JPH03247541A - Method and device for burning fly ash granulated material - Google Patents

Abstract

PURPOSE:To inexpensively obtain a good burned article in high yield at the time of laminating a fly ash granulated material on the moving grate of a kiln and passing the material successively through the drying and preheating zone, burning zone, cooling zone, etc., to continuously burn the material by controlling the oxygen amt., temp., etc., necessary for the combustion reaction in the burning zone. CONSTITUTION:A fly ash granulated material 1 is laminated on the moving grate 4 of the kiln isolated from the atmosphere, passed successively through the drying and preheating zone 6, igniting zone 7, burning zones 9 and 10, cooling zone 11, etc., and treated with the gas current circulating from the upper part to lower part. A part of the combustion gas in the burning zones 9 and 10 is mixed with combustion air, the oxygen concn., gas flow rate at the inlet of the burning zones and gas temp. are adjusted, and the combustion gas is circulated to the burning zones 9 and 10 to burn the material. Air is supplied to the cooling zone 11 to cool the burned material, and the waste cooling gas is circulated to the drying and preheating zone 6. The excess gas unnecessary for the circulation in the burning zone combustion gas and the outlet gases from the drying and preheating zone and igniting zone are discharged outside the system. Consequently, the amt. of oxygen necessary for the combustion reaction in the burning zones 9 and 10, circulating gas amt. and temp. are controlled, and the material is continuously calcined.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method and apparatus for producing artificial lightweight aggregate for effectively utilizing coal ash generated from coal-fired power generation facilities and the like.

[Conventional technology]

Coal ash generated from coal-fired power plants contains unburned carbon, which is mixed with clay, etc., granulated or molded, and fired in a linear moving grate or rotary kiln to produce the molded granules. It is possible to burn off the residual carbon content and give the shaped uniform particles the strength as a lightweight aggregate.

FIG. 3 shows the firing flow of the conventional method, showing the steps from granulating a coal ash mixture to firing in a grate to taking out the product.

In Fig. 3, an ignition burner 4 is a fuel oil (or gas) 2
The surface layer is heated to 1200°C by the blown air 3 and ignited. The surface of the formed uniform grains 1 in the upper layer is heated to 1200°C, and some excess air causes ignition combustion (
Residual carbon in the coal ash contained in the grains and coke powder added during granulation are ignited and burned).

After passing through the ignition zone, the feed gas for combustion is provided by air 14 being drawn in from below.

The layer of molded uniform grains 1 is characterized by the progress of combustion inside the grains in the upper layer,
Combustion progresses toward the lower layer (ignition to the lower layer). At this time, if oxygen in the air is consumed by combustion inside the grains in the upper layer, combustion to the lower layer is restricted. Also,
If an excessive amount of air is supplied, the combustion temperature will rise, so
The temperature will be controlled by the amount of suction air.

In addition, in Fig. 3, 9 is exhaust gas, 10 is finished product, and 11 is
12 is fly ash, 12 is additive (charcoal, bentonite, etc.), 13 is pan-type pelletizer, 15 is pallet,
16 is a chain gear, 17 is a wind box, and 18 is a main duct.

[Problem to be solved by the invention]

The quality of coal ash generated from power plants (residual carbon content, sintering temperature) varies by coal type and over time depending on the type of coal used as fuel and operating conditions.

Therefore, it is not possible to produce a good fired product by granulating or molding such coal ash through a simple firing process due to temperature changes due to combustion of residual carbon and differences in sintering temperature depending on the type of coal.

An example of the melting point of coal ash is given in the literature (Fuel Temperature Society Journal Vol. 64 No. 10 (
(1985)), it is 1300°C for Ashibetsu coal and 1500°C for Australian A coal. There is a 200°C difference in melting point between the two. Therefore, if the appropriate temperature for sintering is determined by Australia A coal, molten matter will be generated and fused with Ashibetsu charcoal, and it cannot be used as an aggregate product. It cannot be used as an aggregate product because it lacks cohesion and becomes easily powdered.

Residual carbon in coal ash varies depending on operating conditions;
There is a fluctuation of 1% to 10% over time. Some of these changes are instantaneous, but most last for several days.

Temperature control in the firing zone for this change in residual carbon in coal ash cannot be solved by adjusting the amount of air suction, and therefore it is not possible to produce a good fired product. Furthermore, since heat recovery from high-temperature exhaust gas is not performed, it is not economically viable.

An object of the present invention is to provide a method for firing carbon-containing granules and an apparatus for the same, which eliminates the drawbacks of the prior art.

[Means to solve the problem]

The present invention consists of: (1) Fly ash granules are stacked on a moving grate in a firing furnace isolated from the atmosphere, and the fly ash granules are fired while forming an airflow that passes through the layer from above to below. In the method, ■ the moving grate passage section is divided into a drying preheating zone, an ignition zone, a firing zone, a cooling zone, and a product discharge zone; ■ a part of the combustion gas in the firing zone is mixed with combustion air;
Air is adjusted to a predetermined oxygen concentration, a predetermined calcination zone inlet gas flow rate, and a predetermined gas temperature and circulated through the calcination zone.■ Air is supplied to the cooling zone to cool the fired fly ash granules, and the exhaust gas after cooling is dried. The amount of oxygen required for the combustion reaction in the firing zone can be reduced by circulating the excess gas in the firing zone combustion gas that is unnecessary for circulation and the exit gas from the drying preheating zone and ignition zone out of the system. A method for firing fly ash granules, characterized by continuous firing while controlling the amount and temperature of circulating gas.

(2) In a device that burns fly ash granules on a moving grate in a kiln isolated from the atmosphere, the kiln consists of five chambers: a pre-drying zone, an ignition zone, a firing zone, a cooling zone, and a product discharge zone. An ignition burner installed in the ignition zone ■ A fan that circulates the exhaust gas that has passed through the firing zone again to the firing zone ■ A means for adding air to the exhaust gas that is circulated by the fan ■ The exhaust gas that has passed through the cooling zone that is Tropical Circulating Fan (1) This is an apparatus for burning fly ash granules, characterized by comprising means for adjusting the gas flow rate at the inlet of the burning zone and the oxygen concentration in the gas.

In addition, in the above-mentioned apparatus of the present invention, in order to utilize combustion exhaust gas and cooling exhaust gas, a grate-type pan-shaped kiln is used, which is arranged in a circular ring, and a part of the circular ring is filled with fly ash granules. In a preferred embodiment, the charging section and the fired lightweight aggregate discharge section are used as the preheating drying ignition zone, the combustion zone, and the cooling zone as described above. The annular firing furnace described above is completely sealed by a water seal mechanism.

[Effect]

In order to properly fire the fly ash granules, it is sufficient that the residual carbon content in the fly ash and the oxygen content in the combustion gas meet the relationship roughly shown by the curve α in Figure 2. The present inventors have confirmed through experiments that it is preferable to keep the value within a certain range above and below the reference value. This figure also shows that in order to obtain a high yield of high-quality products (lightweight aggregates), the oxygen-containing gas must be adjusted to match the residual carbon content in the fly ash, and the gas temperature in the firing zone of the fly ash granules must be adjusted carefully. This suggests that it must be supplied with In other words, this oxygen content is controlled by mixing combustion air into the combustion exhaust gas, but as the residual carbon content in fly ash increases, the amount of oxygen required for firing the granules is reduced by increasing the oxygen concentration. When supplied, this residual carbon burns all at once and the firing temperature becomes too high, causing melting of the surface of the granules and formation of lumpy fused substances, which is important for maintaining stable continuous operation.

In the method and apparatus of the present invention, the fired product (5
The temperature is about 00 to 1200°C.

The air supplied to cool the fly ash passes through the cooling zone from the top to the bottom and is warmed. This gas is then circulated to the preheating drying zone of the lightweight aggregate production equipment to cool the fly ash granules ( It can be effectively used for preheating drying (wet condition).

〔Example〕

FIG. 1 shows an example of the apparatus of the present invention and an embodiment of the method of the present invention using this apparatus, with the annular center section unfolded along the movement of the raw material.

In FIG. 1, fly ash, bentonite or clay as a binder, and water are mixed and stirred in a mixer (not shown), and then granulated material 1 is granulated in a pan-shaped pelletizer. Then, they are sequentially charged into an annular firing furnace 3 isolated from the atmosphere. Note that this granulated material 1 has been charged into the annular firing furnace 3 in advance and is fired).
layered evenly on top of the protective material).

In the drying preheating zone 6, the granulated material 1 on the grate 4 is in a wet state, so in order to dry and preheat it and hasten ignition in the ignition zone 7, the exhaust gas llb from the cooling zone 11 is passed through the circulation fan 19.
It is circulated and supplied through. This circulating gas 6a is a gas used for air cooling of the fired pellets 2, and since the temperature is 300 to 400°C due to heat recovery from the fired pellets 2, it promotes dry preheating of the wet granules 1. .

In the ignition zone 7, the dry and preheated granules 1 are passed through the ignition burner 8.
Raise the temperature to over 1000℃ and ignite it. The fuel 14 of this ignition burner 8 may be any fuel such as coal, oil, gas, etc., and is combusted with air 20 (or ?a) supplied via an air supply fan 15.

The firing zones 9 and 10 are divided into a firing chamber (I) 9 and a firing chamber (■) 10. In the firing chamber (■) 9, the granules are heated from the top to the bottom of the stacked granules 1. Due to the self-combustion effect of the residual carbon contained in the grating 1, the firing reaction progresses as the grate 4 moves. A similar firing reaction proceeds in the firing chamber (I[) 10 as well. In addition, firing chamber (■) 9, firing chamber (
II) Gases 9b and 10b discharged from 10 are converted into combustion gas 2 containing almost no oxygen via circulation fan 18.
1 and mixed with the air introduced via the air supply fan 17.

The oxygen concentration of the mixed gas is measured by an oxygen analyzer 23, and the amount of air from the air supply fan 17 is adjusted by a regulating valve 25 so that a predetermined oxygen concentration is achieved. Then, the firing zone inlet gas 27 whose oxygen concentration has been adjusted is supplied to the firing chamber (I) 9 and the firing chamber (II).
The gas flow rate is adjusted as No. 10 supply gases 9a and 10a by a gas flow meter 24 and a gas adjustment valve 2G, and the gases are supplied to each firing chamber. Surplus gas 22 is exhausted outside the system.

Although the function of the cooling zone 11 has been described above, this cooling air 11a is supplied via the air supply fan 16.

The granulated material l on the grate 4 passes through the drying preheating, ignition, firing, and cooling processes described above, and is then transferred to the crusher 1 in the discharge zone 12.
3 becomes fired pellet 2.

Note that the outlet gas 6b of the drying pre-heating zone 6, the outlet gas vent b of the ignition chamber 7, and the surplus gas 22 of the circulating gas in the firing chamber are exhausted to the outside of the system.

In order to stabilize the firing temperature in the firing zones 9 and 10 and to prevent heating, the firing zone inlet gas 27 is cooled to a required temperature by a cooler 28.

Further, the necessity of the cooler 28 and the temperature after cooling of the calcination zone inlet gas 27 vary depending on the amount of residual carbon in the fly ash.

Furthermore, since the sintering zone inlet gas 27 contains moisture and SOx, the temperature of the sintering zone inlet gas 27 is preferably 135° C. or higher in order to prevent equipment corrosion due to condensation of SO5.

〔Effect of the invention〕

According to the method and apparatus of the present invention, since combustion gas containing combustion oxygen corresponding to the residual carbon content in the fly ash, which is a raw material, is supplied to the firing zone, the residual carbon content in the fly ash does not fluctuate. However, it is possible to control the firing temperature, and the gas heated in the cooling chamber is circulated to the drying preheating chamber, making effective use of waste heat, resulting in high quality products (lightweight). Aggregate) can be obtained in high yield and economically.

[Brief explanation of drawings]

Figure 1 is a diagram showing the flow of raw materials and gas of an annular grate type firing furnace according to an embodiment of the present invention, and Figure 2 is a diagram showing the residual carbon content and supply to understand the appropriate firing conditions for fly ash. FIG. 3 is a diagram showing the relationship between the oxygen content in the gas, and is a diagram showing one embodiment of a conventional annular grate type firing furnace.

Claims (2)

[Claims] (1) A method for firing fly ash granules, in which the fly ash granules are stacked on a moving grate of a firing furnace isolated from the atmosphere, and the process is performed while forming an airflow that passes through the layer from above to below, [1] The moving grate passage section is divided into a dry pre-preparation zone, an ignition zone, a firing zone, a cooling zone, and a product discharge zone. Adjust the concentration, gas flow rate at the inlet of the firing zone, and gas temperature to a prescribed gas temperature and circulate it through the firing zone [3] Supply air to the cooling zone to cool the fired fly ash granules and dry the exhaust gas after cooling. [4] Excess gas unnecessary for circulation out of the firing zone combustion gas and the exit gas from the drying preheating zone and ignition zone are discharged to the outside of the system. A method for firing fly ash granules, characterized by continuous firing while controlling the amount of oxygen, the amount of circulating gas, and temperature. (2) A device for firing fly ash granules on a moving grate in a firing furnace isolated from the atmosphere. Furnace [2] An ignition burner disposed in the ignition zone [3] A fan that circulates the exhaust gas that has passed through the firing zone back to the firing zone [4] Means for adding air to the exhaust gas that is circulated by the fan [5] The above A fan for circulating the exhaust gas that has passed through the cooling zone to the drying and pre-heating zone; [6] A fly ash granule comprising means for adjusting the gas flow rate at the inlet of the calcination zone and the oxygen concentration in the gas. Baking equipment.