JP2009001857A - Slab extraction ratio determining method of continuous heating furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a slab extraction ratio determining method of a continuous heating furnace having a plurality of heating furnaces, and capable of smoothly and adequately controlling the operation of the heating furnaces even when the combustion is performed in the heating furnaces while hot slabs and cold slabs are mixed therein. <P>SOLUTION: In the slab extraction ratio determining method, the slab extraction ratio is calculated by using the coefficient indicating the heating capacity of heating furnaces and the load factor indicating the heating load of slabs in a continuous heating furnace having a plurality of slab heating furnaces. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for determining a slab extraction ratio of a continuous heating furnace for hot rolled material.

  In a continuous heating furnace for hot-rolled material, the slab charged in the furnace passes through the pre-tropical zone, heating zone and soaking zone, and in order to reach the rolling target extraction temperature at the heating furnace outlet. The temperature is raised by heating. In order to manage the heating temperature of such a continuous heating furnace, the temperature of each zone is usually set, and combustion management is performed so that the slab is heated to this temperature.

  Further, the continuous heating furnace has a two-furnace configuration so that the heating capacity exceeds the rolling capacity, and the operation of the heating furnace that performs hot rolling by alternately extracting slabs from the first heating furnace and the second heating furnace. A furnace method is adopted.

  Furthermore, in order to prevent the rolling line from being stopped due to insufficient heating of the slab and to stabilize the operation of the heating furnace, the slab extraction ratio of the first heating furnace and the second heating furnace is fixed at 1: 1. There are many.

  The case described above is stable when there are a large number of slabs to be heated that have the same size, such as thickness and width. In recent years, from the viewpoint of energy saving, hot strip slabs (hereinafter sometimes abbreviated as hot strips) cast by a continuous casting apparatus have been actively introduced into a continuous heating furnace at as high a temperature as possible. However, in addition to the hot piece slab, cold slabs (hereinafter sometimes abbreviated as cold pieces) stored in the slab yard or light slabs with a small slab size can be mixed and operated. There are many cases where this is unavoidable.

  In such a case, trying to satisfy the target temperature at the time of slab extraction in all slabs causes problems such as a rapid temperature rise in each furnace and a longer in-furnace time than necessary, resulting in fuel loss. Or the rolling line is stopped due to insufficient heating.

  As these solutions, in Patent Document 1, the slab charged in the second heating furnace is different from the slab charged in the first heating furnace when the steel type is different and the in-furnace time is limited. A technique is disclosed in which priority is given to extraction of a slab from a two-heating furnace so as not to cause deterioration due to overheating of the slab and insufficient heating due to fluctuations in the in-furnace time.

However, even with this method, when there are a plurality of slab sizes and steel types, the extraction pitch from the heating furnace is limited, and the heating furnace becomes a bottleneck process and there is a problem that the operation efficiency decreases.
Japanese Patent Laid-Open No. 11-12656

  Therefore, the present invention is a continuous heating furnace having a plurality of heating furnaces, and even when the heating furnace is burned by mixing the hot piece slab and the cold piece slab, the heating furnace can be operated smoothly and appropriately. It aims at providing the slab extraction ratio determination method of a heating furnace.

  The present invention has been made to solve the above-described problems of the prior art.

  That is, the first invention calculates a slab extraction ratio in a continuous heating furnace having a plurality of slab heating furnaces, using a coefficient representing the heating capacity of the heating furnace and a load coefficient representing the heating load of the slab. Is a method for determining a slab extraction ratio.

  According to a second aspect of the present invention, the load factor indicates the in-furnace time required for slab heating, the slab thickness of each slab, the furnace charging temperature, the temperature difference between the extraction target slab temperature and the heating zone slab temperature, respectively. The slab extraction ratio determination method according to the first aspect of the invention is characterized in that the coefficient is converted into a coefficient.

  A third invention is the slab extraction ratio determination method according to the second invention, wherein the slab extraction ratio is calculated using the equation (1).

  In calculating and determining the extraction ratio of the slab, overheating and insufficient heating can be reduced by using a load coefficient representing the heating load of the slab.

  An example of the equipment configuration of a continuous heating furnace to which the present invention is applied is shown in FIG.

  FIG. 2 is a side view of the continuous heating furnace, in which the slab is charged into the furnace from the charging side, preheated in the pre-tropical zone and sequentially sent in the direction of the arrow, toward the extraction target temperature in the heating zone. It is heated in earnest, soaking in the tropical zone, soaking so that there is no temperature difference between the outer surface of the slab and the center, and when reaching the extraction target temperature, it is carried out from the extraction side and subjected to hot rolling. Combustion gas used to heat the slab flows in the pretropical direction opposite to the slab flow and is discharged from the flue.

  FIG. 1 is a plan view of a continuous heating furnace, which is an example in which there are two continuous heating furnaces (No. 1 furnace, No. 2 furnace). In the operation of the No. 1 and No. 2 furnaces, each furnace has two rows of slabs. The simplest example of slab extraction in such a heating furnace arrangement is to extract the first slab of the first furnace, then the second slab, and then the second slab of the second furnace, 4 The slabs in the row are extracted and this order is repeated. The extraction ratio of the slab in this case is 1st furnace: 2nd furnace = 2 pieces: 2 pieces = 1: 1.

  However, such slabs can be extracted when the heating capacity of the No. 1 furnace and the No. 2 furnace are equal and the slab types (slab dimensions, hot pieces, cold pieces, etc.) are the same. The slab extraction ratio is the ratio of the number of slab extractions.

  In reality, there are differences in the slab varieties charged in each furnace. For example, when all the light slab slab is charged into the No. 2 furnace, the slab thickness of the light slab slab is about 100mm compared to the 250mm cross-section slab, so the time to reach the extraction target temperature is also compared with the 250mm cross-section slab. And about half. The light slab is a slab name for manufacturing a thin steel plate having a thickness of 10 mm or less, and the slab thickness is thinner than that of a normal slab.

  Therefore, the extraction ratio when heating the light block slab usually needs to be changed to 1: 2 to 1: 3 with respect to the first furnace: second furnace = 1: 1.

  On the other hand, when a hot piece is also charged into the No. 2 furnace, the hot piece and the light slab slab may be over-baked and scale damage may occur in the extraction ratio matched to the cold piece. Further, the in-furnace time becomes longer than necessary, and the fuel efficiency is lowered.

  Thus, when slabs having different thicknesses and charging temperatures are mixed, an operation method of the heating furnace in which the extraction ratio of the slab is changed between the No. 1 furnace and the No. 2 furnace becomes necessary.

  Therefore, it is necessary to operate the heating furnace with a variable extraction ratio according to the type of slab to be charged (slab size, hot piece, cold piece, etc.).

The method for determining the slab extraction ratio in the heating furnace operating method with variable slab extraction ratio will be described below.
1. Coefficientization of heating load of slab In order to change the extraction ratio depending on the heating capacity and slab type (slab size, hot piece, cold piece, etc.), it is necessary to make the heating load of each slab a coefficient.

  Then, the test which investigates the in-furnace time until it reaches extraction temperature 1140 degreeC after charging a slab into a furnace about the 1st furnace and the 2nd furnace was done for slab thickness and the slab charging temperature as a parameter.

  The test level is 4 levels of slab thickness of 100 mm, 150 mm, 180 mm, 250 mm, and the slab charging temperature is 4 levels of normal temperature (cold slab), 200 ° C., 400 ° C., 600 ° C. (hot piece slab), The extraction target temperature (slab average temperature) was 1140 ° C.

  The result was evaluated based on the in-furnace time from the introduction of the slab into the pre-tropical zone until reaching 1140 ° C. The test results are shown in FIGS.

  Fig. 3 shows the furnace No. 1 (1CF) and No. 2 furnace (2CF) when the charging temperature to the heating furnace is changed to room temperature, 200 ° C, 400 ° C, 600 ° C using a slab having a thickness of 250 mm. It is the result of having tested the in-furnace time until extraction average slab temperature in 1140 reaches 1140 degreeC. The horizontal axis indicates the temperature of the slab charged, and the vertical axis indicates the in-furnace time from slab charging to extraction.

  The higher the slab charging temperature, the greater the latent heat of the slab brought into the furnace, so that the slab burns faster and the in-furnace time is shorter. The reason for the longer time in the No. 2 furnace is due to the difference in the structure of the heating furnace such as the combustion burner and the hearth structure.

  FIG. 4 shows the load coefficient in heating (the slab loading of the first furnace) based on the time when the hot piece having a slab temperature of 400 ° C. was charged into the first furnace based on the in-furnace time obtained in FIG. The numerical value representing the required in-furnace time until the slab is burned up when the in-furnace time of a hot piece having a heat input temperature of 400 ° C. is 1.0 is displayed for each slab charging temperature and for each furnace. Therefore, the basic tendency is the same as in FIG.

  FIG. 5 shows that the average temperature of the extracted slabs in the No. 1 furnace and No. 2 furnace is 1140 ° C. when the slab temperature is normal temperature (20 ° C., cold slab) and the slab thickness is changed to 100 mm, 150 mm, 180 mm, 250 mm. It is the result of having tested the in-furnace time until it reaches to. It can be seen that the slab thickness greatly affects the slab burn-up time (in-furnace time).

FIG. 6 shows the in-furnace time obtained in FIG. 5 with the slab thickness of 250 mm and the slab charging temperature of 400 ° C. as a standard, and the load factor is converted into the slab thickness and the furnace as in the case of FIG. It is. The basic trend is the same as in FIG.
2. Calculation of extraction ratio The extraction ratio is changed for the purpose of securing the required in-furnace time until slab burn-up by extending the in-furnace time of the slab that takes time to reach the extraction temperature.

  The in-furnace time of the continuous heating furnace is determined by the slab width and the rolling pitch when the extraction ratio is No. 1 furnace: No. 2 furnace = 1: 1 (formula (3)).

When the extraction ratio is 1: 1 (2: 2) (FIG. 1)
Furnace time = furnace length (m) / slab width (m) / rolling pitch (main / Hr) × 4 (3)
However, the in-furnace time required to burn up differs depending on the heating capacity of the heating furnace and the slab type, and the in-furnace time can be adjusted by changing the extraction ratio.

  In the calculation of the extraction ratio, attention is paid to the heating zone (FIG. 1) that has a great influence on the slab burn-up, and the slab varieties existing in the heating zone and the heating results are taken into consideration. That is, it calculates using the load coefficient shown in FIG.

  Specifically, it is desirable to calculate the load coefficient using Equation (1) with three parameters K1, K2, and K3.

  α is obtained by converting the heating capacity of the No. 2 furnace from the in-furnace time when the heating capacity of the No. 1 furnace is 1, and in this embodiment, the No. 1 and No. 2 furnaces in FIGS. From the difference in in-furnace time, when the first furnace is 1.0, the second furnace is 0.86. That is, when slabs having the same conditions are charged into the No. 1 and No. 2 furnaces, it can be seen that the No. 2 furnace requires more time for the slabs to reach the target extraction temperature. Therefore, α is a coefficient representing the heating capacity determined by characteristics such as the structure of the heating furnace.

  K1 is a load coefficient obtained by converting the influence on the in-furnace time due to the difference in the slab thickness. The time required for the 250 mm slab to reach the target extraction temperature is about 2.6 times for the 100 mm slab. Doubled.

  K2 is a load coefficient obtained by coefficientizing the influence of the temperature of the slab charged into the continuous heating furnace (furnace charging temperature) on the in-furnace time, and the coefficient when the slab temperature 400 ° C. is 1.0. Show. The higher the slab charging temperature, the greater the latent heat that is brought into the furnace, and the shorter the time required for the slab to reach the target extraction temperature.

  K3 is a load coefficient obtained by coefficientizing the difference between the extraction target slab temperature of the continuous heating furnace and the heating zone outlet side slab temperature (equilibrium entry slab temperature). The larger the temperature difference, the longer the time spent in the soaking zone. In this case, it is necessary to add fuel to the heating zone to increase the temperature.

  Further, the load coefficient described above is preferably tabulated in advance as shown in Table 1, for example.

  In addition, the extraction ratio of the slab of the present invention can be used both when the temperature management of the continuous heating furnace is automatically controlled and when the manual management is performed.

  By applying the extraction ratio determination method of the present invention using the coefficient α (= 0.86) and the load coefficients K1, K2, and K3 representing the heating capacity in the equation (2) and Table 1, the slab operation is changed. However, the rapid rise in the furnace temperature was suppressed, contributing to a reduction in fuel consumption. Moreover, the scale flaw defect accompanying the increase in route time could be reduced by 0.02%, and the non-heat generation rate due to slab firing delay could be reduced by 0.2%.

The method of the present invention can also be applied to a heating furnace such as a billet.

It is a top view of a continuous heating furnace. It is a side view which shows an example of a continuous heating furnace. It is a figure which shows the relationship between slab charging temperature and in-furnace time. It is a figure which shows the relationship between slab charging temperature and a load coefficient. It is a figure which shows the relationship between slab thickness and in-furnace time. It is a figure which shows the relationship between slab thickness and a load coefficient.

Claims (3)

  In a continuous heating furnace having a plurality of slab heating furnaces, a slab extraction ratio is determined by calculating a slab extraction ratio using a coefficient indicating the heating capacity of the heating furnace and a load coefficient indicating the heating load of the slab. Method.   The load factor is a factorization of the in-furnace time required for slab heating with respect to each slab thickness, furnace charging temperature, temperature difference between the extraction target slab temperature and the heating zone slab temperature. The slab extraction ratio determination method according to claim 1, wherein the slab extraction ratio is determined. The slab extraction ratio determination method according to claim 2, wherein the slab extraction ratio is calculated using equation (1).

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