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7/31/2019 Lam Ngot Khi
1/27
Bi vit c hon thnh di s hng dn ca PGS. TS. Nguyn Th Minh Hin
B mn CN Hu c- Ha du. HBK.HN(bi vit ch c tnh cht tham kho; khng l ti liu hay gio trnh chnh thc no)
M u................................................................................................................... 1
Tng quan v cc cng ngh lm ngt kh t nhin v kh ng hnh ................ 2
I. Gii thiu chung .......................................................................................................2II. Qu trnh hp ph....................................................................................................3
II.1 C s ha l..................................................................................................................3II.2. Mt s cht hp ph c th dng lm ngt kh ......................................................4
III. Qu trnh hp th ...................................................................................................4III.1. C s ha l ...............................................................................................................4III.2. Qu trnh hp th ha hc..........................................................................................5
III.3. Qu trnh hp th vt l .............................................................................................9III.4. Qu trnh t hp.......................................................................................................12
V. Qu trnh lm ngt kh bng phng php hp th ha hc s dng dung mimonoetanol amin (MEA)...........................................................................................13
H tr tnh ton, thit k thp hp th lm ngt khbng phng php hp th ha hc s dng dung mi MEA .............................17
I. Cn bng vt cht ca thp hp th ........................................................................17III. Cn bng nhit lng ca thp hp th................................................................20IV. Thit k thp hp th ...........................................................................................22
Ti liu tham kho............................................................................................... 26
7/31/2019 Lam Ngot Khi
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7/31/2019 Lam Ngot Khi
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Lm sch kh khi H2S,CO2 v cc hp cht hu c cha lu hunh
Tng quan v cc cng ngh lm ngt kh t nhin vkh ng hnh
I. Gii thiu chung
Trong thnh phn ca kh t nhin v kh ng hnh bn cnh thnh phn
chnh l cc hydrocacbon no cn c cha mt lng ng k cc tp cht c tnh
axit nh cacbonic (CO2), hydrosunfua (H2S) v cc hp cht cha lu hunh
khc nh oxyt lu hunh cacbon (COS), disunfua cacbon (CS2), mecaptan
(RSH)... Cc tp cht k trn l cc tp cht khng mong mun trong qu trnh
khai thc, ch bin, vn chuyn, s dng v bo qun kh cho mc ch lm
nguyn liu t, tng hp hu c-ha du... S tn ti ca cc kh axit gy nns n mn kim loi, gim hiu qu ca cc qu trnh xc tc, lm ng c xc
tc, gy nhim mi trng, c hi cho ngi s dng... Bn cnh s c mt
hm lng cao CO2 trong kh cng lm gim nhit chy ca kh, gim hiu
qu ca qu trnh vn chuyn kh.
Vi cc nguy hi trnh by, th s c mt ca cc cu t mang tnh axit
trong kh cn phi c khng ch mt hm lng nh nhm gim thiu
nhng tc hi m cc kh axit ny gy ra cho thit b, my mc, mi trng v
sinh vt. Cng ha lin bang Nga quy nh hm lng H2S khng c vt qu
22mg/m3 cn M quy nh kht khe hn: hm lng H2S khng c vt qu
5,7mg/m3; nng CO2 trong khong 1~2% th tch...
Do vy qu trnh lm ngt kh l mt qu trnh quan trng v khng th thiu
trong bt k nh my ch bin kh no.
Trn th gii c rt nhiu nghin cu nhm lm sch kh t nhin v
kh ng hnh khi cc cu t axit bng cc phng php hp ph v phng
php hp th. Vic la chn cc phng php lm ngt kh cn ch nh gi
thnh phn ca nguyn liu bao gm c tp cht m trong kh thnh phm yu
cu phi loi b. Mt s tp cht khi tc dng vi cc dung mi c th hnh
thnh cc hp cht ha hc m trong giai on ti sinh s khng b phn hy
(phn ng khng thun nghch trong iu kin qu trnh). iu ny dn n
gim hot tnh dung mi v kt qu l dung mi mt hon ton hot tnh.
Huy NL-H.U.T 2
7/31/2019 Lam Ngot Khi
4/27
Lm sch kh khi H2S,CO2 v cc hp cht hu c cha lu hunh
Thc t cho thy, nhng lng tp cht nh i khi li gy nhng nh
hng rt ln n vic la chon dung mi hoc cng ngh lm sch kh. T l
H2S/CO2 trong kh nguyn liu cn phi c cc nh cng ngh xem xt thn
trng do nng H2S trong cc kh axit l yu t quyt nh la chn cngngh, phng php lm sch kh, phng php x l v thu hi cht thi ca
cng ngh...
Di y xin trnh by cc phng php v cng ngh lm ngt kh v
ang c p dng trn th gii c mt ci nhn tng quan v quy trnh quan
trng ny.
II. Qu trnh hp phII.1 C s ha l
Hp ph l qu trnh ht cc cht ln b mt xp ca cht rn nh cc i
lc trn b mt. Cc vt liu ny c gi l cht hp ph, cht b ht gi l cht
b hp ph. Lc hp ph ha hc do lc ht phn t Vanderwall tc dng trong
khong khng gian gn st b mt gi l hp ph vt l.
Mi phn t b hp ph (pha kh hay lng) u gim t do, nn hp ph
lun km theo s ta nhit.
Khi tin hnh la chn cht hp ph trong cng nghip cn ch ti cc
yu cu sau:
-Cht hp ph c b mt ring ln.-C hp ph chn lc.-C tr lc nh i vi dng kh.-C th ti sinh d dng.-Thi gian lm vic lu.- bn c chu s rung ng v cc tc ng trong nhiu cng
on ca qu trnh.
Trong cng ngh lm ngt kh nu dng phng php hp ph s p ng
tt vi kh c hm lng H2S, RSH trung bnh v thp. Phng php c chn
Huy NL-H.U.T 3
7/31/2019 Lam Ngot Khi
5/27
Lm sch kh khi H2S,CO2 v cc hp cht hu c cha lu hunh
lc cao, H2S thu c c tinh khit cao, t chu nh hng ca p sut. Chi
ph cho cht hp th l tng i thp.
Nhng nhc im ln ca qu trnh hp ph trong lm ngt kh l qu
trnh xy ra chm, cht hp ph kh ti sinh, hiu qu ca qu trnh thp nnphng php s dng cht hp ph l t ph bin.
II.2. Mt s cht hp ph c th dng lm ngt kh
Silicagel, Al2O3, than hot tnh, zeolit.
Cc oxit kim loi: Fe2O3, ZnO,...
III. Qu trnh hp th
III.1. C s ha l
Hp th l qu trnh pha lng ht pha kh. Kh c ht gi l cht b hp
th, cht lng dng ht gi l cht hp th. i km vi qu trnh hp th l
qu trnh nh hp th.
Hp th v nh hp th l hai qu trnh chuyn khi c bn c s dng
tch cc cu t khng mong mun ra khi kh t nhin v kh ng hnh. Bn
cht ha l ca qu trnh l s hnh thnh cn bng pha gia hai pha kh-lng do
s khuch tn ca cc cht t pha n sang pha kia. ng lc ca qu trnh
khuch tn l s chnh lch p sut ring phn gia cc cu t trong pha lng v
pha kh. Nu p sut ring phn ca cc cu t trong pha kh ln hn trong pha
lng th s xy ra qu trnh hp th (cht lng hp th cht kh), cn ngc li th
xy ra qu trnh nh hp thu (cht kh c tch ra khi pha lng) Thc t, tnh
ton ng lc ca qu trnh khuch tn
c tnh qua nng cc cu t, v psut ring phn t l thun vi nng .
Cht hp th cn tha mn cc yu cu sau:
-C kh nng hp th chn lc-C p sut hi bo ha b mt mt dung mi trong qu trnh l b nht.-Nhit dung ring b, tiu tn nng lng cho qu trnh ti sinh nh.-Nhit si khc xa vi nhit i si ca cht b hp th, nh th d
dng ti sinh dung mi bng chng ct.
Huy NL-H.U.T 4
7/31/2019 Lam Ngot Khi
6/27
Lm sch kh khi H2S,CO2 v cc hp cht hu c cha lu hunh
-Nhit ng rn thp, khng b ng rn ti nhit lm vic.- nht ca cht hp th nh.-Khng to thnh kt ta khi hp th.-t n mn, t bay hi, mt mt t trong qu trnh.-C bn nhit v bn oxy ha-Khng c hi cho con ngi v mi trng.-Gi thnh r, d kim.Trong nh my ch bin kh ni ring v trong cng ngh lc-ha du ni
chung qu trnh hp th c s dng kh ph bin. Qu trnh hp th v nh
hp th
c tin hnh theo mt chu trnh kn v lin tc. tch cc cu t c tnh axt trong kh t nhin v kh ng hnh ng i
ta s dng ch yu l cc qu trnh hp th [2] bi tnh hiu qu v kinh t ca
n. Di y l cc qu trnh hp th c phn loi theo c im tng tc ca
kh axit vi dung mi (cht hp th): hp th ha hc v hp th vt l.
III.2. Qu trnh hp th ha hc
Cc qu trnh hp th ha hc lm sch kh bng dung mi l nhng dung
dch nc alkanolamin (monoetanol amin, dietanol amin, diglycol amin...) chng
da trn phn ng ha hc ca cc hp cht khng mong mun vi alkanolamin.
Cc qu trnh amin m bo lm sch trit kh khi H2S, CO2 vi p
sut v nng lm vic ca chng trong kh ban u khc nhau, ha tan cc
hydrocacbon trong nhng cht hp th ny khng cao. Thit b v cng ngh ca
qu trnh n gin v bn.
Nhc im c bn ca qu trnh l khng tch c ton b H2S, CO2,
RSH, COS v CS2. Mc tch mercaptan v cc hp cht cha lu hunh khc
thp, tng tc ca mercaptan, COS v CS2 vi mt s dung mi k trn to
thnh hp cht khng th ti sinh c trong iu kin ca qu trnh. Mun ti
sinh dung mi khi c mt mercaptan, COS v CS2 trong kh t nhin v kh ng
hnh cn phi c bc tun hon ca cht hp th cao, tiu hao nhit lng ln.
Mt iu cn lu rng cht hp th v sn phm tng tc ca chng vi cc
Huy NL-H.U.T 5
7/31/2019 Lam Ngot Khi
7/27
Lm sch kh khi H2S,CO2 v cc hp cht hu c cha lu hunh
tp cht cha trong kh c th lm tng tnh n mn thit b, i hi vt liu v
cng ngh ch to thit b tn km.
S gia tng nng cht hot ng v mc bo ha dung mi bi H 2S
v cc hp cht khng mong mun khc s lm tng tnh n mn ha hc.V vykh nng hp th ca cc dung mi ny thng b hn ch bi mc bo ha
gii hn cho php ca cc cht hp th bng cc kh axit.
Bng 1 di y a ra mt vi tnh cht ho l cn bn ca alkanolamin.
Bng 1: Tnh cht ha l c bn ca MEA, DEA, DIPA, DGA
MEA DEA DIPA DGA
Khi lng phn t 61 105,1 133,2 105,1
Khi lng ring (kg/m3) 1018 1090 989 1055
Nhit si (0C) p sut
110 Pa 171 --- 248,7 221
660 Pa 100 187 167 ---
1320 Pa 69 150 133 ---
p sut hi bo ha (Pa)
20
0
C
48 1,33 1,33 1,33
Nhit ng c (0C) 10,5 28 42 9,5
nht tuyt i (Pa.s)0,241
( 200C)0,38
( 300C)0,198
( 450C)0,026
( 240C)
ha tan trong nc(%KL)
200Chon ton 96,4 87 hon ton
Nhit ha hi (J/kg)
1.105Pa1486,4 1205,9 722,5 917,4
Di y l mt s cng ngh lm ngt kh s dng qu trnh hp th ha
hc c ng dng ph bin trn th gii.
III.2.1. Qu trnh lm ngt kh bng dietanol amin (DEA) [2]
Qu trnh lm ngt kh bng phng php hp th ha hc s dng dung
mi l dietanol amin (DEA). Nng DEA trong dung dch ph thuc vo nng
kh axit trong nguyn liu ban u, bo ha kh axit ca dung dch thay
i t 20% ti 30% khi lng. Nu nng trong dung dch ca kh axit l
Huy NL-H.U.T 6
7/31/2019 Lam Ngot Khi
8/27
7/31/2019 Lam Ngot Khi
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Lm sch kh khi H2S,CO2 v cc hp cht hu c cha lu hunh
III.2.3 Qu trnh lm ngt kh bng iglycolamin (DGA) [2]
Qu trnh s dng dung mi l dung dch nc diglycolamin (DGA) vi
nng cht hot ng 60%-65% khi lng. Vi nng cao nh vy dung
mi c th lm sch trit kh t nhin v kh ng hnh khi H 2S (n5,7mg/m3). Tng tc ca DGA vi CO2, COS, CS2 v mercaptan to thnh cc
hp cht d ti sinh. Trong qu trnh ti sinh kh nng thu hi CO2, COS, CS2 v
mercaptan l tng i cao. bo ha ca dung dch DGA c th t ti 40-50
lt kh axit trn 1 lt dung dch.
Qu trnh rt thun li khi lm ngt kh nguyn liu c hm lng kh axit
t 1,5% ti 8%. ha tan cc hydrocacbon trong kh nguyn liu v hot tnh
n mn ca dung mi l khng cao. Tht thot dung mi trong qu trnh l b.
III.2.4. Qu trnh lm ngt kh bng monoetanol amin (MEA) [1, 2]
Qu trnh s dung mi l dung dch nc monoetanol amin (MEA). Nng
MEA khng c vt qu 15-20% th tch. Khi bo ha dung dch MEA c
nng cao hn bng cc kh axit th vn tc n mn kim loi tng.
Trong thit k h thng lm sch kh t nhin v kh ng hnh bng MEA
cc nh k thut nhn thy rng nng kh axit i ra t dy thp hp th phikhng ln hn 65-75% nng cn bng (theo t l vi kh nguyn liu ban u).
Khi mc bo ha dung dch phi khng ln hn 0,3-0,4 mol/mol MEA.
u im ca qu trnh l lm sch trit kh khi H2S v CO2 trong mt
khong p sut ring phn rng. MEA c tnh n nh ha hc cao, ti sinh d
dng, kh nng phn ng cao, cng ngh v thit b n gin c bn cao khi
vn hnh ng. Dung mi MEA rt t hp th hydrocacbon nn trong qu trnh
ti sinh c th thu hi cho qu trnh sn xut lu hunh.Nhc im ca qu trnh l mc bo ha dung dch thp, lu lng
ring ln v chi ph vn hnh cao (cao hn 25-40% so vi DGA). Cc tp cht
nh CO2, COS, CS2, HCN, SO2, SO3 khi tng tc vi dung mi to thnh hp
cht cao phn t khng ti sinh c hoc kh ti sinh, lm mt hot tnh ca
cht hp th, tng tnh to bt v tnh n mn ca dung mi. V vy khi c COS
v CS2 qu trnh khng c ng dng. Mc thu hi mercaptan v cc hp
cht hu c cha l
u hunh khc thp. Tng khuynh h
ng to bt khi c cchydrocacbon lng, sunfua st, thiosufit v cc sn phm phn hy MEA.
Huy NL-H.U.T 8
7/31/2019 Lam Ngot Khi
10/27
Lm sch kh khi H2S,CO2 v cc hp cht hu c cha lu hunh
III.3. Qu trnh hp th vt l
Cc qu trnh lm sch kh bng phng php hp th vt l cc cu t axit
trong kh t nhin v kh ng hnh bng dung mi hu c (propylen cacbonat,
imetyl ete polyetylenglycol, N-metyl pirrolidon...). Chng da trn hp th vt lch khng phi l cc phn ng ha hc nhqu trnh hp th ha hc.
Trn nguyn tc cc dung mi hu c c th s dng lm sch ton b
kh khi H2S, CO2, RSH, COS v CS2 khi p sut ring phn ca chng ln trong
iu kin hp th. Cht hp th thng khng si bt, khng n mn thit b, c
nhit ng c thp... Vi cc u im ny th vic s dng dung mi hu c
cho qu trnh rt thch hp khi p dng ti nhng vng c iu kin nhit kh
hu lnh.
Khi p sut ring phn ca cc hp cht khng mong mun cao, qu trnh
lm sch kh bng dung mi hu c c yu cu chi ph u t v vn hnh t hn
i vi vic thc hin qu trnh hp th ha hc bng amin. Vic ti sinh cht
hp th vt l din ra trong nhiu trng hp khng cn cp nhit m nh gim
p sut h thng.
Nhc im c bn ca qu trnh l dung mi hu c c s dng li hp
th thng i tt cc hydrocabon. Nhiu trng hp vic lm sch kh l cha
trit . Bng 2 di y trnh by mt vi tnh cht vt l ca mt s dung mi
hp th vt l thng gp
Bng 2: Tnh cht vt l ca mt s dung mi hp th vt l
Propylencacbonat DMEPEG NMP
Nhit si (0
C) 242 151 275Nhit nng chy (0C) -49 22-29 24
Khi lng ring 250C (kg/m3) 1200 1000 1000
Khi lng phn t 102 280 99
nht 250C (Pa.s) 6,64.10-6 5,8.10-3 1,87
p sut hi bo ha 250C (Pa) 0.666 1,33 133,3
Nhit dung ring (KJ/(kg.)) ---2,43
( 250
C)
1,67
( 200
C)
Huy NL-H.U.T 9
7/31/2019 Lam Ngot Khi
11/27
Lm sch kh khi H2S,CO2 v cc hp cht hu c cha lu hunh
Di y l mt s cng ngh lm ngt kh s dng qu trnh hp th vt
l c ng dng ph bin trn th gii.
III.3.1. Qu trnh Flour[2]
Qu trnh c nghin cu bi cng ty Flour. H thng cng nghip u
tin c xy dng M nm 1960 lm sch kh thin nhin khi CO2 (45%
th tch) v H2S (70mg/m3). Cht hp th c s dng rng ri l
propylencacbonat. Propylencacbonat ha tan tt H2S, CO2, RSH, COS, CS2 v
cc hydrocacbon; c tc dng n mn yu i vi thp cacbon thng thng, bn
v mt ha hc trong iu kin qu trnh, c p sut hi bo ha thp.
Qu trnh Flour c th s dng lm sch kh thin nhin, du m vinng CO2 cao v t l H2S/CO2 thp. iu kin thun li nht l m bo c
p sut ring phn tng cng ca cc cu t axit trong kh nguyn liu ln hn
0,4MPa. Nhit hp th trong khong t 0 n 60C. Ti sinh cht hp th
khng cn cp nhit m bng cch gim p sut qua tng bc ca h thng (c
thit b phn ly). Qu trnh hp th mt lng ng k cc hydrocabon nn
khng th s dng lm nguyn liu cho h thng sn xut lu hunh.
III.3.2. Qu trnh Selecsol[2]
Qu trnh Selecsol c nghin cu bi cng ty Ellaid Chemical
Corporation vo cui nhng nm 60. Cht hp th c s dng l eteimetyl
polyetylenglycol (DMEPEG); dung mi ny khng c, bn v mt ha hc
trong iu kin qu trnh, khng si bt, khng c tnh n mn, d b phn hy
khi lm sch nc thi bng vi sinh vt, c tnh chn lc cao. Bng nhng ci
tin cng ngh qu trnh c th lm sch trit kh thin nhin c nng H2S
v CO2 cao v trung bnh (qu trnh hp th c 97% H2S v 85% CO2). Kh
nng ha tan ca DMEPEG i vi cc hp cht khc nhau tng nh sau:
C2H6
7/31/2019 Lam Ngot Khi
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Lm sch kh khi H2S,CO2 v cc hp cht hu c cha lu hunh
c tnh ca dung mi DMEPEG l m bo hp th chon lc H2S vi s
hin din ca CO2. iu ny l rt c ngha khi tin hnh lm sch hai bc, bc
th 1 c th thu c nguyn liu tt sn xut lu hunh cn bc th 2 ta c
nguyn liu sn xut CO2 thng phm. V vy qu trnh Selecsol c th chiu qu khi cn sn xut ng thi c hai sn phm. Hiu qu ca qu trnh
tng cng vi s tng p sut lm vic v nng CO 2, H2S trong kh nguyn
liu.
Qu trnh Selecsol c tnh uyn chuyn cao, nng cc cu t axit trong
kh ban u c th thay i trong mt khong rng m khng lm gim cht
l
ng ca qu trnh lm ngt kh. Ch nhit ty theo i t
ng dao ng t 10ti 150C, p sut c gi trong khong 6,8-7 MPa. Ti sinh cht hp th bng
cch gim p theo tng bc ca h thng m khng cn cp nhit.
III.3.3. Qu trnh Purizol[2]
Qu trnh ny c nghin cu bi cng ty Lurgi, h thng cng nghip
u tin c xy dng c vo nm 1963 lm sch kh thin nhin khi
H2S v CO2.
Cht hp th c s dng l N-metylpirrolydon (NMP). NMP khng c,
ha tan tt H2S, CO2, RSH v hydrocacbon, hp th hi nc, khng c tc dng
n mn, bn v mt ha hc, d phn hy khi lm sch nc thi bng phng
php vi sinh, c trng bi tnh chon lc cao v m bo hp th chn lc H2S
khi c mt CO2 ( 200C v 0,1MPa ha tan H2S ln gp 10 ln CO2). Quy
trnh cng ngh Purizol khi c mt hydrocacbon lng d to bt. Do p sut hi
bo ha ca NMP ln nn mt mt dung mi cao nu khng p dng cc bin
php thch hp.
Ch cng ngh ca qu trnh hp th: nhit cht hp th 20-280C,
nhit kh nguyn liu trong cc i tng khc nhau dao ng trong khong
t 0 ti 150C, p sut c gi trong khong 5-7,5 MPa.
Ti sinh cht hp th c th bng cch gim p sut qua tng bc h thng
m khng cn cp nhit, nu lm sch trit ta p dng bin php tit lu p
sut v cp nhit.
Huy NL-H.U.T 11
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Lm sch kh khi H2S,CO2 v cc hp cht hu c cha lu hunh
III.4. Qu trnh t hp
Qu trnh t hp lm sch kh t nhin v kh ng hnh khi cc cu t
axit bng hn hp dung dch nc alkanolamin vi dung mi hu c nh
sulfolan, metanol... Chng da trn hp th vt l cc hp cht khng mongmun bng dung mi hu c v tng tc ha hc vi alkanolamin, l phn phn
ng tch cc ca cht hp th. Qu trnh kt hp c nhiu u im ca hp
th vt l v hp th ha hc, ni bt l vic lm sch trit H 2S, CO2, RSH,
COS v CS2 khi kh t nhin v kh ng hnh.
Nhc im c bn ca qu trnh l s hp th tng i tt cc
hydrocacbon. iu ny lm hn ch vic thu hi sn xut lu hunh sau khi
tin hnh ti sinh cht hp th.c trng cho qu trnh t hp l qu trnh sulfinol. Qu trnh c
nghin cu bi cng ty Sell (M), h thng cng nghip u tin c a vo
s dng nm 1964. Cht hp th c s dng l hn hp dung dch nc
diizopropanolamin vi sulfinol (xiclotetrametilensulfon). Hn hp gm 30%
diizopropanolamin, 64% sulfolan v 6% nc c gi l Sulfinol. Thnh phn
cht hp th c th thay i ph thuc vo cht lng kh ban u.
Bng 3: Tnh cht ha l ca diizopropanolamin v sulfolan
Diizopropanolamin Sulfolan
Nhit si (0C) 248 288
Nhit nng chy (0C) 42 8-10
Khi lng ring 250C (kg/m3) --- 1,27
Khi lng phn t 133,2 ---
nht (Pa.s) 0,192 ( 480C) 0,99.10-2 ( 250C)
p sut hi bo ha 250C (Pa) 1,33 ---
Sulfinol ha tan tt H2S, CO2, RSH, COS , CS2 v hydrocacbon. N bn
nhit v bn ha. C nhit dung ring v p sut hi bo ha thp. c th c s
dng lm sch ton b kh kh khi cc hp cht cha lu hunh v oxy
khng mong mun; cho php tin hnh lm sch ton b kh khi mercaptan,
CS2 ng thi; mt mt do tng tc ha hc ca dung mi vi CO2 l khng
ng k (s phn hy trong cng nghip t hn MEA 4-8 ln). Kh nng hp thca sulfinol cao hn MEA khong 2 ln.
Huy NL-H.U.T 12
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Lm sch kh khi H2S,CO2 v cc hp cht hu c cha lu hunh
Qu trnh hot ng hiu qu nht khi m bo t l cc cu t axit trong
kh H2S/CO21 v p sut ring phn ca chng 7-8MPa. bo ha ca
sulfinol c th t 85% (cao hn ca MEA vi ln). V vy thc hin qu trnh
sulfinol cn tun hon dung dch t hn, chi ph vn hnh thp hn. Nhng thc
t cng cho thy khi p sut ring phn nh th s dng dung mi MEA v
Sulfinol hiu qu l nh nhau.
V. Qu trnh lm ngt kh bng phng php hp th ha hc sdng dung mi monoetanol amin (MEA)
Phng php ny c s dng t nm 1930, hin nay c ng dng rt
rng ri. Qu trnh tng tc ca H2S v CO2 vi MEA c m t bng cc
phn ng sau:
2HO-C2H
4NH
2+ H
2S (HO-C
2H
4-NH
3)
2S
(HO-C2H
4-NH
3)
2S + H
2S 2HO-C
2H
4-NH
3HS
Hay HO-C2H
4-NH
2+ H
2S HO-C
2H
4-NH
3HS
2HO-C2H4-NH2 + CO2 + H2O (HO-C2H4-NH3)2CO3
(HO-C2H
4-NH
3)
2CO
3+ CO
2+ H
2O 2HO-C
2H
4NH
3HCO3
Hay HO-C2H
4-NH
2+ CO2 + H2O HO-C2H4-NH3HCO3
Hoc 2HO-C2H
4-NH
2+ CO
2HO-C
2H
4-NHCOO-NH
3-C
2H
4-HO
Hiu ng nhit ca phn ng l: khi tng tc H2S v CO2 vi dung dch
MEA tng ng l 1905 v 1917,6 KJ/kg.
nhit thp cc phn ng xy ra t tri sang phi, nhit cao phn
ng xy ra t phi sang tri. Trong trng hp u H2S v CO2 lin kt vi cht
hp th, trong trng hp th hai din ra s phc hi cht hp th v tch cc kh
axit c MEA hp th (H2S v CO2). Qu trnh hp th H2S v CO2 bng MEA
xy ra p sut cao v nhit t 25 ti 400C, cn ti sinh cht hp th MEA
thc hin p sut gn p sut kh quyn v nhit trn 1500
C. S nguynl cng ngh lm sch kh khi H2S v CO2 bng MEA c m t hnh 1:
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Lm sch kh khi H2S,CO2 v cc hp cht hu c cha lu hunh
Hnh 1: S nguyn l cng ngh hp th bng MEA
1-Thp hp th 2,3,4-Thit b phn ly
5,6-Thit b lm ngui bng khng kh 7,8-Thit b lm lnh bng nc
9-Thit b trao i nhit 10-Thp nh hp th
11-Reboiler
I-Kh nguyn liu II-Kh sch (kh ngt)III-Dung mi bo ha IV-Kh phn ly
V-Dung mi nh hp th mt phn VI-Kh axit
VII-Dung mi ti sinh tun hon tr li thp hp th
Nhn trn s hnh 1 ta thy kh nguyn liu c a vo thp hp th
1 pha di y thp c nhit khong t 10 ti 400C, n c ti bng
dung mi MEA c cho vo t nh thp hp th 1. T nh thp kh sch (kh
ngt) i ra, cn pha di y thp hp th cht hp th bo ha kh axit (nhit
cht hp th bo ha khong 55-600C). Kh sch sau thit b phn ly 2 c
a ti ni s dng. Cht hp th bo ha i vo thit b phn ly 3, y nh s
tit lu dung dch, cc hydrocacbon b hp th s c tch ra v c th c
a i s dng lm nhin liu. Sau thit b phn ly 3 cht hp th bo ha kh
axit c un nng trong thit b trao i nhit 9 n nhit khong t 95 0C ti
1000Cri c a vo phn gia ca thp nh hp th 10. Ti thp nh hp th
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Lm sch kh khi H2S,CO2 v cc hp cht hu c cha lu hunh
10, cc kh axit, nc, hydrocacbon cn st s c bay hi. p sut lm vic ca
thp nh hp th l 0,15MPa, nhit ca y thp nh hp th 10 c gi
trong khong 115-1300C nh t nng dung mi i ra t y thp bng thit b
gia nhit y thp (reboiler) 11.Hn hp kh axit, nc, hydrocacbon i ra t nh thp nh hp th 10
c lm lnh qua thit b trao i nhit bng khng kh 6 v bng nc 8. Sau
hn hp hai pha i vo thit b phn ly 4, y nc c tch ra khi kh
axit v hydrocacbon. Nc thit b phn ly 4 c hi lu nh thp nh hp
th 10 nhm loi tr s li cun MEA ln cng sn phm nh. Kh axit c
a ti khu sn xut lu hunh. Dung dch MEA sau khi ti sinh c a qua
thit b trao i nhit tn dng nhit, qua thit b lm ngui bng khng kh 5,
thit b lm lnh bng nc 7 c tr li thp hp th 1 nhit 35-450C .
Qu trnh lm sch kh thin nhin v kh ng hnh khi H2S v CO2
bng MEA yu cu nng MEA khng c vt qu 15-20% th tch. Khi
bo ha cc dung dch c nng cao hn bng cc kh axit th vn tc n mn
kim loi tng (dung dch MEA tinh khit khng c tnh n mn). Mi lin quan
gia nng dung dch v vn tc n mn nh vy lm hn ch kh nng tng
hiu qu ca qu trnh lm sch kh bng MEA. Tuy nhin trong nhng nm gn
y nh vic nghin cu cc cht c ch n mn xut hin kh nng tng nng
cht hp th trong dung dch ti 30% th tch, nn qu trnh MEA tr nn c
li hn. Hn na, kh khai thc t m Bch H c p sut ring phn ca cc cu
t kh axit l thp nn p dng quy trnh lm ngt kh bng MEA l hp l v hiu
qu (qu trnh lm sch bng MEA c ngh dng lm sch kh khi H2Sv CO2 khi p sut ring phn ca chng khng ln hn 0,6-0,7 Mpa [2]).
u im ca qu trnh l lm sch trit kh khi H2S v CO2 trong mt
khong p sut ring phn rng. MEA c tnh n nh ha hc cao, ti sinh d
dng, kh nng phn ng cao, gi thnh r v d kim. Cng ngh v thit b n
gin c bn cao khi vn hnh ng. Dung mi MEA tng i kh hp th
hydrocacbon nn trong qu trnh ti sinh c th thu hi cho qu trnh sn xut
lu hunh.
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Lm sch kh khi H2S,CO2 v cc hp cht hu c cha lu hunh
Nhc im ca qu trnh l mc bo ha dung dch thp, lu lng
ring ln v chi ph vn hnh cao (cao hn 25-40% so vi DGA). Cc tp cht
nh CO2, COS, CS2, HCN, SO2, SO3 khi tng tc vi dung mi to thnh hp
cht cao phn t khng ti sinh c hoc kh ti sinh, lm mt hot tnh cacht hp th, tng tnh to bt v tnh n mn ca dung mi. V vy khi c COS
v CS2 qu trnh khng c ng dng. Mc thu hi mercaptan v cc hp
cht hu c cha lu hunh khc thp. Tng khuynh hng to bt khi c cc
hydrocacbon lng, sunfua st, thiosufit v cc sn phm phn hy MEA cng
nhcc tp cht c hc v mt s dng cht c ch n mn ri vo h thng.
Theo s liu ca Kempbel vn tc phn hy MEA do tng tc khng
thun nghch ca MEA vi CO2, COS v CS2 c th t 3,35kg/1000m3 CO2;
1kg/1m3 COS; 1kg/1m3 CS2. Cc hp cht hu c cha lu hunh (mercaptan,
iunfua, thiophen...) cha trong kh t nhin v kh ng hnh thc t khng
tng tc vi MEA. loi cc tp cht c hc v sn phm ca phn ng
khng thun nghch ngi ta p dng nhiu bin php khc nhau nh lc, bay
hi trong bnh c bit... Nng ca cc sn phm ny trong dung mi khng
c vt qu 0,1-0,5%.
loi tr s to bt ngi ta cho thm vo dung dch MEA ph gia
chng to bt (0,001-0,0015% khi lng) nh cc ch phm KE-10-12, KE-10-
21 ca Lin X... iu ny cho php gim tht thot dung mi, h thng hot
ng n nh hn, tng nng sut.
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Lm sch kh khi H2S,CO2 v cc hp cht hu c cha lu hunh
Huy NL-H.U.T 17
h tr Tnh ton, thit k thp hp th lm ngt khbng phng php hp th ha hc s dng dung mi MEA
iu kin lm vic ca thp hp th ty thuc vo yu cu lm sch, nng sut,
nng MEA v.v... m thay i trong mt phm vi hp (cc s liu a ra di
y c tnh cht tham kho, khi tnh ton vi cc ni dung c th cn tnh lp ti
khi cn bng vt liu v cn bng nng lng c tha mn m tm ra ch
lm vic thch hp cho thp):
Nhit kh nguyn liu vo thp: Tv = 38oC
Nhit dung dch MEA ti sinh: Tts = 44C
p sut lm vic trong thp hp th: P = 3,5 MPa
Dung dch MEA nn chn c nng 15% (theo khi lng) c tun
ton lin tc. C th coi qu trnh ti sinh MEA l hon ton khng c mt mt,
suy hao.
Kh sau khi ra khi thp hp th yu cu hm lng H2S khng qu
0,001 phn th tch; hm lng CO2 khng qu 0,005 phn th tch.
GrI. Cn bng vt cht ca thp hp th
Dng kh nguyn liu Gv c a vo phn di
ca thp hp th, cn kh sch Gr c a ra t nh
thp. Dung dch nc monoetanol amin Ats c a vo
t trn ca thp, cn dung dch bo ho cc cu t axit
Abh
c a ra t y thp.
Ats
GvDung dch nc monoetanol amin hp th cc cu
t axit, trong thp hp th xy ra cc phn ng ho
hc sau:Abh
2OHCH2CH2NH2 + CO2 + H2O (OHCH2CH2NH3)2CO3 (1)
(OHCH2CH2NH3)2CO3 + CO2 + H2O 2OHCH2CH2NH3HCO3 (2)
2OHCH2CH2NH2 + H2S (OHCH2CH2NH3)2S (3)
(OHCH2CH2NH3)2S + H2S 2OHCH2CH2RNH3HS (4)
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Lm sch kh khi H2S,CO2 v cc hp cht hu c cha lu hunh
Cc cu t axit v cc hydrocacbon nh b ho tan mt phn trong
dung dch nc MEA
Phng trnh cn bng vt cht ca thp hp th:
Gv + Ats = Gr + Abh
trong :Gv : lu lng khi lng ca kh nguyn liu i vo thp hp th (kg/h)
Ats : lu lng khi lng ca dung mi MEA 15% ti sinh tun hon tr
li thp hp th (kg/h)
Gr : lu lng khi lng ca kh sch ra khi thp hp th (kg/h)
Abh : lu lng khi lng ca dung dch MEA bo ha ra khi thp hp
th (kg/h)
II.1. Tnh lu lng khi lng ca kh nguyn liu vo thp (GV)
II.2. Lu lng khi lng ca dung mi MEA 15% ti sinh (Ats)
Da vo ton c xy dng bng
cc s liu thc nghim [4] c tnh by
hnh 2 ta xc nh c khi lng
ring ca MEA 15% trong nc ti nhit
ti vo thp hp th tts = 440C l ts=
996 (kg/m3).
Xc nh lu lng th tch MEA
ti vo thp trong mt n v thi gian
bng cch ni suy th c m t
hnh 3 vi ph thuc vn tc kh nguyn
liu vo v tng hm lng kh axit axit
trong kh nguyn liu Hnh 2: Ton xc nh khi lngring ca dung dch etanolamin nc
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Lm sch kh khi H2S,CO2 v cc hp cht hu c cha lu hunh
Hnh 3: th tra cu tc tun hon ca dung dch MEA [3]
II.3. Lu lng khi lng kh sch ra khi thp hp th
So vi propan, butan, pentan th metan, etan tan ng k trong dung mi.
Lng metan, etan ha tan trong mt n v thi gian (m3/h) c tnh theo cng
thc sau:
4 4 2ht CH CH H O
273V = .V .
T+273; 2 6 2 6 2ht C H C H H O
273V = .V .
T+273
trong :VH2O : lu lng th tch nc c trong dung dch MEA (m
3/h)
CH4, C2H6 : ha tan ca CH4, C2H6 trong nc ti nhit t v p sut
thng (m3/m3)
II.4. Lu lng khi lng dung dch MEA bo ha ra khi thit b
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Lm sch kh khi H2S,CO2 v cc hp cht hu c cha lu hunh
III. Cn bng nhit lng ca thp hp th
Phng trnh cn bng nhit lng ca thp hp
th:Qr
Qv + Qts + Qa = Qr + QbhQts
Trong :
Qv : Lng nhit ca dng kh nguyn liu mang vo
thp (kW). Qa
Qts : Lng nhit dung dch MEA ti sinh mang vo
thp (kW). Qv
Qa : Lng nhit ta ra do hp th cc cu t (kW).QbhQr : Lng nhit m kh sch mang ra khi thp (kW).
Qbh : Lng nhit m dung dch MEA bo ha mang ra khi thp (kW).
III.1. Lng nhit ca kh nguyn liu mang vo thp (QV)
III.2. Lng nhit do dung dch MEA ti sinh mang vo (Qts)
Lng nhit do dung dch MEA ti sinh mang vo thp hp th c xc
nh bng cng thc:
Qts = Ats . HL
ts
Trong
Ats l lu lng khi lng dung mi MEA 15% ti sinh tun hon tr li
thp hp th.
HLts: entanpy ca dung mi MEA 15% ti nhit t=440C (kJ/kg)
Dung mi c ti sinh hon ton nn c th coi entanpi ca dung dchMEA ti sinh bng entanpy ca dung dch MEA 15%. Khi entanpy c
tnh theo cng thc:
HLts = Cp. t
Cp : Nhit dung ring ca dung mi MEA 15% ti t = 440C (KJ/kg.).
Cp c xc nh bng cch tra th c a ra hnh 4:
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Lm sch kh khi H2S,CO2 v cc hp cht hu c cha lu hunh
Hnh 4: th tra nhit dung ring ca MEA ti cc nng khc nhau1- Nc tinh khit 2- MEA 15% 3- MEA 30% 4- MEA 50%
III.3. Lng nhit ta ra do hp th cc cu t (Qa)
III.4. Lng nhit theo dng kh sch mang ra khi thp (Qr)
III.5. Lng nhit do dung dch MEA bo ha mang ra khi thp (Qbh)
III.6. Lng nhit do mt mt
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Lm sch kh khi H2S,CO2 v cc hp cht hu c cha lu hunh
IV. Thit k thp hp th
IV.1. Tnh ng knh ca thp hp th
ng knh thp hp th c tnh theo cng thc:
( )( )
35
360035
1800
+
++
=CK
GCK
L
D
o
KLK
o
L
a
trong : L l lu lng cht hp th bo ho i ra khi thp, kg/s.
L l khi lng ring ca cht hp th bo ho, kg/m3.
K l khi lng ring ca kh nguyn liu, kg/m3.
Ko = 0,3 l h s ca a lm vic.C = 480 l h s vi cht hp th khi khong cch gia cc
a l 0,6m.
IV.2. Tnh chiu cao ca thp hp th
Chiu cao ca thp hp th c xc nh bng cng thc
Hw = Ht + H0 + Hd
trong :
Ht : chiu cao nh thp thp (m)
H0 : chiu cao phn gn a (m)
Hd : chiu cao y thp (m)
Ta chn chiu cao ca nh thp v y thp H t = Hd = 1,5 (m)
Chiu cao thp phn c gn a c tnh theo cng thc:
0 0( 1).wH N h=
trong :
Nw: s a lm vic.
h0: khong cch gia cc a ng vi ng knh Da =3 (m) = 3000 (mm).
Theo [5, tr.169] nu ta la chn loi thp hp th l loi chp lm bng
thp h0 = 600 (mm) = 0,6 (m).
S a lm vic thc t ca thp c tnh theo cng thc:
LT
wNN
=
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Lm sch kh khi H2S,CO2 v cc hp cht hu c cha lu hunh
NLT: s a l thuyt
: h s s dng hu ch ca a. H s ny thng khng vt qu
25% - 40% [2] nn ta chn =30%=0,3
S a l thuyt cn thit m bo h s tch ca mt cu t trong thp
vi h s tch khng i trong tng a. S a l thuyt c xc nh bng
cng thc:
lg(1 )
lg(1 )
a
LTN
=
trong :
a: h s tch cc cu t trong thp hp th.
: h s tch trong cc a.
H s tch cc cu t trong thp hp th c tnh da vo hng s cn
bng pha kh (ch tnh vi CO2 v H2S, hp th C1, C2 th b qua)
,.
. .i i cb
T
Mm m
R T=
Vy hng s cn bng pha kh mCO2, mH2S no ln hn th tnh theo h s
tch pha kh .
H s tch trung bnh ca cc a c tnh theo cng thc:
. .
1a
K
K A h
We
=
trong :
K: h s chuyn khi khi hp th ha hc.
A: b mt tip xc pha.ha: chiu cao ca lp kh, chn ha=0,059 (m).
WK: Tc quy c ca dng kh trong iu kin lm vic (m/s).
Tnh K - h s chuyn khi khi hp th ha hc c tnh thng qua h s
chuyn khi khi hp th vt l:
1
1
K L
Km
=
+
K; L : h s chuyn khi trong pha kh lng (m/h).
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Lm sch kh khi H2S,CO2 v cc hp cht hu c cha lu hunh
m: hng s cn bng pha trong thp hp th vi h s hiu chnh vi lc
ion ca dung dch do hp th ha hc.
K - h s chuyn khi trong pha kh bng: K = Ks.Fw=A.WKm.hn.Fw
Ks h s chuyn khi trong pha kh tnh cho mt n v lm vic ca a
vi Fw=7m2
A=41700; WK=0,29; m=1; n=0,5; h=0,04
K = 41700 . 0,291 . 0,040,5 . 7 = 16933 (m/h).
L - h s chuyn khi trong pha lng bng: L = Ls.Fw=A.WKm.hn.Fw
Ls h s chuyn khi trong pha lng tnh cho mt n v lm vic ca
a Fw=7m2
A=240; WK=0,29; m=0,35; n=0,58; h=0,04
L = 240 . 0,290,35. 0,040,58 . 7 = 169 (m/h)
Qua cc s liu tnh ton c trn ta c h s tch trung bnh ca cc a.
Vy tnh c s a l thuyt:
v s a thc t:
Chiu cao thp phn c gn a:Vy chiu cao ton thp:
IV.3. Mt s tnh ton cc chi tit ca chp trn [5]
a) ng knh ng hi chn dh = 100 (mm).b) S chp phn b trn a:
2
20,1.h
D
n d=
vi D l ng knh trong ca thp (mm)
dh l ng knh trong ca ng hi (mm)
c) Chiu cao chp pha trn ng hi:2 0,25. hh d=
d) ng knh chp:
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Lm sch kh khi H2S,CO2 v cc hp cht hu c cha lu hunh
2 2( 2 )ch h h ch
d d d = + +
vi ch l chiu dy chp thng ly t 2-3 (mm).
e) Khong cch t mt a ti chn chp S = 0 25 (mm) chn = 2 (mm)f) Chiu cao mc cht lng trn khe chp h1 = 1540 (mm) chn = 20 (mm)g) ng knh ng chy chuyn:
4.
3600. . . .
x
c
x c
Gd
z =
trong : Gx: lu lng lng trung bnh i trong thp (kg/h)
x: khi lng ring ca lng (kg/m3).
z = 2 s ng hy chuyn.
c: tc lng chy trong ng chy chuyn ly bng 0,15 (m/s)
h) Khong cch t a ti chn ng chy chuyn:1
0,25.c
S d=
i) Khong cch t tm ng chy chuyn ti tm chp gn nht:1 1
2 2
c ch
c ch
d dt l = + + + +
trong : dc b dy ng chy chuyn, thng ly c = 2 4 (mm); l1 khong
cch nh nht gia chp v ng chy chuyn, thng chn l1=75 (mm).
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Lm sch kh khi H2S,CO2 v cc hp cht hu c cha lu hunh
Ti liu tham kho
[1]. Nguyn Th Minh Hin, Cng ngh ch bin kh t nhin v kh ng hnh,NXB Khoa hc v K Thut, H Ni, 2006.
[2]. M.A. Berlin, V.G. Gortrencop, H.P. Volcop, Cng ngh ch bin kh t
nhin v kh du m (bn ting Vit).
[3]. Kunhexov, Tnh ton cc qu trnh cng ngh ch bin kh (bn ting Nga),
1983.
[4]. S tay qu trnh v thit b cng ngh ha cht, Tp 1, NXB Khoa hc v K
thut, H Ni 2004.
[5]. S tay qu trnh v thit b cng ngh ha cht, Tp 2, NXB Khoa hc v K
thut, H Ni 2004.