Flue gas recycling system and method for heat-conducting oil furnace

Abstract

The invention discloses a flue gas recycling system and method for a heat-conducting oil furnace, and relates to the technical field of industrial equipment control, and the method comprises the following steps: collecting operation data of the heat-conducting oil furnace; identifying the operation state of the boiler as different control stages; analyzing a current core target, wherein the current core target comprises inhibition of nitrogen oxide generation, prevention of low-temperature corrosion of a tail flue or improvement of the net energy efficiency of the system; based on a control stage and a current core target, combining the numerical association relationship of the oxygen concentration, the carbon monoxide concentration and the nitrogen oxide concentration, and dynamically analyzing a flue gas recirculation amount operation interval; in the flue gas recirculation amount operation interval, the opening degree of a recirculation valve is simulated, and the comprehensive influence of each adjustment on exhaust gas heat recovery and fan energy consumption is evaluated; and the opening degree of the recirculation valve enabling the comprehensive influence to reach the optimal value is selected as a control instruction, and an execution mechanism is driven to act.

Description

Technical Field

[0001] This invention relates to the field of industrial equipment control technology, specifically to a flue gas recycling system and method for thermal oil furnaces. Background Technology

[0002] Thermal oil heaters, as important thermal energy equipment, are widely used in industries such as chemical, textile, and printing and dyeing. The direct emission of the high-temperature flue gas generated during their operation results in significant heat waste, and the pollutants such as nitrogen oxides in the flue gas also pose a threat to the environment. Flue gas recirculation technology, by guiding a portion of the flue gas back into the furnace, can effectively reduce the exhaust gas temperature, improve thermal efficiency, and suppress nitrogen oxide formation, making it an important energy-saving and consumption-reducing method.

[0003] Traditional flue gas recirculation control methods often employ fixed ratios or simple feedback regulation based on a single parameter. This approach fails to adequately consider the dynamic characteristics of boiler operation and the conflict between multiple objective requirements. When boiler load fluctuates rapidly, prioritizing efficiency may lead to instantaneous NOx emissions exceeding limits; during cold starts or low-load operation, excessive pursuit of waste heat recovery may result in acid dew point corrosion in the tail flue due to excessively low temperatures. Current technology lacks a control method capable of intelligently balancing and dynamically optimizing multiple objectives such as safety, environmental protection, and economy based on real-time boiler operating conditions. This results in existing systems often achieving good results only under specific operating conditions, failing to achieve comprehensive optimal operation across the entire operating range, encompassing safety, efficiency, and low emissions. Summary of the Invention

[0004] The purpose of this invention is to provide a flue gas recycling system and method for thermal oil furnaces to solve the problems raised in the prior art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for recycling flue gas from a thermal oil furnace, the method comprising:

[0006] S100: Collect operating data of the thermal oil boiler, including boiler load, flue gas temperature, oxygen concentration, carbon monoxide concentration, nitrogen oxide concentration and recirculation fan power in the flue gas. The data collection process ensures that the data is continuous and without loss.

[0007] S200. Based on the boiler load and flue gas temperature, the boiler operating status is identified into different control stages, including the load change stage, the safety prevention stage, and the steady-state optimization stage.

[0008] S300. Based on the control phase, analyze the current core objectives. The current core objectives include suppressing nitrogen oxide generation, preventing low-temperature corrosion of the tail flue, or improving the net energy efficiency of the system. The core objectives have a unique priority in the corresponding control phase, and other objectives are subject to the constraint of not exceeding the bottom line of safety and environmental protection, so as to ensure the targeted nature of the objectives.

[0009] S400: Based on the control phase and current core objectives, and combined with the numerical correlation between oxygen concentration, carbon monoxide concentration and nitrogen oxide concentration, dynamically analyze the operating range of flue gas recirculation.

[0010] S500: Within the flue gas recirculation volume operating range, simulate the recirculation valve opening and evaluate the comprehensive impact of each adjustment on flue gas heat recovery and fan energy consumption; select the recirculation valve opening that achieves the optimal comprehensive impact as the control command to drive the actuator to operate.

[0011] According to the above scheme, step S200 includes:

[0012] S210. Obtain the flue gas temperature and compare it with the acid dew point temperature threshold. The acid dew point temperature threshold is preset based on the current fuel composition and flue gas humidity through thermodynamic calculations. If the flue gas temperature is lower than the acid dew point temperature threshold, the boiler is determined to be in a condition with low-temperature corrosion risk, and the control stage is identified as a safety prevention stage.

[0013] S220. If the flue gas temperature is not lower than the acid dew point temperature threshold, the boiler load change rate is obtained and its absolute value is calculated. The boiler load change rate is calculated by the ratio of the load difference between two adjacent sampling periods to the sampling period, and it is determined whether the absolute value of the boiler load change rate continuously exceeds the load change threshold within the continuous time window. The continuous time window is a pre-set fixed duration used to filter out misjudgments caused by instantaneous load fluctuations. The load change threshold is pre-calibrated based on the rated load of the thermal oil boiler and the operating safety boundary.

[0014] S230. If the absolute value of the boiler load change rate exceeds the load change threshold, the boiler is determined to be in dynamic adjustment mode, and the control stage is identified as the load change stage.

[0015] S240. If the absolute value of the boiler load change rate does not exceed the load change threshold, the boiler is determined to be in a relatively stable thermal state, and the control stage is identified as the steady-state optimization stage.

[0016] According to the above scheme, if the control phase is identified as a load change phase, the current core objective will be to suppress the generation of nitrogen oxides.

[0017] If the control phase is identified as the safety prevention phase, then the current core objective is to prevent low-temperature corrosion of the tail flue.

[0018] If the control phase is identified as the steady-state optimization phase, then the current core objective is to improve the system's net energy efficiency.

[0019] According to the above scheme, step S400 includes:

[0020] S410. Obtain the current control phase and core objectives;

[0021] S420. Select the corresponding preset boundary calculation rules according to the core objectives. The preset boundary calculation rules are a set of quantitative calculation rules pre-established based on the combustion mechanism and thermodynamic principles of thermal oil furnaces. Each core objective corresponds to a unique boundary calculation rule.

[0022] S430. Based on the selected boundary calculation rules and combined with the real-time collected oxygen concentration, carbon monoxide concentration and nitrogen oxide concentration, a numerical correlation model of oxygen concentration, carbon monoxide concentration and nitrogen oxide concentration is established to quantify the synergistic effect of the three on the recirculation amount, and calculate the upper and lower limits of the flue gas recirculation amount operation range to ensure the rationality and safety of the operation range.

[0023] According to the above scheme, the preset boundary calculation rules include: when the core objective is to suppress the generation of nitrogen oxides, the selected boundary calculation rules are constrained by the instantaneous generation rate of nitrogen oxides to calculate the lower limit of flue gas recirculation; when the core objective is to prevent low-temperature corrosion of the tail flue, the selected boundary calculation rules are constrained by ensuring that the temperature of the mixed flue gas is higher than the acid dew point temperature to calculate the upper limit of flue gas recirculation; when the core objective is to improve the net energy efficiency of the system, the selected boundary calculation rules are constrained by maintaining complete combustion to calculate the lower limit of flue gas recirculation, and constrained by the exhaust gas temperature not being lower than the design optimum to calculate the upper limit of flue gas recirculation.

[0024] According to the above scheme, step S500 includes:

[0025] S510. With a preset step size, generate a set of candidate sequences of recirculation valve opening from the lower limit to the upper limit within the flue gas recirculation volume operating range; the preset step size is a uniformly distributed opening adjustment increment to ensure that the candidate sequence completely covers the entire operating range, and the difference between adjacent candidate opening values ​​is fixed, with no omissions or repetitions.

[0026] S520. For each candidate opening value in the candidate sequence, based on the ideal gas law and the heat exchange law, the flue gas mass and energy balance relationship is established. Based on the flue gas mass and energy balance relationship, the exhaust gas temperature when the candidate opening value is adopted is predicted. Based on the fan characteristic curve, which is the power-opening relationship curve calibrated at the time of the fan's delivery, the operating power of the recirculation fan under the candidate opening value is predicted.

[0027] S530. For each candidate opening value, calculate the system net benefit index based on its corresponding predicted flue gas temperature and predicted fan power. The system net benefit index is the net value of flue gas heat recovery power and fan operating power consumption. Among them, the flue gas heat recovery power is calculated by multiplying the difference between the predicted flue gas temperature and the flue gas temperature before recirculation, the flue gas mass flow rate, and the flue gas constant pressure specific heat capacity. The fan operating power consumption is the predicted fan power.

[0028] S540. Traverse and compare the system net benefit index corresponding to all candidate opening values. The traversal process is carried out in order of the opening of the candidate sequence from small to large to ensure that the system net benefit index corresponding to each candidate opening value is included in the comparison. Select the candidate opening value that makes the system net benefit index reach the global maximum value and lock the candidate opening value as the optimal recirculation valve opening command.

[0029] S550: The optimal recirculation valve opening command is sent to the actuator of the recirculation valve. The actuator operates smoothly according to the preset adjustment rate to ensure that the valve opening gradually reaches the command value, avoiding the impact of instantaneous opening changes on the combustion stability of the thermal oil furnace and the heat exchange system, and driving the valve to operate to the command opening.

[0030] A flue gas recycling system for a thermal oil furnace, the system comprising a data acquisition module, an operating condition identification module, an operation analysis module, a decision-making module, and an execution drive module;

[0031] The data acquisition module is used to collect the operating data of the thermal oil boiler, including boiler load, flue gas temperature, oxygen concentration, carbon monoxide concentration, nitrogen oxide concentration and recirculation fan power in the flue gas.

[0032] The operating condition identification module is connected to the data acquisition module by signal. It is used to receive operating data, identify the boiler operating status as a load change stage, a safety prevention stage, or a steady-state optimization stage, and determine the current core objective based on the control stage.

[0033] The operation analysis module, connected to the data acquisition module and the operating condition identification module, is used to receive operating data, control stages and current core objectives, and dynamically calculate the upper and lower limits of the flue gas recirculation volume operating range by combining the numerical correlation between oxygen concentration, carbon monoxide concentration and nitrogen oxide concentration.

[0034] The decision-making module, connected to the operation analysis module and the data acquisition module, is used to generate a candidate sequence of recirculation valve opening within the flue gas recirculation volume operation range, predict the corresponding operating parameters and calculate the system net benefit index, and screen out the optimal recirculation valve opening command.

[0035] The execution drive module, connected to the decision module, is used to receive the optimal recirculation valve opening command and drive the recirculation valve actuator to operate to the commanded opening.

[0036] According to the above scheme, the working condition identification module includes a working condition identification unit and a target decision unit;

[0037] The operating condition identification unit is used to receive boiler load and flue gas temperature data transmitted by the data acquisition module. By comparing the flue gas temperature with the acid dew point temperature threshold and judging whether the absolute value of the boiler load change rate exceeds the load change threshold, the boiler operating status is identified as the load change stage, the safety prevention stage, or the steady-state optimization stage.

[0038] The target decision unit is connected to the operating condition identification unit and is used to determine the current core objective based on the identified control stage, such as suppressing nitrogen oxide generation, preventing low-temperature corrosion of the tail flue, or improving the net energy efficiency of the system.

[0039] According to the above scheme, the operation analysis module includes a rule selection unit and an interval calculation unit;

[0040] The rule selection unit is used to receive the current core target transmitted by the working condition identification module and select the corresponding preset boundary calculation rules. The preset boundary calculation rules include rules constrained by suppressing the instantaneous generation rate of nitrogen oxides, rules constrained by ensuring that the temperature of the mixed flue gas is higher than the acid dew point temperature, and rules constrained by maintaining complete combustion and exhaust gas temperature not lower than the design optimum value.

[0041] The interval calculation unit is connected to the rule selection unit and the data acquisition module respectively. It is used to calculate the upper and lower limits of the flue gas recirculation volume operation interval based on the selected preset boundary calculation rules and the real-time collected oxygen concentration, carbon monoxide concentration and nitrogen oxide concentration.

[0042] According to the above scheme, the decision-making module includes a candidate sequence unit, a parameter prediction unit, and a net profit optimization unit;

[0043] The candidate sequence unit is used to receive the flue gas recirculation volume operation range transmitted by the operation analysis module, and generate a candidate sequence of recirculation valve opening from the lower limit to the upper limit with a preset step size.

[0044] The parameter prediction unit is connected to the candidate sequence unit and the data acquisition module respectively. It is used to predict the exhaust temperature based on the relationship between flue gas quality and energy balance for each candidate opening value, and to predict the operating power of the recirculation fan based on the fan characteristic curve.

[0045] The net revenue optimization unit is connected to the parameter prediction unit. It is used to calculate the system net revenue index based on the predicted flue gas temperature and fan operating power, iterates and compares the system net revenue index corresponding to all candidate opening values, and selects the optimal recirculation valve opening command that makes the index reach the global maximum value.

[0046] Compared with the prior art, the beneficial effects of the present invention are:

[0047] 1. This invention ensures that nitrogen oxide emissions meet standards when the load changes, avoids tail corrosion when the load is low, maximizes the net energy efficiency of the system in steady state, and improves the reliability of operation under all working conditions by accurately identifying different operating stages and matching core objectives.

[0048] 2. This invention dynamically calculates the operating range based on the numerical correlation of flue gas components, and uses boundary constraints to ensure combustion completeness and flue gas temperature safety, avoiding equipment damage and emission exceedances caused by excessive or insufficient recirculation, thereby reducing system operation risks;

[0049] 3. This invention selects the optimal opening degree through the net benefit optimization logic within the interval, accurately balances the smoke exhaust heat recovery benefit and fan energy consumption, avoids ineffective energy consumption, maximizes energy-saving benefits and reduces industrial production energy consumption under the premise of ensuring safety and environmental protection. Attached Figure Description

[0050] Figure 1 This is a flowchart illustrating the steps of a flue gas recycling method for a thermal oil furnace according to the present invention.

[0051] Figure 2 This is a schematic diagram of a flue gas recycling system for a thermal oil furnace according to the present invention. Detailed Implementation

[0052] 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.

[0053] Example: Figures 1-2 As shown, the present invention provides a technical solution: a method for recycling flue gas from a thermal oil furnace, the method comprising:

[0054] S100. Collect operating data of the thermal oil boiler, including boiler load, flue gas temperature, oxygen concentration, carbon monoxide concentration, nitrogen oxide concentration, and recirculation fan power. Ensure continuous and complete data collection during the acquisition process. For example, synchronously collect the following data at a frequency of 1Hz: Boiler load L current =9.5MW, flue gas temperature T exh current =165℃, flue gas oxygen concentration O2=3.5%, carbon monoxide concentration CO=80ppm, nitrogen oxide concentration NOx=150mg / Nm 3 The current power P of the recirculation fan fan current=15kW, this is just an example and is not a limitation.

[0055] S200. Based on the boiler load and flue gas temperature, the boiler operating status is identified into different control stages, including the load change stage, the safety prevention stage, and the steady-state optimization stage.

[0056] Specifically, step S200 includes:

[0057] S210. Obtain the flue gas temperature and compare it with the acid dew point temperature threshold. The acid dew point temperature threshold is preset based on the current fuel composition and flue gas humidity through thermodynamic calculations. If the flue gas temperature is lower than the acid dew point temperature threshold, the boiler is determined to be in a condition with a risk of low-temperature corrosion, and the control phase is identified as a safety prevention phase. For example, compare the current flue gas temperature with the acid dew point temperature threshold; the acid dew point temperature threshold T... dp The temperature is set at 120℃; this is a conservative safety value calculated based on the typical sulfur content of fuel oil and the water content of flue gas through thermodynamic balance; since the current flue gas temperature of 165℃ is greater than the acid dew point temperature threshold of 120℃, it does not meet the conditions for the safety prevention stage.

[0058] S220. If the flue gas temperature is not lower than the acid dew point temperature threshold, the boiler load change rate is obtained and its absolute value is calculated. The boiler load change rate is calculated by the ratio of the load difference between two adjacent sampling periods to the sampling period, and it is determined whether the absolute value of the boiler load change rate continuously exceeds the load change threshold within the continuous time window. The continuous time window is a pre-set fixed duration used to filter out misjudgments caused by instantaneous load fluctuations. The load change threshold is pre-calibrated based on the rated load of the thermal oil boiler and the operating safety boundary.

[0059] S230. If the absolute value of the boiler load change rate exceeds the load change threshold, the boiler is determined to be in dynamic adjustment mode, and the control stage is identified as the load change stage.

[0060] S240. If the absolute value of the boiler load change rate does not exceed the load change threshold, the boiler is determined to be in a relatively stable thermal state, and the control stage is identified as the steady-state optimization stage.

[0061] For example: Calculate the absolute value of the boiler load change rate over the past minute. If the load was 9.3 MW one minute ago, then the absolute value of the boiler load change rate is: |ΔL| = |(9.5-9.3) MW / 1min| = 0.2 MW / min; Determine whether the absolute value of the boiler load change rate |ΔL| is within the continuous time window t. window The load change threshold ΔL is continuously exceeded within 5 minutes. th(0.2MW / min); Upon inspection, |ΔL| has not consistently exceeded 0.2MW / min in the past 5 minutes, therefore the load variation stage condition is not met; the current state is determined to be the steady-state optimization stage; this is only an example and is not a limitation.

[0062] S300. Based on the control phase, analyze the current core objectives. The current core objectives include suppressing nitrogen oxide generation, preventing low-temperature corrosion of the tail flue, or improving the net energy efficiency of the system. The core objectives have a unique priority in the corresponding control phase, and other objectives are subject to the constraint of not exceeding the bottom line of safety and environmental protection, so as to ensure the targeted nature of the objectives.

[0063] Specifically, if the control phase is identified as a load variation phase, the current core objective is to suppress nitrogen oxide generation; if the control phase is identified as a safety prevention phase, the current core objective is to prevent low-temperature corrosion of the tail flue; if the control phase is identified as a steady-state optimization phase, the current core objective is to improve the system's net energy efficiency. For example, if the current phase is identified as a steady-state optimization phase, the current core objective is to improve the system's net energy efficiency.

[0064] S400: Based on the control phase and current core objectives, and combined with the numerical correlation between oxygen concentration, carbon monoxide concentration and nitrogen oxide concentration, dynamically analyze the operating range of flue gas recirculation.

[0065] Specifically, step S400 includes:

[0066] S410. Obtain the current control phase and core objectives;

[0067] S420. Select the corresponding preset boundary calculation rules according to the core objectives. The preset boundary calculation rules are a set of quantitative calculation rules pre-established based on the combustion mechanism and thermodynamic principles of thermal oil furnaces. Each core objective corresponds to a unique boundary calculation rule.

[0068] The preset boundary calculation rules include: when the core objective is to suppress the generation of nitrogen oxides, the selected boundary calculation rules are constrained by suppressing the instantaneous generation rate of nitrogen oxides to calculate the lower limit of flue gas recirculation; when the core objective is to prevent low-temperature corrosion of the tail flue, the selected boundary calculation rules are constrained by ensuring that the temperature of the mixed flue gas is higher than the acid dew point temperature to calculate the upper limit of flue gas recirculation; when the core objective is to improve the net energy efficiency of the system, the selected boundary calculation rules are constrained by maintaining complete combustion to calculate the lower limit of flue gas recirculation, and constrained by the exhaust gas temperature not being lower than the design optimum to calculate the upper limit of flue gas recirculation.

[0069] For example: Based on the core objective, select the corresponding preset boundary calculation rule; in this embodiment, the preset boundary calculation rule is: to maintain complete combustion as the lower limit of the calculation constraint, and to ensure that the exhaust gas temperature is not lower than the design optimum value as the upper limit of the calculation constraint.

[0070] Lower limit calculation rules: To ensure stable combustion, set an upper limit for CO concentration (e.g., 100 ppm) and a lower limit for O2 concentration (e.g., 2.5%) as constraints; use a combustion model to deduce the minimum recycling amount V that satisfies these constraints. min ;

[0071] Upper limit calculation rule: Ensure that the exhaust gas temperature is not lower than the optimal exhaust gas temperature T. opt (160℃); Calculations using a heat balance model ensure that the temperature of the mixed flue gas is not lower than the optimal exhaust temperature T. opt Maximum recirculation amount V max The current flue gas flow rate is G. total The temperature is T exh current The temperature of the recirculated flue gas is T. recirc The ambient temperature is T amb The relationship between the data is: (G total ×T exh current -V max ×(T exh current -T amb )) / G total ≥T opt The maximum recycle amount V is calculated. max This is just an example and is not intended to be limiting.

[0072] S430. Based on the selected boundary calculation rules and combined with the real-time collected oxygen, carbon monoxide, and nitrogen oxide concentrations, a numerical correlation model of oxygen, carbon monoxide, and nitrogen oxide concentrations is established to quantify the synergistic effect of the three on the recirculation amount. The upper and lower limits of the flue gas recirculation amount operating range are calculated to ensure the rationality and safety of the operating range. The numerical correlation model is used to characterize the comprehensive response of the coupling relationship between oxygen, carbon monoxide, and nitrogen oxide concentrations to the dilution and cooling effect of recirculated flue gas. For example, when calculating the range, it is necessary to ensure that the combustion state indicated by the combination of O2 and CO is in the high-efficiency and stable zone under the set recirculation amount, while the NOx generation trend is suppressed.

[0073] For example: based on the selected boundary calculation rules, combined with real-time collected data on oxygen concentration (O2) (3.5%), carbon monoxide concentration (CO) (80ppm), and nitrogen oxide concentration (NOx) (150mg / Nm³),... 3 The data is used to execute boundary calculation rules;

[0074] Calculate the lower limit value V minBoth O2 and CO concentrations are better than the combustion stability constraints, i.e., O2 > 2.5% and CO < 100 ppm. Based on the preset combustion model, determine the minimum recycle amount V that satisfies the complete combustion constraint. min 1000 Nm 3 / h; Increasing the amount of recirculation will dilute the oxygen concentration in the furnace and may affect the combustion stability; The preset combustion model establishes a quantitative relationship between the amount of recirculation, the measured oxygen concentration, the amount of carbon monoxide generated, and the minimum oxygen concentration required to ensure complete combustion, and solves for the minimum amount of recirculation under the constraint conditions.

[0075] Calculate the upper limit value V max To ensure that the exhaust gas temperature is not lower than the design optimum value T opt =160℃, calculated based on a heat balance model; where, the total flue gas volume flow rate G total 50000 Nm 3 / h, current flue gas temperature T exh current The temperature is 165℃, and the ambient temperature is T. amb The temperature is 25℃; substituting into the formula, we get: V max =1786Nm 3 / h;

[0076] Therefore, the current operating range for flue gas recirculation is [1000, 1786] Nm. 3 / h is just an example and is not a limitation.

[0077] S500: Within the flue gas recirculation volume operating range, simulate the recirculation valve opening and evaluate the comprehensive impact of each adjustment on flue gas heat recovery and fan energy consumption; select the recirculation valve opening that achieves the optimal comprehensive impact as the control command to drive the actuator to operate;

[0078] Specifically, step S500 includes:

[0079] S510. With a preset step size, generate a set of candidate sequences of recirculation valve opening from the lower limit to the upper limit within the flue gas recirculation volume operating range; the preset step size is a uniformly distributed opening adjustment increment to ensure that the candidate sequence completely covers the entire operating range, and the difference between adjacent candidate opening values ​​is fixed, with no omissions or repetitions.

[0080] For example: in the interval [1000, 1786] Nm 3 Within / h, with a flow rate step size of: (1786-1000) / 10≈78.6Nm 3 / h, rounded up to 80Nm 3 / h, generating candidate sequences: [1000, 1080, 1160, 1240, 1320, 1400, 1480, 1560, 1640, 1720, 1786]Nm 3 / h; This is just an example and is not a limitation;

[0081] S520. For each candidate opening value in the candidate sequence, based on the ideal gas law and the heat exchange law, the flue gas mass and energy balance relationship is established. Based on the flue gas mass and energy balance relationship, the exhaust gas temperature when the candidate opening value is adopted is predicted. Based on the fan characteristic curve, which is the power-opening relationship curve calibrated at the time of the fan's delivery, the operating power of the recirculation fan under the candidate opening value is predicted.

[0082] For example: for each candidate opening value in the candidate sequence, predict the exhaust gas temperature based on the relationship between flue gas mass and energy balance, and predict the fan power based on the fan characteristic curve.

[0083] Flue gas temperature prediction: using a simplified heat balance model: T pred i =(G total ×T exh current -V i ×(T exh current -T amb )) / G total Among them, T pred i V represents the predicted flue gas temperature corresponding to the i-th candidate flow rate. i Represented as candidate recirculation flow, G total Expressed as total flue gas volumetric flow rate; in V i =1400Nm 3 Taking / h as an example, T is calculated. pred i =161.08℃;

[0084] Wind turbine power prediction: Based on the wind turbine characteristic curve P pred i =a×V+b, where P pred i The values ​​are: a represents the predicted fan power; 'a' represents the fan power-flow characteristic coefficient, describing the slope or sensitivity of the fan power change with flow rate, determined by the fan's aerodynamic performance and operating efficiency, and is a key parameter of the fan's factory characteristic curve; 'b' represents the fan no-load / inherent power coefficient, representing the inherent power consumed by the fan to overcome its own mechanical friction and maintain basic operation; where a = 0.003, b = 5; and in V... i =1400Nm 3 Taking / h as an example, P is calculated. pred i =0.003×1400+5=9.2kW;

[0085] S530. For each candidate opening value, calculate the system net benefit index based on its corresponding predicted flue gas temperature and predicted fan power. The system net benefit index is the net value of flue gas heat recovery power and fan operating power consumption. Among them, the flue gas heat recovery power is calculated by multiplying the difference between the predicted flue gas temperature and the flue gas temperature before recirculation, the flue gas mass flow rate, and the flue gas constant pressure specific heat capacity. The fan operating power consumption is the predicted fan power.

[0086] For example: Calculate the system's net return metric Net for each candidate value. i ;

[0087] Flue gas heat recovery power: ΔP heat i =T exh current -T pred i )×G total mass ×C p ; where G total mass It is the total flue gas mass flow rate, where G total mass =G total ×ρ, where ρ is the density of flue gas under standard conditions, which is 1.3 kg / Nm³. 3 Then G total mass =50000Nm 3 / h×1.3kg / Nm 3 / 3600s / h=18.06kg / s; with V i =1400Nm 3 For example, / h, T pred i =161.08℃, ΔT=3.92℃, then ΔP heat i =3.92×18.06×1.05=74.4kW; Wind turbine operating power consumption: P pred i =9.2kW; System net revenue indicator Net i =ΔP heat i -P pred i =65.2kW; This is just an example and is not a limitation.

[0088] S540. Iterate and compare the system net benefit index corresponding to all candidate opening values. The iteration process proceeds in ascending order of the opening value of the candidate sequence, ensuring that the system net benefit index corresponding to each candidate opening value is included in the comparison. Select the candidate opening value that makes the system net benefit index reach the global maximum value, and lock the candidate opening value as the optimal recirculation valve opening command; for example: iterate and compare all Net... i Exhaustive search is used as the optimization algorithm; it is calculated that when V i =1560Nm 3 / h, Net i Once the maximum value is reached, the optimal recirculated flue gas volumetric flow rate V is locked. optimal =1560Nm 3 / h is used as the optimal flow rate setting value;

[0089] S550: The optimal recirculation valve opening command is sent to the actuator of the recirculation valve. The actuator operates smoothly according to the preset adjustment rate, ensuring that the valve opening gradually reaches the command value, avoiding the impact of instantaneous sudden changes in opening on the combustion stability of the thermal oil furnace and the heat exchange system, and driving the valve to the command opening; for example: the optimal recirculation flue gas volume flow rate V optimal =1560Nm 3 / h is converted into the corresponding valve opening command, and sent to the actuator at a preset adjustment rate of no more than 5% opening change per minute to drive the valve to move smoothly to the target opening; this is only an example and is not a limitation.

[0090] This invention provides another technical solution: a flue gas recycling system for a thermal oil furnace, the system comprising a data acquisition module, a working condition identification module, an operation analysis module, a decision-making module, and an execution drive module;

[0091] The system comprises the following modules: a data acquisition module for collecting operating data from the thermal oil boiler, including boiler load, flue gas temperature, oxygen concentration, carbon monoxide concentration, nitrogen oxide concentration, and recirculation fan power; an operating condition identification module connected to the data acquisition module for receiving operating data, identifying the boiler operating status as a load fluctuation stage, a safety prevention stage, or a steady-state optimization stage, and determining the current core objective based on the control stage; an operation analysis module connected to the data acquisition and operating condition identification modules for receiving operating data, control stage, and current core objective, dynamically calculating the upper and lower limits of the flue gas recirculation volume operating range based on the numerical correlation of oxygen, carbon monoxide, and nitrogen oxide concentrations; a decision module connected to the operation analysis and data acquisition modules for generating a candidate sequence of recirculation valve opening degrees within the flue gas recirculation volume operating range, predicting corresponding operating parameters, calculating the system net benefit index, and selecting the optimal recirculation valve opening command; and an execution drive module connected to the decision module for receiving the optimal recirculation valve opening command and driving the recirculation valve actuator to the commanded opening degree.

[0092] Specifically, the operating condition identification module includes an operating condition identification unit and a target decision unit. The operating condition identification unit receives boiler load and flue gas temperature data transmitted by the data acquisition module. By comparing the flue gas temperature with the acid dew point temperature threshold and determining whether the absolute value of the boiler load change rate exceeds the load change threshold, it identifies the boiler operating status as a load change stage, a safety prevention stage, or a steady-state optimization stage. The target decision unit is connected to the operating condition identification unit and is used to determine the current core objective based on the identified control stage, such as suppressing nitrogen oxide generation, preventing low-temperature corrosion of the tail flue, or improving the system's net energy efficiency.

[0093] Specifically, the operation analysis module includes a rule selection unit and an interval calculation unit. The rule selection unit receives the current core objective transmitted by the operating condition identification module and selects the corresponding preset boundary calculation rules. The preset boundary calculation rules include rules constrained by suppressing the instantaneous generation rate of nitrogen oxides, rules constrained by ensuring that the temperature of the mixed flue gas is higher than the acid dew point temperature, and rules constrained by maintaining complete combustion and ensuring that the exhaust gas temperature is not lower than the design optimum value. The interval calculation unit is connected to the rule selection unit and the data acquisition module respectively. It is used to calculate the upper and lower limits of the flue gas recirculation operation interval based on the selected preset boundary calculation rules and combined with the real-time collected oxygen concentration, carbon monoxide concentration, and nitrogen oxide concentration.

[0094] Specifically, the decision-making module includes a candidate sequence unit, a parameter prediction unit, and a net benefit optimization unit. The candidate sequence unit receives the flue gas recirculation volume operation range transmitted by the operation analysis module and generates a candidate sequence of recirculation valve openings from the lower limit to the upper limit with a preset step size. The parameter prediction unit is connected to both the candidate sequence unit and the data acquisition module. For each candidate opening value, it predicts the exhaust gas temperature based on the relationship between flue gas mass and energy balance, and predicts the recirculation fan operating power based on the fan characteristic curve. The net benefit optimization unit is connected to the parameter prediction unit. It calculates the system net benefit index based on the predicted exhaust gas temperature and fan operating power, iterates and compares the system net benefit index corresponding to all candidate opening values, and selects the optimal recirculation valve opening command that makes the index reach the global maximum value.

[0095] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for recycling flue gas from a thermal oil furnace, characterized in that: The method includes: S100. Collect the operating data of the thermal oil furnace, including boiler load, flue gas temperature, oxygen concentration, carbon monoxide concentration, nitrogen oxide concentration and recirculation fan power in the flue gas. S200. Based on the boiler load and the flue gas temperature, the boiler operating status is identified into different control stages, including a load change stage, a safety prevention stage, and a steady-state optimization stage. S300. Based on the control phase, analyze the current core objectives, which include suppressing nitrogen oxide generation, preventing low-temperature corrosion of the tail flue, or improving the net energy efficiency of the system. S400. Based on the control stage and the current core objective, and combined with the numerical correlation between the oxygen concentration, carbon monoxide concentration and nitrogen oxide concentration, dynamically analyze the flue gas recirculation volume operating range. S500. Within the operating range of the flue gas recirculation volume, simulate the opening degree of the recirculation valve and evaluate the comprehensive impact of each adjustment on the exhaust heat recovery and fan energy consumption; select the recirculation valve opening degree that makes the comprehensive impact reach the optimal value as the control command to drive the actuator to act.

2. The method for flue gas recycling in a thermal oil furnace according to claim 1, characterized in that: Step S200 includes: S210. Obtain the flue gas temperature and compare it with the acid dew point temperature threshold. If the flue gas temperature is lower than the acid dew point temperature threshold, determine that the boiler is in a condition with low-temperature corrosion risk and identify the control stage as the safety prevention stage. S220. If the flue gas temperature is not lower than the acid dew point temperature threshold, then obtain the rate of change of the boiler load, calculate its absolute value, and determine whether the absolute value of the rate of change of the boiler load continuously exceeds the load change threshold within a continuous time window. S230. If the absolute value of the boiler load change rate exceeds the load change threshold, the boiler is determined to be in dynamic adjustment mode, and the control stage is identified as the load change stage. S240. If the absolute value of the boiler load change rate does not exceed the load change threshold, the boiler is determined to be in a relatively stable thermal state, and the control phase is identified as the steady-state optimization phase.

3. The method for flue gas recycling in a thermal oil furnace according to claim 1, characterized in that: If the control phase is identified as the load variation phase, then the current core objective is determined to be to suppress the generation of nitrogen oxides; If the control phase is identified as the safety prevention phase, then the current core objective is determined to be preventing low-temperature corrosion of the tail flue. If the control phase is identified as the steady-state optimization phase, then the current core objective is determined to improve the system's net energy efficiency.

4. The method for flue gas recycling in a thermal oil furnace according to claim 1, characterized in that: Step S400 includes: S410. Obtain the current control phase and the core objective; S420. Select the corresponding preset boundary calculation rule according to the core objective; S430. Based on the selected boundary calculation rules and combined with the real-time collected oxygen concentration, carbon monoxide concentration and nitrogen oxide concentration, the upper and lower limits of the flue gas recirculation volume operating range are calculated.

5. A method for recycling flue gas from a thermal oil furnace according to claim 4, characterized in that: The preset boundary calculation rules include: when the core objective is to suppress the generation of nitrogen oxides, the selected boundary calculation rules are constrained by suppressing the instantaneous generation rate of nitrogen oxides to calculate the lower limit of flue gas recirculation; when the core objective is to prevent low-temperature corrosion of the tail flue, the selected boundary calculation rules are constrained by ensuring that the temperature of the mixed flue gas is higher than the acid dew point temperature to calculate the upper limit of flue gas recirculation; when the core objective is to improve the net energy efficiency of the system, the selected boundary calculation rules are constrained by maintaining complete combustion to calculate the lower limit of flue gas recirculation, and constrained by the exhaust gas temperature not being lower than the design optimum to calculate the upper limit of flue gas recirculation.

6. The method for flue gas recycling in a thermal oil furnace according to claim 1, characterized in that: Step S500 includes: S510. Within the flue gas recirculation volume operating range, generate a set of candidate recirculation valve openings from the lower limit to the upper limit with a preset step size. S520. For each candidate opening value in the candidate sequence, based on the relationship between flue gas mass and energy balance, predict the exhaust gas temperature when adopting the candidate opening; based on the fan characteristic curve, predict the operating power of the recirculation fan under the candidate opening. S530. For each candidate opening value, calculate the system net benefit index based on its corresponding predicted flue gas temperature and predicted fan power; the system net benefit index is the net value of flue gas heat recovery benefit and fan operating power consumption. S540. Iterate through and compare the system net benefit index corresponding to all candidate opening values, filter out the candidate opening value that makes the system net benefit index reach the global maximum value, and lock the candidate opening value as the optimal recirculation valve opening command. S550: The optimal recirculation valve opening command is sent to the actuator of the recirculation valve to drive the valve to the commanded opening.

7. A flue gas recycling system for a thermal oil furnace, characterized in that: The system includes a data acquisition module, a working condition identification module, an operation analysis module, a decision-making module, and an execution-driven module; The data acquisition module is used to collect the operating data of the thermal oil furnace, including boiler load, flue gas temperature, oxygen concentration, carbon monoxide concentration, nitrogen oxide concentration and recirculation fan power in the flue gas. The operating condition identification module is signal-connected to the data acquisition module and is used to receive the operating data, identify the boiler operating status as a load change stage, a safety prevention stage, or a steady-state optimization stage, and determine the current core objective based on the control stage. The operation analysis module is connected to the data acquisition module and the operating condition identification module. It is used to receive operating data, control stages and current core targets, and dynamically calculate the upper and lower limits of the flue gas recirculation volume operating range by combining the numerical correlation between oxygen concentration, carbon monoxide concentration and nitrogen oxide concentration. The decision module is connected to the operation analysis module and the data acquisition module. It is used to generate a candidate sequence of recirculation valve opening within the flue gas recirculation volume operation range, predict the corresponding operating parameters and calculate the system net benefit index, and screen out the optimal recirculation valve opening command. The execution drive module is connected to the decision module and is used to receive the optimal recirculation valve opening command and drive the recirculation valve actuator to operate to the commanded opening.

8. A flue gas recirculation system for a thermal oil furnace according to claim 7, characterized in that: The working condition identification module includes a working condition identification unit and a target decision unit; The operating condition identification unit is used to receive boiler load and flue gas temperature data transmitted by the data acquisition module. By comparing the flue gas temperature with the acid dew point temperature threshold and determining whether the absolute value of the boiler load change rate exceeds the load change threshold, the boiler operating status is identified as a load change stage, a safety prevention stage, or a steady-state optimization stage. The target decision unit is connected to the operating condition identification unit and is used to determine the current core objective as suppressing nitrogen oxide generation, preventing low-temperature corrosion of the tail flue, or improving the net energy efficiency of the system based on the identified control stage.

9. A flue gas recirculation system for a thermal oil furnace according to claim 7, characterized in that: The operation analysis module includes a rule selection unit and an interval calculation unit; The rule selection unit is used to receive the current core target transmitted by the working condition identification module and select the corresponding preset boundary calculation rules; the preset boundary calculation rules include rules constrained by suppressing the instantaneous generation rate of nitrogen oxides, rules constrained by ensuring that the temperature of the mixed flue gas is higher than the acid dew point temperature, and rules constrained by maintaining complete combustion and exhaust gas temperature not lower than the design optimum value. The interval calculation unit is connected to the rule selection unit and the data acquisition module respectively, and is used to calculate the upper and lower limits of the flue gas recirculation volume operation interval based on the selected preset boundary calculation rules and combined with the real-time collected oxygen concentration, carbon monoxide concentration and nitrogen oxide concentration.

10. A flue gas recirculation system for a thermal oil furnace according to claim 7, characterized in that: The decision-making module includes a candidate sequence unit, a parameter prediction unit, and a net profit optimization unit. The candidate sequence unit is used to receive the flue gas recirculation amount operation range transmitted by the operation analysis module, and generate a candidate sequence of recirculation valve opening from the lower limit to the upper limit with a preset step size. The parameter prediction unit is connected to the candidate sequence unit and the data acquisition module respectively, and is used to predict the exhaust temperature based on the relationship between flue gas quality and energy balance for each candidate opening value, and predict the operating power of the recirculation fan based on the fan characteristic curve. The net revenue optimization unit is connected to the parameter prediction unit and is used to calculate the system net revenue index based on the predicted flue gas temperature and fan operating power, iterate and compare the system net revenue index corresponding to all candidate opening values, and select the optimal recirculation valve opening command that makes the system net revenue index reach the global maximum value.

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