RU2372288C1 - Method of producing crystalline sodium chloride from underground brine - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used for producing crystalline sodium chloride from underground brine. The method of producing crystalline sodium chloride involves purification of underground brine from mechanical impurities, multistage evaporation and crystallisation, separation of the solid phase. Evaporation at the first stage is done in direct contact of evaporated brine with products of combustion of gaseous or liquid fuel with subsequent utilisation of energy obtained by the gas-vapour mixture at other stages.

EFFECT: invention allows for reducing encrustation of heating surfaces during evaporation of underground brine with high content of calcium and magnesium chlorides.

2 dwg, 1 tbl, 3 ex

Description

The invention relates to the chemical technology of inorganic substances and is intended for the industrial production of crystalline sodium chloride from underground sodium chloride brine with a molar ratio of the number of calcium and magnesium ions to the amount of sodium ions (hereinafter f) of more than 0.05 (1:20) in the presence of sulfate and she. The invention can also be used to concentrate aqueous solutions of non-volatile substances.

Sodium chloride (salt) is a raw material for large-scale production of chlorine and caustic soda by electrolysis of pure brine saturated with salt. The cost of imported rock or lake salt, from which the necessary brine is currently obtained, is constantly increasing. In this regard, the task is set to use in the production of chlorine and caustic soda sodium chloride from the local underground sodium chloride brine, which is available in large areas.

Underground brine has a complex composition. Sodium chloride of the quality necessary for electrolysis can be obtained from it using brine or crystallization methods.

Brine methods include the removal of undesirable impurities from the underground brine by physicochemical methods and the subsequent production of concentrated brine. Such processes fit well with the technology of production of chlorine and caustic soda by diaphragm electrolysis, in which there is a recycle of crystalline sodium chloride [Yakimenko L. M., Pasmanik M. I. Handbook for the production of chlorine, caustic soda and basic chlorine products. - M., Chemistry, 1976]. However, when f is of the order of 0.10, up to 300 kg of sludge is generated per ton of purified sodium chloride during the removal of calcium and magnesium ions.

In the production of chlorine and caustic soda by modern membrane electrolysis, sodium chloride recycling is carried out in the form of a dilute solution (anolyte), which is brought to a saturated state with crystalline sodium chloride. For such productions, the underground sodium chloride brine must be processed by crystallization methods, which provide for the preparation of crystalline sodium chloride from the underground brine.

Currently, there is a powerful industry for the production of crystalline sodium chloride of food grade (sodium chloride) from various brines.

A known method of producing table salt from contaminated with impurities raw materials, for example from a brine of underground dissolution of rock salt [patent 2075440 RU. The method of obtaining table salt. IPC C01D 3/06, publ. 1997.03.20]. The method includes multi-stage evaporation of the brine to obtain a 30-40% suspension of crystalline salt, dilution of the suspension with a mother liquor to a concentration of crystalline salt of 10-20%, classification of the suspension in a hydrocyclone, separation of crystalline salt in washing centrifuges. The method is used with an f value of less than 0.01.

A known method of complex processing of iodine-bromine-containing sodium chloride water [RU patent 2132819. The method of complex processing of hydromineral raw materials. IPC C01D 3/06, publ. 1999.07.10]. The method includes six-fold evaporation of iodine-bromine-containing water with a total mineralization of about 17 kg / m ³ , extraction of iodine and bromine from concentrated brine using chemical reagents, subsequent concentration of the brine with crystallization of edible salt. This method is used with a value of f = 0.03.

There is a method of producing table salt from produced water, produced simultaneously with oil and gas using for evaporation of heat from the combustion of associated gas [Patent 2167286 RU. The method of obtaining table salt. IPC C01D 3/08, publ. 2001.05.20]. The technical salt obtained at first is dissolved in distilled water and re-evaporated, which increases the cost of the process.

A known method of producing table salt from produced water, incidentally produced with oil and gas [patent 2211802 RU. A method of producing table salt from produced water of an oil field. IPC C01D 3/08, publ. 2003.09.

10]. The method includes cleaning the source formation water from mechanical impurities, iron salts, evaporating the formation water in a thermocompression evaporator with precipitation of sodium chloride, the evaporation being carried out until the residual fluid density is from 1310 to 1398 kg / m ³ .

However, these methods are unsuitable for producing crystalline sodium chloride from underground brines with a high content of calcium and magnesium chlorides, in the presence of which inlaying of heating surfaces occurs in the first stages, and the boiling temperature and viscosity of the mother liquor significantly increase in the last stages of evaporation.

As a prototype of this invention, a method for producing table salt from halite raw materials contaminated with clay insoluble impurities, anhydride and gypsum, including its dissolution, purification from insoluble impurities and the isolation of crystalline sodium chloride in a multi-stage vacuum crystallization unit [patent 2056355 RU. The method of obtaining table salt. IPC C01D 3/04, publ. 1996.03.20]. Crystallization is carried out in the presence of seeds with NaCl and CaSO ₄ , the solids content is maintained at 15%, and crystalline sodium chloride is removed in two streams. Pure NaCl crystals larger than 0.1 mm are obtained, which are separated from CaS0 ₄ crystals less than 0.06 mm in hydrocyclones and then released from the mother liquor in centrifuges. The mother liquor from the last case is heated to a temperature of 114 ° C and served to dissolve the halite raw material.

The initial brine directed to evaporation has a total mineralization of 330 kg / m ³ and a molar ratio of the number of calcium ions to the amount of sodium ions f = 0.006, which ensures high-quality crystalline sodium chloride.

The disadvantage of this method is the fast inlay of heating surfaces during evaporation of underground sodium chloride brines with a high content of calcium and magnesium ions.

The aim of the invention is the development of technology to process underground brine with a molar ratio of the number of calcium and magnesium ions to the amount of sodium ions more than 0.05 in the presence of sulfate ion.

This goal is achieved in that the evaporation in the first stage is carried out with direct contact of the evaporated brine with the combustion products of gaseous or liquid fuels, followed by utilization of the energy of the resulting vapor-gas mixture at other stages.

The thermal energy of the gas-vapor mixture is utilized at one or two other stages of brine evaporation and crystallization, the overpressure energy is utilized in the gas engine using the energy obtained to drive the air compressor.

Figure 1 presents the scheme for obtaining crystalline sodium chloride with three blocks of evaporation and crystallization. Figure 2 shows a diagram for the preparation of crystalline sodium chloride with four blocks of evaporation and crystallization and the temperature of evaporation in the first stage of 120-200 ° C.

The table shows the data of an example of obtaining crystalline sodium chloride from underground brine in an installation with three blocks of evaporation and crystallization.

Installation for implementing this method in one of the possible options includes three blocks 1, 2 and 3 with equipment for evaporation, crystallization and separation of the solid phase, figure 1. The blocks are arranged sequentially along the movement of the evaporated brine, and different pressure is maintained in the evaporation apparatus in accordance with the inequality P ₁ > P ₃ > P ₂ . Block 1 is equipped with an evaporator with direct contact of the evaporated brine with fuel combustion products, and blocks 2 and 3 are equipped with evaporators with heat transfer through a solid wall.

In the evaporator of block 1 serves the source brine 4, gaseous or liquid fuel 5 and air 6 with a slight excess. In it, with direct contact of liquid and fuel combustion products, oxidation of Fe ²⁺ occurs, heating of the brine, partial evaporation of water, crystallization of CaSO ₄ . From the evaporator, the vapor-gas mixture 7 is sent to block 3. The resulting suspension is concentrated, and then the sludge 8 containing mechanical impurities, crystalline CaSO ₄ , iron hydroxides and other substances is separated in a centrifuge. The separated intermediate brine 9 is sent to block 2.

In the apparatus for crystallizing block 2 from an intermediate brine 9 at low pressure P ₂ <P ₃ <P _1, water is evaporated and a suspension of sodium chloride is obtained. For evaporation, the thermal energy of the gas-vapor stream 10 is used with the condensation of part of the water vapor and the steam-gas-liquid stream 11 is withdrawn from the system. The water 12 evaporated from the brine is sent to the vacuum system. The resulting suspension is concentrated, and then the first part of crystalline sodium chloride 13 is separated in a centrifuge. The mother liquor 14 is sent to block 3.

The evaporation and crystallization apparatus of block 3 is heated with a gas-vapor mixture 7 from block 1. Condensate 16 is separated from the obtained vapor-gas-liquid stream 15, and the gas-vapor stream 10 is sent to block 2. As a result of evaporation, crystallization, and separation of the heterogeneous mixture, a vaporized water stream 17 is obtained, the second part of crystalline sodium chloride 18 and the final brine 19. The heat energy of the vaporized water stream 17 is used, for example, to heat the source air 6.

The obtained crystalline sodium chloride is washed from the mother liquor and sent to the preparation of a brine for electrolysis or for drying.

More complex is the installation, which has 4 or more stages of evaporation and crystallization with a temperature of evaporation in the first stage of 120-200 ° C, Fig.2. Such a plant is equipped with an additional evaporation stage 20, a compressor for compressing the air 21, and an engine 22 that runs on compressed gas. The pressure in the evaporation zones is maintained in accordance with the inequality P ₁ > P ₃ > P ₂ > P ₂₀ .

Blocks 1 and 3 work in the same way as in a three-stage installation, but the gas-vapor stream 7 has a pressure of 0.2-1.5 MPa and a temperature of 120-200 ° C. In block 3, the thermal energy of this stream is utilized, condensate 16 is separated from the outlet vapor-gas-liquid stream 15 and a compressed vapor-gas stream 10 is obtained. The pressure energy of stream 10 is utilized in the gas engine 22 with expansion to atmospheric pressure. The spent stream 23 is discharged into the atmosphere, the resulting mechanical energy is used in the drive of the compressor 21.

The stream of secondary steam 17 from block 3 is heating for block 2, and the stream of secondary steam 12 of block 2 is heating for block 20. Condensates 24 and 25 are removed from the installation, secondary steam 26 of block 20 is sent to the vacuum system. Crystalline sodium chloride from stream 18, which is inferior in quality to sodium chloride from stream 13, is completely or partially returned to block 1.

In the process of obtaining crystalline sodium chloride, the concentration of salts of iodine, bromine and other valuable components in the final brine 19 in relation to the concentration in the initial brine 4 increases 6-10 times. Therefore, the final brine 19 should be further processed with the associated production of magnesia, iodine, bromine, liquid or solid anti-icing mixtures.

Example 1. The process of obtaining crystalline sodium chloride by this method is considered on the example of processing an underground brine of a medium-carbon coal-bearing aquifer complex from the Cheboksary trough in a plant with three evaporation and crystallization units. Quantitative data were obtained by calculation using the ChemCAD simulation program using published data on the joint solubility of sodium, calcium, and calcium sulfates.

The initial underground brine with a density of 1143 kg / m with a molar ratio of the number of calcium and magnesium ions to the number of sodium ions f = 0.10 contains 186 g / dm ^{3 of} sodium chloride.

The process of evaporation and crystallization is calculated at the following values of pressure (absolute) and temperature:

block 1-145 kPa and 107 ° C; block 2 - 8 and 49; block 3 - 20 and 80; stream 7 - 145 kPa and 107 ° C; stream 11 - 115 and 69; stream 15 - 135 and 93.

The obtained data on the number and composition of the streams before washing the product streams 13 and 18 with a pure NaCl solution per 1 ton of product are presented in the table. The amount of evaporated water is 5139 kg / t of NaCl, including a stream of 12 - 3873 kg / t. 197 m ³ methane is spent on the process, air for methane burning is supplied with a 5% excess.

By washing wet sodium chloride (streams 13, 18) with pure brine, the content of dissolved calcium and magnesium salts is reduced by an order of magnitude and the resulting product is used to produce chlorine and caustic soda. After drying, table salt is obtained from it.

Example 2. The process is carried out in accordance with example 1, but the fuel is low-sulfur fuel oil, the consumption of which is 174 kg. Moreover, compared with example 1, the volume of combustion products increases by 1.4%, and the amount of carbon dioxide in them - by 41.4%, resulting in an increase in the mass flow rate of combined-cycle flows 7, 15, 10 and 11. Mass flow rates and compositions other flows are identical to those presented in the table for example 1.

Example 3 (comparative). When applying the brine from example 1 to the installation of the controlled vacuum crystallization of the prototype in the first stage, the heating surface is quickly inlaid with calcium sulfate and it is impossible to obtain high-quality crystalline sodium chloride for a long time.

Examples 1 and 2 show that this method allows the production of pure crystalline sodium chloride from underground sodium chloride brine with a molar ratio of calcium and magnesium to sodium ions of more than 0.05 in the presence of sulfate ion.

At the first stage, the crystallization of calcium sulfate occurs in the liquid volume upon direct contact of the products of fuel combustion with brine, which eliminates the harmful inlay of the missing solid heating surface and increases the installation mileage between cleanings.

Since the cost of 1 GJ of thermal energy of the combustion products of gaseous or liquid fuels is approximately two times lower than the cost of 1 GJ of thermal energy of water vapor, and the thermal energy generated in the first stage of the gas-vapor stream is utilized in the subsequent stages of evaporation, the method is economical.

When using this method, after condensation of the evaporated water per 1 ton of NaCl, 5 m ³ / t of distillate is simultaneously obtained, which completely covers the need for the production of chlorine and caustic soda.

Magnesium, iodine, bromine can be produced from a concentrated waste solution of calcium and magnesium chlorides, and liquid or solid anti-icing mixtures can be obtained.

The number and composition of the streams of the process for producing crystalline sodium chloride in a plant with three evaporation and crystallization blocks before washing product streams 13 and 18 with a pure NaCl solution Parameter Name Value for stream four 8 9 13 fourteen eighteen 19 1 Consumption, kg 6241 28.44 3873 835.4 1266 218.9 439.2 2 Composition, wt.% NaCl sol. 16.56 18.59 26.56 0.90 17.97 0.22 4.36 CaCl ₂ sol. 3.01 3.38 4.83 0.71 14.31 2.01 40,2 CaSO ₄ sol. 0.185 0,054 0,077 0.011 0,077 0,032 0.058 NaCl Crystal 94,99 94,99 CaSO ₄ crystals 30.00 0.153 0.583 Water rest

Claims (1)

A method of obtaining crystalline sodium chloride from an underground brine, including cleaning the brine from mechanical impurities, multi-stage evaporation and crystallization, separation of the solid phase, characterized in that the evaporation in the first stage is carried out by direct contact of the evaporated brine with the products of combustion of gaseous or liquid fuels, followed by energy recovery the resulting vapor-gas mixture at other stages.

Images