Combustion optimization control method and system for gas-fired boiler

Abstract

The invention relates to the technical field of boiler combustion control, in particular to a combustion optimization control method and system for a gas-fired boiler, and the method specifically comprises the following steps: presetting a target value; collecting data; deviation analysis; dynamically adjusting; and load change response. The tail flue gas oxygen content and the NOx concentration serve as double feedback signals, and hierarchical closed-loop control logic is established. Firstly, oxygen content target values under different loads are calibrated, so that the combustion reference is ensured; and secondly, in the control process, the air volume is corrected according to the oxygen content deviation, and the FGR system is linked to carry out special inhibition on NOx, so that the problem that in traditional control, the air volume and the FGR system are in consideration is solved. The method is particularly suitable for the open-loop control gas-fired hot water boiler, the optimal air-fuel ratio can be achieved through dynamic adjustment, and therefore the heat efficiency of the boiler is improved to the maximum extent while low emission is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of boiler combustion control technology, and in particular to a method and system for optimizing combustion control of gas-fired boilers. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] With increasingly stringent environmental regulations, especially those concerning nitrogen oxides (NOx)... x With increasingly stringent emission limits for pollutants such as carbon dioxide (CO), combustion control technology for gas-fired boilers faces greater challenges. Traditional gas-fired boiler control methods rely primarily on manual experience or simple proportional adjustments, which typically struggle to simultaneously achieve both high-efficiency combustion and low emissions.

[0004] In actual operation, combustion efficiency and pollutant generation are contradictory. Insufficient airflow (low oxygen) leads to incomplete combustion, producing black smoke and carbon monoxide (CO), resulting in fuel waste and environmental pollution; excessive airflow (high oxygen) removes a large amount of heat, reducing boiler thermal efficiency, while excessively high oxygen concentration and furnace temperature promote the formation of thermal NO. x The large-scale generation of NOx. Existing NOx suppression and regulation modules (such as flue gas recirculation systems, FGR) can effectively reduce NO. x However, the timing and depth of its intervention often lack precise linkage with real-time changes in oxygen content.

[0005] Therefore, how to dynamically and accurately adjust the air supply volume and circulating flue gas volume according to the real-time load changes and flue gas emission parameters of the boiler, so that the boiler always operates under the best combustion conditions, is an urgent problem to be solved. Summary of the Invention

[0006] The purpose of this invention is to address the aforementioned shortcomings by providing a method and system for optimizing combustion control in gas-fired boilers.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a combustion optimization control method for gas-fired boilers, specifically including the following steps: S100 sets a target value for the oxygen content in the tail gas and determines the NO content based on the emission limits table for air pollutants from newly built boilers. x Target value; The S200 is equipped with oxygen and nitrogen oxide sensors to simultaneously collect data on the oxygen and NO content of the exhaust gas during combustion. x Real-time parameters of concentration; S300, for collecting oxygen content and NO x Real-time parameters of concentration, comparing oxygen content with NO. xTo determine the target value, conduct a deviation analysis. S400 dynamically adjusts the air supply volume based on deviation analysis and controls the flue gas volume through the existing nitrogen oxide suppression and regulation module; S500: Dynamically adjust the target value of oxygen content according to the load changes during boiler combustion, and repeat steps S200-S400 to control the flue gas volume.

[0008] Furthermore, the method for determining the target value of the oxygen content in the tail gas in S100 includes: S110, based on boiler type, burner type and low nitrogen emission requirements, determine the theoretical target range of flue gas oxygen content under rated load; S120: After the boiler is started from a cold state, during the low load stage of heating up in the hot state, the oxygen content is set to be higher than the theoretical target range of the rated load. By adjusting the air volume or the gas / air ratio, CO ≤ 100ppm and combustion is stable. S130 increases the boiler load to 100% of the rated load and determines the lower and upper limits of oxygen content by bidirectionally adjusting the air supply volume; S140, under 75% and 50% load conditions, gradually increases the oxygen content based on the rated load oxygen content, with the entire process maintaining CO ≤ 100ppm, no visible black smoke, no flashback / flameout in the furnace, and NO... x Meeting emission standards and maintaining stable positive pressure in the furnace are the core criteria for judgment.

[0009] Furthermore, the low load is 30% to 50% load, during which the oxygen content is 0.8% to 1.0% higher than the theoretical target range of the rated load.

[0010] Furthermore, the method for determining the lower and upper limits of oxygen content in S130 includes: S131, gradually reduce the air supply volume and adjust it to CO equal to or greater than 100ppm, which is determined as the lower limit of oxygen content; S132, gradually increase the air supply volume and adjust to NO. x Exceeding the standard or a significant decrease in boiler efficiency will be determined as the upper limit of oxygen content. S133, Select a value between the lower and upper limits of the oxygen content: CO ≤ 50 ppm, NO ≤ 50 ppm. x The intermediate value that meets the standard and ensures stable combustion is used as the preset target value for oxygen content under rated load.

[0011] Furthermore, 75% load: The oxygen content is 0.3% to 0.5% higher than the rated load; 50% load: The oxygen content is 0.8% to 1.0% higher than the rated load.

[0012] Furthermore, S300 specifically includes: Deviation analysis of the gas / air ratio: If the actual oxygen content of the tail gas is less than the lower limit of oxygen content, it is judged as insufficient air volume. If the actual oxygen content of the tail gas is greater than the upper limit of oxygen content, it is judged as excessive air volume. NO x Perform deviation analysis: If the actual NO x When the concentration exceeds the target value, the existing nitrogen oxide suppression and regulation mechanism is triggered. If the actual NO x The concentration should not exceed the target value; maintain the current adjustment state.

[0013] Furthermore, step S400 specifically includes: Gas / air ratio adjustment: When insufficient air volume is detected, the fan air volume is increased, and the adjustment range is positively correlated with the gas / air ratio deviation value. When the air volume is determined to be excessive, the fan air volume is reduced, and the adjustment range is positively correlated with the gas / air ratio deviation value. NO x adjust: When the actual NO x When the concentration exceeds the target value, increase the circulating flue gas volume to suppress NO. x generate; When NO x When the concentration drops below the target value, gradually reduce the circulating flue gas volume back to the initial state.

[0014] The combustion optimization control system for gas-fired boilers includes: The data acquisition module is used to collect real-time flue gas parameters and operating condition parameters from the boiler tail section. The controller, with a built-in control model, is used to compare real-time parameters with target values ​​and perform deviation analysis. The execution adjustment module is used to dynamically adjust the air supply volume based on deviation analysis, and to link with the existing nitrogen oxide suppression adjustment module to control the circulating flue gas volume.

[0015] The beneficial effects of this invention are reflected in: This invention relates to the relationship between the oxygen content of the tail gas and NO. x Concentration serves as a dual feedback signal, establishing a hierarchical closed-loop control logic. First, the target oxygen content under different loads is calibrated (especially through CO and NO). x The boundary conditions determine the optimal range, ensuring the baseline for combustion; secondly, during the control process, not only is the air volume corrected based on the oxygen content deviation, but the FGR system is also linked to control NO. xThis targeted suppression method solves the problem of "paying attention to one aspect while neglecting another" in traditional control methods. It is particularly suitable for condensing boilers, enabling enhanced condensation through dynamic adjustment, thereby maximizing boiler thermal efficiency while ensuring low emissions. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the steps of the method of the present invention. Detailed Implementation

[0017] 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 a part of the embodiments of the present invention, and not all of them. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other. 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.

[0018] Specific implementation of the method Please see Figure 1 This embodiment provides a combustion optimization control method for a gas-fired boiler, which is applied to a gas-fired hot water boiler with a rated load of 160t / h.

[0019] Step S100: Target value preset First, based on the boiler and local "low nitrogen" emission requirements (such as NO... x ≤30mg / m 3 Based on Table 1, the theoretical target range for flue gas oxygen content under rated load is initially determined to be 2.0%~2.8%. Meanwhile, according to the "Boiler Air Pollutant Emission Standard" and as shown in Table 2, the NO content is determined... x The target value is 30 mg / m³ 3 .

[0020] Table 1. Adjustment and Control Table for Excess Air Coefficient in Gas-fired Boilers

[0021] Table 2. Emission Concentration Limits for Air Pollutants from Newly Built Boilers

[0022] Steps S110-S140: On-site calibration of oxygen content target value Cold start: After the boiler starts, it operates at 30% load. To ensure stable combustion, the oxygen content is set at 3.8% (about 1.0% higher than the theoretical target range) to ensure that the fuel and air are fully mixed under low load and to avoid incomplete combustion (CO exceeding the standard) caused by local oxygen deficiency in the furnace. At the same time, the oxygen content is maintained within the target range by adjusting the burner damper actuator or the gas / air ratio valve, while monitoring CO to ensure that CO ≤ 100 ppm.

[0023] Calibration under rated load: Gradually increase the boiler load to 100% of the rated load, and monitor O2, CO, and NO in conjunction with the load. x Three indicators.

[0024] Fine-tune towards lower oxygen levels: Gradually reduce the air supply volume and observe the decrease in oxygen content while focusing on CO: If CO starts to rise to 100ppm, record the oxygen content at this time and determine this value as the lower limit of oxygen content.

[0025] Fine-tune towards higher oxygen levels: Gradually increase the air supply volume, observe the increase in oxygen content, and focus on monitoring NO. x And boiler efficiency: when NO is observed x Concentration increased to 30 mg / m³ 3 When the oxygen content exceeds the critical value and the flue gas heat loss increases (boiler efficiency decreases), record the oxygen content at this time and determine this value as the upper limit of oxygen content.

[0026] Determine the optimal value: Between the "lower limit" and "upper limit" of oxygen content, select a value of CO ≤ 50 ppm and NO ≤ 50 ppm. x The intermediate value that meets the standard, has stable combustion in the furnace, and has low boiler vibration is the preset oxygen content target value under rated load.

[0027] Oxygen content correction for partial load After determining the rated load, test the oxygen content at 75% and 50% load respectively. Gradually increase the oxygen content as the load decreases, following the correction principle: 75% load: Oxygen content is 0.3%~0.5% higher than the rated load; 50% load: Oxygen content is 0.8%~1.0% higher than the rated load; Even after correction, CO must still be kept below 100ppm, and combustion must be free of backfire and flameout (flameout needs to be a key concern for fully premixed burners). At 75% load, a new target value is set by increasing the preset oxygen content target value by 0.4%. At this point, CO ≤ 100 ppm and NO x ≤30mg / m 3 It burns stably.

[0028] At 50% load, increase by 1.0% to set a new target value. At this point, CO ≤ 100 ppm, NOx ≤30mg / m 3 It burns stably.

[0029] Step S200: Data Acquisition Zirconia oxygen sensors and NDIR (non-dispersive infrared) nitrogen oxide sensors are deployed in the boiler tail flue to collect real-time oxygen and NO content data. x Concentration data is collected simultaneously with the boiler's current load signal.

[0030] Step S300: Deviation Analysis The controller receives real-time data.

[0031] Oxygen content deviation: The target value is greater than the real-time value, and the real-time value is close to the lower limit but has not yet triggered a CO alarm. This is judged as "slightly insufficient air volume".

[0032] NO x Deviation: Target value > Real-time value, judged as "NO" x "Meets the standard".

[0033] Step S400: Dynamic Adjustment Air volume adjustment: When the air volume is determined to be "insufficient", the controller issues a command to increase the speed of the variable frequency fan by 2% (the adjustment range is positively correlated with the deviation value of 0.2%), thereby increasing the air volume. The adjustment range is positively correlated with the air-fuel ratio deviation value. When the air volume is determined to be excessive, the fan air volume is reduced, and the adjustment range is the same.

[0034] NO x Inhibition: Due to NO x To achieve the target, gradually reduce the flue gas volume to its initial state while maintaining the current FGR valve opening unchanged. When the actual NO... x When the concentration exceeds the target value, the controller activates the existing nitrogen oxide suppression auxiliary module to increase the circulating flue gas volume and suppress NO. x generate.

[0035] Step S500: Load Change Response When the boiler load decreases from 100% to 70%, the controller, based on a preset curve (load-oxygen content relationship), increases the target oxygen content value by 0.4% (approximately 0.4% higher than the rated value) from the preset target value. Then, steps S200-S400 are repeated to optimize the adjustment under the new target value until the oxygen content stabilizes around 3.0%, and NO... x Not exceeding the standard.

[0036] A combustion optimization control system for a gas-fired boiler, used to perform a method according to one embodiment, includes: Data acquisition module: consisting of an oxygen sensor, NO... xIt consists of a sensor, a CO sensor, a flue gas temperature sensor, and a load transmitter, and is installed in the boiler tail flue and steam / hot water pipeline to collect real-time operating data.

[0037] Controller: A PLC, DCS, or embedded industrial controller is used. It contains a control model programmed into it, which includes the logic algorithms for steps S100-S500 in the embodiments, as well as preset load-oxygen content target value curves and CO / NO... x Boundary protection values, etc. The controller receives signals from the data acquisition module, performs deviation analysis, and outputs control commands.

[0038] The control module includes a blower frequency converter and damper actuators (for regulating the air supply volume), as well as a flue gas recirculation valve actuator that is linked to the existing nitrogen oxide suppression control module (i.e., the FGR system). When the controller issues a command, the control module precisely adjusts the air supply volume and the recirculated flue gas volume.

[0039] The above system enables a complete closed-loop control from "parameter perception → intelligent decision-making → precise execution → feedback correction", ensuring that the gas boiler is always in an optimized combustion state with high efficiency and low emissions across the entire load range.

[0040] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0041] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0042] Additionally, "multiple" refers to two or more.

[0043] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for optimizing combustion control in a gas-fired boiler, characterized in that, Specifically, the following steps are included: S100 sets a target value for the oxygen content in the tail gas and determines the NO content based on the emission limits table for air pollutants from newly built boilers. x Target value; The S200 is equipped with oxygen and nitrogen oxide sensors to simultaneously collect data on the oxygen and NO content of the exhaust gas during combustion. x Real-time parameters of concentration; S300, for collecting oxygen content and NO x Real-time parameters of concentration, comparing oxygen content with NO. x To determine the target value, conduct a deviation analysis. S400 dynamically adjusts the air supply volume based on deviation analysis and controls the flue gas volume through the existing nitrogen oxide suppression and regulation module; S500: Dynamically adjust the target value of oxygen content according to the load changes during boiler combustion, and repeat steps S200-S400 to control the flue gas volume.

2. The combustion optimization control method for a gas-fired boiler according to claim 1, characterized in that, The method for determining the target value of oxygen content in the tail gas of S100 includes: S110, based on boiler type, burner type and low nitrogen emission requirements, determine the theoretical target range of flue gas oxygen content under rated load; S120: After the boiler is started from a cold state, during the low load stage of heating up in the hot state, the oxygen content is set to be higher than the theoretical target range of the rated load. By adjusting the air volume or the gas / air ratio, CO ≤ 100ppm and combustion is stable. S130 increases the boiler load to 100% of the rated load and determines the lower and upper limits of oxygen content by bidirectionally adjusting the air supply volume; S140, under 75% and 50% load conditions, gradually increases the oxygen content based on the rated load oxygen content, with the entire process maintaining CO ≤ 100ppm, no visible black smoke, no flashback / flameout in the furnace, and NO... x Meeting emission standards and maintaining stable positive pressure in the furnace are the core criteria for judgment.

3. The combustion optimization control method for a gas-fired boiler according to claim 2, characterized in that: The low load refers to a load of 30% to 50%, during which the oxygen content is 0.8% to 1.0% higher than the theoretical target range of the rated load.

4. The combustion optimization control method for a gas-fired boiler according to claim 2, characterized in that, The methods for determining the lower and upper limits of oxygen content in S130 include: S131, gradually reduce the air supply volume and adjust it to CO equal to or greater than 100ppm, which is determined as the lower limit of oxygen content; S132, gradually increase the air supply volume and adjust to NO. x Exceeding the standard or a significant decrease in boiler efficiency will be determined as the upper limit of oxygen content. S133, Select a value between the lower and upper limits of the oxygen content: CO ≤ 50 ppm, NO ≤ 50 ppm. x The intermediate value that meets the standard and ensures stable combustion is used as the preset target value for oxygen content under rated load.

5. The combustion optimization control method for a gas-fired boiler according to claim 1, characterized in that: 75% load: The oxygen content is 0.3% to 0.5% higher than the rated load; 50% load: The oxygen content is 0.8% to 1.0% higher than the rated load.

6. The combustion optimization control method for a gas-fired boiler according to claim 1, characterized in that, Specifically, S300 includes: Deviation analysis of the gas / air ratio: If the actual oxygen content of the tail gas is less than the lower limit of oxygen content, it is judged as insufficient air volume. If the actual oxygen content of the tail gas is greater than the upper limit of oxygen content, it is judged as excessive air volume. NO x Perform deviation analysis: If the actual NO x When the concentration exceeds the target value, the existing nitrogen oxide suppression and regulation mechanism is triggered. If the actual NO x The concentration should not exceed the target value; maintain the current adjustment state.

7. The combustion optimization control method for a gas-fired boiler according to claim 1, characterized in that, Step S400 specifically includes: Gas / air ratio adjustment: When insufficient air volume is detected, the fan air volume is increased, and the adjustment range is positively correlated with the gas / air ratio deviation value. When the air volume is determined to be excessive, the fan air volume is reduced, and the adjustment range is positively correlated with the gas / air ratio deviation value. NO x adjust: When the actual NO x When the concentration exceeds the target value, increase the circulating flue gas volume to suppress NO. x generate; When NO x When the concentration drops below the target value, gradually reduce the circulating flue gas volume back to the initial state.

8. A gas-fired boiler combustion optimization control system, configured to execute the gas-fired boiler combustion optimization control method according to any one of claims 1-7, characterized in that, include: The data acquisition module is used to collect real-time flue gas parameters and operating condition parameters from the boiler tail section. The controller, with a built-in control model, is used to compare real-time parameters with target values ​​and perform deviation analysis. The execution adjustment module is used to dynamically adjust the air supply volume based on deviation analysis, and to link with the existing nitrogen oxide suppression adjustment module to control the circulating flue gas volume.

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