JPS649259B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing artificial lightweight fine aggregate used as concrete aggregate for civil engineering or construction. Generally, artificial lightweight fine aggregate is made by heating shale, clay, slate, etc. to a temperature of 1,120°C, generating gas from inside the raw material in the temperature range where it becomes semi-molten, and then distributing it into the melt. It is wrapped in a porous structure and is used as aggregate for lightweight concrete for civil engineering construction, Spritton elements for high-grade interiors and exteriors, gravel and sand for filtration, etc. It is characterized by stable specific gravity, viscosity distribution, and strength, and low thermal conductivity, about 1/3 of that of ordinary concrete. Furthermore, during production, the raw materials are pulverized, sieved and fired, and a rotary kiln is conventionally used for the firing. However, when firing in a rotary kiln, it takes a relatively long time for the raw material to reach a foaming, semi-molten state. Since they are heated in contact with each other, they have the disadvantage that in a half-molten state, the raw material particles fuse together to form clinker, and problems such as adhesion to the furnace wall and formation of rings tend to occur. Also,
In the case of a rotary kiln, temperature control during firing is difficult, and conditions for stable operation are difficult to establish, which is a fatal drawback in producing artificial lightweight fine aggregate. The present invention aims to eliminate the drawbacks caused by firing in a rotary kiln as described above. In a fluidized fluidized furnace, the foaming temperature is reached in a very short time, and the raw material particles are in a state of intense fluidity in the furnace, so there is a risk of them fusing together. It was completed by focusing on the fact that firing at a higher temperature is possible because it is easier to control the temperature. The raw material was preheated and dried using a preheater and the ultrafine powder contained in the raw material was dispersed and removed, while the raw material that had been preheated and dried and the ultrafine powder was dispersed and removed was fed quantitatively to the secondary preheater by a quantitative feeder and preheated. After that, the particles are fed to a fluidized fluidized furnace and fired while controlling the flow rate and firing temperature by utilizing the flow state of the particles in the fluidized fluidized furnace.Furthermore, the product is preheated and dried using a primary preheater and the sensible heat of the product is recovered. This is done by using the hot air generated by , by controlling the flow rate to reduce the carry-over ratio, and by providing a notch that makes the slope continuous from the tip of the overflow pipe the same as the diameter of the freeboard part and making it continuous with the overflow pipe, the estimation in the freeboard part can be improved. By installing a pipe with many small holes on the furnace wall at the lower end of the slope, and blowing air along the furnace wall from the small holes, we were able to secure long-term stable firing. The temperature distribution of the firing temperature was controlled by mixing steam into the fuel spray air, and the temperature distribution of the firing temperature was controlled by blowing air into the raw material charging pipe. It is characterized by controlling the distribution. EMBODIMENT OF THE INVENTION Hereinafter, the manufacturing method of the artificial lightweight fine aggregate based on this invention is demonstrated based on the Example shown in the drawing. FIG. 1 is a system diagram illustrating the method for producing artificial lightweight fine aggregate according to the present invention.
The product enters the primary preheater 3 via the product cooler 17, which will be described later, and is preheated and dried by hot air generated by recovering product sensible heat from the product cooler 17. mmφ
below) are dispersed and removed. The raw material, which has been preheated and dried and from which ultrafine powder has been dispersed and removed, is put into a service hopper 5 via a conveyor 4, and is quantitatively supplied to a secondary preheater 7 by a quantitative supply device 6 connected to the service hopper 5. The raw material, which has been preheated in the secondary preheater 7 by the combustion exhaust gas from the carryover separator 8, is introduced into the fluidized bed furnace 9 through the raw material charging pipe 15. The fluidized fluidized furnace 9 is heated by a burner 11 and maintained at a predetermined temperature (for example, 1115°C to 1125°C), and the raw material introduced into the fluidized fluidized furnace 9 is heated and foamed, and the fine powder is carried by the air flow. The powder is then separated from the gas stream by the carry-over separator 8, and the particles other than the fine powder overflow from the overflow pipe 16, and both enter the product cooler 17, where they are cooled and taken out as a product. Note that the fluidizing air sent to the fluidized fluidized furnace 9 is supplied to the lower part of the fluidized fluidized furnace 9 via a heat exchanger 10 provided in a freeboard section (upper chamber) 91 of the fluidized fluidized furnace 9 by a Roots blower 13. Air is fed into the fluidized bed furnace 9 through a nozzle 12 , and air is fed into the product cooler 17 via a Roots blower 14 . In addition, the exhaust gas of the circulating air of the secondary preheater 7 and the air of the primary preheater 3 which has recovered product sensible heat in the product cooler 17 are discharged from the exhaust blower 18 to the outside of the system. When artificial lightweight fine aggregate is used as aggregate for concrete, its particle size distribution becomes a problem, and in particular, it is required that the amount passing through a 0.3 mm sieve is 20% or more, and the amount passing through a 0.074 mm sieve is small. There is. Therefore, in order to satisfy this requirement, it is necessary to use powerful pulverizing equipment in the raw material pulverizing process, and as a result,
Approximately 10% of the material passed through the 0.074mm sieve.
If this is fed into a fluidized fluidized furnace as it is, the temperature inside the furnace will become extremely unstable, making it easy to form clinker. Therefore, as mentioned above, the raw material is preheated in the primary preheater 3 and the ultrafine powder (0.074 mmφ) is
Separating and removing is preferable in terms of stable operation and improvement of product quality. In addition, preheating the raw material is important in reducing the amount of moisture in raw materials such as shale that contain a large amount of moisture (15 to 20%) (described later), and together with the quantitative supply of the raw material, it constitutes the present invention. This is an important key to achieving this goal. Factors that determine the specific gravity of artificial lightweight fine aggregate include, in addition to the expandability of the raw material, the thermal history of the raw material during calcination, the calcination temperature, and the residence time of the raw material at that temperature. It has been confirmed that the specific gravity differs depending on the particle size of the raw material. For example, Table 1 shows typical particle size distribution and specific gravity of fluidized fine aggregate.

[Table] As can be seen from Table 1, as the particle size decreases, the specific gravity increases. Therefore, in order to obtain lighter fine aggregate, the smaller the particle size, the more preferable it is to perform firing at a higher temperature and longer residence time, but in the case of fluidized firing, the tendency is the opposite. Fluidized firing is a method of firing particles by flowing them in the air at a speed lower than the terminal velocity of the particles, but this terminal velocity differs depending on the particle size and specific gravity. For example, Table 2 shows the relationship between particle size and terminal velocity.

[Table] However, as a result of the test, in order to maintain a good fluidity state and burn heavy oil well in the furnace, two steps are required.
It has been confirmed that a flow velocity (superficial velocity) of approximately 3.5 m/sec is required, and from this and Table 2, 50 m/sec is required.
% or more exceeds the terminal velocity, resulting in carry over and not staying in the fluidized bed furnace.
This means that the problem that the smaller the particle size is, the more difficult it is to reduce the specific gravity unless it is fired at a high temperature and long residence time cannot be solved, making it difficult to reduce the weight of the aggregate as a whole. As a countermeasure against this problem, the present invention provides that the fluidized bed furnace 9 has a freeboard section 91 and an inclined section 92, as shown in FIG.
The diameter of the freeboard part 91 is made larger than that of the fluidizing part 93 to lower the flow velocity of the freeboard part 91, and the freeboard part 91 is sufficient to absorb the fine particles that have carried over the fluidizing part 93. We try to make it flow while ensuring a suitable temperature and residence time. However, by making the diameters of both parts 91 and 93 different, a new problem arises in that fine particles tend to accumulate in the inclined part 92 and become clinker. However, as an effective means to prevent this, , the tip of the overflow pipe 16 is attached to the lower end of the inclined part 92, and a notch 94 is provided to make the inclined part 92 continuous from the tip the same as the diameter of the freeboard part 91, so that the freeboard part 91 and the inclined part 92 are connected to each other. What is necessary is to make it easier to take out the flowing fine particles as overflow. In addition, the inclined portion 92
Due to the shape of the wall surface of the fluidized bed furnace 9, almost no upward flow velocity can be obtained, so fine particles are likely to accumulate on the wall surface of the fluidized bed furnace 9. It is effective to arrange the furnace wall at the lower end of the furnace and blow out air along the furnace wall from small holes. On the other hand, a fluidized fluidized furnace is characterized by the fact that the temperature inside the furnace is constant and easy to control compared to a rotary kiln, but when burning heavy oil in the burner 11 in the furnace, the temperature distribution inside the furnace depends on the combustion state. To,
In particular, there is a problem that variations occur in the temperature distribution in the vertical direction. Since the firing temperature must be controlled at the highest temperature in the furnace, if there is variation in temperature distribution, the average temperature will be low. In general, the combustion mechanism of heavy oil in a fluidized fluid furnace is different from normal combustion, and it is thought that the sprayed heavy oil first adheres to the surface of the fluidized particles in the form of a film, where it vaporizes and burns. Therefore, the factors that affect the combustion state of heavy oil are: (1) the spray state of heavy oil (heavy oil temperature, the amount of atomizing air and steam), (2) the flow state and specific surface area of fluidized particles, and (3) the spray state of heavy oil. Vaporization rate (depending on the surface temperature of the fluidized particles and the temperature of the incoming air) (4) The mixing state of the fluidizing air and heavy oil. Now, as shown in Figure 3, when we measure the temperature at four points, 60 cm (A), 110 cm (B), 140 cm (C), and 200 cm (D) from the lower end of the flow section 9, we find that the combustion of heavy oil When the combustion speed is too fast, the temperature distribution becomes (A) → (B) → (C) → (D), which tends to create clinker at the bottom of the fluidized bed furnace 9, and conversely, when the combustion speed of heavy oil is slow, the temperature distribution is as follows. is (D)→(C)→(B)→
It was confirmed that clinker was easily formed in the inclined portion 92 as shown in (A). Therefore, a state between the two is most preferable in terms of temperature stability and temperature distribution width, and empirically, B → 1125°C, A, C → 1115°C, D →
A temperature distribution such as 1070°C is best. In order to achieve such temperature distribution, the above (1) to (4)
The method is considered based on various factors, but the biggest factor that controls these is the amount of raw material charged per unit time, followed by the moisture content and particle size distribution of the raw material. Good too. That is, as the amount of raw material charged increases, the combustion rate of heavy oil decreases, and even if the water content of the raw material decreases and the particle size distribution leans toward the smaller side, the combustion rate increases. Therefore, in order to maintain an appropriate temperature distribution in response to these fluctuations, if steam is mixed into the fuel spray air,
It can reduce the burning rate of heavy oil. Furthermore, if there are many fine particles that should become carry-over in the raw material, the combustion rate becomes faster and clinker tends to form in the lower part of the fluidized bed furnace. This is because the fine particles flow from the raw material charging pipe to the lower part of the fluidized bed furnace through the low flow velocity on the wall surface of the fluidized bed. To prevent this, connect a pipe for blowing air to the raw material charging pipe. At the same time, this air blows away the fine particles to the inside of the fluidized bed furnace where the flow rate is high.
It is sufficient to prevent it from flowing down to the lower part of the fluidized bed furnace due to the rising air current. As described above in detail based on the embodiments shown in the drawings, according to the method for producing artificial lightweight fine aggregate according to the present invention, stable operation is possible because the flow rate and temperature are reliably controlled. This has the effect of stabilizing the specific gravity, particle size distribution, and strength of the product.

[Brief explanation of drawings]

Fig. 1 is a system diagram explaining the manufacturing method according to the present invention, Fig. 2 is a cross-sectional view of the essential parts of the fluidized bed furnace used in the manufacturing method according to the present invention, and Fig. 3 is an explanatory diagram of the temperature distribution in the fluidized bed furnace. be. In the drawing, 3 is a primary preheater, 6 is a constant supply device,
7 is a secondary preheater, 9 is a fluidized furnace, 91 is a freeboard part, 92 is an inclined part, 93 is a fluidized part, 94 is a notch part, and 95 is a pipe.

Claims (1)

[Scope of Claims] 1. The pulverized and sieved raw material is preheated and dried in a primary preheater using hot air generated by recovering product sensible heat, while the ultrafine powder contained in the raw material is dispersed and removed. After preheating and drying and dispersing and removing the ultrafine powder, the raw material is quantitatively supplied to the secondary preheater by a quantitative supply device, and after preheating, the raw material is divided into a freeboard section, an inclined section, and a flowing section, and the diameter of the freeboard section is adjusted. is supplied to a fluidized furnace with a diameter larger than that of the fluidized section, and the flow rate is controlled to reduce the flow velocity in the freeboard section and the carryover ratio, and steam is mixed into the air for fuel spraying or air is mixed into the raw material bagging pipe. 1. A method for producing artificial lightweight fine aggregate, which comprises firing the same while controlling the temperature distribution of the firing temperature. 2. By providing a notch that makes the slope continuous from the tip of the overflow pipe the same as the diameter of the freeboard part and making it continuous with the overflow pipe, accumulation in the freeboard part is prevented and long-term stable firing is ensured. A method for producing an artificial lightweight fine aggregate according to claim 1, characterized in that: 3 A pipe with many small holes is installed on the furnace wall at the lower end of the slope, and air is blown out along the furnace wall from the small holes to prevent buildup on the slope and ensure long-term stable firing. A method for producing an artificial lightweight fine aggregate according to claim 1 or 2, characterized in that: