Waste incineration method and waste incineration device

Abstract

To reduce a concentration of carbon monoxide contained in exhaust gas discharged from a waste incinerator.SOLUTION: In a waste incineration method, when incinerating waste in an incinerator having a combustion chamber in which waste is burned while being transported by a fire grate, recirculated exhaust gas supply means branches off at least a part of exhaust gas in the incinerator as recirculated exhaust gas, and oxygen supply means mixes oxygen-containing gas with the recirculated exhaust gas to generate mixed gas, and supplies it to the combustion chamber, where the fire grate is configured to have a drying fire grate, a combustion fire grate, and a post-combustion fire grate along a direction in which the waste is transported. The waste incineration method adjusts an oxygen concentration in the mixed gas supplied from below to the combustion fire grate to be larger than 25% and equal to or less than 35%, and adjusts the oxygen concentration in the gas supplied to the vicinity of the outlet through which the exhaust gas is discharged from the combustion chamber to be larger than 25% and equal to or less than 35%.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a waste incineration method and a waste incineration apparatus. [Background technology]

[0002] Conventionally, a combustion technology called O2 / CO2 combustion, oxygen combustion, or Oxy-fuel combustion has been proposed. Patent Document 1 discloses a waste treatment device and a waste treatment method that apply O2 / CO2 combustion. In the technology described in Patent Document 1, first, urban waste is incinerated with oxygen (O2) obtained by separating nitrogen (N2) from air. After recovering heat from the exhaust gas generated by the incineration of this urban waste, a part of the exhaust gas is supplied to the incineration process to control the incineration temperature. In addition to controlling the incineration temperature, water (H2O) and carbon dioxide (CO2) are recovered from the exhaust gas after heat recovery.

[0003] Specifically, the method for incinerating municipal waste described in Patent Document 1 is carried out as follows. That is, in order to control the temperature inside the incinerator to 800 to 1200°C, a part of the incineration flue gas (high concentration CO2) circulated in the system is circulated and supplied to the produced oxygen (O2) to mix it. The weight ratio of municipal waste to the circulated incineration flue gas is 1 to 12 times, preferably 4 to 8 times, the amount of incineration flue gas per unit of municipal waste. As a result, in the incinerator, waste such as municipal waste is incinerated mainly in an atmosphere of oxygen and incineration flue gas, that is, an atmosphere containing mainly carbon dioxide (CO2) and water vapor (H2O). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 5-126324 Summary of the Invention [Problem to be solved by the invention]

[0005] Patent Document 1 discloses that the temperature inside the incinerator is controlled by adjusting the weight ratio of the circulated incineration exhaust gas to 1 to 12 times the amount of waste. However, the technology described in Patent Document 1 does not disclose any specific incineration method other than the above, and there was a problem as to whether or not combustibility in the incinerator was guaranteed. Therefore, in order to ensure combustibility in the incinerator, there was a need to develop a specific technology that completely combusts the waste and reduces the carbon monoxide (CO) contained in the exhaust gas.

[0006] The present invention has been made in consideration of the above, and its object is to provide a waste incineration method and a waste incineration apparatus that can reduce the carbon monoxide contained in the exhaust gas discharged from a waste incinerator. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems and achieve the object, one embodiment of the waste incineration method of the present invention is a waste incineration method in which, when waste is incinerated in an incinerator having a combustion chamber in which the waste is transported by a grate and burned, at least a portion of the exhaust gas from the incinerator is branched off as recirculated exhaust gas by a recirculated exhaust gas supply means, and an oxygen supply means mixes an oxygen-containing gas with the recirculated exhaust gas to generate a mixed gas which is supplied to the combustion chamber, wherein the grate is configured to have a drying grate, a combustion grate, and a post-combustion grate along the transport direction of the waste, and the oxygen concentration of the mixed gas supplied from below to the combustion grate is adjusted to be greater than 25% and less than 35%, and the oxygen concentration of the gas supplied to the vicinity of an outlet from which the exhaust gas is discharged from the combustion chamber is greater than 25% and less than 35%.

[0008] In one embodiment of the waste incineration method of the present invention, in the above-mentioned invention, the gas supplied to the post-combustion grate is the recirculated exhaust gas, or the oxygen concentration of the gas supplied to the post-combustion grate is adjusted to less than 5%.

[0009] In one aspect of the waste incineration method of the present invention, in the above invention, the gas supplied to the drying grate is the recirculated exhaust gas, or the oxygen concentration of the gas supplied to the drying grate is adjusted to less than 5%.

[0010] In one embodiment of the waste incineration method of the present invention, in the above-mentioned invention, the oxygen concentration of the gas supplied into the combustion chamber from a front-stage nozzle provided above the drying grate and the combustion grate is set to 15% or more and 25% or less.

[0011] In one embodiment of the waste incineration method of the present invention, in the above invention, the gas supplied into the combustion chamber from a rear nozzle provided above the combustion grate and the rear combustion grate is used as the recirculated exhaust gas, or the oxygen concentration of the gas supplied into the combustion chamber from the rear nozzle is adjusted to less than 5%.

[0012] A waste incineration method according to one embodiment of the present invention, in the above invention, measures the carbon monoxide concentration using a carbon monoxide measuring means configured to be capable of measuring the carbon monoxide concentration and provided downstream in the waste transport direction within the combustion chamber, and adjusts the oxygen concentration in the mixed gas supplied into the combustion chamber based on the measured carbon monoxide concentration.

[0013] A waste incineration method according to one embodiment of the present invention, in the above invention, adjusts the oxygen concentration of the mixed gas supplied into the combustion chamber based on at least one measurement value of the furnace temperature, oxygen concentration, and carbon monoxide concentration measured by a first measuring means provided upstream in the combustion chamber along the waste transport direction and configured to be capable of measuring the furnace temperature, oxygen concentration, and carbon monoxide concentration, and a second measuring means provided near an outlet from which exhaust gas is discharged from the combustion chamber and configured to be capable of measuring the furnace temperature, oxygen concentration, and carbon monoxide concentration.

[0014] A waste incineration apparatus according to one embodiment of the present invention comprises an incinerator having a combustion chamber in which waste is burned while being transported by a grate, a recirculated exhaust gas supply means configured to be able to branch off at least a portion of the exhaust gas from the incinerator as recirculated exhaust gas and supply it to the incinerator, an oxygen supply means configured to be able to supply a gas containing oxygen as a main component to the incinerator, and a gas mixing means for mixing the recirculated exhaust gas supplied by the recirculated exhaust gas supply means with the gas containing oxygen as a main component supplied by the oxygen supply means to generate a mixed gas, wherein the grate has a drying grate, a combustion grate, and a post-combustion grate along the direction in which the waste is transported, and is configured so that the oxygen concentration in the mixed gas supplied from below the combustion grate can be adjusted to be greater than 25% and less than 35%, and the oxygen concentration of the gas supplied from the combustion chamber to the vicinity of an outlet from which exhaust gas is discharged can be adjusted to be greater than 25% and less than 35%.

[0015] A waste incineration apparatus according to one embodiment of the present invention is configured in the above-mentioned invention so that the gas supplied to the post-combustion grate is the recirculated exhaust gas, or the oxygen concentration of the gas supplied to the post-combustion grate can be adjusted to less than 5%.

[0016] A waste incineration apparatus according to one embodiment of the present invention is configured in the above-mentioned invention so that the gas supplied to the drying grate is the recirculated exhaust gas, or the oxygen concentration of the gas supplied to the drying grate can be adjusted to less than 5%.

[0017] A waste incineration apparatus according to one embodiment of the present invention is configured in the above-mentioned invention so that the oxygen concentration of the gas supplied into the combustion chamber from the drying grate and a pre-stage nozzle provided above the combustion grate can be adjusted to between 15% and 25%.

[0018] A waste incineration apparatus according to one embodiment of the present invention is configured in the above-mentioned invention so that the gas supplied into the combustion chamber from a rear nozzle provided above the combustion grate and the rear combustion grate is the recirculated exhaust gas, or the oxygen concentration of the gas supplied into the combustion chamber from the rear nozzle can be adjusted to less than 5%.

[0019] A waste incineration apparatus according to one aspect of the present invention, in the above invention, further comprises a carbon monoxide measuring means configured to be capable of measuring carbon monoxide concentration downstream in the waste transport direction within the combustion chamber, and is configured to be able to adjust the oxygen concentration in the mixed gas supplied into the combustion chamber based on the carbon monoxide concentration measured by the carbon monoxide measuring means.

[0020] A waste incineration apparatus according to one embodiment of the present invention, in the above invention, comprises a first measuring means provided upstream in the combustion chamber along the waste transport direction and configured to be capable of measuring the furnace temperature, oxygen concentration, and carbon monoxide concentration, and a second measuring means provided downstream in the combustion chamber along the waste transport direction and configured to be capable of measuring the furnace temperature, oxygen concentration, and carbon monoxide concentration, and is configured to be able to adjust the oxygen concentration in the mixed gas supplied into the combustion chamber based on at least one measurement value of the furnace temperature, oxygen concentration, and carbon monoxide concentration measured by the first measuring means and the second measuring means. Effect of the Invention

[0021] According to the waste incineration method and waste incineration apparatus of the present invention, it is possible to reduce the carbon monoxide contained in the exhaust gas discharged from the waste incinerator. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is a diagram showing the overall configuration of a waste incineration system according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a diagram showing conditions within a combustion chamber of a waste incinerator according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In all the drawings of the embodiment, the same or corresponding parts are denoted by the same reference numerals. Furthermore, the present invention is not limited to the embodiment described below.

[0024] In describing the embodiment of the present invention, the inventor conducted intensive research. First, the inventor conducted research on problems related to the conventional technology. According to the inventor's findings, in order to completely combust waste, it is necessary to thoroughly mix and stir the combustible gas from the waste and the oxygen (O2) in the oxidizer. By completely combusting the waste, the carbon monoxide concentration (CO concentration) in the exhaust gas can be reduced. In other words, it is considered that complete combustion of the waste can be ensured by controlling to reduce the CO concentration in the exhaust gas. Therefore, the inventor conducted research on a method for reducing the CO concentration in the exhaust gas in a stoker-type waste incinerator that applies the technology of O2 / CO2 combustion, oxygen combustion, or Oxy-fuel combustion. As a result of the inventor's intensive research, it was found that the CO concentration in the exhaust gas can be reduced by using a mixed gas of oxygen (O2) and recirculated exhaust gas circulated in the system as an oxidizer and changing the oxygen concentration of the oxidizer depending on the location where it is blown in.

[0025] The inventor also devised a method for changing the oxygen concentration as desired by controlling the mixing amount and mixing ratio of the recirculated exhaust gas to the oxygen using the recirculated exhaust gas as a diluent. Based on this, the inventor conducted various experiments and studies on a method for reducing the CO concentration in the exhaust gas by changing the oxygen concentration in the oxidizing agent supplied to the waste in a stoker-type waste incinerator. As a result of intensive studies, the inventor devised the following method as a specific method for changing the oxygen concentration in the oxidizing agent.

[0026] That is, in a stoker-type waste incinerator, a plurality of grates are provided in the combustion chamber according to the type of waste to be burned, specifically, a drying grate, a combustion grate, and a post-combustion grate are provided from the upstream side along the waste transport direction. Furthermore, the present inventor has considered a method of independently controlling the gas supplied to the drying grate, the combustion grate, and the post-combustion grate. That is, the present inventor has considered a method of controlling the oxygen concentration of the gas supplied to the drying grate, the combustion grate, and the post-combustion grate, and in particular, of setting the oxygen concentration of the gas supplied to the combustion grate to a different oxygen concentration from that of the other grates, thereby reducing the CO concentration in the exhaust gas.

[0027] As a result, the inventors have found that in order to completely combust the waste on the grate, it is preferable to use an oxygen-rich gas (O2-rich gas) with an oxygen concentration of more than 25% and not more than 35% as the oxidizing agent to be supplied from below to the combustion grate, which is the central primary combustion region along the transport direction. This allows the combustible gas generated from the waste and the oxygen (O2) contained in the oxidizing agent to be sufficiently mixed and stirred, so that the waste can be efficiently and completely combusted and the CO concentration in the exhaust gas can be reduced. Furthermore, the inventors have also found that in order to further reduce the CO concentration in the exhaust gas, it is preferable to focus on supplying an O2-rich gas with an oxygen concentration of more than 25% and not more than 35% to the downstream side along the transport direction of the waste in the combustion chamber, specifically, near the upper part of the post-combustion grate, for example, near the outlet of the combustion chamber, which is the secondary combustion region.

[0028] The drying grate constituting the drying stage does not require a large amount of oxygen (O2) for combustion because it is an area where the moisture in the waste is mainly evaporated and dried. Therefore, the present inventor considered supplying only recirculated exhaust gas (hereinafter, recirculated exhaust gas) or low-O2 gas with an O2 concentration adjusted to less than 5% to the drying grate. According to the inventor's findings, the drying grate includes an area where the waste is mainly ignited and initially burned, so it is also possible to supply the above-mentioned high-O2 gas as necessary. Similarly, since the post-combustion grate constituting the post-combustion stage is an area after the waste is burned off, it is preferable that the gas supplied from below for ash carbonation of the incineration ash is only recirculated exhaust gas or low-oxygen gas with an oxygen concentration of less than 5%.

[0029] Furthermore, the present inventor has devised a method of providing sensors at at least two locations in the waste incinerator and adjusting the above-mentioned oxygen concentration based on the measurement values ​​by the sensors. More specifically, in the waste incinerator, sensors are provided at least at two locations, upstream (in front of the furnace) and downstream (in rear of the furnace) along the waste transport direction. These sensors measure the furnace temperature, oxygen concentration, and carbon monoxide concentration. In this case, the relationship between the measured value of the carbon monoxide concentration and the oxygen concentration of the gas supplied to the drying grate is tabulated or constructed as a learning model by machine learning or the like, so that the oxygen concentration of the oxidizer can be controlled so that the carbon monoxide concentration is reduced. As a result, the oxygen concentration in the oxidizer supplied to the grate or near the outlet of the combustion chamber is controlled according to the furnace temperature, oxygen concentration, and carbon monoxide concentration measured by the sensors, thereby ensuring high (robust) complete combustion in the waste incinerator.

[0030] Furthermore, the present inventor also studied the oxidizer to be supplied above the grate of the waste incinerator, i.e., into the combustion chamber. The present inventor came up with the idea of ​​making the oxygen concentration of the oxidizer different depending on the position where the oxidizer is supplied into the combustion chamber. That is, when the waste incinerator is, for example, a counterflow furnace, the oxygen concentration of the oxidizer is made different depending on the installation position of a plurality of nozzles (ceiling nozzles) provided on the ceiling. Specifically, the oxygen concentration of the oxidizer supplied into the combustion chamber from the front ceiling nozzle, which is upstream along the waste transport direction, is set to an O2-containing gas with an oxygen concentration of 15% to 25%. If the oxygen concentration of the O2-containing gas is set to less than 15%, the possibility of insufficient combustion and an increase in carbon monoxide concentration increases. On the other hand, the gas supplied into the combustion chamber from the rear ceiling nozzle, which is downstream, is set to an O2-low concentration gas with an oxygen concentration of less than 5%, or only recirculated exhaust gas.

[0031] In addition, if the waste incinerator is a double-flow incinerator, the oxidant supplied from the high-temperature air draft fan (HADF) to the combustion chamber shall be O2-containing gas with an oxygen concentration of 15% or more and 25% or less, and the gas supplied from the recirculated draft fan (RDF) to the combustion chamber shall be low-O2 concentration gas with an oxygen concentration of less than 5%, or only recirculated exhaust gas.

[0032] Based on the above studies, the present inventor has devised an incineration method capable of reducing CO in exhaust gas by adjusting the oxygen concentration according to the supply position of the oxidizing agent. One embodiment of the present invention described below was devised by the present inventor through the above diligent studies.

[0033] (Waste incineration system) 1 and 2 are diagrams showing the overall configuration of a waste incineration system according to an embodiment of the present invention and the state inside the combustion chamber of the waste incinerator, respectively. As shown in FIG. 1, the waste incineration system according to this embodiment includes a waste incinerator 1 to which O2 / CO2 combustion technology is applied. The waste incinerator 1 is, for example, a grate-type waste incinerator, and includes a combustion chamber 2 and a waste inlet 3. The combustion chamber 2 burns waste, such as industrial waste and household garbage. The waste inlet 3 is disposed above the upstream side (left side in FIG. 1) along the flow direction of the waste W in the combustion chamber 2, and is configured so that the waste W can be input into the combustion chamber 2. A boiler 4 is connected above the downstream side (right side in FIG. 1) along the flow direction of the waste W of the combustion chamber 2.

[0034] As shown in FIG. 1 and FIG. 2, a grate (stoker) 5 is provided at the bottom of the combustion chamber 2 to burn the waste W while moving it. The grates 5 are provided in the order of drying grate 5a, combustion grate 5b, and post-combustion grate 5c from the side closer to the waste inlet 3, i.e., from the upstream side. In the drying grate 5a, mainly drying, ignition, and initial combustion of the waste W are performed. In the combustion grate 5b, mainly pyrolysis and partial oxidation of the waste W are performed. On the combustion grate 5b, carbon monoxide (CO) generated by pyrolysis, pyrolysis gas containing hydrocarbons, and solids (fixed carbon) are burned as the main combustion. On the post-combustion grate 5c, the remaining unburned waste is completely burned as post-combustion. After complete combustion, the combustion ash (incineration ash) falls and is discharged from the incineration ash discharge section 6.

[0035] A wind box 7 is provided below the combustion chamber 2. Specifically, wind boxes 7a, 7b, and 7c are provided below the drying grate 5a, the combustion grate 5b, and the post-combustion grate 5c in the combustion chamber 2, respectively. The wind boxes 7 (7a, 7b, and 7c) can function as part of a gas mixing means for mixing gases supplied from multiple systems, and in this embodiment, can function as a gas mixing means for mixing the recirculated exhaust gas with a gas mainly composed of O2.

[0036] The area downstream of the combustion chamber 2 and near the inlet of the boiler 4 connected to the outlet of the combustion chamber 2 constitutes a secondary combustion chamber 11 that burns unburned gas in the gas discharged from the combustion chamber 2. The secondary combustion chamber 11 is connected to the upper part of the downstream side (right side in FIG. 1) of the combustion chamber 2 in the direction of waste flow. Secondary combustion gas is blown into the secondary combustion chamber 11 through a pipe line equipped with a blower and a damper (neither shown). In the secondary combustion chamber 11, unburned gas (unburned gas) in the combustion gas generated in the combustion chamber 2 is burned (secondary combustion), and the exhaust gas after secondary combustion has its heat recovered by the boiler 4.

[0037] The boiler 4, which recovers heat from exhaust gas, is divided into three sections by two deflection sections 12, 13 that bend the flow path of the exhaust gas. The boiler 4 includes a first radiation chamber 14, a second radiation chamber 15, and a convection heat transfer chamber 16, from the upstream side along the flow direction of the exhaust gas. The upstream part along the flow direction of the exhaust gas of the first radiation chamber 14, to which exhaust gas is supplied from the waste incinerator 1, becomes the secondary combustion chamber 11. The first radiation chamber 14 and the second radiation chamber 15 are connected to each other at their upper parts, and the lower part of the second radiation chamber 15 is connected to the lower part of the convection heat transfer chamber 16. The exhaust section 4A of the boiler 4 is connected to a dust collector 18 composed of a bag filter or the like via a flue 17.

[0038] The boiler 4 has an inner wall made of a refractory wall, and the first radiant chamber 14 and the second radiant chamber 15 are provided with heat transfer tubes (not shown) formed of piping for circulating steam, arranged in a dense manner on the outside of the refractory wall forming the inner wall. The convection heat transfer chamber 16 is provided with a heat transfer tube (not shown) in the internal space through which the exhaust gas flows. The boiler 4 is formed by the first radiant chamber 14 and the second radiant chamber 15 as an evaporator. A plurality of, for example, three superheaters 16A are formed by a part of the convection heat transfer chamber 16. In the first radiant chamber 14 and the second radiant chamber 15, the heat transfer tubes arranged on the outside of the refractory wall and through which water flows are configured as a radiant heat transfer surface that receives radiant heat from the exhaust gas and generates steam.

[0039] The convection heat transfer chamber 16 includes, from the upstream side (lower side) along the flow direction of the exhaust gas, a superheater 16A and an economizer 16B. The superheater 16A includes a group of heat transfer tubes in which a plurality of heat transfer tubes arranged horizontally are arranged in multiple stages in the height direction, and the group of heat transfer tubes constitutes a convection heat transfer surface. The superheater 16A further superheats the steam generated in the evaporator through heat exchange with the exhaust gas, turning it into high-temperature, high-pressure superheated steam.

[0040] The economizer 16B is provided downstream (above) of the superheater 16A. The economizer 16B is provided with heat transfer tubes, receives condensate obtained by condensing the steam generated in the boiler 4 and used to drive a steam turbine (not shown) in a condenser (not shown), and heats the water by the heat remaining in the exhaust gas after the steam is superheated by the superheater 16A. As a result, the water is heated by heat exchange with the exhaust gas, and heated water is generated and supplied to the evaporator. Note that the economizer 16B may not be provided in the convection heat transfer chamber 16, but may be provided outside the boiler 4 downstream as a separate economizer, or both an in-boiler economizer and a separate economizer may be provided. A screen tube (not shown) is provided at the most upstream portion (lower portion) of the convection heat transfer chamber 16 with heat transfer tubes arranged in a flag shape, and is configured to cool the exhaust gas introduced into the convection heat transfer chamber 16 and solidify the gaseous or mist-like dust components to be separated as dust from the exhaust gas. An evaporator may be provided upstream or downstream of the superheater 16A in the convection heat transfer chamber 16.

[0041] The exhaust gas from the waste incinerator 1 after secondary combustion in the secondary combustion chamber 11 is introduced into the boiler 4, and steam is generated by the evaporators in the first radiation chamber 14 and the second radiation chamber 15. The generated steam is then made into superheated steam by the superheater 16A in the convection heat transfer chamber 16.

[0042] The exhaust gas from which heat has been recovered by the boiler 4 is supplied to a dust collector 18, such as a bag filter, through a flue 17. In the flue 17, caustic soda, hydrated lime, activated carbon, and the like are added to the exhaust gas. The dust collector 18 collects and removes dust contained in the exhaust gas. An induced draft fan 19 is connected to the dust collector 18. The induced draft fan 19 induces exhaust gas from the waste incinerator 1 and supplies at least a portion of the induced exhaust gas to the wind box 7 for circulation to the waste incinerator 1. The non-circulated exhaust gas from the dust-removed exhaust gas is supplied to a chimney 20 and released into the atmosphere.

[0043] A recirculated exhaust gas supply line 30 is provided from the exhaust gas duct (flue) on the outlet side of the dust collector 18, as a recirculated exhaust gas supply means, which sends a portion of the exhaust gas after dust removal by the dust collector 18 as recirculated exhaust gas to the wind box 7 below the grate 5.

[0044] A cooling tower 31 as a water separation means and a PSA unit 32 as a carbon dioxide capture means are sequentially provided on the recirculated exhaust gas supply line 30. The cooling tower 31 separates water (H2O) from the recirculated exhaust gas and discharges it. The PSA unit 32 separates a portion of carbon dioxide (CO2) from the recirculated exhaust gas from which water has been removed, for example, by pressure swing adsorption (PSA), and then exhausts or captures the separated CO2. Note that a nitrogen PSA unit may be separately provided that separates and discharges nitrogen (N2) from the recirculated exhaust gas from which water has been removed, thereby increasing the CO2 concentration in the recirculated exhaust gas.

[0045] The recirculated exhaust gas supply line 30 has branch lines 30a, 30b, and 30c that are branched to be able to supply the recirculated exhaust gas to each of the wind boxes 7a to 7c. The recirculated exhaust gas supply line 30 also has branch lines 30d and 30e for supplying the recirculated exhaust gas to the combustion chamber 2. The branch line 30d is connected to a rear nozzle 39 provided in the combustion chamber 2. The branch line 30e is connected to a branch line 35e of an oxygen supply line 35 that is connected to a blower 36 (described later) and to an injection nozzle 40 provided in the vicinity of the secondary combustion chamber 11.

[0046] The recirculated exhaust gas supply line 30 is provided with a recirculated exhaust gas flow rate adjustment unit 34 as a recirculated exhaust gas flow rate adjustment means for adjusting the flow rate, which is made of a damper, a valve, or the like. The recirculated exhaust gas flow rate adjustment unit 34 is composed of a plurality of recirculated exhaust gas flow rate adjustment units 34a, 34b, 34c, 34d, and 34e corresponding to the branch lines 30a to 30e, respectively.

[0047] The recirculated exhaust gas flow rate adjusting units 34a-34c are provided corresponding to the branch lines 30a-30c of the recirculated exhaust gas supply line 30 and the wind boxes 7a-7c communicating with the branch lines 30a-30c, respectively. The recirculated exhaust gas flow rate adjusting unit 34d is provided corresponding to the branch line 30d of the recirculated exhaust gas supply line 30 and the rear nozzle 39 in the combustion chamber 2 communicating with the branch line 30d. The recirculated exhaust gas flow rate adjusting unit 34e is provided corresponding to the branch line 30e of the recirculated exhaust gas supply line 30.

[0048] In addition, an oxygen supply line 35 capable of supplying gas containing oxygen (O2) as a main component (hereinafter, O2-main component gas), i.e., gas with an O2 concentration of 50% or more, specifically, oxygen gas with an O2 concentration of nearly 100% separated from air by a technique such as cryogenic separation or PSA method, is connected to the branch lines 30a, 30b, 30c, and 30e of the recirculation exhaust gas supply line 30. A blower 36 is connected to the oxygen supply line 35.

[0049] The oxygen supply line 35 has branch lines 35a, 35b, and 35c that are branched to be able to supply O2 gas to each of the wind boxes 7a to 7c. The branch lines 35a to 35c are connected to the branch lines 30a to 30c, respectively. The oxygen supply line 35 constituting the oxygen supply means is configured to be able to supply oxygen (O2) to each of the branch lines 30a to 30c. As a result, the recirculated exhaust gas and O2 gas are mixed by the branch lines 30a to 30c and the branch lines 35a to 35c. In this case, the recirculated exhaust gas supply line 30 and the oxygen supply line 35 constitute the gas mixing means. Note that the branch lines 35a to 35c of the oxygen supply line 35 may be directly connected to the wind boxes 7a to 7c, respectively, to mix the recirculated exhaust gas and O2 gas in the wind boxes 7a to 7c. In this case, the gas mixing means is constituted by the wind box 7, the recirculated exhaust gas supply line 30, and the oxygen supply line 35. Further, the oxygen supply line 35 has a branch line 35e corresponding to the blowing nozzle 40, which merges the O2 main component gas with the branch line 30e.

[0050] The wind box 7a and the drying grate 5a corresponding to the wind box 7a are supplied with recirculated exhaust gas that is mainly composed of recirculated exhaust gas and has a relatively low O2 concentration, for example, with the O2 concentration adjusted to less than 5%. That is, the wind box 7a is configured to be able to supply recirculated exhaust gas or low-O2 concentration gas to the drying grate 5a from below with the O2 concentration appropriately adjusted.

[0051] The wind box 7b and the combustion grate 5b corresponding to the wind box 7b are supplied with an O2-rich gas, for example, an O2 concentration adjusted to be higher than 25% and not higher than 35%, as an oxidizer adjusted to have a relatively high O2 concentration. That is, the wind box 7b is configured to be able to supply the O2-rich gas, which has a relatively high O2 concentration, to the combustion grate 5b from below.

[0052] The wind box 7c and the post-combustion grate 5c corresponding to the wind box 7c are supplied with recirculated exhaust gas that is mainly composed of recirculated exhaust gas and has a relatively low O2 concentration, for example, an O2 concentration adjusted to less than 5%. That is, the wind box 7c is configured to be able to supply low-O2 concentration gas or recirculated exhaust gas, which has a relatively low O2 concentration, from below to the post-combustion grate 5c.

[0053] Further, the oxygen supply line 35 is provided with an oxygen flow rate adjustment unit 37 as an oxygen flow rate adjustment means configured with a damper or a valve for adjusting the flow rate. The oxygen flow rate adjustment unit 37 is composed of oxygen flow rate adjustment units 37a, 37b, and 37c. The oxygen flow rate adjustment units 37a to 37c are provided on the branch lines 35a to 35c of the oxygen supply line 35, respectively. The oxygen flow rate adjustment unit 37e is provided on the branch line 35e of the oxygen supply line 35.

[0054] A front-stage nozzle 38 and a rear-stage nozzle 39 are provided in the combustion chamber 2. The front-stage nozzle 38 and the rear-stage nozzle 39 each function as a counterflow nozzle.

[0055] The front nozzle 38 is provided above the gap between the drying grate 5a and the combustion grate 5b, for example, on the ceiling of the combustion chamber 2. The front nozzle 38 is supplied with, for example, an O2-containing gas with an O2 concentration adjusted to 15% or more and 25% or less as an oxidizing agent adjusted to have a relatively high O2 concentration. That is, the front nozzle 38 is configured to be able to supply an O2-containing gas with a relatively high O2 concentration to the region between the drying grate 5a and the combustion grate 5b in the combustion chamber 2.

[0056] The rear nozzle 39 is provided above the area between the combustion grate 5b and the rear combustion grate 5c, for example, on the ceiling of the combustion chamber 2. The rear nozzle 39 is supplied with recirculated exhaust gas that is mainly composed of recirculated exhaust gas and has a relatively low O2 concentration, for example, with an O2 concentration adjusted to less than 5%. Note that the rear nozzle 39 may be supplied with low-O2 concentration gas in which an O2-containing gas or an O2-main component gas is mixed with the recirculated exhaust gas to adjust the O2 concentration. That is, the rear nozzle 39 is configured to be able to supply recirculated exhaust gas or low-O2 concentration gas with a relatively low O2 concentration to the area between the combustion grate 5b and the rear combustion grate 5c in the combustion chamber 2, for example, near the periphery of the burnout point of the waste.

[0057] An injection nozzle 40 is provided in the secondary combustion chamber 11 at the outlet of the combustion chamber 2. The injection nozzle 40 is connected to the branch line 30e of the recirculated exhaust gas supply line 30 and the branch line 35e of the oxygen supply line 35. The injection nozzle 40 is supplied with, for example, an O2-rich gas having an O2 concentration adjusted to be higher than 25% and not higher than 35%, as an oxidizer adjusted to have a relatively high O2 concentration. That is, the injection nozzle 40 is configured to be able to supply the O2-rich gas having a relatively high O2 concentration to a region near the outlet of the combustion chamber 2 and at the inlet of the secondary combustion chamber 11.

[0058] A sensor group 51 serving as a first measuring means is provided upstream along the transport direction of the waste W in the combustion chamber 2. The sensor group 51 is configured to be able to measure at least the temperature, O2 concentration, and carbon monoxide concentration (CO concentration) at the installed position. The sensor group 51 transmits the measured sensor values ​​such as the temperature, O2 concentration, and CO concentration to the control unit 50.

[0059] Further, a sensor group 52 as a carbon monoxide measuring means or a second measuring means is provided on the downstream side along the transport direction of the waste W in the combustion chamber 2. The sensor group 52 measures at least the temperature, O2 concentration, CO concentration, and nitrogen oxide concentration (NO x The sensor group 52 is configured to be able to measure the temperature, O2 concentration, CO concentration, and NO xThe sensor values ​​such as concentration are transmitted to the control unit 50.

[0060] Specifically, the control unit 50 includes a processor such as a CPU (Central Processing Unit), a DSP (Digital Signal Processor), and an FPGA (Field-Programmable Gate Array), and a main storage unit such as a RAM (Random Access Memory) and a ROM (Read Only Memory) (none of which are shown). The control unit 50 may also be configured as an information processing device such as a computer equipped with a storage unit. In this case, the storage unit of the control unit 50 includes a storage medium selected from a volatile memory such as a RAM, a non-volatile memory such as a ROM, an EPROM (Erasable Programmable ROM), a hard disk drive (HDD, Hard Disk Drive), and a removable medium. The removable medium is, for example, a Universal Serial Bus (USB) memory, or a disk storage medium such as a Compact Disc (CD), a Digital Versatile Disc (DVD), or a Blu-ray (registered trademark) Disc (BD). The storage unit may also be configured using a computer-readable storage medium such as an externally mountable memory card.

[0061] (Waste incineration method) Incineration by the waste incineration system configured as above will be described. As shown in Fig. 2, in the waste incinerator 1 according to this embodiment, a layer of waste W is formed on the drying grate 5a, the combustion grate 5b, and the post-combustion grate 5c. Specifically, the waste W in the upstream range (front portion) along the waste transport direction of the drying grate 5a, which is located directly above the drying grate 5a and corresponds to the lower portion of the waste inlet 3, is dried and ignited to start combustion.

[0062] As shown in FIG. 2, in the downstream range (rear) of the drying grate 5a, initial combustion is carried out in which a part of the waste W starts to burn after drying and the waste W starts to be pyrolyzed and partially oxidized. The region in which initial combustion is carried out after the waste W is dried is called the combustion start region. The waste W on the drying grate 5a is dried and ignited in the upstream range on the drying grate 5a, and combustion starts in the downstream range and initial combustion is carried out. Here, when the waste W is incinerated, moisture evaporates on the drying grate 5a, and then pyrolysis and partial oxidation reactions occur, starting to generate pyrolysis gas.

[0063] Next, after the waste W starts to burn downstream of the drying grate 5a, pyrolysis gas begins to be generated by pyrolysis and partial oxidation of the waste W, and a part of the waste W is burned. Here, the waste W on the combustion grate 5b undergoes pyrolysis and partial oxidation, and pyrolysis gas, which is a combustible gas, is generated. On the combustion grate 5b, the generated pyrolysis gas and the solid content of the waste W are burned. On the combustion grate 5b, the pyrolysis and partial oxidation of the waste W are actively performed, and the generated pyrolysis gas burns with a flame, and the solid content of the waste W is burned in the combustion region, and the region up to the point where the combustion with the flame is completed (the burn-out point) is defined as the main combustion region. On the combustion grate 5b, the waste W is substantially almost burned.

[0064] In addition, an O2-containing gas is supplied into the combustion chamber 2 from a front nozzle 38 above the drying grate 5a and the combustion grate 5b. In this case, a gas combustion region S1 is formed below the front nozzle 38 in the combustion chamber 2 by a mixed gas of the O2-containing gas supplied from the front nozzle 38 and the pyrolysis gas generated by the combustion of the waste W. The pyrolysis gas that is not combusted in the gas combustion region S1 and becomes unburned gas is transported downstream in the combustion chamber 2.

[0065] After the waste W is burned, unburned matter such as fixed carbon in the remaining waste W is completely burned on the post-combustion grate 5c. From the post-stage nozzle 39 above the combustion grate 5b and the post-combustion grate 5c, the O2-low concentration gas or recirculated exhaust gas is supplied toward the burnout point S3 on the combustion grate 5b or the post-combustion grate 5c. In this case, downstream of the post-stage nozzle 39, secondary combustion is performed in the secondary combustion zone S2 by the O2-low concentration gas or recirculated exhaust gas supplied from the post-stage nozzle 39 and the pyrolysis gas of the unburned matter transported from the gas combustion zone S1.

[0066] The area downstream of the burnout point S3 on the post-combustion grate 5c becomes a post-combustion area where the solid unburned matter (char) in the waste W is burned. From the post-combustion area, an O2-rich gas having an O2 concentration of more than 25% and not more than 35% is supplied from the blowing nozzle 40 to the vicinity of the outlet of the combustion chamber 2 and the vicinity of the inlet of the secondary combustion chamber 11. As described above, a waste layer is formed mainly on the drying grate 5a and the combustion grate 5b, and an incineration ash layer is formed downstream of the post-combustion grate 5c.

[0067] As shown in FIG. 1, in the waste incineration system, the mixture ratio of the recirculated exhaust gas supplied through the recirculated exhaust gas supply line 30 and the O2-based gas supplied through the oxygen supply line 35 can be adjusted by adjusting the flow rate by the recirculated exhaust gas flow rate adjusting unit 34 and the flow rate by the oxygen flow rate adjusting unit 37. That is, the control unit 50 can control the flow rate of the recirculated exhaust gas by controlling the recirculated exhaust gas flow rate adjusting units 34a to 34e, and can control the flow rate of the O2-based gas by controlling the oxygen flow rate adjusting units 37a to 37e. In addition, the control unit 50 can control the O2 concentration of the O2-containing gas supplied to the front nozzle 38. With the above configuration, the control unit 50 can individually and independently control the O2 concentration of the gas supplied to the wind box 7 (7a to 7c), the grate 5 (5a to 5c), the front nozzle 38, and the rear nozzle 39.

[0068] For example, as shown in Fig. 2, the O2-based gas and the recirculated exhaust gas with high CO2 concentration are mixed in the branch lines 30a-30c, 35a-35c below the grate 5. This allows the control of the O2 concentration by the control unit 50 to selectively supply only the recirculated exhaust gas or a low O2 concentration gas with an O2 concentration of less than 5% to the drying grate 5a and the post-combustion grate 5c, and selectively supply a high O2 concentration gas with an O2 concentration of more than 25% and not more than 35% to the combustion grate 5b. The O2-based gas and the recirculated exhaust gas may be mixed in the wind boxes 7a-7c to adjust and control the O2 concentration.

[0069] In addition, the control unit 50 controls the recirculation exhaust gas flow rate adjustment unit 34 and the oxygen flow rate adjustment unit 37 based on the sensor values ​​supplied from the sensor groups 51 and 52. First, the control unit 50 acquires various measurement values ​​(sensor values) from the sensor groups 51 and 52 in the waste incinerator 1 at all times or as needed.

[0070] Specifically, the control unit 50 acquires a measured value of the CO concentration from the sensor group 52. When the acquired CO concentration exceeds a first predetermined value, the control unit 50 performs control to increase the O2 concentration of the gas supplied to the drying grate 5a, the combustion grate 5b, and the post-combustion grate 5c. Conversely, when the acquired CO concentration is less than a second predetermined value, the control unit 50 performs control to decrease the O2 concentration of the gas supplied to the drying grate 5a, the combustion grate 5b, and the post-combustion grate 5c. Furthermore, the control unit 50 can control the individual O2 concentrations of the gases supplied to the front nozzle 38, the rear nozzle 39, and the blowing nozzle 40 so as to suppress the generation of carbon monoxide (CO) and decrease the CO concentration in the exhaust gas. That is, the control unit 50 adjusts the O2 concentration of the mixed gas supplied into the combustion chamber 2 based on the CO concentration measured by the sensor group 52.

[0071] According to the embodiment described above, O2-rich gas having an O2 concentration of more than 25% and not more than 35% is supplied into the combustion chamber 2 from below the combustion grate 5b and from the injection nozzle 40, whereby the waste W can be completely combusted in the combustion chamber 2 and the CO concentration in the exhaust gas discharged from the combustion chamber 2 can be reduced.

[0072] In addition, within the waste incinerator 1, the drying grate 5a, the combustion grate 5b, the post-combustion grate 5c, the front-stage nozzle 38 which supplies high O2 concentration gas to the upper area between the drying grate 5a and the combustion grate 5b, the rear-stage nozzle 39 which supplies low O2 concentration gas or recirculated exhaust gas to the burn-out point S3 of the waste W, and the blowing nozzle 40 which supplies high O2 concentration gas near the exit of the combustion chamber 2, are each individually adjusted in O2 concentration while gas is supplied to the waste incinerator 1. This makes it possible to individually control the O2 concentration for each supply location according to the increase or decrease in CO concentration, thereby reducing the CO concentration in the exhaust gas discharged from the waste incinerator 1.

[0073] Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above-mentioned embodiments, and various modifications based on the technical ideas of the present invention are possible. For example, the numerical values ​​given in the above-mentioned embodiments are merely examples, and numerical values ​​different from these may be used as necessary. The present invention also includes configurations in which the components of the above-mentioned embodiments and each modification are appropriately combined. Further effects and modifications can be easily derived by those skilled in the art. The broader aspects of the present invention are not limited to the specific details and representative embodiments shown and described above. Thus, various modifications are possible without departing from the spirit or scope of the general inventive concept as defined by the appended claims and equivalents thereof.

[0074] For example, in the above-mentioned embodiment, an incinerator using a counterflow furnace has been described as an example of the waste incinerator 1, but an incinerator using a double-flow furnace may also be used. In this case, in the above-mentioned embodiment, the front nozzle 38 can be replaced with a high-temperature air blower (HADF), and the rear nozzle 39 can be replaced with a recirculation blower (RDF). [Explanation of symbols]

[0075] 1 Waste incinerator 2. Combustion chamber 3 Waste input port 4. Boiler 4A Exhaust section 5. Grate 5a drying grate 5b Combustion grate 5c Post-combustion grate 6. Ash discharge section 7,7a,7b,7c Wind box 11 Secondary combustion chamber 12,13 Turning section 14 1st radiation room 15 Second radiation room 16 Convection Heat Transfer Chamber 16A superheater 16B Economizer 17 Flue 18 Dust collector 19 Induced draft fan 20 Chimney 30 Recirculated exhaust gas supply line 30a, 30b, 30c, 30d, 30e, 35a, 35b, 35c, 35e Branch lines 31 Cooling Tower 32 PSA Department 34,34a,34b,34c,34d,34e Recirculation exhaust gas flow rate adjustment section 35 Oxygen supply line 36 Blower 37,37a,37b,37c,37d,37e Oxygen flow rate adjustment section 38 Front stage nozzle 39 Rear nozzle 40 Blowing nozzle 50 Control section 51,52 Sensor group

Claims

1. A method for incinerating waste in an incinerator having a combustion chamber in which waste is transported by a fire grate and combusted, comprising the steps of: branching at least a portion of the exhaust gas from the incinerator as recirculated exhaust gas by a recirculated exhaust gas supply means; and mixing an oxygen-containing gas with the recirculated exhaust gas by an oxygen supply means to generate a mixed gas, and supplying the mixed gas to the combustion chamber, comprising: The grate is configured to have a drying grate, a combustion grate, and a post-combustion grate along the waste transport direction; The oxygen concentration in the mixed gas supplied from below the combustion grate is adjusted to be higher than 25% and not higher than 35%; The oxygen concentration of the gas supplied to the vicinity of the outlet where the exhaust gas is discharged from the combustion chamber is set to be higher than 25% and not higher than 35%. Waste incineration methods.

2. The gas supplied to the post-combustion grate is the recirculated exhaust gas, or the oxygen concentration of the gas supplied to the post-combustion grate is adjusted to less than 5%.

2. The waste incineration method according to claim 1.

3. The gas supplied to the drying grate is the recirculated exhaust gas, or the oxygen concentration of the gas supplied to the drying grate is adjusted to less than 5%.

2. The waste incineration method according to claim 1.

4. The oxygen concentration of the gas supplied into the combustion chamber from a front stage nozzle provided above the drying grate and the combustion grate is set to 15% or more and 25% or less.

2. The waste incineration method according to claim 1.

5. The gas supplied into the combustion chamber from a rear-stage nozzle provided above the combustion grate and the rear-stage combustion grate is used as the recirculated exhaust gas, or the oxygen concentration of the gas supplied into the combustion chamber from the rear-stage nozzle is adjusted to less than 5%.

2. The waste incineration method according to claim 1.

6. measuring a carbon monoxide concentration by a carbon monoxide measuring means configured to be capable of measuring a carbon monoxide concentration and provided downstream in the direction of transport of the waste in the combustion chamber; The oxygen concentration of the mixed gas to be supplied into the combustion chamber is adjusted based on the measured carbon monoxide concentration.

2. The waste incineration method according to claim 1.

7. The oxygen concentration of the mixed gas supplied into the combustion chamber is adjusted based on at least one of the measured values ​​of the furnace temperature, the oxygen concentration, and the carbon monoxide concentration measured by a first measuring means provided upstream in the combustion chamber along the direction in which the waste is transported and configured to be capable of measuring the furnace temperature, the oxygen concentration, and the carbon monoxide concentration, and a second measuring means provided near an outlet through which exhaust gas is discharged from the combustion chamber and configured to be capable of measuring the furnace temperature, the oxygen concentration, and the carbon monoxide concentration.

2. The waste incineration method according to claim 1.

8. An incinerator having a combustion chamber in which waste is transported by a fire grate and burned; A recirculated exhaust gas supply means configured to branch off at least a portion of the exhaust gas from the incinerator as a recirculated exhaust gas and supply it to the incinerator; An oxygen supply means configured to be able to supply a gas containing oxygen as a main component to the incinerator; A waste incineration apparatus comprising: a gas mixing means for mixing the recirculated exhaust gas supplied by the recirculated exhaust gas supply means with a gas containing oxygen as a main component supplied by the oxygen supply means to generate a mixed gas, The grate has a drying grate, a combustion grate, and a post-combustion grate along the waste transport direction; The oxygen concentration in the mixed gas supplied from below the combustion grate can be adjusted to be greater than 25% and less than 35%, and the oxygen concentration in the gas supplied to the vicinity of the outlet from which the exhaust gas is discharged from the combustion chamber can be adjusted to be greater than 25% and less than 35%. Waste incineration equipment.

9. The gas supplied to the post-combustion grate is the recirculated exhaust gas, or the oxygen concentration of the gas supplied to the post-combustion grate can be adjusted to less than 5%.

9. A waste incineration apparatus according to claim 8.

10. The gas supplied to the drying grate is the recirculated exhaust gas, or the oxygen concentration of the gas supplied to the drying grate can be adjusted to less than 5%.

9. A waste incineration apparatus according to claim 8.

11. The oxygen concentration of the gas supplied into the combustion chamber from a front-stage nozzle provided above the drying grate and the combustion grate can be adjusted to 15% or more and 25% or less.

9. A waste incineration apparatus according to claim 8.

12. The gas supplied from a rear-stage nozzle provided above the combustion grate and the rear-stage combustion grate into the combustion chamber is the recirculated exhaust gas, or the oxygen concentration of the gas supplied from the rear-stage nozzle into the combustion chamber can be adjusted to less than 5%.

9. A waste incineration apparatus according to claim 8.

13. The method further includes providing a carbon monoxide measuring means configured to be capable of measuring a carbon monoxide concentration on a downstream side along a waste transport direction in the combustion chamber, The oxygen concentration of the mixed gas supplied into the combustion chamber is adjustable based on the carbon monoxide concentration measured by the carbon monoxide measuring means.

9. A waste incineration apparatus according to claim 8.

14. A first measuring means is provided on an upstream side in the direction of transport of the waste in the combustion chamber and configured to be able to measure an in-furnace temperature, an oxygen concentration, and a carbon monoxide concentration; A second measuring means is provided downstream in the direction of transport of the waste in the combustion chamber and configured to be capable of measuring an in-furnace temperature, an oxygen concentration, and a carbon monoxide concentration; The oxygen concentration of the mixed gas supplied into the combustion chamber can be adjusted based on at least one of the measured values ​​of the furnace temperature, the oxygen concentration, and the carbon monoxide concentration measured by the first measuring means and the second measuring means.

9. A waste incineration apparatus according to claim 8.

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