WO2021090153A1

WO2021090153A1 - Method of water demineralisation and product obtained thereof

Info

Publication number: WO2021090153A1
Application number: PCT/IB2020/060288
Authority: WO
Inventors: Giedrius RUTKAUSKAS; Nicolai Arion
Original assignee: Uab "Arionex Lt"
Priority date: 2019-11-05
Filing date: 2020-11-03
Publication date: 2021-05-14
Also published as: LT6826B; LT2019526A

Abstract

The technology is designed for demineralisation (desalination) of water for technological needs. The technology does not generate polluting waste from the demineralisation process. Desalinated water is used in industrial processes to protect equipment from salt deposits or as a diluent for liquid products in solutions to prevent additional impurities – salts in the water. The technology is based on the principle of ion exchange. Filtration of water through cation exchange and anion exchange resin removes salts (cations and anions) from the water by converting them to H+ and OH- ions. Cation-exchange resin is regenerated with concentrated nitric acid, and anion exchange resin is regenerated with ammonia aqueous solution. Composition of the regeneration product is close to the composition of complex mineral fertilizers, therefore, depending on composition of water that is fed for demineralisation, it is suitable for production of liquid or dry complex mineral fertilizers.

Description

METHOD OF WATER DEMINERALISATION AND PRODUCT OBTAINED THEREOF

TECHNICAL FIELD

The invention relates to demineralisation (desalination) of water that is used as feed water for steam boilers or for other technological purposes, and, more particularly, to a method for zero- waste demineralisation and a product made in such way.

BACKGROUND ART

Demineralised water is used in industrial processes to protect equipment (steam or water heating boilers, turbines, etc.) from salt deposits or as a diluent for solutions, liquid products, to avoid additional impurities -salts in the water. Water demineralisation technologies, which remove salts from the water, produce wastewater that is concentrated with amounts of salts. Today, in order to reduce environmental pollution, the standards for wastewater that is discharged into the environment have been setting the norms for concentrations of salts and for particular chemical elements. As a result, industries face the problem of wastewater discharges, especially when there are no other wastewater streams that could dilute the wastewater coming from demineralisation process.

Common ion-exchange technology comprises filtration of water through the ion exchange resin. The water is filtered through the cationic charge and the cations (converted to the H ion) are removed from the water, then the water is filtered through the anionic charge and the anions (converted to the OH ion) are removed from the water. In this way, salts are removed from the water. When the ion exchange resins are exhausted, they are regenerated. Sulfuric acid (H2SO4) of 0.5-2.5% or hydrochloric acid (HCI) of 4-5% is used for the regeneration of the cation resin, and sodium hydroxide (NaOH) of 4-5% or potassium hydroxide KOH (4-6%) is used for the anionic resin regeneration (Purolite Engineering Manual-Puropack packed-Bed Technology, 1999).

Nitric acid (HNO₃) of 4-6% can also be used for cationic resin regeneration.

In conventional ion-exchange technologies, the amount of wastewater during regeneration comprises 5-15% compared to the amount of the produced (demineralised) water. The mineralisation of wastewater is usually resulted at 5-20 g/L, in addition, the wastewater is enriched with the reagents used in regeneration and with the formed-from-them salts, i.e. NaCI, NaSC>4, and NaNC>₃.

In reverse-osmosis technology, two water streams are separated under high pressure - one stream is desalinated water, and the other stream is concentrated water. Such technology produces 25-15% of concentrated water (wastewater) and 75-85% of demineralised water. During reverse osmosis, the inlet water is concentrated by 4-5 times, i.e. if the salinity of the raw water is 500 mg/L, then the salinity of the concentrate will be 2-2.5 g / L.

Both technologies produce certain amount of wastewater with a correspondingly high salinity and make environmental pollution that is undesirable.

U.S. Pat. No. 3,956,115 discloses the peculiarities of the regeneration of ion-exchange resins with concentrated HNO₃ and NH solutions. This patent describes the regeneration of ion resins enriched with only one type of ion - NH₄ and NO₃, by treating condensates contaminated with ammonium nitrate ions, but does not describe the possibility of regenerating ionic resins enriched with Ca, Mg, Na, Cl, S0₄ ions in desalination waters.

U.S. Pat. No. 5,951 ,874 discloses the closest prior art. The patent describes the possibilities of water reduction in ion exchange systems using surface water for treatment, but does not disclose whether the wastewater reduction measures that are used are possible for regenerations with HNO3 and NH₃ solutions. This patent discloses regenerations only with solutions of HCI, H₂S0₄, NaCI, and NaOH.

The invention does not have the above-mentioned disadvantages associated with water demineralisation methods and includes additional advantages.

BRIEF DESCRIPTION OF THE INVENTION

This method is based on ion exchange, i.e. filtering the water through the ion-exchange resin to remove salt ions from the water and, after exhausting (fully loading) of the resins, regenerating it with higher concentration salt solutions, thereby restoring the original ionic capacity of the resin. Due to the recovery materials used, the resulting effluent composition and the small amount of effluent generated during resin regeneration, the resulting effluent/solution is used as a raw material in the production of mineral fertilizers. In this way, the method of demineralisation is zero effluent and zero waste.

Advantages of the method:

1. Regeneration of the cation exchange resin is made with HNO3 solution of 30-50%. Regeneration of the anion exchange resin is done with NH3 solution of 15-25%.

2. The amount of effluent during regeneration is 0.4-1%, compared to the amount of water produced during the filter cycle. The salinity of effluent is 100-180g/L.

3. The effluents from the process are concentrated and their composition is suitable to be used as an ingredient in the production of complex mineral fertilizers. 4. This technology is zero effluent and zero waste because of the fact that all wastewater is used as a raw material in the production of mineral fertilizers.

5. The resulting concentration is 5-times higher (compared to a conventional regeneration system with non-concentrated reagents), which is more cost-effective, as the use of effluent as a raw material for dry fertilizer production significantly reduces energy consumption for evaporation of water and the use of liquid fertilizers significantly saves storage space, and transportation costs.

When using conventional technology, after obtaining effluent with mineralisation of 20 g/L and in order to achieve an effluent salinity of 150 g/L, we should have to evaporate the remaining water. Evaporation technology is expensive in terms of operation and investment, and environmentally harmful due to the high energy consumption.

BRIEF DESCRIPTION OF FIGURES

Fig. 1 shows a schematic of the water demineralisation system.

DETAILED DESCRIPTION OF THE INVENTION

It should be understood that numerous specific details are set out in order to provide a complete and comprehensive description of the embodiment of the invention. However, the skilled person will understand that the level of details of embodiment examples does not limit the embodiment of the invention, which can be embodied without such specific instructions. Well-known methods, procedures and components have not been described in detail to make sure that embodiment examples are not misleading. Furthermore, this description should not be construed as limiting exemplary embodiments provided, but merely as an implementation thereof.

Although exemplary embodiments of the invention or aspects thereof, as illustrated and described, include many components that are depicted in a particular common space or location, some components may also be remote. It should also be understood that the examples given are not limited to the components described but also include other elements required for their functioning and interaction with other components, the existence of which is self-explanatory and therefore not detailed.

Demineralisation of water that is used for boiler feed or for other technological purposes, involves the supply of inlet water by pump P5. Valves V1 , V13, V2 are open. The water passes through the cation exchange column C and the anion exchange column A, enters the tank T6 and overflows. Other valves closed, pumps off. When the required amount of water has been put through, regeneration is performed.

Regeneration of column C is performed as follows: Fraction 1 - HNO₃ solution is fed by pump P1 with valves V3 and V9 open. After passing the 4L solution (water is expelled from the ion-exchange column and pipelines), V9 is closed, V12, V14 are opened.

Fraction 2 - when the required amount of regeneration solution is passed through, P1 is switched off and the valves are closed. V5, V12, V14 are opened, demineralised water is pumped by pump P3 to expel the solution. The fraction is injected into the tank T5.

Fraction 3 - V14 is closed, V19 is opened. The fraction is injected into the tank T8. The valves close, the pump switches off.

From the tank T8, pump P7 pumps water through column A, through valves V18, V11 , and V10. Concentrated HNO₃ solution is added to the tank T 1 for subsequent regeneration.

Regeneration of column A is performed as follows:

Fraction 1 - the solution of NPU is fed by the pump P4, while the valves V4, V11 , and V10 are open. After passing through 4L of solution (water is expelled from the ion-exchange column and pipelines), V10 is closed, and V14 is opened.

Fraction 2 - when the required amount of regeneration solution is pumped, P4 is switched off and the valves are closed. V6, V11 , V14 are opened, the demineralised water is pumped by the pump P3 to expel the solution. The fraction is injected into the tank T5.

Fraction 3 - V14 is closed, V15 is opened, and the fraction is transferred into the T7.

From the tank T7, the appropriate volume of solution is added into the tank T4, thus diluting the additional concentrated NPU before the regeneration solution is used for the next regeneration.

Fraction 4 - V15 is closed, V10 is opened. The fraction is transferred into T2.

Before starting the next cycle, recirculation is performed through the tank T6 by the pump P6, while the valves V7, V13, and V2 are open. Circulation is carried out until desalinated water of suitable quality is obtained.

After starting a new filtration cycle, pump P2 is switched on and the water of the first and the fourth fractions from the tank T2 is introduced into the incoming water flow at the speed of 3-4 L/h.

The process (demineralisation of water) takes place by passing water through ion-exchange resin, the water flowing from the bottom up. Water first flows through the filter bed of strong acid cation exchange resin, then through the filter bed of weak alkaline (basic) anion-exchange resin. Packed bed units’ technology for the resin charge is used (the filter is nearly completely filled with ion-exchange resin, and just a little free space is allowed to accommodate the ion-exchange resin swelling). 1. Demineralisation process is operated in accordance with the following formulas:

Cation exchange charge:

CaCI, MgCI, NaCI, CaS0₄, MgS0₄, NaS0₄, Ca(HC0₃), Mg(HC0₃), Na(HC0₃), + R-H <=> R- (Ca, Mg, Na) + H(CI,S0₄) + C0

Anion exchange charge:

H(CI, S0₄) + C0₂ + R-OH <=> R-(CI, S0₄, C0₂) + H₂0

For the demineralisation process, cation exchange charge is used - strong acid cation exchange resin and weak alkaline (basic) anion exchange resin.

2. Regeneration process is operated in accordance with the following formulas:

Cation exchange charge:

R-(Ca, Mg, Na) + HN0₃ <=> R-H + Ca(N0₃)₂, Mg(N0₃)₂, NaN0₃ Anion exchange charge:

R-(CI, S0₄, C0₂ ) + NH₄OH <=> R-OH + (NH₄)₂S0₄, NH₄CI + NH₄C0₂

Regeneration process of the cation exchange charge

Regeneration is performed in the opposite direction compared to the process - from top to bottom.

The cation exchange resin is regenerated with nitric acid of 30-50%. The solution is fed, and then the desalinated water is fed to expel the regenerating solution.

During regeneration, 3 wastewater fractions are separated:

Fraction 1 contains 2-10% of the total salts. This amount of water is returned to the beginning of the process.

Fraction 2 contains 85-95% of the total salts. This amount of effluent is mixed with the effluent of the second fraction of the anion exchange charge.

Fraction 3 contains 20-40% of excess FIN0₃. This amount of wastewater is passed through the anion exchange charge. The water is returned to the beginning of the process after passing the anion exchange charge.

Regeneration process of the anion exchange charge

The anion exchange charge is regenerated with NFI₃ solution of 15-25%, and then demineralised water is fed to wash the solution. During regeneration, 4 wastewater fractions are separated:

Fraction 1 contains 2-10% of the total salts. This amount of water is returned to the beginning of the process. Fraction 2 contains 82-96% of the total salts. This amount of effluent is mixed with the effluent of the second fraction of the cation exchange charge.

Fraction 3 contains 25% of excess FINO₃. This solution is used to prepare the NFI₃ solution for the next regeneration.

Fraction 4 is returned to the beginning of the process.

Upon completion of the feed and expulsion of the regeneration solutions, water is circulated through the cation exchange and anion exchange columns until a purified water with quality of 15-25 pS/cm is obtained. After recirculation, the inlet water is supplied and new demineralisation cycle is started.

The regeneration product is a solution of 10-18% (100-180 g/L). In terms of its composition, this solution is close to the nitrogen-based mineral fertilizer composition and can therefore be used as an ingredient in a raw material for production of complex fertilizers or as a component of liquid complex fertilizers. Composition of the resulting product directly depends on the composition of the inlet water and is different for each water source. For this reason, nearby markets have to consider the use of regeneration product depending on each water source, specifics company's (potential user of the technology) production, its use as a raw material for fertilizer production, or the use as liquid fertilizers. If further demineralisation of water is required, mixed resin filtration technology or electrodeionization technology is used after the described technology. Preliminary composition of the regeneration product is given in the table below.

Table 1 :

Methods and materials To verify the operation of the process, tests were performed. For the tests, a water treatment station was used, comprising: the cation exchange column, the anion exchange column, chemically resistant pumps, the containers for water, the reagents, and the solutions.

All apparatuses are connected by plastic pipes, resistant to the solutions used, fitted with appropriate fittings. The station is partially automated (level of automation - monitoring of critical parameters, automatic stopping when critical parameters are exceeded).

Test materials:

Strong acid cation exchanger, amount - 14L Specification:

Weak base anion exchanger, amount - 12L Specification:

Solutions used for filter regeneration:

HNOs acid - 58%

NH₃ aqueous ammonia solution - 25%

Measuring instruments used for the tests: a) electrical conductivity meter (installed: Chemitec 30; portable: WTW 82362 Cond 330i) b) pH meter (portable: Hach HQ40d) c) thermometer installed 0-60°C - 4 pcs. d) rotameter (flow meter), installed 50-500 L/h - 4 pcs. e) water volume pulse meter - 1 pc.

EMBODIMENT OF THE INVENTION

In order to implement the invention, experiments have been performed, which are presented here as examples of the implementation of the technology.

The water is fed to the cation exchange column, then the water is fed to the anion exchange column. The flow of treated water is from the bottom up. The treated water is collected in the treated water tank and overflows during the process. Part of the desalinated water is used for preparation of regenerative solutions and for the expulsion of regenerants during the regeneration process. Regenerative solutions are fed from top to bottom.

Inlet water:

Origin: municipal water Temperature: 10-15 °C • Conductivity: 530 -540 pS/cm Inlet water analysis:

Water flow: 250L/h Water pressure: 3 atm

Regeneration was performed under the following conditions:

Results

The filter cycle (amount of water from regeneration to regeneration) comprises 2500L (10 hours). Quality of demineralised water is 10-15 pS/cm.

Amount of regeneration product that is obtained: 13L.

Regeneration product comprises 0.53% of the amount of water produced (2500L).

Composition of regeneration product that is obtained:

On the whole, 14 purification cycles and 14 regenerations were performed. The data are presented from the 6^th experiment. For all cycles, filter cycle remained stable, at 2500L ± 15L. This indicates that ion exchangers are regenerated efficiently. Quality of demineralised water was stable. Composition of the regeneration product solution is suitable for production of liquid or dry mineral complex fertilizers with microelements.

Although the present description includes numerous characteristics and advantages of the invention together with structural details and features, the description is given as an example of the invention embodiment. There may be changes in the details, especially in the form, size and layout of materials without departing from the principles of the invention, in accordance with the widely understood definition of terms used in claims.

Claims

1 . A method of demineralisation of water to remove salts from the surface water or the deep water, comprising regenerating the cation exchange resin and regenerating the anion exchange resin after passing the filtered water through a filter with the cationic resin and passing the filtered water through the anionic resin, characterized in that: a) the filter with cation exchange resin is regenerated with nitric acid of 30-50%, b) the filter with anion exchange resin is regenerated with ammonia water solution of 15-25%.

2. The product obtained by the method according to claim 1 , which is a product of cationic and anionic regeneration, comprising complex compounds of salts that were present in water before the start of filtration and from a solution of nitrogen, nitric acid and ammoniacal water.

3. The product according to claim 2, wherein the product is a liquid complex mineral fertilizer.

4. Use of the product according to claims 2 or 3 as a raw material for production of liquid or bulk mineral complex fertilizers, or for direct soil fertilization.