JPS6333937Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a vertical calcining furnace placed between a cement raw powder preheating device and a calcining furnace.
Reduce NOx emissions from the raw material preheating device by burning the supplied fuel while suppressing the generation of NOx (nitrogen oxides), and effectively denitrifying NOx contained in the combustion furnace exhaust gas as necessary. At the same time, the vertical shape for cement raw powder enables efficient calcining of raw cement powder by maximizing the use of air extracted from the clinker cooler while reducing the amount of combustion air required in the calciner. This invention relates to improvements in calciners, and in particular provides a calciner structure suitable for pulverized coal fuel.

Modern cement calcining equipment is constructed by disposing a calcining furnace with an independent heat source between a raw material preheating device and a calcining furnace. FIG. 1 is a diagrammatic system diagram showing the steps of preheating, calcining, firing, and cooling cement raw material powder, and the solid arrows in the figure indicate the flow of hot air, and the dashed arrows indicate the flow of the raw material powder. The outline of the device is as follows.
It consists of a raw material preheating device 1, a calcining furnace 2, a calcining furnace 3 such as a rotary kiln, and a clinker cooler 4, and the cement raw material powder supplied from the raw material input chute 5 passes through each of the first to fourth cyclones _C1 to _C4. On the other hand, the high-temperature exhaust gas from the firing furnace 3 and the calcining furnace 2 is sucked by the induced draft fan 7a and rises inside the raw material preheating device ₁ , so that the raw material _is Heat exchange between the powder and the hot gas is repeated. The preheated raw material powder is introduced into the calciner 2 from the fourth cyclone _C4 through the chute. On the other hand, combustion occurs in the calciner 2 by the high temperature secondary combustion air introduced from the clinker cooler 4 and the fuel supplied together with the primary combustion air from the burner 6a serving as a fuel supply device. The raw material powder is calcined by receiving the heat of combustion and the heat of the furnace exhaust gas. The calcined raw material powder enters the lowermost cyclone _C5 from the calciner 2 together with the combustion gas and is separated, then enters the calciner 3 through a chute and enters the burner 6 installed at the lower end of the calciner 3.
The clinker undergoes necessary heat treatment in the kiln 3 by the combustion heat of the fuel supplied from b, and is then cooled in the cooler 4. Note that air for cooling the clinker is supplied by the forced 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 firing furnace 3 as described above. However, excess air is discharged through the dust collector 9 by the induced draft fan 7b. Then, the clinker from the clinker cooler 4 and the dust collector 9 is transported to the next process by a conveyor 11.

Figure 2 is a conceptual diagram showing the structure near the calciner in Figure 1 in more detail. Using these diagrams, the structure and function of the calciner when pulverized coal is used as fuel is explained as follows. be.

That is, in this configuration example, the rigid calcining furnace 2 has a cylindrical shape and is composed of a lower combustion chamber 2a and an upper mixing chamber 2b, which communicate with each other with a constriction part 2c as a boundary.
The lower end of a gradually reduces its cross section downward, and is connected to the firing furnace 3 through the connection housing 12 through the opening 2d.
It is connected to the. Further, a bleed air duct 13 for guiding secondary combustion air from the cooler 4 is opened and connected to the lower side wall of the combustion chamber 2a, and a cyclone in the second stage from the bottom of the raw material preheating device 1 is installed at an appropriate position. Preheating material input chute 14 from C ₄ , and 1
A burner 6a is installed into which pulverized coal is blown together with air. Furthermore, the combustion gas outlet 2e of the mixing chamber 2b
is connected to the lowest stage cyclone _C5 of the raw material preheating device 1. When using these devices, 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 nitrogen and oxygen in the combustion air combine. This generates a large amount of so-called thermal NOx. these
NOx rises and flows into the combustion chamber 2a from the lower opening 2d of the calciner 2 while remaining contained in the calciner exhaust gas. On the other hand, preheating raw material is supplied to the combustion chamber 2a from the second stage cyclone _C4 from the bottom via the input chute 14, and pulverized coal as fuel is supplied to the burner 6.
The raw material powder and pulverized coal are mixed and stirred in the combustion chamber 2a to form a spouted bed.

Secondary air for combustion is supplied to the spouted bed through the extraction duct 13 to combust the pulverized coal, but the combustion temperature is kept low due to the presence of raw material powder. If there is sufficient combustion air in this state, the nitrogen contained in the pulverized coal will combine with the oxygen in the combustion air to generate a large amount of so-called fuel NOx. The NOx generated in the calciner 3 and the calciner 2 is discharged from the raw material preheating device together with the exhaust gas, polluting the air. In order to reduce the amount of NOx discharged, the extraction duct 13 from the cooler 4 is vertically branched off into duct 13 as shown in FIG.
a opens and connects to the lower side wall of the mixing chamber 2b,
A method has been proposed in which, when pulverized coal is burned in the combustion chamber 2a, a state of oxygen deficiency is created to create a reducing gas atmosphere, suppressing the generation of NOx due to nitrogen contained in the pulverized coal, while at the same time decomposing and denitrifying NOx contained in the calciner exhaust gas rising and flowing in from the lower end of the combustion chamber, and then introducing the resulting mixture into the mixing chamber 2b through the narrowed section 2c, mixing it with additional combustion air sucked in through the branch duct 13a, completely combusting the combustible components contained in the reducing gas, and then discharging it into the lowest cyclone C _5. However, in these conventional techniques, the additional combustion air supplied from the branch duct 13a flows into the mixing chamber 2b in a state of almost constant speed sucking in with the rising reducing gas, and is only stirred and mixed by turbulence generated in the mixing chamber 2b when the reducing gas passes through the narrowed section 2c, so the mixing effect of the reducing gas and the additional air is very small. Therefore, if it is attempted to completely combust the combustible components in the reducing gas in the mixing chamber 2b, it becomes necessary to introduce a large amount of excess air, which not only reduces the thermal performance of the device, but also generates secondary NOx due to excess oxygen during the combustion of the reducing gas. Conversely, if the amount of excess air is reduced, the combustible components in the reducing gas continue to burn in the following cyclone, which causes operational problems such as the occurrence of a material blockage accident at the bottom of the cyclone. Furthermore, since the cross-sectional area of the branch duct 13a must be much smaller than that of the calciner main body 2 in terms of layout, in order to ensure the amount of additional air for combustion introduced into the mixing chamber 2b through the branch duct 13a, it is necessary to provide resistance to the passing air by installing an air flow control damper 15 in the extraction duct 13 after the branch, which increases the driving power of the exhaust gas induction fan 7a.

In addition, separately from the burner 6a arranged above the bleed air inlet, the calcination furnace exhaust gas inlet 2d at the lower end of the calcination furnace is installed.
A fuel supply device 6c is additionally installed between the pulverized coal fuel and the bleed air inlet, and a part of the pulverized coal fuel or a liquid fuel such as heavy oil is supplied into the firing furnace exhaust gas rising from the fuel supply device 6c to improve reducing properties. Forms a gas atmosphere and decomposes and decomposes NOx contained in the firing furnace exhaust gas.
Denitrification can be performed.

In view of the above-mentioned circumstances, we have proposed a method and device that can significantly improve the mixing effect of the reducing gas rising in the calciner and the additional air for combustion, and also that can easily control the suppression of NOx generation. He invented it and filed a separate patent application as Japanese Patent Application No. 55-5952. The specific means is to use a forced air blower to feed additional air for combustion from multiple points around the circumference of the calciner near the constriction part 2c in a direction that intersects the reducing gas flow rising inside the calciner. This improves the mixing effect of the reducing gas and the additional air for combustion, thereby reducing excess air.At the same time, controlling the speed of the forced blower or manipulating the damper opening can improve the mixing effect of the reducing gas and additional combustion air. It was possible to adjust the quantitative ratio of secondary air and additional air, thus easily controlling the generation of NOx, and achieving the goal of always keeping it at a stable low level.However, the heat resistance and Because it is necessary to use relatively low-temperature clean air as additional air for combustion due to wear resistance, the utilization rate of high-temperature air from the cooler decreases slightly, and extra power is required to drive the forced air blower. Accompanied by new problems.

The present invention solves the above problems of the conventional technology,
We aim to provide a furnace structure that can achieve virtually complete combustion in the calciner while reducing the amount of excess air, easily control NOx generation at a constant low level, and at the same time efficiently calcining cement raw material powder. It is something to do.

Therefore, the feature of the present invention is that a plurality of air bleed ducts from the clinker cooler are opened on almost the same plane of the side wall of the calciner, and at least one of these openings is opened in a plane above the opening. A fuel supply device is installed at a position within the width of the bleed duct to introduce initial combustion air, and a fuel supply device is not installed near at least one other opening to simply introduce additional combustion air. That's the point.

The present invention will be explained below based on the drawings.

FIG. 4 is a cross-sectional view showing one embodiment of the present invention, and FIGS. 5 and 6 are cross-sectional views showing other embodiments of the present invention. Note that in these drawings, the same reference numerals indicate the same parts.

Explaining FIG. 4, the bleed duct 13 is branched into two and opens at the side wall of the calciner 2.
At this time, the opening cross-sectional area of one bleed duct 13a with respect to the side wall of the calciner 2 is different from that of the other bleed duct 13a.
It is formed to be larger than that of b,
Both bleed ducts 13a and 13b are connected to the side wall of the calciner 2 facing each other. Also, the bleed air duct 13
A burner 6a as a fuel supply device is installed at a position within the width of the bleed air duct 13a in plan view on the side wall of the calciner 2 located above a. Damper 15
a is arranged. As described above, by providing the fuel supply device in the side wall of the calciner 2 at a position within the width of the bleed duct 13a in plan view, the fuel supplied from this fuel supply device and the bleed duct 13a
The initial stage of combustion proceeds at a low air ratio due to the combustion air supplied from the combustion chamber.

By adopting the above configuration, although a sufficient amount of air is supplied as a whole for combustion of the supplied fuel, some of the air is supplied to the bleed air duct 13 which is not equipped with a burner 6a nearby.
Since the fuel is introduced into the calciner 2 from b, decomposition of the fuel and partial combustion reaction proceed under oxygen-deficient conditions in the initial stage of combustion in the calciner, resulting in local reduction. A toxic gas atmosphere is formed.

Since the above-mentioned combustion mode is adopted, the generation of fuel NOx due to nitrogen in the fuel in the calciner is small.

As the reducing gas flows upward through the calciner, it is gradually mixed and stirred with additional combustion air introduced from the bleed air duct 13b, and is discharged from the calciner after substantially completing the combustion reaction.

At this time, when the additional combustion air mixes and joins with the combustion air introduced from the extraction duct 13a during the initial combustion stage of the fuel, the fuel in the calciner increases.
Since the amount of NOx generated increases, additional combustion air is introduced from a position a certain distance away from the initial combustion air introduction opening.

At this time, if the amount of combustion air from the bleed air duct 13a decreases, the combustibility will decrease, and conversely, if the amount of air increases, the amount of NOx generated will tend to increase.
The amount of combustion air introduced from each bleed duct is determined by an air volume distribution damper 15a installed at a branch of the bleed duct 13.
Optimally adjusted by This makes it possible to easily control the amount of NOx generated even when operating conditions change, making it possible to always keep it stable and low. Furthermore, when controlling these, the extraction duct 1
Since there is almost no difference in the passage resistance of the combustion secondary air between the bleed air duct 13a and the bleed air duct 13b, the introduction ratio of the secondary air from each air bleed duct can be adjusted without causing any extra pressure loss. Furthermore, since the additional air for combustion is introduced from near the bottom of the calciner, its residence time is sufficiently long until it is discharged from the calciner. (see figure)
By providing this, sufficient mixing of the additional air and the reducing gas is achieved based on the diffusion effect due to speed increase and deceleration in the throttle section, and therefore, substantially complete combustion is achieved even with a small amount of excess air.

According to empirical knowledge, it is necessary to make the cut-off combustion air larger than the additional combustion air, and a ratio of about 2:1 is appropriate, depending on the relative positional relationship of the respective openings.

Next, referring to FIG. 5, the air bleed duct 13', which is the air bleed duct 13 branched into two, is further branched into two air bleed ducts 13a' and 13' as shown in the figure.
b' are arranged in pairs on both sides of the calcining furnace 2, respectively. In this case as well, the cross-sectional area of the opening of the air bleed duct 13a' is larger than that of the air bleed duct 13b', as in the previous embodiment.
The burner 6a is located above a' and within the width of the bleed duct 13a' in plan view, and the bleed duct 1
An air volume distribution damper 15b is attached to 3b'. It should be noted that even with such a configuration, the same effect as that shown in FIG. 4 can be expected, so a description thereof will be omitted.

FIG. 6 shows an embodiment in which a plurality of openings are formed by a vertical partition wall installed in an air bleed duct. opening 13
A fuel supply device 6a is disposed at a position above the opening 13a'' and within the width of the opening 13a'' in plan view, and no fuel supply device is disposed at the central opening, and the Air volume distribution damper 15c on the side
is installed. Effects due to this kind of configuration
The effect is also the same as in FIG. The present invention is effective for any solid fuel, liquid fuel, or gaseous fuel containing nitrogen as a fuel, and the fuel supply device is not limited to a form other than a burner, such as a pulverized coal input chute.

As described above, according to the present invention, the following effects can be expected.

(A) NOx generation can always be kept low and can be easily controlled.

Further, NOx in the firing furnace exhaust gas can be denitrated in the lower part of the calcining furnace, if necessary.

(B) Since there is little difference in ventilation resistance between the paths of the initial combustion air and the additional combustion air, there is no extra pressure drop in the distribution of each air amount, and cooler bleed air can be used as additional combustion air, so the fuel efficiency of the system is improved. is high.

(C) Since the residence time of the additional combustion air in the calciner is long, sufficient mixing is achieved and complete combustion can be achieved with a small amount of excess air.

[Brief explanation of the drawing]

Figure 1 is a diagrammatic system diagram showing the conventional cement clinker manufacturing process, Figure 2 is a conceptual diagram of the vicinity of the calciner in Figure 1, and Figure 3 is a conceptual diagram of the vicinity of the calciner in another conventional example. , FIG. 4 is a cross-sectional view showing one embodiment of the present invention, and FIGS. 5 and 6 are cross-sectional views showing other embodiments of the present invention. 1... Raw material preheating device, 2... Calcining furnace, 2a...
Combustion chamber, 2b...mixing chamber, 2c...throttle section, 3...
...Kilning furnace, 4...Clinker cooler, 6a, 6
b, 6c... Fuel supply device, 7... Induced draft fan,
13, 13a, 13a', 13a'', 13b, 13
b', 13b''...Bleed air duct, 15a, 15b, 1
5c...Air volume distribution damper, 16...Partition wall.

Claims (1)

[Scope of Claim for Utility Model Registration] (1) Arranged between the raw material preheating device and the firing furnace, with a firing furnace exhaust gas inlet at the lower end and an outlet for combustion exhaust gas and calcining raw material powder near the upper end. let me,
In a vertical calcination furnace for cement raw material powder, in which a bleed air duct from a clinker cooler, a fuel supply device, and an input chute for preheated cement raw material powder are connected to the side wall, the bleed duct is installed on almost the same plane as the side wall of the calciner. has a plurality of openings, a fuel supply device is disposed above at least one opening and within the width of the bleed duct in plan view, and no fuel supply device is disposed in at least one opening. Vertical calcining furnace for cement raw material powder. (2) The cement raw material according to claim 1 of the utility model registration claim, in which the total cross-sectional area of the opening in which the fuel supply device is disposed in the upper position is larger than the total cross-sectional area of the opening in which the fuel supply device is not disposed. Vertical calcining furnace for powder.