JP2020082035A - Coal ash volume reduction method - Google Patents

Abstract

To provide a coal ash volume reduction method where efficient coal ash volume reduction is achieved and the elution of heavy metals can be equal to a reference value or less.SOLUTION: A coal ash volume reduction method includes: an ignition loss amount adjustment step 100 adjusting the ignition loss amount of coal ash to a predetermined value; an Na amount adjustment step 200 adjusting an Na amount in an Na source mixed in coal ash to a predetermined value; a mixing step 300 mixing an Na source amount adjusted by the Na amount adjustment step 200 to coal ash whose ignition loss amount is adjusted by the ignition loss amount adjustment step 100; a heating step 400 where microwaves with a predetermined frequency are irradiated onto a mixture mixed by the mixing step 300 in a predetermined time for increasing the temperature of the mixture to a predetermined temperature and the mixture is sintered; and a cooling step 500 cooling a sintered material heated by the heating step 400 by a predetermined cooling method.SELECTED DRAWING: Figure 1

Description

The present invention relates to a coal ash volume reduction method for effectively utilizing coal ash.

Patent Document 1 (Japanese Patent Laid-Open No. 2006-117478) is intended to significantly reduce the reaction temperature and reaction time by using a method such as atmospheric pressure steam curing for the curing process of the coal ash cured body, Coal ash, calcareous raw material, reinforcing fiber, water, and a mixture of siliceous raw material and calcareous raw material 100 parts by weight of solid content, a mixed material containing 8 parts by weight or less of solid content of sodium hydroxide was molded. Then, a coal ash cured product, which is pre-dried at a predetermined temperature, solidified by atmospheric pressure steam curing or microwave-hydrothermal curing, and post-dried, and an energy-saving production method thereof are disclosed. Further, by adding sodium hydroxide to the mixture of coal ash and calcareous raw material, curing in the curing step is promoted, mechanical strength is improved, and there is no deformation in the drying step, which is excellent in dimensional stability. It is disclosed that a high-strength molded product can be obtained, and it is further disclosed that the addition amount of sodium hydroxide is desirably 8 parts by weight or less. Furthermore, the use of microwave drying for pre-drying and post-drying is disclosed.

Patent Document 2 (Japanese Unexamined Patent Publication No. 2018-58027) is an adsorbent containing cesium and strontium derived from coal ash, wherein the adsorbent contains a zeolite precursor as a main component, and is amorphous. Disclosed is a method for producing an adsorbent containing a high quality alumina silicate and a zeolitized alumina silicate. In this patent document 2, the manufacturing method is a step of adding an alkaline aqueous solution to coal ash and heating at 70 to 120° C. to obtain a zeolite precursor, and a step of separating the zeolite precursor from the aqueous solution containing the zeolite precursor. It is disclosed that the heating means is a microwave.

Patent Document 3 (Japanese Patent Laid-Open No. 9-30857) discloses a sintered body formed by sintering coal ash generated from a pulverized coal burning coal-fired boiler such as fly ash, cinder ash, and bottom ash, and then sintering the coal ash. To do. In Patent Document 3, since it is not possible to sufficiently grasp the physical properties as the weight loss of the sintered body by the conventional Blaine specific surface area, ignition loss value, etc., regarding the coal ash containing carbon, the carbon amount can be calculated as the BET specific surface area. It is disclosed that a good quality coal ash is selected as a sinter loss by selecting the quality index as a control index together with the particle size represented by the residual amount on the screen as a control index, and obtaining a high-strength, non-cracked sinter. It

Patent Document 4 (Japanese Patent Laid-Open No. 56-54267) discloses that coal ash (including fly ash and clinker) obtained from a coal-fired power plant, includes phosphoric acid, polymerized phosphoric acid, phosphorous acid, hypophosphorous acid, and those Disclosed is a curable composition obtained by mixing at least one selected from the group consisting of salts. This Patent Document 4 discloses that coal ash is hardened by kneading phosphoric acid with coal ash. Further, if dilute phosphoric acid is used, the hardening time tends to be long and the strength tends to be low. It is disclosed that when is used, the curing time is shortened and the strength is increased. Also, in the examples, it is disclosed to use 2.78% Igros coal ash.

JP, 2006-117478, A JP, 2018-58027, A JP-A-9-30857 Japanese Patent Laid-Open No. 56-54267

In recent years, from the viewpoint of recycling coal ash, hardening and weight reduction of coal ash have become important issues. In a coal-fired power plant, crushed coal powder is burned in a boiler and its thermal energy is converted into electricity, but the particles of coal ash are melted by this combustion and float in the hot combustion gas, As the temperature decreases toward the outlet, it becomes spherical and is captured by the dust collector. The main components of the coal ash generated by this are "silica" and "alumina", which are used as raw materials for cement raw materials, concrete admixtures, fillers, shielding materials, soil/ground improvement materials, etc. Used, the rest is landfilled. However, from the viewpoint of cost and environmental protection, it is now difficult to secure a new disposal site, and if the landfill site continues to be used, it is necessary to reduce the amount of coal ash produced by the plant. There is. Furthermore, the sintering and hardening of coal ash is also expected to lead to the development of new structural materials.

In addition, coal ash and sintered body contain heavy metals such as hexavalent chromium, arsenic, selenium, fluorine, and boron, although the amount is small, and the elution of these heavy metals from the final product is below the standard value. There must be.

For this reason, the present invention provides a method for reducing the volume of coal ash that can achieve efficient volume reduction of coal ash and further reduce the elution of heavy metals to a reference value or less.

Therefore, the volume-reducing method according to the present invention comprises an igross amount adjusting step of adjusting the igross amount of the coal ash to a predetermined value, and a Na amount of Na source mixed with the coal ash to a predetermined value. Amount adjustment step, a mixing step of mixing the coal ash of which the amount of igross has been adjusted by the igross amount adjusting step and the amount of the Na source adjusted by the Na amount adjusting step, and the mixture mixed by the mixing step have a predetermined In order to raise the temperature, a heating step of irradiating the mixture with microwaves of a predetermined frequency for a predetermined time to sinter, and a cooling step of cooling the sinter heated by the heating step by a predetermined cooling method Composed.

It is desirable that the predetermined value of the Igros amount is 10% by weight or less based on the weight of coal ash, preferably in the range of 4.4 to 7.2% by weight, and more preferably 6% by weight. Regarding the adjustment of the amount of coal ash, it is possible to adjust the amount of coal ash by mixing coal ash with different amounts of ignition (ignition loss) generated at each predetermined power plant. For example, the amount of coal ash (Shin-Onoda ash) generated at the Shin-Onoda power plant is about 3%, whereas the amount of coal ash (Mizushima ash) generated at the Mizushima power plant is about 17%. Therefore, when the amount of Shin Onoda ash is increased, the amount of Igros decreases, and when the amount of Mizushima ash is increased, the amount of Igros increases.

The amount of Na is in the range of 0.5 to 2.33% by weight, preferably in the range of 1.0 to 1.5% by weight, and more preferably 1.0% by weight, based on the weight of coal ash. Is desirable. The Na source is preferably a sodium hydroxide solution or a sodium chloride solution, and seawater is preferably used instead of the sodium chloride solution.

The frequency of the microwave applied in the heating step is preferably 2.45 GHz±0.5 GHz, and the component applied to the mixture is preferably the electric field component. Further, in this heating step, it is desirable to heat to a temperature of 800° C. or higher, particularly 1200° C. or higher by irradiating with microwaves. Also, the time required to reach the predetermined temperature changes depending on the amount of Na described above.

The cooling method of the cooling step differs depending on the use of the final product, and it is desirable to gradually cool the final product in a state where the sintered shape is retained, and it is preferable to use the clinker final product when the final product is desired. It is desirable to quench rapidly. Further, regarding rapid cooling, there are atmospheric quenching and underwater quenching.

According to the present invention, the coal ash having a predetermined proportion of Igros is further mixed with a Na source having a predetermined amount of Na, so that it can be heated to a predetermined temperature in a short time, and the density ratio before and after melting. Therefore, the volume can be reduced to about 50% at the maximum. Further, it becomes possible to keep the elution of heavy metals within the standard value when they are extinguished/melted.

It is the block diagram which showed the outline of the volume reduction method which concerns on this invention. FIG. 5 is a characteristic diagram showing a relationship between μ wave irradiation time and surface temperature for compositions having different amounts of igross. It is a characteristic diagram which showed the relationship between the μ wave irradiation time and the surface temperature of coal ash with different Na amounts. FIG. 3 is a characteristic diagram showing the relationship between microwave irradiation time and surface temperature when the amount of NaOH is changed in coal ash with an Igros amount of 10.0%. FIG. 6 is a characteristic diagram showing the relationship between the microwave irradiation time and the surface temperature when the amount of NaOH is changed in coal ash having an igloss amount of 7.7%. FIG. 4 is a characteristic diagram showing the relationship between microwave irradiation time and surface temperature when the amount of NaOH is changed in coal ash with an Igros amount of 6.5%. FIG. 7 is a characteristic diagram showing the relationship between microwave irradiation time and surface temperature when the amount of NaOH is changed in coal ash with an igloss amount of 5.8%. It is a characteristic diagram which showed the relationship between the microwave irradiation time and the surface temperature when the amount of NaOH is changed in the coal ash with an amount of 5.0% of gross. FIG. 7 is a characteristic diagram showing the relationship between microwave irradiation time and surface temperature when the amount of NaOH is changed in coal ash with an amount of 4.4% igross. FIG. 4 is a characteristic diagram showing the relationship between the microwave irradiation time and the surface temperature when the amount of NaOH is changed in coal ash with an Igros amount of 4.2%. 6 is a graph showing the relationship between the concentration of NaOH and the heating time when the amount of igloss is 5.8%. FIG. 4 is a characteristic diagram showing the relationship between microwave irradiation time and surface temperature in the case of salt, seawater, and tap water when the amount of igross is 5.8%. It is the table which showed the elution test result of the heavy metals of coal ash and a sintered body.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

The volume reduction method according to the present invention, as shown in FIG. 1, an igross amount adjusting step 100 for adjusting the igross amount of coal ash to a predetermined value, and a Na amount of a Na source mixed with the coal ash to a predetermined value. A Na amount adjusting step 200 of adjusting the value of the above, a mixing step 300 of mixing the coal ash having an igros amount adjusted by the igros amount adjusting step and a Na source of the amount adjusted by the Na amount adjusting step, and a mixing step. In order to raise the temperature of the mixture mixed by 300 to a predetermined temperature, a heating step 400 of irradiating the mixture with a microwave having a predetermined frequency for a predetermined time and sintering the mixture, and a sintered product heated by the heating step 400 And a cooling step 500 for cooling with a predetermined cooling method.

The adjustment of the igross amount in the igross amount adjusting step 100 is performed by, for example, a coal ash (New Onoda ash) generated from the Shin-Onoda power plant having a low igross amount (ignition loss) of around 3% and a high igros amount of around 17%. It is possible by mixing with coal ash (Mizushima ash) generated from the Mizushima power plant. Table 1 below shows the adjustment of the amount of Igros, where A is Shin Onoda ash and B is Mizushima ash.

In order to determine the optimum amount of Igros to be blended with the coal ash, only the samples 1 to 7 and Shin Onoda ash described in Table 1 were put into a container (ceramic) and surrounded by a heat insulating container, Microwaves (μ waves) were irradiated in a microwave oven to heat (500 W). After the start of μ wave irradiation, the sample was taken out from the microwave oven as appropriate, and the surface temperature of the sample was measured from the hole provided in the upper part of the heat insulating container with an irradiation thermometer. The target temperature was 1100°C. After completion of heating, the sample was cooled in a room while being surrounded by a heat insulating material, and the state of sintering and melting (spouting of sample, sintering, melting) was confirmed. The result is shown in FIG. In FIG. 2, sample 1 (dotted line +), sample 2 (dotted line Δ), sample 3 (dotted line ◇), sample 4 (dotted line □), sample 5 (dotted line ◯), sample 6 (dotted line ×), sample 7 ( The experimental results of the dotted line ■) and Shin Onoda ash (solid line ×) are shown as characteristic lines. In addition, the legend of the label described in each is shown (spouting of sample, sintering, melting). Large, medium, small, and nothing are selected from the experimental results as the spray, and ◯: whole, □: large part, Δ: medium to small part, ×: none is selected from the experimental result as the sintering/melting. ..

As a result of the experiment shown in FIG. 2, it was generally observed that the temperature rise became smaller as the amount of igross decreased, for example, from Sample 1 (10% of the amount of igros). Also, from the irradiation time of the μ wave and the temperature rising time, and the experimental results of jetting, sintering and melting, Sample 2 (igloss amount 7.7%) to Sample 6 (igloss amount 4.4%) were favorable. It was found that the results (spouting: none, sintering: most (□)) were shown, and the experimental results of sample 4 (igloss amount 5.8%) were (squirt: none, sintering: most (□)). , Melting: Most (□)), which proved to be the most suitable.

As a result, in the igross amount adjusting step 100, a coal ash mixture (mixed ash) having an igross amount of 10% or less is obtained by mixing the coal ash having a large igross amount (for example, Mizushima ash) and the coal ash having a low igross amount (Shin Onoda ash). (Sample 1) is formed. Preferably, a coal ash mixture having a large amount of igros (for example, Mizushima ash) and a coal ash having a low amount of igros (Shin Onoda ash) and having an amount of igros between 4.4 and 7.7% is used. (Mixed ash) is formed (Samples 2, 3, 5, 6, 7). More preferably, a coal ash having a large amount of igros (for example, Mizushima ash) and a coal ash having a small amount of igros (Shin Onoda ash) are mixed to form a coal ash mixture (mixed ash) having an amount of 5.8% ( Sample 4).

As for the amount of Na mixed in the mixed ash obtained in the igross amount adjusting step 100, as shown in FIG. 3, the amount of NaOH added to the mixed ash having an amount of 5.8% was changed from 10% to 1%. As a result of heating with microwaves, it was found that the temperature could easily be raised up to the addition amount of 10% to 3%. There may be a decrease.

Further, FIGS. 4 to 10 show experimental results in which the amount of added Na was changed in the coal ash mixture containing different amounts of Igros. Sodium hydroxide (NaOH) was used as the Na additive in these experiments. As the respective experimental results, in the experimental results shown in FIG. 4, when the amount of Igros was 10% and the amount of NaOH was 1% to 3%, there was no jetting and the temperature rise time (1200°C arrival time) was 20 minutes or less. there were. In the experimental results shown in FIG. 5, when the amount of igloss was 7.7% and the amount of NaOH was 1% to 3%, there was no jetting and the temperature rise time (1200° C. arrival time) was 20 minutes or less. In the experimental results shown in FIG. 6, when the Igros amount was 6.5% and the NaOH was 1% to 3%, there was no jetting and the temperature rise time (1200° C. arrival time) was 20 minutes or less. In the experimental results shown in FIG. 7, when the amount of igloss was 5.8% and the amount of NaOH was 1% to 3%, there was no jetting and the temperature rise time (1200° C. arrival time) was 30 minutes or less. In the experimental results shown in FIG. 8, when the amount of Igros was 5.0% and the amount of NaOH was 1% to 3%, there was no jetting and the temperature rise time (1200° C. arrival time) was 40 minutes or less. In the experimental results shown in FIG. 9, when the amount of igross was 4.4% and the amount of NaOH was 1% to 3%, there was no jetting and the temperature rising time (1200° C. arrival time) was 40 minutes or less. According to the experimental results shown in FIG. 10, when the amount of Igros was 4.2% and the amount of NaOH was 1% to 3%, there was no jetting and the temperature rise time (1200° C. arrival time) was 45 minutes or less. Further, in the case of Shin Onoda ash only (igloss amount 3%), when NaOH was 1% to 3%, there was no jetting and the temperature rise time (1200°C arrival time) was 120 minutes or less.

From the above, as the optimum conditions, when the NaOH was 1 to 3% and the amount of Igros was 5.8% to 10%, the temperature rising time was short and there was no jetting, but it was mostly sintered (□). In this case, since the amount of NaOH is 1 to 3% and the amount of Igros is 5.8%=about 6%, it can be estimated that these conditions are the optimum conditions. Further, as shown in FIG. 11, from the experimental results for obtaining the relationship between the concentration of NaOH and the heating time when the igloss amount is 5.8%, the heating time is the highest when the NaOH amount is 2.33%. Turned out to be short.

Furthermore, as shown in FIG. 12, it is possible to use sodium chloride (NaCl) instead of the above-mentioned sodium hydroxide as the Na amount additive. When the sodium content of sodium chloride was set to 1.725% Na and 2.875% Na to the mixed ash having an igloss amount of 5.8%, it took 30 minutes to reach 1200°C without spraying. It was It is also possible to use seawater instead of sodium chloride. In the case of seawater, an experiment was conducted with a Na content of 1.339% Na, but many jettings were detected, but the temperature rising time was as short as about 20 minutes.

In the mixing step 300, the coal ash mixture set to a predetermined igros amount by the above-mentioned igross amount adjusting step 100 is mixed with a Na source set to a predetermined Na amount, such as sodium hydroxide, sodium chloride or seawater. It

The coal ash mixture mixed with the predetermined amount of Na in the mixing step 300 is heated in the heating step 400. The frequency of the microwave irradiated in this heating step is preferably 2.45 GHz±0.5 GHz, and the component with which the mixture is irradiated is preferably the electric field component. This is because the energy received by the coal ash mixture from microwaves is proportional to the sum of (complex permittivity) x (microwave electric field strength squared) and (complex permeability) x (microwave magnetic field strength squared). .. From the results of the resonance perturbation method, it became clear that the microwave heating of the coal ash mixture has a large contribution by the complex permittivity and the electric field. Therefore, it is presumed that efficient heating can be achieved by irradiating the microwave electric field. Accordingly, in the heating step 400, the microwave having the above-described conditions is applied to raise the temperature to 1200° C., for example.

The coal ash mixture heated in the heating step 400 is sintered and then cooled in the cooling step 500. The cooling method in the cooling step 500 varies depending on the intended use of the final product, and when it is desired to obtain the final product in a state where the sintered shape is maintained, the cooling is performed gradually. If it is desired to use the clinkerized final product as a sand substitute material, etc., quench it. This makes it possible to obtain the desired end product.

The result of the heavy metal elution test for this final product is shown in FIG. In this dissolution test, the method for preparing the test solution is according to the Announcement No. 46 appendix, and the mixed ash A (Shin Onoda ash: Mizushima ash = 4; 1) and the mixed ash B (Misumi ash: Mizushima ash = In the case of 4:1), the comparison is made between the case where sodium hydroxide is 1.5% as the Na source and the case where it is 1.0%. As a result, it was proved that, when sodium hydroxide was added, the elution standard was cleared for all heavy metals.

As described above, according to the volume reduction method of the present invention, the coal ash having a predetermined proportion of igros is further mixed with the Na source having the predetermined Na amount, so that it is heated to the predetermined temperature in a short time. It is possible to reduce the volume up to about 50% from the density ratio before and after melting. In addition, it is possible to keep the elution of heavy metals within the standard value when they are extinguished/melted.

100 Igros amount adjustment process 200 Na amount adjustment process 300 Mixing process 400 Heating process 500 Cooling process

Claims (7)

An igross amount adjusting step of adjusting the igross amount of the coal ash to a predetermined value,
A Na amount adjusting step of adjusting the Na amount of the Na source mixed with the coal ash to a predetermined value,
A mixing step of mixing the coal ash having the amount of igros adjusted by the amount of igros adjustment step and the amount of the Na source adjusted by the step of adjusting the amount of Na;
In order to raise the temperature of the mixture mixed by the mixing step to a predetermined temperature, a heating step in which the mixture is irradiated with microwaves of a predetermined frequency for a predetermined time and sintered,
And a cooling step of cooling the sintered product heated by the heating step by a predetermined cooling method. The predetermined value of the Igros amount is 10% by weight or less, preferably within a range of 4.4 to 7.7% by weight, more preferably 6% by weight, based on the weight of coal ash. 1. The volume reduction method described in 1. Regarding the adjustment of the amount of the coal ash, the amount of the coal ash is adjusted by mixing the coal ash having a different amount of ignition (ignition loss) generated at each predetermined power plant. The volume reduction method described in 2. The amount of Na is in the range of 0.5 to 2.33% by weight, preferably in the range of 1.0 to 1.5% by weight, and more preferably 1.0% by weight, based on the weight of coal ash. 4. The volume reducing method according to claim 1. The volume reduction method according to any one of claims 1 to 4, wherein the Na source is a sodium hydroxide solution or a sodium chloride solution, or seawater is used instead of the sodium chloride solution. .. The frequency of the microwave irradiated in the heating step is preferably 2.45 GHz±0.5 GHz, and the component irradiated to the mixture is an electric field component. Volume reduction method according to one. In the cooling method of the cooling step, depending on the intended use of the final product, gradual cooling may be performed when the final product is in a state where the sintered shape is maintained, or rapid cooling is performed when the clinkerized final product is desired. The volume reduction method according to any one of claims 1 to 6, characterized in that