Oslo crystallizer system and freezing crystallization process

Abstract

The invention discloses an Oslo crystallizer system which comprises a water inlet tank, the water inlet tank is sequentially connected with a first-stage heat exchanger, a second-stage heat exchanger and an Oslo crystallizer, the Oslo crystallizer is further connected with a settler and a centrifugal machine, the settler is connected with the second-stage heat exchanger through a supernatant circulating pipeline, the second-stage heat exchanger is further provided with a supernatant outlet, and the centrifugal machine is connected with the settler. The centrifugal machine is further connected with the Oslo crystallizer through a filtrate circulating pipeline, and a solid discharge port is further formed in the centrifugal machine; and the top of the Oslo crystallizer is connected with a steam pipeline through a heat pump. Meanwhile, the invention further provides a freezing crystallization process adopting the system. The Oslo crystallizer system can solve the problem that salt separation is not thorough due to factors such as performance attenuation of a nanofiltration unit membrane element and the recovery rate in nanofiltration salt separation. According to the freezing crystallization process, a large freezing crystallization process is directly adopted, and the salt separation efficiency is high.

Description

Technical Field

[0001] The invention belongs to the technical field of zero-discharge of coal chemical wastewater, and in particular relates to an Oslo crystallizer system and a freezing crystallization process. Background Art

[0002] Coal chemical industry has great strategic significance for my country's energy structure and security. With the rapid development of coal chemical industry in recent years, water resources and environmental problems have become increasingly prominent, requiring coal chemical projects to implement "zero discharge" of wastewater, so as to achieve the purpose of saving water resources and clean production. This is also the inevitable way to solve the above contradictions. The salty wastewater of coal chemical industry mainly comes from the synthesis gas washing wastewater, circulation system drainage, desalination system drainage, and reuse system concentrated water in the production process. After the salty wastewater is further concentrated and reused, the salt mass fraction of the remaining concentrated water is not less than 1%, which is called concentrated brine. Due to the high salt concentration, it has an inhibitory and toxic effect on microorganisms, so it is difficult to achieve "zero discharge" treatment of high-concentration brine through biochemical methods.

[0003] Highly concentrated brine contains a large amount of soluble inorganic salts, such as Cl - 、SO4 2- 、Na + , Ca 2+ Plasma, in order to stabilize, render harmless and utilize the crystallized salt as a resource, it is necessary to separate the salt.

[0004] At present, among the methods for separating salt from high-concentrated brine, one is to use high-pressure nanofiltration membranes for separation, but the separation effect decreases as the membrane performance and recovery rate decrease. Another method is to use high-temperature evaporation crystallization to achieve Na 2 SO 4 Separation from NaCl crystal salt; this method has low investment cost, but the product quality is greatly affected by the incoming water and requires a high salt / nitrate ratio.

[0005] In addition to the above two methods, there is also a cold salt separation process, that is, cooling crystallization to obtain sodium sulfate crystals, and further evaporating sodium chloride crystal salt from the crystallization mother liquor. The cold salt separation process is short, has strong resistance to fluctuations in salt content in upstream water, has high purity of crystallized salt, and low temperature is conducive to reducing the corrosion of crystallized salt to equipment. In the cold salt separation technology of the prior art, the external circulation freezing pipe is easily blocked, resulting in poor freezing effect, affecting the salt separation effect, and cannot be operated stably for a long period of time with high efficiency. Summary of the invention

[0006] In view of the defects of the prior art, the present invention provides an Oslo crystallizer system, which can avoid the influence of membrane performance and recovery rate on salt separation in nanofiltration salt separation; at the same time, the present invention also provides a freezing crystallization process using the Oslo crystallizer system, avoiding the influence of blockage of the external circulation freezing pipe in the prior art on incomplete salt separation.

[0007] An Oslo crystallizer system comprises a water inlet tank, wherein the water inlet tank is sequentially connected to a primary heat exchanger, a secondary heat exchanger and an Oslo crystallizer, the Oslo crystallizer is also respectively connected to a settler and a centrifuge, the settler is connected to the secondary heat exchanger via a supernatant liquid circulation pipeline, the secondary heat exchanger is also provided with a supernatant liquid outlet, the centrifuge is also connected to the Oslo crystallizer via a filtrate circulation pipeline, and the centrifuge is also provided with a solid discharge outlet; the top of the Oslo crystallizer is connected to a steam pipeline via a heat pump.

[0008] Preferably, the heat pump is also connected to a mixing condenser, and the mixing condenser is sequentially connected to a liquid seal tank and a refrigeration unit, and the refrigeration unit is also connected to the mixing condenser through an internal circulation pipeline.

[0009] Preferably, the Oslo crystallizer is a cooling Oslo crystallizer.

[0010] Preferably, the primary heat exchanger and the secondary heat exchanger are both plate heat exchangers.

[0011] Preferably, a refrigerant is provided in the refrigerating unit. More preferably, the refrigerant is tetrafluoroethane.

[0012] A freezing crystallization process, using the above system, comprises the following steps: (i) The high-salt concentrated water enters the water inlet tank, is pumped to the first-stage heat exchanger for precooling, and then enters the second-stage heat exchanger for precooling; (ii) After precooling, the crystals enter the Oslo crystallizer, and the steam from the steam pipeline provides power for the heat pump, takes away the heat of the Oslo crystallizer, reduces the temperature of the Oslo crystallizer to 0-10°C, and crystals precipitate in the Oslo crystallizer; (III) The crystals precipitated from the Oslo crystallizer are pumped to a centrifuge for solid-liquid separation. The filtrate obtained by separation is returned to the Oslo crystallizer through a filtrate circulation pipeline for secondary freezing and crystallization. The solid sodium sulfate obtained by separation is discharged from the solid discharge port, melted by hot melting, and then used as Na 2 SO 4 The evaporation crystallizer is used for evaporation crystallization, and the precipitated solid is centrifuged and dried to obtain solid Na 2 SO 4 The mother liquor obtained by evaporation and crystallization and the liquid obtained by centrifugation are returned to the evaporation and crystallization, hot melt and Oslo crystallizer for circulation; (iv) The supernatant in the Oslo crystallizer is pumped to the settler for secondary sedimentation. The supernatant after sedimentation enters the secondary heat exchanger through the supernatant circulation pipeline, and the feed of the secondary heat exchanger is precooled, and then discharged from the supernatant outlet and collected. After precooling, it is evaporated and crystallized in a NaCl crystallizer until solids are precipitated, and then centrifuged and dried to obtain solid NaCl. The mother liquor produced by evaporation and crystallization is divided into two paths, one is returned to the Oslo crystallizer to provide salt-nitrate balance, and the other is sent to the miscellaneous salt crystallization system to ensure the purity and whiteness of sodium chloride.

[0013] Preferably, the heat pump is also connected to a mixing condenser, and the mixing condenser is sequentially connected to a liquid seal tank and a refrigeration unit, and the refrigeration unit is also connected to the mixing condenser through an internal circulation pipeline.

[0014] Preferably, in step (ii), the heat pump takes away the heat from the Oslo crystallizer, enters the mixing condenser, cools it to 20-30°C, enters the liquid seal tank, and then pumps it to the refrigeration unit to cool it to 0°C, and then returns to the mixing condenser through the internal circulation pipeline.

[0015] Preferably, the Na 2 SO 4 The evaporation crystallizer adopts a single-effect evaporation crystallizer, and the NaCl crystallizer adopts a forced circulation evaporation crystallizer.

[0016] Preferably, the high-concentration brine has a TDS of 15%-17%, a total hardness of ≤1 mg / L, a COD of ≤400 mg / L, and a silicon content of ≤200 mg / L.

[0017] Advantages of the present invention: (1) The Oslo crystallizer system provided by the present invention can solve the problem of incomplete salt separation in nanofiltration salt separation due to factors such as attenuation of the performance of the nanofiltration unit membrane element and the recovery rate, and can be widely used in the separation of monovalent salt and divalent salt in the fields of coal chemical wastewater treatment, chemical industry, and other fields. It has the characteristics of convenient operation, high automation efficiency, versatility and reliability, and has strong applicability and practical application value; (2) The freezing crystallization process provided by the present invention directly adopts a large freezing crystallization process with high salt separation efficiency, which can avoid the poor freezing effect and incomplete salt separation caused by the blockage of the external circulation freezing pipe in the traditional nanofiltration + external circulation pipe freezing salt separation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A schematic structural diagram of the Oslo crystallizer system of the present invention; Among them, 1-water inlet tank, 2-primary heat exchanger, 3-secondary heat exchanger, 4-Oslo crystallizer, 5-settler, 6-centrifuge, 7-mixing condenser, 8-liquid seal tank, 9-refrigeration unit. DETAILED DESCRIPTION

[0019] Example 1 An Oslo crystallizer system comprises a water inlet tank 1, wherein the water inlet tank 1 is sequentially connected to a primary heat exchanger 2, a secondary heat exchanger 3, and an Oslo crystallizer 4, wherein the Oslo crystallizer 4 is also respectively connected to a settler 5 and a centrifuge 6, wherein the settler 5 is connected to the secondary heat exchanger 3 via a supernatant liquid circulation pipeline, wherein the secondary heat exchanger 3 is also provided with a supernatant liquid outlet, wherein the centrifuge 6 is also connected to the Oslo crystallizer 4 via a filtrate circulation pipeline, wherein the centrifuge 6 is also provided with a solid discharge outlet; and the top of the Oslo crystallizer 4 is connected to a steam pipeline via a heat pump.

[0020] Preferably, the Oslo crystallizer 4 is a cooling type Oslo crystallizer.

[0021] Preferably, the primary heat exchanger 2 and the secondary heat exchanger 3 are both plate heat exchangers.

[0022] The Oslo crystallizer system can achieve the initial separation of monovalent salt and divalent salt from the highly concentrated brine produced by zero discharge, as follows: (1) The high-salt concentrated water enters the water inlet tank 1. Since the incoming water temperature is relatively high, reaching 80-90°C, it is pumped to the primary heat exchanger 2 for pre-cooling (the primary heat exchanger is cooled by circulating water), and then enters the secondary heat exchanger 3 for pre-cooling (the secondary heat exchanger is cooled by the supernatant discharged from the Oslo crystallizer); (2) After precooling, the crystal enters the Oslo crystallizer 4, and the steam from the steam pipeline provides power for the heat pump, takes away the heat of the Oslo crystallizer 4, and reduces the temperature of the Oslo crystallizer 4 to 0-10°C, and crystals are precipitated in the Oslo crystallizer 4; (3) The crystals precipitated from the Oslo crystallizer 4 are pumped to the centrifuge 6, where solid-liquid separation is achieved through centrifugation. The filtrate obtained through the separation is returned to the Oslo crystallizer 4 through the filtrate circulation pipeline for secondary freezing crystallization. The solid sodium sulfate obtained through the separation is discharged from the solid discharge port for standby use. (4) The supernatant in the Oslo crystallizer 4 is pumped to the settler 5 for secondary sedimentation to ensure that no crystals are precipitated in the supernatant after sedimentation. The supernatant after sedimentation enters the secondary heat exchanger 3 through the supernatant circulation pipeline to precool the feed of the secondary heat exchanger 3, and then is discharged from the supernatant outlet for standby use; It can be seen that the Oslo crystallizer system can convert Na 2 SO 4The solid sodium sulfate discharged from the solid discharge port in step (3) can be further processed to obtain Na 2 SO 4 In step (4), the salt mainly contained in the supernatant discharged from the supernatant outlet is NaCl, which can be further evaporated and crystallized to obtain solid NaCl, thereby achieving Na 2 SO 4 and NaCl separation.

[0023] Example 2 On the basis of the above-mentioned embodiment 1, the heat pump is further connected to a mixing condenser 7, and the mixing condenser 7 is sequentially connected to a liquid seal tank 8 and a refrigeration unit 9, and the refrigeration unit 9 is also connected to the mixing condenser 7 through an internal circulation pipeline.

[0024] Preferably, a refrigerant is provided in the refrigerating unit 9. More preferably, the refrigerant is tetrafluoroethane.

[0025] The heat pump takes away the heat of the Oslo crystallizer 4, enters the mixing condenser 7, cools it to 20-30°C, enters the liquid seal tank 8, and then is pumped to the refrigeration unit 9 to cool it to 0°C, and then returns to the mixing condenser 7 through the internal circulation pipeline, and circulates in sequence.

[0026] Example 3 A freezing crystallization process, using the system of Example 1 above, comprises the following steps: (1) The high-salt concentrated water enters the water inlet tank 1. Since the incoming water temperature is relatively high, reaching 80-90°C, it is pumped to the primary heat exchanger 2 for precooling, and then enters the secondary heat exchanger 3 for precooling; (2) After precooling, the crystal enters the Oslo crystallizer 4, and the steam from the steam pipeline provides power for the heat pump, takes away the heat of the Oslo crystallizer 4, and reduces the temperature of the Oslo crystallizer 4 to 0-10°C, and crystals are precipitated in the Oslo crystallizer 4; (3) The crystals precipitated from the Oslo crystallizer 4 are pumped to the centrifuge 6 for solid-liquid separation through centrifugation. The filtrate obtained through the separation is returned to the Oslo crystallizer 4 through the filtrate circulation pipeline for secondary freezing crystallization. The solid sodium sulfate obtained through the separation is discharged from the solid discharge port, melted by hot melting, and then used as Na 2 SO 4 The evaporation crystallizer is used for evaporation crystallization, and the precipitated solid is centrifuged and dried to obtain solid Na 2 SO 4 The mother liquor obtained by evaporation and crystallization and the liquid obtained by centrifugation are returned to the evaporation and crystallization, hot melt and Oslo crystallizer 4 for circulation; (4) The supernatant in the Oslo crystallizer 4 is pumped to the settler 5 for secondary sedimentation. The supernatant after sedimentation enters the secondary heat exchanger 3 through the supernatant circulation pipeline, and the feed of the secondary heat exchanger 3 is precooled. Then, it is discharged from the supernatant outlet and collected into the NaCl buffer tank. After precooling, it is evaporated and crystallized in the NaCl crystallizer until solid is precipitated. Then, it is centrifuged and dried to obtain solid NaCl. The mother liquor produced by evaporation and crystallization is divided into two paths. One path is returned to the Oslo crystallizer 4 to provide salt-nitrate balance, and the other path is sent to the impurity salt crystallization system to ensure the purity and whiteness of sodium chloride.

[0027] Preferably, the Na 2 SO 4 The evaporation crystallizer adopts a single-effect evaporation crystallizer, and the NaCl crystallizer adopts a forced circulation evaporation crystallizer.

[0028] Preferably, the high-concentration brine has a TDS of 15%-17%, a total hardness of ≤1 mg / L, a COD of ≤400 mg / L, and a silicon content of ≤200 mg / L.

[0029] Example 4 On the basis of the above-mentioned embodiment 3, the heat pump is further connected to a mixing condenser 7, which is in turn connected to a liquid seal tank 8 and a refrigerating unit 9, and the refrigerating unit 9 is also connected to the mixing condenser 7 through an internal circulation pipeline. The heat pump takes away the heat of the Oslo crystallizer 4, enters the mixing condenser 7, cools it to 20-30°C, enters the liquid seal tank 8, and then pumps it to the refrigerating unit 9 to cool it to 0°C, and then returns to the mixing condenser 7 through the internal circulation pipeline.

Claims

1. An Oslo crystallizer system, comprising a water inlet tank (1), characterized in that: The water inlet tank (1) is sequentially connected to a primary heat exchanger (2), a secondary heat exchanger (3), and an Oslo crystallizer (4); the Oslo crystallizer (4) is also respectively connected to a settler (5) and a centrifuge (6); the settler (5) is connected to the secondary heat exchanger (3) via a supernatant liquid circulation pipeline; the secondary heat exchanger (3) is also provided with a supernatant liquid outlet; the centrifuge (6) is also connected to the Oslo crystallizer (4) via a filtrate circulation pipeline; the centrifuge (6) is also provided with a solid discharge outlet; and the top of the Oslo crystallizer (4) is connected to a steam pipeline via a heat pump.

2. The Oslo crystallizer system according to claim 1, characterized in that: The heat pump is also connected to a mixing condenser (7), and the mixing condenser (7) is connected in sequence to a liquid seal tank (8) and a refrigeration unit (9), and the refrigeration unit (9) is also connected to the mixing condenser (7) via an internal circulation pipeline.

3. The Oslo crystallizer system according to claim 1 or 2, characterized in that: The Oslo crystallizer (4) is a cooling type Oslo crystallizer.

4. The Oslo crystallizer system according to claim 3, characterized in that: The primary heat exchanger (2) and the secondary heat exchanger (3) are both plate-type heat exchangers.

5. The Oslo crystallizer system according to claim 2, characterized in that: The refrigeration unit (9) is provided with a refrigerant.

6. A freezing crystallization process, characterized in that: The method is carried out using the system described in claim 1, comprising the following steps: (a) Incoming high-salt concentrated water enters the water inlet tank (1), is pumped to the primary heat exchanger (2) for precooling, and then enters the secondary heat exchanger (3) for precooling; (ii) after precooling, the crystals enter the Oslo crystallizer (4), where the steam from the steam pipeline provides power for the heat pump, removes the heat of the Oslo crystallizer (4), and reduces the temperature of the Oslo crystallizer (4) to 0-10° C., causing crystals to precipitate in the Oslo crystallizer (4); (iii) the crystals precipitated from the Oslo crystallizer (4) are pumped to a centrifuge (6) for solid-liquid separation by centrifugation. The filtrate obtained by separation is returned to the Oslo crystallizer (4) through a filtrate circulation pipeline for secondary freezing crystallization. The solid sodium sulfate obtained by separation is discharged from a solid discharge port, melted by hot melting, and then evaporated and crystallized by a Na2SO4 evaporation crystallizer. The precipitated solid is centrifuged and dried to obtain solid Na2SO4. (iv) The supernatant in the Oslo crystallizer (4) is pumped to the settler (5) for secondary sedimentation. The supernatant after sedimentation enters the secondary heat exchanger (3) through the supernatant circulation pipeline, and the feed of the secondary heat exchanger (3) is precooled. The supernatant is then discharged from the supernatant outlet and collected. After precooling, the supernatant is evaporated and crystallized in a NaCl crystallizer until solids are precipitated. The solid NaCl is then obtained by centrifugation and drying.

7. A freeze crystallization process according to claim 6, characterized in that: The heat pump is also connected to a mixing condenser (7), and the mixing condenser (7) is connected in sequence to a liquid seal tank (8) and a refrigeration unit (9), and the refrigeration unit (9) is also connected to the mixing condenser (7) via an internal circulation pipeline.

8. A freeze crystallization process according to claim 7, characterized in that: In step (ii), the heat pump takes away the heat from the Oslo crystallizer (4), enters the mixing condenser (7), cools the temperature to 20-30°C, enters the liquid seal tank (8), is then pumped to the refrigeration unit (9), cools the temperature to 0°C, and then returns to the mixing condenser (7) through the internal circulation pipeline.

9. A freeze crystallization process according to claim 6, 7 or 8, characterized in that: The Na2SO4 evaporation crystallizer adopts a single-effect evaporation crystallizer, and the NaCl crystallizer adopts a forced circulation evaporation crystallizer.

10. A freeze crystallization process according to claim 6, 7 or 8, characterized in that: The high-concentration brine has a TDS of 15%-17%, a total hardness of ≤1 mg / L, a COD of ≤400 mg / L, and a silicon content of ≤200 mg / L.

Images