AU617698B2

AU617698B2 - Method and apparatus for separating clay from and then dewatering ultra fine coal

Info

Publication number: AU617698B2
Application number: AU24079/88A
Authority: AU
Inventors: Edward Harris Greenwald Sr.
Original assignee: Individual
Current assignee: Individual
Priority date: 1987-10-22
Filing date: 1988-10-20
Publication date: 1991-12-05
Anticipated expiration: 2008-10-20
Also published as: GB8824760D0; GB2211440A; FR2622203A1; FR2622203B1; NZ226661A; IN170718B; CA1330427C; GB2211440B; DE3836064A1; AU2407988A

Description

I b S F Ref: 75722 FORM COMMONWEALTH OF AUSTRALIA z 8 PATENTS ACT 1952 6 1 7 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: Class Int Class Complete Specification Lodged: Acceptid: Published: Priority: Related Art: p; Name and Address of Applicant: Edward Harris Greenwald, Sr.

S9 92 Nancy Lane McMurray Pennsylvania 15317 °o UNITED STATES OF AMERICA o Address for Service: Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, k1 Market Street Sydney, New South Wales, OX., Australia S Complete Specification for the invention eti 4 tled: 0 09 o o a Method and Apparatus for Separating Clay From and Then 0' Dewaterink Ultra Fine Coal 00060 The following statement is a full description of this invention, includi-ig the best method of performing it known to me/us 5845/4 >T<ji^III Ill 111 1 I 1 ii il i n i i1 ABSTRACT OF THE DIS LOSURE A method and apparatus for dewatering an aqueous coal slurry includes imparting high shear forces to the aqueous coal slurry in the presence of a peptizing agent to render coal particles hydrophobic by stripping clay from the coal particles and peptizing the clay in the aqueous medium of the slurry. -he slurry is separati.ng to recover ccal particles and the aqueous mediumt is draining medium from the hydrophobic surface of the coal particleEs.

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METHOD AND APPARATUS FOR SEPARATING CLAY FROM AND THEN DEWATERING ULTRA FINE COAL BACKGROUND OF THE INVENTION 1. Field of the Invention: This invention relates to a method and apparatus for dewatering ultra fine coal and more particularly to dewatering an aqueous coal slurry after separating peptized clay from coal particles in a slurry thereof.

2. Description of the Prior Art: In United States patent 4,537,599 there is disclosed a process for removing sulfur and ash, particularly clay and pyrite from the surface of coal particles. A peptized slurry of coal particles is treated to separate clay and pyrite from the coal and weaken chemically bonded contaminants on the coal surface. The clay and pyrite oo. particles are dispersed as a colloid in an aqueous medium of the slurry. To maintain the colloidal Ssuspension, the pH of the slurry is adjusted by the addition of a normalizer. The slurry is then beneficated in a centrifuge and in froth-flotation cells to recover coal particles greater than two microns. Thereafter, an aqueous coal slurry is again formed and the pH is adjusted to maintain contaminants as colloids in the aqueous medium of the slurry during treatment with sonic energy and ozone. Thereafter, the aqueous coal slurry with the aqueous medium 4

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i containing colloidal contaminants is classified to again separate coal particles from contaminants., The cleaned coal product recovered from this process can be used for diverse purposes, one use as disclosed in U.S. Patent No. 4,662,894, is as a feed stock for the preparation of a coal water mixture.

The cleaned coal product is first separated so that coal particles of different size classifications form two or more coal feed streams which are delivered to separate surge vessels in a liquid medium. The feed stream comprised of coal particles having the smallest size are again classified to discard a minus two micron fraction which is comprised mainly of contaminants, particularly clay, and thereafter selected quantities of each of the coal feed streams are mixed together in the presence of a dispersing agent to form a coal-water mixture.

o It is a time consuming and costly, particularly in terms of energy requirements, to 20 reduce the water content of a mass of coal particles, particularly in instances where the coal particles after cleaning to remove clay and pyrite are to be used in the form of a feed stock having a low moisture content for any of diverse purposes such as for a 25 coal-water mix. The moisture content of the cleaned S4I>1 i c coal after classification in the centrifuge according to the process of U.S. Patent No. 4,537,599, is usually about 32% to 36% by weight and no significant moisture reduction occurs even after several days residence in storage. When an aqueous coal water slurry is dewatered in a conventional belt press, it was found that the moisture content was about 36%.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method and apparatus for economically reducing the water content of an aqueous coal slurry to a greater extent then heretofore possible without using sensible heat.

It is a further object of the present 15 invention to provide a method and apparatus for economically dewatering a mass of ultra fine coal particles by treating the coal particles as part of a aqueous slurry wherein the coal particles are rendered hydrophobic and clay contaminants stripped from the surface of the coal particles are treated so as to 4 4 flow freely from the mass of coal particles in the aqueous medium.

l It is a further object of the present 4444 448 invention to provide a method and apparatus for 4 dewatering an aqueous coal slurry wherein the slurry i3 -4is subjected to high shear forces in the presence of a peptizing agent so that hydrophllic clay particles strippe, From the coal particles are rendered readily separable with the aqueous medium from the coal particles by treatment of the iqueous coal slurry with vibratory energy which can take the form of an 'r stream to drive aqueous medium from the coal particles.

More particularly, according to the present invention, there is provided a method of treating an aqueous slurry of clay contaminated ultra fine coal particles, the method including the steps of: placing the aqueous slurry of clay contaminated ultra fine coal particles and a peptizing agent in a stripping chamber; treating the slurry by mechanically stripping clay contaminants from the surfaces of the coal particles to impart a hydrophobic property to the S coal particles and peptize the clay contaminants in the aqueous medium of 1.5 the slurry; ^o dewatering the treated slurry by using the hydrophobic property of ooo the coal particles to form a dilatant coal mass in a manner to materially increase the removal of the aqueous medium along with removal of peptized clay therewith from the coui particles of the slurry; and recovering a dilatant coal mass comprised of ultra fine coal particles from the dewatered slurry, In the apparatus of the present invention there is provided a vessel wherein coal particles in an aqueous medium are subject to high shear forces as by mixing, in the presence of a peptizing agent which 0 GSA/4Z is added to the aqueous medium in the vessel, and means for imparting vibratory energy to the aqueous coal slurry recovered from the vessel while allowing an aqueous medium to drain from the coal particles.

These features and advantages of the present invention as well as others will be more fully understood when the following description is read in light of the accompanying drawings in which: Figure 1 is a schematic illustration of one arrangement of apparatus of the present invention which is a; suitable to carry out of the method thereof; Figure 2 is a schematic illustration of a second embodiment of the apparatus of the present it 15 invention which is also suitable to carry out the method of the present invention; Figure 3 is a schematic illustration of the 9, t third embodiment of the present invention.

Figure 4 is a schematic illustration of a third embodiment of the apparatus of the present invention which is also suitable to carry out the method thereof; '4I Figure 5 is an enlarged view in section of the coal withdraw portion of a classifier included in the apparatus of Figure 4; and Figures 6, 7 and 8 are graphs illustrating the moisture reduction effect on dialant and hydrophobic coal particles according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to Figure 1, there is illustrated a mixing vessel 10 into which there is added a coal feed stock, which is indicated by reference numeral 12, the feed stock may be freshly mined coal or coal salvage from silt ponds or other suitable sources. The feed stock can be an aqueous slurry, as for example, the underflow from a static thickener or other thickening device common to the practice of coal procep-ing. Untreated ultra-fine coal may comprise the feed stock for the process and apparatus of the present invention. Such coal generally has constituent components of: coal of varying purity; high ash impure coal or bone; clay and clay shales; pyrite/marcasite; and various other high ash carbonous and non-carbonous rocks and minerals.

If desired, the feed stock can be cleaned coal particles derived from other coal cleaning process I, after treatment for removal of any hydrocarbon containment from the surfaces of coal particles that are to be peptized. Preferably the feed stock is made lii i up of coal particles typically 100 mesh or less but can be 4 mesh or less, Tyler series. The vessel also receives water, if required, which is introduced by line 14 to form an aqueous slurry in the vessel to which there is also added a peptizing agent by way of line 16. Preferably the aqueous coal slurr' contains to 35% solids by dry weight. The peptiting agent is added as one sttp in the forming of the aqueous coal slurry. Any one of a number of substances can form the peptizing agent, an example of one peptizing agent is sodium hexametaphosphate which is effective in a pH range of about 6.8 to about 8.0. Another peptizing agent which is not pH sensitive is ,fe Praestaminol which is available from Stockhausen.

15 In the forming of the peptized coal slurry, a motor 18 is energized to rotate a mixer blade O that is submerged in the tank. The mixer is operated 8000 S, for a period of time, usually at least 5 minutes under operating conditions that impart high shear forces to the coal water slurry. During the high shear 4 mixing/peptizing period, a high degree of aeration or air entrainment takes place including solubilizing of 4m air in the water of the slurry. Thus there is 4cs4*4 solubilized air in the water on the surface of the 4 25 coal particles. The application of high shear forces tl breaks the adhesion and ionic bonds which bond clay particles. The mixing of the slurry in the peptizing vessel, peptizes the clay particles and deagglomeration occurs which renders the individual coal impurities, other than clay, and clay particles into a state of discreteness. The individual clay particles fall within a typical size range of between 0.68 to 2.0 micrometers and interact with a peptizing agent to effect an ionic exchange thereby imparting to the clay particles e, strong negative electrokinetic charge. The peptized clay particles become discrete and become suspended as a colloid in the associated water of the slurry. Under these conditions, the individual coal particles attain a state of 15 discreteness from clay and other coal impurities *a released from the face surfaces of the coal particles.

444. Once free of adhered clay, the coal particles are t rerndered hydrophobic. In the event the selected 8 t i peptizing agent requires a pH adjustment to the aqueous slurry, then according to the demands of the particular peptizing agent a suitable neutralizing t* agent is introduced into the vossel to bring about the j i>m required pH adjustment.

4 t 4 i I_ The treated aqueous slurry is then discharged from the vessel 10 by line 22 to a wet screening apparatus 24 having three tandem arranged vibrating screens 26, 28 and 30 where the aqueous phase along with peptized clay particles and other undersized contaminants drain from the coal particles which remain on the screens. After the initial drainage of a predominant liquid part of the aqueous phase, the vibrating screen, imparts energy to the coal particles which are now in a state of dilatancy.

The energy causes an expulsion of surface moisture from the coal particles along with clay particles associated therewith. It can be expected that the moisture content of the overflow product will be reduced from an initial 70-75% moisture by weight down to 30-31% percent moisture content when discharged from the vibrating screens. The reduced moisture s Sontent is significantly less than the usual 40% which is obtained without peptization and attendant clay desliming.

The wet screening apparatus illustrated in Figure 1 is of the type well known in the art and made by Derrick Manufacturing Company of Buffalo, New York.

The three screen panels 26, 28 and 30 are mounted on a Sexcited by a high speed vibrating m 25 frame which is excited by a high speed vibrating motor 32. The screen panels preferably have screens having a 400 mesh (37um) size. Typically, the screen panels vibrate at 3600 cycles per minute which is a high frequency vibration having a low amplitude to rapidly expel aqueous liquid including clay, which may be still present, from the coal particles. The aqueous coal slurry is distributed across the width of the first screen panel 27 by a head box 34. The screen panels are inclined to the horizontal in a manner such that the screening surfaces extend downwardly to a terminal end where the top screen product passes to an underlying collector 36 which directs the top screen product to discharge line 38. The aqueous liquid medium, peptized clay, other undersized contaminants 0 t 15 and undersized coal particles pass through the screens and are collected in an inclined underlying tray B0 for discharge from the machine by conduit 42.

o" The solids of the underflow are ,-37um fractions which can be discarded or when dfAired the 20 residual coal content can be recovered by treatment in o 4

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0 94 o l froth flotation cells or in a high speed centrifuge.

The peptized condition of the underproduct greatly enhances the separation process by froth cells. The 0osa coal is more amenable to the action of the frothing 25 agent and the efficiency of coal recovery is improved.

B ft t i i When a high speed centrifuge is used, a cut should be made at about 2, um because the clay is predominantly contained in the um fraction. To be economical feasible the plus 2, um. of the -37 ,um fraction must be mainly coal. The burden on the centrifuge is reduced due the initial separation by the vibrating screens. In Figure 1 conduit 42 is illustrated schematically in which clay and other contaminants conducted by the conduit are discharged into a silt pond or a waste area generally indicated by reference numeral 44. The screen over product recovered from the vibrating screens is delivered by line 38 to a vibrating hopper 46 or if desired the top screen pT duct may be 'delivered first to a belt press 48.

When the coal mass is delivered by line 38 from the vibrating screens to the vibrating hopper 46, the coal particles collect in a hopper chamber wherein vibrating tubes 52 are arranged as fingers as shown in Figure 1, extending along the height of the 20 coal mass and angularly at the bottom portion to exit sites in one of two stopping bottom wall sections.

The tubes 52 are perforated and packed with long S. grained filter media. A motor 54 coupled through an eccentric 56 to vibrator frame imparts low frequency large amplitude vibration to the tubes 52. The tubes 0a 4 ii0$ 0 j e deliver liquid collected in the hopper chamber to drainage ports 58 which comr.unicate with a drain box The hopper chamber 50 has an opening in the other slopping bottom walls which communicate with a discharge chamber 62 having helical flight attachments 64 on a shaft 66 driven by a motor 68. Coal particles are carried by the flight attachments from the bottom of the hopper chamber to a discharge header box 70 for delivery by line 77. The incoming coal particles in line 38 typically have a moisture content of 30-31% by weight. After about 29 minutes treatment time in the vibrating hopper, the moisture content is reduced to 24% by weight.

Energy can be imparted to the mass of coal in the hopper chamber 50 by other means than mechanically operative vibrator device. Such other A means can take the form of perforated tubes extending to 6 6 in the coal mass in a manner similar to tubes 52. The 4 perforated tubes connected with a header by which 20 compressed air can be delivered to the tube and S'exhausted through the perforated openings to the coal mass. Such streams of compressed air permeating the S,0o coal mass transfers sufficient energy to drive moisture from the surface of the coal particles.

i 12 -i When it is desired to speed up the dewatering process, the coal particles in line 38 are first mixed with a small quantity, typically 1% ligninsolfunate by weight of coal particles in a ribbon type mixer 74 and then the admixture of coal particles and ligninsolfunate are feed to the hopper chamber 50. After about 10 minutes treatment in the vibrating hopper, the moisture content of the coal is reduced to about 24% by weight when discharged from the hopper. No further moisture reduction will occur beyond 10 minutes treatment time with the ligninsolfunate in the hopper 46. The ligninsolfunate has an affinity for carbon and therefore drives adhered moisture on the coal from the coal particle A surprising result resides in tb discov, that the removal of the clay renders the resulting coal particles particularly suitable for extruding operations to produce a product which can be more o easily handled and shipped. Ultra fine clay 4t4s 4 4 020 containing coal without dewatering including desliming, according to the present invention, cannot be extruded without a moisture reduction to below about 10% by weight and the addition of expensive lubricants and binders. The extruder is identified by <r 25 reference numeral 76.

13 The feed stream in line 38 can be fed alternatively to a chamber 78 of the belt press 48 and discharged under gravity onto a first endless belt which carries the coal Jrater burden beyond a roller 82A to a second endless belt 84. The belts 80 and 84 are sieve belts made of synthetic fiber so that liquid, p rticularly water, can freely pass from the coal particles on and between the belts on a horizontal drainage section 86 and in a roller pressing section 88B. Liquid draining from the belts isi collected in a container 90. The coal and liquid mixture between the belts entering section 88A is subject to high pressures and shearing forces as the belts pass along a tortuous path formed by rollers 88B which are connected to a suitable drive. Other rollers 88C and 88D as well as roller 88A are removably mounted to control tensioning of the belts 4S by actuators. The dewatered feed stream is discharged from between the belts at 88E. The coal mass 20 recovered from the belt press is ready for use.

4 SI The hydrophobic characteristic of the mass of recovered coal particles from the vibration hopper or belt press even without the addition of ligninsolfunate undergoes an accelerated reduction to 25 the moisture content. Upon exposure to the 1 14

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U 4.4 atmosphere, a constant rate drying period is initiated during which the surface of the coal mass is entirely wet. Evaporation takes place at whatever rate is dictated by the surrounding conditions of air temperature, humidity and replacement rate of air and coal particle moistuvro. An upward change in the temperature of the cake whether induced internally or by external means, results in an expansion of the solubilized air. This results in creation of internal pressure on the entrained moisture in capillaries and interspaces between coal particles. Net effect of this is to accelerate the capillary migration, or wicking of the internal moisture toward the surface of the coal mass and in turn, the reduction of time required for the evaporative process to be totally effective.

l The wet screening apparatus is surprisingly Seffective and produced a dramatic reduction to the 1 water content to the top screen product. Prior to the 20 present invention, it was not possib?2 to reduce the water content of a clay contaminated mass of -100 mesh (-150, um) coal particles recovered from an aqueous slurry below about 40% by weight. Moreover, a more t II surprising result is the'dramatic decrease of the ash 25 content of the various fractions of the minus -100 I[ I I44 4 1

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mesh (-150, um) screen over-product when compared with a wet sieve analysis of a pepti-ed head sample of the feed to a Derrick screen equipped to separate at a nominal 400 mesh or 37,um. The results are given in Table I.

TABLE I Weight Mesh Head Sample Tie m -um.

100X325 32.1 32.1 325X400 5,1 37.2 400X500 42.9 500 67.1 100.0 Dry Ash Over- Product Head Sample Cum. Cum.

66.0 66.0 15.9 15.9 10.6 76.6 17.2 16.1 6.0 82.6 20.3 16.6 17.4 100.0 45.6 32.1 Over- Product Cum 8.2 8.2 11.6 8.7 12.9 39.8 14.4 Wet sieve analyses show the transfer of the higher ash clay and other minus 37,u.m. impurities to the screen under product by way of the passage of the aqueous solution through the screen openings. This can be seen by comparison of the dry ash content of the screen over product fractions with those of the under product fractions. The results are given in Table II.

r t 4, 8 4' 4 4 *44 $444 .4 4 4 .4 'I 4 4 #8 4 48 I 8 4 *4 TABLE II Weight Over- Mesh Pro-uc 100X325 66.0 66.0 325X400 10.6 76.6 400X500 6.0 82.6 500 17.4 100.0 Under- Product 0.1 0.3 0.6 0.7 5.7 6.4 93.6 100.0 Dry Ash Over- 8.2 8.2 11.6 8.7 12.9 9.0 39.8 14.4 Under- 13,4 131 20.7 19.8 45.8 45.4 8.8 4 0 44

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1 r In this test the cumulative recovery of coal values in the plus 25, um fraction of the feed as calculated on an ash balance basis was found to be 99.2%.

In Figure 2 there is illustrated a further embodiment of the present invention, in which vessel like the embodiment of Figure 1, receives.; coal feedstock, water and a peptizing agent from supply lines 12, 14 and 16, respectively. The feed stock is mixed under high shear forces by motor 18, and the mixing process is carried out for a sufficient period of time to peptize clay particles which are driven from the surface of the coal particles. The mixture is delivered from the vessel 10 to a head box of a vibrating sieve bend 94 where the aqueous phase including peptized clay and undersized solids drain to a collection pan 96 from the mass of coal particles on curved screen assembly 98. The screen assembly is *r 'vibrated by drive motor 100 at a high frequency, e.g.

3600 cycles per minute at a low amplitude motion. The 20 under product including an aqueous phase is carried away by a drain line 102. The over-product from sieve bend 98 is delivered by way of a hopper collector 104 to a pug mill 106. The fraction in drain line 102 is a deliLvered to a vibrating screen assembly 108 which can 44 25 be the same as screen assembly 24 described i S117 GSA/4Z k oi¢ i II14 I" R 1 hereinbefore and shown in Figure 1. The screen overproduct is delivered by line 110 to the pug mill 106.

This arrangement of apparatus has the advantage of offering a greater residence time by the underflow in line 102 on a vibrator screen 108 so that the moisture on the face surfaces of the coal particles can be acted upon for a longer period of time as the coal particles pass along the vibrating screens. The product fed to the pug mill 106 is mixed with ligninsolfunate, a binder or other agent delivered by line 112 to the pug mill and mixed therein with the coal particles. The product discharged from the pug mill is delivered by line 114 to vibrating hopper 116.

After dewatering in hopper 116, the coal particles form into suitable extruded shapes by extruder 118 for shipment. Instead of extruder 118, if desired, the product from the vibrating hopper can be feed to a eq rotating peltatizum drum, disc or pin mixer where the coal particles are agglomerated into pellets.

In Figure 3, like the embodiments of Figures 1 and 2, vessel 10 receivee coal feedstock, water, and a peptizing agent from supply lines 12, 14 and 16, respectively. Mixing occurs under high shear force 441 conditions produced by blade 20 driven by motor 18.

its 25 The coal slurry is delivered by line 22 to a vibrating 18 4 1 screen assembly 120 which is the same as screen assembly 24. The screen under products can be discarded by line 122 and the screen over product is delivered to a pug mill 124 which includes a helical mixing blade 126. Ligninsolfunate is mixed with the coal particles in the pug mill to speed up the dewatering process. Aqueous liquid drains from the coal slurry in the pug mill by line 130. The coal particles can then be treated according to embodiments of Figures 1 and 2 downstream of assembly 24.

in the embodiment of the invention shown in Figures 4 and 5, like the embodiments of Figures 1, 2 and 3, a vessel 10 receives coal feedstock, water and peptizing agent in lines 12, 14 and 16 respectively.

The feedstock, initial pulping water and peptizing agent are introduced into the peptizing tank to produce a slurry having from 10% to 45% dry solids.

9* The slurry is mixed for a period of time, under conditions imparting high shear forces to the coal 20 particles. Usually a mixing time of at least minutes is required. Should the peptizing agent be pH sensitive, then a pH adjustment is made to the aqueous coal slurry by the addition of a suitable neutralizing agent before the addition of the peptizing agent. This is particularly true when 19 i. sodium hexametaphosphate is used. Other peptizing agents which are not pH dependent are well known and can be selected for use. As explained previously, the mixing of the slurry in the peptizing vessel, peptizes the clay particles and deagglomeration occurs which renders the individual coal impurities other than clay and clay particles into a state of discreteness. The individual clay particles fall within a typical size range of between 0.68 to 2.0 micrometers and interact with a peptizing agent to effect an ionic exchange thereby imparting to the clay particles a strong negative electrokinetic charge. The peptized clay particles become discrete and become suspended as a colloid in the associated water of the slurry.

The peptize slurry after mixing, is transferred by line 22 to a dilution tank 132 wherein the percent of dry solids making up the coal water slurry is adjusted by lowering the percent to permit unhindered settling of unpeptized particles larger than the point of classification size as well as unhindered upward migration of water, clay and such other particles of coal and associated unpeptized material that are smaller in particle size than the chosen point of classification. Typically, it is desired to adjust the solid content of the slurry with I II -cr

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the addition of water from supply line 134 whereby the dry solid content is a maximum of 10 percent but not less than 2.5 percent. Solids are kept in solution in dilution tank by means of stirring blades 136 driven by motor 138. The slurry from the dilution tank is then delivered by a flow line connected to a metering pump 140 into an upcurrent classifier 142. The point of entry in the classifier by the diluted coal water slurry is at the site of dispersion dispenser 144.

The dispenser is a generally conical member having the apex thereof directed upward whereby a slurry entering the classifier proceeds against the inter conical wall of the disperser so that the slurry rebounds and is directed toward the truncated conical bottom 146 of the upcurrent classifier. The dispenser can take the form of a rotating perforated arm driven by the *oa* velocity of the aqueous slurry exiting from the perforations.

The slurry introduction procedure provides st 20 guiding for the particles of coal to settle in the manner of a sediment. Water with peptized clay as a colloid therein along with small coal particles and other minerals of lesser size migrate to a point of 4 4t 4* classification along a reverse coarse of travel and 25 pass upwardly towards the discharge opening 148 at the

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4- 21 4 44; top of the classifier. The classifier is constructed so as to siphon off the effluent in a quiescent and controlled manner. Since the settled coal particles and non-clay mineral particles are rendered dilatant and hydrophobic in the peptization process as opposed to a non-dilatant, hydrophilic properties of clay and of a mixture of clay, coal and others associated minerals. The settled particles in the truncated conical bottom 146, of the classifier arrange themselves in a manner conducive to the exclusion of the presence of water and its accompanying peptized clay load imposed by the overlying column of liquid.

Low frequency, high amplitude vibrations, generated by a vibrator 150 driven by motor 142 are imposed on the conical bottom 146 which serves as an inducement to the resistance of the introduction of water into the settled material at the conical bottom. To eliminate ft S* the possibility of rat holing, it may be necessary in some instance- to install an inverted cone in the *0M 20 interior of the conical bottom so as to create an annular opening between the cone and conical bottom 146 of a proper width through which settled particles can pass in their downward movement towards a 4 t I, discharge conveyor screw assembly 154 wh4ich draws off quantities of coal particles from the classifier.

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As best shown in Figure 5, an upset cone 156 is fit into the interior of the conical bottom of the separator in a spaced relation from the conical bottom 146 to form angular opening between the two cones.

The width of the opening is selected so that cone particles can pass in their downward movement towards a discharge assembly 154. As the settled particles become compacted in the annular gap, free water migrates to the interface between the compacted mass and the surface of the conical bottom. Further, dewatering is achieved by a series of horizontally arranged annular rings 158 and 160 which are installed as shown in Figure 5 on the cone 156 and annular bottom 146, respectively, to interrupt the continuity of the flow path. The rings may be packed with noncorroding metal wool so as to provide an unobstructed free passage for captured water to exit at the S. ring through a portal opening in the side wall of the classifier. Each ring will produce a constant 1, 20 discharge of water from the classifier.

4 Point size of classification is a function of the vertical distance between the point of t1. dispersion/distribution and the velocity of the upward moving column of water and its load of colloidal clay and ultra fine particles. In turn, velocity is a 23 i 4 44

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function of the area dimensions of the vessel, percent of dry solids in the slurry and volumetric rate of introduction of slurry into the up-current classifying vessel. Since the characteristic of each raw feedstock and the market requirements for the end product to be recovered from it are site specific and the largest size clay platelet is smaller that 2,um, a classification point of 2,um for most coals should prove desirable. However, higher points of classification, such as 10um and even as large as um, may be found more suitable to effect the desired degree of ash reduction to be attained in the process.

Ash reduction is limited to the total of the ash of the clay minerals that can be peptized. In the majority of coals, this should be sufficient to reduce 0 the ash in the finished product to a point acceptable to the market place. Since pyrite occurs as circular 4844 platelets in all sizes in ultra-fine raw coal, all free Coto Spyrite in the peptized slurry of a finer size than the point of classification will report to the tailings and the sulfur content of the recovered product will 4 be commensurately reduced.

4" The effect of rendering the recovered particles dilatant and hydrophobic along with ~u ~I compaction through vibration allows removal of the product from the classifier at an initial moisture level of about 27 percent as compared to a moisture content of about 34 percent should the product be repulped and then dewatered in a high speed centrifuge. Recovery by centrifuging of an unpeptized -100 mesh (-150, um) feedstock produces a cake having a minimum of 40 percent moisture and more likely in the range of 50 percent to 60 percent moisture. By way of comparison, the moisture content of the underflow from an up-curreht classifier feed of an ultra-fine unpeptized raw coal slurry will rarely be less than 65 percent.

Within the initial hour after discharge from the vessel, natural drainage will eliminate all of the free water. During this period and continuing thereafter until all of the unbound water has been eliminated, the evaporation phenomenon is in effect.

For example, without thermal, assist the moisture .i content of a layer of product 1/2" to 3/4" thick will be reduced at the rate of 1.2 percent per hour until air dry equilibrium is reached.

If the product is mixed with a small amount of ligninsolfunate and then exposed to the ambient 25 atmosphere in a layer of similiar thickness without moving air, the natural evaporation phenomenon results in a reduction of the remaining unbound moisture at the rate of 3.6 percent per hour.

It is necessary to understand that ultrafine coal that has been stripped of all clay through the peptization process has entirely different physical characteristics than those of a normal coal/clay association. In addition to the dewatering phenomenon, this change in characteristics permits the reforming of ultra-fine coal into larger, more marketable forms by extrusion, pelleti.ing or pressing. Generally, this is not presently economically possible with unpeptizad ultrafine coal- In the graph of Figure 6, a drying test is demonstrated by a comparison between peptized and unpeptized centrifuge cakes about 3/4" in thickness without the addition of ligninsolfunate in a 115 degrees F forced air atmosphere. As can be seen from Figure 6, graph line 162 indicates the per cent ao reduction of moisture in a processed cake comprised of dilatant coal particles and graph line 164 show's a reduction to moisture contact of a raw cake comprised of coal particles that are not dilatant. A a dramatically increased amount of moisture is drawn a t o" 26 00 o 00 6 B from the dilatant coal particles as can be seen from a comparison of graph lines 168 and 170. The percent of the moisture content in the processed cake was found to ,-crease as shown by graph line 168 to about 2 percent within about 3 1/2 hours after processing according to the present invention. An unprocessed filter cake did rot obtain a corresponding percent moistura content until about 14 hours after treatment as shown by graph line 170.

Figure 7 illustrates, by two sets of gr&ph curves, the percent reduction to the moisture content of a peptized classifier coal product in a drying test wherein the ambient temperature was ?5 degrees F.

average in static atmospheric air. Graph line 172 shows the dramatic reduction to the percent of the moisture content in the classifier product which is mixed with one percent by weight ligninsolfunate as compared with graph line 174 which shows the percent reduction to the moisture content in the same classifier product but without the addition of ligninsolfunate. There was about a 47% moisture reduction to the treated peptized product within the 2 first five hours as compared with only about a 13% reduction during the same time period of an untreated peptized product. Similarly, the percent of moisture 27

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in the classifier product treated with ligninsolfunate dropped rapidly as can be seen by graph line 176 as compared with graph line 178 which shows the percent of moisture content of the classifier product without the addition of ligninsolfunate.

In Figure 8, the effect of heated forcea air at 360 degrees F. verses 90 degrees F. ambient still air on the moisture reduction of a peptized extruded classifier product is shown by pairs of graph lines.

In the drying test depicted by the graph lines of Figure 8, classifier product samples are treated with one percent ligninsolfunate. One sample was exposed to forced air at 350 degrees F, while another sample was exposed to'still air at 90 degrees F. ambient.

The percent reduction of moisture content in the forced air classifier product is shown by graph line 180, and it can be seen that within the first minutes, a very dramatic moisture reduction occurs as compared with the moisture reduction of the classifier 20 product in still air as shown by graph line 182. The effect on the moisture content of the classifier *44( product under forced air condition shows that within about 15 minutes as depicted by graph line 184 there 4,,4 was a percent moisture reduction that could not be 25 achieved in still air until about a lapsed time of

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q or more minutes as depicted by graph line 186. Thus, as can be clearly understood by those skilled in the art, the effect of ligninsolfunate greatly enhances the speed at which dewatering of the mass of coal particles occurs.

While the present invention has been described in connection with the preferred embodiment of the various figures, it is to be understood that other similar embodiments may be used or modifications and additions may be made to the described embodiment for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims.

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Claims

1. A method of treating clay contaminated ultra fine coal particles, said method including the steps of: forming an aqueous slurry of clay contaminated ultra fine coal particles; mechanically stripping clay contaminants from the surfaces of the coal particles while subdividing the size of the clay contaminant to clay platelets; peptizing the clay platelets to impart a state of discreetness in the aqueous slurry; collecting a mass of dilatant coal particles in a superimposed relation upon a dilatant coal layer, said dilatant coal layer being defined by forming an aqueously permeable barrier comprised of a dilatant coal layer of collected coal particles from said slurry upon a barrier; using the dilatancy of said dilatant coal mass in combination with an applied force for dewatering the coal mass by draining aqueous medium along with peptized clay platelets from the coal mass; and recovering the coal mass,

2. The method according to claim 1 wherein said step of mechanically stripping clay contaminants includes imparting high shear forces to the slurry containing the clay contaminated ultra-fine coal particles,

3. The method according to claim 2 wherein said step of mechanically stripping clay contaminants includes separating the clay contaminants from the coal particles without selective flocculation of the coal particles. 4, The method according to claim 1 wherein said step of forming an aqueously permeable barrier includes collecting coal particles from the slurry after clay contaminants are mechanically stripped from the coal surface while allowing aqueous medium along with peptized clay platelets to permeate the dilatant coal layer and form a discard fraction The method according to claim 1 wherein said step of using the dilatancy of the dilatant coal mass includes treating the coal mass with an air flow for said dewatering.

6. The method according to claim I wherein said step of using the dilatancy of the dilatant coal mass includes treating the coal mass with mechanical energy for said dewatering, 30 STA/1447h Irl i

7. The method according to claim 1 wherein said step of forming an aqueously permeable barrier includes wet screening the aqueous slurry after said step of peptizing the clay platelets.

8. The method according to claim 1 wherein said peptizing agent comprises a sufficient amount of sodium hexametaphosphate to act as a peptizing agent.

9. The method according to claim 1 wherein said step of using the dilatancy includes subjecting the dilatant coal mass to a treatment medium sufficient to effect removal of aqueous medium from the dilatant coal mass. The method according to claim 1 wherein said step of collecting a mass of dilatant coal particles includes wet screening the slurry containing peptized clay platelets to recover a screen over-product comprised of said mass of dilatant coal particles.

11. The method according to claim 1 wherein said step of forming an aqueous permeable barrier includes depositing an initial volume of aqueous slurry on an aqueously pervious support member to form said dilatant coal layer and allowing additional quantities of coal particles to collect on the barrier forming said dilatant coal mass by said step of collecting,

12. The method according to claim 11 wherein said step of using the dllatancy includes treating said dilatant coal mass in a dewatering °o chamber. 13, The method according to claim 1 wherein said step of forming an aqueously permeable barrier includes feeding the slurry including peptized clay platelets into an up-current classifier and collecting coal a particles at the bottom of said classifier and wherein said step of collecting a mass includes collectig further quantities of clay particles at the bottom of said classifier while witndrawing aqueous medium including peptized clay from the upper portions of the classifier.

14. The method according to claim 1 Including the further steps of: mixing lignosulfonate with the coal mass derived from said step of recovering; and forming an agglomerated extruded mass of coal particles after a mixture of said lignosulfonate. The method according to claim 1 wherein said step of using the dilatapcy includes impacting the dilatant coal mass with a fluid medium. 31 R STA/1447h I

16. A method for recovering ultra fine coal particles from a clay-containing aqueous slurry substantially as hereinbefore described with reference to the accompanying drawings.

17. Coal recovered by the method of any one of claims 1 to 16,

18. An apparatus for treating an aqueous slurry of clay contaminated ultra fine coal particles substantially as hereinbefore described with reference to the accompanying drawings. DATED this SEVENTEENTH day of SEPTEMBER 1991 Edward Harris Greenwald, Sr. Patent Attorneys for the Applicant SPRUSON FERGUSON S32 STA/1447h