Waste incineration method and waste incineration device

Abstract

To suppress generation of a nitrogen oxide in 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 measures a nitrogen oxide concentration near an outlet where exhaust gas is discharged from the combustion chamber using a nitrogen oxide measurement means configured to be able to measure the nitrogen oxide concentration, and adjusts an oxygen concentration in the gas supplied to the drying fire grate based on the measured nitrogen oxide concentration.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] Traditionally, O 2 / CO 2 A combustion technology called oxygen combustion, or Oxy-fuel combustion has been proposed. 2 / CO 2 A waste treatment device and a waste treatment method using combustion are disclosed. In the technology described in Patent Document 1, first, nitrogen (N 2 ) is separated to obtain oxygen (O 2 After recovering heat from the exhaust gas generated by the incineration of this municipal waste, a portion of the exhaust gas is supplied to the incineration process to control the incineration temperature. In addition to controlling the incineration temperature, water (H 2 O) and carbon dioxide (CO 2 ) to be collected.

[0003] Specifically, the municipal waste incineration method 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, the produced oxygen (O 2 ), whereas the incineration exhaust gas (high concentration CO 2 A part of the municipal waste is circulated and mixed with the circulated incineration exhaust gas. The weight ratio of the municipal waste to the circulated incineration exhaust gas is 1 to 12 times, preferably 4 to 8 times, the municipal waste to incineration exhaust gas. In this way, in the incinerator, waste such as municipal waste is mainly exposed to an atmosphere of oxygen and incineration exhaust gas, that is, mainly carbon dioxide (CO 2 ) and water vapor (H 2 It is incinerated in an atmosphere containing [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] In the above-mentioned Patent Document 1, the amount of nitrogen oxides (NO x However, Patent Document 1 does not disclose any specific incineration methods other than those described above, and only discloses a general action regarding whether or not NOx can be suppressed. Therefore, in order to actually suppress the generation of NOx, it is considered necessary to develop a more specific technology that goes beyond the general action. Therefore, there has been a demand for the development of a more specific technology that can reduce the generation of NOx in waste incinerators.

[0006] The present invention has been made in view of the above, and an object of the present invention is to provide a waste incineration method and a waste incineration apparatus that can reduce the generation of nitrogen oxides in 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 incinerating waste in an incinerator having a combustion chamber in which waste is transported by a grate and combusted, 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 and supplies it to the combustion chamber, wherein the grate is configured to have a drying grate, a combustion grate, and a post-combustion grate along the direction in which the waste is transported, and a nitrogen oxide measuring means configured to be able to measure the nitrogen oxide concentration measures the nitrogen oxide concentration near the outlet where the exhaust gas is discharged from the combustion chamber, and the oxygen concentration in the gas supplied to the drying grate is adjusted based on the measured nitrogen oxide concentration.

[0008] In the waste incineration method according to one aspect of the present invention, in the above-mentioned invention, the oxygen concentration of the gas supplied to the combustion grate is adjusted to be higher than 25% and not higher than 35%.

[0009] 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%.

[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 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 and 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 a nitrogen oxide measuring means configured to be able to measure the nitrogen oxide concentration is provided near the outlet where the exhaust gas is discharged from the combustion chamber, and the oxygen concentration in the gas supplied to the drying grate can be adjusted based on the nitrogen oxide concentration measured by the nitrogen oxide measuring means.

[0013] The waste incineration apparatus according to one aspect of the present invention is configured in such a way that the oxygen concentration of the gas supplied to the combustion grate can be adjusted to a value higher than 25% and equal to or lower than 35%.

[0014] In this configuration, the waste incineration apparatus according to one embodiment of the present invention is configured 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%.

[0015] 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 a pre-stage nozzle provided above the drying grate and the combustion grate can be adjusted to between 15% and 25%.

[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 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%. Effect of the Invention

[0017] According to the waste incineration method and waste incineration apparatus of the present invention, it is possible to reduce the generation of nitrogen oxides in a waste incinerator. [Brief description of the drawings]

[0018] [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

[0019] 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.

[0020] In describing the embodiments of the present invention, the inventors have conducted extensive research. First, the inventors have examined the problems associated with the prior art. 2 / CO 2 The nitrogen oxides (NOx) generated during the combustion of waste using the combustion, oxygen combustion, or oxy-fuel combustion technologies are mostly fuel-NOx (Fuel-NOx) generated from the nitrogen contained in the waste. 2 / CO 2 We investigated methods to reduce NOx, including fuel NOx, in stoker-type waste incinerators that use combustion, oxygen combustion, or oxy-fuel combustion technology.

[0021] The inventors have discovered that oxygen (O 2 The inventor has devised a method for reducing fuel NOx in exhaust gas based on two-stage combustion technology, which is generally recognized as a NOx reduction technology, by using a mixed gas of fuel NOx and recirculated exhaust gas circulated in the system as an oxidizer and changing the oxygen concentration of the oxidizer depending on the location of injection. The inventor has also devised a method for arbitrarily changing the oxygen concentration by using the recirculated exhaust gas mixed with oxygen as a diluent to control the mixing amount and mixing ratio of the recirculated exhaust gas to the oxygen. Based on this, the inventor has conducted various experiments and studies on a method for reducing NOx by variously changing the oxygen concentration in the oxidizer supplied to the waste in a stoker-type waste incinerator. As a result of intensive studies, the inventor has devised the following method as a specific method for changing the oxygen concentration in the oxidizer.

[0022] That is, in a stoker-type waste incinerator, a plurality of grates are provided 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 direction of waste transport. Furthermore, the present inventors have found that the nitrogen oxides (NO x Based on the nitrogen oxide concentration in the combustion grate, the inventor has devised a method for adjusting the oxygen concentration of the oxidizer supplied from below to the drying grate. According to the findings obtained from the experiments by the inventor, in order to completely burn the waste on the grate, it is preferable to set the oxygen concentration of the oxidizer supplied from below to the central combustion grate along the conveying direction to 15% or more and 25% or less. In addition, in order to carbonize the incineration ash on the grate, it is also preferable to set the gas supplied from below to the downstream post-combustion grate to be only recirculated exhaust gas or a low-oxygen gas with an oxygen concentration of less than 5%. In this way, the inventor has devised a method for adjusting the oxygen concentration of the gas supplied to the drying grate based on the nitrogen oxide concentration in the vicinity of the outlet of the combustion chamber in order to reduce NOx after setting the oxygen concentrations of the gas supplied to the combustion grate and the gas supplied to the post-combustion grate to be different from each other.

[0023] Specifically, sensors are provided at least in two locations in the waste incinerator, and the oxygen concentration is adjusted based on the measurement values ​​from the sensors. More specifically, sensors are provided at least in two locations in the waste incinerator, on the upstream side (front of the furnace) and downstream side (rear of the furnace) along the waste transport direction. At least the two sensors on the upstream and downstream sides measure the furnace temperature, oxygen concentration, and carbon monoxide (CO) concentration, and the downstream sensor further measures nitrogen oxides (NO x In this case, the relationship between the measured value of the nitrogen oxide 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 it is possible to control the oxygen concentration of the oxidizer so as to reduce the nitrogen oxide concentration. Note that a separate sensor may be further provided to measure the nitrogen oxide concentration.

[0024] Furthermore, the inventors have also studied the oxidizer supplied above the grate of the waste incinerator, i.e., into the combustion chamber. The inventors have come up with the idea of ​​varying the oxygen concentration of the oxidizer depending on the position where the oxidizer is supplied into the combustion chamber. Specifically, they have found that it is desirable to set the oxygen concentration of the oxidizer supplied to the exhaust gas discharge portion of the combustion chamber to be higher than 25% and lower than 35%.

[0025] Here, when the waste incinerator is, for example, a counterflow incinerator, the oxygen concentration of the oxidizer is varied depending on the installation positions 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 15% to 25%. 2 The gas is the gas containing O 2 If the oxygen concentration of the contained gas is less than 15%, there is a possibility that combustion will be insufficient, and if the oxygen concentration is higher than 25%, there is a high possibility that the concentration of nitrogen oxides will increase. On the other hand, if the gas supplied to the combustion chamber from the downstream ceiling nozzle is O2 with an oxygen concentration of less than 5%, 2 Only low concentration gas or recirculated exhaust gas.

[0026] In addition, if the waste incinerator is a double-flow incinerator, the oxygen concentration of the oxidizer supplied from the high-temperature air draft fan (HADF) to the combustion chamber must be between 15% and 25%. 2 The gas to be supplied to the combustion chamber from the recirculated draft fan (RDF) is O2-containing gas with an oxygen concentration of less than 5%. 2 Only low concentration gas or recirculated exhaust gas.

[0027] Based on the above studies, the present inventor has devised an incineration method that can reduce NOx by controlling 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.

[0028] (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 a combustion chamber of a waste incinerator, respectively. As shown in FIG. 1, the waste incineration system according to this embodiment includes 2 / CO 2 The system includes a waste incinerator 1 to which 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) in the direction of the flow of the waste W within 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 to the upper part of the combustion chamber 2 on the downstream side (right side in FIG. 1) in the direction of the flow of the waste W.

[0029] 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.

[0030] An air box 7 is provided below the combustion chamber 2. Specifically, air 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 air boxes 7 (7a, 7b, and 7c) can function as part of a gas mixing means for mixing gases supplied from a plurality of systems. In this embodiment, the recirculated exhaust gas and O 2 The gas mixture can function as a gas mixing means for mixing the gas having the main component.

[0031] 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 combustion chamber 2 downstream in the direction of waste flow (right side in FIG. 1). 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 portions (unburned gas) of the pyrolysis gas in the combustion gas generated in the combustion chamber 2 are burned (secondary combustion), and the exhaust gas after secondary combustion is heat recovered by the boiler 4.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] A cooling tower 31 as a water separation means and a PSA section 32 as a carbon dioxide recovery means are sequentially provided on the recirculated exhaust gas supply line 30. The cooling tower 31 separates moisture (H 2 The PSA unit 32 separates and discharges carbon dioxide (CO O) from the recirculated exhaust gas from which moisture has been removed, for example, by a pressure swing adsorption (PSA) method. 2 ) and then the separated CO 2 The nitrogen (N 2 ) is separated and discharged, and the CO in the recirculated exhaust gas is 2 A nitrogen PSA section for increasing the concentration may be provided separately.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] In addition, the branch lines 30a, 30b, 30c, and 30e of the recirculation exhaust gas supply line 30 are supplied with oxygen (O 2 ) as its main component (hereafter, O 2 Main component gas), i.e. O 2 Gas with a concentration of 50% or more, specifically, O separated from air by techniques such as cryogenic separation or PSA method 2 An oxygen supply line 35 capable of supplying oxygen gas having a concentration close to 100% is connected to the oxygen supply line 35. A blower 36 is connected to the oxygen supply line 35.

[0044] The oxygen supply line 35 is connected to each of the wind boxes 7a to 7c. 2 The oxygen supply line 35, which constitutes the oxygen supply means, supplies oxygen (O 2 ) can be supplied. Thus, the recirculated exhaust gas and O 2 In this case, the recirculated exhaust gas supply line 30 and the oxygen supply line 35 constitute a gas mixing means. The branch lines 35a to 35c of the oxygen supply line 35 are directly connected to the wind boxes 7a to 7c, respectively, so that the recirculated exhaust gas and the O 2 In this case, the gas mixing means is composed of the wind box 7, the recirculated exhaust gas supply line 30, and the oxygen supply line 35. The oxygen supply line 35 corresponds to the blowing nozzle 40 and is connected to the O 2 There is a branch line 35e that merges the main component gas with the branch line 30e.

[0045] The wind box 7a and the drying grate 5a corresponding to the wind box 7a are provided with, for example, a gas mixture mainly consisting of recirculated exhaust gas. 2 Concentrations are relatively low, e.g. O 2 Recirculated exhaust gas with a concentration of less than 5% or O 2 Concentrations are relatively high, e.g. O 2 O2 concentration adjusted to greater than 25% and less than 35% 2 That is, the wind box 7a supplies O 2 to the drying grate 5a from below. 2 The concentration is appropriately adjusted to recirculate exhaust gas, O 2 Low concentration gas, or O 2 The gas supply system is configured to be capable of supplying high concentration gas.

[0046] The wind box 7b and the combustion grate 5b corresponding to the wind box 7b are provided with O 2 The oxidizing agent, which is adjusted to a relatively high concentration, is, for example, O 2O2 concentration adjusted to greater than 25% and less than 35% 2 That is, the wind box 7b is arranged to supply O 2 Relatively high concentration of O 2 The gas supply system is configured to be capable of supplying high concentration gas.

[0047] The wind box 7c and the post-combustion grate 5c corresponding to the wind box 7c are mainly composed of recirculated exhaust gas. 2 Concentrations are relatively low, e.g. O 2 The recirculated exhaust gas, the concentration of which is adjusted to less than 5%, is supplied to the wind box 7c. 2 Relatively low concentration of O 2 It is configured to be capable of supplying low-concentration gas or recirculated exhaust gas.

[0048] 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.

[0049] 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.

[0050] The pre-stage nozzle 38 is provided above between the drying grate 5a and the combustion grate 5b, for example, on the ceiling of the combustion chamber 2. 2 The oxidizing agent, which is adjusted to a relatively high concentration, is, for example, O 2 O2 concentration adjusted to 15% to 25% 2 That is, the pre-stage nozzle 38 supplies O 2 to the region between the drying grate 5a and the combustion grate 5b in the combustion chamber 2. 2 Relatively high concentration of O 2 The gas containing element is configured to be able to be supplied.

[0051] The rear nozzle 39 is provided above 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 provided with O 2 , which is mainly composed of recirculated exhaust gas. 2 Concentrations are relatively low, e.g. O 2 The recirculated exhaust gas, the concentration of which is adjusted to less than 5%, is supplied to the rear nozzle 39. 2 Gases contained and O 2 The main component gas is mixed with the recirculated exhaust gas to 2 Adjusted concentration of O 2 A low-concentration gas may be supplied. That is, the rear nozzle 39 supplies O 2 to the area between the combustion grate 5b and the rear combustion grate 5c in the combustion chamber 2, for example, in the vicinity of the burnout point of the waste. 2 Recirculated exhaust gas or O with relatively low concentration 2 It is configured to be able to supply low concentration gas.

[0052] The secondary combustion chamber 11 at the outlet of the combustion chamber 2 is provided with an injection nozzle 40. 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 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. 2 The oxidizing agent, which is adjusted to a relatively high concentration, is, for example, O 2 O2 concentration adjusted to greater than 25% and less than 35% 2 That is, the injection nozzle 40 is supplied with O 2 Relatively high concentration of O 2 The high-concentration gas is adapted to be supplied to a region adjacent to the outlet of the combustion chamber (2) and at the inlet of the secondary combustion chamber (11).

[0053] A sensor group 51 is provided on the upstream side in the direction of transport of the waste W in the combustion chamber 2. The sensor group 51 measures at least temperature, O 2 The sensor group 51 is configured to be able to measure the temperature, O concentration, and carbon monoxide concentration (CO concentration). 2 The sensor values ​​such as the concentration, CO concentration, etc. are transmitted to the control unit 50.

[0054] Further, a sensor group 52 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 temperature, O 2 concentration, CO concentration, and nitrogen oxide concentration (NO x The sensor group 52 is configured to be able to measure the temperature, O 2 concentration, CO concentration, and NO x The sensor values ​​such as concentration are transmitted to the control unit 50. The sensor group 52 constitutes a nitrogen oxide measuring means.

[0055] 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.

[0056] (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.

[0057] 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.

[0058] 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.

[0059] In addition, O 2 is introduced into the combustion chamber 2 from a front nozzle 38 above the drying grate 5a and the combustion grate 5b. 2 In this case, the O 2 gas supplied from the front-stage nozzle 38 is supplied below the front-stage nozzle 38 in the combustion chamber 2.2 A gas combustion region S1 is formed by a mixture of the contained gas 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.

[0060] After the waste W is burned, the remaining unburned matter such as fixed carbon in the waste W is completely burned on the post-combustion grate 5c. 2 A low-concentration gas or a recirculated exhaust gas is supplied. In this case, the O 2 supplied from the rear nozzle 39 is supplied downstream of the rear nozzle 39. 2 Secondary combustion is carried out in the secondary combustion zone S2 by the low-concentration gas or recirculated exhaust gas and the pyrolysis gas of the unburned matter transported from the gas combustion zone S1. The area behind the burnout point S3 on the post-combustion grate 5c is the post-combustion zone where the solid unburned matter (char) in the waste W is burned. 2 High-concentration gas is supplied. 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.

[0061] As shown in FIG. 1, in a waste incineration system, recirculated exhaust gas is supplied through a recirculated exhaust gas supply line 30, and O is supplied through an oxygen supply line 35. 2 The mixing ratio with the main component gas can be adjusted by adjusting the flow rate by the recirculation exhaust gas flow rate adjustment unit 34 and by adjusting the flow rate by the oxygen flow rate adjustment unit 37. That is, the control unit 50 can control the flow rate of the recirculation exhaust gas by controlling the recirculation exhaust gas flow rate adjustment units 34a to 34e, and can control the O flow rate by controlling the oxygen flow rate adjustment units 37a to 37e. 2 The flow rate of the main component gas can be controlled. 2 Gas content O 2With the above configuration, the control unit 50 can control the O 2 concentration of the gas supplied to the wind box 7 (7a to 7c), the grate 5 (5a to 5c), the front nozzle 38, the rear nozzle 39, and the blowing nozzle 40. 2 It is possible to control the concentrations individually.

[0062] For example, as shown in Figure 2, 2 Main component gas and CO 2 The recirculated exhaust gas with a high concentration of oxygen is mixed with the recirculated exhaust gas in the branch lines 30a to 30c, 35a to 35c below the grate 5. 2 By controlling the concentration, the drying grate 5a and the post-combustion grate 5c can be fed with only recirculated exhaust gas or with O 2 O concentrations less than 5% 2 Low-concentration gas is selectively supplied to the combustion grate 5b. 2 O concentration is greater than 25% and less than 35% 2 It is possible to selectively supply high concentration gas. 2 The main component gas and the recirculated exhaust gas are mixed in the wind boxes 7a to 7c, and O 2 The concentration may be adjusted to control the amount.

[0063] The control unit 50 also 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 constantly or at any time acquires various measurement values ​​(sensor values) from the sensor groups 51 and 52 in the waste incinerator 1. Specifically, the control unit 50 acquires NO x The control unit 50 acquires the measured value of the NO concentration. x When the concentration exceeds the first predetermined value, the O 2 Decrease the concentration to O 2 On the other hand, the control unit 50 controls the obtained NO x When the concentration becomes less than the second predetermined value, the O 2 of the gas supplied to the drying grate 5a is 2 By increasing the concentration, O 2The control unit 50 controls the O2 concentration of each of the gases supplied to the front nozzle 38, the rear nozzle 39, and the blowing nozzle 40 so as to reduce the amount of NOx generated. 2 It is also possible to control the concentration.

[0064] According to the embodiment described above, in the waste incinerator 1, the drying grate 5a, the combustion grate 5b, the post-combustion grate 5c, and the area between the drying grate 5a and the combustion grate 5b are provided with O 2 The front nozzle 38 supplies high-concentration gas, and the O 2 A rear nozzle 39 for supplying low-concentration gas or recirculated exhaust gas, and an O 2 For each of the nozzles 40 supplying high-concentration gas, 2 By adjusting the concentration while supplying gas to the waste incinerator 1, O 2 Since the concentration can be controlled individually for each supply location, the NOx in the exhaust gas discharged from the waste incinerator 1 can be reduced.

[0065] 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.

[0066] 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]

[0067] 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; measuring a nitrogen oxide concentration by a nitrogen oxide measuring means configured to be able to measure a nitrogen oxide concentration in the vicinity of an outlet where exhaust gas is discharged from the combustion chamber; The oxygen concentration in the gas supplied to the drying grate is adjusted based on the measured nitrogen oxide concentration. Waste incineration methods.

2. The oxygen concentration of the gas supplied to the combustion grate is adjusted to be greater than 25% and less than 35%.

2. The waste incineration method according to claim 1.

3. 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.

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. 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; a nitrogen oxide measuring means configured to be able to measure a nitrogen oxide concentration in the vicinity of an outlet through which exhaust gas is discharged from the combustion chamber; The oxygen concentration in the gas supplied to the drying grate can be adjusted based on the nitrogen oxide concentration measured by the nitrogen oxide measuring means. Waste incineration equipment.

7. The oxygen concentration of the gas supplied to the combustion grate can be adjusted to be higher than 25% and lower than 35%.

7. A waste incineration apparatus according to claim 6.

8. 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%.

7. A waste incineration apparatus according to claim 6.

9. 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.

7. A waste incineration apparatus according to claim 6.

10. 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%.

7. A waste incineration apparatus according to claim 6.

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