Waste incineration method and waste incineration apparatus

Abstract

To promote the carbonation of incinerated ash and the immobilization of heavy metals in waste incinerators. [Solution] A waste incineration method comprising incinerating waste in an incinerator that burns the waste and discharges it as incinerated ash, wherein the incinerator comprises a combustion chamber for burning the waste, the combustion chamber has an ash carbonation region in which carbonation treatment is performed on the incinerated ash, at least a portion of the exhaust gas from the incinerator is branched off as circulating exhaust gas by a circulating exhaust gas supply means, the circulating exhaust gas is supplied to the ash carbonation region, and the temperature of the ash carbonation region is adjusted to 400°C or more and 600°C or less by adjusting the flow rate of the circulating exhaust gas based on measurements by a temperature sensor capable of measuring the temperature of the ash carbonation region.

Description

Technical Field

[0001] The present invention relates to a waste incineration method and a waste incineration apparatus, and is particularly suitable for application to the stabilization of incineration ash of a waste incinerator that performs combustion using a mixed gas of oxygen and carbon dioxide.

Background Art

[0002] In recent years, there has been a demand for technologies to effectively utilize incineration residues (hereinafter referred to as incineration ash) discharged from waste incinerators as resources. Since incineration ash contains harmful substances, particularly heavy metals, when the elution amount of heavy metals from incineration ash exceeds the standard value, it becomes difficult to effectively utilize incineration ash as a resource. Therefore, it is necessary to perform a so-called detoxification treatment of incineration ash, such as removing heavy metals from incineration ash or stabilizing heavy metals to make the elution amount from incineration ash below the standard value. Since the heavy metals contained in incineration ash are mainly lead (Pb), the heavy metals targeted for the detoxification treatment of incineration ash are mainly lead.

[0003] Techniques for suppressing and immobilizing the elution of lead as a heavy metal contained in incineration ash have been variously studied, and there is a method of reducing the solubility in water by reacting lead contained in incineration ash with carbon dioxide to form a carbonate. Specifically, by changing lead oxide (PbO) to lead carbonate (PbCO3), the solubility in water decreases, making it poorly soluble and suppressing elution from incineration ash. In addition, since incineration ash is basic, the pH of the eluate is high. Regarding the pH of incineration ash, the pH of incineration ash is made into a low pH region where heavy metals are poorly soluble by reacting calcium oxide (CaO) or calcium hydroxide (Ca(OH)2) contained in incineration ash with carbon dioxide (CO2) to form calcium carbonate (CaCO3). Lead (Pb), which has a high content among the heavy metals contained in incineration ash, is an amphoteric metal, so by subjecting incineration ash, which exhibits strong basicity, to a treatment to lower the pH to a poorly soluble region, the elution amount of lead (Pb) can be reduced.

[0004] As a method for detoxifying such incinerated ash, the technology described in Patent Document 1 is known. Patent Document 1 discloses a technology for detoxifying incinerated ash, in which the incinerated ash discharged from the waste incinerator is carbonated by passing heated exhaust gas discharged from the waste incinerator through the ash, thereby promoting the immobilization of lead (Pb).

[0005] In the technology described in Patent Document 1, the following four locations can be cited as reaction sites for the carbonation of incinerated ash: firstly, the reaction tower below the incinerated ash discharge chute; secondly, the incinerated ash storage tank for storing incinerated ash extracted from the incinerated ash extraction device below the waste incineration chute; thirdly, the incinerated ash storage tank for storing incinerated ash extracted from the wet ash removal device below the incinerated ash discharge chute; and fourthly, the post-combustion grate. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2003-340397 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, in the conventional technology described above, the carbon dioxide (CO2) concentration in the exhaust gas emitted from the waste incinerator is low, on the order of 10%, so a long residence time is necessary to sufficiently promote the carbonation of the incinerated ash and the immobilization of heavy metals such as lead. Therefore, there has been a need for a technology that can further promote the carbonation of incinerated ash and the immobilization of heavy metals in waste incinerators.

[0008] The present invention has been made in view of the above, and its object is to provide a waste incineration method and waste incineration apparatus that can promote the carbonation of incinerated ash and the immobilization of heavy metals in a waste incinerator. [Means for solving the problem]

[0009] To solve the above-mentioned problems and achieve the objective, a waste incineration method according to one aspect of the present invention is a waste incineration method in which waste is incinerated in an incinerator that burns the waste and discharges it as incinerated ash, wherein the incinerator comprises a combustion chamber for burning the waste, and the combustion chamber has, along the flow direction of the waste, an initial combustion region in which initial combustion is performed after the waste is dried, a main combustion region for burning the solid components of the waste and the generated combustible gas, a post-combustion region for burning the unburned components of the waste to produce incinerated ash, and an ash carbonation region in which carbonation treatment is performed on the incinerated ash, wherein at least a portion of the exhaust gas of the incinerator is branched off as circulating exhaust gas by a circulating exhaust gas supply means, and then an oxygen supply means mixes the circulating exhaust gas with a gas mainly composed of oxygen to produce a mixed gas with a carbon dioxide concentration of 50% or more, and the mixed gas is supplied to the initial combustion region, the main combustion region and the post-combustion region in the combustion chamber, and the circulating exhaust gas is supplied to the ash carbonation region.

[0010] In one aspect of the present invention, the waste incineration method is characterized in that the ash carbonation region is located at a lower position than the post-combustion region.

[0011] In one aspect of the present invention, the waste incineration method is characterized in that the temperature in the ash carbonation region is adjusted to 400°C or more and 600°C or less.

[0012] In one aspect of the present invention, a waste incineration method is provided in which the carbon dioxide concentration of the circulating exhaust gas is adjusted to 80% or more.

[0013] A waste incineration method according to one aspect of the present invention separates and removes a portion of the nitrogen contained in the circulating exhaust gas in the above invention.

[0014] A waste incineration apparatus according to one aspect of the present invention is a waste incineration apparatus comprising an incinerator that burns waste and discharges it as incinerated ash, the apparatus comprising: a combustion chamber for burning the waste; a circulating exhaust gas supply means configured to branch off at least a portion of the exhaust gas from the incinerator as circulating exhaust gas and supply it to the combustion chamber; an oxygen supply means configured to supply a gas mainly composed of oxygen to the combustion chamber; and a mixed gas with a carbon dioxide concentration of 50% or more by mixing the circulating exhaust gas supplied by the circulating exhaust gas supply means and the gas mainly composed of oxygen supplied by the oxygen supply means. The combustion chamber comprises a gas mixing means, wherein the combustion chamber has, along the flow direction of the waste, a drying grate where initial combustion takes place after the waste has been dried, a combustion grate for burning the solid components of the waste and the generated combustible gases, a post-combustion grate for burning the unburned components of the waste to produce incinerated ash, and an ash carbonation grate for carbonation treatment of the incinerated ash, the gas mixing means is configured to supply the mixed gas to the drying grate, the combustion grate, and the post-combustion grate, and the circulating exhaust gas supply means is configured to supply the circulating exhaust gas to the ash carbonation grate.

[0015] In one aspect of the present invention, the waste incineration apparatus is configured such that the ash carbonation grate is positioned lower than the post-combustion grate, separated by a step.

[0016] A waste incineration apparatus according to one aspect of the present invention is configured such that the temperature of the ash carbonation grate can be adjusted to 400°C or more and 600°C or less.

[0017] A waste incineration apparatus according to one aspect of the present invention is configured to adjust the carbon dioxide concentration of the circulating exhaust gas to 80% or more.

[0018] A waste incineration apparatus according to one aspect of the present invention further comprises a nitrogen separation means for separating and removing a portion of the nitrogen contained in the circulating exhaust gas, as described above. [Effects of the Invention]

[0019] According to the waste incineration method and waste incineration apparatus of the present invention, it is possible to promote carbonation of incineration ash and immobilization of heavy metals in a waste incinerator.

Brief Description of the Drawings

[0020] [Figure 1] FIG. 1 is a diagram showing the overall configuration of a waste incineration apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing the configuration of a grate portion of a waste incineration apparatus according to a modified example of an embodiment of the present invention.

Embodiments for Carrying Out the Invention

[0021] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In all the drawings of the following embodiment, the same or corresponding parts are denoted by the same reference numerals. Further, the present invention is not limited to the embodiment described below.

[0022] In describing the embodiment of the present invention, the intensive studies conducted by the present inventors will be described. First, the present inventors examined the problems regarding the prior art. That is, according to the findings of the present inventors, in a waste incinerator in a conventional waste incineration apparatus, the carbon dioxide (CO2) contained in the exhaust gas discharged is at a low concentration on the order of about 10%. Even if such exhaust gas with a low CO2 concentration is circulated to perform carbonation of incineration ash, a long residence time is required to sufficiently promote carbonation, so it is necessary to increase the equipment capacity. Therefore, the present inventors conducted studies and conceived that it is preferable to increase the CO2 concentration in order to promote carbonation of incineration ash in the waste incinerator and immobilization of heavy metals such as lead.

[0023] Furthermore, the present inventors studied a method for increasing the concentration of CO2 in a waste incinerator, and devised a method of generating a mixed gas of O2 gas and CO2 gas (hereinafter referred to as O2 / CO2 mixed gas) as a combustion-supporting gas by recirculating a part of the combustion exhaust gas and mixing it with a gas containing oxygen (O2) as a main component (hereinafter also referred to as O2 gas).

[0024] That is, CO2 greatly contributes to the carbonation of incineration ash and the immobilization of lead as heavy metals. If CO2 gas with a high CO2 concentration can be supplied to the incineration ash, the carbonation of the incineration ash and the immobilization of heavy metals can be promoted. The carbonation reaction in which calcium oxide (CaO) or calcium hydroxide (Ca(OH)2) contained in the incineration ash reacts with CO2 to form calcium carbonate (CaCO3) is promoted more as the temperature is higher. Therefore, the temperature around the incineration ash is preferably high, but when the temperature exceeds 600°C, the decomposition reaction of the generated CaCO3 may start. Therefore, it is preferable to adjust the temperature around the incineration ash to 400°C or higher and 600°C or lower by adjusting the flow rate of the combustion exhaust gas, but it is not necessarily limited thereto.

[0025] Based on the above studies, the present inventors further studied and devised a method of further providing an ash carbonation stage for carbonating incineration ash in the combustion chamber. By providing an ash carbonation stage in the combustion chamber of the incinerator, in the carbonation of incineration ash and the immobilization of heavy metals such as lead, it becomes less susceptible to the influence of radiation due to combustion occurring in the incinerator. By providing the ash carbonation stage, an ash carbonation region where the carbonation of the incineration ash is performed can be formed, and the temperature control in the ash carbonation stage also becomes easier.

[0026] Furthermore, the inventors conducted detailed experiments and studies on the devised ash carbonation stage. The inventors recirculated at least a portion of the circulating exhaust gas discharged from the waste incinerator and mixed it with O2 gas to produce an O2 / CO2 mixed gas, which was then supplied to the waste incinerator. As a result, the inventors found that it was possible to reduce the concentration of N2 in the exhaust gas (N2 concentration) and increase the concentration of CO2 in the exhaust gas (CO2 concentration) to 50% or more. In other words, by producing such a combustion-supporting gas and supplying it to the waste incinerator, the nitrogen (N2) contained in the supplied combustion-supporting gas is significantly reduced compared to the conventional case where air is supplied as the combustion-supporting gas to the waste incinerator, making it possible to increase the CO2 concentration in the combustion exhaust gas to 50% or more. This promotes the carbonation of incinerated ash and promotes the fixation of heavy metals, especially lead (Pb). Furthermore, by supplying an O2 / CO2 mixed gas as a combustion-supporting gas into the waste incinerator, it becomes possible to promote the combustion of waste in the incinerator.

[0027] Here, in the case of a stoker-type incinerator, the inventors devised a method of installing the ash carbonation stage after the post-combustion region of the incinerator and supplying the circulating exhaust gas to the ash carbonation stage independently of other regions within the combustion chamber. This allows a gas mainly composed of carbon dioxide (CO2) with a CO2 concentration of 50% or more to be supplied to the ash carbonation stage, which is the final stage in the combustion chamber. Since the waste on the ash carbonation stage is incinerated ash from which combustion has been completed, the incinerated ash on the ash carbonation stage can be efficiently carbonized, promoting the immobilization of heavy metals such as lead (Pb). Furthermore, in order to further suppress radiation from combustion to the incinerated ash, the inventors also devised a configuration in which the ash carbonation stage is installed at a lower position with a predetermined step difference from the upper surface of the post-combustion grate that constitutes the post-combustion region in the stoker-type incinerator.

[0028] Furthermore, the inventors have also conceived of a configuration in which a temperature sensor is installed in the ash carbonation stage, and the flow rate of the circulating exhaust gas is adjusted based on measurements taken by the temperature sensor. This allows the temperature on the ash carbonation stage to be adjusted to a temperature that can further promote the carbonation of incinerated ash and the immobilization of heavy metals, for example, a temperature of 400°C to 600°C. The embodiment of the present invention described below was devised by the inventors through the above-mentioned diligent research.

[0029] (Waste Incineration Equipment) Figure 1 shows the overall configuration of a waste incineration apparatus according to one embodiment of the present invention. The waste incineration apparatus according to this embodiment includes a waste incinerator 1. 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 waste. The waste inlet 3 is located upstream (left side in Figure 1) above the combustion chamber 2 along the flow direction of waste W, and is configured to allow waste W to be fed into the combustion chamber 2. A boiler 4 is connected to the upper downstream side (right side in Figure 1) of the combustion chamber 2 along the flow direction of waste W.

[0030] At the bottom of the combustion chamber 2, there is a grate (stoker) 5 for burning the waste W while moving it. The grates 5 are arranged in the following order from the side closest to the waste input port 3, i.e., the upstream side: drying grate 5a, combustion grate 5b, post-combustion grate 5c, and ash carbonation grate 5d.

[0031] In the waste incinerator 1 according to this embodiment, layers of waste W are formed on the drying grate 5a, the combustion grate 5b, the post-combustion grate 5c, and the ash carbonation grate 5d. By burning the waste W, multiple combustion regions are formed in the space within the combustion chamber 2 on the waste W on the respective drying grate 5a, combustion grate 5b, post-combustion grate 5c, and ash carbonation grate 5d.

[0032] In the drying grate 5a, the drying and initial combustion of the waste W primarily takes place. Specifically, the waste W in the upstream area (front part) of the drying grate 5a, located directly above the drying grate 5a and corresponding to the area below the waste input port 3, is dried, ignited, and combustion begins. Above the downstream area (rear part) of the drying grate 5a, an initial combustion region is formed where the waste W has been dried and the combustion of a portion of the waste W has begun, resulting in the start of thermal decomposition and partial oxidation of the waste W. In other words, the waste W on the drying grate 5a is dried and ignited in the upstream area of ​​the drying grate 5a, and then combustion begins in the downstream area, resulting in the formation of an initial combustion region for the waste W. The initial combustion region is the area where, after the combustion of the waste W has begun in the downstream part of the drying grate 5a, combustible gases begin to be generated by the thermal decomposition and partial oxidation of the waste W, and a portion of the waste W burns.

[0033] On the combustion grate 5b, the waste W is primarily subjected to thermal decomposition and partial oxidation. On the combustion grate 5b, the main combustion occurs, burning of carbon monoxide (CO) and hydrocarbons generated by thermal decomposition, as well as solid components (fixed carbon). Specifically, when waste W is incinerated on the combustion grate 5b, evaporation of water occurs, followed by thermal decomposition and partial oxidation reactions, which begin to generate combustible gas. The generated combustible gas and solid components of waste W are burned on the combustion grate 5b. On the combustion grate 5b, the waste W is substantially almost completely burned, and the main combustion region of waste W is formed. The main combustion region is the region on the combustion grate 5b where the thermal decomposition and partial oxidation of waste W are actively occurring, generating combustible gases that burn with flames, and where the solid components of waste W are also burning. This region extends to the point where the combustion with flames is completed (burnout point).

[0034] On the post-combustion grate 5c, post-combustion is performed to completely burn any remaining unburned material in the waste. Specifically, the region on the post-combustion grate 5c beyond the burnout point becomes the post-combustion region where solid unburned material (char) in the waste W is burned. After the waste W is burned, any remaining unburned material such as fixed carbon in the waste W is completely burned on the post-combustion grate 5c. The waste W on the post-combustion grate 5c forms the post-combustion region. The post-combustion region is the region on the post-combustion grate 5c where the unburned material in the waste W is burned and the waste W is converted into incinerated ash.

[0035] On the ash carbonation grate 5d, after the waste W is incinerated into ash, a carbonation treatment is performed. Specifically, on the ash carbonation grate 5d, a carbonation treatment is performed using carbon dioxide (CO2) contained in the combustion exhaust gas discharged from the waste incinerator 1, for example, the circulating exhaust gas discharged from the dust collector 18 described later. The ash carbonation region is the region where carbonation treatment is performed on the incinerated ash.

[0036] In the ash carbonation region, CO2 reacts with heavy metals, mainly lead (Pb), contained in the incinerated ash, causing Pb to carbonize and become sparingly soluble. This suppresses the leaching of Pb from the incinerated ash. In addition, in the ash carbonation region, CO2 contained in the circulating exhaust gas reacts with calcium oxide (CaO) contained in the incinerated ash to produce calcium carbonate (CaCO3). This lowers the pH of the incinerated ash, creating a sparingly soluble region where Pb is poorly soluble, further suppressing the leaching of Pb from the incinerated ash. After the carbonation treatment, the incinerated ash is discharged by dropping from the incinerated ash discharge section 6.

[0037] As described above, a waste layer is mainly formed on the drying grate 5a and the combustion grate 5b, an incineration ash layer is formed downstream of the post-combustion grate 5c, and carbonation treatment is carried out on the ash carbonation grate 5d.

[0038] A wind box 7 is provided at the bottom of the combustion chamber 2. Specifically, wind boxes 7a, 7b, 7c, and 7d are provided at the bottom of the drying grate 5a, combustion grate 5b, post-combustion grate 5c, and ash carbonation grate 5d within the combustion chamber 2, respectively. Wind boxes 7a to 7c of the wind box 7 can function as part of a gas mixing means for mixing multiple gases, and in this embodiment, they can function as a gas mixing means for mixing circulating exhaust gas with a gas mainly composed of O2.

[0039] The area downstream of the combustion chamber 2 and near the inlet of the boiler 4, which is connected to the outlet of the combustion chamber 2, constitutes a secondary combustion chamber 11 for burning 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 on the downstream side (right side in Figure 1) in the direction of waste flow. Secondary combustion gas is blown into the secondary combustion chamber 11 by a pipeline (neither shown) equipped with a blower and a damper. In the secondary combustion chamber 11, the unburned portion of the combustible gas in the combustion gas generated in the combustion chamber 2 (unburned gas) is burned (secondary combustion), and the exhaust gas after secondary combustion is recovered as heat by the boiler 4.

[0040] The boiler 4, which recovers heat from exhaust gas, is divided into three sections by two deflection sections 12 and 13 that bend the exhaust gas flow path. The boiler 4 comprises a first radiating chamber 14, a second radiating chamber 15, and a convection heat transfer chamber 16, starting from the upstream side along the direction of exhaust gas flow. The upstream part of the first radiating chamber 14, which is supplied with exhaust gas from the waste incinerator 1, along the direction of exhaust gas flow, becomes the secondary combustion chamber 11. The first radiating chamber 14 and the second radiating chamber 15 are connected at their upper parts, and the lower part of the second radiating 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 via a flue 17 to a dust collector 18 consisting of a bag filter and the like.

[0041] The boiler 4 has an inner wall made of refractory material, and the first radiating chamber 14 and the second radiating chamber 15 are provided with heat transfer tubes (not shown) formed by steam piping densely arranged on the outside of the refractory material walls that make up the inner wall. The convection heat transfer chamber 16 has heat transfer tubes (not shown) in the internal space through which exhaust gas flows.

[0042] The boiler 4 consists of an evaporator comprising a first radiating chamber 14 and a second radiating chamber 15. A portion of the convection heat transfer chamber 16 forms multiple superheaters, for example, three superheaters 16A. In the first radiating chamber 14 and the second radiating chamber 15, heat transfer tubes, which are located outside the refractory walls and through which water flows, are configured as radiant heat transfer surfaces that receive radiant heat from the exhaust gas and generate steam.

[0043] The convection heat transfer chamber 16 comprises a superheater 16A and an economizer 16B, arranged from the upstream side (downward) along the direction of exhaust gas flow. The superheater 16A comprises a group of heat transfer tubes arranged in multiple stages in the height direction, with multiple heat transfer tubes arranged horizontally, 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 to produce superheated steam at high temperature and pressure. The economizer 16B is located downstream (above) of the superheater 16A and has heat transfer tubes arranged to receive condensate that has been condensed in a condenser (not shown) from the steam generated in the boiler 4 and used to drive the steam turbine (not shown). The economizer 16B heats the condensate using the residual heat in the exhaust gas after the steam has been superheated in the superheater 16A, thereby heating the water through heat exchange with the exhaust gas to produce heated water, which is then supplied to the evaporator.

[0044] Furthermore, the economizer 16B may be installed outside the boiler 4 as a separate economizer downstream of the boiler 4, rather than being installed inside the convection heat transfer chamber 16, or both an internal economizer and a separate economizer may be installed. At the uppermost (lower) part of the convection heat transfer chamber 16, a screen tube (not shown) is provided 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 gaseous or mist-like dust components, separating them from the exhaust gas as dust. Evaporators may also be provided upstream or downstream of the superheater 16A inside the convection heat transfer chamber 16.

[0045] The exhaust gas from the waste incinerator 1, after secondary combustion in the secondary combustion chamber 11, is introduced into the boiler 4, where steam is generated by the evaporators in the first and second radiating chambers 14 and 15. The generated steam is then superheated by the superheater 16A in the convection heat transfer chamber 16.

[0046] The exhaust gas, from which heat has been recovered by the boiler 4, is supplied through the flue 17 to a dust collector 18, which consists of, for example, a bag filter. In the flue 17, substances such as caustic soda, slaked lime, and activated carbon 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 draws exhaust gas from the waste incinerator 1 and supplies at least a portion of the drawn exhaust gas to the wind box 7 to recirculate it back to the waste incinerator 1. The exhaust gas that is not recirculated after dust removal is supplied to the chimney 20 and released into the atmosphere.

[0047] A circulating exhaust gas supply line 30 is provided from the exhaust gas duct (flue) on the outlet side of the dust collector 18, which serves as a means for supplying circulating exhaust gas. This line supplies a portion of the exhaust gas after dust removal by the dust collector 18 to the wind box 7 below the grate 5 as circulating exhaust gas.

[0048] The circulating exhaust gas supply line 30 is sequentially equipped with a cooling tower 31 as a water separation means and a nitrogen PSA (Pressure Swing Adsorption) section 32 as a nitrogen separation means for separating nitrogen gas by pressure fluctuation adsorption. The cooling tower 31 separates and discharges water (H2O) from the circulating exhaust gas. The nitrogen PSA section 32 discharges nitrogen (N2) from the circulating exhaust gas from which water has been removed, increasing the CO2 concentration in the circulating exhaust gas. Alternatively, an oxygen PSA section 33 may be provided, branched off from the circulating exhaust gas supply line 30, which separates oxygen (O2) and carbon dioxide (CO2) by pressure fluctuation adsorption and then returns the O2 to the circulating exhaust gas supply line 30.

[0049] The circulating exhaust gas supply line 30 has branch lines 30a, 30b, 30c, and 30d that are branched to supply gas to each of the wind boxes 7a to 7d. The circulating exhaust gas supply line 30 is provided with a circulating exhaust gas flow rate adjustment unit 34, which is a means of adjusting the flow rate of circulating exhaust gas consisting of a damper or valve. The circulating exhaust gas flow rate adjustment unit 34 consists of circulating exhaust gas flow rate adjustment units 34a, 34b, 34c, and 34d provided in each of the branch lines 30a to 30d of the circulating exhaust gas supply line 30, corresponding to the wind boxes 7a to 7d.

[0050] The branch lines 30a to 30c of the circulating exhaust gas supply line 30 are connected to an oxygen supply line 35 capable of supplying a gas mainly composed of oxygen (O2), i.e., a gas with an O2 concentration of 50% or more (hereinafter referred to as O2 gas). A blower 36 is provided in the oxygen supply line 35. The oxygen supply line 35 has branch lines 35a, 35b, and 35c that are branched to supply O2 gas to each of the wind boxes 7a to 7c.

[0051] Branch lines 35a to 35c are each connected to branch lines 30a to 30c. The oxygen supply line 35, which constitutes the oxygen supply means, is configured to supply oxygen (O2) to each of the branch lines 30a to 30c. As a result, the circulating 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 gas mixing means is composed of the circulating exhaust gas supply line 30 and the oxygen supply line 35. Alternatively, the branch lines 35a to 35c of the oxygen supply line 35 may be directly connected to the wind boxes 7a to 7c, and the circulating exhaust gas and O2 gas may be mixed inside the wind boxes 7a to 7c. In this case, the gas mixing means is composed of the wind boxes 7 (7a to 7c), the circulating exhaust gas supply line 30, and the oxygen supply line 35.

[0052] Furthermore, the oxygen supply line 35 is provided with an oxygen flow rate adjustment unit 37, which serves as an oxygen flow rate adjustment means consisting of a damper or valve to adjust the flow rate. The oxygen flow rate adjustment unit 37 consists of oxygen flow rate adjustment units 37a, 37b, and 37c. The oxygen flow rate adjustment units 37a to 37c are provided in the branch lines 35a to 35c of the oxygen supply line 35, respectively.

[0053] The mixing ratio of the circulating exhaust gas supplied through the circulating exhaust gas supply line 30 and the O2 gas supplied through the oxygen supply line 35 can be adjusted by adjusting the flow rate by the circulating exhaust gas flow rate adjustment unit 34 and the oxygen flow rate adjustment unit 37. The circulating exhaust gas flow rate adjustment unit 34 and the oxygen flow rate adjustment unit 37 constitute a carbon dioxide concentration adjustment means for adjusting the CO2 concentration in the O2 / CO2 mixed gas, which is a mixed gas of circulating exhaust gas and oxygen (O2). In this embodiment, the carbon dioxide concentration adjustment means makes it possible to adjust the CO2 concentration of the O2 / CO2 mixed gas supplied to the drying grate 5a, the combustion grate 5b, and the post-combustion grate 5c to typically 50% or more, preferably 60% or more, and more preferably 80% or more.

[0054] With the above configuration, the gas mainly composed of O2 and the circulating exhaust gas with a high concentration of CO2 are mixed in the branch lines 30a-30c and 35a-35c below the grate 5, respectively, and selectively supplied to the dry grate 5a, the combustion grate 5b, and the post-combustion grate 5c as a supporting gas, the O2 / CO2 mixed gas. Alternatively, the gas mainly composed of O2 and the circulating exhaust gas with a high concentration of CO2 may be mixed in the wind chambers 7a-7c to produce the supporting gas, the O2 / CO2 mixed gas.

[0055] The branch line 30d in the circulating exhaust gas supply line 30 is connected to the wind box 7d at the bottom of the ash carbonation grate 5d. The circulating exhaust gas flow rate adjustment unit 34d provided in the branch line 30d is configured to adjust the flow rate of the circulating exhaust gas supplied to the ash carbonation grate 5d through the wind box 7d. Since the circulating exhaust gas is a gas that mainly contains CO2, the circulating exhaust gas flow rate adjustment unit 34d constitutes a carbon dioxide flow rate adjustment means that adjusts the flow rate of CO2 in the circulating exhaust gas supplied to the ash carbonation grate 5d.

[0056] (Adjustment of the temperature of incinerated ash in the ash carbonation region) The circulating exhaust gas flow rate adjustment unit 34d is configured to adjust the temperature of the ash carbonation region by adjusting the flow rate of the circulating exhaust gas based on a signal input from a temperature sensor 38 capable of measuring the temperature of the ash carbonation region. It is preferable to adjust the temperature in the ash carbonation region to, for example, 400°C to 600°C using the circulating exhaust gas flow rate adjustment unit 34d. By controlling the temperature of the incineration ash layer on the ash carbonation grate 5d to a range of 400 to 600°C, the reaction in which CaO or Ca(OH)2 contained in the incineration ash reacts with the high concentration of CO2 in the circulating exhaust gas to produce CaCO3 can be promoted, and the treatment to bring the pH of the incineration ash to a low pH range in which lead is poorly soluble can be promoted. For this reason, it is more preferable to set the temperature of the incineration ash layer in the ash carbonation region to a range of 400 to 600°C because the reaction to produce CaCO3 proceeds with high efficiency.

[0057] As described above, by providing an ash carbonation grate 5d in the combustion chamber 2 and creating a carbonation region, the detoxification treatment of incinerated ash on the post-combustion grate 5c can be sufficiently carried out, eliminating the need for further detoxification treatment after the incinerated ash is discharged, thus reducing treatment costs. Furthermore, by providing an ash carbonation grate 5d downstream of the post-combustion grate 5c in the combustion chamber 2, the carbonation of incinerated ash and the immobilization of heavy metals such as Pb are less affected by radiation from combustion occurring on the dry grate 5a and combustion grate 5b.

[0058] (Waste Incineration Methods) Next, in this embodiment, we will describe the case in which an O2 / CO2 mixed gas is supplied from the wind box 7c below the post-combustion grate 5c. Note that in the following description, the post-combustion grate 5c and its corresponding parts can be replaced to the extent possible with the dry grate 5a and its corresponding parts, and the combustion grate 5b and its corresponding parts.

[0059] In other words, in this embodiment, O2 gas is supplied from below the post-combustion grate 5c in addition to the circulating exhaust gas and mixed with it, and the O2 / CO2 mixed gas is supplied from the wind box 7c to the incinerated ash on the post-combustion grate 5c. A carbon dioxide concentration control means (not shown) adjusts the amount of circulating exhaust gas supplied by the circulating exhaust gas flow rate adjustment unit 34c and the amount of oxygen supplied by the oxygen flow rate adjustment unit 37c so that the CO2 concentration of the O2 / CO2 mixed gas is within a predetermined range, specifically 50% or more.

[0060] A carbon dioxide concentration measuring means for measuring the CO2 concentration of the O2 / CO2 mixed gas may be provided in the space below the post-combustion grate 5c or above the post-combustion grate 5c, and based on the measured CO2 concentration, the circulating exhaust gas flow rate adjustment means and the oxygen flow rate adjustment means may be controlled by a carbon dioxide concentration control means so that the carbon dioxide concentration of the O2 / CO2 mixed gas is within a predetermined range.

[0061] Furthermore, the CO2 concentration of the circulating exhaust gas can be determined, and the amount of carbon dioxide supplied by the circulating exhaust gas can be derived from the amount of circulating exhaust gas supplied below the post-combustion grate 5c. The CO2 concentration of the mixed gas, which is a mixture of circulating exhaust gas and O2 gas, can be calculated. Based on the calculated CO2 concentration, the carbon dioxide concentration control means can control the circulating exhaust gas flow rate means and the oxygen flow rate means so that the CO2 concentration of the O2 / CO2 mixed gas is 50% or more. In this way, the CO2 concentration of the exhaust gas discharged from the waste incinerator 1 can also be set to 50% or more.

[0062] It is also possible to omit the nitrogen PSA section 32 as a nitrogen separation means. In this case as well, by supplying an O2 / CO2 mixed gas to the grate 5, particularly the post-combustion grate 5c, the nitrogen (N2) gas content, i.e., the N2 concentration, in the circulating exhaust gas is reduced. As the N2 concentration decreases in the circulating exhaust gas, the CO2 concentration increases, making it possible to increase the CO2 concentration of the gas supplied to the grate 5 of the waste incinerator 1.

[0063] (Operating procedures for waste incineration equipment) In the operation method of the waste incineration apparatus according to this embodiment configured as described above, first, when waste W is fed into the waste input port 3, the waste W is extruded by an extruder (not shown) and supplied to the drying grate 5a. The waste W moves sequentially from the drying grate 5a to the combustion grate 5b, the post-combustion grate 5c, and the ash carbonation grate 5d through the operation of the drying grate 5a, the combustion grate 5b, the post-combustion grate 5c, and the ash carbonation grate 5d, forming a layer of waste W on the grate 5.

[0064] A mixed O2 / CO2 gas is supplied as a combustion-supporting gas to the drying grate 5a, the combustion grate 5b, and the post-combustion grate 5c, respectively, via branch lines 30a, 35a, 30b, 35b, 30c, and 35c. Primary air may also be supplied from a primary air supply line (not shown) during startup, etc. Circulating exhaust gas is supplied to the ash carbonation grate 5d via branch line 30d. As a result, the waste W is dried and then burned on the drying grate 5a and the combustion grate 5b, then further burned on the post-combustion grate 5c to become incinerated ash, and after carbonation treatment on the ash carbonation grate 5d, it is discharged from the incinerated ash discharge section 6.

[0065] (modified version) Next, a modified version of the waste incineration apparatus according to this embodiment will be described. Figure 2 shows the configuration of the grate portion of the waste incineration apparatus according to a modified version of this embodiment. As shown in Figure 2, in the modified version, the ash carbonation grate 5e, which is configured similarly to the ash carbonation grate 5d, is provided at a lower position, separated from at least the preceding post-combustion grate 5c by a predetermined step, for example, a step of about 1 m. The other configurations are the same as in the embodiment described above.

[0066] By providing an ash carbonation grate 5e, which forms a carbonation region, in the combustion chamber 2 of the waste incinerator 1, at a lower position after the post-combustion grate 5c and separated by a step, the carbonation of incinerated ash and the immobilization of heavy metals such as Pb are less affected by radiation from combustion occurring in the drying grate 5a and combustion grate 5b within the combustion chamber 2.

[0067] According to the embodiment described above, the incinerated ash that has undergone post-combustion on the post-combustion grate 5c is supplied to the ash carbonation grate 5d to perform carbonization treatment. This treatment reacts the CO2 contained in the circulating exhaust gas with the Pb contained in the incinerated ash to form carbon oxides, making them sparingly soluble. This efficiently promotes the detoxification of the incinerated ash within the combustion chamber 2 of the waste incinerator 1. Therefore, carbonization of the incinerated ash and the immobilization of heavy metals such as Pb can be promoted in the waste incinerator 1, and since there is no need for further detoxification treatment after the incinerated ash is discharged, treatment costs can be reduced.

[0068] Although embodiments of the present invention have been specifically described above, the present invention is not limited to the embodiments described above, and various modifications are possible based on the technical idea of ​​the present invention. For example, the numerical values ​​given in the embodiments described above are merely examples, and different numerical values ​​may be used as needed. Combinations of the components of each embodiment and each modification described above are also included in the present invention. Furthermore, further effects and modifications can be easily derived by those skilled in the art. Broader aspects of the present invention are not limited to the specific details and representative embodiments expressed and described above. Therefore, various modifications are possible without departing from the spirit or scope of the overall concept of the invention as defined by the appended claims and their equivalents. [Explanation of symbols]

[0069] 1. Waste Incinerator 2 Combustion chambers 3. Waste Inlet 4 Boiler 4A Exhaust section 5 Fire grates 5a drying grate 5b Combustion grate 5c Post-combustion grate 5d, 5e Ash Carbonated Grate 6. Incineration ash discharge section 7,7a,7b,7c,7d Wind box 36 Blower 11 Secondary combustion chamber 12,13 Change 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 Chimneys 30 Circulating exhaust gas supply line 30a, 30b, 30c, 30d, 35a, 35b, 35c Branch line 31 Cooling Tower 32 Nitrogen PSA section 33 Oxygen PSA Section 34,34a,34b,34c,34d Circulating exhaust gas flow rate adjustment section 35. Oxygen supply line 37,37a,37b,37c Oxygen flow rate adjustment section 38 Temperature Sensor

Claims

1. A waste incineration method comprising incinerating the waste in an incinerator that burns the waste and discharges it as incinerated ash, The incinerator comprises a combustion chamber for burning the waste, The combustion chamber has an ash carbonation region in which carbonation treatment is performed on the incinerated ash, The circulating exhaust gas supply means divertes at least a portion of the exhaust gas from the incinerator as circulating exhaust gas. The circulating exhaust gas is supplied to the ash carbonation region. The temperature of the ash carbonation region is adjusted to 400°C to 600°C by adjusting the flow rate of the circulating exhaust gas based on measurements taken by a temperature sensor capable of measuring the temperature of the ash carbonation region. Waste incineration methods.

2. The carbon dioxide concentration of the circulating exhaust gas is adjusted to 80% or higher. The waste incineration method according to claim 1.

3. A portion of the nitrogen contained in the circulating exhaust gas is separated and removed. The waste incineration method according to claim 1.

4. A waste incineration apparatus equipped with an incinerator that burns waste and discharges it as incinerated ash, A combustion chamber for burning the aforementioned waste, A circulating exhaust gas supply means configured to branch off at least a portion of the exhaust gas from the incinerator as circulating exhaust gas and supply it to the combustion chamber, A temperature sensor and A circulating exhaust gas flow rate adjustment unit adjusts the flow rate of the circulating exhaust gas, Equipped with, The combustion chamber has an ash carbonation grate in which the incinerated ash is subjected to carbonation treatment, The circulating exhaust gas supply means is configured to supply the circulating exhaust gas to the ash carbonation grate via the circulating exhaust gas flow rate adjustment unit, The temperature sensor is provided to measure the temperature in the ash carbonate grate, Based on measurements by the temperature sensor, the flow rate of the circulating exhaust gas is adjusted by the circulating exhaust gas flow rate adjustment unit, thereby adjusting the temperature in the ash carbonation grate to between 400°C and 600°C. Waste incineration equipment.

5. The system is configured to allow adjustment of the carbon dioxide concentration of the circulating exhaust gas to 80% or more. The waste incineration apparatus according to claim 4.

6. The system further comprises a nitrogen separation means for separating and removing a portion of the nitrogen contained in the circulating exhaust gas. The waste incineration apparatus according to claim 4.

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