Process for internal regeneration of ion exchanger resins in mixed bed filters, and mixed bed filters for carrying out the process

The invention relates to a process for internal regeneration of mixed bed filters in which, after the exhausted ion exchanger mass has been separated into the two components and these have been regenerated and washed out, the exchanger layer in the region of the cation exchanger/anion exchanger interface is selectively removed from the mixed bed filter, the cation exchanger remaining in the filter is mixed with the anion exchanger remaining in the filter for the new loading stage, the ion exchanger mass removed from the filter is added again, when the work cycle has ended, to the exhausted ion exchanger mass before or during the separation into cation exchanger and anion exchanger, and, after the separation, the loading stage is started again with the regeneration of the cation exchanger and anion exchanger; and also to a mixed bed filter for carrying out the process.

The invention relates to a new process for internal regeneration of 
exhausted cation and anion exchanger resins in mixed bed filters, and a 
mixed bed filter for carrying out the process. 
Mixed bed filters are ion exchanger filters filled with cation exchangers 
and anion exchangers. During the loading operation, the cation exchangers 
and anion exchangers are in the form of an intimate mixture. For 
regeneration of the loaded exchanger, the mixed bed is separated 
hydraulically into the cation exchanger and anion exchanger on the basis 
of the different specific gravities of these two components, and in 
particular into a lower layer of the cation exchangers of higher specific 
gravity and a lower layer of the anion exchangers of lower specific 
gravity. After the separation, the cation exchanger and anion exchanger 
are regenerated separately and washed out. 
Mixed bed filters are known and, since effective demineralisation can be 
achieved with them, are also frequently used in practice. However, mixed 
bed filters have the serious disadvantage that regeneration of the 
exhausted ion exchangers presents considerable difficulties because only 
incomplete sorting of the mixed bed into cation exchanger and anion 
exchanger is possible. The imcomplete separation into cation exchanger and 
anion exchanger has the result that, when the cation exchanger is 
regenerated, the anion exchanger particles contained therein become loaded 
with the regenerating agent intended for the cation exchanger, and when 
the anion exchanger is regenerated, the cation exchanger particles 
contained therein become loaded with the regenerating agent intended for 
the anion exchanger. 
In the case of mixed bed filters with internal regeneration, the 
mis-loading of cation and anion exchangers caused by the incomplete 
separation is accompanied by unavoidable mis-loading of the ion exchanger 
components close to the cation exchanger/anion exchanger interface as a 
result of penetration of the regenerating agent of the one component into 
the layer of the other component. 
In the loading stage, the mis-loading leads to a reduction of the quality 
of the liquid treated; in addition, mis-loading is one reason why only 
disproportionately low operating capacities are achieved with mixed beds. 
To avoid mis-loading by penetration of the regenerating agent for the one 
component into the layer of the other component and the reduction in the 
quality of the treated liquids and reduction in the operating capacity 
thereby caused, it has been proposed to carry out the regeneration not 
internally, that is to say in the mixed bed filter itself, but externally, 
that is to say in separate vessels outside the mixed bed filter. In this 
external regeneration, the exchanger mass is conveyed hydraulically from 
the mixed bed filter into a separating column. The two components are 
separated in this column by backwashing. After the one of the components 
has been transferred to a third vessel, each of the two components is 
regenerated and washed out by itself. The two components are then conveyed 
back into the mixed bed filter and mixed there for the next loading stage. 
Although penetration of the regenerating agent for the one component into 
the layer of the other component and the mis-loading caused by this 
penetration are avoided by external regeneration, mis-loading of the ion 
exchangers as a result of incomplete separation into cation exchanger and 
anion exchanger and the consequences of this mis-loading (low operating 
capacity and unsatisfactory quality of the liquid treated) are not 
avoided. Contamination of the particular ion exchanger component by 
particles of the opposite component is, of course, highest close to the 
cation exchanger/anion exchanger interface. It has therefore been proposed 
(see, for example, German Auslegeschrift No. 2,631,414; British Patent 
Specification No. 1,498,139), in order to reduce the mis-loading, and 
consequences thereof, caused by incomplete separation, also to separate 
off, after the one component, for example the cation exchanger, has been 
discharged, the mixed resin zone remaining between the two components 
after external separation of the mixed bed into cation exchanger and anion 
exchanger, and not to utilise this zone in the regeneration process, but 
to store it in a separate container and to add it again only to the spent 
mixed bed of the next work cycle before the separation into cation, 
exchanger and anion exchanger. 
Mis-loading is largely avoided with the aid of this special process for 
external regeneration of ion exchangers in mixed bed filters, and as a 
result substantial improvement in the operating capacity and the quality 
of the treated liquid is achieved, in comparison with the operating 
capacity and quality of the treated liquid which are obtained with mixed 
bed filters with internal regeneration. Nevertheless, these special 
processes, for example the process described in German Auslegeschrift 
2,631,414, have found only very restricted application, because, in fact, 
the processes and the devices necessary to carry them out are much too 
expensive. 
Addition to the ion exchanger mass of a resin which does not participate in 
the ion exchange and which interposes itself between the anion exchanger 
and the cation exchanger on sorting has been proposed as another measure 
for improving the operating capacity of mixed bed filters with internal 
regeneration and the quality of the liquids treated with them (see, for 
example, German Patent Specification No. 971,771; and U.S. Pat. No. 
2,666,741). Immediate contact between the cation exchanger and anion 
exchanger is intended to be avoided by these separating layer resins. If 
the outlet for the regenerating agent streams is placed in this 
intermediate layer of inert resin, the danger of penetration of the 
individual regenerating agent solutions into the opposite component is 
certainly reduced. However, the incomplete sorting and the mis-loading 
caused thereby cannot be improved by the use of the separating layer 
resins. Rather, the introduction of a third inert component also has the 
disadvantage that the ion exchanger mass is diluted by the volume content 
of the third component (about 20%), and the operating volume capacity of 
the mixed bed filter is thus further reduced. In addition, the separation 
boundaries for cation exchanger/separating resin and anion 
exchanger/separating resin are less sharply defined than the boundary 
between the two ion exchangers in the two-component system, because the 
difference in specific gravity between the inert resin and the particular 
ion exchanger is only half the difference between the two ion exchangers. 
A change in specific gravity even of only one of the three components, as 
frequently occurs in operation in practice, or a change in the particle 
size, for example by abrasion, therefore leads directly to insufficient 
separation of ion exchanger and inert resin. This means, however, that the 
volume of the one exchanger component is increased by the volume of the 
inert resin, and that the separation boundary with respect to the other 
exchanger component is in this way displaced to above or below the central 
drainage originally located in the middle of the layer of the separating 
resin. This, however, is an even more adverse situation than already 
exists in the simple mixed bed filters. The property of the separating 
resins of tending to float when air is blown into the mixed bed also leads 
to further complications. The intended effect of the separating resins as 
an intermediate layer is lost by this floating. 
This means that even with the aid of separating layer resins, the technical 
problem of eliminating or at least reducing the difficulties which occur 
during regeneration in mixed bed filters with internal regeneration and 
thereby of achieving a higher operating capacity and an improved quality 
of the liquid treated, cannot be solved. 
It has now been found that the technical problem described above can be 
solved in a surprisingly simple manner if, in mixed bed filters with 
internal regeneration, after separation of the exhausted resin mass into 
cation exchanger and anion exchanger and regeneration and washing out of 
the two components, the exchanger layer in the region of the cation 
exchanger/anion exchanger interface is removed from the filter in 
particular selectively and without the adjacent ion exchanger layers being 
whirled, only then the cation exchanger remaining in the filter is mixed 
with the anion exchanger remaining in the filter for the loading stage, 
the loading stage is carried out, the ion exchanger mass removed from the 
filter is added to the exhausted ion exchanger mass before or during the 
separation into the components and, when the separation has ended, the 
work cycle is started again with regeneration of the cation exchanger and 
anion exchanger. 
In mixed bed filters with internal regeneration, the central drainage is 
necessarily in or in the immediate vicinity of the cation exchanger/anion 
exchanger interface, since any displacement from the interface into one of 
the components leads to increased mis-loading of these components by the 
regenerating agent for the opposite component. Therefore for mixed bed 
filters with internal regeneration, the phrase "in the region of the 
cation exchanger/anion exchanger interface" means the same as the phrase 
"in the region of the central drainage". 
The ion exchanger layer removed from the filter consists of a mixture of 
cation exchanger and anion exchanger which essentially contains all of the 
mis-loaded cation exchanger and anion exchanger. 
By the removal, according to the invention, of this ion exchanger layer in 
the region of the cation exchanger/anion exchanger interface (=in the 
region of the central drainage), no mis-loading, but only completely 
regenerated cation exchanger and anion exchanger participate in the 
loading stage. The operating capacity of the mixed bed filter is thus 
decisively increased and the quality of the treated liquid is 
substantially improved. 
The invention thus relates to a process for internal regeneration of mixed 
bed filters in which the separation of the exhausted ion exchanger mass of 
the mixed bed into cation exchanger and anion exchanger is carried out by 
means of upward-flowing liquid and the cation exchanger and anion 
exchanger are regenerated and washed out, which is characterised in that, 
after separation of the exhausted ion exchanger mass and regeneration and 
washing out of the two components, the ion exchanger layer in the region 
of the cation exchanger/anion exchanger interface is selectively removed 
from the mixed bed filter without the adjacent ion exchanger layers being 
whirled, the cation exchanger remaining in the filter is mixed with the 
anion exchanger remaining in the filter for the new loading stage, the ion 
exchanger mass removed from the filter is again added, when the loading 
stage has ended, to the exhausted ion exchanger mass before or during 
separation into cation exchanger and anion exchanger and, when the 
separation has ended, the work cycle is started again with regeneration of 
the cation exchanger and anion exchanger. 
The ion exchanger layer to be removed, according to the invention, from the 
mixed bed filter is transferred to a separate storage vessel. From there, 
it is added again to the ion exchanger remaining in the mixed bed filter 
before or during the separation, if necessary after rinsing to remove fine 
portions and/or after addition of new ion exchanger as a replacement for 
fines and/or other similar special treatments. It is essential that the 
ion exchanger mass to be removed, according to the invention, from the 
mixed bed filter participates, together with the mixed bed mass remaining 
in the filter, in the separation operation and in the regeneration 
operation which follows the separation into cation exchanger and anion 
exchanger, before it is removed again, as described, before mixing of the 
cation exchanger and anion exchanger for the loading stage. 
The thickness of the resin layer to be removed according to the invention, 
from the region of the cation exchanger/anion exchanger interface (=the 
region of the central drainage), depends on the sharpness of the cation 
exchanger anion exchanger separation boundary; the sharper the separation 
boundary, the lower can be the thickness of the layer of resin to be 
removed. Conversely, the more indistinct the separation boundary, the 
greater must be the thickness of the resin layer to be removed. 
Apart from depending on the difference between the specific gravities of 
the cation exchanger and the anion exchanger, the sharpness of the 
separation boundary particularly depends on the uniformity of the 
distribution of liquid during the hydraulic separation, the regeneration 
and the washing out. Since, according to the invention, even thick layers 
of resin can be removed without problems from the region around the 
central drainage, the process according to the invention does not depend 
on whether sharp or not so sharp separation of the cation exchanger from 
the anion exchanger is achieved and hence also does not depend on the 
distribution of the liquid in the filter or on mistakes by the operating 
personnel. The process according to the invention gives constantly good, 
reproducible results, independently of the sharpness of the cation 
exchanger/anion exchanger separation boundary, if the thickness (D) of the 
resin layer to be removed from the mixed bed filter is appropriately 
chosen in size. The most advantageous thickness for a specific case is 
determined empirically. 
In general, it has proved appropriate for the thickness (D) (see FIG. 1), 
in the filter, of the resin layer to be removed to be 100 to 500 mm, that 
is to say in each case 50 to 250 mm above and below the central drainage, 
preferably 200 to 400 mm, that is to say in each case 100 to 200 mm above 
and below the central drainage. 
Removal of the ion exchanger layer in the region of the cation 
exchanger/anion exchanger interface can be effected in a particularly 
simple manner by hydraulic conveying. Surprisingly, it has been found 
that, in the hydraulic conveying proposed according to the invention, no 
whirling of the ion exchanger layers adjacent to the resin layer to be 
removed occurs. 
The uniform non-whirling conveying, required for the process according to 
the invention, of the particular resin layer from the region of the 
central drainage can be achieved, for example, hydraulically by inserting 
vertically into the layered ion exchanger mass of the mixed bed filter as 
many ascending tubes (9) as are required such that the distance between 
the ascending tube and the filter wall or, in the case of several 
ascending tubes, between the ascending tubes and the filter wall and 
adjacent ascending tubes is about the same and does not exceed certain 
values, and the ascending tube(s) (9) is/are inserted into the ion 
exchanger mass to a depth such that the end(s) of the ascending tube(s) in 
the ion exchanger mass is/are in the lower boundary surface, if hydraulic 
pressure is conveyed from the top, or in the upper boundary surface, if 
hydraulic pressure is conveyed from the bottom, of the ion exchanger layer 
(7) to be removed from the filter. In order to achieve technically 
reasonable flow rates of about 0.1 to 3 m/second, preferably 0.4 to 2 
m/second, in the ascending tube (9) or the ascending tubes (9), the ratio 
of free filter cross-section to free cross-section of the ascending tube 
or, in the case of several ascending tubes, to the sum of the free 
cross-sections of the individual ascending tubes, should be about 300:1 to 
500:1. 
Hydraulic conveying of ion exchangers from ion exchanger filters, for 
example mixed bed filters, is known per se. However, in this known 
hydraulic conveying, the ascending tubes or ascending tube are/is inserted 
down to the bottom of the filter and the ion exchanger mass is forced out 
of the filter in its entirety, without paying attention to whirling. The 
hydraulic conveying according to the invention differs from this known 
hydraulic conveying in that a specific intermediate layer is thereby 
removed selectively from the ion exchanger mass without whirling of the 
ion exchanger mass adjacent to this intermediate layer. 
The invention thus also relates to a mixed bed filter with internal 
regeneration for carrying out the claimed process. This mixed bed filter 
according to the invention is characterized in that it consists of a 
filter apparatus which is customary for mixed bed filters with internal 
regeneration, e.g. a container equipped with dosable liquid feed and 
outflow lines, the cylindrical section of this container being closed at 
the bottom by a device which is permeable to liquid, on which the ion 
exchanger mass consisting of cation exchanger and anion exchanger rests 
and in which there is a central drainage at the level of the theoretical 
cation exchanger/anion exchanger interface, which filter apparatus is 
equipped by a device providing for the selective removal from the filter 
of the ion exchanger layer in the region of the cation exchanger/anion 
exchanger interface without the adjacent ion exchanger layers being 
whirled. 
An especially simple and effective device for the selective removal of the 
ion exchanger layer in the region of the cation exchanger/anion exchanger 
interface from the filter is provided by one or more ascending tube(s) 
inserted vertically into the ion exchanger mass and connected to a storage 
vessel, the opening(s) of this (these) tube(s) dipping into the ion 
exchanger mass being in the lower or upper interface of the resin layer to 
be conveyed out of the filter, depending on whether the liquid for the 
hydraulic conveying is passed into the filter from the top or from the 
bottom, this (these) ascending tube(s) being arranged uniformly in the 
cross-section of the filter such that the distance(s) (a) between the 
ascending tube(s) (centre of the tube) and the filter wall do(es) not 
exceed a certain value, the value of 400 mm, and-in the case of several 
ascending tubes-the distances of the individual ascending tubes from one 
another, which are optionally different, do also not exceed a certain 
value, the value of 800 mm. 
The distance(s) between the ascending tube (centre of the tube) and the 
filter wall is (are) preferably 150 to 300 mm; the distances between 
ascending tube (centre of the tube) and ascending tube (centre of the 
tube), which are optionally different, are preferably 300 to 600 mm. 
The internal diameter of the ascending tubes is advantageously 10 to 50 mm, 
preferably 10 to 25 mm. 
It has proved appropriate to match the distance (a) between the ascending 
tube (centre of the tube)/container wall and the thickness (D) of the 
resin layer to be removed, according to the invention, from the region of 
the central drainage with one another, and in particular such that the 
ratio a:D is at most 4:1, preferably 2:1 to 1:1. 
The resin layer to be removed from the region of the central drainage is 
preferably conveyed through ascending tubes inserted vertically into the 
resin mass from the top (see FIGS. 1 and 3). A preferred embodiment of the 
mixed bed filter according to the invention is shown schematically in 
FIGS. 1, 2 and 3. In this embodiment the mixed bed filter according to the 
invention consists of a container (1) equipped with closable liquid feed 
and outflow lines (2) and (3), the cylindrical section of this container 
being closed at the bottom by a device (4) which is permeable to liquid, 
for example a nozzle tray, on which the ion exchanger mass consisting of 
cation exchanger (5) and anion exchanger (6) rests; in which there is a 
central drainage (8) at the level of the theoretical cation 
exchanger/anion exchanger interface (=level of the cation exchanger 
filling), and which is provided with one or more ascending tube(s) (9) 
inserted vertically into the ion exchanger mass and connected to a storage 
vessel (10) the opening(s) of this these tube(s) (9) dipping into the ion 
exchanger mass being in the lower or upper interface of the resin layer 
(7) to be conveyed out of the container (1), depending on whether the 
liquid for the hydraulic conveying is passed in from the top, that is to 
say through line (2), or from the bottom, that is to say through line (3), 
and in which the ascending tube(s) (9) is/are arranged uniformly in the 
cross-section of the container (1) such that the distance/distances (a) 
between the ascending tube (centre of the tube) and the container wall 
do(es) not exceed the value of 400 mm and-in the case of several ascending 
tubes (9)-the distances of the individual ascending tubes (9) from one 
another, which are optionally different, do not exceed the value of 800 
mm. 
the process according to the invention and the operation of the mixed bed 
filter according to the invention may be illustrated with the aid of the 
mixed bed filter according to the invention, shown schematically in FIG. 
1: 
Step A (filling of the filter and regeneration of the ion exchanger): 
The space between the lower nozzle tray (4) and the central drainage (8) in 
the container (1) is filled with cation exchanger (5). A layer of anion 
exchanger (6) is introduced on the cation exchanger (5). Each of the two 
components is then regenerated separately. For this, the regenerating 
agents for the two components can be passed through the components in 
different directions: in cocurrent from the top downwards; in this case, 
the regenerating agent for the anion exchanger, that is to say the 
regenerating base, is fed in through line (2) and taken off through the 
central drainage (8), and the regenerating agent for the cation exchanger 
(5), that is to say the regenerating acid, is fed through the central 
drainage (8) and taken off through line (3); or in countercurrent; in this 
case, the regenerating base is fed in through line (2) and the 
regenerating acid is fed in through line (3) and the regenerating agents 
flowing out are taken off together at the central drainage (8). After 
regeneration, washing out of the ion exchangers is carried out in the same 
manner as the regeneration. 
Step B (removal, according to the invention, of the resin layer (7) in the 
region of the central drainage (8): 
(a) In the case of hydraulic conveying of the resin layer (7) by pressure 
from the top onto the ion exchanger mass; feeding in of the liquid 
effecting conveying, through line (2); in this method of conveying, the 
end of the ascending tube (9) dipping into the ion exchanger mass is in 
the lower boundary surface of the resin layer (7) to be removed from the 
filter. When washing out of the two components (5) and (6) has ended, 
liquid is forced into the container (1) through line (2), with valve (13) 
closed and valve (11) open. The anion exchanger layer (6) falls to the 
same extent as the resin layer (7) is conveyed through the ascending tube 
(9) into the storage vessel (10). As soon as the resin layer (7) has 
disappeared, the feed of liquid through (2) is ended by closing valve 
(12). At the same time, valve (11) is also closed. 
(b) Innstead of being conveyed by pressure from the top, the resin layer 
(7) can also be conveyed to the storage vessel (10) by pressure from the 
bottom via ascending tube (9). In this conveying method, the end of the 
ascending tubes (9) dipping into the ion exchanger mass is in the upper 
boundary surface of the resin layer (7) to be removed from the filter. In 
this case, liquid is forced through line (3) into the container (1), with 
valve (12) closed and valve (11) open, until the layer of resin (7) is in 
the storage vessel (10). 
Conveying according to (a) is preferred, that is to say by pressure of 
liquid from the top. 
When the resin layer (7) has been removed from the container (1) and the 
ion exchangers remaining in the container (1) have been mixed by blowing 
in air, the regeneration stage has ended and the loading stage (step C) 
starts. 
Step C (loading stage): 
The liquid to be treated enters the container (1) through line (2), flows 
through the mixed bed built up in step B from the top downwards and leaves 
the container (1) as worked-up liquid via line (3). 
Step D (recycling of the resin layer (7) removed from the region of the 
central drainage (8) in step (B): 
When the loading stage (step C) has ended, valve (11) is opened and the 
resin in the storage vessel (10) is recycled into the container (1) 
through the ascending tube (9) and is there subjected to separation and 
regeneration (step E) together with the exhausted ion exchanger mass of 
the mixed bed. 
Recycling of the resin mass in the storage vessel (10) can also be effected 
during the separation (sorting) of the exhausted ion exchanger mass of the 
mixed bed. 
Step E (separation and regeneration of the resin mass exhausted in the 
loading stage (step C) and of the resin mass recycled from the storage 
vessel (10)): 
The exhausted resin mass of the mixed bed and the resin mass recycled from 
the storage vessel (10) are separated by backwashing in an 
upwards-directed stream of liquid, that is to say by passing in liquid 
through line (3), into the cation exchanger (5) and an ion exchanger (6). 
Each of the two components, which are again in separate layers, is then 
regenerated separately as described in step (A). The regeneration is again 
ended with step B (transfer of the resin layer (7) into the storage vessel 
(10). 
The resin layer (7) to be removed, according to the invention, from the 
filter should essentially contain all the mis-loaded cation exchanger and 
anion exchanger. The thickness (D), required to achieve this aim, of the 
resin layer (7) symmetrically surrounding the central drainage (8) is 
determined empirically. The distance (d) which the bottom end of the 
ascending tubes (9) must be from the central drainage (8) is given by the 
required thickness (D). This distance (d) is D/2. Depending on whether 
conveying is effected with pressure from the top or from the bottom, the 
end of the ascending tubes (9) dipping into the ion exchanger mass is at a 
distance (d) of D/2 either below or above the central drainage (8). The 
desired thickness (D) of the resin layer (7) to be removed from the region 
of the central drainage (8) can be adjusted particularly easily if the 
ascending tubes (9) are adjustable in length. 
The storage vessel (10) is advantageously closed at the top by a device 
which is permeable to liquid but impermeable to ion exchanger. This device 
enables liquid to be drawn off continuously from the storage vessel, 
without ion exchanger also being discharged. 
The disappearance of the resin layer (7) during transfer into the stock 
vessel (10) can be monitored, for example, by the falling of the upper 
edge of the anion exchanger (6) in the viewing glass (14) (see FIG. 2) or 
by the volume of resin conveyed into the storage vessel (10). Monitoring 
of the volume of resin conveyed into the storage vessel (10) can be 
effected particularly easily if the storage vessel (10) is designed as a 
measurement vessel. The amount, that is to say also the thickness (D) of 
the resin layer (7) conveyed, is given directly by the volume of resin 
conveyed. 
The resin layer (7) conveyed into the storage vessel (10) can be recycled 
through ascending line (9). However, recycling can also be effected by a 
separate recycling line (15) (see FIG. 3). 
A further advantageous embodiment of the mixed bed filter according to the 
invention can consist in a funnel-like widening of the bottom end of the 
ascending tubes (9) intended for removal, according to the invention, of 
the resin layer (7). The resin layer (7) can be drawn off particularly 
uniformly with the aid of this/these ascending tube(s) (9) widened in a 
funnel-like manner. The cross-section of the funnel-like widening of the 
ascending tube is advantageously 2 to 10 times, preferably 4 to 6 times, 
one cross-section of the ascending tube. 
Apart from the advantages of higher operating capacity and improved quality 
of the treated liquid which have already been mentioned, the process 
according to the invention offers the following advantages: 
In the procedure of the process according to the invention, the full volume 
capacity of the mixed bed fillings is retained and the difference in 
acidic gravity of the cation exchanger and anion exchanger is fully 
utilised. Furthermore, a substantially improved utilisation of the 
regenerating agents and hence a substantial reduction in the consumption 
of regenerating agents is achieved with the aid of the process according 
to the invention. This improved utilisation is caused on the one hand by 
the fact that, in the process according to the invention, the layer 
heights of the two components are always great enough for efficient 
regeneration. The improved utilisation of regenerating agent is caused on 
the other hand by the fact that the ion exchanger mass removed from the 
filter is essentially in regenerated form. Since the cation exchanger has 
a lower specific gravity in the H form than in the form loaded with metal 
cations, this regenerated cation exchanger forms, after the separation, 
the top zone of the cation exchanger layer, through which the regenerating 
agent flows through last, whilst the exhausted cation exchanger forms the 
bottom zone of the cation exchanger layer, through which the regenerating 
agent flows through first. This zoning of the cation exchanger during 
regeneration leads to a particularly complete regeneration of the loaded 
cation exchanger and to a particularly good utilisation of the 
regenerating agent. 
In the process according to the invention, the cation exchanger and the 
regenerating agent for the anion exchanger can be passed through the layer 
of ion exchanger in question either in the same direction, e.g. both from 
the top downwards or both from the bottom upwards, or in opposite 
directions to each other. In the process according to the invention, it is 
particularly advantageous to pass the two regenerating agents in opposite 
directions to each other. In this procedure, the regenerating agent for 
the anion exchanger is fed in from the top, and taken off at the central 
drainage together with the cation exchanger regenerating agent, which is 
fed in from the bottom. Since the regenerating chemicals become spent on 
flowing through the two exchanger layers, their regenerating action is 
lowest after flowing through the exchanger layers, that is to say in the 
region of the central drainage. Since, according to the invention, 
precisely this ion exchanger mass in the region of the central drainage is 
removed, participation of insufficiently regenerated exchanger in the 
loading stage is prevented. This leads to an increase in the total 
capacity of the mixed bed filter and to a reduction in the slipping of 
ions during demineralisation, that is to say to an increase in the quality 
of the liquid treated. 
This advantageous embodiment of the process according to the invention is 
of particular importance for reducing displacement slips if the mixed bed 
is operated not only in the H/OH form but, as is usual for the 
purification of ammoniacal condensates, also in the NH.sub.4 /OH form. The 
ammonia contained in the condensate has the effect of displacing the 
cations and anions, especially the Na.sup.+, Cl.sup.- and SO.sub.4.sup.-- 
ions, which may still remain in the mixed bed after regeneration. 
The smaller the number of these ions which remain on the two components 
after regeneration, the smaller also the displacement slip. 
A further advantage of the process according to the invention is that not 
only is the consumption of regenerating agent reduced, but also the amount 
of water required for washing out the excess regenerating agent is 
reduced, since washing out of the ion exchanger mass in the region of the 
central drainage can be shortened; during hydraulic removal, this ion 
exchanger mass is in any case rinsed and moreover does not participate in 
the loading stage.

EXAMPLE 1 
A mixed bed filter constructed according to FIG. 1 is used. The container 
(1) has a diameter of 800 mm, its free internal cross-section is 0.5 
m.sup.2, and its cylindrical height, measured from the bottom nozzle tray 
(4), is 4,000 mm. The central drainage (8) is located at a distance of 
1,000 mm from the bottom nozzle tray (4). Container (1) is equipped with 5 
ascending tubes (9) (internal diameter: 15 mm) which are uniformly divided 
over the container cross-section, dipped into the ion exchanger mass from 
the top and are adjustable in the depth to which they dip in. 
The filter column (1) is filled with 500 liters of strongly acid cation 
exchanger in the Na form (specific gravity: 1.24) and 500 liters of 
strongly basic anion exchanger in the Cl form (specific gravity: 1.08). 
Demineralised water containing 1 ppm of Na ions, 1.5 ppm of Cl ions and 
0.04 ppm of SiO.sub.2 and having a conductivity of 5 .mu.S/cm is used for 
loading the regenerated mixed bed. 
For the regeneration, 120 g of HCl (100% strength) in the form of 6% 
strength aqueous HCl/liter of cation exchanger and 120 g of NaOH (100% 
strength) in the form of 4% strength aqueous NaOH/liter of anion exchanger 
are passed through the ion exchanger in question, in each case from the 
top downwards. The sodium hydroxide solution which drains out of the anion 
exchanger is taken off at drainage (8) and the aqueous hydrochloric acid 
which drains out of the cation exchanger is taken off at valve (13). 
After the regeneration, each ion exchanger is washed out until the 
conductivity of the wash water flowing out is only 10 .mu.S/cm. (Total 
amount of wash water required: 8,500 liters). 
From the region of the central drainage (8), a layer of resin of defined 
thickness D given in Table 1 (1/2 D above and 1/2 D below the cental 
drainage) is conveyed hydraulically through tube (9) into the stock vessel 
(10), which is designed as a measuring vessel. The conveying rate in the 
ascending tubes (9) is 1 m/second. 
The cation exchanger and anion exchanger remaining in the filter are mixed 
by bubbling in compressed air in a known manner. The mixed bed is loaded 
with the demineralised water described above, at a rate of 40 m.sup.3 
/hour (flow direction: from the top downwards). After an operating time of 
half an hour, the residual amounts of sodium and chloride ions remaining 
in the water draining out of the mixed bed and the conductivity of the 
water are determined. The residual values (in ppb) and conductivities (in 
.mu.S/cm) found are likewise shown in Table 1. To determine the capacity 
of the mixed bed, the total amount of water which can be passed through 
the mixed bed before the conductivity in the water draining out has risen 
to 0.5 .mu.S/cm is measured. These amounts of water (in bed volumes of 
mixed bed) are also shown in Table 1. 
TABLE 1 
______________________________________ 
Residual values 
D* Na Cl Conductivity 
Total throughput 
[mm] [ppb] [.mu. S/cm] [BV-MB]** 
______________________________________ 
0 5 6 0.15 4,100 
100 4 7 0.10 4,400 
200 0.8 1 0.06 4,900 
300 0.5 0.6 0.054 5,100 
400 0.5 0.5 0.056 5,150 
______________________________________ 
*D = thickness of the layer of resin removed from the region of the 
central drainage 
**BVMB = bed volumes of mixed bed 
When the mixed bed is exhausted, the ion exchanger mass stored in the 
storage vessel (10) is recycled into the container (1) via line (9). The 
combined ion exchanger mass is separated into the cation exchanger and 
anion exchanger by a stream of liqid entering through line (3), and is 
regenerated again with the stated amounts of hydrochloric acid and sodium 
hydroxide solution. 
EXAMPLE 2 
The procedure described in Example 1 is followed; however, in deviation 
from Example 1, the ion exchangers are regenerated with only 60 g of HCl 
(100% strength)/liter of cation exchanger and 60 g of NaOH (100% 
strength)/liter of anion exchanger. 
The results obtained after regeneration with the smaller amount of 
regenerating agent are summarised in Table 2. 
TABLE 2 
______________________________________ 
Residual values 
T Na Cl Conductivity 
Total throughput 
[mm] [ppb] [.mu. S/cm] [BV-MB] 
______________________________________ 
0 22 25 0.27 2,900 
100 20 25 0.18 3,050 
200 1.5 2 0.09 3,280 
300 0.5 0.7 0.06 4,220 
400 0.5 0.7 0.058 4,700 
______________________________________ 
EXAMPLE 3 
The procedure followed is as described in Example 2, with the only 
difference that the acid solution is passed through the cation exchanger 
from the top and the sodium hydroxide solution is passed through the anion 
exchanger from the bottom, and the two regenerating agents draining out 
are removed together through the central drainage (8). Washing out of the 
regenerating agents is carried out in the same direction as the 
regeneration, in particular in Experiment (a) until the conductivity value 
in the liquid draining from the central drainage (8) is 30 .mu.S/cm 
(amount of wash water required: 8,000 liters) in Experiment (b) until the 
conductivity value in the liquid draining from the central drainage (8) is 
150 .mu.S/cm (amount of wash water required 3,000 liters). The results 
obtained after regenerating in the manner described are summarised in 
Tables 3a and 3b. 
TABLE 3a 
______________________________________ 
Residual values 
D Na Cl Conductivity 
Total throughput 
[mm] [ppb] [.mu. S/cm] [BV-MB] 
______________________________________ 
0 15 19 0,20 3500 
100 11 15 0,15 3750 
200 1,2 1,5 0,07 4020 
300 0,4 0,7 0,058 4300 
400 0,4 0,6 0,056 4900 
______________________________________ 
TABLE 3b 
______________________________________ 
Residual values 
D Na Cl Conductivity 
Total throughput 
[mm] [ppb] [.mu. S/cm] [BV-MB] 
______________________________________ 
0 25 35 0.29 2,200 
100 22 32 0.26 2,500 
200 10 15 0.20 2,900 
300 1.5 2 0.08 4,000 
400 0.8 1 0.06 4,500 
______________________________________ 
EXAMPLE 4 
The procedure followed is as described in Example 1; however, instead of 
the demineralised water used in Example 1, a completely demineralised 
water containing 0.8 mg of NH.sub.3 /liter and 0.015 mg of Na ions/liter 
and having a pH value of 9.3 is used. 
In this demineralisation experiment, the sodium concentration in the water 
draining out of the mixed bed filter is determined. The release of sodium 
ions from the mixed bed filter is a result of converting the cation 
exchanger into the ammonium form by the loading water. The sodium slip 
which occurs, that is to say the amount of sodium displaced by the 
ammonia, is a measure of the degree of mis-loading and regeneration of the 
cation exchanger. 
The sodium concentrations found in the runnings (in ppb) are shown in Table 
4. 
TABLE 4 
______________________________________ 
Residual value at the time 
D of the NH.sub.3 breakthrough 
[mm] Na [ppb] 
______________________________________ 
0 35 
100 25 
200 10 
300 3 
400 1 
______________________________________ 
The data in Table 4 show that if the thickness D of the ion exchanger layer 
(7) removed from the region of the central drainage is sufficient, 
virtually no ion slip now occurs. 
EXAMPLE 5 
The procedure followed is as described in Example 1, except that the resin 
layer (7) of defined thickness D is discharged from the region of the 
central drainage (8) into the storage vessel (10) not by pressure on the 
ion exchanger mass from the top but by pressure from the bottom. In this 
case, the water used for the conveying enters through tube (3). The ends 
of the ascending tubes (9) are at the top boundary surface of the resin 
layer (7) to be removed from the filter. The conveying rate in the 
ascending tubes (9) is 2.5 m/second. 
The change in direction of the conveying water feed leads to no change in 
the properties of the mixed bed during the loading stage. Rather, the same 
residual values, conductivity values and total throughputs as shown in 
Table 1 in Example 1 are achieved for the individual layer thicknesses D. 
EXAMPLE 6 
The procedure followed is as described in Example 1, with the only 
difference that the ascending tubes (9) are inserted into the ion 
exchanger mass not from the top but, as shown in FIG. 2, from the bottom 
and the resin layer (7) of defined thickness D to be removed from the 
region of the central drainage (8) os conveyed into a storage vessel (10) 
below the container (1), and in particular in experimental series (a) by 
hydraulic pressure from the top and in experimental series (b) by 
hydraulic pressure from the bottom. In experimental series (a), the ends 
of the ascending tubes (9) dipping into the ion exchanger mass were in the 
bottom boundary surface of the resin layer (7) to be conveyed out of the 
container (1); the flow rate in the ascending tubes (9) was 1 m/second. In 
experimental series (b), the ends of the ascending tubes (9) dipping into 
the ion exchanger mass were in the top boundary surface of the resin layer 
(7) to be conveyed out of the container (1). The flow rate in the 
ascending tubes (9) was 2.5 m/second. 
The change in direction in which the resin layer (7) removed from the 
region of the central drainage (8) was conveyed out of the container (1) 
resulted in no change at all in the properties of the mixed bed during the 
loading stage. Rather, the same residual values, conductivity values and 
total throughputs as given in Table 1 in Example 1 were achieved for the 
individual layer thickness D.