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TIU CHUN VIT NAM

TCVN 5968 : 1995

ISO 4219: 1979

CHT LNG KHNG KH - XC NH CC HP CHT KH CA LU HUNH TRONG KHNG KH

XUNG QUANH - THIT B LY MUAir quality - Determination of gaseous sulphur compounds in ambient air - sampling equipment

Gii thiu

xc nh cc hp cht kh ca lu hunh trong khng kh xung quanh th bc u tin l phi thumu kh v cho hp th cc hp phn cn xc nh vo mt mi trng lng thch hp. Cc mi trnghp th v mt vi iu kin ly mu c th thay i ty theo phng php. Tiu chun ny quy nh ccchi tit cn thit ca thit b, do khng cn m t thit b mt cch k lng trong tng tiu chun nnglin quan n phng php xc nh cc hp cht kh ca lu hunh na. Phng php ly mu ctrnh by trong TCVN 5969: 1995 (ISO 4220: 1983) v TCVN 5978: 1995 (ISO 4221: 1983).

1. Phm vi p dng

Tiu chun ny quy nh nhng yu cu chung v thit b ly mu khng kh xung quanh xc nh cchp cht kh ca lu hunh, c bit l lu hunh dioxit (SO2)

Tiu chun ny c p dng cho vic ly mu khng kh xung quanh xc nh SO2 v cc hp chtkhi khc ca lu hunh nh nh ngha trong iu 3

2. Tiu chun trch dn

Tiu chun ny p dng cng vi cc tiu chun sau:

- TCVN 5969: 1995 (ISO 4220) - Cht lng khng kh - Xc nh ch s nhim khng kh bi cc khaxit - Phng php chun pht hin im cui vi cc cht ch th mu hoc bng do in th.

- TCVN 5978: 1995 (ISO 4221) - Cht lng khng kh - Xc nh nng khi lng ca SO2 trongkhng kh xung quanh - Phng php so mu dng Thorin.

Nhng tiu chun ny m t nhng chi tit b sung lin quan n thit b ly mu, dung dch hp th vquy trnh ly mu.

Thit b ly mu c m t cng c th p dng ly mu xc nh cc hp cht khc.

3. nh ngha

Cc hp cht kh ca lu hunh: SO2 cc hp cht kh khc ca lu hunh v cc kh axit ha tan ctrong nc v c xc nh theo phng php ca TCVN 5969: 1995.

4. Nguyn tc

Ht khng kh qua bnh hp th by cc hp cht kh ca lu hunh. Trong nhng iu kin nht nh(c ni r trong mt tiu chun ph hp) cn phi lc khng kh loi bi khi gy cn tr.

5. Thit b

V cc hp cht kh ca lu hunh rt d phn ng nn tt c cc b phn ca thit b ly mu tip xc

vi khng kh cha cc hp cht ny phi c lm bng vt liu thch hp. Nhng vt liu ny khnghp th bt k mt hp phn no cn xc nh v khng phn ng vi chng sinh ra cc sn phm cth nh hng n s xc nh tip theo hoc lm gim nng cc thnh phn kh.

Thit b bao gm cc b phn ch yu sau y:

- u ht kh;

- ng ni;

- B lc bi v gi ;

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- Bnh hp th:

- B lc bo v;

- Bm ly mu.

- ng h o kh hoc b iu chnh dng kh; mi b phn c m t trong cc mc t 5 1 n 5.7.

S lp t mt h thng in hnh ch r trn hnh l.

5.1. u ht kh

Tiu chun ny ch lin quan n vic xc nh cc hp cht kh ca lu hunh nn u ht kh khngcn c kt cu c bit ca u ht kh. Nhng nu u ht kh c th b tip xc vi ma th dng mtci phu ln ngc bo v nh trong hnh 2.

Nu c nh tin hnh nhng xc nh khc, chng hn xc nh nng d khi en vi cng thit b(xem iu 2) th khng kh phi c ht qua u ht c ng knh ph hp.

5.2. ng ni

5.2.1. Kch thc

ng knh trong ca ng phi t 6 n 8mm v mt trong ca ng phi trn tru.

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5.2.2. Vt liu

Cng vi vo yu cu chung i vi vt liu, cc cht do c dng phi trnh c hot tnh quangha v tt hn nn ph bng vt liu c dn nhit thp.

Ton ng ng phi kn kht. Nn nh k ra sch ng ng. C th s dng cc vt liu sau ytheo th t gim dn tnh hiu qu.

a) Polytetrafloretylene (PTFE): Mc d tr v ha hc nhng PTFE khng do v kh ghp ni. Vicghp ni vi PTFE c th lm c khi dng cc u ni c sn bng PTFE. Cng v PTFE cng do vykhng nn dng PTFE lm ng dn ca bnh hp th. Vi cao su chu chn khng l vt liu c dngv n mm, kn v khng nh hng n mu v cc thnh phn quan tm c kh b;

b) Thy tinh. Thy tinh dn, nn ghp ni cc b phn th dng ng bng PVC mm;

c) Polypropylene (polyetelene).

Cc cht dng ra sch ng ni phi khng c lu hunh.

5.3. B lc bi

Lp rp phi kn v vy mt dng c kp gi ph hp cn c s dng cng vi mt m hnh khuyn.Khi c ht ln qua ci lc.

5.3.1. Vt liu lcVt liu lc phi tr ha hc vi cc hp cht ca lu hunh v khng ht m. Ci lc c hiu qu cao(99% ) i vi cc ht ln hn 0,3Pm.

Nu ci lc c s dng n gin l ch loi bi (n gy tr ngi vi phng php phn tch) th cilc thch hp l mt lp bng si polystylene. Ci lc ny c hiu q cao gim p sut thp v vt liutr. Cng c th s dng cc loi ci lc tr khc

Khng nn dng vt liu lc bng si thy tnh v n rt d phn ng.

Ch thch: Trong iu kin m cao, ci lc bi c th b m v do hp th mt vi hp cht calu hunh t khng kh i qua n. Lc cn phi ghi ch trong bo co phn tch. Vic lm nng ci lctrong iu kin nh vy l khng nn v c th xy ra cc phn ng ph.

Song trong mt vi iu kin kh hu cng cn m ci lc n trn im sng.

5.3.2. Gi

Gi ci lc phi c lm t vt liu tr, v d bng PVC

5.4. Bnh hp th

C cu ca bnh hp th trong ng dung dch hp th ph thuc vo php phn tch s p dng vvo tc dng ly mu. Cn tham kho tiu chun ph hp

5.5. B lc bo v

Nu cht hp th lng c s dng th c th phi t mt ci by gia bnh hp th v ng h o kh(hoc b iu chnh dng kh) bo v nhng thit b khi b h hi do nhng git dung dch hp th v(hoc) cc kh c hi gy ra. Cu to ca ci by khng hn nh, min l khng kh khng c php ltvo h thng qua k h (thng l khi ht nh).

5.6. ng h o kh hoc b iu chnh dng kh.

tnh nng ng phi bit th tch khng kh c ly. Th tch c o nht bng phng phptch phn, chng hn bng cch dng ng h o kh bng. N c th ghi th tch khi c ly mt cchchnh xc tc dng ang c s dng. C th dng h thng iu chnh dng bng cch s dngmt l6 iu tit. Dng s c kim tra lc bt u v lc kt thc thi gian ly mu u ht kh bngmt thit b nh mt ng h o dng c b mt thay i m bo rng tc dng khng thay i dol b bt mt phn.

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Vic hiu chun nhng ng h hoc nhng l ny c th c tin hnh bng cch so snh vi mtng h o kh t phng th nghim, ng h ny chnh n phi c hiu chun trc trong vng 2nm.

5.7. Bm ly mu

Thit b thch hp nht ly mu l mt bm kh c dng khng i.

Kiu bm nn chn theo tc dng kh nh trc v thc t rt kh iu chnh tc dng ca bmbng cch bin i in th. Nu bm khng c t sau ng h o kh th n phi tht kn.

6. Lp t

Cn lp t thit b trong mi trng sao cho thit b khng b tip xc vi nhit qu cao hoc quthp, hoc trc tip vi nh nng mt tri trong thi gian di. Sp xp u ht kh (5.l) sao cho xa michng ngi k c thit b ly mu, t nht l lm v cao hn 3m trn vng rng c b mt bng phng.ng ni hoc phu phi hng thng xung di.

Phi cn thn trnh t u ht kh nhng ni gn ngun nhim nh ng khi thp hoc l

Ch thch: Chn v tr c nng i din cho mt vng a l, s im cn thit bao trm vng nh s v i tng ca cc tiu chun khc.

Sp xp ng ni (5.2) sao cho khng c nhng ch vng cun trong nc c th tch gp li v khngc nhng ch cong vi bn knh nh hn 50mm. iu ny c bit quan trng nu ch s khi en cngc xc nh trn cng thit b.

di tng ca ng ni gia u ht kh v bnh hp th (5.4) nn cng ngn cng tt v trong mitrng hp phi nh hn 6m.

Phi kim tra kn ca tt c cc mi ni gia cc b phn ca thit b.