CA1325067C - Method of removing pyritic sulphur from coal - Google Patents

Abstract

TITLE
"A Method of Removing Pyritic Sulphur from Coal"

INVENTORS
Richard D. Coleman Serge Croteau Charles E. Capes ABSTRACT OF DISCLOSURE
Pyritic sulphur is removed from coal by mixing agglomerating oil with a slurry of the coal containing discrete particles of carbonaceous material and pyritic sulphur, and other mineral matter that may be present, the oil being added in an amount less than about 3 wt % of the total solids present in the slurry, and then micro-agglomerating the carbonaceous particles. Pyritic sulphur, while showing a tendency to be hydrophobic, and having an affinity for the agglomerating oil, is weaker in either of these properties than carbonaceous coal, and so by adding a starving amount of agglomerating oil it preferentially agglomerates the carbonaceous particles leaving pyritic sulphur and mineral matter that may be present as discrete particles in the water. Aeration/skimming of the micro-agglomerates is then carried out. The skimmed micro- agglomerates are washed in water in low speed mixers to release weakly clinging pyritic sulphur from them, and then aeration/skimmed from the washing water, newly released pyritic sulphur and any other newly released inorganic substances.

Description

- 132S067 `:
1 This invention relates to a method of removlng pyritic sulphur from coal.
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It has already been proposed in Unlted States Patent No. 4,284,413, dated August 18, 1981, "In-Line Method fot the Beneficiation of Coal and the Formation of A Coal-In-Oil Combustible Fuel Therefrom", C.E. Capes et al, to provide an in-line method for the beneficlation of coal and the formulation of a coal-ln-oll combustible fuel whereln the coal is wet pulverized, micro-agglomerated with light oil to di~sociate a large amount of inorganic lmpurltles and some water, agglomerated with heavy oil to form relatively larger agglomerates and dissociate mainly water with some inorganic impurities, and then mixed wlth further heavy oil to form the coal-in-oll combustlble fuel.
~, It has already been proposed in United States Patent NoO 3,655,066, dated May 23, 1972, Beneficlation of Coals", C.E. Capes et al, to add a brldglng llquid to an aqueous, clay contalning slurry of coal flnes, then agltate the resultant mixture to form coal 2gglomerates dispersed in a slurry of the resldual clay and ash impuritlesl and then ~;
separate the coal agglomerates by sklmming them through an overflow spout in a float-slnk tank. The separation of the coal agglomerates may be assisted by introducing a multltude of air bubbles at the bottom of the float sink tank.
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It h2s ~lso been proposed in Brltish Patent Appllcatlon No. 2,143,155A, published Feb. 6, 1985, "A Method of Separating Fine Coal Particles from Refuse", G.A. Wasson et al, to separate flne coal partlcles from refuse by mlxing oll and water with a coal-refuse solids mixture ~;~
., , ";

:' '' ", at hlgh shear agitatlon conditlons, to form a floccular mlxture comprislng flocs of oil and fLne coal partlcles and unflocculated refu~e ln water, floatlng the flocs in a flotation means, and separatlng the flocs of oll and coal partlcles from a substantlal portlon of the water.

It has also been proposed ln Unlted States Patent y No. 4,272,250, dated June 9, 1981, "Process for Removal of Sulphur and Ash from Coal", E.H. Burk, Jr., to reduce the sulphur and ash content of coal particles by addlng a mlnor amount of hydrocarbon oil to an aqueou9 slurry 10of the coal partlcles to effect aggregatlon of the coal particles lnto coal-oil aggregates (flocs) wlth gas (air) lncorporated lnto or on the -aggregates to modlfy thelr density, then gravitatlonally separatlng the aggregates and recoverlng them with a reduced sulfur content. The aggregatlon and the lncorporatlon of air may be effected slmultaneously, .:
15and a partlal separatlon of the denslty modlfied coal/oil aggregrates from the slurry, as by sklmmlng, screenlng may be effected (column 11, llnes 10 - 18) but further processing (centrlfugal separation~ 18 customarlly requlred to recover the carbon heatlng values. The resultlng ` ~;
coal product can exhlblt a diminished non-pyritic sulphur content:

20 for example, ln some coals up to 30X by welght of nos~-pyrltlc sulphur may be removed. Addltios~ally, reduction in ash content is typically from about 20 to 80 wt ~, or even hlgher, aod pyrltic sulphur reduCtion 18 -~
typlcally from abou~ 40 to 90 wt X or even hlgher. ~ ;

~urk, Jr., et al., column 12, llnes 65 - 68, teache~ that the recovered coal partlcle~ may be sub~ected to further treatment. The only treatmer~t of the coal-oll flocY taught by Burk, Jr., et al 18 by washing ~ ;~
them ~ith a llght oil, see column 12, lines 56 - 59, and thls will produce -~
a coal-oll slurry conta~lng any ~mpurltles present in the flocs.

132~0~7 I While the process of E.H. Burk, Jr., et al has proved to be useful~ a problem still exists in that pyritic sulphur partlcles present in the coal slurry also absorb agglomeratlng oil and tend to be agglomerated or flocculated wlth the carbonaceous psrtlcles of t~e coal, and so are difficult to separate, see for example, "Coal Desulfurlzatlon", ACS Symposium Series 64, American Chemical Society, 1977.

Applicants have found that, - . ,,.` .
i) a consistently much better sulphur reductlon 18 obtalned lf '~.
micro-agglomerates are formed ln flrst mixing means with very little agglomeratlng oil, the micro-agglomerates are aerated in a first aeratlng tank to render them buoyant and .
are then skimmed from the other slurry components, and ii) even wlth step 1) there is undesirably large carry over of pyritic sulphur particles that are weakly attached to .
the micro-agglomerates and that, wlth no further additlon -:
of agglomerating oil, a dramatlc reduction of the pyritlc sulphur content can be consistently obtained if the skimmed micro-agglomerates are mixed in a second mlxer with ~ :
wa~hing water to form a dense slurry of washed micro- : -agglomerates which may readily be aerated in a second -~
aerating tank and then skimmed from the washing water. ~ .

According to the present invention there is provided a method of removing pyritic sulphur from carbonaceous coal, comprising; . -132~067 a) violently mixing, in a first mixing means, an agglomerating oil with an :
aqueous slurry of the coal, the slurry comprising water, liberated carbonaceous particles of the coal, liberated surface conditioning agent additive free pyritic sulphur particles, and liberated particles of any other inorganic substances present in the coal, the agglomerating oil being mixed in an amount less than about 3 wt % of the total solids present in the slurry : .
measured on a dry basis, : .
~ .
(b) continuing the violent mixing in the first mixing means until open : .
structured, chain-like micro-agglomerates are formed in the slurry consisting predominantly of carbonaceous particles of the coal and agglomerating oil, `
with predominant amounts of the surface conditioning agent additive free :
pyritic sulphur and any other inorganic substances present remaining -separated from the agglomerates in the water, ~

(c) removing the slurry from the first mixing means, : :

Id) aerating the slurry in a first aerating means to render the micro~
agglomerates buoyant in the water, ~ ~
:
(e) skimming the buoyant micro-agglomerates from the water, ;~ , (f) mixing washing water with the skimmed micro-agglomerates in a ~ -second mixing means to produce, using only the agglomerating oil already ` .
present, a dense slurry of washed micro-agglomerates with newly released -.
pyritic sulphur separated therefrom and present in the washing water, (g) removing the dense slurry from the second mixing means, -~h~ aerating the dense slurry in a second aerating means to render the washed micro-agglomerates buoyant, and " :;: -1) separating the washed, buoyant, micro-agglomerates from the washing water ln the second aeratlng mean6.

In thls patent speclfication, llberated carbonaceous partlcles 5 of the coal includes wholly carbonaceous particles, and carbonaceous partlcles contalnlng some lnorganic substances.

The amount of agglomerating oil added to the aqueous slurry may be less than about 1.5 wt X of the total welght of the sollts present ln 10 the slurry measured on a dry basls.
, - :. :, A frothing agent may be added to the slurry, in an amount in the range of about Q.0025 to 0.05 wt X of the total weight of the solids content of the slurry, before the micro-agglomerates are formed.
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The amount of agglomerating oil added may be less than about 1 wt X, and a frothing agent may be added to the slurry, in an amount in the ran~e of about 0.0025 to O.OS wt X, based on the total weight of the sollds content of the slurry.

In other eDIbodiments of the preseDt lnventlon the vlolent mixing 15 carried out in at least one high shear mixer, and the open-structured, chaln-like micro-agglomerates are broken down and reformed into open-structured, chaln-like micro-agglomerates in at least one relatively 25 low shear mlxer, bPfore being aerated, to separate further water from the agglomerates.

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~ -` 132~0~7 1 In yet other embodlments of the present invention, af~er being ~kinmled from the washing water, the washed, buoyant micro-agglomerates are mixed with further agglomerating oil, broken down and reformed into relatLvely larger agglomerates to release water and are then separated 5 from the released water. :~

In the accompanying drawings which illustrate, by way of ~-example, embodlments of the present invention, Flgure I ls a photograph of 8 typlcal mlcro-agglomerate containing slurry that was obtained in tests that were carrled out to verify the present invention, :.'" .
Figure 2 is 8 graph of results from the test~ showing the wt X
of carbonaceous coal (CC ~) recovered, based on the carbonaceous content of the origlnal slurry, plotted against the wt X of agglomerating oil (A0 %) used, based on the total solids content of the original slurry, :~

Flgure 3 is a graph of results from the tests showing the wt X
of pyritlc sulphur (PS ~) separated, of that prese~t in the orlginal slurry, plotted agalnst the same wt % of agglomeratlng oll (A0 ~) given in Flgure 2, : ~:

Figure 4 i8 a flow diagram of an apparatus for removlng pyritic 25 sulphur from carbonaceous coal, and :: :~
" ' Flgure 5 is a graph of test results, using an apparatus genPrally of the type shown in Figure 4, wherein the equivalent l~bs. of ~

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132~067 l sulphur dioxlde in the treated coal that would be generated on burning the coal, based on the thermal value of the coal content (S02) ls plotted against the wt% ash present (WA%) ln the micro-agglomerates.

In tests to verify the present inventlon a coal slurry of coal fines from Prince Mine, Cape Breton Island, Nova Scotla, Canata, was used.
The coal slurry was taken from the feed to a conventional f~lotation recovery circuit in use at the mine and consequently had a hlgh pyritlc ~ i sulphur content. The coal slurry also had a hlgh clay content, which ~ormally affects both froth flotation and oll agglomeration, and does not respond favourably to froth flotation. Tbe agglomeratlng oll used was No.
4 fuel oil.
' "' In these tests, a laboratory blender was used to mix the slurry with different amounts of agglomerating oll and form micro-agglomerates. i~
Initially the laboratory blender mlxed the slurry ant the agglomeratlng oil at high speed for 30 seconds followed by 2 minutes of lower speed mlxing for agglomerate growth.

Figure 1 18 a photograph oi a typical ~lurry contalnlng micro-agglomerates that wss obtained by tbe tests, The micro-agglomerates of the slurry shown ln Figure 1 are clearly open structured, chaln-llke micro-agglomerates. .
~ ~
The slurries obtained were treated in dlfferent ways to remove the m$cro-agglomerates from them, and the re ved micro-agglomerates were 13250~7 l waslled and analyzed for the wt X carbonaceous coal content (CCZ) and the wt ~ pyrieic sulphur separated from them (PS %) in relation to the wt % of agglomerating oil (A0 %) used based on the total sollds content of the slurry.

In Figure 2, the te~t results for the wt ~ carbonaceous coal content obtained ln the microagglomerates (CC %), based on~the carbonaceos content of the origlnal ~lurry, are plotted graphically against the wt Z
of agglomerating oil (A0 %) used.

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In Figure 3, the test results for the wt X pyrltic sulphur separated from the micro-agglomerates are plotted graphically against the wt Z of agglomerating oil (A0 X) used. In both of the Figures 2 and 3, 0 represents screening the micro-agglomerates from the slurry and then washing them wlth water, 0 represents aeratlng the slurry to render the micro-agglomerates buoyant, s~imming the buoya~t micro-Z0 agglomerates from the surface of the slurry and then wsshlng them with water, and -~

represents the same treatment as thst designated 0 except that a frothing ag~nt marketed under the trademark "Aerofroth" by Cyanamid Csnads Ltd., Mcntreal, Conads, was ;-mixed w~th the slurry before the micro-agglomerates were formed. The amount of frothing agent added was about 0.05 wt ~ of the total weight of the sollds.
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1325~7 I In all cases the skimmed micro-agglomerates were washed with water by mixing them with washing water to produce a dense slurry of washed mlcro-agglomerates, with newly released pyritic sulphur separated therefrom and present ln the washing water, and then separatlng the wa~hed micro-agglomerates by aeration/skimming them from the washing water and newly released pyritic sulphur.

It will be seen from the Figures 2 and 3 that using the screen recovery represented by ~ , required the addition of about 4 wt X
agglomerating oil, ln order to obtain washed micro-agglomerates with a high carbonaceous content (CC Z) yield. Under these condltlons, as shown in Figure 3 the pyrltic sulphur (PS %) separated from the micro-agglomerates is less than 40 wt X. In contrast, when less tha~ about 3 wt X agglomerating oil was used and the aeration/skimmed micro-agglomerates recovered were washed as represented by 0 or ~ , in accordance with the present inve~tion, a negligible 1088 in the carbonaceous content (CC X) is ~ :
incurred while the separation of pyrltic sulphur (PS X) dramatically increased to at least about 70 wt Z. .:

Figures 2 and 3 also show that even better results are conslstently obtained, by the processes designated 0 or ~ , when less than about 1.5 wt X of agglomerating oil was used in tbat at least about 88X ~;
micro-agglomerates carbonaceous content was obtained with a pyritic sulphur separatio~ (PS %) consistently of at least about 80%. Better still, lf the frother is added in the process designated- , the amount of agglomeratiqg oil can be reduced to less than about 1 wt % and a micro-agglomerate content (CC X) of at least about 88 wt Z consistently obtained with at least about 80 wt X pyritic sulphur separation (PS X) _ g _ - ,' ': '' ', ~: : ' ' - . :::

13250~7 ~

1 consLstently obtained. More recent tests have shown that similar results can be consistently obtalned with the frothlng agent being added to the slurry in amount in the range of about 0.0025 to 0.5 wt X of the total solid6 content of the slurry, before the micro-agglomerates are formed, aeration/skimmed and washed. Consistently obtained means that the results are not only repeatedly obtained for more or less identical tests, but under suitable conditions, can consistently be obtalned for other coals.

These results are surprislng ln ~lew of the high clay content of the slurry.

The test results suggested that although pyrltic sulphur tends to be hydrophobic and have an affinlty for the agglomeratlng oll in the --same manner as carbonaceous coal, the hydrophobicity and affinlty for oil of the pyrltic sulphur are weaker than they are for carbonaceous coal.
Thus by adding less than about 3 wt X of agglomerating oil, based on the total weight of the solids content of the slurry, the system i~ starved of agglomerating oil to such an extent that only sufflclent 18 present to preferentially be adsorbed by the carbonaceous coal and to form micro-agg~omerates therewith. The amount of agglomerstlng oil added beingsufficient only for the formulation of micro-agglomerates. Thus a ma~or . .
portiGn of the pyritic sulphur present in the slurry remains ln the form of discrete particles which are separable in two steps from the micro-agglomerates, i) by the aeratlon/sklmming separation of the micro-25 agglomerates from pyritic sulphur in the slurry, followed by, ~ ~ ;
ii) wa6hing to separate the micro-agglomerates from further pyritic sulphur that is weakly attached to the micro-agglomerate~, and ae~ation - ;~
skimmlag the washed micro-agglomerates from the washlng water and the -,:: . -urther pyritic sulphur.
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13250~7 1 It should be pointed out, that adding less than about 3 wt ~ of agglomerating oil in accordance with the present invention is far less than the conventi~nal amount of at least 5 wt ~ used which produces conventional, relatively larger agglomerates containing a substsntial portion of the pyritic sulphur. It should also be noted that it i8 not possible with the applicants very low addition of less than about 3 wt of agg10merating oil to produce anything othe than open structured, chain-like mlcro-agglomerates a typical example of which is shown ln Figure 1.

While lt is true as a general statement to say that le6s than about 3 wt % of agglomerating oil should be added, it should be borne in mind that, in practice, the actual amount of agglomerating oil that is added, while being less than about 3 wt %, depends on the type of oil used ;~
and the type and conditioD of the coal being treated. Furthermore the amount of agglomerating oil is not the only parameter which determlnes whether micro-agglomerates are formed because this, among other things needs to be ad~usted depeDding on the nature of the coal surfsce (for example, has it been oxidized or not), the particle si2ie, the compatibility of the type of oil used with the type of carboDaceous coal being agglomerated, the magnitude of, and the time for, the violent mixing that is used. Thus the amount of agglomeratlng oil used in any particular test will not necessarily be the same as that required for another test.
, ,.

No. 2 fuel oil has also been used~with good results in similar tests to those given above.

Tu m ing now to Figure 4, there i8 shown a flow dlagram of a large scale method of removing pyritic sulphur from carboDaceous coal.

~.-,-', ~3250~7 In Figure 4 there is generally shown a method of removing pyritic sulphur from carbonaceous coal, comprising:
:"
~a) violently mixing, in a first mixing means comprising high shear mixers 1 to 3, an agglomerating oil with an aqueous slurry of the coal, the slurry comprising water, liberated carbonaceous particles of the coal, liberated .
surface conditioning agent additive free pyritic sulphur particles of the coal, ;~
and li~arated particles of any other inorganic substances present in the coal, the agglomerating oil being mixed in an amount. Iess than about 3 wt % of ; :the total solids present in the slurry measured on a dry basis, ~ ~ : ,' (b) continuing the violent mixing in the high speèd mixers 1 to 3 until m open structured, chain-like micro-agglomerates are formed comprising ~ .
carbonaceous particles of the coal and agglomerating oil with amounts of ~:
the surface conditioning additive free pyritic sulphur and any other inorganic ~ ~
substances present remaining separated from the agglomerates in the water, . ~ -(c) removing the slurry from the high speed mixers, ~ ~.
'.",.
~d) aeratin~ the slurry in a first aerating means, in the form of an aeration ~ :
tank 4, to render the micro-agglomerates buoyant in the water, (e~ skimming the buoyant micro-agglomerates from the water in the :
aeration tank 4 by means of a skimmer belt 6, - - .

12 .
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l f) mixing washing water wlth the skimmed micro-agglomerates in a second mixing means comprising two relatively low JY
shear mixers 8 and 10 to produce, using~t~e agglomerating oil already present, a dense slurry of washed micro-agglomerates with newly released pyritic sulphur separated therefrom and present in the washing water, g) removing the dense slurry from the second mlxing means, ~ ~
~ ' h) aerating the deDse slurry in a second aerating meaDs comprising aeration tank 14 to render the washed micro-agglomerates buoyant, and i) separating the washed, buoyant, micro-agglomerate6, by means of a skimmer belt 12 from the washlng water in the :~
aeration tank 14.

The aqueous slurry of coal ls fed from a ~upply 18 where any rea~ents such as frother~ or condltions are added, if requlred whlle the : :
:,, agglomerating oil is fed along a feed line 20.

The high shear mixers 1 to 3 are preferably of the type described and claimed in U~ited States Patent No, 4,610,547, dated Septem~er 9, 1986, Apparatus For Disperslon A Particulate Material In A - :
Liquid , Bennett et al, wherein, as shown in that patent, the slurry passes upwardly through a cylindrical container passed a lower, flat impeller blade type turbine rotor, an intermedlate knife impeller blade 132~067 l type turbine rotor and an upper pitched impeller blade type turbine rotor.
As previously stated, micro-agglomerates of carbonaceous coal particle are aggLomerated from the coal slurry in the relatively high shear, impeller blades 1 to 3.

~ n this embodiment the micro-agglomerates, water and pyritic sulphur together with any other inorganic impurities originally present in the coal slurry are passed to two relatively low shear, impeller blade mixers 22 and 24 each having four, radial flow, flat impeller blades, two of which are show~ aad designated 26, 28 and 30 and 32, respectively. The relatively low shear, impeller blade mixers 22 and 24 are each provided wlth four baffles, two of which are showa for each mixer 22 and 24 and deslgnated 34, 36 and 38 and 40, respectively. The baffles, such as those designated 34, 35 and 38, 40, reduce any flow around the lmpeller blade -shaft, caused by the flat impeller blades such as those desigaated 26, 2B
and 30 and 32, of the micro-agglomerates, water and pyritic sulphur together with any other inorganic lmpurltles present 80 that the --predomlnant flow is radially outwardly rom the lmpeller blates such as -those designated 26, 28 and 30, and 32, and tben lnwardly rebounding along curved paths over and under the impeller blades, such as those designated 26, 28 and 30 and 32, generally towards a central point between them. The b~ffles such a~ those designated 34, 36 and 38, 40 are spaced from the containers in whlch they are situated to avoid the formation of ~tagnant arPas between the baffles, such as those desigaated 34, 36 and 38 and 40 and their re~pectlve containers.
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While not essential, the relatively low shear mixers 12 and 14 promo~2 further gr~wth of open structured, chain-like micro-agglomerates , '-~' 132~067 1 and help to release further pyritic sulphur particles and other inorganic impurities present together with water. As previously stated, the low amount of agglomerating oil that has been added is ~ot sufficlent for relatlvely larger, more robust agglomerates to be formed even in the relatively low shear mixers 12 and 14.
:' The mlcro-agglomerates that are skimmed by a skimmer belt 6 are passed, together with washing water along feed line 42, to the two relatively low shear impeller blade mixers 8 and 10, which are 8imilar to the low speed mixers 22 and 24, where the micro-agglomerates are washed to separate weakly attached pyritic sulphur from them and produce a dense slurry of washed micro-agglomerates with newly released pyrltic s~ulphur separated therefrom.

The washed micro-agglomerstes are separated from the newly released pyrltic sulphur, any other newly released inorganics and washing water by the aeration tank 14 and skimmer belt 12.

Preferably the washed micro-agglomerates that are skimmed by the ~immer belt 12 are passed to two relatively low shear impeller blade mlxers 44 and 46, whlch are similar to the low speed mixers 8, 10, 22 and 24, where the washed micro-agglomerates are broken-down with additional agglomerating oil and formed into an aqueous slurry containlng relatively ~-larger agglomerates. This has the advant~ge that further water i8 separated f}om the carbonaceous material. A balling disc, paddle mixer, or other means of size enlargement, may be used in place of the low speed mixer~ 44 and 46.

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13250~7 1 The aqueou~ slurry is then passed to an aeration tank 48 where -~
the relatively larger agglomerates are aerated and rendered buoyant, and then skimmed from the water by skimmer belt 50.
: ' - -. .' The relatively larger agglomerates are passed from the aeratlon tank 48 to a separator, in this embodiment a screen bowl type separator 52, to be dewatered and then deposited on a conveyor belt 54 for storage - ~
or further treatment. ~ ~-' ', . ~' ~
The separated water from the aeration tanks 4, 14 and 48, containing pyritic sulphur together with any other inorganic impurlties originally present in the coal, is passed to a separator, in this ~ --embodiment a solid bowl separator 56, where the inorganlc impurities are d2watered and passed to a conveyor 58 for disposal.
In further tests to verlfy the present invention, using a pilot plant generally described with reference to ~igure 4, a thlckened, aqueous mlxture of coal fines, from a coal washlng plant located ln Union County, ~entucky, U.S.A., was processed. The aqueous mixture of coal fines had an 20 lnitial equlYa~ent sulphur content of 10 lbs of sulphur dioxide per h million B.T.U.'s, and contalned 50 wt X of ash on a dry basis.

The results of these tests are ~hown graphically in ~igure 5, where the total ~ulphur content of the washed micro-agglomerates, in terms 25 of the equivalent lbs of sulphur dioxide (SO2), that would be generated on burining the coal, per million B.T.U.'s is plotted against the weight a~n (WA ~), dry basis, present in the washed agglomerates.

13250~7 ~
1 In Figure 5, represents screened micro-agglomerates with no wash, represents screened micro-agglomerates whlch were washed and screened once more, represent~ micro-agglomeratea whlch were aerated and skimmed by means of a skimmer belt, but were not washed, and ~0 :,, represent~ micro-agglomerates whlch were aerated and skimmed by means of a sklmmer belt, and then washed and recovered ;~
according to the present invention. :;

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It will be seen that using the present lnventlon there was a dramatlc reduction in the sulphur content of the micro-agglomerates as ~:
well as a dramatic reduction in the ash content.

The micro-agglomerate~ produced ln the tests, using an 2pparatus .
generally of the type shown ln Flgure 4, were open structured, chaln-llke mlcro-agglomerates of the type shown ln Plgure 1.
:
In co-pending Canadian patent Applicatlon No. 543,310 , flled July 29, 1987, 'A Method of Separatlng Carbonaceous Coal From An Aqueous Co~l Sturry , Capes et al, there is descrlbed a process compriolng flrst agglomeratlng carbonaceous coal with agglomeratlng oll to form open ~tructured, chain-like, micro-agglomerates and then form relatlvely ::
' ''' 132~0~7 ~:
l larger, less open structured more robust agglomerates to provlde a mixture of both types of agglomerates. The relatively larger agglomerates may be screen separated while the micro-agglomerates are rendered buoyant by aeration and then skimmed from the water and inorganic particles.~ In the :~ .
tests carried out for this process, about 5 or 8 wt % agglomerating oil was used based on the total weight of the solids content of the slurry, and, as shown in the Figures 2 and 3, the addition of o~ly~4 wt X ~-agglomerating oil i~ sufficlent to reduce the pyrltic sulphur to less than ~`:
40%. From this it will be see~ that this Capes et al process will not 10 give a high separation of pyritic sulphur. :.
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Claims (5)

1. A method of removing pyritic sulphur from carbonaceous coal, comprising:

a) violently mixing, in a first mixing means, an agglomerating oil with an aqueous slurry of the coal, the slurry comprising water, liberated carbonaceous particles of the coal, liberated surface conditioning agent additive-free pyritic sulphur particles of the coal, and liberated particles of any other inorganic substances present in the coal, the agglomerating oil being mixed in an amount less than about 3 wt % of the total solids present in the slurry measured on a dry basis, said amount being only sufficient to be preferentially absorbed by the carbonaceous coal.

b) continuing the violent mixing in the first mixing means until open structured, chain-like micro-agglomerates are formed comprising carbonaceous particles of the coal and agglomerating oil, with predominant amount of the surface conditioning agent additive-free pyritic sulphur and any other inorganic substances present remaining separated from the agglomerates in the water, c) removing the slurry from the first mixing means, d) aerating the slurry in a first aerating means to render the micro-agglomerates buoyant in the water, e) skimming the buoyant micro-agglomerates from the water, f) mixing washing water with the skimmed micro-agglomerates in a second mixing means to produce, using only the agglomerating oil already present, a dense slurry of washed micro-agglomerates with newly released pyritic sulphur separated therefrom and present in the washing water, g) removing the dense slurry from the second mixing means, h) aerating the dense slurry in a second aerating means to render the washed micro-agglomerates buoyant, and i) separating the washed, buoyant, micro-agglomerates from the washing water in the second aerating means.

2. A method according to claim 1, wherein the amount of agglomerating oil added to the aqueous slurry is less than about 1.5 wt % of the total weight of the solids present in the slurry measured on a dry basis.

3. A method according to claim 1, wherein a frothing agent is added to the slurry, in an amount in the range of about 0.0025 to 0.05 wt % of the total weight of the solids content of the slurry, before the micro-agglomerates are formed.

4. A method according to claim 1, wherein the violent mixing is carried out in at least one high shear mixer, and the open structured, chain-like micro-agglomerates are broken down and reformed into open-structured, chain-like agglomerates in at least one relatively low shear mixer before being aerated.

5. A method according to claim 1, wherein, after being skimmed from the washing water, the washed, buoyant micro-agglomerates are mixed with further agglomerating oil, broken down and reformed into relatively larger agglomerates to release further water and then separated from the released water.