JPS6012899B2 - Calcination method of powder raw materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for calcining powder raw materials such as cement raw materials, and particularly to a method for effectively reducing and removing nitrogen oxides in kiln exhaust gas.

In recent years, a so-called rotary kiln with a calciner, in which a calciner is provided between the rotary kiln and the suspension preheater, has been widely adopted as cement firing equipment.

This is intended to increase the specific firing rate of the kiln by distributing part of the heat load of the kiln to the falsification furnace. On the other hand, recently, nitrogen oxides contained in kiln exhaust gas have become a problem, and methods to remove nitrogen oxides without installing special denitrification equipment have been considered. There is nothing effective. For example, the first
As shown in the figure, a denitrification burner f is provided in the lower cone h of a false dawn furnace e, which is provided between a rotary kiln a and a separation cyclone b, and has a false dawn burner c and a child heating raw material introduction pipe d. In the method of removing nitrogen oxides from the kiln exhaust gas, since the denitrification burner f is close to the secondary air inlet g, it is difficult to form a reducing atmosphere and it is not very effective. Further, if the denitrification burner f is provided below the lower cone portion h, there is no raw material, so the temperature becomes high and a coating is formed. In addition, the solid line arrow in the figure shows the flow of gas, and the dotted line arrow shows the flow of powder raw material. In the present invention, a fuel supply device such as heavy oil or pulverized coal is installed in the raw material conduit that feeds preheated powder raw material into the riser duct, and carbon monoxide in the gas in the upper part of the riser duct, which is mainly composed of kiln exhaust gas, is Nitrogen oxides in the kiln exhaust gas are controlled by controlling the fuel supplied to the fuel Z supply device to maintain a reducing atmosphere in the riser duct to an appropriate value between 0.5 and 3%. An example of this will be described with reference to FIG. 2.

In Fig. 2, 1 is a rigid calcining furnace consisting of a combination of a cylinder and an inverted cone of the principal, 2 is a secondary air introduction section consisting of a secondary air introduction chamber, 3 is a false scale burner, and 4 is a rising duct. .

That is, in the lower part of the calcining furnace 1, there is a secondary air introduction part 2 for introducing combustion air into the furnace 1 while giving a swirling force to the combustion air.
and a plurality of temporary brick burners 3, and a riser duct 4 connects the bottom of the secondary air introduction section 2 and an inlet chamber 5 at the bottom of the rotary kiln 12. Exhaust gas from the kiln 12 is introduced into the furnace 1. A preheating raw material conduit 7 for supplying the heated powder raw material from the lower part of the final stage cyclone 6 of the suspension preheater 19 is connected to this riser duct 4. A fuel supply device 8 such as powdered coal is provided. Further, the preliminary furnace 1 is connected to a separation cyclone via a gas conduit 9, and a raw material chute 11 from the lower part of the cyclone 10 is connected to the inlet chamber 5. Further, a carbon monoxide analyzer 13 is installed near the connection between the riser duct 4 and the pseudo-dark furnace 1, and a controller 1 that operates based on the measured value of this analyzer 13 is provided.
4, and a flow control valve 1 controlled by this controller 14.
5 is provided to control the amount of fuel sent to the fuel supply device 8. In addition, 16 is a clinker cooler,
This cooler 16 and the secondary air introducing section 2 are connected by a secondary air duct 17, and 18 is connected to the preheater 1.
This is a raw material supply device for supplying powdered raw materials to 9. In the powder raw material temporary bran apparatus configured as described above, the powder raw material is preheated by the suspension preheater 19 and then supplied to the riser duct 4 via the preheated raw material conduit 7, and the fuel is supplied from the fuel supply device 8. It joins with the child heat raw material and is supplied to the riser duct 4 via the child heat raw material conduit 7.

Here, when using two types of fuel, liquid fuel such as heavy oil and solid fuel such as pulverized coal, it is preferable to supply the liquid fuel to the preliminary burner 3 and the solid fuel to the fuel supply device 8. . Further, high-temperature exhaust gas from the rotary kiln 12 is introduced into the rising duct 4 from the lower part, and the raw materials and fuel are suspended in the high-temperature exhaust gas. This gas normally contains about 2% oxygen, but in the present invention, the purpose is not to completely burn the fuel in the riser duct 4, but rather to use the kiln exhaust gas from the rotary kiln 12. Since the purpose is to effectively remove nitrogen oxides from the inside, the amount of fuel from the fuel supply device 8 is controlled so as to maintain the inside of the rising duct 4 in a reducing atmosphere. That is, the carbon monoxide concentration in the inner part of the riser duct 4 is measured with the carbon monoxide analyzer 13, and this measured value is 0.
．． If it is less than 5%, increase the flow control valve 15 via the controller 14 to increase the amount of fuel supplied from the fuel supply device 8 to the riser duct 4, so that the measured value becomes 3%. If it is larger, the controller 14 conversely reduces the opening degree of the flow control valve 15 to reduce the amount of fuel. In other words, the amount of fuel is controlled so that the carbon monoxide concentration of the gas in the upper part of the riser duct 4 is between 0.5 and 3%. In this case, 3 to 10% of the amount of fuel used in the kiln was appropriate.By doing this, the inside of the riser duct 4 was maintained in a reducing atmosphere, and the high temperature atmosphere caused by the kilnter exhaust gas was maintained. By being sagging,
In the riser duct 4, nitrogen oxides contained in the gas from the rotary kiln 12 are removed. In particular, in the case of cement raw materials, calcium oxide, calcium carbonate, iron oxide, etc. in the cement raw materials supplied from the preheated raw material introduction pipe 7 to the riser duct 4 act as catalysts, and carbon monoxide acts as a reducing agent. , the removal of nitrogen oxides contained in the kiln exhaust gas is carried out very conveniently. In addition, the denitrated kiln exhaust gas is continuously introduced from below into the temporary aging furnace 1 together with the powder raw material and fuel, and at the same time, the secondary air from the clinker cooler 16 and the fuel from the calcining burner 3 are also introduced from below from below. The fuel is continuously introduced into the furnace 1, and the complete calcination of the fuel and the raw material is carried out in the falsifying furnace 1. Of course, the amount of air introduced into the calcining furnace 1 from the secondary air introduction part 2 is provided in an amount necessary for combustion of the fuel from the fuel supply device 8 and the calcining burner 3. As described above, the present invention provides a fuel supply device in the raw material conduit connected to the riser duct that connects the calciner and the bottom of the rotary kiln, and mainly supplies the kiln exhaust gas in the upper part of the riser duct. The carbon monoxide concentration in the gas to be used is 0.5 to 3.
The amount of fuel supplied by the fuel supply device is controlled while measuring with a carbon monoxide analyzer, and the inside of the riser duct is maintained in a reducing atmosphere, so that the nitrogen oxidation of the kiln exhaust gas is controlled. In addition, the control of the amount of fuel supplied and the operation of maintaining a reducing atmosphere can be easily automated, especially those that have a catalytic effect on the components of powder raw materials, such as cement raw materials. When substances are included, their reduction and removal is carried out even more effectively.

Moreover, since fuel is supplied to the raw material conduit, if the fuel is heavy oil, it will be heated by the heat of the raw material, vaporized, and introduced into the rising duct; Since the raw material is preheated and uniformly diffused into the riser duct along with the raw material, there is no need for a complicated fuel supply device such as a burner that requires primary air to diffuse the fuel, and the device can be installed alone. It can be simplified, etc.
The effects of the present invention are extremely large.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway elevational view showing an example of a conventional method, and FIG. 2 is a partially cutaway elevational view showing an example of an apparatus for carrying out the method of the present invention. 1... False furnace, 2... Secondary air introduction section, 3... False burner, 4... Standing duct, 5... Inlet chamber, 6... preheater final stage cyclone, 7... child heating raw material conduit,
8... Fuel supply device, 9... Gas pipe, 1
0... Separation cyclone, 11... Raw material chute, 12... Rotary kiln, 13... Carbon monoxide analyzer, 14... Controller, 15...・・・
...Flow control valve, 16...Clinker cooler, 1
7... Next air duct, 18... Raw material supply device, 19... Suspension fan. Rejita. Multi 1 drawing Multi 2 drawing

Claims (1)

[Claims] 1. A calcining furnace installed vertically between the rotary kiln and the suspension preheater, a rising duct located directly below this calcining furnace and connecting the calcining furnace and the kiln bottom of the rotary kiln, and a raw material conduit connected to the riser duct to input preheated powder raw material from the suspension preheater, and a secondary air conduit for introducing secondary air from the clinker cooler into the calciner. In a powder raw material sintering apparatus having an introduction part and a calcination burner, a fuel supply device is provided at an appropriate position of the raw material conduit connected to the riser duct, and the riser duct and the calcination furnace are connected. A carbon monoxide analyzer is installed near the section, and using the measured value by this analyzer as a guideline, the carbon monoxide concentration in the gas in the upper part of the rising duct, which is mainly composed of kiln exhaust gas, is a value between 0.5 and 3%. The method is characterized in that the amount of fuel supplied to the fuel supply device provided in the raw material conduit is controlled to maintain a reducing atmosphere in the riser duct so that nitrogen oxides in the kiln exhaust gas are reduced and removed. Calcining method for powder raw materials.