Waste incineration equipment

Abstract

A waste incineration facility (1) is provided with: an exhaust gas flow path (4) through which exhaust gas discharged from an incinerator (3) flows; a wet scrubbing tower (43) provided in the exhaust gas flow path (4); a recirculating exhaust gas line (6) which is connected to an extraction position (P1) on the downstream side of the exhaust gas flow path (4) than the wet-type smoke washing tower (43), extracts a part of the exhaust gas flowing through the exhaust gas flow path (4) as recirculating exhaust gas, and supplies the recirculating exhaust gas into the incinerator (3); an oxygen mixing unit (66) that mixes high-concentration oxygen with the recirculation exhaust gas flowing through the recirculation exhaust gas line (6); and a methanation device (51) that generates a methane-containing gas by reacting the exhaust gas, which passes through the extraction position (P1) and flows through the exhaust gas flow path (4), with hydrogen gas. The recirculated exhaust gas supplied into the incinerator (3) is the main gas of the combustion gas used for incinerating waste in the incinerator (3).

Description

Technical Field

[0001] The invention relates to waste incineration equipment.

[0002] [Reference to related applications]

[0003] This application claims the benefit of priority from Japanese patent application JP2023-18400 filed on February 9, 2023, the entire disclosure of which is incorporated into this application. Background Art

[0004] In recent years, attempts have been made in waste incineration equipment to separate carbon dioxide from the exhaust gas discharged from the incinerator and to generate methane from the separated carbon dioxide. For example, in the combustion system of Japanese Patent Laid-Open No. 2022-161757 (Document 1), carbon dioxide is selectively separated from the exhaust gas discharged from the combustion device, and the separated carbon dioxide is used to synthesize methane gas with hydrogen generated by a water electrolysis device. In the combustion system, an exhaust gas recirculation mechanism is also provided to recirculate a portion of the exhaust gas discharged from the combustion device in the combustion device, and the oxygen generated by the water electrolysis device is mixed with the recycled exhaust gas and supplied to the combustion device.

[0005] In the processing device of Japanese Patent Laid-Open No. 2021-135024 (Document 2), the combustion chamber and the methanation reactor are connected by a combustion exhaust gas transfer line, and the exhaust gas discharged from the combustion chamber is transferred to the methanation reactor via a boiler, a cooling tower, a dust collector and a scrubber. A carbon dioxide reflux line is connected between the dust collector and the scrubber, and a portion of the exhaust gas is returned to the combustion chamber through the carbon dioxide reflux line. In addition, oxygen and hydrogen are generated from water by an electrolysis device, the generated oxygen is mixed with the exhaust gas returned to the combustion chamber, and the generated hydrogen is supplied to the methanation reactor. The flow rate of hydrogen transferred to the methanation reactor is controlled based on the flow rate of carbon dioxide flowing into the methanation reactor.

[0006] Furthermore, in the combustion system of Document 1, the main components of the exhaust gas generated are carbon dioxide, water vapor, and residual oxygen. However, since there is no structure to remove water from the exhaust gas returning to the incinerator (combustion device) (recirculation), the amount of water vapor in the gas circulating in this path is high. The exhaust gas temperature tends to drop in the flow path that returns a portion of the exhaust gas to the incinerator, which can lead to condensation in piping, fans, and other components, causing corrosion. Furthermore, in the combustion system of Document 1, the high water concentration makes it difficult to achieve a high concentration of carbon dioxide in the exhaust gas. To increase the methane concentration in the gas discharged from the methanation device (methanation reactor), a structure is required to separate carbon dioxide from the exhaust gas and supply it to the methanation device. In the treatment device of Document 2, a cooling tower is installed between the incinerator (combustion chamber) and the dust collector. However, the exhaust gas passing through the cooling tower remains hot, so water removal is insufficient. As in Document 1, condensation is prone to occur in the exhaust gas recirculation path. Summary of the Invention

[0007] The present invention is directed to waste incineration facilities, and an object thereof is to suppress the occurrence of condensation and the like in a path for recirculating exhaust gas, and to easily increase the methane concentration in the gas exhausted from a methanation device.

[0008] Embodiment 1 of the present invention is a waste incineration equipment, which includes: an incinerator for incinerating waste; an exhaust gas flow path for circulating exhaust gas discharged from the incinerator; a dust collector arranged in the exhaust gas flow path; a wet smoke scrubber arranged in the exhaust gas flow path at a position further downstream than the dust collector, spraying a water-containing liquid into the exhaust gas; a recirculating exhaust gas pipeline connected to a take-out position in the exhaust gas flow path further downstream than the wet smoke scrubber, taking out the exhaust gas flowing in the exhaust gas flow path. a portion of the exhaust gas is used as recycled exhaust gas and supplied to the incinerator; an oxygen mixing unit is used to mix high-concentration oxygen having a higher oxygen concentration than air with the recycled exhaust gas flowing in the recycled exhaust gas pipeline; and a methanation device is used to react the exhaust gas that passes through the take-out position and flows in the exhaust gas flow path with hydrogen supplied from a hydrogen supply source to generate a methane-containing gas, wherein the recycled exhaust gas supplied to the incinerator is the main gas of the combustion gas used for incineration of the waste in the incinerator.

[0009] The present invention can suppress the occurrence of condensation in the exhaust gas flow path and the recirculating exhaust gas line. Furthermore, the carbon dioxide concentration in the exhaust gas can be increased, thereby easily increasing the methane concentration in the gas exhausted from the methanation device.

[0010] A second embodiment of the present invention is the waste incineration facility of the first embodiment, wherein a carbon dioxide separation unit for separating carbon dioxide from the exhaust gas is not provided in a path of the exhaust gas from the incinerator to the methanation device.

[0011] Embodiment 3 of the present invention is the waste incineration equipment of embodiment 1 (which may be embodiment 1 or embodiment 2), wherein the oxygen mixing section includes a water electrolysis device, the water electrolysis device electrolyzes water to generate oxygen and hydrogen, the high-concentration oxygen includes the oxygen generated by the water electrolysis device, and the water electrolysis device also serves as the hydrogen supply source.

[0012] Embodiment 4 of the present invention is the waste incineration equipment of Embodiment 1 (which can be any one of Embodiments 1 to 3), which further includes: a heat exchanger for heating the recycled exhaust gas by heat exchange between the exhaust gas in the exhaust gas flow path that is more upstream than the wet scrubber and the recycled exhaust gas flowing in the recycled exhaust gas pipeline.

[0013] Embodiment 5 of the present invention is the waste incineration equipment of any one of Embodiments 1 to 4, which further includes: an oxygen concentration measuring unit for measuring the oxygen concentration of the exhaust gas flowing into the methanation device; a dilution unit for mixing a dilution gas having an oxygen concentration lower than that of the exhaust gas into the exhaust gas between the extraction position in the path of the exhaust gas and the methanation device; and a control unit for mixing the dilution gas into the exhaust gas through the dilution unit when the measured value of the oxygen concentration measuring unit becomes greater than a specified value.

[0014] Embodiment 6 of the present invention is the waste incineration equipment of embodiment 5, wherein the dilution gas includes the methane-containing gas.

[0015] Embodiment 7 of the present invention is the waste incineration equipment of embodiment 5 (which may be embodiment 5 or embodiment 6), which further includes: a gas separation device for separating nitrogen from the methane-containing gas, and the dilution gas contains nitrogen separated by the gas separation device.

[0016] The above-mentioned object and other objects, features, aspects and advantages will become clear from the following detailed description of the present invention with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] [ Figure 1 ] is a block diagram showing the structure of a waste incineration plant.

[0018] [ Figure 2 ] is a diagram showing another example of waste incineration equipment.

[0019] [ Figure 3 ] is a diagram showing another example of waste incineration equipment.

[0020] [ Figure 4 ] is a diagram showing another example of waste incineration equipment.

[0021] [ Figure 5 ] is a diagram showing another example of waste incineration equipment.

[0022] [ Figure 6 ] is a diagram showing another example of waste incineration equipment.

[0023] [ Figure 7 ] is a diagram showing another example of waste incineration equipment.

[0024] [ Figure 8 ] is a diagram showing another example of waste incineration equipment. DETAILED DESCRIPTION

[0025] Figure 1 It is a block diagram showing the structure of a garbage incineration device 1 according to one embodiment of the present invention. The garbage incineration device 1 is a waste incineration device, and includes a garbage pit 2, an incinerator 3, an exhaust gas flow path 4, and a control unit 10. The control unit 10 is, for example, a computer including a central processing unit (CPU), and is responsible for the overall control of the garbage incineration device 1. The garbage pit 2 is a waste pit that stores garbage as waste. The incinerator 3 is, for example, a stoker type, and incinerates the garbage fed from the garbage pit 2. The exhaust gas flow path 4 is a flue for the exhaust gas discharged from the incinerator 3 to circulate. In Figure 1 In the example shown in FIG. 4 , the exhaust gas flow path 4 is a flow path from the incinerator 3 to a chimney 45 described below. Figure 1 In FIG. 4 , only the arrows between the incinerator 3 and the boiler tube group 41 described below are denoted by reference numeral 4 .

[0026] The waste incineration facility 1 further includes a boiler tube assembly 41, a filter-type dust collector 42 (hereinafter referred to as "dust collector 42"), an air-to-air heat exchanger 61, a wet smoke scrubber 43, an exhaust fan 44, and a chimney 45. The boiler tube assembly 41, dust collector 42, air-to-air heat exchanger 61, wet smoke scrubber 43, exhaust fan 44, and chimney 45 are arranged in the exhaust gas flow path 4 in order from upstream to downstream in the exhaust gas flow direction (i.e., from the incinerator 3 toward the chimney 45).

[0027] The boiler tube group 41 generates steam using the exhaust gas discharged from the incinerator 3 as a heat source. The dust collector 42 is a so-called filter bag that captures fly ash contained in the exhaust gas through filter cloth. On the upstream side of the dust collector 42, a powdered exhaust gas treatment agent can be supplied to the exhaust gas, and the fly ash and the exhaust gas treatment agent are captured in the dust collector 42. The exhaust gas treatment agent can be used to remove sulfur oxides, hydrogen chloride, dioxins, mercury compounds, etc. The temperature of the exhaust gas at the outlet of the dust collector 42 is, for example, 150°C to 200°C. The exhaust gas passing through the dust collector 42 flows into the gas-to-gas heat exchanger 61.

[0028] The gas-to-gas heat exchanger 61 exchanges heat between the exhaust gas discharged from the dust collector 42 and the recirculated exhaust gas flowing through the recirculated exhaust gas line 6 described below. The wet scrubber 43 sprays a liquid containing an alkaline agent, such as caustic soda, and water into the exhaust gas. This lowers the exhaust gas temperature to a roughly constant temperature of, for example, 30°C to 70°C, and removes sulfur oxides, hydrogen chloride, and other substances contained in the exhaust gas. The wet scrubber 43 serves as a desulfurization unit, removing sulfur oxides from the exhaust gas, and also as a desalination unit, removing hydrogen chloride from the exhaust gas. By removing sulfur oxides, hydrogen chloride, and other substances, corrosion of the piping, the methanation unit 51, and the gas separation unit 71 described below can be prevented, and the life of the devices can be extended. As described above, the exhaust gas passing through the wet scrubber 43 maintains a roughly constant temperature, and the amount of water vapor (water vapor per unit volume) contained in the exhaust gas is also roughly constant, measured as saturated water vapor at that temperature. The exhaust fan 44 forms a gas flow from upstream to downstream in the exhaust gas flow path 4 (ie, a gas flow from the incinerator 3 to the chimney 45 ). The exhaust gas passing through the exhaust fan 44 is exhausted from the chimney 45 to the outside.

[0029] The waste incineration equipment 1 further includes a recirculating exhaust gas pipeline 6, a fan 62, and an oxygen mixing unit 66. The recirculating exhaust gas pipeline 6 is a flow path for the recirculating exhaust gas described below to flow. One end of the recirculating exhaust gas pipeline 6 is connected to the extraction position P1 on the downstream side of the wet scrubber 43 in the exhaust gas flow path 4. Figure 1 In the example, the extraction position P1 is a position between the wet scrubber 43 and the exhaust fan 44. A portion of the exhaust gas circulating in the exhaust gas flow path 4 is extracted as recycled exhaust gas through the recycled exhaust gas pipeline 6. In the exhaust gas flow path 4, the wet scrubber 43 is provided at a position further upstream than the extraction position P1, so the recycled exhaust gas extracted from the extraction position P1 has a substantially constant amount of water vapor. The other end of the recycled exhaust gas pipeline 6 is connected to the incinerator 3, and the recycled exhaust gas is supplied to the incinerator 3. Figure 1 In FIG. 6 , only the arrow connected to the removal position P1 is denoted by reference numeral 6 .

[0030] The gas-to-gas heat exchanger 61 and fan 62 described above are provided in the recirculating exhaust gas line 6. In one example of the waste incineration facility 1, the gas-to-gas heat exchanger 61 and fan 62 are arranged in this order from the upstream side of the recirculating exhaust gas flow toward the downstream side (i.e., in a direction away from the extraction position P1). In the gas-to-gas heat exchanger 61, heat is exchanged between the recirculating exhaust gas whose temperature has been lowered in the wet scrubber 43 and the exhaust gas before passing through the wet scrubber 43, thereby heating the recirculating exhaust gas. This suppresses the occurrence of condensation and the like in the recirculating exhaust gas line 6. Furthermore, since the flow rate of the exhaust gas is greater than the flow rate of the recirculating exhaust gas, the temperature of the recirculating exhaust gas can be efficiently increased. The fan 62 forms a flow of the recirculating exhaust gas from the upstream side to the downstream side of the recirculating exhaust gas line 6. A preheater for heating the recirculating exhaust gas can be provided in the recirculating exhaust gas line 6 as needed.

[0031] The oxygen mixing section 66 includes a water electrolysis device 67. The water electrolysis device 67 generates oxygen (O2) and hydrogen (H2) by electrolysis of water. In the oxygen mixing section 66, the gas containing the oxygen generated by the water electrolysis device 67 is supplied to the recirculating exhaust gas pipeline 6 as high-concentration oxygen and mixed in the recirculating exhaust gas. The high-concentration oxygen may be a mixture of the oxygen generated by the water electrolysis device 67 and other gases such as air, or a gas containing only oxygen. High-concentration oxygen is a gas having an oxygen concentration (volume concentration) higher than that of air. The oxygen concentration of the high-concentration oxygen is, for example, 50% (volume %) or more, preferably 65% ​​or more, more preferably 80% or more, and still more preferably 100%.

[0032] In the recirculating exhaust gas line 6, high-concentration oxygen is mixed in to obtain a recirculating exhaust gas having a higher oxygen concentration than the exhaust gas at extraction point P1, and this gas is supplied to the incinerator 3 as combustion gas. The combustion gas is used to burn the waste in the incinerator 3. Furthermore, in the oxygen mixing section 66, the amount of high-concentration oxygen mixed with the recirculating exhaust gas can be changed using a damper or the like. Meanwhile, the hydrogen generated by the water electrolysis unit 67 is supplied to the methanation unit 51 described below. In the recirculating exhaust gas line 6, the order of the gas-to-gas heat exchanger 61 and the fan 62, as well as the mixing position of the high-concentration oxygen, can be arbitrarily determined.

[0033] During normal operation of the waste incineration equipment 1, it is preferred that almost no combustion gas (air, etc.) other than the recycled exhaust gas mixed with a high concentration of oxygen is supplied to the incinerator 3, and it is more preferred that the combustion gas supplied to the incinerator 3 through the gas pipe is only the recycled exhaust gas. In this way, the amount of exhaust gas discharged from the chimney 45 of the waste incineration equipment 1 can be greatly reduced. Moreover, since almost no air is supplied as the combustion gas, the concentration of nitrogen (N2) in the exhaust gas and the recycled exhaust gas becomes lower, and the concentration of carbon dioxide (CO2) becomes higher. In one example, in a steady state, the carbon dioxide concentration in the exhaust gas and the recycled exhaust gas becomes about 50%, which becomes higher than the nitrogen concentration. Therefore, in the incinerator 3, the combustion of waste is carried out in a gas environment with a high carbon dioxide concentration. In the combustion of waste in such a gas environment, it is believed that nitrogen oxides (NO X In the recycled exhaust gas supplied to the incinerator 3, for example, the carbon dioxide concentration is 10% to 70%, the nitrogen concentration is 5% to 60%, and the oxygen concentration is 18% to 24%.

[0034] As described above, in the preferred waste incineration facility 1, the combustion gas supplied to the incinerator 3 via the gas pipe is solely recycled exhaust gas. However, within the scope of understanding that the recycled exhaust gas supplied to the incinerator 3 constitutes the primary combustion gas, a small amount of air may be supplied via the gas pipe as part of the combustion gas (i.e., not as leaked air, etc.). In practice, leaked air, etc. (for example, air that enters with the waste during loading) is also used for combustion. The primary combustion gas may comprise, for example, at least 50% of the combustion gas, preferably at least 65%, more preferably at least 80%, and even more preferably 100%. Furthermore, air may be used as the combustion gas during the initial operation of the waste incineration facility 1. By minimizing the amount of air supplied to the incinerator 3 from outside the system and continuing operation, the amount of nitrogen contained in the exhaust gas gradually decreases, allowing the exhaust gas supplied to the methanation device 51 to primarily consist of carbon dioxide, water, and residual oxygen. When such an operation is performed, the concentration of carbon dioxide contained in the exhaust gas becomes high, and therefore the carbon dioxide can be efficiently reacted by the methanation device 51 .

[0035] The waste incineration equipment 1 further includes an exhaust gas supply line 5, a methanation device 51, an oxygen concentration measuring unit 52, a connecting line 7, a gas separation device 71, and a dilution unit 8. One end of the exhaust gas supply line 5 is connected to the downstream side of the extraction position P1 in the exhaust gas flow path 4. Figure 1In the example, one end of the exhaust gas supply line 5 is connected between the exhaust fan 44 and the chimney 45. The other end of the exhaust gas supply line 5 is connected to the methanation device 51. A portion of the exhaust gas flowing in the exhaust gas flow path 4 is taken out through the exhaust gas supply line 5 and supplied to the methanation device 51. As described below, the exhaust gas supplied to the methanation device 51 is used for the generation of methane (CH4), so it will be referred to as "raw exhaust gas" below. The raw exhaust gas does not flow into the recirculating exhaust gas line 6 and is the exhaust gas that passes through the extraction position P1. The oxygen concentration measuring unit 52 measures the oxygen concentration of the raw exhaust gas flowing in the exhaust gas supply line 5. The measured value of the oxygen concentration measuring unit 52 is output to the control unit 10 mentioned above.

[0036] The methanation unit 51 reacts carbon dioxide contained in the raw material exhaust gas with hydrogen supplied from the water electrolysis unit 67 to produce methane. In the methanation unit 51, methane and water are synthesized using a catalyst, for example, a Sabatier reaction. The produced methane, along with the remaining components of the raw material exhaust gas (including unreacted carbon dioxide) and unreacted hydrogen, is discharged from the methanation unit 51 as methane-containing gas. The methane-containing gas may contain all or part of the produced water in the form of water vapor.

[0037] The connecting line 7 connects the methanation device 51 with the gas separation device 71. The methane-containing gas discharged from the methanation device 51 is supplied to the gas separation device 71 via the connecting line 7. The gas separation device 71 extracts nitrogen from the methane-containing gas. The gas separation device 71 is, for example, a nitrogen generating device of the pressure swing adsorption (PSA) type. In the steady state of the waste incineration equipment 1, the nitrogen contained in the methane-containing gas comes from the air leaking into the incinerator 3 or the incinerated garbage, etc. The methane-containing gas after the nitrogen is extracted has a high methane concentration and can be used as various fuels, etc. A portion of the extracted nitrogen flows into the first dilution line 81 described below, and the rest is discharged to the outside. All of the nitrogen can flow into the first dilution line 81 or be discharged to the outside.

[0038] The dilution section 8 includes a first dilution line 81 and a second dilution line 82. One end of the first dilution line 81 is connected to the gas separation device 71, and nitrogen flows into the first dilution line 81. The other end of the first dilution line 81 is connected to the exhaust gas supply line 5. A damper 86 is provided in the first dilution line 81. By opening the damper 86, nitrogen is mixed with the raw exhaust gas flowing through the exhaust gas supply line 5. The nitrogen mixed with the raw exhaust gas is a dilution gas with a lower oxygen concentration than that of the raw exhaust gas. The amount of nitrogen mixed can be varied by adjusting the opening of the damper 86.

[0039] One end of the second dilution line 82 is connected to the connecting line 7, and the other end is connected to the exhaust gas supply line 5. A damper 87 is provided in the second dilution line 82. Opening the damper 87 allows a portion of the methane-containing gas flowing through the connecting line 7 to be mixed with the raw exhaust gas flowing through the exhaust gas supply line 5. In the methanation unit 51, oxygen contained in the raw exhaust gas reacts with hydrogen to produce water. Therefore, the methane-containing gas mixed with the raw exhaust gas is a dilution gas with a lower oxygen concentration than that in the raw exhaust gas. The amount of methane-containing gas mixed can be varied by adjusting the opening of the damper 87.

[0040] As described above, when hydrogen is supplied from the water electrolysis unit 67 to the methanation unit 51, it is undesirable from safety perspectives if the oxygen concentration of the raw off-gas mixed with the hydrogen is too high. Therefore, if the oxygen concentration measured by the oxygen concentration measuring unit 52 exceeds a predetermined threshold (e.g., 5% to 15%), the control unit 10 determines that the raw off-gas is in a high oxygen concentration state and performs a process to dilute the oxygen in the raw off-gas.

[0041] In the first treatment example under high oxygen concentration conditions, the damper 86 of the first dilution line 81 is opened to supply nitrogen extracted from the gas separation unit 71 to the exhaust gas supply line 5, where it is mixed with the raw exhaust gas. This reduces the oxygen concentration in the raw exhaust gas mixed with hydrogen in the methanation unit 51. The amount of nitrogen mixed can be adjusted appropriately based on the oxygen concentration of the raw exhaust gas. If the value measured by the oxygen concentration measuring unit 52 falls below the threshold, the damper 86 of the first dilution line 81 is closed, stopping the supply of nitrogen to the exhaust gas supply line 5.

[0042] In the second treatment example, by opening the damper 87 of the second dilution line 82, methane-containing gas flowing through the connecting line 7 is supplied to the exhaust gas supply line 5 and mixed with the raw exhaust gas. This reduces the oxygen concentration in the raw exhaust gas. The amount of methane-containing gas mixed can be appropriately adjusted based on the oxygen concentration in the raw exhaust gas. If the value measured by the oxygen concentration measuring unit 52 falls below the threshold, the damper 87 of the second dilution line 82 is closed, stopping the supply of methane-containing gas to the exhaust gas supply line 5. The first and second treatment examples can be combined, in which case nitrogen and methane-containing gas are mixed with the raw exhaust gas.

[0043] Under high oxygen concentration conditions, methane production in the methanation unit 51 can be stopped. For example, a damper (not shown) is provided in the exhaust gas supply line 5. Closing the damper stops the supply of raw exhaust gas to the methanation unit 51. In other words, all exhaust gas passing through the exhaust fan 44 is discharged through the chimney 45. This stops methane production in the methanation unit 51. Furthermore, under high oxygen concentration conditions, the oxygen mixing unit 66 can be used to reduce the amount of high-concentration oxygen mixed in the recirculated exhaust gas, thereby also lowering the oxygen concentration of the raw exhaust gas.

[0044] As described above, the waste incineration facility 1 includes a recycled exhaust gas line 6 and an oxygen mixing unit 66. The recycled exhaust gas line 6 is connected to the extraction point P1 in the exhaust gas flow path 4, extracts a portion of the exhaust gas flowing in the exhaust gas flow path 4 as recycled exhaust gas, and supplies it to the incinerator 3. The oxygen mixing unit 66 mixes the recycled exhaust gas flowing in the recycled exhaust gas line 6 with oxygen having a higher concentration than that of air. Furthermore, the recycled exhaust gas supplied to the incinerator 3 serves as the main combustion gas used for incineration of waste in the incinerator 3. Thus, in the waste incineration facility 1, the amount of exhaust gas discharged from the chimney 45 can be significantly reduced. Furthermore, the waste incineration facility 1 further includes a methanation device 51, which reacts the exhaust gas (raw exhaust gas) flowing through the exhaust gas flow path 4 through the extraction point P1 with hydrogen supplied from a hydrogen supply source to generate a methane-containing gas. As described above, by generating methane from the exhaust gas, the amount of exhaust gas discharged from the chimney 45 can be further reduced.

[0045] Here, the Figure 1A comparative example of a waste incineration facility using a wet scrubber 43 in a waste incineration facility 1 will be described. In this comparative example, no water removal mechanism is provided in the circulation path where the exhaust gas from the incinerator 3 passes through the exhaust gas flow path 4, the extraction point P1, and the recycled exhaust gas line 6 and returns to the incinerator 3. Consequently, the amount of water vapor in the gas circulating in the circulation path increases. In the recycled exhaust gas line 6, the temperature of the exhaust gas tends to drop, which may cause condensation within the piping or on the fan 62, leading to corrosion. Furthermore, the high water concentration makes it difficult to achieve a high concentration of carbon dioxide in the exhaust gas, potentially hindering the combustion of waste in the high carbon dioxide concentration atmosphere of the incinerator 3. Furthermore, it is difficult to increase the carbon dioxide concentration in the raw material exhaust gas, and therefore difficult to increase the methane concentration in the gas discharged from the methanation device 51. In other words, in order to increase the methane concentration in the gas exhausted from the methanation device 51, a structure for separating carbon dioxide from the exhaust gas (carbon dioxide separation unit) is required, which increases the manufacturing cost, installation area, and power consumption of the waste incineration equipment.

[0046] In contrast, in Figure 1 In the waste incineration facility 1, a wet scrubber 43 is installed in the exhaust gas flow path 4, downstream of the dust collector 42. The extraction point P1 connected to the recirculating exhaust gas line 6 is located downstream of the wet scrubber 43. The wet scrubber 43 sprays a water-containing liquid onto the exhaust gas, thereby lowering the temperature of the exhaust gas flowing through the exhaust gas flow path 4. This reduces the amount of water vapor contained in the exhaust gas and the moisture concentration in the gas circulating in the circulation path. As a result, the occurrence of condensation and the like can be suppressed in the exhaust gas flow path 4 and the recirculating exhaust gas line 6. Furthermore, the carbon dioxide concentration in the exhaust gas and the recirculating exhaust gas can be increased, enabling the combustion of waste in an atmosphere with a high carbon dioxide concentration in the incinerator 3 and easily increasing the methane concentration in the gas discharged from the methanation device 51.

[0047] As mentioned above, in Figure 1 In the waste incineration facility 1, the CO2 concentration in the exhaust gas can be increased. Therefore, a CO2 separation unit for separating CO2 from the exhaust gas is not provided in the exhaust gas path from the incinerator 3 to the methanation device 51. This reduces the manufacturing cost, installation area, and power consumption of the waste incineration facility 1. Alternatively, depending on the design of the waste incineration facility 1, a CO2 separation unit can be provided to supply the CO2 separated from the exhaust gas to the methanation device 51.

[0048] The oxygen mixing unit 66 preferably includes a water electrolysis device 67 that electrolyzes water to generate oxygen and hydrogen. Furthermore, the high-concentration oxygen includes the oxygen generated by the water electrolysis device 67, and the water electrolysis device 67 also serves as the hydrogen supply source. As described above, the water electrolysis device 67 can simultaneously generate oxygen for the high-concentration oxygen and hydrogen for methane generation, thereby simplifying the structure of the waste incineration facility 1.

[0049] A gas-to-gas heat exchanger 61 is preferably provided to heat the recirculated exhaust gas by exchanging heat between the exhaust gas flowing upstream of the wet scrubber 43 in the exhaust gas flow path 4 and the recirculated exhaust gas flowing through the recirculated exhaust gas line 6. This ensures that the exhaust gas is more reliably cooled to a predetermined temperature within the wet scrubber 43, effectively removing sulfur oxides, hydrogen chloride, and other substances contained in the exhaust gas. Furthermore, the recirculated exhaust gas can be efficiently heated, further suppressing the occurrence of condensation and other substances in the recirculated exhaust gas line 6, and allowing the recirculated exhaust gas to be preferably used as combustion gas.

[0050] The waste incineration equipment 1 preferably further includes an oxygen concentration measuring unit 52, a dilution unit 8, and a control unit 10. The oxygen concentration measuring unit 52 measures the oxygen concentration of the exhaust gas (raw material exhaust gas) flowing into the methanation device 51. The dilution unit 8 is located between the extraction position P1 in the exhaust gas path and the methanation device 51, and can mix a dilution gas having an oxygen concentration lower than that of the exhaust gas into the exhaust gas. When the measured value of the oxygen concentration measuring unit 52 reaches or exceeds a predetermined value, the control unit 10 mixes the dilution gas into the exhaust gas via the dilution unit 8. This prevents the oxygen concentration of the exhaust gas flowing into the methanation device 51 from becoming too high.

[0051] The dilution gas preferably includes a methane-containing gas. In this case, the dilution gas can be easily prepared, and unreacted carbon dioxide contained in the methane-containing gas can be used to generate methane, thereby further reducing the amount of carbon dioxide emitted.

[0052] The waste incineration facility 1 preferably further includes a gas separation device 71 for separating nitrogen from the methane-containing gas, and the dilution gas contains the nitrogen separated by the gas separation device 71. This allows a gas containing a high concentration of methane to be obtained, and the dilution gas can be easily prepared.

[0053] In the waste incineration equipment 1, the chimney 45, the gas-to-gas heat exchanger 61, the gas separation device 71, etc. can also be omitted. In the case where the methane generation capacity of the methanation device 51 is high, such as Figure 2As shown in the example of , the chimney 45 can be omitted and all the exhaust gas passing through the exhaust fan 44 can be supplied as raw exhaust gas to the methanation device 51. Depending on the temperature of the exhaust gas flowing into the wet scrubber 43 or the temperature of the recycled exhaust gas flowing in the recycled exhaust gas pipeline 6, the exhaust gas can be Figure 3 As shown in the example of , the gas-to-gas heat exchanger 61 is omitted, and heat exchange between the exhaust gas flowing in the exhaust gas flow path 4 and the recirculated exhaust gas flowing in the recirculated exhaust gas line 6 is not performed. Based on the methane concentration obtained in the methane-containing gas, the methane concentration can be calculated as follows: Figure 4 As shown in the example of , the gas separation device 71 is omitted and the methane-containing gas discharged from the methanation device 51 is directly used as fuel. Figure 5 In FIG. 4 , an example is shown in which the chimney 45 and the gas-to-gas heat exchanger 61 are omitted. Figure 6 In FIG, an example is shown in which the chimney 45 and the gas separation device 71 are omitted. Figure 7 In FIG. 1 , an example is shown in which the gas-to-gas heat exchanger 61 and the gas separation device 71 are omitted. Figure 8 , an example is shown in which the chimney 45, the gas-to-gas heat exchanger 61, and the gas separation device 71 are omitted.

[0054] The waste incineration plant 1 can be modified in various ways.

[0055] The oxygen mixing unit 66 can be a component that generates oxygen from a substance other than water. For example, a PSA-type oxygen generator that extracts oxygen from air can be used. Alternatively, it can be an oxygen storage unit for storing oxygen. For example, the oxygen storage unit can be a gas container such as a gas tank. The hydrogen supply source for the methanation unit 51 can be a gas tank storing hydrogen.

[0056] The position where the oxygen concentration is measured by the oxygen concentration measuring unit 52 can be set in the exhaust gas flow path 4. Furthermore, the position where the dilution gas is supplied by the dilution unit 8 can be set downstream of the extraction position P1 in the exhaust gas flow path 4 (between the extraction position P1 and the connection position of the exhaust gas supply line 5). Figures 1 to 8 In the waste incineration equipment 1, the oxygen concentration measuring unit 52 and the dilution unit 8 can be omitted.

[0057] The incinerator 3 may be an incinerator other than a stoker type (eg, a fluidized bed furnace, a kiln, etc.). The garbage incineration facility 1 may be used as a waste incineration facility for incinerating general waste or industrial waste other than garbage.

[0058] The configurations in the above-described embodiment and various modifications may be appropriately combined as long as they do not contradict each other.

[0059] While the invention has been described and illustrated in detail, the above description is illustrative and not restrictive, and therefore, it is understood that various modifications and variations are possible without departing from the scope of the invention.

[0060] Explanation of Figure Numbers

[0061] 1: Waste incineration equipment

[0062] 3: Incinerator

[0063] 4: Exhaust gas flow path

[0064] 6: Recirculation exhaust gas pipeline

[0065] 8: Dilution section

[0066] 10: Control Department

[0067] 42: Dust collector

[0068] 43: Wet smoke scrubber

[0069] 51: Methanation unit

[0070] 52: Oxygen concentration measurement unit

[0071] 61: Air-to-air heat exchanger

[0072] 66: Oxygen mixing unit

[0073] 67: Water electrolysis device

[0074] 71: Gas separation device

[0075] P1: Take out position

Claims

1. A waste incineration device comprising: incinerators, which burn waste; an exhaust gas flow path for the exhaust gas discharged from the incinerator to flow; A dust collector, disposed in the exhaust gas flow path; a wet scrubber disposed in the exhaust gas flow path at a position downstream of the dust collector and configured to spray a water-containing liquid onto the exhaust gas; a recirculating exhaust gas line connected to a take-off position in the exhaust gas flow path, downstream of the wet scrubber, for taking out a portion of the exhaust gas flowing in the exhaust gas flow path as recirculating exhaust gas and supplying it to the incinerator; an oxygen mixing unit for mixing high-concentration oxygen having a higher oxygen concentration than air with the recirculation exhaust gas flowing through the recirculation exhaust gas line; as well as a methanation device for reacting the exhaust gas that has passed through the extraction position and flows in the exhaust gas flow path with hydrogen supplied from a hydrogen supply source to generate a methane-containing gas; The recycled exhaust gas supplied to the incinerator is a main gas of the combustion gas used for incineration of the waste in the incinerator.

2. The waste incineration plant according to claim 1, wherein A carbon dioxide separation unit for separating carbon dioxide from the exhaust gas is not provided in the path of the exhaust gas from the incinerator to the methanation device.

3. The waste incineration plant according to claim 1, wherein The oxygen mixing unit includes a water electrolysis device, which electrolyzes water to generate oxygen and hydrogen. The high-concentration oxygen gas includes oxygen gas generated by the water electrolysis device. The water electrolysis device also serves as the hydrogen supply source.

4. The waste incineration equipment according to claim 1, further comprising: The heat exchanger heats the recirculated exhaust gas by exchanging heat between the exhaust gas upstream of the wet scrubber in the exhaust gas flow path and the recirculated exhaust gas flowing through the recirculated exhaust gas line.

5. The waste incineration plant according to any one of claims 1 to 4, further comprising: an oxygen concentration measuring unit for measuring the oxygen concentration of the exhaust gas flowing into the methanation device; a diluting unit capable of mixing a dilution gas having an oxygen concentration lower than that of the exhaust gas into the exhaust gas between the extraction position and the methanation device in the path of the exhaust gas; and The control unit mixes the dilution gas into the exhaust gas via the dilution unit when the measured value of the oxygen concentration measuring unit becomes equal to or greater than a predetermined value.

6. The waste incineration plant according to claim 5, wherein The dilution gas includes the methane-containing gas.

7. The waste incineration equipment according to claim 5, further comprising: a gas separation device for separating nitrogen from the methane-containing gas, The dilution gas includes nitrogen separated by the gas separation device.

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