Method for manufacturing fertilizer raw materials, method for manufacturing fertilizer, fertilizer raw materials

Abstract

To provide a method for more efficiently recovering phosphorus components usable as fertilizer raw materials from two types of industrial waste that were previously discarded: sludge from thermal power plants and sewage sludge, thereby enabling the production of fertilizer raw materials. [Solution] A method for producing fertilizer raw materials, comprising a mixing step of mixing calcium-containing by-products obtained from a thermal power plant with sewage sludge, and an incineration step of incinerating the mixture of sewage sludge and by-products to obtain incinerated ash which is used as a fertilizer raw material.

Description

Technical Field

[0001] The present invention relates to a method for producing a fertilizer raw material, a method for producing a fertilizer, and a fertilizer raw material.

Background Art

[0002] In recent years, the depletion of phosphorus resources has become a global problem. In Japan, which relies almost 100% on imports, ensuring a stable supply of phosphorus resources is an important issue. It is known that sewage contains phosphorus, and attempts have been made to separate phosphorus into the sludge side during sewage treatment and add a calcium component to the sewage sludge to recover phosphorus as calcium phosphate. The recovered calcium phosphate is easily soluble in the root acid of plants and can be used as a fertilizer raw material.

[0003] On the other hand, in addition to carbon dioxide gas, the exhaust gas discharged from a thermal power plant contains coal containing heavy metals, nitrogen oxides (NOx), sulfur dioxide gas, etc., and each is removed by a dust collector, a denitration device, and a desulfurization device. At that time, a slurry containing calcium sulfate is discharged from the desulfurization device, and the slurry is dehydrated to become gypsum and a desorbed liquid. This desorbed liquid is separated into sludge and desorbed liquid through two-stage coagulation sedimentation and disposed of as industrial waste. Incidentally, the sludge generated by the second-stage coagulation sedimentation contains a large amount of calcium carbonate and magnesium carbonate.

[0004] As a treatment method for recovering phosphorus from sewage sludge, for example, it is disclosed in Patent Document 1 below.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] A sewage treatment process for treating wastewater such as domestic wastewater generally includes a water treatment process for purifying the sewage and separating and removing sludge from the sewage; a sludge treatment process for concentrating and dewatering the sludge separated and removed in the water treatment process to obtain dewatered sludge; and an incineration process for burning the dewatered sludge in an incinerator.

[0007] When dewatered sludge is incinerated, the resulting phosphorus pentoxide (P2O5) is highly viscous and can adhere to the furnace walls, causing the silica sand to clump together. To prevent this, inorganic coagulants such as polyferric sulfate or polyaluminum chloride are added to the dewatered sludge to raise the melting point of the phosphorus compounds, thereby preventing them from adhering to the furnace walls. However, the iron phosphate and aluminum phosphate produced by adding inorganic coagulants are insoluble in phosphate acids and therefore cannot be used as fertilizer raw materials. For this reason, to recover phosphorus components from dewatered sludge, it is necessary to install separate phosphorus recovery equipment and perform a process of treating the sludge with acid or alkali to extract the phosphorus components.

[0008] Furthermore, the large amount of sludge discharged from the aforementioned thermal power plants needs to be properly treated as industrial waste, and there is a desire to reduce the costs associated with this treatment.

[0009] The object of the present invention is to provide a method for more efficiently recovering phosphorus components that can be used as fertilizer raw materials and producing fertilizer raw materials using two types of industrial waste that were conventionally discarded: sludge from thermal power plants and sewage sludge. [Means for solving the problem]

[0010] The characteristics of the method for producing fertilizer raw materials according to the present invention are a mixing step of mixing a calcium-containing by-product obtained from a thermal power plant with sewage sludge, The key feature is that it includes an incineration process in which the mixture of the aforementioned sewage sludge and the aforementioned by-products is incinerated, and the resulting incinerated ash is used as a fertilizer raw material.

[0011] By-products obtained from thermal power plants, which generate lime, gypsum, etc. during desulfurization, contain at least calcium, and sewage sludge usually contains at least phosphorus. Therefore, according to this configuration, by mixing by-products obtained from thermal power plants with sewage sludge and incinerating them, incinerated ash containing calcium phosphate can be obtained and used as a fertilizer raw material. Thus, it is possible to produce fertilizer raw materials useful for plant cultivation using two types of industrial waste that were conventionally discarded: by-products from thermal power plants and sewage sludge, thereby reducing the amount of industrial waste to be disposed of.

[0012] Furthermore, according to this configuration, the by-products obtained from the thermal power plant contain at least calcium components (e.g., calcium carbonate), and by adding these to sewage sludge, it is possible to prevent the adhesion of phosphorus compounds to the furnace walls without adding conventional inorganic flocculants such as polyferric sulfate or polyaluminum chloride. In addition, since the calcium phosphate produced by the incineration process is absorbable by plants, it can be used directly as a fertilizer raw material without the need to install separate phosphorus recovery equipment.

[0013] In the method for producing fertilizer raw materials according to the present invention, it is preferable that the by-product further contains magnesium.

[0014] According to this configuration, by mixing a by-product containing magnesium with sewage sludge and incinerating it, incinerated ash containing not only calcium phosphate but also magnesium phosphate, which is also useful as fertilizer, can be obtained and used as a fertilizer raw material.

[0015] In the method for producing fertilizer raw materials according to the present invention, the incineration step is preferably carried out in a fluidized bed incinerator using silica sand.

[0016] With this configuration, the silica sand used in the fluidized bed incinerator stably supplies silicon, which is useful as fertilizer, to the incinerated ash, eliminating the need to add silicon separately.

[0017] In the method for producing fertilizer raw materials according to the present invention, it is preferable that the incineration temperature in the incineration step is 850°C or higher and 930°C or lower.

[0018] With this configuration, the combustion reaction proceeds more reliably and the incineration process is promoted, so that incinerated ash containing calcium phosphate and other substances can be obtained efficiently.

[0019] The characteristics of the fertilizer manufacturing method according to the present invention are a mixing step of mixing a calcium-containing by-product obtained from a thermal power plant with sewage sludge, The key feature is the use of fertilizer raw materials produced by a method for manufacturing fertilizer raw materials that includes an incineration process, which uses incinerated ash obtained by incinerating a mixture of the aforementioned sewage sludge and the aforementioned by-products as fertilizer raw material, and a method for manufacturing fertilizer raw materials that encompasses this process.

[0020] By-products obtained from thermal power plants contain at least calcium, and sewage sludge typically contains at least phosphorus.

[0021] Therefore, with this configuration, by mixing by-products obtained from a thermal power plant with sewage sludge and incinerating them, incinerated ash containing calcium phosphate can be obtained, and fertilizer can be manufactured using this as a fertilizer raw material.

[0022] Therefore, it is possible to manufacture fertilizers useful for plant cultivation using two types of industrial waste that were previously discarded: by-products from thermal power plants and sewage sludge, thereby reducing the amount of industrial waste that needs to be disposed of.

[0023] Furthermore, according to this configuration, the by-products obtained from thermal power plants contain at least calcium components (such as calcium carbonate), and by adding these to sewage sludge, it is possible to prevent the adhesion of phosphorus compounds to the furnace walls without adding conventional inorganic flocculants such as ferric polysulfate or polyaluminum chloride. In addition, since the calcium phosphate produced by the incineration process is absorbable by plants, it can be used directly as a fertilizer raw material to manufacture fertilizer without the need to install separate phosphorus recovery equipment.

[0024] In the method for producing a fertilizer according to the present invention, the incineration step is carried out in a fluidized bed incinerator using silica sand, and preferably further includes a step of producing a fused phosphate fertilizer by mixing the incineration ash obtained in the incineration step with phosphate ore.

[0025] <s According to this configuration, since silicon useful as a fertilizer is stably replenished in the incineration ash by the silica sand used in the fluidized bed incinerator, there is no need to separately add silicon. Further, since silicon is sufficiently present in the incineration ash, when producing a fused phosphate fertilizer by mixing the incineration ash and phosphate ore, the release reaction of fluorine contained in the phosphate ore is promoted, and a fused phosphate fertilizer of better quality can be produced.

[0026] The fertilizer raw material according to the present invention is characterized by including incineration ash obtained by incinerating a mixture of a by-product containing calcium obtained from a thermal power plant and sewage sludge.

[0027] According to this configuration, since it is produced using two industrial wastes, namely, a by-product derived from a thermal power plant and sewage sludge, which were conventionally discarded, it is possible to provide a fertilizer raw material with a low raw material cost.

Brief Description of the Drawings

[0028] [Figure 1] It is a diagram showing the manufacturing process of the fertilizer. [Figure 2] It is a diagram showing the manufacturing process (modified example) of the fertilizer.

Mode for Carrying Out the Invention

[0029] 〔Embodiment〕 Hereinafter, embodiments of the present invention will be described. [Method for Producing Fertilizer Raw Material] As shown in Figure 1, the method for producing fertilizer raw materials according to the present invention includes a mixing step (#1) in which a calcium-containing by-product obtained from a thermal power plant (hereinafter referred to as calcium-containing by-product) is mixed with sewage sludge obtained from a sewage treatment facility, and an incineration step (#2) in which the incinerated ash obtained by incinerating the mixture of sewage sludge and calcium-containing by-product is used as fertilizer raw material. In this embodiment, it is performed as part of the sewage treatment process. A general sewage treatment process includes a water treatment step for purifying sewage and separating and removing sludge from the sewage, a sludge treatment step for concentrating and dewatering the sludge separated and removed in the water treatment step to obtain dewatered sludge, and a sludge incineration step for incinerating the dewatered sludge in an incinerator.

[0030] (Calcium-containing by-product) In this invention, a thermal power plant refers to a power plant that generates electricity using fuels such as coal, oil, natural gas, or biomass fuel, and whose exhaust gas is subjected to desulfurization treatment by at least a desulfurization unit. A slurry containing calcium sulfate is obtained from the desulfurization unit through the desulfurization treatment, and this slurry is then dewatered to obtain coal and / or gypsum and a desorbed liquid.

[0031] In this invention, the calcium-containing by-product refers to sludge containing at least calcium after the above-mentioned detached liquid has been subjected to coagulation treatment. This sludge contains at least calcium, but may also contain magnesium. The obtained sludge may be dewatered using a known dewatering method as needed to form a cake, thereby reducing its volume and weight and improving combustion efficiency.

[0032] The eluent is typically subjected to a two-stage coagulation and sedimentation treatment. The first stage of coagulation yields sludge mainly containing heavy metals such as iron phosphate and aluminum phosphate, while the second stage of coagulation yields sludge mainly containing calcium carbonate, magnesium carbonate, and magnesium hydroxide. Therefore, it is desirable to use the sludge obtained from the second stage of coagulation as the calcium-containing by-product.

[0033] (Sewage sludge obtained at a sewage treatment plant) In this invention, sewage sludge refers to sludge obtained from sewage treatment facilities that treat sewage such as domestic wastewater. Specifically, as described later, this includes primary sedimentation sludge obtained in the primary sedimentation tank in the water treatment process for separating and removing sludge from sewage, and excess sludge obtained in the final sedimentation tank in the same water treatment process.

[0034] Sewage flowing into a sewage treatment plant first undergoes a water treatment process. After large debris and sand are removed in the grit tank, the sewage is sent to the primary sedimentation tank, where it is slowly flushed to obtain primary sludge, which is fine debris and other sediment. Next, the supernatant water from the primary sedimentation tank is sent to a reaction tank, where air is blown in and activated sludge treatment is performed, in which microorganisms decompose the water's pollutants (organic matter). The sewage that has undergone activated sludge treatment in the reaction tank is sent to the final sedimentation tank, where it is separated into excess sludge and supernatant water. The supernatant water is disinfected in a disinfection facility before being discharged into rivers or the sea. It is desirable that the sludge obtained in the water treatment process be concentrated and dewatered in the subsequent sludge treatment process using known concentration methods to obtain dewatered sludge.

[0035] (Mixing process) Sewage sludge obtained at a sewage treatment plant is mixed with calcium-containing by-products (sludge) (#1). The mixing method is not particularly limited and may be carried out using a known mixer.

[0036] (Incineration process) The mixture of sewage sludge and calcium-containing by-products obtained in the mixing process is incinerated in an incinerator (#2). When this mixture is heated, the phosphorus contained in the sewage sludge reacts with the calcium contained in the calcium-containing by-products to produce calcium phosphate, and the resulting incineration ash contains calcium phosphate. If the calcium-containing by-products contain magnesium, magnesium phosphate is also produced, so the incineration ash contains both calcium phosphate and magnesium phosphate.

[0037] The incineration temperature in the incineration process is preferably between 850°C and 930°C, and more preferably between 880°C and 930°C. Within this temperature range, the combustion reaction proceeds more reliably, promoting the incineration process, and thus allowing for the efficient production of incinerated ash containing calcium phosphate and the like.

[0038] Furthermore, the incineration process is preferably carried out in a fluidized bed incinerator that uses silica sand as the fluidized bed. In the fluidized bed incinerator, a mixing process (#1) in which calcium-containing by-products and sewage sludge are mixed, and an incineration process (#2) in which the ash obtained by incinerating the mixture of sewage sludge and calcium-containing by-products is used as a fertilizer raw material is carried out in sequence. Alternatively, the sewage sludge and calcium-containing by-products may be mixed and incinerated within the fluidized bed incinerator. That is, as shown in Figure 2, the mixing process and the incineration process may be carried out almost simultaneously in the fluidized bed incinerator (mixing and incineration processes (#1, #2)).

[0039] When using a fluidized bed incinerator, silicon, which is useful as fertilizer, is stably supplied to the incinerated ash from silica sand, so basically there is no need to add silicon. However, silicon may be supplemented as needed, in which case, for example, sand used in the grit chambers of sewage treatment plants may be added in the mixing process (#1).

[0040] As described above, the incinerated ash produced contains calcium phosphate and magnesium phosphate, which are absorbable by plants, and therefore can be used as a fertilizer raw material. Since this incinerated ash is produced using two types of industrial waste—by-products from thermal power plants and sewage sludge—which were previously discarded, it can provide a fertilizer raw material with low raw material costs.

[0041] [Fertilizer manufacturing method] In this embodiment, the case of producing fused phosphate fertilizer as a fertilizer will be described. As shown in Figure 1, the method for producing fertilizer according to the present invention includes a mixing step (#1) of mixing the calcium-containing by-product with sewage sludge, an incineration step (#2) of using the incinerated ash obtained by incinerating the mixture of sewage sludge and calcium-containing by-product as a fertilizer raw material, and a step (#3) of producing fused phosphate fertilizer by mixing the incinerated ash obtained in the incineration step with phosphate rock.

[0042] Fused phosphate fertilizer is also called fused phosphate, and phosphate fertilizer is phosphate root (PO4 3- It is an amorphous silicate fertilizer containing ). Because it is not crystalline, it does not have a clear chemical structure, but its main components are Ca3(PO4)2 and Ca2SiO4.

[0043] The raw materials typically used to produce fused phosphate fertilizer are phosphate rock, fusion aids (minerals containing magnesium and silicon, such as serpentinite, dolomite, and peridotite), and fuel. However, in this embodiment, incinerated ash obtained by the above-described method for producing fertilizer raw materials is used instead of fusion aids. Examples of phosphate rock include medium-grade phosphate rock with a relatively low P2O5 content, and recalcitrant phosphate rock that is not suitable for acid decomposition using wet phosphoric acid or superphosphate. Examples of fuel include coke, coal, and heavy oil.

[0044] As shown in Figure 2, the process for producing incinerated ash is basically the same as the method for producing fertilizer raw materials described above, but a fluidized bed incinerator using silica sand as the fluidized bed is used.

[0045] The incinerated ash, phosphate rock, and fuel obtained by the above-described method for producing fertilizer raw materials can be used as raw materials to produce fused phosphate fertilizer by a known fused phosphate fertilizer production process (#3). The fused phosphate fertilizer production process includes a mixing step in which the above-mentioned incinerated ash, phosphate rock, and fuel are mixed to form the raw materials; a melting step in which the raw materials are put into a blast furnace and melted; a water granulation step in which the molten body of the fused phosphate fertilizer is crushed with water; and a drying and crushing step in which the water-granulated fused phosphate fertilizer is dried and crushed.

[0046] According to the fertilizer manufacturing method of the present invention, silicon useful as a fertilizer is stably supplied to the incinerated ash by silica sand used in the fluidized bed incinerator (and sand from the sedimentation basin of a sewage treatment plant, etc., which may be added as needed), so there is no need to add silicon separately. Furthermore, because sufficient silicon is present in the incinerated ash, when the incinerated ash and phosphate rock are mixed to produce fused phosphate fertilizer, the detachment reaction of fluorine contained in the phosphate rock is promoted, making it possible to produce fused phosphate fertilizer of higher quality. [Industrial applicability]

[0047] The method for producing fertilizer raw materials according to the present invention can be suitably used, for example, in the production of fused phosphate fertilizer.

Claims

1. A mixing process in which calcium-containing by-products obtained from a thermal power plant are mixed with sewage sludge, A method for producing fertilizer raw materials, comprising an incineration step of using incinerated ash obtained by incinerating a mixture of the sewage sludge and the by-product as fertilizer raw material.

2. The method for producing a fertilizer raw material according to claim 1, wherein the by-product further contains magnesium.

3. The method for producing fertilizer raw materials according to claim 1, wherein the incineration step is carried out in a fluidized bed incinerator using silica sand.

4. A method for producing fertilizer raw materials according to any one of claims 1 to 3, wherein the incineration temperature in the incineration step is 850°C or higher and 930°C or lower.

5. A mixing process in which calcium-containing by-products obtained from a thermal power plant are mixed with sewage sludge, A method for producing fertilizer, comprising: an incineration step in which incineration ash obtained by incinerating a mixture of the aforementioned sewage sludge and the aforementioned by-products is used as a fertilizer raw material; and a method for producing fertilizer raw materials that uses a fertilizer raw material produced by a method for producing fertilizer raw materials that includes this step.

6. The incineration process is carried out in a fluidized bed incinerator using silica sand. The method for producing fertilizer according to claim 5, further comprising the step of mixing the incinerated ash obtained in the incineration step with phosphate rock to produce fused phosphate fertilizer.

7. Fertilizer raw material containing incinerated ash obtained by incinerating a mixture of calcium-containing by-products obtained from thermal power plants and sewage sludge.

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