Apparatus for measuring bath level in a basic oxygen furnace to determine lance height adjustment

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is directed to a device for determining proper oxygen lance height adjustment for a basic oxygen furnace (BOF) operation, and in particular, it is directed to laser based measuring apparatus capable of being positioned above the mouth of a BOF vessel so that repeated distance measurements to a target area within the vessel may be taken to provide a collection of measurement readings that are used to determine proper oxygen lance height adjustment for each or any selected heat manufactured during a steelmaking campaign. The laser-based measuring device includes an extendable optical head mounted within a protective air-cooled housing attached to an oxygen lance crane assembly, and a combined laser transmitter/receiver unit that communicates with the optical head from a remote position. The air-cooled housing is positioned above the mouth of a BOF at a location that provides the optical head with access to a line of sight extending down through the oxygen lance crane assembly, through a lance opening provided in the off-gas hood, and into the mouth of the BOF vessel. The laser-based measuring device further includes a spring loaded cylinder that is selectively operated to both remove a protective cover from an opening provided in the air-cooled housing, and extend the optical head outward from a stored position within the housing. The optical head is extended outward through the housing opening and into a line of sight down through the lance crane assembly, through the BOF mouth, and into the vessel interior. The spring loaded cylinder also selectively operated to retract the extended optical head back into its stored position within the housing and replace the protective cover over the housing opening. In its closed position, the protective cover shields the optical head and associated mechanisms from dust and fume generated during the BOF steelmaking process. Additionally, the air-cooled housing may also include a hinged or removable panel for convenience during maintenance and repair.

2. Brief Description of the Related Art

There has been a long felt need within the steelmaking industry to develop a more precise method for determining oxygen lance height adjustment. Correct lance height adjustment is critical to proper mixing at the steel/slag interface in a BOF steelmaking operation. In the past, such lance height adjustments were determined by calculations based on a once a day topographic measurement of the vessel interior. For example, a typical BOF heat cycle generally begins when an empty hot metal charging ladle arrives at the pouring station after the ladle has been used to charge a previous heat. A charge calculation is then made for the next scheduled heat and the ladle is filled with a calculated amount of molten iron. The charge calculation is generally made using a mass-energy balance model. The charge model calculates the weights of hot metal, cold pig iron, steel scrap, and flux materials that are used to produce a specified weight, temperature, and chemical analysis of steel at the end of the oxygen blow. In many BOF shops a predetermined weight of hot metal and scrap is weighed out early based upon the once a day topographical measurement of the vessel interior, and the final weights are obtained by trimming either the hot metal, the scrap, or both after the charge calculation for the heat has been completed. In the past, molten metal bath level was calculated using a once a day topographical or profile measurement of the vessel interior along with the charge model calculations. However, such calculations are inaccurate due to changing vessel shape. For example, after a finished heat is tapped, BOF vessels are rocked back and forth to provide a slag-splash coating that solidifies on the refractory lining to provide a protective coating against refractory erosion. Slag-splash coating is done before the remaining slag is poured from the vessel into a waiting slag car.

Slag splashing practice, in combination with the erosive effects of the hostile steelmaking process on the refractory lining, creates a dynamic, continuously changing interior space within the BOF vessel. As a result, bath level calculations of the past, based on a once-a-day vessel profile measurement, are inaccurate and may result in placing the oxygen lance either too high or too low with respect to the slag/metal interface. If an oxygen lance is positioned low, the velocity of the oxygen causes molten metal and slag to erupt from the vessel creating a hazardous condition. Low lance placement also causes skull to build up on the lance and causes overheating that reduces lance tip life. This condition also lowers the iron oxide content in the slag layer that floats on the surface of the molten metal bath. If a lance is positioned high, it becomes more difficult to lower the carbon level in the molten metal bath. A high lance will also generate higher oxygen levels in the cone portion of the furnace and a higher iron oxide content in the slag, both of which will cause excessive refractory wear.

Vessel measurements are taken only once a day because present state of the art vessel measuring devices and techniques require operators to take the vessel out of service so that the measuring apparatus, for example a laser device, can be moved into a measuring position in front of the BOF vessel. Such operations are time consuming and expensive with respect to productivity. For example, at the Bethlehem Steel Sparrows Point operation, it takes between about 45-50 minutes to produce a heat of steel, and each BOF vessel produces about 20 heats of steel per day. In a best case scenario, it takes operators about 20-30 minutes to take a vessel interior profile measurement. Therefore, from a lost-time viewpoint, such profile measurements are generally spaced apart as far as practical to avoid driving down steel production.

Various laser-based measuring devices are in use for detecting molten metal bath levels. For example, U.S. Pat. Nos. 5,190,717 and 5,090,603, issued to Bayliss, disclose a laser based metal pouring system for applying a molten metal coating to the surface of a steel substrate. The apparatus uses laser probes to measure coating thickness and to maintain a constant bath level in the pot. However, although Bayliss broadly teach using a laser beam to measure the level of a molten metal bath contained within a vessel, the drawing figures show an unprotected laser probe positioned above the molten metal bath. The Bayliss laser probe operates in an antiseptic environment as compared to the dust-laden, hostile environment above the mouth of a BOF converter. Therefore, Bayliss fails to recognize the problems associated with placing an electro/optical device within the hostile environment above a BOF steelmaking vessel, and his disclosure completely fails to provide any teaching or suggestion for overcoming such problems.

Another laser-based measuring device is shown in U.S. Pat. No. 4,899,994 granted to Zhidkov, et al. The 994 patent teaches mounting a γ radiation transmitter and a γ radiation receiver above the mouth of a BOF steelmaking vessel to measure the level of molten metal in the vessel. Such devices are very hazardous from a radiation viewpoint, and would likely not be used in the United States due to their high radiation levels. However, because such γ radiation devices are likely not affected by high dust levels, the disclosure fails to address dust related problems associated with a BOF steelmaking operation. Accordingly, the inventors fail to teach, or even suggest, protecting their sensor from the hostile environment above a BOF vessel.

Therefore, there is a long felt need within the industry to provide a safe, radiation free, measuring device that will allow operators to make repeated vessel measurements in the hostile BOF steelmaking environment to determine critical O

2

lance height adjustments with respect to the slag/metal interface without reducing productivity.

SUMMARY OF THE INVENTION

Accordingly, it is therefore a first object of the present invention to provide improved accuracy in oxygen lance height adjustment in a BOF steelmaking operation.

It is another object of the present invention to provide a measuring device capable of measuring distance to a target area within a steelmaking vessel without decreasing steelmaking productivity.

It is still another object of the present invention to provide a measuring device capable of measuring distance to a target area within a steelmaking vessel while the lance crane assembly associated with the steelmaking vessel is in a steelmaking position.

It is another object of this invention to provide a measuring device capable of measuring distance to a target area within a steelmaking vessel before the start of each heat produced during a steelmaking campaign.

It is still another object of the present invention to provide a measuring device capable of being located at a permanent operating position within the hostile environment above the mouth of a BOF steelmaking vessel.

Another object of this invention is to provide an improved method for determining lance height adjustment with respect to a calculated bath surface of a selected heat based upon a continuing series of measurement readings to a target area within a metallurgical vessel.

Other objects and advantages of the present invention will become apparent as a description thereof proceeds. In satisfaction of the foregoing objects and advantages, the present invention provides a measuring device adapted to measure a distance to a target area within a metallurgical refining vessel while an associated lance crane assembly is in its refining position above the metallurgical vessel. The measuring device includes an optical head that is positioned to direct to the target area an energy beam received from an energy source, and to direct to a processor an energy beam reflected from the target area. The optical head is contained within a housing and is attached to a movable mounting that may be selectively extended to expose the optical head to the target area, and selectively retracted to shield the optical head within the housing when measurements are not being taken.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now made to the drawings of the invention wherein:

FIG. 1

is an elevation view showing the preferred embodiment of the present measuring device installed above the mouth of a BOF steelmaking vessel.

FIG. 2

is an enlarged view of a portion of the measuring device installation shown in FIG.

1

.

FIG. 3

is a cross-section view taken through the housing of the preferred embodiment of the present measuring device invention.

FIG. 4

is a cross-section view similar to

FIG. 3

showing the measuring device extended to a measuring position above the mouth of a BOF vessel.

FIG. 5

is an isometric view of an alternate measuring device embodiment.

FIG. 6

is a cross-section view taken along the lines 6—6 of FIG.

5

.

FIG. 7

is an alternate embodiment of the present invention.

FIG. 8

is a graph illustrating the data listed in TABLE A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention advances the art of determining critical oxygen lance height adjustment to properly place a BOF oxygen lance with respect to the slag/metal interface (bath elevation) during an oxygen blow into the BOF steelmaking vessel. A typical BOF heat cycle generally begins when the charging ladle arrives at the hot metal pouring station. A charge calculation, based upon a mass-energy balance model, is made for the scheduled heat, and the charge model calculates the weights of hot metal, cold pig iron, steel scrap, and flux materials required to produce a specified weight, temperature, and chemical analysis of the desired steel product being manufactured in the vessel. In many BOF shops, a predetermined amount of hot metal and scrap may be weighed out early, and final weight adjustments are made by trimming the predetermined materials after the charge for the heat is calculated.

In the past, such charge calculations were used in combination with a once a day laser based topographic measurement of the vessel lining to calculate an estimated bath level for each heat produced throughout the day. Such estimated bath level calculations are inaccurate because continuous increasing or decreasing slag buildup along the vessel lining changes the available steelmaking capacity (vessel volume) from one heat to the next. As a result, once a day laser measurements often provide a false indication of vessel volume, and such misinformation may result in a calculated bath level error and improper adjustment of the oxygen lance height for the O

2

blow. Improper lance height adjustment can cause various problems in a BOF steelmaking operation. For example, if the O

2

lance is positioned above or within the slag/metal interface, the slag cover floating on the surface is over oxidized, and excess amounts of FeO produced during such over oxidization causes accelerated refractory wear along the upper lining of the vessel. On the other hand, if the O

2

lance penetrates too deep into the molten metal bath, too far below the slag/metal interface, poor mixing occurs at the interface and the decarburization rate of the steelmaking process decreases. Reduced decarburization reduces productivity because it slows the reduction of iron into steel, and reduced decarburization drives up steelmaking costs by consuming excess amounts of oxygen and expensive additives. Additionally, a deep penetrating O

2

lance tip will cause excessive refractory wear along the vessel bottom lining, thereby decreasing service life of the vessel which also decreases productivity and increases costs.

The present invention overcomes such past problems by providing a laser based measuring device capable of taking slag surface measurements after each heat and vessel bottom lining measurements before each heat produced during a BOF campaign while the lance crane assembly is in its steelmaking position.

Referring to

FIGS. 1 and 2

of the drawings, a state-of-the-art BOF steelmaking operation comprises a basic oxygen furnace

1

, an off-gas hood

2

, attached to appropriate environmental apparatus such as a wet scrubber to prevent steelmaking fume and dust from reaching the atmosphere, and an oxygen lance

3

for injecting oxygen below the surface of the molten metal bath contained in the BOF steelmaking vessel

1

. The oxygen lance

3

is mounted to a lance crane assembly

4

comprising a carriage

5

that travels either downward along a crane structure

6

to insert the oxygen lance into the steelmaking vessel

1

, or travels upward along crane structure

6

to remove the oxygen lance from the steelmaking vessel. A lance opening

8

in the off-gas hood

2

provides lance access to the vessel interior. The vertical traveling carriage

5

also enables operators to adjust the oxygen lance height with respect to the level of the slag/metal interface of the heat being manufactured in the vessel.

In the past, when operators took once a day measurements of the vessel lining, it was necessary for steelmakers to (a) raise carriage

5

to withdraw lance

3

from the vessel; (b) rotate the vessel from the upright steelmaking position to a horizontal position, exposing the vessel interior to the laser apparatus positioned on the operating floor; (c) moving a vessel measuring device (not shown) into a measuring position adjacent the mouth of the horizontal vessel; (d) measure the profile of the vessel interior; (e) move the vessel measuring device away from its measuring position; (f) rotate the vessel back to the upright steelmaking position; (g) lower carriage

5

to insert lance

3

back into the steelmaking vessel; and (h) adjust lance height based upon calculations using the once a day profile measurement of the vessel interior. In a best case scenario, such an 8-step measuring process will take between 20-30 minutes to complete, and therefore, is impractical for taking frequent vessel measurements throughout a BOF steelmaking campaign.

In the preferred embodiment of the present laser based measuring device invention, the measuring device

10

is attached to the BOF structure

4

a

at a location above the mouth of the BOF converter

1

. The laser based measuring device

10

includes a housing

11

having an open end

12

along the oxygen lance side of the housing, and a movable cover

13

. Cover

13

is adapted to fit over opening

12

and is responsive to a drive means

14

by way of a connecting frame

15

that fastens the drive means to the removable cover. The optical head portion

16

of a laser system is fastened to frame

15

so that when drive means

14

is operated, both the laser head

16

and cover

13

follow frame

15

from a stored position to an extended measuring position that aligns the optical head in a line of sight

30

down through the crane structure

6

, through lance opening

8

(FIG.

1

), and into the steelmaking vessel

1

. Additionally, as shown in

FIGS. 3-4

, frame

15

is supported on wheels

17

that maintain frame

15

, laser head

16

, and cover

13

in a horizontal plane when drive means

14

is operated. An aiming laser

43

may be provided to sight and align the laser measuring device

10

to the selected target area(s) during initial installation of the device or when the device is moved for routine maintenance and/or repair.

Referring to

FIG. 7

, housing

11

may include one or more baffles or panels

46

that are positioned to provide a reduced the size of the opening

12

a

that more approximates the size and shape of the laser head

16

extending or retracting therethrough. The extendable door portion

13

a

(moveable cover) is sized to overlap opening

12

a

as shown by the phantom lines

47

and a seal

48

to prevent steelmaking fume and dust from entering the inside space of housing

11

when door

13

a

is in a retracted closed position against the baffles

46

. Additionally, the smaller size opening

12

a

provided by baffles

46

makes it more difficult for dust to enter housing

11

when the laser head

16

is extended to the measuring position shown in FIG.

7

.

Referring again to

FIGS. 3-4

, the preferred drive means

14

is an air cylinder and includes a spring mechanism

17

biased toward the retracted position to maintain cover

13

in a closed position over opening

12

when the laser-based measuring device is not in use. It should be understood, however, that the drive means is not limited to a pneumatic cylinder and that any suitable drive means may be used to extend laser head

16

to the line of sight measuring position

30

without departing from the scope of this invention. For example, the drive means may comprise a hydraulic cylinder, a rack and pinion arrangement, or any other electromechanical device known in the art to achieve the same results. As shown in

FIG. 4

, housing

11

may include a removable service panel

18

that provides access to the housing interior space for servicing the optical head

16

and its associated mechanism.

Referring again to

FIGS. 1-4

, the preferred laser based measuring device

10

includes laser electronics

19

located within a friendlier environment remote from the BOF vessel. The laser electronics communicate with the optical head

16

through a twin fiber optic cable

20

, and includes a laser source to selectively generate an energy beam transmitted along a first fiber optic cable

20

a

to optical head

16

, and a photodetector, or the like, for generating an electrical output signal indicative of distance based upon reflected energy that is received from optical head

16

along a second fiber optic cable

20

b

. The output signal indicative of distance is sent to a computer

26

located in pulpit

9

where a resident program processes the signal for use in calculations that determine oxygen lance height adjustment for the current heat.

The twin fiber optic cable

20

is enclosed within a protective braided cable

21

that shields the fiber optic cables

20

a

and

20

b

from the hostile steelmaking environment. Cable

21

also houses an air line

22

having one end attached to the pneumatic drive means

14

and its opposite end attached to a pressurized air supply

28

controlled by a solenoid valve

27

. A second air supply line

23

is housed within braided cable

21

to provide an air purge

24

injected into the interior space of housing

11

. The air purge is injected into housing

10

at a pressure of about 90 psig and at a temperature sufficient to maintain the interior space below about 140° F. In some instances, the air supply line

23

may be attached to a cooled pressurized air supply

28

to inject a cooling air purge

24

into the interior space of housing

11

. The forced air purge also creates a positive pressure within housing

11

when the protective cover is closed. The positive pressure prevents steelmaking fume and dust from entering the housing and contaminating the optical head and drive mechanism during the steelmaking operation. Additionally, the air purge also provides an outward airflow, or an air wipe, through opening

12

when cover

13

is opened to extend the optical head into the line of sight

30

. The air wipe flow shields the open interior of housing

11

from dust and fume during measuring operations.

As more clearly shown in

FIGS. 1 and 2

, because the laser electronics

19

and the optical head

16

are spaced apart, the improved laser based measuring device provides a compact measuring tool capable of being inserted into small spaces above a metallurgical vessel. The smaller size device, with its extendable optical head

16

, makes it possible to install the laser based measuring device

10

adjacent the carriage travel path

31

so that only the optical head portion

16

needs to be extended into the narrow line of sight

30

that is available down through the lance crane structure

6

into the mouth of the BOF vessel

1

. This arrangement enables operators to make vessel interior measurements without a need to rotate the vessel from its steelmaking position as described in the above prior 8-step vessel measuring process. Therefore, the improved laser-based measuring device provides means for measuring selected target areas within a metallurgical vessel before or after every or any selected heat produced during a manufacturing campaign without affecting productivity.

In instances where the equipment arrangement provides a wider clearances at the line of sight into the metallurgical vessel, an alternate measuring device without an extendable drive means, may be used to take measurements to target areas within the metallurgical vessel. One example of such an alternate measurement device

10

a

is shown in

FIGS. 5 and 6

. The alternate embodiment includes a stationary optical head

16

fastened within a housing

11

a

. The housing includes a solenoid (not shown) actuated sliding panel or shutter

13

a

that is operated to an open position to expose the optical head

16

to the line of sight

30

extending to the target area within the metallurgical vessel, and is operated to a closed position to shield the optical head within housing

11

a

when measurements are not being taken, for example during metallurgical refining operations. The optical head receives energy beams transmitted along fiber optic cable

20

a

, and transmits reflected energy beams along the second fiber optic cable

20

b

of twin cable housed within the braided cable

21

as heretofore described above. Housing

11

a

also includes a removable panel

18

a

similar to the preferred embodiment to provide access to the housing interior.

Housing

11

a

is attached to the vessel structure

40

via a mounting arm

41

having a first end attached to a pivot mount

25

and a second end

42

attached to housing

11

a

. An air line

23

, attached to the pressurized air source

28

(FIG.

1

), provides an air purge flow

24

into the interior space of the housing

11

a

. Alternatively, as described in the preferred embodiment, the air purge may be conveyed along the braided cable

21

to cool both the fiber optic cables

20

a

and

20

b

and the interior space of housing

11

a.

A horizontal adjustment means

44

, and a vertical adjustment means

45

is provided to enable technicians to align optical head

16

along the line of sight to the target area within the vessel.

The following description is directed to a method for determining lance height adjustment using the preferred laser-based measuring device

10

. It should be understood, however, that the alternate embodiment

10

a

, or other measuring device, may be operated in a similar manner by one skilled in the art without departing from the scope of this invention.

Referring to

FIG. 1

, the preferred laser-based measuring device

10

is operated by a controller normally located in pulpit

9

on the charge floor of the BOF shop. The controller may be either a person who manually operates the laser-based measuring device, or the controller may be a computer

26

and resident program that automatically sends output signals along cable

25

to operate the laser based measuring device. The present disclosure describes operating the laser based measuring device

10

with a computerized controller

26

. However, and it should be understood that measuring device

10

may just as well be manually operated by a person without departing from the scope of this invention.

At the start of a steelmaking cycle, controller

26

sends an output signal along a first line within cable

25

to activate solenoid valve

27

that controls the flow of air along feed line

29

extending from the pressurized air supply

28

. In response to the output signal, solenoid valve

27

is opened to release a flow of pressurized air along line

22

housed within braided cable

21

(

FIGS. 3-4

) and the pressurized air exerts a force against the piston within drive means

14

. The applied force compresses spring

17

and moves frame

15

outward from housing

11

to align laser head

16

along the line of sight

30

to the target area at the vessel bottom lining. As shown in

FIG. 4

, when frame

15

is extended outward from housing

11

, cover

13

follows the frame away from its closed position over end

12

of the housing and thereby provides an opening that enables the laser optical head

16

to be extended to the line of sight

30

position that communicates with the interior of the metallurgical or steelmaking vessel.

After laser head

16

is extended into the line of sight

30

, the laser or energy source within the laser electronics box

19

is activated by an output signal from controller

26

. In response to the signal, an energy beam is generated and transmitted along the first fiber optic cable

20

a

to the optics in laser head

16

, and the laser optics redirect the energy beam along the line of sight

30

to the target area within the vessel. The energy beam impacts upon the target and the reflected energy beam is received by the laser optics in head

16

and is further transmitted along the second fiber optic cable

20

b

to a photodetector housed within the laser electronics box

19

. The photodetector, or other device capable of achieving the same results, converts the reflected energy beam into an amplified electrical signal indicative of distance to the target area, and the amplified signal is transmitted along a second line within cable

25

to controller

26

. The resident program processes the incoming amplified electrical signal to provide an initial measurement or base line reading to the vessel bottom lining, and the base line reading is stored for later use in determining an increasing or decreasing slag buildup trend on the vessel lining. The base line reading may be displayed on a monitor for use by operating personnel. After the initial base line reading is taken, and after the controller sends a signal to deactivate the laser source, solenoid valve

27

receives an output signal from controller

26

to close the pressurized air supply valve. In response, the compressed spring

17

forces frame

15

and the attached laser head

16

and cover

13

back to their retracted stored and closed positions respectively to protect the laser optics and related mechanisms from the fume and dust generated during the steelmaking process (FIG.

3

).

The steelmaking vessel

1

is charged with steel scrap and molten iron delivered from the blast furnace. When the charge is completed, the oxygen lance

3

is lowered through hood opening

8

to a lance height related to a calculated bath level for the heat based upon the charge calculations and the once a day profile reading described above. After the lance is adjusted to its proper height with respect to the calculated bath level or elevation, oxygen is blown into the molten metal bath to reduce the molten iron into steel.

At the end of the heat, after the oxygen blow is stopped, it is a normal practice for steelmakers to take a sample of the molten steel for analysis purposes. During this time, while the operators are waiting for their analysis results, and while the molten metal bath is relatively quiet or still, controller

26

sends an output signal to activate the solenoid valve

27

and extend laser head

16

outward to its line of sight measuring position

30

. At least one distance reading is taken to a target area on the surface of the molten slag cover floating on the metal bath by generating an energy beam as heretofore described. The energy beam is reflected back from the slag cover and is transmitted to the photodetector as herein described, and the resulting amplified electrical signal, indicative of a distance to the surface of the slag cover, is received by controller

26

where it is further processed by the resident program to provide a slag level reading that is stored with a continuing history of such readings used to calculate bath level elevations for proper oxygen lance height adjustments. The slag level reading may also be displayed on the monitor for use by operating personnel.

After the slag level reading is taken, the laser head

16

is retracted to its stored position within housing

11

and cover

13

is closed to protect the laser measuring apparatus during the tapping operation. If the analysis results are positive, the steelmaking vessel is rotated to the tap side and the molten steel is drained from the BOF vessel. When slag begins to appear in the tap stream, the vessel is rotated to the upright position and the slag splash process coats the refractory lining with molten slag. Any molten slag remaining after splash coating is poured from the vessel into a waiting slag car.

When the steelmaking vessel

1

is completely drained of molten slag, after the slag pour off and before the next charge, the empty hot vessel is rotated to its upright steelmaking position and controller

26

once again sends a signal that extends the optical head

16

to its measuring position along the line of sight

30

. The laser source within box

19

is activated by the controller and generates an energy beam that is transmitted along fiber optic cable

20

a

to laser head

16

. The laser head redirects the energy beam along the line of site

30

to the target area at the vessel bottom lining to take a slag build-up reading. The new slag build-up reading is stored with a continuing history of such slag build-up readings, and the resident program compares the base line reading with both the slag build-up history and the slag level history to determine if there is a trend toward an increase or decrease of slag build-up on the vessel lining (slag build-up trend). The resident program then calculates the slag/metal interface (bath level elevation) to determine proper lance height adjustment for the next heat based upon the charge calculation figures for the next heat, the slag build-up trend, and a calculated slag volume estimate for the heat. In response to the calculated bath level elevation, controller

26

sends a signal that regulates the carriage drive mechanism and moves carriage

5

along the crane structure

6

to a location that properly adjusts the oxygen lance tip height with respect to the calculated slag/metal interface for the next scheduled heat. Alternatively, the calculated slag/metal interface and/or the next lance tip position is displayed on the monitor so operators can manually adjust the lance tip elevation with respect to the slag/metal interface.

In the preferred method for determining lance tip height adjustment, the laser-to-target measurements are repeated for each heat produced during a steelmaking campaign, and the continuing history of slag level measurements and slag build-up measurements are compared with the base line and a once a day vessel profile reading to determine the slag build-up trend. However, it should be understood that operators may choose to skip target area measurements on certain selected scheduled heats without departing from the scope of this invention. For example, operators may choose to take laser-to-target measurements every second, or every third heat, etc., without departing from the scope of this invention. The improved measurement device

10

enables operators to take a multiplicity of distances readings throughout the day, or throughout an entire steelmaking campaign because the improved device eliminates any need to remove the vessel from operation when laser-to-target measurements are being taken.

Referring to the graph shown in

FIG. 8

, plotted from the data listed in Table A below, the continuing history of measurement data that was heretofore not available, provides more accurate lance tip height adjustments than such lance height adjustments of the past that were based on a once a day vessel profile measurement. For example, referring to the Table A, column “B” labeled “Lance Height Setting”,and to the corresponding plot “B” shown in

FIG. 8

, past lance tip height adjustments were made in response to a lance height calculation that was based upon a once-a-day profile measurement, a charge calculation, and a slag thickness calculation. The lance position was adjusted to agree with the calculation, and it remained at the calculated elevation until operators were able to take a new profile measurement (about 24-hours). For instance, column “B”,and corresponding plot “B” in

FIG. 8

, show an adjusted lance tip height of 114 inches above a theoretical or calculated bath elevation (i.e. above “0”) for the last heats 2873 through 2876 of an earlier steelmaking cycle. This 114 inch lance tip elevation is based upon an earlier vessel profile reading that was used to calculate the theoretical bath elevation from which the lance height was adjusted. The recorded data shows that a new vessel profile measurement (Profile Reading #1) was taken between Vessel No. 2 heats 2876 and 2877. Based upon this new profile reading a new theoretical bath elevation was calculated and the lance tip height was adjusted to 110 inches accordingly. The lance tip remained at

110

inches until the next profile measurement (Profile Reading #2) was taken between heats 2889 and 2890. Based upon the #2 profile reading, a new theoretical bath level was calculated and the lance tip height was adjusted to 116 inches above zero for the next steelmaking cycle, (about 24-hours).

Referring to Table A, columns “A-F” and the corresponding plotted data in

FIG. 8

, the apparatus and method of the present invention was used to determine proper lance tip height adjustment for each heat produced in the steelmaking cycle extending from heat number 2877 through heat number 2889. The distance measurements taken from the measuring device

10

to the selected target within the steelmaking vessel

1

(

FIG. 1

) are shown in columns “C” and “D”. Column “C” lists the distance readings from the measuring device to a target area at the vessel bottom lining, and the recorded information enables operators to determine an increasing or decreasing slag buildup trend on the vessel lining. Column “D” lists the distance from the measuring device to a target area on the surface of the slag blanket floating on the molten metal bath, and the recorded information is used, in combination with a calculated slag blanket thickness, to determine a theoretical bath elevation or “0” from which the lance tip adjustment is measured. Column “E” shows the difference in calculated theoretical bath elevations for successive heats, and column “F” lists the calculated lance tip height based upon the differences shown in column “E”.

TABLE A

“F”

“B”

“C”

“D”

“E”

New

Date

“A”

Lance

Empty

Full

Bath

Lance

Year

Heat

Height

Vessel

Vessel

Height

Height

2000

No.

Setting

Reading

Reading

Difference

Setting

6/18

2873

114

788

703

111

↓

2874

114

786

702

1

112

2875

114

788

704

−2

110

2876

114

790

705

−1

109

Profile Reading #1

2877

110

789

706

−1

109

2878

110

789

705

1

110

2879

110

790

704

1

111

2880

110

788

702

2

113

2881

110

791

701

1

114

2882

110

790

700

1

115

6/19

2883

110

791

701

−1

114

↓

2884

110

789

699

2

116

2885

110

788

698

1

117

2886

110

790

700

−2

115

2887

110

790

700

0

115

2888

110

796

702

−2

113

2889

110

795

701

1

114

Profile Reading #2

2890

116

793

700

1

117

2891

116

793

701

−1

116

2892

116

793

701

0

116

If we compared the calculated lance tip height adjustments listed in column “F” with the once-day 110 inch adjustment determined by profile reading #1, we see that the new measuring device and method greatly improves the accuracy of such lance height adjustments. For example, in heat number 2885, the 110 inch lance height adjustment has an error of more than 6% when compared to the more accurate corresponding lance height adjustment shown in column “F”.

Additionally, when it is established that there is consistent accuracy between the last lance height adjustment in a given steelmaking cycle, for example heat 2876, and the first lance height adjustment in the next steelmaking cycle, where the adjustment is based upon a profile reading, for example Profile Reading #1, operators may elect to extend the cycle time between vessel profile measurements. Such extended cycle times will dramatically improve steelmaking productivity. To illustrate, if the cycle between successive profile measurements were extended to say 48-steelmaking periods, a vessel would produce one extra heat of steel every two days and thereby increase productivity by about 7,800 tons of steel per year.

While this invention has been described as having a preferred design and method of operation, it is understood that it is capable of further modifications, uses, and/or adaptations following in general the principle of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains, and as may be applied to the essential features set forth herein, and fall within the scope of the invention limited by the appended claims. For example, while the preferred embodiment shows and describes using a laser as an energy source, any energy source capable of generating a signal indicative of distance to the target area may be used to determine the slag/metal interface and/or lance height adjustment without departing from the scope of this invention. Such exemplary energy sources may include any of the light, radar, or microwave wavelengths.

Number	Name	Date	Kind
3395908	Woodcock	Aug 1968	A
3610601	Bishop	Oct 1971	A
3663204	Jungwirth	May 1972	A
3701518	Herff	Oct 1972	A
3708159	De Bray	Jan 1973	A
3727897	Bennett	Apr 1973	A
4365788	Block	Dec 1982	A
4413810	Tenberg et al.	Nov 1983	A
4880212	Hägglund et al.	Nov 1989	A
4899994	Zhidkov et al.	Feb 1990	A
5090603	Bayliss	Feb 1992	A
5190717	Bayliss	Mar 1993	A
5827474	Usher et al.	Oct 1998	A
6228142	Shin et al.	May 2001	B1

Apparatus for measuring bath level in a basic oxygen furnace to determine lance height adjustment

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