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Application and research of dry-type filtration dust collection technology in large tunnel construction
Advanced Powder Technology xxx (2017) xxx–xxx
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Advanced Powder Technology journal homepage: www.elsevier.com/locate/apt
Original Research Paper
Application and research of dry-type filtration dust collection technology in large tunnel construction Shihang Li a,b, Fubao Zhou a,b,c,⇑, Fei Wang a,b, Biao Xie a,b a
Key Laboratory of Gas and Fire Control for Coal Mines, Ministry of Education, China University of Mining and Technology, Xuzhou 221116, China School of Safety Engineering, China University of Mining and Technology, Xuzhou 221116, China c State Key Laboratory of Coal Resources and Mine Safety, China University of Mining and Technology, Xuzhou 221116, China b
a r t i c l e
i n f o
Article history: Received 7 February 2017 Received in revised form 4 September 2017 Accepted 3 October 2017 Available online xxxx Keywords: Dry-type filtration Dust collector Large tunnel Filter cartridge Dust suppression efficiency
a b s t r a c t Large amounts of rock dust are produced in the process of constructing large tunnels. It then accumulates in the tunnel where, because it is difficult to disperse, it is a serious threat to workers’ health; more than 90% of dust is respirable. Traditional methods to reduce rock dust concentrations, such as a water spray, ventilation, and foam are not effective. Therefore, a new dry-type filtration dust collection method is put forward to use in the construction of large tunnels, and a dry-type filtration dust collection device is designed. Experiments and field application of the dry-type filtration dust collection device were carried out. Experimental results showed that the total dust suppression efficiency reached 98.41% and the leakage rate was 7.86% with the dry-type filtration dust collector. The field application in the Chaoyang tunnel indicated that the efficiency of the dry-type dust collector in suppressing total and respirable dust was 98.13% and 97.86%, respectively. During lining trolley shotcreting operations, the total dust concentration decreased from 253.41 mg/m3 to 29.97 mg/m3 and the respirable dust concentration dropped from 226.73 mg/m3 to 28.85 mg/m3. The dust collection system also reached the optimal dust removal efficiency in two other tunnel construction operations and made an obvious improvement in the environment behind the dust collection system in the large tunnel. The dry-type filtration dust collector effectively improves the rock dust collection efficiency and makes up for the problem of inadequate treatment of respirable dust by the traditional methods. Ó 2017 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
1. Introduction In order to solve inconveniences caused by traffic pressure, the construction of tunnels and underground projects (such as railway tunnels, highway tunnels, and municipal pipelines) has become an inevitable trend. The total mileage of railway and highway tunnels reached 25,721.9 km by the end of 2015 in China, and maintained rapid growth, where large tunnel construction was the emphasis but also the main difficulty [1–3]. Rock dust is one of the primary air contaminants in large tunnel construction. Controlling it has become a new challenge due to the high dust concentration, rapid speed of diffusion, number of dust sources, and remote discharge distance. There are several operations, such as tunnel face blasting, lining trolley shotcreting, and tunnel face mucking, that produce large amounts of rock dust, more than 90% of which is respirable
⇑ Corresponding author at: School of Safety Engineering, China University of Mining and Technology, Xuzhou 221116, China. E-mail address: [email protected] (F. Zhou).
dust (that is, have particle sizes less than 7.07 lm) [4]. Anyone working in the tunnel is exposed to high levels of respirable rock dust, which can lead to pneumoconiosis or silicosis, incurable diseases that seriously endanger workers’ health [3,5]. Various collecting technologies have been developed and applied, all over the world, to control rock dust in large tunnel construction [6–8]. They have played important roles in reducing rock dust but still have obvious drawbacks. For instance, water sprays not only have low efficiencies against rock dust, but also consume large amounts of water. Worse still, spraying nozzles are easily blocked and damaged subject to the bad water quality in tunnels [9–12] and demand for high water pressure is hard to meet practically [13,14]. In addition, water has a high surface tension, and rock dust is mostly hydrophobic, so water cannot easily capture respirable rock dust, especially that less than 2 lm in diameter [10,15]. It is also very difficult to dilute and eliminate rock dust purely by ventilation due to the large amount of dust generated, high degree of dust distribution, and high SiO2 content [16,17]. Foam technology is effective at suppressing respirable dust, but
https://doi.org/10.1016/j.apt.2017.10.003 0921-8831/Ó 2017 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
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related research shows that its drawbacks include large pressure losses and a demand for high-pressure water. In some cases, it is hardly forms an effective cover for dust sources in a large tunnel [11,18]. Besides, the foam that covers dust sources obstructs workers’ view, and the high cost of the foam agent severely limits its application at large tunnel construction sites [19,20]. Therefore, controlling dust in large tunnel construction has become the focus of scholarly research. Due to advantages including efficiency, not needing water, and the ability to be used without causing secondary pollution, drytype filtration dust collectors have been extensively applied in modern industrial production, but it less used underground [21]. In order to effectively solve the problem of dust pollution in the process of large tunnel construction, a new dry-type dust collection technology is proposed. In addition, the dry-type filtration dust collector and collection system were developed and designed independently. This is the first systematic research on the dry-type filtration dust collection technology in the large tunnel construction, which could be of great significance in guiding its field application. Therefore, this study will provide an important foundation for the application of dry-type filtration dust collection technology to large tunnel construction, making it an efficient method increase worker health and safety. 2. The dry-type filtration dust collection method and device in large tunnel construction A new dry-type filtration dust collection method for use in large tunnel construction has been put forward as shown in Fig. 1. It takes the existing high voltage and compressed air in the tunnel as its source of operating and cleaning power. Firstly, the drytype filtration dust collector is moved to the desired position, the extraction fan is turned on, and the dust-laden gas is sucked into the exhaust hood under the negative pressure of the extraction fan, entering the filter chamber through an air duct. Secondly, gravity causes some large particles in the dusty gas to settle, and the fine dust is captured on the outer wall of the filter cartridge in the filter chamber. Then the gas passing through the wall of the filter cartridge enters the cleaning chamber and is discharged through the extraction fan. Thirdly, as the thickness of the dust cake deposited on the surface of the filter cartridge increases with dust suppression, resistance also increases. The process of cleaning
begins when the surface resistance of the filter cartridge reaches a certain value, after which compressed air is sprayed into the filter cartridge, at high velocity, through a nozzle on the injection pipe, and the rock dust on the outer wall of the filter cartridge is blown down to the deposition chamber. Finally, the rock dust in the deposition chamber is transported to the flat dust discharge valve when the scraper conveyor is turned on, and the collected dust is discharged when the flat discharge valve is pulled. Fig. 2 shows the dry-type filtration dust collector created by the authors. It consists of a shell, filtration system, cleaning system, discharging system, extraction fan. It is 7040 mm long 1300 mm wide 1050 mm high; weight 2000 kg; has inlet and outlet 600 mm in diameter; uses a FBCD No. 5.6/2⁄11 extraction fan (with rated voltage, power, and air flow of 380/660 V, 22 kW, 200–280 m3/min, respectively), 100 filter cartridges, 20 pulse valves, compressed air at pressures between 0.5 and 0.7 MPa; and has a total filtration area of 240 m2. The electrical motor of the scraper conveyor YBK2-80M2-2 has a rated voltage and powder of 380/660 V and 0.75 kW, respectively. The filtration system consists mainly of pleat-type metal mesh filter cartridges fixed with three bolt connections. A single filter cartridge has the following dimensions: 145 mm outer diameter 80 mm inner diameter 600 mm depth, initial filtration accuracy 15 lm, 60 pleats 20 mm deep, and a filtration area of 2.4 m2. The pleat-type structure can significantly increase the filtration area, and the metal mesh filter material has a good flame-retardant and anti-static effect as addition to its role as a support, which can increase the service life of the filter cartridge. There is no dust on the new filter cartridge during the initial operation of the drytype filtration dust collector, but after a few minutes a thin layer of dust cake is formed on the surface of the filter material. This dust cake, which is 0.3–0.5 mm thick, is called the primary dust cake; the dust which is re-deposited on it is secondary dust cake. The main role of the filter material is to form the primary dust cake and support its frame; the function of filtration relies mostly on the primary dust cake [22]. Fig. 3(a) –(c) shows the filter material, in different states, magnified 1000 times under a scanning electron microscope. Fig. 3(a) illustrates that the unused metal mesh filter material looks smooth, without any foreign materials on it; it can be clearly observed that the metal fibers are knitted together and combine tightly, with a fiber gap of at most 15 lm. Fig. 3(b) shows the used
Fig. 1. The dry-type filtration dust collection method.
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Fig. 2. The dry-type filtration dust collection device.
Fig. 3. Scanning electron microscope views of the surface of the filter material under three conditions (a. unused filter material, b. used filter material after one clean, and c. used filter material after thorough cleaning).
metal mesh filter material after once cleaning. Once cleaning means that pulse valve was opened only once when the gas pressure is 0.5 MPa, and then the pressure gas was injected into the filter cartridge, making partial dust on the outer wall of filter cartridge shocked down. As shown in Fig. 3(b), the surface of filter material is covered with dust, and the fiber gaps are filled with dust particles. Fig. 3(c) shows the used metal mesh filter material after thorough cleaning. Thorough cleaning means that pulse valve was opened several times to cleaning until the pressure drop of the filter no longer decreased. There is little dust on the surface of filter material, and the fiber gap has not yet been completely blocked. Large gaps between fibers exist compared with the once cleaning
filter material. The dust removed from the filter material is the secondary dust cake and the residual dust on the surface of filter material is considered the primary dust cake after once cleaning. Thorough cleaning destroyed the primary dust cake and the secondary dust cake. The filtration effect is optimal in terms of filtration precision and resistance after once cleaning. As shown in Fig. 4, the cleaning system includes pulse valves (SMF-Q-20, working pressure 0.3–0.8 MPa), air valves (CM3PM08, working pressure 0–1 MPa), nozzles, injection pipes, an air tank (10 L), and rubber tubes, among others. The injection pipe is made of a seamless pressure tube, and the number of injection holes on it is contingent on the number of filter cartridges. The cleaning
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compressed air source in the tunnel, with rubber pipes 30 mm in diameter, and the extraction fan and electrical motor are connected to high voltage power sources. 3. Performance test of dry-type filtration dust collector 3.1. Experimental apparatus
Fig. 4. The dust cleaning system.
system is an important part of the dry-type filtration dust collector, and there are many academic studies on the cleaning system of the dry-type filtration dust collector. Chi et al. [23] found that the size of the gap between the nozzle and diffuser is important to avoid incomplete cleaning and enhance the cleaning potential for a ceramic filter cartridge. Ju et al. [24] found that an induced nozzle can enhance the pressure distribution inside the cartridge and improve pulse-jet cleaning efficiency. Li et al. [25] improved the dust cleaning effect by placing a cone installation in the filter cartridge. A well designed cleaning system is conducive to improving cleaning efficiency, reducing cleaning frequency, saving energy consumption, and increasing the life of the filter cartridge. Furthermore, a scraper conveyor is arranged at the bottom of the dust collector and each side of the deposition has a dust discharge flat valve. The discharge system uses the scraper conveyor to collect dust and the dust discharge flat valve to discharge dust, which can effectively reduce the height of the device and increase the air-tightness of the dust collector. A dry-type filtration dust collection system used for ventilation and dust suppression in large tunnel construction has been designed following the specifications above. The dust collector is fixed on a trailer platform and its inlet is connected to a 1000 mm long 500 mm wide dust exhaust hood, via an air duct 600 mm in diameter and 6 m long. The extraction fan outlet is connected to an air duct 600 mm in diameter, the length of which can be adjusted according to demand; here it is 5 m long. The air duct is sustained by a convenient moving support. The dry-type filtration dust collector air tube is connected to an existent
A schematic of the test rig, which follows the general technical conditions for mine dust collector of the People’s Republic of China MT 159-2005 [26], is shown in Fig. 5. The experimental apparatus consists of the dry-type filtration dust collector, an extraction fan, a connecting pipe, and other systems. The dry-type filtration dust collector is connected to the extraction fan by an iron air duct that is 2 m long and 600 mm in diameter. The dust collector inlet is connected to the inlet pipe (a 6 m long iron air duct, 600 mm in diameter), and the dust collector outlet is connected to the outlet pipe (a 7.2 m long iron air duct, 600 mm in diameter). In addition, the experimental apparatus includes a u114/1.5 type powder feeder with a range of 0–3.3 kg/min, two L-type sampling tubes, two sampling funnels into which a 40 mm diameter filter membrane can be loaded, four pressure taps which are uniformly distributed in the same cross section, a pitot tube, two LZB-15 type glass flowmeters, a 2XZ-4A type pump with a pumping rate of 14.4 m3/h, a DYM3 type aneroid barometer, an AZ8205 type differential pressure gauge, a ZX-0.1 type mercury thermometer, fly ash (particles less than 80 lm, of which 14% are less than 10 lm and 48% are less than 30 lm), two regulating valves used to adjust the gas flow of the glass flowmeter, a release valve to regulate the quantity of pump, some filter membranes (polypropylene fiber, diameter: 40 mm), and a JJ124BC type electronic analytical balance with a range of 0–120 g. 3.2. Measurement of air volume The extraction fan was opened, and the atmospheric pressure at the experimental site and the temperature in the inlet and outlet of the experimental device were measured with the aneroid barometer and the mercury thermometer, respectively. The ‘‘negative” joint of the differential pressure gauge was connected to the four pressure mouths in the inlet pipe (450 mm away from the inlet) with the rubber tube to measure the static pressure. The ‘‘positive” and ‘‘negative” joints of the differential pressure gauge were connected to the total pressure and static pressure ports, respectively, of the pitot tube; this was then inserted into the hole in the outlet pipe 6 m from the outlet of the extraction fan, to measure the outlet dynamic pressure. The measurements are listed in Table 1. The inlet air volume, outlet air volume, and air leakage rate of the dust collector were calculated with Eqs. (1)–(3) [26] respectively.
Fig. 5. A diagram of the experimental device.
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S. Li et al. / Advanced Powder Technology xxx (2017) xxx–xxx Table 1 Air volumes measured by the dust collector. Parameters
Atmospheric pressure (Pa)
Inlet temperature (°C)
Outlet temperature (°C)
Inlet pipe relative static pressure (Pa)
Outlet pipe dynamic pressure (Pa)
Measured data
99830 – – –
34.5 34.5 34.6 –
36.1 36.2 36.2 –
82.32 83.79 89.67 91.14
94.65 93.22 90.35 91.79
Average data
99830
34.53
36.13
86.73
92.50
q01 ¼ 18:866aed1 2
2
q02 ¼ 18:866d2
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi DPð273:15 þ t 1 Þ=Pa 60
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi DPd ð273:15 þ t2 Þ=Pa 60
x ¼ ðq02 q01 Þ=q01 100
ð1Þ
and the tot c al dust suppression efficiency, can be calculated using Eqs. (4) and (5), respectively.
ð2Þ
c ¼ ðm2 m1 Þ=q 3600=t
ð4Þ
ð3Þ
g ¼ ðc1 c2 Þ=c1 100
ð5Þ
where q01 and q02 (m3/min) are the inlet and outlet air volume, respectively; d1 and d2 (m) are the diameters of the inlet and outlet pipe, respectively; DP (Pa) is the static pressure 0.75 d1 from the inlet; Pa (Pa) is the atmospheric pressure at the experimental site;t 1 and t 2 (°C) are the temperatures in the inlet and outlet of the experimental device, respectively; P d (Pa) is the dynamic pressure 6 m from the outlet of the extraction fan; x (%) is the air leakage rate of the dust collector; and ae is the compound coefficient where a and e are the flow and expansion coefficients, respectively. Here, a tapered inlet manifold was used to measure flow, so ae = 0.96. This method can effectively avoid measurement error when an anemometer is used, and improve the accuracy of the inlet and outlet air volume measurements. According to Table 1 and Eqs. (1)–(3), the inlet air volume, outlet air volume, and air leakage rate of the dust collector are 202.26 m3/min, 218.15 m3/min, and 7.86%, respectively. 3.3. Measurement of dust suppression efficiency Firstly, the extraction fan was opened after blank filter membranes were weighed and put into the sampling funnels. Secondly, the pump was turned on when the system worked at steady state, and adjustments to the control valves and the release valve kept the flow rates of glass flowmeters F1 and F2 constant at 1.2 m3/h, making the gas flow rate of the sampling tube equal to the pipe. Thirdly, the powder feeder was opened and maintained at a feed rate of 240 g/min, and counting began. Finally, the powder feeder, extraction fan, and pump were off simultaneously after 120 s and the filter membranes were weighed again. The dust concentration in the inlet and outlet pipes of the collector were collected simultaneously, eight times, using the filter membrane method. The measurement data are listed in Table 2. The dust concentration in the collector’s inlet and outlet pipes,
In these equations, m1 (mg) is the weight of the blank filter membrane, m2 (mg) is the weight of the filter membrane after dust collection, q (m3/h) is the sampling flow value, t (s) is sampling time, (mg/m3) represents the dust concentration in the pipe, and g represents the dust suppression efficiency. For the sake of convenience, c1 (mg/m3) is chosen to represent the dust concentration in the inlet pipe, and c2 (mg/m3) is the dust concentration in the outlet pipe. This method is more accurate than using a dust testing instrument to measure dust concentration. According to Table 2, Eqs. (4) and (5), the dust suppression efficiency of the dry-type filtration dust collector is 98.41%.
4. Field application and measurements Chaoyang is a large tunnel on a section of the Beijing-Shenyang passenger line in Chaoyang city, Liaoning province, China. The Chaoyang tunnel is 6750 m long with an arched section, which includes two inclined shafts, that is 107 m2 (12.6 m wide and 8.5 m high). The 1# inclined shaft was arranged in the line of DIK 409 + 500 (409.5 km from the tunnel entrance) and is 300 m in length with a longitudinal slope of 9%. The 2# inclined shaft was arranged in the line of DIK 410 + 700 (410.7 km from the tunnel entrance) and is 385 m in length, with a longitudinal slope of 10%. At present, 1150 m of the 2# inclined shaft has been excavated in the direction of Shenyang, with 320 m remaining. Forced ventilation is used in the tunnel; a main forced fan (power: 2 ⁄ 110 kW, air flow: 2850 m3/min) and an auxiliary forced fan (power: 2 ⁄ 110 kW, air flow: 2850 m3/min) are installed at the entrance and approximately 700 m from the exit of the 2# inclined shaft, respectively. There is a 0.5 m clearance between the outlet of the main forced fan air duct (1.5 m in diameter) and the inlet of the auxiliary forced fan air duct (same diameter). Fig. 6 illustrates the layout of
Table 2 Dust measurements from filter membranes in the inlet pipe and outlet pipe. Position Inlet pipe
Before sampling (mg) Measured Data (mg)
Average data (mg) Outlet pipe
Measured data (mg)
Average data (mg)
After sampling (mg)
661.3 663.4 661.8 660.1 661.588
663.7 660.3 662.9 659.2
686.6 692.5 683.7 684.2 684.400
679.2 687.4 675.5 686.1
663.4 661.8 660.6 663.0 661.563
660.1 659.3 662.7 661.6
663.7 662.2 660.8 663.2 661.925
660.4 660.2 663.1 661.8
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Fig. 6. The layout of the dry-type filtration dust collection system on-site at the Chaoyang tunnel.
dry-type filtration dust collection system on-site at the Chaoyang tunnel. The main forced fan pushed fresh air into the tunnel face from the entrance of the 2# inclined shaft. Without the dry-type filtration dust collection system, visibility was low, dust and smoke were diffuse, the recirculating air was serious, and the air flow was slow behind the lining trolley, which seriously endangers workers’ health. Due to the limited space available and the undulating terrain in front of the lining trolley in the Chaoyang tunnel, the dry-type filtration dust collector was placed at the rear of the lining trolley for field application. A series of tests were carried out under three different operation conditions, including tunnel face blasting, lining trolley shotcreting, and tunnel face mucking. The optimum dust suppression efficiency was achieved during lining trolley shotcreting, the validation for which will be shown below. As shown in Fig. 7, the dust concentration fell significantly in the tunnel with the dry-type filtration dust collector, and the visibility behind the lining trolley improved dramatically.
When the dry-type filtration dust collector was turned on during the lining trolley shotcreting operation, the dust exhaust hood was arranged 3 m behind the spraying point and moved with it. A direct-reading dust-measuring instrument (CCZ-1000, Changshu Deyu Mine Mechanical Co., Ltd., China) was used to monitor the concentrations of total and respirable dust. The measuring points were 1 m in front of the dust exhaust hood and at the dust collector outlet, respectively. Both were 1 m above the ground. Measurements were taken three times, each lasting 60 s, at both points. The measurement data for different days are shown in Fig. 8 and indicate that the dust concentration at the position of dust collector outlet can be controlled below 6 mg/m3. Therefore, the equipment ran stably while being used. After using the dust collector, the average concentrations of total dust and respirable dust declined from 285.4 to 5.33 mg/m3 and 237.8 to 5.08 mg/m3, respectively. Using Eq. (5), the efficiency of the dust collector in the field was calculated to be 98.13% and 97.86%, respectively, in terms of total and respirable dust suppression. The field test value of total dust suppression efficiency was lower than the
Fig. 7. Comparisons of tunnel environment before and after using the dry-type filtration dust collector during lining trolley shotcreting (a. before dust is suppressed, b. the field application of the dry-type dust collection system, c. after dust is suppressed with the dry-type filtration dust collector).
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Fig. 8. Dust concentrations after using the dry-type filtration dust collector during lining tunnel shotcreting operations. a–f shows the average values of dust concentration (t. d.: total dust, r.d.: respirable dust) measured on days 1, 5, 10, 15, 20, and 25, respectively.
experimental value of 98.41%. This was mainly because a small amount of dusty gas in the tunnel mixed with the outlet gas during the field application, which increased the value of the outlet dust concentration. To further prove the effectiveness of the dry-type filtration dust collector, it was turned on during the lining trolley shotcreting, and data were taken at points 0–20 m behind the dust collector outlet. The total dust concentration contour line and the dust concentration distribution on the center line behind the dust collector outlet during shotcreting operations are shown in Figs. 9 and 10, respectively. The dust concentration was lowest at the outlet of the dust collector and increased with distance from the outlet. Since the outlet airflow was restricted by the tunnel wall, the contour line
was not completely symmetrical. As seen from Figs. 8–10, the dry-type filtration dust collector can effectively reduce dust concentrations generated by lining trolley shotcreting. As the distance from the outlet increased, the total dust concentration increased gradually from 5.33 mg/m3 and reached 29.56 mg/m3 13 m behind the outlet of the dust collector, then tended to a relatively stable state. Likewise, the respirable dust concentration increased gradually from 5.08 mg/m3 and reached 28.86 mg/m3 14 m behind the outlet of the dust collector, and then maintained a relatively stable state. Based on the above analyses, the concentration of dust suppressed was steady 15 m behind the dust collector; therefore, the dust suppression efficiency 15 m behind the dust collector was
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Fig. 9. The contour line of total dust concentration behind dust collector outlet during lining tunnel shotcreting operations.
Fig. 10. The distribution of dust concentrations (t.d.: total dust, r.d.: respirable dust) on a center line behind dust collector outlet during lining tunnel shotcreting operations.
taken as that of the dust collection system. That dust concentration was measured for one month under three different operations, including tunnel face blasting, lining trolley shotcreting, and tunnel face mucking. The measurement data and average concentration are shown in Fig. 11. The average concentration of total and respirable dust declined from 314.20 to 48.20 mg/m3 and 286.41 to 46.12 mg/m3, respectively, during tunnel face blasting; from 253.41 to 29.97 mg/m3 and 226.73 to 28.85 mg/m3, respectively, during lining trolley shotcreting; and from 285.91 to 50.32 mg/ m3 and 251.59 to 47.23 mg/m3, respectively, during tunnel face mucking operations. According to Eq. (5), the total rock dust suppression efficiencies of the dry-type filtration dust collection system under tunnel face blasting, lining trolley shotcreting, and tunnel face mucking conditions were 84.66%, 88.17%, and 82.40%, respectively. The respirable rock dust suppression efficiencies were 83.90%, 87.28%, and 81.23%, respectively. The highest dust suppression efficiency was achieved during lining trolley shotcreting followed by tunnel face blasting; the lowest was obtained during tunnel face mucking. This is mainly because the dust exhaust hood was close to the rock dust generation point, and the dusty air was sucked into the dust collector before the rock dust diffused completely. The dust generated in the tunnel face blasting operation had diffused when it reached the dust exhaust hood, so the capacity for air purification was limited. The rock dust settled at the bottom of the tunnel was raised by trucks during tunnel face mucking, which polluted the purification gas; and resulted in the lowest rock dust suppression efficiency. The particle sizes of the rock dust that collected at the bottom of dust collector were measured using a laser particle size analyzer (S 3500, Microtrac Inc., America). The test result is shown in Fig. 12. The rock dust particles were mainly concentrated in 0.818–13.08 lm range; more than 85% was less than 7.07 lm in size, or respirable. The results of the particle size tests were basically in agreement with those from the direct-reading dust-measuring instrument.
Fig. 11. The dust concentration 15 m behind the dust collector in the tunnel during a. tunnel face blasting, b. lining trolley shotcreting, and c. tunnel face mucking.
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References
Fig. 12. Distribution of rock particle sizes at the bottom of dust collector.
5. Conclusion A new method and device have been designed to collect dust from large tunnel construction using a dry-type filtration system. The device is structured like a long box, with filter cartridges, air controlled pulse jet for cleaning and collection of the scraper conveyor. It uses the existing high voltage and compressed air in the tunnel as its source of operating and cleaning power. Experimental test results showed that with the dry-type filtration dust collector, the total rock dust suppression efficiency reached 98.41%, and that the inlet air volume, outlet air volume, and air leakage rate of the dust collector was 202.26 m3/min, 218.15 m3/min, and 7.86%, respectively. The field application in the Chaoyang tunnel indicated that the dry-type filtration dust collector had total and respirable dust suppression efficiencies of 98.13% and 97.86%, respectively; that is, the dry-type filtration dust collector performed well in the field. For lining trolley shotcreting operations, the total dust concentration decreased from 253.41 mg/m3 to 29.97 mg/m3, the respirable dust concentration dropped from 226.73 mg/m3 to 28.85 mg/m3, and the total and respirable dust suppression efficiencies were 84.77% and 83.86%, respectively. The system also reached optimal dust suppression efficiencies in three kinds of tunnel construction operations, and the purification of respirable dust is particularly significant. From these results, it can be inferred that there are wide prospects for the application of dry-type filtration dust collection technology. Acknowledgements This work was supported by the Fundamental Research Funds for the Central Universities [grant number 2014XT02]; the Program for Changjiang Scholars and Innovative Research Team in University [grant number IRT13098]; and the Priority Academic Program Development of Jiangsu Higher Education Institutions.
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Advanced Powder Technology journal homepage: www.elsevier.com/locate/apt
Original Research Paper
Application and research of dry-type filtration dust collection technology in large tunnel construction Shihang Li a,b, Fubao Zhou a,b,c,⇑, Fei Wang a,b, Biao Xie a,b a
Key Laboratory of Gas and Fire Control for Coal Mines, Ministry of Education, China University of Mining and Technology, Xuzhou 221116, China School of Safety Engineering, China University of Mining and Technology, Xuzhou 221116, China c State Key Laboratory of Coal Resources and Mine Safety, China University of Mining and Technology, Xuzhou 221116, China b
a r t i c l e
i n f o
Article history: Received 7 February 2017 Received in revised form 4 September 2017 Accepted 3 October 2017 Available online xxxx Keywords: Dry-type filtration Dust collector Large tunnel Filter cartridge Dust suppression efficiency
a b s t r a c t Large amounts of rock dust are produced in the process of constructing large tunnels. It then accumulates in the tunnel where, because it is difficult to disperse, it is a serious threat to workers’ health; more than 90% of dust is respirable. Traditional methods to reduce rock dust concentrations, such as a water spray, ventilation, and foam are not effective. Therefore, a new dry-type filtration dust collection method is put forward to use in the construction of large tunnels, and a dry-type filtration dust collection device is designed. Experiments and field application of the dry-type filtration dust collection device were carried out. Experimental results showed that the total dust suppression efficiency reached 98.41% and the leakage rate was 7.86% with the dry-type filtration dust collector. The field application in the Chaoyang tunnel indicated that the efficiency of the dry-type dust collector in suppressing total and respirable dust was 98.13% and 97.86%, respectively. During lining trolley shotcreting operations, the total dust concentration decreased from 253.41 mg/m3 to 29.97 mg/m3 and the respirable dust concentration dropped from 226.73 mg/m3 to 28.85 mg/m3. The dust collection system also reached the optimal dust removal efficiency in two other tunnel construction operations and made an obvious improvement in the environment behind the dust collection system in the large tunnel. The dry-type filtration dust collector effectively improves the rock dust collection efficiency and makes up for the problem of inadequate treatment of respirable dust by the traditional methods. Ó 2017 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
1. Introduction In order to solve inconveniences caused by traffic pressure, the construction of tunnels and underground projects (such as railway tunnels, highway tunnels, and municipal pipelines) has become an inevitable trend. The total mileage of railway and highway tunnels reached 25,721.9 km by the end of 2015 in China, and maintained rapid growth, where large tunnel construction was the emphasis but also the main difficulty [1–3]. Rock dust is one of the primary air contaminants in large tunnel construction. Controlling it has become a new challenge due to the high dust concentration, rapid speed of diffusion, number of dust sources, and remote discharge distance. There are several operations, such as tunnel face blasting, lining trolley shotcreting, and tunnel face mucking, that produce large amounts of rock dust, more than 90% of which is respirable
⇑ Corresponding author at: School of Safety Engineering, China University of Mining and Technology, Xuzhou 221116, China. E-mail address: [email protected] (F. Zhou).
dust (that is, have particle sizes less than 7.07 lm) [4]. Anyone working in the tunnel is exposed to high levels of respirable rock dust, which can lead to pneumoconiosis or silicosis, incurable diseases that seriously endanger workers’ health [3,5]. Various collecting technologies have been developed and applied, all over the world, to control rock dust in large tunnel construction [6–8]. They have played important roles in reducing rock dust but still have obvious drawbacks. For instance, water sprays not only have low efficiencies against rock dust, but also consume large amounts of water. Worse still, spraying nozzles are easily blocked and damaged subject to the bad water quality in tunnels [9–12] and demand for high water pressure is hard to meet practically [13,14]. In addition, water has a high surface tension, and rock dust is mostly hydrophobic, so water cannot easily capture respirable rock dust, especially that less than 2 lm in diameter [10,15]. It is also very difficult to dilute and eliminate rock dust purely by ventilation due to the large amount of dust generated, high degree of dust distribution, and high SiO2 content [16,17]. Foam technology is effective at suppressing respirable dust, but
https://doi.org/10.1016/j.apt.2017.10.003 0921-8831/Ó 2017 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
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related research shows that its drawbacks include large pressure losses and a demand for high-pressure water. In some cases, it is hardly forms an effective cover for dust sources in a large tunnel [11,18]. Besides, the foam that covers dust sources obstructs workers’ view, and the high cost of the foam agent severely limits its application at large tunnel construction sites [19,20]. Therefore, controlling dust in large tunnel construction has become the focus of scholarly research. Due to advantages including efficiency, not needing water, and the ability to be used without causing secondary pollution, drytype filtration dust collectors have been extensively applied in modern industrial production, but it less used underground [21]. In order to effectively solve the problem of dust pollution in the process of large tunnel construction, a new dry-type dust collection technology is proposed. In addition, the dry-type filtration dust collector and collection system were developed and designed independently. This is the first systematic research on the dry-type filtration dust collection technology in the large tunnel construction, which could be of great significance in guiding its field application. Therefore, this study will provide an important foundation for the application of dry-type filtration dust collection technology to large tunnel construction, making it an efficient method increase worker health and safety. 2. The dry-type filtration dust collection method and device in large tunnel construction A new dry-type filtration dust collection method for use in large tunnel construction has been put forward as shown in Fig. 1. It takes the existing high voltage and compressed air in the tunnel as its source of operating and cleaning power. Firstly, the drytype filtration dust collector is moved to the desired position, the extraction fan is turned on, and the dust-laden gas is sucked into the exhaust hood under the negative pressure of the extraction fan, entering the filter chamber through an air duct. Secondly, gravity causes some large particles in the dusty gas to settle, and the fine dust is captured on the outer wall of the filter cartridge in the filter chamber. Then the gas passing through the wall of the filter cartridge enters the cleaning chamber and is discharged through the extraction fan. Thirdly, as the thickness of the dust cake deposited on the surface of the filter cartridge increases with dust suppression, resistance also increases. The process of cleaning
begins when the surface resistance of the filter cartridge reaches a certain value, after which compressed air is sprayed into the filter cartridge, at high velocity, through a nozzle on the injection pipe, and the rock dust on the outer wall of the filter cartridge is blown down to the deposition chamber. Finally, the rock dust in the deposition chamber is transported to the flat dust discharge valve when the scraper conveyor is turned on, and the collected dust is discharged when the flat discharge valve is pulled. Fig. 2 shows the dry-type filtration dust collector created by the authors. It consists of a shell, filtration system, cleaning system, discharging system, extraction fan. It is 7040 mm long 1300 mm wide 1050 mm high; weight 2000 kg; has inlet and outlet 600 mm in diameter; uses a FBCD No. 5.6/2⁄11 extraction fan (with rated voltage, power, and air flow of 380/660 V, 22 kW, 200–280 m3/min, respectively), 100 filter cartridges, 20 pulse valves, compressed air at pressures between 0.5 and 0.7 MPa; and has a total filtration area of 240 m2. The electrical motor of the scraper conveyor YBK2-80M2-2 has a rated voltage and powder of 380/660 V and 0.75 kW, respectively. The filtration system consists mainly of pleat-type metal mesh filter cartridges fixed with three bolt connections. A single filter cartridge has the following dimensions: 145 mm outer diameter 80 mm inner diameter 600 mm depth, initial filtration accuracy 15 lm, 60 pleats 20 mm deep, and a filtration area of 2.4 m2. The pleat-type structure can significantly increase the filtration area, and the metal mesh filter material has a good flame-retardant and anti-static effect as addition to its role as a support, which can increase the service life of the filter cartridge. There is no dust on the new filter cartridge during the initial operation of the drytype filtration dust collector, but after a few minutes a thin layer of dust cake is formed on the surface of the filter material. This dust cake, which is 0.3–0.5 mm thick, is called the primary dust cake; the dust which is re-deposited on it is secondary dust cake. The main role of the filter material is to form the primary dust cake and support its frame; the function of filtration relies mostly on the primary dust cake [22]. Fig. 3(a) –(c) shows the filter material, in different states, magnified 1000 times under a scanning electron microscope. Fig. 3(a) illustrates that the unused metal mesh filter material looks smooth, without any foreign materials on it; it can be clearly observed that the metal fibers are knitted together and combine tightly, with a fiber gap of at most 15 lm. Fig. 3(b) shows the used
Fig. 1. The dry-type filtration dust collection method.
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Fig. 2. The dry-type filtration dust collection device.
Fig. 3. Scanning electron microscope views of the surface of the filter material under three conditions (a. unused filter material, b. used filter material after one clean, and c. used filter material after thorough cleaning).
metal mesh filter material after once cleaning. Once cleaning means that pulse valve was opened only once when the gas pressure is 0.5 MPa, and then the pressure gas was injected into the filter cartridge, making partial dust on the outer wall of filter cartridge shocked down. As shown in Fig. 3(b), the surface of filter material is covered with dust, and the fiber gaps are filled with dust particles. Fig. 3(c) shows the used metal mesh filter material after thorough cleaning. Thorough cleaning means that pulse valve was opened several times to cleaning until the pressure drop of the filter no longer decreased. There is little dust on the surface of filter material, and the fiber gap has not yet been completely blocked. Large gaps between fibers exist compared with the once cleaning
filter material. The dust removed from the filter material is the secondary dust cake and the residual dust on the surface of filter material is considered the primary dust cake after once cleaning. Thorough cleaning destroyed the primary dust cake and the secondary dust cake. The filtration effect is optimal in terms of filtration precision and resistance after once cleaning. As shown in Fig. 4, the cleaning system includes pulse valves (SMF-Q-20, working pressure 0.3–0.8 MPa), air valves (CM3PM08, working pressure 0–1 MPa), nozzles, injection pipes, an air tank (10 L), and rubber tubes, among others. The injection pipe is made of a seamless pressure tube, and the number of injection holes on it is contingent on the number of filter cartridges. The cleaning
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compressed air source in the tunnel, with rubber pipes 30 mm in diameter, and the extraction fan and electrical motor are connected to high voltage power sources. 3. Performance test of dry-type filtration dust collector 3.1. Experimental apparatus
Fig. 4. The dust cleaning system.
system is an important part of the dry-type filtration dust collector, and there are many academic studies on the cleaning system of the dry-type filtration dust collector. Chi et al. [23] found that the size of the gap between the nozzle and diffuser is important to avoid incomplete cleaning and enhance the cleaning potential for a ceramic filter cartridge. Ju et al. [24] found that an induced nozzle can enhance the pressure distribution inside the cartridge and improve pulse-jet cleaning efficiency. Li et al. [25] improved the dust cleaning effect by placing a cone installation in the filter cartridge. A well designed cleaning system is conducive to improving cleaning efficiency, reducing cleaning frequency, saving energy consumption, and increasing the life of the filter cartridge. Furthermore, a scraper conveyor is arranged at the bottom of the dust collector and each side of the deposition has a dust discharge flat valve. The discharge system uses the scraper conveyor to collect dust and the dust discharge flat valve to discharge dust, which can effectively reduce the height of the device and increase the air-tightness of the dust collector. A dry-type filtration dust collection system used for ventilation and dust suppression in large tunnel construction has been designed following the specifications above. The dust collector is fixed on a trailer platform and its inlet is connected to a 1000 mm long 500 mm wide dust exhaust hood, via an air duct 600 mm in diameter and 6 m long. The extraction fan outlet is connected to an air duct 600 mm in diameter, the length of which can be adjusted according to demand; here it is 5 m long. The air duct is sustained by a convenient moving support. The dry-type filtration dust collector air tube is connected to an existent
A schematic of the test rig, which follows the general technical conditions for mine dust collector of the People’s Republic of China MT 159-2005 [26], is shown in Fig. 5. The experimental apparatus consists of the dry-type filtration dust collector, an extraction fan, a connecting pipe, and other systems. The dry-type filtration dust collector is connected to the extraction fan by an iron air duct that is 2 m long and 600 mm in diameter. The dust collector inlet is connected to the inlet pipe (a 6 m long iron air duct, 600 mm in diameter), and the dust collector outlet is connected to the outlet pipe (a 7.2 m long iron air duct, 600 mm in diameter). In addition, the experimental apparatus includes a u114/1.5 type powder feeder with a range of 0–3.3 kg/min, two L-type sampling tubes, two sampling funnels into which a 40 mm diameter filter membrane can be loaded, four pressure taps which are uniformly distributed in the same cross section, a pitot tube, two LZB-15 type glass flowmeters, a 2XZ-4A type pump with a pumping rate of 14.4 m3/h, a DYM3 type aneroid barometer, an AZ8205 type differential pressure gauge, a ZX-0.1 type mercury thermometer, fly ash (particles less than 80 lm, of which 14% are less than 10 lm and 48% are less than 30 lm), two regulating valves used to adjust the gas flow of the glass flowmeter, a release valve to regulate the quantity of pump, some filter membranes (polypropylene fiber, diameter: 40 mm), and a JJ124BC type electronic analytical balance with a range of 0–120 g. 3.2. Measurement of air volume The extraction fan was opened, and the atmospheric pressure at the experimental site and the temperature in the inlet and outlet of the experimental device were measured with the aneroid barometer and the mercury thermometer, respectively. The ‘‘negative” joint of the differential pressure gauge was connected to the four pressure mouths in the inlet pipe (450 mm away from the inlet) with the rubber tube to measure the static pressure. The ‘‘positive” and ‘‘negative” joints of the differential pressure gauge were connected to the total pressure and static pressure ports, respectively, of the pitot tube; this was then inserted into the hole in the outlet pipe 6 m from the outlet of the extraction fan, to measure the outlet dynamic pressure. The measurements are listed in Table 1. The inlet air volume, outlet air volume, and air leakage rate of the dust collector were calculated with Eqs. (1)–(3) [26] respectively.
Fig. 5. A diagram of the experimental device.
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S. Li et al. / Advanced Powder Technology xxx (2017) xxx–xxx Table 1 Air volumes measured by the dust collector. Parameters
Atmospheric pressure (Pa)
Inlet temperature (°C)
Outlet temperature (°C)
Inlet pipe relative static pressure (Pa)
Outlet pipe dynamic pressure (Pa)
Measured data
99830 – – –
34.5 34.5 34.6 –
36.1 36.2 36.2 –
82.32 83.79 89.67 91.14
94.65 93.22 90.35 91.79
Average data
99830
34.53
36.13
86.73
92.50
q01 ¼ 18:866aed1 2
2
q02 ¼ 18:866d2
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi DPð273:15 þ t 1 Þ=Pa 60
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi DPd ð273:15 þ t2 Þ=Pa 60
x ¼ ðq02 q01 Þ=q01 100
ð1Þ
and the tot c al dust suppression efficiency, can be calculated using Eqs. (4) and (5), respectively.
ð2Þ
c ¼ ðm2 m1 Þ=q 3600=t
ð4Þ
ð3Þ
g ¼ ðc1 c2 Þ=c1 100
ð5Þ
where q01 and q02 (m3/min) are the inlet and outlet air volume, respectively; d1 and d2 (m) are the diameters of the inlet and outlet pipe, respectively; DP (Pa) is the static pressure 0.75 d1 from the inlet; Pa (Pa) is the atmospheric pressure at the experimental site;t 1 and t 2 (°C) are the temperatures in the inlet and outlet of the experimental device, respectively; P d (Pa) is the dynamic pressure 6 m from the outlet of the extraction fan; x (%) is the air leakage rate of the dust collector; and ae is the compound coefficient where a and e are the flow and expansion coefficients, respectively. Here, a tapered inlet manifold was used to measure flow, so ae = 0.96. This method can effectively avoid measurement error when an anemometer is used, and improve the accuracy of the inlet and outlet air volume measurements. According to Table 1 and Eqs. (1)–(3), the inlet air volume, outlet air volume, and air leakage rate of the dust collector are 202.26 m3/min, 218.15 m3/min, and 7.86%, respectively. 3.3. Measurement of dust suppression efficiency Firstly, the extraction fan was opened after blank filter membranes were weighed and put into the sampling funnels. Secondly, the pump was turned on when the system worked at steady state, and adjustments to the control valves and the release valve kept the flow rates of glass flowmeters F1 and F2 constant at 1.2 m3/h, making the gas flow rate of the sampling tube equal to the pipe. Thirdly, the powder feeder was opened and maintained at a feed rate of 240 g/min, and counting began. Finally, the powder feeder, extraction fan, and pump were off simultaneously after 120 s and the filter membranes were weighed again. The dust concentration in the inlet and outlet pipes of the collector were collected simultaneously, eight times, using the filter membrane method. The measurement data are listed in Table 2. The dust concentration in the collector’s inlet and outlet pipes,
In these equations, m1 (mg) is the weight of the blank filter membrane, m2 (mg) is the weight of the filter membrane after dust collection, q (m3/h) is the sampling flow value, t (s) is sampling time, (mg/m3) represents the dust concentration in the pipe, and g represents the dust suppression efficiency. For the sake of convenience, c1 (mg/m3) is chosen to represent the dust concentration in the inlet pipe, and c2 (mg/m3) is the dust concentration in the outlet pipe. This method is more accurate than using a dust testing instrument to measure dust concentration. According to Table 2, Eqs. (4) and (5), the dust suppression efficiency of the dry-type filtration dust collector is 98.41%.
4. Field application and measurements Chaoyang is a large tunnel on a section of the Beijing-Shenyang passenger line in Chaoyang city, Liaoning province, China. The Chaoyang tunnel is 6750 m long with an arched section, which includes two inclined shafts, that is 107 m2 (12.6 m wide and 8.5 m high). The 1# inclined shaft was arranged in the line of DIK 409 + 500 (409.5 km from the tunnel entrance) and is 300 m in length with a longitudinal slope of 9%. The 2# inclined shaft was arranged in the line of DIK 410 + 700 (410.7 km from the tunnel entrance) and is 385 m in length, with a longitudinal slope of 10%. At present, 1150 m of the 2# inclined shaft has been excavated in the direction of Shenyang, with 320 m remaining. Forced ventilation is used in the tunnel; a main forced fan (power: 2 ⁄ 110 kW, air flow: 2850 m3/min) and an auxiliary forced fan (power: 2 ⁄ 110 kW, air flow: 2850 m3/min) are installed at the entrance and approximately 700 m from the exit of the 2# inclined shaft, respectively. There is a 0.5 m clearance between the outlet of the main forced fan air duct (1.5 m in diameter) and the inlet of the auxiliary forced fan air duct (same diameter). Fig. 6 illustrates the layout of
Table 2 Dust measurements from filter membranes in the inlet pipe and outlet pipe. Position Inlet pipe
Before sampling (mg) Measured Data (mg)
Average data (mg) Outlet pipe
Measured data (mg)
Average data (mg)
After sampling (mg)
661.3 663.4 661.8 660.1 661.588
663.7 660.3 662.9 659.2
686.6 692.5 683.7 684.2 684.400
679.2 687.4 675.5 686.1
663.4 661.8 660.6 663.0 661.563
660.1 659.3 662.7 661.6
663.7 662.2 660.8 663.2 661.925
660.4 660.2 663.1 661.8
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Fig. 6. The layout of the dry-type filtration dust collection system on-site at the Chaoyang tunnel.
dry-type filtration dust collection system on-site at the Chaoyang tunnel. The main forced fan pushed fresh air into the tunnel face from the entrance of the 2# inclined shaft. Without the dry-type filtration dust collection system, visibility was low, dust and smoke were diffuse, the recirculating air was serious, and the air flow was slow behind the lining trolley, which seriously endangers workers’ health. Due to the limited space available and the undulating terrain in front of the lining trolley in the Chaoyang tunnel, the dry-type filtration dust collector was placed at the rear of the lining trolley for field application. A series of tests were carried out under three different operation conditions, including tunnel face blasting, lining trolley shotcreting, and tunnel face mucking. The optimum dust suppression efficiency was achieved during lining trolley shotcreting, the validation for which will be shown below. As shown in Fig. 7, the dust concentration fell significantly in the tunnel with the dry-type filtration dust collector, and the visibility behind the lining trolley improved dramatically.
When the dry-type filtration dust collector was turned on during the lining trolley shotcreting operation, the dust exhaust hood was arranged 3 m behind the spraying point and moved with it. A direct-reading dust-measuring instrument (CCZ-1000, Changshu Deyu Mine Mechanical Co., Ltd., China) was used to monitor the concentrations of total and respirable dust. The measuring points were 1 m in front of the dust exhaust hood and at the dust collector outlet, respectively. Both were 1 m above the ground. Measurements were taken three times, each lasting 60 s, at both points. The measurement data for different days are shown in Fig. 8 and indicate that the dust concentration at the position of dust collector outlet can be controlled below 6 mg/m3. Therefore, the equipment ran stably while being used. After using the dust collector, the average concentrations of total dust and respirable dust declined from 285.4 to 5.33 mg/m3 and 237.8 to 5.08 mg/m3, respectively. Using Eq. (5), the efficiency of the dust collector in the field was calculated to be 98.13% and 97.86%, respectively, in terms of total and respirable dust suppression. The field test value of total dust suppression efficiency was lower than the
Fig. 7. Comparisons of tunnel environment before and after using the dry-type filtration dust collector during lining trolley shotcreting (a. before dust is suppressed, b. the field application of the dry-type dust collection system, c. after dust is suppressed with the dry-type filtration dust collector).
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Fig. 8. Dust concentrations after using the dry-type filtration dust collector during lining tunnel shotcreting operations. a–f shows the average values of dust concentration (t. d.: total dust, r.d.: respirable dust) measured on days 1, 5, 10, 15, 20, and 25, respectively.
experimental value of 98.41%. This was mainly because a small amount of dusty gas in the tunnel mixed with the outlet gas during the field application, which increased the value of the outlet dust concentration. To further prove the effectiveness of the dry-type filtration dust collector, it was turned on during the lining trolley shotcreting, and data were taken at points 0–20 m behind the dust collector outlet. The total dust concentration contour line and the dust concentration distribution on the center line behind the dust collector outlet during shotcreting operations are shown in Figs. 9 and 10, respectively. The dust concentration was lowest at the outlet of the dust collector and increased with distance from the outlet. Since the outlet airflow was restricted by the tunnel wall, the contour line
was not completely symmetrical. As seen from Figs. 8–10, the dry-type filtration dust collector can effectively reduce dust concentrations generated by lining trolley shotcreting. As the distance from the outlet increased, the total dust concentration increased gradually from 5.33 mg/m3 and reached 29.56 mg/m3 13 m behind the outlet of the dust collector, then tended to a relatively stable state. Likewise, the respirable dust concentration increased gradually from 5.08 mg/m3 and reached 28.86 mg/m3 14 m behind the outlet of the dust collector, and then maintained a relatively stable state. Based on the above analyses, the concentration of dust suppressed was steady 15 m behind the dust collector; therefore, the dust suppression efficiency 15 m behind the dust collector was
Please cite this article in press as: S. Li et al., Application and research of dry-type filtration dust collection technology in large tunnel construction, Advanced Powder Technology (2017), https://doi.org/10.1016/j.apt.2017.10.003
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Fig. 9. The contour line of total dust concentration behind dust collector outlet during lining tunnel shotcreting operations.
Fig. 10. The distribution of dust concentrations (t.d.: total dust, r.d.: respirable dust) on a center line behind dust collector outlet during lining tunnel shotcreting operations.
taken as that of the dust collection system. That dust concentration was measured for one month under three different operations, including tunnel face blasting, lining trolley shotcreting, and tunnel face mucking. The measurement data and average concentration are shown in Fig. 11. The average concentration of total and respirable dust declined from 314.20 to 48.20 mg/m3 and 286.41 to 46.12 mg/m3, respectively, during tunnel face blasting; from 253.41 to 29.97 mg/m3 and 226.73 to 28.85 mg/m3, respectively, during lining trolley shotcreting; and from 285.91 to 50.32 mg/ m3 and 251.59 to 47.23 mg/m3, respectively, during tunnel face mucking operations. According to Eq. (5), the total rock dust suppression efficiencies of the dry-type filtration dust collection system under tunnel face blasting, lining trolley shotcreting, and tunnel face mucking conditions were 84.66%, 88.17%, and 82.40%, respectively. The respirable rock dust suppression efficiencies were 83.90%, 87.28%, and 81.23%, respectively. The highest dust suppression efficiency was achieved during lining trolley shotcreting followed by tunnel face blasting; the lowest was obtained during tunnel face mucking. This is mainly because the dust exhaust hood was close to the rock dust generation point, and the dusty air was sucked into the dust collector before the rock dust diffused completely. The dust generated in the tunnel face blasting operation had diffused when it reached the dust exhaust hood, so the capacity for air purification was limited. The rock dust settled at the bottom of the tunnel was raised by trucks during tunnel face mucking, which polluted the purification gas; and resulted in the lowest rock dust suppression efficiency. The particle sizes of the rock dust that collected at the bottom of dust collector were measured using a laser particle size analyzer (S 3500, Microtrac Inc., America). The test result is shown in Fig. 12. The rock dust particles were mainly concentrated in 0.818–13.08 lm range; more than 85% was less than 7.07 lm in size, or respirable. The results of the particle size tests were basically in agreement with those from the direct-reading dust-measuring instrument.
Fig. 11. The dust concentration 15 m behind the dust collector in the tunnel during a. tunnel face blasting, b. lining trolley shotcreting, and c. tunnel face mucking.
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References
Fig. 12. Distribution of rock particle sizes at the bottom of dust collector.
5. Conclusion A new method and device have been designed to collect dust from large tunnel construction using a dry-type filtration system. The device is structured like a long box, with filter cartridges, air controlled pulse jet for cleaning and collection of the scraper conveyor. It uses the existing high voltage and compressed air in the tunnel as its source of operating and cleaning power. Experimental test results showed that with the dry-type filtration dust collector, the total rock dust suppression efficiency reached 98.41%, and that the inlet air volume, outlet air volume, and air leakage rate of the dust collector was 202.26 m3/min, 218.15 m3/min, and 7.86%, respectively. The field application in the Chaoyang tunnel indicated that the dry-type filtration dust collector had total and respirable dust suppression efficiencies of 98.13% and 97.86%, respectively; that is, the dry-type filtration dust collector performed well in the field. For lining trolley shotcreting operations, the total dust concentration decreased from 253.41 mg/m3 to 29.97 mg/m3, the respirable dust concentration dropped from 226.73 mg/m3 to 28.85 mg/m3, and the total and respirable dust suppression efficiencies were 84.77% and 83.86%, respectively. The system also reached optimal dust suppression efficiencies in three kinds of tunnel construction operations, and the purification of respirable dust is particularly significant. From these results, it can be inferred that there are wide prospects for the application of dry-type filtration dust collection technology. Acknowledgements This work was supported by the Fundamental Research Funds for the Central Universities [grant number 2014XT02]; the Program for Changjiang Scholars and Innovative Research Team in University [grant number IRT13098]; and the Priority Academic Program Development of Jiangsu Higher Education Institutions.
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Please cite this article in press as: S. Li et al., Application and research of dry-type filtration dust collection technology in large tunnel construction, Advanced Powder Technology (2017), https://doi.org/10.1016/j.apt.2017.10.003