JPS5834419B2 - Powder material firing equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for firing powder materials such as cement raw materials.

In recent years, firing methods with a calciner have become mainstream as new firing methods, but the present invention suppresses the amount of nitrogen oxides in the exhaust gas of the firing equipment using the above method, and
The purpose is also to improve the performance of the device.

Nitrogen oxides have recently attracted particular attention as one of the photochemical causative substances that are harmful to the human body, and there is an urgent need to take measures to reduce them.

For example, in the case of cement raw material firing equipment, the rotary kiln, which is the main part of the equipment, must maintain an extremely high combustion temperature, which inevitably generates large amounts of nitrogen oxides. be.

Therefore, taking measures to control it is an urgent issue in terms of pollution control.

According to the present invention, the nitrogen oxides generated in the rotary kiln can be actively removed in the calciner, which is a part of the equipment, so there is no need to install a denitrification device outside the equipment system, and the nitrogen oxides in the exhaust gas can be removed. It becomes possible to suppress oxides to, for example, 5011 plO% (02 conversion) or less.

Furthermore, the present invention is characterized in that the fuel consumption of the apparatus can be reduced without affecting the quality of the fired linker, production capacity, continuous operation, etc.

First, the firing method with a calciner is a method in which fuel is dispersedly burned in a calciner and a rotary kiln, and the calcining reaction of the material is efficiently carried out in the former, and the firing reaction is efficiently carried out in the latter.

An array of conventional equipment for this firing method is shown in FIG.

That is, in FIG. 1, the powder material input from the material supply device a is preheated by the material preheater, and then input into the calcination furnace C having the fuel supply device m, where the calcination reaction takes place. After completing 80 to 95 layers, it is collected by separator d and sent to rotary kiln f via material conduit e.

Further, secondary air for combustion in the calciner C is introduced into the calciner C from a cooler g by a rotary kiln f or an independent secondary air duct h.

The material fed into a rotary kiln f having a fuel supply device t is heated to a predetermined temperature (for example, about 1450°C in the case of cement raw materials) to generate clinker minerals, etc., and then fed into a cooler g. cooled down.

The exhaust gas of the rotary kiln f is led to the calciner C through the kiln outlet duct i, and together with the gas brought in the furnace C, it is sucked and discharged by the exhaust fan k through the separator d1 material preheater and the exhaust gas duct j. Ru.

Note that the exhaust gas from the rotary kiln f may be guided to the outlet of the furnace C by the kiln outlet duct i' without passing through the calciner C.

The above is an example of a conventional firing apparatus with a calcining furnace, and the method of suppressing nitrogen oxides in this apparatus can be roughly divided into two types: one using a rotary kiln and the other using a calcining furnace.

The following is an overview and the shortcomings and problems.

(1) Suppression method in rotary kiln It is known that the amount of nitrogen oxides generated increases exponentially as the combustion temperature increases.

However, mainly by radiation heat transfer, the material to be fired can be efficiently heated to a high temperature (for example, approximately 1450°C in the case of firing cement materials).
) In a rotary kiln whose purpose is to heat up to 100% of nitrogen, the firing temperature is kept at an extremely high temperature, which inevitably generates a large amount of nitrogen oxides.

Therefore, suppressing the amount of nitrogen oxides generated in this rotary kiln leads to a reduction in nitrogen oxides in the entire apparatus, but in this case, there are the following problems.

0) Use of a special burner The amount of nitrogen oxides generated during combustion of fuel can be reduced to a certain extent by using a burner with a special structure.

For example, in experiments using this special burner in a furnace that uses combustion air at room temperature, a nitrogen oxide reduction rate of 20 to 30% has been obtained.

However, in the case of a rotary kiln for cement, for example, high-temperature secondary air of 800° C. or higher is used, so the combustion rate of the fuel becomes high and a high-temperature flame of 1800 to 2000° C. is formed.

Due to such differences in combustion conditions, in the case of combustion in a rotary kiln, it is not possible to obtain the nitrogen oxide reduction rate as shown in the above experimental results.

(b) Method using a low combustion air ratio Combustion of fuel at a low combustion air ratio is effective in suppressing the formation of nitrogen oxides.

As a concrete example, FIG. 3 shows actual measurement results of combustion air settling and the amount of nitrogen oxides generated Q (Nm/h) in a rotary kiln in a cement raw material combustion apparatus with a calciner.

However, in this case, in order to obtain the effect of reducing nitrogen oxides, the combustion air ratio is extremely low (for example, 1.00
~1.05) Operation not only increases the length of the flame, leading to a decrease in the quality of the kiln product, but also, especially in the case of cement combustion, increases the alkali, chlorine, and This promotes the circulation of volatile substances such as SO3 within the equipment, causing problems such as adhesion of coatings and intensification of adult insects, which greatly impedes the production capacity and continuous operation of the equipment.

Therefore, this method cannot be expected to significantly and stably suppress nitrogen oxides.

(2) In a calciner or calcining area for the purpose of carrying out a calcining reaction of nitrogen oxide diluted materials, the temperature is relatively low, such as 800 to 1000°C. Since combustion is performed, the amount of nitrogen oxides generated per fuel is only about 1Nm/Kt, which is very small compared to that of rotary kill, although it varies depending on the nitrogen content in the fuel and the combustion air ratio.

In a calciner equipped with a calciner, if the calcining rate of the material at the rotary kiln entrance is 85 to 95%, the amount of fuel given to the calciner is 5% of the amount of fuel supplied to the entire device.
5 to 65%, so the nitrogen oxides of, for example, lQNm/Kt contained in the exhaust gas of the rotary kiln are diluted by the low nitrogen oxide gas brought in the calcining furnace.
The nitrogen oxides per fuel for the entire system, ie the concentration of nitrogen oxides in the exhaust gas, is reduced to approximately 5 Nm/Kt.

However, under normal operating conditions, as discussed below,
Since the calcining furnace cannot actively denitrate the nitrogen oxides in the rotary kiln exhaust gas, it is not possible to achieve a nitrogen oxide concentration as low as, for example, 2''/Kt.

Next, FIG. 2 shows an embodiment of the apparatus of the present invention. In FIG. The exhaust gas from the rotary kiln 6 is introduced into the furnace 3 along with the combustion air from the calciner 3, and is passed through a separator together with the gas brought in the furnace. 5. The process of passing through the material preheater 2, suctioning and discharging by the exhaust fan 14 is the same as the above-mentioned first process.
This is the same as the case of the conventional device shown in the figure.

Further explaining FIG. 2, the following are added as its constituent factors.

(1) Auxiliary grilling chamber 4 The auxiliary grilling chamber 4 includes at least combustion air introduction means 19.
is provided.

However, the air introduction means 19 may be provided directly at the upper part of the calciner 3, the outlet of the calciner, or the separator 5, but in that case, the auxiliary combustion chamber 4 has an integral structure with the calciner 3 or the separator 5. You may do so.

Further, it is preferable to increase the combustion efficiency of the chamber 4 by swirling or dispersing the combustion air before introducing it into the chamber 4.

(2) Means for adjusting the combustion air ratio of the calciner 3 A gas analyzer 22 is provided at the calciner outlet 9 to analyze the exhaust gas of the calciner 3 in order to determine the combustion air ratio of the calciner 3.

Further, the combustion air ratio of the furnace 3 is adjusted by an air volume adjustment damper 20 provided in the air duct.

(3) Means for adjusting the combustion air ratio of the auxiliary board-grilling chamber 4 A gas analyzer 23 is provided at the auxiliary board-grilling chamber outlet 10 to analyze the exhaust gas of the auxiliary board-grilling chamber 4 in order to determine the combustion air ratio of the auxiliary board-grilling chamber 4. It is.

Note that when the air introducing means 19 is provided in the separator 5 or the like, the gas analyzer 23 is provided at the gas outlet of the separator 5.

The combustion air ratio in the chamber 4 is adjusted by an air volume adjustment damper 21.

Note that the gas analyzers 22 and 23 in (2) and (3) above may be replaced with air volume measuring devices using venturi tubes or the like.

In the powder material sintering apparatus configured in this way,
The operating methods of the preheater 2, rotary kiln 6, etc. are the same as before, but for the calciner 3, the air volume is adjusted so that the combustion air ratio determined by gas analysis at the calciner outlet 9 is 1.2 or less. Adjust the adjustment damper 20.

That is, when the combustion air ratio is made larger than 1.2,
This is because the amount of carbon monoxide generated during the combustion process of fuel in the calciner 3 is significantly reduced, and the desired denitrification effect in the calciner 3 cannot be achieved.

Further, the amount of combustion air introduced into the auxiliary grilling chamber 4 is adjusted by the damper 21 so that there is no unburned matter in the exhaust gas from the auxiliary grilling chamber 4 measured by the gas analyzer 23.

Next, the denitration action in the calcining furnace 3 and the action of the auxiliary board firing chamber 4 will be explained.

(1) Denitrification in the calciner 3 Denitrification in the calciner 3 is possible by setting the combustion air ratio of the furnace 3 to 1.2 or less, especially 1.1 to 1.0. , the effect becomes larger as the air ratio becomes smaller.

Here, the entrance of the calcining furnace 3, that is, the rotary kiln 6
Time roars 2. Amount of nitrogen oxides generated (Nrn'/)
Then, the amount of nitrogen oxides at the calcined outlet 9 (Nrrl/h
), the denitrification effect of the calciner 3 can be more clearly understood.

To explain this using an example, Fig. 4 shows the combustion air ratio of the calciner 3 on the horizontal axis and the calciner nitrogen oxide outlet ratio R on the vertical axis, and the actual measurement results are shown as a solid line. It is indicated by α.

Now, nitrogen oxides (so-called FUE, ff NOX) are produced from the nitrogen content of the heavy fuel oil supplied to the calciner 3.
) is determined when the amount of nitrogen oxides in the exhaust gas of the rotary kiln 6 is 1.0 when the combustion air ratio of the calciner 3 is 1.05.
In this case, since it is about 0.2, the inlet/outlet ratio R is about 1.2 when nitrogen oxides in the exhaust gas of the rotary kiln 6 are not denitrated.

The generation rate of nitrogen oxides due to the nitrogen content of this fuel gradually increases with the combustion air ratio, so the inlet/outlet ratio when the nitrogen oxides in the exhaust gas of the rotary kiln 6 are not denitrated in the calciner 3 is the result of actual measurements. It looks like the dotted line β.

Therefore, the denitrification effect of the calciner 3 is clearly shown as the difference between the dotted line β and the solid line α.

The denitrification effect in the calciner 3 uses calcium oxide (Cab) and iron oxide in the materials floating in the furnace as denitrification catalysts, and in the process of burning the fuel supplied into the furnace by the fuel supply means 16. This is due to the strong reducing power of carbon monoxide (Co) produced.

As is clear from FIG. 4, the denitrification effect of the calciner 3 becomes more pronounced as the combustion air ratio of the furnace 3 is lowered. This is because the amount of reducing agent CO generated during the combustion process is large.

(2) Function of the auxiliary board firing chamber 4 As is clear from the explanation of the function of the calcining furnace 3 above, the calcining furnace 3
Operating the furnace with a lower combustion air ratio is effective for denitrification, but on the other hand, unburned matter remains in the exhaust gas from the furnace 3, which reduces the thermal efficiency of the furnace 3.

In order to solve this problem, an auxiliary board firing chamber 4 is provided at the rear of the calcining furnace 3.

That is, since the air necessary to completely burn the unburned components from the calcining chamber 3 is effectively fed into the auxiliary baking chamber 4, the gas discharged from the separator 5 contains unburned components. is not included.

In other words, the auxiliary board firing chamber 4 plays the role of completely burning the unburned content from the calcining furnace 3.

Moreover, the material that could not be sufficiently calcined in the calcining furnace 3 due to the amount of heat due to the secondary combustion that occurs in the auxiliary board firing chamber 4,
Since it is completely calcined, the separated materials in the separator 5,
That is, there is no variation in the calcining rate of the material fed to the rotary kiln 6, the operation of the rotary kiln 6 is stabilized, and a linker of good quality can be obtained.

Furthermore, since the heat load on the calcining furnace 3 is reduced by the installation of the auxiliary board firing chamber 4, combustion is performed in a lower temperature gas atmosphere, and the thermal efficiency of the entire apparatus is improved.

In addition, in the auxiliary board firing chamber 4, there are
Since the amount of introduced air is adjusted by the damper 21 of the air duct 19, the combustion air ratio of the furnace 3 can be adjusted according to the required denitrification rate.

Furthermore, adjusting the combustion air ratio of the calciner 3 does not reduce the thermal efficiency of the entire device.

Next, an example of actual measurement data when cement is fired using the apparatus shown in FIG. 1 and the apparatus shown in FIG. 2 will be shown.

First, in the case of Fig. 1, the fuel oil supply ratio is set to 40% to rotary kiln F and 60% to calciner C, and the combustion air ratio of calciner C maintains the calcining reaction at approximately 90%. In order to
Since it was not possible to lower the value below 1.15, 1.
15, the amount of nitrogen oxides discharged from rotary kiln f is l Q Nm / K t per hour,
This was diluted in the calciner C, and nitrogen oxides of 5N111''/hour were discharged from the calciner C.

On the other hand, in the case of Fig. 2, even if unburned matter occurs in the calciner 3, it can be re-burned in the auxiliary board burning chamber 4, so the combustion air ratio of the calciner 3 is reduced to 1. Keep it at .05 and set the others to 1st.
When the experiment was carried out under almost the same conditions as in the case shown in the figure, the amount of nitrogen oxides discharged from the rotary kiln 6 was 1QNm/K.
b, the amount of nitrogen oxides discharged from the auxiliary board firing chamber 4 is 2.2 Nm/Kb, and the calcination rate of the raw material is approximately 9.
It was 0%.

That is, it was confirmed that the denitrification effect in the calcining furnace 3 in the case of FIG. 2 was large.

Therefore, the present invention eliminates the need to provide a special denitrification device outside the device system as in the past, and also eliminates the use of special reducing agents and catalysts for the sole purpose of denitrification, making it extremely economical to remove NOx from the device. Reduce the amount of nitrogen oxides to 1/2 to 1/2 of the normal amount.
3, that is, it can be suppressed to about 2 Nm/Kt or less.

Furthermore, there are no operational obstacles associated with conventional denitrification-only equipment, and operation and maintenance costs are also saved.

Moreover, since the calcining of the material is carried out in a dispersed manner in the calcining furnace and the auxiliary board burning chamber installed after it, the process of burning unburned materials is highly efficient, and the fuel consumption of the equipment can be reduced. In addition, rotary kilns and other calcining furnaces can be operated at the optimum combustion air ratio regardless of the generation of nitrogen oxides. It is possible to prevent coaching generation, etc.

Moreover, since materials with uniform calcining rates are supplied to the rotary kiln and other firing furnaces, there is no coating attached to the entrance of the firing zone in the rotary kiln, and stable operation is possible. The effect is extremely large.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a conventional device, FIG. 2 is an explanatory diagram of an embodiment of the present invention, and FIG. 3 is an explanatory diagram showing the relationship between the combustion conditions of a rotary kiln and the amount of nitrogen oxides in the kiln exhaust gas. Fourth
The figure is an explanatory diagram showing the relationship between the combustion conditions of the calciner and the nitrogen oxide inlet/outlet ratio of the calciner. 1... Material supply device, 2... Material preheating device, 3...
・Calcination furnace, 4... Auxiliary plate baking chamber, 5... Separator, 6.
... Rotary kiln, 7... Cooler, 8... Calciner gas inlet, 9... Calciner outlet, 10... Auxiliary board baking chamber outlet, 11... Air duct, 12...・Kiln gas duct, 13...Exhaust gas duct, 14...Exhaust fan, 1
5, 16...Fuel supply means, 17...Material supply means 18...Material conduit, 19...Air introduction means, 20
．． 21... Air volume adjustment damper, 22, 23... Gas analyzer.

Claims (1)

[Claims] 1. It has a gas inlet for introducing a mixed gas of exhaust gas from the combustion furnace and combustion air, a means for supplying the material to be calcined, a means for supplying fuel, and an outlet for the gas entraining the calcined material. It is equipped with a calcined furnace, and a separator that introduces the gas accompanying the calcined material, separates it into the calcined material and the gas, and discharges these from separate outlets. A calcining furnace such as a rotary kiln having a material conduit for introducing calcined material from a container and a fuel supply means separate from the calciner, furthermore, An apparatus for sintering powdered materials, comprising means for introducing combustion air between the vicinity of a gas outlet and a separator to combust unburned matter in a gas stream present after calcination.