Fertilizing method of sewage sludge incinerated ash

Abstract

To provide a fertilizing method of waste sludge incinerated ashes, the method capable of obtaining a phosphorous-containing organic fertilizer material whose heavy metal concentrations are reduced as much as possible while maintaining a phosphorus concentration contained in the sewage sludge incinerated ashes.SOLUTION: A fertilizing method of waste sludge incinerated ashes includes: classifying the waste sludge incinerated ashes into three kinds of a fine particle group, a middle particle group and a coarse particle group using an elbow jet classifier; and reusing the classified middle particle and coarse particle group as the phosphorus-containing organic fertilizer material. A classification point between the fine particle group and the middle particle group in the classification is adjusted to 10 μm or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a method for converting sewage sludge incineration ash into fertilizer, and in particular to a method for classifying phosphorus-containing sewage sludge incineration ash and reusing a portion of the classified sewage sludge incineration ash as a raw material for phosphorus-containing fertilizer. [Background technology]

[0002] Patent Document 1 below discloses a method for reusing phosphorus-containing sewage sludge incineration ash, in which the sewage sludge incineration ash is classified into coarse powder and fine powder, and the coarse powder with a low phosphorus concentration is used as a cement raw material, while the fine powder with a high phosphorus concentration is used as a raw material for phosphorus recovery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-212579 Summary of the Invention [Problem to be solved by the invention]

[0004] When using phosphorus-containing sewage sludge incineration ash as a raw material for phosphorus-containing fertilizer, it is possible to use fine powder, which has a higher phosphorus concentration than coarse powder. However, the fine powder also contains high concentrations of heavy metals such as cadmium, arsenic, and lead. Because heavy metals are ingested by humans via plants, it is desirable to keep the concentration of heavy metals in the raw material for phosphorus-containing fertilizer as low as possible.

[0005] The present inventors have conducted extensive research and have discovered that when classifying wastewater into three types, namely, a fine particle group, a medium particle group, and a coarse particle group, using an elbow jet classifier, by changing the classification points of the fine particle group and the medium particle group, the phosphorus concentrations of the medium particle group and the coarse particle group before classification can be maintained while heavy metals are concentrated in the fine particle group, thereby lowering the heavy metal concentrations of the medium particle group and the coarse particle group.

[0006] The present disclosure has been made based on the above findings, and aims to provide a method for converting sewage sludge incineration ash into fertilizer, which can obtain a raw material for a phosphorus-containing fertilizer in which the concentration of heavy metals contained in the sewage sludge incineration ash is reduced as much as possible while maintaining the phosphorus concentration. [Means for solving the problem]

[0007] To solve the above problems, a first aspect of the present disclosure relates to a method for converting phosphorus-containing sewage sludge incineration ash into fertilizer. The method for converting sewage sludge incineration ash into fertilizer includes using an elbow jet classifier to classify the sewage sludge incineration ash into three particle groups: fine, medium, and coarse. The classified medium and coarse particles are reused as raw materials for a phosphorus-containing fertilizer, and the classification points for the fine and medium particle groups are adjusted to 10 μm or less. The lower limit of the classification point can be adjusted in consideration of the recovery rate, for example, to 5 μm.

[0008] The second aspect has the following characteristics in addition to the first aspect: When the sewage sludge incineration ash contains potassium and arsenic, the classification point is adjusted to be within the range of 7 μm to 9 μm. [Effects of the Invention]

[0009] According to the first aspect, by adjusting the classification point between the fine particle group and the medium particle group in classification using an elbow jet classifier to 10 μm or less, the phosphorus concentration of the classified medium particle group and the coarse particle group can be maintained at the phosphorus concentration of the sewage sludge incineration ash before classification. Furthermore, heavy metals are concentrated in the classified fine particle group, and as a result, the heavy metal concentrations of the medium particle group and the coarse particle group can be made as low as possible compared with the heavy metal concentration of the sewage sludge incineration ash before classification. Therefore, the classified medium particle group and the coarse particle group can be reused as valuable raw materials for phosphorus-containing fertilizer.

[0010] According to the second aspect, the potassium concentration of the raw material for a phosphorus-containing fertilizer can be made higher and the arsenic concentration can be made lower than those of sewage sludge incineration ash. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a diagram showing the flow of a method for converting sewage sludge incineration ash into fertilizer according to an embodiment. [Figure 2] 1 is a graph showing the relationship between the classification points of the fine particle group and the medium particle group and the element concentrations of each element in the classified medium particle group and the classified coarse particle group, respectively. [Figure 3] 1 is a graph showing the particle size distribution before classification and the particle size distribution of each of the fine particle group, medium particle group, and coarse particle group classified by adjusting the classification point to 10 μm. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments will be described with reference to the drawings. Common or corresponding elements in each drawing are designated by the same reference numerals, and descriptions thereof will be simplified or omitted. In each drawing, illustration of some components may be omitted for convenience of drawing.

[0013] FIG. 1 is a diagram showing the flow of a method for converting sewage sludge incineration ash into fertilizer according to an embodiment. As shown in FIG. 1, first, phosphorus-containing sewage sludge incineration ash (hereinafter also referred to as "sludge incineration ash") 3 is prepared by incinerating sludge 1 in an incinerator 2. Sludge 1 is, for example, sewage sludge collected from a sewage treatment plant. This type of sewage sludge generally contains fertilizer components such as phosphorus, potassium, and calcium, as well as heavy metals such as cadmium, lead, and arsenic. The following description will be given taking as an example a case where sludge incineration ash 3 contains at least phosphorus and potassium as fertilizer components, as well as the heavy metals cadmium, lead, and arsenic.

[0014] Next, the sludge incineration ash 3 is supplied to an elbow jet classifier 4. The elbow jet classifier 4 is a classifier that utilizes the Coanda effect. The elbow jet classifier 4 is equipped with an edge 41 inside, and is configured so that the classification point can be adjusted by adjusting the position (angle) of the edge 41. Since such elbow jet classifiers 4 are well known, further detailed explanation will be omitted. Using the elbow jet classifier 4, the sludge incineration ash 3 is classified into three types: a fine particle group 51, a medium particle group 52 having an average particle size larger than that of the fine particle group 51, and a coarse particle group 53 having an average particle size larger than that of the medium particle group 52.

[0015] In this embodiment, the classified medium particle group 52 and coarse particle group 53 are reused as a phosphorus-containing fertilizer raw material 6. Fertilizer manufacturers produce desired fertilizers by adding necessary elements such as nitrogen to the phosphorus-containing fertilizer raw material 6. Therefore, in order to increase the value of the phosphorus-containing fertilizer raw material 6 provided to fertilizer manufacturers, it is necessary to increase the phosphorus concentration of the medium particle group 52 and the coarse particle group 53 and to decrease the heavy metal concentration.

[0016] As mentioned above, the inventors have conducted extensive research and have come to the following discovery: That is, by adjusting the position (angle) of the edge 41 of the elbow jet classifier 4 to change the classification point between the fine particle group 51 and the medium particle group 52 (hereinafter also referred to as the "classification point on the fine particle group 51 side"), the medium particle group 52 and the coarse particle group 53 can maintain the phosphorus concentration of the sludge incineration ash 3 before classification, while the heavy metal concentrations of the medium particle group 52 and the coarse particle group 53 can be made lower than the heavy metal concentration of the sludge incineration ash 3 before classification.

[0017] Furthermore, based on the above findings, the inventors conducted a test in which the classification point (angle of edge 41) on the fine particle group 51 side was changed to 5 μm, 7.5 μm, 10 μm, and 15 μm by adjusting the angle of edge 41 to investigate the optimal classification conditions. The test results obtained will be explained below with reference to FIG. 2. In this test, the feed rate of the sludge incineration ash 3 was set to 0.5 g / min. It was confirmed that changing the classification point to a value smaller than 5 μm significantly reduced the recovery rate.

[0018] FIG. 2 is a graph showing the relationship between the classification points of the fine particle group 51 and the medium particle group 52 and the element concentrations of each element in the classified medium particle group 52 and the classified coarse particle group 53. Five elements, phosphorus (P), potassium (K), cadmium (Cd), lead (Pb), and arsenic (As), are illustrated in FIG. 2. The lower limit of the classification point for the fine particle group 51 was adjusted to 5 μm in consideration of the recovery rate. The dashed lines in the figure indicate the concentration (wt%) of each element contained in the sludge incineration ash 3 before classification. The concentrations of cadmium, lead, and arsenic contained in the sludge incineration ash 3 before classification were all below the heavy metal allowable values ​​under the Fertilizer Control Act. However, the present disclosure can also be applied when the heavy metal allowable values ​​are exceeded. The heavy metal allowable values ​​are 5 mg / kg for cadmium, 100 mg / kg for lead, and 50 mg / kg for arsenic.

[0019] With reference to the graph for phosphorus on the upper left, it was confirmed that adjusting the classification point on the fine particle group 51 side to a range of 5 μm or more and 10 μm or less allows the classified medium particle group 52 and coarse particle group 53 to maintain the phosphorus concentration before classification, that is, it is possible to maintain high phosphorus concentrations in the medium particle group 52 and coarse particle group 53. Furthermore, with reference to the graph for potassium on the upper right, it was confirmed that adjusting the classification point on the fine particle group 51 side to a range of 5 μm or more and 10 μm or less, preferably 9 μm or less, allows the potassium concentration in the medium particle group 52 and coarse particle group 53 to be higher than the potassium concentration before classification.

[0020] Furthermore, by referring to the graphs of heavy metals (cadmium, lead, and arsenic) in the middle and bottom rows, it was confirmed that by adjusting the classification point on the fine particle group 51 side to the range of 5 μm or more and 10 μm or less, the heavy metal concentrations in the medium particle group 52 and coarse particle group 53 can be made lower than before classification. This is thought to be due to the concentration of heavy metals in the fine particle group 51.

[0021] Here, referring to the arsenic graph in the lower part, when the classification point on the fine particle group 51 side is adjusted to 5 μm, the arsenic concentration of the medium particle group 52 and the coarse particle group 53 becomes slightly higher than the arsenic concentration of the sludge incineration ash 3 before classification. Therefore, it has been confirmed that when the classification point on the fine particle group 51 side is adjusted to 6 μm or more, preferably 7 μm or more and 10 μm or less, the arsenic concentration of the classified medium particle group 52 and the coarse particle group 53 becomes lower than the arsenic concentration of the sludge incineration ash 3 before classification.

[0022] Considering the above, it is preferable to adjust the classification point on the fine particle group 51 side to 10 μm or less, and to adjust it to a range of 5 μm to 10 μm in consideration of the recovery rate. Furthermore, if it is desired to increase the potassium concentration of the medium particle group 52 and the coarse particle group 53 compared to the potassium concentration of the sludge incineration ash 3 before classification, it is preferable to adjust the classification point to a range of 7 μm to 9 μm inclusive. Furthermore, if it is desired to decrease the arsenic concentration of the medium particle group 52 and the coarse particle group 53 compared to the arsenic concentration of the sludge incineration ash 3 before classification, it is preferable to adjust the classification point to 7 μm or more. Furthermore, if it is desired to increase the potassium concentration of the medium particle group 52 and the coarse particle group 53 compared to the potassium concentration of the sludge incineration ash 3 before classification and decrease the arsenic concentration of the medium particle group 52 and the coarse particle group 53 compared to the arsenic concentration of the sludge incineration ash 3 before classification, it is preferable to adjust the classification point to a range of 7 μm to 9 μm inclusive. The classification point between the medium particle group 52 and the coarse particle group 53 (hereinafter also referred to as the "classification point on the coarse particle group 53 side") is not particularly limited and can be adjusted in consideration of the recovery rate, for example, to 50 μm. The classification point on the coarse particle group 53 side does not affect the concentrations of each element in the medium particle group 52 and the coarse particle group 53, so further explanation will be omitted.

[0023] Furthermore, the inventors measured the particle size distribution (volume-based particle size distribution) of the sludge incineration ash 3 before classification and the particle size distributions of the fine particle group 51, medium particle group 52, and coarse particle group 53 classified by adjusting the classification point to 10 μm by adjusting the edge 41 using a particle size distribution measuring device, and obtained the measurement results shown in Figure 3. A laser diffraction type particle size measuring device, for example, can be suitably used as the particle size distribution measuring device. Figure 3 is a graph showing the particle size distribution before classification and the particle size distributions of the fine particle group 51, medium particle group 52, and coarse particle group 53 classified by adjusting the classification point to 10 μm. As shown in Figure 3, the median diameter D 50 The median diameter D of the fine particle group 51 obtained by classifying the sludge incineration ash 3 having a diameter of about 25 μm 50 The median diameter D of the medium particle group 52 was confirmed to be approximately 6 μm. 50 is about 27 μm, and the median diameter D 50 was approximately 48 μm.

[0024] Although not shown, when the classification point on the fine particle group 51 side was adjusted for multiple sludge incineration ash 3 obtained from multiple sludge 1 collected at different locations and the concentrations of each element in the medium particle group 52 and the coarse particle group 53 were measured, it was confirmed that the results showed roughly the same trends as those shown in Figure 2. Therefore, it is believed that the above-mentioned adjustment range of the classification point on the fine particle group 51 side can also be applied when using other sludge incineration ash 3.

[0025] Furthermore, if the sludge 1 is collected from the same location, the ratio of each element contained in the sludge incineration ash 3 usually does not change significantly over time. Therefore, once the classification point on the fine particle group 51 side (and the coarse particle group 53 side) is adjusted as described above, there is no need to frequently readjust the classification point (edge ​​41 angle). However, if the ratio of each element in the sludge incineration ash 3 changes significantly due to some influence, it is preferable to perform composition analysis and weight measurement on the fine particle group 51, medium particle group 52, and coarse particle group 53 using the analysis and measurement device 7, and readjust the classification point (edge ​​41 angle) based on those results. As a known fluorescent X-ray analyzer can be used as the analysis and measurement device 7, detailed description thereof will be omitted here.

[0026] According to this embodiment, by adjusting the classification point between the fine particle group 51 and the medium particle group 52 in the classification of sludge incineration ash 3 using the elbow jet classifier 4 to 10 μm or less, the phosphorus concentration of the classified medium particle group 52 and coarse particle group 53 can be maintained at the phosphorus concentration of the sludge incineration ash 3 before classification. Furthermore, heavy metals are concentrated in the classified fine particle group 51, and as a result, the heavy metal concentrations of the medium particle group 52 and coarse particle group 53 can be made as low as possible compared with the heavy metal concentration of the sludge incineration ash 3 before classification. Therefore, the classified medium particle group 52 and coarse particle group 53 can be reused as valuable phosphorus-containing fertilizer raw material 6.

[0027] In addition, by adjusting the classification point between the fine particle group 51 and the medium particle group 52 to be within the range of 7 μm or more and 9 μm or less, the potassium concentration of the medium particle group 52 and the coarse particle group 53 can be made higher than the potassium concentration of the sludge incineration ash 3 before classification, and the arsenic concentration of the medium particle group 52 and the coarse particle group 53 can be made as low as possible compared to the arsenic concentration of the sludge incineration ash 3 before classification.

[0028] Although the embodiments of the present disclosure have been described above, the present disclosure is not limited to the above embodiments and can be implemented in various modifications within the scope of the present disclosure. In the above embodiments, the case where the lower limit value of the fine particle group 51 side is adjusted to 5 μm has been described as an example, but it can be adjusted to a range of, for example, 4.5 μm or more and 5.5 μm or less depending on the recovery rate of the fine particle group 51. [Explanation of symbols]

[0029] 1...sludge, 2...incinerator, 3...sludge incineration ash, 4...classifier, 41...edge adjustment unit, 51...fine particle group, 52...medium particle group, 53...coarse particle group, 6...raw material for phosphorus-containing fertilizer, 7...analysis and measurement device

Claims

1. A method for converting phosphorus-containing sewage sludge incineration ash into fertilizer, comprising: classifying the sewage sludge incineration ash into three types of particles, namely, a fine particle group, a medium particle group, and a coarse particle group, using an elbow jet classifier; and reusing the classified medium particle group and the classified coarse particle group as raw materials for a phosphorus-containing fertilizer, A method for converting sewage sludge incineration ash into fertilizer, characterized in that the classification point between the fine particle group and the medium particle group in the classification is adjusted to 10 μm or less.

2. 2. The method for converting sewage sludge incineration ash into fertilizer according to claim 1, The sewage sludge incineration ash contains potassium and arsenic, A method for converting sewage sludge incineration ash into fertilizer, characterized in that the classification point is adjusted to be within the range of 7 μm or more and 9 μm or less.

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