US3627295A - Blow lance arrangement - Google Patents

Abstract

A blow lance arrangement for controlling flow of gas through a blow lance arranged to blow gas onto the upper surface of a metal bath by moving the end of a spindle arranged in a longitudinal passage of the blow lance from a retracted position located upwardly spaced from a restricted throat portion of the passage through the throat portion to advanced positions into the outwardly flaring nozzle portion of the passage.

Description

United States Patent [72] Inventors JyoDoi Kanagawa-ken;

Kunio Yoshioka, Kanagawa-ken, both of Japan [2]] App]. No. 32,997

[22] Filed Apr. 29, 1970 [45] Patented Dec. 14, 1971 [73] Assignee Nippon Kokan Kabushiki Kaisha Tokyo, Japan [32] Priority July 27, 1966 [33] Japan Original application July 26, 1967, Ser. No. 656,241, now abandoned. Divided and this application Apr. 29, 1970, Ser. No. 32,997

[54] BLOW LANCE ARRANGEMENT 6 Claims, 12 Drawing Figs.

[52] U.S. Cl 266/34 L,

75/59 [51] Int. Cl C2lc 7/00 [50] Field of Search 266/34,

DIG. 3, DIG 4; 75/59, 60

[56] References Cited UNITED STATES PATENTS 3,346,190 l0/l967 Shepherd 75/60 X FOREIGN PATENTS 216,032 7/196] Austria i. 266/34 224,669 l2/l962 Austria.... 266/34 995,688 6/1965 Great Britain.v 266/34 l,()()3,5 l4 9/[965 Great Britain 266/34 Primary l-jxamim'n-Gerald A. Dost Almrnvy-Michacl S. Striker ABSTRACT: A blow lancc arrangement for controlling How of gas through a blow lance arranged to blow gas onto the upper surface of a metal bath by moving the end of a spindle arranged in a longitudinal passage of the blow lance from a retracted position located upwardly spaced from a restricted throat portion of the passage through the throat portion to ad vanced positions into the outwardly flaring nozzle portion of the passage.

PATENIED BEE I 4 mm ISOOO- IZ-OOO lOOOO IO-O SHEET 3 OF 6 Tl Ifi 6 Pr Q "Van ab;

Pr 7 /cm abs In) #901" k who ymmm 4 BLOW LANCE ARRANGEMENT CROSS-REFERENCE TO RELATED APPLICATION The present application is a division of our copending patent application Ser. No. 656,241, filed July 26, 1967, entitled Method of Making steel," and now abandoned.

DETAILED DESCRIPTION OF THE INVENTION This invention relates to a blow lance arrangement.

As well known the converter operation may comprise inserting a water cooled lance through the opening in an upright furnace, blasting industrially pure oxygen onto the surface of steel bath containing hot metal as main raw material from a height in the order of l-2 m. to form a fire spot, thereby effecting a quick oxidizing reaction. In such an operation, i.e. in a refining process for obtaining steel having required chemical analysis values from hot metal with addition of some scrap, the proper oxidation of above charged raw materials is complicated. It has been a long-pending question in industrial circles how to properly control flow rate and pressure of the oxygen used. In the LD process, especially in the last blowing stage, as a consequence of the decrease of decarburizing reaction, it is well known that the boiling drops. In order to cope with the phenomenon of rapid increase of [N], which is caused by the air drawn into the furnace owing to considerable reduction of internal pressure of the furnace, the oxygen jet pressure should be increased. However when the pressure of oxygen supplied is raised, the flow rate of oxygen is also increased. This produces a bad effect, namely the increase of oxygen content in the steel. Nevertheless, under present circumstances where no appropriate measure for solving this problem exists, a step such as increase of the pressure of the oxygen supplied, neglecting said undesirable effect of blowing at a lowered lance height above bath is taken. In this case the method of controlling flow rate and pressure of oxygen with a lowered height has naturally a limit, because the possibility of deformation and burning of the nozzle increases and the area of the oxygen jet which comes into contact with the steel bath is considerably reduced.

Moreover with increase of furnace capacity, the use of plu ral lances has been proposed, because a single lance provides limited reaction. However, this method is impracticable due to difficulties in an actual equipment. As a substitute for this method, a multinozzle, that is, a nozzle provided with three or four holes to jet oxygen has been suggested. However similarly to a usual single hole nozzle, it is unable to perform an operation, in which only increase of oxygen pressure is obtained without increasing its blow rate, or vice versa, in correspondence to the oxidizing reaction. The present invention aims to overcome the shortcomings of nozzles (including nozzle system) hitherto proposed and used, and to solve their com mon shortcomings.

According to the present invention, firstly, one and the same lance permits to select an optional flow rate or pressure of oxygen as desired according to respective steps of blowing and it is possible to eliminate the necessity of changing the lance height above the bath or the oxygen flow rate and to permit, under the same conditions of oxygen supply, to change the flow rate or pressure of the jet hitting upon the surface of the bath and in some cases also the shape and area of the fire spot, as desired, secondly, when applied to a large-sized converter in which the bath tends to be shallow, the lance also permits to use the furnace to its maximum efficiency, and thirdly, irrespective of the capacity of the furnace, the efficiency and yield can be improved and at the same time such a phenomenon as superoxidation of the bath can be prevented, so as to reduce oxygen, nitrogen and other impurities in the steel, so that a good quality steel can be obtained.

Now to consider oxygen flow rate and pressure in connection with a sectional area of lance, there seems to be a relation:

wherein V: Flow rate of oxygen NmP/min.

P: Oxygen pressure kg./cm.

K: Constant 1.04 Nmfilkg. min., 300 K.

a: Sectional area cm. (constant) It can be seen that if the flow rate changes, the pressure also changes proportionally and vice versa, because the sectional area at a point of the lance does not change but remains constant. The inventors of the present application discovered in their examination that the blowing function in the use of oxygen can be easily and basically varied by adjusting the sec tional area of the throat portion of the lance nozzle. The known characteristics of the supersonic oxygen jet has a function that, different from static oxidation reaction in open hearth furnace, its impact pressure forms a depression on the bath surface and then accelerates agitation and circulation of the bath, thereby oxidizing the bath directly. It is well know that for obtaining such an impact pressure, the sectional area of the nozzle throat has a great effect and is determined in connection with the expansion ratio of the cross section of the nozzle outlet. Briefly it may be said that a jet velocity is obtained by the driving pressure elevated by throttling the passage of oxygen, followed by jetting said oxygen at an appropriate inclination angle. This is why the inventors selected the nozzle throat as point for controlling flow rate and pressure of the oxygen jet during the blowing performance.

Now, if the flow rate of oxygen is constant, it is possible by changing the sectional area of the throat to obtain an oxygen pressure corresponding to this change. The converse is also possible. An effective and appropriate flow rate or pressure must be held in accordance with respective steps in the blowing operation. An attempt to control the sectional area of the throat merely by inserting a spindle of appropriate diameter into the throat of a single-hole nozzle left in place showed a very good result.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a partially broken front view of an embodiment of the present invention;

FIG. 2 is a sectional view of the lower portion of lance of the same;

FIG. 3 is a sectional view along A-A of FIG. 2;

FIGS. 4 and 5 show respectively embodiments of nozzle mechanism;

FIGS. 6 and 7 show graphs of flow rate of oxygen and its pressure according to change of the sectional area of the throat portion of the nozzle mechanism of FIG. 41;

FIGS. 8 and 9 show graphs of oxygen and nitrogen content as used effects of FIG. 4 nozzle applied to practical operation;

FIG. shows in a graph the relation between jet inclination angle in noule mechanism of FIG. 5 and gross yields;

FIG. Ill similarly shows an example of the relation between and point [C] and slag T.Fe; and

FIG. 12 is an explanatory view of the tire spot on the bath surface during the use of the nozzle shown in FIG. 5.

An explanation will be given as follows with reference to an embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, a lance hanger mechanism 1 is identical with a prior art mechanism, and on both sides thereof are formed a supporter I". In an intermediate portion of the supporter I", other supporters I are formed near the joint portion of lance pipe 8. A selysin transmitter 2 provided in the upper portion of the lance L senses the position of the spindle I3 inserted into the lance and said position is transmitted, for instance, to a furnace operation room in the form of electric signals for indication. The furnace operator can know the position of spindle 13 in the lance by this indication and then operate a small motor 3 to fix spindle 13 in the position corresponding to the reaction in the furnace through the medium of a gear mechanism. In this case, in order to limit up and down movement of the spindle 13, a limit switch is preferably attached. Handle 4 serves for manual driving of spindle 13. A stufiing box at the portion of the oxygen supply pipe which is pierced by spindle 13 prevents leakage of oxygen gas at this location. The lance body is tightly connected with the oxygen supply pipe 8 by a coupling, and inlet pipe 9 and outlet pipe 10 for cooling water communicating with passages 17, 18 concentrically outside around oxygen flow-in tubular passage 16 are likewise connected to the valve body. The gland 20 serves for sealing the joint portion of oxygen flow-in pipe 16 and inlet pipe 9. Support members 11 and 12 are provided for supporting oxygen supply pipe 8, cooling water inlet pipe 9 and outlet pipe 10.

Into oxygen flow-in pipe 16 of the lance of above construction, spindle 13 is inserted movably up and down as aforementioned for such a distance that the head of spindle 13 reaches approximately the head of the lance nozzle in the lower limit of movement of the spindle. Such structure is of importance for obtaining the optimum jet conditions in the present invention. Spindle 13 which is eminently efiective by itself may prove more effective, if appropriately tapered in the head member 14. The head member 14 may be changed during a blowing operation and spindle 13 is connectable with a head member by screw mechanism 21 for simple and quick change of said head member and easy mounting and dismounting of head members of various shapes. Further for preventing vibration of the spindle, which causes irregular change of sectional area of the nozzle throat during a blowing operation, a spindle holder 15 is fixed to spindle 13 and engaging the inner surface of oxygen flow-in passage 16.

Generally, there is a limit in the impact pressure applied on the bath by the oxygen jet during blowing. The sectional area of nozzle throat TT shown in FIGS. 4 and 5 is designed in relation to the flaring of the nozzle outlet opening E-E shown in FIG. 4 in such a manner that no splash from the depression thereof is formed by the jet impact pressure. Such sectional area of throat can be changed by the depth of insertion of the spindle head. The diameter of spindle throat B-B should be determined carefully so that the driving pressure I reaches the maximum pressure required at the nozzle exit C-C. Such driving pressure I and nominal impact pressure in the singlehole nozzle can be changed by movement of spindle 13 so as to cope with any reaction in furnace, and easily controlled in small steps.

These proportional relative dimensions vary in accordance with changes of capacity and shape of the furnace. If the head of the spindle is appropriately tapered from the portion facing the nozzle throat so as to change sectional areas of said head progressively, more effectiveness will be obtained.

FIG. 6 shows the flow rate of oxygen in accordance with variation of the nozzle sectional area TT by changing the position of the spindle head of FIG. 4, on the supposition that oxygen supply pressure is constant. FIG. 7 shows the driving pressure I in accordance with variation of the throat sectional area on the supposition that oxygen flow rate is constant. In this example, blowing is carried out at the oxygen flow rate of 12x10 NmF/hr. and the pressure of 8 kg./cm. with the spindle head pulled up to the position shown in dotted line in the uppermost part of FIG. 4. In the last stage of blowing performance, the nozzle head tip point is lowered to the end of the lance and blowing is continued with said spindle head in the position 14b. The distance of the lance was kept constantly 1,350 mm. from the upper surface of the metal bath.

As condition of blowing at that time, the oxygen driving pressure P, was increased approximately to l5 l g./cm. abs, while the flow rate of the oxygen was maintained. FIG. 8 shows in a graph results of experiments establishing the oxygen constant of a melt relatively to the carbon content at the end of operations made by adjusting relation between said pressure and flow rate by above-mentioned lance conditions. FIG. 9 consolidates numerous results of experiments on [N] relatively to [C] at the end of similar operations. In FIG. 8, the percentages of [C] and [O] at the end of the blowing operation are lower in the operation using the lance of the present invention than in operation using an ordinary lance. In FIG. 9 to all values of C at the end of the blowing operation the percentage of [N] to [C] is lower when a lance of the present invention is used. Especially when an ordinary lance is used, [N] increases linearly from a position at about 0.07 percent of end point [C], whereas when the lance of the present invention is used, [N] decreases progressively with decrease of end point [C] so that in steel having low end point [C] undesirable effect of [N] can be markedly improved.

Such advantage can be attributed to the fact that the rate of flow of oxygen and its pressure for blowing can be easily selected as desired by the present invention. Namely in the last stage of the blowing operation, the agitation of the bath weakens with advancement of decarburization and the furnace pressure markedly drops with the tendency of becoming lower than atmospheric pressure so that the air drawn into the furnace abruptly increases [N]. Accordingly, in order to cope with such a phenomenon, oxygen supply pressure is commonly raised. However in ordinary lances, the increase of oxygen supply pressure cannot avoid the increase of the flow rate, resulting in an unnecessary superoxidation of the bath and the slag, to cause increase of said [0]. However the use of a lance of the present invention enables to control flow rate or pressure of oxygen as desired. Thus the increase of oxygen pressure, as a countermeasure to the drop of furnace pressure in the last stage' of blowing performance, does not cause an increase of the oxygen flow rate so that the phenomenon of superoxidation of the bath can be avoided. It is apparent from above explanation that the more the end point of [O] is lowered, the greater will be the beneficial effects of a lance of the present invention. Further,'the controlling of the oxygen flow rate or its pressure during blowing as desired can effectively eliminate [P], [S] [N] and other impurities in the steel.

To sum up effects and merits obtained by experimental operations, when the oxygen flow rate is changed while the oxygen pressure is kept constant, the velocity of decarburization can be changed without change of [0] in the steel and T, Fe in the slag, and at the same time such a slopping which is generally apt to occur can be completely prevented.

Conversely, when the oxygen pressure is changed, while the oxygen flow rate is kept constant, [0] and [P] in the steel and T, Fe in the slag can easily be controlled without changing the velocity of decarburization, which is not obtainable with lance constructions according to the prior art.

The shape of the passage through the nozzle head is also of importance and preferably the cross section of the passage gradually increases from the throat TT toward the bottom end, as shown in FIG. 5. This can basically change the fire spot made by an ordinary nozzle so as to cope with increase of surface area of the bath.

The essential feature of said nozzle passage resides in the degree of taper as aforementioned. Although a taper must of course be decided in relation to the degree of an ordinary nozzle taper, it can be said that the taper should be constructed in such a manner as to demonstrate its maximum efficiency when it is used in a normal single-hole nozzle.

Now when the spindle head 14c in FIG. 5 is lowermost positioned, the impact area on the bath surface increases and looks like a ring, as shown in FIG. 12b. Such ring-shaped fire spot, concentric with the furnace wall becomes well capable of coping with an increase of the bath surface area. This nozzle construction can be said to be ideal for a furnace near the end of life or in which the bath has been shallowed by increase of furnace capacity. In the here exemplified operation, keeping the oxygen flow rate constant, the driving pressure with the head 14c positioned at the lowermost limit, as shown in TABLE Position of Spindle Uppermost Limit Lowermost Limit The table shows that the agitation and circulation of the bath were active with eminent results as shown in FIGS. 10 and 111. FIG. 10 compares the tapping yield obtained by progressively changing the degree of taper in FIG. with that obtained by single-hole nozzle lance used in the same furnace. This shows that the operation using a nozzle construction of the present invention results in a higher tapping yield than a single-hole nozzle irrespectively of degree of the spindle head taper, and, when jet inclination angle 6 is not less than 6, the tapping yield by using our nozzle is superior to that of three-hole nozzle. FIG. 11 shows the percentage of T, Fe in the slag in relation to the final percentage of carbon, compared with those obtainable when a three-hole nozzle was used. it can be said that this cannot too much demonstrate the usefulness of nozzle mechanism of the present invention. These goods results are attributed to the fact that, as shown in H0. 12, the jet obtained by the present invention forms a ringshaped fire spot concentrally with the furnace wall and that agitation and circulation of the bath produced by said fire spot could well cope with an increased surface area ofthe bath. It is needless to repeat that such bath conditions also showed an eminent result in removing impurities from the steel such as [P] and [S], to say nothing of [O] and [N]. Although, in above-mentioned method, we increased the oxygen pressure while maintaining a constant oxygen flow rate, the relation between flow rate and pressure of oxygen may be changed freely in accordance with the shape of the furnace and blowing condition for an appropriate operation as mentioned in connection with nozzle mechanism shown in FIG. 4.

As above mentioned, the lance for steel making according to the present invention enables to make an effective and appropriate blow of oxygen onto a metal bath which completes blowing in a short time and can well cope with a shallow bath being caused by using the furnace at short intervals and increasing the capacity of the furnace, thereby bringing about a high yield and quality. Moreover the lance of the present invention is of rigid and simplified construction and can be very easily operated. Said lance can be made by a simple modification of an ordinary single-hole lance.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention, and therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended l. A blow lance arrangement for blowing gas on a metal bath, said arrangement comprising, in combination, support means; an elongated blow lance supported on one of the ends thereof on said support means with the other end thereof adapted to be located adjacent to a metal bath, said blow lance being formed with an axial passage therethrough having adjacent to said other end a throat portion of a predetermined length and of an open cross section smaller than the remainder of said passage and downstream of said throat portion an outwardly flaring passage portion of a greater length than that of said throat portion and extending between the latter and said other end of said blow lance; means for feeding gas under pressure in the region of said one end of said blow lance into said axial passage thereof; and means for changing the open cross section of said throat portion and that of said outwardly flaring passage portion and comprising spindle means arranged in said passage and comprising a cylindrical rod and a tapering head on one end of said rod, said tapering head having a maximum diameter smaller than the diameter of said throat portion and a length substantially equal to that of said flaring passage portion, and means connected to the other end of said rod for moving said spindle means in longitudinal direction of said passage between a retracted position in which the free end of said tapering head is located between said one end of said blow lance and said throat portion and an advanced position in which said free end is adjacent to said other end of said blow lance.

2. An arrangement as defined in claim 1, wherein said spindle means comprises a cylindrical rod, a pair of tapering spindle heads, and cooperating attaching means on corresponding ends of said rod and said spindle heads for selectively attaching said heads to said rod, each of said heads having at the attaching end a cross section equal to that of said rod and one of said heads tapering from the region of said attaching end towards the free end thereof and the other of said heads flaring outwardly toward said free end to a cross section smaller than that of said throat portion.

3. An arrangement as defined in claim 1, and including indicating means cooperating with said spindle means for indicating the position of the latter relative to said blow lance.

4. An arrangement as defined in claim 1, wherein said spindle head is removably attached at one end thereof to said one end of said rod, and wherein said one end of said spindle head has a diameter equal to that of said one end of said rod and tapers from said one end of said head toward the free end thereof.

5. An arrangement as defined in claim 11, wherein said spin dle head is removably attached at one end thereof to said one end of said rod, and wherein said one end of said spindle head has a diameter equal to that of said one end of said rod, and wherein said spindle head flares from said one end thereof outwardly to its free end.

6. An arrangement as defined in claim 5, wherein said cone angle of said outwardly flaring spindle head is substantially equal to the cone angle of said outwardly flaring passage portion of said nozzle.

Claims (6)

1. A blow lance arrangement for blowing gas on a metal bath, said arrangement comprising, in combination, support means; an elongated blow lance supported on one of the ends thereof on said support means with the other end thereof adapted to be located adjacent to a metal bath, said blow lance being formed with an axial passage therethrough having adjacent to said other end a throat portion of a predetermined length and of an open cross section smaller than the remainder of said passage and downstream of said throat portion an outwardly flaring passage portion of a greater length than that of said throat portion and extending between the latter and said other end of said blow lance; means for feeding gas under pressure in the region of said one end of said blow lance into said axial passage thereof; and means for changing the open cross section of said throat portion and that of said outwardly flaring passage portions and comprising spindle means arranged in said passage and comprising a cylindrical rod and a tapering head on one end of said rod, said tapering head having a maximum diameter smaller than the diameter of said throat portion and a length substantially equal to that of said flaring passage portion, and means connected to the other end of said rod for moving said spindle means in longitudinal direction of said passage between a retracted position in which the free end of said tapering head is located between said one end of said blow lance and said throat portion and an advanced position in which said free end is adjacent to said other end of said blow lance.

2. An arrangement as defined in claim 1, wherein said spindle means comprises a cylindrical rod, a pair of tapering spindle heads, and cooperating attaching means on corresponding ends of said rod and said spindle heads for selectively attaching said heads to said rod, each of said heads having at the attaching end a cross section equal to that of said rod and one of said heads taperIng from the region of said attaching end towards the free end thereof and the other of said heads flaring outwardly toward said free end to a cross section smaller than that of said throat portion.

3. An arrangement as defined in claim 1, and including indicating means cooperating with said spindle means for indicating the position of the latter relative to said blow lance.

4. An arrangement as defined in claim 1, wherein said spindle head is removably attached at one end thereof to said one end of said rod, and wherein said one end of said spindle head has a diameter equal to that of said one end of said rod and tapers from said one end of said head toward the free end thereof.

5. An arrangement as defined in claim 1, wherein said spindle head is removably attached at one end thereof to said one end of said rod, and wherein said one end of said spindle head has a diameter equal to that of said one end of said rod, and wherein said spindle head flares from said one end thereof outwardly to its free end.

6. An arrangement as defined in claim 5, wherein said cone angle of said outwardly flaring spindle head is substantially equal to the cone angle of said outwardly flaring passage portion of said nozzle.

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