Control method and system for realizing low-nox combustion in tubular heating furnace

Abstract

Disclosed in the present invention are a control method and system for realizing low-NOx combustion in a tubular heating furnace. The control method comprises: monitoring in real time whether the NOx concentration exceeds a preset upper limit, whether the temperature in a convection chamber and the temperature in a radiant chamber are within a preset temperature range, and whether the pressure in the convection chamber is within a preset pressure range, and performing coordinated regulation in time, so that low-NOx emission can be ensured while the combustion requirements for low energy consumption, high combustion efficiency, and high safety are satisfied, thereby facilitating low-cost transformation and application of existing control systems, and having remarkable value and important significance for achieving energy saving and emission reduction of industries using tubular heating furnaces.

Description

A control method and control system for achieving low NOx combustion in a tubular furnace Technical Field

[0001] This invention relates to a control method and control system for achieving low NOx combustion in a tubular furnace, belonging to the field of furnace combustion control technology. Background Technology

[0002] A tubular furnace is a continuously operating heating device with combustion. It typically consists of a radiant chamber, a convection chamber, a burner, a waste heat recovery system, and a flue gas duct system. Its main advantages are high heating temperature and large heat transfer capacity, and it is widely used in the petrochemical, natural gas chemical, and organic chemical industries. The working principle of a tubular furnace is to utilize the heat released by the combustion of fuel within the furnace chamber to provide a heat source for the flowing material in the furnace tubes, enabling it to reach the temperature required for chemical reactions or subsequent processes.

[0003] NOx is a general term for nitrogen oxides, typically including NO and NO2, and is a harmful air pollutant. Because tubular furnaces often use gas as fuel, and the composition of this fuel gas is relatively complex, large amounts of nitrogen oxides are produced during high-temperature combustion and incomplete combustion. High NOx emissions not only pollute the environment, but incomplete fuel combustion also leads to resource waste. Therefore, low NOx emissions have become an important technical indicator for tubular furnaces. In the petrochemical industry, current standards stipulate that NOx emissions from furnace flue gas must be controlled below 50 mg / m³. 3 the following.

[0004] Currently, the main solutions for achieving low NOx emissions are low NOx combustion technology and flue gas denitrification technology. However, because flue gas denitrification technology has problems such as large investment and high operating costs, tubular heaters mainly use low NOx combustion technology to reduce NOx generation.

[0005] Chinese patent document CN105698212 discloses a combustion method and device for energy saving and NOx reduction in a petrochemical heating furnace. The method involves blowing air into the bottom and middle of the furnace to mix with fuel gas for combustion, controlling the volume percentage of oxygen in the flue gas after combustion to be 4%–6%. The heating furnace includes a furnace body, with combustion nozzles at the bottom connected to a fuel gas inlet pipe and a main air inlet pipe. The main air inlet pipe is connected to a fan. An intermediate air inlet pipe is located in the middle of the furnace body and connected to the main air inlet pipe, with an intermediate air regulating valve installed on the intermediate air inlet pipe. Although this patent achieves low NOx emissions by controlling the oxygen content in the flue gas after combustion, a total air intake volume of 10,000–20,000 m³ is required to achieve the desired oxygen volume percentage of 4%–6%. 3 / h, the air intake rate blown into the middle of the heating furnace is 5% to 7% of the total air intake rate, while the gas feed rate is 50 to 100 Nm³. 3 / h. Clearly, in this combustion technology, the amount of auxiliary air used is far greater than the amount of fuel gas fed. The increase in the excess air coefficient leads to increased heat loss in the flue gas, thus causing a decrease in the thermal efficiency of the heater. The thermal efficiency of the heater affects the safety and economy of production operations; only by simultaneously improving the quality of the heater's flue gas and its thermal efficiency can we meet environmental protection requirements, reduce energy consumption, and improve economic benefits.

[0006] However, existing research indicates that while reducing the flame zone temperature in the furnace reduces the amount of thermal NOx generated, the stability of flame combustion also decreases, making it highly susceptible to safety hazards such as flameout and flameout. Furthermore, as the furnace load decreases, the average furnace temperature drops, leading to a significant reduction in thermal NOx. However, this temperature drop also results in incomplete fuel combustion, causing a rapid increase in fuel-based NOx, with the increase far exceeding the decrease in thermal NOx. Ultimately, this results in NOx generation generally trending in the opposite direction to the furnace load change. Additionally, fluctuations in fuel gas pressure not only cause uneven temperature distribution within the furnace but also cause flame deflection and erosion of the furnace tubes, making them prone to localized overheating and overheating of the working fluid, potentially leading to tube rupture. This also results in slow NOx emission control response from the furnace.

[0007] In other words, for tubular furnaces, due to the process characteristics they employ, there are technical challenges such as multivariable, nonlinear, and multi-objective constraints in controlling the simultaneous improvement of flue gas quality and thermal efficiency. There is an urgent need in this field for a control technology that can ensure NOx emissions meet standards while also having low energy consumption, high combustion efficiency, and good safety to achieve low NOx combustion in tubular furnaces. However, to date, there have been no reports of effective control technologies that can meet this requirement.

[0008] Summary of the Invention

[0009] In view of the above-mentioned problems and needs of the existing technology, the purpose of this invention is to provide a control method and control system for achieving low NOx combustion in a tubular furnace, which can meet the requirements of low energy consumption, high combustion efficiency and high safety while ensuring low NOx emissions.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A control method for achieving low NOx combustion in a tubular furnace includes a tubular furnace and fuel gas and combustion air supply pipelines connected to the furnace. It also includes a main controller and an air-fuel ratio controller for monitoring the ratio of combustion air flow to fuel gas flow. The tubular furnace includes a convection chamber and a radiation chamber, and a flue gas baffle at the outlet of the convection chamber. At the outlet of the convection chamber, a convection chamber temperature sensor for monitoring the temperature inside the chamber, a convection chamber pressure sensor for monitoring the pressure inside the chamber, and a NOx analyzer for monitoring the NOx concentration in the flue gas at the outlet of the convection chamber are provided. The radiant chamber is equipped with a radiant chamber temperature sensor at its outlet for monitoring the temperature inside the chamber; the fuel gas delivery pipeline is equipped with a fuel gas pressure reducing valve for adjusting the fuel gas intake flow rate, a fuel gas flow controller for regulating the fuel gas flow rate, and a fuel gas flow meter located on the pipeline downstream of the fuel gas pressure reducing valve; the combustion air delivery pipeline is equipped with a duct regulating baffle for adjusting the combustion air intake flow rate, a combustion air flow controller for regulating the combustion air flow rate, and a combustion air flow meter located on the pipeline downstream of the duct regulating baffle; the control method comprises the following sequential steps:

[0012] S1) The main controller determines whether the measured value of NOx concentration is less than the preset upper limit of NOx concentration. If yes, proceed to step S2); otherwise, jump to step S4.

[0013] S2) The main controller determines whether the measured values ​​of the temperature in the convection chamber and the temperature in the radiation chamber are less than their respective preset lower limit values. If at least one of them is yes, then jump to step S4); otherwise, proceed to step S3.

[0014] S3) The main controller determines whether the measured values ​​of the temperature in the convection chamber and the temperature in the radiation chamber are greater than their respective preset upper temperature limits. If at least one of them is, then jump to step S5); otherwise, jump to step S6.

[0015] S4) Increase the opening of the air duct regulating damper and regulate the fuel gas flow rate by the preset air-fuel ratio; when the signal to increase the opening of the air duct regulating damper ends, return to step S1);

[0016] S5) Reduce the opening of the fuel gas pressure reducing valve and regulate the combustion air flow rate by the preset air-fuel ratio. When the signal of reducing the opening of the fuel gas pressure reducing valve ends, return to step S1).

[0017] S6) The main controller determines whether the measured pressure value in the convection chamber is within the preset pressure range. If yes, it returns to step S1); otherwise, it adjusts the opening of the flue gas damper to make the measured pressure value in the convection chamber within the preset pressure range.

[0018] In one implementation scheme, step S4) involves the following specific steps for regulating fuel gas flow:

[0019] S41) The combustion air flow meter sends the real-time monitored combustion air flow value to the air-fuel ratio controller;

[0020] S42) The air-fuel ratio controller calculates the required increase in fuel gas flow rate based on the preset air-fuel ratio and sends it to the fuel gas flow controller.

[0021] S43) The fuel gas flow controller controls the opening of the fuel gas pressure reducing valve to increase, while the fuel gas flow meter feeds back the real-time monitored fuel gas flow value to the air-fuel ratio controller.

[0022] One implementation scheme, step S5), specifically involves the following steps to achieve combustion air flow regulation:

[0023] S51) The fuel gas flow meter sends the real-time monitored fuel gas flow value to the air-fuel ratio controller;

[0024] S52) The air-fuel ratio controller calculates the required reduction in combustion air flow based on the preset air-fuel ratio and sends it to the combustion air flow controller.

[0025] S53) The combustion air flow controller reduces the opening of the air duct regulating baffle, while the combustion air flow meter feeds back the real-time monitored combustion air flow value to the air-fuel ratio controller.

[0026] One implementation scheme, step S6), specifically involves the following steps to regulate the pressure inside the convection chamber:

[0027] If the measured pressure in the convection chamber is greater than the upper limit of the preset pressure range, the opening of the flue gas damper will be increased; if the measured pressure in the convection chamber is less than the lower limit of the preset pressure range, the opening of the flue gas damper will be decreased.

[0028] A control system for achieving low NOx combustion in a tubular furnace includes a tubular furnace and a fuel gas supply pipeline and a combustion air supply pipeline connected to the furnace. It also includes a main controller and an air-fuel ratio controller for monitoring the ratio of combustion air flow to fuel gas flow. The tubular furnace includes a convection chamber and a radiation chamber, and a flue gas baffle at the outlet of the convection chamber. At the outlet of the convection chamber, there is a convection chamber temperature sensor for monitoring the temperature inside the convection chamber, a convection chamber pressure sensor for monitoring the pressure inside the convection chamber, and a NOx analyzer for monitoring the NOx concentration in the flue gas at the outlet of the convection chamber. At the outlet of the radiation chamber, there is a radiation chamber temperature sensor for monitoring the temperature inside the radiation chamber. The fuel gas supply pipeline is equipped with a system for regulating fuel gas flow. The system comprises a fuel gas pressure reducing valve for regulating the intake flow rate, a fuel gas flow controller for regulating the fuel gas flow rate, and a fuel gas flow meter located on the pipeline downstream of the fuel gas pressure reducing valve; a duct regulating baffle for regulating the intake flow rate of the combustion air and a combustion air flow controller for regulating the combustion air flow rate, and a combustion air flow meter located on the pipeline downstream of the duct regulating baffle, wherein the system further comprises a high-value selector and a low-value selector, the signal input terminals of the high-value selector and the low-value selector are both communicatively connected to the signal output terminal of the main controller, the signal output terminal of the high-value selector is communicatively connected to the signal input terminal of the combustion air flow controller, and the signal output terminal of the low-value selector is communicatively connected to the signal input terminal of the fuel gas flow controller.

[0029] In one embodiment, the signal output terminals of the fuel gas flow meter and the combustion air flow meter are both communicatively connected to the signal input terminal of the air-fuel ratio controller, and the signal output terminal of the air-fuel ratio controller is communicatively connected to the signal input terminals of the fuel gas flow controller and the combustion air flow controller, respectively.

[0030] One embodiment further includes a fuel gas pressure controller, the signal output terminal of which is communicatively connected to the signal input terminal of a fuel gas flow controller, and the signal output terminal of the fuel gas flow controller is communicatively connected to a fuel gas pressure reducing valve.

[0031] In a preferred embodiment, fuel gas pressure sensors are provided on both the front and rear pipelines of the fuel gas pressure reducing valve, and the fuel gas pressure sensors are communicatively connected to the fuel gas pressure controller.

[0032] In a preferred embodiment, the device further includes a signal processor, the signal input terminal of which is communicatively connected to the convection chamber temperature sensor, the convection chamber pressure sensor, the NOx analyzer, and the radiation chamber temperature sensor, respectively, and the signal output terminal of which is communicatively connected to the signal input terminal of the main controller.

[0033] In a preferred embodiment, the system further includes a convection chamber pressure controller, wherein the signal output terminal of the convection chamber pressure controller is communicatively connected to the flue gas damper, and the signal input terminal of the convection chamber pressure controller is communicatively connected to the signal output terminal of the signal processor.

[0034] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0035] This invention, through real-time monitoring and coordinated control of parameters such as NOx concentration, temperature in the convection and radiation chambers, pressure in the convection chamber, and air-fuel ratio, not only ensures low NOx emissions but also simultaneously meets the combustion requirements of low energy consumption, high combustion efficiency, and high safety. Furthermore, it is easy to retrofit existing control systems at low cost, and has significant value and importance for energy conservation and emission reduction in industries using tubular furnaces. Attached Figure Description

[0036] Figure 1 is a flowchart of a control method for achieving low NOx combustion in a tubular furnace according to an embodiment of the present invention;

[0037] Figure 2 is a schematic diagram of a control system for achieving low NOx combustion in a tubular furnace according to an embodiment of the present invention. The arrows in the figure indicate the flow direction, the solid lines indicate the gas pipelines, and the dashed lines indicate the signal paths.

[0038] The labels in the diagram are as follows:

[0039] 1. Tubular furnace; 1-1. Convection chamber; 1-2. Radiant chamber; 1-3. Flue gas baffle; 1-4. Convection chamber temperature sensor; 1-5. Convection chamber pressure sensor; 1-6. NOx analyzer; 1-7. Radiant chamber temperature sensor; 1-8. Convection chamber pressure controller;

[0040] 2. Fuel gas delivery pipeline; 2-1. Fuel gas pressure reducing valve; 2-2. Fuel gas flow controller; 2-3. Fuel gas flow meter; 2-4. Fuel gas pressure controller; 2-5. Fuel gas pressure sensor;

[0041] 3. Combustion air supply pipeline; 3-1. Air duct regulating baffle; 3-2. Combustion air flow controller; 3-3. Combustion air flow meter;

[0042] 4. Main controller; 5. Air-fuel ratio controller; 6. High-value selector; 7. Low-value selector; 8. Signal processor. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0044] The technical solutions provided by the embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0045] Example

[0046] Please refer to Figure 1. This embodiment provides a control method for achieving low NOx combustion in a tubular furnace, which includes the following sequential steps:

[0047] S1) The main controller determines whether the measured value of NOx concentration is less than the preset upper limit of NOx concentration. If yes, proceed to step S2); otherwise, jump to step S4.

[0048] S2) The main controller determines whether the measured values ​​of the temperature in the convection chamber and the temperature in the radiation chamber are less than their respective preset lower limit values. If at least one of them is yes, then jump to step S4); otherwise, proceed to step S3.

[0049] S3) The main controller determines whether the measured values ​​of the temperature in the convection chamber and the temperature in the radiation chamber are greater than their respective preset upper temperature limits. If at least one of them is, then jump to step S5); otherwise, jump to step S6.

[0050] S4) Increase the opening of the air duct regulating damper and regulate the fuel gas flow rate by the preset air-fuel ratio; when the signal to increase the opening of the air duct regulating damper ends, return to step S1);

[0051] S5) Reduce the opening of the fuel gas pressure reducing valve and regulate the combustion air flow rate by the preset air-fuel ratio. When the signal of reducing the opening of the fuel gas pressure reducing valve ends, return to step S1).

[0052] S6) The main controller determines whether the measured pressure value in the convection chamber is within the preset pressure range. If yes, it returns to step S1); otherwise, it adjusts the opening of the flue gas damper to make the measured pressure value in the convection chamber within the preset pressure range.

[0053] In this embodiment, the specific steps for implementing fuel gas flow regulation in step S4) are as follows:

[0054] S41) The combustion air flow meter sends the real-time monitored combustion air flow value to the air-fuel ratio controller;

[0055] S42) The air-fuel ratio controller calculates the required increase in fuel gas flow rate based on the preset air-fuel ratio and sends it to the fuel gas flow controller.

[0056] S43) The fuel gas flow controller controls the opening of the fuel gas pressure reducing valve to increase, while the fuel gas flow meter feeds back the real-time monitored fuel gas flow value to the air-fuel ratio controller.

[0057] In this embodiment, the specific steps for controlling the combustion air flow in step S5) are as follows:

[0058] S51) The fuel gas flow meter sends the real-time monitored fuel gas flow value to the air-fuel ratio controller;

[0059] S52) The air-fuel ratio controller calculates the required reduction in combustion air flow based on the preset air-fuel ratio and sends it to the combustion air flow controller.

[0060] S53) The combustion air flow controller reduces the opening of the air duct regulating baffle, while the combustion air flow meter feeds back the real-time monitored combustion air flow value to the air-fuel ratio controller.

[0061] In this embodiment, the specific operation of step S6) to regulate the pressure in the convection chamber is as follows:

[0062] If the measured pressure in the convection chamber is greater than the upper limit of the preset pressure range, the opening of the flue gas damper will be increased; if the measured pressure in the convection chamber is less than the lower limit of the preset pressure range, the opening of the flue gas damper will be decreased.

[0063] Please refer to Figure 2. This embodiment provides a control system for achieving low NOx combustion in a tubular furnace, including a tubular furnace 1, a fuel gas supply pipeline 2 and a combustion air supply pipeline 3 connected to the tubular furnace 1, a main controller 4, and an air-fuel ratio controller 5 for monitoring the ratio of combustion air flow to fuel gas flow. The tubular furnace 1 includes a convection chamber 1-1, a radiation chamber 1-2, and a flue gas baffle 1-3 located at the outlet of the convection chamber. A flue gas baffle 1-3 for monitoring convection is provided at the outlet of the convection chamber 1-1. The convection chamber temperature sensor 1-4 is used to monitor the indoor temperature, the convection chamber pressure sensor 1-5 is used to monitor the pressure inside the convection chamber, and the NOx analyzer 1-6 is used to monitor the NOx concentration in the flue gas at the outlet of the convection chamber. A radiation chamber temperature sensor 1-7 is installed at the outlet of the radiation chamber 1-2 to monitor the temperature inside the radiation chamber. A fuel gas pressure reducing valve 2-1 is installed on the fuel gas delivery pipeline 2 to regulate the fuel gas intake flow rate, and a fuel gas flow controller 2-2 is installed to regulate the fuel gas flow rate. The system includes a fuel gas flow meter 2-3 on the rear pipeline; a duct regulating baffle 3-1 for adjusting the intake flow of combustion air and a combustion air flow controller 3-2 for regulating the flow of combustion air are provided on the combustion air supply pipeline 3, along with a combustion air flow meter 3-3 on the pipeline behind the duct regulating baffle 3-1; it also includes a high-value selector 6 and a low-value selector 7, the signal input terminals of the high-value selector 6 and the low-value selector 7 are both communicatively connected to the signal output terminal of the main controller 4, the signal output terminal of the high-value selector 6 is communicatively connected to the signal input terminal of the combustion air flow controller 3-2, and the signal output terminal of the low-value selector 7 is communicatively connected to the signal input terminal of the fuel gas flow controller 2-2; the signal output terminals of the fuel gas flow meter 2-3 and the combustion air flow meter 3-3 are both communicatively connected to the signal input terminal of the air-fuel ratio controller 5, and the signal output terminal of the air-fuel ratio controller 5 is communicatively connected to the signal input terminals of the fuel gas flow controller 2-2 and the combustion air flow controller 3-2, respectively.

[0064] As a preferred embodiment, the control system further includes a fuel gas pressure controller 2-4, the signal output terminal of which is communicatively connected to the signal input terminal of the fuel gas flow controller 2-2, and the signal output terminal of the fuel gas flow controller 2-2 is communicatively connected to the fuel gas pressure reducing valve; a fuel gas pressure sensor 2-5 is provided on both the front and rear pipelines of the fuel gas pressure reducing valve 2-1, and the fuel gas pressure sensor 2-5 is communicatively connected to the fuel gas pressure controller 2-4.

[0065] As a preferred embodiment, the control system described in this embodiment further includes a signal processor 8. The signal input terminal of the signal processor 8 is communicatively connected to the convection chamber temperature sensor 1-4, the convection chamber pressure sensor 1-5, the NOx analyzer 1-6, and the radiation chamber temperature sensor 1-7, respectively. The signal output terminal of the signal processor 8 is communicatively connected to the signal input terminal of the main controller 4.

[0066] As a preferred embodiment, the control system described in this embodiment further includes a convection chamber pressure controller 1-8, the signal output terminal of which is communicatively connected to the flue gas damper 1-3, and the signal input terminal of which is communicatively connected to the signal output terminal of the signal processor 8.

[0067] Referring again to Figures 1 and 2, the control process for achieving low NOx combustion in the tubular furnace using the control system provided in this embodiment is specifically described below:

[0068] NOx analyzers 1-6 monitor the NOx concentration in the flue gas at the outlet of the convection chamber 1-1 of the tubular furnace 1 in real time and send the detection signal to the signal processor 8 in real time. The signal processor 8 amplifies, filters, and performs analog-to-digital conversion on the signal before outputting it to the main controller 4. At the same time, the convection chamber temperature sensor 1-4 monitors the temperature inside the convection chamber 1-1 of the tubular furnace 1 in real time and sends the detection signal to the signal processor 8 in real time. The signal processor 8 amplifies, filters, and performs analog-to-digital conversion on the signal before outputting it to the main controller 4. The radiation chamber temperature sensor 1-7 monitors the temperature inside the radiation chamber 1-2 of the tubular furnace 1 in real time and sends the detection signal to the signal processor 8 in real time. The signal processor 8 amplifies, filters, and performs analog-to-digital conversion on the signal before outputting it to the main controller 4.

[0069] S1) The main controller 4 determines whether the measured NOx concentration value is less than the preset upper limit of NOx concentration (for example, according to current standards, this upper limit can be set to 50 mg / m³). 3 If yes, proceed to step S2); otherwise, skip to step S4.

[0070] S2) The main controller 4 determines whether the measured values ​​of the temperature in the convection chamber and the temperature in the radiation chamber are less than their respective preset lower limit values ​​(the lower limit values ​​mentioned here can be obtained from the design manual of the specific tubular heating furnace used). If at least one of them is yes, then jump to step S4); otherwise, proceed to step S3.

[0071] S3) The main controller 4 determines whether the measured values ​​of the temperature in the convection chamber and the temperature in the radiation chamber are greater than their respective preset upper temperature limits (the upper temperature limits mentioned here can be obtained from the design manual of the specific tubular heating furnace used). If at least one of them is yes, then jump to step S5); otherwise, jump to step S6.

[0072] S4) The main controller 4 outputs an increase signal to the high-value selector 6. The high-value selector 6 outputs the received increase signal to the combustion air flow controller 3-2. After receiving the increase signal, the combustion air flow controller 3-2 increases the opening of the air duct regulating damper. The combustion air flow meter 3-3 monitors the combustion air intake flow in real time and simultaneously feeds it back to the air-fuel ratio controller 5. The air-fuel ratio controller 5 calculates the required increase in fuel gas flow based on the preset air-fuel ratio (the air-fuel ratio mentioned here can be obtained from the design standard of the specific combustion conditions) and sends it to the fuel gas flow controller 2-2. The fuel gas flow controller 2-2 outputs the flow increase signal to the fuel gas pressure controller 2-4. The fuel gas pressure controller 2-4 then adjusts the flow increase signal according to the received flow increase signal. The opening of the fuel gas pressure reducing valve 2-1 is increased. The fuel gas pressure sensors 2-5 installed on the pipelines before and after the fuel gas pressure reducing valve 2-1 transmit the pressure data before and after the fuel gas pressure reducing valve 2-1 back to the fuel gas pressure controller 2-4 in real time, so as to assist the fuel gas pressure controller 2-4 in more accurately controlling the valve opening of the fuel gas pressure reducing valve 2-1. At the same time, the fuel gas flow meter 2-3 feeds back the real-time monitored fuel gas intake flow value to the air-fuel ratio controller 5. The air-fuel ratio controller 5 calculates the actual air-fuel ratio at this time based on the actual fuel gas intake flow, and corrects and controls the combustion air flow according to the calculation result. This step is repeated until the main controller 4 no longer outputs an increase signal to the high value selector 6, and then returns to step S1.

[0073] S5) The main controller 4 outputs a reduction signal to the low-value selector 7. The low-value selector 7 outputs the received reduction signal to the fuel gas flow controller 2-2. After receiving the reduction signal, the fuel gas flow controller 2-2 outputs it to the fuel gas pressure controller 2-4. The fuel gas pressure controller 2-4 controls the opening of the fuel gas pressure reducing valve 2-1 to decrease according to the received flow reduction signal. The fuel gas pressure sensors 2-5 installed on the pipelines before and after the fuel gas pressure reducing valve 2-1 transmit the pressure data before and after the fuel gas pressure reducing valve 2-1 back to the fuel gas pressure controller 2-4 in real time to assist the fuel gas pressure controller 2-4 in more accurately controlling the valve opening of the fuel gas pressure reducing valve 2-1. The fuel gas flow meter 2-3 monitors the fuel gas intake flow in real time and feeds it back to the air conditioner. The air-fuel ratio controller 5 calculates the required reduction in combustion air flow rate based on a preset air-fuel ratio (which can be obtained from the design standards for specific combustion conditions) and sends it to the combustion air flow controller 3-2. The combustion air flow controller 3-2 controls the opening of the duct regulating damper 3-1 to decrease based on the received flow reduction signal. At the same time, the combustion air flow meter 3-3 feeds back the real-time monitored combustion air intake flow rate to the air-fuel ratio controller 5. The air-fuel ratio controller 5 calculates the actual air-fuel ratio based on the actual intake flow rate of the combustion air and corrects and regulates the fuel gas flow rate. This step is repeated until the main controller 4 no longer outputs a reduction signal to the low-value selector 7, and then returns to step S1.

[0074] S6) The convection chamber pressure sensor 1-5 monitors the pressure inside the convection chamber 1-1 of the tubular furnace 1 in real time and sends the detection signal to the signal processor 8 in real time. The signal processor 8 amplifies, filters, and converts the signal from analog to digital before outputting it to the main controller 4. The main controller 4 determines whether the measured pressure value inside the convection chamber is within the preset pressure range (the pressure range mentioned here can be obtained from the design manual of the specific tubular furnace used). If yes, it returns to step S1). Otherwise, it adjusts the opening of the flue gas damper 1-3 to make the measured pressure value inside the convection chamber within the preset pressure range (specifically, if the measured pressure value inside the convection chamber is greater than the upper limit of the preset pressure range, the opening of the flue gas damper 1-3 is increased by the convection chamber pressure controller 1-8; if the measured pressure value inside the convection chamber is less than the lower limit of the preset pressure range, the opening of the flue gas damper 1-3 is decreased by the convection chamber pressure controller 1-8).

[0075] As can be seen from the above, this invention, through real-time monitoring and coordinated control of parameters such as NOx concentration, temperature in the convection and radiation chambers, pressure in the convection chamber, and air-fuel ratio, can not only ensure low NOx emissions, but also simultaneously meet the combustion requirements of low energy consumption, high combustion efficiency, and high safety. Furthermore, it is easy to retrofit existing control systems at low cost, and has significant value and importance for energy conservation and emission reduction in industries that use tubular heating furnaces.

[0076] Finally, it should be pointed out that the above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A control method for achieving low NOx combustion in a tubular furnace, comprising a tubular furnace and a fuel gas supply pipeline and a combustion air supply pipeline connected to the tubular furnace, further comprising a main controller and an air-fuel ratio controller for monitoring the ratio of combustion air flow rate to fuel gas flow rate; the tubular furnace includes a convection chamber and a radiation chamber, and a flue gas baffle disposed at the outlet of the convection chamber; a convection chamber temperature sensor for monitoring the temperature inside the convection chamber, a convection chamber pressure sensor for monitoring the pressure inside the convection chamber, and a NOx concentration in the flue gas at the outlet of the convection chamber are disposed at the outlet of the convection chamber. The NOx analyzer includes a radiation chamber temperature sensor at the outlet of the radiation chamber for monitoring the temperature inside the chamber; a fuel gas pressure reducing valve for adjusting the fuel gas intake flow rate and a fuel gas flow controller for regulating the fuel gas flow rate, along with a fuel gas flow meter located on the pipeline downstream of the fuel gas pressure reducing valve, are installed on the fuel gas delivery pipeline; a duct regulating baffle for adjusting the combustion air intake flow rate and a combustion air flow controller for regulating the combustion air flow rate, along with a combustion air flow meter located on the pipeline downstream of the duct regulating baffle, are also included in the analyzer. The control method includes the following sequential steps: S1) The main controller determines whether the measured value of NOx concentration is less than the preset upper limit of NOx concentration. If yes, proceed to step S2); otherwise, jump to step S4. S2) The main controller determines whether the measured values ​​of the temperature in the convection chamber and the temperature in the radiation chamber are less than their respective preset lower limit values. If at least one of them is yes, then jump to step S4); otherwise, proceed to step S3. S3) The main controller determines whether the measured values ​​of the temperature in the convection chamber and the temperature in the radiation chamber are greater than their respective preset upper temperature limits. If at least one of them is, then jump to step S5); otherwise, jump to step S6. S4) Increase the opening of the air duct regulating damper and regulate the fuel gas flow rate by the preset air-fuel ratio; when the signal to increase the opening of the air duct regulating damper ends, return to step S1); S5) Reduce the opening of the fuel gas pressure reducing valve and regulate the combustion air flow rate by the preset air-fuel ratio. When the signal of reducing the opening of the fuel gas pressure reducing valve ends, return to step S1). S6) The main controller determines whether the measured pressure value in the convection chamber is within the preset pressure range. If yes, it returns to step S1); otherwise, it adjusts the opening of the flue gas damper to make the measured pressure value in the convection chamber within the preset pressure range.

2. The control method according to claim 1, characterized in that, The specific steps for achieving fuel gas flow regulation in step S4 are as follows: S41) The combustion air flow meter sends the real-time monitored combustion air flow value to the air-fuel ratio controller; S42) The air-fuel ratio controller calculates the required increase in fuel gas flow rate based on the preset air-fuel ratio and sends it to the fuel gas flow controller. S43) The fuel gas flow controller increases the opening of the fuel gas pressure reducing valve, while the fuel gas flow meter monitors the flow in real time. The fuel gas flow rate value is fed back to the air-fuel ratio controller.

3. The control method according to claim 1, characterized in that, Step S5) The specific steps for controlling the combustion air flow are as follows: S51) The fuel gas flow meter sends the real-time monitored fuel gas flow value to the air-fuel ratio controller; S52) The air-fuel ratio controller calculates the required reduction in combustion air flow based on the preset air-fuel ratio and sends it to the combustion air flow controller. S53) The combustion air flow controller reduces the opening of the air duct regulating baffle, while the combustion air flow meter feeds back the real-time monitored combustion air flow value to the air-fuel ratio controller.

4. The control method according to claim 1, characterized in that, Step S6) The specific operation for achieving pressure regulation in the convection chamber is as follows: If the measured pressure in the convection chamber is greater than the upper limit of the preset pressure range, the opening of the flue gas damper will be increased; if the measured pressure in the convection chamber is less than the lower limit of the preset pressure range, the opening of the flue gas damper will be decreased.

5. A control system for achieving low NOx combustion in a tubular furnace, comprising a tubular furnace and a fuel gas supply pipeline and a combustion air supply pipeline connected to the tubular furnace, further comprising a main controller and an air-fuel ratio controller for monitoring the ratio of combustion air flow rate to fuel gas flow rate; the tubular furnace includes a convection chamber and a radiation chamber, and a flue gas baffle disposed at the outlet of the convection chamber; a convection chamber temperature sensor for monitoring the temperature inside the convection chamber, a convection chamber pressure sensor for monitoring the pressure inside the convection chamber, and a NOx concentration in the flue gas at the outlet of the convection chamber are disposed at the outlet of the convection chamber. The NOx analyzer includes a radiation chamber temperature sensor at the outlet of the radiation chamber for monitoring the temperature inside the chamber; a fuel gas pressure reducing valve for adjusting the fuel gas intake flow rate and a fuel gas flow controller for regulating the fuel gas flow rate, along with a fuel gas flow meter located on the pipeline downstream of the fuel gas pressure reducing valve, are provided on the fuel gas delivery pipeline; a duct regulating baffle for adjusting the combustion air intake flow rate and a combustion air flow controller for regulating the combustion air flow rate, along with a combustion air flow meter located on the pipeline downstream of the duct regulating baffle, are provided on the combustion air delivery pipeline; its characteristic is that: It also includes a high-value selector and a low-value selector. The signal input terminals of the high-value selector and the low-value selector are both communicatively connected to the signal output terminal of the main controller. The signal output terminal of the high-value selector is communicatively connected to the signal input terminal of the combustion air flow controller, and the signal output terminal of the low-value selector is communicatively connected to the signal input terminal of the fuel gas flow controller.

6. The control system according to claim 5, characterized in that: The signal output terminals of the fuel gas flow meter and the combustion air flow meter are both communicatively connected to the signal input terminal of the air-fuel ratio controller. The signal output terminal of the air-fuel ratio controller is communicatively connected to the signal input terminals of the fuel gas flow controller and the combustion air flow controller, respectively.

7. The control system according to claim 5, characterized in that: The control system further includes a fuel gas pressure controller, the signal output terminal of which is communicatively connected to the signal input terminal of a fuel gas flow controller, and the signal output terminal of the fuel gas flow controller is communicatively connected to a fuel gas pressure reducing valve.

8. The control system according to claim 7, characterized in that: Fuel gas pressure sensors are installed on both the front and rear pipelines of the fuel gas pressure reducing valve, and the fuel gas pressure sensors are communicatively connected to the fuel gas pressure controller.

9. The control system according to claim 5, characterized in that: The control system further includes a signal processor, whose signal input terminal is communicatively connected to the convection chamber temperature sensor, the convection chamber pressure sensor, the NOx analyzer, and the radiation chamber temperature sensor, respectively, and whose signal output terminal is communicatively connected to the signal input terminal of the main controller.

10. The control system according to claim 9, characterized in that: The control system further includes a convection chamber pressure controller, the signal output terminal of which is communicatively connected to the flue gas damper, and the signal input terminal of which is communicatively connected to the signal output terminal of the signal processor.

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