JPH0251089B2 - - Google Patents

Description

Detailed Description of the Invention <Related Technical Field> The present invention is directed to a combustion control device for mixed gas, which is often used in hot stoves and the like in steel plants. The present invention relates to a combustion control device for preferentially using a gas with fluctuations in temperature as a mixed gas.

<Prior art> The gases used as fuel in hot blast stoves (hereinafter referred to as furnaces) in steel plants are generally coke oven gas (hereinafter referred to as COG), blast furnace gas (hereinafter referred to as COG), etc.
A mixed gas (called BFG) is used. Since these gases are supplied via a gas holder, they can be supplied continuously and their calorific value is relatively stable. Therefore, to control the flow rate of these gases, the output of the mixed gas flow controller, which uses the furnace temperature controller output as the set value, is used as a master signal, and this is passed through the ratio setting device as the set value of each gas flow controller. Furthermore, the air flow rate supplied to the furnace is realized by a combustion control device with a relatively simple basic configuration, which uses the output of the temperature controller as a set value and controls the air flow rate through an appropriate air-fuel ratio setting means. ing.

By the way, in addition to the above-mentioned COG and BFG, the gases generated in steel plants include converter gas (hereinafter referred to as LDG), which is generated in batches from the converter. Because the quantity fluctuates widely, it is rarely used as fuel and most of it is discarded.

<Objective of the present invention> However, in order to save energy in the entire plant and reduce total equipment costs, it is necessary to effectively use this batchwise generated converter gas as fuel for a continuous combustion control device. This is desirable.

The present invention provides combustion control that mixes this batchwise generated gas into continuously supplied gas to utilize as much of it as possible without affecting the load as much as possible and without requiring the installation of new gas holders. The purpose is to provide equipment.

<Summary of the Invention> The structural feature of the device of the present invention is that a first gas that is continuously supplied and has a stable calorific value is mixed with a second gas that is generated in batches and has a fluctuating calorific value. and a combustion control device in which the ratio of the flow rate controllers for the first gas and the second gas is set using the output of the flow rate controller for the mixed gas as a master signal, Predict setting signals to the first and second gas flow rate controllers so that the calorific value of the mixed gas does not fluctuate based on the flow rate signal and the calorific value signals of the first and second gases. The present invention comprises a feed forward means for calculating, and a feedback means for comparing the calorific value signal of the mixed gas with the calorific value set value and periodically correcting the output of the feed forward means. .

<Example> Fig. 1 is a block diagram showing one implementation row of the present invention, Fig. 2
The figure is an explanatory diagram showing changes in the flow rate and calorific value of each gas,
FIGS. 3 and 4 are flowcharts showing the signal processing procedure of the feed forward means and feedback means which constitute the main part of the present invention.

In FIG. 1, 1 is a supply source of COG, 2 is a gas holder thereof, 3 is a supply branch pipe, 4 is a supply source of BFG, 5 is a gas holder, and 6 is a supply branch pipe. COG and BFG can be continuously supplied to each branch pipe 3, 6, and form a first gas whose calorific value is approximately constant. 7 is the supply source of LDG, and 8 is its supply branch pipe. This gas does not have a gas holder and is supplied to the branch pipe 8 in batches, forming a second gas whose calorific value also changes with time. .

In Fig. 2, A and A' are the flow rate and calorific value showing an _example of LDG production. Period T ₂ ,
Third period T ₃ of 10-15 minutes, fourth period T ₄ of 15-25 minutes, 25
When divided into the fifth period T ₅ of ~40 minutes, the first period T ₁ and the fifth period T ₅ are zero, and the second period T ₂ is 20000Nm ³ /h,
40000Nm ³ /h in the third stage T ₃ , and in the fourth stage T ₄
Approximately 23,000Nm ³ /h (shown in parentheses) is generated, but excluding the amount consumed by other equipment, the amount is 5,800Nm ³ /h in the second period, 11,600Nm 3 /h in the third period, and 11,600Nm ³ /h in the fourth period. Approximately 6670Nm ³ /h is available surplus gas. The calorific value q _L of this gas is 1000 kcal/Nm ³ in the second period T ₂ as shown in A', but
In the third period T ₃ and the fourth period T ₄ , it fluctuates greatly to 2300 kcal/Nm ³ .

On the other hand, the calorific value Q _B of BFG is almost constant at 650 kcal/Nm ³ as shown in Figure 3 B', and the calorific value Q _C of COG is 4134 kcal/Nm3 as shown in Figure 3 C'.
It is almost constant at ^Nm3 .

A main pipe 9 is supplied with a mixed gas of the branch pipes 3, 6, and 8, and the mixed gas is supplied to the combustion furnace 10. Reference numeral 11 denotes an air supply source, which is supplied to the combustion furnace 10 together with the mixed gas through an air pipe 12. 13 is the temperature sensor of the combustion furnace, and 14 is the output of this sensor.
The temperature controller receives the PV value, and the SV is the temperature setpoint. Reference numeral 15 denotes a flow rate controller that receives the output of the temperature controller as a mixed gas flow rate set value F _M. 16
is a differential pressure flow meter that measures the flow rate of mixed gas, 17
18 is a temperature/pressure corrector, 19 is a mixed gas temperature sensor, and 20 is also a mixed gas pressure sensor, and the outputs of these sensors are given to the temperature/pressure corrector 18. There is. 2
1 is a specific gravity corrector, which outputs specific gravity signals ρ _C , ρ _B , ρ _L for each gas.
Then, the specific gravity correction is executed using the signal ρ _M from the calculation unit that calculates the specific gravity of the mixed gas based on the flow rate set value of each gas (described later), and the flow rate f _M in the standard state of the mixed gas is sent to the flow rate controller 15 PV. Supply as value.
23 is a calorimeter that measures the calorific value q _M of the mixed gas.

24 is a differential pressure flowmeter that measures the COG flow rate;
25 is an arithmetic unit for square rooting the output, and 26 is a temperature/
The pressure compensator 27 is a COG temperature sensor, and 28 is a COG pressure sensor, and the outputs of these sensors are given to the temperature/pressure compensator 26. 2
9 is a specific gravity corrector, which receives the output ρ _C of the specific gravity sensor 30 and executes specific gravity correction to calculate the COG in the standard state.
The flow rate f _C of is transmitted as the PV value of the flow rate controller 31 of the COG. 32 is driven by the output of this controller
This is a COG flow control valve.

33 is a differential pressure flowmeter that measures the flow rate of BFG,
34 is an arithmetic unit for square rooting the output, and 35 is a temperature/
The pressure compensator 36 is a BFG temperature sensor, 37 is a BFG pressure sensor, and the outputs of these sensors are given to the temperature/pressure compensator 35. 3
8 is a specific gravity corrector, which receives the output ρ _B of the specific gravity sensor 39 and performs specific gravity correction, and calculates the BFG in the standard state.
The flow rate f _{B of} is transmitted as the PV value of the flow rate controller 40 of the BFG. 41 is driven by the output of this controller
This is a BFG flow control valve.

42 is a differential pressure flow meter that measures the flow rate of LDG;
43 is an arithmetic unit for square rooting the output, and 44 is a temperature/
The pressure compensator 45 is a temperature sensor of LDG, 45 is a pressure sensor of LDG as well, and the outputs of these sensors are given to the temperature/pressure compensator 44. 4
7 is a specific gravity corrector, which receives the output ρ _L of the specific gravity sensor 48 and performs specific gravity correction to determine the LDG in the standard state.
The flow rate f _L is transmitted as the PV value of the flow rate controller 49 of the LDG. 50 is driven by the output of this controller
This is an LDG flow control valve. 51 is the calorific value of LDG
q It is a calorimeter that measures _L.

The outputs ρ _C , ρ _B , ρ _L of the specific gravity sensors 30, 39, 48 for each gas are supplied to the specific gravity corrector for the flow rate signal of each gas, and the specific gravity ρ _M of the mixed gas is calculated in advance and the specific gravity is The mixed gas specific gravity calculator 22 is supplied to the corrector 21 . Furthermore, COG,
For BFG, specific gravity correction can be omitted if it is thought that there is little variation in gas components. Furthermore, if the calorimeters 23 and 51 include a differential pressure type flow rate measurement section, density correction is also required for this flow rate measurement output.

Since COG and BFG are primary gases with stable calorific values, a calorimeter is not provided to measure the calorific values, and the calorific values are set at known set values Q _C , respectively.
Q _B is used.

A dotted line block 52 is a flow rate setting calculation section for each gas which is the main part of the present invention, and includes a feedforward calculation section 521 and a feedback calculation section 522.
It becomes more. The feed forward calculation section includes a second
The flow rate signal f _L of the gas LDG, the calorific value signal q _L , the known calorific value signals Q _C and Q _B of the first gas, and the master signal MV which is the output of the mixed gas flow rate controller 15 are input, and the COG, BFG , LDG flow rate set value F _C , F _B ,
F _L and its coefficients K _C , K _B , K _L are calculated, and K _C・F _C
is the set value of COG flow controller 31 as K _B・F _B
is the setting value of the BFG flow rate controller 40, _KL・
F _L is supplied as a set value to the flow rate controller 49 of the LDG.

The feedback calculation unit 522 is given the mixed gas calorific value signal q _M and the manually set target value Q _M , and calculates the coefficient K _C of the feedback circuit,
Correct K _B and K _L periodically.

Next, the operation of the apparatus of the present invention will be explained.

As much as possible (preferably all) of the batchwise generated second gas is used to mix it with the first gas and combust it, and in addition, the first gas is In order to change the flow rate setting of the second gas, it is necessary to keep the theoretical combustion gas amount G ₀ (combustion gas amount when combustion is performed with the theoretical air amount) or the theoretical air amount A ₀ constant.

Here, it is difficult to make the theoretical air amount A ₀ completely constant by changing only the mixing ratio of the mixed gas, but according to the ROSIN formula, the calorific value per unit volume is Q (kcal/Nm ³ ), then A ₀ =0.875/1000・Q Nm ³ /Nm ³ (Q=500
~3000kcal/ ^Nm3 )(1) A ₀ =1.09/1000・Q~ ^0.25Nm3 / ^Nm3 (Q=4
It is said that it can be approximated by 000 to 7000kcal/Nm ³ )(2). This means that if the calorific value per unit volume is constant, the theoretical air amount A ₀ is also approximately constant.

Focusing on this characteristic, the present invention has developed a set value for each gas flow rate so as to consume as much of the second gas as possible while keeping the calorific value per unit volume of the mixed gas constant, without using complicated calculations or additional equipment. change.

First, the setting of each gas flow rate by feedforward calculation will be explained. Now α, β, and γ are respectively
When LDG, BFG, and COG have their own constants, the calorific value q _M of the mixed gas is: q _M = αq _L + βQ _B + γQ _C (3) α + β + γ = 1 (4) Also, the flow rate setting of gases LDG, BFG, and COG The values are expressed as F _L = αF _M (5) F _B = βF _M (6) F _C = γF _M (7). Here, F _M is a value corresponding to the operation output value MV of the temperature controller 14.

First, assuming that the second gas LDG given in batches is completely consumed, the LDG flow rate signal f _L and
Calculating α from F _M , α=f _L /F _M (8) Based on this tentatively determined α, calculating γ from equations (3) and (4), γ=q _M −Q _B +α(Q _B −q _L )/Q _C −Q _B (9). If the result of equation (9) is negative, γ=0. Therefore, at this time, the COG flow rate set value F _C is F _C =γF _M =0 (10). Then, by substituting this result into equations (3) and (4), α
When calculated, α=q _M +Q _B /q _L +Q _B (11) From this, the flow rate setting value F _L of LDG is F _L = α・F _M = q _M +Q _B /q _L +Q _B・F _M (12). Next, since F _C and f _L are known, the flow rate setting value F _{B of the BFG is determined as F B =} F _M − F _C − f _L (13).

If the calculation result of equation (9) is positive, α of equation (8),
With γ in equation (9), F _L = α・F _M = f _L (14) F _C = γ・F _M = q _M −Q _B +α(Q _B −q _L )/Q _C −Q _B (15 ) F _B = F _M −F _C −f _L (16) The set value of each flow rate can be determined.

In this way, α is temporarily determined on the assumption that all the second gas is used, and α is recalculated with γ = 0, that is, the COG of the first gas is set to zero, according to the polarity of γ calculated as a result. Finally, calculate β, and γ>0
That is, when COG is required, β is determined by using the initially determined γ as is.

In other words, if the flow rate or calorific value of the second gas that is generated in batches is large, even if the COG of the first gas is set to zero, it is still necessary to reduce the set value of the second gas, and there are cases where it is not possible to consume all of the gas. occurs. In this case, the surplus gas will be used for other purposes or will be discarded if no gas holder is provided.

The values of F _C , F _L , and F _B calculated by the feed forward calculation unit 521 are the results of using the value of the output q _L of the calorimeter 51, which has a large dead time and response speed. The set value is not necessarily the optimum value that keeps the calorific value of the mixed gas constant. A gas calorimeter generally used as a calorimeter has a dead time of about 27 seconds and a time constant of about 45 seconds, and the time required for 99% response is about 4 minutes. Therefore, in operation using the set values calculated using equations (3) to (16),
q _M may deviate from a constant value. Therefore, the calorific value q _M of the mixed gas and the manually set constant target value Q _M are compared at regular intervals, and when the difference exceeds a certain value, each gas calculated by the feed forward calculation section Another feature of the present invention is that a feedback calculation section 522 is provided for correcting the flow rate setting value.

The values actually supplied as set values to each flow rate controller are the values K C, F _C , F _L , and F _C multiplied by the coefficients _{K C} , K _L , _{and K B.} Supply K _B and F _B as set values. In the initial setting, K _C = K _L = K _B = 1,
From the next correction cycle, the above coefficients are corrected using the output of the feedback calculation means. For simplicity, K _L = 1
An example will be explained in which K _C and K _B are fixed and changed.

The feed forward and feedback calculating section is executed by software at a constant program cycle using a computer. The coefficients K _C and K _B are changed when the difference between the previous setting value and the current setting value is greater than a certain value, that is, |F ⁿ _C −F ^n-1 _C |>ε _C (17) | When F ⁿ _B −F ^n-1 _B |>ε _B (18), changes in K _C and K _B are executed.

Calculation of K _C and K _B is performed as follows.
When equations (3) to (12) are used as the calculation formulas for the previous calculation cycle, and the constants in the current calculation cycle are α', β', and γ', the following relational expression holds true.

q _M = α′q _L +β′Q _B +γ′Q _C (19) α′+β′+γ′=1 (20) α=α′ (21) From this relational expression, β′ and γ′ can be calculated using the same method as above. Calculate and let the ratio of the previous β and γ be the current coefficients K _B and K _C.

That is, K _B = β'/β (22) K _C = γ'/γ (23) Judgment results of equations (17) and (18), |F ⁿ _C −F ^n-1 _C |<
If ε _C or |F ⁿ _B −F ^n-1 _B | < ε _B , the coefficient K _B
Or, the correction of K _C is not executed.

FIG. 3 is a flowchart when the above-described feed forward and feedback calculations are processed by software.

The coefficients K _B and K _C are corrected based on the determination results of equations (17) and (18), but on the other hand, the change in the calorific value q _M of the mixed gas from the set value Q _M | q _M −Q _M | is monitored, and when |q _M −Q _M | > ε _M is established, a timer that takes dead time and time constant into account is started, and when the timer counts up, |q _M −Q _M | is further restarted. When ｜q _M −Q _M ｜＞ε _M holds true, K _B , K _C
I am trying to perform the following calculations.

FIG. 4 is a flowchart when this process is executed by software.

That is, |q _M −Q _M | exceeds a certain value, and |F ⁿ _B −
When F ^n-1 _B | or |F ⁿ _C −F ^n-1 _C | exceeds a certain value, the coefficients K _B and K _C are corrected by feedback calculation. In the above modification, the coefficient K _L was always set to 1 for simplicity, but it is also possible to include this K _L in the modification.

Next, an example of operation to which the present invention is applied will be briefly explained with reference to FIG. First, in the first period _T1 , as shown in A, the production of the second gas LDG is zero, and as shown in B and B', the flow rate of BFG is 21400Nm ³ /h, the calorific value is 650kcal/Nm ³ , and the amount of COG As shown in C and C', the flow rate is 2640Nm ³ /h, the calorific value is 4134kcal/Nm ³ , and the mixed gas flow rate f _M of both is as shown in D and D'.
24000Nm ³ /h, calorific value is 21400/24000×650＋2640/24000×4134≒1033kcal/N
m ³ , and manually set this as the constant calorific value Q _M. Next, in the second period _T2 , LDG is generated at 5800Nm ³ /h and its calorific value is 1000kcal/Nm ³ . Assuming that all this gas is used, α=5800/24000, and q _M
BFG, COG so that = Q _M = 1033kcal/Nm ³
Calculating the setting value of BFG is F _B = 16144Nm ³ /
h, COG is F _C =2056Nm ³ /h. 3rd period T ₃
In the fourth period T ₄ , the amount of LDG produced and the amount of heat generated increase, so the value of γ will be negative in calculations using all of the generated LDG. LDG as a result of recalculation
The flow rate setting value F _L of BFG is 5571Nm ³ /h, and the flow rate setting value F _B of BFG is 18430Nm ³ /h. In order to make q _M and Q _M the same, during this period T ₃ and T ₄ , LDG shown by the dotted line
Since the gas cannot be completely consumed, it must be disposed of appropriately, and if a gas holder is not provided, it will be discarded.
Next, in the fifth period _T5 , the generation of LDG becomes zero again, so the flow rate set values F _B and F _C of BFG and COG become the same as in the first period. Through this kind of operation, the calorific value q _M of the mixed gas is kept at a constant value throughout the 1st to 5th periods.
It becomes possible to make maximum use of LDG generated in the second to fourth periods while maintaining _QM .

<Effect> As explained above, according to the present invention, the second gas, which is generated in batches and which has a large variation in calorific value, is mixed with the gas which is continuously supplied and has a stable calorific value, thereby minimizing the fluctuation in the load. Up until now, we had no choice but to dispose of most of the waste.
By effectively utilizing LDG, etc., it is possible to further promote energy conservation of the entire plant.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
The figure is an explanatory diagram showing changes in the flow rate and calorific value of each gas,
FIGS. 3 and 4 are flowcharts showing the signal processing procedure of the feed forward means and feedback means which constitute the main part of the present invention. 1... Coke oven gas supply source, 4... Blast furnace gas supply source, 7... Converter gas supply source, 10... Hot stove, 11... Air supply source, 14... Temperature controller,
15...Mixed gas flow rate controller, 31, 40, 49
...Flow rate controller for each gas, 23, 51...Calorimeter, 52...Flow rate setting calculation unit, 151...
Feedback calculation section, 152...Feedback calculation section.

Claims (1)

[Claims] 1. A first gas that is continuously supplied and has a stable calorific value and a second gas that is generated in batches and has a fluctuating calorific value are mixed and used, and the output of the mixed gas flow rate controller is A combustion control device in which a ratio is set by a flow rate controller of the first gas and a second gas as a master signal, the master signal, the flow rate signal of the second gas, the first gas,
a feed forward means for predicting and calculating set values for the first and second gas flow rate controllers so that the calorific value of the mixed gas does not fluctuate based on the calorific value signal of the second gas; A mixed gas combustion control device comprising feedback means for comparing the calorific value signal and the calorific value set value and periodically correcting the output of the feedforward means.