JP5946721B2 - Method for producing phosphate fertilizer - Google Patents

Description

  The present invention relates to a method for producing phosphate fertilizer, and more particularly, to a method for producing phosphate fertilizer from phosphorus contained in sewage of a sewage treatment facility and phosphorus contained in sludge generated in the sewage treatment process.

  Phosphorus, one of the three elements of fertilizer, depends on phosphate ore for its raw material, and in Japan, where mineral resources are scarce, all of it is imported. Phosphorite ore is expected to be depleted in the future and may become extremely difficult to obtain in the future. How to efficiently recover high-quality phosphorus from sewage containing a large amount of phosphorus, or recycle it However, this is an issue of technological development in Japan.

  Some of Japan's sewage treatment facilities already have melting furnaces, and add calcium sources or magnesium sources to the sewage dewatered sludge to control the melting temperature to make molten slag. However, this molten slag is not intended to be used as fertilizer, but is intended to be used for civil engineering materials such as roadbed materials or simply to reduce the volume to reduce the final disposal amount. The above problem of use is not considered at all.

  Therefore, for the purpose of fertilization, for example, in Patent Document 1, an iron-based flocculant is added to sewage, the phosphorus component contained in the sewage is settled, the sediment is collected together with sludge, and these are dehydrated and incinerated. After obtaining sludge incineration ash with a high concentration of phosphorus component, add coke, magnesium oxide, etc. to this sludge incineration ash and heat it in a melting furnace to selectively discharge molten slag to the granulation tank. A method for producing a safe fertilizer having a high phosphorus component concentration by quenching and granulating is described.

Japanese Patent Laid-Open No. 2003-112988

  However, in the method for producing phosphorus fertilizer described in the above-mentioned patent document, the incineration step for converting dehydrated sludge into incineration ash and the melting step for melting into fertilizer are separate, so heat energy is used to obtain sludge incineration ash. In addition, since a large amount of heat energy is required in the melting process at a higher temperature and a large amount of energy is consumed, there is a problem that the manufacturing cost increases.

  Therefore, the present invention has been made in view of the above-described problem, and a phosphoric acid fertilizer manufacturing method capable of obtaining fertilizer of excellent quality at low cost by effectively utilizing phosphorus contained in sewage. The purpose is to provide.

In order to achieve the above object, the present invention is a method for producing phosphate fertilizer, wherein a calcium source is added to sewage sludge containing phosphorus generated in a sewage treatment facility, and a melting furnace of an existing sewage treatment facility is used. And firing at a firing temperature of 1150 ° C. or higher and 1350 ° C. or lower .

  According to the present invention, since the phosphoric acid fertilizer is fired using an existing melting furnace, the initial investment cost can be greatly reduced.

  That is, since the present invention only diverts the existing melting furnace as a firing furnace, the equipment for adding the calcium source or the magnesium source can be diverted as it is, so that additional capital investment is required. do not do.

Conventionally, phosphorus recovery products and sewage sludge were melted and fertilized in the final process, but in the present invention, a firing process having a processing temperature lower than that of melting is adopted, so that energy consumption can be reduced, and manufacturing costs can be reduced. Leading to a significant reduction. Furthermore, by firing in the above temperature range, the phosphoric acid fertilizer phosphoric acid solubility ( the proportion of P ₂ O ₅ content is soluble phosphoric acid) and silicic acid solubility (SiO ₂ content) The ratio of soluble silicic acid among them can be increased.

  In the manufacturing method of the said phosphate fertilizer, the calcium oxide (CaO) content rate of the said phosphate fertilizer can be 35 mass% or more and 60 mass% or less. This makes it possible to adjust the components suitable for producing a phosphoric acid fertilizer excellent in phosphoric acid availability and silicic acid availability even by firing.

  In the method for producing phosphate fertilizer, the melting furnace may be a coke bed furnace, a swirl melting furnace, or a surface melting furnace.

  In the method for producing phosphate fertilizer, the sewage in the sewage treatment facility is concentrated, a phosphorus recovery material is added to the concentrated sewage, the phosphorus in the sewage is reacted with the recovery material, and then dehydrated. While obtaining the said phosphorus collection | recovery thing and sewage sludge, the said calcium source can also be mixed and baked with the phosphorus collection | recovery thing and sewage sludge obtained by dehydration.

  As mentioned above, according to this invention, the manufacturing method of the phosphate fertilizer which can collect | recover phosphorus from sewage at low cost can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is a whole block diagram which shows an example of the system which enforces the manufacturing method of the phosphate fertilizer concerning this invention. It is a graph which shows the relationship between CaO density | concentration of a baked product, and a melting start temperature. It is a whole block diagram which shows the other example of the system which enforces the manufacturing method of the phosphate fertilizer concerning this invention.

  Next, an embodiment for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows an example of a system for carrying out a method for producing a phosphate fertilizer according to the present invention. This phosphate fertilizer production system 1 is roughly divided to concentrate sewage S1 brought into a sewage treatment plant, and dehydrated sludge. The water treatment equipment 2 separated into S9 and the dehydrated filtrate W3, the dewatered sludge S9 separated in the water treatment equipment 2 and the composition adjusting agent A2 are mixed and fired, and pulverized and sized to grind the fired product It consists of the mixed firing equipment 4 which performs

  The water treatment facility 2 concentrates the suspended sediment and mud in the sewage S1 and sends them to the gravity concentration tank 19, and the organic matter, nitrogen, phosphorus, etc. from the first sedimentation basin 5 after finishing the sedimentation treatment. A biological treatment tank 6 for treating sewage water S2 containing microorganisms, a final sedimentation tank 7 for precipitating the activated sludge S3 treated in the biological treatment tank 6 over time, and discharging the supernatant water D, and a final sedimentation tank Centrifugal concentrator 8 for further concentrating surplus sludge S4 from 7 by centrifugal force, methane fermentation tank 9 for decomposing concentrated sludge S5 from centrifugal concentrator 8 and concentrated sludge S6 from gravity concentration tank 19, and methane fermentation tank The storage tank 10 that stores the sludge S7 discharged from 9 and the dehydrator 11 that separates the sludge S8 discharged from the storage tank 10 into the dehydrated sludge S9 and the dehydrated filtrate W3.

  The mixing and firing facility 4 incinerates the mixer 14 for adding the composition regulator A2 as a calcium source to the dehydrated sludge S9 separated by the concentration and separation facility 2 and mixing the mixture M supplied from the mixer 14. Stoker-type incinerator 15 and a surface melting furnace originally installed for the purpose of melting incinerator I, calcination furnace 16 used for firing incinerator I, and pulverization that pulverizes calcined product B1 to a desired size The machine 17 and the pan pelletizer 18 which granulates by adding the granulation auxiliary agent A3 to the pulverized fired product B2.

  The stoker-type incinerator 15 is generally installed in a sewage treatment plant in order to incinerate dehydrated sludge. Instead of the stoker-type incinerator 15, an incinerator such as a fluidized bed furnace or a multistage furnace is used. It can also be used.

  The sewage sludge in the present invention is the dehydrated sludge or sludge before dehydration obtained in various processes of the sewage treatment facility, the dehydrated sludge or the dried sludge obtained by drying the sludge, the carbonized sludge, or the incinerated sludge that has been incinerated. .

  The composition adjuster A2 is a calcium source added to obtain a calcinable phosphate fertilizer, and is used to make the calcium oxide content of the phosphate fertilizer 35% by mass or more. In general, since sewage sludge has a low calcium content, it is necessary to mix calcium sources to supplement calcium in the phosphate fertilizer. When sewage sludge and the calcium source are fired, the solubility of phosphoric acid and the solubility of silicic acid in the obtained fired product (phosphate fertilizer) are increased. On the other hand, when the calcium oxide content of the baked product is 60% by mass or more, the phosphorus content itself in the phosphate fertilizer is lowered and the fertilization effect is reduced, or the soil pH increases when fertilized on farmland. There is a risk of inhibiting the growth of.

  Examples of the calcium source include calcium carbonate, calcium oxide, calcium hydroxide, calcium phosphate, calcium chloride, calcium sulfate, limestone, quicklime, slaked lime, cement, steel slag, gypsum, quick-cone sludge (including its dry matter), waste mortar, Waste concrete, livestock droppings such as chicken droppings can be used. Among these, calcium carbonate and limestone are preferable because they are easily available and have a high calcium content.

In addition to the composition modifier A2, a silica source or a magnesium source may be further added. In general, sewage sludge contains a large amount of silica (SiO ₂ ), so there are few cases where a silica source is added. However, it is necessary to supplement the silica source when the sewage sludge has a low SiO ₂ content. is there. Examples of the silica source in this case include at least one selected from silica, silica sand, sand, diatomaceous earth, shirasu, raw conslag, waste mortar, waste concrete, acidic volcanic ash, acidic volcanic rock, and calcium silicate.

  When supplementing the phosphoric acid fertilizer with a bitter earth component, the magnesium source includes at least one selected from magnesium hydroxide, magnesium oxide, magnesia, dolomite, ferronickel slag, peridotite, serpentinite, and the like.

  In addition, as a method of preparing each raw material, for example, after firing a part of sewage sludge in an electric furnace or the like, the oxide in the fired ash is quantified, and based on the quantitative value and a predetermined composition, each raw material is The method of mixing is mentioned. The oxide can be quantified by a fundamental parameter method using a fluorescent X-ray apparatus. Since the ash content of sewage sludge and the chemical composition of ash vary from day to day, it is desirable to determine the rate of addition of calcium oxide to sewage sludge after grasping the correlation between these annual fluctuation ranges and sewage treatment conditions. . However, for the sake of accuracy, a part of the sewage sludge is fired with an electric furnace or the like as frequently as possible, and based on the chemical composition in the fired product, the desired content of calcium oxide in the phosphate fertilizer is obtained. It is preferable to correct the addition rate so that

  The solubility of phosphoric acid is the mass ratio (%) of soluble phosphoric acid to the total phosphoric acid in phosphate fertilizer, and the solubility of silicic acid is the total solubility in phosphate fertilizer. It is a mass ratio (%) of soluble silicic acid to silicic acid. The amount of soluble phosphoric acid is determined by the ammonium vanadomolybdate method specified in the fertilizer analysis method (Agricultural and Environmental Technology Research Institute, Ministry of Agriculture, Forestry and Fisheries), and the amount of soluble silicic acid is determined by the perchloric acid method specified in the same method. Can be measured. In addition, quantification of the oxide in a raw material or a phosphate fertilizer can be performed by a fundamental parameter method using a fluorescent X-ray apparatus.

FIG. 2 shows the relationship between the calcium oxide (CaO) concentration of the fired product and the melting start temperature for the sewage sludge incineration ash a, the sewage sludge incineration ash b, and the sewage sludge incineration ash c. The sewage sludge incineration ash a has a CaO content of 7.6% by mass and a P ₂ O ₅ content of 15.6% by mass, and the sewage sludge incineration ash b has a CaO content of 12.6% by mass. The P ₂ O ₅ content is 25.5% by mass, and the sewage sludge incinerated ash c has a CaO content of 10.8% by mass and a P ₂ O ₅ content of 38.9% by mass. The melting start temperature is a temperature at which the upper flat surface of the powder pellet formed by adding calcium carbonate to the sewage sludge incinerated ash and press-molded into a cylindrical shape is hemispherical by heating.

  As is apparent from this graph, the melting start temperature rises as the calcium oxide concentration of the fired product increases, and if the calcium oxide content of the fired product is increased to 35% by mass or more, it can be taken out as a fired product without melting. Can do.

  As the firing furnace 16, for example, an existing surface melting furnace installed in this sewage treatment facility is used as described above. When a coke bed furnace, a swirl melting furnace or the like is installed, these furnaces can be used instead of the surface melting furnace. Since these melting furnaces were originally operated at a temperature higher than the above-mentioned calcination temperature in order to obtain a melt, there is no problem as a heat-resistant structure even if used for calcination. Therefore, if necessary, it is necessary to modify the structure so that the mixture M does not stay in the furnace, is uniformly heated in the furnace, and the fired product is smoothly discharged out of the furnace.

  In particular, when a swirl melting furnace or a surface melting furnace is used as a firing furnace, it is necessary to provide a highly fire-resistant movable device for extruding or scraping the fired product out of the furnace. Further, when the coke bed furnace is used as a firing furnace, it is preferable because the fired product itself moves sequentially from the upper part to the lower part of the furnace, so that it is not necessary to greatly modify the discharge port. The firing furnace 16 can sew sewage sludge and the like at 1150 ° C. or higher and 1350 ° C. or lower, preferably 1200 ° C. or higher and 1300 ° C. or lower.

  If necessary, the raw material before firing may be granulated to prevent outflow from the discharge port and stabilize discharge. Examples of the granulating apparatus include a bread type pelletizer, a bread type mixer, an agitation granulator, a briquette machine, a roll press, and an extrusion molding machine. In particular, the bread type is superior in terms of convenience and production efficiency. A pelletizer is preferred. In addition, in order to improve granulation property (moldability), you may add excipient | fillers, such as polyvinyl alcohol and methylcellulose, to the powdery baked product before granulation. However, these excipients burn and disappear upon firing in the firing furnace 16. The granulation before firing is a step that is arbitrarily selected in consideration of the sintering reaction, dischargeability from the firing furnace 16, and the like.

  The fired product discharged from the firing furnace 16 (melting furnace) is a massive sintered product having a particle size of about 1 cm for a large one and about 5 cm on average for a small one about 10 cm. Since the particle size cannot be distributed as a fertilizer product, the particle size range is roughly pulverized by the pulverizer 17 so that the particle size range is between 1 mm and 5 mm, and sized by sieving or the like. As the pulverizer 17, for example, a jaw crusher, a hammer crusher, or the like is preferable because the baked product can be prevented from being excessively pulverized. A general-purpose vibrating screen can be used for the sieving operation.

  In the firing step and the pulverization step, a portion having a particle size of 1 mm or less is generated. In such a case, the sieving part of the above sizing process or the pulverized whole amount of the baked product is granulated with a pan pelletizer so that the particle size range is centered between 1 mm and 5 mm, and sieved. Perform sizing by etc.

  Instead of the pan pelletizer 18, an apparatus that can be expected to have the same granulation effect can be used, and a bread mixer, a stirring granulator, a briquette machine, a roll press, an extrusion molding machine, or the like may be used. A bread-type pelletizer is preferable in terms of convenience and production efficiency. In the case of granulation, it is preferable that the particle passing through the sizing step or the total amount of the fired product is adjusted to a particle size of 100 μm or less with a general-purpose ball mill.

  For the granulation aid A3, polyvinyl alcohol, methylcellulose, or the like can be used. Moreover, in this process, depending on the use of the fertilizer, components of silicic acid and phosphoric acid can be added as appropriate, and other fertilizer components such as nitrogen, potassium and bitter earth can be newly added. A commercially available vibration sieving device can be used as the sizing device.

  The granulation molding and sizing process is necessary to adjust the particle size of the fertilizer in order to suppress the generation of dust and facilitate the handling of the fertilizer when fertilizing agricultural land, and to fully demonstrate the fertilizer effect It is an optional step that is selected if there is.

  Next, operation | movement of the phosphate fertilizer manufacturing system 1 which has the said structure is demonstrated, referring FIG.

  The sewage S1 that has flowed into the phosphate fertilizer production system 1 is led to the first settling basin 5 and the suspended matter and mud that are likely to settle in the first settling basin 5 are concentrated and sent to the gravity concentration tank 19, and the sewage S2 containing organic matter etc. It supplies to the biological treatment tank 6 and processes with microorganisms.

  The activated sludge S3 generated in the biological treatment tank 6 is precipitated in the final sedimentation tank 7 over time, and the precipitated sludge is supplied to the centrifugal concentrator 8 as surplus sludge S4, and the supernatant obtained in the final sedimentation tank 7 is supplied. Release water D. A part of the excess sludge S4 is usually returned to the biological treatment tank 6.

  Excess sludge S4 from the final sedimentation basin 7 is concentrated by the centrifugal concentrator 8 and supplied to the methane fermentation tank 9 together with the concentrated sludge S6 stored in the gravity concentration tank 19. In the methane fermentation tank 9, the concentrated sludges S5 and S6 are decomposed by microorganisms, and the generated sludge S7 is temporarily stored in the storage tank 10, and then the sludge S8 is supplied to the dehydrator 11 and solid-liquid separated to obtain the dehydrated sludge S9. .

  Next, the dewatered sludge S9 is supplied to the mixer 14 and mixed together with the composition regulator A2 as a calcium source. After the homogenized mixture M is supplied to the stoker incinerator 15 and incinerated, the incinerated material I is fired in the firing furnace 16 in a temperature range of 1150 ° C. to 1350 ° C., preferably 1200 ° C. to 1300 ° C. By baking in these temperature ranges, the phosphate solubility and the silicic acid solubility of the obtained phosphate fertilizer are increased. Next, the fired product B1 is pulverized by a pulverizer 17 and granulated and formed to have a desired size together with the granulation auxiliary agent A3 by a pan pelletizer 18 at a later stage.

  The dewatered sludge S9 charged into the mixer 14 may be sewage sludge that has been dried, carbonized, or incinerated.

  Further, instead of incineration after mixing the dewatered sludge S9 and the composition adjusting agent A2, the composition adjusting agent A2 may be mixed after incineration of the dehydrated sludge and fired in the firing furnace 16.

  Furthermore, the composition adjusting agent A2 can be mixed in the mixer 14 with respect to the dried or carbonized sewage sludge, and can be directly baked in the baking furnace 16 without being burned in the stoker type incinerator 15.

  Next, another example of a system that implements the method for producing phosphate fertilizer according to the present invention will be described with reference to FIG.

  Specifically, in the system 21 illustrated in FIG. 3, the recovered material A1 is added to the storage tank 10. Since the sludge S7 stored in the storage tank 10 has a higher phosphorus concentration than other places in the system 21, phosphorus can be efficiently recovered. In the case where carbon dioxide is generated in the methane fermentation tank 9 and the recovered material A1 is added to the sludge S7 containing carbonic acid, the phosphorus recovery performance by the recovered material A1 is reduced, but the amount of recovered material A1 is increased. Alternatively, this can be dealt with by adjusting the pH of the sludge S7 with alkali before introducing the recovered material A1 into the sludge S7.

  As the recovery material A1, a recovery material containing calcium, for example, amorphous calcium silicate can be preferably used. This amorphous calcium silicate has high affinity with phosphorus, is porous, has a specific surface area. Therefore, phosphorus adsorption capacity is high and phosphorus can be selectively and efficiently adsorbed. In addition, calcium hydroxide, calcium chloride, and the like can be used.

  Next, operation | movement of the phosphate fertilizer manufacturing system 21 which has the said structure is demonstrated, referring FIG. In addition, since the operation | movement to the methane fermenter 9 is the same as that of the phosphate fertilizer manufacturing system 1 of FIG. 1, the description is omitted.

  The sludge S7 generated in the methane fermentation tank 9 is supplied to the storage tank 10, the phosphorus recovery material A1 is added to the storage tank 10, and the phosphorus contained in the sludge S7 is adsorbed on the phosphorus recovery material A1 and settled. Next, the sludge S8 from the storage tank 10 is supplied to the dehydrator 11, and solid-liquid separation is performed to obtain the dehydrated sludge S9 and the phosphorus recovery product AP, and the obtained dehydrated filtrate W3 is returned to the gravity concentration tank 19. Return to sedimentation basin 5 together with W1 etc.

  The dewatered sludge S9 and the phosphorus recovery product AP obtained by solid-liquid separation are mixed together with the composition adjusting agent A2 by the mixer 14, and the mixture M is supplied to the stoker incinerator 15 and incinerated. Firing is carried out in a temperature range of not less than 1 ° C and not more than 1350 ° C, preferably not less than 1200 ° C and not more than 1300 ° C. This increases the solubility of phosphoric acid and the solubility of silicic acid in the resulting phosphate fertilizer. Thereafter, the baked product B1 is pulverized by a pulverizer 17, and granulated and sized so as to have a desired size together with the granulation auxiliary agent A3 by a pan pelletizer 18 at a later stage.

  In the above example, the case where the phosphorus recovery material A1 is added to the storage tank 10 that can efficiently recover phosphorus has been described. However, the present invention is not limited to this addition place, and is further upstream of this sewage treatment facility. It is also possible to use this process. For example, in the methane fermentation tank 9, surplus sludge S4 transported from the final sedimentation tank 7 to the centrifugal concentrator 8, activated sludge S3 transported from the biological treatment tank 6 to the final sedimentation tank 7, or return water W1 from the gravity concentration tank 19 It can also be added.

  Further, instead of adding the recovered material A1 to the sewage, the recovered material A1 is added to the dehydrated filtrate W3 having a higher phosphorus concentration than other places in the system 1, and the phosphorus contained in the dehydrated filtrate W3 is added to the recovered material A1. The phosphorus recovery product AP adsorbing phosphorus can be obtained by solid-liquid separation, and the phosphorus recovery product AP and dehydrated sludge S9 can be supplied to the mixer 14 together with the composition modifier A2.

  In these systems, the addition position of the composition adjusting agent A2 is not limited to the mixer 14, and may be added to the sludge S8 between the storage tank 10 and the dehydrator 11, and in that case, the composition adjusting agent A2 is also subject to solid-liquid separation by the dehydrator 11, but an increase in the load on the dehydrator 11 is not a problem when the amount of the composition regulator A2 added and the moisture content of the sludge S8 are taken into consideration. Moreover, the mixer 14 becomes unnecessary.

  In the present invention, in order to produce phosphoric acid fertilizer by firing the phosphorus recovery product and the like, in addition to heat treatment at a lower temperature than the melting method, a calcium-based component adjuster that does not contain chlorine or the like. Since it is used, corrosion of the firing furnace 16 is reduced.

DESCRIPTION OF SYMBOLS 1,21 Phosphate fertilizer manufacturing system 2 Water treatment equipment 4 Mixed baking equipment 5 First sedimentation tank 6 Biological treatment tank 7 Final sedimentation tank 8 Centrifugal concentrator 9 Methane fermentation tank 10 Storage tank 11 Dehydrator 14 Mixer 15 Stoker type incinerator 16 Firing furnace 17 Pulverizer 18 Pamperetizer 19 Gravity concentration tank

Claims (4)

A method for producing a phosphate fertilizer, characterized in that sewage sludge generated in a sewage treatment facility and a calcium source are fired at a firing temperature of 1150 ° C or higher and 1350 ° C or lower using a melting furnace of an existing sewage treatment facility.   2. The method for producing phosphate fertilizer according to claim 1, wherein the calcium oxide content of the phosphate fertilizer is 35 mass% or more and 60 mass% or less. The said melting furnace is a coke bed furnace, a swirl melting furnace, or a surface melting furnace, The manufacturing method of the phosphoric acid fertilizer of Claim 1 or 2 characterized by the above-mentioned. Concentrate sewage in the sewage treatment facility,
After adding a recovery material to the concentrated sewage and reacting phosphorus in the sewage with the recovery material, dewatering to obtain a phosphorus recovery product and sewage sludge,
The method for producing a phosphate fertilizer according to claim 1 , 2 or 3 , wherein the calcium source is mixed with the phosphorus recovery product and sewage sludge obtained by dehydration and calcined.

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