Fully premixed combustion low-nitrogen steam boiler

Abstract

A fully premixed combustion low-nitrogen steam boiler relates to the technical field of steam boilers and comprises a box body and a plurality of standardized boiler modules sequentially arranged along a mounting cavity of the box body. The boiler module is composed of a boiler body, a full premixing burner, a negative pressure steam pocket and a symmetrical tubular heat exchanger. Spiral grooves are formed in the walls of the furnace body combustion cavities and communicated with the water heating cavities, so that water flow forms a thin-layer water film to strengthen heat exchange and prevent local dry burning, and the adjacent furnace body combustion cavities are communicated to realize smoke cascade transmission; hot air flow spirally circulates to prolong the heat exchange time, the full-premixing combustor is combined with the impeller to diffuse fuel gas, the metal fiber net forms low-temperature diffusion flames, and generation of nitric oxide is remarkably inhibited; the negative-pressure steam pocket accelerates evaporation in a negative-pressure environment, so that the steam production rate is increased; flue gas forms a U-shaped loop through the flow guide structure and flows through the tubular heat exchanger. The modular design supports on-demand combination and later expansion, the overall structure is high in heat efficiency, low in emission and safe and reliable in operation, and the multi-working-condition load requirement is met.

Description

Technical Field

[0001] This invention relates to the field of steam boiler technology, and in particular to a fully premixed combustion low-NOx steam boiler. Background Technology

[0002] In the current industrial boiler field, traditional steam boiler designs often face a series of technical challenges and limitations. First, most traditional boilers adopt a single, integrated structure. While this design performs well in certain application scenarios, it lacks flexibility and adaptability when facing evaporation demands of different scales. It cannot be quickly customized and adjusted according to the actual needs of users, resulting in long production cycles, high costs, and significant inconvenience during later expansion or maintenance.

[0003] Furthermore, traditional burners typically employ partial premixing or diffusion combustion. While these methods can meet basic heating requirements, incomplete combustion leads to high nitrogen oxide (NOx) emissions, negatively impacting the environment. Simultaneously, low combustion efficiency results in low energy utilization, increasing operating costs.

[0004] Furthermore, the existing internal structure design of boilers fails to fully utilize thermal energy. For example, the heat transfer path between the combustion chamber and the heat exchange device is relatively short, resulting in a large amount of waste heat in the flue gas not being effectively recovered, leading to higher exhaust gas temperatures and further reducing overall thermal efficiency. Moreover, traditional boilers struggle to achieve cascaded heat utilization, resulting in uneven heat load distribution among modules and a tendency for localized overheating, which affects the service life and safety of the equipment.

[0005] In addition, in terms of steam generation, traditional boilers mostly adopt atmospheric or slightly positive pressure operation modes, which not only limits the saturation temperature of water and affects the steam production rate, but may also lead to steam-water entrainment problems, reduce steam dryness, and increase the difficulty of subsequent processing.

[0006] To address the shortcomings of the existing technologies, this invention proposes a fully premixed combustion low-NOx steam boiler. Through modular design, optimized burner structure, and improved heat exchange system, it aims to improve the boiler's flexibility, thermal efficiency, and environmental performance, overcoming many deficiencies of traditional boilers. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, the present invention discloses a fully premixed combustion low-NOx steam boiler.

[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0009] A fully premixed combustion low-NOx steam boiler, comprising:

[0010] The housing has an internal mounting cavity;

[0011] Boiler modules, which are multiple modules installed sequentially from the head end to the tail end of the housing;

[0012] The boiler module includes:

[0013] The furnace body is a horizontally arranged ring-shaped structure. The inner cavity of the furnace body is a combustion chamber, and a water heating chamber is provided between the combustion chamber and the outer wall of the furnace body. The cavity wall of the combustion chamber is provided with a spiral groove structure extending into the combustion chamber. The spiral groove structure is connected to the water heating chamber. The combustion chambers of two adjacent furnace bodies are connected accordingly.

[0014] The fully premixed burner is installed inside the combustion chamber, and the hot gas flow generated by the combustion of the fully premixed burner flows spirally along the spiral groove structure of the combustion chamber;

[0015] The negative pressure steam pack is installed on the top of the furnace body. The negative pressure steam pack is connected to the water heating chamber of the furnace body through multiple convection pipes; and the tops of two adjacent negative pressure steam packs are connected in parallel through negative pressure steam pipes.

[0016] The tubular heat exchangers consist of two symmetrically installed between the negative pressure steam drum and the fully premixed burner. The water passage chamber of the tubular heat exchanger is connected to the water heating chamber of the furnace body; and the flue gas chambers of the two adjacent tubular heat exchangers are connected accordingly.

[0017] The flue gas chambers of the two tubular heat exchangers of the boiler module located at the head end of the box are connected in series via elbows; the flue gas chamber of one of the tubular heat exchangers of the boiler module located at the tail end of the box is connected to the combustion chamber of the boiler module furnace body via a guide hood, and the flue gas chamber of the other tubular heat exchanger is connected to the chimney.

[0018] Preferably, the fully premixed burner comprises:

[0019] The air intake pipe has one end inserted into the combustion chamber of the furnace body;

[0020] The water-cooled sleeve is fitted outside the pipe body located inside the combustion chamber with the air inlet pipe. One end of the water-cooled sleeve is sealed to the outer wall of the air inlet pipe, and the other end is connected to the water heating chamber of the furnace body.

[0021] The gas pipe is installed inside the gas inlet pipe;

[0022] The impeller is rotatably connected to the hollow bracket inside the gas pipe outlet; the gas is blown out of the gas pipe to drive the impeller to rotate, and the gas diffuses circumferentially under the action of the centrifugal force of the impeller.

[0023] The combustion tube has its middle section connected to the outlet end of the intake pipe; both ends of the combustion tube are closed, and multiple air outlets are arranged in an array on the tube body.

[0024] The ignition needle is installed on the water-cooling jacket, and the cable of the ignition needle is run through the water-cooling jacket.

[0025] The blower is installed at the air inlet end of the air inlet pipe.

[0026] Preferably, the impeller comprises:

[0027] The rotating shaft is rotatably connected at one end to the hollow bracket inside the gas pipe outlet, and at the other end extends out of the gas pipe;

[0028] The wheel is vertically and securely connected to the extended end of the rotating shaft;

[0029] The curved blades are multiple blades spaced apart along the circumference of the wheel, and the curved blades are located on one side of the wheel corresponding to the gas pipe.

[0030] Preferably, the combustion tube is wrapped with a metal fiber mesh.

[0031] Preferably, both ends of the combustion tube are provided with cones, and the tips of the two cones are arranged opposite each other.

[0032] Preferably, the outlet port of the air inlet pipe is provided with multiple conical diffuser meshes at intervals, and the tips of two adjacent conical diffuser meshes are arranged opposite to each other.

[0033] Preferably, the bottom of the boiler module is connected to a converter pipe, which is connected to the top of the negative pressure steam chamber of the boiler module, and a water pump is installed on the pipe.

[0034] Preferably, a water pipe connected to the two tubular heat exchangers is installed at the top position between the two tubular heat exchangers of the boiler module, and the water pipes of adjacent boiler modules are connected in series; an air pipe for supplying air to the fully premixed burner is installed at the bottom position between the two tubular heat exchangers, and the air pipes of adjacent boiler modules are connected in series.

[0035] Preferably, a filter is installed at the air inlet end of the air pipe.

[0036] Preferably, a preheating heat exchanger, which is connected to the air inlet end of the air pipe, is installed between the flow guide and the corresponding tubular heat exchanger.

[0037] By employing the technical solution described above, the present invention has the following beneficial effects:

[0038] (1) The present invention has a simple structure and adopts a modular design. Each module has a standardized evaporation capacity specification, and the number of modules can be flexibly combined according to user needs to achieve rapid customization and on-site assembly. This design not only significantly shortens the production and installation cycle and reduces logistics and construction costs, but also supports later expansion and improves the availability and adaptability of the system.

[0039] (2) The furnace body of this invention adopts a horizontally arranged ring-shaped structure, and the inner combustion chamber wall is machined with inwardly extending spiral grooves, so that the flowing water forms a thin water film, effectively reducing the heat transfer resistance and accelerating the heat conduction rate. In addition, the spiral groove structure can promote the stable flow of steam and water two-phase flow, enhance the convective heat transfer effect, and prevent the occurrence of local dry burning. Adjacent furnace bodies are connected through a sealed interface to ensure smooth flow of flue gas between modules, realize heat gradient transfer, balance the heat load distribution of each burner, and avoid local overheating problems.

[0040] (3) The negative pressure steam package of this invention utilizes a negative pressure environment to reduce the saturation temperature of water, thereby accelerating the evaporation process and increasing the steam production per unit time. At the same time, the negative pressure suction effect helps to reduce steam-water entrainment, improve steam dryness, reduce working pressure, and enhance operational safety. The tubular heat exchanger enables multi-stage recovery of flue gas waste heat, significantly reducing the exhaust gas temperature and improving overall thermal efficiency.

[0041] (4) The fully premixed burner of this invention integrates an intake pipe, a gas pipe, and a cooling device. The intake pipe is cooled and protected by a water-cooled jacket, extending component lifespan while preheating the combustion air and improving thermal efficiency. The impeller design ensures uniform gas diffusion and thorough premixing with air, guaranteeing combustion stability and suppressing localized high-temperature zones, effectively reducing nitrogen oxide generation. The outer circumference of the combustion pipe is wrapped with a metal fiber mesh, promoting the formation of a low-temperature diffused flame, further reducing the peak flame temperature and decreasing nitrogen oxide emissions. The design of the conical body and conical diffuser mesh optimizes airflow distribution, ensuring uniform distribution of premixed gas along the pipe body and improving mixing uniformity.

[0042] (5) This invention achieves a forced circulation loop by setting a converter pipe at the lowest point of the furnace body and connecting it to the top of the negative pressure steam chamber, and equipping it with a high-temperature resistant centrifugal water pump. Hot water rapidly flashes to generate steam under negative pressure, while simultaneously promoting the replenishment of low-temperature water in the heating chamber, accelerating the steam-water circulation rate, and improving the steam generation response speed and steam production stability. The frequency-controlled water pump can adjust the circulation flow rate according to load requirements, achieving energy-saving operation, and maintaining necessary circulation under low load to prevent stagnation.

[0043] (6) The design of adding water and air pipes in this invention ensures a balanced distribution of water flow and temperature in each module heat exchanger, avoiding differences in heat exchange efficiency caused by hydraulic imbalance. The addition of the preheating heat exchanger enables the cascade utilization of flue gas waste heat. The preheated air increases the temperature of the air entering the furnace, reduces fuel consumption in the main combustion zone, and further improves the boiler's thermal efficiency. The flue gas temperature is further reduced after two heat exchanges, reducing exhaust heat loss. At the same time, the preheated air promotes more complete fuel combustion and reduces pollutant emissions. Attached Figure Description

[0044] Figure 1 This is a three-dimensional structural diagram of the present invention;

[0045] Figure 2 A three-dimensional structural diagram showing the connection of multiple boiler modules;

[0046] Figure 3 A schematic diagram showing the connection of multiple boiler modules;

[0047] Figure 4 This is a three-dimensional structural diagram of the boiler module;

[0048] Figure 5 This is a structural schematic diagram of the boiler module;

[0049] Figure 6 This is the rear view of the boiler module;

[0050] Figure 7 This is a side view of the boiler module;

[0051] Figure 8 This is a sectional view of the furnace body;

[0052] Figure 9 This is a schematic diagram of the installation structure of the elbow;

[0053] Figure 10 This is a schematic diagram of the chimney's installation structure.

[0054] Figure 11 This is a cross-sectional view of a fully premixed burner;

[0055] Figure 12 This is a schematic diagram of the impeller structure;

[0056] Figure 13 This is a schematic diagram of the installation structure of the preheating heat exchanger.

[0057] In the diagram: 1. Box body; 2. Furnace body; 3. Fully premixed burner; 3-1. Inlet pipe; 3-2. Water-cooled jacket; 3-3. Gas pipe; 3-4. Impeller; 3-41. Shaft; 3-42. Disc; 3-43. Arc blade; 3-5. Combustion tube; 3-6. Ignition needle; 3-7. Blower; 3-8. Metal fiber mesh; 3-9. Conical body; 3-10. Conical diffuser; 4. Negative pressure steam tank; 5. Tubular heat exchanger; 6. Elbow; 7. Flow guide; 8. Chimney; 9. Flow converter pipe; 10. Water pump; 11. Water pipe; 12. Air pipe; 13. Filter; 14. Preheating heat exchanger. Detailed Implementation

[0058] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0059] In the description of this invention, it should be noted that the terms "upper" and "lower" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed when in use. They are only used to facilitate the description of this invention and to simplify the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0060] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "joining," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0061] Example 1:

[0062] Combined with appendix Figures 1-10 A fully premixed combustion low-NOx steam boiler includes a housing 1 and multiple boiler modules. The housing 1 forms the overall protective outer shell of the boiler, with an internal enclosed mounting cavity. The multiple boiler modules are arranged sequentially along the axial direction of the mounting cavity in the housing 1, from one end to the other, as shown in the attached diagram. Figures 2-5 As shown; the inner wall of the housing 1 is filled with insulation material between it and the boiler module. The boiler module adopts a standardized design, with single module rated evaporation capacities including 2 tons / hour and 5 tons / hour, etc. During production, the number of modules can be flexibly combined according to the user's required evaporation capacity, realizing rapid product customization and on-site assembly, significantly shortening the production and installation cycle, and reducing logistics and construction costs; the modular structure supports later expansion and improves system availability.

[0063] Specifically, as shown in the attached document Figure 4 As shown, the boiler module includes a furnace body 2, a fully premixed burner 3, a negative pressure steam drum 4, and a tubular heat exchanger 5. (See attached diagram) Figure 8As shown, the furnace body 2 is a horizontally arranged ring-shaped structure. The inner cavity of the furnace body 2 forms a combustion chamber, and the outer wall of the combustion chamber forms an annular water heating chamber between the outer wall of the furnace body 2 and the outer shell of the furnace body 2. The surface of the combustion chamber wall is machined with a spiral groove structure extending into the combustion chamber. The spiral cavity formed by the spiral groove is connected to the water heating chamber, allowing water in the water heating chamber to flow into the spiral cavity to participate in heat exchange. The ends of the combustion chambers of two adjacent furnace bodies 2 are connected through flanges with sealing gaskets or welded interfaces to form a continuous and through combustion flue gas channel. This allows high-temperature flue gas to flow sequentially through the combustion chambers of each boiler module, realizing heat transfer in stages, improving the overall thermal efficiency of the system, and balancing the heat load distribution of each burner to avoid local overheating.

[0064] The spiral groove structure of the combustion chamber wall adopts a rectangular cross-section design with a groove width smaller than the groove depth. This structure allows the water flowing into the spiral chamber to form a thin water film, reducing heat transfer resistance, accelerating the heat conduction rate, and promoting rapid and uniform vaporization of water. The groove depth provides sufficient water volume to maintain stable vapor-liquid two-phase flow, enhances water flow disturbance, strengthens convective heat transfer effect, and avoids the risk of local dry burning.

[0065] As attached Figure 7 As shown, the fully premixed burner 3 is fixedly installed in the combustion chamber of the furnace body 2. The high-temperature flue gas generated by combustion flows along the spiral flow channel formed by the spiral groove structure, which significantly prolongs the residence time of the flue gas in the combustion chamber and increases the radiation and convection heat transfer area. The centrifugal effect generated by the spiral flow makes the flue gas flow closely against the cavity wall, enhances the boundary layer disturbance, and improves the heat transfer coefficient. At the same time, the rising disturbance of the bubbles in the spiral groove cavity promotes the natural circulation of water in the water heating chamber.

[0066] The negative pressure steam boiler 4 is installed directly above the furnace body 2 and is connected to the upper part of the water heating chamber through multiple convection pipes, forming a steam-water separation space. The tops of the negative pressure steam boilers 4 of adjacent boiler modules are connected in parallel via negative pressure steam pipes. An external vacuum pump or induced draft fan maintains a stable negative pressure in the system through the negative pressure steam pipes. The negative pressure environment reduces the saturation temperature of the water, accelerates the evaporation process, and increases the steam production per unit time. The negative pressure suction effect causes the steam to quickly leave the water surface, reduces steam-water entrainment, increases steam dryness, and reduces the working pressure inside the boiler, enhancing operational safety. The outlet of the negative pressure steam pipe can be connected to an external steam-water separation device to further obtain high-dryness steam.

[0067] Two tubular heat exchangers 5 are symmetrically arranged between the lower part of the negative pressure steam drum 4 and the upper part of the fully premixed burner 3. Their water passage chambers are connected to the water combustion chamber of the furnace body 2 through pipes. In adjacent boiler modules, the flue gas chamber of the tubular heat exchanger 5 at the tail end of the previous module is connected to the corresponding flue gas chamber of the tubular heat exchanger 5 at the head end of the next module through a sealed connecting pipe, so that the flue gas flows through all the tubular heat exchangers 5 in sequence, realizing multi-stage recovery of flue gas waste heat and significantly reducing the exhaust gas temperature.

[0068] As attached Figure 9As shown, the two tubular heat exchangers 5 of the boiler module at the head end of the housing 1 are connected in series via elbow 6; as attached Figure 10 As shown, in the boiler module at the tail end of box 1, the flue gas chamber of one side of the tubular heat exchanger 5 is connected to the combustion chamber outlet of the boiler module's furnace body 2 via the guide hood 7, and the flue gas chamber on the other side is connected to the chimney 8. High-temperature flue gas flows from the combustion chamber of the furnace body 2 at the head end along the spiral groove to the combustion chamber of the furnace body 2 at the tail end, is introduced into the tubular heat exchanger 5 on one side of the tail end via the guide hood 7, flows through the elbow 6 and then flows in the opposite direction through the tubular heat exchanger 5 on the other side, and is finally discharged from the chimney 8, forming a U-shaped flue gas flow loop, which allows the flue gas to sweep across the heat exchange tube bundle twice, extending the heat exchange path and improving the heat absorption efficiency.

[0069] The flow guide shroud 7 consists of a circular shell closed at one end and connected to the combustion chamber outlet flange at the other end, and a flow guide pipe. One end of the flow guide pipe is connected to the flue gas inlet of the tubular heat exchanger 5, and the other end is tangentially connected to the inner wall of the circular shell. It utilizes the original spiral momentum of the flue gas to achieve smooth deflection, reducing flow resistance and eddy current losses, and ensuring stable airflow into the heat exchanger. A high-temperature resistant observation window is provided at the head end of the furnace body 2 and the combustion chamber end of the casing 1. If a double-layer heat-resistant quartz glass structure is used, it facilitates real-time observation of the flame shape, color, and carbon buildup, providing a basis for combustion regulation and preventative maintenance, and improving operational reliability.

[0070] During operation, water is first injected and pressurized into the water chambers of each boiler module's tubular heat exchanger 5. The water then fills the water-burning chamber and spiral chamber of the furnace body 2 through the connecting path. After the water-burning chamber is full, it enters the negative pressure steam chamber 4 through the convection pipe. The water level in the chamber is maintained at 1 / 4 to 1 / 3 of its volume by the level gauge. Before startup, the blowers 3-7 perform a pre-purging procedure to remove residual gases. Subsequently, the ignition needles 3-6 ignite the gas, and the fully premixed burner 3 starts working. The fuel gas and air are premixed and then combusted. The flame directly radiates heat to the combustion chamber wall, and the heat is efficiently transferred to the water in the water-burning chamber. Fully premixed combustion ensures thorough mixing of air and fuel gas, resulting in uniform combustion temperature distribution and effectively suppressing the formation of thermal nitrogen oxides. The high-temperature flue gas generated by combustion flows from the head end to the tail end along the spiral groove, sequentially heating the water in the water-burning chamber of each boiler body 2. After reaching the tail end, the flue gas flows through the guide shroud 7 into the flue gas chamber of the tubular heat exchanger 5, where it undergoes counter-current heat exchange with the cold water in the water passage chamber. The cold water is preheated and then flows back to the water heating chamber, reducing the heat load in the main combustion zone. After two stages of heat exchange, the exhaust temperature of the flue gas is significantly reduced. Once the steam output of the negative pressure steam drum 4 stabilizes, the control system alternately switches all premixed burners 3 except for the head end to low-fire or intermittent operation. The directional flue gas flow generated by the head end combustion maintains the heat exchange requirements of the subsequent modules, achieving on-demand energy supply and reducing fuel consumption and equipment start-up and shutdown frequency under partial load conditions.

[0071] Example 2:

[0072] Combined with appendix Figure 7 , 11According to Embodiment 1, a fully premixed combustion low-NOx steam boiler, based on Embodiment 1, includes an inlet pipe 3-1, a water-cooled jacket 3-2, a gas pipe 3-3, an impeller 3-4, and a combustion pipe 3-5. One end of the inlet pipe 3-1 extends into the combustion chamber of the furnace body 2; the water-cooled jacket 3-2 is fitted around the outer periphery of the pipe section located in the chamber. One end of the water-cooled jacket 3-2 is sealed and welded to the outer wall of the inlet pipe 3-1, and the other end is connected to the water-heating chamber of the furnace body 2. The circulating water in the water-heating chamber is used to cool and protect the inlet pipe 3-1, preventing high-temperature thermal erosion and extending the service life of the components. At the same time, the heat absorbed by the cooling water preheats the combustion air flowing through the inlet pipe 3-1, improving the thermal energy utilization rate. A gas pipe 3-3 is installed inside the intake pipe 3-1. A hollow bracket is fixed inside the outlet end of the gas pipe, and an impeller 3-4 is installed outside. The impeller 3-4 is rotatably connected to the hollow bracket through a high-temperature bearing. When the gas is ejected, it drives the impeller 3-4 to rotate. The centrifugal force is used to make the gas diffuse evenly in the circumference and fully premix with the air in the intake pipe 3-1 to form a uniform combustible mixture, which ensures combustion stability and avoids local high temperature zones.

[0073] As attached Figure 12 As shown, the impeller 3-4 includes a rotating shaft 3-41, a wheel disk 3-42, and arc-shaped blades 3-43; one end of the rotating shaft 3-41 is rotatably connected to the hollow support, and the other end extends out of the gas pipe 3-3; the wheel disk 3-42 is vertically fixed to the extended end of the rotating shaft 3-41; multiple arc-shaped blades 3-43 are arranged at equal intervals around the wheel disk 3-42 and are located on the side of the wheel disk 3-42 facing the gas outlet of the gas pipe 3-3. The arc-shaped profile matches the airflow direction, reduces flow resistance, and improves turbulent mixing efficiency.

[0074] As attached Figure 11 As shown, the combustion tube 3-5 is sealed and connected to the outlet end of the intake tube 3-1 in the middle, with both ends closed, and multiple outlet holes are evenly distributed on the tube wall. An ignition needle 3-6 is installed on the water-cooled jacket 3-2, with its cable led out from inside the jacket of the water-cooled jacket 3-2. Cooling water provides thermal protection for the cable, preventing high-temperature damage to the insulation layer and ensuring ignition reliability. The cable of the ignition needle 3-6 can be a high-temperature resistant cable. The intake end of the intake tube 3-1 is connected to a variable frequency blower 3-7, providing a stable and controllable combustion air flow and adjusting the air-fuel ratio in conjunction with the gas supply system. The combustion tube 3-5 is tightly wrapped with a metal fiber mesh 3-8. Its high porosity and thermal conductivity promote the formation of a low-temperature diffused flame on the mesh surface, expanding the combustion area, reducing the peak flame temperature, and effectively suppressing the generation of nitrogen oxides. Inside the combustion tube 3-5, there are cones 3-9 with opposite tips at both ends to guide and disperse the airflow axially, ensuring that the premixed gas is evenly distributed along the tube and that the flow rate of each outlet is consistent. Multiple cone diffuser meshes 3-10 are arranged at intervals inside the outlet port of the inlet pipe 3-1. The tips of adjacent cone diffuser meshes 3-10 are arranged opposite each other, causing the airflow to be refracted and disturbed multiple times, further improving the uniformity of the mixture of gas and air.

[0075] Example 3:

[0076] Combined with appendix Figure 6 A fully premixed combustion low-NOx steam boiler, based on Embodiment 1 or 2, has its lowest point at the bottom of the boiler module's furnace body 2 connected to the top steam space of the negative pressure steam chamber 4 via a converter pipe 9. A high-temperature resistant centrifugal water pump 10 is installed on the converter pipe 9. When the water pump 10 is running, it forcibly transports the water heated to near saturation temperature at the bottom of the boiler body 2's water chamber to the upper part of the negative pressure steam chamber 4. The hot water rapidly flashes to generate steam under negative pressure, while simultaneously promoting the downward replenishment of low-temperature water in the water chamber, forming a forced circulation loop. This design significantly accelerates the steam-water circulation rate, improves the steam generation response speed and steam production stability, enhances the uniformity of water temperature distribution inside the boiler body 2, and avoids overheating at the bottom or insufficient boiling in certain areas. The water pump 10 adopts frequency conversion control, which can adjust the circulation flow rate according to load demand to achieve energy-saving operation and maintain necessary circulation to prevent stagnation under low load.

[0077] Example 4:

[0078] Combined with appendix Figure 4 , 5 7, 10, and 13, a fully premixed combustion low-NOx steam boiler, based on any of embodiments one to three, has a water pipe 11 installed between the tops of the two tubular heat exchangers 5 in each boiler module. The water pipes 11 of adjacent modules are connected in series to form a continuous water supply loop running through all modules, ensuring a balanced water flow and temperature distribution in the heat exchangers of each module and avoiding differences in heat exchange efficiency caused by hydraulic imbalance. An air pipe 12 is installed between the bottoms of the two tubular heat exchangers 5 to supply combustion air to the fully premixed burner 3. The air pipes 12 of adjacent modules are connected in series to form a unified air distribution network, ensuring that each burner receives combustion air with stable flow and balanced pressure. A removable filter 13 is installed at the main air inlet of the air pipe 12, with a built-in multi-layer stainless steel filter screen to effectively intercept dust and impurities in the air, preventing burner nozzle blockage, metal fiber mesh 3-8 contamination, or impeller 3-4 jamming, and extending the service life of key components.

[0079] As attached Figure 13 As shown, a preheating heat exchanger 14 is added between the outlet of the flow guide 7 and the inlet of the flue gas chamber of the corresponding tubular heat exchanger 5. It has a shell and tube structure. The flue gas chamber inlet of the preheating heat exchanger 14 is connected to the outlet of the flow guide 7, and the flue gas chamber outlet is connected to the inlet of the flue gas chamber of the tubular heat exchanger 5. The air chamber inlet introduces ambient air through the filter 13, and the air outlet is connected to the air inlet end of the air pipe 12.

[0080] During operation, the medium-temperature flue gas flowing out of the combustion chamber first enters the flue gas chamber of the preheating heat exchanger 14 after passing through the guide shroud 7, where it exchanges heat with the combustion air in the air chamber. Then, it enters the tubular heat exchanger 5 to complete the main heat exchange. Simultaneously, the combustion air is preheated to 80℃~120℃ by the waste heat from the flue gas, and then distributed to each fully premixed burner 3 via the air pipe 12. This design achieves cascade utilization of waste heat from the flue gas: the preheating heat exchanger 14 recovers heat from the flue gas to preheat the combustion air, increasing the temperature of the air entering the furnace, reducing fuel consumption in the main combustion zone, and improving boiler thermal efficiency; after two heat exchanges, the exhaust gas temperature is further reduced, decreasing exhaust heat loss; the preheated air promotes more complete fuel combustion, further reducing pollutant emissions.

[0081] The parts of this invention not described in detail are prior art. It will be apparent to those skilled in the art that this invention is not limited to the details of the above exemplary embodiments, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be regarded as exemplary and non-limiting in all respects, and are intended to encompass all changes falling within the meaning and scope of equivalents within this invention.

Claims

1. A low NOx steam boiler with full premix combustion, characterized in that, include: The housing (1) has an internal mounting cavity; The boiler module consists of multiple units installed sequentially from the head end to the tail end along the housing (1); The boiler module includes: The furnace body (2) is a horizontally arranged ring-shaped structure. The inner cavity of the furnace body (2) is a combustion chamber. A water heating chamber is provided between the combustion chamber and the outer wall of the furnace body (2). The cavity wall of the combustion chamber is provided with a spiral groove structure extending towards the combustion chamber. The spiral groove structure is connected to the water heating chamber. The combustion chambers of two adjacent furnace bodies (2) are connected accordingly. The fully premixed burner (3) is installed in the combustion chamber. The hot airflow generated by the combustion of the fully premixed burner (3) flows spirally along the spiral groove structure of the combustion chamber. The negative pressure steam pack (4) is installed above the furnace body (2). The negative pressure steam pack (4) is connected to the water heating chamber of the furnace body (2) through multiple convection pipes; and the tops of two adjacent negative pressure steam packs (4) are connected in parallel through negative pressure steam pipes. The tubular heat exchangers (5) are two symmetrically installed between the negative pressure steam drum (4) and the fully premixed burner (3). The water passage of the tubular heat exchangers (5) is connected to the water heating chamber of the furnace body (2); and the flue gas chambers of the two adjacent tubular heat exchangers (5) are connected accordingly. Among them, the flue gas chambers of the two tubular heat exchangers (5) of the boiler module located at the head end of the box (1) are connected in series through elbows (6); the flue gas chamber of one of the tubular heat exchangers (5) of the boiler module located at the tail end of the box (1) is connected to the combustion chamber of the boiler module furnace body (2) through a guide hood (7), and the flue gas chamber of the other tubular heat exchanger (5) is connected to the chimney (8).

2. The fully premix-combustion low-NOx steam boiler as claimed in claim 1, wherein The fully premixed burner (3) includes: The air inlet pipe (3-1) has one end inserted into the combustion chamber of the furnace body (2); The water-cooled sleeve (3-2) is fitted outside the pipe body of the air inlet pipe (3-1) located inside the combustion chamber. One end of the water-cooled sleeve (3-2) is sealed to the outer wall of the air inlet pipe (3-1), and the other end is connected to the water-burning chamber of the furnace body (2). The gas pipe (3-3) is installed inside the air inlet pipe (3-1); The impeller (3-4) is rotatably connected to the hollow bracket inside the gas outlet of the gas pipe (3-3); the gas is blown out from the gas pipe (3-3) to drive the impeller (3-4) to rotate, and the gas diffuses circumferentially under the action of the centrifugal force of the impeller (3-4); The combustion tube (3-5) has its middle section connected to the outlet end of the intake pipe (3-1); both ends of the combustion tube (3-5) are closed, and multiple outlet holes are arranged in an array on the tube body; Ignition needle (3-6) is installed on water cooling sleeve (3-2), and the cable of ignition needle (3-6) is passed through water cooling sleeve (3-2); The blower (3-7) is installed at the air inlet end of the air inlet pipe (3-1).

3. The fully premix-combustion low-NOx steam boiler as claimed in claim 2, wherein The impeller (3-4) includes: The rotating shaft (3-41) is rotatably connected at one end to the hollow bracket inside the gas outlet end of the gas pipe (3-3), and the other end extends out of the gas pipe (3-3). The wheel (3-42) is vertically and securely connected to the extended end of the rotating shaft (3-41); The curved blades (3-43) are multiple ones arranged circumferentially along the wheel (3-42), and the curved blades (3-43) are located on the side of the wheel (3-42) corresponding to the gas pipe (3-3).

4. The fully premix-combustion low-NOx steam boiler as claimed in claim 2, wherein The combustion tube (3-5) is wrapped with a metal fiber mesh (3-8).

5. The fully premixed combustion low-NOx steam boiler as described in claim 2 or 4, characterized in that, The combustion tube (3-5) has a cone (3-9) at both ends, and the tips of the two cones (3-9) are arranged opposite each other.

6. The fully premixed combustion low-NOx steam boiler as described in claim 2, characterized in that, The air inlet pipe (3-1) has multiple conical diffuser meshes (3-10) spaced apart at the air outlet port, with the tips of two adjacent conical diffuser meshes (3-10) facing away from each other.

7. The fully premixed combustion low-NOx steam boiler as described in claim 1, characterized in that, The bottom of the boiler body (2) of the boiler module is connected to a converter pipe (9), which is connected to the top of the negative pressure steam package (4) of the boiler module, and a water pump (10) is installed on the pipe.

8. The fully premixed combustion low-NOx steam boiler as described in claim 1, characterized in that, A water pipe (11) connected to the two tubular heat exchangers (5) is installed at the top position between the two tubular heat exchangers (5) of the boiler module, and the water pipes (11) of the two adjacent boiler modules are connected in series; an air pipe (12) for supplying air to the fully premixed burner (3) is installed at the bottom position between the two tubular heat exchangers (5), and the air pipes (12) of the two adjacent boiler modules are connected in series.

9. The fully premixed combustion low-NOx steam boiler as described in claim 8, characterized in that, The air inlet end of the air pipe (12) is equipped with a filter (13).

10. The fully premixed combustion low-NOx steam boiler as described in claim 8 or 9, characterized in that, A preheating heat exchanger (14) connected to the air inlet end of the air pipe (12) is installed between the flow guide (7) and the corresponding tubular heat exchanger (5).

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