JP6261706B1 - How to clean fly ash - Google Patents

Abstract

An object of the present invention is to provide a fly ash cleaning method capable of suppressing the amount of water supplied for cleaning the fly ash. A method for cleaning fly ash according to the present invention includes a mixing step of mixing fly ash collected from exhaust gas neutralized with an alkaline neutralizing agent and cleaning water, and the mixing step. A solid-liquid separation step of obtaining a dehydrated cake and washed water by solid-liquid separation of the mixed solution of the fly ash and the washed water, wherein in the mixing step, the washed water is at least Recycle as part of the wash water until the soluble evaporation residue in the mixture is at least 20%. [Selection] Figure 2

Description

  The present invention relates to a fly ash cleaning method for cleaning fly ash generated when waste is incinerated.

  Since the acidic exhaust gas generated when the waste is incinerated cannot be discharged out of the system as it is, for example, as described in Patent Document 1, an alkaline neutralizing agent is blown and neutralized. After that, fly ash is collected and discharged out of the system through a chimney or the like. Various toxic substances such as salts generated by the neutralization reaction, unreacted neutralizers, and heavy metals are mixed in the fly ash collected from the neutralized exhaust gas as described above. Although the fly ash has utility value such as being used for landfill or cement raw material, it cannot be used in a state containing harmful substances. For this reason, various types of fly ash cleaning equipment have been proposed in the past for cleaning fly ash mixed with harmful substances.

  For example, the fly ash washing facility described in Patent Literature 1 includes a fly ash water washing device for washing fly ash and a dehydrator for dehydrating the washed fly ash. The fly ash cleaning equipment is configured such that fly ash and washing water are mixed by a fly ash water washing device to elute salts, neutralizing agents, and the like into the washing water. And the liquid mixture of the fly ash and washing water discharged | emitted from the fly ash water washing apparatus is spin-dry | dehydrated with a dehydrator, and this liquid mixture is isolate | separated into a spin cake and waste water.

  In the above fly ash cleaning facility, the dehydrated cake is put into a cement kiln when it is used as a cement raw material. The wastewater is purified by a wastewater treatment facility and discharged.

JP 2007-83144 A

  In the above conventional fly ash cleaning equipment, the drainage is discharged, so every time the fly ash is washed, new washing water must be supplied to the fly ash water washing device, and a large amount of water is washed to wash the fly ash. Wash water is required. As described above, the conventional fly ash washing equipment has a problem that a large amount of washing water is required for washing the fly ash, and there is room for improvement.

  Then, this invention makes it a subject to provide the washing method of the fly ash which can suppress the supply amount of the washing water for washing | cleaning fly ash in view of this situation.

Applicants have decided that the washed water obtained as a result of mixing fly ash collected from exhaust gas that has been neutralized with an alkaline neutralizing agent with washing water includes a plurality of types of salts, neutralizing agents, heavy metals, etc. Although the substance was dissolved, it was confirmed that there was no problem even if it was reused for cleaning fly ash.
Specifically, the applicant has determined that if the soluble evaporation residue in the mixed liquid of fly ash and washing water is kept lower than a predetermined concentration, the dissolved substance in the mixed liquid does not precipitate and precipitates. It was confirmed that washed water could be used without problems for washing fly ash because problems such as obstruction of the flow path with objects did not occur easily.
That is, the fly ash cleaning method according to the present invention was obtained by the mixing step of mixing the fly ash collected from the exhaust gas neutralized with an alkaline neutralizer and the washing water, and the mixing step. A step of obtaining a soluble evaporation residue concentration in a mixture of the fly ash and the washing water, a solid-liquid separation step of obtaining a dehydrated cake and washed water by solid-liquid separation of the mixture. In the mixing step, the washed water (excluding water obtained by washing the dehydrated cake) is used as at least a part of the washing water, and the soluble evaporation residue in the mixed solution is Reuse until at least 20%.

  When the washed water obtained in the solid-liquid separation process is reused for the fly ash washing, the washed water is concentrated. However, the fly ash washing method of the above configuration has a soluble evaporation residue in the mixed solution. Since the fly ash is washed with the washed water until it becomes at least 20%, the washed water can be reused as the washing water, so that the amount of water supplied for the washing water can be suppressed.

  As one aspect of the present invention, a neutralizing agent comprising an alkali metal may be used as the alkaline neutralizing agent.

  According to this configuration, since the neutralizing agent made of an alkali metal is used as the alkaline neutralizing agent, the pH of the washed water can be kept low. Therefore, the amount of chemicals required for neutralizing the washed water can be suppressed, and the washed water can be easily neutralized.

  As another aspect of the present invention, a sodium-based neutralizing agent is used as the neutralizing agent comprising the alkali metal, and in the mixing step, a soluble evaporation residue in the mixed solution is 20% or more and 35%. The washed water may be reused as at least part of the washed water so that

  According to such a configuration, among the neutralizing agents composed of alkali metals, the salts generated when using a sodium-based neutralizing agent are used when the neutralizing agents composed of other alkali metals such as potassium are used. It is more soluble in water than the salts produced (highly soluble in water). Therefore, if the soluble evaporation residue is 35% or less, the fly ash can be washed with washed water with almost no dissolved substance being deposited. Therefore, according to such a configuration, it is possible to wash fly ash in a state in which dissolved substances hardly precipitate, while increasing the soluble evaporation residue in the mixed solution, and sufficiently reuse the washed water. Can do.

  Moreover, as another aspect of the present invention, the fly ash cleaning method may include a rinsing step of rinsing the dehydrated cake.

  According to such a configuration, since the dewatering cake is provided with a rinsing step, the dewatering cake can be made into a property suitable for reuse, for example, as a cement raw material.

  As another aspect of the present invention, in the mixing step, water that has been rinsed and rinsed in the rinsing step may be reused as at least part of the washing water.

  According to such a configuration, the rinsed water used in the rinsing step can be used for washing the fly ash, so that the rinsed water can be effectively used.

  As mentioned above, according to this invention, the washing | cleaning method of the fly ash which can suppress the supply amount of the washing water for washing | cleaning fly ash can be provided.

FIG. 1 is a configuration diagram of a waste incineration facility, and is a configuration diagram for explaining a flow from generation of fly ash to washing of fly ash. FIG. 2 is a configuration diagram of the fly ash cleaning apparatus. FIG. 3 is a graph showing changes in pH of the wash water with time. FIG. 4 is a graph showing a change in electric conductivity of washing water with time. FIG. 5 is a graph showing the relationship between the liquid-solid ratio between the water used for cleaning the fly ash (the total of the wash water and the rinse water) and the fly ash and the desalting rate.

  In this embodiment, the soluble evaporated residue means the total amount of dissolved substances in water. The soluble evaporation residue is often expressed as ppm or mg / l as a ratio of dissolved substance to water, but in this embodiment, it is expressed as% as a ratio of dissolved substance to water. The soluble evaporation residue is obtained by heating water (raw water) in which dissolved substances are dissolved at 105 ° C. to evaporate the water, and dividing the weight of the residue by the weight of the raw water or the volume of the raw water. It is calculated by. In the present embodiment, the soluble evaporation residue is a ratio of dissolved substances to the weight of water, and is obtained by dividing the weight of the residue by the weight of raw water.

  The fly ash cleaning method of this embodiment includes a mixing step of mixing fly ash collected from exhaust gas neutralized with an alkaline neutralizing agent and cleaning water, and the flying ash obtained in the mixing step. A solid-liquid separation step of solid-liquid separation of a mixed solution of ash and the washing water to obtain a dehydrated cake and washed water. In the mixing step, the washed water is reused as at least a part of the washing water until the soluble evaporation residue in the mixed solution becomes at least 20%. Specifically, in the mixing step, the washed water is reused as at least part of the washing water so that the soluble evaporation residue in the mixed solution is 20% or more and 35% or less. May be.

  Further, the fly ash cleaning method of the present embodiment includes a rinsing step of rinsing the dehydrated cake, and in the mixing step, the rinsed water rinsed from the dehydrated cake in the rinsing step is at least part of the washing water. May be reused as

  In this embodiment, a neutralizing agent made of an alkali metal is used as the alkaline neutralizing agent (hereinafter referred to as a neutralizing agent). Specifically, a sodium-based neutralizer is used as the neutralizer comprising the alkali metal. The neutralizing agent will be described later.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The fly ash cleaning method of the present embodiment is performed, for example, when cleaning fly ash generated in a waste incineration facility 100 as shown in FIG.

  A waste incineration facility 100 includes an incinerator 1 for incinerating waste, a boiler 2 for heat recovery of exhaust gas discharged from the incinerator 1, and the temperature of water supplied to the boiler 2 by the exhaust gas. The economizer 3 to be raised, the temperature reducing tower 4 for cooling the exhaust gas, the neutralizing agent introduction unit 7 for neutralizing the exhaust gas cooled by the temperature reducing tower 4, and the neutralized exhaust gas are dedusted And a fly ash cleaning device 6 for cleaning fly ash collected from the dust removal device 5.

As the incinerator 1, for example, a gasification melting furnace, a stoker type incinerator, or a fluidized bed type incinerator can be adopted. The exhaust gas discharged from the incinerator 1 contains acidic gases such as hydrogen chloride (HCl) and sulfur oxide (SOx). The acidic exhaust gas discharged from the incinerator 1 is heat recovered by the boiler 2 and the economizer 3 and sent to the temperature reducing tower 4.

  The temperature reducing tower 4 is configured to spray water in the tower, for example. The temperature reducing tower 4 cools the acidic exhaust gas by bringing it into contact with the sprayed water, and discharges it outside the tower. The temperature-decreasing tower 4 may be discharged outside the tower after neutralizing the acidic exhaust gas by spraying alkaline water.

  The neutralizer charging unit 7 is provided downstream of the temperature reducing tower 4 and upstream of the dust removing device 5. In the present embodiment, the neutralizing agent charging unit 7 is connected to a pipe connecting the temperature reducing tower 4 and the dust removing device 5, and is configured to supply the neutralizing agent to the exhaust gas discharged from the temperature reducing tower 4. Yes. The neutralizing agent is supplied to the exhaust gas in a powder, slurry, or liquid state.

Examples of the neutralizing agent to be introduced into the acidic exhaust gas include neutralizing agents made of alkaline earth metals such as slaked lime (Ca (OH) ₂ ) and dolomite (CaMg (CO ₃ ) ₂ ), and sodium bicarbonate (NaHCO _3). ), Caustic soda (NaOH), sodium carbonate (Na ₂ CO ₃ ), potassium hydrogen carbonate (KHCO ₃ ), potassium hydroxide (KOH), potassium carbonate (K ₂ CO ₃ ), etc. It is done.

  As a neutralizing agent thrown into acidic exhaust gas, one type of neutralizing agent may be sufficient, and what mixed multiple types of neutralizing agent may be sufficient. In the present embodiment, the neutralizing agent is preferably a neutralizing agent made of an alkali metal. Specifically, a sodium-based neutralizer is preferable, and sodium bicarbonate is particularly preferable.

The acidic exhaust gas is neutralized by introducing a neutralizing agent. For example, a salt such as calcium chloride (CaCl ₂ ) or calcium sulfate (CaSO ₄ ) is generated by a neutralization reaction between acidic exhaust gas and slaked lime. A salt such as sodium chloride (NaCl) or sodium sulfate (Na ₂ SO ₄ ) is generated by the neutralization reaction between the acidic exhaust gas and sodium bicarbonate. Further, a salt such as potassium chloride (KCl) or potassium sulfate (K ₂ SO ₄ ) is generated by a neutralization reaction between acidic exhaust gas and potassium hydrogen carbonate. The neutralizing agent is excessively administered to the acidic exhaust gas so that the neutralization treatment is not unreacted. Therefore, in the fly ash collected by the dust remover 5, the salt generated by the neutralization reaction and the unreacted neutralizer are mixed.

Among the sulfates produced by the neutralization reaction between the acidic exhaust gas and the neutralizer, the sulfate produced by reacting with the alkaline earth metal is more than the sulfate produced by reacting with the alkali metal. Has low solubility in water. For example, the solubility of calcium sulfate (CaSO ₄ ) in 100 ml of water at 20 ° C. is about 0.24 g, whereas the solubility of sodium sulfate (Na ₂ SO ₄ ) in 100 ml of water at 20 ° C. is about 20 g. Yes, the solubility of potassium sulfate (K ₂ SO ₄ ) is about 11 g. Therefore, from the viewpoint of washing fly ash with water, it is preferable to use a neutralizing agent made of an alkali metal as the neutralizing agent, and it is more preferable to use a sodium-based neutralizing agent.

  As the dust remover 5, for example, a bag filter, a cyclone dust collector, an electric dust collector or the like can be adopted. The dust removing device 5 of the present embodiment is a bag filter. In this embodiment, the fly ash collected by the dust removing device 5 is collected together with the fly ash collected from the boiler 2, the economizer 3, and the temperature reducing tower 4 in the fly ash accumulating part P, and the fly ash cleaning described later Charged into the mixing section 61 of the apparatus 6. However, the fly ash collected by the dust removing device 5 and the fly ash collected from the boiler 2, the economizer 3, and the temperature reducing tower 4 may be distinguished and washed by the fly ash cleaning device 6. The exhaust gas discharged from the dust removing device 5 is discharged outside the waste incineration facility 100 in a harmless state through a chimney or the like. When nitrogen oxides (N O x) and dioxins (D X Ns) are contained in the exhaust gas, a catalyst tower (not shown) is provided downstream of the dust removing device 5, and the exhaust gas contains nitrogen oxides. After (N O x) and dioxins (D X N s) are removed, they are discharged out of the waste incineration facility 100. Reference symbol A represents exhaust gas discharged outside the system.

  The fly ash cleaning device 6 is configured to wash the fly ash with water and dehydrate the mixture of the fly ash and the wash water. As shown in FIG. 2, the fly ash cleaning device 6 of this embodiment includes a mixing unit 61 for mixing fly ash and cleaning water, and a mixed liquid of fly ash and cleaning water mixed in the mixing unit 61. A solid-liquid separation unit 62 that obtains a dehydrated cake containing fly ash and washed water by solid-liquid separation of W, and a dehydrated cake for discharging the dehydrated cake obtained by the solid-liquid separation unit 62 out of the system A discharge path 63, a drain path 64 for draining the washed water obtained in the solid-liquid separation unit 62, and a re-flow for feeding the washed water obtained in the solid-liquid separation unit 62 to the mixing unit 61 as washing water. A use path 65 and a pump 66 that supplies the mixed liquid W discharged from the mixing unit 61 to the solid-liquid separation unit 62 are provided. The fly ash cleaning apparatus 6 of the present embodiment further includes a rinse water supply path 68 that supplies rinse water for rinsing the dewatered cake.

  The washing water is water supplied to the mixing unit 61 for washing fly ash, and is used for washing washed water, rinsed water, and fly ash that are reused for washing fly ash. This is a concept including cleaning water and cleaning raw water prepared separately from rinsed water. Washed water is water in a state in which salt mixed in fly ash and unreacted neutralizing agent (hereinafter also referred to as “salts”) are eluted, and water obtained in the solid-liquid separation unit 62 Means. The washed water is water treated as washing water when supplied to the mixing unit 61.

  The mixing unit 61 includes a mixing tank 611 into which fly ash and washing water are charged, and a stirring unit 612 for stirring the fly ash and washing water in the mixing tank 611. The mixing unit 61 is a part for eluting salts mixed in the fly ash into the wash water. The mixing unit 61 supplies fly ash and washing water into the mixing tank 611 by supplying fly ash into the mixing tank 611 and supplying raw water for cleaning (represented by reference symbol D) or washed water. It is configured to store. In this embodiment, washing of fly ash is performed by batch operation, but may be performed continuously.

  The mixed liquid W is stirred for a predetermined time in the mixing tank 611, and when the salts in the fly ash are eluted and the rise of the soluble evaporation residue of the mixed liquid W stops, the mixed liquid W is supplied to the solid-liquid separation unit 62 via the pump 66. Be transported. Therefore, the liquid mixture W discharged | emitted from the mixing part 61 (mixing tank 611) is a state in which the washing | cleaning fly ash from which salts were removed, and the washed water in which salts were dissolved were mixed.

  The solid-liquid separator 62 is configured to dehydrate the mixed solution W to obtain a dewatered cake containing fly ash and washed water. That is, the solid-liquid separation unit 62 includes a concentration unit 621 that concentrates the liquid mixture W and accumulates dehydrated cake, and a liquid recovery unit 622 that recovers washed water obtained by concentrating the liquid mixture W. The solid-liquid separation unit 62 of the present embodiment is a filter press machine that separates the mixed liquid W into solid and liquid by, for example, a filter press (squeezing) using a filter cloth. For example, in the filter press, the liquid mixture W obtained in the mixing unit 61 is pumped to the concentration unit 621 by the pump 66, so that the concentration of solid content (fly ash) is higher than that of the liquid mixture W through the filter cloth. The mixed solution W is separated into a dehydrated cake having a high concentration and washed water having a solid content lower than that of the mixed solution W.

  The solid-liquid separation unit 62 of the present embodiment is configured to rinse the dewatered cake with rinse water in order to reduce the chlorine concentration of water in the dehydrated cake. That is, the solid-liquid separation unit 62 is configured to be able to supply rinse water to the concentration unit 621. In the present embodiment, the solid-liquid separation unit 62 is configured such that the rinse water is pumped to the concentration unit 621 by the pump 66 and the washed water contained in the dewatered cake in the concentration unit 621 is replaced with the rinse water. . The solid-liquid separation unit 62 is configured to be able to separate the rinsed water from the dehydrated cake. In this way, the solid-liquid separation unit 62 is configured to be able to perform the rinsing step, so that the washed water in the dehydrated cake is replaced with rinse water to reduce the chlorine concentration of the dehydrated cake, and the dehydrated cake. Can be used as a cement raw material. The solid-liquid separation unit 62 may be, for example, a belt press machine or a centrifugal dehydrator.

  The dehydrated cake discharge path 63 is a path for discharging the dehydrated cake concentrated by the solid-liquid separator 62 to the outside of the system. The dehydrated cake discharge path 63 is connected to the concentration unit 621 of the solid-liquid separation unit 62 or configured to receive the dehydrated cake discharged from the concentration unit 621. The dehydrated cake is taken out of the system through the dehydrated cake discharge path 63 and is reused for landfill, cement raw material, and the like. A symbol B represents a dehydrated cake discharged out of the system.

  The drainage path 64 is a path for draining the washed water and the rinsed water obtained from the solid-liquid separation unit 62 out of the system. The drainage path 64 is connected to the liquid recovery unit 622 of the solid-liquid separation unit 62. The wastewater discharged from the fly ash cleaning device 6 is sent to another purification treatment facility (not shown) via the drainage path 64 and subjected to purification treatment. The symbol C represents washed water or rinsed water that is drained out of the system.

  That is, the solid-liquid separation unit 62 is configured such that the concentration unit 621 is connected to the dewatered cake discharge path 63 and the liquid recovery unit 622 is connected to the drainage path 64, so Is configured to be discharged out of the solid-liquid separator 62.

  The reuse path 65 is a path for supplying water that has been washed by the solid-liquid separation unit 62 to the mixing unit 61 as washing water. One end of the reuse path 65 is connected to a storage facility (not shown) such as a tank, and the other end is open to the mixing unit 61. Specifically, the washed water discharged from the solid-liquid separator 62 is stored in a storage facility such as a tank via the drainage path 64 and is pumped by a separately provided pump (not shown). Water is supplied to the mixing unit 61 via the reuse path 65.

  The pump 66 transfers the mixed liquid W discharged from the mixing unit 61 to the solid-liquid separation unit 62. The pump 66 is configured to be able to transfer rinse water to the concentration unit 621. The pump 66 is interposed in a transfer pipe 67 that connects the mixing unit 61 and the solid-liquid separation unit 62.

  The rinse water supply path 68 is a path for supplying rinse water to the concentration unit 621 of the solid-liquid separation unit 62. The rinse water supply path 68 of this embodiment is connected to the transfer pipe 67. Specifically, the rinse water supply path 68 is connected to an upstream pipe 671 provided on the suction side of the pump 66 in the transfer pipe 67. The rinse water is pumped by the pump 66 and is sent to the solid-liquid separation unit 62 via the downstream pipe 672 provided on the discharge side of the pump 66. For example, tap water, industrial water, ground water, or industrial waste water is adopted as the rinse water. Symbol E represents rinse water introduced into the system.

  This completes the description of the waste incineration facility 100. Hereinafter, the fly ash cleaning method will be described more specifically.

  When the washed water is reused for the fly ash washing, the washed water is reused for the fly ash washing within the range where no precipitate is generated in the mixed solution W, and used for the fly ash washing. This has led to a significant reduction in the amount of washing water used. Specifically, when a neutralizing agent made of an alkaline earth metal is used as a neutralizing agent for neutralizing fly ash, when the soluble evaporation residue in the mixed solution W is about 20%, It was confirmed that precipitates were generated in the mixed solution W. Moreover, when the neutralizing agent which consists of alkali metals was used, even if the soluble evaporation residue in the liquid mixture W was 20% or more, it confirmed that a precipitate did not arise. Further, when a sodium-based neutralizing agent was used, it was confirmed that no precipitate was formed if the soluble evaporation residue was 35% or less.

  The fly ash collected in the fly ash accumulating part P is put into the mixing tank 611, and the raw water for washing is supplied to the mixing part 61 so that the liquid-solid ratio of the washing water and the fly ash is 5 to 10 in the mixing tank 611. Is introduced. In the mixing step, the stirrer 612 is driven to stir the fly ash and the cleaning raw water for a predetermined time in the mixing tank 611, and the salts mixed in the fly ash are eluted into the cleaning raw water. The mixing of the fly ash and the raw water for washing is referred to as the first washing operation, and the washed water obtained in the solid-liquid separation step after the first washing operation is referred to as first washed water. When the first washing operation is completed, the soluble evaporation residue in the mixed solution W is confirmed.

In general, fly ash before washing contains a larger amount of chloride than sulfate. Since the solubility of chlorides such as calcium chloride (CaCl ₂ ), sodium chloride (NaCl), and potassium chloride (KCl) is 15 g or more with respect to 100 ml of water at 20 ° C., at the end of the first washing operation, Usually, the soluble evaporation residue in the mixed solution W is 20% or less.

  After the mixing step, the process proceeds to a solid-liquid separation step. In the solid-liquid separation step, the liquid mixture W is passed through the solid-liquid separation unit 62 for solid-liquid separation (dehydration) to obtain a dehydrated cake containing fly ash and first washed water. After the solid-liquid separation step, the first washed water discharged from the solid-liquid separation unit 62 is returned to the mixing unit 61 via the reuse path 65 or stored in a storage facility such as a tank. Subsequently, the dehydrated cake obtained in the solid-liquid separation unit 62 is transferred to a rinsing process.

  In the rinsing step, rinse water is supplied to the concentration unit 621 of the solid-liquid separation unit 62, and the first washed water in the dehydrated cake is replaced with rinse water. In the rinsing step, the rinsing water is introduced into the concentrating unit 621 through the rinsing water supply path 68 so that the liquid-solid ratio between the rinsing water and the fly ash is 2.5 to 5. By rinsing the dehydrated cake with rinse water, the chlorine concentration of the dehydrated cake can be lowered. Specifically, the chlorine concentration in the cement is preferably 350 ppm or less. When the dehydrated cake is used as a cement raw material, it is necessary to reduce the chlorine concentration in the dehydrated cake as much as possible. For example, the chlorine concentration of the entire dehydrated cake including solids and moisture is preferably 1% or less. The chlorine concentration in the dehydrated cake after drying is more preferably 1% or less. As a result of lowering the chlorine concentration in the dehydrated cake, for example, when the chlorine concentration in the dehydrated cake after drying is reduced to 1%, about 3% fly ash can be used as a cement raw material.

The moisture content of the dehydrated cake after dehydration is A%, and the chlorine concentration in the dehydrated cake after rinsing is X%. When the chlorine concentration in the dried dehydrated cake used as a cement raw material is Y%, A, X, and Y have the following relationship.
Y = 100 · X / (100-A)
That is, in the rinsing step, the target value of the chlorine concentration in the dried dehydrated cake is determined, and from the moisture content of the dehydrated cake, the value to which the chlorine concentration needs to be reduced relative to the dehydrated cake after rinsing is calculated, Rinse the dehydrated cake so that the chlorine concentration in the dehydrated cake is below this value.

  For example, even if the concentration of chlorine contained in the solid content of the dehydrated cake is as close to zero as possible, the water in the dehydrated cake before rinsing is washed water with a relatively high soluble evaporation residue, The chlorine concentration in the fly ash after drying may exceed 1%. Therefore, in the present embodiment, the chlorine concentration of the entire dehydrated cake is lowered, and the dehydrated cake is rinsed in the rinsing step so that the chlorine concentration becomes an appropriate cement raw material. After the rinsing step, the rinsed water discharged from the solid-liquid separation unit 62 is stored in a storage facility (not shown) such as a tank.

  Next, a method for reusing washed water in the mixing step will be described. Hereinafter, the process of supplying washed water or rinsed water to the mixing tank 611 is referred to as a reuse process. The reuse step may be performed in parallel with the solid-liquid separation step or the rinsing step, or may be performed after the solid-liquid separation step and the rinsing step are completed. This embodiment demonstrates the case where a reuse process is implemented after a solid-liquid separation process and a rinse process are complete | finished. The storage facility in which the first washed water is stored and the storage facility in which the rinsed water is stored are connected to the reuse path 65, and the reuse path 65 is connected to a pump (not shown) from each storage facility. It is configured to be able to pump water through. In the reuse process, when the washed water is insufficient, the rinsed water may be supplied to the mixing tank 611 as washing water. In the reuse process, raw water for cleaning can be supplied as cleaning water.

  The fly ash collected in the fly ash accumulating part P is put into the empty mixing tank 611, and the mixing ratio is adjusted so that the liquid-solid ratio of the washing water and the fly ash is 5 to 10 in the mixing tank 611. The first cleaned water is supplied as cleaning water through the use path 65. Subsequently, the process proceeds to the mixing step, and the fly ash and the wash water as the first washed water are stirred for a predetermined time in the mixing tank 611 as in the first washing operation, and the salts mixed in the fly ash are removed. Elute in wash water. With this washing operation as the second washing operation, the washed water obtained in the solid-liquid separation step after the second washing operation is referred to as second washed water. When the second washing operation is completed, the soluble evaporation residue in the mixed solution W is confirmed. Then, the above washing operation is repeated until the soluble evaporation residue in the mixed solution W reaches 20% (or 35% or less). Since the solid-liquid separation step and the rinsing step after the mixing step are the same as the already described solid-liquid separation step and the rinsing step, the description will not be repeated.

  For example, the mixing step and the rinsing step are performed with the liquid / solid ratio of washing water and fly ash being 5, and the liquid / solid ratio of rinsing water and fly ash being 2.5, and the mixed solution is obtained at the end of the fifth washing operation. Assume that the soluble evaporation residue in W reaches 20%. In this case, when the raw water for cleaning is used in all of the five cleaning operations, the cleaning water is used 37.5 times ((5 + 2.5) × 5) as much as the fly ash. On the other hand, when the washed water is reused as washing water in all five washing operations as in this embodiment, it is 17.5 times as much as fly ash (5 + 2.5 × 5). This means that the washing water was used. As is clear from this, by reusing the washed water, it is possible to save about 20 times as much water as the fly ash.

  In addition, when a neutralizer based on sodium is used as the neutralizer, the neutralizer composed of an alkaline earth metal or a neutralizer composed of another alkali metal such as potassium is used more than the neutralizer. Since the solubility of the salt produced by the sum is high, the washed water can be reused until the soluble evaporation residue in the mixed solution W becomes 20% or more and 35% or less. Therefore, the number of times the washed water can be reused is increased compared to the case of using a neutralizing agent made of an alkaline earth metal or a neutralizing agent made of another alkali metal such as potassium as the neutralizing agent. Can be further saved.

  Here, a large amount of sodium chloride is present in the fly ash neutralized with the sodium-based neutralizer. Although the solubility of sodium chloride in 100 ml of water at 20 ° C. is about 36 g, the upper limit of the soluble evaporation residue in the mixed solution W is set to 35% in consideration of the presence of sulfate.

  Washed water after the soluble evaporation residue exceeds 35% is sent to another purification treatment facility such as a neutralization treatment facility via the drainage path 64 and subjected to purification treatment. Alternatively, the washed water after the soluble evaporation residue exceeds 35% may be evaporated and solidified. In this case, since the washed water with a high salt concentration is evaporated and solidified, the thermal energy required for the evaporation and solidification can be suppressed compared with the case where the washed water with a low salt concentration is evaporated and solidified. It is. In this embodiment, since a sodium-based neutralizer (same as a neutralizer made of alkali metal) is used, the pH of the washed water is higher than that when a neutralizer made of alkaline earth metal is used. Low (see FIG. 3), it can also save the chemicals required for neutralization of washed water.

  Hereinafter, the operation of the present embodiment will be summarized. According to the fly ash washing method of the present embodiment, the washed water obtained in the solid-liquid separation step is reused for washing the fly ash. In the method, the fly ash is washed with the washed water until the soluble evaporation residue in the mixed solution W is at least 20%, so the washed water can be reused as the washing water. Can be suppressed.

  Moreover, in the said embodiment, since the neutralizing agent which consists of alkali metals is used as an alkaline neutralizing agent, pH of wash water can be restrained low. Therefore, the amount of chemicals required for neutralizing the washed water can be suppressed, and the washed water can be easily neutralized.

  Further, according to the above embodiment, among the neutralizers made of alkali metal, the salts generated when using the sodium-based neutralizer use the neutralizer made of other alkali metals such as potassium. It is more soluble in water than the salts produced (high solubility in water). Therefore, if the soluble evaporation residue is 35% or less, the fly ash can be washed with washed water with almost no dissolved substance being deposited. Therefore, according to such a configuration, fly ash can be washed in a state where almost no dissolved substances are deposited while increasing the soluble evaporation residue in the mixed solution W, and the washed water is sufficiently reused. be able to.

  Moreover, according to the said embodiment, since the dehydrating cake is provided with the rinse process, it can be set as the property suitable for reuse, such as making a dehydrated cake into a cement raw material.

  Moreover, according to the said embodiment, since the rinsed water used at the rinse process can be used for washing | cleaning of fly ash, rinsed water can be used effectively.

  In the above embodiment, when a neutralizer made of an alkali metal is used as the neutralizer, the pH of the washed water is lowered as compared with the case of using a neutralizer made of an alkaline earth metal as the neutralizer. can do. Specifically, as shown in FIG. 3, when comparing sodium bicarbonate ash neutralized with baking soda and slaked lime ash neutralized with slaked lime, from the start to the end of stirring, It can be seen that the pH of the wash water (or washed water) is lower than the pH of the slaked lime ash wash water (or washed water). As can be seen from FIG. 3, the pH of the washed water can be kept low by using an alkali metal neutralizing agent, so that the amount of chemicals required for neutralizing the washed water can also be reduced. And the burden on the neutralization process is reduced. In FIG. 3, the liquid-solid ratio is 7.5 (washing water 5 times, rinsing water 2.5 times).

  Further, as shown in FIG. 4, in the above embodiment, when a neutralizing agent made of an alkali metal is used as the neutralizing agent, compared with a case where a neutralizing agent made of an alkaline earth metal is used as the neutralizing agent. In addition, the dissolution rate of salts in the wash water is fast. Therefore, by using a neutralizing agent made of an alkali metal as the neutralizing agent, the mixing step can be shortened, and the fly ash washing treatment capability can be increased. Specifically, the electric conductivity of washing water (or washed water) of sodium bicarbonate ash exceeds 9 S / m at the same time when stirring is started, and then slightly increases. This shows that when sodium bicarbonate ash is washed, most of the salts are eluted almost simultaneously with stirring. On the other hand, the electrical conductivity of the slaked lime ash washing water (or washed water) gradually increases in 20 minutes after stirring. From this, it can be seen that when slaked lime ash is washed, it takes time to elute the salts. As described above, since alkali metal salts dissolve faster in water than alkaline earth metal salts, when a neutralizer made of an alkali metal is used as a neutralizer, the mixing step is shortened. be able to.

Furthermore, in the above embodiment, by using a neutralizing agent made of an alkali metal as a neutralizing agent, compared with the case of using a neutralizing agent made of an alkaline earth metal as a neutralizing agent, the desalination rate is reduced Can be high. Specifically, as shown in FIG. 5, sodium bicarbonate ash and slaked lime ash are washed at the same liquid-solid ratio, and the liquid-solid ratio is 7.5 times (washing water 5 times, rinsing water 2.5 times). Increase 10 times (5 times washing water, 5 times rinse water), 12.5 times (10 times washing water, 2.5 times rinse water), and 15 times (10 times washing water, 5 times rinse water). As a result, it was found that the desalting rate of baking soda ash was higher than the desalting rate of slaked lime ash, and the baking salt ash had a high desalting rate even when the liquid-solid ratio was low. As apparent from FIG. 5, when sodium bicarbonate ash is used, a high desalting rate can be obtained even if the liquid-solid ratio is small, so that the size of the mixing tank 611 can be reduced. In the present embodiment, the desalination rate Z% is calculated by the following equation, where B is the chlorine concentration of the fly ash before cleaning, and C% is the chlorine concentration of the fly ash after cleaning.
Z = ((B−C) / B) · 100

  It should be noted that the fly ash cleaning method of the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

  Although the said embodiment demonstrated the case where the washing method of fly ash was implemented when wash | cleaning the fly ash which generate | occur | produced in the waste incineration facilities 100, it is not limited to this. The fly ash cleaning method can be implemented in various facilities having an incineration process such as a coal-fired power plant.

  Although not particularly mentioned in the above embodiment, the rinsed water can be reused as rinse water.

  In the above embodiment, the case where the washed water and the rinsed water are reused by supplying water to the mixing unit 61 has been described, but the present invention is not limited to this. The washed water and the rinsed water may be reused by being supplied to the mixing unit of another fly ash washing apparatus, or may be reused in another waste incineration facility.

  Although not particularly mentioned in the above embodiment, the mixing unit 61 may include means for measuring the soluble evaporation residue in the mixed solution W, and the soluble evaporation residue in the mixed solution W is predetermined. An operator or the like may be notified when this value is reached.

DESCRIPTION OF SYMBOLS 100 ... Waste incineration facility, 1 ... Incinerator, 2 ... Boiler, 3 ... Economizer, 4 ... Temperature-reduction tower, 5 ... Dust removal apparatus, 6 ... Fly ash washing apparatus, 7 ... Neutralizer input part, 61 ... Mixing part 611 ... Mixing tank, 612 ... Agitation unit, 62 ... Solid-liquid separation unit, 621 ... Concentration unit, 622 ... Liquid recovery unit, 63 ... Dehydrated cake discharge path, 64 ... Drainage path, 65 ... Reuse path, 66 ... Pump , 67 ... Transfer piping, 671 ... Upstream piping, 672 ... Downstream piping, 68 ... Rinsing water supply path, A ... Exhaust gas, B ... Dehydrated cake, C ... Washed water or rinsed water, D ... Raw water for washing, E ... Rinse water, P ... Fly ash accumulation part

Claims (5)

A mixing step of mixing the fly ash collected from the exhaust gas neutralized with an alkaline neutralizer and the washing water, and a mixture of the fly ash obtained in the mixing step and the washing water A step of obtaining a soluble evaporation residue concentration, and a solid-liquid separation step of obtaining a dehydrated cake and washed water by solid-liquid separation of the mixed solution. In the mixing step, the washed water ( Washing fly ash that is reused until at least 20% of the soluble evaporation residue in the mixed solution is used as at least a part of the washing water ) except for the water obtained by washing the dehydrated cake Method. The method for cleaning fly ash according to claim 1, wherein a neutralizing agent comprising an alkali metal is used as the alkaline neutralizing agent. As the neutralizing agent comprising the alkali metal, a sodium-based neutralizing agent is used, and in the mixing step, the soluble evaporation residue in the mixed solution is 20% or more and 35% or less. The method for washing fly ash according to claim 2 , wherein the washed water is reused as at least a part of the washing water. The method for washing fly ash according to any one of claims 1 to 3 , further comprising a rinsing step of rinsing the dehydrated cake. The method for washing fly ash according to claim 4 , wherein in the mixing step, the rinsed water rinsed from the dehydrated cake in the rinsing step is reused as at least a part of the washing water.

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