Drying system and drying method

Abstract

The present invention relates to a drying system and drying method for receiving and drying multiple types of sludge with different properties, and aims to make it easier to maintain a constant drying efficiency even when dealing with multiple types of sludge with different properties. [Solution] The system comprises multiple hoppers 10, a mixer 20 for mixing the input materials from the multiple hoppers 10, and a dryer 30 for drying the mixture mixed in the mixer 20. The multiple hoppers 10 include multiple sludge hoppers 11, 12, and 13, which are distinguished according to the properties of the sludge received, and a fiber hopper 14 for adding fiber.

Description

[Technical Field]

[0001] This invention relates to a drying system and a drying method for drying multiple types of sludge with different properties. [Background technology]

[0002] Sewage treatment plants generate multiple types of sludge with different properties. For example, when wastewater is treated using the activated sludge method after passing through a final sedimentation tank, excess sludge is generated. Sludge contains both organic and inorganic components, and examples of organic components include phosphate compounds and fibrous material. In excess sludge, the fibrous material is reduced through the activated sludge method, but it tends to contain a large amount of phosphate compounds. Phosphate compounds can cause blockages in exhaust gas ducts and other systems when dried sludge is incinerated. Therefore, in order to reduce the proportion of phosphate compounds as much as possible, raw sludge with a higher fibrous content (primary sedimentation sludge) generated in the primary sedimentation tank is sometimes added to the excess sludge to create mixed raw sludge. Furthermore, concentrated sludge, which is obtained by concentrating excess sludge or raw sludge, is converted into digester gas from some of the organic components, resulting in digested sludge with a reduced organic content and a higher inorganic content.

[0003] The applicant has previously made several proposals for drying sludge generated at sewage treatment plants (for example, Patent Document 1), but it has been found that when drying sludge, if aggregation (granulation) occurs in the sludge during drying due to liquid crosslinking or solid crosslinking, the contact area with the heat transfer medium decreases, and the drying efficiency decreases. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2011-33224 [Overview of the project] [Problems that the invention aims to solve]

[0005] The likelihood of liquid crosslinking and solid crosslinking varies depending on the properties of the sludge. Therefore, when attempting to dry multiple types of sludge with different properties in a common dryer, it becomes difficult to maintain a consistent drying efficiency.

[0006] In view of the above phenomena, the present invention aims to provide a drying system and drying method that makes it easier to maintain a constant drying efficiency even when dealing with multiple types of sludge with different properties. [Means for solving the problem]

[0007] The drying system that solves the above problems is: A drying system that accepts multiple types of sludge with different properties and dries the sludge, Multiple hoppers, A mixer for mixing the input materials introduced from the aforementioned multiple hoppers, The system includes a dryer for drying the mixture mixed in the aforementioned mixer, The aforementioned plurality of hoppers are characterized by the provision of a plurality of sludge hoppers distinguished according to the properties of the received sludge, and a fiber hopper for adding fiber.

[0008] This invention assumes that sludge contains organic matter (e.g., phosphate compounds) that functions as a binder for solid crosslinking. Based on this assumption, the inventors focused on the fibrous content in the sludge. When the fibrous content is low, the fibrous content is covered by particles other than fibrous content, reducing the porosity characteristic of fibrous content. As a result, particles other than fibrous content are more likely to undergo solid crosslinking by the organic matter that functions as a binder, and are more likely to agglomerate (granulate). Conversely, when the fibrous content is present at a certain concentration or higher, the voids in the fibrous content inhibit the agglomeration of particles other than fibrous content that contain binder components, resulting in less agglomeration. With the above drying system, it becomes possible to investigate the properties of the received sludge (e.g., the ratio of fibrous content) in advance or at the time of acceptance, and adjust the input amount and input ratio for each type of sludge with different properties. For example, if the sludge has a low fibrous content, it can be mixed with sludge that has a high fibrous content in the mixer to increase the fibrous content. Alternatively, the fibrous content can also be increased by adding fibrous content from the fibrous content hopper to the mixer and mixing it. As a result, even with multiple types of sludge with different properties, the occurrence of solid crosslinking can be suppressed, making it easier to maintain a consistent drying efficiency.

[0009] The mixer and the dryer may be separate units or a single unit.

[0010] Furthermore, the properties of the sludge may include not only the ratio of fiber content but also the amount of water it contains. If the water content is high, there is a risk of liquid crosslinking occurring. For this reason, the mixer may be used to mix sludge with high water content with sludge with low water content to reduce the water content. In addition, the amount of oil content and the ratio of inorganic content can also be considered. A high oil content makes it easier for liquid crosslinking to form, and a high inorganic content, similar to fiber content, inhibits the aggregation of particles containing binders other than inorganic components.

[0011] Also, The dryer may be characterized in that, in addition to drying the mixture mixed in the mixer, it also dries the sludge fed in from one of the plurality of sludge hoppers.

[0012] If the sludge received in the sludge hopper is suitable sludge with a high fiber content, it can be directly fed from the sludge hopper to the dryer for drying without mixing in the mixer, thereby improving work efficiency.

[0013] Also, The aforementioned dryer is of the conduction heat transfer type and is equipped with an electric motor that serves as a driving source for agitating the material to be dried inside. The system may also be characterized by having a control unit that controls at least one of the following based on a value representing the moisture content of the dried product or the object being dried in the dryer and the current value flowing to the electric motor: the input ratio of fiber to be fed into the mixer, the amount of sludge fed from the sludge hopper into the mixer, and the amount of mixture fed from the mixer into the dryer.

[0014] According to this drying system, a high moisture content suggests that agglomeration is occurring due to liquid crosslinking. Therefore, if the moisture content is high, at least one of the input amounts of sludge from the sludge hopper to the mixer and the input amount of the mixture is reduced (including reducing it to 0) to suppress the occurrence of liquid crosslinking. Also, if agglomeration occurs due to crosslinking, the agglomeration becomes resistance to stirring and the current value increases. Therefore, if the current value is high when the moisture content is not high, it suggests that agglomeration is occurring due to solid crosslinking, and the input ratio of the fiber is increased to suppress the occurrence of solid crosslinking.

[0015] The dried product dried in the dryer may be the dried product discharged from the inside of the dryer, or the dried product remaining inside immediately before being discharged (the same applies hereinafter). The value representing moisture content may be the value of moisture directly measured with a moisture meter, or the value representing moisture content obtained by measuring the temperature of the dried product or the object being dried, or the temperature itself if a correspondence between the measured temperature and moisture content has been established (the same applies hereinafter).

[0016] Further, the control unit may control at least one of the input amount of the fiber component added from the fiber component hopper to the mixer, the input amount of the sludge input from the sludge hopper to the mixer, and the input amount of the mixture input from the mixer to the dryer, based on a value representing the moisture content of the dried product dried by the dryer or the object to be dried being dried by the dryer, and the value of the current flowing through the electric motor. By increasing the input amount of the fiber component, as a result, the ratio of the fiber component of the object to be dried staying inside the dryer increases, and the occurrence of solid crosslinking is suppressed. Alternatively, if sludge containing a large amount of fiber component is received, by increasing the input amount of the sludge hopper that has received the sludge, as a result, the ratio of the fiber component of the object to be dried staying inside the dryer increases, and the occurrence of solid crosslinking can be suppressed. Also, by controlling at least one of the input amount of the sludge input from the sludge hopper to the mixer and the input amount of the mixture input from the mixer to the dryer, the occurrence of liquid crosslinking can be suppressed.

[0017] In addition, when the mixer and the dryer are integrated, there is no need to control the input amount of the mixture input from the mixer to the dryer (the same applies hereinafter).

[0018] Also, The dryer is of a conduction heat transfer type, It may be characterized by including a control unit that controls at least one of the input ratio of the fiber component input to the mixer, the input amount of the sludge input from the sludge hopper to the mixer, and the input amount of the mixture input from the mixer to the dryer, based on a value representing the moisture content of the dried product dried by the dryer or the object to be dried being dried by the dryer, and a value representing the bulk density of the dried product or the object to be dried.

[0019] Since the fiber component that the present inventor focused on this time has voids, a value representing the bulk density (apparent density), which is the mass per unit volume including those voids, is obtained. When the fiber component is below a certain concentration, the fiber component is compressed by the aggregation of particles other than the fiber component, and the porosity characteristic of the fiber component is lost, resulting in an increase in the bulk density. On the other hand, when the fiber component is above a certain concentration, the aggregation of particles other than the fiber component is inhibited, and the porosity of the fiber component is maintained. As a result, when the fiber component is above a certain concentration, the bulk density becomes lower. Therefore, a correlation exists between the ratio of the fiber component of the material to be dried staying inside the dryer, the bulk density of the material to be dried, and further the bulk density of the dried product dried by the dryer. In this drying system, by utilizing these correlations, if the value representing the bulk density is high, it is suspected that aggregates are generated by solid cross-linking, and the input ratio of the fiber component is increased to suppress the occurrence of solid cross-linking. Also, here too, if the value representing the moisture is high, at least one of the input amounts of the sludge input from the sludge hopper to the mixer and the input amount of the mixture is decreased (including decreasing to 0) to suppress the occurrence of liquid cross-linking.

[0020] The value representing the bulk density may be a measured value, an estimated value, or a value obtained indirectly (the same applies hereinafter). For example, if a sampling container for accommodating the dried product discharged from the inside of the dryer is provided, the bulk density of the dried product can be calculated from the volume of the dried product accommodated in the sampling container and the mass of the dried product accommodated in the sampling container. Alternatively, if a sampling container for accommodating the material to be dried extracted from the inside of the dryer is provided, the bulk density of the material to be dried can be calculated from the volume of the material to be dried accommodated in the sampling container and the mass of the material to be dried accommodated in the sampling container.

[0021] Furthermore, the control unit may control the input amount of at least one of the following: the amount of fiber added to the mixer from the fiber hopper, the amount of sludge added to the mixer from the sludge hopper, and the amount of the mixture added to the dryer from the mixer, based on a value representing the moisture content of the dried product or the material being dried in the dryer and a value representing the bulk density of the dried product or the material being dried. By increasing the input amount of fiber, the proportion of fiber in the material being dried that remains inside the dryer increases, thereby suppressing the occurrence of solid crosslinking. Alternatively, if sludge containing a large amount of fiber is being accepted, increasing the input amount of the sludge hopper that accepts the sludge will also increase the proportion of fiber in the material being dried that remains inside the dryer, thereby suppressing the occurrence of solid crosslinking. In addition, by controlling the input amount of at least one of the following: the amount of sludge added to the mixer from the sludge hopper and the amount of the mixture added to the dryer from the mixer, the occurrence of liquid crosslinking can be suppressed.

[0022] Furthermore, the control unit may control at least one of the following based on a value representing the moisture content of the dried product or the object being dried in the dryer, the current value flowing to the electric motor, and a value representing the bulk density of the dried product or the object being dried: the ratio of fiber to be fed into the mixer, the amount of sludge fed from the sludge hopper into the mixer, and the amount of mixture fed from the mixer into the dryer.

[0023] The drying method that solves the above problem is: A drying method for receiving multiple types of sludge with different properties and drying said sludge, A sludge supply process that supplies sludge to separate sludge hoppers according to the properties of the sludge received, A mixing step which involves either sludge mixing, in which sludge is introduced from multiple sludge hoppers and mixed with other sludge to obtain a mixture, or fiber addition mixing, in which sludge is introduced from one or more sludge hoppers and fiber is also introduced from a fiber hopper and mixed with the sludge to obtain a mixture; The system is characterized by comprising a drying step of drying the mixture obtained in the mixing step.

[0024] According to this drying method, in the sludge supply step, sludge is supplied to separate sludge hoppers according to the properties of the sludge (e.g., fiber content). The properties of the sludge supplied to the sludge hopper are determined either by investigating them before supplying them to the sludge hopper or by determining them based on previous investigation results. In the mixing step, the amount of sludge added is adjusted for each type of sludge with different properties. For example, if the sludge has a low fiber content, it can be mixed with sludge that has a high fiber content in the sludge mixing step to increase the fiber content. Alternatively, the fiber content can also be increased by adding fiber during mixing. As a result, even with multiple types of sludge with different properties, the occurrence of solid crosslinking can be suppressed, making it easier to maintain a consistent drying efficiency.

[0025] In addition to the fiber content, the properties of the sludge may also include the amount of water, oil, or inorganic content.

[0026] Furthermore, the drying step may be a step in which the mixture mixed in the mixing step is introduced and the introduced mixture is dried, or a step in which the mixture mixed in the container in the mixing step is dried in the container (the same applies hereinafter).

[0027] Also, The drying process is a process in which the material to be dried is dried by conductive heat transfer while being agitated by the driving force of an electric motor. The method may be characterized by adjusting at least one of the following based on a value representing the moisture content of the dried product or the object being dried in the drying process and the current value flowing through the electric motor during stirring in the drying process: the ratio of fiber added in the mixing process, the amount of sludge added from the sludge hopper in the mixing process, and the amount of the mixture mixed in the mixing process added to the drying process.

[0028] If the moisture content value is high, it is suspected that aggregates are being formed by liquid crosslinking. In this case, the amount of sludge added from the sludge hopper in the mixing step and the amount of the mixture added to the drying step are reduced (including reduced to 0), thereby suppressing the occurrence of liquid crosslinking in the drying step. On the other hand, if the current value is high when the moisture content value is not high, it is suspected that aggregates are being formed by solid crosslinking. In this case, the proportion of fiber added in the mixing step is increased, thereby suppressing the occurrence of solid crosslinking in the drying step.

[0029] The dried product in the above drying process may, for example, be the dried product discharged from inside the dryer, or the dried product remaining inside immediately before being discharged (the same applies hereinafter).

[0030] Furthermore, based on a value representing the moisture content of the dried product or the material being dried in the drying process, and the current value flowing through the electric motor during stirring in the drying process, the amount of fiber added from the fiber hopper, the amount of sludge added from the sludge hopper in the mixing process, and the amount of the mixture mixed in the mixing process added to the drying process may be adjusted. Increasing the amount of fiber added will result in an increase in the fiber content of the material being dried, thereby suppressing the occurrence of solid crosslinking in the drying process. Alternatively, if sludge containing a large amount of fiber is accepted, increasing the amount of sludge from the sludge hopper that accepted the sludge in the mixing process will also result in an increase in the fiber content of the material being dried, thereby suppressing the occurrence of solid crosslinking in the drying process. In addition, the occurrence of liquid crosslinking can be suppressed by adjusting the amount of sludge added from the sludge hopper in the mixing process and the amount of the mixture mixed in the mixing process added to the drying process.

[0031] Furthermore, if the drying step is a step of drying the mixture mixed in the container in the mixing step within the same container, then the amount of the mixture mixed in the mixing step added to the drying step will not be adjusted (the same applies hereinafter).

[0032] Also, The drying process is a process of performing drying by conductive heat transfer, The method may be characterized by adjusting at least one of the following based on a value representing the moisture content of the dried product or the object being dried in the drying process and a value representing the bulk density of the dried product or the object being dried: the ratio of fiber added in the mixing process, the amount of sludge added from the sludge hopper to the mixing process, and the amount of the mixture mixed in the mixing process added to the drying process.

[0033] If the moisture content value is high, it is suspected that aggregates are being formed by liquid crosslinking. In this case, the amount of sludge input from the sludge hopper in the mixing step and the amount of the mixture mixed in the mixing step input into the drying step are reduced (including reduced to 0), thereby suppressing the occurrence of liquid crosslinking in the drying step. On the other hand, if the moisture content value is low and the bulk density value of the dried product is high, it is suspected that aggregates are being formed by solid crosslinking. In this case, the proportion of fiber input in the mixing step is increased, thereby suppressing the occurrence of solid crosslinking in the drying step.

[0034] Furthermore, based on a value representing the moisture content of the dried product or the object being dried in the drying process, and a value representing the bulk density of the dried product or the object being dried, the input amount of at least one of the following may be adjusted: the amount of fiber added from the fiber hopper, the amount of sludge added from the sludge hopper, and the amount of the mixture mixed in the mixing process added to the drying process. Increasing the input amount of fiber will result in an increase in the fiber content of the object being dried, thereby suppressing the occurrence of solid crosslinking in the drying process. Alternatively, if sludge containing a large amount of fiber is accepted, increasing the input amount of the sludge hopper that accepted the sludge in the mixing process will also result in an increase in the fiber content of the object being dried, thereby suppressing the occurrence of solid crosslinking in the drying process. In addition, the occurrence of liquid crosslinking can be suppressed by adjusting the input amount of at least one of the following: the amount of sludge added from the sludge hopper in the mixing process and the amount of the mixture mixed in the mixing process added to the drying process.

[0035] Furthermore, based on a value representing the moisture content of the dried product or the object being dried in the drying process, the current value flowing through the electric motor during stirring in the drying process, and a value representing the bulk density of the dried product or the object being dried, at least one of the following may be adjusted: the ratio of fiber added in the mixing process, the amount of sludge added from the sludge hopper in the mixing process, and the amount of the mixture mixed in the mixing process added to the drying process. [Effects of the Invention]

[0036] According to the present invention, it is possible to provide a drying system and drying method that makes it easier to maintain a constant drying efficiency even when dealing with multiple types of sludge with different properties. [Brief explanation of the drawing]

[0037] [Figure 1] This is a diagram showing the configuration of the drying system in this embodiment. [Figure 2](a) is a table summarizing an example of the materials contained in the hopper of drying system 1 shown in Figure 1, and (b) is a table showing a specific example of the input pattern in drying system 1 shown in Figure 1. [Figure 3] This is a front view showing a portion of the dryer in the drying system of this embodiment, with the inside visible. [Figure 4] Figure 3 is a cross-sectional view of the area near the discharge port of the dryer 30. [Figure 5] (a) is a graph showing the relationship between the retained mass of the material to be dried and the current value flowing to the electric motor of the rotary scraping member, (b) is a table summarizing the trend in the relationship between bulk density and the possibility of agglomeration, and (c) is a table summarizing the trend in the relationship between moisture and the possibility of agglomeration. [Figure 6] These are magnified images of dried sludge with low fiber content and dried sludge with high fiber content, observed under a microscope. [Figure 7] (a) is a table showing the combined results of the possibility of aggregate formation from moisture, the possibility of aggregate formation from current value, and the possibility of aggregate formation from bulk density; (b) is a table showing an example of timer control that gradually increases the fiber input ratio; and (c) is a table showing an example of timer control that gradually decreases the fiber input ratio. [Figure 8] (a) is a table showing the relationship between the change in current value and the fiber content coefficient A, (b) is a table showing the relationship between the change in bulk density and the fiber content coefficient B, and (c) is a table showing the relationship between the value obtained by multiplying the fiber content coefficients A and B and the change in fiber content. [Figure 9] Figure 1 is a flowchart of the drying method implemented in the drying system shown. [Modes for carrying out the invention]

[0038] Embodiments of the present invention will be described below with reference to the drawings.

[0039] <Drying system configuration> Figure 1 shows the configuration of the drying system according to this embodiment.

[0040] The drying system 1 shown in Figure 1 accepts multiple types of sludge with different properties. These multiple types of sludge include mixed raw sludge, excess sludge, digested sludge, and raw sludge (monosettled sludge).

[0041] This drying system 1 comprises multiple hoppers 10, a mixer 20, a dryer 30, a bulk density measuring device 40, a dried product discharge equipment 50, and a control unit 60. In Figure 1, the solid gray line connected to the control unit 60 represents a signal line, and the black arrows represent the flow of material.

[0042] The hopper 10 consists of four hoppers: the first hopper 11, the second hopper 12, the third hopper 13, and the fourth hopper 14. Note that the number of hoppers is not limited to four; two or more are acceptable.

[0043] Figure 2(a) is a table summarizing an example of the materials contained in the hopper of drying system 1 shown in Figure 1.

[0044] The table in Figure 2(a) shows six types of sludge with different properties, labeled Sludge 1 to Sludge 6. Sludge 2 is a type of sewage sludge called excess sludge. The fibrous content of excess sludge is reduced through the activated sludge process. The crude fiber content of Sludge 2 was measured to be 3 wt%-DS (Dry Solid). The moisture content of Sludge 2 was measured to be 84% WB. Note that "% WB" is a unit notation used to indicate the moisture content on a wet basis, representing the amount of water relative to the total mass.

[0045] Sludge 3 is a type of sewage sludge called digested sludge. Digested sludge is sludge with reduced organic content because some of the organic matter is converted into digester gas. The crude fiber content of sludge 3 was measured to be 4 wt%-DS. The moisture content of sludge 3 was measured to be 83% WB.

[0046] Sludge samples 1, 4, 5, and 6 are all mixed raw sludge. Mixed raw sludge is made by adding raw sludge with a higher fiber content (primary sedimentation sludge) generated in the primary sedimentation tank to excess sludge. For sludge 1, the crude fiber content was measured at 35 wt%-DS and the moisture content was measured at 74%WB. For sludge 4, the crude fiber content was measured at 30 wt%-DS and the moisture content was measured at 77%WB. For sludge 5, the crude fiber content was measured at 25 wt%-DS and the moisture content was measured at 79%WB. For sludge 6, the crude fiber content was measured at 23 wt%-DS and the moisture content was measured at 80%WB.

[0047] It can be seen that mixed raw sludge has a higher fiber content compared to surplus sludge and digested sludge. Furthermore, it can be seen that even among mixed raw sludges, the fiber content can differ. The first hopper 11 shown in Figure 1 is a hopper that contains sludge with a relatively high fiber content (sludge with a relatively high fiber content), and contains sludge 1 or sludge 4 shown in Figure 2(a). The second hopper 12 is a hopper that contains sludge with a relatively low fiber content (sludge with a relatively low fiber content), and contains sludge 2 or sludge 3 shown in Figure 2(a). The third hopper 13 is a hopper that contains sludge with an intermediate fiber content (sludge with an intermediate fiber content), and contains sludge 5 or sludge 6 shown in Figure 2(a). Although the sludge with the highest crude fiber content is sludge 1 with a crude fiber content of 35 wt%-DS, sludge with an even higher crude fiber content than sludge 1 may also be placed in the first hopper 11.

[0048] Furthermore, the table shown in Figure 2(a) also shows materials such as fiber. This fiber can be crushed waste paper, crushed wood or wood chips, or a mixture of these. As an example, the crude fiber content was measured to be 50 wt%-DS, and the moisture content was measured to be 45%WB. The fourth hopper 14 shown in Figure 1 is a hopper that contains the fiber shown in Figure 2(a). This fiber does not necessarily need to contain sludge as a component other than fiber, and it is preferable that it does not contain sludge.

[0049] In the drying system 1 shown in Figure 1, when multiple types of sludge are received, the received sludge is distributed to the first hopper 11 to the third hopper 13 according to its fiber content (wt%-DS), based on data from the facility where the received sludge was generated, past performance, or analysis results at the time of receipt.

[0050] The mixer 20 shown in Figure 1 is a two-shaft paddle-type mixer, but it is not limited to this type. The material contained in the hopper 10 may be fed into the mixer 20, or it may be fed directly into the dryer 30. In other words, the drying system 1 shown in Figure 1 is presented as a system in which multiple feeding patterns can be selected.

[0051] Figure 2(b) is a table showing a specific example of the input pattern in the drying system 1 shown in Figure 1. In this example, the amount of material input to the dryer 30 per hour is set to 1000 kg.

[0052] The thick solid arrows in Figure 1 represent input pattern 1. In this input pattern 1, sludge with a relatively high fiber content is directly fed from the first hopper 11 to the dryer 30. The table in Figure 2(b) shows two specific examples of input pattern 1. In example 1, sludge 1 is directly fed into the dryer 30 at an input rate of 1000 kg / h, and in example 2, sludge 4 is directly fed into the dryer 30 at an input rate of 1000 kg / h.

[0053] The dashed arrow in Figure 1 represents input pattern 2. In this input pattern 2, sludge is fed into the mixer 20 from the first hopper 11 and the second hopper 12, respectively. That is, two types of sludge, one with a relatively high fiber content and the other with a relatively low fiber content, are fed into the mixer 20. The two types of sludge are mixed in the mixer 20 and then fed into the dryer 30 as mixed sludge. The table in Figure 2(b) shows four specific examples of input pattern 2. In example 1, sludge 1 is fed into the mixer 20 from the first hopper 11 at a rate of 575 kg / h, and sludge 2 is fed into the mixer 20 from the second hopper 12 at a rate of 425 kg / h. In example 2, sludge 1 is fed into the mixer 20 from the first hopper 11 at a rate of 579 kg / h, and sludge 3 is fed into the mixer 20 from the second hopper 12 at a rate of 421 kg / h. In Example 3, sludge 4 is fed into the mixer 20 from the first hopper 11 at a rate of 754 kg / h, and sludge 2 is fed into the second hopper 12 at a rate of 245 kg / h. In Example 4, sludge 4 is fed into the mixer 20 from the first hopper 11 at a rate of 756 kg / h, and sludge 3 is fed into the second hopper 12 at a rate of 244 kg / h.

[0054] The dashed arrow in Figure 1 represents input pattern 3. In this input pattern 3, sludge is fed into the mixer 20 from the second hopper 12 and fiber is fed into the fourth hopper 14. That is, sludge with a relatively low fiber content and fiber are fed into the mixer 20, and the sludge and fiber are mixed in the mixer 20 before being fed into the dryer 30 as sludge with added fiber. The table in Figure 2(b) shows two specific examples of input pattern 3. In example 1, sludge 2 is fed into the mixer 20 from the second hopper 12 at a rate of 796 kg / h, and fiber is fed into the mixer 20 from the fourth hopper 14 at a rate of 204 kg / h. In example 2, sludge 3 is fed into the mixer 20 from the second hopper 12 at a rate of 794 kg / h, and fiber is fed into the mixer 20 from the fourth hopper 14 at a rate of 206 kg / h.

[0055] The dotted arrow in Figure 1 represents input pattern 4. In this input pattern 4, sludge is fed into the mixer 20 from the third hopper 13 and fibrous material is fed into the fourth hopper 14. That is, sludge with an intermediate fibrous content and fibrous material are fed into the mixer 20, and the sludge and fibrous material are mixed in the mixer 20 before being fed into the dryer 30 as sludge with added fibrous material. Note that there are also cases where the amount of fibrous material fed into the fourth hopper 14 is 0 kg / h. The table in Figure 2(b) shows two specific examples of input pattern 4. In Example 1, sludge 5 is fed into the mixer 20 from the third hopper 13 at an input rate of 1000 kg / h, and the amount of fibrous material fed into the fourth hopper 14 is 0 kg / h. In Example 2, sludge 6 is fed into the mixer 20 from the third hopper 13 at a rate of 972 kg / h, and fiber is fed into the fourth hopper 14 at a rate of 28 kg / h.

[0056] The thick dashed arrow in Figure 1 represents input pattern 5. In this input pattern 5, sludge with an intermediate fiber content is directly fed from the third hopper 13 into the dryer 30. The table in Figure 2(b) shows two specific examples of input pattern 5. In example 1, sludge 5 is directly fed into the dryer 30 at an input rate of 1000 kg / h, and in example 2, sludge 6 is directly fed into the dryer 30 at an input rate of 1000 kg / h.

[0057] The material moisture content (%WB) values ​​in the table in Figure 2(b) are the moisture content values ​​for each material shown in Figure 2(a). The input dry matter amount (kg / h) values ​​in the table in Figure 2(b) are calculated using the formula: input amount × (1 - material moisture content / 100). The material crude fiber content (wt%-DS) values ​​in the table in Figure 2(b) are the crude fiber content values ​​for each material shown in Figure 2(a). The fiber content (kg / h) values ​​in the table in Figure 2(b) are calculated using the formula: input dry matter amount × material crude fiber content / 100. When two types of materials are mixed, the fiber content values ​​for each material are added together to obtain the total value. The mixed crude fiber content (wt%-DS) values ​​in the table in Figure 2(b) are calculated using the formula: (total fiber content / total input dry matter amount) × 100. The moisture content (%WB) value at the time of mixing in the table in Figure 2(b) is calculated by summing the values ​​obtained from the formula (amount added × moisture content of each material / 100), dividing the sum of the amounts added (1000 kg), and multiplying by 100.

[0058] Next, we will describe in detail the dryer 30 shown in Figure 1. This dryer 30 is a conduction heat transfer type dryer. However, a hot air dryer or the like may also be used.

[0059] Figure 3 is a front view showing a portion of the dryer of the drying system of this embodiment, with a section cut away to reveal the inside. Note that in Figure 3, the internal components of the main shell 31 are simplified to make the internal structure easier to see.

[0060] As shown in Figure 3, the dryer 30 is equipped with a main shell 31. The main shell 31 is generally cylindrical with both ends closed. The main shell 31 is supported by a machine frame (not shown) that extends horizontally. In Figure 3, the extension direction of the main shell 31 is left to right. This extension direction of the main shell 31 coincides with the axial direction of the rotation axis of the multi-tube heating tube 32, which will be described later. Hereafter, this axial direction of the multi-tube heating tube 32 (the extension direction of the main shell 31) may be simply referred to as the axial direction.

[0061] The main shell 31 is provided with an inlet 311, an outlet 312, a carrier gas inlet 313, an exhaust port 314, and an electric motor 317. The inlet 311 is an opening for introducing the material to be dried R (see Figure 4), and there are four of them provided at predetermined intervals in the axial direction at the upper end of the main shell 31. Depending on the axial length of the main shell 31, there may be one to three or five or more inlet 311. For example, if the sludge 1 in Example 1 of Input Pattern 1 described above is the material to be dried R, this sludge 1 is supplied to each inlet 311 in predetermined amounts and at predetermined time intervals. In Example 1 of Input Pattern 2, the mixed sludge discharged from the mixer 20 is supplied to each inlet 311 in predetermined amounts and at predetermined time intervals. The main shell 31 is also provided with a viewing window (not shown) so that the inside of the main shell 31 can be visually observed.

[0062] The discharge port 312 is an opening through which the material to be dried R, which is introduced from the input port 311, dries while remaining inside the main shell 31, reducing its moisture content and becoming a dried product D, which is then discharged. This discharge port 312 is located on the right side of the main shell 31 in Figure 3, on the side of the main shell 31 (the side of the main shell 31 on the near side of the paper in Figure 3). The discharge port 312 is provided with a fixed weir plate 3120 and a movable weir plate 3121. The fixed weir plate 3120 is fixed to the main shell 31 so as to cover the middle portion of the discharge port 312, so as to form openings in the upper and lower portions of the discharge port 312. On the other hand, the movable weir plate 3121 is located on the opposite side of the main shell 31 so as to overlap the fixed weir plate 3120, and is driven by a cylinder (not shown) to slide up and down. When the movable weir plate 3121 is slid upward, the lower part of the discharge port 312 opens, and the dried product D is discharged from this opening. On the other hand, when the movable weir plate 3121 is lowered by the cylinder, the opening is closed, and the discharge of the dried product D stops. By changing the height position of the movable weir plate 3121, the opening area of ​​the opening can be changed, and the amount of dried material R that remains in the main shell 31 can be adjusted. In addition, a chute 3122 is positioned in the part of the main shell 31 where the discharge port 312 is provided.

[0063] A bulk density measuring device 40 is connected to this chute 3122. The material to be dried R, which is fed in from the input port 311, moves from left to right inside the main shell 31 shown in Figure 3, and is eventually discharged as dried product D from the discharge port 312, and is sent to the bulk density measuring device 40 through the chute 3122. The bulk density measuring device 40 will be described in more detail later, but the installation position of the bulk density measuring device 40 may be downstream of the dried product discharge equipment 50. In the main shell 31 shown in Figure 3, the left side is the input port side and the right side is the discharge port side. The main shell 31 may be installed on a machine frame or the like in a state where it extends in a direction that is slightly inclined downward from the input port side to the discharge port side.

[0064] The carrier gas inlet 313 is an inlet for introducing carrier gas, which is supplied by a supply blower and heated to approximately 120°C by a heater, into the main body shell 31. The exhaust port 314 is an inlet for exhausting vapor evaporated from the material to be dried R, along with the carrier gas introduced from the carrier gas inlet 313, to the outside of the main body shell 31. The carrier gas introduced into the main body shell 31 from the carrier gas inlet 313 flows along the upper part of the main body shell 31, which is the surface layer of the material to be dried R that remains inside the main body shell 31, and is exhausted from the exhaust port 314 along with the vapor evaporated from the material to be dried R. Hereinafter, the gas exhausted from this exhaust port 314, i.e., the vapor and carrier gas, will be collectively referred to as the outlet gas. The exhaust port 314 is equipped with an outlet thermometer 3141 for measuring the temperature of the outlet gas.

[0065] The exhaust path connected to the exhaust port 314 is equipped with a dust collector and an exhaust blower (not shown). The outlet gas exhausted from the exhaust port 314 is sent to the dust collector, where it undergoes predetermined processing such as removal of fine particles, and then exhausted outdoors via the exhaust blower, etc. Alternatively, it may be exhausted outdoors after passing through a deodorizing device. Furthermore, a portion of the exhaust gas may be introduced into the main body shell 31 as a carrier gas through a second carrier gas port (not shown), resulting in partial carrier gas circulation, full carrier gas circulation, or no carrier gas circulation at all. In the case of carrier gas circulation, the exhaust gas is dehumidified by a condenser and scrubber, reheated by an air heater, and then circulated. Alternatively, superheated steam may be used as the carrier gas; in this case, the superheated steam is condensed by a condenser and scrubber and drained. The pressure inside the main body shell 31 is adjusted by the exhaust blower, etc., to be maintained at a pressure slightly lower than atmospheric pressure.

[0066] The electric motor 317 is the drive source that rotates the multi-tube heating tube 32, which is located inside the main body shell 31 (described later). The driving force generated by the electric motor 317 is transmitted to the hollow shaft 321 on the input side via the drive transmission mechanism 3171, causing the hollow shaft 321 to rotate. The current value flowing through the electric motor 317 is constantly monitored by the control unit 60 shown in Figure 1.

[0067] The main shell 31 houses a multi-tube heating tube 32 and several angle brackets 33 and other components attached to it. The multi-tube heating tube 32 is rotatably positioned within the main shell 31 around a rotation axis. The multi-tube heating tube 32 has a hollow shaft 321, a rotary joint 322, several heating tubes 323, an inlet-side header 324, and an outlet-side header (not shown). The hollow shaft 321 is provided at each end of the rotation axis of the multi-tube heating tube 32. This hollow shaft 321 is supported by a bearing (not shown) and rotates when driven by an electric motor 317. As the hollow shaft 321 rotates, all the heating tubes 323, the inlet-side header 324, the outlet-side header, and the angle brackets 33 rotate as well. The rotary joint 322 is connected to each hollow shaft 321.

[0068] Multiple heating tubes 323 extend along the rotation axis of the multi-tube heating tube 32, spaced apart from each other. Each heating tube 323 is supplied with saturated steam introduced from the rotary joint 322 on the inlet side. The temperature of the saturated steam is approximately 150°C to 170°C. A disc-shaped inlet-side header 324 is provided at the inlet-side end of each heating tube 323. In Figure 3, the outlet side is hidden and not visible because it is depicted as the outer surface of the main body shell 31, but an outlet-side header is provided at the outlet-side end of each heating tube 323. The outlet-side header has the same shape as the inlet-side header 324 and is positioned symmetrically to the inlet-side header 324 in Figure 3.

[0069] The inlet-side header 324 and the outlet-side header are hollow, with a space through which gas passes. Each of the multiple heating tubes 323 has its outlet end inserted into the outlet-side header and its inlet end inserted into the inlet-side header 324. When saturated steam is supplied from the rotary joint 322 on the inlet side, this saturated steam passes from the inlet-side header 324 through each heating tube 323 to the outlet-side header. This maintains the heating tubes 323 at a substantially constant temperature in the axial direction. The condensate generated from the saturated steam in the heating tubes 323 generally flows towards the outlet side and accumulates at the bottom of the outlet-side header. The condensate accumulated in the outlet-side header is drained to the outside of the dryer 30 by a drainage device (not shown).

[0070] Each of the multiple angles 33 is stretched between the input-side header 324 and the output-side header, with a predetermined rotational distance between them on the outer circumference of the heating tube 323. Therefore, as described above, when the hollow shaft 321 rotates, the angles 33 also rotate. The angles 33 are made of, for example, equal-leg angle steel. Multiple lifters 331 and feed vanes 332 are fixed to the angles 33 at intervals in the axial direction.

[0071] The angle 33 functions as a frame that reinforces the multi-tube heating tube 32 and also serves as a mounting base for the lifter 331 and the feed vane 332. When the multi-tube heating tube 32 rotates, the angle 33 and the lifter 331 and feed vane 332 fixed to the angle 33 also rotate together, and the angle 33, lifter 331 and feed vane 332 each scrape up the material to be dried R that is retained inside the main body shell 31. In other words, in this embodiment, the angle 33, lifter 331 and feed vane 332, including the heating tube 323, constitute an example of a configuration that agitates the material to be dried inside, and the electric motor 317 constitutes an example of a drive source for that agitation.

[0072] The lifter 331 is positioned closest to the inner wall of the main shell 31, and its rotation scrapes up the material to be dried R that remains inside the main shell 31. The lifter 331 is attached to the angle 33 in a spiral shape with the rotation axis of the multi-tube heating tube 32 as its central axis. The feed vane 332 is also fixed to the angle 33 at an angle with respect to the axial direction. As a result, the lifter 331 and the feed vane 332 gradually move the material to be dried R that remains inside the main shell 31 towards the discharge port by scraping it up through rotation.

[0073] Figure 4 is a cross-sectional view of the area near the discharge port of the dryer 30 shown in Figure 3. Note that the bulk density measuring device 40 connected to the chute 3122 is omitted from the illustration in Figure 4.

[0074] As shown in Figure 4, the main body shell 31 is a hollow member having a cross-sectional shape in which a roughly U-shaped lower portion and an arc-shaped upper portion are joined. The heating tube 323, the inlet-side header 324 (see Figure 3), the outlet-side header (not shown), the angle 33, the lifter 331, and the feed vane 332 (see Figure 3) rotate clockwise in Figure 4, as indicated by the thick solid arc-shaped arrows. Figure 4 also shows a virtual rotation axis O, which is the rotational axis of the heating tube 323, the inlet-side header 324, the angle 33, the lifter 331, and the feed vane 332.

[0075] Stainless steel pipes are used for the heating tubes 323. The multiple heating tubes 323 shown in Figure 4 are arranged in multiple rows in a regular hexagonal shape around the rotation axis O. A gap of 40 to 50 mm is formed between the heating tubes 323. The diameter, gaps, and arrangement shape of the heating tubes 323 are appropriately set depending on the type and amount of material to be dried R and the size of the main shell 31. The arrangement shape may be, for example, a circular arrangement. Alternatively, the arrangement shape may be asymmetrical with respect to the rotation axis O as a result of removing the heating tubes on the outer circumference that interfere during rotation. The material to be dried R placed inside the main shell 31 is scraped up along the scraping surface 3101 of the inner circumferential surface 310 of the main shell 31 by the angle 33, lifter 331, or feed vane 332. The heating tubes 323 also exert a scraping action on the material to be dried R. This scraping surface 3101 is the surface that comes into contact with the inner circumferential surface 310 as the material to be dried R inside the main shell 31 is scraped up by the rotation of the lifter 331. The material to be dried R, scraped up by the angle 33, lifter 331, or feed vane 332, comes into contact with the heating tube 323 and falls through the gap in the heating tube 323 while drying.

[0076] As described above, the angle 33 spans between the input-side header 324 and the discharge-side header, extending along the axial direction, with a total of 18 angle 33s provided at equal intervals of 20 degrees around the rotation axis O. One end of the angle 33 in the axial direction is fixed to the outer circumference of the input-side header 324, and the other end in the axial direction is fixed to the outer circumference of the discharge-side header.

[0077] As described above, the lifter 331 is arranged spirally with the rotation axis O as the centerline. In the semicircular portion below the main shell 31, the lifter 331 is attached to the angle 33, protruding radially in a virtual circle centered on the rotation axis O, such that the distance between its tip and the inner surface of the main shell 31 is between 20 mm and 30 mm. This lifter 331 is a plate-like shape with a V-shaped cross-section formed by bending a rectangular steel plate. The base of the lifter 331 is fixed to the radially protruding portion of the angle 33, so that the tip is bent toward the downstream side in the rotational direction relative to the radial direction. Because the tip of the lifter 331 is bent toward the downstream side in the rotational direction, the material to be dried R that is scooped up is less likely to fall. The distance between the lifter 331 and the inner surface of the main shell 31, and the cross-sectional shape of the lifter 331 are appropriately set depending on the type and amount of material to be dried R and the size of the main shell 31.

[0078] Figure 4 also shows the movable weir plate 3121 slid upward, with the entire lower portion of the discharge port 312 open. In Figure 4, the material to be dried R that is retained inside the main shell 31 is shown in gray, and it is retained in the lower left-leaning position inside the main shell 31. The way the material to be dried R is being scraped up by the angle 33 and lifter 331 is shown by thick dotted arrows. Furthermore, the water vapor evaporating from the material to be dried R is shown by thin dashed arrows.

[0079] The material remaining inside the main shell 31 is collectively referred to as the material to be dried R, and the material discharged from the outlet 312 is collectively referred to as the dried product D. However, the state of the material to be dried R (moisture content, particle size, etc.) immediately before being discharged from the outlet 312 inside the main shell 31 is almost the same as the state of the dried product D.

[0080] The volume of material R to be dried is adjusted to between 30% and 50% of the total volume of the multi-tube heating tube 32 by the fixed weir plate 3120 and the movable weir plate 3121. Normally, the volume of material to be dried is adjusted by changing the discharge rate by setting the timer on the movable weir plate 3121. However, if a malfunction occurs in the movable weir plate 3121, or if the change in volume is large and it is difficult to adjust the volume using the movable weir plate 3121, the material R to be dried will be discharged beyond the fixed weir plate 3120.

[0081] By adjusting the volume of material to be dried R within the main shell 31 to 30% to 50% of the total volume of the multi-tube heating tube 32, a portion of the multi-tube heating tube 32 is exposed in the upper region (the hatched region in Figure 4). This exposes the outlet gas, which consists of the carrier gas introduced into the main shell 31 from the carrier gas inlet 313 and exhausted from the exhaust port 314, and the water vapor evaporated from the material to be dried R, thereby raising the temperature of the outlet gas. Hereinafter, the region in which a portion of the multi-tube heating tube 32 is exposed will be referred to as the exposed region e. If the volume of material to be dried R within the main shell 31 is small, the area of ​​the exposed region e increases, and the area to which heat is supplied to the outlet gas also increases. Conversely, if the volume of material to be dried is large, the area of ​​the exposed region e decreases, and the area to which heat is supplied to the outlet gas also decreases. As the area to which heat is supplied to the outlet gas increases, the temperature of the outlet gas exhausted from the exhaust port 314 rises, and as the area decreases, the temperature falls. Thus, there is a correlation between the stagnant volume related to the area to which heat is supplied and the temperature of the outlet gas. The stagnant volume can be calculated from the temperature of the outlet gas using the calibration curve described later. The amount of carrier gas introduced into the main shell 31 from the carrier gas port 313 remains constant.

[0082] The inventors have previously verified the relationship between the retention rate of the material to be dried R within the main shell 31 (percentage of the total volume of the multi-tube heating tube 32) and the temperature of the outlet gas (°C). As a result, they obtained a calibration curve showing that if the retention rate of the material to be dried R within the main shell 31 (y) decreases, the temperature of the outlet gas (x) decreases. The equation "y = -ax + b" representing this calibration curve is stored in the control unit 60 shown in Figure 1.

[0083] Next, the bulk density measuring device 40 provided in the drying system 1 of this embodiment will be described.

[0084] The bulk density measuring device 40 is a device for measuring the bulk density of dried product D supplied from the discharge port 312 of the main shell 31 through the chute 3122. As shown in Figure 3, the bulk density measuring device 40 includes a sampling container 41, a load cell 42, a level gauge 43, a supply-side control valve 44, a discharge-side control valve 45, a supply-side flexible chute 46, a discharge-side flexible chute 47, and a PLC (programmable logic controller) (not shown). By controlling the supply-side control valve 44 and the discharge-side control valve 45 under the control of the PLC, the dried product D supplied to the sampling container 41 through the supply-side flexible chute 46 is contained in the sampling container 41. The load cell 42 measures the mass of the sampling container 41. The mass of the empty sampling container 41 is measured in advance by the load cell 42, and this measured value (hereinafter referred to as the tare value) is stored in the PLC. The level gauge 43 detects when a predetermined volume of dried product D is contained in the sampling container 41. That is, the volume of dried product D when it reaches the detection position of the level gauge 43 is measured in advance before the dryer 30 is operated, and this predetermined volume value is also stored in the PLC. When it is detected that a predetermined volume of dried product D is contained in the sampling container 41, the PLC returns the supply-side control valve 44 to the closed state. In this way, the mass of the sampling container 41 containing the predetermined volume of dried product D can be measured by the load cell 42. The PLC calculates the bulk density (apparent density) of the dried product D by subtracting the stored tare value from the measured mass value and dividing the result by the predetermined volume value, which is also stored, and transmits the calculated value to the control unit 60 of the drying system 1 shown in Figure 1. Since the dried material R immediately before being discharged from the discharge port 312 has been dried to the target moisture content, the bulk density value of the dried product D can also be said to be the bulk density value of the dried material R immediately before being discharged from the discharge port 312.

[0085] Once the mass measurement by the load cell 42 is complete, the PLC opens the discharge-side control valve 45 and discharges the dried product D contained in the sampling container 41 from the discharge-side flexible chute 47.

[0086] On the other hand, if mass measurement by the load cell 42 is not required, both the supply-side control valve 44 and the discharge-side control valve 45 are left open, allowing the dried product D to pass through the sampling container 41 and be discharged from the discharge-side flexible chute 47. Alternatively, a separate discharge route for the dried product D may be provided, allowing it to reach the dried product discharge equipment 50 without passing through the bulk density measuring device 40 from the discharge port 312.

[0087] Next, we will describe the dried product discharge equipment 50 provided in the drying system 1 of this embodiment.

[0088] As shown in Figure 3, the dried product discharge equipment 50 has a discharge-side conveyor 51 and a discharge-side moisture meter 52. The dried product D is discharged from the discharge-side flexible chute 47 to the discharge-side conveyor 51 and transported to the next process by the discharge-side conveyor 51. The discharge-side conveyor 51 can be a screw conveyor, a flight conveyor, or a belt conveyor. The discharge-side moisture meter 52 irradiates the dried product D being transported on the discharge-side conveyor 51 with infrared light from above and calculates the moisture content (%WB) from the reflected light. The moisture value calculated by the discharge-side moisture meter 52 is also transmitted to the control unit 60 shown in Figure 1. Furthermore, since there is often a correlation between the temperature of the dried product D and the moisture content of the dried product D, it is also possible to measure the temperature of the dried product D and determine a value representing the moisture content from that temperature. For this reason, the measurement data of the temperature of the dried product D may be transmitted to the control unit 60, and the control unit 60 may determine a value representing the moisture content from the temperature. Alternatively, if a correspondence between product temperature and moisture content is required, the moisture content value can be substituted with the product temperature value. The configuration of the drying system 1 of this embodiment has now been described.

[0089] <Retention mass of dried material R> The outlet gas temperature is measured by the outlet thermometer 3141 shown in Figure 1, and the measured value is transmitted to the control unit 60. As described above, the control unit 60 stores the equation "y = -ax + b", which represents a calibration curve that shows that the outlet gas temperature (x) decreases as the retention rate (y) of the material to be dried within the main shell 31 decreases. From this equation, the control unit 60 calculates the retention rate of the material to be dried within the main shell 31 (percentage of the total volume of the multi-tube heating tube 32) at the time the outlet gas temperature is measured. The control unit 60 also stores the value of the total volume of the multi-tube heating tube 32, and from this volume value and the calculated retention rate, the retention volume of the material to be dried within the main shell 31 is determined.

[0090] Furthermore, the bulk density measuring device 40 periodically measures and calculates the bulk density (apparent density) of the dried product D (for example, every 30 minutes, 1 hour, or 4 hours). The calculated value is transmitted to the control unit 60 and stored. Note that the dried product R immediately before being discharged from the discharge port 312 corresponds to a dried product that has been dried to the target moisture content. Therefore, the bulk density value of this dried product D is the same as the bulk density value of the dried product R immediately before being discharged from the discharge port 312. By multiplying the bulk density value by the previously determined retained volume value, the retained mass of the dried product R that has been dried to the target moisture content within the main body shell 31 can be determined.

[0091] Furthermore, it is also possible to directly measure the retained mass of the dried material R by placing a load cell capable of measuring the total mass of the dryer 30, pre-measuring the mass of the tare bag of the dryer 30 itself, and subtracting this tare bag mass from the total mass of the dryer 30.

[0092] Furthermore, the drying material R is removed from the main shell 31, and its bulk density is measured using a bulk density measuring device (not shown) with the same configuration as the bulk density measuring device 40. The moisture content of the drying material R is also measured. By multiplying the bulk density value of the drying material R measured here by the previously determined retained volume value, the retained mass of the drying material R can be determined. The bulk density value and the value representing the moisture content of the drying material R are also transmitted to the control unit 60 and stored.

[0093] Next, we will explain the aggregation (granulation) within the main shell 31 of the dryer 30 shown in Figure 3.

[0094] Sludge contains organic components (e.g., phosphate compounds) that function as binders for solid crosslinking. Liquid crosslinking can also occur due to the moisture content in the sludge. Therefore, agglomeration is likely to occur when drying sludge.

[0095] If agglomeration (granulation) occurs during the drying of the material R due to solid or liquid crosslinking, the contact area with the heating tube 323 decreases, reducing the drying efficiency. More specifically, agglomerates adhere to the heat transfer surface of the heating tube 323, directly reducing the heat transfer area, or the particle size of the material R increases, reducing its surface area, which in turn reduces the contact area with the heat transfer surface of the heating tube 323, thus reducing the drying efficiency. Furthermore, agglomeration hinders the rotation of rotary scraping members such as the angle 33, lifter 331, and feed vane 332. In other words, agglomerates get trapped between the inner circumferential wall of the main shell 31 and the rotary scraping members, creating resistance to rotation. As a result, the current flowing to the electric motor 317 increases.

[0096] <Relationship between the retained mass of the material being dried R and the current value> For example, by combining the various materials shown in Figure 2(a) and adjusting the amount fed into the dryer 30 shown in Figure 3, the retained mass was changed, and the current value flowing through the electric motor 317 for each retained mass was measured. No agglomeration occurred in the main body shell 31 during the measurement of the current value.

[0097] Figure 5(a) is a graph showing the relationship between the retained mass of the material to be dried R and the current flowing to the electric motor of the rotary scraping member.

[0098] As the retained mass (x') of the material being dried R increases, the current value (y') also increases, confirming that there is a proportional relationship between the retained mass of the material being dried R and the current value. The control unit 60 stores the equation "y'=cx'+d" which represents the graph shown in Figure 5(a).

[0099] Compared to the graph shown in Figure 5(a), the likelihood of aggregate formation is higher in the upper part of the graph and lower in the lower part.

[0100] As described above, the control unit 60 also stores the bulk density values ​​of the dried product D and the material to be dried R transmitted from the bulk density measuring device 40, and can determine the retained volume of the material to be dried R from the outlet gas temperature to obtain the retained mass of the material to be dried R. Alternatively, the retained mass of the material to be dried R can be directly measured with a load cell. In addition, the control unit 60 constantly monitors the current value flowing to the electric motor 317. In the following description, when representing the value at the time of measurement, PV (Present Value) will be appended to the end. The control unit 60 calculates the retained quality amount PV value (x') of the material to be dried R. PV ) and the design current reference value (y') when the retention quality amount PV value is determined. PV From this, using the equation "y'=cx'+d" which represents the graph shown in Figure 5(a), it is possible to determine whether the likelihood of agglutination is high, low, or somewhere in between (medium). In making this determination, if the value is above the first determination line, which is represented by a dotted line obtained by adding the value of n (where n is a positive number) to the value of d on the solid line graph shown in Figure 5(a), it is determined that the likelihood of agglutination is high. If the value is below the second determination line, which is represented by a dashed line obtained by subtracting the value of n (where n is a positive number) from the value of d on the solid line graph, it is determined that the likelihood of agglutination is low. If the value is between the first and second determination lines, it is determined to be the medium level as described above.

[0101] <About fiber content> Furthermore, sludge also contains fiber, which is a type of organic matter.

[0102] Figure 6 shows magnified images of dried sludge with low fiber content and dried sludge with high fiber content, observed under a microscope.

[0103] This dried sludge is produced by determining the ratio of raw sludge to excess sludge during the dewatering process at a sewage treatment plant, mixing it with concentrated sludge, and then drying it. The photo on the left is a magnified view of dried sludge with low fiber content, where raw sludge (primerized sludge) accounts for 20-40% and the remainder is excess sludge. The photo on the right is a magnified view of dried sludge with high fiber content, where raw sludge (primerized sludge) accounts for 50-70% and the remainder is excess sludge. The distance between the vertical lines shown in each magnified photo is 50 μm.

[0104] Comparing the magnified images on the left and right, a difference in porosity is observed depending on the amount of fiber. In the magnified image on the left, because there is little fiber, the fiber is covered by non-fiber particles P. These non-fiber particles P contain binder components, and during the drying process, the fiber is compressed, forming solid crosslinks with the non-fiber particles P. As a result, the porosity of the fiber is lost. On the other hand, in the magnified image on the right, there is a lot of fiber F, and the opposite is true. That is, the fiber is present in a way that prevents the aggregation of non-fiber particles, making aggregation of non-fiber particles less likely, and thus maintaining the porosity of the fiber. Thus, since the porosity of the dried sludge product changes depending on the amount of fiber, the porosity of the dried material R remaining in the main shell 31 also changes depending on the amount of fiber. In other words, if there is little fiber, the porosity of the dried material R remaining in the main shell 31 will be low, and the bulk density (apparent density) will be high. Conversely, if the fibrous content is high, the porosity of the material R being dried within the main shell 31 increases, and the bulk density (apparent density) decreases. Therefore, if the bulk density of the material R being dried to the target moisture content is obtained, the amount of fibrous content in the material R can be estimated.

[0105] <Relationship between bulk density and the likelihood of aggregate formation> For example, using various materials shown in Fig. 2(a), sludge samples with different mixing ratios of raw sludge (primary sedimentation sludge) with a high fiber content and excess sludge with a low fiber content, and sludge samples of only excess sludge were prepared, dried in the dryer 30 shown in Fig. 3, and it was confirmed whether aggregates were generated. Also, for the dried products of each sludge sample, the bulk density value of the dried product D was obtained with the bulk density measuring device 40 shown in Fig. 3. Further, the material to be dried R during drying was taken out from inside the main body shell 31, and the bulk density value of the material to be dried R was also obtained with a bulk density measuring device having the same configuration as the bulk density measuring device 40 shown in Fig. 3.

[0106] Fig. 5(b) is a table summarizing the relationship trend between the bulk density and the possibility of aggregate generation.

[0107] When the bulk density is 450 kg / m 3 or less, the possibility of aggregate generation is low. When the bulk density is 650 kg / m 3 or more, the possibility of aggregate generation tends to be high. Also, when the bulk density is higher than 450 kg / m 3 and less than 650 kg / m 3 in some cases aggregates may occur and in some cases they may not occur, and the possibility of aggregate generation is moderate.

[0108] Also, from the trend shown in Fig. 5(b), when the bulk density is 450 kg / m 3 or less, the amount of fiber in the sludge is large and the possibility of aggregate generation is low. When the bulk density is 650 kg / m 3 or more, the amount of fiber in the sludge is small and the possibility of aggregate generation is high. When the bulk density is higher than 450 kg / m 3 and less than 650 kg / m 3If the value is less than 100Wt%-DS, the amount of fiber in the sludge is moderate, and the possibility of agglomeration is also moderate. The inventors continued testing and found that when the total solid content of the sludge to be dried is set to 100Wt%-DS, the solid content of the fiber is preferably in the range of 20%Wt%-DS to 35Wt%-DS. If the value is less than 20Wt%-DS, there is insufficient fiber, and the possibility of solid agglomeration arises. On the other hand, if the fiber content exceeds 35Wt%-DS, the possibility of solid agglomeration is considerably reduced, but the fibers connect with each other, resulting in a bulky state with many spaces (a fluffy state), which reduces the contact area with the heat transfer medium such as the heating tube 323, and thus the drying efficiency decreases. In other words, a high porosity of fiber reduces the bulk density, increasing the amount of material to be dried R remaining on the outer periphery of the heat transfer section, and reducing the amount that falls into the inside of the heat transfer section, thus lowering the contact efficiency and, as a result, the drying efficiency decreases. Furthermore, an increase in porosity makes the material too light, causing it to fly up during scraping, which impairs contact with the heating tube 323 and reduces drying efficiency. In the case of hot air drying, the material may also be blown up by the hot air. Moreover, an increase in porosity leads to a larger volume, which reduces the residence time in the drying space of the main body shell 31, among other problems.

[0109] <Relationship between moisture content and the likelihood of aggregate formation> For example, using the various materials shown in Figure 2(a), several sludge samples with different amounts of water content were prepared and dried in the dryer 30 shown in Figure 3 to test whether or not aggregates were generated. In addition, the moisture content (%WB) of each dried sludge sample was determined using the discharge-side moisture meter 52 installed in the dried product discharge equipment 50 shown in Figure 3. Furthermore, the material being dried R was extracted from the main shell 31 during the drying process, and the moisture content (%WB) of that material R was also determined using a moisture meter.

[0110] Figure 5(c) is a table summarizing the trend in the relationship between moisture content and the likelihood of aggregate formation due to liquid crosslinking.

[0111] When the moisture content was 15% WB or less, the likelihood of agglutination due to liquid crosslinking was low, while when the moisture content was 30% WB or more, the likelihood of agglutination due to liquid crosslinking tended to be high. Furthermore, when the moisture content was higher than 15% WB but less than 30% WB, agglutination due to liquid crosslinking may or may not occur, resulting in a moderate likelihood of agglutination.

[0112] The cause of liquid crosslinking is that the material being dried R inside the main shell 31 is generally excessively moist. By reducing the moisture content of the material being dried R inside the main shell 31, the liquid crosslinking of the material being dried R inside the main shell 31 weakens, and the aggregates collapse. Therefore, by measuring the moisture content, it is possible to determine whether or not liquid crosslinking is occurring. If it is determined that liquid crosslinking is occurring, the amount of sludge input should be reduced to lower the moisture content of the material being dried R inside the main shell 31.

[0113] <Hopper feeding control> The following explanation will focus on the input control of multiple types of hoppers 10.

[0114] In this control process, the relationship between the retained mass of the material to be dried R and the current flowing to the electric motor of the rotary scraping member, as explained using Figure 5(a), the relationship between bulk density and the likelihood of agglomeration, as explained using Figure 5(b), and the relationship between moisture and the likelihood of agglomeration, as explained using Figure 5(c), are all taken into consideration for a comprehensive determination.

[0115] Figure 7(a) is a table showing the combined results of the possibility of aggregate formation from moisture, the possibility of aggregate formation from current value, and the possibility of aggregate formation from bulk density.

[0116] The bulk density measuring device 40 shown in Figure 3 calculates the bulk density (apparent density) of the dried product D at predetermined intervals (in the following explanation, this interval will be set to 1 hour, but is not limited to 1 hour). The bulk density (apparent density) of the drying material R, which is partially dried and removed from the main shell 31, is also calculated at predetermined intervals (in the following explanation, this interval will be set to 1 hour, but is not limited to 1 hour). In addition, "high," "medium," and "low" data representing the possibility of agglutination from moisture, "high," "medium," and "low" data representing the possibility of agglutination from current values, and "high," "medium," and "low" data representing the possibility of agglutination from bulk density are updated, and the control unit 60 makes a decision in the input control based on the updated data.

[0117] If the likelihood of agglutination from moisture is "high" (No. 1-9), liquid crosslinking should be suspected. As mentioned above, the cause of liquid crosslinking is excessive moisture in the material being dried, and this can be resolved by reducing the amount of sludge added to remove moisture from the material being dried. Therefore, if the likelihood of agglutination from moisture is "high", the amount of sludge added should be reduced. The reduction in the amount of sludge added should be 0.7 times the standard amount (e.g., 1000 kg / h) if the reduction is significant (No. 1-4), 0.8 times if the reduction is moderate (No. 5-6), and 0.9 times if the reduction is slight (No. 7-9). If the likelihood of agglutination from moisture is moderate, the amount of sludge added should remain at the standard amount.

[0118] On the other hand, if the likelihood of aggregate formation from moisture is "low" (No. 19-27), the amount of sludge added will be increased to further improve drying efficiency. The increase in the amount of sludge added will be 1.3 times the amount of the "standard" amount if it is a large increase (No. 19-22), 1.2 times if it is a moderate increase (No. 23-25), and 1.1 times if it is a small increase (No. 26-27).

[0119] Since all of the various types of hoppers 10 use a screw conveyor system for loading, the rotation speed of the screw is changed. Specifically, the control unit 60 slows down the rotation speed of the screw when decreasing the loading amount and speeds up the rotation speed of the screw when increasing the loading amount. Alternatively, the rotation speed of the screw can be kept constant, and the loading amount can be increased or decreased by changing the length of the rotation time and the stopping time. If a belt conveyor system is used instead of a screw conveyor system, the loading amount can be increased or decreased by changing the transport speed or the length of the transport time and stopping time. In addition to speed control and time control of screw conveyors and belt conveyors, mass control may also be performed using a weighing conveyor with a weighing unit installed on the conveyor.

[0120] In addition, in the cases of input patterns 2, 3, and 4, the amount of material fed from the first hopper 11, second hopper 12, and third hopper 13 to the mixer 20 may be kept constant, while the amount of mixed sludge and sludge with added fiber fed from the mixer 20 to the dryer 30 may be increased or decreased.

[0121] If the probability of agglutination based on the current value is "high," then the formation of solid crosslinking is suspected. Similarly, if the probability of agglutination based on bulk density is "high," then the formation of solid crosslinking is also suspected. If the formation of liquid crosslinking is not suspected (the probability of agglutination from moisture is "medium" or "low"), and the formation of solid crosslinking is suspected, then the solid concentration of fibrous material in the sludge being dried may be increased. In other words, the ratio of fibrous material added may be increased from the "standard" ratio (No. 10-13, 19-22). By doing so, the solid concentration of organic material (e.g., phosphate compounds) that functions as a binder for solid crosslinking in the sludge decreases. In addition, as the ratio of fibrous material increases, the aggregation of particles other than fibrous material is inhibited. As a result, particles other than fibrous material become less likely to aggregate. Furthermore, if the probability of agglomeration based on the current value is "low," but the probability of agglomeration based on bulk density is "high" (No. 16, 25), the fiber content input ratio remains at the "standard" ratio.

[0122] The input patterns that allow for changing (increasing or decreasing) the fiber content input ratio are limited to input pattern 2 (single dotted line), input pattern 3 (double dotted line), and input pattern 4 (dotted line), as shown in Figure 1. When sludge is being input using input pattern 2 (single dotted line), the control unit 60 increases the input amount to the first hopper 11, which contains sludge with a relatively high fiber content (sludge 1 and sludge 4 shown in Figure 2(a)), based on the increase rate and fiber content change described later. If the total input amount remains at the "standard" input amount, the control unit 60 decreases the input amount to the second hopper 12, which contains sludge with a relatively low fiber content (sludge 2 and sludge 3 shown in Figure 2(a)), by the amount by which the input amount to the first hopper 11 has been increased. Furthermore, when sludge is being input using input pattern 3 (double dotted line), the control unit 60 increases the input amount to the fourth hopper 14, which contains fiber content instead of sludge, based on the increase rate and fiber content change described later. If the total input volume remains at the "standard" input volume, the input volume to the second hopper 12, which contains sludge with a relatively low fiber content, is reduced by the amount by which the input volume to the fourth hopper 14 is increased. Furthermore, even when sludge is being input according to the dotted input pattern 4, the control unit 60 increases the input volume to the fourth hopper 14, which contains fiber, based on the increase rate and fiber content change described later. If the total input volume remains at the "standard" input volume, the input volume to the third hopper 13, which contains sludge with an intermediate fiber content, is reduced by the amount by which the input volume to the fourth hopper 14 is increased.

[0123] On the other hand, if the possibility of agglomeration based on the current value is "low," or if the possibility of agglomeration based on bulk density is "low," there may be too much fiber. If there is too much fiber, the high porosity of the fiber reduces the bulk density, increasing the amount of material to be dried R that remains on the outer periphery of the heat transfer section. This reduces the amount that falls into the heat transfer section, lowering the contact efficiency and consequently reducing the drying efficiency. In addition, the increased porosity makes the material too light, causing it to be blown around during scraping, which also impairs contact with the heating tube 323 and reduces the drying efficiency. Furthermore, the increased porosity increases the volume, leading to problems such as a reduced residence time within the main shell 31. For these reasons, the solid concentration of fiber in the sludge to be dried may be reduced. In other words, the fiber input ratio may be reduced from the "standard" ratio. In this case, the possibility of agglomeration from moisture is "medium" or "low," and both the possibility of agglomeration from current value and the possibility of agglomeration from bulk density are "low" (No. 18, 27), and the possibility of agglomeration from moisture is "low," the possibility of agglomeration from current value is "low," and the possibility of agglomeration from bulk density is "medium" (No. 26). When sludge is being fed in the input pattern 2 shown by the dashed dot line, the control unit 60 reduces the amount of sludge fed into the first hopper 11, which contains sludge with a relatively high fiber content, based on the reduction rate and fiber content change described later. If the total amount of sludge fed remains at the "standard" amount, the control unit 60 increases the amount of sludge fed into the second hopper 12, which contains sludge with a relatively low fiber content, by the amount by which the amount of sludge fed into the first hopper 11 has been reduced. Furthermore, when sludge is being fed according to feeding pattern 3 indicated by the dashed dots, the control unit 60 reduces the amount of sludge fed into the fourth hopper 14 containing fiber based on the reduction rate and fiber content change described later. If the total amount of sludge fed remains at the "standard" amount, the control unit 60 increases the amount of sludge fed into the second hopper 12, which contains sludge with relatively less fiber, by the amount by which the amount of sludge fed into the fourth hopper 14 has been reduced.Furthermore, even when sludge is being fed according to the dotted line feeding pattern 4, the control unit 60 reduces the amount of sludge fed into the fourth hopper 14 containing fiber based on the reduction rate and fiber content change described later. If the total amount of sludge fed remains at the "standard" amount, the control unit 60 increases the amount of sludge fed into the third hopper 13, which contains sludge with an intermediate fiber content, by the amount by which the amount of sludge fed into the fourth hopper 14 has been reduced.

[0124] The above explanation assumes that the total input amount remains at the "standard" amount, but there are also cases where the total input amount is increased or decreased. The total input amount is decreased when liquid crosslinking is suspected in addition to solid crosslinking. In other words, it corresponds to a case where the possibility of agglomeration from moisture is "high". On the other hand, the total input amount is increased when the drying efficiency is further improved. In other words, it corresponds to a case where the possibility of agglomeration from moisture is "low". When the total input amount is increased or decreased, the input ratio of fiber will be increased or decreased based on the total input amount after the increase or decrease.

[0125] The control unit 60 outputs an input rate change signal to the target hopper, instructing it to change the input rate of fiber. The input rate of the target hopper at the start of input is used as the reference rate.

[0126] Figure 7(b) is a table showing an example of timer control for gradually increasing the fiber input ratio.

[0127] The rate at which the input ratio of the target hopper is increased is fixed, and in the initial stage, the rate is 1.05 times. Therefore, the input ratio is increased to 1.05 times the "standard" ratio. As described above, the bulk density value of the dried product D or the material to be dried R is calculated every hour, and every hour, data on the possibility of three types of aggregate formation (moisture content, current value, bulk density) is updated, and the control unit 60 performs a reassessment of the input control based on the updated data. This reassessment is based on the result of inputting for one hour at an input ratio increased to 1.05 times the "standard" ratio. If, as a result of the reassessment, the updated data also indicates that the input ratio of fiber should be increased (No. 10-13, 19-22), the control unit 60 increases the input ratio to 1.1 times the "standard" ratio. The rate of increase increases by 0.05 every hour until a predetermined upper limit is reached.

[0128] Figure 7(c) is a table showing an example of timer control that gradually reduces the fiber content.

[0129] The rate at which the input ratio of the target hopper is reduced (reduction rate) is also fixed uniformly, and in the initial stage, the reduction rate is 0.95 times. Therefore, the input ratio is reduced to 0.95 times the "standard" ratio, and input is performed for one hour. Here again, every hour, a reassessment is performed with the updated data, and if the reassessment results in a case where the input ratio of fiber is reduced even with the updated data (No. 18, 26-27), the control unit 60 reduces the input ratio to 0.9 times the "standard" ratio. The reduction rate decreases by 0.05 every hour until it reaches a predetermined lower limit.

[0130] The input control based on the possibility of agglomeration has been explained using Figure 7 above, but it is also possible to control the input based on changes in moisture content, electric motor 317 current value, and bulk density value. For example, if the moisture content increases, the electric motor 317 current value also increases, and the bulk density value also increases, it is determined that liquid crosslinking has occurred, and the amount of sludge input is reduced. If the moisture content is constant or decreasing, the electric motor 317 current value increases, and the bulk density value also increases, it is determined that solid crosslinking has occurred, and the fiber input ratio is increased. If the moisture content increases, the electric motor 317 current value is constant, and the bulk density value increases, it is determined that liquid crosslinking has occurred, and the amount of sludge input is reduced. If the moisture content is constant, the electric motor 317 current value decreases, and the bulk density value also decreases, the fiber input ratio is reduced.

[0131] Furthermore, while the above explanation described a control example combining data on three possible causes of agglomeration, it is also possible to perform control using only two types of data: the possibility of agglomeration from moisture and the possibility of agglomeration from current values. In this control case, the occurrence of liquid crosslinking is determined based on the possibility of agglomeration from moisture, and the occurrence of solid crosslinking is determined based on the possibility of agglomeration from current values. That is, if the possibility of agglomeration from moisture is "high" (No. 1-9), the amount of sludge input is reduced, and if the possibility is "low" (No. 19-27), the amount of sludge input is increased. Furthermore, if the probability of agglutination from moisture is "medium" or "low" and the probability of agglutination from current value is "high" (Nos. 10-12, 19-21), the fiber input ratio is increased at the rate shown in Figure 7(b). If the probability of agglutination from moisture is "medium" or "low" and the probability of agglutination from current value is "low" (Nos. 16-18, 25-27), the fiber input ratio is decreased at the rate shown in Figure 7(c). Alternatively, control may be performed by combining data on only two types of probabilities: the probability of agglutination from moisture and the probability of agglutination from bulk density. In this control, the occurrence of liquid crosslinking is determined based on the probability of agglutination from moisture, and the occurrence of solid crosslinking is determined based on the probability of agglutination from current value. That is, if the probability of agglutination from moisture is "high" (Nos. 1-9), the amount of sludge input is reduced, and if the probability is "low" (Nos. 19-27), the amount of sludge input is increased. Furthermore, if the possibility of agglutination from moisture is "medium" or "low" and the possibility of agglutination from bulk density is "high" (No. 10, 13, 16, 19, 22, 25), the fiber content is increased at the rate shown in Figure 7(b). If the possibility of agglutination from moisture is "medium" or "low" and the possibility of agglutination from bulk density is "low" (No. 12, 15, 18, 21, 14, 27), the fiber content is decreased at the rate shown in Figure 7(c).

[0132] Furthermore, in controlling the fiber input ratio, proportional control may be used instead of the timer control explained using Figures 7(b) and 7(c).

[0133] Figure 8(a) is a table showing the relationship between the change in current value and the fiber component coefficient A.

[0134] The current value (y') in the equation "y'=cx'+d" representing the graph shown in Figure 5(a) is used as the reference value, and at this reference value, the change in current value is "0". The change in current value is the current value (y') at the time of measurement relative to this reference value. PV This represents the change in the current value. As shown in Figure 8(a), the fiber content coefficient A is associated with the change in current value within a range from a lower limit of 0.5 to an upper limit of 1.5. When the change in current increases, the fiber content coefficient A becomes a higher value, and when the change in current decreases, the fiber content coefficient A becomes a lower value; the change in current and the fiber content coefficient A are proportional. If the fiber content coefficient A is higher than 1, it means that the fiber content input ratio will be increased from the "reference" ratio, and the higher the fiber content coefficient A, the higher the fiber content input ratio. Conversely, if the fiber content coefficient A is lower than 1, it means that the fiber content input ratio will be decreased from the "reference" ratio, and the lower the fiber content coefficient A, the lower the fiber content input ratio. The control unit 60 constantly monitors the current value flowing through the electric motor shown in Figure 1, so it can constantly grasp changes in the current value and update the fiber content coefficient A at all times.

[0135] Figure 8(b) is a table showing the relationship between the change in bulk density and the fiber content coefficient B.

[0136] The table in Figure 8(b) uses the bulk density values ​​shown in Figure 5(b). Among the bulk density values, "550," which represents a moderate amount of fiber in the sludge, is used as the baseline value, and at this baseline value, the change in bulk density is "0." The change in bulk density is the change in the measured bulk density value measured by the bulk density measuring device 40 relative to this baseline value. As shown in Figure 8(b), the change in bulk density is associated with a fiber content coefficient B within the range of a lower limit of 0.5 to an upper limit of 1.5. When the change in bulk density increases, the fiber content coefficient B becomes a high value, and when the change in bulk density decreases, the fiber content coefficient B becomes a low value; therefore, there is a proportional relationship between the change in bulk density and the fiber content coefficient B. If the fiber content coefficient B is higher than 1, it means that the fiber content input ratio will be increased from the "baseline" ratio, and the higher the fiber content coefficient B, the higher the fiber content input ratio. Conversely, if the fiber content coefficient B is lower than 1, it means that the fiber content input ratio will be reduced from the "standard" ratio, and the lower the fiber content coefficient B, the lower the fiber content input ratio. The fiber content coefficient B can be updated every hour because the bulk density measuring device 40 outputs the measured value every hour.

[0137] Figure 8(c) is a table showing the relationship between the values ​​obtained by multiplying fiber content coefficients A and B and the amount of change in fiber content.

[0138] To change the fiber content ratio in response to both changes in current value and bulk density, we multiply the fiber content coefficient A, which corresponds to the change in current value, by the fiber content coefficient B, which corresponds to the change in bulk density. The lower limit of fiber content coefficient A is 0.5, and the lower limit of fiber content coefficient B is also 0.5, so the lower limit of the product of the two is 0.25. On the other hand, the upper limit of fiber content coefficient A is 1.5, and the upper limit of fiber content coefficient B is also 1.5, so the upper limit of the product of the two is 2.25. The amount of fiber content change is allocated to the value obtained by multiplying fiber content coefficient A and fiber content coefficient B, between the lower limit of 0.25 and the upper limit of 2.25. The value obtained by multiplying fiber content coefficient A and fiber content coefficient B and the amount of fiber content change are proportional.

[0139] The control unit 60 increases or decreases the fiber input ratio based on the fiber content change. As described above, the fiber content coefficient A can be updated at any time, so the fiber content change amount also changes continuously in accordance with the continuous change in fiber content coefficient A, and the control of the fiber input ratio becomes a continuous linear control. Note that since the fiber content coefficient B is updated every hour, the fiber content change amount may also be calculated every hour.

[0140] Furthermore, while the fiber content ratio is changed here in response to both changes in current value and changes in bulk density, it is also possible to change the fiber content ratio in response only to changes in current value, or in response only to changes in bulk density. In other words, the fiber content ratio may be increased or decreased based solely on fiber content coefficient A, or it may be increased or decreased based solely on fiber content coefficient B.

[0141] <Drying method> Figure 9 is a flowchart of the drying method implemented in the drying system shown in Figure 1.

[0142] In the drying system shown in Figure 1, the sludge receiving process in step S1 accepts multiple types of sludge with different properties. Here, six types of sludge with different properties, as shown in Figure 2(a), are accepted.

[0143] In the sludge supply process of step S2, the sludge received in step S1 is supplied to separate sludge hoppers according to its properties. That is, when multiple types of sludge are received, the received sludge is supplied to the first hopper 11 to the third hopper 13 according to its fiber content (wt%-DS), based on data from the facility where the received sludge was generated, past performance, or analysis results at the time of receipt. Sludge 1 and sludge 4 shown in Figure 2(a) are supplied to the first hopper 11, which contains sludge with a relatively high fiber content; sludge 2 and sludge 3 are supplied to the second hopper 12, which contains sludge with a relatively low fiber content; and sludge 5 and sludge 6 are supplied to the third hopper 13, which contains sludge with an intermediate fiber content.

[0144] In the mixing process of step S3, one of the multiple input patterns shown in Figure 2(b) is used to input the material into the mixer 20, where the material is mixed. Specifically, sludge with a relatively high fiber content is input into the mixer 20 from the first hopper 11, and sludge with a relatively low fiber content is input into the second hopper 12 (input pattern 2), and the two types of sludge are mixed in the mixer 20. Alternatively, sludge with a relatively low fiber content is input into the mixer 20 from the second hopper 12, and fiber is input from the fourth hopper 14 (input pattern 3), and the sludge and fiber are mixed in the mixer 20. Or, sludge with an intermediate fiber content is input into the mixer 20 from the third hopper 13, and fiber is input from the fourth hopper 14 (input pattern 4), and the sludge and fiber are mixed in the mixer 20.

[0145] In step S4, the input process, the mixture mixed in the mixer 20 is fed into the dryer 30. The mixer 20 may be equipped with a cushion hopper on the discharge side, and the amount fed into the dryer 30 may be adjusted using the cushion hopper. Alternatively, sludge with a relatively high fiber content may be directly fed into the dryer 30 from the first hopper 11 (input pattern 1), or sludge with an intermediate fiber content may be directly fed into the dryer 30 from the third hopper 13 (input pattern 5). The material is fed into the dryer 30 through the input port 311, and the material to be dried R (sludge) remains inside the main shell 31.

[0146] In the drying process of step S5, the material to be dried R, which has been placed in the dryer 30, is dried. That is, as the material to be dried R is conveyed toward the discharge port 312 while being agitated within the main shell 31, the material to be dried R comes into contact with the heating tube 323, etc., and its moisture content decreases. While this drying process is being carried out, the control unit 60 constantly monitors the current value of the electric motor 317 that agitates the material to be dried R within the main shell 31.

[0147] Furthermore, the drying material R is removed from the main shell 31 during the drying process, its bulk density is determined using a bulk density measuring device, and its moisture content is measured using a moisture meter. The bulk density and moisture values ​​of the drying material R are transmitted to the control unit 60. After moisture measurement is complete, the drying material R is brought to the discharge conveyor 51.

[0148] In the transport process of step S6, the dried product D discharged from the dryer 30 is transported to the next process. Specifically, the dried product D discharged from the discharge port 312 of the main shell 31 is discharged from the dryer 30 through the chute 3122 and first sent to the bulk density measuring device 40. In the bulk density measuring device 40, once every hour, the dried product D is placed in the sampling container 41, the bulk density (apparent density) of the dried product D is calculated, and the calculated bulk density value is transmitted to the control unit 60. The dried product D for which the bulk density has been calculated is discharged from the sampling container 41 to the discharge-side conveyor 51. If the bulk density cannot be measured, the dried product D passes through the sampling container 41 and is discharged to the discharge-side conveyor 51.

[0149] The dried product D, discharged onto the discharge conveyor 51, is transported to the next process by the discharge conveyor 51. During this transport, the moisture content of the dried product D is calculated by the discharge moisture meter 52, and the calculated moisture value is transmitted to the control unit 60.

[0150] Of the steps S1 to S6 described above, at least steps S3 to S6 are carried out continuously. As a result, the mixing process (step S3) and the conveying process (step S6) are carried out simultaneously. While the mixing process (step S3) and the conveying process (step S6) are carried out simultaneously, the control unit 60 controls the amount of sludge input as described above, and the control in the control unit 60 is reflected in the mixing process (step S3) and the input process (step S4). That is, based on the possibility of agglomeration determined from the value representing the moisture content of the dried product D or the material to be dried R calculated in the conveying process (step S6), either the input amount from each hopper (first hopper 11 to fourth hopper 14) in the mixing process (step S3) or the amount of the mixture mixed in the mixing process (step S3) to be input into the drying process (step S5) is adjusted. Note that both input amounts may be adjusted. Furthermore, the control unit 60 controls the fiber content input ratio as described above while the mixing process (step S3) to the conveying process (step S6) are being carried out simultaneously, and the control in the control unit 60 is reflected in the mixing process (step S3). Specifically, the fiber content input ratio in the mixing process (step S3) is adjusted based on the possibility of agglomeration or fiber content coefficient A, which is determined from the current value flowing to the electric motor during stirring in the drying process (step S5), and the possibility of agglomeration or fiber content coefficient B, which is determined from the bulk density of the dried product D or the material to be dried R.

[0151] According to the drying system 1 and drying method of this embodiment, by ensuring that a certain amount or more of fiber is present in the material to be dried R (sludge), the occurrence of agglomeration during drying can be suppressed by the size of the porosity of the fiber. Furthermore, by changing the mixing ratio in the preceding process (mixing process) based on the operating data of the dryer during operation, the amount of fiber in the material to be dried R can be kept within a certain range, and the porosity during drying will also be within a certain range. As a result, the bulk density will also be within a certain range, so the volume fluctuation of the material to be dried R will be small, and the residence time will also be within a certain range, enabling stable operation of the dryer 30. Moreover, by suppressing the occurrence of agglomeration, which is a factor that significantly changes the capacity of the dryer 30 in sewage sludge treatment, the change in drying efficiency (contact efficiency of the material to be dried R to the heating pipe 323) will be small, enabling stable treatment during drying. In addition, the time during which the dryer 30 is stopped due to agglomeration will be reduced, and the loss due to the reduction in processing volume will be reduced. Furthermore, manual operation by the operator due to material fluctuations will also be reduced.

[0152] The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the claims. For example, in the embodiments described above, the mixer 20 and the dryer 30 were separate devices, but the mixer 20 may be omitted, and mixing may be performed using the stirring function of the dryer 30, and drying may be performed without re-adding the mixture after mixing. In other words, a mixer and dryer may be used.

[0153] Furthermore, as shown in Figure 2(a), sludge 1 is sludge with relatively low moisture content, and sludge 2 is sludge with relatively high moisture content. The hoppers may be separated based solely on the moisture content of the sludge, or they may be separated by considering both moisture content and fiber content. Alternatively, the hoppers may be separated by the type of sludge, such as mixed raw sludge, excess sludge, raw sludge (monosettled sludge), and digested sludge.

[0154] Furthermore, the multiple hoppers 10 may include hoppers specifically for storing organic components other than fiber components, or hoppers specifically for storing inorganic components.

[0155] Furthermore, although bulk density and moisture content were determined for both the dried product D and the product being dried R, a correlation was observed between the bulk density of the dried product D and the bulk density of the product being dried R, and a correlation was also observed between the moisture content of the dried product D and the moisture content of the product being dried R. Therefore, it would suffice to determine only one of them. [Explanation of Symbols]

[0156] 1. Drying System 10 Multiple hoppers 11. Hoppers No. 1 12. Hoppers No. 2 13. Third Hopper 14. Hoppers No. 4 20 Mixer 30 Dryer 31 Main shell 311 Inlet 312 Outlet 317 Electric motor 32 Multi-tube heating tube 323 Heating tube 40. Bulk density measuring device 50 Dry product discharge equipment 52 Moisture meter 60 Control Unit R Material to be dried D Dry product

Claims

1. A drying system that accepts multiple types of sludge with different properties and dries the sludge, Multiple hoppers, A mixer for mixing the input materials introduced from the aforementioned multiple hoppers, The system includes a dryer for drying the mixture mixed in the aforementioned mixer, The drying system is characterized in that the aforementioned plurality of hoppers include a plurality of sludge hoppers distinguished according to the properties of the received sludge, and a fiber hopper for adding fiber.

2. The drying system according to claim 1, characterized in that the dryer dries the mixture mixed in the mixer, as well as the sludge introduced from one of the plurality of sludge hoppers.

3. The aforementioned dryer is of the conduction heat transfer type and is equipped with an electric motor that serves as a driving source for agitating the material to be dried inside. The drying system according to claim 1 or 2, further comprising a control unit that controls at least one of the following based on a value representing the moisture content of the dried product or the object being dried in the dryer and the current value flowing through the electric motor: the input ratio of fiber to be fed into the mixer, the amount of sludge fed from the sludge hopper into the mixer, and the amount of mixture fed from the mixer into the dryer.

4. The aforementioned dryer is of the conductive heat transfer type, The drying system according to claim 1 or 2, further comprising a control unit that controls at least one of the following: the ratio of fiber to be fed into the mixer, the amount of sludge fed from the sludge hopper to the mixer, and the amount of mixture fed from the mixer to the dryer, based on a value representing the moisture content of the dried product or the object being dried in the dryer and a value representing the bulk density of the dried product or the object being dried.

5. A drying method for receiving multiple types of sludge with different properties and drying said sludge, A sludge supply process that supplies sludge to separate sludge hoppers according to the properties of the sludge received, A mixing step which involves either sludge mixing, in which sludge is introduced from multiple sludge hoppers and mixed with other sludge to obtain a mixture, or fiber addition mixing, in which sludge is introduced from one or more sludge hoppers and fiber is also introduced from a fiber hopper and mixed with the sludge to obtain a mixture; A drying method characterized by comprising a drying step of drying the mixture obtained in the mixing step.

6. The drying process is a process in which the material to be dried is dried by conductive heat transfer while being agitated by the driving force of an electric motor. The drying method according to claim 5, characterized in that, based on a value representing the moisture content of the dried product dried in the drying step or the object to be dried in the drying step, and the current value flowing to the electric motor during stirring in the drying step, at least one of the following is adjusted: the ratio of fiber added in the mixing step, the amount of sludge added from the sludge hopper in the mixing step, and the amount of the mixture mixed in the mixing step added to the drying step.

7. The drying process is a process of performing drying by conductive heat transfer, The drying method according to claim 5, characterized in that, based on a value representing the moisture content of the dried product or the object being dried in the drying process and a value representing the bulk density of the dried product or the object being dried, at least one of the following is adjusted: the ratio of fiber added in the mixing process, the amount of sludge added from the sludge hopper in the mixing process, and the amount of the mixture mixed in the mixing process added to the drying process.

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