JPH02183793A - Drying control method and device for ladle - Google Patents

Abstract

PURPOSE:To provide a substantial uniform drying so as to get a predetermined distribution of temperature at anywhere within a ladle positively within a time as short as possible by a method wherein a drying initial stage is applied at a combustion in a high air ratio and then gradually the air ratio is decreased and during and after the intermediate drying stage, the combustion is carried out with an air ratio of about 1. CONSTITUTION:Combustion air and fuel gas are injected into a ladle. When it is dried, a drying initial stage is applied with an air ratio of about 5 to 10, then the air is gradually decreased and then the intermediate and subsequent drying stage, the combustion is carried out with the air ratio being about 1. With this arrangement, at the initial drying stage, it is uniformly heated with a high air ratio, a dehydration effect and a ladle agitating effect can be improved. After that, the air ratio is gradually decreased and the combustion gas can be increased so as to be applied for a high temperature heating. In this way, the controlling is carried out to enable a temperature to be varied along a desired distribution curve and so the inner circumferential surface temperature within the ladle is made uniform in a depth direction of the ladle.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is directed to a conveyor belt (hot metal pot, molten steel, tundish, etc.) used for transporting molten metal such as molten ore in a blast furnace or the like. The present invention relates to a drying control method and apparatus.

[Conventional technology]

Generally, ladle is lined with refractory bricks or monolithic refractories, but after long-term use, the ladle is eroded by the smelt ore inside, causing wear or damage. As a result, if the service life limit is exceeded, interim repairs or rebuilding will be carried out. However, since these refractories generally contain moisture, it is necessary to heat and dry them as a dehydration treatment after repair. cause an explosion). If this drying process is carried out too quickly, it may cause cracks or explosions, so it must be carried out carefully while controlling the temperature.

On the other hand, if the ladles are dried slowly over time, many ladles must be prepared to accommodate a large amount of molten metal, and work such as transporting and processing the molten metal takes longer. I don't like it.

A gas burner is generally used as a drying means.

Coke gas is generally used as the fuel gas for the gas burner, and is mixed with combustion air and blown onto the inner peripheral surface of the ladle.

[Problem to be solved by the invention]

Conventionally, when drying a ladle, the temperature inside the ladle has been controlled to have a substantially uniform temperature distribution.

In addition, the optimal temperature distribution pattern in the pot over time (
Characteristic curve) is uniquely determined by calculation according to the type, thickness, size of the pot, etc. of the refractory, and therefore,
How to control the temperature change of the target pot over time is determined on a self-help basis. Naturally, it is ideal to control the temperature inside the pot according to the predetermined temperature distribution pattern.

However, none of the conventional methods can fully satisfy the uniform distribution of temperature inside the pot; for example, even if a predetermined temperature distribution pattern is achieved at the top of the pot, the temperature distribution at the bottom of the pot deviates greatly from the predetermined curve. It ends up. Moreover, the opposite case is also possible. For this reason, attempts have been made to improve the structure of the gas burner so that the entire inner surface of the pot can be heated more or less uniformly in an efficient manner, but this has not yet been achieved (for example, Japanese Patent Laid-Open No. 60-247464). , Japanese Unexamined Patent Publication No. 111887/1987).

[Means to solve the problem]

It is an object of the present invention to provide a control method and apparatus that can reliably perform substantially uniform drying in any part of the ladle so as to draw a predetermined temperature distribution in the shortest possible time.

To achieve this objective, the present invention provides that when blowing combustion air and fuel gas into a ladle and drying it,
The structure is characterized in that combustion is performed at a high air ratio of 5 to 10 in the initial stage of drying, and then the air ratio is gradually lowered, and combustion is performed at an air ratio of approximately 1 from the middle stage of drying onwards.

The apparatus of the present invention for carrying out this method includes a burner combustion apparatus that injects combustion air and fuel gas into a ladle, and burns at a high air ratio of 5 to 10 in the initial stage of drying, and then gradually increases the air ratio. The present invention is characterized in that it has an air ratio control means that lowers the air ratio and performs combustion at an air ratio of approximately 1 after the middle of the drying period.

Preferably, the burner combustion device has a coaxial flow gas burner in which an outer pipe for ejecting combustion air and an inner pipe for ejecting fuel gas are disposed coaxially, and a continuous gas burner is provided near the tip of the inner pipe. An expanding diameter portion is formed, and a plurality of openings are provided at approximately equal intervals along the circumferential direction of the diameter expansion portion.

[For production]

At the initial stage of drying, excessive air is supplied, resulting in a high air ratio of 5 to 10.
Combustion occurs at , and then the amount of supplied air is gradually reduced to bring the air ratio to approximately 1.

In this way, by changing the ratio of air to fuel gas (air ratio) between the initial stage and the middle stage of drying, uniform heating is carried out at a relatively low temperature in the early stage of drying, with the aim of dehydration effect and stirring effect in the pot. After that, lower the air ratio to approximately 1,
To make it possible to increase the amount of fuel gas so as not to interfere with high-temperature heating. By performing such control,
It is possible to change the temperature along the desired distribution curve,
Therefore, the inventors of the present invention have experimentally confirmed that the temperature of the inner peripheral surface of the ladle is approximately uniform in the depth direction of the ladle.

Air ratio control is performed by an air ratio control means, which controls the amount of air supplied to the gas burner and, if necessary, the amount of fuel gas supplied.

A gas burner has a tube for ejecting combustion air and a tube for ejecting fuel gas independently on a concentric circle, and therefore, the amount of each ejected can be easily controlled.

Generally, if the air ratio is set to an excess air amount of 5 to IO, the flame will be blown out. This is because such a high air ratio tends to cause a so-called blow-up phenomenon in which the flame is formed far from the base of the burner tile, and as a result, the flame is blown out. Therefore, even if an attempt was made to increase the air ratio in order to improve the stirring effect, it would not be possible to create such a high air ratio with conventional burner structures, and the air ratio was generally limited to 3).

Therefore, the applicant of the present application previously proposed a gas burner in Utility Application No. 63-23066 that could maintain the flame in a stable state without causing the combustion gas blow-up phenomenon even when the air ratio was increased to 10. .

In the apparatus of the present invention, for example, an air ratio of 5 to 10 can be achieved by using this gas burner (described in detail later).

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 schematically shows the basic concept of the present invention.

In addition, in the following examples, subscripts c and a indicate that they relate to coke gas and air, respectively.

The ladle IO is equipped with a gas burner 11, which will be described later, on its upper part, from which fuel gas (coke gas) Gc and combustion air Ga at a desired air ratio are supplied.

One or more thermometers (thermocouples) 15 are provided within the ladle 10 to detect the temperature of the ladle IO. A temperature signal S from the thermometer 15 is input manually to the control device 20 .

The control device 20 constantly monitors the temperature inside the pot based on this temperature signal St, controls the Gc flow rate by the control valve Vc so that the desired set temperature is reached, and based on this controls the Ga by the control valve Va to maintain the predetermined air ratio. Controlled by The control flow will be described later (FIG. 3).

The ultimate objective of the present invention is how to approximate the temperature inside the pot to a desired heating curve (heating time-heating temperature characteristics). The ideal heating curve itself that provides a uniform temperature condition within the pot is well known, and an example thereof is shown in FIG. The ideal heating curve shown in FIG. 2 shows different curves depending on the size of the pan to be dried, the material, the type of molten metal, etc., but the tendency of the characteristic curve is -. That is, the temperature is raised to about 200°C in the initial stage of drying (about 16 to 17 hours from the start of heating), then heated to about 300°C (about 30 hours after the start of drying), and finally to 1000°C.
(drying completes in about 45 hours). If the heating temperature is time-controlled along this curve, the temperature will be approximately uniform no matter where you measure it in the pot.

Various methods have been tried in the past to approximate this curve, but none of them have yielded sufficiently satisfactory results. In other words, there was a partial deviation from the ideal curve, resulting in uneven temperature distribution within the steel.

According to the present invention, when the combustion air and fuel gas are spouted into the ladle and dried, the initial stage of drying is performed at a high air ratio of 5.
- IO, and then the air ratio was gradually lowered so that the air ratio was approximately 1 from the middle of the drying period onwards. As a result, at the initial stage of drying, high-temperature air is used to uniformly heat the product, improving the dehydration effect and the stirring effect in the pot, and after that, the air ratio is gradually lowered to make it possible to increase the amount of fuel gas for high-temperature heating.

By performing such control, it is possible to change the temperature along the desired distribution curve, and it has been experimentally confirmed that the temperature on the inner circumferential surface of the ladle is approximately uniform in the depth direction of the ladle. did. The experimental results are shown in Figure 2. As shown in the figure,
It can be seen that the temperatures inside the pot measured at three different height positions of the pot (Fig. 2), ■, ■, and ■ (Fig. 2), all approximately correspond to the ideal characteristic diagram (set temperature).

FIG. 2 also shows the relationship between such characteristics and the air ratio and Gc flow rate.

In the case of the example shown in FIG. 2, the "early stage of drying" referred to in the present invention corresponds to about 17 hours after the start of heating. During this time, the temperature inside the pot reached approximately 180°C. "Drying stage" is generally about 1/3 of the heating end time.
It corresponds to the degree.

FIG. 3 shows an example of a control flowchart of the present invention.

The timer routine shown in FIG. 3 is assumed to be executed (counted up) every five minutes, for example (step 301). Further, the counter C is cleared each time during initial operation.

When heating is started, a map of the set temperature T previously stored in the memory is read (step 303), and the measured temperature detected by the thermometer 15 is compared with the set temperature (step 305). If the temperature is the same as the set temperature, the same Gc is maintained. In step 305, if the detected temperature is higher than the set temperature, reduce Gc (step 309),
If it is low, conversely, Gc is increased (step 307).

Next, the process proceeds to step 311, where the characteristic map for the air ratio stored in advance in the memory is read, and the air 11G at that time is read.
a is calculated (step 313), and the Ga flow rate is controlled to achieve the air ratio (step 315). Note that once Gc is determined, Ga is uniquely determined by calculation according to the air ratio.

The above operation is repeated at predetermined time intervals (for example, every 5 minutes) until a predetermined drying time (for example, 45 hours) is reached. In step 317, if C becomes greater than 45 hours, all heating operations (burners, etc.) are stopped.

In the example shown in Fig. 2, the air ratio in the early stage of drying (approximately 17 hours after the start of heating) was set to approximately 8, and then in the middle stage of drying (approximately 17 hours after the start of heating).
It was maintained at 3 for about 30 hours after the start of heating, and then finally lowered to about 1.1.

Fig. 4.5 shows an example of the structure of a high air ratio gas burner used in the present invention.

As mentioned above, this gas burner was disclosed in the applicant's earlier application (Utility Application No. 63-23066), and its construction will be briefly explained below.

The gas burner shown in Figure 4.5 basically has an outer tube 1 that blows out combustion air and an inner tube 2 that blows out fuel gas (e.g. coke gas), and these are arranged coaxially to form a coaxial flow. It's a gas burner. Combustion air Ga flows through the outer tube 1 as shown by arrow 3, while fuel gas Gc flows through the inner tube 2 as shown by arrow 4. Inner pipe 2 along fuel gas flow direction 4
has an enlarged diameter portion 5 that continuously expands near its tip,
Its tip ends as a run-up section 6. 7 is the enlarged diameter part 5
It shows a plurality of openings formed at approximately equal intervals along the circumferential direction. Combustion air flows from the outer tube 1 into the inner tube 2 through this open lower (indicated by arrow 8).

According to the above-described configuration, the flow velocity of the combustion air is lower in the enlarged diameter portion 5 in the outer tube 1 than in the discharging portion at the tip thereof, and the pressure thereof is higher. On the other hand, the fuel gas has a higher flow rate and a lower pressure in the enlarged diameter section 5 in the inner tube 2 than in the discharge section.

That is, by providing the enlarged diameter portion 5, the combustion air in the outer tube 1 has a higher pressure than the fuel gas in the inner tube 2. As a result, the enlarged diameter portion 5
A sufficient blowout effect of combustion air can be obtained due to the pressure difference through the open lower part formed in the lower part.

The ratio of the inner diameter b1 of the inner tube 2 to the inner diameter b2 of the run-up section 6 (
In other words, the difference between the minimum diameter at the start part and the maximum diameter at the end part of the enlarged diameter part 5)
is preferably 1.1 to 2.0. This inner diameter ratio (b2
/bl) is less than 1.1, a sufficient pressure difference will not be generated between the outer tube 1 and the inner tube 2 at the enlarged diameter portion 5, resulting in insufficient combustion air gas mixing effect. Also, conversely, the inner diameter ratio (b2
Even if /b+) exceeds 2.0, the mixing effect of combustion air gas is almost the same as when the inner diameter ratio = 2.0, but since the area of the air discharge part is combusted, the flow velocity increases, and the flame blowout increases. This phenomenon is likely to occur, and the pressure drop increases, which increases the capacity of the air blowing equipment, resulting in the problem of increased equipment costs.

Next, find the inner diameter a of the outer tube l and the inner diameter of the inner tube.

The ratio (a, /bl>) is preferably 2.0 to 3.0 so that the above-mentioned mixing effect can be obtained at an air ratio of 3 to 10, and at the same time, the generation of unburned parts and blowout do not occur.

The ratio (12/βl) between the axial length β2 of the run-up section 6 and the axial length L of the enlarged diameter portion 5 is most preferably 0.2 to 1.0. If the ratio is less than this, the combustion air mixed with the fuel gas will be directed outward from the burner discharge port under the influence of the enlarged diameter portion 5, so that the combustion air mixed with the fuel gas from the inner pipe will not be well mixed, and blowout will occur. Moreover, when lx/it becomes 1.0 or more, the ignition point comes inside the run-up section 6, so the temperature at the burner outlet becomes high, and the durability deteriorates significantly.

The shape of the opening lower is not particularly limited, and generally a circular or rectangular shape is adopted. The number of open lowers (fuel gas jet ports) occupies 30% to 80% of the circumference of the expanded diameter portion 50, and is preferably arranged symmetrically with respect to the coaxial flow. 30%
If the occupancy is less than 80%, the mixing effect will be insufficient;
In this case, the structural strength of the enlarged diameter portion 5 becomes insufficient.

As mentioned above, by using a coaxial flow gas burner, it becomes possible to increase the air ratio, which was conventionally limited to 3, to 10. In this case, it has been experimentally confirmed that the combustion gas does not blow up and the flame remains stable.

〔Effect of the invention〕

As described above, according to the present invention, combustion is performed at a high air ratio of 5 to 1 O in the initial stage of drying, and then the air ratio is gradually lowered, and combustion is performed at an air ratio of approximately 1 from the middle stage of drying onwards, thereby achieving the desired It has been experimentally confirmed that the temperature can be changed along the distribution curve of tin, and that the temperature of the inner peripheral surface in the tin is approximately uniform in the depth direction of the tin.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of an apparatus for implementing the ladle drying control method according to the present invention, FIG. 2 is a diagram showing experimental results of the present invention, and FIG. 3 is a control flowchart of the present invention. FIG. 4 is a longitudinal sectional view showing an example of a gas burner used in the present invention, and FIG. 5 is a sectional view taken along the line V-ν in FIG. 4. l...Outer tube, 2...Inner tube, 5...Enlarged diameter part, 7...Opening, 10...L
11... Gas burner, 15... Thermometer,
2o...control device. Figure 4

Claims (1)

[Claims] 1. When blowing combustion air and fuel gas into a ladle and drying them, combustion is performed at a high air ratio of 5 to 10 in the initial stage of drying, and then the air ratio is gradually lowered. A ladle drying control method characterized by burning at an air ratio of approximately 1 from the middle of the drying period onwards. 2. A ladle drying control device that blows out combustion air and fuel gas into the ladle and dries the ladle while controlling its temperature, the device blowing out combustion air and fuel gas into the ladle. and an air ratio control means that performs combustion at a high air ratio of 5 to 10 during the initial stage of drying, and then gradually lowers the air ratio to perform combustion at an air ratio of approximately 1 from the middle stage of drying onwards. Ladle drying control device. 3. The burner combustion device has an outer tube that blows out combustion air;
It has a coaxial flow gas burner coaxially disposed with an inner tube that spouts fuel gas, and has an enlarged diameter section that continuously expands near the tip of the inner tube, and a gas burner that extends in the circumferential direction of the enlarged diameter section. 3. The ladle drying control device according to claim 2, further comprising a plurality of openings provided at substantially equal intervals along the ladle.