hydrocyclone model simulation.pdf

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No. 1998.100

Hydrocyclone Model Simulation: A Design Tool for Dewatering Oil

Sands Plant Tailings

A.I.A. Salama, CANMET, Devon, Alberta, Canada; and T. Kizior, Syncrude Canada,

Fort McMurray, Alberta, Canada

Abstract

Design of classifying hyd rocyclone d ewatering ci rcuits for oil

sands plant tailings requires careful evaluation of d ewatering

levels as a function of the cyclone cut size, variations in the

cyclone me chanical dimensions, and th roughput . The avail-

ability of reliable models can simplify this p rocess and p rovide

valuable information that enables the design engineer to

understand the p rocess and evaluate di fferent options ( e.g.,

single- or two-stage cyclone ar rangement, cut size, per cent solids in underflow and feed, and number of cyclones).

A hyd rocyclone model simulation app roach has been

developed at the CANME T Western Resea rch Cent re (CWRC)

for designing d ewatering and fine particle sepa ration ci rcuits.

The app roach is based on an existing empirical model. Utiliz-

ing a cyclone manufactu rer’s published data, some modifica-

tions have been d eveloped and int egrated into the model.

Plant tailings characteristics, cyclone me chanical dimen-

sions, and ope rating conditions a re utilized in the CWRC

modeling simulation . The computer results are presented in 3-

D graphs and cor responding 2-D maps showing the cyclone

mass recovery, per cent solids by mass in underflow and ove r- flow, and cut size as functions of the cyclone ap ex diameter

and cyclone th roughput (i. e., inlet p ressure or pressure drop).

The graphs and maps a re useful in visualizing and illust rating

the effects of ope rating conditions on cyclone performanc e.

The p roposed computer simulation app roach has been

demonst rated th rough the design of d ewatering ci rcuits for oil

sands plants . The design includes evaluation of hyd rocyclone

performance and d ewatering l evels. A summary of the results

is presented.

Introduction

Conway, 1985 adopted an approach based on Plitt’s mode

(Plitt, 1976), where the cyclone mechanical dimensions are

adjusted in a prescribed manner until the desired cut size is

achieved. Also the manufacturer’s cyclone capacity data are

used to determine the required number of cyclones. No

attempt was made to check the cyclone underflow per cent

solids (e.g., cyclone operating in rope mode or plugged)

While the approach may be valid in some cases, it does noprovide a thorough insight into cyclone performance as the

operating conditions are changed. Again, Plitt’s model is used

in the computer simulation approach adopted in this paper

The cyclone mechanical dimensions are kept fixed except the

apex and vortex finder diameters are changed according to

selected manufacturer values. It is known that the apex diame-

ter has significant effects on cyclone performance (per cen

solids and mass recovery). For a particular cyclone size, inlet

diameter, and overflow diameter, two sets of apex diameters

and feed volumetric flow rates are used to study their effects

on cyclone performance (cut size, underflow mass recovery

and underflow and overflow per cent solids by mass).

In general, the hydrocyclone model simulation objective

may be stated as: start with given oil sands plant tailings char-

acteristics and try to predict hydrocyclone performance, in

particular, cyclone underflow and overflow per cent solids by

mass, underflow mass recovery, and cyclone cut size. These

steps are summarized in the following table.

Input Data

Solids particle size distribution

Feed solids and fluid mass rates

Feed % solids (mass)

Solids specific gravity

Carrier fluid specific gravity

Carrier fluid viscosity

Desired cut size, D

50 *

Model and Intermediate Data

Number of cyclones

Cyclone geometrical dimensions

Cut size

range

Underflow/overflow mass split

Sharpness of separation

Pressure drop/capacity**

Model tuning parameters

Output Data

Overflow % solids (mass)

Underflow % solids (mass)

Overflow solids and fluid mass rates

Underflow solids and fluid mass rates

Underflow % mass recovery

Product particle size distributions


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* D50 is the cyclone cut size (i.e., particle size which has a 50–50 chance of reporting to either the underflow or the overflow streams).

**Pressure drop is defined as the difference between inlet pressure and overflow pressure.

CWRC Hydrocyclone Model

Simulation Approach

In Plitt’s model, the cyclone model predictions can be deter-

mined by utilizing four fundamental parameters expressed in

terms of the operating design variables (Plitt, 1976). These

parameters are:

• Separation cut size D

50

• Flow split between overflow and underflow

• Sharpness of separation

• Capacity/pressure drop

By determining these parameters, a complete mass balance

together with size distribution of the cyclone products can be

achieved. Plitt’s empirical model was developed based on alarge amount of data collected over wide ranges of operating

conditions. The CWRC computer simulation utilized Plitt’s

model with some changes. These changes were derived based

on Krebs Engineers (KE) published data. The details of Plitt’s

model are given elsewhere (Plitt, 1971, 1976, and further

work by Plitt and Kawatra, 1979; Flintoff et al, 1987, see

Svarovsky, 1984); however, the modifications are presented

next.

Pressure – Flow Rate – Cyclone SizeCorrelation

Based on Krebs published data the following correlation has

been derived

(1)

where K

c

is a coefficient and is dependent on the cyclone size

and p (pressure drop across the cyclone) and Q (cyclone feed

volumetric flow rate) are expressed in psi and USgpm, respec-tively. However, it is straightforward to adjust K

c

so that p and

Q can be expressed in different units. A set of nominal values

of K

c

are given in this table.

The K

c

values could be changed around the nominal values

to give similar relationships between p and Q for the same

cyclone size. If, for a given cyclone size and known p and Q at

a particular operating conditions, then by back substitution of

these values in Equation 1 a new K

c

can be determined. Mular

and July 1978 (and reported in Wills, 1992) utilized Krebs

published data and derived a similar form for determining the

cyclone maximum capacity as

(2)

where K

c

= 9.4 x 10

-3

and using SI units.

Cyclone Cut Size Correlation

Based on KE published data and using nonlinear regression, a

correlation for the corrected cut size D

50c

can be determined

as

(3)

where a viscosity term is added and F

D50c

includes units con-

version. KE engineers have derived a similar form with slight

changes to the powers (Gottfried et al, 1982). The differencebetween the actual cut size D

50

and the corrected cut size D

50c

is the actual cut size obtained using the actual classification

curve (i.e., including water bypass to underflow).

D K = cc D 0.4982.12

D

c

4" 6" 10" 15" 20" 26" 30" 33" 44" 50"

K

c

0.481 0.603 0.417 0.374 0.468 0.527 0.619 0.616 0.475 0.539

Q K c Dc D2.12

p0.498

=

r DD

m 0.51.483010

..

)1.9-1( C p

D. F = D

.

c D50c 50c


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Case Study

In late 1997, Syncrude Canada Ltd. decided that the hydrocy-

clone could be a viable process technology for dewatering

plant tailings. The plant approached CWRC to carry out a

computer modeling simulation and preliminary engineering

design, and to produce in-depth data that would provide a

basis for the engineering and installation phases of the devel-

opment.

The plant tailings sand has a typical direct particle size-

mass distribution as shown in Table 1. This particle size distri-

bution is used as part of the input files to the CWRC modeling

simulation. Note that a top particle size of 250 m

m is used in

the cyclone computer models. The direct mass distribution is

used to generate the cumulative mass distribution. Close

examination of the cumulative mass distribution indicates that

the desired cut size is in the range of 20–40 m

m.

Computer Input Data

Based on the tailings characteristics, slurry flow rate, and par-ticle size distribution, a set of cyclone sizes (10", 15", 20")

and a set of feed per cent solids by mass (35%, 40%, 50%,

60%) were selected. The solids and liquid specific gravities

are 2.65 and 1, respectively. Using a nominal pressure drop

across the cyclone, a set of feed volumetric flow rates (using

Equation 1) was selected. This allowed better presentation of

the results and facilitated visualization of the effects of feed

volumetric flow rate and apex diameter on the underflow and

overflow per cent solids, cut size, and mass recovery. Using

plant tailings total volumetric flow rate in USgpm and Krebs

published data, the number of cyclones can be determined.

Such values are determined by assuming nominal values of

cyclone feed volumetric flow rate. There was no attempt toadjust the calculated number of cyclones to meet KE design.

This adjustment can be made at the design stage.

KE cyclone mechanical dimensions, in particular, the vor-

tex finderBapex distance and cyclone inlet diameter for the

10-, 15-, and 20-inch Krebs cyclones, were kept constant dur-

ing computer simulation. Two settings around Krebs cyclone

overflow diameters were selected. A set of underflow diame-

ters was selected rather than two settings around Krebs nomi-

nal values. This made it possible to evaluate the effect of

underflow orifice diameter on cyclone performance. Cyclone

performance is very sensitive to apex diameter and to lesser

extent to cyclone inlet pressure, as will be shown later.

Computer Simulation Results

The single-stage cyclone performance predictions at maxi-

mum underflow mass recoveries for different operating set-

tings are summarized in Table 2, where “*” indicates that the

apex is overcrowded (small apex) and sends coarse particles to

the overflow stream, and “recovery” indicates mass recovery.

The maximum mass recoveries were obtained at low overflow

and apex diameters. The corrected D

50c

is dependent on the

actual cut size D

50

and the water split (bypass) to the under-

flow.

A selected set of three-dimensional (3-D) graphs and corre

sponding two-dimensional (2-D) maps (for single-stage 15"

and 20" cyclones and 40% and 50% feed solids by mass) are

presented in Figures 1-6. These figures are typical of the com-

puter results obtained and are presented to demonstrate theeffects of apex diameter and cyclone pressure drop (feed volu-

metric flow rate, Equation 1) on cyclone performance. Figures

1 and 3 are 3-D graphs for the 15" cyclone with 40% feed sol

ids and overflow diameters of 5" and 6", respectively. Figure 2

is the 2-D map corresponding to the 3-D graph in Figure 1

Figures 4 and 5 are 3-D graphs for the 20" cyclone with 50%

feed solids and overflow diameters of 7" and 8", respectively

Figure 6 is the 2-D map corresponding to the 3-D graph in

Figure 5.

In general, the simulation results for the 10-inch cyclone

showed flat surfaces for the underflow per cent solids (i.e.

constant high values) over the selected ranges of feed volu-

metric flow rate and apex diameter. This is because the 10-inch cyclone tends to separate at a low cut size and, as a result

the apex becomes overcrowded resulting in higher underflow

per cent solids. The underflow mass recovery and per cent sol-

ids over the selected ranges of apex diameters exhibited

opposing trends (see Figures 1, 3, 4, and 5). The underflow

mass recovery and cyclone actual cut size D

50a

over the

selected ranges of apex diameters exhibited opposing trends

(see Figures 1, 3, 4, and 5). Cyclone performance (in particu-

lar the underflow mass recovery, underflow per cent solids

and cut size D

50

) is strongly affected by the apex diameter. In

the selected range of 20% of the nominal feed volumetric flow

rate, the model predictions show unexpectedly small effects othe feed volumetric flow rate (see Figures 1, 3, 4, and 5). Low

settings of overflow diameters and high settings of apex diam

eters produce higher underflow mass recovery with lower per

cent solids. This is due to forcing more solids and water to the

underflow stream. On the other hand, low settings of overflow

and apex diameters produce higher underflow mass recoveries

and per cent solids. Furthermore, as the feed per cent solids

increases the underflow mass recovery decreases.

A two-stage cyclone circuit was simulated where the over

flow of stage I is fed to stage II. Stages I and II underflows

were combined to form the circuit underflow. Based on the

results of single-stage cyclone simulation the suitable apex

settings did not change very much in relation to the feed percent solids. As a result, the same settings used in the single-

stage simulation were repeated for the two-stage simulation

The two-stage cyclone circuit performance predictions at the

selected settings are summarized in Table 3. The results indi-

cated that the two-stage cyclone circuit mass recoveries are

much higher than the single-stage cyclone recoveries; how-

ever, the underflow per cent solids is lower in the two-stage

cyclone circuit than in the single-stage cyclone. The per cent

solids differential decreases as the feed per cent solids


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4

increases. Therefore, the two-stage cyclone circuit is recom-

mended for feed with higher per cent solids (50–60%).

The computer simulation results are predictive in nature

and supplementary experimental work is needed to support

the predictions

Conclusion

A hydrocyclone model simulation approach for designing

dewatering and fine particle separation circuits has been

developed at the CANMET Western Research Centre

(CWRC). The approach utilizes an existing empirical model

and some modifications based on a cyclone manufacturer’s

published data are integrated into the model. The published

data on cyclone mechanical dimensions and operating condi-

tions are used in the development of the modeling simulation.

The computer results are presented in 3-D graphs and corre-

sponding 2-D maps showing the cyclone mass recovery, mass

per cent solids in underflow and overflow, and cut size as

functions of the cyclone apex diameter and cyclone through-put.

The results obtained from an oil sands plant utilizing this

computer simulation approach are briefly summarized and

presented.

The usefulness of the CWRC model simulation has been

demonstrated by the utilization of the results in the course of

full-scale implementation at several oil sand plants applica-

tions.

Acknowledgment

This work was supported in part by the Federal Panel on

Energy Research and Development (PERD). The authors

would like to thank Syncrude Canada Ltd. for permission to

publish the present work.

References

1. Conway, T.M., 1985. “A computer program for prediction

of hydrocyclone performance, parameters, and product-

size distributions”, Mintek-Report No. M233

, Randburg,

South Africa.

2. Flintoff, B.C., Plitt, L.R., and Turak, A.A., 1987.

“Cyclone modeling: a review of present technology”,

CIM Bulletin 80:905, 39–50.3. Gottfried, B.S., Luckie, P.T., and Tierney, J.W., 1982.

“Computer simulation of coal preparation plants”, U.S.

Dept. of Energy, DOE/PC/30144-T7, DE 83004279,

December.

4. Mular, A.L. and Jull, N.A., 1978. “The selection of

cyclone classifier, pumps and pump boxes for grinding

circuits”, Mineral Processing Plant Design

, AIMME,

New York.

5. Plitt, L.R., 1971. “The analysis of solid-solid separation

in classifiers”, CIM Bulletin

64:70: 42–47.

6. Plitt, L.R., 1976. “A mathematical model of the hydrocy-

clone classifier”, CIM Bulletin

69:776: 114–123.7. Plitt, L.R. and Kawatra, S.K., 1979. “Estimating the cut

size of classifiers without particle size measurement”,

Int

J Min Proc

5: 369–378.

8. Svarovsky, L., 1984. “Hydrocyclones”

, Holt, Reinhart,

and Winston, New York.

9. Wills, B.A., 1992. “Mineral Processing Technology”

, 5

th

Edition, Pergamon Press, New York.


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Table 1: Sand Cumulative Mass and Direct Mass Distributions With Particle Size

* Overcrowded apex (small apex)

Table 2: Single-Stage Simulation Results

Size

(

m

m)

Cumulative Mass

(%)

Size

(

m

m)

Direct Mass

(%)

- 10 9.02 - 10 9.02

- 20 12.54 10 - 20 3.52

- 40 20.15 20 - 40 7.61

- 80 26.54 40 - 80 6.39

- 90 32.46 80 - 90 5.92

- 100 39.31 90 - 100 6.85

- 150 78.69 100 - 150 39.38

- 200 95.77 150 - 200 17.08

- 250 100.00 + 200 4.23

Total 100

Cyclone Feed

Solids %

Cyclone

Diameter

Cyclone

Underflow

Cut Size D50a

(

m

m)

Solids % Recovery %

35 %

10"

15"

20"

75.3

63.3

64.7

82.8

87.2

79.1

38

37

52

40 %

10"

15"

20"

77.2

67.3

69.4

74.1

82.3

76.3

65

*

42

60

50 %

10"

15"

20"

78.0

75.1

75.8

57.6

75.7

67.6

117

*

62

87

60 %

10"

15"

20"

79.1

76.3

73.7

46.9

61.2

50.8

158

*

109

150


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Overcrowded apex (small apex)

Table 3: Two-Stage Simulation Results

Figure 1: 3-D Simulation Results for 40% Feed Solids, 15" Cyclone, 5" D

o

Cyclone

Feed Solids

%

Cyclone

Diameter

Stage I

Cyclone

Under-

flow

Stage II

Cyclone

Under-

flow

Two-

Stage

Cyclone

Circuit

Solids%Recovery%

D

50a

m

mSolids%Recovery%

D

50a m

mSolids%Recovery%

35%

10"15"20"

75.363.364.7

82.887.279.1

383752

15.911.418.1

45.253.350.7

262336

57.047.649.6

90.694.090.0

40%

10"15"20"

77.267.369.4

74.182.376.3

65

*

4260

31.818.524.3

57.755.552.9

292539

62.352.654.9

89.092.188.8

50%

10"15"20"

78.075.175.8

57.675.767.6

117

*

62

87

61.033.842.1

66.561.157.5

413049

71.562.564.6

85.890.686.2

60%

10"15"20"

79.176.373.7

46.961.250.8

158

*

110150

75.358.363.3

60.664.255.3

705397

77.570.069.7

79.086.178.0


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