JPH0324422B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing artificial lightweight aggregate used as concrete aggregate for civil engineering or construction. In general, artificial lightweight aggregates are made of shale, clay, slate, etc., which are heated to, for example, 1120°C, gas is generated from inside the raw material in the temperature range where it becomes semi-molten, and this is added to the melt. It is wrapped to form an aggregate with a porous structure, and is used for purposes such as lightweight concrete aggregate for civil engineering construction, Spritton elements for high-grade interiors and exteriors, gravel and sand for filtration, etc. Its specific gravity, particle size distribution, and strength are stable, and its apparent specific gravity is 1.2 to 1.6, about 1/2 that of natural aggregate, and its thermal conductivity is low, about 1/3 that of ordinary concrete. Also,
The manufacturing process involves firing raw materials having a particle size within a predetermined range, and a rotary kiln has conventionally been 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, it is difficult to control the temperature during firing, and it is difficult to establish conditions for stable operation, which is a fatal drawback in the production of artificial lightweight aggregates. In order to eliminate the drawbacks caused by firing in a rotary kiln, the inventors of the present invention discovered that in a fluidized fluidized furnace, the foaming temperature is reached in a very short time, and the raw material particles are in a violent fluid state in the furnace, so that they fuse together. Focusing on the fact that firing at higher temperatures is possible because there is less danger and temperature control is easier, we pre-heat and dry the crushed and sieved raw materials in a primary preheater, and reduce the ultra-fine powder contained in the raw materials. While preheating and drying, the raw material from which ultrafine particles have been dispersed and removed is supplied quantitatively to a secondary preheater using a quantitative supply device for preheating, and then supplied to a fluidized fluidized furnace, where the particles flow. He filed an application for an invention characterized by firing the flow rate and firing temperature while controlling the flow rate and firing temperature by utilizing the
-148810, Japanese Unexamined Patent Publication No. 58-55363). In this application, for example, liquid fuel heavy oil is used as the fuel,
This heavy oil is sprayed directly into the fluidized furnace and combusted in the furnace, but in this case, the temperature inside the furnace has a considerable height distribution in the vertical and horizontal directions, and the firing temperature is the highest in the furnace. Since temperature must be used for control, it was found that the greater the variation in temperature distribution, the lower the average temperature and the heavier the product specific gravity. Furthermore, it has been found that even when the maximum temperature is controlled, under certain conditions, higher temperature areas may occur in some areas, causing unexpected fusion phenomena. The present invention was proposed in view of the above circumstances, and uses liquid or gaseous fuel as the firing fuel when firing the particles while controlling the flow rate and firing temperature by utilizing the flow state of the particles in the fluidized fluidized furnace. In some cases, the pulverized solid auxiliary fuel is also used in combination with a supply means separate from the firing fuel. EMBODIMENT OF THE INVENTION Hereinafter, the manufacturing method of the artificial lightweight 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 aggregate according to the present invention. For example, raw material that has been crushed and sieved and configured to have a particle size within a predetermined range is transported from a raw material tank 1 to a conveyor. 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, which will be described later. 0.074mmφ or less) 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 carrier separator 8, is introduced into the fluidized bed furnace 9 through the raw material charging pipe 15. The fluidized bed furnace 9 has a pulverized solid fuel supply port 19
Fine powder solid fuel such as coal supplied from a to 19e, or in the case of liquid or gaseous fuel, the firing fuel supplied from the burner 11 and the supply port 1
It is heated by the fine powder solid auxiliary fuel supplied from 9a to 19e to a predetermined temperature (for example, 1100°C to
The raw material introduced into the fluidized bed furnace 9 is heated and foamed, and the fine powder is carried by the air flow and separated from the gas flow by the carry-over separator 8, and other than the fine powder is passed through the overflow pipe. 16
Both of them enter the product cooler 17 where they are cooled and taken out as a product. Further, the fluidizing air sent to the fluidized furnace 9 is supplied to the Roots blower 1.
3, the freeboard part (upper chamber) of the fluidized bed furnace 9
Air is sent into the fluidized furnace 9 through a heat exchanger 10 provided at 9a and into the fluidized fluidized furnace 9 through a nozzle 12 provided at the bottom of the fluidized fluidized furnace 9, and air is sent into the product cooler 17 by a roots blower 14. Ru. Furthermore, 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. In the above embodiment, the case where the primary and secondary preheaters 3 and 7 are used is explained as an example, but the present invention is not limited to this, and the present invention is not limited to this. Needless to say, this includes everything that can supply raw materials. When artificial lightweight aggregate is used as aggregate for concrete, its particle size distribution poses a problem, especially
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. 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, for example, the primary preheater 3
Preheating the raw materials and separating and removing the ultrafine powder (0.074 mmφ) is preferable in terms of stable operation and improvement of product quality. In addition, preheating the raw materials will prevent a large amount of moisture (15-20
This is important in this example in terms of lowering the amount of water in raw materials such as shale containing (%). Factors that determine the specific gravity of artificial lightweight aggregates 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 varies 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 mm/sec is required, and from this and Table 2, 50
% 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. On the other hand, the fluidized fluidized furnace 9 is characterized by the fact that the temperature inside the furnace is constant and easy to control compared to the rotary kiln. However, when using liquid firing fuel and burning heavy oil in the burner 11, However, there is still a problem in that the temperature distribution within the furnace, particularly in the vertical direction, varies. As mentioned above, the firing temperature must be controlled at the maximum temperature in the furnace, so if there are variations 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) heavy oil atomization state (heavy oil temperature, amount of atomizing air and steam), (2) flow state and specific surface area of fluidized particles, and (3) vaporization of heavy oil. Velocity (depending on the surface temperature of the fluidized particles and the temperature of the inlet air) (4) The mixing state of the fluidizing air and heavy oil, etc. Now, as shown in Figure 2, 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 9b as shown in (A). Therefore, a state intermediate between the two is most preferable in terms of temperature stability and temperature distribution width, and empirically, a temperature distribution of around 1100° 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 in the raw material that should become carryover, 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 through the low-flow area on the wall of the fluidized bed furnace to the lower part of the fluidized bed furnace.To prevent this, connect the pipe for blowing air from the raw material charging pipe. At the same time, this air can be used to blow away the fine particles to the inside of the fluidized fluidized furnace where the flow rate is high, so that they are carried by the upward air current and do not flow down to the lower part of the fluidized fluidized furnace. On the other hand, in the present invention, in order to enhance the effect of controlling the firing temperature in the fluidized fluidized furnace 9, when heavy oil is used as the firing fuel, in addition to the burner 11, fine solid auxiliary fuel injection pipes 19a to 19e such as coal powder etc.
is inserted into the fluidized fluidized furnace 9 to mix the pulverized solid auxiliary fuel with the firing fuel. The combustion mechanism of firing fuel such as heavy oil and fine powder solid auxiliary fuel is that in the case of heavy oil, it starts to gasify as soon as it is sprayed into the furnace, and when it exceeds its boiling point, it instantly gasifies and burns and flows to the upper part of the furnace. When pulverized coal is concentrated, it tends to raise the temperature in the upper part of the furnace.However, in the case of pulverized coal, when it is blown into the furnace, it moves violently and is rapidly dispersed and burned within the furnace. It has the effect of making the temperature distribution uniform. Therefore, no localized high-temperature areas are generated, and the oxygen utilization rate in the air inside the furnace is increased. By utilizing this combustion mechanism, the present invention reduces the width of the temperature distribution in the vertical and horizontal directions within the furnace, eliminates the fusion phenomenon caused by the occurrence of localized high temperatures, and thereby increases the specific gravity. This is said to have made it possible to manufacture lightweight products. Now, as shown in Figure 2, we measured the correlation of the temperature distribution with the horizontal direction at 60 cm (A), 110 cm (B), and 140 cm (C) from the lower end of the fluidized bed furnace 9. The results were obtained and the specific gravity of the product was 1.30.

[Table] When 50% of the heavy oil (in terms of calorific value) was replaced with fine coal powder in the same equipment, the temperature distribution was as shown in Table 4, and the product specific gravity was the same, 1.30.

[Table] As is clear from this result, it is clear that the temperature control at the center of the furnace is more uniform at around 1100°C when the pulverized solid auxiliary fuel is used in combination. Note that the above combustion mechanism also applies to the case where pulverized solid fuel is used as the combustion fuel, and it is possible to control the temperature to a desired uniformity by adjusting the number, position, supply amount, etc. of the supply ports 19a to 19e. As described above in detail based on the embodiment shown in the drawings, according to the method for producing artificial lightweight 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 for explaining the manufacturing method according to the present invention, and FIG. 2 is an explanatory diagram of temperature distribution in a fluidized bed furnace. In the drawing, 3 is a primary preheater, 6 is a constant supply device,
7 is a secondary preheater, 9 is a fluidized furnace, 9a is a freeboard part, 9b is an inclined part, 11 is a burner, 19a-
19e is a fine powder solid fuel supply port.

Claims (1)

[Claims] 1. When feeding a raw material having a particle size within a predetermined range to a fluidized fluidized furnace and firing it while controlling the flow rate and firing temperature by utilizing the flow state of the particles in the fluidized fluidized furnace, liquid or gaseous fuel is used as the firing fuel. In this case, a method for producing an artificial lightweight aggregate, characterized in that a fine powder solid auxiliary fuel is used in combination with a supply means different from the calcination fuel.