GB2331257A

GB2331257A - A mineral separation process

Info

Publication number: GB2331257A
Application number: GB9805163A
Authority: GB
Inventors: John Mcculloch; Heinz Holter
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-11-17
Filing date: 1998-03-12
Publication date: 1999-05-19
Also published as: GB9805163D0; GB9724232D0; GB2331257A9

Abstract

A process for mineral separation employs a cylindrical separation vessel 1 having an axial inlet 6 for raw material feed, an involute inlet 2 for separating medium which induces vortical flow within the vessel, an axial outlet 4 for low density material and an outlet 8 for high density material. To optimise the process, the pressure of the separation is monitored and is used to control the feed rate of the separation medium into the vessel. The process is particularly useful for the separation of fractions of coal from a process stream of coal containing fractions of differing densities.

Description

1 2331257 IMPROVEMENTS IN OR RELATING TO MINERAL SEPARATION This invention

is concerned with improvements in or relating to mineral processing techniques.

In particular the invention has reference to a method of controlling the separation of mineral particles of different densities using a carrier fluid eg a dense medium, and also has reference to apparatus for use in such a method.

The present invention has especial, although not exclusive, reference to the separation of fractions of coal from a process stream of coal containing fractions of differing densities.

Cyclonic separation techniques have long been known in the field of mineral processing and the forces acting with the conventional cyclone have been well documented. The conventional cyclone essentially comprises a cylindrical inlet section with a tangential feed and an axial outlet through the vortex finder tube, the inlet section leading to a frustoconical section with an outlet nozzle. The principal force within the cyclone during its operation is centrifugal force which varies considerably between the central region where it far exceeds that obtaining adjacent the cyclone wall. There are essentially four flow patterns within an operating cyclone. The first flow pattern generated within the cyclone is rotational as the stream of solid fluid, eg liquid, matrix is introduced tangentially to the inlet section around the vortex finder tube. The second is downward as the medium flows down the wall and discharges through the outlet nozzle, and the third is upward as medium flows upwards, following the central air column, and discharges at the top of the vessel. The fourth flow pattern is inward since the medium must pass to the centre of the cyclone for the flow to exhaust either at the top or the bottom.

The efficacy of the separation mechanism is of prime importance and in large measure is driven by market requirements. Accordingly there is a clear need for. the capacity to control the separation thereby to ensure that it is both efficient and satisfies the demands from the market in terms of product quality consistently. The operating parameters are crucial to the achievement of this end and whilst the conventional cyclone is effective in principle, the degree to which its operation characteristics can be modified is limited.

2 One type of alternative separating vessel to the conventional cyclone is that disclosed in British Patents Nos 2 147 831, 2 199 518, which consists of a cylindrical vessel having its axis angularly orientated at between 20' and 30' to the horizontal. The vessel has two inlets, one axial inlet for raw mineral feed, and a second involute inlet for a separating medium, there being an axial outlet adjacent the medium inlet for the low density fractions and an involute outlet for the high density fractions. A vortical extractor unit is connected to the involute outlet for extraction of the high density materials through a large outlet under controlled flow with a minimum of separating medium. The low density mineral basically remains axially within the vessel and discharges through the axial outlet. It will thus be seen that this alternative separating vessel operates in distinctly different manner from the conventional cyclone in which latter the separating medium and the mineral flow together into the cyclone, whereas in clear contradistinction the improved and alternative vessel, known by the Registered Trade Mark 'LARCOIDEMS', provides for the discrete flows of mineral and separating medium.

Furthermore, the 'LARCODEMS' unit, in contrast to other dense medium separation vessels, permits separation of a significantly wider granular size range. For example, granular material of different densities, sized between 120mm to 0.5mm, can be processed in a single vessel, whereas conventionally two different dense medium separation vessels are required for this size range: for example a combination of bath type dense medium separators and jigs or a combination of dense medium baths and dense medium cyclones was used.

However, practical operation of the 'LARCODEMS' vessel has shown that product quality varies to an extent which highlights the need to provide efficient and effective control of the process parameters to provide for greater consistency. The relative density dictates in large measure the product quality and accordingly the parameters which control this 'cut point' require careful attention. In particular, it has been found that a balanced, controlled rate of flow of the separating medium must be achieved. The establishment of a balanced fl ow ensures the generation of a strong vortex within the vessel which extends into the raw feed inlet at the upper end of the vessel thereby encouraging the induction of feed into the vessel.

It is of course the case that the physical characteristics, namely size and capacity, of the separation vessel play a pivotal role in the ultimate efficiency of the separation process and have to be selected according to the specific application in 3 terms of the feed material, the product type and size range, and the throughput levels required.

It is an object of the present invention to provide an improved method of controlling the performance of a mineral separation process.

It is a further object of the present invention to provide apparatus for the improved method.

Accordingly, the invention provides as a first aspect in a mineral separation process in which raw feed material in discrete form is fed to one end of a cylindrical vessel and a separating medium is fed to another end of the vessel in such manner as to induce vortical flow within the vessel, a method of controlling the separation includes the steps of monitoring the pressure of the separation, and varying the feed rate of the separation medium into the vessel in response to any pressure variation.

Conveniently, the pressure of the separation is monitored by detecting the pressure of the separation medium. Alternatively, the pressure of the separation can be monitored by detecting the pressure associated with the separation vessel, for example the exit pressure of the high density material.

Advantageously, the separation medium may be fed to the vessel by a variable speed pump. In the alternative, the separation medium is fed to the vessel by a fixed head gravity system.

The feed of the separation medium to the vessel is controlled to provide the requisite volume delivery and pressure in accordance with the pressure parameter monitored, thereby to secure that separation efficiency is maximised on a continuous basis, the pressure of the separation being indicative of the vortex strength.

The method of the invention also includes the steps of monitoring and controlling the feed rate of the raw mineral to give consistency.

in a preferred method the inlet pressure of the dense medium is controlled within a range defined by the ratio between the inlet pressure head and the internal diameter of the vessel. In particular the pressure is governed to lie within the range 6:1 to 15:1 being the ratio between the static inlet pressure head and the 4 internal diameter of the pressure vessel. The internal diameter of the separation vessel may range from 850 mm to 1500 mm but other sizes outside this range are possible.

Advantageously, the ratio between the static inlet pressure head and the internal diameter of the vessel is 9:1.

According to a second aspect of the invention there is provided apparatus for mineral separation including a generally cylindrical vessel, an involute inlet for a separating medium at or towards one end of the vessel, an axial feed inlet for raw mineral at the other end of the vessel, an axial outlet for low density material adjacent the involute inlet, an involute outlet for high density material adjacent the raw mineral inlet, feed means for the separating medium, pressure sensing means for detecting the pressure of the separation, and control means for varying the feed of the separation medium in response to the detected pressure of the separation.

1 1 Conveniently, the feed means may be a variable speed pump and the pressu sensing means may be a transducer providing continuous on-line measurements.

The pressure sensing means may be associated with the feed line for the separation medium or may in the alternative be associated with the high density material outlet or elsewhere within the vessel.

The high density material outlet may be connected to a vortex extractor unit which is employed to enhance the discharge through the said outlet.

Conveniently the size of the internal diameters of the low density material outlet and of the high density material outlets is determined in relation to the internal diameter of the separation vessel. Advantageously the ratio of the internal diameter of the high density material outlet to the internal diameter of the separation vessel lies in the range 1:7 to L4.5, and the ratio of the internal diameter of the low density material outlet to the internal diameter of the separation vessel lies in the range 1:6 to L4.

It has also been found that for optimisation of the operation of the apparatus there is relationship between the internal diameter of the material feed inlet and the internal diameter of the vessel. Advantageously the ratio of the former to the latter lies in the range L3. 5 and L4.5.

It will be understood that the influence of wear of the various elements in the apparatus is taken into account in the practical control of the method of separation. In this connection, the use of a variable speed pump referred to above compensates for any variation in dimensional parameters.

The control means may advantageously include a 3 term P.l.D. control loop, either as a discrete control loop or as part of a P.L.C. control system. The control means may be provided with a manual override for use in the event of pressure transducer failure.

By way of example, a method and an apparatus for controlling a mineral separation process are described with reference to the accompanying drawings in which:

Figure 1 is a diagrammatic representation of a separation vessel for use in the present invention; and Figure 2 is a circuit diagram of a control means for the mineral separation process.

Referring to the drawings, in Figure 1 there is shown a separation vessel 1 which is of generally cylindrical form with an involute inlet 2 for a separating medium at one end thereof and an adjacent axial outlet 4 for low density material. An axial inlet 6 for raw mineral feed is provided at the other end of the vessel 1 and an involute outlet 8 for high density material is located at said other end adjacent the axial inlet 6. The outlet 8 is connected to a vortical extractor unit 10 for enhancing the discharge of high density material. In practice, the vessel 1 is orientated with its axis at between 20' and 30'.

Dimensionally, by way of example, the ratio of the internal diameter of the high density outlet 8 to the internal diameter of the vessel 1 lies in the range 1:7 to L4.5, and the ratio of the internal diameter of the low density outlet 4 to the internal diameter of the vessel 1 lies in the range 1:6 to L4. Additionally, the ratio of the internal diameter of the inlet 6 to the internal diameter of the vessel 1 lies in the range 13.5 to L4.5.

Referring now to Figure 2, the vessel 1 is shown diagrammatically with separating medium feed line 20 extending from a pump 22 supplied from a storage sump 24. The pump 22 is driven by a variable speed drive motor shown at 26 provided with control means 28 in the form of a closed loop automatic control system which 6 advantageously includes a 3 term P.l.D. control loop, either as a discrete control loop or as part of a P.L.C. control system.

A pressure sensing transducer 30 is provided in the feed line 20 to give continuous on-line measurements of the separating medium pressure and is connected to the control means 28.

In operation raw mineral, for example raw untreated coal, is fed into the inlet 6 and at the same time a continuous feed of separating medium is introduced through inlet 2 into the vessel thereby to induce vortical flow, the raw coal being drawn into the vessel by the separating medium. The low density material exits through the outlet 4 whilst the high density fraction discharges through outlet 8 and passes to the vortex extractor unit 10.

The pressure of the separating medium feed in line 20 is constantly monitored since it is a determinant of the flow conditions within the vessel 1 and thus the operational efficiency of the separation. Any variation of the pressure will affect the strength of the vortex and accordingly appropriate and remedial action is necessary to re-establish the pressure at the preset value. In this respect, the control means 28 is preset to a desired pressure level and any deviation therefrom triggers a response in the form of a control signal to the variable speed motor 26 of the pump 22 thereby to vary the speed to effect the requisite modulation of the pressure in line 20 to give stable separating medium feed to the vessel 1.

The pressure of the dense medium at the inlet is modulated in accordance with a ratio between the static inlet pressure head and the internal diameter of the vessel 1 and conveniently lies in the range 6: 1 and 15:1, preferably approximately 9:1.

The control means can be preset at the desired pressure level manually or can be calculated using the actual separating medium relative density signal or set point, and manually selected constant K, thus Pset = pgKD where P = feed pressure set point (kPa) p = separating medium density (kg/M3) g = gravitational acceleration (9.81 m/s2) D = vessel diameter (m) K = constant (chosen ratio of inlet pressure head to vessel internal diameter) 7 The output signal from the control means 28 varies the speed of the pump 22 to ensure stable feed pressure at the desired value to ensure the correct vortex strength and thus optimise separation efficiency in accordance with process requirements.

The variable speed motor 26 drives the pump 22 at its rated output which for example may give a 20:1 speed ratio at constant torque.

The employment of a variable speed pump affords certain advantages over a fixed head gravity fed system and essentially these advantages are more flexibility to enable optimisation of control to suit feed conditions, significantly less head room required and capital cost savings. It is however to be understood that the invention also encompasses a mineral separation process in which a fixed head gravity fed system is used.

It is further to be understood that whilst the emphasis of the present invention has been focused upon the monitoring of pressure for the purpose of maintaining the performance of the separation process, it is nonetheless important as indicated supra that the physical characteristics of the vessel are selected dependent upon the process regime in which it is to operate. Additionally the specific elements in the overall apparatus design require careful selection to ensure that for given -throughputs and raw material specifications the necessary vortex structure and strength are achieved. The specification of the feed equipment, for example the pump, for the separating medium is chosen accordingly to match performance criteria and requirements.

The invention has applicability to any mineral processing system utilising a vessel of the kind described which requires the consistency of product quality to the extent afforded by the monitored and controlled pressure parameter of the invention.

8

Claims

1. A mineral separation process in which raw feed material in discrete form is fed to one end of a cylindrical separation vessel and a separating medium is fed to another end of the vessel in such manner as to induce vortical flow within the vessel, a method of controlling the separation includes the steps of monitoring the pressure of the separation, and varying the feed rate of the separation medium into the vessel in response to any pressure variation.

2.

A process according to Claim 1 in which the pressure of the separation is monitored by detecting the pressure of the separation medium.

3. A process according to Claim 1 in which the pressure of the separation is monitored by detecting the pressure associated with the separation vessel.

4. A process according to any one of the preceding claims in which the inlet pressure of the dense medium is controlled in accordance with the ratio of the static inlet pressure head and the internal diameter of the vessel.

5. A process according to Claim 4 in which the ratio lies within the range 6:1 and 15:1.

6. A process according to Claim 5 in which the ratio is approximately 9:1.

7. A process according to any one of the preceding claims in which the separation medium is fed to the vessel by a variable speed pump.

8. A process according to Claim 7 as dependent on Claim 2 in which the speed of the pump is varied in response to a variation in pressure of the separation medium feed.

9. A process according to Claim 1 in which the separation medium is fed to the vessel by a fixed head gravity system.

10.. Apparatus for mineral separation including a generally cylindrical vessel, an involute inlet for a separating medium at or towards one end of the vessel, an axial feed inlet for raw mineral at the other end of the vessel, an axial outlet for low density material adjacent the involute inlet, an involute outlet for high density material adjacent the raw mineral inlet, feed means for the separating 9 medium, pressure sensing means for detecting the pressure of the separation, and control means for varying the feed of the separation medium in response to the detected pressure of the separation.

11.Apparatus according to Claim 10 in which the feed means for the separating medium is a variable speed pump and the pressure sensing means is a transducer providing continuous on-line measurements.

12. Apparatus according to Claim 10 or 11 in which pressure sensing means is associated with the feed line for the separation medium.

13. Apparatus according to any one of Claims 10 to 12 in which the ratio of the internal diameter of the high density outlet to the internal diameter of the vessel lies in the range 1:7 to L4.5.

14. Apparatus according to any one of Claims 10 to 13 in which the ratio of the internal diameter of the low density material outlet to the internal diameter of the vessel lies in the range 1:6 to L4.

15. Apparatus according to any one of Claims 10 to 14 in which the ratio of the internal diarnter of the material feed inlet to the internal diameter of the vessel lies in the range L3.5 to L4.5.

16. Apparatus according to Claim 10 or 11 in which the pressure sensing means is associated with the high density material outlet or elsewhere within the vessel.

17. Apparatus according to any one of Claims 10 to 16 in which the high density material outlet may be connected to a vortex extractor unit.

18. A mineral separation process substantially as hereinbefore described with reference to the accompanying drawings.

19. Apparatus for mineral separation substantially as hereinbefore described with reference to the accompanying drawings.