JP4315841B2 - Artificial aggregate firing method and firing apparatus - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method and apparatus for firing artificial aggregates, and in particular, when unburned carbon in coal ash is reduced and fired when artificial aggregates are fired using coal ash with high unburned carbon in a rotary kiln. The present invention relates to a proper firing method and firing apparatus.

When coal is burned, coal ash corresponding to about 10% of its mass is generated. Due to the recent increase in coal-fired thermal power plants, the amount of coal ash generated has increased, and there is a need for an effective method for its use.

When other components are added to the coal ash as necessary, pretreatment such as granulation is performed and then fired, a sintered product having an appropriate strength is obtained and can be used as an aggregate for concrete. Thus, various attempts have been made to produce these artificial aggregates from coal ash and to make effective use thereof.

However, since the first purpose of coal-fired thermal power plants is to provide stable and high-quality power, it is difficult to expect supply of coal ash, which is a by-product, at a certain quality. Eventually, the quality of the generated coal ash varies depending on the power plant or even the same power plant, depending on the brand of coal used and the operating conditions. In particular, the value of so-called unburned carbon, in which carbon in coal remains without being completely burned, varies greatly depending on coal ash, and ranges from less than 1% by mass to several mass%, and sometimes more than 10% by mass. The current situation is that

When calcining artificial aggregate using coal ash as a raw material, unburned carbon in the coal ash is lost by burning in a temperature range of about 600 to 1000 ° C. (calcined range), and a temperature range of about 1200 ° C. or higher. The coal ash powder is fused in the (calcined region) to become a sintered product, which becomes particles having the strength required for the artificial aggregate.

However, when the amount of unburned carbon in the coal ash exceeds 1.5% by mass, the entire amount is not burned in the calcined region, and a part is brought into the calcined region. When the unburned carbon burns after the coal ash powder starts to fuse in the firing zone, bubbles are generated in the sintered product due to the generated carbon dioxide, or in severe cases it may explode, causing high strength artificial There was a phenomenon that aggregates could not be obtained.

Therefore, in Patent Document 1, a projection is provided in a portion corresponding to a temperature region of 800 to 1000 ° C. in the calcined region in the rotary kiln used for firing the artificial aggregate, and coal ash which is a fired product. A technique has been provided in which the agglomerated material is scraped to improve contact with oxygen in the combustion gas so that unburned carbon is sufficiently burnt and removed during the calcining region.

On the other hand, in Patent Document 2, a rotary calcining furnace in which an air supply pipe is installed in the granule charging side half zone of the furnace body and a pulverized coal feeding pipe is installed in the calcined product discharge side half zone. Discloses a method for producing an artificial aggregate using coal ash as a main raw material, characterized in that firing in an oxidizing atmosphere and firing in a reducing atmosphere are continuously performed in one furnace body. ing. And it is supposed that the unburned carbon in coal ash burns with the external oxygen in the air supplied from this air supply pipe.

JP-A-6-265271 JP 2001-163646 A

However, in the technique of Patent Document 1, in order to perform a mechanical operation of providing a protrusion in a high temperature region of 800 to 1000 ° C. and scooping up an object to be fired, the conditions for operating the equipment are severe. It was difficult to leave the object for a long time, and there was a problem that the effect was not sustained unless the rotary kiln was frequently stopped and the protrusions were repaired.

Moreover, the structure of the rotary baking furnace with the air supply pipe | tube etc. which were disclosed by patent document 2 is complicated, and it is difficult to maintain the soundness of this baking furnace for a long period of time by operation at high temperature. Furthermore, as disclosed in FIG. 3 of Patent Document 2, when the air supply pipe enters the vicinity of the furnace shaft and air is introduced from there to the furnace bottom direction, the air almost flies away from the furnace together with the combustion gas. The unburned carbon in the material to be fired rolling in the lower half of the rotary firing furnace has a problem that it is difficult to burn.

Therefore, the present invention has been made in view of the problems in the countermeasure against unburned carbon in the firing of the above-mentioned conventional artificial aggregate, and fires the artificial aggregate using coal ash having high unburned carbon in a rotary kiln as a raw material. It is an object of the present invention to provide a firing method capable of sufficiently reducing unburned carbon in coal ash in the calcining region and capable of continuous operation for a long period of time in a high temperature atmosphere in terms of equipment, and a firing apparatus used in the method. .

In order to solve the above-mentioned problem, the present inventors have conducted intensive studies, and as a result, a nozzle is inserted from the kiln bottom of the rotary kiln, and a gas having an oxygen concentration of 10% or more is blown from the nozzle toward the object to be fired. The present inventors have found that it is effective for burning unburned carbon and have completed the present invention.

That is, the invention of claim 1 is a gas having an oxygen concentration of 10% or more by inserting a nozzle from the kiln bottom of a rotary kiln in firing an artificial aggregate in which coal ash is a main raw material and the granulated raw material is fired in a rotary kiln. This is a method for firing an artificial aggregate, which is characterized in that the material is blown from a nozzle toward an object to be fired.

Generally, so-called excess air with an oxygen concentration of 2 to 10% remains at the bottom of the kiln in the combustion gas of the burner discharged from the rotary kiln when the artificial aggregate is fired. However, high-temperature gas has high viscosity (generally, the viscosity coefficient of gas increases in proportion to the square root of its absolute temperature), and the material to be fired, that is, the raw material granule fed from the kiln bottom. If even a small amount of unburned carbon contained in the coal ash burns, the inert combustion product gas generated thereby covers the fired material layer that rolls in the lower half of the rotary kiln, thereby causing the excess. Air cannot effectively contact the remaining amount of unburned carbon, and as a result, most of the unburned carbon in the coal ash is not burned off.

Therefore, according to the invention of claim 1, since a gas having an oxygen concentration of 10% or more is blown from the nozzle toward the object to be fired, unburned carbon can be burned by oxygen contained in the gas. Further, since the gas is blown toward the object to be fired, the inert combustion product gas that has covered the layer to be fired is blown off, and the opportunity for direct contact between the excess air in the combustion gas of the burner and the object to be fired occurs. Further, the combustion of unburned carbon can be promoted.

The invention according to claim 2 is the method for firing an artificial aggregate according to claim 1, wherein the insertion position of the nozzle is in a temperature range of 600 to 1000 ° C. in the rotary kiln.

The position of the blowout hole of the inserted nozzle in the rotary kiln axial direction is preferably in a temperature region called a so-called calcining region of 600 to 1000 ° C. Below 600 ° C., unburned carbon in coal ash is not preferable because it does not burn even in the presence of oxygen. When the temperature exceeds 1000 ° C., the fired particles mainly composed of coal ash start to soften and fuse, but if the unburned carbon inside burns at this time, the carbon dioxide that is generated generates sintered bubbles. If it is severe, it will explode and it will not be possible to obtain a strong artificial bone material.

According to a third aspect of the present invention, the flow rate of gas blown from the nozzle is 1/100 or more and 1/5 or less of an amount commensurate with the amount of oxygen required to burn all unburned carbon in coal ash fed into the rotary kiln. The method for firing an artificial bone according to claim 1, wherein the method is a method for firing an artificial bone.

Here, the amount commensurate with the amount of oxygen required to burn all unburned carbon is:
Gas flow rate (Nm ³ / min) = carbon amount (kg / min) × 22.4 (Nm ³ / kmol) ÷ 12 (kg / kmol) × 100 ÷ oxygen concentration in gas (%)
This is the amount required.

If the flow rate of the gas blown from the nozzle is less than 1/100 of the amount of oxygen required to burn all the unburned carbon in the coal ash sent to the rotary kiln, the oxygen in the gas is unburned carbon. Both the effect of burning the gas and the effect of the gas blowing off the inert combustion product gas that covered the layer to be fired are both small, and good results cannot be obtained.

With respect to the effect aimed at by the present invention, the gas flow rate blown from the nozzle exceeds 1/5 of the amount of oxygen required for burning all the unburned carbon in the coal ash fed into the rotary kiln. The amount of gas is excessive, and not only the equipment cost and power cost become excessive, but the gas normally blown from the nozzle is much lower in temperature than the combustion gas of the rotary kiln, which results in lowering the temperature of the firing system. Absent. This numerical value is more preferably 1/10 or less.

Invention of Claim 4 uses the coal ash whose unburned carbon is 1.5 mass% or more as a raw material, It is a firing method of the artificial aggregate of Claims 1-3 characterized by the above-mentioned.

Since the present invention prevents the unburned carbon in the coal ash from adversely affecting the firing of the artificial aggregate, when using coal ash whose unburned carbon is 1.5 mass% or more as a raw material, The effect can be used effectively.

In the invention according to claim 5, the property of the artificial aggregate obtained by the main firing is that the absolute dry density value is 1.50 g / cm 3 or more and 2.10 g / cm 3 or less, and the water absorption value is 24 hours. It is 0.1% or more and 6% or less, and the value of the compressive load is 0.5 kN or more of aggregate having a diameter of 5 to 10 mm, or 1.0 kN or more of aggregate having a diameter of 10 to 15 mm. It is a baking method of the artificial aggregate as described in 1-4.

The firing method of the present invention can prevent the generation of bubbles and explosion in the sintered product due to the combustion of unburned carbon, so that the absolute dry density value is 1.50 g / cm 3 or more, 2.10 g / cm 3 or less, and 24 hours. Dense and strong with a water absorption value of 0.1% or more and 6% or less, and a compressive load value of 0.5kN or more aggregate with a diameter of 5mm to 10mm, or 1.0kN or more aggregate with a diameter of 10mm to 15mm. This is a firing method for obtaining a high-quality artificial aggregate.

The invention of claim 6 is a rotary kiln and is inserted in the vicinity of the furnace center axis in the vicinity of the kiln bottom of the rotary kiln, and in the radial direction from the vicinity of the furnace center axis at a position corresponding to a temperature range of 600 to 1000 ° C. And a nozzle having one or a plurality of gas blowing holes in a direction.

When the calcining apparatus of the present invention is used, unburned carbon in coal ash can be sufficiently reduced during the calcining region of 600 to 1000 ° C., and the apparatus can be operated continuously for a long time while a high temperature atmosphere exists. is there.

According to the present invention, even when an artificial aggregate is fired using coal ash with high unburned carbon in a rotary kiln, unburned carbon in the coal ash can be sufficiently reduced in the calcined region, and a dense and high-strength artificial man-made. In addition to being able to fire the aggregate, firing at a high temperature can also be performed continuously for a long time in terms of equipment.

In the present invention, coal ash is used as the main raw material for the artificial aggregate. Coal ash is discharged from a coal-fired power plant, and is adjusted in particle size using fly ash that is scattered from a pulverized coal boiler and collected by an electric dust collector, PFBC ash that is collected from a circulating fluidized bed boiler, etc. It can be used with no raw powder. If necessary, various types of cements as a binder, bentonite as a binder, kaolin mineral, sodium silicate, lignin contained in the waste liquid during pulp production, and the like are added to the coal ash. Furthermore, a component adjusting material is added as necessary. The component adjusting material is added to adjust the softening and melting temperature of the raw material mainly composed of coal ash. For example, silica powder and kaolin as the SiO ₂ source, alumina powder and aluminum as the Al ₂ O ₃ source As the CaO source such as ash, lime powder, cement, gypsum and the like are used.

After mixing the above raw materials, granulate. Any method can be used as long as the granulation can be molded to a particle size within the specified range. Rolling granulation using a pan pelletizer, press granulation using a pressure molding machine, Henschel mixer (Mitsui Engineering & Shipbuilding Co., Ltd., registration) Agitation granulation using a trademark) or the like can be used.

Next, the granulated raw material is fired to produce an artificial aggregate. As a baking apparatus, it is preferable to use a rotary kiln because mass production is possible and a homogeneous fired product can be obtained.

FIG. 1 shows an example of an artificial aggregate firing apparatus according to the present invention. The artificial aggregate baking apparatus 1 includes a rotary kiln 2, a burner 4, a kiln butt housing 5, a raw material chute 6, and the like.

The granulated raw material 8 fed from the raw material chute 6 installed on the kiln bottom side moves while rolling in the rotary kiln 2 as an object to be fired 3. On the other hand, a burner 4 is installed on the front side of the kiln, and burns fuel heavy oil, pulverized coal, etc., and heats the rotary kiln 2. As combustion air, secondary air (not shown) is supplied from the front of the kiln, and primary air (not shown) is also supplied through the burner 4.

The combustion gas 10 generated by the combustion of the burner 4 shows a temperature of 1200 ° C. or higher necessary for sintering the artificial aggregate at the highest point, and the temperature of the fired article 3 is heated or dissipated as it flows to the bottom of the kiln. Is lowered to 600 ° C. or less when flowing out from the kiln bottom. Moreover, the oxygen concentration of the normal combustion gas 10 is about 2 to 10% in the kiln bottom.

In the present invention, the nozzle 7 is inserted along the furnace center axis in the vicinity of the furnace center axis in the vicinity of the kiln bottom of the rotary kiln 2. The nozzle 7 has one or a plurality of gas blowout holes at positions corresponding to a temperature region in which the temperature in the rotary kiln is 600 to 1000 ° C. from the vicinity of the furnace center axis in the radial direction and the direction in which the object to be fired exists. Provide.

A gas having an oxygen concentration of 10% or more is supplied to the nozzle 7 from a blower (not shown), and is blown out from the gas blowing hole in the radial direction and in the direction in which the object to be fired exists. As the gas, it is convenient to use air having an oxygen concentration of 21% as it is. However, if air at normal temperature is blown in, the temperature of the firing system will decrease, so if a gas with a temperature of about 100 to 600 ° C and an oxygen concentration of 10% or more can be used in the combustion exhaust gas of nearby equipment, use it It is preferable to do. The nozzle 7 is made of a heat-resistant metal such as SUS310 or is used by protecting the periphery of the steel pipe with a refractory material.

FIG. 2 shows a cross-sectional view of the artificial aggregate firing apparatus 1 according to the present invention at the position AA ′. In FIG. 2, the refractory 12 is omitted. As shown in this figure, a gas 9 having an oxygen concentration of 10% or more is blown out from the nozzle 7, and the direction thereof is the radial direction of the rotary kiln and the direction in which the object to be fired 3 exists, that is, B. The direction shown. It is preferable that the plurality of blowout holes of the nozzle 7 respectively change the angle and cover the range of B.

In FIG. 1, by the action of the gas 9 blown out from the nozzle 7, the fired product 3 that has sufficiently burned the unburned carbon is prevented from generating bubbles and explosion in the sintered product due to the burning of the unburned carbon. The temperature is raised while rolling in the direction, and the powder particles of the raw material are fused at a firing temperature of 1200 ° C. or more, and become a high-strength artificial aggregate 11 and discharged from the rotary kiln 2.

The artificial aggregate thus fired has an absolute dry density value of 1.50 g / cm 3 or more and 2.10 g / cm 3 or less, and a 24-hour water absorption value of 0.1% or more and 6% or less, Further, it is a dense and high-strength artificial aggregate with a compressive load value of 0.5 kN or more of aggregate having a diameter of 5 mm to 10 mm or 1.0 kN or more of aggregate having a diameter of 10 mm to 15 mm.

Coal ash discharged from a coal-fired power plant (unburned carbon: 2.1% by mass) is mixed with 15% by mass of ordinary Portland cement as a binder, and the mixed powder is hydrated with a pan pelletizer. The granulated raw material was granulated to a particle size of 5 to 15 mm at an amount of 15% by mass and cured for 2 hours in an atmosphere at a curing temperature of 85 ° C. and a relative humidity of 90% or more by a rotary curing machine.

Next, it was fired in a rotary kiln (φ1.5 m × 20 mL) at a feed rate of 1.4 tons / hour, a residence time of 1.2 hours, and a firing temperature of 1270 ° C. At this time, a pipe made of SUS310 (diameter 3 cm) having 10 outlet holes was inserted into a rotary kiln at a position of 620 to 800 ° C. (position of 3 to 5 m from the bottom of the kiln), and a gas with an oxygen concentration of 19% was inserted into each of the rotary kilns. It was sent in an amount of 450L per minute. Under this condition, the fired product of Example 1 was obtained.

In Example 2, coal ash (unburned carbon: 3.0% by mass) discharged from a coal-fired power plant is used as a main raw material, 12% by mass of ordinary Portland cement as a binder, and 3% by mass of bentonite. This mixed powder is granulated with a pan pelletizer to a particle size of 5 to 15 mm with a moisture content of 18% by mass, and cured for 2 hours in a rotary curing machine at an curing temperature of 85 ° C. and a relative humidity of 90% or more. And used as a raw material for granulation.

Next, it was fired in a rotary kiln (φ1.5 m × 20 mL) at a feed rate of 1.2 tons / hour, a residence time of 1.3 hours, and a firing temperature of 1250 ° C. At this time, a pipe made of SUS310 (diameter 3 cm) provided with 10 blowout holes was inserted into a rotary kiln at a position of 710 to 900 ° C. (position of 3 to 6 m from the kiln bottom), and a gas with an oxygen concentration of 15% was inserted into each rotary kiln. It was sent in an amount of 300L per minute. Under this condition, the fired product of Example 2 was obtained.

In Example 3, coal ash (unburned carbon: 2.8% by mass) discharged from a coal-fired power plant is used as the main raw material, and 18% by mass of calcium carbonate as a binder and 7% by mass of bentonite are mixed. The mixed powder was granulated with a pan pelletizer at a water content of 18% by mass to a particle size of 5 to 15 mm to obtain a granulated raw material.

Next, it was fired in a rotary kiln (φ1.5 m × 20 mL) at a feed rate of 1.0 ton / hour, a residence time of 1.5 hours, and a firing temperature of 1230 ° C. At this time, a pipe made of SUS310 (diameter 3 cm) having 10 outlet holes is inserted into a rotary kiln at a position of 620 to 750 ° C. (position of 3 to 6 m from the bottom of the kiln), and a gas having an oxygen concentration of 19% is inserted into each rotary kiln. It was sent in an amount of 150L / min. Under this condition, the fired product of Example 3 was obtained.

In Comparative Example 1, the coal ash (unburned carbon: 2.1% by mass) discharged from a coal-fired power plant is mixed as a main raw material, and 15% by mass of ordinary Portland cement as a binder is mixed. Was granulated to a particle size of 5 to 15 mm with a water content of 15% by mass with a pan pelletizer, and cured for 2 hours in an atmosphere at a curing temperature of 85 ° C. and a relative humidity of 90% or more by a rotary type curing machine to obtain a granulated raw material.

Next, it was fired in a rotary kiln (φ1.5 m × 20 mL) at a feed rate of 0.7 tons / hour, a residence time of 1.6 hours, and a firing temperature of 1270 ° C. Under this condition, the fired product of Comparative Example 1 was obtained. In order to obtain high-quality artificial aggregates compared to the examples, the amount of raw material input had to be drastically reduced.

In Comparative Example 2, 15% by mass of coal ash (unburned carbon: 2.1% by mass) discharged from a coal-fired power plant and 15% by mass of ordinary Portland cement as a binder are mixed. Was granulated to a particle size of 5 to 15 mm with a water content of 15% by mass with a pan pelletizer, and cured for 2 hours in an atmosphere at a curing temperature of 85 ° C. and a relative humidity of 90% or more by a rotary type curing machine to obtain a granulated raw material.

Next, it was fired in a rotary kiln (φ1.5 m × 20 mL) at a feed rate of 1.4 tons / hour, a residence time of 1.2 hours, and a firing temperature of 1270 ° C. At this time, a pipe made of SUS310 (diameter 3 cm) having 10 blowout holes is inserted into a rotary kiln at a position of 620 to 800 ° C. (position of 3 to 5 m from the bottom of the kiln), and air with an oxygen concentration of 15% is inserted into the rotary kiln. It was sent in an amount of 900L per minute. Under this condition, the fired product of Comparative Example 2 was obtained. In order to obtain high quality artificial aggregates compared to the examples, the amount of air blown in had to be reduced.

The results of Examples 1 to 3 and Comparative Examples 1 and 2 are shown in (Table 1).

(Table 1)

As is clear from the results shown in Table 1, in Examples 1 to 3 in which the present invention was carried out, a fired product having good physical properties as an artificial aggregate was obtained.

It is the schematic of the artificial aggregate baking apparatus which concerns on this invention. It is AA 'sectional drawing of the artificial aggregate baking apparatus which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Artificial aggregate baking apparatus 2 Rotary kiln 3 To-be-fired object 4 Burner 5 Kiln bottom housing 6 Raw material chute 7 Nozzle 8 Granulation raw material 9 Gas 10 Combustion gas 11 Artificial aggregate 12 Refractory

Claims (6)

In the firing of artificial aggregate in which coal ash is the main raw material and the granulated raw material is fired in a rotary kiln, a nozzle is inserted from the bottom of the kiln of the rotary kiln, and a gas having an oxygen concentration of 10% or more is directed from the nozzle to the object to be fired. A method for firing an artificial aggregate, characterized by blowing. The method for firing an artificial aggregate according to claim 1, wherein the insertion position of the nozzle is in a temperature range of 600 to 1000 ° C. in the rotary kiln. The gas flow rate blown from the nozzle is 1/100 or more and 1/5 or less of an amount commensurate with the amount of oxygen required to burn all unburned carbon in coal ash fed into the rotary kiln. Item 3. A method for firing an artificial aggregate according to Item 1 or 2. The method for firing an artificial aggregate according to any one of claims 1 to 3, wherein coal ash containing 1.5% by mass or less of unburned carbon is used as a raw material. The properties of the artificial aggregate obtained by the main firing are such that the absolute dry density value is 1.50 g / cm 3 or more and 2.10 g / cm 3 or less, and the 24-hour water absorption value is 0.1% or more and 6% or less. 5. The artificial aggregate according to claim 1, wherein the value of the compressive load is 0.5 kN or more of aggregate having a diameter of 5 to 10 mm, or 1.0 kN or more of aggregate having a diameter of 10 to 15 mm. Firing method. A rotary kiln and one near the furnace center axis near the kiln bottom of the rotary kiln, one at a position corresponding to a temperature range of 600 to 1000 ° C., from the vicinity of the furnace center axis in the radial direction and in the direction of presence of the object to be fired. An artificial aggregate baking apparatus comprising: a nozzle having a plurality of gas blowing holes.

Images