JPH0812002B2 - Fly ash modification method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for modifying fly ash used as a concrete admixture or a civil engineering / building material. More specifically, it relates to a reforming method for reducing the ignition loss and the MB adsorption amount of fly ash having a large ignition loss and a large methylene blue adsorption amount (hereinafter referred to as MB adsorption amount) among the fly ash generated in a coal combustion boiler.

In the above, fly ash refers to ash collected from a flue gas of a coal burning boiler (including a pulverized coal burning boiler) by a dust collector, and ignition loss refers to fly ash of 750 ± 50 ° C. It is the weight loss when heated to constant weight (according to JIS A6201) and represents the unburned carbon content of fly ash. The amount of MB adsorbed is the amount of methylene blue reagent adsorbed by fly ash (according to the Cement Association Standard Test Method (CAJS I-61)), which is a quantitative value for the highly active unburned carbon contained in fly ash. It is shown in the figure.

In recent years, in coal-fired boilers, the use of domestic coal has decreased and the use of overseas coal has increased. Generally, however, since overseas coal is less likely to ignite than domestic coal, coal is not completely burned and coal is not burned. The amount of unburned carbon contained in the ash increases,
The melting point of overseas coal ash is higher than that of domestic coal ash, and the coal ash does not melt into glass in the coal combustion boiler and the activity of unburned carbon does not decrease, so fly ash with large ignition loss and large MB adsorption amount is used. It is increasing. Furthermore, in order to reduce the emission of nitrogen oxides from the coal-fired boiler, it has become possible to reduce the amount of combustion air and to lower the combustion temperature. The production of large fly ash is increasing.

Fly ash is used as a concrete admixture or as a civil / building material, but not all fly ash can be used for this purpose. This is because fly ash, which has a large loss on ignition or a large amount of adsorbed MB, has a large unburned carbon content or a large activity of unburned carbon, and the amount of air to adsorb the air entraining agent is large. It becomes difficult to control the amount of air, and the amount of air when using these fly ash as a concrete admixture or a civil engineering / building material becomes improper. As a result, there arises a problem that the concrete mixed with fly ash becomes inferior in quality that cracks easily occur. Therefore, it becomes necessary to modify the fly ash.

[0005]

2. Description of the Related Art Conventional modification techniques include a modification technique by a separation method and a modification technique by a chemical method. As an example of the modification technology by the separation method, fly ash is classified by wind force, electrostatic classification,
Depending on the vibrating fluidized bed or rocking table, the dielectric constant,
Fly ash with a small ignition loss was selected and collected by utilizing the difference in specific gravity and particle size.The modification technology by these separation methods is the loss on ignition included in the fly ash before modification. The fly ash having a small size was separated and collected, and it did not reduce the loss on ignition and the amount of MB adsorbed, and was extremely insufficient both in terms of quality and quantity.

Further, as a typical modification technique by a chemical method, a modification technique described in JP-B-4-70529 (conventional example I) and a modification technique described in JP-B-4-21089 (conventional technique). Example II) is proposed.

In the conventional example I, the coal ash is mixed with the exhaust gas containing dust at the outlet of the coal ash reforming furnace and preheated, then separated from the exhaust gas and supplied to the coal ash reforming furnace, and the coal ash reforming furnace is also supplied. It is characterized by supplying oxygen-enriched air at 5 degrees Celsius.
The unburned carbon content is removed at a temperature of 00 to 1000 degrees,
It is described that it can be used as a raw material for cement and a mixed material for cement.

In the conventional example II, when the fly ash discharged from the coal-fired boiler and the industrial furnace is re-combusted in the processing furnace, the temperature of the furnace wall of the processing furnace is 700 to 1 ° C.
It is characterized by the fact that the re-combustion air supplied to the processing furnace is maintained at 100 degrees and is swirl flow, and the unburned carbon content can be reduced to 5% or less, and it is effectively used as a cement admixture or a raw material for ceramics. It is described that it is possible.

[0009]

However, the conventional example I has the following drawbacks. Since oxygen-enriched air is used, dedicated equipment such as an oxygen-enrichment device, an oxygen-enriched air fan, and an oxygen-enriched air supply nozzle is required, resulting in high equipment cost. Although it is described that unburned carbon content can be reduced, there is no description about the amount of MB adsorbed.

The conventional example II has the following drawbacks. A special structure is required, such as a nozzle or the like for making the re-combustion air a swirl flow, and the equipment cost increases. It is described that the unburned carbon content can be reduced to 5% or less, but the MB adsorption amount is not described at all.

As can be seen from the above-mentioned typical prior art, it seems that the reduction of unburned carbon content has been achieved in the past, but the present situation is that the reduction of the amount of adsorbed MB has not been solved. It was Even if the amount of unburned carbon decreases, if the amount of MB adsorbed is large, problems such as cracking of concrete occur due to the phenomenon of adsorbing air entraining agent. Therefore, the Cement Standards Test Method (CAJS I- 61
In (), the measurement standard of MB adsorption amount is set, and it is customary to set the transaction condition that MB adsorption amount is 0.3 mg / g or less. However, in reality, the reduction of MB adsorption amount has not been sufficiently solved. However, fly ash was not sufficiently used as a concrete admixture material or wall material, mortar, fly ash cement, and other civil engineering and building materials, and many fly ash were still disposed of by landfilling.

In view of such circumstances, the present invention reduces the ignition loss of fly ash and the amount of adsorbed MB to reduce the amount of adsorbed MB, concrete admixture materials such as dams, piers, and tunnels, or wall materials, mortar, fly ash cement, and other civil engineering and construction. It is an object of the present invention to provide a reforming method that can be used as a material and is suitable for mass production.

Further, as a result of diligent research conducted by the present inventors on why the reduction of the amount of adsorbed MB was insufficient, until now, generally, the loss on ignition and the amount of adsorbed MB have a correlation, and the loss on ignition decreases. It was thought that the amount of MB adsorbed would decrease, but with fly ash of 5% or less, which is required as fly ash for concrete admixtures or civil engineering / construction materials, the amount of ignition decreased and MB adsorbed. It was found that there is no correlation between the amounts, and the MB adsorption amount fluctuates even with the same loss on ignition. It was also found that due to this, the amount of MB adsorbed cannot be effectively reduced. An object of the present invention is to provide a reforming method that can surely reduce the amount of MB adsorbed among the newly discovered phenomena.

[0014]

According to the reforming method of the present invention, fly ash is heated at a temperature of 580 to 680 degrees Celsius for 30 to 30 degrees Celsius.
It is characterized by reducing the ignition loss and the MB adsorption amount by heating in an oxidizing atmosphere for 10 minutes or more. The above heating temperature and heating time are related to each other. When the heating temperature is 580 degrees Celsius, the heating time is 30 minutes or more, and when the heating temperature is 680 degrees Celsius, the heating time is 10 minutes or more. It is necessary to satisfy these conditions,
Even in the region where the ignition loss and the MB adsorption amount have no correlation, the condition is to reduce not only the ignition loss but also the MB adsorption amount.

[0015]

As a general tendency, the smaller the ignition loss of fly ash, the smaller the amount of MB adsorbed. Therefore, by heating, the ignition loss and M
Both the B adsorption amount can be reduced. However, in the fly ash with a loss on ignition of around 5% or less required as a fly ash for concrete admixture or civil engineering / construction materials, there is no correlation between the loss on ignition and the amount of MB adsorbed, and the same loss on ignition is lost. However, the amount of MB adsorbed varies. As a result of diligent research by the present inventor on this point, when the fly ash is heated to burn the unburned carbon content to reduce the ignition loss, the MB adsorption amount due to the reduction of the unburned carbon content and the unburned carbon content are reduced. It was newly found that it is based on the phenomenon that the increase in the amount of MB adsorbed by the increase in the activity of carbon content occurs simultaneously.

Therefore, in the region where the correlation is weak, even if the fly ash is heated to reduce the unburned carbon content, even if the ignition loss becomes small due to the increase in the activity of the unburned carbon content, MB adsorption is reduced. The volume may not decrease. However, it was confirmed that if the conditions of the heating temperature and the heating time based on the present invention are observed, not only the ignition loss but also the MB adsorption amount is greatly reduced.

Further, since it is heated in an oxidizing atmosphere, no special equipment is required, and fly ash having a large ignition loss and a large MB adsorption amount can be reformed separately from the coal-fired boiler, so that it can be inexpensively modified in large quantities. Can be quality.

[0018]

EXAMPLES Next, the reforming method of the present invention will be described in detail. It should be noted that in the following description, JIS loss is large and JIS
Fly ash that does not conform to A6201 or has a large MB adsorption amount that is not specified in JIS A6201 is called modified ash.
Fly ash that conforms to JIS A6201 and has a small MB adsorption amount is called modified ash.

First, an experiment was conducted to confirm in which temperature range the unburned carbon content burns when the ash requiring reforming is heated. FIG. 2 shows a differential thermogravimetric simultaneous measurement device used in the combustion experiment (model TG / DTA3 manufactured by Seiko Instruments Inc.
0) is a block diagram, 1 is a sample (fly ash), 2 is a standard sample (a substance that does not generate heat), 3 is a sample holder, 4 is a differential thermocouple, 5 is a temperature measuring thermocouple, and 6 is an electric furnace. Is.

The experimental results using the above apparatus are shown in FIG.
FIG. 1 is a graph showing a tendency that the heating temperature of the modified ash and the unburned carbon content of the modified ash are burned to reduce the weight.
G (Derivative Thermogravimetry) is called differential thermogravimetry, which is a time differential value of thermogravimetric (TG), and indicates a weight change per unit time. DTA (Differential ThermalAn
(alysis) is called differential heat, in which a sample and a standard sample are heated under the same thermal conditions, and the temperature difference generated between the two is displayed in voltage. TG (Thermogravimetry) is called thermogravimetry and indicates the sample weight at the measurement temperature.

In FIG. 1, point A is the starting point of the differential thermogravimetric change (DTG), which means that the weight loss due to the combustion of the unburned carbon content starts at 380 degrees Celsius. Reference B is a point at which the differential thermogravimetric change (DTG) is completed, and the temperature at this time is 680 degrees Celsius. As a result, fly ash can reach 380 to 68 degrees Celsius.
It can be seen that it burns in the range of 0 degree. It can be seen that the most weight loss due to combustion is around 600 degrees Celsius. The point C is the point where the slope of the differential heat value (DTA) curve is to the upper right, which means heat generation, that is, combustion of unburned carbon content.

Burning in the above temperature range generally decreases the ignition loss and the MB adsorption amount in a correlated manner. However, as described above, the ignition loss decreases in a certain region. Even if the MB adsorption amount does not decrease, a phenomenon occurs. For example, FIGS. 3-4 show 380 degrees Celsius, 480 degrees Celsius.
FIG. 4 is a graph recording loss on ignition and MB adsorption amount when fly ash is heated at 580 ° C., 580 ° C., and 680 ° C. As shown in FIG. 4, the loss on ignition at 580 ° C. and 680 ° C. is Although it becomes zero, as shown in FIG. 3, the amount of MB adsorbed does not become zero, and about 0.05 mg / g remains, and the amount of MB adsorbed per unit amount of unburned carbon content is not constant.

Therefore, in order to clarify the above phenomenon, the present inventor investigated the unburned carbon content activity as an index showing the influence of the unburned carbon content on the MB adsorption amount. The unburned carbon content activity a is defined as follows. a = [{MB adsorption amount (mg / g) -0.05 (mg / g)} / loss on ignition (%)] × 100 The effect of heating temperature and heating time on the unburned carbon activity a is shown in FIG. Show. There is a minimum point of activity at a heating temperature of 480 degrees Celsius for 20 minutes, at a heating temperature of 580 degrees Celsius for 5 minutes, and at a heating temperature of 680 degrees Celsius for 3 minutes, and the activity increases at other heating times. You can see that Therefore, the amount of MB adsorbed can be reduced by heating under the condition that the unburned carbon content is low in activity. The conditions are 580 to 680 degrees Celsius and 30
Oxidizing atmosphere for 10 minutes or more.

It should be noted that the ash requiring reforming may burn unburned carbon content even at temperatures of 680 degrees Celsius or higher, but as the temperature rises, the ash requiring reforming softens and melts, then melts and the particle size increases. , Fly ash is out of the condition of JIS A 6201 fineness of 2400 cm ² / g or more, which is usually used when using concrete as a concrete admixture or as a civil engineering / construction material. Therefore, the lower limit of the heating temperature is 38 degrees Celsius.
0 degree, the upper limit is 680 degrees Celsius.

Next, an experiment was conducted to reform the unburned carbon content of the ash requiring reforming in the heat treatment furnace under the above-mentioned temperature and time conditions, and the reduction rate of ignition loss and the reduction rate of MB adsorption amount were confirmed.
The heat treatment furnace used was 2000 mm wide and 1000 mm high.
mm, length 3000 mm, fueled by butane gas, 60 degrees Celsius
Heated at 0 degrees for 1 hour. The results are shown in Tables 1 and 2.

Table 1 * MB adsorption amount Ignition loss mg / g% Standard-JIS 0.3 or less 5 or less Before reforming: 0.41 9.71 After reforming: 0.10 1.01 * MB adsorption amount is specified in JIS A6201 standard. Absent.

Table 2 Compressive strength ratio SiO ₂ specific gravity Specific surface area Unit water content ratio Moisture 28 days 91 days %%% cm ² / g %% Standard JIS JIS JIS JIS JIS JIS JIS JIS 60 or more 70 or more 45 or more 1.98 or more 2400 or more 102 or less 1 or less Before modification: 70.1 82.8 51.8 2.20 4480 101.7 0.18 After modification: 67.7 83.0 52.6 2.18 4190 97.0 0.08

As shown in Table 1, the loss on ignition is 9.71%.
Then, the modified ash with an MB adsorption amount of 0.41 mg / g is 60 degrees Celsius.
When kept at 0 ° C for 1 hour, the loss on ignition was 1.01% and the amount of MB adsorbed was reduced to 0.1 mg / g. From this result, it is understood that the property is modified so as to satisfy the qualities such as loss on ignition of 5% or less and MB adsorption amount of 0.3 mg / g or less, which are generally required as a concrete admixture material or a civil engineering / construction material. Furthermore, in the reforming method of the present invention, as shown in Table 2, it was confirmed that the compression strength ratio, SiO ₂ , specific gravity, specific surface area, unit water content ratio, and various conditions of moisture all satisfy JIS A6201. It was

In the above experiment, the heating temperature was 600 degrees Celsius.
However, if the temperature is lower than 380 degrees Celsius, the same effect can be obtained because unburned carbon content is burned, and the above effect can be obtained at a temperature higher than 600 degrees Celsius for the same reason. It is a thing.

According to the present invention, fly ash is only burned in an oxidizing atmosphere. Therefore, fly ash can be reformed in a large amount by preparing an ordinary combustion furnace without any special equipment. It is a thing.

[0031]

As described above, according to the present invention, fly ash can be used as a concrete admixture material or a modified ash suitable for civil engineering and building materials. In the electric power industry, the amount of reformed ash to be disposed of as industrial waste is reduced by increasing the amount of reformed ash collected. Inject air to reduce unburned carbon content of coal ash,
The load on the coal-fired boiler is kept constant to homogenize the quality of the coal ash, and a coal-fired boiler with a special structure is installed, such as extending the combustion time of the coal to collect the modified ash. ing. Even in this way, the electricity industry only used 610,000 tons of concrete admixture and 1.05 million tons of civil engineering and construction materials out of the 3.65 million tons of fly ash generated in 1991, leaving about 1.99 million tons. Landfills are disposed of as industrial waste.

On the other hand, according to the present invention, since the ash requiring reforming can be reformed separately from the coal-fired boiler, an economical coal brand can be selected for the coal-fired boiler, and an excessive combustion air is not added. Therefore, the generation of nitrogen oxides is suppressed, the emission of air pollutants can be reduced, there are no operational restrictions for collecting reformed ash, and economical operation is possible. It is not necessary to have a special structure, and it becomes possible to plan, design, and adopt an economical coal-fired boiler.

Further, the coal-fired boiler used outside the electric power industry generally has a smaller capacity than the coal-fired boiler used in the electric power industry, cannot retain sufficient combustion residence time of coal in the coal-fired boiler, and is a concrete admixture. Or civil engineering
In general, it is difficult to produce fly ash suitable for building materials. In addition to about 1.9 million tons of reformed ash that has been disposed of as industrial waste in the electric power industry such as landfill, these industries The ash requiring modification, which has been disposed of as landfill or the like as waste, can be modified into a concrete admixture material or a civil engineering / construction material according to the present invention, which is a great advantage.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a heating temperature of a ash requiring reforming and a rate at which unburned carbon content of the ash is burned to reduce weight.

FIG. 2 is a block diagram of a differential thermogravimetric simultaneous measurement apparatus used in a heating experiment.

FIG. 3 is a graph showing the relationship between heating temperature and MB adsorption amount.

FIG. 4 is a graph showing the relationship between heating temperature and loss on ignition.

FIG. 5 is a graph showing the tendency of unburned carbon activity a.

[Explanation of symbols]

1 sample (fly ash) 2 standard sample 3 sample holder 4 differential thermocouple 5 temperature measuring thermocouple 6 electric furnace A starting point where differential thermogravimetric change increases B point where differential thermogravimetric change ends C differential thermal value is upper right Point a: Unburned carbon activity

Claims (1)

[Claims] 1. A fly ash characterized by reducing the ignition loss and the amount of adsorbed methylene blue by heating the fly ash at a temperature of 580 to 680 ° C. for 30 to 10 minutes or more in an oxidizing atmosphere. Reforming method.