US 3134579 A
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Description (OCR text may contain errors)
y 25, 1964 c. H. BOOTH, sR
' METHOD OF TREATING FLUE DUST Filed Aug. 22, 1962 III IN VEN TOR.
United States Patent Filed Aug. 22, 1962, Ser. No. 218,733 4 Claims. (31. 2s9 149 This invention relates to a method of coating ore particles, flue dust, precipitator dust, fly ash, dolomite, limestone and like materials with foamed bituminous material or its equivalent to render such materials useful for handling as charges for blast furnaces and the like.
The present invention is particularly designed to bond flue dust of magnetic or non-magnetic materials into lumps which may be charged into a furnace without the need for sintering or pelletizing which is expensive.
The present invention makes use of bituminous foam such as has been used for preparing road materials from aggregates such as the well-known blacktopping materials employed in highway construction, the bitumen being supplied to a mixing chamber in which the dust is agitated by mixing paddles and steam is mixed with the bitumen to produce the foam for bonding the dust.
The present invention deals with the proportioning or metering of the dust in certain proportions to the bonding bitumen material with regulated pressures for the steam and bitumen and the maintenance of predetermined temperatures during the mixing operation.
The invention will become more apparent from a consideration of the accompanying drawing constituting a part hereof in which like reference characters designate like parts and in which:
FIGURE 1 is a view in perspective diagrammatically illustrating apparatus for coating powderous materials such as flue dust with a steamed bitumen to bond the same in accordance with the present invention; and
FIGURE 2 is a vertical cross-sectional view of a nozzle for supplying the steamed bitumen to the mixing chamber.
In the drawing, the numeral 1 designates the housing of a pug mill in which are mounted shafts 2 and 3 with mixing paddles 4, the shafts being driven by sprocket chain 5 connected to a suitable source of power such as an electric motor. The housing 1 is provided with a sliding door 6 which allows the material to be transferred from the mill toa mixing chamber 7 where the bitumen coated material is more thoroughly mixed by rods 8 mounted on a shaft 9 driven by sprocket chain 10 connected to a source of power and the finished material is finally dumped through an opening controlled by a sliding door 11. A plurality of mixing nozzles 12 are provided in the upper part of the pug mill housing 1, these nozzles being connected to steam lines 13 and lines 14 leading to a source of bitumen such as a supply tank 15. The steam lines 13 are connected to a boiler 16. The steam pressure is controlled by a pressure regulator 17 and a gauge 18 is provided in the steam line 13, together with a Ivalve 19 for shutting off the steam supply to the pug mill.
The bitumen is pumped into the line 14 by a pump 20 operated by a motor 21 and the pressure is controlled by pressure regulator 22, a gauge 23 indicating the pressure in the line 14. A valve 24 controls the volume flow. The pug mill 1 is provided with a cover 25 which has an automatic feed mechanism 26 mounted thereon. A screw feed designated by the line 27 supplies the flue dust from a hopper 28 below a flue dust storage bin 29 to regulate the volume feeding to the pug mill to obtain a proportion of 97% dust to 3% bitumen as regulated by the valve 24. The pressure of the bitumen is regulated at 20 pounds and the bitumen is heated in the tank to a temperature of substantially 290 F. The steam pressure is 50 pounds and an increase of 1% bitumen is required for each v10 pound drop of steam pressure. As shown in FIGURE 2, the nozzle 12 has an opening 30 and the steam nozzle 13 is spaced from the opening 30 a distance to entrain the bitumen as the steam is emitted from the opening 31 so that the mixture of bitumen and steam produces a foam which is fed from a plurality of the nozzles 12 into the mixing chamber of the pug mill 1.
The pug mill chamber is heated by means of electrical heating coils or steam lines 32 to maintain a constant temperature of F. The operation of the abovedescribed apparatus and the steps of the process of bonding flue dust into solid particles or balls is briefly as follows:
The flue dust that has been collected in bins 29 is fed by the screw feed 27 from the hopper 28 into the automatic feed box 26 from which it is fed into the mixing chamber of the pug mill in regulated quantities and the heated bitumen and the steam is fed in regulated quantities to the nozzles 12 to maintain a ratio of 97% dust to 3% bitumen. The steam at 50 pounds pressure and the bitumen pressure at a temperature of 290 mix to create a foam that is sprayed into the chamber of the pug mill to cover the particles of dust. By maintaining the material at 160 F., the pug mill is operated for one minute at a speed of 60 rpm. or until the flue dust has become a flowable mass. It is then dropped into the rod mill chamber 7 where it is mixed for approximately two minutes at a speed of 30 r.p.m. The rod mill 7 is not heated and the slow mixing action and drop in temperature and increase in the mixing time changes the flowable mass to a semi-solid mass which is formed into balls or lumps the size of which is controlled by the spacing of the rods 8 and the speed of rotation of the shaft 9.
The above-described process converts dust to semi-solid or solid particles which can be charged into blast furnaces without any dust passing to the stack as is the case where dust has been pelletized or used in sintering processes. Also, instead of making furnace charges, fly ash and other materials may be reduced to a semi-solid state by this process and used for roadways, parking areas, driveways, tennis courts and the like. It is evident that the material can be used on any fine materials of a magnetic or nonmagnetic material for various uses.
Although one embodiment of the invention has been herein illustrated and described, it will be evident to those skilled in the art that various modifications may be made in the details of construction without departing from the principles herein set forth.
1. In the method of converting flue dust and the like to a semi-solid state by the use of a pug mill having spaced paddles which comprises the steps of;
(a) charging a pre-determined quantity of flue dust into the pug mill,
(b) spraying a foam consisting of steam and bitumen into the flue dust while the dust is subjected to a mixing action to cover each particle of dust,
(c) continuing the mixing action of the material in the presence of heat until the mixture has become a flowable mass,
(d) lowering the temperature of the mass and continuing to mix the same to form a semi-solid substance in the shape of compact masses, and,
(e) and controlling the size of the compact masses by v regulating the speed of the mixing action.
2. The method set forth in claim 1 in which the mix- 1 ture is in the proportion of approximately 97% flue dust and 3% bitumen and the steam is at approximately 50 Patented May 26, 1964 pounds pressure and the temperature at which the initial References Cited in the file of this patent mixing action takes place is approximately 160.
3. The method as set forth in claim 2 in which the UNITED STATES PATENTS percentage of bitumen used is increased by 1% with each 1,531723 Alsdoff 31, 1925 drop of 10 pounds of steam pressure. 5 2,572,068 Sommer 9 4. The method set forth in claim 1 in which the charge of the mixture from a fiowable mass to a semi-solid com- FOREIGN PATENTS pact mass takes place in a second mixing chamber that 227,733 Australia Apr. 20, 1960 is unheated and the mass is mixed at relatively slow speed. 818,3 84 Great Britain Aug. 19, 1959