Method and device for treating high-salt high-concentration waste liquid by low-temperature evaporator

Abstract

The present application relates to waste liquid treatment technical field, disclose a kind of low-temperature evaporator processing high-salt high-concentration waste liquid method and equipment.The method: the feed flow of feed waste liquid and feed salt concentration are detected and the secondary steam production forecast value is calculated;According to the secondary steam production forecast value, the target speed of centrifugal steam compressor is calculated, and the target value of vacuum degree of vacuum evaporator is calculated according to the feed salt concentration;The first running speed of centrifugal steam compressor is adjusted in real time until the target speed of compressor is reached, and the first running vacuum degree of vacuum evaporator is adjusted synchronously until the target value of vacuum degree is reached;The concentrated liquid discharged from vacuum evaporator is supersaturated crystallization, and the crystal slurry is obtained, and the crystal slurry is solid-liquid separated, and solid salt product and mother liquor are obtained.The present application solves the technical problem that the heat transfer efficiency of existing MVR evaporation system decreases and runs unstable under variable load condition, and then realizes the stable resource disposal of high-salt waste liquid.

Description

Technical Field

[0001] This invention relates to the field of waste liquid treatment technology, and in particular to a method and equipment for treating high-salt, high-concentration waste liquid using a low-temperature evaporator. Background Technology

[0002] Evaporation treatment of high-salt / high-concentration wastewater is a key step in achieving zero discharge of industrial wastewater, and mechanical vapor recompression (MVR) technology is widely used due to its energy efficiency advantages. However, existing MVR evaporation systems generally adopt a fixed compression ratio and fixed vacuum degree operation mode. Once the system control parameters are set under design conditions, they are not adjusted. This leads to a severe mismatch between the processing capacity of the steam compressor and the actual secondary steam output when the feed flow rate or salt concentration fluctuates, resulting in a significant decrease in heat transfer efficiency and a significant increase in system energy consumption.

[0003] In existing technologies, the operating pressure of vacuum evaporators is usually set based on the saturated vapor pressure of pure water, without compensating for the boiling point rise effect of high-salt waste liquid. This results in the actual heat transfer temperature difference deviating from the design value, unstable evaporation intensity, and difficulty in ensuring the concentration ratio. Consequently, it is impossible to dynamically couple and optimize according to real-time operating conditions. Under wide load fluctuation conditions, the system's operational stability is poor, the quality of feed to the crystallization section fluctuates greatly, and the solid-liquid separation effect is unstable, which restricts the overall efficiency of high-salt waste liquid resource utilization treatment. Summary of the Invention

[0004] The main objective of this invention is to provide a method and equipment for treating high-salt and high-concentration waste liquid using a low-temperature evaporator. This invention solves the technical problems of decreased heat transfer efficiency and operational instability of existing MVR evaporation systems under variable load conditions by adaptively and collaboratively controlling the speed of the centrifugal steam compressor and the vacuum degree of the vacuum evaporator. This enables the stable resource-based treatment of high-salt waste liquid and improves the robustness and energy efficiency of the process.

[0005] To achieve the above objectives, the present invention provides a method for treating high-salt, high-concentration waste liquid using a low-temperature evaporator, comprising the following steps:

[0006] The feed flow rate and feed salt concentration of the waste liquid were detected, and the predicted value of secondary steam production was calculated.

[0007] The target compressor speed of the centrifugal steam compressor is calculated based on the predicted secondary steam output, and the target vacuum level of the vacuum evaporator is calculated based on the feed salt concentration.

[0008] Adjust the centrifugal steam compressor to its first operating speed in real time until the compressor reaches its target speed, and simultaneously adjust the vacuum evaporator to its first operating vacuum level in real time until the vacuum level reaches its target value.

[0009] The concentrated liquid discharged from the vacuum evaporator is subjected to supersaturated crystallization to obtain a crystal slurry, and the crystal slurry is subjected to solid-liquid separation to obtain a solid salt product and a mother liquor.

[0010] Optionally, in a first implementation of the first aspect of the present invention, detecting the feed flow rate and feed salt concentration of the feed waste liquid and calculating the predicted value of secondary steam production includes:

[0011] Detect the feed flow rate and feed salt concentration of the wastewater;

[0012] The waste liquid density is obtained by adding the waste liquid density benchmark value to the result of multiplying the feed salt concentration by the density ratio coefficient.

[0013] Based on the feed flow rate, the waste liquid density, and the feed salt concentration, the amount of water evaporated is obtained by dividing the difference between the feed salt concentration and the target concentrated salt concentration by the target concentrated salt concentration and then multiplying it by the product of the feed flow rate and the waste liquid density.

[0014] The predicted value of secondary steam production is obtained by multiplying the evaporation water volume by the preset flash loss correction coefficient.

[0015] Optionally, in a second implementation of the first aspect of the present invention, calculating the target compressor speed of the centrifugal steam compressor based on the predicted secondary steam output value, and calculating the target vacuum level of the vacuum evaporator based on the feed salt concentration, includes:

[0016] Using the reference steam processing capacity under the rated operating conditions of the centrifugal steam compressor as the set reference steam capacity, the difference between the predicted value of the secondary steam output and the set reference steam capacity is obtained to get the steam output difference value. The steam output difference value is multiplied by the preset speed adjustment coefficient to obtain the speed adjustment amount.

[0017] The compressor target speed is obtained by superimposing the speed adjustment amount with the set reference speed corresponding to the rated operating condition.

[0018] The boiling point elevation is calculated based on the feed salt concentration, and the target vacuum level of the vacuum evaporator is calculated based on the boiling point elevation and the preset heat transfer temperature difference.

[0019] Optionally, in a third implementation of the first aspect of the present invention, calculating the boiling point elevation based on the feed salt concentration, and calculating the target vacuum level of the vacuum evaporator based on the boiling point elevation and a preset heat transfer temperature difference, includes:

[0020] Substitute the feed salt concentration into the boiling point elevation function, and sum the product of the first-order coefficient of the salt concentration and the product of the second-order coefficient of the salt concentration and the square of the feed salt concentration to obtain the boiling point elevation value.

[0021] The target saturation temperature of pure water is obtained by subtracting the boiling point rise and the preset heat transfer temperature difference from the compressed steam temperature, and the target vacuum value of the vacuum evaporator is calculated based on the target saturation temperature of pure water.

[0022] Optionally, in a fourth implementation of the first aspect of the present invention, the target saturation temperature of pure water is obtained by subtracting the boiling point rise and the preset heat transfer temperature difference from the compressed steam temperature, and the target vacuum degree of the vacuum evaporator is calculated based on the target saturation temperature of pure water, including:

[0023] The target saturation temperature of pure water is obtained by subtracting the boiling point rise from the compressed steam temperature and the sum of the preset heat transfer temperature difference. The target saturation temperature of pure water is then substituted into the Antoni equation for forward solution to obtain the initial pressure value.

[0024] The initial pressure value is substituted back into the Antoni equation to calculate the pure water saturation temperature. The difference between the calculated pure water saturation temperature and the target pure water saturation temperature is used to obtain the temperature deviation value. If the temperature deviation value exceeds the convergence threshold, the pressure value is corrected according to the deviation direction and the solution is solved again in the forward direction. This process is repeated until the temperature deviation value converges to within the convergence threshold to obtain the target vacuum value.

[0025] Optionally, in a fifth implementation of the first aspect of the present invention, adjusting the real-time first operating speed of the centrifugal steam compressor until the target speed of the compressor is reached, and simultaneously adjusting the real-time first operating vacuum of the vacuum evaporator until the target vacuum value is reached, includes:

[0026] The target output frequency of the inverter is calculated based on the target speed and number of pole pairs of the compressor. The motor frequency of the centrifugal steam compressor is adjusted in an S-curve acceleration manner until the difference between the real-time first operating speed fed back by the encoder and the target speed of the compressor converges to within the speed tolerance.

[0027] The vacuum degree deviation value is obtained by subtracting the real-time first operating vacuum degree of the vacuum evaporator from the target vacuum degree value collected by the vacuum degree sensor. The product of the vacuum degree deviation value and the valve opening adjustment coefficient is superimposed on the reference opening to adjust the vacuum pump inlet opening of the electric regulating valve until the difference between the first operating vacuum degree and the target vacuum degree value converges to within the pressure tolerance.

[0028] Optionally, in a sixth implementation of the first aspect of the present invention, the method for treating high-salt, high-concentration waste liquid using a low-temperature evaporator further includes:

[0029] The secondary steam temperature, secondary steam pressure, actual secondary steam flow rate, and liquid phase temperature inside the evaporator at the outlet of the vacuum evaporator are collected.

[0030] The heat transfer efficiency index value is obtained by dividing the difference between the secondary steam temperature and the liquid phase temperature in the evaporator by the preset heat transfer temperature difference. The heat transfer efficiency index value is then subtracted from the target heat transfer efficiency to obtain the heat transfer efficiency deviation value. The product of the heat transfer efficiency deviation value and the speed compensation coefficient is then added to the first operating speed to obtain the second operating speed.

[0031] The difference between the actual secondary steam flow rate and the predicted secondary steam output is divided by the predicted secondary steam output to obtain the steam output deviation value. The product of the steam output deviation value and the vacuum adjustment coefficient is then added to the first operating vacuum level to obtain the second operating vacuum level.

[0032] Optionally, in a seventh implementation of the first aspect of the present invention, a heat transfer efficiency index value is obtained by dividing the difference between the secondary steam temperature and the liquid phase temperature in the evaporator by a preset heat transfer temperature difference; a heat transfer efficiency deviation value is obtained by subtracting the heat transfer efficiency index value from the target heat transfer efficiency; and a second operating speed is obtained by adding the product of the heat transfer efficiency deviation value and the speed compensation coefficient to the first operating speed.

[0033] The heat transfer efficiency index value is obtained by dividing the difference between the secondary steam temperature and the liquid phase temperature in the evaporator by the preset heat transfer temperature difference. The heat transfer efficiency index value is then compared with the target heat transfer efficiency to obtain the heat transfer efficiency deviation value.

[0034] The speed compensation amount is obtained by multiplying the product of the ratio of the heat transfer efficiency deviation value to the target heat transfer efficiency and the ratio of the preset heat transfer temperature difference to the reference heat transfer temperature difference, and then multiplying it by the speed compensation reference coefficient. The speed compensation amount is then added to the first operating speed to obtain the second operating speed.

[0035] Optionally, in an eighth implementation of the first aspect of the present invention, the concentrated liquid discharged from the vacuum evaporator is subjected to supersaturated crystallization to obtain a crystal slurry, and the crystal slurry is subjected to solid-liquid separation to obtain a solid salt product and a mother liquor, comprising:

[0036] The concentrated liquid discharged from the vacuum evaporator is input into the DTB type forced circulation crystallizer. When the TDS detection value of the concentrated liquid reaches the crystallization trigger threshold, the concentrated liquid is driven by the circulation pump to circulate along the guide tube at a set circulation flow rate to perform supersaturated crystallization and obtain crystal slurry.

[0037] The crystal slurry is fed into a horizontal screw discharge centrifuge, and solid-liquid separation is performed on the crystal slurry at a preset speed and separation factor to obtain solid salt product and mother liquor.

[0038] The present invention also provides a device for treating high-salt, high-concentration waste liquid using a low-temperature evaporator, comprising:

[0039] The detection module is used to detect the feed flow rate and feed salt concentration of the feed waste liquid and calculate the predicted value of secondary steam production.

[0040] The calculation module is used to calculate the target compressor speed of the centrifugal steam compressor based on the predicted value of the secondary steam output, and to calculate the target vacuum value of the vacuum evaporator based on the feed salt concentration.

[0041] The adjustment module is used to adjust the real-time first operating speed of the centrifugal steam compressor until the target speed of the compressor is reached, and to simultaneously adjust the real-time first operating vacuum of the vacuum evaporator until the target vacuum value is reached.

[0042] The crystallization module is used to supersaturate the concentrated liquid discharged from the vacuum evaporator to obtain crystal slurry, and to perform solid-liquid separation on the crystal slurry to obtain solid salt product and mother liquor.

[0043] In summary, this invention solves the technical problems of decreased heat transfer efficiency and operational instability in existing MVR evaporation systems under variable load conditions by adaptively and collaboratively controlling the dual parameters of centrifugal steam compressor speed and vacuum evaporator degree. In the feed detection stage, the feed salt concentration and feed flow rate are converted into accurate predicted values ​​of secondary steam production by combining the waste liquid density relationship with material balance, providing reliable input for subsequent dual-parameter calculations. In the speed calculation stage, based on a linear correlation model calibrated from the compressor performance curve, the deviation in secondary steam production is directly mapped to the speed adjustment, achieving dynamic matching between the compressor's processing capacity and the actual evaporation load. In the vacuum degree calculation stage, the boiling point elevation relationship between the primary and secondary terms of salt concentration is introduced, combined with the Antoni equation iterative convergence algorithm, to accurately correlate the target vacuum degree value with the actual boiling point characteristics of the waste liquid, eliminating the systematic deviation of the heat transfer temperature difference under a fixed vacuum degree setting. In the execution stage, the inverter S-curve acceleration adjustment and the closed-loop control of the electric regulating valve opening operate in parallel, ensuring the stability and accuracy of both parameters reaching the target values. In the feedback correction stage, the heat transfer efficiency deviation value drives speed compensation, and the steam production deviation value drives vacuum fine-tuning, forming a dual closed-loop real-time correction mechanism that enables the system to maintain a high-efficiency heat transfer state under wide flow fluctuation conditions. The concentrate is subjected to forced circulation crystallization triggered by the TDS threshold and horizontal spiral centrifugation separation, achieving stable resource utilization of high-salt waste liquid. Attached Figure Description

[0044] Figure 1 This is a schematic diagram of the steps of a method for treating high-salt, high-concentration waste liquid using a low-temperature evaporator according to an embodiment of the present invention;

[0045] Figure 2 This is a structural block diagram of a low-temperature evaporator for treating high-salt, high-concentration waste liquid in an embodiment of the present invention.

[0046] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0047] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0048] Reference Figure 1 This embodiment provides a method for treating high-salt, high-concentration waste liquid using a low-temperature evaporator, including the following steps:

[0049] S1, detect the feed flow rate and feed salt concentration of the feed waste liquid and calculate the predicted value of secondary steam production;

[0050] S2, calculate the target compressor speed of the centrifugal steam compressor based on the predicted value of secondary steam production, and calculate the target vacuum value of the vacuum evaporator based on the feed salt concentration;

[0051] S3, adjust the real-time first operating speed of the centrifugal steam compressor until the compressor target speed is reached, and simultaneously adjust the real-time first operating vacuum of the vacuum evaporator until the vacuum target value is reached;

[0052] S4. The concentrated liquid discharged from the vacuum evaporator is subjected to supersaturated crystallization to obtain crystal slurry, and the crystal slurry is subjected to solid-liquid separation to obtain solid salt product and mother liquor.

[0053] In one example, the feed flow rate and feed salt concentration of the feed waste liquid are detected, and the predicted secondary steam production is calculated, including:

[0054] Detect the feed flow rate and feed salt concentration of the wastewater;

[0055] The waste liquid density is obtained by adding the waste liquid density benchmark value to the result of multiplying the feed salt concentration by the density ratio coefficient.

[0056] Based on the feed flow rate, waste liquid density, and feed salt concentration, the amount of water evaporated is obtained by dividing the difference between the feed salt concentration and the target concentrated salt concentration by the target concentrated salt concentration, and then multiplying it by the product of the feed flow rate and the waste liquid density.

[0057] Multiply the evaporation water volume by the preset flash loss correction factor to obtain the predicted value of secondary steam production.

[0058] In this example, the physicochemical parameters of the feed waste liquid, including feed flow rate and feed salt concentration, are monitored in real time. The feed flow rate is acquired using a high-precision electromagnetic flowmeter installed on the feed pipeline, which outputs a 4-20mA standard signal with a sampling period of 100 milliseconds. The feed salt concentration is acquired in real time using an online conductivity meter with a measurement range covering 0-100,000 μS / cm, and determined using an empirical fitting formula. The conductivity values ​​were converted to salt concentration values ​​(in mg / L), and an empirical fitting formula was obtained by fitting the formula to a large number of laboratory waste liquid samples. The goodness of fit R0 was calculated. 2 =0.998. Set the baseline value for the waste liquid density as ρ0 = 1.0 g / cm³. 3 Simultaneously, a density proportionality coefficient k = 0.000756, directly proportional to the salt concentration, is set. The waste liquid density baseline value ρ0 is then compared with the feed salt concentration C. in Adding the results of multiplying by the density proportionality coefficient k, we get the waste liquid density ρ = ρ0 + k × C in Its unit is g / cm³ 3 This method is suitable for chloride-sulfate type wastewater systems with TDS concentrations ranging from 35,000 to 80,000 mg / L. After calculating the waste liquid density, the parameters are based on the feed flow rate Q, waste liquid density ρ, and feed salt concentration C. in Estimate the amount of water that needs to be evaporated to achieve the target concentrated salt concentration C. out The system design setpoint is 280,000 mg / L. The formula for calculating the evaporation rate W is W = Q × (C...). in -C out ) C in -C out This indicates the degree of deviation between the original salt concentration and the target concentration. The ratio of the difference to the target concentration reflects the required evaporation ratio. Multiplying this by the product of the feed flow rate and density yields the volume of water that the system needs to evaporate per unit time. The evaporation volume needs to account for losses caused by flash evaporation, droplet carryover, and heat transfer lag during system operation. Therefore, a preset correction coefficient α = 0.97 is introduced. The value of α was obtained through multiple rounds of experiments. The corrected predicted secondary steam production value is G. 蒸汽 =α×W, the predicted steam production result obtained by multiplying the evaporation water volume by the correction coefficient is used as the input for the coordinated control of compressor speed regulation and vacuum degree.

[0059] In one example, the target compressor speed of the centrifugal steam compressor is calculated based on the predicted secondary steam output, and the target vacuum level of the vacuum evaporator is calculated based on the feed salt concentration, including:

[0060] Using the reference steam processing capacity under the rated operating conditions of the centrifugal steam compressor as the set reference steam capacity, the difference between the predicted value of secondary steam production and the set reference steam capacity is obtained. The steam production difference is then multiplied by the preset speed adjustment coefficient to obtain the speed adjustment amount.

[0061] The compressor target speed is obtained by superimposing the speed adjustment amount with the set reference speed corresponding to the rated operating conditions;

[0062] The boiling point elevation is calculated based on the feed salt concentration, and the target vacuum level of the vacuum evaporator is calculated based on the boiling point elevation and the preset heat transfer temperature difference.

[0063] In this example, the compressor's design capacity under rated operating conditions is used as the baseline setting parameter, i.e., the baseline steam quantity is set. This value is set to 4.5 t / h, corresponding to the set reference speed. The speed is 1100 rpm. Real-time predicted secondary steam production value. The data comes from the flow rate and salt concentration calculation module, and the calculation method is the product of the evaporation rate and the correction factor. ,in This is an empirical correction factor. The required evaporation water volume is calculated. The difference between the predicted secondary steam production and the set baseline steam production is obtained as the steam production difference. The difference represents the deviation of the system's current load from the design conditions, serving as the basis for speed control. The output difference is used... With the preset speed adjustment coefficient Multiply to obtain the speed adjustment amount. ,in This is a constant determined after performance curve fitting and safety factor conversion, and its value is taken as 95 rpm·h / t. For example, if t / h, then (5.18-4.5)=64.6 rpm. The target operating speed is obtained by superimposing the speed adjustment amount with the reference speed. The target operating speed is used as the target input for the inverter's adjustment frequency, and is smoothly adjusted at a rate of 50 rpm / s using an S-shaped acceleration / deceleration curve to prevent sudden shocks from causing mechanical stress on the compressor impeller. Simultaneously, to achieve efficient heat energy utilization, the boiling point elevation of the waste liquid inside the evaporator is calculated based on the current feed salt concentration. This value reflects the effect of salt concentration on the vapor-liquid phase equilibrium temperature, and the calculation formula is as follows: ,in The feed salt concentration is expressed in mg / L. This formula is an empirical fit and is applicable to common high-salinity wastewater systems. After obtaining the boiling point elevation, the optimal heat transfer temperature difference required to maintain the system is considered. Calculate the target vacuum level. The optimal heat transfer temperature difference is an empirical function determined by the salt concentration, expressed as follows: ,in This represents the actual salt concentration inside the evaporator, slightly higher than... It can be accessed through Approximate estimation. By consulting the water vapor property table, and setting the initial vacuum level... Obtaining the boiling point of pure water The actual boiling point of the waste liquid is obtained by adding the boiling point elevation value to the boiling point elevation value. ,by °C to estimate compressed steam temperature and calculate heat transfer temperature difference and the target heat transfer temperature difference If a deviation exists, the vacuum degree is iterated according to the following modified model: The process is iterated repeatedly until the heat transfer temperature difference approaches the optimal value, thus obtaining the target vacuum level. .

[0064] In one example, the boiling point elevation is calculated based on the feed salt concentration, and the target vacuum level of the vacuum evaporator is calculated based on the boiling point elevation and a preset heat transfer temperature difference, including:

[0065] Substitute the feed salt concentration into the boiling point elevation function, and sum the product of the first-order coefficient of the salt concentration and the product of the second-order coefficient of the salt concentration and the square of the feed salt concentration to obtain the boiling point elevation value.

[0066] The target saturation temperature of pure water is obtained by subtracting the boiling point rise and the preset heat transfer temperature difference from the compressed steam temperature, and the target vacuum value of the vacuum evaporator is calculated based on the target saturation temperature of pure water.

[0067] In this example, the feed salt concentration Substituting the empirical function model of boiling point elevation as input variables, the model adopts a quadratic polynomial form, specifically expressed as follows: ,in, The coefficient of the first-order term of salt concentration is... The coefficient of the quadratic term of salt concentration. The unit is mg / L, and the coefficient units have been normalized for direct compatibility with temperature (°C). In actual calculations, the feed salt concentration is substituted into the coefficients of the first-order term and multiplied to obtain the product value of the first-order term. Then, the square of the feed salt concentration was substituted into the coefficients of the quadratic term to obtain... Add the two results together to obtain the boiling point elevation. This represents the degree of boiling point rise relative to pure water at the current salt concentration. To deduce the target saturation temperature under pure water conditions, a backward analysis is performed, combining the theoretical outlet temperature of the compressed steam and the heat transfer requirements. The temperature of the compressed steam... The temperature difference between the set value (slightly higher than the boiling point of the liquid phase) and the liquid phase is the actual heat transfer temperature difference. To achieve optimal heat transfer, the heat transfer temperature difference must be equal to the preset optimal heat transfer temperature difference. Therefore, by subtracting the sum of the boiling point rise and the optimal heat transfer temperature difference from the current compressed steam temperature, the following relationship can be constructed: T sat,目标 This is the target pure water saturation temperature, representing the saturated temperature of the evaporator's internal gas-liquid coexistence required to achieve a closed heat transfer temperature difference in the absence of dissolved salts. Based on the target saturation temperature, the corresponding saturation pressure value can be derived by consulting standard water vapor property tables or using interpolation methods. This is the target vacuum level that the vacuum evaporator should maintain under current operating conditions.

[0068] In one example, the target saturation temperature of pure water is obtained by subtracting the boiling point elevation and the preset heat transfer temperature difference from the compressed steam temperature. Based on this target saturation temperature, the target vacuum level of the vacuum evaporator is calculated, including:

[0069] The target saturation temperature of pure water is obtained by subtracting the boiling point rise from the compressed steam temperature and the sum of the preset heat transfer temperature difference. The target saturation temperature of pure water is then substituted into the Antoni equation for forward solution to obtain the initial pressure value.

[0070] The initial pressure value is substituted back into the Antoni equation to calculate the pure water saturation temperature. The difference between the calculated pure water saturation temperature and the target pure water saturation temperature is used to obtain the temperature deviation value. If the temperature deviation value exceeds the convergence threshold, the pressure value is corrected according to the deviation direction and the solution is solved again in the forward direction. This process is repeated until the temperature deviation value converges to within the convergence threshold, and the target vacuum value is obtained.

[0071] In this example, the temperature of the compressed steam is used. Starting from this point, subtract the boiling point elevation caused by the concentration of dissolved salts. and the preset optimal heat transfer temperature difference The target saturation temperature under pure water conditions was calculated. ,Right now By substituting the target saturation temperature into the Antoni equation and solving it in the forward direction, the corresponding initial saturation pressure value can be obtained. The general form of the Antoni equation is:

[0072]

[0073] in Pressure (unit: mmHg or kPa, depending on the parameters) Temperature (in °C) , , Let be the Antoine constant for water vapor. (Using...) After substituting the values ​​into the equation to obtain the initial pressure value, to verify that this pressure numerically corresponds to the target temperature, the obtained initial pressure... Substituting back into the Antoni equation, the corresponding saturation temperature is calculated again using inverse calculation. The calculated temperature is then compared with the set target saturation temperature, and the difference is calculated. If the temperature deviation Exceeding the preset convergence threshold (e.g.) This indicates that the current pressure does not accurately correspond to the target thermodynamic conditions. Therefore, the pressure value is corrected according to the direction of the deviation: if the calculated temperature is too high, it means the initial pressure is too high, and the pressure value is reduced; otherwise, the pressure is increased. The correction method uses a simple iterative method or Newton's correction method. After each adjustment, the pressure is substituted back into the Antoni equation for a forward solution to obtain a new temperature value and update the deviation, forming a cyclic iterative process. The iteration continues until the temperature deviation value is reached. The convergence pressure value is the target vacuum level, calculated by converging until it does not exceed the threshold. .

[0074] After obtaining the target vacuum value, the process also includes: substituting the target vacuum value into the Antoni equation for a forward solution to obtain the evaporation saturation temperature of the vacuum evaporator under the current target vacuum value; subtracting the preset feed temperature difference from the evaporation saturation temperature to obtain the preheating target temperature; calculating the difference between the preheating target temperature and the actual feed temperature collected by the Pt100 temperature sensor to obtain the preheating temperature deviation value; and superimposing the product of the preheating temperature deviation value and the preheating valve adjustment coefficient with the reference opening of the heating steam inlet valve of the plate heat exchanger to adjust the opening of the heating steam inlet valve until the difference between the actual feed temperature and the preheating target temperature converges to within the temperature tolerance.

[0075] In one example, the centrifugal steam compressor's real-time first operating speed is adjusted until the compressor's target speed is reached, and the vacuum evaporator's real-time first operating vacuum level is simultaneously adjusted until the target vacuum level is reached, including:

[0076] The target output frequency of the inverter is calculated based on the target speed of the compressor and the number of pole pairs. The motor frequency of the centrifugal steam compressor is adjusted in an S-curve acceleration manner until the difference between the real-time first operating speed fed back by the encoder and the target speed of the compressor converges to within the speed tolerance.

[0077] The vacuum deviation value is obtained by subtracting the real-time first operating vacuum value of the vacuum evaporator from the target vacuum value using a vacuum sensor. The product of the vacuum deviation value and the valve opening adjustment coefficient is then superimposed on the reference opening to adjust the vacuum pump inlet opening of the electric regulating valve until the difference between the first operating vacuum value and the target vacuum value converges to within the pressure tolerance.

[0078] In this example, in the compressor speed control process, the compressor target speed is... This requires controlling the motor by outputting a frequency from a frequency converter, and the conversion relationship between frequency and speed depends on the number of pole pairs of the motor. The calculation formula is: ,in The target output frequency of the frequency converter, in Hz. This represents the number of pole pairs of the compressor motor, which can be 1 or 2, determined based on the actual configuration parameters. After obtaining the target frequency, the control system uses an S-curve acceleration method to dynamically adjust the motor frequency. S-curve control ensures a smooth transition during frequency rise, preventing mechanical shock to the compressor impeller due to sudden frequency changes, thus improving equipment lifespan and operational stability. During the frequency change of the inverter output, the encoder monitors the operating speed of the compressor shaft in real time. and the set target speed The difference is calculated to obtain the speed deviation. The speed deviation value is used as the feedback reference for frequency adjustment until... When the speed converges to within the allowable tolerance range (e.g., ±5 rpm), it indicates that the motor has achieved the desired speed response, and the compressed steam volumetric flow rate matches the actual load. Simultaneously, in the pressure regulation stage of the vacuum evaporator, the initial operating vacuum level inside the evaporator is collected in real time by a vacuum sensor. And compared with the target vacuum value obtained earlier through thermodynamic parameters. By comparing the values, the pressure deviation was calculated. This serves as the input for the next control command. Since the vacuum level adjustment of the evaporator depends on the pumping capacity of the vacuum pump, the specific mechanism involves adjusting the opening of the electrically operated regulating valve at the vacuum pump inlet. The valve is controlled using a proportional control model, and the adjustment formula is as follows: ,in The reference opening degree for stable operation of the vacuum pump is set to 45%. This is the valve opening adjustment coefficient, expressed as a percentage per kPa, for example, 0.8% / kPa. According to the formula above, if the current pressure is too high, i.e. ,but This leads to the opening degree Increasing the valve opening increases the pumping rate to reduce evaporator pressure; conversely, decreasing it decreases the opening to reduce the pumping rate. When the adjusted opening is actuated by the actuator and applied to the electric valve, the evaporator pressure changes accordingly and is monitored and updated by the vacuum sensor, feeding back to the control system for the next iteration. This process continues until… Once the pressure converges to within the preset tolerance range (e.g., ±0.1 kPa), it is considered that the current vacuum level has met the set thermodynamic operation requirements, and the system enters the steady-state operation stage.

[0079] In one example, the method for treating high-salt, high-concentration waste liquid using a low-temperature evaporator also includes:

[0080] Collect the secondary steam temperature, secondary steam pressure, actual secondary steam flow rate, and liquid phase temperature inside the evaporator at the outlet of the vacuum evaporator;

[0081] The heat transfer efficiency index value is obtained by dividing the difference between the secondary steam temperature and the liquid phase temperature in the evaporator by the preset heat transfer temperature difference. The heat transfer efficiency index value is then subtracted from the target heat transfer efficiency to obtain the heat transfer efficiency deviation value. The product of the heat transfer efficiency deviation value and the speed compensation coefficient is then added to the first operating speed to obtain the second operating speed.

[0082] The difference between the actual secondary steam flow rate and the predicted secondary steam output is divided by the predicted secondary steam output to obtain the steam output deviation value. The product of the steam output deviation value and the vacuum degree adjustment coefficient is added to the first operating vacuum degree to obtain the second operating vacuum degree.

[0083] In this example, the outlet temperature of the secondary steam is collected by thermocouples and pressure transmitters deployed in the outlet pipe of the vacuum evaporator. Export pressure Then, an immersion temperature sensor installed near the liquid level collects the liquid phase temperature of the waste liquid inside the evaporator. At the same time, the actual flow rate of the secondary steam is obtained by combining the vortex flow meter installed on the pipeline. After data collection, the actual heat transfer temperature difference is calculated based on the difference between the hot and cold end temperatures, and then divided by the set optimal heat transfer temperature difference. The heat transfer efficiency index value is obtained. ,Right now:

[0084]

[0085] This value reflects the degree to which the actual heat transfer temperature difference is achieved compared to the theoretical optimal value; ideally, it should be 1.0. The calculated value... The difference between the value and the target value (set to 1.0) yields the heat transfer efficiency deviation value. This deviation value serves as the basis for correcting the operating status of the steam compressor. Based on the sign of the deviation, it determines whether to increase the compression ratio to increase the heat transfer temperature difference or decrease the compression ratio to lower the hot-end temperature. The heat transfer efficiency deviation value is then multiplied by a preset speed compensation coefficient. The speed compensation coefficient has units of rpm and is dimensionless. Its value is derived from actual debugging experience or control algorithm models; for example, it might be set to 30 rpm corresponding to a 5% deviation. The product result is the value to be added to the current first operating speed. Speed ​​correction amount The updated second operating speed was obtained. The rotational speed is output in real time by the control system to the frequency converter, achieving closed-loop feedback control of the compressor speed. Simultaneously, to ensure that the steam load output level is consistent with the theoretical prediction, error monitoring and adaptive vacuum correction are performed on the secondary steam flow rate. The theoretical secondary steam output prediction value is known. The relative deviation between the actual flow and the predicted value is defined as:

[0086]

[0087] Steam production deviation reflects the actual performance of the system's current evaporation intensity. If the actual evaporation is higher than predicted, it indicates that evaporation is stronger than expected; conversely, if the actual evaporation is lower than predicted, it indicates that evaporation is weaker than expected. Vacuum degree adjustment coefficient Multiply to obtain the pressure correction amount. This coefficient, expressed in kPa / percentage, represents the pressure correction required for a given unit of steam production deviation. This pressure correction is then added to the current initial operating vacuum level. The second operating vacuum level was obtained. The control system updates the opening degree of the electric regulating valve or the pumping speed command of the vacuum pump in real time, adjusting the absolute pressure value inside the evaporator to converge towards the target evaporation intensity.

[0088] The process involves superimposing the product of the heat transfer efficiency deviation and the speed compensation coefficient onto the first operating speed, and superimposing the product of the steam production deviation and the vacuum adjustment coefficient onto the first operating vacuum. It also includes: within each control cycle, subtracting the actual heat transfer efficiency index value collected after execution at the second operating speed from the target heat transfer efficiency to obtain the speed-corrected residual deviation value; dividing the product of the speed-corrected residual deviation value and the current speed compensation coefficient by the sum of the square norm and regularization factor of the current input vector to obtain the speed compensation coefficient correction amount; superimposing the speed compensation coefficient correction amount onto the current speed compensation coefficient to obtain the updated speed compensation coefficient; similarly, with the second operating speed... The residual value of the actual steam output deviation after the second operating vacuum is updated according to the same projection update rule to obtain the updated vacuum adjustment coefficient. The updated speed compensation coefficient and the updated vacuum adjustment coefficient are stored in the coefficient history array. The average value of the coefficients within the sliding window is used as the speed compensation coefficient and vacuum adjustment coefficient for the next control cycle. This process is repeated until the coefficient changes in two adjacent control cycles converge to within the coefficient stability threshold. The converged speed compensation coefficient is used to compensate for the heat transfer efficiency deviation to obtain the second operating speed. The converged vacuum adjustment coefficient is used to correct the steam output deviation to obtain the second operating vacuum.

[0089] After obtaining the second operating speed and the second operating vacuum, the process also includes: comparing the measured TDS value of the concentrated liquid at the outlet of the vacuum evaporator with the feed salt concentration using an online conductivity meter to obtain the actual concentration ratio; subtracting the target concentration ratio from the actual concentration ratio to obtain the concentration ratio deviation value; multiplying the concentration ratio deviation value by the feed flow rate adjustment coefficient to obtain the feed flow rate correction amount; adding the feed flow rate correction amount to the current feed flow rate; adjusting the output frequency of the feed pump inverter to obtain the corrected feed flow rate; multiplying the concentration ratio deviation value by the vacuum degree compensation coefficient to obtain the vacuum degree compensation amount; adding the vacuum degree compensation amount to the vacuum degree target value to obtain the corrected vacuum degree target value; replacing the original vacuum degree target value with the corrected vacuum degree target value; and re-triggering the electric regulating valve to adjust the opening to within the pressure tolerance.

[0090] In one example, the heat transfer efficiency index value is obtained by dividing the difference between the secondary steam temperature and the liquid phase temperature inside the evaporator by the preset heat transfer temperature difference. The difference between the heat transfer efficiency index value and the target heat transfer efficiency is used to obtain the heat transfer efficiency deviation value. The product of the heat transfer efficiency deviation value and the speed compensation coefficient is added to the first operating speed to obtain the second operating speed, including:

[0091] The heat transfer efficiency index value is obtained by dividing the difference between the secondary steam temperature and the liquid phase temperature in the evaporator by the preset heat transfer temperature difference. The heat transfer efficiency index value is then compared with the target heat transfer efficiency to obtain the heat transfer efficiency deviation value.

[0092] The speed compensation amount is obtained by multiplying the product of the ratio of the heat transfer efficiency deviation value to the target heat transfer efficiency and the ratio of the preset heat transfer temperature difference to the reference heat transfer temperature difference, and then multiplying it by the speed compensation reference coefficient. The speed compensation amount is then added to the first operating speed to obtain the second operating speed.

[0093] In this example, the secondary steam temperature at the evaporator outlet is collected in real time. Liquid phase temperature of waste liquid in evaporator The difference between the two can be expressed as the actual heat transfer temperature difference of the current system, i.e. Then, using the preset optimal heat transfer temperature difference As a standard, the heat transfer efficiency index value is obtained by dividing the actual temperature difference by the optimal temperature difference. , expressed as:

[0094]

[0095] The index value reflects the degree to which the current heat transfer capacity has achieved its theoretical optimum; ideally, it should be close to the target value of 1.0. The heat transfer efficiency index value is compared with the set target heat transfer efficiency. Subtracting (set to 1.0) yields the heat transfer efficiency deviation value. one The deviation characterizes the degree of discrepancy between the current thermodynamic state and the ideal heat transfer conditions. The deviation is converted into a speed compensation variable with operating condition adaptability. Two proportional terms are constructed, representing the ratio of the heat transfer efficiency deviation to the target heat transfer efficiency. and the current preset heat transfer temperature difference Relative to the system reference heat transfer temperature difference (e.g., set to 15°C) ratio Multiplying the two ratios above yields a comprehensive adjustment factor, which can be adjusted in intensity based on the system's current operating efficiency and design heat load. This comprehensive adjustment factor is then compared with the set speed compensation reference coefficient. Multiply to obtain the speed compensation amount. Its complete expression is:

[0096]

[0097] in The speed gain coefficient, set to 30 rpm, represents the recommended adjustment range under a 5% heat transfer deviation and a reference heat load. Increase to the current first operating speed The updated second operating speed was obtained. The second operating speed is adjusted by the frequency output of the inverter, which affects the compressor motor to achieve dynamic increase or decrease compensation of the actual steam compression capacity and stably maintain the optimal temperature difference between the hot and cold ends of the evaporator.

[0098] In one example, the concentrate discharged from the vacuum evaporator is subjected to supersaturated crystallization to obtain a crystal slurry, which is then subjected to solid-liquid separation to obtain a solid salt product and a mother liquor, including:

[0099] The concentrated liquid discharged from the vacuum evaporator is fed into the DTB type forced circulation crystallizer. When the TDS detection value of the concentrated liquid reaches the crystallization trigger threshold, the circulating pump drives the concentrated liquid to circulate along the guide tube at the set circulation flow rate to perform supersaturated crystallization of the concentrated liquid and obtain crystal slurry.

[0100] The crystal slurry is fed into a horizontal screw discharge centrifuge, and solid-liquid separation is performed on the crystal slurry at a preset speed and separation factor to obtain solid salt products and mother liquor.

[0101] In this example, the high-concentration waste liquid discharged from the bottom of the vacuum evaporator is stably introduced into a DTB-type forced circulation crystallizer through a level control valve. The crystallizer is a vertical cylindrical structure with a coaxially mounted guide tube inside to create a stable internal flow circulation path. An axial-flow stirring paddle system is also provided to enhance the fluid turbulence intensity, ensuring uniform distribution of suspended matter and preventing crystal deposition. When the concentrated liquid entering the crystallizer is monitored by an online TDS detection device, its total dissolved solids concentration reaches the set crystallization trigger threshold, for example, 250,000 to 280,000 mg / L. This crystallization trigger threshold is close to the saturation solubility of many inorganic salts (such as NaCl and Na2SO4). At this point, the system automatically determines that the crystallization conditions are met and starts the crystallization circulation pump with a set circulation rate. The concentrated liquid is drawn from the bottom of the crystallizer and heated to the 77-80°C range by an external heater, and then introduced into the crystallizer through the guide tube, achieving high-speed forced circulation within a closed path. Heating raises the liquid temperature, but localized cooling and micro-flash evaporation occur due to pressure release and circulating agitation, resulting in a highly supersaturated state in the concentrate. This promotes the precipitation of dissolved salts in a nucleation-growth mode, forming a solid-liquid coexisting slurry system. Once the slurry concentration and crystal particle size meet the process requirements, the slurry is continuously or intermittently discharged from the side outlet of the crystallizer and fed into a horizontal screw discharge centrifuge for solid-liquid separation. The centrifuge adopts a horizontal cylindrical structure and is equipped with a differential speed-controlled screw conveyor system to achieve continuous feeding. Its design speed is 2800 rpm, corresponding to a separation factor of up to 1850, causing the suspended crystals to be rapidly thrown outward under centrifugal force and conveyed along the screw to the discharge end. During the separation process, the solid phase is a crystalline salt product with a water content that can be stably controlled below 3%, which can meet the process requirements for direct packaging or further drying. The liquid phase is the mother liquor, which still contains some uncrystallized salt and residual impurities. It has high conductivity, TDS and COD values ​​and is refluxed to the crystallizer inlet or sent back to the front-end evaporation unit for further concentration.

[0102] Before the concentrated liquid discharged from the vacuum evaporator is input into the DTB-type forced circulation crystallizer, the process includes: substituting the feed salt concentration and the liquid phase temperature inside the evaporator into the solubility relationship function, and summing the product of the solubility reference value, the solubility temperature coefficient, and the liquid phase temperature inside the evaporator, and the solubility concentration coefficient and the feed salt concentration to obtain the salt solubility under the current operating conditions; multiplying the salt solubility by the preset supersaturation coefficient to obtain the crystallization trigger TDS threshold, and using the crystallization trigger TDS threshold to replace the fixed threshold for comparison and judgment between the concentrated liquid TDS detection value and the crystallization trigger condition; subtracting the concentrated liquid TDS detection value from the crystallization trigger TDS threshold to obtain the supersaturation margin value; when the supersaturation margin value is greater than zero, triggering the circulation pump to start and driving the concentrated liquid to circulate along the guide tube at a set circulation flow rate to perform supersaturated crystallization of the concentrated liquid to obtain crystal slurry.

[0103] Reference Figure 2 This embodiment provides a device for treating high-salt, high-concentration waste liquid using a low-temperature evaporator, comprising:

[0104] Detection module 1 is used to detect the feed flow rate and feed salt concentration of the feed waste liquid and calculate the predicted value of secondary steam production.

[0105] Calculation module 2 is used to calculate the target compressor speed of the centrifugal steam compressor based on the predicted value of secondary steam production, and to calculate the target vacuum value of the vacuum evaporator based on the feed salt concentration.

[0106] Adjustment module 3 is used to adjust the real-time first operating speed of the centrifugal steam compressor until the compressor target speed is reached, and to simultaneously adjust the real-time first operating vacuum of the vacuum evaporator until the vacuum target value is reached.

[0107] Crystallization module 4 is used to supersaturate crystallize the concentrated liquid discharged from the vacuum evaporator to obtain crystal slurry, and then perform solid-liquid separation on the crystal slurry to obtain solid salt product and mother liquor.

[0108] In this embodiment, the specific implementation of each unit in the above device embodiment is described in the above method embodiment, and will not be repeated here.

[0109] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, apparatus, article, or method that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, apparatus, article, or method. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, apparatus, article, or method that includes that element.

[0110] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for treating high-salinity, high-concentration waste liquid by a low-temperature evaporator, characterized in that, include: The feed flow rate and feed salt concentration of the waste liquid were detected, and the predicted value of secondary steam production was calculated. The target compressor speed of the centrifugal steam compressor is calculated based on the predicted secondary steam output value, and the target vacuum level of the vacuum evaporator is calculated based on the feed salt concentration. Specifically, this includes: using the reference steam capacity under rated operating conditions of the centrifugal steam compressor as the set reference steam capacity; subtracting the predicted secondary steam output value from the set reference steam capacity to obtain the steam output difference; multiplying the steam output difference by a preset speed adjustment coefficient to obtain the speed adjustment amount; superimposing the speed adjustment amount with the corresponding set reference speed under rated operating conditions to obtain the compressor target speed; and substituting the feed salt concentration into the boiling point elevation function, using the first-order coefficient of the salt concentration and the feed... The boiling point elevation is obtained by summing the product of salt concentrations, the quadratic coefficient of salt concentration, and the square of the feed salt concentration. The target saturation temperature of pure water is obtained by subtracting the sum of the boiling point elevation and the preset heat transfer temperature difference from the compressed steam temperature. The target saturation temperature of pure water is then substituted into the Antone equation for forward solving to obtain the initial pressure value. The initial pressure value is then substituted back into the Antone equation to calculate the saturation temperature of pure water. The difference between the calculated saturation temperature of pure water and the target saturation temperature of pure water is obtained to obtain the temperature deviation value. If the temperature deviation value exceeds the convergence threshold, the pressure value is corrected according to the deviation direction and the forward solution is repeated. This process is repeated until the temperature deviation value converges to within the convergence threshold to obtain the target vacuum value. Adjust the centrifugal steam compressor to its first operating speed in real time until the compressor reaches its target speed, and simultaneously adjust the vacuum evaporator to its first operating vacuum level in real time until the vacuum level reaches its target value. The concentrated liquid discharged from the vacuum evaporator is subjected to supersaturated crystallization to obtain a crystal slurry, and the crystal slurry is subjected to solid-liquid separation to obtain a solid salt product and a mother liquor.

2. The method of claim 1, wherein the low-temperature evaporator is a falling film evaporator. The feed flow rate and feed salt concentration of the wastewater are detected, and the predicted value of secondary steam production is calculated, including: Detect the feed flow rate and feed salt concentration of the wastewater; The density of the waste liquid is obtained by adding the density reference value of the waste liquid to the result of multiplying the feed salt concentration by the density ratio coefficient. Based on the feed flow rate, the waste liquid density, and the feed salt concentration, the amount of water evaporated is obtained by dividing the difference between the feed salt concentration and the target concentrated salt concentration by the target concentrated salt concentration and then multiplying it by the product of the feed flow rate and the waste liquid density. The predicted value of secondary steam production is obtained by multiplying the evaporation water volume by the preset flash loss correction coefficient.

3. The method of claim 1, wherein the low temperature evaporator is a falling film evaporator. Adjusting the centrifugal steam compressor's real-time first operating speed until the compressor's target speed is reached, and simultaneously adjusting the vacuum evaporator's real-time first operating vacuum level until the target vacuum level is reached, includes: The target output frequency of the inverter is calculated based on the target speed and number of pole pairs of the compressor. The motor frequency of the centrifugal steam compressor is adjusted in an S-curve acceleration manner until the difference between the real-time first operating speed fed back by the encoder and the target speed of the compressor converges to within the speed tolerance. The vacuum degree deviation value is obtained by subtracting the real-time first operating vacuum degree of the vacuum evaporator from the target vacuum degree value collected by the vacuum degree sensor. The product of the vacuum degree deviation value and the valve opening adjustment coefficient is superimposed on the reference opening to adjust the vacuum pump inlet opening of the electric regulating valve until the difference between the first operating vacuum degree and the target vacuum degree value converges to within the pressure tolerance.

4. The method of claim 3, wherein the low-temperature evaporator is a multiple-effect evaporator. The method for treating high-salt, high-concentration waste liquid using a low-temperature evaporator also includes: The secondary steam temperature, secondary steam pressure, actual secondary steam flow rate, and liquid phase temperature inside the evaporator at the outlet of the vacuum evaporator are collected. The heat transfer efficiency index value is obtained by dividing the difference between the secondary steam temperature and the liquid phase temperature in the evaporator by the preset heat transfer temperature difference. The heat transfer efficiency index value is then subtracted from the target heat transfer efficiency to obtain the heat transfer efficiency deviation value. The product of the heat transfer efficiency deviation value and the speed compensation coefficient is then added to the first operating speed to obtain the second operating speed. The difference between the actual secondary steam flow rate and the predicted secondary steam output is divided by the predicted secondary steam output to obtain the steam output deviation value. The product of the steam output deviation value and the vacuum adjustment coefficient is then added to the first operating vacuum level to obtain the second operating vacuum level.

5. The method of claim 4, wherein the low temperature evaporator is a multiple effect evaporator. The heat transfer efficiency index value is obtained by dividing the difference between the secondary steam temperature and the liquid phase temperature inside the evaporator by a preset heat transfer temperature difference. The heat transfer efficiency index value is then subtracted from the target heat transfer efficiency to obtain a heat transfer efficiency deviation value. The product of the heat transfer efficiency deviation value and the speed compensation coefficient is added to the first operating speed to obtain the second operating speed, including: The heat transfer efficiency index value is obtained by dividing the difference between the secondary steam temperature and the liquid phase temperature in the evaporator by the preset heat transfer temperature difference. The heat transfer efficiency index value is then compared with the target heat transfer efficiency to obtain the heat transfer efficiency deviation value. The speed compensation amount is obtained by multiplying the product of the ratio of the heat transfer efficiency deviation value to the target heat transfer efficiency and the ratio of the preset heat transfer temperature difference to the reference heat transfer temperature difference, and then multiplying it by the speed compensation reference coefficient. The speed compensation amount is then added to the first operating speed to obtain the second operating speed.

6. The method of claim 1, wherein the low temperature evaporator is a multiple effect evaporator. The concentrated liquid discharged from the vacuum evaporator is subjected to supersaturated crystallization to obtain a crystal slurry, and the crystal slurry is subjected to solid-liquid separation to obtain a solid salt product and a mother liquor, comprising: The concentrated liquid discharged from the vacuum evaporator is input into the DTB type forced circulation crystallizer. When the TDS detection value of the concentrated liquid reaches the crystallization trigger threshold, the concentrated liquid is driven by the circulation pump to circulate along the guide tube at a set circulation flow rate to perform supersaturated crystallization and obtain crystal slurry. The crystal slurry is fed into a horizontal screw discharge centrifuge, and solid-liquid separation is performed on the crystal slurry at a preset speed and separation factor to obtain solid salt product and mother liquor.

7. An apparatus for treating high-salinity, high-concentration waste liquid by a low-temperature evaporator, characterized in that, The steps for implementing the method for treating high-salt, high-concentration waste liquid using a low-temperature evaporator according to any one of claims 1 to 6 include: The detection module is used to detect the feed flow rate and feed salt concentration of the feed waste liquid and calculate the predicted value of secondary steam production. The calculation module is used to calculate the target compressor speed of the centrifugal steam compressor based on the predicted value of the secondary steam output, and to calculate the target vacuum value of the vacuum evaporator based on the feed salt concentration. The adjustment module is used to adjust the real-time first operating speed of the centrifugal steam compressor until the target speed of the compressor is reached, and to simultaneously adjust the real-time first operating vacuum of the vacuum evaporator until the target vacuum value is reached. The crystallization module is used to supersaturate the concentrated liquid discharged from the vacuum evaporator to obtain crystal slurry, and to perform solid-liquid separation on the crystal slurry to obtain solid salt product and mother liquor.

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