WO2010004941A1 - Method and apparatus for removing unburned carbon in fly ash - Google Patents

Abstract

Disclosed are a method and apparatus for removing unburned carbon in fly ash that yields high-quality modified fly ash at high throughput by increasing the dehydration kinetics and efficiency in the dehydration process, without decreasing the efficiency of sink-float separation in a flotation process. A method for removing unburned carbon in fly ash comprising a slurrification process (20), in which water (w) is added to fly ash (FA) to produce a slurry, a surface modification process (21), in which a collecting agent (c) is added to the slurry, a foaming agent addition process (22), in which a foaming agent (f) is added to the slurry, a flotation process (23), in which the slurry is sink-float separated into a precipitate and a float, and a precipitation dehydration process (26), in which a slurry of the precipitate obtained by the flotation process (23) is dehydrated, wherein the slurry is dehydrated after the flotation process (23) by means of a circulation concentration process (24) in which the precipitate slurry obtained by the flotation process (23) is circulated between an intermediate tank, where the precipitate slurry is temporarily stored, and a centrifugal dehydrator, and this dehydrated slurry is then transported to the precipitate dehydration process (26).

Description

Method and apparatus for removing unburned carbon in fly ash

The present invention relates to a method and apparatus for removing unburned carbon in fly ash, and more particularly, to remove unburned carbon from fly ash generated in a coal-fired thermal power plant and the like, and to remove fly ash and unburned unburned carbon. The present invention relates to a method for effectively using carbon.

In coal-fired thermal power plants, finely pulverized coal is burned in a boiler and the energy is converted into electricity. The ash particles melted by this combustion float in the high-temperature combustion gas, and the temperature drops at the boiler outlet. The ash particles become spherical fine particles and are collected by an electrostatic precipitator, and these particles are called fly ash.

The fly ash is used as a raw material for cement and artificial lightweight aggregate, concrete admixture, and the like. However, when fly ash is used as an admixture for concrete, unburned carbon in the fly ash absorbs the AE water reducing agent and the like, reducing the workability of the concrete. In addition, when concrete is placed, unburned carbon floats, and there are problems such as the occurrence of a black portion at the joint portion of the concrete. Furthermore, when there is much unburned carbon in fly ash, there also exists a problem that the quality of the artificial lightweight aggregate will fall.

Here, since the unburned carbon content is currently 1-5% by weight in Japan and 16-18% by weight in Vietnam, it is usually difficult to use as a cement raw material.

In order to solve the above problem, a method is disclosed in which water is added to fly ash to form a slurry, and a collection agent and a foaming agent are added, and unburned carbon is removed by flotation separation (for example, non-patent literature). 1).

Fig. 3 shows the process of the unburned carbon removal method using flotation separation. First, in the slurrying step, water is added to fly ash containing unburned carbon generated in a thermal power plant or the like to obtain a slurry having a slurry concentration of about 15% by weight. Next, in the surface modification step, about 0.5% by weight of light oil or kerosene or the like as a scavenger is added to the fly ash in the slurry, and further stirred to collect the scavenger particles ( Oil) is in close contact with each other, making it more lipophilic. Next, in the foaming agent addition step, a foaming agent is added to the slurry whose surface has been modified, and flotation separation is performed using a flotation machine. Unburnt carbon that has been made oleophilic is recovered as a suspended matter, Fly ash is recovered as a precipitate.

On the other hand, in the suspended matter dehydration step, the unburned carbon is dehydrated by a filter press dehydrator or the like and recovered as a floss cake (dehydrated cake). The floss cake can be referred to as concentrated unburned carbon and can be used as an auxiliary fuel.

On the other hand, in the precipitate dewatering step, the fly ash is dewatered by a filter press dehydrator or the like and collected as a fly ash cake (dehydrated cake). The fly ash cake is a high-quality fly ash having an unburned carbon content of 0.5% by weight or less, and can be used as a cement admixture or a mixture.

Mitsui Engineering & Ship Technical Report No. 192 (2007-11)

However, in the flotation separation method described in Non-Patent Document 1, after adding water or the like to fly ash to form a slurry, the slurry is again dehydrated by a dehydrator to recover the floss cake and fly ash cake as a product. When the concentration is low, the dehydration process takes time, and when the slurry concentration is high, the efficiency of flotation separation is deteriorated.

In particular, when a filter press type dehydrator is used, the dehydration effect is high (highly effective in reducing the water content), but it takes a lot of time to send the slurry between the filters and further squeeze it, and the entire plant Is a bottleneck in the amount of processing.

That is, the reduction in the processing time in the dehydration process is directly linked to the reduction in the overall processing time in the plant.

In addition, the filter press dehydrator is a very expensive device, and in order to increase the throughput in the plant, conventionally, the enlargement of the filter press dehydrator has become an indispensable condition, which processes fly ash. Because of this, the construction cost of the plant increased.

Furthermore, due to the above factors, when the slurry concentration is increased for the purpose of shortening the dewatering time, the fluidity of the slurry is lowered and the efficiency of the flotation separation is greatly reduced, so that it is recovered. The amount of floss cake (unburned carbon) as a product is reduced, and the quality of the fly ash cake (modified fly ash) is deteriorated as the unburned carbon content is increased.

The present invention has been made to solve the above-described problems, and its purpose is to increase the dewatering speed and efficiency in the dewatering step without reducing the efficiency of the flotation separation in the flotation step, thereby increasing the throughput. It is an object of the present invention to provide a method for removing unburned carbon in fly ash and an apparatus therefor that can provide a high quality modified fly ash.

In addition, it is configured to circulate and use water generated in the plant, thereby suppressing the generation of waste associated with fly ash treatment and removing unburned carbon in fly ash with less environmental impact. It is to provide a method and apparatus thereof.

In order to achieve the above object, a method for removing unburned carbon in fly ash according to the present invention includes a slurrying step of adding water to fly ash to form a slurry, and a surface modification for adding a collecting agent to the slurry. A foaming agent adding step for adding a foaming agent to the slurry, a flotation step for flotation-separating the slurry into a precipitate and a suspended matter, and the precipitate obtained in the flotation step In the method for removing unburned carbon in fly ash comprising a precipitate dewatering step for dewatering the slurry, an intermediate tank and a centrifugal separation type for temporarily storing the slurry of the precipitate obtained in the flotation step after the flotation step The slurry is dehydrated by a circulation concentration step of concentrating by circulating between dehydrators, and the dehydrated slurry is conveyed to the precipitate dehydration step.

It was possible to increase the dewatering efficiency in the precipitate dewatering step by lowering the water content of the slurry to some extent in the circulation concentration step as a pretreatment before the precipitate dewatering step. That is, since the concentration of the slurry sent to the precipitate dewatering step has increased, the mass of the precipitate (fly ash) in the slurry sent to the dehydrator per unit time increases, and the processing time per unit amount in the dewatering step is shortened. It became possible.

Along with this increase in dewatering efficiency, it becomes possible to increase the amount of fly ash treated in the plant, or the size of the dehydrator used in the dewatering process can be reduced, thereby reducing the cost of plant construction. It has become possible.

Further, since the dehydration can be performed to some extent in the circulation concentration step, it is possible to reduce the concentration of the slurry in the flotation step by using a larger amount of water than the conventional method without the circulation concentration step. . As the slurry concentration decreased, the separation efficiency of unburned carbon improved, and the types of fly ash that could be treated increased.

In the method for removing unburned carbon in the fly ash, the precipitate obtained in one of the flotation steps is treated in a circulation concentration step and a precipitate dehydration step to recover the modified fly ash as a product, On the other hand, the suspended matter obtained is dehydrated in a suspended matter dewatering step, and unburned carbon is recovered as a product.

This method makes it possible to produce modified fly ash as a raw material for cement and the like, and unburned carbon that can be used as an auxiliary fuel as a product.

In the above-described method for removing unburned carbon in fly ash, the liquid phase recovered in the circulation concentration step may be reused by returning part or all of the liquid phase to one or both of the slurrying step and the foaming agent addition step. It is characterized by doing.

By this method, water necessary for the treatment of fly ash can be circulated as much as possible and reused in the system, so it is possible to reduce the environmental impact of wastewater. The amount of water required can be reduced.

In the method for removing unburned carbon in the fly ash, the slurry concentration in each step of the slurry is 5 to 20 wt% in the surface modification step, 5 to 20 wt% in the flotation step, and the circulation concentration. The circulation time in the circulation concentration step and the supply amount of the liquid phase to be reused are controlled so as to be 10 to 30% by weight in the step.

By controlling the slurry concentration in the circulation concentration process, it became possible to operate the dehydrator in the dehydration process efficiently.

In the above-described method for removing unburned carbon in fly ash, in the circulation concentration step, circulation is performed so that the slurry concentration after the circulation concentration step is increased by 2 to 10% by weight with respect to the slurry concentration before the circulation concentration step. It is characterized by controlling circulation in the concentration process.

An apparatus for removing unburned carbon in fly ash for achieving the above-mentioned object is that a slurry tank, a surface reformer, a condition tank, and a flotation machine are connected in that order through a slurry transport pipe, In the apparatus for removing unburned carbon in fly ash, one of which is connected to a modified fly ash slurry tank, a centrifugal dehydrator and a precipitate dehydrator, and the other is connected to a floss tank and a float dehydrator. A slurry tank is mixed with fly ash, which is an object to be treated, to form a slurry, the slurry is mixed with the collecting agent with the surface reformer, a foaming agent is added to the slurry in the condition tank, The slurry is subjected to flotation separation with a flotation machine, and one of the precipitates is circulated and concentrated by circulating the modified fly ash slurry tank and the centrifugal dehydrator, and then the precipitates. Water machine performs dehydration and the other flotage to dwell the floss reservoir, characterized in that subsequent to the arrangement above to perform a dehydration treatment by suspended matter dehydrator.

In the apparatus for removing unburned carbon in the fly ash, the centrifugal dehydrator is a fluid cyclone.

The use of a liquid cyclone improved the throughput per unit time compared to a dehydrator using a filter or the like, enabling continuous treatment. In addition, it is unnecessary to replace the filter.

In the above-described apparatus for removing unburned carbon in fly ash, the modified fly ash is recovered as a product from the modified fly ash slurry dehydrator, which is the precipitate dewaterer, and the floss dewaterer, which is the float dewaterer The floss containing unburned carbon is collected as a product.

In the above-described apparatus for removing unburned carbon in fly ash, both the modified fly ash slurry dehydrator and the floss dehydrator are filter press dehydrators.

By using a filter press type dehydrator as the dehydrator, it is possible to strongly squeeze the slurry, and produce the modified fly ash and unburned carbon, which are the products, as a dehydrated cake with extremely low moisture content. Became possible.

In the apparatus for removing unburned carbon in the fly ash, the liquid phase recovered by the centrifugal dehydrator may be reused by returning a part or all of the liquid phase to one or both of the slurry tank and the condition tank. It is characterized by having constituted so.

* By circulating water in the equipment, the amount of water required is reduced, and it is possible to reduce the environmental load caused by drainage.

According to the method and apparatus for removing unburned carbon in fly ash according to the present invention, the throughput is increased by increasing the dehydration speed and efficiency in the dehydration step without reducing the efficiency of flotation separation in the flotation step. It has become possible to provide a method and apparatus for removing unburned carbon in fly ash that can provide a large number of high-quality modified fly ash.

In addition, it is configured to circulate and use the water generated in the equipment, thereby suppressing the generation of waste associated with fly ash treatment and removing unburned carbon in fly ash with less environmental impact. It has become possible to provide a method and its apparatus.

FIG. 1 is a process diagram of an example in which the method of the present invention is carried out. FIG. 2 is a schematic diagram of one embodiment of the apparatus of the present invention. FIG. 3 is a process diagram of a conventional fly ash processing plant.

Hereinafter, the present invention will be specifically described with reference to embodiments shown in the drawings. FIG. 2 shows an outline of an apparatus for removing unburned carbon in fly ash, which is one of the embodiments of the present invention, and FIG. 1 shows a process diagram thereof.

(Process in plant)
Fly ash FA generated in a thermal power plant or the like is supplied to the fly ash receiving tank 10. The fly ash FA is in a fine powder form, and unburned carbon is attached to the surface of the fine powder. First, in the slurrying process 20, in order to process these, fly ash FA is thrown into the slurry tank 4, and water (circulated water) w is added to make a slurry (slurry process 20).

The slurry fly ash FA is sent to the surface reformer 5 in the next step by the slurry transfer pump 11. Here, for example, oil such as light oil or kerosene is added as a scavenger c, stirred to adsorb unburned carbon to the scavenger c, and the slurry whose surface has been modified is sent to the condition tank 6 (surface modification). Step 21).

In the condition tank 6, the foaming agent f is added (foaming agent addition step 22), and the slurry to which the foaming agent f is added is sent to the flotation machine 7. The slurry is stirred and unburned carbon is sent to the floss slurry tank 8 as a suspended matter. The modified fly ash RFA from which unburned carbon has been removed is sent to the modified fly ash slurry tank 9 as a precipitate (flotation step 23).

On the other hand, the unburned carbon sent to the floss slurry tank 8 is sent to a filter press type floss dehydrator. The unburned carbon is dehydrated (floating matter dewatering step 25) and recovered as a product floss cake (unburned carbon) FL.

On the other hand, the modified fly ash RFA sent to the modified fly ash slurry tank 9 (intermediate tank) circulates the fly ash slurry concentrated cyclone (liquid cyclone) and the modified fly ash slurry tank 9 to remove water, The concentration is increased (circulation concentration step 24).

The slurry having an increased slurry concentration is sent to the filter press type modified fly ash slurry dewatering machine 3, dehydrated (precipitate dehydration step 26), and recovered as a product fly ash cake (modified fly ash RFA). .

Here, the water recovered by the fly ash slurry concentration cyclone 1 is reused in the slurry tank 4 or the condition tank 6. The recovered water can be used for adjusting the concentration of the slurry.

(Range of slurry concentration in each device)
The slurry concentration that can be processed in each apparatus and the range of the optimum slurry concentration are shown in Table 1.

In the flotation step 23, when the slurry concentration increases, the fluidity of the slurry decreases and the efficiency of the flotation separation decreases, so the slurry concentration has a low value.

From (Table 1), it is desirable that the slurry concentration is treated at 30% by weight in the surface modification step 21, 10% by weight in the flotation step 23, and 30% by weight in the sediment dehydration step 26. In the conventional method, when the slurry concentration is lowered in the middle of the process (for example, the flotation step 23), it is necessary to process the slurry in the lower stage in the subsequent stage.

However, according to the present invention, even if, for example, the slurry concentration is lowered in the flotation step 23 to increase the efficiency of the flotation separation, the precipitate dewatering step 26 supplies a high concentration slurry with good dewatering efficiency. Is possible. This is due to the circulation concentration step 24 before the sediment dehydration step 26.

(Circulating concentration process)
The effect of the circulation concentration step 24 in the apparatus (plant) of the present invention will be described below. For example, the slurry whose slurry concentration is adjusted to 15% by weight in the slurrying step 20 is also 15% by weight in the surface modification step 21. This is because the trapping agent c and foaming agent f added in the middle are less than 1% by weight with respect to the weight of the slurry, so that the slurry concentration is hardly affected.

Next, the slurry concentration of the modified fly ash slurry recovered as a precipitate in the flotation step 23 is 15% by weight.

In the past, the slurry having a slurry concentration of 15% by weight was supplied to the modified fly ash slurry dehydrator 3 and dewatered. However, in the circulation concentration step 24, the slurry concentration was increased to 30% by weight. Let's consider the case.

For example, assuming that the mass of the fly ash cake recovered from the dehydrator 3 is 15, the mass of the slurry to be treated and the time required for it are shown in (Table 2). Here, the dehydrator 3 is a filter press-type dehydrator, and, as a batch type in which the slurry is introduced and then compressed by a filter, the pressing time is fixed at 5.5 minutes. This is because the pressing time is defined by the quality of the fly ash cake recovered as a product.

As can be seen from (Table 2), when the slurry concentration is high (30%), the mass of slurry to be supplied to the dehydrator 3 is reduced (50), so the slurry inflow time is shortened to 2.5 minutes. The entire dehydration time can be reduced to 8.0 minutes.

In the apparatus of the present invention, when the amount of fly ash to be processed (the amount of fly ash to be supplied) is considered to be constant, the time required for the process is reduced by 24% (8.0 minutes / 10.5 minutes = 0.762), it is possible to reduce the scale of the plant.

In addition, although many filters of the filter press type dehydrator are expensive, the present invention makes it possible to reduce the filtration area required for the treatment by 24% as well as the time reduction.

As described above, according to the present invention, by increasing the dewatering speed and efficiency in the dewatering step 26 without reducing the efficiency of the flotation separation in the flotation step 23, a high-quality modified fly ash RFA with a high throughput can be obtained. It is possible to provide a method and an apparatus for removing unburned carbon in the obtained fly ash.

In addition, it is configured to circulate and use water w generated in the plant, thereby suppressing the generation of waste associated with fly ash treatment and reducing the environmental impact of unburned carbon in fly ash. The provision of the removal method and the apparatus was realized.

1 Liquid Cyclone (Fly Ash Slurry Concentrated Cyclone)
2 Floating material dehydrator (Floss dehydrator)
3 Precipitate dewatering machine (modified fly ash slurry dewatering machine)
4 Slurry tank 5 Surface reformer 6 Condition tank 7 Flotation machine 8 Floss slurry tank 9 Reformed fly ash slurry tank 10 Fly ash receiving tank 11 Slurry transfer pump 20 Slurry process 21 Surface reform process 22 Foaming agent addition process 23 Flotation process 24 Circulation concentration process 25 Float dewatering process 26 Precipitate dewatering process w Circulating water FA Fly ash c Collection agent f Foaming agent FL Floss RFA Modified fly ash

Claims (10)

A slurrying step of adding water to fly ash to form a slurry, a surface modifying step of adding a collecting agent to the slurry, a foaming agent adding step of adding a foaming agent to the slurry, and precipitating the slurry In a method for removing unburned carbon in fly ash comprising a flotation step of flotation and separation into a product and a floating material, and a precipitate dehydration step of dewatering the slurry of the precipitate obtained in the flotation step
After the flotation step, the slurry of the precipitate obtained in the flotation step is dehydrated by a circulation concentration step of concentrating by circulating between the intermediate tank temporarily stored and the centrifugal dehydrator, and this dehydrated slurry Is transported to the precipitate dehydration step, and a method for removing unburned carbon in fly ash. The precipitate obtained in one of the flotation steps is treated in a circulation concentration step and a precipitate dehydration step to recover the modified fly ash as a product, and the floating matter obtained in the other is dehydrated in the float dehydration step, The method for removing unburned carbon from fly ash according to claim 1, wherein unburned carbon is recovered as a product. The fly according to claim 1 or 2, wherein the liquid phase recovered in the circulation concentration step is reused by returning a part or all of the liquid phase to one or both of the slurrying step and the foaming agent addition step. A method for removing unburned carbon in ash. Circulating concentration step so that the slurry concentration in each step of the slurry is 5-20 wt% in the surface modification step, 5-20 wt% in the flotation step, and 10-30 wt% in the circulating concentration step. The method for removing unburned carbon in fly ash according to any one of claims 1 to 3, wherein the circulation time in the tank and the supply amount of the liquid phase to be reused are controlled. The circulation concentration step is controlled to circulate in the circulation concentration step so that the slurry concentration after the circulation concentration step is increased by 2 to 10% by weight with respect to the slurry concentration before the circulation concentration step. Item 5. The method for removing unburned carbon in fly ash according to any one of Items 1 to 4. A slurry tank, a surface reformer, a condition tank, and a flotation machine are connected in that order through a slurry transport pipe, and one of the flotation machines is connected to a modified fly ash slurry tank, a centrifugal dehydrator, and a sediment dehydrator. In the device for removing unburned carbon in the fly ash, which is in communication with the other, the floss tank and the suspended matter dehydrator.
Mix the fly ash and water to be treated in the slurry tank to form a slurry, mix the slurry and the collecting agent in the surface reformer, add a foaming agent to the slurry in the condition tank, The slurry is subjected to flotation separation with the flotation machine, and one precipitate is circulated and concentrated by circulating the reformed fly ash slurry tank and the centrifugal dehydrator, and then with the precipitate dehydrator. An apparatus for removing unburned carbon in fly ash, characterized in that a dewatering process is performed, the other floating substance is retained in the froth tank, and then the dewatering process is performed by the floating substance dehydrator. The apparatus for removing unburned carbon in fly ash according to claim 6, wherein the centrifugal dehydrator is a fluid cyclone. The modified fly ash is recovered as a product from the modified fly ash slurry dehydrator, which is the precipitate dewaterer, and the floss containing unburned carbon is recovered as a product from the floss dewaterer, which is the float dewaterer. The apparatus for removing unburned carbon in fly ash according to claim 6 or 7, characterized in that it is configured. The apparatus for removing unburned carbon in fly ash according to any one of claims 6 to 8, wherein both the modified fly ash slurry dehydrator and the floss dehydrator are filter press dehydrators. 10. The liquid phase recovered by the centrifugal dehydrator is reused by returning a part or all of the liquid phase to one or both of the slurry tank and the condition tank. The apparatus for removing unburned carbon in fly ash according to any one of the above.

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