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

• Θ - 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 easier in the

industry. The new nomenclature will refer to actual cyclone diameter.

The “throw away” cyclone will be more simplistic, consisting of two loose parts only and will

prevent inward steps due to incorrect assembly and the potential loss of diamonds.

Hawkeye measurements will enable the end user to predict when a cyclone should be replaced

once a database of history has been built up.

Cone Inspection

Front View

LH Cyclone

RH Cyclone

LH inlet

1 2

3456

Material Flow

10.0 References

1) Reeves, TJ & Platt, BI 1988, ‘Maximizing efficiency in dense medium plants’, The Third

Samancor Symposium on Dense Medium Separation 29 February – 1 March 1988, Riviera

International Hotel and Country Club Vereeniging, South Africa.

2) Bekker, E 2012, ‘DMS Cyclone Presentation – DMS Basics’.

3) Communication with J Engelbrecht, Director International Business Division, January 2013.

4) Dos Santos, R 2011, ‘Hawkeye for Cyclones – Tools and Inspection Procedure’.