RU2522602C1 - Method of water softening - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method includes mechanical activation by passing a water flow through a membrane system with holes with d diameter not larger than 1 mm with a ratio of a flow section to 10%, with pressure variation from 0.05 to 0.5 MPa, water alkalisation with a water ammonia solution in an amount of 0.003÷0.05 wt % and separation of an insoluble sediment from the processed water. The length of hole channel L is selected by condition L≥10d, where d is a diameter of one hole. Separation of the insoluble sediment from the processed water is performed in centrifuges of a setting type with pulsing or auger discharge of the sediment.

EFFECT: increased efficiency of the water softening process, reduction of energy consumption and reduction of concentration of an introduced alkalising solution.

3 cl, 1 tbl

Description

The proposed method relates to water treatment and can be used both at home and in production conditions for softening water containing a large amount of hardness salts, as well as for clarification and purification of recycled and waste water from agriculture, food and chemical industries.

A known method of water softening [RF Patent 2106316, publ. 03/10/1998], by introducing with stirring calcium compounds, for example calcium hydroxide, followed by introducing with stirring alkali metal compounds, sedimentation of sediment, separation of clarified water from the precipitate. A mixture of K ₂ CO ₃ and KOH is used as an alkali metal compound, with K ₂ CO ₃ used in an amount determined by the dependence 48-53 Zh, where Zh is the constant hardness of the source water, and KOH is used in an amount of not more than 50 mg / l, while KOH is introduced with stirring into softened water not earlier than 30 minutes after the introduction of K ₂ CO ₃ . After settling and separating the settled water from the precipitate, the softened water is neutralized with an acid, for example phosphoric acid, to pH 8. In order to intensify the method, the softened water is preheated to 35-50 ° C.

The disadvantages of this method are multi-stage, increasing the duration of the process of water softening, as well as a slow decrease in the hardness of the softened water.

Closest to the proposed method is a method of water softening [RF Patent No. 2462422, publ. 09/27/2012], including alkalization of water with an aqueous solution of ammonia in an amount of 0.072 wt.%, Heating water to 40 ° C, stirring in the range from 1650 rpm to 17000 rpm for 45 s, settling for 2-10 minutes and filtering through a fiber filter of thermoplastics with a fiber diameter of 2.8 μm. Due to mixing in water, conditions are created for the development of cavitation processes, with developed cavitation in one milliliter of cavitating liquid contains from 10 ³ to 10 ⁵ air bubbles. There is a degassing. As a result of mechanical action, reactions with molecules of the medium and other solids are facilitated, water becomes unstable, and CaCO ₃ , MgCO ₃ , Fe (OH) ₃ precipitate.

The main disadvantages of the prototype method are the low level of degassing of dissolved gases, which takes place under the development of cavitation processes, high energy consumption for mechanical mixing and heating of water to 40 ° C, and the need for a special fiber filter made of thermoplastics with a fiber diameter of 2.8 μm. In addition, settling the solution for 10 minutes leads to an increase in the duration of the process.

The present invention is the creation of a method of water softening, which allows to improve the quality of drinking water, accelerate the process of softening and reduce energy consumption.

The technical result consists in increasing the efficiency of the process of water softening, in reducing energy consumption and reducing the concentration of the introduced alkalizing solution.

The specified technical result is achieved in that in the method of water softening, including, like the prototype, alkalization with an aqueous solution of ammonia, mechanical activation and the release of insoluble precipitate from the treated water, unlike the prototype, mechanical activation is carried out by passing a stream of water through a membrane system with holes with a diameter d of not more than 1 mm with a flow ratio of up to 10%, with a pressure drop of 0.05 to 0.5 MPa, then alkalized with an aqueous solution of ammonia in an amount of 0.003 ÷ 0.05 wt.%.

It is advisable that the length of the channel of the holes L of the membrane system be selected from the condition L≥10d, where d is the diameter of one hole, which corresponds to the established mode of gas-liquid flow at a given temperature.

It is advisable to isolate insoluble sludge from the treated water in centrifuges of a settling type with pulsating or screw discharge of sludge.

To accelerate the process of water softening, we propose to carry out water treatment by increasing the contact surface area of the phases, which is carried out by obtaining microbubble gas-liquid media of increased gas content, when the water flows through the membrane system, the hydrostatic pressure passes into the dynamic pressure and the dissolved gases are extracted from the water. A method of softening water from hardness salts involves increasing the contact surface area of the phases by isolating the gas phase from the initial solution in the form of gas bubbles from 5 to 50 μm, alkalizing water to pH 8-10 with aqueous ammonia in an amount of 0.003 ÷ 0.05 wt.% . The increase in the surface area of the contact of the phases avoids the process of heating water to 40 ° C, which is necessary in the known methods.

Many of the physical properties of water can reversibly change as a result of its filling with air bubbles. Due to the passage of the membrane system by the water flow, in which, due to the transfer of hydrostatic pressure to dynamic pressure (the potential energy is converted into kinetic energy), the dissolved gases are extracted from water, thereby creating conditions for the development of a gas-liquid medium with a large specific contact surface area of the phases. There is a degassing. It is known that excess free carbon dioxide, in contrast to equilibrium, is very active and is called aggressive, being one of the main causes of pipeline corrosion. Part of it, acting on calcium carbonate, turns it into hydrogen carbonate, and the other goes into equilibrium carbonic acid to keep it in solution. As a result of the increase in the surface area of the phase contact, reactions with molecules of the medium and other solids are facilitated, the crystal lattice is broken, and water becomes unstable and a precipitate of CaCO ₃ , MgCO ₃ , Fe (OH) ₃ precipitates.

A method of water softening is as follows. The source water at room temperature is fed into a gas-liquid reactor, where the initial aqueous solution is mechanically activated by passing a water stream through a system of holes with a diameter d of not more than 1 mm with a flow ratio of up to 10%, with a pressure drop of 0.05 to 0.5 MPa . When a water flow passed through a system of holes with a diameter of 0.25-0.5 mm in diameter, clogging of channels was observed by growing crystals of calcium carbonate precipitate, which is consistent with the analysis of the precipitate isolated during crystallization using an NewView 5022 interference microscope (Zygo Inc. USA) , which indicate that the size of the crystals, their equivalent diameter, varies in the range from 834 nm to 20 μm, and the sizes of the aggregates reach up to 750 μm, so we chose a hole diameter that excludes clogging of holes with a diameter of n e more than 1 mm. The indicated ratio of the flow cross section up to 10% was used because, with this ratio, the opening angle of the gas-liquid stream jet does not exceed 13%, which corresponds, according to the laws of hydrodynamics, to the optimal flow of gas-liquid systems and is confirmed by practical results. Further, in order to remove hardness salts, water is made alkaline with an aqueous solution of ammonia NH ₄ OH supplied by the dispenser in an amount of 0.003 ÷ 0.05 wt.% (See table). The need to reduce the amount of ammonium hydroxide added to intensify the crystallization process is associated with sanitary norms and rules for drinking water. As a result of the calculations of the equilibrium and working concentrations of ammonium hydroxide in the solution, the following values of the concentrations of ammonium hydroxide are shown in the table: where the minimum concentration value of 0.002% corresponds to a degree of softening of 47%, and the maximum value of the degree of softening to 93% is achieved starting from the concentration of hydroxide ammonia 0.03% and further. When the concentration of ammonium hydroxide is 0.05%, the curve of the degree of softening goes to a "plateau" and therefore the addition of excess ammonium hydroxide is impractical.

Under such processing conditions, the precipitate of hardness salts crystallizes upon standing for up to 3 minutes, forming an aragonite form of calcium carbonate. The brittle and loose aragonite sediment is easily destroyed and washed off by a stream of water. The appearance of aragonite in water leads to the destruction of the already formed scale, due to the fact that these crystals become centers of recrystallization. Next, the resulting aragonite precipitate is removed by centrifugation in a settling type centrifuge with pulsating or auger discharge of the sediment. Following the claimed method, it is possible to achieve a degree of water softening in an amount of from 47 to 93% at room temperature.

After separation of the precipitate, to reduce to pH 7-8, water can be filtered through zeolite. Purified water is supplied to the consumer.

The proposed method of cleaning is economical, increases the degree of purification of water from hardness salts, and can be used both independently to soften water and as one of the stages of water treatment.

Table Mass concentration of ammonia solution,% The degree of softening,% 0.002 47 0.003 67 0.006 77 0.012 90 0.018 91 0,023 92 0,03 93 0.05 93 0.06 93

Claims (3)

1. A method of water softening, including alkalization with an aqueous solution of ammonia, mechanical activation and the release of insoluble precipitate from the treated water, characterized in that the mechanical activation is carried out by passing a water stream through a membrane system with holes with a diameter d of not more than 1 mm with a passage ratio of up to 10 %, with a pressure drop from 0.05 to 0.5 MPa, then alkalized with an aqueous solution of ammonia in an amount of 0.003 ÷ 0.05 wt.%. 2. The method of water softening according to claim 1, characterized in that the length of the channel of the holes L is selected from the condition L≥10d, where d is the diameter of one hole. 3. The method of water softening according to claim 1, characterized in that the isolation of insoluble sediment from the treated water is carried out in centrifuges of a settling type with pulsating or screw discharge of the sediment.