JP7183066B2 - Sludge treatment method and sludge treatment equipment - Google Patents

Description

TECHNICAL FIELD The present invention relates to a sludge treatment method and a sludge treatment apparatus.

Sludge that is separated as solids when treating sewage or wastewater still contains a large amount of water, so the sludge is dewatered during sludge treatment. However, due to the physical and chemical properties of sludge, mechanical dehydration as it is usually does not work. Therefore, various chemicals are sometimes added as a pretreatment before dehydration.

For example, Non-Patent Document 1 discloses adding an inorganic flocculant and a calcium agent as a pretreatment for dewatering sludge. As inorganic flocculants, polyvalent metal salts (iron salts, aluminum salts, etc.) are generally used. The inorganic flocculant has the effect of neutralizing and flocculating negatively charged colloidal particles contained in sludge. Slaked lime (Ca(OH) ₂ ) is mainly used as a calcium agent. Calcium agents have a chemical dehydration-assisting effect and a physical dehydration-assisting effect. As an example of the former, it has the effect of ionizing in water and aggregating colloidal particles. Examples of the latter include the effect of acting as a support between sludge colloid particles to maintain gaps through which liquid can flow, and the effect of acting as nuclei for floc formation.

Further, Patent Document 1 discloses a technique of injecting carbon dioxide into digested sludge to adjust the pH of the digested sludge to a range suitable for using an inorganic flocculant.

JP 2017-159216 A

Masaki Kamimura (1973) "Effect of flocculants in thickening and dehydration of sludge", Environmental Technology, Environmental Technology Study Group, Vol. 2, No. 12, pp. 919-927

However, since the pretreatment process as in Non-Patent Document 1 requires the introduction of chemicals, costs are incurred for that purpose. Specifically, purchase costs for the above-mentioned inorganic flocculant and calcium agent are incurred, and their existence cannot be ignored.

In addition, although the technology described in Patent Document 1 may reduce the purchase cost of the pH adjuster, there is still room for development of a method for using carbon dioxide gas in sludge treatment.

An object of one aspect of the present invention is to provide a sludge treatment method in which the purchase cost of chemicals is suppressed.

The present inventors have conceived that the introduction of a carbon dioxide-containing gas into sludge in the pretreatment of the sludge dehydration process can replace the function of the calcium agent, and have completed the present invention.

A sludge treatment method according to one aspect of the present invention includes a precipitation step of introducing a carbon dioxide-containing gas into the raw sludge to precipitate an insoluble carbonate; a mixing step of adding and incorporating the insoluble carbonate into the sludge flocs; and a dewatering step of dewatering the sludge after the mixing step.

A sludge treatment apparatus according to one aspect of the present invention includes a precipitation device that introduces a carbon dioxide-containing gas into the raw sludge through an introduction device and precipitates an insoluble carbonate; raw sludge treated by the precipitation device; and an inorganic flocculant. and a pH adjuster to incorporate the insoluble carbonate into sludge flocs; and a dewatering device for dewatering the sludge after being treated by the mixing device; It is a device different from a mixing device.

According to one aspect of the present invention, it is possible to provide a sludge treatment method in which the purchase cost of chemicals is suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows typically by comparison the sludge-treatment method which concerns on one Embodiment of this invention, and the conventional sludge-treatment method. (a) shows the pretreatment for the dehydration step in the prior art, and (b) shows the pretreatment for the dehydration step in one embodiment of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows typically the sludge processing apparatus which concerns on one Embodiment of this invention. It is a flow figure showing a flow of processing of a sludge processing method concerning one embodiment of the present invention.

Examples of embodiments of the present invention will be described in detail below, but the present invention is not limited to these. The contents described in each of the following items can also be appropriately used in other items. The present invention is not limited to the following embodiments, and various modifications are possible within the scope of the claims. Therefore, embodiments obtained by appropriately combining technical means disclosed in different embodiments are also included in the technical scope of the present invention.

Unless otherwise specified in this specification, "A to B" representing a numerical range means "A or more and B or less". All scientific and patent documents mentioned herein are hereby incorporated by reference.

[Comparison between the present invention and conventional technology]
FIG. 1 is a diagram schematically showing a comparison between a sludge treatment method according to one embodiment of the present invention and a conventional sludge treatment method. As explained in the section [Prior art], in the conventional sludge treatment method, (i) in the mixing step S2, an inorganic flocculant, a pH adjuster and a calcium agent are put into the mixing device 2, and (ii) thereafter, In the aggregation step S3, the polymer flocculant was put into the aggregation device 3 ((a) in FIG. 1). Here, the calcium agent has the function of (i) serving as a nucleus for floc formation and (ii) serving as a support between sludge particles to increase water flowability.

On the other hand, the sludge treatment method in one aspect of the present invention includes a precipitation step S1 of introducing a carbon dioxide-containing gas into the raw sludge, and then a mixing step of adding an inorganic flocculant and a pH adjuster to the raw sludge that has undergone the precipitation step S1. S2 and, optionally, a flocculation step S3 of adding a polymer flocculant to the raw sludge that has passed through the mixing step S2 (FIG. 1(b)).

Here, the precipitation step S1 and the mixing step S2 are not performed at the same time. In one example, the precipitation device 1 in which the precipitation step S1 is performed and the mixing device 2 in which the mixing step S2 is performed are different devices. Alternatively, even if the precipitation device 1 and the mixing device 2 are the same device, the precipitation step S1 and the mixing step S2 are not performed at the same time (for example, after stopping the introduction of the carbon dioxide-containing gas, the inorganic flocculant and Add pH adjuster). As will be described later, the preferred pH differs between the precipitation step S1 and the mixing step S2. Therefore, it is preferable that the precipitation device 1 and the mixing device 2 are different devices.

A carbon dioxide-containing gas is introduced into the precipitation device 1 through the introduction device 1a. Then, due to the reaction with carbon dioxide, at least part of the inorganic ions in the sludge are precipitated as insoluble carbonates (calcium carbonate, magnesium carbonate, manganese carbonate, etc.). These carbonates act as nuclei for flocculation as well as supports between sludge particles. In other words, the same effect as when a calcium agent is added can be obtained.

Thus, according to the sludge treatment method according to one aspect of the present invention, it is possible to suppress the input amount of the calcium agent. Therefore, it is possible to reduce the purchase cost of the calcium preparation as compared with the conventional method.

It should be noted that if the amount of calcium agent to be added can be suppressed as compared with the prior art, it can be said that the present invention is effective. That is, in the method according to one embodiment of the present invention, it is not necessary to set the dosage of the calcium agent to zero.

[Sludge treatment equipment]
FIG. 2 is a diagram schematically showing a sludge treatment apparatus according to one embodiment of the present invention. Each part included in the sludge treatment apparatus 100 will be described below with reference to FIG. The sludge treatment apparatus 100 illustrated in FIG. 2 is provided with a precipitation device 1, a mixing device 2 and a dehydration device 4, and a carbon dioxide-containing gas is introduced into the precipitation device 1 through the introduction device 1a. It is configured. With such a configuration, the sludge treatment apparatus 100 can exhibit the above-described effect of the present invention (suppression of the input amount of the calcium agent).

The sludge treatment apparatus 100 is also provided with a flocculation device 3, a drying device 5, a thermal decomposition device 6, a reforming device 7, a combustion device 8, and an ash separation device 9, which are optional configurations. With such a configuration, the sludge treatment apparatus 100 can (i) supply gas containing high-concentration carbon dioxide generated during sludge treatment to the precipitation step S1, and (ii) high A fuel gas containing a concentration of hydrogen can be removed.

The sludge supplied to the sludge treatment apparatus 100 is not particularly limited. Examples of such sludge include, in addition to sewage sludge, organic sludge derived from industries such as the paper/pulp industry, chemical industry, and food manufacturing industry, human waste treatment sludge, and organic sludge derived from the livestock industry. . Below, sewage sludge is mentioned as a typical example and demonstrated. However, the invention is also applicable to other types of sludge.

Examples of sewage sludge include raw sludge, activated sludge and digested sludge.

[Precipitation device and introduction device, mixing device, aggregation device]
In the precipitation device 1, carbon dioxide-containing gas is introduced into the raw sludge through the introduction device 1a to precipitate insoluble carbonate. The insoluble carbonate precipitated at this time serves as a nucleus for floc formation in the mixing step S2 or as a support between sludge particles in the dehydration step S4, thereby functioning as a dehydration aid. The raw sludge from which the insoluble carbonate is precipitated is sent to the mixing device 2 .

In the mixing device 2, an inorganic flocculant and a pH adjuster are added to the raw sludge to incorporate the insoluble carbonate into the sludge flocs (to form sludge flocs with the insoluble carbonate as the nucleus).

The sludge after being treated by the mixing device 2 may optionally be sent to the flocculating device 3 . In the flocculating device 3, a polymer flocculant is added to the sludge. For example, if the polymer flocculant is introduced into the pipe that transfers the sludge treated by the mixing device 2 to the dewatering device, the flocculating device 3 need not be provided separately. Further, since the addition of the polymer flocculant itself is also a step of optional configuration, the flocculation step S3 may be omitted. However, from the viewpoint of improving the dehydration efficiency, it is preferable to provide the aggregation step S3 and add the polymer flocculant.

In this way, the raw sludge that has undergone the treatment in the precipitation device 1, the mixing device 2 (and optionally the flocculation device 3) is flocculated into flocculated sludge. The obtained flocculated sludge is supplied to the dehydrator 4 . The water separated in the step of obtaining flocculated sludge is appropriately treated in a wastewater treatment facility and then discharged outside through a discharge channel, or may be reused in the treatment facility as reused water.

The introduction device 1 a introduces a carbon dioxide-containing gas into the raw sludge in the precipitation device 1 . Carbon dioxide contained in this gas has the function of precipitating insoluble carbonate. As a result, the sludge treatment apparatus 100 can suppress the input amount of the calcium agent.

In FIG. 2, the carbon dioxide-containing gas generated in the combustion device 8 is introduced into the deposition device 1 through the introduction device 1a. However, the source of the carbon dioxide-containing gas introduced into the deposition apparatus 1 through the introduction apparatus 1a is not particularly limited. However, the mode of introducing the carbon dioxide-containing gas generated in the combustion device 8 into the precipitation device 1 through the introduction device 1a is (i) a high degree of freedom in the design and installation position of the sludge treatment device 100, and (ii) Since the carbon dioxide-containing gas that would otherwise be discarded is used, the cost reduction effect is further enhanced. In order to obtain this effect, it is sufficient to introduce at least part of the carbon dioxide-containing gas generated in the combustion device 8 into the deposition device 1 . In other words, it is not necessary to introduce all of the carbon dioxide-containing gas generated in the combustion device 8 into the deposition device 1 .

Moreover, in FIG. 2, the calcium oxide after having separated ash by the ash separator 9 is supplied to the precipitation apparatus 1. As shown in FIG. Although this is an arbitrary configuration, by adopting such a configuration, the amount of calcium agent to be introduced into the precipitation apparatus 1 from outside the apparatus can be further reduced.

The concentration of carbon dioxide contained in the carbon dioxide-containing gas introduced into the precipitation device 1 through the introduction device 1a is preferably 10% by volume or more, where the total volume of the carbon dioxide-containing gas is 100% by volume. It is more preferably 20% by volume or more. As will be described later, the sludge treatment apparatus 100 has a structure in which an inorganic calcium compound is circulated among the thermal decomposition apparatus 6, the combustion apparatus 8, and the reforming apparatus 7. Therefore, combustion containing high-concentration carbon dioxide in the combustion apparatus 8 Gas can be generated. In this regard, it is preferable to introduce at least part of the combustion gas generated in the combustion device 8 into the deposition device 1 .

(Difference in suitable pH between precipitation step and mixing step)
Here, the difference in suitable pH between the precipitation step S1 and the mixing step S2 will be described. In the precipitation step S1, a suitable pH for precipitating the insoluble carbonate is 7.0 to 8.0. Therefore, in the precipitation step S1, the pH of the raw sludge is preferably adjusted to 7.0 to 8.0 by introducing the carbon dioxide-containing gas. On the other hand, in the mixing step S2, the pH is preferably 5.0 to 7.0 (more preferably 5.0 to 6.0) to obtain the effect of the inorganic flocculant. That is, it is not necessarily the optimum condition to subject the raw sludge that has undergone the precipitation step S1 to the mixing step S2 as it is, and it is preferable to change the pH of the raw sludge with a pH adjuster in the mixing step S2.

Therefore, in one embodiment of the invention, the precipitation step S1 and the mixing step S2 are not performed simultaneously. As an example of such a sludge treatment method, there is a method in which the precipitation device 1 in which the precipitation step S1 is performed and the mixing device 2 in which the mixing step S2 is performed are different devices. As another example, the precipitation device 1 and the mixing device 2 are the same device, but the precipitation step S1 and the mixing step S2 are not performed at the same time (for example, after stopping the introduction of the carbon dioxide-containing gas, method of adding an inorganic coagulant and a pH adjuster). From the viewpoint that continuous sludge treatment is possible (the pH in the apparatus does not have to be changed for each step), it is preferable to use separate apparatuses for the precipitation apparatus 1 and the mixing apparatus 2 .

In order to obtain the effect of suppressing the input amount of the calcium agent, it is preferable that the sludge supplied to the precipitation apparatus 1 contain an inorganic component whose carbonate is insoluble in water. The content of the inorganic component whose carbonate is insoluble in water is preferably 0.07% by weight or more, with the weight of the sludge (including water) supplied to the precipitation apparatus 1 being 100% by weight. 0.24% by weight or more is more preferable, and 0.48% by weight or more is even more preferable. Examples of inorganic components in which carbonates are insoluble include calcium, magnesium, manganese, copper and zinc. These inorganic components are generally present in sludge in an ionic form, but may also be present in other forms. It should be noted that not all of the inorganic components contained in the sludge need to be “inorganic components whose carbonates are insoluble in water”, and some of them are “inorganic components whose carbonates are insoluble in water”. is enough.

When calcium is contained in the sludge, the precipitated calcium carbonate functions as an inorganic calcium compound that circulates in the thermal decomposition device 6, the combustion device 8, and the reforming device 7, in addition to the function as the calcium agent described above. can function. In other words, if calcium is contained in the sludge, the amount of inorganic calcium compound to be introduced into the thermal decomposition device 6, reforming device 7 and combustion device 8 can be reduced as needed. Therefore, from the viewpoint of cost, it is desirable that the sludge contain calcium. The calcium content is preferably 0.07% by weight or more, more preferably 0.24% by weight or more, more preferably 0.48% by weight, where the weight of the sludge (including water) supplied to the precipitation apparatus 1 is 100% by weight. % or more is more preferable.

The precipitation device 1 is not particularly limited as long as it is a device capable of flocculating raw sludge to obtain flocculated sludge.

[Dehydrator]
The dewatering device 4 removes a separated liquid containing water from the flocculated sludge supplied from the mixing device 2 or flocculating device 3 to obtain dehydrated sludge. The obtained dehydrated sludge is supplied to the drying device 5 . The separated liquid removed from the flocculated sludge is properly treated in the wastewater treatment facility and then discharged to the outside through the discharge channel, or may be reused in the treatment facility as reused water.

The dehydrator 4 is not particularly limited as long as it can remove the separated liquid from the flocculated sludge. Specific examples of the dehydrator 4 include a pressurized dehydrator (belt press, filter press, screw press, etc.) or a mechanical dehydrator (centrifugal dehydrator, etc.).

[Drying device]
The drying device 5 evaporates at least part of the water contained in the dehydrated sludge supplied from the dewatering device 4 as water vapor. Part of the steam generated by the drying device 5 is supplied to the thermal decomposition device 6 as dry steam. This dry steam is used to thermally decompose the dried sludge supplied to the thermal decomposition device 6 . The rest of the water vapor generated by the drying device 5 is discharged to the outside.

Furthermore, the drying device 5 supplies the dry sludge from which moisture has been removed to the thermal decomposition device 6 . If desired, the drying device 5 may supply a portion of the dried sludge to the combustion device 8 . The dried sludge supplied to the combustion device 8 is combusted as a heat source.

The drying device 5 is not particularly limited as long as it is a device capable of drying dehydrated sludge to obtain dried sludge. Moreover, the drying device 5 is an optional device. That is, when the amount of water contained in the dehydrated sludge obtained by the dewatering device 4 is sufficiently small, the drying device 5 may not be provided. In this case, the dehydrated sludge obtained in the dewatering device 4 is supplied to the thermal decomposition device 6 .

[Pyrolyzer]
The thermal decomposition device 6 thermally decomposes the dry sludge supplied from the drying device 5 (or the dehydrated sludge supplied from the dehydration device 4). This thermal decomposition is carried out in the presence of steam, the heating temperature is 400 ° C. to 900 ° C. (preferably 600 ° C. to 800 ° C.), the residence time is 0.1 hours to 2 hours (preferably 0.5 hours to 1 hour). A new inorganic calcium compound may be supplied to the pyrolyzer 6 as necessary.

The pyrolysis products obtained by the pyrolyzer 6 are supplied to the combustion device 8 . On the other hand, the pyrolysis gas obtained by the pyrolyzer 6 is supplied to the reformer 7 .

The thermal decomposition device 6 is not particularly limited as long as it can thermally decompose dried sludge (or dehydrated sludge).

(Generation of pyrolysis gas)
In the pyrolyzer 6, pyrolysis is carried out by the reaction shown below, and finally pyrolysis gas is generated.

First, dried sludge (or dehydrated sludge) is pyrolyzed in the presence of water vapor and converted into pyrolysis gas and solid residue by the reaction shown in equation (1) below:
Dry sludge (C, H, O, N, S) + _H2O → Thermal decomposition gas ( _H2 , CO, _CO2 , _{CmHn , H2S} , _NH3 ) + C (charcoal) + ash … (1).

Thermal decomposition gases produced by the reaction of formula (1) include hydrogen (H ₂ ), carbon monoxide (CO), carbon dioxide (CO ₂ ), hydrogen sulfide (H ₂ S), ammonia (NH ₃ ), methane ( CH ₄ ) and a hydrocarbon-based gas (C _m H _n ; containing tar components) as main components. Solid residues include charcoal and ash. The ash is a compound containing P, Si, Al, Fe, Mg, Ca, Na and K and the like.

Further, a portion of the charcoal reacts with water vapor to convert to carbon dioxide and hydrogen, as shown in equation (2) below:
C(charcoal)+ _2H2O → _CO2 + _2H2 (2).

Furthermore, as shown in the following formula (3), carbon monoxide contained in the pyrolysis gas reacts with water vapor and is converted to carbon dioxide:
CO + H ₂ O → CO ₂ + H ₂ (3).

(concentration of hydrogen)
Most of the hydrogen sulfide contained in the pyrolysis gas reacts with the inorganic calcium compounds (mostly converted into calcium oxide by heating) deposited in the sludge in the coagulation process, and is fixed as calcium sulfide ( See formula (4) below):
CaO+ _H2S →CaS+ _H2O (4).

In addition, carbon dioxide generated by the reactions represented by the above formulas (1) to (3) reacts with calcium oxide and is immobilized as calcium carbonate (CaCO ₃ ) (see formula (5) below):
CaO+ _CO2 → _CaCO3 (5).

As shown in formula (4), most of the hydrogen sulfide contained in the pyrolysis gas is immobilized as calcium sulfide, resulting in an increase in the concentration of hydrogen in the pyrolysis gas. In addition, as shown in formula (5), only carbon dioxide in the pyrolysis gas is absorbed by calcium oxide, so rightward equilibrium shift occurs in the reactions shown in formulas (1) to (3), resulting in Hydrogen concentration in pyrolysis gas increases.

(Thermal decomposition product)
The pyrolysis products produced in the pyrolyzer 6 include inorganic calcium compounds (calcium carbonate, calcium oxide, etc.) in addition to charcoal and ash, which are solid residues produced in the reaction of formula (1). ing. The pyrolysis products are sent to combustion device 8 .

In the sludge treatment apparatus 100, (i) calcium oxide is supplied from the combustion apparatus 8 to the reformer 7, and (ii) calcium oxide and calcium carbonate are supplied from the reformer 7 to the thermal decomposition apparatus 6. supplied. Thus, the sludge treatment apparatus 100 has a structure in which inorganic calcium compounds (calcium oxide and calcium carbonate) are circulated among the thermal decomposition apparatus 6, the combustion apparatus 8 and the reforming apparatus 7.

[Reformer]
The reformer 7 steam-reforms the pyrolysis gas supplied from the pyrolysis device 6 to further increase the hydrogen concentration in the pyrolysis gas. The pyrolysis gas with the hydrogen concentration further increased in this way is recovered as a gas containing hydrogen at a high concentration after cooling. A new inorganic calcium compound may be supplied to the reformer 7 as necessary.

The reformer 7 is not particularly limited as long as it is a device capable of steam reforming the pyrolysis gas.

In the reformer 7, steam reforming of the pyrolysis gas is performed as follows. As mentioned above, the pyrolysis gas contains hydrogen, carbon monoxide, methane, and hydrocarbon-based gases (containing tar components). As shown in formulas (3) and (6), carbon monoxide and hydrocarbon-based gases contained in the pyrolysis gas are reformed into hydrogen and carbon dioxide using calcium oxide as a catalyst:
CO + H ₂ O → CO ₂ + H ₂ (3)
_CmHn + _H2O- > _H2 + _CO2 (6) _.

The carbon dioxide produced at this time is absorbed by calcium oxide as shown in formula (5). In this way the concentration of hydrogen in the pyrolysis gas is further increased:
CaO+ _CO2 → _CaCO3 (5).

[Combustion device]
The combustion device 8 burns the thermal decomposition products supplied from the thermal decomposition device 6 to produce combustion products and combustion gas. Among the combustion products, calcium oxide is separated and circulated to the reformer 7 . Air or an oxygen-containing gas and a combustion gas serving as a heat source are supplied from the outside to the combustion device 8 . If necessary, the combustion device 8 may be supplied with fresh inorganic calcium compounds.

The combustion device 8 may be supplied with dried sludge from the drying device 5 . The dried sludge supplied at this time is combusted as an additional heat source in addition to the combustion gas. By burning the dried sludge, the amount of combustion gas supplied from the outside can be reduced, so that the amount of energy used can be reduced.

Combustion device 8 is not particularly limited as long as it is a device capable of burning thermal decomposition products.

(Concentration of carbon dioxide)
In the combustion device 8, combustion products and combustion gases are produced by the following reactions. First, the air or oxygen-containing gas and the charcoal contained in the pyrolysis products are combusted to produce carbon dioxide (see equation (7) below). Calcium oxide and carbon dioxide are generated from calcium carbonate contained in the thermal decomposition products (see formula (8) below). Further, air or oxygen-containing gas reacts with calcium sulfide contained in the thermal decomposition products to produce gypsum (calcium sulfate; CaSO ₄ ) (see formula (9) below).

C(charcoal)+ _O2 → _CO2 (7)
_CaCO3 →CaO+ _CO2 (8)
CaS+ _2O2 → _CaSO4 (9).

In this manner, combustion gas containing high-concentration carbon dioxide is obtained from the combustion device 8 . That is, in addition to the carbon dioxide produced by burning the charcoal, the carbon dioxide absorbed as calcium carbonate in the thermal decomposition device 6 and the reformer 7 is also released, increasing the carbon dioxide concentration in the combustion gas. At least part of the combustion gas containing high-concentration carbon dioxide is introduced into the precipitation device 1 through the introduction device 1a. Here, not all of the combustion gases need be introduced into the condenser 1 .

Equation (8) can also be interpreted as a regeneration reaction of calcium oxide. This calcium oxide is separated by a calcium oxide separation device (such as a cyclone, not shown) and supplied to the reformer 7 . Furthermore, part of the regenerated calcium oxide may be supplied to the precipitation device 1 . Calcium oxide supplied to the precipitation device 1 functions as a calcium agent. That is, in the precipitation step S1, even when the amount of the insoluble carbonate precipitated by the introduction of the carbon dioxide-containing gas is insufficient, the regenerated calcium oxide is supplied, so the calcium agent to be added from the outside can be reduced. be able to.

Ash is separated by an ash separator 9 (such as a cyclone) and discharged to the outside.

[Modification 1 of sludge treatment equipment]
Although FIG. 2 employs a design in which the inorganic calcium compound is circulated between the pyrolyzer 6, the combustion device 8 and the reformer 7, these devices may simply be the combustion device. That is, the design may be such that dried sludge (or dehydrated sludge) is supplied directly to the combustion device and burned.

[Modification 2 of sludge treatment device]
The above description mainly describes the case where the precipitation device 1 and the mixing device 2 are different devices. However, the precipitation device 1 and the mixing device 2 (and optionally the agglomeration device 3) may be the same device.

[Sludge treatment method]
FIG. 3 is a flowchart showing the process flow of the sludge treatment method according to one embodiment of the present invention. The sludge treatment method illustrated in FIG. 3 includes precipitation step S1, mixing step S2 and dehydration step S4. With such a configuration, the sludge treatment method according to one embodiment of the present invention can exhibit the above-described effect of the present invention (suppression of the input amount of the calcium agent).

Moreover, the sludge treatment method according to one embodiment of the present invention also includes, as an optional configuration, a flocculation step S3, a drying step S5, a thermal decomposition step S6, a reforming step S7, and a combustion step S8. With such a configuration, the sludge treatment method according to one embodiment of the present invention provides (i) a gas containing a high concentration of carbon dioxide generated in the process of treating sludge and supplying it to the precipitation step S1. and (ii) a fuel gas containing a high concentration of hydrogen can be extracted.

In addition, you may provide a conveyance process between said each process. By providing a conveying process, sludge can be treated continuously.

Each step constituting the sludge treatment method according to one embodiment of the present invention will be described below. However, with respect to the content that overlaps with the content described in the item [Sludge treatment device], the description will be simplified or omitted.

[Precipitation step, mixing step and aggregation step]
In the precipitation step S1, the mixing step S2 and the optional aggregation step S3, raw sludge is aggregated to obtain aggregated sludge. Among them, in the precipitation step S1, a carbon dioxide-containing gas is introduced into the raw sludge. In the mixing step S2, an inorganic coagulant and a pH adjuster are added to the raw sludge. In the flocculation step, a polymer flocculant is added to the raw sludge. The flocculated sludge thus obtained is subjected to the dehydration step S4. The water separated in the step of obtaining flocculated sludge is appropriately treated in a wastewater treatment facility and then discharged outside through a discharge channel, or may be reused in the treatment facility as reused water.

The carbon dioxide introduced in the precipitation step S1 has the function of precipitating insoluble carbonate. Therefore, the sludge treatment method according to one embodiment of the present invention can suppress the input amount of the calcium agent.

The source of the carbon dioxide-containing gas introduced in the precipitation step S1 is not particularly limited. In one embodiment, at least part of the carbon dioxide-containing gas introduced in the precipitation step S1 is the carbon dioxide-containing gas generated in the combustion step S8 described below.

Moreover, in the precipitation step S1, calcium oxide separated from the solid matter remaining after the combustion step S8 may be put into the raw sludge.

In addition, suitable conditions for the carbon dioxide-containing gas introduced in the precipitation step S1 and the raw sludge supplied to the precipitation step S1 to the aggregation step S3 are described in the item [Precipitation device and introduction device, mixing device, aggregation device]. is as described.

[Dehydration process]
In the dehydration step S4, the flocculated sludge obtained in the mixing step S2 (or flocculation step S3) is dehydrated to obtain dehydrated sludge. That is, in the dehydration step S4, the separated liquid containing water is removed from the flocculated sludge. A specific method for dewatering flocculated sludge is not particularly limited. The obtained dehydrated sludge is subjected to the drying step S5.

[Drying process]
In the drying step S5, at least part of the water contained in the dewatered sludge obtained in the dewatering step S4 is evaporated as water vapor to obtain dried sludge. Part of the steam generated in the drying step S5 is used as dry steam for thermal decomposition of the dried sludge in the thermal decomposition step S6. The rest of the water vapor generated by the drying step S5 is discharged to the outside. Also, part of the dried sludge may be used as a heat source in the combustion step S8. The obtained dried sludge is subjected to the thermal decomposition step S6.

A specific method for drying the dehydrated sludge is not particularly limited. Further, when the amount of water contained in the dewatered sludge obtained in the dewatering step S4 is small, the drying step S5 may not be provided. In this case, the dehydrated sludge obtained in the dehydration step S4 is supplied to the thermal decomposition step S6.

[Thermal decomposition process]
In the thermal decomposition step S6, the dry sludge obtained in the drying step S5 (or the dehydrated sludge obtained in the dehydration step S4) is thermally decomposed to obtain thermal decomposition products and thermal decomposition gas. This thermal decomposition is carried out in the presence of steam, the heating temperature is 400 ° C. to 900 ° C. (preferably 600 ° C. to 800 ° C.), the residence time is 0.1 hours to 2 hours (preferably 0.5 hours to 1 hour). If necessary, a new inorganic calcium compound may be supplied externally.

In the thermal decomposition step S6, thermal decomposition is performed by the reaction described in the item [Thermal Decomposition Apparatus]. The pyrolysis gas generated by this pyrolysis is supplied to the reforming step S7. On the other hand, thermal decomposition products generated by thermal decomposition are supplied to the combustion step S8.

In addition, the inorganic calcium compound circulates between the thermal decomposition step S6, the combustion step S8 and the reforming step S7. This point is as described in the item (Thermal Decomposition Products).

A specific method for thermally decomposing dry sludge (dehydrated sludge) is not particularly limited.

[Reforming process]
In the reforming step S7, the pyrolysis gas obtained in the pyrolysis step S6 is steam-reformed to further increase the hydrogen concentration in the pyrolysis gas. The pyrolysis gas with the hydrogen concentration further increased in this way is recovered as a gas containing hydrogen at a high concentration after cooling. If necessary, a new inorganic calcium compound may be supplied externally.

A specific method for steam reforming the pyrolysis gas is not particularly limited.

[Combustion process]
The combustion step S8 burns the thermal decomposition products obtained in the thermal decomposition step S6 to produce combustion products and combustion gas. Among the combustion products, calcium oxide is separated and recycled to the reforming step S7. In the combustion step S8, air or an oxygen-containing gas and a combustion gas serving as a heat source are supplied from the outside. A new inorganic calcium compound may be supplied from the outside in the combustion step S8.

Dried sludge may be supplied to the combustion step S8 from the drying step S5. The dried sludge supplied at this time is combusted as an additional heat source in addition to the combustion gas. By burning the dried sludge, the amount of combustion gas supplied from the outside can be reduced, so that the amount of energy used can be reduced.

The combustion gas obtained in the combustion step S8 contains high-concentration carbon dioxide. Therefore, it is preferable to introduce at least part of this combustion gas in the deposition step S1.

A specific method for burning the thermal decomposition product is not particularly limited.

〔summary〕
The present invention includes the following configurations.
<1>
A precipitation step S1 in which a carbon dioxide-containing gas is introduced into the raw sludge to precipitate an insoluble carbonate;
A mixing step S2 of adding an inorganic flocculant and a pH adjuster to the raw sludge that has undergone the precipitation step S1 and incorporating the insoluble carbonate into the sludge flocs;
A dewatering step S4 for dewatering the sludge after passing through the mixing step S2;
A sludge treatment method, comprising:
<2>
A sludge treatment method further comprising a dewatered sludge combustion step S8 performed after the dewatering step S4,
The sludge treatment method according to <1>, wherein at least part of the carbon dioxide-containing gas introduced in the precipitation step S1 is the carbon dioxide-containing gas generated in the combustion step S8.
<3>
<1> or <2>.
<4>
The sludge treatment method according to any one of <1> to <3>, wherein the pH of the raw sludge is adjusted to 7.0 to 8.0 by the precipitation step S1.
<5>
The raw sludge to be subjected to the precipitation step S1 contains an inorganic component,
At least a portion of the inorganic component has a carbonate insoluble in water,
When the weight of the raw sludge (including water) to be subjected to the precipitation step S1 is 100% by weight, the content of the inorganic component is 0.07% by weight or more, any of <1> to <4> or the sludge treatment method according to one.
<6>
The sludge treatment method according to <5>, wherein the inorganic component whose carbonate is insoluble in water is one or more selected from the group consisting of calcium, magnesium, manganese, copper and zinc.
<7>
A precipitation device 1 that introduces a carbon dioxide-containing gas into the raw sludge through the introduction device 1a and precipitates an insoluble carbonate;
A mixing device 2 that mixes the raw sludge treated by the precipitation device 1 with an inorganic flocculant and a pH adjuster to incorporate the insoluble carbonate into the sludge flocs;
A dewatering device 4 for dewatering the sludge after being treated by the mixing device 2;
with
A sludge treatment apparatus 100 which is a device different from the precipitation device 1 and the mixing device 2 .
<8>
It further comprises a combustion device 8 for burning the sludge dehydrated by the dehydration device 4,
The sludge treatment apparatus 100 according to <7>, wherein at least part of the carbon dioxide-containing gas introduced by the introduction device 1a is the carbon dioxide-containing gas generated in the combustion device 8.

[Other aspects of the present invention]
The present invention also includes the following configurations.

[1]
An introduction step of introducing a carbon dioxide-containing gas into the raw sludge and precipitating an insoluble carbonate;
A dehydration step S4 for dewatering the flocculated sludge generated by the introduction step;
a thermal decomposition step S6 in which the sludge after the dehydration step S4 is thermally decomposed in the presence of water vapor or superheated steam to obtain thermal decomposition products and combustible gas;
a combustion step S8 of burning the thermal decomposition products to obtain combustion products;
A reforming step S7 for producing a fuel gas having a higher hydrogen concentration than the combustible gas from the combustible gas by steam reforming using calcium oxide;
A sludge treatment method comprising
Between the thermal decomposition step S6, the combustion step S8 and the reforming step S7, the inorganic calcium compound is circulating,
The sludge treatment method, wherein at least part of the carbon dioxide-containing gas introduced in the introduction step is the carbon dioxide-containing gas generated in the combustion step S8.

According to the above configuration, the inorganic calcium compound (calcium oxide, calcium carbonate, etc.) circulates among the thermal decomposition step S6, the combustion step S8, and the reforming step S7. Therefore, the carbon dioxide generated in the thermal decomposition step S6 and the reforming step S7 is adsorbed as calcium carbonate and released again as carbon dioxide in the combustion step S8. As a result, a carbon dioxide-containing gas with a high carbon dioxide concentration is obtained. Since the gas containing this high-concentration carbon dioxide is introduced in the introduction step, it is possible to reduce the input amount of the calcium agent for flocculating the raw sludge.

[2]
An introduction step of introducing a carbon dioxide-containing gas into the raw sludge and precipitating calcium carbonate;
A dehydration step S4 for dewatering the flocculated sludge generated by the introduction step;
a thermal decomposition step S6 in which the sludge after the dehydration step S4 is thermally decomposed in the presence of water vapor or superheated steam to obtain thermal decomposition products and combustible gas;
a combustion step S8 of burning the thermal decomposition products to obtain combustion products;
A reforming step S7 for producing a fuel gas having a higher hydrogen concentration than the combustible gas from the combustible gas by steam reforming using calcium oxide;
A sludge treatment method comprising
Between the thermal decomposition step S6, the combustion step S8, and the reforming step S7, the inorganic calcium compound is circulated, and at least part of the inorganic calcium is derived from the calcium carbonate precipitated in the introducing step. Sludge treatment method.

According to the above configuration, at least part of the inorganic calcium compounds (calcium oxide, calcium carbonate, etc.) circulating between the thermal decomposition step S6, the combustion step S8, and the reforming step S7 is precipitated from the raw sludge. Calcium carbonate can be substituted. Therefore, in these steps, the amount of externally added inorganic calcium compound can be reduced.

The "introduction step" in [1] and [2] is a step combining the precipitation step S1 and the mixing step S2 (and optionally the aggregation step S3). At this time, the precipitation step S1 and the mixing step S2 may be performed simultaneously or sequentially.

[3]
A salt precipitation device that introduces a carbon dioxide-containing gas into the raw sludge through the introduction device 1a and precipitates an insoluble carbonate;
a dewatering device 4 for dewatering the sludge after being processed by the salt precipitation device;
a thermal decomposition device 6 for thermally decomposing the sludge after being treated by the dehydration device 4 in the presence of water vapor or superheated steam to obtain thermal decomposition products and combustible gas;
a combustion device 8 for burning the pyrolysis products to obtain combustion products;
A reformer 7 for producing a fuel gas having a higher hydrogen concentration than the combustible gas from the combustible gas by steam reforming using calcium oxide;
A sludge treatment apparatus 100 comprising
Between the thermal decomposition device 6, the combustion device 8 and the reforming device 7, an inorganic calcium compound is circulated,
The sludge treatment apparatus 100, wherein at least part of the carbon dioxide-containing gas introduced in the salt precipitation apparatus is the carbon dioxide-containing gas generated in the combustion apparatus 8.

[4]
A salt precipitation device that introduces a carbon dioxide-containing gas into the raw sludge through the introduction device 1a and precipitates calcium carbonate;
a dewatering device 4 for dewatering the sludge after being processed by the salt precipitation device;
a thermal decomposition device 6 for thermally decomposing the sludge after being treated by the dehydration device 4 in the presence of water vapor or superheated steam to obtain thermal decomposition products and combustible gas;
a combustion device 8 for burning the pyrolysis products to obtain combustion products;
A reformer 7 for producing a fuel gas having a higher hydrogen concentration than the combustible gas from the combustible gas by steam reforming using calcium oxide;
A sludge treatment apparatus 100 comprising
Between the thermal decomposition device 6, the combustion device 8 and the reforming device 7, an inorganic calcium compound is circulated, and at least part of the inorganic calcium is precipitated in the salt precipitation device. A sludge treatment device 100 derived from calcium carbonate.

The configuration [3] provides the same effect as the configuration [1], and the configuration [4] provides the same effect as the configuration [2].

The "salt precipitation device" in [3] and [4] is a device combining the precipitation device 1 and the mixing device 2 (and optionally the aggregation device 3). At this time, the precipitation device 1 and the mixing device 2 may be the same device or different devices.

1: precipitation device 1a: introduction device 2: mixing device 4: dehydration device 8: combustion device 100: sludge treatment device S1: precipitation process S2: mixing process S4: dehydration process S8: combustion process

Claims (8)

A precipitation step of introducing a carbon dioxide-containing gas into the raw sludge to precipitate an insoluble carbonate;
A mixing step of adding an inorganic flocculant and a pH adjuster to the raw sludge that has undergone the precipitation step and incorporating the insoluble carbonate into the sludge flocs;
A dehydration step for dewatering the sludge after passing through the mixing step;
A sludge treatment method, comprising: A sludge treatment method further comprising a step of burning sludge after dehydration, which is performed after the dehydration step,
The sludge treatment method according to claim 1, wherein at least part of the carbon dioxide-containing gas introduced in the precipitation step is carbon dioxide-containing gas produced in the combustion step. 3. According to claim 1 or 2, wherein the concentration of carbon dioxide contained in the carbon dioxide-containing gas introduced in the precipitation step is 10% by volume or more when the total volume of the carbon dioxide-containing gas is 100% by volume. The described sludge treatment method. The sludge treatment method according to any one of claims 1 to 3, wherein the pH of the raw sludge is adjusted to 7.0 to 8.0 by the precipitation step. The raw sludge to be subjected to the precipitation step contains inorganic components,
At least a portion of the inorganic component has a carbonate insoluble in water,
5. Any one of claims 1 to 4, wherein the content of the inorganic component is 0.07% by weight or more when the weight of the raw sludge (including water) to be subjected to the precipitation step is 100% by weight. The sludge treatment method described in . The sludge treatment method according to claim 5, wherein the inorganic component whose carbonate is insoluble in water is one or more selected from the group consisting of calcium, magnesium, manganese, copper and zinc. a precipitation device that introduces a carbon dioxide-containing gas into the raw sludge through the introduction device and precipitates an insoluble carbonate;
A mixing device that adds an inorganic flocculant and a pH adjuster to the raw sludge treated by the precipitation device and incorporates the insoluble carbonate into the sludge flocs;
a dewatering device for dewatering the sludge after being treated by the mixing device;
with
A sludge treatment device, which is a device different from the precipitation device and the mixing device. It further comprises a combustion device for burning the sludge dehydrated by the dehydration device,
8. The sludge treatment apparatus according to claim 7, wherein at least part of the carbon dioxide-containing gas introduced by said introduction device is carbon dioxide-containing gas generated in said combustion device.

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