Sludge drying system and sludge drying method

Abstract

The phosphorus in the sludge is thought to be the cause of the formation of hard granular material and adhesion inside the dryer during the drying process, but no measures were taken to suppress this effect. [Solution] The present invention is a sludge drying system or sludge drying method that solves the problem by receiving the sludge into corresponding storage tanks according to the phosphorus content in the sludge, leveling out the phosphorus content, and performing a drying treatment.

Description

Technical Field

[0001] The present invention relates to a sludge drying treatment system and a sludge drying treatment method containing a phosphorus component.

Background Art

[0002] Sludges generated by water treatment include various types such as raw sludge, mixed raw sludge, excess sludge, or digested sludge. After drying these to reduce the moisture content and obtaining a dried product, incineration treatment such as supplying this dried product to an incinerator for incineration is carried out at sludge treatment plants. In recent years, due to the advancement of water treatment, especially the phosphorus content in sewage treatment sludge is high and may become even higher in the future.

[0003] According to Non-Patent Document 1, it is shown that deposits considered to be caused by phosphorus in the sludge incineration process cause blockages in flues and the like, hindering the incineration treatment. Therefore, as a means to suppress adhesion, a method of adding an additive that reacts with phosphorus to form a high-melting-point compound to dehydrated sludge has also been shown. Excess sludge is shown in Non-Patent Document 2 to be sludge with a high phosphorus content, followed by digested sludge.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] Based on the inventor's experience in drying sludge at various locations, regarding the effects of phosphorus in the drying process, it was hypothesized that phosphorus is the cause of sludge adhesion to heat transfer surfaces and the formation of hard, granular dried material as the sludge granulates during the drying process. The adhesion that occurs on the heat transfer surface causes a decrease in drying capacity in conduction heat transfer dryers. In both conductive heat transfer dryers and hot air dryers, strong adhesion can occur, leading to increased workload and strain on the equipment's functions during the removal process. Large, hard dried particles can get stuck in narrow spaces inside a dryer, for example, increasing the load on rotating parts or agitators within the dryer. In incinerators, hard particles take longer to burn completely, or large particles impair fluidity, resulting in longer burning times. When such phenomena occur over a relatively short period, automatic control systems are often insufficient to cope, and operators may have to readjust operating conditions, such as interrupting drying or incineration operations. Furthermore, in the long term, this is likely to cause deterioration of parts and components in dryers and incinerators, wear on contact surfaces, or damage.

[0006] On the other hand, regarding sludge treatment plants, some treatment plants dry (and incinerate) only one type of sludge, but many treatment plants generate and treat multiple types of sludge, such as raw sludge, mixed raw sludge, excess sludge, or digested sludge. In such treatment plants, it is common practice to dry the sludge under uniform conditions regardless of the type of sludge. Furthermore, there are many sludge treatment plants that accept various types of sludge brought in from nearby locations (such as nearby businesses) and process them by drying. In such sludge treatment plants, it is common practice to process the sludge in the order in which it was received. The sludge received from various locations is generally dewatered using a dewatering machine, transported by truck or other means, and then received and stored in a storage tank. However, the sludge from each location is not necessarily of the same type. Therefore, the sludge stored in the tank accumulates in a sequential manner, resulting in a varied concentration distribution of phosphorus components within the tank.

[0007] Even within a single treatment plant where multiple types of sludge are generated, the drying process is not carried out by differentiating the physical properties of each type of sludge. In typical storage tanks, sludge is discharged from the bottom and sent to a drying process (dryer). Therefore, the sludge received in the storage tank is dried in order from the bottom of the tank upwards, and the drying operation conditions changed irregularly during the drying process depending on the type of sludge being sent (supplied to the dryer). In the midst of these changes, when excess sludge with a particularly high phosphorus content was supplied to the dryer, it would adhere to the inside of the dryer, reducing heat transfer efficiency and making it difficult to dry the sludge to the target moisture content. Alternatively, hard particles could form, increasing the load on the stirring device, and in severe cases, even forcing the stirring device to shut down. The inventors concluded that these operational problems were due to the phosphorus content.

[0008] In the incineration process, Non-Patent Document 1 indicates that the incinerated ash is analyzed, and the amount of additives added is adjusted according to the phosphorus content. This method requires time for analysis, and there is a significant time lag before the analysis results are reflected in the incineration process, making it not an effective way to add additives. Furthermore, because it is impossible to know what phosphorus content the sludge supplied to the incinerator has, there is the cumbersome task of frequently analyzing the phosphorus content in the incinerated ash.

[0009] The reason these problems arise is that, fundamentally, when drying multiple types of sludge, there is no concept of obtaining information (data) on the phosphorus content of the supplied sludge before drying or incineration and using that information for each treatment. More specifically, this is because there is no concept of classifying sludge according to its phosphorus content and then leveling out the phosphorus content before drying or incinerating it. The present invention aims to address these problems by providing a sludge drying system and a sludge drying method that can be used for drying treatment with a leveled phosphorus content, or for incineration treatment that follows the drying treatment. [Means for solving the problem]

[0010] In other words, the sludge drying treatment system described in claim 1 is characterized by receiving the sludge into a storage tank corresponding to the phosphorus content in the sludge.

[0011] Furthermore, the sludge drying treatment system described in claim 2 is characterized in that, in addition to the requirements described in claim 1, the sludge supplied from the storage tank to the drying treatment is a combination of sludge from a storage tank that stores sludge with a high phosphorus content and sludge from a storage tank that stores sludge with a low phosphorus content.

[0012] Furthermore, the sludge drying treatment system described in claim 3 is characterized in that, in addition to the requirements described in claim 2, information regarding the phosphorus content is used in the incineration treatment.

[0013] Furthermore, the sludge drying treatment system described in claim 4 is characterized in that, in addition to the requirements described in claim 3, an additive that forms a compound with phosphorus in the dried material during the incineration treatment is added to the dried material.

[0014] Furthermore, the sludge drying treatment method described in claim 5 is characterized by receiving the sludge into a storage tank corresponding to the phosphorus content in the sludge.

[0015] Further, the sludge drying treatment method according to claim 6, in addition to the requirements according to claim 5, is characterized in that the sludge supplied from the storage tank for the drying treatment is a combination of sludge from a storage tank storing sludge with a high phosphorus content and sludge from a storage tank storing sludge with a low phosphorus content.

[0016] Further, the sludge drying treatment method according to claim 7, in addition to the requirements according to claim 6, is characterized in that information regarding the phosphorus content is used in the incineration treatment.

[0017] Further, the sludge drying treatment method according to claim 8, in addition to the requirements according to claim 7, is characterized in that an additive that forms a compound with phosphorus in the dried product is added to the dried product in the incineration treatment. And the problems are solved by means of the configurations of the inventions described in each of these claims.

Effects of the Invention

[0018] According to the invention described in claim 1 or claim 5, it becomes possible to easily equalize the phosphorus content in the sludge during the drying treatment. As a result, the phosphorus content in the dried product after the drying treatment is also equalized.

[0019] Further, according to the invention described in claim 2 or claim 6, it becomes possible to easily equalize the phosphorus content and suppress the influence of sludge with a high phosphorus content on the drying treatment.

[0020] Further, according to the invention described in claim 3 or claim 7, information on the phosphorus content in the drying treatment is efficiently used in the incineration treatment after the drying treatment.

[0021] Further, according to the invention described in claim 4 or claim 8, it becomes possible to efficiently generate a high melting point compound of the additive and phosphorus in the incineration treatment after the drying treatment.

Brief Description of the Drawings

[0022] [Figure 1] This is a basic configuration diagram of the sludge drying treatment system of the present invention. [Modes for carrying out the invention]

[0023] The following describes in detail the sludge drying treatment system and sludge drying treatment method according to the present invention. [Examples]

[0024] Figure 1 is a basic configuration diagram of the sludge drying treatment system D in the present invention, showing the flow of receiving sludge into a storage tank through receiving treatment, drying the sludge, and incinerating the resulting dried material.

[0025] Regarding the relationship between sludge and storage tanks, if a sludge treatment plant accepts sludge generated at various locations in the vicinity (such as nearby businesses), it will accept the sludge into the appropriate storage tank (storage tank 1, storage tank 2, ..., storage tank n in Figure 1) according to the phosphorus content in the sludge. Even if a treatment plant does not accept sludge from other locations, it will accept various types of sludge generated within its own treatment plant into corresponding storage tanks according to the phosphorus content of the sludge. Providing storage tanks according to the phosphorus content of the sludge in this way is effective in leveling out the phosphorus content to suppress the effect of phosphorus in the subsequent sludge drying treatment.

[0026] Here, the phosphorus content refers to the phosphorus content per unit of dry weight of the sludge. Dry matter weight refers to the weight of a dry product, excluding the weight of water. For example, a phosphorus content of 1 wt%-ds means that the phosphorus content per unit dry weight (i.e., -ds) of the sludge is 1 wt%. The phosphorus content is analyzed before or after the sludge is received into each storage tank, and the analytical value (phosphorus content) is used in the drying process described later. These analytical values ​​are input into a PLC (Programmable Logic Controller), such as a PLC that controls drying or incineration processes, and are entered into the PLC by an operator or analyst. If sludge is being sent from various nearby locations, the analytical values ​​measured at those locations may be automatically input into the PLC via telecommunications lines or the like.

[0027] Furthermore, if the sludge is generated from the same water treatment method in various nearby locations, or if the water treatment method within the facility has not been changed, then it is generally the case that there will not be significant fluctuations in the phosphorus content over a short period of time, and analysis values ​​are not required each time the sludge is received. Furthermore, for long-term fluctuations such as seasonal variations, the moving average of the phosphorus analysis values ​​can be calculated using the time-series information (data) of the phosphorus analysis values ​​stored in the PLC, and this information (data) can also be used as supplementary data. In addition to the phosphorus analysis values, measurements of the sludge's moisture content and other information (data) are also input into the PLC and used as part of the sludge's information.

[0028] If numerous storage tanks are installed according to the phosphorus content, it becomes possible to improve the accuracy of equalizing the phosphorus content accordingly. However, it is also sufficient if each storage tank accepts sludge with a phosphorus content within a certain range. For example, sludge with a phosphorus content ranging from 4 wt% to over 3 wt% can be stored in storage tank 1 in Figure 1, while sludge with a phosphorus content ranging from 3 wt% to over 2 wt% can be stored in storage tank 2. The information on the phosphorus content (analytical value) of the sludge received into the storage tank can be used directly for the drying process. If sludge remains in the storage tank before acceptance, the average phosphorus content can be calculated from the weight, moisture content, and phosphorus content of the remaining sludge and the newly accepted sludge, and this calculated value can be used. Alternatively, for example, in the case of storage tank 1 mentioned above, a representative value of the phosphorus content of the sludge in storage tank 1 could be set to 3.5 wt%, and for storage tank 2, it could be set to 2.5 wt%, and these representative values ​​could be used. The phosphorus content information for each storage tank will be used in the drying process described later.

[0029] The sludge supplied from each storage tank to the dryer 2 is supplied by combining the sludge from the storage tank with a high phosphorus content and the sludge from the storage tank with a low phosphorus content along the transport path. For conveying, screw conveyors or the like are used, and it is preferable to equip the confluence with a sludge mixer, such as a paddle mixer. Any device capable of transporting sludge, such as a sludge pump, will suffice.

[0030] The sludge supplied from each storage tank to the dryer 2 is delivered quantitatively, for example, by adjusting the rotation speed of the screw dischargers located at the bottom of each storage tank. Furthermore, each storage tank is equipped with, for example, a load cell, and a signal regarding the total weight of the storage tank is input from the load cell to the PLC. The PLC then calculates the weight of the sludge inside the storage tank by subtracting the empty weight of the storage tank, which is pre-programmed into the PLC, from the total weight, and this value is stored in the PLC. As the sludge is discharged by the screw discharger and the total weight of the storage tank decreases, the supply rate of sludge supplied to the dryer 2 is calculated by the PLC based on the time required for discharge.

[0031] The moisture content of each sludge sample can be measured very quickly, even along the sludge's transport route, using, for example, an infrared moisture meter. The moisture content signal is input to the PLC, and the PLC calculates the dry weight (supply rate as dry weight) supplied to the dryer 2 from this moisture content and the sludge supply rate mentioned above. Since the phosphorus content of each storage tank, or a representative value of the above-mentioned content, is pre-entered into the PLC by the operator or others, the average phosphorus content of the supplied sludge is calculated by the PLC based on the ratio of this content to the dry weight of the sludge supplied from each storage tank to the dryer 2. For example, if the excess sludge supplied to dryer 2 has a supply rate of 1000 kg / h, a moisture content of 75% WB, and a phosphorus content of 3.5 wt%-ds, and the raw sludge has a supply rate of 1000 kg / h, a moisture content of 75% WB, and a phosphorus content of 1.5 wt%-ds, then the average phosphorus content of the sludge when these two types of sludge are combined and supplied to dryer 2 will be 2.5 wt%-ds. Since this content does not change even after drying, it also serves as information (data) on the phosphorus content of the dried product after drying. Furthermore, in order to equalize the phosphorus content in the sludge supplied for drying, it is not only necessary to supply two types of sludge as described above, but it is also acceptable to supply a combination of three or more types of sludge.

[0032] The impact of a high phosphorus content on the inside of dryer 2 is presumed to become apparent when the water in the sludge has evaporated and a certain degree of drying has progressed. Therefore, as sludge with a high phosphorus content and sludge with a low phosphorus content are mixed and dried in dryer 2, or if a sludge mixer is provided, its mixing action also contributes to suppressing the effect of sludge with a high phosphorus content in dryer 2. In addition, the operating conditions for the drying process, which correspond to the phosphorus content of the combined sludge, can be pre-programmed into the PLC. The PLC will then automatically adjust the operating conditions for the drying process according to the combination of sludge supplied to the dryer 2, enabling operation that either further suppresses the effects of phosphorus or increases drying capacity. If the combination of sludge with high phosphorus content and sludge with low phosphorus content changes, the amount of sludge supplied to dryer 2 will also need to be changed. Therefore, the operating conditions of the drying process, including those corresponding to the amount of sludge supplied, will also need to be changed.

[0033] The phosphorus content of the sludge at the stage supplied to dryer 2 can be determined by the operator through information provided by the PLC, i.e., displayed on a display installed on the control panel, and the operator can change the operating conditions of the drying process according to that content. The operator can also determine the weight of sludge stored in each storage tank based on information provided by the PLC, and input a desired sludge supply amount into the PLC. It is also possible for the operator to select a storage tank to which the sludge is supplied and to perform the drying process there. Based on the provided information, it is also possible to set an upper limit on the phosphorus content in the sludge supplied to the drying process by the operator in the PLC, and program the PLC to automatically adjust the supply of sludge from each storage tank to meet that upper limit.

[0034] Furthermore, depending on the conditions of the treatment plant, it is possible that a large amount of excess sludge with a high phosphorus content is stored, while only a small amount of sludge with a low phosphorus content is stored, or that no sludge other than excess sludge is stored at all. In this case, it is preferable to provide a storage tank for storing materials containing a large amount of fiber components, and to supply the materials containing a large amount of fiber components from this storage tank to the dryer 2 in combination with, for example, the surplus sludge mentioned above, which has a high phosphorus content. Materials containing a large amount of fiber do not necessarily have to contain sludge; other materials are also acceptable. This material preferably has a low phosphorus content, and even more preferably contains no phosphorus at all. Materials primarily composed of fibers include, for example, shredded waste paper. Other examples of waste materials besides recycled paper include agricultural waste such as rice bran and rice husks. By performing the drying process while the material contains a high amount of fiber, the effects of phosphorus are suppressed, making it less likely for the dried material to become hard granules, and thus reducing its adhesion to the inside of the dryer 2.

[0035] Dryer 2 may be either a hot air dryer that evaporates moisture using hot air, or a conduction heat transfer dryer that evaporates moisture using a heating medium. According to the present invention, the dried material discharged from the dryer 2 is standardized with minimal fluctuation in phosphorus content. This dried material is supplied to the incinerator 3 and becomes the material to be burned in the combustion region of the incinerator 3. The dried material discharged from dryer 2 is in the form of fine powder, granules, or granules.

[0036] As mentioned above, even if the phosphorus concentration of the incinerated material (dried material) is standardized, it is difficult to prevent flue blockage due to accumulated deposits from years of use during the incineration process. Therefore, Non-Patent Literature 1 indicates that in the incineration process, additives containing components such as iron and aluminum must be supplied to the incinerator 3 to prevent blockage of the flue and other parts by deposits thought to be caused by phosphorus. In this invention as well, the above-mentioned substance is added, which reacts with phosphorus to produce a high-melting-point compound. As mentioned above, the PLC stores information (data) on the phosphorus content during the drying process, so the required amount of the additive is calculated using this information in the PLC. Of course, information (data) on the phosphorus content can also be used to optimize the operating conditions of incinerator 3 during the incineration process. The additives may be in powder or liquid form. If a powder is to be used as an additive, a fine powder is preferable to improve uniformity during mixing.

[0037] One way to homogenize the required amount of additive with the dried material is to supply the additive to the incinerator 3 through a separate route, and then homogenize it within the incinerator 3 through the stirring function or fluidization action of the incinerator 3. In this method, since the dried material or its combustion product is mixed with the additives inside the incinerator 3, it is difficult to say that phosphorus and the additives will react with a high probability of contact to evenly produce high-melting-point compounds. Therefore, it may be necessary to supply an excessive amount of additives to increase the probability of contact. Alternatively, an additive can be added to the sludge stored in the storage tank, or to the sludge in the transport path supplied to the dryer 2, in an amount corresponding to the phosphorus content of each type of sludge. However, uniformly adding additives to sludge with high moisture and viscosity is not easy.

[0038] In light of these means, it is preferable that the additive be supplied to the dried material discharged from the dryer 2. It is more preferable to merge the conveying path for the dry material with the conveying path for the additive, and then homogenize them using a mixer after the merger. If the dried material is granular, it may be necessary to crush the dried material before feeding it into the mixer. As a result, the dried material and additives are supplied to the incinerator 3 in a homogenized state, making it easier for the phosphorus in the dried material to react with the additives, thus ensuring the reliable formation of high-melting-point compounds. The dried material mixed with additives can be supplied directly to the incinerator 3, but it may also be temporarily stored in a storage tank for incinerators and then supplied to the incinerator 3 from that tank.

[0039] When there is a large difference in specific gravity between the dry material and the additive, the dry material and the additive tend to separate inside the incinerator 3, especially in a fluidized bed type combustion furnace. Therefore, it is preferable that the above-mentioned mixer mixes the dry material and the additive while spraying water or binder liquid to form a granulated state before supplying it to the incinerator 3. Incinerator 3 may be of any type: fluidized bed, stoker, or fixed-bed with agitation.

[0040] From here, we will explain the drying process and the mixing of additives in relation to logistics. First, for example, if no new sludge is supplied to each storage tank during the drying process, the amount of sludge supplied from each storage tank to the dryer 2 is calculated by the PLC (Power Line Program) so that the sludge weight in each storage tank becomes zero at the end of the drying operation. This calculated value is then set as the supply amount from each storage tank. Based on this set value, the rotation speed of the motors of the screw dischargers for each storage tank is adjusted, for example, via an inverter. During this drying process, there will be no change in the phosphorus content of the dried material. This phosphorus content information (data) is used as information on the dried material obtained through the drying process to calculate the amount of additives needed for the subsequent incineration process.

[0041] Next, we will explain a case where, for example, sludge from storage tank 1 and storage tank 2 are supplied to the dryer 2, and new sludge is supplied to storage tank 1 at that time. The weight of the sludge in storage tank 1 immediately after new sludge is supplied is calculated by the PLC, and a new supply amount is set and supplied from storage tank 1 to dryer 2. At this time, the ratio of the amount of sludge supplied from storage tank 1 to the amount of sludge supplied from storage tank 2 changes, so the phosphorus content supplied to dryer 2 also changes. This change, or information (data) such as the phosphorus content and sludge supply amount after the change, is stored in the PLC and used for drying. As mentioned above, operating conditions corresponding to the amount of sludge and the phosphorus content are pre-set in the PLC, so it can also be used to change the operating conditions of dryer 2 in response to changes in the sludge conditions. This change also manifests in the dried material discharged from dryer 2 as a change in the discharge rate and phosphorus content of the dried material, appearing a certain time after the change in the sludge supply rate begins. Therefore, the amount of additives added to the dried product will also be changed after a certain period of time in response to this change.

[0042] The time it takes for sludge (or dried material) to travel from each storage tank to the dryer 2, where it is supplied, depends on the amount of sludge supplied to the dryer 2 and the related operating conditions of the dryer 2. This can be determined through design or trial operation. Therefore, the relationship between the transfer time corresponding to the amount of sludge supplied from each storage tank is determined in advance or during trial operation and entered into the PLC. For example, if the amount of sludge supplied from storage tank 1 changes, and the PLC stores information (data) indicating that it takes 1 hour for this change to appear in the dried material just before it is supplied to the mixer, then the amount of additives added will be changed 1 hour after operation with the new sludge supply setting begins. In other words, when the amount of sludge supplied from the storage tanks is changed, the set supply values ​​from each storage tank and the corresponding transfer time are changed, and then, as described above, the conditions for adding additives are changed. Similarly, the conditions for drying and incineration are also changed. Because the present invention reveals information (data) on the phosphorus content at the stage of supplying the sludge to the drying treatment, it can be said that this method involves significantly less time lag and effort compared to methods that analyze incinerated ash and reflect that analysis in the amount of additives added.

[0043] Regarding the transfer time, since sludge (or dried material) does not necessarily move by piston flow, when the amount of sludge supplied changes, if the change is in the direction of increasing the amount of additives added, or in the direction of increasing the phosphorus content, it is preferable to calculate the transfer time by multiplying the transfer time information (data) stored in the PLC by a coefficient of less than 1, and use this transfer time as the timing for changing the conditions. This coefficient is also a coefficient that is pre-set in the PLC. This makes it possible to avoid situations where, even if logistics do not involve piston flow, for example, there is a shortage of additives relative to the amount of phosphorus in the incinerator 3.

[0044] As described above, the present invention describes an example of incinerating dried material. However, before adding additives to the dried material, it is also possible to separate dried material with a phosphorus content within a predetermined range from the transport path from the dryer 2 to the incinerator 3, thereby utilizing the dried material as a soil conditioner or fertilizer. [Explanation of symbols]

[0045] D Sludge drying treatment system 1 storage tank 2 Dryer 3 Incinerator

Claims

1. A sludge drying treatment system that receives sludge into a storage tank corresponding to the phosphorus content of the sludge.

2. The sludge drying treatment system according to claim 1, characterized in that the sludge supplied from the storage tank to the drying treatment is a combination of sludge from a storage tank that stores sludge with a high phosphorus content and sludge from a storage tank that stores sludge with a low phosphorus content.

3. The sludge drying treatment system according to claim 2, characterized in that the information regarding the phosphorus content is used in the incineration treatment.

4. The sludge drying treatment system according to claim 3, characterized in that an additive that forms a compound with phosphorus in the dried material during the incineration treatment is added to the dried material.

5. A sludge drying method characterized by comprising: an receiving treatment in which the sludge is received into a storage tank corresponding to the phosphorus content in the sludge; and a drying treatment in which the sludge received in the receiving treatment is dried to obtain a dried product.

6. The sludge drying method according to claim 5, characterized in that the drying treatment is a treatment in which sludge obtained by combining sludge from a storage tank that stores sludge with a high phosphorus content and sludge from a storage tank that stores sludge with a low phosphorus content is dried.

7. The sludge drying treatment method according to claim 6, characterized in that it includes an incineration treatment in which the dried material obtained in the drying treatment is incinerated using information regarding the phosphorus content.

8. The sludge drying treatment method according to claim 7, characterized in that the incineration treatment is a treatment in which a dried material to which an additive that forms a compound with phosphorus is added is incinerated.

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