Numerical simulation of the centrifugal separator for

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Jun 6, 2014 - Numerical simulation of the centrifugal separator for oil-water emulsion. Ph.D. ... Problems with free surface belong to a class of multiphase ...
Advanced Materials Research Vols. 945-949 (2014) pp 944-950 © (2014) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMR.945-949.944

Online: 2014-06-06

Numerical simulation of the centrifugal separator for oil-water emulsion Ph.D., associate professor Kharkov Nikita1, a Ph.D., associate professor Ermak Olga2, b Engineer, Aver’yanova Olesya3, c 1

Saint-Petersburg State Polytechnical University, Russia

2

Saint-Petersburg State Polytechnical University, Russia

3

Saint-Petersburg State Polytechnical University, Russia

a

b

c

[email protected], [email protected], [email protected]

Keywords: oil refining, centrifugal separator, flow swirling, numerical simulation, two-phase flows

Abstract. Calculation of a centrifugal water oil separator is shown. The separator represents alternative method of purifying water of oil inclusions and sludge (at a concentration up to 12%). The problems of creating a computational mesh, defining boundary conditions, separation two phases of oil-water emulsion and efficiency of separation are considered. Introduction Existing oil sedimentation tanks intended for cleaning oil-water emulsion is large-sized equipment (capacity of about 100 m3), where working fluid temperature is maintained at 50 C, which is very energy consuming [1, 2]. As less power expensive way of cleaning oil-water emulsion it is offered to use centrifugal separators. The first stage of calculation the separator design is made in the software package ANSYS Fluent. From the obtained results the conclusions on further optimization of separator design and calculation methods are made. Geometric model and problem statement

Fig. 1 Geometric model of the separator 1 - input stream; 2 - output of clean product; 3 – water and sluge outlet; 4 - output stream for recirculation. Problems with free surface belong to a class of multiphase applications [3-6]. Calculation was carried out in a two-phase nonstationary statement by solving the Navier-Stokes equations connecting Volume of Fluid (VOF) model (specialized on solutions with free surface) [7-22]. Principal All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, www.ttp.net. (ID: 92.62.61.159-21/07/15,09:24:10)

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possibility to realize effective cleaning of oil in similar construction of a separator and possible ways of process optimization is researched. Computational mesh and boundary conditions

Fig. 2 Computational mesh (full model) - 1106460 cells Figure 2 shows a block-structured hexahedral mesh finer to the walls for correct modeling processes proceeding in the boundary layer. Calculation of the full model in the two-phase statement requires considerable resources of computer time [23-29]. In this cases more efficient use the model with periodic boundary conditions.

Fig. 3 Geometrical model with periodic boundaries The mesh size for sector of 1/6 models is equal 184660 cells (approximately 6 times less than the full model). Comparison of calculations in a single-phase full-staged model and model with periodic boundary conditions (Fig. 4, 5) showed that excluded from consideration the drainage channel has no effect on the velocity field and pressure.

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Fig. 4 Distribution graphs of velocity module along the longitudinal control lines y = 0 m (left - separator axis); y = 0.25 m (right)

Fig. 5 Distribution graphs of the total pressure along the longitudinal control lines y = 0 m (left - separator axis); y = 0.25 m (right) Further analysis is performed on the model with periodic boundary conditions (Fig. 6)

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Fig. 6 Boundary conditions with oil fraction at the inlet set in the axial region Setting the oil-water emulsion with a certain concentration ratio was not possible, so the concentration of water and oil are given zonally. All the water inlet is defined at a central portion thus modeled the most difficult option in terms of separation. Conditions for solving the problem and results • •

• • •



On the inlet boundary value of speed – 2 m/s (flow rate is 43. 2 m3/h) At the boundaries of outlet 1, 2, 3, the outflow of fluid given in the ratio of the total flow rate: outlet 1 – 5 % outlet 2 – 75% outlet 3– 20% On other boundary condition is given wall, no-slip condition is realized During the solution is obtained, the process comes to a steady state after about 1 second since the beginning of the movement In the simulation were used Segregated solver (the equations of continuity, impulses, turbulence are solved consistently) and PRESTO scheme (PREssure STaggering Option) oriented to solution problems with swirling flow Courant number is set 0.25

Due to low velocities (except interscapular channel guide vanes - up to 10 m/s) and large values of the viscosity (140 cSt and 1 cSt for oil and water, respectively), the problem was solved in the laminar formulation.

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Fig. 7 Water surface visualization The table 1 shows the results of a calculation for the most «difficult» case from the point of view of separation is shown. Water has to move from the axial region to the periphery, even in this case there is a positive result. Table 1 Calculation results The water concentration at inlet [%]

12%

5.7%

2.2%

Boundaries

Flow rate [m3/h]

Water flow rate [m3/h (%)]

Oil flow rate [m3/h (%)]

Oil inlet

38

-

-

Water inlet

5,2

-

-

Cleared oil

2,2

0 (0)

2,28 (6)

Draining

8,672

0,312 (6)

8,36 (22)

Recirculation

32,4

4,888 (94)

27,36 (72)

Oil inlet

40,8

-

-

Water inlet

2,4

-

-

Cleared oil

2,2

0 (0)

2,2 (5,4)

Draining

8,6

0,132 (5,5)

8,486 (20,8)

Recirculation

32,4

2,268 (94,5)

30,11 (73,8)

Oil inlet

42,25

-

-

Water inlet

0,95

-

-

Cleared oil

2,2

0 (0)

2,323 (5,5)

Draining

8,6

0,019 (2)

8,45 (20)

Recirculation

32,4

0,931 (98)

31,47 (74,5)

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Summary 1. Despite the "difficult" input conditions obtained positive results of oil separation. 2. However, in the calculation model guide vanes make turbulent perturbations in the flow. To account for this phenomenon is required to connect the turbulence model. To solve the problems with the swirling flow is recommended to connect seven-parametric Reynolds stress model (RSM turbulence model). This model allows the calculation of non-isotropic turbulent flow observed in swirling flows. Calculation problem connecting RSM turbulence model will be conducted in in subsequent papers. 3. Further optimization of construction of the device is possible in the following directions: - regulation of the boundary conditions at the outlet flow - correction of guide vanes construction to reduce turbulence in the flow References [1] G.J. Hirasaki, C.A. Miller, O.G. Raney, D.T. Nguyen. J. Hera, M.K. Poindexter: Separation of produced emulsions from surfactant enhanced oil recovery processes. 2011. Energy and fuels. Vol. 25. No. 2. pp. 555-561. [2] A. Silset, A. Hannisdal, P.V. Hemmingsen, J. Sjöblom: Emulsions of heavy crude oils. II. viscous responses and their influence on emulsion stability measurements. 2010. Journal of dispersion science and technology. Vol. 31. No. 10. pp. 1432-1445. [3] Spalart P.R., Shur, M.L.: On the sensitization of turbulence models to rotational and curvature. 1997. Aerospace Science and Technology. Vol. 1, No. 5. pp. 297-302. [4] A.I. Khrabriy, D.K. Zaicev, E.M. Smirnov: Numerical modeling of flow with free surface based on the method VOF. 2013. Works of CRI acad. A.N. Krylov. No. 78 (362). pp. 53-64. [5] C.W. Hirt, B.D Nichols: Volume of fluid (VOF). Method for the dynamics of free boundaries. 1981. Journal of Computational Physics. Vol. 39. pp. 201-226. [6] R. Wemmenhove: Numerical simulation of two-phase flow in offshore environments: PhD thesis. 2008. University of Groningen, pp. 121-125. [7] A.A. Khalatov: Theory and practice of swirling flows. 1989. AS USSR. Institute of Engineering Thermophysics. - Kiev: Science. Dumka - 192 p. - ISBN 5-12-000927-1. [8] A.A. Girgidov, K.I. Streletc, N.I. Vatin: Numerical simulation of three-dimensional velocity field in the cyclone. 2011. Magazine of Civil Engineering. No. 5 (23). pp. 5-9. [9] N.I. Vatin, T.N. Mikhailova: Computation of cross correlation function of induced potential for developed turbulent flow with axisymmetric mean velocity profile. 1986. Magnetohydrodynamics New York, N.Y., 22 (4), pp. 385-390. [10] N.I. Vatin: Weight vector of conduction transducer of a correlation flowmeter. 1985. Magnetohydrodynamics New York, N.Y., 21 (3), pp. 316-320. [11] V.P. Bocheninskii, N.I. Vatin, V.S. Shmarov: Results of investigation of transient processes in liquid metal loops with MHD Pumps. 1981. Trudy LPI (374), pp. 20-23. [12] V.N. Bukhartsev, M.R. Petrichenko: Conditions of mechanical-energy balance of an integral flow with a variable rate. 2001. Hydrotechnical Construction 35 (4) pp. 189 -194. [13] D.V. Platonov, A.V. Minakov, A.A. Dekterev, A.V. Sentyabov: Numerical modeling of spatio flows with flow swirling. 2013. Computer studies and modeling. Vol. 5. No.4. pp. 635-648. [14] M.O. Gagne: Turbulence modeling of swirling flow in a sudden expansion geometry. 1997. Degree: M.A.Sc. Technical University of Nova Scotia (Canada).

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[15] A.V. Shvab, A.G. Chepel: Modeling of swirling turbulent flow in a separator with biconical plates. 2010. Journal of engineering physics and thermophysics. Vol. 83. No. 2. pp. 338-345. [16] S. Jakirlic, K Hanjalic, C. Tropea: Modeling rotating and swirling turbulent flows: a perpetual challenge. 2002. AIAA Journal. Vol. 40. No. 10. pp. 1984-1996. [17] R. Thundil Karuppa Raj, V. Ganesan: Study on the effect of various parameters on flow development behind vane swirlers. 2008. International journal of thermal sciences. Vol. 47. No. 9. pp. 1204-1225. [18] J. Vondal, J. Hajek: Swirling flow prediction in model combuster with axial guide vane swirler. 2012. Chemical engineering transactions. Vol. 29. pp. 1069-1074. [19] N. Pourmahmoud, A. Hassanzaden, S.E. Rafiee, M. Rahim: Three-dimentional numerical investigation of effect of convergent nozzles on the energy separation in a vortex tube. 2012. Heat and technology. Vol. 30. No. 2. pp. 133-140. [20] M.-Z.P. Ismadi, P. Meunier, A. Fouras, K. Hourigan: Experimental control of vortex breakdown by density effects. 2011. Physics of fluids. Vol. 23. No. 3. pp. 034104-9. [21] I.A. Belov, S.A. Isaev: Modeling of turbulent flows, SPb, BGTU, 2001, 108 p. [22] A.K. Panov, R.R. Usmanova, V.G. Zaikov, G.E. Zaikov: Complex aerohydrodynamic research and the effectiveness or arresting dispersed particles for barbotage-rotation. 2007 Journal of Applied Polymer Science 104 (4), pp. 2088-2091. [23] Y. Liu, L.X. Zhou, C.X. Xu: Numerical simulation of instaneous flow structure of swirling and non-swirling coaxial-jet particle-laden turbulence flows. 2010. Physica A: Statistical Mechanics and its Applications. Vol. 389. No. 23. pp. 5380-5389. [24] R. Hreiz, C. Gentric, N. Midoux: Numerical investigation of swirling flow in cylindrical cyclones. 2011. Chemical engineering research and design. Vol. 89. No. 12. pp. 2521-2539. [25] A. Escue, J. Cui: Comparison of turbulence models in simulating swirling pipe flows. 2010. Applied Mathematical Modelling. Vol.34, Iss. 10. pp. 2840-2849. [26] M.A. Abdoh, I.M. Kolesnikov: Kinetics of allocation of water from a water black oil emulsion. 2006. Chemistry and Technology of Fuels and Oils. No. 6. pp. 31-32. [27] B. Pardowitz, U. Tapken, R. Sorge, P.U. Thamsen, L. Enghardt: Rotating Instability in an Annular Cascade: Detailed Analysis of the Instationary Flow Phenomena. 2013. Journal of Turbomachinery. Vol. 136. Iss. 6, pp. 061017. [28] L.O. Diehl, D.P. Morales, F.G. Antes, J.S.F. Pereira, J.N.G. Paniz, E.M.M. Flores, M.P.S De Fatima, R.C.L. Guimaraes: Separation of heavy crude oil emulsion using microwave radiation for further crude oil analysis. 2011. Separation science and technology. Vol. 46. No. 8. pp. 1358-1364. [29] E.R. Binner, J.P. Robinson, S.W. Kingman, E.H. Lester. B.J. Azzopardi, G.Dimitrakis, J. Briggs: Separation of oil/water emulsion in continuous flow using microwave heating. 2013. Energy and fuels. Vol. 27. No. 6. pp. 3173-3178.

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Numerical Simulation of the Centrifugal Separator for Oil-Water Emulsion 10.4028/www.scientific.net/AMR.945-949.944