JP2005134098A - Method for treating burned ash - Google Patents

Abstract

[PROBLEMS] To improve soil without causing growth disturbance of agricultural products by treating incinerated ash by a simple and inexpensive method that replaces complicated and time-consuming methods such as cement solidification and melting and suppressing boron elution. The purpose is to make it available as a material.
SOLUTION: Lime is burned in a combustion furnace (A), the haiku gas is treated with an electric dust collector, and the resulting dust collection ash (EP ash) is used as a main fuel in the combustion furnace (B). A method for treating incinerated ash by which the amount of boron in incinerated ash that has been burned again with the addition of a calcium source is reduced to 1.0 mg / l or less by a dissolution test method based on Notification No. 18 of the 2003 Environment Agency. Preferably, the combustion furnace (A) is a coal stalker furnace and the combustion furnace (B) is a fluidized bed combustion furnace.

Description

The present invention relates to a method for treating incineration ash, and more particularly to a method for treating incineration ash that can be used as a soil improvement material. Since the present invention meets the elution reference value of boron, which is one of the substances regulated by the Soil Contamination Countermeasures Law enacted in February 2003 by the Ministry of the Environment, coal containing a large amount of boron is burned in a combustion furnace. Then, the exhaust gas generated at that time is treated with an electric dust collector (EP), and the EP ash is burned again in a combustion furnace using coal as a main fuel and a calcium source can be added. The present invention relates to a method for treating incineration ash that makes the elution amount of boron contained therein 1.0 mg / l or less to make incineration ash that can be used as a soil improvement material.

Boron-containing soil is eluted with rainwater and mixed with groundwater or agricultural water. It is known that plants consume a large amount of boron and inhibit growth. For this reason, boron insolubilization technology will play an important role in areas with soil containing boron.

Meanwhile, incineration ash such as household waste incineration ash, coal combustion ash (coal ash) from thermal power plants and paper mills, sewage sludge combustion ash, various industrial wastes, etc. contain boron, Since the coal ash originally contains several to several hundred mg / kg of boron in the coal, the content of boron or boron compounds is high. In addition, since most of the incinerated ash is used for landfilling, there is a concern that it will be eluted by rain or the like and adversely affect plants. In addition, since there is a shortage of landfills for incineration ash, it is desirable to make effective use of incineration ash in order to reduce the increase in environmental pollution caused by increasing the number of landfills.

In order to render the incinerated ash harmless, it is conceivable to melt at a high temperature of 1500 ° C., for example, and to cool and solidify it. In addition, as a means for stabilizing ash, cement solidification, treatment with chemicals, extraction treatment with acid or other solvents have been proposed.

In the processing method for melting and solidifying (for example, refer to Patent Document 1), the solid matter produced is not uniform even though it consumes enormous heat energy to melt the ash, and is not suitable for landfill. The ash component melts after landfill, which is not enough.

In the processing method of solidifying ash with cement (for example, see Patent Document 2), even if solidified due to the properties of ash, the solidified product may not be durable. For example, cement is weathered and ash components are eluted. Contamination due to this is considered.

A calcium-based material, alkali material, amorphous alumina, activated alumina as a solidifying material, and water added to zeolite, allophane, bentonite as a fixing material, and cured for a certain period of time from room temperature to 200 ° C. to solidify or fix (Patent Document 3) (See below), but curing takes time.

Further, a method of melting a molten ash by adding a mixture mainly composed of a silicate compound containing an alkali metal and an alkaline earth metal (see, for example, Patent Document 4) has also been proposed. Although it decreases, it still needs to be heated to 1300 ° C. or higher, and this method is not practical for using ash for inexpensive applications such as soil amendments.

On the other hand, in the method of making the ash component insoluble with an inorganic or organic chemical and stabilizing it (for example, see Patent Document 5), several steps are required for the treatment, the cost is high, and it is used in the treatment step. It is necessary to consider the post-treatment of the drug, which is not preferable. In addition, extraction processing with a solvent such as an acid (see, for example, Non-Patent Document 1) requires a long time and requires a large-scale facility, which is not suitable for practical use.

Furthermore, when incineration ash is used as a snow-melting agent or a soil conditioner to improve acidic soil, there are limited ways to suppress elution of heavy metals and boron, etc., more than in landfills, such as cementing with cement. It is a situation that must be said to be out of the question. As described above in detail, each of the ash treatment means considered in the conventional knowledge has fundamental difficulties, and no very satisfactory treatment has been proposed.
JP 2000-5727 A JP 2001-310175 A Japanese Patent Laid-Open No. 9-271738 JP 2001-310175 A Japanese Patent No. 3005617 Obayashi Institute of Technology Report No65 P96-100 (2002)

The present invention provides a simple and inexpensive method for suppressing the dissolution of boron from ash discharged from a coal boiler such as a thermal power plant instead of the complicated and time-consuming method of cement solidification and melting as described above. In this way, the incineration ash is intended to be usable as a soil conditioner without causing the growth of agricultural products due to boron.

In order to solve the above-mentioned problems, the present inventors have investigated the reaction in a furnace, particularly in a fluidized bed combustion furnace, and as a result, calcium contained in limestone for desulfurization reacts with boron in a high temperature region, It has been found that immobilization is also effective. Further, it was found that this effect is more effective as the amount of boron contained in the ash is larger, and the present invention has been achieved.
This application includes the following inventions.

(1) Coal is burned in a combustion furnace (A), the exhaust gas is treated with an electric precipitator, and the resulting dust collection ash (Electronic Precipitator ash, hereinafter abbreviated as EP ash) is a combustion furnace ( B) Incineration ash that uses coal as the main fuel and burns again with the addition of calcium source to reduce the boron content to 1.0 mg / l or less according to the dissolution test method based on Environmental Agency Notification No. 18 of 2003 Processing method.

(2) The incineration ash treatment method according to (1), wherein the combustion furnace (A) is a coal stalker furnace, and the combustion furnace (B) is a fluidized bed combustion furnace.

(3) The weight ratio of coal to the calcium source (as CaO) when burning in the combustion furnace (B) is 100/1 to 100/20, and the incinerated ash according to (1) or (2) Processing method.

(4) The calcium source used in the combustion furnace (B) is any one of limestone, dolomite, scallops, paper sludge, and waste paper basket, or a combination of any ratio (1) The processing method of incineration ash of any one of-(3).

(5) The incineration ash treatment method according to any one of (1) to (4), wherein the furnace temperature of the combustion furnace B is 700 ° C. or higher and 900 ° C. or lower.

 By re-burning coal ash (EP ash) in a combustion furnace to which a calcium source can be added, elution of boron contained in incinerated ash can be suppressed, so it can be used as a soil improver without affecting the environment. . Furthermore, since the unburned carbon contained in the EP ash from the first coal boiler can be effectively used as the fuel for the next coal boiler, the amount of coal there can be reduced and it is economical.

The present invention is a method for suppressing the dissolution of boron contained in incinerated ash, and is configured as follows in order to solve the technical problems described above. That is, according to the present invention, relatively high concentrations of boron and boron compounds are collected in the EP ash obtained by collecting the exhaust gas generated when coal is burned with an electric dust collector. On the other hand, since a large amount of unburned carbon remains in the EP ash, it is used as a part of the coal fuel to burn again with the coal in the combustion furnace B in which the calcium source can be directly input.

The function of limestone used for desulfurization in a fluidized bed combustion furnace is achieved by the calcium contained in the limestone reacting with sulfur contained in the coal at a high temperature to become gypsum. On the other hand, the reaction with boron is not fully understood, but boron or boron compounds contained in coal and EP ash are vaporized, which reacts with calcium, and boron is incorporated into the compounds mainly composed of calcium. Estimated.

The coal used in the present invention may be either domestic coal or foreign coal, and the type of coal such as peat and lignite is not limited. Coal contains several ppm to less than 300 ppm of boron in domestic coal, but in the present invention, the boron elution suppression effect is excellent, so it is not necessary to select coal with particularly low boron content. .

The combustion furnace A used in the present invention is preferably a furnace having a structure in which the concentrations of boron and boron compounds in fly ash are increased, and for that purpose, a stalker furnace not having a structure to which a calcium source is added is suitable. On the other hand, both the pulverized coal combustion furnace and the fluidized bed combustion furnace have a structure that uses limestone as a calcium source for desulfurization. Therefore, the bottom ash contains a lot of boron compounds, but fly ash contains boron and boron compounds. This is not preferable because the amount of is small and the processing efficiency is lowered.

A stalker furnace is a furnace that can burn various miscellaneous goods, and is a combustion furnace that is used in many factories because it is simpler and cheaper than pulverized coal combustion furnaces and fluidized bed combustion furnaces. .
The ash discharged from this furnace (EP ash) is mixed with unburned coal and is not economical to be discharged as it is. Since EP ash has a fine particle size, it is optimal for use as a soil conditioner. However, since it contains a large amount of vaporized boron, it cannot be used as a soil conditioner.

The combustion furnace B used in the present invention may be a pulverized coal combustion furnace, a fluidized bed combustion furnace, or a coal gasification furnace as long as it can add a calcium source. A pulverized coal combustion furnace or a fluidized bed combustion furnace capable of adding a calcium source used to immobilize sulfur is preferable, and more specifically, a fluidized bed combustion furnace having a structure that can be easily charged is the best. The fluidized bed combustion furnace has a structure in which a heating section such as coal is combusted in a fluidized state with a medium such as gas or sand, and is excellent in terms of thermal efficiency.

It is possible to change the structure of the stalker furnace and add limestone to suppress the elution of boron, but it is possible to add limestone in the stalker furnace, but limestone is boron contained in coal due to the structure of the furnace. It is not practical because it reacts little with sulfur and falls to the bottom of the furnace and only the amount of incinerated ash increases, and changing the structure of a stalker furnace is not practical.

Even if the combustion furnace A used in the present invention is a fluidized bed combustion furnace, and the latter combustion furnace B is also a fluidized bed combustion furnace, both furnaces can use limestone, etc. effective. However, as mentioned above, fluidized bed combustion furnaces have high equipment costs, and the addition of limestone to the two furnaces increases the absolute amount of incinerated ash that is discarded, handling, ash treatment, and cost. The load increases.

The weight ratio of coal to limestone when burning in a fluidized bed combustion furnace is preferably in the range of 100/1 to 100/20, more preferably in the range of 100/2 to 100/10. Is good. If the weight ratio is less than 100/1, sulfur and boron cannot be collected sufficiently. Conversely, if the weight ratio exceeds 100/20, the proportion of secondary materials increases compared to fuel. Is not practical because it reduces not only economically, but also increases the total amount of incinerated ash, which takes time and cost.

The calcium source used in the fluidized bed combustion furnace is either one of calcium-based materials such as limestone, dolomite, scallops, or high calcium content materials such as paper sludge and waste paper lees characteristically discharged from paper mills, Alternatively, any combination of ratios can be used.

Further, there is no problem even if at least one of zeolite, allophane, and bentonite is used alone or in combination in any ratio and used as a reaction promoting aid for promoting the reaction between boron and calcium. . When the incinerated ash already contains a calcium source or a reaction promoting aid, the amount of these newly added can be adjusted.

The furnace temperature in the combustion furnace A of the present invention is preferably 600 ° C. to 800 ° C., and if it exceeds 800 ° C., boron or boron compounds are almost discharged out of the system, which is not preferable from the environmental point of view. Since the efficiency of EP) is reduced, it is further undesirable. On the other hand, the in-furnace temperature of the combustion furnace B of the present invention is preferably 700 ° C. or more and 900 ° C. or less, and if it is less than 700 ° C., the calcium carbonate contained in the limestone has not completely changed to calcium oxide. Also, the reactivity with boron is not good. If the temperature exceeds 900 ° C., the limestone is overburned, the surface of the limestone is vitrified, and the surface area is reduced, which makes it difficult to collect sulfur and boron, which is not preferable.

The incinerated ash obtained by the present invention has a boron amount of 1.0 mg / l or less by a dissolution test based on 2003 Environmental Agency Notification No. 18 “Solution Method of Soil Elution Standard”.
If the amount of boron is 1.0 mg / l or less, it is considered to be within the standards of the “Soil Contamination Countermeasures Law”, and incinerated ash whose boron elution is suppressed within that range can be effectively used as a soil conditioner. It becomes.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is of course not limited by these examples, and the implementation thereof is not departed from the gist of the present invention. Aspects can be changed.

1) Boron Elution Method In each of the following examples and comparative examples, the boron elution test was conducted in accordance with Notification No. 18 of the 2003 Environment Agency. In other words, the fly ash collected by the electric dust collector (EP) in the flue of the stoker furnace or the fly ash collected by the bag filter installed in the flue of the fluidized bed combustion furnace is air-dried. After removing the gravel and wood pieces, the aggregate is pulverized and then passed through a non-metallic 2 mm sieve and mixed well. From this sample, 50 g is put into a 500 cc polyethylene container with a lid, and hydrochloric acid is added to pure water to adjust the pH to 6.0, so that the total amount becomes 500 cc. This prepared sample solution was shaken continuously (shaking width 4-5 cm, frequency 200 times / min) for 6 hours at room temperature and atmospheric pressure using an industrial waste elution shaker (manufactured by Taitec Corporation). This solution was allowed to stand for 30 minutes, and then centrifuged at about 3000 rpm for 20 minutes. The supernatant was filtered through a membrane filter having a pore size of 0.45 μm, the filtrate was taken, the amount required for quantification was accurately measured, and this was used as a test solution.

2) Measuring method of boron The test solution was analyzed with ICP-OES (inductively coupled plasma optical emission spectrometer, manufactured by Rigaku / Spectoro, CIROS-120 type), and the amount of eluted boron was quantified.

Example 1
Furnace A is a stalker furnace, Furnace B is an actual machine using a fluidized bed combustion furnace, Furnace A burns coal (Australia), Furnace B uses EP A ash and coal (Australia) as fuel Then, limestone was added to the coal so that the weight ratio in terms of calcium was 100: 5 and burned. The temperature inside the furnace A was 750 ° C., and the temperature inside the furnace B was 800 ° C. The fly ash discharged from the furnace B was used as a test sample, and analyzed by the above elution method and measurement method to determine the elution amount of boron. The results are shown in Table 1.

Example 2
The types of the furnace A and the furnace B are the same as those in Example 1, but the furnace A burns coal (Australia), the furnace B uses EP ash of the furnace A and coal (Australia) as fuel, coal In contrast, dolomite and paper sludge were added and burned so that the weight ratio in terms of calcium was 100: 8. The temperature inside the furnace A was 750 ° C., and the temperature inside the furnace B was 780 ° C. The fly ash discharged from the furnace B was used as a test sample, and analyzed by the above elution method and measurement method to determine the elution amount of boron. The results are shown in Table 1.

Example 3
The types of the furnace A and the furnace B are the same as those in Example 1. In the furnace A, coal (produced in China) is burned, and in the furnace B, EP ash of the furnace A and coal (produced in China) are used as fuel. On the other hand, scallops and waste paper cake were added and burned at a calcium-converted weight ratio of 100: 2. The temperature inside the furnace A was 740 ° C., and the temperature inside the furnace B was 800 ° C. The fly ash discharged from the furnace B was used as a test sample, and analyzed by the above elution method and measurement method to determine the elution amount of boron. The results are shown in Table 1.

Comparative Example 1
Furnace A is a stalker furnace, and furnace B is also a stalker furnace. In furnace A, coal (Australia) was burned, and in furnace B, the EP ash of coal in furnace A and coal (Australia) were burned. . In furnace A and furnace B, no calcium source is added. The temperature inside the furnace A was 750 ° C., and the temperature inside the furnace B was 800 ° C. The fly ash discharged from the furnace B was used as a test sample, and analyzed by the above elution method and measurement method to determine the elution amount of boron. The results are shown in Table 1.

Comparative Example 2
There was no furnace A, and furnace B was a one-stage combustion method of a fluidized bed combustion furnace. In furnace B, limestone was added to coal (Indonesian coal) so as to be 100: 5 in terms of calcium and burned. The temperature of furnace B was 780 ° C. The fly ash discharged from the furnace B was used as a test sample, and analyzed by the above elution method and measurement method to determine the elution amount of boron. The results are shown in Table 1.

Comparative Example 3
The temperature inside the furnace A was 850 ° C., and the temperature inside the furnace B was 680 ° C. The fly ash discharged from the furnace B was used as a test sample and analyzed by the above elution method and measurement method to determine the boron elution amount. The results are shown in Table 1.

 As apparent from Table 1, using a stalker furnace for furnace A and a fluidized bed combustion furnace for furnace B, EP ash and coal of furnace A were burned in furnace B. The calcium source to be added is limestone, dolomite and paper sludge are added in Example 2, scallops and waste paper lees are added in Example 3, and the ratio of coal to calcium and the temperature in the furnace are stored in the respective claims of the present invention. In this case, the elution amount of boron from the ash discharged from the furnace B can be set to 1.0 mg / l or less.

On the other hand, when both the furnaces A and B are stalker furnaces as in Comparative Example 1 and no calcium source is added, elution of boron can hardly be suppressed, so that the reference value is greatly exceeded. Although Comparative Example 2 is a one-stage combustion method without furnace A, even if a large amount of limestone is added to furnace B, the elution amount of boron can be suppressed as compared with Comparative Example 1, but the reference value cannot still be cleared. Furthermore, in Comparative Example 3, the temperature of the combustion furnace (A) was set higher than that in Example 1, but since the temperature in the furnace B into which limestone was charged was low, the limestone did not act effectively, and the boron elution amount was a comparative example. It becomes more than 2 and exceeds the reference value.

 As described above, since the boron elution amount can be suppressed to 1.0 mg / l or less by burning in two stages by a simple method, the incineration double factor obtained by the two-stage combustion is used as a soil improvement material. It became possible to do.

Claims (5)

Coal is burned in a combustion furnace (A), and the exhaust gas is discharged into an electric precipitator (Electronic Pre).
Dust ash (Electronic Precip) obtained by processing with a cipitator
Iterator ash) is a combustion furnace (B), coal is the main fuel, incinerated ash burned again with the addition of calcium source, the boron content by the dissolution test method based on 2003 Environment Agency Notification No. 18 1.0mg / L or less incinerated ash treatment method. The method for treating incinerated ash according to claim 1, wherein the combustion furnace (A) is a coal stalker furnace, and the combustion furnace (B) is a fluidized bed combustion furnace. The weight ratio of coal to calcium source (as CaO) when burning in the combustion furnace (B) is 1
It is 00/1 to 100/20, The processing method of the incineration ash of Claim 1 or 2 characterized by the above-mentioned. The calcium source used in the combustion furnace (B) is any one of limestone, dolomite, scallops, paper sludge and waste paper cocoons, or a combination of arbitrary ratios. Incineration ash treatment method according to any one of items The method for treating incineration ash according to any one of claims 1 to 4, wherein the temperature in the furnace of the combustion furnace B is 700 ° C or higher and 900 ° C or lower.