Method for controlling a sodium bicarbonate crystallization process

Abstract

The present application belongs to the technical field of sodium bicarbonate preparation, and particularly relates to a method for regulating the crystallization process of sodium bicarbonate. The method comprises driving the crystal slurry to circulate in the crystallizer, using the difference in settling velocity to gather the crystals with a particle size of 150-300 microns in the settling zone at the bottom of the reactor; arranging an electrode array in the settling zone, applying a high-frequency signal of 10 to 100 kHz to reconstruct the spatial impedance distribution matrix; calculating the anisotropy coefficient and the impedance gradient modulus; discretizing the impedance distribution matrix, establishing the mapping relationship between the physical coordinates and the nozzle group matrix at the bottom of the tank, and matching the target nozzle group trigger instruction of the abnormal material; when the needle-shaped crystal or agglomerate determination condition is met, the control unit determines the trigger instruction according to S3, and injects high-pressure mother liquor into the nozzle group at the corresponding position. The abnormal material is subjected to fixed-point physical shearing or forced deagglomeration, so as to realize the regulation of the crystal particle size and morphology.

Description

Technical Field

[0001] This invention belongs to the field of sodium bicarbonate preparation technology, specifically relating to a method for controlling the sodium bicarbonate crystallization process. Background Technology

[0002] Sodium bicarbonate, also known as baking soda, is widely used in the pharmaceutical, food, and industrial fields. Its crystal size and morphology, such as needle-like crystals or aggregates, directly determine the purity, flowability, and dissolution rate of the product. However, existing production processes still have limitations in terms of control. First, existing online monitoring methods are mostly based on photoelectric sensing or sampling analysis, which makes it difficult to obtain spatial impedance distribution information in the high-concentration crystal slurry region at the bottom of the crystallizer. Because the settling zone is located in a complex circulating flow field, non-uniform flow field disturbances often cause measurement artifacts in the monitoring data, making it impossible to capture the nascent stage of needle-like crystal over-standardization or local agglomeration in real time.

[0003] Secondly, when product quality abnormalities are found, such as an increase in the proportion of needle-like crystals, existing systems often adjust process parameters, such as changing the overall stirring speed or feed temperature. However, this often leads to complete instability of the flow field inside the crystallizer and has a long response time, making it difficult to effectively intervene in the agglomeration dead zone generated at the bottom of the vessel. Summary of the Invention

[0004] To address the aforementioned problems in the prior art, this invention provides a method for controlling the crystallization process of sodium bicarbonate.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for controlling the crystallization process of sodium bicarbonate is provided, comprising the following steps: S1. Drive the crystal slurry to circulate in the crystallizer, and use the difference in settling velocity to gather crystals with a particle size of 150–300 μm into the settling zone at the bottom of the reactor. S2. Arrange an electrode array in the settlement zone and apply a high-frequency signal of 10 to 100 kHz to reconstruct the spatial impedance distribution matrix. ; Calculate the anisotropy coefficient and impedance gradient magnitude The calculation formula is as follows: ; ; in, Here are the anisotropy coefficients; The impedance gradient magnitude; This is the largest component in the principal value of the impedance tensor; This is the smallest component in the principal value of the impedance tensor; Let be the rate of change of impedance along the space normal direction; when When the needle-like crystals are deemed to be excessive, This was determined to be due to crystal aggregation. S3. Discretize the spatial impedance distribution matrix into multiple three-dimensional monitoring sub-regions, establish a partition mapping relationship between the monitoring sub-regions and the bottom nozzle group, and match the target nozzle group trigger command of the monitoring sub-region where the abnormal material is located. S4. When the criteria for determining needle-like crystals or agglomerates are met, the control unit injects high-pressure mother liquor into the nozzle group in the corresponding area according to the trigger command determined in S3; the pressure difference between the high-pressure mother liquor and the main current field satisfies: ; in, The pressure difference ranges from 0.1 to 0.5 MPa. The injection pressure of the high-pressure mother liquor; This represents the pressure of the mainstream field in the settlement zone.

[0006] Preferably, step S2 further includes: A preset reference value for system background impedance is provided to characterize the non-deposition state. ; Real-time acquisition of steady-state impedance data of the electrode array and compare it with the background impedance reference value. Compare and obtain the impedance dynamic fluctuation index. ; When detected The rate of change within the preset monitoring period is lower than the threshold. When the impedance value remains constant, it is determined that there is a sedimentation dead zone in the settling area, and a cleaning command is generated to trigger the bottom nozzle group to execute a full-coverage pulse jet cleaning program.

[0007] Preferably, the nozzle groups are logically addressed according to spatial proximity and divided into multiple nozzle groups; step S4 includes the following sub-steps: (a) Real-time acquisition of local impedance data for the target monitoring sub-region and its N neighboring monitoring sub-regions, construction of impedance covariance matrix, and calculation of regional impedance correlation coefficients between the target sub-region and each neighboring sub-region. ; (b) When the abnormal characteristic value of the target sub-region meets the triggering condition, the region impedance correlation coefficient is retrieved. And select all that satisfy The nozzle groups corresponding to adjacent sub-regions are designated as nozzle groups to be linked, among which... The preset associated trigger threshold; (c) The control unit issues a synchronous blowing command to the target nozzle group and the selected nozzle group to be linked, the command including a phase delay parameter. ,pass Set the blowing start time for each adjacent nozzle group relative to the nozzle group, where =0.1−2s.

[0008] Preferably, the associated trigger threshold The value range is 0.75–0.90.

[0009] Preferably, the partition mapping relationship between the monitoring sub-region and the nozzle group at the bottom of the reactor is preset through a geometric calibration procedure based on the geometric distribution of the electrode array and the actual coverage quadrant of each nozzle group at the bottom of the reactor.

[0010] Preferably, the crystallizer includes a central guide tube and an axial flow propulsion device; the central guide tube is vertically fixed at the crystallizer axis position, and the axial flow propulsion device is installed at the bottom of the central guide tube; the top overflow port of the central guide tube is connected to the annular flow channel of the settling zone, and the ratio of the cross-sectional area of ​​the central guide tube to the cross-sectional area of ​​the annular flow channel is 0.8–1.2.

[0011] Preferably, the settling zone is located within the bottom cone section of the crystallizer, which is shaped like an inverted cone, and the nozzle group is arranged in a multi-row, multi-column matrix array on the inner bottom wall of the bottom cone section; The spray direction of each of the nozzle groups forms an angle of 30°–60° with the central axis.

[0012] Preferably, the nozzle group includes: a valve body, a valve core slidably connected to the valve body, and a return spring disposed on the back of the valve core; When the high-pressure mother liquor is injected, the valve core opens under hydraulic pressure, overcoming the load of the return spring. When the injection stops, the return spring drives the valve core back to its original position and achieves a seal. The load of the return spring is 5–10 N.

[0013] Preferably, the inner wall of the settling zone is provided with a flow stabilizing cavity, each of the nozzle groups is embedded in the flow stabilizing cavity, and the opening of the flow stabilizing cavity is covered with a porous mesh plate, the porosity of the porous mesh plate being 60%–80%.

[0014] Preferably, the temperature difference between the high-pressure mother liquor injection temperature and its mainstream field temperature in step S4 is controlled within a certain range. Within.

[0015] This invention provides a method for controlling the crystallization process of sodium bicarbonate. The beneficial effects of this invention are as follows: By using the jetting effect of high-pressure mother liquor, abnormal materials are subjected to targeted physical shearing or forced depolymerization, thereby achieving control over crystal particle size and morphology. Attached Figure Description

[0016] Figure 1 This is a schematic flowchart of the method for controlling the sodium bicarbonate crystallization process proposed in this invention. Figure 2 This is a three-dimensional view of the crystallizer in the method for controlling the sodium bicarbonate crystallization process proposed in this invention; Figure 3 This is a front view of the crystallizer in the method for controlling the sodium bicarbonate crystallization process proposed in this invention. Figure 4 This is one of the cross-sectional views of the crystallizer in the method for controlling the sodium bicarbonate crystallization process proposed in this invention; Figure 5 This is the second cross-sectional view of the crystallizer in the method for controlling the sodium bicarbonate crystallization process proposed in this invention; Figure 6 This is the third cross-sectional view of the crystallizer in the method for controlling the sodium bicarbonate crystallization process proposed in this invention; Figure 7 This is a schematic diagram of the nozzle group in the method for controlling the sodium bicarbonate crystallization process proposed in this invention.

[0017] Explanation of reference numerals in the attached figures: 1. Crystallizer; 2. Central guide tube; 3. Axial flow propulsion device; 4. Settling zone; 5. Overflow port; 6. Nozzle group; 7. Flow stabilizing cavity; 8. Perforated mesh plate; 9. Electrode array. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Please see Figures 1-7 As shown, the specific embodiments provided by the present invention are as follows: like Figure 1 As shown, an embodiment of the present invention proposes a method for controlling the crystallization process of sodium bicarbonate. In the specific implementation process, the crystal slurry in the crystallizer 1 is first driven to circulate in a large manner. Utilizing the dynamic sedimentation difference of crystal particles in the fluid, qualified crystals with a particle size between 150 and 300 μm are continuously guided to converge in the sedimentation zone 4 at the bottom of the reactor, providing a relatively stable material environment for subsequent monitoring and control.

[0020] Within the aforementioned settling zone 4, a multi-channel electrode array 9 is uniformly arranged along the axial and radial directions. The processing unit applies a high-frequency excitation signal of 10–100 kHz to the electrode array 9 via an excitation source, acquires electrical response data between each electrode, and reconstructs the spatial impedance distribution matrix within the settling zone 4. Based on this matrix, the anisotropy coefficient is calculated. and impedance gradient magnitude Among them, the anisotropy coefficient The calculation formula is Used to characterize the degree of conduction anisotropy caused by the dominant growth of needle-like crystals along the polar axis; impedance gradient magnitude The calculation formula is ,in This represents the rate of change of impedance along the spatial normal, used to quantify the difference in resistivity distribution caused by crystal aggregation density. When When the growth of needle-like crystals is deemed excessive, it is determined that the growth exceeds the standard. When this occurs, it is determined that the crystals have aggregated.

[0021] It should be noted that the underlying data acquisition and calculation process for reconstructing the spatial impedance distribution matrix in step S2 is based on the principle of electrical impedance tomography. Since the spatial resolution of industrial EIT / ERT technology typically exhibits regional characteristics, this invention does not employ stringent single-point physical coordinate calculation, but rather uses regional positioning logic.

[0022] After identifying the abnormal state, the processing unit discretizes the spatial impedance distribution matrix into multiple three-dimensional monitoring sub-regions, such as dividing them into northeast quadrants, southwest quadrants, etc., and establishes a partition mapping relationship between the monitoring sub-regions and the bottom nozzle group 6, thereby constructing a partition mapping relationship database. Based on this database, the abnormal region where the needle-like crystals or agglomerates are located is identified, and a trigger command for the target nozzle group 6 in that region is generated.

[0023] Based on the trigger command, the control unit activates nozzle group 6 within the corresponding area to inject high-pressure mother liquor into the abnormal material area. During the injection process, the pressure difference between the mother liquor and the mainstream field in the settling zone meets the following requirements: Among them, pressure difference Controlled within the range of 0.1–0.5 MPa To inject pressure, Mainstream market pressure.

[0024] By using the jetting effect of high-pressure mother liquor, abnormal materials are subjected to regional physical shearing or forced depolymerization, thereby achieving control over crystal size and morphology.

[0025] In a preferred embodiment of the present invention, a system background impedance reference value is first preset. This benchmark value characterizes the standard impedance distribution state of sedimentation zone 4 when there is no crystal accumulation and only normal circulating crystallization suspension exists.

[0026] During the control process, the processing unit acquires the steady-state impedance data of the electrode array 9 in real time. and with By performing difference comparison, the impedance dynamic fluctuation index can be calculated and obtained. .

[0027] The index This reflects the activity level of material distribution within the current monitoring area. The system continuously tracks the data within a preset monitoring period. The changing trend. If the monitoring data exhibits the following characteristics: Right now The rate of change within this period is lower than a preset threshold, and the corresponding impedance value If the temperature remains constant for an extended period, the processing unit determines that a crystal deposition dead zone has formed within settling zone 4. At this point, the system generates a cleaning command, triggering the nozzle group 6 array located at the bottom of the reactor to execute a full-coverage pulse jet cleaning program. This process utilizes the energy impact of the pulsed fluid to forcibly disrupt the particle structure within the deposition dead zone, causing it to re-enter the circulating flow field, thereby ensuring the continuous dynamic equilibrium of the crystallization system.

[0028] like Figures 2 to 7 As shown, in another preferred embodiment of the present invention, for complex working conditions such as large-scale crystal agglomeration or abnormal growth, the matrix of nozzle group 6 set at the bottom of the crystallizer is logically addressed in advance according to spatial proximity. Based on this, the blowing action in step S4 is refined into the following sub-steps: First, during step (a), the processing unit acquires real-time data on the target monitoring sub-area and its surroundings. The system uses local impedance data corresponding to each adjacent sub-region. Based on the data stream acquired synchronously through multiple channels, the system constructs an impedance covariance matrix and calculates the impedance correlation coefficient between the target sub-region and each adjacent sub-region through matrix operations. The impedance correlation coefficient The calculation formula is: ; in, For target sub-region With adjacent sub-regions The covariance of the corresponding local impedance data, These represent the standard deviations of the corresponding impedance data. This coefficient can characterize the spatial coherence of abnormal material distribution in different quadrants or regions.

[0029] Subsequently, the system proceeds to the linkage screening stage in step (b). When the abnormal characteristic value of the target sub-region meets the preset triggering conditions, the system retrieves and searches for the calculated impedance correlation coefficient. Select all that satisfy The adjacent sub-regions (and their corresponding nozzle groups 6) are combined and arranged into 6 groups of nozzles to be linked. This is the preset associated trigger threshold. When At this point, in a physical sense, the crystal agglomeration or needle-like crystal network in the target region has crossed the shear coverage radius of a single nozzle group 6, indicating that the anomalous region exhibits significant spatial continuity. This screening logic ensures that the system only intervenes in anomalous regions with actual physical impact, effectively preventing additional disturbances to the overall steady-state flow field of the crystallizer caused by indiscriminate blowing.

[0030] Finally, in the timing control phase of step (c), the control unit issues synchronous blowing commands to the target nozzle group 6 and the selected nozzle groups 6 to be linked. These commands not only include the injection action but also specifically embed phase delay parameters. The system uses Set the injection start time of each adjacent nozzle group 6 relative to the central target group, and set the value range of this parameter to be [value missing]. By using this control, the system can locally induce pressure pulses in the settling zone, which, compared to single-point synchronous blowing, can perform more efficient full-coverage physical disturbance and forced depolymerization on large-scale abnormal crystallization networks.

[0031] In a preferred embodiment of the present invention, the associated triggering threshold is further defined. The value range is 0.75–0.90.

[0032] Specifically, in the actual operating conditions of the settling zone 4 of crystallizer 1, due to the high-frequency turbulence of the local flow field and the randomness of crystal particle settling, the impedance data between different sensor channels inevitably suffer from environmental noise interference. When set... At times, the system is overly sensitive to weak signal fluctuations, easily misinterpreting background noise caused by random fluid disturbances as spatial expansion of material agglomeration, thus frequently triggering ineffective linkage jetting. Conversely, when set... At times, the conditions for triggering the linkage are too stringent. Due to the natural damping and attenuation characteristics of high-concentration crystal slurry on high-frequency electrical signals, even if substantial needle-like crystal interlacing or large-scale aggregation has occurred in adjacent regions, the system struggles to collect strong correlation features above this threshold. This leads to a delayed response or even failure of the linkage mechanism, allowing abnormal crystal clusters to escape from the control region.

[0033] Therefore, strictly controlling the associated trigger threshold within the range of 0.75–0.90 can achieve the best balance between filtering out fluid dynamic noise artifacts and capturing abnormal material spatial cross-linking characteristics, thus maximizing the hit rate of group linkage intervention and the macroscopic stability of the crystallization flow field.

[0034] In a preferred embodiment of the present invention, the mapping relationship between the monitoring sub-region and the bottom nozzle group 6 is preset based on the geometric distribution characteristics of the electrode array 9 and the actual mechanical installation position of each nozzle group 6 at the bottom of the reactor, through a built-in geometric calibration program. During the crystallizer assembly or system initialization phase, the calibration program first establishes a unified spatial reference coordinate system in the crystallizer settling zone. Subsequently, the effective detection node coordinates of each sensing channel in the electrode array 9, along with the physical outlet coordinates and spray coverage envelope of the bottom nozzle group 6, are synchronously projected into this reference coordinate system.

[0035] Since the spatial impedance distribution matrix reconstructed by electrode array 9 is essentially a discretized grid of the continuous flow field, this geometric calibration program uses a spatial topology algorithm to spatially overlap and match the virtual discrete grid containing impedance characteristics with the effective shear disturbance region of the actual nozzle group 6. Based on the matching results, the system establishes a static partition mapping relationship database, establishing a preset mapping relationship between each monitoring sub-region and the corresponding nozzle group 6.

[0036] Through this pre-defined geometric calibration, when the processing unit identifies an abnormal feature that meets the triggering conditions of needle-like or clustered structures in a certain part of the impedance matrix, the control system can skip the complex positioning calculation process and directly perform instruction addressing through the partitioned mapping database, which greatly reduces the system's computing power requirements.

[0037] In a preferred embodiment of the present invention, the crystallizer 1 is provided with a central guide tube 2 and a matching axial flow propulsion device 3 inside its main body.

[0038] The central guide tube 2 is vertically suspended and fixed along the central axis of the crystallizer 1 to ensure the central symmetry of the internal circulating flow field; the axial flow propulsion device 3 is installed at the bottom of the central guide tube 2. During operation, the axial flow propulsion device 3 rotates at high speed to generate axial thrust, driving the supersaturated mother liquor and small-diameter crystal slurry at the bottom to flow from bottom to top along the interior of the central guide tube 2 until they reach the overflow port 5 at the top of the guide tube. Subsequently, the crystal slurry overflows the overflow port 5 and flows back into the annular flow channel formed between the outer wall of the central guide tube 2 and the inner wall of the crystallizer 1, flowing back from top to bottom to the settling zone 4.

[0039] Specifically, in this embodiment, the ratio of the internal cross-sectional area of ​​the central guide tube 2 to the cross-sectional area of ​​the annular flow channel is limited to the range of 0.8 to 1.2. If this ratio is too small, the downward flow velocity in the annular gap will be too low, and some crystals will settle prematurely near the vessel wall or even deposit and form scale before reaching the target particle size. Conversely, if this ratio is too large, the downward flow velocity in the annular gap will be too fast, and the strong fluid drag will disrupt the steady-state environment of the bottom settling zone 4, causing small needle-like crystal nuclei that do not meet the particle size requirements to be forcibly drawn into the bottom monitoring and control zone, seriously interfering with the accuracy of electrical monitoring.

[0040] In a preferred embodiment of the present invention, the settling zone 4 is physically located within the bottom cone section of the crystallizer 1, which is shaped like an inverted cone. It can utilize gravity settling and the natural guiding effect of the inclined surface to allow the crystals descending from the outer annular channel to naturally converge and concentrate at the bottom.

[0041] On the inner bottom wall of this bottom cone section, the nozzle group 6 is densely arrayed in a multi-row, multi-column matrix. Regardless of where abnormal material settles into the bottom cone section, the system can call upon one or more of the nearest nozzle groups 6 to provide omnidirectional coverage, completely eliminating physical blind spots and intervention blind zones of the bottom actuator.

[0042] Furthermore, the injection direction of each nozzle group 6 forms an angle of 30°–60° with the central axis of the crystallizer 1. If the injection angle is too small, the high-pressure jet will directly impact the descending mainstream flow field in the opposite direction, which will not only cause great kinetic energy loss, but also easily lift the agglomerates that have not been completely deagglomerated back to the upper flow field, resulting in control failure; if the injection angle is too large, the jet is prone to wall adhesion effect, causing energy to be dissipated by friction on the vessel wall, weakening the penetrating and destructive force on the suspended material.

[0043] In a preferred embodiment of the present invention, the nozzle group 6 is mainly composed of a valve body, a valve core slidably connected to the valve body, and a return spring disposed on the back of the valve core.

[0044] During normal crystallization cycles and when there are no material abnormalities in the target area, nozzle group 6 is in standby mode. At this time, relying on the physical preload of the back return spring, the valve core is driven to slide forward and return to its original position, so that the end of the valve core is tightly fitted with the outlet end of the valve body to achieve a physical seal. This normally closed sealing state can completely prevent the backflow of high-concentration, supersaturated sodium bicarbonate slurry into the nozzle group 6 under static pressure.

[0045] When the control unit issues a targeted injection command, the high-pressure mother liquor is injected into the valve body. Under hydraulic pressure, the valve core overcomes the mechanical load of the return spring, opens the injection channel, and allows the high-pressure jet to be ejected and perform depolymerization on the crystals. When the mother liquor injection stops, the hydraulic pressure inside the valve body decreases, the return spring releases the accumulated elastic potential energy, and pushes the valve core back to the sealed position.

[0046] Specifically, in this embodiment, the load of the return spring is limited to the range of 5–10 N. If the load of the return spring is less than 5 N, under the static pressure of the liquid column at the bottom of the crystallizer 1, the spring force will be insufficient to overcome the environmental pressure at the bottom of the vessel to maintain the tight fit of the valve port, which can easily lead to sealing failure and crystal slurry leakage. Conversely, if the load of the return spring is greater than 10 N, the high-pressure mother liquor must have an extremely high opening and overflow pressure difference to forcibly open the valve port. This not only unnecessarily increases the energy loss of the system's liquid supply pump, but also causes excessive mechanical fatigue and high-frequency impact wear on the sealing contact surfaces of the valve body and valve seat during the pulse jet process of frequent opening and closing of the valve core.

[0047] In a preferred embodiment of the present invention, the inner wall of the settling zone 4 is provided with a concave flow stabilizing cavity 7 corresponding to each nozzle group 6. Each nozzle group 6 is deeply embedded inside the flow stabilizing cavity 7, which effectively avoids direct and continuous mechanical scouring and abrasive wear on the valve body of the nozzle group 6 caused by the high-concentration circulating crystal slurry in the crystallizer 1.

[0048] At the external opening of the flow stabilizing cavity 7, i.e., at the interface between the flow stabilizing cavity 7 and the main flow field of the settling zone 4, a perforated mesh plate 8 is installed. When the nozzle group 6 is in a closed, silent period, the mesh plate, as a purely mechanical physical isolation layer, can effectively intercept large crystal particles or dense aggregates in the settling zone 4, preventing them from backflowing and filling the flow stabilizing cavity 7 due to gravity settling, thereby ensuring that the jet channel of the nozzle group 6 is always unobstructed; while when the nozzle group 6 is opened instantaneously to perform high-pressure jetting, the jet needs to pass through the mesh plate to enter the main flow field.

[0049] Specifically, in this embodiment, the porosity of the porous mesh plate 8 is defined as between 60% and 80%. If the porosity is less than 60%, the solid area of ​​the mesh plate is too large, which will generate a large local water resistance to the outwardly sprayed high-pressure mother liquor, causing severe throttling and dissipation of jet kinetic energy at this point, weakening its depolymerization and destructive force on abnormal materials after entering the mainstream field; conversely, if the porosity is greater than 80%, the solid support skeleton of the mesh plate will become too thin, which will not only be unable to withstand the long-term mechanical stress impact of the high-pressure pulse jet and be prone to fatigue fracture, but its physical blocking and interception efficiency against external suspended crystals will also be greatly reduced.

[0050] In a preferred embodiment of the present invention, when the high-pressure mother liquor is injected in step S4, the control unit will link the heat exchange and temperature compensation module of the crystallization system to control the temperature difference between the high-pressure mother liquor to be injected and the mainstream field temperature of the sedimentation zone 4 to be entered within ±2°C.

[0051] If the injection temperature of the high-pressure mother liquor is significantly lower than the mainstream field (i.e., the negative temperature difference exceeds 2°C), a large amount of cold fluid will be injected into the settling zone 4 in the form of high-speed pulses. This will cause a local supercooling effect at the nozzle group 6 outlet and in the jet-affected area, significantly increasing the solute supersaturation in that region. This will easily induce uncontrolled primary nucleation, generating a large number of crystal nuclei out of thin air. Conversely, if the injection temperature of the high-pressure mother liquor is significantly higher than the mainstream field (i.e., the positive temperature difference exceeds 2°C), the local high temperature will break the supersaturation state in that region, causing the mother liquor to locally transform into an unsaturated dissolved state. At this time, the high-pressure jet will not only physically collide and depolymerize, but will also produce a surface erosion effect on the crystals that have already grown to the required standard, destroying the complete crystal form and surface smoothness of the crystals, resulting in overall quality degradation.

[0052] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for controlling the crystallization process of sodium bicarbonate, characterized in that, Includes the following steps: S1. Drive the crystal slurry to circulate in the crystallizer, and use the difference in settling velocity to gather crystals with a particle size of 150–300 μm into the settling zone at the bottom of the reactor. S2. Arrange an electrode array in the settlement zone and apply a high-frequency signal of 10 to 100 kHz to reconstruct the spatial impedance distribution matrix. ; Calculate the anisotropy coefficient and impedance gradient magnitude The calculation formula is as follows: ； ； in, Here are the anisotropy coefficients; The impedance gradient magnitude; This is the largest component in the principal value of the impedance tensor; This is the smallest component in the principal value of the impedance tensor; Let be the rate of change of impedance along the space normal direction; when When the needle-like crystals are deemed to be excessive, This was determined to be due to crystal aggregation. S3. Discretize the spatial impedance distribution matrix into multiple three-dimensional monitoring sub-regions, establish a partition mapping relationship between the monitoring sub-regions and the bottom nozzle group, and match the target nozzle group trigger command of the monitoring sub-region where the abnormal material is located. S4. When the criteria for determining needle-like crystals or agglomerates are met, the control unit injects high-pressure mother liquor into the nozzle group in the corresponding area according to the trigger command determined in S3; the pressure difference between the high-pressure mother liquor and the main current field satisfies: ； in, The pressure difference ranges from 0.1 to 0.5 MPa. The injection pressure of the high-pressure mother liquor; This represents the pressure of the mainstream field in the settlement zone.

2. The method for controlling the sodium bicarbonate crystallization process according to claim 1, characterized in that, Step S2 further includes: A preset reference value for system background impedance is provided to characterize the non-deposition state. ; Real-time acquisition of steady-state impedance data of the electrode array and compare it with the background impedance reference value. Compare and obtain the impedance dynamic fluctuation index. ; When detected The rate of change within the preset monitoring period is lower than the threshold. When the impedance value remains constant, it is determined that there is a sedimentation dead zone in the settling area, and a cleaning command is generated to trigger the bottom nozzle group to execute a full-coverage pulse jet cleaning program.

3. The method for controlling the sodium bicarbonate crystallization process according to claim 1, characterized in that, The nozzle groups are logically addressed according to spatial proximity and divided into multiple nozzle groups; step S4 includes the following sub-steps: (a) Real-time acquisition of local impedance data for the target monitoring sub-region and its N neighboring monitoring sub-regions, construction of impedance covariance matrix, and calculation of regional impedance correlation coefficients between the target sub-region and each neighboring sub-region. ; (b) When the abnormal characteristic value of the target sub-region meets the triggering condition, the region impedance correlation coefficient is retrieved. And select all that satisfy The nozzle groups corresponding to adjacent sub-regions are designated as nozzle groups to be linked, among which... The preset associated trigger threshold; (c) The control unit issues a synchronous blowing command to the target nozzle group and the selected nozzle group to be linked, the command including a phase delay parameter. ,pass Set the blowing start time for each adjacent nozzle group relative to the nozzle group, where =0.1−2s.

4. The method for controlling the sodium bicarbonate crystallization process according to claim 1, characterized in that, The associated trigger threshold The value range is 0.75–0.

90.

5. The method for controlling the sodium bicarbonate crystallization process according to claim 1, characterized in that, The mapping relationship between the monitoring sub-region and the nozzle group at the bottom of the reactor is preset through a geometric calibration procedure based on the geometric distribution of the electrode array and the actual coverage quadrant of each nozzle group at the bottom of the reactor.

6. The method for controlling the sodium bicarbonate crystallization process according to claim 1, characterized in that, The crystallizer includes a central guide tube and an axial flow propulsion device; the central guide tube is vertically fixed at the crystallizer axis position, and the axial flow propulsion device is installed at the bottom inside the central guide tube; the top overflow port of the central guide tube is connected to the annular flow channel of the settling zone, and the ratio of the cross-sectional area of ​​the central guide tube to the cross-sectional area of ​​the annular flow channel is 0.8–1.

2.

7. The method for controlling the sodium bicarbonate crystallization process according to claim 1, characterized in that, The settling zone is located in the bottom cone section of the crystallizer, which is shaped like an inverted cone. The nozzle group is arranged in a multi-row, multi-column matrix on the inner bottom wall of the bottom cone section. The spray direction of each of the nozzle groups forms an angle of 30°–60° with the central axis.

8. The method for controlling the sodium bicarbonate crystallization process according to claim 7, characterized in that, The nozzle group includes: a valve body, a valve core slidably connected to the valve body, and a return spring disposed on the back of the valve core; When the high-pressure mother liquor is injected, the valve core opens under hydraulic pressure, overcoming the load of the return spring. When the injection stops, the return spring drives the valve core back to its original position and achieves a seal. The load of the return spring is 5–10 N.

9. The method for controlling the sodium bicarbonate crystallization process according to claim 8, characterized in that, The inner wall of the settling zone is provided with a flow stabilizing cavity, and each of the nozzle groups is embedded in the flow stabilizing cavity. The opening of the flow stabilizing cavity is covered with a porous mesh plate, and the porosity of the porous mesh plate is 60%–80%.

10. The method for controlling the sodium bicarbonate crystallization process according to claim 1, characterized in that, The temperature difference between the high-pressure mother liquor injection temperature and its mainstream field temperature in step S4 is controlled within a certain range. Within.

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