A porous medium combustion device with two-stage flue gas circulation

Abstract

A porous medium combustion device with two-stage flue gas circulation belongs to the technical field of energy and environmental devices. It includes a furnace surrounded by a furnace wall, the furnace is filled with a porous medium material layer, an air distribution plate is arranged at the bottom of the porous medium material layer, a mixing chamber is formed between the porous medium material layer and the air distribution plate, a nozzle is arranged on the side wall of the furnace located in the mixing chamber, and the furnace located below the air distribution plate forms a bellows; the furnace flue gas circulation pipe is placed in the middle of the furnace, the furnace flue gas circulation pipe passes through the porous medium material, the mixing chamber, and the bellows, and the bottom end of the furnace flue gas circulation pipe is connected to the venturi; the upper part of the furnace is connected to the flue, the flue is connected to the flue gas circulation pipeline outside the furnace, the flue gas circulation pipeline outside the furnace is connected to the fan, and the downstream of the fan is connected to the venturi. The present invention greatly expands the low calorific value gas treatment range of porous medium combustion technology, and is particularly suitable for gas sources with small flow rates and dispersed emission sources.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy and environmental devices, and in particular relates to a porous medium combustion device with a two-stage flue gas circulation. Background Art

[0002] To improve air quality, both domestic and international efforts are increasing the use of clean fuels such as natural gas. This includes increasing the development and import of natural gas, while also exploring other unconventional gases as clean alternative energy sources. Currently, industrial processes still produce a significant amount of low-quality, low-calorific-value gases, which are not readily utilized. Combustion methods can be used to convert these low-quality gases into harmless substances, enabling efficient and clean utilization of unconventional energy sources, reducing greenhouse gas emissions, and protecting the environment.

[0003] Unconventional gas fuels exhibit significant variations in flow rate and composition, sometimes containing a very low proportion of combustible components. For example, the volume content of methane in coal mining exhaust gas is even less than 1%, resulting in a very low calorific value. The large amount of non-combustible gas reduces the combustion temperature and combustion rate, significantly reducing combustion stability and exceeding the combustion range of conventional burners. To improve the combustion stability of such gases, one can (a) utilize the heat recovery and heat storage capabilities of porous media materials; (b) increase the initial reaction temperature, lower the lean combustion limit, and even achieve spontaneous combustion, thereby increasing the combustion rate, shortening the ignition delay time, and enhancing combustion stability; and (c) simultaneously minimize flue gas losses and achieve thermal self-sustaining of the combustion system. Consequently, a reciprocating porous media combustion technology has emerged, capable of processing low-calorific-value gases with a lean combustion limit as low as 0.026. However, due to the complex structure and difficult operation and maintenance of multiple moving parts such as switching valves, it is often only suitable for high-flow applications and lacks flexibility.

[0004] The unidirectional flow porous media combustion technology, on the other hand, has a simple structure, no moving parts, and is more flexible in handling flow rates, making it suitable for dispersed, small-flow emission sources. Currently, the initial reaction temperature of unidirectional flow porous media combustion technology is generally not high, and the lean combustion limit gas equivalence ratio is generally between 0.4 and 0.5, which greatly limits the ability to treat low-calorific-value gases. In order to recover the flue gas waste heat, part of the flue gas waste heat can be recovered from the air through a preheater in the flue, or a fan can be used to directly extract part of the flue gas and send it to the inlet of the combustion device to increase the initial reaction temperature. However, due to the influence of the fan and pipeline materials, whether it is air preheating or tail flue gas circulation, the temperature of the preheat recovery medium is generally not higher than 500°C, and the degree of improvement in the combustion stability of low-calorific-value gases is still limited. In addition, due to the presence of porous media materials, it is difficult to organize a large-scale gas circulation in the furnace to promote the heating of the fresh intake air by the high-temperature flue gas. Summary of the Invention

[0005] The present invention reduces exhaust heat loss to a great extent, greatly expands the low calorific value gas treatment range of porous medium combustion technology, and is particularly suitable for gas sources with small flow rates and dispersed emission sources.

[0006] A multi-media combustion device with two-stage flue gas circulation comprises a furnace surrounded by a furnace wall, the furnace is filled with a porous medium material layer, an air distribution plate is arranged at the lower part of the porous medium material layer, a mixing chamber is formed between the porous medium material layer and the air distribution plate, a nozzle is arranged on the side wall of the furnace located in the mixing chamber, and a bellows is formed in the furnace located below the air distribution plate; a furnace flue gas circulation pipe is placed in the middle of the furnace, the furnace flue gas circulation pipe passes through the porous medium material, the mixing chamber, and the bellows, and the bottom end of the furnace flue gas circulation pipe is connected to a venturi; the upper part of the furnace is connected to a flue, the flue is connected to a flue gas circulation pipeline outside the furnace, the flue gas circulation pipeline outside the furnace is connected to a fan, and the downstream of the fan is connected to the venturi.

[0007] During operation, the fan extracts part of the low-temperature flue gas in the flue through the flue gas circulation pipeline outside the furnace and sends it to the Venturi. The Venturi draws the high-temperature flue gas from the upper part of the furnace through the flue gas circulation pipe inside the furnace. The Venturi then sends the mixed flue gas into the bellows and into the mixing chamber through the air distribution plate; the fuel gas enters the mixing chamber through the gas nozzle; after the circulating flue gas and the fuel gas are mixed in the mixing chamber, they enter the porous medium material and flow upward and burn, and the flue gas enters the upper part of the furnace. Part of the high-temperature flue gas is sucked and circulated by the Venturi through the flue gas circulation pipe inside the furnace, and part of the flue gas enters the flue after cooling; part of the flue gas entering the flue is sent to the Venturi by the fan to draw the high-temperature flue gas, and part of it leaves the combustion device. As mentioned above, a two-stage circulation of the tail flue gas and the high-temperature flue gas in the furnace is formed through the fan and the Venturi. The circulated flue gas participates in combustion again, and the cycle continues.

[0008] In this invention, using a high-temperature blower, the flue gas temperature can reach 500°C (144°F), while the high-temperature flue gas from the flue gas circulation pipe within the furnace reaches over 1000°C (144°F). This mixed flue gas is then mixed with the fuel gas from the nozzle. This two-stage circulating flue gas mixture maximizes waste heat recovery, rapidly heating the premixed gas and enabling stable combustion of low-calorific value fuels that are difficult to burn under normal conditions.

[0009] In the present invention, the low calorific value gas being processed may or may not contain oxygen. If it does not contain oxygen or the oxygen content is insufficient to support complete combustion, it can be mixed with an appropriate amount of air and then fed into the mixing chamber through a nozzle. During operation, the flue gas circulation flow rate can also be adjusted to adapt to fluctuations in the concentration and flow rate of combustible gases of the low calorific value gas, and the oxygen concentration in the furnace can also be adjusted. Through two-stage flue gas circulation, high-temperature, low-oxygen combustion of low calorific value gases can be achieved, expanding the lean combustion limit of the gases that can be processed, and being applicable to a wider range of low calorific value gas sources, while ensuring stable combustion and reducing nitrogen oxide emissions.

[0010] This invention provides a multi-media combustion device with two-stage flue gas recirculation. This device utilizes a high-temperature fan to achieve external recirculation of tail flue gas. A flue gas return pipe is installed within the furnace, and the externally recirculated flue gas is passed through a venturi ejector to extract the high-temperature flue gas from the furnace, achieving internal recirculation of the high-temperature flue gas. The recirculated flue gas is then mixed with low-calorific value gases and burned within the porous medium, allowing the fuel to burn in a high-temperature, low-oxygen atmosphere. This broadens the fuel's flammability limit, improves combustion stability, and significantly reduces pollutant emissions. This significantly reduces exhaust heat loss and expands the range of low-calorific value gas treatment capabilities of porous medium combustion technology, making it particularly suitable for gas sources with low flow rates and dispersed emission sources. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a structural schematic diagram of the multi-media combustion device of the present invention. DETAILED DESCRIPTION

[0012] Below in conjunction with specific embodiment, further set forth the present invention.Should be understood that these embodiments are only used to illustrate the present invention and are not used in limiting the scope of the present invention.In addition, should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall equally within the scope limited by the appended claims of the application.

[0013] A multi-media combustion device with two-stage flue gas circulation includes a furnace 3 surrounded by a furnace wall 4, the furnace 3 is filled with a porous medium material layer 5, an air distribution plate 7 is arranged at the lower part of the porous medium material layer 5, a mixing chamber 11 is formed between the porous medium material layer 5 and the air distribution plate 7, a nozzle 6 is arranged on the side wall of the furnace 3 located in the mixing chamber 11, and a bellows 10 is formed in the furnace located below the air distribution plate 7; an in-furnace flue gas circulation pipe 2 is placed in the middle of the furnace 3, the in-furnace flue gas circulation pipe 2 passes through the porous medium material layer 5, the mixing chamber 11, and the bellows 10, and the bottom end of the in-furnace flue gas circulation pipe 2 is connected to a venturi 8; the upper part of the furnace 3 is connected to a flue 1, the flue is connected to a flue gas circulation pipeline 12 outside the furnace, the out-furnace flue gas circulation pipeline 12 is connected to a fan 9, and the downstream of the fan 9 is connected to the venturi 8.

[0014] During operation, fan 9 extracts some of the low-temperature flue gas from flue 1 through flue gas circulation line 12 outside the furnace and sends it to venturi 8. Venturi 8 draws the high-temperature flue gas from the upper part of furnace 3 through flue gas circulation pipe 2 inside the furnace. Venturi 8 then sends the mixed flue gas into bellows 10 and into mixing chamber 11 through air distribution plate 7. Combustion gas enters mixing chamber 11 through gas nozzle 6. The circulating flue gas mixes with the combustion gas in mixing chamber 11 and then flows upward into porous dielectric layer 5, where combustion occurs. The flue gas enters the upper part of furnace 3. Some of the high-temperature flue gas is drawn and circulated by venturi 8 through flue gas circulation pipe 2 inside the furnace. Some of the flue gas cools and enters flue 1. After entering the flue, some of the flue gas is sent by fan 11 to venturi 8 to extract the high-temperature flue gas. As described above, fan 9 and venturi 8 form a two-stage circulation system of tail flue gas and high-temperature flue gas from the furnace. The recycled flue gas participates in combustion again, and the cycle repeats.

[0015] In the present invention, if a high-temperature blower is used, the flue gas temperature from flue duct 1 can reach 500°C, while the high-temperature flue gas from flue gas circulation pipe 2 in the furnace is above 1000°C. The mixed flue gas is then mixed with the fuel gas from nozzle 6. This two-stage circulating flue gas mixing maximizes waste heat recovery from the flue gas, rapidly heating the premixed gas and enabling stable combustion of low-calorific value fuels that are difficult to burn under normal conditions.

[0016] In the present invention, the low calorific value gas being processed may or may not contain oxygen. If it does not contain oxygen or the oxygen content is insufficient to support complete combustion, it can be mixed with an appropriate amount of air and then fed into the mixing chamber through the nozzle 6. During operation, the flue gas circulation flow rate can also be adjusted to adapt to fluctuations in the concentration and flow of combustible gases of the low calorific value gas, and the oxygen concentration in the furnace can also be adjusted. Through two-stage flue gas circulation, high-temperature, low-oxygen combustion of low calorific value gases can be achieved, expanding the lean combustion limit of the gases that can be processed, and being applicable to a wider range of low calorific value gas sources, while ensuring stable combustion and reducing nitrogen oxide emissions.

[0017] To overcome the shortcomings of existing porous media combustion technology, such as low preheating temperatures and difficulty organizing airflow circulation within the furnace, the present invention proposes a porous media combustion device with two-stage flue gas circulation. This device uses a fan to achieve external circulation of low-temperature flue gas at the rear, and then uses a venturi to achieve internal circulation of high-temperature flue gas within the furnace, producing a high-temperature mixed flue gas. (a) The resulting flue gas temperature is even higher than the auto-ignition temperature of the combustible components, significantly expanding the lean combustion phase of the calorific value gas and achieving stable thermal oxidation of low-concentration combustible components. (b) The two-stage flue gas circulation significantly improves the utilization of flue gas waste heat, rapidly heating the premixed gas to promote the combustion system's self-heat maintenance, enabling stable combustion of low-calorific value fuels that are difficult to burn under normal conditions. (c) It also reduces the oxygen concentration within the furnace, which helps reduce NOx emissions. Based on these characteristics, the two-stage flue gas circulation can achieve high-temperature, low-oxygen, clean combustion of low-calorific value gases.

[0018] The low calorific value gas being processed can contain or not contain oxygen. When fed into the combustion device, air can be added to adjust the oxygen concentration of the mixed gas to meet combustion requirements. Compared to air preheating technology, direct flue gas recycling also has the following advantages: (a) reducing temperature difference losses; (b) if the low calorific value gas itself contains sufficient oxygen to meet the combustion requirements of its internal combustible components, only flue gas recycling is required for waste heat recovery, eliminating the need to introduce additional air, thereby reducing unnecessary heating losses.

Claims

1. A porous medium combustion device with two-stage flue gas circulation, characterized in that The porous medium combustion device is used for processing low calorific value gas, comprising a furnace (3) surrounded by a furnace wall (4), the furnace (3) is filled with a porous medium material layer (5), an air distribution plate (7) is arranged below the porous medium material layer (5), a mixing chamber (11) is formed between the porous medium material layer (5) and the air distribution plate (7), a nozzle (6) is arranged on the side wall of the furnace (3) located in the mixing chamber (11), and a wind box (11) is formed in the furnace below the air distribution plate (7). 0); The furnace flue gas circulation pipe (2) is placed in the middle of the furnace (3), and the furnace flue gas circulation pipe (2) passes through the porous medium material layer (5), the mixing chamber (11), and the wind box (10). The bottom end of the furnace flue gas circulation pipe (2) is connected to the venturi (8); the upper part of the furnace (3) is connected to the flue (1), the flue is connected to the furnace external flue gas circulation pipeline (12), the furnace external flue gas circulation pipeline (12) is connected to the fan (9), and the downstream of the fan (9) is connected to the venturi (8); The fan (9) extracts the low-temperature flue gas from the flue (1) through the flue gas circulation pipeline (12) outside the furnace and sends it to the venturi (8). The venturi (8) draws the high-temperature flue gas after combustion from the upper part of the furnace (3) through the flue gas circulation pipe (2) inside the furnace. Through the fan (9) and the venturi (8), a two-stage circulation of the tail flue gas and the high-temperature flue gas inside the furnace is formed.

2. The porous media combustion device with two-stage flue gas circulation according to claim 1 is characterized in that The low calorific value gas being treated may contain oxygen or not contain oxygen. If it does not contain oxygen or the oxygen content is insufficient to support complete combustion, it will be mixed with air and sent into the mixing chamber through a nozzle. During operation, the flue gas circulation flow rate is adjusted to adapt to fluctuations in the concentration and flow of the low calorific value combustible gas, or to adjust the oxygen concentration in the furnace.

Images