waste incineration facility

Abstract

To enable attention amount to come closer to a target value while drastically reducing amount of exhaust gas.SOLUTION: A waste incineration facility 1 includes: a recirculation exhaust gas line 6 for taking out part of exhaust gas flowing in an exhaust gas flow passage 4 as recirculation exhaust gas and supplying the recirculation gas into an incinerator 3; an oxygen mixing section 5 for mixing high concentration oxygen gas of which oxygen concentration is higher than that of air with the recirculation exhaust gas flowing in the recirculation exhaust gas line 6; mixing ratio change sections 81-83 for changing a mixing ratio between the recirculation exhaust gas and the high concentration oxygen gas, which are to be supplied from a predetermined gas supply position in the incinerator 3 into the incinerator 3; attention amount measurement sections 36-38 for measuring at least one of steam amount generated by heat of the exhaust gas, a temperature in the incinerator 3 and an oxygen concentration at an outlet of the incinerator 3 as attention amount; and a control section 10 for controlling the mixing ratio change sections 81-83 so as to cause a measurement value of the attention amount to come closer to a predetermined target value. Main gas of combustion gas to be supplied into the incinerator 3 via a gas pipe is the recirculation gas with which the high concentration oxygen gas is mixed.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a waste incineration plant. [Background technology]

[0002] Conventionally, in waste incineration facilities, a portion of the exhaust gas flowing through the exhaust gas flow path is extracted as recirculated exhaust gas and supplied to the incinerator. The use of recirculated exhaust gas makes it possible to reduce the amount of exhaust gas from the waste incineration facility. In the incineration plant of Patent Document 1, a combustion adjustment gas wind box is installed below the combustion stoker in the slow combustion zone, and a low-oxygen gas supply pipe for supplying low-oxygen gas and a high-oxygen gas supply pipe for supplying high-oxygen gas are connected to the combustion adjustment gas wind box. A flue gas recirculation system is used as the low-oxygen gas source, and the oxygen concentration of the high-oxygen gas is set to 21 to 30 volume %. When the main steam volume falls below the target steam volume, gas containing high-oxygen gas is supplied to the combustion adjustment gas wind box. When the main steam volume exceeds the target steam volume, low-oxygen gas is supplied to the combustion adjustment gas wind box.

[0003] Patent Document 2 discloses a combustion device that incinerates a fuel layer on a stoker with primary combustion air or the like from below the fuel layer. The device is provided with a recirculated exhaust gas supply path that recirculates exhaust gas from the incinerator to the incinerator, an oxygen supply device, a first oxygen supply path that supplies oxygen from the oxygen supply device to the primary combustion air, a third oxygen supply path that supplies oxygen from the oxygen supply device to the recirculated exhaust gas, a switching device that switches the supply of oxygen from the oxygen supply device between the first oxygen supply path and the third oxygen supply path, and a control device that controls the switching device based on the results of measurement of the incinerator temperature and / or the oxygen concentration at the incinerator outlet. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-71238 [Patent Document 2] Patent No. 4359536 Summary of the Invention [Problem to be solved by the invention]

[0005] As mentioned above, in Patent Documents 1 and 2, the amount of steam, the temperature of the incinerator, or the oxygen concentration at the incinerator outlet is set as a quantity of interest, and control is performed to bring the quantity of interest closer to a target value. However, because primary combustion air is supplied to the incinerator, that is, because the main combustion gas supplied to the incinerator is air, there is a limit to how much exhaust gas can be reduced. Therefore, there is a need for a method to bring the quantity of interest closer to a target value while significantly reducing the amount of exhaust gas.

[0006] The present invention has been made in view of the above-mentioned problems, and aims to bring the quantity of interest closer to the target value while significantly reducing the amount of exhaust gas. [Means for solving the problem]

[0007] The invention described in claim 1 is a waste incineration facility, comprising: an incinerator for incinerating waste; an exhaust gas flow path through which exhaust gas discharged from the incinerator flows; and a dust collector provided in the exhaust gas flow path. a wet smoke washing tower provided downstream of the dust collector in the exhaust gas flow path; In the exhaust gas flow path wet smoke washing towera recirculation exhaust gas line connected to an extraction position downstream of the incinerator, extracting a portion of the exhaust gas flowing through the exhaust gas flow path as recirculation exhaust gas and supplying it into the incinerator; an oxygen mixing section that mixes high-concentration oxygen gas having an oxygen concentration higher than that of air with the recirculation exhaust gas flowing through the recirculation exhaust gas line; a mixing ratio changing section that changes the mixing ratio of the recirculation exhaust gas and the high-concentration oxygen gas that is supplied into the incinerator from a predetermined gas supply position in the incinerator; and a quantity of interest measuring device that measures at least one of the amount of steam generated by the heat of the exhaust gas, the temperature inside the incinerator, and the oxygen concentration at the outlet of the incinerator as a quantity of interest. and a control unit that controls the mixing ratio changing unit so that the measured value of the quantity of interest approaches a predetermined target value, wherein the combustion gas supplied into the incinerator through a gas pipe is the recirculated exhaust gas mixed with the high-concentration oxygen gas, the incinerator has a primary combustion chamber and a secondary combustion chamber, a grate unit is provided at the bottom of the primary combustion chamber, and the gas supply positions of the combustion gas in the incinerator are provided below the grate unit, (B) a side wall unit surrounding the secondary combustion chamber, and (C) (C1) a ceiling unit covering above a part of the grate unit in the primary combustion chamber, or (C2) a side wall unit surrounding the primary combustion chamber. 。

[0009] Claim 2 The invention described in , abandoned A waste incineration facility, an incinerator for incinerating waste; an exhaust gas flow path through which exhaust gas discharged from the incinerator flows; a dust collector provided in the exhaust gas flow path; and a recirculation exhaust gas line connected to an extraction position in the exhaust gas flow path downstream of the dust collector, for extracting a portion of the exhaust gas flowing through the exhaust gas flow path as recirculation exhaust gas and supplying it into the incinerator; a carbon dioxide recovery device that is provided downstream of the extraction position in the exhaust gas flow path and recovers carbon dioxide from the exhaust gas; and, from the exhaust gas that has passed through the carbon dioxide capture device , with a higher oxygen concentration than air A high-concentration oxygen gas is generated and introduced into the recirculation exhaust gas flowing through the recirculation exhaust gas line. On the other hand, the high concentration oxygen gas Mix The incinerator is provided with an oxygen mixing unit, a mixing ratio changing unit that changes the mixing ratio of the recirculated exhaust gas and the high-concentration oxygen gas that are supplied into the incinerator from a predetermined gas supply position in the incinerator, a quantity of interest measuring unit that measures at least one of the amount of steam generated by the heat of the exhaust gas, the temperature inside the incinerator, and the oxygen concentration at the outlet of the incinerator as a quantity of interest, and a control unit that controls the mixing ratio changing unit so that the measured value of the quantity of interest approaches a predetermined target value. The combustion gas supplied is the recirculated exhaust gas mixed with the high-concentration oxygen gas, the incinerator has a primary combustion chamber and a secondary combustion chamber, a grate section is provided at the bottom of the primary combustion chamber, and the gas supply positions of the combustion gas in the incinerator are (A) below the grate section, (B) a side wall section surrounding the secondary combustion chamber, (C) (C1) a ceiling section covering above a part of the grate section in the primary combustion chamber, or (C2) a side wall section surrounding the primary combustion chamber. The invention described in claim 3 is a waste incineration facility described in claim 1 or 2, further comprising a waste pit for storing waste before it is fed into the incinerator, and an extracted gas line for extracting gas from the waste pit as extracted gas, and the oxygen mixing section generates the high-concentration oxygen gas from the extracted gas and mixes it with the recirculated exhaust gas flowing through the recirculated exhaust gas line.

[0010] Claim 4 The invention described in claim 1 or 2 In the waste incineration facility described above, the flow rate of the gas supplied from the gas supply position in the incinerator into the incinerator is approximately constant.

[0011] Claim 5 The invention described in claim 1 or 2 In the waste incineration facility described above, the amount of interest includes the amount of steam, and the control unit controls the mixing ratio changing unit so that the measured value of the amount of steam approaches a predetermined target value, thereby changing the oxygen concentration of the combustion gas supplied into the incinerator from the gas supply position below the grate unit.

[0012] Claim 6 The invention described in claim 1 or 2 In the waste incineration facility described above, the quantity of interest includes the temperature inside the incinerator, and the control unit controls the mixing ratio changing unit so that the measured value of the temperature inside the incinerator approaches a predetermined target value, thereby changing the oxygen concentration of the combustion gas supplied into the incinerator from the gas supply position of the ceiling, the side wall surrounding the primary combustion chamber, or the side wall surrounding the secondary combustion chamber.

[0013] Claim 7 The invention described in claim 1 or 2 In the waste incineration facility described above, the amount of interest includes the oxygen concentration at the outlet of the incinerator, and the control unit controls the mixing ratio changing unit so that the measured value of the oxygen concentration at the outlet approaches a predetermined target value, thereby changing the oxygen concentration of the combustion gas supplied into the incinerator from the gas supply position on the side wall portion surrounding the secondary combustion chamber. [Effects of the Invention]

[0014] According to the present invention, it is possible to bring the quantity of interest closer to the target value while significantly reducing the amount of exhaust gas. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a block diagram showing the configuration of a waste incineration facility according to a first embodiment. [Figure 2] FIG. 1 is a diagram showing the configuration of a garbage pit and an incinerator. [Figure 3]FIG. 10 is a diagram showing another example of a configuration for supplying primary combustion gas to a grate portion. [Figure 4] FIG. 10 is a block diagram showing the configuration of a waste incineration facility according to a second embodiment. [Figure 5] FIG. 10 is a block diagram showing another example of a waste incineration facility. [Figure 6] FIG. 10 is a block diagram showing the configuration of a waste incineration facility according to a third embodiment. [Figure 7] FIG. 10 is a block diagram showing another example of a waste incineration facility. [Figure 8] FIG. 10 is a block diagram showing the configuration of a waste incineration facility according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] (First embodiment) FIG. 1 is a block diagram showing the configuration of a waste incineration plant 1 according to a first embodiment of the present invention. The waste incineration plant 1 is a waste incineration facility and includes a waste pit 2, an incinerator 3, an exhaust gas flow path 4, and a control unit 10 (see FIG. 2, which will be described later). The control unit 10 is, for example, a computer equipped with a CPU or the like, and is responsible for overall control of the waste incineration plant 1. The waste pit 2 is a waste pit that stores waste, which is waste. The incinerator 3 incinerates the waste thrown into the waste pit 2. The exhaust gas flow path 4 is a flue through which exhaust gas discharged from the incinerator 3 flows. In the example of FIG. 1, the exhaust gas flow path 4 is a flow path from the incinerator 3 to a chimney 47, which will be described later. In FIG. 1, only the arrow between the incinerator 3 and a boiler tube group 41, which will be described later, is labeled with the symbol 4. The waste pit 2 and the incinerator 3 will be described in detail later.

[0017] The waste incineration facility 1 further includes a boiler tube group 41, a filter-type dust collector 42 (hereinafter simply referred to as "dust collector 42"), a wet smoke scrubber 43, a carbon dioxide capture device 44, an exhaust gas reheater 45, an induced draft fan 46, and a chimney 47. The boiler tube group 41, the dust collector 42, the wet smoke scrubber 43, the carbon dioxide capture device 44, the exhaust gas reheater 45, the induced draft fan 46, and the chimney 47 are provided in the exhaust gas flow path 4, and are arranged in this order from the upstream side to the downstream side in the flow direction of the exhaust gas (i.e., from the incinerator 3 toward the chimney 47).

[0018] The boiler tube group 41 generates steam using the flue gas discharged from the incinerator 3 as a heat source. The dust collector 42 is a so-called bag filter, and collects fly ash contained in the flue gas using a filter cloth. A powdered flue gas treatment agent may be supplied to the flue gas upstream of the dust collector 42, and the flue gas treatment agent may be collected together with the fly ash in the dust collector 42. The flue gas treatment agent is used to remove sulfur oxides, hydrogen chloride, dioxins, mercury compounds, etc. The temperature of the flue gas at the outlet of the dust collector 42 is, for example, 150°C to 200°C. The flue gas that has passed through the dust collector 42 flows into the wet smoke scrubber 43.

[0019] The wet smoke scrubber 43 sprays a liquid containing an alkaline agent such as caustic soda and water into the flue gas. This lowers the temperature of the flue gas to, for example, 30°C to 70°C, and removes sulfur oxides, hydrogen chloride, and the like contained in the flue gas. The wet smoke scrubber 43 is a desulfurization section that removes sulfur oxides from the flue gas, and also a demineralization section that removes hydrogen chloride from the flue gas.

[0020] The carbon dioxide capture unit 44 captures carbon dioxide from the flue gas that has passed through the wet scrubber 43. One example of the carbon dioxide capture unit 44 captures carbon dioxide by chemical absorption and includes an absorption tower and a regeneration tower. In the absorption tower, for example, a liquid containing amine and water is sprayed into the flue gas, and the carbon dioxide is absorbed by the liquid. That is, carbon dioxide is removed from the flue gas. The liquid that has absorbed the carbon dioxide is sent to the regeneration tower and heated, and the carbon dioxide is extracted and captured. The captured carbon dioxide is used for methanation to produce methane, or is stored underground (CCUS (Carbon dioxide Capture, Utilization, and Storage)). In the waste incineration plant 1 that is provided with the recirculation flue gas line 6 described below, the carbon dioxide concentration in the flue gas is high, making CCUS easy to perform. The carbon dioxide capture unit 44 may capture carbon dioxide by a method other than chemical absorption.

[0021] As described above, the wet smoke scrubber 43 and the carbon dioxide capture device 44 remove predetermined components from the flue gas by supplying a liquid containing water to the flue gas that has passed through the dust collector 42. The flue gas that has passed through the wet smoke scrubber 43 and the carbon dioxide capture device 44 is a gas that contains large amounts of water, oxygen, and nitrogen.

[0022] The exhaust gas reheater 45 heats the exhaust gas using, for example, steam from a boiler (boiler tube group 41) as a heat medium. The induced draft fan 46 forms a gas flow from upstream to downstream in the exhaust gas flow path 4 (i.e., a gas flow from the incinerator 3 to the chimney 47). The exhaust gas that has passed through the induced draft fan 46 is discharged to the outside from the chimney 47. The waste incineration plant 1 may be provided with a reducing agent supply unit that sprays a reducing agent such as ammonia water into the incinerator 3, and non-catalytic denitrification (SNCR) may be performed.

[0023] The waste incineration system 1 further includes a recirculated flue gas line 6, a fan 66, a preheater 67, and an oxygen mixing unit 5. The recirculated flue gas line 6 is a flow path through which the recirculated flue gas described below flows. One end of the recirculated flue gas line 6 is connected to an extraction position P1 in the flue gas flow path 4 downstream of the dust collector 42. In the example shown in FIG. 1, the extraction position P1 is located between the wet smoke scrubber 43 and the carbon dioxide capture device 44. The recirculated flue gas line 6 extracts a portion of the flue gas flowing through the flue gas flow path 4 as recirculated flue gas. Because the carbon dioxide capture device 44 is located downstream of the extraction position P1 in the flue gas flow path 4, the recirculated flue gas extracted at the extraction position P1 has a high carbon dioxide concentration and a low oxygen concentration. The other end of the recirculated flue gas line 6 is connected to the incinerator 3, and the recirculated flue gas is supplied into the incinerator 3. In FIG. 1, only the arrow connected to the extraction position P1 is labeled with the symbol 6. Depending on the design of the waste incineration facility 1, the take-out position P1 may be provided between the dust collector 42 and the wet smoke washing tower 43, or may be provided downstream of the carbon dioxide capture device 44.

[0024] The fan 66 and the preheater 67 are provided in the recirculated exhaust gas line 6. In one example of the waste incineration facility 1, the preheater 67 and the fan 66 are arranged in this order from the upstream side to the downstream side in the flow of the recirculated exhaust gas (i.e., in the direction away from the take-out position P1). Two preheaters (first and second preheaters) may be used, with the first preheater, the fan 66, and the second preheater being arranged in this order from the upstream side to the downstream side. The order of the fan 66 and the preheater 67 in the recirculated exhaust gas line 6 may be determined arbitrarily.

[0025] The fan 66 forms a flow of the recirculated exhaust gas from the upstream side to the downstream side of the recirculated exhaust gas line 6. The preheater 67 can heat the recirculated exhaust gas using, for example, steam from a boiler (boiler tube group 41) as a heat medium. The preheater 67 may only heat the recirculated exhaust gas as necessary.

[0026] The oxygen mixing unit 5 is a device that generates high-concentration oxygen gas from air, having a higher oxygen concentration (volume concentration) than air, and is, for example, a PSA oxygen gas generator. The oxygen mixing unit 5 is connected to the recirculation exhaust gas line 6 via the oxygen mixed gas line 50, and the high-concentration oxygen gas generated in the oxygen mixing unit 5 is mixed with the recirculation exhaust gas flowing through the recirculation exhaust gas line 6. In an example in which a first preheater, a fan 66, and a second preheater are provided, the high-concentration oxygen gas may be mixed between the fan 66 and the second preheater. The order of the first preheater, the fan 66, and the second preheater and the mixing position of the high-concentration oxygen gas may be determined arbitrarily. By mixing the high-concentration oxygen gas, recirculation exhaust gas having a higher oxygen concentration than the exhaust gas at the discharge position P1 is obtained and supplied to the incinerator 3. The high-concentration oxygen gas has an oxygen concentration sufficiently higher than that of air, and the oxygen concentration is, for example, 50% by volume or more, preferably 65% ​​by volume or more, and more preferably 80% by volume or more. As will be described later, the high-concentration oxygen gas may be generated from sources other than air.

[0027] FIG. 2 is a diagram showing the configuration of the waste pit 2 and the incinerator 3. As described above, waste is stored in the waste pit 2 before being dumped into the incinerator 3, and a waste sediment layer 91 is formed. In a preferred waste incineration facility 1, a double-door structure is provided on the platform 22 connected to the waste pit 2. Specifically, an outer door 221 and an inner door 222 are provided between the platform 22 where waste collection trucks stop and the waste pit 2. When a waste collection truck dumps waste into the waste pit 2, the outer door 221 is opened with the inner door 222 closed, and the waste is dumped from the waste collection truck. The waste is temporarily held between the inner door 222 and the outer door 221. When the waste collection truck has finished dumping the waste, the outer door 221 is closed, and then the inner door 222 is opened. This allows the waste to be dumped into the waste pit 2. After the waste has been dumped into the waste pit 2, the inner door 222 is closed. With the above-mentioned double door structure, it is possible to reduce the amount of air that flows into the garbage pit 2.

[0028] The incinerator 3 comprises an input hopper 31, a waste supply section 32, a primary combustion chamber 33, and a secondary combustion chamber 34. Waste is input into the input hopper 31 from the waste pit 2 by the waste crane 23. The waste supply section 32 has a pusher or screw feeder or the like, and supplies waste from the bottom of the input hopper 31 into the primary combustion chamber 33.

[0029] At the bottom of the primary combustion chamber 33, a drying grate section 331, a combustion grate section 332, a post-combustion grate section 333, and a discharge port 334 are arranged in this order away from the waste supply section 32. In the drying grate section 331, the combustion grate section 332, and the post-combustion grate section 333, waste is transported from the waste supply section 32 toward the discharge port 334 by a well-known transport operation. In each of the drying grate section 331, the combustion grate section 332, and the post-combustion grate section 333, a primary combustion gas (described below) is ejected into the primary combustion chamber 33, combusting the waste along the way. The burned waste (mainly ash) is discharged outside the primary combustion chamber 33 through the discharge port 334. At least one nozzle 336 is provided in a ceiling section 335 covering the top of the post-combustion grate section 333. Auxiliary gas (described below) is ejected into the primary combustion chamber 33 from the nozzle 336. The auxiliary gas agitates the gas in the primary combustion chamber 33. The nozzle 336 may be provided on the side wall surrounding the primary combustion chamber 33 (including the rear wall near the outlet 334).

[0030] The secondary combustion chamber 34 is a space surrounded by the side wall, and directly continues from the primary combustion chamber 33, forming a flow path for exhaust gas discharged from the primary combustion chamber 33. In the example of FIG. 2, the secondary combustion chamber 34 is an upward-facing space with a flow path area sufficiently smaller than the floor area of ​​the primary combustion chamber 33. Multiple nozzles 341 are provided on the side wall of the secondary combustion chamber 34, and secondary combustion gas, described below, is ejected from the multiple nozzles 341. This burns unburned gas generated in the primary combustion chamber 33. The secondary combustion chamber 34 is part of the incinerator 3, and the flow path downstream from the outlet of the secondary combustion chamber 34 is the previously described exhaust gas flow path 4. In FIG. 2, the area where the boiler tube group 41 is provided is designated by the reference numeral 41.

[0031] In the example of FIG. 2, the recirculation exhaust gas line 6 branches into a first branch line 61, a second branch line 62, and a third branch line 63. The first branch line 61 branches into multiple lines that connect to the wind boxes of the drying grate section 331, the combustion grate section 332, and the post-combustion grate section 333, respectively. The second branch line 62 branches into multiple lines that connect to multiple nozzles 341, respectively. The third branch line 63 connects to a nozzle 336 in the ceiling section 335. Dampers 811, 821, and 831 are provided in the first branch line 61, the second branch line 62, and the third branch line 63, respectively. The dampers 811, 821, and 831 are electrically connected to the control unit 10. The flow rate of the recirculation exhaust gas flowing through each of the branch lines 61 to 63 can be adjusted by the dampers 811, 821, and 831. In order to precisely adjust the flow rate of the recirculated exhaust gas, a flow meter or the like may be provided (the same applies to branch lines 51 to 53 described later).

[0032] The oxygen mixed gas line 50 branches into a first branch line 51, a second branch line 52, and a third branch line 53. The first branch line 51, the second branch line 52, and the third branch line 53 are connected to the first branch line 61, the second branch line 62, and the third branch line 63, respectively, of the recirculation exhaust gas line 6. The first branch line 51, the second branch line 52, and the third branch line 53 are provided with dampers 812, 822, and 832, respectively. The dampers 812, 822, and 832 are electrically connected to the control unit 10. The flow rate of the high-concentration oxygen gas flowing through each of the branch lines 51 to 53 can be adjusted by the dampers 812, 822, and 832.

[0033] A mixture of the recirculated exhaust gas flowing through the first branch line 61 and the high-concentration oxygen gas flowing through the first branch line 51 is supplied as primary combustion gas into the primary combustion chamber 33. The primary combustion gas contains oxygen and is used to combust waste in the primary combustion chamber 33. The primary combustion gas is supplied below the drying grate section 331, the combustion grate section 332, and the post-combustion grate section 333 (hereinafter collectively referred to as "grate sections 331-333"). Dampers 811 and 812 provided in the first branch lines 51 and 61 are mixture ratio change sections 81 that change the mixture ratio of the high-concentration oxygen gas and the recirculated exhaust gas in the primary combustion gas. A damper 811 is provided in the first branch line 61 upstream of the connection position of the first branch line 51 (the same applies to the damper 821 in the second branch line 62 and the damper 831 in the third branch line 63).

[0034] A mixture of the recirculated exhaust gas flowing through the second branch line 62 and the high-concentration oxygen gas flowing through the second branch line 52 is supplied as secondary combustion gas into the secondary combustion chamber 34. The secondary combustion gas is a gas containing oxygen, and is used to combust unburned gas in the secondary combustion chamber 34. The secondary combustion gas is supplied to a nozzle 341 in the side wall. Dampers 821 and 822 provided in the second branch lines 52 and 62 are mixture ratio change units 82 that change the mixture ratio of the high-concentration oxygen gas and the recirculated exhaust gas in the secondary combustion gas.

[0035] A mixture of the recirculated exhaust gas flowing through the third branch line 63 and the high-concentration oxygen gas flowing through the third branch line 53 is supplied as auxiliary gas into the primary combustion chamber 33. The auxiliary gas is a gas containing oxygen, and is used to agitate the gas in the primary combustion chamber 33 and to combust unburned gas. In the example of FIG. 2, the auxiliary gas is supplied to a nozzle 336 in the ceiling portion 335. Dampers 831 and 832 provided in the third branch lines 53 and 63 are a mixture ratio change unit 83 that changes the mixture ratio of the high-concentration oxygen gas and the recirculated exhaust gas in the auxiliary gas.

[0036] The waste incineration system 1 further includes a steam amount measurement unit 36, an oxygen concentration measurement unit 37, and an in-furnace temperature measurement unit 38. The steam amount measurement unit 36 ​​measures the amount of steam discharged from the boiler tube group 41 (hereinafter referred to as the "boiler-generated steam amount"). The steam is used, for example, for power generation. The oxygen concentration measurement unit 37 measures the oxygen concentration at the outlet of the secondary combustion chamber 34, i.e., the outlet of the incinerator 3, using a sensor provided at the outlet (hereinafter referred to as the "furnace outlet oxygen concentration"). The in-furnace temperature measurement unit 38 measures the temperature inside the primary combustion chamber 33 using a sensor provided inside the primary combustion chamber 33. As described below, the in-furnace temperature measurement unit 38 may also measure the temperature inside the secondary combustion chamber 34. The steam amount measurement unit 36, the oxygen concentration measurement unit 37, and the in-furnace temperature measurement unit 38 are electrically connected to the control unit 10.

[0037] The control unit 10 performs control based on the measured values ​​of the quantities of interest, which are the amount of steam generated by the boiler measured by the steam amount measurement unit 36, the oxygen concentration at the furnace outlet measured by the oxygen concentration measurement unit 37, or the temperature inside the primary combustion chamber 33 (or the temperature inside the secondary combustion chamber 34) measured by the furnace temperature measurement unit 38. The steam amount measurement unit 36, the oxygen concentration measurement unit 37, and the furnace temperature measurement unit 38 are quantity of interest measurement units that measure the quantities of interest.

[0038] In a first control example of the control unit 10, a target value for the amount of steam generated by the boiler, which is a quantity of interest, is set, and the mixing ratio changing unit 81 provided on the first branch line 51, 61 is controlled so that the measured value of the amount of steam generated by the boiler by the steam amount measuring unit 36 ​​approaches the target value. Specifically, when the measured value of the amount of steam generated by the boiler is lower than the target value, the opening of the damper 811 in the mixing ratio changing unit 81 is made smaller (compared to the previous opening) and the opening of the damper 812 is made larger. This increases the ratio of high-concentration oxygen gas in the mixed gas of the recirculated exhaust gas and high-concentration oxygen gas, and primary combustion gas with a higher oxygen concentration (compared to the previous oxygen concentration) is supplied into the primary combustion chamber 33 from below the grate units 331-333. As a result, the measured value of the amount of steam generated by the boiler increases.

[0039] Furthermore, when the measured value of the amount of steam generated by the boiler is higher than the target value, the opening of damper 811 in the mixture ratio changing unit 81 is increased and the opening of damper 812 is decreased. This reduces the ratio of high-concentration oxygen gas in the mixed gas, and primary combustion gas with a low oxygen concentration is supplied into the primary combustion chamber 33 from below the grate units 331 to 333. As a result, the measured value of the amount of steam generated by the boiler decreases.

[0040] As described above, the mixture ratio of the recirculated exhaust gas and the high-concentration oxygen gas in the mixed gas (i.e., the oxygen concentration of the primary combustion gas) is changed by the mixture ratio change unit 81, and the amount of steam generated by the boiler is controlled to be approximately constant at a target value. The oxygen concentration of the primary combustion gas (as well as the secondary combustion gas and auxiliary gas) is, for example, 30% by volume or less, and typically 25% by volume or less. The oxygen concentration is, for example, greater than 0% by volume, and preferably 3% by volume or more. In the mixture ratio change unit 81, the change in the mixture ratio of the recirculated exhaust gas and the high-concentration oxygen gas may be achieved by a configuration other than the dampers 811 and 812 (for example, a fan, etc.) (the same applies to the mixture ratio change units 82 and 83).

[0041] It is preferable that the flow rate of the mixed gas (gas for primary combustion) supplied into the incinerator 3 from below the fire grate sections 331-333 be approximately constant before and after the change in the mixture ratio of the recirculated exhaust gas and the high-concentration oxygen gas by the mixture ratio change section 81. If the flow rate of the mixed gas is maintained within a range of ±20% of its average value (for example, the average value for one day) before and after the change in the mixture ratio, it can be said that the flow rate of the mixed gas is approximately constant. It is preferable that the flow rate of the mixed gas be maintained within a range of ±15% of its average value before and after the change in the mixture ratio, and more preferably within a range of ±10%. The same applies before and after the change in the mixture ratio by the mixture ratio change sections 82, 83.

[0042] In the second control example of the control unit 10, a target value for the furnace outlet oxygen concentration, which is a quantity of interest, is set, and the mixture ratio changing unit 82 provided on the second branch line 52, 62 is controlled so that the value of the furnace outlet oxygen concentration measured by the oxygen concentration measuring unit 37 approaches the target value. Specifically, when the measured value of the furnace outlet oxygen concentration is lower than the target value, the opening of the damper 821 in the mixture ratio changing unit 82 is reduced, and the opening of the damper 822 is increased. This increases the ratio of high-concentration oxygen gas in the mixed gas of the recirculated exhaust gas and high-concentration oxygen gas, and secondary combustion gas with a high oxygen concentration is supplied from the nozzle 341 into the secondary combustion chamber 34. As a result, the measured value of the furnace outlet oxygen concentration increases.

[0043] Furthermore, when the measured value of the furnace outlet oxygen concentration is higher than the target value, the opening of the damper 821 in the mixture ratio changing unit 82 is increased, and the opening of the damper 822 is decreased. This reduces the ratio of high-concentration oxygen gas in the mixed gas, and secondary combustion gas with a low oxygen concentration is supplied from the nozzle 341 into the secondary combustion chamber 34. As a result, the measured value of the furnace outlet oxygen concentration decreases. As described above, the mixture ratio of the recirculated exhaust gas and high-concentration oxygen gas in the mixed gas (i.e., the oxygen concentration of the secondary combustion gas) is changed by the mixture ratio changing unit 82, and the furnace outlet oxygen concentration is controlled to be approximately constant at the target value. As described above, in a preferred mixture ratio changing unit 82, the flow rate of the secondary combustion gas supplied from the nozzle 341 into the incinerator 3 is approximately constant before and after changing the mixture ratio of the recirculated exhaust gas and high-concentration oxygen gas.

[0044] In the third control example of the control unit 10, a target value for the temperature inside the primary combustion chamber 33, which is a quantity of interest, is set, and the mixture ratio change unit 83 provided on the third branch line 53, 63 is controlled so that the temperature measured by the furnace temperature measurement unit 38 inside the primary combustion chamber 33 approaches the target value. Specifically, when the measured temperature inside the primary combustion chamber 33 is lower than the target value, the opening of the damper 831 in the mixture ratio change unit 83 is reduced and the opening of the damper 832 is increased. This increases the ratio of high-concentration oxygen gas in the mixed gas of the recirculated exhaust gas and high-concentration oxygen gas, and auxiliary gas with a high oxygen concentration is supplied from the nozzle 336 into the primary combustion chamber 33. As a result, the measured temperature inside the primary combustion chamber 33 increases.

[0045] Furthermore, when the measured temperature in the primary combustion chamber 33 is higher than the target value, the opening of the damper 831 in the mixture ratio change unit 83 is increased and the opening of the damper 832 is decreased. This reduces the ratio of high-concentration oxygen gas in the mixed gas, and auxiliary gas with a low oxygen concentration is supplied from the nozzle 336 into the primary combustion chamber 33. As a result, the measured temperature in the primary combustion chamber 33 decreases. As described above, the mixture ratio of the recirculated exhaust gas and the high-concentration oxygen gas in the mixed gas (i.e., the oxygen concentration of the auxiliary gas) is changed by the mixture ratio change unit 83, and the temperature in the primary combustion chamber 33 is controlled to be approximately constant at the target value. As described above, in a preferred mixture ratio change unit 83, the flow rate of the auxiliary gas supplied from the nozzle 336 into the incinerator 3 is approximately constant before and after changing the mixture ratio of the recirculated exhaust gas and the high-concentration oxygen gas. Note that depending on the design of the waste incineration plant 1, the nozzle 336 may not be provided in the primary combustion chamber 33. In this case, the third control example is not performed.

[0046] The furnace temperature measuring unit 38 may measure the temperature inside the secondary combustion chamber 34 using a sensor provided inside the secondary combustion chamber 34. In this case, a target value for the temperature inside the secondary combustion chamber 34 is set in the control unit 10, and the mixture ratio changing units 82, 83 are controlled so that the temperature measured by the furnace temperature measuring unit 38 inside the secondary combustion chamber 34 approaches the target value. Specifically, when the measured temperature inside the secondary combustion chamber 34 is lower than the target value, secondary combustion gas with a high oxygen concentration is supplied from the nozzle 341 into the secondary combustion chamber 34, and auxiliary gas with a high oxygen concentration is supplied from the nozzle 336 into the primary combustion chamber 33. As a result, the measured temperature inside the secondary combustion chamber 34 increases.

[0047] Furthermore, when the measured temperature value in the secondary combustion chamber 34 is higher than the target value, secondary combustion gas with a low oxygen concentration is supplied from the nozzle 341 into the secondary combustion chamber 34, and auxiliary gas with a low oxygen concentration is supplied from the nozzle 336 into the primary combustion chamber 33. As a result, the measured temperature value in the secondary combustion chamber 34 decreases. As described above, the oxygen concentrations of the secondary combustion gas and the auxiliary gas are changed by the mixture ratio change units 82, 83, and the temperature in the secondary combustion chamber 34 is controlled to be approximately constant at the target value. Note that if the nozzle 336 is not provided in the primary combustion chamber 33, the temperature in the secondary combustion chamber 34 may be controlled only by changing the oxygen concentration of the secondary combustion gas.

[0048] In controlling the amount of steam generated by the boiler (first control example), in addition to changing the oxygen concentration of the primary combustion gas, the oxygen concentration of the secondary combustion gas and / or the oxygen concentration of the auxiliary gas may be changed.In controlling the furnace outlet oxygen concentration (second control example), in addition to changing the oxygen concentration of the secondary combustion gas, the oxygen concentration of the primary combustion gas and / or the oxygen concentration of the auxiliary gas may be changed.In controlling the temperature inside the incinerator (third control example), the oxygen concentration of the primary combustion gas may be changed.

[0049] Furthermore, two or more of the boiler-generated steam amount, the furnace outlet oxygen concentration, and the incinerator internal temperature may be focused on as quantities of interest, and control of the two or more quantities of interest may be performed in parallel. In this case, if the objects to be changed (the oxygen concentration of the primary combustion gas, the oxygen concentration of the secondary combustion gas, or the oxygen concentration of the auxiliary gas) overlap in the control of the two or more quantities of interest, the amount of change of the objects to be changed may be determined, for example, taking into consideration weights respectively set for the two or more quantities of interest.

[0050] As described above, the waste incineration system 1 includes the recirculated exhaust gas line 6 that extracts a portion of the exhaust gas flowing through the exhaust gas flow path 4 as recirculated exhaust gas and supplies it to the incinerator 3, and the oxygen mixing unit 5 that mixes high-concentration oxygen gas, which has a higher oxygen concentration than air, with the recirculated exhaust gas flowing through the recirculated exhaust gas line 6. In the waste incineration system 1, by mixing the high-concentration oxygen gas with the recirculated exhaust gas and using it as combustion gas in the incinerator 3, it is possible to increase the amount of recirculated exhaust gas extracted from the exhaust gas flow path 4 compared to when air is mixed with the recirculated exhaust gas. As a result, it is possible to easily reduce the amount of exhaust gas flowing in the exhaust gas flow path 4 downstream of the connection position of the recirculated exhaust gas line 6 (i.e., extraction position P1).

[0051] Furthermore, in the waste incineration plant 1, almost no air is supplied to the incinerator 3 from outside, except for air brought into the incinerator 3 by the waste and air flowing into the incinerator 3 via the feeding hopper 31. In detail, almost all of the combustion gas supplied to the incinerator 3 through the gas pipe is recirculated flue gas supplied to the incinerator 3 from the recirculated flue gas line 6, i.e., recirculated flue gas mixed with high-concentration oxygen gas. This makes it possible to significantly reduce the amount of flue gas discharged from the chimney 47 in the waste incineration plant 1. Note that air may be supplied to the incinerator 3 from outside during initial operation.

[0052] Here, we will describe a comparative example of a waste incineration system that supplies gases (e.g., air) with a constant oxygen concentration as the primary combustion gas, secondary combustion gas, and auxiliary gas. In this comparative example of a waste incineration system, the flow rate of the primary combustion gas, secondary combustion gas, or auxiliary gas is increased or decreased so that the target quantity approaches a target value, such as the amount of steam generated by the boiler, the oxygen concentration at the furnace outlet, or the temperature inside the incinerator. In this case, the amount of exhaust gas discharged from the incinerator 3 fluctuates greatly, which increases the power consumption of the induced draft fan 46.

[0053] In response to this, the waste incineration system 1 is provided with mixing ratio change units 81-83 that change the mixing ratio of the recirculated exhaust gas and the high-concentration oxygen gas supplied into the incinerator 3 from a predetermined gas supply position in the incinerator 3. The target quantity measurement units (steam amount measurement unit 36, oxygen concentration measurement unit 37, and furnace temperature measurement unit 38 in the above example) measure at least one of the target quantities: the amount of steam generated by the heat of the exhaust gas, the temperature inside the incinerator 3, and the oxygen concentration at the outlet of the incinerator 3. The control unit 10 controls the mixing ratio change units 81-83 so that the measured target quantity approaches a predetermined target value. In this way, by changing the oxygen concentration of the mixed gas supplied into the incinerator 3 from the gas supply position, fluctuations in the amount of exhaust gas discharged from the incinerator 3 can be suppressed. As a result, it is possible to easily bring the target quantity closer to the target value while reducing the power consumption of the induced draft fan 46.

[0054] Preferably, the flow rate of the mixed gas supplied from the gas supply position into the incinerator 3 is kept approximately constant. This further suppresses fluctuations in the amount of exhaust gas discharged from the incinerator 3, and further reduces the power consumption of the induced draft fan 46. In addition, the pressure inside the incinerator 3 is kept approximately constant, enabling stable and safe operation. Depending on the waste incineration conditions, the mixture ratio of the recirculated exhaust gas and the high-concentration oxygen gas may be changed while changing the flow rate of the mixed gas.

[0055] Preferably, the target amount includes the steam amount described above, and the gas supply position in the incinerator 3 is located below the grate sections 331-333. This allows the steam amount to easily approach the target value. Furthermore, even when low-calorie waste is supplied to the incinerator 3, the low-calorie waste can be appropriately incinerated by increasing the oxygen concentration of the primary combustion gas. In other words, the combustion of the low-calorie waste does not require the use of a combustion enhancer such as fossil fuel, thereby reducing running costs. Furthermore, the combustion temperature can be maintained at a high temperature during such low-load operation, making it possible to flexibly handle low-calorie waste, flood-damaged waste, sludge, and the like. When low-calorie waste is supplied to the incinerator 3, the oxygen concentration of the primary combustion gas may be increased while the flow rate of the primary combustion gas is reduced, thereby efficiently combusting the low-calorie waste.

[0056] Preferably, the quantity of interest includes the oxygen concentration at the outlet of the incinerator 3, and the gas supply position in the incinerator 3 is provided in the side wall surrounding the secondary combustion chamber 34 of the incinerator 3. This makes it possible to easily bring the oxygen concentration at the outlet of the incinerator 3 close to the target value.

[0057] Incidentally, when the flow rate of secondary combustion gas (secondary combustion air) is increased or decreased as in the waste incineration system of the comparative example, if the oxygen concentration at the outlet of the incinerator 3 is high, the flow rate of the secondary combustion air is reduced. In this case, the discharge speed of the secondary combustion air from the nozzle decreases, reducing the penetration force of the secondary combustion air and resulting in insufficient stirring in the secondary combustion chamber 34. As a result, incomplete combustion is more likely to occur and carbon monoxide (CO) is more likely to be generated. In contrast, in the waste incineration system 1, if the oxygen concentration at the outlet of the incinerator 3 is high, secondary combustion gas with a low oxygen concentration is supplied. This maintains a constant penetration force, allowing sufficient stirring within the secondary combustion chamber 34 and suppressing incomplete combustion. NOx emissions can also be appropriately reduced.

[0058] Preferably, the quantity of interest includes the temperature inside the incinerator 3, and the gas supply position in the incinerator 3 is located on the ceiling 335 covering a portion of the grate sections 331-333, on the sidewall surrounding the primary combustion chamber 33 of the incinerator 3, or on the sidewall surrounding the secondary combustion chamber 34 of the incinerator 3. This allows the temperature inside the incinerator 3 to easily approach the target value, enabling stable operation of the waste incineration system 1. Furthermore, when the flow rate of the secondary combustion gas or auxiliary gas is increased or decreased, as in the waste incineration system of the comparative example, if the flow rate becomes excessively low, incomplete combustion is likely to occur, making it more likely that carbon monoxide will be generated. In contrast, the waste incineration system 1, which changes the oxygen concentration of the secondary combustion gas or auxiliary gas, can suppress incomplete combustion as described above.

[0059] FIG. 3 shows another example of a configuration for supplying primary combustion gas to the grate sections 331-333. In FIG. 3, a first branch line 61 of the recirculation exhaust gas line 6 branches into multiple lines 61a, 61b, and 61c, which are connected to the wind boxes of the drying grate section 331, the combustion grate section 332, and the post-combustion grate section 333, respectively. The first branch line 51 of the oxygen-mixed gas line 50 also branches into multiple lines 51a, 51b, and 51c, which are connected to the multiple lines 61a, 61b, and 61c, respectively. A damper for the mixing ratio changing section 81a is provided in the lines 51a and 61a, which allows the mixing ratio of the recirculation exhaust gas and the high-concentration oxygen gas supplied into the incinerator 3 from below the drying grate section 331 to be changed. Lines 51b and 61b are provided with a damper for a mixing ratio changing unit 81b, which can change the mixing ratio of the recirculated exhaust gas and the high-concentration oxygen gas supplied into the incinerator 3 from below the combustion grate unit 332. Lines 51c and 61c are provided with a damper for a mixing ratio changing unit 81c, which can change the mixing ratio of the recirculated exhaust gas and the high-concentration oxygen gas supplied into the incinerator 3 from below the post-combustion grate unit 333.

[0060] In the example of FIG. 3, the control unit 10 also individually controls the mixing ratio changing units 81a-81c so that the measured value of a quantity of interest (e.g., the amount of steam generated by the boiler) approaches a predetermined target value. This allows the quantity of interest to approach the target value with high accuracy. Preferably, the flow rate of gas supplied into the incinerator 3 from below each of the grate units 331-333 is approximately constant. This suppresses fluctuations in the amount of exhaust gas discharged from the incinerator 3 and reduces the power consumption of the induced draft fan 46. Note that, similar to the grate units 331-333, multiple mixing ratio changing units may be provided for the multiple nozzles 341 in the secondary combustion chamber 34, respectively, so that the mixing ratio of the recirculated exhaust gas and the high-concentration oxygen gas supplied into the incinerator 3 from each nozzle 341 can be individually changed. The same applies when multiple nozzles 336 are provided in the primary combustion chamber 33.

[0061] (Second embodiment) Fig. 4 is a block diagram showing a waste incineration plant 1 according to a second embodiment of the present invention. In the waste incineration plant 1 of Fig. 4, the waste pit 2 and the oxygen mixing section 5 are connected by an extracted gas line 21, which is a gas flow path. Gas in the waste pit 2 is extracted as extracted gas and supplied to the oxygen mixing section 5 via the extracted gas line 21. Other components are the same as those of the waste incineration plant 1 of Fig. 1, and the same components are designated by the same reference numerals.

[0062] A fan 212 and a deodorizer 72 are provided in the extracted gas line 21, in this order, from the garbage pit 2 toward the oxygen mixing section 5. The order of the fan 212 and the deodorizer 72 may be reversed. Extracted gas deodorized by an activated carbon layer or the like in the deodorizer 72 is supplied to the oxygen mixing section 5, and high-concentration oxygen gas is generated by concentrating oxygen from the extracted gas. The high-concentration oxygen gas is mixed with the recirculated flue gas flowing through the recirculated flue gas line 6 via the oxygen-mixed gas line 50 and supplied to the incinerator 3. The remaining gas (mainly nitrogen gas) after oxygen concentration in the oxygen mixing section 5 is discharged outside the waste incineration plant 1. The oxygen mixing section 5 may take in ambient air as needed, for example, when the required amount of high-concentration oxygen gas cannot be generated using the extracted gas alone.

[0063] As described above, the oxygen mixing section 5 in Figure 4 is provided with an extracted gas line 21 that extracts gas from within the garbage pit 2 as extracted gas, and the negative pressure within the garbage pit 2 is appropriately maintained. This prevents odors from leaking from the garbage pit 2 to the outside. In addition, high-concentration oxygen gas is generated from the extracted gas, mixed with the recirculated exhaust gas, and used as combustion gas in the incinerator 3. This increases the amount of recirculated exhaust gas extracted from the exhaust gas flow path 4, and reduces the amount of exhaust gas discharged from the chimney 47.

[0064] Furthermore, since almost all of the combustion gas supplied to the incinerator 3 via the gas pipe is recirculated exhaust gas mixed with high-concentration oxygen gas, it is possible to significantly reduce the amount of exhaust gas discharged from the chimney 47. Furthermore, the control unit 10 controls the mixing ratio change units 81-83 so that the measured value of the amount of attention approaches a predetermined target value (see FIG. 2). This makes it possible to suppress fluctuations in the amount of exhaust gas discharged from the incinerator 3, and as a result, it is possible to reduce the power consumption of the induced draft fan 46 while easily bringing the amount of attention close to the target value. The same applies to the waste incineration plants 1 of the third and fourth embodiments described below.

[0065] The deodorizing device 72 does not necessarily have to be provided on the extracted gas line 21, but may be provided on the discharge path leading from the oxygen mixing section 5 to the outside, as shown in FIG. 5. In the oxygen mixing section 5 of FIG. 5, the oxygen contained in the extracted gas (and air) is concentrated to generate high-concentration oxygen gas, which is then mixed with the recirculated exhaust gas. Meanwhile, the remaining extracted gas, i.e., the gas remaining after oxygen concentration, is discharged to the outside via the deodorizing device 72. In the configuration of FIG. 5, the flow rate of gas flowing through the deodorizing device 72 is smaller than in the configuration of FIG. 4. This allows the use of a smaller deodorizing device 72, thereby reducing the manufacturing costs of the waste incineration plant 1.

[0066] (Third embodiment) FIG. 6 is a block diagram showing a waste incineration plant 1 according to a third embodiment of the present invention. In the waste incineration plant 1 of FIG. 6, an oxygen enrichment device 5a is provided instead of the oxygen mixing section 5 in the waste incineration plant 1 of FIG. 1. The oxygen enrichment device 5a is disposed in the flue gas flow path 4 between the carbon dioxide capture device 44 and the flue gas reheater 45. The oxygen enrichment device 5a is connected to the recirculation flue gas line 6 via an oxygen mixed gas line 50. An extracted gas line 21 is further connected to the oxygen enrichment device 5a. A gas-gas heat exchanger 71 is provided in the flue gas flow path 4 and the recirculation flue gas line 6. The other configuration is the same as in FIG. 1, and the same components are designated by the same reference numerals.

[0067] In the gas-gas heat exchanger 71, heat is exchanged between the flue gas flowing from the dust collector 42 to the wet smoke scrubber 43 in the flue gas flow path 4 and the recirculated flue gas flowing in the recirculated flue gas line 6. This makes it possible to efficiently heat the recirculated flue gas whose temperature has been reduced in the wet smoke scrubber 43 in a waste incineration plant 1 in which the take-out position P1 is provided downstream of the wet smoke scrubber 43. The gas-gas heat exchanger 71 may also be used in other waste incineration plants 1. In the example of FIG. 6, a preheater is omitted in the recirculated flue gas line 6, but a preheater may be provided if necessary. Furthermore, a preheater may be provided instead of the gas-gas heat exchanger 71. If the gas-gas heat exchanger 71 is not provided, the take-out position P1 may be provided between the dust collector 42 and the wet smoke scrubber 43.

[0068] The oxygen enrichment device 5a in FIG. 6 is supplied with exhaust gas that has passed through the carbon dioxide recovery device 44. In the extracted gas line 21, the fan 212 extracts extracted gas from the garbage pit 2 and supplies it to the oxygen enrichment device 5a via the deodorizing device 72. External air may also be supplied to the oxygen enrichment device 5a as needed. The oxygen enrichment device 5a generates high-concentration oxygen gas from these gases, and is, for example, a PSA device similar to the oxygen mixing unit 5 described above. In this embodiment, the oxygen enrichment device 5a adsorbs and separates nitrogen (N2) gas from these gases and directs it to the exhaust gas reheater 45. The remaining gas (mainly oxygen (O2) gas and carbon dioxide (CO2) gas) is directed to the recirculated exhaust gas line 6 via the oxygen mixed gas line 50 and mixed with the recirculated exhaust gas. The gas mixed with the recirculated exhaust gas is high-concentration oxygen gas with a higher oxygen concentration than air and is used as combustion gas (combustion oxidant) in the incinerator 3. The gas (mainly nitrogen gas) guided to the exhaust gas reheater 45 is guided to a chimney 47 via an induced draft fan 46 and released into the atmosphere. Note that an adsorbent that adsorbs oxygen may be used in the oxygen enrichment device 5a. The same applies to the oxygen mixing section 5 described above.

[0069] As described above, in the waste incineration plant 1 of Figure 6, the oxygen enrichment device 5a is provided in the flue gas flow path 4. The oxygen enrichment device 5a is an oxygen mixing section that generates high-concentration oxygen gas with a high oxygen concentration from the flue gas that has passed through the carbon dioxide recovery device 44 and the gas extracted from the garbage pit 2, and mixes this with the remaining carbon dioxide into the recirculated flue gas that flows through the recirculated flue gas line 6. This makes it possible to reduce the amount of carbon dioxide emitted from the flue gas that has passed through the carbon dioxide recovery device 44.

[0070] In addition, an extracted gas line 21 is provided to extract gas from within the garbage pit 2 as extracted gas, thereby appropriately maintaining a negative pressure within the garbage pit 2. Then, the oxygen enrichment device 5a generates high-concentration oxygen gas from the extracted gas and mixes it with the recirculated flue gas flowing through the recirculated flue gas line 6. This makes it possible to increase the amount of recirculated flue gas extracted from the flue gas flow path 4 compared to when the extracted gas is mixed directly with the recirculated flue gas or when it is supplied directly to the incinerator 3.

[0071] In the waste incineration plant 1, a wet smoke scrubber 43 is provided in the flue gas flow path 4 between the dust collector 42 and the extraction position P1 of the recirculated flue gas. In the gas-gas heat exchanger 71, the recirculated flue gas is heated by heat exchange between the flue gas upstream of the wet smoke scrubber 43 in the flue gas flow path 4 and the recirculated flue gas flowing in the recirculated flue gas line 6. In this way, the recirculated flue gas from which a portion of the flue gas has been extracted (i.e., gas with a lower flow rate than the flue gas in the flue gas flow path 4) is heated by the high-temperature flue gas flowing in the flue gas flow path 4, thereby efficiently increasing the temperature of the recirculated flue gas.

[0072] In the waste incineration plant 1 of Figure 6, depending on the oxygen content of the flue gas that has passed through the carbon dioxide capture device 44, the flue gas may not need to be supplied to the oxygen enrichment device 5a. In this case, in the oxygen enrichment device 5a, high-concentration oxygen gas is extracted from the gas extracted from the garbage pit 2 and from the outside air, and mixed with the recirculated flue gas. Meanwhile, gases other than the high-concentration oxygen gas (mainly nitrogen gas) are discharged to the flue gas reheater 45. Furthermore, the flue gas that has passed through the carbon dioxide capture device 44 may, for example, be guided downstream of the oxygen enrichment device 5a without passing through the oxygen enrichment device 5a, and mixed with the gas (nitrogen gas, etc.) discharged from the oxygen enrichment device 5a.

[0073] As shown in FIG. 7, a deodorizer 72 may be disposed between the oxygen enrichment device 5a and the flue gas reheater 45. In this case, the remaining gas after oxygen enrichment in the oxygen enrichment device 5a passes through the deodorizer 72 and is then discharged to the outside through a chimney 47. Furthermore, the flue gas that has passed through the carbon dioxide capture device 44 may be guided downstream of the deodorizer 72 without passing through the oxygen enrichment device 5a and the deodorizer 72, and mixed with the gas (nitrogen gas, etc.) discharged from the deodorizer 72. Depending on the configuration of the waste incineration plant 1, the deodorizer 72 may be omitted. Furthermore, the extracted gas does not have to be supplied to the oxygen enrichment device 5a.

[0074] (Fourth embodiment) Fig. 8 is a block diagram showing a waste incineration plant 1 according to a fourth embodiment of the present invention. In the waste incineration plant 1 of Fig. 8, a carbon dioxide utilization device 44a is provided instead of the carbon dioxide capture device 44 in the waste incineration plant 1 of Fig. 1, and the flue gas reheater 45, induced draft fan 46, and chimney 47 are omitted. Other configurations are the same as those of the waste incineration plant 1 of Fig. 1.

[0075] As shown in FIG. 8, the carbon dioxide utilization device 44a is provided downstream of the extraction position P1 in the flue gas flow path 4. The carbon dioxide utilization device 44a is a device that utilizes flue gas to produce a predetermined product. In one example, methane gas or the like is produced from the flue gas by methanation. In another example, solid carbonates are produced from the flue gas by mineralization. Note that components other than carbon dioxide contained in the flue gas may also be included in the product. A waste incineration plant 1 equipped with the carbon dioxide utilization device 44a can significantly reduce the amount of flue gas emitted into the atmosphere. In other waste incineration plants 1, the carbon dioxide utilization device 44a may be provided instead of the carbon dioxide capture device 44, as in FIG. 8. Alternatively, both the carbon dioxide capture device 44 and the carbon dioxide utilization device 44a may be provided. In this case, for example, the carbon dioxide captured by the carbon dioxide capture device 44 is used to produce a predetermined product in the carbon dioxide utilization device 44a.

[0076] The waste incineration plant 1 can be modified in various ways.

[0077] In the above embodiment, almost no air is supplied from outside into the incinerator 3. However, depending on the design of the waste incineration facility 1, air may be supplied into the incinerator 3 via a gas pipe as part of the combustion gas (gas containing oxygen). In this case, to sufficiently reduce the amount of exhaust gas, it is preferable that the main combustion gas supplied into the incinerator 3 via the gas pipe be recirculated exhaust gas mixed with high-concentration oxygen gas. The main combustion gas is, for example, a gas that accounts for 50% or more by volume of the combustion gas. Even when air is supplied into the incinerator 3 via the gas pipe as part of the combustion gas, it is preferable that the air account for less than 50% by volume of the combustion gas. The air is more preferably less than 35% by volume, and even more preferably less than 20% by volume.

[0078] In the above embodiment, the recirculated exhaust gas line 6 is connected to the primary combustion chamber 33 and secondary combustion chamber 34 of the incinerator 3, and the recirculated exhaust gas mixed with high-concentration oxygen gas is used as primary combustion gas and secondary combustion gas, but the recirculated exhaust gas line 6 may also be connected only to the primary combustion chamber 33 or secondary combustion chamber 34.

[0079] If the oxygen concentration of the exhaust gas that has passed through the carbon dioxide capture device 44 is sufficiently higher than that of air, the exhaust gas may be mixed as high-concentration oxygen gas into the recirculated exhaust gas. In this case, the carbon dioxide capture device 44 is regarded as an oxygen mixing section.

[0080] The incinerator 3 may be an incinerator other than a stoker-type incinerator (for example, a fluidized bed furnace, a kiln furnace, etc.). The waste incineration facility 1 may be used as a waste incineration facility for incinerating general waste other than waste and industrial waste.

[0081] The configurations in the above-described embodiment and each modification may be combined as appropriate as long as they are not mutually contradictory. [Explanation of symbols]

[0082] 1. Waste incineration facility 2. Garbage pit 3 Incinerator 4 Exhaust gas flow path 5 Oxygen mixing section 5a Oxygen enrichment device 6 Recirculation exhaust gas line 10 Control Unit 21 Extraction gas line 33 Primary combustion chamber 34 Secondary combustion chamber 36 Steam volume measurement section 37 Oxygen concentration measurement unit 38 Furnace temperature measurement section 42 Dust collector 44 Carbon dioxide capture equipment 81-83, 81a-81c Mixing ratio change section 331~333 Grate section 335 Ceiling 336,341 nozzles P1 Extraction position

Claims

1. A waste incineration facility comprising: an incinerator for incinerating waste; an exhaust gas flow path through which exhaust gas discharged from the incinerator flows; a dust collector provided in the exhaust gas flow path; a wet smoke washing tower provided downstream of the dust collector in the exhaust gas flow path; a recirculation flue gas line connected to an extraction position downstream of the wet smoke scrubber in the flue gas flow path, extracting a portion of the flue gas flowing through the flue gas flow path as recirculation flue gas and supplying it into the incinerator; an oxygen mixing section that mixes high-concentration oxygen gas having an oxygen concentration higher than that of air with the recirculation exhaust gas flowing through the recirculation exhaust gas line; a mixing ratio changing unit that changes the mixing ratio of the recirculated exhaust gas and the high-concentration oxygen gas supplied into the incinerator from a predetermined gas supply position in the incinerator; a quantity of interest measurement unit that measures at least one of the amount of steam generated by the heat of the exhaust gas, the temperature inside the incinerator, and the oxygen concentration at the outlet of the incinerator as a quantity of interest; a control unit that controls the mixing ratio changing unit so that the measured value of the amount of interest approaches a predetermined target value; Equipped with The combustion gas supplied into the incinerator through a gas pipe is the recirculated exhaust gas mixed with the high-concentration oxygen gas, The incinerator has a primary combustion chamber and a secondary combustion chamber, and a grate is provided at the bottom of the primary combustion chamber; The gas supply position of the combustion gas in the incinerator is (A) below the grate portion; (B) a sidewall portion surrounding the secondary combustion chamber; (C) (C1) a ceiling portion covering an upper portion of the grate portion in the primary combustion chamber, or (C2) a side wall portion surrounding the primary combustion chamber; A waste incineration facility characterized by being installed in.

2. A waste incineration facility, an incinerator for incinerating waste; an exhaust gas flow path through which exhaust gas discharged from the incinerator flows; a dust collector provided in the exhaust gas flow path; a recirculation exhaust gas line connected to an extraction position downstream of the dust collector in the exhaust gas flow path, extracting a portion of the exhaust gas flowing through the exhaust gas flow path as recirculation exhaust gas and supplying it into the incinerator; a carbon dioxide recovery device that is provided in the exhaust gas flow path downstream of the extraction position and that recovers carbon dioxide from the exhaust gas; an oxygen mixing section that generates high-concentration oxygen gas having an oxygen concentration higher than that of air from the exhaust gas that has passed through the carbon dioxide recovery device and mixes the high-concentration oxygen gas with the recirculation exhaust gas flowing through the recirculation exhaust gas line; a mixing ratio changing unit that changes the mixing ratio of the recirculated exhaust gas and the high-concentration oxygen gas supplied into the incinerator from a predetermined gas supply position in the incinerator; a quantity of interest measurement unit that measures at least one of the amount of steam generated by the heat of the exhaust gas, the temperature inside the incinerator, and the oxygen concentration at the outlet of the incinerator as a quantity of interest; a control unit that controls the mixing ratio changing unit so that the measured value of the amount of interest approaches a predetermined target value; Equipped with The combustion gas supplied into the incinerator through a gas pipe is the recirculated exhaust gas mixed with the high-concentration oxygen gas, The incinerator has a primary combustion chamber and a secondary combustion chamber, and a grate is provided at the bottom of the primary combustion chamber; The gas supply position of the combustion gas in the incinerator is (A) below the grate portion; (B) a sidewall portion surrounding the secondary combustion chamber; (C) (C1) a ceiling portion covering an upper portion of the grate portion in the primary combustion chamber, or (C2) a side wall portion surrounding the primary combustion chamber; A waste incineration facility characterized by being installed in.

3. The waste incineration facility according to claim 1 or 2, a waste pit for storing waste before being fed into the incinerator; an extraction gas line for extracting gas from the waste pit as an extraction gas; Furthermore, a waste incineration facility characterized in that the oxygen mixing section generates the high-concentration oxygen gas from the extracted gas and mixes it with the recirculated exhaust gas flowing through the recirculated exhaust gas line.

4. The waste incineration facility according to claim 1 or 2, A waste incineration facility characterized in that the flow rate of gas supplied from the gas supply position in the incinerator into the incinerator is approximately constant.

5. The waste incineration facility according to claim 1 or 2, the quantity of interest includes the vapor quantity; A waste incineration facility characterized in that the control unit controls the mixing ratio change unit so that the measured value of the steam amount approaches a predetermined target value, thereby changing the oxygen concentration of the combustion gas supplied into the incinerator from the gas supply position below the grate unit.

6. The waste incineration facility according to claim 1 or 2, the quantity of interest includes a temperature within the incinerator; A waste incineration facility characterized in that the control unit controls the mixing ratio change unit so that the measured temperature inside the incinerator approaches a predetermined target value, thereby changing the oxygen concentration of the combustion gas supplied into the incinerator from the gas supply position of the ceiling, the side wall surrounding the primary combustion chamber, or the side wall surrounding the secondary combustion chamber.

7. The waste incineration facility according to claim 1 or 2, the quantity of interest includes an oxygen concentration at an outlet of the incinerator; A waste incineration facility characterized in that the control unit controls the mixing ratio change unit so that the measured value of the oxygen concentration at the outlet approaches a predetermined target value, thereby changing the oxygen concentration of the combustion gas supplied into the incinerator from the gas supply position on the side wall portion surrounding the secondary combustion chamber.

Images