JP2006003013A - Sewage sludge treatment method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sewage sludge treatment method and its device capable of burning sewage sludge, collecting the incinerated ash in a combustion exhaust gas by a dust collector, and stably solidifying the incinerated ash with simple operation to make a solid material of high strength. <P>SOLUTION: The sewage sludge and calcium-containing substance are supplied to a fluidized bed furnace kept at high temperatures of about 800-950°C to burn the sewage sludge, then high-temperature combustion exhaust gas is cooled, the incinerated ash existing in the exhaust gas is collected by the dust collector, and the water is added to the collected incinerated ash to granulate/solidify the incinerated ash. Further the amount of the calcium-containing substance supplied to the fluidized bed furnace is controlled to adjust a ratio MC/(MS+MA) of the amount MC(mol) of a calcium component in the calcium-containing substance supplied to the fluidized bed furnace and MS+MA obtained by adding the amount MS(mol) of a silicon component in the sewage sludge and the amount MA(mol) of an aluminum component in the sewage sludge to be 0.1 2. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  TECHNICAL FIELD The present invention relates to a method and apparatus for treating sewage sludge, which allows incineration ash generated when incinerating sewage sludge to be a solid having good handling properties and high strength by simple means. .

Sludge generated by sewage treatment is increasing with the spread of sewerage. This sludge is mainly treated by landfill, but in recent years, landfill disposal has become difficult from the viewpoint of landfill reduction and the environment.
For this reason, in the treatment of sewage sludge, ways to reduce sludge and effectively use sludge are being sought. For example, a method in which sludge is dehydrated and composted and used as an organic soil conditioner, or a method in which dehydrated sludge is incinerated and incinerated ash is disposed of in landfill has been implemented.
However, even if the sludge is dehydrated and composted, harmful heavy metals are contained and its use is limited, so this method has not been adopted so much, and more methods for landfilling the incinerated ash have been implemented.

  However, even if the volume of incinerated ash is reduced, it is still difficult to secure a landfill. Therefore, a method for reusing and effectively using sludge incineration ash as a resource has been proposed. For example, incineration ash is heated and melted and then cooled, slag is converted into slag and used as an aggregate of building materials, incineration ash is compression-molded and used as brick, cement and other binders are added to incineration ash There are a method of using it as a lightweight aggregate or a method of using incinerated ash as a part of a cement raw material.

  However, melting and firing of sewage sludge incineration ash has problems such as consuming a great amount of heat and requiring special equipment. Further, the method of solidifying using a binder such as cement requires a binder, which is costly and causes an increase in the amount of disposal.

  In addition, as a method for incinerating waste such as sludge, an additive containing calcium as a main component is added to the high-temperature combustion exhaust gas from the incinerator, and hydrogen chloride and sulfur oxide generated in the incinerator are added to the additive. After removing by adsorbing calcium, a waste incineration method is proposed in which the additive is recovered as fine powder dust and scattered dust, molded, and steam autoclaved to obtain detoxified solids. (For example, refer to Patent Document 1).

This method can remove hydrogen chloride and sulfur oxides in exhaust gas, and incineration fly ash containing additives recovered by a dust collector is easy to handle without using high-temperature treatment or other binders. Also, it has the advantage that it can be disposed of as a solid material that can prevent elution of heavy metals and the like.
However, since the hydraulic property necessary for adding water to the dust collected by the dust collector and solidifying it is not sufficient, it is necessary to acclimate it with a steam autoclave in order to obtain a high-strength hydraulic solid material.

JP 55-35870 A

  The present invention has been made in view of the above circumstances, supplying sewage sludge and calcium-containing material to a high-temperature fluidized bed furnace, reacting the incineration residue with calcium oxide in the fluidized bed furnace, and incineration exhaust gas. Incineration fly ash (hereinafter simply referred to as incineration ash) with uniform composition and excellent hydraulic properties is collected with a dust collector, and the incineration ash is made into a solid solid with high strength by simple operation. It is an object of the present invention to provide a method and apparatus for treating sewage sludge.

The present invention has been made to achieve the above-described problems, and has been solved by the following means.
A method for treating sewage sludge, supplying sewage sludge and calcium-containing substances to a fluidized bed furnace maintained at a high temperature of about 800 to 950 ° C., incinerating the sewage sludge, cooling the high-temperature combustion exhaust gas, The incinerated ash present inside was collected with a dust collector, and water was added to the collected incinerated ash to granulate and solidify.

  The amount MC (mol) of calcium component in the calcium-containing substance supplied to the fluidized bed furnace, the amount MS (mol) of silicon component in sewage sludge, and the amount MA (mol) of aluminum component in sewage sludge. In the calcium-containing substance supplied to the fluidized bed furnace, the supply amount of the calcium-containing substance supplied to the fluidized bed furnace is controlled such that the ratio MC / (MS + MA) to the added MS + MA is 0.1-2. It is also characterized in that the supply amount of the calcium-containing substance is controlled so that the ratio Ma / Mb of the calcium component weight Ma and the nitrogen component weight Mb in the sewage sludge is 0.1 to 0.45.

A treatment apparatus for sewage sludge, a fluidized bed furnace for incinerating sewage sludge, a quantitative feeder for quantitatively supplying sewage sludge and calcium-containing materials to the fluidized bed furnace, and a quantitatively supplied sewage sludge and calcium-containing material Are supplied individually or mixed into the fluidized bed furnace, a cooling tower for cooling the high-temperature combustion exhaust gas discharged from the fluidized bed furnace, and incineration ash in the cooled exhaust gas is collected. A dust collector, a smoke treatment device for treating the exhaust gas removed by the dust collector, and a granulator for adding water to the incinerated ash collected by the dust collector to granulate and solidify .
It is also characterized by comprising a kneader for adding water to the incinerated fly ash collected by the dust collector and kneading in advance, and a molding machine for molding and solidifying the mixture kneaded by the kneader.

Supply sewage sludge and calcium-containing material to a fluidized bed furnace maintained at a high temperature, incinerate the sludge in the fluidized bed furnace, and burn the incineration residue and calcium oxide in the fluidized bed furnace in a uniformly mixed state By carrying out the reaction, the incinerated ash becomes a fired product made of SiO ₂ , Al ₂ O ₃ , CaO or the like having a uniform composition in the fluidized bed furnace and excellent hydraulic properties. For this reason, the incineration ash in the incineration exhaust gas collected by the dust collector is easy to handle compared to dust with a simple operation of adding water and granulating, and it has a stable and high strength. It can be a solid.

According to the method and apparatus for treating sewage sludge of the present invention, a method of solidifying by adding a binder to a conventional collected dust, a method of acclimating and solidifying using a high-pressure reactor, firing and melting treatment at a high temperature. Compared with the method of solidifying, there is an advantage that addition of a binder and high-temperature heat treatment are unnecessary.
In addition, acclimatization equipment such as an autoclave for solidification is not required. For this reason, it is economical because sewage sludge can be treated efficiently at low cost.
In addition, since it is not necessary to add a binder or the like to the collected dust, it is possible to suppress an increase in by-products and waste.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments, and can be implemented with appropriate modifications.
FIG. 1 is a schematic view showing a configuration example of an apparatus for treating sewage sludge according to the present invention. 1 is a circulating fluidized bed furnace for incinerating sewage sludge (hereinafter simply referred to as a fluidized bed furnace), 2 is a cyclone that separates unburned solids contained in the exhaust gas and returns the separated matter into the furnace, Air preheater, 4 is a preheater for white smoke prevention, 5 is a fan for white smoke prevention, 6 is a cooling tower, 7 is a dust collector such as a bag filter, 8 is a flue gas treatment device such as a washing tower, 9 is an exhaust gas The fan 10 is a chimney for releasing the treated exhaust gas to the atmosphere.

11 is an ash hopper for storing incinerated ash collected by a dust collector, 12 is a metering feeder mounted at the outlet of the ash hopper 11, 13 is a granulator, and 14 is a granulated product receiver.
100 is a sewage treatment facility, 101 is a sewage sludge dewatering machine, and 102 is a dewatered sludge hopper. Reference numeral 103 denotes a limestone hopper, in which fine powdered limestone that is a calcium-containing substance is stored.
Reference numerals 104 and 105 denote fixed-quantity feeders attached to the discharge ports of the dewatered sludge hopper 102 and the limestone hopper 103, respectively, and 106 denotes a feeder for mixing the dehydrated sludge and limestone and putting them into the fluidized bed furnace 1.

  Therefore, the sewage sludge generated in the sewage treatment facility 100 is dehydrated by the dehydrator 101 and stored in the dewatered sludge hopper 102. The dehydrated sludge in the dehydrated sludge hopper 102 is supplied in a fixed amount from the quantitative supply device 104 to the supply device 106, and the limestone in the limestone hopper 103 is supplied in a fixed amount from the quantitative supply device 105 into the supply device 106. Are fed into the fluidized bed furnace 1 while being mixed by the feeder 106.

The sludge is incinerated in the fluidized bed furnace 1, and the incombustible portion becomes incineration residue. On the other hand, the limestone supplied into the fluidized bed furnace 1 together with the dehydrated sludge is decomposed in the fluidized bed furnace 1 under a high temperature condition of about 800 to 950 ° C. to become calcium oxide (CaO). Then, a solid phase reaction between the incineration residue of sludge mainly composed of SiO _2, Al ₂ O _{3 and the} like and CaO proceeds under a high temperature condition around 900 ° C., and CaO · SiO ₂ , 2CaO · SiO ₂ , CaO · Al It becomes a fired product such as ₂ O ₃ . These fired products are also discharged from the fluidized bed furnace 1 along with the combustion exhaust gas as incinerated ash.

High-temperature exhaust gas (for example, about 900 ° C.) generated in the fluidized bed furnace 1 is introduced into a cyclone 2 provided in the fluidized bed furnace 1. Unburned substances in the exhaust gas are separated by the cyclone 2, the separated parts are returned to the fluidized bed furnace 1 and incinerated, and the incineration residue similarly reacts with calcium oxide in the fluidized bed furnace 1 and fires. It becomes a thing. In the case of a fluidized bed furnace using a fluidized medium such as silica sand, the fluidized medium is also collected by the cyclone 2 and returned to the fluidized bed furnace 1. A part is scattered with the exhaust gas, and is collected by the dust collector 7 in the subsequent stage.
Since silica sand as a fluidized medium has a large particle size and is a very stable substance, it hardly reacts with the calcium component supplied into the fluidized bed furnace 1 at a temperature around 900 ° C.

  The high temperature exhaust gas leaving the cyclone 2 is introduced into the air preheater 3. In the air preheater 3, the high temperature exhaust gas is heat-exchanged with the combustion air supplied into the fluidized bed furnace 1 to reach about 500 ° C. The exhaust gas that has reached about 500 ° C. is supplied to the white smoke prevention preheater 4 in order to obtain heated air for white smoke prevention, which will be described later, and is heat-exchanged with the air supplied by the fan 5.

The exhaust gas from the white smoke prevention preheater 4 is introduced into a cooling tower 6 such as a water spray type. The air heated by the white smoke prevention preheater 4 is introduced into the inlet of the subsequent chimney 10 through the pipe L to raise the temperature of the exhaust gas discharged from the chimney 10 to prevent the generation of white smoke.
The exhaust gas sent to the cooling tower 6 takes into consideration the prevention of the production of harmful organic chlorine compounds such as dioxins and the heat resistance of the filter cloth when using a bag filter capable of collecting fine dust as the dust collector 7. It is cooled to about 200 ° C. or lower.

The cooled exhaust gas is introduced into the dust collector 7, and dust in the exhaust gas is removed.
The exhaust gas that has passed through the dust collector 7 is partially removed from the fluidized bed furnace 1 by adding limestone in the fluidized bed furnace 1, but the remaining hydrogen chloride, sulfur oxide, hydrogen cyanide, etc. In order to remove harmful substances, water and an alkaline solution such as sodium hydroxide are sprayed and treated through a flue gas treatment device 8, and the treated exhaust gas is discharged from a chimney 10 to the atmosphere by an induction fan 9. .
In addition to the bag filter, various types such as an electric dust collector and a moving bed dust collector can be used as the dust collector 7.

  Further, when harmful chlorine compounds such as dioxins or mercury are present in the exhaust gas, carbonaceous adsorbent powders such as activated carbon and activated coke are added to the exhaust gas before the dust collector 7 and adsorbed to the dust collector 7. It can be efficiently removed by collecting with.

When nitrogen oxides are present in the exhaust gas, a denitration tower (not shown) filled with a denitration catalyst is provided in the front stage of the cooling tower 6 or the rear stage of the dust collector 7, and the exhaust gas at the inlet of the denitration tower is provided. Nitrogen oxide can be removed by injecting ammonia into the substrate. As the catalyst filled in the denitration tower, a carbonaceous catalyst such as a TiO ₂ —V ₂ O ₅ catalyst or active coke can be used.

The incinerated ash collected by the dust collector 7 is stored in the ash hopper 11, and this collected incinerated ash is supplied to the granulator 13 together with water such as treated water from the sewage treatment facility via the quantitative feeder 12. Granulate and solidify. That is, it is possible to obtain pellets having a particle size of 1 to 15 mm and a compressive strength of 8 kg / cm ² or more simply by adding water, granulating and drying in the sun. When granulated by heating with low-temperature steam of about 50 to 100 ° C., it is possible to obtain an excellent solid having a compressive strength of 20 kg / cm ² or more.

  As the granulator 13, water is added to the incinerated ash, and granulated (including molding) and solidified at the same time as mixing, and a pan-type or drum-type rolling granulator, or water is added to the incinerated ash Various kinds of materials such as an extrusion molding machine and a press molding machine that are previously kneaded and then molded and solidified can be used. Among them, the rolling granulator is inexpensive and excellent in operability.

  As the calcium-containing substance to be supplied to the fluidized bed furnace 1 in the present invention, limestone, calcium carbonate, calcium oxide, calcium hydroxide, ores such as various shells and dolomite containing a large amount of calcium can be used.

  The calcium-containing material is obtained by adding the amount MC (mol) of the calcium component in the calcium-containing material, the amount MS (mol) of the silicon component in the sewage sludge, and the amount MA (mol) of the aluminum component in the sewage sludge. Is supplied into the fluidized bed furnace 1 so that the ratio MC / (MS + MA) is 0.1-2.

That is, the ratio MC / (MS + MA) = 0.1-2.
By supplying the calcium-containing substance into the fluidized bed furnace 1 maintained at a high temperature of about 800 to 950 ° C., the incineration residue and calcium oxide are uniformly dispersed and mixed in the fluidized bed furnace 1, and the efficiency baked products such as _{CaO · SiO 2, 2CaO · SiO} 2, CaO · Al 2 O 3 is produced better solid phase reaction proceeds. In particular, CaO · Al ₂ O ₃ and 2CaO · SiO ₂ have hydraulic properties, and are therefore effective for making incineration ash into a solid substance.

If the above ratio is less than 0.1, solids having sufficient strength cannot be obtained, and if it exceeds 2, the calcium content becomes excessive, and the unreacted calcium content increases and sufficient solidification cannot be achieved. , Alkalis may elute and cause secondary pollution.
In addition, since the sewage sludge dehydrated using slaked lime or the like may have a high calcium content, the amount of the calcium-containing substance supplied into the fluidized bed furnace 1 may be reduced accordingly.

  In particular, the ratio Ma / Mb between the weight Ma of the calcium component in the calcium-containing substance supplied into the fluidized bed furnace 1 and the weight Mb of the nitrogen component in the sewage sludge is 0.1 to 0.45. For example, the calcium-containing material has a ratio MC / MN of 0.035 to 0.16 between the amount MC (mol) of the calcium component in the calcium-containing material and the amount MN (mol) of the nitrogen component in the sewage sludge. 2, the content of nitrogen oxides and hydrogen cyanide in the combustion exhaust gas generated in the fluidized bed furnace 1 can be reduced as shown in FIG. The present inventors have found that the burden on the exhaust gas treatment facility 8 can be reduced, and filed a patent application earlier (Japanese Patent Application No. 2003-093932).

In FIG. 2, the vertical axis represents the contents of hydrogen cyanide (HCN) and nitrogen oxide (NOx) in the combustion exhaust gas.
From the figure, by adjusting the supply amount of the calcium-containing material so that Ma / Mb is 0.1 to 0.45, both the HCN concentration and the NOx concentration in the exhaust gas generated from the fluidized bed furnace 1 are appropriate. It is possible to suppress the concentration.

  Usually, the ratio MN of the amount MN (mol) of nitrogen component in the sewage sludge and the MS + MA obtained by adding the amount MS (mol) of silicon component in the sewage sludge and the amount MA (mol) of aluminum component in the sewage sludge Since / (MS + MA) is about 4, Ma / Mb is 0.1 to 0.45 (corresponding to 0.035 to 0.16 as MC / MN). MC / (ratio) of MC + (mol) of the amount of calcium component in the contained material, MS + MA of the amount of silicon component MS (mol) in the sewage sludge and the amount MA (mol) of aluminum component in the sewage sludge. MS + MA) corresponding to about 0.14 to 0.64. And this value exists in the range of 0.1-2 which is a value required in order to obtain incineration ash with good hydraulic property.

  That is, by adjusting the supply amount of the calcium-containing substance so that Ma / Mb is 0.1 to 0.45, the load on the exhaust gas treatment facility 8 can be reduced, and the solidification of the collected incineration ash is easy. There is an effect that can be done.

  The water content of the dewatered sludge supplied into the fluidized bed furnace 1 is normally about 80% or less with the dehydrator 101 in order to maintain good combustion of the sludge in the fluidized bed furnace 1 and to reduce fuel consumption. Preferably, it is dehydrated to about 70% or less. By keeping the temperature in the fluidized bed furnace 1 high and stable, incinerated ash that is a uniform and excellent hydraulic property can be obtained.

If the water content is too high, the temperature in the fluidized bed furnace 1 will not rise and will not be stable, so that a good fired product cannot be obtained. Moreover, if incineration of sludge is not performed sufficiently, unburned components such as carbon in the incineration ash collected by the dust collector 7 increase, and incineration ash with good hydraulic properties cannot be obtained.
Conversely, in order to obtain dehydrated sludge with a very low water content, a large amount of expensive chemicals are required or an expensive dehydrator is required, which is not economical.

In the present invention, since the sewage sludge and the calcium-containing substance are supplied into the fluidized bed furnace 1 maintained at a high temperature, the firing reaction in the fluidized bed furnace 1 proceeds under uniform conditions, and the hydraulic property Since the calcium-containing substance in an amount suitable for the production of a fired product excellent in the above is supplied into the fluidized bed furnace 1, there is a feature that a fired product having a uniform composition and excellent hydraulic properties can be obtained.
The incinerator to be used is the fluidized bed furnace 1 and the incinerated ash and the calcium-containing substance are uniformly mixed under a high temperature condition and the firing reaction proceeds, so that a fired product that is uniform and has good hydraulic properties is obtained. Suitable for

As the fluidized bed furnace 1, a bubble type fluidized bed furnace or a circulating fluidized bed furnace can be used. A type in which a fluid medium such as silica sand is added to the fluidized bed furnace 1 can also be used.
In FIG. 1, sewage sludge and calcium-containing substances are mixed and supplied into the fluidized bed furnace 1 using a single feeder 106, but two feeders are provided and each is individually fluidized bed. It is also possible to supply into the furnace 1.

The apparatus shown in FIG. 1 was used to incinerate sewage sludge. A sewage sludge and fine limestone containing SiO _2, 45 wt%, Al ₂ O _3, 16 wt%, CaO, 3 wt% as an ash composition were supplied to a circulating fluidized bed furnace maintained at 850 to 900 ° C.
The amount of limestone supplied to the circulating fluidized bed furnace is the amount MC (mol) of calcium component in limestone, the amount MS (mol) of silicon component in sewage sludge, and the amount MA (mol) of aluminum component in sewage sludge. The ratio MC / (MS + MA) to MS + MA with the addition of was changed to 0.05, 0.1, 0.5, 1.0, 2.0, and 3.0, respectively. The incinerated ash collected by the dust collector was added with 25% of water using a drum-type rolling granulator, granulated and dried to produce pellets having a diameter of about 3 to 10 mm.

The compression strength (kg / cm ² ) of the obtained granulated product was 5, 7, 8, 9, 8, and 6, respectively.
That is, by controlling the amount of calcium-containing material supplied to the fluidized bed furnace 1 so that the value of MC / (MS + MA) is in the range of 0.1 to 2, it is possible to obtain pellets with high strength. .

  The method of the present invention does not add a calcium-containing substance to a flue or the like where the temperature of exhaust gas in which the calcination reaction is difficult to proceed is reduced, but as described above, the sewage sludge and the calcium-containing substance are mixed in the high-temperature fluidized bed furnace 1. Incineration residue and calcium compound are uniformly dispersed and mixed in the fluidized bed furnace 1 and the firing reaction proceeds effectively due to the high temperature state. For this reason, since the incinerated ash collected by the dust collector 7 has a uniform composition and excellent hydraulic properties, a solid material having excellent strength can be obtained only by a simple operation of adding water and granulating. Can do.

Since the granulated product obtained by the treatment method and apparatus of the present invention is a spherical molded product having a particle size of about 1 to 15 mm and a compressive strength of 8 kg / mm ² or more, a flower fertilizer, snow melting agent, desulfurizing agent, ground improvement agent Can be used.

Moreover, since it has a favorable function also as a deodorizing agent such as a sludge digester in a sewage treatment plant, it can be used as a deodorizing agent for various odorous gases.
Further, the shape and particle size of the granulated product can be adjusted as suitable for use in each application. For example, when using a drum type rolling granulator, it is possible to adjust the particle size of the spherical product by changing the granulation time and the number of rotations of stirring.

It is the schematic which shows the structural example of the apparatus which processes the sewage sludge by this invention. It is the graph which showed the relationship between the value of Ma / Mb at the time of incinerating sewage sludge, and the nitrogen oxide density | concentration in the waste gas generated from a fluidized bed furnace, and hydrogen cyanide density | concentration.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fluidized bed furnace 2 Cyclone 3 Air preheater 4 White smoke prevention preheater 5 White smoke prevention fan 6 Cooling tower 7 Dust collector 8 Smoke treatment device 9 Induction fan 10 Chimney 11 Ash hopper 12 Fixed supply machine 13 Granulator 14 Granulated product receiver 100 Sewage treatment equipment 101 Dehydrator 102 Dehydrated sludge hopper 103 Limestone hopper 104, 105 Fixed amount feeder 106 Feeder

Claims (5)

  Sewage sludge and calcium-containing material are supplied to a fluidized bed furnace maintained at a high temperature of about 800 to 950 ° C., the sewage sludge is incinerated, the high-temperature combustion exhaust gas is cooled, and the incineration fly ash present in the exhaust gas is collected by a dust collector A method for treating sewage sludge, characterized in that the sewage sludge is collected by using water and granulated and solidified by adding water to the collected incinerated fly ash.   The amount MC (mole) of calcium component in the calcium-containing substance supplied to the fluidized bed furnace, the amount MS (mole) of silicon component in sewage sludge, and the amount MA (mole) of aluminum component in sewage sludge. The treatment of sewage sludge according to claim 1, wherein the supply amount of the calcium-containing substance supplied to the fluidized bed furnace is controlled so that the ratio MC / (MS + MA) to the added MS + MA is 0.1-2. Method.   The calcium-containing material is adjusted so that the ratio Ma / Mb of the weight component Ca of the calcium component in the calcium-containing material supplied to the fluidized bed furnace and the weight component Mb of the nitrogen component in the sewage sludge is 0.1 to 0.45. The method for treating sewage sludge according to claim 1, wherein the supply amount is controlled.   A fluidized bed furnace for incinerating sewage sludge, a quantitative feeder for supplying sewage sludge and a calcium-containing substance to the fluidized bed furnace, respectively, and a fixed quantity of sewage sludge and a calcium-containing substance supplied individually to the fluidized bed furnace, or A mixed supply unit, a cooling tower for cooling the high-temperature combustion exhaust gas discharged from the fluidized bed furnace, a dust collector for collecting incinerated fly ash in the cooled exhaust gas, and the dust collector A sewage sludge treatment apparatus comprising: a flue gas treatment apparatus for treating exhaust gas; and a granulator for granulating and solidifying by supplying incinerated fly ash and water collected by the dust collector. The sewage comprising: a kneader for adding water to the incinerated fly ash collected by the dust collector and kneading in advance; and a molding machine for molding and solidifying the mixture kneaded by the kneader. Sludge treatment equipment.

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