Low NOx emission combustion device suitable for boiler

Abstract

The invention discloses a low-NOx-emission combustion device suitable for a boiler. The low-NOx-emission combustion device comprises a boiler hearth. The boiler furnace comprises a main combustion area, a reduction area and a burnout area which are sequentially arranged from bottom to top. A plurality of tar atomizing spray guns for spraying atomized tar are arranged on the furnace wall of the main combustion area / reduction area, and a plurality of pyrolysis gas nozzles for spraying pyrolysis gas are arranged on the furnace wall of the reduction area, or a plurality of tar pyrolysis gas nozzles for spraying tar-containing pyrolysis gas are arranged on the furnace wall of the main combustion area / reduction area. The tar is sprayed into the high-temperature and low-oxygen main combustion area, the tar and cracking components of the tar efficiently participate in the NOx conversion process, in-situ removal of NOx in the combustion process can be achieved, flue gas is used as fluidization and heat source gas of the pyrolyzing furnace, large-scale pyrolysis can be economically achieved, and the high tar yield is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of nitrogen oxide emission reduction technology for boilers, and particularly to a low-NOx emission combustion device suitable for boilers. Background Technology

[0002] Solid fuels typically contain nitrogen (N), which generates NOx during combustion, necessitating flue gas denitrification treatment. With increasingly stringent national emission standards, the cost of flue gas denitrification is rising. Reducing NOx levels during combustion can significantly lower these costs.

[0003] The NOx produced during boiler combustion is mostly fuel-type NOx (originating from the nitrogen in the fuel itself), with a small amount being thermal NOx (originating from N2 in the air). Thermal NOx production is primarily dependent on combustion temperature, with higher levels at higher temperatures (typically >1800K) and lower levels at lower temperatures. Fuel-type NOx is also affected by combustion temperature, but is also significantly influenced by the local combustion atmosphere. In a reducing atmosphere, NOx precursors (HCN, NH3, etc.) can be effectively reduced to N2, while in an oxidizing atmosphere, they are easily oxidized to NOx (NO, NO2, N2O, etc.).

[0004] (1) Staged combustion technology

[0005] To ensure complete combustion of fuel, the amount of air supplied during combustion (oxygen content) is usually higher than the required amount of air, with the excess air coefficient α (actual air volume / theoretical required air volume) typically between 1.1 and 1.2. Although the higher oxygen content ensures complete combustion of fuel, the excess oxygen in the combustion environment can also easily lead to a large amount of NOx precursors being converted into NOx, increasing the cost of subsequent flue gas denitrification.

[0006] Staged combustion technology moves the amount of air required for partial combustion upwards, thus dividing the combustion process into stages. Along the height of the furnace, the furnace can be divided into the main combustion zone (α<1, the area of ​​intense coal combustion, high temperature, and relatively low oxygen content), the reduction zone (moderate combustion temperature and low oxygen content), and the burnout zone (α>1, unburned particles continue to burn, and high oxygen content).

[0007] Under this technology, all pulverized coal enters the furnace from the main combustion zone, while only about 80% of the air enters from the same zone. Therefore, the main combustion zone is in a fuel-rich, oxygen-deficient combustion state. On the one hand, incomplete combustion lowers the combustion temperature (reducing localized high-temperature zones and decreasing the formation of thermal NOx); on the other hand, it creates a reducing combustion atmosphere (preventing the large-scale conversion of NOx precursors into NOx). Consequently, the NOx content generated during the intense combustion of pulverized coal is relatively low. Simultaneously, because the incomplete combustion process in the main combustion zone produces a significant amount of reducing components (CO, H2, unburned coke, etc.), the generated NOx can be effectively removed by these reducing components through homogeneous or heterogeneous reduction reactions in the suitable temperature and low oxygen content of the reducing zone, further reducing the NOx content. Then, in the burnout zone, the remaining combustion air (approximately 20%) is fed into the furnace to ensure the complete combustion of unburned components.

[0008] (2) Re-ignition technology

[0009] Reburning technology utilizes reducing reburning fuels during combustion to effectively reduce already generated NOx. For example... Figure 1 As shown, when staged combustion technology is used, reducing reburning fuel is fed into the furnace in the reduction zone, which effectively reduces the generated NOx while providing heat through combustion.

[0010] Under this technology, only 80%–90% of the fuel is fed into the furnace from the main combustion zone. Simultaneously, air staging technology maintains the main combustion zone in an oxygen-deficient combustion state, effectively reducing the NOx content generated during the intense combustion process. Meanwhile, the remaining approximately 10%–20% of the reburning fuel (reducing secondary fuels, such as pure CH4, natural gas, fuel pyrolysis gas, etc.) is fed into the furnace from the reduction zone. While releasing heat during combustion, it efficiently reduces the NOx already generated in the main combustion zone. Although a certain amount of NOx may also be generated during the combustion of this reburning fuel (some reburning fuel contains N), this area remains in an oxygen-deficient state, resulting in a low NOx content. Finally, under the action of burnout air, the fuel is fully combusted.

[0011] Prior art, disclosed in CN111140865B, is a composite reduction type low NOx emission device suitable for power plant boilers. This device includes a coal-water slurry generation mechanism, a coal-water slurry pyrolysis mechanism, and a composite reduction type combustion device. The coal-water slurry generation mechanism generates coal-water slurry and injects it into the coal-water slurry pyrolysis mechanism via a coal-water slurry spray gun, producing coal-water slurry pyrolysis gas rich in CO and H2. After separation, the coal-water slurry pyrolysis gas is fed into the reduction zone of the composite reduction type combustion device along with ammonia through a combined pyrolysis gas and ammonia nozzle (37) to remove NOx generated during combustion.

[0012] The prior art disclosed in CN105987379B discloses a boiler unit in which a pulverized coal pyrolysis furnace is used to pyrolyze pulverized coal to produce pyrolysis gas and coke. After being separated by a gas-solid separator, the pyrolysis gas is introduced into the furnace reduction zone through a reburning gas pipeline to remove the generated NOx, while the residual carbon is sent to the area above the main combustion zone through a residual carbon conveying pipeline for continued combustion.

[0013] The prior art disclosed in CN111140865B is a composite reducing low-NOx emission device suitable for power plant boilers, aiming to effectively remove NOx generated in the main combustion zone of the furnace using a composite reducing agent (coal-water slurry pyrolysis gas and ammonia). However, the pyrolysis gas mainly consists of small-molecule CO, H2, and CO2, which has limited NOx removal efficiency. Furthermore, the coal-water slurry pyrolysis gas contains a significant amount of water vapor, which, upon entering the furnace, may not only lower the combustion temperature but also increase the water vapor content in the flue gas and increase exhaust heat loss. In addition, the introduction of ammonia as a denitrification agent requires strict control of the low oxygen content to prevent the large-scale conversion of injected NH3 into NOx, which would negatively impact combustion efficiency. Simultaneously, the injection amount of ammonia fuel needs precise control to prevent excessive ammonia fuel from escaping.

[0014] The prior art disclosed in CN105987379B describes a boiler unit that uses pyrolysis gas (mainly composed of small-molecule CO, H2, CO2, etc.) as a denitrification reducing agent to remove NOx generated during combustion in the main combustion zone, while the remaining unburned coke is introduced above the main combustion zone for complete combustion. However, this scheme also suffers from low denitrification efficiency of the pyrolysis gas components.

[0015] Therefore, how to improve NOx removal efficiency and minimize NOx removal costs has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0017] In view of the above-mentioned deficiencies of the prior art, the present invention provides a low NOx emission combustion device suitable for boilers, with the aim of improving NOx removal efficiency and minimizing NOx removal costs.

[0018] To achieve the above objectives, the present invention discloses a low-NOx emission combustion device suitable for boilers, including a boiler furnace;

[0019] The boiler furnace includes a main combustion zone, a reduction zone, and a burnout zone arranged sequentially from bottom to top;

[0020] The furnace wall of the main combustion zone / reduction zone is equipped with a plurality of tar atomizing spray guns for spraying atomized tar, and the furnace wall of the reduction zone is equipped with a plurality of pyrolysis gas nozzles for spraying pyrolysis gas.

[0021] Alternatively, the furnace wall of the main combustion zone / reduction zone may be provided with several tar pyrolysis gas nozzles for injecting tar-containing pyrolysis gas.

[0022] Preferably, the cross-section of the boiler furnace is square or rectangular, or square or rectangular with chamfers, and multiple layers of burners are provided on each side of the furnace wall along the height direction of the boiler furnace; the airflow injected by the multiple layers of burners on the four sides of the furnace wall forms a rotating main airflow channel;

[0023] Each of the burners is fixed to the furnace wall of the boiler furnace or to the chamfered furnace wall between two adjacent inner walls, and the corresponding flame direction is tangent to the cylindrical channel formed by the main airflow.

[0024] Each furnace wall in the main combustion zone / reduction zone is provided with one or more tar atomizing spray guns or one or more tar pyrolysis gas nozzles within a range D on one side of the center line.

[0025] The injection direction of each of the tar atomizing spray guns or each of the tar pyrolysis gas nozzles is either tangential or antitangential to the cylindrical channel formed by the main airflow.

[0026] Preferably, each furnace wall in the main combustion zone is provided with two or more layers of tar atomizing spray guns or two or more layers of tar pyrolysis gas nozzles; the number of each layer of tar atomizing spray guns or each layer of tar pyrolysis gas nozzles is one or more.

[0027] Preferably, it further includes a combustion module for generating the heat required for pyrolysis, and a pyrolysis module for generating the tar-containing pyrolysis gas;

[0028] The combustion module includes a blower, a flue gas heat exchanger, a primary air chamber, a combustion air distribution plate, an ash collection device, a combustion chamber, a heat storage wall, a first cyclone separator, and a first return material mechanism;

[0029] The pyrolysis module consists of a fluidizing air chamber, a pyrolysis air distribution plate, a pyrolysis chamber, a second cyclone separator, and a second return material mechanism.

[0030] More preferably, the second cyclone separator is connected to all of the tar pyrolysis gas nozzles via insulated pipes.

[0031] More preferably, it also includes a tar module for separating the tar-containing pyrolysis gas into tar and pyrolysis gas;

[0032] The tar module includes an electric tar trap, a tar buffer tank, and a booster pump;

[0033] The electro-tar trap is connected to the second cyclone separator to obtain the tar-containing pyrolysis gas after gas-solid separation, separate the tar-containing pyrolysis gas into tar and pyrolysis gas, and deliver the pyrolysis gas to the pyrolysis gas nozzle and the tar to the tar buffer tank.

[0034] The tar buffer tank is connected to all the tar atomizing spray guns via an insulated pipeline equipped with a booster pump.

[0035] More preferably, the blower introduces air to exchange heat with high-temperature flue gas in the flue gas heat exchanger to form primary air and secondary air;

[0036] The primary air passes through the combustion air distribution plate above the primary air chamber, carrying the bed material and fuel above the combustion air distribution plate upward into the combustion chamber;

[0037] The secondary air is supplied into the combustion chamber from above the dense phase zone of the bed material;

[0038] The flue gas in the combustion chamber carries some fine bed material and unburned coke into the first cyclone separator;

[0039] The first cyclone separator, through centrifugal separation, inputs most of the solid particles, including bed material and unburned particles, into the first return material mechanism via the downcomer, and then sends them back to the combustion chamber to continue participating in the combustion process. The high-temperature flue gas after gas-solid separation enters the flue gas heat exchanger to release heat, which is used to heat the primary air and the secondary air required for combustion. Then, part of the flue gas enters the fluidizing air chamber of the pyrolysis module, and part of the flue gas enters the horizontal or vertical flue of the boiler furnace for heat exchange.

[0040] The combustion air distribution plate is equipped with an air cap, and the circulating heat-carrying bed material is reasonably set according to the fluidization requirements. The fuel feed port is arranged above the dense phase zone of the circulating heat-carrying bed material.

[0041] The combustion chamber is equipped with a heat storage wall at the top.

[0042] More preferably, the flue gas entering the fluidized air chamber carries the fluidized fuel particles into the pyrolysis chamber via the pyrolysis air distribution plate, so that the fluidized fuel particles are fully heated and pyrolyzed to produce pyrolysis gas and tar.

[0043] A hood is provided on the pyrolysis cloth air plate;

[0044] The pyrolysis gas containing tar is separated by the second cyclone separator, which collects the unburned particles carried out by the flue gas. These particles are then mixed with the return material from the first return mechanism via the second return mechanism, or sent separately into the combustion chamber for combustion.

[0045] More preferably, a coke collection device is provided at the bottom of the pyrolysis chamber to periodically collect unburned coke particles and send them to the combustion chamber for combustion.

[0046] The pyrolysis air distribution plate is inclined;

[0047] The pyrolysis chamber is equipped with a flue gas temperature detection device to monitor the pyrolysis temperature and maintain it within the range of 450 to 600°C.

[0048] The beneficial effects of this invention are:

[0049] This invention achieves in-situ removal of NOx during combustion by injecting tar into the high-temperature, low-oxygen main combustion zone, and by utilizing the efficient participation of tar and its pyrolysis components in the NOx conversion process.

[0050] This invention utilizes flue gas as the fluidizing and heat source gas in a pyrolysis furnace, which can economically achieve large-scale pyrolysis and ensure a high tar yield.

[0051] The following will further explain the concept, specific structure, and technical effects of the present invention in conjunction with the accompanying drawings, so as to fully understand the purpose, features, and effects of the present invention. Attached Figure Description

[0052] Figure 1 A schematic diagram of re-ignition technology in the prior art is shown.

[0053] Figure 2 The diagram shows a schematic of a device for spraying atomized tar and pyrolysis gas through a tar atomizing spray gun and a pyrolysis gas nozzle, respectively, according to an embodiment of the present invention.

[0054] Figure 3 This diagram illustrates the structure of an apparatus for injecting pyrolysis gas containing tar through a tar pyrolysis gas nozzle according to an embodiment of the present invention.

[0055] Figure 4 This diagram illustrates a tangential installation method of a tar atomizing spray gun on a wall-mounted tangential boiler according to an embodiment of the present invention.

[0056] Figure 5 This diagram illustrates a tangential installation method of a tar atomizing spray gun on a tangentially shaped boiler in one embodiment of the present invention.

[0057] Figure 6 This diagram illustrates a reverse-cut installation method of a tar atomizing spray gun on a wall-mounted tangential boiler, according to an embodiment of the present invention.

[0058] Figure 7 The diagram shows a single-layer, multi-group atomizing spray gun installation method on a wall-mounted tangential boiler according to an embodiment of the present invention. Detailed Implementation

[0059] Example: Figure 2 and Figure 3 As shown, a low NOx emission combustion device suitable for boilers includes a boiler furnace 21;

[0060] The boiler furnace 21 includes a main combustion zone, a reduction zone, and a burnout zone arranged sequentially from bottom to top;

[0061] The furnace wall in the main combustion zone / reduction zone is equipped with several tar atomizing spray guns 19 for spraying atomized tar, and the furnace wall in the reduction zone is equipped with several pyrolysis gas nozzles 20 for spraying pyrolysis gas.

[0062] Alternatively, the furnace wall in the main combustion zone / reduction zone may be equipped with several tar pyrolysis gas nozzles 22 for injecting tar-containing pyrolysis gas.

[0063] The boiler furnace 21 of this invention mainly utilizes the heat released from fuel combustion to heat the circulating working fluid (usually water) in each heating surface to generate working fluid steam, which then drives the steam turbine to generate electricity. During this process, fuel combustion produces a significant amount of NOx (mostly fuel-based, some thermal-based), and NOx removal from the flue gas requires the input of a large amount of ammonia fuel, posing a risk of ammonia escape and incurring considerable costs. Therefore, this invention utilizes tar and pyrolysis gas for denitrification during combustion, reducing the cost of subsequent flue gas denitrification. Specifically, atomized tar is sprayed into the boiler furnace 21 through a tar atomizing spray gun 19 and thoroughly mixed with the combustion flue gas. The tar and its components, such as small-molecule hydrocarbons, CO, and H2 generated during thermal cracking, reduce the generated NOx or react with NOx precursors (HCN, NH3, and other nitrogen-containing substances) to prevent NOx formation, thereby reducing the NOx content. At the same time, the pyrolysis gas (mainly CH4, CO, H2, etc.) that enters the furnace through the pyrolysis gas nozzle 20 is used to reduce the NOx that has been generated, thereby further reducing the NOx content in the flue gas.

[0064] Alternatively, pyrolysis gas containing tar can be directly sent to the boiler furnace 21 through an insulated pipe, and then sent into the boiler furnace 21 through the tar pyrolysis gas nozzle 22 installed in the main combustion zone or reduction zone of the boiler furnace 21. At the same time, the pyrolysis gas and tar are used to achieve efficient removal of NOx during the combustion process.

[0065] This invention utilizes tar to efficiently remove NOx during the combustion process, thereby reducing the cost of flue gas denitrification.

[0066] In traditional reburning schemes, pyrolysis gas is mainly used as a reducing component to react with NOx already generated during combustion, thereby reducing the NOx content in the flue gas. However, studies have shown that compared with tar cracking components, CH4, CO, H2, etc., are not as efficient at reducing already generated NOx.

[0067] Therefore, this invention utilizes tar components and their pyrolysis products to participate in the NOx conversion process, that is, to undergo a reduction reaction with already generated NOx, or to react directly with NOx precursors (HCN, NH3, etc.), thus avoiding the generation of large amounts of NOx. Therefore, this invention can more efficiently reduce the NOx content during combustion and lower the cost of flue gas denitrification.

[0068] This invention utilizes combustion flue gas with an oxygen content of 3% to 4% by volume as a pyrolysis atmosphere to prevent excessive fuel gasification and increase tar yield.

[0069] In large-scale industrial applications, fuel gasification is often used to generate pyrolysis gas, which is then used in the re-combustion process to reduce NOx emissions. Therefore, the pyrolysis atmosphere is typically air or water vapor. The gaseous volatiles produced under this atmosphere are mostly pyrolysis gases (primarily H2, CO, CO2, etc., with low levels of hydrocarbons like CH4), while the tar content is low, thus limiting the reduction effect on NOx. To obtain a higher tar yield using pyrolysis, N2 or inert gases are usually used as the pyrolysis atmosphere, resulting in higher costs for industrial applications.

[0070] This invention proposes using the high-temperature flue gas after combustion in the combustion chamber as a fluidizing carrier, which also functions as a heat carrier. This enables the complete pyrolysis of fuel at extremely low oxygen levels, generating a large amount of tar along with the pyrolysis gas, which is then used in the subsequent tar denitrification process. Furthermore, by using high-temperature flue gas as the heat transfer fluid, this invention avoids the drawbacks of using circulating bed material as the heat carrier in some engineering practices (bed material circulation consumes energy), effectively improving the energy utilization efficiency of the device.

[0071] In some embodiments, the cross-section of the boiler furnace 21 is square or rectangular, or square or rectangular with chamfers, and multiple layers of burners are provided on each side of the furnace wall along the height direction of the boiler furnace 21; the airflow injected by the multiple layers of burners on the four sides of the furnace wall forms a rotating main airflow channel;

[0072] Each burner is fixed on the furnace wall of the boiler furnace 21 or on the chamfered furnace wall between two adjacent inner walls, and the corresponding flame direction is tangent to the cylindrical channel formed by the main airflow.

[0073] On each furnace wall of the main combustion zone / reduction zone, within a range D on one side of the center line, there is one or more tar atomizing spray guns 19 or one or more tar pyrolysis gas nozzles 22.

[0074] When the injection direction of the tar atomizing spray gun 19 or the tar pyrolysis gas nozzle 22 is tangential to the cylindrical channel formed by the main airflow, the D value shall not be greater than 2 / 3 of the half width of the furnace and shall be between the burner and the centerline of the furnace; when the injection direction of the tar atomizing spray gun 19 or the tar pyrolysis gas nozzle 22 is reverse tangential to the cylindrical channel formed by the main airflow, the D value shall not be greater than 2 / 3 of the half width of the furnace.

[0075] The spray direction of each tar atomizing spray gun 19 or each tar pyrolysis gas nozzle 22 is either tangential or antitangential to the cylindrical channel formed by the main airflow.

[0076] like Figures 4 to 7 As shown, in some embodiments, each furnace wall in the main combustion zone is provided with two or more layers of tar atomizing spray guns 19 or two or more layers of tar pyrolysis gas nozzles 22; the number of each layer of tar atomizing spray guns 19 or each layer of tar pyrolysis gas nozzles 22 is one or more.

[0077] In practical applications, there are multiple options for the arrangement of the tar atomizing spray gun 19 on the boiler furnace 21.

[0078] like Figures 4 to 7 As shown, the tar atomizing spray gun 19 can be installed on a wall-mounted tangentially round boiler with a square / rectangular cross-section. Figure 4 It can also be installed on a square / rectangular boiler with chamfered corners. Figure 5 ), which can be tangential to the cylindrical channel formed by the main airflow ( Figure 4 , Figure 5 It can also be reverse-tangential with the cylindrical channel formed by the main airflow. Figure 6 ), allowing for the installation of a single spray gun on each wall ( Figures 4 to 6 Multiple spray guns can also be installed. Figure 7 It can be installed in one layer or multiple layers along the height of the boiler furnace 21 (not shown in the diagram).

[0079] There are several ways to install the tar pyrolysis gas nozzle 22 in the boiler furnace 21: it can be wall-mounted, corner-mounted, or a combination of both; it can be tangential to or counter-tangential to the main airflow in the furnace; it can be a single nozzle or multiple nozzles installed on each wall; it can be installed in one layer or multiple layers along the height of the boiler furnace 21 (no schematic diagram provided); it can be installed in the main combustion zone, the burnout zone, or both.

[0080] In some embodiments, the system further includes a combustion module for generating the heat required for pyrolysis and a pyrolysis module for generating tar-containing pyrolysis gas.

[0081] The combustion module includes a blower 1, a flue gas heat exchanger 2, a primary air chamber 3, a combustion air distribution plate 4, an ash collection device 5, a combustion chamber 6, a heat storage wall 7, a first cyclone separator 8, and a first return material mechanism 9;

[0082] The pyrolysis module consists of a fluidizing air chamber 10, a pyrolysis air distribution plate 11, a pyrolysis chamber 13, a second cyclone separator 14, and a second return material mechanism 15.

[0083] In some embodiments, the second cyclone separator 14 is connected to all tar pyrolysis gas nozzles 22 via insulated pipes.

[0084] In practical applications, the pyrolysis gas containing tar, after being separated by the second cyclone separator 14, is directly sent to the boiler furnace 21 through an insulated pipe. It is then connected to the pyrolysis gas nozzle 22 installed in the main combustion zone of the boiler furnace 21 and sent into the boiler furnace 21. At the same time, the pyrolysis gas and tar are used to achieve efficient removal of NOx during the combustion process.

[0085] In some embodiments, a tar module is also included for separating tar-containing pyrolysis gas into tar and pyrolysis gas;

[0086] The tar module includes an electro-tar trap 16, a tar buffer tank 17, and a booster pump 18;

[0087] The tar trap 16 is connected to the second cyclone separator 14 to obtain tar-containing pyrolysis gas after gas-solid separation, separates the tar-containing pyrolysis gas into tar and pyrolysis gas, and delivers the pyrolysis gas to the pyrolysis gas nozzle 20 and the tar to the tar buffer tank 17.

[0088] The tar buffer tank 17 is connected to all the tar atomizing spray guns 19 via an insulated pipeline equipped with a booster pump 18.

[0089] In practical applications, the tar-containing pyrolysis gas after gas-solid separation enters the electric tar collector 16, where the tar is captured under the action of an electric field and then stored in the tar buffer tank 17. Subsequently, it is pressurized by the booster pump 18 and sent to the tar atomizing spray gun 19.

[0090] The tar buffer tank 17 and its upstream and downstream pipelines require insulation to maintain good tar fluidity, facilitating delivery to the tar atomizing spray gun 19 via the booster pump 18. The purpose of the tar buffer tank 17 is to continuously supply the stored tar to the tar atomizing spray gun 19 during coke collection in the pyrolysis chamber, thereby reducing the NOx content generated during combustion in the boiler furnace 21.

[0091] In some embodiments, blower 1 introduces air, which exchanges heat with high-temperature flue gas in flue gas heat exchanger 2 to form primary air and secondary air;

[0092] The primary air passes through the combustion air distribution plate 4 above the primary air chamber 3, carrying the bed material and fuel above the combustion air distribution plate 4 upward into the combustion chamber 6. In practical applications, the primary air mainly serves to fluidize the bed material / fuel and provide oxygen for the initial stage of combustion. The preheated primary air first enters the primary air chamber 3, and then enters the combustion chamber 6 through the combustion air distribution plate 4, carrying the bed material and fuel above the combustion air distribution plate 4 upward to complete the fuel combustion process.

[0093] Secondary air is supplied to combustion chamber 6 from above the dense phase zone of the bed material; in practical applications, secondary air provides the remaining air required for fuel combustion.

[0094] The flue gas in combustion chamber 6 carries some fine bed material and unburned coke into the first cyclone separator 8;

[0095] During combustion, by properly controlling the fluidizing velocity, the flue gas can carry some fine bed material and unburned coke into the first cyclone separator 8.

[0096] The first cyclone separator 8, through centrifugal separation, inputs most of the solid particles, including bed material and unburned particles, into the first return material mechanism 9 via the downcomer, and then sends them back to the combustion chamber 6 to continue participating in the combustion process. The high-temperature flue gas after gas-solid separation enters the flue gas heat exchanger 2 to release heat, which is used to heat the primary and secondary air required for combustion. Then, part of the flue gas enters the fluidized air chamber 10 of the pyrolysis module, and part of the flue gas enters the horizontal or vertical flue of the boiler furnace 21 for heat exchange.

[0097] An air cap is installed on the combustion air distribution plate 4, and the circulating heat-carrying bed material is reasonably set according to the fluidization requirements. The fuel feed port is arranged above the dense phase zone of the circulating heat-carrying bed material.

[0098] In practical applications, the bed material and fuel are piled on the combustion air distribution plate, and the bed material is fluidized by primary air blowing.

[0099] The type and quantity of circulating heat transfer bed material should be set appropriately to facilitate fluidization.

[0100] The bed material circulates primarily within the combustion chamber, where the high temperature allows for rapid heating of newly supplied fuel.

[0101] The combustion chamber 6 is equipped with a heat storage wall 7 at the top. In practical applications, the heat from fuel combustion can be fully utilized to heat the flue gas entering the fluidized air chamber 10. The material of the heat storage wall 7 can be selected according to actual needs.

[0102] In some embodiments, the flue gas entering the fluidized air chamber 10 carries the fluidized fuel particles into the pyrolysis chamber 13 after passing through the pyrolysis air distribution plate 11, so that the fluidized fuel particles are fully heated and pyrolyzed to produce pyrolysis gas and tar.

[0103] A hood is installed on the pyrolysis air distribution plate 11;

[0104] The pyrolysis gas containing tar is separated by the second cyclone separator 14, which collects the unburned particles carried out by the flue gas. The unburned particles are then mixed with the return material from the first return mechanism 9 via the second return mechanism 15, or sent separately to the combustion chamber 6 for combustion.

[0105] In some embodiments, a coke collection device 12 is installed at the bottom of the pyrolysis chamber 13. This device periodically collects unburned coke particles and sends them to the combustion chamber 6 for combustion. Since the fluidized air in the pyrolysis chamber 13 is flue gas with extremely low oxygen content, after the fuel in the pyrolysis chamber 13 undergoes pyrolysis to release pyrolysis gas and tar, the remaining solid coke cannot be fully burned. Furthermore, because the pyrolysis chamber 13 is in a fluidized bed state, unburned particles cannot be effectively carried to the second cyclone separator 14 and then fed into the combustion chamber 6 via the second return material mechanism 15 for combustion. Therefore, the coke collection device 12 is necessary. In practical applications, a pneumatic conveying method can be selected to deliver the periodically collected coke into the combustion chamber 6.

[0106] The pyrolysis air distribution plate 11 is inclined; in practical applications, this makes it easier to collect unburned particles.

[0107] A flue gas temperature detection device is installed in pyrolysis chamber 13 to monitor the pyrolysis temperature and maintain it within the range of 450–600℃. In practical applications, the pyrolysis temperature is adjusted according to different fuels, typically within the range of 450–600℃, to maximize tar production.

[0108] In some embodiments, the boiler furnace 21 further includes a primary air-coal nozzle, a secondary air nozzle connected to the burner, and a burnout air nozzle connected to the burnout zone.

[0109] In practical applications, heating surfaces of various levels are arranged in the upper part of the furnace and in the horizontal / vertical flues, which can be determined according to actual needs.

[0110] In practical applications, the position of the tar atomizing spray gun 19 / tar pyrolysis gas nozzle 22 on the boiler furnace can be adjusted.

[0111] In addition to the horizontal position of the tar atomizing spray gun 19 on the boiler furnace 21 being freely adjustable, its vertical position in the boiler furnace 21 can also be adjusted as needed. For example, it can be arranged in the main combustion zone of the boiler furnace 21 (to react with NOx precursors and generated NOx), or in the reburning zone, i.e., the reduction zone, to react with already generated NOx, or in the upper part of the reduction zone near the bottom of the burnout zone.

[0112] The pyrolysis gas nozzle 20 is the same as the tar atomizing spray gun 19, and can be adjusted as needed in the horizontal position on the boiler furnace 21 and in the vertical direction of the boiler furnace 21.

[0113] Arrangement of burners and secondary / tertiary air nozzles in boiler furnace 21

[0114] The arrangement of the burners and secondary / tertiary air nozzles on the boiler furnace 21 can be set according to the actual situation. That is, it can be corner installation (four corners cut circle), wall installation (wall cut circle), or a combination of wall and corner installation (mixed cut circle).

[0115] Methods for separating tar and pyrolysis gas

[0116] The separation of tar from pyrolysis gas can be achieved using either an electrostatic tar trap or a cooling tar separator (which separates the gas and liquid by condensing the tar through cooling). When using a cooling heat exchanger, the heat from the pyrolysis gas containing tar can be absorbed by the heat exchange equipment and used for subsequent tar cooling heating and insulation of tar pipelines.

[0117] Feeding method in the pyrolysis chamber

[0118] The pyrolysis chamber uses a fixed-bed intermittent feeding method, therefore, residual solid coke needs to be collected periodically. Under suitable conditions, a chain grate furnace or a reciprocating grate furnace can be used to achieve stable continuous feeding.

[0119] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A low-NOx emission combustion device suitable for boilers; characterized in that, Including the boiler furnace (21); The boiler furnace (21) includes a main combustion zone, a reduction zone and a burnout zone arranged sequentially from bottom to top; The furnace wall of the main combustion zone / reduction zone is provided with a number of tar atomizing spray guns (19) for spraying atomized tar, and the furnace wall of the reduction zone is provided with a number of pyrolysis gas nozzles (20) for spraying pyrolysis gas. Alternatively, the furnace wall of the main combustion zone / reduction zone may be provided with several tar pyrolysis gas nozzles (22) for injecting tar-containing pyrolysis gas.

2. The low NOx emission combustion device for boilers according to claim 1, characterized in that, The cross-section of the boiler furnace (21) is square / rectangular or square / rectangular with chamfers. Multiple burners are provided on each side of the furnace wall along the height direction of the boiler furnace (21). The airflow injected by the multiple burners on the four sides of the furnace wall forms a rotating main airflow channel. Each of the burners is fixed to the furnace wall of the boiler furnace (21) or the chamfered furnace wall between two adjacent inner walls, and the corresponding flame direction is tangent to the cylindrical channel formed by the main airflow. Each furnace wall of the main combustion zone / reduction zone is provided with one or more of the tar atomizing spray guns (19) or one or more of the tar pyrolysis gas nozzles (22) within a range D on one side of the center line. The spray direction of each of the tar atomizing spray guns (19) or each of the tar pyrolysis gas nozzles (22) is either tangential or antitangential to the cylindrical channel formed by the main airflow.

3. The low NOx emission combustion device for boilers according to claim 1, characterized in that, Each furnace wall in the main combustion zone is provided with two or more layers of the aforementioned tar atomizing spray guns (19) or two or more layers of the aforementioned tar pyrolysis gas nozzles (22); the number of each layer of the aforementioned tar atomizing spray guns (19) or each layer of the aforementioned tar pyrolysis gas nozzles (22) is one or more.

4. The low-NOx emission combustion device for boilers according to claim 1, characterized in that, It also includes a combustion module for generating the heat required for pyrolysis, and a pyrolysis module for generating the tar-containing pyrolysis gas; The combustion module includes a blower (1), a flue gas heat exchanger (2), a primary air chamber (3), a combustion air distribution plate (4), an ash collection device (5), a combustion chamber (6), a heat storage wall (7), a first cyclone separator (8), and a first return material mechanism (9). The pyrolysis module consists of a fluidizing air chamber (10), a pyrolysis air distribution plate (11), a pyrolysis chamber (13), a second cyclone separator (14), and a second return material mechanism (15).

5. The low NOx emission combustion device for boilers according to claim 4, characterized in that, The second cyclone separator (14) is connected to all the tar pyrolysis gas nozzles (22) via insulated pipes.

6. The low NOx emission combustion device for boilers according to claim 4, characterized in that, It also includes a tar module for separating the tar-containing pyrolysis gas into tar and pyrolysis gas; The tar module includes an electric tar trap (16), a tar buffer tank (17), and a booster pump (18). The electro-tar trap (16) is connected to the second cyclone separator (14) to obtain the tar-containing pyrolysis gas after gas-solid separation, separate the tar-containing pyrolysis gas into tar and pyrolysis gas, and deliver the pyrolysis gas to the pyrolysis gas nozzle (20) and deliver the tar to the tar buffer tank (17). The tar buffer tank (17) is connected to all the tar atomizing guns (19) via an insulated pipeline equipped with the booster pump (18).

7. The low NOx emission combustion device for boilers according to claim 4, characterized in that, The blower (1) introduces air, which exchanges heat with high-temperature flue gas in the flue gas heat exchanger (2) to form primary air and secondary air; After the primary air passes through the combustion air distribution plate (4) above the primary air chamber (3), it carries the bed material and fuel above the combustion air distribution plate (4) upward into the combustion chamber (6). The secondary air is sent into the combustion chamber (6) from above the dense phase zone of the bed material. The flue gas in the combustion chamber (6) carries some fine bed material and unburned coke into the first cyclone separator (8). The first cyclone separator (8) centrifugally separates most of the solid particles, including bed material and unburned particles, into the first return material mechanism (9) through the downcomer, and then sends them back to the combustion chamber (6) to continue participating in the combustion process. The high-temperature flue gas after gas-solid separation enters the flue gas heat exchanger (2) to release heat and heat the primary air and secondary air required for combustion. Then, part of the flue gas enters the fluidized air chamber (10) of the pyrolysis module, and part of the flue gas enters the horizontal or vertical flue of the boiler furnace (21) for heat exchange. The combustion air distribution plate (4) is equipped with an air cap, and the circulating heat-carrying bed material is reasonably set according to the fluidization requirements. The fuel feed port is arranged above the dense phase zone of the circulating heat-carrying bed material. The combustion chamber (6) is provided with a heat storage wall (7) at the top.

8. The low NOx emission combustion device for boilers according to claim 7, characterized in that, The flue gas entering the fluidized air chamber (10) carries the fluidized fuel particles into the pyrolysis chamber (13) after passing through the pyrolysis air distribution plate (11), so that the fluidized fuel particles are fully heated and pyrolyzed to produce pyrolysis gas and tar. A wind cap is provided on the pyrolysis air distribution plate (11); The tar-containing pyrolysis gas is separated by the second cyclone separator (14), and the unburned particles carried out by the flue gas are collected and mixed with the return material of the first return material mechanism (9) via the second return material mechanism (15), or sent separately into the combustion chamber (6) for combustion.

9. The low NOx emission combustion device for boilers according to claim 8, characterized in that, The bottom of the pyrolysis chamber (13) is equipped with a coke collection device (12), which periodically collects unburned coke particles and sends them to the combustion chamber (6) for combustion. The pyrolysis air distribution plate (11) is set at an angle; A flue gas temperature detection device is installed in the pyrolysis chamber (13) to monitor the pyrolysis temperature and maintain the pyrolysis temperature in the range of 450 to 600°C.

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