Multotec Process Equipment (Pty) Ltd
Introduction The sizing of cyclones for dense medium separation, like most other things in this industry, is a combination of art and science. The selection process within itself is not complex, but there are a number of factors which must be taken into consideration to ensure that the cyclone size which has in the best separation efficiency is selected. Main Categories The selection process can be divided into the following main categories i.e. Inputs This covers feed parameters, yield, and design parameters which result in a mass balance. Diameter The full range of cyclone diameters which apply to the input data are calculated. Constraints The outputs of the diameter process are then checked against the following constraints: Top size Breaking size Spigot capacity requirement Number of cyclones and feed volume Selection At this stage the final selection is made, taking materials of construction, inlet shape and distributor into account.
The categories can be graphically depicted as follows:
Each of the categories will now be considered in greater detail. Inputs
Feed The minimum information required is the following: Tons per hour solids (dry). Particle density of the feed. Top size of the feed being treated. In order to ensure the best possible cyclone selection a full feed particle size distribution is required, but is unfortunately not always available. Yield The yield is required to determine the cyclone mass balance. The best possible information can be derived if a feed washability is provided. This enables the yield to be accurately determined and the sinks density can be calculated. Once again, this information is not readily available for many processes due to, amongst other factors, the density of separation. The next test is for the yield to be supplied by the end user. This can be determined by a mass balance around a plant or the results of pilot scale test work. If this is not available, then an estimate will have to be made based upon similar operations / applications. Design Parameters These cover the required ore to medium ratio and operating head and are the subject of much controversy. In general, industry standards apply but these change with time and it is important to know which standards were used, especially when evaluating existing plants. Mass Balance With the above information, it is possible to set up a mass balance for the application.
The next step is to calculate the relevant parameters for all the cyclone diameters which can be used for all the application. Top size The process starts with the 250 mm diameter cyclone. The first step is to check the top size, which the cyclone can handle, compared to the top size of the feed. The top size capability of cyclones ranging in diameter from 250 mm to 800 mm is shown in Figure1.
Figure 1 The cyclone diameter must be incremented until one which can handle the top size is found. Cyclone Capacity A table of cyclone capacities for cyclones fitted with a barrel extension is shown in Table 1. Calculate the number of cyclones required to handle the total volume based upon the mass balance. It is important to remember to round up i.e. 1.3 becomes 2. Spigot Capacity The total available spigot capacity can be calculated by multiplying the rounded up number of cyclones with the spigot capacities shown in Figure 2.
Spigot capacity (m3/
50.0 45.0 40.0 35.0 30.0 25.0 20.0 15.0 10.0 5.0 0.0 250 360 420 510 610 660 710 3.5 4.6 7.4 9.6 13.1 10.0 19.3 14.8 21.1 27.6 24.7 32.3 28.6
Standard Hi Capacity37.3 36.3
Figure 2 Please note that both standard and high capacity spigots are available and the calculation should be done for both. If the available spigot capacity is less than the required spigot capacity, recalculate N based upon the maximum spigot capacity. New Cyclone Diameter The number of cyclones required is the greater of N and N*. If the number of required cyclones is more than 1, increment the cyclone diameter and repeat the process until N=1 ore the cyclone diameter exceeds 800 mm.
Constraints The output from the previous category must now be checked against the constraints that apply to this application.
This is a graphical process to ensure that everything is taken into consideration. Top Size Using figure 1, plot the feed top size. This will very quickly verify whether all the possible cyclone diameters under the diameter category have been evaluated and whether a square or rectangular inlet is appropriate for a given cyclone diameter. Breakaway Size If a full particle size distribution has not been supplied, then this graph must be skipped. If a distribution has been provided, then plot the percentage finer than the breakaway size for each cyclone. The following guidelines can be used:
% Finer 0-5 % 5-15 % >15 % Spigot Requirements
Comment Acceptable On the limit Reduce cyclone diameter
The total available spigot capacity must be plotted against the required spigot capacity from the mass balance. This will assist to determine which cyclone diameters can be used and whether a standard or high capacity spigot is required. Number of Cyclones Calculate the total feed volume based upon the number of cyclones required and using the capacity figures in Table 1. Plot the required volume on the same graph. Note, that if the cyclone is spigot controlled, the calculated volume will be much higher than that based upon the feed medium to ore ratio.
Selection All the information required to make the final selection is now available.
Materials of Construction The standard materials of construction, which are available, are: Cast iron Engineered alumina tiles Silicon carbide It is important to decide at this stage what the appropriate material of construction is as the cyclone supplier may not have all the diameters available in all the materials. (Note, all the information supplied in this paper is based upon cast iron). Cyclone Diameter The cyclone diameter and number of cyclones must now be selected using the following guidelines: Always use the largest diameter cyclone possible, taking the break away size into account. This will simplify the design and operation.
If multiple cyclones have to be used, for N=2, it is possible to ensure good distribution. If N>4, then it is better to consider modules with individual modules having N=2,3,4. Inlet Shape Where square and rectangular inlets are available, the following guidelines apply: Square inlets can be used where a large top size must be accommodated or a low differential is required. Rectangular inlets are used to ensure a high differential. This is especially helpful for high density separations (>3.2) as the circulating medium density can be reduced and the inventory of medium is reduced. Pulp Distribution Where N>1, a distributor is required. A two way distributor can be designed to ensure that equal solids and liquid distribution is achieved. For N>2, distribution becomes increasing complex. Note that no static distributor can remove a bias which already exists. Engineered ceramic tiles are the preferred lining for pulp distributors as they give good wear life and can easily be designed to fit any distributor. Example An example illustrating the use of this procedure follows: Diamond Application Inputs Feed Tph Particle density Top size Psd Yield Washability Input Estimated : : : not supplied not supplied 1.5 % : : : : 100 2.6 (Kimberlite) 25 mm not supplied, however bottom size on screen deck is 1.6 mm
Design Parameters Ore: medium ratio Operating head Mass balance Feed Solids (tph) Volume solids (m/h) Medium (m/h) Total medium (m/h) Diameter Top size Dc = 250 Top size = 18 mm (Figure 1) > 25 mm 100 38.5 288.8 327.3 Floats 98.5 37.9 202.2 240.1 Sinks 1.5 0.6 86.6 87.2 : : 7.5:1 12 D
Increment Dc Dc = 360 Square top size = 25 mm
Cyclone Capacity Cyclone capacity @ 12 D = 79 m/h (Table 1) N = 327.3/79 = 4.15 = 5 Spigot Capacity Total capacity (standard) = 5 x 7.4 = 37 m/h ore Total capacity (hi capacity) = 5 x 9.6 = 48 m/h ore > 0.6 m/h ore required New Cyclone Diameter Increment Dc Dc = 420 mm Repeat process
No of Cyclones , Total Volu
Summary of Results Dc 360 420 510 610 710 Inlet shape Square Square / Rect. Square / Rect. Square / Rect. Rect. N 5 3 2 2 1 Spigot capacity (m/h) 37 30 29.6 42.2 28.6
Number of Cyclones
1000 395 345 358
5 3 2 2 1
0.1 250 360 420 510 610 660 710 0.0393 800 0.0420
Selection Materials of Construction Cast iron is suitable for this application
Cyclone Diameter Both the 420 and 510 mm cyclones will be acceptable. In terms of distribution, 2 cyclones is better than 3, which would support the choice of the 510 mm cyclone. The breakaway size for the 510 mm cyclone is 1.7 mm and the bottom deck is 1.6 mm so performance will not be sacrificed. Constraints Top Size60
Square Rectangular Feed topsize43 42
40 34 30 25 20 18 18 24 30 25 30 33
0 250 360 420 510 610 660 710 800
Breakaway Size Not meaningful without the size distribution.
Spigot capacity (m3/
Standard Hi Capacity Required9.6 13.1 10.0
27.6 19.3 14.8 21.1
0.1 250 360 420 510 610 660 710 800
Not a constraint N = 2 and Dc = 510 mm Inlet Shape Square inlet is recommend