JPH0347133B2 - - Google Patents

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for introducing fuel and combustion bleed air into a calciner for raw material powder in a modern sintering apparatus for raw material powder such as cement and alumina. This relates to a device that burns the supplied fuel while suppressing the generation of fuel NOx (nitrogen oxides) in the furnace and reduces the NOx content in the exhaust gas. The firing device for cement will be explained below.

[Prior Art] As shown in FIG. 3, a cement firing apparatus is constructed by disposing a calcining furnace 2 having an independent heat source between a raw material preheating device 1 and a calcining furnace 3. Therefore, with reference to FIG. 3, the equipment configuration of this type of cement firing apparatus and the process of processing raw material powder will be explained. still,
The solid arrows in the figure indicate the flow of hot air, and the dashed arrows indicate the flow of raw material powder. The cement firing apparatus includes a raw material preheating device 1 comprising cyclones C1 to C3 and a duct 7, a calcining furnace 2 with an attached cyclone C4, a calcining furnace 3 such as a rotary kiln, and a clinker cooler 4. Raw material input chute 5
The cement raw material powder supplied from the first to third cyclones C1 to C3 sequentially descends, while the high-temperature exhaust gas from the calcining furnace 3 and the calcining furnace 2 is sucked by the induced draft fan 8 and passes through the raw material preheating device 1. Heat exchange between the raw material powder and the high-temperature gas is repeated within the duct 7 and within the cyclones C1 to C3.
The preheated raw material powder is introduced into the calciner 2 from the third cyclone C3 through the preheated raw material chute 14. On the other hand, a bleed air duct 13 from the clinker cooler 4
Combustion occurs in the calciner 2 by high-temperature combustion bleed air introduced into the calciner 2 through the burner 6a and fuel supplied together with the primary combustion air from the burner 6a as a fuel supply device, and the combustion The raw material powder is calcined by receiving the heat and the heat of the firing furnace exhaust gas. After the calcined raw material powder enters the cyclone C4 from the calciner 2 together with the combustion gas and is separated,
The material enters the calcining furnace 3 from the calcining raw material chute 15 through the inlet end cover 12, undergoes necessary heat treatment in the calcining furnace 3 by the combustion heat of fuel supplied from the burner 6b installed at the lower end of the calcining furnace 3, and becomes clinker. After it cools down, it is cooled by a cooler 4. Incidentally, air for cooling the clinker is supplied by the forced air blower 10, and a part of the air whose temperature has been raised by exchanging heat with the clinker is distributed and introduced into the calcining furnace 2 and the calcining furnace 3 as described above. However, excess air is exhausted by the induced draft fan 9. The clinker discharged from the clinker cooler 4 is then conveyed to the next process by a conveyor 11.

Next, the structure and function of the calciner 2 in the above-mentioned cement firing apparatus will be explained in detail with reference to FIG. 4. That is, the calcining furnace 2 has a cylindrical vertical shape in this configuration example, and is composed of a lower combustion chamber 2a and an upper mixing chamber 2b that communicate with each other with a constriction part 2c as a boundary, and the lower end of the combustion chamber 2a is located at the lower end of the combustion chamber 2a. The cross section is gradually reduced toward the inverted cone-shaped part, and the opening 2d opens the inlet end cover 1.
It is connected to the firing furnace 3 via 2. Further, in the lower side wall of the combustion chamber 2a, a bleed air duct 13 that guides combustion bleed air from the cooler 4 in the radial or tangential direction is opened and connected to the inlet 2e, and the combustion chamber A burner 6a is installed facing the combustion bleed air flowing into the combustion chamber 2a, and a preheated raw material chute 14 from the cyclone C3 of the raw material preheating device 1 is connected to an appropriate position on the side wall of the combustion chamber 2a. The gas and calcined raw material powder outlet 2f are connected to the cyclone C4.

In the cement firing apparatus described in FIGS. 3 and 4, NOx is generated by combustion by the burner 6b installed in the firing furnace 3 and combustion by the burner 6a installed in the calcining furnace 2.

In the firing furnace 3, fuel is supplied from the burner 6b and the combustion atmosphere formed in the firing furnace 3 is at a very high temperature, so that a large amount of so-called thermal NOx, which is a combination of nitrogen and oxygen in the combustion air, is generated. These NOx remain contained in the calciner exhaust gas and rise into the combustion chamber 2a from the lower opening 2d of the calciner 2.
Inflow. On the other hand, in the combustion chamber 2a, a cyclone C3
The preheated raw material powder is supplied from the combustion chamber 2a through the chute 14, and is mixed and stirred in the combustion chamber 2a to form a spouted bed.

In the calciner 2, combustion bleed air is introduced into the spouted bed from the bleed air inlet 2e, and the fuel blown into the bleed air from the burner 6a is combusted. Because of the presence of raw material powder, the combustion temperature is maintained low. If there is sufficient combustion air under these conditions, the nitrogen contained in the fuel will combine with the oxygen in the combustion air to generate so-called fuel NOx, especially when the fuel contains a large amount of nitrogen such as pulverized coal. The amount of NOx generated also increases. Occurred in these firing furnaces 3 and 2
NOx is discharged from the raw material preheating device 1 together with the exhaust gas, polluting the atmosphere.

Conventionally, in order to reduce such NOx emissions, a burner 6c was provided between the bleed air inlet 2e of the calciner 2 and the calciner exhaust gas inlet 2d, and a burner 6c was installed to drain the fuel into the rising calciner exhaust gas. There is a known method that decomposes NOx and denitrates by supplying a reducing gas atmosphere in an inverted cone-shaped part.

[Problem to be solved by the invention]

However, due to the burner 6c mentioned above,
Decomposition and denitrification of NOx are effective in reducing thermal NOx in the calciner exhaust gas, but the burner 6c cannot suppress the generation of fuel NOx in the calciner combustion chamber.

In order to investigate the cause of fuel NOx generation in the calciner, we conducted a detailed study of the combustion conditions in the calciner and found the following. That is, the combustion air in the calciner includes high-temperature bleed air from the bleed air inlet 2e, primary combustion air and fuel conveying air from the burner 6a (in the case of solid fuel), and surplus air in the calciner exhaust gas. However, if the fuel is supplied directed to the fuel bleed air, the combustion bleed air and the air introduced from the burner are consumed during the initial combustion of the fuel. The air ratio of these initial combustion air (the ratio between the amount of air supplied for combustion and the theoretical amount of air required for combustion of fuel) is the ratio of fuel supply to the firing furnace and calciner, the amount of surplus air in the exhaust gas of the firing furnace, , varies depending on the amount of excess air that should be included in the calciner exhaust gas, but in general
It ranges from 1.1 to 1.3.

On the other hand, in the temperature range (800 to 1100℃) inside the calciner, the air ratio during fuel combustion and the fuel NOx
The relationship between the amount generated and the amount generated is not yet fully understood, and the type of fuel, nitrogen content in the fuel,
It is influenced by many factors such as the mode of fuel introduction and the concentration of raw material powder in the combustion atmosphere. However, in general, the relationship between the conversion rate of nitrogen contained in fuel to NOx and the air ratio tends to be as shown in Figure 5 (NOx
Challenge to ・Co-authored by Keiji Kato, Katsuya Nagata, Koji Himi・Published by Japan Energy Technology Association・Showa
(See Figures 5 and 3 on page 116, first published on August 20, 1951).
That is, on average, when the air ratio is below about 1.1 to 1.2, the amount of NOx generated decreases rapidly as the air ratio decreases.
On the other hand, when the air ratio is about 1.4 to 1.5 or higher, the amount of NOx generated increases slowly, and the combustion conditions in the calciner according to the conventional method are as an example
1.2), and at an air ratio of 1.1 to 1.3, a considerable amount of nitrogen in the fuel is converted to NOx. Furthermore, these fuel NOx are generated significantly in the initial stage of combustion, and especially when solid fuel such as pulverized coal with a high nitrogen content is used as fuel, a large amount of fuel NOx is generated in the calciner. , the NOx decomposition effect of burner 6c is due to this fuel.
It is not enough to remove NOx, and it is emitted from the raw material preheating equipment, causing air pollution.

The present invention solves the above problems of the prior art,
A method for introducing fuel and combustion bleed air into a calciner that can significantly reduce the amount of NOx generated when burning fuel in the calciner and also partially denitrate NOx contained in the exhaust gas of the calciner. The purpose is to provide

[Means to solve the problem]

In order to achieve the above object, the method of introducing fuel and combustion bleed air into a calciner for raw material powder of the present invention is as follows:
Calciner exhaust gas was introduced from the lower end of the calciner, and combustion bleed air from the clinker cooler was introduced from the side to burn the fuel, and most of the preheated raw material powder supplied to the calciner was calcined. Later, in a method for introducing fuel and combustion bleed air into a raw material powder calciner in which combustion gas and calcined raw material powder are discharged from the vicinity of the upper end, the combustion bleed air is placed on substantially the same plane of the side wall of the calciner. When a plurality of inlets are opened and fuel is supplied from each inlet toward the combustion bleed air introduced into the calciner, the air ratio at at least one bleed air inlet is 1.0 or less, and at least the other Fuel and/or combustion bleed air is unevenly distributed to each bleed air inlet so that the air ratio at one bleed air inlet is 1.0 or more.

[Effect]

Air ratio at least one bleed air inlet is 1.0
If the fuel and/or combustion bleed air is unevenly distributed to each bleed air inlet so that the air ratio at at least one other bleed air inlet is 1.0 or more, the bleed air with an air ratio of 1.0 or less When the fuel introduced from the bleed air intake is combusted, the conversion rate to fuel NOx is close to zero, and even if the air ratio increases when the fuel introduced from the other bleed air intakes is combusted, the conversion rate will not increase proportionally. , the average conversion rate of both becomes smaller, and the overall amount of fuel NOx generated decreases.

〔Example〕

The present invention will be described in detail below based on the drawings, but the drawings show specific examples of implementation, and the present invention is not limited to these illustrated examples. Alternatively, the same implementation can be performed even if a part of the design is changed.

FIG. 1 is a cross-sectional view of a calciner combustion chamber for carrying out the method of the invention. The bleed air duct 13 from the clinker cooler is branched into two branches and opens on substantially the same plane of the side wall of the calciner, facing toward the center of the calciner. At this time, the inlet cross-sectional area of one bleed air inlet 13a to the calciner 2 is different from the other bleed air inlet 13b.
is formed to be larger than that of. Further, fuel supply devices 6a, 6a having substantially the same capacity are arranged above the respective bleed air introduction ports 13a, 13b so as to direct the combustion bleed air introduced into the calciner. Further, an air volume distribution damper 16 is attached to a branch portion of the air bleed duct 13. In addition, when the fuel supply devices at the two bleed air intake ports have the same capacity, in order to keep the air ratio at one bleed air intake port to 1.0 or less, the ratio of the amount of bleed air introduced from the bleed air intake ports 13a and 13b must be adjusted. It is necessary to have a difference of 3:2 or more.

That is, the one in FIG.
The same amount of fuel is supplied from the bleed air inlets 13a and 6b, and the combustion bleed air is introduced from the bleed air inlets 13a and 13b so that the total air amount has the same air ratio as before (for example, 1.2). The amount of air from the inlet 13 of the bleed air duct 13 is varied.
In b, the air ratio is 1.0 or less (for example, 0.9), and in the inlet 13a of the extraction duct 13, the air ratio is 1.0 or more (for example, 1.5), and the air is distributed unevenly with a difference (for example, 0.6) between the two. The structure is as follows.

The conversion of the nitrogen content in the fuel into fuel NOx in the case of FIG. 1 described above will be explained with reference to FIG. 2. Note that point S indicates a case where the air ratio is 1.2 due to the same amount of combustion bleed air at the two bleed air inlets. Increase the combustion bleed air at the bleed air inlet 13a and raise the air ratio to 1.5.
Then, the conversion rate will be point A. On the other hand, if the combustion bleed air equivalent amount increased at the bleed air inlet 13a is reduced at the bleed air inlet 13b, the air ratio becomes 0.9 and the conversion rate becomes point B near zero. In the end, half of the fuel generates almost no fuel NOx, and the other half generates more fuel NOx during combustion, but
On average, the conversion rate is intermediate and corresponds to point M. In the end, the difference between point S and point M is fuel
NOx decreases. In other words, if the combustion bleed air is unevenly distributed to each bleed air intake so that the air ratio at one bleed air intake is 1.0 or less and the air ratio at the other bleed air intake is 1.0 or more, then one bleed air The fuel NOx at the inlet becomes near zero, and the fuel NOx at the other bleed air inlet increases, but as long as the conversion rate curve shows the trend shown in Figure 2 (a convex curve diagonally upward on the left), the overall fuel NOx will definitely decrease.

Further, in the bleed air inlet 13b of FIG. 1, in the initial stage of combustion, fuel decomposition and partial combustion reaction proceed under oxygen-deficient conditions, and a local reducing gas atmosphere is formed. Because of this combustion mode, not only is the generation of fuel NOx due to the nitrogen content in the fuel during combustion in the calciner significantly suppressed, but also the reduction The gas subsequently flows in from the lower opening 2d of the calciner and mixes with a portion of the ascending calciner exhaust gas, which serves to decompose and reduce NOx contained in the exhaust gas.

Further, the bleed air inlet ports 13a and 13b are opened on almost the same plane of the side wall of the calciner, and the combustion gas generated near the inlet ports gradually mix with each other as it flows upward, and passes through the constriction part 2c. and introduced into the mixing chamber 2b. And the aperture part 2
Stirring and mixing are promoted by the diffusion effect due to acceleration and deceleration when passing through the combustion chamber 2b and the turbulent flow generated in the mixing chamber 2b, and the combustible components contained in the combustion gas are completely combusted in the mixing chamber 2b. Well, opening 2f
It is discharged to cyclone C4.

At this time, if the amount of combustion air extracted from the extraction air inlet 13b decreases more than appropriate, the combustibility will decrease and the unburned content in the calciner exhaust gas will increase, or it will be necessary to increase the amount of surplus air in the exhaust gas. occurs, and conversely, the bleed air inlet 1
If the amount of combustion bleed air from 3b increases, the amount of NOx generated tends to increase, so the amount of combustion bleed air introduced from each bleed air duct is optimally adjusted by the air volume distribution damper 16 installed at the branch part of the bleed air duct 13. be done. This allows NOx to be maintained even when operating conditions fluctuate.
The amount generated can be easily controlled and always kept stable and low. It goes without saying that the amount of fuel supplied to each bleed air inlet can be adjusted as well as the amount of combustion bleed air introduced.

In the above explanation, in order to keep the air ratio at least one bleed air inlet to 1.0 or less, fuel supply devices with approximately the same capacity are arranged but the bleed air inlets are configured to have different cross-sectional areas. This effect can also be achieved by making the cross-sectional area of each bleed air inlet almost the same, but by arranging fuel supply devices with different capacities to each bleed air inlet. It is necessary to select a capacity with a difference of 3:2 or more. Furthermore, the same effect can be obtained by arranging both the size of the bleed air inlet and the capacity of the fuel supply device to be different for each bleed air inlet, which allows the amount of fuel and combustion bleed air to be unevenly distributed. The NOx reduction effect increases as the amount of fuel supplied to the bleed air inlet on the side that forms the reducing gas atmosphere increases within a range that does not inhibit combustibility in the calciner.

Furthermore, even when three or more bleed air inlets are opened, the air ratio at at least one bleed air inlet is
NOx emissions can be maintained low by distributing fuel and/or combustion bleed air to a level below 1.0.

In these calcining furnaces, the cross-sectional shape of the calcining furnace,
Also, the type of fuel and the type and arrangement of the fuel supply device can be freely selected depending on the purpose. For example, when solid fuel is used, a fuel supply chute can be provided in place of the burner 6a, and the powdered solid fuel can be dropped and introduced into the combustion chamber 2a by gravity.
It is also possible to combine this with other means for suppressing NOx generation or denitration, such as installing a separate burner in the inverted cone-shaped portion of the combustion chamber 2a. Furthermore,
Type of raw material preheating device (cyclone type, tower type, etc.),
The number of series, the number of stages, the number of cyclones constituting each stage, etc. are not limited at all.

〔Effect of the invention〕

The method of introducing fuel and combustion bleed air into a calciner for raw material powder according to the present invention is to open a plurality of inlets for the combustion bleed air on substantially the same plane of the side wall of the calciner, and When supplying fuel toward the combustion bleed air introduced into the bleed air, the air ratio at at least one bleed air intake port is 1.0 or less, and the air ratio at at least one other bleed air intake port is 1.0 or more. The fuel and/or combustion bleed air is unevenly distributed to each bleed air intake port, and the conversion rate to fuel NOx is close to zero at the bleed air intake port where the air ratio is 1.0 or less, and the other bleed air intakes are distributed accordingly. Even if the air ratio increases at the mouth, the conversion rate does not increase proportionally, so the average conversion rate of both becomes small, and the amount of fuel NOx generated in the calciner as a whole can be reduced.

In addition, a local reducing gas atmosphere is formed at the bleed air inlet where the air ratio is 1.0 or less, and this reducing gas continues to flow in from the lower opening of the calciner and become part of the ascending calciner exhaust gas. The mixture decomposes and decomposes a portion of the thermal NOx contained in the firing furnace exhaust gas.
This will reduce the NOx content in the exhaust gas of the entire cement kiln.

Furthermore, the bleed air duct opens on almost the same plane as the side wall of the calciner, and the combustion gas produced at the inlet is gradually mixed with each other as it flows upward, so that combustible components contained in the combustion gas are mixed with each other. Complete combustion is achieved.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a calcining furnace for carrying out the method of the present invention, and FIG. 2 is a graph showing the relationship between the conversion rate and air ratio at each bleed air inlet in the case of FIG. 1.
Figure 3 is a diagram showing the equipment configuration of the cement firing equipment and the processing process of raw material powder. Figure 4 is a diagram showing the configuration of the calciner in Figure 3 and the conventional NOx reduction method. Figure 5 is a diagram showing the calciner. 2 is a graph showing a trend of the relationship between the conversion rate of nitrogen content in the fuel and the air ratio. 1... Raw material preheating device, 2... Calcining furnace, 2a...
Combustion chamber, 2b...mixing chamber, 2c...throttle section, 2e
... Bleed air inlet, 3 ... Calcining furnace, 4 ... Clinker cooler, 6a, 6b6c ... Fuel supply device, 8
...Induced draft fan, 13...Bleed air duct, 13a,
13b...Bleed air inlet, 14...Preheating raw material chute, 15...Calculating raw material chute, 16...Air volume distribution damper, C1-C4...Cyclone.

Claims (1)

[Claims] 1 Introducing the calciner exhaust gas from the lower end of the calciner, and introducing combustion bleed air from the clinker cooler from the side to burn the fuel, and calcining most of the preheated raw material powder supplied to the calciner. After that, in a method for introducing fuel and combustion bleed air into a raw material powder calciner in which combustion gas and calcined raw material powder are discharged from the vicinity of the upper end, the combustion When opening multiple bleed air inlets and supplying fuel toward the combustion bleed air introduced into the calciner from each inlet, the air ratio at at least one bleed air inlet is 1.0 or less, and A calcining furnace for raw material powder, characterized in that fuel and/or combustion bleed air is distributed unevenly to each bleed air inlet so that the air ratio at at least one other bleed air inlet is 1.0 or more. How to introduce fuel and combustion bleed air to.