JP2556480B2 - Nitrogen oxide reduction device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to nitrogen oxides (NO
The present invention relates to a device for reducing NOx, and particularly to a device suitable for reducing NOx in a combustion device in which coal is pulverized and burned.

[Conventional technology]

In large boilers for businesses such as large boilers for thermal power plants, conversion from petroleum-based fuels to other fuels, particularly coal, is being actively promoted. The reserves of coal are very large, but the properties differ considerably depending on the coal producing area, and considering future coal demand, it cannot always be said that the coal of the specified properties will always be secured. Therefore, it is necessary to further improve the technology for burning coal of various properties toward the future. Also, in the case of coal combustion, as a matter of course, the amount of air pollutants, especially NOx, emitted during combustion must be kept low.

As a method for reducing NOx in a combustion apparatus, methods such as adoption of a low NOx burner, installation of a two-stage combustion equipment, and installation of a flue gas denitration apparatus have been conventionally implemented singly or in combination.

FIG. 7 is a conventional control system diagram for implementing the above method. In the figure, 1 is a boiler input signal generator, 2 is an economizer outlet O ₂ meter, 3 is a combustion air flow meter, 4 is an O ₂ setter, 5
Is a subtractor, 6 is an O ₂ integrator, 7 is an O ₂ adder, 8 is a subtractor,
9 is a controller, 10, 13 and 20 are manual / automatic setting devices, 11 is an air flow rate adjusting damper, 12 is an opening setting device, 14 is a two-stage combustion air control damper, 15 is a economizer outlet NOx meter, 16 is an NH ₃ flow meter, 17,1
8 is a computing unit, 19 is a controller, and 21 is an NH ₃ injection control valve.

Regarding the control of NOx, the air amount corresponding to 10 to 30% of the combustion air amount is divided into burner air and wind box air, and the two-stage combustion air control damper 14 is operated. As a result, first, the NOx generation amount at the furnace outlet of the combustion device (boiler) is suppressed, and the NH ₃ injection amount into the flue gas denitration device and the NOx amount in the exhaust gas are monitored by the NH ₃ flow meter 16 and the NOx meter 15. N
By controlling the injection amount of NH _{3 with} the H ₃ injection control valve 21,
We were trying to reduce the amount of Ox.

During this control, the opening of the burner register is fixed and the combustion device is operated. That is, the opening degree of the burner register is fixed to the opening degree set on the basis of the adjustment result of the trial operation when the burner is ignited, and the burner register is closed when the burner is exhausted.

[Problems to be solved by the invention]

As mentioned above, in order to secure a stable supply of coal, it is necessary to import many types of coal, and the types of coal supplied to the combustion equipment tend to change rapidly. Driving is desired.

However, the conventional combustion apparatus does not perform control corresponding to the properties of coal such as the N content, so that the effect of reducing NOx is not sufficiently obtained.

In view of such a background, the object of the present invention is to achieve sufficient NOx reduction effect, and also to reduce the power cost of the pulverized powder machine as much as possible, and to extend the life of the pulverized coal machine. To provide a reduction device.

[Means for solving problems]

In order to achieve the above object, the present invention is an apparatus for supplying pulverized coal pulverized by a pulverized coal machine to a burner and burning the pulverized coal machine, wherein the pulverized coal machine adjusts the average particle size of the pulverized coal, for example, a particle size such as a vane. Controlling means, for coal with high nitrogen content, reduce the average particle size of the pulverized coal sent from the pulverized coal machine, and for coal with low nitrogen content, delivered from the pulverized coal machine. The average particle size of the pulverized coal is adjusted by the particle size adjusting means so as to increase the average particle size of the pulverized coal.

[Action]

The present invention, as described above, grasps the relationship between the nitrogen content of coal-NOx generation-power cost and life of the pulverized coal machine, and divides the coal to be used into those with a high nitrogen content and those with a low nitrogen content. When using coal with a high nitrogen content, the amount of NOx generated can be effectively suppressed by pulverizing the coal so that the average particle size of the pulverized coal becomes smaller.

On the other hand, coal with a low nitrogen content is essentially
Since the amount of NOx generated is smaller than that of coal with a high nitrogen content, it is not necessary to reduce the average particle size of pulverized coal so much.
For this reason, the pulverized coal is suppressed from being finely pulverized within the range where the NOx generation amount does not increase, and the power cost of the pulverized coal machine is reduced by that amount and the service life is extended.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. FIG. 9 is a vertical sectional view of a ball mill used in the embodiment of the present invention.

The crushing section of this ball mill uses an electric motor through a speed reducer 52.
From the lower crushing wheel 53 rotating at 51, the crushing balls 60 arranged in the circumferential direction of the lower crushing wheel 53, and the upper crushing wheel 55 (fixed type) arranged above these crushing balls 60 It is configured. The upper crushing wheel 55 is pressed in the direction of the crushing balls 60 by the pressure device 62, and by rotating the lower crushing wheel 53, the crushing balls 60 sandwiched between the upper and lower crushing wheels 55, 53 are placed on the lower crushing wheel 53. To roll.

The coal supplied from the coal feeding pipe 58 is bitten between the lower crushing wheel 53 and the crushing balls 60 and crushed, and the lower crushing wheel 53 is crushed.
It moves to the outside of the crushing ball 60 by the centrifugal force caused by the rotation of.

The hot air supplied from the air duct 59 is blown into the outer periphery of the lower crushing wheel 53, and the crushed coal particles are blown up to the upper part of the device. And crushed coal is a guide vane
A turning force is given by 56 and flows into the classifier hopper 57. Due to this turning force, the pulverized coal having a small diameter is pneumatically transported to the burner of the combustion device through the pulverized coal pipe 61. On the other hand, large-sized coal particles are processed in the classifier hopper 57 by their own weight and are re-ground in the crushing section.

Since the turning force applied to the pulverized coal can be changed by changing the angle of the guide vanes 56, the angle of the guide vanes 56 can be adjusted to adjust the classification degree of the classifier, that is, the average particle size of the pulverized coal supplied to the burner. it can.

FIG. 10 is a vertical sectional view of a pulverized coal machine having a rotary classifier. The coal supplied from the chute 85 is crushed by being caught between the crushing roller 73 supported by the arm 76 and the rotary table 72. The crushed coal particles fly up to the upper part of the device by hot air, enter the rotary classifier 77, and are classified by the vanes 86 rotated by the motor 88 via the shaft 87. Therefore, in the case of this rotary classifier 77, by controlling the rotation speed of the vane 86, the degree of classification of the classifier, that is, the average particle size of the pulverized coal supplied to the burner can be adjusted.

In the embodiment of the present invention, a pulverized coal machine having a ball mill shown in FIG. 9 or a rotary classifier shown in FIG. 10 is used.

Figure 3 shows the fuel ratio of coal (fixed carbon / volatile matter) and NOx.
It is a characteristic view which shows the relationship with the generation amount. In this test, pulverized coal having a fuel ratio of 1, 3 and 4 (all of which has a N content of 1.1 to 1.2% in the coal) was burned and the amount of NOx produced was measured. As is clear from the results of this test, the higher the fuel ratio, the greater the amount of NOx generated.

FIG. 4 is a characteristic diagram showing the relationship between the N content rate in coal and the NOx generation amount. In this test, the air ratio was set to 1.3 and pulverized coal was burned to measure the amount of NOx produced. The numerical value attached to the characteristic curve indicates the fuel ratio.
As is clear from the test results, the higher the N content in the coal, the greater the amount of NOx generated, and conversely, the lower the N content in the coal, the lower the amount of NOx generated.

FIG. 5 is a characteristic diagram showing the relationship between the oxygen concentration at the outlet of the economizer (ECO) and the ratio of unburned ash in combustion [upper (A)] and NOx ratio [lower (B)]. . A, b in the figure,
C indicates the difference in particle size of pulverized coal, and the average particle size increases in the order of a, b, and c (a <b <c). As is clear from this test result, the particle size of pulverized coal has a great influence on its combustion, and the smaller the particle size of pulverized coal, the less unburned components in ash and the amount of NOx generated.

FIG. 6 is a characteristic diagram showing the relationship between the burner port air ratio and the NOx ratio in pulverized coal having different particle sizes. In this test, 200 mesh pass is about 70% pulverized coal (a), about 82%
Pulverized coal (b), about 84% pulverized coal (c), and about 86% pulverized coal (d) are used. Therefore, the average particle size of pulverized coal is (a)>(b)> (c )> (D). As is clear from the test results, pulverized coal having a smaller particle size produces less NOx at the same air ratio, and pulverized coal having the same particle size produces less NOx at a lower air ratio.

The present inventors have confirmed the following points by conducting various combustion experiments.

(1) Most NOx generation in coal combustion is due to NOx generated by N content in fuel (so-called fuel NOx).

(2) The N content release amount at the time of volatile content release in coal increases as the proportion of volatile content increases.

(3) If the pulverized coal is miniaturized, the flame holding property and ignitability immediately downstream of the burner will be good, and the temperature will be high. In addition, the char itself is a small-diameter particle. The release rate of N in the inside becomes high.

(4) If the pulverized coal is fine, N content is released in a short time in the reduction zone formed in the central area of the burner that burns this pulverized coal, so the conversion rate of N content to NOx becomes low, As a result, the amount of NOx generated is reduced.

From the above characteristic diagrams and findings of various combustion experiments ,. The higher the N content in coal, the greater the amount of NOx generated.

. By making the pulverized coal finer, it is possible to reduce the amount of NOx generated and the amount of unburned matter in ash.

. It is not necessary to make the pulverized coal finer than necessary because the amount of NOx generated is essentially small in coal with a low N content. On the contrary, if the coal is refined more than necessary, the power cost for pulverization will be high, and the parts of the pulverized coal machine will be consumed so much that the life of the coal will be shortened. No need.

The present invention is constructed based on this view.

FIG. 1 is a control system diagram showing a first embodiment of the present invention.

The NOx concentration measured by the economizer outlet NOx meter 15 is input to the calculator 17. NH ₃ flow meter 16
The injected NH ₃ flow rate measured at is input as a correction value, and the controller 19 and the manual / automatic setting device 20 are used to supply the NH ₃ injection amount control valve 21.
Control the opening of.

The combustion air flow meter 3 measures the flow rate of the combustion air, and the opening degree measuring device 12, the two-stage combustion adder 32, the manual / automatic setting device 13
After that, the opening degree of the two-stage combustion air flow rate control damper 14 is adjusted. In this case, the opening degree adjustment of the two-stage combustion air flow rate control damper 14 is corrected based on the NOx concentration target value signal of the NOx setting device 25 described later.

The signal from the boiler input signal generator 1 passes through the O ₂ setter 4 and the subtracter 5 outputs the O ₂ output from the economizer outlet O ₂ meter _2.
The concentration signal is subtracted, further reaches the O ₂ adder 7 via the O ₂ integrator 6, is added to the above-mentioned raw boiler input signal, and reaches the subtractor 8. This signal is further adjusted by the controller 9, manual / automatic setting device
The air flow rate adjustment damper 11 is operated via 10.

The NOx concentration target value signal set in the NOx setter 25 is
It is input to the two-stage combustion adder 32 via the two-stage combustion bias device 31 and corrects the opening adjustment of the two-stage combustion air flow rate control damper 14.

Further, the NOx concentration target value signal set in the NOx setting device 25 reaches the adder 28 via the bias device 27, is added to the boiler input signal input via the classifier vane opening setting device 26, and is manually operated. / Controls the openings of the classifier vanes 30 of a plurality of ball mills via the automatic setting device 10.

In the present embodiment, when using coal with a high N content, the vane opening of the classifier is reduced within the vibration control of the pulverized coal machine to determine the average particle size of the pulverized coal sent from the pulverized coal machine. The opening degree of the two-stage combustion air flow rate control damper 14 is increased as the size is reduced (for example, 200 mesh pass is about 86%). On the other hand, when using coal with a low N content,
The average particle size of the pulverized coal sent from the pulverized coal machine is increased (for example, 200 mesh pass is about 70%), and the opening degree of the two-stage combustion air flow rate control damper 14 is reduced to operate.
In addition, the N content content is obtained in advance by analysis for each type of charcoal.

The bias device 27 outputs a signal for adjusting the average particle size of pulverized coal according to the N content, and a signal for adjusting the opening degree of the two-stage combustion air flow rate control damper 14 according to the N content. Is output from the two-stage combustion bias device 31
Is.

When the load of the combustor is up to about 40 to 60%, the two-stage combustion air flow rate control damper 14 is closed, and the guide vane opening of the pulverized coal classifier is "small" or "medium". To do. FIG. 8 specifically shows the vane opening.
Curve A in the figure indicates vane opening "small", curve B indicates vane opening "medium", and curve C indicates vane opening "large". The two-stage combustion air flow rate control damper 14 is automatically opened based on the NOx setting device 25 as the load of the combustion device increases.

FIG. 2 shows another embodiment. This embodiment is constructed so as to perform control more accurately than the above embodiments.

That is, from the control system of the classifier vane 30,
Signal switch 29 between automatic setter 28 and classifier vane 30
Is installed, to which the burner extinguishing signal calculator 31 is connected.

Further, a gain controller 33 is installed for the two-stage combustion air flow rate damper control system, and the NOx concentration setting signal from the NOx setting device 25 via the two-stage combustion air flow rate damper opening degree controller 32 is used as a correction value. Is entered. Further, a signal switch 34 is installed between the manual / automatic setting device 13 and the two-stage combustion air flow rate damper 14, and a pulverized coal machine stop signal setting device 35 is connected thereto.

With the above configuration, the NOx output from the NOx setter 25
The concentration target value signal issues an opening signal to both the two-stage combustion air flow rate damper 14 and the classifier vane 30. At this signal pressure, for example, if the signal is 4 to 20 mmAq,
When showing a pressure of 16 mmAq, the two-stage combustion air flow damper 14
Is adjusted, and in the case of 15 to 20 mmAq, in addition to this, the opening of the classifier vane 30 is also controlled, and is controlled in series. Here, the two-stage combustion air flow rate damper
When the NOx control signal of 14 becomes high, the opening degree of the two-stage combustion air flow rate damper 14 is controlled in the opening direction and the classifier vane 30 is controlled in the throttling direction.

Also in this embodiment, when a high N coal is supplied to the furnace, the two-stage combustion air flow rate damper 14 is adjusted to near full opening, and the opening degree of the classifier vane 30 is reduced so that the inside of the classifier is reduced. The particle size of the pulverized coal is reduced by increasing the swirling force at, and the increase of NOx generation amount and ash generation amount is prevented.
On the other hand, when low N coal is supplied, the two-stage combustion air flow damper 14 is throttled and the opening of the classifier vane 30 is opened within the range where the NOx generation amount does not rise, and the power cost of the pulverized coal machine is reduced. To reduce

〔The invention's effect〕

The present invention, as described above, grasps the relationship between the nitrogen content of coal-NOx generation-power cost and life of the pulverized coal machine, and divides the coal to be used into those with a high nitrogen content and those with a low nitrogen content. When using coal with a high nitrogen content, the amount of NOx generated can be effectively suppressed by pulverizing the coal so that the average particle size of the pulverized coal becomes smaller.

On the other hand, coal with a low nitrogen content is essentially
Since the amount of NOx generated is smaller than that of coal with a high nitrogen content, it is not necessary to reduce the average particle size of pulverized coal so much.
Therefore, it is possible to suppress the pulverization of the pulverized coal within the range where the NOx generation amount does not increase, reduce the power cost of the pulverized coal machine by that amount, and extend the service life.

[Brief description of drawings]

FIG. 1 is a control system diagram of a nitrogen oxide reduction apparatus showing a first embodiment of the present invention, FIG. 2 is a control system diagram of a nitrogen oxide reduction apparatus showing a second embodiment of the present invention, and FIG. The figure shows the fuel ratio and NO
Fig. 4 is a characteristic diagram showing the relationship with the x value, Fig. 4 is a characteristic diagram showing the relationship between the N content rate and the NOx value, and Fig. 5 is the oxygen concentration at the economizer outlet and the unburned ash content and NOx ratio. Fig. 6 shows the relationship between NOx and burner port air ratio at different pulverized coal particle sizes.
Fig. 7 is a characteristic diagram showing the relationship with the ratio, Fig. 7 is a control system diagram of a conventional nitrogen oxide reduction device, Fig. 8 is a characteristic diagram showing the relationship between the coal feed rate, the pulverized coal particle size and the mill load factor, the 9th. FIG. 1 is a vertical sectional view of a ball mill used in an embodiment of the present invention, and FIG. 10 is a vertical sectional view of a pulverized coal machine having a rotary classifier. 11 …… Air flow control damper, 14 …… Two-stage combustion air flow damper, 25 …… NOx concentration setter, 26 …… Classifier vane opening setter, 30,56 …… Classifier vane, 35 …… Pulverized coal machine stop signal setter, 57 …… Classifier hopper, 77 …… Rotary classifier, 86 …… Rotary vane.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nakashita Adult 6-9 Takaracho, Kure City Bab Kotsk Hitachi Co., Ltd. Kure Factory (56) References JP 57-19506 (JP, A) Actual development Sho 57- 178940 (JP, U)

Claims (1)

(57) [Claims] 1. A device for supplying pulverized coal pulverized by a pulverized coal machine to a burner and burning the pulverized coal machine, wherein the pulverized coal machine has a particle size adjusting means for adjusting an average particle size of the pulverized coal, For high coal, reduce the average particle size of the pulverized coal delivered from the pulverized coal machine, and for coal with a low nitrogen content, increase the average particle size of the pulverized coal delivered from the pulverized coal machine. Thus, the nitrogen oxide reducing apparatus is configured such that the average particle size of the pulverized coal is adjusted by the particle size adjusting means.