JPS62248918A - Method of controlling combustion for hot blast furnace - Google Patents

Abstract

PURPOSE:To attempt increased accuracy in combustion control free from effects of disturbances by carrying out flow rate control of a supplied fuel gas or composition ratio control according to the difference between a set temperature and the actually measured temperature of heat accumulating silica bricks of a hot blast furnace. CONSTITUTION:A plurality of silica brick thermometers 3 are inserted at different places of thc silica bricks of a heat accumulating chamber 2 in order to find out whether or not the silica brick temperature meets a set value. The outputs of those thermometers are inputted to a computer 4 and a change-over switch 5, and one out of a plurality of silica brick thermometers 3 is selected, In a silica brick temperature regulator 8 a standard temperature of the silica bricks in the heat accumulating cham ber 2 is set up and it is compared with an actually measured temperature, and an output in accordance with the difference is given to an automatic selector 9. The automatic selector 9 selects the lower output from the output of the silica brick temper ature regulator 8 and the output of a gas flow rate setting device 10 to control a hydraulic operator 12 and the flow rate of a gas sent to a combustion chamber 1 is controlled. Since combustion control is made by the direct detection of heat accumu lating silica brick temperature as noted above, it is possible to eliminate effects of disturbances.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a combustion control method for a hot blast furnace in blast furnace operation.

[Conventional technology]

In addition to fire resistance, hot volume stability, and dust resistance, the qualities required of refractory materials for forming the walls of hot blast furnaces include load softening properties, especially at high temperatures. Recently, silica brick has been used as a material that satisfies these requirements. However, although this silica brick has the above-mentioned properties, the volume changes significantly due to the transformation of tridymite and cristobalite between 100 and 350°C and the transformation of quartz between 500 and 600°C, which causes thermal stress. There is a problem with doing so. Therefore, it is necessary to limit the range of use of silica bricks to high-temperature areas, and the lower limit control value is 550.
It is defined as °C.

However, after the blast furnace operation shifted to oil-less operation, the air temperature has decreased significantly. When the blast temperature decreases and the load on the hot-blast stove becomes low, the furnace heat of the hot-blast stove also decreases. However, as mentioned above, the lower limit control value for silica bricks has become a bottleneck, and excessive combustion has been forced in actual operations. For this reason, it has become a big problem in the management of the furnace body equipment and the energy-saving operation of hot air stoves.

As a countermeasure to this problem, for example, JP-A-54-140
In the invention disclosed in Publication No. 305, the temperature inside the hot air stove is maintained at a high temperature by detecting the dome temperature of the hot air stove, and varying the gas analysis, gas mixture ratio, combustion air ratio, etc. Further, in the invention described in Japanese Patent Application Laid-Open No. 49-64505, equipment maintenance is attempted by equipping a hot air stove with a temperature control system based on dome temperature, exhaust gas temperature, etc.

[Problem that the invention seeks to solve]

However, in the method of controlling by dome temperature, the dome temperature itself does not represent the absolute value of the amount of heat stored in the hot air stove, and is directly influenced by the combustion flame. This causes large variations, making stable operation impossible.

In addition, in a method that controls combustion based on exhaust gas temperature,
This exhaust gas temperature is easily influenced by the temperature of the ventilation air because it is the heated exhaust gas of the guisotar that has been cooled by the ventilation during ventilation. The same applies to the case of controlling the dome temperature. Furthermore, the temperature of the exhaust gas is also affected by the ventilation ratio when, for example, only two of the four hot stoves are ventilated. Furthermore, since there is a time delay between the temperature change of the hot air stove and the temperature change of the exhaust gas, controllability is poor when the temperature of the exhaust gas is used for control. Therefore, although the detected gas temperature can serve as a guideline for combustion management, as a method of controlling the amount of heat storage, it is susceptible to the above-mentioned disturbances.

In addition, a computer-based furnace heat control system has been implemented, but the system is too complex. For example, when two reactors are ventilated, the air flow rate for furnace repair is not clear, and it is difficult to accurately analyze components such as fuel and exhaust gas. It is not operated online because it is vulnerable to external disturbances and lacks security.

Therefore, in actual operation, the amount of combustion gas that controls the amount of heat storage is often artificially controlled. However, artificial control cannot avoid large variations in the amount of heat storage due to individual differences, differences in combustion management methods, and neglect during busy times, which causes a decrease in thermal efficiency. .

The present invention was developed in view of such conventional problems, and an object of the present invention is to improve control accuracy while being less susceptible to external disturbances.

[Means for solving problems]

In order to achieve this objective, the hot blast furnace combustion control method of the present invention provides fuel to be supplied according to the difference between the actually measured temperature of the heat storage silica brick part of the hot blast stove and the preset temperature of the heat storage silica brick part. It is characterized by controlling the gas flow rate or mixture ratio.

[Effect]

In the present invention, focusing on the fact that the temperature of the heat storage silica brick best represents the amount of heat stored in the hot air stove, a thermometer is attached to the heat storage silica brick part, and the output of this thermometer is input to the silica brick temperature controller. do. The setting value of this controller is set in advance, for example, close to the minimum limit value of the required amount of heat storage, so that the amount of heat storage takes into account the maximum heat storage temperature during the combustion period and the lower limit control temperature during the ventilation period. To automatically reduce the amount of combustion gas to a lower limit value when the measured temperature of a silica brick reaches a set temperature.

The measured temperature can be obtained as a continuous measurement value or an intermittent measurement value. The difference between the measured temperature and the set temperature changes from moment to moment from the start to the end of combustion. On the other hand, the schedule of the combustion period is determined by the operating conditions of the hot blast furnace, that is, the operating conditions of the blast furnace. Therefore, in the present invention, the necessary energy, that is, the flow rate of fuel gas and calories, are controlled in order to make the deviation that changes from moment to moment zero within a set time.

As a result, the upper limit of the temperature of the silica brick becomes almost constant, excessive combustion is suppressed, and the amount of heat storage can be kept constant at a minimum value, thereby making it possible to save energy.

〔Example〕

Hereinafter, the features of the present invention will be specifically explained with reference to Examples.

In a hot-blast oven, there are two steps: one is to burn fuel and store heat in bricks using the amount of heat generated, and the other is to heat an object by flowing the heated object into the bricks where the heat is stored in a flow opposite to the combustion gas. As a characteristic of the furnace, the temperature of the dome of the furnace is determined by the flame temperature of the combustion gas.

On the other hand, the temperature at the lower end of the heat storage chamber is determined by the temperature of the object to be heated.

Therefore, it is particularly important to heat the object to be heated to a specified temperature in just the right amount and in order to achieve combustion management, efficiency, and cost savings.

The key point to this is how much heat can be stored in combustion.

In the present invention, a heat storage thermometer is installed on the heat storage silica brick that best represents the heat storage amount of the furnace, for example, at the center of the furnace height, so that the heat storage temperature approaches a predetermined set value. The amount of combustion is automatically controlled. As a result, the amount of heat storage becomes constant.

Here, there are the following three methods as combustion control methods.

■ Heat storage, a method of setting the combustion amount from the average value of the heat storage temperature of the heating cycle and its rate of change.

■ If the heat storage temperature during heat storage exceeds a certain set value,
How to reduce combustion.

■ A method of increasing the combustion amount when the heat storage temperature during heat storage is below a certain set value.

Any of these methods (1) to (2) can be automatically controlled by a computer or digital instrumentation. Furthermore, methods (1) and (2) can also be controlled by a simple analog instrumentation system.

FIG. 1 is a flowchart of automatic control for implementing the combustion control method of the present invention.

In FIG. 1, 1 and 2 are a combustion chamber and a heat storage chamber, respectively, which constitute a hot blast stove. A plurality of silica brick thermometers 3 are inserted into the silica brick, which is the heat storage body of the heat storage chamber 2, at different locations. Measure the temperature of the core,
Check whether each set value is satisfied.

Each output of this silica brick thermometer 3 is input to a computer 4 and a changeover switch 5. The changeover switch 5 selects one of the plurality of silica brick thermometers 3. The selected temperature output is input to a silica brick temperature controller 8 via transducers 6 and 7. A reference temperature of the silica bricks in the heat storage chamber 2 is set in this silica brick temperature controller 8, and this reference temperature is compared with the actual measured temperature, and an output corresponding to the deviation is sent to the next automatic selector 9. give to

The B gas flow rate setting device IO sets the maximum value of the flow rate of B gas, that is, blast furnace gas. and automatic selector 9
selects the lower one of the output of the silica brick temperature controller 8 and the output of the B gas flow rate setting device IO, and supplies it to the next B gas flow rate controller 11. This B gas flow rate regulator 11 controls a hydraulic actuator 12 based on the output signal of the automatic selector 9, and adjusts the flow rate of B gas sent to the combustion chamber l.

Note that an exhaust gas thermometer 13 is provided in the flow path between the heat storage chamber 2 and the flue, as in the conventional case, and its output is input to the computer 4.

In addition, the silica brick thermometer 3 is placed at one point on the inner side of the iron shell in the radial direction of the furnace, a relatively outer side, or a central portion of the heat storage silica brick, and is controlled based on the temperature of this portion, or It may be provided in the inner part of the skin, the relatively outer part, and the central part, respectively, and control the temperature based on the temperature of that part. Furthermore, more preferable results can be obtained by determining the amount of heat storage from the volume and specific heat of the silica brick based on the temperature at that location and managing the amount of heat storage as an index.

Next, the operation of the automatic control system having the above configuration will be explained.

+11 At the beginning of combustion, the temperature of the silica brick, that is, the heat storage temperature θ is low, and there is a large difference from the set temperature θ. Therefore, the output of the silica brick temperature controller 8 is a full-open output (maximum output).

Further, the automatic selector 9 is configured to select the lower level of the output of the silica brick temperature controller 8 and the output of the B gas flow rate setting device 10.
The output of 0 is selected, and combustion is performed at the gas flow rate according to the set value of the B gas flow rate setting device 10.

(2) As the temperature θ of the silica brick increases, the difference from the set temperature θR of the silica brick controller 8 becomes smaller. As a result, the output of the silica brick controller 8 decreases. and,
When the temperature θ of the silica brick reaches the set value θ, the output of the silica brick temperature controller 8 becomes lower than the output of the B gas flow rate setting device IO. Therefore, the automatic setting device 9 automatically selects the output of the silica brick controller 8. This results in
The B gas flow rate controller 11 gives a command to the hydraulic actuator 12 based on an output corresponding to the temperature deviation to control the amount of B gas.

Note that in step (2), the B gas flow rate controller 1
By setting the lower limit (or upper limit) of the output of 1 to a certain value in advance, when the output from the silica brick temperature controller 8 is selected, the lower limit (or upper limit) of B
It can be set by the gas flow rate controller 11. As a result, even when the temperature deviation between the set temperature θ2 of the temperature controller 8 and the temperature θ of the silica brick is large, the B
The gas amount is automatically regulated to a flow rate corresponding to the lower limit value (upper limit value), suppressing the rise in the temperature of the silica brick, and controlling the temperature to a constant value.

In addition, by setting the flow rate ratio C/B of C gas (coke oven gas) and B gas to a constant value, the flow rate control is performed to increase or decrease the amount of C gas in accordance with the increase or decrease in the amount of B gas. .

With such a control method, the temperature of the silica brick can be suppressed to the minimum necessary temperature, and fluctuations in the temperature of the silica brick can be suppressed. Furthermore, it becomes possible to control the lower control limit value for the silica brick at the extreme limit. This makes it possible to achieve both energy-saving operation and equipment maintenance management at the same time.

Table 1 shows the operational results of a hot blast furnace using the method of the present invention in comparison with the conventional method of controlling exhaust gas temperature.

Table 1 As can be seen from Table 1, by using the method of the present invention, it is possible to significantly reduce the temperature variation of the hot air stove, so the silica brick temperature and the air blowing temperature can be controlled to the lower limit range without damaging the furnace body. In addition, by operating according to the method of the present invention,
Thermal efficiency was also improved, resulting in significant energy savings in operation.

In this example, a method is described in which combustion control is performed according to the temperature of the silica brick by controlling the flow rate of B gas, but combustion control can be similarly performed by controlling the blending ratio of B gas. Of course it can be done.

〔Effect of the invention〕

As described above, in the present invention, combustion control is performed by directly detecting the temperature of the heat storage silica brick, which represents the amount of heat storage. Therefore, the influence of disturbance can be eliminated compared to the conventional method of indirectly detecting the temperature of the regenerative furnace from the temperature of the exhaust gas. Furthermore, since direct detection is used, deterioration in controllability due to time delay can be suppressed. Furthermore, since it is a direct control method based on the temperature of the heat storage silica brick, there is no variation in combustion, and it is resistant to external disturbances such as changes in air volume and calorie fluctuations, resulting in combustion that minimizes the amount of heat storage and lowers the exhaust gas temperature. becomes possible.

In addition, since the temperature of the heat storage silica brick is controlled to be constant, it is possible to control the temperature at the lowest control limit of the silica stone, making it possible to maintain equipment and save energy at the same time.

[Brief explanation of drawings]

FIG. 1 is a flowchart of a control system for implementing the control method according to the present invention.

Claims (1)

[Claims] 1. It is characterized by controlling the flow rate or blending ratio of the fuel gas to be supplied according to the difference between the measured temperature of the heat storage silica brick part of the hot air stove and the preset temperature of the heat storage silica brick part. Combustion control method for hot stove.