lam ngot khi

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


2/27


3/27

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


4/27


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


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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


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-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


7/27


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


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9/27


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


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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


11/27


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


12/27


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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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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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:

Huy NL-H.U.T 13


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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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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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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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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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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

Huy NL-H.U.T 18


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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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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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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

Huy NL-H.U.T 21


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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

=

Huy NL-H.U.T 22


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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).

Huy NL-H.U.T 23


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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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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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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.

lam ngot khi

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