JP6434725B2 - Method for melting phosphorus-containing material and method for operating melting furnace - Google Patents

Description

  In the present invention, when a phosphorus-containing material such as sewage sludge is melt-treated, the phosphorus component contained in the phosphorus-containing material is prevented from being volatilized into the exhaust gas, and the phosphorus component is captured in the slag. The present invention relates to a method for melting a contained material and a method for operating a melting furnace.

  Sludge generated at a sewage treatment plant is slag by melting in a melting furnace for the purpose of volume reduction, stabilization and reuse.

  For example, as shown in FIG. 8, polyferric sulfate, which is an example of a flocculant, is added to the concentrated sludge and agglomerated, and then dehydrated by the dehydrator 1 and the dehydrated sludge stored in the storage pit 2 is sequentially dried. A pretreatment step in which the dried sludge dried in 3 is stored in the hopper 4, a melting step in which the sewage sludge whose water content is adjusted and reduced in the pretreatment step is sequentially introduced from the hopper 4 into the melting furnace 5 and melted. The molten slag is made into a slag through a cooling step in which it is cooled and solidified.

  The exhaust gas discharged from the melting furnace 5 is processed through a waste heat boiler 6, a dry electrostatic precipitator 7, a flue gas treatment tower 8, and a wet electrostatic precipitator 9, and the return water of the wet electrostatic precipitator 9 is purified by a water treatment facility. Yes.

  In recent years, in order to prevent eutrophication of wastewater after sewage treatment, a dephosphorization process is performed by advanced treatment of sewage, and the concentration of phosphorus components contained in excess sludge generated at a sewage treatment plant has increased. When melting such sewage sludge with a high concentration of phosphorus component, if the phosphorus component in the sludge volatilizes in the melting furnace and moves to the flue along with dust, it becomes a phosphate compound with high adhesion and corrosivity. Various countermeasures have been proposed to cause problems such as flue blockage and exhaust gas treatment equipment corrosion.

  In Patent Document 1, an appropriate value of the Fe / P ratio is determined as an empirical rule in the correlation between the Fe / P ratio in the sewage sludge and the ignition loss VTS in advance, and the sewage sludge as the melt is analyzed to obtain Fe. The iron component is added to the sewage sludge before being introduced into the melting furnace so that the Fe / P ratio of the analysis value and VTS are larger than the appropriate value of the rule of thumb, so that the phosphorus component can be removed from the slag side. The technology to capture is proposed.

By the way, when melting sewage sludge in a melting furnace, if it is melted as it is, the melting point of the sludge increases, and there is a possibility that the meltability may deteriorate, so it is processed to lower the melting point by adjusting the sludge components in advance. ing. Usually, slaked lime Ca (OH) ₂ , silica sand (SiO ₂ ) or the like is added to the sludge so that the basicity represented by CaO / SiO ₂ [w / w] falls within a predetermined range.

  Even if the phosphorus component, which is an acidic oxide in the sludge, is volatilized by a reduction reaction that occurs during the melting process, it immediately binds to the added iron and is captured in the slag as a metal iron phosphide (metal phosphorus compound).

  In addition, it is known that ferrous oxide (FeO) also exhibits a melting point lowering action, and when the sludge contains ferrous oxide (FeO), the melting point tends to decrease.

  In Patent Document 2, before introducing sludge into a melting furnace, a phosphorus fixing substance made of a trivalent metal is added to sludge containing moisture, and phosphorus and phosphoric acid in the sludge are generated in the slag generated in the furnace. A sludge melting method is proposed in which a phosphorus fixing substance is reacted to fix it as a metal phosphorus compound or metal phosphate compound. As the phosphorus fixing substance, ferric oxide, ferric hydroxide, ferric chloride, sulfuric acid Trivalent iron compounds such as diiron and aluminum compounds such as aluminum oxide, aluminum hydroxide, and aluminum sulfate are disclosed. This technology focuses on the characteristic that phosphorus, which is a pentavalent element, easily binds to a trivalent metal.

JP 2006-15173 A Japanese Patent Laid-Open No. 2001-9500

  However, all of the above-described conventional techniques are techniques for capturing a phosphorus component as a metal compound in slag, and if such metal-like particles are mixed in the slag, for example, as concrete aggregate or cement raw material. There is a problem in that it cannot be reused as it is, and a separate separation / separation process, which is expensive for removing the metallic particles, is required.

In addition, when the technique disclosed in Patent Document 1 is employed, a basicity adjusting agent is added to the sludge to ensure a solubility of 60% or more at about 1300 ° C., and the basicity (CaO / SiO ₂ ) Must be adjusted to a narrow range of 0.4 to 0.8, but it often fails to follow the fluctuations in the composition of the target sludge and often deviates from this range, causing problems in stable operation. was there. For this reason, the furnace must be operated at a higher melting temperature, and it becomes difficult to effectively suppress the volatilization of the phosphorus component, as well as causing refractory wear and increasing the consumption of fossil fuels. there were.

  Furthermore, unoxidized iron powder generates heat when it reacts with moisture, so it must be added to the sludge immediately before being introduced into the melting furnace in order to avoid ignition accidents, etc. There was also a problem that it was not distributed. Therefore, in order to prevent volatilization of the phosphorus component, iron powder must be added excessively to the sludge, and as a result, the metal particles mixed in the slag, that is, the metal phosphorus compound containing iron phosphide increases. It was. Especially in recent years, the price of iron powder has been rising, and the running cost for melting phosphorus-containing materials including sewage sludge while avoiding the volatilization of phosphorus components has become very high, so the cost of recycling slag is also high In addition, there is a need for an economical treatment method.

  In view of the above-mentioned problems, the object of the present invention is to reduce the contamination of the phosphorous component, while suppressing the volatilization of the phosphorous component and reducing the mixing of the metal phosphorous compound containing iron phosphide in the slag. It is in providing a method and a method of operating a melting furnace.

In order to achieve the above-described object, the first characteristic configuration of the phosphorus-containing material melting method according to the present invention is that phosphorus is 0.04 wt% or more of the dry substance equivalent as described in claim 1 of the claims. A pretreatment step for adjusting the water content of the contained phosphorus-containing material, a melting step for melting the phosphorus-containing material whose water content has been adjusted in the pretreatment step into a melting furnace, and a melting generation in the melting step A cooling step of solidifying the slag by cooling, wherein the iron compound addition step of adding a trivalent iron compound to the phosphorus-containing material is the pretreatment step or before and after the pretreatment step soluble run, in the previous SL melting step, the phosphorus-containing material in a reducing atmosphere trivalent iron compounds added in the iron compound addition step is retained is reduced to divalent iron compounds Doing, it is possible to prevent the volatilization of phosphorus component contained in the phosphorus-containing material, in terms of capturing the slag phosphorus component while suppressing transition to the metal-containing phosphorus compound iron phosphide phosphorus component.

If trivalent iron compounds Unlike iron powder, since there is no risk of heat generation be added to the phosphorus-containing substances wet, such as sewage sludge, preprocessing step of adjusting the water content relative to the phosphorus-containing substances Alternatively, it can be added before or after that, so that the phosphorus-containing substance and the iron compound can be sufficiently mixed so that they are homogeneously distributed. When mixtures of such trivalent iron compound and a phosphorus-containing material is charged into the melting furnace, the melting point lowering action by ferrous oxide (FeO) produced from trivalent iron compound melting process expression For example, when the melting temperature is about 1300 ° C., it is possible to ensure a solubility of 60% or more in a range wider than the preferable basicity of the phosphorus-containing material with respect to iron of 0.4 to 0.8, and in the melt. The new finding that volatilization of the phosphorus component of the slag is suppressed and the phosphorus is trapped in the slag in a form that is not a metal phosphorus compound.

According to the new knowledge, since the basicity adjustment range is widened, the amount of the basicity adjusting agent used is small, and the slag is reduced by the adjusted basicity and the melting point lowering effect of ferrous oxide (FeO). Since the melting temperature of can be further lowered, the volatilization amount of the phosphorus component can be greatly reduced. Moreover, unlike the case where iron powder (Fe) is added, there is no possibility of heat generation , so that it can be sufficiently mixed with the phosphorus-containing substance in advance, so that it is not necessary to add an excessive amount of iron compound, and as a result, it is mixed into the slag. The amount of metal particles containing a metal phosphorus compound can also be greatly reduced. Such an iron compound can be obtained at a lower price than the price of iron powder, which has been on the rise in recent years, so that the running cost can be greatly reduced overall, and the obtained slag can be effectively reused.

  In the second characteristic configuration, as described in claim 2, in addition to the first characteristic configuration described above, the phosphorus-containing substance is sewage sludge, and the water content of the sewage sludge is adjusted in the pretreatment step. It is in.

  Sewage sludge is an object of suitable melting treatment as a phosphorus-containing substance, and the melting treatment is efficiently performed by adjusting moisture from the sewage sludge in the pretreatment step.

In the third characteristic configuration, as described in claim 3, in addition to the first or second characteristic configuration described above, in the iron compound addition step, the amount of iron (Fe) is reduced to a dry substance equivalent amount DS ( The trivalent iron compound is added so as to fall within a range of 1 to 8 wt% with respect to (Dry Solid).

As iron (Fe) content is in the range of 1～8Wt% relative to the dry matter equivalent amount DS (Dry Solid), the amount of trivalent iron compound that will be added to the phosphorus-containing material is adjusted, the melt Even if the temperature is relatively low, it becomes possible to secure a solubility of 60% or more, and phosphorus can be effectively trapped in the slag while suppressing the volatilization of the phosphorus component.

The fourth characterizing feature of the can, as noted in the claim 4, in addition from the first described above in the third one characteristic feature of the trivalent iron compounds that are used in the iron compound addition step, tetroxide ferric _{(Fe 3 O} 4), ferric oxide _{(Fe 2 O} 3), ferric hydroxide (Fe _{(OH) 3),} ferric chloride (FeCl _3), ferric sulfate ( Fe _{2 (SO 4) 3)} lies in a either one or more.

Trivalent iron compound that will be added to the phosphorus-containing material is not limited to one type, tetraoxide ferric _{(Fe 3 O} 4), acid ferric _{(Fe 2 O} 3), the hydroxide ferric (Fe _{(OH) 3),} ferric (FeCl ₃₎ chloride, Ru can be used either one kind or plural kinds of ferric sulfate _{(Fe 2 (SO 4) 3} ).

  In the fifth feature configuration, as described in claim 5, in addition to any of the first to fourth feature configurations described above, a basicity adjuster is added to the phosphorus-containing material to improve the phosphorus-containing material. The basicity adjustment step of adjusting the basicity so as to fall within the range of 0.2 to 1.0 is performed before the melting step.

  When the basicity of the phosphorus-containing substance is adjusted to a range of 0.2 to 1.0, ferrous oxide produced during melting treatment from a divalent or trivalent iron compound added in the iron compound addition step Combined with the melting point lowering effect expressed by (FeO), it is possible to ensure a preferable solubility at a relatively low melting point.

  In the sixth feature configuration, as described in claim 6, in addition to any one of the first to fourth feature configurations described above, a basicity adjuster is added to the phosphorus-containing material to improve the phosphorus-containing material. The basicity adjustment step for adjusting the basicity so as to fall within the range of 0.7 ± 0.1 is that the basicity adjustment step is executed before the melting step.

  When the basicity of the phosphorus-containing substance is adjusted to a range of 0.7 ± 0.1, ferrous oxide produced during the melting treatment from the divalent or trivalent iron compound added in the iron compound addition step Combined with the melting point lowering action expressed by (FeO), it becomes possible to secure a preferable solubility at a lower melting point, and to effectively suppress the volatilization of the phosphorus component.

  In the seventh feature configuration, as described in claim 7, in addition to the sixth feature configuration described above, the ratio of iron (Fe) phosphorus (P) silica (Si) (= Fe / (P + Si) [mol / Mol]) is included in the iron compound addition step so that the iron compound is added so that the iron compound is in the range of 0.2 to 0.8, and the iron phosphorus silica ratio adjustment step is performed before the melting step. There is in point to perform.

  When the iron compound is added so that the iron-phosphorus-silica ratio is in the range of 0.2 to 0.8 in the iron compound addition step, a preferable flow rate can be secured with a very low melting point compared to the conventional one, Volatilization of the phosphorus component can be effectively suppressed, and the amount of fossil fuel used can be suppressed.

  In addition to any of the fifth to seventh feature configurations described above, the eighth feature configuration is the addition of the iron compound so that the solubility is 60% or more. The step and the basicity adjustment step are performed before the melting step.

  By adjusting the addition amount of the iron compound added in the iron compound addition step and the addition amount of the basicity adjusting agent added in the basicity adjustment step, stable melting treatment can be performed at a relatively low melting point. The volatilization of the phosphorus component can be effectively suppressed.

  As described above, according to the present invention, it is possible to reduce the mixing of the metal phosphorus compound containing iron phosphide in the slag while suppressing the volatilization of the phosphorus component. It has become possible to provide a method for operating a melting furnace.

Explanatory drawing of the melting processing method of phosphorus content material by the present invention (A), (b) Explanatory drawing of melting furnace (A) is a characteristic diagram of basicity and solubility of sludge to which iron powder or ferric oxide is added, (b) is iron (Fe) phosphorus (P) of sludge to which iron powder or ferric oxide is added Characteristic diagram of silica (Si) ratio (= Fe / (P + Si)) and phosphorus immobilization rate Characteristic diagram of basicity and flow rate of sludge with respect to iron (Fe) content (A) is explanatory drawing of slag obtained by melting the sludge which added ferric oxide, (b) is explanatory drawing of slag obtained by melting the sludge which added iron powder. (A)-(c) is explanatory drawing of a solubility test (A) is an explanatory view showing an example of a state in which phosphorus is captured by a slag in a form that is not a metal, that is, a state in which the phosphorus element is taken into the glass via oxygen atoms that become bridges, and (b) is an element of phosphorus Explanatory drawing showing an example in which is incorporated in a state that does not contain oxygen atoms and exhibits metallic properties such as extensibility, gloss, and high thermal conductivity Illustration of conventional sewage sludge melting treatment method

  Hereinafter, embodiments of a method for melting a phosphorus-containing material and a method for operating a melting furnace according to the present invention will be described.

FIG. 1 shows a melting treatment method when the phosphorus-containing substance is sewage sludge. Concentrated sludge extracted as surplus sludge from a sewage treatment apparatus that performs biological treatment using an activated sludge method, a membrane separation activated sludge method, or the like is ferric sulfate {(Fe ₂ OH) _n (SO4), which is an example of a flocculant. ) _{3-n / 2} } _m is added and agglomerated, and then dehydrated by a dehydrator 1 such as a screw press or a filter press and stored in the storage pit 2. In this case, the water content of the dewatered sludge is about 70 to 85%.

The dehydrated sludge stored in the storage pit 2 is added with slaked lime (Ca (OH) ₂ ) or SiO ₂ as a basicity adjusting agent and ferric oxide (Fe ₂ O ₃ ) as a trivalent iron compound. Then, it is put into a steam-type dryer 3 and dried with stirring and becomes dry sludge, which is stored in the hopper 4. In addition, the moisture content of dry sludge becomes about 20 to 30% by this drying process.

The process of agglomerating, dewatering, and drying the concentrated sludge is a pretreatment step that adjusts the moisture in the sewage sludge (here, removes moisture), and the step that adds the basicity adjuster becomes the basicity adjustment step that oxidizes the sewage sludge. The step of adding ferric iron (Fe ₂ O ₃ ) is the iron compound addition step. The iron compound addition step may be executed in any step as long as it is executed before or after the pretreatment step described above.

  In addition, as a method of adjusting the moisture in the pretreatment step, a method using a mechanical mechanism such as a filter press, centrifugal dehydration, screw press, etc., direct or indirect using reaction heat by chemical reaction, retained heat of steam or exhaust gas, etc. A heating method, a method of adding waste paper, dried sludge, or the like can be used to relatively reduce moisture.

  Sewage sludge to which the water content is adjusted to 30% or less suitable for melting in the pretreatment step and the basicity adjusting agent and the trivalent iron compound are added is sequentially fed from the hopper 4 to the melting furnace 5 through the conveyor mechanism. The slag that has been melted and melted in the melting furnace 5 is then cooled and solidified. As the melting furnace, a surface melting furnace, an electric melting furnace, a swirling melting furnace, a coke bed furnace, or the like can be used. In particular, a swirling melting furnace or a surface melting furnace can be suitably used. In this embodiment, a rotary surface melting furnace belonging to the surface melting furnace is used.

  As shown in FIG. 2, the rotary surface melting furnace 5 has a bottomed structure in which an inner cylinder 53 standing around a ceiling portion 52 in which a combustor 51 is disposed and an outlet 54 formed in the center of the bottom portion. The outer cylinder 55 is disposed around the common axis, and includes a rotation mechanism that rotates the outer cylinder 55 around the axis, and the outer cylinder 55 is configured to be rotatable with respect to the inner cylinder 53.

  The combustor 51 is composed of a burner that mixes and burns fuel supplied from a fuel tank and air supplied from a blower so that the temperature of the molten slag becomes approximately 1300 ° C. by adjusting the amount of fuel supplied. In addition, the temperature of the main combustion chamber 56 is adjusted.

  The dried sludge charged into the storage portion 57 formed between the inner cylinder 53 and the outer cylinder 55 is supplied to the main combustion chamber 56 from the lower edge of the inner cylinder 53 by the relative rotation of the inner cylinder 53 and the outer cylinder 55. The The exposed surface of the sludge is melted by the combustion flame of the combustor 51, and is dripped and discharged as molten slag from the spout 54 formed at the center of the bottom surface of the main combustion chamber 56. The molten slag dripped from the tap outlet 24 is rapidly cooled in a water tank disposed below to become a granulated slag.

  That is, the melting step is performed in the rotary surface melting furnace 5, and the cooling step for cooling and solidifying the slag melted in the melting step is performed in the water tank disposed below the spout 54.

  Returning to FIG. 1, the exhaust gas discharged from the melting furnace 5 is processed through a waste heat boiler 6, a dry electrostatic precipitator 7, a flue gas processing tower 8, and a wet electrostatic precipitator 9. In the purification process.

When such a kneaded mixture of ferric oxide (Fe ₂ O ₃ ) and sludge is put into the melting furnace, the periphery of ferric oxide (Fe ₂ O ₃ ) is reduced in the process of melting the sewage sludge. The melting point lowering action is expressed by the reduced ferrous oxide (FeO) that is formed into an atmosphere. For example, when the melting temperature is about 1300 ° C., the preferable basicity of sludge for iron is less than 0.4 to 0.8. A solubility of 60% or more can be secured over a wide range, and the volatilization of the phosphorus component in the sludge is suppressed, so that phosphorus is captured in the slag in a form that is not metal. That is, the phosphorus component in the sewage sludge is trapped in the slag in a non-metal form while suppressing the transition to the metal phosphorus compound containing iron phosphide.

  FIG. 7 (a) shows the bonding state of some elements constituting the glass (slag), and the state in which phosphorus (P) is captured by the slag in a form that is not a metal (in the figure, a one-dot chain line) A portion surrounded by a circle) is illustrated. That is, the phosphorus element (P) is trapped in the glass via the oxygen atom (O) that becomes a bridge.

  FIG. 7B shows an example of the state in which the phosphorus element (P) is incorporated in the slag in a state that does not include an oxygen atom for bridging and exhibits metallic properties such as ductility, gloss, and high thermal conductivity. It is shown. This becomes metal particles such as a metal phosphorus compound containing iron phosphide.

If ferric oxide (Fe ₂ O ₃ ) is used instead of iron powder (Fe), not all of the phosphorus is captured in the slag in a non-metallic form, and some of it is made of iron phosphide. It is trapped by the slag in the form, and part of it will be volatilized, but most of the ferric oxide (Fe ₂ O ₃ ) becomes ferrous oxide (FeO) and is fixed to the slag, and in the sewage sludge It means that most of the phosphorus contained is trapped in the slag in a non-metallic form.

The entire main combustion chamber does not have to be a reducing atmosphere, and at least the periphery of ferric oxide (Fe ₂ O ₃ ) only needs to be a reducing atmosphere. In such an environment, organic substances contained in the sludge are thermally decomposed. This is realized by a reducing gas such as carbon monoxide which is generated when

On the other hand, when the inside of the furnace is made a reducing atmosphere for a long time, iron is reduced from slag of lFeO-mP ₂ O ₅ -nCaO-oSiO ₂ system (l, m, n, and o are arbitrary integers) to form metal particles. As the phosphorus component is volatilized, the local reducing atmosphere or the weak reducing atmosphere is a better condition for trapping the phosphorus component in the slag.

That is, as shown in FIG. 2 (b), the material to be melted put into the melting furnace is melted from the surface and dropped from the outlet 54 in the center of the bottom, but the molten slag layer L1 and the unmelted In the boundary region with the layer L2, the organic component contained in the melt is thermally decomposed to form a reducing atmosphere. Under such a reducing atmosphere, ferric oxide (Fe ₂ O ₃ ) is reduced to ferrous oxide (FeO), which functions as a melting point depressant for slag, as shown in FIG. It is fixed to the slag in a manner. Since melting | fusing point of slag falls, volatilization of phosphorus is suppressed and iron is capture | acquired by slag, without couple | bonding as a metal phosphorus compound. That is, it may be reducible in the vicinity where the material to be melted, which is a phosphorus-containing material, changes to slag, and the inside of the furnace may be either an oxidizing atmosphere or a reducing atmosphere.

  Since the adjustment range is wider than the preferable basicity of 0.4 to 0.8 of the sludge with respect to iron powder (Fe), the amount of the basicity adjusting agent used can be reduced, and the adjusted basicity and the first oxidation Since the melting point of the slag can be further lowered by the melting point lowering action by iron (FeO), the volatilization amount of the phosphorus component that causes blockage or corrosion of the exhaust gas treatment facility or the like can be greatly reduced.

Unlike iron powder (Fe), trivalent iron compounds such as ferric oxide (Fe ₂ O ₃ ) remove heat from sewage sludge because there is no risk of heat generation even when added to wet sludge. Can be added at any time before or after the pretreatment step, and therefore, unlike the case of adding iron powder (Fe), an opportunity to sufficiently knead with sludge can be secured in advance, so an excessive amount of iron compound is added. And can be uniformly dispersed. As a result, the amount of metal particles mixed in the slag can be greatly reduced.

  Divalent or trivalent iron compound so that the amount of iron (Fe) falls within the range of 1 to 8 wt%, preferably 3 to 5 wt% with respect to the dry substance equivalent DS (Dry Solid) in the iron compound addition step Is preferably added, and even when the melting temperature is relatively low, a solubility of 60% or more can be secured, and phosphorus is effectively trapped in the slag while suppressing volatilization of the phosphorus component. Will be able to.

The iron compound added in the iron compound addition step is not limited to the trivalent iron compound but may be a divalent iron compound. The trivalent iron compound is not limited to ferric oxide (Fe ₂ O ₃ ), but ferric hydroxide (Fe (OH) ₃ ), ferric chloride (FeCl ₃ ), and ferric sulfate (Fe _2). Any one or more of (SO ₄ ) ₃ ), polyferric sulfate {(Fe ₂ OH) _n (SO 4) _{3 -n / 2} } _{m, and the} like can be suitably used. In the present embodiment, ferric sulfate {(Fe ₂ OH) _n (SO 4) _{3-n / 2} } _m used for agglomerating the concentrated sludge is added, and then ferric oxide (Fe ₂ The iron compound addition step is realized such that O ₃ ) is added.

Moreover, as a bivalent iron compound used at an iron compound addition step, ferrous oxide (FeO), ferrous hydroxide (Fe (OH) ₂ ), ferrous chloride (FeCl ₂ ), ferrous sulfate Any one or more of (FeSO ₄ ), ferric tetroxide (Fe ₃ O ₄ ), ferrous carbonate (FeCO ₃ ) and the like can be suitably used. A combination of divalent and trivalent iron compounds may be used.

For example, ferric oxide (Fe ₂ O ₃ ) becomes ferric tetroxide (Fe ₃ O ₄ ) by the following reduction reaction, and is further reduced to ferrous oxide (FeO).
3Fe ₂ O ₃ + CO → 2Fe ₃ O ₄ + CO ₂
Fe ₃ O ₄ + CO → 3FeO + CO ₂

For example, ferric chloride (FeCl ₃ ) becomes ferric oxide (Fe ₂ O ₃ ) by the following hydrolysis reaction, and further becomes ferrous oxide (FeO) by a reduction reaction.
2FeCl ₃ + 3H ₂ O → Fe ₂ O ₃ + 6HCl

For example, ferric hydroxide (Fe (OH) ₃ ) becomes ferric oxide (Fe ₂ O ₃ ) by the following thermal decomposition reaction, and further becomes ferrous oxide (FeO) by a reduction reaction.
2Fe (OH) ₃ → Fe ₂ O ₃ + 3H ₂ O

For example, ferric sulfate (Fe ₂ (SO ₄ ) ₃ ) becomes ferric oxide (Fe ₂ O ₃ ) by the following thermal decomposition reaction, and further becomes ferrous oxide (FeO) by a reduction reaction.
Fe ₂ (SO ₄ ) ₃ → Fe ₂ O ₃ + 3SO ₃

For example, ferrous sulfate (FeSO ₄ ) becomes ferric oxide (Fe ₂ O ₃ ) by the following reduction reaction, and further reduced to ferrous oxide (FeO).
4FeSO ₄ + C → 2Fe ₂ O ₃ + 4SO ₂ + CO ₂

For example, ferrous carbonate (FeCO ₃ ) becomes ferrous oxide (FeO) by the following thermal decomposition reaction.
FeCO ₃ → FeO + CO ₂

  Further, it is preferable that the basicity adjusting step for adjusting the basicity of the sewage sludge to be in the range of 0.2 to 1.0 by adding a basicity adjusting agent to the sewage sludge is performed before the melting step. Compared with the addition of iron powder (Fe), combined with the melting point lowering effect expressed by ferrous oxide (FeO) produced during the melting treatment from the trivalent iron compound added in the iron compound addition step Therefore, it is possible to secure a preferable solubility at a low melting point.

  More preferably, the basicity adjustment step of adjusting the basicity of the sewage sludge to a range of 0.7 ± 0.1 by adding a basicity adjusting agent to the sewage sludge is performed before the melting step, and an iron compound is added. Combined with the melting point depressing action expressed by the ferrous oxide (FeO) produced during the melting process from the trivalent iron compound added in the step, it becomes possible to secure a preferable solubility at a lower melting point. The volatilization of the phosphorus component can be effectively suppressed.

  Furthermore, the iron phosphorous silica in which the iron compound is added so that the iron (Fe) phosphorous (P) silica (Si) ratio (= Fe / (P + Si) [mol / mol]) falls within the range of 0.2 to 0.8. Preferably, the ratio adjustment step is included in the iron compound addition step, and the iron-phosphorus-silica ratio adjustment step is performed before the melting step.

  When the iron compound is added so that the iron-phosphorus-silica ratio falls within the range of 0.2 to 0.8 in the iron compound addition step, a preferable solubility can be secured at a very low melting point compared to the conventional case. The phosphorus immobilization rate is 80% or more, so that the volatilization of the phosphorus component can be effectively suppressed and the amount of fossil fuel used can be suppressed.

  Furthermore, it is preferable to perform the iron compound addition step and the basicity adjustment step before the melting step so that the solubility is 60% or more, and to perform a stable melting process at a relatively low temperature. And the volatilization of the phosphorus component can be effectively suppressed.

  That is, for a melting furnace that melts sewage sludge whose moisture has been adjusted and removed, the amount of iron (Fe) in the sewage sludge is in the range of 1 to 8 wt% with respect to the dry substance equivalent DS (Dry Solid). Thus, it is preferable to operate so as to melt the sewage sludge in such a state that the divalent or trivalent iron compound is added and stirred and then charged into the melting furnace so that the periphery of the iron compound is in a reducing atmosphere.

  In addition, there is no restriction | limiting in the order of a basicity adjustment step and an iron compound addition step, It is good also as a step which mixes a basicity adjustment agent and an iron compound in advance, and adds together.

  INDUSTRIAL APPLICABILITY The present invention can be suitably used for a phosphorus-containing material containing 0.04 wt% or more of phosphorus in terms of dry matter. As such a phosphorus-containing material, in addition to sewage sludge, field soil, livestock manure The present invention is also suitably used for human waste sludge, phosphorus-containing ore residues, and the like. For example, 0.5 to 3 wt% sewage sludge, 0.04 to 1 wt% in field soil, 0.5 to 3 wt% in livestock manure, and 2-3 wt% in manure sludge. ing.

Below, the experimental result of the melting characteristic at the time of adding a trivalent iron compound to sewage sludge is demonstrated.
FIG. 3A shows iron powder (Fe) or ferric oxide (Fe ₂ O ₃ ) with respect to sample sludge in which basicity adjusting agent was added to sewage sludge after pretreatment to change the basicity. It shows the solubility characteristics when the test piece to which is added) is heated at 1300 ° C. using an electric furnace. In the figure, the characteristic indicated by the broken line is the characteristic of iron powder, and the characteristic indicated by the solid line is the characteristic of ferric oxide.

  The iron (Fe) phosphorus (P) silica (Si) ratio (= Fe / (P + Si) [mol / mol]) of the sample sludge is 0.45, and the amount of iron powder or ferric oxide added is dry, respectively. It is 5 wt% with respect to the substance conversion amount DS (Dry Solid).

As shown in FIGS. 6 (a), 6 (b), and 6 (c), the degree of dissolution means that a test piece is filled on one end side of a ship-shaped magnetic board, and the magnetic board is placed so that the filling portion is on the upper side. Measure the state of the test piece when it is left at a predetermined angle (5 °) and left in an electric furnace maintained at a predetermined temperature for a predetermined time (15 minutes), then taken out and cooled at room temperature. The value is calculated based on the following equation.
Dissolution rate (M value) = (L−L ₀ ) / L ₀ × 100

  Usually, the temperature at which the solubility is 60% is evaluated as the melting point, the melting furnace can be operated at a solubility of 40%, and if the solubility is 60% or more, it is judged that the meltability is high. . The magnetic board has a length of 150 mm, a width of 20 mm, and a height of 70 mm, and is formed in a capacity of about 10 ml. The length of the test piece filled in the magnetic board is set to 70 mm.

As shown in FIG. 3 (a), when iron powder is added, it is possible to ensure a solubility of 60% or more in a basicity range of about 0.4 to 0.8 (R-Fe). On the other hand, when ferric oxide was added, it was found that a solubility of 60% or more can be secured in a basicity range of about 0.2 to 1.0 (R—Fe ₂ O ₃ ). .

  That is, when ferric oxide is added, the basicity adjustment range in which a solubility of 60% or more can be ensured is widened, so that the addition amount of the basicity adjusting agent can be suppressed low. .

  And, it becomes possible to ensure a very high solubility within a range of 0.7 ± 0.1, and when the basicity is adjusted within this range, the melting temperature is about 50 ° C. lower than 1300 ° C. The melting furnace can be operated well. As a result, it has been found that the volatilization of the phosphorus component contained in the sludge can be more effectively suppressed.

  In FIG. 3 (b), iron powder or ferric oxide was added to the sample sludge whose basicity was adjusted to 0.7 by adding a basicity adjusting agent to the sewage sludge after pretreatment. The phosphorus immobilization rate is shown when a test piece with a different (Fe) phosphorus (P) silica (Si) ratio (= Fe / (P + Si) [mol / mol]) is heated at 1300 ° C. using an electric furnace. Has been. In the figure, the characteristic indicated by the broken line is the characteristic of iron powder, and the characteristic indicated by the solid line is the characteristic of ferric oxide.

  As apparent from the characteristics shown by the solid line in FIG. 3B, when ferric oxide is added and the iron (Fe) phosphorus (P) silica (Si) ratio of the sample sludge is adjusted to 0.2, it is about 80. % Phosphorous immobilization rate was obtained, and it was found that a high phosphorus immobilization rate of about 90% was obtained when adjusted to 0.4 or more.

  In the characteristic diagram, data obtained by adding ferric oxide to such sludge and operating in an actual furnace are plotted with black triangles. In the actual furnace, the basicity is adjusted to a range of 0.7 ± 0.1, and the iron (Fe) phosphorus (P) silica (Si) ratio is set to 0.35, 0.45, 0.51. The data that was run and sampled at that time is indicated by black triangles.

  From the above, it is preferable to adjust the iron (Fe) phosphorus (P) silica (Si) ratio to a range of 0.2 to 0.8, more preferably to a range of 0.25 to 0.55, It became clear that adjusting to the range of 0.30 to 0.50 is most preferable. By adjusting the iron (Fe) phosphorus (P) silica (Si) ratio in the range of 0.30 to 0.50, phosphorus can be well fixed in the slag while suppressing the addition amount of ferric oxide. This is also preferable in that the running cost can be suppressed. Lowering the phosphorus immobilization rate can reduce the running cost required for iron compounds, but increases the frequency of cleaning dust adhering to exhaust gas treatment facilities and flue. Therefore, it is also possible to adjust at least the phosphorus immobilization rate to about 60% in consideration of the cleaning frequency. It has been confirmed that the same tendency exists even when the basicity is in the range of about 0.2 to 1.0.

  FIG. 4 shows a sample sludge having a basicity in the range of about 0.2 to 1.2 in a range where the iron (Fe) amount is 3 to 5 wt% in terms of the weight ratio to the dry substance equivalent DS (Dry Solid). The solubility characteristics when ferric oxide is added are shown. It is the characteristic at the time of heating at 1300 degreeC using an electric furnace. Although it depends on the basicity, it has been found that if the amount of iron (Fe) is adjusted to fall within the range of 3 to 5 wt% with respect to the dry substance equivalent DS, a solubility of 60% or more can be secured over a wide range. did.

  5 (a) and 5 (b), the basicity is adjusted to 0.7, and iron powder or ferric oxide is added so that the amount of iron (Fe) is less than the dry substance equivalent DS. The photograph of the slag when the test piece adjusted to 3 wt% is melted at 1300 ° C is shown. FIG. 5A shows the slag when ferric oxide is added, and FIG. 5B shows the slag when iron powder is added.

When iron powder (Fe) is added to the sludge, it is observed that spherical metal particles are deposited on the slag (see an area surrounded by white circles in FIG. 5B). Component analysis of the metal particles revealed that it was a metal phosphorus compound containing iron (Fe) or iron phosphide (Fe ₂ P) as a main component. On the other hand, in FIG. 5A, ferrous oxide (Fe ₂ O ₃ ) added to the sludge was reduced to ferrous oxide (FeO) in a state where almost no metal particles could be confirmed. It was confirmed that phosphorus was trapped in the slag in a non-metal form without being dissolved in the slag in a state and combining the phosphorus component in the sludge as iron and a metal phosphorus compound.

The ferric oxide used in this example was a powder having a median diameter of 11 μm (d ₅₀ ). However, it can be used from a powder having a median diameter of about 1 mm (d ₅₀ ), and the particle size can be increased from the viewpoint of increasing the reaction rate. The finer is more preferable.

  The “iron powder”, “ferric oxide” or “iron compound” described in the present specification and the like are not limited to those having a purity of 100%, but include cases where some impurities are included. In other words, if “iron powder”, a part of the compound is a compound such as iron oxide, and if it is an iron compound, iron remains in the form of a compound without iron. In other words, the description mainly means the one containing the substance. Further, the iron compound may be a mixture of different iron compounds.

1: Dehydrator 2: Storage pit 3: Dryer 4: Hopper 5: Melting furnace

Claims (8)

A pretreatment step for adjusting the water content of the phosphorus-containing material containing 0.04 wt% or more of the dry matter equivalent of phosphorus, and a phosphorus-containing material whose water content has been adjusted in the pretreatment step is charged into the melting furnace A melting step of a phosphorus-containing substance, comprising: a melting step for melting; and a cooling step for cooling and solidifying the slag melt-generated in the melting step,
Run the iron compound addition step of adding the trivalent iron compound to the phosphorus-containing material wherein the preprocessing step or before and after, in the previous SL melting step, trivalent iron compounds added in the iron compound addition step 2 By melting the phosphorus-containing material in a reducing atmosphere that is reduced and retained by a valent iron compound, the phosphorous component contained in the phosphorus-containing material is prevented from being volatilized and the metal phosphorus compound containing iron phosphide as the phosphorus component A method for melting a phosphorus-containing substance, in which the phosphorus component is captured by the slag while suppressing the transfer of water.   The method for melting a phosphorus-containing substance according to claim 1, wherein the phosphorus-containing substance is sewage sludge, and the moisture of the sewage sludge is adjusted in the pretreatment step. In the iron compound addition step, according to claim 1 or 2 wherein the trivalent iron compound as fall within the scope of 1～8Wt% relative iron (Fe) weight dry substance equivalent amount DS (Dry Solid) is added Method for melting phosphorus-containing material. Trivalent iron compounds that are used in the iron compound addition step, tetroxide ferric _{(Fe 3 O} 4), acid ferric _{(Fe 2 O} 3), ferric hydroxide (Fe (OH) ₃ ) Melting of a phosphorus-containing substance according to claim 1, which is one or more of ferric chloride (FeCl ₃ ) and ferric sulfate (Fe ₂ (SO ₄ ) ₃ ) Processing method.   The basicity adjusting step of adding a basicity adjusting agent to the phosphorus-containing material so that the basicity of the phosphorus-containing material is in the range of 0.2 to 1.0 is performed before the melting step. A method for melting a phosphorus-containing substance according to any one of 1 to 4.   The basicity adjustment step of adjusting the basicity of the phosphorus-containing material so that the basicity of the phosphorus-containing material falls within a range of 0.7 ± 0.1 by adding a basicity adjusting agent to the phosphorus-containing material is performed before the melting step. A method for melting a phosphorus-containing substance according to any one of 1 to 4.   Iron-phosphorus-silica ratio adjustment in which the iron compound is added so that the iron (Fe) phosphorus (P) silica (Si) ratio (= Fe / (P + Si) [mol / mol]) falls within the range of 0.2 to 0.8. The method for melting a phosphorus-containing substance according to claim 6, wherein a step is included in the iron compound adding step, and the iron-phosphorus-silica ratio adjusting step is executed before the melting step. The melting treatment of a phosphorus-containing substance according to any one of claims 5 to 7, wherein the iron compound addition step and the basicity adjustment step are executed before the melting step so that the solubility is 60% or more. Method.