GB2038653A

GB2038653A - Dressing Slurries

Info

Publication number: GB2038653A
Application number: GB7921970A
Authority: GB
Original assignee: Kloeckner Humboldt Deutz AG
Current assignee: Kloeckner Humboldt Deutz AG
Priority date: 1978-12-27
Filing date: 1979-06-25
Publication date: 1980-07-30
Also published as: FR2445164A1; ES478034A1; DE2856351A1; FR2445164B1; BE874315A; GB2038653B; ZA791194B

Abstract

A method of dressing slurries, more particularly coal slurries, comprises mixing the slurry with selectively acting additive (e.g. oil, oil/water emulsion) and feeding the mixture to a separating apparatus (5) for the purpose of separation into a predominantly solid phase (21) and a predominately liquid phase (22). Homogeneous mixing of the slurry with the additive is undertaken by the separating apparatus. A device for performing the method comprises the separating apparatus (5), a pump (3) for feeding slurry in a container (1) along pipes (2, 4) to the separating apparatus (5), a container (6) for the additive and a mixing element (9) in the pipe line (4). The container (6) is connected to the mixing element (9) by a supply line (7) containing a flow control valve (8). An emulsifier may be provided for emulsifying the additive. <IMAGE>

Description

SPECIFICATION A method and device for dressing slurries The invention relates to a method and a device for dressing slurries, more particularly coal slurries.

The progressive mechanisation in the extraction of coal, more particularly hard coal, and the constantly increasing demands for dressing of coal lead to an ever-increasing amount of slurry, more particularly slurries in the fine grain and very fine grain range. As the water content of products of the dressing process with a fine or very fine grain size is exceptionally high and the conventional dehydration methods and devices which have been used until now are frequently unable to bring this valuable product up to a usable quality.

A large slurry yield is produced for example when conveying the coal by pipeline. A turbid liquid with a solid content of approximately 650 g/l is normally used. In a specific example, a grain size distribution of between 3.5mm and 50 microns is present as follows: Grain size group Proportion (mm) lO/obywtJ 3.5 - 1.0 8 1.0 - 0.5 16 0.5 - 0.125 48 0.125 - 0.063 12 0.063 - 0 16 Furthermore, it is known fact that the ash content in the coal increases disporportionately as the fineness increases.For example, the following ash contents were established in hard coal from the Ruhr: Grain size Proportion Ash (mum) (O/obywt) (O/obywt) +10.0 1.1 2.1 10.0 - 6.3 4.3 2.1 6.3 - 3.15 5.9 2.7 3.15 - 1.0 23.2 3.8 1.0 - 0.5 14.0 5.5 0.5 - 0.315 11.5 10.1 0.315 - 0.125 7.9 28.6 0.125 - 0.063 7.1 12.8 0.063 - 0 25.00 28.6 The rising contents of ash in the fine and very fine grain range of the coal makes it desirable to provide a sorting process during dehydration of the fine slurry in order to prevent the quality of the dehydrated proportion of the coal as far as possible from being impaired by high proportions of ash.

A method of dressing slurries, more particularly when dressing hard coal is known whereby in the first place it is proposed that the solid contained in the slurry should be classified at a separation grain size within the limits 0.03 mm and 0.15 mm into a very fine grain range and into a coarser fraction of the slurry, after which the coarser fraction is brought into an optimum distribution of its grain size and subjected subsequently to dehydration and the fraction rich in very fine grains is supplied to an attached sorting and dehydration process while adding selectively acting flocculation and agglomeration agents.

(German Offenlegungsschrift No. 47 554). The known method provides forthe fraction of the slurry which is rich in very fine grains and has liquid hyd rocarbonsto be treated in a so-called re-moistening reactor i.e. for it to be homogenised into an intimate mixture after which the homogenised slurry/mixture of hydrocarbons is subsequently sorted and dehydrated with the aid of a separating device such as a filter or centrifuge.

The considerable technological costs of this are regarded as a disadvantage and these costs are characterized by the sequence of expensive process steps such as the classification of the grain sizes for example, subsequent setting of the optimum grain size distribution of at least one classified proportion of the material, subsequent treatment of one of the fractions with agglomeration agents by means of a re-moistening process in a separate re-moistening reactor, and finally sorting and dehydration carried out separately from these preparatory dressing steps.

The aim of the present invention is to dress large quantities of slurry to form a valuable product by means of economic measures and devices, the residual water content of the said valuable product and its proportions of ash being as low as possible in the very fine grain range. More particularly, the preparatory dressing steps are to be limited to a minimum and the expensive classification and setting of a definite grain size distribution as well as the costly use of a separate re-moistening process, are to be avoided as far as possible.

According to the invention, there is provided a method of dressing slurries, more particularly coal slurries, in which the slurry is mixed with a selectively acting additive and is fed to a separating apparatus for the purpose of of separation into a predominantly solid phase and a predominantly liquid phase, wherein homogeneous mixing of the slurry with the additive is undertaken by the separating apparatus.

The following advantages are provided by the invention: a) Omission of a separate re-moistening process and the re-moistening reactor required therefor.

b) Saving energy and wear since the turbulence in the region of the inlet chamber of the separating apparatus which acts dynamically and makes the coal hydrophobic with the additive is used for the purpose of moistening the particles of coal with hydrocarbons instead of an ag itator -- such as a turbo mixer or a high-speed homogenising mill operating with shearing forces.

c) Reducing the quantity of hydrocarbon additive added.

The separating apparatus desirably comprises a centrifuge preferably a solid sleeve sieve centrifuge.

The intimate mixing of the slurry with the additive preferably takes place in the region of the feed chamber of the centrifuge. As a result, there is the advantage that optimum homogenisation takes place as a result of utilising the high turbulence prevailing in this feed chamber without an additional separate re-moistening machine and additional energy being necessary. By completing the moisten ing process in the region of the artificial gravitational field the latter is clearly affected advantageously in a surprising manner.

According to one embodiment of the invention, the additive comprises an oil which may be mineral oil or oil waste recovered from used oils and fats.

Consequently, there is the advantagethatthe prob lem of disposing of what was previously a waste product is overcome and a product for use in the method according to the invention is obtained at lit tle or no expense because it is no longer necessary to especiallyselectthetypes of oil added as the addi tive, for example according to their viscosity, because of the exceptionally intensive moistening effect which is achieved surprisingly by the invention. For this reason the use of any desired oils obtained from waste oils and fats etc. is possible with the invention without any risk being taken.

According to another embodiment of the invention, the additive may comprise an emulsion, preferably an oil/water emulsion.

Any desired hydrocarbon can be used to manufacture the emulsion without damage to its consistency and there is no longer the necessity of heating to increase the viscosity when adding heavy bunker oils for example.

The use of an emulsion gives the advantage that it contains oil in very fine droplets whereby the distribution of this oil is promoted to an exceptional degree on the large active surface for the purpose of moistening the fine coal.

The emulsion preferably comprises an unstable or semi-stable emulsion, i.e. an emulsion with a short half-life. This has the advantage that the emulsion breaks down at the moment of contact with the solid particles into the components: water and oil, whereby oil is deposited on the oleophilic solid particles of the coal and water passes into the liquid together with the tailings. As a result the moistening and selectivity effects of the additive are optimised.

A preferred measure provides forthe emulsion to be produced with the aid of ultrasonics. The advantage of this lies in the fact that the intensity of the acoustic irradiation and the period of action can be adjusted as desired so that the stability of the emulsion can be controlled optimally with regard to operation within wide limits.

Another advantageous measure provides for an emulsifier of the same type to be used to produce the emulsion of the "water-in-oil" type.

As a further advantage provided by the invention there is the fact that a pasty consistency hydrocarbon, for example wax, fat, stearin, etc. can be used as the additive as an emulsion in liquid phase. Without the measure of emulsifying these materials there would be no opportunity of using them as an additive when dressing coal slurries. The invention was the first to be able to use pasty consistency hydrocarbons as additives, its use in a method on which the invention is based forthe purpose of dressing slurry was not previously considered possible.

A refinement of the method provides for the slurry to have a grain size between 0 and 5 mm, preferably between 0 and 1 mm.

The advantage as compared to known methods in which the grain range of the slurry must be set in the very fine grain range within narrower limits lies in the fact that the preparatory classification can be reduced to a minimum of the previous method.

Furthermore, in a surprising manner it has proved to be advantageous for a slightly more widely spread out grain spectrum to be subjected to the dehydration process whereby the residual water content is lower in comparison to known methods and moreover the agglomeration capacity of the dehydrated coal is affected in a favourable manner.

As a result of the method stages normally preceding the method of dressing coal slurry in accordance with the invention - for example a flotation stage - the slurry in the very fine grain range can lie within the limits of between 5 and 65 microns. The use of the method in accordance with the invention has proved to be exceptionally advantageous in this grain range. Another preferred sorting effect is achieved for example in this grain range so that ash contents in the predominantly liquid phase of up to 87% are achieved and considerably below the starting value in the valuable solid product.

A device for carrying out the method in accordance with the invention comprises a separating apparatus having feed means for slurry and means for the separate extraction of predominantly liquids and predominantly solids and a device for introducing an additive to the slurry.

According to one embodiment of the invention, the device for adding the additive comprises a reser voirvessel, a supply line containing a flow control valve, and a device for introducing the additive into the feed of slurry to the separating apparatus.

According to another embodiment of the invention, the device for adding the additive comprises a device for producing an emulsion, a supply line containing a flow control valve and a disperser for adding proportionate amounts of the emulsion to the slurry. The supply line desirably also contains a controllable metering pump.

The invention will now be further described, by way of example, with reference to the drawings, in which :- Figure 1 shows a block circuit diagram of a device according to the invention having a device for feeding additive into the slurry supply of the separating apparatus; and Figure 2 shows a block circuit diagram of a modified device according to Figure 1 having an additional emulsifier device.

In Figure 1 the slurry/water mixture is removed from a container 1. A removal pipe 2 with a pump 3 conveys the slurry through a supply line 4 into a separating apparatus 5. A container 6 for the additive is connected by a line 7 and a quantity control valve 8 arranged therein to the supply line 4 via a mixing element 9.

The mixing element 9 may for example be an injector which automatically aspirates, such as is known per se for introducing materials into the flow of a liquid or gaseous medium.

Slurry together with a proportion of additive arrives via the supply line 4 in the feed chamber 10 of the separating apparatus 5 and is intimately mixed together in the prevailing turbulence region and is homogenised and cross-linked. Thus the additive is distributed extremely finely and evenly over the active surface of the fine coal particles whereby the additive is deposited on the particles of coal as a result of the oleophilic properties of the coal particles. Owing to capillary forces, these particles tend to be bonded by otherveryfine coal particles into larger agglomerates which are subsequently easily and safely separated off in the gravitational field of the dynamic separating apparatus, preferably a centrifuge, from the liquid phase.The predominantly solid product is removed at 21 and the predominantly liquid is removed at 22 from the separating apparatus 5.

The arrangement according to Figure 2, in which the same parts are provided with the same reference numerals, is distinguished from the arrangement according to Figure 1 essentially by the presence of an emulsifying device. This emulsifying device comprises an emulsifying vessel 11, into which opens a supply line for water 12 having a quantity control element 13, a supply line 14 for hydrocarbon with a quantity control element 15 and a supply line 16 for emulsifiers with a quantity control element 17.

A line 18 for the emulsion having a controllable metering positive displacement pump 19 and an additional control element 20 leads from the emulsifying vessel 11 to the mixing element 9 arranged in the slurry supply line 4 and from there into the feed chamber 10 of the separating apparatus 5. The predominantly solid product is removed at 21 and the predominantly liquid at 22 from the separating apparatus 5. The invention will now be described in greater detail with reference to the following example.

Example Coal slurry was used in the grain limits between 500 and 10 microns with a solid/water ratio of 47.5 to 52.5% by volume or 55.9 to 44.1% by weight and a solid content of 665 g/l. The slurry was mixed up in a container having a capacity of 5 m3 which is equipped with an agitator for preventing sedimentation.

The slurry was then fed to a solid sieve centrifuge with the aid of a slurry pump by means of a supply line having a 3-inch diameter. Commercial oil with viscosity of 200E was passed into the centrifuge directly in front of the opening of the slurry supply from a 200-litre capacity tank with the aid of a flocculation agent pump via an exactly set throttle element and a throughflow indicator with the aid of a sepa rate conveyor line having a 1/4 inch diameter.

As a compartive test of the invention, three tests were carried out: Test No. 1 without the addition of oil, Test No. 2 with 3.5% addition of oil and Test No. 3 with 3.5% addition of oil in an aqueous emulsion.

The emulsion was produced for the purpose of the test in a separate settling container with a highspeed mixer agitator by adding 0.3% methylose from each volume part of oil and two volume parts of water at a temperature of +35C.

The results of the tests are shown in the th ree following tables: Test No. 1 without the addition of oil Grain Feed Product Liquid size (O/obywtl (%bywt) (%bywt) group (mm) Solid Ash Coal Ash Solid Ash + 500 9.5 5.0 8.5 4.4 + 250 24.7 6.7 23.9 6.1 + 125 24.2 11.3 25.8 9.0 + 63 17.2 15.9 19.6 11.8 0.1 22.3 + 45 2.3 24.6 4.6 13.6 + 38 22.1 37.9 20.3 29.1 - 38 - - - - 99.9 42.3 Test No. 2 with the addition of 3.5% oil Grain Feed Product Liquid size (%bywt) (%bywt) (%bywt) group (mum) Solid Ash Coal Ash Solid Ash + 500 9.0 5.4 5.8 4.4 + 250 25.4 6.9 21.0 6.0 + 125 21.8 12.0 27.7 8.4 + 63 19.0 14.5 29.2 9.8 + 45 3.1 14.0 5.4 10.0 0.9 18.8 + 38 21.7 40.1 10.9 24.6 - 38 - - - - 99.1 75.8 Test No. 3 with the addition of3.5% oil in emulsion Grain Feed Product Liquid size (%bywt) (%bywt) (%bywt) group (mm) Solid Ash Coal Ash Solid Ash + 500 8.6 4.8 4.4 4.0 + 250 26.1 6.8 19.6 5.7 + 125 22.8 11.6 29.6 7.9 + 63 16.0 15.6 19.6 10.2 0.6 26.8 + 45 26.5 35.9 26.5 20.1 + 38 - - - - - 38 - - - 99.4 86.9 It is shown that when dressing slurry without the addition of oil a relatively high residual proportion of ash remains in the product whereby the liquid has an ash content of 42.3%. The liquid has a dark coloration and still contains considerable proportions of very fine coal.

In test No. 2,3.5% oil is added. The ash content in the product is markedly reduced as compared to Test No. 1, as can be seen by comparing the tables.

The concentration of the ash in the liquid is significantly higher at 75.8% as compared to 42.3% without the addition of oil.

In Test No.3, another reduction in the ash content in the product can be seen by comparing the Tables.

The ash content in the liquid amounts to 86.9%, has a light grey coloration and is clearly distinguished not only from the liquid of Test No. 1, but also from the liquid of Test No. 2.

The invention is not restricted to the abovedescribed embodiments but deviations therefrom and refinements of the devices may be made without departing from the scope of invention as defined by the appended claims.

Claims

1. A method of dressing slurries, more particularly coal slurries, in which the slurry is mixed with a selectively acting additive and is fed to a separating apparatusforthe purpose of separation into a predominantly solid phase and a predominantly liquid phase, wherein homogeneous mixing of the slurry with the additive is undertaken by the separating apparatus.

2. A method according to Claim 1, wherein the separating apparatus comprises a centrifuge.

3. A method according to Claim 2, wherein the centrifuge is a solid sleeve sieve centrifuge.

4. A method according to Claim 2 or Claim 3, wherein intimate mixing of the slurry with the additive takes place in the region of the feed chamber of the centrifuge.

5. A method according to any one of Claims 1 to 4, wherein the additive comprises oil.

6. A method according to Claim 5, wherein the oil is mineral oil.

7. A method according to Claim 5, wherein the oil is oil waste recovered from used oils and fats.

8. A method according to one of Claims 1 to 4, wherein the additive comprises an emulsion.

9. A method according to Claim 8, wherein the emulsion is an oil/water emulsion.

10. A method according to Claim 8 or 9 wherein the emulsion is an unstable or semi-stable emulsion, i.e. an emulsion with a low half-life.

11. A method according to any one of Claims 8 to 10, wherein the emulsion is produced with the aid of ultrasonics.

12. A method according to any one of Claims 8 to 11, wherein an emulsifier is used in orderto produce a "water-in-oil" type of emulsion.

13. A method according to any one of Claims 1 to 4, wherein the additive comprises a pasty consistency hydrocarbon.

14. A method according to Claim 13, wherein the hydrocarbon comprises wax, fat or stearin.

15. A method according to Claim 13, or Claim 14, wherein the additive comprises an emulsion in liquid phase.

16. A method according to any preceding claim, wherein the slurry has a grain range between 0 and 5 mm.

17. A method according to any preceding claim, wherein the slurry has a grain size between 0 and 1 mm.

18. A method according to any preceding claim, wherein the slurry has a grain size between 5 and 65 microns.

19. A device for carrying out the method claimed in any one of the preceding claims, which device comprises a separating apparatus having feed means for slurry and means for the separate extrac tion of predominantly liquids and the predominantly solids and a device for adding an additive to the slurry.

20. A device according to Claim 19, wherein the device for adding the additive comprises a reservoir vessel, a supply line containing a flow control valve and a device for introducing the additive into the feed of slurry to the separating apparatus.

21. A device according to Claim 19, wherein the device for adding the additive comprises a device for producing an emulsion, a supply line containing a flow control valve and a disperser for adding prnpor- tionate amounts of the emulsion to the slurry.

22. A device according to Claim 21, wherein the supply line also contains a controllable metering pump.

23. A method of dressing slurries substantially as described herein with reference to the drawings.

24. A device for dressing slurries substantially as described herein with reference to the drawings.