Energy-saving brine purification process

Abstract

Provided in the present invention is an energy-saving brine purification process. The process comprises: low-pressure flash evaporation, involving: inputting salt-containing brine 1 comprising sodium carbonate as a main component and sodium chloride and sodium sulfate as impurities into a one-stage flash evaporator or a multi-stage flash evaporator for flash evaporation and concentration, so as to obtain brine 2, wherein the flash evaporator is provided with an independent vacuum system, and the temperature and the pressure of the multi-stage flash evaporator gradually decrease; crystallization of sodium carbonate decahydrate, involving: inputting the brine 2 into a crystallizer for low-temperature crystallization, so as to obtain crystal mush; centrifugal separation, involving: subjecting the crystal mush to centrifugal separation, so as to obtain a sodium carbonate decahydrate filter cake; and heating a centrifugal mother liquor, then returning same to the crystallizer, and dissolving the filter cake, so as to obtain a low-salt brine. The energy-saving brine purification process of the present invention can eliminate constraints on the temperature of the input salt-containing brine and the concentration of sodium carbonate, continuously and efficiently remove inorganic salt and nitrate impurities in the salt-containing brine, achieve waste heat recovery and utilization, and finally obtain a high-purity low-salt brine.

Description

Energy-saving brine purification process TECHNICAL FIELD

[0001] The present application relates to the technical field of natural soda production, in particular to an energy-saving brine purification process. BACKGROUND

[0002] Natural soda production mainly utilizes natural soda ore (Na2CO3·NaHCO3·2H2O) or soda stone ore (NaHCO3) to produce sodium carbonate monohydrate through dissolution and subsequent production processes. In addition to Na2CO3 and NaHCO3, there are also salt and nitre impurities such as NaCl and Na2SO4 in natural soda ore or soda stone ore. These impurities enter the brine after dissolution and accumulate in the production process of heavy sodium carbonate, ultimately affecting the crystallization and precipitation of sodium carbonate monohydrate, so these salt and nitre impurities must be removed.

[0003] In view of the salt and nitre impurities in the brine, the existing process often uses ten-water sodium carbonate process to recover the crystallization effluent to maximize resource utilization. It is worth noting that the ten-water sodium carbonate production process in the production process of sodium carbonate monohydrate is used to treat high-sodium carbonate content and high-temperature salt-containing brine prepared in the upstream process, so in the actual process flow, the ten-water sodium carbonate production process is limited by the concentration and temperature of the input brine. Patent CN112850753A discloses a natural soda production process using natural soda ore or soda stone ore as raw material, which first produces ten-water sodium carbonate, and then uses the ten-water sodium carbonate product to produce sodium carbonate monohydrate, thereby reducing the content of sodium chloride / sodium sulfate impurities in the sodium carbonate product. In this technical solution, the concentration of Na2CO3 in the brine input into the ten-water sodium carbonate production is 21-24wt%, and the temperature is about 100℃, and the further utilization of waste heat in the process flow is lacking in the ten-water sodium carbonate production. SUMMARY

[0004] In view of the deficiencies in the prior art, the present application discloses an energy-saving brine purification process, which purifies salt and nitre impurities such as sodium chloride and sodium sulfate in the brine through low-pressure flash evaporation, ten-water sodium carbonate crystallization, centrifugal separation and dissolution, etc. This purification process is not limited by the temperature of the brine and the concentration of sodium carbonate in the brine, can effectively remove salt and nitre impurities and realize waste heat recovery and utilization, and obtain high-purity low-salt brine.

[0005] In order to achieve the above technical purposes, the present application proposes an energy-saving brine purification process, which comprises the following steps:

[0006] (1) Low-pressure flash evaporation: inputting salt-containing brine 1 with main component sodium carbonate and including sodium chloride and sodium sulfate impurities into a primary flash evaporator or a multi-stage series flash evaporator for flash evaporation and concentration to obtain brine 2; the flash evaporator is provided with an independent vacuum system, and the temperature and pressure of the multi-stage series flash evaporator are gradually reduced;

[0007] (2) Sodium carbonate decahydrate crystallization: the brine 2 is input into a crystallizer for low-temperature crystallization to obtain a crystal slurry containing sodium carbonate decahydrate crystals;

[0008] (3) Centrifugal separation: the crystal slurry is subjected to centrifugal separation to obtain a sodium carbonate decahydrate filter cake; the centrifugal mother liquor is returned to the crystallizer after being heated.

[0009] (4) Dissolution: the sodium carbonate decahydrate filter cake is dissolved to obtain a low-salt brine.

[0010] In the above technical solution, a two-stage waste heat coupled salt-containing brine flash concentration process is provided, and specifically:

[0011] The research and development team of the present application innovatively provides a recirculation loop including a mother liquor heater on the sodium carbonate decahydrate crystallizer. After the crystal slurry is separated to obtain sodium carbonate decahydrate solids from the crystallizer, the mother liquor is heated by the mother liquor heater and then returned to the crystallizer, thereby supplementing part of the heat source to the crystallizer and promoting further flash concentration of the liquid in the crystallizer. In the technical solution of the present application, the brine 2 is subjected to low-temperature crystallization in the crystallizer. The main body of the crystallizer is designed to maintain an appropriate residence time and crystallization temperature of the salt-containing brine. In the specific process, the appropriate mother liquor circulation reflux flow can be set. The heat source can be continuously supplemented to the crystallizer to promote flash concentration, so that the concentration of sodium carbonate in the crystallizer is maintained above the crystallization point, and the appropriate crystallization temperature of the overall target product is maintained to improve the crystallization efficiency.

[0012] In addition, in the technical solution of the present application, one or more stages of low-pressure flash concentration process is provided to flash concentrate the brine input into the process, thereby increasing the concentration of the target product (sodium carbonate) in the salt-containing brine 1, so as to improve the efficiency of the subsequent crystallization process. When multiple stages of low-pressure flash concentration are used, the pressure and temperature gradient of the flash evaporators arranged in series are reduced. Thus, through the low-pressure flash concentration coupled with the crystallization flash, the process of the present application can meet the crystallization needs of salt-containing brine with different temperatures and target product concentrations, effectively remove salt and nitrate impurities in the salt-containing brine, and effectively utilize waste heat.

[0013] In a further example of the present application, the low-pressure flash concentration process can be selected to include 1-4 stages of flash concentration, and more further, two or three stages of low-pressure flash concentration can be provided. In the actual process, appropriate low-pressure flash concentration technology can be selected according to the conditions of the plant waste heat, equipment investment, and land occupation, etc.

[0014] In the present application, a vacuum system is provided at the top of the flash evaporator for controlling the pressure of the flash evaporator. In a further example of the present application, the vacuum system of the flash evaporator uses a spray device and a vacuum pump or an inter-wall heat exchanger and a vacuum pump to maintain negative pressure.

[0015] In a further example of the present application, when the vacuum system uses a spraying device and a vacuum pump to maintain negative pressure, the spraying water used by the spraying device has a temperature lower than the temperature of the flash vapor in the corresponding flash tank by more than 5℃, thereby improving the operability of the process; in addition, in the actual process, the number of stages of low-pressure flash evaporation can be determined according to the temperature of the spraying water and the specifications of the spraying device used, and the pressure and temperature of each stage of low-pressure flash evaporation are further determined.

[0016] In a further example of the present application, in the low-pressure flash evaporation process, the vacuum system of at least one flash evaporator uses a partition wall heat exchanger and a vacuum pump to maintain negative pressure, and the circulating medium of the partition wall heat exchanger is low-salt brine, thereby achieving energy coupling utilization and reducing process energy consumption.

[0017] In a further example of the present application, the flash evaporator is provided with a waste heat heater, which can use factory waste heat as a heat source, and through the gradient setting of the pressure and temperature of each stage of the series-connected flash tank, different temperature waste heat can be flexibly utilized and the process flow can be simplified, thereby achieving staged utilization of the heat source and heat recovery; optionally, the temperature of the heat source of the waste heat heater is higher than the temperature of the liquid in the corresponding flash tank by more than 5℃, thereby further improving the operability of the process.

[0018] In the technical solution of the present application, the waste heat heater and the mother liquor heater can optionally both use factory waste heat as a heat source; in a further example of the present application, the waste heat heater and the mother liquor heater can be used in combination, thereby further enhancing the flexibility of the process of the present application and making it applicable to a wider range of factory waste heat utilization conditions.

[0019] In the present application, the brine 2 obtained through low-pressure flash evaporation is further flash evaporated, concentrated and cooled in a crystallizer, and sodium carbonate decahydrate crystals are precipitated; in a further example of the present application, the temperature of the sodium carbonate decahydrate crystals is 10-20℃, and the pressure is 1-3kpaA.

[0020] In a further example of the present application, the crystallizer is provided with a vacuum system, which uses a spraying device and a vacuum pump to maintain negative pressure; further, the spraying device sprays low-temperature water at 4-10℃, which is obtained by a compression refrigeration ice machine.

[0021] In a further example of the present application, the compression refrigeration ice machine includes at least two stages of series-connected condensers, and the circulating medium used by the first stage of condensers is low-salt brine, thereby further improving the energy coupling utilization efficiency of the present application.

[0022] A recirculation loop including a mother liquor heater is provided between the crystallizer of step (2) and the centrifuge of step (3). The centrifugal mother liquor is heated by the mother liquor heater and then returned to the crystallizer through the recirculation loop to supplement part of the heat source to the crystallizer to promote further flash evaporation and concentration of the liquid in the crystallizer.

[0023] Compared with the prior art, the application has the beneficial effects that: in the application, the centrifugal mother liquor is returned to the sodium carbonate decahydrate crystallizer after being heated, and part of the heat source is supplemented to the crystallizer to promote the further flash evaporation and concentration of the liquid in the crystallizer, and the low-pressure flash evaporation is combined with the flash evaporation of the crystallizer, so that the energy-saving type bittern purification process can break away from the restrictions of the temperature and the sodium carbonate concentration of the input salt-containing bittern, continuously and efficiently remove the salt and nitrate impurities in the salt-containing bittern, and realize the waste heat recovery and utilization, and finally obtain high-purity low-salt bittern. BRIEF DESCRIPTION OF DRAWINGS

[0024] The drawings constituting a part of the specification of the application serve to provide a further understanding of the application, and the illustrative embodiments of the application and the description thereof serve to explain the application, and do not constitute an improper limitation on the application. In the drawings:

[0025] Figure 1 shows the flow chart of the energy-saving type bittern purification process according to Embodiment 1 of the application;

[0026] Figure 2 shows the flow chart of the energy-saving type bittern purification process according to Embodiment 3 of the application. DETAILED DESCRIPTION

[0027] In order to facilitate the understanding of the application, the application will be described more fully below, and the preferred embodiments of the application are given. However, it should be understood that these embodiments are only used for more detailed description, and should not be understood as limiting the application in any form, i.e. not intended to limit the protection scope of the application.

[0028] Embodiment 1

[0029] An energy-saving type bittern purification process, as shown in the flow chart of Figure 1, the process comprises the following steps:

[0030] (1) Low-pressure flash evaporation: the salt-containing bittern 1 with the main component of sodium carbonate and including sodium chloride and sodium sulfate impurities is input into a primary flash evaporator or a multi-stage series flash evaporator for flash evaporation and concentration, to obtain bittern 2; the flash evaporator is provided with an independent vacuum system, and the temperature and pressure of the multi-stage series flash evaporator are stepwise reduced.

[0031] Optionally, the low-pressure flash evaporation process includes 1-4 stages of flash evaporation and concentration.

[0032] Optionally, the vacuum system of the flash evaporator uses a spray device or a shell-and-tube heat exchanger to maintain negative pressure with a vacuum pump.

[0033] Further optionally, when the vacuum system uses a spray device and a vacuum pump to maintain negative pressure, the temperature of the spray water used by the spray device is lower than the temperature of the flash evaporation gas in the corresponding flash tank by more than 5℃.

[0034] Further, the vacuum system of the at least one flash evaporator uses a heat exchanger with a vacuum pump to maintain negative pressure, and the circulating medium of the heat exchanger is low-salt brine.

[0035] Optionally, the flash evaporator is provided with a waste heat heater; and further optionally, the temperature of the heat source of the waste heat heater is higher than the temperature of the liquid in the corresponding flash tank by 5℃ or more.

[0036] Optionally, the waste heat heater and / or the mother liquor heater of the present embodiment use factory waste heat, waste heat or external heat source as the heat source; and further optionally, the waste heat heater and / or the mother liquor heater use factory waste heat as the heat source.

[0037] (2) Sodium carbonate decahydrate crystallization: the brine 2 is input into a crystallizer to perform low-temperature crystallization, to obtain a crystal slurry containing sodium carbonate decahydrate crystals.

[0038] Optionally, the temperature of the sodium carbonate decahydrate crystallization is 10-20℃, and the pressure is 1-3kpaA.

[0039] Optionally, the crystallizer is provided with a vacuum system, and the vacuum system uses a spraying device and a vacuum pump to maintain negative pressure.

[0040] Further optionally, the spraying device sprays low-temperature water at 4-10℃, and the low-temperature water is obtained by using a compression refrigeration ice machine.

[0041] Further optionally, the compression refrigeration ice machine includes at least two series-connected condensers, and the circulating medium used in the first-stage condenser is low-salt brine.

[0042] Optionally, the flash evaporator and the crystallizer use bottom stirring to make the liquid level in the container update faster, which is conducive to the control of the supersaturation in the flash evaporator and the crystallizer.

[0043] (3) Centrifugal separation: the crystal slurry is subjected to centrifugal separation to obtain sodium carbonate decahydrate filter cake; and the centrifugal mother liquor is returned to the crystallizer after being heated.

[0044] Optionally, the centrifugal separation process further includes washing the sodium carbonate decahydrate filter cake to further remove impurities in the filter cake; and further optionally, industrial water is used to wash the sodium carbonate decahydrate filter cake.

[0045] (4) Dissolution: the sodium carbonate decahydrate filter cake is dissolved to obtain low-salt brine.

[0046] Embodiment 2

[0047] The present embodiment shows the process of using the energy-saving brine purification process shown in the embodiments to purify brine under specific working conditions. It should be noted that the present embodiment is only a better display and does not limit the protection scope of the present application.

[0048] Specifically, the process comprises the following steps:

[0049] (1) Two-stage low-pressure flash evaporation: the discharge liquid from a sodium carbonate crystallizer is neutralized by caustic soda to obtain a salt-containing brine 1, which mainly comprises Na2CO3: 26.6wt%, NaCl: 2.8wt%, and Na2SO4: 0.43wt%; the flow rate of the salt-containing brine 1 is 920t / h, and the temperature is 103℃. The salt-containing brine 1 is cooled and concentrated by two-stage low-pressure flash evaporation, wherein the first-stage flash evaporation pressure is 36kPaA, and the second-stage flash evaporation pressure is 6kPaA; the first-stage flash evaporator uses a partition heat exchanger + a liquid ring vacuum pump to provide low pressure, and the cold source of the heat exchanger is low-salt brine; the second-stage flash evaporator uses a circulating water spray + a liquid ring vacuum pump to provide low pressure, and after flash evaporation, a brine 2 containing 29.1% of Na2CO3 is obtained.

[0050] It should be noted that the two-stage low-pressure flash evaporation is combined and shown in Fig. 1 for the purpose of simplicity, and the protection scope of the present application is not limited thereby.

[0051] (2) Sodium carbonate decahydrate crystallization: the brine 2 is further flash evaporated and crystallized in a crystallizer to obtain a crystal slurry containing sodium carbonate decahydrate crystals. The flash evaporation pressure is 1.3kPaA, and the crystallization temperature is 10-20℃; the top of the crystallizer is maintained at negative pressure by using a low-temperature water spray + a steam ejector + a liquid ring vacuum pump. The temperature of the upper water of the low-temperature water is 4℃, and the flow rate is 16000m 3 / h.

[0052] Optionally, a compression refrigeration ice machine is arranged to prepare low-temperature water at 2-7℃.

[0053] It should be noted that the crystallization process of sodium carbonate decahydrate is carried out in a low-temperature crystallizer, and a person skilled in the art can select a low-temperature crystallizer with a suitable structure based on the present application through non-creative labor, and the technical solutions thus formed are within the protection scope of the present application. Optionally, the crystallizer is bottom-stirred.

[0054] (3) Centrifugal separation: a pusher centrifuge is used to separate the crystal slurry to obtain a filter cake of 610t / h, and industrial water is used to wash the filter cake, and the consumption of the industrial water is 48t / h. The mother liquor of 1370t / h is obtained by centrifugation, of which 196t / h is discharged as waste liquid, and the remaining 1174t / h is returned to the crystallizer after being heated to about 30℃ by a low-pressure steam in a crystallizer heater.

[0055] (4) Dissolution: the filter cake is dissolved by using the condensate to obtain low-salt brine, and the composition of the low-salt brine is Na2CO3: 28wt%, NaCl: 0.19wt%, and Na2SO4: 0.03wt%, and the output flow rate is 774t / h.

[0056] Optionally, part of the heat required in the dissolution process comes from a compression refrigeration ice machine.

[0057] After the treatment of the brine 1 by the energy-saving brine purification process of the embodiment, the content of the impurities (sodium chloride and sodium sulfate) in the brine 1 is reduced from 3.23wt% to 0.22wt%.

[0058] Embodiment 3

[0059] The embodiment shows an energy-saving brine purification process under a specific working condition. It should be noted that the embodiment is only a better display and does not limit the protection scope of the present application. As shown in FIG. 2, the process includes the following steps:

[0060] (1) Low-pressure flash evaporation: 50℃, 235t / h of brine 1 containing 20wt% of sodium carbonate, 1.76wt% of sodium chloride, 0.11wt% of sodium sulfate, and the rest of water is input into a two-stage series flash evaporator for flash evaporation and concentration to obtain brine 2;

[0061] The pressure of the first-stage flash evaporator is 10kpaA, and the temperature is 50℃.

[0062] A first-stage external circulation heater is provided, which is heated by 75℃ process condensate recovered in the plant to provide the heat required for flash evaporation.

[0063] A liquid ring vacuum pump is provided at the top of the flash evaporator to maintain the system pressure, and a first-stage spray cooling is provided before the vacuum pump, which is cooled by spraying the return water of the vacuum system at the top of the second-stage flash evaporator, and the spraying water temperature is 30℃.

[0064] The pressure of the second-stage flash evaporator is 5.3kpaA, and the temperature is 38℃.

[0065] A second-stage external circulation heater is provided, which is heated by 60℃ process condensate at the outlet of the first-stage external circulation heater to provide the heat required for flash evaporation.

[0066] A liquid ring vacuum pump is provided at the top of the flash evaporator to maintain the system pressure, and a second-stage spray cooling is provided before the vacuum pump, which is cooled by spraying the circulating water, and the spraying water temperature is 25℃.

[0067] The composition of the brine 2 is: 30.1wt% of sodium carbonate, 2.66wt% of sodium chloride, 0.17wt% of sodium sulfate, and the rest of water.

[0068] The amount of process condensate is 1440t / h.

[0069] The flow rate of the spraying circulating water of the vacuum system is 4700m 3 / h.

[0070] It should be noted that the two-stage low-pressure flash evaporation is combined and displayed in FIG. 2 for the purpose of simplicity, and this does not limit the protection scope of the present application.

[0071] (2) Sodium carbonate decahydrate crystallization: the brine 2 is input into a crystallizer to perform low-temperature crystallization to obtain a crystal slurry containing sodium carbonate decahydrate crystals;

[0072] The temperature of the sodium carbonate decahydrate crystals is 10-20°C, and the pressure is 1-3 kPa A.

[0073] The vacuum system of the crystallizer uses low-temperature water spraying at 4-10°C + steam injection + liquid ring vacuum pump to maintain negative pressure, and the low-temperature water is prepared by a compression refrigeration ice machine.

[0074] Optionally, the compression refrigeration ice machine includes at least two series-connected condensers, wherein the circulating medium used by the first condenser is low-salt brine.

[0075] (3) Centrifugal separation: the crystal slurry is subjected to centrifugal separation to obtain sodium carbonate decahydrate filter cake.

[0076] After the crystal slurry is subjected to centrifugal separation, 115 t / h of sodium carbonate decahydrate crystals are obtained, containing 5 wt% of liquid.

[0077] The mother liquor obtained by centrifugal separation is 207.5 t / h, of which 22.5 t / h is discharged as waste liquid, and the remaining 185 t / h is heated to 30°C by a mother liquor heater and then returned to the crystallizer, and the heat flow is the top one-stage spray cooling return water of a one-stage flash evaporator.

[0078] Optionally, the centrifugal separation process further includes washing the sodium carbonate decahydrate filter cake to further remove impurities in the filter cake; further optionally, industrial water is used to wash the sodium carbonate decahydrate filter cake.

[0079] (4) Dissolution: the sodium carbonate decahydrate filter cake is dissolved with the outlet process condensate of a two-stage external circulation heater to obtain low-salt brine, containing 26.5 wt% of sodium carbonate, 0.54 wt% of sodium chloride, 0.03 wt% of sodium sulfate, and the rest being water.

[0080] After being treated by the energy-saving brine purification process of the embodiment, the content of impurities (sodium chloride and sodium sulfate) in the salt-containing brine 1 is reduced from 1.87 wt% to 0.57 wt%.

[0081] It should be noted that the above content is a further detailed description of the present application in combination with specific embodiments, and the specific implementation of the present application should not be limited to these descriptions; the process data of the embodiment does not limit the technical solution, but only demonstrates one specific working condition. For ordinary skilled persons in the technical field to which the present application belongs, without departing from the concept of the present application, a number of simple improvements and refinements can be made, which should be regarded as falling within the scope of protection of the present application.

Claims

1. An energy-saving brine purification process, characterized in that: The following steps are involved: (1) Low-pressure flash evaporation: brine 1, the main component of which is sodium carbonate and contains sodium chloride and sodium sulfate as impurities, is fed into a single-stage flash evaporator or a multi-stage series flash evaporator for flash evaporation and concentration to obtain brine 2; the flash evaporator is provided with an independent vacuum system, and the temperature and pressure of the multi-stage series flash evaporator are stepped down; (2) Crystallization of sodium carbonate decahydrate: The brine 2 is input into a crystallizer for low-temperature crystallization to obtain a slurry containing sodium carbonate decahydrate crystals; (3) Centrifugal separation: The slurry is centrifuged to obtain a sodium carbonate decahydrate filter cake; the centrifuged mother liquor is heated and returned to the crystallizer; (4) Dissolution: The sodium carbonate decahydrate filter cake is dissolved to obtain low-salt brine.

2. The energy-saving brine purification process according to claim 1, characterized in that: The low-pressure flash evaporation process includes 1-4 stages of flash evaporation concentration.

3. The energy-saving brine purification process according to claim 1, characterized in that: The vacuum system of the flash evaporator adopts a spray device and a vacuum pump or a partition wall heat exchanger and a vacuum pump to maintain negative pressure.

4. The energy-saving brine purification process according to claim 3, characterized in that: When the vacuum system uses a spray device and a vacuum pump to maintain negative pressure, the temperature of the spray water used by the spray device is lower than the temperature of the flash gas in the corresponding flash tank by more than 5°C.

5. The energy-saving brine purification process according to claim 3, characterized in that: The vacuum system of at least one flash evaporator adopts a partition wall heat exchanger and a vacuum pump to maintain negative pressure, and the circulating medium of the partition wall heat exchanger is low-salt brine.

6. The energy-saving brine purification process according to claim 1, characterized in that: The flash evaporator is provided with a waste heat heater.

7. The energy-saving brine purification process according to claim 1, characterized in that: The crystallization temperature of the sodium carbonate decahydrate is 10-20° C., and the pressure is 1-3 kPaA.

8. The energy-saving brine purification process according to claim 1, characterized in that: The crystallizer is provided with a vacuum system, and the vacuum system adopts a spray device and a vacuum pump to maintain negative pressure.

9. The energy-saving brine purification process according to claim 8, characterized in that: The spraying device sprays low-temperature water at 4-10° C., and the low-temperature water is obtained by a compression refrigeration ice machine.

10. The energy-saving brine purification process according to claim 9, characterized in that: The compression refrigeration ice machine comprises at least two stages of condensers connected in series, wherein the circulating medium used by the first stage condenser is the low-salt brine.

11. The energy-saving brine purification process according to claim 1, characterized in that: A recirculation loop including a mother liquor heater is provided between the crystallizer of step (2) and the centrifuge of the centrifugal separation in step (3).

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