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The effect of particle humidity on separation efficiency for an axial cyclone separator
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16 January 2019 Advanced Powder Technology xxx (xxxx) xxx 1
Contents lists available at ScienceDirect
Advanced Powder Technology journal homepage: www.elsevier.com/locate/apt
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Original Research Paper
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The effect of particle humidity on separation efficiency for an axial cyclone separator
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Yuan Li a,⇑, Guoliang Qin a, Zhiyi Xiong c,d, YunFeng Ji a, Ling Fan b
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a
School of Energy and Power Engineering, Xi’an Jiaotong University, No. 28, Xianning West Road, Xi’an, Shaanxi 710049, China Sinopec Si Chuan to Eastern China Transmission Gas Pipeline Co. Ltd., No. 126, Guanggu Road, Donghu New Technology Development Zone, City of Wuhan, Hubei Province 430020, China c College of Mechanical and Transportation Engineering, China University of Petroleum-Beijing, 18 Fuxue Road, Changping, Beijing, China d Beijing Key Laboratory of Process Fluid Filtration and Separation, 18 Fuxue Road, Changping, Beijing, China b
a r t i c l e
i n f o
Article history: Received 1 May 2018 Received in revised form 22 November 2018 Accepted 7 January 2019 Available online xxxx Keywords: Cyclone separator Particle humidity Collection efficiency Grade efficiency
a b s t r a c t The objective of this study is to investigate the effects of particle humidity on the inlet particle size distribution, overall efficiency, grade efficiency and cut size diameter for an axial cyclone separator with inner diameter of 150 mm. The collection and grade efficiencies of the cyclone separator were measured by on-line method for inlet velocities, particle concentration and particle humidity in the ranges of 12– 18 m/s, 30–500 mg/m3 and 8–30‰, respectively. By employing a set of fixed parameters for inlet velocity and particle concentration, the effect of particle humidity on separation efficiency was investigated. The experimental results show that the volume ratio of larger particle increases with the increasing of particle humidity due to particle agglomeration. When the inlet velocity and particle humidity remain constant, the collection and grade efficiencies improve greatly as the increasing of the particle concentration because of the particle aggregation. However, it was noticed that the grade efficiencies did not always increased with the increasing of particle humidity under the same conditions of inlet velocity and particle concentration. The trends of grade efficiency curves for different particle humidity change at the particle diameter of approximately 10 lm. The grade efficiency improves with the increasing of particle humidity when the particle diameter is larger than 10 lm, while a contrary tendency is observed when the particle diameter is smaller than 10 lm. Ó 2019 Published by Elsevier B.V. on behalf of The Society of Powder Technology Japan. All rights reserved.
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1. Introduction
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Many processing stations such as compressor station and distribution station are necessary along the long-distance pipeline of natural gas transportation according to the requirement of pressurization and distribution. These stations are commonly equipped with multicyclone separators and filter separators to remove sand, light hydrocarbons, water droplets and other impurities from the natural gas. Most of the multicylone separators are composed of several parallel single axial cyclone separators with cylinder diameter of 50–150 mm. The axial cyclone separators are usually utilized to remove the harmful or nuisance moist particles, light hydrocarbons and water droplets. The characteristic air flow pattern of an axial cyclone separator consists of an inner and an outer vortex, both spiraling in the same
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⇑ Corresponding author.
sense, with the outer vortex descending into the cyclone separator, reversing its direction and exiting the cyclone separator through the vortex finder located in the cyclone roof [1,2]. As the rotation motion, the particles are carried in the gas to experience the effects of the centrifugal force. Thus, the particles were carried to the cyclone separator wall and separate from the air flow. This is however a simplified perspective and belies the profound effects of dust concentration and particle interaction on separation performance. It is well established that as the concentration of dust increases the overall separation efficiency of the cyclone separator increases. The improvement in the cyclone separator performance has been noted to commence at dust loading as low as 0.00014 kg/m3, which resulted in the assertion that there is no lower limit of dust concentration which does not demonstrate enhance cyclonic performance [3]. The improvement in performance with increased dust loading varies with cyclone separator geometry and the inlet velocity [4]. The influence of geometry on cyclonic performance with increased dust loading is not as
E-mail address: [email protected] (Y. Li). https://doi.org/10.1016/j.apt.2019.01.002 0921-8831/Ó 2019 Published by Elsevier B.V. on behalf of The Society of Powder Technology Japan. All rights reserved.
Please cite this article as: Y. Li, G. Qin, Z. Xiong et al., The effect of particle humidity on separation efficiency for an axial cyclone separator, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.01.002
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significant as inlet velocity [5]. Except very low velocities, lower inlet velocities have greater impact on performance improvement than higher velocities [3,6]. The mechanism of increased dust loading how to improve the overall separation efficiency is not fully understood. However, the two main arguments revolve around theories of critical dust loading and particle agglomeration, with both effects taking place in or immediately after the cyclone inlet. Although there is strong experimental evidence supporting unclassified separation [5], the critical load theory also implies that below this limit load, improvement in separation performance with increased dust loading does not occur; this is however at odds with the observed behavior [3]. In contrast to the concept of critical load, Mothes & Löffler [7] proposed that particle agglomeration contributes to the improvement in cyclone performance with increased dust loading. The agglomeration of large and small particles makes the separation of finer particles from the airstream more likely, and this hypothesis is also supported by Ji et al. [4]. However, there was concern that agglomeration alone would not account for the magnitude of the effect on separation efficiency [8]. Particle agglomeration within a downcomer tube of a cyclone has been observed by phase Doppler anemometry (PDA) [9], lending credence to the agglomeration hypothesis. However there is agreement that the minima frequently observed in separation grade efficiency graphs, corresponding to finer particle sizes, are indeed a result of the agglomeration of fine particles [8,10]. The PACys model (Particle Agglomeration in Cyclones) was developed to predict the phenomenon of particle collection in reverse flow cyclones by taking into account the agglomeration phenomenon in turbulent flows [11–13]. Furthermore, Paiva et al. [14] built a model to predict the collection efficiency of gas cyclones in a more realistic way. In particular, they optimized cyclones using this model, and the results show very high collection efficiencies for submicrometer particles. They concluded that the hypothesis of particle agglomeration within the cyclone turbulent flow seems a sound justification for collection efficiencies observed higher than predicted for smaller particles in a gas-cyclone, being expectable with recirculation which will result in a more significant effect. The effect of particle agglomeration and attrition on the separation efficiency of a Stairmand cyclone was investigated by Haig et al. [15], and evidence of the agglomeration of fine particles occurring within the cyclone body was initially observed. As shown above, several studies have been performed to investigate and evaluate the effects of dry particle agglomeration on the separation efficiency. However, only few studies have discussed the effects of particle humidity on the separation efficiency. Ahuja [16] used a wetted wall cyclone separator to increase the overall collection efficiency, and Kim et al. [17] simply measured the effect of mist water on the collection efficiency. Both of the researchers concluded that the collection efficiency of the fine particles dramatically increases with the humidity. Therefore, it is important to fully investigate the change rules of particle size distribution, collection efficiency and grade efficiency with the increasing of particle humidity.
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2. Experiments
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The cyclone separator used in this study had an axial inlet with eight guide vanes, and its detailed geometry and dimensions are shown in Fig. 1. A schematic of the test rig is shown in Fig. 2. The dust-laden gas entered the cyclone separator and was taken off by a blower. The Pitot tube was used to measure the cross-section gas velocity in the tube. The experiments were carried out at the atmospheric pressure and ambient temperature. The laboratory temperature,
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Fig. 1. Geometry and dimensions of the cyclone separator.
atmospheric pressure and air relative humidity were checked and recorded frequently to improve the accuracy of the calculated air flow within the test rig through the air density and the standard equation for Pitot tubes. Throughout the experiments the air relative humidity was ranged between 25 and 40%, room temperature was between 20 and 30 °C and atmospheric pressure varied between 99,800 and 102,000 Pa. A powder dispersion generator, BEG-1000 by Palas, was used to feed particles continuously into the inlet gas. A similar method adopted by other researchers [4,15,18] was employed to calculate the particle concentration, as the mass flow divided by the flow rate. Model Welas-2000 aerosol spectrometer by Palas was used for online measurement of particle concentrations and particle size distributions based on particle numbers at a sampling flow rate of 5 L/min. The range of measured particle number concentration was from 0 to 105 particles/cm3 and the particle size distribution was
Please cite this article as: Y. Li, G. Qin, Z. Xiong et al., The effect of particle humidity on separation efficiency for an axial cyclone separator, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.01.002
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blower
bag filter smapling nozzle manometer
compressed air
pitot
smapling nozzle
inclined manometer sensor dust feeder
welas system
PC test cyclone Fig. 2. Schematic of cyclone separator test rig.
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between 0.3 and 40 lm. Sampling nozzles with different diameters were used for different flow rates in the isokinetic sampling of the dust-laden gas at the inlet and outlet of the cyclone separator. The downstream sensor is positioned more than ten pipe diameters from the elbow tube to eliminate sampling issues due to a swirling flow. The collection and grade efficiencies of the cyclone separator were measured at inlet velocities of 12–18 m/s and particle concentrations of 30–500 mg/m3 at atmospheric pressure and room temperature, respectively. Calcium carbonate was used as solid particles with a physical density of 2700 kg/m3, and the particle size ranged from 0.6 to 40 lm. In order to remove the particles’ moisture, the solid particles were dried more than two hours by a dryer before experiment. Then these dried solid particles were put in a closed agitator, and the water was sprayed into the agitator by a humidifier, so particles and water vapor were stirred completely. The quantity of particles and water was weighed, respectively. The different particle humidity was controlled by adding water vapor to the dried solid particles. The particle humidity was defined as,
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H¼
mw 100% ms þ mw
ð1Þ
where H, mw and ms are the particle humidity, the quality of water vapor and dried solid particles, respectively. The particle humidity changed among 8–30‰ in experiments. In order to control the particle humidity, the dried solid particles were weighed firstly, and then the quality of water vapor was calculated and weighed according to the value of particle humidity.
3. Results and discussion
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3.1. Particle size distribution
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Model Welas-2000 is an aerosol spectrometer, also known as optical particle counter (OPC), which measures the particle size (equivalent spherical optical particle size) base on the intensity of scattered light of single particle. Accordingly, the counting distribution (dN/N), volume distribution (dV/V), volume and mass concentration of particles can be obtained. By using the formula of sphere volume, the volume distribution of particles can be chan-
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Particle size volume ration dv/v
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Particle humidity 0‰ 8‰ 10‰ 15‰ 20‰ 25‰ 30‰
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Particle size diameter / m Fig. 3. The effect of humidity on inlet particle size distribution.
Please cite this article as: Y. Li, G. Qin, Z. Xiong et al., The effect of particle humidity on separation efficiency for an axial cyclone separator, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.01.002
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0.055
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Particle humidity 8‰ 10‰ 15‰ 20‰ 25‰ 30‰
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(a) Particle size distributions based on number ration
(b) Particle size distributions based on volume ration
Fig. 4. The effect of humidity on outlet particle size distribution.
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Overall efficiency /%
Overall efficiency /%
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Particle humidity 30‰ 25‰ 20‰ 15‰ 10‰ 8‰
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Fig. 5. The effect of humidity on overall efficiency.
Please cite this article as: Y. Li, G. Qin, Z. Xiong et al., The effect of particle humidity on separation efficiency for an axial cyclone separator, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.01.002
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Particle humidity:30‰ Particle concentration 3 30 mg/m 3 50 mg/m 3 100 mg/m 3 200 mg/m 3 300 mg/m 3 500 mg/m
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Grade efficiency /%
Grade efficiency /%
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Particle humidity:20‰ Particle concentration 3 30 mg/m 3 50 mg/m 3 100 mg/m 3 200 mg/m 3 300 mg/m 3 500 mg/m
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Particle humidity:25‰ Particle concentration 3 30 mg/m 3 50 mg/m 3 100 mg/m 3 200 mg/m 3 300 mg/m 3 500 mg/m
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Grade efficiency /%
Grade efficiency /%
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Particle relative humidity:15‰ Particle concentration 3 30 mg/m 3 50 mg/m 3 100 mg/m 3 200 mg/m 3 300 mg/m 3 500 mg/m
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Partilce diameter / m
Particle diameter / m Fig. 6. The effect of particle concentration on grade efficiency (inlet velocity is 18 m/s).
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ged and calculated from the counting distribution, shown as follows:
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pD3
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i Ni dV D3 N i ¼P 6 3 ¼ P60i 3 p D 60 V i N i¼1 Di N i
i¼1
6
ð2Þ
i
where i is the number of channels for measuring particle size, 1 i 60, Di is the particle size, 0.6 lm Di 40 lm, N i is the counting number of the particle corresponding to Di . In these experiments, the mixture of dried solid particles and water vapor was premixed by the dust feeder to ensure the same dispersion, which had been verified by Ji et al. [4]. However, the particle size distributions for different humidity are not the same at the inlet sampling position. Fig. 3 shows the effect of humidity on particle size distribution at the cyclone inlet with 14 m/s inlet velocity and 300 mg/m3 particle concentration. As shown in Fig. 3, the volume of large agglomerated particle increases with the increasing of particle humidity at the inlet. There are many fine (<10 lm) particles in the mixture with lower humidity 8‰ compared to the others. Agglomeration, or coagulation, is the primary inter-particle occurrence among aerosol particles. When aerosol particles collide due to their relative motion, the particles may adhere to each other and form larger particles known as agglomerates. Kinematic coagulation arises when the relative motion of the particle is the result of an external force, such as the centrifugal force as is the case with cyclones [19]. The main adhesive force
is the van der Waals force, which is due to complementary dipoles (concentrations in electric charge) forming in neighboring particles and producing an attractive force. The surface force also plays a strong role. This force arises from liquid molecules being absorbed by the particle surface and surface tension, as a result of capillary action, which adhere the particle to a surface. Therefore, more fine particles form larger particles with the increasing of humidity. Particle size distributions of different particle humidity measured at the downstream of the cyclone are shown in Fig. 4 at the same inlet velocity and particle concentration as the upstream. Although there are some differences among the particle size distributions based on volume ration, the particle size distributions based on number ration are almost the same. Because most of bigger particles were separated by the cyclone, so there are few effects of particle humidity on particle size distribution of the downstream of the cyclone.
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3.2. Overall efficiency
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The effects of particle humidity on overall efficiency are showed in Fig. 5, in which the inlet velocity, particle concentration and humidity in the ranges of 12–18 m/s, 30–500 mg/m3 and 8–30‰, respectively. Utmost care is taken while determining the overall efficiency since there is a possibility of the escape of fines. To account for any possible experimental errors due to this, each experiment was repeated six times for obtaining the overall effi-
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Please cite this article as: Y. Li, G. Qin, Z. Xiong et al., The effect of particle humidity on separation efficiency for an axial cyclone separator, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.01.002
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Grade efficiency /%
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Inlet velocity: 18 m/s 3 Particle concentration: 100 mg/m Particle humidity: 8‰ 10‰ 15‰ 20‰ 25‰ 30‰
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Inlet velocity: 18 m/s 3 Particle concentration: 500 mg/m Particle humidity: 8‰ 10‰ 15‰ 20‰ 25‰ 30‰
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Particle diameter / m Fig. 7. The effect of humidity on grade efficiency.
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ciency of the cyclone separator. The measure errors are shown in Fig. 5. It is observed that the overall efficiency increases with the increasing of particle humidity. This is to be expected since more fine particles form larger particles at higher humidity, and larger particles are easy to be separated. The efficiency varied from 58.5% to 69.53% under humidity 8‰ and from 63.07% to 80.18% under humidity30‰ with the inlet velocity 18 m/s, corresponding to particle concentration between 30 mg/m3 and 500 mg/m3. Thus, there is a remarkable increase in the overall efficiency with the increasing of particle humidity under the condition of same inlet velocity and particle concentration. However, it may be observed that the larger particles are the major contribution to the overall efficiency increase. The substantial change in the separation efficiency of smaller particles with a lesser proportion is not reflected in the overall efficiency. In addition, the overall efficiency also increases with the increasing of particle concentration, which has been investigated by other researches [3,4,6]. 3.3. Grade efficiency
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Grade efficiency (gi ) is the separation efficiency of a given particle size for cyclone. In the upstream and downstream of the cyclone, the mass frequency or volume frequency of the particles with a certain size (dp ) is f dp in;i and f dp out;i , respectively. Grade
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efficiency can be calculated by the following formula:
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gi ¼
! C out f dp out;i 100% 1 C in f dp in;i
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ð3Þ
where C in and C out are the mass concentration of the particle in upstream and downstream, respectively. Fig. 6 shows the separation grade efficiency of the cyclone separator with different particle concentration for inlet velocity 18 m/ s, at different humidity. As shown in Fig. 6, when the inlet velocity and particle humidity are the same, the improvement of grade efficiency with the increase of particle concentration from 30 to 500 mg/m3 is clearly observed. The series of data points from the repeated tests are shown along with their average, with each series also being an average of six sampling periods. The graphs clearly show the effect of particle concentration on grade efficiency. Many researches [4,7,15] have observed that the effect of particle concentration on the particle grade efficiency may be important due to particles agglomeration. There are more fine particles form larger ones with the increasing of particle concentration. The effect of agglomeration had been illustrated by the upstream and downstream particle distributions [4,15]. The removal of particles is primarily due to the effects of the centrifugal force which is directly proportional to the particle mass characterized by the particle diameter, when considering the particle as sphere. The ‘tail’ formations at very fine particle sizes, which is known to press the entire grade efficiency curve upwards, are often seen
Please cite this article as: Y. Li, G. Qin, Z. Xiong et al., The effect of particle humidity on separation efficiency for an axial cyclone separator, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.01.002
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Inlet velocity: 18 m/s 3 Particle concentration: 100 mg/m Particle humidity: 8‰ 10‰ 15‰ 20‰ 25‰ 30‰
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Grade efficiency /%
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ation configuration). As shown in Fig. 10, the liquid bridge may exist between particles, but there are few of agglomeration particles existed in the form of the third configuration according to the particle humidity. When agglomeration particles enter into the cyclone separator, several forces will work at each particle, such as centrifugal force, attraction force, drag force, and so on. Among these forces, the centrifugal force and drag force determine the agglomeration particles’ configuration. Assuming an agglomeration particle (shown in Fig. 9) does not disperse to two particles, although the tangential velocities of these two particles are same, the centrifugal force for each particle is different. If the difference in drag is larger than the attraction force, the agglomeration particle will be dispersed to two separate particles. The number of agglomeration particle increases with the increasing of particle humidity in the cyclone separator inlet (shown in Fig. 3), so the probability of particle dispersion also increases with the increasing of particle humidity. As a result, the ratio of escaped particles to inlet particles increases with the increasing of particle humidity. Therefore, the grade efficiency decreased with the increasing of particle humidity. However, almost all of the larger particles (>10 lm) can be separated by cyclone separator, so particle humidity has few effects on larger particles’ grade efficiency. Data indicative of particle de-agglomeration occurring in small scale reverse-flow cyclone separators for use in dry powder inhaler (DPI) was observed and reported by Cheng [20]. The cyclone separator efficient is decreased as particle dispersion inevitably
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experimentally due to the effect of high solid loading. Thus, low solid loading was used (ranged from 30 to 500 mg/m3) in these experiments. Considering the cohesive nature of the test dust, it is possible that small particles agglomerate in the inlet and being separated in the cyclone as form of agglomerates and then show up in the disperser when the agglomerates break up during dispersion, so the grade efficiency curves measured by on-line method are flat. Furthermore, the number of fine particles measured in cyclone separator outlet may be more than that of in cyclone separator inlet, which caused negative grade efficiency for the fine particle. The similar phenomenon for the grade efficiency curves has been observed by other researchers [7,15] using on-line method. The effect of particle humidity on grade efficiency is shown in Fig. 7 for inlet velocity 18 m/s, in order to observe the effect clearly, the positive grade efficiency of Fig. 7 is shown in Fig. 8. It can be found that the grade efficiencies do not always increase with the increasing of particle humidity. When the particle diameter is less than 10 lm, the grade efficiency for the lower particle humidity is higher than that of the higher particle humidity. However, an opposite tend is observed when the particle diameter is larger than 10 lm. Because the maximum particle humidity is only 30‰ in this work, the agglomeration particles are not able to exist in the statuses shown in Fig. 9. Thus, the agglomeration particles are present in the statuses shown in Fig. 10 (only give two particles agglomer-
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Grade efficiency /%
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Inlet velocity: 18 m/s 3 Particle concentration: 500 mg/m Particle humidity: 8‰ 10‰ 15‰ 20‰ 25‰ 30‰
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Fig. 8. The effect of humidity on grade efficiency (positive grade efficiency).
Please cite this article as: Y. Li, G. Qin, Z. Xiong et al., The effect of particle humidity on separation efficiency for an axial cyclone separator, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.01.002
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Fig. 9. Status of agglomeration particles.
liquid
liquid
Fig. 10. Particles agglomeration configuration.
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Cut size diameter / m
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Inlet velocity: 18 m/s Particle concentration 3 100 mg/m 3 200 mg/m 3 300 mg/m 3 500 mg/m
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Particle humidity /‰ Fig. 11. Cut size diameter versus particle humidity at different particle concentration.
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4. Conclusion
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This study investigated the effect of particle humidity on inlet particle size distribution, overall efficiency, and grade efficiency of an axial cyclone separator. In addition, the change rules of cut size diameter according to particle humidity changes were also studied. More and more fine particles formed larger ones with the increasing of particle humidity. However, more agglomeration particles dispersed into fine ones again in the inner side of the cyclone separator. As a result, the trends of grade efficiency curves for different particle humidities change at the particle diameter of approximately 10 lm under the same conditions of inlet velocity and particle concentration. The grade efficiency improves with the increasing of particle humidity when the particle diameter is larger than 10 lm, while a contrary tendency is observed when the particle diameter is smaller than 10 lm. However, the overall separation efficiency increases with the increasing of particle humidity when the inlet velocity and particle concentration remain constant.
372
Acknowledgements
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The authors gratefully acknowledge the support provided by the National Natural Science Foundation of China (Grant No. 51776155) and Sinopec Si Chuan to Eastern China Transmission Gas Pipeline Co. Ltd. Sincere thanks are due to reviewers for their careful and valuable comments.
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References
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[1] C. Cortes, A. Gil, Modeling the gas and particle flow inside cyclone separators, Prog. Energy Combust. Sci. 33 (2007) 409–452. [2] G. Gong, Z. Yang, S. Zhu, Numerical investigation of the effect of helix angle and leaf margin on the flow pattern and the performance of the axial flow cyclone separator, Appl. Math. Model. 36 (2012) 3916–3930. [3] A.C. Hoffmann, H. Arends, H. Sie, An experimental investigation elucidating the nature of the effect of solids loading on cyclone performance, Filtr. Sep. 28 (1991) 188–193. [4] Z. Ji, Z. Xiong, X. Wu, et al., Experimental investigation on a cyclone separator performance at an extremely low particle concentration, Powder Technol. 191 (2009) 254–259. [5] A.C. Hoffmann, A.V. Santen, R.W.K. Allen, Effects of geometry and solid loading on the performance of gas cyclones, Powder Technol. 70 (1992) 83–91. [6] F.L. Fassani, L.G. Jr, A study of the effect of high inlet solids loading on a cyclone separator pressure drop and collection efficiency, Powder Technol. 107 (2000) 60–65. [7] H. Mothes, F. Löffler, Prediction of particle removal in cyclone separators, Int. Chem. Eng. 28 (1988) 51–55. [8] A.C. Hoffmann, L.E. Stein, Gas Cyclones and Swirl Tubes, 2nd ed., Springer, Berlin, 2008. [9] S. Obermair, C. Gutschi, Flow pattern and agglomeration in the dust outlet of a gas cyclone investigated by phase Doppler anemometry, Powder Technol. 156 (2005) 34–42. [10] R.L. Salcedo, Collection efficiencies and particle size distribution from sampling cyclones-comparison of recent theories with experimental data, Canadian J. Chem. Eng. 71 (1993) 20–27. [11] M. Sommerfeld, Validation of a stochastic Lagrangian modelling approach forinter-particle collisions in homogeneous isotropic turbulence, Int. J. Multiph. Flow 27 (2001) 1829–1858. [12] C.A. Ho, M. Sommerfeld, Modelling of micro-particle agglomeration in turbulent flows, Chem. Eng. Sci. 57 (2002) 3073–3084. [13] M. Sommerfeld, S. Lain, From elementary processes to the numerical predictionof industrial particle-laden flows, Multiph. Sci. Technol. 21 (2009) 123–140. [14] J. Paiva, R. Salcedo, P. Araujo, Impact of particle agglomeration in cyclones, Chem. Eng. J. 162 (2010) 861–876.
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that the cut size diameter decreases with the increasing of particle concentration, while increases with the increasing of particle humidity. Because the cut size diameter is anti-proportional to the grade efficiency, the cut size diameter also can be illustrated that the grade efficiency of fine particles decreases with the increasing of particle humidity.
increases the number of fine particles which are susceptible to escape. However, the overall efficiency increases with the increasing of particle humidity since the quantity of larger particles is far larger than that of fine ones, the phenomenon that overall efficiency increased but the grade efficiency of fine particle decreased with the increasing of particle humidity is not self-contradiction. The cut size diameter refers to the particle diameter when the separation efficiency is 50% is an important parameter to evaluate the separation efficiency of cyclone separator. The cut size diameters at different particle humidities are determined from the grade efficiency curves (shown in Fig. 7). Fig. 11 shows the cut size diameter and particle humidity of the cyclone separator at different particle concentrations. As shown in the figure, the cut size diameters are dependent on both particle humidity and particle concentration. Although there are some fluctuations existed in the values of cut size diameters, the overall trends are same. It can be seen
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[15] C.W. Haig, A. Hursthouse, R.J. Lories, et al., The effect of particle agglomeration and attrition on the separation efficiency of a Stairmand cyclone, Powder Technol. 258 (2014) 110–124. [16] S.M. Ahuja, Wetted wall cyclone – a novel concept, Powder Technol. 204 (2010) 48–53. [17] G.N. Kim, W.K. Choi, C.H. Jung, The development and performance evaluation of a cyclone train for the removal of contaminated hot particulate in a hot cell, Sep. Purif. Technol. 55 (2007) 313–320.
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[18] Z. Xiong, Z. Ji, X. Wu, Development of a cyclone separator with high efficiency and low pressure drop in axial inlet cyclones, Powder Technol. 253 (2014) 644–649. [19] W.C. Hinds, Aerosol Technology, 2nd ed., Wiley Interscience, 1998. [20] S.J. Cheng, Numerical and Experimental Study of Cyclone Separator for Aerosol Drug Delivery, Clare Hall College, University of Cambridge, 2012.
Please cite this article as: Y. Li, G. Qin, Z. Xiong et al., The effect of particle humidity on separation efficiency for an axial cyclone separator, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.01.002
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Contents lists available at ScienceDirect
Advanced Powder Technology journal homepage: www.elsevier.com/locate/apt
2
Original Research Paper
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The effect of particle humidity on separation efficiency for an axial cyclone separator
8
Yuan Li a,⇑, Guoliang Qin a, Zhiyi Xiong c,d, YunFeng Ji a, Ling Fan b
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a
School of Energy and Power Engineering, Xi’an Jiaotong University, No. 28, Xianning West Road, Xi’an, Shaanxi 710049, China Sinopec Si Chuan to Eastern China Transmission Gas Pipeline Co. Ltd., No. 126, Guanggu Road, Donghu New Technology Development Zone, City of Wuhan, Hubei Province 430020, China c College of Mechanical and Transportation Engineering, China University of Petroleum-Beijing, 18 Fuxue Road, Changping, Beijing, China d Beijing Key Laboratory of Process Fluid Filtration and Separation, 18 Fuxue Road, Changping, Beijing, China b
a r t i c l e
i n f o
Article history: Received 1 May 2018 Received in revised form 22 November 2018 Accepted 7 January 2019 Available online xxxx Keywords: Cyclone separator Particle humidity Collection efficiency Grade efficiency
a b s t r a c t The objective of this study is to investigate the effects of particle humidity on the inlet particle size distribution, overall efficiency, grade efficiency and cut size diameter for an axial cyclone separator with inner diameter of 150 mm. The collection and grade efficiencies of the cyclone separator were measured by on-line method for inlet velocities, particle concentration and particle humidity in the ranges of 12– 18 m/s, 30–500 mg/m3 and 8–30‰, respectively. By employing a set of fixed parameters for inlet velocity and particle concentration, the effect of particle humidity on separation efficiency was investigated. The experimental results show that the volume ratio of larger particle increases with the increasing of particle humidity due to particle agglomeration. When the inlet velocity and particle humidity remain constant, the collection and grade efficiencies improve greatly as the increasing of the particle concentration because of the particle aggregation. However, it was noticed that the grade efficiencies did not always increased with the increasing of particle humidity under the same conditions of inlet velocity and particle concentration. The trends of grade efficiency curves for different particle humidity change at the particle diameter of approximately 10 lm. The grade efficiency improves with the increasing of particle humidity when the particle diameter is larger than 10 lm, while a contrary tendency is observed when the particle diameter is smaller than 10 lm. Ó 2019 Published by Elsevier B.V. on behalf of The Society of Powder Technology Japan. All rights reserved.
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1. Introduction
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Many processing stations such as compressor station and distribution station are necessary along the long-distance pipeline of natural gas transportation according to the requirement of pressurization and distribution. These stations are commonly equipped with multicyclone separators and filter separators to remove sand, light hydrocarbons, water droplets and other impurities from the natural gas. Most of the multicylone separators are composed of several parallel single axial cyclone separators with cylinder diameter of 50–150 mm. The axial cyclone separators are usually utilized to remove the harmful or nuisance moist particles, light hydrocarbons and water droplets. The characteristic air flow pattern of an axial cyclone separator consists of an inner and an outer vortex, both spiraling in the same
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⇑ Corresponding author.
sense, with the outer vortex descending into the cyclone separator, reversing its direction and exiting the cyclone separator through the vortex finder located in the cyclone roof [1,2]. As the rotation motion, the particles are carried in the gas to experience the effects of the centrifugal force. Thus, the particles were carried to the cyclone separator wall and separate from the air flow. This is however a simplified perspective and belies the profound effects of dust concentration and particle interaction on separation performance. It is well established that as the concentration of dust increases the overall separation efficiency of the cyclone separator increases. The improvement in the cyclone separator performance has been noted to commence at dust loading as low as 0.00014 kg/m3, which resulted in the assertion that there is no lower limit of dust concentration which does not demonstrate enhance cyclonic performance [3]. The improvement in performance with increased dust loading varies with cyclone separator geometry and the inlet velocity [4]. The influence of geometry on cyclonic performance with increased dust loading is not as
E-mail address: [email protected] (Y. Li). https://doi.org/10.1016/j.apt.2019.01.002 0921-8831/Ó 2019 Published by Elsevier B.V. on behalf of The Society of Powder Technology Japan. All rights reserved.
Please cite this article as: Y. Li, G. Qin, Z. Xiong et al., The effect of particle humidity on separation efficiency for an axial cyclone separator, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.01.002
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significant as inlet velocity [5]. Except very low velocities, lower inlet velocities have greater impact on performance improvement than higher velocities [3,6]. The mechanism of increased dust loading how to improve the overall separation efficiency is not fully understood. However, the two main arguments revolve around theories of critical dust loading and particle agglomeration, with both effects taking place in or immediately after the cyclone inlet. Although there is strong experimental evidence supporting unclassified separation [5], the critical load theory also implies that below this limit load, improvement in separation performance with increased dust loading does not occur; this is however at odds with the observed behavior [3]. In contrast to the concept of critical load, Mothes & Löffler [7] proposed that particle agglomeration contributes to the improvement in cyclone performance with increased dust loading. The agglomeration of large and small particles makes the separation of finer particles from the airstream more likely, and this hypothesis is also supported by Ji et al. [4]. However, there was concern that agglomeration alone would not account for the magnitude of the effect on separation efficiency [8]. Particle agglomeration within a downcomer tube of a cyclone has been observed by phase Doppler anemometry (PDA) [9], lending credence to the agglomeration hypothesis. However there is agreement that the minima frequently observed in separation grade efficiency graphs, corresponding to finer particle sizes, are indeed a result of the agglomeration of fine particles [8,10]. The PACys model (Particle Agglomeration in Cyclones) was developed to predict the phenomenon of particle collection in reverse flow cyclones by taking into account the agglomeration phenomenon in turbulent flows [11–13]. Furthermore, Paiva et al. [14] built a model to predict the collection efficiency of gas cyclones in a more realistic way. In particular, they optimized cyclones using this model, and the results show very high collection efficiencies for submicrometer particles. They concluded that the hypothesis of particle agglomeration within the cyclone turbulent flow seems a sound justification for collection efficiencies observed higher than predicted for smaller particles in a gas-cyclone, being expectable with recirculation which will result in a more significant effect. The effect of particle agglomeration and attrition on the separation efficiency of a Stairmand cyclone was investigated by Haig et al. [15], and evidence of the agglomeration of fine particles occurring within the cyclone body was initially observed. As shown above, several studies have been performed to investigate and evaluate the effects of dry particle agglomeration on the separation efficiency. However, only few studies have discussed the effects of particle humidity on the separation efficiency. Ahuja [16] used a wetted wall cyclone separator to increase the overall collection efficiency, and Kim et al. [17] simply measured the effect of mist water on the collection efficiency. Both of the researchers concluded that the collection efficiency of the fine particles dramatically increases with the humidity. Therefore, it is important to fully investigate the change rules of particle size distribution, collection efficiency and grade efficiency with the increasing of particle humidity.
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2. Experiments
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The cyclone separator used in this study had an axial inlet with eight guide vanes, and its detailed geometry and dimensions are shown in Fig. 1. A schematic of the test rig is shown in Fig. 2. The dust-laden gas entered the cyclone separator and was taken off by a blower. The Pitot tube was used to measure the cross-section gas velocity in the tube. The experiments were carried out at the atmospheric pressure and ambient temperature. The laboratory temperature,
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Fig. 1. Geometry and dimensions of the cyclone separator.
atmospheric pressure and air relative humidity were checked and recorded frequently to improve the accuracy of the calculated air flow within the test rig through the air density and the standard equation for Pitot tubes. Throughout the experiments the air relative humidity was ranged between 25 and 40%, room temperature was between 20 and 30 °C and atmospheric pressure varied between 99,800 and 102,000 Pa. A powder dispersion generator, BEG-1000 by Palas, was used to feed particles continuously into the inlet gas. A similar method adopted by other researchers [4,15,18] was employed to calculate the particle concentration, as the mass flow divided by the flow rate. Model Welas-2000 aerosol spectrometer by Palas was used for online measurement of particle concentrations and particle size distributions based on particle numbers at a sampling flow rate of 5 L/min. The range of measured particle number concentration was from 0 to 105 particles/cm3 and the particle size distribution was
Please cite this article as: Y. Li, G. Qin, Z. Xiong et al., The effect of particle humidity on separation efficiency for an axial cyclone separator, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.01.002
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blower
bag filter smapling nozzle manometer
compressed air
pitot
smapling nozzle
inclined manometer sensor dust feeder
welas system
PC test cyclone Fig. 2. Schematic of cyclone separator test rig.
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between 0.3 and 40 lm. Sampling nozzles with different diameters were used for different flow rates in the isokinetic sampling of the dust-laden gas at the inlet and outlet of the cyclone separator. The downstream sensor is positioned more than ten pipe diameters from the elbow tube to eliminate sampling issues due to a swirling flow. The collection and grade efficiencies of the cyclone separator were measured at inlet velocities of 12–18 m/s and particle concentrations of 30–500 mg/m3 at atmospheric pressure and room temperature, respectively. Calcium carbonate was used as solid particles with a physical density of 2700 kg/m3, and the particle size ranged from 0.6 to 40 lm. In order to remove the particles’ moisture, the solid particles were dried more than two hours by a dryer before experiment. Then these dried solid particles were put in a closed agitator, and the water was sprayed into the agitator by a humidifier, so particles and water vapor were stirred completely. The quantity of particles and water was weighed, respectively. The different particle humidity was controlled by adding water vapor to the dried solid particles. The particle humidity was defined as,
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H¼
mw 100% ms þ mw
ð1Þ
where H, mw and ms are the particle humidity, the quality of water vapor and dried solid particles, respectively. The particle humidity changed among 8–30‰ in experiments. In order to control the particle humidity, the dried solid particles were weighed firstly, and then the quality of water vapor was calculated and weighed according to the value of particle humidity.
3. Results and discussion
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3.1. Particle size distribution
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Model Welas-2000 is an aerosol spectrometer, also known as optical particle counter (OPC), which measures the particle size (equivalent spherical optical particle size) base on the intensity of scattered light of single particle. Accordingly, the counting distribution (dN/N), volume distribution (dV/V), volume and mass concentration of particles can be obtained. By using the formula of sphere volume, the volume distribution of particles can be chan-
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0.06
Particle size volume ration dv/v
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Particle humidity 0‰ 8‰ 10‰ 15‰ 20‰ 25‰ 30‰
0.05 0.04 0.03 0.02 0.01 0.00 -5
0
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Particle size diameter / m Fig. 3. The effect of humidity on inlet particle size distribution.
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0.055
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Particle size volume ration dV/V
Particle size number ration dN/N
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Particle humidity 8‰ 10‰ 15‰ 20‰ 25‰ 30‰
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Particle humidity 8‰ 10‰ 15‰ 20‰ 25‰ 30‰
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Particle diameter / m
(a) Particle size distributions based on number ration
(b) Particle size distributions based on volume ration
Fig. 4. The effect of humidity on outlet particle size distribution.
82 80 78
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Overall efficiency /%
Overall efficiency /%
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Particle humidity 30‰ 25‰ 20‰ 15‰ 10‰ 8‰
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Particle concentration /mg/m
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Particle concentration /mg/m
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Particle concentration /mg/m (d) v=12m/s
Fig. 5. The effect of humidity on overall efficiency.
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Particle humidity:30‰ Particle concentration 3 30 mg/m 3 50 mg/m 3 100 mg/m 3 200 mg/m 3 300 mg/m 3 500 mg/m
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Grade efficiency /%
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Particle humidity:20‰ Particle concentration 3 30 mg/m 3 50 mg/m 3 100 mg/m 3 200 mg/m 3 300 mg/m 3 500 mg/m
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Particle humidity:25‰ Particle concentration 3 30 mg/m 3 50 mg/m 3 100 mg/m 3 200 mg/m 3 300 mg/m 3 500 mg/m
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Grade efficiency /%
Grade efficiency /%
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Particle relative humidity:15‰ Particle concentration 3 30 mg/m 3 50 mg/m 3 100 mg/m 3 200 mg/m 3 300 mg/m 3 500 mg/m
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Partilce diameter / m
Particle diameter / m Fig. 6. The effect of particle concentration on grade efficiency (inlet velocity is 18 m/s).
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ged and calculated from the counting distribution, shown as follows:
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pD3
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i Ni dV D3 N i ¼P 6 3 ¼ P60i 3 p D 60 V i N i¼1 Di N i
i¼1
6
ð2Þ
i
where i is the number of channels for measuring particle size, 1 i 60, Di is the particle size, 0.6 lm Di 40 lm, N i is the counting number of the particle corresponding to Di . In these experiments, the mixture of dried solid particles and water vapor was premixed by the dust feeder to ensure the same dispersion, which had been verified by Ji et al. [4]. However, the particle size distributions for different humidity are not the same at the inlet sampling position. Fig. 3 shows the effect of humidity on particle size distribution at the cyclone inlet with 14 m/s inlet velocity and 300 mg/m3 particle concentration. As shown in Fig. 3, the volume of large agglomerated particle increases with the increasing of particle humidity at the inlet. There are many fine (<10 lm) particles in the mixture with lower humidity 8‰ compared to the others. Agglomeration, or coagulation, is the primary inter-particle occurrence among aerosol particles. When aerosol particles collide due to their relative motion, the particles may adhere to each other and form larger particles known as agglomerates. Kinematic coagulation arises when the relative motion of the particle is the result of an external force, such as the centrifugal force as is the case with cyclones [19]. The main adhesive force
is the van der Waals force, which is due to complementary dipoles (concentrations in electric charge) forming in neighboring particles and producing an attractive force. The surface force also plays a strong role. This force arises from liquid molecules being absorbed by the particle surface and surface tension, as a result of capillary action, which adhere the particle to a surface. Therefore, more fine particles form larger particles with the increasing of humidity. Particle size distributions of different particle humidity measured at the downstream of the cyclone are shown in Fig. 4 at the same inlet velocity and particle concentration as the upstream. Although there are some differences among the particle size distributions based on volume ration, the particle size distributions based on number ration are almost the same. Because most of bigger particles were separated by the cyclone, so there are few effects of particle humidity on particle size distribution of the downstream of the cyclone.
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3.2. Overall efficiency
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The effects of particle humidity on overall efficiency are showed in Fig. 5, in which the inlet velocity, particle concentration and humidity in the ranges of 12–18 m/s, 30–500 mg/m3 and 8–30‰, respectively. Utmost care is taken while determining the overall efficiency since there is a possibility of the escape of fines. To account for any possible experimental errors due to this, each experiment was repeated six times for obtaining the overall effi-
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Grade efficiency /%
Grade effiency /%
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Inlet velocity: 18 m/s 3 Particle concentration: 100 mg/m Particle humidity: 8‰ 10‰ 15‰ 20‰ 25‰ 30‰
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Partilce diameter / m
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Inlet velocity: 18 m/s 3 Particle concentration: 500 mg/m Particle humidity: 8‰ 10‰ 15‰ 20‰ 25‰ 30‰
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Particle diameter / m Fig. 7. The effect of humidity on grade efficiency.
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ciency of the cyclone separator. The measure errors are shown in Fig. 5. It is observed that the overall efficiency increases with the increasing of particle humidity. This is to be expected since more fine particles form larger particles at higher humidity, and larger particles are easy to be separated. The efficiency varied from 58.5% to 69.53% under humidity 8‰ and from 63.07% to 80.18% under humidity30‰ with the inlet velocity 18 m/s, corresponding to particle concentration between 30 mg/m3 and 500 mg/m3. Thus, there is a remarkable increase in the overall efficiency with the increasing of particle humidity under the condition of same inlet velocity and particle concentration. However, it may be observed that the larger particles are the major contribution to the overall efficiency increase. The substantial change in the separation efficiency of smaller particles with a lesser proportion is not reflected in the overall efficiency. In addition, the overall efficiency also increases with the increasing of particle concentration, which has been investigated by other researches [3,4,6]. 3.3. Grade efficiency
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Grade efficiency (gi ) is the separation efficiency of a given particle size for cyclone. In the upstream and downstream of the cyclone, the mass frequency or volume frequency of the particles with a certain size (dp ) is f dp in;i and f dp out;i , respectively. Grade
271
efficiency can be calculated by the following formula:
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gi ¼
! C out f dp out;i 100% 1 C in f dp in;i
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ð3Þ
where C in and C out are the mass concentration of the particle in upstream and downstream, respectively. Fig. 6 shows the separation grade efficiency of the cyclone separator with different particle concentration for inlet velocity 18 m/ s, at different humidity. As shown in Fig. 6, when the inlet velocity and particle humidity are the same, the improvement of grade efficiency with the increase of particle concentration from 30 to 500 mg/m3 is clearly observed. The series of data points from the repeated tests are shown along with their average, with each series also being an average of six sampling periods. The graphs clearly show the effect of particle concentration on grade efficiency. Many researches [4,7,15] have observed that the effect of particle concentration on the particle grade efficiency may be important due to particles agglomeration. There are more fine particles form larger ones with the increasing of particle concentration. The effect of agglomeration had been illustrated by the upstream and downstream particle distributions [4,15]. The removal of particles is primarily due to the effects of the centrifugal force which is directly proportional to the particle mass characterized by the particle diameter, when considering the particle as sphere. The ‘tail’ formations at very fine particle sizes, which is known to press the entire grade efficiency curve upwards, are often seen
Please cite this article as: Y. Li, G. Qin, Z. Xiong et al., The effect of particle humidity on separation efficiency for an axial cyclone separator, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.01.002
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ation configuration). As shown in Fig. 10, the liquid bridge may exist between particles, but there are few of agglomeration particles existed in the form of the third configuration according to the particle humidity. When agglomeration particles enter into the cyclone separator, several forces will work at each particle, such as centrifugal force, attraction force, drag force, and so on. Among these forces, the centrifugal force and drag force determine the agglomeration particles’ configuration. Assuming an agglomeration particle (shown in Fig. 9) does not disperse to two particles, although the tangential velocities of these two particles are same, the centrifugal force for each particle is different. If the difference in drag is larger than the attraction force, the agglomeration particle will be dispersed to two separate particles. The number of agglomeration particle increases with the increasing of particle humidity in the cyclone separator inlet (shown in Fig. 3), so the probability of particle dispersion also increases with the increasing of particle humidity. As a result, the ratio of escaped particles to inlet particles increases with the increasing of particle humidity. Therefore, the grade efficiency decreased with the increasing of particle humidity. However, almost all of the larger particles (>10 lm) can be separated by cyclone separator, so particle humidity has few effects on larger particles’ grade efficiency. Data indicative of particle de-agglomeration occurring in small scale reverse-flow cyclone separators for use in dry powder inhaler (DPI) was observed and reported by Cheng [20]. The cyclone separator efficient is decreased as particle dispersion inevitably
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experimentally due to the effect of high solid loading. Thus, low solid loading was used (ranged from 30 to 500 mg/m3) in these experiments. Considering the cohesive nature of the test dust, it is possible that small particles agglomerate in the inlet and being separated in the cyclone as form of agglomerates and then show up in the disperser when the agglomerates break up during dispersion, so the grade efficiency curves measured by on-line method are flat. Furthermore, the number of fine particles measured in cyclone separator outlet may be more than that of in cyclone separator inlet, which caused negative grade efficiency for the fine particle. The similar phenomenon for the grade efficiency curves has been observed by other researchers [7,15] using on-line method. The effect of particle humidity on grade efficiency is shown in Fig. 7 for inlet velocity 18 m/s, in order to observe the effect clearly, the positive grade efficiency of Fig. 7 is shown in Fig. 8. It can be found that the grade efficiencies do not always increase with the increasing of particle humidity. When the particle diameter is less than 10 lm, the grade efficiency for the lower particle humidity is higher than that of the higher particle humidity. However, an opposite tend is observed when the particle diameter is larger than 10 lm. Because the maximum particle humidity is only 30‰ in this work, the agglomeration particles are not able to exist in the statuses shown in Fig. 9. Thus, the agglomeration particles are present in the statuses shown in Fig. 10 (only give two particles agglomer-
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Fig. 8. The effect of humidity on grade efficiency (positive grade efficiency).
Please cite this article as: Y. Li, G. Qin, Z. Xiong et al., The effect of particle humidity on separation efficiency for an axial cyclone separator, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.01.002
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Fig. 9. Status of agglomeration particles.
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Particle humidity /‰ Fig. 11. Cut size diameter versus particle humidity at different particle concentration.
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This study investigated the effect of particle humidity on inlet particle size distribution, overall efficiency, and grade efficiency of an axial cyclone separator. In addition, the change rules of cut size diameter according to particle humidity changes were also studied. More and more fine particles formed larger ones with the increasing of particle humidity. However, more agglomeration particles dispersed into fine ones again in the inner side of the cyclone separator. As a result, the trends of grade efficiency curves for different particle humidities change at the particle diameter of approximately 10 lm under the same conditions of inlet velocity and particle concentration. The grade efficiency improves with the increasing of particle humidity when the particle diameter is larger than 10 lm, while a contrary tendency is observed when the particle diameter is smaller than 10 lm. However, the overall separation efficiency increases with the increasing of particle humidity when the inlet velocity and particle concentration remain constant.
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Acknowledgements
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The authors gratefully acknowledge the support provided by the National Natural Science Foundation of China (Grant No. 51776155) and Sinopec Si Chuan to Eastern China Transmission Gas Pipeline Co. Ltd. Sincere thanks are due to reviewers for their careful and valuable comments.
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References
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[1] C. Cortes, A. Gil, Modeling the gas and particle flow inside cyclone separators, Prog. Energy Combust. Sci. 33 (2007) 409–452. [2] G. Gong, Z. Yang, S. Zhu, Numerical investigation of the effect of helix angle and leaf margin on the flow pattern and the performance of the axial flow cyclone separator, Appl. Math. Model. 36 (2012) 3916–3930. [3] A.C. Hoffmann, H. Arends, H. Sie, An experimental investigation elucidating the nature of the effect of solids loading on cyclone performance, Filtr. Sep. 28 (1991) 188–193. [4] Z. Ji, Z. Xiong, X. Wu, et al., Experimental investigation on a cyclone separator performance at an extremely low particle concentration, Powder Technol. 191 (2009) 254–259. [5] A.C. Hoffmann, A.V. Santen, R.W.K. Allen, Effects of geometry and solid loading on the performance of gas cyclones, Powder Technol. 70 (1992) 83–91. [6] F.L. Fassani, L.G. Jr, A study of the effect of high inlet solids loading on a cyclone separator pressure drop and collection efficiency, Powder Technol. 107 (2000) 60–65. [7] H. Mothes, F. Löffler, Prediction of particle removal in cyclone separators, Int. Chem. Eng. 28 (1988) 51–55. [8] A.C. Hoffmann, L.E. Stein, Gas Cyclones and Swirl Tubes, 2nd ed., Springer, Berlin, 2008. [9] S. Obermair, C. Gutschi, Flow pattern and agglomeration in the dust outlet of a gas cyclone investigated by phase Doppler anemometry, Powder Technol. 156 (2005) 34–42. [10] R.L. Salcedo, Collection efficiencies and particle size distribution from sampling cyclones-comparison of recent theories with experimental data, Canadian J. Chem. Eng. 71 (1993) 20–27. [11] M. Sommerfeld, Validation of a stochastic Lagrangian modelling approach forinter-particle collisions in homogeneous isotropic turbulence, Int. J. Multiph. Flow 27 (2001) 1829–1858. [12] C.A. Ho, M. Sommerfeld, Modelling of micro-particle agglomeration in turbulent flows, Chem. Eng. Sci. 57 (2002) 3073–3084. [13] M. Sommerfeld, S. Lain, From elementary processes to the numerical predictionof industrial particle-laden flows, Multiph. Sci. Technol. 21 (2009) 123–140. [14] J. Paiva, R. Salcedo, P. Araujo, Impact of particle agglomeration in cyclones, Chem. Eng. J. 162 (2010) 861–876.
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that the cut size diameter decreases with the increasing of particle concentration, while increases with the increasing of particle humidity. Because the cut size diameter is anti-proportional to the grade efficiency, the cut size diameter also can be illustrated that the grade efficiency of fine particles decreases with the increasing of particle humidity.
increases the number of fine particles which are susceptible to escape. However, the overall efficiency increases with the increasing of particle humidity since the quantity of larger particles is far larger than that of fine ones, the phenomenon that overall efficiency increased but the grade efficiency of fine particle decreased with the increasing of particle humidity is not self-contradiction. The cut size diameter refers to the particle diameter when the separation efficiency is 50% is an important parameter to evaluate the separation efficiency of cyclone separator. The cut size diameters at different particle humidities are determined from the grade efficiency curves (shown in Fig. 7). Fig. 11 shows the cut size diameter and particle humidity of the cyclone separator at different particle concentrations. As shown in the figure, the cut size diameters are dependent on both particle humidity and particle concentration. Although there are some fluctuations existed in the values of cut size diameters, the overall trends are same. It can be seen
Please cite this article as: Y. Li, G. Qin, Z. Xiong et al., The effect of particle humidity on separation efficiency for an axial cyclone separator, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.01.002
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[15] C.W. Haig, A. Hursthouse, R.J. Lories, et al., The effect of particle agglomeration and attrition on the separation efficiency of a Stairmand cyclone, Powder Technol. 258 (2014) 110–124. [16] S.M. Ahuja, Wetted wall cyclone – a novel concept, Powder Technol. 204 (2010) 48–53. [17] G.N. Kim, W.K. Choi, C.H. Jung, The development and performance evaluation of a cyclone train for the removal of contaminated hot particulate in a hot cell, Sep. Purif. Technol. 55 (2007) 313–320.
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[18] Z. Xiong, Z. Ji, X. Wu, Development of a cyclone separator with high efficiency and low pressure drop in axial inlet cyclones, Powder Technol. 253 (2014) 644–649. [19] W.C. Hinds, Aerosol Technology, 2nd ed., Wiley Interscience, 1998. [20] S.J. Cheng, Numerical and Experimental Study of Cyclone Separator for Aerosol Drug Delivery, Clare Hall College, University of Cambridge, 2012.
Please cite this article as: Y. Li, G. Qin, Z. Xiong et al., The effect of particle humidity on separation efficiency for an axial cyclone separator, Advanced Powder Technology, https://doi.org/10.1016/j.apt.2019.01.002
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