Low-nitrogen combustion control system of rotary cement kiln

Abstract

The invention relates to the field of cement production thermal control, in particular to a cement rotary kiln low-nitrogen combustion control system which comprises a state monitoring module, a reaction evaluation module, a strategy execution module and a verification optimization module. Direct and real-time monitoring of combustion state parameters of a key area in the furnace is realized, and then balance analysis of carbon-oxygen reaction and nitrogen-oxygen reaction is carried out based on the combustion state parameters, so that the root causes of insufficient carbon-oxygen reaction in a reduction area, too high temperature in a main combustion area or uneven mixing of system gas and materials are accurately diagnosed; and then, a specific diagnosis reason is accurately matched with a quantitative adjustment action, and dynamic factors such as a deviation change rate are introduced to carry out adjustment quantity correction, so that high-coupling-degree closed-loop control of monitoring-diagnosis-adjustment is formed, the dependence on artificial experience is reduced, and the control accuracy and the self-adaptive capability of the system are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of cement production thermal control, and particularly relates to a cement rotary kiln low-nitrogen combustion control system. BACKGROUND

[0002] In the cement industry production, the rotary kiln decomposing furnace is one of the main links of producing nitrogen oxides, in order to meet the increasingly stringent environmental emission standards, the development and application of effective nitrogen oxides emission reduction technology has become the inevitable requirement of the industry development.

[0003] In the prior art, based on the cement rotary kiln, the staged combustion technology combined with the selective non-catalytic reduction denitration technology is usually used to reduce the concentration of nitrogen oxides in the tail gas, and the technology uses the fuel itself or the intermediate product to reduce the generated nitrogen oxides by constructing a specific combustion atmosphere and temperature field in different sections of the decomposing furnace, such as the reduction zone and the main combustion zone.

[0004] However, the existing process control system based on the staged combustion has the following limitations in actual application, specifically: 1. The traditional monitoring means are mostly arranged at the kiln tail outlet, and can only reflect the final emission result. Since the thermal system in the decomposing furnace is complex, the chemical reaction state of the reduction zone and the main combustion zone cannot be analyzed in real time and dynamically, so it is difficult for the operator to master the real-time balance state of the carbon-oxygen reaction and the nitrogen-oxygen reaction in the furnace.

[0005] 2. The coupling degree of fault diagnosis and adjustment strategy is low. When the emission index is not up to standard, the existing technology often relies on artificial experience or simple PID adjustment for intervention, which cannot quickly and accurately diagnose the root cause, and it is difficult to realize the deep coupling matching of fuel, air volume and reaction zone, and even may lead to carbon monoxide exceeding the standard, resulting in insufficient adaptability of the system in long-term operation. SUMMARY

[0006] In order to overcome the shortcomings in the background art, the embodiments of the present application provide a cement rotary kiln low-nitrogen combustion control system, which can effectively solve the problems involved in the above background art.

[0007] The purpose of the present application can be achieved by the following technical scheme: a cement rotary kiln low-nitrogen combustion control system, comprising: a state monitoring module, a reaction evaluation module, a strategy execution module and a verification optimization module.

[0008] The state monitoring module is connected with the reaction evaluation module, the reaction evaluation module is connected with the strategy execution module, and the strategy execution module and the verification optimization module are connected.

[0009] The state monitoring module acquires combustion state parameters in real time through a plurality of sensors arranged in the decomposing furnace and the outlet flue, and the combustion state parameters include oxygen content, carbon monoxide content, nitrogen monoxide concentration and temperature.

[0010] The reaction assessment module performs a balance analysis of carbon-oxygen and nitrogen-oxygen reactions based on the combustion state parameters to assess the staged combustion and denitrification status in the decomposition furnace. If the denitrification status is not up to standard, the diagnosis is that the cause is at least one of the following: insufficient carbon-oxygen reaction in the reduction zone, excessively high temperature in the main combustion zone, or uneven mixing of gas and feed in the system.

[0011] The strategy execution module matches corresponding adjustment actions based on the diagnosed cause. The adjustment actions include at least one of the following: adjustment of the fuel and air volume ratio in the reduction zone, adjustment of the fuel input in the main combustion zone, or adjustment of the overall air volume.

[0012] The verification and optimization module verifies the compliance of kiln tail flue gas emissions based on nitric oxide concentration and ammonia slip concentration after the preset time for the adjustment action has been executed, and archives the data of the entire process for the purpose of optimizing control parameters.

[0013] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects: (1) The present invention realizes direct and real-time monitoring of combustion state parameters in key areas of the furnace by deploying a multi-sensor network in the reduction zone and outlet flue of the decomposition furnace, overcoming the lag and one-sidedness of traditional monitoring only at the kiln tail.

[0014] (2) By analyzing the carbon-oxygen reaction and nitrogen-oxygen reaction based on thermodynamic equilibrium and statistical correlation, this invention can dynamically and quantitatively assess the denitrification status and diagnose the root causes of insufficient carbon-oxygen reaction in the reduction zone, excessively high temperature in the main combustion zone, and uneven mixing of gas and feed in the system.

[0015] (3) By precisely matching specific diagnostic causes with quantitative adjustment actions and introducing dynamic factors such as the rate of change of deviation to correct the adjustment amount, the present invention forms a highly coupled closed-loop control of monitoring-diagnosis-adjustment, which reduces the dependence on human experience and effectively improves the accuracy of control and the adaptive ability of the system. Attached Figure Description

[0016] The present invention will be further described with reference to the accompanying drawings, but the embodiments in the drawings do not constitute any limitation on the present invention. For those skilled in the art, other drawings can be obtained based on the following drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the module connection of the present invention.

[0018] Figure 2 This is a schematic diagram of the carbon-oxygen reaction equilibrium analysis process of the present invention.

[0019] Figure 3 This is a flowchart illustrating the logic of the fuel and air volume ratio adjustment action in the reduction zone of this invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Reference Figure 1 As shown, the present invention provides a low-NOx combustion control system for a cement rotary kiln, comprising: a status monitoring module, a reaction evaluation module, a strategy execution module, and a verification and optimization module.

[0022] The state monitoring module is connected to the reaction evaluation module, the reaction evaluation module is connected to the strategy execution module, and the strategy execution module is connected to the verification and optimization module.

[0023] The status monitoring module collects combustion status parameters in real time through multiple sensors deployed in the decomposition furnace and the outlet flue. These combustion status parameters include oxygen content, carbon monoxide content, nitrogen monoxide concentration, and temperature.

[0024] The specific arrangement process of the multiple sensors deployed in the decomposition furnace and the outlet flue is as follows: On the vertical or near-vertical furnace wall section located between the main combustion zone and the subsequent section in the downward direction of the material, dominated by a reducing atmosphere, at least one physical section is selected as a representative monitoring section. The representative monitoring section should meet the following requirements: it should avoid the orthogonal projection area of ​​the feed inlet, nozzle, or other locations with severe airflow disturbance, and it should also be located within 1 / 3 to 2 / 3 of the theoretical height of the reduction zone in the vertical direction of the furnace body, so as to ensure that the monitoring information can reflect the main state of the reduction reaction.

[0025] At this representative monitoring section, sampling holes are evenly distributed at equal angles along the circumference of the furnace body, with no fewer than four holes. High-temperature thermocouples, oxygen content sensors, and carbon monoxide content sensors are installed to obtain data reflecting the temperature, oxygen concentration, and carbon monoxide concentration in the reduction zone.

[0026] The high-temperature thermocouple can be exemplarily configured as a type B thermocouple, with its measuring end located inside the sampling hole and extending into the furnace atmosphere to avoid interference from the furnace wall boundary layer and directly contact the main airflow in the reduction zone; the oxygen content sensor can be exemplarily configured as a zirconia solid electrolyte oxygen sensor, with its probe inserted into the sampling hole and extending into the furnace to a depth flush with or close to the measuring end of the thermocouple; the carbon monoxide content sensor can be exemplarily configured as an electrochemical gas sensor, with the sampling tube inlet located inside the sampling hole and extending to a depth consistent with the measuring end of the thermocouple.

[0027] After connecting the flue gas outlet flange at the top of the decomposition furnace, the vertical or horizontal flue section before the first turn or connection to other branches is taken as a straight pipe section, and a cross-section with stable airflow is selected. The cross-section with stable airflow should meet the following conditions: First, it is located in the middle of the straight pipe section, and the distance from the upstream outlet flange and the first downstream turning component is not less than twice the equivalent diameter of the flue, so as to ensure that the distribution of flue gas velocity field and concentration field at this cross-section tends to be stable and reduce local eddy interference; Second, the inner wall of the flue at this cross-section should be flat, free of obstacles, and convenient for equipment installation and maintenance.

[0028] At the selected monitoring section, multiple monitoring holes are evenly opened along the circumference of the flue wall. The specific number of monitoring holes is determined according to the shape of the flue cross section: when the flue is a circular cross section, at least 3 monitoring holes are evenly arranged along the same circumference; when the flue is a rectangular cross section, at least 1 monitoring hole is opened at the center of each of its long side walls, and additional monitoring holes can be added to the short side walls according to monitoring needs.

[0029] The monitoring hole is made of a heat-resistant steel pipe base, with its axis perpendicular to the flue wall. The end extending into the inside of the flue is flush with the inner wall of the flue, and a connecting flange is provided on the outside for installing monitoring devices or sealing blind plates.

[0030] The following monitoring device is installed through the monitoring hole: an online analyzer based on the principle of chemiluminescence, which uses a composite sampling probe with dust filtration and heating insulation functions to collect gas from the central area of ​​the flue through the monitoring hole, and then transports it to the analyzer's gas chamber through an insulated pipeline. The analyzer measures and outputs the nitric oxide concentration value in real time.

[0031] A thermocouple temperature measuring device is composed of a retractable armored thermocouple array. It is installed on the monitoring hole through a dedicated multi-channel sealing flange. Its measuring end can be positioned point by point along the radial direction of the flue under mechanical drive, so as to obtain the temperature values ​​at at least three different radial positions from the flue wall to the central area within the same monitoring section.

[0032] This invention achieves direct and real-time monitoring of combustion state parameters in key areas of the furnace by deploying a multi-sensor network in the reduction zone and outlet flue of the decomposition furnace, overcoming the lag and one-sidedness of traditional monitoring only at the kiln tail.

[0033] The reaction assessment module performs a balance analysis of carbon-oxygen and nitrogen-oxygen reactions based on the combustion state parameters to assess the staged combustion and denitrification status in the decomposition furnace. If the denitrification status is not up to standard, the diagnosis is that the cause is at least one of the following: insufficient carbon-oxygen reaction in the reduction zone, excessively high temperature in the main combustion zone, or uneven mixing of gas and feed in the system.

[0034] Reference Figure 2 As shown, the specific process of the carbon-oxygen reaction balance analysis is as follows: obtain the oxygen content, carbon monoxide content, and temperature of the reduction zone of the decomposition furnace in real time.

[0035] Based on the temperature, the pre-stored reaction equilibrium constant-temperature relationship is invoked to determine the target chemical equilibrium constant at the current temperature.

[0036] The method for establishing the pre-stored reaction equilibrium constant-temperature relationship is as follows:

[0037] For key carbon-oxygen reactions in the reduction zone, including incomplete combustion and Boudouar reactions, the standard Gibbs free energy changes of each reaction at different temperatures were obtained based on standard thermodynamic data.

[0038] Based on thermodynamic formulas, the theoretical correspondence between the equilibrium constants of each reaction and the corresponding temperatures is calculated and stored as a dataset.

[0039] Based on the target chemical equilibrium constant and real-time oxygen content, the theoretical equilibrium concentration of carbon monoxide in the reduction zone under current conditions is dynamically calculated by solving the chemical equilibrium equation. The calculation process specifically includes: taking the incomplete combustion reaction as the object, and using the definition of its chemical equilibrium constant, establishing a constraint relationship equation between the partial pressures of various relevant gaseous components under equilibrium conditions. In this equation, the target chemical equilibrium constant and the oxygen partial pressure are known input parameters, while the equilibrium partial pressures of carbon monoxide and carbon dioxide are variables to be determined.

[0040] The real-time oxygen partial pressure is calculated directly by multiplying the total flue gas pressure by the volume percentage concentration of oxygen. Specifically, if the oxygen content sensor measures an oxygen concentration of 5.2% in the flue gas and a total flue gas pressure of 100,000 Pa, then the oxygen partial pressure is 5,200 Pa.

[0041] The Boudouar reaction equilibrium constant corresponding to the real-time temperature is used to establish a second equilibrium relationship between this constant and the theoretical equilibrium partial pressures of carbon monoxide and carbon dioxide. At the same time, based on the total amount of carbon in the fuel fed into the furnace and the flow rate of the flue gas in the reduction zone, the total carbon partial pressure corresponding to the carbon in the flue gas is calculated, and a material conservation equation is established in which the sum of the equilibrium partial pressures of carbon monoxide and carbon dioxide equals the total carbon partial pressure.

[0042] By combining the second equilibrium relationship with the material conservation equation, and eliminating the equilibrium partial pressure of carbon dioxide through algebraic operations, an explicit functional relationship is obtained between the equilibrium partial pressure of carbon monoxide, the total partial pressure of carbon, and the Boudouar reaction equilibrium constant.

[0043] Substituting the explicit functional relationship obtained above into the constraint equation, the theoretical equilibrium partial pressure of carbon monoxide is solved, and the theoretical equilibrium partial pressure of carbon monoxide is converted into volume concentration according to Dalton's law of partial pressure, thus obtaining the theoretical equilibrium concentration of carbon monoxide.

[0044] The real-time carbon monoxide content is compared with the theoretical equilibrium concentration of carbon monoxide. By aligning the real-time carbon monoxide content with the theoretical equilibrium concentration calculated using the same time base, the two are converted into the same concentration characterization unit according to the ideal gas law.

[0045] The theoretical equilibrium concentration value is subtracted from the measured concentration value to obtain the carbon monoxide concentration deviation value, and the trend of this deviation value is continuously tracked and analyzed.

[0046] The specific process of the nitrogen-oxygen reaction balance analysis is as follows: First, the nitrogen monoxide concentration and corresponding average temperature data at the outlet of the decomposition furnace are collected synchronously at a preset sampling period. The instantaneous value of nitrogen monoxide concentration is obtained by real-time measurement by the nitrogen oxide analyzer and output after preprocessing, as well as the temperature of each point measured by multiple thermocouple temperature measuring devices at the same time and on the same monitoring section. The average temperature of the flue gas on the section is obtained after calculation.

[0047] The preset sampling period is dynamically set based on the rate of change of the flue gas parameters at the decomposition furnace outlet. The specific setting method includes: acquiring high-frequency time-series data of nitric oxide concentration and flue gas temperature during a stable operating phase; performing frequency domain analysis on the high-frequency time-series data to obtain its power spectrum; defining the highest frequency corresponding to a specific proportion of cumulative energy in the power spectrum to the total energy, such as 95%, as the highest frequency component of the effective fluctuation; and setting the sampling frequency to no less than twice the highest effective frequency according to the Nyquist sampling theorem, with the sampling period being the reciprocal of the sampling frequency, which can be set to 20 seconds for example.

[0048] Next, the instantaneous values ​​of nitric oxide concentration and their corresponding average temperatures are stored in timestamp order, forming the original nitric oxide concentration sequence and the original temperature sequence, respectively. Simultaneously, the validity of each data point is verified, and data points exceeding a preset reasonable physical range are automatically removed. This preset reasonable physical range is set based on process theory and equipment measurement limits; for example, the preset nitric oxide concentration is 0-1500. The average temperature is preset to .

[0049] Then, a moving average was applied to the two valid original sequences to generate a nitric oxide concentration time series and a temperature time series for subsequent equilibrium analysis and trend identification.

[0050] Using the current acquisition time as the reference point, which refers to the most recent valid data sampling time point that triggers the correlation index calculation, the system uses this sampling time point as the reference point to backtrack by a preset time window, which is usually 10 to 30 minutes. From the nitric oxide concentration time series and the average temperature time series, all data points whose timestamps fall within the preset time window are extracted respectively, thereby obtaining two one-to-one corresponding data segments of equal length.

[0051] A univariate linear regression analysis was performed on the extracted nitric oxide concentration data segment and the average temperature data segment. In this embodiment, the least squares method was used for fitting, with the average temperature data segment as the independent variable and the nitric oxide concentration data segment as the dependent variable. The fitted straight line equation was obtained by solving the equation, and the slope of the fitted straight line equation was used as a real-time correlation index characterizing the sensitivity of nitric oxide concentration to changes in average temperature within the current time window.

[0052] Based on the temperature distribution data of the outlet flue, at each sampling time, the real-time temperature values ​​of multiple radial measurement points within the same monitoring section are obtained from the multi-point thermocouple temperature measuring device to form a temperature distribution sample set. The arithmetic mean and standard deviation of the sample set are calculated. The standard deviation of the temperature distribution quantitatively characterizes the degree of uniformity of the temperature of the outlet flue section.

[0053] The real-time correlation index is compared with the baseline correlation index range obtained from the statistical analysis of the system's historical stable operation data, and the real-time trend of the temperature distribution standard deviation is analyzed simultaneously.

[0054] The methods for obtaining the benchmark correlation index range include, but are not limited to: during the historical stable operation phase, continuously collecting and storing real-time correlation index data under normal operating conditions to form a historical dataset, performing statistical analysis on the historical dataset, calculating its mean and standard deviation, and determining a confidence interval by adding or subtracting a certain number of times the standard deviation, such as ±2 times the standard deviation, based on the mean. The confidence interval is the benchmark correlation index range.

[0055] The concentration deviation values ​​and trends obtained from the carbon-oxygen reaction balance analysis, the real-time correlation index obtained from the nitrogen-oxygen reaction balance analysis and its comparison with the benchmark range, and the standard deviation of the outlet flue temperature distribution and its changing trend are used to evaluate the staged combustion and denitrification status in the decomposition furnace. If the denitrification status is not up to standard, the diagnosis is that the cause is at least one of the following: insufficient carbon-oxygen reaction in the reduction zone, excessively high temperature in the main combustion zone, or uneven mixing of gas and feed in the system.

[0056] The strategy execution module matches corresponding adjustment actions based on the diagnosed cause. The adjustment actions include at least one of the following: adjustment of the fuel and air volume ratio in the reduction zone, adjustment of the fuel input in the main combustion zone, or adjustment of the overall air volume.

[0057] The specific process for diagnosing the cause includes: based on the balance analysis results of the carbon-oxygen reaction, if the carbon monoxide concentration deviation value is consistently positive and shows an upward trend, it is determined that the carbon-oxygen reaction in the reduction zone is insufficient.

[0058] It should be noted that the continuously positive carbon monoxide concentration deviation indicates that the actual carbon monoxide concentration is consistently higher than the thermodynamic equilibrium concentration under the current operating conditions. This reveals that the chemical reaction process in the reduction zone lags behind the theoretical equilibrium state, and is a direct quantitative manifestation of insufficient reaction. Furthermore, the upward trend of the carbon monoxide concentration deviation indicates that this insufficient reaction is dynamically aggravating or continuously deteriorating.

[0059] The upward trend refers to obtaining a sequence of carbon monoxide concentration deviation values ​​over a continuous monitoring period, and then using the least squares method to perform linear fitting on the sequence. If the slope of the fitted line is greater than zero, it is determined that the carbon monoxide concentration deviation value is showing an upward trend.

[0060] Reference Figure 3 As shown, when the diagnostic cause includes insufficient carbon-oxygen reaction in the reduction zone, it is configured to perform a fuel and air volume ratio adjustment action in the reduction zone. The specific process includes: determining the adjustment target and its adjustment direction based on the positive sign characteristic of the carbon monoxide concentration deviation value and the real-time oxygen content.

[0061] If the real-time oxygen content is higher than the oxygen content benchmark value, it is determined that the combustion air input flow rate to the reduction zone of the decomposition furnace should be reduced; otherwise, it is determined that the fuel input flow rate to the reduction zone of the decomposition furnace should be increased.

[0062] The oxygen content benchmark value is the median value of the optimal control range obtained from historical stable operation data.

[0063] Using the carbon monoxide concentration deviation as the basic input, multiply it by the preset adjustment coefficient of the corresponding adjustment object to obtain the theoretical adjustment amount of the adjustment object.

[0064] In this embodiment, the preset adjustment coefficient of the corresponding adjustment object refers to the control gain parameter associated with the combustion air input flow rate to the reduction zone of the decomposition furnace or the fuel input flow rate to the reduction zone of the decomposition furnace. It is determined in advance through historical calibration tests. Specifically, under the condition that the decomposition furnace is in stable operating condition, multiple sets of known small step change experiments are applied to the adjustment object, and the steady-state response change of the carbon monoxide concentration deviation value is recorded. By analyzing the corresponding data of multiple sets of adjustment amount change and deviation value change, the average correlation between the two is established, and the proportional coefficient of the correlation is determined as the preset adjustment coefficient.

[0065] The rate of change of the carbon monoxide concentration deviation is calculated in real time, i.e., its first time derivative.

[0066] When the rate of change is positive, it indicates that the concentration deviation is widening and the degree of deviation of the reaction state in the reduction zone from equilibrium is worsening. Therefore, the previously calculated theoretical adjustment amount is multiplied by a preset correction factor greater than 1 to obtain the final adjustment amount.

[0067] The preset correction factor is determined by analyzing the correlation between the rate of change of carbon monoxide concentration deviation in historical operation and the additional adjustment amount actually applied that can effectively suppress the expansion of the deviation. The specific calibration process is as follows: First, when the system is in a condition with a stable carbon monoxide concentration deviation, the rate of change of the deviation value is recorded to quantify its deterioration trend.

[0068] Subsequently, based on the theoretical adjustment amount, an additional step adjustment amount of known magnitude is applied.

[0069] Monitor and record the magnitude of the additional adjustment amount when the worsening trend of carbon monoxide concentration deviation is effectively suppressed after applying this additional step adjustment amount.

[0070] Repeat the above steps to obtain multiple sets of data pairs, each set containing a specific rate of change and its corresponding additional adjustment that can effectively suppress the trend.

[0071] Finally, by performing linear regression analysis on these data pairs, the proportional relationship between the intensity of the deterioration trend and the required additional adjustment amount is established. This proportional relationship is then normalized by combining the static deviation level under typical operating conditions with the theoretical adjustment amount, and a fixed coefficient value greater than 1 is calculated. This coefficient value is then determined as the preset correction factor.

[0072] When the rate of change is non-positive, in order to maintain smooth adjustment and avoid overshoot, the theoretical adjustment value is directly used as the final adjustment value without amplification.

[0073] The specific process for diagnosing the cause also includes: based on the equilibrium analysis results of the nitrogen-oxygen reaction:

[0074] a. If the real-time correlation index is higher than the baseline correlation index range, it is determined that the temperature of the main combustion zone is too high. The logic is as follows: The real-time correlation index quantitatively characterizes the instantaneous sensitivity of the outlet nitric oxide concentration to the average temperature. In the staged combustion process of the decomposition furnace, the generation rate of thermal nitrogen oxides is extremely sensitive to temperature, especially in the high-temperature zone where it increases exponentially. When the actual temperature of the main combustion zone is too high or there is local overheating, even if the average temperature of the outlet section may still be within the normal range, the surge in nitrogen oxide generation in the high-temperature zone will lead to a significant increase in the overall nitric oxide concentration at the outlet in response to changes in the average temperature, resulting in an abnormally high correlation index. The specific method for determining that the correlation index is higher than the baseline correlation index range is as follows: The real-time correlation index of the latest calculated multiple consecutive sampling periods is compared with the upper limit of the pre-stored baseline correlation index range. If the real-time correlation index of multiple consecutive sampling periods is greater than the upper limit of the baseline correlation index range, it is determined that the real-time correlation index is higher than the baseline correlation index range. The multiple consecutive sampling periods can be exemplarily set to 3.

[0075] When the diagnostic cause includes excessively high main combustion zone temperature, it is configured to perform a main combustion zone fuel input adjustment action, which is logically consistent with the fuel and air volume ratio adjustment action in the reduction zone. The specific process includes:

[0076] Calculate the first difference between the real-time correlation index and the upper limit of the benchmark correlation index range, and use its absolute value as the basic adjustment intensity.

[0077] Calculate the rate of change of the real-time correlation index within a preset time window.

[0078] If the rate of change is positive, the basic regulation intensity and the trend factor are weighted and superimposed according to a preset weight to obtain the corrected total regulation intensity coefficient. The real-time fuel input flow rate is multiplied by this total regulation intensity coefficient to obtain the final fuel flow rate regulation amount.

[0079] The trend factor is a dimensionless trend strength value obtained by comparing the calculated rate of change of the real-time correlation index with a preset reference rate of change.

[0080] The preset weights are determined in advance based on the analysis of the impact of basic deviations and trend changes on the control effect in historical data. If the adjustment command is mainly based on the current static deviation, while also taking into account the dynamic trend, the weight of the basic adjustment intensity can be set to 0.7 for example, and the weight of the trend factor can be set to 0.3 for example.

[0081] If the rate of change is non-positive, the real-time fuel input flow rate is multiplied by the basic regulation intensity to obtain the final fuel flow rate regulation amount.

[0082] b. If the standard deviation of the temperature distribution continues to increase and exceeds its historical normal fluctuation range, it is determined that the gas-fuel mixture in the system is uneven. The logic is as follows: the uniformity of the temperature distribution of the outlet flue section directly reflects the uniformity of the flow field organization and the mixing of fuel, materials and air in the furnace. When the gas-fuel mixture is uneven, it will lead to an imbalance in the spatial distribution of heat release and transfer in the furnace. At the flue outlet, the temperature is higher in some areas and lower in some areas, which will significantly increase the standard deviation of the cross-sectional temperature distribution. The determination of continuous increase is consistent with the logic of the above determination that the carbon monoxide concentration deviation value is on the rise. The "exceeding its historical normal fluctuation range" is defined as: the current temperature distribution standard deviation exceeds the upper limit of normal fluctuation determined by the statistical analysis of the standard deviation data during the historical stable operation period. The historical normal fluctuation range can be taken as the 5%-95th percentile of the historical standard deviation data. When both the continuous increase and exceeding the historical range conditions are met at the same time, the system determines that the gas-fuel mixture is uneven.

[0083] When the diagnostic cause includes uneven mixing of system air and material, it is configured to perform an overall airflow adjustment action. The determination of the adjustment amount also adopts logic based on deviation and rate of change correction. The specific process includes:

[0084] Obtain the upper limit of the historical statistical normal fluctuation range of the temperature distribution standard deviation, and obtain the current benchmark total air volume of the system.

[0085] The second difference between the standard deviation of the temperature distribution and its upper limit value is calculated in real time. The second difference is divided by the upper limit value to obtain the relative deviation degree characterizing the current degree of mixing unevenness.

[0086] The rate of change of the standard deviation of the temperature distribution within a first preset time window is calculated, and the rate of change is divided by the maximum fluctuation range under historical normal operating conditions to obtain the normalized rate of change.

[0087] The comprehensive adjustment coefficient is obtained by multiplying the relative deviation degree by the normalized rate of change and the preset prediction feedforward coefficient.

[0088] The product of the normalized rate of change and the preset prediction feedforward coefficient is used as the relative deviation degree characterizing the future degree of mixing unevenness.

[0089] The physical meaning of the prediction feedforward coefficient is: the foresight time required to offset the lag in the dynamic response of the system. The value of this coefficient is determined by the system identification method, specifically: applying a known step disturbance to the system, recording the dynamic response curve of the temperature distribution standard deviation, and extracting the dominant lag time constant of the system from the curve. The prediction feedforward coefficient is the ratio of the dominant lag time constant of the system to the sampling period, and is used to convert the rate of change into a predictive adjustment amount.

[0090] The comprehensive adjustment coefficient is multiplied by the current baseline total air volume, and the product is used as the total adjustment amount of the overall air volume adjustment.

[0091] This invention, through thermodynamic equilibrium and statistical correlation analysis of carbon-oxygen and nitrogen-oxygen reactions, can dynamically and quantitatively assess the denitrification status and diagnose the root causes of insufficient carbon-oxygen reaction in the reduction zone, excessively high temperature in the main combustion zone, and uneven mixing of gas and feed in the system.

[0092] Among them, the above three judgment conditions are independent of each other and can be met individually or simultaneously.

[0093] It should be noted that when the diagnostic results include only one of the following: insufficient carbon-oxygen reaction in the reduction zone, excessively high temperature in the main combustion zone, or uneven mixing of gas and feed in the system, the system is determined to be a single-cause fault, and the strategy execution module will directly generate and execute the standardized adjustment command corresponding to the single cause.

[0094] When the diagnostic results contain two or all three causes, the system determines it to be a mixed-cause fault. In this case, the system generates and executes a sequence of adjustment instructions according to the following preset priority order:

[0095] If the temperature in the main combustion zone is too high, the corresponding adjustment command will be generated and executed immediately.

[0096] If the system's gas-material mixing is uneven, then after executing the previous instruction, the corresponding adjustment instruction will be generated and executed.

[0097] If the carbon-oxygen reaction in the reduction zone is insufficient, then after executing all higher-priority instructions, the corresponding adjustment instruction will be generated and executed.

[0098] It should also be noted that after each adjustment command is executed, a short stabilization period can be waited for, and then the latest data from the status monitoring module can be used to quickly reassess the situation before deciding whether to continue executing subsequent priority commands, in order to avoid over-adjustment or conflicts.

[0099] This invention precisely matches specific diagnostic causes with quantitative adjustment actions and introduces dynamic factors such as the rate of deviation change to correct the adjustment amount, forming a highly coupled closed-loop control of monitoring-diagnosis-adjustment. This reduces reliance on human experience and effectively improves the accuracy of control and the system's adaptability.

[0100] The verification and optimization module verifies the compliance of kiln tail flue gas emissions based on nitric oxide concentration and ammonia slip concentration after the preset time for the adjustment action has been executed, and archives the data of the entire process for the purpose of optimizing control parameters.

[0101] The preset duration can be determined by the implementer based on the thermal inertia of the decomposer, the response time of the adjustment action, and the flue gas flow time. It can be set to 20 minutes for example. If the standard deviation of the nitric oxide concentration or ammonia escape concentration sequence is still significantly higher than its historical average level at the end of the preset duration, the preset duration can be appropriately increased. If the key emission parameters reach stability within a time much shorter than the current preset duration after multiple adjustment actions are performed, the preset duration can be appropriately decreased.

[0102] The specific process for verifying the compliance of kiln tail flue gas emissions is as follows: After the adjustment action is completed, within the preset time period, the instantaneous value of nitric oxide concentration output by the flue gas analyzer at the kiln tail chimney and the instantaneous value of ammonia slip concentration output by the ammonia slip analyzer at the downstream selective non-catalytic reduction outlet are collected synchronously at a fixed sampling frequency. These constitute nitric oxide concentration time series and ammonia slip concentration time series, respectively. After removing invalid data points introduced by instrument backflushing, calibration and other operations from the nitric oxide concentration time series and ammonia slip concentration time series, the arithmetic mean of all valid data is calculated.

[0103] From its historical database, retrieve the long-term average concentration of nitric oxide and the long-term average concentration of ammonia escape obtained during the historical stable and compliant operation phase. The long-term average is the average calculated based on all valid data within that phase.

[0104] By comparing the corresponding arithmetic mean with the long-term average, we obtain the first ratio representing the nitric oxide concentration and the second ratio representing the ammonia escape concentration.

[0105] If both the first ratio and the second ratio are less than or equal to 1, the verification result is that the kiln tail flue gas emission meets the standard; otherwise, the verification result is that it does not meet the standard.

[0106] The above description is merely an example and illustration of the structure of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the structure of the invention or exceed the scope defined by the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A low-NOx combustion control system for a cement rotary kiln, characterized in that, include: The status monitoring module collects combustion status parameters in real time through multiple sensors deployed in the decomposition furnace and the outlet flue. The combustion status parameters include oxygen content, carbon monoxide content, nitrogen monoxide concentration and temperature. The reaction assessment module performs a balance analysis of carbon-oxygen reaction and nitrogen-oxygen reaction based on the combustion state parameters to assess the staged combustion and denitrification status in the decomposition furnace. If the denitrification status is not up to standard, the diagnosis is that the cause is at least one of the following: insufficient carbon-oxygen reaction in the reduction zone, excessively high temperature in the main combustion zone, or uneven mixing of gas and feed in the system. The strategy execution module matches corresponding adjustment actions based on the diagnosed cause. The adjustment actions include at least one of the following: adjustment of the fuel and air volume ratio in the reduction zone, adjustment of the fuel input in the main combustion zone, or adjustment of the overall air volume. The verification and optimization module verifies the compliance of kiln tail flue gas emissions based on nitric oxide concentration and ammonia slip concentration after the preset time for the adjustment action has been executed, and archives the data of the entire process for the purpose of optimizing control parameters.

2. The low-NOx combustion control system for a cement rotary kiln according to claim 1, characterized in that, The specific process of deploying multiple sensors in the decomposition furnace and outlet flue is as follows: On the wall of the reduction zone section of the decomposition furnace, at least one physical cross section is selected as a representative monitoring section. At this monitoring section, multiple sampling holes are uniformly opened along the circumference of the furnace body, and high-temperature thermocouples, oxygen content sensors and carbon monoxide content sensors are installed to obtain the temperature, oxygen concentration and carbon monoxide concentration of the reduction zone. On the straight pipe section from the decomposition furnace outlet to the downstream flue, a section with stable airflow is selected, and multiple monitoring holes are opened on the flue wall of the section. A nitrogen oxide analyzer and a multi-point thermocouple temperature measuring device are installed to obtain the nitrogen monoxide concentration in the flue gas and the temperature distribution of the outlet flue, respectively.

3. The low-NOx combustion control system for a cement rotary kiln according to claim 2, characterized in that, The specific process for conducting carbon-oxygen reaction equilibrium analysis based on the aforementioned combustion state parameters is as follows: The oxygen content, carbon monoxide content, and temperature in the reduction zone of the decomposition furnace are collected in real time. Based on the temperature, the target chemical equilibrium constant at the current temperature is determined by calling the pre-stored reaction equilibrium constant-temperature relationship. Based on the target chemical equilibrium constant and the real-time oxygen content in the reduction zone, the theoretical equilibrium concentration of carbon monoxide in the reduction zone under the current conditions is dynamically calculated by solving the chemical equilibrium equation. The real-time carbon monoxide content is compared with the theoretical equilibrium concentration of carbon monoxide to generate a real-time concentration deviation value, and the trend of the deviation value is continuously tracked and analyzed.

4. The low-NOx combustion control system for a cement rotary kiln according to claim 3, characterized in that, The specific process for conducting nitrogen-oxygen reaction equilibrium analysis based on the aforementioned combustion state parameters is as follows: The concentration of nitric oxide and the corresponding average temperature at the outlet of the decomposition furnace were collected synchronously at a preset sampling period, and the time series of nitric oxide concentration and the time series of average temperature were constructed respectively. Using the current acquisition time as a reference point, extract the corresponding data segment within a preset time window from the nitric oxide concentration time series and the average temperature time series; Based on the nitric oxide concentration data segment and the average temperature data segment within the preset time window, a real-time correlation index is calculated to characterize the sensitivity of nitric oxide concentration to changes in average temperature. Based on the temperature distribution data of the outlet flue, calculate its temperature distribution standard deviation; The real-time correlation index is compared with the baseline correlation index range obtained from the statistical analysis of the system's historical stable operation data, and the real-time trend of the temperature distribution standard deviation is analyzed simultaneously.

5. A low-NOx combustion control system for a cement rotary kiln according to claim 4, characterized in that, The specific process for establishing the real-time correlation index is as follows: A linear fit is performed between the nitric oxide concentration data segment and the average temperature data segment, and the slope of the resulting fitted line is used as the real-time correlation index.

6. A low-NOx combustion control system for a cement rotary kiln according to claim 4, characterized in that, The specific process for diagnosing the cause is as follows: Based on the equilibrium analysis results of the carbon-oxygen reaction, if the carbon monoxide concentration deviation value is consistently positive and shows an upward trend, it is determined that the carbon-oxygen reaction in the reduction zone is insufficient. Based on the equilibrium analysis results of the nitrogen-oxygen reaction: a. If the real-time correlation index is higher than the baseline correlation index range, then the main combustion zone temperature is determined to be too high; b. If the standard deviation of the temperature distribution continues to increase and exceeds its historical normal fluctuation range, it is determined that the gas-material mixing in the system is uneven; Among them, the above three judgment conditions are independent of each other and can be met individually or simultaneously.

7. A low-NOx combustion control system for a cement rotary kiln according to claim 3, characterized in that, When the diagnostic cause includes insufficient carbon-oxygen reaction in the reduction zone, it is configured to perform a fuel and air volume ratio adjustment action in the reduction zone, the specific process of which includes: Based on the positive sign of the carbon monoxide concentration deviation and the real-time oxygen content, the target for regulation and its direction of regulation are determined. If the real-time oxygen content is higher than the oxygen content benchmark value, it is determined to reduce the combustion air input flow to the reduction zone of the decomposition furnace; otherwise, it is determined to increase the fuel input flow to the reduction zone of the decomposition furnace. Using the carbon monoxide concentration deviation value as the basic input, multiply it by the preset adjustment coefficient of the corresponding adjustment object to obtain the theoretical adjustment amount of the adjustment object; The rate of change of the carbon monoxide concentration deviation value is calculated in real time. If the rate of change is positive, the theoretical adjustment amount is multiplied by a preset correction factor to obtain the final adjustment amount. If the rate of change is non-positive, the theoretical adjustment amount will be directly used as the final adjustment amount.

8. A low-NOx combustion control system for a cement rotary kiln according to claim 4, characterized in that, When the diagnostic cause includes excessively high main combustion zone temperature, it is configured to perform a main combustion zone fuel input adjustment action, the specific process of which includes: Calculate the first difference between the real-time correlation index and the upper limit of the range of the benchmark correlation index obtained from the statistical analysis of the system's historical stable operation data; The absolute value of the first difference is used as the basis for determining the adjustment intensity of the fuel flow reduction. Calculate the rate of change of the real-time correlation index within a preset time window; If the rate of change is positive, the basic adjustment intensity and a trend factor normalized by the absolute value of the rate of change are weighted and superimposed according to a preset weight to obtain the corrected total adjustment intensity coefficient. If the rate of change is non-positive, then the basic adjustment intensity coefficient is directly used as the total adjustment intensity coefficient; The real-time fuel input flow rate of the main combustion zone is obtained, and the real-time fuel input flow rate is multiplied by the total adjustment intensity coefficient to obtain the final determined fuel flow rate reduction.

9. A low-NOx combustion control system for a cement rotary kiln according to claim 4, characterized in that, When the diagnostic cause includes uneven mixing of system air and material, it is configured to perform an overall airflow adjustment action, the specific process of which includes: Obtain the upper limit of the historical statistical normal fluctuation range of the temperature distribution standard deviation, and obtain the current benchmark total air volume of the system; The second difference between the standard deviation of the temperature distribution and its upper limit value is calculated in real time, and the second difference is divided by the upper limit value to obtain the relative deviation degree characterizing the degree of mixing unevenness; Calculate the rate of change of the standard deviation of the temperature distribution within a first preset time window; By integrating the relative deviation degree with the rate of change, a comprehensive adjustment coefficient is obtained; The comprehensive adjustment coefficient is multiplied by the current baseline total air volume, and the product is used as the total adjustment amount of the overall air volume adjustment.

10. A low-NOx combustion control system for a cement rotary kiln according to claim 1, characterized in that, The specific process for verifying the compliance of kiln tail flue gas emissions is as follows: Within the preset time period, the nitrogen monoxide concentration sequence and ammonia escape concentration sequence of the kiln tail flue gas are obtained, and the arithmetic mean of the sequences is calculated. Retrieve the long-term average values ​​of nitric oxide concentration and ammonia slip concentration from historical statistics during periods of stable and compliant operation; The arithmetic mean and the long-term mean are compared to obtain the first ratio representing the nitric oxide concentration and the second ratio representing the ammonia escape concentration, respectively. If both the first ratio and the second ratio are less than or equal to 1, the verification result is that the kiln tail flue gas emission meets the standard; otherwise, the verification result is that it does not meet the standard.

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