System for preparing alkali and removing hardness by evaporating and crystallizing sodium chloride mother liquor

Abstract

The system comprises an evaporative crystallization sodium chloride mother liquor tank, a reaction tank, a solid-liquid separator, an adjusting tank, an ammonium chloride crystallizer, a first centrifugal machine, a first micro-washer, a second centrifugal machine, a first dryer, an ammonium chloride storage tank and the like which are connected in sequence. According to the device, the evaporated and crystallized sodium chloride mother liquor is used as a raw material for preparing the baking soda, CO2 can be absorbed in the baking soda preparation process, carbon reduction and emission reduction are realized, sodium carbonate is prepared from the baking soda through calcination, sodium chloride which is poorer in sale is converted into sodium carbonate which is smoother in sale, and the additional value of byproducts is improved. And the byproduct sodium bicarbonate is reused in a hardness removal system of the high-salinity wastewater, so that the medicament cost for treating the high-salinity wastewater is reduced.

Description

Technical field:

[0001] The utility model relates to the technical field of high-salt wastewater treatment, in particular to an alkali production and hardness removal system using evaporation and crystallization of sodium chloride mother liquor. Background technology:

[0002] The rapid growth of industrial production has also generated a large amount of high-salinity wastewater. This high-salinity wastewater typically undergoes pretreatment to remove suspended solids and hardness, followed by advanced oxidation or Fenton treatment to remove organic matter. The wastewater is then concentrated using thermal or membrane methods before entering a crystallization process to recover sodium chloride and sodium sulfate. However, issues such as the marketability of the byproduct salt produced in the crystallization process have limited the development and application of this process. Utility model content:

[0003] The utility model aims to provide a system for preparing alkali and removing hardness by evaporating and crystallizing sodium chloride mother liquor, which has high added value of by-products and low cost of reagents.

[0004] The utility model is implemented by the following technical solutions: an evaporation crystallization sodium chloride mother liquor alkali production and hardness removal system, which includes an evaporation crystallization sodium chloride mother liquor tank, a reaction tank and a solid-liquid separator connected in sequence through pipelines; the supernatant outlet of the solid-liquid separator is connected to the inlet of the regulating tank; the regulating tank, the ammonium chloride crystallizer and the first centrifuge are connected in sequence through pipelines; the solid material outlet of the first centrifuge is connected to the inlet of a first micro-washer, the outlet of the first micro-washer is connected to the inlet of a second centrifuge, the solid material outlet of the second centrifuge is connected to the inlet of a first dryer, and the outlet of the first dryer is connected to the inlet of an ammonium chloride storage tank;

[0005] The outlet of the carbon dioxide storage tank and the outlet of the ammonia storage tank are both connected to the reaction tank;

[0006] The substrate outlet of the solid-liquid separator is connected to the inlet of the third centrifuge, the solid material outlet of the third centrifuge is connected to the inlet of the second micro-washer, the outlet of the second micro-washer is connected to the inlet of the fourth centrifuge, the solid material outlet of the fourth centrifuge is connected to the inlet of the second dryer, the outlet of the second dryer is connected to the sodium bicarbonate storage tank, and the sodium bicarbonate storage tank is respectively connected to the hardness removal tank and the inlet of the calcining furnace of the high-salt wastewater treatment system.

[0007] Furthermore, the dewatering outlet of the first centrifuge and the washing liquid outlet of the second centrifuge are both connected to the reaction tank.

[0008] Furthermore, the dewatering outlet of the third centrifuge and the washing liquid outlet of the fourth centrifuge are both connected to the regulating tank.

[0009] Advantages of this utility model:

[0010] (1) The utility model uses evaporated crystallized sodium chloride mother liquor as a raw material for preparing baking soda. At the same time, CO2 can be absorbed during the preparation process of baking soda, thereby achieving carbon reduction and emission reduction. Baking soda is prepared into sodium carbonate by calcination, and sodium chloride with poor sales is converted into sodium carbonate with better sales, thereby increasing the added value of the by-product.

[0011] (2) The by-product sodium bicarbonate is recycled into the high-salinity wastewater hardness removal system, thereby reducing the cost of chemicals for high-salinity wastewater treatment. Description of the drawings:

[0012] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0013] Figure 1 This is a schematic diagram of the structure of an evaporation and crystallization sodium chloride mother liquor alkali production and hardness removal system.

[0014] Evaporation and crystallization of sodium chloride mother liquor tank 1, reaction tank 2, solid-liquid separator 3, regulating tank 4, ammonium chloride crystallizer 5, first centrifuge 6, first micro-washer 7, second centrifuge 8, first dryer 9, ammonium chloride storage tank 10, carbon dioxide storage tank 11, ammonia water storage tank 12, third centrifuge 13, second micro-washer 14, fourth centrifuge 15, second dryer 16, hardness removal tank 17 of high-salt wastewater treatment system, calcining furnace 18, and sodium bicarbonate storage tank 19. Specific implementation method:

[0015] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0016] like Figure 1As shown, a sodium chloride mother liquor evaporation and crystallization alkali production and hardness removal system includes an evaporation and crystallization sodium chloride mother liquor tank 1, a reaction tank 2, and a solid-liquid separator 3 connected in sequence by pipelines; the supernatant outlet of the solid-liquid separator 3 is connected to the inlet of a regulating tank 4; the regulating tank 4, an ammonium chloride crystallizer 5, and a first centrifuge 6 are connected in sequence by pipelines; the solid material outlet of the first centrifuge 6 is connected to the inlet of a first micro-washer 7, the outlet of the first micro-washer 7 is connected to the inlet of a second centrifuge 8, the solid material outlet of the second centrifuge 8 is connected to the inlet of a first dryer 9, and the outlet of the first dryer 9 is connected to the inlet of an ammonium chloride storage tank 10;

[0017] The outlet of the carbon dioxide storage tank 11 and the outlet of the ammonia storage tank 12 are both connected to the reaction tank 2;

[0018] The substrate outlet of the solid-liquid separator 3 is connected to the inlet of the third centrifuge 13, the solid material outlet of the third centrifuge 13 is connected to the inlet of the second micro-washer 14, the outlet of the second micro-washer 14 is connected to the inlet of the fourth centrifuge 15, the solid material outlet of the fourth centrifuge 15 is connected to the inlet of the second dryer 16, the outlet of the second dryer 16 is connected to the sodium bicarbonate storage tank 19, and the sodium bicarbonate storage tank 19 is respectively connected to the inlets of the hardness removal tank 17 and the calcining furnace 18 of the high-salt wastewater treatment system.

[0019] In one embodiment, the deionized water outlet of the first centrifuge 6 and the washing liquid outlet of the second centrifuge 8 are both connected to the reaction tank 2, so that the deionized water and the uncrystallized materials in the washing liquid are returned to the reaction tank to continue the reaction, thus avoiding waste.

[0020] In one embodiment, the dewatering outlet of the third centrifuge 13 and the washing liquid outlet of the fourth centrifuge 15 are both connected to the regulating tank 4, so that the ammonium chloride in the dewatering water and the washing liquid is returned to the regulating tank 4, and then the ammonium chloride product is obtained after crystallization in the ammonium chloride crystallizer 5, thereby avoiding waste.

[0021] In this embodiment, the solid-liquid separator 3 is purchased from Zhucheng Loncin Environmental Protection Machinery Technology Co., Ltd., and the model is LXCW1.

[0022] In this embodiment, the first centrifuge 6, the second centrifuge 8, the third centrifuge 13, and the fourth centrifuge 15 are all purchased from Zhejiang Light Machinery Centrifuge Manufacturing Co., Ltd., and the model is P-60.

[0023] In this embodiment, the first micro-washer 7 and the second micro-washer 14 are both produced by Qingzhou Lusheng Sand Mining Machinery Co., Ltd., and the model is TXR1020.

[0024] In this embodiment, the first dryer 9 and the second dryer 16 are both PLG type continuous disc dryers produced by Changzhou Nanfang Drying Equipment Co., Ltd.

[0025] The system works as follows:

[0026] First, the evaporated crystallized sodium chloride mother liquor enters the baking soda production process section: sodium bicarbonate is produced in the reaction tank by adding ammonia solution and absorbing carbon dioxide. The supernatant and precipitate are separated by the action of the solid-liquid separator 3. The precipitate is removed from most of the water by the third centrifuge 13. The liquid obtained by centrifugation enters the regulating tank 4. The precipitate obtained by the third centrifuge 13 is then passed through the second micro-washer 14 to wash away other impurities and ammonium chloride on the surface of the precipitate. It is then dried in the second dryer 16 to obtain high-purity sodium bicarbonate. A portion of the sodium bicarbonate enters the hardness removal process section as a hardness removal agent. The pH is adjusted to pH = 11 by adding sodium hydroxide to meet the hardness removal requirements before hardness removal is carried out. A portion of the sodium bicarbonate is calcined to produce soda ash.

[0027] The supernatant obtained by separation in the solid-liquid separator 3, as well as the precipitate and washing liquid separated by the third centrifuge 13 and the fourth centrifuge 15, all enter the regulating tank 4, which mainly contains a large amount of ammonium chloride. They then enter the ammonium chloride crystallizer 5 for crystallization, and the precipitate is passed through the first centrifuge 6 to remove part of the water. The liquid obtained by centrifugation enters the reaction tank 1. The obtained precipitate then passes through the first micro-washer 7 to wash away other impurities on the precipitate surface, and is dried in a dryer to obtain high-purity ammonium chloride.

[0028] Working principle: First, the mother liquor of sodium chloride is evaporated and crystallized to enter the baking soda process section. In this process section, ammonia solution is added and carbon dioxide is absorbed to prepare baking soda as raw material (principle: CO2+NH4OH+NaCl→NaHCO3+NH4Cl). Then, sodium bicarbonate is precipitated by centrifugation and then washed twice to prepare high-purity sodium bicarbonate. Sodium bicarbonate can be subsequently calcined to prepare soda ash. Sodium bicarbonate can also be put into the hardness removal process section and sodium hydroxide is added to maintain its pH at 11 to achieve the purpose of hardness removal (principle: OH - +HCO - →CO3 2- +H2O, CO3 2- +Ca 2+ →CaCO3↓,OH - +Mg 2+ →Mg(OH)2↓. The formed CaCO3 and Mg(OH)2 are both insoluble compounds that can be precipitated from the water. This eliminates the need for the cost of adding other reagents and the increase in the total salt content of the entire system, reducing operating costs during the treatment process. The clear liquid after the reaction centrifugation is used for ammonium chloride crystallization. The resulting precipitate is partially removed by centrifugation, and the liquid obtained by centrifugation enters the reaction tank. The precipitate obtained by the centrifuge is then passed through a micro-washer to wash away other impurities on the precipitate surface, and then dried in a dryer to obtain high-purity ammonium chloride.

[0029] System application case 1 of this embodiment:

[0030] The system of this embodiment was used to treat the mother liquor of sodium chloride evaporated and crystallized from a sewage treatment plant. The sample composition is shown in Table 1. The concentration of the mother liquor of sodium chloride evaporated and crystallized was 409901 mg / L. The product then entered the baking soda production process, where ammonia water was added and carbon dioxide was introduced. The product reacted at 35°C to produce sodium bicarbonate, which was then separated into solid and liquid and centrifuged twice before drying to a purity of 99.78%. The crystallized sodium bicarbonate then entered the calcination process to produce sodium carbonate, with a purity of up to 99.98%. The sodium bicarbonate then entered the hardness removal system, providing bicarbonate ions to the system. Sodium hydroxide was added to adjust the pH to 11, which could reduce the hardness to <30 mg / L. The centrifuge and supernatant entered the regulating tank. The product was then crystallized through ammonium chloride, centrifuged, and then micro-washed to remove other impurities on the surface of the precipitate. The product was then dried in a dryer to obtain 98.75% ammonium chloride.

[0031] Table 1: Component test data of sodium chloride mother liquor from evaporation and crystallization in a sewage treatment plant

[0032]

[0033] System application case 2 of this embodiment:

[0034] The system of this embodiment was used to treat the mother liquor of sodium chloride evaporated and crystallized from a sewage treatment plant. The sample composition is shown in Table 2, and the concentration of the mother liquor of sodium chloride evaporated and crystallized was 466220 mg / L. The product then entered the baking soda production process, where ammonia and carbon dioxide were added, reacting at 35°C to produce sodium bicarbonate. Through solid-liquid separation and two centrifugal cycles, the product was then dried to a purity of 99.84%. The crystallized sodium bicarbonate then entered the calcination process to produce sodium carbonate, with a purity of up to 99.92%. The sodium bicarbonate then entered the hardness removal system, providing bicarbonate ions. Sodium hydroxide was added to adjust the pH to 11, reducing the hardness to <30 mg / L. The centrifuge and supernatant entered the regulating tank. The product was then crystallized with ammonium chloride, centrifuged, and then micro-washed to remove impurities on the precipitate surface. The product was then dried in a dryer to yield 98.85% ammonium chloride.

[0035] Table 2: Component test data of sodium chloride mother liquor from evaporation and crystallization in a sewage treatment plant

[0036]

[0037] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A system for alkali production and hardness removal from evaporative crystallization of sodium chloride mother liquor, characterized in that: It includes an evaporation crystallization sodium chloride mother liquor tank, a reaction tank, and a solid-liquid separator connected in sequence through pipelines; the supernatant outlet of the solid-liquid separator is connected to the inlet of the regulating tank; the regulating tank, the ammonium chloride crystallizer, and the first centrifuge are connected in sequence through pipelines; the solid material outlet of the first centrifuge is connected to the inlet of a first micro-washer, the outlet of the first micro-washer is connected to the inlet of a second centrifuge, the solid material outlet of the second centrifuge is connected to the inlet of a first dryer, and the outlet of the first dryer is connected to the inlet of an ammonium chloride storage tank; The outlet of the carbon dioxide storage tank and the outlet of the ammonia storage tank are both connected to the reaction tank; The substrate outlet of the solid-liquid separator is connected to the inlet of the third centrifuge, the solid material outlet of the third centrifuge is connected to the inlet of the second micro-washer, the outlet of the second micro-washer is connected to the inlet of the fourth centrifuge, the solid material outlet of the fourth centrifuge is connected to the inlet of the second dryer, the outlet of the second dryer is connected to the sodium bicarbonate storage tank, and the sodium bicarbonate storage tank is respectively connected to the hardness removal tank and the inlet of the calcining furnace of the high-salt wastewater treatment system.

2. A alkali-making and hardness-removing system for evaporating and crystallizing sodium chloride mother liquor according to claim 1, characterized in that: The dewatering outlet of the first centrifuge and the washing liquid outlet of the second centrifuge are both connected to the reaction tank.

3. A alkali-making and hardness-removing system for evaporating and crystallizing sodium chloride mother liquor according to claim 1, characterized in that: The dewatering outlet of the third centrifuge and the washing liquid outlet of the fourth centrifuge are both connected to the regulating tank.

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