A low-nitrogen combustor for a roasting furnace based on cyclone and staged combustion

Abstract

The present application relates to the technical field of combustor, in particular to a kind of low-nitrogen combustor of roasting furnace natural gas based on cyclone and staged combustion, solve the problem that more nitrogen oxides can be produced in the combustor in the prior art;It includes outer sleeve, inner sleeve and inner core tube, the outer sleeve is sleeved on the outside of inner sleeve, air flow channel is formed between the outer sleeve and inner sleeve, the inner core tube is connected to the inside of inner sleeve, the inner sleeve is formed with natural gas flow channel through inner core tube, the inner wall of outer sleeve is formed with first rifling, the inner wall of inner sleeve is formed with second rifling, spiral groove is formed on the inner core tube and penetrates both ends;The scheme utilizes multiple rifling structures to make air and gas produce cyclone, improve mixing effect, enhance the radiation heat transfer effect of combustion in the furnace on furnace wall, increase the thermal efficiency of equipment, reduce energy waste, compared with conventional direct injection type combustor, NOx is reduced by 40.7%, and flame length is nearly 2 times of conventional direct injection type.

Description

Technical Field

[0001] This invention relates to the field of burner technology, and specifically to a low-NOx burner for natural gas in a roasting furnace based on swirl and staged combustion. Background Technology

[0002] Natural gas has wide applications in both industrial and residential sectors, and its pollutant emissions have a significant impact on the social environment and human health. Nitrogen oxides, in particular, are well-known air pollutants. Natural gas burners are key equipment in industrial and residential thermal systems, and their output power, energy consumption, and pollutant emissions have a significant impact on the economic indicators of kilns.

[0003] Currently, the traditional burners used in domestic prebaked anode roasting furnaces have simple structures, poor functionality, and short service lives. Because the roasting process in these furnaces does not employ air distribution principles, but instead relies on high-speed air introduced by high negative pressure within the furnace to provide oxygen, and because the direct-injection structure and injection principle of traditional burners make it difficult for natural gas to fully mix with the high-speed oxygen, this results in problems such as short flame length, unstable flame, high peak temperatures at the burner outlet while the average temperature inside the furnace is low, large amounts of thermal nitrogen oxides are generated during the heating phase, and incomplete combustion. This inefficient combustion caused by outdated combustion equipment significantly increases the waste of fossil fuels and the emission of pollutants in production processes with long roasting cycles.

[0004] The existing burners have the following specific problems:

[0005] 1. The final firing temperature of the calcining furnace is above 1100°C. When the temperature is above 900°C, nitrogen oxides increase by 7-8 times for every 100°C increase.

[0006] 2. The temperature reaction zone is small, and the local flame temperature exceeds 1600°C, resulting in the formation of a large amount of thermal NOx.

[0007] 3. Although dry non-catalytic reduction is currently used for nitrogen reduction, the amount of nitrogen oxides generated during combustion is too large. Furthermore, the reduction of nitrogen oxides by SNCR relies on the ammonia produced in the pyrolysis reaction to selectively reduce NOx in the flue gas, which has a limited degree of reaction. As a result, the workshop monitoring system sometimes shows nitrogen oxides exceeding 50mg, affecting production.

[0008] 4. When nitrogen oxide levels exceed limits, large quantities of urea are used. In severe cases, this can lead to temporary furnace shutdowns, resulting in significant heat loss and waste, and increasing production costs in the workshop.

[0009] Solution: Suppressing the large-scale generation of thermal NOx during combustion, and then using urea to catalytically reduce the remaining NOx after suppression, is a good way to save energy, save costs, and ensure production. This solution is to explore and invent a new burner to reduce NOx generation during combustion. Summary of the Invention

[0010] Based on the above description, the present invention provides a low-NOx burner for natural gas in a roasting furnace based on swirl and staged combustion, in order to solve the problem that burners in the prior art produce a large amount of nitrogen oxides.

[0011] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0012] A low-NOx natural gas burner for a roasting furnace based on swirl and staged combustion is characterized by comprising an outer sleeve, an inner sleeve, and an inner core tube. The outer sleeve is fitted over the outer sleeve, forming an air flow channel between the outer sleeve and the inner sleeve. The inner core tube is fitted over the inner sleeve, having a first gas flow channel inside and a second gas flow channel on the inner core tube. The first and second gas flow channels communicate to form a natural gas flow channel. The inner wall of the outer sleeve has a first rifling, and the inner wall of the inner sleeve has a second rifling. The inner core tube has a spiral groove penetrating both ends.

[0013] Based on the above technical solution, the present invention can be further improved as follows.

[0014] Furthermore, the inner core tube is sleeved in the middle of the inner sleeve. The portion of the inner sleeve that sleeves the inner core tube is defined as the middle section, the portion outside the middle section facing the nozzle is defined as the front section, and the portion outside the middle section away from the nozzle is defined as the rear section. The inner diameter of the rear section is larger than that of the middle section, and the inner diameter of the middle section is larger than that of the front section.

[0015] Furthermore, the second rifling includes an A sub-rifling formed in the front section and a B sub-rifling formed in the middle section.

[0016] Furthermore, the rotation direction of the A rifling groove is opposite to that of the B rifling groove.

[0017] Furthermore, the A rifling groove rotates in the same direction as the first rifling groove.

[0018] Furthermore, the rotation direction of the spiral groove is the same as the rotation direction of the B-type rifling.

[0019] Furthermore, the front section of the inner sleeve has a contraction zone, the outer diameter of which is smaller than that of the middle section, and a tapered guide surface is formed at the connecting line of the contraction zone.

[0020] Furthermore, the number of the first rifling grooves and the number of the B rifling grooves are the same, and the number of the A rifling grooves is half that of the B rifling grooves.

[0021] Furthermore, the number of the first rifling and the B rifling is 12, and the number of the A rifling is 6.

[0022] Furthermore, a tapered sleeve is fitted onto the rear section, and the end of the outer sleeve abuts against the tapered sleeve.

[0023] Compared with the prior art, the technical solution of this application has the following beneficial technical effects:

[0024] 1. The new low-NOx burner achieves an average temperature 24°C higher than conventional burners in the roasting furnace combustion process, which enhances the radiative heat transfer effect of combustion in the furnace on the furnace walls, increases the thermal efficiency of the equipment, and reduces energy waste.

[0025] 2. The new low-NOx burner reduces NOx by 40.7% compared to conventional direct-injection burners in the calcining furnace combustion process.

[0026] 3. The flame length of the new low-NOx burner is nearly twice that of the conventional direct injection type. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the overall structure provided for an embodiment of the present invention;

[0028] Figure 2 for Figure 1 Cross-sectional view;

[0029] Figure 3 for Figure 2 A schematic diagram of the structure after the inner core tube is removed;

[0030] Figure 4 This is a schematic diagram of the inner core tube structure;

[0031] Figure 5 This is a schematic diagram of the combustion chamber structure;

[0032] Figure 6 A chart comparing the temperatures of the three burners;

[0033] Figure 7 Charts showing NOx emissions for three types of burners;

[0034] Figure 8 The diagram shows the flame length of three types of burners.

[0035] The attached diagram lists the components represented by each number as follows:

[0036] 1. Outer tube; 2. Inner tube; 21. Front section; 22. Middle section; 23. Rear section; 24. Contraction zone; 3. Inner core tube; 4. First rifling; 5. A sub-rifling; 6. B sub-rifling; 7. Spiral groove; 8. Conical sleeve. Detailed Implementation

[0037] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings, which illustrate embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be thorough and complete.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0039] It is understood that spatial relation terms such as "below," "under," "below," "below," "above," "above," etc., can be used here to describe the relationship between one element or feature shown in the figure and other elements or features. It should be understood that, in addition to the orientation shown in the figure, spatial relation terms also include different orientations of the device in use and operation. For example, if the device in the figure is flipped, the element or feature described as "below" or "below" of the other element or feature will be oriented "above" the other element or feature. Therefore, the exemplary terms "below" and "below" can include both upper and lower orientations. Furthermore, the device may also include other orientations (e.g., rotated 90 degrees or other orientations), and the spatial descriptive terms used herein will be interpreted accordingly.

[0040] It should be noted that when one element is considered to be "connected" to another element, it can be directly connected to the other element or connected to the other element through an intermediary element. In the following embodiments, "connection" should be understood as "electrical connection," "communication connection," etc., if the connected circuits, modules, units, etc., have the transmission of electrical signals or data between them.

[0041] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising,” “including,” or “having,” etc., specify the presence of the stated feature, whole, step, operation, component, part, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof.

[0042] like Figure 1-4 The diagram illustrates a low-NOx natural gas burner for a roasting furnace based on swirl and staged combustion. It includes an outer sleeve 1, an inner sleeve 2, and an inner core tube 3. The outer sleeve 1 is fitted over the inner sleeve 2, forming an air flow channel between them. The inner sleeve 2 has a first gas flow channel inside. The inner core tube 3 is fitted inside the inner sleeve 2, and has a second gas flow channel. The first and second gas flow channels communicate to form a natural gas flow channel. The inner wall of the outer sleeve 1 has a first rifling groove 4, and the inner wall of the inner sleeve 2 has a second rifling groove. The inner core tube 3 has a spiral groove 7 extending through both ends, which serves as the second gas flow channel. The first rifling groove 4 alters the airflow to cause it to rotate, while the second rifling groove and spiral groove 7 alter the combustion gas flow to cause it to rotate. The swirl creates a rotating jet of air or combustion gas, promoting thorough mixing of the gas and air, extending the residence time, and improving flame stability.

[0043] The inner core tube 3 is sleeved in the middle of the inner sleeve 2. The portion of the inner sleeve 2 that sleeves the inner core tube 3 is defined as the middle section 22. The portion of the middle section 22 facing the nozzle is defined as the front section 21. The portion of the middle section 22 away from the nozzle is defined as the rear section 23. The inner diameter of the rear section 23 is larger than that of the middle section 22, and the inner diameter of the middle section 22 is larger than that of the front section 21. A tapered sleeve 8 is sleeved on the rear section 23. The end of the outer sleeve 1 abuts against the tapered sleeve 8. Several support members are provided between the outer sleeve 1 and the inner sleeve 2.

[0044] The second rifling includes sub-rifling A 5 formed in the front section 21 and sub-rifling B 6 formed in the middle section 22. Sub-rifling A 5 and sub-rifling B 6 rotate in opposite directions. The core of swirling combustion technology is the central recirculation zone generated in the center of the airflow due to the negative pressure gradient. When the fuel or air mixture passes through the swirler, a strong swirling effect is generated near the burner outlet in the furnace, forming a high-temperature flue gas recirculation zone, which greatly increases fuel ignition and flame stability.

[0045] Preferably, the rotation direction of sub-rifling 5 is the same as that of the first rifling 4.

[0046] Preferably, the rotation direction of the spiral groove 7 is the same as the rotation direction of the B-rifling 6.

[0047] The front section 21 of the inner sleeve 2 has a contraction zone 24, the outer diameter of which is smaller than that of the middle section 22. A tapered guide surface is formed at the connecting line of the contraction zone 24. The increased diameter of the air flow channel at the contraction zone 24, in conjunction with the narrowing of the gas flow channel at the front section 21, improves the air-gas mixing efficiency at the burner nozzle.

[0048] In this design, the number of first rifling grooves 4 and B rifling grooves 6 is the same, and the number of A rifling grooves 5 is half that of B rifling grooves 6. Specifically, the number of first rifling grooves 4 and B rifling grooves 6 is 12, and the number of A rifling grooves 5 is 6.

[0049] The following is a simulation calculation for this scheme:

[0050] I. Model Establishment

[0051] (1) Turbulence model

[0052] The time-averaged RANS equations add Reynolds stress and turbulent transport terms, which cause the RANS equations to become unclosed. Therefore, to close the RANS equation solution process, additional flow equations need to be introduced. The Reynolds number in the flame space of the aluminum melting furnace is much greater than the critical Reynolds number, and the flow process is entirely turbulent. Therefore, the Realizable model commonly used in swirl burners, combined with the standard wall function method, is used to solve for the turbulent characteristics.

[0053] (2) Combustion model and radiation model

[0054] The reaction model of CH4 with O2 in the air employs a two-step reaction vortex breakup model. The combustion products in the flue contain a large amount of triatomic gas, which therefore emits radiation. The P-1 model has significant advantages in solving problems related to heat transfer in high-temperature gases, and its energy diffusion equation is relatively easy to solve. Therefore, the P-1 model was selected in this study to solve the radiation problem of the furnace gas.

[0055] (3) Burner model

[0056] The combustion chamber has a longitudinal depth of 5140 mm, a length of 6600 mm, and a thickness of 360 mm. Figure 5 As shown. Due to the influence of mesh generation, half of the combustion chamber was selected as the computational domain for numerical simulation.

[0057] (4) Natural gas burner model

[0058] There are three types of natural gas burner nozzle models: (A) direct injection burner (currently used in Suotong Jiayuguan), (B) ordinary swirl type, and (C) this scheme.

[0059] II. Solution Methods and Boundary Conditions

[0060] In the numerical simulation of combustion, the SIMPLE algorithm was used to solve the coupled velocity and pressure equations. The pressure interpolation scheme was PRESTO!, and the remaining variables (momentum, composition, and energy, etc.) were solved using a second-order upwind scheme. To ensure the accuracy of the calculation, the residuals of the continuity equation were set to 10⁻⁴, the residuals of the velocity, energy, and radiation equations were set to 10⁻⁶, and the residuals of the composition equations were set to 10⁻⁵. The average velocity and temperature at the outlet of the aluminum melting furnace in the computational domain were also monitored.

[0061] (1) Natural gas inlet

[0062] The fuel is assumed to be pure CH4. During the calculation, the velocity inlet boundary condition is applied to the fuel nozzle, the velocity at the fuel nozzle is set to 50.154 m / s, and the temperature is assumed to be 303 K.

[0063] (2) Combustion air inlet

[0064] A velocity inlet boundary is used, and the velocity magnitude is calculated based on the fuel flow rate, air excess coefficient, and inlet area; the velocity is 2.6 m / s, and the air excess coefficient is 2.1. The air is preheated to 1323 K through the cooling section.

[0065] (3) Wall conditions

[0066] The heat exchange between the combustion chamber wall and the environment adopts a comprehensive heat exchange boundary condition with both convection and radiation, and both are assumed to be fixed walls without slippage. The convection heat transfer coefficient is taken as 15 W / m²·K, and the wall emissivity is taken as 0.65.

[0067] (4) Fire exit

[0068] The standard constant pressure outlet boundary is applied to the fire channel outlet, with an outlet pressure of -25 Pa.

[0069] III. Simulation Results

[0070] like Figure 6 As shown, the three columns for each model, from left to right, represent the outlet temperature, peak temperature, and average temperature.

[0071] Peak temperature:

[0072] 1. Conventional direct injection has the highest output, with a larger fuel velocity and more concentrated distribution.

[0073] 2. The conventional swirl type and this scheme significantly reduce fuel consumption, as the fuel is more dispersed after swirling, allowing combustion to occur in a low-fuel environment.

[0074] 3. This design has the lowest temperature, greater swirl intensity in the burner, and more uniform fuel distribution, thus reducing the excessive concentration in the high-temperature zone.

[0075] Average temperature:

[0076] This design achieves the highest average temperature, 24°C higher than conventional designs and 16°C higher than ordinary swirl furnaces. It enhances the radiative heat transfer from combustion within the furnace to the furnace walls, increasing equipment thermal efficiency and reducing energy waste.

[0077] like Figure 7 The figure shows the NOx generation of each burner.

[0078] NOx peak:

[0079] Standard direct injection: 1357ppm; ordinary swirl injection: 926ppm; this solution: 804ppm.

[0080] This solution reduces NOx by 40.7% compared to conventional direct injection burners and by 15.1% compared to ordinary swirl burners.

[0081] like Figure 8 As shown, Figure 8 The 1500K flame profiles for three different burners are shown in the figure.

[0082] 1. The flame area of ​​this 1500K is much larger than that of conventional direct injection and ordinary swirl type, and the flame length is nearly twice that of conventional direct injection and about 1.5 times that of ordinary swirl type.

[0083] 2. This design has the largest reaction area and the longest flame length, which can increase the temperature level inside the furnace and enhance the radiation effect of the flame on the furnace wall.

[0084] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A low-NOx burner for a roasting furnace based on swirl and staged combustion, characterized in that, It includes an outer sleeve, an inner sleeve, and an inner core tube. The outer sleeve is fitted over the outside of the inner sleeve, and an air flow channel is formed between the outer sleeve and the inner sleeve. The inner core tube is fitted inside the inner sleeve. The inner sleeve has a first gas flow channel, and the inner core tube has a second gas flow channel. The first gas flow channel and the second gas flow channel are connected to form a natural gas flow channel. The inner wall of the outer sleeve has a first rifling, the inner wall of the inner sleeve has a second rifling, and the inner core tube has a spiral groove that extends through both ends. The inner core tube is sleeved in the middle of the inner sleeve. The part of the inner sleeve that sleeves the inner core tube is defined as the middle section. The part outside the middle section that faces the nozzle is defined as the front section. The part outside the middle section that is far away from the nozzle is defined as the rear section. The inner diameter of the rear section is larger than that of the middle section. The inner diameter of the middle section is larger than that of the front section. The second rifling includes an A sub-rifling formed in the front section and a B sub-rifling formed in the middle section; the A sub-rifling and the B sub-rifling rotate in opposite directions; the A sub-rifling and the first rifling rotate in the same direction; the spiral groove rotates in the same direction as the B sub-rifling.

2. The low-NOx burner for a roasting furnace based on swirl and staged combustion according to claim 1, characterized in that, The front section of the inner sleeve has a contraction zone, the outer diameter of which is smaller than that of the middle section, and a tapered guide surface is formed at the connecting line of the contraction zone.

3. The low-NOx burner for a roasting furnace based on swirl and staged combustion according to claim 1, characterized in that, The number of the first rifling groove and the number of the B rifling groove are the same, and the number of the A rifling groove is half that of the B rifling groove.

4. A low-NOx burner for a roasting furnace based on swirl and staged combustion according to claim 3, characterized in that, The number of the first rifling groove and the B rifling groove is 12, and the number of the A rifling groove is 6.

5. A low-NOx natural gas burner for a roasting furnace based on swirl and staged combustion according to claim 1, characterized in that, A tapered sleeve is fitted onto the rear section, and the end of the outer sleeve abuts against the tapered sleeve.

Images