FR2482476A1 - Regeneration ion exchange resins with brine - involves recycling part of brine to a brine saturation vessel - Google Patents

Abstract

The process in which brine is passed from a concn. station through the bed is characterised in a region of salt saturation at the concn. station, in discarding the initial effluent from the regeneration and in returning the later effluent to the concn. station to concentrate it. It is carried out in an appts. comprising a saturation salt bed in a concn. vessel, means to start and stop the fresh brine circulation and the return brine flow, and means to control the brine level in the vessel. The process preserves the amt. of brine used, enables less appts. to be used and it is also simpler.

Description

 The present invention relates to the regeneration of ion exchange resins in the presence of brine and more especially, the conservation of salt by predetermined recycling of the brine.

 The recovery of the brine used to regenerate ion exchange resins is an accepted procedure. However, as is commonly done, this recovery imposes constraints on equipment and technique which prohibit this practice and limit the resulting savings. The use of more than one brine tank is classic, whether or not it is a special attempt to recover the brine. Examples are described in US Patents NO 2,689,218 (see Figure 1), NO 3,977,968 (see Figure 2) and in the document entitled "Demineralization by Ion Exchange" (see page 44) by "Applebaum-Academic Press", 1968.

The main object of the present invention is to conserve salt during the regeneration of ion exchange resins in the presence of brine, to simplify the regeneration of ion exchange resins with recovered brine and to reduce the need for equipment for ensure the regeneration of ion exchange resins by a recovered brine.

The object of the invention is also to carry out the above operations using a single brine tank.

The invention will be described in more detail with reference to the accompanying drawings by way of non-limiting example and in which
Figure 1 schematically shows an apparatus according to the present invention
FIGS. 2 to 7 are simplified schematic representations of the same apparatus at successive stages of the regeneration of the resins and of the recovery of the brine; and
Figure 8 is a graph giving the hardness to
tale and salt concentration depending on the volume of the ef
regenerating agent flows from a resin bed
during such regeneration.

According to the essential characteristics of the invention, the brine is passed from a concentration station over and through a bed of an ion exchange resin to be regenerated, the initial part of the agent effluent is discarded of regeneration discharged from this bed and the rest of the regeneration rag effluent from said bed is returned to the concentration station in order to reconcentrate it.

 More particularly, the brine coming from a mass of the latter located near a bed of salt contained in a saturator is evacuated from the latter and is injected into a column containing a bed of ion exchange resin and a contiguous mass of liquid to be treated by passing it through the resin, the treatment being temporarily interrupted. The injection station is located in the liquid mass and close to the resin / liquid interface which is sometimes called hereinafter "intermediate station" because it is located between the volume of the liquid mass and the resin bed. Brine is passed through the resin bed; the initial part of the used brine which is discharged from the bed is discarded; and the part of the brine which is subsequently discharged from the bed is brought back to the preceding place situated above the salt bed where it is concentrated to be used in a similar manner.

 Figure 1 shows schematically on the left a conventional column 10 containing an ion exchange resin and on the right a salt tank 30 constituting the saturator as well as the connection piping, the valves and the accessory equipment. A service liquid inlet pipe 11 comprising a valve V1 penetrates into the top of the column and ends near this top by an upper distributor 21. A service liquid outlet pipe 12 leaves from a manifold 22 placed in a bottom material 29 (gravel, etc.) in the lower extreme part of the column and comprises a valve V2 after which it extends to a station of use (not shown). A pipe 13 for the outlet of the liquid backwashing device comprising a valve V3 is connected to the inlet pipe 11 between the valve V1 and the column 10. A pipe 14 for entering the backwashing liquid comprising a valve V4, a pipe 15 for rinsing liquid outlet comprising a valve a low flow outlet pipe 16 comprising a valve S6 and a brine recovery pipe 17 comprising a valve V7 are connected to the outlet pipe 12 between the bottom of the column and the valve V2.

A brine transfer pipe 18 in which a pump 40 and a valve V8 are incorporated extend from a lower layer of bottom material 39 contained in the tank 30 to an intermediate level inside the column 10 to end with an intermediate distributor 28 placed in the part of the service liquid 24 which is located immediately above the bed of ion exchange resin 26 and which is juxtaposed at the resin / liquid interface. Line 19 for entering the low-flow rinsing liquid comprising a valve V9 connects line 12 to line 18 between valve V8 and the intermediate distributor 28. A layer 34 of brine located in the upper part of the tank 30 covers the salt bed 36 located in the lower part of this tank. A float-controlled switch 32, represented at the upper left end of the salt tank, makes it possible to start the pump 40 when the tank contains sufficient brine and prevents said pump from operating when the brine has fallen to a minimum operating level (shown in phantom). A float-controlled switch 31 shown at the upper right end of the salt tank closes an outlet valve V10 of the recovery line to prevent overflow of the brine A pressure-sensitive switch 37 located between the inlet and outlet valves exit
V7 and V10 of the recovery line also fulfills a control function which will be described later.

To simplify, we will consider that FIG. 1 illustrates by way of example the normal service treatment of an intake liquid (for example drinking water or water intended for use in a commercial or industrial process), this liquid filling the upper part of the column 10 and passing through the resin to exit the column and end up in a remote place of use (not shown)
The service liquid inlet (and rinsing) and service liquid outlet valves V1 and M2 respectively, located in the inlet and outlet lines 11 and 12 are open and all the other valves are closed. The present invention will be better understood with the aid of FIGS. 2 to 7 representing the successive stages which reproduce certain parts of FIG. 1 and which show the appropriate settings of the valves for the successive stages during the implementation of the invention, the open valves being mainly represented.

 FIG. 2 illustrates a countercurrent washing step which normally takes place between the service step (FIG. 1) and the step of regenerating the resin using brine. During backwashing, the only valves open are the inlet valve V4 of line 14 through which the cool water passes into the bottom of the column and the outlet valve V3 of line 13 through which the liquid backwash is removed from the top of the tank or column 10.

FIG. 3 illustrates the initial step of removing the brine from the tank 30 to inject it into the resin column 10 in order to regenerate the bed of ion exchange resin 26 which it contains. The pump 40 sucks the brine 34 through the salt bed 36 and the undercoat 39 to transfer it to the resin column. via line 18, the transfer valve V8 of the latter being open. A valve V6 for discharging the residual liquid incorporated in the outlet pipe 16 is open so as to eliminate the first part of the effluent from the regeneration fluid or spent brine after it has passed through the resin bed.

All other valves are closed during this step.

The brine is injected not at the top of the column but at an intermediate level located between the top and the base, immediately above the top of the resin bed, via the distributor 28, which can be in the form of a cross to ensure regular bed cover.

The brine admitted is discharged through the resin bed and is then discharged from the bottom of the column as described. During this transfer of brine, its level drops in the salt tank, which lowers the floats of the two switches 31 and 32 which open the valve V10 of the recovery line 17 which, however, is still closed by its valve V7 finally, stop the pump 40 when the brine surface drops to a level just above the salt bed. This indicates the end of the regeneration step, as illustrated in FIG. 4, when the valve V8 closes and the valve V9 opens to communicate with the intermediate distributor 28; valve V6 is also closed and valve V7 is open. Ejection (by escaping water) or gravity feed can replace pumping as an appropriate means of injecting brine.

FIG. 5 represents the brine recovery stage during which a slow injection of water into the resin column via the distributor 28 pushes back the brine present in the resin bed and the adjacent layers of liquid through the intermediate recovery line 17 and two inlet and outlet valves
V7 and V10 in the upper part of the tank 30. When a sufficient quantity of the effluent of the regeneration fluid has been brought back into the salt tank to cause the closure of the outlet valve V10 (having meanwhile closed switch 32), as shown in FIG. 6, the back pressure detected by switch 37 increases appreciably.

When the pressure sensitive switch closes by closing the inlet valve V7 of the recovered brine and the inlet valve V9 of the low-flow rinsing fluid and by opening the inlet valve V1 of the pipe 11 and valve
V5 of the line 15 for discharging the rinsing liquid.

This rapid rinsing step continues for an appropriate period after which the service cycle shown in FIG. 1 resumes. An associated control circuit, etc., which ensures the consequences of actuation of the inter
pressure sensitive switch can have any
classic shape and therefore is not shown.

Figure 8 graphically shows results
typical of the process described in the first place by plotting the
concentration, in percent by weight depending on the volume
regeneration fluid effluent from the column
resin. The thrown part (about the first two thirds)
of the regenerating fluid effluent which is now light
diluted, is designated by A and the final part recovered
of this effluent is designated by B. The total hardness is in
dotted line and the salt concentration in solid line,
it is obvious that part B contains a good half of
all of the salt (area below the curve), while
most hardness constituents (at least three
about quarters) is contained in part A. Thus, the pre
sente invention keeps half the salt while
by reducing the residual hardness to a tolerable value.

The example on which Figure 8 is based is described below.

Example
A column having an internal diameter of 14 cm and a height of 157.5 cm is used. It is filled with a cationic resin (of the softener type with a sodium zeolite wearer) up to a height of approximately 66 cm (approximately 10 dm 3).

The brine saturation tank has an internal diameter of 19.7 cm and a height of 104 cm. The bottom material is placed at the bottom to a thickness of 6.35 cm followed by a layer of about 7.6 cm of gravel. On the latter, a thickness of 45.7 cm of rock salt is placed. Water is added to a height of about 40.6 cm above the salt level. Water and salt are mixed until a certain degree of saturation is obtained. The concentration of brine extracted from the saturator is approximately 23 80.

 The cationic resin is exhausted and then regenerated with saturated brine. The regenerating agent is injected at a level situated approximately 15.2 cm above the bed by means of an intermediate distributor (see FIG. 1).

 The flow rate for regeneration is 320 ml / min (0.2 1 / dom2). The residual regeneration liquid is collected in the form of 640 ml samples and up to 13.5 samples for analysis. A total of 8.64 1 of brine is used, which is equivalent to 0.252 g / cm3 (resulting capacity 0.126 g / cm3).

The rinsing which follows is carried out at a flow rate of 320 ml / min (0.2 1 / dm2) and the rinsing liquid is also collected in the form of 640 ml samples at the rate of 21.5 samples which are analyzed also. The rinsing is continued for an additional 25 minutes at a flow rate of 640 ml / min (0.4 1 / dm2).

The column is then put into service and exhausted.

During subsequent regenerations, half of the salt by weight of the samples collected (N 20 to N 29) is returned to the brine tank (see table I for the results of the test
N 3: typical regeneration). Salt and water are added so that the specifications of the brine tank correspond to those mentioned above. The above procedure is repeated.

A brine sample is also collected during regeneration. A total of eight tests are carried out under these conditions. See table II for capacities, leaks, etc.

The exchange capacity is indicated in grams per cubic decimetres.

TABLE I
of NaCl and% hardness of the samples - test N 3
Sample N% NaCl% hardness
1 0.02
8 0.78 1.31
9 3.12 3.14
10 5.85 * 5.26
11 8.58 7.49
12 11.7 9.31
13 14.04 11.34
14 16.9 12.15
15 18.7 11.95
16 20.54 11.34
18 23.14 9.31
20 23.92 7.29
22 24.44 5.87
24 24.96 4.86
28 7.54 0.95
30 1.30 0.07
Brine 25.22 TABLE II - Capacity
Hardness loss Test capacity N Total, Max liters (ppm) Average Starting hardness Brine hardness (g / dm3 1 2634 6.0 3.7 246 ppm 0.035% 2 2650 2.0 1.0 238 ppm 1.033% 3 2748 3.0 1.1 244 ppm 1.378% 4 2559 3.0 3.0 242 ppm 1.884% 5 2613 1.0 0.5 231 ppm 2.046% 6 2642 2.0 1.0 220 ppm 2.208% 7 4232 2.0 1.3 145 ppm 2.574% 8 5409 1.0 1.0 138 ppm 2.552%
Average = 63.17
The coarse salt dosage is 0.252 kg / dm3 of resin. The resulting degree of regeneration is 0.126 kg of
NaCl per dm3 for a regeneration efficiency of 0.126 = 1.994 g for 6.48 g of hardness removed, which equi63.17 is worth approximately 170 Dó of the theoretical value. For tap water with a total hardness of 235 ppm (as CaCO3), the brine solution reaches an equilibrium value, after eight regenerations, of 2.6 Ó of the total hardness based on saturated brine . This does not affect the total loss of hardness of 3 ppm, nor significantly the exchange capacity.

Normally, at a dose of 0.096 kg of NaCl per dm3 of resin (prior art), the operating capacity would only be 43.78 g / dm3, but the process of the present invention at a dose of 0.096 kg of NaCl per dm3 removes approximately 61.8 g per dm3 (approximately 130 of the theoretical efficiency of the salt), a yield for which the previous methods would have required approximately 0.192 kg of NaB1 per dm3. Thus, the present invention allows users of ion exchange resins to recover at least half of the salt used for the regeneration of brine, by means of a simple apparatus which can be supplied in the form of spare parts so as to adapt it to existing installations to ensure better regeneration. No additional container is required in addition to the brine tank cooperating with the resin column. Recycling brine is simple, as just described.

 Although the invention has been described in its application to a cation exchange resin, it is also applicable to anion exchange resins, whether on the chloride cycle or the combined chloride and hydroxide cycle. It goes without saying that numerous modifications can be made to the method and to the apparatus described and shown without departing from the scope of the invention.

Claims (7)

 1. Method for regenerating ion exchange resins in the presence of brine, in which the brine is passed from a concentration station through a bed of an ion exchange resin intended to be regenerated, method characterized in that that it consists in using a region of saturation of salt at the concentration station, in throwing away the initial part of the effluent of the regeneration fluid discharged from this bed and in bringing back to the concentration station the amount of the effluent of the regeneration later discharged from the bed to reconcentrate it.  2. Method according to claim .1, characterized in that a mass of liquid is contiguous to the bed of ion exchange resin, said process -consistent, with a view to passing the brine through the resin, -to inject the brine in this mass of liquid at an intermediate location near the resin / liquid interface. 3. Method according to claim 1, characterized in that it consists in throwing into this initial part of the effluent of the regeneration fluid at most about half of the salt of the brine applied to the resin bed.  4. Method according to claim 1, characterized in that it consists in throwing into this first part of the effluent of the regeneration fluid at least about three quarters of the total hardness removed from the resin bed during this regeneration. 5. Apparatus in the form of spare parts usable with a column of ion exchange resin to facilitate its regeneration by brine using a brine concentration tank, apparatus characterized in that it comprises a bed of salt saturation in the brine concentration tank, a device intended to allow and prevent the circulation of fresh brine from the tank in the column and, as a variant, the flow of the used brine from the column into the tank and a device for adjusting the level of brine in the tank 6. Apparatus according to claim 5, characterized in that it comprises a brine concentration tank to be used as the only tank containing brine during the regeneration step and a brine distributor located at an intermediate level which is intended to be installed in the column.  7. Apparatus according to claim 5, characterized in that the first device comprises a circulation device intended to transfer the brine from the tank into the column to regenerate the resin.