Evaporative concentration process for nitrate production

Abstract

The present application relates to the technical field of nitrate preparation, and provides an evaporation concentration process for nitrate preparation, which comprises the following steps: determining concentration process parameters and safety control thresholds corresponding to the nitrate to be concentrated based on the characteristic type of the nitrate to be concentrated, setting a system energy consumption control target, calculating initial operating pressures of each evaporator, constructing a multi-dimensional prediction matrix and a pressure correction prediction matrix, and predicting pressure pre-adjustment values of each evaporator to adjust the operating pressures of each evaporator in advance to obtain a concentrated nitrate solution with a target concentration. Through the synergistic design of the three-effect evaporation process, pressure dynamic regulation and early prediction correction, the present application not only realizes the differentiated adaptation of nitrate with different characteristics, but also establishes a quantitative correlation between the system energy consumption control target and the operating pressure, significantly reduces energy consumption waste, upgrades the regulation mode to active prediction, reduces parameter fluctuations, and improves the product concentration qualification rate and production stability.

Description

Technical Field

[0001] This invention belongs to the field of nitrate preparation technology, specifically relating to an evaporation and concentration process for nitrate preparation. Background Technology

[0002] Nitrates are a key raw material in agriculture, chemical industry, and pharmaceutical industry. Their preparation process requires core steps such as raw material reaction, solid-liquid separation, evaporation and concentration, and crystallization and purification. Among these, evaporation and concentration is the core step that determines the product concentration, purity, and production energy consumption. By removing water from dilute nitrate solutions, the concentration is increased from 15%-25% to the target range of 70%-80%, providing qualified raw materials for subsequent crystallization processes. This step accounts for 60%-80% of the total energy consumption of nitrate production and is a key breakthrough for energy conservation and consumption reduction in the industry.

[0003] To reduce evaporation energy consumption, the industry has gradually shifted from traditional single-effect evaporation processes to triple-effect evaporation processes (which connect three evaporators in series, using the secondary steam generated in the previous effect as a heat source for the next effect, thus achieving multiple uses of thermal energy). Compared to single-effect evaporation, this reduces energy consumption by more than 30%, making it the current mainstream energy-saving technology. However, considering the current production status of the nitric acid and nitrate industry, existing triple-effect evaporation processes and related technologies still have many core drawbacks that urgently need to be addressed: (1) In the existing triple-effect evaporation process, the operating pressure of each evaporator is a fixed set value. It is not adapted to the characteristics of nitrates such as heat sensitivity and easy scaling, nor is it dynamically adjusted according to the changes in solution concentration and equipment heat exchange status. For heat-sensitive nitrates (such as ammonium nitrate), the fixed boiling point is close to its thermal decomposition temperature, resulting in a product decomposition rate of 5%-8%, which reduces product purity and poses safety hazards. For easy-to-scale nitrates (such as potassium nitrate), the solute is easy to precipitate and adhere to the heat exchange tube wall at the fixed boiling point, causing equipment scaling and blockage, which seriously interrupts the continuity of production. At the same time, the fixed operating pressure cannot be adapted to the boiling point change law of solutions with different concentrations, resulting in a decrease in thermal energy utilization efficiency and further aggravating energy waste.

[0004] (2) The existing triple-effect evaporation process only achieves basic energy saving by utilizing steam step by step. It has not established a quantitative correlation model between the system energy consumption control target and the operating pressure of each evaporator. There is no clear energy consumption benchmark in the production process, and it is impossible to accurately compensate for the heat exchange efficiency decay and solution concentration fluctuation of different evaporators.

[0005] (3) Most existing triple-effect evaporation processes adopt a real-time feedback passive adjustment mode, which only starts parameter adjustment after detecting abnormalities such as boiling point exceeding the standard or sudden increase in energy consumption. This lag leads to large fluctuations in process parameters, which not only reduces the product concentration qualification rate, but may also cause a chain of problems such as thermal nitrate decomposition and easy-to-scale nitrate scaling due to short-term boiling point exceeding the standard, which cannot meet the production requirements of high precision and high stability. Summary of the Invention

[0006] This invention provides an evaporation and concentration process for nitrate preparation, thereby solving at least one of the aforementioned technical problems. This invention is achieved through the following technical solution: An evaporation and concentration process for nitrate preparation includes the following steps: S1. Identify the characteristic type of the nitrate to be concentrated. Based on the characteristic type of the nitrate to be concentrated, the intelligent control system retrieves the preset thermal characteristic parameter library to determine the concentration process parameters and safety control thresholds corresponding to the nitrate to be concentrated. S2. Set the system energy consumption control target. Based on the concentration process parameters corresponding to the nitrate to be concentrated, calculate the initial operating pressure of each evaporator under the constraint of the safety control threshold, and start the concentration based on the initial operating pressure of each evaporator. S3. The nitrate to be concentrated flows through each series of evaporators for continuous concentration. The intelligent control system collects the process data of each evaporator in real time and constructs a multi-dimensional prediction matrix based on the real-time collected process data of each evaporator. The multi-dimensional prediction matrix includes a temperature fluctuation prediction matrix, an energy consumption deviation prediction matrix, and a raw material characteristic prediction matrix. S4. Based on the characteristics of the nitrate to be concentrated and the production stage, dynamically adjust the dynamic weights corresponding to the multi-dimensional prediction matrix, and construct a pressure correction prediction matrix based on the multi-dimensional prediction matrix and its corresponding dynamic weights. Based on the pressure correction prediction matrix, predict the pressure pre-adjustment value of each evaporator in the next monitoring cycle, and adjust the operating pressure of each evaporator in advance based on the pressure pre-adjustment value of each evaporator in the next monitoring cycle, so as to finally obtain the nitrate concentrated solution of the target concentration.

[0007] Preferably, step S1 includes: S11. Identify the characteristic type of the nitrate to be concentrated. The characteristic types of the nitrate to be concentrated include heat-sensitive nitrates and easily scale-forming nitrates. S12. The intelligent control system retrieves the preset thermal characteristic parameter library and matches the concentration process parameters corresponding to the characteristic type of the nitrate to be concentrated, including basic thermal characteristic data and the adaptation parameters of each evaporator. S13. Based on the basic thermal characteristic data and the adaptation parameters of each evaporator, set a corresponding safety control threshold for each evaporator in series.

[0008] Preferably, step S13 includes: S131. For nitrates to be concentrated that are heat-sensitive, the safety control threshold is set at 90% of their thermal decomposition temperature. S132. For nitrates to be concentrated that are characterized as easily scaling nitrates, the safety control threshold is set to their scaling critical temperature. S133. Set safety control thresholds according to the number of evaporator stages. As the number of evaporator stages increases, the safety control threshold corresponding to each evaporator decreases.

[0009] Preferably, step S2 includes: S21. Set the system energy consumption control target through the human-machine interaction module of the intelligent control system and determine the benchmark value of the amount of live steam required for unit water evaporation; S22. Retrieve the concentration process parameters corresponding to the nitrate to be concentrated from the preset thermal characteristic parameter library, including the specific heat capacity and boiling point data under different pressures in the basic thermal characteristic data, as well as the rated heat exchange efficiency, rated heat transfer area and pressure correction coefficient in the adaptation parameters of each evaporator. S23. Using an energy consumption backward calculation algorithm, under the constraint of safety control threshold, and guided by the system energy consumption control target, calculate the initial operating pressure of each evaporator to ensure that the initial operating pressure of each evaporator forms a pressure gradient that decreases step by step. S24. Verify whether the boiling point of the nitrate solution corresponding to the initial operating pressure of each evaporator is lower than the corresponding safety control threshold. If not, adjust the pressure correction coefficient in the adaptation parameters of each evaporator and repeat step S23 until the safety constraint conditions are met.

[0010] Preferably, step S3 includes: S31. The nitrate to be concentrated is continuously fed into the first-stage evaporator at a preset flow rate through the feed control equipment; S32. The intelligent control system collects the actual boiling point of the nitrate solution in each evaporator, the actual energy consumption of the system, and the initial concentration of the raw materials in real time from the process data of each evaporator. S33. Based on the actual boiling point of the nitrate solution in each evaporator, the actual energy consumption of the system, and the initial concentration of the raw materials, a multi-dimensional prediction matrix is ​​constructed. The multi-dimensional prediction matrix includes a temperature fluctuation prediction matrix, an energy consumption deviation prediction matrix, and a raw material characteristic prediction matrix.

[0011] Preferably, step S4 includes: S41. Based on the nitrate solution concentration in each evaporator, determine the production stage, and based on the characteristic type of the nitrate to be concentrated, the actual heat exchange efficiency of each evaporator in the process data of each evaporator, and the nitrate solution concentration in each evaporator, determine the dynamic weights corresponding to the temperature fluctuation prediction matrix, energy consumption deviation prediction matrix and raw material characteristic prediction matrix. S42. Assign the corresponding dynamic weights to the temperature fluctuation prediction matrix, energy consumption deviation prediction matrix, and raw material characteristic prediction matrix, respectively. S43. Construct a pressure correction prediction matrix based on the temperature fluctuation prediction matrix, energy consumption deviation prediction matrix, and raw material characteristic prediction matrix and their corresponding dynamic weights. Predict the pressure pre-adjustment value of each evaporator in the next monitoring cycle based on the pressure correction prediction matrix. S44. Based on the pressure pre-adjustment value of each evaporator in the next monitoring cycle, adjust the operating pressure of each evaporator in advance to ensure that the boiling point of nitrate in each evaporator does not exceed the safety control threshold and the system energy consumption is stable within the system energy consumption control target range. S45. After the concentrated nitrate solution flows through all the evaporators in series, the final concentrated nitrate solution of the target concentration is obtained, completing the evaporation and concentration process.

[0012] Preferably, step S41 determines the dynamic weights corresponding to the temperature fluctuation prediction matrix, energy consumption deviation prediction matrix, and raw material characteristic prediction matrix, including: S411. The production stage is determined based on the concentration of nitrate solution in the first-stage evaporator. When the concentration of nitrate solution is <30%, it is the start-up stage, and when the concentration of nitrate solution is ≥30%, it is the stable stage. S412. Assign basic weights to the temperature fluctuation prediction matrix, energy consumption deviation prediction matrix, and raw material characteristic prediction matrix according to the characteristic type of the nitrate to be concentrated. , and : When the nitrate to be concentrated is a heat-sensitive nitrate, the basic weight for the start-up phase is allocated as follows: , , The basic weights for the stable phase are allocated as follows: , , ; When the nitrate to be concentrated is a scaling-prone nitrate, the basic weight for the start-up phase is allocated as follows: , , The basic weights for the stable phase are allocated as follows: , , ; S413. Determine whether weight adjustment is needed. If weight adjustment is not needed, then the basic weights corresponding to the temperature fluctuation prediction matrix, energy consumption deviation prediction matrix, and raw material characteristic prediction matrix are determined. , and That is, the dynamic weights corresponding to the temperature fluctuation prediction matrix, energy consumption deviation prediction matrix, and raw material characteristic prediction matrix; Otherwise, the revised base weights will be used as dynamic weights; The situations requiring weight adjustment include: If the actual heat exchange efficiency decay rate of any evaporator during the current monitoring period Then the evaporator corresponding to Increase by 0.05-0.1; If the concentration of nitrate solution in the evaporator is off ,but Increase by 0.05-0.1; the revised dynamic weights still meet the requirements. .

[0013] Preferably, step S43 predicts the pressure pre-adjustment value of each evaporator in the next monitoring cycle based on the pressure correction prediction matrix, including: S431. Extract the pressure correction base value of each evaporator in the pressure correction prediction matrix: pressure correction base value of the first stage evaporator, pressure correction base value of the intermediate stage evaporator, and pressure correction base value of the last stage evaporator. S432. Calculate the correlation deviation parameters for each evaporator. The correlation deviation parameters include the deviation between the actual operating pressure and the initial operating pressure, the actual heat exchange efficiency decay rate, and the deviation between the actual nitrate solution concentration and the target nitrate solution concentration. S433. Based on the correlation deviation parameter, correct the pressure correction baseline value to obtain the pressure pre-adjustment value for each evaporator in the next monitoring cycle, including the pressure pre-adjustment value for the first-stage evaporator. Pressure pre-adjustment value of intermediate evaporator Pressure pre-adjustment value of the final stage evaporator .

[0014] Preferably, step S43, which predicts the pressure pre-adjustment value of each evaporator in the next monitoring cycle based on the pressure correction prediction matrix, further includes step S434, which includes: Verify whether the pressure pre-adjustment value of each evaporator is within the pressure adjustment range in the corresponding evaporator's adaptation parameters: if it exceeds the pressure adjustment range, take the boundary value of the pressure adjustment range as the final pressure pre-adjustment value of the corresponding evaporator; if it does not exceed the range, directly use the pressure pre-adjustment value as the final pressure pre-adjustment value of the corresponding evaporator. And the corrected gradient must ensure If the gradient is reversed, then for each evaporator , , Fine-tune the gradient, with an adjustment increment ≤ 0.02 atm, until the gradient meets the requirements; among which, The actual operating pressure of the first-stage evaporator in the process data of each evaporator, The actual operating pressure of the intermediate evaporator in the process data of each evaporator, This refers to the actual operating pressure of the final stage evaporator in the process data of each evaporator.

[0015] Preferably, an evaporation and concentration process for nitrate preparation further includes an ultrasonic anti-scaling linkage control step, specifically: The intelligent control system captures the boiling point change trend of each evaporator based on the temperature fluctuation prediction matrix, and simultaneously combines the actual heat exchange efficiency and the decay of the rated heat exchange efficiency of each evaporator to determine whether there is a scaling trend. When the boiling point of any evaporator continues to rise for two consecutive monitoring cycles and the actual heat exchange efficiency decays compared with the rated heat exchange efficiency, it is determined that the evaporator has a scaling trend and ultrasonic linkage control is activated.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention identifies the characteristic type of the nitrate to be concentrated, sets differentiated safety control thresholds for each stage of the evaporator based on a preset thermal characteristic parameter library, and then dynamically adjusts the boiling point of the solution by pressure. This ensures that the boiling point of heat-sensitive nitrates is precisely controlled below the thermal decomposition temperature, effectively preventing thermal decomposition, and the boiling point of easily scaling nitrates is controlled below the scaling critical temperature, reducing solute precipitation. By constructing three prediction matrices—temperature fluctuation prediction matrix, energy consumption deviation prediction matrix, and raw material characteristic prediction matrix—the invention captures parameter change trends in advance and dynamically adjusts the pressure based on the prediction results. This upgrades the control mode from real-time feedback passive adjustment to proactive adjustment based on advance prediction, reducing parameter fluctuation amplitude and avoiding chain problems such as nitrate decomposition and scaling caused by lag, thereby improving product concentration qualification rate and production stability. Attached Figure Description

[0017] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This invention provides a flowchart of an evaporation and concentration process for nitrate preparation. Detailed Implementation

[0018] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0019] Example 1: This embodiment of the invention provides an evaporation and concentration process for nitrate preparation, such as... Figure 1 As shown, it includes the following steps: S1. Identify the characteristic type of the nitrate to be concentrated. Based on the characteristic type of the nitrate to be concentrated, the intelligent control system retrieves the preset thermal characteristic parameter library to determine the concentration process parameters and safety control thresholds corresponding to the nitrate to be concentrated. S2. Set the system energy consumption control target. Based on the concentration process parameters corresponding to the nitrate to be concentrated, calculate the initial operating pressure of each evaporator under the constraint of the safety control threshold, and start the concentration based on the initial operating pressure of each evaporator. S3. The nitrate to be concentrated flows through each series of evaporators for continuous concentration. The intelligent control system collects the process data of each evaporator in real time and constructs a multi-dimensional prediction matrix based on the real-time collected process data of each evaporator. The multi-dimensional prediction matrix includes a temperature fluctuation prediction matrix, an energy consumption deviation prediction matrix, and a raw material characteristic prediction matrix. S4. Based on the characteristics of the nitrate to be concentrated and the production stage, dynamically adjust the dynamic weights corresponding to the multi-dimensional prediction matrix, and construct a pressure correction prediction matrix based on the multi-dimensional prediction matrix and its corresponding dynamic weights. Based on the pressure correction prediction matrix, predict the pressure pre-adjustment value of each evaporator in the next monitoring cycle, and adjust the operating pressure of each evaporator in advance based on the pressure pre-adjustment value of each evaporator in the next monitoring cycle, so as to finally obtain the nitrate concentrated solution of the target concentration.

[0020] In this embodiment, the nitrates to be concentrated include heat-sensitive nitrates and scale-prone nitrates.

[0021] In this embodiment, the intelligent control system is a dedicated control system that integrates core functions such as data acquisition, parameter retrieval, matrix operation, and pressure regulation, and is used to realize the automated and intelligent control of the nitrate evaporation and concentration process.

[0022] In this embodiment, the preset thermal characteristic parameter library is a standardized and specialized database that pre-stores various core data related to the nitrate evaporation and concentration process. It can accurately match the characteristics of the nitrate to be concentrated, providing data support for process parameter calculation, safety control threshold setting, and pressure adjustment.

[0023] In this embodiment, the concentration process parameters corresponding to the nitrate to be concentrated include basic thermal characteristic data and adaptation parameters for each evaporator. The basic thermal characteristic data are related to the physicochemical properties of the nitrate itself, directly determining the safety boundary and core efficiency of the evaporation and concentration process. Specifically, these include specific heat capacity, thermal decomposition temperature, scaling critical temperature, and boiling point data under different pressures. The adaptation parameters for each evaporator are process adaptation data related to the evaporator equipment connected in series, used to match the nitrate characteristic type and concentration conditions. Specifically, these include rated heat exchange efficiency, rated heat transfer area, pressure adjustment range, and pressure correction coefficients adapted to different nitrate types.

[0024] In this embodiment, the safety control threshold is a process safety upper limit set based on the characteristics of the nitrate to be concentrated and the operating conditions of the evaporator. It is used to constrain the operating conditions inside the evaporator to ensure that the nitrate does not undergo thermal decomposition or precipitate solute scale during the evaporation and concentration process. The safety control thresholds are different for different types of nitrate and different stages of evaporators.

[0025] In this embodiment, the system energy consumption control target is a pre-set benchmark value used to constrain the energy consumption of the nitrate evaporation and concentration process. The core of this target is the amount of live steam required for the evaporation of a unit of water. The actual energy consumption must be kept within a reasonable fluctuation range of the system energy consumption control target.

[0026] In this embodiment, the initial operating pressure of each evaporator is the initial operating pressure of each evaporator in series calculated before the start of the evaporation and concentration process, based on the concentration process parameters corresponding to the nitrate to be concentrated and under the constraint of the safety control threshold. The initial operating pressure of each evaporator shows a gradient distribution that decreases step by step, and is the basic operating parameter for starting the concentration of the evaporator.

[0027] In this embodiment, based on the concentration process parameters corresponding to the nitrate to be concentrated, and under the constraint of the safety control threshold, the calculation of the initial operating pressure of each evaporator refers to: using the basic thermal characteristic data in the concentration process parameters corresponding to the nitrate to be concentrated, such as the boiling point and specific heat capacity of nitrate, and the adaptation parameters of each evaporator, such as the rated heat exchange efficiency and rated heat transfer area, as the core calculation basis, and taking "the boiling point of the nitrate solution in each evaporator does not exceed the corresponding safety control threshold" as the inviolable safety boundary, quantitative calculation is performed through a dedicated energy consumption backward calculation algorithm, and finally the initial operating pressure of each evaporator that meets the energy-saving target and safety requirements is obtained, while ensuring that the pressure of each evaporator forms a gradually decreasing gradient.

[0028] In this embodiment, the process data of each evaporator is a series of core data collected in real time by the intelligent control system, reflecting the operating status and process progress of the evaporator. Specifically, these include: the actual boiling point of the nitrate solution in each evaporator, the actual operating pressure of each evaporator, the concentration of the nitrate solution in each evaporator, the actual energy consumption of the system (i.e., the amount of live steam actually consumed per unit of water evaporation), the actual heat exchange efficiency of each evaporator, and the initial concentration of the raw materials.

[0029] In this embodiment, the temperature fluctuation prediction matrix is ​​used to capture and predict the rate of change and fluctuation trend of the boiling point of the solution in each evaporator in the next monitoring cycle, based on the boiling point data of each evaporator in the historical monitoring cycle.

[0030] The energy consumption deviation prediction matrix is ​​used to predict the energy consumption deviation trend in the next monitoring period based on the deviation data between the actual energy consumption of the system and the system energy consumption control target in the historical monitoring period.

[0031] The raw material characteristic prediction matrix is ​​used to capture and predict the fluctuation trend and deviation range of raw material concentration in the next monitoring period based on the raw material concentration data of historical monitoring periods.

[0032] In this embodiment, the nitrate production process is mainly divided into a start-up phase and a stabilization phase.

[0033] In this embodiment, the pressure correction prediction matrix is ​​a comprehensive prediction matrix that integrates multi-dimensional prediction matrices and corresponding dynamic weights, used to quantitatively output the pressure pre-adjustment value of each evaporator in the next monitoring cycle.

[0034] In this embodiment, the pressure pre-adjustment value of each evaporator is calculated based on the pressure correction prediction matrix and is the amount of pressure change that each evaporator needs to adjust in the next monitoring cycle, including the adjustment direction and adjustment magnitude.

[0035] The working principle and beneficial effects of the above technical solution are as follows: First, the characteristic type of the nitrate to be concentrated is identified. The intelligent control system retrieves the basic data and evaporator adaptation parameters corresponding to the nitrate to be concentrated from the preset thermal characteristic parameter library, and then determines the safety control threshold of each evaporator. Second, the system energy consumption control target is set, that is, the baseline value of the amount of live steam required for unit water evaporation. Based on the thermal energy utilization logic of the triple-effect evaporation process, live steam is introduced into the first-stage evaporator to heat the dilute solution. The generated secondary steam is used as the heat source of the intermediate-stage evaporator. The secondary steam generated in the intermediate stage is then used as the heat source of the final-stage evaporator. The final-stage secondary steam is condensed and recovered. The initial operating pressure of each evaporator is calculated through an energy consumption backward calculation algorithm. A pressure gradient is formed, with the first stage higher than the intermediate stage and the intermediate stage higher than the final stage. Since pressure is positively correlated with boiling point, the boiling point of the solution in each evaporator decreases step by step. The intelligent control system collects process data from each evaporator in real time and constructs three prediction matrices: a temperature fluctuation prediction matrix, an energy consumption deviation prediction matrix, and a raw material characteristic prediction matrix. These matrices capture the trend of parameter changes. Finally, based on the characteristics of the nitrate to be concentrated and the production stage, the weights of the multi-dimensional prediction matrices are dynamically adjusted and integrated to construct a pressure correction prediction matrix. This matrix predicts the pre-adjustment value of the pressure for each evaporator in advance. By adjusting the pressure to change the boiling point, it ensures that the boiling point of each evaporator is always below the safe control threshold, while maintaining stable energy consumption and achieving the set system energy consumption control target.

[0036] This invention identifies the characteristic type of the nitrate to be concentrated, sets differentiated safety control thresholds for each stage of the evaporator based on a preset thermal characteristic parameter library, and then dynamically adjusts the boiling point of the solution by pressure. This ensures that the boiling point of heat-sensitive nitrates is precisely controlled below the thermal decomposition temperature, effectively preventing thermal decomposition, and the boiling point of easily scale-forming nitrates is controlled below the critical scaling temperature, reducing solute precipitation and solving the problem of equipment scaling and clogging. Simultaneously, the pressure is dynamically adjusted according to changes in solution concentration to adapt to the boiling point patterns at different concentrations, improving thermal energy utilization efficiency and reducing energy waste. By setting clear system energy consumption control targets, and using an energy consumption backward calculation algorithm, the system energy consumption control targets and the relationship between each evaporator are established. The quantitative correlation of the generator operating pressure, combined with the multi-stage utilization logic of thermal energy in the triple-effect evaporation process, enables precise energy consumption control. At the same time, the energy consumption deviation prediction matrix captures the energy consumption fluctuation trend and performs targeted pressure compensation to solve the problem of inaccurate energy consumption compensation. By constructing three prediction matrices—temperature fluctuation prediction matrix, energy consumption deviation prediction matrix, and raw material characteristic prediction matrix—parameter change trends are captured in advance. Based on the prediction results, the pressure is dynamically adjusted, upgrading the control mode from real-time feedback passive adjustment to proactive adjustment based on advance prediction. This reduces the amplitude of parameter fluctuations and avoids chain problems such as nitrate decomposition and scaling caused by lag, thereby improving the product concentration qualification rate and production stability.

[0037] Example 2: Based on Example 1, step S1 includes: S11. Identify the characteristic type of the nitrate to be concentrated. The characteristic types of the nitrate to be concentrated include heat-sensitive nitrates and easily scale-forming nitrates. S12. The intelligent control system retrieves the preset thermal characteristic parameter library and matches the concentration process parameters corresponding to the characteristic type of the nitrate to be concentrated, including basic thermal characteristic data and the adaptation parameters of each evaporator. S13. Based on the basic thermal characteristic data and the adaptation parameters of each evaporator, set a corresponding safety control threshold for each evaporator in series.

[0038] The working principle and beneficial effects of the above technical solution are as follows: First, by determining whether the nitrate to be concentrated is heat-sensitive or prone to scaling, the core requirements for subsequent control are clarified. Heat-sensitive nitrates need to avoid thermal decomposition, and prone-scaling nitrates need to avoid crystallization. Second, based on the identification results, the intelligent control system retrieves matching basic thermal characteristic data and adaptation parameters for each evaporator from a preset thermal characteristic parameter library. For heat-sensitive nitrates, the thermal decomposition temperature is retrieved; for prone-scaling nitrates, the critical scaling temperature and critical scaling concentration are retrieved. The adaptation parameters for each evaporator include the rated heat transfer area and pressure regulation range of each stage of the evaporator, ensuring that the retrieved parameters are highly compatible with the nitrate characteristic type and equipment operating conditions. Finally, based on the retrieved parameters, safety control thresholds are set for the first-stage evaporator, intermediate-stage evaporator, and final-stage evaporator. The safety control thresholds must match the pressure gradient of the triple-effect evaporation process. The highest pressure in the first-stage evaporator corresponds to the highest safety control threshold, and the lowest pressure in the final-stage evaporator corresponds to the lowest safety control threshold, ensuring that the boiling point of the solution in each stage of the evaporator is both below the safety control threshold and compatible with the temperature transfer of the secondary steam.

[0039] This invention's characteristic type identification and parameter retrieval targeting make subsequent pressure and boiling point control more targeted, avoiding safety risks caused by parameter mismatch; it sets individual safety control thresholds for each stage of the evaporator, making safety constraints more aligned with the pressure gradient and boiling point distribution of the triple-effect evaporation process, further reducing the probability of heat-sensitive nitrate decomposition and easily scaled nitrate scaling; the precise correlation between basic thermal characteristic data and the adaptation parameters of each evaporator improves the accuracy of subsequent initial operating pressure calculations and controls the initial pressure deviation within a reasonable range.

[0040] Example 3: Based on Example 2, step S13 includes: S131. For nitrates to be concentrated that are heat-sensitive, the safety control threshold is set at 90% of their thermal decomposition temperature. S132. For nitrates to be concentrated that are characterized as easily scaling nitrates, the safety control threshold is set to their scaling critical temperature. S133. Set safety control thresholds according to the number of evaporator stages. As the number of evaporator stages increases, the safety control threshold corresponding to each evaporator decreases.

[0041] In this embodiment, the safety control threshold is allocated according to the number of evaporator stages. As the number of evaporator stages increases, the safety control threshold corresponding to each evaporator decreases, specifically: The series evaporators are divided into three stages according to the process flow: the first-stage evaporator (corresponding to the feed end), the intermediate-stage evaporator, and the final-stage evaporator (corresponding to the discharge end). The operating pressure of each evaporator shows a decreasing gradient: first-stage evaporator > intermediate-stage evaporator > final-stage evaporator. The boiling point of the corresponding nitrate solution also decreases at each stage. To match this pressure gradient and boiling point change, the safety control threshold is synchronously differentiated according to the number of stages. The safety control threshold of the first-stage evaporator is set to the highest. For each subsequent stage of evaporator, its safety control threshold is lowered accordingly (the reduction range is adapted to the evaporator pressure gradient and solution boiling point gradient). The safety control threshold of the final-stage evaporator is the lowest, ensuring that the boiling point of the solution in each stage of evaporator is lower than the corresponding safety control threshold, and that the overall process meets the safety requirements.

[0042] The working principle and beneficial effects of the above technical solution are as follows: For heat-sensitive nitrates, whose thermal decomposition temperature is relatively low, a safety control threshold is set at 90% of the thermal decomposition temperature to reserve a safety buffer, thereby avoiding the risk of thermal decomposition by lowering the boiling point. For easily scale-forming nitrates, whose critical scaling temperature is the key boundary for solute precipitation, the safety control threshold is directly set at the critical scaling temperature to prevent solute precipitation from the source. Simultaneously, considering the pressure gradient characteristics of the triple-effect evaporation process—the higher the pressure, the higher the boiling point of the solution—the safety control threshold is allocated according to the number of evaporator stages, with the highest threshold for the first-stage evaporator, followed by the second-stage evaporator, and the lowest for the final-stage evaporator. This ensures that the boiling point of each stage of evaporator is below the corresponding safety control threshold and adapts to the temperature decrease pattern of secondary steam from the first-stage to the final-stage evaporator, ensuring efficient heat transfer.

[0043] The present invention provides a 10% buffer space for the safety control threshold of heat-sensitive nitrates, which significantly reduces their decomposition risk; the safety control threshold of easily scaling nitrates is directly matched with the scaling critical temperature, which reduces the probability of solute precipitation and extends the equipment cleaning cycle; the design of adapting the safety control threshold to the pressure gradient improves the utilization rate of secondary steam heat energy and further reduces energy consumption; the graded safety control threshold setting makes the safety boundary of each stage of evaporator clearer and eliminates the chain risk of overheating and scaling.

[0044] Example 4: Based on Example 1, step S2 includes: S21. Set the system energy consumption control target through the human-machine interaction module of the intelligent control system and determine the benchmark value of the amount of live steam required for unit water evaporation; S22. Retrieve the concentration process parameters corresponding to the nitrate to be concentrated from the preset thermal characteristic parameter library, including the specific heat capacity and boiling point data under different pressures in the basic thermal characteristic data, as well as the rated heat exchange efficiency, rated heat transfer area and pressure correction coefficient in the adaptation parameters of each evaporator. S23. Using an energy consumption backward calculation algorithm, under the constraint of safety control threshold, and guided by the system energy consumption control target, calculate the initial operating pressure of each evaporator to ensure that the initial operating pressure of each evaporator forms a pressure gradient that decreases step by step. S24. Verify whether the boiling point of the nitrate solution corresponding to the initial operating pressure of each evaporator is lower than the corresponding safety control threshold. If not, adjust the pressure correction coefficient in the adaptation parameters of each evaporator and repeat step S23 until the safety constraint conditions are met.

[0045] In this embodiment, the energy consumption backward calculation formula in step S23 is as follows: ; in, For the first The initial operating pressure of each evaporator is expressed in standard atmospheres, i.e., atm. The number of stages in the evaporator is represented by the first, second, and third evaporators, which correspond to the first-stage evaporator, the intermediate-stage evaporator, and the final-stage evaporator, respectively. This is a dimensionless correction factor, with units of standard atmospheres per square meter, i.e. The parameters are pre-stored in a preset thermal characteristic parameter library and calibrated by the characteristics of the evaporator equipment and the type of nitrate. The target for system energy consumption control is the baseline value of the amount of live steam required for a unit of water evaporation, expressed in tons of live steam / ton of evaporated water, which is dimensionless. The specific heat capacity of the nitrate solution to be concentrated is the amount of heat required to raise the temperature of a unit mass of nitrate solution by 1 degree Celsius. It is derived from a preset thermal characteristic parameter library and is expressed in kJ / (kg·℃). For the first The temperature rise and boiling point difference of the nitrate solution in each evaporator, i.e., the first The difference between the boiling point of the solution at the inlet and the boiling point of the solution at the outlet of the evaporator is derived from a preset thermal characteristic parameter library, and the unit is degrees Celsius (°C). For the first The rated heat exchange efficiency of an evaporator is the ratio of the actual heat exchange capacity to the theoretical heat exchange capacity of the evaporator. It is dimensionless and comes from the evaporator's adaptation parameters in a preset thermal characteristic parameter library. For the first The latent heat of vaporization of water under the operating pressure of an evaporator, that is, the heat required for a unit mass of water to change from liquid to gas under this pressure, is expressed in kJ / kg. For the first The rated heat transfer area of ​​an evaporator, i.e. the effective area inside the evaporator used for heat exchange, is derived from the evaporator's adaptation parameters in a preset thermal characteristic parameter library. The pressure correction factor is dimensionless and derived from the evaporator adaptation parameters in the preset thermal characteristic parameter library, which are used to adapt to the characteristics of the nitrates to be concentrated. Different parameters are corresponding to heat-sensitive nitrates and easily fouling nitrates. value.

[0046] In this embodiment, if the conditions are not met, the pressure correction coefficient in the adaptation parameters of each evaporator is adjusted, and step S23 is executed again, specifically including: After verification, if the boiling point of the nitrate solution corresponding to the initial operating pressure of a certain evaporator is found to be greater than or equal to the safety control threshold of the evaporator, it is determined that the safety constraint is not met. In this case, adjustments are made according to the degree of non-compliance: if the boiling point is slightly higher than the safety control threshold, and the difference is ≤3℃, then the pressure correction coefficient is increased. "Direction adjustment, Increasing the pressure can lower the calculated initial operating pressure, thereby lowering the boiling point; if the boiling point is significantly higher than the safety control threshold (difference > 3°C), then the pressure should be increased in a stepwise manner. "Method adjustment, i.e., doubling; pressure correction coefficient" The single adjustment range is ±0.02-0.05, and the adjustment must be maintained afterward. Within the preset range, i.e., heat-sensitive nitrates ∈0.85-0.90, nitrates are prone to scaling. ∈0.90-0.95, to avoid exceeding the device's compatibility range; the adjusted value will be... Substitute the energy consumption backward calculation formula and recalculate the initial operating pressure of each evaporator until the boiling point corresponding to the initial operating pressure of all evaporators is less than the safety control threshold, and the pressure gradient is maintained as "first stage > middle stage > last stage".

[0047] The working principle and beneficial effects of the above technical solution are as follows: First, the system energy consumption control target is set through the human-computer interaction module, clarifying the baseline value of the amount of live steam required for unit water evaporation, thus providing a clear benchmark for energy consumption control. Second, concentration process parameters matching the characteristic type of the nitrate to be concentrated are retrieved from a preset thermal characteristic parameter library, including specific heat capacity, boiling point data under different pressures, rated heat exchange efficiency of the evaporator, rated heat transfer area, and pressure correction coefficient. Next, an energy consumption backward calculation algorithm is used, based on the principle of energy conservation, to quantitatively correlate the system energy consumption control target with parameters such as specific heat capacity, rated heat transfer area, and latent heat of vaporization, calculating the initial operating pressure of each stage of the evaporator. This ensures that the pressure gradient conforms to the principle that the first stage is higher than the intermediate stage, and the intermediate stage is higher than the final stage, so that the secondary steam generated by the first stage live steam heating can meet the heating needs of the intermediate stage, and the secondary steam generated by the intermediate stage can meet the heating needs of the final stage, realizing multi-stage utilization of thermal energy. Finally, check whether the boiling point corresponding to the initial pressure of each evaporator is lower than the safety control threshold. If it is not met, adjust the pressure correction coefficient. Increasing the coefficient can reduce the pressure and thus reduce the boiling point. Recalculate until all evaporators meet the safety constraints to ensure the continuous and stable operation of the triple-effect evaporation process.

[0048] The energy consumption backward calculation algorithm establishes a quantitative correlation between the system energy consumption control target and the operating pressure, thus reducing the deviation between the actual system energy consumption and the system energy consumption control target. The dynamic adjustment and secondary verification of the pressure correction coefficient ensure that the boiling point of each stage of the evaporator is strictly below the safety control threshold, reducing the risk of heat-sensitive nitrate decomposition. The secondary steam of the triple-effect evaporation process is utilized in stages, which significantly reduces energy consumption compared with the single-effect evaporation process and reduces the energy consumption fluctuation range compared with the existing triple-effect evaporation process without algorithm support. The introduction of parameters such as rated heat transfer area and specific heat capacity improves the accuracy of initial pressure calculation, so that the pressure deviation is controlled within a reasonable range.

[0049] Example 5: Based on Example 1, step S3 includes: S31. The nitrate to be concentrated is continuously fed into the first-stage evaporator at a preset flow rate through the feed control equipment; S32. The intelligent control system collects the actual boiling point of the nitrate solution in each evaporator, the actual energy consumption of the system, and the initial concentration of the raw materials in real time from the process data of each evaporator. S33. Based on the actual boiling point of the nitrate solution in each evaporator, the actual energy consumption of the system, and the initial concentration of the raw materials, a multi-dimensional prediction matrix is ​​constructed. The multi-dimensional prediction matrix includes a temperature fluctuation prediction matrix, an energy consumption deviation prediction matrix, and a raw material characteristic prediction matrix.

[0050] In this embodiment, the formula for constructing the temperature fluctuation prediction matrix is: ; in: This is the temperature fluctuation prediction matrix for the nth monitoring period; This represents the total number of historical monitoring periods. , where is a positive integer; The number of stages in the evaporator is represented by the first, second, and third evaporators, which correspond to the first-stage evaporator, the intermediate-stage evaporator, and the final-stage evaporator, respectively, for a total of three evaporators. For the first Within the monitoring cycle, the first The actual boiling point of the nitrate solution in the evaporator, in °C. This is the monitoring cycle number, with a value range of [value range missing]. ; The dimension of the temperature fluctuation prediction matrix is Line × Columns, first row first The actual boiling point values ​​of the nitrate solution in each evaporator during each monitoring cycle, from row 2 to row 3. The difference in the actual boiling point of the nitrate solution in each evaporator within two adjacent monitoring periods is used to reflect the rate of change and fluctuation trend of the actual boiling point of the nitrate solution in each evaporator. For the first The monitoring cycle and the first Within each monitoring cycle, the first-stage evaporator... The difference between the actual boiling point values ​​of the nitrate solution inside the evaporator and so on. For the first The monitoring cycle and the first Within the monitoring cycle, the first The difference between the actual boiling point values ​​of the nitrate solutions in each evaporator.

[0051] In this embodiment, the formula for constructing the energy consumption deviation prediction matrix is: ; in: This is the energy consumption deviation prediction matrix for the nth monitoring period; For the first The actual energy consumption of the system within a monitoring cycle, i.e., the actual amount of live steam consumed per unit of water evaporation, is expressed in tons of live steam per ton of evaporated water, and is dimensionless. This is the monitoring cycle number, with a value range of [value range missing]. ; The target for system energy consumption control is the baseline value of the amount of live steam required for a unit of water evaporation. It is dimensionless and the unit is tons of live steam / ton of evaporated water. The energy consumption deviation prediction matrix has 3 rows × The matrix contains all dimensionless elements, with the first row being the first column. The first row contains the raw data of the actual system energy consumption for each monitoring period. The second row contains the absolute deviation data of the actual system energy consumption from the system energy consumption control target for each monitoring period. The third row contains the relative deviation data of the actual system energy consumption from the system energy consumption control target for each monitoring period, which are used to reflect the deviation trend and deviation magnitude of the system energy consumption. For the first The absolute deviation between the actual energy consumption of the system and the system energy consumption control target within each monitoring cycle is dimensionless. For the first The relative deviation between the actual energy consumption of the system and the system energy consumption control target within each monitoring cycle is dimensionless and presented as a percentage.

[0052] In this embodiment, the formula for constructing the raw material characteristic prediction matrix is: ; in: This is the raw material characteristic prediction matrix for the nth monitoring period; For the first The initial concentration of raw materials within the monitoring period, i.e., the first monitoring period... The actual concentration of dilute nitrate solution at the feed inlet of the first-stage evaporator within each monitoring cycle is dimensionless and expressed as a percentage (%). This is the monitoring cycle number, with a value range of [value range missing]. ; For the front The average concentration of dilute nitrate solution at the feed inlet of the first-stage evaporator within a monitoring period, dimensionless, in percentage (%), calculated using the following formula: ; The raw material characteristic prediction matrix has a dimension of 3 rows × The matrix contains all dimensionless elements, with the first row being the first column. The first row contains the raw data of the initial concentration of raw materials for each monitoring period. The second row contains the difference in the initial concentration of raw materials between two adjacent monitoring periods, reflecting the rate of change of the initial concentration of raw materials. The third row contains the normalized ratio of the initial concentration of raw materials to the average concentration for each monitoring period, which is used to reflect the fluctuation trend and relative deviation of the raw material concentration. For the first The monitoring cycle and the first The difference in initial concentration of raw materials within each monitoring period, dimensionless, in percentage (%), reflects the rate of change of initial concentration of raw materials; For the first Within each monitoring period, it reflects the normalized ratio of the initial concentration of raw materials to the average concentration. It is dimensionless and used to eliminate the influence of the absolute value of the initial concentration of raw materials, so as to more accurately capture the trend of concentration fluctuation.

[0053] The working principle and beneficial effects of the above technical solution are as follows: First, the nitrate to be concentrated is fed into the first-stage evaporator at a preset flow rate through the feed control equipment, ensuring feed stability and providing a foundation for subsequent parameter stability. Second, core data such as the actual boiling point of the nitrate solution in each stage of the evaporator, the actual energy consumption of the system, and the initial concentration of the raw material are collected. These data directly reflect the boiling point change trend, the degree of energy consumption deviation, and the fluctuation of the raw material concentration. Finally, based on historical data from at least five monitoring periods, three prediction matrices are constructed. The temperature fluctuation prediction matrix captures the rate and trend of boiling point change in each evaporator through the boiling point difference between adjacent periods; the energy consumption deviation prediction matrix reflects the energy consumption deviation pattern through the difference and proportion between the actual system energy consumption and the system energy consumption control target; and the raw material characteristic prediction matrix captures the raw material concentration fluctuation trend through the concentration difference and its ratio to the average concentration. The three prediction matrices together provide data support for the prediction of subsequent pressure pre-adjustment values, enabling pressure control to shift from passive feedback to advance prediction.

[0054] The temperature fluctuation prediction matrix can accurately capture the actual boiling point change trend of nitrate solution in each evaporator, providing a forward-looking basis for pressure adjustment at the temperature level; the energy consumption deviation prediction matrix can quantify the energy consumption deviation pattern, making pressure adjustment at the energy consumption level more accurate; the raw material characteristic prediction matrix can identify raw material concentration fluctuations in advance, avoiding boiling point anomalies caused by concentration changes; and a multi-dimensional prediction matrix is ​​constructed based on historical data from multiple monitoring cycles to ensure the reliability of the prediction results, laying a solid foundation for the construction of the subsequent pressure correction prediction matrix and reducing the prediction deviation of the pressure pre-adjustment value.

[0055] Example 6: Based on Example 1, step S4 includes: S41. Based on the nitrate solution concentration in each evaporator, determine the production stage, and based on the characteristic type of the nitrate to be concentrated, the actual heat exchange efficiency of each evaporator in the process data of each evaporator, and the nitrate solution concentration in each evaporator, determine the dynamic weights corresponding to the temperature fluctuation prediction matrix, energy consumption deviation prediction matrix and raw material characteristic prediction matrix. S42. Assign the corresponding dynamic weights to the temperature fluctuation prediction matrix, energy consumption deviation prediction matrix, and raw material characteristic prediction matrix, respectively. S43. Construct a pressure correction prediction matrix based on the temperature fluctuation prediction matrix, energy consumption deviation prediction matrix, and raw material characteristic prediction matrix and their corresponding dynamic weights. Predict the pressure pre-adjustment value of each evaporator in the next monitoring cycle based on the pressure correction prediction matrix. S44. Based on the pressure pre-adjustment value of each evaporator in the next monitoring cycle, adjust the operating pressure of each evaporator in advance to ensure that the boiling point of nitrate in each evaporator does not exceed the safety control threshold and the system energy consumption is stable within the system energy consumption control target range. S45. After the concentrated nitrate solution flows through all the evaporators in series, the final concentrated nitrate solution of the target concentration is obtained, completing the evaporation and concentration process.

[0056] In this embodiment, the pressure correction prediction matrix is: ; in: The pressure correction prediction matrix for the nth monitoring period has a dimension of 3 rows and 1 column. The dynamic weights of the temperature fluctuation prediction matrix are dimensionless. ; The dynamic weights of the energy consumption deviation prediction matrix are dimensionless. ; The dynamic weights of the raw material property prediction matrix are dimensionless. ; The constraints for dynamic weights are: ; This is the temperature-pressure dimension conversion coefficient, with units of atm / ℃, pre-stored in a preset thermal characteristic parameter library, used to convert the temperature dimension of the temperature fluctuation prediction matrix into the pressure dimension. This is the energy consumption deviation pressure dimension conversion coefficient, with the unit atm. It is pre-stored in a preset thermal characteristic parameter library and is used to convert the dimensionless data of the energy consumption deviation prediction matrix into pressure dimension. This is the concentration-pressure dimension conversion coefficient, with units of atm / %, pre-stored in a preset thermal characteristic parameter library, used to convert the concentration data of the raw material characteristic prediction matrix into pressure dimensions; for The transpose of the matrix; The influence weight vector of the temperature fluctuation prediction matrix has dimensions of . Rows x 1 column, dimensionless, value range is Used for The data in each column are weighted to highlight the impact of key monitoring periods; The influence weight vector of the energy consumption deviation prediction matrix has a dimension of . Rows x 1 column, dimensionless, value range is Used for The data in each column is weighted; The influence weight vector of the raw material characteristic prediction matrix has dimensions of . Rows x 1 column, dimensionless, value range is Used for The data in each column is weighted.

[0057] The working principle and beneficial effects of the above technical solution are as follows: First, the production stage is determined based on the nitrate solution concentration in the first-stage evaporator. A nitrate solution concentration below 30% indicates the start-up stage, while a concentration above or equal to 30% indicates the stable stage. The start-up stage needs to balance energy consumption and safety, while the stable stage emphasizes safety and concentration stability. Combining the nitrate characteristics and the actual heat exchange efficiency and nitrate solution concentration of each stage of the evaporator, the dynamic weights of three prediction matrices—temperature fluctuation prediction matrix, energy consumption deviation prediction matrix, and raw material characteristic prediction matrix—are determined. For heat-sensitive nitrates, temperature safety is emphasized, while for easily fouling nitrates, concentration stability is emphasized. Second, the dynamic weights are assigned to the corresponding prediction matrices, and a pressure correction prediction matrix is ​​constructed through matrix operations. This pressure correction prediction matrix is ​​a three-row, one-column matrix, corresponding to the pressure correction base values ​​for the first, intermediate, and final stages of the evaporator, respectively. The dynamic adjustment of the weights makes the matrix fusion more suitable for the current operating conditions. Next, based on this pressure correction prediction matrix, the pressure pre-adjustment values ​​for each evaporator in the next monitoring cycle are predicted. By adjusting the operating pressure, the boiling point of the solution is changed; an increase in pressure raises the boiling point, and a decrease in pressure lowers the boiling point. Finally, adjust the operating pressure of each stage of evaporator in advance according to the pressure pre-adjustment value to ensure that the boiling point is always below the safety control threshold, while maintaining the pressure gradient of the first stage being higher than the intermediate stage and the intermediate stage being higher than the last stage, so as to ensure that the secondary steam is utilized step by step and the energy consumption is stable within the target range. The introduction of dynamic weights in this invention makes matrix fusion more adaptable to changes in production stages and operating conditions, improving the prediction accuracy of pressure pre-adjustment values; by adjusting the pressure to precisely control the boiling point of the solution, the fluctuation range of boiling point in each stage of evaporator is reduced, and the product concentration deviation is reduced; the maintenance of the pressure gradient ensures the stability of the secondary steam thermal energy utilization rate, and the deviation between the actual energy consumption of the system and the system energy consumption control target is controlled within a reasonable range; the risk of decomposition of heat-sensitive nitrates is reduced, and the scaling cycle of easily scaling nitrates is extended.

[0058] Example 7: Based on Example 6, step S41 determines the dynamic weights corresponding to the temperature fluctuation prediction matrix, energy consumption deviation prediction matrix, and raw material characteristic prediction matrix, including: S411. The production stage is determined based on the concentration of nitrate solution in the first-stage evaporator. When the concentration of nitrate solution is <30%, it is the start-up stage, and when the concentration of nitrate solution is ≥30%, it is the stable stage. S412. Assign basic weights to the temperature fluctuation prediction matrix, energy consumption deviation prediction matrix, and raw material characteristic prediction matrix according to the characteristic type of the nitrate to be concentrated. , and : When the nitrate to be concentrated is a heat-sensitive nitrate, the basic weight for the start-up phase is allocated as follows: , , The basic weights for the stable phase are allocated as follows: , , ; When the nitrate to be concentrated is a scaling-prone nitrate, the basic weight for the start-up phase is allocated as follows: , , The basic weights for the stable phase are allocated as follows: , , ; S413. Determine whether weight adjustment is needed. If weight adjustment is not needed, then the basic weights corresponding to the temperature fluctuation prediction matrix, energy consumption deviation prediction matrix, and raw material characteristic prediction matrix are determined. , and That is, the dynamic weights corresponding to the temperature fluctuation prediction matrix, energy consumption deviation prediction matrix, and raw material characteristic prediction matrix; Otherwise, the revised base weights will be used as dynamic weights; The situations requiring weight adjustment include: If the actual heat exchange efficiency decay rate of any evaporator during the current monitoring period Then the evaporator corresponding to Increase by 0.05-0.1; If the concentration of nitrate solution in the evaporator is off ,but Increase by 0.05-0.1; the revised dynamic weights still meet the requirements. .

[0059] In this embodiment, the formula for calculating the actual heat exchange efficiency attenuation rate of the evaporator is: ; in, For the first The actual heat exchange efficiency decay rate of each evaporator; For the first The rated heat exchange efficiency of each evaporator is derived from the evaporator's adaptation parameters in a preset thermal characteristic parameter library; For the first The actual heat exchange efficiency of an evaporator is derived from the process data collected in real time by the intelligent control system.

[0060] In this embodiment, the actual heat exchange efficiency decay rate of an evaporator Then the evaporator corresponding to Increased by 0.05-0.1, specifically including, for the first One evaporator: like ,but Increase by 0.05; if ,but Increase by 0.08; if ,but Increased by 0.1.

[0061] In this embodiment, if the concentration of nitrate solution in the evaporator deviates... ,but Increased by 0.05-0.1. Specifically, this includes: For the first The actual concentration of nitrate solution in each evaporator The target concentration of the nitrate solution is 70%-80%; if ,but Increase by 0.05; if ,but Increase by 0.08; if ,but Increased by 0.1.

[0062] The working principle and beneficial effects of the above technical solution are as follows: First, the production stage is determined based on the nitrate solution concentration in the first-stage evaporator, and the basic weight allocation is clarified. Thermosensitive and easily fouling nitrates correspond to different basic weights in the start-up and stable stages, respectively. Second, the actual heat exchange efficiency decay rate and nitrate solution concentration deviation of each stage of the evaporator are monitored within the current monitoring period. If the actual heat exchange efficiency decay rate of a certain evaporator exceeds 5%, it indicates a decrease in the equipment's heat exchange capacity, requiring an increase in the basic weight α of the temperature fluctuation prediction matrix to enhance the pressure control at the temperature level and compensate for the impact of heat exchange efficiency decay on the boiling point. If the nitrate solution concentration deviation of a certain evaporator exceeds 3%, it indicates that concentration fluctuations affect the concentration effect, requiring an increase in the basic weight of the raw material characteristic prediction matrix to enhance the pressure control at the concentration level. Finally, the dynamic weights after the basic weight correction must ensure... By adjusting other weights to make up for the deficiencies, the corrected dynamic weights can still support precise pressure control after matrix fusion.

[0063] This invention employs a weighted correction based on the actual heat exchange efficiency decay rate, enabling pressure regulation to compensate for changes in equipment status and reduce the impact of evaporator heat exchange efficiency decay on boiling point. A weighted correction based on concentration deviation allows pressure regulation to adapt to raw material concentration fluctuations, reducing the impact of concentration deviation on product quality. The corrected dynamic weights make the pressure pre-adjustment value more closely match real-time operating conditions, improving the boiling point stability of each stage of the evaporator and increasing the product concentration qualification rate. The weight correction process does not disrupt the pressure gradient, maintaining stable secondary steam thermal energy utilization.

[0064] Example 8: Based on Example 6, step S43 is based on the pressure correction prediction matrix. Predict the pre-adjustment values ​​for the pressure of each evaporator in the next monitoring cycle, including: S431. Extract the pressure correction base value of each evaporator in the pressure correction prediction matrix: pressure correction base value of the first stage evaporator, pressure correction base value of the intermediate stage evaporator, and pressure correction base value of the last stage evaporator. S432. Calculate the correlation deviation parameters for each evaporator. The correlation deviation parameters include the deviation between the actual operating pressure and the initial operating pressure, the actual heat exchange efficiency decay rate, and the deviation between the actual nitrate solution concentration and the target nitrate solution concentration. S433. Based on the correlation deviation parameter, correct the pressure correction baseline value to obtain the pressure pre-adjustment value for each evaporator in the next monitoring cycle, including the pressure pre-adjustment value for the first-stage evaporator. Pressure pre-adjustment value of intermediate evaporator Pressure pre-adjustment value of the final stage evaporator .

[0065] In this embodiment, the pressure correction prediction matrix It is a 3x1 matrix, with the first row corresponding to the first-stage evaporator. Pressure correction baseline value The second row corresponds to the intermediate evaporator ( Pressure correction baseline value The third row corresponds to the final stage evaporator ( Pressure correction baseline value .

[0066] In this embodiment, the deviation between the actual operating pressure and the initial operating pressure is: ;in, For the first The actual operating pressure of each evaporator For the first Initial operating pressure of each evaporator, in atm; Actual heat exchange efficiency decay rate: ; in, Let be the rated heat exchange efficiency of the j-th evaporator. Let be the actual heat exchange efficiency of the j-th evaporator; Deviation between actual nitrate solution concentration and target nitrate solution concentration: ;in, For the first The actual nitrate solution concentration in each evaporator The target nitrate solution concentration is set at 70%-80%.

[0067] In this embodiment, the pressure correction base value is corrected based on the associated deviation parameter, and the correction formula is as follows: ; in, , , These are preset correction coefficients corresponding to the deviations of actual operating pressure from initial operating pressure, actual heat exchange efficiency attenuation rate, and actual nitrate solution concentration from target nitrate solution concentration, respectively. The units are: heat-sensitive nitrate concentration... , , Nitrate is prone to scaling. , , , which are pre-stored in a preset thermal characteristic parameter library.

[0068] The working principle and beneficial effects of the above technical solution are as follows: First, the pressure correction baseline values ​​for each stage of the evaporator in the pressure correction prediction matrix are extracted, including the pressure correction baseline values ​​for the first-stage evaporator, the intermediate-stage evaporator, and the final-stage evaporator. These pressure correction baseline values ​​serve as the initial pressure adjustment basis after matrix fusion. Second, three major related deviation parameters are calculated: the deviation between the actual operating pressure and the initial operating pressure reflects the degree of current pressure deviation from the benchmark; the actual heat exchange efficiency decay rate reflects the heat exchange status of the equipment; and the deviation between the actual nitrate solution concentration and the target nitrate solution concentration reflects the concentration effect. These parameters quantify the difference between the current operating condition and the ideal state. Next, the pressure correction baseline values ​​are corrected based on preset correction coefficients. These preset correction coefficients are set differently according to the nitrate characteristic type, with heat-sensitive nitrates... Higher values ​​are chosen to enhance pressure deviation correction; nitrates are prone to scaling. Higher values ​​are selected to enhance concentration deviation correction. During the correction process, the deviation parameters are normalized to ensure dimensional matching. Finally, the pressure pre-adjustment values ​​of each stage of the evaporator are obtained, so that the pressure adjustment can specifically compensate for the operating condition deviation.

[0069] The introduction of the associated deviation parameter in this invention makes pressure adjustment more targeted and improves the accuracy of the pressure pre-adjustment value; normalization processing ensures dimensional matching and avoids abnormal pressure adjustment caused by calculation errors; preset correction coefficients are set differently according to characteristic types, making pressure control more suitable for the core needs of different nitrates, further reducing the risk of thermal decomposition of heat-sensitive nitrates and the probability of scaling of easily scaling nitrates; the corrected pressure pre-adjustment value reduces the deviation between the actual pressure and the ideal pressure of each stage of evaporator and reduces the fluctuation range of boiling point.

[0070] Example 9: Based on Example 8, step S43 further includes step S434, which includes: Verify whether the pressure pre-adjustment value of each evaporator is within the pressure adjustment range in the corresponding evaporator's adaptation parameters: if it exceeds the pressure adjustment range, take the boundary value of the pressure adjustment range as the final pressure pre-adjustment value of the corresponding evaporator; if it does not exceed the range, directly use the pressure pre-adjustment value as the final pressure pre-adjustment value of the corresponding evaporator. And the corrected gradient must ensure If the gradient is reversed, then for each evaporator , , Fine-tune the gradient, with an adjustment increment ≤ 0.02 atm, until the gradient meets the requirements; among which, The actual operating pressure of the first-stage evaporator in the process data of each evaporator, The actual operating pressure of the intermediate evaporator in the process data of each evaporator, This refers to the actual operating pressure of the final stage evaporator in the process data of each evaporator.

[0071] The working principle and beneficial effects of the above technical solution are as follows: First, it verifies whether the pressure pre-adjustment value of each stage of the evaporator is within the corresponding pressure adjustment range. This pressure adjustment range is the safe operating boundary of the evaporator equipment. If it exceeds the pressure adjustment range, the boundary value is taken as the final pressure pre-adjustment value to avoid the pressure exceeding the equipment's tolerance range and causing equipment damage. Second, it verifies whether the adjusted pressure gradient meets the requirements. This gradient is the core guarantee for the staged utilization of secondary steam in the triple-effect evaporation process. If the gradient reverses, the intermediate evaporator cannot utilize the secondary steam from the first-stage evaporator, and the final-stage evaporator cannot utilize the secondary steam from the intermediate evaporator, leading to a sharp increase in energy consumption. If gradient reversal occurs, the pre-adjustment values ​​of each stage pressure should be fine-tuned, with the adjustment range not exceeding 0.02 atm. Priority should be given to fine-tuning the pressure of the final-stage evaporator to ensure gradient restoration and to guarantee the secondary steam flow direction and thermal energy utilization efficiency.

[0072] The verification of the pressure adjustment range of the present invention ensures that the pressure adjustment does not exceed the safety boundary of the equipment, prolonging the service life of the evaporator; the forced verification of the pressure gradient guarantees the multi-level utilization mechanism of thermal energy in the triple-effect evaporation process, avoiding the sudden increase in energy consumption caused by gradient reversal and improving the energy consumption stability; the limitation of the fine-tuning amplitude ensures the smooth pressure adjustment, avoiding the drastic fluctuation of the boiling point caused by gradient correction and reducing the fluctuation amplitude of the boiling point of each stage of the evaporator; the dual verification forms a safety line for pressure adjustment, enhancing the reliability of the process operation.

[0073] Example 10:

[0074] Based on Example 6, an evaporation concentration process for nitrate preparation further includes an ultrasonic anti-scaling linkage control step, specifically: The intelligent control system captures the boiling point change trend of each evaporator based on the temperature fluctuation prediction matrix, and simultaneously combines the attenuation of the actual heat transfer efficiency and the rated heat transfer efficiency of each evaporator to determine whether there is a scaling trend; when the boiling point of any evaporator continuously rises in two consecutive monitoring cycles and the actual heat transfer efficiency shows attenuation compared to the rated heat transfer efficiency, it is determined that there is a scaling trend in this evaporator, and the ultrasonic linkage control is started.

[0075] In this example, when the cumulative increase in the boiling point of the evaporator in two consecutive monitoring cycles is ≥1°C and the attenuation of the actual heat transfer efficiency compared to the rated heat transfer efficiency is ≥3%, a scaling warning is triggered.

[0076] In this example, the ultrasonic linkage control includes: reducing the operating pressure of the evaporator with a scaling trend by 0.02 atm to slow down the scaling rate by reducing the solution boiling point; at the same time, triggering the ultrasonic transducer supporting this evaporator to start working. The working frequency of the ultrasonic transducer is 20 - 40 kHz, the power is 500 - 1000 W, and it stops working after continuously working for 5 minutes to break up the potential scale layer in advance.

[0077] If the scaling warning standard is still met after the ultrasonic linkage control, shorten the working interval of the ultrasonic transducer to 30 minutes until the boiling point rise amplitude <1°C and the actual heat transfer efficiency attenuation <3%, stop the high-frequency working of the ultrasonic transducer, and restore the conventional pressure control mode to ensure that the boiling point of this evaporator never exceeds the corresponding safety control threshold.

[0078] The working principle and beneficial effects of the above technical solution are as follows: First, the intelligent control system calls the constructed temperature fluctuation prediction matrix to capture the boiling point change trend of each evaporator, and at the same time obtains the actual heat transfer efficiency data of each evaporator, compares it with the rated heat transfer efficiency in the preset heat characteristic parameter library, and analyzes the attenuation of the heat transfer efficiency; the fouling trend is determined by two indicators of boiling point change and heat transfer efficiency attenuation. When the boiling point of a certain evaporator continuously rises in two consecutive monitoring periods and the actual heat transfer efficiency shows attenuation compared with the rated heat transfer efficiency, it is preliminarily determined that there is a fouling trend. Second, a clear fouling warning standard is set. When the cumulative increase in the boiling point of the evaporator in two consecutive monitoring periods reaches or exceeds 1°C, and the actual heat transfer efficiency decays by 3% or more compared with the rated heat transfer efficiency, the fouling warning is officially triggered. Then, the operating pressure of this evaporator is lowered by 0.02 atm, and the positive correlation between pressure and boiling point is used to lower the solution boiling point, slowing down the fouling rate from the thermodynamic level; at the same time, the ultrasonic transducer supporting this evaporator is triggered to start working. After the ultrasonic transducer works continuously for 5 minutes according to the preset parameters, it stops, and the potential fouling layer on the heat transfer tube wall is scattered in advance through ultrasonic vibration, avoiding the attachment and growth of the fouling layer. Finally, the fouling trend determination logic is repeated in the next monitoring period. If the fouling warning standard is still met, the working interval of the ultrasonic transducer is shortened to 30 minutes, and continuous linkage control is carried out until the boiling point increase amplitude is lower than 1°C and the actual heat transfer efficiency decay is lower than 3%. The high-frequency operation of the ultrasonic transducer is stopped, and the conventional pressure control mode is restored to ensure that the boiling point of the evaporator never exceeds the corresponding safety control threshold during the entire linkage process; The present invention predicts the fouling trend through two indicators, realizes the early identification of fouling risks, and the linkage of pressure reduction and ultrasonic anti-fouling. It not only slows down the fouling formation rate from the thermodynamic level but also scatters the potential fouling layer through physical vibration. The dual effects significantly extend the fouling cycle of the evaporator, reduce the number of shutdown cleanings, and improve production continuity; during the linkage control process, only the pressure is slightly adjusted and strictly controlled within the safety control threshold range, avoiding the risk of thermal-sensitive nitrate decomposition caused by anti-fouling operations, and taking into account both the anti-fouling effect and production safety.

[0079] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these changes and modifications.

Claims

1. An evaporation and concentration process for nitrate preparation, characterized in that, Includes the following steps: S1. Identify the characteristic type of the nitrate to be concentrated. Based on the characteristic type of the nitrate to be concentrated, the intelligent control system retrieves the preset thermal characteristic parameter library to determine the concentration process parameters and safety control thresholds corresponding to the nitrate to be concentrated. S2. Set the system energy consumption control target. Based on the concentration process parameters corresponding to the nitrate to be concentrated, calculate the initial operating pressure of each evaporator under the constraint of the safety control threshold, and start the concentration based on the initial operating pressure of each evaporator. S3. The nitrate to be concentrated flows through each series of evaporators for continuous concentration. The intelligent control system collects the process data of each evaporator in real time and constructs a multi-dimensional prediction matrix based on the real-time collected process data of each evaporator. The multi-dimensional prediction matrix includes a temperature fluctuation prediction matrix, an energy consumption deviation prediction matrix, and a raw material characteristic prediction matrix. S4. Based on the characteristics of the nitrate to be concentrated and the production stage, dynamically adjust the dynamic weights corresponding to the multi-dimensional prediction matrix, and construct a pressure correction prediction matrix based on the multi-dimensional prediction matrix and its corresponding dynamic weights. Based on the pressure correction prediction matrix, predict the pressure pre-adjustment value of each evaporator in the next monitoring cycle, and adjust the operating pressure of each evaporator in advance based on the pressure pre-adjustment value of each evaporator in the next monitoring cycle, so as to finally obtain the nitrate concentrated solution of the target concentration.

2. The evaporation and concentration process for nitrate preparation according to claim 1, characterized in that, Step S1 includes: S11. Identify the characteristic type of the nitrate to be concentrated. The characteristic types of the nitrate to be concentrated include heat-sensitive nitrates and easily scale-forming nitrates. S12. The intelligent control system retrieves the preset thermal characteristic parameter library and matches the concentration process parameters corresponding to the characteristic type of the nitrate to be concentrated, including basic thermal characteristic data and the adaptation parameters of each evaporator. S13. Based on the basic thermal characteristic data and the adaptation parameters of each evaporator, set a corresponding safety control threshold for each evaporator in series.

3. The evaporation and concentration process for nitrate preparation according to claim 2, characterized in that, Step S13 includes: S131. For nitrates to be concentrated that are heat-sensitive, the safety control threshold is set at 90% of their thermal decomposition temperature. S132. For nitrates to be concentrated that are characterized as easily scaling nitrates, the safety control threshold is set to their scaling critical temperature. S133. Set safety control thresholds according to the number of evaporator stages. As the number of evaporator stages increases, the safety control threshold corresponding to each evaporator decreases.

4. The evaporation and concentration process for nitrate preparation according to claim 1, characterized in that, Step S2 includes: S21. Set the system energy consumption control target through the human-machine interaction module of the intelligent control system and determine the benchmark value of the amount of live steam required for unit water evaporation; S22. Retrieve the concentration process parameters corresponding to the nitrate to be concentrated from the preset thermal characteristic parameter library, including the specific heat capacity and boiling point data under different pressures in the basic thermal characteristic data, as well as the rated heat exchange efficiency, rated heat transfer area and pressure correction coefficient in the adaptation parameters of each evaporator. S23. Using an energy consumption backward calculation algorithm, under the constraint of safety control threshold, and guided by the system energy consumption control target, calculate the initial operating pressure of each evaporator to ensure that the initial operating pressure of each evaporator forms a pressure gradient that decreases step by step. S24. Verify whether the boiling point of the nitrate solution corresponding to the initial operating pressure of each evaporator is lower than the corresponding safety control threshold. If not, adjust the pressure correction coefficient in the adaptation parameters of each evaporator and repeat step S23 until the safety constraint conditions are met.

5. The evaporation and concentration process for nitrate preparation according to claim 1, characterized in that, Step S3 includes: S31. The nitrate to be concentrated is continuously fed into the first-stage evaporator at a preset flow rate through the feed control equipment; S32. The intelligent control system collects the actual boiling point of the nitrate solution in each evaporator, the actual energy consumption of the system, and the initial concentration of the raw materials in real time from the process data of each evaporator. S33. Based on the actual boiling point of the nitrate solution in each evaporator, the actual energy consumption of the system, and the initial concentration of the raw materials, a multi-dimensional prediction matrix is ​​constructed. The multi-dimensional prediction matrix includes a temperature fluctuation prediction matrix, an energy consumption deviation prediction matrix, and a raw material characteristic prediction matrix.

6. The evaporation and concentration process for nitrate preparation according to claim 1, characterized in that, Step S4 includes: S41. Based on the nitrate solution concentration in each evaporator, determine the production stage, and based on the characteristic type of the nitrate to be concentrated, the actual heat exchange efficiency of each evaporator in the process data of each evaporator, and the nitrate solution concentration in each evaporator, determine the dynamic weights corresponding to the temperature fluctuation prediction matrix, energy consumption deviation prediction matrix and raw material characteristic prediction matrix. S42. Assign the corresponding dynamic weights to the temperature fluctuation prediction matrix, energy consumption deviation prediction matrix, and raw material characteristic prediction matrix, respectively. S43. Construct a pressure correction prediction matrix based on the temperature fluctuation prediction matrix, energy consumption deviation prediction matrix, and raw material characteristic prediction matrix and their corresponding dynamic weights. Predict the pressure pre-adjustment value of each evaporator in the next monitoring cycle based on the pressure correction prediction matrix. S44. Based on the pressure pre-adjustment value of each evaporator in the next monitoring cycle, adjust the operating pressure of each evaporator in advance to ensure that the boiling point of nitrate in each evaporator does not exceed the safety control threshold and the system energy consumption is stable within the system energy consumption control target range. S45. After the concentrated nitrate solution flows through all the evaporators in series, the final concentrated nitrate solution of the target concentration is obtained, completing the evaporation and concentration process.

7. The evaporation and concentration process for nitrate preparation according to claim 6, characterized in that, Step S41 determines the dynamic weights corresponding to the temperature fluctuation prediction matrix, energy consumption deviation prediction matrix, and raw material characteristic prediction matrix, including: S411. The production stage is determined based on the concentration of nitrate solution in the first-stage evaporator. When the concentration of nitrate solution is <30%, it is the start-up stage, and when the concentration of nitrate solution is ≥30%, it is the stable stage. S412. Assign basic weights to the temperature fluctuation prediction matrix, energy consumption deviation prediction matrix, and raw material characteristic prediction matrix according to the characteristic type of the nitrate to be concentrated. , and : When the nitrate to be concentrated is a heat-sensitive nitrate, the basic weight for the start-up phase is allocated as follows: , , The basic weights for the stable phase are allocated as follows: , , ; When the nitrate to be concentrated is a scaling-prone nitrate, the basic weight for the start-up phase is allocated as follows: , , The basic weights for the stable phase are allocated as follows: , , ; S413. Determine whether weight adjustment is needed. If weight adjustment is not needed, then the basic weights corresponding to the temperature fluctuation prediction matrix, energy consumption deviation prediction matrix, and raw material characteristic prediction matrix are determined. , and That is, the dynamic weights corresponding to the temperature fluctuation prediction matrix, energy consumption deviation prediction matrix, and raw material characteristic prediction matrix; Otherwise, the revised base weights will be used as dynamic weights; The situations requiring weight adjustment include: If the actual heat exchange efficiency decay rate of any evaporator during the current monitoring period Then the evaporator corresponding to Increase by 0.05-0.1; If the concentration of nitrate solution in the evaporator is off ,but Increase by 0.05-0.1; the revised dynamic weights still meet the requirements. .

8. The evaporation and concentration process for nitrate preparation according to claim 6, characterized in that, Step S43 predicts the pressure pre-adjustment value of each evaporator in the next monitoring cycle based on the pressure correction prediction matrix, including: S431. Extract the pressure correction base value of each evaporator in the pressure correction prediction matrix: pressure correction base value of the first stage evaporator, pressure correction base value of the intermediate stage evaporator, and pressure correction base value of the last stage evaporator. S432. Calculate the correlation deviation parameters for each evaporator. The correlation deviation parameters include the deviation between the actual operating pressure and the initial operating pressure, the actual heat exchange efficiency decay rate, and the deviation between the actual nitrate solution concentration and the target nitrate solution concentration. S433. Based on the correlation deviation parameter, correct the pressure correction baseline value to obtain the pressure pre-adjustment value for each evaporator in the next monitoring cycle, including the pressure pre-adjustment value for the first-stage evaporator. Pressure pre-adjustment value of intermediate evaporator Pressure pre-adjustment value of the final stage evaporator .

9. The evaporation and concentration process for nitrate preparation according to claim 8, characterized in that, It also includes step S434, which includes: Verify whether the pressure pre-adjustment value of each evaporator is within the pressure adjustment range in the corresponding evaporator's adaptation parameters: if it exceeds the pressure adjustment range, take the boundary value of the pressure adjustment range as the final pressure pre-adjustment value of the corresponding evaporator; if it does not exceed the range, directly use the pressure pre-adjustment value as the final pressure pre-adjustment value of the corresponding evaporator. And the corrected gradient must ensure If the gradient is reversed, then for each evaporator , , Fine-tune the gradient, with an adjustment increment ≤ 0.02 atm, until the gradient meets the requirements; among which, The actual operating pressure of the first-stage evaporator in the process data of each evaporator, The actual operating pressure of the intermediate evaporator in the process data of each evaporator, This refers to the actual operating pressure of the final stage evaporator in the process data of each evaporator.

10. The evaporation and concentration process for nitrate preparation according to claim 6, characterized in that, It also includes an ultrasonic anti-scaling linkage control step, specifically: The intelligent control system captures the boiling point change trend of each evaporator based on the temperature fluctuation prediction matrix, and simultaneously combines the actual heat exchange efficiency and the decay of the rated heat exchange efficiency of each evaporator to determine whether there is a scaling trend. When the boiling point of any evaporator continues to rise for two consecutive monitoring cycles and the actual heat exchange efficiency decays compared with the rated heat exchange efficiency, it is determined that the evaporator has a scaling trend and ultrasonic linkage control is activated.

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