JP7243677B2 - Furnace bottom temperature raising method and blast furnace start-up method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for raising the temperature of the bottom of a blast furnace whose operation has been stopped, which is used to start air blowing after raising the temperature of the contents of the bottom, and a method for starting up the blast furnace using the method.

The blast furnace was installed at the lower part of the tuyeres, where the iron ore was heated, reduced, and melted using high-temperature air blown through holes called tuyeres and high-temperature reducing gas generated by the reaction of oxygen with coke and pulverized coal. This facility discharges pig iron and slag from the taphole to the outside of the furnace for production. During normal operation of the blast furnace, stable operation of the blast furnace is possible because the reaction heat in the furnace and the heat supply from the tuyeres are in balance. However, due to operational troubles, equipment troubles, etc., it may be necessary to stop blowing air to the blast furnace. In addition, it may be necessary to rest the blast furnace for a long period of time for repair work due to aging of the blast furnace. During the wind break, the temperature of the charged material and the molten material (hereinafter referred to as "furnace heat") in the furnace decreases due to heat removal from the furnace body and air intake from the tuyeres.

When the furnace heat is lowered, the viscosity of the slag increases, part of it solidifies, and it becomes difficult to discharge the hot metal slag from the tap hole. When air is blown in such a state, the molten iron and slag generated by the hot gas generated in front of the tuyere raise the liquid level of molten iron slag in the lower part of the furnace. At this time, the temperature of the molten iron slag remaining at the bottom of the furnace is raised by the molten iron slag supplied from the upper part of the tuyeres, and if the furnace heat level is gradually restored, there is no problem. However, if the furnace heat does not recover and the liquid level of the molten iron slag reaches the level of the tuyeres and the tuyeres are clogged, the means for supplying heat to the furnace will be cut off, leading to a furnace cooling accident, resulting in a huge economic loss. bring loss.

Conventionally, the following method has been used as a recovery method from a furnace cooling accident. That is, first, while the wind is not blowing, all but one or two tuyeres above the taphole are blocked with a refractory material or the like, and oxygen is blown in through the taphole and unblocked tuyeres. As a result, after the semi-molten material between the taphole and the tuyere is discharged from the taphole, the space created in the furnace is filled with coke, and then air blowing is started. Then, a cycle is established in which the temperature of the hearth bottom is raised by the hot gas flowing between the tap hole and the tuyeres, and the hot metal slag produced by the blowing of the air is smoothly discharged. After that, open the adjacent tuyeres and gradually increase the number of open tuyeres to restore normal operation. However, these steps take 1-2 months. In addition, since the blowing of oxygen is performed manually, it is a work with high safety risks.

Since the furnace heat is low when the reactor is started up after a rest period, there is a high risk of the above-mentioned furnace cooling accident. Conventionally, in order to start the furnace without causing an accident, the coke ratio in the furnace was increased to enter a rest period, and after blowing air, heat compensation was performed until pulverized coal blowing could start. was going Other methods include blowing oxygen gas through the tap hole to burn the carbonaceous materials and pig iron in the furnace to generate heat to raise the temperature of the bottom of the blast furnace. A blast furnace blast start method and a hearth temperature raising burner have been proposed that can be installed to burn fuel, efficiently heat the hearth, and start up in a short time from a long pause. (Patent Documents 1 and 2).

JP 2016-30833 A JP 2013-221184 A

The method of raising the temperature of the hearth using a furnace bottom heating burner can be said to be an extremely efficient method because heat is directly supplied to the temperature-lowered melt or solidified matter on the hearth to raise the temperature. Combustible gas such as natural gas and combustion-supporting gas containing oxygen are blown into the furnace from the furnace bottom heating burner installed at the tap hole, and heat can be supplied to the filling in the furnace bottom. . In addition, combustion-supporting gas containing oxygen can be blown from a burner to burn coke in the furnace, or heat can be supplied by oxidizing iron in the furnace. In the present invention, combustible gas and combustion-supporting gas blown from the burner are collectively called heating gas. However, in using this method, there was a problem that it was difficult to rationally determine the position to install the burner and its combustion time. The main purpose of burner combustion is to sufficiently raise the temperature of the melted or solidified material existing between the taphole and the tuyere directly above it, melt it and discharge it from the taphole, and then generate it at the tip of the tuyere by blowing air. It is to facilitate discharge of slag and molten iron out of the furnace. Therefore, in order to stably start up the blast furnace, it is desirable to install a burner at the tap hole that can effectively raise the temperature. Generally, a blast furnace has two to four tapholes per blast furnace, and this is a suitable method for predicting which taphole a burner should be installed to effectively raise the temperature of the hearth bottom. was not known.

Moreover, it was also difficult to determine a suitable time for burning the combustible gas blown from the burner. The amount of heat that can be supplied from the taphole is smaller than the amount of heat that can be supplied by burning coke in the furnace by blowing hot air from the tuyeres. Therefore, in order to start up the blast furnace early, it is preferable to switch to blowing air from the tuyeres as early as possible. In particular, when the heat radiation from the blast furnace is large, it is difficult to compensate for the heat radiation only by the burner installed at the tap hole, so it is desirable to quickly blow air from the tuyeres. In other words, the heat from the burner installed at the tap hole sufficiently increases the temperature at the tip of the tuyere, and the air blowing from the tuyere makes it possible to burn the coke in the furnace at the tip of the tuyere at an early stage. If it can be done, the blast furnace can be started up early, and the expansion of the solidified layer due to increased heat dissipation can be suppressed.

The inventors have studied how the temperature inside the blast furnace is increased by the burner installed at the taphole, and completed the present invention. That is, the present inventors have found a suitable method of estimating how the conditions inside the furnace change (how the temperature rises) according to the burner combustion time, and determining the burner combustion time according to the estimation results. The temperature rise behavior in the furnace after burner combustion also differs depending on the conditions in the furnace before burner combustion. This is because the amount of heat removed from the furnace changes depending on the length of the blast furnace shutdown time (breathing time) until just before burner combustion. This is because the difference affects the temperature rise due to subsequent burner combustion and the time at which the burner should be fired. If the combustion time of the burner is sufficiently long, the amount of heat supplied to the vicinity of the burner increases. However, since the inside of the furnace is a packed bed filled with lump coke, the gas blown into the furnace from the tip of the burner does not reach a remote position from the tip of the burner, so the temperature does not rise and heat removal progresses, and the melting inside the furnace Adverse effects such as a further reduction in material fluidity or a further growth of solidified layers grown in the furnace may occur. That is, it is necessary to accurately estimate the specifications such as the burner combustion time and the amount of burner combustion gas required to raise the temperature of the area between the tap hole and the tuyere to the desired temperature according to the furnace conditions. Become.

An object of the present invention is to provide a suitable method for raising the temperature of the hearth bottom for quickly restarting a blast furnace whose operation has been stopped using a burner installed at the tap hole of the blast furnace, and starting up the blast furnace using the method. It is to propose a method.

As a result of extensive studies to solve the above problems, the inventors used a simulation model to estimate the temperature of the melted material in the lower part of the furnace or the thickness and shape of the solidified layer before the shutdown of the blast furnace (before the shutdown of the wind). Based on the results, a method for determining preferable combustion conditions for a burner installed at the taphole (hereinafter sometimes referred to as a taphole burner) was found. Specifically, based on the thickness of the solidified layer estimated by the simulation model, a tap hole that can effectively raise the temperature of the tip of the tuyere using a tap hole burner is identified, and a burner is installed at that tap hole. Heat transfer calculations are used to estimate how long the combustion time will allow the temperature of the blast furnace to be raised by blowing air from the tuyeres. Then, after the furnace bottom is heated under these conditions, hot air is quickly blown from the tuyeres, so that the stopped blast furnace can be started up quickly.

A first aspect of the method for raising the temperature of the hearth bottom of the present invention is to raise the temperature of the hearth bottom by blowing a heating gas into the furnace from a burner provided at the tap hole of the hearth bottom of a blast furnace whose operation has been stopped. In the temperature raising method of No., the step of estimating the shape of the solidified layer grown at the bottom of the furnace during shutdown, and in a plurality of tapholes, between the taphole and the tuyere immediately above the taphole a step of estimating the average thickness of the solidified layer; and the tap hole with the smallest estimated average thickness, or the tap hole with the second smallest estimated average thickness when there are three or more tap holes. A method for raising the temperature of the bottom of the furnace, comprising a step of installing a burner in the mouth and blowing a heating gas into the furnace from the burner to raise the temperature of the bottom of the furnace.

In a second aspect of the method for raising the temperature of the hearth bottom of the present invention, heating gas is blown into the furnace from a burner provided at the tap hole of the hearth bottom of a blast furnace whose operation has been stopped to raise the temperature of the hearth bottom. In the method for raising the temperature of the furnace bottom, the step of estimating the shape of the solidified layer grown on the furnace bottom while the operation is stopped, and raising the temperature during the combustion of the heating gas blown from the burner using the estimated solidified layer shape as the boundary condition. A method for raising the temperature of a furnace bottom, comprising the steps of: estimating a temperature distribution in a furnace bottom; and determining, based on the temperature distribution, the time for burning a heating gas blown from a burner.

In addition, in the first aspect,
(1) After burning the heated gas to be blown in for a determined combustion time or longer, the burner is moved to another taphole and the heated gas blown in from the burner is burned;
In the first aspect and the second aspect,
(2) The burner has a heavy-tube structure including an inner tube and an outer tube through which gas flows, and has a cap that covers the ends of the inner tube and the outer tube and is removable in the blast furnace. ,
are considered to be preferred embodiments.

Furthermore, in the method for starting up a blast furnace of the present invention, in the above-described method for raising the temperature of the hearth bottom, after the heating gas is blown from the burner, a gas containing oxygen at 1000 ° C. or higher is blown from the tuyere immediately above the burner. It is a method of starting up a blast furnace by blowing in and burning coke in the furnace.

According to the method for raising the temperature of the hearth bottom of the present invention, it is possible to effectively raise the temperature of the lower part of the blast furnace while the operation is stopped, so that the blast furnace can be restarted smoothly.

4 is a flow chart showing steps up to estimation of burner combustion conditions in the furnace bottom temperature raising method of the present invention. FIG. 4 is a diagram showing the shape of a solidified layer grown on the hearth estimated by the boundary element method; FIG. 4 is a diagram showing solidified layer lines at respective positions in the circumferential direction that have grown on the hearth, estimated by the boundary element method. FIG. 4 is a diagram showing smoothed solidification layer lines at respective positions in the circumferential direction that have grown on the hearth, estimated by the boundary element method. FIG. 3 is a diagram showing a three-dimensional region of the hearth bottom to be calculated by the simulator and a division diagram thereof; FIG. 10 is a diagram showing a temperature distribution in the vicinity of the burner calculated by a simulator from the start of burner combustion to 15 hours later; 1(a) and 1(b) are diagrams each showing an example of the structure of a burner that is preferably used in the method for raising the temperature of the hearth of the present invention.

Hereinafter, embodiments and effects of the present invention will be described.
FIG. 1 is a flow chart showing the flow until the thickness of the solidified layer and the taphole burner combustion time are determined using a simulation model in the present invention. In the present invention, first, in order to estimate the conditions inside the furnace before burner combustion, a simulation model is used to estimate the thickness and shape of the solidified layer grown inside the furnace.

Various methods for calculating the thickness of the solidified layer in the furnace are conceivable. The method described in the above document assumes that the interface of the solidified layer is an isotherm of the solidification temperature of pig iron (1150°C), performs heat transfer calculations by the boundary element method (BEM), and measures the temperature with a thermocouple in an actual furnace. This is a method of successively calculating a solidification interface that minimizes the error between the measured value of the furnace bottom temperature and the temperature calculation result by the boundary element method (steps 1 to 3). Fig. 2 shows the shape of the solidified layer on the hearth estimated by this method. Thermocouples are generally installed at a plurality of positions in the circumferential direction and the height direction of the blast furnace at the bottom of the blast furnace below the tuyeres. As shown in FIG. 2, the shape of the solidified layer can be calculated in each direction of the furnace bottom where there are thermocouples for measuring the temperature of the furnace bottom.

Next, in step 4, the calculation result of the vertical cross section is three-dimensionalized. Examples are shown in FIGS. 3 and 4. FIG. FIG. 3 shows the calculation results of the solidification layer lines at each position in the circumferential direction of the blast furnace side by side. By interpolating between the solidified layer lines in FIG. 3, it is possible to smoothly convert the shape of the solidified layer at the bottom of the furnace into three dimensions. Fig. 4 shows the result of dividing the solidified layer lines in Fig. 3 at a pitch of 5° in the circumferential direction, and displaying the solidified layer height at each divided position as a value obtained by quadratic spline interpolation of the solidified layer lines in Fig. 3. show. If the solidified layer height at each position division position in FIG. 4 and the solidified layer height at the actual measurement points are developed in a circumferential shape, the solidified layer shape in the lower part of the furnace can be three-dimensionalized.

Next, in step 5, region division for calculation is performed. FIG. 5 is a three-dimensional computational domain including the furnace bottom and side wall bricks, and the solidified layer region of FIG. The three-dimensional region in FIG. 5 is divided into regions for heat transfer calculation, and physical property values such as thermal conductivity, specific heat, and density for heat transfer calculation are set for each divided element.

Next, in step 6, a tap hole for inserting a burner and burning is selected. This step 6 may be performed before step 5. In step 6 of the flow chart of FIG. 1, the tap hole where the burner is installed is determined for heat transfer calculation. However, the heat transfer calculation may be omitted, the tap hole where the burner should be installed may be specified based on the calculated shape of the solidified layer, and the work of raising the temperature of the hearth bottom may be performed. The inventors found that when a burner is installed at a taphole where the average thickness of the solidified layer between the taphole and the tuyere directly above the taphole is small and heating is performed, the tip of the tuyere is effectively I found that it can be heated.

That is, from the shape of the solidified layer estimated in step 4, the average thickness of the solidified layer in the horizontal direction between the taphole and the tuyere immediately above the taphole is estimated, and the estimated average thickness of the taphole or If there are three or more tap holes, a burner is installed at the tap hole with the second smallest estimated average thickness, and heating gas is blown into the furnace from the burner to raise the bottom of the furnace. Warm is preferred. At this time, if the solidified layer spreads horizontally to the center of the furnace at the height of the tap hole, the horizontal thickness from the average height of the top surface of the horizontally spread solidified layer to the height of the tuyere can be used. Further, the height of the upper surface of the solidified layer at the center of the furnace may be used instead of the average height of the upper surface of the solidified layer.

In step 7, the combustion conditions such as the amount of oxygen to be blown, the fuel gas, the combustion time, and the trajectory of the combustion gas in the packed bed are input. Combustion conditions may be determined according to the capability of the burner and the amount of heat to be supplied. The trajectory of the gas can be determined based on the pressure distribution in the furnace considering the estimated situation in the furnace. In addition, the solidified layer at the bottom of the furnace is rarely filled with solidified pig iron or slag without any gaps. Most of them do. If the tip of the furnace inside the burner installed at the taphole is clogged with a solidified layer and ventilation is poor, prior to combustion of the taphole burner, pure oxygen is blown into the solidified pig iron to oxidize and heat the solidified layer. The burner should be combusted after melting. Also, the combustion temperature of the combustion gas (adiabatic flame temperature) is calculated from the composition of oxygen and fuel gas (step 9).

上記の式においてTは炉底の凝固物、コークス等の内容物の温度、Tgは燃焼ガス温度、ρは密度、Cpは比熱、λは熱伝導率、x,y,zは分割要素の座標、hはガスの対流および輻射による熱伝達係数を表す。 Under the above conditions, unsteady calculation of the temperature rise behavior of the hearth bottom when the burner is fired at the hearth bottom is performed (steps 10 to 13). Specifically, each element obtained by dividing the heat transfer equation shown below for calculation is solved by a numerical analysis method such as a finite difference method or a finite volume method.

In the above formula, T is the temperature of solidified material at the bottom of the furnace, coke, etc., Tg is the combustion gas temperature, ρ is the density, Cp is the specific heat, λ is the thermal conductivity, and x, y, z are the coordinates of the dividing elements. , h represent the convective and radiative heat transfer coefficients of the gas.

Here, the target temperature of the tuyere tip temperature is set to a temperature (approximately 800° C.) or higher at which coke starts to burn due to blowing air from the tuyere. However, the coke in the furnace when the operation is stopped is often covered with molten materials such as pig iron and slag. Combustion may not be able to continue steadily even at possible temperatures. Therefore, the target temperature is preferably 1500° C. or higher, more preferably 2000° C. or higher.

Fig. 6 shows the temperature distribution in the vicinity of the burner after the start of combustion when the solidified layer is obtained as shown in Fig. 4 for an actual blast furnace during a long period of rest, and the burner is inserted into the tap hole and burned. . It can be seen that the temperature of the in-furnace solidified material rapidly rises from the tip of the tap hole through which the combustion gas of the burner flows to the region of the tuyere. Twelve hours after the start of combustion, the temperature at the tip of the tuyere exceeded 2000° C. At this point, it can be determined that it became possible to blow air from the tuyere to burn the coke in the furnace. Therefore, in this blast furnace, the burner installed at the tap hole where the calculation was performed can continue to burn for 12 hours under the same conditions as in the calculation, and then immediately start blowing air from the tuyere. After heating is performed for a predetermined period of time by the burner installed at the taphole, and air can be blown from the tuyere, the taphole burner is moved to another taphole, and multiple positions of the blast furnace are installed. Heating may be performed so that air can be blown from the tuyeres.

For comparison, FIG. 6 also shows the results when heating was continued even after the temperature at the tip of the tuyere reached 2000°C. After 15 hours from the start of combustion, the temperature rise in the area between the tip of the tap hole and the tuyere is maintained at 2000°C, but the temperature rise in the area away from the trajectory of the combustion gas is stagnant. That is, since the purpose of this burner is to raise the temperature of the area between the tap hole and the tuyere, the purpose is achieved 12 hours after the start of combustion, and the combustion is continued thereafter. However, a large temperature rise effect cannot be obtained. This is probably because under these combustion conditions, even if the combustion time increases, the amount of heat input hardly contributes to the increase in temperature, and the amount of heat dissipated increases. That is, 12 hours from the start of combustion is an appropriate burner combustion time. In this way, the present invention makes it possible to estimate the appropriate combustion conditions and combustion time of the burner in just the right amount, which contributes to the early start-up of a blast furnace that is currently out of operation.

The burner may have a structure capable of blowing combustible gas and combustion-supporting gas at the same time. An example of the structure is one having a multi-pipe structure including an inner tube and an outer tube through which gas flows. When the combustible gas and the combustion-supporting gas are blown from the burner, the combustible gas is blown from either the inner tube or the outer tube, and the combustion-supporting gas (for example, oxygen or air) is blown from the other. When the combustion-supporting gas is blown from the burner to burn the coke in the blast furnace, the combustion-supporting gas is blown from one or both of the inner tube and the outer tube. At this time, the burner may be cooled by blowing an inert gas (for example, nitrogen) from the outside of the outer tube so that the temperature of the burner does not rise too much. Alternatively, when no combustible gas is blown, for example, a combustible gas may be blown from the inner tube and an inert gas for cooling may be blown from the outer tube.

Also, the tip of the burner may be provided with a cap that covers the ends of the inner tube and the outer tube and that is removable in the blast furnace. By providing such a cap, when the burner is installed in the blast furnace, the burner can be installed in the blast furnace while gas such as air is circulated from the inner tube to the outer tube to cool the burner. After the installation is completed, for example, by melting and removing the cap by the heat in the blast furnace, heated gas can be blown into the blast furnace from the inner and outer tubes, and the work of installing the burner to the taphole can be simplified. Efficient and safe. An example of such a burner structure is shown in FIGS. 7(a) and 7(b).

FIGS. 7(a) and 7(b) are diagrams respectively showing an example of the structure of a burner preferably used in the method for raising the temperature of the furnace bottom of the present invention. The burner 1 shown in FIGS. 7(a) and 7(b) has a double tube structure of an inner tube 21 and an outer tube 22 through which gas flows, and a cap covering the ends of the inner tube 21 and the outer tube 22. 23. When the cap 23 is present as shown in FIG. 7A, the gas blown from the gas introduction port 24 of the inner tube 21 is discharged from the gas discharge port 25 of the outer tube 22 without leaking to the outside. On the other hand, when the cap 23 does not exist as shown in FIG. 7(b), the gas blown from the gas introduction port 24 of the inner tube 21 is supplied into the furnace. Therefore, the burner 1 has a function of cooling the burner 1 by flowing gas from the inner tube 21 to the outer tube 22 in a state where the cap 23 is present, and cooling by the flow of gas from the inner tube 21 to the outer tube 22 is performed. It has a function of stopping and melting the cap 23 and blowing heating gas into the furnace from the inner tube 21 and/or the outer tube 22 of the burner 1 to raise the temperature of the bottom of the furnace.

Examples of the present invention will be described below. Combustion was started by inserting a furnace bottom heating burner into the tap hole for a real blast furnace that had been out of operation for a long period of time. On the other hand, before the start of combustion, the relationship between the combustion time of the burner and the temperature distribution in the furnace was estimated using a simulator according to the flow chart shown in Fig. 1. A simulator was used to estimate the combustion time during which the temperature of the region between the tap hole and the tuyere would be sufficiently increased, and the same time as this estimated time was used as the combustion time in the actual furnace.

When the burner was pulled out from the tap hole after the end of combustion, it was confirmed that a large amount of molten material was immediately discharged from the tap hole and the temperature in the vicinity of the tap hole was sufficiently raised. After the molten material was discharged, a draft of gas from the taphole to the tuyere was confirmed, so it was also confirmed that a space was secured between the taphole and the tuyere. The temperature at the tip of the tuyere was also raised to 2000°C, confirming the validity of the simulation. Afterwards, hot air at 1100°C was blown from the tuyere, and the coke at the tip of the tuyere burned smoothly. The heating of the blast furnace could be continued and the blast furnace could be started up quickly.

According to the method for raising the temperature of the furnace bottom according to the present invention, it is possible to effectively raise the temperature of the lower part of the furnace during shutdown, not only for restarting the blast furnace but also for various vertical melting furnaces other than the blast furnace. can also provide a method for raising the temperature of the furnace bottom.

1 Burner 21 Inner Tube 22 Outer Tube 23 Cap 24 Gas Inlet 25 Gas Outlet 26 Thermometer

Claims (5)

In a method for raising the temperature of the bottom of a blast furnace whose operation has been stopped, heating gas is blown into the furnace from a burner provided at the tap hole of the bottom of the furnace to raise the temperature of the bottom of the furnace,
estimating the shape of the solidified layer grown on the bottom of the furnace during shutdown;
estimating an average thickness of a solidified layer between a plurality of tap holes and a tuyere immediately above the tap hole;
Install the burner at the tap hole with the smallest estimated average thickness, or at the tap hole with the smallest or second smallest estimated average thickness when there are three or more tap holes, A method for raising the temperature of the bottom of a furnace, comprising the step of blowing a heating gas into the furnace from a burner to raise the temperature of the bottom of the furnace. In a method for raising the temperature of the bottom of a blast furnace whose operation has been stopped, heating gas is blown into the furnace from a burner provided at the tap hole of the bottom of the furnace to raise the temperature of the bottom of the furnace,
estimating the shape of the solidified layer grown on the bottom of the furnace during shutdown;
a step of estimating the temperature distribution of the furnace bottom, which rises in temperature during combustion of the heating gas blown from the burner, from the estimated solidified layer shape;
and determining a time for burning the heating gas blown from the burner based on the temperature distribution. In the method for raising the temperature of the furnace bottom according to claim 2,
A method for raising the temperature of the bottom of the furnace, comprising burning the heated gas to be blown in for a predetermined combustion time or more, and then moving the burner to another tap hole and burning the heated gas to be blown from the burner. In the method for raising the temperature of the furnace bottom according to any one of claims 1 to 3,
The burner has a heavy-tube structure including an inner tube and an outer tube through which gas flows, and has a cap that covers the ends of the inner tube and the outer tube and is removable in the blast furnace. heating method. Using the method for raising the temperature of the furnace bottom according to any one of claims 1 to 4,
A method for starting up a blast furnace, comprising blowing a heating gas from a burner and then blowing a gas containing oxygen at a temperature of 1000°C or higher from a tuyere directly above the burner to burn coke in the furnace.

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