GB2143155A

GB2143155A - A method of separating fine coal particles from refuse

Info

Publication number: GB2143155A
Application number: GB08415829A
Authority: GB
Inventors: George A Wasson; Robert E Douglas
Original assignee: Conoco Inc
Current assignee: ConocoPhillips Co
Priority date: 1983-06-27
Filing date: 1984-06-21
Publication date: 1985-02-06
Also published as: DE3421932A1; PL248417A1; GB8415829D0; AU2833684A; ZA844193B

Abstract

A method of separating fine coal particles from refuse in a coal-refuse mixture comprises the steps as follows: a) mixing water and oil with a feed coal-refuse solids mixture comprising fine coal particles and fine refuse particles, said fine coal and refuse particles being less than 1.41 mm in size, in a weight ratio of oil to solids of from 0.5:100 to 2:100 at high shear agitation conditions to form a floccular mixture comprising flocs of oil and fine coal particles and unflocculated refuse in water, b) floating said flocs of oil and coal particles from said floccular mixture in a flotation means to separate said floccular mixture into a floated floccular clean coal and oil product and refuse, said clean coal and oil product comprising said flocs of oil and fine coal particles in water, and c) separating said flocs of oil and fine coal particles from a substantial portion of said water to recover a fine coal and oil product. o

Description

SPECIFICATION A method of separating fine coal particles from refuse This invention concerns a method of separating fine coal particles from refuse, utilising differential floatation of flocs of oil and fine coal particles.

US-A-3,043,426 (Noon) discloses a black water clarification treatment using a froth cell.

Noon states that the purpose of the conditioner is to assure that each particle of coal has come in contact with the reagent which is usually a small amount of oil such as kerosene and the frothing material such as methyl isobutylcarbinol or other suitable agents known in the art for producing the results as seen in column 3 lines 3 to 8.

Chen et al in Mineral Matters, March 1 983 discloses a recovery process for fine coal using oil agglomeration at elevated oil and water temperatures.

US-A-4,033,729 (Capes et al) discloses a method for separating inorganic material from coal using light hydrocarbon liquid and mixing an aqueous agglomerating liquid.

US-A-3,665,066 (Capes et al) discloses beneficiation of coal for producing balled coal product of coal fines involving mixing a bridging liquid with coal fines and agitating the formed mixture in an aqueous medium to cause agglomeration of the coal particles.

None of these disclosures effectively address and solve the problem of separating fine coal particles, e.g. of the type present in a blackwater pond, from refuse such as shale and clay.

A coal preparation plant is a series of processing stages for separating coal from refuse in a mixture of coal and refuse from the coal mine. Such plants often use one or more heavy media separators, coal jigs, screens and froth flotation units. Coal preparation plants always produce a proportion of fine coal particles admixed with refuse; this mixture is commonly stored in a socalled "black water pond". The separation of coal from this mixture, efficiently and economically, is a longstanding problem in the art.

According to the present invention we provide a method of separating fine coal particles from refuse in a coal-refuse mixture comprising the steps as follows: (a) mixing water and oil liquids with a feed coal-refuse solids mixture comprising fine coal particles and fine refuse particles, said fine coal and refuse particles being less than 1.41 mm in size (less than 14 mesh on the US standard sieve scale), in a weight ratio of oil to solids of from 0.5:100 to 2::100 at high shear agitation conditions to form a floccular mixture comprising flocs of oil and fine coal particles and unfloccuated refuse in water, said flocs of oil and fine coal particles comprising a substantial portion of said fine coal particle from said feed coal-refuse mixture, (b) floating said flocs of oil and coal from said floccular mixture in a flotation means to separate said floccular mixture into a floated floccular clean coal and oil product and refuse, said clean coal and oil product comprising said flocs of oil and fine coal particles in water, and c) separating said flocs of oil and fine coal particles from a substantial portion of said water to recover a fine coal and oil product.

Refuse as used herein refers to the substantially inorganic mixture of solids separated from coal by solids separating apparatus such as froth flotation units. Refuse often includes shale and/or clay.

Kerosene as used herein refers to hydrocarbon liquid having a boiling range from 1 80 to 300"C. Preferably kerosene is used with a specific gravity of about 0.8 and is derived from petroleum. The preferred kerosene used in accordance with the invention may have a substantial aliphatic fraction.

High shear agitation or high shear mixing as used herin refers to mixing in a vessel wherein the stirrer blade face is substantially perpendicular to its direction of travel. Preferably, the stirrer tip velocity is approximately 5.588 m/s (approximately 1100 feet per minute) in high shear agitation. The solids and liquid are given a substantial horizontal component in the direction of flow resulting from high shear agitation.

Flocs of coal and oil formed in the high shear agitation or mixing are believed to be particles of coal adhered together by oil with entrapped air. The effective specific gravity of the flocs may e.g. vary from 0.3 to 0.98 depending upon the proportion of residue in the black water pond solids, the coal particle size, entrapped air, and other factors.

The flocs or floccules of coal, oil and water dewater much more readily than non-flocculated coal due to the decrease of fine coal particles and the oil reduces the adhesion between the water and coal particles.

One embodiment of our invention is illustrated schematically and by way of example only in the accompanying drawing, which shows a flow diagram of a process according to our invention.

With more particular reference to the drawing, water in line 1 is fed along with oil such as kerosene from line 2 into line 3 which connects to mixer 4 which may be an emulsifier. The mixer 4 is stirred by stirrer 5. The stirring action of the mixer 4 forms a well mixed or emulsified mixture of oil and water. The emulsified mixture of oil and water leaves the mixer 4 through line 6. The coal slurry in line 7 is added to the emulsified mixture in line 6. The source of the slurry in line 7 may be a black water pond. The mixture of coal, oil and water in line 8 is fed into high shear agitator 9. High shear agitator 9 is mixed by mixer 10. Flocs of coal and oil are formed in the high shear agitator 9. A slurry of flocs, refuse and water leaves the higher shear agitator 9 through line 11.Line 11 is connected to the flotation apparatus 1 2. Flotation apparatus 1 2 may be a froth flotation cell. Alternatively, separation of the flocs from the refuse may be by flotation with or without gentle stirring. A portion of the mixture flowing through line 11 may be passed through line 1 9 and screened by a screen 1 3. This step is optional. The solids recovered from the screen 1 3 are passed through line 14 into line 1 5 which connects with a mechanical drying apparatus 1 6 which may for example be a filter. The liquid may be recycled from screen 1 3 through line 20.Clean coal is recovered from the mechanical drying unit 16, which may be a filter, through line 1 7. Filtrate from the filter 1 6 passes through line 18 to the high shear agitator 9. The liquid from the screen 1 3 is passed back to line 11. The refuse leaves the flotation apparatus through line 21.

In the high shear agitator 9 oil and coal particles are mixed and it is believed form agglomerates or floccules of coal either partially or totally coated with oil. The oil on the surface of the coal particles adheres forming agglomerates or floccules of coal and oil particles. These agglomerates or floccules have an effective size sufficient for feed to the froth cell. In the froth cell, the small air bubbles adhere to and entrapped in the oil-coal agglomerates or floccules effectively lowering their density thus allowing them to more rapidly float to the surface of the froth cell.

The following Table shows results using the present invention. Black water pond solids were taken from four different mine sites. The percent coal recovery on a moisture and ash free basis ranges from more than 93 to 98 percent by weight.

The black water pond solids from each source are mixed with kerosene. The proportion of kerosene to solids is from 0.5:100 to 2:100 by weight.

A floccular mixture is formed from high shear mixing in the mixing vessel.

The floccular mixture is passed through a froth flotation cell 12.

The floccular mixture comprises flocs of oil and fine coal particles suspended in water with unflocculated refuse.

The flocs of fine coal and oil are recovered from the froth cell.

The ratio of solids to liquid feed in the mixing vessel is from about 1:5 to 1:1. Preferably, this ratio is from 1:1.5 to 1:3, on a weight basis.

The fine coal particles of the pond solids may be less than 1.41 mm (less than 14 mesh on the US standard sieve scale). This method is also effective for separating minus 0.074 mm (- 200 mesh) coal and refuse; commercially available processes cannot efficiently accept such a fine feed.

The bulk density of the froth generated in cell 12, using 2 percent kerosene is about 801.4 kg/m3 (about 50 Ibs/ft3).

TABLE Low-oil Agglomeration2 Feed1 Wt% Ash MAF3 Product4 Source % -400 Mesh* Wt% Ash Product Reject Recovery Moisture Jenkinjones 64 21 6-9 83-86 96-98 25-28 Mathies 47 37 8 90-92 > 93 24-26 Arkwright 46 28 6-7 89-91 > 94 24-27 Blacksville 35 28 5-6 83-86 > 95 24-25 1Blackwater pond solids 2Kerosene at 1-2 wt% of Feed 3MAF Recovery = Moisture and ash-free percent recovery 45.1 x 10-2m2(0.55 ft2) batch filter - 40 x 60 mesh stainless steel filtering screen (rectangular openings 0.25 X 0.42 mm).

NOTE: All wt% ash on dry basis * minus 0.037mm

Claims

1. A method of separating fine coal particles from refuse in a coal-refuse mixture comprising the steps as follows: a) mixing water and oil liquids with a feed coai-refuse solids mixture comprising fine coal particles and fine refuse particles, said fine coal and refuse particles being less than 1.41 mm in size (less than 14 mesh on the US standard sieve scale), in a weight ratio of oil to solids of from 0.5:100 to 2::100 at high shear agitation conditions to form a floccular mixture comprising flocs of oil and fine coal particles and unflocculated refuse in water, said flocs of oil and fine coal particles comprising a substantial portion of said fine coal particle from said feed coal-refuse mixture, b) floating said fiocs of oil and coal from said floccular mixture in a flotation means to separate said floccular mixture into a floated floccular clean coal and oil product and refuse, said clean coal and oil product comprising said flocs of oil and fine coal particles in water, and c) separating said flocs of oil and fine coal particles from a substantial portion of said water to recover a fine coal and oil product.

2. The method of claim 1 wherein said step (b) is carried out in the absence of a frothing material.

3. The method of claim 1 or 2 further comprising sceening at least a portion of said floccular mixture to form a screened clean coal mixture of flocs of coal and oil in water and then separating said flocs from said water to form a portion of said fine coal product.

4. The method of claim 3 wherein said separating in step (c) comprises screening.

5. The method of any of the preceding claims wherein said high shear agitation is at a stirrer tip velocity of about 5.588 m/s (about 1100 feet per minute).

6. The method of any of the preceding claims wherein said fine coal and oil product comprises more than 90 percent by weight on a moisture and ash free basis of said fine coal particles of said feed coal mixture.

7. The method of any of the preceding claims wherein said oil in said water-oil emulsion is kerosene.

8. The method of any of the preceding claims wherein said refuse comprises shale or clay.

9. The method of claim 1 wherein at least a substantial portion of said coal-refuse mixture comprises black water pond solids.

10. The method of any of the preceding claims wherein in step (b) said floccular mixture is contacted with fine bubbles in a froth flotation means without any frothing agent present.

11. The method of any of the preceding claims wherein the ratio of coal refuse solids to water and oil liquids is from 1:1 to 1:5 by weight.

1 2. The method of any of the preceding claims wherein said water and oil liquids are emulsified to form a water-oil emulsion and said emulsion is added to said coal-refuse solids mixture prior to mixing in step (a).

1 3. The method of any of the preceding claims wherein said fine coal particles are less than 0.149 mm in size (less than 100 mesh on the US standard sieve scale).

1 4. The method of claim 1, substantially as described herein with reference to the accompanying drawing.

1 5. The method of claim 1, substantially as illustrated in the Table herein.

1 6. Fine coal particles, separated from refuse by the method defined in any of claims 1 to 15.