RU44670U1 - SYSTEM OF DEEP SALTATION OF FRESH AND SALTONIC WATERS - Google Patents

Abstract

The utility model relates to the field of power engineering and can be used to obtain deeply desalted water from natural fresh and brackish waters. The deep desalination system of natural fresh and brackish waters contains a clarification unit connected in series, a clarification water treatment installation on ion-exchange filters, and a reverse osmosis desalination membrane installation. According to a utility model, a reverse osmosis unit has at least two reverse osmosis unit stages connected in series along the direction of the concentrate with booster pumps installed between these stages, as well as connection lines between the specified units, each stage of the reverse osmosis unit is equipped with membranes operating under operating pressure, necessary for the efficient processing of this stage concentrate. The use of concentrate from the stages of the reverse osmosis installation for the regeneration of ion-exchange filters is provided. For water with a high content of organic compounds, the clarified water treatment plant contains H-Na-cation exchange resin and Cl-ionite filters, and the concentrate removal line from the reverse osmosis unit and the alkaline solution removal line from the Н-ОН-ionization stage of the permeate are connected to the Cl-ionite filter, the acid solution withdrawal line from the H-OH ionization stage and the spent solution line from the Cl-ionite filter are connected to the H-Na-cation exchange filter.

Description

The utility model relates to the field of power engineering and can be used to obtain deeply desalted water from natural fresh and brackish waters.

Currently, at a number of thermal power plants for deep water desalination, a system is used that consistently includes a clarification unit (clarifiers and mechanical filters), reverse osmosis (UOO) as the first stage of desalination and H-OH-ionite filters as the second stage of desalination [1, 2] - analogues. The disadvantage of this system is the increased consumption of concentrate (purge water) due to the shallow concentration of the treated water in the DOE and, accordingly, the low consumption of permeate (demineralized water) after the DOE. The indicated drawback is the result of the fact that the DOE does not provide for an increase in the working pressure providing constant conditions for the reverse osmosis process as the salt content of the concentrate increases. In addition, this drawback is a consequence of a simplified pre-treatment scheme, which does not allow carbonate hardness to be removed deep enough from water. Another drawback of the system according to [1, 2] is the discharge of spent regeneration solutions from the H-OH ionization stage containing high concentrations of reactive acid and alkali.

Known adopted as a prototype system of deep desalination of fresh and brackish water, containing sequentially included clarification unit, a treatment plant for clarified water on ion-exchange filters and a desalination membrane installation of reverse osmosis [3]. The process of reverse osmosis desalination in the installation of the prototype is carried out at a constant value of the applied pressure in devices with the same membrane elements, with significant values of the discharge of concentrate 15-30%, which correspond

low values of the ratio of permeate to concentrate costs n = 2.3-5.7. Such a desalination system makes it possible to ensure the operating mode of UO without the formation of mineral deposits in the membrane elements with a relatively shallow concentration of the treated water. At the same time, this system, like [1, 2], does not allow increasing permeate production, and therefore, increasing the ratio of permeate to concentrate costs and it is useful to use the concentrate as a regenerant of the Na-cation exchange filter due to the low concentration of sodium salts in it. As a result of these features of the prototype, the water consumption for own needs as a whole for the installation of desalination remains quite high 23.5-51.4% of the flow rate of the obtained demineralized water. This flow rate is due to a significant amount of concentrate discharge of 15-30% of the flow rate of the initial treated water (or 17.6-42.8% of the flow rate of demineralized water), as well as the flow of water for own needs of the H- or Na-cationite filters that are included in front of the UOE, which usually accounts for 5-6% of the flow rate of cationic water (or 5.9-8.6% of the flow rate of the obtained demineralized water). In total, according to the installation, the water consumption for own needs is 23.5-51.4% of the flow rate of the obtained demineralized water.

The disadvantage of the prototype should also include:

- relatively high values of hardness and alkalinity in the source water before DOE,

- shallow desalination of water (7-50 μS / cm of electrical conductivity) due to the lack of an additional stage of H-OH ionization of permeate,

- pollution of membrane elements with organo-containing deposits during the treatment of water with a high content of organic substances (including man-caused origin).

The achievable results of the utility model are:

- a significant increase in the yield of permeate from the reverse osmosis unit and a decrease in the concentrate flow rate, which correspond to higher values of the ratio of permeate flow rate to the concentrate 7-99;

- improving the quality of demineralized water (up to <0.5 μS / cm of electrical conductivity);

- reduction of discharges of concentrated solutions by desalination steps and, accordingly, reduction of water consumption for the plant’s own needs (up to 3-17% of the flow rate of deeply desalted water obtained).

The indicated results are ensured by the fact that in a deep desalination system of natural fresh and brackish waters containing a clarification unit in series, a clarification water treatment unit on ion-exchange filters and a reverse osmosis desalination unit, according to a utility model, the reverse osmosis unit has at least two connected in series along the movement of the concentrate steps of the reverse osmosis apparatus with booster pumps installed between the indicated steps, and that there are also connection lines between the specified plants, and each subsequent stage of the reverse osmosis installation is equipped with membranes operating at the working pressure necessary for processing the concentrate of the previous stage. In this case, the ion-exchange clarified water treatment plant may contain H-Na filters or Na-cation exchange filters, and after the installation of reverse osmosis, the installation of H-OH ionization of permeate is switched on. Moreover, the concentrate removal line from the reverse osmosis unit is connected to the Na-cation exchange filter, the acid solution withdrawal line from the Н-ОН ionization stage of the permeate is connected to the Н-cation exchange filter or to the clarified water line in front of the Na-cation exchange filter, and the alkaline solution removal line from that steps to the Na-cation exchange filter.

With a high content of organic compounds, the clarified water treatment plant may contain Cl-ionite or H-Na-

cation exchange and Сl-ion exchange filters. The line for the removal of concentrate from the reverse osmosis unit and the line for the removal of alkaline solution from the Н-ОН-ionization stage of the permeate are connected to the Cl-ion filter.

The acid solution withdrawal line from the Н-ОН ionization stage and the spent solution line from the Cl-ionite filter are connected to the Н-Na-cation exchange filter.

In the proposed system, the content of hardness ions in the water entering the reverse osmosis plant is 3-5 μg-equiv / l, and alkalinity is (0.1-0.2) mg-equiv / l, i.e. significantly lower than in the prototype.

Deep softening and decarbonization of feed water make it possible to eliminate contamination of membrane elements even with deep concentration of water, corresponding to the declared values of the ratio of permeate to concentrate expenditures in the range n = 7-99.

The prevention of organic deposits on the membrane surface is ensured by additional purification of clarified water on a Cl-ionite filter loaded with organoabsorbing anion exchange resin, and the required efficiency of organic matter absorption is achieved due to deep regeneration of the anion exchange resin by the reverse osmosis unit concentrate and spent alkaline solution of the OH-anion exchange filter of the Н-ОН-ionization stage permeate.

The selected ranges of the ratio of permeate to concentrate expenditures are justified by the extreme conditions for the operation of UOE on deeply softened and decarbonized fresh or brackish water.

The process of reverse osmosis desalination of water is carried out under the influence of pressure, the value of which exceeds the value of the osmotic pressure. Thus, the value of the working pressure that ensures the separation process (permeate and concentrate) is determined by the difference between the applied and osmotic pressures - ΔР.

As the salt content of the concentrate increases at a constant value of the applied pressure, the working pressure ΔР decreases, which leads to a decrease in the productivity of the membranes.

The characteristic range of the total salinity of natural waters is 100-1250 mg / l. In the process of reverse osmosis desalination, concentration occurs, respectively, to the salinity of, respectively, brackish and saline waters. The membrane elements of the corresponding type used in the practice of desalination of such waters have limitations on the salt content of the concentrate ~ 5000 mg / l - brackish water and ~ 10000 mg / l - saline water. This limitation is due to the fact that when the salinity of the concentrate is within the specified limits, the pressure created is ~ 1.6 MPa and ~ 4.0 MPa for the corresponding type of membranes provides the necessary parameters of the reverse osmosis process. When the salt content of the concentrate is higher than 5000 mg / l and 10 000 mg / l due to the increase in osmotic pressure, the applied pressure (1.6 MPa and 4.0 MPa) for the corresponding types of reverse osmosis membranes is not enough to ensure their nominal performance. As a result, the process of reverse osmosis desalination is disrupted and leads to a decrease in the performance of reverse osmosis membranes and the installation as a whole and a deterioration in the quality of permeate.

Let us consider the process of desalination in an installation with blocks of reverse osmosis membrane devices (modules) assembled in two or more stages (in the direction of the concentrate), assembled in a parallel-serial circuit and equipped with two types of reverse osmosis membrane elements (for example, BW for desalination of brackish water and HR for desalination of salted water). The installation provides for an increase in the applied pressure of not more than 1.6 MPa in the first stage and up to 3.5-4.0 MPa in the last stage, while ensuring the necessary speed of the solution (concentrate) in the pressure channels above the surface of the membranes in the filter elements (at least 1 m / s).

For low-saline waters with a salinity of 100 mg / l, the optimal desalination conditions will be characterized by a value of n = 99, which corresponds to the operating mode of the reverse osmosis unit with a concentrate flow rate of 1.0% of the feed water flow. At

In this case, the salt content of the concentrate is close to the limit according to the operating conditions of the membranes. At n <99, the concentrate consumption increases and the permeate yield decreases, in addition, the salt content of the concentrate and its regenerating ability with respect to the strongly acidic Na-filter cation exchange resin are reduced. That is, the operating mode of the DOE is not optimal.

At n> 99 as a result of an increase in the osmotic pressure, the productivity of the installation decreases to 90% of the nominal, and the salt content of permeate also increases.

For waters with a salinity of 1250 mg / l, the optimal desalination conditions will be characterized by a value of n = 7, which corresponds to the operation mode of the reverse osmosis unit with a concentrate flow rate of 12.5% of the feed water flow. In this case, the salt content of the concentrate is close to the limit according to the operating conditions of the membranes. When n <7, the concentrate consumption increases and the permeate yield decreases, in addition, the salt content of the concentrate and its regenerating ability with respect to the strongly acidic Na-filter cation exchanger decrease. That is, the operating mode of DOE is also not optimal.

At n> 7 as a result of an increase in the osmotic pressure, the productivity of the installation decreases to 85% of the nominal, and the salt content of permeate also increases.

Thus, the reduced range of the ratio of permeate consumption to concentrate (n = 7-99) is determined on the basis that, for values of n> 99, even for waters with initial salinity of 100 mg / l, the maximum salt content of the concentrate exceeds 10,000 mg / l and for values of n <7, even for waters with initial salinity of 1250 mg / l, the salinity of the concentrate is significantly lower than permissible.

Figure 1, as one example of the implementation of the utility model, schematically depicts a deep desalination system (SGO), in which at the pretreatment stage, in addition to clarifier (O) and mechanical filters (M), H- and Na-cation exchange filters are provided; figure 2 -

another example of the implementation of a utility model in the form of an SSS, in which, at the pretreatment stage, instead of an H-cation exchange filter, a device for acidifying water is provided; figure 3 is another example of the implementation of the utility model in relation to the source water with a high content of organic compounds, in which at the stage of pre-treatment additionally provides Cl-anion exchange filter to remove organic substances.

SGO according to the utility model contains a clarification unit as a part of clarifier (O) 1, and mechanical (clarification) filters (M) 2, H-cation exchange filter (H) 3, Na-cation exchange filter (Na) 4 (Fig. 1), H -Na-cation exchange filter (H, Na) 3,4, Сl-ion exchange filter (Сl) 5 (Fig. 3), as well as a pump 6 for the first stage, УОО 7 for the first desalination step-up pump 8 for the second stage (or pumps the second and third) stages, UOO 9 of the second (or second and third) desalination stage, H-ion filter 10, OH-ion filter 11, concentrate line 12, permeate line 13, lines 14, 15, respectively, the supply of source water and the removal of deeply demineralized water, as well as the line 16, 17 of the supply to the ion exchange filters and the discharge of acid and alkali, respectively.

The system according to the utility model (figure 1, 2) works as follows. The source water is preliminarily supplied to the clarification unit, where clarifier 1, mechanical filter 2, H-cation exchange filter 3 (Fig. 1) and Na-cation exchange filter 4 pass sequentially. Softened decarbonized water is pumped 6 to the first desalination unit UOE 7, then, using a booster pump 8, under higher pressure, it enters UOO 9 to the second stage of desalination. Permeate from both desalination stages via line 13 is fed sequentially to H- and OH-ionite filters 10 and 11, respectively. For regeneration, sulfuric acid is fed to the OH-anionite filter through line 16 for line 16, and caustic soda is fed to line 2 through line 17 . The concentrate from UOO 9 of the second or last stage of desalination and the spent alkali solution from the OH-ionite filter 11 are supplied, respectively, along lines 12 and 17 to the regeneration of the Na-cation exchange filter (FIGS. 1 and 2), Cl-

ion exchange filter (figure 3). The spent acid solution from the H-cation exchange filter 10 is fed through line 16 to the regeneration of the H-cation exchange filter (Fig. 1), the acidification of clarified water in front of the Na-cation exchange filter (Fig. 2), and the regeneration of the H-Na-cation exchange filter (Fig. 2). 3). The spent concentrate after the Cl-ionite filter 5 is fed through line 12 to the regeneration of the H-Na-cationite filter 3, 4 (Fig. 3).

Example 1. The clarified water p. Kama after processing in clarifier 1 and on mechanical filters (Fig. 1) enters H-Na cation on filters 3, 4 loaded with weakly and strongly acidic cation exchangers (MAC-3 and KU-2-8), respectively, then deeply softened and decarbonated water is supplied for reverse osmosis desalination to sequentially mounted blocks of UOO 7 and 9 membrane devices. The first stage 7 of the devices is equipped with BW membrane elements operating at pressures up to 1.6 MPa. The last stage of these devices is equipped with HR membrane elements operating under a pressure of not more than 4.0 MPa.

The obtained permeate is fed to ion-exchange desalination on H-OH filters loaded respectively with KU-2-8 cation exchanger and AB-17-8 anion exchanger.

Table 1 shows the compositions of clarified, H-Na-cationized water, permeate and concentrate reverse osmosis unit, desalted permeate after H-OH-ionite filters.

The desalination process is carried out with a concentrate flow rate of 2.86% of the feed water flow rate with a ratio of permeate to concentrate flow rate n = 34.

Table 1 Composition indicators Clarified water H-Na-cationic water Permeate Concentrate Permeate after H-OH filters Hardness, mEq / dm ³ 1,0 0.005 0.00012 0.17 0,0 Ca ²⁺ , - "- 0.6 0.003 0.00007 0.10 0,0 Mg ²⁺ , - "- 0.4 0.002 0.00005 0,07 0,0 Alkalinity, - "- 0.6 0.2 0.005 6.82 0,0 Na, mg / dm ³ 91.2 105 2,625 3583 0.11 Сl ^- , - "- 122 122 3.05 4162 0.1 SO ₄ ^2- , - “- 43 43 1,075 1467 traces SiO ₃ ^2- , - “- 3.0 3.0 0,075 102,4 0.005 Salt content, - "- 293 285 7,125 9727 <0.3 Electric wires., - "- - 440 eleven - <0.5 COD, mgO / dm ³ 1,2 1,0 0.3 24.7 -

Example 2. The clarified water p. Kama after treatment in the clarifier and on the mechanical filters of the installation (Fig. 2) is acidified with an spent sulfuric acid solution and fed to Na-cation on filters loaded with strongly acidic cation exchange resin (KU-2-8), then deeply softened and decarbonized water is fed to reverse osmosis desalination , in sequentially mounted blocks of membrane apparatuses UOO 7 and 9. The first stage 7 is equipped with BW membrane elements operating at pressures up to 1.6 MPa. The last stage of these devices is equipped with HR membrane elements operating under a pressure of not more than 4.0 MPa.

The obtained permeate is fed to ion-exchange desalination on H-OH-ion-exchange filters loaded respectively with KU-2-8 cation exchanger and AB-17-8 anion exchanger.

Table 2 shows the compositions of clarified, acidified Na-cationized water, permeate and reverse osmosis concentrate, desalted permeate after H-OH filters.

The desalination process is carried out with a concentrate flow rate of 3.13% of the feed water flow rate with a ratio of permeate to concentrate flow rate n = 30.87. To acidify the clarified water, the spent solution of the H-cation exchange filter of the Н-ОН-post-desalination permeate stage is supplied. For the regeneration of the Na-cation exchange filter, the concentrate of the reverse osmosis unit is fed, and then the spent alkali solution after regeneration of the OH-anion exchange filter of the permeate pre-desalination stage.

table 2 Composition indicators Clarified water Acidified and Na-cationic water Permeate Concentrate Permeate after H-OH filters Hardness, mEq / dm ³ 1,0 0.005 0.00012 0.156 0,0 Ca ²⁺ , - "- 0.6 0.003 0.00007 0,094 0,0 Mg ²⁺ , - "- 0.4 0.002 0.00005 0,062 0,0 Alkalinity, - "- 0.6 0.2 0.005 6.23 0,0 Na, mg / dm ³ 91.2 114.2 2.85 3560 0.12 Сl ^- , - "- 122 122 3.05 3803 0.1 SO ₄ ^2- , - “- 43 62,2 1.55 1940 traces SiO ₃ ^2- , - “- 3.0 3.0 0,075 93.5 0.005 Salt content, - "- 293 313.7 7.84 9780 <0.3 Conducting., - "- - 448 11.2 - <0.5 COD, mgO / dm ³ 1,2 1,0 0.3 22.7 -

Example 3. The clarified water of the river. Kama after processing in clarifiers and on mechanical filters (Fig. 3) enters H-Na-cation on a filter loaded with strongly acid and weakly acid cation exchange resin (KU-2 and MAC-3) and Cl-ionization on a filter loaded with organo-absorbing anion exchange resin (Marathon 11), then deeply softened, decarbonized and purified from organic substances water is supplied to reverse osmosis desalination, to sequentially mounted blocks of membrane devices 7 and 9. The first stage 7 is equipped with BW membrane elements operating at pressures up to 1.6 Pa. The last stage of these devices is equipped with HR membrane elements operating under a pressure of not more than 4.0 MPa.

The resulting permeate is fed to ion-exchange desalination on H-OH filters loaded respectively with KU-2-8 cation exchanger and AB-17-8 anion exchanger.

Table 3 shows the compositions of clarified, H-Na-Cl-ionized water, permeate and reverse osmosis concentrate, desalted permeate after H-OH filters.

The desalination process is carried out with a concentrate flow rate of 3.05% of the feed water consumption with a ratio of permeate to concentrate consumption n = 31.8. For the regeneration of the Cl-ion exchanger filter, the concentrate of the reverse osmosis unit is supplied, and then the spent alkali solution after regeneration of the OH-anion exchanger filter of the stage of additional desalination of permeate.

The spent acid solution is fed to the regeneration of the H-Na-cation exchange filter of the H-Na-cationization stage after the regeneration of the H-cation exchange filter of the H-OH-post-desalination of permeate and the spent solutions after the Cl-ion filter.

Table 3 Composition indicators Clarified water H-Na-Cl-ionized bath water Permeate Concentrate Permeate after H-OH filters Hardness, mEq / dm ³ 1,0 0.005 0.00012 0.176 0,0 Ca ²⁺ , - "- 0.6 0.003 0.00007 0.1056 0,0 Mg ²⁺ , - "- 0.4 0.002 0.00005 0,07 0,0 Alkalinity, - "- 0.6 0.2 0.005 7.04 0,0 Na, mg / dm ³ 91.2 105 2,625 3698 0.11 Сl ^- , - "- 122 147 3,675 5177 0.1 SO ₄ ^2- , - “- 43 nine 0.225 317 traces SiO ₃ ^2- , - “- 3.0 3.0 0,075 105.66 0.005 Salt content, - "- 293 276 6.9 9721 <0.3 Conducting., - "- - 436 10.9 - <0.5 COD, mgO / dm ³ 1,2 1,0 0.3 25.57 -

Sources of information:

1. The use of reverse osmosis in the desalination of water to power the steam generators of TPPs and nuclear power plants. - Mamet A.P., Sitnyakovsky Yu.A. - Thermal Engineering, 2000, No. 7, pp. 20-22.

2. Comparison of the efficiency of ionic and reverse osmosis desalination of water. - Mamet A.P., Sitnyakovsky Yu.A. - Electric stations, 2002, No. 6, p. 63-66.

3. USSR patent No. 1820895, C 02 F 1/42, 1991.

Claims (3)

1. A system for deep desalination of natural fresh and brackish water, comprising a clarification unit in series, a clarification water treatment unit on ion-exchange filters, a desalination membrane reverse osmosis unit, characterized in that the reverse osmosis unit has at least two stages connected in series along the direction of the concentrate movement reverse osmosis devices with booster pumps installed between the indicated steps, as well as connecting lines between the indicated installations, and each stage of the reverse osmosis installation is equipped with membranes operating under the working pressure necessary for the efficient processing of the concentrate of this stage. 2. The deep desalination system according to claim 1, characterized in that the clarified water treatment plant contains H-Na filters or Na-cation exchange filters, and after the reverse osmosis installation, the N-OH-ionization of permeate is turned on, and the concentrate removal line from reverse osmosis the unit is connected to Na-cation exchange filters, the acid solution drainage line from the Н-ОН-ionization stage of permeate is connected to the Н-cationite filter or clarified water line, and the alkaline solution removal line from the same stage to the Na-cation exchange filter. 3. The deep desalination system according to claim 1, water with a high content of organic compounds, characterized in that the clarified water treatment plant contains H-Na-cationite and Cl-ionite filters, and a concentrate removal line from the reverse osmosis unit and an alkaline solution removal line from the stage The Н-ОН-ionization of the permeate is connected to the Cl-ionite filter, the line for removing the acid solution from the Н-ОН-ionization stage and the waste solution line from the Cl-ionite filter are connected to the Н-Na-cation exchange filter.