GB2221856A - Coal fines recovery plant - Google Patents

Abstract

Apparatus for the preparation of particles in a slurry in accordance with their size and weight comprising interconnected cyclones and spirals in a network with input water. The ratios of dry solids to water at the respective positions in the network are preferably as indicated in Table 1 (not shown) to within an accuracy of plus or minus 10%.

Description

Coal Fines Recovery Plant The invention relates to plant for the recovery of mineral substances such as coal from slurries containing these particles in a mixture with finer particles of the mineral and particles of other and unwanted material, such as stones and clay.

In the winning of coal, it is common practice for the coal to be washed to rid it of extraneous matter so as to present the coal relatively clean and dust-free. However, the particles removed from the coal during washing, referred to as fines, contain significant quantities of coal dust, and circumstances arise in which it is economic to attempt to recover the coal from the fines.

It is known to use cyclones for the separation of slurries in accordance with the size of the solid particles contained therein and it is also known to use spiral separators for the separation of slurries according to the weight of the particles contained therein. However, both the cyclones and the spirals are theoretically capable of operation in a wide range of conditions of input and output, and the inventors have devised an arrangement of cyclones and spirals in an associated flow diagram to produce a particularly efficient separation of wanted particles from unwanted.

According to the invention there is provided apparatus for the separation of particles in a slurry in accordance with their size and weight comprising interconnected cyclones and spirals in a network with input water, wherein the ratios of dry solids to water at the respective positions in the network are as indicated in Table 1 to within an accuracy of plus or minus 10% and preferably within an accuracy of plus or minus 5%.

Preferably the ratios represent relative proportions of dry solids and water passing in an hour and preferably again the feed of slurry to the network comprises 60 tons of dry solids per hour in 440 cubic metres of water per hour.

Embodiments of the invention will now be described by way of example and with reference to the accompanying drawings of which the single figure is a flow diagram representing a plant for the separation of a slurry comprising coal fines in water so as to recover therefrom coal particles substantially free from contaminants such as stones and clay and from water.

As shown in the figure the plant comprises a network 1 comprising six 350 cm diameter cyclones arranged in parallel and represented by reference 2, four 250 cm diameter cyclones arranged in parallel and represented by reference 3 and four further 250 cm diameter cyclones arranged in parallel and represented by reference 4, a bank of ten twin-start separating spirals arranged in parallel and represented by reference 5, a further bank of eight twin-start spirals arranged in parallel and represented by reference 6 and two static sieves of 0.2 mm mesh arranged in parallel and represented by reference 7. Cyclones 2 are arranged over spirals 5, cyclones 3 are arranged over spirals 6 and cyclones 4 are arranged over sieves 7 and all are arranged over an inclined concrete surface 8 for the collection of any spillage.

Raw slurry is fed by means of pump 9 via a pipe 10 containing an automatic shut-off valve 11 to a preliminary separating unit 12 whence a refined slurry is fed into and through the network - which produces a refined slurry discharged to an output secticn 1'3 co=vriting -a 6t cm wi'de adia'i' slowing stock pile conveyor 14 terminating over a drainage slab 15.

Water is introduced into the plant from a tank 17 by means of a pump 16 acting through an automatic shut-off valve 18. The tank 17 is fed with mains water from a pipe 19 controlled by a valve 20 together with waste water returned from the network 1 via pipe 21 and after settlement in a settling tank 22.

Turning now to the preliminary separating unit 12, slurry is fed from the pipe 10 at a rate of 60 tons per hour of dry solids in 440 cubic metres of water to a feed box 23 which feeds a 1300 cm wide sieve bend 24 having a 1.5 mm mesh.

Material passing through the mesh feeds into a tank 25 whilst other material is fed into a 1500 cm x 3000 cm scalping screen 26 having a 2 mm mesh.

Water is delivered to the plant by means of the pump 16 at a rate of 141.7 cubic metres per hour, and of this volume 30 cubic metres per hour is fed to the screen 26, washing finer particles including coal fines into the tank 25 and delivering larger particles, including stones, together with some water onto a conveyor 27 terminating over and depositing its load onto a waste slab 28. Typically the discharge onto the conveyor 27 comprises 2 tons per hour of dry solids in 0.4 cubic metres of water.

The tank 25 discharges into a pipe 29 which in turn empties, together with other discharges to be described below into a feed sump 30 from which the network 1 is fed by means of pump 31.

Slurry is fed from the tank 25 in a ratio of 58.0 tons per hour of dry solids in 469.6 cubic metres of water, and the other feeds mentioned, but not described as yet in detail, augment this to an input of 62.6 tons per hour of dry solids in 559.0 cubic metres of water. A water feed pipe 32, connected back to the valve 18 also leads into the sump 30 via a valve 33, but in the preferred mode of operation no water is fed into the sump thereby.

Reference will now be made to the arrangement of units constituting the network 1 and to the ratio of dry solids to water passing along various sections of pipe leading from or into specific units of the network. The ratios are referred to in the figure by blocks carrying reference numbers prefixed by the letter R, and the values are reproduced in the Table below. Thus, for example, the feed pump 31 delivers slurry at a rate of 62.6 tons per hour in 559.0 cubic metres of water per hour, and those values are indicated in the Table against the reference R1.

The slurry delivered by pump 31 is fed to the cyclones 2, regarded in the figure for simplicity as a single unit, it being understood in relation to these cyclones and the other cyclones 3, 4, the spirals 5, 6 and the sieve 7, that the inputs mentioned represent input shared amongst all the parallel units, and the outputs represent the total outputs from all the units in the group.

By operation of the cyclones 2 the slurry fed thereto is divided into two fractions differing in respect of the particle size of the solid component. Thus a slurry comprising the larger particles and having a solids to water ratio R2 is discharged downwardly to a 20-way distributor 34 from which any overflow returns to the sump 30. The finer particles are discharged from the cyclones 2 into a separating tank 35. This slurry has a solids to water ratio R3. It will be observed that the sum of the solids in R2 and R3 aq4is th*-solid..roportioa sIPRl and.similarly the"sumQf the water proportions of R2 and R3' equals the water proportion of R1, and it is to be understood that throughout the network the various ratios are mathematically correct in this way.

Water is supplied to the network from valve 18 free, of course, of any solids content, so ratio R4 shows zero dry solids and 141.7 cubic metres of water. This quantity of water is divided into two streams 36, 37 giving ratios respectively R5 and R6. A proportion of the water of R5 is diverted along pipe 38 under control of valve 39, and the remainder, R8 is again divided, 30 cubic metres per hour of water being introduced into the screen 26 as previously mentioned and the rest, R7, entering the distributor 34.

From the tank 35, a proportion of the slurry of ratio R9 containing the larger of the particles is returned to the sump 30, whilst the larger fraction R10 in which the solids are predominently fine clay particles are discharged along with other discharges to be referred to below into effluent sump 40.

The distributor 34 distributes a slurry having a ratio R11 into the spirals 5 which together discharge the lighter solid particles (mainly coal) in a ratio R12 into a second stage sump 41, whilst the heavier particles (including stone, shale and lumps of clay) are discarded in a slurry of ratio R13 into the effluent sump 40.

The slurry entering sump 41 has a ratio R14 made up of a slurry R12 plus a slurry R15 to be described below, whilst a proportion of the water of stream 37, controlled by valve 42 and having a solid free ratio R16 also enters the sump 41.

From the sump 41 the mixed slurries are fed by means of pump 42 in a ratio R46 into the set of cyclones 3. These operate in a similar fashion to the cyclones 2 in that the larger particles are discharged in a ratio R17 to a 16-way distributor 43 whilst the smaller particles, in the form of a slime of ratio R18 are discharged into a tank 44. From the tank 44 the finest particles, predominantly of clay, are discharged in a ratio R19 into the effluent sump 40 whilst the larger particles are returned to the sump 41 in the ratio R15 already referred to.

Water from valve 39 in ratio R20 combines with the slurry R17 from cyclones 3 in the distributor 43 resulting in a feed slurry R21 entering the set of spirals 6. These operate to separate out the heavier particles in a ratio R22 which are discharged to the effluent sump 40. It will be observed that the slurries R13 and R22 combine to form the ratio R23 of unwanted particles.

The lighter particles from the spirals 6 representing ratio R24 are transferred into a product sump 45, augmented by a slurry of ratio R25 (to be referred to below) to form a combined slurry R26. A proportion of the flow 37 of water, controlled by valve 46 and representing ratio R27 is added to the product sump 45 which is discharged therefrom by pump 47 in ratio R28 to the final set of cyclones 4.

The smaller particles from cyclones 4 are discharged in ratio R29 into a tank 48 from which the very smallest particles are discharged in ratio R30 into the effluents of 40. It will be observed that the finer particle discharges from the tanks or head boxes 35, 44, and 48 combine so that R10 combines with R19 to form R31, R31 and R30 combine to form R32.

The larger particles from the head box 48 are discharged in ration R33 to the product sump 45t combining with a slnrry of ratio 34' (to be described)- to form the ratio R25" (already described).

The larger particles from the cyclones 4 are discharged in a ratio R35. Water from the stream 37, controllled by valve 49 and representing solids-free ratio R36 combine with slurry R35 to form an input slurry R37 for the static sieves 7. The finer particles are discharged from the sieves 7 in a ratio R38 into a splitter box 50 whilst the coarsest particles are discharged in a ratio R39 onto the de-watering screen 51 of 0.5 mm mesh previously referred to. A portion of the water flow 37 controlled by valve 52 and having a solids-free ratio R40 is introduced into the sieves 7 to assist the passage of material therethrough.

The slurry R39 contains most of the wanted particles of coal, but the discharge R38 may contain some useful material, so whilst half of the slurry entering the split box 50 is discharged in a ratio R39 into the effluent pump 40, a similar fraction R45 is returned to the first feed sump 30 to be recycled through the network.

The slurry R41 entering the effluent sump 40 comprises a combination of slurries R23 (already mentioned) with R42 which in turn is a combination of R32 and R45, both previously mentioned.

The effluent sump 40 is discharged by means of pump 52 along pipe 21 previously mentioned. The fluid has a large proportion of dry solids as shown by the ratio R43, but it will be understood that the solid matter is primarily unwanted matter. The liquid is fed to the tank 22 to which a flocculant is added for the purpose of precipitating the solid matter which is discharged therefrom by pump 53, whilst the supernatant liquid is added to the tank 17 as previously mentioned.

The solid matter retained by the mesh of the screen 51 is discharged onto the conveyor 14; it has a ratio R44 which is low in water, whilst the solids content is high in coal particles of largest size. The material is discharged from the conveyor 14 onto drainage slab 15 from which some of the water content drains away into a sump 52 whence it is discharged by a pump 53 to enter the feed box 23 in the preliminary treatment zone 12.

The inclined surface 8 which collects any fluids leaking from the plant, including any overflows from the sumps 41, 45 and 40, discharges to a sump 54 whence they are discharged by the pump 55 again to enter the feed box 23.

Whilst the plant described is intended to be adjusted so that the ratios of solids to water represented by R1 to R46 are expressed in tons and cubic metres respectively per hour, it is to be understood that the invention contemplates the same ratios passing in equal periods and are less than or greater than an hour. Whilst the precise figures as indicated in the table are preferred, it is within the scope of the invention that any one or more of the ratios may be varied by 5% or even 10%.

TABLE 1 Dry Solids Water (tons/hour) (cu metres per hour) R1 62.6 559.0 R2 35.8 47.8 R3 26.8 511.2 R4 - 141.7 R5 - 99.6 R6 - 42.1 R7 - 33.9 R8 - 63.9 R9 3.5 74.2 R10 23.3 437.0 R11 35.18 81.7 R12 27.0 72.9 R13 8.8 8.8 R14 32.6 211.1 R15 5.6 138.2 R16 - 22.1 R17 24.6 35.7 R18 8.0 197.5 R19 2.4 59.3 R20 - 35.7 R21 24.6 71.4 R22 6.7 6.7 R23 15.5 15.5 R24 17.9 64.7 R25 11.9 165.4 R26 29.8 230.1 R27 - 5.0 R28 29.8 235.1 R29 8.0 202.4 R30 1.2 48.7 R31 25.7 496.3 Dry Solids Water (tons/hour) (cu metres per hour) R32 26.9 545.0 R33 6.8 153.7 R34 5.1 11.7 R35 21.8 32.7 R36 - 7.5 R37 21.8 40.2 R38 2.2 30.4 R39 19.6 17.3 R40 - 7.5 R41 43.5 575.7 R42 28.0 560.2 R43 43.5 575.7 R44 14.5 5.6 R45 1.1 15.2 R46 32.6 233.2 The invention provides a novel arrangement of cyclones and spiral separators in conjunction with other items of separation equipment, and the various pumping arrangements and recycling of partially filtered slurries may or could constitute inventive aspects of this disclosure either singly or in combination, and the Applicant reserves the right to claim any aspect or combination of apparatus method which is or is shown to be a novel and inventive feature or combination in the future.

Claims (12)

1. Apparatus for the separation of particles in a slurry in accordance with their size and weight comprising interconnected cyclones and spirals in a network with input water, wherein the ratios of dry solids to water at the respective positions in the network are as indicated in Table 1 to within an accuracy of plus or minus 10%.

2. Apparatus for the separation of particles in a slurry according to Claim 1, wherein the ratios of dry solids to water at the respective positions in the network are as indicated in Table 1 to within an accuracy of plus or minus 5%.

3. Apparatus for the separation of particles in a slurry according to Claims 1 or 2, wherein the ratios represent relative proportions of dry solids and water passing in an hour.

4. Apparatus for the separation of particles in a slurry according to any one of Claims 1 - 3, wherein the feed of slurry to the network comprises 60 tons of dry solids per hour in 440 cubic metres of water per hour.

5. Apparatus for the separation of particles in a slurry according to Claim 1, substantially as herein described with reference to the accompanying drawings.

6. Apparatus for the separation of particles in a slurry in accordance with their size and weight comprising interconnected cyclones and spirals arranged in a sequence network and means for inputting water into the network and also including means for maintaining the ratios of dry solids to water at respective positions in the network within predetermined tolerances.

7. Apparatus according to Claim 6, wherein there are two or more stages each comprising cyclone spearation means followed in sequence by a spiral separator, and the stages are connected in sequence so that discharge from the spiral separator of one stage is supplied to the cyclone means of the next stage.

8. Apparatus according to Claim 7 wherein a last stage comprises cyclone means followed in sequence by a sieve separator, the output from the sieve separator is fed to a de-watering screen from whence the de-watering material is fed to a slewing stock pile conveyor.

9. Apparatus according to Claim 6, 7 or 8, wherein the apparatus comprises an input scalping screen stage from whence the discharge is fed to the first cyclone/spiral stage.

10. Apparatus according to any of Claims 4 to 9, wherein the output of each spiral of each cyclone/spiral stage is fed to a sump, and a pump supplies the material from the sump to the next cyclone/spiral stage.

11. Apparatus according to any of Claims 6 to 10, wherein the separated material from each cyclone is returned to a head box from whence separation takes place, and at least one of the separated fractions is returned to the cyclone at the same stage.

12. A method for the separation of particles in a slurry in accordance with their size and weight wherein interconnected sequentially arranged cyclones and spirals are used and wherein water is supplied to the network so as to maintain the ratios of dry solids and water at respective positions in the network within predetermined limits.