JP2008221205A - Dust collection method of exhaust gas from sludge incinerator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dust collection method of exhaust gas from sludge incinerator capable of separating incinerated ash contained in an exhaust gas from a sludge incinerator into high-temperature fly ash containing extremely small amount of deposition of heavy metals such as As and Se, and low-temperature fly ash containing a large amount of heavy metals such as As and Se. <P>SOLUTION: The exhaust gas from the sludge incinerator 1 is supplied to a high-temperature cyclone 3 at 700°C or more to collect the high-temperature fly ash, thereafter the low-temperature fly ash is collected by a dust collector 5. In this invention, the separation limit particle size of the high-temperature cyclone 3 is adjusted, or the high-temperature fly ash collected by the high-temperature cyclone 3 is classified, so that the high-temperature fly ash having the minimum particle size of 10 μm or more is recovered. The amount of elution of heavy metals from this high-temperature coarse fly ash satisfies environmental standards. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for collecting dust from sludge incinerator exhaust gas generated when incinerating sewage dewatered sludge.

  Various techniques have been developed for the treatment of sewage dewatered sludge generated from sewage treatment plants, but the mainstream is the incineration process. Dust collection ash collected from the exhaust gas from this sludge incinerator contains a small amount of heavy metal, and when buried as it is, As, Se, F, and B exceed the elution standards stipulated in the soil environmental standards. May leach into the soil. Incidentally, the elution standard values are 0.01 mg / L for As and Se, 0.8 mg / L for F, and 1.0 mg / L for B. For this reason, in order to effectively use sludge incineration ash generated in large quantities, it is necessary to take elution prevention means, which has been an obstacle to effective use.

  Therefore, the inventors of the present invention supplied the exhaust gas from the sludge incinerator to a high-temperature cyclone at 700 ° C. or higher to collect high-temperature dust collection ash, and then collected the low-temperature dust collection ash with a dust collector installed at the subsequent stage. The technology to be developed has been proposed as Patent Document 1. This technology utilizes the fact that heavy metals such as As and Se evaporate at 700 ° C or higher, so that they do not remain in the high-temperature dust collection ash. is there. As, Se, etc. in the exhaust gas pass through the high-temperature cyclone in a gas state, but as the exhaust gas temperature subsequently drops, they condense and adhere to the surface of the incineration ash, and are collected at a low temperature by a dust collector of about 200 to 350 ° C at the subsequent stage. Collected with dust ash.

According to the method of Patent Document 1, a relatively large amount of high-temperature dust ash with a small residual amount of heavy metals such as As and Se and heavy metals such as As and Se (hereinafter simply referred to as heavy metals) are included. Separation and collection into a relatively small amount of low-temperature dust collection ash is possible, and effective use of high-temperature dust collection ash can be achieved. However, recently, there is an increasing demand for further reducing the amount of elution of heavy metals from dust collection ash than before. For this reason, there has been a demand for a novel dust collection method for sludge incinerator exhaust gas that can further reduce the elution amount of heavy metals.
JP 2006-116526 A

  The present invention has been made to meet the above-mentioned demands. The incineration ash contained in the sludge incinerator exhaust gas is composed of a high-temperature dust collection ash with a very small amount of residual heavy metals and a low-temperature collection containing a large amount of heavy metals. An object of the present invention is to provide a method for collecting dust from sludge incinerator exhaust gas that can be separated and collected into dust ash.

  As a result of repeated studies by the present inventors to solve this problem, heavy metals easily adhere to the surface of fine ash even among incinerated ash. For example, fine ash having a particle size of 10 μm or less among high-temperature dust ash is used. It was found that the amount of elution of heavy metals can be reduced by cutting only coarse ash. This phenomenon is presumed to be because the specific surface area increases as the particle size decreases, and the amount of heavy metals deposited per unit weight increases. In addition, the present inventors have confirmed that the elution reduction effect is also seen in P, F, and B that are not explicitly disclosed in Patent Document 1.

  The present invention has been completed on the basis of such knowledge. The invention of claim 1 is that after exhaust gas from a sludge incinerator is supplied to a high temperature cyclone at 700 ° C. or higher to collect high temperature dust ash. In a dust collection method for sludge incinerator exhaust gas that collects low temperature dust ash with a filtration dust collector, high temperature dust ash with a minimum particle size of 10 μm or more is recovered by adjusting the separation limit particle size of the high temperature cyclone It is characterized by doing. The separation limit particle size of the high temperature cyclone can be adjusted, for example, by blowing purge air from the lower part of the cyclone.

  Further, in order to solve the same problem, the invention according to claim 2 is that the exhaust gas from the sludge incinerator is supplied to a high-temperature cyclone at 700 ° C. or higher to collect high-temperature dust collection ash, and then separately collected by a separate dust collector. In a dust collection method for exhaust gas from a sludge incinerator that collects dust collection ash, the collected high temperature dust collection ash is classified and the high temperature dust collection ash having a minimum particle size of 10 μm or more is recovered. It is.

  In these first and second inventions, high-temperature dust ash that is collected at a high temperature of 700 ° C. or higher, has a minimum particle size of 10 μm or more, and does not contain fine ash having a particle size of 10 μm or less is recovered. To do. As described above, when the particle size is reduced, the specific surface area is increased, and the adhesion amount of P and heavy metals per unit weight is increased. Therefore, fine ash having a particle size of 10 μm or less is cut and the minimum particle size is set to 10 μm or more. For example, the elution amount of P and heavy metals from the high temperature dust ash can be further reduced. Note that the cut fine ash is collected by a filtration dust collector such as a bag filter or an electric dust collector.

Preferred embodiments of the present invention are shown below.
In FIG. 1, 1 is a sludge incinerator. Here, a fluidized bed incinerator is used in which air is blown from the bottom to form a fluidized bed. The sewage dewatered sludge is thrown into the sludge incinerator 1 by the sludge supply pump 2 and incinerated at 800 to 1000 ° C. However, the type of the sludge incinerator 1 is not particularly limited.

  The exhaust gas from the sludge incinerator 1 is guided to the high temperature cyclone 3. The high-temperature cyclone 3 has a collection temperature of 700 ° C. or higher and separates incinerated ash and exhaust gas contained in the exhaust gas. The vaporization temperature of P is 277 ° C, the vaporization temperature of As is 613 ° C, and the vaporization temperature of Se is 685 ° C. If the collection temperature is set to 700 ° C or higher, P, As, and Se are almost incinerated ash. It does not remain and moves to the latter stage with the exhaust gas. In addition, since some of the acidic components such as SOx and NOx contained in the incineration ash also move to the subsequent stage together with the exhaust gas, the incineration ash exhibits alkalinity of pH 8-9. A preferred collection temperature is 800 to 850 ° C.

  Many cyclones conventionally used in this technical field are designed to collect incinerated ash having a separation limit particle size of 3 to 5 μm, that is, a particle size of 3 to 5 μm or more. Incineration ash larger than the diameter is collected as high temperature dust ash. However, in the present invention, by adjusting the separation limit particle size of the high temperature cyclone 3 upward, the minimum particle size is set to 10 μm or more, and high temperature dust ash not containing fine ash having a particle size of 10 μm or less is recovered. A method for adjusting the separation limit particle size will be described later.

  When the particle size distribution of the incinerated ash in the fluidized bed incinerator is measured, the average particle size is around 30 μm, the weight ratio occupied by fine ash with a particle size of 10 μm or less is about 6 to 7%, and the weight ratio occupied by fine ash with a particle size of 20 μm or less is It is about 20%. In the present invention, the separation limit particle size may be set to an arbitrary value of 10 μm or more. However, when the separation limit particle size is set to be larger than 30 μm, the recovery rate of the high-temperature dust ash in the high-temperature cyclone 3 is reduced. This deviates from the purpose of collecting as much high-temperature dust ash as possible with a low heavy metal elution amount. For this reason, it is preferable to set the separation limit particle size within a range of 10 μm or more and 30 μm or less.

  In the present invention, the high temperature dust ash collected by the high temperature cyclone 3 is collected in a high temperature state of 700 ° C. or higher and does not contain fine ash having a separation limit particle size or less. As described above, since the fine ash has a large specific surface area and a relatively large amount of P and heavy metals per unit weight, the recovered high-temperature dust ash is made up of P and heavy metals by cutting the fine ash. It becomes clean ash with very small elution amount. Although specific numerical values are shown in the data of the examples, incineration ash having a particle size of 5 to 10 μm has an elution amount of P and As about 10 times larger than that of incineration ash having a particle size larger than that, and this is cut. In particular, the amount of elution of P and As can be greatly suppressed.

  In addition, since fine ash has a large specific surface area and a relatively large amount of acidic components such as SOx and NOx per unit weight, the collected high-temperature dust ash is alkaline with a pH of 10 to 11 by cutting the fine ash. Presents. For this reason, it becomes possible to suppress the elution of ash without adding lime which has been conventionally used as an ash elution suppression means.

  Thus, this high temperature dust collection ash has cleared the soil environmental standard, can be embedded as it is, and can also be effectively used as it is without taking elution prevention means. Furthermore, since the elution amount of P is suppressed in this high temperature dust collection ash, the problem of product strength reduction due to the mixing of P, which has occurred when incinerated ash is used as a cement material or a cement-based solidifying agent-added civil engineering material, can be solved.

  Moreover, as described above, the weight ratio occupied by fine ash having a particle size of 10 μm or less in the total incinerated ash is about 6 to 7%, and the weight ratio occupied by fine ash having a size of 20 μm or less is about 20%. Is set to 10 to 20 μm, the amount of high-temperature dust collection ash recovered by the high-temperature cyclone 3 does not decrease so much.

  The separation limit particle size of the high-temperature cyclone 3 can be freely set when newly designed and manufactured. However, the existing high-temperature cyclone 3 can be adjusted by blowing purge air from the lower portion of the high-temperature cyclone 3 as shown in FIG. That is, as the purge air is blown, an upward flow is formed inside the cyclone and the fine particles to be dropped are blown up, so that the separation limit particle size can be shifted to the larger diameter side. The separation limit particle size can be freely adjusted by changing the air volume of the purge air.

  In this way, after collecting clean high-temperature dust collection ash in which the elution amount of P and heavy metals is extremely low, the exhaust gas is cooled to about 200 to 350 ° C. in the cooling tower 4. At this stage, P and heavy metals condense and adhere to the surface of the incinerated ash, so the low-temperature dust ash is collected by the dust collector 5 such as a bag filter or a ceramic filter. Since a large amount of P and heavy metals adhere to this low-temperature dust collection ash, post-treatment such as fixing P and heavy metals is separately performed and finally disposed. The exhaust gas that has passed through the dust collector 5 is desulfurized and demineralized by the scrubber 6 and released, but contains almost no P and heavy metals.

  In the invention of claim 1 explained above, the separation limit particle size of the high temperature cyclone 3 is adjusted so that the minimum particle size is 10 μm or more and the high temperature dust ash not containing fine ash having a particle size of 10 μm or less is recovered. In the invention of claim 2 shown in FIG. 3, a high-temperature cyclone 3 having a separation limit particle size similar to the conventional one is used. In this case, since fine ash having a particle size of 10 μm or less is contained in the high-temperature dust collection ash, classification is performed by the classifier 7 to separate the fine ash having a particle size of 10 μm or less.

  Since this fine ash contains a relatively large amount of P and heavy metals than the coarse ash, it is disposed with the low-temperature dust collection ash collected by the filtration dust collector 5. Coarse ash not containing fine ash having a particle size of 10 μm or less is a clean ash with an extremely low elution amount of P and heavy metals.

  A sewage sludge dewatering cake containing a relatively large amount of P and As generated from a certain sewage treatment plant is incinerated in a fluidized bed incinerator having a furnace temperature of 820 ° C., and the exhaust gas is obtained by the method of the present invention shown in FIG. Processed. First, as a comparative example, high temperature cyclone purge air was stopped, high temperature dust ash was collected at a dust collection temperature of 800 ° C., and an elution test for P and heavy metals was conducted by a method stipulated in environmental standards. Was 0.002 mg / L and cleared the standard value of 0.01 mg / L, but As was 0.016 mg / L and exceeded the standard value of 0.01 mg. The elution amount of P was 1.33 mg / L.

  On the other hand, the separation limit particle size of the high-temperature cyclone is adjusted by blowing purge air (about 37% of the exhaust gas amount) according to the method of the present invention, and only the high-temperature dust collection ash not containing fine ash having a particle size of 10 μm or less. In this case, the elution amount of Se was 0.002 mg / L as in the above comparative example, but the elution amount of P was 0.05 mg / L or less, and As was a quantification limit value of 0.0. The level dropped below 005 mg / L to an undetectable level.

  In addition, when the high temperature dust ash collected in the comparative example was classified and the elution amount of As was measured according to the particle size, the elution amount of As from fine ash of 10 μm or less reached 0.06 mg / L. It was confirmed that the removal of this part enabled the collection of clean ash with a low As elution amount.

  As shown in the data of this example, according to the present invention, the incineration ash contained in the sludge incinerator exhaust gas is a high-temperature dust collection ash that can clear environmental standards with very little P and heavy metal adhesion, and these Can be separated and collected into low-temperature dust ash containing a relatively large amount of ash, which is advantageous for effective use of incinerated ash.

It is a flowchart which shows embodiment of invention of Claim 1. It is a flowchart which shows other embodiment of invention of Claim 1. It is a flowchart which shows embodiment of invention of Claim 2.

Explanation of symbols

1 Sludge incinerator 2 Sludge supply pump 3 High temperature cyclone 4 Cooling tower 5 Dust collector 6 Scrubber 7 Classifier

Claims (3)

  In the dust collection method of sludge incinerator exhaust gas, the exhaust gas from the sludge incinerator is supplied to the high temperature cyclone at 700 ° C or higher to collect the high temperature dust ash, and then the low temperature dust ash is collected by the dust collector. A dust collection method for exhaust gas from a sludge incinerator, wherein the high temperature dust collection ash having a minimum particle size of 10 μm or more is recovered by adjusting the separation limit particle size of the sludge.   In the dust collection method of the sludge incinerator exhaust gas, the exhaust gas from the sludge incinerator is supplied to the high temperature cyclone at 700 ° C or higher to collect the high temperature dust ash and then the low temperature dust ash is collected by the dust collector. A method for collecting dust from a sludge incinerator exhaust gas, wherein the collected high-temperature dust ash is classified and the high-temperature dust ash having a minimum particle size of 10 μm or more is recovered.   The method for collecting dust from a sludge incinerator exhaust gas according to claim 1, wherein the separation limit particle size of the high-temperature cyclone is adjusted by blowing purge air from the lower part of the cyclone.

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