Modular molten salt cascade waste heat recovery method and system using semicoke coal gas waste heat

Abstract

The application discloses a modular molten salt step-by-step waste heat recovery method and system utilizing semi-coke coal gas waste heat, and the method comprises the following steps: obtaining monitoring data of at least smoke gas temperature, flow and component concentration of a semi-coke coal gas outlet, and dynamically dividing different temperature interval corresponding waste heat gradient interval according to the monitoring data; generating a distribution scheme containing molten salt flow and heat exchange path for each temperature interval based on the waste heat gradient interval; controlling the molten salt pump valve system according to the distribution scheme, driving molten salts with different melting points to flow through the multi-stage heat exchanger of the corresponding temperature interval in sequence, completing the step-by-step heat absorption and energy storage of the molten salt; and transporting the high-temperature molten salt obtained after the step-by-step heat absorption to the molten salt mixing pressure stabilizing tank for temperature and pressure equalization treatment, realizing the optimized recovery of semi-coke coal gas waste heat. By using the embodiment of the application, the step-by-step efficient recovery and stable output of energy can be realized, and the system adaptability and waste heat utilization rate are improved.

Description

Technical Field

[0001] This invention belongs to the field of semi-coke gas technology, and in particular, it is a modular molten salt cascade waste heat recovery method and system for utilizing the waste heat of semi-coke gas. Background Technology

[0002] In recent years, the production of semi-coke has generated a large amount of medium- and high-temperature coal gas, which carries high-grade and abundant waste heat resources. Efficient recovery and utilization of this waste heat is of great significance for energy conservation and emission reduction. Currently, common waste heat recovery methods mostly employ single-medium or fixed-process heat exchange, which are difficult to adapt to the complex composition and large parameter fluctuations of semi-coke coal gas. These methods generally suffer from poor system adaptability, easy coking and blockage, and inaccurate matching of waste heat grade, resulting in low overall recovery efficiency. Existing technologies also lack effective means for the fine-grained classification and storage of coal gas waste heat according to temperature ranges, leading to serious waste of high-grade heat energy. Summary of the Invention

[0003] The purpose of this invention is to provide a modular molten salt cascade waste heat recovery method and system for utilizing the waste heat of semi-coke gas, so as to overcome the shortcomings of the existing technology, realize efficient cascade energy recovery and stable output, and improve system adaptability and waste heat utilization rate.

[0004] One embodiment of this application provides a modular molten salt cascade waste heat recovery method utilizing the waste heat of semi-coke gas, the method comprising:

[0005] Acquire monitoring data on flue gas outlet, including at least flue gas temperature, flow rate, and component concentration, and dynamically divide waste heat gradient intervals corresponding to different temperature ranges based on the monitoring data;

[0006] Based on the waste heat gradient range, the heat absorption characteristics of molten salts with different melting points in the modular molten salt thermal storage unit are matched to generate an allocation scheme for each temperature range, including molten salt flow rate and heat exchange path.

[0007] According to the allocation scheme, the molten salt pump valve system is controlled to drive molten salts with different melting points to flow sequentially through multi-stage heat exchangers in the corresponding temperature range for segmented heat absorption and energy storage, thus completing the cascade heat absorption and energy storage of the molten salt.

[0008] The high-temperature molten salt obtained after the cascade heat absorption is transported to the molten salt mixing and stabilizing tank for temperature and pressure equalization. The molten salt medium that meets the set temperature and pressure parameters is then output to the heat application system to achieve optimized recovery of waste heat from semi-coke gas.

[0009] Another embodiment of this application provides a modular molten salt cascade waste heat recovery system utilizing the waste heat of semi-coke gas, the system comprising:

[0010] The acquisition module is used to acquire monitoring data of at least flue gas temperature, flow rate and component concentration at the outlet of semi-coke gas, and dynamically divide the waste heat gradient intervals corresponding to different temperature intervals based on the monitoring data.

[0011] The generation module is used to match the heat absorption characteristics of molten salts with different melting points in the modular molten salt thermal storage unit based on the waste heat gradient range, and generate an allocation scheme including molten salt flow rate and heat exchange path for each temperature range.

[0012] The heat exchange module is used to control the molten salt pump valve system according to the distribution scheme, drive molten salt with different melting points to flow sequentially through a multi-stage heat exchanger in the corresponding temperature range, perform segmented heat absorption and energy storage, and complete the cascade heat absorption and energy storage of the molten salt.

[0013] The output module is used to transport the high-temperature molten salt obtained after the cascade heat absorption to the molten salt mixing and stabilizing tank for temperature and pressure equalization, and output the molten salt medium that meets the set temperature and pressure parameters to the heat application system to realize the optimized recovery of waste heat from semi-coke gas.

[0014] Another embodiment of this application provides a storage medium storing a computer program, wherein the computer program is configured to execute the method described in any of the preceding claims when running.

[0015] Another embodiment of this application provides an electronic device including a memory and a processor, wherein the memory stores a computer program and the processor is configured to run the computer program to perform the method described in any of the preceding claims.

[0016] Compared with existing technologies, this invention provides a modular molten salt cascade waste heat recovery method utilizing the waste heat of semi-coke gas. This method acquires monitoring data at the semi-coke gas outlet, including at least the flue gas temperature, flow rate, and component concentration, and dynamically divides different temperature ranges into waste heat gradient zones based on the monitoring data. Based on these waste heat gradient zones, a distribution scheme including molten salt flow rate and heat exchange path is generated for each temperature range. The molten salt pump valve system is controlled according to the distribution scheme, driving molten salts with different melting points to flow sequentially through multi-stage heat exchangers in the corresponding temperature ranges, completing the cascade heat absorption and energy storage of the molten salt. The high-temperature molten salt obtained after cascade heat absorption is transported to a molten salt mixing and stabilizing tank for temperature and pressure equalization, achieving optimized recovery of the semi-coke gas waste heat. This enables efficient cascade energy recovery and stable output, improving system adaptability and waste heat utilization. Attached Figure Description

[0017] Figure 1 A hardware structure block diagram of a computer terminal for a modular molten salt cascade waste heat recovery method utilizing semi-coke gas waste heat, provided in an embodiment of the present invention.

[0018] Figure 2 A schematic diagram of a modular molten salt cascade waste heat recovery method for utilizing the waste heat of semi-coke gas, provided for an embodiment of the present invention;

[0019] Figure 3 This is a schematic diagram of a modular molten salt cascade waste heat recovery system utilizing the waste heat of semi-coke gas, provided as an embodiment of the present invention. Detailed Implementation

[0020] The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0021] The present invention first provides a modular molten salt cascade waste heat recovery method for utilizing the waste heat of semi-coke gas. This method can be applied to electronic devices, such as computer terminals, specifically ordinary computers.

[0022] The following detailed explanation uses a computer terminal as an example. Figure 1 This is a hardware structure block diagram of a computer terminal for a modular molten salt cascade waste heat recovery method utilizing semi-coke gas waste heat, provided as an embodiment of the present invention. Figure 1 As shown, the computer device includes a processor, memory, and network interface connected via a system bus, wherein the memory may include non-volatile storage media and internal memory.

[0023] See Figure 2 The present invention provides a modular molten salt cascade waste heat recovery method utilizing the waste heat of semi-coke gas, which may include the following steps:

[0024] S201, acquire monitoring data of at least flue gas temperature, flow rate and component concentration at the outlet of semi-coke gas, and dynamically divide the waste heat gradient intervals corresponding to different temperature intervals based on the monitoring data.

[0025] Specifically, real-time monitoring data, including at least flue gas temperature, flow rate, and component concentration, can be collected at the semi-coke gas outlet pipeline to obtain the raw monitoring dataset;

[0026] This step is the foundational data source for the cascade recovery of waste heat from semi-coke gas. Its core is to capture key thermal and compositional parameters of the semi-coke gas outlet in real time using high-precision, high-reliability sensing equipment. These parameters include: flue gas temperature determining the waste heat grade (high-temperature waste heat can be used for high-temperature molten salt endothermic treatment, while low-temperature waste heat is suitable for low-melting-point molten salt); flow rate determining the total waste heat (affecting molten salt flow distribution); and component concentration (such as H2S and CO) determining the material selection and safety threshold of the heat exchange equipment (to avoid equipment damage caused by corrosive components). These three factors together form the core basis for subsequent waste heat gradient division. It is necessary to clearly define the hardware selection, range and accuracy design, acquisition frequency, and data format for each parameter. Each step must be combined with the actual operating conditions of the semi-coke gas (outlet temperature typically 300~800℃, flow rate 1000~3000 Nm³). 3 / h (containing trace amounts of corrosive components) provides specific examples to ensure the integrity and accuracy of the original data.

[0027] Data acquisition frequency: Based on the fluctuation characteristics of semi-coke gas operating conditions (load adjustment cycle of about 1 minute), the acquisition frequency is set to 1Hz (1 set of data per second) – temperature and flow data need to be acquired at high frequency to capture dynamic fluctuations. Although component concentration data changes more slowly, 1Hz acquisition can ensure timely detection of anomalies (such as a sudden increase in H2S) and avoid equipment damage.

[0028] The original monitoring dataset is formatted as follows: It uses a structured format of "timestamp + temperature + flow rate + CO concentration + H2S concentration," with the timestamp accurate to milliseconds (format YYYYMMDDHHMMSSfff). Each parameter retains its corresponding decimal places. Example data is shown below:

[0029] 20251001083000123, 725.3℃, 2850.5Nm 3 / h, 6.8%VOL, 42.3ppm;

[0030] 20251001083001456, 723.8℃, 2845.2Nm 3 / h, 6.9%VOL, 41.8ppm;

[0031] 20251001083002789, 726.1℃, 2852.1Nm 3 / h, 6.7%VOL, 43.1ppm.

[0032] The data is stored in real time in a MySQL database on the industrial control computer, with the table name "LantanGas_OriginalData", providing the original data source for subsequent preprocessing.

[0033] The original monitoring dataset was cleaned and outlier removed. A moving average filtering algorithm was used to smooth temperature fluctuations and generate preprocessed monitoring data.

[0034] I. Data Cleaning and Outlier Removal:

[0035] Outlier detection method: The "physical threshold method + 3σ principle" is used for dual detection to ensure that the outliers are not caused by equipment failure or data noise.

[0036] II. Implementation of the moving average filtering algorithm:

[0037] Algorithm principle: Moving average filtering selects N consecutive data points (window size N) and calculates their arithmetic mean as the filtered data at the current time. The formula is: x_filtered(t) = (x(t) + x(t-1) + ... + x(t-N+1)) / N, where x(t) is the original data at time t, x_filtered(t) is the filtered data, and N is the window size. The larger N is, the stronger the filtering effect, but the more obvious the data lag; the smaller N is, the smaller the lag, but the weaker the filtering effect. It needs to be selected in combination with the data fluctuation characteristics.

[0038] Parameter design: For the temperature fluctuation of semi-coke gas (cycle about 10 seconds, fluctuation range ±5℃), select window size N=5 (i.e. take the current time and the previous 4 times for a total of 5 data points), and take into account the filtering effect and lag (lag time 4 seconds, much smaller than the working condition adjustment cycle of 1 minute, no impact).

[0039] III. Validation and Formatting of Preprocessed Data:

[0040] Pre-processed monitoring data format: Follow the format of "timestamp + temperature + flow rate + CO concentration + H2S concentration". Temperature and flow rate should be retained to one decimal place, and component concentrations should be retained to one decimal place (CO) or one decimal place (H2S). Example data:

[0041] 20251001083000123, 725.3℃, 2850.5Nm 3 / h, 6.8%VOL, 42.3ppm;

[0042] 20251001083001456, 723.8℃, 2845.2Nm 3 / h, 6.9%VOL, 41.8ppm;

[0043] 20251001083002789, 723.8℃, 2852.1Nm 3 / h, 6.7%VOL, 43.1ppm;

[0044] 20251001083003123, 726.1℃, 2848.7Nm 3 / h, 6.8%VOL, 42.5ppm;

[0045] 20251001083004456, 724.7℃, 2849.2Nm 3 / h, 6.9%VOL, 42.1ppm.

[0046] The data is stored in the database table "LantanGas_PreprocessedData" to provide input for subsequent dynamic density clustering.

[0047] Based on the preprocessed monitoring data, the dynamic density clustering algorithm is used to analyze the characteristics of flue gas temperature distribution, automatically identify temperature concentration areas, and generate temperature distribution clustering results.

[0048] I. Selection and Principle of Dynamic Density Clustering Algorithm:

[0049] Algorithm Selection: The DBSCAN (Density-Based Spatial Clustering of Applications with Noise) algorithm was chosen. Its advantages include: no need to pre-specify the number of clusters (changes in the operating conditions of semi-coke gas can lead to changes in the number of temperature concentration regions, such as 2-3), automatic identification of clusters of arbitrary shapes (temperature concentration regions may be continuous intervals, not circular), and the elimination of noise points (temperature deviations caused by minor fluctuations in operating conditions), perfectly adapting to the dynamic characteristics of semi-coke gas temperature distribution. Core Concept Explanation:

[0050] ε (neighborhood radius): The area around a data point that is less than ε is considered the neighborhood of that point, and is used to determine density;

[0051] MinPts (Minimum Number of Points): If a point has at least MinPts data points in its neighborhood, then that point is a "core point", and the continuous area formed by core points is a cluster.

[0052] Cluster: A region consisting of a core point and all data points reachable from it;

[0053] Noise points: Data points that are neither core points nor reachable from any core points are identified as anomalies caused by fluctuations in operating conditions.

[0054] II. Dynamic adjustment of key parameters:

[0055] Traditional DBSCAN uses fixed values ​​for ε and MinPts, which cannot adapt to the dynamic fluctuations in the temperature of semi-coke gas. Therefore, it needs to be adjusted in real time based on pre-processed temperature data.

[0056] Dynamic calculation of ε: ε = k × σ_T, where σ_T is the standard deviation of the preprocessed temperature data (reflecting the amplitude of temperature fluctuations), and k is an adjustment factor (set to 2.0 to ensure coverage of 95% of normal fluctuation data). Example: If the preprocessed temperature data has σ_T = 15℃, then ε = 2.0 × 15 = 30℃, meaning the neighborhood radius is 30℃, ensuring that temperature data within the same concentrated area are mutually accessible.

[0057] The dynamic calculation of MinPts is as follows: MinPts = ceil (N_total × r), where N_total is the total amount of data in the current analysis window (taking 100 data points, approximately 100 seconds of temperature data, covering 1-2 operating cycles), and r is a scaling factor (set to 0.1 to ensure that there are enough data points in the neighborhood of the core point, avoiding overly fine clustering). Example: If N_total = 100, then MinPts = ceil (100 × 0.1) = 10, meaning that a temperature point is considered a core point only if there are at least 10 data points in the 30℃ neighborhood.

[0058] III. Clustering process and results example:

[0059] Taking 100 preprocessed temperature data points (with some key data extracted: 725.3, 723.8, 724.7, 715.6, 715.9, 708.5, 712.3, 520.4, 518.7, 525.1, 519.3, 522.6, 328.9, 332.5, 325.7, 330.1) as an example, the clustering process is as follows:

[0060] Data preprocessing: Arrange the temperature data in chronological order, take the most recent 100 data points, and calculate σ_T=15℃, ε=30℃, and MinPts=10.

[0061] Core point identification:

[0062] For data points near 720℃ (e.g., 725.3℃), count the number of data points within their 30℃ neighborhood (420~750℃): a total of 45 data points ≥ MinPts=10, which are identified as core points;

[0063] For data points near a temperature of 520℃ (e.g., 520.4℃), the number of data points in the neighborhood (490~550℃) is 38 (≥10), which are identified as core points.

[0064] For data points with a temperature around 330℃ (e.g., 328.9℃), the number of data points in the neighborhood (300~360℃) with a total of 15 (≥10) points is determined to be core points.

[0065] For data points near a temperature of 600℃ (e.g., 605.2℃, only 1 data point), the number of data points in the neighborhood is 2 < 10, and the data points are identified as noise points.

[0066] Cluster generation:

[0067] Cluster 1 (High Temperature Cluster): Composed of a core point around 720℃ and its reachable data points, with a temperature range of 690~750℃ (750-690=60℃, containing 45 data points);

[0068] Cluster 2 (Medium-temperature cluster): Composed of a core point around 520℃ and its reachable data points, with a temperature range of 490~550℃ (containing 38 data points);

[0069] Cluster 3 (Low Temperature Cluster): Composed of a core point near 330℃ and its reachable data points, with a temperature range of 300~360℃ (containing 15 data points).

[0070] Noise points: Two data points, including 605.2℃, were determined to be deviations caused by brief adjustments to the operating conditions and will not be included in subsequent analysis.

[0071] IV. Validation of Clustering Results:

[0072] Verification metrics:

[0073] Silhouette Coefficient: Calculates the silhouette coefficient of each cluster, with a value ranging from -1 to 1. The closer to 1, the better the clustering effect. In the example, the silhouette coefficient of cluster 1 is 0.85, cluster 2 is 0.82, and cluster 3 is 0.78, all ≥0.75, indicating excellent clustering effect.

[0074] Cluster purity: Data points within each cluster originate from the same temperature concentration region under the same operating condition, with no overlap (e.g., the high-temperature cluster contains only full-load data, and the medium-temperature cluster contains only half-load data), purity = 100%;

[0075] Noise point percentage: ≤2% (in the example, 2 / 100=2%, which meets the requirements).

[0076] Temperature distribution clustering results output: Output in the format of "cluster number + temperature range + number of data points + cluster type", example:

[0077] Cluster 1: High-temperature cluster, temperature range 690~750℃, number of data points 45, cluster type = high-grade waste heat;

[0078] Cluster 2: Medium-temperature cluster, temperature range 490~550℃, number of data points 38, cluster type = medium-grade waste heat;

[0079] Cluster 3: Low temperature cluster, temperature range 300~360℃, number of data points 15, cluster type = low grade waste heat;

[0080] This result provides a temperature basis for subsequent division of waste heat gradient intervals based on flue gas composition.

[0081] Based on the temperature distribution clustering results and combined with the flue gas component concentration characteristics, the temperature range for efficient waste heat recovery is dynamically divided, and a waste heat gradient range division scheme is generated.

[0082] I. Mechanisms influencing flue gas component concentration:

[0083] The impact of key components (H2S, CO) in semi-coke gas on waste heat recovery is mainly reflected in:

[0084] The corrosive effects of H2S: At high temperatures (>600℃), H2S will undergo a sulfidation reaction with the carbon steel material of the heat exchanger, which will accelerate the corrosion rate of the material (the corrosion rate increases by 2 to 3 times for every 100℃ increase in temperature). When the H2S concentration is >50ppm, the risk of corrosion above 600℃ increases significantly, and the upper limit of the high temperature range needs to be limited.

[0085] Safety impact of CO: CO is a flammable component. When the CO concentration is >10% VOL and the temperature is >700℃, if air leaks into the heat exchanger, it may cause deflagration. The upper limit of the high temperature range should be controlled to not exceed 700℃ (when the CO concentration is >10%).

[0086] Efficiency constraints in the low-temperature range: When the temperature is < 300℃, the waste heat grade is too low, and the heat absorption efficiency of low-melting-point molten salt is < 50% (energy recovery cost is higher than the benefit). Therefore, the lower limit of the low-temperature range should be set at 300℃, and waste heat below this temperature should not be recovered.

[0087] II. Dynamic adjustment of interval boundaries:

[0088] Taking the clustering results from step three (cluster 1: 690~750℃, cluster 2: 490~550℃, cluster 3: 300~360℃) and the preprocessed component data (C_H2S=42ppm, C_CO=6.8% VOL) ​​as an example, the adjustment process is as follows:

[0089] Adjustment of the high-temperature cluster (cluster 1):

[0090] The original temperature range was 690~750℃, C_H2S=42ppm<50ppm (low corrosion risk), C_CO=6.8% VOL<10% (no risk of deflagration). However, the long-term tolerance temperature of the heat exchanger material needs to be considered (long-term tolerance temperature of carbon steel ≤750℃). Therefore, the upper limit of the high temperature range is retained at 750℃, and the lower limit is adjusted to 700℃ (the low temperature end of 690~700℃ is eliminated to ensure that the residual heat grade is high enough to match the 600℃ melting point of sodium nitrate-potassium nitrate molten salt). The adjusted high temperature range is 700~750℃.

[0091] Adjustment of the mesothermal cluster (cluster 2):

[0092] The original temperature range was 490~550℃, and C_H2S=42ppm. The corrosion rate in this temperature range is low (about 0.1mm / year, within the allowable range). There is no risk of CO deflagration. Moreover, this temperature range is suitable for sodium nitrate-sodium nitrite molten salt with a melting point of 400℃. Therefore, the boundary was only slightly adjusted to 500~550℃ (the low temperature end of 490~500℃ was removed to improve the residual heat quality). The adjusted medium temperature range is 500~550℃.

[0093] Adjustment of the low-temperature cluster (cluster 3):

[0094] The original temperature range is 300~360℃. The lower limit of 300℃ meets the efficiency requirements (it is compatible with magnesium chloride-calcium chloride molten salt with a melting point of 200℃ and has an endothermic efficiency of >60%). The upper limit of 360℃ poses no corrosion or safety risks. Therefore, the original range is retained. The adjusted low temperature range is 300~360℃.

[0095] Ineffective waste heat range: Waste heat below 300℃ (e.g., 250℃) is not recovered because its grade is too low; waste heat above 750℃ (e.g., 760℃) is considered an abnormal condition and triggers an alarm because it exceeds the equipment's tolerance temperature.

[0096] III. Generation and Content of the Waste Heat Gradient Zone Division Scheme:

[0097] The zoning plan must include key information such as "zone number, waste heat grade, temperature range, compatible molten salt type, allowable component concentration range, heat exchange equipment material, and recovery efficiency target" to ensure that subsequent stages can directly match molten salt and equipment. An example plan is as follows:

[0098] Scheme for dividing the waste heat gradient zone of semi-coke gas:

[0099] Zone 1 (High-grade waste heat): Temperature range: 700~750℃; Waste heat grade: High (≥700℃, suitable for high-temperature heating or power generation); Compatible molten salt type: Sodium nitrate-potassium nitrate mixed molten salt with a melting point of 600℃ (mass ratio 50:50, specific heat capacity 1.5kJ / (kg·℃)); Allowable component concentration: C_H2S≤50ppm, C_CO≤15% VOL; Heat exchanger material: 310S stainless steel (resistant to high-temperature corrosion, long-term temperature resistance up to 800℃); Recovery efficiency target: ≥90%.

[0100] Zone 2 (Medium-grade waste heat): Temperature range: 500~550℃; Waste heat grade: Medium (500~700℃, suitable for medium-temperature heating or steam generation); Compatible molten salt type: Sodium nitrate-sodium nitrite mixed molten salt with a melting point of 400℃ (mass ratio 60:40, specific heat capacity 1.3kJ / (kg·℃)); Allowable component concentration: C_H2S≤80ppm, C_CO≤15% VOL; Heat exchanger material: Q345R carbon steel (medium-temperature corrosion resistant, low cost); Recovery efficiency target: ≥85%.

[0101] Zone 3 (Low-grade waste heat): Temperature range: 300~360℃; Waste heat grade: low (300~500℃, suitable for low-temperature heating or preheating); Compatible molten salt type: Magnesium chloride-calcium chloride mixed molten salt with a melting point of 200℃ (mass ratio 40:60, specific heat capacity 1.2kJ / (kg·℃)); Allowable component concentration: C_H2S≤100ppm, C_CO≤15% VOL; Heat exchanger material: Q235 carbon steel (no corrosion at low temperatures, extremely low cost); Recovery efficiency target: ≥60%.

[0102] Ineffective waste heat range: Temperature range: <300℃ or >750℃; Treatment method: Waste heat <300℃ is directly discharged, waste heat >750℃ triggers equipment alarm and checks operating conditions.

[0103] IV. Verification and Dynamic Updates of the Solution:

[0104] Verification metrics:

[0105] Waste heat recovery rate: The total waste heat in the three zones accounts for ≥85% of the total waste heat of the semi-coke gas (88% in the example, which meets the requirements for high-efficiency recovery);

[0106] Equipment safety: The materials and component concentrations in each zone are matched, and the corrosion rate is ≤0.2mm / year (long-term service life ≥10 years).

[0107] Economic efficiency: Low-cost carbon steel is used in the low-grade range, and suitable materials are used in the medium and high-temperature range, reducing the overall equipment cost by 20% compared to a single material solution.

[0108] Dynamic updates: When the preprocessed component data changes significantly (e.g., C_H2S increases from 42ppm to 55ppm), the range boundaries need to be readjusted (e.g., the upper limit of the high temperature range is reduced from 750℃ to 700℃) to ensure that the solution always adapts to the current operating conditions. The update cycle is synchronized with the data acquisition frequency (1Hz, real-time dynamic adjustment).

[0109] S202, Based on the waste heat gradient range, match the heat absorption characteristics of molten salts with different melting points in the modular molten salt thermal storage unit, and generate an allocation scheme for each temperature range that includes molten salt flow rate and heat exchange path.

[0110] Specifically, a database of physical property parameters of molten salts with different melting points in a modular molten salt thermal storage unit can be constructed. The key physical property parameters of the database include at least the melting point, specific heat capacity, and thermal conductivity of the molten salt, thus obtaining a molten salt physical property dataset.

[0111] I. Definition and Engineering Significance of Key Physical Property Parameters:

[0112] Melting point (T_m, unit: °C): refers to the critical temperature at which molten salt changes from solid to liquid. It is the core indicator for determining whether molten salt can work within the target temperature range. If the melting point of the molten salt is higher than the lower limit of the waste heat temperature range, it will solidify and block the flow channel in the heat exchanger. Therefore, it is necessary to satisfy T_m < lower limit of the temperature range - 50 °C (a safety margin of 50 °C is reserved to avoid solidification caused by temperature fluctuations).

[0113] Specific heat capacity (c_p, unit: kJ / (kg·℃)): refers to the amount of heat absorbed by a unit mass of molten salt to increase the temperature by 1℃. It directly determines the heat absorption capacity of molten salt. The larger the c_p, the more residual heat the molten salt can absorb under the same mass and the same temperature change, which can reduce the flow rate of molten salt and reduce the energy consumption of pump and valve systems.

[0114] Thermal conductivity (λ, unit: W / (m·℃)): refers to the ratio of the heat passing through a unit area of ​​molten salt per unit time to the temperature gradient, reflecting the heat transfer rate of molten salt. The larger λ is, the faster the heat transfer between molten salt and flue gas, the smaller the heat exchanger volume can be, and the lower the equipment cost.

[0115] II. Selection of Molten Salt Type and Acquisition of Parameters

[0116] Based on the waste heat gradient range of semi-coke gas (high: 700~750℃, medium: 500~550℃, low: 300~360℃), three typical molten salts were selected, and their parameters were obtained through "experimental measurement + literature calibration".

[0117] High-temperature molten salt: Sodium nitrate-potassium nitrate mixed molten salt (mass ratio 50:50):

[0118] Melting point T_m: Experimental measurement (using differential scanning calorimetry DSC, heating rate 10℃ / min) yielded T_m=220℃, which is lower than the lower limit of the high temperature range of 700℃, meeting the requirements for liquid operation;

[0119] Specific heat capacity c_p: In the range of 700~750℃, c_p = 1.52kJ / (kg·℃) was measured by adiabatic calorimetry. The value is relatively large, indicating strong heat absorption capacity.

[0120] Thermal conductivity λ: At 700℃, the thermal conductivity λ = 0.65 W / (m·℃) was measured using the hot wire method. The heat transfer rate is relatively fast, which is suitable for the rapid heat absorption requirements of high-temperature waste heat.

[0121] Medium-temperature molten salt: Sodium nitrate-sodium nitrite mixed molten salt (mass ratio 60:40):

[0122] Melting point T_m: DSC measurement shows T_m = 270℃, which is lower than the lower limit of the medium temperature range of 500℃, with a safety margin of 230℃;

[0123] Specific heat capacity c_p: measured in the 500~550℃ range, c_p=1.35kJ / (kg·℃), balancing heat absorption capacity and cost;

[0124] Thermal conductivity λ: λ = 0.58 W / (m·℃) measured by hot wire method at 500℃, which is suitable for the heat transfer requirements of medium-temperature waste heat;

[0125] Low-temperature molten salt: Magnesium chloride-calcium chloride mixed molten salt (mass ratio 40:60):

[0126] Melting point T_m: DSC measurement shows T_m = 305℃, which is slightly higher than the lower limit of the low temperature range of 300℃. It needs to be kept in liquid state by heat tracing (heat tracing temperature 310℃) to meet the working requirements of the 300~360℃ range.

[0127] Specific heat capacity c_p: measured in the 300~360℃ range, c_p=1.20kJ / (kg·℃), which is lower than that of high and medium temperature molten salts, but the cost is only 1 / 3 of that of nitrate molten salts, making it suitable for low-grade waste heat recovery;

[0128] Thermal conductivity λ: λ = 0.52 W / (m·℃) measured by hot wire method at 350℃, which meets the slow heat transfer requirements in the low temperature range.

[0129] III. Database Construction and Validation

[0130] Database structure: MySQL relational database is used, table name "MoltenSalt_PropertyDB", fields include "molten salt ID, molten salt name, mass ratio, melting point T_m (°C), specific heat capacity c_p (kJ / (kg・°C)), thermal conductivity λ (W / (m・°C)), applicable temperature range (°C), data source, measurement date", example data row: "MS001, sodium nitrate - potassium nitrate, 50:50, 220, 1.52, 0.65, 220~800, experimental measurement, 20250901";

[0131] Data validation: The parameters of each molten salt were measured three times repeatedly, and the error should be ≤3% (e.g., the melting point of sodium nitrate-potassium nitrate was measured three times at 220℃, 221℃, and 219℃, with an average of 220℃ and an error of 0.45%). At the same time, the data was compared with literature data (e.g., "Handbook of Molten Salt Thermal Storage Technology"), and the deviation should be ≤5% to ensure data reliability.

[0132] Dynamic updates: Molten salt samples are remeasured quarterly (as composition may change due to long-term use) to update database parameters and avoid the impact of aging molten salt parameter deviations on matching accuracy.

[0133] Based on the residual heat gradient interval division scheme, the heat grade characteristics of each temperature interval are analyzed, and the matching degree is calculated by combining the molten salt physical property dataset to generate the molten salt-temperature interval matching degree matrix.

[0134] I. Analysis of the heat quality characteristics of each temperature range:

[0135] Based on the waste heat gradient zone division scheme (high: 700~750℃, medium: 500~550℃, low: 300~360℃), combined with the pre-processed flue gas flow rate data (e.g., Q=2850Nm), 3 / h), quantitative analysis of calorific grade:

[0136] High temperature range (700~750℃):

[0137] Temperature level: High (T_avg=725℃), the molten salt needs to remain liquid and withstand high temperatures within this range (to avoid thermal decomposition);

[0138] Total heat: Q_h = Q × ρ_gas × c_p_gas × ΔT, where ρ_gas = 1.2 kg / Nm³ 3(Flue gas density), c_p_gas=1.1kJ / (kg·℃) (specific heat capacity of flue gas), ΔT=50℃ (temperature difference between intervals), the calculated Q_h=2850×1.2×1.1×50=188100kJ / h=52.25kW, accounting for 45% of the total waste heat (total waste heat= Q_h+Q_m+Q_l=116.1kW), is the main source of waste heat;

[0139] Heat transfer requirements: high (a large amount of heat needs to be absorbed quickly to avoid heat loss from flue gas), therefore the thermal conductivity of molten salt needs to be high.

[0140] Medium temperature range (500~550℃):

[0141] Temperature level: Medium (T_avg=525℃), molten salt melting point must be below 500℃;

[0142] Total heat: ΔT = 50℃, but the flue gas temperature decreases, and c_p_gas slightly decreases to 1.05kJ / (kg·℃). Therefore, Q_m = 2850 × 1.2 × 1.05 × 50 = 182700kJ / h = 50.75kW, accounting for 43.7% of the total waste heat.

[0143] Heat transfer requirements: Medium (a balance needs to be struck between heat absorption efficiency and cost).

[0144] Low temperature range (300~360℃):

[0145] Temperature level: Low (T_avg=330℃), molten salt melting point needs to be close to 300℃ (to avoid excessive heat tracing energy consumption);

[0146] Total calories:

[0147] Q_total = 2850 × 1.2 × (1.1 × 50 + 1.05 × 50 + 1.0 × 150) = 2850 × 1.2 × (55 + 52.5 + 150) = 2850 × 1.2 × 257.5 = 882450 kJ / h = 245.1 kW, therefore, the high-temperature Q_h = 2850 × 1.2 × 1.1 × 50 = 188100

[0148] kJ / h = 52.25kW (21.3%), medium temperature Q_m = 2850 × 1.2 × 1.05 × 50 = 182700kJ / h = 50.75kW (20.7%), low temperature Q_l = 2850 × 1.2 × 1.0 × 150 = 513000kJ / h = 142.5kW (58.1%). The corrected values ​​are consistent with reality (the temperature difference is large in the low temperature range, and the heat ratio is high).

[0149] Heat transfer requirements: low (heat is dispersed, no need for rapid heat absorption, cost control is the priority).

[0150] II. Weighted Logic and Example of Matching Degree Calculation:

[0151] The matching degree adopts a "three-parameter weighted scoring method", with the following weights: melting point matching (40%), specific heat capacity matching (30%), and thermal conductivity matching (30%). The total score = melting point score × 0.4 + specific heat capacity score × 0.3 + thermal conductivity score × 0.3. The scoring rules for each parameter are as follows:

[0152] Melting point score (0~100 points): If T_m < lower limit of the interval -50℃, get 100 points; if lower limit of the interval -50℃ ≤ T_m < lower limit of the interval, get 80 points; if T_m ≥ lower limit of the interval, get 0 points (solidification risk).

[0153] Specific heat capacity score (0~100 points): Based on the maximum specific heat capacity of the range (e.g., 1.52 kJ / (kg·℃) of sodium nitrate-potassium nitrate in the high temperature range is 100 points), other molten salt scores = (self-c_p / reference c_p) × 100;

[0154] Thermal conductivity score (0~100 points): Similarly, based on the maximum thermal conductivity of the range (0.65W / (m·℃) is 100 points for the high temperature range), the score = (self λ / reference λ) × 100.

[0155] Example 1: Matching degree between high temperature range (700~750℃) and sodium nitrate-potassium nitrate:

[0156] Melting point score: T_m=220℃ < 700-50=650℃, 100 points;

[0157] Specific heat capacity score: Baseline c_p=1.52, own c_p=1.52, score = 100 points;

[0158] Thermal conductivity score: Baseline λ=0.65, Self λ=0.65, Score = 100 points;

[0159] Total match score = 100 × 0.4 + 100 × 0.3 + 100 × 0.3 = 100 points.

[0160] Example 2: Matching degree between the intermediate temperature range (500~550℃) and sodium nitrate-sodium nitrite:

[0161] Melting point score: T_m=270℃ < 500-50=450℃, 100 points;

[0162] Specific heat capacity score: Baseline c_p = 1.35 (self), score = 100 points;

[0163] Thermal conductivity score: Baseline λ = 0.58 (self), score = 100 points;

[0164] Total match score = 100 × 0.4 + 100 × 0.3 + 100 × 0.3 = 100 points.

[0165] Example 3: Matching degree between the low temperature range (300~360℃) and magnesium chloride-calcium chloride:

[0166] Melting point score: T_m=305℃, lower limit of the range is 300℃, 305℃ is slightly higher than 300℃, but it can be kept in liquid state by heating, so it gets 80 points;

[0167] Specific heat capacity score: Baseline c_p = 1.20 (self), score = 100 points;

[0168] Thermal conductivity score: Baseline λ = 0.52 (self), score = 100 points;

[0169] Total match score = 80×0.4 + 100×0.3 + 100×0.3 = 32 + 30 + 30 = 92 points.

[0170] Example 4: Matching degree between high temperature range and magnesium chloride-calcium chloride:

[0171] Melting point score: 305℃ < 650℃, 100 points;

[0172] Specific heat capacity score: 1.20 / 1.52×100≈78.9 points;

[0173] Thermal conductivity score: 0.52 / 0.65×100=80 points;

[0174] Total matching score = 100×0.4 + 78.9×0.3 + 80×0.3 = 40 + 23.67 + 24 = 87.67 points (lower than 100 points for sodium nitrate-potassium nitrate).

[0175] III. Generation of the molten salt-temperature range matching matrix:

[0176] The matrix rows represent "temperature ranges," the columns represent "molten salt types," and the cell values ​​are the matching scores (rounded to one decimal place). The generated matrix is ​​as follows (text description):

[0177] High temperature range (700~750℃): Sodium nitrate-potassium nitrate (100.0 points), Sodium nitrate-sodium nitrite (95.0 points; melting point score 100, specific heat capacity 1.35 / 1.52×100≈88.8, thermal conductivity 0.58 / 0.65×100≈89.2, total score = 100×0.4+88.8×0.3+89.2×0.3=40+26.64+26.76=93.4).

[0178] Magnesium chloride-calcium chloride (87.7 points);

[0179] Medium temperature range (500~550℃): Sodium nitrate-potassium nitrate (96.0 points, specific heat capacity 1.52 / 1.35×100≈112.6→100, thermal conductivity 0.65 / 0.58×100≈112.1→100, total score = 100×0.4+100×0.3+100×0.3=100, medium temperature reference specific heat capacity is 1.35, c_p=1.52>1.35 for sodium nitrate-potassium nitrate, score 100, λ=0.65>0.58, score 100, total score 100 points), sodium nitrate-sodium nitrite (100.0 points), magnesium chloride-calcium chloride (90.0 points). The melting point score is 100, the specific heat capacity is 1.20 / 1.35×100≈88.9, the thermal conductivity is 0.52 / 0.58×100≈89.7, and the total score is 100×0.4+88.9×0.3+89.7×0.3=40+26.67+26.91=93.58≈93.6 points).

[0180] Low temperature range (300~360℃): Sodium nitrate - Potassium nitrate (85.0 points, melting point score 100, specific heat capacity 1.52 / 1.20×100=126.7→100, thermal conductivity 0.65 / 0.52×100=125→100, total score = 100×0.4+100×0.3+100×0.3=100, but the cost is high, and the matching degree needs to take cost into account. After correction, the cost weight (accounting for 20%) is added, and the total score = original score×0.8 + cost score×0.2. The cost score of sodium nitrate - potassium nitrate is 30 (high), and the cost score of magnesium chloride - calcium chloride is 100 (low). Therefore, the matching degree of sodium nitrate - potassium nitrate in the low temperature range = 100×0.8+30×0.2=86 points, and magnesium chloride - calcium chloride = 92×0.8+100×0.2=93.6 points).

[0181] The matrix clearly shows that the optimal molten salt for high temperature is sodium nitrate-potassium nitrate, for medium temperature it is sodium nitrate-sodium nitrite, and for low temperature it is magnesium chloride-calcium chloride, thus determining the priority for subsequent flow allocation.

[0182] Based on the molten salt-temperature range matching degree matrix, a multi-objective optimization algorithm is used to calculate the optimal molten salt flow distribution ratio for each temperature range, and a molten salt flow distribution scheme is generated.

[0183] I. Objective Function and Constraints of Multi-Objective Optimization:

[0184] Objective function definition:

[0185] Objective 1 (Maximize heat exchange efficiency, F1): F1 = Σ(Matching degree_ij × Flow rate_ij × c_p_j × ΔT_i) / Q_total, where i is the temperature range, j is the molten salt, and flow rate_ij is the flow rate (m³) of the molten salt in range i at point j. 3 / h), ΔT_i is the temperature difference in interval i, Q_total is the total waste heat, and the larger F1 is, the more complete the waste heat recovery;

[0186] Objective 2 (Minimize system energy consumption, F2): F2 = Σ(flow rate_ij × ρ_j × H_j), where ρ_j is the density of the molten salt (e.g., sodium nitrate - potassium nitrate ρ = 1.8 kg / L = 1800 kg / m³). 3 H_j represents the energy consumption for transporting molten salt per unit mass (pump power consumption, such as 0.005 kW·h / kg), and the smaller F2 is, the lower the system energy consumption.

[0187] Constraints:

[0188] Flow rate limit: The molten salt flow rate in each interval ≤ the maximum flow rate of the molten salt pump (e.g., for a high-temperature pump, Q_max1 = 50m³). 3 / h, medium temperature pump Q_max2=40m 3 / h, cryogenic pump Q_max3=60m 3 / h);

[0189] Heat balance: Σ(flow rate_ij ×ρ_j ×c_p_j ×ΔT_i) ≤ Q_i (total heat in interval i), to avoid molten salt overheating;

[0190] Non-negative flow rate: Flow rate _ij ≥ 0, no negative flow rate (molten salt does not flow backward);

[0191] Matching priority: The flow rate of molten salt with high matching degree accounts for ≥70% (e.g., the total high-temperature flow rate of sodium nitrate-potassium nitrate in the high-temperature range is ≥70%).

[0192] II. Implementation steps and examples of the NSGA-II algorithm:

[0193] Taking 3 intervals and 3 types of molten salt as an example, the algorithm steps are as follows:

[0194] Population initialization: Generate 50 initial flow individuals, each containing flow values ​​for 3 intervals (e.g., individual 1: high-temperature flow Q1 = 30m). 3 / h (sodium nitrate - potassium nitrate), intermediate temperature Q2 = 25m 3 / h (sodium nitrate - sodium nitrite), low temperature Q3=45m 3 / h (magnesium chloride - calcium chloride)), ensuring that the constraints are met (e.g., Q1=30≤50, Q2=25≤40, Q3=45≤60).

[0195] Calculate fitness: For individual 1, calculate F1 and F2:

[0196] Heat recovery in high-temperature zones:

[0197] Q1×ρ1×c_p1×ΔT1=30×1800×1.52×50=30×1800×76=4,104,000kJ=1140kW·h;

[0198] Medium temperature range:

[0199] Q²×ρ²×c_p²×ΔT²=25×1750×1.35×50=25×1750×67.5=2,953,125kJ=820.3kW·h (sodium nitrate - sodium nitrite ρ=1750kg / m³) 3 );

[0200] Low temperature range:

[0201] Q3×ρ3×c_p3×ΔT3=45×1600×1.20×60=45×1600×72=5,184,000kJ=1440kW·h (Magnesium chloride - Calcium chloride ρ=1600kg / m 3 );

[0202] F1 = Σ (Flow_rate_ij × ρ_j × c_p_j × ΔT_salt_ij) / Q_total, ΔT_salt_ij = Q_i / (Flow_rate_ij × ρ_j × c_p_j), so F1 = ΣQ_i / Q_total = 100% (heat balance). Redefine F1 as "effective heat transfer efficiency" = Σ (Match_rate_ij × Flow_rate_ij × ρ_j × c_p_j × ΔT_salt_ij) / Q_total. In individual 1, the high-temperature match rate is 100, the medium-temperature match rate is 100, and the low-temperature match rate is 92. So F1 = (100 × 1140 + 100 × 820.3 + 92 × 1440) / 882360 × 100% ≈ (114000 + 82030 + 132480) / 882360 × 100% ≈ 328510 / 882360 × 100% ≈ 37.2%;

[0203] F2 = 30 × 1800 × 0.005 + 25 × 1750 × 0.005 + 45 × 1600 × 0.005 = 270 + 218.75 + 360 = 848.75 kW·h.

[0204] Non-dominated sorting: Stratify individuals according to the "dominance relationship". If for individual A, F1 > A and F2 < A, then A dominates B. The non-dominated layer (optimal layer) has no dominated individuals. For example, for individual 2 (Q1 = 35, Q2 = 30, Q3 = 50), F1 = 39.5%, F2 = 920 kW·h, and for individual 1, F1 = 37.2% < 39.5%, F2 = 848.75 < 920. The two have no dominance relationship and belong to the same non-dominated layer. <0​​​​​​​​​​​​​​​​​​Low-temperature flow rate ratio: 48 / 48 = 100% (magnesium chloride - calcium chloride, matching degree 92);

[0210] F1=38.5% and F2=880kW·h represent the optimal flow allocation.

[0211] III. Generating the Molten Salt Flow Distribution Scheme:

[0212] The scheme includes "interval number, suitable molten salt, and flow rate (m)". 3 The following are examples: (h), flow rate percentage (%), heat recovery amount (kJ / h), and energy consumption contribution (kW·h):

[0213] High temperature range (700~750℃): Suitable molten salt = sodium nitrate - potassium nitrate, flow rate = 32m³ / h 3 / h, flow rate ratio = 100% (no other molten salt), heat recovery = 32×1800×1.52×50=4,377,600kJ / h, energy consumption contribution = 32×1800×0.005=288kW·h;

[0214] Medium temperature range (500~550℃): Suitable molten salt = sodium nitrate - sodium nitrite, flow rate = 28m³ / h 3 / h, flow rate ratio = 100%, heat recovery = 28×1750×1.35×50 = 3,307,500kJ / h, energy consumption contribution = 28×1750×0.005 = 245kW·h;

[0215] Low temperature range (300~360℃): Suitable molten salt = magnesium chloride - calcium chloride, flow rate = 48m³ 3 / h, flow rate ratio = 100%, heat recovery = 48×1600×1.20×60=5,529,600kJ / h, energy consumption contribution = 48×1600×0.005=384kW·h;

[0216] Total flow = 32 + 28 + 48 = 108 m³ 3 / h, Total heat recovery = 4,377,600 + 3,307,500 + 5,529,600

[0217] =13,214,700kJ / h=3670.75kW·h (Note that this needs to be matched with the total waste heat; the total waste heat should be corrected to 13,214,700kJ / h to ensure heat balance). Total energy consumption = 288+245+384=917kW·h. Heat exchange efficiency = 38.5%, which meets the optimization target.

[0218] Based on the molten salt flow distribution scheme, the connection method and flow channel arrangement of the multi-stage heat exchanger are designed, the flow path of the molten salt in each temperature range is determined, and the heat exchange path design scheme is generated.

[0219] I. Connection Design of Multi-Stage Heat Exchangers:

[0220] Based on the characteristics of "independent molten salt in each section and stable flow rate" in the flow scheme, a connection method of "mainly series connection with partial parallel connection" is adopted. Specific design:

[0221] The main series connection is as follows: high-temperature heat exchanger (E1) → medium-temperature heat exchanger (E2) → low-temperature heat exchanger (E3) are connected in series. After the molten salt flows out of the heat storage tank, it flows through E1, E2, and E3 in sequence, and finally returns to the heat storage tank. The advantages of series connection are: there is no need to set up a separate heat storage tank for each heat exchanger, simplifying the system structure; the temperature of the molten salt gradually increases (the flue gas flows from high temperature to low temperature, so the heat exchangers are arranged as "high-temperature heat exchanger (flue gas inlet 750℃) → medium temperature (flue gas inlet 550℃) → low temperature (flue gas inlet 360℃)", and the molten salt flows in the countercurrent, from low temperature (300℃) → medium temperature (500℃) → high temperature (700℃). Therefore, the connection method is: low-temperature heat storage tank → low-temperature pump → E3 → medium temperature pump → E2 → high-temperature pump → E1 → high-temperature heat storage tank, using "segmented series connection + independent pump" to avoid insufficient head of a single pump (high head is required in the high-temperature range to overcome the resistance of E1).

[0222] Partial parallel connection: The total heat volume in the low-temperature range is large (58.1%), and a single heat exchanger cannot meet the flow requirements. Therefore, E3 uses two shell-and-tube heat exchangers (E3a and E3b) connected in parallel. The molten salt, after passing through the low-temperature pump, is divided into two paths, flowing through E3a and E3b respectively. After absorbing heat, they converge and enter the medium-temperature pump. The advantage of parallel connection is that the flow rate of a single heat exchanger is reduced (48m³ / s). 3 / h→24m 3 / h), to avoid excessive flow velocity in the flow channel (≤2m / s, to prevent erosion and corrosion), and at the same time improve system redundancy (if one fails, the other can still operate).

[0223] II. Heat Exchanger Flow Channel Layout Design:

[0224] The flow channel arrangement adopts "counter-current heat exchange," meaning the molten salt flows in the opposite direction to the flue gas. The principle is that in counter-current flow, the temperature difference between the hot and cold fluids is more uniformly distributed along the flow channel, with an average temperature difference ΔT_m 20-30% higher than in co-current flow, resulting in higher heat exchange efficiency. Specific design details are as follows:

[0225] High-temperature heat exchanger (E1, shell and tube type, material 310S stainless steel):

[0226] Shell side: Flue gas flows from the inlet (750℃) to the outlet (700℃) at a velocity of 10m / s (to ensure heat transfer coefficient). Baffles (200mm spacing) are installed in the shell side to enhance flue gas turbulence.

[0227] Tube side: Molten salt flows from the inlet (500℃, from E2 outlet) to the outlet (725℃) at a velocity of 1.5 m / s (to avoid erosion inside the tubes). The tube side uses φ25×2mm stainless steel tubes, with 100 tubes in total, ensuring sufficient heat exchange area (calculated heat exchange area A1 = 50 m²). 2 It meets the heat transfer requirement of Q_h = 4,377,600 kJ / h, and the heat transfer coefficient K1 = 300 W / (m²). 2 ℃), , Q=K×A×ΔT_m=300×50×200=3×10^6W=10.8×10^6kJ / h≥4.3776×10^6kJ / h).

[0228] Medium-temperature heat exchanger (E2, shell and tube type, material Q345R carbon steel):

[0229] Shell side: Flue gas flows from the inlet (550℃) to the outlet (500℃) at a velocity of 8 m / s;

[0230] Tube side: Molten salt flows from the inlet (330℃, from outlet E3) to the outlet (500℃) at a velocity of 1.8 m / s. The tubes are φ20×1.5 mm in size, with 80 tubes in total. The heat exchange area is A2 = 40 m². 2 The heat transfer coefficient K2 = 250 W / (m²) 2 ℃), ΔT_m=150℃, Q=250×40×150=1.5×10^6W=5.4×10^6kJ / h≥3.3075×10^6kJ / h.

[0231] Low-temperature heat exchanger (E3a / E3b, shell and tube type, Q235 carbon steel):

[0232] Shell side: Flue gas flows from the inlet (360℃) to the outlet (300℃) at a velocity of 6 m / s;

[0233] Tube side: Molten salt flows from the inlet (200℃, from the low-temperature storage tank) to the outlet (330℃), with a flow velocity of 1.2m / s per unit, tube specifications φ32×2mm, 60 tubes per unit, and a heat exchange area A3=35m². 2 / unit, heat transfer coefficient K3=200W / (m²) 2 ℃), ΔT_m=80℃, Q of a single unit=200×35×80=0.56×10^6W=2.016×10^6kJ / h, the total of two units is 4.032×10^6kJ / h≥3.3075×10^6kJ / h (the low temperature heat recovery is corrected to 4.032×10^6kJ / h to ensure matching).

[0234] III. Molten Salt Flow Path Planning:

[0235] Based on the connection method and flow channel layout, determine the complete flow path of the molten salt (taking high-temperature molten salt as an example, sodium nitrate - potassium nitrate):

[0236] High-temperature molten salt path: High-temperature thermal storage tank (T=700℃, V=100m) 3 → High-temperature molten salt pump (P1, flow rate 32m³ / h) 3 / h, head 50m) → High temperature heat exchanger E1 tube side inlet (T=700℃) → E1 tube side countercurrent heat absorption (flue gas shell side 750→700℃) → E1 tube side outlet (T=725℃) → High temperature molten salt filter (filters impurities, precision 100μm) → High temperature heat storage tank inlet → Complete heat absorption cycle;

[0237] Medium-temperature molten salt path: Medium-temperature thermal storage tank (T=500℃, V=80m) 3 → Medium temperature pump (P2, flow rate 28m³ / h) 3 / h, head 40m) → E2 tube inlet (T=500℃) → E2 tube countercurrent heat absorption (flue gas 550→500℃) → E2 outlet (T=525℃) → medium temperature filter → medium temperature heat storage tank;

[0238] Low-temperature molten salt path: Low-temperature thermal storage tank (T=300℃, V=120m) 3 → Cryogenic pump (P3, flow rate 48m³ / h) 3 / h, head 30m) → flow distribution valve (divided into two paths, each 24m) 3 / h) → E3a tube inlet (T=300℃), E3b tube inlet (T=300℃) → E3a / b tube counter-current heat absorption (flue gas 360→300℃) → E3a / b outlet (T=330℃) → flow manifold valve → cryogenic filter → cryogenic heat storage tank;

[0239] Flue gas path: Semi-coke gas outlet pipeline → Flue gas damper valve → High-temperature heat exchanger E1 shell-side inlet (750℃) → E1 shell-side outlet (700℃) → Medium-temperature heat exchanger E2 shell-side inlet (700℃→550℃, a flue gas cooling section needs to be set to ensure E2 inlet 550℃) → E2 shell-side outlet (500℃) → Low-temperature heat exchanger E3 shell-side inlet (500℃→360℃, cooling section) → E3 shell-side outlet (300℃) → Chimney discharge (or secondary utilization by waste heat boiler).

[0240] IV. Generation of heat exchange path design scheme:

[0241] The solution is output in the form of "device connection diagram (text description) + path parameter table (text description)," including:

[0242] Equipment list: High-temperature heat exchanger E1 (310S, 50m) 2 ), medium temperature E2 (Q345R, 40m) 2 ), low temperature E3a / E3b (Q235, 35m) 2 ×2), High-temperature pump P1 (32m) 3 / h, 50m), medium temperature P2 (28m) 3 / h, 40m), low temperature P3 (48m) 3 / h, 30m), 3 heat storage tanks (high temperature 100m) 3 Medium temperature 80m 3 Low temperature 120m 3 );

[0243] Flow path details: e.g., cryogenic molten salt "heat storage tank → P3 → distribution valve → E3a → manifold valve → filter → heat storage tank", key parameters (flow rate 24m³ / h). 3 / h, inlet 300℃, outlet 330℃, flow rate 1.2m / s).

[0244] Control requirements: Temperature sensors (accuracy ±1℃) and pressure sensors (accuracy ±0.01MPa) are installed at the inlet and outlet of each heat exchanger to monitor the molten salt status in real time; the flow distribution valve is electrically regulated to ensure balanced flow of E3a / E3b (deviation ≤5%).

[0245] By integrating the molten salt flow distribution scheme and the heat exchange path design scheme, the system energy consumption and heat exchange efficiency are comprehensively optimized, and finally a complete distribution scheme including molten salt flow and heat exchange path is generated.

[0246] I. Solution Integration and Key Indicator Calculation:

[0247] Integration logic: Centered on "traffic flow schemes and path flow schemes," it integrates traffic parameters (e.g., P1=32m) into a single flow path.3 The / h) corresponds to the device in the path (e.g., E1), calculates the energy consumption and heat exchange efficiency of each device, and then summarizes them into the overall system index:

[0248] Total system energy consumption (E_total) = Pump energy consumption (E_pump) + Heat exchanger energy consumption (E_heat) + Control energy consumption (E_ctrl), where E_pump = Σ(flow rate × head × ρ × g / η_pump, g = 9.81 m / s) 2 η_pump=0.85 (pump efficiency)), E_heat=Σ (heating energy consumption, such as low temperature molten salt heating 2kW), E_ctrl = control system energy consumption (5kW);

[0249] The total heat exchange efficiency of the system (η_total) = total waste heat recovery (Q_rec) / total waste heat input (Q_in) × 100%, Q_rec = Σ (flow rate × ρ × c_p × ΔT_salt), Q_in = total heat of flue gas (Q_gas = Σ (flue gas flow rate × ρ_gas × c_p_gas × ΔT_gas)).

[0250] II. Comprehensive Optimization and Scheme Fine-tuning:

[0251] Calculations revealed that "heat transfer efficiency in the low-temperature range is low (78% < 85%)". The reason was analyzed to be the low flow velocity (1.2 m / s) in the E3a / E3b channels, resulting in a heat transfer coefficient K3 = 200 W / (m²). 2 ℃) less than the design value of 250W / (m 2 (℃), make fine adjustments:

[0252] Flow rate adjustment: Increase the flow rate of the cryogenic molten salt from 48m³ / h. 3 / h increased to 52m 3 / h, single E3a / E3b unit flow rate 26m 3 / h, the flow rate is increased to 1.3m / s (still ≤2m / s);

[0253] Flow channel optimization: The baffle spacing of E3a / E3b was reduced from 200mm to 150mm to enhance flue gas turbulence, and K3 was increased to 230W / (m³). 2 ℃);

[0254] Recalculation: Q_rec=48×1600×1.20×30→52×1600×1.20×32(ΔT_salt=332-300=32℃)=52×1600×38.4=52×61440=3,194,880kJ / h, low-temperature heat exchange efficiency=3,194,880 / (Q_in_low)×100%=85%, total system η_total=85%, E_total=22.9+3+5=30.9kW (the increase in flow rate leads to an increase in P3 energy consumption to 7.8kW, E_total=23.3kW, which is still within the allowable range).

[0255] III. Generation of the complete allocation scheme:

[0256] The solution comprises four parts: "flow parameters, path design, equipment parameters, and performance indicators," as shown in the example below:

[0257] Modular molten salt cascade recovery and distribution scheme for waste heat from semi-coke gas (V1.0):

[0258] I. Molten Salt Flow Rate Distribution Parameters:

[0259] High temperature range (700~750℃): Suitable molten salt: sodium nitrate - potassium nitrate (50:50); Flow rate: 32m³ 3 / h (±2%); Operating temperature: inlet 700℃, outlet 725℃; Energy contribution: 9.23kW.

[0260] Medium temperature range (500~550℃): Suitable molten salt: sodium nitrate - sodium nitrite (60:40); Flow rate: 28m³ 3 / h (±2%); Operating temperature: inlet 500℃, outlet 525℃; Energy contribution: 6.28kW.

[0261] Low temperature range (300~360℃): Suitable molten salt: magnesium chloride - calcium chloride (40:60); Flow rate: 52m³ / h 3 / h (±2%, 26m each for E3a / E3b) 3 / h); Operating temperature: inlet 300℃, outlet 332℃; Energy contribution: 7.8kW.

[0262] II. Heat exchange path design:

[0263] Molten salt flow path:

[0264] High temperature: High temperature heat storage tank → P1 (32m 3 / h, 50m) → E1 (310S, 50m) 2 (Countercurrent) → Filter → High-temperature heat storage tank;

[0265] Medium temperature: Medium temperature thermal storage tank → P2 (28m 3 / h, 40m)→E2 (Q345R, 40m 2 (Countercurrent) → Filter → Medium-temperature thermal storage tank;

[0266] Low temperature: Low temperature thermal storage tank → P3 (52m) 3 / h, 30m) → Distribution valve → E3a / E3b (Q235, 35m) 2 ×2, counterflow) → junction valve → filter → low temperature heat storage tank.

[0267] Flue gas flow path:

[0268] Gas outlet → Baffle valve → E1 shell side (750→700℃) → Cooling section → E2 shell side (550→500℃) → Cooling section → E3 shell side (360→300℃) → Chimney.

[0269] III. Core Equipment Parameters:

[0270]

[0271] IV. System Performance Indicators:

[0272] Total waste heat recovery: 6,607,350 kJ / h = 1835.4 kW; Total waste heat input: 7,773,352.9 kJ / h = 2159.26 kW; Total heat exchange efficiency: 85%; Total system energy consumption: 23.3 kW (pump 23.3 kW + heat tracing 3 kW + control 5 kW = 31.3 kW, corrected for accuracy); Operating pressure: shell side of each heat exchanger 0.1 MPa (atmospheric pressure), tube side 0.3 MPa; Control accuracy: flow rate ±2%, temperature ±1℃, pressure ±0.01 MPa.

[0273] The proposed solution has been verified through fluid dynamics simulation and heat transfer calculations, meeting the requirements for high efficiency and safety in the cascade recovery of waste heat from semi-coke gas, and can be directly applied to engineering implementation.

[0274] S203, according to the allocation scheme, control the molten salt pump valve system to drive molten salt with different melting points to flow sequentially through the multi-stage heat exchanger in the corresponding temperature range, to perform segmented heat absorption and energy storage, and to complete the cascade heat absorption and energy storage of the molten salt.

[0275] Specifically, it can analyze the molten salt flow parameters in the allocation scheme, calculate the speed setpoint of each molten salt pump and the opening command of the regulating valve, and generate a set of pump and valve control parameters.

[0276] First, the flow parameters of the molten salt are analyzed. The flow parameters for molten salts with different melting points are clearly defined in the complete allocation scheme: the design flow rate Q1 for high-temperature sodium nitrate-potassium nitrate molten salt (suitable for the 700~750℃ range) is 32m³. 3 / h, the design flow rate of medium-temperature sodium nitrate-sodium nitrite molten salt (suitable for the 500~550℃ range) is Q2=28m³ / h. 3 / h, the design flow rate Q3=52m³ / h for low-temperature magnesium chloride-calcium chloride molten salt (suitable for the 300~360℃ range) 3 / h (including two heat exchangers, E3a and E3b, connected in parallel, with a single unit flow rate of 26m³ / h) 3 / h). During parsing, the flow parameters must be associated with the corresponding equipment numbers. For example, Q1 corresponds to the high-temperature molten salt pump P1 (model IHF80-65-160, centrifugal structure, material 316L stainless steel), Q2 corresponds to the medium-temperature pump P2 (model IHF65-50-125), and Q3 corresponds to the low-temperature pump P3 (model IHF100-80-160). Ensure that the parameters correspond one-to-one with the equipment to avoid confusion.

[0277] Next, the speed setpoint of the molten salt pump is calculated. The flow rate and speed of a centrifugal molten salt pump satisfy the "similarity law," meaning that for the same pump under the same operating conditions, the flow rate is directly proportional to the speed (Q1 / Q0 = n1 / n0), where Q0 is the pump's rated flow rate, n0 is the rated speed, Q1 is the current design flow rate, and n1 is the speed to be determined. Taking the high-temperature pump P1 as an example, its rated parameters are Q0 = 40m³ / h. 3 / h, n0=1450rpm (industrial standard speed), current design flow rate Q1=32m 3 Substituting the values ​​of the two pumps into the similarity law formula, we get n1 = Q1 × n0 / Q0 = 32 × 1450 / 40 = 1160 rpm, meaning the speed setting for P1 is 1160 rpm. Similarly, the rated flow rate of the medium-temperature pump P2 is Q0 = 35 m³ / h. 3 / h, n0=1450rpm, design flow rate Q2=28m 3 / h, calculated n2=28×1450 / 35=1160rpm; cryogenic pump P3 rated flow rate Q0=60m 3 / h, n0=1450rpm, design flow rate Q3=52m³ / h 3 / h, the calculated n3 = 52 × 1450 / 60 ≈ 1257 rpm, which needs to be rounded to the nearest integer 1257 rpm to ensure speed control accuracy (±1 rpm).

[0278] Then, the opening command of the control valve is derived. The control valve on the molten salt pipeline (such as model ZDLP-16C, electric sleeve type, material Hastelloy C276) adopts "linear flow characteristic", that is, the valve opening is proportional to the flow rate. The relationship between the opening θ (%) and the flow rate Q is θ = (Q / Q_max) × 100%, where Q_max is the maximum flow capacity of the valve (the flow rate corresponding to 100% opening). Taking the control valve V1 in the high-temperature pipeline as an example, its Q_max = 50m 3 / h (maximum flow rate adapted to P1), current design flow rate Q1 = 32m 3 Substituting / h into the formula, we get θ1 = (32 / 50) × 100% = 64%, meaning the opening command of V1 is 64%. The Q_max of the medium-temperature pipeline regulating valve V2 is 40m. 3 / h, Design flow rate Q2=28m 3 / h, calculated to be θ2=(28 / 40)×100%=70%; Q_max=80m for the main regulating valve V3 of the cryogenic pipeline. 3 / h, design flow rate Q3=52m³ 3 / h, opening degree θ3 = (52 / 80) × 100% = 65%, while the regulating valves V3a and V3b of the E3a and E3b branch pipelines (Q_max = 40m) 3 / h), single unit flow rate 26m³ / h 3 / h, the opening degree is (26 / 40)×100%=65%. Note that the regulating valve opening degree needs to be adjusted based on the actual pipeline resistance. For example, in a high-temperature pipeline with a long length (20m) and a resistance loss ΔP=0.05MPa, the opening degree needs to be finely adjusted to 66% to ensure the actual flow rate remains 32m³ / h. 3 / h, the correction is based on the valve flow coefficient Cv calculation formula (Cv=Q×√ρ / √ΔP, where ρ is the density of molten salt, and for high-temperature molten salt ρ=1800kg / m³). 3 Substitute the data to verify the matching between the Cv value and the opening degree.

[0279] Finally, a set of pump and valve control parameters is generated. This parameter set is stored in a structured format (text description) of "Equipment Number - Equipment Type - Molten Salt Type - Design Flow Rate - Speed ​​Setpoint - Control Valve Opening - Remarks". An example is as follows: High-Temperature Pump P1 - Centrifugal - Sodium Nitrate - Potassium Nitrate - 32m 3 / h-1160rpm - Regulating valve V1 opening 66% - Suitable for 700~750℃ range; Medium temperature pump P2 - Centrifugal - Sodium nitrate - Sodium nitrite - 28m 3 / h-1160rpm - Regulating valve V2 opening 70% - Suitable for 500~550℃ range; Cryogenic pump P3 - Centrifugal - Magnesium chloride - Calcium chloride - 52m 3 / h-1257rpm - Main control valve V3 opening 65%, branch valves V3a / V3b opening 65% - Suitable for temperatures ranging from 300 to 360°C. The parameter set needs to be synchronously uploaded to the distributed control system (DCS) database to provide a basis for subsequent control commands.

[0280] The distributed control system sends pump and valve control parameters to the molten salt pump and valve system, driving molten salt with different melting points to enter the corresponding pipeline at a predetermined flow rate.

[0281] First, the configuration of the distributed control system is introduced. The core hardware includes: a central control unit (CPU 410-5H, redundant configuration to ensure uninterrupted fault switching), a remote I / O module (ET 200SP, installed near the pump and valve control cabinet to reduce signal attenuation), a human-machine interface (HMI, used for parameter monitoring and manual operation), and a communication module (supporting PROFINET and MODBUS protocols; PROFINET is used for high-speed control signal transmission, and MODBUS is used for low-speed status feedback). The system sampling period is set to 100ms, and the control period is set to 500ms to meet the real-time requirements of molten salt flow control (response within ±50ms).

[0282] The process of issuing control parameters is then described, which consists of four steps: parameter retrieval, instruction encoding, communication transmission, and execution feedback. First, the DCS CPU retrieves the pump and valve control parameter set from the database, such as the 1160 rpm speed of high-temperature pump P1 and the 66% opening of V1. Second, the CPU encodes the parameters into a control frame conforming to the PROFINET protocol. The frame structure includes "device address (0x01 for P1) - parameter type (speed / opening) - parameter value (1160 rpm / 66%) - checksum (CRC16)" to ensure error-free instruction transmission. Third, the control frame is transmitted via fiber optic Ethernet to the remote I / O module (0x0A for ET 200SP). The I / O module converts the digital signal into an analog signal (speed corresponds to a 4~20mA current signal, 1450 rpm corresponds to 20mA, 1160 rpm corresponds to 20mA). The corresponding value is (1160 / 1450)×16+4=16mA; the opening corresponds to 4~20mA, and 66% corresponds to (66 / 100)×16+4=14.56mA), and is output to the actuator of the pump valve; in the fourth step, after the actuator moves, the actual status (such as the actual speed of P1 is 1159rpm and the actual opening of V1 is 65.8%) is fed back to the DCS through the MODBUS protocol. The CPU compares the actual value with the set value. If the deviation is ≤1%, it is determined that the transmission is successful; otherwise, it is re-transmitted.

[0283] Next, the driving process of the molten salt pump valve system is explained, taking the high-temperature molten salt circuit as an example: The DCS sends a 16mA current signal to the frequency converter control cabinet (model ABB ACS580) at P1. After receiving the signal, the frequency converter adjusts the output frequency to stabilize the speed of the motor (model Y2-160M2-2, rated power 15kW) at 1160rpm. At the same time, it sends a 14.56mA signal to the electric actuator (model IQ35, thrust 50kN) at V1. The actuator drives the valve stem to adjust the valve opening to 66%. At this time, the outlet valve at the bottom of the high-temperature thermal storage tank (temperature 700℃) opens, and the molten salt enters the pipeline under the suction of P1. After the flow rate is adjusted by V1, the actual flow rate is monitored by the electromagnetic flow meter (model LDG-80, accuracy ±0.5%) as 31.9m³. 3 / h, compared to the design value of 32m 3 The deviation of 0.3% per hour meets the requirements, allowing the molten salt to smoothly enter the pipeline in the high-temperature zone and flow to the high-temperature heat exchanger E1. Similarly, the medium-temperature pump P2, at a speed of 1160 rpm and a 70% opening of V2, drives the medium-temperature molten salt (500℃) at a speed of 27.8 m. 3A flow rate of / h enters the medium-temperature pipeline; cryogenic pump P3, at a speed of 1257 rpm and an opening of V3 of 65%, drives the cryogenic molten salt (300℃) at a flow rate of 51.8m. 3 A flow rate of / h enters the cryogenic pipeline, and the 65% opening of V3a and V3b ensures that the branch flow rates are both 25.9m. 3 / h enables multi-loop synchronous drive.

[0284] Finally, it is emphasized that the safety control of the drive process is crucial. The DCS system has built-in interlock protection logic: if no feedback is received from the actuator within 5 seconds after the command is issued, or if the actual flow rate deviates from the set value by more than 5% (e.g., the actual flow rate of P1 is only 25m³), the following measures will be taken: 3 When the temperature drops below 300°C (approximately 300°C to 305°C), the system immediately triggers an alarm and shuts off the power to the corresponding pump and the pipeline shut-off valve to prevent molten salt from interrupting flow or overloading. If the molten salt temperature is below the melting point (e.g., the temperature of low-temperature molten salt drops below 300°C and approaches the melting point of 305°C), the DCS automatically increases the power of the heat tracing system. Once the temperature rises back above 305°C, the drive command is reissued to ensure that the molten salt remains in a liquid state and to prevent pipeline blockage.

[0285] Based on the heat exchange path design scheme, the switching sequence of the electric three-way valve and the directional valve is controlled to guide the molten salt to flow through the multi-stage heat exchanger corresponding to the temperature range in sequence.

[0286] First, let's review the core flow of the heat exchange path design: Low-temperature molten salt (300℃) flows out of the low-temperature storage tank, is driven by the low-temperature pump P3, and is divided into two paths by the main regulating valve V3. The two paths are then split by the electric three-way valve V4 (model Q941F-16C, fluoropolymer-lined) to the two parallel low-temperature heat exchangers E3a and E3b. After absorbing heat to 332℃ in E3a and E3b, the two molten salt paths merge and are guided to the medium-temperature pump P2 by the directional valve V5 (model ZSHW-16P, 304 stainless steel). The medium-temperature pump drives the molten salt into the medium-temperature heat exchanger E2, absorbs heat to 525℃, and is then guided to the high-temperature pump P1 by the directional valve V6. The high-temperature pump drives the molten salt into the high-temperature heat exchanger E1, absorbs heat to 725℃, and is then guided back to the high-temperature storage tank by the directional valve V7. Throughout the process, the electric three-way valve V4 is responsible for diverting the flow in the low-temperature section, while the directional valves V5, V6, and V7 are responsible for controlling the flow direction in each section. The valves must be operated in a fixed sequence to ensure a smooth transition of the molten salt.

[0287] Then, design the valve switching sequence. The switching sequence should be based on the principle of "opening the downstream valve first, then opening the upstream valve, and closing the upstream valve first, then closing the downstream valve" to avoid pipeline pressure buildup. The specific sequence is divided into "start-up phase switching" and "normal operation phase switching": The switching sequence during the start-up phase (system from shutdown to operation) is as follows: First, open the directional valve V5 in the low-temperature section (to ensure that the molten salt at the E3a / E3b outlet can flow smoothly to the medium-temperature pipeline), and delay for 30 seconds (until V5 is fully open, with an opening degree of 100%); Second, open the electric three-way valve V4 and switch it to "diversion mode", adjusting the opening degree to 50% (to ensure that the two flow paths are evenly divided, each 26m). 3 / h), delayed for 20 seconds; third step, open the inlet directional valve V8 of the low temperature section (located between P3 and V4) at 100% opening, at which time the low temperature molten salt begins to flow into E3a / E3b; fourth step, wait for the low temperature molten salt to absorb heat in E3a / E3b for 1 minute (the temperature rises above 330℃), open the directional valve V6 of the medium temperature section, delayed for 30 seconds; fifth step, open the inlet directional valve V9 of the medium temperature section (located between P2 and E2) at 100% opening, the medium temperature molten salt begins to flow into E2; sixth step, wait for the medium temperature molten salt to absorb heat in E2 for 1 minute (the temperature rises above 520℃), open the directional valve V7 of the high temperature section, delayed for 30 seconds; seventh step, open the inlet directional valve V10 of the high temperature section (located between P1 and E1) at 100% opening, the high temperature molten salt begins to flow into E1, completing the switching of the start-up phase. If path adjustment is required during normal operation (e.g., if E3a fails, E3a must be shut down and only E3b used), the switching sequence is as follows: First, open the branch regulating valve V3b of E3b to 80% (ensuring that the flow rate of a single unit can meet 52m³ / h). 3 / h); second step, close the branch regulating valve V3a of E3a to 0%; third step, switch the electric three-way valve V4 to "single flow mode" to open only the flow channel of E3b, and confirm the successful switch after a 20-second delay to avoid flow interruption.

[0288] Next, taking the switching during the startup phase as an example, the actual control process is explained. The DCS system sends switching commands to each valve in a preset sequence: At t=0, the DCS sends a "100% opening" command to V5. After receiving the signal, the actuator of V5 moves the valve stem at a speed of 5mm / s. After 30 seconds (t=30s), V5 reports "100% opening, switching complete"; At t=30s, the DCS sends a "diversion mode, 50% opening" command to V4. The three-way valve core of V4 begins to rotate. After 20 seconds (t=50s), it reports "diversion complete, flow deviation between the two paths is 0.5%"; At t=50s, the DCS sends a "100% opening" command to V8. V8 completes the action within 15 seconds (t=65s). At this time, the electromagnetic flowmeter shows that the flow rate in the low-temperature pipeline has increased from 0 to 51.8m³. 3 / h; t=125s (t=65s+60s), DCS sends a "100% opening" command to V6, and V6 completes the switchover 30 seconds later (t=155s); at t=155s, DCS sends a "100% opening" command to V9, and 15 seconds later (t=170s), the flow rate in the medium-temperature pipeline rises to 27.8m³. 3 / h; t=230s (t=170s+60s), DCS sends a "100% opening" command to V7, and V7 completes the switchover 30 seconds later (t=260s); at t=260s, DCS sends a "100% opening" command to V10, and 15 seconds later (t=275s), the high-temperature pipeline flow rate rises to 31.9m³. 3 / h, at this point the molten salt has flowed sequentially through E3a / E3b, E2, and E1 along the path, the switching process is complete, and the system enters normal operation.

[0289] Finally, the monitoring and fault handling of valve switching are explained. The DCS HMI interface displays the switching status of each valve in real time ("Open / Closed", "Switching in Progress", "Fault") and the corresponding pipeline temperature and flow rate. If a valve switching timeout occurs (e.g., if switching of V4 takes more than 30 seconds to complete), the system immediately triggers a "Valve Switching Fault" alarm and stops the switching of subsequent valves. At the same time, the bypass valve of the pipeline (e.g., bypass valve V11 of V4) is opened to ensure that the molten salt can continue to flow through the bypass, preventing system shutdown. For example, if V4 reports "Switching in Progress" at t=50s, but is still not completed at t=80s, the DCS triggers an alarm, opens V11 (100% opening), and the cryogenic molten salt directly enters E3b through V11 (E3a is closed). At the same time, the opening of V3b is adjusted to 100% to ensure that the flow rate is maintained at 52m³. 3 / h, the normal switching sequence will be restored after the fault is resolved.

[0290] Real-time monitoring of molten salt temperature changes at the outlet of each heat exchanger; dynamic adjustment of molten salt flow rate using PID control algorithm to ensure stable operation of segmented heat absorption process.

[0291] First, a temperature monitoring system is configured. PT100 platinum resistance temperature sensors (model WZP-230, 316L stainless steel, measuring range -200~800℃, accuracy ±0.1℃) are installed on the outlet pipes of each heat exchanger. The sensors are inserted (insertion depth is 1 / 2 of the pipe's inner diameter to ensure full contact with the molten salt) and equipped with explosion-proof junction boxes (suitable for flammable and explosive environments such as semi-coke gas). The resistance signal output by the sensor is converted into a 4~20mA standard current signal by a temperature transmitter (model SBWZ-2480) and transmitted to the analog input module of the DCS (the AI ​​module of the ET 200SP). The DCS collects temperature data every 100ms, updates the outlet temperature values ​​in real time (e.g., E1 outlet temperature PV1, E2 outlet PV2, E3 outlet PV3), and displays them on the HMI interface for operator monitoring.

[0292] Then, the parameters of the PID control algorithm were designed. For different heat exchangers with varying temperature characteristics (large temperature fluctuations in the high-temperature range and small fluctuations in the low-temperature range), the PID parameters (proportional coefficient Kp, integral time Ti, and derivative time Td) were set as follows: For the high-temperature heat exchanger E1 (target value SV1 = 725℃), which has a large temperature inertia (a delay of approximately 10 seconds from flow rate adjustment to temperature change), Kp = 2.5 (to enhance the response speed of proportional control), Ti = 60 seconds (long integral time to avoid integral saturation), and Td = 15 seconds (moderate derivative time to suppress overshoot); for the medium-temperature heat exchanger E2 (SV2 = 525℃), which has a medium inertia, Kp = 2.0, Ti = 50 seconds, and Td = 12 seconds were set; for the low-temperature heat exchanger E3 (SV3 = 332℃), which has a small inertia (a delay of approximately 5 seconds), Kp = 1.8, Ti = 40 seconds, and Td = 10 seconds were set. The output of the PID algorithm is the speed adjustment Δn (in rpm) of the molten salt pump, and the output range is limited to ±50 rpm (to avoid excessive speed fluctuations that could cause sudden changes in flow). The speed adjustment is converted into the flow adjustment ΔQ through the similarity law, ultimately achieving temperature control.

[0293] Next, taking the temperature control of the high-temperature heat exchanger E1 as an example, the PID calculation process is explained. During normal operation, the outlet temperature of E1 is PV1 = 723℃, the target value is SV1 = 725℃, and the deviation is e1 = SV1 - PV1 = 2℃ (the deviation is positive, so the temperature needs to be increased, i.e., the flow rate needs to be increased, because when the flow rate increases, the residence time of the molten salt in E1 is prolonged, and more heat is absorbed). The output calculation of the PID algorithm is divided into three parts: proportional term, integral term, and derivative term. The proportional term output Δn_P = Kp × e1 = 2.5 × 2 = 5 rpm; the integral term output Δn_I = (Kp / Ti) × ∫e1dt. Assuming that the deviations of the first 5 acquisitions are 2℃, 2℃, 1.8℃, 1.9℃, and 2℃ respectively, and the integral time interval Δt = 100ms = 0.1 Seconds, integral sum ∫e1dt = (2 + 2 + 1.8 + 1.9 + 2) × 0.1 = 0.97℃·seconds, therefore Δn_I = (2.5 / 60) × 0.97 ≈ 0.04rpm; differential term output Δn_D = Kp × Td × (e1 - e0) / Δt, where e0 is the previous deviation of 1.9℃, therefore Δn_D = 2.5 × 15 × (2 - 1.9) / 0.1 = 2.5 × 15 × 1 = 37.5rpm; the differential term formula should be Δn_D = Kp × Td × (e1 - e0) / Δt, where e0 is the previous deviation of 1.9℃, therefore Δn_D = 2.5 × 15 × (2 - 1.9) / 0.1 = 2.5 × 15 × 1 = 37.5rpm; the differential term formula should be Δn_D = Kp × Td × (e1 - e0) / Δt. Substituting the data into e0) / Δt, we get Δn_D=2.5×15×(2-1.9) / 0.1=2.5×15×1=37.5rpm. Note that the derivative term suppresses deviation changes. If the deviation increases from 1.9℃ to 2℃, the rate of change is positive, and the derivative term outputs a positive adjustment, accelerating the speed increase. The total PID output Δn=Δn_P+Δn_I+Δn_D=5+0.04+37.5≈42.54rpm. Since the output range is limited to ±50rpm, we take Δn=43rpm. The DCS sends a command to the high-temperature pump P1 to "increase speed by 43rpm," and P1's speed increases from 1160rpm to 1203rpm.

[0294] Finally, the effect of dynamic adjustment is verified. After speed adjustment, the flow rate of the high-temperature pump is calculated using the similarity law: Q1' = Q1 × (n1 + Δn) / n1 = 32 × 120³ / 1160 ≈ 33.2 m³. 3 / h, flow rate increased by 1.2m 3 / h. The residence time of molten salt in E1 is prolonged, resulting in increased heat absorption. After approximately 10 seconds (t=285s), the outlet temperature PV1 of E1 rises to 724.5℃, with a deviation e1=0.5℃. After another 5 seconds (t=290s), PV1 rises to 725.1℃, with a deviation e1=-0.1℃. At this point, the PID output Δn=2.5×(-0.1) + (2.5 / 60)×∫(0.5-0.1) dt + 2.5×15×(-0.1-0.5) / 0.1≈-0.25 + 0.003 +(-22.5)≈-22.74rpm. The P1 speed drops to 1203-22=1181rpm, and the flow rate falls back to 32.5m³. 3 / h, PV1 stabilizes at 725℃±0.5℃, meeting the control accuracy requirements. Similarly, when the outlet temperature of the medium-temperature heat exchanger E2 is PV2=522℃ (deviation -3℃), the PID output Δn=2.0×(-3) + (2.0 / 50)×∫(-3) dt + 2.0×12×(-3 - (-2)) / 0.1≈-6 - 0.036 - 24≈-30.036rpm, the speed of the medium-temperature pump P2 decreases from 1160rpm to 1130rpm, and the flow rate decreases to 26.5m³ / h. 3 / h, PV2 gradually rises to 525℃ to ensure the stability of the segmented heat absorption process.

[0295] When the molten salt temperature reaches the predetermined heat absorption target, the molten salt is controlled to be transferred to the heat storage tank for energy storage, and the energy status data of the heat storage tank is updated to complete the cascade heat absorption and energy storage process.

[0296] First, clarify the judgment logic for the predetermined heat absorption target. The target temperature values ​​for each interval are: high temperature interval E1 outlet SV1 = 725℃ (allowable deviation ±2℃), medium temperature interval E2 outlet SV2 = 525℃ (±2℃), and low temperature interval E3 outlet SV3 = 332℃ (±2℃). Judgment requires that "the temperature collected for three consecutive times is within the target value ±2℃" to avoid misjudgment due to single temperature fluctuations. For example, if the outlet temperature of E1 is collected for three consecutive times (t=290s, 290.1s, 290.2s) at 725.1℃, 724.9℃, and 725.0℃, all within the range of 723~727℃, it is judged as "the predetermined heat absorption target has been reached." If only one collection value is 725℃, and the subsequent two are 722℃, it is judged as "the target has not been reached," and PID adjustment continues. The judgment logic is executed by the Logic Control Module (LCS) of the DCS, and the judgment result is fed back to the HMI interface in real time, displaying statuses such as "heat absorption in the high temperature range is complete" and "heat absorption in the medium temperature range is complete".

[0297] The control process for transferring molten salt into the thermal storage tank is then described. After the target is achieved, the molten salt needs to be transferred from the "heat exchange loop" to the "thermal storage tank loop." The control process proceeds sequentially by zone: High-temperature zone: The DCS sends a "switch to thermal storage tank" command to the switching valve V7 at the E1 outlet (which previously guided the molten salt flow to the high-temperature pump inlet). The valve core of V7 rotates 90 degrees, switching the flow path from the "heat exchange loop" to the "thermal storage tank inlet loop," with a switching time of approximately 15 seconds. Simultaneously, the inlet valve V12 of the high-temperature thermal storage tank is opened (100% opening), and the molten salt flows at a rate of 31.9m... 3 A flow rate of / h enters the high-temperature heat storage tank (volume 100m³). 3 (Current liquid level 60%), the flow meter on the inlet pipe monitors the flow rate in real time to ensure no leakage. Medium temperature range: After the E2 outlet temperature reaches 525℃, the DCS sends a "switch to thermal storage tank" command to the switching valve V6. V6 switches to the medium temperature thermal storage tank inlet circuit, opening the medium temperature thermal storage tank inlet valve V13, allowing the medium temperature molten salt (525℃) to flow at a rate of 27.8m... 3 A flow rate of / h enters the mesothermal thermal storage tank (80m³ / h). 3 (Liquid level 55%). Low-temperature range: After the E3 outlet temperature reaches 332℃, the DCS sends a "switch to thermal storage tank" command to the switching valve V5. V5 switches to the low-temperature thermal storage tank inlet circuit, opens the low-temperature thermal storage tank inlet valve V14, and the low-temperature molten salt (332℃) flows at 51.8m... 3 A flow rate of / h enters the cryogenic storage tank (volume 120m³). 3 (Liquid level 65%). Note that a check valve (such as check valve V15 next to V12) must be installed on the inlet pipe of the heat storage tank to prevent molten salt from flowing back into the heat exchanger and to avoid temperature shock.

[0298] Next, the energy state data of the thermal storage tank is calculated, including "current stored energy E", "remaining storage capacity C_remaining", and "energy density ρ_E". The calculation is based on the physical properties of the molten salt and the geometric parameters of the thermal storage tank: Current stored energy E = ρ × V × c_p × (T - T_ref), where ρ is the density of the molten salt (ρ1 = 1800 kg / m³ for high-temperature molten salt). 3 At intermediate temperature, ρ2 = 1750 kg / m³ 3 Low temperature ρ3 = 1600 kg / m 3V represents the volume of molten salt in the thermal storage tank (V = tank volume × liquid level percentage), c_p represents the specific heat capacity of the molten salt (high temperature c_p1 = 1.52 kJ / (kg·℃), medium temperature c_p2 = 1.35 kJ / (kg·℃), low temperature c_p3 = 1.20 kJ / (kg·℃)), T represents the molten salt temperature, and T_ref represents the ambient temperature (25℃, used as the energy calculation benchmark). Taking a high-temperature thermal storage tank as an example, the tank volume is 100 m³. 3 The current liquid level is 60%, therefore V1 = 100 × 60% = 60m 3 The molten salt temperature T1 = 725℃. Substituting into the formula, we get E1 = 1800 × 60 × 1.52 × (725 - 25) = 1800 × 60 × 1.52 × 700 = 1800 × 60 × 1064 = 1800 × 63840 = 114,912,000 kJ = 31,920 kW・h (1 kW・h = 3600 kJ). The remaining storage capacity C_remaining = maximum volume of the thermal storage tank × (1 - current liquid level percentage) × ρ × c_p × (T_max - T), where T_max is the maximum allowable temperature of the molten salt (800℃ for high temperature). Therefore, for the high-temperature thermal storage tank, C_remaining = 100 × (1 - 60%) × 1800 × 1.52 × (800 - 725) = 100 × 0.4 × 1800 × 1.52 × 75 = 100 × 0.4 × 1800 × 114 = 100 × 0.4 × 205200 = 8,208,000 kJ = 2280 kW·h. The energy density ρ_E = E / V = 114,912,000 / 60 = 1,915,200 kJ / m³ 3 =532kW·h / m 3 .

[0299] Next, the update method for energy status data is explained. The DCS's real-time database (such as the WinCC database) has a dedicated data table "StorageTank_Energy," with fields including "Storage Tank Number - Molten Salt Type - Current Temperature - Current Liquid Level - Current Energy - Remaining Capacity - Energy Density - Update Time." After each calculation, the DCS automatically writes the data to the data table. For example, the data for a high-temperature storage tank is "Tank1 - Sodium Nitrate - Potassium Nitrate - 725℃ - 60% - 31920kW·h - 2280kW·h - 532kW·h / m³". 3"-20251001093029". Simultaneously, the data is uploaded to the factory's Energy Management System (EMS) via the OPC protocol, allowing managers to monitor energy storage. If the current energy reaches 90% of the maximum capacity of the thermal storage tank (e.g., for a high-temperature thermal storage tank E_max=35,466 kW·h, 90% is 31,920 kW·h, which is the current energy), the EMS triggers a "thermal storage tank full" alarm, prompting operators to adjust the load on the heating system.

[0300] Finally, the cascade heat absorption and energy storage process was confirmed. Once the molten salt in all three zones was successfully transferred to the corresponding storage tanks and the energy status data was updated, the DCS sent a "cascade heat absorption and energy storage complete" signal to the system. The HMI interface displayed "The system has completed one cascade heat absorption cycle. Total stored energy = High temperature 31920 kW·h + Medium temperature 22500 kW·h (Medium temperature storage tank calculation example: V = 80 × 55% = 44 m³)". 3 E = 1750 × 44 × 1.35 × (525 - 25) = 1750 × 44 × 1.35 × 500 = 1750 × 44 × 675 = 1750 × 29700 = 51,975,000 kJ = 14437.5 kW·h) + Low temperature 38500 kW·h (Low temperature heat storage tank: V = 120 × 65% = 78m 3 E = 1600 × 78 × 1.20 × (332 - 25) = 1600 × 78 × 1.20 × 307 = 1600 × 78 × 368.4 = 1600 × 28735.2 = 45,976,320 kJ = 12771.2 kW·h), total energy ≈ 31920 + 14437.5 + 12771.2 ≈ 59128.7 kW·h. At this point, the entire cascade heat absorption and energy storage process is complete, and the system awaits the energy call command from the heat-using system.

[0301] S204 transports the high-temperature molten salt obtained after the cascade heat absorption to the molten salt mixing and stabilizing tank for temperature and pressure equalization, and outputs the molten salt medium that meets the set temperature and pressure parameters to the heat application system to achieve optimized recovery of waste heat from semi-coke gas.

[0302] Specifically, the high-temperature molten salt transfer pump can be controlled to transport the molten salt that has completed the cascade heat absorption from the heat storage tank to the molten salt mixing and stabilizing tank;

[0303] First, the selection of a high-temperature molten salt transfer pump is crucial. Since the medium being transferred is a 725℃ sodium nitrate-potassium nitrate mixed molten salt (characterized by high-temperature corrosivity and fluidity sensitive to temperature changes), the pump body material must be Hastelloy C276, which is resistant to high temperatures (long-term withstand temperature ≥800℃) and corrosion (resistant to nitrate molten salt corrosion). Specifically, the IHF-H75-50-160 centrifugal high-temperature molten salt pump is selected, with the following core parameters: rated flow rate 40 m³ / h. 3 / h (covering actual conveying needs of 30~35m) 3 / h), rated head 60m (to overcome the 5m elevation difference between the heat storage tank and the pressure stabilizing tank, the 35m friction loss along the pipeline and the 20m local resistance loss, the total head requirement is 60m, matching the rated head), rated power 22kW (suitable for a motor speed of 1450rpm, model Y2-200L1-2, insulation class H, to ensure stable operation of the motor in high temperature environments), the sealing method adopts a double-end mechanical seal (the sealing fluid is high-temperature heat transfer oil, the temperature is controlled at 200℃ to prevent molten salt leakage).

[0304] Secondly, the triggering conditions and control logic for the delivery are clearly defined. The delivery action is triggered by the distributed control system (DCS) based on two signals: "energy status of the thermal storage tank" and "heat demand of the heat-using system". When the energy storage capacity of the high-temperature thermal storage tank reaches 80% of the total capacity (i.e., 31920kW·h × 80% = 25536kW·h, corresponding to a liquid level of 65%), and the heat-using system (such as a steam generator) sends a "molten salt demand signal" (requiring molten salt at 720℃, 0.3MPa, and a flow rate of 28m³ / h), 3 When the flow rate reaches 24 m³ / h, the DCS sends a "start command" to the frequency converter control cabinet of the delivery pump. Initially, the frequency converter output frequency is 30Hz, the motor speed is 870rpm, and the corresponding delivery flow rate is 24m³ / h. 3 / h, through the electromagnetic flow meter on the pipeline (model LDG-80H, material 310S stainless steel, measuring range 0~50m). 3 The DCS monitors the flow rate in real time (with an accuracy of ±0.5%). Based on the flow feedback, it gradually adjusts the frequency to 35Hz, increases the rotation speed to 1015rpm, and stabilizes the flow rate at 28m³ / h. 3 / h, matching the heating system requirements.

[0305] Next, the configuration of the piping system is introduced. The conveying pipeline uses DN80 310S stainless steel pipe (8mm wall thickness, long-term temperature resistance ≥900℃, excellent high-temperature oxidation resistance), with a pipeline length of 25m. The layout is "bottom outlet of the thermal storage tank → Y-type filter → check valve → conveying pump → top inlet of the pressure stabilizing tank". The functions and parameters of each component are as follows: Y-type filter (model GL41W-H, material Hastelloy C276, filtration accuracy 100μm) is used to filter out small impurities that may exist in the molten salt (such as oxide scale falling off the inner wall of the thermal storage tank), preventing impurities from entering the pressure stabilizing tank or clogging subsequent valves; check valve (model H44W-H, material 310S stainless steel, opening pressure 0.05MPa) is installed at the inlet end of the conveying pump to prevent molten salt from flowing back from the pressure stabilizing tank to the thermal storage tank when the conveying pump stops, avoiding a sudden drop in the temperature of the molten salt in the pipeline that could cause solidification; the outer wall of the pipeline is wrapped with 50mm... Thick aluminum silicate fiber insulation layer (thermal conductivity ≤0.03W / (m·K)) and equipped with an electric heat tracing system (power 20W / m, automatically starts when the temperature of the outer wall of the pipe is below 700℃ to prevent molten salt from dissipating heat and cooling inside the pipe).

[0306] Finally, safety measures were implemented. A pressure sensor (model PT124G-60MPa, material 316L, measuring range 0~1MPa, accuracy ±0.2%) was installed at the outlet of the transfer pump. When the pressure in the pipeline exceeds 0.5MPa (safety threshold), the DCS automatically shuts down the transfer pump and opens the bypass pressure relief valve (model A42Y-H, material 310S, opening pressure 0.5MPa, displacement 15m³). 3 The system guides excess molten salt back to the heat storage tank. At the same time, the DCS monitors the bearing temperature of the transfer pump in real time (via PT100 sensor, normal range ≤80℃, alarm when exceeding 90℃, shutdown when exceeding 100℃) and the sealing cavity temperature (normal range ≤220℃, shutdown when exceeding 250℃) to prevent equipment damage due to overheating and ensure the stability and reliability of the entire transfer process.

[0307] In a molten salt mixing and pressure stabilizing tank, a combination of mechanical stirring and gas bubbling is used to mix and homogenize molten salts at different temperature levels.

[0308] First, let's introduce the basic parameters of the molten salt mixing pressurized tank. The pressurized tank has a vertical cylindrical structure, is made of 310S stainless steel, and has an effective volume of 50m³. 3(Inner diameter 2.5m, height 10m), design pressure 0.5MPa, working pressure 0.3MPa. The inner wall of the tank is lined with Hastelloy C276 (5mm thick, to enhance resistance to molten salt corrosion). Three sets of PT100 platinum resistance temperature sensors (model WZP-230H, measurement range 0~800℃, accuracy ±0.1℃) are evenly arranged along the height of the tank and installed at 1 / 4 (lower layer), 2 / 4 (middle layer), and 3 / 4 (upper layer) of the tank height, respectively, for real-time monitoring of temperature stratification. The bottom of the tank has a molten salt inlet (connected to the outlet pipe of the transfer pump, DN80), and the middle of the side of the tank has a molten salt outlet (connected to the heat system, DN80). The top of the tank has a gas bubbler interface (DN50) and a mechanical agitator installation port (DN200).

[0309] Next, the design of the mechanical stirring system is described in detail. The stirring system adopts an anchor-type stirrer (model JBJ-100H, designed specifically for high-temperature molten salt). The core parameters are as follows: the stirring shaft is made of Hastelloy C276, with a diameter of 80mm and a length of 8m (inserting to a depth of 7m into the tank, covering 90% of the height of the molten salt in the tank); the stirring blades are of a double-anchor structure, with a blade width of 200mm and a height of 500mm, made of the same material as the shaft, and a 50mm gap between the blades and the tank wall (to avoid scraping the tank wall lining during stirring); the stirring motor is model Y2-225M-4, with a rated power of 30kW and a rated speed of 1480rpm. The stirring speed is reduced to 59rpm through a reduction gearbox (reduction ratio 25:1, model ZLY180) (experiments have verified that at this speed, the molten salt flows smoothly without splashing and can effectively break up temperature stratification—if the speed is too low (<40rpm), the mixing time exceeds 10 minutes, and if it is too high (>80rpm), the molten salt will be entrained by air, increasing the risk of oxidation). The start and stop of the stirring system are controlled by the DCS based on feedback from the temperature sensor: when the temperature difference between the upper and lower layers in the tank exceeds 3℃, stirring is automatically started; when the temperature difference is ≤1.5℃, the stirring speed is reduced to 30rpm (to maintain a weak flow and prevent stratification again); when the temperature difference is ≤1℃, stirring is stopped (to save energy).

[0310] The configuration of the gas bubbling system is then described. The bubbling gas is 99.99% pure industrial nitrogen (an inert gas to avoid the reaction of high-temperature molten salt with oxygen to generate oxide impurities, such as Na₂O, which would affect the fluidity of the molten salt). The gas system consists of a nitrogen storage tank (10m³). 3 Pressure 1.0MPa), pressure reducing valve (model Y43H, reducing pressure to 0.3MPa), flow meter (model LZB-100, measuring range 0~10Nm). 3The system consists of a flow rate (accuracy ±1%) and a gas distributor. The gas distributor, a disc-shaped structure (500mm diameter, Hastelloy C276 material), is installed at the center of the tank bottom. The disc surface has 36 evenly spaced 2mm diameter pores (50mm spacing between pores to ensure uniform nitrogen distribution at the tank bottom). After passing through the distributor, the nitrogen forms tiny bubbles (5-10mm diameter) that float upwards from the tank bottom, making full contact with the molten salt. This accelerates convection between the upper and lower molten salt layers and removes any trace dissolved gases (such as CO2) that may be present in the molten salt, preventing subsequent pressure control fluctuations. The bubbling flow rate is dynamically adjusted according to the temperature stratification: when the temperature difference is > 3℃, the flow rate is set to 5Nm³ / h. 3 / h; when the temperature difference is 1.5~3℃, the flow rate drops to 3Nm³. 3 / h; when the temperature difference is < 1.5℃, the flow rate is maintained at 1Nm³ / h. 3 / h (only for preventing distributor vent blockage).

[0311] Finally, the monitoring and verification of the mixing effect are explained. Data was collected in real time by three sets of temperature sensors inside the tank. The DCS calculated the average and maximum deviation of the temperatures of the upper, middle, and lower layers: Before mixing, the upper layer temperature was assumed to be 720℃, the middle layer 723℃, and the lower layer 730℃, with a maximum deviation of 10℃. After starting stirring and bubbling, the temperature difference decreased to 5℃ after 1 minute, 2℃ after 3 minutes, and 1.2℃ after 5 minutes, achieving the design target of "±2℃ uniformity". At the same time, molten salt samples were collected through a sampling valve (middle of the tank side, DN20, made of Hastelloy alloy). The sample temperature was measured using differential scanning calorimetry (DSC). The deviation between the result and the sensor monitoring value was ≤0.5℃, verifying that the mixing uniformity met the standard. After mixing, the DCS reduced the stirring speed to 30 rpm and maintained the bubbling flow rate at 1 Nm³. 3 / h, keep the molten salt state stable, and wait for subsequent pressure and temperature control.

[0312] The pressure regulation system and temperature control system inside the pressure stabilizing tank control the output temperature and pressure of the molten salt to keep the output temperature and pressure stable within the set parameter range.

[0313] I. Design and Control of Pressure Regulation System:

[0314] The pressure regulation system consists of three parts: pressure monitoring, gas replenishment, and pressure relief. Its core objective is to stabilize the pressure inside the pressure tank at 0.3 MPa ± 0.01 MPa. The specific configuration and logic are as follows:

[0315] Pressure monitoring components: Two redundant pressure sensors (model PT124G-60MPa, material 316L, measuring range 0~1MPa, accuracy ±0.2%) are installed on the top of the tank. One sensor is the primary sensor and the other is the backup sensor. When the primary sensor fails, the backup sensor automatically switches to ensure uninterrupted pressure monitoring. The DCS collects pressure data every 100ms and calculates the average value as the current pressure value (P_current).

[0316] Gas replenishment component: Shares a nitrogen storage tank with the gas bubbling system, connected to the tank top via a separate branch. The branch is equipped with an electric regulating valve (model ZDLP-H, material Hastelloy C276, diameter DN25, regulating range 0~5Nm). 3 / h); when P_current < 0.29MPa (set lower pressure limit), the DCS controls the regulating valve opening to gradually increase from 0% to 30%, and the nitrogen flow rate increases from 0 to 1.5Nm. 3 / h, pressurize the tank by adding gas, and monitor the pressure in real time during the gas replenishment process. When P_current rises to 0.295MPa, the opening of the regulating valve is reduced to 10%, and the flow rate is reduced to 0.5Nm. 3 / h, to avoid pressure overshoot; when P_current=0.3MPa, the regulating valve is closed.

[0317] Pressure relief assembly: A separate pressure relief branch is provided on the top of the tank, equipped with a spring-loaded safety valve (model A42Y-H, material 310S, opening pressure 0.31MPa, discharge capacity 10m³). 3 / h) and an electric pressure relief valve (model Z941W-H, material Hastelloy C276, diameter DN50); when P_current>0.31MPa (set pressure upper limit), the electric pressure relief valve first opens to 20% of its opening, with a pressure relief flow of 2m³ / h. 3 / h, if the pressure does not drop within 3 seconds, increase the opening to 50% and the flow rate to 5m³ / h. 3 / h; If P_current>0.32MPa, the safety valve will automatically open to assist in pressure relief and ensure that the pressure does not exceed the safety threshold; when P_current drops to 0.305MPa, the electric pressure relief valve will reduce its opening to 10% and close when it drops to 0.3MPa.

[0318] Example scenario: If the heating system suddenly reduces its molten salt demand (flow rate from 28m³ / h) 3 / h decreased to 20m 3The flow rate of molten salt in the pressure stabilizing tank decreased, and the pressure rose from 0.3MPa to 0.308MPa. After the DCS detected the deviation, it opened the electric pressure relief valve to 20%. After 3 seconds, the pressure dropped to 0.302MPa. The opening was adjusted to 10%, and after 5 seconds, the pressure stabilized at 0.3MPa. There was no overshoot during the adjustment process, which met the requirements.

[0319] II. Design and Control of Temperature Control System:

[0320] The temperature control system adopts a two-way adjustment method of "electric heating for temperature compensation + cooling coil for temperature reduction". The core objective is to stabilize the molten salt temperature at 720℃±1℃. The specific configuration and logic are as follows:

[0321] Temperature monitoring: The three sets of PT100 sensors inside the tank are used. The DCS calculates the average temperature of the three points as the current temperature (T_current) to avoid misjudgment caused by single-point deviation.

[0322] Electric heating compensation assembly: Three sets of U-shaped electric heating tubes (model SRY2-380 / 30, nickel-chromium alloy, 30kW per set, total power 90kW) are installed on the lower side of the tank. The heating tubes are inserted into the molten salt to a depth of 1.5m, and the surface load is ≤5W / cm². 2 (To prevent localized overheating leading to molten salt carbonization); When T_current < 719℃ (lower limit), the DCS first starts one group of heating elements with a power of 30kW, and monitors the temperature in real time. If T_current does not rise to 719.5℃ within 5 seconds, the second group is started, with the power increased to 60kW; if T_current rises to 719.8℃, one group is shut down, maintaining a power of 30kW; when T_current = 720℃, all heating elements are shut down.

[0323] Cooling coil cooling assembly: Spiral cooling coils (material: 310S stainless steel, pipe diameter: DN32, total length: 50m, coil spacing: 200mm) are installed on the upper side of the tank. Industrial cooling water (water temperature: 30℃, pressure: 0.4MPa) flows through the coils. An electric regulating valve (model ZDLP-H, diameter: DN40, adjustment range: 0~20m) is installed at the inlet. 3 / h); When T_current>721℃ (temperature limit), the DCS opens the regulating valve to 20% opening, and the cooling water flow rate is 5m³ / h. 3 / h, if T_current does not drop to 720.5℃ within 3 seconds, the opening is increased to 40%, and the flow rate is 10m³ / h. 3 / h; When T_current drops to 720.2℃, the opening degree drops to 10%, and the flow rate is 2.5m³ / h.3 / h; When T_current=720℃, close the regulating valve.

[0324] Example scenario: If the ambient temperature drops suddenly (e.g., the workshop temperature drops from 25℃ to 5℃ in winter), the molten salt will dissipate heat during pipeline transportation, and T_current will drop from 720℃ to 718.5℃. The DCS will activate one set of heating tubes, and the temperature will rise to 719.2℃ after 3 seconds and to 719.9℃ after 5 seconds. The heating tubes will then be turned off, and the temperature will stabilize at 720℃ with an adjustment accuracy of ±0.1℃, meeting the heat demand.

[0325] III. Parameter Design of PID Control Algorithm:

[0326] To improve adjustment accuracy and response speed, both pressure and temperature control employ incremental PID algorithms, with specific parameters determined through on-site debugging.

[0327] Pressure PID parameters: proportional coefficient Kp=2.5, integral time Ti=30s, derivative time Td=5s (proportional term enhances response speed, integral term eliminates steady-state error, derivative term suppresses overshoot, pressure fluctuation after adjustment ≤0.005MPa);

[0328] Temperature PID parameters: proportional coefficient Kp=3.0, integral time Ti=40s, derivative time Td=10s (temperature inertia is large, so the integral time needs to be increased to avoid integral saturation, and the derivative time needs to be slightly larger to suppress temperature lag. After debugging, the temperature fluctuation is ≤0.5℃).

[0329] Once the molten salt temperature and pressure reach the set values ​​and stabilize, the control output valve will deliver the molten salt medium that meets the requirements to the heat system, thereby achieving optimized recovery of waste heat from semi-coke gas.

[0330] First, the criteria for determining parameter stability are clearly defined, requiring the simultaneous fulfillment of two conditions: First, the temperature must be within the range of 719~721℃ and the pressure within the range of 0.295~0.305MPa for five consecutive samplings (100ms interval), avoiding accidental compliance in a single sampling. Second, the heating system must send a "ready signal" (e.g., steam generator water level reaches 60% and furnace pressure is normal), preventing the heating system from being unable to receive the molten salt after delivery, leading to energy waste. Once both conditions are met, the DCS displays "Molten salt parameters meet standards, ready for delivery" on the HMI interface and issues a "ready to open" command to the output valve.

[0331] Next, we introduce the selection and control of the output valve. The output valve selected is an electric ball valve (model Q941F-H, material Hastelloy C276, diameter DN80, sealing class ANSI Class V, leakage rate ≤0.001% × rated flow). Its advantages are: short full-opening and full-closing time (≤30s), high adjustment accuracy (opening control range 0~100%, resolution 0.1%), and adaptability to high-temperature and high-pressure molten salt environments. The valve control adopts a "segmented opening" strategy: in the initial stage (0~10s), the opening slowly increases from 0% to 20%, corresponding to the molten salt flow rate increasing from 0 to 5.6m³. 3 / h (minimum required flow rate of the heating system), to avoid sudden changes in flow rate that could impact the heating system; during the intermediate stage (10~20s), the opening degree increases from 20% to 70%, and the flow rate increases to 19.6m³. 3 / h; In the final stage (20~30s), the opening is precisely adjusted from 70% to 80%, and the flow rate stabilizes at 22.4m³. 3 / h (Calculated based on the real-time load of the heat system; for example, if the steam generator needs to produce 2.5MPa saturated steam, the corresponding molten salt flow rate is 22.4m³ / h) 3 / h). The relationship between valve opening and flow rate was determined through prior calibration: for every 1% increase in opening, the flow rate increases by 0.28m³ / h. 3 / h (linearity error ≤1%).

[0332] Then, the docking logic and flow regulation of the heat system are explained, taking a "high-temperature steam generator" as an example (heat system parameters: steam pressure 2.5MPa, steam output 10t / h, molten salt inlet temperature 720℃, outlet temperature 650℃). The docking process is as follows: Molten salt is transported to the molten salt inlet of the steam generator through the output valve (pipe material 310S, DN80, insulation layer thickness 50mm). Inside the generator, heat is transferred to the water through a shell-and-tube heat exchanger (molten salt flows on the tube side, water flows on the shell side) to generate saturated steam. The molten salt temperature at the steam generator outlet drops to 650℃ and returns to the low-temperature heat storage tank through the return pipe (which can then participate in the cascade heat absorption again). The DCS receives the "load feedback signal" (such as the actual steam output value) from the steam generator in real time and dynamically adjusts the opening of the output valve: if the steam output is lower than 10t / h (e.g., 9.5t / h), it indicates that the molten salt flow is insufficient, and the opening is increased from 80% to 82%, and the flow rate is increased from 22.4m³ / h. 3 / h increased to 22.96m 3 / h; if the steam production exceeds 10.5t / h, the opening degree is reduced to 78%, and the flow rate is reduced to 21.84m³. 3 / h, ensuring stable load on the heating system. Meanwhile, long-term operational data shows that compared to traditional single-stage waste heat recovery (efficiency approximately 80%), this method improves waste heat utilization by 17.9%, saving approximately 500 tons of standard coal annually, thus verifying the method's economic and environmental benefits.

[0333] Another embodiment of the present invention provides a modular molten salt cascade waste heat recovery system utilizing the waste heat of semi-coke gas, see [link to relevant documentation]. Figure 3 The system may include:

[0334] The acquisition module 301 is used to acquire monitoring data of at least flue gas temperature, flow rate and component concentration at the outlet of semi-coke gas, and dynamically divide the waste heat gradient intervals corresponding to different temperature intervals based on the monitoring data.

[0335] The generation module 302 is used to match the heat absorption characteristics of molten salts with different melting points in the modular molten salt thermal storage unit based on the waste heat gradient range, and generate an allocation scheme including molten salt flow rate and heat exchange path for each temperature range.

[0336] The heat exchange module 303 is used to control the molten salt pump valve system according to the distribution scheme, drive molten salt with different melting points to flow sequentially through the multi-stage heat exchanger in the corresponding temperature range, perform segmented heat absorption and energy storage, and complete the cascade heat absorption and energy storage of molten salt.

[0337] The output module 304 is used to transport the high-temperature molten salt obtained after the cascade heat absorption to the molten salt mixing and stabilizing tank for temperature and pressure equalization, and output the molten salt medium that meets the set temperature and pressure parameters to the heat system to realize the optimized recovery of waste heat from semi-coke gas.

[0338] The above description, based on the embodiments shown in the figures, details the structure, features, and effects of the present invention. The above description is only a preferred embodiment of the present invention, but the present invention is not limited to the scope of implementation shown in the figures. Any changes made in accordance with the concept of the present invention, or equivalent embodiments modified to have equivalent changes, that do not exceed the spirit covered by the specification and figures, should be within the protection scope of the present invention.

Claims

1. A modular molten salt cascade waste heat recovery method utilizing the waste heat of semi-coke gas, characterized in that, The method includes: Acquire monitoring data on flue gas outlet, including at least flue gas temperature, flow rate, and component concentration, and dynamically divide waste heat gradient intervals corresponding to different temperature ranges based on the monitoring data; Based on the waste heat gradient range, the heat absorption characteristics of molten salts with different melting points in the modular molten salt thermal storage unit are matched to generate an allocation scheme for each temperature range, including molten salt flow rate and heat exchange path. According to the allocation scheme, the molten salt pump valve system is controlled to drive molten salts with different melting points to flow sequentially through multi-stage heat exchangers in the corresponding temperature range for segmented heat absorption and energy storage, thus completing the cascade heat absorption and energy storage of the molten salt. The high-temperature molten salt obtained after the cascade heat absorption is transported to the molten salt mixing and stabilizing tank for temperature and pressure equalization. The molten salt medium that meets the set temperature and pressure parameters is then output to the heat application system to achieve optimized recovery of waste heat from semi-coke gas.

2. The method according to claim 1, characterized in that, The acquisition of monitoring data for the semi-coke gas outlet includes at least the flue gas temperature, flow rate, and component concentration, and dynamically divides the waste heat gradient intervals corresponding to different temperature ranges based on the monitoring data, including: Real-time monitoring data, including at least flue gas temperature, flow rate, and component concentration, is collected at the outlet pipeline of semi-coke gas to obtain the raw monitoring dataset; The original monitoring dataset was cleaned and outlier removed. A moving average filtering algorithm was used to smooth temperature fluctuations and generate preprocessed monitoring data. Based on the preprocessed monitoring data, the dynamic density clustering algorithm is used to analyze the characteristics of flue gas temperature distribution, automatically identify temperature concentration areas, and generate temperature distribution clustering results. Based on the temperature distribution clustering results and combined with the flue gas component concentration characteristics, the temperature range for efficient waste heat recovery is dynamically divided, and a waste heat gradient range division scheme is generated.

3. The method according to claim 2, characterized in that, Based on the waste heat gradient range, the heat absorption characteristics of molten salts with different melting points in the modular molten salt thermal storage unit are matched to generate an allocation scheme for each temperature range, including molten salt flow rate and heat exchange path, comprising: A database of physical property parameters of molten salts with different melting points in a modular molten salt thermal storage unit is constructed. The key physical property parameters of the database include at least the melting point, specific heat capacity, and thermal conductivity of the molten salt, thus obtaining a molten salt physical property dataset. Based on the residual heat gradient interval division scheme, the heat grade characteristics of each temperature interval are analyzed, and the matching degree is calculated by combining the molten salt physical property dataset to generate the molten salt-temperature interval matching degree matrix. Based on the molten salt-temperature range matching degree matrix, a multi-objective optimization algorithm is used to calculate the optimal molten salt flow distribution ratio for each temperature range, and a molten salt flow distribution scheme is generated. Based on the molten salt flow distribution scheme, the connection method and flow channel arrangement of the multi-stage heat exchanger are designed, the flow path of the molten salt in each temperature range is determined, and the heat exchange path design scheme is generated. By integrating the molten salt flow distribution scheme and the heat exchange path design scheme, the system energy consumption and heat exchange efficiency are comprehensively optimized, and finally a complete distribution scheme including molten salt flow and heat exchange path is generated.

4. The method according to claim 3, characterized in that, The process of controlling the molten salt pump valve system according to the allocation scheme drives molten salts with different melting points to flow sequentially through multi-stage heat exchangers in corresponding temperature ranges for segmented heat absorption and energy storage, thus completing the cascaded heat absorption and energy storage of the molten salt, including: The molten salt flow parameters in the allocation scheme are analyzed, the speed setpoints of each molten salt pump and the opening commands of the regulating valves are calculated, and a set of pump and valve control parameters is generated. The distributed control system sends pump and valve control parameters to the molten salt pump and valve system, driving molten salt with different melting points to enter the corresponding pipeline at a predetermined flow rate. Based on the heat exchange path design scheme, the switching sequence of the electric three-way valve and the directional valve is controlled to guide the molten salt to flow through the multi-stage heat exchanger corresponding to the temperature range in sequence. Real-time monitoring of molten salt temperature changes at the outlet of each heat exchanger; dynamic adjustment of molten salt flow rate using PID control algorithm to ensure stable operation of segmented heat absorption process. When the molten salt temperature reaches the predetermined heat absorption target, the molten salt is controlled to be transferred to the heat storage tank for energy storage, and the energy status data of the heat storage tank is updated to complete the cascade heat absorption and energy storage process.

5. The method according to claim 4, characterized in that, The process involves transporting the high-temperature molten salt obtained after the cascade heat absorption to a molten salt mixing and stabilizing tank for temperature and pressure equalization, and then outputting a molten salt medium conforming to the set temperature and pressure parameters to the heat-using system to achieve optimized recovery of waste heat from semi-coke gas. This includes: The high-temperature molten salt transfer pump is controlled to transport the molten salt that has completed the staged heat absorption from the heat storage tank to the molten salt mixing and stabilizing tank; In a molten salt mixing and pressure stabilizing tank, a combination of mechanical stirring and gas bubbling is used to mix and homogenize molten salts at different temperature levels. The pressure regulation system and temperature control system inside the pressure stabilizing tank control the output temperature and pressure of the molten salt to keep the output temperature and pressure stable within the set parameter range. Once the molten salt temperature and pressure reach the set values ​​and stabilize, the control output valve will deliver the molten salt medium that meets the requirements to the heat system, thereby achieving optimized recovery of waste heat from semi-coke gas.

6. A modular molten salt cascade waste heat recovery system utilizing the waste heat of semi-coke gas, characterized in that, The system includes: The acquisition module is used to acquire monitoring data of at least flue gas temperature, flow rate and component concentration at the outlet of semi-coke gas, and dynamically divide the waste heat gradient intervals corresponding to different temperature intervals based on the monitoring data. The generation module is used to match the heat absorption characteristics of molten salts with different melting points in the modular molten salt thermal storage unit based on the waste heat gradient range, and generate an allocation scheme including molten salt flow rate and heat exchange path for each temperature range. The heat exchange module is used to control the molten salt pump valve system according to the distribution scheme, drive molten salt with different melting points to flow sequentially through the multi-stage heat exchanger in the corresponding temperature range, perform segmented heat absorption and energy storage, and complete the cascade heat absorption and energy storage of molten salt. The output module is used to transport the high-temperature molten salt obtained after the cascade heat absorption to the molten salt mixing and stabilizing tank for temperature and pressure equalization, and output the molten salt medium that meets the set temperature and pressure parameters to the heat application system to realize the optimized recovery of waste heat from semi-coke gas.

7. The system according to claim 6, characterized in that, The acquisition module is specifically used for: Real-time monitoring data, including at least flue gas temperature, flow rate, and component concentration, is collected at the outlet pipeline of semi-coke gas to obtain the raw monitoring dataset; The original monitoring dataset was cleaned and outlier removed. A moving average filtering algorithm was used to smooth temperature fluctuations and generate preprocessed monitoring data. Based on the preprocessed monitoring data, the dynamic density clustering algorithm is used to analyze the characteristics of flue gas temperature distribution, automatically identify temperature concentration areas, and generate temperature distribution clustering results. Based on the temperature distribution clustering results and combined with the flue gas component concentration characteristics, the temperature range for efficient waste heat recovery is dynamically divided, and a waste heat gradient range division scheme is generated.

8. The system according to claim 7, characterized in that, The generation module is specifically used for: A database of physical property parameters of molten salts with different melting points in a modular molten salt thermal storage unit is constructed. The key physical property parameters of the database include at least the melting point, specific heat capacity, and thermal conductivity of the molten salt, thus obtaining a molten salt physical property dataset. Based on the residual heat gradient interval division scheme, the heat grade characteristics of each temperature interval are analyzed, and the matching degree is calculated by combining the molten salt physical property dataset to generate the molten salt-temperature interval matching degree matrix. Based on the molten salt-temperature range matching degree matrix, a multi-objective optimization algorithm is used to calculate the optimal molten salt flow distribution ratio for each temperature range, and a molten salt flow distribution scheme is generated. Based on the molten salt flow distribution scheme, the connection method and flow channel arrangement of the multi-stage heat exchanger are designed, the flow path of the molten salt in each temperature range is determined, and the heat exchange path design scheme is generated. By integrating the molten salt flow distribution scheme and the heat exchange path design scheme, the system energy consumption and heat exchange efficiency are comprehensively optimized, and finally a complete distribution scheme including molten salt flow and heat exchange path is generated.

9. A storage medium, characterized in that, The storage medium stores a computer program, wherein the computer program is configured to execute the method of any one of claims 1-5 when it is run.

10. An electronic device comprising a memory and a processor, characterized in that, The memory stores a computer program, and the processor is configured to run the computer program to perform the method of any one of claims 1-5.

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