JP2012172867A - Auxiliary burner and electric furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an auxiliary burner causing no clogging in a nozzle and having good maintenance properties.SOLUTION: The auxiliary burner includes a fuel injection pipe 20 and an oxygen gas injection pipe 30 disposed in the outer circumferential part of the fuel injection pipe, and the burner has a discharge flow rate of ≥40 m/s. The drawing margin L (mm) of the oxygen gas injection pipe, the inner diameter D (mm) of the burner top end and the discharge flow rate V (m/s) of the burner satisfy the relationship of expression (1): L/D≥-0.033×V+3.341. The auxiliary burner is useful for assisting combustion of an electric furnace.

Description

  The present invention relates to an auxiliary burner and an electric furnace.

  In a DC or AC electric furnace, iron scrap in the furnace is melted by discharging radially between the inner wall and scrap of the furnace or between the electrodes using an electrode disposed near the center of the furnace. At this time, the iron scrap existing in the radial region from the position of the electrode toward the inner wall dissolves quickly, but there is a portion where the dissolution is insufficient between the electrodes (hereinafter referred to as “cold spot”). To do. The iron scrap in the cold spot melts slowly and an unbalance occurs in the melting speed of the iron scrap in the furnace. The dissolution rate of iron scrap is limited by the dissolution rate of the cold spot.

  For this reason, conventionally, an auxiliary burner that radiates a flame toward the cold spot is installed, and the iron scrap located at the cold spot is preheated, cut, and melted by the auxiliary burner.

  For example, in Patent Document 1, oxygen gas for scattering nonflammable materials and scrap cutting is ejected from the center, fuel is ejected from the outer periphery of the oxygen gas, and combustion oxygen gas is ejected from the outer periphery of the fuel. In order to achieve this, a triple pipe configuration is provided, and in order to increase the speed of the oxygen gas ejected from the central portion, a constricted portion is provided at the tip of the central oxygen gas ejecting tube, and the combustion oxygen gas ejected from the outermost periphery In order to impart swirl to the electric furnace, a high-speed pure oxygen auxiliary burner for an electric furnace in which swirl vanes are installed in an annular space formed by a fuel jet pipe and a combustion oxygen gas jet pipe has been proposed.

  For example, Patent Document 2 proposes a high-speed pure oxygen auxiliary burner for an electric furnace having a triple tube configuration. In Patent Document 3, a triple-structure auxiliary burner is used in an electric furnace, and a theoretical combustion ratio α of oxygen to fuel α, oxygen basic unit A, fuel basic unit B, carbon blending amount C of dissolved raw material, dissolved raw material A technique is disclosed in which the silicon blending amount D is controlled within a predetermined range to prevent the tip of the burner from being blocked by splash or incombustible material, thereby achieving efficient electric furnace operation.

Patent Document 4 and Patent Document 5 disclose a technique that enables the auxiliary combustion burner to swing in the left-right direction to promote the melting of the raw material, so that powder, gas, and the like can be uniformly blown into the furnace body. Has been.

JP-A-10-009524 JP 2002-54805 A JP 2001-158908 A JP 2003-004382 A JP 2004-053129 A

  However, the conventional auxiliary burner still has a problem that the tip of the burner is likely to be clogged by the splash during operation of the electric furnace. For this reason, there is a problem that the maintenance of the burner takes a lot of man-hours and the operating rate of the electric furnace also decreases.

  The present invention has been made in order to solve the problems of the conventional auxiliary combustion burner, and has no nozzle clogging, good maintainability, and an auxiliary combustion burner and an electric furnace that can increase the productivity of the electric furnace. The purpose is to provide.

As a result of intensive studies to achieve the above object, the present inventors have obtained the following knowledge necessary for preventing nozzle clogging.
1) The discharge flow rate needs to be 40 m / s or more.
2) It is preferable that the ratio between the nozzle pull-in allowance and the nozzle diameter is within a predetermined range in relation to the discharge flow rate.
2) A higher flow rate at the nozzle tip is preferred.
3) The installation angle of the burner is preferably large.

  This invention is made | formed based on said knowledge, and makes a summary the auxiliary | assistant combustion burner shown to following (A)-(C), and the electric furnace shown to (D).

(A) An electric furnace auxiliary burner comprising a fuel injection pipe and an oxygen gas injection pipe disposed on the outer periphery thereof, the discharge flow rate being 40 m / s or more, and satisfying the following formula (1) An auxiliary combustion burner characterized by that.
L / D ≧ −0.033 × V + 3.341 (1)
However, the meaning of each symbol in the above formula is as follows.
L: Oxygen gas ejection pipe retraction allowance (mm)
D: Inner diameter of burner tip (mm)
V: Burner discharge flow rate (m / s)

  (B) The auxiliary fuel burner according to (A), wherein the fuel ejection pipe includes an oxygen gas ejection inner pipe having a constricted portion at the tip and a fuel ejection inner pipe for ejecting liquid or gaseous fuel.

(C) The auxiliary burner according to (A) or (B), which satisfies the following formula (2).
L / D ≧ 0.8 (2)
However, the meaning of each symbol in the above formula is as follows.
L: Oxygen gas ejection pipe retraction allowance (mm)
D: Inner diameter of burner tip (mm)

  (D) An electric furnace that uses the auxiliary burners (A) to (C) described above and has a depression angle of 25 ° or more.

  Since the auxiliary combustion burner of the present invention has no nozzle clogging and good maintainability, the productivity of the electric furnace can be increased.

Sectional drawing which shows the example of the auxiliary combustion burner which concerns on this invention Sectional drawing which shows the other example of the auxiliary combustion burner which concerns on this invention Sectional drawing which shows the other example of the auxiliary combustion burner which concerns on this invention The figure which shows the usage example of the auxiliary combustion burner which concerns on this invention The figure which shows the relationship between discharge flow rate and L / D value

  1-3 is a figure which shows the example of the auxiliary combustion burner which concerns on this invention, and FIG. 4 is a figure which shows the usage example of the auxiliary combustion burner which concerns on this invention. Note that the rear end portion of the auxiliary burner is omitted in any of FIGS.

  As an auxiliary combustion burner according to the present invention, for example, as shown in FIG. 1, an auxiliary combustion burner (burner having a double pipe structure) 10 including a fuel injection pipe 20 and an oxygen gas injection pipe 30 disposed on the outer periphery thereof is provided. Can be used. In the auxiliary combustion burner 10, it is preferable that the swirl vane 40 is provided. The swirl vane 40 is for swirling the combustion oxygen gas ejected from the outer periphery to cause a swirl flow. Thereby, mixing of fuel gas and combustion oxygen gas can be promoted.

  The auxiliary burner according to the present invention may be attached with a protective hood at the tip as necessary, and the combustion oxygen gas ejection pipe has a water cooling structure so as to cope with a high temperature atmosphere in the electric furnace. It is good to leave.

  However, the double-tube burner has a limit on the discharge flow rate, and the mixing of the fuel gas and the oxygen gas may be insufficient. Therefore, it is preferable to use the triple-tube burner shown below. FIG. 2 shows a burner when gaseous fuel is used, and FIG. 3 shows a burner when liquid fuel is used.

  As shown in FIG. 2, the auxiliary combustion burner 11 according to the present invention is an auxiliary combustion burner including, for example, a fuel injection pipe 20 and an oxygen gas injection pipe 30 disposed on the outer periphery thereof. The fuel injection pipe 20 of the auxiliary burner 11 is the same as that of the burner having the double pipe structure, but includes an oxygen gas injection inner pipe 21 and an inner pipe (fuel injection inside) for jetting gaseous fuel provided on the outer peripheral side thereof. Tube) 22. In this auxiliary combustion burner 11, cutting oxygen gas is jetted from the central portion, gaseous fuel is jetted from the outer peripheral portion of this oxygen gas, further, combustion oxygen gas is jetted from the outer periphery, and mixed at the nozzle tip, Form a flame. In this auxiliary burner 11, since the cutting oxygen gas ejected from the oxygen gas ejection inner pipe 21 is accelerated at the throttle portion 23, a core flame can be formed at the center of the flame, and the flame can be lengthened. The cold spot can be effectively heated.

  In this auxiliary combustion burner 11 as well, a swirl vane 40 is provided to swirl the combustion oxygen gas ejected from the outer periphery to cause a swirl flow and promote mixing of the fuel gas and the combustion oxygen gas. preferable.

  As shown in FIG. 3, the auxiliary combustion burner 12 according to the present invention is an auxiliary combustion burner including, for example, a fuel injection pipe 20 and an oxygen gas injection pipe 30 disposed on the outer periphery thereof. The fuel jet pipe 20 of the auxiliary burner 12 is the same as that of the burner having the double pipe structure, but includes an inner pipe (fuel jet inner pipe) 25 for jetting liquid fuel therein, and an oxygen gas jet provided on the outer peripheral side thereof. And an inner tube 26. In this auxiliary combustion burner 12, liquid fuel is ejected from the central portion, liquid fuel atomization and scrap cutting oxygen gas is ejected from the outer peripheral portion of this liquid fuel, and combustion oxygen is ejected from the outer peripheral portion of this cutting oxygen gas. Oxygen gas is ejected.

  And in this auxiliary combustion burner 12, it is preferable to provide the throttle part 27 which makes the jet speed of the liquid fuel and the cutting oxygen gas high at the tip of the oxygen gas jet inner pipe 26 in order to atomize the liquid fuel. Moreover, it is preferable to provide swirl vanes 40 for stirring and mixing the mixture of liquid fuel and oxygen gas and further the combustion oxygen gas ejected from the outer periphery.

  In the auxiliary combustion burner 12, the liquid fuel ejected from the central portion and the cutting oxygen gas are mixed at the distal end portion of the oxygen gas ejection tube 26, and further, a throttle portion 27 provided at the distal end portion of the oxygen gas ejection tube 26. At this time, the liquid fuel is sheared by the cutting oxygen gas flowing from the oxygen gas ejection pipe 26 into the liquid fuel ejection pipe 25 and passes through the throttle portion 27. Then, it collides with the inner wall surface of the throttle part 27, and is atomized and atomized by the shock wave of the collision.

  The mixture of atomized liquid fuel and oxygen gas is stirred and mixed by the combustion oxygen gas and the swirl vanes 40. In this way, liquid fuel is atomized and the mixture of the atomized liquid fuel and oxygen gas is ejected at a high speed, so that scattering of combustion supporting materials such as a solvent is promoted and the mixture and combustion are performed. The oxidation exothermic reaction with the working oxygen gas proceeds rapidly, a high-temperature combustion flame is obtained, and the fusing of scrap is promoted. In addition, the swirling blades swirl the combustion oxygen gas ejected from the outermost periphery to cause a swirl flow, so that the mixture of the atomized liquid fuel and cutting oxygen gas and the combustion oxygen gas is abruptly mixed. Done. Furthermore, a sharp flame can be formed at the tip of the burner by these synergistic effects.

  Here, even when any of the above burners is used, the discharge flow rate needs to be 40 m / s or more. This is because if the discharge flow rate is less than 40 m / s, nozzle clogging due to splash adhesion cannot be prevented. The discharge flow rate is preferably 50 m / s or more, and more preferably 60 m / s or more. Even if the discharge flow rate is increased, the effect of preventing nozzle blockage is saturated, so the upper limit of the discharge flow rate is preferably 130 m / s. More preferred is 120 m / s or less, and even more preferred is 110 m / s or less.

However, nozzle clogging due to splash adhesion cannot be prevented only by adjusting the discharge flow rate. However, the drawing-in allowance (mm) of the oxygen gas ejection pipe is L (L in FIGS. 1 to 3), the inner diameter (mm) of the burner tip is D (D in FIGS. 1 to 3), and the burner discharge flow rate (m / s). ) Is V, nozzle blockage can be suppressed if the following expression (1) is satisfied.
L / D ≧ −0.033 × V + 3.341 (1)

If L, D, and V are adjusted within the range that satisfies the above formula (1), the effect of preventing nozzle blockage will be drastically improved, but L / D should be limited to the range that satisfies the following formula (2). This makes it easier to prevent nozzle clogging. L / D is particularly preferably in a range that satisfies the following formula (3).
L / D ≧ 0.8 (2)
L / D ≧ 1.2 (3)

  From the viewpoint of prevention of nozzle clogging, it is preferable that the value of L / D is large. However, if the value is too large, the burner tip may be melted by flame. Therefore, L / D is preferably 3.0 or less. More preferred is 2.8 or less, and even more preferred is 2.5.

  The above auxiliary burner can be used for melting a cold spot of an electric furnace. That is, as shown in FIG. 4, the electric furnace 60 has an electrode 50 at the top, and the auxiliary burner 13 is installed at a position higher than the slag surface of the molten metal 70 on the wall surface of the electric furnace 60. The number of auxiliary burners installed is not particularly limited, but a plurality of auxiliary burners are preferably installed. In particular, in the case of alternating current, it is preferable to install three in order to melt the cold spot between the electrodes. Here, θ shown in FIG. 4 is an angle formed by the axial direction of the auxiliary burner and the horizontal plane, and is called a dip angle. The dip angle is preferably 25 ° or more from the viewpoint of preventing nozzle clogging. There is no restriction on the upper limit of the dip angle, but if it becomes too steep, it becomes impossible to inject a flame in a wide range, so it is preferable to set it to 35 °.

  The burner main body is usually fixed outside the electric furnace main body or the electric furnace, but in the present invention, it is desirable to fix the burner main body to the electric furnace main body. The reason is that since the electric furnace body tilts, when the burner is fixed outside the electric furnace, it is necessary to separate the burner from the electric furnace body every time it is tilted, resulting in poor productivity. On the other hand, when fixing to the electric furnace main body, since the burner moves in synchronization with the electric furnace main body, the burner can be tilted while being inserted into the electric furnace. It is preferable that the burner is fixed to the electric furnace in a state where the burner can be inserted and pulled out. Thus, when the burner is not used, such as during tilting, the burner can be extinguished and pulled out from the electric furnace body, so that splash can be prevented from adhering to the burner. It is preferable to provide a lid at the opening of the electric furnace for inserting and extracting the burner. The lid is used to close the opening when the burner is pulled out. This reliably prevents the splash from adhering to the burner. The lid preferably has a heat insulating material attached. When using the burner, auxiliary combustion can be started quickly by inserting the burner into the opening of the electric furnace.

  In the example shown in FIGS. 2 and 3, the throttle portion is provided in order to increase the flow velocity from the oxygen gas ejection pipe. However, it is desirable that the flow velocity of the oxygen gas be Mach 0.1 to 3.0. If the flow rate is less than Mach 0.1, it is difficult to blow off non-combustible materials such as soot solvent, and it is not possible to expect the fusing acceleration effect due to the exposure of the iron scrap surface, and it may be impossible to suppress clogging of the burner tip. On the other hand, if it exceeds Mach 3.0, it is necessary to increase the size of the oxygen gas supply equipment, and equipment investment costs are required, but the effect is saturated. For this reason, it is preferable that the flow rate of oxygen gas is set to Mach 0.1 to 3.0.

  It should be noted that when the scrap is initially charged in the electric furnace, there is scrap near the burner, so it is important to shorten the flame length. In other words, it is desirable to shorten the flame length at first and to increase the flame length when the scrap melts. The flame length is adjusted by changing the ratio of the oxygen gas supply amount at the center and the oxygen gas supply amount for combustion.

  Three auxiliary burners (triple tube configuration, liquid fuel used (see FIG. 3)) having the same L and D values were prepared. About these auxiliary combustion burners, the dip angle was set to 35 ° in an electric furnace, and the clogged state of the nozzle tip was confirmed. Thereafter, the same experiment was conducted on auxiliary burners having different values of L and D. The result is shown in FIG. In FIG. 5, “×” indicates that the nozzle is blocked within 2 days from the start of use, and “◯” indicates that the nozzle has not been blocked after 18 days from the start of use. Yes.

  As shown in FIG. 5, in the example where the discharge flow rate is less than 40 m / s, nozzle clogging occurred regardless of the value of L / D. In addition, even when the discharge flow rate was 40 m / s or more, nozzle clogging occurred in an example that did not satisfy “L / D ≧ −0.033 × V + 3.341”. On the other hand, in the example where the discharge flow rate was 40 m / s or more and “L / D ≧ −0.033 × V + 3.341” was satisfied, the nozzle clogging could be prevented over a long period of time.

  Since the auxiliary combustion burner of the present invention has no nozzle clogging and good maintainability, the productivity of the electric furnace can be increased.

10, 11, 12, 13 Auxiliary burner 20 Fuel ejection pipe 21 Oxygen gas ejection inner pipe 22 Fuel ejection inner pipe 23 Throttle section 25 Fuel ejection inner pipe 26 Oxygen gas ejection inner pipe 27 Throttle section 30 Oxygen gas ejection pipe 40 Swivel blade 50 Electrode 60 Electric furnace 70 Molten metal

Claims (4)

An electric furnace auxiliary burner comprising a fuel ejection pipe and an oxygen gas ejection pipe disposed on the outer periphery thereof, characterized in that its discharge flow rate is 40 m / s or more and satisfies the following formula (1): An auxiliary combustion burner.
L / D ≧ −0.033 × V + 3.341 (1)
However, the meaning of each symbol in the above formula is as follows.
L: Oxygen gas ejection pipe retraction allowance (mm)
D: Inner diameter of burner tip (mm)
V: Burner discharge flow rate (m / s)   The auxiliary fuel burner according to claim 1, wherein the fuel ejection pipe includes an oxygen gas ejection inner pipe having a constricted portion at a distal end portion, and a fuel ejection inner pipe for ejecting liquid or gaseous fuel. The auxiliary combustion burner according to claim 1 or 2, wherein the following formula (2) is satisfied.
L / D ≧ 0.8 (2)
However, the meaning of each symbol in the above formula is as follows.
L: Oxygen gas ejection pipe retraction allowance (mm)
D: Inner diameter of burner tip (mm)   An electric furnace characterized in that the auxiliary burner according to any one of claims 1 to 3 is used, and the dip angle is 25 ° or more.

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