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Publication numberUS3701518 A
Publication typeGrant
Publication dateOct 31, 1972
Filing dateOct 3, 1969
Priority dateOct 3, 1969
Also published asCA949316A, CA949316A1, DE2045602A1, DE2045602B2
Publication numberUS 3701518 A, US 3701518A, US-A-3701518, US3701518 A, US3701518A
InventorsHerff Louis M
Original AssigneeBerry Metal Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Oxygen lance control arrangement for basic oxygen furnace
US 3701518 A
Abstract
A ranging radar system is employed in combination with the oxygen blowing lance of a basic oxygen furnace to make an absolute measurement of the distance between the lance and the level of molten material within the furnace vessel. This measurement may be made while the level of molten material is quiescent, i.e., before the oxygen blowing operation is started, and may be used either to calibrate the existing lance drum indicator or directly as a measurement of lance height in the overall computer control of the furnace. In the alternative, the measurement of lance height from the molten surface may be made during the oxygen blowing operation and may be employed for accurate lance positioning during blow or the accurate repositioning of the lance in the event a reblow operation is required to obtain a desired quality of steel for a particular heat.
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United States Patent Herfi [54] OXYGEN LANCE CONTROL ARRANGEMENT FOR BASIC OXYGEN FURNACE [72] Inventor: Louis M. Herfi, Pittsburgh, Pa.

[73] Assignee: Berry Metal Company, Harmony,

[22] Filed: Oct. 3, 1969 [2i] Appl. No.: 863,609

[52] US. Cl. ..266/34 LM [5 1] Int. Cl. ..C21c 7/00 [58] Field of Search ....266/34 R, 34 L, 34 LM, 34 T, 266/41; 75/59, 60

[56] References Cited UNITED STATES PATENTS 1,674,947 6/1928 Bunce et al ..266/43 2,883,279 4/1959 Graef et al. ..266/34 R 3,378,366 4/1968 Borowski et al ..75/60 3,396,960 8/1968 Maatsch ..266/34 L 3,505,062 4/1970 Woodcock ..75/60 FOREIGN PATENTS OR APPLICATIONS 1,434,231 1/1965 France ..266/34 LM [451 Oct. 31, 1972 Primary Examiner-Gerald A. Dost Attorney-Mason, Kolehmainen, Rathbum & Wyss [57] ABSTRACT A ranging radar system is employed in combination with the oxygen blowing lance of a basic oxygen furnace to make an absolute measurement of the distance between the lance and the level of molten material within the furnace vessel. This measurement may be made while the level of molten material is quiescent, i.e., before the oxygen blowing operation is started, and may be used either to calibrate the existing lance drum indicator or directly as a measurement of lance height in the overall computer control of the furnace. In the alternative, the measurement of lance height from the molten surface may be made during the oxygen blowing operation and may be employed for accurate lance positioning during blow or the accurate repositioning of the lance in the event a reblow operation is required to obtain a desired quality of steel for a particular heat.

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LOUIS M. HERFF,

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OXYGEN LANCE CONTROL ARRANGEMENT FOR BASIC OXYGEN FURNACE The present invention relates to a top blown oxygen steelmaking converter such as the basic oxygen furnace, and, more particularly to a system and method for measuring and controlling the position of the oxygen blowing lance relative to the surface of the molten material within the converter in such manner as to optimize the efficient production of steel in such a converter.

In a conventional steelmaking converter of the top blowing type, commonly known as a basic oxygen furnace, a fire brick lined vessel open only at the top is employed into which is first loaded up to percent of scrap iron. Molten iron which has been reduced from iron ore to iron in a blast furnace by removing impurities, is then moved directly from the blast furnace to the converter and is dumped into the top of the vessel. Various other ingredients called additives, which are necessary for proper slag formation and chemical conversion of the iron, are also added to the molten material in the vessel. A hollow pipe, called an oxygen lance, is then lowered through the upright top of the vessel to a position such that the tip of the lance is near the surface of the molten material. Pure oxygen is then supplied to the top end of the lance and issues from the lance tip in the form of one or more downwardly directed high velocity jets of oxygen which impinge upon the surface of the molten material with such force as to produce craters or cavities in the molten metal. This direct supply of oxygen is employed without any source of heat other than the heat created from the chemical reaction of the pure oxygen with the hot iron,

to produce steel. While a complete steelmaking cycle may last as long as minutes, oxygen is blown only over a short portion of this cycle and may last as little as 12 to 18 minutes. When oxygen is blowing, the vessel itself is filled with fumes, sparks and dust to the extent that there is no visibility within the vessel. in addition, the air space around the vessel is often filled with flying sparks rendering it difficult or impossible to approach the vessel from the sides. The operations of the vessel are controlled from a platform, aptly known as the pulpit, which is related to the top or open end of the vessel and to the side thereof so as to be out of the way of a hood which is positioned above the upright vessel and acts as a fume catcher to divert the fumes up a Smokestack.

According to conventional practice, the oxygen lance is controlled by an operator who decides at what level the lance tip should be positioned and energizes a motor control system which actuates a lance crane comprising a suitable cable and drum arrangement the drum being rotated to lower the lance into the open top of the vessel. A lance height indicator, which may be controlled from a slide wire transmitter driven from the lance drum, is employed to provide an indication of the position of the lance tip. However, since the lance may be as long as 70 feet, is quite heavy and must be raised and lowered a distance of many feet during each steelmaking heat cycle, the lance drum indicator does not give an accurate indication of the position of the lance tip due to stretching of the crane cables during the raising and lowering operations. Also, since the oxygen lance is subjected to relatively high temperatures during the blowing operation, it may expand as much as 4 or 5 inches in length, thus rendering any initial measurement of lance tip position considerably in error.

Furthermore, and most importantly, the lance operator has no way of accurately determining the position of the lance tip relative to the level of the molten material within the vessel. This is because the level of the molten iron within the vessel will vary from heat to heat, depending upon the amount of scrap iron and molten iron which is supplied from the blast furnace. Furthermore, as the refractory lining of the vessel is worn away the level of the molten bath, even assuming that identical amounts of iron are added during each heat, correspondingly decreases. Also, when the refractory lining is coated with lime to seal the cracks between bricks the lime tends to collect in the bottom of the vessel and is not removed when the vessel is emptied. This buildup of lime may become as much as a foot or more in the bottom of the vessel and may greatly change the level of the molten material which is dumped in on top of the buildup of lime in the vessel.

At the present time, the actual distance between lance tip and molten material can be measured only by attaching a steel rod to the lance, lowering the lance until the tip of the rod is immersed in the liquid steel, letting the immersed portion of the rod melt in the liquid steel, and then moving the lance vertically out of the vessel and the hood and measuring the remaining rod length. In some plants such a measurement is made every day, while in others, such a measurement is made every shift. However, the refractory wear and subsequent lowering of the molten iron level between these measurements is neglected. Furthermore, such a measurement is made when no oxygen is blown and, of course, does not provide any indication of the dynamic operation of the basic oxygen furnace. Thus, at the present time, there exists no control arrangement by means of which the lance operator may accurately position the lance tip relative to the level of the molten material in the vessel.

It is, therefore, a primary object of the present invention to provide a new and improved control arrangement for positioning an oxygen lance relative to the surface of the molten material within the vessel of a top blowing oxygen converter.

It is another object of the present invention to provide a new and improved control arrangement for indicating and/or positioning an oxygen lance relative to the molten material within the vessel wherein reflection of an electromagnetic wave transmitted downwardly from the lance is employed to determine the distance between the lance tip and the level of the molten material within the vessel.

It is a further object of the present invention to provide a new and improved oxygen lance positioning system wherein an electromagnetic wave is generated and is transmitted downwardly through one of the nozzles in the lance tip and is reflected back through said nozzle to a receiver, a signal proportional to the elapsed time between transmitted and reflected waves being employed as a control parameter in either an open loop or a closed loop control system.

It is a still further object of the present invention to provide a new and improved oxygen lance position indicator system wherein inaccuracies due to elongation of the cable employed to lower the lance into the vessel are eliminated.

it is another object of the present invention to provide a new and improved oxygen lance positioning system wherein at least one of the nozzles in the lance tip which is employed to form a high velocity oxygen jet during the oxygen blowing period of the process, also acts as a transmitting and receiving antenna for an electromagnetic wave transmitted downwardly through the nozzle and reflected upwardly therethrough from the surface of the molten material in the vessel.

It is a further object of the present invention to provide a new and improved arrangement by means of which the conventional lance drum indicator may be accurately calibrated prior to the initiation of the oxygen blowing operation, so that this indicator may be employed during subsequent portions of the process to provide accurate positioning or repositioning of the lance tip as desired.

While it is desirable initially to position the oxygen lance accurately with respect to the molten metal at the start of the oxygen blowing operation, it is also necessary to reposition the oxygen lance tip to a different position during later periods of the blowing operation. Thus, the lance tip is originally positioned relatively far away from the level of the molten material, at a distance of from say 80 to 120 inches, during the socalled pre-ignition portion of the oxygen blowing process in which silicon is preferentially oxidized. Once the silicon in the melt has been substantially completely oxidized, the lance tip must be moved substantially closer to the level of the molten material in the vessel in order to provide the proper spacing between lance tip and metal bath for most efficient mixing action with the melt and carbon removal. However, once the oxygen blowing operation is initiated the surface of the melt becomes violently heaving and oscillatory so that the level of the molten metal relative to the lance tip is constantly changing during the oxygen blowing operation. Under present operating procedures, the lance operator can merely make a hopefully educated guess as to the distance between the lance tip and the violently heaving liquid metal within the vessel and lower the lance tip to a point which he believes will give the desired carbon removal. Also, if a reblow is required after the main oxygen blowing operation is completed, it is necessary to reposition the lance either at a high level for heating the steel without further decarbonization or at a lower level for decarbonization within increased heating of the steel.

While certain arrangements have been heretofore proposed for the dynamic control of a basic oxygen furnace these arrangements have not made any attempt to measure the constantly varying distance between the lance tip and the heaving surface of the molten material in the vessel nor have these arrangements attempted to employ such a measurement as a control parameter useful in the dynamic control of the basic oxygen furnace during the oxygen blowing operation. In general, these prior art process control arrangements have attempted to determine the rate of decarbonization or carbon removal during the early phases of the oxygen blowing operation by analyzing the gases given off during the oxygen blowing operation so as to determine the carbon content of such gases. One such arrangement measures the carbon and oxygen compounds in the waste gases for a given period of time together with the amount of oxygen blown during the same period of time and calculates from these measurements a carbon oxidation rate.

A set of characteristic decarbonization curve is thus derived empirically. At some point during the middle of latter phases of the blowing operation, the temperature of the molten bath is obtained by lowering a sinker thermocouple into the molten metal so as to determine an actual point on the temperature curve. This information is then employed to correct the blowing operation, primarily by changing the amount of oxygen which is being blown, so that the desired carbon end point and the desired end point temperature will be achieved to provide the desired quality of steel.

Such arrangements for dynamic control of the basic oxygen furnace are necessarily approximations since they depend upon attempted correlations of the actual furnace operation with a set of ideal curves rather than relying upon an actual measurement of what is going on in the furnace during the blowing operation. Furthermore, a considerable amount of time is required to analyze the exhaust gases and determine carbon content so that the resulting control parameter lags considerably behind the actual events taking place in the furnace and cannot be used for the direct dynamic coritrol of the oxygen blowing operation.

It is, therefore, a further object of the present invention to provide a new and improved control arrangement for a basic oxygen furnace wherein the actual distance between the lance tip and the surface of the molten material in the vessel during the oxygen blowing operation may be employed as a control parameter.

It is another object of the present invention to provide a new and improved control arrangement for a basic oxygen furnace wherein an indication is provided during the oxygen blowing operation of the constantly varying distance between the lance tip and the heating surface of the molten material in the vessel, said indication being useful in the dynamic control of the oxygen blowing operation.

It is still another object of the present invention to provide a new and improved control arrangement for a basic oxygen furnace whereby the oxygen blowing lance may be positioned to different points relative to the heaving surface of the molten material during the oxygen blowing operation to provide optimum operating conditions for the furnace.

It is a further object of the present invention to pro vide a new and improved arrangement for measuring the amount of heaving of the molten metal surface during the oxygen blowing operation so that maximum efficiency during pre-ignition and carbon removal stages of the process may be achieved without causing an excessively unstable condition to arise which could produce sparking and furnace ejections such as slopping.

It is another object of the present invention to provide a new and improved dynamic control arrangement for a basic oxygen furnace wherein the motion of the heaving surface molten material in the vessel during the oxygen blowing operation is analyzed to provide information which can be used to control lance height and oxygen blowing rate to provide optimum conversion of iron into steel.

Briefly, in accordance with one aspect of the present invention, a radar system, which may be of the pulsed, FM/CW or phase modulation type, is provided which includes an electromagnetic wave generator arranged to transmit an electromagnetic wave through one of the nozzles in the lance tip which is also employed to form a high velocity oxygen jet during the oxygen blowing operation. The electromagnetic wave which is transmitted downwardly to the surface of the molten material in the vessel and is reflected back through said nozzle to a suitable receiving means, which may also be positioned within the lance. The elapsed time between transmitted and reflected waves is then employed to determine the actual distance between the lance tip and the surface of the molten material in the vessel. An output signal which may be in either analog or digital form, is then provided which accurately indicates the actual distance between the lance tip and the surface of the molten metal in the vessel. This distance signal may be employed in any one of several ways. First, as the oxygen lance is initially lowered into the open top of the vessel before the oxygen blowing operation is started, an indication of lance tip distance from the quiescent level of the melt may be provided at a selected point. The lance operator is thus informed of the actual distance to the quiescent level of the melt and may position the lance tip accurately at the desired location for the start of oxygen blowing. Furthermore, he can at the same time calibrate his existing lance drum indicator so that the lance drum indicator may thereafter be used for subsequent re-positioning of the lance tip to different levels during the oxygen blowing operation and reblow.

The above described lance separation signal may also be continuously employed to provide an indication of the frequency and amplitude characteristics of the heaving surface of the molten material during the actual oxygen blowing operation. With this information, either the lance height or oxygen blowing rate, or both, may be controlled either manually or by automatic process control means, which may include a computer, so as to set up a desired amplitude of standing wave in the molten liquid during various portions of the oxygen blowing operation to provide optimum efficiency of the conversion process. For example, the lance separation signal may be employed to position the lance during the pre-ignition period for optimum removal of silicon without loss of energy due to mixing of the steel which would be experienced if the lance were too close to the level of the liquid. Also, as slag is formed during the initial stages of the oxygen blowing operation the lance separation signal may be employed to determine and control the maximum amplitude of heaving of the molten material so that sparking and slopping does not occur. After the pre-ignition period, the lance may be accurately lowered to the desired point at which optimum carbon removal is achieved while limiting the instability of the heaving liquid within the vessel. Finally, if a reblow is necessary after the initial blowing operation has been completed, the lance separation signal may be employed to position the lance tip relatively far from the level of the liquid if additional heat is required or relatively close to the surface of the liquid if additional mixing and carbon removal is required to achieve the desired carbon end point and temperature end point for a desired quality of steel.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings in which:

FIG. 1 is a side elevational view, partly in section, of a basic oxygen furnace employing an oxygen lance positioning system in accordance with the present invention;

FIG. 2 is a sectional view taken along the lines 22 of FIG. 1;

FIG. 3 is a block diagram of the major electronic components of the positioning and control system of the present invention shown in conjunction with a diagrammatic representation of the oxygen lance;

FIG. 4 is a sectional view of the tip of the oxygen blowing lance of FIG. 3 but taken on a somewhat larger scale and illustrating the manner in which electromagnetic waves are transmitted and received through one of the nozzles of the lance tip;

FIG. 5 is a sectional view taken along the lines 5-5 of FIG. 4;

FIG. 6 is a side elevational view of the lance top adaptor unit provided at the upper end of the oxygen blowing lance in the system of FIG. 1;

FIG. 7 is a plan view of the lance top adaptor of FIG.

FIG. 8 is a left-side view of the lance adaptor portion of FIG. 6;

FIG. 9 is a cross sectional view of the lance top adaptor of FIG. 6, taken on a somewhat larger scale, and illustrating the manner in which the transmitted and received electromagnetic signals are supplied to the upper end of the lance;

FIG. 10 is a sectional view taken along the lines l0- 10 of FIG. 9;

FIG. 11 is a detailed block diagram of the major components of one type of transmitting and receiving radar system which may be employed to determine the separation of the lance tip from the surface of the molten material in the vessel of the basic oxygen furnace;

FIG. 12a is a timing diagram showing the relationship between transmitted and received signals when linear modulation is used in the system of FIG. I 1;

FIG. 12b is a timing diagram of the beat frequency characteristic when linear modulation is used as shown in FIG. 12a;

FIG. 13 is a frequency component diagram illustrating the various beat frequency components of the received signal in the system of FIG. 1 1;

FIG. 14a is a timing diagram showing the relationship between transmitted and received signals when sinusoidal modulation is employed in the system of FIG. 11;

FIG. 14b is a timing diagram of the beat frequency obtained with sinusoidal modulation as in FIG. 14a;

FIG. 15a is an energy-frequency characteristic of a typical received spectrum when linear modulation is used in FIG. 1 1;

FIG. 15b is an energy-frequency characteristic of the received signal when sinusoidal modulation is employed in the system of FIG. 11;

FIG. 16 is a side elevational view of a lance top adaptor arrangement wherein an alternative embodiment is employed for transmitting electromagnetic waves to the lance tip;

FIG. 17 is a lefthand side view of the arrangement of FIG. 16;

FIG. 18 is a block diagram of the major system components employed in a short-pulse ranging radar system which may be used in the arrangement of FIGS. 16 and 17;

FIG. 19 is a side elevational view of a lance top adaptor portion of an alternative embodiment of the invention wherein a further alternative arrangement for transmitting electromagnetic waves to the lance tip is employed;

FIG. 20 is a sectional side elevational view of the lance tip portion of the arrangement of FIG. 19, shown on a somewhat larger scale, and illustrating the manner in which electromagnetic waves are transmitted through one of the nozzles of the lance tip;

FIG. 21 is a side elevational view, partly in section, of a further alternative embodiment of the invention wherein a ranging radar system is provided outside the oxygen blowing lance to measure the distance to the molten material within the vessel of the basic oxygen furnace; and

FIG. 22 is a side elevational view ofa still further embodiment of the invention wherein a ranging radar system is employed to provide an indication of lance height with respect to a fixed reference plane, this indication being usable in place of the conventional lance drum indicator.

Referring now to the drawings, and more particularly to FIGS. 1 and 2 thereof, the oxygen lance positioning system of the present invention is shown therein in connection with a basic oxygen furnace which includes an open top vessel indicated generally at which is lined with some 2 to 3 feet of refractory material 32 and is adapted to receive scrap iron and molten iron directly from the blast furnace, as indicated generally at 34.

conventionally, the vessel 30 is provided with trunion pins 36 which are journaled in suitable bearings, one of these pins being arranged to be driven so that the vessel may be tilted for the loading and emptying operations. A hood 38 is provided above the open mouth of the vessel 30 when this vessel is positioned vertically, and is adapted to carry off the fumes and exhaust gases produced during the steelmaking operation. The top of the hood 38 is provided with a central opening 40 (FIG. 2) through which an oxygen blowing lance, indicated generally at 42, may be lowered downwardly through the entire hood 38 and into the open top of the vessel 30 until the lance 42 is positioned somewhat above the surface 44 of the molten material 34 within the vessel 30. Since the vessel 30 may have a height of some to feet and the hood 38 is likewise of substantial height, the lance 42 conventionally has a length of about 70 feet in order to extend through the hood 38 and into the vessel 30 to a position a few feet above the surface of the molten material within the vessel 30. Accordingly, the oxygen blowing lance 42 is arranged to be suspended from a carriage 46 which is movably mounted on a vertically extending frame indicated generally at 48, and is suspended on the end of a cable 54. To this end, the lance top adaptor portion 50 is provided with an eye 52 which is arranged to be connected to a hook secured to the carriage 46. The frame 48 comprises a pair of vertically extending I beam members 56 and 58 (FIG. 2) which are connected together at the top and bottom ends thereof by means of triangularly shaped end plates 60 and 62, these end plates being journaled for rotation about a vertical axis by means of the bearings 64 and 66.

In order to swing the frame 48 about the vertical axis of the bearings 64, 66, a lance slewing motor is mounted on the frame 48 and is arranged to drive a pinion gear 72 which is in engagement with a fixed segment gear 74 so that the oxygen blowing lance 42 may be swung in the arc ofa circle as indicated at 76 in FIG. 2. Normally, a second oxygen blowing lance 42a is mounted on an associated frame 48a and may be used alternately with the lance 42. When one of the oxygen blowing lances is not being used it is swungto a parked position as indicated in FIG. 2 by the position of the lance 42a. The active oxygen blowing lance 42 is swung to an operative position over the opening 40 in the hood 38. When the lance is properly positioned with respect to the hood opening 40, a hoist drive motor 80 is energized so that the cable 54 is paid out and the lance 42 is lowered through the hood 38 and into the top of the vessel 30.

In accordance with the present invention, a microwave transmitter, indicated generally at 82, is arranged to develop an electromagnetic wave which is conveyed by means of a flexible coaxial cable 84 to the lance top adaptor portion 50. This electromagnetic wave is conveyed through the inside of the lance 42 to the tip portion thereof and issues from one of the nozzles provided in the lance tip for developing high velocity jets of oxygen which impinge upon the surface 44 of the molten material 34 in the vessel 30. A suitable crystal detector is provided within the lance tip portion or at the receiver circuitry 82, and is adapted to receive the reflected wave which bounces back from the reflec' tive surface 44 within the vessel 30 as well as a small portion of the transmitted signal. Beat frequency components resulting from these transmitted and reflected signals are supplied by way of a flexible coaxial cable 86 to suitable receiver circuitry within the unit 82 and the resultant lance distance signal is supplied by way of the conductor 88 to the control pulpit room 90 and the computer room 92 which normally house the control facilities for operating the basic oxygen furnace.

Referring now to FIGS. 3 to 15, inclusive, wherein the details of the lance positioning system described generally heretofore are shown, the top adaptor portion 50 of the lance 42 is illustrated as comprising a frame consisting of top and bottom members 94 and 96 (FIG. 6) and side members 98 and 100, the eye 52 being secured to the top member 94 by means of the right angle brackets 102 and 104. The eye plate 52 is preferably pivotally mounted to the brackets 102 and 104 so as to permit the lance 42 to hang directly downwardly and the center line of the opening 106 provided in the eye 52 is offset from the center line of the lance 42 to achieve a plumb attitude when the lance is suspended from a hook placed within the opening 106, as will be readily understood by those skilled in the art.

Oxygen may be introduced through either arm 110 or arm 112 of a Y-shaped oxygen header 114 which opens downwardly by means of a common offset central pipe 116 into the top of a housing 118 into which the water inlet pipe 120 and the water outlet pipe I22 are connected. The oxygen lance 42 comprises a central pipe 124 which is usually eight inches in diameter, an intermediate concentric pipe 126 which is usually 10 inches in diameter and an outer pipe 128 which is concentric with the pipes 124 and 126 and is usually 12 inches in diameter.

As best illustrated in FIG. 9, the central portion 116 of the Y-shaped header 114 is secured to a collar 130 which is positioned on the upper end of the housing 118 and the central oxygen pipe 124 is secured to an annular ring 132 positioned within the housing 118 so that oxygen supplied to either of the inlet pipes 110 or 112 is supplied directly to the interior of the central pipe 124.

In order to cool the oxygen blowing lance 42, and particularly the tip portion thereof, cooling water is introduced from the pipe 120 into the chamber 134 of the housing 118 and is supplied to the space 136 between the pipes 124 and 126. The cooling water travels downwardly adjacent the central oxygen pipe 124 to the lance tip and is forced upwardly through the space 138 between the pipes 126 and 128 to the water outlet pipe 122. The housing 118 is preferably seated on a platform 140 which extends between the side members 98 and 100 of the top adaptor frame, the housing 118 being provided with a bottom flange 142 which is adapted to seat on the platform 140. The lance tip portion, indicated generally at 150, is preferably cast as an integral unit from substantially pure copper and is secured to the bottom ends of intermediate pipe sections 124a, 126a, and 128a by means of the welds 152, 154 and 156 (FIG. 4). The pipe sections 124a and l28a are in turn connected to the pipes 124 and 128 by means of the steel-to-steel welds 152a and 156a and the pipe section 126a is connected to the pipe 126 through an expansion joint 154a. In the illustrated embodiment the lance tip 150 is provided with four oxygen jet forming nozzles 158, 160, 162 and 164, each of these nozzles comprising a converging portion such as the portion 164a of the nozzle 164, a throat portion 164b and a diverging portion 164c. conventionally, oxygen supplied to the upper end of the central pipe 124 issues from all four of the nozzles 158, 160, 162 and 164 in the form of high velocity jets of oxygen, traveling at approximately twice the local speed of sound and having sufficient force to form craters or cavities in the surface 44 of the molten material within the vessel 30.

In accordance with an important feature of the present invention, one of these nozzles, such as the nozzle 164, is employed as a microwave antenna to which an electromagnetic wave is supplied from the interior of the pipe 124. This electromagnetic wave which issues from the nozzle 164 travels downwardly from the lance tip 150 until it strikes the surface of the molten material 44 in the vessel 30 and is then reflected back through the nozzle 164 which new acts as a microwave receiving antenna and is utilized to determine the spacing or separation between the lance tip 150 and the reflecting surface 44. More particularly, an electromagnetic wave is developed by the generator 170 (FIG. 3) and is supplied by way of the flexible coaxial cable 84 to a coaxial cable fitting 172 which is mounted in the wall of the central vertically extending oxygen pipe section 116. A coaxial cable 174 is connected to the coaxial connector 172 internally of the pipe 116 and extends downwardly through the center of the oxygen pipe 124 within a small pipe 176 which is mounted within the pipe 124 by means of brackets 178 which are spaced along the length of the pipe 124 and are secured to the inside of this pipe by means of the mounting brackets 180 and 182.

Somewhat below the end of the pipe 176, the coaxial cable 174 is connected through a type N coax fitting 180 to a microwave hybrid unit 182, a dummy load 184 being connected to the hybrid 182 through the fitting 186. The transmitted electromagnetic wave is then supplied through the fittings 188 and 190 to a coaxial cable-to-2.25 inch circular wave guide transition member or antenna 192. The flared transition member or directive antenna 192 is seated on and secured to the upper end of a perforated metal cylinder 194 the bottom edge of which rests on the inner bottom wall 196 of the lance tip 150. The cylinder 194 acts as a short section of circular wave guide so as to transmit the electromagnetic wave downwardly from the end of the transition member 192 to the converging portion 164a of the nozzle 164 and the interior of the cylinder 194 is preferably coated with a thin layer of conductive material such as copper, to reduce losses'in transmission of the electromagnetic wave therethrough. The cylinder 194 is perforated so as to permit the entrance of oxygen into the cylinder 194 and hence to the nozzle 164. However, the perforations in the cylinder 194 are of the proper diameter and spacing so as to contain the electromagnetic wave within the cylinder 194 so that it may be propagated downwardly to the converging portion 164a. For example, the perforations in the cylinder 194 may be 0.125 to 0.200 inch diameter holes. lt should be noted that the cylinder 194 will necessarily introduce some pressure drop since it will provide some obstruction to the flow of oxygen to the nozzle which flow may be in the order of 6,000 standard cu. ft. per min. Accordingly, the cylinder 194 must be strong enough to withstand this pressure drop and the highest pressure is on the outside of the cylinder 194 and tends to crush the cylinder. The cylinder 194 may be of steel and have a wall thickness of 0.125 in., the perforations in the cylinder wall being formed by drilling holes of a suitable diameter to accomplish the above-described objectives or, alternatively, the holes may be more economically provided by punching. If the holes are punched they can be square holes with sides oriented vertically so that better streamlining and less pressure drop is produced than with round holes. In the alternative, the cylinder 194 may be made of a material consisting of a porous matrix of small metallic shot material bonded together by suitable sintering techniques to provide a mesh-like cylinder having about 10 percent of its surface area consisting of voids through which oxygen can flow. Such a material has a smooth internal surface for transmission of the electromagnetic wave without dissipating energy in higher order modes while at the same time being less expensive and easier to fabricate than a steel cylinder. The length of the cylinder 194 is chosen so that sufficient oxygen can be admitted through the openings in the cylinder 194 to provide the required flow of oxygen to the entrance of the nozzle 164 with an acceptable pressure drop. For example, the cylinder 194 may be of steel and have a perforated length of 8 in. in which 960 holes of 0.l 25 in. diameter are symmetrically arranged. However, it

will be understood that other ratios of length to number of holes can be used so long as the area of the holes is at least four times the area of the throat 164b of the nozzle 164. The cylinder 194 is preferably supported within the lance tip 150 by means of an arcuate upstanding boss portion 198 which extends upwardly from the bottom surface 196 of the tip portion 150, the cylinder 194 being secured as by welding or brazing to the boss 198 as indicated at 200. Preferably the boss 198 is provided with openings 202 so as to permit the maximum amount of oxygen to be admitted to the interior of the cylinder 194.

Since the perforated cylinder 194 necessarily offers some impediment to oxygen flow to the nozzle 164, if only one of the four nozzles of the lance tip 150 were so impeded, the lance jets would tend to energize preferentially the lowest unsymmetrical mode of oscillation of the liquid pool 34 within the vessel 30 which in turn would tend to produce undesired slopping. In addition, if only one of the four nozzles is impeded, a force would be developed tending to move the lance sidewise away from the center of the vessel, due to the fact that the force of the oxygen jet through the unimpeded nozzles would be greater than the force through the nozzle 164 and since these nozzles are directed at an angle to the vertical center line of the lance 42, a sidewise component of thrust would thus be developed. In order to overcome these difficulties, the nozzle 162 which is diametrically opposite the nozzle 164 is also provided with a perforated metal cylinder 240 of the same length as the cylinder 194, the cylinder 240 being closed at its upper end by means of a cover plate 242. The bottom end of the cylinder 240 is seated on the surface 196 of the tip 150 and an arcuate boss 244, similar to the boss 198 is provided for support of the cylinder 240. The cylinder 240 is perforated in the same manner as the cylinder 194 so that oxygen issuing from the nozzle 162 has exactly the same force as the oxygen jet emitted from the nozzle 164. The other two nozzles 158 and 160 are balanced with respect to the nozzles 162 and 164, and hence do not require matching cylinders such as the cylinders 194 and 240. If an oxygen blowing lance having three nozzles is used then all three nozzles should preferably be balanced.

The electromagnetic wave which is transmitted downwardly through the wave guide section 194 is propagated downwardly through the converging, throat and diverging portions of the nozzle 164 and is emitted in the form of a directed microwave signal from the bottom end of the lance tip 105 in the direction of the longitudinal axis of the nozzle 164. The transmitted wave is reflected back from the surface 44 of the molten material in the vessel 30 and re-enters the nozzle 164, is propagated upwardly through the diverging and converging portions of this nozzle and the wave guide section 194 to the flared transition member 192 so that a received signal is developed at the output 204 of the hybrid 182. This received signal, together with a small portion of the transmitted signal which appears at the output 204 of the hybrid 182 due to leakage within the hybrid, is supplied by way of the fitting 206 to a crystal detector 208. The output from the crystal 208 is supplied by way of the fitting 210 to a coaxial cable 212 and the cable 212 extends upwardly through the pipe 176 within the lance 42 to the other input of the coaxial cable connector 172 in the top adaptor portion 50. The cable 212 is connected through the connector 172 to the flexible receiver coaxial cable 86 outside the pipe section 116 and the cable 86 is connected to the electromagnetic wave receiving circuitry indicated generally at 214 in FIG. 3. As mentioned heretofore, the crystal detector 208 may be located adjacent the receiver circuitry 214 and the transmitted and reflected signals developed in the output 204 of the hybrid 182 may, if desired, be transmitted directly over the cables 212 and 86 to this crystal. Such an arrangement has the advantage that spurious signals which may appear in the hybrid output will be attenuated in transmission to the receiving crystal.

In the receiving circuitry 214 the signal transmitted over the cable 86 is processed to develop an output signal proportional to the distance of the lance tip 150 from the reflecting surface 44 within the vessel 30, as will be described in more detail hereinafter in connection with the detailed circuit diagram and timing wave forms shown in FIGS. 11 to 15, inclusive. This output signal is transmitted over the conductor 88 to a lance distance signal display unit 220 in the control room 90. A lance drum indicator 222 is provided in the control room 90 and indicates the position of the lance drum as the lance 42 is lowered by means of the driving motor 80.

Conventionally, the lance drum indicator 222 is energized from a slide wire transmitter driven from the lance drum and indicates the position of this drum to the operator within the control room 90. However, as indicated heretofore, the reading of the drum indicator 222 is under current practice, in error due to stretching of the supporting cable 54 and also due to thermal elongation of the oxygen blowing lance 42 when it is heated up. Furthermore, and most importantly, the distance between the lance tip and the surface of the molten material in the vessel 30 is not given by the drum indicator 222 because this level may vary with many factors such as the amount and character of the scrap iron used in the heat, the thickness of the refractory lining 32, and the buildup of lime in the bottom of the vessel 30. The lance distance signal display unit 220 does, however, in accordance with the present invention, provide a true indication of the distance between the lance tip and the reflecting surface of the molten material in the vessel 30.

The lance distance signal displayed on the unit 220 may be used in several different ways. First, this distance signal may be used to make a quiescent measurement of the distance between the lance tip 150 and the reflecting surface within the vessel 30 before oxygen blowing is begun and hence before the surface of the molten material becomes violently heaving and churning as it does when oxygen is being blown. This quiescent measurement is made as the oxygen lance 42 is being lowered into the vessel 30 as it approaches the point where the lance is to be stopped and oxygen blowing started for the pre-ignition process. When the lance 42 reaches the desired distance above the surface 44, as indicated on the unit 220, the operator can use the distance signal thus displayed to calibrate the reading of the lance drum indicator 222 at this same point. Thus, the operator is informed that whereas the conventional lance drum indicator indicates, for example,

that the lance tip 150 is positioned l20 in. above the surface 44, this lance tip is actually positioned 108 in. from the surface 44, due to the above-discussed factors which influence lance tip position and the level of the molten material in the vessel 30. Once this calibration is made for the drum indicator 222, the indicator 222 may then be usedduring the actual oxygen blowing operation to re-position the lance tip 150, as required during the various operations during the heat, including the re-positioning of the lance tip at the proper height if a re-blow operation is necessary. Under these conditions, the operator manually controls the lance crane controls 224, i.e., the lance driving motor 80, the controls for releasing additives from the bins 226 into the vessel 30 at the proper times during the heat, and the oxygen control valve 228 for controlling the flow of oxygen to the pipe 1 10, all as indicated by the dotted line 223 in FIG. 3.

It is also contemplated that the lance distance signal, which is obtained before the oxygen blowing operation is started, may be fed to a computer 230 where it is stored and utilized during the oxygen blowing operation in place of the signal conventionally generated by the lance drum transmitter. The computer 230 may, for example, be of the type described in the article entitled "Dynamic Control of Basic Oxygen Steel Process" by Keenan, Carlson and Martz appearing in Instruments and Control Systems for May 1967 pages 139 to 144, inclusive. The computer control system described in said article is intended to function with data derived from the chemical analysis of the exhaust gases from the vessel 30 and measurement of the bath temperature with a sinker thermocouple and controls lance position and oxygen flow to obtain the desired temperature and carbon content end points, for a desired quality of steel. As indicated generally heretofore, such a computer control arrangement is relatively slow acting because it depends upon gas analysis of the carbon removal rate in the initial stages of the heat and other on-line data. However, by employing the accurate lance distance signal developed by the ranging radar system of the present invention, the computer 230 is able to control the process more accurately and closer duplication of results with different heats is made possible.

It is also contemplated that the lance distance signal developed by the display unit 220 may be employed during the actual oxygen blowing operation and while the molten material within the vessel 30 is heaving and churning. Furthermore, since the oxygen jet emitted from the nozzle 164 produces a crater or cavity in the surface 44 of the molten material, this dynamic lance distance signal will be a measure of the actual distance between lance tip 150 and the bottom of the crater or cavity thus formed.

During the oxygen blowing operation the basic oxygen furnace may be considered as a process which includes the oxygen jets, the molten material, or melt, within the vessel, which may be considered as a body of liquid capable of various modes of oscillatory motion, and the interaction between the jets and the melt. When the oxygen jets strike the melt they produce a curtain or spray of droplets of steel and/or slag from each crater and part of these droplets are entrained and driven back into the melt by so-called jet pumping. As a Vol.4... 7

result, energy is periodically added to the melt by the oxygen jets which results in oscillatory motion of the melt within the vessel 30. This oscillatory motion may be made up of many modes, both diametral and circumferential, depending upon many factors including the shape of the vessel 30, the mass, viscosity, slag-iron ratio, or slag composition of the melt, etc. Furthermore, depending upon the jet coupling to the melt the amplitude of this oscillatory motion may become so large as to cause the system to become unstable and cause sparking or slopping of the molten material out of the top of the vessel. Also, under certain conditions of acoustical feedback within the jet its pressure may drop abruptly thus causing a marked decrease in the amplitude of oscillation of the melt.

It will thus be seen that while the basic oxygen furnace is affected by many factors which cannot be detected directly, the direct dynamic measurement of variations in the level of the melt in the vicinity of the jet craters, by means of the above-described lance distance signal provides a new control parameter which may be used to correct other process parameters which cannot themselves be measured and thereby provide for the more efficient production of steel by means of the basic oxygen process. In this connection, it will be understood that the dynamic lance distance signal will contain frequency components corresponding to each of the modes of oscillation of the melt within the vessel 30 and the amplitudes of these various frequency components may be correlated and compared to provide an indication of optimum performance at various times during the oxygen blowing operation. Furthermore, by controlling oxygen flow to the lance the amplitude of oscillatory motion of the melt may be maintained at a high level to provide optimum mixing and shorten the overall process, without introducing instability of the melt which causes sparking or slopping. If the amplitude of the standing waves becomes excessive, the oxygen pressure may be reduced or the lance 42 may be raised to avoid instability. Also, under some conditions of incipient instability, the lance 42 may be moved sidewise within the opening in the hood 38, by controlling the slewing motor 70, so that the mass of the melt is excited at a different point and less inphase energy is supplied to this oscillating mass by the oxygen jets.

Variation in power distribution between the various frequency components of the lance distance signal may also be employed to control the process. For example, at the beginning of the heat most of the energy may be concentrated in the lowest frequency of oscillation of the melt, because the scrap tends to damp higher frequency components, so that the melt may have a tendency to slop around. As the scrap melts and slag is formed, some energy is transferred to the higher frequency components. By analyzing the relative amplitudes of the frequency components of the lance distance signal and changes in these amplitudes during the process, information is thus obtained about the process which could not be obtained directly.

Considering now in more detail the electronic circuits employed to develop the above-described electromagnetic wave and to process the received or reflected signal to recover information indicating the distance between the lance tip and the reflecting sur-

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US3727897 *Feb 17, 1971Apr 17, 1973Avco CorpLance with distance measuring sub-system
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US20110209579 *Feb 26, 2010Sep 1, 2011Nupro CorporationSystem for furnace slopping prediction and lance optimization
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Classifications
U.S. Classification266/86, 266/94, 266/245, 266/226, 342/124, 266/80
International ClassificationC21C5/46, C21C5/30, G01F23/284
Cooperative ClassificationC21C5/30, C21C5/4673
European ClassificationC21C5/30, C21C5/46K