High chrome dense medium cyclone migration and CHROME DENSE MEDIUM CYCLONE MIGRATION AND WEAR ......

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Transcript of High chrome dense medium cyclone migration and CHROME DENSE MEDIUM CYCLONE MIGRATION AND WEAR ......

  • HIGH CHROME DENSE MEDIUM CYCLONE MIGRATION AND WEAR

    MEASUREMENTS

    F Bornman

    Multotec Process Equipment

    Abstract

    Reeves and Platt1 stated that dense medium separation is one of the most complex unit

    processes in mineral processing today particularly if cyclones are used. The complexity of the

    process and large number of design and operating variables has meant that the process has

    largely remained more art than science.

    The cyclone forms the core of the dense medium separation process and is part of the reason

    why the Diamond industry remained with high chrome as a material of construction. More cost

    effective ceramic lined cyclones can fail catastrophically and result in major losses of diamonds.

    Multotec Process Equipment offers two ranges of high chrome cast iron dense medium

    cyclones. The paper describes the ratios for the different cyclones and the necessity to change

    the cyclone nomenclature.

    Cyclones are replaced based on wear and performance which are dependent on ore

    characteristics and tonnage throughput. The Hawkeye software maintenance system was

    developed to predict the wear on the different components and hence the replacement dates.

  • 1.0 Introduction

    The following nomenclature is used for a cyclone:

    Dc - the inside diameter of a cyclone in mm

    Di the diameter of the feed opening in mm

    Dvf - the diameter of the overflow opening in mm

    Du - the diameter of the underflow opening in mm

    - the cone angle in degrees

    Bl - The length of the barrel in mm

    Figure 1 Dense medium cyclone

  • The Dutch State Mines (DSM) manual recommended certain standard ratios for the dense

    medium cyclone:

    Table 1 DSM cyclone ratios

    Cyclone diameter Feed opening

    1 0.2

    Cyclone diameter Vortex finder

    1 0.43

    Cyclone diameter Spigot

    1 0.3

    Cyclone operating head D

    Coal 9

    Industrial minerals and ores 15-40

    Cyclone cone angle 20 degrees

    2.0 Different cyclone designs

    There is basically two different designs i.e.

    C & CL design

    CE & CEL design

    The L donates a lug design at the flanges to replace solid or loose flanges. The main advantage

    of the L design is the saving in material and hence the cost of the cyclone.

    Both designs use the scrolled evolute design for the inlet which proved the best design from a

    capacity and wear point of view.

    Data collected on a cast iron densifier proved the advantages of the scrolled evolute design as

    shown in table 2:

    Table 2 Cast iron densifier data

    Inlet design Material of construction

    Wear life (hours)

    Tangential Ni hard 2 450

    Tangential High chrome 950

    Evolute High chrome 1450

    Scrolled evolute High chrome 2300

  • The basic design of the tangential and the scrolled evolute design are shown in figures 2 & 3.

    Figure 2 Tangential inlet Figure 3 Scrolled evolute inlet

    2.1 C design

    The C-range of cyclones is one of the earliest cyclone designs by Multotec for dense medium

    applications as shown in figure 4. This range was originally designed with an evolute entry of

    the inlet and later converted to the scrolled evolute design. Note the 360 degree cast iron

    flanges on the inlet head, barrel, cone and spigot segments.

    Tangential Inlet Scrolled Evolute Inlet

  • Figure 4 High chrome cyclone range

    Initially both square and rectangular inlet nozzles were supplied; however, standardization on

    square nozzle inlets was implemented to rationalize the part inventory. This enables the cyclone

    to treat the maximum size of particle possible as the design of the inlet had an insignificant

    influence on the efficiency.

    The table below shows the standard ratios for the C design. This is in line with the original DMS

    ratios and gives excellent efficiencies and a very stable operation.

    Table 3 Cyclone ratios for C design cyclones

    Component Ratio

    Inlet nozzle to cyclone diameter Di = 0.2Dc

    Overflow outlet to cyclone diameter Do = 0.43Dc

    Underflow outlet to overflow diameter Du = 0.5 to 0.8Do

  • Figure 5 Cyclone ratios for C design cyclones

    Table 4 Range for C design cyclones

    Cyclone size Actual diameter (mm)

    C250 250

    C360 350

    C420 420

    C510 510

    C610 610

    C660 660

    C710 710

    C900 900

  • 2.2 CE design

    The CE-range of cyclones was designed with the following objectives in mind:

    To produce a cyclone with the same capacity, performance and wear life as the C

    design, but at a lower cost

    To produce a cast iron cyclone that had component compatibility with the classification

    range of cyclones

    Figure 6 CE design

    The end result was a cyclone which had a diameter slightly smaller than an equivalent C design

    (hence cheaper), but had equivalent process performance. This was achieved principally

    through an increase in the inlet nozzle size from 0.2D to 0.23D.

  • Table 5 Cyclone ratios for CE design cyclones

    Component Ratio

    Inlet nozzle to cyclone diameter Di = 0.23Dc

    Overflow outlet to cyclone diameter Do = 0.43Dc

    Underflow outlet to overflow diameter Du = 0.5 to 0.8Do

    Table 6 Range for CE design cyclones

    Cyclone size Actual diameter (mm)

    CE420 390

    CE510 470

    CE610 570

    3.0 Comparison between C & CL versus CE & CEL cyclones

    The internal diameter of the CE/CEL cyclone range is smaller than the C, and the inlet nozzle is

    larger. The net result is that the volumetric capacities of the two types of cyclones are

    approximately the same as shown in tables 7 & 8.

    Table 7 C/CL cyclone capacities

    Cyclone Type Actual Diameter (mm)

    Inlet Nozzle Equivalent (mm)

    Capacity at 9D (m3/hr slurry)

    Capacity at 15D (m3/hr slurry)

    C420 420 85 95 123

    C510 510 101 148 191

    C610 610 122 225 290

    Table 8 CE/CEL cyclone capacities

    Cyclone Type Actual Diameter (mm)

    Inlet Nozzle Equivalent (mm)

    Capacity at 9D (m3/hr slurry)

    Capacity at 15D (m3/hr slurry)

    CE420 390 90 99 128

    CE510 470 108 145 187

    CE610 570 131 224 289

  • 4.0 New consolidated cyclone range

    In order to prevent any misunderstanding in the industry it was decided to rationalize the design

    and the nomenclature for all the cyclone designs as one range called the L range as shown in

    table 9.

    Table 9 CL cyclone range

    Cyclone size Actual diameter (mm) Inlet open area

    CL200 200 0.2D

    CL250 250 0.2D

    CL300 300 0.2D

    CL350 350 0.2D

    CL390 390 0.23D

    CL420 420 0.2D

    CL470 470 0.23D

    CL510 510 0.2D

    CL570 570 0.23D

    CL610 610 0.2D

    CL660 660 0.2D

    CL710 710 0.2D

    CL900 900 0.2D

    CL1150 1150 0.2D

    5.0 New Developments

    The maintenance cost of the dense medium cyclones in a diamond plant is low in comparison to

    other treatment costs and is estimated to be in the order of 0.1%. It makes therefore economic

    sense to replace the cyclone as a unit rather than replacing individual components as it is the

    core of the process.

    A cone/spigot combination was developed as a throw away unit once the cyclone reached the

    end of its lifetime. Similar to this, an inlet head/vortex finder combination exists for the C900

    cyclone which can be extended to the smaller diameter cyclones. The benefit of this is that the

    cyclone now effectively only consists of two loose parts the inlet head/vortex finder and

    cone/spigot combination. This saves assembly time and also eliminates the risk of off-centre

    joints that may affect the efficiency of the separation.

  • Figure 7 Cone/spigot combination

    Figure 8 Inlet head/vortex finder combination

    8.0 Planning of the maintenance of the dense medium cyclones through the use of

    Hawkeye software

    Plant maintenance can have its challenges in terms of time, the availability of people, the

    availability of equipment and the availability of stocks.

    Hawkeye is a predictive maintenance software program developed by Multotec. The objectives

    were:

    Determine the expected life based on the wear rate and performance data as a function

    of tonnages treated

    Predict the replacement date

    In the case of the high chrome cast iron cyclone, Ultrasonic Testing (UT) with high frequency

    sound energy is used to make thickness measurements from which the wear rate can be

    calculated.

  • The cone is divided into imaginary planes as shown in figure 9. Measurements are taken of the

    cone at different points. The cast iron thickness is measured. The measurements are repeated

    at certain intervals based on time or tonnage treated.

    Figure 9 Hawkeye setup

    A profile can now be drawn up of the wear pattern. The following data is recorded in the

    Hawkeye database:

    The date of inspection

    The cyclone description

    Equipment number

    Operating pressure

    Throughput (t/hr)

    Wear measurements

    9.0 Conclusions

    Cast iron is still the preferred material of construction for the diamond industry due to the

    potential catastrophic failure of ceramic materials.

    Standardizing on one cast iron cyclone range will make cyclone identification e