What is claimed is:
1. A process for beneficiating coal comprising:
(a) dividing a coal feed into two fractions based on particle size; (b) dividing a first of said two fractions from step (a) , which contains larger-size particles, into three subtractions based on density, with the least dense subtraction containing predominantly coal, with the densest subfraction containingpredominantly non-coal material, and with the mid-density subtraction containing a combination of coal and non-coal material; (c) comminuting said mid-density subtraction; (d) dividing the second of said two fractions from step (a) , which contains smaller-size particles, into at least three fractions based on particle size;
(e) discarding as refuse a first of said fractions from step (d) , which contains the smallest-size particles;
(f) separately processing the remaining fractions from step (d) in dense medium separation units, with the dense medium comprising liquid and suspended magnetic particles, to separate each fraction into a clean coal overflow and a refuse underflow;
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(g) separately recovering magnetic particles from both overflow and underflow following dense medium separation of a second of said fractions from step (d) , which contains larger-size particles processed in step (f) , by draining and then rinsing with water on a screen or sieve followed by removal of magnetic particles from the rinse water by magnetic separation; and (h) separately recovering magnetic particles from both overflow and underflow following dense medium separation of a third of said fractions from step (d) , which contains smaller-size particles processed in step (f), by magnetic separation.
2. The process of Claim 1, wherein the comminuted mid-density subtraction from step (c) is further processed with the second fraction from step (a) which contains smaller-size particles than the first fraction of step (a) . 3. The process of Claim 1, wherein the least dense subtraction in step (b) comprises at least about 85 weight percent coal.
4. The process of Claim 1, wherein the least dense subtraction in step (b) comprises at least about 90 weight percent coal.
5. The process of Claim 1, wherein the least dense subtraction in step (b) comprises at least about 95 weight percent coal.
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6. The process of Claim 1, wherein the amount of magnetic particles which is not recovered in step (g) is less than four pounds per ton of material subjected to magnetic particle recovery in step (g) . 7. The process of Claim 1, wherein the amount of magnetic particles which is not recovered in step (g) is less than ten pounds per ton of material subjected to magnetic particle recovery in step (g) .
8. The process of Claim 1, wherein the total amount of magnetic particles recovered in steps (g) and (h) is at least about 99 weight percent.
9. The process of Claim 1, wherein at least about 75 weight percent of inorganic sulfur is separated from said coal feed. 10. The process of Claim 1, wherein at least about 85 weight percent of inorganic sulfur is separated from said coal feed.
11. The process of Claim 1, wherein the resulting clean coal products contain at least about 65 percent of the total heating value of said coal feed.
12. The process of Claim 1, wherein the resulting clean coal products contain at least about 80 percent of the total heating value of said coal feed.
13. The process of Claim 1, wherein magnetic separation in steps (g) and (h) consists essentially of separation in wet drum magnetic separators.
14. The process of Claim 1, wherein the coal feed is divided into said two fractions in step (a) wherein said
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first fraction comprises particles, at least 90 percent of which are larger than about 0.5 mm in size, and wherein said second fraction comprises particles, at least 90 percent of which are smaller than about 0.5 mm in size. 15. The process of Claim 1, wherein the coal feed is divided into said fractions in step (a) wherein said first fraction contains particles larger than from about 0.25 mm to about 1 mm in size, and wherein said second fraction contains particles smaller than from about 0.25 mm to about 1 mm in size.
16. The process of Claim 1, wherein said second fraction from step (a) is divided into two subtractions based on particle size, and wherein the first of said two subtractions, which contains larger-size particles, is processed the same process as said first fraction from (a) is processed in steps (b) through (h) , and wherein the second of said two subtractions is processed the same as said second fraction from step (a) is processed in steps (d) through (h) . 17. The process of Claim 1, wherein said second fraction from step (a) is divided into two subtractions based on particle size, and wherein the first of said two subtractions contains particles larger than about 0.4 mm to 0.6 mm, and wherein the second of said subtractions contain particles smaller than about 0.4 mm to 0.6 mm.
18. The process of Claim 1,. wherein the second of said fractions from step (d) , which contains larger-size
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particles, is processed the same as said first fraction from step (a) is processed in steps (b) through (h) .
19. The process of Claim 1, wherein said least dense subtraction from step (b) comprises overflow from density separation wherein the density of separation occurs at a specific gravity within about 0.1 specific gravity units of the specific gravity of the coal being processed.
20. The process of Claim 1, wherein said least dense fraction from step (b) comprises overflow from a density separation wherein the density of separation occurs at a specific gravity from about 1.2 to about 1.4.
21. The process of Claim 1, wherein said densest subtraction from step (b) comprises underflow from a density separation wherein the density of separation occurs at a specific gravity of at least 0.5 specific gravity units in excess of the specific gravity of the coal being processed.
22. The process of Claim 1, wherein said densest subtraction from step (b) comprises underflow from a density separation wherein the density of separation occurs at a specific gravity from about 1.8 to about 2.1.
23. The process of Claim 1, wherein said densest subtraction from step (b) comprises underflow from a density separation wherein the density of separation occurs at a specific gravity of at least 0.35 specific gravity units in excess of the specific gravity of the coal being processed.
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24. The process of Claim 1, wherein the coal feed comprises anthracite coal, and wherein said densest subtraction from step (b) comprises underflow from a density separation wherein the density of separation occurs at a specific gravity of at least 0.3 in excess of the specific gravity of said anthracite coal.
25. The process of Claim 1, wherein said second fraction from step (a) is divided into three fractions based on particle size in step (d) . 26. The process of Claim 1, wherein said first fraction from step (d) , which is discarded in step (e) , comprises the overflow from a classifying cyclone.
27. The process of Claim 1, wherein said first fraction from step (d) , which is discarded in step (e) , comprises the overflow from a classifying cyclone, and wherein the average velocity of the feed of said first fraction through the inlet orifice by which the particles enter the cyclone feed chamber is at least 60 feet per second. 28. The process of Claim 1, wherein said first fraction from step (d) , which is discarded in step (e) , comprises the overflow from a classifying cyclone, and wherein the average velocity of the feed of said first fraction through the inlet orifice by which the particles enter the cyclone feed chamber is at least 90 feet per second.
29. The process of Claim 1, wherein said first fraction from step (d) , which is discarded in step (e) ,
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comprises the overflow from a classifying cyclone, and wherein the volumetric flow rate of feed into the classifying cyclone is such that the residence time of particles to be classified is sufficient to achieve effective classification of the particles.
30. The process of Claim 1, wherein said first fraction from step (d) , which is discarded in step (e) , comprises the overflow from a classifying cyclone, and wherein the volumetric flow rate of feed into the classifying cyclone is within the range for the industry design standards for the particular cyclone configuration.
31. The process of Claim 1, wherein said first fraction from step (d) , which is discarded in step (e) , comprises the overflow from a classifying cyclone, and wherein the classification of particles comprising said first fraction are classified in the classifying cyclone according to particle settling velocity.
32. The process of Claim 1, wherein said first fraction from step (d) , which is discarded in step (e) , predominantly comprises particles smaller than from about 0.01 mm to about 0.025 mm in size.
33. The process of Claim 1, wherein said second fraction from step (a) , which contains smaller-size particles, is divided into three fractions based on particle size, with the first of said three fractions having a maximum particle size of from about 0.4 mm to about 0.6 mm and a minimum particle size of from about 0.085 mm to about 0.125 mm, with the second of said
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fractions having a maximum particle size of from about 0.085 mm to about 0.125 mm and a minimum particle size of from about 0.01 mm to about 0.025 mm, and with the third of said fractions having a maximum particle size of from about 0.01 mm to about 0.025 mm.
34. The process of Claim 1, wherein the dense medium separation units in step (f) comprise dense medium cyclones, and wherein the average velocity of the feed through the inlet orifice by which the particles enter a cyclone feed chamber is at least 30 feet per second.
35. The process of Claim 1, wherein the dense medium separation units in step (f) comprise dense medium cyclones, and wherein the average velocity of the feed through the inlet orifice by which the particles enter a cyclone feed chamber is at least 60 feet per second.
36. The process of Claim 1, wherein the dense medium separation units in step (f) comprise dense medium cyclones, and wherein the average velocity of the feed through the inlet orifice by which the particles enter a cyclone feed chamber is at least 90 feet per second.
37. The process of Claim 1, wherein the dense medium separation units in step (f) comprise dense medium cyclones, and wherein the volumetric flow rate of feed into the dense medium cyclones is such that the residence time of particles to be separated is sufficient to achieve effective separation of the particles.
38. The process of Claim 1, wherein the dense medium separation units in step (f) comprise dense medium
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cyclones, and wherein the volumetric flow rate of feed into the dense medium cyclones is within the range for the industry design standards for the particular cyclone configuration. 39. The process of Claim 1, wherein the dense medium in step (f) comprises water and magnetite particles.
40. The process of Claim 1, wherein the dense medium in step (f) comprises water and magnetite particles and at least about 60 weight percent of the magnetite particles are from about 2 microns to about 10 microns in size.
41. The process of Claim 1, wherein the dense medium in step (f) comprises water and magnetite particles and at least about 75 weight percent of the magnetite particles are from about 2 microns to about 10 microns in size. 42. The process of Claim 1, wherein the dense medium in step (f) comprises water and magnetite particles and no more than about 10 weight percent of the magnetite particles are less than about 2 microns in size.
43. The process of Claim 1, wherein the dense medium in step (f) comprises water and magnetite particles and no more than about 25 weight percent of the magnetite particles are smaller than about 3 microns in size.
44. The process of Claim 1, wherein the dense medium in step (f) comprises water and magnetite particles and at least about 10 weight percent of the particles are greater than about 7 microns in size.
45. The process of Claim 1, wherein the dense medium in step (f) comprises water and magnetite particles and
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wherein said magnetite particles are produced from reduction of hematite wherein during said reduction, the hematite is subjected to a maximum temperature of from about 900°C to about 1000βC. 46. The process of Claim 1, wherein the dense medium in step (f) comprises water and magnetite particles and wherein said magnetite particles are produced from reduction of hematite wherein said reduction, takes place under such conditions of residence time and temperature that crystal growth of magnetite produced is limited such that magnetite particles produced are of a size such that at least about 60 weight percent of such magnetite particles are from about 2 microns to about 10 microns in size. 47. The process of Claim 1, wherein the dense medium in step (f) comprises water and magnetite particles and wherein said magnetite particles are produced from reduction of hematite wherein said reduction, takes place under such conditions of residence time and temperature that crystal growth of magnetite produced is limited such that magnetite particles produced are of a size such that at least about 75 weight percent of such magnetite particles are from about 2 microns to about 10 microns in size. 48. The process of Claim 1, wherein recovery of dense medium in step (f) comprises water and magnetite particles, and wherein said magnetite particles are produced by spray roasting an aqueous solution of iron chloride at a maximum
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te perature in the reactor of from about 900βC to about lOOO-c.
49. The process of Claim 1, wherein the dense medium in step (f) comprises water and magnetite particles and wherein said magnetite particles are produced by spray roasting an aqueous solution of iron chloride under such conditions of residence time and temperature that crystal growth of magnetite produced is limited such that magnetite particles produced are of a size such that at least about 60 weight percent of such magnetite particles are from about 2 microns to about 10 microns in size.
50. The process of Claim 1, wherein the dense medium in step (f) comprises water and magnetite particles and wherein said magnetite particles are produced by spray roasting an aqueous solution of iron chloride under such conditions of residence time and temperature that crystal growth of magnetite produced is limited such that magnetite particles produced are of a size such that at least about
75 percent of such magnetite particles are from about 2 microns to about 10 microns in size.
51. The process of Claim 1, wherein recovery of dense medium particles in step (h) is by magnetic separation in wet drum magnetic separators arranged in a rougher-cleaner- scavenger circuit with, the scavenger unit containing a rare earth magnet.
52. The process of Claim 1, wherein said magnetic separation in step (g) is in one or more wet drum magnetic separators.
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53. The process of Claim 1, wherein said third fraction from step (d) , which is processed in step (h) as overflow to produce a clean coal product, is dewatered by centrifugal separation, and wherein paper fibers are added to said clean coal product prior to said dewatering.
54. The process of Claim 1, wherein said third fraction from step (d) , which is processed in step (h) as overflow to produce a clean coal product, is agglomerated, and wherein paper fibers are added to said clean coal product prior to said agglomeration.
55. The process of Claim 1, wherein the dense medium separation units in step (f) are dense medium cyclones, and wherein said dense medium cyclones are capable of separating a fraction of coal feed comprising particles smaller than from about 0.4 mm to about 0.6 mm in size and larger than from about 0.085 mm to about 0.125 mm in size with a probable error of less than 0.05.
56. The process of Claim 1, wherein the dense medium separation units in step (f) are dense medium cyclones, and wherein said dense medium cyclones are capable of separating a fraction of coal feed comprising particles smaller than from about 0.4 mm to about 0.6 mm in size and larger than from about 0.085 mm to about 0.125 mm in size with a probable error of less than 0.035. 57. The process of Claim 1, wherein the dense medium separation units in step (f) are dense medium cyclones, and wherein said dense medium cyclones are capable of separating a fraction of coal feed comprising particles
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s aller than from about 0.085 mm to about 0.125 mm in size and larger than from about o.oio to about 0.025 mm in size with a probable error of less than 0.08.
58. The process of Claim 1, wherein the dense medium separation units in step (f) are dense medium cyclones, and wherein said dense medium cyclones are capable of separating a fraction of coal feed comprising particles smaller from about 0.085 mm to about 0.125 mm in size and larger than from about 0.010 to about 0.025 mm in size with a probable error of less than 0.12.
59. The process of Claim 1, wherein non-magnetic effluent liquid following removal of magnetic particles by magnetic separation in step (h) is used to dilute feed to said magnetic separation unit in step (h) . 60. The process of Claim 1, wherein cleaned effluent liquid following removal of magnetic particles in step (g) is added to said second of said fractions in step (d) , which contains larger-size particles processed in step (f) , prior to said processing in step (f) .
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61. A process for beneficiating coal comprising:
(a) dividing the coal feed into at least three fractions based on particle size;
(b) discarding as refuse a first of said fractions from step (a) , which first fraction contains the smallest-size particles;
(c) separately processing the remaining fractions from step (a) in dense medium separation units, with dense medium comprising liquid and magnetic particles, to separate each fraction into a clean coal overflow and a refuse underflow;
(d) separately recovering magnetic particles from both overflow and underflow following dense medium separation of a second fraction from (a) , which contains larger-size particles processed in step (c) , by draining and then rinsing with water on a screen or sieve followed by removal of dense medium magnetic particles from the rinse water by magnetic separation; and
(e) separately recovering magnetic particles from both overflow and underflow following dense medium separation of a third fraction from (a) , which contains smaller-size particles processed in step (c) , by magnetic separation.
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62. The process of Claim 61, wherein, in step (d) , water is added to said second of said fractions from step (d) following draining on a screen or sieve, and prior to rinsing on a screen or sieve. 63. The process of Claim 61, wherein the amount of magnetic particles which is not recovered in step (d) is less than four pounds per ton of material subjected to magnetic particle recovery in step (d) .
64. The process of Claim 61, wherein the amount of magnetic particles which is not recovered in step (d) is less than ten pounds per ton of material subjected to magnetic particle recovery in step (d) .
65. The process in Claim 61, wherein the total amount of magnetic particles recovered in steps (d) and (e) is at least about 99 weight percent.
66. The process of Claim 61, wherein at least about 75 weight percent of inorganic sulfur is separated from said coal feed.
67. The process of Claim 61, wherein at least about 85 weight percent of inorganic sulfur is separated from said coal feed.
68. The process of Claim 61, wherein the resulting clean coal products contain at least about 65 percent of the total heating value of said coal feed. 69. The process of Claim 61, wherein the resulting clean coal products contain at least about 80 percent of the total heating value of said coal feed.
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70. The process of Claim 61, wherein magnetic separation in steps (d) and (e) consists essentially of magnetic separation in wet drum magnetic separators.
71. The process of Claim 61, wherein said coal feed is divided into three fractions based on particle size in step (a) .
72. The process of Claim 61, wherein said first fraction from step (a) , which is discarded in step (b) , comprises the overflow from a classifying cyclone. 73. The process of Claim 61, wherein said first fraction from step (a) , which is discarded in step (b) , comprises the overflow from a classifying cyclone, and wherein the average velocity of the feed of said first fraction through the inlet orifice by which the particles enter the cyclone feed chamber is at least 60 feet per second.
74. The process of Claim 61, wherein said first fraction from step (a) , which is discarded in step (b) , comprises the overflow from a classifying cyclone, and wherein the average velocity of the feed of said first fraction through the inlet orifice by which the particles enter the cyclone feed chamber is at least 90 feet per second.
75. The process of Claim 61, wherein said first fraction from step (a) , which is discarded in step (b) , comprises the overflow from a classifying cyclone, and wherein the volumetric flow rate of feed into the classifying cyclone is such that the residence time of
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particles to be classified is sufficient to achieve effective classification of the particles.
76. The process of Claim 61, wherein said first fraction from step (a) , which is discarded in step (b) , comprises the overflow from a classifying cyclone, and wherein the volumetric flow rate of feed into the classifying cyclone is within the range for the industry design standards for the particular cyclone configuration.
77. The process of Claim 61, wherein said first fraction from step (a) , which is discarded in step (b) , comprises the overflow from a classifying cyclone, and wherein the classification of particles comprising said first fraction are classified in the classifying cyclone according to particle settling velocity. 78. The process of Claim 61, wherein said first fraction from step (a) which is discarded in step (b) predominantly comprises particles smaller than from about 0.01 mm to about 0.025 mm in size.
79. The process of Claim 61, wherein the coal feed is divided into three fractions based on particle size, with the first fraction having a maximum particle size of from about 0.4 mm to about 0.6 mm and a minimum particle size from about 0.085 mm to about 0.125 mm, with the second fraction having a maximum particle size from about 0.085 mm to about 0.125 mm and a minimum particle size of from about 0.01 mm to about 0.025 mm, and with the third fraction having a maximum particle size of from about 0.01 mm to about 0.025 mm.
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80. The process of Claim 61, wherein the dense medium separation units in step (c) comprise dense medium cyclones, and wherein the average velocity of the feed through the inlet orifice by which the particles enter a cyclone feed chamber is at least 30 feet per second.
81. The process of Claim 61, wherein the dense medium separation units in step (c) comprise dense medium cyclones, and wherein the average velocity of the feed through the inlet orifice by which the particles enter a cyclone feed chamber is at least 60 feet per second.
82. The process of Claim 61, wherein the dense medium separation units in step (c) comprise dense medium cyclones, and wherein the average velocity of the feed through the inlet orifice by which the particles enter a cyclone feed chamber is at least 90 feet per second.
83. The process of Claim 61, wherein the dense medium separation units in step (c) comprise dense medium cyclones, and wherein the volumetric flow rate of feed into the dense medium cyclones is such that the residence time of particles to be separated is sufficient to achieve effective separation of the particles.
84. The process of Claim 61, wherein the dense medium separation units in step (c) comprise dense medium cyclones, and wherein the volumetric flow rate of feed into the dense medium cyclones is within the range for the industry design standards for the particular cyclone configuration.
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85. The process of Claim 61, wherein the dense medium in step (c) comprises water and magnetite particles.
86. The process of Claim 61, wherein the dense medium in step (c) comprises water and magnetite particles and at least about 60 weight percent of the magnetite particles are from about 2 microns to about 10 microns in size.
87. The process of Claim 61, wherein the dense medium in step (c) comprises water and magnetite particles and at least about 75 weight percent of the magnetite particles are from about 2 microns to about 10 microns in size.
88. The process of Claim 61, wherein the dense medium in step (c) comprises water and magnetite particles and no more than about 10 weight percent of the magnetite particles are less than about 2 microns in size. 89. The process of Claim 61, wherein the dense medium in step (c) comprises water and magnetite particles and no more than about 25 weight percent of the magnetite particles are smaller than about 3 microns in size.
90. The process of Claim 61, wherein the dense medium in step (c) comprises water and magnetite particles and at least about 10 weight percent of the particles are greater than about 7 microns in size.
91. The process of Claim 61, wherein the dense medium in step (c) comprises water and magnetite particles and wherein said magnetite particles are produced from reduction of hematite wherein during said reduction, the hematite is subjected to a maximum temperature of from about 900°C to about 1000"C.
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92. The process of Claim 61, wherein the dense medium in step (c) comprises water and magnetite particles and wherein said magnetite particles are produced from reduction of hematite wherein said reduction, takes place under such conditions of residence time and temperature that crystal growth of magnetite produced is limited such that magnetite particles produced are of a size such that at least about 60 weight percent of such magnetite particles are from about 2 microns to about 10 microns in size.
93. The process of Claim 61, wherein the dense medium in step (c) comprises water and magnetite particles and wherein said magnetite particles are produced from reduction of hematite wherein said reduction, takes place under such conditions of residence time and temperature that crystal growth of magnetite produced is limited such that magnetite particles produced are of a size such that at least about 75 weight percent of such magnetite particles are from about 2 microns to about 10 microns in size.
94. The process of Claim 61, wherein the dense medium in step (c) comprises water and magnetite particles, and wherein said magnetite particles are produced by spray roasting an aqueous solution of iron chloride at a maximum temperature in the reactor of from about 900°C to about 1000°C.
95. The process of Claim 61, wherein recovery of dense medium particles in step (e) is by magnetic
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separation in wet drum magnetic separators arranged in a rougher-cleaner-scavenger circuit with the scavenger unit containing a rare earth magnet.
96. The process of Claim 61, wherein coal feed in step (a) is comprised of a middling fraction which has been comminuted to a maximum particle size of from about 0.6 mm to about 0.4 mm.
97. The process of Claim 61, wherein said third fraction from step (a) , which is processed in step (e) as overflow to produce a clean coal product, is dewatered by centrifugal separation, and wherein paper fibers are added to said clean coal product prior to said dewatering.
98. The process of Claim 61, wherein said third fraction from step (a) , which is processed in step (e) as overflow to produce a clean coal product, is agglomerated, and wherein paper fibers are added to said clean coal product prior to said agglomeration.
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99. A process for separating solid particles by dense medium separation with dense medium comprising water and magnetic particles, wherein at least about 60 percent of said magnetic particles are from about 2 microns to about 10 microns in size.
100. The process of Claim 99, wherein said magnetic particles comprise magnetite.
101. The process of Claim 99, wherein at least about 75 weight percent of said magnetic particles are from about 2 microns to about 10 microns in size.
102. The process of Claim 99, wherein said dense medium comprises water and magnetite particles and no more than about 10 weight percent of the magnetite particles are smaller than about 2 microns in size. 103. The process of Claim 99, wherein no more than about 25 weight percent of said magnetic particles are smaller than about 3 microns in size.
104. The process of Claim 99, wherein at least about 10 weight percent of said magnetic particles are larger than 7 microns in size.
105. The process of Claim 99, wherein said solid particles to be separated comprise coal feed particles less than a size from about 0.6 mm to about 0.4 mm.
106. The process of Claim 99, wherein said dense medium comprises water and magnetite particles, and wherein said magnetite particles are produced from reduction of hematite wherein during said reduction, the hematite is
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subjected to a maximum temperature in the reactor of from about 900"C to about 1000βC.
107. The process of Claim 99, wherein said dense medium comprises water and magnetite particles and wherein said magnetite particles are produced from reduction of hematite wherein said reduction, takes place under such conditions of residence time and temperature that crystal growth of magnetite produced is limited such that magnetite particles produced are of a size such that at least about 60 weight percent of such magnetite particles are from about 2 microns to about 10 microns in size.
108. The process of Claim 99, wherein said dense medium comprises water and magnetite particles and wherein said magnetite particles are produced from reduction of hematite wherein said reduction, takes place under such conditions of residence time and temperature that crystal growth of magnetite produced is limited such that magnetite particles produced are of a size such that at least about 75 weight percent of such magnetite particles are from about 2 microns to about 10 microns in size.
109. The process of Claim 99, wherein said dense medium comprises water and magnetite particles, and wherein said magnetite particles are produced by spray roasting an aqueous solution of iron chloride at a maximum temperature in the reactor of from about 900°C to about 1000°C.
110. The process of Claim 99, wherein said dense medium comprises water and magnetite particles and wherein said magnetite particles are produced by spray roasting an
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aqueous solution of iron chloride under such conditions of residence time and temperature that crystal growth of magnetite produced is limited such that magnetite particles produced are of a size such that at least about 60 weight percent of said magnetite particles are from about 2 microns to about 10 microns in size.
111. The process of Claim 99, wherein said dense medium comprises water and magnetite particles and wherein said magnetite particles are produced by spray roasting an aqueous solution of iron chloride under such conditions of residence time and temperature that crystal growth of magnetite produced is limited such that magnetite particles produced are of a size such that at least about 75 weight percent of said magnetite particles are from about 2 microns to about 10 microns in size.
112. The process of Claim 99, wherein said dense medium comprises water and magnetite particles, and wherein said magnetite particles are produced from reduction of hematite and wherein the reduction takes place in a rotary kiln reactor, with hematite feed in one end and magnetite product discharge at the opposite end, with a burner flame introduced into the reactor at the discharge end, with restricted oxygen to the burner, and with additional natural gas injected into the reactor to maintain a reducing environment.
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113. A process for recovering dense medium following dense medium separation of solid particles comprising:
(a) employing a dense medium comprising water and magnetic particles, wherein at least about 60 weight percent of said magnetic particles are from about 2 microns to about 10 microns in size; and
(b) recovering said dense medium with a magnetic particle recovery unit comprising magnetic separators.
114. The process of Claim 113, wherein said magnetic particles comprise magnetite.
115. The process of Claim 113, wherein at least about 75 weight percent of said magnetic particles are from about 2 microns to about 10 microns in size.
116. The process of Claim 113, wherein no more than about 10 weight percent of said magnetic particles are smaller than about 2 microns in size.
117. The process of Claim 113, wherein no more than about 25 weight percent of said magnetic particles are smaller than 3 microns in size.
118. The process of Claim 113, wherein at least about 10 weight percent of said magnetic particles are larger than about 7 microns in size. 119. The process of Claim 113, wherein dense medium magnetic particles are recovered following dense medium separation of coal feed containing particles having a maximum particle size of from about 0.6 mm to about 0.4 mm.
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120. The process of Claim 113, wherein said dense medium in step (a) is used in dense medium separation of coal, wherein the coal feed is split into at least two fractions based on particle size, prior to dense medium separation, wherein magnetic particles are recovered separately from each fraction, wherein smaller-particle- size fractions are diluted, prior to magnetic particle recovery, with effluent comprising cleaned fluid exiting the magnetic particle recovery unit for treating said smaller-particle-size fraction, and wherein cleaned fluid exiting the magnetic particle recovery unit for treating larger-particle-size fractions is added to a smaller particle-size fraction prior to dense medium separation of said smaller-particle-size fraction. 121. The process of Claim 113, wherein said dense medium comprises water and magnetite particles and wherein said magnetite particles are produced from reduction of hematite wherein during said reduction, the hematite is subjected to a maximum temperature of from about 900°C to about 1000°C.
122. The process of Claim 113, wherein said dense medium comprises water and magnetite particles and wherein said magnetite particles are produced from reduction of hematite wherein said reduction, takes place under such conditions of residence time and temperature that crystal growth of magnetite produced is limited such that magnetite particles produced are of a size such that at least about
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60 percent of such magnetite particles are from about 2 microns to about 10 microns in size.
123. The process of Claim 113, wherein said dense medium comprises water and magnetite particles and wherein said magnetite particles are produced from reduction of hematite wherein said reduction, takes place under such conditions of residence time and temperature that crystal growth of magnetite produced is limited such that magnetite particles produced are of a size such that at least about 75 weight percent of such magnetite particles are from about 2 microns to about 10 microns in size.
124. The process of Claim 113, wherein said dense medium comprises water and magnetite particles, and wherein said magnetite particles are produced by spray roasting an aqueous solution of iron chloride at a maximum temperature in the reactor of from about 900°C to about 1000°C.
125. The process of Claim 113, wherein said dense medium comprises water and magnetite particles, and wherein said magnetite particles are produced from reduction of hematite and wherein the reduction reaction takes place in a rotary kiln reactor, with hematite feed in one end and magnetite product discharge at the opposite end, with a burner flame introduced into the reactor at the discharge end, with restricted oxygen to the burner, and with additional natural gas injected into the reactor to maintain a reducing environment.
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126. A process for producing magnetite by reduction of hematite comprising:
(a) heating hematite in a reactor under reducing conditions; and (b) subjecting the hematite to a maximum temperature in said reactor of from about 900°C to about 1000°C.
127. The process of Claim 126, wherein said hematite is subjected to maximum temperatures in the reactor of from about 180°C to about 1000"C.
128. The process of Claim 126, wherein said hematite is produced by spray roasting of an aqueous solution of iron chloride at a maximum temperature of from about 900βC to about 1000°C. 129. The process of Claim 126, wherein said hematite is produced from pyrohydrolysis of iron chloride.
130. The process of Claim 126, wherein oxygen to reactor burners is restricted, and additional hydrogen or natural gas is injected into said reactor to maintain a reducing environment.
131. The process of Claim 126, wherein the reduction occurs in a tunnel reactor, with hematite fed into one end of the reactor and magnetite product discharged from the other end, with the hematite being heated as it moves between feed and discharge ends, and with the hematite subjected to a maximum temperature of from about 900°C to about 1000βC.
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132. The process of Claim 126, wherein at least about 60 weight percent of the magnetite particles are from about 2 microns to about 10 microns in size.
133. The process of Claim 126, wherein at least about 75 weight percent of the magnetite particles are from about
2 microns to about 10 microns in size.
134. The process of Claim 126, wherein no more than about 10 weight percent of the magnetite particles have a size smaller than about 2 microns. 135. The process of Claim 126, wherein no more than about 25 percent of the magnetite particles have a size smaller than about 3 microns.
136. The process of Claim 126, wherein at least about 10 weight percent of the magnetite particles are larger than about 7 microns in size.
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137. A process for classifying solid particles according to particle settling velocities comprising:
(a) forming a slurry comprising solid particles to be classified and water; and (b) feeding the slurry to a classifying cyclone, wherein the average velocity of the feed through the inlet orifice by which the slurry enters the cyclone feed chamber is at least about 60 feet per second. 138. The process of Claim 137, wherein the volumetric flow rate of feed into the classifying cyclone is such that the residence time of solid particles in the cyclone is sufficient to achieve effective classification of the solid particles. 139. The process of Claim 137, wherein the volumetric flow rate of feed into the classifying cyclone is within the range for the industry design standards for the particular cyclone configuration.
140. The process of Claim 137, wherein the solid particles to be classified comprise coal feed particles.
141. The process of Claim 137, wherein the solid particles to be classified are smaller than a size from about 0.4 mm to about 0.6 mm.
142. The process of Claim 137, wherein the solid particles to be classified are smaller than from about
0.085 mm to about 0.125 mm.
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143. The process of Claim 137, wherein the solid particles are to be classified predominantly according to particle size.
144. The process of Claim 137, wherein the solid particles are to be classified at a size of about 15 microns .(0.015 mm).
145. The process of Claim 137, wherein the average inlet velocity of feed entering the cyclone feed chamber, in step (b) , is at least about 90 feet per second.
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146. A process for separating solid particles by density in one or more dense medium cyclones wherein the average velocity of feed through the inlet orifice by which the particles enter a cyclone feed chamber is at least about 30 feet per second.
147. The process of Claim 146, wherein the solid particles to be separated comprise coal feed particles.
148. The process of Claim 146, wherein the dense medium comprises water and magnetic particles. 149. The process of Claim 146, wherein the dense medium comprises water and magnetite.
150. The process of Claim 146, wherein the average velocity of feed through said inlet orifice by which feed particles enter said cyclone feed chamber is at least about 60 feet per second.
151. The process of Claim 146, wherein the average velocity of feed through said inlet orifice by which feed particles enter said cyclone feed chamber is at least about 90 feet per second. 152. The process of Claim 146, wherein the dense medium cyclones are capable of separating a fraction of coal feed comprising particles smaller than from about 0.4 mm to about 0.6 mm in size and larger than from about 0.085 mm to about 0.125 mm in size with a probable error of less than 0.05.
153. The process of Claim 146, wherein the dense medium cyclones are capable of separating a fraction of coal feed comprising particles smaller than from about 0.4
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mm to about 0.6 mm in size and larger than from about 0.085 mm to about 0.125 mm in size with a probable error of less than 0.035.
154. The process of Claim 146, wherein the dense medium cyclones are capable of separating a fraction of coal feed comprising particles smaller than from about 0.085 mm to about 0.125 mm in size and larger than from about 0.010 mm to about 0.025 mm in size with a probable error of less than 0.08. 155. The process of Claim 146, wherein the dense medium cyclones are capable of separating a fraction of coal feed containing particles smaller than from about 0.085 mm to about 0.125 mm in size and larger than from about 0.010 to about 0.025 mm in size with a probable error of less than 0.12.
156. The process of Claim 146, wherein the dense medium comprises water and magnetic particles and at least about 60 percent of said magnetic particles are from about 2 microns to about 10 microns in size. 157. The process of Claim 146, wherein the dense medium comprises water and magnetic particles and at least about 75 percent of said magnetic particles are from about 2 microns to about 10 microns in size.
158. The process of Claim 146, wherein the dense medium comprises water and magnetic particles and no more than about 10 percent of said magnetic particles are smaller than about 2 microns in size.
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159. The process of Claim 146, wherein the dense medium comprises water and magnetic particles and no more than about 25 percent of said magnetic particles are smaller than about 3 microns in size. 160. The process of Claim 146, wherein the dense medium comprises water and magnetic particles and at least about 10 percent of said magnetic particles are greater than about 7 microns in size.
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161. A process for beneficiating coal comprising:
(a) removing particles of a size less than about 15 microns; and
(b) further beneficiating the remaining coal particles to separate coal from non-coal material.
162. The process of Claim 161, wherein the removal of particles in step (a) is in a classifying cyclone.
163. The process of Claim 161, wherein beneficiation in step (b) is by dense medium cyclone.
164. The process of Claim 161, wherein the solid particles to be separated comprise coal particles of a size less than from about 0.4 mm to about 0.6 mm.
165. The process of Claim 161, wherein the average velocity of coal feed through the inlet orifice by which the particles enter a cyclone feed chamber is at least about 60 feet per second.
166. The process of Claim 161, wherein the average velocity of coal feed through the inlet orifice by which the particles enter a cyclone feed chamber is at least about 90 feet per second.
167. The process of Claim 161, wherein the average velocity of coal feed through the inlet orifice by which the particles enter a cyclone feed chamber is such that the residence time of particles to be classified is sufficient to achieve effective classification of the coal feed particles.
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168. The process of Claim 161, wherein the volumetric flow rate of feed into the classifying cyclone is such that the residence time of particles to be classified is sufficient to achieve effective classification of the particles.
169. The process of Claim 161, wherein the removal of particles in step (a) occurs in a classifying cyclone according to particle settling velocity.
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170. A process for beneficiating coal comprising:
(a) dividing the coal feed into two fractions based on particle size?
(b) dividing the larger-particle-size fraction from (a) into three subtractions based on density, with the least dense subtraction comprising predominantly pure coal, with the densest subtraction comprising predominantly non-coal, and with the mid-density subfraction comprising a combination of coal and non-coal material; and
(c) comminuting the mid-density fraction from (b) for further processing with the smaller-particle-size fraction from (a) .
171. The process of Claim 170, wherein said least dense subfraction from step (b) results from density separation wherein the density of separation is within 0.1 specific gravity units of the coal.
172. The process of Claim 170, wherein said least dense subfraction in step (b) results from density separation wherein the density of separation is at a specific gravity from about 1.2 to about 1.4.
173. The process of Claim 170, wherein the densest subfraction in step (b) is produced by density separation wherein the density of separation is at least 0.5 specific gravity units greater than the specific gravity of the coal.
174. The process of Claim 170, wherein the densest subfraction in step (b) results from density separation
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where the density of separation is at a specific gravity from about 1.8 to about 2.1.
175. The process of Claim 170, wherein the dense medium separation in step (b) takes place in dense medium cyclones.
176. The process of Claim 170, wherein the least dense subfraction in step (b) comprises at least about 90 weight percent coal.
177. The process of Claim 170, wherein the least dense subfraction in step (b) comprises at least about 95 weight percent coal.
178. The process of Claim 170, wherein the least dense subfraction in step (b) comprises at least about 85 weight percent coal.
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179. A process for separating coal particles based on size comprising:
(a) forming a mixture of coal feed and water;
(b) providing multiple classifying cyclones arranged in series; and
(c) ■ feeding to classifying cyclones overflow from a directly succeeding classifying cyclone and underflow from a directly preceding cyclone, wherein overflow from the first classifying cyclone in series and underflow from the last classifying cyclone in series comprise the separated product streams. 180. The process of Claim 179, wherein the coal to be separated comprises particles smaller than about 0.5 mm in ' size.
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181. A process for dewatering coal comprising adding paper fibers to the coal and subsequent centrifugal separation of coal and water.
182. The process of Claim 181, wherein the coal comprises particles less than about 0.105 microns in size.
183. The process of Claim 181, wherein the paper fibers comprise of newsprint fibers.
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184. A method for agglomerating coal particles comprising adding paper fibers to the coal and pelletizing, briqueting or otherwise compacting the coal particles and paper fibers into an agglomerated form. 185. The process of Claim 184, wherein the coal comprises particles less than about 0.105 microns in size. 186. The process of Claim 184, wherein the paper fibers are comprised of newsprint fibers.
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