Denitrification system with combustion and heating in the flue

Abstract

The present invention is a denitrification system for heating up by combustion in a flue, including a flue before denitrification, a flue for denitrification treatment, and a control system. A heat exchanger is connected to the flue before denitrification and the flue for denitrification treatment, and a low-temperature flue gas channel before denitrification and a high-temperature flue gas channel after denitrification are arranged in the heat exchanger; an SCR denitrification reactor and a flue gas sampling structure are arranged in the flue for denitrification treatment; a direct-fired heating device is arranged in the flue before denitrification, and the direct-fired heating device includes a plurality of flame burners, the center line of the flame stream of each flame burner is tangent to an imaginary tangent circle, the flame injection direction of each flame burner is arranged opposite to the direction of the flue gas flow, and the flame injection length of each flame burner is arranged to be adjustable. The direct-fired heating device is arranged in the present invention to directly heat up the flue gas, so as to promote the flue gas temperature to reach the temperature range of the ideal denitrification reaction of the catalyst, realize the expected denitrification reaction, meet the ultra-low emission requirements, and improve the economic benefits of equipment operation.

Description

Technical Field

[0001] The invention relates to the technical field of flue gas denitration, and in particular to a denitration system with combustion and heating in a flue. Background Art

[0002] The control of air pollution is an important part of environmental governance. With the development of industry and the improvement of living standards, people are paying more and more attention to environmental issues and atmospheric environmental protection issues.

[0003] Nitrogen oxides (NOx) are a major type of atmospheric pollutant and one of the main factors in the formation of acid rain, photochemical smog and PM2.5 pollution. At present, industrial sources of NOx emissions in my country account for more than 70% of the total NOx emissions. The control emission technologies of NOx in industrial flue gas mainly include combustion control technology and post-combustion control technology. Combustion control technology includes low-nitrogen combustion technology, reburning technology and flue gas recirculation technology. Among the post-combustion control technologies, selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR) and SCR-SNCR hybrid technology are the main technologies. Considering economic and technical benefits, selective catalytic reduction is the most effective NOx post-control technology.

[0004] The coal combustion process will produce a large amount of air pollutants such as SO2 and NOx, causing serious air pollution and economic losses. The pollutants in the flue gas emitted by thermal power, steel and other industries are diverse, and strict requirements are put forward for the emission of NOx. The purpose of denitrification is mainly to remove nitrogen monoxide (NO) and nitrogen dioxide (NO2).

[0005] The proportion of nitric oxide (NO) in flue gas to nitrogen oxide (NOx) is very high, often above 90%. Nitric oxide is a polluting gas. When it is directly discharged into the atmosphere, it is easy to pollute the atmosphere, soil and water sources. Therefore, when factories discharge flue gas, especially when the flue gas contains nitric oxide, they need to denitrify the flue gas. Among them, the existing flue gas denitrification technologies are mainly dry and wet. Compared with the wet flue gas denitrification technology, the main advantages of dry flue gas denitrification technology are: low basic investment, simple equipment and process, high efficiency of removing NOx, no wastewater and waste treatment, and not easy to cause secondary pollution.

[0006] The completion of the SCR reaction requires the use of a catalyst. Currently, the most widely used is a medium-temperature catalyst with an operating temperature of 320 to 450°C, so the reaction temperature of catalytic reduction denitrification should be controlled at 320 to 450°C. When the reaction temperature is lower than 300°C, side reactions will occur on the catalyst surface. Ammonia reacts with sulfur trioxide and water to generate (NH4)2SO4 or NH4SO4 to reduce the reaction with NOx. The product adheres to the catalyst surface, blocking the catalyst channels and micropores, reducing the catalyst activity. In addition, if the reaction temperature is higher than the applicable temperature of the catalyst, the catalyst channels and micropores will deform, thereby deactivating the catalyst. Therefore, ensuring the appropriate reaction temperature is the key to the normal operation of the selective catalyst reduction method. Low boiler load or low atmospheric temperature will cause the SCR inlet temperature to be lower than the catalyst operating temperature. Among them, SCR denitrification requires a temperature window of 300 to 400°C. NOx is reduced to N2 under the action of the catalyst and NH3, and the denitrification efficiency can reach more than 90%.

[0007] In the denitrification process, the flue gas needs to be heated to a preset temperature before the denitrification process can be carried out efficiently and stably. In the prior art, the flue gas heating is often achieved by setting a heating source below the denitrification flue and allowing the high-temperature gas to rise and mix evenly with the flue gas to achieve the heating purpose. However, since the denitrification system pipelines are generally long in size, heat loss is inevitably caused during the rising process of the high-temperature gas below the mixing layer. At the same time, during the rising process of the high-temperature gas, the axial mixing length with the flue gas is long enough, but the radial mixing surface cannot be guaranteed to be large enough, so the complete and uniform mixing of the high-temperature gas and the flue gas cannot be guaranteed.

[0008] In the steel, metallurgy and coal chemical industries, the exhaust gas temperature of sintering machines and other equipment is relatively low. In order to meet the subsequent denitrification treatment or other process requirements in the SCR equipment, the exhaust gas needs to be heated. There are many ways to heat the flue gas, such as directly adding a heat exchanger, setting up electric heating, etc., which use high-temperature heat sources for heating. These methods require additional heat sources, resulting in high operating costs.

[0009] In addition, since a large amount of blast furnace gas, converter gas, coke oven gas and other fuel gases are usually generated in industrial equipment in the steel, metallurgy and coal chemical industries. Therefore, in the prior art, many companies will use these fuel gases to set up a separate heating furnace outside the flue, and set up one or more blast furnace gas or coke oven gas burners according to the power of the heating furnace. The fuel gas in the burner is burned to produce high-temperature flue gas, and the high-temperature flue gas is sent into the flue through a branch and mixed with the original flue gas in the flue to achieve heating of the original flue gas. Since the above method needs to set up a separate heating furnace outside the flue, on the one hand, the investment cost is relatively high, and on the other hand, after the high-temperature flue gas after the combustion of the fuel gas is mixed with the original flue gas in the flue, the total amount of flue gas in the flue will increase sharply, thereby causing a greater impact on the flue system, and also causing the problem of insufficient output of the existing induced draft fan.

[0010] At present, the environmental protection situation in the steel industry is becoming increasingly severe, and steel companies need to carry out ultra-low emission transformation in steps. The most commonly used technology in steel plants that have implemented low-emission transformation is to build a set of SCR denitrification equipment, and then use the steel plant's own blast furnace gas to heat the flue gas, so as to meet the denitrification inlet flue gas temperature requirements.

[0011] Blast furnace gas is not easy to ignite due to its low calorific value. Generally, an insulated ignition duct with a separate castable is used. Natural gas or light oil gun is used for ignition first. After the temperature in the ignition duct is raised, blast furnace gas is introduced for combustion. Finally, the high-temperature flue gas after combustion is mixed into the denitrification flue to heat the denitrification flue gas. Although blast furnace gas has a low calorific value, it burns in an insulated flue, and the high-temperature flue gas it produces can reach a temperature of 1200-1400°C. During the ignition process, if natural gas or an oil gun is used for ignition, the combustion temperature will be even higher, reaching 1500-1700°C, while the operating temperature of ordinary refractory castables is around 1300°C, which can easily cause the ignition air duct castable to fall off, and then the air duct steel plate will be deformed by high temperature and its life will be shortened; if refractory castables with better performance, such as alumina hollow ball castables, are used, the manufacturing cost will be greatly increased due to their high price; in addition, there is also the prior art that uses a large excess air coefficient to reduce the combustion flue gas temperature, but this method will greatly increase the additional air required for heating, thereby requiring more gas, resulting in poor economic efficiency.

[0012] In the prior art, there is a denitrification system for direct combustion and heating of low-load flue of boiler (CN209576247U), a direct-fired temperature-raising heating device for denitrification system (CN 209501296 U), and a flue gas heating system (CN 110160066 A). The direct-fired furnaces thereof all adopt a counter-arrangement mode, and the flue gas heating area is small, and it is impossible to heat the flue with a large cross-section. The temperature of the area close to the flame area of ​​the direct-fired furnace is higher, and the temperature of the area close to the walls around the flue is lower. The airflow mixing effect on the cross-sectional axis is poor, which is not conducive to the rapid transfer and uniform distribution of heat; the flame combustion area is relatively fixed, and it is impossible to achieve ideal mixing of the airflow and rapid transfer of heat on the flue cross section, and it is impossible to achieve uniform temperature distribution.

[0013] Therefore, the inventor, relying on his many years of experience and practice in related industries, proposes a denitrification system with combustion and heating in the flue to overcome the defects of the prior art. Summary of the invention

[0014] The purpose of the present invention is to provide a denitrification system with combustion and heating in the flue to overcome the problems existing in the prior art. A direct-fired heating device is arranged in the present invention to directly heat the flue gas, so as to promote the flue gas temperature to reach the temperature range of the ideal denitrification reaction of the catalyst, realize the expected denitrification reaction, meet the ultra-low emission requirements, and improve the economic benefits of equipment operation.

[0015] The object of the present invention is achieved in this way. A denitrification system with combustion and temperature increase in a flue comprises a flue before denitrification, a flue for denitrification treatment and a control system, wherein a flue before denitrification is provided with a flue gas inlet at the first end of the flue before denitrification, a flue gas outlet at the first end of the flue for denitrification treatment, and a second end of the flue before denitrification and a second end of the flue for denitrification treatment are sealed and connected; a heat exchanger is connectedly arranged on the flue before denitrification and the flue for denitrification treatment, and a low-temperature flue gas channel before denitrification and a high-temperature flue gas channel after denitrification are arranged in the heat exchanger; an SCR denitrification reactor is arranged between the second end of the denitrification treatment flue and the heat exchanger, and a flue gas sampling structure is arranged on the denitrification treatment flue between the SCR denitrification reactor and the heat exchanger, and the flue gas sampling structure is arranged perpendicular to the axial direction of the denitrification treatment flue; the denitrification An ammonia uniform distribution structure is arranged on the front flue between the second end thereof and the heat exchanger, at least two ammonia uniform distribution structures are arranged at intervals on the ammonia uniform distribution structure, each of the ammonia uniform distribution units is arranged perpendicularly to the axial direction of the flue before denitrification, and a flue gas sampling hole corresponding to each ammonia uniform distribution unit is arranged on the flue gas sampling structure; a direct-fired heating device is arranged between the second end of the flue before denitrification and the ammonia uniform distribution structure, the direct-fired heating device comprises a plurality of flame burners penetrating the side wall of the flue before denitrification, the center line of the flame stream of each flame burner is tangent to an imaginary tangent circle, the flame injection direction of each flame burner is arranged opposite to the flue gas flow direction, and the flame injection length of each flame burner is arranged to be adjustable; the SCR denitrification reactor and the direct-fired heating device are both electrically connected to the control system.

[0016] In a preferred embodiment of the present invention, a flue gas analyzer, a flue gas velocity measuring instrument and a first temperature detection device are arranged between the heat exchanger and the ammonia spray uniform distribution structure, a second temperature detection device is arranged in the SCR denitrification reactor, an ammonia analyzer is connected to the flue gas sampling structure, the flue gas analyzer is used to measure the content of nitrogen oxides in the flue gas, and the flue gas velocity measuring instrument is used to measure the flue gas flow rate in the flue before denitrification; the ammonia analyzer is used to detect the amount of ammonia in the flue gas after denitrification treatment by the SCR denitrification reactor, the first temperature detection device and the second temperature detection device are used for real-time temperature monitoring, and the flue gas analyzer, the flue gas velocity measuring instrument, the first temperature detection device, the ammonia analyzer and the second temperature detection device are all electrically connected to the control system.

[0017] In a preferred embodiment of the present invention, the multiple flame burners of the direct-fired heating device constitute at least two burner groups, and the number of the burner groups is an even number; the center line of the flame stream of each flame burner in each burner group is tangent to an imaginary tangent circle, and the center line of each flame stream of two adjacent burner groups is opposite to the cutting direction of the imaginary tangent circle; the center axis of each flame burner is set at a first angle to the horizontal direction, and the center axis of each flame burner is set at a second angle to the vertical direction.

[0018] In a preferred embodiment of the present invention, the first angle ranges from 10° to 50°, and the second angle ranges from 15° to 85°.

[0019] In a preferred embodiment of the present invention, each of the flame burners includes a combustion stabilizing flue structure, a flame injection port is arranged at a first end of the combustion stabilizing flue structure, and a central axis of the combustion stabilizing flue structure constitutes a central axis of the flame burner; a combustion-supporting chamber and a gas chamber are connected at a second end of the combustion stabilizing flue structure; a combustion stabilizing center hole is axially arranged on the combustion stabilizing flue structure, the combustion stabilizing center hole constitutes a combustion mixing chamber, an igniter is arranged in the combustion mixing chamber, and the igniter is electrically connected to a control system; a combustion-supporting gas inlet is connected to the combustion-supporting gas chamber, and a gas inlet is connected to the gas chamber; an ejector is penetrated through the gas chamber and the combustion-supporting gas chamber, the ejector is coaxially arranged with the combustion stabilizing flue structure, the ejector is used to accelerate the combustible gas in the gas chamber to be ejected into the combustion mixing chamber, a necked ejection channel is formed between the combustion-supporting gas chamber and the combustion mixing chamber, and the combustion-supporting gas in the combustion-supporting gas chamber is ejected into the combustion mixing chamber through the ejection channel.

[0020] In a preferred embodiment of the present invention, the combustion stabilizing flue structure includes a combustion stabilizing inner tube and a combustion stabilizing outer tube that are coaxially and radially spaced apart, the cross-section of the combustion stabilizing inner tube being a closed contour formed by splicing multiple circular arcs, the cross-section of the combustion stabilizing outer tube being a circle, a combustion stabilizing annular space is formed between the combustion stabilizing inner tube and the combustion stabilizing outer tube, and the combustion stabilizing annular space is filled with a refractory castable material unit.

[0021] In a preferred embodiment of the present invention, a flame detector and a temperature detector are arranged in the combustion mixing chamber, and both the flame detector and the temperature detector are electrically connected to the control system; the flame detector is used to detect the flame burning condition in the combustion mixing chamber, and the temperature detector is used to detect the temperature in the combustion mixing chamber.

[0022] In a preferred embodiment of the present invention, the ejector includes a straight pipe section, a contraction section, a throat section, an expansion section and a straightening section, the straight pipe section is located in the fuel gas chamber, and the contraction section, the throat section, the expansion section and the straightening section are located in the combustion-supporting gas chamber; an air inlet is provided at the first end of the straight pipe section, the second end of the straight pipe section is connected to the first end of the contraction section, the diameter of the contraction section is gradually contracted from the first end to the second end, the second end of the contraction section is connected to the first end of the throat section, the second end of the throat section is connected to the first end of the expansion section, the diameter of the expansion section is gradually expanded from the first end to the second end, the second end of the expansion section is connected to the first end of the straightening section, and the second end of the straightening section is provided with an air outlet.

[0023] In a preferred embodiment of the present invention, the rectifying section includes a rectifying inner tube and a rectifying outer tube which are coaxially and radially spaced apart, the cross-section of the rectifying inner tube is a closed contour formed by splicing multiple arc segments, the cross-section of the rectifying outer tube is a circle, a rectifying annular space is formed between the rectifying inner tube and the rectifying outer tube, and the rectifying annular space is filled with a refractory castable material unit.

[0024] In a preferred embodiment of the present invention, the flue before denitrification and the flue for denitrification treatment are arranged vertically, the second end of the flue before denitrification and the second end of the flue for denitrification treatment are connected by a horizontal flue, and a horizontal rectifying grid is arranged at the outlet of the horizontal flue.

[0025] In a preferred embodiment of the present invention, the control system includes a measurement data summary and analysis module, which is used to calculate the nitrogen oxide load based on the measurement data of the flue gas analyzer, the flue gas velocity measuring instrument and the ammonia analyzer, and calculate the ammonia injection amount of each ammonia injection unit based on the nitrogen oxide load.

[0026] In a preferred embodiment of the present invention, each of the flame burners is fixedly arranged on the side wall of the flue before denitration, and the first angle and the second angle are fixedly arranged.

[0027] In a preferred embodiment of the present invention, each of the flame burners is adjustably disposed on the side wall of the flue before denitration, and the first angle and the second angle are adjustable.

[0028] As described above, the denitration system with combustion and heating in the flue provided by the present invention has the following beneficial effects:

[0029] (1) In the flue combustion heating denitration system provided by the present invention, a direct-fired heating device is arranged in the flue before denitration, and the heat of the flame combustion of the flame burner is used to directly heat the flue gas, thereby improving the heat utilization efficiency and reducing the heat loss; the flame injection direction of the flame burner is arranged opposite to the direction of the flue gas flow, thereby promoting rapid and efficient heat exchange between the flue gas and the high-temperature flame, shortening the time required for heat exchange, reducing the flue length required for uniform flue gas temperature, and promoting uniform temperature in the flue;

[0030] (2) Multiple flame burners form a swirl zone to achieve a dynamic swirl effect of the flue gas, promote the turbulent flow of the flue gas, promote the heat exchange between the flue gas and the high-temperature flame, shorten the length of the heat exchange area in the flue, and achieve temperature uniformity;

[0031] (3) The flame burner adopts ejector jet technology, which reduces the load of the system fan, reduces the resistance loss of the flue, and improves the stability of equipment operation; the cross-section of the stable combustion inner tube and the rectifying section of the ejector of the stable combustion flue structure is spliced ​​by multiple arc sections, which increases the contact area between the combustible gas and the combustion-supporting gas, while maintaining the stability of combustion, and achieving a good gathering effect of the jet flame, avoiding premature divergence and attenuation of the flame, ensuring that the flames ejected by multiple flame burners have higher kinetic energy, and efficiently stirs the flue gas turbulently to promote heat exchange; at the same time, the multi-arc circular cross-section structure can reduce the local oxygen content of the combustible gas combustion, reduce the local high temperature of the flame burner, avoid the generation of NOx, and achieve low-nitrogen combustion;

[0032] (4) In the denitration system of the present invention, the heat exchanger uses the high-temperature flue gas after denitration to preheat the low-temperature flue gas before denitration, making full use of the waste heat and reducing the energy consumption required for heating by the direct-fired heating device; the flue gas sampling hole of the flue gas sampling structure is arranged corresponding to the ammonia injection unit of the ammonia injection uniform distribution structure, and the sampling is accurate, which is conducive to the control of the ammonia injection amount; the direct-fired heating device directly heats the flue gas, causing the flue gas temperature to reach the temperature range of the ideal denitration reaction of the catalyst, thereby achieving the expected denitration reaction, meeting the ultra-low emission requirements, and improving the economic benefits of equipment operation;

[0033] (5) In the denitrification system of the present invention with combustion and heating in the flue, no spoiler or guide plate is required in the flue before denitrification and the flue for denitrification treatment, which simplifies the equipment structure and makes the whole system simple and convenient to manufacture and install, and easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The following drawings are only intended to illustrate and explain the present invention, and are not intended to limit the scope of the present invention.

[0035] in:

[0036] Figure 1: It is a schematic diagram of the denitrification system of the present invention in which the flue gas is burned and heated when the flue gas enters from bottom to top.

[0037] Figure 2 :for Figure 1 Schematic diagram of the structure inside the flue before denitrification.

[0038] Figure 3 :for Figure 2 Middle AA section view.

[0039] Figure 4 : is a side view of a flame burner of the present invention.

[0040] Figure 5 : is a cross-sectional view of a flame burner of the present invention.

[0041] Figure 6 :for Figure 5 Center B view.

[0042] Figure 7 : is a schematic diagram of the ejector of the present invention.

[0043] Figure 8 :for Figure 7 Center C view.

[0044] Fig. 9 : It is a schematic diagram of the denitrification system of the present invention in which the flue gas is burned and heated when the flue gas enters from top to bottom.

[0045] Fig.10 :for Fig. 9 Schematic diagram of the structure inside the flue before denitrification.

[0046] In the figure:

[0047] 100. Denitrification system with combustion and heating in the flue;

[0048] 1. Heat exchanger;

[0049] 2. SCR denitrification reactor;

[0050] 3. Flue gas sampling structure;

[0051] 4. Ammonia spraying uniform distribution structure;

[0052] 5. Direct combustion heating device;

[0053] 50. Imaginary tangent circle; 51. Flame burner; 511. Stable combustion flue structure; 512. Flame jet nozzle; 513. Stable combustion center hole; 514. Stable combustion inner tube; 515. Stable combustion outer tube; 52. Combustion-supporting chamber; 521. Combustion-supporting chamber inlet; 53. Combustion chamber; 531. Combustion inlet; 54. Ignitor; 55. Ejector; 551. Straight pipe section; 552. Contraction section; 553. Throat section; 554. Expansion section; 555. Rectification section; 5551. Rectification inner tube; 5552. Rectification outer tube; 556. Inlet pipe opening; 557. Exhaust pipe opening; 56. Flame detector; 57. Temperature detector; 58. Refractory casting material unit;

[0054] 61. Flue gas analyzer; 62. Flue gas velocity measuring instrument; 63. First temperature detection device; 64. Ammonia analyzer; 65. Second temperature detection device;

[0055] 91. Flue duct before denitrification; 911. Front side wall; 912. Rear side wall; 92. Denitrification treatment flue; 93. Flue gas inlet; 94. Flue gas outlet; 95. Horizontal flue; 96. Rectifier grille; 97. Turning elbow; 98. Guide plate. DETAILED DESCRIPTION

[0056] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described with reference to the accompanying drawings.

[0057] The specific embodiments of the present invention described herein are only used to explain the purpose of the present invention and cannot be understood as limiting the present invention in any way. Under the guidance of the present invention, technicians can conceive of any possible variations based on the present invention, which should be considered to belong to the scope of the present invention. It should be noted that when an element is referred to as "arranged on" another element, it can be directly on the other element or there can also be a central element. When an element is considered to be "connected" to another element, it can be directly connected to the other element or there may be a central element at the same time. The terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a mechanical connection or an electrical connection, or it can be the internal communication of two elements, it can be directly connected, or it can be indirectly connected through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to the specific circumstances. The terms "vertical", "horizontal", "up", "down", "left", "right" and similar expressions used herein are only for illustrative purposes and do not represent the only implementation method.

[0058] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used herein includes any and all combinations of one or more related listed items.

[0059] like Figures 1 to 10 As shown, the present invention provides a denitrification system 100 with combustion and heating in a flue, including a flue 91 before denitrification, a flue 92 for denitrification treatment and a control system (not shown in the figure), a flue 93 is arranged at the first end of the flue 91 before denitrification, a flue 94 is arranged at the first end of the flue 92 for denitrification treatment, and a second end of the flue 91 before denitrification and a second end of the flue 92 for denitrification treatment are sealed and connected.

[0060] A heat exchanger 1 is provided in communication with the flue 91 before denitrification and the flue 92 for denitrification treatment. The heat exchanger 1 is provided near the flue gas inlet 93 and the flue gas outlet 94. A low-temperature flue gas channel before denitrification and a high-temperature flue gas channel after denitrification are provided in the heat exchanger 1 (the low temperature and high temperature here are relative, and the temperature of the flue gas entering through the flue gas inlet is lower than the temperature of the flue gas after denitrification treatment). An SCR denitrification reactor 2 is provided between the second end of the denitrification treatment flue and the heat exchanger. The heat exchanger 1 utilizes the high-temperature post-denitrification flue gas with a higher temperature after passing through the SCR denitrification reactor to preheat the low-temperature pre-denitrification flue gas with a lower temperature before entering the SCR denitrification reactor, thereby making full use of the waste heat and reducing the energy consumption required for heating the flue gas before denitrification.

[0061] A flue gas sampling structure 3 is arranged between the SCR denitration reactor 2 and the heat exchanger 1 on the denitration treatment flue 92, and the flue gas sampling structure 3 is arranged perpendicularly to the axial direction of the denitration treatment flue 92; an ammonia spraying uniform distribution structure 4 is arranged between the second end of the flue 91 before denitration and the heat exchanger 1, and at least two ammonia spraying units are arranged at intervals on the ammonia spraying uniform distribution structure 4, and each ammonia spraying unit is arranged perpendicularly to the axial direction of the flue 91 before denitration, and a flue gas sampling hole corresponding to each ammonia spraying unit is arranged on the flue gas sampling structure 3; before denitration, a flue gas sampling hole corresponding to each ammonia spraying unit is arranged on the flue gas sampling structure 3; A direct-fired heating device 5 is arranged between the second end of the flue 91 and the ammonia uniform distribution structure 4. The direct-fired heating device 5 includes a plurality of flame burners 51 penetrating the side wall of the flue before denitrification. The center line of the flame flow of each flame burner 51 is tangent to an imaginary tangent circle 50. The flame injection direction of each flame burner 51 is arranged opposite to the flue gas flow direction, and the flame injection length of each flame burner 51 is adjustable. The SCR denitrification reactor 2 and the direct-fired heating device 5 are both electrically connected to the control system.

[0062] The method of directly heating the flue gas in the flue can not only save the amount of flue gas, but also greatly save the engineering cost and the land in the factory. The existing method of directly heating the flue gas in the flue has certain technical difficulties: the negative pressure in the flue is large, and the burner is not easy to burn stably; the flue gas directly in contact with the flame has a high temperature rise, while the flue gas far from the flame has a low temperature rise, so the flue gas temperature is uneven; the scouring of the flame by the flue gas can easily cause the flame to be extinguished; the ignition point of the combustible gas is high, and the inert gas content is high, which is not easy to burn stably. The direct-fired heating device for the denitrification system of the present invention can effectively solve the above problems.

[0063] like Figure 1 , Figure 2 As shown, in a specific embodiment of the present invention, in the flue before denitration, before direct combustion heating, the flue gas flows from bottom to top, and the center line of the flame flow of the flame burner in the direct combustion heating device 5 of the present invention is oriented toward the direction of the flue gas flow, and is arranged opposite to the direction of the flue gas flow (from top to bottom and in an inclined state); Figure 1 As shown, the flame burner 51 is tilted downward, and the flame and the flue gas before heating flow in opposite directions, which increases the turbulence degree of heat exchange between the high-temperature flue gas and the original flue gas, shortens the time required for heat exchange, increases the contact area between the flame and the flue gas, and increases the time for heat exchange between the high-temperature flame and the flue gas, which is beneficial to the uniformity of the flue gas temperature.

[0064] like Fig. 9 , Fig.10 As shown, in another specific embodiment of the present invention, in the flue before denitration, before direct combustion heating, the flue gas flows from top to bottom, and the center line of the flame flow of the flame burner in the direct combustion heating device 5 of the present invention is toward the direction of the flue gas flow, and is arranged opposite to the direction of the flue gas flow (from bottom to top, and in an inclined state); Figure 2 As shown, the flame burner 51 is arranged to be inclined upward.

[0065] The flame spray length of each flame burner 51 can be adjusted, and the diameter and height position of the imaginary tangent circle tangent to the center line of the flame flow of each flame burner can be adjusted accordingly. Different swirl mixing area controls can be achieved under different flue gas flow conditions. The position of the high temperature zone of the flame in the flue is adjustable to achieve dynamic adjustment of flue gas mixing.

[0066] The ammonia uniformly distributed structure 4 includes a plurality of ammonia spraying areas arranged at intervals in the cross-sectional direction of the flue 91 before denitrification, each ammonia spraying area has the same area, each ammonia spraying area forms an independent ammonia spraying unit, each ammonia spraying unit is arranged at intervals in the cross-sectional direction of the flue 91 before denitrification, at least 2 ammonia spraying units are arranged horizontally, and at least 2 ammonia spraying units are arranged vertically, and the flue gas sampling structure 3 includes flue gas sampling holes corresponding to each ammonia spraying area one by one.

[0067] In the denitration system for combustion and heating in the flue provided by the present invention, a direct-fired heating device is arranged in the flue before denitration, and the heat of the flame combustion of the flame burner is used to directly heat the flue gas, thereby improving the utilization efficiency of heat and reducing heat loss; the flame injection direction of the flame burner is arranged opposite to the direction of the flue gas flow, thereby promoting rapid and efficient heat exchange between the flue gas and the high-temperature flame, shortening the time required for heat exchange, reducing the flue length required for uniform flue gas temperature, and promoting uniform temperature in the flue; multiple flame burners form a swirl zone, realizing a dynamic swirl effect of the flue gas, promoting turbulent flow of the flue gas, and promoting the smooth flow of the flue gas and the high-temperature flame. heat exchange, shortening the length of the heat exchange area in the flue and achieving temperature uniformity; in the denitrification system of combustion and heating in the flue of the present invention, the heat exchanger uses the high-temperature flue gas after denitrification to preheat the low-temperature flue gas before denitrification, making full use of the waste heat and reducing the energy consumption required for heating by the direct-fired heating device; the flue gas sampling holes of the flue gas sampling structure are arranged corresponding to the ammonia injection units of the ammonia injection uniform distribution structure, and the sampling is accurate, which is conducive to the control of the ammonia injection amount; the direct-fired heating device directly heats the flue gas, causing the flue gas temperature to reach the temperature range of the ideal denitrification reaction of the catalyst, thereby realizing the expected denitrification reaction, meeting the ultra-low emission requirements, and improving the economic benefits of equipment operation.

[0068] Further, if Figure 1 As shown, a flue gas analyzer 61, a flue gas velocity measuring instrument 62 and a first temperature detection device 63 are arranged between the heat exchanger 1 and the ammonia spraying uniform distribution structure 4. The flue gas analyzer 61 can also be arranged between the heat exchanger 1 and the flue gas inlet 93. The ammonia analyzer 64 is connected to the flue gas sampling structure 3. A second temperature detection device 65 is arranged in the SCR denitration reactor 2. The second temperature detection device 65 can also be arranged downstream of the SCR denitration reactor 2. The flue gas analyzer 61 is used to measure the content of nitrogen oxides in the flue gas. The flue gas velocity measuring instrument 62 is used to measure the content of nitrogen oxides in the flue gas. For measuring the flue gas flow rate in the flue before denitrification; the ammonia analyzer 64 is used to detect the amount of ammonia in the flue gas after denitrification treatment by the SCR denitrification reactor, the first temperature detection device 63 and the second temperature detection device 65 are used for real-time temperature monitoring, the first temperature detection device 63 detects the flue gas temperature before the direct-fired heating device 5, and calculates the theoretical heat required by the flame burner, the flue gas analyzer 61, the flue gas velocity measuring instrument 62, the first temperature detection device 63, the ammonia analyzer 64 and the second temperature detection device 65 are all electrically connected to the control system.

[0069] In the denitration system, the second temperature detection device 65 is arranged downstream of the SCR denitration catalyst to detect the actual temperature of the flue gas undergoing the denitration reaction. If the temperature is within the process requirement range, there is no need to adjust the flow rate and proportion of the flame burner 51. If the temperature is lower than the process requirement, the combustion calorific value of the flame burner 51 is increased to further increase the flue gas temperature; if the temperature is higher than the process requirement, the combustion calorific value of the flame burner 51 is reduced to further reduce the flue gas temperature; the combustion heat released by the flame burner 51 is feedback-controlled by the second temperature detection device 65 to control the flue gas temperature within the optimal temperature range of the denitration reaction.

[0070] Further, if Figure 2 , Figure 3 As shown, the direct-fired heating device 5 adopts the swirl effect of Laval nozzle injection, and the multiple flame burners 51 of the direct-fired heating device 5 constitute at least two burner groups, and the number of burner groups is an even number; the center line of the flame stream of each flame burner 51 of each burner group is tangent to an imaginary tangent circle 50, and the center line of each flame stream of two adjacent burner groups is set opposite to the cutting direction of the imaginary tangent circle; the central axis of each flame burner 51 is set at a first angle α to the horizontal direction, and the central axis of each flame burner 51 is set at a second angle to the vertical direction. The center line of each flame stream of two adjacent burner groups is set opposite to the cutting direction of the imaginary tangent circle, that is, the center line of each flame stream of two adjacent burner groups and the cutting direction of the imaginary tangent circle adopt opposite swirl methods, which eliminates the impact of the two groups of swirl flame burners and realizes the stable operation of the swirl. The number of burner groups is an even number to ensure the stable operation of the heating device.

[0071] Furthermore, the first angle α is in the range of 10° to 50°, preferably in the range of 15° to 30°; the second angle is in the range of 15° to 85°, preferably in the range of 30° to 65°.

[0072] In a specific embodiment of the present invention, the flue 91 before denitration is a rectangular flue and is arranged vertically. The center line of the two opposite side walls (front side wall 911 and rear side wall 912) of the flue 91 before denitration is the hedging center line. The flame burners are divided into two groups, each burner group includes four flame burners 51, and the flame burners are in the form of tangential combustion. The gas streams of the flame burners are fed in a tangential manner, and each flame burner 51 forms an octagonal double tangential combustion structure. The center line of the flame streams ejected by each group of flame burners is tangent to the same imaginary tangential circle (ellipse or circle), and the rotation directions of the two groups of imaginary tangential circles (ellipse or circle) are opposite, one is clockwise and the other is counterclockwise.

[0073] In actual engineering applications, flame burners can be appropriately added to the front side wall 911 and the rear side wall 912 according to the cross-sectional size of the flue 91 before denitrification; flame burners can also be appropriately added to the other two side walls of the flue 91 before denitrification.

[0074] like Figure 3 As shown, in a specific embodiment of the present invention, the angles between the eight flame burners and the side walls of the vertical flue 91 before denitrification (i.e., the second angles) are β1, β2, β3, β4, β5, β6, β7, and β8, respectively, ranging from 15° to 85°, and preferably ranging from 30° to 65°.

[0075] Each flame burner can be adjusted on the side wall of the flue before denitration, and the first angle and the second angle are adjustable; the flame burner 51 can adopt a full swing form of up and down, left and right swing (that is, the first angle and the second angle are adjustable), which can realize the dynamic adjustment of the flame jet flow of the flame burner 51; the flame burner 51 can also adopt a fixed method, and each flame burner is fixedly set on the side wall of the flue before denitration, and the first angle and the second angle are fixed. By adjusting the flame length of the flame burner, the size of the imaginary tangent circle can be dynamically adjusted, and the swirl mixing effect of different flue gas ranges can be realized, and the uniformity of flue gas temperature can be achieved.

[0076] Further, if Figure 4 , Figure 5 , Figure 6 As shown, each flame burner 51 includes a combustion-stabilizing flue structure 511, which is a cylindrical structure. A flame ejection port 512 is arranged at the first end of the combustion-stabilizing flue structure 511, and the central axis of the combustion-stabilizing flue structure 511 constitutes the central axis of the flame burner; a combustion-supporting chamber 52 and a combustion gas chamber 53 are connected at the second end of the combustion-stabilizing flue structure 511; a combustion-stabilizing center hole 513 is axially penetrated on the combustion-stabilizing flue structure 511, and the combustion-stabilizing center hole 513 constitutes a combustion mixing chamber, and a point is arranged in the combustion-stabilizing flue structure 511. The igniter 54 is electrically connected to the control system; a combustion-supporting gas inlet 521 is connected to the combustion-supporting gas chamber 52, and a gas inlet 531 is connected to the gas chamber 53; an ejector 55 is passed through the gas chamber 53 and the combustion-supporting gas chamber 52, and the ejector 55 is coaxially arranged with the combustion stabilizing flue structure 511, and the ejector 55 is used to accelerate the combustible gas in the gas chamber 53 to the combustion mixing chamber, and a necked ejector channel is formed between the combustion-supporting gas chamber 52 and the combustion mixing chamber, and the combustion-supporting gas in the combustion-supporting gas chamber 52 is ejected to the combustion mixing chamber through the ejector channel.

[0077] The flame burner 51 adopts the ejector jet technology, which reduces the load of the system fan, reduces the resistance loss of the flue, and improves the stability of the equipment operation. The combustion gas inlet 521 and the gas inlet 531 are connected to the corresponding pipelines through flanges, and a flow meter and a flow regulating valve are arranged on the corresponding pipelines. The flow meter and the flow regulating valve are electrically connected to the control system. The required amount of combustible gas and combustion-supporting gas is calculated according to the control model using the detection data of the first temperature detection device 63, and the flow regulating valve (electric regulating valve) is used to adjust the flow until the flow reaches the predetermined demand.

[0078] The combustion-supporting gas can be connected to the flue gas after the heat exchanger in the flue before denitrification through a pipeline, and the flue gas in the flue before denitrification can be used as the combustion-supporting gas for the combustion reaction of the flame burner to achieve combustion of the combustible gas under low oxygen concentration conditions, avoid the generation of NOx, and achieve low-nitrogen combustion of the fuel gas.

[0079] The combustible gas entering the flame burner can be blast furnace gas, converter gas, coke oven gas, natural gas, etc., or a mixture of blast furnace gas, converter gas, coke oven gas or natural gas. The combustion-supporting gas entering the flame burner can be air, pure oxygen, or the original flue gas in the flue containing a certain amount of oxygen.

[0080] Further, if Figure 5 , Figure 6 As shown, the stable combustion flue structure 511 includes a stable combustion inner tube 514 and a stable combustion outer tube 515 which are coaxially and radially spaced apart. The cross section of the stable combustion inner tube 514 is a closed contour formed by splicing multiple arcs, and the cross section of the stable combustion outer tube 515 is a circular configuration. A stable combustion annular space is formed between the stable combustion inner tube 514 and the stable combustion outer tube 515, and the stable combustion annular space is filled with a refractory casting material unit 58. The cross section of the stable combustion inner tube 514 is formed by splicing multiple arcs, which increases the contact area between the high-temperature flame and the flue gas, promotes the heat exchange of the flue gas, and is conducive to maintaining a good gathering effect of the combustion flame, increasing the flame length, and avoiding the premature divergence and attenuation of the flame.

[0081] Further, if Figure 5 As shown, a flame detector 56 and a temperature detector 57 are arranged in the combustion mixing chamber, and both the flame detector 56 and the temperature detector 57 are electrically connected to the control system; the flame detector 56 is used to detect the flame burning condition in the combustion mixing chamber. If the flame is extinguished, the igniter is re-ignited through the control system to achieve stable combustion of the flame burner. The flame detector 56 is an electronically controlled ignition device; the temperature detector 57 is used to detect the temperature in the combustion mixing chamber. If the local temperature is too high, the flow rate and proportional relationship of the combustible gas and the combustion-supporting gas are adjusted through the control system to reduce the temperature of the combustion mixing chamber and achieve low NOx combustion.

[0082] Further, if Figure 7 , Figure 8 As shown, the ejector 55 includes a straight pipe section 551, a contraction section 552, a throat section 553, an expansion section 554 and a rectification section 555. The straight pipe section 551 is located in the combustion chamber 53, and the contraction section 552, the throat section 553, the expansion section 554 and the rectification section 555 are located in the combustion-supporting chamber 52. The first end of the straight pipe section 551 is provided with an air inlet 556, and the second end of the straight pipe section 551 is connected to the first end of the contraction section 552. The diameter of the contraction section 552 increases from the first end to the second end. It is gradually contracted, the second end of the contraction section 552 is connected to the first end of the throat section 553, the second end of the contraction section 552 and the throat section 553 are smoothly transitioned by an arc, the second end of the throat section 553 is connected to the first end of the expansion section 554, the diameter of the expansion section 554 is gradually expanded from the first end to the second end, the second end of the expansion section 554 is connected to the first end of the rectification section 555, the second end of the rectification section 555 is provided with an air outlet 557, and the air outlet 557 is in the ejection channel. In a specific embodiment of the present invention, the length of the expansion section 554 is 6 to 10 times the diameter of the throat section 553, preferably in the range of 7 to 9 times, and the length of the rectification section 555 is not less than 100 mm. The distance between the air outlet 557 of the ejector and the bottom of the combustion mixing chamber is between 100 and 300 mm, preferably in the range of 150 to 250 mm.

[0083] Further, if Figure 8 As shown, the rectifying section 555 includes a rectifying inner tube 5551 and a rectifying outer tube 5552 which are coaxially and radially spaced apart. The cross section of the rectifying inner tube 5551 is a closed contour formed by splicing multiple arcs. The cross section of the rectifying outer tube 5552 is circular. A rectifying annular space is formed between the rectifying inner tube 5551 and the rectifying outer tube 5552. The rectifying annular space is filled with a refractory casting material unit 58. The multi-arc circular cross section of the rectifying section 555 can promote the combustible gas to maintain the multi-arc circular cross section and spray forward after it leaves the gas outlet 557. The multi-arc circular cross section shape increases the contact area between the combustible gas and the combustion-supporting gas, while maintaining the stability of the combustion. At the same time, the jet flame has a good gathering effect, avoiding the premature divergence and attenuation of the flame, ensuring that the flames sprayed by the multiple flame burners have high kinetic energy, and efficiently stirs the flue gas in the flue to promote heat exchange. At the same time, the multi-arc circular cross-section structure can reduce the local oxygen content of the combustible gas combustion, reduce the local high temperature of the flame burner, avoid the generation of NOx, and achieve low-nitrogen combustion.

[0084] Further, if Figure 1As shown, the flue 91 before denitration and the flue 92 for denitration are arranged vertically, and the second end of the flue 91 before denitration and the second end of the flue 92 for denitration are connected through a horizontal flue 95, and a horizontal rectifying grid 96 is arranged at the outlet of the horizontal flue 95. The flue 91 before denitration can be connected to the horizontal flue 95 through a turning elbow 97. In order to allow the flue gas to pass smoothly, a guide plate 98 is arranged in the horizontal flue 95, and the guide plate 98 plays a guiding role for the flue gas. The heated flue gas flows through the horizontal flue 95 through the turning elbow 97 and then passes through the rectifying grid 96, so as to achieve further mixing of the flue gas and ammonia, and at the same time, the energy is mixed to achieve uniform flue gas temperature. The flue gas and ammonia mixed gas pass through the rectifying effect of the rectifying grid, so that the flue gas and ammonia mixed gas can enter the catalyst of the SCR denitration reactor uniformly and vertically, and realize the efficient, rapid and uniform reaction of nitrogen oxides and ammonia in the flue gas under the catalytic effect of the catalyst.

[0085] Furthermore, the control system includes a measurement data summary and analysis module, which is used to calculate the nitrogen oxide load based on the measurement data of the flue gas analyzer, the flue gas velocity measuring instrument and the ammonia analyzer, and calculate the ammonia injection amount of each ammonia injection unit based on the nitrogen oxide load.

[0086] The flue gas velocity measuring instrument 62 is used to measure the flue gas velocity in each different horizontal area in the flue before denitrification; the flue gas analyzer 61 is used to measure the content of nitrogen oxides in the flue gas, and the nitrogen oxide removal load is calculated by a computer program. The measurement data summary and analysis module is used to calculate the nitrogen oxide load according to the flue gas flow rate and flue gas composition in each area, and the required ammonia injection amount in each area is calculated according to the nitrogen oxide load. An ammonia injection branch pipe is arranged on the ammonia injection uniform distribution structure 4, and an electric regulating valve or a pneumatic regulating valve is arranged on the ammonia injection branch pipe. The control system adjusts the ammonia injection amount in each area through the electric regulating valve or the pneumatic regulating valve, and monitors the actual ammonia injection amount according to the flow meter on the ammonia injection branch pipe; the ammonia analyzer 64 is used to detect the ammonia amount (i.e., ammonia escape amount) in the flue gas after denitrification treatment by the SCR denitrification reactor, and the ammonia injection amount is controlled according to the ammonia escape amount in each area. When the ammonia escape amount exceeds the set value, the system prompts that the ammonia injection amount in the corresponding area is too large, and the ammonia injection amount in the area is reduced accordingly to achieve the minimum ammonia consumption and ammonia escape amount.

[0087] The following is an example in which the flue gas inlet 93 is located at the bottom of the flue before denitration to illustrate the working process of the denitration system 100 for heating up by combustion in the flue of the present invention:

[0088] The original flue gas (unpurified flue gas before denitrification) enters the flue combustion and heating denitrification system 100 of the present invention from the flue gas inlet 93, and first passes through the heat exchanger 1 to preheat the flue gas. The heated flue gas flows through the flue gas analyzer 61 and the flue gas velocity measuring instrument 62, and the ammonia spraying uniform distribution structure 4 performs ammonia spraying operation. The injected ammonia is mixed with the flue gas, and the flue gas mixed with ammonia continues to rise. The flue gas temperature is measured by the first temperature detection device 63. The flame burner of the direct-fired heating device 5 performs efficient combustion of the combustible gas and the combustion-supporting air, and the injection swirl effect of multiple flame burners is used to promote the rapid mixing and heat exchange of the high-temperature gas and the flue gas, thereby further increasing the temperature of the flue gas and ammonia mixed gas.

[0089] The heated flue gas flows through the horizontal flue 95 through the turning elbow 97 and then through the rectifying grid 96, so as to achieve further mixing of the flue gas and ammonia, and at the same time, energy mixing is performed to achieve uniform flue gas temperature. The flue gas and ammonia mixed gas is rectified by the rectifying grid, so that the flue gas and ammonia mixed gas can enter the catalyst of the SCR denitration reactor evenly and vertically, so as to achieve efficient, rapid and uniform reaction of nitrogen oxides and ammonia in the flue gas under the catalytic effect of the catalyst;

[0090] The flue gas mixture after passing through the catalyst of the SCR denitrification reactor flows through the flue gas sampling structure 3, and the ammonia analyzer 64 detects the ammonia content in the mixed gas to control the ammonia concentration to be lower than the set value. If the ammonia content exceeds the set value, it is fed back to the control system to reset the ammonia injection amount of the ammonia injection uniform distribution structure 4, and at the same time adjust the ammonia injection amount of the ammonia injection unit, continuously monitor the residual ammonia content downstream of the SCR denitrification reactor and make it meet the set value. After the denitrification mixed gas enters the heat exchanger 1, it flows through the flue gas outlet 94 and enters the downstream dust collector (existing technology).

[0091] As described above, the denitration system with combustion and heating in the flue provided by the present invention has the following beneficial effects:

[0092] (1) In the flue combustion heating denitration system provided by the present invention, a direct-fired heating device is arranged in the flue before denitration, and the heat of the flame combustion of the flame burner is used to directly heat the flue gas, thereby improving the heat utilization efficiency and reducing the heat loss; the flame injection direction of the flame burner is arranged opposite to the direction of the flue gas flow, thereby promoting rapid and efficient heat exchange between the flue gas and the high-temperature flame, shortening the time required for heat exchange, reducing the flue length required for uniform flue gas temperature, and promoting uniform temperature in the flue;

[0093] (2) Multiple flame burners form a swirl zone to achieve a dynamic swirl effect of the flue gas, promote the turbulent flow of the flue gas, promote the heat exchange between the flue gas and the high-temperature flame, shorten the length of the heat exchange area in the flue, and achieve temperature uniformity;

[0094] (3) The flame burner adopts ejector jet technology, which reduces the load of the system fan, reduces the resistance loss of the flue, and improves the stability of equipment operation; the cross-section of the stable combustion inner tube and the rectifying section of the ejector of the stable combustion flue structure is spliced ​​by multiple arc sections, which increases the contact area between the combustible gas and the combustion-supporting gas, while maintaining the stability of combustion, and achieving a good gathering effect of the jet flame, avoiding premature divergence and attenuation of the flame, ensuring that the flames ejected by multiple flame burners have higher kinetic energy, and efficiently stirs the flue gas turbulently to promote heat exchange; at the same time, the multi-arc circular cross-section structure can reduce the local oxygen content of the combustible gas combustion, reduce the local high temperature of the flame burner, avoid the generation of NOx, and achieve low-nitrogen combustion;

[0095] (4) In the denitration system of the present invention, the heat exchanger uses the high-temperature flue gas after denitration to preheat the low-temperature flue gas before denitration, making full use of the waste heat and reducing the energy consumption required for heating by the direct-fired heating device; the flue gas sampling hole of the flue gas sampling structure is arranged corresponding to the ammonia injection unit of the ammonia injection uniform distribution structure, and the sampling is accurate, which is conducive to the control of the ammonia injection amount; the direct-fired heating device directly heats the flue gas, causing the flue gas temperature to reach the temperature range of the ideal denitration reaction of the catalyst, thereby achieving the expected denitration reaction, meeting the ultra-low emission requirements, and improving the economic benefits of equipment operation;

[0096] (5) In the denitrification system of the present invention with combustion and heating in the flue, no spoiler or guide plate is required in the flue before denitrification and the flue for denitrification treatment, which simplifies the equipment structure and makes the whole system simple and convenient to manufacture and install, and easy to implement.

[0097] The above description is only an illustrative embodiment of the present invention and is not intended to limit the scope of the present invention. Any equivalent changes and modifications made by any person skilled in the art without departing from the concept and principle of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A denitration system for heating up by combustion in a flue, comprising a flue before denitration, a flue for denitration treatment and a control system, wherein a flue gas inlet is arranged at the first end of the flue before denitration, a flue gas outlet is arranged at the first end of the flue for denitration treatment, and a second end of the flue before denitration and a second end of the flue for denitration treatment are arranged in a sealed communication; characterized in that: A heat exchanger is arranged in communication with the flue before denitrification and the flue for denitrification treatment, and a low-temperature flue gas channel before denitrification and a high-temperature flue gas channel after denitrification are arranged in the heat exchanger; an SCR denitrification reactor is arranged between the second end of the flue for denitrification treatment and the heat exchanger, and a flue gas sampling structure is arranged on the flue for denitrification treatment between the SCR denitrification reactor and the heat exchanger, and the flue gas sampling structure is arranged perpendicular to the axial direction of the flue for denitrification treatment; an ammonia uniform distribution structure is arranged on the flue before denitrification between the second end thereof and the heat exchanger, and at least two ammonia spraying units are arranged on the ammonia uniform distribution structure at intervals, and each of the ammonia spraying units is connected to the denitrification treatment flue. The axial direction of the pre-denitration flue is vertically arranged, and the flue gas sampling structure is provided with flue gas sampling holes corresponding to each ammonia spraying unit; a direct-fired heating device is arranged between the second end of the pre-denitration flue and the ammonia spraying uniform distribution structure, and the direct-fired heating device includes a plurality of flame burners penetrating the side wall of the pre-denitration flue, the center line of the flame stream of each flame burner is tangent to an imaginary tangent circle, the flame spraying direction of each flame burner is arranged opposite to the direction of the flue gas stream, and the flame spraying length of each flame burner is adjustable; the SCR denitration reactor and the direct-fired heating device are both electrically connected to the control system; A flue gas analyzer, a flue gas velocity measuring instrument and a first temperature detection device are arranged between the heat exchanger and the ammonia spraying uniform distribution structure, a second temperature detection device is arranged in the SCR denitration reactor, an ammonia analyzer is connected to the flue gas sampling structure, the flue gas analyzer is used to measure the content of nitrogen oxides in the flue gas, and the flue gas velocity measuring instrument is used to measure the flue gas flow velocity in the flue before denitration; The ammonia analyzer is used to detect the amount of ammonia in the flue gas after denitration treatment by the SCR denitration reactor, the first temperature detection device and the second temperature detection device are used for real-time temperature monitoring, and the flue gas analyzer, the flue gas velocity measuring instrument, the first temperature detection device, the ammonia analyzer and the second temperature detection device are all electrically connected to the control system; The multiple flame burners of the direct-fired heating device constitute at least two burner groups, and the number of the burner groups is an even number; the center line of the flame stream of each flame burner of each burner group is tangent to an imaginary tangent circle, and the center line of each flame stream of two adjacent burner groups is arranged in opposite directions to the cutting direction of the imaginary tangent circle; the center axis of each flame burner is arranged at a first angle to the horizontal direction, and the center axis of each flame burner is arranged at a second angle to the vertical direction; 8. The flame burner of claim 7, wherein the flames of the combustion-stabilizing flue gas are directed to a first end of the combustion-stabilizing flue gas structure and a second end of the combustion-stabilizing flue gas structure is connected to a combustion-supporting gas chamber and a fuel gas chamber. A combustion-stabilizing center hole is axially provided on the combustion-stabilizing flue gas structure, and the combustion-stabilizing center hole forms a combustion mixing chamber. An igniter is provided in the combustion mixing chamber, and the igniter is electrically connected to a control system. A combustion-supporting gas inlet is connected to the combustion-supporting gas chamber, and a fuel gas inlet is connected to the fuel gas chamber. An ejector is provided in the fuel gas chamber and the combustion-supporting gas chamber, and the ejector is coaxially provided with the combustion-stabilizing flue gas structure. The ejector is used to accelerate the combustion of the fuel gas in the fuel gas chamber and eject it into the combustion mixing chamber. A necked ejector passage is formed between the combustion-supporting gas chamber and the combustion mixing chamber, and the combustion-supporting gas in the combustion-supporting gas chamber is ejected into the combustion mixing chamber through the ejector passage. The flue before denitration and the flue for denitration treatment are arranged vertically, the second end of the flue before denitration and the second end of the flue for denitration treatment are connected through a horizontal flue, and a horizontal rectifying grid is arranged at the outlet of the horizontal flue.

2. The denitration system with combustion and heating in the flue as claimed in claim 1, characterized in that: The first angle ranges from 10° to 50°, and the second angle ranges from 15° to 85°.

3. The denitration system with combustion and heating in the flue as claimed in claim 1, characterized in that: The combustion-stabilizing flue structure includes a combustion-stabilizing inner tube and a combustion-stabilizing outer tube which are coaxially and radially spaced apart. The cross section of the combustion-stabilizing inner tube is a closed contour formed by splicing multiple arc segments, and the cross section of the combustion-stabilizing outer tube is a circle. A combustion-stabilizing annular space is formed between the combustion-stabilizing inner tube and the combustion-stabilizing outer tube, and the combustion-stabilizing annular space is filled with a refractory castable material unit.

4. The denitration system with combustion and heating in the flue as claimed in claim 1, characterized in that: A flame detector and a temperature detector are arranged in the combustion mixing chamber, and both the flame detector and the temperature detector are electrically connected to the control system; the flame detector is used to detect the flame combustion condition in the combustion mixing chamber, and the temperature detector is used to detect the temperature in the combustion mixing chamber.

5. The denitration system with combustion and heating in the flue as claimed in claim 1, characterized in that: The ejector includes a straight pipe section, a contraction section, a throat section, an expansion section and a rectification section, the straight pipe section is located in the fuel gas chamber, the contraction section, the throat section, the expansion section and the rectification section are located in the combustion-supporting gas chamber; an air inlet is arranged at the first end of the straight pipe section, the second end of the straight pipe section is connected to the first end of the contraction section, the diameter of the contraction section is gradually contracted from the first end to the second end, the second end of the contraction section is connected to the first end of the throat section, the second end of the throat section is connected to the first end of the expansion section, the diameter of the expansion section is gradually expanded from the first end to the second end, the second end of the expansion section is connected to the first end of the rectification section, and an air outlet is arranged at the second end of the rectification section.

6. The denitration system with combustion and heating in the flue as claimed in claim 5, characterized in that: The rectifying section comprises a rectifying inner tube and a rectifying outer tube which are coaxially and radially spaced apart. The cross section of the rectifying inner tube is a closed contour formed by splicing multiple arc segments. The cross section of the rectifying outer tube is a circle. A rectifying annular space is formed between the rectifying inner tube and the rectifying outer tube. The rectifying annular space is filled with a refractory castable material unit.

7. The denitration system with combustion and heating in the flue as claimed in claim 1, characterized in that: The control system includes a measurement data summary and analysis module, which is used to calculate the nitrogen oxide load based on the measurement data of the flue gas analyzer, the flue gas velocity measuring instrument and the ammonia analyzer, and calculate the ammonia injection amount of each ammonia injection unit based on the nitrogen oxide load.

8. The denitration system with combustion and heating in the flue as claimed in claim 1, characterized in that: Each of the flame burners is fixedly arranged on the side wall of the flue before denitration, and the first angle and the second angle are fixedly arranged.

9. The denitration system with combustion and heating in the flue as claimed in claim 1, characterized in that: Each of the flame burners is adjustably arranged on the side wall of the flue before denitration, and the first angle and the second angle are adjustable.

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