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**Frank Th., Schneider J., Yu Q., Wassen E.:**- "Experimental and Numerical Investigation of Particle Separation in a Symmetrical Double Cyclone Separator"
- 8th Int. Symposium on Gas-Particle Flows,
- ASME Fluids Engineering Division Summer Meeting,
- San Francisco, CA, U.S.A., July 18-22, 1999.
- CD-ROM Proceedings, Paper No. FEDSM99-7865, pp. 1-10.

- (*) Chemnitz University of Technology
- Faculty of Mechanical Engineering and Process Technology
- Research Group of Multiphase Flow
- Reichenhainer Straße 70
- 09107 Chemnitz, Germany
- Email : drth.frank@arcor.de
- Phone : +49 (371) 531 46 43
- Fax : +49 (371) 531 46 44
- (**) Flensburg University of Applied Sciences
- Institut of Process Technology
- Dept. of Mechanical Process Technology
- Kanzleistraße 91-93
- 24943 Flensburg, Germany
- Phone : +49 (461) 805 512
- Fax : +49 (461) 805 300

- multiphase flow, gas-particle flow
- particle separation, gas cleaning
- cyclone separator, symmetrical double cyclone separator
- CFD, computational fluid dynamics, parallel computing
- Lagrangian approach, PSI-Cell model, numerical particle tracking

(There is a PDF version of this abstract available (contains figure and gives better printing output).)

Disperse multiphase flows are very common for processes in mechanical and thermal process technology (e.g. gas-particle or gas-droplet flows, coal combustion, pneumatical conveying, erosion phenomena). Furthermore processes for the separation of solid particles from gases or fluids and for the classification and particle size analysis are an important field of interest in process technology.

The paper deals with the experimental and numerical investigation of the
particle precipitation in a special class of cyclone separators, the so called
symmetrical double cyclone separator (see
figure).
This type of cyclones
was developed by the * Gesellschaft für Luft- und Umwelttechnik mbH,
Eckernförde/Germany* (LUT ltd.).
By using this type of cyclone the secondary flow along the lid, which is
observed in standard cyclones, can be avoided. In the case of a secondary
flow along the lid small particles can move directly from the inlet to the
clean gas exit bypassing the main vortex flow in the conical part of the cyclone.
The diagonal secondary
flow induced by the walls of the conical parts of the symmetrical double
cyclone leads to enrichment of the particle phase along the walls. The
secondary flow is led to the walls of the sedimentation chamber by special
shielding or guiding equipment attached at the lower end of the conical part
of the cyclone to the outer diameter of the vortex finder tubes.
In this flow region along the walls of the sedimentation chamber also
smaller particles are able to agglomerate and to
sedimentate as larger agglomerates in the sedimentation chamber.

In comparison with conventional cyclone separators and other kinds of special cyclones better particle precipitation can be achieved with this special type of a symmetrical double cyclone separators. This means that the cut-off particle diameter d_50 for the particle precipitation rate T (d_P) (with T (d_50) = 0.5) can be significantly decreased. For a diameter of the separation chamber of the cyclone of 40mm a cut-off particle diameter d_50 of less than 100 nanometers has been measured. Even for diameters of the separation chamber of about 200-250mm values for the cut-off particle diameter d_50 less than 1 micrometer could be measured (Schneider98, Bachmann96, Wieck97).

Experiments described in this paper were carried out at the Flensburg University of Applied Sciences. In a series of experiments a symmetrical double cyclone separator with a diameter of the separation chamber of 230 mm has been investigated. Particles have been dispersed with the RBG 1000 and the particle size measurements have been carried out using the particle sizer PCS 2000, both made by the PALLAS GmbH, Karlsruhe/Germany. For the particle phase calcium carbonate particles were used, produced under the trading name OMYACARB 2--GU by OMYA GmbH, Köln/Germany. So the particle phase used in the experiments for investigation of particle precipitation in the symmetrical double cyclone separator can be characterized by the mean particle diameter d_50,3 of the distribution sum Q_3 (d_P) of about 2.5 micrometers which corresponds to an aerodynamic diameter of about 4.1 micrometers.

The experimental results for the particle precipitation rates in the symmetrical double cyclone have been compared with numerical predictions for three different variations of the cyclone geometry. For these numerical simulations a 3-dimensional Lagrangian approach developed by Frank et al. (Frank92, Frank96b, Frank97c, Frank98a) was used. The numerical method is based on the modified Navier-Stokes solver FAN-3D (Peric92a, Peric92b) which is able to calculate 3-dimensional, steady, incompressible flows in complex geometries using non-orthogonal, boundary fitted, block-structured numerical grids. Due to the complex flow geometry of the investigated cyclone separators numerical grids with up to 95 different grid blocks and about 350.000 grid cells had to be designed for the numerical calculations of the gas-particle flow.

The disperse phase is treated by the Lagrangian approach where a large number of particle trajectories is calculated throughout the flow domain. For the formulation of particles equation of motion a small density ratio rho_F / rho_P is assumed. So the drag force, the lift force due to fluid shear (Saffman force), the pressure force, the gravitational and added mass force are taken into account (Frank97c, Frank98a). Particle precipitation rates were obtained from the calculation of about 10.000 particle trajectories with a particle diameter distribution in the range of d_P = 0.6 - 20.0 micrometers and by analyzing the number of particles reaching the particle hopper vs. the number of particles reaching the clean gas exit.

The numerical investigations for the precipitation of limestone particles (rho_P=2700 kg/m^3) were carried out for three different geometrical configurations of the symmetrical double cyclone using a constant gas inlet velocity of u_F = 25 m/s. In a first numerical simulation the influence of the gap width between the apex cone and the inner cyclone wall on the particle precipitation rate has been investigated. In a second numerical experiment the spiral inflow into the cyclone main body has been changed to a tangential inflow.

The numerical flow simulations confirm the expected main vortex flow structure known from cyclone theory and from experimental observations. The numerical predictions especially confirm the substantial contribution for particle precipitation of the recirculation of a certain gas volume flow rate from the cyclone main body through the gap at the apex cone into the particle hopper. The obtained numerical results for the particle precipitation rates are in good agreement with the experimentally predicted precipitation rates.

- Bachmann Ch., Schulz U., 1996
- "Experimentelle Ermittlung der Abscheideleistung von Hochleistungsentstaubern für feste Partikeln aus Gasen - Effektivität und Wirtschaftlichkeit"
- Diploma thesis, Flensburg University of Applied Sciences.

- Frank Th., 1992
- "Numerische Simulation der feststoffbeladenen Gasströmung im horizontalen Kanal unter Berücksichtigung von Wandrauhigkeiten"
- PhD Thesis, Techn. University Bergakademie Freiberg, Germany.

- Frank Th., Wassen E., 1996
- "Parallel Solution Algorithms for Lagrangian Simulation of Disperse Multiphase Flows"
- Proc. 2nd Int. Symposium on Numerical Methods for Multiphase Flows, ASME Fluids Engineering Division Summer Meeting
- San Diego, California, USA, July 7-11, 1996, Vol. 1, pp. 11-20.

- Frank Th., Wassen E., Yu Q., 1997
- "A 3-dimensional Lagrangian Solver for disperse multiphase flows on arbitrary, geometrically complex flow domains using block-structured numerical grids"
- Int. Symposium on Gas-Particle Flows, ASME Fluids Engineering Division Summer Meeting
- Vancouver, BC, Canada, June 22-26, 1997, CD-ROM Proceedings, FEDSM97-3590.

- Frank Th., Wassen E., Yu Q., 1998
- "Lagrangian prediction of disperse gas-particle flow in cyclone separators"
- ICMF '98 - 3rd International Conference on Multiphase Flow 1998
- Lyon, France, June 8.-12., 1998, CD-ROM Proceedings, Paper No. 217, pp. 1-8.

- Peric M., 1992
- "Ein zum Parallelrechnen geeignetes Finite-Volumen-Mehrgitterverfahren zur Berechnung komplexer Strömungen auf blockstrukturierten Gittern mit lokaler Verfeinerung"
- Abschluß bericht zum DFG-Vorhaben Pe 350/3-1 im DFG-Habilitandenstipendiumprogramm
- Stanford University, USA.

- Schreck E., Peric M., 1992
- "Parallelization of implicit solution methods"
- ASME Fluids Engineering Conference
- June 22-23, 1992, Los Angeles (CA), USA.

- Schneider J., 1998
- "Abscheideleistung eines symmetrischen Doppelzyklons"
- Research report of LTU ltd., Eckernförde, Germany
- to be published in Chemie-Ingenieur-Technik, 1999.

- Wieck T., Hofeditz U., 1997
- "Konstruktion und Fertigung unterschiedlicher Varianten von Zyklonabscheidern - Experimenteller Vergleich der Abscheideleistung"
- Diploma thesis, Flensburg University of Applied Sciences.

- Title
- Contents
- Different types of experimentally investigated symmetrical double cyclone separators - I
- Different types of experimentally investigated symmetrical double cyclone separators - II
- Functional diagram of symmetrical double cyclone separators
- Scheme of experimental test rig at FH Flensburg
- Technical data of experimental investigations
- Separation performance of cyclones ZA and ZS - experimental investigations
- Comparison of a standard cyclone and symmetrical double cyclone ZT
- The Eulerian-Lagrangian approach MISTRAL / PartFlow-3D - I
- The Eulerian-Lagrangian approach MISTRAL / PartFlow-3D - II
- Equations of motion of the fluid phase
- The 3-dimensional equations of motion for the disperse phase - I
- Equations of motion of the disperse phase - II
- Particle-wall interaction
- Models for erosion prediction in gas-particle flows
- Separation rate T(x) and distribution functions q(x) and Q(x)
- Numerical prediction of the particle separation rate T(X)
- Comparison of experimentally predicted separation rates for ZS18, ZS30 and ZT30
- Comparison of numerically predicted separation rates for ZS18, ZS30 and ZT30 - I
- Comparison of numerically predicted separation rates for ZS18, ZS30 and ZT30 - II
- Particle separation in symmetrical double cyclones
- Particle separation rates for symmetrical double cyclones of different size
- Numerical mesh for the double cyclone with spiral inflow ZS30
- Fluid flow field in the double cyclone ZS30 (x-z-plane)
- Detail of the fluid flow field for ZS30 in the vicinity of the apex cone (x-z-plane)
- Fluid flow field in the double cyclone ZS30 (y-z-plane)
- Detail of the fluid flow field for ZS30 in the vicinity of the apex cone (y-z-plane)
- Particle trajectories in ZS18 - I
- Particle trajectories in ZS18 - II
- Particle trajectories in ZS18 - III
- Particle separation in symmetrical double cyclones ZS18 and ZS30 - I
- Particle separation in symmetrical double cyclones ZS18 and ZS30 - II
- Numerical mesh for the double cyclone with spiral inflow ZT30
- Fluid flow field in the double cyclone ZT30 (x-z-plane)
- Detail of the fluid flow field for ZT30 in the vicinity of the apex cone (x-z-plane)
- Fluid flow field in the double cyclone ZT30 (y-z-plane)
- Detail of the fluid flow field for ZT30 in the vicinity of the apex cone (y-z-plane)
- Particle trajectories in ZT30 - I
- Particle trajectories in ZT30 - II
- Particle trajectories in ZT30 - III
- Distribution of the mean particle diameter for the ZT30 cyclone
- Wall erosion in ZT30 cyclone (y-z-plane)
- Wall erosion in ZT30 cyclone (x-z-plane)
- Particle number density distribution in ZT30 cyclone
- Particle separation in symmetrical double cyclones ZS18 and ZS30 - I
- Particle separation in symmetrical double cyclones ZS18 and ZS30 - II
- Parallel computation of gas-particle flow in cyclone separators
- Conclusions

Dr. Thomas Frank, last modified : March 30, 1999