JP3362065B2 - Coal ash reforming 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 reforming a large amount of coal ash generated in a coal-fired thermal power plant, etc., and particularly to a state in which the coal ash can be used as a cement admixture, a building material, an aggregate, etc. It relates to a method of reforming up to.

[0002]

2. Description of the Related Art In recent years, the installation of coal-fired boilers has been increasing due to energy diversification measures. A large amount of dust (ash) is contained in the waste gas of a coal-fired boiler. This coal ash is usually mostly recovered by a dry electrostatic precipitator or a dry precipitator such as a multi cyclone.

[0003] Conventionally, among the collected ash, one having a low unburned carbon content is called fly ash and is utilized as a fly ash cement raw material or a cement admixture. However, most are dumped in landfills.

The fly ash used for fly ash cement has various disadvantages such as blackening of the surface of the product and adsorption of an admixture for concrete when the amount of free unburned carbon is large. Therefore, JIS
According to A 6201, the loss on ignition, which is mostly unburned carbon, is specified to be 5% or less.

However, recently, NOx (nitrogen oxide)
A low NOx combustion system has been implemented in response to stricter regulations, but this increases the amount of unburned carbon mixed in fly ash, making it difficult to use fly ash as a cement admixture advantageously. Has become. Therefore, it is necessary to remove unburned carbon from fly ash.

As a conventional method for removing unburned carbon, Japanese Patent Application Laid-Open No. 64-80477 discloses a technique utilizing an oscillating fluidized bed. This method utilizes the fact that the specific gravity of particles that contain a large amount of unburned carbon is lower than the specific gravity of particles that do not contain unburned carbon, and density classification is performed in a fluidized bed whose fluidized state is stabilized by vibration. This is a method of separating and removing fuel carbon.

In this technique, air is sent at a rate of 1 to 4 times the air flow velocity (minimum fluidization rate) at which the entire bed starts to fluidize while vibrating the fluidized bed at a frequency of about 3 Hz, and no bubbles are generated. Density classification is performed while maintaining a stable flow state.

[0008]

However, the actual coal ash contains a large amount of highly adherent fine particles having a particle size of 10 μm or less. On the other hand, in the above-mentioned conventional technique, since the air velocity (superficial velocity) is low, it is difficult to stably fluidize the actual coal ash containing fine particles having strong adhesion.

In order to prevent this, it is necessary to previously remove fine particles having a particle size of 10 μm or less from the raw material coal ash. However, the pretreatment for removing a large amount of fine particles from coal ash requires a large-scale facility, which makes the system complicated, costly, and unrealistic. Also, the particle size 10
Since many fine particles having a particle size of 10 μm or less are contained in particles effective as a cement admixture (Japanese Patent Publication No. 2-49264), removal of particles having a particle size of 10 μm or less is not preferable in terms of utilization.

An object of the present invention is to remove unburned carbon in coal ash by using an oscillating fluidized bed for an actual coal ash containing fine particles having strong adherence and having a particle size of 10 μm or less,
The purpose is to enable efficient separation and removal of particles having a low density that contain a relatively large amount of unburned carbon.

[0011]

The present invention has a particle size of 10 μm.
Reformation of coal ash to reduce the amount of unburned carbon in coal ash by separating low density particles containing relatively large amount of unburned carbon by using a vibrating fluidized bed than the coal ash containing the following particles: In the method, the superficial velocity of fluidized air in the vibrating fluidized bed is 0.5 to 4.0 cm / sec, and the frequency is 10
It relates to a method for reforming coal ash at a frequency of not less than Hz and an amplitude of 0.1 to 2.0 mm.

[0012]

When the density classification is performed using the fluidized bed, the biggest cause of the separation is the mixing of particles. Possible causes of the mixing of particles are uneven distribution of air flow, generation of bubbles, interaction with walls, etc., among which the influence of bubbles is remarkable.

On the other hand, in order to increase the separation efficiency, it is necessary to increase the porosity in the fluidized bed so that particles having a difference in specific gravity can easily move to each other. For that purpose, it is effective to increase the flow velocity of the fluidizing air introduced into the fluidized bed to provide as many spaces as possible between the particles. However, if the flow rate is simply increased, large bubbles tend to be generated, so that particles are mixed and the separation efficiency is rather lowered. 10 μm with strong adhesion, especially as coal ash
When the following fine particles are contained, larger bubbles are likely to be generated and the mixing of the particles is promoted, which is not preferable.

In order to solve the above-mentioned trade-off, the present inventor examined in detail the relationship between the superficial velocity and vibration conditions of fluidized air, and the state of bubbles and the mixed state of particles. And, in this process, although the bubbles are generated under the condition that the flow velocity is high such that the bubbles are generated in the vibrating fluidized bed, the particles are not mixed at all, or only a small amount is mixed. We have found that there are unique conditions that do not occur.

As a result, the separation of the particles from each other is promoted by the fine air bubbles, and at the same time, the mixing of the particles is suppressed. As a result, coal ash containing fine particles of 10 μm or less can be extremely efficiently classified in density. became.

The unique condition region discovered by the present inventor is defined by the superficial velocity of fluidized air and the vibration frequency and amplitude as vibration conditions.

In the present invention, the superficial velocity of the fluidized air is intentionally set in the region where bubbles are generated. Specifically, it is 0.5 to 4.0 cm / sec, and more preferably 1.0 to 3.0 cm / sec.

If the superficial velocity is less than 0.5 cm / sec, a uniform flow state cannot be obtained due to channeling, uneven distribution of flow, etc., so that separation is not performed. Sky tower speed is 4.
When it exceeds 0 cm / sec, the bubbles become large and the inside of the layer is vigorously stirred, so that the mixing is promoted and the separation effect is reduced, and the number of particles that fly out is increased and the effective component is lost.

Regarding the frequency, there is an optimum condition within the range of 10 Hz or higher, although it depends on the grain size composition.
If the frequency is too low, channeling etc. will occur and uniform fluidization will not be possible, so separation will not occur. The frequency is more preferably 60 Hz or less. When the frequency exceeds 60 Hz, it becomes difficult to increase the amplitude and it is necessary to increase the mechanical strength, which leads to an increase in the cost of the device itself.

The amplitude is 0.1 to 2.0 mm, more preferably 0.3 to 1.0 mm. When the amplitude is less than 0.1 mm, the vibration is not physically transmitted, so that the effect due to the vibration is not exhibited. If the amplitude exceeds 2.0 mm, physical voids are generated between the dispersion plate and the powder layer, which promotes the generation of large bubbles and violent mixing of the particles themselves, making it impossible to obtain a good flow state. .

The present invention utilizes the fact that the specific gravity of particles containing a large amount of unburned carbon is lower than the specific gravity of particles containing no unburned carbon, and attempts to separate particles containing a large amount of unburned carbon by density classification. To do. However, when treating a material having a wide particle size distribution, such as coal ash, the effect of particle size classification may appear and a particle having a large particle size may sink into the layer.

Therefore, by removing the large-sized particles having a particle size of 100 μm or more before carrying out the modification treatment of the present invention, it is possible to prevent the large-sized particles from sinking into the layer. At this stage, for example, a bubbling fluidized bed or an air classifier can be used, but the present invention is not limited thereto.

[0023]

EXAMPLES More specific examples will be described below.
In order to obtain a vibrating fluidized bed, an apparatus schematically shown in FIG. 1 was prototyped and used.

Raw coal ash was quantitatively supplied from the hopper 1 for supplying coal ash through the vibrating feeder 2. Fluidizing gas was supplied to the wind box from the lower part of the main body by the air supply device 3, and the fluidizing gas was sent to the fluidized bed 5 through the gas dispersion plate 4 to fluidize the coal ash in the fluidized bed 5.

At this time, vertical vibration was applied from the lower part of the fluidized bed body by the rotary vibration generator 6. Particles having a large amount of unburned carbon that have been density-classified in the fluidized bed 5 and floated near the surface are sucked by a nozzle 7 mounted slightly above the surface, discharged to the outside of the system, and then a bag filter 8 is used. Recovered.

The desired product was passed through the moat weir 9 so as not to mix with the unburned carbon-rich particles on the upper part of the fluidized bed. The product then flows over the overflow weir 10 and into the product reservoir 11. The product collecting device 12 periodically sucks and collects the product. In the product reservoir 12, air is supplied from below to constantly fluidize the product in order to prevent clogging of the product due to retention.

Using the above apparatus, the unburned carbon content was 8.
5% of raw coal ash was modified. However, in order to suppress the influence of the particle size classification, particles having a particle size of 100 μm or more were removed in advance. Superficial velocity when processing coal ash,
The amplitude and frequency were changed as shown in Table 1. And
The state of the fluidized bed was observed and the ratio of unburned carbon in the obtained product was measured.

[0028]

[Table 1]

As can be seen from Table 1, the superficial velocity is 0.2, 0.
In the case of 3 cm / sec, the flow is insufficient and the superficial velocity is
In the case of 5.0 cm / sec, the mixing becomes large. Further, when the frequency is 5 Hz, the fluidization is not uniform. Amplitude is 2.5
When it becomes cm, the mixing becomes large. Within the scope of the present invention, it has become possible to obtain products with a loss on ignition of 5% or less, most of which is unburned carbon.

[0030]

As described above, according to the present invention,
When coal ash containing fine particles having a strong adherence with a particle size of 10 μm or less is modified by an oscillating fluidized bed, even if bubbles are generated, the particles are not mixed at all or are slightly mixed. It can be processed under conditions that only occur.

As a result, the separation of the particles from each other is promoted by the fine air bubbles, and at the same time, the mixing of the particles is suppressed. As a result, the coal ash containing the particles can be extremely efficiently classified in density.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of an unburned carbon removing apparatus suitable for carrying out the method for reforming coal ash according to the present invention.

[Explanation of symbols]

1 Coal ash supply hopper 2 vibrating feeder 3 Air supply device 4 gas dispersion plate 5 fluidized bed 6 Rotational vibration generator 7 nozzles 8 bug filters 9 Moguri weir 10 overflow weir 11 product pool 12 Product collection device

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takuo Nojiri 7-34, Minamienkajima, Taisho-ku, Osaka-shi Osaka Cement Co., Ltd. Central Research Laboratory (72) Inventor Yasuharu Utsunomiya 7-chome, Minamienkajima, Taisho-ku, Osaka 1-34 Osaka Cement Co., Ltd. Central Research Laboratory (72) Inventor Seiya Kamei 7-34, Minami Enkajima, Taisho-ku, Osaka City Osaka Cement Co., Ltd. Central Research Laboratory (56) Reference JP-A-64-80477 ( JP, A) JP 60-61050 (JP, A) JP 52-2492 (JP, A) JP 5-337442 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B07B 1/00-15/00 B01J 8/00-8/46

Claims (4)

(57) [Claims] 1. An unburned carbon amount in coal ash is separated by separating low density particles containing relatively large amount of unburned carbon from a coal ash containing particles of 10 μm or less by using an oscillating fluidized bed. A method of reforming coal ash for reducing the superficial velocity of fluidized air in the vibrating fluidized bed, wherein
The vibration flow is set to 0.5 to 4.0 cm / sec at which bubbles are generated.
The frequency of vibration given to the layer is 10 Hz or more, and the amplitude is 0.
A method for reforming coal ash, which is 1 to 2.0 mm. 2. The method for reforming coal ash according to claim 1, wherein the superficial velocity is set to 1.0 to 3.0 cm / sec. 3. The method for reforming coal ash according to claim 1, wherein the amplitude is 0.3 to 1.0 mm. 4. Particle size of 10 prior to reforming coal ash.
The method for reforming coal ash according to claim 1, wherein particles of 0 μm or more are removed from the coal ash.