8/21/2019 Ti liu l hi

1/38

122

Chng 7. Ch nc ca l hi

v cc phng php thu nhn hi sch

7.1. Cc tp cht trong nc thin nhin v nhng ch tiu chtlng ca nc

7.1.1. Cc tp cht trong nc thin nhin

Theo kch thc ht c th chia cc tp cht thnh 3 nhm:+ Tp cht th gm cc ht c kch thc >100 nanomet (1

nanomet = 10-9m);+ Tp cht keo gm cc ht c kch thc t 1-100

nanomet;+ Tp cht dng phn t gm cc ht c kch thc < 1

nanomet.Nhng tp cht th lm c nc thin nhin v l nhng tpcht c kh, gm ct, t st v cc ht c ngun gc khong vngun gc hu c.

Vt cht keo c kch thc ht nm gia vt cht th v vtcht dng phn t. Cc cht keo khng lng mc d thi gian rtdi. Cc hp cht ca silic, nhm, st v cc cht hu c hnh thnhdo phn hy ng vt v thc vt nm trong nc thin nhin trng thi keo n phn tn.

Cc mui, axit, kim v cc kh ha tan trong nc thuc vcc cht phn tn dng phn t v dng ion.

Thnh phn ca nc thin nhin c xc nh bi cc ion

sau: K+, Ca2+, Mg2+, Na+, Cl-, SO42-, HSiO32-. Cc ion cn li nh:CO3

2-, H+, OH-, NH4+, NO2

-, NO32-, Fe2+, Cu2+, thng c trong

nc thin nhin vi mt lng khng ng k, song chng c nhhng quan trng n cc tnh cht ca nc ni chung cng nhcc c im ca nc trong l hi, trong ng nc cp v trongbnh ngng ca tuabin.

Ngun chnh sinh ra cc ion Ca2+ trong n c thin nhin l vi CaCO3v mt ngun khc l thch cao CaSO 4.2H2O. Cc ionMg2+ c trong n c khi ha tan dolomit (MgCO3.CaCO3) do cCO2t do trong n c.

8/21/2019 Ti liu l hi

2/38

123

7.1.2. Nhng ch tiu cht lng nc

Nhng ch tiu quan trng nht ca cht lng nc gm chm lng cc cht l lng, cht kh, cng ton phn v ccthnh phn ca n, kim ton phn v cc thnh phn ca n,nng cc ion hydro v hm lng cc cht kh ha tan c tcdng n mn kim loi nhO 2v CO 2.

c cht lng y ca nc ngi ta xc nh thmhm lng cc ion Ca2+, Mg2+, Na+, Cl-, cc ion cacbonat, sunfat,silicat v cc hp cht ca st, nhm.1. Hm lng cc cht l lng tnh bng mg/kg.2. Cht kh ca nc l s lng cc cht keo v phn t c ngungc hu c v ngun gc khong khng bay hi v c ha tantrong nc, tnh bng mg/kg. Cht kh c xc nh bng cch chomu nc lc s b bc hi sau sy phn khng bay hi 1100C n khi khi lng khng thay i.

3. cng ca nc : l mt trong nhng ch tiu quan trng nhtca cht lng nc dng cho l hi nht l l hi nh my nhitin.

+ cng ton phn ca nc H0 bng tng nng cacc ion canxi ( cng canxi HCa) v cc ion magie ( cng magieHMg), tnh bng mgl/kg hay gl/t hay gl/kg:

H0= H Ca+ H Mg (7-1) tnh i nng canxi v magie t n v mg/kg sang

mgl/kg ta chia nng ca chng cho khi lng ng lng cacc cation y, tc l:

,04,20

CH

2Ca

Ca

+

= mgl/kg (7-2)

,16,12

CH

2Mg

Mg

+

= mgl/kg, (7-3)

trong : +2Ca

C v +2MgC l nng cc ion Ca2+ v Mg 2+c trong

nc, mgl/kg;20,04 v 12,16 l khi lng ng lng ca Canxi v

Magie. cng ton phn ca nc c phn thnh cng

cacbonat v cng khng cc bonat.

8/21/2019 Ti liu l hi

3/38

124

+ cng cacbonat ca nc HC sinh ra ch yu do c cccanxi bicacbonat Ca(HCO3)2 v magie bicacbonat Mg(HCO 3)2 trongnc.

+ cng khng cacbonat ca nc HKC: cng ny sinhra do c cc clorua, sunfat v cc mui khng cacbonat khc caCanxi v Magie nh: CaCl2, MgCl2, CaSO4, MgSO4, CaSiO3,MgSiO3,..

cng khng cacbonat cn gi l cng vnh cu.Do cng ton phn ca nc H0mt mt l bng tng

cc cng canxi v magie v mt khc bng tng cc cngcacbonat v khng cacbonat.

Phn loi nc thin nhin theo cng ton phn nhsau:H0< 1,5 mgl/kg n c c cng nh;H0 = 1,5 - 3,0 mgl/kg n c c cng trung

bnh;H0= 3,0 - 6,0 mgl/kg n c c cng nng cao;H0= 6,0 12,0 mgl/kg n c c cng cao;

H0> 12,0 mgl/kg n c c cng rt cao.4. kim tng qut ca nc K0 (mgl/kg) l tng nng ccanion OH-, HCO3

-, CO32-, PO4

3-, HSiO3-, SiO3

2- v cc mui ca ccaxit hu c yu c trong nc.

Ty thuc vo cc anion gy ra kim m ngi ta phnbit thnh:

a- kim hydrat Kh do c ion hydroxyl OH - trong n cto ra;

b- kim cacbonat KC do c ion cacbonat CO 32- trongnc;

c- kim bicacbonat KbCdo c cc b160d- icacbonat HCO

3

-trong n c.5. Cc vt cht hu c

Vic xc nh trc tip nng cc vt cht hu c thc tkhng th lm c, nn hm lng ca chng c xc nh bngcon ng gin tip khi xc nh oxy ha ca nc dng kalipemanganat KMnO4lm cht oxy ha trong mi tr ng axit.6. Nng ion hydro

Cc ion hydro H+ v hydroxyl OH - sinh ra trong n c dophn hy nc:

H2O H++ OH - (7-4)

8/21/2019 Ti liu l hi

4/38

125

Cc ion H+ c th c trong dung dch do phn hy cc axit,v d:

HCl H ++ Cl - (7-5)Cc ion OH-sinh ra do phn hy cht kim, v d:

NaOH Na ++ OH - (7-6)Trong nc nguyn cht v ha hc 230C th cc nng

+HC v OHC bng 10

-7g ion/kg v chng c tr ng phn ng trung

ha cht lng. Trong mi trng axit +HC > 10-7 g ion/kg > OHC ,

trong mi trng kim th ngc li +HC < 10-7g ion/kg < OHC

C th biu din phn ng ca dung dch mt cch thuntin hn qua ch s PH hay POH, chng l logarit m ca nng cc ion tng ng.

Trong mi trng trung ha PH = 7 = POH. Mi trng axitc pH < 7 < POH, mi trng kim c pH > 7 > POH.

Tnh axit v tnh kim PH

Axit yuTrung haKim yuKim mnh

4,0 6,57,0

7,5 1011 14

7. Cc cht kh ha tan trong nc.Cc cht kh nhN 2, O2, CO2, ha tan trong nc. CO2v O 2

c tc dng gy n mn kim loi. ha tan ca cc cht kh trongnc ph thuc vo nhit ca nc v phn p sut ca kh phatrn mt nc.

7.1.3. Cht lng nc thin nhin

Nc thin nhin gm nc b mt nhn c sng, h, bin,h cha nc nhn to v nc ngm. Cht lng nc b mt nhtl nc sng h thay i theo thi gian v ma trong mt nm, ngthi theo chiu di sng cht lng nc cng khc nhau.

Nc sng thng cha mt s lng tng i khng lncc mui ha tan khong 500 600 mg/kg. Nc sng thng ccc cation Ca2+, Mg2+, Na+ v cc anion HCO 3

-, SO42-, Cl-. Ch tiu

pH ca nc sng thng bng 6,57,5.

8/21/2019 Ti liu l hi

5/38

126

Nc sng thng cha mt s lng nht nh cc cht llng v dao ng trong phm vi rng ty thuc vo lng nc ma.

Nc h v bin c t l cc cation v anion gn nh nhau.Hm lng mui ca nc h v bin gn bng 35 g/kg. Cc ionchnh ca nc bin l Na+ v Cl -. cng ton phn ca nc hnm trong phm vi 215 225 mgl/kg, trong cng cacbonatbng khong 15 mgl/kg

Nc ngm c thnh phn ha hc rt khc nhau. Nc dit cha mt lng ng k CO2ha tan, st v H 2S.

7.2. Nhim v ch nc ca l hi.

Nc cp cho l hi cc nh my in gm nc ngng catuabin v nc b sung c x l b li tn tht nc v hi.

cc nh my nhit in ng ng hi thun ty cc tn thtnc v hi gm hi tiu th truyn ng c cu ph, thi bitro bm bn cc b mt t, thng hi lm mt b qu nhit trong

lc t l, chn tuabin hi v r r nhng ch h trn nghi, ng nc; tn tht ny khng ln hn 1 3% sn lng nhmc ca phn xng l hi. V th nc cp cho l hi gm 96 98% nc ngng ca tuabin v 24 % nc b sung.

cc trung tm nhit in l ng nc ngng v nc bsung dao ng trong phm vi rt rng ty thuc c tnh ca cc btiu th nhit (nc nng, hi trch t tuabin c tr li nc haykhng, hi ly t b qu nhit), trong mt s trng hp nc bsung t n 4050% v c th ln hn. i khi nc ngng do ccb tiu th hi tr v b bn nn khng th dng ngay lm nccp cho l hi c.

Cc tp cht khng mong mun c nh

cc mui v hp chtca cc kim loi nng thm nhp vo nc theo cc ng khcnhau. Ngun sinh ra cc tp cht ch yu l lt (r) nc lm lnhqua cc ch h trong cc bnh gia nhit cung cp nhit ca mngnhit,

S c mt ca cc tp cht trong nc cp c th dn n tora cu cn bm trn b mt t ca l hi v ph hy ch lmvic bnh thng ca l, lm xu cht lng hi v n mn cc chitit kim loi ng hi v nc.

V th l hi lm vic lin tc v kinh t th nhim v cach nc phi:

8/21/2019 Ti liu l hi

6/38

127

1- Ngn nga hoc gim thiu s to thnh cu bm trncc b mt truyn nhit (b mt t);

2- Ngn nga hoc gim thiu qu trnh n mn kim loing nc v hi;

3- m bo thu c hi c sch yu cu.7.3. S to thnh cu cn trong l hi v ng nc cp

Nc cp ca l hi lun lun cha mt lng nht nh ccvt cht ha tan nh nhng hp cht v c khng bay hi v cccht bay hi (cht kh).

Mi cht ha tan trong nc (tr cc cht kh, cc axitcacbonic v silicic) u b phn hy hon ton tc l chng l cccht in phn mnh. Cc axit cacbonic v silicic l cc cht inphn yu.

Nc l l dung dch nc ca cc hp cht ha hc khcnhau, trong nc l xy ra qu trnh ha l phc tp v kt qu l

tch pha rn ra khi dung dch trc tip bm chc trn b mt kimloi, gi l cu bm hoc trng thi cc ht l lng trong nc l,gi l bn. Bn cng tch t li th hoc bin thnh cht xp khngbm vo b mt kim loi v c th d dng x ra ngoi hoc bmvo b mt kim loi gi l cu th cp.

S tch pha cng ra khi nc l c th xy ra do nhngnguyn nhn sau:

1- Do xy ra phn ng gia cc cht khc nhau c trongnc;

2- Do gim ha tan mt s mui khi tng nhit (ccmui c h s ha tan m);

3- Do tng nng mui trong nc l khi bay hi.S phn ng gia cc hp cht khc nhau nm trong nc

c t nng v bc hi c th dn n to thnh v tch cc chtkh ha tan ra khi dung dch. Cc cht ny l CaSO4, CaCO3,MgCO3, CaSiO3, v MgSiO3, cc hydroxyt Ca(OH)2v Mg(OH) 2,

Qu trnh lng cc hp cht kh ha tan ni trn tun theoquy lut tch s ha tan. Quy lut ny ni rng trong dung dchbo ha ca cht kh ha tan th tch s nng cc ion nm trongdung dch nhit cho l i lng khng i:

constTHA.CnnACnn

==+ , (7-7)

8/21/2019 Ti liu l hi

7/38

128

trong :[Cn

+] v [An-] l nng cc cation v anion trong nc;

TH l gi tr bng s ca tch s ha tan, gi tr nykhng i nhit cho vi cht cho trc.

Do nu +> nnAC A.CTH nn th dung dch ch a bo ha

v cc cht cn s khng lng. Nu +< nnAC A.CTH nn th dungdch qu bo ha v xy ra qu trnh lng cn.

Cho nn tch s ha tan c trng gii hn ha tan cacht in phn nhit cho v ph thuc vo bn cht ha hcca cht y.

V d tch s ha tan ca mt s cht nm trong ncc din t nhsau:

4CaSO

2

4

2 THSO.Ca =+

4MgSO

2

4

2 THSO.Mg =+

3CaSiO

2

3

2 THSiO.Ca =+

S gim ha tan ca mt s cht khi tng nhit cngdn n lng cn. V d cc mui ha tan ca canxi v magie c hs ha tan m. Quan h gia ha tan ca cc cht to thnh cuch yu v mt s hp cht d ha tan vi nhit c minh hatrong cc hnh v 7.1 v 7.2.

S tch (lng) cc cht cha trong nc cp ra khi dungdch xy ra ch yu di dng tinh th. S kt tinh cc cht c thxy ra trn b mt kim loi v trong th tch dung dch. Nhng trungtm ca qu trnh kt tinh bao gm nhm ca b mt, cc ht keov cc bt kh nm trong dung dch, cc ht l lng. Cc cht tothnh cu l nhng cht b kt tinh trn b mt kim loi di dng

cc cht lng th rn lin kt chc vi kim loi.

8/21/2019 Ti liu l hi

8/38

129

Nhng cht b kt tinh trong th tch nc l di dng cctinh th l lng trong dung dch gi l bn.

Cc hp cht ca canxi v magie t ha tan c mt trongnc l chnh l cc cht to thnh cu bm.

CaSiO3to ra cu cng dnh cht vo vch ng kim loi. Cuny c mK/W12,0= tc l nh hn 400 ln so vi h s dnnhit ca thp cacbon thng thng. Cho nn khi c lp cu ny rt

mng cng lm tng r rt nhit vch ng. CaSO4

cng l cuchc, n c mK/W33,223,0 = . CaCO3 c th to ra cc cucng hay bn. Cc hp cht silicat ca magie nh MgSiO 3,3MgO.2SiO2.2H2O to ra bn v d thi ra ngoi.

S to thnh cu cng trn b mt ng sinh hi xy ra do ktqu ca cc qu trnh ha l v in ha phc tp, khng nhng cccht to thnh cu m c cc oxyt kim loi (st, nhm, km), cckim loi nguyn cht (ng) v cc cht d ha tan u tham giavo cc qu trnh sinh cu.

Hnh 7.1. ha tan cacc cht to thnh cuch yu c trong nc

Hnh 7.2. ha tan camt s hp cht d hatan c trong nc

8/21/2019 Ti liu l hi

9/38

130

Cu sinh ra trong l hi c cc tnh cht vt l v tnh chtha hc khc nhau.

Nhng ch tiu ch yu ca cu l xp, cng v khnng dn nhit. Ty theo cng v xp ca cu m xc nhc cu to v thnh phn ha hc ca cu v kh nng c th thicu bng bin php c kh hay khng. dn nhit ca cu tythuc cu to v thnh phn ha hc ca cu.

m bo s lm vic bnh thng ca l hi cn m boch lm vic khng sinh ra cu. Mun vy mt mt phi lmmm tht su nc b sung v kh hin tng lt nc tun hontrong bnh ngng, mt khc phi m bo cht lng cn thit canc l.

Mc du c nhiu bin php dng nng cao cht lngnc cp v nc l nhng vn c cu sinh ra nn phi dng binphp c kh hay dng axit thi cu ra ngoi.

chng ng cu l cc hp cht ca st, ng trong ngsinh hi v ng qu nhit (cc loi ny to ra l thng v r kim)

cn phi duy tr nng st v ng trong nc l v nc cp mc ti thiu bng cch kh kh ha tan trong nc.

Bng 7.1. Gi tr trung bnh ca h s dn nhit ca mt s cu cnDng cu v thnh phn ha

hc ca n c tnh ca cuH s dn nhit

W/mK,

Cu cha du Cng 0,116 - 0,175

Cu silicat (c hm lng SiO2bng hoc ln hn 20 25%)

Cng 0,058- 0,232

Cu thch cao (c hm lngCaSO4n 50%)

Rn, chc 0,580 - 2,900

Cu cacbonat (c hm lngCaCO3+ MgCO 3ln hn 50%)

T bt khng nhhnh n l

cng0,580 - 7,000

Cu hn hp gm thch cao,cacbonat, silicat canxi v magie

Cng, chc 0,800 - 3,500

7.4. Qu trnh n mn kim loi b mt truyn nhit

8/21/2019 Ti liu l hi

10/38

131

S n mn kim loi b mt t ca l hi l s ph hy kimloi di tc dng ca mi trng xung quanh (hi, nc, khi) docc qu trnh ha hc v in ha hc.

Qu trnh ph hy kim loi do tng tc ha hc trc tipgia kim loi vi mi trng xung quanh l s n mn ha hc.

S n mn in ha hc khc vi s n mn ha hc chcc phn ng xy ra c km theo sinh ra dng in.

C cc dng n mn sau (hnh v 7.3):S n mn ng u l s ph hy kim loi xy ra vi tc nhnhau trn ton b hay hu nh trn ton b b mt tip xc vi mitrng n mn (xm thc).

Trong trng hp n mn khu vc th s ph hy kim loixy ra trn tng phn ca b mt. n mn khu vc thng c ccdng sau: n mn im, vt, gia cc tinh th, xuyn ngang tinh thv la chn.

n mn vt xut hin trn tng phn nh ca b mt, nhngthng t n su ng k. ng knh vt khoang nc cabao hi bng 45mm, v nhng ng sinh hi c khi thy cc hrt ln b ph bi mt lp oxyt st dy. Khi ng knh vt bng0,21mm th gi l n mn im v thng n mn im gy ra ccl xuyn thng nn n mn im l nguy him nht.

S ph hy kim loi trn bin ca cc ht gi l n mn giacc tinh th. Khi y bn c hc ca kim loi b gim v c thhnh thnh cc vt rn gia cc tinh th. Dng n mn ny c nhng ng thp stenit.

Khi n mn xuyn qua tinh th th vt rn i xuyn qua htkim loi.

Hnh 7.3. Cc dng nmn kim loi.1-ng u;

2-vt lot;3-im;4-gia cc tinh th;5-xuyn ngang tinh th.

8/21/2019 Ti liu l hi

11/38

132

Tt c cc dng h hng kim loi do n mn u c th ctrong l hi v thng c s kt hp mt s dng h hng do nmn.

Tc n mn u v n mn vt c xc nh theo gim khi lng ca phn t b n mn, tnh bng g/m2h hay theochiu su n mn tnh bng mm/nm.

Khi chn tc n mn cho php trong ng nc cp cnphi k n s tng ln ca hm lng tp cht trong nc cp, chyu l cc hp cht st t ha tan. Cc sn phm n mn trong nccp lm tng hm lng bn trong l hi, bn ny cng tham giavo s to ra cu bm trn b mt t. Khi nc lu ng trongvng tun hon vi tc nh th bn nm li ng gp hay titdin vo ca ng sinh hi do lm gim tit din cho nc i hocc th lm tc ng nc.

Khng cho php xy ra s ph hy kim loi do n mn giacc tinh th v n lm gim bn c hc ca kim loi mc d tntht khi lng nh hn nhiu so vi n mn u v n mn vt.

Trong bng 7.2 cho bit s phn loi cng n mn ccng sinh hi v ng hm nc. (Thi hn phc v ca ng l 20 nmc ly lm c s tnh tc n mn cho php).

Bng 7.2. Cng n mn cc ng sinh hi v ng hm nc(thi hn phc v ca ng l 20 nm)

Tc n mn vtlot, mm/nm

Tc nmn u,mm/nm

c tnh caqu trnh n

mnTrung p Cao p

Trung,cao p

Vt nt do nmn

Thc t l

khng c

0,00

0,05

0,00

0,05

0,00

0,02

Khng c

n mn yu 0,05 0,10

0,00 0,20

0,03 0,08

Khng c

n mn chophp

0,10 0,15

0,20 0,30

0,08 0,12

Khng c

n mn mnh 0,15 0,60

0,30 1,20

0,13 0,40

Pht hin c

n mn s c 0,60 1,20 0,40 Pht hin thy

8/21/2019 Ti liu l hi

12/38

133

phng nga n mn v ngn nga cc sn phm n mn lm bnnc cp cn phi bit c ch v cc iu kin tin hnh qu trnhn mn.

Trong l hi c c n mn ha hc v n mn in ha hcv nhiu khi c hai qu trnh ny xy ra ng thi.

* n mn ha hc thun ty: v d n mn ca hi n ctrong cc ng ca b qu nhit do oxy ha kim loi bi hi qunhit:

3Fe + 4 H2O Fe 3O4+ 4H 2 (7-8)Dng n mn ny c c tnh ng u. Mng oxyt st

Fe3O4 c tc dng bo v b mt ng khi b n mn tip theo. cc ng sinh hi n mn do hi nc ch xy ra khi ph hy thyng ca chng nhphn lp hn hp hi n c v ngng tun hon.

Nhng yu t c bn nh hng n cng n mn hinc l nhit v thnh phn ha hc ca kim loi. i vi thpcacbon nhit < 5000C th tc n mn hi nc c tr s nh.Khi tip tc tng nhit th tc n mn tng ln nhanh chng.

Khi b sung cc nguyn t hp kim nhMo, Cr, Ni vo thpth tnh n nh chng n mn bi hi nc ca thp s tng ln.

* n mn in ha hc: Nhiu qu trnh n mn kim loitrong l hi l qu trnh in ha hc. S n mn ny xy ra do tcdng ca cc kh c hot tnh n mn nhO 2, CO2, ca dung dchcc cht in phn (cc mui, cc axit, cc cht kim) c sinh radng in i t phn ny n phn khc ca kim loi. S d sinh radng in v khi kim loi tip xc vi cc cht in phn th trn bmt kim loi sinh ra cc pin in rt nh. Nguyn nhn xut hincc pin in nh ch yu l do tnh khng ng nht v in hahc ca b mt phn chia gia kim loi v cht in phn do b mt

kim loi khng ng nht, khi c cu bm trn tng phn ca bmt t, do cht in phn c nng khc nhau v do phn bkhng ng u cc sn phm n mn trn b mt kim loi.

Hiu in th ca cc pin in (gy n mn) ch ng ktrong giai on u khi sinh ra cc pin in y, sau mt khong thigian rt ngn hiu in th ny s gim xung r rt. S gim hiuin th ban u ca cc in cc ca pin in nh khi c dng ini qua gi l s phn cc. V th s phn cc s lm gim cng n mn. S phn cc b gim i khi trong cht in phn c cc chtc kh nng phc hi th in cc. Nhng cht nhvy gi l chtkh cc v qu trnh gim phn cc gi l qu trnh kh cc.

8/21/2019 Ti liu l hi

13/38

134

Ngi ta phn bit s kh cc anot v s kh cc catot. Skh cc anot c c trng bng s chuyn kim loi vo dung dchv gii phng cc (in t) electron; s kh cc catot c trng bis tip nhn cc electron ca cht kh cc v do cng dngin n mn s tng ln.

Cht kh cc (n mn) hot tnh nht l oxy ha tan trongnc, n gy ra s kh cc catot rt mnh do nhn cc electron vto ra cc ion hydroxyl:

4e + O2+2H 2O 4OH- (7-9)

Cc ion hydro nm trong nc cng gy ra s kh cc catot(s kh cc hydro) do kt hp cc electron m chng bin thnh ccphn t hydro:

2e + 2H+ H 2 (7-10)Kt qu ca cc qu trnh n mn l anot c s tng nng

cc ion kim loi, cn catot c s tch t cc ion OH-. Khi chngtng tc vi nhau s to ra hydroxyt st hai:

Fe2++ 2OH - Fe(OH) 2 (7-11)

Khi trong nc c oxy ha tan th Fe(OH)2 chuyn thnhFe(OH)3khng ha tan trong n c:4Fe(OH)2+ O 2+ 2H 2O 4Fe(OH) 3 (7-12)

Qu trnh ny lm gim nng cc ion st trong dung dch anot v do dn n tng cng s n mn do kh cc anot. CO2t do c trong nc cng lm tng qu trnh n mn v khi ngthi c O2v CO 2 trong n c s xy ra song song cc qu trnh khcc oxy v kh cc hydro. Cho nn iu kin quan trng phngnga n mn in ha hc l kh kh cho nc, tc l thi O2 vCO2ra khi n c.

7.5. Ch nc ca l hi

Ch nc ca l hi phi c t chc nh th no m bo s lm vic tin cy v kinh t ca l v hi sn xut ra ccht lng cao.

Trc ht phi m bo cht lng nc cp, phi c nhngyu cu nht nh i vi cc tp cht c trong nc cp cho l hi.Ch nc l hi c bao hi khc l hi trc lu. l hi cbao hi ch nc c xc nh bi p sut hi, cn l hi trclu th cht lng nc cp phi nh nhau i vi bt k p sutno.

8/21/2019 Ti liu l hi

14/38

135

Vic t chc tt ch nc ca l hi s ngn nga s sinhcu v loi tr s n mn v gim s bm mui trong phn truynhi ca tuabin.

7.5.1. Ch nc ca l hi c bao hi (l hi tun hon tnhin)

Tiu chun cht lng nc cp cho l hi c bao hi phitha mn nhng yu cu trong bng 7.3.

Bng 7.3. Tiu chun cht lng nc cp cho l hi c bao hi,tun hon t nhin.Hm lng cho php ti a trong nc cp

p suthi trongbao hi

ca l,Mpa

cngtonphn,

gl/kg

Axitsilictnhi

sangSiO3

2-,g/kg

Oxyha

tan,g/kg

Hp chtst tnhi sang

Fe,g/kg

Hpchtngtnh

isangCu,g/kg

Du,mg/k

g

< 4,04,010,0

>10,0

15105

10050

302010

753520

2010

31

0,5

pH ca nc cp phi nm trong phm vi 7,0 8,5.Vic hn ch i lng ny v hm lng oxy trong nc nhmngn nga n mn in ha hc trong ng hi nc ca l hi.

Khng th m bo ch lm vic ca l hi khng c cuch bng cch tun theo cc tiu chun cht lng nc cp m cn

phi thi ra ngoi l cc tp cht c trong nc l bng cch x lintc, x nh k v x l nc bn trong l hay x l nc l (phng php hiu chnh). x l nc l thng dngnatriphotphat Na3PO4. Khi tng r rt kim ca nc l ngi tadng natri hidrophotphat Na2HPO4, nhng cht ny kt hp vi cccht to thnh cu ri tch ra khi dung dch di dng bn v cx ra ngoi, phng php ny gi l phng php photphat ha ncl. Cc phn ng ha hc xy ra nhsau:

2Mg(HCO3)2+ 2Na 3PO4 Mg 3(PO4)2 + 6NaHCO3; (7-13)2Ca(HCO3)2 + 2Na 3PO4 Ca 3(PO4)2 + 6NaHCO3; (7-14)

8/21/2019 Ti liu l hi

15/38

136

Trong phng php ny cc cation Ca2+ kt hp vi cc ionphotphat to ra Ca3(PO4)2 hoc ng vi kim xc nh canc s to ra hydroxyl apatit Ca10(PO4)6(OH)2, cn cc ion Mg

2+slng di dng photphat 3 magie Mg3(PO4)2. C hai hp cht ny tha tan trong nc.

Photphat ha nc l bng cch cho vo bao hi mt lngphotphat tng tc vi cht to thnh cu c trong nc l vcn dmt l ng no . Trong iu kin nh vy th hm l ngcc ion Ca2+ v Mg 2+ trong n c s nh n mc loi tr c ssinh cu. Lng dPO 4

3-bng khong 7 15 mg/l.Phng php khc bo v kim loi khi b tc dng ca kim

nng cao trong l hi l gim tnh n mn ca nc l bng cchduy tr mt t l nht nh gia nng kim hydrat v cc ionkhc.

Tiu chun cht lng nc l v ch x l phi c xcnh cho tng l hi trn c s th nghim nhit ha. Cn lu lphi m bo thu c hi c cht lng ph hp vi yu cu.

7.5.2. Ch nc ca l hi trc lu.

nhng l hi trc l u khng c b phn phn ly amar thton b nc cp c bc hi. V khng c x ra ngoi nn mitp cht c trong nc cp hoc s bm ln b mt t ca l hihoc bay theo hi vo tuabin.

Do vy phi t ra nhng yu cu kht khe i vi chtlng nc cp cho l hi trc lu khng c b phn ly m (xembng 7.4).

Bng 7.4. Tiu chun cht l

ng n

c i vi l hi trc l

ukhng c b phn ly m

Cc ch tiu cht lng nc cpHm lng cho

php ti a- cng ton phn, gl/kg 1- Axit silic tnh i sang SiO3

2-, g/kg 20- Cc hp cht Natri tnh i sang Na2SO4, g/kg 50- pH 7,0-8,5- Hm lng oxy ha tan, g/kg 10

8/21/2019 Ti liu l hi

16/38

137

- Hm lng hp cht st tnh i sang Fe, g/kg 20- Hm lng hp cht ng i sang Cu, g/kg 10- Hm lng du, mg/l Ch c vt

ngn nga n mn ng hi nc ca l hi trc lu

cn kh kh bng nhit tht tt cho nc cp, pH ca nc cp

8/21/2019 Ti liu l hi

17/38

138

HCO3-+ OH - H 2O + CO3

2- (7-16a)CO2+ 2OH

- H 2O + CO32- (7-16b)

Ion CO32- kt hp vi ion Ca 2+ to ra CaCO 3 t ha tan v lng

xung:Ca2++ CO 3

2- CaCO 3 (7-17)

Khi OH

-

t

ng tc vi Mg

2+

s to ra magie hydroxyt t ha tan:Mg2++ OH - Mg(OH) 2 (7-18)Cho nn vi chuyn cc mui canxi ca cng cacbonat

(ca nc) v mi mui magie thnh cn. Ngoi ra vi lm lng st,mt phn axit silicic v lin kt vi CO2. Khi b sung Na2CO3 thion cacbonat CO3

2- phn ng vi Ca 2+ ca cng khng cacbonat to ra CaCO3:

CO32-+ Ca 2+ CaCO 3 (7-19)

Khi tng tc gia x a v vi th sinh ra NaOH, cht nytham gia vo phn ng lng cn:

Ca(OH)2+ Na 2CO3 2NaOH + CaCO 3 (7-20)

Khi lng cc mui ca cng cacbonat th hm l

ng muitrong nc mm gim xung. S kt tinh v tch cn s b chm likhi c cht hu c trong nc. V th tng cng qu trnh thng thi vi vic lm mm nc ngi ta cng tin hnh keo tnc. lm vic ny phi t nng nc mm v a vo mtlng d cht phn ng. Khi khng t nng th cng c thgim n 1,41,8 mgl/l, khi kim bng 2,0 2,5 mgl/l m tnng 70800C th cng gim n 0,30,35 mgl/l.

7.6.2. X l nc bng phng php trao i ion (cation vanion).

Dng phng php lng cn khng th lm mm hon tonnc thin nhin. V th thng dng s phi hp, trong x ls b bng cch lng cn v kt thc bng phng php trao i ion.

X l nc bng phng php trao i ion da vo kh nngca mt s cht thc t khng ha tan trong nc gi l cc chttrao i ion hay ionit, cht ny lm thay i thnh phn ion canc theo hng mong mun.

X l bng trao i ion khc v nguyn l vi phng phplng cn ch tp cht c thi ra khi nc khng to ra cn vvic x l ny khng yu cu nh lng (pha ch) lin tc cht

8/21/2019 Ti liu l hi

18/38

139

phn ng. Do vy vic vn hnh thit b x l nc bng trao i ionn gin hn, kch thc thit b nh hn, hiu qu x l cao hnnhiu so vi thit b x l bng phng php lng cn.

Thi gian ca chu trnh lm vic ca thit b trao i ionc xc nh bi dung tch trao i ca ionit tc l kh nng traoi ion ca n. Sau mt thi gian lm vic th kh nng trao i ionca ionit gim i do phi hon nguyn (ti sinh) khi phckh nng trao i ion ban u ca ionit.

7.6.2.1. X l nc bng phng php trao i cation

Cc cation thng dng l Natri NaR, hydro HR v amoniNH4R, trong R l gc ca cationit. Vt liu cationit cn c bn c hc, bn ha hc v c kh nng trao i ion ln. Dungtch hp th biu th bng gam ng lng cc ion canxi v magietnh cho 1 m3 ht.

Khi dng cationit natri th xy ra s trao i ion theo cc

phn ng sau:Ca2++ 2Na +R- Ca 2+R2

-+ 2Na + (7-21a)Mg2++ 2Na +R- Mg 2+R2

-+ 2Na + (7-21b)hoc:

2NaR + Ca(HCO3)2 CaR 2+ 2NaHCO 3; (7-21c)2NaR + CaSO4 CaR 2+ Na 2SO4; (7-21d)2NaR + CaCl2 CaR 2+ 2NaCl; (7-21e)

2NaR + Mg(HCO3)2 MgR 2+ 2NaHCO 3; (7-21f)2NaR + MgSO4 MgR 2+ Na 2SO4; (7-21g)2NaR + MgCl2 MgR 2+ 2NaCl. (7-21h)

Do qu trnh trao i cation m cng cn li ca nc

gim n 10 gl/kg v thp hn, kim v cc thnh phn anionkhng thay i cn hm lng mui th tng ln mt t. Nhc imc bn ca trao i cation Natri NaR l bin i cng cacbonatthnh natri bicacbonat lm tng kim natri ca nc l, v trongl hi NaHCO3 c bin thnh Na2CO3v NaOH:

Ca(HCO3)2+ 2Na+R- Ca 2+R2+ 2NaHCO 3; (7-22a)

2NaHCO3 Na 2CO3+ CO 2 + H2O; (7-22b)Na2CO3+ H 2O 2NaOH + CO 2 . (7-22c)

hon nguyn NaR ta dng NaCl c nng 6 8%, phn ngxy ra nhsau:

8/21/2019 Ti liu l hi

19/38

140

CaR + 2NaCl 2NaR + CaCl 2; (7-23a)MgR + 2NaCl 2NaR + MgCl 2. (7-23b)

Khi dng cationit hydro ta c cc phn ng sau:Ca2++ 2H +R- Ca 2+R2

- + 2H +; (7-24a)Mg2++ 2H +R- Mg 2+R2

-+ 2H +; (7-24b)hoc:

2HR + Ca(HCO3)2 CaR 2+ 2H 2O + CO2; (7-25a)2HR + Mg(HCO3)2 MgR 2+ 2H 2O + CO2; (7-25b)

2HR + CaSO4 CaR 2+ H 2SO4; (7-25c)2HR + MgCl2 MgR 2+ 2HCl; (7-25d)2HR + CaCl2 CaR 2+ 2HCl. (7-25e)

Kt qu l cng ton phn gim n 10 gl/kg v thphn, cng cacbonat c kh hon ton, do hm lng muigim i v kh c kim ca nc. V trong qu trnh trao iHR mi cation trong nc c thay th bng H+ nn cc sunfat,clorua, v nitrat canxi.. c trong dung dch s bin thnh cc axitkhong t do (H2SO4, HCl,......) do tnh axit ca nc tng ln.Thng ngi ta phi hp hai phng php trao i NaR v HR kim ca nc sau khi qua bnh NaR c trung ha bi axitsinh ra khi nc i qua bnh HR (hnh v 7.4)

Hnh 7.4. S b tr cc bnh trao i cation NaR v HRa-khi trao i cation Na; b-khi b tr ni tip bnh HR v bnh NaR; c-khi kt hp

HR v NaR trong mt bnh; d-khi b tr song song bnh HR v bnh NaR. 1-ng

8/21/2019 Ti liu l hi

20/38

141

cp nc cng; 2-bnh NaR; 3-bnh ha tan mui; 4-b dung dch; 5-b nc ra ngc; 6-ng nc mm i ra; 7-thng cha H2SO4; 8-bnh HR; 9-b phnthi CO2; 10-qut gi;11-b cha nc trung gian; 12-bm; 13-bnh NaR cp 2

HCO3-+ H + H 2O + CO2 (7-26)

hon nguyn HR ta dng axit sunfuric c nng 1,01,5%

hay axit clohydric. Khi dng H2SO4 ti sinh HR s xy ra phnng sau:

CaR2+ H 2SO4 2HR + CaSO 4; (7-27a)MgR2+ H 2SO4 2HR + MgSO 4. (7-27b)

Khi dng cationit amon cng ca nc gim n cn rtnh nhng cc mui amon to thnh khi a vo l hi s b phnhy nhit to ra NH3 v cc axit:

NH4Cl NH 3 + HCl; (7-28a)(NH4)2SO4 2NH 3 + H 2SO4;... (7-28b)

S c mt ca NH3v oxy trong n c s gy n mn cc hp

kim ng. Thng s dng phi hp phng php ny vi phngphp trao i NaR. hon nguyn cationit amon ta dng cc mui amon:

CaR2+ 2NH 4Cl 2NH 4R + CaCl2 (7-29)

7.6.2.2. X l nc bng phng php trao i anion

Cc anion ca mui v axit trong nc s trao i vi gcca anionit theo phn ng sau:

2RaOH + H2SO4= Ra 2SO4+ 2H 2O (7-30a)RaOH + HCl = RaCl + H2O (7-30b)

Ngi ta cng dng cc anionit khc nhau nh: Ra2CO

3,

RaHCO3Trao i anion s kh c trit cc axit trong nc, v

th ngi ta t bnh HR trc bnh trao i anion

7.6.3. Cc phng php x l nc khc:

- Dng in trng, t trng, siu m x l nc cho ccl hi cng nghip.

- Chng ct nc ly hi v sau cho hi ngng t lithnh nc ngng lm nc cp cho l hi.

8/21/2019 Ti liu l hi

21/38

142

7.7. sch ca hi

7.7.1. Yu cu v sch ca hi

Cht lng hi do l sn xut ra gm cc thng s (p sutv nhit ) v sch ca hi tc l s lng v thnh phn cacc tp cht nhcc mui v kh cha trong hi.

Mc lm vic kinh t ca tuabin hi ph thuc ng kvo cc thng s ca hi v vo sch ca hi. Cc tp cht chatrong hi c bit l cc mui s bm vo cc ng ca b qu nhitv vo phn truyn hi ca tuabin hi.

Khi mui bm vo phn truyn hi ca tuabin hi s gy huqu c hi:

- Lm gim kinh t ca tuabin v nhm ca cnh quttng ln v bin dng (profile) ca cc rnh b sai i, s lm tng tntht thy lc.

- Lm tng ging p gia cc tng tuabin do lm tng ngsut trong cc cnh qut v tng p sut trong cc chn du, to stng ging p gia cc tng lm gim lu lng hi qua tuabin v do lm gim cng sut ca tuabin, kt qu l khng sn sut innng.

Nu c cu d ha tan bm trn cnh qut th c th ratuabin bng hi m, mun vy phi gim cng sut trong mt s gi(c th gim n cn 50% cng sut nh mc). Nhng cu kh hatan trong nc nh SiO 2 v cu cha Cu khng th kh bng cchdng nc ra m ra phc tp hn, c khi phi m tuabin ra co sch cu bm tc l dng dung dch kim, dng phng php ckh.

Thng s hi cng cao th yu cu i vi sch ca hicng tng ln.

Phi dng cc bin php khc nhau thu c hi sch tcl hi c cha t tp cht (bay hi v khng bay hi).

Cc tp cht bay hi gm: N2, NH3, CO2v H 2. Tr CO2cncc kh khc khng tham gia to thnh cn bn trong tuabin.

Cc tp cht khng bay hi c trong hi gm cc cht rnha tan hay l lng trong nc l. Cc tp cht khng bay hi nyc th bm trong ng hi. Hm lng cc tp cht khng bay hinm trong hi bo ha c th biu din nhsau:

8/21/2019 Ti liu l hi

22/38

143

g/kg,CK01.0C nph += (7-31)

hay

g/kg,C100

KC nh = (7-32)

trong :

Cnl hm lng cc tp cht trong nc l, g/kg ;K l h s bay mui: pKK += , %;

l m ca hi, %;Kp l h s phn b hp cht cho gia hi bo ha v

nc si, %.Yu cu c bn i vi cht lng hi l duy tr cc tp cht

khng bay hi c trong hi mc m bo s lm vic catuabin trong mt thi gian di m khng c s gim r rt kinh tv khng hn ch cng sut. Trong bng 7.5 gii thiu tiu chuncht lng ca hi.

Bng 7.5. Tiu chun cht lng hi.Hm lng cho php ti a trong hip sut

hi tuabin,Mpa

Cc hp cht natritnh i sang

Na2SO4, g/kg

Axit silic tnh isang SiO3

2-,g/kg

CO2t do,g/kg

< 4410>10

200300200

5080

20302030

102051027

sch ca hi qu nhit l hi c bao hi c xc nhbi sch ca hi bo ha, v vy ta phi bit nguyn nhn lm

bn hi bo ha v c bin php thu c hi bo ha sch.

7.7.2. Nguyn nhn lm bn hi bo ha:

Nguyn nhn c bn lm bn hi bo ha l cc git nc lb cun theo hi. Trong cc git m do hi cun theo c cha ccmui ha tan hay mui l lng v cc ht bn mn. Nguyn nhnth hai lm bn hi bo ha l c mt s mui nh: mui Silic, st,ng, ha tan trong hi bo ha cao p.

8/21/2019 Ti liu l hi

23/38

144

m bo hi c sch cao nht khi cht lng nc cp cho th phi lm sao thu c hi bo ha c kh ti a vgim nng ca cc cht ha tan trong hi n mc ti thiu.

7.8. S cun c hc cc git m theo hi bo ha

m ca hi bo ha ph thuc vo nhiu yu t nh: phti ca l, chiu cao ca khoang hi, hm lng mui ca nc l viu kin cp hn hp hi nc vo bao hi ca l hi.

Khi cc bt hi i ra khi mt nc th v ca bt b v ra vto ra mt s nht nh cc git m ln v mt tp hp cc git mmn.

Khi si bt hi qua nc th kch thc v s lng cc gitm c sinh ra ph thuc vo ng nng ca bt hi vo cc thngs vt l ca nc, ca hi v hm lng mui trong nc l.

Khi tng tc chuyn ng ca cc bt hi qua mt bchi th mt mt lm tng s lng cc git m c sinh ra v mt

khc s git m c kch thc ln cng tng ln.S tng ng nng ca dng hn hp hi nc khi cp hnhp ny vo khoang hi ca bao hi cng s lm tng s lng vkch thc cc git m.

Ngi ta xc nh m ca hi ph thuc vo ph tica l hi (xem hnh v 7.5) v c th biu din nhsau:

nDA= (7-33)

Ngi ta phn bit ba vng trong quan h x = f(D)

Hnh 7.5. Quan h gia mca hi v ph ti l hi.

8/21/2019 Ti liu l hi

24/38

145

Vng 1: ng vi m rt nh ca hi %01,0 , 10n .Bi vy hi c sch cao nht khi l lm vic ph ti ng

vi u vng th hai c 43=n . Ph ti m bt u tng rrt m ca hi v do tng r rt h s bay mui

( 100.C

CK

n

h= )c gi l ph ti ti hn. Nh vy cc l hi caop v siu cao p cn phi lm vic trong phm vi ph ti d i tihn.

Ph ti ca khng gian hi v ph ti ca mt bc hi c nhhng n cht lng phn ly cc git m ra khi hi. Ph ti ca ltnh cho 1m3th tch khoang hi v cho 1m 2mt bc hi gi l sutph ti ca khoang hi tnh bng m3/ m3s hay kg/m3s hoc sut phti ca mt bc hi m3/m2s hay kg/m2s:

s/mm,V

10".v.DR 33

h.K

3

v = hay skg/m,V

DR 3

h.K

'

v =

s/mm,F

10".v.DR

23

h.b

3

S = hay skg/m,F

D'R

2

h.b

S=

Sut ph ti cao ca c khoang hi v ca mt bc hi slm gim kch thc ca bao hi tc l gim gi thnh bao hi. Tuynhin kh v sch ca hi s cao hn khi sut ph ti hikhng cao qu v khng thp qu.

Thc ra khi khoang hi c chiu cao nh th cc git m bnra t mt bc hi c th bay n tn ming cc ng ly hi ra v c

th b dng hi ko ra khi bao hi. Khi tng chiu cao khoang hitc l gim sut ph ti ca n th mt phn ng k cc git m lnc nng n chiu cao nht nh s ri tr li mt bc hi.

iu ni trn cng ph hp vi ngha vt l ca c hai ilng sut ph ti ca khoang hi v ca mt bc hi ni trn,th nguyn ca ph ti khoang hi (1/s) l i lng nghch o cathi gian lu li ca hi trong bao hi; khi tng chiu cao khoanghi tc l gim ph ti ca n th thi gian lu li ca hi trong baohi s tng ln, iu ny to iu kin gim m ca hi. Thnguyn ca ph ti mt bc hi [m/s] l tc quy dn ca hi tnh

8/21/2019 Ti liu l hi

25/38

146

cho ton b b mt bc hi. Tc quy dn ca hi cng nh th sgit nc b dng hi ko theo s cng t v m ca hi s gimxung.

Cho nn sut ph ti ca khoang hi v ca mt bc hi lnhng yu t quan trng xc nh s cun m theo hi ra khi baohi v do xc nh m ca hi bo ha.

Quan h gia m ca hi v chiu cao khoang hi khi phti mt bc hi khng i v hm lng mui khng i c chotrong hnh v 7.6. T hnh v ta thy rng khi tng chiu cao khoanghi th m ca hi lc u gim r rt, sau bt u mtchiu cao nht nh m gn nh khng thay i. Cho nn chiucao khoang hi ch cn ln hn chiu cao nng ln ti a ca ccgit m, thng chiu cao khoang hi bng 0,50,6m hay ti abng 0,81m l .

Hm lng mui ca nc l c nh hng ln n hmlng ca hi. Ngi ta chng minh rng hm lng mui cahi t l vi hm lng mui ca nc l, khi vt nng ti hn

y th hm lng mui ca hi s tng ln r rt. V th m bo sch cn thit ca hi th hm lng mui ca nc l khngc ln hn gi tr nm trong pham vi (vng) di ti hn (xemhnh v 7.7).

Khi tng hm lng mui trong nc l vt trn mt gi trnht nh v ty thuc vo thnh phn mui v p sut hi s xy raqu trnh sinh bt. Khi lp bt c chiu cao ng k th s cun mcng tng ln r rt v do m ca hi tng ln mnh.

Hnh 7.6. Quan h gia mca hi v chiu cao khoang hi.

Hnh 7.7. Quan h gia m cahi v hm lng mui ca nc l.

8/21/2019 Ti liu l hi

26/38

147

S cun mnh cc git m v do bay nhiu mui theo hicng cn do s si bng ca nc trong bao hi. Nguyn nhn sibng l do khi lng ring ca cc lp nc b bo ha bi cc bthi b gim i t ngt, do lm tng th tch ca hn hp trongbao hi v lm cho mc nc tng ln (bng ln).

7.9. ha tan ca cc cht trong hi.

Ngi ta xc nh bng nghin cu v thc nghim rngtrong khi hin tng cun cc git m theo hi l ngun chnh lmbn hi c p sut bt k th i vi hi c p sut > 6 MPa ngunrt quan trng lm bn hi cng l s cun chn lc mt s vt chttheo hi nhSiO 2, cc mui ca natri (NaCl, Na2SO4, Na2SiO3, ).

Nghin cu nhng quy lut cun chn lc cc cht k trntheo hi ngi ta thy nguyn nhn chnh ca qu trnh l hatan tng i cao ca cc cht trong hi cao p.

ha tan ca cc cht trong hi c mt s c im l:1- Cc cht c ha tan c chn lc trong hi, tc l trongnhng iu kin hon ton ging nhau (i vi hi qu nhit th psut v nhit nhnhau, i vi hi bo ha th p sut v nng cc cht trong nc nhnhau) th ha tan trong hi ca cc hpcht khc nhau.

2- Kh nng cho ha tan ca hi tng ln khi tng p sut. ha tan ca cc cht trong hi bo ha c c trng bi h sphn b, l t s gia hm lng ca cc cht ha tan trong hiChv hm l ng ca cc cht y trong nc Cn:

%,100.

C

CK

n

hp = . (7-34)

p sut thp ha tan ca hu ht cc hp cht v c khng bayhi ca nc l trong hi bo ha l rt nh.

Ty theo mc tng p sut m ha tan ca cc chttrong hi (s tng ln) v h s phn b ca chng tng ln. Ngita chng minh bng thc nghim rng ln ca h s phn bca a s cc hp cht v c nm trong khoang hi ph thuc chyu vo p sut (p sut ny xc nh mt ca hi v nc).

H s phn b tng ng vi dng tn ti nh nhau ca tpcht ha tan trong pha hi v pha nc xc nh theo biu thc:

8/21/2019 Ti liu l hi

27/38

148

n

nl

hpK

= , (7-35)

trong : Sh, Snll mt hi v n c l;n l s phn t H2O dng thy ha tp cht cho, mi hp

cht c gi tr n ring v khng ph thuc vo nhit .Cc cht in phn rt yu nh oxyt st, nhm, c n < 1;

cc cht in phn yu (axit silicic, H2SiO3) c n = 1 3; cc chtin phn mnh c n = 49.

Trong hi qu nhit c th c cc cht sau y ha tan:NaCl, NaOH, CaCl2, Na2SiO3, Ca(OH)2, Na2SO4, CaSO4, . . .(hnh v7.8). ha tan ca cc cht rn trong hi qu nhit t n gi trln ngay c cc p sut trung bnh, nhng p sut ny ha tanca cc cht trn trong hi bo ha l rt nh.

cng mt nhit qu nhit (hi qu nhit) khi tng psut v mt hi qu nhit th ha tan ca cc hp cht v ctrong hi s tng ln.

7.10. Cc phng php thu c hi sch

thu c hi sch trong cc l hi c bao hi ta phigim s lng cc git nc l trong hi v gim hm lng cc vtcht ha tan trong hi.

Hnh 7.8. ha tan ca mt s mui v hydroxit trong hi qu nhit 30

8/21/2019 Ti liu l hi

28/38

149

Gim m ca hi bo ha bng cch phn ly m ra khihi, gim hm lng cc tp cht ha tan trong hi bng cch gimnng cc tp cht trong nc l v ra hi qua lp nc schthng l nc cp. Gim hm lng mui ca nc l bng cchnng cao sch ca nc cp hay tng cng x l, tin hnh bchi theo cp.

7.10.1. Phn ly m ra khi hi.

Cc thit b phn ly m ra khi hi phi tha mn nhng yucu sau:

1- Gim c ng nng ca dng hn hp hi nc kthp vi vic p tht mn cc git m v tch c mtkhi lng ti a cc git nc ra khi hi.

2- Phi c kh nng phn b ng u hi trong khoang hica bao hi nhm gim tc ca hi, c nhvy mim bo qu trnh phn ly t nhin t hiu qu cao.

3- Cn thc hin phn ly c hc trong thit b do sinh ra cccc ly tm khi dng hi chuyn ng cong.cc l hi c bao hi dng cc thit b phn ly khc nhau

nh: tm chn, ca chp, tm c khoan l, xyclonMi thit b phn ly p ng c mt hay ng thi hai, ba

yu cu k trn. nng cao hiu qu phn ly t nhin m ra khi hi do

hiu khi lng ring ca nc v ca hi th tc dng hi trongkhoang hi phi nh. Tc ny cng nh th s git m trongdng hi s cng t v gm ch yu l nhng git mn.

Ngi ta t chc qu trnh phn ly gm 2 giai on:

Giai on th nht yu cu lm gim (tt) ng nng ca dng hnhp hi nc t ng i vo bao hi v tch lng m chnh ra khihi. Giai on ny cn gi l giai on phn ly hi khi nc.Giai on th hai sy kh hi n mc c th v gim m nkhong 0,01 0,005%, giai on ny cn gi l giai on phn lym ra khi hi v l giai on chnh.

Di y s trnh by s , nguyn l lm vic v cch btr mt s thit b phn ly m t trong bao hi ca l hi.

*Tm chn:Tm chn l thit bi phn ly n gin nht, ct trong khoang hi ca bao hi . Ngi ta t tm chn ring chotng dy ng , tm chn t nghing 450 so vi h ng dng hi

8/21/2019 Ti liu l hi

29/38

150

m bo dng hn hp hi nc p vo chng m hn (hnh v7.9).

* Ca chp: y nh lc ly tm sinh ra khi dng hi m ingot m thc hin c qu trnh phn ly t nhin (hnh v7.10).

* Tm c khoan l: m bo cp ng u hn hp hinc vo bao hi v ly hi ra khi bao hi ngi ta cn t cc tmkhoan l chm di mt nc v ch hi i vo ng qu nhit, ccl khoan c ng knh 510 mm v s l c tnh ton mbo tr lc ca tm khng ln hn 300350 Pa.

t tm khoan l thp hn mc nc cho php thp nht mtkhong 50100 mm tng tr lc chuyn ng ca hn hp hinc do m bo ph ti ng u ca mt bc hi v hi i ra tmt bc hi vi tc nh nht, khi hi khng th ko theo cc

git m ln.Mt trong nhng bin php hiu qu nht gim ngnng ca dng hn hp l cp khi lng chnh ca hn hp vodi mc nc trong bao hi.

t tm khoan l trc ch ly hi ra cng c tc dnglm cn bng tr lc ca mi dng hi v m bo s dng ton btit din bao hi, iu ny c nh hng n ng u ca phti mt bc hi v ph ti khoang hi ca bao hi.

Hnh 7.9. Tm chn t chhn hp hi nc i vo bao hi.

Hnh 7.10. Ca chp.a-un trn; b-un c gc nhn

8/21/2019 Ti liu l hi

30/38

151

* Thit b phn ly kiuxyclon: Khi nc l c hmlng mui cao v c khuynhhng sinh bt th cc xyclon ttrong bao hi s t c hiuqu cao ca qu trnh phn ly hira khi m. Hn hp c cptip tuyn vo xyclon. Khi hnhp hi nc i vo xyclon ngnng ca dng b gim., do tc

dng ca lc ly tm m nc bnn n vch xyclon v chyxung di theo mt trongxyclon. Xyclon c ng knhbng 300400 mm v chiu caobng 500650 mm (hnh v7.11).

Hnh 7.11. Xyclon t trong bao hi.a-s xyclon; b-b tr xyclon trong bao hi.

12. Xyclon t ngoi bao hi.p; 2-hn hp hi nc i vo xyclon;o xoy; 4-tm c khoan l; 5-ng ly hi

ng thi khng kh; -ng x; 8-ng nc9-nc t bao hi n; 10-chc ch thp

8/21/2019 Ti liu l hi

31/38

152

u d i ca xyclon t mt ci y cho nc i thnhvng, gia y v thn c cc cnh hng chuyn ng xoy ca

nc thnh chuyn ng thng ng v dng chy m vo khoangnc.

Khi t xyclon loi tr c s sinh bt v si bng canc, khng c si bng v nc v hi sau khi vo xyclon schuyn ng theo hai hng khc nhau, khng c sinh bt v lc lytm s nn cc bt n vch xyclon v ph hy bt nhanh chng.

u im ny ca xyclon cho php dng xyclon c trongtrng hp nc l c hm lng mui v kim cao. Do khngth tng kch thc bao hi nn ngi ta t cc xyclon bn ngoibao hi tng c chiu cao khng gian hi v to ra mt bc hiquay bn trong xyclon (hnh v 7.12).

Chiu cao khoang nc ca xyclon ngoi bng 22,5 m vchiu cao phn hi khong 1,5 2,5m, ng knh trong ca xyclonbng 300500 mm. Tc hi ch i vo tip tuyn bng 6,0m/s, trong thn xyclon bng 5,5 m/s. V hiu qu phn ly phthuc tc vo ca hi nn ngi ta tng tc vo xyclon n1012m/s v c th n 20 m/s. Nhng khi phi kim tra mc tun hon tin cy ca vng tun hon ni vo xyclon.

Vic dng xyclon ngoi cho php thu c hi rt sch ngayc khi nc l c mui cao. Do xyclon ngoi c dng lmkhoang mui ca l hi c bc hi theo cp.

7.10.2. Ra hi

Khi tng p sut nhng yu cu v sch ca hi v v vicgim hm lng SiO2 trong hi ngy cng tng, v ngay c khi bchi theo cp v dng xyclon ngoi cng khng th m bo ccht lng hi yu cu. Kh khn chnh sinh ra l do khi tng psut th mc cun SiO2theo hi bo ha cng tng ln.

Ra hi gim hm lng mui tng v c bit l gimSiO2trong hi.

8/21/2019 Ti liu l hi

32/38

153

Bn cht ca vic ra hi l cho hi cn lm sch tip xcvi lp nc cp hay lp nc ca khoang sch. C nhiu phngphp cho hi tip xc vi nc sch nh:

- Phun nc cp vo khoang hi ca bao hi;- Cho cc dng (tia) hi nh i qua trn b mt c ra

bng nc cp;- Cho hi khuch tn (si bt) qua lp nc cp.Khi hi c ra th cc git nc c nng mui cao nm

trong hi s pha trn vi nc sch v li trong nc sch phnln cc mui cha trong n. ng thi cc cht ha tan trong hicng s chuyn sang cho nc, v ha tan ca cc cht trongnc cao hn nhiu so vi trong hi ngay c khi p sut cao. Hisau khi ra, c sy trong khoang hi v sau i vo cc ng cab qu nhit.

Bin php cho hi khuch tn qua lp nc cp l bin phpra hi c hiu qu nht (hnh v 7.13). Chiu dy lp nc rabng 4050 mm l tt nht. Nu < 40 mm th hiu qu ra gim i

r rt.

Hnh 7.13. S thit b ra hi kiu cho hi khuch tn qua lp nc cp.a-b tr thit b ra hi trong bao hi; b-tm c khoan l t nm ngang;

c-tm c khoan l v c mng t di

8/21/2019 Ti liu l hi

33/38

154

Hiu qu ra do khuch tn (si bt) ph thuc ch yu 2yu t:

- Hm lng cc tp cht trong nc ra;- H s bay cc tp cht theo hi c ra.

1. Hm lng tp cht trong nc ra c xc nh trc ht bicht lng nc ra v ph thuc vo phn nc cp a vo rahi:

%,100.D

DZ

nc

r= (7-36)

trong :Dr l l u lng nc a vo thit b ra, kg/s;Dncl l ng nc cp vo l, kg/s.Khi tng Dr , hiu qu ra tng ln tc l l ng tp cht

trong nc ra v do hm lng tp cht trong hi gim xung.Cht lng nc ra s xu i khi tng nng cc tp cht

trong nc l; s d nhvy v khi h s bay mui K 1khng i nutng hm lng cc tp cht trong nc l th hm lng ca chngtrong hi trc khi ra s tng ln. Hm lng cc tp cht trongnc ra cn ph thuc vo h s bay cc cht cng vi hi trckhi ra. Nu nng cc tp cht trong nc l cng cao th nhhng ca K1 n hm l ng cc tp cht trong nc ra v do trong hi c ra s cng ln.

Nh vy hm l ng cc tp cht trong nc ra ph thucvo:

- S lng v cht lng nc a vo thit b ra;- H s bay cc cht theo hi trc khi ra;- Hm lng cc tp cht trong nc l.

H s bay cc cht theo hi trc thit b ra bng: 1p11 KK += ,

v sau thit b ra: 2p22 KK += ,

trong :

1 v 2 l m ca hi tr c v sau khi ra, %;1

pK v2

pK l h s phn b c tr ng hm lng cc tp cht

ha tan trong hi trc v sau khi ra, %. Trong thc t khi tnh ton sch ca hi c th ly 1pK =

2

pK .

8/21/2019 Ti liu l hi

34/38

155

Vic ra hi c thc hin trong khoang hi ca bao hi.ng knh ca bao hi phi khng nh hn 1400 1800mm c khng gian lp t thit b ra hi.

Kt qu ca vic ra hi bng nc cp l hm lng cccht rn ha tan trong hi sau khi ra, c bit l axit silicic gim ihng chc ln. Hiu qu ra cng cao khi lng nc ra cng ln.Lng nc cp dng ra hi c th bng 25 100% lng nccp vo bao hi.

7.10.3. Bc hi theo cp

Bn cht ca phng php bc hi theo cp l to ra trong l2, 3 hay nhiu vng tun hon c lp c nng nc l khcnhau. Mun vy ngi ta t trong bao hi cc vch ngn chiakhoang nc thnh 2, 3 khoang, do cng chia cc b mt sinhhi thnh s vng tun hon tng ng c lp vi nhau. Nc cpc a vo khoang sch c kch thc ln nht v gi l cp bc

hi th nht. Nc khoang sch c tho sang khoang mui (cpbc hi th 2), . . . .(hnh v 7.14 v 7.15).

Hnh 7.14. S bc hi hai cp c khoang mui trong bao hi.1-bao hi; 2-ng dn hi ra; 3-ng gp di ca ng tun hon;

4-ng sinh hi; 5-ng nc xung; 6-ng nc cp;7-ng nc x lin tc t bao hi; 8-vch ngn trong bao hi.

8/21/2019 Ti liu l hi

35/38

156

Nng mui trong nc s tng ln t nng mui trongnc cp Cnc n nng mui trong n c x Cx. Lc xtng i ca mi cp l rt ln nhng ln x tuyt i ca tonb l hi li rt nh. Hm lng mui trong cp bc hi th nht rtnh m lng hi sinh ra cp ny l ln nht. Dng bc hi theocp c th tng ng k nng nc x m cht lng hi khngb xu i. Do dng bc hi theo cp gim lng nc x hoc c th dng nc cp c hm lng mui cao hn.

Hm lng mui ca hi khi dng bc hi theo cp c xcnh theo cc cng thc sau:

Khi c 2 cp bc hi:

mg/kg,C100

nC

100

n100C 11h

111

h11

h +

= ; (7-37)

Khi c 3 cp bc hi:

mg/kg,C100

nC100

nC100

nn100C

111

h

11111

h

111

h

11111

h ++

= (7-38)trong : n11v n 111 l sn l ng hi ca cp bc hi th hai v thba, %.

8/21/2019 Ti liu l hi

36/38

157

Hnh 7.15. S bc hi ba cp c xyclon t ngoi bao hi.1-bao hi; 2-xyclon t ngoi; 3-ng gp di ca vng tun hon;4-ng sinh hi; 5-ng nc xung; 6-ng nc cp;

7-ng nc x lin tc t xyclon ngoi; 8-ng dn nc t bao hi vo xyclon ngoi;9-ng dn hi t xyclon ngoivo bao hi; 10-ng ly hi ra;

11-vch ngn trong bao hi.

* Hm lng mui th trong hi ca tng cp bc hi cxc nh nhsau:

;mg/kg,C100

kC 1nl

11

h = (7-39a)

;mg/kg,C100

kC 11nl

211

h = (7-39b)

mg/kg,C100

kC 111nl

3111

h = . (7-39c)

Trong cc cng thc trn k hiu:k1, k2, k3 l h s bay cc cht theo hi t cp bc hi th 1,

th 2, th 3, %;1

nlC ,11

nlC ,111

nlC l hm l ng mui ca nc l trong cp bc hi th1, th 2, th 3, mg/kg.

8/21/2019 Ti liu l hi

37/38

158

Vic cho bc hi theo cp s lm gim hm lng muitrong nc l tc l lm gim hm lng mui trong hi, do chtlng hi tng ln. ng thi bc hi theo cp cng c coi l binphp x l hiu chnh nc trong l.

7.10.4. X lin tc v x nh k ca l hi

Ty thuc cc yu cu v sch ca hi m nng muitrong nc l phi khng c ln hn mt gi tr xc nh. Munvy phi tin hnh x lin tc ra khi l hi mt lng nc l cnng mui cao nht. Trong s bc hi theo cp vic x lintc c thc hin khoang mui. Cng vi x lin tc ta cng cnphi x nh k l hi, vic thc hin cc ng gp di ca dnng sinh hi hay bao nc (balng di) ca l c hai bao hi v ch thp nht ca cc l hi nh. Mi ca vn hnh phi x nh k 1n 2 ln, thi gian x ko di khong 2 n 5 pht.

x l hipth ng tnh bng phn trm ca sn lng l

hi, tc l:%,100.

D

Dp x= (7-40)

trong : Dx l lng nc x, kg/s;D l sn lng hi nh mc ca l hi, kg/s.

Lng nc cp vo l hi Dncbng:Dnc= D + D x, kg/s. (7-41)

S cn bng mui ca l hi c trnh by trn hnh7.16. Phng trnh cn bng mui ca l hi c bao hi khi khng

c cu cn bm c dng sau:

( ) xxhncx CDCDCDD +=+ , (7-42)hay: (100 + p) Cnc= 100 C h+ p C x,

(7-43)trong : Cnc, Ch, Cx l hm l ngmui trong nc cp, trong hi vtrong nc x, mg/kg.

8/21/2019 Ti liu l hi

38/38

159

Thng thng x l hi p = 0,51,0 %, ti a p = 3%.Gii phng trnh (7-43) khi

cho bit x l p ta xc nh chm lng mui trong nc x(nc l) nhsau:

( ) p C100Cp100Chnc

x += . (7-

44)

Khi coi hm lng mui trong hi bng khng (Ch=0) v ly x l p = 1% ta xc nh c hm lng mui trong nc xbng:

( )nc

nc

nlx C1011

C1100CC =

+== (7-45)

T biu thc (7-45) ta thy rng hm l

ng mui ca n

cl ln hn 101 ln hm lng mui ca nc cp. V vy thuc hi c sch cao ta phi gim hm lng mui ca nc lbng cch tng cng x l.

Hnh 7.16. S cnbn mui ca l hi.