US2854136A - Method and apparatus for separating solid materials of different specific gravities - Google Patents

Description

Sept. 30, 1958 P. H. GILLIE ETAL METHOD AND APPARATUS FOR SEPARATING SOLID MATERIALS OF DIFFERENT SPECIFIC GRAVITIES 2 Sheets-Sheet 1 Filed Aug. 22, 1955 STIRRER CLEAN COAL DISCHARGE RAW FEED INTERMEDIATE REFUSE INTERMEDIATE REFUSE AIR PIPE CHAMBER REFUSE INVENTORS PERCY H. GILLIE REFUSE WILLIAM NOONE ATTORNEY Sept. 30, 1958 P. H. GILLIE ET AL 2,854,136

METHOD AND APPARATUS FOR SEPARATING SOLID MATERIALS OF DIFFERENT SPECIFIC GRAVITIES Filed Aug. 22, 1955 2 Sheets-Sheet 2 INTERMEDIATE REFUSE LRAW FEED WATER AND SAND INLET CLEAN COAL DI5CHARGE INTERMEDIATE REFUSE PERFORATED l5 PLATE CLEAN COAL DISCHARGE PERFORATED PLATE INTERMEDIATE REFUSE WATER AIR P PE INTERMEDIATE REFUSE WATER 5' REFUSE REFUSE GATE CHAMBER I 5 I REFUSE I GATE INVENTORS PERCY H.GILI IE WILLIAM H. NOONE Mm M ATT RNEY United States Patent F METHOD AND APPARATUS FOR SEPARATING SOLID MATERIALS OF DIFFERENT SPECIFIC GRAVITIES Application August 22, 1955, Serial No. 529,721

2 Claims. (Cl. 209-158) This invention relates to the separation of materials of different specific gravities and more particularly refers to new and improved methods and apparatus for effecting the separation of coal from refuse in an artificial dense medium of sand suspended in water.

- 'An object of the present invention is to provide an improved process and apparatus for effecting more perfect separation of clean coal from raw coal in a water-sand medium. v Another object is to provide an efiicient economical process and apparatus for classifying a mixture of raw coal in a sand-water medium to produce a clean coal with a lower ash content at a high rate of throughput.

A further object of the present invention is to provide apparatus for removing impurities from coal which is simple and economical in construction and flexible in operation.

A still further object of the present invention is to provide an improved method and apparatus simple in design and without increase in cost of power for effecting cyclic agitation of the sand-water suspension containing raw coal undergoing classification.

Other objects and advantages of the present invention will be apparent from the following description and accompanying drawing.

in accordance with the present invention improved separation of solid materials of different specific gravities, such as raw coal, to effect finer separation of the desired solid material (clean coal of lower ash content) from the heavier impurities in the materials of different specific gravities may be accomplished in a process involving maintaining a dense medium of comminuted solid matter, such as sand, of greater specific gravity than water and substantially insoluble therein, and constituting a fluid mass having a specific gravity greater than that of the lightest of the materials (clean coal) in the mixture of materials to be separated, maintaining the dense medium in a mildly agitated condition by the introduction of water, mechanically stirring to effect rotation of the dense medium, introducing the mixture of solid materials of different specific gravities into the top of the dense medium thereby causing the mixture of materials to flow in the same direction with the rotating dense medium and to stratify in the order of their relative specific gravities with the lightest materials (clean coal) floating on top of the dense medium, overflowing the floating solid material at a point remote from and downstream from the point of introduction of the mixture of different specific gravities, discharging materials of heavier specific gravities from the bottom of the dense medium, restraining intermediate specific gravity materials suspended beneath the lighter material (clean coal) which are to be floated off the top of the dense medium from being carried upward by a rising current with a 2,854,136 Patented Sept. 30, 1958 floating lighter material and thereby contaminating the lighter material by interposing a substantially horizontal perforated plate disposed upstream and a short distance beneath the point of overflow of the light material, said perforated plate having holes of a sufl'icient number and size to permit a free flow of sand and water therethrough, but small enough in size to prevent the passage of intermediate specific gravity material therethrough, and discharging said intermediate specific gravity materials from a point beneath said perforated plate.

Apparatus for separating solid materials of different specific gravities comprising in combination a tank, preferably of conical shape, containing a dense medium of comminuted solids insoluble in water and suspended in water to provide a fluid mass having a specific gravity greater than the lighter of the mixture of material of different specific gravities, an inlet for the introduction of comminuted. solids and water into the top of the tank for maintaining the Volume of dense medium substantially constant in the tank, water inlets into the tank below the surface of the dense medium therein for agitating the dense medium, a stirrer adapted to maintain rotational motion of the dense medium in the tank, an inlet near the top of the tank for the introduction of solid materials of different specific gravities to be subjected to classification in a tank, a discharge weir for the overflow of lighter specific gravity material from the top of the dense medium disposed at a point downstream and remote from the introduction of materials of different specific gravities, a substantially horizontal perforated plate disposed a short distance beneath and upstream of the discharge weir, said plate having holes of sufficient number and size to permit the free flow therethrough of water and comminuted solids, but of a size small enough to restrain'the passage therethrough of materials of intermediate specific gravities slightly lower than that of the lighter material floating over the discharge weir, a refuse chamber beneath the tank for collection of the heavy specific gravity material sinking in the dense medium, a gate interposed between the bottom of the tank and the top of the refuse chamber adapted to be opened and closed for the control of the discharge of heavy specific gravity material into the refuse chamber, and a gate at the bottom of the refuse chamber adapted to be opened and closed to control the discharge of heavy specific gravity material from the refuse chamber.

In the operation of classifying apparatus as illustrated by the Chance cone there is provided a refuse chamber at the bottom of the cone with a gate interposed between the bottom of the cone and the top of the refuse chamber and a gate at the bottom of the chamber. These gates are operated alternately and intermittently in a cycle of about 30 seconds duration. Stated in other words, the top gate is quickly opened to permit discharge of refuse from the bottom of the cone into the refuse chamber and then quickly closed. Thereafter the bottom gate is quickly opened to discharge refuse from the refuse chamber and then quickly closed to complete the cycle, which cycle is continuously repeated. We have found a means of modifying the equipment with insignificant cost in construction to effect automatic intermittent agitation of the cone contents without any increase in power or labor costs. We accomplished this effect by attaching a breather pipe to the refuse chamber with the other end of the breather pipe open to the atmosphere and with a check valve interposed in the breather pipe which permits the flow only into the breather pipe and prevents any flow of material out of the breather pipe. In the operation of the gates of the I refuse chamber, the bottom gate is opened and closed so rapidly that a partial vacuum is created in the refuse chamber. However, with the breather pipe attached to the refuse chamber air from the atmosphere enters the refuse chamber to fill the void left by the discharge of the refuse from the refuse chamber. When the top refuse gate opens, the inrush of the refuse and water from the cone into the refuse chamber is at such a rapid rate that the air in the refuse chamber is compressed and forced to travel up through the cone as an air bubble. This bubble of air produces a beneficial action by destroying the blanket of intermediate gravity material which is in the lower part of the cone and then escapesto the atmosphere from the open top of the cone. The use of air in the manner described as contrasted with the use of a liquid has the added advantage of not altering the concentration and volume of the cone contents.

Figure 1 is a perspective view in partial section illustrating one method of-carrying out the present invention. Figure 2 is an elevation in section of the apparatus in Figure 1. Figure 3 is a plan view taken along line 33 of Figure 2.

Referring to Figure 1, an open vessel for effecting separation of impurities from coal, designated generally by numeral v1, consists of a conical portion 2 having a top diameter of 13'6" witha 4' cylindrical top 3. Extending down from the bottom of conical section 2 may be provided, if desired, a suitable classifying column 4 which may be merely a hollow cylindrical conduit. Beneath classifying column 4 may be provided, if desired,

found satisfactory for separating clean coal from its impurities. Materially decreasing the density of the sandwater suspension tends to cause some of the clean coal to be pulled down with the refuse thereby causing loss of valuble product. Materially increasing the density of the sand-water mixture will result in flotation of intermediate refuse out with the clean coal.

The laminar plate 15 is installed so that it will interpose itself between the lower specific gravity material, clean coal, which is being carried around the cone at the top of the dense medium of sand suspended in water and the intermediate gravity material which is being carried upward by the rising current toward overflow weir 13. Perforated plate 15 is constructed as a circular segment and so installed that its beginning point is approximately counterclockwise from the sand and water inlet 8. The other end of plate 15 extends to about the center line of discharge weir 13. Plate 15 is approximately in thickness with 1":perforations 16 on 1%" center, which perforations permit the free flow of water and sand therethrough but restrain the intermediate gravity material which is a size greater than the diameter of thepperforations. If desired a small side plate 17 (Figure 3) may be attached to project downwardly from perforated plate 15 extending from the intersection of the plate'edge and center line of the cone to the discharge weir. Plate-15 maybe suspended and supported by any suitable means refuse chamber 5 with air operated refuse gate 6 interposed between column 4 and chamber 5 to regulate the discharge of heavy refuse from the cone. At the bottom of refuse chamber 5 is refuse gate 7 which controls the discharge of the refuse from chamber 5. In operation sand and water are pumped into'the top of cone 1 through line 8 at the approximate rate of 1500 gallons per minute with the sand being 20% by volume. This mixture is agitated by stirrer 9 which rotates at approximately 9 R. P. M. in a counterclockwise direction ,indicated by the arrow in Figure 3. The purpose of'this rotation is to keep the sand in suspension and also provide a means of propelling the raw coal around the vessel, the raw coal being sent in at a chute.11, approximately 180 from the sand and water inlet. Additional" water .is introduced into the sand-water suspension through a plurality of water inlets 12 disposed at spaced points intermediate to the top and'bottorn of the cone to aid in maintaining the sand and water mixture in Vessel 1 in a floating condition along with the agitation provided by stirrer 9;

The raw coal sent in at chute 11 flows tangentially in a counterclockwise direction around the cone, and as it flows around the cone, the artificial dense medium created by the sand suspension in the water and the rising currents from the water introduced through line 12 creates Y a specific gravity condition whereby the heavier refuse particles sink to the bottom of the cone and the clean coal particles are floated around the cone and flowout of the cone over the discharge lip.13 and thence into conventional screening apparatus 14 for the separation .of sand and water and gradation of the clean coal into different sizes. The overflow over lip 13 is at the approximate rate of 4,000 gallons per minute, composed of the clean coal particles, sand and water,-the clean coal amounting to approximately 168 tons per hour.

The rate of discharge of the refuse through the mechanical inter-lock gates 6 and 7 is controlled by automatic timing devices and operates on approximately 30 second cycles, this discharge being at the rate of about 92 tons per hour. The density of the sand-water medium may be regulated to some extent by the proportion of sand relative to water introduced into vessel 1. In general a density of approximately 1.35 specific gravity has been such as -threaded rods, not shown in the. drawing, which are arranged to allow adjustment of the plate vertically in the-cylindrical section of the cone. In practice we have vobtained good operation with the plate 15 a distance of 18' from the top of section 3 ;and about 6". below'weir 13. Laminar plate- 15 by itself will not produce the im- 7 proved results in separating the refuse from the coalunl'ess used in conjunction with an ejector tube 18 for the discharge of the u intermediate gravity material. Ejector tubedS is idisposedapproximately 5' from the top [of section 3 and approximately 45 upstream from thecenter of discharge weir 13. 'As the heavier material passes overflow lip 13 it begins to descend due to the absence of the rising currents. Removal of this heavier material is facilitated by ejector tube 19 disposed approximately 7 below the top of section 3 and approximately v4S" downstream from the center line of discharge weir- 13. Although nota preferredmethod of construction,;plate '15 may be tilted at a small angle from thehoriiontal without too great impairment of the operation.

Refuse accumulating in the bottom-of column 4 is cyclicly discharged into refuse chamber 5 by opening and closing of refuse gate 6. Alternate and intermittent opening of refuse gate 7 discharges the refuse from chamber 5 onto refuse screen 21 which separates the sand and water from the refuse. The discharge of refuse from chamber 5 i by opening gate 7 creates a void in chamber 5 causing air from the atmosphere to flow down through breather pipe 22 and check valve 23 into chamber 5. Check valve;23 prevents reverse flow in pipe 22. The down flow of refuse and water into chamber 5 when gate 6 is opened forces the trapped air in chamber 5 upwardly through vessel 1 thereby destroying the blanket of intermediate gravity material in the lower part of cone 2. In this mannerautomatic intermittent agitation of the cone contents is accomplished by the simple addition of a breather pipe and check valve and without additional power and operating,

diate refuse discharge conduit 19 may be provided at a point below conduit 18. Additional water is introduced into vessel 1 through line 12. Air pipe 22 is provided for the entrance of air into chamber 5.

The following comparative example illustrates the advantages of the present invention. For purposes of comparison a Harewood Colliery raw coal was subjected to flotation in a sand-water medium in apparatus substantially as illustrated in Figure 1, except that the apparatus was not provided with perforated plate 15 and with breather pipe 22. Even with a low feed rate of 220 tons per hour raw coal the ash content of the clean coal was 3.83%.

In a similar operation with raw coal from the same source, but with the apparatus provided with perforated plate 15, breather pipe 22 and check valve 23, we found we could increase the feed rate to 260 tons per hour raw coal and obtain a clean coal containing 2.87% ash which is appreciably less than that obtained when operating in the conventional manner.

Analyses of the clean coals obtained from the conventional operation and the operation in accordance with the present invention as carried out in the comparative tests are shown in Table I and Table 11 below.

TABLE I Analysis of clean coal in operation without perforated plate and breather pipe Separation 1.39 sp. gr.

TABLE II Analysis of clean coal in operation with perforated plate and breather pipe Sp. Gr. Percent Percent Wgt. Ash

Total 100.0 2. 87

Separation 1.32 sp. gr.

As will be noted from Table I the clean coal has an ash content of 3.85% and a specific gravity of 1.39 which is higher than the specific gravity of the sand-water medium which has a specific gravity of 1.35. Also, it will be noted that almost 7% of the clean coal had a specific gravity higher than the 1.35, and also this fraction had a high ash content ranging from 13.40 to 23.91 thereby demonstrating that this material of intermediate refuse and ash content was carried over with the clean coal.

In Table II it will be noted that the clean coal had a specific gravity of 1.32 which is lower than the 1.35 specific gravity of the sand-water medium. Also, only 2.5% of the coal had a specific gravity of above 1.35 and that this small fraction had an ash content ranging from 11.77 to 22.11. The operation in accordance with the present invention reduced the ash content of the clean coal by approximately 25% and, furthermore, operated at an increased capacity of 40 tons per hour.

an inlet for the introduction of comminuted solids and I water into the top of the tank for maintaining the volume of dense medium substantially constant in the tank, water-inlets into the tank below the surface of the dense medium therein for agitating the dense medium, a stirrer adapted to maintain rotational motion of the dense medium in the tank, an inlet near the top of the tank for the introduction of solid materials of different specific gravities to be subjected to classification in the tank, a discharge weir for the overflow of lighter specific gravity material from the top of the dense medium disposed at a point downstream and remote from the introduction of materials of different specific gravities, a substantially horizontal perforated plate disposed a short distance beneath and upstream of the discharge weir, said plate having holes of sufficient number and size to permit the free flow therethrough of Water and comminuted solids, but of a size small enough to restrain the passage therethrough of materials of intermediate specific gravities slightly lower than that of the lighter material floating over the discharge weir, an outlet beneath said plate for the discharge of intermediate specific gravity materials, a refuse chamber beneath the tank for collection of the heavy specific gravity material sinking in the dense medium, a gate interposed between the bottom of the tank and the top of the refuse chamber adapted to be intermittently opened and closed for the control of the discharge of heavy specific gravity material into the refuse chamber, a gate at the bottom of the refuse chamber adapted to be alternately and intermittently opened and closed to discharge the heavy specific gravity material from the refuse chamber, and a breather pipe having a check valve connected to the refuse chamber and open to the atmosphere for the passage of air into the refuse chamber during discharge of refuse from the bottom of the refuse chamber, said check valve being constructed to permit the flow of air from the atmosphere through the breather pipe into the refuse chamber and to bar the fiow of materials from the refuse chamber out through the breather pipe.

2. Apparatus for separating solid materials of different specific gravities comprising in combination a tank for containing a dense medium of comminuted solids insoluble in water and suspended in water to provide a fluid mass having a specific gravity greater than the lighter of the mixture of materials of different specific gravities, an inlet for the introduction of comminuted solids and water into the top of the tank for maintaining the volume of dense medium substantially constant in the tank, Water-inlets into the tank below the surface of the dense medium therein for agitating the dense medium, a stirrer adapted to maintain rotational motion of the dense medium in the tank, an inlet near the top of the tank for the introduction of solid materials of different specific gravities to be subjected to classification in the tank, a discharge weir for the overflow of lighter specific gravity material from the top of the dense medium disposed at a point downstream and remote from the introduction of materials of different specific gravities, a substantially horizontal perforated plate disposed a short distance beneath and upstream of the discharge weir, said plate having holes of sufiicient number and size to permit the free flow therethrough of water and comminuted solids, but of a size small enough to restrain the passagetherethrough of materials of intermediate specific gravities slightly lower than that of the lighter material floating over the discharge weir, an outlet beneath said plate for the discharge of intermediate specific gravity materials, and an outlet for the discharge of materials of heavier specific gravity from the bottom of the dense medium.

UNITED. STATES PATENTS Allen :June 21, 1904 Andrews Dec. 6, 1932 Chance Feb. 27,1934 Chance July 17, 1934 Rakowsky Dec. 13, 1955'

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