JPH0781151B2 - High efficiency NOx control method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an operation method for reducing nitrogen oxides in exhaust gas when burning many types of coal in the same furnace in a pulverized coal combustion apparatus, The present invention relates to a furnace control method suitable for achieving high efficiency and reducing NOx.

[Conventional technology]

The following can be said regarding NOx in the exhaust gas in a boiler or the like in which a large number of types of coal are burned in the form of fine powder in the same boiler as the fuel. Fuel ratio (fixed carbon / volatile matter)
The higher the value, the higher the NOx generation. That is, the N content contained in the coal is distributed without being unevenly distributed in the volatile content and the fixed carbon. The lower the fuel ratio, the higher the N content release rate at the time of volatile content release, and the higher the fuel ratio, the greater the N content. N minutes of remain in the char. Then, the N content in the volatile matter is released in a short time in the reducing atmosphere in the central region of the burner, so the conversion rate to NOx is low, while the N content remaining in the char is in the oxidizing atmosphere. Combustion underneath is forced and the conversion rate to NOx becomes high (see Fig. 7). The higher the N content in the fuel, the higher the NOx (see Fig. 2). Furnace outlet O ₂ (hereinafter E
NOx value is affected by CoO ₂ (Fig. 4 NOx)
See curve). In the case of the same coal type, the NOx value and the unburned ash content are incompatible with ECoO ₂ , and therefore the operating method that reduces NOx has the characteristic of increasing the unburned ash content (Fig. 4). (Refer to the unburned component curve). Even when ECoO _{2 is} constant, the unburned content in the ash with respect to the fuel ratio changes depending on the particle size of the pulverized coal (Fig. 3).

As described in FIG. 5, basically, as a control method for burning various types of coal having different fuel ratios and N content in the fuel in the same furnace and suppressing NOx within the environmental regulation value, as shown in FIG. B) Lower NOx level due to low NOx burner,
(B) Installation of two-stage combustion equipment and changes in the two-stage combustion ratio,
(C) It has been controlled by the method of mounting the flue gas denitration device and changing the NH ₃ injection ratio for the denitration device.

FIG. 5 shows an example of a conventional pulverized coal burning boiler structure, and FIG. 6 shows an example of NOx control. In FIG.
Coal is sent from a coal bunker 20 through a coal feeder 21 to a pulverized coal machine 22 and pulverized to produce pulverized coal. The pulverized coal from the pulverized coal machine 22 is supplied to the furnace 1 by the pulverized coal burner 24 via the pulverized coal pipe 23 and forms the flame 2 together with the combustion air from the wind box 14. An air register 25 and a two-stage combustion NOx port 26 are present in the wind box 14.

Then, the adjustment of the combustion air is performed by the air flow rate control tamper 12 arranged at the inlet of the strong pressure blower 11 in proportion to the fuel amount of the coal feeder 21. The air from the ventilation fan 11 is split and one flow is preheated by the air preheater 4 using the exhaust heat gas from the furnace 2, and then the two-stage combustion air flow control damper 10 or burner inlet It is sent into the furnace 1 via the air damper 13. The air flow control damper 12 is an EC
It was feedback controlled by oO ₂ total 32. The other flow of the split air is passed through the primary fan 15 and further split, and is partially preheated by the air preheater 4 to become hot air 16 and cold air 17 which has not been preheated through the temperature control damper 18. After being mixed and temperature-controlled, it is fed into the pulverized coal machine 22 through the pulverized coal machine primary air flow control damper 19.

Regarding NOx control, fine powder is obtained by controlling the opening degree of the two-stage combustion air flow rate control damper 10 in which an amount corresponding to 10 to 30% of the combustion air amount is separated and sent as the two-stage combustion air. The air ratio of the burner port of the charcoal burner 24 is controlled to suppress the NOx generation amount at the furnace 1 outlet first. Further, the NH ₃ injection rate injected into the flue gas denitration device (hereinafter referred to as De-NOx device) 3 by the pipe 34 is controlled by the NH ₃ injection amount control valve 33 while being monitored by the NOx meter 31 in the exhaust gas. The outlet NOx of the chimney 7 was controlled. An electric dust collector 5 and an induced draft fan 6 are provided in the middle of the flue 8.

Next, FIG. 6 will be described.

First, the control of the air flow rate control damper 12 will be described.

An air flow rate request signal is created by the boiler input signal BID (101). This air flow rate request signal is created by adding the excess air ratio so as to be the air flow rate request signal required for combustion. The excess air ratio is calculated by setting the ECoO ₂ setting according to the load by the calculator (104), subtracting it by the ECoO ₂ measurement signal (102) and the subtractor (105), and integrating the deviation by the integrator (106). It becomes an excess air ratio signal. Boiler input signal (10
1) and the excess air ratio signal (output of the integrator (106)) are added by the adder (107) to form an air flow rate request signal. This air flow rate request signal and the air flow rate measurement signal AF (103) are subtracted (1
In step 08), the air flow rate control damper (12) is adjusted by a controller (proportional integrator) (109) so that the deviation becomes zero. The H / A (air preheater 110, 113, 120) is an automatic manual switching device and is normally used in an automatic state. When the operator manually adjusts, the H / A is switched to manual and adjusted.

Next, the control of the two-stage combustion air flow rate control damper 10 will be described. This is a control that determines the control damper opening according to the boiler combustion air flow rate. The air flow rate measurement signal A / F (103)
The damper opening setting is created by the calculator (112) by the output signal of the calculator (112) and the two-stage combustion air flow rate control damper (1
Adjust 0).

Further, the control of the NH ₃ injection flow rate control valve (33) will be described.

The NH ₃ injection flow rate control is performed by adjusting the NH ₃ injection amount according to the NOx amount in the exhaust gas. The NH ₃ injection amount request signal is the combustion air amount (corresponding to the exhaust gas amount) AF (103) and N in the exhaust gas.
It is created by multiplying the Ox measurement signal (115) by the multiplier (117). The NH ₃ injection amount request signal ((117) output signal) and the NH ₃ measurement signal (116) are subtracted by the subtractor (118) and the deviation is zero by the controller (proportional integrator) (119). ₃ Adjust the injection flow control valve 33.

By the way, since the required NOx level is decreasing year by year, it is common to use the two-stage combustion air flow rate control damper 10 at the maximum opening as a result of optimization and adjust it with the NH ₃ injection rate. It has become.

According to this method, basically, the ECoO ₂ concentration is basically controlled by a program control (6th load) corresponding to a load (fuel amount).
(Figure 104) was assembled. Therefore, when burning many types of coal in the same furnace, ECoO _{2 was} set higher based on the highly fueled coal that produces a large amount of both NOx and unburned ash.

And, even when burning a low fuel ratio coal that has a low fuel ratio, that is, it is easy to burn and also lowers NOx, it is not possible to operate by lowering the effective ECoO ₂ in order to increase the efficiency and reduce the power factor in the plant. It remained.

[Problems to be solved by the invention]

The above-mentioned conventional technology is a low volatility coal (see FIG. 4) that has low unburned content and is easy to reduce NOx from the viewpoint of high efficiency operation by using many types of coal in the same furnace. However, it is not possible to operate with a low ECoO ₂ concentration, which is effective as a means of reducing exhaust gas loss and lowering the in-house rate. Thus, despite the addition it can decrease NH ₃ injection rate can decrease NOx by lowering the ECoO ₂ concentration in these coal, in order to not easily made operated to lower the ECoO ₂ concentration, to lower NH ₃ also efforts to There was therefore no high efficiency operation.

This kind of operation method imports coal from a number of coal-producing areas and burns it in the same furnace from the viewpoint of risk dispersion in a country without resources such as Japan, and at the same time the furnace becomes a large-capacity furnace. In addition, the degree of change in coal type is increasing in relation to the size of the mineral ship, and the demand for improved efficiency is becoming stronger day by day.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention first inputs the fuel ratio and the N content in the fuel among the coal properties that have entered the bunker that has arrived to the computer as input items for control. On the other hand, from the data obtained in the furnace or a similar furnace, the computer calculates (a) NOx (see FIG. 2) correction factor for N content, (b) NOx and unburned content (E) for ECoO ₂ concentration. (See FIG. 4), (c) NOx with respect to fuel ratio (see FIG. 7), and unburned content (see FIG. 3) (d) Relationship between NH ₃ injection rate and denitrification rate (known from the past). Keep it. The smoke outlet NOx value (local regulation value) is known in advance as a control target value, so within the range of the NOx value, ECo
Cost calculation of exhaust gas loss and in-house ratio with respect to O ₂ concentration, EC
Calculation of loss cost (unburned component cost) due to increase of unburned component with respect to oO ₂ concentration and cost calculation for NH ₃ injection rate determined by the NOx value. Then, based on the calculation results, the ECoO ₂ concentration that maximizes the efficiency (minimum loss) is found, and the bias rate is added to the conventional ECoO ₂ concentration program and output as a control signal automatically.
The control described above is performed, for example, with an intelligent jet type NO.
x Control unit.

[Action]

NOx when changing the ECoO ₂ concentration in a pulverized coal combustion furnace,
The behavior of unburned matter in the ash is shown in FIG. First, NOx
Let's take a look at
₂ N generated in the downstream of the burner when the concentration became low
Ox undergoes a reducing action in an air-deficient atmosphere, part of which is reduced to stable N ₂ , and the NOx value decreases. Decrease in NOx
It has the effect of lowering the NH ₃ injection rate in NOx, and also reduces the generation of acid ammonium sulfate in the air preheater and reduces A / H clogging. Next, when the ECoO ₂ concentration of the unburned matter becomes low, the combustion rate decreases due to oxygen deficiency, and therefore the unburned carbon in the unburned matter in the ash still has a calorific value of 8,000 Kcal / kg, for example. Have,
Unburned loss increases with fuel loss.

On the other hand, the air preheater outlet gas temperature is generally low even under low load.
Since it is designed to balance about 130 ° C and about 145 ° C at high load, the higher the ECoO ₂ concentration is, the more the exhaust gas amount increases, and in addition to the dry exhaust gas loss, the air moisture loss also increases, and The power of the high-pressure draft fan and the induction draft fan 6 for transferring the exhaust gas becomes large.

These are very complicatedly involved in multiple variables, and in order to achieve optimization, it is necessary to comprehensively judge the factors of the multiple variables. Since it changes frequently, cost control can be optimized if control is performed using, for example, an intelligent NOx control device.

〔Example〕

A specific embodiment will be described with reference to FIG. The control circuit on the right side of the drawing has the same function and function as those of the prior art (see the left side of FIG. 6). As shown on the left side of the figure,
An intelligent NOx controller is added to the ECoO ₂ control circuit in advance, and then the predictable fuel ratio and N content in coal are input (201). This fuel ratio and N content may be input as a signal as a result of the continuous analyzer,
You may enter it manually. In the NOx controller, for example, NOx and unburned fuel content with respect to the fuel ratio are predicted by a data file or a calculation formula (load static characteristic) (20
2). After that, NOx is corrected by N minutes according to N minutes in the fuel (203). Based on this NOx value, the NH ₃ injection rate can be determined based on the De-NOx characteristics (204). It is judged whether the NOx value in the injection rate is within the limit of the local regulation value (2
05). Within limits, then, NH ₃ injection rate cost, the exhaust gas loss and house index (206) further unburned cost (207)
Is repeatedly calculated in the NOx-limited ECoO ₂ to select the minimum loss value (208). Based on this, the bias rate is added to the O ₂ program control setting value adopted in the conventional technique (209) to obtain the O ₂ concentration. Of course ECoO ₂
The minimum value for furnace safety is given as the lower limit for the concentration.

Thus, using the intelligent NOx controller, NOx
When controlled, the ECoO ₂ concentration set value for the load (although it is impossible unless there is some margin in the NOx characteristics and unburned content characteristics) changes due to different fuels, and is Although it is confusing, when coal other than the high fuel ratio coal, which is the base of the ECoO ₂ concentration, arrives, it becomes possible to lower the ECoO ₂ concentration, thus reducing exhaust gas loss and NH ₃ injection rate. In addition to enabling high-efficiency operation, the conversion rate from SO _{2 to} SO ₃ and the leak NH ₃ are reduced, so NH ₄ (H) SO ₄ (acidic ammonium sulfate) remains as a problem when installing a De-NOx device. The clogging of A / H due to), that is, the rise of draft loss can be reduced.

In addition, the characteristics of the convection heat transfer part when the amount of exhaust gas decreases, which is a concern with a decrease in the concentration of ECoO ₂ , that is, for example, the reheat steam temperature characteristic, the problem that has not been achieved is parallel damper control of exhaust gas and / or exhaust gas recirculation. There is no problem because it can be handled by controlling the gas amount.

NOx concentration in the chimney outlet is a 60 ppm, the future at present the NOx damper NH ₃ injection rate into operated at substantially full open or constant opening De-NOx is considered as the main regulator, ECoO ₂
The reason why NOx control can be proposed is that the high-efficiency and low-NOx burner called NR burner was developed, and there was an answer to some extent between how to use this burner to further improve the efficiency. .

〔The invention's effect〕

According to the present invention, (1) When a fuel other than the high-fuel-ratio coal, which is the base for setting the ECoO ₂ concentration (NOx, unburned matter) among the various types of coal, is received, the low ECoO ₂ concentration operation is performed. Since this is possible, the most efficient operation is possible.

(2) As the ECoO ₂ concentration decreases, A / H clogging due to acidic ammonium sulfate can be reduced, and running costs as well as maintenance phi can be reduced.

(3) Since the optimum ECoO ₂ concentration can be calculated in the control device when performing one-man control for multiple coals,
Ideal for labor-saving plants.

[Brief description of drawings]

FIG. 1 shows an intelligent control device according to the present invention, and FIG. 2 shows a burner air ratio and a fuel ratio which are substantially constant.
NOx characteristic diagram when N minute is changed, Fig. 3 is O ₂ constant, unburned component characteristic diagram when the fuel ratio is changed, and Fig. 4 is an unburned component and NOx characteristic diagram when O _{2 is} changed, 5th The figure shows an example of a conventional boiler system, FIG. 6 shows a conventional combustion air amount control system, and FIG. 7 shows when the N content in the fuel is almost the same and the fuel ratio changes. 3 is a NOx characteristic diagram of FIG.

Claims (1)

[Claims] 1. A control for controlling NOx in flue gas within a regulated value in a combustion furnace in which multiple types of coal having different fuel ratios (fixed carbon / volatile matter) and N content in fuel are burned in the same furnace. By inputting the fuel ratio of the coal to be used from now on and the N content in the fuel in advance to the circuit, the efficiency calculation based on the load static characteristic can be calculated in the exhaust gas O ₂ (ECoO
₂ ) Calculated from factors such as concentration, unburned content in ash, and NH ₃ injection amount, find the ECoO ₂ concentration that maximizes efficiency, output it, and automatically control the combustion air amount based on that concentration Therefore, a high-efficiency NOx control method characterized by setting a control circuit for controlling NOx.