A porous medium burner suitable for hydrogen-blended natural gas

Abstract

This invention relates to a porous media burner and its combustion method suitable for hydrogen-blended natural gas, belonging to the field of gas combustion technology. It includes a gas premixing chamber, a gas-air ejector, a swirl plate, a direct current plate, a preheating zone, an air preheating channel, a preheated air inlet, a shell, a combustion zone, combustion zone I, combustion zone II, and temperature measuring electrodes. It is suitable for the combustion of 0-100% hydrogen-blended natural gas, which helps reduce pollutant emissions and prevent flame instability phenomena such as flameout and flashback.

Description

Technical Field

[0001] This invention relates to the field of gas combustion technology, and in particular to a porous medium burner and combustion method suitable for hydrogen-blended natural gas. Background Technology

[0002] Common gas burners provide convective and radiant heating of high-temperature flue gas through free flame combustion. This combustion method results in a large temperature gradient near the flame surface, extremely uneven temperature distribution, unstable combustion, localized high temperatures, and incomplete combustion. These localized high temperatures lead to the generation of a large amount of thermal nitrogen oxides, while incomplete combustion results in the generation of a large amount of carbon monoxide, ultimately causing pollutant emissions to fail to meet standards.

[0003] If pure hydrogen or hydrogen-blended natural gas is used as fuel, the flame propagation speed is high, the flame elongation rate is high, and the risk of backfire and flameout also increases, causing safety hazards.

[0004] Porous media combustion technology is a novel combustion method that has developed in the international combustion field over the past decade. Compared to "open flame" combustion, which involves localized high temperatures, this type of combustion does not have an open flame. The temperature and uniformity of the combustion surface can be significantly improved, and the formation of pollutants such as NOx (e.g., nitric oxide and nitrogen dioxide) is significantly reduced (by more than 70%), with NOx below 30 ppm and CO below 10 ppm. Direct emissions can meet environmental protection requirements. Furthermore, the presence of solid porous media (infrared radiation coefficient > 0.9) greatly enhances the efficiency of radiative heat transfer. Since solid radiation has no wavelength selectivity for infrared radiation, its radiative heat transfer capacity is greatly enhanced compared to flue gas, resulting in a significant increase in combustion heat utilization efficiency (in some cases, even exceeding 50%). Summary of the Invention

[0005] Therefore, it is necessary to provide a porous media burner to address the above problems, enabling it to be used for the stable combustion of hydrogen-blended natural gas with a hydrogen blending ratio of 0-100%, thus solving the problems of flame stability and pollutants.

[0006] The hydrogen-blended natural gas air premixer has tangentially distributed Venturi ejectors at the bottom of the premixer chamber, with a gas injection device at the inlet end of the Venturi ejectors; a guide plate is provided at the upper end of the hydrogen-blended natural gas air premixing chamber, with a DC plate in the middle, a protection zone inside the DC plate, a preheating zone and a combustion zone with two sections of pores at the upper end of the DC plate; a swirler is provided outside the guide plate, with a preheating zone and a combustion zone at the upper end of the swirler; and an air preheating interlayer channel is provided on the outer wall of the burner.

[0007] Firstly, the fuel gas is supplied by a gas injector connected to the Venturi ejector; secondly, air can be supplied by the entrainment effect of the Venturi ejector, and a portion of the air can also be supplied by the air preheating channel to meet and regulate the air that allows the fuel gas to burn completely; the two are further premixed in the premixing chamber, above which a baffle plate, a combustion chamber and an ignition needle are arranged in sequence.

[0008] The ejector is a Venturi tube, which is tangentially and uniformly arranged with the premixing chamber. There are two or three Venturi tubes in total. The ejector is arranged at an angle of 0° to 15° with the horizontal plane of the premixing chamber. This tangential rotating premixing arrangement allows the gas and air to be more fully premixed while maintaining a certain flow velocity in the longitudinal direction.

[0009] The preheating interlayer channel is used to introduce preheated air, and its heat is provided by the porous medium region. The heat of the porous medium region is transferred by the outer wall with a certain thermal conductivity. The number of channels corresponds to the number of ejectors. When there are 2 ejectors, there are 2 preheating interlayer channels, which are arranged symmetrically at 90° with the ejectors outside the burner. When there are 3 ejectors, there is 1 preheating interlayer channel.

[0010] The guide plate has a frustum-shaped and cylindrical structure. A direct current plate is located in the center, with circular holes of 15mm diameter. The direct current plate contains a porous medium with a porosity of 0.2-0.3 to prevent backfire and promote better gas mixing. The overall plate thickness is 10-30mm. Specifically, the openings can be either small or large diameter, but the total opening area accounts for 40-70%. The porous medium material can be metal spheres or foam ceramics. A swirl plate is located on the outer side of the guide plate, with 2mm wide holes arranged in a 360° pattern to ensure uniform mixing and stable combustion of the hydrogen-blended natural gas. The swirl plate has a horizontal inclination of 10°-15° and a vertical inclination of 15°. This overall arrangement of the guide plate ensures that the premixed gas enters the porous medium region uniformly and comprehensively, avoiding localized overheating or underheating, reducing thermal stress concentration in the porous medium, and thus improving the burner's service life.

[0011] The porous medium is divided into a preheating zone and a combustion zone at the upper end of the swirl plate, and into a preheating zone, combustion zone I, and combustion zone II at the upper end of the DC plate. The porous medium material is one of ceramic spheres, honeycomb ceramic plates, foam ceramic plates, metal mesh plates, and foam metal plates.

[0012] The porous medium has a porosity of 0.2-0.4% and a thickness of 30 mm in the preheating zone, a porosity of 0.4-0.8% and a thickness of 30 mm in the combustion zone, a porosity of 0.4-0.6% and a thickness of 15 mm in combustion zone I, and a porosity of 0.6-0.8% and a thickness of 15 mm in combustion zone II. This increasing porosity arrangement of the porous medium serves two purposes: firstly, to prevent the risk of backfire, and secondly, to promote uniform combustion, thereby improving safety.

[0013] The porous media combustion device has a temperature measuring device in the preheating zone, combustion zone, and combustion zone I to measure the temperature of the porous media area. The highest temperature measured is 1500℃. The temperature measuring device is used to enable the burner to regulate the air volume. When the temperature in the preheating zone is higher than that in the combustion zone, the occurrence of backfire will cause the burner to increase the air volume in the air preheating channel, thereby avoiding the occurrence of dangerous situations.

[0014] The method of increasing the equivalence ratio allows the equivalence ratio of the premixed gas to be controlled between 0.8 and 1.4, thus ensuring stable combustion of hydrogen-blended natural gas.

[0015] The mixing of hydrogen into natural gas increases the combustion temperature, which promotes the formation of thermal NOx. Uneven temperature also leads to increased NOx emissions. The baffle and porous media structure used in this invention allow the gas to diffuse into every area of ​​the porous media region, thereby promoting uniform combustion, reducing NOx emissions, and improving the burner's service life while reducing emissions. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall structure of the burner of the present invention.

[0017] Figure 2 This is a schematic diagram of the burner guide plate of the present invention viewed from top to bottom.

[0018] Figure 3 This is a schematic diagram of the burner guide plate of the present invention viewed from bottom to top.

[0019] Reference numerals: 1. Gas premixing chamber; 2. Gas-air ejector; 3. Swirl plate; 4. Direct current plate; 5. Preheating zone; 6. Air preheating channel; 7. Preheated air inlet; 8. Outer shell; 9. Combustion zone; 10. Combustion zone I; 11. Combustion zone II. Detailed Implementation

[0020] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0021] This invention provides a porous media burner suitable for hydrogen-blended natural gas. For example... Figure 1 As shown, it includes a gas premixing chamber 1, a gas-air ejector 2, a swirl plate 3, a direct current plate, a preheating zone, an air preheating channel, a preheated air inlet, an outer shell, a combustion zone, combustion zone I, combustion zone II, and a temperature measuring electrode.

[0022] The swirl plate 3 and the DC plate 4 form the guide plate.

[0023] Gas-air ejectors 2 are installed on both sides of the gas premixing chamber 1. The ejectors adopt a venturi tube structure, and a gas injector is installed at the inlet end of the ejector. The gas can be 0%-100% hydrogen-blended natural gas. The gas-air ejectors are arranged tangentially along the premixing chamber. The gas injector needs to introduce gas at a certain speed to entrain the surrounding air for primary premixing. When the primary premixed gas enters the premixing chamber, it will be premixed again with the air entering from the air preheating channel 6 to form a premixed gas with a certain equivalence ratio. Part of the premixed gas enters the porous medium preheating zone, combustion zone I, and combustion zone II sequentially through the intermediate DC plate. The other part of the premixed gas enters the porous medium preheating zone and combustion zone through the outer swirl plate and is ignited by the ignition needle at the top. Heat is transferred through the thermal conductivity and radiation of the porous medium material, and finally the gas is stably burned in the porous medium combustion zone.

[0024] A guide plate is installed above the gas premixing chamber. The guide plate consists of two parts, generally in the form of a frustum plus a cylinder. One part is a direct current plate, which is a cylindrical structure with a diameter of 60 mm. Multiple small holes are evenly distributed on the direct current plate, and a porous medium region with a porosity of 0.2-0.3 is arranged in the small holes for protection. The porous medium region is made of foam microspheres or foam ceramic structure. The outer side of the guide plate consists of swirl plates with a horizontal inclination of 10-15° and a vertical inclination of 15°. The rectangular holes have a width of 1-2 mm and a length of 15 mm.

[0025] Because hydrogen-blended natural gas has the characteristics of fast combustion speed, unstable combustion, and easy backfire, we set up a porous media area to play a stabilizing role. In addition, the purpose of the guide plate structure is: the premixed gas passing through the DC plate has a high longitudinal velocity. After ignition from the top of the burner, in order to prevent backfire, a porous media structure with stepped pores is set up. Only a preheating zone and a combustion zone with porous media are set up above the swirl plate.

[0026] Considering the relatively high longitudinal velocity of the DC flow, a three-layer porous media structure is arranged above the DC plate to prevent the flame from becoming unstable. The three porous layers are, in sequence, a preheating zone with a thickness of 30 mm and a porosity of 0.2-0.4, a combustion zone I with a thickness of 15 mm and a porosity of 0.4-0.6, and a combustion zone II with a thickness of 15 mm and a porosity of 0.6-0.8. Above the swirl plate, only two layers of porous media are arranged, with the two porous structures being, in sequence, a preheating zone with a thickness of 30 mm and a porosity of 0.2-0.4, and a combustion zone with a thickness of 30 mm and a porosity of 0.4-0.8.

[0027] An air preheating interlayer channel 6 is provided at location 8 of the outer casing to achieve a certain degree of waste heat recovery. The burner casing is made of a metal material with a certain thermal conductivity, preventing excessive heat from being supplied to the air preheating interlayer channel, which could lead to combustion of the premixed gas in the premixing chamber and cause a dangerous situation. The interlayer channel is arranged normally to the ejector and tangentially to the premixing chamber. In addition, temperature measuring electrodes are arranged in the preheating zone, combustion zone I, and combustion zone. When the temperature in the combustion zone and combustion zone II is higher than that in the preheating zone, it indicates that a flashback has occurred. The preheating air inlet will automatically adjust to increase the input air volume to prevent the occurrence of dangerous situations.

[0028] Combustion of hydrogen-blended natural gas reduces CO emissions but increases NOx emissions. This is partly because the hydrogen blending raises the temperature, while the presence of baffles allows for well-organized flow of the combustion gas into the porous medium. Within this porous medium, the gas is preheated and combusted, with the flame filling the entire medium and eliminating combustion "dead zones." Furthermore, the inherent properties of the porous medium itself result in more uniform combustion, eliminating localized high and low temperature zones, thus reducing NOx and CO emissions.

[0029] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0030] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A porous media burner suitable for hydrogen-blended natural gas, characterized in that, include: The hydrogen-blended natural gas air premixer has tangentially distributed Venturi ejectors at the bottom of the premixer chamber, with a gas injector at the inlet end of each Venturi ejector. A guide vane is located at the top of the hydrogen-blended natural gas air premixer chamber, with a direct current plate in the middle. A protection zone is located within the direct current plate. A preheating zone and two stepped combustion zones (Zone I and Zone II) with two pore sizes are located at the top of the direct current plate. A cyclone separator is located outside the guide vane, with a preheating zone and a combustion zone at the top of the cyclone separator. An air preheating interlayer channel is located on the outer wall of the burner. A portion of the premixed gas enters the porous medium preheating zone, combustion zone I, and combustion zone II sequentially through the intermediate DC plate, while the other portion of the premixed gas enters the porous medium preheating zone and combustion zone through the outer swirl plate. The porosity of the combustion zone is 0.8% and the thickness is 30 mm; the porosity of combustion zone I is 0.4% and the thickness is 15 mm; and the porosity of combustion zone II is 0.6% and the thickness is 15 mm. The combustion zone I and the combustion zone II are located inside the combustion zone; The porous media combustion device has a set of temperature measuring devices in the preheating zone, combustion zone and combustion zone I.

2. The porous media burner suitable for hydrogen-blended natural gas according to claim 1, characterized in that: The ejector is a Venturi tube, and the premixed gas is injected tangentially into the premixing chamber. There are two or three ejectors, and the ejectors are arranged at an angle of 0° to 15° to the horizontal plane of the premixing chamber.

3. The porous media burner suitable for hydrogen-blended natural gas according to claim 1, characterized in that: The guide plate is a combination of a frustum and a cylinder; a DC plate is provided in the middle, and the protection zone is a porous medium in the middle of the DC plate. The porosity of the porous medium is 0.2%-0.3% to prevent backfire and better promote gas mixing. The overall plate thickness is 10-30mm.

4. The porous media burner suitable for hydrogen-blended natural gas according to claim 3, characterized in that: The guide plate has a swirl plate on the outer side in the middle, with a horizontal inclination of 10-15° and a vertical inclination of 15°.

5. The porous media burner suitable for hydrogen-blended natural gas according to claim 4, characterized in that: The preheating interlayer channel is used to introduce air, and its number corresponds to the number of ejectors. When there are 2 ejectors, there are 2 preheating interlayer channels, which are arranged symmetrically at 90° with the ejectors outside the burner. When there are 3 ejectors, there is 1 preheating interlayer channel.

6. The porous media burner suitable for hydrogen-blended natural gas according to claim 1, characterized in that: The porous medium is divided into a preheating zone and a combustion zone at the upper end of the swirl plate, and into a preheating zone, combustion zone I, and combustion zone II at the upper end of the DC plate. The porous medium is made of one of the following materials: ceramic spheres, honeycomb ceramic plates, foam ceramic plates, metal mesh plates, and foam metal plates.

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