A combustion method and combustion system

Abstract

The application discloses a combustion method and a combustion system. The combustion method comprises the following steps: carrying out combustion in a combustion furnace, wherein the combustion furnace comprises a first combustion-supporting gas inlet, a first fuel gas inlet, two groups of regenerative burners, a second combustion-supporting gas inlet, a second fuel gas inlet, two groups of diffusion burners and a flue gas duct. The regenerative burners and the diffusion burners are combined to realize different working modes in different combustion stages, so that the qualified emission of nitrogen oxides is ensured, energy consumption is saved, the working requirements of the combustion furnace are met, the purposes of energy saving, fast melting rate of target metals, small burning loss of the diffusion burners and low nitrogen are realized, and the combustion method has great application value.

Description

Technical Field

[0001] This application belongs to the field of combustion furnace technology, and particularly relates to a combustion method and combustion system. Background Technology

[0002] Currently, burners widely used in industrial furnaces and kilns are basically divided into cold air burners, cold air preheating burners, regenerative burners, and diffused burners. Each of these burners has its own advantages and disadvantages. Cold air burners have low flame temperatures and high energy consumption. X Low emissions; cold air preheating burners increase flame temperature and reduce energy consumption, but are still considered high-energy-consuming products; regenerative burners greatly increase the temperature of the combustion air by recovering and utilizing waste heat from flue gas, so their flame temperature can usually reach over 1600℃. At the same time, due to the recovery and utilization of waste heat, energy consumption can often reach a very low standard, but they are extremely prone to generating large amounts of NO in high-temperature environments. X x is a positive integer, which is not environmentally friendly; ordinary diffuse burners have a non-concentrated flame, an unsatisfactory combustion state, and a high CO content in the flue gas, resulting in high energy consumption, but the heated material has low burn loss. Summary of the Invention

[0003] This application provides a combustion method and a combustion system, aiming to provide an energy-saving and environmentally friendly combustion method.

[0004] On the one hand, this application provides a combustion method, comprising:

[0005] The method is carried out in a combustion furnace, which includes a first auxiliary gas inlet, a first gas inlet, two sets of regenerative burners, a second auxiliary gas inlet, a second gas inlet, two sets of diffused burners, and a flue gas duct. The method includes:

[0006] In the first mode, the first auxiliary gas inlet and the first gas inlet are opened, and combustion is carried out using two sets of regenerative burners;

[0007] In the second mode, one set of regenerative burners is shut down and another set of regenerative burners is used for combustion. At the same time, the second auxiliary gas inlet and the second gas inlet are opened and a set of diffuse burners are used for combustion. The second mode is started when the nitrogen oxide content of the flue gas in the exhaust duct reaches the first preset value.

[0008] In the third mode, the first auxiliary gas inlet and the first gas inlet are closed, and the two sets of regenerative burners are shut down. Combustion is carried out using two sets of diffuse burners. The third mode is started when the nitrogen oxide content in the flue gas in the exhaust duct reaches the second preset value.

[0009] Optionally, the second mode can be started when the nitrogen oxide content in the flue gas in the exhaust duct reaches a third preset value, wherein the nitrogen oxide content is such that the second preset value ≤ the third preset value ≤ the first preset value.

[0010] Optionally, in the second mode, the heat from the flue gas in the combustion furnace is used to heat the gas in the first combustion gas inlet to achieve heat recovery.

[0011] Optionally, after the second mode begins, the combustion furnace exhibits a temperature change that first decreases and then increases, wherein the lowest temperature of the combustion furnace is 800℃~1200℃, or 900℃~950℃.

[0012] Optionally, the temperature at the outlet of the smoke exhaust duct is 150℃~200℃ or 170℃~190℃.

[0013] Optionally, in the second and third modes, the air-fuel ratio ranges from 10 to 13:1, and the fuel quantity is 100 to 110 m³. 3 / h.

[0014] Optionally, in the second mode, the ratio of the volumetric flow rate of the first gas inlet and the second gas inlet is gradually switched from 9:1 to 5:5, or from 7:3 to 6:4.

[0015] Optionally, in the third mode, when the energy consumption of the combustion furnace reaches the preset energy consumption value, the system switches to the second mode.

[0016] Secondly, this application provides a combustion system used in the combustion method of the first aspect, comprising:

[0017] The combustion furnace includes: a first auxiliary gas inlet, a first gas inlet, a second auxiliary gas inlet, a second gas inlet, and a flue gas duct, used for combustion treatment;

[0018] A regenerative combustion assembly is used to supply combustion gas to the combustion furnace through the first combustion gas inlet; and to supply combustion gas to the combustion furnace through the first combustion gas inlet, and to ignite the combustion gas via a regenerative burner;

[0019] A diffused combustion assembly is used to supply combustion gas to the combustion furnace through the second combustion gas inlet; and to supply combustion gas to the combustion furnace through the second combustion gas inlet, which is then combusted by a diffused burner.

[0020] Optionally, the combustion system may also include:

[0021] The first auxiliary gas inlet pipe is connected to the first auxiliary gas inlet and is used to transport auxiliary gas to the combustion furnace;

[0022] A heat transfer device is connected to the flue gas duct and the first combustion gas intake duct, respectively, to conduct the heat of the flue gas to the first combustion gas intake duct for heating the combustion gas.

[0023] Optionally, the combustion system may also include:

[0024] A nitrogen oxide detection device is installed in the flue gas duct or flue gas outlet to detect the nitrogen oxide content in the flue gas in order to switch the working mode of the combustion furnace.

[0025] An energy consumption detection device is installed in the gas inlet pipeline of the combustion furnace to detect energy consumption in order to switch the working mode of the combustion furnace.

[0026] The combustion method and system of this application, based on the existing combustion furnace, combine a regenerative burner and a diffuse burner to achieve different working modes at different combustion stages. This ensures that nitrogen oxide emissions are within acceptable limits, saves energy, and meets the working requirements of the combustion furnace. It achieves the goals of energy saving, fast melting rate of the target metal, low burn-off of the diffuse burner, and low nitrogen content, and has great application value. Attached Figure Description

[0027] Figure 1 A wiring diagram of a combustion system according to an embodiment of this application is shown;

[0028] Figure 2 The interface of the burner according to an embodiment of this application is shown;

[0029] Figure 3 An interface showing gas control parameters according to an embodiment of this application is illustrated;

[0030] Figure 4 An interface showing the smoke exhaust control parameters according to an embodiment of this application is provided;

[0031] Figure 5 The flue gas detection results of Comparative Example 1 of this application are shown;

[0032] Figure 6 The flue gas detection results of the first mode of Embodiment 1 of this application are shown;

[0033] Figure 7 The flue gas detection results of the second mode of Embodiment 1 of this application are shown;

[0034] Figure 8 The flue gas detection results of the third mode of Embodiment 1 of this application are shown;

[0035] Figure 9 The detection results of gas flow rate in Embodiment 1 of this application are shown. Detailed Implementation

[0036] The features and exemplary embodiments of various aspects of this application will be described in detail below. To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are intended only to explain this application and not to limit it. For those skilled in the art, this application can be implemented without some of these specific details. The following description of the embodiments is merely to provide a better understanding of this application by illustrating examples of this application.

[0037] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising..." does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes said element.

[0038] In traditional technology, burners used in industrial furnaces are basically classified into: cold air burners, cold air preheating burners, regenerative burners, and diffused burners. Each of these burners has its advantages and disadvantages. Cold air burners have low flame temperatures, high energy consumption, and low nitrogen oxide emissions; cold air preheating burners increase flame temperatures and reduce energy consumption, but are still considered high-energy-consuming products; regenerative burners, by recovering and utilizing waste heat from flue gas, significantly increase the temperature of the combustion air, so their flame temperatures can typically reach over 1600℃. Simultaneously, due to the recovery of waste heat, energy consumption is often very low, but in high-temperature environments, they are prone to generating large amounts of NO. X It is not environmentally friendly; ordinary diffused burners have a non-concentrated flame, an unsatisfactory combustion state, and a high CO content in the flue gas, resulting in high energy consumption, but the heated material has low burn loss.

[0039] Combustion methods

[0040] On the one hand, this application provides a combustion method, comprising:

[0041] The method is carried out in a combustion furnace, which includes a first auxiliary gas inlet, a first gas inlet, two sets of regenerative burners, a second auxiliary gas inlet, a second gas inlet, two sets of diffused burners, and a flue gas duct. The method includes:

[0042] In the first mode, the first auxiliary gas inlet and the first gas inlet are opened, and combustion is carried out using two sets of regenerative burners;

[0043] In the second mode, one set of regenerative burners is shut down and another set of regenerative burners is used for combustion. At the same time, the second auxiliary gas inlet and the second gas inlet are opened and a set of diffuse burners are used for combustion. The second mode is started when the nitrogen oxide content of the flue gas in the exhaust duct reaches the first preset value.

[0044] In the third mode, the first auxiliary gas inlet and the first gas inlet are closed, and the two sets of regenerative burners are shut down. Combustion is carried out using two sets of diffuse burners. The third mode is started when the nitrogen oxide content in the flue gas in the exhaust duct reaches the second preset value.

[0045] In the embodiments of this application, the first combustion-supporting gas can be air or oxygen. The second combustion-supporting gas can be coal gas, marsh gas, etc.

[0046] In this embodiment, both the first preset value and the second preset value are the nitrogen oxide content of the flue gas in the exhaust duct. The first preset value can be 90-100 mg / m³. 3 The second preset value can be 90-100 mg / m². 3 In this embodiment, the second mode begins when the nitrogen oxide content in the flue gas in the exhaust duct reaches a first preset value. This first preset value, after conversion, is closest to the environmental protection indicators for the emitted flue gas, thus extending the second mode duration as much as possible to reduce energy consumption and the wear of the diffused burner. Switching at this time has a positive effect on energy saving and nitrogen reduction. The third mode begins when the nitrogen oxide content in the flue gas in the exhaust duct reaches a second preset value. This second preset value is set based on experience and is closely related to the furnace temperature. Switching at this time primarily aims to reduce nitrogen oxides and ensure environmental protection.

[0047] In the embodiments of this application, in the first mode, when the material is first put into the furnace, the temperature inside the combustion furnace is low, and concentrated firepower is needed to raise the temperature. At this time, a regenerative burner can be used. The burner is in a high-efficiency working state, with a high melting rate and low energy consumption. In addition, due to the low furnace temperature, the amount of nitrogen oxides is also less.

[0048] In the embodiments of this application, in the second mode, typically during the middle of melting, the furnace temperature gradually increases, and the requirement for concentrated firepower decreases. To suppress the formation of nitrogen oxides, a mode in which a regenerative burner and a diffuse burner are used for simultaneous combustion can be adopted. At this time, since the regenerative burner can recover waste heat, the combustion air temperature is high but energy consumption does not increase. Furthermore, since some fuel is still burned through the regenerative burner, the resulting flue gas reduces the oxygen content of the combustion air in the diffuse burner, thus keeping the final flue gas emissions at a low nitrogen level.

[0049] In the embodiments of this application, the third mode is generally in the later stage of combustion in the combustion furnace, at a high temperature stage, and the requirement for the heating rate is not high; the main issue to be addressed is nitrogen oxides. At this time, the system switches to a fully diffused burner mode. The combustion air can be entirely exchanged for heat through the regenerator, but the fuel has already entered the furnace through the diffused burner to participate in combustion. Because combustion and air do not undergo the premixing process in the regenerator within the burner, combustion occurs entirely inside the furnace, resulting in a wide flame range and a flue gas entrainment effect over a large area, achieving a high-temperature, low-oxygen, low-NOx combustion effect.

[0050] In some embodiments, the first preset value is greater than the second preset value. The first and second preset values ​​are compared after being converted to actual atmospheric nitrogen oxide values. While meeting environmental protection requirements, the usage time of pure dispersion burners can be reduced, thus lowering burner wear.

[0051] In some embodiments, the second mode is initiated when the nitrogen oxide content in the flue gas in the exhaust duct reaches a third preset value, wherein the nitrogen oxide content satisfies the following relationship: second preset value ≤ third preset value ≤ first preset value.

[0052] In this embodiment, the first, second, and third preset values ​​are converted to actual atmospheric nitrogen oxide values ​​and then compared. The second preset value, after conversion, is close to, but less than, the environmental protection index for emitted flue gas, leaving a certain margin. This setting allows for the emission of more environmentally friendly flue gas and also extends the duration of the second mode, enabling switching at this point to simultaneously consider both environmental protection and energy consumption indicators.

[0053] In some embodiments, in the second mode, the heat from the flue gas inside the combustion furnace heats the gas in the first combustion-supporting gas inlet to achieve heat recovery.

[0054] In this embodiment, the two sets of burners alternate periodically. While one burner is burning, the other burner draws in high-temperature flue gas, which undergoes regenerative heating to heat the air, thus obtaining high-temperature combustion air. In this way, ambient temperature combustion air can be heated to a temperature only 100°C lower than the flue gas temperature inside the furnace, thereby achieving extremely high heating efficiency.

[0055] In some embodiments, the combustion method further includes: obtaining the oxygen content of the flue gas in the exhaust duct;

[0056] The emission value of nitrogen oxides in the atmosphere is obtained based on the content and oxygen content of the first, second, or third preset value in the flue gas.

[0057] Based on a comparison between the stated emission values ​​and standard nitrogen oxide emission values, if the difference between the stated emission values ​​and the standard nitrogen oxide emission values ​​is within the range of 0-2 mg / m³... 3 .

[0058] In some embodiments, after the second mode begins, the combustion furnace exhibits a temperature change that first decreases and then increases, wherein the lowest temperature of the combustion furnace is 800°C to 1200°C, or 900°C to 950°C. This temperature change refers to the temperature variation along the height of the combustion furnace. This is because the combustion zone of the gas in a regenerative burner is more concentrated, while the combustion zone of a diffuse burner is more dispersed, resulting in a temperature change along the height of the combustion furnace. When solid fuel, such as solid coal, is present in the combustion furnace, this temperature change can suppress the formation of CH4 in the gas and promote CH4 conversion, resulting in gas (composition) with low CH4 content. Simultaneously, it can also promote the cracking and conversion of tar in the gas, reducing the tar content. Furthermore, it can prevent coal melting in this area, ensuring stable combustion, obtaining gas (gas fuel) with a high effective gas ratio, and ensuring complete combustion of the gas. When using 100% natural gas as fuel, the temperature change in the combustion furnace, characterized by an initial decrease followed by an increase, refers to the temperature variation along the height of the furnace. This is because the combustion zone of the gas is more concentrated in regenerative burners, while the combustion zone is more dispersed in diffused burners, resulting in a temperature change along the furnace's height. This ensures that the fuel furnace provides a stable supply of fuel, thereby increasing the melting rate of the target metal.

[0059] In some embodiments, the temperature at the outlet of the flue gas duct is 150°C to 200°C, or 170°C to 190°C. At these temperatures, it is advantageous to control the oxygen content in the flue gas, thereby allowing the preset value of nitrogen oxides in the flue gas to be higher than the standard emission level in the air during the conversion process.

[0060] In some embodiments, in the second and third modes, the air-fuel ratio ranges from 10 to 13:1, and the fuel quantity is 100-110 m³ / h. 3 / h. Controlling the air-fuel ratio and fuel quantity as described above is beneficial for smooth combustion.

[0061] In some embodiments, in the second mode of the combustion furnace, the volumetric flow rate ratio of the first gas inlet and the second gas inlet gradually switches from 9:1 to 5:5, or from 7:3 to 6:4. Controlling the gas distribution in the second mode facilitates the gradual replacement of regenerative burner combustion with parallel combustion of both regenerative and diffuse burners. This extends the operating time of the regenerative burner as much as possible while reducing nitrogen oxide emissions in the flue gas, ensuring they do not exceed standards. It also helps maintain a stable or steadily rising furnace temperature. In the method of this application, a smaller proportion of gas used in the regenerative burner results in lower nitrogen oxide formation.

[0062] In some embodiments, in the third mode, when the energy consumption of the combustion furnace reaches a preset energy consumption value, the system switches to the second mode. Later in this combustion mode, based on a comprehensive consideration of nitrogen oxide emissions and energy consumption, when the energy consumption reaches a preset energy consumption value according to the energy consumption-related indicators measured by the detection device or calculated by the system, the system can gradually switch to the second mode, increasing the range of selectable combustion modes. In this mode, nitrogen oxide emissions still need to meet environmental protection requirements.

[0063] Combustion system

[0064] Secondly, this application provides a combustion system used in the combustion method of the first aspect, as shown in Figure 1, comprising:

[0065] The combustion furnace includes: a first auxiliary gas inlet, a first gas inlet, a second auxiliary gas inlet, a second gas inlet, and a flue gas duct, used for combustion treatment;

[0066] A regenerative combustion assembly is used to supply combustion gas to the combustion furnace through the first combustion gas inlet; and to supply combustion gas to the combustion furnace through the first combustion gas inlet, and to ignite the combustion gas via a regenerative burner;

[0067] A diffused combustion assembly is used to supply combustion gas to the combustion furnace through the second combustion gas inlet; and to supply combustion gas to the combustion furnace through the second combustion gas inlet, which is then combusted by a diffused burner.

[0068] In this embodiment, the combustion system, based on an existing combustion furnace, combines a regenerative burner and a diffused burner to achieve different operating modes at different combustion stages. This ensures qualified nitrogen oxide emissions while maximizing energy savings, and meets the operational requirements of the combustion furnace. It achieves energy conservation, rapid melting rate of materials within the furnace, and low nitrogen content due to the diffused burner, demonstrating significant application value. During combustion, the burner can be controlled as follows: Figure 2 As shown, combustion parameter control can be achieved as follows: Figure 3 As shown, the smoke exhaust control parameters can be as follows: Figure 4 As shown.

[0069] In some embodiments, the combustion system further includes:

[0070] The first auxiliary gas inlet pipe is connected to the first auxiliary gas inlet and is used to transport auxiliary gas to the combustion furnace;

[0071] A heat transfer device is connected to the flue gas duct and the first combustion gas intake duct, respectively, to conduct the heat of the flue gas to the first combustion gas intake duct for heating the combustion gas.

[0072] In some embodiments, the combustion system further includes:

[0073] A nitrogen oxide detection device is installed in the flue gas duct or flue gas outlet to detect the nitrogen oxide content in the flue gas in order to switch the working mode of the combustion furnace.

[0074] An energy consumption detection device is installed in the gas inlet pipeline of the combustion furnace to detect energy consumption in order to switch the working mode of the combustion furnace.

[0075] According to the embodiments of this application, the nitrogen oxide detection device can be a portable flue gas analyzer; the energy consumption detection device can be an instrument that measures energy consumption-related indicators or the energy consumption calculated by relevant parameters can reach a preset energy consumption value.

[0076] In some embodiments, the combustion system further includes:

[0077] A furnace pressure detection device is installed on the furnace wall to detect furnace pressure.

[0078] A furnace temperature detection device is installed on the furnace wall to detect the temperature inside the furnace.

[0079] According to the embodiments of this application, the furnace pressure detection device and the furnace temperature detection device can better understand and monitor the status of the combustion system, and achieve an effective balance between energy consumption and nitrogen oxide emissions.

[0080] Example

[0081] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0082] Example 1

[0083] A combustion method, comprising:

[0084] The method is carried out in a combustion furnace, which includes a first auxiliary gas inlet, a first gas inlet, two sets of regenerative burners, a second auxiliary gas inlet, a second gas inlet, two sets of diffused burners, and a flue gas duct. The method includes:

[0085] In the first mode, the first auxiliary gas inlet and the first gas inlet are opened, and combustion is carried out using two sets of regenerative burners;

[0086] In the second mode, one set of regenerative burners is shut down, and another set of regenerative burners is used for combustion. Simultaneously, the second auxiliary gas inlet and the second gas inlet are opened, and a set of diffusion burners is used for combustion. The second mode is initiated when the nitrogen oxide content in the flue gas reaches a first preset value of 90 mg / m³. 3 (Converted to actual atmospheric nitrogen oxide values);

[0087] In the third mode, the first auxiliary gas inlet and the first gas inlet are closed, and both sets of regenerative burners are shut down. Combustion is then performed using two sets of dispersion burners. The third mode is initiated when the nitrogen oxide content in the flue gas in the exhaust duct reaches a second preset value; the first preset value is greater than the second preset value, which is 95 mg / m³. 3 (Converted to actual atmospheric nitrogen oxide values).

[0088] Comparative Example 1

[0089] The difference between this comparative example and the embodiment is that only regenerative burners are used, in two sets.

[0090] Comparative Example 2

[0091] The difference between this comparative example and the embodiment is that only two sets of diffuse burners are used. This has the disadvantages of high energy consumption and low melting rate.

[0092] Performance testing

[0093] The testing equipment used was a Testo 330-2 portable flue gas analyzer.

[0094] The nitrogen oxide content in the exhaust gas of the examples and comparative examples was detected using a portable flue gas analyzer. Figure 5-8 As shown, the nitrogen oxide values ​​in the image are measured values, while the nitrogen oxide values ​​in the table are converted from the values ​​in the image.

[0095] The melting rate and energy consumption are calculated based on the gas flow meter and the amount of material fed into the EV300 intelligent volume corrector. For example... Figure 9 As shown in Table 1.

[0096] Table 1. Nitrogen oxide content and energy consumption values ​​for the examples and comparative examples (at a baseline oxygen content of 12%).

[0097]

[0098]

[0099] Based on the above analysis, it can be seen that the nitrogen oxide emissions of the regenerative burner modified with this scheme have been significantly reduced, meeting the national environmental protection standards. Furthermore, there is no significant difference in melting rate and energy consumption; when used for melting scrap aluminum, the melting rate remains at 7.8 T / h, and the energy consumption is 58 Nm³. 3 / T, further reducing energy consumption.

[0100] It should also be noted that the exemplary embodiments mentioned in this application describe methods or systems based on a series of steps or apparatus. However, this application is not limited to the order of the above steps; that is, the steps can be performed in the order mentioned in the embodiments, or in a different order, or several steps can be performed simultaneously.

[0101] The above description is merely a specific implementation of this application. Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, modules, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here. It should be understood that the protection scope of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the protection scope of this application.

Claims

1. A combustion method, comprising: The method is carried out in a combustion furnace, which includes a first auxiliary gas inlet, a first gas inlet, two sets of regenerative burners, a second auxiliary gas inlet, a second gas inlet, two sets of diffused burners, and a flue gas duct. The method includes: In the first mode, the first auxiliary gas inlet and the first gas inlet are opened, and combustion is carried out using two sets of regenerative burners. The first mode is set when the material is just put into the furnace. In the second mode, one set of regenerative burners is shut down and another set of regenerative burners is used for combustion. At the same time, the second auxiliary gas inlet and the second gas inlet are opened and a set of diffusion burners are used for combustion. The second mode is started when the nitrogen oxide content of the flue gas in the exhaust pipe reaches the first preset value. The second mode is set in the middle of melting. In the third mode, the first auxiliary gas inlet and the first gas inlet are closed, and the two sets of regenerative burners are closed. Combustion is carried out using two sets of diffuse burners. The third mode is started when the nitrogen oxide content in the flue gas in the exhaust pipe reaches the second preset value. The third mode is set in the later stage of combustion in the combustion furnace. In the third mode, when the energy consumption of the combustion furnace reaches the preset energy consumption value, it switches to the second mode.

2. The combustion method according to claim 1, characterized in that, In the second mode, the heat from the flue gas inside the combustion furnace heats the gas in the first combustion-supporting gas inlet to achieve heat recovery.

3. The combustion method according to claim 1 or 2, characterized in that, After the second mode begins, the combustion furnace exhibits a temperature change that first decreases and then increases, wherein the lowest temperature of the combustion furnace is 800℃~1200℃; and / or, The temperature at the outlet of the exhaust duct is 150℃~200℃.

4. The combustion method according to claim 1 or 2, characterized in that, In the second and third modes, the air-fuel ratio ranges from (10-13):1, and the fuel quantity is 100-110m³. 3 / h.

5. The combustion method according to claim 1 or 2, characterized in that, In the second mode, the volumetric flow rate ratio of the first gas inlet and the second gas inlet of the combustion furnace is gradually switched from 9:1 to 5:5, or from 7:3 to 6:4.

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