MVR (Mechanical Vapor Recompression) and single-effect or multi-effect self-adaptive collaborative evaporative crystallization system and process for hydrochloric acid washing mother liquor of incineration fly ash

Abstract

The invention discloses an MVR (Mechanical Vapor Recompression) and single-effect or multi-effect self-adaptive collaborative evaporative crystallization system and process for hydrochloric acid washing mother liquor of incineration fly ash. The MVR and single-effect or multi-effect self-adaptive collaborative evaporative crystallization system comprises a controller as well as an MVR pre-concentration unit, a single-effect / multi-effect fine concentration unit, a concentrator, a filter and a filtrate storage tank which are connected in sequence. The MVR pre-concentration unit preliminarily concentrates the hydrochloric acid washing mother liquor of the incineration fly ash in an energy-saving manner. The single-effect / multi-effect fine concentration unit is used for receiving the discharged material of the MVR pre-concentration unit and completing the accurate concentration of the calcium chloride solution and the removal of carnallite. And the concentrator and the filter are used for separating and concentrating the generated NaCl / KCl carnallite. The controller coarsely adjusts the steam adjusting valve according to the effect number, the feeding flow metered by the flowmeter and the predicted value of the total salt concentration of the fed and discharged materials of the single-effect / multi-effect fine concentration unit; calculating the calcium chloride concentration of the filtrate according to the filtrate density and the filtrate temperature obtained by the density meter and the thermometer, and finely adjusting the steam regulating valve based on the difference between the calculated calcium chloride concentration and the target calcium chloride concentration of the filtrate, so that the calcium chloride concentration of the filtrate reaches the standard.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization and chemical separation technology, specifically to a treatment system and process for the complex mother liquor generated after hydrochloric acid washing of incineration fly ash, which can be used to prepare flaky calcium chloride dihydrate products that meet national standards. Background Technology

[0002] With the continuous expansion of municipal solid waste incineration, the resource utilization of incineration fly ash, classified as hazardous waste (HW18 category), has become a focus of the industry. Currently, hydrochloric acid washing is commonly used to recover valuable metals and extract calcium chloride as a byproduct. However, the resulting mother liquor has a complex and highly fluctuating composition, and the calcium chloride content is high. 2+ The concentration typically varies between 5 wt% and 25 wt%, while containing 3 wt% to 12 wt% Na. + K + Alkali metal ions.

[0003] To obtain industrial-grade calcium chloride dihydrate (alkali metal chloride ≤5%) conforming to GB / T 26520-2011 standard, the mother liquor needs to be concentrated to a CaCl2 mass fraction of 44%-54%, so that most of the NaCl / KCl precipitates out in advance and is removed by solid-liquid separation. Then, the mother liquor is further concentrated to 68%-74%, cooled for crystallization, and dried to obtain calcium chloride dihydrate conforming to the standard.

[0004] The applicant has proposed a resource-based treatment process for the reaction mother liquor of waste incineration fly ash and hydrochloric acid. For details, please refer to the patent specification with publication number CN112225242A. Specifically, the mother liquor adopts a scheme of first removing impurities and then evaporating and crystallizing to separate salts. First, excess calcium hydroxide and calcium sulfate are removed, and then the mixed salts mainly composed of sodium chloride and potassium chloride are separated by evaporation and crystallization. The mother liquor can be used to prepare two products: in the first path, the mother liquor is further concentrated and then cooled and crystallized to obtain calcium chloride dihydrate flakes; in the second path, the mother liquor is concentrated or diluted to a calcium chloride content of about 45%, and then granulated and dried in a fluidized bed.

[0005] Existing evaporation technologies mainly employ two approaches: 1. Mechanical vapor recompression (MVR) evaporation system: High energy efficiency (approximately 25-40 kg of steam per ton of water), but limited by compressor temperature rise (single unit ≤20℃, two units in series ≤35℃). Combined with the heat transfer temperature difference, its applicable solution boiling point is generally no more than 125℃, with little operational flexibility, and it is not suitable for high-boiling-point solutions such as calcium chloride. 2. Single-effect or multi-effect evaporation system: It can achieve high-temperature concentration, but the energy consumption is too high (steam consumption per ton of water ≥ 300 kg), and the economy is poor, but the operation is highly flexible.

[0006] More importantly, because the mother liquor contains Na + K +Plasma, during the evaporation process, forms a multi-component eutectic system, leading to: 1) The actual boiling point is significantly higher than that of pure CaCl2 or saturated NaCl or potassium chloride solution. For example, when the concentration of CaCl2 is 33wt%, if NaCl / KCl is saturated, the actual boiling point can reach 121.4℃, while the boiling point of pure CaCl2 solution at the same concentration is only about 113℃, a deviation of more than 8℃. 2) Different actual CaCl2 concentrations at the same density due to different impurity ratios; 3) If the conductivity, temperature or density of the slurry in the evaporator is used as the control parameter, it is very easy to make a misjudgment and cause the product quality to be out of control.

[0007] Therefore, the existing single evaporation mode is unable to meet the three core requirements of energy efficiency, stability and product quality control.

[0008] Therefore, there is an urgent need to develop a new type of evaporation crystallization system that can achieve intelligent collaborative operation between the high-efficiency energy-saving section of MVR and the single-effect / multi-effect high-temperature stable section, and ensure full-process automation and high-quality output through a precise monitoring and feedback control mechanism. Summary of the Invention

[0009] To address the aforementioned technical problems and shortcomings in this field, the present invention provides an MVR (Mechanical Vapor Reduction) system and process for hydrochloric acid washing mother liquor from incinerated fly ash, along with single-effect or multi-effect adaptive synergistic evaporation crystallization. This system features high efficiency, energy saving, and stability, and can achieve the following objectives: 1) In the event of fluctuations in feed composition (Ca... 2+ Na + K + 1) Achieve dynamic matching and material balance between MVR and single / multi-effect systems under conditions of concentration change; 2) Precisely control the evaporation rate of single / multi-effect systems while ensuring efficient operation of MVR, so that the mass fraction of CaCl2 in the filtrate after solid-liquid separation is maintained at 44%-54% and the residual NaCl / KCl content is less than 3.5wt%; 3) Overcome the distortion problem of traditional physical parameters (such as boiling point, density, and conductivity) in multi-component systems and establish a reliable concentration estimation model.

[0010] The specific technical solution is as follows: In a first aspect, the present invention provides an MVR and single-effect or multi-effect adaptive synergistic evaporation crystallization system for incineration fly ash hydrochloric acid washing mother liquor, including a controller and an MVR pre-concentration unit, a single-effect / multi-effect fine concentration unit, a concentrator, a filter and a filtrate storage tank connected in sequence. A flow meter is installed between the MVR pre-concentration unit and the single-effect / multi-effect fine concentration unit for preliminary measurement of the feed flow rate of the single-effect / multi-effect fine concentration unit; The single-effect / multi-effect condensing unit includes a steam regulating valve for regulating the steam flow rate entering the single-effect / multi-effect condensing unit; A monitoring point is set between the filter and the filtrate storage tank, connecting a density meter and a thermometer; the density meter is used to obtain the density of the filtrate; the thermometer is used to obtain the temperature of the filtrate. The controller connects to a flow meter, steam regulating valve, density meter, and thermometer. It is used to: coarsely adjust the steam regulating valve based on the number of effects of the single-effect / multi-effect concentrator, the feed flow rate measured by the flow meter, and the predicted total salt concentration of the feed and discharge of the single-effect / multi-effect concentrator; and simultaneously calculate the calcium chloride concentration of the filtrate based on the density and temperature of the filtrate obtained by the density meter and thermometer, and finely adjust the steam regulating valve based on the difference between the calculated calcium chloride concentration and the target calcium chloride concentration of the filtrate, so that the calcium chloride concentration of the filtrate meets the standard.

[0011] In some preferred embodiments, the filtrate is refluxed to the MVR pre-concentration unit if the calcium chloride concentration is below the standard.

[0012] In some preferred embodiments, the concentration of calcium chloride in the filtrate is calculated based on piecewise linear interpolation, specifically including: Create a temperature-density-calcium chloride concentration dataset; Determine the filtrate temperature obtained by the thermometer The narrowest temperature range in the dataset. , , These are the temperature points in the dataset; Based on the temperature in the data The density-calcium chloride concentration relationship is established, and the first filtrate concentration corresponding to the filtrate density obtained from the density meter is calculated using linear interpolation. Specifically, this includes: first determining the filtrate density obtained from the density meter. The temperature The narrowest density range in the density-calcium chloride concentration relationship. , , Temperature The density value in the density-calcium chloride concentration relationship is used to calculate the concentration of the first filtrate using the following formula. : , Temperature Density in the density-calcium chloride concentration relationship , The corresponding calcium chloride concentration; Based on the temperature in the data The density-calcium chloride concentration relationship is established, and the second filtrate concentration corresponding to the filtrate density obtained from the density meter is calculated using linear interpolation. Specifically, this includes: first determining the filtrate density obtained from the density meter. The temperature The narrowest density range in the density-calcium chloride concentration relationship. , , Temperature The density value in the density-calcium chloride concentration relationship is used to calculate the concentration of the second filtrate using the following formula. : , Temperature Density in the density-calcium chloride concentration relationship , The corresponding calcium chloride concentration; Based on the concentration of the first filtrate Second filtrate concentration The concentration of the third filtrate was calculated by performing linear interpolation along the temperature direction. The specific calculation formula is as follows: Based on the concentration of the third filtrate The density of the filtrate obtained by the densitometer was calculated from the concentration offset caused by NaCl / KCl miscellaneous salts. The temperature of the filtrate obtained by the thermometer True calcium chloride concentration in the filtrate : This refers to the set total mass fraction of NaCl / KCl mixed salts. Generally speaking, The value should not exceed 3.5%, and for further examples, the range could be 1%-3.5%, etc.

[0013] Furthermore, the MVR pre-concentration unit is used to concentrate the mother liquor to: a boiling point 12-25°C higher than that of pure water under the same pressure, a total salt concentration controlled at 20wt%-55wt% (e.g., 40wt%, 50wt%, etc.), and a CaCl2 concentration increased to 20wt%-40wt%.

[0014] In some preferred embodiments, the operating temperature of the MVR pre-concentration unit is 90-125°C.

[0015] Furthermore, the single-effect / multi-effect concentrator unit is used to concentrate the slurry from the MVR pre-concentrator unit to (i.e., the output of the single-effect / multi-effect concentrator unit) a total salt concentration of 30wt%-65wt% and a CaCl2 concentration of 25wt%-45wt%, promoting the precipitation of NaCl and KCl.

[0016] In some preferred embodiments, the operating temperature of the single-effect / multi-effect concentration unit is 70-110°C. Furthermore, in the filtrate separated by the filter, the mass fraction of CaCl2 is 44%-54%, and the total amount of NaCl and KCl does not exceed 3.5 wt%.

[0017] In some preferred embodiments, the MVR and single-effect or multi-effect adaptive synergistic evaporation crystallization system for the incinerated fly ash hydrochloric acid washing mother liquor further includes a three-stage concentration and cooling crystallization unit. The three-stage concentration and cooling crystallization unit is connected to a filtrate storage tank and is used for the final concentration of the filtrate and product preparation. Specifically, it includes: re-evaporating the filtrate to achieve a CaCl2 concentration of 68wt%-74wt%, and then allowing it to enter a cooling crystallizer to precipitate CaCl2·2H2O crystals.

[0018] In a second aspect, the present invention provides an MVR and single-effect or multi-effect adaptive synergistic evaporation crystallization process for incinerated fly ash hydrochloric acid washing mother liquor, employing the MVR and single-effect or multi-effect adaptive synergistic evaporation crystallization system for incinerated fly ash hydrochloric acid washing mother liquor described in the first aspect. The MVR and single-effect or multi-effect adaptive synergistic evaporation crystallization process of the incinerated fly ash hydrochloric acid washing mother liquor includes: The MVR pre-concentration unit performs preliminary energy-saving concentration of hydrochloric acid washing mother liquor from incinerated fly ash. The single-effect / multi-effect fine concentration unit receives the output from the MVR pre-concentration unit and completes the precise concentration of calcium chloride solution and removal of impurities; The concentrator and filter separate the NaCl / KCl impurities produced during concentration; The controller coarsely adjusts the steam regulating valve based on the number of effects of the single-effect / multi-effect concentrator, the feed flow rate measured by the flow meter, and the predicted total salt concentration of the feed and discharge of the single-effect / multi-effect concentrator. At the same time, it calculates the calcium chloride concentration of the filtrate based on the density and temperature of the filtrate obtained by the densitometer and thermometer, and finely adjusts the steam regulating valve based on the difference between the calculated calcium chloride concentration and the target calcium chloride concentration of the filtrate to ensure that the calcium chloride concentration of the filtrate meets the standard.

[0019] The steam regulating valve is coarsely adjusted based on the number of effects in the single-effect / multi-effect concentrator, the feed flow rate measured by the flow meter, and the predicted total salt concentration of the feed and discharge of the single-effect / multi-effect concentrator. The initial steam consumption is calculated using the following formula, and the steam regulating valve is then coarsely adjusted based on the initial steam consumption: Initial steam flow rate = a × (1 - b / c) × feed mass flow rate; 'a' represents the effect parameter value, for example, 1.1 for the first effect and 0.55 for the second effect; b represents the predicted total salt concentration of the feed to the single-effect / multi-effect concentrator unit; c represents the predicted total salt concentration of the output from the single-effect / multi-effect concentrator unit.

[0020] This invention relates to an MVR (Mechanical Vapor Removal) system for incinerating fly ash and hydrochloric acid washing mother liquor, combined with a single-effect or multi-effect adaptive evaporation and crystallization system. This system utilizes an MVR combined with a single-effect or multi-effect tandem evaporation and crystallization device. Through precise control of process boundaries and an innovative soft-sensoring method for concentration measurement, it achieves efficient removal of impurities and produces high-quality calcium chloride dihydrate. The core innovation of this invention lies in setting the monitoring point at the clarified liquid stage after impurity removal, avoiding interference from suspended particles in the slurry with measurement accuracy. It combines a piecewise linear interpolation algorithm to estimate the calcium chloride concentration in real time, and employs an adaptive control strategy using a feedforward coarse adjustment and feedback fine adjustment steam regulating valve to ensure stable operation of the system under fluctuating feed composition conditions. The final product conforms to the GB / T 26520-2011 standard.

[0021] Compared with the prior art, the beneficial effects of this invention are as follows: (1) Control the MVR to operate at high efficiency: the boiling point is 12-25℃ higher than that of pure water under the same pressure, the total salt concentration is controlled at 20wt%-55wt%, and the CaCl2 concentration is increased to 20wt%-40wt%, to avoid over-limit operation or low-load operation.

[0022] (2) Single-effect / multi-effect can take over the subsequent precise concentration task, so that the CaCl2 content in the filtrate after desalting is 44wt%-54wt% and the dissolved salt content is ≤3.5wt%; monitoring of the clear liquid stage after desalting completely avoids interference from multiple components.

[0023] (3) The alkali metal chloride content in the final product is ≤5wt%, which conforms to GB / T 26520-2011 standard. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of an MVR and single-effect or multi-effect adaptive synergistic evaporation crystallization system for incinerated fly ash hydrochloric acid washing mother liquor according to the present invention. Detailed Implementation

[0025] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0026] See Figure 1 A MVR and single-effect or multi-effect adaptive synergistic evaporation crystallization system for incinerating fly ash hydrochloric acid washing mother liquor includes a controller 18 and an MVR pre-concentration unit, a single-effect / multi-effect fine concentration unit, a concentrator 13, a filter 14, a filtrate storage tank 15, and a tertiary concentration and cooling crystallization unit (not shown) connected in sequence.

[0027] The MVR pre-concentration unit includes an MVR pre-liquid tank 1, a feed pump 2, an MVR heater 3, a first circulation pump 4, an MVR crystallizer 5, and a steam compressor 6. The MVR heater 3, the MVR crystallizer 5, and the first circulation pump 4 are connected to form a first slurry circulation loop. The MVR crystallizer 5 is connected to the MVR heater 3 through the steam compressor 6.

[0028] The single-effect / multi-effect slurry concentrator unit includes a single-effect / multi-effect heater 10, a single-effect / multi-effect crystallizer 8, a second circulation pump 9, and a condenser 12. The MVR crystallizer 5 is connected to the single-effect / multi-effect crystallizer 8 via a first feed pump 7. A flow meter 20 is installed between the first feed pump 7 and the single-effect / multi-effect crystallizer 8 for preliminary metering of the feed flow rate to the single-effect / multi-effect slurry concentrator unit. The single-effect / multi-effect heater 10, the second circulation pump 9, and the single-effect / multi-effect crystallizer 8 are connected to form a second slurry circulation loop. The single-effect / multi-effect crystallizer 8 is connected to the condenser 10. The single-effect / multi-effect heater 10 is equipped with a steam regulating valve 19 for regulating the steam flow rate entering the single-effect / multi-effect slurry concentrator unit. The single-effect / multi-effect heater 10 is connected to the concentrator 13 via a second feed pump 11.

[0029] A monitoring point connecting a density meter 16 and a thermometer 17 is installed between the filter 14 and the filtrate storage tank 15 (e.g., the connecting pipeline between the filter 14 and the filtrate storage tank 15, the inlet position of the filtrate storage tank 15, etc.). The density meter 16 is used to obtain the density of the filtrate. The thermometer 17 is used to obtain the temperature of the filtrate.

[0030] The controller 18 is connected to the flow meter 20, the steam regulating valve 19, the densitometer 16, and the thermometer 17. It is used to: coarsely adjust the steam regulating valve 19 based on the feed flow rate measured by the flow meter 20 and the predicted total salt concentration of the feed and discharge of the single-effect / multi-effect concentrator; at the same time, it calculates the calcium chloride concentration of the filtrate based on the density and temperature of the filtrate obtained by the densitometer 16 and the thermometer 17, and finely adjusts the steam regulating valve 19 based on the difference between the calculated calcium chloride concentration and the target calcium chloride concentration of the filtrate, so that the calcium chloride concentration of the filtrate meets the standard.

[0031] The dilute slurry at the top outlet of the concentrator 13 is refluxed through a pipeline connected to the single-effect / multi-effect crystallizer 8. The concentrated slurry at the bottom goes to the filter 14 to filter out impurities. If the calcium chloride concentration of the filtrate does not meet the standard, it is refluxed back to the MVR pre-liquid tank 1 through the reflux pipeline. After the filtrate meets the standard, it goes to the filtrate storage tank 15.

[0032] The three-stage concentration and cooling crystallization unit is used for the final concentration of the filtrate and product preparation, including equipment such as a deep concentration unit, a cooling crystallizer, a centrifuge, and a dryer.

[0033] A method for MVR (Mechanical Vapor Recycling) and single-effect or multi-effect adaptive synergistic evaporation crystallization of incinerated fly ash hydrochloric acid washing mother liquor, employing, for example... Figure 1The MVR of the above-mentioned incineration fly ash hydrochloric acid washing mother liquor and single-effect or multi-effect adaptive synergistic evaporation crystallization system are shown.

[0034] The MVR and single-effect or multi-effect adaptive synergistic evaporation crystallization process of the incinerated fly ash hydrochloric acid washing mother liquor includes: The MVR pre-concentration unit performs preliminary energy-saving concentration of the incineration fly ash hydrochloric acid washing mother liquor, i.e., primary concentration. The initial fly ash hydrochloric acid washing mother liquor in the MVR pre-liquid tank 1 is fed into the MVR heater 3 at a set flow rate via the feed pump 2. The first circulation pump 4 is started, and low-pressure steam is introduced into the MVR heater 3 to begin heating and concentration. Steam is emitted from the top of the MVR crystallizer 5. The steam compressor 6 is started, pressurizing the steam emitted from the top of the MVR crystallizer 5 and then feeding it back into the MVR heater 3 for recycling. Evaporation and concentration are carried out at 90-115℃. By adjusting the frequency converter of the steam compressor 6 and adding a small amount of low-pressure steam, the MVR pre-concentration unit is kept in a high-efficiency and stable operating state. The CaCl2 concentration is increased to 25wt%-40wt%, and some NaCl / KCl begins to precipitate, forming a low-concentration MVR crystallization slurry of mixed salts.

[0035] In the MVR pre-concentration unit, the mixed salt solution is concentrated to a boiling point that is 12-25°C higher than that of pure water under the same pressure. At this point, the total salt concentration is controlled at 20wt%-55wt%, some sodium chloride has crystallized out, and the CaCl2 concentration is about 20wt%-40wt%. Furthermore, it is within the high-efficiency range of the MVR compressor, achieving energy-saving concentration.

[0036] The single-effect / multi-effect concentrator unit receives the output from the MVR pre-concentrator unit and completes the precise concentration of calcium chloride solution and removal of impurities, i.e., secondary concentration. The MVR crystallization slurry enters the single-effect / multi-effect crystallizer 8 through the first feed pump 7 and is metered by the flow meter 20. The second circulation pump 9 is started. Based on the feed flow rate and the predicted total salt concentration of the feed to the single-effect / multi-effect heater 10, the controller 18 calculates the required steam flow rate for the single-effect / multi-effect concentrator unit (positive feedback control of steam flow rate). The steam flow rate of the single-effect / multi-effect concentrator unit is adjusted by controlling the steam regulating valve 19, and steam is introduced into the single-effect / multi-effect heater 10 for heating, evaporation, and concentration, which promotes the precipitation of more NaCl / KCl and increases the calcium chloride concentration. The steam generated at the top of the single-effect / multi-effect crystallizer 8 is condensed by the condenser 12.

[0037] Based on the number of effects in the single-effect / multi-effect concentrator, the predicted total salt concentration of the MVR crystallization slurry (feed to the single-effect / multi-effect concentrator), the predicted total salt concentration of the effluent from the single-effect / multi-effect concentrator, and the feed flow rate of the single-effect / multi-effect concentrator, an initial steam consumption calculation formula is established to ensure the system operates at an optimal starting point, reduce adjustment time, and achieve positive feedback control. After positive feedback control, the filtrate after multi-effect concentrator removal of impurities and salts approaches the control target.

[0038] Initial steam flow rate = a × (1 - b / c) × feed mass flow rate; 'a' represents the effect parameter value, for example, 1.1 for the first effect and 0.55 for the second effect; b represents the predicted total salt concentration of the feed to the single-effect / multi-effect concentrator unit; c represents the predicted total salt concentration of the output from the single-effect / multi-effect concentrator unit.

[0039] The discharge from the single-effect / multi-effect heater 10 enters the concentrator 13 via the second feed pump 11. The concentrator 13 and the filter 14 separate the NaCl / KCl mixed salts produced during concentration. Specifically, the salt-containing slurry discharged from the single-effect / multi-effect heater 10 is thickened by the concentrator 13, and then the NaCl / KCl mixed salt filter cake is separated by the filter 14 to obtain a relatively pure calcium chloride filtrate. If the quality does not meet the standards, it is first circulated to the MVR pre-liquid tank 1.

[0040] The controller 18 calculates the calcium chloride concentration in the filtrate based on the density and temperature of the filtrate obtained from the densitometer 16 and thermometer 17, and fine-tunes the steam regulating valve 19 (feedback control of steam flow) based on the difference between the calculated calcium chloride concentration and the target calcium chloride concentration in the filtrate, so that the calcium chloride concentration in the filtrate meets the standard. Specifically, the densitometer 16 and thermometer 17 collect the density and temperature of the filtrate after desalination in real time, and set the content of impurities in the filtrate to a fixed value, not exceeding 3.5%. The controlled variable is defined as the calcium chloride concentration after desalination (control range: 44%-50%), and the manipulated variable is the steam flow rate. Based on the real-time collected filtrate density and temperature signals, the system calculates the concentration feedback through soft sensing technology; the deviation between this feedback value and the set value is sent to the controller 18 to generate a PID control command, which overcomes process disturbances and achieves constant concentration control by fine-tuning the opening of the steam regulating valve 19. When the calcium chloride concentration meets the standard after desalination, the filtrate stops circulating and is collected in the filtrate storage tank 15.

[0041] The slurry discharged from the MVR pre-concentration unit enters the single-effect / multi-effect fine concentration unit for further concentration until the mass fraction of CaCl2 in the filtrate after solid-liquid separation reaches 44%-54%, ensuring that the total mass content of dissolved sodium chloride / potassium chloride does not exceed 3.5%, thus achieving precise concentration.

[0042] The filtrate from storage tank 15 is pumped back into the three-stage concentration and cooling crystallization unit for three-stage concentration until the CaCl2 concentration reaches 68wt%-74wt%, meeting the requirements for subsequent cooling crystallization. The concentrated solution enters the cooling crystallizer to cool to 40-50℃, precipitating calcium chloride dihydrate crystals. After drying, calcium chloride dihydrate product conforming to GB / T 26520-2011 standard is obtained, achieving compliant production of calcium chloride products.

[0043] Through the above design, this invention fully leverages the energy-saving advantages of MVR in the low-to-medium concentration range while avoiding the problem of efficiency degradation in the high-boiling-point range.

[0044] When the feed flow rate of the MVR pre-concentration unit is stable, the evaporation boiling point of the MVR changes due to fluctuations in the content of sodium chloride, potassium chloride, and calcium chloride in the feed. Under the condition of ensuring stable operation of the MVR, the evaporation rate of the MVR changes. Therefore, the feed rate and salt concentration entering the single-effect / multi-effect concentrator are fluctuating and uncertain, and it is necessary to monitor the feed flow rate of the single-effect / multi-effect concentrator.

[0045] When the feed rate and salt content of the single-effect / multi-effect evaporation and concentration unit fluctuate, the steam volume is adaptively adjusted to ultimately and precisely control the single-effect / multi-effect evaporation and concentration, so that the mass fraction of CaCl2 in the filtrate after solid-liquid separation reaches 44%-54%, and the total mass content of dissolved sodium chloride / potassium chloride does not exceed 3.5%, so that the subsequent products meet the quality requirements.

[0046] This invention ensures stable final product quality through positive feedback adaptive control under fluctuating feeding conditions.

[0047] Feedforward control: By monitoring the fluctuations in the feed to the single-effect / multi-effect concentrator and predicting the total salt concentration, the steam flow rate of the single-effect / multi-effect concentrator is set to counteract disturbances and provide a rapid response.

[0048] Feedback control: By monitoring the concentration of the final product (or a parameter strongly correlated with it), the steam output of the single-effect / multi-effect condensing unit is finely adjusted to ensure control accuracy and eliminate errors that cannot be covered by the feedforward model.

[0049] This invention successfully stabilizes a production process with significant upstream fluctuations at a strict quality output target by dynamically adjusting a key operating variable (steam quantity).

[0050] The concentration calculated by the aforementioned soft sensing technique is specifically based on piecewise linear interpolation to calculate the calcium chloride concentration in the filtrate, including: Create a temperature-density-calcium chloride concentration dataset; Determine the filtrate temperature obtained by the thermometer The narrowest temperature range in the dataset. , , These are the temperature points in the dataset; Based on the temperature in the data The density-calcium chloride concentration relationship is established, and the first filtrate concentration corresponding to the filtrate density obtained from the density meter is calculated using linear interpolation. Specifically, this includes: first determining the filtrate density obtained from the density meter. The temperature The narrowest density range in the density-calcium chloride concentration relationship. , , Temperature The density value in the density-calcium chloride concentration relationship is used to calculate the concentration of the first filtrate using the following formula. : , Temperature Density in the density-calcium chloride concentration relationship , The corresponding calcium chloride concentration; Based on the temperature in the data The density-calcium chloride concentration relationship is established, and the second filtrate concentration corresponding to the filtrate density obtained from the density meter is calculated using linear interpolation. Specifically, this includes: first determining the filtrate density obtained from the density meter. The temperature The narrowest density range in the density-calcium chloride concentration relationship. , , Temperature The density value in the density-calcium chloride concentration relationship is used to calculate the concentration of the second filtrate using the following formula. : , Temperature Density in the density-calcium chloride concentration relationship , The corresponding calcium chloride concentration; Based on the concentration of the first filtrate Second filtrate concentration The concentration of the third filtrate was calculated by performing linear interpolation along the temperature direction. The specific calculation formula is as follows: Based on the concentration of the third filtrate The density of the filtrate obtained by the densitometer was calculated from the concentration offset caused by NaCl / KCl miscellaneous salts. The temperature of the filtrate obtained by the thermometer True calcium chloride concentration in the filtrate : This represents the set total mass fraction of NaCl / KCl mixed salts.

[0051] The following provides the usage as follows: Figure 1 Specific embodiments of the above-mentioned MVR and single-effect or multi-effect adaptive synergistic evaporation crystallization system and process for incineration fly ash hydrochloric acid washing mother liquor are shown below: Fly ash at a rate of 1 t / h, after leaching with hydrochloric acid and neutralization purification, yields approximately 3.71 m³ of calcium chloride mother liquor. 3 / h, the initial CaCl2 concentration is approximately 20wt%, containing approximately 6wt% NaCl and approximately 3wt% KCl. Using... Figure 1 The above-mentioned incineration fly ash hydrochloric acid washing mother liquor is subjected to evaporation and crystallization treatment using an MVR system and process with single-effect or multi-effect adaptive synergistic evaporation and crystallization. The operation steps are as follows: S1, MVR pre-concentration (energy-saving stage): The purified mother liquor is fed into the MVR pre-liquid tank 1 and then into the MVR pre-concentration unit via the feed pump 2. In the MVR heater 3, it is heated by low-pressure steam and compressed steam in a cycle. The mother liquor then enters the MVR crystallizer 5 via the first circulation pump 4. The secondary steam at the top of the MVR crystallizer 5 is pressurized and heated by the steam compressor 6 and then returned to the MVR heater 3 as a heat source for high-efficiency evaporation and concentration.

[0052] During this stage, approximately 1.54 t / h of water is evaporated and removed. When the boiling point of the solution in MVR crystallizer 5 increases by 21.4°C compared to pure water under the same pressure, it is determined to have entered the high-boiling-point zone, and steam compressor 6 operates at high efficiency. Analysis results of the slurry sample at the bottom of MVR crystallizer 5: total salt concentration ≈ 50 wt%, sodium chloride and potassium chloride crystal salts ≈ 17 wt%, CaCl2 concentration ≈ 33 wt%.

[0053] S2, single-effect positive feedforward control of steam flow for evaporation and concentration: The concentrated slurry is conveyed to the single-effect heater via the first feed pump 5 at a flow rate of 2.17 m³ / s. 3 The predicted total salt concentration of the feed to the single-effect / multi-effect condensing unit is 48%, and the total salt concentration of the output is 55%. Using the controller 18 and the initial steam consumption calculation formula for the single-effect / multi-effect condensing unit (initial steam flow rate = a × (1-b / c) × feed mass flow rate), the required steam flow rate for the single-effect unit is calculated to be 0.3 t / h. A "heating" command is sent to the single-effect crystallizer to start the steam supply. The steam flow rate is controlled at approximately 0.3 t / h via the steam regulating valve 19, maintaining a standby state until stable operation.

[0054] S3, Separation of mixed salts: The salt-containing slurry discharged from the single-effect crystallizer is thickened by the concentrator 13 and then separated into NaCl / KCl mixed salt filter cake by the filter 14 to obtain a relatively pure calcium chloride filtrate. If the quality does not meet the standard, it is first circulated to the MVR front tank 1.

[0055] S4, single-effect feedback control of steam flow to achieve precise evaporation and concentration: The system enables an impurity-corrected concentration soft measurement algorithm: Density meter 16 acquires filtrate density in real time. =1499 kg / m 3 Thermometer 17 was used to collect the temperature of the filtrate. =87.8℃, set the total mass fraction of NaCl / KCl mixed salts =3.5%.

[0056] Calculation process: Step 1: Determine the temperature range: The temperature of 87.8℃ falls between 85℃ and 95℃, therefore the density of 1499 kg / m³ needs to be calculated separately at 85℃ and 95℃. 3 The corresponding concentration is then interpolated along the temperature direction.

[0057] Table 1 provides the known temperature-density-calcium chloride concentration dataset, with density in kg / m³. 3 Concentration unit: wt%.

[0058] Table 1 Step 2: Calculate the concentration at 85℃: Density-concentration data at 85℃: Density: [1472, 1489, 1507, 1525, 1544, 1563, 1582, 1602]; Concentration: [43, 44, 45, 46, 47, 48, 49, 50]; Density 1499 kg / m³ 3 It is between 1489 and 1507, corresponding to concentrations of 44 and 45.

[0059] Density ratio = (1499-1489) / (1507-1489) = 10 / 18 ≈ 0.5556; Concentration at 85℃ = 44 + 0.5556 × (45 - 44) = 44.5556%.

[0060] Step 3: Calculate the concentration at 95℃: Density-concentration data at 95℃: Density: [1462, 1479, 1497, 1515, 1533, 1552, 1571, 1591]; Concentration: [43, 44, 45, 46, 47, 48, 49, 50]; Density 1499 kg / m³3 It is between 1497 and 1515, corresponding to concentrations of 45 and 46.

[0061] Density ratio = (1499-1497) / (1515-1497) = 2 / 18 ≈ 0.1111; Concentration at 95℃ = 45 + 0.1111 × (46 - 45) = 45.1111%.

[0062] Step 4: Interpolate in the temperature direction: Temperature ratio = (87.8-85) / (95-85) = 2.8 / 10 = 0.28; Concentration at 87.8℃ =85℃ concentration + temperature ratio × (95℃ concentration - 85℃ concentration) = 44.5556 + 0.28 × (45.1111 - 44.5556) = 44.7111%.

[0063] Based on a concentration at 87.8℃ The density of the filtrate obtained by the densitometer was calculated from the concentration offset caused by NaCl / KCl miscellaneous salts. The temperature of the filtrate obtained by the thermometer True calcium chloride concentration in the filtrate : have to The concentration is 42.2011%, lower than the set calcium chloride concentration (44%-54%). The controlled target is set between 46%-50%. The deviation between the feedback value (42.2011%) and the set value is sent to the controller 18 to generate a PID control command. By fine-tuning the opening of the steam regulating valve 19, the steam flow rate is gradually increased. When the steam flow rate is 0.39 t / h: Real-time data collection =1582 kg / m 3 , =91.8℃; set up =3.5%; The concentration at 91.8℃ was calculated using the piecewise linear interpolation method described above. It is 49.37%.

[0064] Based on a concentration of 91.8℃ The density of the filtrate obtained by the densitometer was calculated from the concentration offset caused by NaCl / KCl miscellaneous salts. The temperature of the filtrate obtained by the thermometer True calcium chloride concentration in the filtrate : have to The concentration was 46.24%. Once the set requirement of 46%-50% was met, the filtrate circulation stopped, and the filtrate was collected in filtrate storage tank 13. The total alkali metal chloride content in the filtrate, after random sampling, was 2.4%-2.6%, meeting the requirements for subsequent precise control.

[0065] S5, continue concentration, cooling, crystallization, and drying: The filtrate in the filtrate storage tank 13 is further concentrated to 68wt%-74wt%, and then sent to a cooling crystallizer to precipitate crystals. After centrifugation, dehydration, and drying, a white flaky calcium chloride dihydrate product is obtained.

[0066] S6, Product Inspection: ICP-OES analysis showed that the total sodium chloride / potassium chloride content in the product was 3.8 wt%, which meets the requirements of GB / T 26520-2011.

[0067] In summary, the MVR and single-effect or multi-effect adaptive synergistic evaporation crystallization system and process for incinerating fly ash hydrochloric acid washing mother liquor of the present invention can adaptively handle different batches of feed without changing the main equipment. The switching and coordinated operation of each unit in the system can be completed automatically by the PLC or DCS control system, and it has fault alarm, interlock protection and remote monitoring functions.

[0068] Furthermore, it should be understood that after reading the above description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims.

Claims

1. A method for MVR (Mechanical Vapor Recycling) combined with single-effect or multi-effect adaptive synergistic evaporation and crystallization system for incinerating fly ash and hydrochloric acid washing mother liquor, characterized in that, Includes a controller and an MVR pre-concentration unit, a single-effect / multi-effect fine concentration unit, a concentrator, a filter, and a filtrate storage tank connected in sequence; A flow meter is installed between the MVR pre-concentration unit and the single-effect / multi-effect fine concentration unit for preliminary measurement of the feed flow rate of the single-effect / multi-effect fine concentration unit; The single-effect / multi-effect condensing unit includes a steam regulating valve for regulating the steam flow rate entering the single-effect / multi-effect condensing unit; A monitoring point is installed between the filter and the filtrate storage tank, connecting a density meter and a thermometer; the density meter is used to obtain the density of the filtrate; the thermometer is used to obtain the temperature of the filtrate. The controller connects to a flow meter, steam regulating valve, density meter, and thermometer. It is used to: coarsely adjust the steam regulating valve based on the number of effects of the single-effect / multi-effect concentrator, the feed flow rate measured by the flow meter, and the predicted total salt concentration of the feed and discharge of the single-effect / multi-effect concentrator; and simultaneously calculate the calcium chloride concentration of the filtrate based on the density and temperature of the filtrate obtained by the density meter and thermometer, and finely adjust the steam regulating valve based on the difference between the calculated calcium chloride concentration and the target calcium chloride concentration of the filtrate, so that the calcium chloride concentration of the filtrate meets the standard.

2. The MVR and single-effect or multi-effect adaptive synergistic evaporation crystallization system for incineration fly ash hydrochloric acid washing mother liquor according to claim 1, characterized in that, If the calcium chloride concentration in the filtrate is below the standard, it should be returned to the MVR pre-concentration unit.

3. The MVR and single-effect or multi-effect adaptive synergistic evaporation crystallization system for incineration fly ash hydrochloric acid washing mother liquor according to claim 1, characterized in that, The calculation of calcium chloride concentration in the filtrate based on piecewise linear interpolation includes: Create a temperature-density-calcium chloride concentration dataset; Determine the filtrate temperature obtained by the thermometer The narrowest temperature range in the dataset. , , These are the temperature points in the dataset; Based on the temperature in the data The density-calcium chloride concentration relationship is established, and the first filtrate concentration corresponding to the filtrate density obtained from the density meter is calculated using linear interpolation. Specifically, this includes: first determining the filtrate density obtained from the density meter. The temperature The narrowest density range in the density-calcium chloride concentration relationship. , , Temperature The density value in the density-calcium chloride concentration relationship is used to calculate the concentration of the first filtrate using the following formula. : , Temperature Density in the density-calcium chloride concentration relationship , The corresponding calcium chloride concentration; Based on the temperature in the data The density-calcium chloride concentration relationship is established, and the second filtrate concentration corresponding to the filtrate density obtained from the density meter is calculated using linear interpolation. Specifically, this includes: first determining the filtrate density obtained from the density meter. The temperature The narrowest density range in the density-calcium chloride concentration relationship. , , Temperature The density value in the density-calcium chloride concentration relationship is used to calculate the concentration of the second filtrate using the following formula. : , Temperature Density in the density-calcium chloride concentration relationship , The corresponding calcium chloride concentration; Based on the concentration of the first filtrate Second filtrate concentration The concentration of the third filtrate was calculated by performing linear interpolation along the temperature direction. The specific calculation formula is as follows: Based on the concentration of the third filtrate The density of the filtrate obtained by the densitometer was calculated from the concentration offset caused by NaCl / KCl miscellaneous salts. The temperature of the filtrate obtained by the thermometer True calcium chloride concentration in the filtrate : This represents the set total mass fraction of NaCl / KCl mixed salts.

4. The MVR and single-effect or multi-effect adaptive synergistic evaporation crystallization system for incineration fly ash hydrochloric acid washing mother liquor according to claim 1, characterized in that, The MVR pre-concentration unit operates at a temperature of 90-125℃ and is used to concentrate the mother liquor to a boiling point 12-25℃ higher than that of pure water under the same pressure, a total salt concentration controlled at 20wt%-55wt%, and a CaCl2 concentration increased to 20wt%-40wt%.

5. The MVR and single-effect or multi-effect adaptive synergistic evaporation crystallization system for incineration fly ash hydrochloric acid washing mother liquor according to claim 1, characterized in that, The single-effect / multi-effect concentrator operates at a temperature of 70-110℃ and is used to concentrate the slurry from the MVR pre-concentrator to a total salt concentration of 30wt%-65wt% and a CaCl2 concentration of 25wt%-45wt%.

6. The MVR and single-effect or multi-effect adaptive synergistic evaporation crystallization system for incineration fly ash hydrochloric acid washing mother liquor according to claim 1, characterized in that, The filtrate after separation by the filter contains 44%-54% CaCl2 by mass, and the total amount of NaCl and KCl does not exceed 3.5 wt%.

7. The MVR and single-effect or multi-effect adaptive synergistic evaporation crystallization system for incineration fly ash hydrochloric acid washing mother liquor according to claim 1, characterized in that, The MVR and single-effect or multi-effect adaptive synergistic evaporation crystallization system for the incinerated fly ash hydrochloric acid washing mother liquor also includes a three-stage concentration and cooling crystallization unit; the three-stage concentration and cooling crystallization unit is connected to the filtrate storage tank and is used for the final concentration of the filtrate and product preparation, specifically including: re-evaporating the filtrate to make its CaCl2 concentration reach 68wt%-74wt%, and then entering the cooling crystallizer to precipitate CaCl2·2H2O crystals.

8. A method for MVR (Mechanical Vapor Recycling) combined with single-effect or multi-effect adaptive synergistic evaporation and crystallization of incinerated fly ash hydrochloric acid washing mother liquor, characterized in that, The MVR system of incinerated fly ash hydrochloric acid washing mother liquor as described in any one of claims 1-7, combined with a single-effect or multi-effect adaptive synergistic evaporation crystallization system; The MVR and single-effect or multi-effect adaptive synergistic evaporation crystallization process of the incinerated fly ash hydrochloric acid washing mother liquor includes: The MVR pre-concentration unit performs preliminary energy-saving concentration of hydrochloric acid washing mother liquor from incinerated fly ash. The single-effect / multi-effect fine concentration unit receives the output from the MVR pre-concentration unit and completes the precise concentration of calcium chloride solution and removal of impurities; The concentrator and filter separate the NaCl / KCl impurities produced during concentration; The controller coarsely adjusts the steam regulating valve based on the number of effects of the single-effect / multi-effect concentrator, the feed flow rate measured by the flow meter, and the predicted total salt concentration of the feed and discharge of the single-effect / multi-effect concentrator. At the same time, it calculates the calcium chloride concentration of the filtrate based on the density and temperature of the filtrate obtained by the densitometer and thermometer, and finely adjusts the steam regulating valve based on the difference between the calculated calcium chloride concentration and the target calcium chloride concentration of the filtrate to ensure that the calcium chloride concentration of the filtrate meets the standard.

9. The MVR and single-effect or multi-effect adaptive synergistic evaporation crystallization process for incineration fly ash hydrochloric acid washing mother liquor according to claim 8, characterized in that, The steam regulating valve is coarsely adjusted based on the number of effects in the single-effect / multi-effect concentrator, the feed flow rate measured by the flow meter, and the predicted total salt concentration of the feed and discharge of the single-effect / multi-effect concentrator. The initial steam consumption is calculated using the following formula, and the steam regulating valve is then coarsely adjusted based on the initial steam consumption: Initial steam flow rate = a × (1 - b / c) × feed mass flow rate; 'a' represents the value of the effect parameter; b represents the predicted total salt concentration of the feed to the single-effect / multi-effect concentrator unit; c represents the predicted total salt concentration of the output from the single-effect / multi-effect concentrator unit.

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