10 cm, 20 cm and 30 cm represented 
5%, 10%; 20% and 30% of bed lifting and perceptible mixing of the one 
meter (100 cm) bed, respectively. Once the up flow produced the given 
amount of bed lifting and perceptible mixing within the bed, a flow of 
water was introduced to vessel 10 in the opposite or downward direction, 
through valve 19, through the bed 16, and out through valve 26. This 
downward flow forced the bed to settle to its original position. This 
series of events was repeated for several different velocities in the 
range of 0.1 cm/sec to 2.0 cm/sec to generate the series of curves 
depicting the relationship of time and velocity required to get a given 
degree of bed lifting and perceptible mixing within the vessel. 
FIG. 4 comprises a series of curves which illustrate the net flow through 
the bed at various up flow velocities for given bed lifting and 
perceptible mixing heights as a percent of total bed height. The data for 
these curves were generated using the vessel described above and were 
obtained in the following manner. An up flow of 4% NaCl was introduced 
through valve 26 upwardly through the bed 16 and out through valve 18 at a 
given velocity between 0.2 cm/sec and 1.2 cm/sec. This flow was maintained 
for a period of time required to lift and mix the bottom of the bed to 
some predetermined height (5 cm, 10 cm, 20 cm, 30 cm, representing 
respectively 5%, 10% 20% and 30% of bed lifting and perceptible mixing of 
the one meter bed) from the bottom of the bed, as shown in FIG. 3, and the 
bed was then re-seated with a flow of water in the opposite or downward 
direction through valve 19 and out valve 26. This downward flow was just 
large enough to return the bed to its original position, before the 
introduction of the next up flow. The volume of the up and down flows were 
measured by collecting them and the difference in their volume was 
determined. The average net up flow rate through the column at each flow 
velocity during this process was calculated as follows: 
##EQU2## 
where the up flow volume was the measured volume (cm.sup.3) of the up 
flow, the down flow was the measured volume (cm.sup.3) of the down flow as 
described above; the cycle time was the up flow time in seconds plus the 
down flow time in seconds; and the net up flow rate was in cm.sup.3 /sec. 
FIG. 5 illustrates two curves which present a plot of percent of 
stoichiometric regeneration chemical utilization and regeneration time at 
given bed lifting and perceptible mixing heights as a percent of total bed 
height for one embodiment of the process. The data was generated using a 
one inch nominal I.D. column, equipped as described in FIG. 1, filled to a 
depth of one meter with IR 120 cation exchange resin from Rohm and Haas. 
The regenerations were done with three pounds of NaCl at a concentration 
of 4% by weight. The up flow velocity was held to 0.8 cm/sec with down 
flow velocities of typically 4 to 6 cm/sec. which gave maximum throughput 
(minimum regeneration times), and a series of regenerations were conducted 
as described for FIG. 1 with the degree of bed lifting and perceptible 
mixing as a percent of total bed height being 5%, 10%, 20%, and 30%. In 
each case the time required to complete the regeneration as well as the 
percent of stoichiometric regeneration chemical utilization was recorded. 
As shown by the data in FIG. 5, increasing the degree of bed lifting and 
perceptible mixing reduced the total regeneration time but caused a 
negative effect on regeneration chemical utilization (higher percent of 
stoichiometric regeneration chemical utilization). Bed lifting and 
perceptible mixing at a range significantly higher than taught by Kunz but 
limited to the first portion of the bed (10-20%) substantially reduced 
regeneration time with only a modest effect on regeneration chemical 
utilization. 
Table 1 further illustrates the difference in regeneration time and the 
percent of stoichiometric regeneration chemical utilization between a 
regeneration according to Kurtz and the present invention. This data was 
based on a bed lifting and perceptible mixing height equal to 15% of the 
total bed height for the present invention. Data for both cases describe 
the NaCl regeneration of a one meter cation exchange bed in a nominal one 
inch column. Although some small loss in regeneration chemical utilization 
versus Kunz at optimum regeneration chemical utilization is experienced 
with the present invention, a significant reduction in regeneration time 
is observed. The regeneration time for the Kunz process can be shortened 
by decreasing the settle time. However, as the Kunz regeneration time 
starts to approach that achieved by the present invention, regeneration 
chemical utilization decays rapidly, and becomes significantly poorer than 
those achievable by the present invention. 
TABLE 1 
______________________________________ 
% OF STOICHIOMETRIC 
REGENERATION 
TIME CHEMICAL 
METHOD REQUIRED UTILIZATION 
______________________________________ 
Kunz at 3.64 Hours 108% 
20 sec. 
settle time 
and no mixing 
Kunz at 2.8 Hours 108% 
15 sec. 
settle time 
and no mixing 
Kunz at 2.22 Hours 150% 
11 sec. settle time 
and no mixing 
CURRENT 1.8 Hours 112% 
INVENTION 
at 15% 
bed lifting and 
perceptible mixing 
______________________________________ 
While the invention has been described in detail with respect to specific 
embodiments thereof, it will be understood by those skilled in the art 
that variations and modifications may be made without departing from the 
essential features thereof.