A distributed multi-profile flue gas injection staged low-NOx combustion device

Abstract

The present invention discloses a distributed multi-profile flue gas injection staged low-nitrogen combustion device, comprising: a cracking furnace, a chimney, an external circulation flue gas return main pipe, a regulating valve, a induced draft fan, a flue gas distribution main pipe, a plurality of flue gas branch regulating dampers, a plurality of flue gas distribution branch pipes, a multi-profile flue gas staged injector and a bottom staged burner; wherein, the chimney is installed on the top of the cracking furnace; the external circulation flue gas return main pipe is connected to the chimney, and the regulating valve and the induced draft fan are both installed on the external circulation flue gas return main pipe; one end of the flue gas distribution main pipe is connected to the end of the external circulation flue gas return main pipe, and the other end of the flue gas distribution main pipe is connected to one end of each flue gas distribution branch pipe; each flue gas branch regulating damper is installed on the corresponding flue gas distribution branch pipe; the other end of each flue gas distribution branch pipe is connected to the corresponding multi-profile flue gas staged injector. The present invention realizes efficient reduction of NOx emissions.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal energy, and particularly relates to a distributed multi-profile flue gas injection staged low-nitrogen combustion device. Background Art

[0002] There are mainly three types of NOx generation, namely thermal NOx, prompt NOx, and fuel NOx. Thermal NOx is generated by the oxidation of nitrogen in combustion air at high temperatures. The generation rate of NO is proportional to the 0.5th power of the oxygen molecule concentration. With the increase of the reaction temperature, the generation of thermal NO follows the Arrhenius law and increases exponentially. Prompt NOx is formed by the combination of nitrogen in the air with oxygen at high temperatures. It is generated within the flame front and is a unique phenomenon in the combustion of hydrocarbon-rich fuels when the excess air coefficient is less than 1. The generation of prompt NOx is not greatly affected by temperature. At a certain temperature, prompt NOx mainly depends on the excess air coefficient. Fuel NOx is generated from nitrogen-containing substances such as NH3 and HCN contained in the fuel itself, or intermediate products such as N, CN, and HCN directly cracked from nitrogen-containing organic compounds in the fuel during the fuel combustion process and then oxidized. There is also a part of NOx directly generated by pyrolysis.

[0003] High-temperature furnace petrochemical process heaters such as cracking furnaces adopt a heating method with multiple burners. Due to their high furnace temperature, they are the main large petrochemical equipment generating NOx emissions. Since high-temperature petrochemical heaters such as cracking furnaces mostly use gas as fuel, the sources of NOx generation are thermal NOx and prompt NOx, among which the main one is thermal NOx. Previously, the method of using low-nitrogen burners was mostly adopted to reduce NOx emissions. With the more stringent requirements for NOx emission indicators, it has been difficult to meet the requirements only by using low-nitrogen burners to reduce NOx emissions. In order to achieve ultra-low NOx emissions, flue gas denitrification is adopted in high-temperature furnace petrochemical process heaters such as cracking furnaces, but the investment cost and operating cost of flue gas denitrification are both very high. Summary of the Invention

[0004] The technical problem solved by the present invention is: overcoming the deficiencies of the prior art, providing a distributed multi-profile flue gas injection staged low-nitrogen combustion device, and achieving efficient reduction of NOx emissions.

[0005] The object of the present invention is achieved by the following technical solutions: A distributed multi-profile flue gas injection and staged low-nitrogen combustion device, comprising: a cracking furnace, a chimney, an external circulation flue gas reflux main pipe, a regulating valve, a forced draft fan, a flue gas distribution main pipe, a plurality of flue gas branch regulating dampers, a plurality of flue gas distribution branches, a plurality of multi-profile flue gas staged injectors and a plurality of bottom staged burners; wherein, the chimney is installed on the top of the cracking furnace; the external circulation flue gas reflux main pipe is connected to the chimney, and the regulating valve and the forced draft fan are both installed on the external circulation flue gas reflux main pipe; one end of the flue gas distribution main pipe is connected to the end of the external circulation flue gas reflux main pipe, and the other end of the flue gas distribution main pipe is connected to one end of each flue gas distribution branch; each flue gas branch regulating damper is installed on the corresponding flue gas distribution branch; the other end of each flue gas distribution branch is connected to the corresponding multi-profile flue gas staged injector; the multi-profile flue gas staged injector is installed at the bottom of the cracking furnace; the bottom staged burner is installed at the bottom of the cracking furnace.

[0006] In the above-mentioned distributed multi-profile flue gas injection and staged low-nitrogen combustion device, the relationship between the flow area of the external circulation flue gas reflux main pipe and the flow area of the flue gas distribution branch is:

[0007] s1≥2ns2;

[0008] wherein, s1 is the flow area of the external circulation flue gas reflux main pipe, s2 is the flow area of the flue gas distribution branch, and n is the number of flue gas distribution branches.

[0009] In the above-mentioned distributed multi-profile flue gas injection and staged low-nitrogen combustion device, the multi-profile flue gas staged injector includes a reflux flue gas inlet, a primary flue gas nozzle, a secondary flue gas nozzle and a tube bundle type rectifier; wherein, one end of the reflux flue gas inlet is connected to the end of the flue gas distribution branch, and the other end of the reflux flue gas inlet is connected to the tube bundle type rectifier; the primary flue gas nozzle and the secondary flue gas nozzle are installed at the upper end of the multi-profile flue gas staged injector.

[0010] In the above-mentioned distributed multi-profile flue gas injection and staged low-nitrogen combustion device, a part of the flue gas is ejected from the primary flue gas nozzle at a horizontal angle; the remaining flue gas is ejected from the secondary flue gas nozzle at an ejection angle α of 15° to 45°.

[0011] In the above-mentioned distributed multi-profile flue gas injection and staged low-nitrogen combustion device, the number of the flue gas branch regulating dampers, the flue gas distribution branches, the multi-profile flue gas staged injectors and the bottom staged burners are all equal.

[0012] The present invention has the following beneficial effects compared with the prior art:

[0013] (1) The present invention extracts the flue gas of a high-temperature furnace process furnace represented by a cracking furnace from the chimney through an induced draft fan. The flue gas flows through the outer circulation flue gas return main pipe and is led to the furnace bottom. The total flow rate of the returned flue gas is adjusted by a regulating valve. The flue gas is distributed to each flue gas distribution branch pipe, and the flue gas volume entering each branch pipe is adjusted by a flue gas branch pipe regulating damper. Then, the branch pipe flue gas flows through the tube bundle rectifier inside the multi-profile flue gas grading injector for rectification to further improve the distribution uniformity. The flue gas is divided into two or more stages and injected into the furnace to participate in the combustion of the bottom burner. Each flue gas grading injector corresponds to a bottom burner. The combination of these devices realizes the distributed flue gas injection cycle. Since the combustion reaction involving the outer circulation flue gas occurs outside the outlet of the bottom burner, it has no impact on the combustion reactions of the central gas gun and the pilot burner that determine the flame stability of the bottom burner. Therefore, the flue gas outer circulation in this way reduces NOx emissions without affecting the combustion stability and regulation ratio of the bottom burner. The effect of achieving low nitrogen emissions is realized without affecting the combustion regulation ratio and stability.

[0014] (2) Through the area and injection angle of the first-stage flue gas nozzle and the second-stage flue gas nozzle of the multi-profile flue gas grading injector of the present invention, the flue gas can be divided into two or more stages and enter the bottom combustion area at different ratios and angles. By adjusting the injection angles of the first-stage flue gas nozzle and the second-stage flue gas nozzle, the bottom flame can be made closer to the furnace wall, avoiding situations such as flame floating and furnace tube overheating caused by low-nitrogen combustion. At the same time, the outer circulation flue gas ejected from the first-stage flue gas nozzle and the second-stage flue gas nozzle will also entrain part of the flue gas inside the furnace into the bottom combustion flame area, thereby greatly increasing the flue gas volume, further reducing the combustion reaction rate, and reducing the oxygen concentration in the bottom combustion area, thus significantly reducing the generation of NOx in the bottom combustion. Through the structural design of the multi-profile flue gas grading injector, the injection ratio and injection angle of each stage can be controlled, thereby regulating the combustion process and ensuring combustion stability and flame rigidity while reducing NOx emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] By reading the detailed description of the preferred embodiments below, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present invention. Moreover, throughout the drawings, the same reference numerals are used to represent the same components. In the drawings:

[0016] Figure 1 is a schematic structural diagram of a distributed multi-profile flue gas injection grading low-nitrogen combustion device provided by an embodiment of the present invention;

[0017] Figure 2 is a top view of the bottom of a distributed flue gas pipeline furnace provided by an embodiment of the present invention;

[0018] Figure 3It is a bottom side view of the distributed flue gas pipeline furnace provided by an embodiment of the present invention;

[0019] Figure 4 It is a structural diagram of a multi-profile flue gas grading injector provided by an embodiment of the present invention;

[0020] Figure 5 It is another structural diagram of a multi-profile flue gas grading injector provided by an embodiment of the present invention;

[0021] Figure 6 It is another structural diagram of a multi-profile flue gas grading injector provided by an embodiment of the present invention;

[0022] Figure 7 It is another structural diagram of a multi-profile flue gas grading injector provided by an embodiment of the present invention;

[0023] Figure 8 It is a schematic diagram of the principle of staged flue gas injection participating in combustion provided by an embodiment of the present invention. Detailed implementation manners

[0024] Hereinafter, exemplary embodiments of the present disclosure will be described in more detail with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present disclosure can be more thoroughly understood and the scope of the present disclosure can be fully conveyed to those skilled in the art. It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other. Hereinafter, the present invention will be described in detail with reference to the drawings and in combination with the embodiments.

[0025] Figure 1 It is a schematic structural diagram of a distributed multi-profile flue gas injection staged low-nitrogen combustion device provided by an embodiment of the present invention; Figure 2 It is a top view of the bottom of the distributed flue gas pipeline furnace provided by an embodiment of the present invention; Figure 3 It is a bottom side view of the distributed flue gas pipeline furnace provided by an embodiment of the present invention. As Figure 1 、 Figure 2 and Figure 3 shown, the device includes a cracking furnace (or other high-temperature process heating furnace) 1, a chimney 2, an outer circulation flue gas return main pipe 3, a regulating valve 4, a induced draft fan 5, a flue gas distribution main pipe 6, a plurality of flue gas branch regulating dampers 7, a plurality of flue gas distribution branch pipes 8, a plurality of multi-profile flue gas grading injectors 9 and a plurality of bottom staged burners 10; wherein,

[0026] The chimney 2 is installed on the top of the cracking furnace 1; the outer circulation flue gas reflux main pipe 3 is connected to the chimney 2, and the regulating valve 4 and the induced draft fan 5 are both installed on the outer circulation flue gas reflux main pipe 3; one end of the flue gas distribution main pipe 6 is connected to the end of the outer circulation flue gas reflux main pipe 3, and the other end of the flue gas distribution main pipe 6 is connected to one end of each flue gas distribution branch pipe 8; the number of the flue gas branch regulating dampers 7, the flue gas distribution branch pipes 8, the multi-profile flue gas grading injectors 9 and the bottom grading burners 10 are all equal; each flue gas branch regulating damper 7 is installed on the flue gas distribution branch pipe 8 corresponding to each flue gas branch regulating damper 7; the other end of each flue gas distribution branch pipe 8 is connected to the multi-profile flue gas grading injector 9 corresponding to each flue gas distribution branch pipe 8; the multi-profile flue gas grading injector 9 is installed at the bottom of the cracking furnace 1; the bottom grading burner 10 is installed at the bottom of the cracking furnace 1. Each flue gas grading injector 9 corresponds to one bottom burner 10.

[0027] The constraint condition between the outer circulation flue gas reflux main pipe 3 and the flue gas distribution pipe 8 is used to improve the uniformity of flue gas distribution.

[0028] s1≥2Ns2

[0029] Wherein, s1 is the flow area of the outer circulation flue gas reflux main pipe, s2 is the flow area of the flue gas distribution pipe, and N is the number of flue gas distribution pipes.

[0030] Such as Figure 4 、 Figure 5 、 Figure 6 and Figure 7 As shown in

[0031] The induced draft fan 5 extracts the flue gas in the chimney 2 through the outer circulation flue gas reflux main pipe 3, adjusts the flue gas flow through the regulating valve 4, then distributes the flue gas to each 8 flue gas distribution branch pipes 8 through the flue gas distribution main pipe 6, and adjusts the flue gas volume entering each branch through the flue gas branch regulating damper 7. The flow area of the flue gas distribution main pipe 6 is more than 2 times the sum of the areas of the connected flue gas distribution branch pipes 8, further ensuring uniform flue gas distribution. Then, the branch flue gas is divided into two or more levels through the multi-profile flue gas grading injector 9 and injected into the furnace to participate in the combustion of the bottom burner. Each flue gas grading injector 9 corresponds to one bottom burner 10.

[0032] After the flue gas enters from the recycled flue gas inlet 11, it is rectified by the tube bundle type rectifier 14. Further rectification ensures that the flue gas flow rate entering each flue gas staged injector 9 is basically the same. A part of the flue gas is ejected from the primary flue gas nozzle 12 at a horizontal angle or an angle close to horizontal. The remaining flue gas is ejected from the secondary flue gas nozzle 13 at an ejection angle of α, and the preferred angle is 15° to 45°. The areas of the primary flue gas nozzle 12 and the secondary flue gas nozzle 13 can be allocated and adjusted according to the flame rigidity and low-nitrogen combustion effect. The primary flue gas nozzle 12 is directly opposite to the peripheral gas spray gun of the bottom burner, and the position of the secondary flue gas nozzle 13 does not overlap with that of the primary flue gas nozzle 12.

[0033] As Figure 8 shown, the externally circulated injected flue gas is divided into two or more stages by the multi-profile flue gas staged injector and is respectively injected into the combustion flame area of the bottom burner to participate in the combustion reaction. Since the combustion reaction participated by the externally circulated flue gas is outside the outlet of the bottom burner and has no influence on the combustion reactions of the central gas gun and the pilot burner that determine the flame stability of the bottom burner, this method of flue gas external circulation to reduce NOx emissions does not affect the combustion stability and regulation ratio of the bottom burner. By adjusting the ejection angles of the primary flue gas nozzle and the secondary flue gas nozzle, the bottom flame can be made closer to the furnace wall, avoiding situations such as flame floating and furnace tube overheating caused by low-nitrogen combustion. At the same time, the externally circulated flue gas ejected from the primary flue gas nozzle and the secondary flue gas nozzle will also entrain part of the flue gas inside the furnace into the bottom combustion flame area, thereby greatly increasing the flue gas volume, further reducing the combustion reaction rate, reducing the oxygen concentration in the bottom combustion area, and thus significantly reducing the generation of NOx in the bottom combustion.

[0034] The flue gas recirculation and staged combustion technologies are combined through the multi-profile injection structure. Part of the flue gas is introduced into the flue gas circulation pipeline by the induced draft fan and injected into the furnace through the multi-profile burner brick, entraining part of the flue gas in the furnace, entering the bottom combustion area, participating in the combustion, and further reducing the NOx emissions on the original basis by reducing the flame temperature, slowing down the combustion reaction process, and reducing the oxygen concentration participating in the NOx reaction.

[0035] In the present invention, the flue gas of a high-temperature furnace process furnace represented by a cracking furnace is extracted from the chimney by an induced draft fan, and the flue gas flows through an external circulation flue gas reflux main pipe and is led to the bottom of the furnace. The total flow rate of the reflux flue gas is regulated by a regulating valve. The flue gas is distributed to each flue gas distribution branch pipe, and the amount of flue gas entering each branch pipe is regulated by a flue gas branch pipe regulating damper. Then, the branch pipe flue gas flows through a tube bundle type flow rectifier inside a multi-profile flue gas staged injector for rectification to further improve the distribution uniformity. The flue gas is divided into two or more stages and injected into the furnace to participate in the combustion of the bottom burner. Each flue gas staged injector corresponds to one bottom burner. The combination of these devices realizes distributed flue gas injection circulation. Since the combustion reaction involving the external circulation flue gas occurs outside the outlet of the bottom burner, it has no impact on the combustion reactions of the central gas gun and the pilot burner that determine the flame stability of the bottom burner. Therefore, the flue gas external circulation in this way reduces NOx emissions without affecting the combustion stability and regulation ratio of the bottom burner. The effect of achieving low nitrogen emissions is realized without affecting the combustion regulation ratio and stability.

[0036] In the present invention, through the areas and injection angles of the first-stage flue gas injection port and the second-stage flue gas injection port of the multi-profile flue gas staged injector, the flue gas can be divided into two or more stages and enter the bottom combustion area at different ratios and angles. By adjusting the injection angles of the first-stage flue gas injection port and the second-stage flue gas injection port, the bottom flame can be made closer to the furnace wall, avoiding situations such as flame floating and furnace tube overheating caused by low-nitrogen combustion. At the same time, the external circulation flue gas ejected from the first-stage flue gas injection port and the second-stage flue gas injection port will also entrain part of the flue gas inside the furnace into the bottom combustion flame area, thereby greatly increasing the amount of flue gas, further reducing the combustion reaction rate, and reducing the oxygen concentration in the bottom combustion area, thus significantly reducing the generation of NOx in the bottom combustion. Through the structural design of the multi-profile flue gas staged injector, the injection ratio and injection angle of each stage can be controlled, thereby regulating the combustion process and ensuring combustion stability and flame rigidity while reducing NOx emissions.

[0037] Under the same operating conditions, the cracking furnace using this device can achieve NOx emissions ≤ 65 mg / Nm³ in a normal operating condition capacity-expanding cracking furnace 3 , and in the special case of decoking, achieve NOx emissions ≤ 75 mg / Nm³ 3 , and steam is not injected in the above operating conditions. At the same time, the combustion stability, regulation ratio remain the same as those before the addition of flue gas external circulation.

[0038] Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A distributed multi-profile flue gas injection and staged low-nitrogen combustion device, characterized in that Including: A cracking furnace (1), a chimney (2), an external circulation flue gas reflux main pipe (3), a regulating valve (4), a draft fan (5), a flue gas distribution main pipe (6), a number of flue gas branch regulating dampers (7), a number of flue gas distribution branch pipes (8), a number of multi-profile flue gas staged injectors (9) and a number of bottom staged burners (10); wherein, The chimney (2) is installed on the top of the cracking furnace (1); The external circulation flue gas reflux main pipe (3) is connected to the chimney (2), and the regulating valve (4) and the draft fan (5) are both installed on the external circulation flue gas reflux main pipe (3); One end of the flue gas distribution main pipe (6) is connected to the end of the external circulation flue gas reflux main pipe (3), and the other end of the flue gas distribution main pipe (6) is connected to one end of each flue gas distribution branch pipe (8); Each flue gas branch regulating damper (7) is installed on the flue gas distribution branch pipe (8) corresponding to each flue gas branch regulating damper (7); The other end of each flue gas distribution branch pipe (8) is connected to the multi-profile flue gas staged injector (9) corresponding to each flue gas distribution branch pipe (8); The multi-profile flue gas staged injector (9) is installed at the bottom of the cracking furnace (1); The bottom staged burner (10) is installed at the bottom of the cracking furnace (1); The relationship between the flow area of the external circulation flue gas reflux main pipe (3) and the flow area of the flue gas distribution branch pipe (8) is: s1≥2ns2; Wherein, s1 is the flow area of the external circulation flue gas reflux main pipe, s2 is the flow area of the flue gas distribution branch pipe, and n is the number of flue gas distribution branch pipes; The multi-profile flue gas staged injector (9) includes a reflux flue gas inlet (11), a flue gas primary nozzle (12), a flue gas secondary nozzle (13) and a tube bundle type rectifier (14); wherein, One end of the reflux flue gas inlet (11) is connected to the end of the flue gas distribution branch pipe (8), and the other end of the reflux flue gas inlet (11) is connected to the tube bundle type rectifier (14); The flue gas primary nozzle (12) and the flue gas secondary nozzle (13) are installed at the upper end of the multi-profile flue gas staged injector (9); Part of the flue gas is ejected from the flue gas primary nozzle (12) at a horizontal angle; the remaining flue gas is ejected from the flue gas secondary nozzle (13) at an ejection angle α of 15° to 45°; The numbers of the flue gas branch regulating dampers (7), the flue gas distribution branch pipes (8), the multi-profile flue gas staged injectors (9) and the bottom staged burners (10) are all equal; The draft fan extracts the flue gas in the chimney through the external circulation flue gas reflux main pipe, adjusts the flue gas flow through the regulating valve, then distributes the flue gas to each flue gas distribution branch pipe through the flue gas distribution main pipe, and adjusts the flue gas volume entering each branch pipe through the flue gas branch regulating damper; the flow area of the flue gas distribution main pipe is more than 2 times the sum of the areas of the connected flue gas distribution branch pipes, further ensuring uniform flue gas distribution; then, the branch flue gas is divided into two or more stages through the multi-profile flue gas staged injector and injected into the furnace to participate in the combustion of the bottom burner; each flue gas staged injector corresponds to one bottom burner.

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