JP6869126B2 - Sludge treatment method and treatment equipment - Google Patents

Description

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

In the sludge treatment step, the sludge is first dehydrated using a dehydrator, and then the dehydrated product (sludge after dehydration) is dried using a dryer. The dried sludge is treated as landfill or industrial waste, and has been effectively used as a fuel resource in recent years. In the drying process, the dried product and exhaust gas (heat medium gas or carrier gas) may be discharged from the dryer in a mixed state, and this mixture is separated from the powder or granular material by using a solid air separator. Separate into gas. Then, the separated gas is released to the atmosphere through a deodorizing step and a dust collecting step.

In the dehydration step, an inorganic flocculant may be injected into the dehydrator. The purpose of injecting this inorganic flocculant is to promote dehydration by a dehydrator and reduce the water content of sludge after dehydration. Generally, the injection rate of the inorganic flocculant is about 2 to 4% with respect to the amount of solid sludge supplied to the dehydrator. That is, the "injection rate (%) of the inorganic coagulant" was obtained by dividing the "product weight of the inorganic coagulant to be injected (kg / h)" by the "solid amount of sludge supplied to the dehydrator (kg / h)". After that, it is the value multiplied by 100 (hereinafter the same). This is because when the injection rate is 5% or more, the rate at which the water content decreases with respect to the injection rate of the inorganic flocculant becomes extremely low, and the cost effectiveness deteriorates.
The "sludge solid matter amount (kg / h) supplied to the dehydrator" is ^{obtained by multiplying the "sludge flow rate (m 3} / h)" by the "sludge concentration (%)" and then multiplying by "10". (The same applies hereinafter). The "product weight of the inorganic coagulant to be injected (kg / h)" is a value obtained by multiplying the "product specific weight of the inorganic coagulant" by the "injection amount of the inorganic coagulant (L / h)" (hereinafter, the same). ).
In some cases, the polymer flocculant is supplied to the dehydrator. In this case, the "polymer coagulant injection rate (%)" is the "product weight of the polymer coagulant to be injected (kg / h)". It is a value obtained by dividing by "the amount of solid sludge supplied to the dehydrator (kg / h)" and then multiplying by 100 (hereinafter, the same applies).

When a continuous hot air dryer is used in the drying step, there is a problem that continuous operation becomes impossible due to the dehydrated product adhering to or accumulating in the dryer depending on the properties of the dehydrated product to be supplied. is there.

Therefore, a main object of the present invention is to provide a sludge treatment method and a treatment device capable of preventing the dehydration from adhering to and accumulating in the continuous hot air dryer.

The present invention that solves the above problems is as follows.
(1) A dehydration process that dehydrates sludge with a dehydrator,
It is a sludge treatment method including a drying step of bringing dehydrated sludge into contact with hot air in a continuous hot air dryer to dry the sludge.
In the dehydration step
An inorganic flocculant is injected into at least one of the sludge before being supplied to the dehydrator and the sludge being dehydrated by the dehydrator.
A method for treating sludge, wherein the injection rate of the inorganic flocculant is 5% or more with respect to the amount of solid sludge supplied to the dehydrator.

(Action effect)
As described above, conventionally, in order to reduce the water content of the dehydrated product discharged from the dehydrator, an inorganic flocculant of about 2 to 4% has been injected.
In the present invention, the inorganic flocculant is injected for a purpose completely different from the conventional one. That is, the inorganic coagulant is injected to control the properties of the dehydrated product discharged from the dehydrator to prevent the dehydrated product from adhering to or accumulating in the continuous hot air dryer.
To achieve this goal, we adopted an injection rate of inorganic flocculants, which was previously avoided due to its inefficiency. Specifically, it was decided to inject 5% or more of the inorganic flocculant with respect to the amount of solid sludge supplied to the dehydrator.
By setting the injection rate of the inorganic flocculant to 5% or more, the properties of the dehydrated product become suitable for drying in the continuous hot air dryer, and the dehydrated product adheres to or accumulates in the continuous hot air dryer. It became possible to prevent that.

(2) The sludge treatment method according to (1) above, wherein the injection rate of the inorganic flocculant is 30% or less with respect to the amount of solid sludge supplied to the dehydrator.

(Action effect)
The more the amount of the inorganic flocculant is more than 5%, the more difficult it is for dehydrated products to adhere and accumulate in the continuous hot air dryer. However, there is a demerit that the drug cost increases as the amount of the inorganic flocculant increases. Therefore, the running cost can be reduced by setting the upper limit of the injection rate of the inorganic flocculant to 30%.

Further, depending on the type of the inorganic flocculant, there is a risk that the inside of the continuous hot air dryer is corroded, and this risk increases as the amount of the inorganic flocculant increases. In particular, ferric sulfate, ferrous sulfate, ferric chloride, aluminum sulfate, and polyaluminum chloride, which are inorganic flocculants containing sulfuric acid and hydrochloric acid, are metal salts dissolved in sulfuric acid or hydrochloric acid. Therefore, when the dehydrated product containing the inorganic flocculant is supplied into the continuous hot air dryer, the sulfur content and hydrogen chloride of the inorganic flocculant are volatilized and mixed in the hot air, and these are mixed at a temperature below the acid dew point. Condensation of the acid component causes a problem that the metal of the dryer is corroded.
Therefore, by setting the upper limit of the injection rate of the inorganic flocculant to 30%, it is possible to reduce the cost and suppress the occurrence of corrosion inside the continuous hot air dryer.

(3) The sludge treatment method according to (2) above, wherein the inorganic flocculant is selected from the group of ferric sulfate, ferrous sulfate, ferric chloride, aluminum sulfate and polyaluminum chloride.

(Action effect)
Although ferric sulfate, ferrous sulfate, ferric chloride, aluminum sulfate, and polyaluminum chloride, which are inorganic flocculants containing sulfuric acid and hydrochloric acid, have the above-mentioned corrosion problems, they should be used in an appropriate amount (30% or less). If there is, there are advantages that corrosion can be suppressed, the coagulation effect is high as compared with other inorganic coagulants, and the running cost is low.

(4) The sludge treatment method according to (1) above, wherein the continuous hot air dryer is a circular tube type airflow dryer or a straight tube type airflow dryer.

(Action effect)
When the continuous hot air dryer is a circular tube type airflow dryer or a straight tube type airflow dryer, dehydrated matter is likely to adhere and accumulate in the dryer. Therefore, when such a dryer is used, it is highly effective to set the injection rate of the inorganic flocculant to 5% or more with respect to the amount of solid sludge supplied to the dehydrator.

(5) The sludge treatment method according to (1) above, wherein the maximum particle size of the dehydrated sludge supplied to the continuous hot air dryer is 60 mm or less.

(Action effect)
There are various factors that cause the dehydrated product to adhere and accumulate in the dryer, but the main factor is that the particle size of the dehydrated product is large. If the maximum particle size of the dehydrated product is larger than 60 mm, it becomes difficult to transport the dehydrated product by hot air from the dryer. In the present invention, by injecting 5% or more of an inorganic flocculant to reduce the maximum particle size of the dehydrated product to 60 mm or less, adhesion / deposition in the dryer can be prevented.

(6) The sludge treatment method according to (1) above, wherein the average particle size of the dehydrated sludge supplied to the continuous hot air dryer is 1 mm to 30 mm.

(Action effect)
When the average particle size of the dehydrated sludge (dewatered product) is within the above range by injecting 5% or more of the inorganic flocculant, it becomes difficult for the sludge to adhere and accumulate in the dryer.

(7) A dehydrator that dehydrates sludge,
It has a continuous hot air dryer that dries the sludge by bringing the dehydrated sludge into contact with hot air.
An inorganic flocculant is injected into at least one of the sludge before being supplied to the dehydrator and the sludge being dehydrated by the dehydrator.
A sludge treatment apparatus comprising an injection means for injecting the inorganic flocculant so that the injection rate of the inorganic flocculant is 5% or more with respect to the amount of solid sludge supplied to the dehydrator.

(Action effect)
It has the same effect as (1) above.

(8) The sludge treatment apparatus according to (7) above, wherein the injection rate of the inorganic flocculant is 30% or less with respect to the amount of solid sludge supplied to the dehydrator.

(Action effect)
It has the same effect as (2) above.

According to the present invention, it is possible to prevent the dehydrated product from adhering to or accumulating in the continuous hot air dryer.

It is a processing flow diagram of the sludge processing apparatus which concerns on this invention.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. It should be noted that the following description and drawings merely show one embodiment of the present invention, and the contents of the present invention should not be construed as being limited to this embodiment.

FIG. 1 is a processing flow diagram of the sludge processing apparatus 1. The processing device 1 includes a hot air generator 4, a continuous hot air dryer 5, a solid air separator 6, and the like. The configuration of the processing device 1 and the processing flow will be described in detail below.

(Sludge W)
The treatment apparatus 1 according to the present invention treats sludge W. Examples of this sludge include surplus sludge, initial sedimentation sludge, mixed raw sludge, mixed sludge, digested sludge, sludge mixed and digested with biomass, and the like, and inorganic substances may be mixed therein. Of these sludges, it is particularly suitable for treating digestive sludge. The sludge W is stored in the sludge storage tank 2 and is supplied to the dehydrator 3 by the supply pump 21.

(Dehydrator 3)
The processing apparatus 1 according to the present invention has a dehydrator 3 for dehydrating sludge W. In the form of FIG. 1, the sludge W is dehydrated by the dehydrator 3 and then sent to the continuous hot air dryer 5.

Examples of the dehydrator 3 include a centrifugal dehydrator, a belt press dehydrator, a screw press dehydrator (including a multi-plate type dehydrator), a rotary press dehydrator, a rotary pressurizing dehydrator, a multiple disc type dehydrator, and the like. Can be mentioned. Of these dehydrators, a centrifugal dehydrator is particularly suitable.

Centrifugal dehydrator 3 includes a dehydrator used in a two-component tempering method in which two types of coagulants are added to sludge W to adjust the properties of sludge W. This two-component tempering type centrifugal dehydrator is suitable for the centrifugal dehydrator 3 of the present invention because it is easy to reduce the maximum particle size and the average particle size of the dehydrated product. The two-component tempering type centrifugal dehydrator includes an in-flight two-component tempering type centrifugal dehydrator and an external two-component tempering type centrifugal dehydrator. The former is two types of coagulants (one type is an inorganic coagulant). , The other type is a polymer flocculant. The same shall apply hereinafter) is a dehydrator that supplies the sludge onboard, and the latter is a dehydrator that supplies two types of flocculants to sludge outside the machine. In the present invention, either type may be used. When one type of coagulant is supplied to the sludge outside the machine and the other type of coagulant is supplied to the sludge inside the machine, it is classified as an external two-component tempering type centrifugal dehydrator for convenience.

The two-component tempering type centrifugal dehydrator 3 is provided with a rotary bowl on the outside, and a screw conveyor is provided in the rotary bowl. A supply port is provided on one end side of the rotary bowl, and a discharge port is provided on the other end side. The sludge W supplied into the rotary bowl from the supply port is carried to the other end side while being agitated by the screw conveyor, and is discharged from the discharge port as dehydrated matter. The sludge W is dehydrated by the centrifugal force generated by the rotation of the rotary bowl in the process of moving in the rotary bowl from one end side to the other end side.

The in-flight two-component tempering type centrifugal dehydrator 3 adds the polymer flocculant HC and the inorganic flocculant IC into the sludge W by injecting them into a rotating bowl. On the other hand, the external two-component tempering type centrifugal dehydrator 3 adds the polymer flocculant HC and the inorganic flocculant IC to the sludge W before being supplied to the rotary bowl.

As the polymer flocculant HC, for example, polyacrylamide-based or polyacrylic acid ester-based ones can be used. Examples of the inorganic flocculant IC include ferric sulfate (particularly, ferric sulfate (polyiron)), ferrous sulfate, ferric chloride, aluminum sulfate and polyaluminum chloride (PAC), and ferric chloride. Etc. can be used. By using these two types of flocculants, the maximum particle size and the average particle size of the dehydrated product can be reduced. Concomitantly, the water content of the dehydrated product can also be reduced.

The injection rate of the inorganic flocculant IC is preferably 5% or more with respect to the amount of solid sludge supplied to the dehydrator 3. For example, when the amount of solid sludge supplied to the dehydrator 3 is 4 m ³ / h, it is preferable to inject an inorganic flocculant IC of ^{0.2 m 3 / h or more.} By injecting 5% or more of the inorganic flocculant IC, the properties of the dehydrated product become suitable for drying of the continuous hot air dryer 5, and the dehydrated product adheres to or accumulates in the continuous hot air dryer 5. You can prevent it from happening.

The properties of the dehydrated product suitable for drying the continuous hot air dryer 5 include various factors such as viscosity, but the most important factor for achieving the object of the present invention is that the particle size of the dehydrated product is small. It is in. This is because if the particle size of the dehydrated product is small, the weight is inevitably lightened, and it becomes easy to carry it with hot air in the dryer. Specifically, the maximum particle size is preferably 60 mm or less, and more preferably 30 mm or less. The average particle size is preferably 1 mm to 30 mm, more preferably 1 mm to 5 mm.

As described above, the more the injection rate of the inorganic flocculant IC is increased to more than 5%, the more difficult it is for dehydrated products to adhere and accumulate in the continuous hot air dryer 5.
However, as the amount of the inorganic flocculant IC increases, the drug cost increases. Further, depending on the type of the inorganic coagulant IC, sulfur and hydrogen chloride volatilize from the inorganic coagulant IC to lower the acid dew point, and sulfuric acid and hydrochloric acid contained in the inorganic coagulant IC are dissolved, so that the continuous hot air dryer 5 Corrodes the inside of. Considering these demerits, it is preferable to set the injection rate of the inorganic flocculant IC to 30% or less.

In addition to the inorganic flocculant IC, the polymer flocculant HC is injected into the two-component tempering type centrifugal dehydrator 3. Like the inorganic flocculant IC, the polymer flocculant HC has a function of coagulating sludge. Therefore, it is preferable that the injection rate of the polymer flocculant HC is changed according to the injection rate of the inorganic flocculant IC. For example, when the injection rate of the inorganic flocculant IC is 5% to 30%, the injection rate of the polymer flocculant HC is about 0.1% to 5% with respect to the amount of solid sludge supplied to the dehydrator 3. Is preferable.

As the in-flight two-component tempering type centrifugal dehydrator, for example, "Technical Information / Research" "Technical Information / Research" "133 2012/12/13 Technical Information <Technology" on the website of the Japan Sewage Works Agency dated April 20, 2015. Introduction> The one described in the column of "In-flight two-component tempering type centrifugal dehydrator" -Realization of low water content dehydrated sludge "can be used.

When the in-flight two-component tempering type centrifugal dehydrator 3 is used, when it is discharged from the discharge port of the dehydrator 3, it is discharged from the inside of the dehydrator 3 having a gravitational acceleration of 2000 to 3000 G, that is, 1 G. Since it is released into the atmosphere of, dehydrated matter will be dispersed. Therefore, the properties of the dehydrated product suitable for drying of the continuous hot air dryer 5, particularly the particle size of the dehydrated product can be easily set in a desired range.

By injecting the inorganic flocculant IC, the water content of the dehydrated product can be lowered concomitantly. For example, when the injection rate of the inorganic flocculant IC is 5% to 30%, the water content of the dehydrated product can be set to about 75% to 79%.

In the present invention, a one-component tempering type centrifugal dehydrator 3 may be used. Either type of the in-flight one-liquid tempering type centrifugal dehydrator 3 or the outside one-liquid tempering type centrifugal dehydrator 3 may be used. When the one-component tempering type centrifugal dehydrator 3 is used, only the inorganic flocculant IC is injected without injecting the polymer flocculant HC. The injection rate of the polymer flocculant HC is the same as in the case of the two-component tempering type centrifugal dehydrator 3. Specifically, the amount of sludge solids supplied to the dehydrator 3 is preferably 5% or more, and the injection rate of the inorganic flocculant IC is more preferably 30% or less.

(Dehydrate carrier 7)
The sludge (dewatered product) discharged from the dehydrator 3 is supplied to the dehydrated product transporter 7. The water content of the dehydrated product is preferably 81% or less, more preferably 78% or less. In FIG. 1, the dehydrator 3 and the dehydration carrier 7 are connected by a pipe 30, and the dehydrated product moves to the dehydration carrier 7 through the inside of the pipe 30. Further, a moisture meter AM is attached to the pipe 30 to measure the amount of moisture contained in the dehydrated product.

As the dehydration carrier 7, a screw conveyor, a belt conveyor, or the like that transports by mechanical power can be used. In FIG. 1, a screw conveyor is used as the dehydration carrier 7. Further, a supply port is provided in the middle portion (near the center) in the longitudinal direction of the screw conveyor 7 in FIG. 1, and the dehydrated product is supplied into the screw conveyor 7 from this supply port.

(Supply method of dehydrated product)
When supplying the dehydrated material to the continuous hot air dryer 5, the amount of the dehydrated material supplied to the continuous hot air dryer 5 (kg-ds / min) is set to X, and the amount of the dehydrated material held by the continuous hot air dryer 5 is set to X. When (kg-ds) is Y, continuous hot air drying is performed so that the average residence time T of the dehydrated product defined by the following formula 1 stays in the continuous dryer is within the range of 0.05 to 10 minutes. It is preferable to supply the machine 5.
T = Y / X ・ ・ ・ Equation 1
The residence time T is preferably in the range of 0.1 to 7 minutes, and more preferably in the range of 0.2 to 5 minutes.
By keeping the amount of dehydrated product supplied to the continuous hot air dryer 5 within the above range, the time for the dehydrated product to stay in the continuous hot air dryer 5 becomes an appropriate value, and a foul odor is generated from the final product. Can be suppressed.

(Maximum particle size)
It is preferable that the dehydrated product carrier 7 is provided with a measuring means for measuring the particle size of sludge (dehydrated product). As a result of measuring the particle size of the dehydrated product, if the maximum particle size of the dehydrated product is higher than the reference value, the dehydrated product is sent to the digestion tank 20, and if it is less than the standard value, the dehydrated product is sent to the continuous hot air dryer 5 To send to. The reference value can be arbitrarily determined, but if the maximum particle size of the dehydrated product is larger than 60 mm, it should be sent to the digestion tank 20, and conversely, if the maximum particle size of the dehydrated product is 60 mm or less, it should be sent to the dryer 5. Is preferable.

When a dehydrated product having a maximum particle size of more than 60 mm is supplied to the continuous hot air dryer 5, there is a high possibility that the dehydrated product adheres to or accumulates in the dryer 5. Then, when the amount of deposit exceeds a certain amount, it becomes necessary to temporarily stop the operation of the dryer 5 and artificially discharge the deposit. In the present invention, long-term continuous operation of the dryer 5 is realized by not supplying a dehydrated product having a maximum particle size of more than 60 mm.

The maximum particle size of sludge is measured by the method described in JIS M 8801 Coal Test Method. Sieve using a sieve with a sieve size of 45 mm, and use calipers to remove the sludge remaining on the sieve. The maximum diameter of the measured value is defined as the maximum particle size.

When the two-component tempering type centrifugal dehydrator 3 is used, the dehydrated product tends to be in uniform granules (granular matter), and the maximum particle size and the average particle size can be easily measured. Therefore, the two-component tempering type centrifugal dehydrator 3 is more suitable than the one-component tempering type centrifugal dehydrator 3.

In some cases, the dehydrated product is not homogeneously granular, that is, the dehydrated product is agglomerated by water or the like. Even if there is a lump of dehydrated product (lump) in this way, it can be supplied to the dryer.

When the two-component tempering type centrifugal dehydrator 3 is used and the injection rate of the inorganic flocculant IC is 5% or more, the dehydrated product tends to become more granular. By granulating the dehydrated product, it becomes easy to stably supply the dehydrated product to the continuous hot air dryer 5. Further, when the dehydrated product is granular, the resistance to the hot air flowing in the continuous hot air dryer 5 is reduced, and there is an advantage that the chance of contact between the hot air and the dehydrated product can be increased.

(Average particle size)
The average particle size is measured by the following method. When the particle size of the dehydrated product is 500 microns or more, sifting is performed by the method described in JIS M 8801 coal test method, and the sieving result is represented by the rosin ramler distribution, when the integrated mass (on the sieving) corresponds to 50%. The particle size of is defined as the average particle size. When the particle size of the dehydrated product is less than 500 microns, the particle size distribution is measured using a laser diffraction type particle size distribution measuring device (for example, trade name SALD-3100, manufactured by Shimadzu Corporation), and the cumulative volume corresponds to 50%. The particle size at the time of sieving is determined as the average particle size.

The average particle size of the dehydrated product may be measured, and if the average particle size is 1 mm to 30 mm, it may be sent to the dryer 5, and if it is outside the range, it may be sent to the digestion tank 20. If the average particle size is larger than 30 mm, there is a high possibility that the dehydrated product adheres to or accumulates in the dryer 5, so it is preferable to perform such control. At the same time, if the average particle size is larger than 30 mm, the dried product is discharged without being sufficiently dried in the dryer 5, and there is a concern that the quality of the dried product, which is the final product, may deteriorate.

(Particle size distribution)
In order to stabilize the operation of the continuous hot air dryer 5, it is preferable to reduce the fluctuation of the particle size distribution of the sewage sludge supplied per unit time. This is because a problem occurs when the value of the particle size distribution changes significantly. Specifically, when the value of the particle size distribution of sludge is large, the water content of the dried product discharged from the dryer 5 tends to be non-uniform, and when the value of the particle size distribution is small, the water content of the dried product tends to be uniform. ..

(Other)
A method of providing a dehydration storage facility (not shown) between the dehydration carrier 7 and the continuous hot air dryer 5 and periodically sending the dehydrated product from the storage facility to the continuous hot air dryer 5 is also considered. be able to.

(Hot air generator 4)
The dehydrated product discharged from the dehydrator 3 is sent to the continuous hot air dryer 5, and is dried in contact with the hot air in the dryer 5. The hot air used in the dryer 5 is generated by the hot air generator 4. Specifically, the burner 4A supplied with fuel F (LPG or the like) from a fuel tank (not shown) heats the compressed air sent from the storage tank 18 for storing the compressed air generated by the air compressor 17. Generates hot air. When the sludge W is sludge, the digestion gas generated when the sludge is digested may be used as the fuel F. The control of the hot air generator 4 measures the outlet temperature of the hot air generator 4 and controls the amounts of fuel F and air A supplied to the hot air generator 4 so as to reach a target temperature.

The hot air temperature is not particularly limited. However, for example, when 5% or more of the inorganic flocculant IC is injected to dehydrate the sludge solid matter supplied to the dehydrator 3 and the dehydrated product is dried in the dryer 5, the hot air temperature is set to 250 ° C. to 500 ° C. It is preferable to set the temperature to ° C. By using hot air in this range, the water content of the sludge after drying (dry sludge) can be set to a value of 10% to 50%, which is suitable for the subsequent treatment.

The hot air temperature is more preferably 350 ° C. to 450 ° C., further preferably 390 ° C. to 410 ° C., and most preferably 400 ° C. When the hot air temperature is low, the dehydrated product cannot be sufficiently dried, and the water content of the dried product becomes high. On the other hand, when the hot air temperature is high, the fuel cost of the hot air generator 4 increases, and the economic efficiency deteriorates. Therefore, in order to balance the economic efficiency of the moisture content of the dried product and the fuel cost, it is most appropriate to set the temperature at around 400 ° C.

(Continuous hot air dryer 5)
The continuous hot air dryer 5 brings the dehydrated product from the dehydrator 3 into contact with the hot air from the hot air generator 4 to dry the dehydrated product into powder or granular material.

The continuous hot air dryer 5 includes (1) a spray dryer, an air flow dryer, a fluidized layer dryer, a rotary dryer, and the like, in which the dehydrated material is dispersed in the hot air and dried (2). ) Transfer the dehydrated material in a stationary state like a ventilation band dryer, tunnel dryer (parallel flow band dryer), spout flow dryer, etc., and bring hot air into contact with the dehydrated material in the transfer process. Examples thereof include those in which the dehydrated material is dried, and (3) a type in which the dehydrated material is mechanically stirred and hot air is brought into contact with the dehydrated material to dry the dehydrated material. The "continuous type" of the continuous type hot air dryer 5 means that it can be operated continuously.

Generally, an indirect heating type dryer (stirring heat transfer type device) is often used, but in the present invention, it is preferable to use the airflow dryer 5 which is cheaper and has excellent maintainability.

There are various types of air flow dryers 5, but when 5% or more of the inorganic flocculant IC is injected into the two-component tempering type centrifugal dehydrator 3 or the one-component tempering type centrifugal dehydrator 3 to dehydrate the dehydrated product. Since the adhesiveness can be weakened, an air flow dryer 5 without a crusher for crushing the dehydrated product can be used.

FIG. 1 shows an example of the airflow dryer 5. The airflow dryer 5 is a circular tube type airflow dryer 5 in which pipes through which hot airflow passes (hereinafter, also referred to as “pipes”) are arranged in an annular shape. In the illustrated airflow dryer 5, the pipe 5a to which the hot air sent from the hot air generator 4 first arrives, the pipe 5b extending upward from the pipe 5a, and the pipe 5b extending horizontally in the direction of turning back from the pipe 5b. It is composed of an existing pipe 5c and a pipe 5d extending downward from the pipe 5c. An R-shaped curved pipe is located between the adjacent pipes (for example, between the pipes 5a and 5b). The lower end of the pipe 5d is joined to the left end of the pipe 5a, and the insides of the pipes are connected to each other at this joint. A dehydrated product supply port 5X is provided in the middle portion of the pipe 5a, and a desiccant discharge port 5Y is provided in the middle portion of the pipe 5d.

The hot air generated by the hot air generator 4 is supplied to the pipe 5a. At the same time, the dehydrated product conveyed by the conveying means 7 falls from the supply port 5X into the hot air (hot air flow) of the pipe 5a. The dehydrated product that has fallen is dispersed in powder particles in hot air. Then, the powder or granular material is instantaneously dried while being sent in parallel with the hot air flow (while being conveyed in the air flow by the hot air). Specifically, the hot air accompanied by the powder or granular material flows in the order of the pipe 5a, the pipe 5b, the pipe 5c, and the pipe 5d, and a part of the hot air is exhausted from the discharge port 5Y to the outside of the vessel. On the other hand, the dehydrated product not exhausted from the discharge port 5Y merges with the hot air newly sent from the hot air generator 4, and flows again to the pipe 5a, the pipe 5b, the pipe 5c, and the pipe 5d, and a part of them flows to the discharge port. It is exhausted from 5Y to the outside of the vessel. As described above, a part of the hot air is exhausted from the discharge port 5Y, and the other hot air circulates in the pipes 5a to 5d. In this way, the newly introduced dehydrated product and the dehydrated product circulating in the pipe are mixed in the pipe, whereby the adhesiveness and the water content are adjusted. That is, in the air flow dryer 5, the dehydrated product is dried by absorbing the heat in the hot air. Therefore, the airflow dryer 5 has a structure that is fundamentally different from that of an indirect heating type dryer that dries when a dehydrated product comes into contact with a heated pipe.

The dehydrated product immediately after being supplied to the circular tube type airflow dryer 5 often flows on the outer peripheral side of each of the pipes 5a to 5d due to the influence of centrifugal force. Then, as the drying of the dehydrated product progresses, the agglomerated state of the dehydrated product is dissolved and the average particle size becomes smaller, so that the dehydrated product flows on the inner peripheral side of each of the pipes 5a to 5d, and the discharge port 5Y provided inside the pipe 5d. Is discharged from.

In the operation of the air flow dryer 5, it is preferable that the wind speed of the hot air in each of the pipes 5a to 5d is 10 m / s or more. More preferably, it is preferably 15 m / s or more in order to smoothly convey the dehydrated product by hot air. More preferably, the dehydrated product supplied from the supply port 5X collides with the circulating hot air at high speed, so that the dehydrated product can be dispersed in the hot air. Therefore, the temperature is preferably 20 m / s or more.

In FIG. 1, a circular tube type airflow dryer 5 in which pipes 5a to 5d are formed in an annular shape is shown. However, the continuous hot air dryer 5 is not limited to the annular one, and may be a straight pipe type airflow dryer in which all the pipes are arranged in a straight line or a substantially straight line. The circular tube type airflow dryer 5 is superior in that the installation space is smaller than that of the straight tube type airflow dryer. However, even in a straight pipe type airflow dryer, if the pipe is extended in the height direction, the installation space can be reduced.

Even if the size of the circular tube type airflow dryer 5 is increased or decreased, there is almost no change in the residence time in which the dehydrated product stays in the dryer 5.

Even if a stirring heat transfer dryer is provided instead of the continuous hot air dryer 5, a part of the separated gas from the solid air separator 6 is returned to the hot air generator 4 to make effective use of the separated gas. good. An airflow dryer with a crusher may be provided as the continuous hot air dryer 5, and a part of the separated gas from the solid air separator 6 may be returned to the hot air generator 4 to make effective use of the separated gas. ..

The continuous hot air dryer 5 of the present invention uses a dryer 5 in which the heat capacity coefficient obtained from the size of the dryer 5 and the temperature and amount of the supplied hot air gas is in the range of ^{2000 to 4000 kcal / m 3 h ° C.} Is preferable. The higher the heat capacity coefficient, the more heat energy can be transferred to the sludge, and that energy can be used to evaporate the water content of the sludge. Since the circular tube type air flow dryer 5 has an extremely high heat capacity coefficient as compared with an indirect heating type dryer such as an inclined disk type dryer, sufficient drying can be performed with a short residence time.

(Heat retention means)
It is preferable that the continuous hot air dryer 5 is provided with heat insulating means (not shown) around each of the pipes 5a to 5d. By providing this heat retaining means, it is possible to prevent the occurrence of dew condensation in the continuous hot air dryer 5, and it is possible to stably discharge the dried product. Examples of this heat retaining means include a heat insulating sheet and a heating tube. Further, in order to prevent dew condensation, it is preferable to provide the same heat retaining means in the piping between the continuous hot air dryer 5 and the solid air separator 6.

(Solid air separator 6)
The hot air whose humidity has increased due to the drying of the powder or granular material is exhausted as exhaust gas from the continuous hot air dryer 5 and sent to the solid air separator 6. Since this exhaust gas contains powder or granular material, it is separated into powder or granular material and a separation gas (gas separated from the powder or granular material) by using a solid air separator 6.

The solid air separator 6 includes, for example, a cyclone that collects dust by centrifugal force, a gravity settling chamber that collects dust by gravity, a mist separator that collects dust by inertia, a bag filter that collects dust by a filter cloth, and filling. A moving particle layer air filter that collects dust by a layer, an electrostatic precipitator that collects dust by electricity, or the like can be used.

(Exhaust treatment)
The separated gas separated from the powder or granular material by the solid air separator 6 is dust-removed by the venturi scrubber 11 that collects dust by washing, and then is sucked by the exhaust fan 12 and carried to the mist separator 13. Then, after being further deodorized by the mist separator 13, it is deodorized by the plasma deodorizer 14 and released into the atmosphere E. The method for treating the separated gas discharged from the solid air separator 6 is not limited to the above contents, and each facility may be appropriately changed.

(Retention of powder and granules)
The powder or granular material accumulated at the lower end of the solid air separator 6 is cut out by the rotary valve 19 and then supplied to the powder or granular material upstream transporter 9 through the pipe 31. If the water content of the powder or granular material at the lower end of the solid air separator 6 is high, the powder or granular material may adhere to the valve and the discharge may not be successful. Therefore, it is preferable to use a rotary valve 19 that is scraped out by a rotary blade.

Further, in the illustrated embodiment, a moisture meter AW is provided in the pipe 31 to measure the water content of the powder or granular material passing through the pipe 31. If the measured moisture content is out of the appropriate range, control such as raising the temperature of the hot air supplied from the hot air generator 4 to the continuous hot air dryer 5 is performed.

As the powder or granular material upstream transporter 9, a screw conveyor, a belt conveyor, or the like that transports by mechanical power can be used. In the illustrated form, a screw conveyor composed of biaxial screws is used. By using a biaxial screw conveyor, the powder or granular material adhering to one shaft can be scraped out by the other rotating blade.

In the screw conveyor 9, the supply port for the powder or granular material is provided in the middle portion in the longitudinal direction of the screw conveyor 9, and the discharge port for the powder or granular material is one end side end in the longitudinal direction of the screw conveyor 9 (right side in the drawing) and others. It is provided at the end side (left side of the drawing). The powder or granular material supplied from the supply port is carried to one end side end by the forward rotation of the screw conveyor 9, and is discharged from the discharge port at one end side end. On the contrary, when the screw conveyor 9 rotates in the reverse direction, the powder or granular material is carried to the other end side end and discharged from the discharge port at the other end side end. In order to store the powder or granular material in a plurality of containers 15 arranged downstream in a well-balanced manner, the screw conveyor 9 is rotated in the forward direction for a certain period of time and then in the reverse direction for the same time. It is preferable that the amount of powder or granular material discharged from one end side end and the amount of powder or granular material discharged from the other end side end are the same amount.

The temperature of the powder or granular material supplied to the screw conveyor 9 is as high as about 65 ° C to 90 ° C. Therefore, it is preferable to make the screw conveyor 9 water-cooled in order to remove the rough heat of the powder or granular material and lower it to about 65 ° C. Specifically, the powder or granular material is cooled from both the outside and the inside by flowing cooling water on the outside of the jacket of the screw conveyor 9 and also flowing water on the inside of the shaft.

The powder or granular material discharged from each discharge port (one end side discharge port and the other end side discharge port) of the screw conveyor 9 passes through the pipe 32 and is supplied to separate powder or granular material downstream conveyors 10. Each of the illustrated powder or granular material downstream conveyors 10 is a uniaxial screw conveyor 10 and has the same structure as the powder or granular material upstream conveyor 9 except that it does not have a cooling function and is a uniaxial screw.

When the screw conveyor 10 rotates in the forward or reverse direction, the powder or granular material is distributed to one end side and the other end side of the screw conveyor 10. Then, the powder or granular material discharged from the one end side discharge port or the other end side discharge port is stored in each container 15 (four containers in the illustrated embodiment) through the pipe 33. In this way, by distributing the powder or granular material to the plurality of containers 15 using the screw conveyor 10, it is possible to prevent the containers 15 from being filled up immediately.

The temperature of the powder or granular material stored in the container 15 may rise due to oxygen or carbon monoxide in the container 15. Therefore, it is preferable to attach a thermometer to the container 15 to monitor the temperature from the outside and supply nitrogen into the container 15 from a nitrogen tank (not shown). Further, a mechanism for dropping water may be provided in the container 15 in case the temperature suddenly rises.

(Other)
Depending on the type of dehydrator 3, the dehydrated product may not be in the form of granules. For example, when a belt press is used for the dehydrator 3, the dehydrated product is often in the form of a sheet. The shape of the dehydrated product may be plate-shaped or columnar. In such a case, it is crushed by a crusher or the like before being supplied to the continuous hot air dryer 5. In this case as well, it can be supplied by simple crushing by injecting an inorganic flocculant. In the present invention, the particle size of the granules after crushing may be measured, it may be determined whether the maximum particle size or the average particle size is desirable, and whether or not the particles may be supplied to the continuous hot air dryer 5 may be determined. ..

(Example 1)
Digestive sludge was used as the sludge. This digested sludge contains 1.8% of TS (Total Solids), 79.8% of VTS (Volatile Total Solids), and fiber content (amount captured by a 100Mesh net). Was 9.4%.

Digestive sludge was supplied to an in-flight two-component tempering type centrifugal dehydrator at 4.2 m ³ / h (100 m ^{3 / day) for dehydration.} 5% of an inorganic flocculant (ferric polysulfate) and 2.4% of a polymer flocculant were injected into this in-flight two-component heat-regulating centrifugal dehydrator. The injection rate of the inorganic flocculant and the polymer flocculant is a ratio to the amount of solid matter of sludge supplied to the dehydrator.

After that, the dehydrated product was sent to the twin-screw conveyor through the piping. Further, when the water content of the dehydrated product was measured using a moisture meter attached to this pipe, it was 79.9%. Further, when the maximum particle size and the average particle size of the dehydrated product were also measured, the maximum particle size was 30 mm and the average particle size was 15 mm. As mentioned above, the maximum particle size was measured using calipers. After sieving, the average particle size was represented by a rosin ramler distribution, and the particle size when the integrated mass (on the sieve) corresponded to 50% was measured as the average particle size.

Next, the dehydrated product was supplied to the circular tube type air flow dryer using a screw conveyor. This supply was performed so that the average residence time T calculated by the above formula 1 was 5 to 7 minutes. Specifically, the amount of sludge dehydrated water supplied to the circular air flow dryer was 25 to 35 kg-ds / h. In addition, the amount of sludge solids (holding amount) that can be stored in the circular tube type airflow dryer was 3 kg-ds.

Next, the dehydrated product was dried using hot air at 400 ° C. in a circular air flow dryer. Then, the dried product discharged from the circular tube type airflow dryer was supplied to the cyclone, and solid air separation was performed by centrifugal force, and the solid product after separation was used as the final product.

(Example 2)
An inorganic flocculant (ferric polysulfate) was injected at 10% into an in-flight two-component tempering type centrifugal dehydrator. Other operating conditions are the same as in the first embodiment.

(Example 3)
20% of an inorganic flocculant (ferric polysulfate) was injected into an in-flight two-component tempering type centrifugal dehydrator. Other operating conditions are the same as in the first embodiment.

(Example 4)
An inorganic flocculant (ferric polysulfate) was injected at 30% into an in-flight two-component tempering type centrifugal dehydrator. Other operating conditions are the same as in the first embodiment.

(Example 5)
40% of an inorganic flocculant (ferric polysulfate) was injected into an in-flight two-component tempering type centrifugal dehydrator. Other operating conditions are the same as in the first embodiment.

(Example 6)
The in-flight two-component tempering type centrifugal dehydrator was injected with 3% of the polymer flocculant without injecting the inorganic flocculant. Other operating conditions are the same as in the first embodiment.

(Example 7)
2% of an inorganic flocculant (ferric polysulfate) was injected into an in-flight two-component tempering type centrifugal dehydrator. Other operating conditions are the same as in the first embodiment.

(Example 8)
An inorganic flocculant (ferric polysulfate) was injected at 4% into an in-flight two-component tempering type centrifugal dehydrator. Other operating conditions are the same as in the first embodiment.

The results of the above examples are shown in Table 1 below.

(result)
It was found that by increasing the injection rate of the inorganic flocculant, the amount of dehydrated products adhering to or accumulating in the dryer can be reduced. Specifically, when the injection rate of the inorganic flocculant was 5%, the operation could be continued although adhesion and accumulation were observed in the dryer. When the injection rate was increased to 10% or more, the amount of adhesion / deposition decreased and the operation became easier. When no injection was performed, the amount of adhesion and accumulation was large and the operation could not be continued.

On the other hand, increasing the injection rate of the inorganic flocculant has the disadvantage of increasing the cost. In addition, it was found that corrosion is likely to proceed due to the sulfuric acid of ferric polysulfate.

From the above results, considering the balance between the amount of adhesion / deposition, cost, and corrosiveness, the injection rate of the inorganic flocculant is preferably 5% or more with respect to the amount of solid sludge supplied to the dehydrator. More preferably, it is 10% or more. The upper limit is preferably 30% or less.

1: Treatment device, 2: Sludge storage tank, 3: Dehydrator, 4: Hot air generator, 5: Continuous hot air dryer, 5a to 5d: Pipe, 5X: Supply port, 5Y: Discharge port, 6: Solid air Separator, 7: Dehydrated transporter, 8: Measuring device, 9: Powder and granular material upstream transporter, 10: Powder and granular material downstream conveyor, 11: Venturi scrubber, 12: Exhaust fan, 13: Mist separator, 14: Plasma deodorizer, 15: container, 17: air compressor, 18: storage tank, 19: rotary valve, 20: digestion tank, 21: supply pump, 31-33: piping, AM: moisture meter, E: atmosphere, F : Fuel, M: Motor, W: Sludge

Claims (8)

A dehydration step of centrifugally dehydrated sludge with a centrifugal dehydrator,
A sludge treatment method comprising a drying step of bringing dehydrated sludge into contact with hot air to dry the sludge in a circular tube type air flow dryer in which pipes through which hot air passes are arranged in a ring shape.
In the dehydration step
Said sludge before feeding to the centrifugal dehydrator, and to at least one of sludge in dewatering in the centrifugal dewatering machine, injecting an inorganic flocculant,
A method for treating sludge, wherein the injection rate of the inorganic flocculant is 5% or more with respect to the amount of solid sludge supplied to the centrifugal dehydrator. The sludge treatment method according to claim 1, wherein the injection rate of the inorganic flocculant is 30% or less with respect to the amount of solid sludge supplied to the centrifugal dehydrator. The sludge treatment method according to claim 2, wherein the inorganic flocculant is selected from the group of ferric sulfate, ferrous sulfate, ferric chloride, aluminum sulfate and polyaluminum chloride. The sludge treatment method according to claim 1, wherein the centrifugal dehydrator is a two-component tempering type centrifugal dehydrator. The sludge treatment method according to claim 1, wherein the maximum particle size of the dehydrated sludge supplied to the circular air flow dryer is 60 mm or less. The method for treating sludge according to claim 1, wherein the average particle size of the dehydrated sludge supplied to the circular air flow dryer is 1 mm to 30 mm. A centrifugal dehydrator that centrifugally dehydrates sludge,
It has a circular tube type airflow dryer in which pipes through which hot air passes are arranged in a ring shape and the sludge is dried by bringing the dehydrated sludge into contact with the hot air.
Said sludge before feeding to the centrifugal dehydrator, and to at least one of sludge in dewatering in the centrifugal dewatering machine, injecting an inorganic flocculant,
A sludge treatment apparatus comprising an injection means for injecting the inorganic flocculant so that the injection rate of the inorganic flocculant is 5% or more with respect to the amount of solid sludge supplied to the centrifugal dehydrator. The sludge treatment apparatus according to claim 7, wherein the injection rate of the inorganic flocculant is 30% or less with respect to the amount of solid sludge supplied to the centrifugal dehydrator.

Images