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An analysis of a reverse pulse cleaning process using high-flow pleated fabric filter cartridges
Accepted Manuscript Title: An Analysis of a Reverse Pulse Cleaning Process using High-Flow Pleated Fabric Filter Cartridges Authors: Yan Cuiping, Zhang Mingxing, Lin Longyuan, Chen Haiyan PII: DOI: Reference:
S0957-5820(17)30372-5 https://doi.org/10.1016/j.psep.2017.10.018 PSEP 1215
To appear in:
Process Safety and Environment Protection
Received date: Revised date: Accepted date:
23-5-2016 9-5-2017 23-10-2017
Please cite this article as: Cuiping, Yan, Mingxing, Zhang, Longyuan, Lin, Haiyan, Chen, An Analysis of a Reverse Pulse Cleaning Process using HighFlow Pleated Fabric Filter Cartridges.Process Safety and Environment Protection https://doi.org/10.1016/j.psep.2017.10.018 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
An Analysis of a Reverse Pulse Cleaning Process using High-Flow Pleated Fabric Filter Cartridges
Yan Cuiping, Zhang Mingxing, Lin Longyuan, Chen Haiyan Key Laboratory of Solid Waste Treatment and Resource Recycle, Ministry of Education, School of Environment and Resource, Southwest University of Science and Technology, Mianyang 621010, China
Graphical abstract
Large-flow filter cartridge (Φ325 × 1000 mm) was experiment
Process of dust dislodgement from filter cartridge was photographed by high-speed camera
Static pressure and duration of peak pressure along the filter cartridge was recorded
The first peak pressure (673 Pa) and the first impact cannot effectively remove the dust cake
The process of quartz particles dislodgement from the entire filter cartridge is not only related to peak pressure but also to duration of peak pressure.
Increase of pulse width can decrease the opportunity of re-suspended dust particles reattached on the bottom of filter cartridge again
1
Highlights
We examine the cleaning characteristics of high-flow filter cartridges.
The quartz particles are dislodgement from the entire filter cartridge.
The particles are removed due to peak pressure and duration of peak pressure.
Increase of pulse width decrease dust reattached on the bottom of filter cartridge.
Abstract: A high-flow fabric filter cartridge with a high pleat ratio, along with a large diameter, and a large filtration area, showed increased susceptibility to incomplete cleaning, caused by the greater variation of pulse airflow in the filter cartridge. In order to investigate the cleaning characteristics of high-flow pleated fabric filter cartridges, a pleated fabric filter cartridge (Φ325×Φ215×1000 mm) was used to the experiment. Then, the peak pressure distribution along the height of the filter cartridge with five measurement locations was recorded using five pressure transducers. The process of dust cake born off the filter cartridge was photographed using a high-speed camera. The cleaning process of a high-flow filter cartridge was examined, and the peak pressure variation on the filter cartridge was determined during the pulse cleaning. The results show the following: the process duration of the dust cake born off the filter cartridge was 372 ms. The maximum peak pressures were 4932, 14026, 3998, 8813, and 1962 Pa from the top to the bottom along the height of the filter cartridge, respectively. The peak pressure and duration formed by the pulse airflow are indicative of the cleaning process of dust cake born off filter cartridge. Although a peak pressure high to 673 Pa appears at location one with the first transient time, only a minor amount of dust particles was born off filter cartridge. Therefore, the process of quartz particles born off the entire filter cartridge was not only related to the peak pressure, but 2
also to the duration. Meanwhile, the experiment shows that an increase in the pulse width can decrease the likelihood of dust particles being reattached on the bottom of the filter cartridge. The peak pressures increase on the filter cartridge when the pleat number decreases from the 155 to 125. This can decrease the incidence of incomplete cleaning. Keywords: filter cartridge, pulse cleaning, reverse airflow, static pressure, dust cake born off
1. Introduction In recent years, the use of pleated fabric filter cartridges in dust collectors has attracted a great deal of attention, due to the fact that the pleated filter cartridges offer a larger filtration surface when compared to the flat-sheet filter bags (if both filters are used in housing of the same size) [1]. Therefore, the pleated fabric filter cartridges used in dust collection technology have the purposes to control particulate emissions, recover valuable particles, and in the high-flow filter cartridges in particular. High-flow filter cartridges can be used to create a high-flow dust collector, which can effectively filter dust-laden airflow higher to 120000 m3/h, even more cleaning for filters has been widely used since the 1950s authors
[8-12]
[6] [7]
[2-5]
. Pulse-jet
. For the filters, some
hold that the reverse airflow played an important role in dust cake born
off (the dust born off the filter cartridge and collected in the hopper) the filters. Certain authors
[13-15]
hold that the medium movement given effect in dust cake born
off the filters. The above studies have shown that the reverse airflow and medium movement were important and essential to achieve cleaning efficiency (defined as the weight pre and post cleaning). However, some authors
[16][17]
have concluded that the
reverse airflow played only a minor role in dust cake born off the filters. Sievert and 3
Löffler
[10]
found that the medium acceleration was related to fabric characteristics
during pulse cleaning. The medium acceleration was at least 300 ms-2 for soft fabric to effective cleaning. Otherwise, the medium acceleration was higher to 2000~5000
ms-2 for nonflexible fabric to effective cleaning. Leubner and Riebel
[18]
have
reported that the peak pressure and the rate to peak pressure (the maximum pressure on the filter) were used to assess the cleaning effect. Dennis
[13]
has reported that the
rate to peak pressure was higher than 600 Pa/ms for the dust cake born off the filters. For the filter cartridge, some authors [19-21] have shown that the peak pressures of pleated filter cartridge have the positive correlation to the cleaning intensity. The main opinions showed that the static peak pressure on the filter cartridge has positive effects on cleaning efficiency. The cleaning process of filter cartridge is different from the flexible bag. This is because that the fabric medium of filter cartridge is different the flexible bag. Qian et al. [22] have show that the cleaning mechanism at the top of the three filter bags is governed by fabric acceleration due to sudden filter media movement, while the peak pulse pressure plays a major role in the lower part of the three filter bags. However, Lo et al.
[23]
have demonstrated that the average static
pressure (static pressure has formed obtained by the dynamic pressure when the reverse airflow encounters the filter medium) on the filter cartridge was more closely correlated to cleaning efficiency than to overpressure, and the top of a filter cartridge was difficult to clean because of the lower pressure generated by the pulse-jet airflow. Ju et al.
[24]
thought that the first positive static peak pressure formed by the first
airflow was a main factor to the cleaning efficiency. Yan et al.
[25]
have demonstrated 4
that the cleaning efficiency increased when the static peak pressure increased. Our team holds that the cleaning performances can be directly related to the static peak pressure on the filter cartridge formed by the pulse airflow [26-29]. However, a pleated fabric filter cartridge with a high pleat ratios (pleat height to pleat width, higher than 4 [1]), a large diameter (diameter of filter cartridge, equal to or higher than 325 mm) and a large filtration area (height of filter cartridge, equal to or higher than 1000 mm) have greater instances of incomplete cleaning (defined as the top part or bottom part have an obviously dust cake after a pulse cleaning) due to large variation of reverse airflow internal the filter cartridge
[30]
. The instances of
filtration velocity and uneven particle deposition on filter medium increases gradually due to incomplete cleaning of filter cartridges. The incomplete cleaning of filter cartridges lead to the greater unsteady of the filtration airflow, thus, the more opportunities the incomplete cleaning is formed. Conversely, the more opportunities the incomplete cleaning is, the greater unsteady the filtration airflow is formed. Therefore, the formed dust cake distribution is ununiformed. Thus, the probability of incomplete cleaning of a filter cartridge is larger than this of a flat-sheet filter bag. An occurrence of incomplete cake detachment or patchy cleaning is shown in Fig. 1. Thus, our team focused on the cleaning process rather than the filtration process. We conducted a series of experiments to study the cleaning performances of the filter cartridges under varied operational parameters [19-21] [24-29]. In this paper, a high-flow fabric filter cartridge (Φ325×Φ215×1000 mm) with a high pleat ratio, along with a large diameter, and a large filtration area, the greater 5
variation of pulse airflow in the filter cartridge increased susceptibility to incomplete cleaning. There was a deficiency in the technical literature concerning the cleaning performance of a filter cartridge during a pulse cleaning. In order to investigate the cleaning characteristics of high-flow pleated fabric filter cartridges, the peak pressure distribution along the height of the filter cartridge and the process of dust born off the filter cartridge are examined, decreasing an incidence of the incomplete cleaning. 2. Materials and methods 2.1. Experimental apparatus In order to examine the reverse airflow on the total cleaning process using high-flow pleated fabric filter cartridges, a filter cartridge (Φ325 × Φ215 × 1000 mm) was installed in the filter. The dust cake born off the filter cartridge, as well as the static pressure on the filter cartridge was examined, reducing an incidence of the incomplete cleaning. Fig. 2 shows a schematic view of the test rig (designed by Mianyang, Liuneng, Powder Equipment Co., Ltd.). The dimensions of the dust collector compartment were length 845× width 585× height 2270 mm. Table 1 shows the filter cartridge dimensions (Φ325×Φ215×1000 mm). Fig. 3 shows that a rigid wire cage supported the filter medium. The rigid wire cage can decrease the deformation of the filter media during pulse cleaning. The pressure transducers were fixed on a rigid wire cage, shown in Fig. 2. The photo and microstructure of the filter cartridge are shown in Fig. 3. The filter medium without surface treatment was composed a polyethylene terephthalate nonwoven filters. The permeability was 150 L/m2*s at a 200 Pa pressure drop. Another filter medium with surface treatment was composed of 6
a layer of polytetrafluoroethene fibers on a polyethylene terephthalate nonwoven filters substrate. The permeability was 80 to 100 L/m2*s at a 200 Pa pressure drop. The induced airflow was produced using a supersonic induced nozzle (VN25PC-50, Australia, Goyen Co., Ltd.) and an air diffuser (CC200, Australia, Goyen Co., Ltd.). The schematic diagrams of the induced nozzle and the diffuser are shown in Fig. 2. The experiment also includes a high-speed camera (FASTCAM APX RS, Japan, Photron Co., Ltd); a pulse-jet valve (DMF-ZM-25s type with a diameter of one inch); a compressed air reservoir; a pulse controller; a screw air compressor; six high precision pressure transducers (S130100, precision is 0.05%, data acquisition rate is 1 kHz, Mianyang Qishiyuan Science and Technology Co., Ltd); an electric charge amplifier (QSY7709); a metal halide lamp (DCI-2000) and a portable data acquisition instrument (QSY-USB-8512E). A hopper was connected to the dust cartridge filter to collect the dust born off the filter cartridge. Fig. 2 shows that the five high-precise pressure transducers were fixed on a rigid wire cage. Those pressure transducers were used to record the static pressure (the dust cake born force from the filter cartridge), along with the duration of the peak pressure on the filter cartridge. A high precise pressure transducer was used to record the outlet pressure of the pulse valve. The high precise pressure transducer was fixed at the location of the pulse tube, which was connected to the pulse valve. The process of dust cake born off the filter cartridge was photographed using a high-speed camera (3000 fps, FASTCAM APX RS, Japan, Photron Co., Ltd), under a 2000 W metal halide lamp. The reverse airflow from the compressed air reservoir was controlled 7
using a pressure regulator, a pulse valve, and a sequential timer/relay that caused the pulse valve opening time and interval to change. The filtration velocity through the filter cartridge was controlled using a fan speed controller. Then, a vibrating feeder was used to disperse the quartz particles. The filtration velocity was set to 0.8 cm/s. The top view of a filter cartridge is shown in Fig. 2. A filter cartridge was fitted with an induced nozzle, along with a pulse valve. A computer running a LabView program was connected to a charge amplifier and a data acquisition instrument, in order to collect the data, and a pulse controller was used to control the pulse valve. After a pulse cleaning, the filter cartridge was taken out and weight. The cleaning efficiency is defined the weight difference. 2.2. Dust test In this experiment, a pleated fabric filter cartridge was used to collect the quartz particles, which were obtained from the grinding. The size distribution was measured using an Laser Particle Sizer (Ⅵ) from the Zhuhai OMEC Instrument Co., Ltd. The mean particle size of particulate matter was 1.5 μm, as shown in Fig. 4. The dust concentration of the quartz was 25 g/m3. 2.3. Experimental design Table 2 shows the experimental parameters during the pulse cleaning. In our previously experiment
[24]
, we found that the cleaning process was complex and the
process of the dust cake born off the filter cartridges was not clear. Usually, the cleaning process is classified as four stages due to pulse valve. The first stage is the time delay to open the pulse valve; the second stage is the time to open the pulse valve; 8
the third stage is the continued opening time of pulse valve; and the fourth stage is the close time of the pulse valve. The four stages correspond to the formed pressure process on the filter cartridge. Therefore, in order to investigate the cleaning process and the process of the dust cake born off the filter cartridge, we designed this experiment. In this experiment, we focused on the cleaning process and the dust cake born off the filter cartridge. The actuation of the cleaning process was managed using a pulse controller. The pulse airflow was in the opposing direction to the normal forward filtration airflow through the filter cartridge. Then, the dust cake born off the filter cartridge, and the static pressures were recorded using a high-speed camera and five pressure transducers, respectively. A high-speed camera was positioned approximately 5 m away from the dust collector, and a metal halide lamp was positioned approximately 2 m away from the dust collector. Five pressure transducers (Φ7 mm) were fixed onto the interface of the rigid wire cage on the filter surfaces. Measurements one, two, three, four, and five were located at the locations of 80, 150, 350, 650, and 850 mm, respectively, from the filter cartridge opening. The sizes of the pressure transducers were smaller than this of the filter cartridge. Therefore, the effects of the pressure transducers on the airflow could be ignored. Each pressure transducer was located at each measurement location. The export signal from the pressure transducer was connected to the import signal from the charge amplifier. The outlet signal of the charge amplifier was then linked to the inlet of the data acquisition instrument. Finally, the export signal from the data acquisition instrument was linked to the computer. Every experiment, the three identical pulses were examined and the 9
average values were obtained. In the data analysis phase, Microsoft dasView 2.0 was employed to obtain and change the data into the pressure data, based on sensor sensitivity and the following formula: P
v K1 K 2
(1),
Where P (MPa) is the measured pressure; v (mV) is the voltage output value; K1 (mv/pC) is a multiple of the charge amplifier; and K2 (pC/MPa) is the sensor sensitivity. In this study, the K1 was magnified 100 times. The sensor sensitivity K2 was 6.5 pC/MPa. 3. Results and discussion 3.1. Effects of the pulse airflow on the peak pressures of the filter cartridge The pulse airflow is a transient unsteady airflow and is a reverse airflow, which is in opposition to the filtration airflow. As illustrated in Fig. 5, the outlet pressures of the pulse valve are obtained using a pressure transducer, which is fixed on the pulse tube. In this study, the induced nozzle and the diffuser can disperse the pulse airflow and change the induced the secondary airflow. The mixture airflow of pulse airflow and the induced airflow (secondary airflow) moved into the filter cartridge and dispersed quickly onto the filter’s internal surface. The mixed airflow beam form a bigger horizontal area at the filter cartridge opening with the induced nozzle and the diffuser, compared to those without induced nozzle and the diffuser
[25] [31]
. Fig. 5
illustrates that the outlet pressures of the pulse valve were formed to a steady phase at the third stage. Fig. 5 shows that the duration of the outlet peak pressure of the pulse 10
valve was approximately 100 ms. Therefore, the duration of the surface peak pressure on the filter cartridge was approximately 100 ms, as shown in Table 3. Then, the surface pressures on the filter cartridge gradually decreased to zero. Table 3 shows that the high pressure variation and long duration of the peak pressure at the top area of the filter cartridge were caused by the incomplete mixture of the jet pressure, strong local velocities, and turbulence due to the short time period of the first stage to the second stage of the pulse valve. Therefore, the initial pressures were triggered at measurements one and two. One peak pressure higher than 673 Pa was recorded at measurement location one, and another peak pressure higher than 427 Pa was recorded at measurement location two, with a transient time. This corresponded to the second stage (25.5 to 60 ms) of the outlet pressures of pulse valve, as shown in Fig. 5. Fig. 5 shows that the incomplete mixture airflow forms the first peak pressure at measurement location one and two. When the airflow goes down the filter cartridge, the airflow appeared to steady airflow. At this moment, the second peak pressures have formed. At the third stage, the pulse airflow appeared to be in the steady stage. The reverse airflow and secondary airflow formed the steady airflow. The steady airflow went into the filter cartridge through the induced nozzle and the diffuser, and formed the steady peak pressures and the duration on the filter cartridge. The steady airflow encountered the filter medium, and some partly dynamic pressures of the steady airflow were changed to static pressures on the filter cartridge. Therefore, maximum peak pressures higher than 4932, 14026, 3998, 8813, and 1962 Pa were recorded from the top of filter cartridge to the bottom, as shown in Table 3. The 11
duration of the maximum peak static pressure was obtained by the duration of the peak pressures of the pulse valve outlet. The peak static pressure distribution was formed along the height of the filter cartridge. The five peak static pressures are averaged and the value is 6746 Pa along the height of the filter cartridge. This is because that the mixed airflow goes into filter cartridge and forms the static pressure at measurement location one through the induced nozzle and diffuser. Then, the axial velocity of the mixed airflow goes down. The mixed airflow expanses and forms the static pressure at measurement location three. The expanded airflow mixes with the airflow from the measurement location one. The mixed airflow form the maximum pressure at measurement location two, therefore, the time to peak pressure is longer than other measurement locations, shown in table 3. Then, the axial velocity of the mixed airflow decreases, which results in decrease of peak static pressure. Otherwise, the pressure variation at the bottom of the filter cartridge is greater than that of the measurement locations. This result indicates that the mixed airflow along the filter cartridge surfaces mixes with the rebounded airflow from the bottom of filter cartridge. Thus, the dynamic pressure is transformed to static pressure at first. Then the static pressure obtains a maximum value and the dynamic pressure decreases. The mixture airflow of reverse airflow and induced airflow occurs to expand. At the same time, the consumption of airflow through filter medium and friction of airflow and filter medium decrease the airflow energy. Therefore, the peak static pressures are obtained by the energy of mixed airflow and consumption airflow. The duration of the maximum peak static pressure on the filter cartridge corresponded to the third stage of 12
the outlet pressures of the pulse valve. From Table 3 and Fig. 5, the reverse airflow and secondary airflow appeared to be in a steady state at the third stage. The dynamic pressures of the mixed airflow were conversed to static pressures when the mixed airflow encountered the filter cartridge. Therefore, the formed peak pressure appeared as a maximum value at the measurement locations. For the different air permeability of filter media, Fig. 6 and Table 4 show that the formed static pressure on the filter cartridge with surface treatment (80-100 L/m2·s) was higher than this without a surface treatment (150 L/m2·s). This result agrees with the result obtained by Zheng et al.
[20]
, who reported
that the peak static pressure on the filter medium with a surface treatment (a multiple layer structure of finer fibers) was higher than that without a surface treatment. This was due to the fact that few reverse airflow pervaded through the filter medium when the porosity of the filter medium was smaller with a surface treatment than that without a surface treatment. Therefore, the dynamic pressures of the reverse airflow were mostly conversed to the static pressures when the airflow encounter on the filter media. The static pressures were formed to a maximum pressure. However, Table 4 shows that the tendency of the peak static pressure distribution along the height of the filter cartridge was similar with and without surface treatments. The smaller porosity of the filter medium was, the higher the observed peak pressure occurred. Fig. 6 shows that the dust particles were not easily into the internal filter medium with a surface treatment. Meanwhile, the formed dust cake looks to be in a porous state. The dust cake will filter the dust-laden airflow as the operational time. Otherwise, the dust 13
particles were easily into the internal filter medium without a surface treatment. Then, the compacting dust cakes were formed on the filter medium’s surface. Table 3 and Fig. 6 show that the dust cake could be readily born off the filter medium with a surface treatment. Therefore, the formed dust cake appeared in to in a porous state, and readily born off the filter cartridge by the pulse airflow. 3.2 Effects of the pulse airflow on the cleaning process of the filter cartridge Firstly, the quartz particles were retained on the filter medium using an induced draft fan. Then, the cleaning process was used. The compressed air was delivered through a blow tube to the nozzle. Fig. 7 shows the process of the dust cake born off the filter cartridge during the pulse cleaning. At this process, the pulse airflow and secondary airflow form the mixture airflow. The mixture airflow has a high velocity and has dynamic pressure. When the airflow goes into the filter cartridge and the airflow has prevented by the filter media. The dynamic pressures of the pulse airflow were conversed to static pressures, and then the static pressure force was formed and the dust cake was born off the filter cartridge by the static pressure force. The higher the static pressure force is, the quicker the dust born off the filter cartridge will be. At the stage of 0 to 12 ms, Fig. 7 shows that a few dust particles were born off the top area of the filter cartridge to the middle area. This was due to the fact that the transient pressure was formed at measurement locations one and two, as shown in Table 3. Although a peak pressure 673 Pa occurs at measurement one with the first transient time, only a minor amount of dust particles were born off the filter cartridge. Then, the maximum peak pressures were 4932, 14026, 3998, 8813 and 1962 Pa from the top 14
area to the bottom area of the filter cartridge. The dust cakes were born off the entire filter cartridge. This process of the dust cakes born off the filter cartridge corresponds to the four stages shown in Fig. 5. Fig. 8 shows the comparison photos of the pre and post pulse cleaning. The entire filter cartridge was filled with quartz particles prior to the pulse cleaning. Then the mostly quartz particles were born off the filter cartridge during the pulse cleaning. After a pulse cleaning, the filter cartridge was taken out. Through the weighting the filter cartridge and the dust, the cleaning efficiencies are defined as the weight difference between pre and post pulse cleaning. The cleaning efficiency is defined the weight difference and is 98%. From Fig. 5 and Fig. 7, although a peak pressure 673 Pa occurs at measurement location one with the first transient time, only a minor amount of dust particles were born off the filter cartridge. This conflicted with the results obtained by Ju et al., as well as Humphries and Madden
[24] [32]
, who reported that the first peak pressure
higher than 300 Pa could effectively remove the dust particles from the filter bag. This was due to the fact that because that the filter medium of the filter cartridge was nonflexible, and had a layer surface treatment with a small porosity, as shown in Fig. 3. The filter medium, and the construction of the filter cartridge were different from that of the filter bag. Therefore, the transient pressure did not form a continuous impact on the filter cartridge. Lu and Tsaï [33] believed that the cleaning efficiency was related to the continuous impact of the reverse airflow on the filter cartridge. Therefore, the process of the quartz particles’ born off the entire filter cartridge was not only related to peak static pressure, but also to the continuous impact of the peak 15
static pressure. The process of the peak static pressure, along with the duration on the filter cartridge surface was indicative of the process of dust cake born off the filter cartridge. Table 3 shows that although the peak static pressure at measurement location five was lower than those at other measurement locations, the majority of the quartz particles were born off the filter cartridge, as shown in Fig. 7 and 8. This conflicted with the results obtained by Yan et al.
[25]
, who reported that the bottom area of the
filter cartridge was filled with dust particles with the increase of the operational time. In Reference [25], the cleaning process was on-line cleaning. In this study, some part cleaning process was off-line cleaning. Fig. 7 shows that the quartz particles were born off the entire filter cartridge. Fig. 5 illustrates that the peak static pressure decreased quickly after 100 ms. However, Fig. 7 shows that the total process of the dust cake born off the filter cartridge was approximately 370 ms. Therefore, the dislodged dust particles’ from the filter cartridge goes into the hopper with a gravitation force after 150 ms. In industrial application, the dislodged dust particles that drop due to gravitation force are induced to the filter medium and reattached on the filter medium, especially the bottom area of the filter medium, by using an induced draft fan. This is likely related to the length of the filter cartridge and the pulse width (opening time of electromagnetic valve controlled using a pulse controller). This result is different from this obtained in previous literature
[24]
. Our
team thought that the peak static pressure was not high to remove the dust particles born off the filter cartridge. In our previous industrial applications, if the height of the 16
high-flow filter cartridge is shorter (equal to 660 mm), the dust particles are not reattached on the bottom of the filter cartridge during in a long period of operational time. In some cases, an increase in the pulse width can decrease the opportunity of dust particles reattached on the bottom area of the filter cartridge in the same experiment shown in Reference
[25]
. Yang et al.
[19]
reported that the pulse width has
only a slight effect on cleaning efficiency. This is due to the fact that their experimental results were obtained in the laboratory. The effect of pulse width on cleaning performance is only on the peak pressure, but not on the cleaning process [19]. Due to the fact that the length (1000 mm) of the filter cartridge used in this study was longer than those used by Lo et al. [23] and Zhang et al. [21], the static pressure variation in our experiment is more complex than that of studies with shorter filter cartridges. Fig. 5 shows that the pulse airflow can prolong the duration of the peak static pressure if the pulse width increases. Therefore, the duration of pulse airflow increase. The formed peak static pressure has a long time in opposing direction to the normal forward airflow. The long-time peak static pressure decrease the incidence of the re-suspend particles reattached to the bottom area of the filter cartridge secondly. In industrial application, another method is to decrease the pleat number. Fig. 9 shows that the cleaning effect of a pleat number high to 125 is better than this of a pleat number high to 155. This is due to the fact that the formed static peak pressures increase when the pleat number decrease from the 155 to 125. This is because that the filter cartridge with pleat number 155 has the lower air permeability than the filter cartridge with pleat number 125. Therefore, the permeable airflow forms the bigger 17
static peak pressure on the filter cartridge. Therefore, the static pressure forces quickly reinforce the dust born off the filter cartridge. The detailed effects of the different pleat number on pulse airflow and cleaning process will be researched in future research. 4. Conclusions The maximum peak pressures are 4932, 14026, 3998, 8813 and 1962 Pa from the top to the bottom along the height of filter cartridge. The duration of the peak pressure on the filter cartridges’ surface are 185, 81.3, 99.2, 78.2 and 93.8 ms, respectively. The five peak static pressures are averaged and the value is 6746 Pa. The process of dust born off the filter cartridge is 372 ms. The pressure variation on filter cartridge’s surface agrees well with the dynamic process of dust cake born off filter cartridge obtained from the High-speed camera. The process of surface pressure variation and duration of the peak static pressure on the filter cartridge are indicative of the process of the dust born off the filter cartridge. A small amount of particulate was seen to be removed at the first recorded peak pressure 673 Pa with a transient time. This was contrary to previous testing conducted by other researchers, which showed that a pressure above 300 Pa produced effective cleaning results. The process of dust cake born off the whole filter cartridge is not only related to peak static pressure, but also to continuous impact of reverse airflow. In industrial application, the particulate matter was reattached to the filter cartridge medium after the completion of the pulse airflow using an induced draft fan through the filter in the normal direction. An increase in pulse width can extend the 18
duration of the peak pressure, and decrease the amount of dust reattached on the filter cartridge. The peak static pressures increase on the filter cartridge when the pleat number decreases from the 155 to 125. This can decrease the incidence of incomplete cleaning. Our next goal is to study the detailed effects of different pleat numbers on the pulse airflow and cleaning process. Acknowledgements This scientific work was financed from the National Natural Science Foundation of China (No. 51508481), Doctor’s Fund of Southwest University of Science and Technology (No. 14ZX7127), and was also supported by the Key Scientific Research Platform of Southwest University of Science and Technology (No. 14tdgk04). References: [1] Li-Ming Lo, Da-Ren Chen, David Y.H. Pui. Experimental study of pleated fabric cartridges in a pulse-jet cleaned dust collector [J]. Powder Technology 197 (2010) 141-149 [2] Ning Mao, Yuping Yao, Mistuhiko Hata, Masashi Wada, Chikao Kanaoka. Comparison of filter cleaning performance between VDI and JIS testing rigs for cleanable fabric filter [J]. Powder Technology 180 (2008) 109-114 [3] Zha Wenjuan, Qian Fuping. Feasibility Analysis of Reforming Electrostatic Precipitator into Cartridge Filter [J]. Journal of Filtration and Separation 23(2013) 21-24, 46 [4] Lin Tingquan, Yu Yuan, Wei Gang, Xu Zhongwei, Yang Chunyu. Application of high-flow filter cartridges in cement plant [J]. Cement Guide for New Epoch 4(2011) 44-45 [5] Zheng Yingjian, Jiang Dong. Recovery of glyphosate by pleated-type cartridges filter [J]. 19
Hangzhou Chemical 41(2011) 36-38 [6] Bai Zhen, Zhang Dianyin. Cleaning pressure characteristics and selection research of pulse filter [J]．Environment protection of metallurgy 6(2002) 68-69 [7] Xavier Simon, Sandrine Chazelet, Dominique Thomas, Denis Bémer, Roland Régnier. Experimental study of pulse-jet cleaning of bag filters Supported by rigid rings [J]. Powder Technology 172(2007) 67-81 [8] R. Dennis, J.E. Wilder, Fabric Filter Cleaning Studies, National Environmental Research Center, 1975 Report EPA 650/2-75-009. [9] I. Theodore, J. Reynolds, A. Corvini, A. Buonicore. Particulate control by pulsed-air baghouse filtration: describing equations and solutions, Proceedings of 2nd Speciality on the User and Fabric Filtration Equipment, Buffalo gd, vol. 90, 1975. [10] J. Sievert, F. Löffler. Dust dislodgement in pulse-jet fabric filters [C]. Proceedings of the First World Congress on Particle Technology, Part IV, Nurnburg West Germany, 1986, pp. 111–126. [11] X.Simon, D.Thomas, D.Bémer, S.Callé, R.Régnier, P.Contal. Influence of cleaning parameter on pulse-jet filter bag performance [J]. Filtration 4 (4) (2004) 253–260. [12] H.C. Lu, C.J. Tsaï, Influence of design and operation parameters on bag-cleaning performance of pulse-jet baghouse [J]. Journal of Environmental Engineering 125 (6) (1999) 583-591. [13] R. Dennis, J.E. Wilder, D.L. Harmon, Predicting pressure loss for pulse jet filters [J]. Journal of the Air Pollution Control Association 31 (9) (1981) 987-992. [14] R.W.K. Allen, H.G.D. Goyder, K. Morris, Modelling medium movement during cleaning of pulse-jet fabric filters [J]. Chemical Engineering Research and Design 77 (3) (1999) 223-230. 20
[15] W.J. Morris, Cleaning mechanisms in pulse jet fabric filters [J]. Filtration and Separation 21 (1) (1984) 50-54. [16] W. Humphries, J.J. Madden, Fabric filtration for coal-fired boilers: dust dislodgement in pulse jet filters [J]. Filtration and Separation 20 (1) (1983) 40-44. [17] M.J. Ellenbecker, D. Leith, Dust removal from non-woven-fabric-cleaning methods needs to be improved [J]. Filtration and Separation 18 (1981) 41-45. [18] Leubner H, Riebel U. Pulse jet cleaning of textile and rigid filter media characteristic parameters. Chemie Ingenieur Technik May 75(5) (2003) 504-514. [19] Yang Di，Chen Haiyan，Li Huaiyu．The influence of the pressure peak and pulse width on the dust-cleaning efficiency of the pulse-jet cartridge filter [J]．Journal of Safety and Environment 5(2008) 73-76 [20] Zheng Juan, Zhang Mingxing, Zhou Qijie, Zhang Yizhi, Cai Guangbei. Pressure peak test and analysis of membrane cartridge filter side wall [J]. China Powder Science and Technology 17(1) (2011) 63-66 [21] Zhang Qing, Chen Haiyan, Ju Min, Chen Jundong．Experiment on induction nozzle improving dust-cleaning efficiency of pulse-jet cartridge filters by induction nozzles [J]. Environment Engineering 30(2012) 62-65 [22] Yunlou Qian, Yuanxia Bi, Mingxing Zhang, Haiyan Chen, Guanjie Xu. Effect of filtration operation and surface treatment on pulse-jet cleaning performance of filter bags [J]. Powder Technology 277 (2015) 82-88 [23] Li-Ming Lo, Shih-Cheng Hu, Da-Ren Chen, David Y.H. Pui. Numerical study of pleated fabric cartridges during pulse-jet cleaning [J]. Powder Technology 198 (2010) 75-81 21
[24] Ju Min, Zhang Mingxing, Chen Jundong, Zhang Qing, Chen Haiyan. Dynamic analysis of dust dislodgement from pulse-jet cartridge filter [J]. Chinese Journal of Environmental Engineering 7(2013) 1091-1094 [25] Cuiping Yan, Guijian Liu, Haiyan Chen. Effect of induced airflow on the surface static pressure of pleated fabric filter cartridges during pulse jet cleaning [J]. Powder Technology 249 (2013) 424-430 [26] Lin Lijun, Chen Haiyan, Zhou Xi, Mu Lan. Experiment of dust-cleaning performances of pulse-jet cartridge filters [J]. Heating Ventilating and Air Conditioning 39(2009) 148-151 [27] Zhang Yizhi, Chen Haiyan, Zheng Juan, Zhang Mingxing. Experiments on cleaning performance of pulse jet filter bag [J]. Journal of Safety and Environment 6(3) (2010) 30-34 [28] Zhou Qijie, Chen Haiyan, Zhang Mingxing, Zheng Juan. Influence of pulse valve injection quantity on dust-cleaning performance of cartridge filters [J]. Heating Ventilating and Air Conditioning 41(6)(2011) 100-105 [29] Zhou Qijie, Chen Haiyan, Zhang Mingxing, Zheng Juan, Wang Yan. The industrial test of pulse bag filter in petroleum coke superfine grinding process [J]. Environmental Engineering 29(4)(2011) 94-98 [30] S. Fotovati, S.A. Hosseini, H. Vahedi Tafreshi, B. Pourdeyhimi. Modeling instantaneous pressure drop of pleated thin filter media during dust loading [J]. Chemical Engineering Science 66 (2011) 4036-4046 [31] Tao Zhendong, Zheng Shaohua. Powder Technology and Equipment [M]. Beijing: Chemical Industry Press, (2003) 249 [32] Humphries W., Madden J.J.. Fabric filtration for coal-fired boilers: dust dislodgement in 22
pulse jet filters [J]. Filtration and Separation 20 (1) (1983): 40-44. [33] Lu H.C., Tsaï C.J.. Influence of design and operation parameters on bag cleaning performance of pulse-jet baghouse [J]. Journal of Environmental Engineering 125 (6) (1999) 583-591.
23
Figures:
Fig.1 Incomplete cleaning photo of high-flow filter cartridge in industrial application
24
Supersonic induced nozzle and air diffuser
Pulse controller
Pulse valve
Computer
pressurized air reservior Transmitter
a rigid wire cage
Clean air 0mm 80mm 150mm
High-speed camera
P
a
350mm
pressure
transducer
Powder feeder
filter 650mm Metal halide lamp
850mm Powder collector
1000mm Baffle Flowmeter
Frequency transformer
Hopper Powder
Induced fan Gate valve
Fig. 2 Schematic view of the test rig
Blowtube
Supersonic induced nozzle Air diffuser
Schematic diagram of supersonic induced nozzle and the air diffuser
Top view of a pleated filter cartridge
25
A filter cartridge
A view from the top of filter cartridge A rigid wire cage
Microstructure of filter medium
Fig. 3 Rigid wire cage and microstructure of filter cartridge with surface treatment
26
100 Cumulative distribution (%) 80 Differential distribution (%)
60 40 20
Size distribution
Fig. 4 Quartz size distribution (µm)
27
700000
Outlet pressures of pulse value (pa)
Third stage 600000 500000 400000
Second stage
Fourth stage
300000 200000 100000
First stage
0 0
50
100
150
200
250
Pulse time (ms)
Fig.5 Outlet pressure variation of pulse valve with diameter 24.5 mm
28
a
b
c
29
d Fig.6 microstructure of the filter medium a. Front microstructure of the filter medium with surface treatment, b. Front microstructure of the filter medium without surface treatment, c. Crosse section microstructure of the filter medium with surface treatment, d. Crosse section microstructure of the filter medium without surface treatment
30
Dust
begin
to
dislodge from the cartridge
0 ms
6ms
12 ms
18 ms
Partially
dust
dislodge
from
the cartridge
24 ms
30 ms
36 ms
42 ms
Dust begin to deposit
from
the cartridge
48 ms
54 ms
60 ms
66 ms
31
72 ms
78 ms
96 ms
102 ms
108 ms
84 ms
114 ms
90 ms
120ms
32
…….partially photos omitted 126 ms
132 ms
Dust has been dislodged from the cartridge
252 ms
312 ms
372ms
Fig.7. Process of dust dislodgement from the filter cartridge vs time for filter medium with the surface treatment
33
b
d
c a
b
d
a. entire filter cartridge b. top of filter cartridge c. middle of filter cartridge d. bottom of filter cartridge c a
c
Fig.8. Comparison photos pre and post pulse cleaning for filter medium with the surface treatment
34
Pleat number 155
Pleat number 125
Filtration area 16m2
Filtration area 12m2
Fig.9 Photo of industrial application during pulse-jet cleaning for filter medium with the surface treatment (tank pressure 0.6MPa)
35
Tables: Table 1 Filter cartridge dimension Parameters Pleat number (n, 个)
125
155
Pleat pitch (W, mm)
8.164
6.58
Pleat height (H, mm)
45
44
Inner diameter (Din, mm)
215
215
Filter length (L, mm)
1000
1000
Filtration area (Af, m )
12
16
Thickness of filter medium (mm)
0.6
0.6
2
(L/m2·s)
Air permeability 80-100 or 150 80-100 Annotation: The filter medium with surface treatment was composed of a layer of polytetrafluoroethene fibers on a polyethylene terephthalate nonwoven filters substrate (air permeability is 80-100 L/m2·s). The filter medium without surface treatment was composed a polyethylene terephthalate nonwoven filters (air permeability is 150 L/m2·s).
36
Table 2 Experimental parameters during the cleaning Parameters Pulse pressure (MPa)
0.6
Pulse valve opening time (ms)
80
Pulse air volume (L)
80
Pulse orifice diameter (mm)
16
distance between nozzle and
50
filter cartridge top (mm) Diffuser height (mm)
102
Filtration velocity (m/min)
0.8
37
Table 3 Static peak pressure and duration on filter cartridge with surface treatment First peak
Maximum
Initial
Time to peak
Duration of
pressure
peak pressure
pressure
pressure
peak pressure
（Pa）
（Pa）
time（ms）
（ms）
（ms）
80
673
4932
0
0
185
150
427
14026
1.3
20.5
81.3
350
-
3998
1.3
1.3
99.2
650
-
8813
1.3
11.5
78.2
850
-
1962
2.5
3.8
93.8
Measurement location（mm）
Annotation: first time of occurred initial pressure is set to 0. First time to peak pressure is set to 0. Other time is set to relatively value.
38
Table 4 Comparison of peak pressure with surface treatment and without surface treatment Measurement point Filter medium 80mm
150mm
350mm
650mm
850mm
Filter medium with surface treatment (Pa)
4932
14026
3998
8813
1962
Filter medium without surface treatment (Pa)
899
1767
790
1013
572
39
S0957-5820(17)30372-5 https://doi.org/10.1016/j.psep.2017.10.018 PSEP 1215
To appear in:
Process Safety and Environment Protection
Received date: Revised date: Accepted date:
23-5-2016 9-5-2017 23-10-2017
Please cite this article as: Cuiping, Yan, Mingxing, Zhang, Longyuan, Lin, Haiyan, Chen, An Analysis of a Reverse Pulse Cleaning Process using HighFlow Pleated Fabric Filter Cartridges.Process Safety and Environment Protection https://doi.org/10.1016/j.psep.2017.10.018 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
An Analysis of a Reverse Pulse Cleaning Process using High-Flow Pleated Fabric Filter Cartridges
Yan Cuiping, Zhang Mingxing, Lin Longyuan, Chen Haiyan Key Laboratory of Solid Waste Treatment and Resource Recycle, Ministry of Education, School of Environment and Resource, Southwest University of Science and Technology, Mianyang 621010, China
Graphical abstract
Large-flow filter cartridge (Φ325 × 1000 mm) was experiment
Process of dust dislodgement from filter cartridge was photographed by high-speed camera
Static pressure and duration of peak pressure along the filter cartridge was recorded
The first peak pressure (673 Pa) and the first impact cannot effectively remove the dust cake
The process of quartz particles dislodgement from the entire filter cartridge is not only related to peak pressure but also to duration of peak pressure.
Increase of pulse width can decrease the opportunity of re-suspended dust particles reattached on the bottom of filter cartridge again
1
Highlights
We examine the cleaning characteristics of high-flow filter cartridges.
The quartz particles are dislodgement from the entire filter cartridge.
The particles are removed due to peak pressure and duration of peak pressure.
Increase of pulse width decrease dust reattached on the bottom of filter cartridge.
Abstract: A high-flow fabric filter cartridge with a high pleat ratio, along with a large diameter, and a large filtration area, showed increased susceptibility to incomplete cleaning, caused by the greater variation of pulse airflow in the filter cartridge. In order to investigate the cleaning characteristics of high-flow pleated fabric filter cartridges, a pleated fabric filter cartridge (Φ325×Φ215×1000 mm) was used to the experiment. Then, the peak pressure distribution along the height of the filter cartridge with five measurement locations was recorded using five pressure transducers. The process of dust cake born off the filter cartridge was photographed using a high-speed camera. The cleaning process of a high-flow filter cartridge was examined, and the peak pressure variation on the filter cartridge was determined during the pulse cleaning. The results show the following: the process duration of the dust cake born off the filter cartridge was 372 ms. The maximum peak pressures were 4932, 14026, 3998, 8813, and 1962 Pa from the top to the bottom along the height of the filter cartridge, respectively. The peak pressure and duration formed by the pulse airflow are indicative of the cleaning process of dust cake born off filter cartridge. Although a peak pressure high to 673 Pa appears at location one with the first transient time, only a minor amount of dust particles was born off filter cartridge. Therefore, the process of quartz particles born off the entire filter cartridge was not only related to the peak pressure, but 2
also to the duration. Meanwhile, the experiment shows that an increase in the pulse width can decrease the likelihood of dust particles being reattached on the bottom of the filter cartridge. The peak pressures increase on the filter cartridge when the pleat number decreases from the 155 to 125. This can decrease the incidence of incomplete cleaning. Keywords: filter cartridge, pulse cleaning, reverse airflow, static pressure, dust cake born off
1. Introduction In recent years, the use of pleated fabric filter cartridges in dust collectors has attracted a great deal of attention, due to the fact that the pleated filter cartridges offer a larger filtration surface when compared to the flat-sheet filter bags (if both filters are used in housing of the same size) [1]. Therefore, the pleated fabric filter cartridges used in dust collection technology have the purposes to control particulate emissions, recover valuable particles, and in the high-flow filter cartridges in particular. High-flow filter cartridges can be used to create a high-flow dust collector, which can effectively filter dust-laden airflow higher to 120000 m3/h, even more cleaning for filters has been widely used since the 1950s authors
[8-12]
[6] [7]
[2-5]
. Pulse-jet
. For the filters, some
hold that the reverse airflow played an important role in dust cake born
off (the dust born off the filter cartridge and collected in the hopper) the filters. Certain authors
[13-15]
hold that the medium movement given effect in dust cake born
off the filters. The above studies have shown that the reverse airflow and medium movement were important and essential to achieve cleaning efficiency (defined as the weight pre and post cleaning). However, some authors
[16][17]
have concluded that the
reverse airflow played only a minor role in dust cake born off the filters. Sievert and 3
Löffler
[10]
found that the medium acceleration was related to fabric characteristics
during pulse cleaning. The medium acceleration was at least 300 ms-2 for soft fabric to effective cleaning. Otherwise, the medium acceleration was higher to 2000~5000
ms-2 for nonflexible fabric to effective cleaning. Leubner and Riebel
[18]
have
reported that the peak pressure and the rate to peak pressure (the maximum pressure on the filter) were used to assess the cleaning effect. Dennis
[13]
has reported that the
rate to peak pressure was higher than 600 Pa/ms for the dust cake born off the filters. For the filter cartridge, some authors [19-21] have shown that the peak pressures of pleated filter cartridge have the positive correlation to the cleaning intensity. The main opinions showed that the static peak pressure on the filter cartridge has positive effects on cleaning efficiency. The cleaning process of filter cartridge is different from the flexible bag. This is because that the fabric medium of filter cartridge is different the flexible bag. Qian et al. [22] have show that the cleaning mechanism at the top of the three filter bags is governed by fabric acceleration due to sudden filter media movement, while the peak pulse pressure plays a major role in the lower part of the three filter bags. However, Lo et al.
[23]
have demonstrated that the average static
pressure (static pressure has formed obtained by the dynamic pressure when the reverse airflow encounters the filter medium) on the filter cartridge was more closely correlated to cleaning efficiency than to overpressure, and the top of a filter cartridge was difficult to clean because of the lower pressure generated by the pulse-jet airflow. Ju et al.
[24]
thought that the first positive static peak pressure formed by the first
airflow was a main factor to the cleaning efficiency. Yan et al.
[25]
have demonstrated 4
that the cleaning efficiency increased when the static peak pressure increased. Our team holds that the cleaning performances can be directly related to the static peak pressure on the filter cartridge formed by the pulse airflow [26-29]. However, a pleated fabric filter cartridge with a high pleat ratios (pleat height to pleat width, higher than 4 [1]), a large diameter (diameter of filter cartridge, equal to or higher than 325 mm) and a large filtration area (height of filter cartridge, equal to or higher than 1000 mm) have greater instances of incomplete cleaning (defined as the top part or bottom part have an obviously dust cake after a pulse cleaning) due to large variation of reverse airflow internal the filter cartridge
[30]
. The instances of
filtration velocity and uneven particle deposition on filter medium increases gradually due to incomplete cleaning of filter cartridges. The incomplete cleaning of filter cartridges lead to the greater unsteady of the filtration airflow, thus, the more opportunities the incomplete cleaning is formed. Conversely, the more opportunities the incomplete cleaning is, the greater unsteady the filtration airflow is formed. Therefore, the formed dust cake distribution is ununiformed. Thus, the probability of incomplete cleaning of a filter cartridge is larger than this of a flat-sheet filter bag. An occurrence of incomplete cake detachment or patchy cleaning is shown in Fig. 1. Thus, our team focused on the cleaning process rather than the filtration process. We conducted a series of experiments to study the cleaning performances of the filter cartridges under varied operational parameters [19-21] [24-29]. In this paper, a high-flow fabric filter cartridge (Φ325×Φ215×1000 mm) with a high pleat ratio, along with a large diameter, and a large filtration area, the greater 5
variation of pulse airflow in the filter cartridge increased susceptibility to incomplete cleaning. There was a deficiency in the technical literature concerning the cleaning performance of a filter cartridge during a pulse cleaning. In order to investigate the cleaning characteristics of high-flow pleated fabric filter cartridges, the peak pressure distribution along the height of the filter cartridge and the process of dust born off the filter cartridge are examined, decreasing an incidence of the incomplete cleaning. 2. Materials and methods 2.1. Experimental apparatus In order to examine the reverse airflow on the total cleaning process using high-flow pleated fabric filter cartridges, a filter cartridge (Φ325 × Φ215 × 1000 mm) was installed in the filter. The dust cake born off the filter cartridge, as well as the static pressure on the filter cartridge was examined, reducing an incidence of the incomplete cleaning. Fig. 2 shows a schematic view of the test rig (designed by Mianyang, Liuneng, Powder Equipment Co., Ltd.). The dimensions of the dust collector compartment were length 845× width 585× height 2270 mm. Table 1 shows the filter cartridge dimensions (Φ325×Φ215×1000 mm). Fig. 3 shows that a rigid wire cage supported the filter medium. The rigid wire cage can decrease the deformation of the filter media during pulse cleaning. The pressure transducers were fixed on a rigid wire cage, shown in Fig. 2. The photo and microstructure of the filter cartridge are shown in Fig. 3. The filter medium without surface treatment was composed a polyethylene terephthalate nonwoven filters. The permeability was 150 L/m2*s at a 200 Pa pressure drop. Another filter medium with surface treatment was composed of 6
a layer of polytetrafluoroethene fibers on a polyethylene terephthalate nonwoven filters substrate. The permeability was 80 to 100 L/m2*s at a 200 Pa pressure drop. The induced airflow was produced using a supersonic induced nozzle (VN25PC-50, Australia, Goyen Co., Ltd.) and an air diffuser (CC200, Australia, Goyen Co., Ltd.). The schematic diagrams of the induced nozzle and the diffuser are shown in Fig. 2. The experiment also includes a high-speed camera (FASTCAM APX RS, Japan, Photron Co., Ltd); a pulse-jet valve (DMF-ZM-25s type with a diameter of one inch); a compressed air reservoir; a pulse controller; a screw air compressor; six high precision pressure transducers (S130100, precision is 0.05%, data acquisition rate is 1 kHz, Mianyang Qishiyuan Science and Technology Co., Ltd); an electric charge amplifier (QSY7709); a metal halide lamp (DCI-2000) and a portable data acquisition instrument (QSY-USB-8512E). A hopper was connected to the dust cartridge filter to collect the dust born off the filter cartridge. Fig. 2 shows that the five high-precise pressure transducers were fixed on a rigid wire cage. Those pressure transducers were used to record the static pressure (the dust cake born force from the filter cartridge), along with the duration of the peak pressure on the filter cartridge. A high precise pressure transducer was used to record the outlet pressure of the pulse valve. The high precise pressure transducer was fixed at the location of the pulse tube, which was connected to the pulse valve. The process of dust cake born off the filter cartridge was photographed using a high-speed camera (3000 fps, FASTCAM APX RS, Japan, Photron Co., Ltd), under a 2000 W metal halide lamp. The reverse airflow from the compressed air reservoir was controlled 7
using a pressure regulator, a pulse valve, and a sequential timer/relay that caused the pulse valve opening time and interval to change. The filtration velocity through the filter cartridge was controlled using a fan speed controller. Then, a vibrating feeder was used to disperse the quartz particles. The filtration velocity was set to 0.8 cm/s. The top view of a filter cartridge is shown in Fig. 2. A filter cartridge was fitted with an induced nozzle, along with a pulse valve. A computer running a LabView program was connected to a charge amplifier and a data acquisition instrument, in order to collect the data, and a pulse controller was used to control the pulse valve. After a pulse cleaning, the filter cartridge was taken out and weight. The cleaning efficiency is defined the weight difference. 2.2. Dust test In this experiment, a pleated fabric filter cartridge was used to collect the quartz particles, which were obtained from the grinding. The size distribution was measured using an Laser Particle Sizer (Ⅵ) from the Zhuhai OMEC Instrument Co., Ltd. The mean particle size of particulate matter was 1.5 μm, as shown in Fig. 4. The dust concentration of the quartz was 25 g/m3. 2.3. Experimental design Table 2 shows the experimental parameters during the pulse cleaning. In our previously experiment
[24]
, we found that the cleaning process was complex and the
process of the dust cake born off the filter cartridges was not clear. Usually, the cleaning process is classified as four stages due to pulse valve. The first stage is the time delay to open the pulse valve; the second stage is the time to open the pulse valve; 8
the third stage is the continued opening time of pulse valve; and the fourth stage is the close time of the pulse valve. The four stages correspond to the formed pressure process on the filter cartridge. Therefore, in order to investigate the cleaning process and the process of the dust cake born off the filter cartridge, we designed this experiment. In this experiment, we focused on the cleaning process and the dust cake born off the filter cartridge. The actuation of the cleaning process was managed using a pulse controller. The pulse airflow was in the opposing direction to the normal forward filtration airflow through the filter cartridge. Then, the dust cake born off the filter cartridge, and the static pressures were recorded using a high-speed camera and five pressure transducers, respectively. A high-speed camera was positioned approximately 5 m away from the dust collector, and a metal halide lamp was positioned approximately 2 m away from the dust collector. Five pressure transducers (Φ7 mm) were fixed onto the interface of the rigid wire cage on the filter surfaces. Measurements one, two, three, four, and five were located at the locations of 80, 150, 350, 650, and 850 mm, respectively, from the filter cartridge opening. The sizes of the pressure transducers were smaller than this of the filter cartridge. Therefore, the effects of the pressure transducers on the airflow could be ignored. Each pressure transducer was located at each measurement location. The export signal from the pressure transducer was connected to the import signal from the charge amplifier. The outlet signal of the charge amplifier was then linked to the inlet of the data acquisition instrument. Finally, the export signal from the data acquisition instrument was linked to the computer. Every experiment, the three identical pulses were examined and the 9
average values were obtained. In the data analysis phase, Microsoft dasView 2.0 was employed to obtain and change the data into the pressure data, based on sensor sensitivity and the following formula: P
v K1 K 2
(1),
Where P (MPa) is the measured pressure; v (mV) is the voltage output value; K1 (mv/pC) is a multiple of the charge amplifier; and K2 (pC/MPa) is the sensor sensitivity. In this study, the K1 was magnified 100 times. The sensor sensitivity K2 was 6.5 pC/MPa. 3. Results and discussion 3.1. Effects of the pulse airflow on the peak pressures of the filter cartridge The pulse airflow is a transient unsteady airflow and is a reverse airflow, which is in opposition to the filtration airflow. As illustrated in Fig. 5, the outlet pressures of the pulse valve are obtained using a pressure transducer, which is fixed on the pulse tube. In this study, the induced nozzle and the diffuser can disperse the pulse airflow and change the induced the secondary airflow. The mixture airflow of pulse airflow and the induced airflow (secondary airflow) moved into the filter cartridge and dispersed quickly onto the filter’s internal surface. The mixed airflow beam form a bigger horizontal area at the filter cartridge opening with the induced nozzle and the diffuser, compared to those without induced nozzle and the diffuser
[25] [31]
. Fig. 5
illustrates that the outlet pressures of the pulse valve were formed to a steady phase at the third stage. Fig. 5 shows that the duration of the outlet peak pressure of the pulse 10
valve was approximately 100 ms. Therefore, the duration of the surface peak pressure on the filter cartridge was approximately 100 ms, as shown in Table 3. Then, the surface pressures on the filter cartridge gradually decreased to zero. Table 3 shows that the high pressure variation and long duration of the peak pressure at the top area of the filter cartridge were caused by the incomplete mixture of the jet pressure, strong local velocities, and turbulence due to the short time period of the first stage to the second stage of the pulse valve. Therefore, the initial pressures were triggered at measurements one and two. One peak pressure higher than 673 Pa was recorded at measurement location one, and another peak pressure higher than 427 Pa was recorded at measurement location two, with a transient time. This corresponded to the second stage (25.5 to 60 ms) of the outlet pressures of pulse valve, as shown in Fig. 5. Fig. 5 shows that the incomplete mixture airflow forms the first peak pressure at measurement location one and two. When the airflow goes down the filter cartridge, the airflow appeared to steady airflow. At this moment, the second peak pressures have formed. At the third stage, the pulse airflow appeared to be in the steady stage. The reverse airflow and secondary airflow formed the steady airflow. The steady airflow went into the filter cartridge through the induced nozzle and the diffuser, and formed the steady peak pressures and the duration on the filter cartridge. The steady airflow encountered the filter medium, and some partly dynamic pressures of the steady airflow were changed to static pressures on the filter cartridge. Therefore, maximum peak pressures higher than 4932, 14026, 3998, 8813, and 1962 Pa were recorded from the top of filter cartridge to the bottom, as shown in Table 3. The 11
duration of the maximum peak static pressure was obtained by the duration of the peak pressures of the pulse valve outlet. The peak static pressure distribution was formed along the height of the filter cartridge. The five peak static pressures are averaged and the value is 6746 Pa along the height of the filter cartridge. This is because that the mixed airflow goes into filter cartridge and forms the static pressure at measurement location one through the induced nozzle and diffuser. Then, the axial velocity of the mixed airflow goes down. The mixed airflow expanses and forms the static pressure at measurement location three. The expanded airflow mixes with the airflow from the measurement location one. The mixed airflow form the maximum pressure at measurement location two, therefore, the time to peak pressure is longer than other measurement locations, shown in table 3. Then, the axial velocity of the mixed airflow decreases, which results in decrease of peak static pressure. Otherwise, the pressure variation at the bottom of the filter cartridge is greater than that of the measurement locations. This result indicates that the mixed airflow along the filter cartridge surfaces mixes with the rebounded airflow from the bottom of filter cartridge. Thus, the dynamic pressure is transformed to static pressure at first. Then the static pressure obtains a maximum value and the dynamic pressure decreases. The mixture airflow of reverse airflow and induced airflow occurs to expand. At the same time, the consumption of airflow through filter medium and friction of airflow and filter medium decrease the airflow energy. Therefore, the peak static pressures are obtained by the energy of mixed airflow and consumption airflow. The duration of the maximum peak static pressure on the filter cartridge corresponded to the third stage of 12
the outlet pressures of the pulse valve. From Table 3 and Fig. 5, the reverse airflow and secondary airflow appeared to be in a steady state at the third stage. The dynamic pressures of the mixed airflow were conversed to static pressures when the mixed airflow encountered the filter cartridge. Therefore, the formed peak pressure appeared as a maximum value at the measurement locations. For the different air permeability of filter media, Fig. 6 and Table 4 show that the formed static pressure on the filter cartridge with surface treatment (80-100 L/m2·s) was higher than this without a surface treatment (150 L/m2·s). This result agrees with the result obtained by Zheng et al.
[20]
, who reported
that the peak static pressure on the filter medium with a surface treatment (a multiple layer structure of finer fibers) was higher than that without a surface treatment. This was due to the fact that few reverse airflow pervaded through the filter medium when the porosity of the filter medium was smaller with a surface treatment than that without a surface treatment. Therefore, the dynamic pressures of the reverse airflow were mostly conversed to the static pressures when the airflow encounter on the filter media. The static pressures were formed to a maximum pressure. However, Table 4 shows that the tendency of the peak static pressure distribution along the height of the filter cartridge was similar with and without surface treatments. The smaller porosity of the filter medium was, the higher the observed peak pressure occurred. Fig. 6 shows that the dust particles were not easily into the internal filter medium with a surface treatment. Meanwhile, the formed dust cake looks to be in a porous state. The dust cake will filter the dust-laden airflow as the operational time. Otherwise, the dust 13
particles were easily into the internal filter medium without a surface treatment. Then, the compacting dust cakes were formed on the filter medium’s surface. Table 3 and Fig. 6 show that the dust cake could be readily born off the filter medium with a surface treatment. Therefore, the formed dust cake appeared in to in a porous state, and readily born off the filter cartridge by the pulse airflow. 3.2 Effects of the pulse airflow on the cleaning process of the filter cartridge Firstly, the quartz particles were retained on the filter medium using an induced draft fan. Then, the cleaning process was used. The compressed air was delivered through a blow tube to the nozzle. Fig. 7 shows the process of the dust cake born off the filter cartridge during the pulse cleaning. At this process, the pulse airflow and secondary airflow form the mixture airflow. The mixture airflow has a high velocity and has dynamic pressure. When the airflow goes into the filter cartridge and the airflow has prevented by the filter media. The dynamic pressures of the pulse airflow were conversed to static pressures, and then the static pressure force was formed and the dust cake was born off the filter cartridge by the static pressure force. The higher the static pressure force is, the quicker the dust born off the filter cartridge will be. At the stage of 0 to 12 ms, Fig. 7 shows that a few dust particles were born off the top area of the filter cartridge to the middle area. This was due to the fact that the transient pressure was formed at measurement locations one and two, as shown in Table 3. Although a peak pressure 673 Pa occurs at measurement one with the first transient time, only a minor amount of dust particles were born off the filter cartridge. Then, the maximum peak pressures were 4932, 14026, 3998, 8813 and 1962 Pa from the top 14
area to the bottom area of the filter cartridge. The dust cakes were born off the entire filter cartridge. This process of the dust cakes born off the filter cartridge corresponds to the four stages shown in Fig. 5. Fig. 8 shows the comparison photos of the pre and post pulse cleaning. The entire filter cartridge was filled with quartz particles prior to the pulse cleaning. Then the mostly quartz particles were born off the filter cartridge during the pulse cleaning. After a pulse cleaning, the filter cartridge was taken out. Through the weighting the filter cartridge and the dust, the cleaning efficiencies are defined as the weight difference between pre and post pulse cleaning. The cleaning efficiency is defined the weight difference and is 98%. From Fig. 5 and Fig. 7, although a peak pressure 673 Pa occurs at measurement location one with the first transient time, only a minor amount of dust particles were born off the filter cartridge. This conflicted with the results obtained by Ju et al., as well as Humphries and Madden
[24] [32]
, who reported that the first peak pressure
higher than 300 Pa could effectively remove the dust particles from the filter bag. This was due to the fact that because that the filter medium of the filter cartridge was nonflexible, and had a layer surface treatment with a small porosity, as shown in Fig. 3. The filter medium, and the construction of the filter cartridge were different from that of the filter bag. Therefore, the transient pressure did not form a continuous impact on the filter cartridge. Lu and Tsaï [33] believed that the cleaning efficiency was related to the continuous impact of the reverse airflow on the filter cartridge. Therefore, the process of the quartz particles’ born off the entire filter cartridge was not only related to peak static pressure, but also to the continuous impact of the peak 15
static pressure. The process of the peak static pressure, along with the duration on the filter cartridge surface was indicative of the process of dust cake born off the filter cartridge. Table 3 shows that although the peak static pressure at measurement location five was lower than those at other measurement locations, the majority of the quartz particles were born off the filter cartridge, as shown in Fig. 7 and 8. This conflicted with the results obtained by Yan et al.
[25]
, who reported that the bottom area of the
filter cartridge was filled with dust particles with the increase of the operational time. In Reference [25], the cleaning process was on-line cleaning. In this study, some part cleaning process was off-line cleaning. Fig. 7 shows that the quartz particles were born off the entire filter cartridge. Fig. 5 illustrates that the peak static pressure decreased quickly after 100 ms. However, Fig. 7 shows that the total process of the dust cake born off the filter cartridge was approximately 370 ms. Therefore, the dislodged dust particles’ from the filter cartridge goes into the hopper with a gravitation force after 150 ms. In industrial application, the dislodged dust particles that drop due to gravitation force are induced to the filter medium and reattached on the filter medium, especially the bottom area of the filter medium, by using an induced draft fan. This is likely related to the length of the filter cartridge and the pulse width (opening time of electromagnetic valve controlled using a pulse controller). This result is different from this obtained in previous literature
[24]
. Our
team thought that the peak static pressure was not high to remove the dust particles born off the filter cartridge. In our previous industrial applications, if the height of the 16
high-flow filter cartridge is shorter (equal to 660 mm), the dust particles are not reattached on the bottom of the filter cartridge during in a long period of operational time. In some cases, an increase in the pulse width can decrease the opportunity of dust particles reattached on the bottom area of the filter cartridge in the same experiment shown in Reference
[25]
. Yang et al.
[19]
reported that the pulse width has
only a slight effect on cleaning efficiency. This is due to the fact that their experimental results were obtained in the laboratory. The effect of pulse width on cleaning performance is only on the peak pressure, but not on the cleaning process [19]. Due to the fact that the length (1000 mm) of the filter cartridge used in this study was longer than those used by Lo et al. [23] and Zhang et al. [21], the static pressure variation in our experiment is more complex than that of studies with shorter filter cartridges. Fig. 5 shows that the pulse airflow can prolong the duration of the peak static pressure if the pulse width increases. Therefore, the duration of pulse airflow increase. The formed peak static pressure has a long time in opposing direction to the normal forward airflow. The long-time peak static pressure decrease the incidence of the re-suspend particles reattached to the bottom area of the filter cartridge secondly. In industrial application, another method is to decrease the pleat number. Fig. 9 shows that the cleaning effect of a pleat number high to 125 is better than this of a pleat number high to 155. This is due to the fact that the formed static peak pressures increase when the pleat number decrease from the 155 to 125. This is because that the filter cartridge with pleat number 155 has the lower air permeability than the filter cartridge with pleat number 125. Therefore, the permeable airflow forms the bigger 17
static peak pressure on the filter cartridge. Therefore, the static pressure forces quickly reinforce the dust born off the filter cartridge. The detailed effects of the different pleat number on pulse airflow and cleaning process will be researched in future research. 4. Conclusions The maximum peak pressures are 4932, 14026, 3998, 8813 and 1962 Pa from the top to the bottom along the height of filter cartridge. The duration of the peak pressure on the filter cartridges’ surface are 185, 81.3, 99.2, 78.2 and 93.8 ms, respectively. The five peak static pressures are averaged and the value is 6746 Pa. The process of dust born off the filter cartridge is 372 ms. The pressure variation on filter cartridge’s surface agrees well with the dynamic process of dust cake born off filter cartridge obtained from the High-speed camera. The process of surface pressure variation and duration of the peak static pressure on the filter cartridge are indicative of the process of the dust born off the filter cartridge. A small amount of particulate was seen to be removed at the first recorded peak pressure 673 Pa with a transient time. This was contrary to previous testing conducted by other researchers, which showed that a pressure above 300 Pa produced effective cleaning results. The process of dust cake born off the whole filter cartridge is not only related to peak static pressure, but also to continuous impact of reverse airflow. In industrial application, the particulate matter was reattached to the filter cartridge medium after the completion of the pulse airflow using an induced draft fan through the filter in the normal direction. An increase in pulse width can extend the 18
duration of the peak pressure, and decrease the amount of dust reattached on the filter cartridge. The peak static pressures increase on the filter cartridge when the pleat number decreases from the 155 to 125. This can decrease the incidence of incomplete cleaning. Our next goal is to study the detailed effects of different pleat numbers on the pulse airflow and cleaning process. Acknowledgements This scientific work was financed from the National Natural Science Foundation of China (No. 51508481), Doctor’s Fund of Southwest University of Science and Technology (No. 14ZX7127), and was also supported by the Key Scientific Research Platform of Southwest University of Science and Technology (No. 14tdgk04). References: [1] Li-Ming Lo, Da-Ren Chen, David Y.H. Pui. Experimental study of pleated fabric cartridges in a pulse-jet cleaned dust collector [J]. Powder Technology 197 (2010) 141-149 [2] Ning Mao, Yuping Yao, Mistuhiko Hata, Masashi Wada, Chikao Kanaoka. Comparison of filter cleaning performance between VDI and JIS testing rigs for cleanable fabric filter [J]. Powder Technology 180 (2008) 109-114 [3] Zha Wenjuan, Qian Fuping. Feasibility Analysis of Reforming Electrostatic Precipitator into Cartridge Filter [J]. Journal of Filtration and Separation 23(2013) 21-24, 46 [4] Lin Tingquan, Yu Yuan, Wei Gang, Xu Zhongwei, Yang Chunyu. Application of high-flow filter cartridges in cement plant [J]. Cement Guide for New Epoch 4(2011) 44-45 [5] Zheng Yingjian, Jiang Dong. Recovery of glyphosate by pleated-type cartridges filter [J]. 19
Hangzhou Chemical 41(2011) 36-38 [6] Bai Zhen, Zhang Dianyin. Cleaning pressure characteristics and selection research of pulse filter [J]．Environment protection of metallurgy 6(2002) 68-69 [7] Xavier Simon, Sandrine Chazelet, Dominique Thomas, Denis Bémer, Roland Régnier. Experimental study of pulse-jet cleaning of bag filters Supported by rigid rings [J]. Powder Technology 172(2007) 67-81 [8] R. Dennis, J.E. Wilder, Fabric Filter Cleaning Studies, National Environmental Research Center, 1975 Report EPA 650/2-75-009. [9] I. Theodore, J. Reynolds, A. Corvini, A. Buonicore. Particulate control by pulsed-air baghouse filtration: describing equations and solutions, Proceedings of 2nd Speciality on the User and Fabric Filtration Equipment, Buffalo gd, vol. 90, 1975. [10] J. Sievert, F. Löffler. Dust dislodgement in pulse-jet fabric filters [C]. Proceedings of the First World Congress on Particle Technology, Part IV, Nurnburg West Germany, 1986, pp. 111–126. [11] X.Simon, D.Thomas, D.Bémer, S.Callé, R.Régnier, P.Contal. Influence of cleaning parameter on pulse-jet filter bag performance [J]. Filtration 4 (4) (2004) 253–260. [12] H.C. Lu, C.J. Tsaï, Influence of design and operation parameters on bag-cleaning performance of pulse-jet baghouse [J]. Journal of Environmental Engineering 125 (6) (1999) 583-591. [13] R. Dennis, J.E. Wilder, D.L. Harmon, Predicting pressure loss for pulse jet filters [J]. Journal of the Air Pollution Control Association 31 (9) (1981) 987-992. [14] R.W.K. Allen, H.G.D. Goyder, K. Morris, Modelling medium movement during cleaning of pulse-jet fabric filters [J]. Chemical Engineering Research and Design 77 (3) (1999) 223-230. 20
[15] W.J. Morris, Cleaning mechanisms in pulse jet fabric filters [J]. Filtration and Separation 21 (1) (1984) 50-54. [16] W. Humphries, J.J. Madden, Fabric filtration for coal-fired boilers: dust dislodgement in pulse jet filters [J]. Filtration and Separation 20 (1) (1983) 40-44. [17] M.J. Ellenbecker, D. Leith, Dust removal from non-woven-fabric-cleaning methods needs to be improved [J]. Filtration and Separation 18 (1981) 41-45. [18] Leubner H, Riebel U. Pulse jet cleaning of textile and rigid filter media characteristic parameters. Chemie Ingenieur Technik May 75(5) (2003) 504-514. [19] Yang Di，Chen Haiyan，Li Huaiyu．The influence of the pressure peak and pulse width on the dust-cleaning efficiency of the pulse-jet cartridge filter [J]．Journal of Safety and Environment 5(2008) 73-76 [20] Zheng Juan, Zhang Mingxing, Zhou Qijie, Zhang Yizhi, Cai Guangbei. Pressure peak test and analysis of membrane cartridge filter side wall [J]. China Powder Science and Technology 17(1) (2011) 63-66 [21] Zhang Qing, Chen Haiyan, Ju Min, Chen Jundong．Experiment on induction nozzle improving dust-cleaning efficiency of pulse-jet cartridge filters by induction nozzles [J]. Environment Engineering 30(2012) 62-65 [22] Yunlou Qian, Yuanxia Bi, Mingxing Zhang, Haiyan Chen, Guanjie Xu. Effect of filtration operation and surface treatment on pulse-jet cleaning performance of filter bags [J]. Powder Technology 277 (2015) 82-88 [23] Li-Ming Lo, Shih-Cheng Hu, Da-Ren Chen, David Y.H. Pui. Numerical study of pleated fabric cartridges during pulse-jet cleaning [J]. Powder Technology 198 (2010) 75-81 21
[24] Ju Min, Zhang Mingxing, Chen Jundong, Zhang Qing, Chen Haiyan. Dynamic analysis of dust dislodgement from pulse-jet cartridge filter [J]. Chinese Journal of Environmental Engineering 7(2013) 1091-1094 [25] Cuiping Yan, Guijian Liu, Haiyan Chen. Effect of induced airflow on the surface static pressure of pleated fabric filter cartridges during pulse jet cleaning [J]. Powder Technology 249 (2013) 424-430 [26] Lin Lijun, Chen Haiyan, Zhou Xi, Mu Lan. Experiment of dust-cleaning performances of pulse-jet cartridge filters [J]. Heating Ventilating and Air Conditioning 39(2009) 148-151 [27] Zhang Yizhi, Chen Haiyan, Zheng Juan, Zhang Mingxing. Experiments on cleaning performance of pulse jet filter bag [J]. Journal of Safety and Environment 6(3) (2010) 30-34 [28] Zhou Qijie, Chen Haiyan, Zhang Mingxing, Zheng Juan. Influence of pulse valve injection quantity on dust-cleaning performance of cartridge filters [J]. Heating Ventilating and Air Conditioning 41(6)(2011) 100-105 [29] Zhou Qijie, Chen Haiyan, Zhang Mingxing, Zheng Juan, Wang Yan. The industrial test of pulse bag filter in petroleum coke superfine grinding process [J]. Environmental Engineering 29(4)(2011) 94-98 [30] S. Fotovati, S.A. Hosseini, H. Vahedi Tafreshi, B. Pourdeyhimi. Modeling instantaneous pressure drop of pleated thin filter media during dust loading [J]. Chemical Engineering Science 66 (2011) 4036-4046 [31] Tao Zhendong, Zheng Shaohua. Powder Technology and Equipment [M]. Beijing: Chemical Industry Press, (2003) 249 [32] Humphries W., Madden J.J.. Fabric filtration for coal-fired boilers: dust dislodgement in 22
pulse jet filters [J]. Filtration and Separation 20 (1) (1983): 40-44. [33] Lu H.C., Tsaï C.J.. Influence of design and operation parameters on bag cleaning performance of pulse-jet baghouse [J]. Journal of Environmental Engineering 125 (6) (1999) 583-591.
23
Figures:
Fig.1 Incomplete cleaning photo of high-flow filter cartridge in industrial application
24
Supersonic induced nozzle and air diffuser
Pulse controller
Pulse valve
Computer
pressurized air reservior Transmitter
a rigid wire cage
Clean air 0mm 80mm 150mm
High-speed camera
P
a
350mm
pressure
transducer
Powder feeder
filter 650mm Metal halide lamp
850mm Powder collector
1000mm Baffle Flowmeter
Frequency transformer
Hopper Powder
Induced fan Gate valve
Fig. 2 Schematic view of the test rig
Blowtube
Supersonic induced nozzle Air diffuser
Schematic diagram of supersonic induced nozzle and the air diffuser
Top view of a pleated filter cartridge
25
A filter cartridge
A view from the top of filter cartridge A rigid wire cage
Microstructure of filter medium
Fig. 3 Rigid wire cage and microstructure of filter cartridge with surface treatment
26
100 Cumulative distribution (%) 80 Differential distribution (%)
60 40 20
Size distribution
Fig. 4 Quartz size distribution (µm)
27
700000
Outlet pressures of pulse value (pa)
Third stage 600000 500000 400000
Second stage
Fourth stage
300000 200000 100000
First stage
0 0
50
100
150
200
250
Pulse time (ms)
Fig.5 Outlet pressure variation of pulse valve with diameter 24.5 mm
28
a
b
c
29
d Fig.6 microstructure of the filter medium a. Front microstructure of the filter medium with surface treatment, b. Front microstructure of the filter medium without surface treatment, c. Crosse section microstructure of the filter medium with surface treatment, d. Crosse section microstructure of the filter medium without surface treatment
30
Dust
begin
to
dislodge from the cartridge
0 ms
6ms
12 ms
18 ms
Partially
dust
dislodge
from
the cartridge
24 ms
30 ms
36 ms
42 ms
Dust begin to deposit
from
the cartridge
48 ms
54 ms
60 ms
66 ms
31
72 ms
78 ms
96 ms
102 ms
108 ms
84 ms
114 ms
90 ms
120ms
32
…….partially photos omitted 126 ms
132 ms
Dust has been dislodged from the cartridge
252 ms
312 ms
372ms
Fig.7. Process of dust dislodgement from the filter cartridge vs time for filter medium with the surface treatment
33
b
d
c a
b
d
a. entire filter cartridge b. top of filter cartridge c. middle of filter cartridge d. bottom of filter cartridge c a
c
Fig.8. Comparison photos pre and post pulse cleaning for filter medium with the surface treatment
34
Pleat number 155
Pleat number 125
Filtration area 16m2
Filtration area 12m2
Fig.9 Photo of industrial application during pulse-jet cleaning for filter medium with the surface treatment (tank pressure 0.6MPa)
35
Tables: Table 1 Filter cartridge dimension Parameters Pleat number (n, 个)
125
155
Pleat pitch (W, mm)
8.164
6.58
Pleat height (H, mm)
45
44
Inner diameter (Din, mm)
215
215
Filter length (L, mm)
1000
1000
Filtration area (Af, m )
12
16
Thickness of filter medium (mm)
0.6
0.6
2
(L/m2·s)
Air permeability 80-100 or 150 80-100 Annotation: The filter medium with surface treatment was composed of a layer of polytetrafluoroethene fibers on a polyethylene terephthalate nonwoven filters substrate (air permeability is 80-100 L/m2·s). The filter medium without surface treatment was composed a polyethylene terephthalate nonwoven filters (air permeability is 150 L/m2·s).
36
Table 2 Experimental parameters during the cleaning Parameters Pulse pressure (MPa)
0.6
Pulse valve opening time (ms)
80
Pulse air volume (L)
80
Pulse orifice diameter (mm)
16
distance between nozzle and
50
filter cartridge top (mm) Diffuser height (mm)
102
Filtration velocity (m/min)
0.8
37
Table 3 Static peak pressure and duration on filter cartridge with surface treatment First peak
Maximum
Initial
Time to peak
Duration of
pressure
peak pressure
pressure
pressure
peak pressure
（Pa）
（Pa）
time（ms）
（ms）
（ms）
80
673
4932
0
0
185
150
427
14026
1.3
20.5
81.3
350
-
3998
1.3
1.3
99.2
650
-
8813
1.3
11.5
78.2
850
-
1962
2.5
3.8
93.8
Measurement location（mm）
Annotation: first time of occurred initial pressure is set to 0. First time to peak pressure is set to 0. Other time is set to relatively value.
38
Table 4 Comparison of peak pressure with surface treatment and without surface treatment Measurement point Filter medium 80mm
150mm
350mm
650mm
850mm
Filter medium with surface treatment (Pa)
4932
14026
3998
8813
1962
Filter medium without surface treatment (Pa)
899
1767
790
1013
572
39