- Email: [email protected]
The dehydration performance evaluation of a new supersonic swirling separator
Journal of Natural Gas Science and Engineering 27 (2015) 1667e1676
Contents lists available at ScienceDirect
Journal of Natural Gas Science and Engineering journal homepage: www.elsevier.com/locate/jngse
The dehydration performance evaluation of a new supersonic swirling separator Xuewen Cao*, Wen Yang College of Pipeline and Civil Engineering, China University of Petroleum, No.66, Changjiang West Road, Qingdao, 266580, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 16 July 2015 Received in revised form 20 October 2015 Accepted 23 October 2015 Available online 28 October 2015
A new supersonic swirling separator with an ellipsoidal central body has been designed, and an indoor experimental system and simulation method are utilised to evaluate the dehydration performance of the designed separator. The dew point depression and adaptability of the separator inlet and outlet working conditions are analysed to evaluate the dehydration performance. The experimental results show that the separator has a good dehydration performance, with the pressure recovery coefficient ranging from 20.6% to 69.8%. The maximum dew point depression is 34.9 C, with the dew point depression decreasing as the pressure recovery coefficient increases, where the former is 18.3 C C at a high pressure recovery coefficient (69.8%). The inlet pressure and inlet temperature have a weak influence on the dehydration performance when the mass flow rate meets the separator working requirement. In addition, dehydration performance is not affected by the liquid outlet pressure. This means that the designed separator can operate normally across a large range of inlet and outlet working conditions. © 2015 Elsevier B.V. All rights reserved.
Keywords: Supersonic swirling separator Dehydration Experiment Simulation Evaluation
1. Introduction Natural gas always contains significant quantities of water vapour when it is exploited from underground sources. The water vapour will condense in the pipeline as the transportation pressure and temperature change, which will cause blockage and corrosion of the pipeline. Therefore, removing the water from the natural gas is a fundamental necessity. Several methodsdincluding absorption, adsorption, cooling, and membrane separationdhave been developed to dehydrate natural gas. A new method called supersonic swirling separation was introduced for natural gas dehydration in 1996 by ENGO and Shell (Jones et al., 2003; Prast et al., 2006; Schinkelshoek et al., 2006). The proposed supersonic swirling separators (‘3S’ and ‘Twister’) work on two major principles, namely condensation separation and cyclone separation at supersonic velocities (Wen et al., 2012a). Due to their advantages, including a compact design, low weight, no need for chemical additives, and unmanned operation (Wen et al., 2011a), extensive studies have been carried out on the separators. Many numerical simulations have been performed. The high-pressure natural gas flow characteristics in supersonic swirling separators
* Corresponding author. E-mail address: [email protected] (X. Cao). http://dx.doi.org/10.1016/j.jngse.2015.10.029 1875-5100/© 2015 Elsevier B.V. All rights reserved.
have been studied with computational fluid dynamics (CFD) technology, and the effects of the real gas and separator geometry on the flow characteristics have been analysed (Jassim et al., 2008a; Jassim et al., 2008b). The effects of inlet pressure, inlet temperature, inlet mass flow rate, back pressure, and shockwaves on the gas-dynamic parameters in separators have also been analysed (Karimi et al., 2009; Malyshkina, 2010, 2009). In addition, the microscopic homogeneous nucleation in rapid expansion without swirling has also been discussed (Jiang et al., 2009; Ma et al., 2009a, 2010). Many experimental studies have focused on the condensation characteristics of the vapour in the nozzle (Wyslouzil et al., 1994, 1997; Heath et al., 2002; Khan et al., 2003; Ghosh et al., 2010; Harshad, 2013). Some numerical work on the swirling characteristics and separator characteristics of the separators has been done by Xuewen Cao by using the FLUENT software to investigate supersonic swirling separators with an ellipsoidal central body (Wen et al., 2011a; Wen et al., 2012b), but the evaluation of the separation characteristics experiment has not been reported until now. There is also a lack of experimental studies on separation characteristics, and only a few experiments have been reported. Experimental results for the Twister show that a maximum dew point depression of 22e28 C can be obtained, but the details of the experimental conditions are not described (Okimoto et al., 2002). A new type of dehydration unit with a different structure from the Twister has been developed and an indoor test has been carried
1668
X. Cao, W. Yang / Journal of Natural Gas Science and Engineering 27 (2015) 1667e1676
out. The effects of the pressure loss ratio, shockwaves, and the flow rate on the dehydration characteristics have been analysed, and the maximum dew point depression is approximately 20 C without any need for external mechanical power or chemicals (Liu et al., 2005). Ma et al. (2009b) also developed a new kind of separator with an inner pyramid, and experimental results showed that the dew point depression can reach 29 C by adopting the proposed droplet enlargement method, which is difficult to use. This paper introduces a new supersonic swirling separator with an ellipsoidal central body, which is proposed to reduce gas flow resistance. The dehydration performance of the designed separator is evaluated using experimental and simulation methods. The effects of the pressure recovery coefficient, inlet pressure, inlet temperature, and liquid outlet pressure on the separation characteristics of the separator are discussed. The effects of the liquid outlet pressure on the separation characteristics are discussed for the first time. 2. Experimental system 2.1. The experimental process The overall experimental system and major experimental set-up are shown in Fig. 1. The detailed separation process is as follows. Compressed air flows through the surge tank and filter, mixes with micro-water mist from a high pressure micro mist humidifier, and then goes into the supersonic swirling separator after being
measured by the vortex flowmeter. The mixture condenses in the supersonic swirling separator. Thereafter, condensed liquid flows out through the liquid outlet driven by centrifugal force. Meanwhile, gas enters the surge tank from the gas outlet of the supersonic swirling separator after it is measured by the vortex flowmeter, and then moves into the air. 2.2. The supersonic swirling separator In this study, a new structure of supersonic swirling separator with an ellipsoidal central body is designed, as shown in Fig. 2. The swirling device consists of 12 vanes turned through 45 . The vanes can ensure that the inlet of the vanes is in line with the direction of the flow to reduce resistance, and the larger outlet angle can produce a larger swirling flow field. The swirling vanes on the central body are helical blades designed with the unequal pitch method, and the helix equation of the vanes is presented in Eq. (1).
8 r ¼ f ðzÞ þ r0 > > > > Zt > > > > > q ¼ uðtÞdt þ q0 < 0 > > Zt > > > > > z¼ vðtÞdt þ z0 > > :
(1)
0
Fig. 1. Experimental system and major setup. 1-Screw compressor; 2,11-Surge tank; 3- Filter; 4- High pressure micro mist humidifier; 5-Valve; 6-Humidifying tank; 7-Heat exchanger; 8,12,13-Self-operated pressure control valve; 9- Vortex flowmeter; 10- Supersonic swirling separator.
X. Cao, W. Yang / Journal of Natural Gas Science and Engineering 27 (2015) 1667e1676
1669
Fig. 2. Structure of supersonic swirling separator designed.
where u(t) and v(t) are the angular velocity and axial velocity, respectively; (r0, q0, z0) is the initial point coordinate; (r, q, z) is the moving point coordinate; and f(z) is the curved surface formed by the moving points. The annular channel between the central body and the wall forms a Laval nozzle, a cyclone separation section, and a diffuser, as shown in Fig. 2. The swirling motion is generated by the swirling vanes on the central body, which are located in the subsonic part of the channel. The wet gas condenses in the Laval nozzle due to the formation of a low temperature and low pressure. The liquid and gas are separated, driven by the centrifugal force in the cyclone separation section, and the kinetic energy of the gas decreases while its static pressure and temperature increase as it moves across the diffuser. According to the designed inlet working parameters (0.6 MPa, 30 C, 300 Nm3/h), the structure of the separator is determined. The whole length of the separator is 945.3 mm; the diameter of the inlet is 80 mm; the inner-wall diameter and central body diameter at the throat are 15.94 mm and 12.00 mm, respectively; and the wall inner diameter and central body diameter at the gas outlet are 15.94 mm and 6.4 mm, respectively. 2.3. The other set-ups An Atlas Copco GA45 VSD screw compressor (Atlas Copco, 2015) is utilised to provide compressed air. Its maximum working pressure and mass flow are 1.3 MPa and 515 Nm3/h, respectively. The screw compressor combines the surge tank installed to ensure the
pressure and mass flow stability at the inlet of the supersonic swirling separator. A high-pressure micro mist humidifier with a 6 MPa maximum working pressure is utilised to add micro-water mist to the compressed air. The diameter range of the micro mist is 0.1e5 mm. The precision of the Yokogawa DY040 Vortex flowmeter is ±0.75%. It is used to measure the inlet and outlet volume flow rate of the supersonic swirling separator. The inlet and gas outlet temperature and the humidity of the supersonic swirling separator are measured by Vaisala HMT3608 humidity/temperature transducers. The precision of the transducers is ±0.2 C and ±1.5% for temperature and humidity, respectively. Rosemount 3051 pressure sensors are mounted at the inlet, gas outlet, and liquid outlet of the supersonic swirling separator. The precision of these sensors is ±0.075%. Pressure adjustment at the inlet, gas outlet, and liquid outlet of the supersonic swirling separator is conducted by a KOSO800 self-operated pressure control valve, and flow rate adjustment is conducted by a Yamatake electric control valve.
2.4. Dehydration performance criterion The effects of the pressure recovery coefficient (gp), inlet pressure, inlet temperature, and liquid outlet pressure on the performance of the designed supersonic swirling separator have been investigated. Dew point depression (DTd) is the criterion used to evaluate the dehydration performance of the separator. The definitions of the pressure recovery coefficient and the dew point depression are presented in Eq. (2) and Eq. (3), respectively.
Fig. 3. Unstructured tetrahedral meshes.
1670
X. Cao, W. Yang / Journal of Natural Gas Science and Engineering 27 (2015) 1667e1676
Fig. 6. Dew point depression at different pressure recovery coefficient of the separator.
Fig. 4. Calculation results at the nozzle outlet axis with different mesh cells. (a)Mach number distribution; (b) Temperature distribution.
gp ¼ ðpout =pin Þ 100%
(2)
where pout and pin are the pressure at the gas outlet and at the wet gas inlet, respectively.
DTd ¼ Tdin Tdout
Fig. 7. Dew point depression at different inlet pressure of the separator.
(3)
Fig. 5. Static temperature distribution in the separator at different pressure recovery coefficient.
X. Cao, W. Yang / Journal of Natural Gas Science and Engineering 27 (2015) 1667e1676
where Tdin and Tdout are the dew point of the gas at the inlet and at the gas outlet, respectively.
3. Numerical approach 3.1. Governing equations The gas flow characteristics in the supersonic swirling separators are described by the continuity equation, the momentum equation, and the energy equation. They are described in Eqs.
1671
(4)e(6).
v ruj ¼ 0 vxj
(4)
" !# vuj vui 2 vul v vp v v ru0 i u0 j þ dij m þ rv uj ui ¼ þ vxj vxi vxj vxj vxi vxj 3 vxl
Fig. 8. Distribution of gas dynamic parameters at different inlet pressure. (a)Mach number; (b) Static temperature; (c) Tangential velocity.
(5)
1672
X. Cao, W. Yang / Journal of Natural Gas Science and Engineering 27 (2015) 1667e1676
v v r u E þ uj p ¼ vxj v j vxj
vT þ ui teff keff vxj
! (6)
where r, u, p are the vapour density, velocity, and pressure, respectively; keff is the effective thermal conductivity; teff is the effective viscous stress; dij is the Kronecker delta; u0 is the velocity fluctuation, and the Reynolds Stress Model was adopted to calculate the Reynolds stress term; E is the total energy; and t is the time. The differencing formulation used in this work is second-order upwind.
. a ¼ 0:457247R2 Tc2 pc
(9)
b ¼ 0:07780RTc =pc
(10)
h pffiffiffiffiffiffiffiffiffiffii2 aðTÞ ¼ 1 þ m 1 T=Tc
(11)
m ¼ 0:37464 þ 1:54226u 0:2699u2
(12)
The mixture rules are as follows: 3.2. Mesh generation
am ¼
In the study, unstructured tetrahedral meshes are generated for the numerical computation due to the twisted vanes and complex sump, as shown in Fig. 3. Four cases with different mesh cells are generated, where there are 276,549, 467,852, 611,258, and 1,278,561 mesh cells, respectively. The Mach number and temperature distribution at the nozzle outlet axis are presented in Fig. 4. The results show that 611,258 mesh cells provide sufficient grid independence for the designed supersonic swirling separator.
XX i
bm ¼
X
0:5 xi xj ai aj 1 kij
(13)
j
x i bi
(14)
i
where R is the universal gas constant; p and T are the gas pressure and temperature, respectively; v is the molar specific volume; Tc and Pc are the critical temperature and critical pressure, respectively; and u is a centric factor. 4. Results and discussion
3.3. Boundary conditions and convergence criterion According to the flow characteristics of the supersonic compressible flow in the supersonic swirling separator, pressure boundary conditions are assigned to the inlet (wet gas inlet) and outlet of the nozzle (gas outlet and liquid outlet). Non-slip and adiabatic boundary conditions are specified for the walls. Pressure inlet: Specify the gauge pressure, static pressure, total temperature, and turbulence parameters. The turbulence strength and viscosity ratio are assigned as turbulence parameters. The turbulence strength (I) can be estimated from the following equation that is derived from an empirical correlation for pipe flows:
I ¼ 0:16ðReÞ1=8
(7)
where Re is the Reynolds number. The turbulent viscosity ratio, mt/m, is directly proportional to the turbulent Reynolds number. Typically, the turbulence parameters are set such that 1 < mt/m < 10. Pressure outlet: No parameters should be specified at the outlet for the supersonic flow. Specify the gauge pressure, total temperature, turbulence strength, and viscosity ratio for the calculation with different pressure recovery coefficient conditions. The convergence criterion is 106 for the energy equation residual error, 103 for other equations' residual error, and the mass flow rate absolute error between the inlet and outlet is less than 0.05%.
Natural gas raises significant safety concerns in a laboratory environment. Hence, a safer alternative air is selected as the carrier gas in our experiments. Different working conditionsdsuch as the different pressure recovery coefficient conditions, different inlet pressure conditions, different inlet temperature conditions, and different liquid outlet pressure conditionsdare used to evaluate the dehydration performance of the separator. 4.1. Effects of pressure recovery coefficient on separator performance The static temperature distribution at different pressure recovery coefficients in the simulation results is shown in Fig. 5. The static temperature at the outlet of the Laval nozzle increases as the pressure recovery coefficient increases, which shows that the expansion ability and water condensation ability decrease as the pressure recovery coefficient increases. That is, the separator has a
3.4. Equation of state The PengeRobinson equation of state (PR EoS), which is frequently utilised to calculate the physical properties of real gas, is used to describe the gas characteristics at different conditions in the supersonic swirling separator in this work. The PR EoS is described as follows:
p¼
RT aaðTÞ v b vðv þ bÞ þ bðv bÞ
(8) Fig. 9. Dew point depression at different inlet temperature of the separator.
X. Cao, W. Yang / Journal of Natural Gas Science and Engineering 27 (2015) 1667e1676
worse dehydration performance when the pressure recovery coefficient is higher, but more pressure energy is recovered. This means that a higher dew point depression can be acquired by sacrificing the gas pressure energy. An appropriate pressure recovery coefficient should be selected to acquire desired dew point depression according to the actual gas treatment requirement. Another thing to be concerned about is shockwaves. Shockwaves will be generated in Laval nozzles when the pressure recovery coefficient is higher than a fixed valve according to gas dynamic theory. The generation of shockwaves in Laval nozzles will destroy the existence of a condensation environment. Hence, an appropriate pressure recovery coefficient should be selected to ensure that condensation occurs.
1673
Experiments have been carried out to evaluate the dehydration performance of the separator and to find out the value of the fixed pressure recovery coefficient. The results are presented in Fig. 6, which shows that the dew point depression decreases as the pressure recovery coefficient increases. The dew point depression is 34.9 C when the pressure recovery coefficient is 20.6%, and it decreases to 18.3 C when the pressure recovery coefficient increases to 69.8%. The effect of the pressure recovery coefficient on the dehydration performance of the separator is significant. A higher dew point depression can be acquired with a larger pressure energy loss in the separator. When the pressure recovery coefficient is higher than 69.8%, the shockwaves enter the separator, and the condensation and separation environment in the
Fig. 10. Distribution of gas dynamic parameters at different inlet temperature. (a)Mach number; (b) Static temperature; (c) Tangential velocity.
1674
X. Cao, W. Yang / Journal of Natural Gas Science and Engineering 27 (2015) 1667e1676
separator will be destroyed. The dew point depression almost becomes zero when the pressure recovery coefficient is higher than 69.8%, showing that 69.8% is the fixed pressure recovery coefficient for this nozzle. The highest dew point depression in our separator is 34.9 C, which occurs when the pressure recovery coefficients is 20.6%. 4.2. Effects of inlet pressure on separator performance The effects of the inlet pressure on the dew point depression, that is, on the condition that the mass flow rate can meet the separator mass flow rate requirement (supersonic flow after throat), have been investigated experimentally. The experimental results are presented in Fig. 7, in which it is shown that the dew point depression decreases at all four different inlet pressures as the pressure recovery coefficient increases, which corroborates the discussion in Section 4.1. In addition, it can be seen that the difference between the dew point depression for the four inlet pressure conditions at a fixed pressure recovery coefficient is small, which illustrates that the influence of the inlet pressure on the dehydration performance of the separator is weak with a fixed pressure recovery coefficient. The distribution of the gas-dynamic parameters in the separator at different inlet pressures in the simulation results are shown in Fig. 8, where it can be seen that the Mach number and static temperature at the Laval nozzle outlet are similar at different inlet pressures with a fixed pressure recovery coefficient, which demonstrates that temperature depressions are similar at a fixed pressure recovery coefficient condition. Meanwhile, the maximum tangential velocity values are similar, indicating similar swirling separation abilities at different inlet pressures. Therefore, the dehydration performances of the separator with different inlet pressures with a fixed pressure recovery coefficient are similar, which corroborates experimental results. The experimental results illustrate that designed separator can operate normally across a large range of inlet pressures when the mass flow rate meets the separator mass flow rate requirement. 4.3. Effects of inlet temperature on separator performance The effects of the inlet temperature on the dew point depression, that is, on the condition that the mass flow rate can meet the separator design mass flow rate requirement, have been investigated experimentally. The experimental results are presented in Fig. 9. The dew point depression variation with respect to the pressure recovery coefficient corroborates the discussion in Section 4.1. A similar conclusion can be obtained from the experimental results. That is, the inlet temperature has a weak influence on the dehydration performance of the separator at a fixed pressure recovery coefficient. The simulation results of the effects of inlet temperature on the distribution of the gas-dynamic parameters in the separator are shown in Fig. 10. The Mach numbers at the Laval nozzle outlet are all 1.40 for the various inlet temperature conditions. Meanwhile, the temperature depressions are all approximately 80 K. The simulation results demonstrate that the separator expansion ability is similar for the separator at the various inlet temperature conditions. In addition, the same maximum tangential velocity at different inlet temperature conditions, approximately 138 m/s, indicates that the separator's swirling separation abilities are the same. According to the above discussion, the inlet temperature has a weak effect on the dew point depression with a fixed pressure recovery coefficient, which is reflected in the experimental results. The experimental results illustrate that our designed separator
can operate normally across a large range of inlet temperatures when the mass flow rate meets the separator mass flow rate requirement. 4.4. Effects of liquid outlet pressure on the separator performance The experimental study of the effects of the liquid outlet pressure on the dew point depression is carried out under the condition that the inlet pressure and gas outlet pressure are kept constant (0.6 MPa and 0.18 MPa, respectively). The experimental results are presented in Fig. 11. As shown in Fig. 11, the influence of the liquid outlet pressure on the water dew point depression is minimal. The experimental results further illustrate that the separation of liquid and gas is not controlled by the liquid outlet pressure, which is a typical inertial separation process that is affected by the centrifugal force, namely tangential velocity, to a large extent. The simulation results of the effects of the liquid outlet pressure on the distribution of the gas-dynamic parameters in the separator are shown in Fig. 12, where it can be seen that the Mach number, static temperature, and tangential velocity at the Laval nozzle outlet are all the same for the various liquid outlet pressures, demonstrating that the separator's dehydration performance is not affected by the liquid outlet pressure. That is, the liquid outlet pressure can be increased to the greatest extent to decrease the amount of slip gas and pressure loss. 5. Conclusions The designed supersonic swirling separator has a good dehydration performance without any chemical agent or external mechanical power. The maximum dew point depression is 34.9 C when the pressure recovery coefficient is 20.6%. The dew point depression can be 18 C with a very high pressure recovery coefficient (69.8%). The pressure recovery coefficient is the main factor that affects the performance of the designed separator. The dew point depression decreases as the pressure recovery coefficient increases, showing that a better dehydration performance can be achieved with a larger pressure energy loss in the separator. The inlet pressure and inlet temperature have a weak influence on the dehydration performance of the separator with a fixed
Fig. 11. Dew point depression at different liquid outlet pressure of the separator.
X. Cao, W. Yang / Journal of Natural Gas Science and Engineering 27 (2015) 1667e1676
1675
Fig. 12. Distribution of gas dynamic parameters at different liquid outlet pressure. gp-l ¼ pout-l/pin, where pout-l is pressure at liquid outlet, and pin is pressure at inlet. (a)Mach number; (b) Static temperature; (c) Tangential velocity.
pressure recovery coefficient, that is, when the mass flow rate meets the separator design mass flow rate requirement. This shows that the designed separator entry condition adaptability is very good. And the dehydration performance is not affected by the liquid outlet pressure. That is, the liquid outlet pressure can be increased to the greatest extent to decrease the amount of slip gas and pressure loss for our designed separator. In conclusion, good dehydration performance has been achieved with the designed separator. Acknowledgement This work is supported by the National Natural Science Foundation of China (NO.51274232 and NO.51406240).
References Atlas Copco, 2015. Atlas Copco Oil-injected Rotary Screw Compressors. http:// elitemotors.ge/files/products/atlascopco/industrial/GA30þ_-90_&_VSD.pdf. Ghosh, D., Bergmann, D., Schwering, R., Wolk, J., Strey, R., Tanimura, S., Wyslouzil, B.E., 2010. Homogeneous nucleation of a homologous series of nalkanes(CiH2iþ2, i¼7-10) in s supersonic nozzle. J. Chem. Phys. 132, 1e17. Harshad, N.P., 2013. Nucleation and Droplet Growth during Co-condensation of Nonane and D2O in a Supersonic Nozzle. The Ohio State University. Heath, C.H., Streletzky, K., Wyslouzil, B.E., Wolk, J., Strey, R., 2002. H2O-D2O condensation in a supersonic nozzle. J. Chem. Phys. 117, 6176e6185. Jassim, E., Abdi, M.A., Muzuchka, Y., 2008a. Computational fluid dynamics study for flow of natural gas through high-pressure supersonic nozzle: part 1. Real gas effects and shockwave. Pet. Sci. Technol. 26, 1757e1772. Jassim, E., Abdi, M.A., Muzuchka, Y., 2008b. Computational fluid dynamics study for flow of natural gas through high-pressure supersonic nozzle: part 2. Nozzle geometry and vorticity. Pet. Sci. Technol. 26, 1773e1785. Jiang, W.M., Liu, Z.L., Liu, H.W., Pang, H.Z., Bao, L.L., 2009. Influences of friction drag
1676
X. Cao, W. Yang / Journal of Natural Gas Science and Engineering 27 (2015) 1667e1676
on spontaneou scondensation in water vapor supersonic flow. Sci. China Ser. E Tech Sci. 52, 2635e2659. Jones, I.P., Guilblert, P.W., Owens, M.P., Hamill, I.S., Montavon, C.A., Penrose, J.M., Prast, B., 2003. The Use of Coupled Solvers for Complex Multi-phase and Reacting Flows. Third International Conference on CFD in the Minerals and Process Industries. CSIRO, Melbourne, Australia. Karimi, A., Abdi, M.A., 2009. Selective dehydration of high-pressure natural gas using supersonic nozzles. Chem. Eng. Process. 48, 560e568. Khan, A., Heath, C.H., Dieregsweiler, U.M., Wyslouzil, B.E., Strey, R., 2003. Homogeneous nucleation rates for D2O in a supersonic laval nozzle. J. Chem. Phys. 119, 3138e3147. Liu, H.W., Liu, Z.L., Feng, Y.X., Gu, K.Y., Yan, T.M., 2005. Characteristics of a supersonic swirling dehydration system of natural gas. Chin. J. Chem. Eng. 13, 9e12. Ma, Q.F., Hu, D.P., Jiang, J.Z., Qiu, Z.H., 2009a. A turbulent Eulerian multi-fluid model for homogeneous nucleation of water vapor in transonic flow. Int. J. Comput. Fluid Dyn. 23, 221e231. Ma, Q.F., Hu, D.P., Jiang, J.Z., Qiu, Z.H., 2009b. A turbulent Eulerian multi-fluid model for homogeneous nucleation of water vapor in transonic flow, Int. J. Comput. Fluid Dyn. 23, 221e231. Ma, Q.F., Hu, D.P., Jiang, J.Z., Qiu, Z.H., 2010. Numerical study of the spontaneous nucleation of self-rotational moist gas in a converging-diverging nozzle. Int. J. Comput. Fluid Dyn. 24, 29e36. Malyshkina, M.M., 2009. The structure of gas dynamic flow in a supersonic separator of natural gas. High. Temp. 46, 69e76. Malyshkina, M.M., 2010. The procedure for investigation of the efficiency of purification of natural gases in supersonic separator. High. Temp. 48, 244e250. Okimoto, F., Brouwer, J.M., 2002. Supersonic gas conditioning. World Oil 223, 89e92. Prast, B., Lammers, B., Betting, M., 2006. CFD for supersonic gas processing. In: Fifth International Conference on CFD in the Process Industries CSIRO (Melbourne, Australia). Schinkelshoek, P., Epsom, H., 2006. Supersonic gas conditioning for NGL recovery. In: 2006 offshore Technology Conference (Houston, Texas, U.S.A). Wen, C., Cao, X.W., Yang, Y., Zhang, J., 2011a. Swirling effects on the performance of supersonic separators for natural gas separator. Chem. Egn. Technol. 34, 1380e1386. Wen, C., Cao, X.W., Yang, Y., Zhang, J., 2011b. Supersonic swirling characteristics of natural gas in convergent-divergent nozzles. Pet. Sci. 8, 114e119. Wen, C., Cao, X.W., Yang, Y., Li, W.L., 2012a. Numerical simulation of natural gas
flows in diffusers for supersonic separator. Energy 37, 195e200. Wen, C., Cao, X.W., Yang, Y., Zhang, J., 2012b. Evaluation of natural gas dehydration in supersonic swirling separators applying the discrete particle method[J]. Adv. Powder Technol. 23, 228e233. Wyslouzil, B.E., Wliemski, G., Beals, M.G., Frish, M.B., 1994. Effect of carrier gas pressure on condensation in a supersonic nozzle. Phys. Fluids 31, 74e83. Wyslouzil, B.E., Cheung, J.L., Wilemski, G., Strey, R., 1997. Small angel neutron scattering from nanodroplet aerosols. Phys. Rev. Lett. 79, 431e434.
Glossary E: [J kg1] total energy I: [-] turbulence intensity keff: [W m1 K1] effective thermal conductivity p: [Pa] pressure pc: [Pa] critical pressure pin: [Pa] pressure at dry air outlet pout: [Pa] pressure at inlet Re: [-] Reynolds number. R: [J mol1 k1] gas constant, 8.314 Jmol1 k1 t: [s] time T: [K] gas temperature Tc: [K] critical temperature Tdin: [K] dew point of gas at inlet Tdout: [K] dew point of gas at gas outlet DT: [K] reduced temperature u: [m s1] gas velocity u0 : [m s1] velocity fluctuation v: [m3 mol1] molar specific volume Greek symbols
gp: [-] specific heat ratio dij: [-] the Kronecker delta r: [kg m3] gas density teff: [-] effective viscous stress u: [-] acentric factor
Contents lists available at ScienceDirect
Journal of Natural Gas Science and Engineering journal homepage: www.elsevier.com/locate/jngse
The dehydration performance evaluation of a new supersonic swirling separator Xuewen Cao*, Wen Yang College of Pipeline and Civil Engineering, China University of Petroleum, No.66, Changjiang West Road, Qingdao, 266580, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 16 July 2015 Received in revised form 20 October 2015 Accepted 23 October 2015 Available online 28 October 2015
A new supersonic swirling separator with an ellipsoidal central body has been designed, and an indoor experimental system and simulation method are utilised to evaluate the dehydration performance of the designed separator. The dew point depression and adaptability of the separator inlet and outlet working conditions are analysed to evaluate the dehydration performance. The experimental results show that the separator has a good dehydration performance, with the pressure recovery coefficient ranging from 20.6% to 69.8%. The maximum dew point depression is 34.9 C, with the dew point depression decreasing as the pressure recovery coefficient increases, where the former is 18.3 C C at a high pressure recovery coefficient (69.8%). The inlet pressure and inlet temperature have a weak influence on the dehydration performance when the mass flow rate meets the separator working requirement. In addition, dehydration performance is not affected by the liquid outlet pressure. This means that the designed separator can operate normally across a large range of inlet and outlet working conditions. © 2015 Elsevier B.V. All rights reserved.
Keywords: Supersonic swirling separator Dehydration Experiment Simulation Evaluation
1. Introduction Natural gas always contains significant quantities of water vapour when it is exploited from underground sources. The water vapour will condense in the pipeline as the transportation pressure and temperature change, which will cause blockage and corrosion of the pipeline. Therefore, removing the water from the natural gas is a fundamental necessity. Several methodsdincluding absorption, adsorption, cooling, and membrane separationdhave been developed to dehydrate natural gas. A new method called supersonic swirling separation was introduced for natural gas dehydration in 1996 by ENGO and Shell (Jones et al., 2003; Prast et al., 2006; Schinkelshoek et al., 2006). The proposed supersonic swirling separators (‘3S’ and ‘Twister’) work on two major principles, namely condensation separation and cyclone separation at supersonic velocities (Wen et al., 2012a). Due to their advantages, including a compact design, low weight, no need for chemical additives, and unmanned operation (Wen et al., 2011a), extensive studies have been carried out on the separators. Many numerical simulations have been performed. The high-pressure natural gas flow characteristics in supersonic swirling separators
* Corresponding author. E-mail address: [email protected] (X. Cao). http://dx.doi.org/10.1016/j.jngse.2015.10.029 1875-5100/© 2015 Elsevier B.V. All rights reserved.
have been studied with computational fluid dynamics (CFD) technology, and the effects of the real gas and separator geometry on the flow characteristics have been analysed (Jassim et al., 2008a; Jassim et al., 2008b). The effects of inlet pressure, inlet temperature, inlet mass flow rate, back pressure, and shockwaves on the gas-dynamic parameters in separators have also been analysed (Karimi et al., 2009; Malyshkina, 2010, 2009). In addition, the microscopic homogeneous nucleation in rapid expansion without swirling has also been discussed (Jiang et al., 2009; Ma et al., 2009a, 2010). Many experimental studies have focused on the condensation characteristics of the vapour in the nozzle (Wyslouzil et al., 1994, 1997; Heath et al., 2002; Khan et al., 2003; Ghosh et al., 2010; Harshad, 2013). Some numerical work on the swirling characteristics and separator characteristics of the separators has been done by Xuewen Cao by using the FLUENT software to investigate supersonic swirling separators with an ellipsoidal central body (Wen et al., 2011a; Wen et al., 2012b), but the evaluation of the separation characteristics experiment has not been reported until now. There is also a lack of experimental studies on separation characteristics, and only a few experiments have been reported. Experimental results for the Twister show that a maximum dew point depression of 22e28 C can be obtained, but the details of the experimental conditions are not described (Okimoto et al., 2002). A new type of dehydration unit with a different structure from the Twister has been developed and an indoor test has been carried
1668
X. Cao, W. Yang / Journal of Natural Gas Science and Engineering 27 (2015) 1667e1676
out. The effects of the pressure loss ratio, shockwaves, and the flow rate on the dehydration characteristics have been analysed, and the maximum dew point depression is approximately 20 C without any need for external mechanical power or chemicals (Liu et al., 2005). Ma et al. (2009b) also developed a new kind of separator with an inner pyramid, and experimental results showed that the dew point depression can reach 29 C by adopting the proposed droplet enlargement method, which is difficult to use. This paper introduces a new supersonic swirling separator with an ellipsoidal central body, which is proposed to reduce gas flow resistance. The dehydration performance of the designed separator is evaluated using experimental and simulation methods. The effects of the pressure recovery coefficient, inlet pressure, inlet temperature, and liquid outlet pressure on the separation characteristics of the separator are discussed. The effects of the liquid outlet pressure on the separation characteristics are discussed for the first time. 2. Experimental system 2.1. The experimental process The overall experimental system and major experimental set-up are shown in Fig. 1. The detailed separation process is as follows. Compressed air flows through the surge tank and filter, mixes with micro-water mist from a high pressure micro mist humidifier, and then goes into the supersonic swirling separator after being
measured by the vortex flowmeter. The mixture condenses in the supersonic swirling separator. Thereafter, condensed liquid flows out through the liquid outlet driven by centrifugal force. Meanwhile, gas enters the surge tank from the gas outlet of the supersonic swirling separator after it is measured by the vortex flowmeter, and then moves into the air. 2.2. The supersonic swirling separator In this study, a new structure of supersonic swirling separator with an ellipsoidal central body is designed, as shown in Fig. 2. The swirling device consists of 12 vanes turned through 45 . The vanes can ensure that the inlet of the vanes is in line with the direction of the flow to reduce resistance, and the larger outlet angle can produce a larger swirling flow field. The swirling vanes on the central body are helical blades designed with the unequal pitch method, and the helix equation of the vanes is presented in Eq. (1).
8 r ¼ f ðzÞ þ r0 > > > > Zt > > > > > q ¼ uðtÞdt þ q0 < 0 > > Zt > > > > > z¼ vðtÞdt þ z0 > > :
(1)
0
Fig. 1. Experimental system and major setup. 1-Screw compressor; 2,11-Surge tank; 3- Filter; 4- High pressure micro mist humidifier; 5-Valve; 6-Humidifying tank; 7-Heat exchanger; 8,12,13-Self-operated pressure control valve; 9- Vortex flowmeter; 10- Supersonic swirling separator.
X. Cao, W. Yang / Journal of Natural Gas Science and Engineering 27 (2015) 1667e1676
1669
Fig. 2. Structure of supersonic swirling separator designed.
where u(t) and v(t) are the angular velocity and axial velocity, respectively; (r0, q0, z0) is the initial point coordinate; (r, q, z) is the moving point coordinate; and f(z) is the curved surface formed by the moving points. The annular channel between the central body and the wall forms a Laval nozzle, a cyclone separation section, and a diffuser, as shown in Fig. 2. The swirling motion is generated by the swirling vanes on the central body, which are located in the subsonic part of the channel. The wet gas condenses in the Laval nozzle due to the formation of a low temperature and low pressure. The liquid and gas are separated, driven by the centrifugal force in the cyclone separation section, and the kinetic energy of the gas decreases while its static pressure and temperature increase as it moves across the diffuser. According to the designed inlet working parameters (0.6 MPa, 30 C, 300 Nm3/h), the structure of the separator is determined. The whole length of the separator is 945.3 mm; the diameter of the inlet is 80 mm; the inner-wall diameter and central body diameter at the throat are 15.94 mm and 12.00 mm, respectively; and the wall inner diameter and central body diameter at the gas outlet are 15.94 mm and 6.4 mm, respectively. 2.3. The other set-ups An Atlas Copco GA45 VSD screw compressor (Atlas Copco, 2015) is utilised to provide compressed air. Its maximum working pressure and mass flow are 1.3 MPa and 515 Nm3/h, respectively. The screw compressor combines the surge tank installed to ensure the
pressure and mass flow stability at the inlet of the supersonic swirling separator. A high-pressure micro mist humidifier with a 6 MPa maximum working pressure is utilised to add micro-water mist to the compressed air. The diameter range of the micro mist is 0.1e5 mm. The precision of the Yokogawa DY040 Vortex flowmeter is ±0.75%. It is used to measure the inlet and outlet volume flow rate of the supersonic swirling separator. The inlet and gas outlet temperature and the humidity of the supersonic swirling separator are measured by Vaisala HMT3608 humidity/temperature transducers. The precision of the transducers is ±0.2 C and ±1.5% for temperature and humidity, respectively. Rosemount 3051 pressure sensors are mounted at the inlet, gas outlet, and liquid outlet of the supersonic swirling separator. The precision of these sensors is ±0.075%. Pressure adjustment at the inlet, gas outlet, and liquid outlet of the supersonic swirling separator is conducted by a KOSO800 self-operated pressure control valve, and flow rate adjustment is conducted by a Yamatake electric control valve.
2.4. Dehydration performance criterion The effects of the pressure recovery coefficient (gp), inlet pressure, inlet temperature, and liquid outlet pressure on the performance of the designed supersonic swirling separator have been investigated. Dew point depression (DTd) is the criterion used to evaluate the dehydration performance of the separator. The definitions of the pressure recovery coefficient and the dew point depression are presented in Eq. (2) and Eq. (3), respectively.
Fig. 3. Unstructured tetrahedral meshes.
1670
X. Cao, W. Yang / Journal of Natural Gas Science and Engineering 27 (2015) 1667e1676
Fig. 6. Dew point depression at different pressure recovery coefficient of the separator.
Fig. 4. Calculation results at the nozzle outlet axis with different mesh cells. (a)Mach number distribution; (b) Temperature distribution.
gp ¼ ðpout =pin Þ 100%
(2)
where pout and pin are the pressure at the gas outlet and at the wet gas inlet, respectively.
DTd ¼ Tdin Tdout
Fig. 7. Dew point depression at different inlet pressure of the separator.
(3)
Fig. 5. Static temperature distribution in the separator at different pressure recovery coefficient.
X. Cao, W. Yang / Journal of Natural Gas Science and Engineering 27 (2015) 1667e1676
where Tdin and Tdout are the dew point of the gas at the inlet and at the gas outlet, respectively.
3. Numerical approach 3.1. Governing equations The gas flow characteristics in the supersonic swirling separators are described by the continuity equation, the momentum equation, and the energy equation. They are described in Eqs.
1671
(4)e(6).
v ruj ¼ 0 vxj
(4)
" !# vuj vui 2 vul v vp v v ru0 i u0 j þ dij m þ rv uj ui ¼ þ vxj vxi vxj vxj vxi vxj 3 vxl
Fig. 8. Distribution of gas dynamic parameters at different inlet pressure. (a)Mach number; (b) Static temperature; (c) Tangential velocity.
(5)
1672
X. Cao, W. Yang / Journal of Natural Gas Science and Engineering 27 (2015) 1667e1676
v v r u E þ uj p ¼ vxj v j vxj
vT þ ui teff keff vxj
! (6)
where r, u, p are the vapour density, velocity, and pressure, respectively; keff is the effective thermal conductivity; teff is the effective viscous stress; dij is the Kronecker delta; u0 is the velocity fluctuation, and the Reynolds Stress Model was adopted to calculate the Reynolds stress term; E is the total energy; and t is the time. The differencing formulation used in this work is second-order upwind.
. a ¼ 0:457247R2 Tc2 pc
(9)
b ¼ 0:07780RTc =pc
(10)
h pffiffiffiffiffiffiffiffiffiffii2 aðTÞ ¼ 1 þ m 1 T=Tc
(11)
m ¼ 0:37464 þ 1:54226u 0:2699u2
(12)
The mixture rules are as follows: 3.2. Mesh generation
am ¼
In the study, unstructured tetrahedral meshes are generated for the numerical computation due to the twisted vanes and complex sump, as shown in Fig. 3. Four cases with different mesh cells are generated, where there are 276,549, 467,852, 611,258, and 1,278,561 mesh cells, respectively. The Mach number and temperature distribution at the nozzle outlet axis are presented in Fig. 4. The results show that 611,258 mesh cells provide sufficient grid independence for the designed supersonic swirling separator.
XX i
bm ¼
X
0:5 xi xj ai aj 1 kij
(13)
j
x i bi
(14)
i
where R is the universal gas constant; p and T are the gas pressure and temperature, respectively; v is the molar specific volume; Tc and Pc are the critical temperature and critical pressure, respectively; and u is a centric factor. 4. Results and discussion
3.3. Boundary conditions and convergence criterion According to the flow characteristics of the supersonic compressible flow in the supersonic swirling separator, pressure boundary conditions are assigned to the inlet (wet gas inlet) and outlet of the nozzle (gas outlet and liquid outlet). Non-slip and adiabatic boundary conditions are specified for the walls. Pressure inlet: Specify the gauge pressure, static pressure, total temperature, and turbulence parameters. The turbulence strength and viscosity ratio are assigned as turbulence parameters. The turbulence strength (I) can be estimated from the following equation that is derived from an empirical correlation for pipe flows:
I ¼ 0:16ðReÞ1=8
(7)
where Re is the Reynolds number. The turbulent viscosity ratio, mt/m, is directly proportional to the turbulent Reynolds number. Typically, the turbulence parameters are set such that 1 < mt/m < 10. Pressure outlet: No parameters should be specified at the outlet for the supersonic flow. Specify the gauge pressure, total temperature, turbulence strength, and viscosity ratio for the calculation with different pressure recovery coefficient conditions. The convergence criterion is 106 for the energy equation residual error, 103 for other equations' residual error, and the mass flow rate absolute error between the inlet and outlet is less than 0.05%.
Natural gas raises significant safety concerns in a laboratory environment. Hence, a safer alternative air is selected as the carrier gas in our experiments. Different working conditionsdsuch as the different pressure recovery coefficient conditions, different inlet pressure conditions, different inlet temperature conditions, and different liquid outlet pressure conditionsdare used to evaluate the dehydration performance of the separator. 4.1. Effects of pressure recovery coefficient on separator performance The static temperature distribution at different pressure recovery coefficients in the simulation results is shown in Fig. 5. The static temperature at the outlet of the Laval nozzle increases as the pressure recovery coefficient increases, which shows that the expansion ability and water condensation ability decrease as the pressure recovery coefficient increases. That is, the separator has a
3.4. Equation of state The PengeRobinson equation of state (PR EoS), which is frequently utilised to calculate the physical properties of real gas, is used to describe the gas characteristics at different conditions in the supersonic swirling separator in this work. The PR EoS is described as follows:
p¼
RT aaðTÞ v b vðv þ bÞ þ bðv bÞ
(8) Fig. 9. Dew point depression at different inlet temperature of the separator.
X. Cao, W. Yang / Journal of Natural Gas Science and Engineering 27 (2015) 1667e1676
worse dehydration performance when the pressure recovery coefficient is higher, but more pressure energy is recovered. This means that a higher dew point depression can be acquired by sacrificing the gas pressure energy. An appropriate pressure recovery coefficient should be selected to acquire desired dew point depression according to the actual gas treatment requirement. Another thing to be concerned about is shockwaves. Shockwaves will be generated in Laval nozzles when the pressure recovery coefficient is higher than a fixed valve according to gas dynamic theory. The generation of shockwaves in Laval nozzles will destroy the existence of a condensation environment. Hence, an appropriate pressure recovery coefficient should be selected to ensure that condensation occurs.
1673
Experiments have been carried out to evaluate the dehydration performance of the separator and to find out the value of the fixed pressure recovery coefficient. The results are presented in Fig. 6, which shows that the dew point depression decreases as the pressure recovery coefficient increases. The dew point depression is 34.9 C when the pressure recovery coefficient is 20.6%, and it decreases to 18.3 C when the pressure recovery coefficient increases to 69.8%. The effect of the pressure recovery coefficient on the dehydration performance of the separator is significant. A higher dew point depression can be acquired with a larger pressure energy loss in the separator. When the pressure recovery coefficient is higher than 69.8%, the shockwaves enter the separator, and the condensation and separation environment in the
Fig. 10. Distribution of gas dynamic parameters at different inlet temperature. (a)Mach number; (b) Static temperature; (c) Tangential velocity.
1674
X. Cao, W. Yang / Journal of Natural Gas Science and Engineering 27 (2015) 1667e1676
separator will be destroyed. The dew point depression almost becomes zero when the pressure recovery coefficient is higher than 69.8%, showing that 69.8% is the fixed pressure recovery coefficient for this nozzle. The highest dew point depression in our separator is 34.9 C, which occurs when the pressure recovery coefficients is 20.6%. 4.2. Effects of inlet pressure on separator performance The effects of the inlet pressure on the dew point depression, that is, on the condition that the mass flow rate can meet the separator mass flow rate requirement (supersonic flow after throat), have been investigated experimentally. The experimental results are presented in Fig. 7, in which it is shown that the dew point depression decreases at all four different inlet pressures as the pressure recovery coefficient increases, which corroborates the discussion in Section 4.1. In addition, it can be seen that the difference between the dew point depression for the four inlet pressure conditions at a fixed pressure recovery coefficient is small, which illustrates that the influence of the inlet pressure on the dehydration performance of the separator is weak with a fixed pressure recovery coefficient. The distribution of the gas-dynamic parameters in the separator at different inlet pressures in the simulation results are shown in Fig. 8, where it can be seen that the Mach number and static temperature at the Laval nozzle outlet are similar at different inlet pressures with a fixed pressure recovery coefficient, which demonstrates that temperature depressions are similar at a fixed pressure recovery coefficient condition. Meanwhile, the maximum tangential velocity values are similar, indicating similar swirling separation abilities at different inlet pressures. Therefore, the dehydration performances of the separator with different inlet pressures with a fixed pressure recovery coefficient are similar, which corroborates experimental results. The experimental results illustrate that designed separator can operate normally across a large range of inlet pressures when the mass flow rate meets the separator mass flow rate requirement. 4.3. Effects of inlet temperature on separator performance The effects of the inlet temperature on the dew point depression, that is, on the condition that the mass flow rate can meet the separator design mass flow rate requirement, have been investigated experimentally. The experimental results are presented in Fig. 9. The dew point depression variation with respect to the pressure recovery coefficient corroborates the discussion in Section 4.1. A similar conclusion can be obtained from the experimental results. That is, the inlet temperature has a weak influence on the dehydration performance of the separator at a fixed pressure recovery coefficient. The simulation results of the effects of inlet temperature on the distribution of the gas-dynamic parameters in the separator are shown in Fig. 10. The Mach numbers at the Laval nozzle outlet are all 1.40 for the various inlet temperature conditions. Meanwhile, the temperature depressions are all approximately 80 K. The simulation results demonstrate that the separator expansion ability is similar for the separator at the various inlet temperature conditions. In addition, the same maximum tangential velocity at different inlet temperature conditions, approximately 138 m/s, indicates that the separator's swirling separation abilities are the same. According to the above discussion, the inlet temperature has a weak effect on the dew point depression with a fixed pressure recovery coefficient, which is reflected in the experimental results. The experimental results illustrate that our designed separator
can operate normally across a large range of inlet temperatures when the mass flow rate meets the separator mass flow rate requirement. 4.4. Effects of liquid outlet pressure on the separator performance The experimental study of the effects of the liquid outlet pressure on the dew point depression is carried out under the condition that the inlet pressure and gas outlet pressure are kept constant (0.6 MPa and 0.18 MPa, respectively). The experimental results are presented in Fig. 11. As shown in Fig. 11, the influence of the liquid outlet pressure on the water dew point depression is minimal. The experimental results further illustrate that the separation of liquid and gas is not controlled by the liquid outlet pressure, which is a typical inertial separation process that is affected by the centrifugal force, namely tangential velocity, to a large extent. The simulation results of the effects of the liquid outlet pressure on the distribution of the gas-dynamic parameters in the separator are shown in Fig. 12, where it can be seen that the Mach number, static temperature, and tangential velocity at the Laval nozzle outlet are all the same for the various liquid outlet pressures, demonstrating that the separator's dehydration performance is not affected by the liquid outlet pressure. That is, the liquid outlet pressure can be increased to the greatest extent to decrease the amount of slip gas and pressure loss. 5. Conclusions The designed supersonic swirling separator has a good dehydration performance without any chemical agent or external mechanical power. The maximum dew point depression is 34.9 C when the pressure recovery coefficient is 20.6%. The dew point depression can be 18 C with a very high pressure recovery coefficient (69.8%). The pressure recovery coefficient is the main factor that affects the performance of the designed separator. The dew point depression decreases as the pressure recovery coefficient increases, showing that a better dehydration performance can be achieved with a larger pressure energy loss in the separator. The inlet pressure and inlet temperature have a weak influence on the dehydration performance of the separator with a fixed
Fig. 11. Dew point depression at different liquid outlet pressure of the separator.
X. Cao, W. Yang / Journal of Natural Gas Science and Engineering 27 (2015) 1667e1676
1675
Fig. 12. Distribution of gas dynamic parameters at different liquid outlet pressure. gp-l ¼ pout-l/pin, where pout-l is pressure at liquid outlet, and pin is pressure at inlet. (a)Mach number; (b) Static temperature; (c) Tangential velocity.
pressure recovery coefficient, that is, when the mass flow rate meets the separator design mass flow rate requirement. This shows that the designed separator entry condition adaptability is very good. And the dehydration performance is not affected by the liquid outlet pressure. That is, the liquid outlet pressure can be increased to the greatest extent to decrease the amount of slip gas and pressure loss for our designed separator. In conclusion, good dehydration performance has been achieved with the designed separator. Acknowledgement This work is supported by the National Natural Science Foundation of China (NO.51274232 and NO.51406240).
References Atlas Copco, 2015. Atlas Copco Oil-injected Rotary Screw Compressors. http:// elitemotors.ge/files/products/atlascopco/industrial/GA30þ_-90_&_VSD.pdf. Ghosh, D., Bergmann, D., Schwering, R., Wolk, J., Strey, R., Tanimura, S., Wyslouzil, B.E., 2010. Homogeneous nucleation of a homologous series of nalkanes(CiH2iþ2, i¼7-10) in s supersonic nozzle. J. Chem. Phys. 132, 1e17. Harshad, N.P., 2013. Nucleation and Droplet Growth during Co-condensation of Nonane and D2O in a Supersonic Nozzle. The Ohio State University. Heath, C.H., Streletzky, K., Wyslouzil, B.E., Wolk, J., Strey, R., 2002. H2O-D2O condensation in a supersonic nozzle. J. Chem. Phys. 117, 6176e6185. Jassim, E., Abdi, M.A., Muzuchka, Y., 2008a. Computational fluid dynamics study for flow of natural gas through high-pressure supersonic nozzle: part 1. Real gas effects and shockwave. Pet. Sci. Technol. 26, 1757e1772. Jassim, E., Abdi, M.A., Muzuchka, Y., 2008b. Computational fluid dynamics study for flow of natural gas through high-pressure supersonic nozzle: part 2. Nozzle geometry and vorticity. Pet. Sci. Technol. 26, 1773e1785. Jiang, W.M., Liu, Z.L., Liu, H.W., Pang, H.Z., Bao, L.L., 2009. Influences of friction drag
1676
X. Cao, W. Yang / Journal of Natural Gas Science and Engineering 27 (2015) 1667e1676
on spontaneou scondensation in water vapor supersonic flow. Sci. China Ser. E Tech Sci. 52, 2635e2659. Jones, I.P., Guilblert, P.W., Owens, M.P., Hamill, I.S., Montavon, C.A., Penrose, J.M., Prast, B., 2003. The Use of Coupled Solvers for Complex Multi-phase and Reacting Flows. Third International Conference on CFD in the Minerals and Process Industries. CSIRO, Melbourne, Australia. Karimi, A., Abdi, M.A., 2009. Selective dehydration of high-pressure natural gas using supersonic nozzles. Chem. Eng. Process. 48, 560e568. Khan, A., Heath, C.H., Dieregsweiler, U.M., Wyslouzil, B.E., Strey, R., 2003. Homogeneous nucleation rates for D2O in a supersonic laval nozzle. J. Chem. Phys. 119, 3138e3147. Liu, H.W., Liu, Z.L., Feng, Y.X., Gu, K.Y., Yan, T.M., 2005. Characteristics of a supersonic swirling dehydration system of natural gas. Chin. J. Chem. Eng. 13, 9e12. Ma, Q.F., Hu, D.P., Jiang, J.Z., Qiu, Z.H., 2009a. A turbulent Eulerian multi-fluid model for homogeneous nucleation of water vapor in transonic flow. Int. J. Comput. Fluid Dyn. 23, 221e231. Ma, Q.F., Hu, D.P., Jiang, J.Z., Qiu, Z.H., 2009b. A turbulent Eulerian multi-fluid model for homogeneous nucleation of water vapor in transonic flow, Int. J. Comput. Fluid Dyn. 23, 221e231. Ma, Q.F., Hu, D.P., Jiang, J.Z., Qiu, Z.H., 2010. Numerical study of the spontaneous nucleation of self-rotational moist gas in a converging-diverging nozzle. Int. J. Comput. Fluid Dyn. 24, 29e36. Malyshkina, M.M., 2009. The structure of gas dynamic flow in a supersonic separator of natural gas. High. Temp. 46, 69e76. Malyshkina, M.M., 2010. The procedure for investigation of the efficiency of purification of natural gases in supersonic separator. High. Temp. 48, 244e250. Okimoto, F., Brouwer, J.M., 2002. Supersonic gas conditioning. World Oil 223, 89e92. Prast, B., Lammers, B., Betting, M., 2006. CFD for supersonic gas processing. In: Fifth International Conference on CFD in the Process Industries CSIRO (Melbourne, Australia). Schinkelshoek, P., Epsom, H., 2006. Supersonic gas conditioning for NGL recovery. In: 2006 offshore Technology Conference (Houston, Texas, U.S.A). Wen, C., Cao, X.W., Yang, Y., Zhang, J., 2011a. Swirling effects on the performance of supersonic separators for natural gas separator. Chem. Egn. Technol. 34, 1380e1386. Wen, C., Cao, X.W., Yang, Y., Zhang, J., 2011b. Supersonic swirling characteristics of natural gas in convergent-divergent nozzles. Pet. Sci. 8, 114e119. Wen, C., Cao, X.W., Yang, Y., Li, W.L., 2012a. Numerical simulation of natural gas
flows in diffusers for supersonic separator. Energy 37, 195e200. Wen, C., Cao, X.W., Yang, Y., Zhang, J., 2012b. Evaluation of natural gas dehydration in supersonic swirling separators applying the discrete particle method[J]. Adv. Powder Technol. 23, 228e233. Wyslouzil, B.E., Wliemski, G., Beals, M.G., Frish, M.B., 1994. Effect of carrier gas pressure on condensation in a supersonic nozzle. Phys. Fluids 31, 74e83. Wyslouzil, B.E., Cheung, J.L., Wilemski, G., Strey, R., 1997. Small angel neutron scattering from nanodroplet aerosols. Phys. Rev. Lett. 79, 431e434.
Glossary E: [J kg1] total energy I: [-] turbulence intensity keff: [W m1 K1] effective thermal conductivity p: [Pa] pressure pc: [Pa] critical pressure pin: [Pa] pressure at dry air outlet pout: [Pa] pressure at inlet Re: [-] Reynolds number. R: [J mol1 k1] gas constant, 8.314 Jmol1 k1 t: [s] time T: [K] gas temperature Tc: [K] critical temperature Tdin: [K] dew point of gas at inlet Tdout: [K] dew point of gas at gas outlet DT: [K] reduced temperature u: [m s1] gas velocity u0 : [m s1] velocity fluctuation v: [m3 mol1] molar specific volume Greek symbols
gp: [-] specific heat ratio dij: [-] the Kronecker delta r: [kg m3] gas density teff: [-] effective viscous stress u: [-] acentric factor