A porous medium combustor based on flow field reconstruction and thermal cycle synergistic stable combustion

Abstract

The present application belongs to the technical field of porous medium combustion, and discloses a porous medium burner based on flow field reconstruction and heat cycle collaborative stable combustion, which comprises a shell and a porous medium arranged in the shell, wherein the porous medium comprises a connecting section and a convex section, the connecting section is connected and fixed with the inner wall of the shell, the convex section is connected with the downstream end face of the connecting section, and the diameter of the convex section is smaller than that of the connecting section, so that an annular free space is formed between the convex section and the inner wall of the shell; the convex section is used for forming a low-speed flow area at the center, and the central part of the flame is stably arranged in the low-speed flow area to form a partially submerged flame; the annular free space is used for forming a flow boundary layer for stabilizing the outer part of the flame; meanwhile, the submerged flame is beneficial to further improving the heat recovery efficiency of the porous medium, so that the effects of flow and heat cycle collaborative stable combustion are realized, and the blowout limit of the flame is improved.

Description

Technical Field

[0001] This invention belongs to the technical field of porous media combustion, and more specifically, relates to a porous media burner based on flow field reconstruction and thermal cycle synergistic stable combustion. Background Technology

[0002] The increasingly severe global warming and dwindling fossil fuel resources have placed higher demands on energy conservation and emission reduction, making the search for environmentally friendly combustion technologies increasingly important. On the one hand, it is necessary to improve the utilization efficiency of hydrocarbon fuels; on the other hand, it is crucial to actively develop zero-carbon fuels, such as ammonia and hydrogen. Porous media combustion technology is an effective solution. The unique structure of porous media causes the fluid micro-elements within it to constantly change their direction of movement, generating a dispersion effect, disrupting the flow boundary layer, and making the fluid movement more complex. This facilitates the formation of a uniform velocity and temperature field, thereby promoting material mixing, lowering combustion temperature, and reducing pollutant emissions. Furthermore, compared to bare tubes, porous media increase the heat exchange area between the fluid and the porous medium by several times or even tens of times, which enhances the heat exchange efficiency between the fluid and the solid framework, increases the combustion speed, and enables the efficient utilization of lean and difficult-to-burn fuels.

[0003] Despite the advantages of porous media combustion, the applicant found in previous studies that in a circular tube with porous media, the flame extinguishing limit (defined as the maximum inlet velocity for maintaining combustion) for a chemically appropriate butane / air premixed gas is only 0.55 m / s (slightly greater than its laminar combustion velocity). The flame is difficult to fix in the porous media, so the heat recovery efficiency of the unburned mixture through the porous media is not high at higher inlet velocities, and the heat recovery effect of the porous media is not fully utilized.

[0004] Existing porous media combustion still faces problems such as difficulty in fixing the flame in porous media, a narrow range of fixed flame velocity, and a small flame extinguishing limit, which bring difficulties to the application of porous media burners. Summary of the Invention

[0005] To address the above-mentioned deficiencies or improvement needs of existing technologies, this invention provides a porous media burner based on flow field reconstruction and thermal cycle synergistic stable combustion. This solves the problems of existing porous media combustion, such as the difficulty in fixing the flame in the porous medium, the narrow velocity range of the fixed flame, and the small flame extinguishing limit. It is beneficial to obtain a fixed flame with a certain velocity range in the porous media burner and obtain a wider stable combustion velocity range.

[0006] To achieve the above objectives, according to the present invention, a porous medium burner based on flow field reconstruction and thermal cycle synergistic combustion stabilization is provided, comprising a shell and a porous medium disposed inside the shell. The porous medium includes a connecting section and a protruding section. The connecting section is fixedly connected to the inner wall of the shell, and the protruding section is connected to the downstream end face of the connecting section. The cross-sectional dimension of the protruding section is smaller than that of the connecting section, such that an annular free space is formed between the protruding section and the inner wall of the shell.

[0007] The protruding section is used to form a low-velocity flow zone at the center of the outer shell, stabilizing the central part of the flame within it to form a partially submerged flame; the annular free space is used to form a stable flow boundary layer on the outer side of the flame at the wall of the outer shell; at the same time, the submerged flame helps to improve the heat recovery efficiency of the porous medium, thereby achieving the effect of coordinated stable combustion of flow and thermal circulation.

[0008] According to the porous media burner based on flow field reconstruction and thermal cycle synergistic combustion stabilization provided by the present invention, the cross-section of the outer shell is circular, polygonal or flat, and the length of the protruding section along the flame flow direction accounts for 10%-90% of the total length of the porous media.

[0009] According to the porous medium burner based on flow field reconstruction and thermal cycle synergistic combustion stabilization provided by the present invention, the equivalent diameter of the protruding section is 20%-80% of the equivalent diameter of the connecting section.

[0010] According to the porous medium burner based on flow field reconstruction and thermal cycle synergistic combustion stabilization provided by the present invention, the cross-sectional size that can obtain the maximum flame extinguishing limit is selected as the optimal cross-sectional size of the protruding section through simulation experiment.

[0011] According to the porous medium burner based on flow field reconstruction and thermal cycle synergistic combustion stabilization provided by the present invention, the placement position of the porous medium in the outer shell is determined according to the requirements of the heat source in actual application.

[0012] According to the porous medium burner based on flow field reconstruction and thermal cycle synergistic combustion stabilization provided by the present invention, the outer shell is a stainless steel shell or a quartz glass shell.

[0013] The porous medium burner based on flow field reconstruction and thermal cycle synergistic combustion stabilization provided by the present invention is a metal wire mesh, porous ceramic or foam metal.

[0014] Overall, compared with the prior art, the porous media burner based on flow field reconstruction and thermal cycle synergistic combustion stabilization provided by the present invention offers the following advantages:

[0015] 1. By appropriately tailoring the structure of the porous medium, an annular free-flow zone is formed between the porous medium and the burner wall in the downstream section. Due to the obstruction of flow by the porous medium, the fluid velocity can be reduced inside the protruding section in the downstream section, forming a low-velocity flow zone in the stable flame center and creating a partially submerged flame. At the same time, a thicker velocity boundary layer is formed at the wall of the annular free space, which helps to stabilize the outer part of the flame within the boundary layer, thereby facilitating the acquisition of a stationary flame within a certain velocity range and a wider stable combustion velocity range.

[0016] 2. The formation of partially submerged flames can enhance the thermal circulation efficiency of porous media, further improve its stable combustion capability and combustion efficiency, thereby helping to improve the flame extinguishing limit. Attached Figure Description

[0017] Figure 1 This is a two-dimensional structural schematic diagram of the porous medium flame-stabilized burner provided by the present invention;

[0018] Figure 2 This is a schematic diagram of the velocity contour lines (black lines) inside and near the porous medium in the burner provided by the present invention, as well as the position of the flame front (colored area);

[0019] Figure 3 This is the heat recovery efficiency of the porous medium during combustion in the burner under different protrusion lengths in a specific embodiment provided by the present invention.

[0020] Figure 4 This is the flame extinguishing limit under different protrusion lengths during combustion inside the burner in a specific embodiment provided by the present invention;

[0021] Figure 5 This is the flame extinguishing limit under different protruding section radii during combustion inside the burner in a specific embodiment provided by the present invention;

[0022] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein:

[0023] 1-Burner inlet; 2-Upstream section; 3-Porous medium; 31-Connecting section; 32-Protruding section; 4-Downstream section; 5-Burner outlet; 6-Shell. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0025] Please see Figure 1 This invention provides a porous medium burner based on flow field reconstruction and thermal cycle synergistic combustion stabilization. The porous medium burner includes a shell 6 and a porous medium 3 disposed inside the shell 6. The porous medium 3 has a pore structure inside and includes a connecting section 31 and a protruding section 32. The connecting section 31 is connected and fixed to the inner wall of the shell 6, and the protruding section 32 is connected to the downstream end face of the connecting section 31. The cross-sectional dimension of the protruding section 32 perpendicular to the incoming flow direction is smaller than the cross-sectional dimension of the connecting section 31, so that an annular free space is formed between the protruding section 32 and the inner wall of the shell 6.

[0026] The protruding section is used to create a low-velocity flow zone at the center of the outer shell, stabilizing the central portion of the flame within it to form a partially submerged flame. The annular free space is used to form a stable flow boundary layer on the outer wall of the outer shell for the outer portion of the flame. Simultaneously, the submerged flame helps to further improve the regenerative efficiency of the porous medium, thereby achieving a synergistic effect of stable combustion through flow and thermal circulation.

[0027] This invention incorporates a porous medium 3 within the burner's outer casing 6. The porous medium 3 reconstructs the flow field distribution within the burner. Specifically, the porous medium 3 includes a connecting section 31 and a protruding section 32. The connecting section 31 forms a uniform flow zone for the porous medium, while the protruding section 32 forms a velocity reduction zone at the center of the porous medium. The connecting section 31 is located upstream of the protruding section 32. After the fuel and oxidant are mixed, they flow into the outer casing 6 from the burner inlet 1, first passing through the connecting section 31. The connecting section 31 serves both to fix the porous medium 3 to the inner wall of the outer casing 6 and to increase the heat exchange area for preheating the unburned gas, while simultaneously ensuring uniform gas flow and a more uniform velocity across the entire cross-section.

[0028] After the fuel and oxidizer mixture is regulated by the connecting section 31, it flows out. Due to the large resistance of the protruding section 32 to the fluid flow in the center of the burner, the fluid will change direction and flow into the annular free space. When the fluid passes through the protruding section 32, a low-velocity flow zone will be formed in the center of the burner. At the same time, the fluid in the annular free space will form a flow boundary layer near the wall. Through the low-velocity flow zone formed in the protruding section 32 and the fully developed flow boundary layer near the wall, the flame can be stabilized and the stable combustion range can be expanded.

[0029] The porous media burner based on flow field reconstruction and thermal circulation synergistic combustion stabilization provided by this invention, by appropriately tailoring the structure of the porous media, forms an annular free flow zone between the porous media and the combustion channel wall. Due to the flow resistance of the porous media, the fluid velocity can be reduced inside the protruding section 32 to form a low-velocity zone, which is beneficial for stabilizing the flame center within the porous media, forming a partially submerged flame. A relatively thick velocity boundary layer is formed at the annular free space wall, which is beneficial for stabilizing the outer part of the flame within the boundary layer. At the same time, the submerged flame helps to further improve the heat recovery efficiency of the porous media, thereby achieving the synergistic stable combustion effect of flow and thermal circulation. Thus, the flame stabilization effect is achieved through the synergy of the protruding section and the boundary layer, which helps to improve the flame extinguishing limit, obtain a stationary flame within a certain velocity range, and obtain a wider stable combustion velocity range.

[0030] In some specific embodiments, a porous media flame stabilization technology based on flow field reconstruction and thermal cycle synergy is disclosed. This technology is mainly aimed at fuels with slow combustion rates or very lean combustible gas mixtures, used to stabilize their flames and expand the flame stabilization range. The provided porous media flame stabilization burner specifically includes a burner inlet 1, an upstream free-flow zone (upstream section 2), a central convex porous media zone (porous medium 3), a downstream free-flow zone (downstream section 4), a burner outlet 5, and a casing 6. Premixed gas enters the burner and, after being ignited, forms a stable flame in the porous media zone. The upstream free-flow zone (upstream section 2), the central convex porous media zone (porous medium 3), and the downstream free-flow zone (downstream section 4) can be coaxially distributed within the burner casing 6.

[0031] The porous media stabilization combustion technology based on flow field reconstruction and thermal cycle synergy provided by this invention significantly improves the purge limit of premixed gas combustion while ensuring a fixed flame position, compared to previous porous media stabilization combustion technologies. Burners designed based on this invention are highly adaptable to various fuels, particularly slow-burning fuels (e.g., ammonia) or very lean combustible gas mixtures (e.g., coal mine gas). Burners designed based on this invention have high maximum output power and a wide adjustable output power range. This invention is versatile, and burners with various structures can be designed based on it.

[0032] In this embodiment, a low-speed zone for a stable flame is formed within the protruding section 32, meaning the gas velocity inside the protruding section 32 is lower than the gas velocity at the annular free space; this makes the flame front inside the burner... Figure 2 The colored area is shown, that is Figure 2The two arrows indicate the positions of the flame front at the protruding section 32 and at the boundary layer, respectively. This creates a low-velocity zone at the center of the burner, allowing this portion of the flame to be immersed in the porous medium, further improving regenerative efficiency. This also enhances the stability of the flame root at the center, thereby further increasing the flame extinguishing limit, achieving a higher velocity range of stationary flame and stable combustion, which is more beneficial for the practical application of the burner.

[0033] In some specific embodiments, the equivalent diameter of the protruding section 32 is 20%-80% of the equivalent diameter of the connecting section 31. This technology can be applied to burners with various cylindrical or other cross-sectional shapes, such as square or irregular shapes, and the specific shape is not limited.

[0034] In some specific embodiments, the optimal cross-sectional size of the protruding segment 32 is selected by means of simulation experiments, which can obtain the maximum flame extinguishing limit and form a stable flame.

[0035] The larger the cross-sectional size of the protruding section 32, the larger the area of ​​submerged combustion, which theoretically is more conducive to improving combustion efficiency and flame extinguishing limit. However, as the cross-sectional size of the protruding section 32 increases, the area of ​​the annular free space will relatively decrease, causing the internal fluid to fail to form a stable flame due to excessive flow velocity. Therefore, the optimal cross-sectional size of the protruding section 32 should be obtained with the aim of maximizing the flame extinguishing limit while ensuring the formation of a stable flame.

[0036] In some specific embodiments, the cross-section of the outer shell 6 is circular or flat, and the length of the protruding section 32 along the flame flow direction accounts for 10%-90% of the total length of the porous medium.

[0037] In some specific embodiments, the placement position of the porous medium 3 within the outer casing 6 is determined based on the actual application requirements for the heat source. That is, the stable flame is mainly distributed inside the protruding section 32, and the protruding section 32 can be positioned at the location requiring the heat source, thereby providing better heat delivery. The burner provided by this invention has good flame stabilization performance and is convenient for practical applications.

[0038] In some specific embodiments, the outer casing 6 is a stainless steel casing 6 or a quartz glass casing 6. It may also be made of other high-temperature resistant materials, and there is no specific limitation.

[0039] In some specific embodiments, the porous medium 3 is one of metal wire mesh, porous ceramic, and foamed metal. It can also be made of other high-temperature resistant materials, and there is no specific limitation.

[0040] In a specific example, an embodiment of the present invention provides a tubular burner filled with a convex porous medium 3, such as... Figure 1 As shown, the burner shell 6 is made of quartz material, with a density, specific heat capacity, thermal conductivity, and normal emissivity of 2650 kg / m³ at room temperature. 3 750 J / (kg·K), 1.4 W / (m 2 ·K) and 0.92. Porous medium 3 is made of 304 stainless steel wire mesh, and its density, specific heat capacity, thermal conductivity and normal emissivity at room temperature are 7980 kg / m³ and 0.92, respectively. 3 500 J / (kg·K), 21.5 W / (m 2 ·K) and 0.8. The length of the free flow zone in the upstream section 2 of the burner is 10 mm, and the total length of the porous medium 3 in the middle section is 10 mm. The burner shell 6 is a circular tube with a total length of 50 mm, an inner diameter of 6 mm, and a wall thickness of 1 mm. The fuel is butane, and the oxidizer is air. Before entering the burner, they are mixed into a combustible gas mixture with a certain equivalence ratio, and then enter the burner through the left inlet. After being ignited, the flame is stable downstream of the porous medium, exhibiting either a submerged flame or a surface flame state. The protruding section 32 of the control group has a length of 0 mm, and the other parameters are the same. The combustion characteristics under different protruding section 32 lengths and radii were numerically simulated using the general CFD calculation software FLUENT 19.0. The results are as follows. Figure 2 , Figure 3 , Figure 4 and Figure 5 As shown, the horizontal axis represents the length of the porous medium protrusion 32. Due to the axial symmetry of the geometry, the horizontal axis also corresponds to the central axis of the burner.

[0041] Figure 2 The figure presents the velocity contours (black lines) inside and near the porous medium 3, as well as the flame front position (colored area), when the butane / air premixed gas equivalence ratio is 1, the radius of the protruding section 32 is 1 mm, and the length of the protruding section 32 is 8 mm. The red line in the figure represents the boundary line of the porous medium. Figure 2 It can be seen that a distinct low-velocity zone is formed within the porous medium protrusion section 32, while a relatively thick velocity boundary layer is formed near the burner wall. These layers are used to stabilize the central and outer parts of the flame, respectively (arrow positions).

[0042] Figure 3The regenerative efficiency (the ratio of heat absorbed by the unburned gas mixture from the porous medium to the total heat input to the burner) of the premixed gas through the porous medium is presented when the butane / air premixed gas equivalence ratio is 1, the radius of the protruding section 32 is 1 mm, and the inlet velocity is 0.5 m / s. Specifically, it shows the regenerative efficiency of the premixed gas through the porous medium 3 when the downstream porous medium lengths are 0 mm (control group), 2 mm, 4 mm, 6 mm, and 8 mm, respectively, during combustion in a tubular burner with an inner diameter of 6 mm. It can be observed that, compared to the control group, the convex porous medium can improve the regenerative efficiency by more than double, thus more effectively preheating the unburned premixed gas and improving combustion stability.

[0043] Figure 4 The purge limits of butane / air premixed gas combustion in a quartz tube are given when the butane / air premixed gas equivalence ratio is 1, the radius of the protruding section 32 of the convex porous medium is 1 mm, and the lengths of the protruding section 32 are 0 mm (control group), 2 mm, 4 mm, 6 mm, and 8 mm. Figure 4 It can be clearly seen that the flame extinguishing limit increases with the length of the protruding section 32. When the length of the protruding section 32 is 8mm, the extinguishing limit reaches 1.05m / s, which is nearly double that of the control group model.

[0044] Figure 5 The purge limit of butane / air premixed gas during combustion in a quartz tube is given when the butane / air premixed gas equivalence ratio is 1, the optimal length of the protruding section 32 is 8 mm, and the radii of the protruding section 32 are 0.5 mm, 1 mm, 1.5 mm, and 2 mm. Figure 5 As shown, the blowout limit gradually increases with the radius of the protruding section 32, reaching a maximum of 1.65 m / s, which is three times the blowout limit of the control group. Further increasing the radius of the protruding section 32 results in an excessively high gas velocity within the annular space, preventing the formation of a stable flame. Therefore, a radius of 2 mm for the protruding section 32 is the optimal structural parameter for enhancing flame stability.

[0045] This invention proposes a porous media-based stable combustion technology based on the synergy of flow field reconstruction and thermal circulation. This technology involves appropriately tailoring the porous media so that the equivalent diameter of the porous media in the downstream section 4 is smaller than the equivalent diameter of the burner, thus creating an annular free space between them. Due to the significant resistance of the porous media to fluid flow, the fluid undergoes a flow direction change when passing through the protruding section 32 of the porous media (i.e., flowing towards the annular free space), thereby forming a low-velocity zone within it, stabilizing the flame center within the porous media. The formation of the submerged combustion mode also enhances heat exchange between the flame and the solid framework of the porous media, thereby significantly improving the regenerative efficiency of the porous media 3. The synergistic effect of flow field reconstruction and thermal circulation significantly improves the range of stable combustion in the porous media. This technology is universally applicable, particularly suitable for fuels with slow combustion rates (e.g., ammonia) or very lean combustible gas mixtures (e.g., coal mine gas).

[0046] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A porous media burner based on synergistic combustion stabilization of flow field reconstruction and thermal circulation, characterized in that, The device includes an outer shell and a porous medium disposed inside the outer shell. The porous medium includes a connecting section and a protruding section. The connecting section is fixedly connected to the inner wall of the outer shell, and the protruding section is connected to the downstream end face of the connecting section. The cross-sectional dimension of the protruding section is smaller than that of the connecting section, so that an annular free space is formed between the protruding section and the inner wall of the outer shell. The protruding section is used to form a low-velocity flow zone at the center of the outer shell, stabilizing the central part of the flame within it to form a partially submerged flame; the annular free space is used to form a stable flow boundary layer on the outer side of the flame at the wall of the outer shell; at the same time, the submerged flame helps to improve the heat recovery efficiency of the porous medium, thereby achieving the effect of coordinated stable combustion of flow and thermal circulation.

2. The porous media burner based on flow field reconstruction and thermal cycle synergistic combustion stabilization as described in claim 1, characterized in that, The outer shell has a circular, polygonal, or flat cross-section, and the length of the protruding section along the flame flow direction accounts for 10%-90% of the total length of the porous medium.

3. The porous media burner based on flow field reconstruction and thermal cycle synergistic combustion stabilization as described in claim 1, characterized in that, The equivalent diameter of the protruding section is 20%-80% of the equivalent diameter of the connecting section.

4. The porous media burner based on flow field reconstruction and thermal cycle synergistic combustion stabilization as described in claim 3, characterized in that, Through simulation experiments, the cross-sectional size that yields the maximum flame extinguishing limit is selected as the optimal cross-sectional size of the protruding section.

5. The porous media burner based on flow field reconstruction and thermal cycle synergistic combustion stabilization as described in any one of claims 1-4, characterized in that, The placement of the porous medium within the housing is determined based on the actual requirements for the heat source in the application.

6. The porous media burner based on flow field reconstruction and thermal cycle synergistic combustion stabilization as described in any one of claims 1-4, characterized in that, The outer casing is made of stainless steel or quartz glass.

7. The porous media burner based on flow field reconstruction and thermal cycle synergistic combustion stabilization as described in any one of claims 1-4, characterized in that, The porous medium is a metal wire mesh, porous ceramic, or foamed metal.

Images