US3197304A

US3197304A - Method for introducing coal into a blast furnace

Info

Publication number: US3197304A
Application number: US144605A
Authority: US
Inventors: Jagdish C Agarwal
Original assignee: United States Steel Corp
Current assignee: United States Steel Corp
Priority date: 1961-10-12
Filing date: 1961-10-12
Publication date: 1965-07-27
Anticipated expiration: 1982-07-27

Description

July 27, 1965 J. c. AGARWAL METHOD FOR INTRODUCING COAL INTO A BLAST FURNACE Filed 061:. 12. 1961 D E S S m A M i FLOW OIVTROL L 5!? TUYERES COLD BLAST MAIN INVENTOR. JAGD/SH C. AGARWAL M/ Attorney United States Patent 3,197,304 METHOD FOR WIRODUCING COAL INTO A BLAST FURNACE .Iagdish C. Agarwal, Penn Hills Township, Allegheny County, Pa, assignor to United States Steel Corporation, a corporation of New Jersey Filed Oct. 12, 1961, Ser. No. 144,605 2 Claims. (Q1. 75-42) This invention relates to an improved method and apparatus for handling pulverized coal introduced to a blast furnace through the tuyeres.

In conventional blast furnace operation, iron ore, metallurgical coke and limestone flux are charged to the top of the furnace, while a hot air blast is blown through the tuyeres. Since proper grades of coke are scarce and costly, every effort is made to use smaller proportions of coke. It is known that the coke consumption can be lowered by introducing fuel with the blast at the tuyeres. Such fuel may be either gaseous, liquid or pulverized solids, and it oxidizes in the furnace to furnish part of the necessary heat. Pulverized coal presents handling problems when used for this purpose. It is necessary to dry the coal so that freezing of condensed moisture in cold weather does not impede its fiow. Furthermore the size range of the coal particles must be controlled for proper regulation of the injection rate.

An object of my invention is to provide an improved method and apparatus for handling pulverized coal in which the coal is sized, dried and injected in regulated quantities through the tuyeres of a blast furnace all in one continuous operation.

A further object is to provide a method and apparatus for handling pulverized coal in which coal particles are dried in a bed fiuidized by air taken from a cold blast main and heated to a suitable drying temperature and subsequently injected along with the air blast to the furnace.

In the drawing:

The single figure is a diagrammatic showing of a coal handling apparatus constructed in accordance with my invention.

My apparatus includes a storage bin containing a supply of crushed coal, a pulverizer 12, conveyors 13 for feeding coal from the bin to the pulverizer, and a screen 14 or equivalent for separating oversize particles from the pulverized product. Usually I screen at 4; inch or inch, and I return oversize particles to the pulverizer for further grinding. A conveyor carries coal particles which pass through the screen to the mouth of a container 16. Two outlet conduits 17 and 17a extend from the bottom of container 16 to alternative hoppers 18 and 18a. I equip these conduits with respective valves 19 and 19a, which seal the upper ends of the hoppers air-tight when closed. I connect compressed air lines 29 and 20a, which contain valves 21 and 21a, to the respective hoppers 18 and 18a. I alternately open one valve 17 or 17a and close the other and thus fill each hopper 18 and 18a in turn with pulverized coal from container 16. I close valve 21 or 21a which leads to the open hopper and open the other to pressurize the closed hopper.

My apparatus includes a fluidized bed dryer 22 and

respective screw conveyors

23 and 23a and downcomers 2d and 24a for continuously feeding pulverized coal from the closed hopper 18 or 18a to said dryer. I continuously withdraw a controlled portion of the compressed air carried by a cold blast main 25 through a line 26 which contains a flow controller 27. Line 26 leads to a compressor 23, thence to a direct-fired heat exchanger 29, and finally to the dryer 22. I compress the air to a pressure of about 50 to 60 p.s.i.g., which is about 20 to 30 pounds higher ice than the pressure in the tuyere zone of a blast furnace. Pressure in the closed hopper 18 or 18a balances pressure in the dryer, while the screw conveyors 23 and 2311 have conventional locks to prevent loss of pressure through the open hopper. I heat the air to a temperature of about 1400 to 1900 F. to maintain a temperature of 220 to 350 F. in the dryer. I control this temperature with a temperature sensing element 30 connected to the dryer and a flowproportioning valve 31 in the fuel line to the heat exchanger operatively connected to said sensing element. Alternatively I can adjust valve 31 manually in accordance with the temperature readings. As another alternative, I can use direct means for preheating the air, such as by burning fuel in the air stream, or I can use other compatible gas than air.

Dryer 22 has a constriction plate 32 which supports a bed of coal particles B. Air from line 26 enters the bottom of the dryer below the constriction plate and passes upwardly therethrough to fluidize the bed. The pressure drop between the dryer and the tuyere zone of the furnace continuously forces air and entrained coal particles from the bed through a series of downcomers 33 which lead to the respective tuyeres of the blast furnace (not shown). I position these downcomers symmetrically around the dryer to ensure that each receives approximately an equal quantity of coal. All the air withdrawn from the main passes through the dryer and ultimately reaches the blast furnace, except for minor leakage. While I prefer that each downcomer lead to a single tuyere, alternatively each can feed coal to two or more tuyeres, or the same dryer can be used for more than one blast furnace. I control the total quantity of coal feeding from the dryer by regulating the speed of the

screw conveyors

23 and 23a and by regulating the compressor 28.

As a specific example to demonstrate how my invention may be practiced, I operated a blast furnace having a 23- foot hearth diameter with a total blast of 65,000 s.c.f./ minute. I bypassed approximately 5 percent of this blast (3,250 s.c.f./min.) from the cold blast main and heated the remainder to the usual temperature of about 1650" F. I compressed the bypassed air from 35 p.s.i.g. to 50 p.s.i.g. and heated it to 1900 F. in a direct-fired heat exchanger. I fed coal to the dryer at a rate of 20 tons an hour, while maintaining a fluidization velocity of 1.5 feet per second and a bed temperature of 300 F. From the bed of the dryer, I fed 20 tons of coal an hour and 3250 sci/minute of air through sixteen downcomers connected to a like number of tuyeres of a furnace. The coal flowed freely and distributed itself uniformly to the diflferent tuyeres where it oxidized, as known in the art. I was able to replace 1.15 pounds of coke for each pound of coal injected at the tuyeres.

From the foregoing description it is seen that my invention affords a simple effective method of handling and sizing pulverized coal injected into the tuyeres of a blast furnace. I dry and inject the coal as part of the blast all in one continuous operation. The individual items which form my apparatus are conventional per se; hence I have not shown nor described them in detail.

While I have shown and described only a single embodiment of my invention, it is apparent that modifications may arise. Therefore, I do not wish to be limited to the disclosure set forth but only by the scope of the appended claims.

I claim:

1. A method of handling pulverized fuel for injection through the tuyeres of a blast furnace comprising continuously feeding fuel particles from one of two alternative sources to a bed, fiuidizing the particles in said bed with heated air maintained at a higher pressure than the pressure at the tuyere zone of the furnace, thereby drying the particles, pressurizing the source from which particles are feeding to the bed to balance the bed pressure, entraining the fuel particles in the fluidizing air, continuously forcing substantially all the fluidizing air and particles en-' trained therein from the bed in approximately equal portions, and directing said portions individually from the bed to the respective tuyeres.

2. A method of handling pulverized fuel for injection through the tuyeres of a blast furnace comprising continuously feeding fuel particles from one of two alternative sources to a bed, fluidizing the particles in said he with air heated to a temperature of about 1400 to 1900 F. and at a pressure about 20 to 30 p.s.i. higher than the pressure at the tuyere zone of the furnace, thereby maintaining a temperature of about 220 to 350 F. in said bed and drying the particles, pressurizing the source from which particles are feeding to balance the bed pressure, entraining the fuel particles in the fiuidizing air, continuously forcing substantially all the fluidizing air and particles entrained therein from the bed in approximately equal portions, and directing said portions individually from the bed to the respective tuyeres.

References Cited by the Examiner UNITED STATES PATENTS 719,320 1/03 Foster 75-42 1,535,174 4/25 McGregor 75--42 1,541,731 6/25 Muguet 75-42 2,420,398 5/47 Kenney 75-42 2,719,083 9/55 Pomykala 75-42 2,841,102 7/58 Mashall 110-106 2,849,968 9/58 Krug 110-106 2,939,411 6/60 Priestley 110-28 3,056,212 10/62 Jamison 34-10 DAVID L. RECK, Primary Examiner.

RAY K. WINDHAM, WINSTON A. DOUGLAS,

Examiners.

Claims

1. A METHOD OF HANDLING PULVERIZED FUEL FOR INJECTION THROUGH THE TUYERES OF A BLAST FURNACE COMPRISING CONTINUOUSLY FEEDING FUEL PARTICLES FROM ONE OF TWO ALTERNATIVE SOURCES TO A BED, FLUIDIZING THE PARTICLES IN SAID BED WITH HEATED AIR MAINTAINED AT A HIGHER PRESSURE THAN THE PRESSURE AT THE TUYERE ZONE OF THE FURNACE, THEREBY DRYING THE PARTICLES, PRESSURIZING THE SOURCE FROM WHICH PARTICLES ARE FEEDING TO THE BED TO BALANCE THE BED PRESSURE, ENTRAINING THE FUEL PARTICLES IN THE FLUIDIZING AIR, CONTINUOUSLY FORCING SUBSTANTIALLY ALL THE FLUIDIZING AIR AND PARTICLES ENTRAINED THEREIN FROM THE BED IN APPROXIMATELY EQUAL PORTIONS, AND DIRECTING SAID PORTIONS INDIVIDUALLY FROM THE BED TO THE RESPECTIVE TUYERES.