RU2412118C2 - Method of seawater desalination - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to seawater desalination and may be used for producing whatever volumes of fresh water. Proposed method comprises seawater treatment on electrolyser made up of cylindrical electrolytic chamber made in the form of insert into main pipeline with axis aligned with that of said electrolytic chamber. Note here that said electrolytic chamber consists of two sections, i.e. one arranged along electrolytic chamber axis and another arranged on its inner surface, and is divided by common cylindrical bulkhead transmitting electric charges into anode and cathode zones with identical geometrical sizes. Note also that at said boundary anode and cathode zones get reversed. In treatment, seawater is passed, first, through one section and, then, through another section.

EFFECT: efficient neutralisation of harmful substances, higher efficiency of desalination.

2 dwg

Description

1. The technical field

The present invention relates to methods for desalination of sea water and can be used to produce virtually any volume of water required for effective use in agricultural, municipal and other industries, from an unlimited source of cheap raw materials - saline groundwater, ocean and sea waters.

2. The level of technology

Technological progress associated with the growing consumption of fresh drinking and industrial water in the municipal, mining, agricultural and other branches of technology causes a growing demand for clean water, which is becoming increasingly scarce due to technogenic pollution of the environment. At the same time, we are surrounded by huge reserves of sea and ocean salt water, plankton and other impurities in which could serve as fertilizer, increasing the fertility of the lands irrigated with desalinated sea water. Still larger reserves of saline water are found in the bowels of the Earth.

Currently, the most common method of desalination of sea water on an industrial scale is electrodialysis, when, using ionite membranes separating the side chambers from the central one, mainly cations or anions of sea water are passed into the side chambers depending on the charge sign on the surface of the ionite membranes (Demineralization by the method of electrodialysis (ionite membranes), trans. from English M., 1963).

There is a method of electrolytic treatment of water in order to improve its properties in a flowing hydraulic system, including three diaphragm electrolysers connected in series, in which water is sequentially processed in the cathode chamber of the first electrolyzer, then in the anode chambers of the second and third electrolyzers (US patent No. 3910829, cl . 204-151, 1975).

The disadvantage of this method is that the water treated in accordance with this method does not meet the requirements for drinking water. In addition, the method requires in addition to three diaphragm electrolyzers the presence of a system that synchronously sets the operating modes of the electrolyzers, which greatly complicates the practical implementation of the method.

A known method of desalination of sea water, comprising mixing ammonia (NH ₃ ) with the source water to form ammonium hydroxide (NH ₄ OH) to react with the NaCl salt molecules present in the source water, and softening the bond in the NaCl molecules, spraying said water in the form of fine sprays in the upper part of a closed process chamber, spraying water with an effective amount of combustion exhaust gas (СО ₂ ) to react with the indicated softened molecules, forming and removing solid substances: sodium carbonate (Na ₂ CO ₃ ) and ammonium chloride (NH ₄ Cl) in the sump located below the specified process chamber (RU No. 2239602, CL C02F 1/00, 2000).

The disadvantages of the analogue are that the dispersion of small sprays is energy-intensive and practically impossible with high desalination productivity, and the use of ammonia and carbon dioxide significantly increases the cost of each unit of the volume of desalinated water. In addition, the method is mainly intended for desalination of water with a maximum salt concentration of 22%, while the highest salt concentration in sea and ocean water does not exceed 5%.

The closest analogue of the claimed proposal, adopted as a prototype, is a method for desalting salt water by repeated electrolysis for a long time, including electrically treating it with direct electric current in an electrolytic chamber separated by a porous partition into anode and cathode space (CN No. 101033093, class C02F 1/461, September 12, 2007).

The disadvantages of the prototype are that multiple and time-consuming electrolysis requires large amounts of energy and time.

3. Disclosure of invention

The objective of the invention is the organization of processing desalinated water passed through an electrolytic cell with minimal time and energy.

The problem is solved due to the fact that in the proposed method of desalination of sea water, it is sequentially processed in an electrolytic cell, which is a cylindrical electrolytic chamber made in the form of an insert in the main pipeline, the axis of which coincides with the axis of the electrolytic chamber, while the electrolytic chamber consists of two sections, in each of which cylindrical electrodes are installed, one of which is installed along the axis of the electrolytic chamber, and the second on its inner surface and, and is divided by a common cylindrical permeable to electric charges partition into anodic and cathodic zones having the same geometric dimensions in both sections, moreover, when changing from one section to another, the anodic and cathodic zones change to the opposite, while sea water is first passed through one , and then through another section.

4. The invention

Implementations of the claimed method are depicted in figure 1, which shows the technological scheme of desalination of sea water, and figure 2, which shows the design (circuit) of the electrolyzer. Figure 1 shows a source of sea water 1, an intake device 2, a supply pipe 3 with a pump station 4, an electrolyzer 5, which is a cylindrical electrolytic chamber made in the form of an insert into the main pipeline, the axis of which coincides with the axis of the chamber, consisting of two sections 11 and 12, located along the flow, in each of which cylindrical electrodes are installed, one of which 14 is installed along the axis of the electrolytic chamber 11 and 12, and the second 13 is installed on its inner surface, while the inner diameter of its cylinder It coincides with the inner surface of the pipeline, and the partition 15 divided by a common cylindrical permeable to electric charges 15 into anode and cathode spaces, which have the same geometric dimensions and are a continuation of one another, and the polarity of the signs of the electrodes in each section is opposite. In the cell section 11, the water flow in the inner space of the cylindrical partition 15 is the cathode region around the cathode 14, and the outer space around the partition 15 is the anode (positively charged) zone. In section 12 of the electrolyzer, the cathode and anode zones are interchanged, which ensures efficient electrolysis of water — its optimal desalination. The described device operates as follows.

Sea water is an electrolyte in which it is present in the most noticeable concentrations, mol / kg: H ₂ O - 53.6; Cl ^- - 0.546; Na ⁺ - 0.469; Mg ²⁺ - 0.0528, - ions that determine the conductivity of the electric current (Izmailov N.A. Electrochemistry of solutions. 3 ed. M., 1976).

Ionic conductivity is provided as follows. Under the influence of the electric field created by connecting the anode (+) and cathode (-) to the direct current source of the electrolyzer, which is a cylindrical electrolytic chamber made in the form of an insert into the main pipeline, the axis of which coincides with the axis of the electrolytic chamber, while the chamber consists of two sections, in each of which cylindrical electrodes are installed, one of which is installed along the axis of the electrolytic chamber, and the second on its inner surface, and divided by a common cylindrical permeable to electric charges partition into anodic and cathodic zones having the same geometric dimensions in both sections, and when changing from one section to another, the anodic and cathodic zones change to the opposite, while sea water is sequentially passed first through one, and then through another section.

In the process of operation of the electrolyzer, positive ions (cations) go to the cathode 14 of section 11 of the cylindrical electrolytic chamber 5 installed on the water supply pipe 3 (Fig. 1), where they receive the electrons that they lack, while negative ions (anions) go to the anode 13, to which they give away excess electrons. Thus, providing the ionic conductivity of the solution, the electrodes neutralize the ions received by them, which turn into atoms of the corresponding substances, which precipitate at the bottom of the sump 7, located behind section 12, i.e. the anions and cations of desalinated water give away excess electrons to the anode or anions and receive the missing electrons from the cathode or from cations, as a result of electron replacement reactions with the simultaneous neutralization of the corresponding charges of both the anions and cations falling out of solution in the sump 7, located behind the electrolytic chamber 5 (FIG. 1).

Water in the anode zone is saturated for a fraction of a second with highly active oxidizing agents: HClO, O ₃ , H ₂ O ₂ , etc., which ensure the destruction of impurities and bacteria.

When hydrated electrons (e ^- _aq ) enter the desalinated water, i.e. surrounded by a solvation shell of e ^- electrons, the source of which is the electrolyzer, at the cathodes and anodes (partly in the volume of water, where there are exchange reactions caused by different values of electron affinity of certain substances), chemical reactions like the following take place (Hart E., Anbar M. Hydrated Electron. M.: “Atomizdat.” 1973. 268 p.):

cathodic reactions:

2Na ⁺ + 2e ^- _aq + SO ₄ ^2- → Na ₂ SO ₄ ↓ (e ^- _aq plays an associative role);

Na ⁺ + Cl ^- + e ^- _aq → NaCl ↓ (e ^- _aq plays an associative role);

Ca ²⁺ + 2e ^- _aq + 2H ₂ O → Ca (OH) ₂ ↓ + H ₂ ↑ (e ^- _aq plays an associative role);

anode reactions:

2Cl ^- - 2е ^- _aq → Cl ₂ ↑;

4OH ^- - 4e ^- _aq → 2H ₂ ↑ + O ₂ ↑;

2Al ⁺⁺⁺ + 3H ₂ O + 6е ^- _aq → Al ₂ O ₃ + 3H ₂ ↑.

During the flow of the source water through the anode space, anodic oxidation products are formed, for example, HClO, ClO ^- , as well as ozone and oxygen, which oxidize microorganisms and organic impurities (plankton, etc.) by the type:

HCNO + 2OH ^- - 2e ^- _aq → H ₂ ↑ + CO ₂ + H ₂ O.

Thus, passing first through the anodic (cathodic), and then the cathodic (anodic) cells of the electrolyzer, seawater undergoes neutralization of both cations and anions, simultaneously providing the dissociation of organic impurities (plankton, etc.) into forms more accessible for assimilation by agricultural by plants.

The electrical parameters of the electrolyzer are established from the condition of ensuring the required degree of desalination of sea water and its hydrogen index based on the fact that with a higher electric field strength, better processing results are provided.

Considering that water with varying degrees of hydrogen index (pH) is desirable for the corresponding technological processes, the necessary water can be obtained by appropriately adjusting the parameters of the electrolyzer, in particular its electric field strength or increasing the electrode contact area. So, it is known that, for example, alkaline water is needed for washing oil or gas wells, acidic for leather processing or for room disinfection, and for most crops, irrigation water with pH> 7.0 is the most favorable, which agronomists call it "living water", in contrast to water with a pH <7.0 ("dead water"). At the same time, certain plant species prefer water with different pH values, up to pH <7.0, which is consumed by solonchak plants that bloom and bear fruit only on solonchaks (Genkel P. A. The main ways of studying the salt tolerance of plants. "Agricultural biology", 1970, vol. 5, No. 2).

As we see, the method according to the proposal can be carried out using an electrolyzer installed on a supply pipe in which cylindrical electrodes are placed, to which a constant electric current is connected. Given the high conductivity of sea water, 4000 times higher than the conductivity of ordinary drinking water, the anode and cathode processes will occur in the entire volume of water passed through the electrolytic chamber.

5. Technical results

The present invention provides a cheap method of producing large volumes of desalinated sea water without the use of expensive chemicals and without significant energy costs, such as electrodialysis or reverse osmosis. In addition, it is possible to process saline underground water, which in the bowels of the Earth contains an order of magnitude more than in the seas and oceans (Furon R. Problems of water on the globe. M., 1966).

In the claimed proposal, chemical reactions occur with the participation of hydrated electrons, the inexhaustible source of which is the surrounding space, including water itself. At the same time, a high productivity of the desalination process, which occurs directly in the pipeline pumping water, is in line with modern land reclamation requirements (tens of cubic meters per second). Solid sediments falling in the sump located after the electrolytic chamber are removed in large quantities (the ratio of water to sludge is approximately 100: 3) and can be used in the mining industry (up to gold mining) and as building materials.

Plankton and a number of salts contained in desalinated water will serve as fertilizer for irrigated lands, and the economic use of sludge falling in sedimentation tanks will both increase the profitability of the desalination process and solve the cleaning problem.

The advantage of the claimed method in comparison with the prototype is that it provides more opportunities for both anodic and cathodic neutralization of harmful substances that are removed from desalinated sea water, at higher technical and economic indicators of the desalination process.

Claims (1)

The method of desalination of sea water, including its sequential processing in an electrolyzer, which is a cylindrical electrolytic chamber, made in the form of an insert into the main pipeline, the axis of which coincides with the axis of the electrolytic chamber, while the electrolytic chamber consists of two sections, each of which has cylindrical electrodes , one of which is installed along the axis of the electrolytic chamber, and the second on its inner surface, and is divided by a common permeable cylindrical for both sections A electric charges partition into anode and cathode zones having the same geometrical dimensions in the two sections, wherein the transition from one section to the other anode and cathode area are reversed, and the sea water is sequentially passed first through one, and then through another section.

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