JP2024151997A - Waste treatment equipment and waste treatment method - Google Patents

Abstract

To provide a waste treatment facility capable of reducing a supply amount of circulation exhaust gas necessary for making incineration ashes harmless, and reducing a load for recovering CO2 from combustion exhaust gas.SOLUTION: A waste treatment facility includes: an incineration device for generating incineration ashes and combustion exhaust gas from waste containing heavy metals; a concentration device for concentrating CO2 in the combustion exhaust gas; and a device for supplying at least part of the concentrated exhaust gas obtained from the concentration device to the incineration device without diluting it.SELECTED DRAWING: Figure 1

Description

The present invention relates to a waste treatment facility and a waste treatment method.

Most of the ash generated when industrial waste and other waste is incinerated is disposed of in landfills, but in recent years, there has been a demand to reduce the amount of landfill waste. For this reason, effective use of the ash as a resource is being considered.

However, since incineration ash contains heavy metals, in order to use the ash as a resource, the heavy metals must be removed from the ash or made less soluble.

As a method for making the insoluble matter, for example, the method described in Patent Document 1 is known. In this method, a part of the combustion exhaust gas from the waste incinerator is introduced from below the post-combustion grate, and the exhaust gas from the waste incinerator (called the circulating exhaust gas) is aerated with the incineration ash on the post-combustion grate. This causes the carbonation reaction of heavy metals such as lead to produce lead carbonate, etc., which makes the insoluble matter difficult to dissolve. At the same time, calcium oxide, etc. contained in the incineration ash is reacted with carbon dioxide to produce calcium carbonate _CaCO3 , and the pH of the incineration ash is lowered to make it difficult to dissolve.

On the other hand, in the method described in Patent Document 1, in order to sufficiently react the components in the incineration ash with the CO ₂ in the exhaust gas, it is necessary to increase the supply amount of the circulating exhaust gas. However, if the supply amount of the circulating exhaust gas is increased, it may have a negative effect on the conditions inside the incinerator, such as the temperature inside the incinerator, and there is also a problem that the load on the circulation equipment increases.

Recently, in order to achieve carbon neutrality, there has also been an increasing demand for the development of technology to capture large amounts of _CO2 from the combustion exhaust gas emitted from waste incinerators.

JP 2020-91068 A

However, in the method for detoxifying incineration ash described in Patent Document 1, the amount of circulating exhaust gas required for sufficient reaction between heavy metal components in the incineration ash and carbon dioxide in the circulating exhaust gas is not sufficiently reduced, and the load on the circulating equipment is not sufficiently reduced. In addition, in the method described in Patent Document 1, the concentration of CO ₂ in the circulating exhaust gas is low, so the concentration of CO ₂ contained in the combustion exhaust gas is also low. Therefore, the method has the problem that when CO ₂ is captured from the combustion exhaust gas to be carbon neutral, the load on the capture equipment used for capturing CO ₂ (hereinafter referred to as the "capture equipment") is large.

In view of the above circumstances, the present invention aims to reduce the amount of circulating exhaust gas required to sufficiently react heavy metal components in the incineration ash with carbon dioxide in the circulating exhaust gas, thereby reducing the load on the circulating equipment during the reaction. Another object of the present invention is to reduce the load on the capture equipment when capturing _CO2 from the combustion exhaust gas.

As a result of intensive research, the inventors have investigated the supply of at least a part of the concentrated exhaust gas prepared by concentrating _CO2 in the combustion exhaust gas discharged from an incineration apparatus as a circulating exhaust gas to the waste incinerator in the incineration apparatus. As a result, the inventors have found that the supply of the circulating exhaust gas can significantly reduce the amount of circulating exhaust gas required to sufficiently react heavy metal components in the incineration ash with carbon dioxide in the circulating exhaust gas. The inventors have also found that by concentrating _CO2 in the combustion exhaust gas, the load on the capture equipment when capturing _CO2 from the concentrated combustion exhaust gas can be reduced.

One aspect of the present invention is
An incineration device that burns waste containing heavy metals to generate incineration ash and combustion exhaust gas;
A concentrating device for concentrating CO ₂ in the combustion exhaust gas discharged from the incineration device;
A concentrated exhaust gas supplying device that supplies at least a portion of the concentrated exhaust gas obtained from the concentrating device to the incineration device as a circulating exhaust gas without diluting it;
The waste treatment facility includes an incineration system.

Another aspect of the present invention is
an incineration step of burning waste containing heavy metals using an incineration device to generate incineration ash and combustion exhaust gas;
A concentration step of concentrating CO ₂ in the combustion exhaust gas generated in the incineration step;
A supply step of supplying at least a portion of the concentrated exhaust gas obtained in the concentration step to the incineration apparatus as a circulating exhaust gas without dilution;
The incinerator waste treatment method includes:

In both the waste treatment facility and the waste treatment method according to one embodiment of the present invention, when treating waste containing heavy metals, the amount of circulating exhaust gas required for sufficient reaction between the heavy metal components in the incineration ash and the carbon dioxide in the circulating exhaust gas is sufficiently reduced. As a result, the load on the circulating facility is sufficiently reduced without adversely affecting the condition inside the furnace, and the load on the recovery facility when recovering _CO2 from the combustion exhaust gas can be reduced.

FIG. 1 is a schematic diagram showing the configuration of a waste treatment facility according to one embodiment of the present invention used in Examples 1 and 2. FIG. 11 is a schematic diagram showing the configuration of a waste treatment facility according to another embodiment of the present invention, which is used in Example 3. FIG. 13 is a schematic diagram showing the configuration of a waste treatment facility according to yet another embodiment of the present invention, used in Example 4. FIG. 1 is a schematic diagram showing an embodiment of a concentrator using a _CO2 separation membrane in the present invention. FIG. 2 is a schematic diagram showing the configuration of a waste treatment facility used in Comparative Example 1.

One embodiment of the present invention will be described below, but the present invention is not limited to this. The present invention is not limited to the configurations described below, and various modifications are possible within the scope of the claims. The technical scope of the present invention also includes embodiments obtained by appropriately combining the technical means disclosed in different embodiments. In this specification, unless otherwise specified, "A to B" representing a numerical range means "greater than or equal to A and less than or equal to B."

[Embodiment 1: Waste treatment facility]
The waste treatment facility according to the first embodiment of the present invention (hereinafter also referred to as "the present waste treatment facility") includes an incineration device that incinerates waste containing heavy metals to produce incineration ash and combustion exhaust gas, a concentrating device that concentrates _CO2 in the combustion exhaust gas discharged from the incineration device, and a concentrated exhaust gas supplying device that supplies at least a portion of the concentrated exhaust gas obtained from the concentrating device to the incineration device as a circulating exhaust gas without diluting it.

Each piece of equipment that makes up this waste treatment facility is described in detail below.

[Incineration equipment]
The incineration apparatus in this waste treatment facility is an apparatus that burns waste containing heavy metals and generates incineration ash and combustion exhaust gas. The incineration apparatus is not particularly limited as long as it is an apparatus that can burn the waste and generate incineration ash and combustion exhaust gas, and an incinerator is generally used. Here, "combustion" means generating incineration ash as a solid content from the waste by thermal decomposition and oxidation, and generating combustion exhaust gas as a gas. In addition, during "combustion", combustible gas may be generated from the waste, and the combustion exhaust gas may be generated from the combustible gas. In addition, during "combustion", solid content other than the incineration ash may be generated from the waste, and the incineration ash may be generated from the solid content other than the incineration ash. When the generation of the incineration ash and the combustion exhaust gas is incomplete, that is, when the generated solid content contains a part of the waste and/or a solid content other than the incineration ash, and/or when the generated gas contains the combustible gas, it is also within the scope of "combustion". In this specification, "combustion" and "incineration" are used with the same meaning.

In one embodiment of the present invention, the waste containing heavy metals is not particularly limited as long as it contains heavy metals, and may be, for example, industrial waste, household waste, etc. The heavy metals are heavy metals that can be rendered harmless by reacting with carbon dioxide (CO ₂ ) in the concentrated exhaust gas described below, and are, for example, lead (Pb) and calcium (Ca).

In the incineration apparatus, the waste containing the heavy metals is burned, and the resulting incineration ash contains residual heavy metals. In this waste treatment facility, as described below, concentrated exhaust gas containing a high concentration of _CO2 is supplied to the incineration apparatus as circulating exhaust gas without dilution. Therefore, the heavy metals remaining in the incineration ash react sufficiently with the _CO2 contained in the concentrated exhaust gas, and are rendered harmless.

Here, in conventional waste treatment facilities, flue gas having a lower _CO2 concentration than the concentrated flue gas is used as the circulating flue gas.

Therefore, when the same waste is to be treated, the waste treatment method using this waste treatment equipment requires a smaller amount of circulating exhaust gas to render the heavy metals harmless than a waste treatment method using conventional waste treatment equipment. Therefore, when treating waste containing heavy metals, this waste treatment equipment can sufficiently reduce the amount of circulating exhaust gas required to sufficiently react between the heavy metal components in the incineration ash and the carbon dioxide in the circulating exhaust gas. This makes it possible to sufficiently reduce the load on the circulation equipment without adversely affecting the conditions inside the furnace.

In addition, in the waste treatment method using this waste treatment facility, the _CO2 contained in the concentrated exhaust gas supplied to the incineration device as a circulating exhaust gas is contained in the combustion exhaust gas discharged from the incineration device, and the _CO2 that has not reacted with the heavy metals is contained in the combustion exhaust gas. Therefore, compared to the waste treatment method using the conventional waste treatment facility, a circulating exhaust gas having a higher concentration of _CO2 circulates through the waste treatment facility. Therefore, the combustion exhaust gas contains a higher concentration of _CO2 . Therefore, the waste treatment method using this waste treatment facility can reduce the load on the capture facility when capturing _CO2 from the combustion exhaust gas.

In this specification, the term "combustion exhaust gas" refers to the gas (gas) discharged from the incineration apparatus, including the gas generated by burning the waste in the incineration apparatus. The "combustion exhaust gas" may also include, for example, the excess air not used for combustion, and the "circulating exhaust gas" described below, which does not react with the heavy metals and is discharged from the incineration apparatus as it is. In addition, in this specification, the term "concentrated exhaust gas" refers to a gas (gas) in which the CO ₂ in the "combustion exhaust gas" is concentrated by the concentrating device, and the CO ₂ concentration is higher than the CO ₂ concentration of the "combustion exhaust gas". In addition, in this specification, the term "circulating exhaust gas" refers to at least a part of the concentrated exhaust gas obtained from the concentrating device, and is supplied to the incineration apparatus by the concentrated exhaust gas supplying device.

Figures 1 to 3 are schematic diagrams showing the configuration of a waste treatment facility according to one embodiment of the present invention. In Examples 1 and 2 described below, it was assumed that the waste treatment facility shown in Figure 1 was used, in Example 3 in Figure 2, and in Example 4 in Figure 3. In the figures, 100 is the waste treatment facility, 10 is the incineration device, 20 is the concentrating device, and 30 is the concentrated gas supply device.

The incineration apparatus 10 comprises a combustion chamber 1 for burning waste, a waste inlet 2 for feeding the waste into the combustion chamber, an air supply port 3 (3a-3c) for feeding air for combustion into the combustion chamber, a secondary combustion chamber 4 for secondary combustion of the unburned combustible gas generated in the combustion chamber 1, and an incineration ash outlet 5 for removing the incineration ash obtained as a result of the combustion of the waste. Here, "secondary combustion" means heating the unburned combustible gas to generate the combustion exhaust gas from the unburned combustible gas. The incineration apparatus also comprises a concentrated exhaust gas supply port 6 for receiving at least a portion of the concentrated exhaust gas. In Figures 1-3, the arrow pointing to the waste inlet 2 indicates the feeding of waste.

Furthermore, the incineration apparatus 10 is equipped with an exhaust gas exhaust pipe 7 for sending the combustion exhaust gas to the concentrating apparatus 20. The air supply port 3 is connected to an air supply means 8. The air supply means 8 is, for example, an air supply line (pipe). By using the air supply means 8, air can be supplied to the incineration apparatus 10 through the air supply port 3. The air supplied to the incineration apparatus 10 is not particularly limited, and for example, air present in the atmosphere can be used as it is.

Here, the air introduced into the combustion chamber 1 can be used not only to burn the waste, but also to cool the combustion chamber 1 and to agitate the waste.

The incineration apparatus 10 may have multiple combustion chambers. When the incineration apparatus 10 has multiple combustion chambers, for example, in a combustion chamber located near the waste inlet 2 (upstream side), the waste undergoes thermal decomposition and partial oxidation, and the combustible gas generated by the thermal decomposition is combusted with solids to obtain a primary combustion product. The primary combustion product then moves to a combustion chamber located near the incineration ash outlet 5 (downstream side), and the unburned content in the primary combustion product is completely combusted in the downstream combustion chamber, and incineration ash is obtained as a combustion product. Therefore, in this case, in order to more efficiently detoxify the heavy metals contained in the incineration ash, it is preferable to supply at least a portion of the concentrated exhaust gas to the combustion chamber from which the incineration ash is obtained. Here, the unburned content in the primary combustion product is a solid content different from the incineration ash.

When the incineration apparatus 10 has multiple combustion chambers, each of the multiple combustion chambers may have an air supply port 3. In Figures 1 to 3, combustion chambers 1a to 1c have air supply ports 3a to 3c, respectively. Furthermore, the amount of air supplied from each air supply port of the multiple combustion chambers may be the same for all combustion chambers, or may be different. The amount of air supplied from each air supply port of the multiple combustion chambers may be appropriately adjusted so that the combustion taking place in each combustion chamber proceeds sufficiently.

Specifically, it is preferable to use a grate-type incinerator as the incineration device 10 equipped with the multiple combustion chambers. The grate-type incinerator has a drying grate, a combustion grate, and a post-combustion grate, and these grates are driven by a grate drive mechanism to incinerate the waste while sending it through.

The configuration of the grate incinerator will now be described with reference to FIG. 1. In addition, in FIGS. 1 to 3 and 5, when the incineration apparatus 10 is the grate incinerator, the grate incinerator is represented by the component number "10", the drying grate is represented by the component number "1a", the combustion grate is represented by the component number "1b", and the post-combustion grate is represented by the component number "1c". The drying grate 1a, the combustion grate 1b, and the post-combustion grate 1c correspond to the combustion chamber.

For example, at the bottom of the combustion chamber of the grate-type incinerator 10, there are provided drying grate 1a, combustion grate 1b, and post-combustion grate 1c, which are grates (stokers) that burn the waste while moving it toward the downstream side. Below the waste inlet 2 of the grate-type incinerator 10, there is provided an extruder that extrudes and supplies the waste fed from the waste inlet 2 onto the drying grate 1a, combustion grate 1b, and post-combustion grate 1c, which are grates of the combustion chamber 1. The grates are provided in the order of drying grate 1a, combustion grate 1b, and post-combustion grate 1c, from the side closest to the waste inlet 2. Of these, a layer of waste is formed mainly on the drying grate 1a and combustion grate 1b, and a layer of incineration ash is formed on the post-combustion grate 1c.

In the drying grate 1a, the waste is dried and ignited. In the combustion grate 1b, the waste is pyrolyzed and partially oxidized. On the post-combustion grate 1c, ignition is carried out to completely burn the unburned solids in the waste. As a result, a layer of incineration ash is formed on the post-combustion grate 1c after the waste is completely burned. The incineration ash is discharged from the incineration ash outlet 5 of the grate incinerator 10.

In one embodiment of the present invention, the air supply ports 3a-3c of the grate incinerator 10 may be provided below the drying grate 1a, the combustion grate 1b, and the post-combustion grate 1c. The grate incinerator 10 may be provided with an air supply means 8 that supplies air for combustion through the air supply ports 3a-3c. The air supply means 8 may be, for example, an air supply line or an air supply line equipped with a blower.

As described above, it is preferable that at least a part of the concentrated exhaust gas is supplied to the combustion chamber where the incineration ash is obtained. Here, the combustion chamber where the incineration ash is obtained is the post-combustion grate 1c, and the incineration ash is obtained in the lower part of the post-combustion grate 1c. Therefore, it is preferable that the concentrated exhaust gas supply device 30 that supplies at least a part of the concentrated exhaust gas to the incineration device without diluting it is a device that supplies at least a part of the concentrated exhaust gas to the lower part of the post-combustion grate 1c. In Figures 1 to 3, at least a part of the concentrated exhaust gas is supplied to the concentrated exhaust gas supply port 6 of the post-combustion grate 1c. In this case, CO ₂ contained in at least a part of the concentrated exhaust gas and heavy metals contained in the incineration ash react sufficiently, so that the heavy metals can be sufficiently detoxified.

The heavy metals are rendered harmless means that the incineration ash satisfies at least one of the following conditions (a) to (d).

(a) The inorganic carbon concentration in the incineration ash is 0.5% by dry weight or more.

(b) The calcium carbonate concentration in the incineration ash is 4.0% by dry weight or more.

(c) The calcium oxide concentration in the incineration ash is 5.0% by dry weight or less.

(d) The pH of the eluate from the incineration ash is 12.0 or less.

The eluate is obtained by conducting a lead elution test on incinerated ash based on the test method set out in the Ministry of the Environment Notification No. 46, Environmental Standards for Soil Contamination. Furthermore, satisfying the requirement of (d) above means lowering the pH of the incinerated ash and bringing it into the poorly soluble range for lead.

Here, in the waste treatment method using this waste treatment facility, if the contact time between the incineration ash and the circulating exhaust gas is increased, the inorganic carbon concentration in (a) increases, and the calcium carbonate concentration in (b) increases. Also, the calcium oxide concentration in (c) decreases, and the pH of the eluate in (d) decreases. Here, the contact time is, for example, the time that the incineration ash is retained on the post-combustion grate 1c when a grate-type incinerator 10 is used.

The combustion conditions in the incineration device 10, such as the combustion temperature and combustion time, are not particularly limited as long as the waste can be burned and the incineration ash and the combustion exhaust gas can be obtained. The combustion conditions can be adjusted appropriately depending on the type and amount of the waste. For example, the combustion temperature is preferably 600°C to 1200°C, and more preferably 800°C to 1000°C. The combustion time is preferably 0.5 hours to 4 hours, and more preferably 1 hour to 3 hours. The combustion temperature means the temperature inside the combustion chamber in the incineration device 10. The combustion time is the time from when the waste is put into the combustion chamber 1 to when the incineration ash is discharged from the incineration ash discharge port 5.

[Concentration device]
The concentrating device 20 in this waste treatment facility 100 is a device that concentrates the CO ₂ in the combustion exhaust gas discharged from the incineration device 10 .

The waste treatment facility 100 may have one concentrating device as shown in FIG. 1, or may have two concentrating devices as shown in FIGS. 2 and 3 (concentrating devices 20, 24), or may have three or more. Incidentally, having two or more concentrating devices means that the waste treatment method using the waste treatment facility 100 is carried out through two or more stages of concentration processes. Also, when the waste treatment facility 100 has two or more concentrating devices, concentrated exhaust gas is supplied to the concentrated gas supply device 30 from the most downstream concentrating device.

The concentrator 20 is connected to the exhaust gas discharge pipe 7 of the incineration device 10, and is also connected to the concentrated exhaust gas supply port 6 via a concentrated gas supply device 30. In addition, in this waste treatment facility 100 that includes two or more concentrators, each of the two or more concentrators is connected via a conduit 9. For example, in the waste treatment facility shown in Figures 2 and 3, the concentrator 20 and the concentrator 24 are connected via a conduit 9.

Here, when the number of concentrating devices is large, the _CO2 contained in the combustion exhaust gas is further concentrated each time it passes through a plurality of concentrating devices, and concentrated exhaust gas with a higher _CO2 concentration can be generated. As a result, when treating waste containing heavy metals, the supply amount of circulating exhaust gas required to sufficiently react the heavy metal components in the incineration ash with the carbon dioxide in the circulating exhaust gas can be significantly reduced compared to the case of using conventional waste treatment equipment. Therefore, it is preferable that the number of concentrating devices is two or more.

On the other hand, if the number of concentrating devices is excessively large, the waste treatment facility 100 may become huge. From this perspective, it is preferable that the number of concentrating devices is four or less, and more preferably three or less.

The concentrating device 20 is not particularly limited as long as it can concentrate the _CO2 in the combustion exhaust gas. Examples of the concentrating device 20 include a device equipped with a _CO2 separation membrane and a device equipped with a substance capable of adsorbing and/or absorbing _CO2 and desorbing CO2. Hereinafter, the substance will be referred to as "substance X".

Concentration of _CO2 using a device equipped with a _CO2 separation membrane is generally more energy-efficient than concentration of _CO2 using the substance X. Therefore, from the viewpoint of reducing the energy required for the waste treatment method using the waste treatment facility 100 and miniaturizing the facility, it is preferable that the concentrator 20 is a device equipped with a _CO2 separation membrane.

The device having the _CO2 separation membrane may be, for example, a device having a configuration shown in Fig. 4. Fig. 4 is a schematic diagram showing an embodiment of a concentrating device 20 using a _CO2 separation membrane. In Fig. 4, 21 is a _CO2 separation membrane, 22 is an inlet part of the feed gas in the concentrating device 20, and 23 is a permeation part of the feed gas. In the figure, a represents the feed gas, b represents the permeation gas, and c represents the non-permeation gas.

Of the components contained in the supply gas a shown in Fig. 4, _CO2 selectively passes through the _CO2 separation membrane 21 and moves to the permeation section 23 shown in Fig. 4. As a result, the concentration of _CO2 increases in the permeation section 23, and the permeation gas b shown in Fig. 4 is prepared. Note that the non-permeation gas c shown in Fig. 4 has a lower _CO2 concentration than the supply gas a.

The _CO2 separation membrane 21 is not particularly limited, and for example, an organic membrane, an inorganic membrane, an ionic liquid membrane, etc. can be used. When the waste treatment facility 100 includes a plurality of concentrating devices 20 each including a _CO2 separation membrane 21, the _CO2 separation membranes 21 in each of the concentrating devices 20 may be the same type of _CO2 separation membrane or different types of _CO2 separation membranes.

In addition, the concentrating device 20 including the substance X can use the substance X instead of the _CO2 separation membrane in the concentrating device 20 having the configuration shown in FIG. 4, for example. In this case, among the components contained in the supply gas a shown in FIG. 4, _CO2 is selectively adsorbed and/or absorbed by the substance. Then, the adsorbed and/or absorbed _CO2 is released to the permeation section 23 in FIG. 4. As a result, the concentration of _CO2 increases in the permeation section 23, and the permeation gas b shown in FIG. 4 is prepared. Note that the non-permeation gas c shown in FIG. 4 has a lower concentration of _CO2 than the supply gas.

The substance X is not particularly limited, and may be, for example, amine, zeolite, activated carbon, or the like. When the waste treatment facility 100 includes a plurality of concentrating devices 20 each including the substance X, the substance X in each of the concentrating devices 20 may be the same type of substance or different types of substances.

Here, when the waste treatment facility 100 is a facility equipped with one concentrating device 20 shown in FIG. 1, the gas a supplied to the concentrating device 20 is the combustion exhaust gas, and the permeating gas b permeating the concentrating device 20 is the concentrated exhaust gas. In addition, at least a part of the concentrated exhaust gas is introduced as a circulating exhaust gas into the incineration device 10, preferably into the combustion chamber from which the incineration ash is obtained, for example, into the post-combustion grate 1c when the incineration device 10 is a grate-type incinerator, without dilution. On the other hand, a remaining part of the concentrated exhaust gas is introduced into the device shown in "A" in FIG. 1, and CO ₂ can be recovered. The device shown in "A" is not particularly limited and may be a device known to those skilled in the art used for recovering CO _2. In addition, a part of the concentrated exhaust gas may be discharged to the outside of the concentrating device 20, as shown by the arrow extending to the right from the concentrating device 20 in FIGS. 1 to 3.

When the waste treatment facility 100 is a facility equipped with two concentrators as shown in Fig. 2, the gas (supply gas) a supplied to the upstream concentrator 20 directly connected to the exhaust gas discharge pipe 7 is the combustion exhaust gas. At this time, the permeation gas b that has permeated the concentrator 20 is supplied as a supply gas to the downstream concentrator 24. The concentrator 24 is, like the concentrator 20, an apparatus equipped with a _CO2 separation membrane, an apparatus equipped with the substance X, or the like. The configuration of the concentrator 24 is the same as that of the concentrator 20 described above.

The permeable gas that has permeated the concentrating device 24 is the concentrated exhaust gas. At least a part of the concentrated exhaust gas is introduced as a circulating exhaust gas into the incineration device 10, preferably into the combustion chamber from which the incineration ash is obtained, for example, into the post-combustion grate 1c when the incineration device 10 is a grate-type incinerator, via the concentrated exhaust gas supply device 30. Meanwhile, the remaining part of the concentrated exhaust gas is introduced into the capture equipment shown in "A" in FIG. 2, similar to the equipment shown in FIG. 1, and CO ₂ can be captured. The capture equipment shown in "A" is not particularly limited and may be a capture equipment known to those skilled in the art for use in capturing CO ₂ .

When the waste treatment facility 100 is a facility equipped with two concentrators as shown in Fig. 3, the gas a supplied to the upstream concentrator 20 is the combustion exhaust gas, as in the facility shown in Fig. 2. At this time, the permeable gas b that has permeated the concentrator 20 is supplied to the downstream concentrator 24 as a supply gas. In the facility shown in Fig. 3, the non-permeable gas in the downstream concentrator 24 is used as the concentrated exhaust gas. Here, the non-permeable gas has a lower _CO2 concentration than the gas supplied from the concentrator 20 to the concentrator 24, but the _CO2 concentration is sufficiently high due to the concentration by the upstream concentrator 20.

Therefore, the apparatus shown in FIG. 3 can also reduce the amount of circulating exhaust gas required to sufficiently react the heavy metal components in the incineration ash with the carbon dioxide in the circulating exhaust gas. Furthermore, in the apparatus shown in FIG. 3, the permeable gas that has permeated the concentrator 24 can be introduced into the capture equipment shown in "A" in FIG. 3, and CO ₂ can be captured. The capture equipment shown in "A" is not particularly limited and may be a capture equipment known to those skilled in the art for use in capturing CO _2. The CO ₂ concentration of the permeable gas that has permeated the concentrator 24 is higher than the CO ₂ concentration in the non-permeable gas. Therefore, the apparatus shown in FIG. 3 can capture CO ₂ from the combustion exhaust gas while reducing the load on the capture equipment compared to the case of capturing CO ₂ from a conventional waste treatment facility.

In the concentrator, the CO ₂ concentration of the permeable gas is preferably at least twice as high as the CO ₂ concentration of the supply gas, and more preferably at least three times as high. In addition, the CO ₂ concentration of the non-permeable gas is preferably at most half as high as the CO ₂ concentration of the supply gas, and more preferably at most one-quarter as high. When the CO ₂ concentrations of the permeable gas and non-permeable gas are within the above-mentioned range relative to the CO ₂ concentration of the supply gas, the CO ₂ concentration of the circulating exhaust gas in the waste treatment facility 100 and the CO ₂ concentration of the combustion exhaust gas discharged from the incineration device 10 can be made higher. As a result, in the waste treatment method using the waste treatment facility 100, the supply amount of the circulating exhaust gas required to sufficiently react the heavy metal components in the incineration ash with the carbon dioxide in the circulating exhaust gas can be further reduced. In addition, CO ₂ can be recovered from the combustion exhaust gas while reducing the load on the recovery facility compared to the case of recovering CO ₂ from a conventional waste treatment facility.

The _CO2 concentrations of the permeate gas and non-permeate gas relative to the _CO2 concentration of the feed gas can be controlled by appropriately adjusting the selectivity in the concentrator and the conditions for concentrating _CO2 .

The selectivity in the concentrator is represented, for example, by the ratio of the rates at which two of the compounds contained in the supply gas permeate the _CO2 separation membrane (permeance ratio). The selectivity is also represented, for example, by the ratio of the rates at which two of the compounds contained in the supply gas are adsorbed and/or absorbed by the substance X. Specific examples of the ratio of the two compounds include the ratios of _CO2 / _N2 , _CO2 / _O2 , and _CO2 / _H2O . The selectivity in the concentrator may vary depending on the type of the _CO2 separation membrane and the substance X.

The conditions for concentrating the _CO2 include, for example, the pressure at which the supply gas is supplied to the concentrator (hereinafter referred to as the "supply pressure"). The conditions also include the ratio of the pressure of the supply gas to the permeable gas in the concentrator (permeable gas pressure/supply gas pressure) (hereinafter referred to as the "pressure ratio"). The method for controlling the supply pressure and the pressure ratio includes, for example, a method of controlling the pressure of the supply gas and/or the pressure of the permeable gas by installing a pressure valve or the like at the supply site of the supply gas and/or the discharge site of the permeable gas in the concentrator.

[Concentrated exhaust gas supply device]
The concentrated exhaust gas supplying device in this waste treatment facility is a device that supplies, as a circulating exhaust gas, at least a part of the concentrated exhaust gas obtained from the device for preparing the concentrated exhaust gas to the incineration device without diluting it.

In detail, the concentrated exhaust gas supplying device is a device that connects the concentrating device and the incineration device, and supplies at least a portion of the concentrated exhaust gas to the incineration device by passing at least a portion of the concentrated exhaust gas through the device. Figures 1 to 3 show how the concentrated exhaust gas supplying device 30 connects the concentrating device 20 or 24, the combustion chamber 1c, and, for example, the post-combustion grate 1c when the incineration device 10 is a grate-type incinerator.

The concentrated exhaust gas supply device is not particularly limited and may be, for example, a conduit. Hereinafter, at least a portion of the concentrated exhaust gas is also referred to as "circulated exhaust gas."

The concentrated exhaust gas supplying device supplies the circulating exhaust gas to the incineration device without diluting it. In this specification, "supplying the circulating exhaust gas to the incineration device without diluting it" means the following. For example, as shown in Figures 1 and 2, when the permeation gas obtained in the concentration device is the concentrated exhaust gas, it means that at least a part of the permeation gas is discharged to the concentrated exhaust gas supplying device without diluting the permeation gas in the permeation section. "Without diluting the permeation gas in the permeation section" means that the permeation gas is not mixed with any gas other than the permeation gas in the permeation section.

As shown in FIG. 3, when the non-permeable gas in the downstream concentrator 24 is used as the concentrated exhaust gas, this means that at least a portion of the non-permeable gas in the downstream concentrator is discharged to the concentrated exhaust gas supply device without diluting it. "Without diluting the non-permeable gas" means that the non-permeable gas is not mixed with any gas other than the non-permeable gas.

In addition, "supplying to the incineration apparatus without dilution" also means that at least a part of the concentrated exhaust gas (circulating exhaust gas) is discharged from the concentrator and does not mix with gases other than the "circulating exhaust gas" when it moves through the concentrated exhaust gas supplying apparatus. That is, the circulating exhaust gas preferably passes through the concentrated exhaust gas supplying apparatus with its _CO2 concentration remaining the same as the _CO2 concentration of the concentrated exhaust gas obtained in the permeation section, or with its _CO2 concentration remaining the same as the CO2 concentration of the non-permeating gas. Examples of gases other than the permeating gas, gases other than the non-permeating gas, and gases other than the "circulating exhaust gas" include sweep gas, etc.

When the incineration apparatus has multiple combustion chambers, as described above, in order to more efficiently detoxify the heavy metals contained in the incineration ash, it is preferable to supply the circulating exhaust gas to the combustion chamber from which the incineration ash is obtained. Therefore, it is preferable that the concentrated exhaust gas supply device is connected to the combustion chamber from which the incineration ash is obtained. Specifically, when the incineration apparatus is a grate-type incinerator, it is preferable that the concentrated exhaust gas supply device is connected below the post-combustion grate. For example, in Figures 1 to 3, the concentrated exhaust gas supply device 30 is connected to the lower part of the post-combustion grate 1c.

The concentrated exhaust gas supplying device may be equipped with a member for controlling the flow rate of the circulating exhaust gas passing through the concentrated exhaust gas supplying device. Examples of such members include a blower. By using such members appropriately, the rate at which the circulating exhaust gas is supplied to the incineration device can be appropriately adjusted so that the reaction between the heavy metal components in the incineration ash and the carbon dioxide in the circulating exhaust gas is sufficiently carried out.

The suitable flow rate of the circulating exhaust gas varies depending on various conditions such as the concentration of heavy metals in the incineration ash, the _CO2 concentration in the circulating exhaust gas, the temperatures of the incineration ash and the circulating exhaust gas, etc. The suitable flow rate of the circulating exhaust gas, i.e., the suitable supply rate of the circulating exhaust gas to the incineration apparatus, is, for example, 100 ^Nm3 /ton (waste) to 2000 ^Nm3 /ton (waste).

The concentrated exhaust gas supplying device may be equipped with a member for controlling the temperature of the circulating exhaust gas passing through the concentrated exhaust gas supplying device. Examples of such members include a heater. By using such members appropriately, the temperature of the circulating exhaust gas supplied to the incineration device can be appropriately adjusted so that the reaction between the heavy metal components in the incineration ash and the carbon dioxide in the circulating exhaust gas is sufficiently carried out.

The temperature of the circulating exhaust gas supplied to the incineration apparatus varies depending on various conditions such as the concentration of heavy metals in the incineration ash, the _CO2 concentration in the circulating exhaust gas, the temperature of the incineration ash, the flow rate of the circulating exhaust gas, etc. A suitable temperature of the circulating exhaust gas supplied to the incineration apparatus is, for example, 130°C to 250°C.

The concentrated exhaust gas supply device may merge with the air supply means, for example, an air supply line (pipe), before being connected to the incineration device. In that case, the air supply port of the incineration device and the concentrated exhaust gas supply port are the same, and a mixture of air and the circulating exhaust gas is supplied to the incineration device from there.

[Embodiment 2: Waste treatment method]
The waste treatment method according to the second embodiment of the present invention (hereinafter also referred to as "the present waste treatment method") includes an incineration process in which waste containing heavy metals is burned using an incineration apparatus to generate incineration ash and combustion exhaust gas, a concentration process in which _CO2 in the combustion exhaust gas generated in the incineration process is concentrated, and a supply process in which at least a portion of the concentrated exhaust gas obtained in the concentration process is supplied to the incineration apparatus as a circulating exhaust gas without being diluted.

This waste treatment method can be carried out using this waste treatment equipment. Therefore, as shown in the above-mentioned "Embodiment 1: Waste Treatment Equipment" section, this waste treatment method requires less circulating exhaust gas to detoxify heavy metals contained in the waste to be treated, compared to conventional waste treatment methods. Therefore, when treating waste containing heavy metals, the method can significantly reduce the amount of circulating exhaust gas required to sufficiently react between the heavy metal components in the incineration ash and the carbon dioxide in the circulating exhaust gas. Therefore, it is possible to significantly reduce the load on the circulating equipment used without adversely affecting the internal conditions of the furnace used.

In addition, in the method, the _CO2 contained in the concentrated exhaust gas supplied to the incineration process as a circulating exhaust gas is unreacted with the heavy metals and is contained in the combustion exhaust _gas discharged from the incineration process. Therefore, compared to the conventional waste treatment method, the circulating exhaust gas having a higher concentration of _CO2 circulates in the waste treatment facility used, and the resulting combustion exhaust gas contains a higher concentration of _CO2 . Therefore, the present waste treatment method can recover _CO2 from the combustion exhaust gas while reducing the load on the recovery facility compared to the case of recovering _CO2 from a conventional waste treatment facility.

The components of the waste treatment facility described in the above section "Embodiment 1: Waste Treatment Facility" can be used as appropriate for the components of the waste treatment method. The incineration process can be performed by the incineration device, the concentration process can be performed by the concentration device, and the supply process can be performed by the concentrated exhaust gas supply device.

The concentration step is preferably a step carried out using a _CO2 separation membrane. The _CO2 separation membrane is as described above.

The incineration process is preferably carried out using a grate-type incinerator that has a drying grate, a combustion grate, and a post-combustion grate, and incinerates the waste while driving these grates with a grate drive mechanism. The grate-type incinerator and its operation are as described above.

The concentration process is preferably carried out through two or more stages. As described above, the concentration process of two or more stages means that the concentration process is carried out using two or more concentration devices, such as the waste treatment facilities shown in Figures 2 and 3.

[summary]
One embodiment of the present invention may include the following inventions [1] to [8].

[1] An incineration apparatus for burning waste containing heavy metals to generate incineration ash and combustion exhaust gas;
A concentrating device for concentrating CO ₂ in the combustion exhaust gas discharged from the incineration device;
A concentrated exhaust gas supplying device that supplies at least a portion of the concentrated exhaust gas obtained from the concentrating device to the incineration device as a circulating exhaust gas without diluting it;
Waste treatment facilities, including:

[2] The waste treatment facility according to [1], wherein the concentrating device is a device equipped with a _CO2 separation membrane.

[3] The waste treatment facility according to [1] or [2], in which the incineration device is a device equipped with a grate-type incinerator having a drying grate, a combustion grate, and a post-combustion grate, and which incinerates waste while driving these grates with a grate drive mechanism.

[4] The waste treatment facility according to any one of [1] to [3], comprising two or more of the concentrating devices.

[5] an incineration step of burning waste containing heavy metals using an incineration device to generate incineration ash and combustion exhaust gas;
A concentration step of concentrating CO ₂ in the combustion exhaust gas generated in the incineration device step;
A supply step of supplying at least a portion of the concentrated exhaust gas obtained in the concentration step to the incineration apparatus as a circulating exhaust gas without dilution;
A waste treatment method comprising:

[6] The waste treatment method according to [5], wherein the concentration step is carried out using a _CO2 separation membrane.

[7] The waste treatment method according to [5] or [6], wherein the incineration apparatus used in the incineration step is a grate-type incinerator having a drying grate, a combustion grate, and a post-combustion grate, and these grates are driven by a grate drive mechanism to incinerate the waste while sending it therethrough.

[8] The waste treatment method according to any one of [5] to [7], in which the concentration step is carried out through two or more stages of the concentration step.

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples.

[Example 1]
As shown in Fig. 1, a waste treatment facility was assumed in which a grate-type incinerator, a concentrating device, and a concentrated exhaust gas supplying device were connected as the respective components of the incineration device. Specifically, it was assumed that a waste treatment facility using a grate-type incinerator was used as the incineration device 10 in the waste treatment facility 100 shown in Fig. 1.

The concentrating device 20 shown in Fig. 1 is a concentrating device in which the yield of _CO2 represented by the following formula (1) is 80%. The recovered gas described below is the gas present at position A in Figs. 1 to 3 and 5. The combustion exhaust gas described below is the gas generated when the waste is assumed to be completely combusted, that is, the theoretical combustion gas described below.

(Flow rate of CO ₂ in the recovered gas [kmol/hour])/(Flow rate of CO ₂ in the combustion exhaust gas [kmol/hour]) (1)
In formula (1), the concentration of _CO2 in the recovered gas present at position A in FIG. 1 was used as the concentration of _CO2 in the recovered gas, and the concentration of _CO2 in the theoretical combustion gas described below was used as the concentration of _CO2 in the combustion exhaust gas.

Furthermore, the material selectivity in the concentrator 20 and the conditions (supply pressure and pressure ratio) when concentrating _CO2 using the concentrator 20 were as shown in Table 1 below. The supply pressure is the pressure of the combustion exhaust gas when it is supplied to the concentrator 20. The pressure ratio is calculated by (pressure of the recovery gas/pressure of the combustion exhaust gas).

Using the waste treatment facility 100 assumed as described above, a simulation was carried out in which waste treatment was carried out under the following conditions.
<Conditions>
The waste to be treated was assumed to have the composition shown in Table 2 below. The composition is expressed by the weight percentage of moisture, and the weight percentages of carbon, hydrogen, and oxygen as combustible matter. The waste was also assumed to contain 50 ppm of lead as a heavy metal.

The supply air from the air supply line 8 was assumed to be dry air. The dry air was composed of 79% by volume of nitrogen ( _N2 ) and 21% by volume of oxygen ( _O2 ).
The combustible matter in the waste was assumed to be completely combusted. The theoretical composition of the combustion exhaust gas (hereinafter referred to as the "theoretical combustion gas") obtained when one ton of the waste was completely combusted is shown in Table 3 below.

The air ratio was set to 1.4. The air ratio is a value calculated by using the theoretical amount of air (volume) required for complete combustion of the waste and the amount of air supplied (volume) as (amount of air supplied)/(theoretical amount of air required for complete combustion of the waste). The theoretical amount of air was calculated assuming that the content of oxygen in the air is 21% by volume relative to the total volume of the air.
Of the air supplied to the grate incinerator 1, 20% by volume was supplied below the post-combustion grate 1c, and the remaining air was supplied below the drying grate 1a and below the combustion grate 1b.
The temperatures of the combustion exhaust gas discharged from the grate incinerator 1, the concentrated exhaust gas discharged from the concentrating device 20, and the circulating exhaust gas supplied to the grate incinerator 1 were each assumed to be 40°C.
- It is assumed that all condensed water generated is removed.
The volume of the circulating flue gas was assumed to be an amount such that (flow rate of _CO2 in the circulating flue gas [kmol/hour])/(flow rate of _CO2 in the concentrated flue gas [kmol/hour]) = 0.2 (20%).
The membrane separation model was assumed to be completely mixed. The completely mixed condition specifically means that the gas concentrations of the feed gas a, the permeable gas b, and the non-permeable gas c shown in Fig. 4 are uniform in the concentrator 20. The feed gas a is the combustion exhaust gas, and the permeable gas b is the concentrated exhaust gas.

[Example 2]
Instead of the concentrator described in Example 1, it was assumed to use a concentrator equipped with a material capable of adsorbing and/or absorbing and desorbing _CO2 , with a _CO2 yield of 80% and a yield of components other than _CO2 of 1%. A simulation of waste treatment was performed under the same conditions as in Example 1, assuming the same waste treatment facility as in Example 1.

[Example 3]
A waste treatment simulation was carried out under the same conditions as in Example 1, except that the waste treatment facility shown in FIG. 1 was replaced with the waste treatment facility shown in FIG.

[Example 4]
A simulation of waste treatment was carried out under the same conditions as in Example 1, except that the waste treatment facility shown in FIG. 1 was replaced with the waste treatment facility shown in FIG.

[Comparative Example 1]
As shown in Fig. 5, the waste treatment facility shown in Fig. 1 was replaced with a waste treatment facility 100' that did not include a concentrator, and the combustion exhaust gas was used as the circulating exhaust gas without being concentrated, and the volume of the combustion exhaust gas was assumed to be 1000 ^Nm3 per ton of the waste. A simulation of waste treatment was carried out under the same conditions as in Example 1, except for these points.

[result]
The results of the simulations for Examples 1 to 4 and Comparative Example 1 are shown in Table 4 below.

"Post-combustion air CO ₂ concentration" in Table 4 means the CO ₂ concentration in the mixed gas of the air supplied below the post-combustion grate 1c and the concentrated exhaust gas, i.e., the circulating exhaust gas. "Flow rate of circulating exhaust gas" in Table 4 means the total amount of circulating exhaust gas supplied below the post-combustion grate 1c. Here, in the simulations in Examples 1 to 4 and Comparative Example 1, the heavy metals are detoxified by the CO ₂ contained in the circulating exhaust gas. Therefore, the "flow rate of circulating exhaust gas" is the amount of circulating exhaust gas required to sufficiently react the heavy metals with the CO ₂ in the circulating exhaust gas. "CO ₂ capture concentration" and "CO ₂ capture flow rate" in Table 4 mean the CO ₂ concentration and the flow rate of the CO ₂ in the capture gas (gas present at position A in Figures 1 to 3 and 5), respectively. Note that the "post-combustion air CO ₂ concentration" and "CO ₂ capture concentration" were evaluated in volume percent in a dry state.

As mentioned above, the waste treatment device and waste treatment method described in Examples 1 to 4 correspond to this waste treatment facility and this waste treatment method.

As shown in Table 4, the waste treatment device and waste treatment method described in Examples 1 to 4 require a smaller supply of circulating exhaust gas to sufficiently react the heavy metals with CO ₂ in the circulating exhaust gas, compared to the waste treatment device and waste treatment method described in Comparative Example 1. In addition, the waste treatment device and waste treatment method described in Examples 1 to 4 have a higher "CO ₂ recovery concentration" than the waste treatment device and waste treatment method described in Comparative Example 1, and it is shown that CO ₂ can be recovered while reducing the load on the recovery equipment compared to when CO ₂ is recovered from a conventional waste treatment facility.

From the above, it was found that the present waste treatment facility and the present waste treatment method can greatly reduce the amount of circulating exhaust gas required to sufficiently react the heavy metal components in the incineration ash with the carbon dioxide in the circulating exhaust gas when treating waste containing heavy metals. As a result, it was found that the load on the circulating facility can be greatly reduced without adversely affecting the condition inside the furnace, and that _CO2 can be captured while reducing the load on the capture facility compared to when _CO2 is captured from a conventional waste treatment facility.

The waste treatment device according to one embodiment of the present invention and the waste treatment method according to one embodiment of the present invention can be suitably used for treating waste containing heavy metals.

REFERENCE SIGNS LIST 100 Waste treatment equipment 100' Waste treatment equipment 10 Incineration equipment, grate type incinerator 20 Concentration equipment 24 Concentration equipment 30 Concentrated gas supply equipment 1 Combustion chamber 1a Combustion chamber, drying grate 1b Combustion chamber, combustion grate 1c Combustion chamber, post-combustion grate 2 Waste inlet 3 Air supply port 3a Air supply port 3b Air supply port 3c Air supply port 4 Secondary combustion chamber 5 Incineration ash outlet 6 Concentrated exhaust gas supply port 7 Exhaust gas exhaust pipe 8 Air supply means 9 Conduit 21 _CO2 separation membrane 22 Supply gas inlet 23 Supply gas permeation section a Supply gas b Permeation gas c Non-permeation gas

Claims (8)

An incineration device that burns waste containing heavy metals to generate incineration ash and combustion exhaust gas;
A concentrating device for concentrating CO ₂ in the combustion exhaust gas discharged from the incineration device;
A concentrated exhaust gas supplying device that supplies at least a portion of the concentrated exhaust gas obtained from the concentrating device to the incineration device as a circulating exhaust gas without diluting it;
Waste treatment facilities, including: The waste treatment facility according to claim 1 , wherein the concentrating device is a device equipped with a CO ₂ separation membrane. The waste treatment facility according to claim 1, wherein the incineration device is a grate-type incinerator having a drying grate, a combustion grate, and a post-combustion grate, and these grates are driven by a grate drive mechanism to incinerate the waste while sending it therethrough. The waste treatment facility according to any one of claims 1 to 3, comprising two or more concentrating devices. an incineration step of burning waste containing heavy metals using an incineration device to generate incineration ash and combustion exhaust gas;
A concentration step of concentrating CO ₂ in the combustion exhaust gas generated in the incineration step;
A supply step of supplying at least a portion of the concentrated exhaust gas obtained in the concentration step to the incineration apparatus as a circulating exhaust gas without dilution;
A waste treatment method comprising: The waste treatment method according to claim 5 , wherein the concentration step is carried out using a CO ₂ separation membrane. The waste treatment method according to claim 5, wherein the incineration device used in the incineration process is a grate-type incinerator having a drying grate, a combustion grate, and a post-combustion grate, and these grates are driven by a grate drive mechanism to incinerate the waste while sending it therethrough. The waste treatment method according to any one of claims 5 to 7, wherein the concentration step is carried out through two or more stages of the concentration step.

Images