JP2018001062A - Sludge treatment method and sludge treatment apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sludge treatment method and a sludge treatment apparatus capable of solving a problem that dewatered sludge cannot be dried by a dryer and capable of obtaining excellent drying at a low cost.SOLUTION: A sludge treatment apparatus includes: a sludge dryer 2; a stoker furnace 3 for incinerating dried sludge by the sludge dryer 2; and main ash transportation means 4 for receiving the main ash dropped and discharged from the stoker furnace 3 and transporting to the sludge dryer 2. The dewatered sludge is charged into the sludge dryer, and the main ash dropped and discharged from the stoker furnace is charged into the sludge dryer in a state where water cooling treatment and a pulverization treatment are not applied and without mixing with the dewatered sludge before charging into the sludge dryer.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a sludge treatment method and a sludge treatment apparatus, and more particularly, to a sludge treatment method and a sludge treatment apparatus in which dehydrated sludge is dried with a sludge dryer and then incinerated with an incinerator.

  Conventionally, when incinerating sewage sludge, generally, the dewatered sludge (also referred to as a dehydrated cake) is previously dehydrated to a predetermined moisture content or lower (for example, 78% or lower) with a dehydrator such as a centrifugal separator. Is put into an incinerator, but dehydrated sludge is thrown into a sludge dryer to reduce the amount of auxiliary fuel used at the time of incineration, and then put into the incinerator after making it into a dry sludge with a specified content or less. There is. Incinerators include fluidized bed furnaces and stoker furnaces equipped with grate, but stoker furnaces used for incineration of dry sludge are generally equipped with a waste heat boiler that is integrated with the furnace. Indirect heating type sludge dryers that use high-temperature steam generated in this waste heat boiler as a heat medium are widely used (Patent Document 1, Non-Patent Document 1, etc.).

  This type of sludge dryer dries dehydrated sludge by heat transfer, but depending on the sludge quality, sludge may not adhere to the heat transfer surface and may not be dried.

  Therefore, conventionally, in the case where good drying cannot be obtained, some kind of auxiliary agent is added. As auxiliaries, slaked lime and dried sludge are often used, and the use of incinerated ash as auxiliaries has also been proposed (Patent Documents 2 to 4, etc.).

Japanese Patent Publication No. 4-76760 Japanese Patent Application Laid-Open No. 56-115311 JP-A-6-257731 JP 2007-127386 A

Takuma Technical Report Vol.22 No.1 (Vol. 42), published in June 2014, Joe Nakanishi, Naoki Co., Ltd., “Kyoto City Toba Water Environmental Conservation Center Stair Furnace Drying and Incineration Equipment Longevity Construction”

  However, when using slaked lime as an auxiliary agent, the cost of slaked lime increases and the running cost becomes expensive. Moreover, when using dry sludge as an auxiliary agent, the amount of sludge thrown into the sludge dryer becomes the total amount of dry sludge as an auxiliary agent, and as a result of increasing the amount of sludge, a large-scale sludge dryer is required.

  On the other hand, in the proposal using incineration ash as an auxiliary agent, it is explained that the effect is exhibited by using powdered incineration ash such as dust collection ash. It is necessary to mix with sludge, and mixing equipment is required separately. Moreover, the incineration ash generated in the stoker furnace is a lump of about 1 to 50 mm of main ash that occupies most of the ash, and usually the main ash contains a large amount of water because it is cooled by water when discharged from the incinerator. However, it could not be used as an auxiliary agent and had to be dried and ground. Furthermore, although fly ash is in the form of powder, the amount generated is very small and is insufficient for use as an auxiliary agent.

  Therefore, the main object of the present invention is to provide a sludge treatment method and a sludge treatment apparatus that solves the phenomenon that dehydrated sludge cannot be dried by a drier and can obtain good drying at low cost.

  In order to achieve the above object, the sludge treatment method according to the present invention does not perform a water cooling process and a crushing process on at least a part of the main ash discharged from the stoker furnace and the step of putting the dehydrated sludge into the sludge dryer In the state and without mixing with the dewatered sludge before charging the sludge dryer, and by mixing the dewatered sludge with the main ash in the sludge dryer and drying the sludge And a step of incinerating the dried sludge in the stoker furnace.

  In the sludge treatment method according to the present invention, the method further includes a step of distributing main ash discharged from the stoker furnace into main ash transported to the sludge dryer and main ash transported to an ash pit or ash bunker. Is preferred.

  The sludge treatment apparatus according to the present invention includes a sludge dryer, a stoker furnace for incinerating sludge dried by the sludge dryer, and at least a part of main ash discharged from the stoker furnace to the sludge dryer. And a main ash returning means to be supplied.

  In the sludge treatment apparatus according to the present invention, the sludge treatment apparatus further includes an ash discharging conveyor for carrying out main ash discharged from the stoker furnace to an ash pit or an ash bunker, and the main ash discharged from the stoker furnace is used as the main ash. It is preferable to provide sorting means for sorting the returning means or the ash removal conveyor.

  According to the present invention, the main ash dropped and discharged from the stoker furnace is massive and has a certain volume. Therefore, the main ash can retain heat during combustion for a longer time than a crushed powder. Therefore, the main ash that has not been subjected to water-cooling treatment and crushing treatment can be put into the sludge dryer at a temperature higher than room temperature, and the heat held by the main ash put into the sludge dryer in this state Can transfer heat to the dewatered sludge and promote the drying of the dewatered sludge in the process of stirring and mixing with the dewatered sludge that is introduced together with the main ash by a screw conveyor or the like in the sludge dryer. Moreover, since main ash does not need to provide a mixing apparatus separately by inputting into a sludge dryer, without mixing with dehydration sludge beforehand, cost can be held down. Furthermore, since the main ash has a maximum diameter of about 1 to 50 mm and has irregularities on the surface, it can also exhibit an effect of cleaning (scraping) the sludge that has adhered to the heat transfer surface of the dryer.

1 is a schematic configuration diagram showing a first embodiment of a sludge treatment apparatus according to the present invention. It is a schematic block diagram which shows 2nd Embodiment of the sludge processing apparatus which concerns on this invention. It is a schematic block diagram which shows 3rd Embodiment of the sludge processing apparatus which concerns on this invention. It is a schematic block diagram which shows 4th Embodiment of the sludge processing apparatus which concerns on this invention. It is a schematic block diagram which shows 5th Embodiment of the sludge processing apparatus which concerns on this invention. It is a schematic block diagram which shows 6th Embodiment of the sludge processing apparatus which concerns on this invention. It is a schematic block diagram which shows 7th Embodiment of the sludge processing apparatus which concerns on this invention. It is a schematic block diagram which shows 8th Embodiment of the sludge processing apparatus which concerns on this invention.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol was attached | subjected to the same or similar component through all embodiment.

  FIG. 1 is a schematic configuration diagram showing a first embodiment of a sludge treatment apparatus according to the present invention. Referring to FIG. 1, a sludge treatment apparatus 1 receives a sludge dryer 2, a stoker furnace 3 that incinerates sludge dried by the sludge dryer 2, and main ash dropped and discharged from the stoker furnace 3. Main ash returning means 4 for conveying to the dryer 2.

  The sludge dryer 2 can be a dryer used for drying dehydrated sludge, particularly an indirect heating type sludge dryer. For example, as shown in the schematic structure of FIG. A casing 2c provided with a discharge port 2b and a jacket through which the heat medium V circulates, and a hollow rotating body 2d that is rotatably provided in the casing 2c to stir and convey sludge and through which the heat medium V circulates. Can be provided. As the heat medium V supplied to the sludge dryer 2, high-temperature steam generated in the waste heat boiler 5 integrated with the stoker furnace 3 can be used. In addition, since the waste heat boiler 5 is well-known, detailed description is abbreviate | omitted.

  In the stalker furnace 3, the dried sludge dried by the sludge dryer 2 is constantly supplied from the hopper 3a by the pusher 3b to the uppermost stage of the grate 3c, 3d in the furnace, and alternately arranged with the fixed grate 3c. Due to the back and forth movement of the movable grate 3d, it comes into contact with the combustion air sent from below the grate in the process of being conveyed from the upper stage to the lower stage, and is dried, ignited and burned by the radiant heat in the combustion chamber 3r. Combustion becomes a burning point at a certain level in the lower part of the grate, and the incineration ash falls and is discharged from the main ash chute 3e at the lower part of the grate. The main ash (falling ash) falling from the gap between the grate 3c and 3d is collected by the falling ash conveyor 6 through the falling ash chute 3f and carried out. The combustion exhaust gas is heat-recovered as steam by the waste heat boiler 5 integrated with the stoker furnace 3 and used as the heat medium V of the sludge dryer 2. In general, “main ash” is incineration residue dropped from the bottom of an incinerator and includes ash from a drop ash conveyor. In this specification, the term “main ash” is as described above. In addition to the incinerated ash falling from the main ash chute 3e, it is used as a term including the falling ash falling from the falling ash chute 3f.

  The main ash discharged from the main ash chute 3e provided at the end of the grate is conveyed by the main ash return means 4 as it is and is put into the sludge dryer 2 without being cooled with water or crushed. In the example shown in FIG. 1, the main ash (falling ash) dropped and discharged through the falling ash chute 3f from the gap between the grate 3c and 3d is conveyed by the falling ash conveyor 6 and discharged from the main ash chute 3e. It is mixed with ash, conveyed to the sludge dryer 2 by the main ash return means 4, and charged into the sludge dryer 2 through the main ash inlet 2e. A part of the falling ash may be returned to the hopper 3a of the stoker furnace. The main ash returning means 4 can be constituted by a belt conveyor, a vibration conveyor, a screw conveyor, or other known conveying means.

  The dewatered sludge dehydrated to a predetermined moisture content or less in advance by a dehydrator 8 such as a centrifugal separator is sludge dried through the supply port 2a at the same time as or before or after the main ash is charged into the sludge dryer 2. The machine 2 is charged. The dried sludge dried by the sludge dryer 2 is discharged from the discharge port 2b, conveyed by the dried sludge conveyor 10, and put into the hopper 3a.

  In the second embodiment of the present invention, as shown in FIG. 2, only the main ash falling from the main ash chute 3e is conveyed to the sludge dryer 2 by the main ash return means 4, and the sludge is passed through the main ash inlet 2e. The dryer 2 is charged. The main ash (falling ash) falling from the falling ash chute 3f is not mixed with the main ash falling from the main ash chute 3e, but is conveyed to the ash pit 7 (or ash bunker) by the falling ash conveyor 6, and the ash pit 7 (Or an ash bunker) and can be carried out to a landfill site by a truck or the like as in the prior art. Other configurations of the second embodiment are the same as those of the first embodiment. Although not shown, the fall ash conveyed by the fall ash conveyor 6 can be water cooled before being put into the ash pit 7.

  Furthermore, in 3rd Embodiment of this invention, as shown in FIG. 3, when the sludge dryer 2 is not provided with the main ash charging port 2a separately from the sludge supply port 2a, the main ash returning means 4 conveys the main ash. Ashes are fed into the sludge dryer 2 through the sludge supply port 2a. Other configurations of the third embodiment are the same as those of the first embodiment.

  In the fourth embodiment of the present invention, as shown in FIG. 4, only the main ash (falling ash) dropped from the falling ash chute 3f is conveyed to the sludge dryer 2 by the main ash returning means 4, and the main ash is charged. The sludge dryer 2 is charged through the mouth 2e. The main ash falling from the main ash chute 3e is transported and stored in the ash pit 7 (or ash bunker) by the ash takeout conveyor 11, and can be carried out to a landfill site or the like by a truck or the like as in the past. Other configurations of the fourth embodiment are the same as those of the first embodiment. Although not shown, the main ash falling from the main ash chute 3e can be supplied to the ash pit 7 after being cooled by an ash cooling device or the like.

  Since the average particle size of the main ash falling from the main ash chute 3e is larger than the average particle size of the main ash falling from the falling ash chute 3f, the main ash falling from the main ash chute 3e and the main ash falling from the falling ash chute 3f By selectively returning the ash to the sludge dryer, the effect as a drying aid is different, and a more suitable system can be selected according to the properties of the sludge.

  As shown in the fifth to seventh embodiments to be described later, the sludge treatment apparatus can include a distribution unit that distributes the main ash discharged from the stoker furnace to the main ash return unit or the ash removal conveyor.

  In the fifth embodiment of the present invention, as shown in FIG. 5, a control damper 12 is provided in the vicinity of the discharge port of the main ash chute 3e, an opening 3g is formed on the side surface of the main ash chute 3e, and an ash is formed in the opening 3g. One end of the delivery conveyor 11 is connected. The control damper 12 is swing-controllable with the upper end as a fulcrum. In the illustrated example, the control damper 12 is directed vertically along the inner wall surface of the main ash chute 3e to drop the main ash chute 3e. The ash falls on the main ash return means 4 as it is, and the control damper 12 is tilted so that the free end of the control damper 12 is directed to one end of the ash removal conveyor 11, whereby the main ash chute 3 e is returned by the control damper 12. The main ash dropping the main ash chute 3e is closed along the slope of the main ash chute 3e, guided to the ash removal conveyor 11 through the opening 3g, and discharged to the ash pit 7. . By controlling the timing of swinging the control damper 12, that is, the opening / closing time of the control damper 12, the amount of main ash charged into the sludge dryer 2 can be controlled.

  In the sixth embodiment of the present invention, as shown in FIG. 6, the main ash return means 4 has an ash drop port 4c formed on the bottom surface of a casing 4b that houses a screw conveyor, a belt conveyor, etc. In order to open and close, a slide gate 13 that is reciprocated in the horizontal direction is provided. An ash removal conveyor 11 is disposed below the ash drop opening 4c so as to receive the main ash falling from the ash drop opening 4c. When the slide gate 13 is open, the main ash falling from the main ash chute 3e falls on the ash removal conveyor 11 from the ash drop opening 4c and is conveyed to the ash pit 7. When the slide gate 13 is closed, the main ash falling from the main ash chute 3e is conveyed to the sludge dryer 2 by the main ash return means 4. By controlling the opening and closing time of the slide gate 13, the amount of main ash charged into the sludge dryer 2 is controlled.

  In the sixth embodiment, an example in which the main ash return means 4 is provided with the ash drop opening 4c and the slide gate 13 is shown. However, as in the seventh embodiment shown in FIG. A slide gate 13 that opens and closes the ash drop opening 11a can also be provided.

  In the eighth embodiment of the present invention, as shown in FIG. 8, a buffer tank 16 is connected downstream of an ash takeout conveyor 15 that conveys the main ash falling from the falling ash chute 3f and the main ash chute 3e. A measuring conveyor 17 is provided below the lower discharge port, and the main ash returning means 4 is arranged on the downstream side of the measuring conveyor 17 so as to receive the main ash conveyed by the measuring conveyor 17. The control damper 16 a provided in the bottom discharge path of the buffer tank 16 is controlled by the control unit 18. The control unit 18 receives the weight signal of the main ash measured by the weighing conveyor 17, and feedback-controls the control damper 16a so that the amount of main ash cut out from the buffer tank 16 becomes a desired amount. When surplus main ash accumulates in the buffer tank 16, it can be taken out from the buffer tank 16 by an ash crane (not shown) or the like and carried out to a landfill site or the like by a truck or the like.

  According to the sludge treatment apparatus having the above-described configuration, the main ash dropped and discharged from the stoker furnace 3 is a lump having a maximum diameter of 1 to 50 mm. Therefore, the heat during combustion is higher than that of the crushed powder. Can be held for a long time. As a result, the main ash that has not been subjected to the water cooling treatment and crushing treatment is put into the sludge dryer 2 at a temperature higher than room temperature, and the heat held by the main ash put into the sludge dryer in this state is sludge. In the process of being stirred and mixed with the dewatered sludge that is put together with the main ash in the dryer 2, heat can be transferred to the dewatered sludge, and the temperature rise of the dewatered sludge can be accelerated and drying can be promoted.

  Moreover, since main ash does not need to provide a mixing apparatus separately by throwing into the sludge dryer 2 without mixing with dewatered sludge beforehand, cost can be held down.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to each example.

  In each example, the dewatered sludge obtained by dewatering the sewage sludge to a water content of 78% with a dehydrator in advance was added to the sludge dryer alone or together with an auxiliary agent, and a drying experiment was performed. Specifically, the water evaporation rate until the water content of the dewatered sludge or the mixture of the dewatered sludge and the auxiliary agent introduced into the sludge dryer was 40% was measured.

The water evaporation rate and water content were calculated by the following formula.
<Moisture evaporation rate>
Moisture evaporation rate (kg-H ₂ O / m ² · hr)
= Moisture evaporation W (kg-H ₂ O / hr) / Heat transfer area (m ² ) (1)
The water evaporation amount W was calculated by the following calculation formula.

x: Dehydrated sludge supply amount (kg / hr) ... Known y: Dehydrated sludge moisture content (%) ... Known x ': Dried sludge creation amount (kg / hr) ... Unknown y': Dry sludge water content Rate (%) ... known W = xx '(2)
xx (1- (y / 100)) = x '* (1- (y' / 100)) (3)
W is calculated by solving the simultaneous equations of the above equations (2) and (3). Since the heat transfer area is known, the water evaporation rate is calculated from the equation (1).
<Moisture content>
The moisture content was measured using a thermostatic bath.

  Measurement conditions: Drying was performed under conditions of 105 ° C. × 24 hours, and the weight was calculated by the following calculation formula (4) from the weight before and after drying.

Moisture content (%) = [(ab) / a] × 100 (4)
Here, a is the weight (g) before drying, and b is the weight (g) after drying.

Example 1
Sludge A: dehydrated sludge (sludge obtained by dewatering sewage sludge with a dehydrator; the same applies hereinafter) Moisture content 78%, ash 19% -DS
(DS: Weight of solid in sludge (Dry Solid))
Auxiliary agent (additive) B: Incinerated ash of sludge A stair-type stoker furnace Same amount as ash in sludge A Sludge A and auxiliary agent B are cooled and pulverized without mixing sludge A and auxiliary agent B in advance. When the mixture was put into a sludge dryer, the water evaporation rate until the water content of the mixture of sludge A and auxiliary agent B reached 40% was 12 kg-H ₂ O / m ² · hr.

Example 2
Sludge A: dehydrated sludge moisture content 78%, ash 19% -DS
Auxiliary agent (additive) C: Incineration ash of sludge A staircase stoker furnace Double amount of ash in sludge A Sludge A and auxiliary C are cooled and ground without mixing sludge A and auxiliary C in advance. When the mixture was put into a sludge dryer, the water evaporation rate until the water content of the mixture of sludge A and auxiliary agent B reached 40% was 14 kg-H ₂ O / m ² · hr.

Comparative Example 1
Sludge A: dehydrated sludge moisture content 78%, ash 19% -DS
Auxiliary agent: None Sludge adhered to the heat transfer surface of the sludge dryer during the test, and continuous operation was not possible.

Comparative Example 2
Sludge A: dehydrated sludge moisture content 78%, ash 19% -DS
Auxiliary agent (additive) D: Crushed material of incinerated ash in sludge A stair-type stoker furnace (median particle size 50 μm) Same amount as ash in sludge A Sludge A and auxiliary D crushed without water cooling Was previously mixed with a mixer and then put into a sludge dryer. The water evaporation rate until the water content of the mixture of sludge A and auxiliary agent D reached 40% was 9 kg-H ₂ O / m ² · hr. Met.

  From the above experiment, it can be seen that Examples 1 and 2 have better drying than Comparative Examples 1 and 2. Therefore, the dewatered sludge is fed into the sludge dryer, and the main ash dropped and discharged from the stepped stoker furnace is mixed with the dehydrated sludge without being subjected to water cooling and crushing treatment and before being fed into the sludge dryer. Without adding the auxiliary by putting it in the sludge dryer (Comparative Example 1), when mixing the auxiliary crushed incineration ash with dehydrated sludge before putting it into the dehydrating dryer (Comparative Example) Compared to 2), it was confirmed that better drying of the dewatered sludge was obtained.

DESCRIPTION OF SYMBOLS 1 Sludge processing apparatus 2 Sludge dryer 3 Stoker furnace 4 Main ash return means 5 Waste heat boiler 6 Falling ash conveyor

Claims (4)

Introducing dehydrated sludge into the sludge dryer;
Charging at least a portion of the main ash discharged from the stoker furnace into the sludge dryer without being mixed with dehydrated sludge without being subjected to water cooling treatment and crushing treatment and before the sludge dryer is charged;
Mixing the dehydrated sludge with the main ash and drying in the sludge dryer to obtain dry sludge;
Incinerating the dried sludge in the stoker furnace;
The sludge processing method characterized by including. 2. The method according to claim 1, further comprising a step of distributing main ash discharged from the stoker furnace into main ash transported to the sludge dryer and main ash transported to an ash pit or ash bunker. Sludge treatment method. A sludge dryer, a stoker furnace for incinerating the sludge dried by the sludge dryer, and a main ash returning means for transporting and feeding at least a part of the main ash discharged from the stoker furnace to the sludge dryer. And a sludge treatment apparatus. An ash takeout conveyor for carrying out main ash discharged from the stoker furnace to an ash pit or ash bunker;
The sludge treatment apparatus according to claim 3, further comprising a distribution unit that distributes the main ash discharged from the stoker furnace to the main ash return unit or the ash removal conveyor.