JPS6122003B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for keeping a hot blast furnace warm during a period when the blast furnace is temporarily suspended for repairs, etc., and its purpose is to prevent damage to the silica bricks inside the blast furnace in order to keep the hot blast furnace warm during the period. This is a method to keep a hot air stove warm with the minimum amount of fuel while preventing

As is well known, for example, hot blast furnaces for blast furnaces burn
That is, while repeating heat storage operation and air blowing, that is, heat dissipation operation, a plurality of hot blast furnaces are sequentially switched to continuously supply high temperature air to the blast furnace.

Therefore, if the blast furnace is temporarily suspended due to repairs, etc.,
Since it is no longer necessary to supply high-temperature air to the blast furnace, the hot blast furnace will generally be shut down, but if the hot blast furnace is in good condition, it will naturally be used for the blast furnace after the blast furnace is restarted. It will be reused as much as possible.
Therefore, when shutting down a hot-blast stove in preparation for reuse, it is necessary to keep the hot-blast stove at a temperature level that will not cause damage to the bricks during the period, or to completely cool it down to room temperature while being careful not to damage the bricks during cooling. There are two options: suspend the program.

In this case, the silica bricks constituting the main part of the hot stove are heated in a temperature range of less than 575°C as shown in Figure 1, A to C, and the mineral components that undergo transformation are quartz, locristobalite, The transformation expansion curve of Hatridymite is shown. Silica bricks undergo rapid contraction or expansion when passing through these transformation points when the temperature is lowered or raised in a hot air stove, and therefore, if the temperature is repeatedly lowered and raised above and below 575°C, cracks and damage to the bricks may occur. It was considered inevitable. For this reason, conventionally, quartz has a temperature of 575℃ or higher, which is the transformation point of quartz.
For example, it was common to keep hot air stoves at a relatively high temperature of about 600°C or higher.

For example, as described in Japanese Patent Publication No. 50-29803, a method of keeping a hot-blast stove warm has been used in which the hot-blast stove is operated as if it were operating, that is, the combustion and blowing operations are alternately performed.

However, with this conventional method, the temperature at the bottom of the silica brick in the heat storage chamber inside the hot air stove cannot be adjusted.
In order to maintain the temperature above about 600°C, the upper part of the heat storage chamber must be maintained at a fairly high temperature, for example, about 1100°C, so there is a large amount of heat loss from the iron shell.

During heat dissipation operations, high-temperature air of approximately 1000℃ is dissipated into the atmosphere.

As a result, the energy and cost required to keep the hot air stove warm is enormous, and keeping the hot air stove warm for a long period of time in this manner poses a major obstacle from the standpoint of energy conservation.

The present invention is a heat insulation method for a hot air stove that eliminates the drawbacks of these conventional methods, and makes it possible to keep a hot air stove warm with a small amount of fuel gas without damaging the silica bricks, checker metal fittings, etc. inside the furnace. It is something.

The gist of the present invention is (1) when maintaining the temperature of the hot blast furnace while the blast furnace is inactive, the temperature of the lowest temperature part of the silica stone brick wall of the hot blast furnace is
Within the range of 300℃ or more and less than 575℃, and the temperature difference between the highest and lowest temperature of the inner side of the brick in the area is 400℃
There is a method of keeping a hot air stove warm, which is characterized by keeping the heat as follows.

The present invention will be explained in detail below. FIG. 2 is a front sectional view showing the overall structure of an external combustion hot air stove, FIG. 3 is a front sectional view showing the overall structure of an internal combustion hot air stove, and FIG. 4 is a horizontal sectional view of the internal combustion hot air stove.

In each figure, 1 is a heat storage chamber, 2 is a combustion chamber, 3 is a mixed cooling chamber, 4 is a dome connecting pipe, 5 is a hot air connecting pipe, 6 is a burner, 7 is a flue valve, 8 is a blower valve,
9 is a hot air valve, 10 is a gas valve, 11 is an air valve, 12
1 is a cold air valve, 13 is an iron shell, 14 is a checker bracket, 15 is a heat storage chamber dome, 16 is a combustion chamber dome,
17 is a dome of the internal combustion type hot air stove, and 18 is a wall portion.

The shaded area is the area in which silica bricks are used for the iron shell lining and the checker bricks in the heat storage chamber in a hot air stove with such a configuration. For example, in the case of the wall of a hot-blast furnace, in order to stop air blowing to the blast furnace and keep the hot-blast furnace warm, the temperature must be lowered from the normal operating state and maintained at a low temperature within a predetermined range. Even in the process of maintaining the temperature within a certain range,
During heat retention, heat is dissipated to the outside of the hot air stove, so heat is supplied to the hot air stove intermittently or continuously. Furthermore, heat dissipation varies depending on heat supply conditions and outside air conditions. Therefore, the temperature inside the brick is also constantly changing.
Heat is generally dissipated from the outer side of the furnace through the insulating bricks, but the heat receiving state of the inner side of the furnace varies depending on the heat supply conditions such as direct combustion. The velocities are greater than those on the outer surface of the furnace.

This is shown in FIGS. 5 and 6. FIG. 5 is an enlarged view of the wall portion 18 in FIGS. 2, 3, and 4.
19 is a silica brick, 20 is an insulation brick, 21 is inside the furnace,
22 represents the outside air, and 13 represents the iron skin. This silica brick 1
FIG. 6 shows the temperature change state of No. 9. 23 in Figure 6
The inner furnace side surface 24 and the furnace outer surface surface 25 of the silica brick 19 are average temperature distributions, with the furnace inner surface temperature T 1 and the furnace outer surface temperature T ₁ .
T ₁ ′. If more heat is supplied than the amount of heat dissipated from this state, the temperature of the inner side surface of the furnace increases as shown in the temperature distribution after heat supply in 26. When the heat supply is eventually interrupted or reduced, the temperature distribution after heat dissipation becomes 27.
T ₂ and T ₃ are the temperature of the inner side of each furnace, and T ₂ ′,
T ₃ ′ is the temperature of each furnace outer surface. When keeping warm in a hot air stove, the temperature changes described above are repeated to some extent. The amount of change is generally large on the inner side of the furnace. For this reason, tensile stress is generally generated in the wall portion in the radial direction in the thickness direction of the silica brick, that is, in the direction where there is a temperature gradient. This stress is greatly influenced by the rate of temperature change and the amount of temperature change, that is, the temperature difference on the inner side surface of the silica brick. The present inventors conducted various investigations and analyzes regarding the tendency of this tensile stress to occur, and obtained results as illustrated in FIG. 7 in the case of an external combustion type hot blast stove. In FIG. 7, the horizontal axis represents the temperature of the outer surface of the furnace wall silica brick, and the vertical axis represents the tensile stress generated in the silica brick.

In Figure 5, curves A and B show the tendency of tensile stress to occur when the temperature difference ΔT on the inner side of the silica brick is 50°C, and curve A shows the rate of temperature change v on the inner side of the silica brick. When is 25℃/hr, curve B is 100℃/hr
Indicates when hr. Curves C and D have a temperature difference ΔT of 200
It shows the tendency of tensile stress to occur when the temperature is 25°C/hr.
Indicates when hr. Curves E and F have a temperature difference ΔT of 400
It shows the tendency of tensile stress to occur when the temperature is 25°C/hr for curve H and 50°C/hr for curve H.
Shown in °C/hr.

These curves have slightly different values because the size of each brick and other brick configurations are slightly different for each hot air stove, but they are almost the same for internal combustion hot air stoves. Curve G indicates the average allowable tensile strength of the brick itself determined from the physical properties of the brick, and curve H indicates the control limit value of the generated tensile stress determined by taking into account the safety factor.

As is clear from Fig. 7, the lower the temperature of the brick itself, the faster the rate of temperature change of the brick itself, and the larger the temperature difference ΔT between the inner sides of the silica brick, the more the tensile force generated in the silica brick of the furnace wall. The stress becomes a large value. Naturally, when the tensile stress generated in the brick exceeds the allowable tensile stress, the brick is torn in the thickness direction (approximately perpendicular to the radial direction) and divided into multiple pieces.

Debris then falls off and damages the brickwork. However, as can be understood from Fig. 7, the rate of temperature change of the silica brick and the inner surface of the silica brick with respect to the temperature of the outer side of the furnace wall silica brick (temperature on the horizontal axis in Fig. 7) during heat retention of the hot stove. If the temperature difference is within a certain condition, the tensile stress generated in the brick is within the allowable tensile stress value or control limit value, so no damage to the brick occurs.
For example, in a temperature range of about 575°C or higher, the generated tensile stress is within control limits under all conditions that can be used in actual work, and there is no risk of damage to the bricks. In addition, in the temperature range of less than 300℃, there is a risk of brick damage unless it is within very limited conditions, and in the temperature range of 300℃ to 575℃, for example, the temperature difference ΔT on the inner side of the furnace can be 400℃ ℃
It is possible to avoid damage to the bricks within this range.

The above is an explanation of an example of a wall part, but needless to say, the silica bricks lining the dome part are basically based on the same design as the wall bricks, and the same heat insulation method as for the wall bricks is applied. good.

Further, in the case of silica checker bricks, it is clear that the direction in which the temperature gradient in the furnace wall bricks is vertical is the vertical direction, since combustion gas and air flow pass in the vertical direction. Therefore, for checker bricks, the temperature of the lowest temperature part of the brick is
It is important to maintain the temperature between 300℃ and 575℃, and to maintain the temperature difference between the top and bottom of each brick within a certain range. This certain range is the same as in the case of wall bricks.
It is sufficient to set the temperature to 400℃ or less.

The present invention has been made based on the above knowledge, and according to the method of the present invention, when keeping a hot blast stove warm for a long period of time, the heat retention temperature of the silica bricks in the hot blast stove is lower than that of the conventional method. The temperature range can be from less than 575 degrees Celsius to about 300 degrees Celsius, which is lower than in the conventional case, and the amount of fuel used for heat insulation can be significantly reduced. In addition, since the heat retention temperature is low, there is no need to cool the checker holder etc. during the heat retention period, making the work extremely simple.

Furthermore, when the temperature drops to as low as 300℃, the silica bricks contract in the furnace walls and dome, creating tensile stress in the furnace circumferential direction, which causes the strength of the mortar joints in the brickwork to be lower than the strength of the bricks. , the mortar joints may crack first. However, in this case, the width of the crack at the joint is about 0.05 to 0.1% of the total circumference in terms of shrinkage rate, and in actual practice, there are about 10 cracks around the circumference, so the width of the crack at one place is extremely small. However, cracks of this magnitude can be closed when the hot stove is heated up for restarting, and the functionality of the brickwork will not be impaired in any way.

Next, embodiments of the present invention will be described.

Immediately after the blowing of the blast furnace is stopped, the temperature inside the hot blast furnace is high, about 1100℃ at the dome, and about 800℃ at the outer side of the furnace wall near the lower end of the silica brickwork in the heat storage chamber.
There is a temperature of ℃. While the temperature inside the furnace is high at the initial stage of cooling, the heat in the upper part of the heat storage chamber is transmitted downward and the temperature of the checker holder etc. increases. It is necessary to cool the checker holder etc. with air. As time passes, the amount of heat storage decreases, and the temperature on the outside of the furnace wall brick furnace near the lower end of the silica brickwork in the heat storage room and on the lower end surface of the silica checker brick reaches a minimum of 300°C.Actually, there are only 1 or 2 temperature measurement points in the furnace circumferential direction. Taking into consideration the fact that there are three locations and the temperature measurement error, the temperature reduction ends when the measured temperature reaches 350 to 400 degrees Celsius, and from then on, the temperature is kept within the predetermined temperature range at this temperature level. By the time the temperature of the outside surface of the furnace wall and brick furnace reached around 550℃ during the temperature drop, the temperature of the checker bracket, etc., would drop to about 350℃ or less even without forced cooling, and the metal would be outside the buckling limit temperature. It is. During the subsequent heat retention period, in order to maintain the brick temperature between 350°C and 400°C, it is only necessary to continue burning a small amount of fuel gas.
As a result of applying the method of the present invention to the heat insulation of an actual hot air stove, it was found that the standard of the conventional method required fuel of about 600 Nm ² /hr of COG per class ² hot blast stove with a heating area of 80,000 m. With this method, the fuel consumption was reduced to approximately 1/3 at approximately 200Nm ² /hr.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the transformation expansion curve of silica stone, Figure 2 is a front sectional view showing the overall structure of an external combustion hot blast stove, Figure 3 is a front sectional view showing the overall structure of an internal combustion hot blast stove, and Figure 4 is a front sectional view showing the overall structure of an internal combustion hot blast stove. The figure is a horizontal sectional view showing the structure of an internal combustion hot air stove, Figure 5 is an enlarged view of the wall 18, Figure 6 is a temperature distribution diagram of the wall silica brick, and Figure 7 is the temperature conditions and stress of the furnace wall silica brick. FIG. 1... Heat storage chamber, 2... Combustion chamber, 3... Mixed cooling chamber,
4...Dome connecting pipe, 5...Hot air connecting pipe, 6...
Burner, 7... Flue valve, 8... Ventilation valve, 9...
Hot air valve, 10... Gas valve, 11... Air valve, 12
...Cold air valve, 13...Iron shell, 14...Checker bracket, 15...Regenerator dome, 16...Combustion chamber dome, 17...Dome of internal combustion hot air stove, 18...
…Wall portion, 19…silica brick, 20…insulation brick,
21...Furnace inside, 22...Outside air, 23...Furnace inner side of silica brick, 24...Furnace outer side of silica brick, 25
... Average temperature distribution, 26 ... Temperature distribution after heat supply.

Claims (1)

[Claims] 1. When keeping the hot blast furnace warm while the blast furnace is idle, the temperature of the lowest temperature part of the silica stone bricks on the walls of the hot blast furnace should be
A method for keeping a hot air stove warm, characterized by maintaining the temperature difference between the highest and lowest temperature of the inner side of the brick in the range of 300°C or higher and lower than 575°C to 400°C or lower.