High-salt trona halogen heat pump wet decomposition and salt-alkali separation process

Abstract

The invention relates to the technical field of sodium carbonate production, and discloses a high-salt trona brine heat pump wet decomposition and salt-alkali separation process which comprises the following steps: S1, a carbonization separation section: carrying out carbonization reaction on high-salt trona brine and carbon dioxide to generate sodium bicarbonate crystals; carrying out solid-liquid separation on the reaction product to obtain sodium bicarbonate crystals and carbonization and washing mother liquor; and S2, a calcination alkali production section: heating and decomposing the sodium bicarbonate crystals to obtain light sodium carbonate and calcination tail gas. S3, heat pump coupling wet decomposition and salt mining work section. According to the method, the heat pump technology and the wet decomposition section are deeply coupled, so that the process energy consumption is remarkably reduced, the synchronous separation and production of the high-value byproduct sodium chloride are realized, and the comprehensive utilization efficiency and the economical efficiency of resources are improved; meanwhile, according to the process, through mother liquor reinjection and condensate water recycling, salt balance and water balance closed circulation in the system is ingeniously constructed, so that long-term stability of the production process is guaranteed, waste liquid discharge is reduced, and the process has the remarkable environmental protection advantage.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of soda production, in particular to a high-salt natural soda brine heat pump wet decomposition and salt-alkali separation process. BACKGROUND

[0002] Soda, i.e. sodium carbonate, is an important basic chemical raw material, widely used in building materials, chemical industry, metallurgy, textile, food and many other fields. Using natural soda brine as raw material to produce soda is one of the important ways to obtain soda. At present, the carbonation process is generally used in industry to treat natural soda brine. The basic principle is to introduce carbon dioxide into the brine, take advantage of the small solubility of sodium bicarbonate in sodium chloride solution, make it crystallize and precipitate, and then filter, wash and send to calcination and decomposition to obtain the final product soda.

[0003] In the existing carbonation process, the carbonation mother liquor produced after the separation of sodium bicarbonate crystals is the key link that determines the overall process technology level, economic benefit and environmental protection level. However, there are several interrelated technical bottlenecks in the existing technology when dealing with this high-salt carbonation mother liquor. The current process usually uses a large amount of fresh industrial steam to heat and decompose the mother liquor (commonly known as "ammonia evaporation" or "wet decomposition") to recover the residual alkali. This method has strong dependence on external energy, resulting in high energy consumption and directly increasing production costs.

[0004] In addition, the existing process often lacks efficient and economic comprehensive utilization means for the high-concentration sodium chloride component in the mother liquor. The focus of process design is mostly limited to alkali recovery, and insufficient attention is paid to the separation and resource utilization of sodium chloride. This makes sodium chloride continue to accumulate in the process circulation system, and the continuous increase in its concentration will in turn inhibit the efficiency of the front-end carbonation reaction, affecting the yield and quality of sodium bicarbonate. In order to maintain system stability, the factory has to discharge a part of high-salt mother liquor regularly, which not only causes the waste of sodium chloride resources, but also poses a potential threat to the environment and increases the burden of environmental treatment.

[0005] At the same time, in order to ensure the purity of the final soda product, the washing step of sodium bicarbonate crystals in the carbonation separation section is indispensable, and this process requires the introduction of external clean water. In the traditional process lacking effective internal water balance control mechanism, the addition of this part of external water will break the water balance of the system, leading to the continuous expansion of the total amount of circulating liquid, which further aggravates the problem of having to discharge waste liquid to maintain balance, making it difficult for the entire production process to form a closed loop with stable material and water balance and full resource utilization. SUMMARY

[0006] In view of the deficiencies of the prior art, the application provides a high-salt natural alkali brine heat pump wet decomposition and salt-alkali separation process, which solves the problems of high energy consumption of mother liquor wet decomposition, waste of associated sodium chloride resources and difficulty in closing material and water balance in the whole process in the high-salt natural alkali brine carbonation method.

[0007] To achieve the above object, the application is implemented by the following technical scheme: a high-salt natural alkali brine heat pump wet decomposition and salt-alkali separation process, comprising the following steps:

[0008] S1, carbonization separation section: carbonization reaction is carried out on high-salt natural alkali brine and carbon dioxide to generate sodium bicarbonate crystals; solid-liquid separation and washing are carried out on the reaction product to obtain sodium bicarbonate crystals and carbonization and washing mother liquor;

[0009] S2, calcination alkali production section: the sodium bicarbonate crystals are heated and decomposed to obtain light sodium carbonate and calcination tail gas; the carbon dioxide in the calcination tail gas is recovered and sent to the carbonization separation section;

[0010] S3, heat pump coupled wet decomposition and salt extraction section:

[0011] The carbonization and washing mother liquor is sent to a wet decomposition tower for wet decomposition;

[0012] All the liquid at the bottom of the wet decomposition tower is sent to a vapor-liquid separation tank operating under reduced pressure to generate negative pressure secondary steam by flashing;

[0013] The negative pressure secondary steam is compressed and pressurized by a steam compressor and then sent back to the bottom of the wet decomposition tower as a heat source;

[0014] The solid-liquid mixture at the bottom of the vapor-liquid separation tank is separated to obtain sodium chloride solids.

[0015] Moreover, the solid-liquid separation in the carbonization separation section is that the carbonization reaction product is first sent to a vacuum belt filter for filtration and washing to obtain a water-containing filter cake; and then the water-containing filter cake is sent to a centrifuge for dewatering to obtain the sodium bicarbonate crystals.

[0016] Moreover, in the heat pump coupled wet decomposition and salt extraction section, the carbonization and washing mother liquor is subjected to multi-stage preheating by multiple preheaters before entering the wet decomposition tower.

[0017] Moreover, the preheating of the carbonization and washing mother liquor is carried out by using, in sequence, the sensible heat of the condensate water of the steam at the top of the wet decomposition tower, the latent heat of part of the uncondensed vapor phase and the sensible heat of the complete liquid collected from the circulating liquid tank at the bottom of the wet decomposition tower.

[0018] Moreover, the solid-liquid mixture taken from the vapor-liquid separation tank is first introduced into a thickener for concentration, and the material at the bottom of the thickener is introduced into a centrifuge for separation to obtain the sodium chloride solid.

[0019] Moreover, the liquid phase obtained after separation of the sodium chloride solid is returned to a circulating liquid tank, and part of the liquid in the circulating liquid tank is injected back into the well after heat exchange with the carbonation and washing mother liquor entering the wet decomposition tower for continuous brine production, so as to maintain the concentration of salt and alkali in the high-salt natural alkali brine.

[0020] Moreover, a part of the condensed water obtained by condensing the steam discharged from the top of the wet decomposition tower is used for washing the sodium bicarbonate crystals in the carbonation separation section.

[0021] Moreover, in the calcination and alkali production section, a drum-type steam soda calcination furnace is used, and steam with a pressure of 2.0-3.2 MPaG is introduced for indirect heating of the sodium bicarbonate crystals.

[0022] Moreover, in the carbonation separation section, the temperature of the carbonation reaction is controlled at 0-60 DEG C, and the pressure is controlled at 0-0.5 MPaG.

[0023] Moreover, the carbon dioxide used in the carbonation separation section is sourced from the carbon dioxide recovered in the calcination and alkali production section and the carbon dioxide discharged from the top of the wet decomposition tower.

[0024] The present application provides a high-salt natural alkali brine heat pump wet decomposition and salt-alkali separation process.

[0025] Advantages:

[0026] 1. The present application deeply couples the heat pump technology with the wet decomposition section to build an efficient internal energy circulation system. Specifically, the low-grade secondary steam generated in the wet decomposition process is used as the heat source after being compressed by a compressor to increase the pressure and temperature, thereby replacing a large amount of high-grade external fresh steam consumption. This design significantly recovers and reuses the latent heat in the system, greatly reduces the overall energy consumption of the entire process, and improves the energy utilization efficiency.

[0027] 2. The present application realizes the comprehensive utilization of resources and product diversification, and significantly improves the overall economy of the process. In the process of treating high-salt mother liquor, the sodium chloride in the solution reaches a supersaturated state and crystallizes out through the continuous evaporation and concentration of the heat pump coupled wet decomposition system, thereby producing high-value sodium chloride by-product while producing main product soda ash. This not only solves the problem of difficult treatment of high-salt mother liquor in traditional processes, but also realizes complete salt-alkali separation, converts the original impurity components into commodities, and extends the value chain.

[0028] 3、The application ensures that the entire production system, especially the core carbonation reaction section, can be operated stably for a long time by constructing a sophisticated material closed loop. In the design, part of the concentrated completion liquid from the wet decomposition section is injected back into the underground brine extraction well, forming a dynamic salt and alkali balance regulation loop. This loop can effectively prevent the unlimited accumulation of sodium chloride in the process cycle, thereby stabilizing the components of the raw brine within an optimized process window, providing a continuous and stable prerequisite for obtaining high-quality sodium bicarbonate crystals.

[0029] 4、The application forms high-purity condensed water by condensing the water vapor evaporated from the top of the wet decomposition tower, which is directly used in the carbonation separation section as a high-quality water source for washing sodium bicarbonate crystals. This design not only realizes the closed loop of process water, greatly reducing the dependence on external fresh water resources, but also maximizes the reduction of production wastewater discharge, meeting the requirements of green chemical industry and sustainable development. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is the overall flow chart of the process of the application;

[0031] Figure 2 is the process structure flow chart of the application;

[0032] Figure 3 is the diagram of the carbonation separation step of the application;

[0033] Figure 4 is the structural schematic diagram of the carbonation separation section of the application;

[0034] Figure 5 is the diagram of the calcination and alkali production step of the application;

[0035] Figure 6 is the structural schematic diagram of the calcination and alkali production section of the application;

[0036] Figure 7 is the diagram of the heat pump coupled wet decomposition and salt extraction step of the application;

[0037] Figure 8 is the schematic diagram of the wet decomposition part of the application. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the application will be described in detail below with reference to the drawings in the specification of the application. Obviously, the described embodiments are only a part of the embodiments of the application, not all embodiments. Based on the embodiments in the application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the application.

[0039] Please refer to the drawings in the specification of the application Figure 1 -Figure 4 The embodiment of the present application provides a high-salt natural alkali brine heat pump wet decomposition and salt-alkali separation process, which comprises the following steps:

[0040] S1, carbonization separation section: the high-salt natural alkali brine is subjected to carbonization reaction with carbon dioxide to generate sodium bicarbonate crystals; the reaction product is subjected to solid-liquid separation and washing to obtain sodium bicarbonate crystals and carbonization and washing mother liquor;

[0041] The core purpose of this section is to convert the sodium carbonate component in the raw material high-salt natural alkali brine into sodium bicarbonate with relatively low solubility in brine through reaction with carbon dioxide according to the principle of chemical equilibrium, and separate it from the liquid phase in the form of crystals, so as to realize the preliminary separation of alkali and salt.

[0042] In the initial stage of the process, the high-salt natural alkali brine from the brine extraction station is mixed with carbon dioxide gas recovered from the subsequent S2 calcination alkali production section and S3 heat pump coupled wet decomposition and salt extraction section. To ensure sufficient reaction, carbon dioxide is supplied in excess, which aims to increase the conversion rate of sodium carbonate and compensate for the loss of carbon dioxide due to the emission of inert gases (such as air) inevitably brought into the system. The initial contact and reaction of brine and carbon dioxide preferably occur in the conveying pipeline before entering the subsequent cooling system to promote mass transfer between gas and liquid phases by utilizing the turbulent effect in the pipeline.

[0043] Subsequently, the gas-liquid mixture enters a forced circulation loop system. This system is the core reaction unit of this section, mainly composed of a carbonation reactor, a forced circulation pump and a cooler. In this circulation loop, the material is continuously circulated and the carbonation reaction is continuously carried out, and the chemical reaction formula is:

[0044] Na2CO3+ CO2+ H2O → 2NaHCO3.

[0045] Since the above carbonation reaction is essentially an acid-base neutralization reaction, it releases a large amount of reaction heat. In order to continuously push the chemical equilibrium to the positive direction that is beneficial to the generation of sodium bicarbonate (product) and effectively reduce the solubility of sodium bicarbonate in sodium chloride solution (application of the principle of common ion effect), the process uses a cooler in the circulation loop to remove the reaction heat from the system in time by using cooling medium such as circulating water or low-temperature water. In this embodiment, the temperature of the carbonation reaction system is preferably controlled in the range of 0-60°C, and the reaction pressure is maintained at 0-0.5 MPaG under slightly positive pressure or pressurized conditions. Lower temperature and higher pressure both have a positive effect on the carbonation reaction and the crystallization rate of sodium bicarbonate.

[0046] The newly generated sodium bicarbonate crystal particles are fine and have strong surface adhesion, which can easily deposit and scale on the inner wall of the pipeline and the surface of the heat exchanger tube bundle, thereby causing serious problems such as pipeline blockage and sharp decline in heat exchange efficiency. In order to ensure the long-term continuous and stable operation of the process, the carbonation reaction and heat removal circulation loop of the present application is specially designed as a 2 to 6 parallel structure. This design allows any one of the parallel structures to be isolated, online dissolved and cleaned or maintained in turn without stopping production, thereby ensuring the continuity and efficiency of the overall production process.

[0047] In the internal structure design of the carbonation reactor, a baffle is specially provided. The baffle is ingeniously used for the physical property that the density of sodium bicarbonate crystals is greater than the density of the solution. The outlet of the circulating liquid is arranged on one side of the baffle, so that the upper clear liquid which is almost free of sodium bicarbonate crystals is mainly extracted by the forced circulation pump, thereby effectively reducing the wear and blockage risk of the circulating pump and the cooler, and ensuring the operation efficiency of the circulating system.

[0048] After sufficient reaction and crystal growth in the circulating system, the material at the bottom of the carbonation reactor has formed a slurry containing a large amount of sodium bicarbonate crystals. The material slurry is pumped to the subsequent solid-liquid separation unit by the carbonation liquid feeding pump. In this embodiment, an optimized two-stage separation combination method is adopted to realize efficient separation and deep dewatering.

[0049] The first stage separation preferably adopts a vacuum belt filter. Its unique structure enables continuous operation of filtration and washing. When the material slurry is transported to the front half of the vacuum belt filter, most of the liquid phase (i.e. carbonation mother liquor) is quickly filtered out under the action of vacuum suction. Subsequently, the filter cake formed runs to the rear half of the belt filter, where the filter cake is washed countercurrently with condensed water obtained from the S3 heat pump coupled wet decomposition and salt extraction section overhead steam condensation. The purpose of this step is to efficiently wash away sodium chloride and other soluble impurities adhering to the surface of sodium bicarbonate crystals, so as to achieve the purpose of desalination and purification.

[0050] The second stage separation adopts a centrifuge. The water-containing filter cake obtained after the vacuum belt filter treatment has a water content of about 20%. In order to significantly reduce the heat energy consumption of the subsequent S2 calcination and caustic soda production section, the filter cake needs to be deeply dewatered. Therefore, the water-containing filter cake is sent to a centrifuge with a higher separation factor, and finally a high-purity sodium bicarbonate crystal with a water content of less than 8% is obtained. In this process, the liquid phase separated by the centrifuge (i.e. centrifugal mother liquor) may contain a small amount of fine crystals that are not effectively intercepted, so it is returned to the feed end of the vacuum belt filter for re-filtration, thereby avoiding the loss of product and improving the overall yield of the material.

[0051] Finally, the output of the carbonation separation section is clearly divided into two parts: solid phase product, i.e. the sodium bicarbonate crystals after deep dehydration, is delivered to the S2 calcination section for subsequent processing; liquid phase product, i.e. the carbonation and washing mother liquor obtained by combining the carbonation mother liquor filtered out by the vacuum belt filter with the washing liquid, is then sent to the S3 heat pump coupled wet decomposition and salt extraction section as the core processing raw material.

[0052] S2, calcination section: heating and decomposing the sodium bicarbonate crystals to obtain light sodium carbonate and calcination tail gas; recovering the carbon dioxide in the calcination tail gas and sending it to the carbonation separation section;

[0053] The core task of this section is to convert the sodium bicarbonate crystals produced by the aforementioned S1 carbonation separation section, which have been deeply dehydrated, into the final product, light sodium carbonate, through a precisely controlled thermal decomposition process, and to efficiently recover the carbon dioxide gas generated in this process, which has important recycling value.

[0054] The sodium bicarbonate crystals delivered from the S1 section have a water content that has been preferably controlled to be below 8%, and this low-moisture material is continuously and uniformly fed into the calcination equipment. In a preferred embodiment of the present application, the calcination equipment is a rotary drum steam soda calciner. This equipment works through the principle of wall-type heat exchange, i.e. a heating pipe bundle is arranged inside the rotating furnace body.

[0055] During operation, high-pressure steam with a pressure of 2.0-3.2 MPaG is introduced into the inside of the heating pipe bundle, wherein a steam pressure of 3.2 MPaG is preferably used to obtain a higher heat exchange temperature (corresponding to a saturated steam temperature of about 215-239°C). As the calciner slowly rotates, the sodium bicarbonate crystals in the furnace are constantly turned over and come into full contact with the high-temperature outer wall of the heating pipe, thereby being uniformly and efficiently indirectly heated.

[0056] According to the chemical properties of sodium bicarbonate, it will begin to rapidly decompose when the temperature reaches above 127°C. The present process uses high-pressure steam far above this decomposition temperature as a heat source, aiming to ensure that the sodium bicarbonate can quickly and completely complete the thermal decomposition reaction, the chemical reaction formula of which is as follows:

[0057]

[0058] In this process, a small amount of free water carried by the sodium bicarbonate crystals is also rapidly vaporized at the same time. The solid phase product generated after this decomposition process, due to its small particle size and low apparent density, is called light sodium carbonate, also known as "light ash".

[0059] The water vapor and carbon dioxide gas generated in the decomposition and vaporization process are discharged from the tail or top of the calciner as calciner tail gas. Due to the difficulty in achieving complete air tightness at the inlet and outlet ends of the calciner, a small amount of air is inevitably brought into the furnace during operation, so the calciner tail gas usually contains about 90% pure carbon dioxide. To achieve the economic and atom economy of the process, this part of carbon dioxide must be recovered and recycled to the S1 carbonization separation section.

[0060] To achieve the above purpose, the calciner tail gas needs to be purified first. Specifically, the high-temperature calciner tail gas is introduced into a direct contact gas washing tower. In the tower, the tail gas is in direct contact with the downwardly sprayed washing water (usually low-temperature water) countercurrently, and intense heat exchange occurs. This process rapidly reduces the temperature of the tail gas, and most of the water vapor contained therein is condensed into liquid water and removed.

[0061] After the above washing, cooling and dehumidification treatment, the high-purity carbon dioxide gas obtained is combined with the carbon dioxide gas recovered from the S3 heat pump coupled wet decomposition and salt recovery section. The combined gas stream is then sent to a carbon dioxide compressor for pressurization, and then returned to the S1 carbonization separation section as a key raw material, thereby forming an internal recycling loop of carbon dioxide.

[0062] On the other hand, the solid product, hot light sodium carbonate, discharged from the calciner head or tail is usually at a temperature of about 200°C. Such a high temperature can cause thermal damage to the packaging materials (such as plastic or paper-plastic composite bags) used in the subsequent metering and packaging processes. Therefore, the hot light ash must be cooled before entering the packaging section.

[0063] In this embodiment, the hot light sodium carbonate is introduced into a dedicated cooling alkali furnace. The structure of the cooling alkali furnace can be flexibly selected according to production needs, for example, a drum-type cooling alkali furnace or a powder flow cooling alkali furnace can be used. In the cooling alkali furnace, the temperature of the light sodium carbonate is stably reduced to below 80°C through indirect or direct heat exchange with a cooling medium (such as cooling water or air). The light sodium carbonate reaching the target temperature can be transferred to the final packaging section to complete the preparation of the product.

[0064] S3, heat pump coupled wet decomposition and salt recovery section:

[0065] The carbonization and washing mother liquor is sent to the wet decomposition tower for wet decomposition;

[0066] All the liquid at the bottom of the wet decomposition tower is sent to a vapor-liquid separation tank operated at reduced pressure to flash produce negative pressure secondary steam;

[0067] The negative pressure secondary steam is compressed to increase the pressure by a steam compressor and then sent back to the bottom of the wet decomposition tower as a heat source;

[0068] The solid-liquid mixture at the bottom of the vapor-liquid separation tank is separated to obtain sodium chloride solids;

[0069] This section is the core innovative unit of the process, and its main purpose is to treat the carbonation and washing mother liquor from the S1 carbonation separation section. It not only aims to efficiently decompose and recover the residual sodium bicarbonate in the mother liquor, but also, through a set of ingeniously designed heat pump coupling systems, to achieve the separation and production of high-value byproduct sodium chloride while significantly reducing energy consumption, and ultimately to form the necessary water balance and salt balance closed-loop circulation for stable operation of the entire process system.

[0070] Specifically, the carbonation and washing mother liquor from the S1 section, before entering the main equipment of this section, the wet decomposition tower, is first subjected to a set of multi-stage series preheaters for sufficient waste heat recovery. The multi-stage series preheater system includes preheater 1, preheater 2, and preheater 3. This is done to maximize the temperature of the feed to reduce the energy demand of the subsequent decomposition process. Preferably, the preheating process is carried out in steps: first, the mother liquor is heat exchanged with the high-temperature condensate from the wet decomposition tower heater in the subsequent section; then, it continues to be heat exchanged with the high-temperature completion liquid taken from the bottom of the tower in this section; if necessary, finally a small amount of primary steam can be used for final supplementary heating to ensure that the temperature of the mother liquor reaches or approaches 100°C when it enters the wet decomposition tower.

[0071] The well-preheated mother liquor enters from the top of the wet decomposition tower, which can have an internal structure in the form of a packed tower, a tray tower, or a combination of both. In the tower, the liquid from top to bottom is in countercurrent contact with the high-temperature steam rising from the bottom, and sufficient mass and heat transfer occurs. In this process, most (usually more than 95%) of the residual sodium bicarbonate in the mother liquor is decomposed, and the reaction is as follows:

[0072] 2NaHCO3→ Na2CO3 + H2O + CO2.

[0073] The generated carbon dioxide gas is desorbed from the liquid phase and discharged from the top of the wet decomposition tower along with a large amount of water vapor, thus completing the decomposition of sodium bicarbonate and the desorption of carbon dioxide.

[0074] It is worth mentioning that the core heat source for decomposing the mother liquor in this section is not a large amount of fresh steam supplied from the outside, but is provided by a set of MVR (mechanical vapor recompression) heat pump systems tightly coupled with the wet decomposition tower. The operation mechanism of this system is as follows:

[0075] The wet decomposition column is operated at normal pressure or slightly positive pressure (preferably at an operating pressure of 0-0.05 MPaG). The liquid withdrawn from the bottom of the column is allowed to flow into a downstream vapor-liquid separation tank by pressure difference; a large amount of circulating liquid, which is pumped from a circulating liquid tank through a circulating pump at the bottom of the column, is heated by the steam at the top of the column and then enters the vapor-liquid separation tank. The vapor-liquid separation tank is maintained at a significant reduced pressure or vacuum state (for example, an absolute pressure of 0.05 MPaA) by suction of a steam compressor. Under this negative pressure condition, the boiling point of the high-temperature liquid entering the tank is significantly reduced, thereby causing violent flashing and generating a large amount of low-pressure secondary steam.

[0076] The steam compressor continuously sucks in the low-pressure, low-grade secondary steam, performs compression work on it, and significantly increases the pressure and temperature of the secondary steam (for example, the pressure is increased to 0.105 MPaA, and the corresponding temperature is about 105°C). The high-temperature and high-pressure steam after "upgrading" is directly sent back to the bottom of the wet decomposition column as the core heat source for heating and decomposing the mother liquor in the column. In this way, an efficient internal energy circulation is formed, that is, the latent heat of the secondary steam generated by the evaporation of the liquid is recovered and upgraded for reuse, thereby replacing a large amount of external energy input.

[0077] As the water in the wet decomposition column is continuously evaporated and the MVR system is circulated and concentrated, the concentration of sodium chloride in the circulating system gradually increases, and when it reaches a supersaturated state, sodium chloride crystals are precipitated. In order to separate and obtain this byproduct, the solid-liquid mixture withdrawn from the bottom of the vapor-liquid separation tank is sent to a subsequent salt extraction unit. Preferably, the solid-liquid mixture first enters a thickener for solid enrichment. The high-concentration crystal slurry with a significantly increased solid content (for example, reaching more than 50%) at the bottom of the thickener is then pumped to a centrifuge for final solid-liquid separation, thereby obtaining the solid sodium chloride product.

[0078] The mother liquor separated by the centrifuge (centrifugal mother liquor) is combined with the clarified liquid at the top of the thickener and then returned to a circulating liquid tank. The circulating liquid tank is the center of the system material scheduling. Most of the liquid in the tank is pumped into a heater heated by the steam at the top of the column and then returned to the vapor-liquid separation tank to continue participating in the flashing cycle.

[0079] It is crucial to maintain the long-term stability of the entire process system, especially the stability of the raw brine salt and alkali concentration. A small amount of liquid is drawn from the circulating liquid tank as a completion liquid. The completion liquid is pumped out from the bottom of the column, and after exchanging heat with the feed mother liquor in the preheater to contribute its sensible heat, it is injected back into the well for brine extraction. This step constitutes the "salt and alkali balance" regulation mechanism of the process, which discharges the sodium chloride enriched in the process cycle from the system in a controlled manner, and at the same time brings the newly dissolved sodium chloride, sodium carbonate and sodium bicarbonate in the ore bed into the production process, thereby ensuring the stability of the carbonization efficiency of the S1 section and avoiding the process fluctuations caused by the unlimited increase of the salt content in the mother liquor.

[0080] Finally, for the gas phase product processing and water balance control of this section: the mixed gas containing carbon dioxide and a large amount of water vapor discharged from the top of the wet decomposition tower first enters the heater, and its latent heat is used to heat the circulating liquid entering this section. In this heat exchange process, most of the water vapor is condensed into clean condensed water. This part of the condensed water is collected and then heat exchanged with the wet decomposition tower feed, and then cooled with circulating water. After that, part of it is sent back to the S1 carbonation separation section as high-quality washing water for washing sodium bicarbonate filter cake; another part can be used as supplementary water for the plant circulating water system. This design not only recovers heat energy, but also realizes internal water circulation, perfectly solving the problem of system total water expansion that may be caused by the introduction of external washing water in the S1 section, forming a closed loop of "water balance". The remaining non-condensable gas (mainly carbon dioxide) after condensation is combined with the carbon dioxide gas recovered from the S2 calcination section and enters the carbon dioxide compressor together, returning to the S1 section for recycling.

[0081] In summary, through the deep coupling of wet decomposition and MVR heat pump, as well as the fine treatment and circulation of liquid and gas phase products, this section not only achieves the goal of energy saving and consumption reduction, but also integrally solves a series of key technical problems such as salt and alkali separation, by-product recovery, system salt balance, and water balance.

[0082] The specific implementation is as follows:

[0083] The high-salt trona brine 647146.02 kg / h from the brine station contains sodium carbonate 35875.73 kg / h, sodium bicarbonate 19758.31 kg / h, water 448496.98 kg / h, sodium chloride 143015 kg / h, and the temperature is 35℃, which enters the carbonation separation section.

[0084] In the carbonation separation section, more than 98% of the sodium carbonate in the high-salt trona brine reacts with excess carbon dioxide from the carbon dioxide compressor and water in the reaction system to form sodium bicarbonate. The reaction product after carbonation is 662420.66 kg / h, containing sodium bicarbonate 76113.96 kg / h, sodium carbonate 318 kg / h, 143015 kg / h, and water 442973.7 kg / h. Unreacted carbon dioxide and inert gas air are discharged from the top of the reactor and out of the carbonation system.

[0085] The carbonization reaction product first enters a vacuum belt filter, where liquid is removed at the front of the belt filter. At the middle and rear of the belt filter, 30,000 kg / h of deionized water is used to wash away any sodium chloride adhering to the surface of the sodium bicarbonate. The filter cake, containing approximately 20% water after the belt filter, enters a centrifuge, producing 62,420.66 kg / h of sodium bicarbonate crystals with a moisture content of less than 8%, comprising 59,433.96 kg / h of sodium bicarbonate, 15 kg / h of sodium chloride, and 2,971.7 kg / h of water.

[0086] Centrifugation yields 630,000 kg / h of carbonization and washing mother liquor, which contains 318 kg / h of sodium carbonate, 16,680 kg / h of sodium bicarbonate, 47,000 kg / h of water, and 143,000 kg / h of sodium chloride.

[0087] The sodium bicarbonate crystals from the centrifuge enter a drum-type steam soda ash calciner heated with 3.2 MPaG steam. The resulting calcined sodium carbonate (light ash) produces 37,515.9 kg / h of light sodium carbonate, which is then cooled and packaged. The light ash contains 37,500 kg / h of sodium carbonate, 0.9 kg / h of water, and 15 kg / h of sodium chloride. The calcining furnace tail gas 25961.76kg / h (nitrogen 835kg / h, oxygen 222kg / h, carbon dioxide 15566.04kg / h, water vapor 9338.63) and the wet decomposition tower top gas 4301.46kg / h (carbon dioxide 4159.51kg / h, water vapor 141.95kg / h) after condensation and cooling enter the scrubbing tower to condense the water vapor therein, and then 20980.01kg / h of gas (nitrogen 835kg / h, oxygen 222kg / h, carbon dioxide 19265.55kg / h, water vapor 657.46kg / h) enters the carbon dioxide compressor and then returns to the carbonization section.

[0088] The carbonized and washed mother liquor, serving as the wet decomposition tower feed, heats up to 58.9°C via heat exchange with the condensate in the wet decomposition tower heater. The liquid at the bottom of the wet decomposition tower completes heat exchange, raising its temperature to 76.4°C, and the primary steam heat exchange temperature is raised to 100°C. Afterward, the mother liquor enters the wet decomposition tower from the top. Sodium bicarbonate decomposes within the wet decomposition tower to produce 4267.51 kg / h of carbon dioxide, which, along with 129,259.22 kg / h of water vapor at approximately 105°C at the top of the tower, enters the wet decomposition tower heater to heat the circulating liquid from the circulating liquid tank. The condensate, along with uncondensed gases, enters the wet decomposition tower feed preheater 1 and then the cooler. 30,000 kg / h of condensate enters the sodium bicarbonate crystallization and washing process, while the remainder enters the circulating water system. The gases enter the scrubber.

[0089] The 1612946 kg / h liquid (sodium carbonate 35127.18 kg / h, sodium bicarbonate 1388.485 kg / h, sodium chloride 438308.7 kg / h, water 1138121.635 kg / h) heated by the wet decomposition tower heater, together with the 625509.01 kg / h liquid (sodium carbonate 10313.88 kg / h, sodium bicarbonate 819.87 kg / h, sodium chloride 143000 kg / h, water 471375.26 kg / h) taken from the bottom of the wet decomposition tower, enters the vapor-liquid separation tank, the flash vapor pressure of which is 0.05 MPaA, and the flow rate is 129035.74 kg / h (carbon dioxide 97.43 kg / h, water vapor 128938.31 kg / h), the steam enters the steam compressor, and after being pressurized to 0.105 MPaA by the compressor, it returns to the bottom of the wet decomposition tower. The 2109419.27 kg / h solid-liquid mixture (sodium carbonate 45678.493 kg / h, sodium bicarbonate 1836.401 kg / h, sodium chloride 581308.7 kg / h, water 1480595.68 kg / h) taken from the bottom of the vapor-liquid separation tank enters the thickener, the supernatant 2086970.4 kg / h (sodium carbonate 45431.422 kg / h, sodium bicarbonate 1826.635 kg / h, sodium chloride 567121.763 kg / h, water 1472590.58 kg / h) returns to the circulating liquid tank, and the other materials in the thickener with a solid content of more than 50% enter the centrifuge. The centrifugal mother liquor 10900.66 kg / h (sodium carbonate 237.382 kg / h, sodium bicarbonate 9.383 kg / h, sodium chloride 2962.502 kg / h, water 7691.39 kg / h) returns to the circulating liquid tank, and the sodium chloride solid containing a small amount of sodium carbonate 11584.21 kg / h (sodium carbonate 9.689 kg / h, sodium bicarbonate 0.383 kg / h, sodium chloride 11224.435 kg / h, water 313.706 kg / h) is taken out to enter the sodium chloride washing and packaging section. The material in the circulating liquid tank 484925.04 kg / h (sodium carbonate 10560.832 kg / h, sodium bicarbonate 417.442 kg / h, sodium chloride 131775.565 kg / h, water 342171.221 kg / h) is injected into the well by the bottom pump after being heated by the wet decomposition tower feed preheater 2, and then returns to the carbonation section. The other material in the circulating liquid tank 1612946 kg / h (sodium carbonate 35127.18 kg / h, sodium bicarbonate 1388.485 kg / h, sodium chloride 438308.7 kg / h, water 1138121.635 kg / h) enters the wet decomposition tower heater through the bottom circulating pump.

[0090] While embodiments of the application have been shown and described, it is to be understood that the embodiments described are merely exemplary of the principles and application of the present application. Numerous modifications and adaptions can be effected without departing from the spirit and scope of the present application, which is not limited to the exact construction and arrangement described. It is intended, therefore, to cover all modifications and adaptions that fall within the scope of the claims and their equivalents.

Claims

1. A high-salt natural alkali brine heat pump wet decomposition and salt-alkali separation process, characterized in that: The following steps are involved: S1, Carbonization and separation section: Carbonization reaction of high-salt natural alkaline brine with carbon dioxide to generate sodium bicarbonate crystals; The reaction product is subjected to solid-liquid separation and washing to obtain sodium bicarbonate crystals and carbonization and washing mother liquor; S2, calcination alkali section: heating and decomposing the sodium bicarbonate crystals to obtain light sodium carbonate and calcination tail gas; recovering the carbon dioxide in the calcination tail gas and sending it to the carbonization separation section; S3, heat pump coupled wet decomposition and salt mining section: sending the carbonized and washed mother liquors into a wet decomposition tower for wet decomposition; All the liquid at the bottom of the wet decomposition tower is sent to the vapor-liquid separation tank under reduced pressure operation, and flash evaporated to produce negative pressure secondary steam; The negative pressure secondary steam is compressed and pressurized by a steam compressor and then sent back to the bottom of the wet decomposition tower as a heat source; The solid-liquid mixture at the bottom of the vapor-liquid separation tank is separated to obtain sodium chloride solid.

2. A high-salt natural alkali brine heat pump wet decomposition and salt-alkali separation process according to claim 1, characterized in that: The solid-liquid separation in the carbonization separation section is specifically as follows: the carbonization reaction product is first sent to a vacuum belt filter for filtration and washing to obtain a water-containing filter cake; and then the water-containing filter cake is sent to a centrifuge for dehydration to obtain the sodium bicarbonate crystals.

3. A high-salt natural alkali brine heat pump wet decomposition and salt-alkali separation process according to claim 1, characterized in that: In the heat pump coupled wet decomposition and salt mining section, the carbonization and washing mother liquors are preheated in multiple stages through multiple preheaters before entering the wet decomposition tower.

4. A high-salt natural alkali brine heat pump wet decomposition and salt-alkali separation process according to claim 3, characterized in that: The carbonization and washing mother liquor is preheated by sequentially utilizing the sensible heat of the condensed water of the wet decomposition tower top steam and the latent heat of part of the uncondensed vapor phase and the sensible heat of the finished liquid extracted from the circulating liquid tank at the bottom of the wet decomposition tower.

5. A high-salt natural alkali brine heat pump wet decomposition and salt-alkali separation process according to claim 1, characterized in that: In the heat pump coupled wet decomposition and salt mining process, the solid-liquid mixture mined from the vapor-liquid separation tank first enters a thickener for concentration, and the material at the bottom of the thickener then enters a centrifuge for separation to obtain the sodium chloride solid.

6. A high-salt natural alkali brine heat pump wet decomposition and salt-alkali separation process according to claim 1, characterized in that: The liquid phase obtained after the separation of the sodium chloride solid is returned to the circulating liquid tank. Part of the liquid in the circulating liquid tank is injected back into the well for continued brine production after heat exchange with the carbonization and washing mother liquor entering the wet decomposition tower to maintain the concentration of salt and alkali in the high-salt natural alkaline brine.

7. A high-salt natural alkali brine heat pump wet decomposition and salt-alkali separation process according to claim 1, characterized in that: A portion of the condensed water obtained by condensing the steam discharged from the top of the wet decomposition tower is used to wash the sodium bicarbonate crystals in the carbonization separation section.

8. The high-salt natural alkali brine heat pump wet decomposition and salt-alkali separation process according to claim 1, characterized in that: In the calcination alkali-making section, a drum-type steam soda ash calcining furnace is used, and steam with a pressure of 2.0 to 3.2 MPaG is introduced to indirectly heat the sodium bicarbonate crystals.

9. A high-salt natural alkali brine heat pump wet decomposition and salt-alkali separation process according to claim 1, characterized in that: In the carbonization separation section, the temperature of the carbonization reaction is controlled at 0-60° C., and the pressure is controlled at 0-0.5 MPaG.

10. A high-salt natural alkali brine heat pump wet decomposition and salt-alkali separation process according to claim 1, characterized in that: The carbon dioxide used in the carbonization separation section comes from the carbon dioxide recovered from the calcination alkali making section and the carbon dioxide discharged from the top of the wet decomposition tower.

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