JPH0637972B2 - Combustion control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a naturally ventilated combustion control device for various heating furnaces, etc., and particularly has a high combustion efficiency even in an excessive state such as load change. A combustion control device that can be maintained.

(Prior Art) This type of combustion control device is required to save energy and improve pollution prevention. The former objective is to reduce the combustion cost by supplying the required amount of air and performing complete combustion to improve the combustion efficiency. The latter objective is to prevent black smoke, that is, the amount of NOx and SOx generated. The aim is to reduce environmental pollution as much as possible. Therefore, in order to satisfy the above two requirements, it is necessary to control the air-fuel ratio to a predetermined value not only in a steady state but also in a transient state such as load change or set value change.

By the way, in the conventional natural ventilation combustion control device, the pressure inside the furnace is controlled to a predetermined value independently of the fuel flow rate, or a specific function operation is performed on the fuel command value to set the pressure inside the furnace. After obtaining the value, there is a method in which the furnace pressure is controlled so as to reach the furnace pressure set value. Therefore, all of these combustion control devices regard the load as constant and perform combustion control without considering the state of load change or the like.

(Problems to be Solved by the Invention) However, the conventional device as described above does not have a problem if the load is always constant, but is empty in the case of an excessive state due to load change or setting value change. The fuel ratio fluctuates greatly, resulting in a reduction in combustion efficiency, causing pollution, and exposing a fatal defect in the combustion system. In particular, in recent years, it is necessary to manufacture the required products in the required quality in the required amount, and to automate the start and stop, and it is inevitable that the load will become more and more fluctuating. In this case, the conventional device as described above cannot cope with the problem at all.

The present invention has been made in view of the above circumstances, and a combustion control device that can sufficiently improve the combustion efficiency by coping with it even in an excessive state due to load change, and can reduce the generation of pollution-causing substances. The purpose is to provide.

[Composition of the Invention] (Means for Solving Problems) A combustion control device according to the present invention includes an adjusting means for detecting a combustion control amount and obtaining a fuel flow rate command signal based on the detected combustion control amount; A first limiting means having at least an upper limit associated with the output of the pressure gauge for limiting the command signal from the adjusting means, and at least a lower limit intended with respect to the output of the fuel flow meter, Second limiting means for limiting the command signal from the adjusting means; fuel flow rate control means for controlling the fuel flow rate operation end by receiving the output of the first limiting means and the output of the fuel flow meter; In the furnace for controlling the in-reactor pressure operating end by obtaining the in-reactor pressure set value required to discharge the total amount of exhaust gas from the output of the limiting means, and receiving the in-reactor pressure set value and the output of the in-reactor pressure gauge. And a pressure control means.

(Operation) Therefore, according to the present invention, by adopting the above-mentioned means, the coefficient (1
+ K ₁ ) as the upper limit, and the coefficient (1-
The lower limit is set to a value obtained by multiplying by k ₂ ) and the fuel flow rate control means controls the fuel flow rate with the limited fuel flow rate command signal as a set value. On the other hand, regarding the total exhaust gas flow rate, the lower limit is a value obtained by multiplying the fuel flow rate command signal by the output of the fuel flow meter by a coefficient (1 + k ₃ ), and the upper limit is a value obtained by multiplying the coefficient (1 + k ₄ ). Then, the total exhaust gas flow rate signal is obtained from this limited fuel flow rate command signal, and the differential pressure necessary to discharge this total exhaust gas flow rate is obtained.
This is used as a set value for the pressure in the furnace to control the pressure in the furnace.

(Embodiment) An embodiment of the device of the present invention will be described below with reference to FIG. In the figure, 1 is a combustion furnace, and a material pipe 2 to be heated is provided in the furnace. Further, the combustion furnace 1 is provided with a burner 3 to which fuel is supplied from a fuel pipe 4 via a fuel flow meter 5 and a fuel flow rate control valve 6 forming a fuel flow rate operation end, and an opening degree of a damper 7 is adjusted. As a result, air is naturally sucked from around the burner 3. Reference numeral 8 denotes a temperature detector that detects the combustion furnace outlet temperature of the raw material, which is a controlled variable of the combustion furnace 1. When the combustion furnace 1 is applied to a boiler, the control amount may be steam pressure or steam flow rate.

The output of the temperature detector 8 is introduced into the temperature adjusting means 9. The temperature adjusting means 9 compares the combustion furnace outlet temperature from the temperature detector 8 with a temperature target value and performs an adjustment calculation to obtain a fuel flow rate command signal A, that is, a master signal of a combustion amount command.
Then, the fuel flow rate command signal is supplied to the first and second limiting means 10 and 11, respectively. The first limiting means 10 is composed of low-order signal selecting means 10a, high-order signal selecting means 10b, coefficient means 10c, 10d, etc.,
Here, the fuel flow rate set value is obtained and sent to the fuel flow rate control means. This fuel flow rate control means is the fuel flow rate control means 12
The fuel flow rate setting value is compared with the output of the fuel flow meter 5 to obtain the operation output of the fuel flow rate. The second limiting means 11 is composed of high-order signal selecting means 11a, low-order signal selecting means 11b, coefficient means 11c, 11d, etc., and the signal selected here is sent to the multiplying means 13. Reference numeral 14 is a multiplying means, and 15 is a furnace pressure adjusting means configured as a furnace pressure control means. 16 is a unit total exhaust gas amount calculation means, 17 is a furnace pressure gauge, 18 is a square root calculation means,
Reference numeral 19 is a dividing means.

Next, the operation of the apparatus configured as described above will be described.
The output of the temperature detector 8 which is the controlled variable of the combustion furnace 1 is introduced into the temperature adjusting means 9, where it is compared with the fuel flow rate target quantity to obtain the fuel flow rate command signal A, and passed through the first limiting means 10. It is provided to the fuel flow rate adjusting means 12. The fuel flow rate adjusting means 12 uses the output of the first limiting means 10 as a target value, performs comparison adjustment calculation by using the output signal of the fuel flow meter 5 as a footback signal, and changes the opening degree of the fuel flow rate adjusting valve 6. Control the fuel flow rate.

On the other hand, the fuel flow rate command signal A which is the output of the temperature control means 9
Are introduced into the second limiting means 11. In the second restriction means 11, the coefficient of the coefficient unit 11c corresponding to the high signal selecting means 11a _{(1-k 3),} defined as _k 3> 0, and the coefficient unit 11d corresponding to the lower signal selecting means 11b
The coefficient of (1 + k ₄ ), k ₄ > 0 is defined, and each coefficient means 1
1c, when the Ff input signals to 11d, each coefficient unit 11c, from _{11d E = (1-k 3} ) · Ff ...... (1) G = (1 + k 4) · Ff ...... (2) becomes Output E and G are taken out. Therefore, the low-order signal selection means 11b compares the signals A and G and selects and outputs the low-level signal of the two signals, while the high-order signal selection means 11 is selected.
In a, the low-order selection signal and the signal E are compared, and the high-level signal of both is selected and output.

In this way, the signal H selected by the second limiting means 11
Is given to the multiplication means 13. In this multiplication means 13,
Unit exhaust gas amount for fuel is G ₀ , unit theoretical air amount is A
₀ , the set excess air ratio is μs, the coefficient is β, and the unit total exhaust gas amount is fds, K = β · fds = β [G ₀ + (μs-1) A ₀ ] from the unit total exhaust gas amount calculation means 16. The following calculation output K is supplied. Therefore, the multiplication means 1
3 multiplies the output H of the second limiting means 11 and the output K of the unit total exhaust gas amount calculating means 16 to obtain a signal β · Fds proportional to the total exhaust gas flow rate set value signal Fds.

K · H = β · fds · H = β · Fds Then, the signal β · Fds proportional to the total exhaust gas flow rate setting value signal Fds is introduced into the multiplying means 14, where it is squared to obtain the furnace internal pressure setting value signal Ps. Obtained and supplied to the in-furnace pressure adjusting means 15.

Here, the relationship between the total exhaust gas flow rate setting value signal Fds and the furnace internal pressure setting value signal Ps is Becomes Here, Fds is represented by the following formula.

Fds = fds · H = {G ₀ + (μs−1) A ₀ } · H (4) By substituting this equation (4) into the equation (3), it is represented by Ps = β ² {G + (μs−1) A ₀ } ² · H ² (5). Here, β is a range correction coefficient, and β = Ff (max) / Fd (max). Ff (max) is the maximum fuel flow rate, Fd (m
ax) is the exhaust gas flow rate at the maximum furnace pressure range. Here, when the expressions (1), (2), and (5) and the operation of the second control means 11 are superposed, (a) when E <A <G, H = A, and Ps = [ β {G ₀ + (μs-1) A ₀ } · A] ² ......
(6) (b) When A ≦ E, H = E = (1-k ₃ ) · Ff, and Ps = [β {G ₀ + (μs−1) A ₀ } · (1-k ₃ ) · Ff ] ² (7) (C) When G ≦ A, H = G = (1-k ₄ ) · Ff, and Ps = [β {G ₀ + (μs−1) A ₀ } · (1-k ₄ ) · Ff] ² (8), and the in-reactor pressure setting signal Ps is limited by the upper limit G and the lower limit E proportional to the fuel flow rate Ff. The in-furnace pressure setting signal Ps thus limited is introduced into the in-furnace pressure adjusting means 15. The in-furnace pressure adjusting means 15 uses the in-reactor pressure setting signal Ps as a target value, and uses the output signal P of the in-reactor pressure gauge 17 as a feedback signal to perform a comparative adjustment calculation to change the opening degree of the damper 7 to change the in-reactor pressure. To control.

Next, the fuel flow rate control system will be described. Furnace pressure gauge 17
Theoretical fuel flow rate Ffp from measured reactor pressure P detected by
And ask It is represented by. Therefore, the square root calculation means 18 calculates the detected pressure P detected by the in-furnace pressure gauge 17 according to the equation (9).
After square rooting at, and leading to the dividing means 19 and dividing by the output K of the unit total exhaust gas amount calculating means 16, Is obtained, which is the same as equation (9) and the estimated fuel flow rate F
fp can be calculated.

Then, the estimated fuel flow rate F obtained as described above
fp is sent to the first limiting means 10. The first limiting means 10 sets the coefficient of the coefficient means 10c corresponding to the low-order signal selecting means 10a to (1-k ₁ ), k ₁ > 0, and the coefficient means 10d corresponding to the high-order signal selecting means 10b.
If the coefficients of (1−k ₂ ), k ₂ > 0 are set, then B = (1 + k ₁ ) · Ffp (11) C = (1-k ₂ ) · Ffp from each coefficient means 10c and 10d. (12) is output. Therefore, the high-order signal selection means 10b compares the signals A and C and selects and outputs the high-level signal of both. Further, the low-order signal selecting means 10a compares the higher signal with B and selects and outputs the low-level signal of the both. That is, (a) when C <A <B, Fs = A (b) when B <A, Fs = B (c) when A <C, Fs = C is selected. This indicates that the fuel flow rate command signal A is limited by the predetermined upper limit B and lower limit C. Here, Ffp in B and C indicates the theoretical fuel flow rate calculated from the pressure in the furnace, which means that the fuel flow rate command signal A is limited within a predetermined upper and lower limit with respect to the theoretical fuel flow rate.

FIG. 2 shows the magnitude relationship between the fuel flow rate command signal A and the signals of the respective parts of the limiting means 10 and 11 in the steady state. In this state, the first limiting means 10 and the second limiting means 11 indicate that the fuel flow rate command signal A is selected.

Next, let us consider how the excess air ratio μ becomes excessive. Now, the fuel flow rate set value signal Fs is expressed by equation (11),
By the equation (12) and the operation of the first limiting means 10, C ≦ Fs ≦ B, that is, (1-k ₂ ) · Ffp ≦ Fs ≦ (1 + k ₁ ) · Ffp.
It can be expressed as (13). Then, by substituting the relations of Ffp · A ₀ · μs = Fa and Fs · A ₀ · μ = Fa into the equation (13), {(1-k ₂ ) / μs} ≦ 1 / μ ≦ {(1 + k ₁ ) / μs}, which is transformed into {μs / (1 + k ₁ )} ≦ μ ≦ {μs / (1-k ₂ )}. Here, assuming k ₁ << 1, k ₂ << 1, {(1-k ₁ ) μs} ≦ μ ≦ {(1 + k ₂ ) μs} ...
(14) That is, the excess air ratio μ is set to (1−k ₁ ) times the set excess air ratio μs by the first limiting means 10.
+ K ₂ ) times the range.

Next, the operation of the second limiting means 11 will be described.
Now, by the expressions (1) and (2) and the operation of the second limiting means 11, the output H of the second limiting means 11 is from E ≦ H ≦ G to (1-k ₂ ) · Ff ≦ H ≦ (1 + k ₄ ) · Ff …… (1
5) is represented. Therefore, when the exhaust gas amount corresponding to (15) is calculated, the unit total exhaust gas amount for the fuel flow rate Ff = G ₀
+ (Μs−1) A ₀ , the total exhaust gas flow rate for varying H = {G ₀ + (μ−1) A ₀ } · Ff. Therefore, substituting these formulas into the formula (15) gives (1) −k ₃ ) · {G ₀ + (μs−1) A ₀ } · Ff ≦
{G ₀ + (μ-1) A ₀ } · Ff ≦ (1-k ₄ ) · {G
₀ + (μs−1) A ₀ } · Ff can be obtained. When this equation is modified, μs−k ₃ {(G ₀ / A ₀ ) + μs−1} ≦ μ ≦ μs +
k ₄ {(G ₀ / A ₀ ) + μs−1)} (16). Here, with heavy oil or propane, G ₀ / A
_Since it becomes ₀ 1, the formula (16) is expressed by (1-k ₃ ) μs ≦ μ ≦ (1 + k ₄ ) · μs (1
7) That is, the excess air ratio μ is set to (1−k ₃ ) times the set excess air ratio μs by the second limiting means 11 to (1
It will be confined in the range of + k ₄ ) times.

Fig. 3 is based on the above examination. Fig. 1, that is, (14)
In equations (17), k ₁ = k ₃ and k ₂ = k _4, and changes in the excess air ratio μ with respect to time when the response of the fuel supply system is slightly faster than that of the air supply system are shown. That is, in the steady state, the excess air ratio is limited to μs, but when the fuel flow rate command signal A sharply increases at time t ₁ due to a sudden change in the set value or a sudden change in the load, the excess air ratio becomes (μ
sk ₁ · μs), and after a while, returns to the steady state. If the fuel flow rate command signal A is suddenly reduced at time t ₂ , the excess air ratio μ is excessively (μs + k ₂ · μ).
s), and after a while, returns to the steady state again. That is, the excess air ratio μ is (1-k ₁ ) · μs ≦ μ ≦ (1 + k ₂ ) · μs ... (1
It is limited to the range of 8).

Therefore, according to the configuration of the above embodiment, the in-reactor pressure gauge 17 is responsive to the fuel flow rate command signal A from the adjusting means 9.
Coefficient (1 + k ₁ ) to the allowable fuel flow rate signal obtained from the output of
The upper limit is the value obtained by multiplying by, and the lower limit is the value obtained by multiplying by the coefficient (1-k ₂ ), and the fuel flow rate control means sets the fuel flow rate with the limited fuel flow rate command signal as a set value. On the other hand, for the total exhaust gas flow rate, the lower limit is a value obtained by multiplying the fuel flow rate command signal A by the output of the fuel flow meter 5 by a coefficient (1-k ₃ ), and the coefficient (1 + k ₄ ).
Add a limit to the value multiplied by, obtain the total exhaust gas flow rate signal from this limited fuel flow rate command signal, obtain the differential pressure required to discharge this total exhaust gas flow rate, and set this to the reactor pressure setting value. Since the furnace pressure is controlled as described above, the excess air ratio μ is controlled not only in the steady state but also in the following range with respect to the set excess air ratio μs at all times. That is, if k ₁ = k ₃ and k ₂ = k ₄ , then μs−k ₁ {μs + (G ₀ / A ₀ ) −1} ≦ μ ≦ μs +
k ₂ {μs (G ₀ / A ₀ ) −1} (19), and generally k ₁ to k ₄ are 0.03 to
If it is set to about 0.05 (3 to 5%), G ₀ / A ₀ 1 for heavy oil, propane, etc., so that the equation (19) is μs (1-k ₁ ) ≦ μ ≦ μs (1 + k ₂ ). It can be approximated by (20), and by setting k ₁ to k ₄ , the excess air ratio μ can be suppressed within a very narrow range regardless of process conditions, and combustion efficiency Energy conservation and pollution prevention can be achieved by improving

In the above embodiment, the set excess air ratio μs is described as a constant value. However, this may be corrected by the combustion amount, exhaust gas O ₂ control, and exhaust gas CO control signals, and calculation processing may be performed using the corrected excess air ratio. Good. In this way, more advanced combustion control can be realized. Further, both the first limiting means 10 and the second limiting means 11 are configured to limit both the upper limit and the lower limit, but in the case where only the basic condition that black smoke is not generated when the load changes is satisfied, for example. In addition, the first limiting means 10 may have a planned upper limit limiting function related to the output of the in-core pressure gauge 17, and the second limiting means 11 may have a planned lower limit limiting related to the output of the fuel flow meter 5. You just have to have a function. In addition, the present invention can be modified in various ways without departing from the scope of the invention.

[Advantages of the Invention] As described in detail above, according to the present invention, the excess air ratio can always be controlled within the predetermined upper and lower limits, so that the combustion efficiency can be improved even when there is a load change. It is possible to provide a natural ventilation combustion control device that can realize safe combustion without the risk of pollution and without any accidental fire.

[Brief description of drawings]

1 to 3 are shown for explaining one embodiment of a combustion control device according to the present invention. FIG. 1 is a block diagram of the device of the present invention, and FIG. 2 is a fuel flow rate command signal and FIG. 3 is a diagram showing a magnitude relationship between signals of respective parts of the first and second limiting means, and FIG. 3 is an explanatory diagram showing a change in excess air ratio with time. 1 ... Combustion furnace, 3 ... Burner, 4 ... Fuel pipe, 5 ...
… Fuel flow meter, 6… Fuel flow control valve, 7… Damper,
8 ... Temperature detector, 9 ... Temperature adjusting means, 10 ... First
Limiting means, 11 ... second limiting means, 12 ... fuel flow rate adjusting means, 13,14 ... multiplying means, 15 ... reactor pressure adjusting means, 16 ... unit total exhaust gas amount calculating means, 17 ...
... furnace pressure gauge, 18 ... square root calculation means, 19 ... division means, 10b, 11a ... high level signal selection means, 10a, 1
1b ... Low-order signal selection means, 10c, 10d, 11c,
11d ... Coefficient means.

Claims (1)

[Claims] 1. A combustion control device comprising a fuel supply system having a fuel flow meter and a fuel flow operating end, and an exhaust gas exhaust system having an in-reactor pressure gauge and an in-reactor pressure operating end. Adjusting means for obtaining a fuel flow rate command signal based on the detected combustion control amount, and first limiting means for limiting the command signal from the adjusting means having at least a predetermined upper limit related to the output of the in-core pressure gauge. And second limiting means for limiting a command signal from the adjusting means, the second limiting means having at least a predetermined lower limit related to the output of the fuel flow meter, the output of the first limiting means and the fuel flow meter. A fuel flow rate control means for receiving the output to control the fuel flow rate control end, and a reactor internal pressure set value necessary for discharging the total amount of exhaust gas are obtained from the output of the second limiting means, and the reactor internal pressure set value Receives the output of the furnace pressure gauge And a furnace pressure control means for controlling the furnace pressure operating end.