Agitation heat transfer drying device and drying method using the same

Abstract

To stably, continuously and efficiently dry an adhesive material, sewage sludge for example, using an agitation heat transfer drying device without adding a chemical or by adding a small amount of chemicals thereto.SOLUTION: The agitation heat transfer drying device comprising a casing 12 provided with a feeder for a drying object MO to be fed therefrom and a dried product discharge port 32, a plurality of rotary shafts 16 horizontally disposed therein parallel to each other, and a plurality of agitation plates 18 rotating with the rotation of the rotary shafts 16 to agitate a drying object to transfer heat to the drying object from a heat medium being fed into the rotary shafts 16 via the agitation plates 18 to dry the drying object, comprises a first feeder 30 disposed on one end and a second feeder 30 and the discharge port 32 on the other end in the longitudinal direction of the casing 12, and at least one or more of third feeders 30 disposed between the first feeder 30 and the second feeder 30.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to an agitation heat transfer drying device, for example, an internal agitation type indirect heating dryer (also called an inclined disk dryer), and a drying method using the same. [Background technology]

[0002] There are various types of dryers available, and the selection is based on factors such as drying performance, required dry moisture content, running costs, and equipment costs.

[0003] Agitation heat transfer drying devices, typified by internal agitation type indirect heating dryers, use a heat medium to agitate materials while drying them through conductive heat transfer.

[0004] This type of internally agitated indirectly heated dryer is known to be used for drying sludge generated during sewage treatment in sewage treatment facilities. However, sludge that is (very) adhesive, such as mixed raw sludge that is a mixture of primary sludge and excess sludge, is difficult to dry using an internal agitation indirect heating dryer.

[0005] The reason for this is that this type of highly adhesive sludge adheres to and covers the heat transfer surfaces of the dryer, reducing the effective heat transfer area and significantly reducing the drying capacity. Another reason is that the sludge that covers the heat transfer surface is difficult to remove even after drying, making it difficult to restore the heat transfer area.

[0006] To address this issue, when drying highly adhesive materials such as mixed raw sludge, it has been necessary to operate the drying process at a very low load, for example, 50% or less, or to add chemicals such as hydrated lime. For example, as exemplified in Patent Document 1, it is known to add hydrated lime in the range of 10% to 100% of the absolute dry weight of the material to be treated.

[0007] On the other hand, as a measure to prevent or suppress adhesion, a return ash method is also known in which a part or most of the dried material is returned to the upstream side of the dryer through a return line and mixed with the material to be dried (see Patent Document 2). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-152695 [Patent Document 2] Jikko No. 52-48457 Summary of the Invention [Problem to be solved by the invention]

[0009] The method of adding chemicals such as slaked lime to reduce the adhesion of sludge and improve its releasability after drying requires constant addition of chemicals, which increases running costs.

[0010] On the other hand, the return ash method involves returning the dried material to reduce the apparent moisture content and covering the surface of the highly adhesive material to be dried with the dried material, thereby reducing adhesion. In this method, the amount of material to be dried must be returned during the drying operation, which is several times, or in some cases several tens of times, the amount of material to be dried, so excessive handling equipment must be provided.

[0011] Therefore, the main object of the present invention is to provide an agitation heat transfer drying apparatus and a drying method using the same that can dry stably, continuously, and efficiently, for example, without adding chemicals or even with only small amounts of chemicals added. [Means for solving the problem]

[0012] The following aspects are included as means for solving the above problems. <First aspect> A stirring and heat transfer drying device comprising: a casing provided with a supply section to which a material to be dried is supplied; a casing provided with a discharge section to which the material to be dried is discharged; a plurality of hollow rotating shafts arranged horizontally in parallel; a plurality of hollow stirring plates on the outer periphery of each of the rotating shafts; and a heat transfer drying device in which heat is transferred from a heat medium supplied into the rotating shafts to the material to be dried via the stirring plates while the material is stirred by the stirring plates which rotate together with the rotation of the rotating shafts; The casing has a first supply section at one end in the longitudinal direction thereof, and a second supply section and the discharge section at the other end thereof, At least one third supply section is provided between the first supply section and the second supply section. Agitation heat transfer drying device.

[0013] <Second aspect> A drying method using an agitation heat transfer drying device in which a plurality of hollow rotating shafts are arranged horizontally in parallel within a casing having a supply section to which a material to be dried is supplied and a discharge section to which a material to be dried is discharged, and a plurality of hollow stirring plates are provided around the outer periphery of each of the rotating shafts, and heat is transferred to the material to be dried by a heat medium supplied into the rotating shafts via the stirring plates while the material is being agitated by the stirring plates that rotate together with the rotating shafts, The stirring heat transfer drying device is The casing has a first supply section at one end in the longitudinal direction thereof, and a second supply section and the discharge section at the other end thereof, At least one third supply unit is provided between the first supply unit and the second supply unit, The material to be dried is supplied from each of the supply units. Agitation heat transfer drying method. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide an agitation heat transfer drying apparatus and a drying method using the same that can perform stable, continuous, and efficient drying when drying using the agitation heat transfer drying apparatus, for example, even when no chemicals are added or only a small amount is added. [Brief explanation of the drawings]

[0015] [Figure 1]10 is a graph illustrating the progress of drying. [Figure 2] 1 is a schematic diagram of an example of equipment including an agitation heat transfer drying device and its peripheral equipment. FIG. [Figure 3] FIG. 10 is an explanatory diagram showing a vertical cross section of a conventional agitation heat transfer drying device where an object to be dried is supplied. [Figure 4] 1 is a horizontal cross-sectional view of a conventional agitation heat transfer drying device showing a supply portion of an object to be dried. [Figure 5] 1 is a graph showing the change in sludge liquid content with respect to the position in the device direction from the inlet to the outlet in a conventional sludge drying process. [Figure 6] 1 is an explanatory diagram showing a vertical cross section of an agitation heat transfer drying device in one embodiment of the present invention, where a supply portion of an object to be dried is provided. FIG. [Figure 7] 1 is an explanatory diagram showing a horizontal cross section of a supply portion of an object to be dried in an agitation heat transfer drying device according to one embodiment of the present invention. FIG. [Figure 8] 1 is a graph showing the change in sludge liquid content at different locations in the device direction from the inlet to the outlet in sludge drying according to one embodiment of the present invention. [Figure 9] FIG. 2 is a schematic horizontal plan view of a first example of a discharge form of dried material. [Figure 10] FIG. 10 is a schematic horizontal plan view of a second example of a discharge form of dried material. [Figure 11] FIG. 1 is a schematic horizontal view of an example of a four-axis agitation heat transfer drying device. DETAILED DESCRIPTION OF THE INVENTION

[0016] In one embodiment of the present invention, the material to be dried may be a liquid-containing material such as sewage sludge, industrial wastewater sludge, food waste, kitchen waste, human waste sludge, livestock manure, plant juice residue, and other various biomass and waste materials. The effects of the present invention are particularly pronounced when drying adhesive materials, such as adhesive sewage sludge, among these types of liquid-containing materials. Here, "adhesion" refers to the property of the material to be dried to adhere to the agitator plate or the rotating shaft. However, it is difficult to make an absolute evaluation of the level of "adhesion," and although it is effective to make such an evaluation based on rheological properties, it is also difficult to establish evaluation criteria for the degree to which the adhesive force is weakened by shearing the material to be dried with the agitator plate. For these reasons, it is difficult to uniformly define "adhesion" and "adhesive material." However, in the case of sewage sludge, mixed sludge of primary sludge discharged from the primary sedimentation tank and excess sludge discharged from the final sedimentation tank, mixed sludge of primary sludge and digested sludge, and mixed sludge of excess sludge and digested sludge can be evaluated as typical ``adhesive materials.'' In the following, an example of sewage sludge as the material to be dried will be mainly described.

[0017] Figure 1 is a graph used to explain the time course of general drying. During the preheating period, the rate at which the product temperature (temperature of the material to be dried) rises does not correspond to the rate at which the liquid content falls. However, once the constant rate drying period begins, when the moisture surrounding the particles of the material to be dried evaporates, the product temperature barely rises, but the rate at which the liquid content falls becomes significantly faster. During the falling rate drying period, when evaporation from the inside of the particles begins, the rate at which the liquid content falls is slower than the rate at which the product temperature rises.

[0018] An agitation heat transfer drying apparatus according to one embodiment of the present invention is installed under an example of equipment including peripheral devices shown in Fig. 2. Fig. 2 shows a conventional example. The agitation heat transfer drying device 10 includes a casing 12 having a supply section to which the material to be dried is supplied and a discharge section from which the material to be dried is discharged.

[0019] The casing 12 may be provided with a cover 14. Furthermore, within the casing 12, a plurality of hollow rotating shafts 16 (for example, two or four shafts) are arranged horizontally in parallel, and a plurality of hollow stirring plates 18 are provided around the outer periphery of each rotating shaft 16. As shown in Figures 2 to 4, the stirring plate 18 is provided perpendicular to the rotating shaft 16, but it can also be provided at an angle to the axis of the rotating shaft 16 to improve stirring and shearing properties.

[0020] The agitation heat transfer drying device 10 dries the material to be dried by agitating the material with an agitator plate 18 that rotates integrally with the rotating shaft 16, while heating the agitator plate 18 with a heat transfer medium (steam or heat transfer oil) 20 supplied into the rotating shaft 16. In the conventional example, as shown in Figures 2 to 4, a supply section 30X for the material to be dried M0 is arranged on the first side (left side of the drawing), and a discharge section 32X for the material to be dried M1 is arranged on the second side (right side of the drawing). In this configuration, the material to be dried M0 supplied into the casing 12 via the supply section 30X is subjected to a drying process while being transferred to the discharge section 32X, and is discharged as a dried material M1.

[0021] The heat medium 20 is also supplied to the casing 12 . The exhaust gas emitted during drying is led to a scrubber 40, where it is cleaned of dust and cooled. After that, a portion of the treated exhaust gas is circulated into the casing 12 as a carrier gas by a circulation fan 42, and the remainder is released into the atmosphere, for example, via a deodorizing device (not shown).

[0022] FIG. 5 shows the change in the liquid content of the sludge from the inlet (supply section 30X) of the material to be dried M0 to the outlet (discharge section 32X) of the material to be dried M1 in the conventional example. For example, a material to be dried M0 having a liquid content of 80% is dried to become a dried material M1 having a liquid content of about 30%. In the case of poor drying, the liquid content of the dried product M1 may be as low as about 70%.

[0023] Depending on the properties of the sludge, as mentioned above, particularly adhesive sludge may adhere to the heat transfer surface of the dryer and cover the surface during the drying process, reducing the effective heat transfer area and causing a significant drop in drying capacity. For example, this may result in poor drying, as shown by "poor drying" in Figure 5, and the target liquid content may not be achieved.

[0024] In contrast, in one embodiment of the present invention, as shown in Figures 6 and 7, the casing 12 has a first supply section at one longitudinal end (left side of the drawing), a second supply section and a discharge section 32 at the other end (right side of the drawing), and further has at least one or more third supply sections between the first supply section and the second supply section.

[0025] The one or more third supply sections may be located on one end side or the other end side with respect to the center CL, which is the center position in the longitudinal direction of the casing 12. In the example shown in FIGS. 6 and 7, the supply units 30 are arranged in four locations in total, with two on one end and two on the other end, sandwiching the center CL.

[0026] In one embodiment of the present invention, it is desirable to further include a step of initially filling the casing 12 with material to be dried that is within the target liquid content range for the discharge section 32, at least from the supply section 30 to the start position of the discharge section 32, before starting continuous supply of the material to be dried M0 through the supply sections 30, 30, etc.

[0027] Continuous supply may be started when a new operation is started or when an operation is restarted after being temporarily stopped due to a problem. As the drying material initially filled into the supply casing 12 of the material to be dried M0, a drying material M1 that has already been dried using the agitation heat transfer drying device 10 can be used.

[0028] When starting a new operation, it is possible to use dried materials from other sewage treatment plants, or dried biomass such as rice husks and sawdust as the dried materials for initial loading.

[0029] In either case, when initially filling the dried material, for example, as shown in Figure 6, it can be fed from two feeding positions 44, one on one end and one on the other end, and then the rotating shaft 16 can be rotated to distribute the dried material inside the casing 12.

[0030] It is preferable that the filling height 46 of the drying material initially filled in the casing 12 is higher than the upper surface of the rotary shaft 16 in the section from the supply section 30 to the discharge section 32 . Furthermore, it is more preferable that the starting position of the discharge section 32 is at a level higher than the discharge start level, for example, the upper end of the discharge weir 50 .

[0031] After the material to be dried has been filled up to a predetermined filling height, the material to be dried is fed into the casing 12 from each feeding section. It is desirable to supply the material to be dried into the casing 12 evenly from each of the supply sections 30, 30.... This "evenly" means that the supply amount per hour from the supply sections 30, 30... is controlled to be approximately equal so that the height of the material to be dried during the drying operation does not fluctuate greatly like the height 48 in conventional drying methods, as shown in Figure 6, but rather the filling height 46 is maintained as much as possible. By performing such control, efficient heat transfer drying can be achieved.

[0032] The amount of material to be dried M0 supplied per hour is preferably 1 / 8 to 1 / 15 of the amount of solid matter of the material to be dried initially charged. If the supply amount is too small, the material to be dried tends to be over-dried, whereas if the supply amount is too large, adhesion tends to occur, resulting in a decrease in the drying speed.

[0033] The dried material in the initially packed state preferably has an average particle size of 0.5 to 2.5 mm, with at least two-thirds of the dried material having a particle size of 2.5 mm or less, and more preferably at least two-thirds of the dried material having a particle size of 2.0 mm or less. The average particle size is measured by the following method: If the particle size of the dehydrated material is 500 μm or more, it is sieved using the method described in JIS M 8801 Coal Testing Method, the sieving results are expressed in Rosin-Rammler distribution, and the particle size when the cumulative mass (on the sieve) corresponds to 50% is defined as the average particle size.

[0034] By initially filling the drying material having the above particle size distribution, the drying material adheres to the surface of the material to be dried supplied into the casing 12, and acts to coat the surface of the material to be dried, which results in a decrease in the adhesiveness of the surface of the material to be dried. In addition, by initially filling the material to be dried when it is supplied, the material to be dried covers (surface coats) the heat transfer surfaces (the surfaces of the agitator plate and the rotating shaft), so even if the material to be dried does not come into sufficient contact with the material to be dried and is sticky, adhesion to the heat transfer surfaces is prevented or suppressed. This makes it less likely that the drying capacity will decrease due to a decrease in the effective heat transfer area, and allows for stable, continuous, and more efficient drying without adding chemicals such as slaked lime, or even with a small amount added. Furthermore, as described above, by setting the initial filling height of the material to be dried higher than the upper surface of the rotating shaft 16 in the section from the supply section 30 to the discharge section 32, the material to be dried tends to overflow the rotating shaft 16 more frequently as the rotating shaft 16 rotates, and kneading and crushing tend to be carried out more reliably.

[0035] On the other hand, if the average particle size is large, the material to be dried will not be coated on the surface of the material to be dried, but will be coated on the surface of the drying material, which will increase the opportunities for the material to be dried to come into contact with the heat transfer surface, and there is a risk that the material to be dried will adhere to the heat transfer surface.

[0036] As a result of the supply mode of the material to be dried according to one embodiment of the present invention, the liquid content of the material to be dried exhibits a distribution shown in FIG. It is shown that although the liquid content is somewhat high in some areas at each supply section position, the liquid content is distributed low throughout the casing 12. When comparing the distribution of fluctuations in this low liquid content in adhesive sewage sludge with the graph of changes in liquid content in the conventional example in Figure 5, there is a marked difference.

[0037] This result shows that in the supply mode of the material to be dried according to the embodiment, the casing 12 has a first supply section 30 at one end in the longitudinal direction, a second supply section 30 and a discharge section 32 at the other end, and at least one or more third supply sections 30 between the first and second supply sections 30, and by supplying the material to be dried from each of the supply sections 30, the material to be dried is supplied to an area with a low liquid content, and is quickly dried to within the target liquid content range. Furthermore, this drying is carried out over the entire area of ​​at least three locations in the longitudinal direction of the casing 12, allowing for stable, continuous, and efficient drying.

[0038] Furthermore, according to the supply mode of the material to be dried in one embodiment of the present invention, when the material to be dried is, for example, sticky sewage sludge, the sticky sewage sludge is mixed and crushed in the low liquid content area as described in the previous section, and moreover, this is carried out over the entire longitudinal area of ​​the casing 12, thereby preventing the sticky sewage sludge from adhering to and covering the heat transfer surface of the drying device, thereby reducing the effective heat transfer area and causing a significant decrease in drying capacity. As a result, it is possible to prevent the drying device from operating at a low load, and also to reduce or eliminate the amount of chemicals such as hydrated lime that need to be added.

[0039] According to one embodiment of the present invention, the liquid content varies little throughout the entire section from the supply section 30 to the discharge section 32 during the drying process. For adhesive sewage sludge, the target liquid content is preferably around 30% or less for stable operation. However, it is not always possible to achieve the target liquid content during operation. Furthermore, even in accordance with one embodiment of the present invention, the properties of the sewage sludge to be treated may change and operation may fluctuate. Therefore, it is desirable to operate the entire section from the supply section 30 to the discharge section 32 so that the liquid content is within a fluctuation range of plus 10% to minus 8% of the target liquid content at the discharge section 32. Furthermore, it is particularly preferable that the fluctuation range W of the target liquid content be set to a single point without any fluctuation range, and be plus or minus 13% or less. For example, if the target liquid content is 27% or less, the fluctuation range is preferably 40% or less. The method for measuring the liquid content is not particularly limited, and any method can be used. Alternatively, the liquid content may be measured by attaching a sensor or the like to the inside of the casing 12, or by sampling the material to be dried during operation or when operation is stopped and measuring the liquid content using a moisture meter.

[0040] The discharge of the dried material can be the same as in the conventional example. Figure 9 shows a configuration in which the dried material that has overflowed a weir 50 provided on the side of the other end of the casing 12 is guided to a discharge box 52, i.e., a discharge section, and discharged from its bottom. The weir 50 and discharge box 52 may be provided not only on both sides, but also on only one side. FIG. 10 shows a configuration in which the dried material that has flowed over a weir 54 provided at the other end of the casing 12 is guided to the discharge portion of the casing 12 and discharged from the bottom thereof.

[0041] According to one embodiment of the present invention, the drying operation involves kneading and crushing at a low liquid content throughout the entire section from the supply section 30 to the discharge section 32. As a result, since no material to be dried is supplied, particularly when the equipment is started up or stopped, the liquid content of the mixture decreases significantly, resulting in over-drying and the mixture potentially catching fire. To prevent over-drying, a water spray can be provided at an appropriate location on the drying equipment, for example, on the top plate, so that the mixture can be humidified as needed.

[0042] Also, it is possible to make the slope downwards on the discharge side as shown by θ in Figure 6. On the other hand, an example of a four-shaft system is shown in Figure 11. [Industrial Applicability]

[0043] The material to be dried in the present invention can be any of a variety of liquid-containing materials, but the effects of the present invention are particularly pronounced when adhesive materials, such as adhesive sewage sludge, are dried. Furthermore, stable, continuous, and efficient drying can be achieved without adding chemicals such as slaked lime, or even with a reduced amount of slaked lime added, which has previously been required to be in the range of 10% to 100% of the absolute dry weight of the material to be treated, as exemplified in Patent Document 1. [Explanation of symbols]

[0044] 10...Agitation heat transfer drying device, 12...Casing, 16...Rotating shaft, 18...Agitation plate, 20...Heat medium, 30X, 30...Supply section, 32X, 32...Discharge section, M0...Material to be dried, M1...Material to be dried, 50, 54...Weir, 52...Discharge box

Claims

1. A stirring and heat transfer drying device comprising: a casing provided with a supply section to which a material to be dried is supplied; a casing provided with a discharge section to which the material to be dried is discharged; a plurality of hollow rotating shafts arranged horizontally in parallel; a plurality of hollow stirring plates on the outer periphery of each of the rotating shafts; and a heat transfer drying device in which heat is transferred from a heat medium supplied into the rotating shafts to the material to be dried via the stirring plates while the material is stirred by the stirring plates which rotate together with the rotation of the rotating shafts; a first supply section at one end of the casing in the longitudinal direction, and a second supply section and the discharge section at the other end; At least one third supply section is provided between the first supply section and the second supply section. Agitation heat transfer drying device.

2. 2. The agitation heat transfer drying apparatus according to claim 1, wherein the number of supply sections for the material to be dried is three or four in total.

3. 3. The agitation heat transfer drying apparatus according to claim 1, further comprising a water sprinkler means for spraying water into the casing.

4. A drying method using an agitation heat transfer drying device in which a plurality of hollow rotating shafts are arranged horizontally in parallel within a casing having a supply section to which a material to be dried is supplied and a discharge section to which a material to be dried is discharged, and a plurality of hollow stirring plates are provided around the outer periphery of each of the rotating shafts, and heat is transferred to the material to be dried by a heat medium supplied into the rotating shafts via the stirring plates while the material is being agitated by the stirring plates that rotate together with the rotating shafts, The stirring heat transfer drying device is a first supply section at one end of the casing in the longitudinal direction, and a second supply section and the discharge section at the other end; At least one third supply unit is provided between the first supply unit and the second supply unit, The material to be dried is supplied from each of the supply units. Agitation heat transfer drying method.

5. 5. The agitation and heat transfer drying method according to claim 4, further comprising a step of initially filling the casing with a material to be dried that is within a target liquid content range for the discharge section at least from the supply section to a start position of the discharge section before starting to supply the material to be dried through the supply section.

6. The agitation heat transfer drying method according to claim 5, wherein the dried material is dried using the agitation heat transfer drying device.

7. 6. The stirring and heat transfer drying method according to claim 4, wherein the fluctuation in liquid content during the drying process is within a range of plus 10% to minus 8% of the target liquid content in the discharge section throughout the entire section from the supply section to the discharge section.

8. The stirring and heat transfer drying method according to claim 4 or 5, wherein the dried product has an average particle size of 0.5 to 2.5 mm, and two-thirds or more of the dried product has a particle size of 2.5 mm or less.

9. 6. The agitation and heat transfer drying method according to claim 5, wherein an initial filling height of the material to be dried is higher than an upper surface of the rotary shaft in a section from the supply section to the discharge section.

10. 6. The agitation heat transfer drying method according to claim 4, wherein the materials to be dried are supplied evenly from each of the supply sections.

11. 7. The method for drying by stirring and heat transfer according to claim 6, wherein the amount of material to be dried supplied per hour is 1 / 8 to 1 / 15 of the amount of solid matter of the material initially charged.

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