JPS6022274B2 - Continuous air flow firing furnace for powder and granular materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vertical furnace having a hollow column structure for continuously heating and firing powder and granular materials in an air stream.

BACKGROUND ART Various vertical furnaces have been developed and proposed for use in heating and firing granular materials such as firing artificial lightweight aggregates, limestone, and dolomite.

In view of the fact that when artificial lightweight aggregate is fired in a rotary kiln, there are problems in terms of prevention of fusion of its descendants, heat transfer bran in the furnace, thermal economy, etc. ``Continuous airflow firing of powder and granular materials in a vertical furnace'' allows for the production of lightweight aggregates with a large particle diameter, easy to prevent fusion of fired materials, and excellent firing processing ability. He first proposed the "Method" (Tokubuta Sho 55-75522, hereinafter referred to as "Sakimanpo"). The present invention relates to a vertical furnace having a hollow tower structure used in the method of this prior application.

'1' is a vertical furnace used for air flow firing of powder and granular material in a subordinate column.
}As shown in Japanese Patent Publication No. 49-48076, this is a vertical furnace with a sky tower structure, which has a combustion chamber in the lower part of the furnace and slits to generate a swirling upward hot gas flow in the furnace, and the fired product is transported from the lower part of the furnace. Discharge and batch operation, Samurai Sekisho 53-12
Like the furnace used in No. 1807, a vertical furnace is equipped with a perforated plate in the lower part of the furnace to straighten the rising air flow, and has a structure that continuously overflows and discharges the fired product. [3] A straightening plate for the rising air flow in the furnace. A structure in which the fired product is sequentially overflowed to the lower stage and discharged after forming a deposited layer of neighboring products at the bottom of the furnace. A vertical furnace with a structure in which an inverted cone-shaped perforated plate is installed around the gas jet nozzle and its surroundings to generate an upward air current, and the fired product is discharged overflow. It is a vertical furnace with an open tower structure in which the fired products are sequentially dropped into the lower part of the furnace, forming a deposited layer of fired products at the bottom of the furnace and then being discharged. These conventional techniques involve forming a fluidized bed, improved spouted bed, swirling spouted bed, packed moving bed, etc. of powder and granular materials in a furnace using an upward air flow of combustion gas, etc., and then heating and firing them.
No matter which type of vertical furnace is used, it is not possible to obtain satisfactory conditions for preventing the fusion of fired products. In either case, due to the mechanism of the furnace, the exhaust gas is at a high temperature that is approximately the same as or higher than the firing temperature. It was found that there is a large room for improvement in terms of the firing processing capacity of the furnace (the amount of spotting per inner mirror of the furnace), which has poor thermal efficiency. As a result of repeated research aimed at achieving this goal, we found that when heating and firing powder and granules by forming a mixed layer of powder and granules in the furnace, it is important to If you use a furnace with the shape and structure that produces the powder, the concentration of powder and granules will be high at the slow end, and a thin mixed layer will be formed at the far end. Then, the gas temperature of the rising air in the upper and lower mixed layers,
A gradient occurs in the temperature of the material (powder and granules). ■ The dilute mixed layer is fired as the highest temperature zone, and the fired product does not pass through this highest temperature zone and accumulate at the bottom of the furnace, but instead is suspended in the rising air current. By using a furnace that allows the air to be discharged from the bottom of the furnace to the outside of the furnace while floating, it becomes easier to adjust the temperature inside the furnace and prevent the baked product from being contaminated by insects, improving the thermal efficiency of the furnace, and reducing the amount of scale per internal mirror in the furnace. We found that it is possible to improve output ability.

The present invention is based on these findings.According to the present invention, in a vertical furnace having a hollow tower structure and having no porous portions in the furnace or the furnace wall for passing airflow, powder particles are placed in the upper part of the furnace. The furnace body has a body inlet and a sedimentation chamber, and the cross-sectional area decreases toward the bottom directly below the sedimentation chamber, and the discharge part of the furnace body has a discharge port for the fired product and an inlet for fuel, etc. and an inlet for fuel, etc. is provided in the furnace wall.

In carrying out the present invention, the furnace body directly below the settling chamber can be composed of an inverted conical section and one straight cylindrical section.

Further, the furnace body directly below the settling chamber can be constructed only of an inverted conical portion. Furthermore, the furnace body directly below the settling chamber can be composed of one straight section and an inverted conical section. The airflow firing furnace according to the present invention is intended to be used for firing granular materials such as lightweight aggregates, which are likely to be deposited at high temperatures. The purpose is also to improve the firing ability, and it can also be used for firing powdery materials such as limestone and dolomite.

In the present invention, the mixed layer of powder and granular material and an updraft is a layer in which the powder and granular material are in contact with an updraft in a vertical furnace with an open column foundation structure, excluding a packed bed of powder and granular material and a simple sedimentation layer. ``A layer in which powder and granules form a fluidized bed, spouted bed, etc. due to rising air currents, and the powder and granules float and circulate.

A specific example of the vertical air flow kiln having a sky tower structure according to the present invention is the first example.
Figure 3 shows a vertical airflow firing furnace with a hollow tower structure, where 2 is a combustion gas outlet, 3 is a powder inlet, 13 is a settling chamber, and 8 is a furnace. This is the port through which the firing fuel (air and/or combustion gas (hereinafter referred to as fuel, etc.)) is introduced upward from the bottom.

4' is an inverted conical portion, and 5 and 7 are tube portions.

The cross section of this straight cylindrical portion is not limited to a circular one, but may be polygonal.The inverted conical portion may also be in the shape of an inverted pyramid.Therefore, the rising air from the bottom of the furnace has a flow velocity of {2} In the furnace shape shown in Fig. 2, it is fast below the inverted conical part and slows above it; '3' In the furnace shape shown in Fig. 3, it becomes slower in the inverted conical part In other words, the flow velocity of the rising air is slow in the wide cross-sectional area of the straight cylinder parts 5, 7 and inverted conical part 4 of the furnace body, and becomes faster in the narrow part. According to the findings of the present inventors, when forming a mixed layer of updraft and granular material in a furnace body having such a shape, "the concentration of granular material is It was found that a large mixed layer 11 (hereinafter referred to as a dense mixed layer) is formed above and below a mixed layer 12 with a small concentration of powder and granules (hereinafter referred to as a thin mixed layer) at high flow speeds. In the present invention, as will be described later, the fired product is discharged from the lower part of the diluted mixing layer 12, that is, from the bottom of the furnace, so even if the granular material fed in a fixed amount into the furnace descends to the mixing layer 12, The entire amount is blown back to the mixed layer 11 by the updraft and circulated.
The flow does not repeat, but what passes through the dilute mixed layer 12 is always discharged in a constant amount. Therefore, due to the combination of this and the above-mentioned differential effect of richness and dilution, even in the steady state during heating and firing, in the mixed layers 11 and 12, the amount of granular material retained, that is, the amount of granular material There is a difference in the amount of floating, circulating, and flowing, and the upper and lower layers as a whole become an incompletely mixed layer.

Generally, in the mixed layer of Hakama Sekisho No. 53-121807 and Mochikai Sho Nezuichiro No. 796, the powder and granules are completely mixed as a whole and the temperature is uniform throughout the layer. On the other hand, if firing is performed using the furnace according to the present invention, the mixed layer 12 will now be the heating center (
(highest temperature range for heating, firing, and lightweight aggregate foaming), the powder and granules in mixed layers 11 and 12 are incompletely mixed as described above, and there is a difference in the retention amount. This causes a difference in the amount of heat and a difference in temperature, that is, the mixed layers 11 and 12
Although the mixed layer is formed continuously and integrally, it creates a low local temperature gradient in the height direction of the furnace and forms a steady state.
As a result, the temperature of the gas discharged from the mixed layer decreases, reducing fuel consumption. Next, a description will be given of the reduction of unevenness in the fired product by the furnace of the present invention and the ability of the furnace to remove phosphorus. Generally, when the mixed layer is a single layer, such as in the above-mentioned Tokuseki Shobou No. 121807, the powder and granules in the calendar are uniform and form a complete mixed layer, and the discharge of the fired product is not an overflow discharge. Therefore, whether the individual particles of the powdered raw material supplied into the furnace are discharged immediately or whether they remain in the furnace for a certain period of time and are sufficiently fired before being discharged depends entirely on probability. It is said that it is necessary to lengthen the residence time of powder and granules in the furnace in order to eliminate unevenness at dawn.
(Refer to pages 146-148 and 176-177, published by Oh, Showa 52).

On the other hand, according to the furnace of the present invention, the furnace is divided into upper and lower layers as described above, and is an incompletely mixed layer as a whole, and the reinforcement material passes through the dilute mixed layer 12 in a relatively high temperature zone. It is then discharged from the bottom of the furnace body. Therefore, the granular raw material fed into the furnace is transferred to all layers in the furnace (the low-temperature mixed layer 11 mentioned above).
and the high-temperature mixed layer 12), and is discharged from the bottom of the furnace with the effect of piston flow, that is, the phenomenon of extrusion flow added to the entire body.

As a result, even if the residence time in the furnace from when the powder and granular material is sent into the furnace to when it is discharged is relatively short, it always passes through the maximum temperature range and is ejected, so it is easy to be fired sufficiently. The unevenness of scales on baked products is reduced.

Further, according to the present invention, in the mixing report 12, the flow rate of the updraft is faster than in the conventional single layer, and the heat transfer effect between the gas (updraft) and the powder and granules is large, and the above-mentioned furnace By reducing the internal residence time, the firing capacity per internal volume of the furnace is improved as in the embodiments described below.

Next, in the furnace of the present invention, a settling chamber is provided in the upper part of the furnace, which has a diameter larger than that of the straight cylindrical part or the inverted conical part, and a mixed layer is formed in the rising air flow, which has a faster flow rate than in the conventional kiln technology. Overall, the retention amount of powder and granular material 0 is small, and
Among them, the mixed layer 12 has a faster flow rate, a thinner powder and granular material, and has a greater fly-catching effect, so that it is possible to reduce the bug sticking phenomenon of the fired product.

As a result, even powder particles with strong fusion properties can be fired and foamed by relatively high-temperature treatment without the use of a ratchet preventive material, making it possible to obtain light and heavy aggregates with a lighter specific gravity. In addition, because the structure of the furnace allows rapid heating in a floating state, when using granules as a late-forming raw material, even if the granules do not have the strength necessary for firing in a rotary kiln, they can be heated quickly.
The surface of the granules is compacted in a short time and can be used without breaking and turning into powder. Inverted conical part 4 of the vertical furnace of the present invention
And the upward opening angle of 10 needs to be 60 degrees or less. This is because if it exceeds this range, the powder particles will accumulate or stagnate on the inner wall of the inverted conical portion, causing adhesion.
In FIGS. 1 to 3, reference numerals 6a to 6d are inlets for fuel, etc. in the side wall, and are burners used for forming the aforementioned temperature gradient, adjusting the maximum temperature and the internal pressure of the discharge section.

The inlet port 0 is not limited to the position shown in FIGS. 1 to 3. Next, reference numeral 9 in FIGS. 1 to 3 is a fired product discharge port, and when forming powder and granules next to each other using the furnace according to the present invention, the powder and granules supplied from the powder and granule inlet 3 are The following describes the effect of the particles staying in the mixed layer, falling down, and being discharged from the outlet 9 at the bottom of the furnace.

The powder and granules supplied from the powder and granule inlet 3 to the mixing layer 11 are fluidized, circulated, and suspended in the mixing layers 11 and 12 and retained for firing.
In this case, a settling chamber 13 is provided in the upper part, so that some of the powder and granules carried by the rising air descend to the mixed layer and stay there (during the grain distribution of the powder and granules, there is a The fine powder is transported out of the furnace from the combustion gas outlet 2 by the rising air), and the balance between the pressure loss of the rising air and the amount of retention in the mixed layer by feeding the powder and granules, that is, the balance expressed by the following equation. W (retention g) = △P (mixed layer differential pressure) descends from the bottom 9 of the furnace by the amount that breaks the
xA (furnace cross-sectional area).

As a result, in the scale formation using the furnace of the present invention, it is possible to continuously feed the granular raw material and continuously discharge the fired product. In calcination using the furnace according to the present invention, the average flow velocity of the upward air current in the mixed bed is operated at higher than the flow start velocity (Umf) of the powder and granules, and the composite material is not discharged overflow but descends through the mixed bed. According to the findings of the present inventors, the reason why it is possible to discharge from the bottom of the furnace is due to the above-mentioned imbalance between pressure loss and retention amount, as well as the difference in the flow velocity of the rising air between the furnace center and the furnace peripheral wall. Presumed. In FIGS. 1 to 3, 8 is a port through which fuel, etc. is introduced upward from the lower part of the furnace, and is used as an updraft to support the mixed layer, adjust the temperature of the mixed layer L12, and descend from the mixed layer. This is necessary in order to discharge the fired products while floating them without accumulating them.

According to the furnace according to the present invention, '1) a dense mixed layer and a dilute mixed layer are continuously formed vertically and fired with a temperature gradient; '2) they are divided like a conventional multi-stage fluidized bed. It should be continuous and integrated instead of being arranged in multiple stages. 3) The powder and granules should have a piston flow as a whole, and the flow should be countercurrent as a whole in relation to the upward airflow. Factors such as having a structure in which the gas is discharged directly from the bottom of the furnace through the highest gas temperature zone of the furnace (instead of a falling discharge), and (5) a settling chamber provided at the top of the furnace work together. It is easy to stabilize the temperature and other furnace conditions, and even fine grains with a female diameter of 5 or less can be fired without using an anti-fusing agent. The smaller the diameter, the easier it is to frame during firing.

However, according to the present invention, in the mixed layer 12 in the highest temperature zone, the amount of granular material retained is small and the flow velocity of the rising air is far, so the particles are floating and flowing in a violent rope state.
As a result, the probability that the particles will come into contact with each other is low, making it difficult for them to fuse together. ), it is possible to obtain lightweight aggregate with a lower specific gravity, the internal fuel consumption is reduced, the capacity for discharging per internal volume of the 8 furnaces is improved, and 'e' the discharge of the fired products is by the overflow discharge method. In some cases, if a small adhering lump occurs in the furnace, it is difficult to discharge it, but in the case of the present invention, it is directly discharged from the bottom of the furnace to the outside of the furnace, so even if a fused small lump occurs, it can be automatically discharged. It has great industrial practical value, such as the fact that it is emitted. Example The inner diameter of the sedimentation chamber 13 is 200 mm, the inner diameter of the straight cylindrical portion 7 is 8 mm, the upward opening angle of the inverted conical portion 4 is 27 degrees, and the total height of the mixed layers 11 and 12 is approximately 44 It is a vertical airflow firing furnace with a shape and structure similar to that shown in Fig. 1, which has three fuel inlet ports on the side wall, a fuel inlet port 8 at the bottom, and a fired product outlet 9. Table 1 shows the results of firing lightweight aggregate using the following methods.

The raw material used was pulverized tributary rock granulated to a size of 1.7 to 2.5 mm.

Further, most of the fired product was discharged and collected from the fired product discharge port 9 at the bottom of the furnace, and a portion was discharged from the combustion gas discharge port 2 at the top of the furnace and collected by a cyclone (not shown). As is clear from Table 1, according to the present invention, the exhaust gas temperature (temperature at the top of the mixed layer 11) is lower than the firing temperature (the highest temperature at the mixed layer 12), and the amount of baked out per internal volume of the furnace is reduced. 427kg/〆・Hr
becomes.

In Table 1, by the way, the ratio is 40 to 60 kg/〆・mark for rotary kilns, and about 200 kg/〆・mark for other fluidized fluidized furnaces.

According to the present invention, a product with a specific gravity of 1.25 was obtained without using an anti-fusing material.

[Brief explanation of the drawing]

1 to 3 are vertical cross-sectional views schematically showing the vertical airflow firing furnace according to the present invention, and in the figures, 2... combustion gas outlet, 3... granular material inlet , 4... Inverted conical portion, 5, 7... Straight cylindrical portion, 6a to 6d...
. . . Side wall fuel inlet, 8 . . . Lower fuel inlet, 9 . . . Burnt material discharge port, 13 . Many diagrams and many diagrams

Claims (1)

[Scope of Claims] 1. A vertical furnace having a hollow column structure and having no porous portions in the furnace or the furnace wall to allow air to pass through, and having a powder inlet and a settling chamber in the upper part, The furnace body has a shape in which the cross-sectional area decreases toward the bottom directly below the chamber, and a fired product outlet and a fuel inlet are provided at the bottom of the furnace body.
A continuous air flow firing furnace for powder and granular materials, characterized in that the furnace wall is provided with an inlet for feeding fuel, etc. 2. The continuous air flow firing furnace for powder and granular materials according to claim 1, wherein the furnace body immediately below the settling chamber includes an inverted conical section and one straight cylindrical section. 3. A continuous air flow firing furnace for powder and granular materials according to claim 1, wherein the furnace body directly below the settling chamber is comprised of only an inverted conical portion. 4. The continuous air flow firing furnace for powder and granular materials according to claim 1, wherein the furnace body directly below the settling chamber comprises one straight cylindrical part and an inverted conical part.