WO2018069909A1

WO2018069909A1 - Process for the extraction of salts and fresh water from seawater or wastewater of various industries

Info

Publication number: WO2018069909A1
Application number: PCT/IL2016/051108
Authority: WO
Inventors: Solomon Flaks
Original assignee: Marine Mineral Resources Ltd
Priority date: 2016-10-13
Filing date: 2016-10-13
Publication date: 2018-04-19

Abstract

Process and plant for desalination of seawater and other salt containing solutions, which allow simultaneously with fresh water to get the salts of magnesium, sodium, potassium and others. The plant structure allows to carry out process in narrow thermal conditions of 98-100°C,in which there is release of the greatest amount of water and gives possibility to use the largest secondary energy, obtained on cooling of both hot solutions and water.

Description

PROCESS FOR THE EXTRACTION OF SALTS AND FRESH WATER FROM

SEAWATER OR WASTEWATER OF VARIOUS INDUSTRIES

The invention is related to extraction sphere of subsoil resources from inexhaustible water sources: oceans, seas, salt lakes, as well as a huge number of various industries salt-containing wastewater. These sources in the future, after the development of new economical methods of their processing, will allow stopping extraction of mineral raw materials by means of expensive mining method. Primarily, it is related to extraction of magnesium chloride MgCl₂, which is widely used for the production of magnesium metal, magnesia cements, high-temperature refractory products and other.

Sea water also contains sodium chloride, NaCl, which is used to produce soda ash - Na₂C0₃, caustic soda, glass, etc., potassium chloride KC1, which is used as a fertilizer, in medical science, etc., lithium chloride - LiCl is used in nuclear power, accumulator batteries, etc., as well as iodides, bromides and other valuable products. Simultaneously with minerals products preparation, large quantity of fresh water is released.

All currently existing technologies of fresh water preparation do not enable at the same time receive a crystalline salt and they throw it back into sea as brines of higher concentration. In all mentioned below processes, for crystalline salt preparation it was proposed to evaporate the brine that requires a lot of energy consumption (US Patent Jis3,670,067, 11.07.1972: PCT RU Va 2005133756/15, 11.01.2005; US Patent JM° 8,021,557, 05.08.2010).

Israeli patent No. 227430, 07.10.2013; PCT / IL 2014/000033 describes the method of simultaneous preparation of both fresh water and crystals mixture of all salts that are in source sea water.

This method disadvantages include the following:

The relatively low efficiency of the process due to operation in up to 95°C temperatures range, where it is possible to use only a low concentration of water in the air that causes necessity, when producing of large quantities of fresh water to apply high pressure fans > 10 kPa, and high efficiency > 40,000 m³ / hour that greatly increases the cost of plants construction. Furthermore, process of patent in question does not allow at stage of fresh water preparation to extract, at least, one salt in in the pure state.

The aim of this invention is development of commercial method and apparatus for integrated processing of sea water and other salt-containing solutions that allows to simplify the technology and reduce the costs related to industrial plant manufacturing and its operation, it should lead to power consumption reduction as to fresh water preparation, which will be lower than 2.5 kW / m³, and to reduction of fresh water and salts cost.

Set aim is achieved due to the use of heat release effect when dissolving air, carbon dioxide and other gases in water, for power consumption dramatic reduction and increase of processing rate of fresh water and salt separation. The chemical interaction of water with dissolving gases and air leads to the formation of new compounds - hydrates, which is accompanied by release of heat, in this case the enthalpy of the system decreases (ΔΗ <0). It is known that the solubility of air in water decreases with temperature increasing and increases with pressure increasing. In practice, it was found that in the time of air-water heat above 96°C, air solubility begins to increase. When dissolving 1 g / mol of air (29 g) in a large amount of water, 5.3 kcal of heat is released in terms of 1 m³ of air 220 kcal Manual DPVA). According to the "Chemist handbook", v. V, p. 35, edition: Moscow-Leningrad, 1966, internal energy (ui) system-to-air in kcal / kg of dry air, as well as internal energy (u₂), as kcal / kg of water in the air were calculated. Obtained data are summarized in Table 1. Also the increase of water content in 1 kg of dry air (0.83m³ of air) at temperature that is above 90°C. Data are shown in Table No. 2

Table No.l.

Properties of air saturated with water steam

Table No.2.

The degree of water content increase of dry air-water system at temperature of 90-99°C

From the data of Table 1 and 2 we can see that maximum plant capacity will be when operating in temperature range of 98-99°C. In this case, at maximum air-water phase saturation with water at 99°C up to 198.20 1 / kg of dry air and cooling of purified steam by 1°C, it is possible to obtain 198.2 - 15.6 = 182.6 liters of fresh water per 1 kg of dry air or 182.6X1.2047 kg /l per 1 m³ of dry air.

Technological scheme of the proposed process is shown in Figure 1.

For testing it was used the brine of "Palmachim" desalting plant of reverse osmosis, at present time the brine is thrown back into the sea. The salts' content in the brine is twice more than in sea water and is: NaCl - 55.18 kg/m³; MgCl₂ - 10.88 kg/m³; KCl - 1.49 kg/m₃; CaS0₄ - 1.4 kg/m³; d = 1.0613 g/cm³.

The brine from desalting plant or seawater from the sea should be pumped into storage tank No.l, from which by means of pump No. 29 the brine reaches through the condenser jacket No.16 heat exchanger, where the one is heated to temperature of 99-100°C. Heating in heat exchanger is carried out by means of automatic hot-water boiler No.2. Hot brine from heat exchanger reaches receiving tank No.6, where from the one continuously is pumped (Pump No.9) through atomizing cones to absorber No.7.

In absorber No.7, atomizing cones are arranged circumferentially in two rows and they spray the brain so as completely to close off entire inner cross section of the absorber. From below with fan No. 30 hot air (99- 100°C) is blown through sprayed brine. Because, when spraying the brine, the size of liquid droplets is less than 500 μπι, contact surface of hot air with brine is large, rapid dissolution of air in the brine and water saturation of the air is carried out quickly. Received water-air mixture should be forwarded into separator No.14, where separation of water-air mixture from brine, saturated with salts that is returned to the absorber, is carried out. At the bottom of absorber No.7 there is thickener No. 8 with barbators, through which air is blown by means of fan No.12. In thickener thorough mixing of flowing off saturated with salts brine from separator to absorber is carried out with hot (99-100°C) air. Barbators operate in foam mode; airflow rate is > lm³/min through lm² solution surface in thickener. Obtained water-air mixture should be also sent to separator No.14, temperature of the mixture at the outlet of the separator and at the inlet of condensing apparatus No.15 reduces to 99°C.

Since the process proceeds at high temperature, the decomposition of bicarbonates of Na, K, Mg, and other elements is carried out, solutions pH increases up to pH = 8-9 and metal chlorides, which are in sea water, settle out as hydroxides Me (OH)x, simultaneously extraction of calcium as gypsum CaSC>4 * 2H₂0 is occurred.

Intensive distillation of fresh water leads to both supersaturated with salts solution and salting of sodium chloride, potassium and others. Because of high solubility of magnesium chloride, its crystals are not formed to concentration of > 35.7%. At such high concentration, salting of NaCl, KCl and other salts in the form of mixed crystals is carried out. The mixture of MgCl₂ solution with salts crystals enters thickener, where in saturated solution the growth of NaCl, KCl, and others crystals is occurred. With increase of the crystals, they are deposited on the bottom of the thickener, which slowly rotating stirrer (2 rev./min.), moves them to central drain device, from it, using the diaphragm pump No.10 the pulp is pumped into the screw crystallizer No.13, which is cooled by source salt-containing brine . Brine supply is carried out by pump No. 29 from receiving tank No.1. Upon cooling pulp of salts and MgCl₂ solution to 25°C, cooling brine is heated to 50-60°C and enters the heat pump No.24, where it participates in fresh water cooling, then it is entered to heat to T = 99- 100°C automatic water-heating boiler No.2. The cooled pulp from crystallizer No.13 enters into carousel-type drum screen No. 25 (mesh size - 0.7 mm), where separation of salts mixtures of NaCl and KC1 from pulp, containing MgCl₂ solution and slick of gypsum CaS0₄ * 2H₂0 and metal hydroxides Me (OH) x, that are in seawater occurs. All products, obtained after drum screen are rich with concentrates and they may be separated in accordance with existing technological schemes.

Separator No. 14 is a tube, diameter and length of which allows maintaining speed of transmission of air- water mixture in the range 1.5-3.0 m/sec. During this time, coagulation of saturated brine and separating it from the air-water phase without use of special droplet separators is taking place. Obtained steam-air mixture containing no salt impurities enters condenser No.15, which should be pumped, through atomizing cones, with 25°C temperature fresh water. Because of contact with cold water, intense condensation of water from steam-air mixture is taking place. At outlet of condenser No.15 and at inlet of heat exchanger No. 16 temperature at 95°C should be maintained. When passing through heat exchanger of water-air mixture - its cooling is carried out using initial brine or sea water to temperature of 50-60°C, at the same time cooling brine is heated to 95°C, then it enters the boiler heat exchanger No.2, where the one is heated to 99-100°C and is discharged into a storage tank No.6, where from it by pump No.9 is directed to absorber No.7, which is the head of the process. From heat exchanger No.16, water-air mixture with temperature of 50-60°C enters separator No.17, where separation of fresh water from air takes place. Fresh water enters heat pump No.24, where it is cooled to 25°C and air with temperature of 50°C enters heat exchanger No.5, where it is heated by hot-water boiler No.2 to 100°C and is directed to absorber No.7, which is the head of the process. Cooled fresh water from heat pump No.24 is pumped by centrifugal pump No.23 into the circulating tank number 19, where from by pump No.20 the one is directed, for direct cooling, to condenser No.15 from circulating tank No.19 the excess water enters tank number 18, and then by pump N°21 it should be directed to tank No.22 for transferring to consumer. All plant is carefully insulated by polyurethane foam, thus reducing heat losses for heat radiation up to 5%. Carried out tests and calculations have shown that the operation of all systems in closed cycles and high degree of heat exchange and heat insulation allow to reduce power costs per lm³ of fresh water to 2.5 kW. Tests were carried out on scaled up laboratory plant with capacity of 42-62 1/h (1-1.5 m day). At the next stage, it was mounted semiproduction experimental plant with capacity of 30-50 m³ /day. On this plant, it is planned to use the Bromide-Lithium absorption heat pump that will allow reducing energy costs up to 0.5kW/m³ of water.

Claims

1. Method and plant for drawing of fresh water and salts from brine, of desalting plants and other salt- containing solutions, comprising:

(i) Absorber completed with bubbler and thickener, allowing obtaining fresh water and partially separated salts.

(ii) Two fans: one of high pressure for carrying out of intense barbotage, the other one of low pressure for circulation of air-water mixture in closed system of plant.

(iii) For replenishment of heat losses we must use automatic hot-water boiler, which can be fired by the cheapest fuel types (coal, gas and other ones that are suitable for local conditions), as well as solar and other thermal plants.

2. The process of claim 1, wherein water-air mixture from absorber enters inclined pipe separator, the diameter of which is several times greater than the diameter of outlet fitting of absorber and the length is 5 meters that allows drastically to reduce flowing speed of water / air mixture, increase contact time of air with water as well as to enhance coagulation of brine and its complete separation from fresh water-air mixture without use of special droplet separators.

3. The process of claims 1 and 2. The process is carried out at temperature of 98-100°C (boiling point of solutions is > 106°C) that allows dramatically increase heat capacity of the system and plant output.

4. The process of claims 1 to 3. At temperature of 98-100°C, process of dissolution of air in water occurs with heat production in the amount of 5.3 kcal per lg/ mole of air (220 kcal per 1 m³ of air).

5. The process of claims 1 to 4. The process is carried out at constant high MgCl₂ concentration of 35-37% in thickener that allows to obtain NaCl, KC1 and other salts in a crystalline form, in the absence of these salts in saturated solution of MgCl₂ as well as concentrators of gypsum CaS0₄ * 2H₂0 and hydroxides of metals that are in sea water.

6. The process of claims 1 to 5. Plant continuous operation is achieved by obtaining saturated MgCl₂ solution (35-37%), followed by continuous charging of initial brine, fresh water removal and continuous discharge of saturated pulp equivalent amount of MgC12 solution with crystals of salts, gypsum and metal hydroxides.

7. The process of claims 1 to 6. When using "Palmachim" brine and its evaporating in an amount of 1000 1/h, it was necessary to select by diaphragm pump of 23.9 1/h saturated pulp (0.4 1/min). Boiling-down degree was 97.6%.

8. The process of claims 1 to 7. Separation of crystalline salts from pulp, containing MgCl₂ saturated solution, gypsum and metal hydroxides can be carried out on standard rotary drum screen with mesh size of 0.7-1.0 mm at rotation velocity of 40-60 rpm.

9. The process of claims 1 to 8. Preparation of pure MgCl₂ solution is carried out by filtration on nutsch-filter of pulp, obtained on drum screen.

10. The process of claims 1 to 9. Electricity consumption, for preparation of 1 m³ of fresh water, is 2.5 kW. It is expected that use of bromide lithium absorption heat pump will reduce electricity consumption to 0.5 kW/m³ of fresh water.