JPS5911334B2 - Continuous airflow firing method for powder and granular materials using a vertical furnace - Google Patents

Description

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

Traditionally, vertical furnaces have been used to heat and sinter various types of powder and granule materials, such as calcination of artificial lightweight aggregates, limestone, and dolomite. Techniques have been proposed in which an improved spouted bed, a swirling spouted bed, a packed moving bed, etc. are formed and then heated and fired.

According to the findings of the present inventors, when artificial lightweight aggregate is fired, the foaming temperature for weight reduction and its fusion temperature are close to each other, making it difficult to touch, and rotary kilns in particular have a poor heat transfer mechanism. Most of the heat is radiated from the furnace wall, and although there is some stirring of the raw materials in the furnace, the movement within the furnace is a continuous packed bed, and when firing under these conditions, there is a risk of fusion. Not only is it difficult to operate smoothly and smoothly, but the thermal efficiency is also poor and it is uneconomical.

In addition, especially when firing lightweight aggregates in a rotary kiln, it is necessary to let them stay in the furnace for a relatively long time (20 to 60 minutes), and because of the heat transfer mechanism described above, coarse particles of 5 skins or more cannot be used. A product with a specific gravity of 1.25 to 1.35 can be obtained, but if the raw material is fine particles with a diameter of 5 mm or less, the foaming component is likely to be oxidized and lost or fused, so the specific gravity of the fired product is 1.25 to 1.35.
Currently, only those with a score of 55 or higher can be obtained.

Generally, when firing lightweight aggregates, it is necessary to perform firing in a high temperature range of 1100°C or higher while controlling the temperature within a narrow temperature range of around 10°C to prevent the fired products from fusion. Furthermore, if the fired product is accumulated and discharged to the outside of the after-furnace, or if the high-temperature fired product is cooled while being deposited, heat is likely to be partially trapped and cause fusion.

Therefore, the present inventors have conducted various studies on airflow firing techniques using a vertical furnace, which has a high heat transfer rate and is thought to be easy to prevent fusion of fired products.

To summarize the air flow firing technology of powder and granular materials using conventional vertical furnaces, (1) % Particle size 5
(2) Unexamined Japanese Patent Application Publication No. 2003-202012 A method in which coarse grain raw material with a diameter of mm or more is supplied, the grains are suspended, dropped, and circulated by a swirling upward hot gas flow, and fired, and the fired product is discharged from the lower part of the furnace and operated in a batch manner. (2) JP-A-Sho As in No. 53-121807, the powder and granules are fluidized by an upward air current passing through a rectifying plate (porous part), and a furnace temperature regulating material is supplied to prevent fusion, and the fired product is continuously treated in a fluidized bed. (3) A multistage fluidized bed is formed by installing a plurality of rectifying plates for upward airflow in the furnace, and the powder and granules are sequentially overflowed and dropped to the lower stage to preheat, bake, and discharge the powder and granules. One that performs cooling, etc. to form a deposited layer of the fired product at the bottom of the furnace, and discharges while preheating the combustion air and cooling the fired product, (4) A method that passes through a rectifier plate as in JP-A No. 54-68796. (5) The above-mentioned (
2)? (3)? Typical techniques include forming a fluidized bed without providing a porous rectifying plate as shown in (4), treating the lower layers as a denser fluidized bed, and discharging the fired material while forming a deposited layer at the bottom of the furnace. Other examples are also considered to be applications, improvements, and modifications of any of the above.

And no matter which of these conventional techniques is combined, (a) satisfactory conditions for preventing fusion of fired products cannot be obtained.
In either case, due to the mechanism of the furnace, the exhaust gas is discharged at a high temperature that is approximately the same as the dawning temperature, so the thermal efficiency is poor. It turns out that there is room for improvement.

The present inventors have conducted further research to achieve the above-mentioned problems in the firing technology for lightweight aggregates, and have found that: Focusing on the fact that the concentration of powder and granules is small in areas where the flow rate is fast and becomes thicker in areas where the flow rate is slow, if a dense mixed layer and a thin mixed layer of powder and granules are continuously formed vertically and fired, In the mixed layer, the gas temperature of the rising air, the material (powder and granular material)
(2) The dilute mixed layer is fired as the highest temperature zone, and the fired product passes through this highest temperature zone and is suspended and suspended in the rising air current while being discharged from the bottom of the furnace. It has been found that by doing so, it is possible to easily adjust the temperature inside the furnace and prevent the sintering of the fired product, improve the thermal efficiency of the furnace, and improve the firing capacity per internal volume of the furnace.

The present invention is based on these findings, and involves supplying powder and granules from the top of a vertical furnace, sending firing fuel, air and/or combustion gas to the furnace, and discharging the combustion gas from the top of the furnace. , and in a continuous air flow firing method in which a mixed layer of powder and granular material and an upward air current is formed and fired in a furnace, a vertical structure having a hollow column structure that does not have a porous part through which the air flow for forming the mixed layer is passed. Using a furnace, a sedimentation layer is placed in the upper part of the furnace, and below that a mixed layer with a low flow rate of updraft (hereinafter referred to as a dense mixed layer) and a mixed layer with a high flow rate (hereinafter referred to as a lean mixed layer) are vertically continuous. The fired product is formed by creating a temperature gradient between both mixed layers, and the fired product that falls due to the imbalance between the updraft from the lower part of the furnace and the amount of granular material retained in the mixed layer is called an updraft. This is a continuous air flow firing method for powder and granular material using a vertical furnace, which is characterized by continuously discharging powder and granules from the bottom of the furnace out of the furnace while suspending and floating them.

The purpose of the present invention is to perform sintering of powder and granules that are easily fused at high temperatures, such as lightweight aggregates, but at the same time, the present invention also aims to improve thermal efficiency and calcination capacity per internal volume of the furnace. It can also be used for firing granular materials such as limestone and dolomite.

In the present invention, the mixed layer of powder and granular material and updraft refers to a packed layer of powder and granular material and a settling layer of powder and granular material among the layers where powder and granular material are in contact with updraft in a vertical furnace with an open column structure. A layer in which powder and granules float, circulate, flow, etc. due to rising air currents.

An example of a vertical furnace with a sky column structure used in the present invention is shown in FIG. 11 is a sedimentation layer of powder, 9a and 9b are straight tower parts, and 10at10b is a cone part.

The straight column section 9a has a wider cross-sectional area of the furnace than the section 9b, and the flow velocity of the rising air current is small, and the mixed layer of the rising air flow and the powder and granular material is a dense mixed layer where a large amount of the powder and granular material stays in the area where the flow velocity is slow. 4
is formed and the dilute mixed layer 5 is formed where the flow velocity is high.

The vertical furnace of the present invention has a hollow column structure and does not have a perforated plate or the like for rectifying the rising air flow inside the furnace or on the furnace wall. Therefore, the mixed layer 4 and the mixed layer 5 are formed vertically and continuously. Ru.

In the mixed layers 4 and 5, which are continuously formed on the upper and lower sides, not only the amount of powder particles retained in the steady state during heating and baking differs, but also the squeezing action of the cone portion 10a and the flow rate of the upward air current in the upper and lower mixed layers are different. Because of this difference, there is a difference in the amount of floating, circulating, and flowing powder between the upper and lower mixing layers and each other, that is, the upper and lower layers as a whole are incompletely mixed.

In general, the above-mentioned JP-A-53-121807 and JP-A-5
In the method of forming a fluidized bed or an improved spouted bed and overflowing and discharging the fired product as in No. 4-68796, the ratio U/TJt of the average flow velocity U of the mixed bed and the terminal velocity Ut of the particles is set to 0.
The present invention is characterized by complete mixing of the entire layer and uniform temperature of the entire layer by operating at a temperature of 1 to 0.3, but the present invention is characterized by operating at a temperature of 2 to 0.6 in the densely mixed layer and %, 0 in the thinly mixed layer. .4～
Operate as 1.0.

Therefore, if the mixing layer 5 is the heating center (the highest temperature zone for firing and foaming), the powder and granules in the mixing layers 4 and 5 are incompletely mixed as described above, and there is a difference in the amount of retention, and there is also a difference in the flow velocity. This causes a difference in the amount of heat transfer and a temperature difference.

In other words, although the mixed layers 4 and 5 are continuous and integrally formed, they create a low-high temperature gradient in the height direction of the furnace to form a steady state, and as a result, the temperature of the gas discharged from the mixed layer increases. and fuel consumption decreases.

Furthermore, as will be described later, the fired product is discharged from the bottom of the furnace rather than overflowing, and in normal embodiments, the sedimentation layer 11 is provided above the dense mixed layer 4 for firing. As mentioned above, the flow rate can be made faster than in the conventional technology, and the powder and granules have a piston flow effect as a whole, so the heat transfer effect between the gas and the powder and granules is significant, and as described later, the furnace The baking capacity per internal volume is improved.

Next, in the present invention, as mentioned above, a mixed layer with a faster flow rate than in the prior art is formed and fired, so the amount of powder particles retained as a whole is small. Since the grains are thin and the stirring effect is strong, it is possible to reduce the phenomenon of fusion in the fired product.

As a result, even powder particles with a strong tendency to fuse can be foamed by relatively high temperature treatment without using an anti-fusing agent, and a lightweight aggregate with a lower specific gravity can be obtained.

In addition, since the heat treatment is carried out in a suspended state, even granulated products can be used without being thermally broken and turned into powder.

It is necessary that the upward opening angle of the cone portion 10a of the vertical furnace used in the present invention be 90° or less.

This is because if it exceeds this range, the powder particles will accumulate on the inner wall of the cone portion and cause fusion.

For more certainty, it is desirable that the angle be 60° or less.

In FIG. 1, reference numerals 6a to 6d are inlets for fuel, etc. in the side wall, and are burners used for forming the aforementioned temperature gradient and adjusting the maximum temperature.

However, this inlet port is not limited to the side wall position of the mixed layer 5.

The amount of granular material retained in the mixed layers 4 and 5 can be calculated from the following equation in relation to the pressure loss of the upward air flow in both layers.

W (retention amount) - △P (mixed layer differential pressure) x A (furnace cross-sectional area) The powder and granules supplied from the powder and granule inlet 3 to the mixing layer 4 are fluidized, circulated, and circulated in the mixing layers 4 and 5. The particles are fired while floating, but since there is a sedimentation layer 11 above the mixed layer 4, the powder particles carried by the rising air descend to the mixed layer and remain there (very fine powders rise The combustion gas is conveyed out of the furnace from the combustion gas outlet 2 by the air current), and then it falls by an amount corresponding to the imbalance between the pressure loss and retention amount due to the feeding of the powder and granules, and is discharged from the bottom of the furnace to the outside of the furnace.

As a result, it is possible to continuously feed the granular raw material and continuously discharge the fired product, and it is only necessary to control the feeding speed.

In the present invention, since the average velocity of the upward air current in the mixed layer is as described above, the operation is performed at a speed higher than Um, (flow start speed), and the fired product descends through the mixed layer even though it is not overflow discharged (falling). According to the findings of the present inventors, the reason why the gas can be discharged 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 updraft between the furnace center and the furnace peripheral wall. Presumed.

According to the present invention, it is necessary to select a retention amount corresponding to the optimum retention time depending on the particle size of the powder raw material, but in this case as well, the suction adjustment by a combustion gas exhaust fan (not shown) is performed to This is achieved by arbitrarily controlling the (mixed layer differential pressure).

In FIG. 1, 7 is a port through which fuel, etc. is introduced upward from the lower part of the furnace, and serves as an updraft that supports the mixed layer, controls the temperature of the mixed layer 5, and controls the fired products falling from the mixed layer. Necessary for holding pull-ups.

And 8 is a fired product discharge port. As mentioned above, the present invention is a technology whose main purpose is to efficiently fire lightweight aggregates that are easy to fuse during or after foaming and firing of powder and granules. 5 is the highest temperature zone, and a temperature gradient is provided between the layer and the rich mixed layer 4, and the fired product must be immediately discharged to the outside of the furnace, unrelated to the furnace pressure system, without being deposited on the bottom of the furnace to prevent fusion. be.

If the negative pressure near the discharge port 8 is large, external air will be sucked in, causing the mixed layer 5 to collapse and the highest temperature zone to shift to the cone portion 10a or near the mixed layer 4, which will cause trouble in controlling the temperature of the furnace. Furthermore, the pressure balance system of the above-mentioned mixed layer pressure difference, retention amount, and descent of the fired product is affected, and the furnace condition becomes unstable.

Therefore, it is desirable to adjust the static pressure near the discharge port to near atmospheric pressure.

The adjustment method is performed by balancing the supply pressure of fuel, air, etc. with the suction by the exhaust fan.

According to the present invention, (1) forming a rich mixed layer and a dilute mixed layer in succession above and below and firing with a temperature gradient;
(2) It is not divided into multiple stages as in conventional multistage fluidized beds, but is continuous and integrated. (3) The powder and granules have a piston flow as a whole, and the upward airflow is countercurrent as a whole. , (4) The fired products are discharged directly from the bottom of the furnace through the highest gas temperature zone of the furnace by falling discharge rather than overflow discharge, and (5) Factors such as providing a sedimentation layer above the mixed layer come into play. (a) It is easy to stabilize the furnace temperature and other furnace conditions, and (a) it is a lightweight aggregate that can be fired without using an anti-fusing agent even with fine grains of particle size 5 or less, and has a lighter specific gravity. (C) Reduced fuel consumption, (d) Increased firing capacity per furnace internal volume, and (e) If the fired product is discharged by overflow discharge method, no melting will occur in the furnace. When small lumps are generated, it is difficult to discharge them, but in the case of the present invention, they are directly discharged from the bottom of the furnace, so even if fused small lumps are generated, they are automatically discharged. There is a practical value called a dog.

Example The inner diameter of the sedimentation layer forming part is 200 mm, the inner diameter of the straight column part 9a is 130 mm, the inner diameter of the straight column part 9b is 70 mm, and the cone part 1
It is a vertical airflow firing furnace with an upward opening angle of 45° and a total height of mixed layers 4 and 5 of approximately 470 mm, with three fuel inlets on the side wall and a fuel inlet at the bottom. 7,
Table 1 shows the results of sintering lightweight aggregate using a sintering furnace having a structure similar to that shown in FIG. 1 and having a sintered product outlet 8.

? The raw material is granulated from crushed shale to a size of 1.2 to 3.3 mm.
I used the one that I made.

Further, most of the fired product was discharged and collected from the lower part of the furnace 8, and a part was discharged from the combustion gas outlet 2 of the upper part 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 (
The temperature at the top of the mixed layer 4) is lower than the firing temperature (the highest temperature at the mixed layer 5), and the firing amount per internal volume of the furnace is 63.
4 ”'/, . . .

By the way, in rotary kiln it is 40~60”/,=
．． H,, about 200~. in other fluidized fluidized furnaces. , that's about it.

According to the present invention, the specific gravity is 1 without using an anti-fusing material.
．． Thirty-five samples were obtained.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a vertical sectional view schematically showing a vertical airflow firing furnace used in the present invention, and in the figure, 2... combustion gas discharge ports, 3...・Powder inlet, 4...Dense mixed layer, 5...Dilute mixed layer, 7...
Lower fuel inlet, 8... Burned product outlet, 9a
, 9b... Straight tower section, 10at10b...
... Cone part, 11 ... Sedimentation layer.

Claims (1)

[Scope of Claims] 1. Powder and granular material to be fired (hereinafter referred to as granular material) is supplied from the upper part of a vertical furnace, and firing fuel, air, and/or combustion gas are sent to the furnace to supply the combustion gas to the furnace. In a continuous air flow firing method in which the powder is discharged from the upper part of the furnace and a mixed layer of powder and granular material and an upward air current is fired in the furnace, the air flow forming the mixed layer does not have a porous part through which the air flow passes. Using a vertical furnace with an open column structure, a sedimentation layer is provided at the top of the furnace, and a mixed layer with a low updraft flow rate and a mixed layer with a high flow rate are formed vertically in succession, thereby achieving both mixing. The fired product is fired by creating a temperature gradient between the layers, and the fired product that falls out of balance between the updraft from the lower part of the furnace and the amount of granular material retained in the mixed layer is suspended and suspended in the updraft. A continuous air flow firing method for powder fluid using a vertical furnace, which is characterized by continuously discharging powder from the bottom of the furnace to the outside of the furnace. 2. At the position where the mixed layer is to be formed, a vertical furnace with a hollow column structure is used, in which a straight cylinder part with a large cross-sectional area is formed at the top and a straight cylinder part with a small cross-sectional area is formed through a cone part at the bottom. A continuous air flow firing method for powder and granular material using a vertical furnace according to claim 1. 3. A continuous air flow firing method for powder and granular material using a vertical furnace according to claim 2, wherein the vertical furnace is used in which the upward opening angle of the cone part is 90 degrees or less. 4. Powder and granular material produced by a vertical furnace according to claims 1 to 3, in which firing fuel, air, and/or combustion gas (hereinafter referred to as fuel, etc.) is sent into the furnace from the lower part and side wall of the furnace for firing. Continuous airflow firing method. 5. Continuous air flow firing of powder and granular materials in a vertical furnace according to claims 1 to 4, in which the fired product is discharged from the furnace while adjusting the pressure at the fired product discharge port of the vertical furnace to near atmospheric pressure. Method.