Apparatus For Operating A Blast Furnace

Abstract

The apparatus includes means for comparing the rate of drop in the height of said burden with a predetermined normal rate of drop, means for indicating when the rate of drop in the burden height decreases a predetermined amount below normal, and means for indicating when the rate of drop in the burden height decreases a further predetermined amount below normal. Means are provided for determining when the blast pressure reaches a predetermined amount above normal and also for determining the rate of rise in the blast pressure. The pressure in the furnace is decreased when the blast pressure reaches the predetermined amount above normal, the rate of rise in the blast pressure reaches a predetermined value, and the rate of drop in the height of said burden decreases the first predetermined amount below normal, or when the blast pressure reaches the predetermined amount above normal and the rate of drop in the height of said burden decreases the second predetermined amount below normal.

Description

This invention relates to a method and apparatus for operating a blast furnace and more particularly for preventing or limiting slips in the furnace. In a blast furnace a charge or burden of iron ore, coke and limestone is periodically introduced into the top of the furnace and air under pressure is introduced into the bottom of the furnace. During the operation of the furnace the burden moves downwardly and the height of the burden is measured between charges. During normal or smooth operation the top of the burden or stockline moves downwardly at a relatively constant rate which is typically about 0.3 ft. per minute although the normal rate of movement may vary in different furnaces. When the furnace burden is not moving at the normal or proper rate, voids in the burden are increasing. If the voids continue to increase and the conditions causing the voids are not corrected the burden eventually will fall resulting in what is known as a "slip." When a slip occurs, the blast gases blow through the voids and create a high pressure in the furnace top. This high top pressure causes safety relief or bleeder valves to open. When these valves open, hot gases and burden material are discharged through the bleeder valves, thus polluting the atmosphere. In many cases a slip may not be of sufficient magnitude to open the bleeder valves. In this case, it is normally referred to as an inside roll. Inside rolls cause a heavy concentration of burden material to be carried out of the furnace and into a dust catcher. This dust catcher must be emptied and the dust disposed of. If the amount of dust collected exceeds the ability to dispose of this material, it can end up as a river pollution problem. It is not uncommon for a typical furnace to slip three or four times a day and have ten or fifteen inside rolls. Many attempts have been made to limit or control these slips, but none have proved satisfactory for various reasons. The parameters previously used are such that the possible occurrence of a slip is not predicted, but the existence of the slip is promptly indicated. Illustrative of the prior art are:

Leone Patent No. 2,625,386 dated 1/13/53

Leone Patent No. 2,814,479 dated 11/26/57

Leone Patent No. 3,092,680 dated 6/4/63

Borgel Patent No. 3,021,126 dated 2/13/62

Miller Patent No. 3,209,344 dated 9/28/65

It is therefore an object of my invention to provide apparatus for determining blast furnace conditions indicating that a slip is imminent.

Another object is to provide such apparatus which is relatively inexpensive.

Still another object is to provide such apparatus which includes means for reliving the conditions leading to a slip.

A further object is to provide a method of operating a blast furnace which eliminates or lessens the severity of slips.

A still further object is to provide a method and apparatus for operating a blast furnace which reduces air and water pollution.

These and other objects will be more apparent after referring to the following specification and attached drawing, in which:

The single FIGURE is a schematic view of a blast furnace and the wiring diagram of my invention.

Referring more particularly to the drawing, reference numeral 2 indicates a blast furnace having a large bell 4 and a small bell 6 at the top thereof. The burden is raised to the top of the furnace by means of skip 8. Blast air passes through a stove 10 to the bustle pipe 12 and enters the bottom of the furnace through tuyeres 14. A burden B in the furnace has a height or stockline S. The level of the stockline may be determined in various ways but that shown includes a test rod 16 connected by means of a wire rope or other flexible member 18 to a drum 20 which is rotated by means of a reversible motor 22. The rotation of the drum is recorded on a stockline recorder 24 such as a Foxboro Model 638-2AS Position Transmitter. The blast furnace gases pass from the furnace 2 through a downcomer 26 to a dust collector 28. In case of a sudden rise in furnace top pressure safety relief or bleeder valves 30 will open. A blast bleeder or snort valve 32 is provided in the air delivery line to quickly lower the pressure of the air blast. The parts so far described are conventional.

According to my invention I connect a D.C. input converter 34 to the output of the stockline recorder 24. This is preferably a Bell and Howell Module No. 19-116 which converts the D.C. output of the recorder 24 to a voltage which varies from 0 to 10 volts as the recorder 24 indicates a stockline height of 20 to 0 feet. The output of converter 34 is connected as one input to a differential amplifier or subtractor 36. This is preferably a Bell and Howell Module No. 19-301 Adder-Subtractor. An integrator 38 provides the second input to subtractor 36. This is preferably a Bell and Howell Module No. 19-407 connected to function as an integrator or ramp function generator. The converter 34 produces an impulse indicative of the actual height of the burden at predetermined time intervals which may be so close as to give a continuous impulse indicating a height-time curve. The integrator 38 produces an impulse indicative of the normal or desired height of the burden at the same predetermined time intervals as converter 34. The slope of its curve or ramp is determined by the setting of potentiometer 40. Thus, during the time that the rod 16 is in the furnace the impulses from converter 34 and integrator 38 are being compared at the same time intervals by subtractor 36. To assure that this occurs automatically after each charge the impulse from converter 34 is connected by lead 42 to the integrator 38 and to a relay 44 which is preferably a Bell and Howell Module No. 19-508. When the rod 16 is withdrawn the output of converter 34 rises so as to operate relay 44 to cause the voltage from converter 34 to be impressed on integrator 38. Then when the rod 16 is lowered onto the burden the initial voltage output of integrator 38 at this time will be the same as the voltage output of converter 34.

It will be seen that the output of subtractor 36 indicates the difference between actual and desired burden movement. This output is connected to relays 46 and 48 of the same type as relay 44. However, relay 46 is set to operate at a first predetermined difference value to indicate that the burden height is falling at a slower than desired rate and relay 48 is set to operate at a second predetermined value higher than the first so as to indicate the presence of substantial voids in the burden. Relay 46 has normally open contacts 46C and 46c1 and relay 48 normally open contacts 48C and 48C1. Contact 46C1 is connected to power lines L1, L2 in series with a horn 49 or other device which informs the workman that the burden is not falling fast enough and contact 48C1 is likewise connected to a similar horn 50.

A blast furnace pressure recorder 52 of any standard type is connected to measure the pressure of the blast air. The output of the recorder 52 is connected to a D.C. input converter 54 of the same type as converter 34. This converts the output of recorder 52 to a voltage which varies from 0 to 10 volts as the recorder 52 indicates a pressure of 0 to 30 p.s.i. The output of converter 54 is connected to a relay 56 of the same type as relay 44 having a normally open contact 56C adjusted to close when the blast pressure is above 20 p.s.i. The output of converter 54 is also connected to a differentiator 58 which is preferably a Bell and Howell Module 19-407 arranged to produce a voltage proportional to the rate of change of blast pressure. The output of differentiator 58 is connected to a relay 60 of the same type as relay 56 and having a normally open contact 60C adapted to close when the pressure is increasing at a rate in excess of 1/2 p.s.i. per minute. Contacts 46C, 56C and 60C are connected in series with a relay coil 62 to power lines L3, L4. Contact 48C is connected in parallel with contacts 46C and 60C. The relay 62 has normally open contact 62C. Contact 62C is connected to power lines L1, L2 in series with a solenoid 64S which operates valve 64 and with a signal horn 66. The valve 64 is connected in air conduit 68 so as to deliver air to an air cylinder 70 which operates snort valve 32.

In operation, the parts will be in the position shown as long as the furnace is operating normally. Assuming that the rod 16 is resting on the burden any of the following situations may occur. If the stockline is not falling fast enough and the actual stockline output from converter 34 lags behind the output of the integrator 38 by 1 volt, the contacts 46C and 46C1 will close and the operator will be warned by signal 49 that the furnace condition is not satisfactory. He may reduce the blast pressure or otherwise try to remedy the situation. However, if the blast pressure rises to a predetermined pressure such as 20 p.s.i. and the blast pressure increases at a rate in excess of 1/2 p.s.i. per minute while contact 46C is still closed relay 62 will operate to close its contact 62C, thus opening snort valve 32 to reduce the pressure in the furnace. When this occurs the furnace burden may move normally downward so as to open contact 46C to cause valve 32 to return to its closed position. However, if a slip should result the bleeder valves 30 will not open and the atmosphere will not be polluted.

Assuming that relays 56 and 60 are in normal position and the condition in the furnace is not corrected, it is probable that additional voids will occur in the burden and that the output of subtractor 36 will reach 3 volts. This will cause contacts 48C and 48C1 to close. Closing of contact 48C1 will cause operation of horn 50 and the operator will be warned that the furnace condition is critical. He will try to remedy the condition by opening snort valve 32. If for any reason he does not do this it is probable that the blast pressure will increase to 20 p.s.i., thus closing contact 56C. Thus, relay coil 62 will be energized so that snort valve 32 will open automatically.

While one embodiment of my invention has been shown and described, it will be apparent that other adaptations and modifications may be made without departing from the scope of the following claims.

Claims

I claim:

1. In a blast furnace having a moving burden therein and including means for introducing pressurized blast air into said furnace adjacent the bottom, means for charging burden into the top of said furnace, means for measuring the height of said burden, means for measuring the pressure of said blast air and means for reducing the pressure in said blast furnace; the improvement comprising:

means for determining the actual rate of burden movement,

means for determining the difference between the actual rate of burden movement and a desired rate of burden movement,

means for determining the rate of change of pressure of blast air, and

means responsive to the difference between actual and desired burden movement rates exceeding a predetermined level and the blast air pressure exceeding a predetermined level and the rate of change of blast air pressure exceeding a predetermined level for actuating said pressure reducing means.

2. In a blast furnace having a moving burden therein and including means for introducing pressurized blast air into said furnace adjacent the bottom, means for charging burden into the top of said furnace, means for measuring the height of said burden, means for measuring the pressure of said blast air and means for reducing the pressure in said blast furnace, the improvement comprising:

means for determining the actual rate of burden movement,

means for determining the difference between the actual rate of burden movement and a desired rate of burden movement, and

means responsive to the difference between actual and desired burden movement rates exceeding a first predetermined level and the blast air pressure exceeding a predetermined level for actuating said pressure reducing means.

3. The combination of claim 2 which includes means for determining the rate of change of pressure of blast air and means responsive to the difference between actual and desired burden movement rates exceeding a second predetermined level greater than said first level and the blast air pressure exceeding a predetermined level and the rate of change of blast air pressure exceeding a predetermined level for actuating said pressure reducing means.

4. The combination of claim 3 which includes an air delivery line in said means for introducing pressurized air into said furnace adjacent the bottom and in which said means for reducing the pressure in said blast furnace is a snort valve in said air delivery line.

5. The combination of claim 3 which includes a first alarm for indicating that the difference between the actual and desired burden movement rates exceeds the first predetermined level and a second alarm for indicating that the difference between the actual and desired burden movement rates exceeds the second predetermined level.