JP7449714B2 - Waste treatment method - Google Patents

Description

The present invention relates to a waste treatment method in which sludge is mixed with waste such as municipal waste and incinerated.

Conventionally, waste treatment methods have been known in which waste such as municipal waste is mixed with sludge obtained by dehydrating human waste sludge or sewage sludge and incinerated in an incineration facility (hereinafter also referred to as "sludge co-combustion") (for example, Patent Documents 1 to 3, etc.). In order to uniformly mix the municipal waste and sludge, for example, as shown in FIG. A method is known, such as supplying a predetermined amount of sludge from 4 to the waste hopper 3. The garbage and sludge supplied to the garbage hopper 3 are mixed in the process of being conveyed to the incinerator 6 through the shooter 5. The illustrated incinerator 6 is a step-type stoker furnace, and combustion air A is supplied from the lower part of the stoker, and garbage and sludge are burned while being stirred on the stoker. The combustion husks on the stoker are discharged as bottom ash from the bottom of the furnace, and the exhaust gas G produced by the combustion is subjected to treatments such as desalination, desulfurization, dust collection, and denitrification at an exhaust gas treatment facility (not shown).

Japanese Patent Application Publication No. 2000-291935 Japanese Patent Application Publication No. 2000-161635 Japanese Patent Application Publication No. 11-257639

Dehydrated sludge obtained by dehydrating human waste sludge, sewage sludge, etc. has a water content of about 70 to 80% and has a low calorific value of generally 2000 kJ/kg or less, so the combustion temperature drops to 850° C. or less. Therefore, auxiliary combustion is required to maintain stable combustion (furnace temperature), and the sludge co-combustion rate remains at about 18% or less.

When sludge is dried, the lower calorific value becomes 9,000 to 11,000 kJ/kg, making combustion easier, but energy is required for drying.

Furthermore, the sulfur component of sludge (sewage sludge) is contained in the combustibles at a rate of about 0.5% to 1.5%, and it is thought that almost the entire amount is transferred to exhaust gas through combustion. Therefore, as the sludge co-combustion rate increases, the SOx concentration also increases, and a large amount of desulfurization agent is required.

Furthermore, if large chunks of sludge (for example, 50 mm or more) are placed in the furnace, the sludge will coagulate and solidify inside the furnace, resulting in incomplete combustion as the sludge does not dry to the inside, and will be transferred to the incineration bottom ash as unburned matter. However, it causes problems such as bad odors at the landfill site.

Furthermore, sludge with a high water content tends to adhere to the conveyor that transports the sludge into the furnace, resulting in poor transportability.

In view of the above-mentioned conventional problems, the present invention enables in-furnace desulfurization, reduces exhaust gas treatment costs, and increases the sludge co-combustion rate, reducing sludge treatment costs and reducing the amount of fly ash generated. The main purpose of the present invention is to provide a waste treatment method that can reduce fly ash disposal costs.

In order to achieve the above object, the present invention provides a waste treatment method in which sludge is mixed with waste and co-incinerated in an incinerator, and slaked lime is added to the exhaust gas from the incinerator before dust collection. , before the sludge is mixed with waste, collected fly ash is added, and the amount of slaked lime added to the exhaust gas is determined by the concentration of unreacted slaked lime in the fly ash and the amount of fly ash added to the sludge. and adjusted based on.

It is preferable that the amount of the fly ash added to the sludge is adjusted based on the concentration of calcium chloride in the fly ash.

Furthermore, in order to achieve the above object, the present invention provides a waste treatment method in which sludge is mixed with waste and co-incinerated in an incinerator, and slaked lime is added to the exhaust gas from the incinerator before dust collection. The collected fly ash is added to the sludge before it is mixed with the waste, and the amount of the fly ash added to the sludge is adjusted based on the calcium chloride concentration in the fly ash.

Preferably, the fly ash is kneaded with the sludge before being mixed with the waste.

The sludge may be extruded before being mixed with the waste, and the fly ash may be sprinkled on the surface of the sludge extrudate.

Before the sludge is mixed with waste, bottom ash that is discharged from the incinerator is further added, and the bottom ash added to the sludge is sieved to a particle size of 1 mm or less. preferable.

Preferably, slaked lime is further added to the sludge before it is mixed with waste, and the amount of slaked lime added to the exhaust gas is further reduced in accordance with the amount of slaked lime added to the sludge.

Preferably, quicklime is further added to the sludge before it is mixed with waste, and the amount of slaked lime added to the exhaust gas is further reduced in accordance with the amount of slaked lime added to the sludge.

It is preferable that the sludge is extruded and co-fired with the waste before being mixed with the waste so that the maximum width of its cross section is less than or equal to a predetermined dimension.

It is preferable that the sludge is extruded to a maximum cross-sectional width of 3 mm to 50 mm, and then processed into a predetermined length.

Preferably, the sludge is cured after extrusion molding, and the sludge after curing is co-fired with the waste.

According to the present invention, by mixing fly ash with sludge and co-incinerating it with waste, it is possible to perform in-furnace desulfurization with unreacted slaked lime in the fly ash, and the amount of in-furnace desulfurization with unreacted slaked lime in the fly ash can be reduced. , the amount of slaked lime injected into the exhaust gas can be reduced, reducing exhaust gas treatment costs, and the absorption of sludge water by calcium chloride, a reaction product in fly ash, improves the ease of loosening and adhesion of sludge, improving combustion efficiency. It is possible to increase the sludge co-combustion rate, eliminate the need for a sludge dryer, reduce sludge treatment costs, and also melt part of the fly ash by burning the sludge, making it difficult to scatter as fly ash. The amount of fly ash generated can be reduced, and the concentration of heavy metals such as Pb in the fly ash can be reduced, so fly ash disposal costs can be reduced.

1 is a process diagram for explaining one embodiment of a waste treatment method according to the present invention. FIG. 3 is a process diagram for explaining another embodiment of the waste treatment method according to the present invention. FIG. 1 is a schematic diagram showing a waste treatment device used in a conventional waste treatment method.

An embodiment of the waste treatment method according to the present invention will be described with reference to the process diagrams of FIGS. 1 and 2. Note that the same or similar components are denoted by the same reference numerals throughout all the figures and all embodiments.

Waste (municipal garbage, hereinafter also simply referred to as "garbage") is first transported to the garbage pit 1. On the other hand, in the example shown in FIG. 1, the sludge is kneaded and molded with additives such as incineration residue, which will be described later, in a kneader 7 and an extrusion molding machine 8, and then transported to a garbage pit 1 or incinerated by a conveyor or other conveyance means. The waste is put into the waste hopper 3 of the furnace 6. Sludge includes sewage sludge (raw sludge, fire extinguishing sludge, surplus sludge), human waste, etc.

The kneading machine 7 is also called a kneader, and a screw type, paddle type, ribbon type, or the like can be used. The extrusion molding machine 8 can extrude sludge (also referred to as sludge mixture) obtained by kneading additives such as incineration residue into an extruded product having a noodle shape, a groove shape in cross section, or the like. The kneading machine 7 and the extrusion molding machine 8 may be integrated.

The garbage is transported from the garbage pit 1 to the garbage hopper 3 by a garbage crane (see reference numeral 2 in FIG. 3 ). In the garbage pit 1, sludge and garbage are stirred and mixed by a garbage crane. The sludge put into the waste hopper 3 is mixed with waste during the process of being supplied into the incinerator 6. The incinerator 6 can be a known stepped stoker furnace. By co-combusting sludge with garbage, low-melting-point substances such as Na and K contained in the sludge are melted by high-temperature combustion, thereby sealing in elements that easily volatilize at low temperatures and reducing the amount of soot and dust generated.

In the incinerator 6, the garbage and the extruded material are burned at a high temperature of 700 to 1000°C to become husks (incineration residue), which fall from the bottom of the incinerator as bottom ash and are discharged as fly ash from the dust collector 9. be discharged. The exhaust gas that has passed through the dust collector 9 is discharged into the atmosphere from a chimney 11 via an induced draft fan 10.

In order to remove acid gases (HCl, SOx) in the exhaust gas generated in the incinerator 6, slaked lime is blown into the exhaust gas in a flue before the dust collector 9. A bag filter is preferably used for the dust collector 9. By spraying a known special reaction aid together with slaked lime, it is possible to prevent clogging of the filter cloth of the bag filter and to promote neutralization of HCl and SOx. Additionally, by spraying activated carbon at the same time as slaked lime, dioxins and mercury can be stably removed.

A part of the fly ash discharged from the dust collector 9 is added to the sludge before being mixed with garbage, and is recycled as an additive to the sludge.

Specifically, in the example shown in FIG. 1, part of the fly ash is supplied to the kneader 7 together with the sludge. In the example shown in FIG. 2, sludge is put into an extruder 8, and the surface of the sludge molded product extruded from the extruder 8 is sprinkled with fly ash by a powder sprinkler 16. The powder dusting machine 16 is not particularly limited in structure as long as it is a machine that can sprinkle powder such as fly ash, preferably evenly, on the surface of an extruded product, but for example, it can sprinkle powder on a turntable. A powder spraying device that uses a cyclone separator to recycle the powder to be sprinkled on the object, and other powder scattering devices may be used. In the example shown in FIG. 2, the kneader 7 in the example of FIG. 1 is omitted. In the example shown in FIG. 1 as well, a part of the fly ash is put into the kneading machine 7 and mixed with the sludge, and then the extruded product is extruded from the extrusion molding machine 8. As shown in the dashed line, It is also possible to further sprinkle fly ash with the powder dusting machine 16, or alternatively, as shown by the two-dot chain line, the extruded product can be extruded from the extrusion molding machine 8 without putting fly ash into the kneading machine 7. The surface can also be sprinkled with fly ash using a powder dusting machine 16.

20 to 100% of the fly ash removed from the dust collector 9 can be recycled as an additive to sludge. The fly ash that is not recycled is transported out of the incineration facility via the fly ash transport device 12 and treated as waste.

The fly ash contains unreacted slaked lime (Ca(OH) ₂ ), and the unreacted slaked lime reacts with SO ₂ in the combustion exhaust gas in the incinerator 6 to form CaSO ₃ and the like, resulting in a concentration of 10 to 80%. A desulfurization rate of about 100% can be obtained.

A part of the fly ash taken out from the dust collector 9 is analyzed by the analyzer 13 to calculate the unreacted slaked lime concentration (wt%) contained in the fly ash, and the unreacted slaked lime concentration in the fly ash and the concentration of unreacted slaked lime in the sludge are calculated. The amount of slaked lime added to the exhaust gas is adjusted based on the amount of fly ash added. That is, adjustment can be made to reduce the amount of slaked lime blown into the exhaust gas in the flue before the dust collector 9 by the amount of unreacted slaked lime contained in the fly ash added to the sludge. The amount added can be calculated, for example, in terms of mass per unit time.

Fly ash contains calcium chloride (CaCl ₂ ) produced by a chemical reaction between slaked lime blown into the exhaust gas and HCl in the exhaust gas. When CaCl ₂ reacts with sludge water, it becomes a hydrate of CaCl _2.2 to 6H ₂ O, and the sludge to which fly ash has been added apparently has a lower water content and becomes easier to loosen. Therefore, the amount of fly ash mixed into the dehydrated sludge can be adjusted so that fly ash with more CaCl ₂ is smaller than fly ash with less CaCl ₂ . Therefore, the analyzer 13 analyzes Ca, Cl, Na, and K in the fly ash, and it is thought that Cl, excluding Cl that combines with NaCl and KCl, combines with Ca to become calcium chloride (CaCl ₂ ). The amount (number of moles) of calcium chloride in the ash can be calculated. Thereby, the amount of fly ash added to the sludge can be adjusted based on the calcium chloride concentration in the fly ash.

In addition to fly ash, slaked lime and/or quicklime can also be added to the sludge. In this case, the amount of slaked lime added to the exhaust gas in the flue before the dust collector 9 can be adjusted by taking into consideration the amount of slaked lime and quicklime added to the sludge. That is, the amount of slaked lime and quicklime added to the sludge can be reduced from the amount of slaked lime blown into the flue before the dust collector 9. When quicklime is added to sludge, the drying of the sludge can be accelerated because quicklime generates heat in the process of reacting with water in the sludge to become slaked lime. When adding slaked lime and/or quicklime to sludge, it can be added to the kneading machine 7 and kneaded with the sludge in the same way as the fly ash described above, or it can be added to the sludge mixture extruded from the extrusion molding machine 8. The powder can also be sprinkled onto the surface of the extruded product using a powder sprinkler 16.

The concentration of acidic gases (HCl, SOx) in the exhaust gas is measured by a known concentration measuring device (not shown), and based on the measured acidic gas concentration, the acidic gas in the exhaust gas is removed. The amount of slaked lime required to be added (injected) to the exhaust gas can be calculated.

By adding fly ash to the sludge as described above, or by adding slaked lime and/or quicklime to the sludge together with the fly ash, the amount of slaked lime blown into the exhaust gas generated in the incinerator 6 can be reduced.

In addition, since fly ash has hygroscopic properties, when it is kneaded with sludge or sprinkled on the surface of a sludge molded product, it absorbs the water content of the sludge, and the water content of the sludge decreases. Improves adhesion to conveyors and other equipment, improving handling.

Furthermore, bottom ash, which falls and is discharged from the bottom of the combustion chamber of the incinerator 6, may be added to the sludge, together with fly ash and the like, before being mixed with the waste.

Part or all of the bottom ash is sieved by a sieve 14 , and only the bottom ash with a particle size of less than a predetermined size, preferably 1 mm or less, is added to the sludge and recycled.

In the example shown in FIG. 1, bottom ash having a predetermined particle size or less is conveyed by a conveyor such as a conveyor, supplied to a kneader 7, and kneaded with sludge. In the example shown in FIG. 2, the surface of the extruded product extruded from the extrusion molding machine 8 is sprinkled with powdered bottom ash having a predetermined particle size or less by the powder sprinkler 16. In the example shown in FIG. 1 as well, bottom ash with a predetermined particle size or less is put into the kneading machine 7, mixed with sludge, and then extruded from the extrusion molding machine 8. , the bottom ash can be further sprinkled with the powder dusting machine 16, or the extruded product can be extruded from the extrusion molding machine 8 without putting the bottom ash into the kneading machine 7, as shown by the two-dot chain line. You can also sprinkle bottom ash on the surface.

When the particle size of the bottom ash mixed with the sludge exceeds 1 mm, it is not preferable because it does not adsorb water in the sludge. If fly ash alone is added to sludge as an auxiliary agent, the amount of fly ash generated is small and may be insufficient, but by adding fly ash and bottom ash to sludge, the ease of sludge and adhesion can be reduced. Improved. The bottom ash that has not been added to the sludge is transported out of the incineration facility via the ash transport device 15 and treated as waste.

The ratio of the total amount of fly ash and bottom ash added to the sludge is preferably 5 to 50 wt% (sludge: fly ash + bottom ash = 100 wt%: 5 to 50 wt%). If the total amount of fly ash and bottom ash added to the sludge is less than 5% by weight, the ease of loosening and adhesion of the sludge mixture will not be improved, and if it exceeds 50% by weight, the low heat generation of the sludge mixture will occur. In addition, the improvement effect on ease of loosening and adhesion reaches a peak, and furthermore, it becomes impossible to maintain a combustion temperature of 850° C. (for 2 seconds) when co-firing with garbage.

Generally, the amount of fly ash generated is less than the amount of bottom ash generated, so when bottom ash is added, the ratio of fly ash to the total amount of fly ash and bottom ash can be about 10 to 30% by weight.

The co-combustion rate of the garbage and sludge mixture, that is, the ratio of the sludge mixture to the total amount of the municipal garbage and sludge mixture, is preferably 2 to 40% by weight. If the co-combustion rate is less than 2% by weight, the reduction in the amount of fly ash generated and the concentration of heavy metals in the fly ash due to sludge co-combustion will be small, and the effect of reducing the amount of chelate added necessary for fly ash treatment will not be achieved. , if it exceeds 40% by weight, the amount of incineration increases and it is necessary to increase the capacity of the incinerator, leading to an increase in processing costs. As mentioned above, a sludge mixture is sludge to which additives such as incineration residue are added, and incineration residue, etc. refers to at least fly ash from the group consisting of fly ash, bottom ash, slaked lime, and quicklime. This includes:

The extruded sludge mixture is preferably cured for about 10 minutes to 2 hours before being introduced into a garbage pit or garbage hopper. This curing makes it easier to loosen the sludge mixture, and the rate of co-combustion of the sludge mixture with waste can be improved by several percent compared to the case without curing.

The maximum width of the cross section (corresponding to the size and shape of the extrusion port of the extruder) of the extruded product of the sludge mixture is desirably 3 mm to 50 mm. If the maximum cross-sectional width of the extruded product is less than 3 mm, it will easily fall from the side wall of the stoker furnace, increasing the possibility that it will be mixed in with the falling ash. If it exceeds 50 mm, it will not burn out in the incinerator and unburned materials becomes more likely to remain.

Further, after extrusion, the extruded product is divided into predetermined lengths (length in the extrusion direction). The length of the extruded product is preferably 3 mm to 50 mm, more preferably 5 mm or more, for the same reason as the maximum cross-sectional width. This is because if the length of the extruded product is less than 5 mm, the cutting device becomes complicated.

The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.

1 Garbage pit
3 Garbage hopper 6 Incinerator 7 Kneading machine 8 Extruder 9 Dust collector 13 Analyzer 14 Sieve 16 Powder dusting machine

Claims (12)

A waste treatment method in which sludge is mixed with waste and co-incinerated in a stoker type incinerator, and slaked lime is added to the exhaust gas from the stoker type incinerator before dust collection,
Before the sludge is mixed with waste, collected fly ash is added,
The amount of slaked lime added to the exhaust gas is determined based on the concentration of unreacted slaked lime in the fly ash and the amount of fly ash added to the sludge, and the amount of unreacted slaked lime contained in the fly ash added to the sludge. said waste disposal method adjusted to reduce only. The waste treatment method according to claim 1, wherein the amount of the fly ash added to the sludge is adjusted based on the calcium chloride concentration in the fly ash. The waste treatment method according to claim 1 or 2 , wherein the fly ash is kneaded with the sludge before being mixed with the waste. The waste treatment method according to any one of claims 1 to 3 , wherein the sludge is extruded before being mixed with the waste, and the surface of the extruded sludge is sprinkled with the fly ash. Before the sludge is mixed with waste, bottom ash from the incinerator is further added,
The waste treatment method according to any one of claims 1 to 4 , wherein the bottom ash added to the sludge is sieved to a particle size of 1 mm or less. The sludge is further added with slaked lime before being mixed with waste;
The waste treatment method according to any one of claims 1 to 5 , wherein the amount of slaked lime added to the exhaust gas is further reduced in accordance with the amount of slaked lime added to the sludge. Quicklime is further added to the sludge before it is mixed with waste;
The waste treatment method according to any one of claims 1 to 6 , wherein the amount of slaked lime added to the exhaust gas is further reduced in accordance with the amount of slaked lime added to the sludge. The waste treatment according to any one of claims 1 to 7 , wherein the sludge, before being mixed with the waste, is extruded so that the maximum width of its cross section is equal to or less than a predetermined size, and is co-incinerated with the waste. Method. The waste treatment method according to claim 8 , wherein the sludge is extruded into a maximum cross-sectional width of 3 mm to 50 mm, and then processed into a predetermined length. The waste treatment method according to claim 8 or 9 , wherein the sludge is cured after extrusion molding, and the cured sludge is co-incinerated with the waste. The waste treatment method according to any one of claims 1 to 10 , wherein the ratio of the amount of fly ash added to the sludge is 5 to 50% by weight. Calculate the concentration of calcium chloride in the fly ash by analyzing Ca, Cl, Na, and K in the collected fly ash,
The waste treatment method according to any one of claims 2 to 11 , wherein the amount of the fly ash added to the sludge is adjusted based on the calcium chloride concentration in the fly ash.