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A performance analysis of inverse two-stage dynamic cyclone separator
Accepted Manuscript A performance analysis of inverse two-stage dynamic cyclone separator
Peiqi Liu, Yintian Ren, Mingyu Feng, Di Wang, Dapeng Hu PII: DOI: Reference:
S0032-5910(19)30241-4 https://doi.org/10.1016/j.powtec.2019.04.002 PTEC 14234
To appear in:
Powder Technology
Received date: Revised date: Accepted date:
23 November 2018 25 March 2019 1 April 2019
Please cite this article as: P. Liu, Y. Ren, M. Feng, et al., A performance analysis of inverse two-stage dynamic cyclone separator, Powder Technology, https://doi.org/10.1016/ j.powtec.2019.04.002
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A Performance Analysis of Inverse Two-stage Dynamic Cyclone Separator Peiqi Liu, Yintian Ren, Mingyu Feng, Di Wang, Dapeng Hu * [email protected] School of Chemical Machinery Engineering, Dalian University of Technology *
Corresponding author.
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Abstract
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On account of low removal efficiency of fine coal, lo w availab le pressure and large range of gas fluctuation during the CBM explo itation process, an inverse two-stage dynamic cyclone separator is proposed to solve these questions. In the present study, the mechanisms and performance of the separator are investigated through the combination of experimental and numerical methods. The results show that the average separation efficiency of the 5 μm particles in the inverse two-stage dynamic cyclone separator is 91 % when the inlet flo w rate of 20,000 m3 /d and
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rotational speed is 1500 rp m. Moreover, it is found that the pressure drop increases with the increase of the impeller speed and flow rate, and it is roughly linear. The internal rotational flow field of the separator is controlled by adjusting
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an external motor so that the device can adapt to a wide range of fluctuations. When the impeller speed is 1500 rp m, the separation efficiency of the particle with a mean diameter of 10 μm reduces by 3 % when the flow rate increases to 125 %
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of the nominal flow and the separation efficiency increases by 3.5 % when the flow rate reduces to 75 % of the nominal flow.
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Keywords: Coalbed methane; Dynamic cyclone; Secondary separation; Pressure drop; Anti-flow fluctuation 1 Introduction
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As an unconventional gas, shallow underground coalbed methane （CBM） is mo re accessible for exp loration and utilizat ion, which contributes significantly to the Chinese energy adjustment
[1,2]
. The diameter of the droplet carried by
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CBM is commonly between 5 and 40 μm. During the mining process, the fine particles in the gas can adversely affect subsequent equipment, which is not conducive to long -term and stable operation of the equip ment. In addition, the flow is always fluctuated during the whole mining process. The mining pressure of the coalbed methane is lo w so the equipment generally has the characteristics of low inlet pressure and low pressure drop. At present, the development of CBM is main ly based on the natural gas techniques. Natural gas dust separation equipment is often used for dust removal. Separation equipment includes gravity sedimentation chambers, filter separators, cyclone separators, etc. [3] The structure of gravity s edimentation room is simp le and easy to maintain, with less resistance and long durability. But the equipment occupies a large space and the separation range of particle size is
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narrow [4-8]. Filter dust collector is better in removing dust especially for fine dust. The filter dust collector has a simple structure and stable operation, but the equipment takes up a large space and the pressure drop is large
[9]
. Cyclone
separator main ly employ centrifugal force to separate particles fro m gas to achieve purif ication. And it has the advantages of high efficiency, simp le operation and large handling capacity. However, limited by the tangential velocity, it is difficult for the traditional cyclone separator to separate the fine particles. What’s more, it has cert ain requirements
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on the inlet pressure.
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In order to improve the separation efficiency of cyclone separator, the scholars in different countries have optimized the structure and the size of the cyclone separator and created the Stairmand equivalent cyclone separator, but it is still difficult to separate fine particles effect ively
[10]
. Therefore, researchers begin to design a kind of dynamic
cyclone separator to improve the separation performance by active rotating part. On the basis of the trad itional cyclone separator, J.J.H. Brouwers improved the rotating filter tube to a rotary particle separator which can separate fine [11-14]
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particles effectively and accomplish the secondary separation
. Aiju Shi presented a rotary cage dynamic cyclone
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with a plurality of blades. This equip ment relies on the cage to accelerate the particles to obtain strong centrifugal force. T. Ch mielniak and A. Bryczkowski employed rotating blades to develop a lower exhaust dynamic cyclone separator with rotating vortex baffle based on Stairmand’s high efficiency cyclone separator and they analyzed the factors that
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affecting the pressure drop of the dynamic cyclone [15,16]. J.Y. Jiao and Y. Zheng designed a dynamic cyclone separator with rotating blades and they investigated the effects of inlet speed and blade speed on the separation efficiency by [17]
. Based on the traditional cyclone separator, Z. Yu designed a new
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numerical simulat ion and experimental research
dynamic cyclone separator and he studied the main factors affect ing the t angential velocity in different regions by [18]
. The results showed that the separation ability can be effectively improved by adding
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simu lation and experiment
dynamic components in the conventional cyclone separator.
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Therefore, a new cyclone separator structure is proposed in this paper, wh ich integrates the drive shaft and overflow pipe into the dynamic cyclone separator to achieve two -stage separation. The two-stage dynamic cyclone separator with the self-rotating center overflo w p ipe can improve the separation efficiency of coalbed methane. And impeller can provide so me kinetic energy to the particles in the CBM to reduce pressure drop. At the same time, the internal flow field can be controlled by the rotating speed of impeller so as to avoid flo w fluctuation wh ich result in the degradation of the separation performance. So, the inverse two-stage dynamic cyclone separator can effectively solve the problems of low removal efficiency of fine coal, lo w effective p ressure and large gas fluctuation range in the process of CBM explo itation. With the co mbination of analysis and experiments, this paper focuses on the effects of
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impeller speed, impeller shape and processing capacity on the performance of the separator. The current investigation of the separator performance, including the separation efficiency, the range of flo w resistance , and pressure loss, can theoretically contribute to the popularization and application of this device. 2 The structure and mechanism of inverse two-stage dynamic cyclone separator The equipment is mainly co mposed of a rotating impeller, a center overflow pipe and a cylinder body, as is shown
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in Figure 1. The rotating impeller is the main power co mponent of the separator, which accelerates the airflow directly
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at high tangential speeds. The center overflow pipe consisting of a lower straight pipe, an expanding pipe and a higher straight pipe, is the core part of the equip ment to realize the two -step separation with a rotating center pipe. Structure of overflow pipe is shown in Figure 2. The speed of the center overflow pipe is controlled by the motor rather than the flow of gas. The flo w field can keep stable within a wide range of fluctuations. The new separator takes advantage of
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the spin of the center overflow pipe to accomplish the second stage separation.
When the separator is under a regular simulat ion, the material gas enters the equipme nt fro m the in let tube and is
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sucked into the central part of the impeller by the negative pressure produced by the high -speed rotating impeller. After leaving the impeller, the fully accelerated gas continues to move downward. At the same time, the partic les which are separated by larger centrifugal force co mpared to that the gas born flow downwards along the tapered cylinder wall to
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the ash silo. The equip ment has co mpleted the first-step separation, which is also called flo w separation. The gas continues to rotate upward and forms an inner cyclone. The residual particles wh ich have not been removed would enter
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the center overflow pipe with the gas. With accelerat ion of the center overflo w p ipe, the particles get a larger tangential velocity and separation happens again. So me of the separated particles flow into the cavity from the hole of the center
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overflow p ipe and then directly return to ash silo through reflu x p ipe, so that the device achieves the second stage
the exhaust pipe.
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separation . The gas cleaned by the two stages of separation enters the exhaust chamber and is finally discharged from
3 Research methods
3.1 Numerical analysis According to the actual scale, the three-dimensional fluid do main model o f the separator is established by Pro -E software. Then the model has been imported to pre-processing software Gambit in meshing. The cyclone’s cross section is in the regular shape of circular, circular ring, or sector. The structure mesh is fully used in the model. The model is divided into several interconnected parts in order to guarantee the quality of the mesh. The hexahedron mesh is used for simp le parts and tetrahedral mesh is used for more co mp lex parts. As for the important flu id domain parts, such as the
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rotating impeller, the grids are divided densely and transited smoothly. The dynamic and static regions are modeled by the independent methods. The grid at the boundary will be suitably densified and the y+ value decided in the range fro m 30 to 60. After d ividing, the grids of each part are connected by the inner connection surfaces (Interface). After the grid-independent test, the number of vo lu me mesh of this model is 458, 928. The three-d imensional geo metry model of the whole machine and the mesh are shown in Figure 3. The mesh of the impeller region is shown in Figure 4.
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Because CBM contains flammable and exp losive gas , air is used instead of CBM in the experiment. In orde r to
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explore the characteristics of the internal flow field of the separator, numerical simu lation analysis is carried out . The results of using RNG k-ε and RSM to simulate cyclone separator are appropriately consistent and the calculation amount of RNG k-ε is less than that of RSM, wh ich proved that RNG k-ε is mo re suitable for engineering applications [19]
. Thus, the RNG κ-ε model has been adopted. For the movable area of the equip ment, the numerical simulat ion is
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carried out with mult iple reference fra me model (M RF) in order to obtain a reasonable flow field d istribution [20]. The particles are s mall and have little influence on each other so that the influence of them on the flo w field is neglected.
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The internal flo w field is analyzed by Lagrangian method. Co mbined with actual working condition, the discrete DPM model is used to simulate the trajectories of particles with different size. Furthermore, boundary condition at the inlet is “velocity inlet”, and the velocity is calculated based on the handlin g capacity and inlet pipe size. The boundary
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condition at the outlet is “outflow”. The standard wall function is chosen for the walls. In order to study the effect of flow fluctuations on the separation efficiency, an observation surface is set at the inle t between the impeller and the
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center overflow pipe. The location of the observation surface is shown in Figure 1 named Section I. 3.2 Experimental study
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In order to test the performance o f the inverse two -stage dynamic cyclone separator, the separation e xperiments are carried out under different working conditions. The schematic diagram of the experimental apparatus and platform
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are shown in Figure 5 and Figure 6, respectively. During the experiment, the liquid is dispersed into droplets of different sizes by atomizer and mixed with air absorbed by pneumatic transport, and then the mixture would be transported to the separator. After two stages of separation, the purified gas is discharged from the exhaust pipe. The trapped liquid enters the ash silo along the wall of the cylinder or through the return pipe. In the experiment, the power of the new separator is provided by an Y132-2 three-phase asynchronous motor whose rated speed is 2890rp m. The speed of the impeller is controlled by a MF-7.5KW-380V digital frequency converter. The flow rate of gas is controlled by the inlet valve and monitored by a rotameter with the accuracy class (indicate the accuracy of the meter) of 1.5 and the range of 0-30000 m3 /d. The liquid volu me is monitored by a rotameter with an accuracy class of 1.5. The total
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pressure drop of the gas is measured by a U type differential pressure meter which is capable of testing the pressure drop. Mediums used in the experiment includes comp ressed air and water. The co mpressed air is supplied by a laboratory comp ressor with the pressure range of 0-1 M Pa and the water is provided by tap water system with room temperature and at mospheric pressure. Figure. 7 shows the size distribution of the droplet with mean d iameter o f 10 μm
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measured by a Phase Doppler Particle Analyzer (PDPA) shown in Figure. 8, which indicates that the sizes of the particles are normally distributed.
In order to study the influence of different shape blades acting on the performance of the separator in the impeller, the experiment provides three types of impellers: straight b lade, p itched blade and backward bent blade, as is shown in
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Figure 9.
4 The performance of inverse two-stage dynamic cyclone separator
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4.1 Separation performance
The rotating impeller is the main power co mponent of the separator, and its rotational speed and structure directly impact the separation performance. Therefo re, in this research, the in fluence of impeller parameters on the separation
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performance is intensively studied by changing the rotational speed and specific structures. By establishing a part icle separation model o f the t wo -stage separator, the velocity vector d istribution shown in
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Figure. 10 is obtained. As is shown in Figure 11, in the cyclone separator, the impeller rotates at high speed so as to form negative pressure in the central area and facilitate the gas entering the impeller center automatically.
Under the
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action of the impeller, the gas is accelerated and enters the cylinder. The gas flows into the center overflow pipe through the cone section of the cylinder. Then the gas enters the exhaust cavity from the central overflo w pipe and is discharged
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fro m the exhaust pipe. The chamber connected to the return line has a high pressure at the edge, and the center of the separator has a low pressure. The particles in the two-stage separation are transported to the ash bin under pressure differences and discharged from the same cavity with the particles in the one-stage separation. The internal velocity distribution of the device is symmetrical, among wh ich there is a large strong swirl region, and the problems of short circuit flow and back mixing can be eliminated, and the reflu x is obvious. Thus, high separation efficiency can be expected. Figure 12 shows the separation efficiency of the simulation results for the new separat or under the inlet volu me flow rate of 20,000 m3 /d and rotating speed of 1000 rp m, 1500 rp m and 2000 rp m. As is shown in the figure, the
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separation efficiency of the device is close to 100 % for the particles with size larger than 10μm when the speed of impeller is 1000 rp m. For the particles below 10 μm, the separation efficiency increases with the speed of impeller. When the impeller speed rises fro m 1000rp m to 2000rp m, the separation efficiency of 5μm part icles increases fro m 87 % to 95 % with the increment of 8 %. It can be seen that the separation efficiency can be significantly imp roved by increasing the impeller speed for the particles with sizes belo w 10μm. The trajectories of the part icles are simu lated by
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DPM numerical method. On the basis of the previous experimental results, the particles are driven into the separator in
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turn with the size of 1μm, 3μm, 5μm, 10μm, 20μm and 40 μm (Figure 1 3). As is shown in Figure. 13, the larger-sized particles can reach the wall quickly, so the separation can be completed in the one-stage separation with high efficiency, while the s maller-sized particles are not easily separated due to the small inert ia force. Thus, separation efficiency is lower and secondary separation will work.
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The experiment is carried out under normal temperature and pressure. With an inlet flow rate of 20,000 m 3 /d, the rotational speed of the impeller equipped with the straight blade is fro m 0 to 2000 rp m by adjusting the MF-7.5K-380V
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type digital frequency converter. In this process, the separation efficiencies of the equip ment under the speed of 1000 rpm, 1200 rp m, 1400 rp m, 1600 rp m, 1800 rp m and 2000 rp m are recorded and the results are shown in Figure 14. The separation efficiency of the equipment increases linearly with the increasing impeller speed. The experimental results
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are basically in co incidence with the simu lation results. The experimental values are slightly higher than the simu lation values, mainly because of the existence of the second agglomeration of liquid in the actual separation process. All in all,
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increasing the speed of impeller in a certain range is conducive to improving the separation efficiency of the separator. The influence of impeller parameters acting on separation efficiency is simu lated before the experiment. Figure 15
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illustrates the simu lation results using different forms o f impellers under an inlet flo w rate o f 20,000 m3 /d and rotational speed is 1500 rp m. As can be seen from the graph, the separation efficiency of the new separator is roughly the same
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with the three types of impellers. The form of the impeller has little effect on the separation performance of part icles larger than 10 μm, and the separation efficiency of all three impellers is close to 100 %. But the effect of impeller types on the separation efficiency is significant for s maller particles. The separation performance of backward bent blade is the best, and the separation efficiency of the 5 μm particles is 93 %. The main reason is that the backward bent blade can transmit the speed of the particles smoothly and the speed difference between the particles and the wall of the cylinder is smaller. And the average separation efficiency of the 5 μm part icles is 91 %. It can be seen that the separator has good separation ability.
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In order to further explore the influence of impeller parameters acting on separation efficiency, the separation performance of three types of blades with different speeds and fixed volu me flow rate is tested. In the performance experiment of the separator, the separation efficiency of the three impellers are obtained by adjusting the impeller speed at the inlet volu me flow rate of 20,000 m3 /d, as is shown in Figure 16. On the whole, the trends of the separation efficiency of the three kinds of impellers are basically the same and increase with the speed of the impellers. Fro m the
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view of separation efficiency, all three types of impellers ensure the separation efficiency mo re than 90 % but there are
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obvious disparities between them. A mong the three types of blades, the separation efficiency of the backward bent blade is the highest, with the efficiency of pitched blade following closely behind, wh ich indicates that they have similar accelerating abilit ies. While the separation efficiency of straight blade is the lowest. For examp le, when the impeller speed is 1500 rp m, the separation efficiency of the straight blade is 94.5 %, which is 2.2 % lower than that of
improved by optimizing the structure of the impeller.
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4.2 Pressure drop
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the pitched blade and 3 % of the backward bent blade. Therefore, the separation efficiency of the separator can be
During the separation process, the gas flows into the center overflow pipe through the cone section of the cylinder. Then the gas enters the exhaust cavity fro m the center overflow p ipe and is discharged fro m the exhaust pipe. In this
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process, the pressure of the gas will d rop due to viscous dissipation and the load loss. This paper investigates the effe cts of pressure drop for the equipment from the perspectives of impeller speed, flow and impeller form.
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The pressure drop of the separator is measured by a U type pressure gauge. The values of pressure drop are recorded when testing the separation performance. Figure 17 - 19 show the pressure drop results under different rotating
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speeds, inlet flow rates and impeller forms.
As can be seen from Figure 17, the simulation values of pressure drop rise from 1000 Pa to 1400 Pa with the
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impeller speed increasing fro m 1000rp m to 2000 rp m, following a roughly linear trend . As can be seen from Figure 18, the simu lation values of pressure drop fro m 800 Pa to 1400 Pa with the flow rate rising fro m 15,000 m 3 /d to 25,000 m3 /d, following a roughly linear trend. This is du e to the loss of dynamic pressure and loading increase with the increasing of impeller speed and flow rate, resulting in the larger pressure drop. Furthermore, the experimental values of pressure drop are larger than the simulation values , and the distribution is coincidence with simulation. As can be seen from Figure 19, the trends of the pressure drop of the three forms of impellers are similar and the trends accord with the relat ionship of the impeller speed and pressure drop. By co mparing the trends of the pressure drop, the pressure drop of the straight blade impeller is the min imu m, while backward bent blade’s pressure drop is the
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maximu m and the pitched blade’s pressure drop is in between. In the process of particle separation, energy loss will cause pressure drop, while in the process of separation, the impeller can provide partial energy to particles, thus reducing pressure drop. Among different forms of blades with the same velocity, the backward bent blade provides the least kinetic energy to the particles, so the pressure drop of the separator equipped with the backward bent blade is greater.
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4.3 Resistance to flow fluctuations
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In order to exp lore the inherent separation mechanis ms of flow fluctuations, the present study numerically simu lates the internal flow o f the separator at the inlet flo w rate of 15,000 m3 /d, 20,000 m3 /d and 25,000 m3 /d. Figure 19 shows the relat ionship between flo w rate and separation efficiency. As is shown in Figure. 20, when the flow rate is between 15,000 m3 /d~25,000 m3 /d, the difference value of separation efficiency of part icles ranging fro m 5 -10 μm is
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less than 5%. It can be seen that with a large fluctuation of the flow rate, the separation efficiency of particles with different sizes changes slightly and even keep a h igh efficiency, which proved that the two-stage separator has a certain
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ability to resist fluctuations . Figure 21 and 22 illustrate the tangential and axial velocity distribution on the section -I respectively. As is shown in Figure 21, as the flow rate increases, the tangential velocity distribution outside the center overflow p ipe is basically the same, and the tangential velocity inside becomes larger. As is shown in Figure. 22, as the
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flow rate increases, the axial velocity increases, which means that the internal residence time of the cyclone is reduced, and the effective separation time is shortened not conducive to separation. It can be preliminarily analyzed that when
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the flow rate is large, the axial velocity of the particles becomes large, so the time of the part icles staying in the separator becomes short, which is disadvantageous for separation, but the tangential velocity also becomes large at the
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same time, wh ich contributes to separation, so the separation efficiency does not change much. Similarly, when the flow rate is s mall, the tangential velocity becomes s mall, which is disadvantageous for separation, but at the same t ime,
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the axial velocity of the particles also becomes small, so the time of the particles staying in the separator becomes longer, wh ich contributes to separation, so the separation efficiency does not change much. Based on the above analysis, we can preliminarily conclude that the separator has the ab ility to resist flow fluctuations. In order to further verify the anti-fluctuations ability of the two-stage separator, the anti-fluctuations experiment is carried out. The no minal flow o f the new separator is 20,000 m3 /d. In order to test the flow fluctuations resistance of the separator, the experiment is carried out at an impeller speed of 1500 rp m and a no minal flo w at rate of 0 -125 %. The experimental results show that the separation efficiency of the separator is close to 100% within the range of 0 -75 % of the nominal flo w rate. Therefo re, a further experiment starts under the nominal flow of 75-125 % (15000-25000 m3 /d)
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and the results are shown in Figure 23. As can be seen fro m the figure, the simulat ion values are lower than the experimental values. The main reason is that the agglomeration of the particles is neglected in the simu lation, so particles that cannot be removed in the simu lation have been part ially removed during the actual separation process . Nevertheless, the experiment and simulation results are basically consistent with each other and the separation efficiency decreases with the increment of flow rate. Under the no minal flow, the separation efficiency is 95 %. The
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separation efficiency reduces by 3 % when the flow rate increases to 125 % of the no minal flow. The separation
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efficiency increases by 3.5 % when the flow rate reduces to 75 % of the nominal flow. It can be seen that with a large fluctuation of the flo w rate, the separation efficiency changes slightly and even keep a high efficiency. Therefo re, the inverse two-stage dynamic cyclone separator can maintain a stable and efficient operation under fluctuating flow, exhibiting good fluctuations resistance ability.
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5 Conclusions
In this paper, the performance of the new separator is studied by experiment and numerical simulat ion, and the
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following conclusions are drawn:
(1) The two-stage dynamic cyclone imp rove device efficiency. The results show that the average separation efficiency of the part icle size with 5 μm in the t wo-stage dynamic cyclone separator is 91 % and 10μm is 100 %
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when in let flo w rate of 20,000 m3 /d and rotational speed is 1500 rp m. At the same time, the separation efficiency can be further improved with the increase of the impeller speed, and can be increased by 5-6 % in
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the speed range.
(2) The two-stage dynamic cyclone includes the impeller inside, wh ich on the one hand can provide the power,
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reducing the pressure drop. The results show that the pressure drop increases by about 400 Pa as the impelle r
m3 /d.
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speed increases from 1000 rp m to 2000 rp m or the volu me flo w rate increases from 15,000 m3 /d to 25,000
(3) The two-stage dynamic cyclone can control the flow field speed and improve the resistance to flow fluctuations. The results show that the separation efficiency maintain stable at close to 100 % when the inlet flow rate changes from 0 to 75 % of the no minal flow rate and the separation efficiency which is linear to the flow rate decreases by about 6.5 % when the flow rate rises from 75 % to 125 % o f the nominal flow. (4) In terms of separation efficiency, the separation efficiency of the backward bent blade is the highest, followed by that of the oblique blade, wh ile that of the straight blade is the lowest. In terms of pressure performance, the pressure drop of backward bent blade is the largest, followed by that of pitched blade, and the straight
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blade is the lowest. Co mb ining the above analyses, the performance of the pitched blade is optimal, which not only ensures high separation efficiency, but also avoids excessive pressure drop.
Acknowledgments This research is supported by “National science and technology major pro ject（2016ZX05066005-002）”and “The
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National Natural Science Foundation of China(21676048)”.
Nomenclature
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D——grain diameter (μm) N——diameter count n——impeller speed (rpm)
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P——pressure (Pa)
X——radial position (mm)
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Q——throughput (m3 /d)
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T——particle residence time (s) V——velocity (m/s)
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Vt ——tangential velocity (m/s) Va——axial velocity (m/s)
η——separation efficiency (%) △P——pressure drop (Pa)
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[20] C. Zhang, Study on pressure performance and separation performance of self-circulation dynamic hydrocyclone.
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Fig.1 Structure and geometry size of separator
Fig.2 Structure of overflow pipe
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Fig. 3 The model and mesh of complete machine
Fig. 4 The mesh of impeller
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Fig. 5 Schematic diagram of experimental apparatus
Fig.6 The experimental platform
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Fig. 7 The size distribution of droplets
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Fig. 8 Measure the droplets diameter using PDPA
(a)straight blade
(b) backward bent blade Fig. 9 The three forms of impellers
(c) pitched blade
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Velocity vector diagram
Tangential velocity diagram
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Fig. 10 Velocity distribution of the cyclone
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(rotational speed is 1500 rpm and inlet flow rate is 15,000 m3/d.)
Fig.11 Static pressure distribution of straight blade rotating impeller model on the section Ⅰ
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Fig. 21 Tangential velocity of section Ⅰunder different inlet flow rate
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A Performance Analysis of Inverse Two-stage Dynamic Cyclone Separator
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Peiqi Liu1, Yintian Ren1, Mingyu Feng1, Di Wang1, Dapeng Hu1
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Highlights
The two-stage dynamic cyclone of backset and concurrent has average separation efficiency of 91% against to particles of 5μm.
The second separation can be realized by using central overflow pipe and the separation efficiency is improved. The inverse two-stage dynamic cyclone separator can effectively maintain gas
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intake continuous in low pressure.
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Peiqi Liu, Yintian Ren, Mingyu Feng, Di Wang, Dapeng Hu PII: DOI: Reference:
S0032-5910(19)30241-4 https://doi.org/10.1016/j.powtec.2019.04.002 PTEC 14234
To appear in:
Powder Technology
Received date: Revised date: Accepted date:
23 November 2018 25 March 2019 1 April 2019
Please cite this article as: P. Liu, Y. Ren, M. Feng, et al., A performance analysis of inverse two-stage dynamic cyclone separator, Powder Technology, https://doi.org/10.1016/ j.powtec.2019.04.002
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A Performance Analysis of Inverse Two-stage Dynamic Cyclone Separator Peiqi Liu, Yintian Ren, Mingyu Feng, Di Wang, Dapeng Hu * [email protected] School of Chemical Machinery Engineering, Dalian University of Technology *
Corresponding author.
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Abstract
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On account of low removal efficiency of fine coal, lo w availab le pressure and large range of gas fluctuation during the CBM explo itation process, an inverse two-stage dynamic cyclone separator is proposed to solve these questions. In the present study, the mechanisms and performance of the separator are investigated through the combination of experimental and numerical methods. The results show that the average separation efficiency of the 5 μm particles in the inverse two-stage dynamic cyclone separator is 91 % when the inlet flo w rate of 20,000 m3 /d and
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rotational speed is 1500 rp m. Moreover, it is found that the pressure drop increases with the increase of the impeller speed and flow rate, and it is roughly linear. The internal rotational flow field of the separator is controlled by adjusting
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an external motor so that the device can adapt to a wide range of fluctuations. When the impeller speed is 1500 rp m, the separation efficiency of the particle with a mean diameter of 10 μm reduces by 3 % when the flow rate increases to 125 %
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of the nominal flow and the separation efficiency increases by 3.5 % when the flow rate reduces to 75 % of the nominal flow.
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Keywords: Coalbed methane; Dynamic cyclone; Secondary separation; Pressure drop; Anti-flow fluctuation 1 Introduction
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As an unconventional gas, shallow underground coalbed methane （CBM） is mo re accessible for exp loration and utilizat ion, which contributes significantly to the Chinese energy adjustment
[1,2]
. The diameter of the droplet carried by
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CBM is commonly between 5 and 40 μm. During the mining process, the fine particles in the gas can adversely affect subsequent equipment, which is not conducive to long -term and stable operation of the equip ment. In addition, the flow is always fluctuated during the whole mining process. The mining pressure of the coalbed methane is lo w so the equipment generally has the characteristics of low inlet pressure and low pressure drop. At present, the development of CBM is main ly based on the natural gas techniques. Natural gas dust separation equipment is often used for dust removal. Separation equipment includes gravity sedimentation chambers, filter separators, cyclone separators, etc. [3] The structure of gravity s edimentation room is simp le and easy to maintain, with less resistance and long durability. But the equipment occupies a large space and the separation range of particle size is
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narrow [4-8]. Filter dust collector is better in removing dust especially for fine dust. The filter dust collector has a simple structure and stable operation, but the equipment takes up a large space and the pressure drop is large
[9]
. Cyclone
separator main ly employ centrifugal force to separate particles fro m gas to achieve purif ication. And it has the advantages of high efficiency, simp le operation and large handling capacity. However, limited by the tangential velocity, it is difficult for the traditional cyclone separator to separate the fine particles. What’s more, it has cert ain requirements
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on the inlet pressure.
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In order to improve the separation efficiency of cyclone separator, the scholars in different countries have optimized the structure and the size of the cyclone separator and created the Stairmand equivalent cyclone separator, but it is still difficult to separate fine particles effect ively
[10]
. Therefore, researchers begin to design a kind of dynamic
cyclone separator to improve the separation performance by active rotating part. On the basis of the trad itional cyclone separator, J.J.H. Brouwers improved the rotating filter tube to a rotary particle separator which can separate fine [11-14]
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particles effectively and accomplish the secondary separation
. Aiju Shi presented a rotary cage dynamic cyclone
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with a plurality of blades. This equip ment relies on the cage to accelerate the particles to obtain strong centrifugal force. T. Ch mielniak and A. Bryczkowski employed rotating blades to develop a lower exhaust dynamic cyclone separator with rotating vortex baffle based on Stairmand’s high efficiency cyclone separator and they analyzed the factors that
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affecting the pressure drop of the dynamic cyclone [15,16]. J.Y. Jiao and Y. Zheng designed a dynamic cyclone separator with rotating blades and they investigated the effects of inlet speed and blade speed on the separation efficiency by [17]
. Based on the traditional cyclone separator, Z. Yu designed a new
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numerical simulat ion and experimental research
dynamic cyclone separator and he studied the main factors affect ing the t angential velocity in different regions by [18]
. The results showed that the separation ability can be effectively improved by adding
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simu lation and experiment
dynamic components in the conventional cyclone separator.
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Therefore, a new cyclone separator structure is proposed in this paper, wh ich integrates the drive shaft and overflow pipe into the dynamic cyclone separator to achieve two -stage separation. The two-stage dynamic cyclone separator with the self-rotating center overflo w p ipe can improve the separation efficiency of coalbed methane. And impeller can provide so me kinetic energy to the particles in the CBM to reduce pressure drop. At the same time, the internal flow field can be controlled by the rotating speed of impeller so as to avoid flo w fluctuation wh ich result in the degradation of the separation performance. So, the inverse two-stage dynamic cyclone separator can effectively solve the problems of low removal efficiency of fine coal, lo w effective p ressure and large gas fluctuation range in the process of CBM explo itation. With the co mbination of analysis and experiments, this paper focuses on the effects of
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impeller speed, impeller shape and processing capacity on the performance of the separator. The current investigation of the separator performance, including the separation efficiency, the range of flo w resistance , and pressure loss, can theoretically contribute to the popularization and application of this device. 2 The structure and mechanism of inverse two-stage dynamic cyclone separator The equipment is mainly co mposed of a rotating impeller, a center overflow pipe and a cylinder body, as is shown
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in Figure 1. The rotating impeller is the main power co mponent of the separator, which accelerates the airflow directly
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at high tangential speeds. The center overflow pipe consisting of a lower straight pipe, an expanding pipe and a higher straight pipe, is the core part of the equip ment to realize the two -step separation with a rotating center pipe. Structure of overflow pipe is shown in Figure 2. The speed of the center overflow pipe is controlled by the motor rather than the flow of gas. The flo w field can keep stable within a wide range of fluctuations. The new separator takes advantage of
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the spin of the center overflow pipe to accomplish the second stage separation.
When the separator is under a regular simulat ion, the material gas enters the equipme nt fro m the in let tube and is
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sucked into the central part of the impeller by the negative pressure produced by the high -speed rotating impeller. After leaving the impeller, the fully accelerated gas continues to move downward. At the same time, the partic les which are separated by larger centrifugal force co mpared to that the gas born flow downwards along the tapered cylinder wall to
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the ash silo. The equip ment has co mpleted the first-step separation, which is also called flo w separation. The gas continues to rotate upward and forms an inner cyclone. The residual particles wh ich have not been removed would enter
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the center overflow pipe with the gas. With accelerat ion of the center overflo w p ipe, the particles get a larger tangential velocity and separation happens again. So me of the separated particles flow into the cavity from the hole of the center
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overflow p ipe and then directly return to ash silo through reflu x p ipe, so that the device achieves the second stage
the exhaust pipe.
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separation . The gas cleaned by the two stages of separation enters the exhaust chamber and is finally discharged from
3 Research methods
3.1 Numerical analysis According to the actual scale, the three-dimensional fluid do main model o f the separator is established by Pro -E software. Then the model has been imported to pre-processing software Gambit in meshing. The cyclone’s cross section is in the regular shape of circular, circular ring, or sector. The structure mesh is fully used in the model. The model is divided into several interconnected parts in order to guarantee the quality of the mesh. The hexahedron mesh is used for simp le parts and tetrahedral mesh is used for more co mp lex parts. As for the important flu id domain parts, such as the
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rotating impeller, the grids are divided densely and transited smoothly. The dynamic and static regions are modeled by the independent methods. The grid at the boundary will be suitably densified and the y+ value decided in the range fro m 30 to 60. After d ividing, the grids of each part are connected by the inner connection surfaces (Interface). After the grid-independent test, the number of vo lu me mesh of this model is 458, 928. The three-d imensional geo metry model of the whole machine and the mesh are shown in Figure 3. The mesh of the impeller region is shown in Figure 4.
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Because CBM contains flammable and exp losive gas , air is used instead of CBM in the experiment. In orde r to
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explore the characteristics of the internal flow field of the separator, numerical simu lation analysis is carried out . The results of using RNG k-ε and RSM to simulate cyclone separator are appropriately consistent and the calculation amount of RNG k-ε is less than that of RSM, wh ich proved that RNG k-ε is mo re suitable for engineering applications [19]
. Thus, the RNG κ-ε model has been adopted. For the movable area of the equip ment, the numerical simulat ion is
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carried out with mult iple reference fra me model (M RF) in order to obtain a reasonable flow field d istribution [20]. The particles are s mall and have little influence on each other so that the influence of them on the flo w field is neglected.
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The internal flo w field is analyzed by Lagrangian method. Co mbined with actual working condition, the discrete DPM model is used to simulate the trajectories of particles with different size. Furthermore, boundary condition at the inlet is “velocity inlet”, and the velocity is calculated based on the handlin g capacity and inlet pipe size. The boundary
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condition at the outlet is “outflow”. The standard wall function is chosen for the walls. In order to study the effect of flow fluctuations on the separation efficiency, an observation surface is set at the inle t between the impeller and the
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center overflow pipe. The location of the observation surface is shown in Figure 1 named Section I. 3.2 Experimental study
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In order to test the performance o f the inverse two -stage dynamic cyclone separator, the separation e xperiments are carried out under different working conditions. The schematic diagram of the experimental apparatus and platform
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are shown in Figure 5 and Figure 6, respectively. During the experiment, the liquid is dispersed into droplets of different sizes by atomizer and mixed with air absorbed by pneumatic transport, and then the mixture would be transported to the separator. After two stages of separation, the purified gas is discharged from the exhaust pipe. The trapped liquid enters the ash silo along the wall of the cylinder or through the return pipe. In the experiment, the power of the new separator is provided by an Y132-2 three-phase asynchronous motor whose rated speed is 2890rp m. The speed of the impeller is controlled by a MF-7.5KW-380V digital frequency converter. The flow rate of gas is controlled by the inlet valve and monitored by a rotameter with the accuracy class (indicate the accuracy of the meter) of 1.5 and the range of 0-30000 m3 /d. The liquid volu me is monitored by a rotameter with an accuracy class of 1.5. The total
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pressure drop of the gas is measured by a U type differential pressure meter which is capable of testing the pressure drop. Mediums used in the experiment includes comp ressed air and water. The co mpressed air is supplied by a laboratory comp ressor with the pressure range of 0-1 M Pa and the water is provided by tap water system with room temperature and at mospheric pressure. Figure. 7 shows the size distribution of the droplet with mean d iameter o f 10 μm
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measured by a Phase Doppler Particle Analyzer (PDPA) shown in Figure. 8, which indicates that the sizes of the particles are normally distributed.
In order to study the influence of different shape blades acting on the performance of the separator in the impeller, the experiment provides three types of impellers: straight b lade, p itched blade and backward bent blade, as is shown in
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Figure 9.
4 The performance of inverse two-stage dynamic cyclone separator
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4.1 Separation performance
The rotating impeller is the main power co mponent of the separator, and its rotational speed and structure directly impact the separation performance. Therefo re, in this research, the in fluence of impeller parameters on the separation
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performance is intensively studied by changing the rotational speed and specific structures. By establishing a part icle separation model o f the t wo -stage separator, the velocity vector d istribution shown in
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Figure. 10 is obtained. As is shown in Figure 11, in the cyclone separator, the impeller rotates at high speed so as to form negative pressure in the central area and facilitate the gas entering the impeller center automatically.
Under the
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action of the impeller, the gas is accelerated and enters the cylinder. The gas flows into the center overflow pipe through the cone section of the cylinder. Then the gas enters the exhaust cavity from the central overflo w pipe and is discharged
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fro m the exhaust pipe. The chamber connected to the return line has a high pressure at the edge, and the center of the separator has a low pressure. The particles in the two-stage separation are transported to the ash bin under pressure differences and discharged from the same cavity with the particles in the one-stage separation. The internal velocity distribution of the device is symmetrical, among wh ich there is a large strong swirl region, and the problems of short circuit flow and back mixing can be eliminated, and the reflu x is obvious. Thus, high separation efficiency can be expected. Figure 12 shows the separation efficiency of the simulation results for the new separat or under the inlet volu me flow rate of 20,000 m3 /d and rotating speed of 1000 rp m, 1500 rp m and 2000 rp m. As is shown in the figure, the
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separation efficiency of the device is close to 100 % for the particles with size larger than 10μm when the speed of impeller is 1000 rp m. For the particles below 10 μm, the separation efficiency increases with the speed of impeller. When the impeller speed rises fro m 1000rp m to 2000rp m, the separation efficiency of 5μm part icles increases fro m 87 % to 95 % with the increment of 8 %. It can be seen that the separation efficiency can be significantly imp roved by increasing the impeller speed for the particles with sizes belo w 10μm. The trajectories of the part icles are simu lated by
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DPM numerical method. On the basis of the previous experimental results, the particles are driven into the separator in
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turn with the size of 1μm, 3μm, 5μm, 10μm, 20μm and 40 μm (Figure 1 3). As is shown in Figure. 13, the larger-sized particles can reach the wall quickly, so the separation can be completed in the one-stage separation with high efficiency, while the s maller-sized particles are not easily separated due to the small inert ia force. Thus, separation efficiency is lower and secondary separation will work.
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The experiment is carried out under normal temperature and pressure. With an inlet flow rate of 20,000 m 3 /d, the rotational speed of the impeller equipped with the straight blade is fro m 0 to 2000 rp m by adjusting the MF-7.5K-380V
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type digital frequency converter. In this process, the separation efficiencies of the equip ment under the speed of 1000 rpm, 1200 rp m, 1400 rp m, 1600 rp m, 1800 rp m and 2000 rp m are recorded and the results are shown in Figure 14. The separation efficiency of the equipment increases linearly with the increasing impeller speed. The experimental results
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are basically in co incidence with the simu lation results. The experimental values are slightly higher than the simu lation values, mainly because of the existence of the second agglomeration of liquid in the actual separation process. All in all,
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increasing the speed of impeller in a certain range is conducive to improving the separation efficiency of the separator. The influence of impeller parameters acting on separation efficiency is simu lated before the experiment. Figure 15
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illustrates the simu lation results using different forms o f impellers under an inlet flo w rate o f 20,000 m3 /d and rotational speed is 1500 rp m. As can be seen from the graph, the separation efficiency of the new separator is roughly the same
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with the three types of impellers. The form of the impeller has little effect on the separation performance of part icles larger than 10 μm, and the separation efficiency of all three impellers is close to 100 %. But the effect of impeller types on the separation efficiency is significant for s maller particles. The separation performance of backward bent blade is the best, and the separation efficiency of the 5 μm particles is 93 %. The main reason is that the backward bent blade can transmit the speed of the particles smoothly and the speed difference between the particles and the wall of the cylinder is smaller. And the average separation efficiency of the 5 μm part icles is 91 %. It can be seen that the separator has good separation ability.
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In order to further explore the influence of impeller parameters acting on separation efficiency, the separation performance of three types of blades with different speeds and fixed volu me flow rate is tested. In the performance experiment of the separator, the separation efficiency of the three impellers are obtained by adjusting the impeller speed at the inlet volu me flow rate of 20,000 m3 /d, as is shown in Figure 16. On the whole, the trends of the separation efficiency of the three kinds of impellers are basically the same and increase with the speed of the impellers. Fro m the
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view of separation efficiency, all three types of impellers ensure the separation efficiency mo re than 90 % but there are
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obvious disparities between them. A mong the three types of blades, the separation efficiency of the backward bent blade is the highest, with the efficiency of pitched blade following closely behind, wh ich indicates that they have similar accelerating abilit ies. While the separation efficiency of straight blade is the lowest. For examp le, when the impeller speed is 1500 rp m, the separation efficiency of the straight blade is 94.5 %, which is 2.2 % lower than that of
improved by optimizing the structure of the impeller.
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4.2 Pressure drop
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the pitched blade and 3 % of the backward bent blade. Therefore, the separation efficiency of the separator can be
During the separation process, the gas flows into the center overflow pipe through the cone section of the cylinder. Then the gas enters the exhaust cavity fro m the center overflow p ipe and is discharged fro m the exhaust pipe. In this
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process, the pressure of the gas will d rop due to viscous dissipation and the load loss. This paper investigates the effe cts of pressure drop for the equipment from the perspectives of impeller speed, flow and impeller form.
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The pressure drop of the separator is measured by a U type pressure gauge. The values of pressure drop are recorded when testing the separation performance. Figure 17 - 19 show the pressure drop results under different rotating
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speeds, inlet flow rates and impeller forms.
As can be seen from Figure 17, the simulation values of pressure drop rise from 1000 Pa to 1400 Pa with the
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impeller speed increasing fro m 1000rp m to 2000 rp m, following a roughly linear trend . As can be seen from Figure 18, the simu lation values of pressure drop fro m 800 Pa to 1400 Pa with the flow rate rising fro m 15,000 m 3 /d to 25,000 m3 /d, following a roughly linear trend. This is du e to the loss of dynamic pressure and loading increase with the increasing of impeller speed and flow rate, resulting in the larger pressure drop. Furthermore, the experimental values of pressure drop are larger than the simulation values , and the distribution is coincidence with simulation. As can be seen from Figure 19, the trends of the pressure drop of the three forms of impellers are similar and the trends accord with the relat ionship of the impeller speed and pressure drop. By co mparing the trends of the pressure drop, the pressure drop of the straight blade impeller is the min imu m, while backward bent blade’s pressure drop is the
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maximu m and the pitched blade’s pressure drop is in between. In the process of particle separation, energy loss will cause pressure drop, while in the process of separation, the impeller can provide partial energy to particles, thus reducing pressure drop. Among different forms of blades with the same velocity, the backward bent blade provides the least kinetic energy to the particles, so the pressure drop of the separator equipped with the backward bent blade is greater.
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4.3 Resistance to flow fluctuations
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In order to exp lore the inherent separation mechanis ms of flow fluctuations, the present study numerically simu lates the internal flow o f the separator at the inlet flo w rate of 15,000 m3 /d, 20,000 m3 /d and 25,000 m3 /d. Figure 19 shows the relat ionship between flo w rate and separation efficiency. As is shown in Figure. 20, when the flow rate is between 15,000 m3 /d~25,000 m3 /d, the difference value of separation efficiency of part icles ranging fro m 5 -10 μm is
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less than 5%. It can be seen that with a large fluctuation of the flow rate, the separation efficiency of particles with different sizes changes slightly and even keep a h igh efficiency, which proved that the two-stage separator has a certain
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ability to resist fluctuations . Figure 21 and 22 illustrate the tangential and axial velocity distribution on the section -I respectively. As is shown in Figure 21, as the flow rate increases, the tangential velocity distribution outside the center overflow p ipe is basically the same, and the tangential velocity inside becomes larger. As is shown in Figure. 22, as the
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flow rate increases, the axial velocity increases, which means that the internal residence time of the cyclone is reduced, and the effective separation time is shortened not conducive to separation. It can be preliminarily analyzed that when
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the flow rate is large, the axial velocity of the particles becomes large, so the time of the part icles staying in the separator becomes short, which is disadvantageous for separation, but the tangential velocity also becomes large at the
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same time, wh ich contributes to separation, so the separation efficiency does not change much. Similarly, when the flow rate is s mall, the tangential velocity becomes s mall, which is disadvantageous for separation, but at the same t ime,
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the axial velocity of the particles also becomes small, so the time of the particles staying in the separator becomes longer, wh ich contributes to separation, so the separation efficiency does not change much. Based on the above analysis, we can preliminarily conclude that the separator has the ab ility to resist flow fluctuations. In order to further verify the anti-fluctuations ability of the two-stage separator, the anti-fluctuations experiment is carried out. The no minal flow o f the new separator is 20,000 m3 /d. In order to test the flow fluctuations resistance of the separator, the experiment is carried out at an impeller speed of 1500 rp m and a no minal flo w at rate of 0 -125 %. The experimental results show that the separation efficiency of the separator is close to 100% within the range of 0 -75 % of the nominal flo w rate. Therefo re, a further experiment starts under the nominal flow of 75-125 % (15000-25000 m3 /d)
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and the results are shown in Figure 23. As can be seen fro m the figure, the simulat ion values are lower than the experimental values. The main reason is that the agglomeration of the particles is neglected in the simu lation, so particles that cannot be removed in the simu lation have been part ially removed during the actual separation process . Nevertheless, the experiment and simulation results are basically consistent with each other and the separation efficiency decreases with the increment of flow rate. Under the no minal flow, the separation efficiency is 95 %. The
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separation efficiency reduces by 3 % when the flow rate increases to 125 % of the no minal flow. The separation
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efficiency increases by 3.5 % when the flow rate reduces to 75 % of the nominal flow. It can be seen that with a large fluctuation of the flo w rate, the separation efficiency changes slightly and even keep a high efficiency. Therefo re, the inverse two-stage dynamic cyclone separator can maintain a stable and efficient operation under fluctuating flow, exhibiting good fluctuations resistance ability.
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5 Conclusions
In this paper, the performance of the new separator is studied by experiment and numerical simulat ion, and the
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following conclusions are drawn:
(1) The two-stage dynamic cyclone imp rove device efficiency. The results show that the average separation efficiency of the part icle size with 5 μm in the t wo-stage dynamic cyclone separator is 91 % and 10μm is 100 %
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when in let flo w rate of 20,000 m3 /d and rotational speed is 1500 rp m. At the same time, the separation efficiency can be further improved with the increase of the impeller speed, and can be increased by 5-6 % in
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the speed range.
(2) The two-stage dynamic cyclone includes the impeller inside, wh ich on the one hand can provide the power,
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reducing the pressure drop. The results show that the pressure drop increases by about 400 Pa as the impelle r
m3 /d.
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speed increases from 1000 rp m to 2000 rp m or the volu me flo w rate increases from 15,000 m3 /d to 25,000
(3) The two-stage dynamic cyclone can control the flow field speed and improve the resistance to flow fluctuations. The results show that the separation efficiency maintain stable at close to 100 % when the inlet flow rate changes from 0 to 75 % of the no minal flow rate and the separation efficiency which is linear to the flow rate decreases by about 6.5 % when the flow rate rises from 75 % to 125 % o f the nominal flow. (4) In terms of separation efficiency, the separation efficiency of the backward bent blade is the highest, followed by that of the oblique blade, wh ile that of the straight blade is the lowest. In terms of pressure performance, the pressure drop of backward bent blade is the largest, followed by that of pitched blade, and the straight
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blade is the lowest. Co mb ining the above analyses, the performance of the pitched blade is optimal, which not only ensures high separation efficiency, but also avoids excessive pressure drop.
Acknowledgments This research is supported by “National science and technology major pro ject（2016ZX05066005-002）”and “The
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National Natural Science Foundation of China(21676048)”.
Nomenclature
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D——grain diameter (μm) N——diameter count n——impeller speed (rpm)
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P——pressure (Pa)
X——radial position (mm)
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Q——throughput (m3 /d)
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T——particle residence time (s) V——velocity (m/s)
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Vt ——tangential velocity (m/s) Va——axial velocity (m/s)
η——separation efficiency (%) △P——pressure drop (Pa)
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References
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[5] X.D. Xiang, Theory and technology of dust removal, Metallurgical industry press, Beijing, 2013. [6] M.Y. Hu, Y. Zhao, Z Liu, Dedusting Technology, Chemical industry press, Beijing, 2006.
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[9] J.S. Zhu, Filter dust removal technology, Journal of filtration & separation. 4(2003) 43-46. [10] J.J. Derksen, Separat ion performance predict ions of a Stairmand high ‐ efficiency cyclone, AICh E Journal. 49
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[11] B. Brouwers, Rotational particle separator: A new method for separating fine particles and mists from gases ,
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[13] J.G.M. Kuerten, H.P. Van Kemenade, J.J.H. Brouwers, Nu merical study of the rotational phase separator sealing impeller, Powder technology. 154 (2005) 73-82. [14] H.Y. Chen, Turbine dust removal technology, Modern Chemical Industry. 23(2003) 49-51. [15] T. Ch mieln iak, A. Bryczko wski, Method of calculation of new cyclone-type separator with swirling baffle and bottom take off of clean gas ——part I: Theoretical approach, Chem. Eng. Process. 41 (2000) 441-448. [16] T. Ch mieln iak, A. Bryczko wski, Method of calculation of new cyclone-type separator with swirling baffle and bottom take off of clean gas ——part II: Experimental verification, Chem. Eng. Process. 41 (2000) 245-254.
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[17] J.Y. Jiao, Y. Zheng, G.G. Sun, J. Wang, Study of the separation efficiency and the flow field of a dynamic cyclone, Separation and Purification Technology. 49 (2006) 157-166. [18] Z. Yu, C.Y. Ma, Nu merical simu lation and experimental study of dynamic cyclone separator, Chemical industry and engineering progress, 33 (2014) 1684-1690. [19] J.Y Wang, Y. Mao, M.L. Liu, J. Wang, Simulat ion of strong swirling flow in a cyclone with a modified RNG k-ε
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[20] C. Zhang, Study on pressure performance and separation performance of self-circulation dynamic hydrocyclone.
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Fig.1 Structure and geometry size of separator
Fig.2 Structure of overflow pipe
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Fig. 3 The model and mesh of complete machine
Fig. 4 The mesh of impeller
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Fig. 5 Schematic diagram of experimental apparatus
Fig.6 The experimental platform
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Fig. 7 The size distribution of droplets
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Fig. 8 Measure the droplets diameter using PDPA
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(b) backward bent blade Fig. 9 The three forms of impellers
(c) pitched blade
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Velocity vector diagram
Tangential velocity diagram
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Fig. 10 Velocity distribution of the cyclone
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(rotational speed is 1500 rpm and inlet flow rate is 15,000 m3/d.)
Fig.11 Static pressure distribution of straight blade rotating impeller model on the section Ⅰ
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Fig. 12 Separation efficiencies under different rotating speed
4）10μm 5）20μm Fig.13 Tracks of different size particles in the separator
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Fig.14 Comparison between the experimental and computational separation efficiencies 105 100
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Fig.17 Pressure drop at different rotating speed
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Fig. 22 Axial velocity of section Ⅰunder different inlet flow rate
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Fig. 23 Separation efficiency under different flow rates
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A Performance Analysis of Inverse Two-stage Dynamic Cyclone Separator
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Highlights
The two-stage dynamic cyclone of backset and concurrent has average separation efficiency of 91% against to particles of 5μm.
The second separation can be realized by using central overflow pipe and the separation efficiency is improved. The inverse two-stage dynamic cyclone separator can effectively maintain gas
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intake continuous in low pressure.
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