A grate-fired boiler and a method of operating the same

Abstract

The present application discloses a layer combustion boiler and its working method, the layer combustion boiler comprises a wind chamber, a grate and a hearth, and further comprises: a combustion chamber arranged above the grate and at the front side of the hearth; a combined quick cooling and heat exchange device: a wind cooling, water cooling and secondary circulating flue gas cooling and heat exchange system is installed between the front supply and the rear arch, which is used for rapidly reducing the center temperature of the hearth and inhibiting the generation of nitrogen dioxide and sulfur dioxide; a secondary air system comprises a first subsystem, the first subsystem is communicated with an outdoor combustion-supporting air pipeline, the secondary flue gas and the combustion-supporting air are mixed and then enter an air superheater and are introduced into the wind chamber; a second subsystem is used for dividing the secondary air into a second part and introducing the second part into an air pipe and spraying the secondary air from the air pipe to form an air curtain; and a third subsystem is used for dividing the secondary air into a third part and introducing the third part into the hearth from the rear side of the hearth. The combined quick cooling and heat exchange device can be independently installed and used, or can be installed and used in combination with the combustion chamber arranged above the grate and at the front side of the hearth.

Description

Technical Field

[0001] This invention relates to the field of boiler technology, and in particular to a stoker-fired boiler and its operating method. Background Technology

[0002] Stoker-fired boilers produce nitrogen oxides (NOx) during combustion. x Nitrogen oxides (NOx) produce harmful gases such as nitrogen oxides (NOx) and sulfides. The mechanisms of NOx formation are complex, mainly including thermal, rapid, and fuel-related processes. Thermal NOx refers to the formation of NOx from the oxidation of nitrogen in the air at high temperatures. x "Rapid combustion" refers to the reaction between nitrogen in the air and hydrocarbon ions in the fuel, such as CH4, during combustion to produce NO. x Fuel type refers to NO produced when nitrogen compounds in fuel undergo thermal decomposition and subsequent oxidation during combustion. x The sulfides produced during combustion are mainly due to the presence of sulfur in fuels such as coal.

[0003] To remove nitrogen oxides, denitrification technology is mainly used. Currently common denitrification technologies include selective catalytic reduction (SCR) and selective non-catalytic reduction (SNCR). The main drawbacks of SCR technology are that, due to the complex composition of flue gas, some pollutants can poison the catalyst; highly dispersed dust particles can cover the catalyst surface, reducing its activity; unreacted NH3 and SO2 in the flue gas react to generate ammonium sulfate and ammonium bisulfate, which easily corrode and clog equipment, while also reducing ammonia utilization, resulting in higher investment and operating costs. The biggest difference between SNCR and SCR is that it does not require a catalyst; the entire reduction process takes place inside the boiler, eliminating the need for a separate reactor. However, when the ammonia reducing agent is injected into the furnace, it can easily cause ammonia escape and also lower the furnace temperature, reducing combustion efficiency.

[0004] In addition, some low-NOx combustion technologies exist that can reduce the proportion of nitrogen in the combustion environment to a certain extent, thereby reducing the burden of subsequent denitrification. However, these technologies still have certain limitations in terms of combustion efficiency.

[0005] Therefore, this invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a stoker-fired boiler and its operating method, which can reduce the generation of nitrogen oxides and improve the combustion efficiency of the stoker-fired boiler.

[0007] To address the above problems, embodiments of the present invention provide a stoker-fired boiler, comprising a wind chamber, a grate, and a furnace, wherein the stoker-fired boiler further comprises:

[0008] A combustion chamber is provided above the grate and at the front of the furnace, and the combustion chamber is in communication with the interior of the furnace.

[0009] Combined rapid cooling heat exchange device: An air-cooled, water-cooled and secondary circulating flue gas cooling heat exchange system is installed between the front supply and the rear arch to rapidly reduce the furnace center temperature and suppress the generation of nitrogen dioxide and sulfur dioxide.

[0010] A secondary air system; the secondary air in the secondary air system is flue gas extracted from the boiler exhaust gas and returned to the boiler for recycling; the secondary air system includes:

[0011] The first subsystem, which is connected to the air chamber, is used to divert secondary air out of the first part and introduce it into the air chamber, and then into the combustion chamber and the furnace.

[0012] The second subsystem is connected to the air duct and is used to divert secondary air from the second part and introduce it into the air duct. The air duct is provided with an air outlet facing the grate, so that the secondary air of the second part is ejected from the air duct to form an air curtain. The combustion chamber and the furnace are located on both sides of the air curtain, and the airflow at the bottom of the air curtain contacts the coal on the grate.

[0013] The third subsystem is used to divert secondary air out of the third section and introduce it into the interior of the furnace from the rear side.

[0014] Optionally, the secondary air accounts for approximately 10-35% of the total boiler flue gas (adjustable according to operating conditions).

[0015] Optionally, a desulfurizing agent may also be circulated inside the duct.

[0016] Optionally, the second subsystem further includes a gas distribution manifold for introducing the second portion of secondary air. The gas distribution manifold includes a first branch and a second branch. The first branch is connected to the air duct, and the second branch is connected to the third subsystem, thereby introducing a portion of the second portion of secondary air into the air duct and another portion into the third subsystem. This results in the gas introduced into the furnace by the third subsystem comprising two streams: the first stream is a portion of the second portion of secondary air introduced from the second branch, and the second stream is the secondary air of the third portion.

[0017] Furthermore, a circulating water pipe is also fitted on the outside of the air duct, thus forming a combined cooling structure in which the circulating water pipe covers the air duct.

[0018] Furthermore, multiple air ducts are arranged in parallel, and the tops of each air duct are connected together by a circulating air manifold. A circulating water manifold is fitted over the outside of the circulating air manifold, and the bottom of the circulating water manifold is connected to a number of circulating water distribution pipes corresponding to the number of air ducts. Each circulating water distribution pipe is fitted over the outside of the air duct, and the bottoms of each circulating water distribution pipe converge to a circulating water distribution pipe. The bottom of the air duct extends from the bottom of the circulating water distribution pipe, and the air outlet and a gas nozzle connected to the air outlet are provided on the extended part.

[0019] Furthermore, the circulating water pipe includes a circulating water manifold pipe, the bottom of which is connected to multiple circulating water diversion pipes, and the bottoms of each circulating water diversion pipe converge to the circulating water diversion pipe.

[0020] Multiple air ducts are arranged in parallel, and the tops of each air duct are connected together by a circulating air manifold; the circulating water drain pipe is sleeved on the outside of the circulating air manifold.

[0021] The bottom of the air duct extends from the bottom of the circulating water pipe, and the air outlet and the gas nozzle connected to the air outlet are provided on the extended part.

[0022] Furthermore, the gas nozzle is replaceable and made of wear-resistant and heat-resistant cast iron material.

[0023] Furthermore, during assembly, the circulating air manifold is first placed into the circulating water pipe, and the position of the gas nozzle is accurately located for welding. Then, the air duct is sealed with a ring weld.

[0024] Furthermore, the surface of the combined cooling structure forms a combustion surface, and the combustion surface is coated with a wear-resistant and thermally conductive castable.

[0025] Optionally, the outer wall of the combustion chamber is also coated with an anti-coking superconducting castable.

[0026] Optionally, the anti-coking superconducting castable comprises the following components in parts by weight:

[0027] 25-50 parts aggregate;

[0028] 10-25 parts of silicon carbide;

[0029] 1-3 parts of flake graphite;

[0030] 3-5 parts silica fume;

[0031] 2-3 parts of metakaolin;

[0032] 3-5 parts mullite powder;

[0033] 2-3 parts of fused cement;

[0034] 4-6 parts of CA-70 pure calcium aluminate;

[0035] 2-3 parts of α-alumina;

[0036] 2-3 parts of high-alumina micro powder;

[0037] 2-3 parts of burnt gemstone powder;

[0038] Borax 0.1-0.2 parts;

[0039] 0.1-0.2 parts of explosion-proof fiber;

[0040] Sodium tripolyphosphate 0.1-0.2 parts;

[0041] 1-2 parts of metallic aluminum powder.

[0042] Optionally, it also includes a flue connected to the furnace, the flue being equipped with a flue gas analysis device for controlling the air volume of the secondary air in the first part, the second part, and the third part according to the composition and content of the flue gas.

[0043] Optionally, if a desulfurizing agent is also present in the duct, the flue gas analysis device further controls the amount of desulfurizing agent used based on the composition and content of the flue gas.

[0044] Optionally, it also includes a flue connected to the furnace, and the flue is also connected to a low-temperature denitrification device.

[0045] Optionally, the flue of the stoker boiler is also connected to a flue gas condensation device.

[0046] The above-mentioned operating method of the stoker-fired boiler includes:

[0047] Through the first subsystem, the secondary air is diverted from the first part and introduced into the air chamber, then enters the combustion chamber to gasify the fuel, and is further sent into the furnace.

[0048] The secondary air is diverted from the second part through the second subsystem and introduced into the air duct, so that the secondary air of the second part is ejected from the air duct to form an air curtain that impacts the coal on the grate, while the air curtain separates the combustion chamber from the bottom of the furnace.

[0049] The secondary air is diverted from the third section through the third subsystem and introduced into the furnace from the front side of the furnace.

[0050] Compared with the prior art, the present invention has the following beneficial effects: The present invention divides a portion of the secondary air in the secondary air system of a stoker boiler into three streams, which respectively pass through the air chamber to the combustion chamber located in the rear arch, enter the air curtain through the air duct, and enter the furnace through the duct in the front arch. The first part of the secondary air can fully gasify the coal and introduce it into the furnace, diluting the nitrogen content in the furnace. The air curtain formed by the second part of the secondary air can seal the surface of the coal layer regardless of its thickness, thereby separating the combustion chamber and the furnace on both sides of the air curtain. At the same time, it can also improve the combustion efficiency near the air curtain. The airflow from the air curtain is from top to bottom, while the airflow from the air chamber is from bottom to top. The two airflows can create an impact, increasing the airflow disturbance and further improving the combustion efficiency. The third part of the secondary air enters from the front arch, making up for the lack of secondary air near the front arch, and complementing the first and second parts of the secondary air to further improve the combustion efficiency. Attached Figure Description

[0051] Figure 1 This is a schematic diagram of the structure of a stoker-fired boiler provided in an embodiment of the present invention;

[0052] Figure 2 for Figure 1 Enlarged structural diagram of the duct section;

[0053] Figure 3 This is a side view of the duct section in one embodiment;

[0054] Figure 4 This is a schematic diagram of the combined cooling structure in one embodiment;

[0055] Figure 5 This is a schematic diagram of the combined cooling structure in another embodiment;

[0056] Figure 6 This is a graph showing the thermal conductivity system count test results of anti-coking superconducting castable and ordinary castable in this embodiment of the invention;

[0057] Figure 7 The graph shows the test results of the mechanical properties and refractoriness of the anti-coking superconducting castable in the embodiments of the present invention;

[0058] Figure 8 This is a schematic diagram of the main structure of the cooling device in the furnace.

[0059] Figure 9 This is a side view of the cooling device in the furnace.

[0060] In the diagram: 1-Air chamber; 2-Grate; 3-Furnace; 31-Rear arch; 32-Front arch; 4-Combustion chamber; 41-Opening; 42-Side wall; 5-Flue gas outlet; 6-Main flue gas duct; 7-Flue gas circulation duct; 8-Secondary air box; 9-First duct; 10-Air pipe; 11-Second duct; 12-Air outlet; 13-Air curtain; 14-Coal seam; 15-Third duct; 16-Feeding cone; 17-Feeding pipe; 18-Flue gas analyzer; 19-Dust collector; 20-Low temperature denitrification device; 21-Desulfurization device; 22-Chimney; 23-Screw feeder; 24-Conveying fan; 25-Gas distribution box; 26-Nozzle; 27-Fan; 28 29-First header pipe; 30-Second header pipe; 31-Circulating air header pipe; 32-Circulating water header pipe sleeve; 33-Circulating water distribution pipe; 34-Gas nozzle; 35-Circulating water header pipe; 36-Annular pipe sealing welding point; 51-Outlet pipe; 52-Hot water collector; 53-Flue gas circulation conveying pipe; 54-Hot water distributor; 55-Circulating flue gas nozzle; 56-Distributor connecting pipe; 57-First circulating flue gas main pipe; 58-Second circulating flue gas main pipe; 59-Circulating water inlet main pipe; 510-Inlet pipe; 511-Circulating water outlet main pipe; 512-Water pipe support device; 517-Side furnace wall. Detailed Implementation

[0061] The principles and spirit of the invention will now be described with reference to several exemplary embodiments illustrated in the accompanying drawings. It should be understood that these embodiments are described merely to enable those skilled in the art to better understand and implement the invention, and are not intended to limit the scope of the invention in any way.

[0062] Please refer to Figures 1-3 This invention provides a stoker-fired boiler, including a wind chamber 1, a grate 2 disposed above the wind chamber 1, and a furnace 3, the furnace 3 including a front arch 32 and a rear arch 31. Furthermore, the stoker-fired boiler also includes:

[0063] A combustion chamber 4 is provided above the grate 2 and in front of the furnace 3, and the combustion chamber 4 is in communication with the interior of the furnace 3. For example, the combustion chamber 4 may have an opening 41 above it, which is in communication with the interior of the furnace 3.

[0064] The stoker-fired boiler also includes a secondary air system. In this embodiment, the boiler furnace 3 has a flue gas outlet 5 connected to a main flue gas duct 6. A secondary air system is connected to the main flue gas duct 6. As an example, a flue gas circulation duct 7 is branched off from the main flue gas duct 6 and connected to a secondary air box 8, thereby extracting the boiler exhaust gas for reuse within the boiler. Therefore, this gas has already undergone combustion once relative to the initial air in the furnace 3, hence the name "secondary air." Furthermore, the secondary air system is further divided into three subsystems: a first subsystem, a second subsystem, and a third subsystem. Wherein:

[0065] The first subsystem, connected to air chamber 1, is used to divert secondary air from the first part and introduce it into air chamber 1, which then enters combustion chamber 4 and furnace 3. As an example, a first pipe 9 can be drawn from the air box of the secondary air system (the airflow entering the air chamber through pipe 9 is mutually adjustable with the airflow of the original air chamber; natural air can be added to the airflow of the original air chamber to meet the oxygen demand for combustion under operating conditions). This pipe then enters air chamber 1 of the stoker-fired boiler. At this time, the air from the secondary air system is introduced into air chamber 1. Specifically, the first part of the secondary air from air chamber 1 corresponding to combustion chamber 4 enters combustion chamber 4, and the first part of the secondary air from air chamber 1 corresponding to furnace 3 enters furnace 3. Since the secondary air is the flue gas after combustion, which contains sulfides, nitrogen oxides, carbon oxides, and other gases relative to the initial air in the furnace, its recirculation into the furnace can dilute the nitrogen ratio in combustion chamber 4 and furnace 3, thus promoting a low-NOx combustion environment. On the other hand, after the first portion of secondary air enters combustion chamber 4, it helps to gasify some of the coal into CO before it is sent into furnace 3, further diluting the nitrogen content. Additionally, gasification promotes more complete combustion, improving combustion efficiency. Furthermore, as circulating flue gas, the secondary air itself has a higher temperature, which also raises the temperature inside furnace 3, further enhancing combustion efficiency. In other embodiments, the first subsystem is connected to an outdoor combustion air duct, and the secondary flue gas mixes with the combustion air before entering the air chamber through an air superheater.

[0066] The second subsystem, connected to the duct 10, is used to divert secondary air from the second part and introduce it into the duct 10. For example, the secondary air from the second part can be drawn out through the second pipe 11 drawn from the secondary air box 8, and then further connected to the duct 10. In this embodiment, the duct 10 can be fixed to the side wall of the combustion chamber 4 near the furnace 3.

[0067] The air duct 10 is provided with an air outlet 12 facing the grate, so that the secondary air of the second part is ejected from the air duct 10 and impacts the surface of the coal bed to form an air curtain 13. The air curtain 13 separates the bottom of the combustion chamber 4 and the bottom of the furnace 3 from each other, that is, the two sides of the air curtain 13 are the combustion chamber 4 and the furnace 3 respectively.

[0068] Since the thickness of the coal layer 14 on the grate 2 is not fixed, the initial laying thickness of the coal layer varies depending on the working conditions. In addition, during the operation of the stoker boiler, the thickness of the coal layer 14 will gradually become thinner as the coal layer 14 burns. However, since the position of the bottom of the combustion chamber 4 is fixed, it cannot be guaranteed that the bottom of the combustion chamber 4 can completely fit with the coal layer 14 under each coal layer thickness. If they cannot fit, a barrier cannot be formed between the bottom of the combustion chamber 4 and the bottom of the furnace 3. In this way, the secondary air that has just entered the combustion chamber 4 may not have time to help the coal gasification before flowing away through the gap between the bottom of the combustion chamber 4 and the bottom of the furnace 3. Therefore, in this embodiment of the invention, an air duct 10 is provided at the bottom of the side wall 42 of the combustion chamber 4 to form an air curtain 13. The advantage of the air curtain 13 is that the farthest distance of the airflow depends on the position of the coal layer 14. That is, no matter how the thickness of the coal layer 14 changes, the airflow will stop only after it comes into contact with the coal layer 14. In this way, the thickness of the coal layer 14 can be disregarded, and a barrier can be formed between the bottom of the combustion chamber 4 and the bottom of the furnace 3 at all times, ensuring the gasification effect in the combustion chamber 4.

[0069] In addition, the advantage of setting up the air curtain 13 is that the airflow of the air curtain 13 is from top to bottom, while the airflow from the air chamber 1 (including the primary air and the secondary air of the first part) is from bottom to top. The two airflows can form an impact, increase the turbulence of the airflow, and further improve the combustion efficiency.

[0070] In some embodiments, the air outlet on the duct includes a plurality of spaced holes. In other embodiments, the air outlet may be designed as a single continuous elongated hole, resulting in a more continuous air curtain.

[0071] The third subsystem is used to divert secondary air from the third section and introduce it into the interior of the furnace 3 from the rear side. For example, a third pipe 15 can be drawn from the secondary air box 8 of the secondary air system, and air is drawn in by the fan 27 and introduced into the rear arch of the furnace 3, and then into the interior of the furnace 3. The secondary air of the third section enters from the rear arch 31, which makes up for the insufficient secondary air near the front arch 32, and complements the secondary air of the first and second sections to further improve combustion efficiency.

[0072] As an example, the secondary circulating air introduced into the secondary air system accounts for approximately 10 to 35% of the total boiler flue gas.

[0073] As an example, desulfurizing agent, such as quicklime, is also circulated within the duct 10, allowing for simultaneous desulfurization within the furnace. For instance, it can be added via a desulfurizing agent feeding device and a feeding pipe 17. As an example, the desulfurizing agent feeding device includes a feeding hopper 16, a screw feeder 23, and a conveying fan 24. The screw feeder 23 controls the amount of desulfurizing agent added, while the conveying fan 24 facilitates the rapid and uniform delivery of the desulfurizing agent into the furnace. Furthermore, since the secondary air within the duct 10 is flue gas from combustion within the furnace, containing sulfur dioxide, it combines with oxygen in the primary air after the air curtain 13 is formed, forming sulfur trioxide under combustion conditions. Sulfur trioxide can be directly desulfurized with water, thus reducing the burden on subsequent desulfurization processes.

[0074] Combination Figures 2-3 As a further improvement, the second subsystem also includes a gas distribution manifold 25. The upstream side of the gas distribution manifold 25 is connected to the second pipe 11 (and also to the feed pipe 17 if desulfurizing agent is introduced). The downstream side of the gas distribution manifold 25 branches into a first branch 251 and a second branch 252. The first branch 251 is introduced from the side of the boiler and connected to the air duct 10. In this embodiment, the bottom of the first branch 251 is a horizontally arranged first manifold pipe 28. The air duct 10 is perpendicular to the first manifold pipe 251a, comprising multiple parallel pipes, thus forming a flue gas air curtain wall. Of course, in other embodiments, the air curtain wall can also be set at an inclined angle, i.e., the angle can be changed according to the engineering conditions. The air curtain wall can form a more compact air duct arrangement, thus creating a more tightly sealed air curtain that isolates the combustion chamber 4 from the furnace interior.

[0075] The second branch 252 extends horizontally along the furnace, converging at its end with the third pipe 15 into the second header pipe 29. A nozzle 26 is then led out from the second header pipe 29, pointing towards the furnace head outlet. The air ejected from the nozzle 26 consists of two streams: the first is secondary air from a portion of the second subsystem, which may carry desulfurizing agent to achieve in-furnace desulfurization at the rear arch position; the other is circulating flue gas without desulfurizing material (i.e., the secondary air from the third section). The ratio of the two circulating flue gas streams can be adjusted as needed (e.g., using a flue gas analyzer).

[0076] Optionally, the outer wall of the combustion chamber 4 is further coated with an anti-coking superconducting castable. The anti-coking superconducting castable has both anti-coking properties and good thermal conductivity. The anti-coking property can prevent corrosion inside the furnace, while the thermal conductivity facilitates the conduction of heat between the combustion chamber 4 and the furnace 3, thereby improving combustion efficiency.

[0077] In this embodiment, the anti-coking superconducting castable comprises the following components in parts by weight:

[0078] Aggregate: Of the aggregate, 9.65 parts are 0-1mm in diameter, 11 parts are 1-3mm in diameter, 15 parts are 3-5mm in diameter, and 12 parts are 5-8mm in diameter. The preferred aggregate is Barmac aggregate obtained from a Barmac crushing machine, which produces finished aggregates that are mostly cubic in shape, with good particle size and fine particle size.

[0079] 18 parts of silicon carbide;

[0080] Two portions of flake graphite;

[0081] 4 parts silica fume;

[0082] 2.5 parts metakaolin;

[0083] 4 parts mullite powder;

[0084] 2.5 parts of electrofused cement;

[0085] 5 parts of CA-70 pure calcium aluminate;

[0086] 2.5 parts of α-alumina;

[0087] 2.5 parts of high-alumina micro powder;

[0088] 2.5 parts of burnt gemstone powder;

[0089] 0.1 parts borax;

[0090] 0.1 part explosion-proof fiber;

[0091] 0.15 parts of sodium tripolyphosphate;

[0092] Two parts of metallic aluminum powder.

[0093] In the above components, the explosion-proof fiber can be polypropylene fiber, etc., to prevent gas explosions. High-alumina micro-powder can be commercially available high-alumina fine powder, and other raw materials can also be purchased commercially. In specific formulation, materials can be prepared in kg units; for example, in the weight parts above, the unit is replaced by kg. Then, the above raw materials are mixed with water to prepare an anti-coking superconducting castable.

[0094] Testing revealed that the anti-coking superconducting castable provided in this embodiment of the invention possesses excellent thermal conductivity, a property not previously reported in related technologies. During testing, a 15kg sample of the superconducting anti-coking castable was taken and tested according to YB / T 4130-2005 "Test Method for Thermal Conductivity of Refractory Materials (Water Flow Plate Method)". Figure 6The results showed that the thermal conductivity of the anti-coking superconducting castable reached 1.050 W / (m·K) at 800℃ on the hot surface and 1.354 W / (m·K) at 1200℃, significantly higher than other types of castables (ordinary castables, tested using the same method, had a thermal conductivity of only 0.511 W / (m·K) at 800℃ and 0.629 W / (m·K) at 1200℃). Furthermore, the anti-coking superconducting castable also exhibited good compressive strength, flexural strength, and refractoriness, as detailed in [see details]. Figure 7 .

[0095] The superconducting anti-coking castable prepared above was coated on the front and rear arches of the stratification transition. After two years of use, no coking was found during furnace maintenance. Therefore, it can be seen that it has good thermal conductivity and good anti-coking performance.

[0096] In the embodiments described above, multiple air ducts 10 form an air-guiding partition wall, separating the combustion chamber 4 and the furnace 3. As an improvement or variation, in some embodiments, circulating water pipes are also fitted over the outer side of the air ducts 10, thus forming a combined cooling structure where circulating water pipes cover the air ducts 10, i.e., a "water + air" partition wall, which separates the combustion chamber 4 and the furnace 3, while simultaneously serving the functions of heat exchange and cooling. A combustion surface is formed on the surface of this combined cooling structure, and an anti-wear and thermally conductive castable is coated on the combustion surface to improve thermal conductivity while preventing wear.

[0097] As an example, combined Figure 4 Multiple air ducts 10 are arranged in parallel, and the tops of each air duct 10 are connected together by a generally horizontally arranged circulating air manifold 30. The circulating air manifold 30 is filled with secondary air (which may carry desulfurizing agent). In this embodiment, the circulating air manifold 30 can refer to the first manifold 28 in the previous embodiment, and its upstream side is connected to the gas distribution manifold 25, which will not be described again here. Further, a circulating water manifold sleeve 301 is fitted over the outside of the circulating air manifold 30, and circulating water is filled into the circulating water manifold sleeve 301 to wrap the circulating air manifold 30. The bottom of the circulating water manifold sleeve 301 is connected to multiple circulating water diversion pipes 302, the number of which corresponds to the number of air ducts 10, so that each circulating water diversion pipe 302 is sleeved on the outside of each air duct 10. The bottoms of each circulating water diversion pipe 302 converge to a generally horizontally arranged circulating water pipe 33. The bottom of the air duct 10 extends from the bottom of the circulating water pipe 33, and the air outlet and the gas nozzle 34 connected to the air outlet are provided in the extended part. The gas nozzle 34 can be a flat nozzle.

[0098] As another example, combined Figure 5The circulating water pipe includes a circulating water manifold 35 through which circulating water flows. Multiple circulating water diversion pipes 302 are connected to the bottom of the circulating water manifold 35, and the bottoms of all circulating water diversion pipes 302 converge at a circulating water diversion pipe 33. Multiple air ducts 10 are arranged in parallel, and their tops are connected together via the circulating air manifold 30. The circulating water diversion pipe 33 is fitted over the circulating air manifold 30 and the outer side of each air duct 10. The bottom of the air duct 10 extends from the bottom of the circulating water diversion pipe 33, and an air outlet and a gas nozzle 34 connected to the air outlet are provided on the extended portion. Optionally, the gas nozzle 34 is replaceable and made of wear-resistant and heat-resistant cast iron. During assembly, the circulating air manifold 30 is first placed into the circulating water diversion pipe 35, and the position of the gas nozzle 34 is accurately located and welded. Then, the air duct 10 is annularly sealed by welding (annular pipe seal welding point 36).

[0099] Optionally, a flue gas analysis device 18 (such as a flue gas analyzer) is installed on the main flue gas duct 6 to control the air volume of the secondary air in the first, second, and third sections according to the composition and content of the flue gas. Optionally, if a desulfurizing agent is also flowing through the duct 10, the flue gas analysis device 18 also controls the amount of desulfurizing agent used according to the composition and content of the flue gas.

[0100] Optionally, a dust collector 19, a low-temperature denitrification device 20, a desulfurization device 21, and a chimney 22 are sequentially connected to the main flue gas duct 6 after the flue gas analysis device 18.

[0101] Optionally, the main flue gas duct 6 of the stoker boiler is also connected to a flue gas condensation device (for example, it can be connected after the chimney or directly replace the chimney). Specifically, a natural power air cooling and flue gas dewhitening device produced by Beijing Yingxiang Borui Refractory Materials Technology Co., Ltd. can be selected, as detailed in the patent publication document CN111964093A.

[0102] The above-mentioned operating method of the stoker-fired boiler includes:

[0103] Through the first subsystem, the secondary air is diverted from the first part and introduced into the air chamber, then enters the combustion chamber to gasify the fuel, and is further sent into the furnace.

[0104] The secondary air is diverted from the second part through the second subsystem and introduced into the air duct, so that the secondary air of the second part is ejected from the air duct to form an air curtain that impacts the coal on the grate, while the air curtain separates the combustion chamber from the bottom of the furnace.

[0105] The secondary air is diverted from the third section through the third subsystem and introduced into the furnace from the front side of the furnace.

[0106] As a further improvement, a cooling system is also provided in the middle of the furnace. As an example, the cooling system includes a water-cooling device and an air-cooling device in the highest combustion zone between the front and rear arches. The water-cooling device includes a hot water collector 52 (which can be fixed by means of a water pipe support device 512) arranged generally horizontally between the two side furnace walls 517. The lower end of the hot water collector 52 is connected to a hot water distributor 54 through a multi-channel distributor connecting pipe 56. The circulating water inlet main pipe 59 and the inlet pipe 510 are located upstream of the hot water distributor 54, and the circulating water outlet main pipe 511 and the outlet pipe 51 are located downstream of the hot water collector 52. In this way, the circulating water can exchange heat in the highest combustion zone, remove a large amount of heat, reduce the temperature of the highest combustion zone, and reduce the generation of nitrogen oxides.

[0107] To make more efficient use of space, the air-cooled device includes a flue gas circulation conveying pipe 53 nested within the hot water distributor 54. This flue gas circulation conveying pipe 53 has air intakes on both sides, for example, connecting to the first circulating flue gas main pipe 57 and the second circulating flue gas main pipe 58, respectively. Both can be led out to the circulating flue gas main pipe of the stoker boiler to receive circulating flue gas. Multiple circulating flue gas nozzles 55 are installed at the lower end of the flue gas circulation conveying pipe 53 to spray flue gas into the high-temperature zone above the coal bed 14, thus partially reducing the temperature of the highest combustion zone. Both the air-cooled and water-cooled devices are externally wrapped with wear-resistant castable refractory and have thermal expansion joints.

[0108] Because nitrogen oxides are generated at their peak between 800 and 1200 degrees Celsius, the purpose of the cooling system is to lower the central combustion temperature, quickly remove heat, and reduce the generation of nitrogen oxides.

[0109] The stoker-fired boiler provided by the embodiments of the present invention mainly reduces the generation of nitrogen oxides through the following synergistic effects:

[0110] 1. Utilizing secondary air mixing increases the blower temperature and reduces the oxygen content, thus preventing the formation of nitrogen oxides. 2. Part of the coal is gasified in the combustion chamber, producing carbon monoxide. Carbon monoxide reacts more readily with oxygen, and in the case of reduced oxygen, it more easily generates carbon dioxide, further reducing nitrogen oxide formation. 3. The three streams of air blown in, with reduced oxygen content, lower the central combustion temperature, reducing nitrogen oxide formation. 4. The cooling device added in the middle aims to quickly remove heat, lower the central temperature, and prevent nitrogen oxide formation.

[0111] This article uses specific examples to illustrate the inventive concept in detail. The description of the above embodiments is only for the purpose of helping to understand the core idea of ​​the present invention. It should be noted that any obvious modifications, equivalent substitutions or other improvements made by those skilled in the art without departing from the inventive concept should be included within the protection scope of the present invention.

Claims

1. A stoker-fired boiler, comprising a wind chamber, a grate, and a furnace, characterized in that, The stoker boiler also includes: A combustion chamber is provided above the grate and at the front of the furnace, and the combustion chamber is in communication with the interior of the furnace. A secondary air system; the secondary air in the secondary air system is flue gas extracted from the boiler exhaust gas and returned to the boiler for recycling; the secondary air system includes: The first subsystem, which is connected to the air chamber, is used to divert secondary air out of the first part and introduce it into the air chamber, and then into the combustion chamber and the furnace. The second subsystem is connected to the air duct and is used to divert secondary air from the second part and introduce it into the air duct. The air duct is provided with an air outlet facing the grate, so that the secondary air of the second part is ejected from the air duct to form an air curtain. The combustion chamber and the furnace are located on both sides of the air curtain, and the airflow at the bottom of the air curtain contacts the coal on the grate. The third subsystem is used to divert secondary air out of the third section and introduce it into the interior of the furnace from the rear side of the furnace. A circulating water pipe is also fitted on the outside of the air duct, thus forming a combined cooling structure in which the circulating water pipe covers the air duct; the surface of the combined cooling structure forms a combustion surface, and the combustion surface is coated with a wear-resistant and heat-conducting castable; the outer wall of the combustion chamber is also coated with an anti-coking superconducting castable. It also includes a combined rapid cooling heat exchange device installed between the front and rear arches of the furnace. The combined rapid cooling heat exchange device includes a water cooling device and an air cooling device. The water cooling device includes a hot water collector, which is connected to a hot water distributor through multiple water distribution pipes. A water outlet pipe and a water inlet pipe are respectively installed on the downstream side of the hot water collector and the upstream side of the hot water distributor. The air cooling device includes a flue gas circulation conveying pipe nested in the hot water distributor. Multiple circulating flue gas nozzles are installed at the lower end of the flue gas circulation conveying pipe.

2. The stoker-fired boiler according to claim 1, characterized in that, The secondary air accounts for 10-35% of the total boiler flue gas.

3. The stoker-fired boiler according to claim 1, characterized in that, The duct also contains a desulfurizing agent, so that the secondary air in the second part carries the desulfurizing agent.

4. The stoker-fired boiler according to any one of claims 1-3, characterized in that, The second subsystem also includes a gas distribution manifold for introducing the second portion of secondary air. The gas distribution manifold includes a first branch and a second branch. The first branch is connected to the air duct, and the second branch is connected to the third subsystem, thereby introducing a portion of the second portion of secondary air into the air duct and another portion into the third subsystem. This results in the gas introduced into the furnace by the third subsystem comprising two streams: the first stream is a portion of the second portion of secondary air introduced from the second branch, and the second stream is the secondary air of the third portion.

5. The stoker-fired boiler according to claim 1, characterized in that, Multiple air ducts are arranged in parallel, and the tops of each air duct are connected together by a circulating air manifold. A circulating water manifold is fitted over the outside of the circulating air manifold, and the bottom of the circulating water manifold is connected to a number of circulating water distribution pipes corresponding to the number of air ducts. Each circulating water distribution pipe is fitted over the outside of the air duct, and the bottoms of all circulating water distribution pipes converge to a circulating water distribution pipe. The bottom of the air duct extends from the bottom of the circulating water distribution pipe, and the air outlet and a gas nozzle connected to the air outlet are provided on the extended part.

6. The stoker-fired boiler according to claim 1, characterized in that, The circulating water pipe includes a circulating water manifold pipe, and the bottom of the circulating water manifold pipe is connected to multiple circulating water diversion pipes, and the bottoms of each circulating water diversion pipe converge into the circulating water diversion pipe. Multiple air ducts are arranged in parallel, and the tops of each air duct are connected together by a circulating air manifold; the circulating water drain pipe is sleeved on the outside of the circulating air manifold. The bottom of the air duct extends from the bottom of the circulating water pipe, and the air outlet and the gas nozzle connected to the air outlet are provided on the extended part.

7. The stoker-fired boiler according to claim 5 or 6, characterized in that, The gas nozzle is replaceable and is made of wear-resistant and heat-resistant cast iron.

8. The stoker-fired boiler according to claim 6, characterized in that, During assembly, first place the circulating air manifold into the circulating water pipe, locate the position of the gas nozzle and weld it, and then perform ring-shaped sealing welding on the air duct.

9. The stoker-fired boiler according to claim 1, characterized in that, The anti-coking superconducting castable comprises the following components in parts by weight: 25-50 parts aggregate; 10-25 parts of silicon carbide; 1-3 parts of flake graphite; 3-5 parts silica fume; 2-3 parts of metakaolin; 3-5 parts mullite powder; 2-3 parts of fused cement; 4-6 parts of CA-70 pure calcium aluminate; 2-3 parts of α-alumina; 2-3 parts of high-alumina micro powder; 2-3 parts of burnt gemstone powder; Borax 0.1-0.2 parts; 0.1-0.2 parts of explosion-proof fiber; Sodium tripolyphosphate 0.1-0.2 parts; 1-2 parts of metallic aluminum powder.

10. The stoker-fired boiler according to claim 1, characterized in that, It also includes a flue connected to the furnace, and the flue is equipped with a flue gas analysis device for controlling the air volume of the secondary air in the first part, the second part and the third part according to the composition and content of the flue gas.

11. The stoker-fired boiler according to claim 10, characterized in that, If a desulfurizing agent is also circulating in the duct, the flue gas analysis device will control the amount of desulfurizing agent used based on the composition and content of the flue gas.

12. The stoker-fired boiler according to claim 1, characterized in that, It also includes a flue connected to the furnace, and the flue is also connected to a low-temperature denitrification device.

13. The stoker-fired boiler according to claim 1, characterized in that, The flue of the stoker boiler is also connected to a flue gas condensation device.

14. The operating method of the stoker-fired boiler according to any one of claims 1-13, characterized in that, include: Through the first subsystem, the secondary air is diverted from the first part and introduced into the air chamber, then enters the combustion chamber to gasify the fuel, and is further sent into the furnace. The secondary air is diverted from the second part through the second subsystem and introduced into the air duct, so that the secondary air of the second part is ejected from the air duct to form an air curtain that impacts the coal on the grate, while the air curtain separates the combustion chamber from the bottom of the furnace. The secondary air is diverted from the third section through the third subsystem and introduced into the furnace from the front side of the furnace.

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