Plant for individually extracting salts from a salt solution

Abstract

The invention relates to devices for individually extracting salts from salt solutions of various origin. The essence of the invention lies in a plant comprising a concentrating unit that includes a multi-stage flash evaporator containing stages having an expansion chamber and a condensation chamber, and at least two salt crystallization units, each of which contains a heater, a boiling chamber and a system for separating and discharging salts, wherein the flash evaporator expansion chamber and the heater, and also the boiling chamber and the flash evaporator expansion chamber, are connected to one another by steam delivery channels. The technical result consists in an increase in the energy efficiency of the plant.

Description

[0001] Plant for separate extraction of salts from brine

[0002] The invention relates to devices for the separate extraction of salts from saline solutions of various origins, in particular from solutions obtained in desalination plants, including membrane-type ones, from wastewater from chemical, metallurgical, agricultural and other types of production, including energy enterprises.

[0003] Methods and devices for extracting salts from saline solutions of various origins are currently being actively developed. The goals of such extraction are to obtain purified water and crystalline products—salts—that are valuable in industry and agriculture. Typically, the process of obtaining pure crystalline salt products from solutions is technologically complex and highly energy-intensive. Furthermore, most solutions contain several types of valuable salts, and their separate extraction significantly increases the energy consumption of the process. Therefore, energy-efficient technical solutions for salt extraction are being developed.One of such technical solutions is a plant for extracting salts from a brine, which is part of a wastewater treatment complex and contains a concentration unit, which includes a flash evaporator (FVE), containing sequentially installed stages, each of which contains an expansion chamber and a condensation chamber, and a salt crystallization unit, which includes a heater, the cavity of which is sequentially connected to the boiling chamber and a system for separating and removing salts, wherein the cavity of the steam space of the boiling chamber is connected to the cavity of the expansion chamber of the FVE stage, and the cavity of the condensation chamber of the FVE stage is provided with a channel for feeding steam into the cavity for circulating the hot coolant of the heater, while the outlet pipe of the cavity for circulating the hot coolant is provided with a channel for removing condensate into the cavity of the condensation chamber of the FVE stage [RU2814341C1, publication date: 28.02.2024].

[0004] A disadvantage of the known technical solution is the impossibility of using it for the separate extraction of salts from saline solutions, due to the fact that the system has only one salt crystallization unit, which does not allow the extraction of individual salts from a multi-component saline solution.

[0005] The prototype chosen is a plant for separate extraction of salts from a brine, containing a concentration unit including a multi-stage flash evaporator (FVE) and two salt crystallization units, the circuit of which includes two crystallizers and three centrifuges for dehydrating the salt; during the operation of the plant, steam from an external source is used as a heating medium for the crystallizers, as well as for the first stage of the FVE [RU6717U1, publication date: 17.06.1996]. The advantage of the prototype over the known technical solution is the possibility of using the plant for the purpose of separate extraction of salts from salt solutions due to the presence of two salt crystallization units in it, in each of which conditions are created for the extraction of different types of salts.

[0006] However, the disadvantage of the prototype remains the relatively low energy efficiency of the installation for the separate extraction of salts from salt solutions, due to the high load on external steam sources used during the operation of the installation, as well as the impossibility of reusing the heat generated by the installation due to the lack of heat exchange between the concentration unit and the salt crystallization units.

[0007] The technical problem that the invention aims to solve is the insufficiently high energy efficiency of the installation for the separate extraction of salts from a brine.

[0008] The technical result that the invention is aimed at achieving consists in increasing the energy efficiency of a plant for the separate extraction of salts from a brine by reusing the heat generated by the concentration unit and the salt crystallization units.

[0009] The essence of the invention is as follows.

[0010] The plant for separate extraction of salts from brine solution contains:

[0011] — a concentration unit, which includes a multi-stage flash evaporator (MEV), containing sequentially installed stages, each of which contains an expansion chamber and a condensation chamber, at the outlet of which there are pipes for discharging the concentrate and distillate, respectively;

[0012] — at least two salt crystallization units, each of which contains a heater, the cavity of which is connected in series with the boiling chamber and the salt separation and removal system, wherein:

[0013] — the cavity of the expansion chamber of the IMV stage is provided with a channel for supplying steam to the cavity for circulating the hot coolant of the heater, while the outlet pipe of the cavity for circulating the hot coolant is provided with a channel for removing condensate into the cavity of the condensation chamber of the IMV stage, and the cavity of the steam space of the boiling chamber is connected to the cavity of the expansion chamber of the IMV stage.

[0014] The unit can be used for the separate extraction of salts from brine solutions, which can include solutions produced at desalination plants, including membrane-based ones, such as seawater, wastewater from chemical, metallurgical, agricultural, and other industries, as well as energy plants. These solutions can undergo pre-treatment before salt extraction to remove suspended solids, organic compounds, and colloidal impurities, which reduces the risk of deposits forming on the heat-exchange surfaces of the concentration unit. These solutions can also undergo additional treatment before being fed to the salt crystallization unit to remove hardness salts and / or seeding agents introduced during the pre-treatment stage.

[0015] The concentration unit increases the brine concentration by distillation, specifically by separating the feed solution into distillate and concentrate. For this purpose, the concentration unit includes a multi-stage flash evaporator (FVE). The FVE circulation circuit comprises sequentially installed stages, each containing an expansion chamber and a condensation chamber, with outlet pipes for concentrate and distillate, respectively. The expansion chamber enables flashing and separation of the brine into steam and concentrate. The bottom of the expansion chamber can be inclined toward the brine outlet. The condensation chamber enables the phase transition of the steam produced in the expansion chamber into distillate and contains a bundle of heat exchange tubes for this purpose.A steam separation device is installed in the wall between the chambers, connecting the interior of the expansion chamber and the interior of the condensation chamber. The steam separation device allows for the separation of condensed moisture from the steam. The steam separation device can be removable, allowing for quick cleaning of any deposits that may form. To heat the brine, the wastewater concentration unit may include one or more head heaters, either installed upstream of the IMV or integrated into the IMV circulation loop and powered by external steam. To maintain the required brine level and remove distillate, the concentration unit is equipped with tanks.

[0016] The salt crystallization unit produces a crystalline salt product from a brine solution through evaporation and can be based on a forced-circulation evaporation system, including a heater whose cavity is connected in series with a flashing chamber and a salt separation and removal system. The flashing chamber can be an expander, a cylindrical vessel with a conical bottom containing a system of devices for flashing the solution. During operation of the salt crystallization unit, the concentrate is fed into the heater, and after the heater, it enters the upper part of the expander, where it flashes (expands) and the temperature drops to saturation. During flashing, the concentration of the brine solution increases by approximately 1-2%, leading to salt crystallization.The concentrate with crystals is transferred to the salt separation and removal system, where the salt crystals are pre-separated from the mother liquor, then the salt pulp is dehydrated and the target crystalline product is obtained, and the mother liquor is returned for further processing back into the crystallization unit circuit.

[0017] The number of salt crystallization units that a plant for the separate extraction of salts from a brine may contain may be equal to n + 1, where n is the number of target salt types to be extracted, and may be at least two. This number of crystallization units within the plant is chosen because the separate extraction of salts from a brine requires the creation of different conditions for their crystallization within the boiling chambers. The extraction of at least one target salt type requires at least two crystallization units, one of which ensures the extraction of the target salt type as a crystalline product free of impurities, while the second ensures the extraction of a mixture of the remaining salts from the solution.

[0018] To improve the energy efficiency of the plant for the separate extraction of salts from brine, the expansion chamber cavity of the IMV stage is equipped with a steam supply channel to the hot coolant circulation cavity of the heater, while the outlet pipe of the hot coolant circulation cavity is equipped with a condensate drain channel to the condensation chamber cavity of the IMV stage. The choice of IMV stage determines the parameters of the supplied steam, which allows for the creation of an optimal temperature for the crystallization of a specific salt, while preventing overheating of the heat exchanger wall and preventing deposits on the heat transfer surface.

[0019] Also, to increase the energy efficiency of the installation for the separate extraction of salts from the brine, the cavity of the steam space of the boiling chamber is connected to the cavity of the expansion chamber of the IMV stage, which makes it possible to use the steam separator of the IMV stage and further use the low-potential secondary steam formed as a result of boiling of the concentrate for heating the brine circulating in the tube bundles located in the cavities of the condensation chambers of the IMV.

[0020] To ensure the operation of the installation and the organization of the regeneration of its heat flows, the cavity for the circulation of the hot coolant of the heater can be connected by a steam supply channel to the higher stage of the IMV, while the cavity of the steam space of the boiling chamber and the channel for removing condensate from the heater can be connected to the lower stages of the IMV.

[0021] Additionally, to ensure the unit's operation, one stage of the IMV can be connected via a steam supply channel to only one cavity for circulating the hot coolant in the heater or to only one cavity in the steam space of the boiling chamber. This allows for the creation of different temperatures in each salt crystallization unit, ensuring optimal crystallization conditions and the highest energy efficiency of the unit. The invention can be manufactured from known materials using known means, demonstrating its compliance with the patentability criterion of "industrial applicability."

[0022] The invention is characterized by a previously unknown set of essential features from the prior art, distinguished in that:

[0023] — the cavity of the expansion chamber of the IMV stage is equipped with a channel for supplying steam to the cavity for circulating the hot coolant of the heater, while the outlet pipe of the cavity for circulating the hot coolant is equipped with a channel for removing condensate into the cavity of the condensation chamber of the IMV stage, which makes it possible for the heater to operate without external heat sources.

[0024] — the cavity of the steam space of the boiling chamber is connected to the cavity of the expansion chamber of the IMV stage, which makes it possible to use the secondary steam generated as a result of boiling of the concentrate to heat the salt solution circulating in the tube bundles located in the cavities of the condensation chambers of the IMV, and thus reduce the load on the head heater or heaters.

[0025] This ensures the achievement of a technical result consisting of increasing the energy efficiency of the installation for the separate extraction of salts from a brine by reusing the heat generated by the concentration unit and the salt crystallization units.

[0026] The invention has a set of essential features previously unknown in the state of the art, which indicates its compliance with the patentability criterion of “novelty”.

[0027] The prior art includes installations for the separate extraction of salts from salt solutions, but none of them are known to provide the possibility of reusing the heat they generate, which is why the invention meets the patentability criterion of “inventive step”.

[0028] The invention is illustrated by the following figures.

[0029] Fig. 1 - Diagram of a wastewater treatment plant including a device for separate extraction of salts from a brine solution.

[0030] Fig. 2 - Simplified diagram of a wastewater treatment plant including a device for the separate extraction of salts from a brine. Fig. 3 - Types of feed solutions from which the inventive system can be used for the separate extraction of salts.

[0031] To illustrate the possibility of implementation and a more complete understanding of the essence of the invention, an embodiment of it is presented below, which can be changed or supplemented in any way, while the present invention is in no way limited to the presented embodiment.

[0032] The unit for the separate extraction of salts from a brine solution includes a concentration unit and two salt crystallization units. It is part of a wastewater treatment complex (industrial wastewater, reverse osmosis concentrate, etc.), which, in turn, includes a wastewater supply pipeline 100, connected to a pre-treatment unit, a unit for the separate extraction of salts from a brine solution, a hardness removal unit, and a cooling unit. The complex also includes a steam supply pipeline.

[0033] The wastewater pre-treatment unit includes a thermal softener 200, a sludge separator 210, a sludge water tank 220, a sludge screw dewaterer 230, a sludge bin 240, a centrate tank 250, a centrate return pump 260, a clarified water tank 270, a pump 280 for feeding clarified water to the evaporator and a unit 290 for preparing and dosing an inhibitor.

[0034] The concentration unit includes a head heater 300 and a vertical flash evaporator (VFE) comprising a housing 310 having expansion chambers, the bottom of which is inclined in the direction of the brine outlet and in which removable steam separation devices 312 are installed, as well as condensation chambers in which tube bundles 314 are installed, while at the outlet of the expansion chambers and condensation chambers there are nozzles for removing the concentrate and distillate, respectively. The concentration unit also includes a circulation water tank 320, a distillate tank 330, a circulation pump 340, and a distillate discharge pump 350.

[0035] The hardness salt removal unit includes a settling tank 400, a clarified concentrate tank 410, a concentrate return pump 420, a lime preparation and dosing unit 430, a sludge collector 440, a screw sludge dewaterer 450, a sludge bin 460, a centrate tank 470, a centrate return pump 480 and a vacuum pump 490. The cooling unit includes a cooling tower 500 and a cooling tower pump 510. The salt crystallization units include concentrate tanks 600 and 700, pumps 610 and 710 for returning concentrate to the crystallization unit circuit, heaters 620 and 720, boiling chambers, which are expanders 630 and 730, circulation pumps 640 and 740, salt crystallizers 650 and 750, centrifuges 660 and 760 for dehydrating salt, and salt bins 670 and 770.

[0036] The cavity of each heater 620 and 720 is connected in series with an expander 630 and 730, respectively, and with the remaining elements of the salt crystallization units, ensuring the separation and removal of salts. The cavity of the steam space of each expander 630 and 730 is connected to the cavity of the expansion chamber of the IMV stage. The cavities of the expansion chambers of the IMV stage are equipped with channels for feeding steam into the cavities for circulating the hot coolant of each heater 620 and 720, while the outlet pipes of these cavities are equipped with channels for removing condensate into the cavities of the condensation chambers of the IMV stages. In this case, the steam supply channels from the expansion chambers of the IMV into the cavity for circulating the hot coolant of each heater 620 and 720 connect them with the higher stages of the IMV, while the cavity of the steam space of each expander 630 and 730 and the condensate drainage channels from the heaters 620 and 720 are connected with the lower stages of the IMV.

[0037] The connection of the remaining listed elements of the complex to each other is carried out by means of pipelines and shut-off valves in accordance with the diagram shown in Fig. 1.

[0038] The invention works as follows.

[0039] At the initial stage, wastewater is fed through pipeline 100 to a pre-treatment unit, specifically thermal softener 200, where it is heated to a temperature of 70°C and treated with steam. This results in the precipitation of hardness salts (CaCO3, CaSC, Mg(OH)2) in the water, which form a sludge, which is then separated from the water in sludge separator 210. The sludge from sludge separator 210 is discharged through sludge water tank 220 to a screw sludge dewaterer 230. The dewatered sludge is accumulated in sludge bin 240 and subsequently unloaded into vehicles. The centrate remaining after sludge dewatering is diverted from dewaterer 230 back to sludge separator 210. The clarified water flow from the sludge separator is treated with a scale inhibitor solution, represented by calcium carbonate, using unit 290, and fed to circulation water tank 320.

[0040] After preliminary treatment, the wastewater flow is concentrated in the circulation circuit of the IMV, which operates as follows.

[0041] Circulation water, consisting of clarified wastewater, is drawn from tank 320 by circulation pump 340 and fed through tube bundles 314 to head heater 300 for heating. Steam supplied from an external source via pipeline PO serves as the heating medium for head heater 300. After head heater 300, the circulating water flow, at a temperature 3-4°C above the saturation temperature in a vacuum, is fed through pipes to the expansion chamber of the IMV stage, where it boils, reducing its temperature to the saturation temperature, resulting in the formation of steam. The resulting steam, passing through steam separation device 312, enters the condensation chamber of the IMV stage, where it condenses on the surface of tube bundles 314, heating the circulating water contained therein.Circulation water, boiling in the IMV stage, flows through transfer devices into each subsequent stage and then into circulation water tank 320, from where it is discharged back into the IMV circulation system by pump 340. Condensate from the condensation chambers is first discharged to distillate tank 330 via a cascade steam trap and then discharged to cooling tower 500 via pump 350 if additional cooling is required, or discharged directly by pump 350 to the purified water consumer.

[0042] When the wastewater solution boils in the expansion chambers of the IMV, the concentration of salts in it increases, resulting in a concentrate being obtained at the outlet of the IMV circuit, which undergoes further processing in the circuit of the hardness salt removal unit as follows.

[0043] The concentrate enters settling tank 400, where suspended particles formed as a result of crystallization during concentration or due to additional reagent treatment of the concentrate in the settling tank using unit 430 settle. The sludge from settling tank 400 is discharged through sludge collector 440 to screw sludge dewaterer 450. The dewatered sludge is accumulated in sludge bin 460 and subsequently unloaded into vehicles. The centrate remaining after sludge dewatering is returned to the IMV circulation system using centrate return pump 480. The clarified concentrate from settling tank 400 flows into the clarified concentrate tank and is returned to the IMV circulation system or to the crystallization units using concentrate return pump 420.

[0044] In the salt crystallization units, separate extraction of sulfate and chloride salts from the clarified concentrate is carried out as follows.

[0045] The clarified concentrate enters tank 600, from where it is fed by pump 610 into the crystallization unit's circulation loop. Here, the concentrate enters heater 620, which uses secondary steam drawn from the cavities of the IMV expansion chambers as the heating medium. The condensate obtained in heater 620 is directed to the IMV condensation chambers and mixed with the distillate stream. The concentrate, with a temperature 2-8°C above the saturation temperature, is discharged into expander 630, where it boils, reducing the temperature to the saturation temperature. During boiling and the removal of a portion of the solution as steam, the concentration of salts in the remaining solution increases, resulting in their crystallization. A portion of the boiling concentrate is diverted as steam to the IMV expansion chambers to heat the circulating water in tube bundles 314.The salt crystal concentrate is pumped via pump 640 into salt crystallizer 650, where the solution is aged and the crystals are preliminarily separated from the mother liquor. The resulting salt pulp is fed to centrifuge 660 for salt dehydration, and the mother liquor is returned for further processing through tank 600. The dehydrated crystalline product is collected in salt bin 670 and subsequently unloaded into trucks or packaged in bags.

[0046] The crystallization unit, designated by positions 700-770, operates on a similar principle and is fed from the circuit of the preceding crystallization unit, designated by positions 600-670. The operating conditions of the crystallization units differ in the conditions created within expanders 630 and 730, specifically the temperature, pressure, concentration of the separated compound, and seed parameters required to extract a particular salt from the solution. This allows for their separate extraction and the production of a pure crystalline product at the outlet of each crystallization unit.

[0047] The proposed plant for the separate extraction of salts from a brine has high energy efficiency due to the fact that it provides the possibility of exchanging coolant, in particular steam, between the steam space of expanders 630 and 730 and the expansion chambers of the IMV stages, which makes it possible to use steam separation devices 312 located in the cavities of these chambers and more efficiently heat the circulating water located in tube bundles 314, thereby reducing the load on heater 300. The proposed plant also has high energy efficiency due to the fact that it provides the possibility of exchanging steam between the expansion chambers of the IMV stages and the cavities for circulating the hot coolant of heaters 620 and 720, which makes it possible to heat the concentrate entering the salt crystallization unit for processing without the use of external heat sources.

[0048] In addition, the exchange of coolant between the said elements of the installation for the separate extraction of salts from salt solutions is organized in such a way as to ensure the possibility of the operation of the installation and the organization of the regeneration of its heat flows, in particular, the intake of steam to ensure the heating of the concentrate in heaters 620 and 720 is carried out from the expansion chambers of the higher stages of the IMV, where the steam has a higher temperature, in comparison with the lower stages of the IMV, which allows it to be used as a source of heating medium in heaters 620 and 720, and the supply of steam from the steam space of expanders 630 and 730 to the expansion chambers of the lower stages of the IMV allows more efficient heating of the circulating water in tube bundles 314, located in the lower stages of the IMV, due to the mixing of superheated steam from expanders 630 and 730 to the steam of the lower stages of the IMV, which has a lower, in comparison with the higher IMV steps, temperature.

[0049] The proposed system can be used for the separate extraction of salts from solutions obtained in desalination plants, including membrane-based ones, and from wastewater from chemical, metallurgical, agricultural, and other industries, including energy plants, while increasing the energy efficiency of the extraction processes. Specifically, the proposed system can be used for the separate extraction of salts from the types of wastewater (source solutions) presented in the table shown in Fig. 3.

[0050] This ensures the achievement of a technical result consisting of increasing the energy efficiency of the installation for the separate extraction of salts from a brine solution by reusing the heat generated by the concentration unit and the salt crystallization units.

Claims

Invention formula 1. An installation for the separate extraction of salts from a brine solution, comprising: — a concentration unit, which includes a multi-stage flash evaporator (MEV), containing sequentially installed stages, each of which contains an expansion chamber and a condensation chamber, at the outlet of which there are pipes for discharging the concentrate and distillate, respectively; — at least two salt crystallization units, each of which contains a heater, the cavity of which is connected in series with the boiling chamber and the salt separation and removal system, wherein: — the cavity of the expansion chamber of the IMV stage is provided with a channel for supplying steam to the cavity for circulating the hot coolant of the heater, while the outlet pipe of the cavity for circulating the hot coolant is provided with a channel for removing condensate into the cavity of the condensation chamber of the IMV stage, and the cavity of the steam space of the boiling chamber is connected to the cavity of the expansion chamber of the IMV stage.

2. The installation according to paragraph 1, characterized in that the cavity for circulation of the hot coolant of the heater is connected by a steam supply channel to the higher stage of the IMV, while the cavity of the steam space of the boiling chamber and the channel for removing condensate from the heater are connected to the lower stages of the IMV.

3. The installation according to paragraph 1, characterized in that one stage of the IMV is connected by a steam supply channel to only one cavity for the circulation of the hot coolant of the heater or to only one cavity of the steam space of the boiling chamber.

4. The installation according to paragraph 1, characterized in that it contains crystallization blocks in a quantity equal to n+1, where n is the number of types of target salts to be extracted.

5. The installation according to item 1, characterized in that the bottom of the expansion chamber has a slope in the direction of the outlet of the saline solution.

6. The installation according to paragraph 1, characterized in that a steam separation device is installed between the expansion and condensation chambers, connecting their internal spaces.

7. The installation according to paragraph 6, characterized in that the steam separation device is removable.

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