Cyclone

Journal of Thermal Science Vol.17, No.3 (2008) 275−280

Received: March 2008 Zhu Zhiping: PhD, Assistant Professor

www.springerlink.com

DOI: 10.1007/s11630-008-0275-7 Article ID: 1003-2169(2008)03-0275-06

Pressure Drop in Cyclone Separator at High Pressure

Zhu Zhiping1, 2 Na Yongjie1 Lu Qinggang1

1. Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190 2. Graduate University of Chinese Academy of Sciences, Beijing 100190

For the design of pressurized circulating fluidized beds, experiments were conducted in a small cyclone with 120 mm in diameter and 300 mm in height at high pressures and at atmospheric temperatures. Influence of air leakage from the stand pipe into the cyclone was specially focused. A semi-empirical model was developed for the predic-tion of the pressure drop of the cyclone separator at different operate pressures with the effect of air leakage and inlet solid loading. The operate pressure, air leakage and inlet solid loading act as significant roles in cyclone pressure drop. The pressure drop increases with the increasing of pressure and decreases with the increasing of the flow rate of air leakage from the standpipe and with the increasing of the inlet solid loading.

Keywords: cyclone separator, pressure drop, air leakage

Introduction

Cyclone separators are widely used in fields of air pollution control, air-solid separation for sampling and industrial applications. A number of studies have been reported in literatures, predicting pressure losses in cy-clones[1]. In simplest models, pressure loss coefficient is based on the ratio of inlet and outlet cross section areas[2]. The main parameters that affect the pressure drop have been taken as the inlet geometry, acceleration, outlet channel dimensions, temperature and friction. In addition, effects of different parameters, such as inlet width and height, radius and height of the outlet pipe, geometry of conical part, temperature, surface roughness and particle concentration were also investigated[3-10]. There are em-pirical and semi-empirical relations in literatures, but none can be used for different type of cyclones and dif-ferent operation parameters[11]. For a cyclone separator of a circulating fluidized bed, more or less gas will leak from the loop seal into the cyclone and destroy the flow structure in the cyclone, especially to a pressurized cir-culating fluidized bed, consequently, the pressure drop in

the cyclone separator will be changed and the separation efficiency will be decreased. In the design and the opera-tion of a cyclone for a pressurized circulating fluidized bed, the effects of gas leakage must be predicted. So far, there is no theoretical or empirical model of pressure drop with gas leakage in high pressurized cyclone sepa-rator.

Our experiments were conducted in a small cyclone separator at high pressure. Influence of air leakage from the stand pipe into the cyclone was specially focused. A semi-empirical model was developed for the prediction of the pressure drop of the cyclone separator at different pressure with the effect of air leakage.

Experiments

The test rig The dimensions of the cyclone used in experiments are

shown in Figure 1. The schematic diagram of the ex-perimental system is shown in Figure 2. Three pressure taps are at the inlet, the outlet and the apex cone of the cyclone separator, separately. The highest working pres-

Cephas

Underline

Cephas

Underline

Cephas

Underline

276 J. Therm. Sci., Vol.17, No.3, 2008

Nomenclature Ain area of cyclone inlet Rin radius of cyclone inlet

Km angular momentum loss parameter RCS radius of the boundary between core region and annual region in separation space

S insert depth of cyclone outlet Rc radius of the boundary between core region and annual region in cyclone outlet

M inlet solid loading inv inlet air velocity

Mf weight of solid particles added into feed bin θv tangential velocity at radius r

Mc weight of solid particles collected in dust hopper θCv tangential velocity at radius Rc

Ma inlet air mass flow rate θCmv mean tangential velocity in outlet

ms inlet solid particle mass flow rate θCSv tangential velocity at radius Ro

Q1 inlet air volume flow rate θwv wall surface tangential velocity of air after suf-fering wall friction force

Q2 leakage air volume flow rate *θwv wall surface tangential velocity of air flow at the

entrance region r radius voz axial velocity in the annular region of outlet Rw radius of cyclone barrel ε the cone slope

Fig. 1 Cyclone separator dimensions (units are in mm)

1. Air compressor; 2. Pressure vessel; 3. Relief valve; 4. High pres-sure ball valve; 5. Mass flowmeter F1; 6. Mass flowmeter F2; 7. Pres-sure balance tube; 8. Feed bin; 9. Cyclone separator; 10. Dust hopper; 11. Bag filter; 12. Control valve; 13. Silencer mounting; 14. Pressure difference transmitter; 15. Pressure difference transmitter; 16. Pressure transmitter.

Fig. 2 The schematic diagram of experimental system

sure was 2 MPa. From an air compressor, a pressure ves-sel and a mass flowmeter, air enters the cyclone separator. A control valve is fixed at the outlet of a bag filter. Si-multaneously adjusting the mass flowmeter and the con-trol valve can control both the air flow rate and pressure.

Experiment procedure

At the beginning of each experiment, add solid parti-cle materials (Mf) into the feed bin, start the air com-pressor and adjust the inlet air flow (Q1) and leakage air flow (Q2) by the mass flowmeters F1 and F2, respectively. Adjust the operate pressure to the set value by the control valve, turn on the high pressure ball valve at the bottom of the feed bin. The pressure drop of the cyclone separa-tor decreased markedly as solid loading. While the pres-sure drop increased suddenly, all solid particles in the feed bin flowed out, the experiment is finished. Adjust the air flow rate (Q1) and (Q2) to zero, fetch and weigh the solid particles in the dust hopper separated by cy-clone separator.

The air leakage rate is defined as, 2

1100%

QQ

χ = × (1)

The inlet solid loading is defined as, a sM m m= (2)

Here, ma is the inlet air mass flow rate and ms the inlet solid particle mass flow rate.

Solid particle materials Quartz sand was used as solid particle material, the

Zhu Zhiping et al. Pressure Drop in Cyclone Separator at High Pressure 277

particle diameters are 0 ~ 0.5 mm and the apparent den-sity was 2502 kg/m3.

Measurement Generally, the pressure drop over a cyclone separator

is a difference of static pressure between the inlet and the outlet. The static pressure at inlet cross-section is uni-formly distributed because there is no swirling motion. It can be easily measured with a pressure tapping on the wall. However, there is strong swirling flow at the outlet pipe. The static pressure measurement becomes compli-cated and difficult. In the past, Stairmand[12] ignored the influence of the swirling flow, of course, it is not precise. Shepherd and Lapple[2] discharged the air directly from the cyclone to atmosphere. Meissner and Löffler[6] meas-ured the static pressure after a flow rectifier. The latter two ways have been widely used in investigation and engineering fields. In our experiments we measured the static pressure with a tapping on the tube wall. The di-ameter of the outlet pipe is changed from 20 mm to 32 mm at the cyclone separator roof to decrease the swirling strength.

Experimental results

1. χ = 0, M = 0 When χ and M are zero, the pressure drop of the cy-

clone separator relative to the operate pressure, shown in Figure 3, decreases with increasing of the operating pres-sure. The effect of the operating pressure on the pressure drop of the cyclone separator is stronger as the inlet air velocity increasing.

0.0 0.4 0.8 1.2 1.6 2.00

2

4

6

8

10

12

Pres

sure

dro

p (k

Pa)

Operate pressure (MPa)

vin = 10 m/s vin = 5 m/s vin = 3 m/s

Fig. 3 Effect of the operating pressure on the pressure drop of

the cyclone separator (χ = 0, M = 0) 2. χ >0, M = 0

While χ >0 and M = 0, as shown in Figure 4, the pres-sure drop of the cyclone separator decreases with in-creasing of the air leakage rate. Air leakage influences the spin intensity making the reduction of pressure drop. 3. χ = 0, M > 0

Change the operating pressure and the inlet solid

loading at the conditions of χ = 0, vin = 5 m/s, 0.03 < M <1.2, the pressure drop of the cyclone separator decreases with the increasing of the inlet solid loading. When the inlet solid loading increased from 0.03 to 0.2, the pres-sure drop of the cyclone separator decreased exponen-tially; but at a higher value of the inlet solid loading, the extent of reduction is small.

At a higher inlet velocity of 10 m/s the pressure drops of the cyclone separator, as shown in Figure 6, also de-crease exponentially with the increasing of the inlet solid loading.

0 2 4 6 8 10 12 140

2

4

6

8

10

12

vin = 10 m/s, P = 0.9 MPavin = 5 m/s, P = 1.9 MPavin = 5 m/s, P = 1.4 MPavin = 5 m/s, P = 0.9 MPavin = 5 m/s, P = 0.3 MPa

Pres

sure

dro

p (k

Pa)

Air leakage rate (%)

Fig. 4 Effect of the air leakage rate on the pressure drop of the cyclone separator (χ >0, M = 0)

0.0 0.2 0.4 0.6 0.8 1.0 1.20

1

2

3

4

5

6

1.9 MPa 1.4 MPa 0.9 MPa 0.3 MPa

Pres

sure

dro

p (k

Pa)

Inlet solid loading (kg/kg)

Fig. 5 Effect of inlet solid loading on pressure drop of cyclone separator (χ = 0, M > 0, vin = 5 m/s)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

2

4

6

8

10

12

0.9 MPa, vin = 10 m/s 0.9 MPa, vin = 5 m/s

Pres

sure

dro

p (k

Pa)

Inlet solid loading (kg/kg) Fig. 6 Effect of inlet solid loading on pressure drop of cy-

clone separator (χ = 0, M > 0, P = 0.9 MPa)

278 J. Therm. Sci., Vol.17, No.3, 2008

Let 12PΔ and 12'PΔ be the pressure drops of the cy-clone separator at M = 0 and M > 0, respectively. As shown in Figure 7, there is a good linear relationship between 12 12P P′Δ Δ and the inlet solid loading in loga-rithm coordinate system, whereas the effect of the oper-ating pressure and the inlet air velocity on this relation-ship is little. We can get an expression as follows,

0.33012

120.128

PM

P−′Δ

= ⋅Δ

(0.03≤M≤1.2) (3)

From this empirical relationship we can obtain the ef-fect of inlet solid loading on pressure drop of the cyclone. Numerous similar empirical relationships have been re-ported [3, 15-16], but all of the numerical values are differ-ent because the cyclone geometry and solid particles used in experiment were different, thus compare the empirical relationship have no actual significance for different cy-clone and operation conditions.

0.1 1

0.01

0.1

1

P = 0.9 MPa, vin

= 10 m/sP = 1.9 MPa, vin = 5 m/sP = 1.4 MPa, v

in = 5 m/s

P = 0.9 MPa, vin

= 5 m/sP = 0.3 MPa, vin = 5 m/s

ΔP' 12

/ΔP 12

（/）


Fig. 7 The relationship between 12 12P P′Δ Δ and inlet solid l oading

Model

Model of pure air The pressure drop of a cyclone consists of local losses

and a friction loss, consists of five parts: an expansion loss at the cyclone inlet, ΔP1; contraction loss at the en-trance of the outlet, ΔP2; friction loss between the air flow and the cyclone wall, ΔP3; swirling loss of the air flow in the separation space, ΔP4; dissipation loss of the air dynamic energy in the outlet, ΔP5. Therefore, the pressure drop of a cyclone separator can be expressed as:

1 2 3 4 5P P P P P PΔ = Δ + Δ + Δ + Δ + Δ (4) The air flow will expand both radially and axially after

entering a cyclone. The expansion loss can be expressed as[13]:

( )

222 in

1 g inw o

1 12

RP v

R R Hπ

ρ⎡ ⎤

Δ = −⎢ ⎥−⎢ ⎥⎣ ⎦

(5)

The contraction loss generates at the entrance of the outlet when the air flow enters the outlet tube because of

an abrupt variety of the flow area. Based on hydrody-namics theory, 2PΔ can be expressed as[14]:

2 2g 2o in

2 inCS o

0.5 12

R RP v

R Rρ⎡ ⎤⎛ ⎞ ⎛ ⎞⎢ ⎥Δ = − ⎜ ⎟ ⎜ ⎟

⎢ ⎥⎝ ⎠ ⎝ ⎠⎣ ⎦ (6)

The friction between the air and the cyclone wall due to the viscosity will result in friction loss. Because of the influence of this viscous friction, the swirling flow is not a combination of a free vortex and a forced vortex, but a combination of a quasi-free vortex and a quasi-forced vortex.

According to Mothes and Löffler’s model of swirling flow pattern[6, 17], the velocity profile in the separated space can be expressed as the following equation set:

θwθ

mw w

1 1

vv

r rKR R

=⎡ ⎤⎛ ⎞+ −⎢ ⎥⎜ ⎟

⎝ ⎠⎣ ⎦

(7)

**b θw

θw *b

1 14 2

v vv h

vhξ

ξ

⎛ ⎞⎜ ⎟= + −⎜ ⎟⎝ ⎠

(8)

2* wθw b

2 inin

w

0.204 0.889

Rv v

RRR

π=

⎛ ⎞−+⎜ ⎟⎜ ⎟

⎝ ⎠

(9)

1b 2

w

Qv

Rπ= (10)

in

w* in

w w

2 arccos 11

2

RRR hh

R R

πππ

π

⎡ ⎤⎛ ⎞− −⎢ ⎥⎜ ⎟⎜ ⎟⎢ ⎥⎝ ⎠= − +⎢ ⎥

⎢ ⎥⎢ ⎥⎣ ⎦

(11)

θw 0m 0

b sinv

Kv

ξξ

ε⎛ ⎞= +⎜ ⎟⎝ ⎠

(12)

21 in inQ R vπ= (13)

Here, *θwv is the wall surface tangential velocity of air

flow at the entrance region, θwv is the wall surface tan-gential velocity of air after suffering wall friction force,

0ξ is the wall friction coefficient for pure air. In Mothes and Löffler’s model, 0 0.0065 ~ 0.0075ξ = , without the influence of the particles concentration.

When air leak from a loop seal occurs, 1 2

b bl 2w

Q Qv v

Rπ−

= = (14)

Therefore, the wall surface tangential velocities of air flow, *

θwv , can be calculated, and the friction loss be-tween the air and the cyclone wall can be expressed as:

( )* 2 23 g θw θw

12

P v vρΔ = − (15)

Zhu Zhiping et al. Pressure Drop in Cyclone Separator at High Pressure 279

From Navier-Stokes equation in cylindrical coordi-nates, the relationship between the pressure and the ve-locity can be simplified by neglecting the axial effects:

2

g θdd

vPr r

ρ= (16)

Thus, the swirling loss can be obtained from:

( )( ){ }w

o

24 g θw m w w

1 1 1R

RP v r K r R R dr

rρ ⎡ ⎤Δ = + −⎣ ⎦∫ (17)

In the outlet tube, the air tangential velocity is very high, and the air flow is a combination of a quasi-free vortex and quasi-forced vortex. The air flow can be di-vided into two regions, a core region and an annual re-gion. The radius of the boundary between the two regions, Rc, equal to o3 3R approximately[18]. The axial veloc-ity in the annular region can be obtained from:

( ) ( )1 2 1 2oz 22 2

oo C

1.5Q Q Q Qv

RR R ππ

+ += =

⎡ ⎤−⎣ ⎦ (18)

In the quasi-free vortex region, the tangential velocity at radius Ro is θCSv , according to the rules of quasi-free vortex flow,

θCSo

C vR

= (19)

And, at radius Rc

θCC

CvR

= (20)

Eliminating the constant C, the following equation can be obtained,

o θCSθC θCS

C3

R vv v

R= = (21)

Thus, the mean tangential velocity θCmv can be cal-culated by the following equation,

θCm θCS θCv v v= (22) Consequently, the pressure loss for the aerodynamic

dissipation in the outlet tube can be obtained from

( )2 25 θCm oz

12 gP v vρΔ = + (23)

Substituting Equation (5), (6), (15), (17) and (23), the pressure drop of a cyclone separator for pure air can be calculated.

Model of dust-laden air According to Equation (3) and (4), we can catch the

influence rule of the inlet solid loading, ( )0.330

1 2 3 4 50.128P M P P P P P−′Δ = ⋅ ⋅ Δ + Δ + Δ + Δ + Δ (24)

Validation of the models Figure 8 and Figure 9 show the comparisons between

the experimental data and the calculate results. In the

range of our experiments, 0.03 < M <1.2, the trend of change on cyclone pressure drop with variety of operat-ing parameters predicted by the models is in accord with the experimental results, the maximum of relative error approximates 25%. From these comparisons, we can draw a conclusion: The model is suitable for predicting the pressure drop over a cyclone separator operating with pressurized, dust-laden air and different air leakage rate.

0 2 4 6 8 10 12 140369

12

P = 0.9 MPa, vin = 10m/s, Calculated data

P = 0.9 MPa, vin = 10m/s, Experimental data

Air leakage rate (%)

01234567



012345



Pres

sure

dro

p (k

Pa) 0.0

0.51.01.52.02.53.03.5



0.00.20.40.60.81.01.21.4



Fig. 8 Comparison between the calculated and experimental

data (χ > 0, M = 0)

Conclusions

The pressure drop of a cyclone separator under differ-ent operating pressure, air leakage rate, inlet velocity and solid loading is investigated.

Based on the experimental results, a semi-empirical model is developed. The comparisons between the ex-perimental data and the calculated results show that the model is suitable for predicting the pressure drop of the cyclone separator operating with pressurized, dust-laden air and different air leakage rate.

Acknowledgment

Financial support from The Ministry of Science and Technology of China (Contract No. 2003AA529220) is

280 J. Therm. Sci., Vol.17, No.3, 2008

sincerely appreciated.

0.0 0.2 0.4 0.6 0.8 1.00.00.51.01.52.02.5


P = 1.9 MPa, vin = 5 m/s, Calculated dataP = 1.9 MPa, vin = 5 m/s, Experimental data

0.00.81.62.43.24.0

P = 0.9 MPa, vin =10 m/s, Calculated data

P = 0.9 MPa, vin =10 m/s, Experimental data

0.00.20.40.60.81.01.2

Pre

ssur

e dr

op (k

Pa)

P = 0.9 MPa, vin = 5 m/s, Calculated data P = 0.9 MPa, vin = 5 m/s, Experimental data

0.00.10.20.30.4

P = 0.3 MPa, vin = 5 m/s, Calculated data P = 0.3 MPa, vin = 5 m/s, Experimental data

0.00.40.81.21.62.0

P = 1.4 MPa, vin = 5 m/s, Calculated dataP = 1.4 MPa, vin = 5 m/s, Experimental data

Fig. 9 Comparison between the calculated and experimental

data (χ = 0, M > 0)

References

[1] A. C. Hoffmann, L. E. Stein. Gas Cyclones and Swirl Tubes: Principles, Design and Operation [M]. Berlin: Springer-Verlag Berlin Heidelberg, 2002.

[2] C. B. Shephered, C. E. Lapple. Flow Pattern and Pressure Drop in Cyclone Dust Collectors [J]. Ind. Eng. Chem., 1939, 31 (8): 972−984.

[3] L. W. Briggs. Effect of dust concentration on cyclone performance [J]. Trans. Am. Inst. Chem. Eng., 1946, 42: 511−526.

[4] Leith David, Mehta Dilip. Cyclone performance and de-sign [J]. Atmospheric Environment, 1973, 7 (5): 527−549.

[5] Yuu Shinichi, Jotaki Tomosada, Tomita Yuji, et al. The reduction of pressure drop due to dust loading in a con-ventional cyclone [J]. Chemical Engineering Science, 1978, 33 (12): 1573−1580.

[6] H. Mothes, F. Löffler. A model for particle separation in

cyclones [J]. Chemical Engineering and Processing, 1984, 18 (6): 323−331.

[7] J. M. Beeckmans, B. Morin. The effect of particulate sol-ids on pressure drop across a cyclone [J]. Powder Tech-nology, 1987, 52 (3): 227−232.

[8] D. L. Iozia, Leith David. Effect of cyclone dimensions on gas flow pattern and collection efficiency [J]. Aerosol Science and Technology, 1989, (10): 491−500.

[9] Hemdan Shalaby, Klaus Wozniak, Wozniak, Günter. Par-ticle-laden flow simulation in a cyclone separator [J]. PAMM, 2006, 6 (1): 547−548.

[10] Liu Chengwen, Wang Lianze, Liu Qiusheng. Experimen-tal study and analysis on drag reduction mechanisms of reducing pressure drop stick in a cyclone separator [J]. Chemical Engineering and Technology, 2006, 29 (4): 495−503.

[11] A. Avci, I. Karagoz. Theoretical investigation of pressure losses in cyclone separators [J]. International Communi-cations in Heat and Mass Transfer, 2001, 28 (1): 107−117.

[12] C. J. Stairmand. Design and performance of cyclone separators [J]. Institution of Chemical Engineers

-Transactions, 1951, 29 (3): 356−373. [13] Zhao Bingtao. A theoretical approach to pressure drop

across cyclone separators [J]. Chemical Engineering and Technology, 2004, 27 (10): 1105−1108.

[14] Akira Ogawa, Osamu Seito, Hisao Nagabayashi. Distri-butions of the tangential velocity on the dust laden gas flow in the cylindrical cyclone [J]. Particulate Science and Technology, 1988, 6 (1): 17−28.

[15] H A.Gil; Luis M. Romeo. Effect of the solid loading on a pressurized fluidized bed combustors cyclone with pneumatic extraction of solids [J]. Chemical Engineering and Technology, 2002, 25: 407−515.

[16] A. P. Baskakov, V. N. Dolgov, Yu M. Goldobin. Aerody-namics and heat transfer in cyclones with particle-laden gas flow [J]. Experimental Thermal and Fluid Science, 1990, 3 (6): 597−602.

[17] H. Mothes, F. Löffler. Prediction of particle removal in cyclone separators [J]. International Chemical Engineer-ing, 1988, 28 (2): 231−240.

[18] Chen Jianyi, Luo Xiaolan, Shi Mingxian. Theoretical analysis on internal flow field of separation space cy-clone separators [J]. Journal of China University of Petroleum, 2006, 30 (6): 83−88.

Documents

Cyclone