JP2007069066A - Method for treating fly ash - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for treating fly ash, in which fly ash in the combustion exhaust gas to be generated from an incinerator or the like is collected, and when chlorine is removed from the collected fly ash, the chlorine content of the collected fly ash is decreased while reducing the cost of a fly ash treatment facility and decreasing the amount of washing water to be used and the amount of waste water to be discharged. <P>SOLUTION: The method for treating fly ash, which is used when the combustion exhaust gas to be generated from the incinerator is treated by removing fly ash in the combustion exhaust gas, adding a desalting agent to the fly ash-removed combustion exhaust gas to react the desalting agent with acidic gas in the combustion exhaust gas and collecting/discharging the desalted residues, comprises a first washing step of roughly washing the removed fly ash with water and subjecting the fly ash-washed water to solid-liquid separation to obtain a dehydrated cake C<SB>1</SB>and filtrate F<SB>1</SB>and a second washing step of finally washing the obtained dehydrated cake C<SB>1</SB>with water and subjecting the dehydrated cake-washed water to solid-liquid separation to obtain a dehydrated cake C<SB>2</SB>and filtrate F<SB>2</SB>. The dehydrated cake C<SB>2</SB>is used as an industrial raw material. The filtrate F<SB>2</SB>is stored and used when the collected fly ash is washed roughly at the next batch or thereafter. The filtrate F<SB>1</SB>obtained at the first washing step is subjected to salt separation treatment to separate the salt thereof. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for treating fly ash in combustion exhaust gas generated from an incinerator or the like, and more particularly to a method for treating fly ash in which fly ash is washed with water to remove chlorine in the fly ash.

  Combustion exhaust gas generated from incineration facilities such as garbage incinerators contains harmful components such as acid gas mainly composed of hydrogen chloride. For this reason, incineration facilities are generally equipped with a wet exhaust gas treatment system that uses a sodium hydroxide aqueous solution in a scrubber or the like, and a dry exhaust gas treatment system that uses an alkaline treatment agent in a bag filter or the like.

  Among these, in a dry exhaust gas treatment system, when a desalinating agent such as slaked lime is introduced into the exhaust gas upstream of the dust collector, it is a reaction product of dust such as incinerated fly ash and a desalting agent in the dust collector. The desalted residue is collected together. Since the recovered material from the dust collector contains a large amount of chlorine due to the mixing of the desalting residue, it cannot be used as an industrial raw material, and most of it is landfilled by chemical treatment or cement solidification.

However, reduction of the amount of landfill disposal has become an issue due to the decrease in the remaining years at existing landfill disposal sites and the difficulty of adding new landfill disposal sites. For this reason, attempts have been made to recycle incineration ash such as fly ash in combustion exhaust gas and use it as a cement raw material. Cement is mainly composed of CaO, SiO ₂ , Al ₂ O ₃ , Fe ₂ O _3, etc., and since wastes containing these can be used as raw materials, various wastes have been used as cement raw materials so far. .

  However, since the fly ash in the combustion exhaust gas contains chlorine, the rebar is easily corroded, and the durability of the reinforced concrete is lowered. For this reason, the JIS standard stipulates that the chlorine content in ordinary cement is 200 ppm or less, and fly ash cannot be used as it is. In particular, if the desalination residue and fly ash having a high chlorine concentration are simultaneously collected and mixed by the dust collector, the chlorine concentration in the fly ash has been further increased.

  Patent Document 1 proposes that after removing dust, hydrogen chloride in the exhaust gas is removed with a sodium-based desalting agent, and the desalted residue is effectively used. However, the chlorine concentration of fly ash has not decreased.

  On the other hand, Patent Document 2 proposes a method of washing incinerated ash with water to wash out chlorine and recycle it into a cement raw material. However, this water washing treatment method does not have a sufficient chlorine removal rate, and the recycling of incinerated ash has been limited to specific applications such as unreinforced concrete such as blocks.

If the amount of cleaning water used is increased, the remaining chlorine can be reduced, but the amount of cleaning water becomes enormous, increasing the equipment cost and energy usage required for wastewater treatment after fly ash treatment. It became a problem and the removal rate of chlorine in fly ash could not be increased. Actually, in the fly ash treatment method, as a means for separating the salt component from the washing wastewater, for example, the evaporation to dryness method can be mentioned. However, the cost of the evaporation to dryness equipment is more than 40% of the total. was there.
JP-A-11-63468 JP 2005-1910 A

  The purpose of the present invention is to collect fly ash in combustion exhaust gas generated from incinerators, etc., and to reduce chlorine from the fly ash, thereby reducing equipment costs and reducing the amount of washing water used and the amount of drainage. Another object of the present invention is to provide a fly ash treatment method that reduces the processing cost and reduces the chlorine content in the incinerated fly ash.

The method for treating fly ash according to the present invention that achieves the above object is to remove fly ash from combustion exhaust gas generated from an incinerator, add a desalting agent to the combustion exhaust gas, and remove the desalting agent in the combustion exhaust gas. In the method for treating fly ash in the combustion exhaust gas treatment for collecting and discharging the desalted residue reacted with the acid gas, the fly ash is washed with coarse water and then solid-liquid separated to obtain a dehydrated cake A first washing step for obtaining C _{1 and} filtrate F _1, and a second washing step for obtaining dehydrated cake C _{2 and} filtrate F ₂ by subjecting the dehydrated cake C ₁ to finish water washing and solid-liquid separation. Using C ₂ as an industrial raw material, storing the filtrate F ₂ and using it in the subsequent batch and subsequent coarse water washing, and separating the salt by subjecting the filtrate F ₁ obtained in the first washing step to salt separation. It is characterized by.

  The fly ash treatment method of the present invention removes fly ash from combustion exhaust gas generated from an incinerator, and then adds a desalting agent to the combustion exhaust gas to react the desalting agent with the acid gas in the combustion exhaust gas. The desalted residue thus collected is collected separately so that the fly ash and the desalted residue are not mixed. Thereby, fly ash is collected independently from combustion exhaust gas, and it becomes possible to reduce the amount of fly ash which should be processed, without raising the chlorine concentration of fly ash. Therefore, in the next water washing step, the amount of fly ash to be processed and the chlorine content can be reduced, and the equipment and processing costs of the water washing step can be greatly reduced.

Moreover, in the water washing step, the residual amount of chlorine in the fly ash can be greatly reduced by washing the fly ash in the first washing step and then washing the finishing ash in the second washing step. become able to. At the same time, the filtrate F ₂ obtained in the second washing step is reused as the washing water in the first washing step, so that the washing water can be effectively used to separate the salt for recovery of the new washing water and salt recovery. it is possible to significantly reduce the amount of Bekiroeki F ₁ be processed. In this way, it is possible to reduce the amount of washing water used and the amount of drainage while reducing the chlorine content in the incineration fly ash, thereby reducing equipment and processing costs.

That is, the treatment method of the present invention collects the fly ash to be treated from the combustion exhaust gas independently of the desalting residue, and effectively uses the filtrate F ₂ that is generated in the middle while washing the fly ash in two stages. By using it, the amount of washing water used and the amount of drainage can be reduced, equipment and processing costs can be reduced, and the chlorine content in the incineration fly ash can be reduced.

The present invention is described in detail below.
FIG. 1 is an explanatory view showing an example of the configuration of an apparatus used in the dust collection process of the fly ash treatment method of the present invention, and FIG. 2 is an apparatus used in the water washing process of the fly ash treatment method of the present invention. It is explanatory drawing which shows an example of a structure of.

  In FIG. 1, the apparatus used for the dust collection processing of fly ash according to the present invention includes a first dust collector 51, a second dust collector 52, and a desalting agent supply means 53. The combustion exhaust gas generated from the incinerator is collected by the first dust collector 51 with priority given to fly ash. Next, a desalting agent is added from the desalting agent supply means 53 to the combustion gas from which fly ash has been removed, and reacts with hydrogen chloride in the combustion gas to produce a desalting residue. The desalted residue is collected by the second dust collector 52. Thereby, acidic gas, such as fly ash and hydrogen chloride, is removed from the combustion gas, and exhausted after necessary processing.

  In FIG. 2, the apparatus used for the water washing process of the fly ash of this invention is the fly ash storage tank 1 which receives the fly ash collected independently as mentioned above, and the fly ash is washed with water to make a slurry. A washing tank 2, a slurry storage tank 3 for storing the slurry after washing, and a solid-liquid separator 5 for separating the slurry into a dehydrated cake and a filtrate are provided. In addition, a dehydrating cake 6 that selectively transfers the solid-liquid separated dehydrated cake to the dehydrated cake receiving tank 7 or the washing tank 2 is provided. The destination of the cake can be selected to the washing tank 2.

Further, a filtrate storage tank 8 and a salt water storage tank 11 are provided to store the filtrate separated by solid-liquid. The filtrate F _{2 for the} second and subsequent finish water washings with low chlorine concentration is stored separately in the filtrate storage tank 8, and the filtrate F _{1 for the first} rough water washing with high chlorine concentration is stored separately in the salt water storage tank 11.

The filtrate F ₂ filtrate reservoir 8 leads to a pipe that communicates with the washing tank 2, it becomes possible to reuse the filtrate F ₂ as washing water. On the other hand, the salt water storage tank 11 that receives the filtrate F ₁ having a high chlorine concentration is sent to the salt separation means 15 via the filtrate transfer pump 10, and is separated into water and salt components by the salt separation means 15. The components are stored in the crystal salt receiving tank 17 through the transfer means 16.

Hereinafter, each process will be described in detail.
The first dust collector 51 and the second dust collector 52 are not particularly limited as long as they can collect fly ash and desalted residue, respectively. Preferably, a bag filter, a cartridge filter, an electric dust collector, a cyclone, etc. are used. Among them, a bug filter is more preferable.

  The desalting agent supply means 53 is not particularly limited as long as it can quantitatively add the desalting agent, and preferably includes a gravimetric quantitative feeder and a capacitive quantitative feeder. Specifically, A biaxial screw type weight feeder equipped with a vibrator or the like, a table feeder, a rotary valve and the like can be exemplified.

  The fly ash storage tank 1 is preferably a cylindrical bowl-shaped hopper, and includes a fly ash cutting machine such as a table feeder, a vibrator, and the like so that the fly ash can be smoothly and rapidly supplied to the washing tank 2. .

  The water washing tank 2 is a batch-type washing means for uniformly mixing fly ash and washing water and dissolving chlorine in the fly ash in washing water at a predetermined solubility. The water rinsing tank 2 is preferably substantially cylindrical and has a conical bottom, so that the washed slurry can be discharged efficiently. Moreover, it has a screw type stirrer and can mix fly ash and washing water uniformly. Furthermore, the water washing tank 2 is a washing tank that can share the rough water washing that is the first washing and the finishing washing that is the second and subsequent washings, and includes means necessary for switching between the two. Yes.

Washing tank 2 is adapted to be able to use the filtrate F ₂ and / or new cleaning water 14 as wash water. The washing water to be used may be any one of the above, or a combination of two or more, and can be appropriately used.

  The slurry storage tank 3 stores the slurry after washing with water and can control the amount of slurry transferred to the solid-liquid separator 5, and is efficient according to the processing capacity of the solid-liquid separator 5. Driving. Moreover, during this dehydration process, the washing tank 2 is in an empty state, and the dehydrated cake that has been subjected to solid-liquid separation can be immediately returned to the washing tank 2. Thereby, the equipment cost and production cost required for water-washing fly ash several times can be reduced. Although there is no restriction | limiting in particular in the slurry storage tank 3, It may be the same shape as the water washing tank 2, and it is preferable that it is an equivalent internal volume. Moreover, in order to prevent the separation of the slurry during storage, it is preferable to have a screw type agitator.

  The solid-liquid separator 5 is an apparatus that separates the slurry transferred from the slurry storage tank 3 into a dehydrated cake (solid phase) and a filtrate (liquid phase). The solid-liquid separator 5 is not particularly limited as long as the slurry can be separated into a solid phase and a liquid phase, and preferred examples include a filter press, a belt press, a centrifugal dehydrator, a screw press, and a rotary press. However, a filter press is preferred because the moisture content of the dehydrated cake can be lowered.

The transfer means 6 is a means that makes it possible to select transfer of the dehydrated cake separated into solid and liquid to the dehydrated cake receiving tank 7 or the washing tank 2. The dehydration cake with a small amount of residual chlorine is transferred to the dehydration cake receiving tank 7, and the dehydration cake with a large amount of residual chlorine is transferred to the washing tank 2, so that the transfer means 6 can select the transfer destination. That is, it is possible to arbitrarily select the number of times that the fly ash is washed with water using a set of washing tank 2 and solid-liquid separator 5. In the present invention, the dewatered cake C ₁ with one water washing is returned to the water washing tank 2 and washed again with water to further reduce the chlorine concentration, and the dehydration with a sufficiently low chlorine concentration by two or more water washings. cake C ₂ is preferably selectively transferred to dewatered cake receiving vessel 7.

  Although there is no restriction | limiting in particular in the transfer means 6, A flight conveyor, a flex belt conveyor, a screw conveyor, etc. are mentioned preferably, A flight conveyor is preferable since horizontal and vertical conveyance are possible especially.

In the present invention, the filtrate F ₂ is stored in the filtrate storage tank 8 and can be used as the first wash water of the fly ash after the next batch. This is because the filtrate F ₂ has a low chlorine concentration and has a remaining capacity for dissolving more chlorine.

On the other hand, the filtrate F ₁ having a high chlorine concentration received in the salt water storage tank 11 is sent to the salt separation means 15 via the filtrate transfer pump 10. The filtrate F ₁ is separated into water and salt components by the salt separation means 15, and the salt components remaining as crystals are stored in the crystal salt receiving tank 17 via the transfer means 16. The separated salt component can be reused for other industrial uses such as snow melting agents, metal refining, and leather processing.

  The water separated in the salt separation means 15 is condensed through a condenser (not shown) or the like, and can be reused as the new washing water 14. In this case, it is possible to further reduce the amount of new washing water replenished from outside the system, which is preferable.

  In the present invention, the salt separation means 15 is not particularly limited, but a salt separation method such as an evaporation / drying method, a crystallization method, and an electrolytic method can be preferably exemplified, and an evaporation / drying method is particularly preferable. Specific examples of the evaporation / drying method include a drum dryer type, a vacuum drying type, and a spray dryer type evaporator / dryer, and a drum dryer type is particularly preferable.

  The fly ash treatment method of the present invention is a treatment method including a dust collection step using at least two dust collectors and a desalting agent supply means, and a washing step having a water washing tank, a slurry storage tank, and a solid-liquid separator. By combining the two processes organically, while reducing the equipment cost, the efficiency of operation and a drastic reduction in the amount of washing water and energy consumption are achieved, and the residual amount of chlorine in the fly ash Therefore, the fly ash and desalted residue generated from the incineration facility can be effectively used as industrial raw materials such as cement raw materials and industrial salts without landfill treatment.

FIG. 3 is a block diagram showing an example of an embodiment of the fly ash treatment method of the present invention.
In FIG. 3, the fly ash treatment method of the present invention uses the first dust collector 51 to collect the fly ash a from the incinerator and collects the fly ash a in the dust collection process. A salt agent d is added to react with the acidic gas in the combustion exhaust gas to produce a desalted residue r, which is collected using the second dust collector 52. Next, in the water washing step, the fly ash a collected independently as described above is received in the fly ash storage tank 1 and transferred to the water wash tank 2, and the fly ash a is washed with coarse water and then separated into solid and liquid. The first washing step for obtaining the dehydrated cake C _{1 and the} filtrate F ₁ and the second washing step for obtaining the dehydrated cake C _{2 and the} filtrate F ₂ by further subjecting the dehydrated cake C ₁ to final water washing and solid-liquid separation. Is included. Moreover, the reuse of dewatered cake C ₂ obtained as an industrial raw material, keep in storing the filtrate F ₂ be used for rough water washing subsequent batch, the filtrate F ₁ and salts separation And recovering the salt. Moreover, it is preferable to advance salt separation efficiently by dissolving the desalting residue r in the filtrate F ₁ and subjecting it to salt separation treatment.

  The treatment method of the present invention collects fly ash a and desalted residue r separately from the combustion exhaust gas generated from the incinerator so that the fly ash is preferentially collected from the combustion exhaust gas. Therefore, the chlorine concentration in the fly ash is not increased, and the amount of fly ash to be processed can be prevented from increasing. Therefore, in the next washing step, the amount of fly ash to be treated and the chlorine content, that is, the total amount of salt components to be separated can be reduced, and the equipment and treatment costs of the washing step can be greatly reduced. .

  The desalting agent d used in the treatment method of the present invention can be appropriately selected from sodium desalting agents and calcium desalting agents, but it is particularly preferable to use sodium desalting agents. These desalting agents react with an acidic gas mainly composed of hydrogen chloride contained in the combustion gas to produce sodium chloride and calcium chloride as the desalting residue, thereby producing harmful substances in the combustion gas. Can be easily separated.

  Sodium-based desalting agents are preferable because sodium chloride as a desalting residue has advantages such as easy handling and easy reuse, high solubility in water and easy separation and crystallization. In addition, in the case of calcium-based desalting agents, the hydrophilicity of the solid component of the slurry is increased due to the disadvantage that calcium chloride, which is a desalting residue, has significant deliquescent properties, and the addition of diatomaceous earth as a reaction aid. While there is a problem that the moisture content of the dehydrated cake becomes high, it is also advantageous that such a problem does not occur in the sodium-based desalting agent.

Preferred examples of the sodium-based desalting agent used in the present invention include sodium bicarbonate NaHCO ₃ , sodium carbonate Na ₂ CO ₃ , and sodium hydroxide NaOH.

Next, in the washing process, the fly ash a collected independently in the dust collection process is received in the fly ash storage tank 1, and a predetermined amount is transferred to the water washing tank 2 and washing water is supplied. Wash water used for rough water washing of the first cleaning step, at the time of steady operation, it is to use a filtrate F ₂ of the second cleaning step, which is stored in the previous batches. It should be noted that new washing water can be used at the start of operation regardless of this. As the new washing water 14, clean water, industrial water, reused water, condensed water obtained in the previous salt separation means, or the like can be used.

  In the coarse water cleaning, the fly ash a and the cleaning water are uniformly mixed using a stirrer or the like so that the chlorine in the fly ash is dissolved in the cleaning water. The time for washing with rough water is preferably 1 minute to 30 minutes, more preferably 5 minutes to 10 minutes. By setting the rough water washing time within this range, it is preferable that as much chlorine as possible in the fly ash can be dissolved and the treatment efficiency can be improved.

The slurry that has been washed with coarse water is transferred to the solid-liquid separator 5 and separated into the dehydrated cake C _{1 and the} filtrate F ₁ . At the time of transfer, a slurry storage tank 3 is provided between the washing tank 2 and the solid-liquid separator 5, and the entire amount of the slurry in the washing tank 2 is transferred to the slurry storage tank 3 while being transferred to the slurry storage tank 3. From the viewpoint of increasing the processing efficiency, it is preferable to transfer the slurry from the slurry storage tank 3 to the solid-liquid separator 5 and perform the solid-liquid separation process simultaneously with the start of the slurry transfer. That is, the total amount of the slurry in the washing tub 2 by transferring the slurry storage tank 3, it is possible to empty the washing tank 2 at an early stage, the dehydrated cake C ₁ which is a solid-liquid separation immediately into washing tank 2 Can accept. Similarly, in the second cleaning step, the fly ash of the next processing batch can be received immediately after the slurry is discharged.

In the solid-liquid separator 5 in the first washing step, the slurry is separated into the dehydrated cake C _{1 and the} filtrate F ₁ . The filtrate F ₁ has a high chlorine concentration and has been disposed of as waste liquid or discarded after the salt component is removed by salt separation treatment such as evaporation to dryness. However, when a large amount of washing water is used to reduce the chlorine concentration remaining in the fly ash, a large amount of filtrate F ₁ is generated, and the equipment cost and energy consumption required for salt separation treatment such as evaporation to dryness are reduced. The problem was that it became enormous. As will be described later, the fly ash treatment method of the present invention reduces the discharge amount of the filtrate F _{1 as} the drainage by reusing the filtrate F ₂ as the washing water for the rough water washing, and the salt separation. The facility cost and energy consumption for processing to recover the salt can be greatly reduced.

In the present invention, the water content of dehydrated cake _{C 1} is preferably 50 wt% or less, more preferably 45 wt% or less, and more preferably If it is 30 to 45 wt%. If the water content in the dewatered cake C ₁ exceeds 50 wt%, the concentration of the salt component remaining in the dehydrated cake C ₁ is increased, when you try to moisture content below 30% by weight, of the solid-liquid separator 5 This increases the burden, requires a reduction in the processing amount per unit time and an increase in the size of the equipment, leading to a reduction in the operating efficiency of other processing equipment, which is not preferable. Prepared water content of dehydrated cake C ₁ into the above range, it is possible to achieve by using a sodium-based dechlorinating agent.

Dewatered cake C ₁ is finishing cleaning is performed is sent to the second cleaning step. The rinsing tank 2 ′ for finishing cleaning may be provided separately from the rinsing tank 2 in the first cleaning step, but it is preferable to share it in order to reduce equipment costs.

In finishing the washing of the second cleaning step, since the chlorine concentration in the dehydrated cake C ₁ is reduced by the rough water washing, washing water to be used, it is preferred to use the novel washing water 14. The supply amount of the new cleaning water 14 at this time becomes the supply amount of new cleaning water into the system. That is intended to supplement the amount of washing water taken out drainage of filtrate F ₁ and with water in the dewatered cake C ₂ out of the system. The smaller the replenishment amount, the lower the operating cost. In addition, the operating conditions of the finish cleaning can be set in the same manner as the above-described rough water cleaning.

  The slurry after the finish cleaning is transferred to the solid-liquid separator 5 ′ preferably through the slurry storage tank 3 in the same manner as in the rough water cleaning. The slurry storage tank 3 and the solid-liquid separator 5 ′ in the second cleaning process may be arranged separately from the slurry storage tank 3 and the solid-liquid separator 5 in the first cleaning process, but are shared in order to reduce equipment costs. It is preferable to do.

In solid-liquid separator 5 'in the second washing step, the slurry is separated into a dehydrated cake C ₂ filtrate F _2. The filtrate F ₂ has a low chlorine concentration and can be reused as washing water for the rough water washing in the first washing step of the next batch. Dewatered cake C _2, after removal of the water content, can be reused as an industrial raw material for a cement raw material. Incidentally, dehydrated cake C ₂ is preferably a chlorine concentration relative to the fly ash solids (fly ash net weight) of 0.1 wt% or less.

Here, dehydrated cake C ₂ to transfer the dewatered cake receiving tank 7 is preferably a chlorine concentration relative to the fly ash solids (fly ash net weight) of 0.1 wt% or less. This dehydrated cake C _2, by removing the water, the chlorine concentration of 0.1 wt% or less of fly ash can be obtained, it can be effectively utilized in the industrial products of the cement raw material.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further, the scope of the present invention is not limited by these Examples.

  When cleaning fly ash with a chlorine concentration of 10% by weight and reducing the chlorine concentration in the fly ash to 0.1% by weight or less, new cleaning methods are used in the treatment method for fly ash in various combustion exhaust gases. The amount of water 14 replenished, the amount of drainage to be treated, and the amount of wastewater treatment energy required for the treatment when using an evaporator / dryer as the salt separation means 15 were compared.

  In addition, the required amount in the case of processing the fly ash of 300 kg / hour for 2 hours and 600 kg of fly ash was simulated. The amount of desalted residue produced is 100 kg / hour for a desalted residue having a chlorine concentration of 50% by weight when a sodium desalting agent is used, and 33.3% by weight for a calcium desalting agent. % Desalted residue is assumed to be 150 kg / hour.

  Furthermore, the amount of energy for drainage treatment was calculated assuming that the amount of energy required for temperature rise and evaporation with respect to the water in the wastewater to be treated by the evaporator / dryer was 2.5 MJ / kg. In addition, it was assumed that it was estimated as 3 significant figures.

<Example 1>
With the fly ash treatment method shown in the block diagram of FIG. 3, the conditions for treating 600 kg of fly ash in 2 hours were simulated during steady operation. In addition, after desalting residue (sodium chloride) 200 kg produced using sodium bicarbonate as a desalting agent is collected separately from fly ash by the second dust collector 52 and dissolved in the salt water storage tank 11, Salt separation treatment was performed.

  Table 1 shows the replenishment amount of the new washing water 14, the amount of drainage to the salt separation means 15, and the amount of drainage treatment energy required for the drainage treatment under the condition that the moisture content of the dehydrated cake is 45% by weight.

<Comparative Example 1>
By the fly ash treatment method shown in the block diagram of FIG. 4, conditions for treating 600 kg of fly ash in 2 hours were simulated during steady operation. In addition, 200 kg of desalted residue (chlorine concentration: 50% by weight) produced by using sodium bicarbonate as a desalting agent is collected together with fly ash by the first dust collector 51, and treated ash having a chlorine concentration of 20% by weight ( Simulation was performed assuming that 800 kg of fly ash + desalted residue) was separated from salt components by washing with water.

  Table 1 shows the replenishment amount of the new washing water 14, the drainage amount to the salt separation means 15, and the drainage treatment energy amount required for the drainage treatment under the condition that the moisture content of the dehydrated cake is 45% by weight.

<Comparative example 2>
By the fly ash treatment method shown in the block diagram of FIG. 4, conditions for treating 600 kg of fly ash in 2 hours were simulated during steady operation. In addition, 300 kg of desalted residue (chlorine concentration: 33.3% by weight) generated using calcium hydroxide as a desalting agent is collected together with fly ash by the first dust collector 51, and the chlorine concentration is 17.8% by weight. The treated ash (fly ash + desalted residue) 900 kg was simulated as a salt component separated by a water washing treatment. However, since the calcium-based desalting agent contains a reaction aid (diatomaceous earth or the like), the moisture content becomes high, so the moisture content of the dehydrated cake is 55% by weight.

  Table 1 shows the replenishment amount of the new washing water 14, the drainage amount to the salt separation means 15, and the drainage treatment energy amount required for the drainage treatment under the condition that the moisture content of the dehydrated cake is 55% by weight.

<Comparative Example 3>
The conditions for treating 600 kg of fly ash in 2 hours during steady operation were simulated by the fly ash treatment method in which the water washing process shown in the block diagram of FIG. 5 is only one stage. In addition, after desalting residue (sodium chloride) 200 kg produced using sodium bicarbonate as a desalting agent is collected separately from fly ash by the second dust collector 52 and dissolved in the salt water storage tank 11, Salt separation treatment was performed.

  Table 1 shows the replenishment amount of the new washing water 14, the drainage amount to the salt separation means 15, and the drainage treatment energy amount required for the drainage treatment under the condition that the moisture content of the dehydrated cake is 45% by weight.

  In order to reduce the chlorine concentration remaining in the fly ash after the dehydration treatment to 0.1% by weight or less, the fly ash and the desalted residue shown in Comparative Examples 1 and 2 are collected in a lump. In the method of washing with water, since the total amount of ash to be treated (fly ash + desalted residue) and salt components to be separated increases, a large amount of washing water is required and discharged to the salt separation means 15. The amount of liquid increases, and the amount of energy required for the drainage treatment becomes enormous. In Comparative Example 2, since the calcium-based desalting agent is used, the amount of desalted residue increases and the moisture content of the dehydrated cake increases, requiring a larger amount of washing water and drainage treatment energy. Was recognized.

  In Comparative Example 3, the fly ash collected separately from the desalting residue is washed only once, so a large amount of washing water is required and the amount of liquid drained to the salt separation means 15 is enormous. It was recognized that the amount of energy required for the drainage treatment was enormous.

On the other hand, it was recognized that Example 1 can reduce the replenishment amount and drainage treatment energy of the new cleaning water 14 by about 40% compared to Comparative Example 1. Therefore, by collecting fly ash independently from the combustion exhaust gas without mixing fly ash and desalted residue, and by effectively using the filtrate F ₂ that is generated in the middle while washing the fly ash in two stages It has been confirmed that the amount of washing water used and the amount of drainage can be reduced to reduce equipment and processing costs, and the chlorine content in incineration fly ash can be reduced.

It is explanatory drawing which shows an example of the apparatus structure of the dust collection process of the processing method of the fly ash which concerns on this invention. It is explanatory drawing which shows an example of the apparatus structure of the water washing process of the processing method of the fly ash which concerns on this invention. It is a block diagram which shows the example of the embodiment of the processing method of the fly ash which concerns on this invention. It is a block diagram which shows the processing method of the fly ash in the comparative examples 1 and 2. It is a block diagram which shows the processing method of the fly ash of the comparative example 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fly ash storage tank 2 Flush tank 3 Slurry storage tank 4 Slurry transfer pump 5 Solid-liquid separator 6 Dehydrated cake transfer means 7 Dehydrated cake receiving tank 8 Filtrate storage tank 9 Filtrate transfer pump 10 Filtrate transfer pump 11 Salt water storage tank 14 New washing water 15 Salt separation means 16 Transfer means 17 Crystal salt receiving tank 18 Exhaust blower 19 Low pressure steam 20 Storage tank 21 Transfer pump 51 First dust collector 52 Second dust collector 53 Desalting agent supply means

Claims (3)

After removing fly ash from the combustion exhaust gas generated from the incinerator, a desalting agent is added to the combustion exhaust gas, and the desalination residue obtained by reacting the desalting agent with the acid gas in the combustion exhaust gas is collected. In the treatment method of the fly ash in the exhaust gas treatment to be discharged,
The fly ash is washed with coarse water and then solid-liquid separated to obtain a dehydrated cake C _{1 and a} filtrate F _{1. The} dehydrated cake C ₁ is washed with finish water and solid-liquid separated to obtain a dehydrated cake. A second washing step of obtaining C _{2 and} filtrate F ₂ , wherein the dehydrated cake C ₂ is used as an industrial raw material, the filtrate F ₂ is stored and used for coarse water washing in the subsequent batch, and the first washing A method for treating fly ash in which the filtrate F ₁ obtained in the step is subjected to salt separation treatment to separate the salt.   The method for treating fly ash according to claim 1, wherein the desalting agent is a sodium-based desalting agent. The fly ash treatment method according to claim 1, wherein the desalted residue is dissolved in the filtrate F ₁ and then subjected to salt separation treatment to recover the salt.

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