Water softening by dialysis
Magnetic water treatment
Literature
Water softening refers to the process of removing hardness cations from it, i.e. calcium and magnesium. In accordance with GOST 2874-82 "Drinking water", water hardness should not exceed 7 mEq/l. Certain types of production require deep softening of process water, i.e. up to 0.05.0.01 mEq/l. Typically used water sources have a hardness that meets drinking water standards and do not require softening. Water softening is carried out mainly during its preparation for technical purposes. Thus, the hardness of water for feeding drum boilers should not exceed 0.005 mEq/l. Water softening is carried out using the following methods: thermal, based on heating water, its distillation or freezing; reagents, in which the ions present in water Ca ( II ) And Mg ( II ) bind with various reagents into practically insoluble compounds; ion exchange, based on filtering softened water through special materials that exchange the ions included in their composition Na ( I) or H (1) into Ca (II) ions and Mg ( II ), contained in dialysis water; combined, representing various combinations of the listed methods.
The choice of water softening method is determined by its quality, the required depth of softening and technical and economic considerations. In accordance with the recommendations of SNiP when softening groundwater, ion exchange methods should be used; when softening surface water, when water clarification is also required, the lime or lime-soda method is used, and when deep softening water, subsequent cationization. The main characteristics and conditions for using water softening methods are given in table. 20.1.
softening water dialysis thermal
To obtain water for domestic and drinking needs, usually only a certain part of it is softened, followed by mixing with source water, while the amount of softened water Qy determined by the formula
where is J o. And. - total hardness of source water, mEq/l; F 0. s. - total hardness of water entering the network, mEq/l; F 0. u. - hardness of softened water, mEq/l.
Water softening methods
| Index | thermal | reagent | ion exchange | dialysis |
| Process characteristics | Water is heated to a temperature above 100°C, which removes carbonate and non-carbonate hardness (in the form of calcium carbonate, hydroxy- and magnesium and gypsum) | Lime is added to the water, which eliminates carbonate and magnesium hardness, as well as soda, which eliminates non-carbonate hardness. | The water to be softened is passed through cation exchanger filters | Source water is filtered through a semi-permeable membrane |
| Purpose of the method | Elimination of carbonate hardness from water used to feed low and medium pressure boilers | Shallow softening while simultaneously clarifying water from suspended solids | Deep softening of water containing a small amount of suspended solids | Deep water softening |
| Water consumption for own needs | - | No more than 10% | Up to 30% or more in proportion to the hardness of the source water | 10 |
| Conditions for effective use: source water turbidity, mg/l | Up to 50 | Up to 500 | No more than 8 | Up to 2.0 |
| Water hardness, mEq/l | Carbonate hardness with a predominance of Ca (HC03) 2, non-carbonate hardness in the form of gypsum | 5.30 | Not higher than 15 | Up to 10.0 |
| Residual water hardness, mEq/l | Carbonate hardness up to 0.035, CaS04 up to 0.70 | Up to 0.70 | 0.03.0.05 prn single-stage and up to 0.01 with two-stage cationization | 0.01 and below |
| Water temperature, °C | Up to 270 | Up to 90 | Up to 30 (glauconite), up to 60 (sulfonite) | Up to 60 |
The thermal method of water softening is advisable to use when using carbonate waters used to feed boilers low pressure, and also in combination with reagent methods of water softening. It is based on a shift in the carbon dioxide equilibrium when it is heated towards the formation of calcium carbonate, which is described by the reaction
Ca (HC0 3) 2 -> CaCO 3 + C0 2 + H 2 0.
The equilibrium is shifted due to a decrease in the solubility of carbon (IV) monoxide caused by an increase in temperature and pressure. Boiling can completely remove carbon (IV) monoxide and thereby significantly reduce calcium carbonate hardness. However, it is not possible to completely eliminate this hardness, since calcium carbonate, although slightly (13 mg/l at a temperature of 18°C), is still soluble in water.
If magnesium bicarbonate is present in water, the process of its precipitation occurs as follows: first, relatively highly soluble (110 mg/l at a temperature of 18 ° C) magnesium carbonate is formed
Mg (HCO 3) → MgC0 3 + C0 2 + H 2 0,
which hydrolyzes during prolonged boiling, resulting in a slightly soluble precipitate (8.4 mg/l). magnesium hydroxide
MgC0 3 +H 2 0 → Mg (0H) 2 +C0 2 .
Consequently, when water is boiled, the hardness caused by calcium and magnesium bicarbonates decreases. When water is boiled, hardness, determined by calcium sulfate, also decreases, the solubility of which drops to 0.65 g/l.
In Fig. 1 shows a thermal softener designed by Kopyev, characterized by the relative simplicity of the device and reliable operation. The treated water, preheated in the apparatus, enters through the ejector onto the socket of the film heater and is sprayed over vertically placed pipes, and flows down through them towards the hot steam. Then, together with the blowdown water from the boilers, it enters the clarifier with suspended sediment through the central supply pipe through the perforated bottom.
The carbon dioxide and oxygen released from the water along with excess steam are discharged into the atmosphere. Calcium and magnesium salts formed during the heating of water are retained in the suspended layer. Having passed through the suspended layer, the softened water enters the collection tank and is discharged outside the apparatus.
The residence time of water in the thermal softener is 30.45 minutes, the speed of its upward movement in the suspended layer is 7.10 m/h, and in the holes of the false bottom 0.1-0.25 m/s.
Rice. 1. Thermal softener designed by Kopyev.
15 - reset drainage water; 12 - central supply pipe; 13 - false perforated bottoms; 11 - suspended layer; 14 - sludge discharge; 9 - collection of softened water; 1, 10 2 - boiler blowing; 3 - ejector; 4 - evaporation; 5 - film heater; 6 - steam release; 7 - ring perforated pipeline for water drainage to the ejector; 8 - inclined separating partitions
Water softening using reagent methods is based on treating it with reagents that form poorly soluble compounds with calcium and magnesium: Mg (OH) 2, CaC0 3, Ca 3 (P0 4) 2, Mg 3 (P0 4) 2 and others, followed by their separation in clarifiers , thin-layer sedimentation tanks and clarification filters. Lime is used as reagents, soda ash, sodium and barium hydroxides and other substances.
Water softening by liming used for high carbonate and low non-carbonate hardness, as well as in cases where it is not necessary to remove non-carbonate hardness salts from water. Lime is used as a reagent, which is introduced in the form of a solution or suspension (milk) into preheated treated water. When dissolved, lime enriches the water with OH - and Ca 2+ ions, which leads to the binding of free carbon monoxide (IV) dissolved in water with the formation of carbonate ions and the transition of hydrocarbonate ions into carbonate ones:
C0 2 + 20H - → CO 3 + H 2 0, HCO 3 - + OH - → CO 3 - + H 2 O.
An increase in the concentration of CO 3 2 - ions in the treated water and the presence of Ca 2+ ions in it, taking into account those introduced with lime, leads to an increase in the solubility product and the precipitation of poorly soluble calcium carbonate:
Ca 2+ + C0 3 - → CaC0 3.
If there is an excess of lime, magnesium hydroxide also precipitates.
Mg 2+ + 20H - → Mg (OH) 2
To accelerate the removal of dispersed and colloidal impurities and reduce the alkalinity of water, coagulation of these impurities with iron (II) sulfate is used simultaneously with liming, i.e. FeS0 4 *7 H 2 0. The residual hardness of softened water during decarbonization can be obtained 0.4-0.8 mg-eq/l more than non-carbonate hardness, and the alkalinity is 0.8-1.2 mg-eq/l. The dose of lime is determined by the ratio of the concentration of calcium ions in water and carbonate hardness: a) at the ratio [Ca 2+ ] /20<Ж к,
b) with the ratio [Ca 2+ ] /20 > J c,
where [CO 2 ] is the concentration of free carbon monoxide (IV) in water, mg/l; [Ca 2+ ] - concentration of calcium ions, mg/l; Fc - carbonate hardness of water, mEq/l; D k - dose of coagulant (FeS0 4 or FeCl 3 in terms of anhydrous products), mg/l; e k- equivalent mass active substance coagulant, mg/mg-eq (for FeS0 4 e k = 76, for FeCl 3 e k = 54); 0.5 and 0.3 - excess lime to ensure greater completeness of the reaction, mEq/l.
The expression D k / e k is taken with a minus sign if the coagulant is introduced before the lime, and with a plus sign if together or after.
In the absence of experimental data, the dose of the coagulant is found from the expression
D k = 3 (C) 1/3, (20.4)
where C is the amount of suspended matter formed during water softening (in terms of dry matter), mg/l.
In turn, C is determined using the dependence
where M and is the content of suspended solids in the source water, mg/l; m- CaO content in commercial lime, %.
Lime-soda method of water softening is described by the following basic reactions:
Using this method, residual hardness can be brought to 0.5.1, and alkalinity from 7 to 0.8.1.2 mEq/l.
Doses of lime D and soda D s (in terms of Na 2 C0 3), mg/l, are determined by the formulas
(20.7)
where is the content of magnesium in water, mg/l; Jn. K. - non-carbonate water hardness, mEq/l.
With the lime-soda method of water softening, the resulting calcium carbonate and magnesium hydroxide can supersaturate solutions and remain in a colloidal dispersed state for a long time. Their transition into coarse sludge takes a long time, especially at low temperatures and the presence of organic impurities in the water, which act as protective colloids. With a large amount of them, water hardness during reagent water softening can be reduced by only 15.20%. In such cases, before softening or during the softening process, organic impurities are removed from the water using oxidizing agents and coagulants. With the lime-soda method, the process is often carried out in two stages. Initially, organic impurities and a significant part of carbonate hardness are removed from the water, using aluminum or iron salts with lime, carrying out the process at optimal conditions coagulation. After this, soda and the rest of the lime are introduced and the water is softened. When removing organic impurities simultaneously with water softening, only iron salts are used as coagulants, since at a high pH value of water necessary to remove magnesium hardness, aluminum salts do not form sorption-active hydroxide. The dose of the coagulant in the absence of experimental data is calculated using formula (20.4). The amount of suspension is determined by the formula
where W o - total water hardness, mEq/l.
Deeper softening of water can be achieved by heating it, adding an excess of precipitating reagent and bringing the softened water into contact with previously formed sediments. When water is heated, the solubility of CaCO 3 and Mg (OH) 2 decreases and softening reactions occur more fully.
From the graph (Fig. 2, a) it is clear that residual hardness, close to theoretically possible, can be obtained only with significant heating of the water. A significant softening effect is observed at 35.40°C; further heating is less effective. Deep softening is carried out at temperatures above 100° C. It is not recommended to add a large excess of the precipitating reagent during decarbonization, since the residual hardness increases due to unreacted lime or if there is magnesium non-carbonate hardness in the water due to its transition to calcium hardness:
MgS0 4 + Ca (OH) 2 = Mg (OH) 2 + CaS0 4
Rice. 2. The influence of temperature (a) and dose of lime (b) on the depth of water softening with lime-soda and lime method
Ca (0H) 2 + Na 2 C0 3 = CaC0 3 + 2NaOH,
but excess lime leads to wasteful overconsumption of soda, increasing the cost of water softening and increasing hydrate alkalinity. Therefore, excess soda is taken at about 1 mEq/L. Water hardness as a result of contact with previously fallen sediment is reduced by 0.3-0.5 mg-eq/l compared to the process without contact with sediment.
The water softening process should be controlled by adjusting the pH of the softened water. When this is not possible, it is controlled by the value of hydrate alkalinity, which is maintained within 0.1-0.2 mg-eq/l during decarbonization, and 0.3-0.5 mg-eq/l during lime-soda softening.
With the soda-sodium method of softening water, it is treated with soda and sodium hydroxide:
Due to the fact that soda is formed by the reaction of sodium hydroxide with bicarbonate, the dose required to add it to water is significantly reduced. If the concentration of bicarbonates in the water is high and the non-carbonate hardness is low, excess soda may remain in the softened water. Therefore, this method is used only taking into account the relationship between carbonate and non-carbonate hardness.
Soda-sodium method Usually used to soften water whose carbonate hardness is slightly higher than non-carbonate hardness. If the carbonate hardness is approximately equal to the non-carbonate hardness, you don’t need to add soda at all, since the amount required to soften such water is formed as a result of the interaction of bicarbonates with caustic soda. The dose of soda ash increases as the non-carbonate hardness of the water increases.
The soda-regenerative method, based on the renewal of soda during the softening process, is used in water preparation and for feeding low-pressure steam boilers
Ca (HC0 3) 2 + Na 2 C0 3 = CaC0 3 + 2NaHC0 3.
Sodium bicarbonate, entering a boiler with softened water, decomposes under the influence high temperature
2NaHC0 3 = Na 2 C0 3 + H 2 0 + C0 2.
The resulting soda, together with the excess soda initially introduced into the water softener, is immediately hydrolyzed in the boiler to form sodium hydroxide and carbon monoxide (IV), which enters the water softener with the purge water, where it is used to remove calcium and magnesium bicarbonates from the softened water. The disadvantage of this method is that the formation of a significant amount of CO 2 during the softening process causes corrosion of the metal and an increase in dry residue in the boiler water.
Barium water softening method used in combination with other methods. First, barium containing reagents are introduced into the water (Ba (OH) 2, BaCO 3, BaA1 2 0 4) to eliminate sulfate hardness, then after clarification of the water, it is treated with lime and soda to soften it. The chemistry of the process is described by the reactions:
Because of high cost reagents, the barium method is used very rarely. It is unsuitable for the preparation of drinking water due to the toxicity of barium reagents. The resulting barium sulfate settles very slowly, so settling tanks or clarifiers are needed large sizes. To introduce BaCO3, flocculators with mechanical stirrers should be used, since BaCO3 forms a heavy, quickly settling suspension.
The required doses of barium salts, mg/l, can be found using the expressions: barium hydroxide (product of 100% activity) D b =1.8 (SO 4 2-), barium aluminate D b =128Zh 0; barium carbonate D in = 2.07γ (S0 4 2-);
Barium carbonate is used with lime. By exposing barium carbonate to carbon dioxide, barium bicarbonate is obtained, which is dosed into the water to be softened. In this case, the dose of carbon dioxide, mg/l, is determined from the expression: D arc. = 0.46 (SO 4 2-); where (S0 4 2-) is the content of sulfates in the softened water, mg/l; γ=1.15.1.20 - coefficient taking into account the loss of barium carbonate.
Oxalate method of water softening based on the use of sodium oxalate and the low solubility of the resulting calcium oxalate in water (6.8 mg/l at 18° C)
The method is distinguished by its simplicity of technological and hardware design, however, due to the high cost of the reagent, it is used to soften small quantities of water.
Phosphating is used to soften water. After reagent softening using the lime-soda method, the presence of residual hardness (about 2 mEq/l) is inevitable, which can be reduced to 0.02-0.03 mEq/l by phosphate softening. Such deep purification allows in some cases not to resort to cation exchange water softening.
Phosphating also achieves greater stability of water, reduces its corrosive effect on metal pipelines and prevents carbonate deposits on the inner surface of pipe walls.
Hexametaphosphate, sodium tripolyphosphate (orthophosphate), etc. are used as phosphate reagents.
The phosphate method of water softening using tri-sodium phosphate is the most effective reagent method. The chemistry of the water softening process with trisodium phosphate is described by the reactions
As can be seen from the above reactions, the essence of the method is the formation of calcium and magnesium salts of phosphoric acid, which have low solubility in water and therefore precipitate quite completely.
Phosphate softening is usually carried out by heating water to 105.150 ° C, achieving its softening to 0.02.0.03 mEq/l. Due to the high cost of trisodium phosphate, the phosphate method is usually used to soften water previously softened with lime and soda. The dose of anhydrous trisodium phosphate (Df; mg/l) for additional softening can be determined from the expression
D F =54.67 (W OST + 0.18),
where Zhost is the residual hardness of softened water before phosphate softening, mEq/l.
Ca 3 (P0 4) 2 and Mg 3 (P0 4) 2 precipitates formed during phosphate softening well adsorb organic colloids and silicic acid from softened water, which makes it possible to identify the feasibility of using this method for the preparation of feed water for medium and high pressure boilers (58 ,8.98.0 MPa).
A solution for dosing sodium hexametaphosphate or sodium orthophosphate with a concentration of 0.5-3% is prepared in tanks, the number of which must be at least two. The internal surfaces of the walls and bottom of the tanks must be coated with corrosion-resistant material. The preparation time for a 3% solution is 3 hours with mandatory stirring with a stirrer or bubbler (using compressed air) way.
Reagent water softening technology uses equipment for preparing and dosing reagents, mixers, thin-layer sedimentation tanks or clarifiers, filters and installations for stabilizing water treatment. The diagram of a pressure water softening installation is shown in Fig. 3
Rice. 3. Water softening plant with a vortex reactor.
1 - hopper with contact mass; 2 - ejector; 3, 8 - supply of source water and removal of softened water; 4 - vortex reactor; 5 - input of reagents; 6 - fast clarification filter; 9 - contact mass release; 7 - softened water tank
This installation does not have a flocculation chamber, since flocs of calcium carbonate precipitate are formed in the contact mass. If necessary, the water before the reactors is clarified.
The optimal structure for softening water using lime or lime-soda methods is vortex reactor (pressure or open spiractor) ( rice. 20.4). The reactor is a reinforced concrete or steel body, narrowed downwards (taper angle 5.20°) and filled to approximately half the height with contact mass. The speed of water movement in the lower narrow part of the vortex reactor is 0.8.1 m/s; the speed of the upward flow in the upper part at the level of drainage devices is 4.6 mm/s. Sand or marble chips with a grain size of 0.2-0.3 mm are used as a contact mass at the rate of 10 kg per 1 m3 of reactor volume. With a helical upward flow of water, the contact mass is suspended, grains of sand collide with each other and CaCO 3 intensively crystallizes on their surface; grains of sand gradually turn into balls correct form. Hydraulic resistance contact mass is 0.3 m per 1 m height. When the diameter of the balls increases to 1.5.2 mm, the largest, heaviest contact mass is released from the lower part of the reactor and a fresh one is added. Vortex reactors do not retain magnesium hydroxide sediment, so they should be used in conjunction with filters installed behind them only in cases where the amount of magnesium hydroxide sediment formed corresponds to the dirt holding capacity of the filters.
With a dirt holding capacity of sand filters equal to 1.1.5 kg/m3 and a filter cycle of 8 hours, the permissible amount of magnesium hydroxide is 25.35 g/m3 (the magnesium content in the source water should not exceed 10.15 g/m3). It is possible to use vortex reactors with a higher content of magnesium hydroxide, but after them it is necessary to install clarifiers to separate magnesium hydroxide.
The consumption of fresh contact mass added using an ejector is determined by the formula G = 0.045QZh, where G- amount of added contact mass, kg/day; AND- water hardness removed in the reactor, mEq/l; Q - installation productivity, m 3 / h.
Rice. 4. Vortex reactor.
1,8 - supply of source water and removal of softened water: 5 - samplers; 4 - contact mass; 6 - air release; 7 - hatch for loading contact mass; 3 - input of reagents; 2 - removal of spent contact mass
In technological schemes of reagent water softening with clarifiers, vertical mixers are used instead of vortex reactors (Fig. 5). In clarifiers it is necessary to maintain constant temperature, not allowing fluctuations of more than 1°C for an hour, since convection currents arise, sediment resuspension and its removal.
A similar technology is used to soften turbid waters containing a large number of magnesium salts. In this case, the mixers are loaded with contact mass. When using clarifiers designed by E.F. Kurgaev, mixers and floc formation chambers are not provided, since the mixing of reagents with water and the formation of sediment flocs occurs in the clarifiers themselves.
The significant height and small volume of sediment compactors allows them to be used for softening water without heating, as well as for desiliconizing water with caustic magnesite. The distribution of the source water by nozzles determines its rotational movement in the lower part of the apparatus, which increases the stability of the suspended layer during fluctuations in temperature and water supply. Water mixed with reagents passes through horizontal and vertical mixing partitions and enters the zone of sorption separation and regulation of the sediment structure, which is achieved by changing the conditions for selecting sediment along the height of the suspended layer, creating the prerequisites for obtaining its optimal structure, which improves the effect of softening and clarification of water. Clarifiers are designed in the same way as for conventional water clarification.
At flow rates of softened water up to 1000 m 3 /day, a water treatment plant of the “Jet” type can be used. The treated water with reagents added to it enters a thin-layer sedimentation tank, then onto a filter.
The Institute of Mining of the Siberian Branch of the Russian Academy of Sciences has developed a reagent-free electrochemical technology for water softening. Using the phenomenon of alkalization at the anode and acidification at the cathode when passing a direct electric current through a water system, the water discharge reaction can be represented by the following equation:
2Н 2 0 + 2е 1 → 20Н - + Н 2,
where e 1 is a sign indicating the ability of hardness salts to dissociate into Ca (II) and Mg (II) cations.
As a result of this reaction, the concentration of hydroxyl ions increases, which causes the binding of Mg (II) and Ca (II) ions into insoluble compounds. From the anode chamber of a diaphragm (belting fabric diaphragm) electrolyzer, these ions pass into the cathode chamber due to the potential difference between the electrodes and the presence of electric field between them.
In Fig. 6 shown technology system installations for softening water using an electrochemical method.
The production plant was installed in the district boiler house, the testing of which lasted about two months. The electrochemical treatment regime turned out to be stable; no deposits were observed in the cathode chambers.
The voltage on the supply busbars was 16 V, the total current was 1600 A. The total productivity of the installation was 5 m3/h, the speed of water movement in the anode chambers was 0.31 n-0.42 m/min, in the gap between the diaphragm and the cathode 0.12- 0.18 m/min.
Rice. 5. Installation of lime-soda water softening.1 ,8 - supply of source water and removal of softened water; 2 - ejector; 3 - hopper with contact mass; 5 input of reagents; 6 - clarifier with a layer of suspended sediment; 7 - fast clarification filter; 4 - vortex reactor
Rice. 6. Installation diagram for electrochemical water softening I - rectifier VAKG-3200-18; 2 - diaphragm electrolyzer; 3, 4 - analyte and catalyte; 5 - pump; 6 - pH meter; 7 - clarifier with a layer of suspended sediment; 8 - clarification fast filter; 9 - discharge into the sewer; 10, 11 - removal of softened water and supply of source water; 12 - flow meter; 13 - exhaust hood
It has been established that from water with W o = 14.5-16.7 mg-eq/l, an anolyte with a hardness of 1.1 - 1.5 mg-eq/l at pH = 2.5-3 and a catholyte with a hardness of 0 are obtained .6-1 mEq/l at pH=10.5-11. After mixing the filtered anolyte and catholyte, the softened water indicators were as follows: the total hardness of liquid was 0.8-1.2 mEq/l, pH = 8-8.5. Electricity costs amounted to 3.8 kW*h/m3.
Chemical, X-ray diffraction, IR spectroscopic and spectral analyzes It was found that the sediment predominantly contains CaC0 3, Mg (OH) 2 and partially Fe 2 0 3 *H 2 0. This indicates that the binding of Mg (II) ions occurs due to hydroxyl ions during the discharge of water molecules at the cathode .
Electrochemical treatment of water before feeding it to cation exchange filters can significantly (15-20 times) increase their operating cycle.
Thermochemical softening is used exclusively in the preparation of water for steam boilers, since in this case the heat spent on heating water is used most efficiently. With this method, water softening is usually carried out at water temperatures above 100°C. More intensive softening of water when heated is facilitated by the formation of heavy and large flakes of sediment, its rapid sedimentation due to a decrease in the viscosity of water when heated, and the consumption of lime is also reduced, since free carbon monoxide (IV) is removed by heating before the introduction of reagents. The thermochemical method is used with or without the addition of a coagulant, since the high density of the sediment eliminates the need to weigh it down during sedimentation. In addition to the coagulant, lime and soda with the addition of phosphates are used, and less often sodium hydroxide and soda. Application of hydroxide Using sodium instead of lime somewhat simplifies the technology for preparing and dosing the reagent, but such a replacement is not economically justified due to its high cost.
To ensure the removal of non-carbonate hardness in water, soda is added in excess. In Fig. Figure 7 shows the effect of excess soda on the residual calcium and total hardness of water during its thermochemical softening. As can be seen from the graphs, with an excess of soda of 0.8 mg/eq/l, calcium hardness can be reduced to 0.2, and total hardness to 0.23 mg/eq/l. With further addition of soda, the hardness decreases even more. The residual magnesium content in water can be reduced to 0.05-0.1 mEq/L with an excess of lime (hydrate alkalinity) of 0.1 mEq/L. In Fig. Figure 20.8 shows a thermochemical water softening installation.
Lime-dolomite method used for simultaneous softening and desiliconization of water at a temperature of 120 ° C. With this softening method, the alkalinity of water treated with lime or lime and soda (without excess) can be reduced to 0.3 mEq/l with a residual calcium concentration of 1.5 mg -eq/l and up to 0.5 mEq/l with a residual calcium concentration of 0.4 mEq/l. The source water is treated with lime-dolomite milk and clarified in a pressure clarifier. Then it passes through pressure anthracite and Na-cationite filters of the first and second stages.
In clarifiers, the height of the clarification zone is taken to be 1.5 m, the speed of the upward flow during liming is no more than 2 mm/s. The residence time of water in the clarifier is from 0.75 to 1.5 hours, depending on the type of contamination being removed. Iron (III) salt coagulant is recommended to be added in an amount of 0.4 mEq/l.
Rice. 7. The effect of excess soda on residual calcium (a) and total (b) water hardness during thermochemical softening
Rice. 8. Installation of lime-soda water softening with phosphate softening: 1 - discharge of sludge from the storage tank 2,3 - collection of softened water; 4 - input of lime and soda; 5, 11 - supply of source water and removal of softened water; 6 - steam input; 7, 8 - thermoreactor of the first and second stages; 9 - introduction of trisodium phosphate; 10 - clarification fast filter
High temperature water softening method used to almost completely soften it. Thermochemical water softening units are usually more compact. They consist of reagent dispensers, thin-layer sedimentation tank or clarifier heaters and filters. Doses of lime D and soda D s, mg/l, for thermochemical water softening
where C and and C c are, respectively, the content of CaO and Na 2 C0 3 in the technical product, %.
Dialysis is a method of separating solutes that differ significantly in molecular weight. It is based on different speeds diffusion of these substances through a semi-permeable membrane separating concentrated and dilute solutions. Under the influence of a concentration gradient (according to the law of mass action), dissolved substances with different speeds diffuse through the membrane towards the dilute solution. The solvent (water) diffuses in the opposite direction, reducing the rate of solute transport. Dialysis is carried out in membrane devices with nitro- and cellulose acetate film membranes. The effectiveness of a semi-permeable membrane for water softening is determined by the high values of selectivity and water permeability, which it must maintain over a long operating time. The selectivity of the membrane can be expressed as follows:
(Zh i - Zh y) /Zh i (20.11)
where Ж в is the concentration of the initial solution (hardness); W and - hardness of softened water.
In practice, the salt reduction coefficient is often used - the content of C and /C arr. It most fully reflects changes in the operation of the membrane associated with its manufacture or exposure to external factors.
There are several hypothetical models for the action of semipermeable membranes.
Hyperfiltration hypothesis assumes the existence of pores in a semi-permeable membrane that allow associates of water molecules and hydrated salt ions to pass through during dialysis. The basis of theoretical developments was the position that water and salts dissolved in it penetrate through a semi-permeable membrane using diffusion and flows through the pores.
Sorption model permeability is based on the premise that on the surface of the membrane and in its pores layer adsorbed bound water, with reduced dissolving ability. Membranes will be semi-permeable if they, at least in the surface layer, have pores that do not exceed twice the thickness of the layer of bound liquid.
Diffusion model is based on the assumption that the components of the system dissolve in the membrane material and diffuse through it. The selectivity of the membrane is explained by the difference in the diffusion coefficients and solubility of the system components in its material.
Electrostatic theory is as follows. When the source water moves in the chamber on one side of the selective (cationite) membrane, and the brine on the other, sodium ions, in the case when the brine is prepared from a solution of table salt, migrate into the membrane and then into the source water, and calcium ions in the opposite direction, i.e. .e. from hard water to brine. Thus, calcium ions are removed from the source water and replaced with non-precipitating sodium ions. At the same time, side processes occur in the chambers that accompany the main dialysis process: osmotic transfer of water, transfer of like ions, diffusion of electrolyte. These processes depend on the quality of the membrane.
The exchange equation between ions contained in the source water and ions in the membrane has the form
Where x, x- other ions contained in the solution and in the membrane.
Equilibrium constant
The exchange equation is written only for the calcium ion, but> in fact it is necessary to take into account the sum of the calcium and magnesium ions. The equilibrium between the brine and the membrane is:
If k1+ k 2 then
where n is an exponent depending on which ions are included in the solution.
From last expression we can conclude that if the equilibrium ratio of sodium ions in brine and hard source water is, for example, 10, then the hardness in the source water will be approximately 100 times less than in the brine. Area, m2, membrane surface
where M is the amount of substance that has passed through the membrane; ΔC av - the driving force of the process, i.e. the difference in the concentrations of the substance on both sides of the membrane; Kd is the mass transfer coefficient, usually determined experimentally or approximately from the expression
β 1 and β 2 are the corresponding coefficients of the rate of transfer of a substance in a concentrated solution to the membrane and from it in a dilute solution; b - membrane thickness; D- diffusion coefficient of the solute.
Hardness of softened water after dialysis:
where C d and C p are the concentrations of salts at the beginning of the apparatus, respectively, in the dialysate and in the brine, mEq/l; And Q p - productivity of the device for dialysate and brine, respectively, m 3 /h; F d and F r - hardness of the dialysate and brine at the beginning of the apparatus, mEq/l; a is a constant determined by the properties of membranes and solutions;; L- length of the path of the solution in the dialysate and brine chambers of the apparatus, m; υ d - speed of movement of the dialysate in the chamber, m/s.
Experimental testing of equation (20.13) on MCC cation exchange membranes showed good convergence of results. Analysis of formula (20.13) shows that reducing the speed of movement of the dialysate in the chambers of the apparatus increases the softening effect; the decrease in the hardness of softened water is directly proportional to the brine concentration.
IN Lately In domestic and foreign practice, magnetic water treatment is successfully used to combat scale formation and encrustation. The mechanism of the influence of a magnetic field on water and its admixture has not been fully clarified, there are a number of hypotheses that E.F. Tebenikhin classified into three groups: the first, which unites most of the hypotheses, relates the effect of a magnetic field on salt ions dissolved in water. Under the influence of a magnetic field polarization and deformation of ions occur, accompanied by a decrease in their hydration, increasing the likelihood of their approach, and in ultimately education crystallization centers; the second assumes the action of a magnetic field on colloidal impurities of water; the third group combines ideas about the possible influence of a magnetic field on the structure of water. This the influence, on the one hand, can cause changes in the aggregation of water molecules, and on the other, disrupt the orientation of the nuclear spins of hydrogen in its molecules.
Treatment of water in a magnetic field is common to combat scale formation. The essence of the method is that when water crosses magnetic lines of force, scale formers are released not on the heating surface, but in the mass of water. The resulting loose sediments (sludge) are removed by blowing. The method is effective in treating waters of the calcium-carbonate class, which make up about 80% of the waters of all reservoirs in our country and cover approximately 85% of its territory.
Treatment of water with a magnetic field has received wide application to combat scale formation in steam turbine condensers, in low-pressure and low-capacity steam generators, in heating networks and hot water supply networks and various heat exchangers, where the use of other water treatment methods is not economically feasible. Compared to water softening, the main advantages of magnetic treatment are simplicity, low cost, safety and almost complete absence of operating costs.
Magnetic processing natural waters(both fresh and mineralized) leads to a decrease in the intensity of scale formation on heating surfaces only if they are oversaturated with both calcium carbonate and calcium sulfate at the time of exposure to a magnetic field and provided that the concentration of free carbon monoxide (IV) is less than its equilibrium concentration . The anti-scale effect of E determines the presence of iron oxides and other impurities in water:
where m n and m m are the mass of scale formed on the heating surface during boiling under the same conditions of the same amount of water, respectively untreated and treated with a magnetic field, g.
The anti-scale effect depends on the composition of the water, the strength of the magnetic field, the speed of water movement and the duration of its stay in the magnetic field and other factors. In practice, magnetic devices with permanent steel or ferrite-barium magnets and electromagnets are used (Fig. 9). Devices with permanent magnets are simpler in design and do not require power from the mains. In devices with an electromagnet, coils of wire are wound around a core (core), creating a magnetic field.
The magnetic device is mounted to pipelines in a vertical or horizontal position using adapter couplings. The speed of water movement in the gap should not exceed 1 m/s. The process of operation of the devices may be accompanied by contamination of the passage gap with mechanical, mainly ferromagnetic impurities. Therefore, devices with permanent magnets must be periodically disassembled and cleaned. Iron oxides are removed from devices with electromagnetic devices by disconnecting them from the network.
The results of MGSU research (G.I. Nikoladze, V.B. Vikulina) showed that for water with a carbonate hardness of 6.7 mcg-eq/l, oxidability of 5.6 mg02/l and salt content of 385.420 mg/l, the optimal magnetic field strength was (10.12.8) * 19 4 A/m, which corresponds to a current strength of 7.8 A.
The installation diagram for magnetic treatment of additional feed water of heating steam boilers is shown in Fig. 20.10.
Recently, devices with external magnetizing coils have become widespread. To magnetize large masses of water, devices with layer-by-layer processing have been created.
In addition to preventing scale formation, magnetic treatment , according to P.P. Strokacha can be used to intensify the process of coagulation and crystallization, accelerate the dissolution of reagents, increase the efficiency of using ion exchange resins, and improve the bactericidal effect of disinfectants.
Rice. 9. Electromagnetic device for anti-scale treatment of water SKV VTI: 1,8 - supply of source and removal of magnetized water; 2 - net; 3 - working gap for passage of magnetized water; 4 - casing; 5 - magnetizing coil; 6 - core; 7 - frame; 9 - lid; 10 – terminals
When designing magnetic devices for water treatment, the following data is specified: the type of device, its performance, the magnetic field induction in the working gap or the corresponding magnetic field strength, the speed of water in the working gap, the time it takes water to pass through the active zone of the device, the type and its voltage for the electromagnetic device or magnetic alloy and magnet dimensions for permanent magnet devices.
Rice. 10. Layout of a magnetic installation for treating boiler water without preliminary purification.
1,8 - source and make-up water; 2 - electromagnetic devices; 3, 4 - stage I and II heaters; 5 - deaerator; 6 - intermediate tank; 7 - charging pump
1. Alekseev L.S., Gladkov V.A. Improving the quality of soft waters. M.,
2. Stroyizdat, 1994
3. Alferova L.A., Nechaev A.P. Closed water systems of industrial enterprises, complexes and districts. M., 1984.
4. Ayukaev R.I., Meltser V.Z. Production and application of filter materials for water purification. L., 1985.
5. Weitzer Yu.M., Miits D.M. High-molecular flocculants in water purification processes. M., 1984.
6. Egorov A.I. Hydraulics of pressure tubular systems in water supply systems wastewater treatment plants. M., 1984.
7. Zhurba M.G. Water purification using granular filters. Lvov, 1980.
" and "Chemical reagent methods of softening water" section "Water" and subsection " " we touched on the topic of combating hardness salts and scale. In previous articles we looked at the actual definition of the word "softening water" and considered that there are several methods of softening - physical, chemical, extrasensory. We also touched upon such reagent methods of water softening as ion exchange and the dosage of antiscalants (antiscale formers). In this article we offer you two subsections - a little about extrasensory methods and a little more about physical methods of water softening.
Psychic and physical methods of softening water are not fully studied and understood. This is probably why the extrasensory way of dealing with hard water is often confused with the physical way of fighting. And, accordingly, they lose money, time and faith in people. Both for the purchase of psychic gadgets and for the repair of equipment that they did not protect from scale. By the way, for a good understanding of the article, we recommend that you first study the materials of the articles “Hard water” and “”, where the basic definitions used in this article are given (such as water softening, scale, hardness, hardness salts, etc.)
So, extrasensory methods are easily confused with physical ones. About the same as the ganzfeld effect with magic. For example, treating water with a magnetic field. This is both a high-quality way to combat scale and a useless extrasensory way of purifying and structuring water.
The difference between physical and extrasensory methods is very simple - if a thing costs little money (on average up to 100 USD), but it is promised that it will accomplish a whole lot of tasks (such as: purify the water of all substances, remove scale, improve health and give youth, structures, accelerates the growth of plants and hair, removes damage, etc.), then this is an extrasensory way of purifying water. We will not dwell on extrasensory methods in detail; they are described in various sources (for example, here), since they are of no use except a hundredth part of what was promised.
By the way, recently there has been a tendency for such softening structurers to become more expensive. So you can run into a very expensive fake, which is advertised as protection against scale. However, usually devices that can actually physically help with scale do not have additional structuring functions.
So, if you want to engage in extrasensory structuring, you need to purchase a special device. If you need to physically soften water, you need to purchase a special device. But not a complex. Although... As you like :) And we will move on to physical methods of dealing with scale.
As mentioned earlier, there are several definitions of the term “water softening”, depending on the stage at which the impact occurs -
Previous methods - ion exchange - are aimed at combating the causes of water hardness. That is, either calcium and magnesium salts are removed from the water, which leads to the creation of soft water.
Accordingly, physical softening methods do not imply soft water in the first sense (water without any hardness salts at all). The result of physical water softening is water that has retained all its hardness salts, but does not harm pipes and boilers - that is, does not form scale. However, after physical treatment, hard water changes its properties - and, as a result, ceases to form scale. That is, it ceases to be tough. And it becomes soft. Of course, if we were engaged in scientific research, we would introduce a difference in the terms “soft water”, that is, water in which there are no hardness salts in principle, and “softened water”, which does not form scale, but may contain hardness salts. However, these are terminological nuances that are not interesting to us. We actually need physical ways to soften water.
There are the following basic physical methods to combat scale:
And we will begin to gradually characterize physical methods of dealing with hard water. We may not cover everything at once in one article, but a series of articles will definitely include the characteristics of each method. Let's start with treating water with a magnetic field, since this type of physical fight against scale is most often confused with extrasensory softening of water.
Treatment of water with a magnetic field is a complex and controversial issue. Without going into details, we can say that effective physical softening of water using a magnetic field is possible only when it is possible to simultaneously take into account a huge number of factors. This:
All these and many other factors influence the effectiveness of magnetic water treatment. Thus, a slight change in the composition of water should be compensated by changes in the specified parameters (for example, water speed and magnetic field intensity). All changes must be monitored and responded to immediately, since the effectiveness of physical water softening using a magnetic field will change in an unknown direction.
But it is possible, and magnetic water treatment is successfully used in many boiler houses. First of all, this happens because in boiler rooms the constancy of most of the listed factors is observed - water flow, water composition, water temperature, pressure, etc.
However, this is almost NOT possible to repeat at home. And when you have a desire to buy a magnet for a pipe in order to save your home from scale, then think a lot, and first of all, think about whether you can organize not only the constancy of the indicators described above, but also find their optimal combination through experiments.
If not, then treating water using a magnetic field in the form of magnets is not for you, and you will get nothing except losing money on buying a magnet and on repairing equipment and pipes. Another way to put it is this: the probability that a pipe magnet will help you is less than 10%. That is, at home, a constant magnetic field approaches extrasensory water softening.
In order to compensate for the variability of water parameters during physical treatment, more modern methods physical softening - for example, using an electronic water softener.
Which will be discussed in the sequel.
Basic methods of water softening
Thermochemical water softening method
Water softening by dialysis
Magnetic water treatment
Literature
Water softening refers to the process of removing hardness cations from it, i.e. calcium and magnesium. In accordance with GOST 2874-82 "Drinking water", water hardness should not exceed 7 mEq/l. Certain types of production require deep softening of process water, i.e. up to 0.05.0.01 mEq/l. Typically used water sources have a hardness that meets drinking water standards and do not require softening. Water softening is carried out mainly during its preparation for technical purposes. Thus, the hardness of water for feeding drum boilers should not exceed 0.005 mEq/l. Water softening is carried out using the following methods: thermal, based on heating water, its distillation or freezing; reagent methods, in which the Ca (II) and Mg (II) ions present in water are bound by various reagents into practically insoluble compounds; ion exchange, based on filtering softened water through special materials that exchange their constituent Na (I) or H (1) ions for Ca (II) and Mg (II) ions contained in dialysis water; combined, representing various combinations of the listed methods.
The choice of water softening method is determined by its quality, the required depth of softening and technical and economic considerations. In accordance with the recommendations of SNiP, ion exchange methods should be used when softening groundwater; when softening surface water, when water clarification is also required, the lime or lime-soda method is used, and when deep softening water, subsequent cationization. The main characteristics and conditions for using water softening methods are given in table. 20.1.
softening water dialysis thermal
To obtain water for domestic and drinking needs, usually only a certain part of it is softened, followed by mixing with source water, and the amount of softened water Q y is determined by the formula
where is J o. And. - total hardness of source water, mEq/l; F 0. s. - total hardness of water entering the network, mEq/l; F 0. y. - hardness of softened water, mEq/l.
Water softening methods
| Index | thermal | reagent | ion exchange | dialysis |
| Process characteristics | Water is heated to a temperature above 100°C, which removes carbonate and non-carbonate hardness (in the form of calcium carbonate, hydroxy- and magnesium and gypsum) | Lime is added to the water, which eliminates carbonate and magnesium hardness, as well as soda, which eliminates non-carbonate hardness. | The water to be softened is passed through cation exchanger filters | Source water is filtered through a semi-permeable membrane |
| Purpose of the method | Elimination of carbonate hardness from water used to feed low and medium pressure boilers | Shallow softening while simultaneously clarifying water from suspended solids | Deep softening of water containing a small amount of suspended solids | Deep water softening |
| Water consumption for own needs | - | No more than 10% | Up to 30% or more in proportion to the hardness of the source water | 10 |
| Conditions for effective use: source water turbidity, mg/l | Up to 50 | Up to 500 | No more than 8 | Up to 2.0 |
| Water hardness, mEq/l | Carbonate hardness with a predominance of Ca (HC03) 2, non-carbonate hardness in the form of gypsum | 5.30 | Not higher than 15 | Up to 10.0 |
| Residual water hardness, mEq/l | Carbonate hardness up to 0.035, CaS04 up to 0.70 | Up to 0.70 | 0.03.0.05 prn single-stage and up to 0.01 with two-stage cationization | 0.01 and below |
| Water temperature, °C | Up to 270 | Up to 90 | Up to 30 (glauconite), up to 60 (sulfonite) | Up to 60 |
The thermal method of water softening is advisable to use when using carbonate waters used to feed low-pressure boilers, as well as in combination with reagent methods of water softening. It is based on a shift in the carbon dioxide equilibrium when it is heated towards the formation of calcium carbonate, which is described by the reaction
Ca (HC0 3) 2 -> CaCO 3 + C0 2 + H 2 0.
The equilibrium is shifted due to a decrease in the solubility of carbon (IV) monoxide caused by an increase in temperature and pressure. Boiling can completely remove carbon (IV) monoxide and thereby significantly reduce calcium carbonate hardness. However, it is not possible to completely eliminate this hardness, since calcium carbonate, although slightly (13 mg/l at a temperature of 18°C), is still soluble in water.
If magnesium bicarbonate is present in water, the process of its precipitation occurs as follows: first, relatively highly soluble (110 mg/l at a temperature of 18 ° C) magnesium carbonate is formed
Mg (HCO 3) → MgC0 3 + C0 2 + H 2 0,
which hydrolyzes during prolonged boiling, resulting in a slightly soluble precipitate (8.4 mg/l). magnesium hydroxide
MgC0 3 +H 2 0 → Mg (0H) 2 +C0 2 .
Consequently, when water is boiled, the hardness caused by calcium and magnesium bicarbonates decreases. When water is boiled, hardness, determined by calcium sulfate, also decreases, the solubility of which drops to 0.65 g/l.
In Fig. 1 shows a thermal softener designed by Kopyev, characterized by the relative simplicity of the device and reliable operation. The treated water, preheated in the apparatus, enters through the ejector onto the socket of the film heater and is sprayed over vertically placed pipes, and flows down through them towards the hot steam. Then, together with the blowdown water from the boilers, it enters the clarifier with suspended sediment through the central supply pipe through the perforated bottom.
The carbon dioxide and oxygen released from the water along with excess steam are discharged into the atmosphere. Calcium and magnesium salts formed during the heating of water are retained in the suspended layer. Having passed through the suspended layer, the softened water enters the collection tank and is discharged outside the apparatus.
The residence time of water in the thermal softener is 30.45 minutes, the speed of its upward movement in the suspended layer is 7.10 m/h, and in the holes of the false bottom 0.1-0.25 m/s.
Rice. 1. Thermal softener designed by Kopyev.
15 - discharge of drainage water; 12 - central supply pipe; 13 - false perforated bottoms; 11 - suspended layer; 14 - sludge discharge; 9 - collection of softened water; 1, 10 - supply of source water and discharge of softened water; 2 - purging of boilers; 3 - ejector; 4 - evaporation; 5 - film heater; 6 - steam release; 7 - ring perforated pipeline for water drainage to the ejector; 8 - inclined separating partitions
Water softening using reagent methods is based on treating it with reagents that form poorly soluble compounds with calcium and magnesium: Mg (OH) 2, CaC0 3, Ca 3 (P0 4) 2, Mg 3 (P0 4) 2 and others, followed by their separation in clarifiers , thin-layer sedimentation tanks and clarification filters. Lime, soda ash, sodium and barium hydroxides and other substances are used as reagents.
Water softening by liming is used when it has high carbonate and low non-carbonate hardness, as well as when it is not necessary to remove salts of non-carbonate hardness from the water. Lime is used as a reagent, which is introduced in the form of a solution or suspension (milk) into preheated treated water. When dissolved, lime enriches the water with OH - and Ca 2+ ions, which leads to the binding of free carbon monoxide (IV) dissolved in water with the formation of carbonate ions and the transition of hydrocarbonate ions into carbonate ones:
C0 2 + 20H - → CO 3 + H 2 0, HCO 3 - + OH - → CO 3 - + H 2 O.
An increase in the concentration of CO 3 2 - ions in the treated water and the presence of Ca 2+ ions in it, taking into account those introduced with lime, leads to an increase in the solubility product and the precipitation of poorly soluble calcium carbonate:
Ca 2+ + C0 3 - → CaC0 3.
If there is an excess of lime, magnesium hydroxide also precipitates.
Mg 2+ + 20H - → Mg (OH) 2
To accelerate the removal of dispersed and colloidal impurities and reduce the alkalinity of water, coagulation of these impurities with iron (II) sulfate is used simultaneously with liming, i.e. FeS0 4 *7 H 2 0. The residual hardness of softened water during decarbonization can be obtained 0.4-0.8 mg-eq/l more than non-carbonate hardness, and the alkalinity is 0.8-1.2 mg-eq/l. The dose of lime is determined by the ratio of the concentration of calcium ions in water and carbonate hardness: a) at the ratio [Ca 2+ ] /20<Ж к,
b) with the ratio [Ca 2+ ] /20 > J c,
where [CO 2 ] is the concentration of free carbon monoxide (IV) in water, mg/l; [Ca 2+ ] - concentration of calcium ions, mg/l; Fc - carbonate hardness of water, mEq/l; D k - dose of coagulant (FeS0 4 or FeCl 3 in terms of anhydrous products), mg/l; e k - equivalent mass of the active substance of the coagulant, mg/mg-eq (for FeS0 4 e k = 76, for FeCl 3 e k = 54); 0.5 and 0.3 - excess lime to ensure greater completeness of the reaction, mEq/l.
The expression D k / e k is taken with a minus sign if the coagulant is introduced before the lime, and with a plus sign if together or after.
In the absence of experimental data, the dose of the coagulant is found from the expression
D k = 3 (C) 1/3, (20.4)
where C is the amount of suspended matter formed during water softening (in terms of dry matter), mg/l.
In turn, C is determined using the dependence
The lime-soda method of water softening is described by the following basic reactions:
Using this method, residual hardness can be brought to 0.5.1, and alkalinity from 7 to 0.8.1.2 mEq/l.
Doses of lime D and soda D s (in terms of Na 2 C0 3), mg/l, are determined by the formulas
(20.7)
where is the content of magnesium in water, mg/l; Jn. K. - non-carbonate water hardness, mEq/l.
With the lime-soda method of water softening, the resulting calcium carbonate and magnesium hydroxide can supersaturate solutions and remain in a colloidal dispersed state for a long time. Their transition into coarse sludge takes a long time, especially at low temperatures and the presence of organic impurities in the water, which act as protective colloids. With a large amount of them, water hardness during reagent water softening can be reduced by only 15.20%. In such cases, before softening or during the softening process, organic impurities are removed from the water using oxidizing agents and coagulants. With the lime-soda method, the process is often carried out in two stages. Initially, organic impurities and a significant part of carbonate hardness are removed from water using aluminum or iron salts with lime, carrying out the process under optimal coagulation conditions. After this, soda and the rest of the lime are introduced and the water is softened. When removing organic impurities simultaneously with water softening, only iron salts are used as coagulants, since at a high pH value of water necessary to remove magnesium hardness, aluminum salts do not form sorption-active hydroxide. The dose of the coagulant in the absence of experimental data is calculated using formula (20.4). The amount of suspension is determined by the formula
where W o - total water hardness, mEq/l.
Deeper softening of water can be achieved by heating it, adding an excess of precipitating reagent and bringing the softened water into contact with previously formed sediments. When water is heated, the solubility of CaCO 3 and Mg (OH) 2 decreases and softening reactions occur more fully.
From the graph (Fig. 2, a) it is clear that residual hardness, close to theoretically possible, can be obtained only with significant heating of the water. A significant softening effect is observed at 35.40°C; further heating is less effective. Deep softening is carried out at temperatures above 100° C. It is not recommended to add a large excess of the precipitating reagent during decarbonization, since the residual hardness increases due to unreacted lime or if there is magnesium non-carbonate hardness in the water due to its transition to calcium hardness:
MgS0 4 + Ca (OH) 2 = Mg (OH) 2 + CaS0 4
Rice. 2. The influence of temperature (a) and dose of lime (b) on the depth of water softening using the lime-soda and lime method
Ca (0H) 2 + Na 2 C0 3 = CaC0 3 + 2NaOH,
but excess lime leads to wasteful overconsumption of soda, increasing the cost of water softening and increasing hydrate alkalinity. Therefore, excess soda is taken at about 1 mEq/L. Water hardness as a result of contact with previously fallen sediment is reduced by 0.3-0.5 mg-eq/l compared to the process without contact with sediment.
The water softening process should be controlled by adjusting the pH of the softened water. When this is not possible, it is controlled by the value of hydrate alkalinity, which is maintained within 0.1-0.2 mg-eq/l during decarbonization, and 0.3-0.5 mg-eq/l during lime-soda softening.
With the soda-sodium method of softening water, it is treated with soda and sodium hydroxide:
Due to the fact that soda is formed by the reaction of sodium hydroxide with bicarbonate, the dose required to add it to water is significantly reduced. If the concentration of bicarbonates in the water is high and the non-carbonate hardness is low, excess soda may remain in the softened water. Therefore, this method is used only taking into account the relationship between carbonate and non-carbonate hardness.
The soda-sodium method is usually used to soften water whose carbonate hardness is slightly higher than non-carbonate hardness. If the carbonate hardness is approximately equal to the non-carbonate hardness, you don’t need to add soda at all, since the amount required to soften such water is formed as a result of the interaction of bicarbonates with caustic soda. The dose of soda ash increases as the non-carbonate hardness of the water increases.
The soda-regenerative method, based on the renewal of soda during the softening process, is used in water preparation and for feeding low-pressure steam boilers
Ca (HC0 3) 2 + Na 2 C0 3 = CaC0 3 + 2NaHC0 3.
Sodium bicarbonate, entering a boiler with softened water, decomposes under the influence of high temperature
2NaHC0 3 = Na 2 C0 3 + H 2 0 + C0 2.
The resulting soda, together with the excess soda initially introduced into the water softener, is immediately hydrolyzed in the boiler to form sodium hydroxide and carbon monoxide (IV), which enters the water softener with the purge water, where it is used to remove calcium and magnesium bicarbonates from the softened water. The disadvantage of this method is that the formation of a significant amount of CO 2 during the softening process causes corrosion of the metal and an increase in dry residue in the boiler water.
The barium method of water softening is used in combination with other methods. First, barium containing reagents are introduced into the water (Ba (OH) 2, BaCO 3, BaA1 2 0 4) to eliminate sulfate hardness, then after clarification of the water, it is treated with lime and soda to soften it. The chemistry of the process is described by the reactions:
Due to the high cost of reagents, the barium method is used very rarely. It is unsuitable for the preparation of drinking water due to the toxicity of barium reagents. The resulting barium sulfate settles very slowly, so large settling tanks or clarifiers are required. To introduce BaCO3, flocculators with mechanical stirrers should be used, since BaCO3 forms a heavy, quickly settling suspension.
The required doses of barium salts, mg/l, can be found using the expressions: barium hydroxide (product of 100% activity) D b =1.8 (SO 4 2-), barium aluminate D b =128Zh 0; barium carbonate D in = 2.07γ (S0 4 2-);
Barium carbonate is used with lime. By exposing barium carbonate to carbon dioxide, barium bicarbonate is obtained, which is dosed into the water to be softened. In this case, the dose of carbon dioxide, mg/l, is determined from the expression: D arc. = 0.46 (SO 4 2-); where (S0 4 2-) is the content of sulfates in the softened water, mg/l; γ=1.15.1.20 - coefficient taking into account the loss of barium carbonate.
The oxalate method of water softening is based on the use of sodium oxalate and the low solubility of the resulting calcium oxalate in water (6.8 mg/l at 18°C)
The method is distinguished by its simplicity of technological and hardware design, however, due to the high cost of the reagent, it is used to soften small quantities of water.
Phosphating is used to soften water. After reagent softening using the lime-soda method, the presence of residual hardness (about 2 mEq/l) is inevitable, which can be reduced to 0.02-0.03 mEq/l by phosphate softening. Such deep purification allows in some cases not to resort to cation exchange water softening.
Phosphating also achieves greater stability of water, reduces its corrosive effect on metal pipelines and prevents carbonate deposits on the inner surface of pipe walls.
Hexametaphosphate, sodium tripolyphosphate (orthophosphate), etc. are used as phosphate reagents.
The phosphate method of water softening using tri-sodium phosphate is the most effective reagent method. The chemistry of the water softening process with trisodium phosphate is described by the reactions
As can be seen from the above reactions, the essence of the method is the formation of calcium and magnesium salts of phosphoric acid, which have low solubility in water and therefore precipitate quite completely.
Phosphate softening is usually carried out by heating water to 105.150 ° C, achieving its softening to 0.02.0.03 mEq/l. Due to the high cost of trisodium phosphate, the phosphate method is usually used to soften water previously softened with lime and soda. The dose of anhydrous trisodium phosphate (Df; mg/l) for additional softening can be determined from the expression
D F =54.67 (W OST + 0.18),
where Zhost is the residual hardness of softened water before phosphate softening, mEq/l.
Ca 3 (P0 4) 2 and Mg 3 (P0 4) 2 precipitates formed during phosphate softening well adsorb organic colloids and silicic acid from softened water, which makes it possible to identify the feasibility of using this method for the preparation of feed water for medium and high pressure boilers (58 ,8.98.0 MPa).
A solution for dosing sodium hexametaphosphate or sodium orthophosphate with a concentration of 0.5-3% is prepared in tanks, the number of which must be at least two. The internal surfaces of the walls and bottom of the tanks must be coated with corrosion-resistant material. The preparation time for a 3% solution is 3 hours with mandatory mixing using a stirrer or bubbling method (using compressed air).
Technological diagrams and structural elements of reagent water softening installations
Reagent water softening technology uses equipment for preparing and dosing reagents, mixers, thin-layer sedimentation tanks or clarifiers, filters and installations for stabilizing water treatment. The diagram of a pressure water softening installation is shown in Fig. 3
Rice. 3. Water softening plant with a vortex reactor.
1 - hopper with contact mass; 2 - ejector; 3, 8 - supply of source water and discharge of softened water; 4 - vortex reactor; 5 - input of reagents; 6 - quick clarification filter; 9 - contact mass release; 7 - softened water tank
This installation does not have a flocculation chamber, since flocs of calcium carbonate precipitate are formed in the contact mass. If necessary, the water before the reactors is clarified.
The optimal structure for softening water using lime or lime-soda methods is a vortex reactor (pressure or open spiractor) (Fig. 20.4). The reactor is a reinforced concrete or steel body, narrowed downwards (taper angle 5.20°) and filled to approximately half the height with contact mass. The speed of water movement in the lower narrow part of the vortex reactor is 0.8.1 m/s; the speed of the upward flow in the upper part at the level of drainage devices is 4.6 mm/s. Sand or marble chips with a grain size of 0.2-0.3 mm are used as a contact mass at the rate of 10 kg per 1 m3 of reactor volume. With a helical upward flow of water, the contact mass is suspended, grains of sand collide with each other and CaCO 3 intensively crystallizes on their surface; gradually the grains of sand turn into balls of the correct shape. The hydraulic resistance of the contact mass is 0.3 m per 1 m height. When the diameter of the balls increases to 1.5.2 mm, the largest, heaviest contact mass is released from the lower part of the reactor and a fresh one is added. Vortex reactors do not retain magnesium hydroxide sediment, so they should be used in conjunction with filters installed behind them only in cases where the amount of magnesium hydroxide sediment formed corresponds to the dirt holding capacity of the filters.
With a dirt holding capacity of sand filters equal to 1.1.5 kg/m3 and a filter cycle of 8 hours, the permissible amount of magnesium hydroxide is 25.35 g/m3 (the magnesium content in the source water should not exceed 10.15 g/m3). It is possible to use vortex reactors with a higher content of magnesium hydroxide, but after them it is necessary to install clarifiers to separate magnesium hydroxide.
The consumption of fresh contact mass added using an ejector is determined by the formula G = 0.045Q Ж, where G is the amount of added contact mass, kg/day; W - water hardness removed in the reactor, mEq/l; Q - installation productivity, m 3 / h.
Rice. 4. Vortex reactor.
1.8 - supply of source water and discharge of softened water: 5 - samplers; 4 - contact mass; 6 - air release; 7 - hatch for loading contact mass; 3 - input of reagents; 2 - removal of spent contact mass
In technological schemes of reagent water softening with clarifiers, vertical mixers are used instead of vortex reactors (Fig. 5). In clarifiers, a constant temperature should be maintained, not allowing fluctuations of more than 1°C, for an hour, since convection currents arise, sediment resuspension and its removal.
A similar technology is used to soften turbid waters containing large amounts of magnesium salts. In this case, the mixers are loaded with contact mass. When using clarifiers designed by E.F. Kurgaev, mixers and floc formation chambers are not provided, since the mixing of reagents with water and the formation of sediment flocs occurs in the clarifiers themselves.
The significant height and small volume of sediment compactors allows them to be used for softening water without heating, as well as for desiliconizing water with caustic magnesite. The distribution of the source water by nozzles causes its rotational movement in the lower part of the apparatus, which increases the stability of the suspended layer during fluctuations in temperature and water supply. Water mixed with reagents passes through horizontal and vertical mixing partitions and enters the zone of sorption separation and regulation of the sediment structure, which is achieved by changing the conditions for selecting sediment along the height of the suspended layer, creating the prerequisites for obtaining its optimal structure, which improves the effect of softening and clarification of water. Clarifiers are designed in the same way as for conventional water clarification.
At flow rates of softened water up to 1000 m 3 /day, a water treatment plant of the “Jet” type can be used. The treated water with reagents added to it enters a thin-layer sedimentation tank, then onto a filter.
The Institute of Mining of the Siberian Branch of the Russian Academy of Sciences has developed a reagent-free electrochemical technology for water softening. Using the phenomenon of alkalization at the anode and acidification at the cathode when passing a direct electric current through a water system, the water discharge reaction can be represented by the following equation:
2Н 2 0 + 2е 1 → 20Н - + Н 2,
where e 1 is a sign indicating the ability of hardness salts to dissociate into Ca (II) and Mg (II) cations.
As a result of this reaction, the concentration of hydroxyl ions increases, which causes the binding of Mg (II) and Ca (II) ions into insoluble compounds. From the anode chamber of a diaphragm electrolyzer (diaphragm made of belting fabric) these ions pass into the cathode chamber due to the potential difference between the electrodes and the presence of an electric field between them.
In Fig. Figure 6 shows a technological diagram of an installation for softening water using an electrochemical method.
The production plant was installed in the district boiler house, the testing of which lasted about two months. The electrochemical treatment regime turned out to be stable; no deposits were observed in the cathode chambers.
The voltage on the supply busbars was 16 V, the total current was 1600 A. The total productivity of the installation was 5 m3/h, the speed of water movement in the anode chambers was 0.31 n-0.42 m/min, in the gap between the diaphragm and the cathode 0.12- 0.18 m/min.
Rice. 5. Installation of lime-soda water softening. 1.8 - supply of source water and removal of softened water; 2 - ejector; 3 - hopper with contact mass; 5 input of reagents; 6 - clarifier with a layer of suspended sediment; 7 - fast clarification filter; 4 - vortex reactor
Rice. 6. Installation diagram for electrochemical water softening I - rectifier VAKG-3200-18; 2 - diaphragm electrolyzer; 3, 4 - analyte and catalyte; 5 - pump; 6 - pH meter; 7 - clarifier with a layer of suspended sediment; 8 - fast clarification filter; 9 - discharge into the sewer; 10, 11 - removal of softened water and supply of source water; 12 - flow meter; 13 - exhaust hood
It has been established that from water with W o = 14.5-16.7 mg-eq/l, an anolyte with a hardness of 1.1 - 1.5 mg-eq/l at pH = 2.5-3 and a catholyte with a hardness of 0 are obtained .6-1 mEq/l at pH=10.5-11. After mixing the filtered anolyte and catholyte, the indicators of softened water were as follows: the total hardness of liquid was 0.8-1.2 mEq/l, pH = 8-8.5. Electricity costs amounted to 3.8 kW*h/m3.
Chemical, X-ray diffraction, IR spectroscopic and spectral analyzes have established that the sediment predominantly contains CaC0 3, Mg (OH) 2 and partially Fe 2 0 3 *H 2
Water is a forced and expensive event, which is a rather complex task associated with great variety pollutants and the appearance of new compounds in their composition. Water purification methods can be divided into 2 large groups: destructive and regenerative. Destructive methods are based on the processes of destruction of pollutants. The resulting decomposition products are removed...
It is produced through the middle and upper collection and distribution devices by directing part of the spent regeneration solution or supplying source water through the recirculation circuit. 1. TYPES OF FILTERS AND FEATURES OF THEIR STRUCTURE Ion filters are classified depending on the principle of operation, as well as on the purposes pursued when water passes through them. 1.1 FIP filters, ...
It is necessary to know the degree of hardness of the water used. Many aspects of our life depend on the hardness of drinking water: how much to use washing powder, whether measures are needed to soften hard water, how long aquarium fish will live in water, whether it is necessary to introduce polyphosphates in reverse osmosis, etc.
There are many ways to determine hardness:
The main cations present in water are calcium, magnesium, manganese, iron, strontium. The last three cations have little effect on water hardness. There are also trivalent cation of aluminum and iron, which at a certain pH form limestone plaque.
Hardness can be of different types:
There are several units of water hardness: mol/m 3, mg-eq/l, dH, d⁰, f⁰, ppm CaCO 3.
Why is water hard? Alkaline earth metal ions are found in all mineralized waters. They are taken from deposits of dolomite, gypsum and limestone. Water sources can have hardness in different ranges. There are several rigidity systems. Abroad they approach it more “harshly”. For example, in our country water is considered soft with a hardness of 0-4 mEq/l, and in the USA - 0-1.5 mEq/l; very hard water in Russia - over 12 mg-eq/l, and in the USA - over 6 mg-eq/l.
The hardness of low-mineralized waters is 80% due to calcium ions. With increasing mineralization, the proportion of calcium ions sharply decreases, and magnesium ions increases.
Most often, surface waters have less hardness than groundwater. The hardness also depends on the season: when the snow melts, it decreases.
The hardness of drinking water changes its taste. The sensitivity threshold for calcium ion is from 2 to 6 mEq/l, depending on the anions. The water becomes bitter and has a bad effect on the digestion process. WHO does not make any recommendations on water hardness, since there is no accurate evidence of its effect on the human body.
Restriction of rigidity is necessary for heating devices. For example, in boilers - up to 0.1 mEq/l. Soft water has low alkalinity and causes corrosion of water pipes. Utilities use special treatments to find a compromise between plaque and corrosion.
There are three groups of water softening methods:
Chemical methods are based on ion exchange. The filter mass is an ion exchange resin. It consists of long molecules that are collected into balls yellow color. Small processes containing sodium ions protrude from the balls.
During filtration, water permeates the entire resin, and its salts replace sodium. Sodium itself is carried away by water. Due to the difference in ion charges, 2 times more salts are washed out than deposited. Over time, the salts are replaced and the resin stops working. Each resin has its own operating period.
The ion exchange resin can be in cartridges or poured into a long barrel - a column. Cartridges are small in size and are used only to reduce the hardness of drinking water. Ideal for softening water at home. An ion exchange column is used to soften water in an apartment or small industry. In addition to the high cost, the column must be periodically loaded with recovered filter mass.
If there are no sodium ions left in the resin of the cartridge, then it is simply replaced with a new one, and the old one is thrown away. When using an ion exchange column, the resin is restored in a special tank with brine. To do this, dissolve the tableting salt. The saline solution regenerates the resin's ability to exchange ions.
The downside is the added ability of water to remove iron. It clogs the resin and renders it completely unusable. You should do a water analysis on time!
There are a number of less popular, but effective ways water softening:
Softening water with soda
The method of softening water using lime is called liming. Slaked lime is used. The carbonate content decreases.
A mixture of soda and lime is most effective. To demonstrate how to soften water at home, you can add soda ash to your washing water. Take 1-2 teaspoons per bucket. Stir well and wait for sediment to form. A similar method was used by women in Ancient Greece using stove ash.
Water after lime and soda is not suitable for food purposes!
Polyphosphates are capable of binding hardness salts. They are large white crystals. Water passes through the filter and dissolves polyphosphates, binding salts.
The disadvantage is the danger of polyphosphates for living organisms, including humans. They are a fertilizer: after entering the reservoir, active growth of algae is observed.
Polyphosphates are also unsuitable for softening drinking water!
Physical methods combat the consequences of high hardness - scale. This is a reagent-free water purification. When using it, there is no reduction in salt concentration, but simply prevents harm to pipes and heating elements. The water becomes soft or, for greater understanding, softened.
The following physical methods are distinguished:
Reagent-free water softening using a magnetic field has many nuances. Efficiency is achieved only if certain rules are observed:
Changing any parameter requires a complete reconfiguration of the entire system. The response must be immediate. Despite the difficulty of controlling parameters, magnetic water softening is used in boiler rooms.
But softening water at home using a magnetic field is almost impossible. If you want to purchase a magnet for a pipeline, think about how you will select and ensure the necessary parameters.
Ultrasound leads to cavitation - the formation of gas bubbles. The likelihood of magnesium and calcium ions meeting increases. Crystallization centers appear not on the surface of the pipes, but in the water column.
When softening hot water ultrasonic crystals do not reach the size required for deposition - scale does not form on heat exchange surfaces.
Additionally, high-frequency vibrations occur, which prevent the formation of plaque: they repel crystals from the surface.
Bending vibrations are detrimental to the formed layer of scale. It begins to break off into pieces that can clog the channels. Before using ultrasound, it is necessary to clean the surfaces from scale.
Reagent-free water softeners based on electromagnetic pulses change the way salts crystallize. Dynamic electrical impulses with different characteristics are created. They go along a winding wire on a pipe. The crystals take the form of long shelves, which are difficult to attach to the heat exchange surface.
During the processing process, carbon dioxide is released, which fights existing limescale and forms protective film on metal surfaces.
This is the first time someone hears about this method. But in fact, everyone has been using it since childhood. This is the boiling of water that is familiar to us.
Everyone has noticed that after boiling water, a precipitate of hardness salts forms. Coffee or tea is made from softer water than tap water.
How long does it take to boil? It's simple: with increasing temperature and its impact, hardness salts become less soluble and precipitate more. During the heating process, carbon dioxide is released. The faster it evaporates, the more limestone plaque forms. A tightly closed lid prevents removal carbon dioxide, and in an open container the liquid quickly evaporates.
When using heat softening, leave the lid of the container slightly open. It is also necessary to ensure the maximum area of salt deposition to accelerate the softening of drinking water.
With a hardness of up to 4 mEq/l, thermal softening is not necessary: the salts will settle more slowly than the water evaporates. The remaining water will have an increased concentration of many impurities.
The hardness of water is determined by the presence in its composition of a certain amount of impurities of soluble magnesium and calcium salts.
Water hardness is determined by the amount of admixture of calcium and magnesium salts.
One of the main criteria by which water quality is determined is its level of hardness. Hardness can be adjusted using various water softening methods.
There are several main types of hardness:
Naturally, almost every person thinks about such a question as the quality of the water they drink.
Water that is supplied to residential buildings through the water supply, undergoes certain levels of filtration, but often these are not enough to ensure drinking water required level of softness.
You can use a piece of silicon to soften water.
Therefore, most people prefer to use additional filters, of which there are a very large number today, using other methods of water softening.
The first signal that the water you drink and from which you cook food for your family is hard is the presence of scale in the kettle and pots where the water is boiled.
Signs of excessive water hardness can include more than just scale. When cooked in such water, vegetables fall apart and meat becomes tougher. White stains remain on plates and glasses after washing.
Drinking excessively hard water can cause health problems.
At the moment, there are a wide variety of methods for softening water.
Water softening is carried out through the use of certain devices, the task of which is to purify water from two types of heavy carbonate salts.
The simplest and most well-known method of softening water since ancient times is to place a small piece of silicon in a container with liquid that will be used for food and drink. The size of such a piece should be approximately 5 by 5 cm. It is enough to clean a three-liter jar of water at a time. It takes about a week to settle the water with silicon.
This is exactly how long this mineral needs to charge and soften the water, neutralizing magnesium and potassium salts.
This method is only suitable for household use.
You can soften water different ways. At the moment, there are the following main methods of water softening:
Physical method. When using this method of softening hardness, the use of chemicals of any kind is excluded. This cleaning method is ideal for softening water that is used in everyday life - for cooking and drinking.
Membrane method. Membrane methods There are several main methods.
One of the most popular subtypes of membrane cleaning is reverse osmosis or electrodialysis. The essence of this method is that water is desalted using pressure. Such water becomes suitable for drinking.
The device for such cleaning contains a membrane, which is a perforated layer made of expensive materials in the filter. Perforation, that is, the application of through holes, is made taking into account the size of the water molecule. This makes it possible to retain on the surface of the membrane any impurities that exceed the size of a water molecule.
Filtration using reverse osmosis is of such high quality that such water can be used not only for drinking, but also in various fields of production, for example, in pharmacology.
The second method of membrane purification is nanofiltration.
Nanofiltration is carried out under low pressure. The main advantage of this method is that water can be obtained exactly to the degree of purification and softness that is necessary for certain purposes. And you can get different cleaning results by replacing the membrane in the filter device.
The main disadvantages of this method include the fact that most of the water undergoing purification remains in the device for a long time.
This situation occurs for the reason that water seeps through the membrane at low speed. In addition, there are more than one filters in such a device, and accordingly, a certain amount of time will be spent passing through each of them.
Reverse osmosis, mechanical filter, as well as air conditioning.
This method is ideal for purifying water not only from impurities of all types, but also from various types of bacteria. Drinking water must be free of bacteria.
That is why air conditioning is usually installed on those devices whose task is to produce drinking water.
However, using such an installation at home is currently a difficult to obtain cleaning method.
Chemical method. For the chemical cleaning method, appropriate chemicals are used. These include sodium chlorine and phosphates.
With this cleaning method, water pipe special dispensers are installed.
But the chemical method can be dangerous because the substances used for cleaning can contribute to the formation of additional impurities, which will result in new sediment.
Ion exchange method. Ion exchange is one of the most technologically advanced simple ways water purification and softening.
Its simplicity lies in the fact that to carry out this process it is not necessary to erect any complex structures.
This method works based on ion exchange.
The main element of such cleaning devices is a gel-like resin. The resin contains a huge amount of sodium. Sodium, in contact with hard water, is exchanged for calcium and magnesium crystals.
Thus, an incredibly simple and quick cleaning water and its softening.
But a household resin cartridge must be replaced from time to time, since sodium tends to leach out of it.
And cartridges used in industry can be restored using a special solution. The cartridge is washed with this solution, and chemical reagents restore the sodium level.
With this method, water is purified very quickly and efficiently. But it cannot be called inexpensive or even accessible. After all, cartridges require considerable expenses, as well as their restoration.
Household jug filters based on this method have low productivity: only a few liters.
To provide drinking water with a sufficient level of purification and softening, it is necessary to additionally use one or more filters based on other methods.
Reagent-free method. In order to understand what a reagent-free method of water softening is, it is worth considering one of the most common methods - magnetic force.
Devices of this cleaning method are based on the use of permanent magnets increased power.
This installation does not require much effort during installation, as well as subsequent dismantling.
It is also incredibly easy to maintain and does not require any special replacement accessories in the form of cartridges or any additional cleaning.
The purification process occurs due to the fact that the magnetic force field passes through the water in a special way. At the same time, heavy salts, which make water hard, change their formula, taking on the shape of needles. This shape makes it possible to rub the affected surfaces. old scale, ultimately eliminating it completely.
Water that will be purified in this way must be room temperature, its flow should not be variable, but constant, as should the speed of its movement.
To neutralize the disadvantages of this method, it was added to the magnetic field electricity. As a result, an installation was invented that combines both types of influence - electromagnetic.
The most common method is the ion exchange softening method.
The main difference between industrial devices for purifying and softening water from household ones is that they have different tank capacities, and additionally use different classes of ion exchange resin.
Since all devices require a recovery period, the volume of water that can pass through them will be strictly defined.
If the volume of water is small, then household appliances can be used.
When we're talking about about large volumes of water, then it makes sense to install duplex softeners.
Such a device consists of two cylinders, which are controlled using one adjacent valve.
Such a device is called a continuous device for the reason that when the water is softened in one cylinder, the resin of the other cylinder has time to recover.
The class of the ion exchange resin also plays a huge role. Household softeners use only food grade resin, but industrial softeners can use different grades of resin.
