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TfNH TOAN KHUfcH TAN BUI THEO MO HINH GAUSS CO K^ D^N VAN T6C ROI COA HAT BUI ThS Nguyen Huy Tie''''n Vipn Khoa hgc va Ky thuat Mdi tmdng Trudng Dal hge XSy dung Tdm tat Hidn nay md hinh Gauss dugc sU du[.]
TfNH TOAN KHUfcH TAN BUI THEO MO HINH GAUSS CO K^ D^N VAN T C ROI COA HAT BUI ThS Nguyen Huy Tie'n Vipn Khoa hgc va Ky thuat Mdi tmdng Trudng Dal hge XSy dung Tdm tat: Hidn md hinh Gauss dugc sU dung kha biin di tinh toSn du bSo d nhiim cdng tSe dSnh giS va du bSo d nhidm mdi trudng khdng Vdi md hinh Gauss, tinb toSn ed nhan mpt sd gia thiit gin dung, dd cd gia thiit IS chit d nhidm khdng ling dgng quS trinh khuich tan Thuc ti, trgng lugng ciia bui Idn hgn rat nhiiu so vdi chat khi, vSy sd xiy hidn tugng ling dgng bui quS trinh khuich tSn BSi bao gidi thidu phuong phSp tinh lan toi ehit d nhiem cd ki din su ling dgng eiia bui quS trinh lan truyin khdng khi, ding thdi tinh toSn so sanh su khSc bidt vi phSn bd ndng dp bui kbi khing ki de'n va ed ki din vpn td'c rai cua bui quS trinh khuich tSn khdng Summary: Currently, Gausses model is used commonly to calculate and predict pollution in assessment of air environment Gausses model, when calculating is based on some assumptions, in which the pollutants are not deposited during their dispersion Actually, gravity of particulate matter is so larger than gases Hence, they are setting down while transferring into atmosphere This paper gives out air pollution dispersion method, which mentions to depositing of particulate matters during transfer Simultaneously, calculation and comparison the difference of particulate matter ambient concentrations between two options: mention or not mention to deposition of the dusts I.OATVANDE o i du bdo d nhiem mdi trUdng cdc ngudn diem cao gdy dd'i vdi mdi trudng khdng xung quanh, cdng tac ddnh gid tde ddng mdi trudng ngUdi ta thudng sd dyng cac md hinh d i tinh todn Mdt nhOmg md hinh dupe sd dung kha phd bien hidn la md hinh Gauss Theo md hinh Gauss, ndng dp C cua chd't d nhiem tai toa dp x, y, z bat ky khdng gian dugc xde djnh nhu sau: ^(x V z) = -^r-^ ( e x p - ^ ) ^ exp ixy.z; 2r7'ua,Oz 2oJ I Trong dP: -(H-Z)^ 2a + exp -(H + Z)2 2a mg/m^ (1) C,,,.,, - ndng dp chit d nhiem tai diim cd tog dp x, y, z, mg/m^; y - khoang edeh tir diim tinh todn trdn mdt ngang din tmc vet khdi, m; z - chiiu cao diim tinh todn, m; TAP CH( KHOA HOC C0NGNGH$XAY DUNG sd3/2008 63 M - tai lupng P nhiim eda ngudn thai, mg/s; u - tdc dp gio trung binh, m/s; Oy, Oj - he sd khuich tan cda chat o nhiem quyen theo phUOng y v^ theo phuong z, m; H - chiiu eao hieu qua cua dng khdi, m Md hinh thudng dupe dp dyng de tinh toan khuech tdn chd't d nhiim Id hoac bui mdi trudng khdng Khi tinh eho byi, ngudi ta da ngim hieu ring day Id byi kich thudc hat rit be, d dang Id Idng vTnh vien khdng vd ed dp khuich tan gidng nhu chit Thue t i hat byi khdng gidng nhu ede chat khi, byi ed khdi lupng ridng Idn hon rat nhiiu (lii hang trdm tdi hang nghin lin) so vdi ede chit khi, vdy bui co van tdc roi tuong ddi Idn, qua trinh lan tmyin, van tde ndy se anh hudng tdi su phdn bd ndng dp eda byi khdng SU L A N G OQNG C O A BUI KHI LAN TRUYEN TRONG KHONG KHi Trong qua trnh khuich tan khdng khi, su ling dpng eda eae hat byi phy thuoc nhiiu vdo kieh thude cda hat byi Vdi cdc hat byi cd kieh thudc > 20 (jm ed van tde roi Idn, se nhanh chdng ling dpng xudng mdt dit theo ehiiu gid thdi Oe ke de'n sy ling dpng qua trinh lan truyen eda byi, Bosanquet vd cdng sy [1] da nghidn edu ly thuyet phuong phdp xdc djnh lupng ling dpng trung binh cda byi, dd ed tinh d i n van tde rdi eda byi diiu kidn thdi tiit ed gid Cudng dd ling dpng trung binh eda hat byi trdn gde cung 45° d eudi hUdng gid dupe xdc djnh nhusau: G - ^ ^ HY U - ^ ' ^ Trong dd: ^f^f^ pu e-^ g/m^s (2) [px! M^ - tai lupng phat thai eua byi, g/s; a - ty Id thdi gian cd gid nim gde cung 45° v i cudi hudng gid; p - he sd khuich tan ddng cda Bosanquet, cd the nhdn p = 0,05; V, - van td'c rOi tu tdi han cda hat byi, m/s; r(1+ v,ypu) - hdm sd gamma r cda dai lupng 1+ v/pu; H - ehiiu eao hieu qua cua dng khdi, m; X - khoang each td ngudn thai tdi diim tinh toan, m Cudng dp ling dpng tren tryc ngudn dupc xde djnh nhu sau: 0-=-^^^^ HY + ^ ^ { ^ f e-^ g/m^.s (3) pu LPXJ Qua edng thdc (2) va (3) cho tha'y vdi cudng dp ling cua byi phy thude vao van tdc roi (v,) tde Id phy thudc vdo dudng kinh (5) va khdi lupng don vi (p) cua hat byi Byi ed 8, p cdng Idn thi eudng dp ling cang cao Do ed van td'c roi eda hat byi, se lam giam dp ndng eda ludng khdi (byi), tde la se lam giam ehiiu cao hidu qua (H) cua ngudn thai vd se cd qua trinh "tach bui" khdi ludng khdi, dd ehinh Id lupng bui ling dpng 64 TAP CHf KHOA HOC C N G N G H X A Y DUNG Sd3/2008 TiNH TOAN KHUECH TAN BUI THEO MO HJNH GAUSS CO KE DEN VAN TOC ROI CUA HAT BUI Theo md hinh Gauss khdng cd sU phan xa cua mdt dd't ddi vdi ludng khdi, mdt dd't hip thy ehit o nhiem, ndng dp chat d nhiim xdc dinh nhU sau: M '(x y.z) -(exp-iy)exp ^y"Z -(H-Z)^ 2o mg/m^ (4) o i dp dyng md hinh Gauss tinh toan khuech tan byi cd ke d i n van tdc roi eda hat bui ta phai hidu chinh: - Oai lupng H md hinh Gauss se dupc hidu chinh bing cdch trd di doan dUdng md hat byi roi dupe khoang thdi gian T Ooan dudng roi cda hat byi se la V,.T md T = X/U (xkhoang each theo true gid tinh td ngudn, u - van tde gid) - Vd tai lupng M Id tai lupng cua cd hat bui dang xem xet, dupc ky hieu Id M,, - Bui ling dpng se bi h i p thy hodn todn bdi mdt dat Khi cong thdc (4) se trd thdnh: C(x y z) =:; ^(exp-i5-)exp ("y.z) 2rTuao, 2o ("-Ơ)ã 2o mg/m-' (5) o i tinh toan dupe theo cdng thdc trdn thi phai biit dp phan c i p cda byi, tdc Id ty Id theo khdi lupng cac loai cd hat eda byi phdt thai vd van tde roi cda hat byi Phdn c i p cda hgt bui theo kich thude thudc vdo loai byi phdt thai.Theo tdi lidu cda Nga thi thudng ngUdi ta phdn chia byi theo c i p cd hat: < 5; 5^10; 10-^20; 20+40; 40-=-60 vd > 60 nm Khi tinh todn mdi cd hat phai lay mdt trj sd dudng kinh trung binh de tinh toan Vdi byi xi mdng, phdn e i p cac cd hat theo cd'p ndu trdn theo khdi lupng nhu sau (ty Id theo sd thdp phdn): 0,37; 0,18; 0,08; 0,06; 0,12; 0,19 vd khdi lupng don vj eda byi xi mdng Id p6= 2840 kg/m^ Tai lupng theo cd hat dupc xdc djnh nhu sau: Mb = ms X M Trong dd: M^ - tai IUpng byi theo c3 hat kich thudc 5, mg/s; ms- ty Id phdn eip cd hgt bui theo khdi lupng; M - tai lupng tdng cdng cda byi, mg/s Van tde rdi cda hat bui dUdc xde djnh theo djnh ludt Stokes [4] nhu sau: p»g5' m/s (6) 18M Trong dd: Pb - khdi lupng ddn vj eua bui, kg/m^ g - gia tde trpng trudng, m/s^; - dudng kinh hat byi, m; \i - hd sd nhdt ddng lue, Pa.s TAP CHI KHOA HOC C O N G N G H $ XAY DUNG SO 3/2008 65 ANH HUdNG CUA VAN TOC ROI TCJl SU PHAN BO NONG DO BUI KHI TINH T O A N THEO MO HJNH GAUSS Oe thay sU khdc biet gida vide xae djnh phdn bd ndng dp bui khdng ke d i n van tde roi theo edng thdc (1) vd cd ke d i n van td'c roi theo cdng thdc (4) theo mo hinh Gauss Xet vi du tinh todn sau day: Vidul: Tinh todn ndng dp byi dng khdi nha may xi mdng gdy tren mdt dd't, dpc theo tryc gid di qua ehan dng khdi, xuoi theo chiiu gid each chdn d'ng khdi khoang Id 2km Khi biit chieu eao hidu qua dng khdi: H = 120 m; tai lupng byi M = 1298.10' mg/s; van tde gid Id m/s; he sd khuich tanCT,= 300m;CT^= 350m; dp nhdt dpng lUc eda khdng n =1,85.10"^ Pa.s; bui xi mdng phan eip cdc ed hat theo khdi lupng nhu sau (ty Id theo sd thdp phan): m