Chương 3 Thiết kế hệ thống đường ống.pdf

8/11/2019 Chng 3 Thit k h thng ng ng.pdf

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Chng 3Thit k h thng ng ng

3.1 ng hc dng chy v h s ma st- Ch ca dng chy c c trng bi chun s

Reynol:

Trong :Q-lu lng th tch (gpm); W-lu lng khi lng(lb/h); d-ng knh trong ca ng (in); - khi lngring (lb/ft3); - nht (cp) NRe 2000: dng chy tng 2000 NRe 4000: dng chy qu 4000 NRe: dng chy ri

Chuyn i n v:(1Pa=1,45.10-4

Psi; 1kg=2,2lb; 1m=3,28ft; 1m3

=264,17g)


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- Hsma st (Friction factor) giadng mi chtvthnh ng ph thuc vo ch ng ca dng chy,

chtlngbmtthnhng


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3.2 ng lc hc dng chy

-Phng trnh Euler

-Phng trnh Bernoulli


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- Tn thtnng lnghL trong phng trnh BernoullicDarcy nghin cuv tnh ton theo cng thc

Trong :

K=f.L/D: hstnthtnnglng v (m/s): vntccami chttrongng

g (m2/s): gia tctrngtrng

f : hsma st giami chtv thnhng L (m): chiudi cang

D =d/12 (m): ngknh thylccang


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- Tn tht nng lng trn quy i ra tn tht p sutP (psi)

- Thay D=d/12; v=0,408.(Q/d2) vo biu thc trnnhn c

- Khi tnh cho L=100 (ft) chiu di

- Thay =62,37.S (62,37 lb/ft3 l khi lng ring canc 600F) s c


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- ivikh v hitnthtp sutctnh

- Nh vy tn tht nng lng trn ngngc chiudi L (ft)

- Tnthtnnglngcadng chykhi qua cc

ph kin ng ng c quy i tngngtheo chiudi (ft) sccho trong ccstay


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- V d: Tnh tn tht p sut ca h thng ng ngc ng knh danh ngha (NPS) l 6, P100=1,02 psi


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3.3 Thit k h thng ng ng3.3.1 Vn tc mi cht trong ng

- Khi mi chtvnchuyntrong ngng,do c tnthtnnglngnn gy ra sgimp cami cht,sgimp ny c gi trtngicao nhngimc tr lc ln: ca vo ngnght, van, chuynhng,chia dng

- Khi mi chttrongnggntrngthi bo ha , sgimp c thgy ra hintngmi chtlngbsi(ha hi) trong ng. khc ph hin tng nyngi ta a ra vn tc cho php ca mi cht itrongng


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3.3.2 Thitkhthngngng

Hthngngngthngcphn lm 2 loi:

- H thng ngng di: l>>d, tn tht cc b rtnh so vi tn thtdcngnn b qua tn thtccb.

- Hthngngngngn: phitnh thm tnthtccb

- Thit k h thng ngng l i tm Q, H, di cncung cp cho h thng ngng khi bit ccthng scc imtiu thnh: Hi ,Qi , Li


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3.2.1 Thitkngngdi- Bi ton thitktrn scgiiquyttheo 3 bc

sau: Bc1: chnngngcbnl ngngvn

ti nng lng ca mi cht ln nht (thng lc Q lnnht hocl di nht)

Bc 2: tnh ton thy lc (tnh ng knh vtn tht ca cc onng) cho ngng chn

Bc3: Kimtra trn ngngnhnh, xem vi

nng lng tnh c ti cho mtngnhnhhay khng? Nukhng phitnh li.

- Kh c cH v Q ta stm ccng sutcabmcnthit.


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- Cn c vo thi trn, tm c vn tc thch hpcho dng mi chtstnh cngknh trong ca

nght cabmly tm

d =(0,408.Q/v)0,5 (in)

- Khi c ngknhngstnh cNRe, tra bngtm

chsma st f, ttnh cP100- Tra bng tm tnp ccbqua cc phkin trn

ngnght ttnh ctnp ton phntrnton bngnght cabmP (psi)


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- Tnh NPSHa:

NPSHa= patm/ - heP/ - pv/

Trong :patm: l p suttrn mtthonghe : chiucao cabmso vimtthong (nhngitrdngkhi bmtcao hnmtthong)

pv: p sutbo ha cami chtnhitlm vic: trnglngring cami cht

- Tra thtm NPSHr cabm

- Kim tra iu kin xm thc: NPSHa>NPSHr, nukhng c thong mn th phi chn li v tr tbm.


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V d:

Hy xc nhkch ngknh v trlccanght

bmly tm.Mi chtl dunngLulngduQ=900 gpmH s S=0,88 (khi lng

ring tngicaduso vinc600F)Khi lng ring ca du=55 lb/ft3nht: =0,6 CphL =18 in


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3.4 Tnh chiudy cang

3.4.1 GiithiuvASME B31

- ASME B31 (American Society of Mechanical Engineers)yl blutcaMdng cho thitkhthngng

ngv cc thitbp lc. ASME B31 bao gmcc phn

B31.1, Power Piping: lut thit k cho h thng

ngngtrong cc nh my in,mi chtl nc,hinclm vicp sutv nhitcao, ngoi racn p dng cho h thng ngng cung cp vphn phihi.

B31.3 process piping: lutthitkcp dngrngri cho h thng ngng trong nh my lc hadu,nh my ha cht,nh my dcphm


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B31.9 building services piping: lut p dng chohthngngngtrong xy dngdn dngv

cng nghip B31.11 slurry transportation piping systems: lut

p dng cho h thng ngng dng vn

chuynhuynph, bn, dng nhiutrong ngnhcng nghipkhai thc m.


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3.4.2 ng sut trong ng

Khi hthngngnghotngsxuthinngsuttrong ng, ty thuc vo ti trng gy ra ng sut mASME chia thnh hai loi:

- ng sut to bi cc ti trng: p sut trong hoc ngoing,trng lngbnthn ngv mi cht,titrnggi,

titrngdo ngt- ngsuttobisgin nnhitcangng

- Ti trng chnh dng tnh ton chiu dy ngngthng l p sut bn trong. Chiu dy ng sau khi tnh

ton theo titrngchnh sckimnghimli.- ngsutcho php cavtliuphthucvo loivtliu

v nhitlm viccangngscquy nhtytheo cc mccaASME B31


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3.4.3 Cng thc tnh chiu dy ng chu p sut trong

Trong :

tm : chiu dy nh nht ca ng(in)P: p sut trong ng (psi)D0: ng knh ngoi ca ng (in)S: ng sut cho php ca vt liu

(psi)E: h s nh hng ca mi hntra theo bng A-1A, A-1BY: h s ph thuc vo nhit lm vic v vt liu lm ng

A: h s chng n mn, mi mnng ngF: h s, thng ly F=0,5


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- Tc n mn (Corrosion) ca thp cc bon trongmi trng nc ph thuc vo nng oxy v

nhitmi trngcbiudintheo th


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3.4.4 Cc bc xc nh kch thc ng danh ngha (NPS)Bc 1: Chn kch thc ng danh ngha (NPS) (AMSE B36.10Mcho thp cc bon; ASME B 36.19M- cho thp hpkim)

gnvingkch trong cangxc nht lu lngvvntccami chtchytrongng.Bc2: trn cstnh chtcami cht,tcnmn, mimnlachnhsmn ABc 3: Xc nh chiu dy ng theo cc cng thc gii

thiuphntrnBc 4: Da vo AMSE B 36.10M v AMSE B36.19M lachnkch thcngdanh nghaNPS c chiudy gnvichiudyngxc nhbc3Bc5: kimtra iukin: chiudyngdanh nghatnh

bc 4 kt hp vi dung sai sn xut phi m bo ln hnchiudyngtnh bc3.Bc 6: kim tra iu kin: ng knh trong cang danhngha lachnbc5 phimbolu lngmi chtyu cu


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- Dung sai: dung sai ca chiu dy ng ph thuc vophngphp snxutng:

i ving sn xut bng phng php cn khngmihn dung sai chiudyngt-12,5% n+0%

ivingsnxutbngphngphp hn tthptmdung sai chiudyng-0,01 (in)

- p sutv nhitthitk L p sutv nhit lnnht c thxuthin khi

hthnglm victrngthinnh

Gi trp sutv nhitthitksquytnhvtliu,phngphp snxutng,chiudy cangvs lachncc phkinngngnh: mtbch,van, cch thcning


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- p sutlnnht

Khi hthngngnglm vicnnh,p suttrong hthng ngng c duy tr n nh v c gi tr nhhnp sutthitk.

Tuy nhin, khi h thng ngng ang trong qu trnhkhi ng hoc do hot ng ca h thng iu khin(ngmvan) hocdo hotngcavan mtchiugyra nhngxung p c gi trlnhnp sutthitkcahthng. Xung p ln nht m h thng cn chu c sctnh theo cng thc

Trong cng thctrn gi trS slytng15-20% so vingsutcho php cavtliu.


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V d1Mtngthp cn khng mihn vnchuynncmm

trong nh my nhitinvi lu lng920 (gpm), vntc nc chuyn ng trong ng l 3(ft/s), p sut canc700 psi, nhit900F (320C). ngcthitksdng trong 8 nm. Nng oxy trong nc 1ppm. Vtliuchtongc k hiuA53 Grade A c ngsutchophp 320C l 10200 psi. Hy lachn kch thcngdanh ngha(NPS).


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V d2: hthngngngcung cpncmmchomtnihinhhnh v:


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Cc thng skthut ng c ng knh danh ngha NPS 8 (DN200) v NPS 12 (DN

300)

Nhitnccpcho nihil 3500

F (1770

C) Lulngnccpcho nihiQ=3000 gal/min Nihitcao hnbm260 ft ( 79,3 m) p sutvnhnh canihi2520 psi p sutcavan p ton nihit2600 psi

Ctp khi van trnngycabmngtl 8700 ft Vtliulmngc k hiuA106 Garde C c S=17500 psi nhit

t-290C n3430C mn tngcngA=0,08 in

Yu cu: Tm chiudy caccng Gi s van an ton ca bm khng hot ng khi ng

van, hy kimtra bncangNPS 8


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3.4.5 Chiudy onngnicong (Ben, Miters)

- ngcong (Ben):

t: chiu dy ng nh nht

P: p sut trong ngD: ng knh ngoi caon ng congS: ng sut cho php cavt liu.

E: h s, ph thuc vonhit lm vicy: h s ph thuc nhit v vt liu lm ng


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- Miters:


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- p sut ln nht trong Miters c tnh theo bngsau:


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thxc nhA v B khi tnh p sutngoi lnnht


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3.5 Kim nghim ng sut trong ng- Kimnghimngsut(kimnghimbn)ngl phn

c vai tr rt quan trng trong qu trnh thit k hthngngng.- Trong phn ny, ngoi ti trng chnh (p sut trong

ng) dng tnh ton chiu dy ca ngng,

ngithitkphich nttc cc ti trngphtc ngln hthngngngnh: trnglng,titrnggi, ngt,gin nnhit,

- Kim nghimng tc l kim tra iu kin ng suttngcngtrongngphithonmn cc iukinbnv iukinmicho php.

- Cc iukinbncho php scquy nhtrong cctiu chunthitk(ASME B31.1; B31.3; )


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3.5.1 Phn loititrng

- Titrngtnh: titrngtnhl titrngtc dnglin

tcln hthngngngtrong qu trnh vnhnhnh: trng lcng v mi cht, p sut, lc tptrung

- Titrngng: titrngng l titrng tc dngln hthngngngtrong mtkhongthigianngnnh: titrnggi, titrngvan xp, ngt,cc xung p khi ngmvan

- Ti trng gin n nhit: ti trng xut hin khingngbnung nng hoclm lnh


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3.5.2 Kim nghim theo ASME B31.3- Khi ngchutitrngtnhv ngth phngtrnh

kimnghimgingviASME B31.1 vihsk=1- Khingchutitrnggin nnhit

trong : Sb: ng sut do m men un gy ra (psi) St : ng sut do m men xon gy ra (psi)

SA : ng sut cho php khi gin n nhit

f: h s tra theo bng


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3.5.3 Kim nghim theo ASME B31.4- ngchutitrngtnh: < 0,54.Sy

- ngchutitrngng:< 0,8 Sy

- ngchutitrnggin nnhit

+ SL< 0,9.Sy

Trong : E: mu unnhicavtliu(psi)

: hsgin nnhitcavtliu(in/in.0

F) : hsPoisson T1 : nhitmi trng; T2: nhit lnnhthocnh

nhtkhi vnhnh ngng Sy : ngsutbindngdocavtliu(psi)


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3.5.4 Kim nghim theo ASME B31.5- Khi ngchutitrngtnhv ngth phngtrnh

kimnghimgingviASME B31.1 vik=1- Khingchutitrnggin nnhit

f: h s, c tra theo th


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3.5.5 Kim nghim theo ASME B31.8

- Khi ng chu ti trng tnh:

Trong : T: h s nhit tra theo bng


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F: hsphthucvo vng al lptngng,tra theo bng

A: vng dn c tha tht: sa mc, ni, nng tri

B: vng bao quanh thnh ph hoc th trnC: thnh ph hoc th trn nhD: thnh ph v th trn ln


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- Khi ng chu ti trng gin n nhit

- Khi ng chu ti trng tng hp

+ < Sy


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t: chiu dy ng (in) P: p sut trong ng (psi) D

0

: ng knh ngoi ca ng (in) MA : mmen un do ti trng tnh gy ra (in.lb) MB : mmen un do ti trng ng gy ra (in.lb) MC : m men un do gin n nhit gy ra (in.lb) Z: mmen chng un ca mt ct ngang (in3) Sh: ng sut cho php ca vt liu nhit lm vic

ca ng (psi) SL : ng sut dc trc (psi) SA: ng sut cho php ca vt liu khi gin n nhit

(psi) Sy : ng sut bin dng do ca vt liu (psi) i: h s k: h s

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Chương 3 Thiết kế hệ thống đường ống.pdf