CN114772668A - Multi-effect evaporative crystallization method and multi-effect evaporative crystallization system - Google Patents
Multi-effect evaporative crystallization method and multi-effect evaporative crystallization system Download PDFInfo
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Abstract
The invention relates to the field of coal chemical wastewater treatment, and discloses a multiple-effect evaporative crystallization method and a multiple-effect evaporative crystallization system, wherein the method comprises the steps of introducing salt-containing wastewater into a 1 st-stage evaporative crystallizer for cyclic concentration, then enabling the salt-containing wastewater to sequentially pass through a 2 nd-nth-stage evaporative crystallizer, and finally precipitating in an nth-stage evaporative crystallization device to obtain crystal salt; each stage of evaporation crystallizer comprises a feed inlet and a strong brine outlet; the (m + 1) th stage evaporation crystallizer is provided with a salt leg, an (m + 1) th stage strong brine outlet and an (m + 1) th stage slurry turning port which are communicated with the salt leg; n is more than or equal to 2, m +1 is more than or equal to n, and m and n are positive integers; when the continuous operation condition is met, the feed liquid in the (m + 1) th level salt leg is subjected to pulp turning and elutriation by using the m-th level strong brine; on the contrary, the feed liquid in the m +1 level salt leg is subjected to pulp turning and elutriation by using the m +1 level strong brine; the continuous operation condition comprises that the feed liquid sedimentation ratio in the nth stage evaporation crystallizer is not less than 15%. The method is beneficial to saving energy consumption and cost and improving the purity and the particle size distribution of the crystallized salt.
Description
Technical Field
The invention relates to the field of coal chemical wastewater treatment, in particular to a multi-effect evaporative crystallization method and a multi-effect evaporative crystallization system.
Background
The zero discharge treatment of the coal chemical industry wastewater mainly utilizes the saline wastewater as resources by the technologies of concentration, salt separation, crystallization and the like, and realizes the purpose of no discharge of the wastewater. In the thermal crystallization technology, a multi-effect evaporation crystallization process is usually adopted to separate out crystal salt, but the crystal salt obtained by the conventional multi-effect crystallization in the prior art has the problems of small particle size, unstable quality and the like, and is not beneficial to resource utilization of the crystal salt.
In order to improve the quality of the crystallized salt, professional equipment such as a salt precipitator and a salt washer are usually adopted in the prior art to elutriate the crystallized salt obtained by evaporative crystallization, but the elutriation mode of additional equipment not only increases the equipment investment cost, but also improves the difficulty of process flow control. For example, CN212941543U discloses a multiple-effect evaporation system, in which an evaporator is provided with a salt leg, which allows the feed liquid in the upstream evaporator to elutriate the crystal slurry in the salt leg, but there is a certain difference in feed liquid concentration between evaporators with different effects, and when the feed liquid concentration in the front-end evaporator is low, the concentration of the feed liquid in the rear-end evaporator is reduced by using the salt leg to perform slurry-tumbling elutriation on the salt leg of the rear-end evaporator, which increases the energy consumption of the evaporator. Therefore, the prior art still lacks effective control on an elutriation mode and a slurry turning flow, and the evaporative crystallizer has low crystallization efficiency, poor quality of crystallized salt and larger production energy consumption.
Disclosure of Invention
The invention aims to solve the problems of lack of effective control on an elutriation mode and a slurry turning flow rate, low crystallization efficiency of an evaporation crystallizer, poor quality of crystallized salt and large production energy consumption in the prior art, and provides a multi-effect evaporation crystallization method and a multi-effect evaporation crystallization system.
In order to achieve the above object, the first aspect of the present invention provides a multi-effect evaporative crystallization method, wherein salt-containing wastewater is subjected to n-stage evaporative crystallization to obtain crystallized salt;
the n-stage evaporative crystallization process comprises the following steps: introducing the salt-containing wastewater into a 1 st-stage evaporative crystallizer for cyclic concentration, then passing through a 2 nd-nth-stage evaporative crystallizer sequentially, and finally precipitating in an nth-stage evaporative crystallization device to obtain crystal salt;
wherein, each stage of evaporation crystallizer comprises a feed inlet and a strong brine outlet;
the m + 1-stage evaporation crystallizer is provided with a salt leg, an m + 1-stage strong brine outlet and an m + 1-stage slurry turning port, wherein the m + 1-stage strong brine outlet and the m + 1-stage slurry turning port are communicated with the salt leg; wherein n is more than or equal to 2, m +1 is more than or equal to n, and m and n are positive integers;
when the continuous operation condition is not met, communicating the m + 1-stage strong brine outlet with the m + 1-stage slurry turning port, and turning and washing the feed liquid in the m + 1-stage salt leg by using the m + 1-stage strong brine;
when the continuous operation condition is met, communicating the m-th stage strong brine outlet with the m + 1-th stage slurry turnover port, and utilizing the m-th stage strong brine to carry out slurry turnover and elutriation on the feed liquid in the m + 1-th stage salt leg;
the continuous operation condition comprises that the feed liquid sedimentation ratio in the nth stage evaporation crystallizer is not less than 15%.
The invention provides a multi-effect evaporative crystallization system, which comprises n stages of evaporative crystallizers and condensers, wherein the n stages of evaporative crystallizers are connected in sequence;
each stage of evaporative crystallizer comprises a crystallizer and a shell and tube heat exchanger, the crystallizer and the heat exchanger are connected with a steam pipeline through a circulating pipeline, and a forced circulating pump is arranged on the circulating pipeline to ensure that feed liquid is circularly concentrated in a separation chamber of the crystallizer and a tube pass of the shell and tube heat exchanger; steam enters the shell pass of the tube type heat exchanger through a steam pipeline to heat the feed liquid in the tube pass;
wherein, a salt leg, an m +1 stage strong brine outlet and an m +1 stage slurry turning port which are communicated with the salt leg are arranged below the m +1 stage crystallizer; the (m + 1) th-level slurry turning port is respectively communicated with the (m + 1) th-level strong brine outlet or the (m + 1) th-level strong brine outlet through a slurry turning and material transferring pipeline and is switched through a material transferring pump arranged on the slurry turning and material transferring pipeline;
wherein n is more than or equal to 2, m +1 is more than or equal to n, and m and n are positive integers.
According to the technical scheme provided by the invention, the pulp turning and elutriating modes are adjusted according to the actual operation condition of the process, so that the efficient operation of evaporative crystallization is ensured, the waste of energy is fully avoided, salt precipitation and salt washing equipment does not need to be arranged independently, and the equipment investment cost is saved. By adopting the multi-effect evaporation crystallization method, the purity and the particle size distribution of the crystallized salt product are effectively improved, wherein the purity of the crystallized salt can be improved to more than 99 percent, and the content of the product with the particle size of more than 100 meshes is improved to more than 92 percent by weight.
Drawings
Fig. 1 is a schematic diagram of the multi-effect evaporative crystallization system in example 1 (n ═ 3).
Description of the reference numerals
1 incoming material pipeline, 2 raw steam pipeline, 3 stage 1 crystallizer
4 circulating pump 5 tubular heat exchanger 6 circulation pipeline
7 slurry turning pipeline 8 slurry turning and material transferring pipeline 9 secondary steam pipeline
10 stage 2 crystallizer 11 transferring pump 12 salt leg
13 3 rd-stage crystallizer 14-view mirror 15 discharge pipeline
16 condenser 17 slurry turning port 18 strong brine outlet
Detailed Description
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and these ranges or values should be understood to encompass values close to these ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
In the invention, n represents the total number of the evaporation crystallizers in the multi-effect evaporation crystallization, and m represents any one of the 1 st-stage evaporation crystallizers.
The first aspect of the invention provides a multi-effect evaporative crystallization method, salt-containing wastewater is subjected to n-stage evaporative crystallization to obtain crystallized salt;
the n-stage evaporative crystallization process comprises the following steps: introducing the salt-containing wastewater into a 1 st-stage evaporative crystallizer for cyclic concentration, then passing through a 2 nd-nth-stage evaporative crystallizer in a downstream manner, and finally precipitating in an nth-stage evaporative crystallization device to obtain crystalline salt;
wherein each stage of evaporation crystallizer comprises a feed inlet and a strong brine outlet;
the m + 1-stage evaporation crystallizer is provided with a salt leg, an m + 1-stage strong brine outlet and an m + 1-stage slurry turning port, wherein the m + 1-stage strong brine outlet and the m + 1-stage slurry turning port are communicated with the salt leg; wherein n is more than or equal to 2, m +1 is more than or equal to n, and m and n are positive integers;
when the continuous operation condition is not met, communicating the m + 1-stage strong brine outlet with the m + 1-stage slurry turning port, and turning and washing the feed liquid in the m + 1-stage salt leg by using the m + 1-stage strong brine;
when the continuous operation condition is met, communicating the m-th stage strong brine outlet with the m + 1-th stage slurry turnover port, and utilizing the m-th stage strong brine to carry out slurry turnover and elutriation on the feed liquid in the m + 1-th stage salt leg;
in the present invention, the continuous operation conditions can be determined by measuring the feed liquid density or the feed liquid sedimentation ratio, and the test mode can be selected conventionally in the art. For example, the density of the nth stage evaporation crystallizer which is generally continuously operated can be 1050-3Preferably 1145-1150kg/m3. Since conventionally used densitometers are easily clogged with crystallized salts on the crystallizer, resulting in inaccurate values, it is preferred that the feed liquid sedimentation ratio can be measured by: and (3) setting a sampling port on a circulating pipeline of the nth-stage evaporative crystallizer, taking 1L of circulating feed liquid from the sampling port by using a measuring cylinder during operation, standing for 10min, wherein the volume of precipitated crystalline salt accounts for the percentage of the total volume of the feed liquid, namely the feed liquid sedimentation ratio. Preferably, the continuous operation conditions include a feed liquid sedimentation ratio in the nth stage evaporative crystallizer of not less than 15%.
According to the invention, in the multi-effect evaporative crystallization, salt-containing wastewater is introduced into a 1 st-stage evaporative crystallizer for cyclic concentration, then sequentially passes through a 2 nd-nth-stage evaporative crystallizer, and finally is separated out in an nth-stage evaporative crystallization device to obtain crystalline salt. For example, when n is 3, the feed liquid after the salt-containing wastewater is concentrated by the 1 st-stage crystallizer is discharged into the 2 nd-stage evaporative crystallizer for continuous concentration, and similarly, the feed liquid concentrated by the 2 nd-stage evaporative crystallizer is discharged into the 3 rd-stage evaporative crystallizer for continuous concentration, and crystallized salt is separated out.
On one hand, the salt legs are arranged on the (m + 1) th-level evaporative crystallizer, impurities such as organic matters, COD (chemical oxygen demand), sylvite and the like are removed by using feed liquid circulating in the system, the growth of crystal salt particles is promoted, the quality of crystal salt products produced by the process is improved, and therefore, salt precipitation and salt washing equipment does not need to be arranged independently, and the equipment investment cost is saved. On the other hand, it can be understood that, by adopting the multi-effect evaporation crystallization method, a certain feed liquid concentration difference exists between evaporators with different effects, and when the feed liquid concentration of the frontmost evaporator is lower, the salt leg of the tail end evaporator is subjected to pulp turning and elutriation by using the feed liquid concentration difference, so that the feed liquid concentration in the tail end evaporator is reduced, and the energy consumption of the tail end evaporator is increased. The inventor finds in research that when the sedimentation ratio of the feed liquid of the nth-stage crystallizer is low and does not meet the continuous operation condition, the feed liquid of the crystallizer is used for pulp turning and elutriation, and when the sedimentation ratio of the tail-end crystallizer meets the continuous operation condition, the feed liquid in the (m + 1) th-stage salt leg is subjected to pulp turning and elutriation and liquor supplementation by using the mth-stage strong brine, so that energy waste can be effectively avoided, and the production efficiency is improved.
According to a preferred embodiment of the invention, the number of evaporative crystallizers is such that: n is more than or equal to 3 and less than or equal to 5, under the preferable condition, the maximum utilization of energy is favorably realized, the advantage of multi-effect evaporation is lost due to too few effects, the temperature difference loss is increased due to too many effects, and the aim of saving energy cannot be fulfilled.
According to a preferred embodiment of the present invention, the continuous operation conditions include a feed liquid sedimentation ratio in the n-th stage evaporative crystallizer of 15 to 30%, preferably 20 to 30%. With the preferred embodiment described above, it is advantageous to maintain sufficient nuclei in the crystallizer to ensure that continuous crystallization occurs, and a too high sedimentation ratio means that too much salt is deposited in the system, which tends to cause the deposition of crystallized salt and clogging of the piping.
According to the invention, the salt-containing wastewater is salt-containing wastewater generated in coal chemical production, preferably, the salt-containing wastewater is strong brine obtained after membrane concentration or MVR concentration; the concentrated brine is the concentrated brine containing sodium chloride or sodium sulfate.
According to a preferred embodiment of the present invention, the TDS of the salt-containing wastewater is 100000-200000 mg/L.
According to a preferred embodiment of the invention, the salt-containing wastewater is heated by steam to obtain heated salt-containing wastewater, and then is introduced into a 1 st-stage evaporative crystallizer for cyclic concentration; the steam carries out circulating heat exchange in the 1 st-stage evaporative crystallizer, and the formed secondary steam flows downstream through each-stage evaporative crystallizer.
According to a preferred embodiment of the invention, the temperature of the saline wastewater after heating is 100-110 ℃, and more preferably 103-107 ℃.
According to a preferred embodiment of the present invention, the steam has a pressure of 0.1-0.6MPa, preferably 0.3-0.5MPa, and a temperature of 120-180 ℃, preferably 140-160 ℃.
According to a preferred embodiment of the invention, the temperature of the feed liquid in the 1 st stage evaporation crystallizer is 100-120 ℃, the temperature of each stage evaporation crystallizer in the n stages evaporation crystallizer is gradually reduced, and the temperature of the feed liquid in the n stage evaporation crystallizer is 60-80 ℃; preferably, the temperature of the feed liquid in the 1 st-stage evaporation crystallizer is 105-115 ℃, the temperature of each stage of evaporation crystallizer in the n-stage evaporation crystallizer is gradually reduced, and the temperature of the feed liquid in the n-stage evaporation crystallizer is 65-75 ℃.
According to a preferred embodiment of the present invention, the feed liquid temperature of the m +1 th stage of evaporative crystallizer is 10-50 deg.C, preferably 12-20 deg.C lower than the feed liquid temperature of the m-th stage of evaporative crystallizer. The temperature difference of each two adjacent stages of evaporative crystallizers can be the same or different, preferably, the temperature gradient between each two adjacent stages of evaporative crystallizers is evenly distributed, and the temperature difference of the adjacent evaporative crystallizers is the same. For example, when n is 3, the feed liquid temperature in the stage 1 evaporative crystallizer is preferably 108-112 ℃, the feed liquid temperature in the stage 2 evaporative crystallizer is preferably 88-92 ℃, and the feed liquid temperature in the stage 3 evaporative crystallizer is preferably 68-72 ℃. By adopting the preferred embodiment, the energy of the previous evaporator can be utilized to the maximum extent, and energy conservation and consumption reduction can be really realized.
According to a preferred embodiment of the present invention, the n-th stage evaporative crystallizer is a vacuum atmosphere, and preferably, the vacuum degree of the n-th stage evaporative crystallizer is 0 to 101.325kPa, and more preferably 10 to 50 kPa. Under the preferable condition, the boiling point of the strong brine in the system is reduced, and the strong brine can still keep an explosive boiling state at a lower temperature.
According to the invention, the dosage of the concentrated brine in the pulp turning and elutriation can be adjusted according to production needs and actual conditions, so that the condition that the pulp turning flow is too large or too small is avoided; preferably, the dosage of the concentrated brine in the slurry tumbling is that the volume ratio of the salt content in the salt legs to the dosage of the concentrated brine is 1: 1-3, preferably 1: 1.5-2.5.
The invention provides a multi-effect evaporative crystallization system, which comprises n stages of evaporative crystallizers and a condenser, wherein the n stages of evaporative crystallizers are sequentially connected with each other;
each stage of evaporative crystallizer comprises a crystallizer and a shell and tube heat exchanger, the crystallizer and the heat exchanger are connected with a steam pipeline through a circulating pipeline, and a forced circulating pump is arranged on the circulating pipeline to ensure that feed liquid is circularly concentrated in a separation chamber of the crystallizer and a tube pass of the shell and tube heat exchanger; steam enters the shell pass of the tube type heat exchanger through a steam pipeline to heat the feed liquid in the tube pass;
wherein, a salt leg, an m +1 stage strong brine outlet and an m +1 stage slurry turning port which are communicated with the salt leg are arranged below the m +1 stage crystallizer;
the (m + 1) th level slurry turning port is respectively communicated with the (m) th level strong brine outlet or the (m + 1) th level strong brine outlet through a slurry turning and material transferring pipeline and is switched by a material transferring pump arranged on the slurry turning and material transferring pipeline;
wherein n is more than or equal to 2, m +1 is more than or equal to n, and m and n are positive integers.
According to the invention, the switching can be flexibly controlled according to the actual production situation. Preferably, when the continuous operation condition is not met, the (m + 1) th level strong brine outlet is communicated with the (m + 1) th level pulp turning port, the (m + 1) th level strong brine is used for carrying out pulp turning and elutriation on the feed liquid in the (m + 1) th level salt leg, and the circulating feed liquid of the crystallizer is used for playing a role in pulp turning and elutriation so as to avoid the deposition of crystallized salt in the salt leg; when the continuous operation condition is met, the m-th-stage strong brine outlet is communicated with the m + 1-th-stage slurry turning port, the m-th-stage strong brine is used for turning and elutriating the feed liquid in the m + 1-th-stage salt leg, and the slurry turning and material transferring pipeline supplies liquid to the evaporation crystallizer and plays a role in turning and elutriating the feed liquid simultaneously, so that the liquid level in the crystallizer is maintained to be stable. The continuous operation condition comprises that the feed liquid sedimentation ratio in the nth stage evaporation crystallizer is not less than 15%.
According to a preferred embodiment of the invention, the sight glasses are arranged on the crystallizers at all levels and the salt legs at all levels, and are used for observing the liquid level of the crystallizers and the pulp-turning elutriation effect, and the pulp-turning elutriation flow rate is controlled by adjusting the opening degree of the valve, so that the situation that the pulp-turning flow rate is too large or too small is avoided.
According to a preferred embodiment of the present invention, an online densitometer is provided on the nth stage crystallizer to monitor the density value or a sampling port is provided in the circulation pipeline of the nth stage evaporative crystallizer to monitor the continuous operation condition, and salt can be continuously discharged when the density value is greater than a set value or the feed-liquid sedimentation ratio is satisfied.
The present invention will be described in detail below by way of examples.
In the following examples, sodium chloride purity was tested according to the test method of Industrial salt Standard (GB/T5462-.
The particle size is measured according to the method of Standard (GB/T13025.1-2012) of the general test methods for the salt industry for determining particle size.
Example 1
The multi-effect evaporative crystallization system is shown in figure 1, wherein n is 3. The salt-containing wastewater raw material is MVR concentrated water obtained by membrane concentration treatment of coal chemical wastewater, and TDS is 200000 mg/L.
The salt-containing wastewater enters a tube side of a tube type heat exchanger 5 through an incoming material pipeline 1 and a forced circulation pump 4, steam 2 enters a shell side of the tube type heat exchanger 5 to heat feed liquid in the tube side, and the pressure of the steam is 0.4MPa and the temperature is 150 ℃. The heated feed liquid is circulated and concentrated in the separation chamber of the 1 st-stage crystallizer 3 and the tube pass of the tube type heat exchanger 5 through a forced circulation pump 4 and a circulation pipeline 6. The feed liquid concentrated by the 1 st-stage crystallizer 3 is discharged into the 2 nd-stage crystallizer 10 for continuous concentration, and similarly, the feed liquid concentrated by the 2 nd-stage crystallizer 10 is discharged into the 3 rd-stage crystallizer 13 for continuous concentration, and the feed liquid is discharged out of the system through a discharge pipeline 15 after crystal salt is separated out. The temperature in the stage 1 crystallizer is about 110 + -2 deg.C, the temperature in the stage 2 crystallizer is about 90 + -2 deg.C, and the temperature in the stage 3 crystallizer is about 70 + -2 deg.C. The degree of vacuum in the stage 3 crystallizer was 20 kPa.
The continuous operation condition is set to be that the feed liquid sedimentation ratio in the 3 rd-stage evaporation crystallizer is 20%, and when the feed liquid sedimentation ratio in the 3 rd-stage evaporation crystallizer is lower than 20%, the material transferring pump controls the slurry turning pipeline 7 to carry out slurry turning and elutriation by utilizing the circulating feed liquid of the crystallizer. When the feed liquid sedimentation ratio in the 3 rd-stage crystallizer is more than or equal to 20%, the material transferring pump transfers the material to the next section, the slurry turning pipeline 7 is stopped, and the slurry turning and transferring pipeline 8 replenishes the next-stage crystallizer and carries out slurry turning and elutriation. The volume ratio of the salt content in the salt leg to the strong brine is 1: 2.
the purity of the sodium chloride crystalline salt collected after continuous operation was 99.1%, wherein the content of crystalline salt with a particle size of more than 100 mesh was 92.9 wt%.
Example 2
The procedure of example 1 was followed except that the ratio of the amount of salt in the salt leg to the amount of concentrated brine was 1: 1.5. the purity of the crystalline salt collected after continuous operation was 98.4%, with a crystalline salt content of 88.2 wt% for particle size (larger than 100 mesh).
Example 3
The procedure of example 1 was followed except that the ratio of the amount of salt in the salt leg to the amount of concentrated brine was 1: 1. the purity of the crystalline salt collected by continuous operation was 97.5%, wherein the content of crystalline salt with a particle size of more than 100 mesh was 83 wt%.
Example 4
The multi-effect evaporation crystallization system is shown in figure 1, wherein n is 3. The salt-containing wastewater raw material is MVR concentrated water obtained by membrane concentration treatment of coal chemical wastewater, and TDS is 100000 mg/L.
The salt-containing wastewater enters a tube side of a tube type heat exchanger 5 through an incoming material pipeline 1 and a forced circulation pump 4, steam 2 enters a shell side of the tube type heat exchanger 5 to heat feed liquid in the tube side, and the pressure of the steam is 0.3MPa and the temperature is 140 ℃. The heated feed liquid is circulated and concentrated in the separation chamber of the 1 st-stage crystallizer 3 and the tube pass of the tube type heat exchanger 5 through a forced circulation pump 4 and a circulation pipeline 6. The feed liquid concentrated by the 1 st-stage crystallizer 3 is discharged into the 2 nd-stage crystallizer 10 for continuous concentration, and similarly, the feed liquid concentrated by the 2 nd-stage crystallizer 10 is discharged into the 3 rd-stage crystallizer 13 for continuous concentration, and the feed liquid is discharged out of the system through a discharge pipeline 15 after crystal salt is separated out. The temperature in the crystallizer of stage 1 is about 100 +/-2 ℃, the temperature in the crystallizer of stage 2 is about 80 +/-2 ℃ and the temperature in the crystallizer of stage 3 is about 60 +/-2 ℃. The degree of vacuum in the stage 3 crystallizer was 10 kPa.
The continuous operation condition is set to be that the feed liquid sedimentation ratio in the 3 rd-stage evaporation crystallizer is 15%, and when the feed liquid sedimentation ratio in the 3 rd-stage evaporation crystallizer is lower than 15%, the material transferring pump controls the slurry turning pipeline 7 to carry out slurry turning and elutriation by utilizing the circulating feed liquid of the crystallizer. When the liquid-liquid sedimentation ratio in the 3 rd-stage crystallizer is more than or equal to 15%, the material-transferring pump transfers the material to the next section, the slurry-turning pipeline 7 is stopped, and the slurry-turning and material-transferring pipeline 8 replenishes the next-stage crystallizer and carries out slurry-turning and elutriation. The volume ratio of the salt content in the salt leg to the strong brine is 1: 2.
the purity of the crystalline salt collected after continuous operation was 98.7% with a crystalline salt content of 91.5 wt% with a particle size (larger than 100 mesh).
Example 5
The multi-effect evaporation crystallization system is shown in figure 1, wherein n is 3. The adopted raw material of the saline wastewater is MVR concentrated water obtained by membrane concentration treatment of coal chemical wastewater, and TDS is 15000 mg/L.
Salt-containing wastewater enters a tube pass of a tube type heat exchanger 5 through an incoming material pipeline 1 by a forced circulation pump 4, steam 2 enters a shell pass of the tube type heat exchanger 5 to heat feed liquid in the tube pass, the pressure of the steam is 0.5MPa, and the temperature is 160 ℃. The heated feed liquid is circulated and concentrated in the separation chamber of the 1 st-stage crystallizer 3 and the tube pass of the tube type heat exchanger 5 through a forced circulation pump 4 and a circulation pipeline 6. The feed liquid concentrated by the 1 st-stage crystallizer 3 is discharged into the 2 nd-stage crystallizer 10 for continuous concentration, and similarly, the feed liquid concentrated by the 2 nd-stage crystallizer 10 is discharged into the 3 rd-stage crystallizer 13 for continuous concentration, and the crystallized salt is separated out and then is discharged out of the system through a discharge pipeline 15. The temperature in the stage 1 crystallizer was about 120. + -. 2 ℃, the temperature in the stage 2 crystallizer was about 100. + -. 2 ℃ and the temperature in the stage 3 crystallizer was about 80. + -. 2 ℃. The degree of vacuum in the stage 3 crystallizer was 50 kPa.
The continuous operation condition is set to be that the feed liquid sedimentation ratio in the 3 rd-level evaporative crystallizer is 30%, and when the feed liquid sedimentation ratio in the 3 rd-level evaporative crystallizer is lower than 30%, the material transfer pump controls the pulp turning pipeline 7, and the circulating feed liquid of the crystallizer is utilized to carry out pulp turning and elutriation. When the liquid-liquid sedimentation ratio in the 3 rd-stage crystallizer is more than or equal to 30%, the material-transferring pump transfers the material to the next section, the slurry-turning pipeline 7 is stopped, and the slurry-turning and material-transferring pipeline 8 replenishes the next-stage crystallizer and carries out slurry-turning and elutriation. The volume ratio of the salt content in the salt leg to the strong brine is 1: 2.5.
the purity of the crystalline salt collected after continuous operation was 98.9% with a crystalline salt content of 92.1 wt% with a particle size (larger than 100 mesh).
Comparative example 1
According to the method of the embodiment 1, except that the switching is not carried out, the feed liquid of the 1 st-stage crystallizer is supplied to the 2 nd-stage crystallizer for liquid supplement and pulp turning and elutriation in the whole operation process, and the feed liquid of the 2 nd-stage crystallizer is supplied to the 3 rd-stage crystallizer for liquid supplement and pulp turning and elutriation. The concentrated brine concentration in both the 2 nd and 3 rd stage crystallizers is reduced, resulting in a prolonged time required for evaporative crystallization, accounting for about 2% reduction in evaporative crystallization efficiency.
Comparative example 2
According to the method of example 1, except that switching is not performed, the outlet of the concentrated brine of the 1 st stage is communicated with the slurry turnover port of the 3 rd stage, the feed liquid of the 1 st stage crystallizer is used for slurry turnover and elutriation of the 3 rd stage crystallizer, the concentration of the concentrated brine in the 3 rd stage crystallizer is reduced, the time required for evaporation crystallization is prolonged, and the efficiency of evaporation crystallization is calculated to be reduced by about 3%.
The results of the above examples and comparative examples show that the multi-effect evaporative crystallization method provided by the invention effectively improves the quality of the crystallized salt, improves the purity and granularity of the crystallized salt, improves the production efficiency, and effectively improves the resource utilization value of the crystallized salt. Wherein, the purity of the crystal salt can reach 99.1 percent, and the content of the crystal salt with the granularity of more than 100 meshes can reach 92.9 percent by weight.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including various technical features being combined in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.
Claims (10)
1. A multi-effect evaporation crystallization method is characterized in that salt-containing wastewater is subjected to n-level evaporation crystallization to obtain crystal salt;
the n-stage evaporative crystallization process comprises the following steps: introducing the salt-containing wastewater into a 1 st-stage evaporative crystallizer for cyclic concentration, then passing through a 2 nd-nth-stage evaporative crystallizer in a downstream manner, and finally precipitating in an nth-stage evaporative crystallization device to obtain crystalline salt;
wherein, each stage of evaporation crystallizer comprises a feed inlet and a strong brine outlet;
the m + 1-stage evaporation crystallizer is provided with a salt leg, an m + 1-stage strong brine outlet and an m + 1-stage slurry turning port, wherein the m + 1-stage strong brine outlet and the m + 1-stage slurry turning port are communicated with the salt leg; wherein n is more than or equal to 2, m +1 is more than or equal to n, and m and n are positive integers;
when the continuous operation condition is not met, communicating the (m + 1) th level strong brine outlet with the (m + 1) th level pulp turning port, and turning and washing the feed liquid in the (m + 1) th level salt leg by using the (m + 1) th level strong brine;
when the continuous operation condition is met, communicating the m-th stage strong brine outlet with the m + 1-th stage slurry turnover port, and utilizing the m-th stage strong brine to carry out slurry turnover and elutriation on the feed liquid in the m + 1-th stage salt leg;
the continuous operation condition comprises that the feed liquid sedimentation ratio in the nth stage evaporation crystallizer is not less than 15 percent.
2. A method according to claim 1, wherein the continuous operating conditions comprise a feed liquid settling ratio in the n-th stage evaporative crystallizer of between 15 and 30%, preferably between 20 and 30%.
3. The method of claim 1, wherein the salt-containing wastewater is concentrated brine after membrane concentration or MVR concentration;
preferably, the TDS of the salt-containing wastewater is 100000-200000 mg/L;
preferably, 3. ltoreq. n.ltoreq.5.
4. The method according to claim 1, wherein the salt-containing wastewater is heated by steam to obtain heated salt-containing wastewater, and then the heated salt-containing wastewater is introduced into a 1 st-stage evaporative crystallizer for cyclic concentration;
preferably, the temperature of the heated salt-containing wastewater is 100-110 ℃, and more preferably 103-107 ℃.
5. Method according to claim 4, wherein the pressure of the steam is between 0.1 and 0.6MPa, preferably between 0.3 and 0.5MPa, and the temperature is between 120 ℃ and 180 ℃, preferably between 140 ℃ and 160 ℃.
6. The method as claimed in claim 5, wherein the temperature of the feed liquid in the 1 st stage of evaporative crystallizer is 100-120 ℃, the temperature of each stage of evaporative crystallizer in the n stages of evaporative crystallizer is gradually decreased, and the temperature of the feed liquid in the n stage of evaporative crystallizer is 60-80 ℃.
7. A method according to claim 6, wherein the feed liquid temperature of the (m + 1) th stage evaporative crystallizer is 10-50 ℃, preferably 12-20 ℃ lower than the feed liquid temperature of the m-th stage evaporative crystallizer;
preferably, the degree of vacuum in the n-th stage evaporative crystallizer is 0 to 101.325kPa, more preferably 10 to 50 kPa.
8. The method of claim 7, wherein the concentrated brine in the panning is used in an amount such that the volume ratio of salt in the salt legs to concentrated brine is 1: 1-3, preferably 1: 1.5-2.5.
9. A multi-effect evaporation crystallization system is characterized by comprising n stages of evaporation crystallizers and condensers, wherein the n stages of evaporation crystallizers are connected in sequence;
each stage of evaporative crystallizer comprises a crystallizer and a shell and tube heat exchanger, the crystallizer and the heat exchanger are connected with a steam pipeline through a circulating pipeline, and a forced circulating pump is arranged on the circulating pipeline, so that feed liquid is circularly concentrated in a separation chamber of the crystallizer and a tube pass of the shell and tube heat exchanger; steam enters the shell pass of the tube type heat exchanger through a steam pipeline to heat the feed liquid in the tube pass;
wherein, a salt leg, an m +1 stage strong brine outlet and an m +1 stage slurry turning port which are communicated with the salt leg are arranged below the m +1 stage crystallizer;
the (m + 1) th-level slurry turning port is respectively communicated with the (m + 1) th-level strong brine outlet or the (m + 1) th-level strong brine outlet through a slurry turning and material transferring pipeline and is switched through a material transferring pump arranged on the slurry turning and material transferring pipeline;
wherein n is more than or equal to 2, m +1 is more than or equal to n, and m and n are positive integers.
10. The system according to claim 9, wherein, a sight glass is arranged on each crystallizer and each salt leg for observing crystallizer liquid level and the pulp-turning and elutriating effect;
preferably, an online densitometer is arranged on the nth stage crystallizer to monitor the density value, or a sampling port is arranged on a circulating pipeline of the nth stage evaporative crystallizer to monitor the continuous operation condition.
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Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2019001571A1 (en) * | 2017-06-29 | 2019-01-03 | 合众高科（北京）环保技术股份有限公司 | Waste water treatment system with buffering device and waste water treatment method therefor |
| CN209438096U (en) * | 2018-10-29 | 2019-09-27 | 内蒙古荣信化工有限公司 | Strong brine multiple-effect evaporation crystal system |
| CN212941543U (en) * | 2020-06-19 | 2021-04-13 | 上海晶宇环境工程股份有限公司 | Multiple-effect evaporation system |
| CN113577799A (en) * | 2021-07-20 | 2021-11-02 | 山东菜央子盐场有限公司 | Application method of MVR heat pump evaporation salt production in multi-effect vacuum salt production process technology |
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2019001571A1 (en) * | 2017-06-29 | 2019-01-03 | 合众高科（北京）环保技术股份有限公司 | Waste water treatment system with buffering device and waste water treatment method therefor |
| CN209438096U (en) * | 2018-10-29 | 2019-09-27 | 内蒙古荣信化工有限公司 | Strong brine multiple-effect evaporation crystal system |
| CN212941543U (en) * | 2020-06-19 | 2021-04-13 | 上海晶宇环境工程股份有限公司 | Multiple-effect evaporation system |
| CN113577799A (en) * | 2021-07-20 | 2021-11-02 | 山东菜央子盐场有限公司 | Application method of MVR heat pump evaporation salt production in multi-effect vacuum salt production process technology |
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