Method and structure for low-nitrogen clean combustion and anti-extinction of coal-fired boiler

Abstract

The application discloses a method and structure for low-nitrogen clean combustion and anti-extinction of a coal-fired boiler, which uses solid fuel to replace diesel oil for ultra-low load stable combustion, and uses a solid fuel stable ignition device to ignite solid fuel entering the coal-fired boiler for the first time; the application can use coal powder as solid fuel for low-cost stable combustion when the coal-fired boiler is operated at an ultra-low load, and replaces the condition that diesel oil is used as boiler stable combustion accompanying fuel under a conventional ultra-low load stable combustion condition, and is beneficial to low-nitrogen clean and high-efficiency combustion of the coal-fired boiler.

Description

Technical Field

[0001] This invention relates to a method and structure for low-NOx clean combustion and anti-flameout in coal-fired boilers, belonging to the field of coal-fired boiler technology. Background Technology

[0002] A coal-fired boiler is a boiler that uses coal as fuel. It is a thermal power equipment that uses the heat released by burning coal in the boiler furnace to heat water or other organic heat carriers (such as heat transfer oil) to a certain temperature (or pressure).

[0003] In existing coal-fired boilers, the boiler output conditions fluctuate constantly during operation. When high output is not required, the boiler needs to be operated at low load. During low-load operation, because coal combustion requires heat absorption and an ignition process, the risk of boiler flameout is high if auxiliary combustion stabilizing materials are not added, especially for boilers burning lean coal or anthracite. The mechanism of combustion stabilization in existing coal-fired boilers relies on achieving continuous fuel supply once the internal heat load of the furnace reaches a certain value. However, due to low load or poor coal quality, the heat load per unit volume may be unstable or below the ignition point, significantly increasing the risk of boiler flameout.

[0004] Therefore, for coal-fired power boilers in my country, the design and subsequent operation of boilers are based on the assumption that a 50% load can meet the daily operating standards. However, with the increasing demand for coal-fired boilers to operate at load reductions below 50%, especially with ultra-low stable combustion loads below 40% becoming a necessity, diesel fuel is needed as a stable fuel for combustion when the load is below 40%. However, using diesel fuel for auxiliary combustion is extremely uneconomical, far exceeding the capacity of coal-fired power plants. This leads to power plants only using diesel fuel for temporary supplementary combustion in special emergency situations; otherwise, they directly shut down the plant. Furthermore, the use of diesel fuel for temporary supplementary combustion results in incomplete combustion due to the mixing and combustion of diesel fuel with solid fuel in the same confined space, leading to a coal-oil co-burning process that is toxic to subsequent dust collectors, desulfurization slurry, and denitrification catalysts.

[0005] Meanwhile, achieving low-NOx, clean, and efficient combustion in coal-fired boilers has always been a concern. However, high-efficiency combustion technology for solid fuels and low-NOx combustion technology are two contradictory technologies. NOx generation in coal-fired power generation is primarily thermal. Reducing NOx generation and emissions fundamentally depends on controlling the temperature of the combustion zone to prevent it from becoming too high. However, low-temperature combustion affects the ignition and combustion rate of solid fuels. The optimal goal is to coordinate the application of these two technologies to achieve the best overall effect, which in practice requires controlling the entire solid fuel combustion process. This requires ensuring reliable solid fuel ignition, adjustable NOx levels, and a sufficiently long combustion time at a certain temperature to ensure complete combustion of the solid fuel.

[0006] Based on the mechanisms of nitrogen oxide (NOx) formation and inhibition, there are two main types of NOx control technologies for thermal power plants: one is controlling NOx formation during combustion, i.e., low-NOx combustion technology, also known as primary measures; the other is treating the generated NOx, i.e., flue gas denitrification technology, also known as secondary measures. Reducing NOx emissions by altering combustion conditions is collectively referred to as low-NOx combustion technology. Among various NOx emission reduction technologies, low-NOx combustion technology is the most widely used, relatively simple, economical, and effective.

[0007] Low-NOx combustion technology refers to technologies that reduce NOx formation and emissions by improving combustion techniques based on the NOx formation mechanism during fuel combustion. Low-NOx combustion technologies in coal-fired power plants include low-NOx burners, staged air combustion technology, and staged fuel combustion technology. Among these, staged air combustion technology is mature, has lower investment and operating costs, and its denitrification efficiency is generally between 10% and 50%. Furthermore, in the retrofitting of older thermal power units, only the boiler furnace needs to be modified to apply staged air combustion technology.

[0008] However, after the current low-NOx burner retrofitting of coal-fired boilers, a series of problems arise, such as increased fly ash combustibles, increased flue gas outlet temperature, reduced boiler combustion efficiency, boiler coking, and easy boiler flameout. The root cause of these problems lies in the fact that to reduce the formation of NOx in the main combustion zone, measures are generally taken to reduce the oxygen content and combustion temperature. This requires maintaining low-oxygen, low-temperature combustion in the main combustion zone, which necessitates reducing the volume of secondary air. However, reducing the air volume in the main combustion zone decreases the efficiency of air-solid fuel mixing and combustion, making it impossible to maintain both the oxygen content in the main combustion zone and stable ignition and combustion in that area. Furthermore, large fluctuations in coal quality in coal-fired power generation boilers, especially at low boiler loads, increase the risk of boiler flameout, particularly for boilers burning lean or anthracite coal. Therefore, while existing air and fuel classification technologies have excellent efficiency in theoretical calculations, in practical applications, the precise control of air and fuel classification becomes the main limiting factor for their low efficiency in actual use.

[0009] Staged air combustion involves completing the fuel combustion process in stages. In the first stage, the amount of air supplied from the main burner to the furnace is reduced to 70-75% of the total combustion air, allowing the fuel to burn under oxygen-deficient, fuel-rich combustion conditions. This reduces the combustion rate and temperature in the combustion zone, but the reducing atmosphere lowers the NOx formation rate, thus inhibiting NOx generation in this combustion process. This zone is the boiler's main combustion reduction zone. In the second stage, to complete the entire combustion process, the remaining air required for complete combustion is introduced into the furnace through secondary air nozzles located above the main burner, mixing with the flue gas produced in the main combustion zone to complete the entire combustion process. Because the air required for the entire combustion process is supplied to the furnace in two stages, it is called staged air combustion. The basic principle of staged fuel combustion is the same as staged air combustion, essentially transforming the staged air entry into the combustion process into a staged fuel entry into the combustion condition. That is, first increasing the fuel input concentration, and then supplementing with fully combusted air and lean fuel for combustion.

[0010] Whether using air staging or fuel staging, a smaller excess air coefficient in the main combustion zone of the boiler results in better NOx suppression, but also more incomplete combustion products, leading to reduced combustion efficiency and a greater likelihood of slagging and corrosion. This is the main reason why low-NOx combustion is inefficient in actual operating conditions. Furthermore, when the load of a coal-fired power plant boiler decreases, the fuel supply drops significantly, increasing the boiler's air margin coefficient and causing a substantial increase in NOx content in the flue gas. Moreover, when the boiler operates at low or ultra-low loads, the risk of boiler flameout is extremely high, regardless of whether air staging or fuel staging is used for control.

[0011] In other words, there is a need for a technology for low-NOx clean combustion and anti-quenching in coal-fired boilers, which can achieve stable combustion of coal at low cost when operating at ultra-low load, while also promoting low-NOx clean and high-efficiency combustion in coal-fired boilers. Summary of the Invention

[0012] In view of this, the purpose of the present invention is to provide a method and structure for low-NOx clean combustion and anti-flameout in coal-fired boilers, which can overcome the shortcomings of the prior art.

[0013] The objective of this invention is achieved through the following technical solution:

[0014] This invention discloses a method for low-NOx clean combustion and anti-flameout in coal-fired boilers. The method uses solid fuel instead of diesel for ultra-low load stable combustion and uses a solid fuel stable ignition device to ignite the solid fuel that is about to enter the coal-fired boiler for the first time.

[0015] The solid fuel stable ignition device delivers combustion-supporting fuel to the nozzle through a gas or fuel supply pipe and an oxygen supply pipe. The nozzle has a mixed combustion zone for pure oxygen and combustion-supporting fuel. Outside the mixed combustion zone is a pure oxygen heating zone. The pure oxygen heated in the pure oxygen heating zone further refines the particle size of the solid fuel passing through the zone and ignites it. Outside the pure oxygen heating zone is a gas film protection device. The gas film protection device prevents the fuel or pure oxygen from impacting the nozzle and causing flameout in the combustion zone. At the same time, it avoids direct contact between the high-temperature pure oxygen in the pure oxygen heating zone and the inner wall of the burner cavity, which would cause corrosion.

[0016] Solid fuel is transported by a powder conveying fan. After passing through a solid fuel stabilizing and igniting device, the solid fuel is controlled to form an open flame or reducing gas after the first ignition.

[0017] By injecting the open flame of solid fuel into the coal-fired boiler after it has ignited, the boiler can avoid the heat absorption and slow ignition or failure of solid fuel to ignite during the ignition process when the solid fuel enters the boiler under ultra-low load conditions. By using the solid fuel in a burning state to directly release heat into the boiler, the heat absorption and ignition process of solid fuel entering the boiler and the delayed heat release are avoided. This avoids the fluctuation of thermal stability in the furnace caused by solid fuel entering the furnace under low load conditions, stabilizes the boiler temperature, and achieves stable combustion of the coal-fired boiler under ultra-low load operation.

[0018] The oxygen supply of the pulverized coal blower is less than the amount of oxygen required for the combustion of solid fuel. The enhancement measures in the solid fuel stable ignition device enable the solid fuel to ignite. The incomplete combustion of solid fuel forms a reducing gas, which inhibits the formation of nitrogen oxides in the burner. The reducing gas is introduced into the main combustion zone of the coal-fired boiler for combustion and to inhibit and reduce the formation of nitrogen oxides.

[0019] The high-temperature fire core at the center of the aforementioned mixed combustion zone transports carbon and oxygen through gas or fuel oil delivery pipes and oxygen delivery pipes, with a C:molar ratio of 1:1. The high-temperature fire core serves as both a heating source for pure oxygen gas and an ignition source for the combustion of solid fuel with high-temperature oxygen.

[0020] As mentioned above, the pure oxygen supplied by the gas film protection device is partially used to enter the pure oxygen heating zone to act as heated pure oxygen, while the other part forms the gas film layer. The high-temperature ignition core heats the pure oxygen gas supplied by the gas film protection device.

[0021] The above-mentioned data are collected by sensors, including the concentration of nitrogen oxides (NOx) D at the SCR inlet, the CO concentration Y at the boiler outlet, the SCR inlet temperature T, the reduction burner temperature Tt, the CO concentration at the reduction burner nozzle, and the flue gas oxygen concentration X. The control center controls the air volume of the secondary air supply device and the pulverized coal fan on the burner. The amount of pulverized coal mixed into the pulverized coal fan is adjusted by the screw conveyor device, thereby controlling the ratio of air volume to pulverized coal in the pulverized coal fan. This enhances the air volume regulation or reducing gas regulation of the main combustion zone and the complete combustion zone of the coal-fired boiler.

[0022] As mentioned above, a heating chamber is installed on the flue gas exhaust pipe of the coal-fired boiler, and the flue gas is heated by a heating device to ensure that the subsequent flue gas reaches the treatment temperature.

[0023] This structure for low-NOx clean combustion and anti-flameout in a coal-fired boiler includes a coal-fired boiler, burners connected to the boiler's internal cavity, a fuel combustion cavity, a solid fuel delivery pipe connected to the combustion cavity, and a pulverized coal blower. A solid fuel stabilizing ignition device is installed within the combustion cavity. This device includes a gas or oil delivery pipe and an oxygen delivery pipe, with nozzles at their ends. A gas film protection device with pure oxygen as a film is installed outside the flame combustion zone of the nozzles. A pure oxygen heating zone is located between the core flame and the gas film protection layer formed by the gas film protection device. The gas film protection device prevents flameout caused by the impact of fuel or gas on the core flame of the nozzles and prevents the high-temperature oxygen in the pure oxygen heating zone from directly contacting the inner wall of the burner cavity.

[0024] The aforementioned oxygen delivery pipe is sleeved on the outside of the gas or fuel delivery pipe and is coaxially arranged. The nozzle is located at the outer end of the oxygen delivery pipe and the gas or fuel delivery pipe. The gas film protection device includes a pure oxygen delivery pipe sleeved on the outside of the gas or fuel delivery pipe and the oxygen delivery pipe and is coaxially arranged. The end of the pure oxygen delivery pipe is sealed with the oxygen delivery pipe. Air holes are distributed on the side wall of one end of the pure oxygen delivery pipe near the nozzle. The air holes are circumferentially distributed on the side wall of the pure oxygen delivery pipe and arranged in multiple rows along the axial direction of the pure oxygen delivery pipe.

[0025] As described above, an annular baffle is provided on the inner wall of the fuel combustion cavity to guide the flow of solid fuel and primary air fuel in the middle of the combustion cavity. A horn-shaped guide plate with openings at both ends and gradually increasing in size along the solid fuel injection direction is provided on the outer side of the ignition end of the solid fuel stable ignition device. The horn-shaped guide plate is connected to the inner wall of the burner by a connecting rod or a connecting plate. An external flow channel for solid fuel is provided between the horn-shaped guide plate and the inner wall of the burner.

[0026] As mentioned above, a flue gas exhaust pipe is provided on the upper side of the coal-fired boiler, a heating chamber is provided on the flue gas exhaust pipe, and a heating device and a flue gas discharge pipe are provided on the heating chamber.

[0027] The aforementioned solid fuel conveying pipe is connected to a solid fuel conveying system, which includes a coal mill. The coal mill is connected to a solid fuel storage tank via a conveyor belt. A spiral auger conveying device connected to the solid fuel conveying pipe is installed on the solid fuel storage tank. Sensors are installed on the coal-fired boiler to collect the concentrations of nitrogen oxides (NOx) D and CO Y before SCR, as well as the SCR inlet temperature T, the reduction burner temperature Tt, the CO concentration at the reduction burner nozzle, and the flue gas oxygen concentration X. The sensors exchange data with the control center. The control center controls the secondary air supply device of the coal-fired boiler and the pulverized coal fan on the burner to regulate the reducing gas and solids in the burner, thereby achieving deep low-NOx clean combustion in the boiler.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] 1. The principle of this invention is as follows: Pure oxygen gas and a small amount of combustion-supporting fuel are transported through different pipelines without premixing, reducing the safety risk of deflagration during premixing. After exiting the nozzles through different pipelines, the gas enters the combustion zone, where the fuel gas and pure oxygen mix and burn in a low-wind-velocity area. This area is enveloped in a pure oxygen atmosphere, achieving complete combustion of the fuel and forming a high-temperature flame core. Simultaneously, the released heat heats the excess pure oxygen gas. A portion of the pure oxygen transported by the gas film protection device enters the pure oxygen heating zone to act as heated pure oxygen, i.e., the excess high-temperature pure oxygen gas. When solid fuel enters the pure oxygen heating zone and is heated, the high-temperature pure oxygen ignites the solid fuel passing through the zone. Another portion of the pure oxygen supplied by the gas film protection device forms a gas film layer. The gas film is formed by supplying pure oxygen through pores in the side wall of the pure oxygen supply pipe. When the fuel and primary air supplied by the burner pass through the flame area of ​​the nozzle, the gas ejected from the pure oxygen supply pipe intercepts and redirects the primary air, thus creating a gas flow buffer zone in and around the pure oxygen heating zone. The ejected gas acts as a protective gas film layer. In this way: firstly, the gas film layer prevents the high-temperature pure oxygen in the pure oxygen heating zone from corroding external materials. Secondly, the gas film layer intercepts and redirects the fuel and primary air, reducing the amount of fuel or primary air directly acting on the flame, thus reducing the risk of core flame extinguishing. Thirdly, in the flame and a small area around it, the gas film can slow down the speed of the fuel or primary air in that area, preventing the fuel or primary air from directly impacting the flame at a high speed and reducing the risk of flameout. At the same time, the gas film only protects the flame area. Inside the burner delivery pipe, a sleeve made of high-temperature resistant special material is provided around the high-temperature fire core of the solid ignition device. The outer circumference of the sleeve has sufficient space with the original inner wall of the burner, so it will not affect the overall delivery speed of the original solid fuel or the spraying effect of the burner. Fourth, because the flame zone of the ignition gun has a high temperature, when solid fuel particles enter this zone, due to the deceleration of the gas film, the solid fuel will remain in this zone for a longer time. The temperature difference caused by the higher temperature in this zone and the longer residence time make the solid fuel particles prone to bursting, further reducing the particle size of the fuel. This is conducive to the ignition and combustion of the fuel and further reduces the risk of flameout. At the same time, in existing coal-fired boilers, the coal particles can generally only reach 90 mesh through physical abrasion before entering the burner. If the coal particles are to be further abraded, it will require greater costs, and the fineness of the particle size is seriously disproportionate to the cost investment, which is not in line with the economic benefits of enterprises. However, by combining the gas film and the flame zone, the purpose of further refining the fuel can be achieved.

[0030] Simultaneously, solid fuel is used to replace diesel for stable combustion. A solid fuel stabilization ignition device is used to ignite the solid fuel before it enters the coal-fired boiler. The air-to-solid fuel ratio in the burner is controlled by a pulverized coal blower and a solid fuel auger, thereby controlling the combustion conditions and generating open flame or reducing gas. Open flame injection into the coal-fired boiler avoids the heat absorption of solid fuel ignition within the boiler, and the heat release from the burning solid fuel is directly achieved in the boiler, stabilizing the boiler temperature and achieving stable combustion in the coal-fired boiler operating at low load. Compared with existing fuels entering the coal-fired boiler... In this method, the solid fuel first absorbs heat, and then releases heat through combustion once the fuel reaches its ignition point. This means the solid fuel, in its combustion state, directly releases heat upon entering the furnace, without absorbing heat from the furnace itself. This prevents the furnace temperature from dropping, completely resolving the problem of primary air and pulverized coal deteriorating combustion conditions under ultra-low load conditions in existing coal-fired boilers, and eliminating the risk of flameout under such conditions. Furthermore, the entire process from the solid fuel entering the furnace to its final discharge through the flue gas pipe reduces heat absorption, as the solid fuel enters the furnace in an ignited state. Therefore, the solid fuel has a longer heat release time in the furnace, which helps increase the furnace temperature, further reducing the risk of flameout and allowing for stable combustion with less fuel. Introducing solid fuel into the furnace in an ignited state ensures a stable open flame under any operating conditions, especially at low boiler loads or with poor coal quality, mitigating the risk of flameout. Simultaneously, the extended direct combustion time of solid fuel within the boiler effectively improves the burnout rate.

[0031] Moreover, compared with existing technologies, which use diesel fuel for stable combustion in coal-fired boilers, resulting in high costs and the risk of poisoning subsequent dust collectors, desulfurization slurry, and denitrification catalysts due to the co-firing of oil and coal, this method has lower costs and is more economical. At the same time, the stable combustion of solid fuel is the same as the fuel used to burn the boiler body, thus eliminating the co-firing of oil and coal and preventing poisoning of subsequent dust collectors, desulfurization slurry, and denitrification catalysts.

[0032] 2. A heating chamber is installed on the flue gas exhaust pipe of the coal-fired boiler. The heating device ensures that the subsequent flue gas reaches the treatment temperature. According to environmental protection requirements, the temperature of the flue gas during treatment should not be lower than 320°C. Therefore, in order to avoid the flue gas temperature from not meeting the standard, it is heated by a heating device. This is especially suitable for situations where the flue gas temperature is too low during low-load combustion.

[0033] 3. Controlling the oxygen supply of the pulverized coal blower to be less than the amount of oxygen required for solid fuel combustion results in incomplete combustion of solid fuel, forming reducing gases. Firstly, these reducing gases inhibit the formation of nitrogen oxides in the burner. Secondly, utilizing an active solid fuel ignition and combustion method, by introducing the combustion flame from the bottom of the furnace (the main combustion zone is also the reduction zone), deepens the reducing atmosphere in the furnace's reduction zone, improving the effect that traditional furnace air staging cannot achieve. That is, the burner pre-forms reducing gases before the solid fuel enters the boiler, and these pre-formed reducing gases then inhibit the formation of nitrogen oxides in the main combustion zone. Simultaneously, it ensures complete combustion of solid fuel, increasing the burnout rate. The active solid fuel ignition and combustion method, by introducing the combustion flame from the bottom of the furnace, addresses combustion stability within the furnace, preventing the risk of flameout or deflagration under low-load conditions.

[0034] 4. Solid fuel stabilizing ignition devices for auxiliary solid fuel combustion are distributed on the coal-fired boiler. This allows reducing gas to be introduced into the main combustion zone of the coal-fired boiler for combustion and inhibits the formation of nitrogen oxides. At the same time, the solid fuel stabilizing ignition device can be used for air depth classification and control, and regulate and control the boiler primary air, secondary air, burnout air and burner reducing air.

[0035] 5. Sensors are installed on the coal-fired boiler to collect the concentrations of nitrogen oxides (NOx) D and CO Y before the SCR inlet, as well as the SCR inlet temperature T, reduction burner temperature, reduction burner nozzle CO concentration, and flue gas oxygen concentration. These sensors exchange data with the control center, which then controls the secondary air supply device and the pulverized coal fan on the burner. This allows for the measurement and collection of parameters such as the NOx concentration D, CO concentration Y, SCR inlet temperature T, reduction burner temperature, reduction burner nozzle CO concentration, and flue gas oxygen concentration at the boiler outlet. Intelligent control is achieved by setting the desired NOx concentration at the outlet (D1), the desired CO concentration at the outlet (Y1), the reduction burner temperature (T1), the reduction burner nozzle CO concentration, and the boiler furnace outlet oxygen content, in conjunction with the proportions of primary air, secondary air, and combustion air.

[0036] 6. The solid fuel stable ignition device includes a burner, on which a fuel combustion cavity, a solid fuel conveying pipe, and a pulverized coal fan are provided. The injection device is a spray gun provided on the burner, which is connected to the inner cavity of the coal-fired boiler. An igniter is provided in the fuel combustion cavity. The solid fuel conveying pipe is connected to a solid fuel conveying system. The solid fuel conveying system includes a coal mill, which is connected to a solid fuel storage tank via a conveyor belt. A spiral auger conveying device connected to the solid fuel conveying pipe is provided on the solid fuel storage tank. With this structure, the coal mill can grind coal into solid fuel, which can be stored in the solid fuel storage tank. The spiral auger conveying device facilitates the sealed and stable conveying of solid fuel to the burner. The sealed conveying helps to ensure the airflow control effect of the pulverized coal fan on the burner.

[0037] 7. An annular baffle is provided on the inner wall of the fuel combustion cavity to guide the flow of solid fuel and primary air fuel in the middle of the combustion cavity. A trumpet-shaped guide plate with openings at both ends and gradually increasing in size along the direction of solid fuel injection is provided on the outer side of the ignition end of the solid fuel stable ignition device. The trumpet-shaped guide plate is connected to the inner wall of the burner by a connecting rod or a connecting plate. An external flow channel for solid fuel is provided between the trumpet-shaped guide plate and the inner wall of the burner. In this way, the annular baffle can guide the flow of solid fuel and primary air fuel in the middle of the combustion cavity, allowing more solid fuel to enter the trumpet-shaped guide plate and be ignited by the pure oxygen heating zone of the solid fuel stable ignition device.

[0038] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will now be described in further detail with reference to the accompanying drawings, wherein:

[0040] Figure 1 This is a schematic diagram of the connection structure of the present invention.

[0041] Figure 2 This is a schematic diagram of the burner connection structure distributed on a coal-fired boiler according to the present invention.

[0042] Figure 3 This is a schematic diagram of the connection structure of the solid fuel stable ignition device of the present invention.

[0043] Figure 4 for Figure 3 A bottom view.

[0044] Figure 5 This is a schematic diagram of the connection structure between the solid fuel stable ignition device and the burner of the present invention.

[0045] Figure 6 A schematic diagram of a structure that forms a buffer gas film within the burner as the fuel direction and the pure oxygen delivery pipe vent direction collide.

[0046] Figure 7 for Figure 6 Layout diagram.

[0047] Figure 8 This is a schematic diagram of the second embodiment of the pore distribution method of the solid fuel stable ignition device of the present invention.

[0048] Figure 9 A schematic diagram of the connection structure for adding exhaust gas treatment to this invention.

[0049] Among them, there is a coal-fired boiler 1; a burner 2; a fuel combustion cavity 2-1; a solid fuel conveying pipe 2-2; a pulverized coal blower 2-3; a solid fuel stabilizing ignition device 3; a gas or oil conveying pipe 3-1; an oxygen conveying pipe 3-2; a nozzle 3-3; a pure oxygen conveying pipe 3-4; a vent 3-5; a flame combustion zone 4; a gas film protection device 5; a gas film protection layer 6; a pure oxygen heating zone 7; an annular baffle 8; a trumpet-shaped guide plate 9; a heating chamber 10; a coal mill 11; a conveyor belt 12; a solid fuel storage tank 13; a screw conveyor 14; and a heating device 15. Detailed Implementation

[0050] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be understood that the preferred embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0051] Example 1:

[0052] like Figures 1-7 As shown, the present invention discloses a method for low-NOx clean combustion and anti-quenching of coal-fired boilers. The method uses solid fuel to replace diesel for ultra-low load stable combustion and uses a solid fuel stable ignition device 3 to ignite the solid fuel that is about to enter the coal-fired boiler 1 for the first time.

[0053] The solid fuel stable ignition device 3 delivers combustion-supporting fuel to the nozzle 3-3 through the gas or fuel oil delivery pipe 3-1 and the oxygen delivery pipe 3-2. The nozzle 3-3 is provided with a mixed combustion zone of pure oxygen and combustion-supporting fuel. A pure oxygen heating zone 7 is provided outside the mixed combustion zone. The pure oxygen heated by the pure oxygen heating zone 7 further refines the particle size of the solid fuel passing through the zone and ignites it. A gas film protection device 5 is provided outside the pure oxygen heating zone 7. The gas film protection device 5 prevents the fuel or pure oxygen from impacting the nozzle 3-3 and causing the flame combustion zone 4 to detach. At the same time, it avoids the high temperature of pure oxygen in the pure oxygen heating zone 7 from directly contacting the inner wall of the burner 2 cavity and causing corrosion.

[0054] Solid fuel is transported by the powder conveying fan 2-3. After passing through the solid fuel stabilizing ignition device 3, the solid fuel is controlled to form an open flame or reducing gas after the first ignition.

[0055] By injecting the open flame of solid fuel after ignition into the coal-fired boiler 1, the boiler can avoid heat absorption and slow ignition or failure of solid fuel to ignite during the ignition process of solid fuel entering the boiler under ultra-low load conditions, thus preventing boiler extinguishing. By using solid fuel in combustion state to directly release heat into the boiler, the heat absorption and ignition process of solid fuel entering the boiler and the delayed heat release are avoided. This avoids the fluctuation of thermal stability in the furnace caused by solid fuel entering the furnace under low load conditions, stabilizes the boiler temperature, and achieves stable combustion of coal-fired boiler 1 under ultra-low load operation.

[0056] The oxygen supply of the pulverized coal blower 2-3 is less than the amount of oxygen required for the combustion of solid fuel. The enhancement measures in the solid fuel stable ignition device 3 enable the solid fuel to ignite. The incomplete combustion of solid fuel forms a reducing gas, which inhibits the formation of nitrogen oxides in the burner 2. The reducing gas is introduced into the main combustion zone of the coal-fired boiler 1 for combustion and to inhibit and reduce the formation of nitrogen oxides.

[0057] The high-temperature fire core at the center of the mixed combustion zone supplies carbon and oxygen through gas or fuel oil supply pipe 3-1 and oxygen supply pipe 3-2, with a C:O2 molar ratio of 1:1. The high-temperature fire core serves as both a heating source for pure oxygen gas and an ignition source for the combustion of solid fuel with high-temperature oxygen.

[0058] The pure oxygen supplied by the gas film protection device 5 is partially used to enter the pure oxygen heating zone 7 as heated pure oxygen, while the other part forms a gas film layer. The high-temperature fire core heats the pure oxygen gas supplied by the gas film protection device 5.

[0059] The concentrations of nitrogen oxides (NOx) at the SCR inlet (D), the CO concentration at the boiler outlet (Y), the SCR inlet temperature (T), the temperature of the reduction burner 2 (Tt), the CO concentration at the nozzle 3-3 of the reduction burner 2, and the oxygen concentration in the flue gas (X) are collected by sensors. The secondary air supply device and the air volume of the pulverized coal feeding fan 2-3 on the burner 2 are controlled by the control center. The amount of pulverized coal mixed into the pulverized coal feeding fan is adjusted by the screw conveyor device 14, thereby controlling the ratio of air volume to pulverized coal in the pulverized coal feeding fan 2-3. This enhances the air volume regulation or reducing gas regulation of the main combustion zone and the complete combustion zone of the coal-fired boiler 1 by the burner 2.

[0060] The structure of this low-NOx clean combustion and anti-extinguishing coal-fired boiler includes a burner 2 connected to the inner cavity of the coal-fired boiler 1. The burner 2 has a fuel combustion cavity 2-1, a solid fuel delivery pipe 2-2 connected to the fuel combustion cavity 2-1, and a pulverized coal blower 2-3. A solid fuel stabilizing ignition device 3 is installed inside the fuel combustion cavity 2-1. The solid fuel stabilizing ignition device 3 includes a gas or oil delivery pipe 3-1 and an oxygen delivery pipe 3-2. A nozzle 3-3 is located at the end of the gas or oil delivery pipe 3-1 and the oxygen delivery pipe 3-2. A gas film protection device 5 with pure oxygen as the film is installed outside the flame combustion zone 4 of the nozzle 3-3. A pure oxygen heating zone 7 is located between the core flame and the gas film protection layer 6 formed by the gas film protection device 5. The gas film protection device 5 prevents the core flame of the nozzle 3-3 from being impacted by fuel or gas, thus preventing flameout, and prevents the high-temperature oxygen in the pure oxygen heating zone 7 from directly contacting the inner wall of the burner 2 cavity.

[0061] The oxygen delivery pipe 3-2 is sleeved on the outside of the gas or fuel delivery pipe 3-1 and is coaxially arranged. The nozzle 3-3 is located at the outer end of the oxygen delivery pipe 3-2 and the gas or fuel delivery pipe 3-1. The gas film protection device 5 includes a pure oxygen delivery pipe 3-4 sleeved on the outside of the gas or fuel delivery pipe 3-1 and the oxygen delivery pipe 3-2 and is coaxially arranged. The end of the pure oxygen delivery pipe 3-4 is sealed with the oxygen delivery pipe 3-2. Air holes 3-5 are distributed on the side wall of the pure oxygen delivery pipe 3-4 near the nozzle 3-3. The air holes 3-5 are circumferentially distributed on the side wall of the pure oxygen delivery pipe 3-4 and arranged in multiple rows along the axial direction of the pure oxygen delivery pipe 3-4.

[0062] An annular baffle 8 is provided on the inner wall of the fuel combustion cavity 2-1 to guide the flow of solid fuel and primary air fuel in the middle of the combustion cavity 2-1. A trumpet-shaped guide plate 9 with openings at both ends and gradually increasing in size along the solid fuel injection direction is provided on the outer side of the ignition end of the solid fuel stable ignition device 3. The trumpet-shaped guide plate 9 is connected to the inner wall of the burner 2 by a connecting rod or a connecting plate. An external flow channel for solid fuel is provided between the trumpet-shaped guide plate 9 and the inner wall of the burner 2.

[0063] The solid fuel conveying pipe 2-2 is connected to the solid fuel conveying system, which includes a coal mill 11. The coal mill 11 is connected to the solid fuel storage tank 13 via a conveyor belt 12. The solid fuel storage tank 13 is equipped with a screw conveyor device 14 connected to the solid fuel conveying pipe 2-2. The coal-fired boiler 1 is equipped with sensors that collect the concentrations of nitrogen oxides (NOx) D and CO Y before SCR, as well as the SCR inlet temperature T, the temperature Tt of the reduction burner 2, the CO concentration at the nozzle 3-3 of the reduction burner 2, and the oxygen concentration X in the flue gas. The sensors exchange data with the control center. The control center controls the secondary air supply device of the coal-fired boiler 1 and the pulverized coal fan 2-3 on the burner 2 to regulate the reducing gas and solids in the burner 2, thereby achieving deep low-NOx clean combustion in the boiler.

[0064] Example 2

[0065] The difference between this embodiment and Embodiment 1 lies in the distribution of pores, such as... Figure 8 As shown, the adjacent two exhaust holes 3-5 are arranged alternately. This arrangement of exhaust holes 3-5 can help form a uniformly distributed gas film, which can improve the protection effect on the flame and ensure stable combustion of the flame.

[0066] Example 3

[0067] like Figure 9 As shown, this embodiment is an improvement on the previous two embodiments. Specifically, a flue gas exhaust pipe is provided on the upper side of the coal-fired boiler 1, a heating chamber 10 is provided on the flue gas exhaust pipe, and a heating device 15 and a flue gas discharge pipe are provided on the heating chamber 10. In this way, a heating chamber 10 is set on the flue gas exhaust pipe of the coal-fired boiler 1, and the heating of the flue gas by the heating device 15 ensures that the subsequent flue gas reaches the processing temperature. The heating device 15 uses a ratio of natural gas (diesel) and oxygen to achieve complete combustion and then heats the flue gas.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments without departing from the technical solution of the present invention and based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A structure for low-NOx clean combustion and anti-quenching in a coal-fired boiler, comprising a coal-fired boiler (1), characterized in that: A burner (2) communicating with the inner cavity of a coal-fired boiler (1) is provided on the coal-fired boiler (1). A fuel combustion cavity (2-1), a solid fuel delivery pipe (2-2) communicating with the fuel combustion cavity (2-1), and a pulverizing fan (2-3) are provided on the burner (2). A solid fuel stabilizing ignition device (3) is provided in the fuel combustion cavity (2-1). The solid fuel stabilizing ignition device (3) includes a gas or oil delivery pipe (3-1) and an oxygen delivery pipe (3-2). (3-1) and the oxygen delivery pipe (3-2) are provided with nozzles (3-3). A gas film protection device (5) with pure oxygen as a film is provided outside the flame combustion zone (4) of the nozzle (3-3). A pure oxygen heating zone (7) is provided between the core flame and the gas film protection layer (6) formed by the gas film protection device (5). The gas film protection device (5) prevents the core flame of the nozzle (3-3) from being blown off by the impact of fuel or gas and prevents the high temperature oxygen in the pure oxygen heating zone (7) from directly contacting the inner wall of the burner (2) cavity. The oxygen delivery pipe (3-2) is sleeved on the outside of the gas or fuel delivery pipe (3-1) and coaxially arranged. The nozzle (3-3) is located at the outer end of the oxygen delivery pipe (3-2) and the gas or fuel delivery pipe (3-1). The gas film protection device (5) includes a pure oxygen delivery pipe (3-4) sleeved on the outside of the gas or fuel delivery pipe (3-1) and the oxygen delivery pipe (3-2) and coaxially arranged. The end of the pure oxygen delivery pipe (3-4) is sealed with the oxygen delivery pipe (3-2). Air holes (3-5) are distributed on the side wall of one end of the pure oxygen delivery pipe (3-4) near the nozzle (3-3). The air holes (3-5) are circumferentially distributed on the side wall of the pure oxygen delivery pipe (3-4) and arranged in multiple rows along the axial direction of the pure oxygen delivery pipe (3-4). An annular baffle (8) is provided on the inner wall of the fuel combustion cavity (2-1) to guide the flow of solid fuel and primary air direction fuel in the middle of the combustion cavity (2-1). A horn-shaped guide plate (9) with openings at both ends and gradually increasing in size along the solid fuel injection direction is provided on the outer side of the ignition end of the solid fuel stable ignition device (3). The horn-shaped guide plate (9) is connected to the inner wall of the burner (2) by a connecting rod or a connecting plate. An external flow channel for solid fuel is provided between the horn-shaped guide plate (9) and the inner wall of the burner (2).

2. The structure for low-NOx clean combustion and anti-flameout in a coal-fired boiler according to claim 1, characterized in that: A flue gas exhaust pipe is provided on the upper side of the coal-fired boiler (1), a heating chamber (10) is provided on the flue gas exhaust pipe, and a heating device (15) and a flue gas discharge pipe are provided on the heating chamber (10).

3. The structure for low-NOx clean combustion and anti-flameout in a coal-fired boiler according to claim 1, characterized in that: The solid fuel conveying pipe (2-2) is connected to the solid fuel conveying system, which includes a coal mill (11). The coal mill (11) is connected to the solid fuel storage tank (13) via a conveyor belt (12). A spiral auger conveying device (14) connected to the solid fuel conveying pipe (2-2) is provided on the solid fuel storage tank (13). Sensors are provided on the coal-fired boiler (1) to collect the concentrations of nitrogen oxides (NOx) D, CO concentration Y, SCR inlet temperature T, burner (2) temperature Tt, CO concentration at burner (2) nozzle (3-3), and flue gas oxygen concentration X. The sensors exchange data with the control center. The control center controls the secondary air supply device of the coal-fired boiler (1) and the pulverized coal fan (2-3) on the burner (2) to regulate the reducing gas and solids in the burner (2), thereby achieving deep low-NOx clean combustion of the boiler.

4. A method for low-NOx clean combustion and anti-quenching of a coal-fired boiler, comprising a structure for low-NOx clean combustion and anti-quenching of a coal-fired boiler as described in any one of claims 1-3, characterized in that, This method uses solid fuel instead of diesel for ultra-low load stable combustion, and uses a solid fuel stable ignition device (3) to ignite the solid fuel that is about to enter the coal-fired boiler (1) for the first time; The solid fuel stable ignition device (3) delivers combustion-supporting fuel to the nozzle (3-3) through the gas or fuel oil delivery pipe (3-1) and the oxygen delivery pipe (3-2). The nozzle (3-3) is provided with a mixed combustion zone of pure oxygen and combustion-supporting fuel. A pure oxygen heating zone (7) is provided outside the mixed combustion zone. The pure oxygen heated by the pure oxygen heating zone (7) further refines the particle size and ignites the solid fuel passing through the zone. A gas film protection device (5) is provided outside the pure oxygen heating zone (7). The gas film protection device (5) prevents the fuel or pure oxygen from impacting the nozzle (3-3) and causing the flame combustion zone (4) to detach. At the same time, it avoids the high temperature pure oxygen in the pure oxygen heating zone (7) from directly contacting the inner wall of the burner (2) cavity and causing corrosion. Solid fuel is transported by a powder conveying fan (2-3). After passing through a solid fuel stabilizing ignition device (3), the solid fuel is controlled to form an open flame or reducing gas after the first ignition. The open flame after solid fuel ignition is injected into the coal-fired boiler (1) to avoid the boiler fire caused by heat absorption and slow ignition or failure of solid fuel to ignite during the process of solid fuel entering the boiler under ultra-low load conditions. The solid fuel in combustion state directly releases heat into the boiler, avoiding the heat absorption and ignition process of solid fuel entering the boiler and delayed heat release. It also avoids the fluctuation of thermal stability in the furnace caused by solid fuel entering the furnace under low load conditions, stabilizes the boiler temperature, and achieves stable combustion of the coal-fired boiler (1) under ultra-low load operation. The oxygen supply of the pulverized coal blower (2-3) is less than the amount of oxygen required for the combustion of solid fuel. The strengthening measures in the solid fuel stable ignition device (3) enable the solid fuel to ignite. The incomplete combustion of solid fuel forms a reducing gas. The reducing gas inhibits the formation of nitrogen oxides in the burner (2). The reducing gas is introduced into the main combustion zone of the coal-fired boiler (1) for combustion and to inhibit and reduce the formation of nitrogen oxides.

5. The method for low-NOx clean combustion and anti-flameout in a coal-fired boiler according to claim 4, characterized in that: The high-temperature fire core at the center of the mixed combustion zone transports carbon and oxygen through a gas or fuel oil delivery pipe (3-1) and an oxygen delivery pipe (3-2), with a C:O2 molar ratio of 1:

1. The high-temperature fire core serves as both a heating source for pure oxygen gas and an ignition source for the combustion of solid fuel with high-temperature oxygen.

6. The method for low-NOx clean combustion and anti-flameout in a coal-fired boiler according to claim 5, characterized in that: The pure oxygen delivered by the gas film protection device (5) is partially delivered into the pure oxygen heating zone (7) to act as heated pure oxygen, and the other part constitutes the gas film layer. The high-temperature fire core heats the pure oxygen gas delivered by the gas film protection device (5).

7. The method for low-NOx clean combustion and anti-flameout in a coal-fired boiler according to claim 4, characterized in that: The concentrations of nitrogen oxides (NOX) at the SCR inlet (D), CO concentration at the boiler outlet (Y), SCR inlet temperature (T), burner (2) temperature (Tt), CO concentration at the burner (2) nozzle (3-3), and flue gas oxygen concentration (X) are collected by sensors. The air volume of the secondary air supply device and the pulverized coal feeding fan (2-3) on the burner (2) is controlled by the control center. The amount of pulverized coal mixed into the pulverized coal feeding fan is adjusted by the screw conveyor (14), thereby controlling the ratio of air volume to pulverized coal in the pulverized coal feeding fan (2-3), thereby strengthening the air volume regulation or reducing gas regulation of the main combustion zone and complete combustion zone of the coal-fired boiler (1) by the burner (2).

8. The method for low-NOx clean combustion and anti-flameout in a coal-fired boiler according to claim 4, characterized in that: A heating chamber (10) is installed on the flue gas exhaust pipe of the coal-fired boiler (1), and the subsequent flue gas is heated by the heating device (15) to ensure that the flue gas reaches the treatment temperature.

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