US 3250016 A
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May 10, 1956 .1. c. AGARWAL METHOD AND APPARATUS FOR PREPARING POWDERED COAL FOR INJECTION INTO A BLAST FURNACE Fild NOV. 8, 1962 Attorney United States .Patent 'O This invention relates to an improved method and u apparatus for preparing powdered coal for injection into a blast furnace.
l The most common practice in operating a blast furnac is to supply all the necessary fuel in the form of coke charged with the burden. However, it is known that part of the coke usually required can be replaced with fuel injected with the blast at the tuyeres. This fuel can be either solid (e.g., powdered coal), liquid or gaseous, and its combustion supplies at least part of the heat required to operate the furnace. Coke charged with the burden has other functions, such as furnishing carbon for reducin-g ore and physically supporting the burden. Fuel injected at the tuyeres cannot serve such purposes, but any replacement of the more costly coke with cheaper fuels leads to worthwhile savings. When powdered coal is' used as the injected fuel, it must irstlbe carefully prepared by drying and sizing.
An object of the present invention is to provide an improved method and apparatus for drying and sizing powdered coal to enable it to be injected into the tuyeres of a blast furnace as replacement for coke.
apparatus for preparing powdered coal in which sensible heat in the top gas from a blast furnace is utilized for drying the coal in a fluidized bed.
A further object is to provide a method and apparatus which offer the foregoing advantages, and in which the gas used for drying the coal subsequently is cleaned and u-sed for injecting the coal into the furnace.
In the drawing:
The single figure is a schematic flowsheet of my method and apparatus.
My apparatus includes a conventional fluidized bed dryer 10 whi-ch contains a perforate partition 12 in its lower portion for supporting a bed B ofrninus 1/2 inch or smaller coal particles. A screw conveyor 13 continuously feeds coal fines to the dryer from a storage bin 14. In accordance with my invention, I introduce -top gas from a blast furnace (not shown) via a line 15 to the bottom of the dryer, where the gas acts to fluidize the bed. This gas commonly is at a temperature within the range of about 350 to 600 F. and a pressure of about 2 to 30 p.s.i.g. Sensible heat in the gas serves to maintain coal in the bed at a temperature of about 250 to 350- F. and thus dri-ves off moisture, leaving the coal with a maximum moisture content of about 4 percent. y I preferably control the temperature automatically with a temperature-sensing element 16 in the dryer, a controller 17 connected to said element and an adju-stable valve 18 which is connected to line 15 and operated by said controller, all which per se are of conventional construction. Valve 18 routes excess top gas through a bypass 19. Alternatively, I can measure the bed temperature and adjust valve 18 manually.
Dried coal discharges from bed B via a line 20 which leadsto a fractionating screen 21. Preferably line 20 is equipped with an automatic mechanism 22 for controlling the bed level in the dryer, as known in the art. Screen 21 has openings of a size to pass particles suit-able for injection into the furnace, commonly minus 1A; inch or minus 1/16 inch. Undersize particles from the screen go to a storage vessel 23. Oversize particles from the screen go to a pulverizer 24 and thence back to the screen in a closed circuit arrangement. Contaminated and moistureladen olf-gas discharges from the top of the dryer via a line 25 which leads to a dust collector 26, for example a cyclone. A line 27 carries dust recovered from the gas in the dust collector to screen 21, where it joins the dried coal from line 20.
Gas from the dust collector 26 and from the bypass 19 goes to a conventional venturi scrubber 28 to which Water is introduced via a line 29. The scrubber is connected to a conventional entrainment separator 30. Waste slurry from the separator goes to a thickener (not shown), while the gas goes to a cooler 31 where it is cooled to a temperature of about F. A line 32, which contains a conventional automatic flow controller 33, carries a portion of the gas from the cooler to a compressor V34, where it is compressed -to approximately p.s.-i.g. A line 35 carries the remainder of the gas from the cooler to blast furnace stoves (not shown) or other equipment where the gas is consumed in the usual way. A line 36, which contains a conventional automatic pressure regulator 37, carries gas from the compressor 34 to a conventional gas dryer 38, where it is dried to a dew point of about 0 to v 20 F. VA line 39 carries gas from the dryer 38 to a gas holder 40. A line 41 carries gas from the holder 40 to the coal storage vessel 23. Gas in the last-named line picks up dried powdered coal from the vessel and transports it to the blast furnace tuyeres (not shown) where it is injected into the furnace. In this manner the hydrogen and carbon monoxide remaining in the top gas likewise `are utilized effectively in the fu-rnace. I use approximately 1/2 to 3 cu. ft. of gas for injecting each pound of coal.
My invention may be modified by heating the compressed and dried gas from the dryer 38 to a temperature up to about 800 F. to eliminate excessiveheat load on the blast furnace. In addition, the compressed top gas can be purified by any conventional method to eliminate carbon dioxide. 'The removal of carbon dioxide improves the efficiency of the blast furnace, because carbon is required to reduce the carbon dioxide to carbon monoxide. The drawing schematically indicates lconventional devices 42 and 43 for preheating the gas and removing carbon dioxide. Also, conventionally compressed and dried air instead of blast-furnace top gas may be used to convey the coal particles to the blast furnace.
A specific example of the practice of my invention is as follows:
I operated a blast furnace having a 23-ft. hearth vdiameter with a hot blast at 65,000 cu. ft./ min` having a ternperature of approximately 1650 F. vI produced approximately 1600 tons/day of hot metal with a coke rate of approximately 1260 lb./THM. During this operation, I obtained approximately 90,000 cu. ft./min. of top gas at a pressure of approximately 9 p.s.i.g. I used minus 1/z-in. Maple Creek coal for injection, and dried this coal from a 10 percent to a 3 percent moisture content at a rate of 10 tons/ hr. in a fluidized-bed dryer. I maintained the drying atmosphere at 250 F. by regulating the amount of top gas introduced to the dryer. The top gas leaving the blast furnace was at a temperature of 410 F. I controlled the gas flow to the dryer so that approximately 17,500 cu. ft./ min. of top gas passed through it. The remainder of the top gas bypassed the dryer and combined with the moisture-ladened top gas leaving the cyclone. I took approximately 400 cu. ft./min. of this top gas, compressed it to approximately 100 p.s.i.g., and then dried it in a conventional silica-gel dryer to a dew point of 10 F. I used this gas to inject 9.28 ton's/ hr. of dried and pulverized coal into the blast furnace.
The advantages of my method are apparent from the above description of the operation. By using the blastfurnace top gas as the drying medium, the need for an external heat source is eliminated. Also, additional equipment is not required to clean the gas leaving the dryer, since it may be combined With the top gas bypassing the dryer and thus processed by the equipment conventional to blast-furnace installations. The explosion hazard usually associated with storing dried and pulverized coal is eliminated by employing an atmosphere of top gas in the coal-storage vessels. In addition, the gas used for injection is compatible with the blast-furnace process.
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.
1. A method of preparing coal for injection into the tuyeres of a blast furnace comprising feeding coal ines to a fluidized bed dryer, introducing top gas from a blast furnace to the dryer to iiuidize the coal fines, utilizingy sensible heat in this gas to drive moisture from the coal, discharging dried coal from the dryer, screen-sizing the dried coal to separate out undersize coal particles having a maximum size of about ls-in. and suitable for injection, pulverizing the oversize coal particles for further screensizing, cleaning, compressing and drying the oit-gas from the dryer, and utilizing this olf-gas for injecting the undersize particles.
2. A method of preparing coal for injection into the tuyeres of a blast furnace comprising feeding coal iines to a iluidized bed dryer, introducing top gas from a blast furnace to the dryer to lluidize the coal lines, said gas being at a temperature of about 350 to 600 F. and a pressure of about 2 to 30 p.s'.i.g., utilizing sensible heat in this gas to drive moisture from the coal and thus lower its moisture content to a maximum of about 4 percent, discharging dried coal from the dryer, screen-sizing the dried coal to separate out coal particles having a maximum size of about 1s-in. and suitable for injection, pulverizing thel oversize coal particles, and again screen-sizing the pulverized coal in a closed circuit arrangement.
3. A method as defined in claim 2 in which off-gas from the dryer is cleaned, compressed, dried and utilized in part for injecting the undersize coal particles.
4. A method of preparing and injecting coal into the tuyeres of a blast furnace comprising feeding coal nes to a tluidized bed dryer, introducing a portion of the top gas from a blast furnace to the dryer to rluidize the coal ines, said gas being at a temperature of about 350 to 600 F. and a pressure of about 2 to 30 p.s.i.g., utilizing sensible heat in this gas to drive moisture from the coal and thus lower its moisture content to a maximum of about 4 percent, discharging dried coal and off-gas from the dryer, screen-sizing the dried coal to separate out coal particles having a maximum size of about 1s-in. and suitable for injection, pulverizing the oversize coal particles, again screen-sizing the pulverized coal in a closed circuit arrangement, collecting dust from said off-gas, combining another portion of the top gas with said off-gas, cleaning and cooling the resulting combined gas, compressing and drying a portion of the cleaned and cooled gas, and utilizing the last-named portion for injecting the dried and sized coal particles into the tuyeres.
5. A method as dened in claim 4 in which the lastnamed portion of the cleaned and cooled gas is preheated to a maximum temperature of about 800 F.
6. A method as defined in claim 4 in which the lastnamed portion of the cleaned and cooled gas is puried to eliminate carbon dioxide.
7. An apparatus for preparing coal for injection into the tuyeres of a blast furnace comprising a liuidized bed dryer, means operatively connected With said dryer for feeding coal fines thereto, means operatively connected with said dryer for introducing blast furnace top gas thereto to fluidize the coal lines and supply sensible heat for driving ofr moisture, a fractionating screen, means for transferring dried coal fines from said dryer to said screen, means for collecting undersize particles from said screen suitable for injection, a pulverizer, means for transferring oversize particles from said screen to said pulverizer and pulverized particles back to said screen in a closed circuit arrangement, means operatively connected with said dryer for cleaning, compressing and drying off-gas therefrom, and means for utilizing this off-gas for injecting undersize coalparticles into the blast furnace tuyeres.
References Cited by the Examiner UNITED STATES PATENTS 1,628,609 5/ 1927 Newhouse 110--106 2,103,453 1 2/ 1937 Graemiger 110-28 2,560,807 7/1951 Lobo 241-24 2,841,125 7/1958 Falla 110-106 X 2,939,411 6/ 1960 Priestley 11028 3,192,068 6/1965 Brandt 34-10 X FOREIGN PATENTS 865,221 2/ 1941 France. 369,330 3/ 1932 Great Britain.
ALDEN D. STEWART, Primary Examiner.
NOMAN YUDKOFF, WILLIAM F. ODEA,
W. C. EVERETT, D. A. TAMBURRO,