Method of removing Fe particulate matters from subway environments

Transcription

1 International Journal of Environmental onitoring and Analysis 5; 3(): -6 Published online Deember 3, 4 ( doi:.648/j.ijema.53. ISSN: (Print); ISSN: (Online) ethod of removing Fe partiulate matters from subway environments Jong-Hun Par, *, Dushin Par Dept. of Railroad Drive and Control, DongYang Univ., Yeongju, Korea Transportation Environmental Researh Team, Korea Railroad Researh Institute, Uiwang, Korea address: jhpar348@gmail.om (Jong-Hun P.), dspar@rri.re.r (Dushin P.) To ite this artile: Jong-Hun Par, Dushin Par. ethod of Removing Fe Partiulate atters from Subway Environments. International Journal of Environmental onitoring and Analysis. Vol. 3, No., 5, pp. -6. doi:.648/j.ijema.53. Abstrat: In subway environments, partiulate matter is generated ontinuously by abrasion between wheels, rails and brae pads, and through ontat between eletri arlines and the pantograph. Partiulate matter, 6-79% of whih is omposed of iron (Fe), is dispersed throughout subway stations, inluding platforms and waiting rooms, by train drafts. This study proposes a method for removal of Fe partiulates from subway tunnels, whih involves mounting magneti dust olletors underneath operating subway trains. A mathematial model is developed to determine the size of dust olletor needed and the minimum period required to remove all Fe partiulate matter aumulated in subway tunnels. When the model was applied to Seoul etropolitan Subway Line 7, whih has an operational duration of years, it was estimated that up to 3 years would be required to remove aumulated partiulate matter if two olletors were mounted on all subway trains. After removal of aumulated partiulate matter, the overall onentration of partiulate matter in the tunnel was shown to derease by 6.6% when dust olletors were mounted on 5% of subway trains. Keywords: Partiulate atter, Subway, agneti Partile Colletor, Passenger Cabin. Introdution Expansion of subway lines results in greater passenger numbers using underground transit [], and so the issue of air quality management in subways is beoming inreasingly important. As suh, Korean regulations require strit management of subway air quality []. Aeleration, deeleration and steering in subway trains are ontrolled using the fritional fore between the wheels and rails. In this proess, signifiant quantities of partiulate matter are generated through abrasion between wheels, rails and brae pads, and from sparing at the ontat between eletri arlines and the pantograph. Studies have shown that 6-79% of partiulate matter in subway ontains Fe [3]. Partiulate matter generated in subway tunnels is dispersed throughout the tunnels and may be spread to platforms and waiting rooms by strong air irulation urrents. The distribution of partiulate matter is at a maximum within the tunnels, with lower onentrations found on platforms and in waiting rooms. Overall onentrations inrease in proportion to operational frequeny [4]. High partiulate onentrations in tunnels may result in environmental pollution, health onsequenes for passengers and worers, eletrial equipment failure, and premature depreiation of failities. Though subway tunnels ontain ventilation systems in onstant operation and are regularly water leaned, improvements in air quality have been minimal. In the Seoul etro, mounted magnets underneath trains have been installed to lower partiulate matter onentrations [5], however these have shown limited effiay in improving air quality, sine the average diameter of aptured partiulate matter is 5 µmor more. This study proposes a magneti dust olletor that an effetively remove partiulate matter from subway environments. The removal mehanism is presented, and an estimate of the quantity of removed partiulate matter using this method is provided. athematial modeling was undertaen to determine the size of dust olletor needed for a given partile diameter, the number of dust olletor sets required to lower overall partiulate matter onentrations in tunnels, and the time needed for partiulate matter removal.

2 Jong-Hun Par and Dushin Par: ethod of Removing Fe Partiulate atters from Subway Environments. aterials and ethods The magneti flux density due to any magnet used to remove Fe partiulate matter varies with the shape and size of the magnet, and the distane from the magnet. Using a plate magnet with width W, length L and thiness T, magneti flux density (B) at a distane x from the enter of the magnet ay be expressed as below [6]. B B tan π x WL 4x + W + L tan WL ( x + T) 4( x + T) + W + L [T(tesla)] () Where, B magneti strength. The magneti flux density of a.5 T (5, Gauss) plate magnet, with width, length and thiness of 5,, and mm, respetively, equation () an be approximate as shown in equation (). 4 3 B b x + b x + b x + b x b [T] () Where, b.38, b -.55, b , b , b Assuming a gap G between two adjaent plate magnets,partiulate iron found at their midpoint (hg/) will be affeted by the adsorptive power of the magnet, by gravity and by air resistane (inluding that generated by train draft passing between the magnets). The adsorptive fore ( F m ) for partiulate matter is proportional to the square of the magneti flux density and the ross-setional area of the partiulate iron, as shown in equation (3) [7]. F m B A A ross setion area [m ] [N], where µ µ permeability of spae 4π An expression may be obtained for the adsorptive power experiened by Fe partiulate matters found at a height h vertially from the surfae of the magnet. This is given by the average of the square of the magneti flux density, as shown in equation (4). B 7 (3) h 8 7 B dx ah + ah + + a8h + a9 [T] (4) h b b b where a, a,, a8 b4b5, a9 b5 9 4 The fore with whih Fe partiulate mattersare adsorbed to a.5t plate magnet is proportional to the square of the diameter (d) of an Fe partile. Equation (5) shows air resistane as a funtion of partile veloity, for partiulate matter adsorbed under the influene of both the magneti fore and gravity [8]. v partile veloity [m/se] Fa 3 πµ adv [N], where d partile diameter [m] µ a visosity of air.8 Equation (6) gives an expression for the veloity of partiulate matter for the ase in whih adsorptive power and air resistane are in equilibrium. ρ pd 3 B v ± g [m/se], 8µ 4 a dρ pµ 5 where g 9.8m/se We an therefore obtain an expression for the time taen for the partiulate matter loated at a distane hfrom the magnet surfae to be adsorbed, equation (7). h 8µ h 3B a t ± g v ρ d 4d p ρpµ [se] The strength of the train draft delivered underneath the arriage as a train passes through a double-tra tunnel may be estimated at up to 4-6% of train veloity []. The under-arriage train draft generated by two subway trains approahing eah other in opposite diretions at a maximum veloity of 8 m/h may be up to 3.6 m/s []. An expression for the maximum train-draft-indued air resistane experiened by partiulate matter passing underneath a subway train is shown in equation (8). (5) (6) (7) u train veloity [m/se] Fw 3 πµ ad( ζ +.6) u [N], where ζ rate of strength of train draft at train bottom (8) The maximum dispersion distane (x) of partiulate matter experiening train draft while passing through two plate magnets is given by equation (9). The width of the magneti olletor must be larger than this, if all Fe partiulate matters passing through the magnets is to be adsorbed. 9µ ag 3B x vt ( ζ +.6 ) u ± g [m], where G gap between two plate magnets ρ 4d pd ρ pµ (9) Hene, the width of two.5t plate magnets arranged 4 mm apart, underneath a subway train traveling at the maximum veloity of 8 m/h,should be larger than 6.4 mm, as shown in table, if they are to adsorb all Fepartiulate matter with diameter >.5 μm.

3 International Journal of Environmental onitoring and Analysis 5; 3(): -6 3 Table. Trapping time and dispersion distane of partiles between two plate of magnets. Items d. µm d.5 µm d5. µm d µm Remar Trapping time (ms) G4 mm Dispersion distane u8 m/h (mm) Conditions: B.5 T, G4 mm If multiple plate magnets are installed in a dust olletor, the shape of the magneti flux, and hene the partiulate iron olletion apability, varies with the layout of the magneti poles. To inrease iron partile olletion apability, magneti poles should fae eah other to reate parallel magneti flux lines, as shown in figure (a). If the same poles are adjaent to eah other, an opposing flux is formed as shown in figure (b), dereasing Fe partiulate matters olletion apability. inrease when dust olletors are mounted lower. There are a number of advantages to mounting dust olletors at the bottom of the T (trailers) of subway trains, suh as worability and spae seurity, as well as trapping effiieny, as shown in table. Although the pratial size of a dust olletor will depend on the installation loation, multiple plate magnets should be spaed equally suh that the ross-setional area perpendiular to travel diretion is at a maximum within the limits of the train dimensions [9] as shown in figure. (a) Faed with opposite poles (b) Faed with same poles Figure. Changes in magneti flux with pole layout. When the plate magnets in a dust olletor are laid out parallel to the travel diretion of a subway train, the width (W) of the magnet should be seleted to ensure that the strength (B) and spaing (G) satisfy equation (9-), for diameter (d). µ G W vt (.6)u µ > ζ + a [m] (9-) db Table. Qualitative assessment of partile trappingdevie mounting position. Positions Safety Worability Spae Effetiveness Roof x x O Lower O O O Front x O O O: Good, : Normal, x: Bad Partiulate matters in tunnels settles faster than in air due to higher speifi gravity, hene, apture effiieny will 3. Results Figure. Struture of partile trapping devie. Par et al. [] reported that the onentration of partiulate matters in subway tunnels in Seoul etro inreases by 9.8 µg/m 3 for eah subway train operating, regardless of diretion. Assuming that partiulate matters dispersed in tunnels has Fe ontents of 7% [3], we an alulate a orresponding inrease in Fe partiulate matters onentration of 6.35 µg/m 3 for eah subway train passing. This partiulate matters may be divided into partiulates aumulated on the floor and subsequently sattered by train draft, and partiulates generated through frition. If the generation rate for new partiulate matter is γ ( ), the quantity (Q) of partiulate matters generated daily in a tunnel an be obtained using equation (). N number of train operation eah day [times/day] 3 Q Nγδ S [ µ g / m day]where S ross setional area of tunnel [m ] 3 δ Inreased partiulate matters [ µ g/m ] () The operational effiieny of a dust olletor depends on the ratio between the ross-setional areas of the dust olletor and the tunnel; these areas vary aording to the size of the train and tunnel struture. Calulations in this study used a double-tra tunnel with a ross-setional area (S ) of 8.37 m, and subway train with a ross-setional area (S ) of 3.6 m. As the spae between the train body and olletor is limited to mm by the struture of the subway train, the maximum ross-setional area of a dust olletor (S ) will be 3.8 m. When a subway train passes through a tunnel, train draft is generated both in front of the train and opposite to the diretion of travel. To onstrut a mathematial model for dust olletor operation, the ratio between these two soures of train draft was approximated as the ratio between the ross-setional area of the dust olletor and the effetive area (S e, S e S S ), where the 'effetive area' is the ross-setional area of the tunnel minus that of the subway train, as shown in equation (). It was assumed that train drafts and partiulate matter onentrations within the ross-setional area perpendiular to the diretion of travel did not vary with loation. Applying equation () to the ross-setional area of the tunnel, an effetive adsorptive area for the dust olletor of 4.45% was alulated.

4 4 Jong-Hun Par and Dushin Par: ethod of Removing Fe Partiulate atters from Subway Environments α S S e S S S 4.45% () If N represents the total number of daily subway train operations, is the number of daily operations with dust olletors mounted, and is the partiulate matter onentration in the tunnel, then a quantity S of Fe partiulate matter is removed, and NδS / ( where ) is generated per unit distane, eah time a subway train with dust olletors mounted is operated. Therefore, the hange in partiulate matter onentration in the tunnel for operational events of trains mounted with dust olletors an be expressed by equation (). S S S + NδS / [µg/m] N + δ [µ µg/m 3 ] () α S S where,,,, initial onentration of iron partile matters Assuming the existene of undeposited partiulate matter floating in the tunnel, an overall redution in partiulate matter onentration requires that the olletor operation rate (i.e., / N ) satisfies equation (3). < δs > N S Equation (4) alulates the sensitivity of partiulate matter onentration in the tunnel to hanges in the ross-setional area of the dust olletor, using Equation (). Sine the partiulate matter onentration in the tunnel inreases with olletor operation rate (i.e., / N ) and dereases with the rosssetional area ratio (i.e., S / S ), the rate of operation and the ross-setional area of the dust olletor must be higher than the ritial values if partiulate matter removal effiieny is to be inreased. N + δ + ( ) ( ) (3) (4) The ross-setional setional area of the dust olletor an be effetively enlarged by mounting two dust olletors with suffiient spae between. Assuming that air passing through a dust olletor installed at the front of a train is mixed with the air in the tunnel suh that partiulate mattersare uniformly distributed in the tunnel, installing two dust olletors on one train should have a similar effet to operating two trains eah installed with a single dust olletor, as shown in equation (5). S S S S + NδS / N 3 + δ [µg/m ] (5) Assuming that partiulate matters generated by a moving train is not disharged outside the tunnel but remains inside, the maximum time required to remove the partiulate matters aumulated in a tunnel using dust olletors an be obtained by dividing the total aumulated amount in the tunnel by the removal amount per day as shown in equation (6). QH D S NδS Where, D no.of days the aumulated Ps are removed H subway operation period[day] With two dust olletors installed with suffiient spaing, the time taen to remove partiulate matters in the tunnel dereases to /(+) ompared with one dust olletor, as shown in equation (7). QH D ( + ) S NδS γh S ( + ) NδS [µg/m] Assuming a generation rate (γ) of Fe partiulate matters in the Seoul etro of %, for an operational duration of years, not all partiulate matters aumulated in the tunnel will be removed even with a dust olletor of ross-setional area ratio 4% mounted on all trains. However, if two 4% dust olletors are mounted on all subway trains with suffiient spae between, all partiulate matter an be removed within 96 days. γh S NδS [day], (6) [day] (7) Table 3. Removal period of Fe partiulate matters from tunnels (unit: day). Figure 3. Sensitivity of partiulate matters onentration to hanges in S S. S /S Dust olletor ( set) Dust olletor ( sets).n.5n N.N.5N N 3%,674 4% 96 5% 6,739 6, %,469, %,333, % 93,5 75 9% 6, % 4, Conditions: 3.6 µg/m 3, δ6.35 µg/m 3, γ%

5 International Journal of Environmental onitoring and Analysis 5; 3(): -6 5 Sine not all aumulated Fepartiulate matters will be floated by train drafts after aumulated in the tunnel is removed, the onentration of partiulate matters in the tunnel will inrease by γδ eah time a subway train operates. Therefore, partiulate matter onentrations in a tunnel an be obtained by equation (8), by again onsidering the number of operations of subway trains mounted with dust olletors. N 3 + γδ [µg/m ], (8) Where,,,,,. The number of dust olletors may be redued after partiulate matters aumulated in the tunnel is removed as long as equation (9) is satisfied. γδs < > (9) N S In this ase, the partiulate matter onentrations in a tunnel dereases to equation () with inreasing number of operation days of subway trains mounted with dust olletors. As a result, partiulate matter onentrations in the entire tunnel will derease to f. f N S γδ () S One all aumulated Fe partiulate matters are removed from the subways in Seoul etro, the onentration of Fepartiulate matters in tunnels will derease from 3.6 µg/m 3 to 5.9 µg/m 3,even when all subway trains are mounted with only one dust olletor with a 4% ross-setional area. This amounts to a 6.6% redution in partiulates in tunnels. If a dust olletor is installed on 5% of all subway trains, Fe partiulate matters will derease from 3.6 µg/m 3 to 3.8 µg/m 3, a 53.% redution in partiulates in tunnels. Table 4. Changes in partiulate matter onentrations in tunnelsusing dust olletorsafter all aumulated partiulate matters are removed. Items Conentration of Fe partiulate matter in tunnels Conentration of partiulate matter in tunnels /N S/S Initial Final Redution Rate Initial Final Redution Rate % 4% % % 8% % % 5% 4% % % 8% % % 4. Conlusion Partiulate matter is being generated ontinuously in subway tunnels through abrasion between wheels, rails and brae diss as well as from spars generated during ontat between eletri arlines and the pantograph during subway operation. Sine high onentrations of partiulate matter in tunnels are dispersed by train drafts throughout the underground spae, partiulate matter generated in tunnels is the main soure of partiulates in the subway environment. Highdensity Fe partiles are rapidly deposited and thus aumulate in tunnels as subway train operation inreases. Partiulate matter aumulated in tunnels not only pollutes the subway environment but also results in malfuntion and shortened life span of the eletroni devies used to ontrol trains and equipment. It is therefore vitally important to remove partiulate matter to improve air quality in underground stations. This study proposed a method for effiient removal of partiulate matter in tunnels, involving magneti dust olletors mounted underneath operating subway trains. A mathematial model was presented to determine the design and operation of these dust olletors. For a dust olletor to effetively adsorb and remove partiulate matter floating in tunnels, it should be designed so that the magnet width in the dust olletor is greater than the dispersion distane of partiulate matter due to train drafts. For a dust olletor mounted underneath a subway train moving at a maximum veloity of 8 m/h, the width of the magnet must be at least 6.4 mm if all partiulate matter of.5 µm diameter or larger is to be adsorbed. It is reommended that magneti dust olletors be installed underneath subway trains. The removal period for partiulate matter urrently aumulated in tunnels may be redued by installing two dust olletors with the maximum spae between them on all operating subway trains. After the partiulate matter aumulated in tunnels is removed, it is expeted that the overall onentration of partiulate matter in tunnels an be redued by 53.% (75.9% of Fe partiulate matter), even when dust olletors are installed on only 5% of all subway trains. Anowledgements The wor desribed in this paper was supported by researh grants on the Railway Tehnology Researh Projet by inister of Land, Infrastruture and Transport (4RTRP-B849-). Referenes [] Seoul City Government, The status of publi transport, aessed on Aug. 6, 4. [] Korea Government, Indoor Air Quality Control in Publi Use Failities, et. At, aessed on Aug. 6, 4.

6 6 Jong-Hun Par and Dushin Par: ethod of Removing Fe Partiulate atters from Subway Environments [3] S.N. Kang, H.J. Hwang el al, Chemial Compositions of Subway Partiles in Seoul, Korea Determined by a Quantitative Single Partile Analysis, Environ. Si. Tehnol., 8, 4 (4), pp [4] J.H. Par, J.C. Par, S.J. Eum, The Estimation of the Diffusion Diretion and Veloity of P in a Subway Station - For the Gaehwasan Station of Subway Line 5 in Seoul, J. Korean Soiety of Transportation Researh,, 9(3), pp [5] Seoul etropolitan Rapid Transit Corporation, Green Car 3 guys will shoulder the responsibility of SRT's tunnels, appeared at the 34th Seoul Affiliated Organization Conferene for best praties of ustomer satisfation and innovative management,. [6] Ahieved at [7] Ahieved at [8] Sott A. Shearer and Jeremy R. Hudson, Fluid ehanis: Stoes Law and Visosity, easurement Laboratory No. 3. [9] Y.B. Choo, Y.O. oon, el al, The disussion of the standard ross-setion of the railway tunnel, YOOSHIN Tehnology Newsletter,, pp [] J.Y. Kim, K.Y. Kim, Experimental and numerial analyses of train-indued unsteady tunnel flow in subway, Tunnelling and Underground Spae Tehnology, 7, (), [] S.D. Kim, J.H. Song, H.G. Lee (4): The Estimation of train-indued wind by Train Operation in Subway Tunnel, Air Conditioning and Refrigeration Engineering Dissertation, 6, [] J.H. Par, H.Y. Woo, J.C. Par, ajor Fators Affeting the Aerosol artiulate Conentration in the Underground Stations, Indoor and Built Environment, 4, 3(5), pp