JPS59140310A - Controlling method of air fuel ratio in hot-blast stove - Google Patents

Abstract

PURPOSE:To prevent the loss of energy by changing forcibly an air ratio to a means air ratio in a previous burning stage when a specified time elapses after completing the change-over of other hot-blast stove in order to keep an optimum burning state. CONSTITUTION:When one hot-blast stove is in the burning stage and the other hot blast stove starts a changing operation, the stove in the burning stage is supplied temporarily with excess air since a gas for burning and air are supplied to every hot-blast stove through a common piping. As the air ratio is decreased by air fuel ratio control, air is supplied insufficiently after the changing operation and a large amt. of gaseous CO is generated. Therefore, the air ratio is changed to the mean air mopt in the previous burning stage when the sepcified time t0 elapses after the changing operation of the other hot-blast stove is completed. The time t0 is determined empirically.

Description

[Detailed description of the invention] The present invention relates to an air-fuel ratio control method for a hot blast stove.

A hot stove burns a mixed gas (M gas) of blast furnace gas (B gas) and coke oven gas (C gas) in a combustion chamber, and passes the generated high-temperature gas through checker bricks in a heat storage chamber. This is a device that stores heat in the blast furnace and uses this stored heat to blow air to the blast furnace. Therefore, a hot air stove has two periods: a combustion period and a blowing period. In addition, three to five hot-blast stoves are usually arranged, and one or two of them are used to blow air to the blast furnace, while the other hot-blast stoves are in a state of combustion, and the heat from the hot-blast stoves that are blowing air has become insufficient. Sometimes, the blast furnace is switched to another hot blast furnace that has completed heat storage, and air is continuously blown to the blast furnace. Incidentally, when blowing air, normally a stun guard barrel two-barrel control is performed in which air is sent to two hot air stoves at the same time with a time difference. When controlling combustion in such a hot-blast stove, in order to maintain a high temperature of the flame of the hot-blast stove and achieve stable and efficient combustion, the O gas concentration and CO gas concentration in the exhaust gas must be kept constant and as much as possible. It is important to maintain the ratio of M gas for combustion to air so that it can be maintained at a low value, and it is undesirable from the point of view of energy saving and the environment to disrupt this balance and emit a high concentration of Co gas. For this reason, conventionally, the air-fuel ratio is explained as follows. The hot air stove 2 includes a combustion chamber 2a and a heat storage chamber 2b, a dome is attached to the upper part of the combustion chamber 2a and the heat storage chamber 2b, and a communication pipe 2c
I have been in contact with you. B gas and primary C gas are mixed to form primary M gas, and secondary C gas is mixed to the primary M gas via the secondary C gas flow path 4 for fine adjustment of the mixture ratio. The M gas is supplied to the combustion chamber 2a via the M gas flow path 6. Additionally, combustion air is supplied to the combustion chamber 2a via an air flow path 8. The M gas flow path 6 and the air flow path 8 are composed of piping that is common to all the hot stoves, and are designed to commonly supply M gas and air to each furnace. ing. The secondary C gas flow path 4 has a secondary C gas flow rate F.
A C gas flowmeter 10 is installed to measure c2, and M
Is there a flow rate of M gas in gas flow path 6? , an M gas flow meter 12 is attached to measure .

An air flow meter 14 for measuring the air flow rate FAIR and a butterfly valve 16 for controlling the air flow rate are attached to the air flow path 8 in this order.

The heat storage chamber 2b of the hot air stove 2 is provided with an exhaust gas passage 18 for discharging the exhaust gas generated by burning the mixture of M gas and air to the outside. A 07 analyzer 20 for detecting residual oxygen concentration is attached.

The C gas flow meter IO is controlled by a microcomputer 24 for control.
The air-fuel ratio calculation means 26 is connected to the input terminal thereof. The M gas flow meter 12 is connected to the input terminal of the air-fuel ratio calculation means 26 of the microcomputer 24 and the air amount calculation means (Fr) 2B.
is connected to the input end of the Further, the air flow meter 14 is connected to an input end of an air flow control means (FIC) 30, and the butterfly valve 16 is connected to an output end of the air flow control means 30. The air-fuel ratio calculation means 26 is connected to the air flow rate control means 30 via the air amount calculation means 28. The 07 analyzer 20 is connected to the process computer 22 via an indicator (X-engine) 31 within the microcomputer 24. This process computer 22
A signal indicating the switching timing between the combustion period and the blowing period of the hot air stove is input to the process computer 2.
2 is connected to a microcomputer 24.

Next, we will discuss the air-fuel ratio control method for the device shown in the FGX diagram. The process computer 22 determines which hot air stove is in the combustion period based on the switching timing signal, and also samples the O7 concentration signal from the 02 analyzer 20 at predetermined time intervals and calculates the air ratio (operated amount) based on the following formula. ) m is calculated and stored.

m(t)=m(t-Δt)+α(SO2-Ao2) −
・・・・・=+1 Also [7, m(t) is the current air ratio, m(t-Δshi) is the previously calculated air ratio, t is the current time, 8t is the sampling interval, α is a constant, S02 is the preset 02 concentration, and Ao2 is the actual 0.02 concentration measured by the 02 analyzer. It is concentration.

That is, sample value proportional control is performed to change the air ratio m to α times the O7 concentration deviation at each sampling interval. The process computer 22 also stores the theoretical air amount AOM l of the primary M gas obtained from the calorie analysis of the primary M gas.
And the value of the secondary C gas theoretical air amount AOC obtained from the calorie analysis of the secondary C gas is stored in advance. The air ratio m1 theoretical air amount AOMI, AOC stored in the process computer 22 is input to the air-fuel ratio calculating means 26 of the microcomputer 24, and the air-fuel ratio calculating means 26
These values and the secondary C input from each flowmeter 1O112
Based on the gas flow rate Fc2 and the M gas flow rate FM, the air-fuel ratio A, 6 of the mixture for combustion guidance is calculated according to the following formula.

Value=mA,) r'M However, Ao is the theoretical air amount of M gas.

The air-fuel ratio 7/1 is input to the air amount calculation means 28, and its product with the M gas flow rate F input from the flow meter 12 is calculated to obtain the set air flow rate Air. This set air flow rate Air is input to the air flow rate control means 3°, and the air flow rate control means 3o controls the butterfly flow based on the difference between the actual air flow rate input from the flow meter 14 and the set air flow rate Air. Controlling the valve 16 by duty ratio control etc.
The air flow rate flowing through the air flow path 8 is controlled to become Air. As a result, the air-fuel ratio of the air-fuel mixture in the combustion chamber is controlled to be A.

However, such conventional air-fuel ratio control has the following problems. That is, three to five hot-blast stoves are usually provided and staggered parallel control is performed, and when one hot-blast stove is in the combustion period, the other hot-blast stoves are switched. At this time, M gas and air for combustion are supplied to each hot-blast stove from piping that is common to all hot-blast stoves, so when switching to other hot-blast stoves, due to control problems, the hot-blast stove in the combustion period is temporarily However, due to combustion conditions with excess air, the residual oxygen concentration in the exhaust gas becomes excessive. Then, an attempt is made to lower the value of the air ratio m by air-fuel ratio control to lower the air flow rate, but since the switching time is short and the followability of the value of the air ratio m is poor, the value of m remains even though the 02 concentration has disappeared after switching. Since the air pressure was low, the lack of air continued for some time, and a large amount of CO gas was generated in the exhaust gas, resulting in the problem of energy loss due to unresolved release of CO gas. This state is expressed as a second time series change.
As shown in the figure. It has also been confirmed that the dome temperature of the hot air stove temporarily drops due to the above energy loss. The main cause of the above problem is the poor responsiveness of the control system, but this poor responsiveness is due to the fact that the air ratio m is calculated by a process computer that takes a long calculation time, and the exhaust gas O.

The main causes include the poor responsiveness of the analyzer and the fact that the process computer controls sampling every few minutes.

The present invention was made to solve the above problems, and it is possible to always maintain an optimal combustion state, keep the flame temperature constant, prevent the dome temperature from dropping, and generate a large amount of CO gas. It is an object of the present invention to provide an air-fuel ratio control method for a hot-blast stove that prevents energy loss by preventing this.

In order to achieve the above object, the configuration of the present invention is such that, in the conventional air-fuel ratio control method of a hot-blast stove, when a predetermined time to has elapsed after switching of another hot-blast stove is completed, the air ratio m is changed to that of the previous combustion period. The average air ratio moptK is forcibly changed. As a result, the value of the air ratio m is changed as shown in FIG.

Here, changing the value of the air ratio m after a predetermined time to has elapsed after the completion of switching is because the residual 0. The time for the concentration to return to zero is the second
As shown in the figure, the time to is determined empirically based on the fact that molding is required after the switching is completed. Also,
The optimal value for changing the value of the air ratio m differs depending on each hot air stove and combustion conditions, so the average m value from the previous combustion is stored in the process computer for each hot air stove, and the value is changed for the next time. Used during combustion.

Next, embodiments of the present invention will be described in detail.

The blast furnace used was operated in staggered parallel fashion using four hot blast furnaces, with a combustion period of 115 minutes, a blowing period of 110 minutes, and a switching period of 15 minutes.If you focus on a particular hot blast furnace, it will take approximately 60 minutes to start combustion. Other hot air stoves will switch over later. The switching of this hot air stove starts at approximately 0 minutes each time, and the blowing and combustion are completed approximately 120 minutes later at 0 minutes, and the air-fuel ratio is controlled every 2 minutes by the process computer. This is done through sampling. Furthermore, blast furnaces perform two-stage combustion in which the amount of fuel input is changed between the first half and the second half of the combustion period. The exhaust gas 02 concentration, M gas flow rate, air flow rate, and air ratio m1 air-fuel ratio A~ in this hot air stove are as shown in FIG. In addition, CO
The gas concentration was not measured online, but according to offline measurements it was 0. It has been confirmed that this occurs frequently when the concentration reaches 0%.

Therefore, in this example, the predetermined time to is 2 minutes, and the average air ratio m0Pt is the average of the air ratios m in the lower A, B, and C3 periods for each hot air stove in the latter half of the previous combustion period. The value was adopted.

A: 27 minutes to 29 minutes B: 37 minutes to 39 minutes C: 47 minutes to 49 minutes The second half of the hour was used because the blast furnace in use uses two-stage combustion; This is because the average air ratio is different. Therefore, it is necessary to use the optimum value for the air ratio mopt depending on the operation. Furthermore, the reason why the average air ratio mopt is determined for each hot-blast stove is that the combustion characteristics differ for each hot-blast stove.

O1 concentration and Co concentration in the exhaust gas in the above example and 0.0 in the exhaust gas subjected to the conventional method. A comparison between the concentration and the Co concentration is shown in FIG. As shown in FIG. 5(b), the O2O and Co concentrations in this example are considerably lower than those in the conventional example shown in FIG. 5(a).
It can be seen that the zero energy loss is reduced. Also, Fig. 6 shows the fluctuation of the dome temperature, and Fig. 6(b)
In the case of the present embodiment shown in FIG. 6(a), the temperature fluctuation at the time of furnace switching is reduced compared to the conventional example shown in FIG. 6(a).

As explained above, according to the present invention, it is possible to suppress CO gas generation due to incomplete combustion when switching hot stoves, prevent energy loss, maintain an optimal combustion state, and prevent a decrease in dome temperature when switching. This has the unique effect of preventing

[Brief explanation of the drawings] Figure 1 is a block diagram showing a conventional air-fuel ratio control system.
Fig. 2 is a diagram showing the variation in the process amount in conventional air-fuel ratio control, Fig. 3 is a diagram showing the change in the air ratio in the present invention, and Fig. 4 is a diagram showing the variation in the process quantity in the implementation furnace. ,
Figure 5 (8) and (b) show the CO in the conventional example and this example.
O20 and 0. 6 (aL(b) is a diagram comparing and showing the fluctuations in the gas concentration. FIG. 6 (b) is a diagram comparing and showing the fluctuations in the dome temperature in the conventional example and the present example. 2...Hot stove, 10 .12.14...Flowmeter, 16...Butterfly valve, 20...O2 analyzer, 22...-process computer, 24...Microcomputer. Figure 2 Figure 3

Claims (1)

[Claims] (1) The combustion period in which combustion gas and air are mixed and burned to store heat and the blowing period in which the stored heat is sent to the blast furnace are switched, and when at least one unit is in the combustion period, the other units are switched. The residual oxygen concentration in the exhaust gas discharged from the hot blast furnaces during the combustion period in a plurality of hot blast stoves is detected, and the air ratio and the combustion are determined based on the deviation between the residual oxygen concentration and a preset set oxygen concentration. The air-fuel ratio is determined by multiplying the theoretical air amount obtained from the calorie analysis value of the combustion gas, and the air-fuel ratio is adjusted so that the ratio of the combustion gas and the air supplied to the hot air stove during the combustion period becomes the air-fuel ratio. The air-fuel ratio control method for a hot-blast stove that controls the amount of air is characterized in that the air ratio is changed to the average air ratio of the previous combustion period when a predetermined time has elapsed after switching of other hot-blast stoves is completed. A method for controlling the air-fuel ratio of a hot-blast stove.