JPS6218503B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a preheating device before firing fine grain raw materials, and provides a preheating device for fine grain raw materials such as limestone, dolomite, etc., which can reduce the amount of fuel consumed during firing of the fine grain raw materials. That is.

The reaction of heat-treating fine raw materials such as calcium carbonate, magnesium carbonate, or materials containing them to obtain quicklime and magnesium oxide is as follows:
It is widely used in various industries, and various devices have been put into practical use.

CaCO ₃ → CaO + CO ₂ MgCO ₃ → MgO + CO ₂ In the above reaction, the decomposition temperature of CaCO ₃ is approximately 800℃
As mentioned above, the decomposition temperature of MgCO ₃ is approximately 550°C or higher, but in recent years there has been a strong demand for low consumption of fuel as a heat source, and one method to achieve this is to preheat the raw material with high-temperature exhaust gas from the kiln. is taken.

However, the high-temperature exhaust gas emitted from the kiln used for preheating contains carbon dioxide contained in the combustion gas generated by the combustion of fuel as a heat source and carbon dioxide generated by heat treatment of raw materials. In addition to being accompanied by fine product particles, the temperature of the exhaust gas discharged from the kiln gradually drops in the raw material preheating section, while the raw material is heated, resulting in the following drawbacks.

In other words, within the range where the temperature in the preheating section is below the decomposition reaction temperature of the raw materials, the product fine particles and carbon dioxide gas in the exhaust gas are recarbonated as shown by the following formula: CaO + CO ₂ → CaCO ₃ Mg + CO ₂ → MgCO ₃ Not only does this cause a reaction that is not intended for any purpose, but the reactants are deposited on the inner wall of the device in the heat exchange section of the preheating section, which deteriorates heat exchange by reducing the volume of the heat exchange section of the preheating section. This often increases pressure loss and makes it difficult to maintain stable operation and continuous long-term operation of the heat treatment equipment.

As a result of intensive research to eliminate the above-mentioned drawbacks of the conventional method, the present inventors have found that the above-mentioned drawbacks can be largely eliminated by lowering the carbon dioxide concentration and temperature in the exhaust gas in the preheating section. This led to the completion of the present invention.

That is, the present invention provides an apparatus in which a plurality of cyclones are stacked above a firing furnace, and a fine grain raw material introduced into the firing furnace is preheated by the firing furnace exhaust gas by the cyclones, etc., in which a plurality of cyclones are installed on the outer wall of a member that guides the firing furnace exhaust gas. The gist of the present invention is to provide a preheating device for a particulate raw material, characterized in that a small hole is provided, and a cover member is provided on the outer wall of the preheating device, the cover member communicating with an air supply source and sealingly covering the small hole.

Hereinafter, the present invention will be explained in detail using FIGS. 1 to 4 based on an example in which limestone is applied to heat treatment.

Figure 1 is a conceptual diagram of the equipment used here.
It consists of a fluidized bed type kiln 1 with an inner diameter of 350 mm and a height of 4 m, a limestone preheating device that combines cyclones 2a, 2b, and 2c, and a collection cyclone 6 for collecting products accompanying the exhaust gas of the kiln 1. has been done. The raw material limestone L is supplied from the raw material conduit 4 to the exhaust gas conduit 3b through which the exhaust gas of the kiln 1 flows,
It exchanges heat with exhaust gas and is collected by cyclone 2a,
It enters the exhaust gas conduit 3c via the raw material conduit 5a, is collected by the cyclone 2b, and while following the flow of the gas from the raw material conduit 5b to the exhaust gas conduit 3b, it is preheated by repeated heat exchange with the exhaust gas, and finally collected by the cyclone 2c. The raw material is then charged into the firing furnace 1 through the raw material conduit 5c. In the firing furnace 1, the air A supplied from the air conduit 11 via the blower 12 burns the fuel F supplied from the fuel conduit 10 to thermally decompose limestone. Quicklime Q obtained by thermal decomposition is taken out from a product conduit 8, and quicklime Q accompanying the exhaust gas from the firing furnace 1 is collected by a collection cyclone 6 and taken out from a product conduit 7. The exhaust gas from the firing furnace 1 that has passed through the collection cyclone 6 is passed through the exhaust gas conduits 3d, 3.
c, 3b, 3a and cyclone 2c, 2b, 2
a sequentially and are discharged from the blower 13.

When this device was used to decompose 100 kg of limestone per hour while changing the temperature inside the kiln 1 in the range of 840 to 960°C, the preheating device (cyclone, exhaust gas pipes, etc.)
The fine particles of quicklime that could not be collected by the collection cyclone 6 and rose with the exhaust gas and the carbon dioxide gas in the exhaust gas cause a recarbonation reaction, and this reaction product can accumulate on the inner wall. found. This tendency is particularly noticeable in the exhaust gas conduit 3. This adhesion to the inner wall of the device is hard in the temperature range of 700 to 800°C.
Furthermore, because the adhesion progresses rapidly, continuous operation of the device is difficult.Those that adhere at temperatures below 700°C are relatively soft, and once they have adhered to a certain extent, they peel off and do not interfere with operation. Figure 2 shows an example of the relationship between the crushing strength of deposits due to recarbonation reaction and temperature, and Figure 3 shows the relationship between the crushing strength of deposits due to recarbonation reaction and temperature, and Figure 3 shows the relationship between CO ₂ concentration in exhaust gas of 30% at a temperature of 730°C.
An example of the relationship between recarbonation reaction rate and reaction time in the case of (curve a) and 20% (curve b) is shown.

Based on the above knowledge, it is possible to prevent the adhesion and accumulation of recarbonation reactants on the inner wall of the preheating device, especially the exhaust gas conduit 3,
To enable continuous operation, a small hole 1 with a diameter of 0.5 to 5 mm is installed in the exhaust gas pipe 3 in the temperature range of 700 to 800 °C.
A plurality of 6 are provided, and a covering member 17 is further provided to sealingly cover the small hole 16, and the member 17 and the blower 14 are connected through a conduit 15 to introduce air from outside the system through the small hole. This prevents it from adhering to the inner wall of the conduit. This is shown in FIG. That is, the firing furnace 1
When the temperature of the cyclone 2c is about 850°C, the temperature at the outlet of the cyclone 2c is about 800°C, and reactants due to the recarbonation reaction are heavily attached to the inner wall of the exhaust gas conduit 3c. Therefore, the air A is guided from the conduit 15 via the blower 14 to the cover member 17 provided on the exhaust gas conduit 3c, and from there passes through the plurality of small holes 16 to the exhaust gas conduit 3c.
The exhaust gas is uniformly introduced into the interior of the exhaust gas conduit 3c, thereby lowering the concentration of carbon dioxide in the exhaust gas passing near the inner wall of the exhaust gas conduit 3c and lowering the temperature. At this time, since the cover member 17 sealingly covers the plurality of small holes 16, the air introduced into the member 17 is evenly introduced from the small holes 16 into the conduit 3c without escaping to the outside. be done.

In this way, by introducing air from outside the system through the plurality of small holes 16 and making the amount of air equal to or more than 3% of the amount of gas flowing inside the system, it is possible to prevent the air from adhering to the inner wall of the exhaust gas conduit 3c, allowing continuous operation. It turned out that it is possible.

Although FIG. 4 shows a case where a plurality of small holes 16 are provided in the exhaust gas conduit 3c to introduce air, if the temperature of the firing furnace 1 is increased, for example, 900
It goes without saying that when the temperature is higher than 700 DEG C., a plurality of small holes 16 may be provided in the exhaust gas conduit 3b, which is in the temperature range of 700 DEG to 800 DEG C., to introduce air to prevent deposition.

As can be understood from the above explanation, the device of the present invention has the following effects.

(1) The air introduced through the small holes in the device wall lowers the carbon dioxide concentration in the exhaust gas passing near the inner wall, and also lowers the temperature, suppressing the progress of the recarbonation reaction.

(2) Furthermore, materials that cause recarbonation reaction products by air introduced through small holes, such as CaO,
Prevents MgO, CO ₂ or recarbonation reactants from reaching the inner walls of the device.

[Brief explanation of the drawing]

Figure 1 shows a schematic diagram of the limestone heat treatment equipment, Figure 2 shows the relationship between the crushing strength of deposits due to recarbonation reaction and temperature, and Figure 3 shows the relationship between recarbonation reaction rate and reaction time. FIG. 4 is a diagram schematically showing a means for introducing air from outside the system in the present invention.

Claims (1)

[Claims] 1 Stack multiple cyclones above the firing furnace,
In a device for preheating the fine grain raw material introduced into the kiln using the kiln exhaust gas using the cyclone or the like, a plurality of small holes are provided in the outer wall of the member that guides the kiln waste gas, and the outer wall is connected to an air supply source. A preheating device for a particulate raw material, characterized in that a covering member is provided for sealingly covering a hole.