B MN CNG NGH HA HC

Academic year: 2014 - 2015

Msc. Nguyen Bao Viet

o Ngc Duy

S tn ch : 2 LT

S tit: - L thuyt: 21

- Bi tp: 9

Ti liu hc tp:

a/ Hc liu bt buc:

- Bi ging Cc qu trnh phn ring, B mn Cng ngh Ha hc, i hc Nng Lm TP.HCM

- Truyn khi, V B Minh, 2009, Nh xut bn HQG TP.HCM.

b/ Hc liu tham kho ghi theo th t u tin:

- Separation Process Principles, 3rd edition, J.D. Seader, E.J. Henley, D. K. Roper, 2011, Wiley-

VCH.

- Chemical Process Equipment Selection & Design, Stanley M.Walas, 1990, Butterworth-

Heinemann

1.1. nh ngha

1.2. Phn loi

1.2.1. Phn tch bng phng php bin i pha

MSA (mass separating agent) : b sung cc cht h tr qu trnh phn tch pha

- Phi chn la c tc cht ph hp vi quy trnh sn xut

- Phc hi tc cht b sung ???

- Tinh sch MSA khi sn phm ???

-Thit k thit b phc tp (kh m hnh ha)

Bng phn loi cc qu trnh phn ring theo PP bin i pha (File PDF)

ESA (energy separating agent): dng nng lng phn tch pha

- Thit k n gin

- Hao tn nng lng

- Sn phm t tp cht

- Ph bin trong cng nghip

1.2.2. Phn tch bng tr lc

1.2.3. Phn tch bng cch s dng cc tc cht rn

1.2.4. Phn tch bng cch s dng cc trng lc

Lc ly tm (centrifugation)

Khuch tn nhit (thermal diffusion)

in ly (electrolysis)

in di (electrophoresis)

1.3.La chn cc gii php cng ngh

1.3.1. Cc yu t nh hng

V d:

1.Tch oxy v nit khi hn hp khng kh bng phng php chng ct

2. Tch m-xylene khi p-xylene

3. Tch benzen v cyclohexane

4. Tch isopropyl alcohol t hn hp vi nc

5. Tch peniciline t nc trong hn hp sn phm ln men

1.3.2. ng dng

1.4. S khuch tn

1.4.1. nh lut Fick

D: h s khuch tn (m2/s)

q: dng khuch tn (mol/m2.s)

C: nng (mol/m3)

xA: nng phn mol (%)

1.4.2. Xc nh h s khuch tn D

* Trong hn hp kh D: cm2

T: K

P: atm

v tng khuch tn ca cc

nguyn t

* Trong hn hp khng in ly (Nonelectrolyte Liquid Mixture)

Phng trnh Stoke-Einstein (ch p dng cho dung dch c nng cht tan thp)

rA: bn knh ht phn tn

: nht pha lin tc (cP)

kB: hng s Boltzmann = R/NA = 1.38x10^-23 J/K

Phng trnh Wilke-Chang (p dng cho dung dch c nng cht tan cao)

vA: th tch ring cht tan A (cm3/mol)

: nc (2.6); methanol (1.9); ethanol (1.5); dung mi khng phn cc (1.0)

* Trong hn hp in ly (Electrolyte Liquid Mixture)

Phng trnh Nerst-Haskell R: 8.314 J/mol.K n: ha tr cc ion F: hng s Faraday = 96500 J/g-equiv : dn in (A/cm2)(V/cm)(g-equiv) Ti nhit khc 25C, cc gi tr trong bng 3.7 phi nhn cho T/(334B)

* S khuch tn ca vt liu sinh hc trong mi trng lng:

Phng trnh Geankoplis:

1.4.3. S khuch tn n nh

A. Khuch tn qua tm phng

12

21..zz

ccADN AAA

B. Khuch tn qua cylinder

)ln(.2.

12

21

rr

ccLDN AAA

B. Khuch tn qua vt hnh cu

12

2121 .....4

rr

ccDrrN AAA

(Mol/s)

(Mol/s)

(Mol/s)

1.4.4. S khuch tn khng n nh

z

A

zAz

cADN

..

zz

A

zzAz

cADN

..dz

t

cA A ..

Flow IN Flow OUT

2

2

.)/()/(

.z

cD

z

zczcD

t

c AzAzzAA

2

2

2

2

2

2

.z

c

y

c

x

cD

t

c AAAA

1.5. Qu trnh truyn khi

* Phng trnh tng qut:

dn

dCADAkN AABCcA A ....

* Cc chun s ph bin trong truyn khi:

AB

ScD

N.

AB

cSh

D

LkN

.

..Re

vLN

Schmidt (tng t Prandtl):

Sherwood (tng t Nusselt):

Reynolds (c trng dng chy):

Stanton .v

kN cSt

Xc nh hng s truyn khi k thng cc phng php thc nghim

Cng thc B mt truyn khi iu kin p dng

Mt phng Chy tng, 0.6 < Sc < 50

Mt phng Chy ri, 0.6 < Sc < 50, Re < 10^8

Mt phng 0.6 < Sc < 50, 5*10^5

Cc phng trnh thc nghim trn ch p dng khi dung dch long (nng phn

mol cht tan A < 5%) . Nu vt qu mc gii hn trn, nh hng ca dng chy

mng l ng k v h s truyn khi k s c thay bng h s truyn khi hiu

chnh k

2

1

21

1

1ln

)1()1()1(

)1('

A

A

AATBA

TBA

x

x

xxx

x

kk

Qu trnh truyn khi gia 2 h Lng Hi

a) L thuyt b) Thc t

)( AbAicA cckn Pha lng:

)( AiAbpA ppkn Pha kh:

Cn bng pha: AiAAi pHc .

cpA

AbAAbA

kkH

cHpn

/1/

.

p dng nh lut Henry:

AAbA

AbAA

Hcp

pHc

/

.

*

*

).().( ** AAbGAbALA ppKccKn

cApGcp

A

L kHkKkk

H

K .

111;

11

Cc phng trnh trn c th bin i theo nng phn mol:

).().( ** AAbyAbAxA yyKxxKn

x

A

yyxyAx k

K

kKkkKK

11;

1

.

11

Ai

AiApycx

x

yKkPkkCk ;.;.;

Trong trng hp bin thin ca x hoc y qu ln nn KA khng phi l hng s:

*

*

;;11

;1

.

11

AAi

AiAbx

AbAi

AAiy

x

x

yyxyyx xx

yym

xx

yym

k

m

kKkkmK

1.1. c tnh h s khuch tn ca hn hp oxygen (A)/ benzen (B) ti 38C v 2 atm.

1.2. c tnh h s khuch tn ca aniline (A) trong nc ti nng 0.5% mol theo

phng php Wike-Chang. Nhit ca dung dch l 20C v nht l 1.01 cP. Th tch

ring ca aniline ti nhit si bnh thng (457.6 K) l 107 cm3/mol.

1.3. c tnh h s khuch tn ca KCl trong nc 18.5C nu bit nht ca nc

ti nhit ny l 1.05cP.

1.4. Khng kh ti 32C c lm m bng cch thi qua mt ng container di 1.2 m

cha y nc. Vn tc khng kh di chuyn l 0.15 m/s. Nhit b mt nc l 20C.

p sut hi nc trong khng kh v trn b mt nc ln lt l 0.01174 atm v

0.02308 atm. nht ng hc ca nc l 1.51x10^-5 (m2/s) v h s khuch tn

khng kh l 2.77x10^-5 (m2/s).

Hy tnh h s truyn khi v lng nc bay hi qua mi n v b rng container

1.5. Kh SO2 (cht A) c hp th bi nc trong mt ct chm ti 50C, 2 atm. tan ti

a ca SO2 trong nc khong 3.43lbmol/ft3 (tng ng 55kmol/m3).

Cho y(Ab) = 0.085 v x(Ab) = 0.001.

H s truyn khi pha lng kc = 0.18 m/h

pha kh kp = 0.040 kmol/(h.m2.kPa)

Vi d liu v ng cn bng ca h SO2 trong nc v kh nh sau:

pSO2 (atm) cSO2 (lbmol/ft3)

0.0382 0.0606 0.1092 0.1700

0.00193 0.00290 0.00483 0.00676

Hy tnh lu lng SO2 b hp th trong cc trng hp sau:

a/ p dng nh lut Henry (coi KA l hng s) v b qua nh hng ca dng chy mng

b/ Xc nh da trn d liu thc v ng cn bng v vn b qua nh hng chy mng

c/ Kt hp c d liu thc v ng cn bng v nh hng ca dng chy mng.

2.1. nh ngha v phn loi

Hp ph (adsorption) l phng php ch

yu trong cng nghip phn loi hn

hp kh, loi b tp cht v thu hi cc hp

cht ha hc c gi tr cao.

Hp ph vt l: ch yu xy ra gia nc

v cc hydrocacbon, khng c phn ng

xy ra.

Hp ph ha hc: c phn ng gia cht

hp ph v cht b hp ph. C th l qu

trnh thun nghch hoc bt thun nghch

Gii hp (desorption): l qu trnh ngc

vi qu trnh hp ph vt l

H s hp ph:

A= L / (K.V)

L: lu lng dng lng

V: lu lng dng kh

K: h s cn bng pha c trng cho mi cht b hp ph

V hiu qu kinh t, gi tr ca A nn nm trong khong 1.25 2.0 trong 1.4 l

ti u. gim lu lng dng lng (cht hp ph) nhm tng hiu qu kinh t th

phi iu chnh cho K gim. Thng thng K s gim khi nhit T thp v p sut

hot ng P cao.

Ngc vi qu trnh hp ph l qu trnh gii hp:

S= 1/A= (K.V)/L

Qu trnh gii php hiu qu khi T cao v P thp (h tr qu trnh bay hi).

Bng 2.1. Cc qu trnh hp ph ph bin trong CNHH

2.2. Thit b

a/ Thp mm (Trayed tower)

b/ Ct chm (Packed Column)

c/ Thp phun

d/ Ct bubble

e/ Ly tm

2.3. Thp mm

Nguyn l:

Dng lng chy t trn xung v

lung kh i t di ln to

thnh 2 vng truyn khi:

Froth regime: cc bt kh hnh

thnh i xuyn qua pha lng

Spray regime: cc git lng hnh

thnh trong pha kh

T l gia cc vng ny ph

thuc vo tc ca lung kh

v dng cht lng (hp ph)

a/ Mm xuyn l

b/ Mm valve

c/ Mm kiu bubble

d/ Kiu hn hp

Bng 2.2. So snh hiu qu cc loi mm

2.3.1. Tnh ton s mm: (phng php th gii tch)

L: lu lng mol pha lng

V: lu lng mol pha kh

X: t l mol gia cht tan v phn cn li trong pha lng = x(1-x)

Y: t l mol gia cht tan v phn cn li trong pha hi = y(1-y)

H s K ti mm n bt k c tnh nh sau:

)1(

)1(

nn

nn

n

nn

XX

YY

x

yK

(2.1)

Cn bng vt cht: '.''.' 110 VYLXVYLX nn (2.2)

Phng trnh hp ph tng qut: )'/'()'/'( 011 VLXYVLXY nn (2.3)

Trong khi hu ht cc gi tr trong

phng trnh 2.3 l yu cu cng

ngh, gi tr L ty thuc vo iu

kin kinh t v bn cht ca qu

trnh hp ph.

L ln: tn km

L nh: khng hp ph

V vy, Lmin l yu t quyt nh

trong tnh ton s mm ca thp

hp ph.

Trong trng hp tng qut, tc ti thiu ca dng cht hp ph c tnh nh sau:

Nu dung dch long, phng trnh tr nn n gin hn:

n

n

n

n KV

xK

y

yyVL '.'.'

01

11min

(2.4)

(2.5)

Lu rng Lmin ph thuc rt nhiu vo K v V. Thc tin ch ra rng cc qu trnh

hp ph trong cng nghip din ra ph bin vi lu lng dng hp ph gia mc 1.1

2 ln Lmin. Trong gi tr 1.5 Lmin d em li h s hp ph ti u A= 1.4

S mm l thuyt xc nh nh sau:

- V ng lm vic theo phng trnh 2.3 vi L = 1.5Lmin (nu khng c thng tin v L)

- V s bc thang gia ng lm vic v ng cn bng t c gi tr u ra nh

yu cu

Nu qu trnh l gii hp, tin hnh tng t

2.3.2. Hiu sut thp mm

a

t

N

NE 0

S mm l thuyt

S mm thc t

Thp mm nhn chung c hiu sut kh thp (10-70%) v ph thuc vo cc yu t chnh sau:

- Tc dng lng v dng kh

- Thnh phn v tnh cht cc pha trong thp

- Thit k ca mm

i vi thit b hp th hydrocacbon, cc phng trnh thc nghim sau c th p dng

c tnh hiu sut thp mm:

a/ Phng php Dickramer (sai s 10%) vi

)log(8.572.190 LE

cPL 6.02.0

b/ Phng php OConell (sai s 15%) 2

0

..log0896.0

..log199.0597.1

L

LL

L

LL MKMKE

(2.6)

(2.7)

2.3.3. Hin tng ngp lt (Flooding)

Mt h thng mm thit k tt phi m bo khi vn

hnh dng lng ch i qua cc rnh trn mm trong khi

lung kh xuyn qua cc l ca mm. Hin tng ngp

lt s xy ra trong 2 trng hp sau:

- Tit din rnh qu nh cht lng c th chy

xung khi lu lng dng kh qu ln. Hin tng ny

c th khc phc nu Ad/A >10% v khong cch gia

cc mm > 24 inch (0.6m).

- Lu lng lng qu cao kt hp lu lng dng kh

cao to nn hin tng ngp lt trn mm (chiu cao

vng froth tng). Thit b thng hot ng n nh

nu lu lng dng kh t 85-90% ngng c th gy

ngp lt. V vy vic xc nh tc ti a ca dng kh

c th dn n hin tng ngp lt rt quan trng.

Tc gy ngp lt (flooding velocity):

5.0

.

V

VLf Cu

(m/s)

Trong C c xc nh da trn h s dng chy FLV

5.0

..

.

L

V

V

LLV

MV

MLF

Mi quan h gia C v FLV c xc nh theo cng thc sau:

FHAFST CFFFC ...

FST: h s sc cng b mt = (/20)^0.2

: sc cng b mt (dyne/cm)

FF: h s foam (nu h khng to foam, FF = 1)

FHA : bng 1 nu Ah/Aa> 0.1

bng 5(Ah/Aa)+0.5 nu 0.06< Ah/Aa

Hnh 2.1. Xc nh CF

theo FLV v khong

cch gia cc mm

H s FLV cng c dng xc nh din tch rnh nc trn mm

2.3.4. Chiu cao thp mm v gim p:

Khi lung kh i qua thp mm, p sut s suy gim do 3 nguyn nhn chnh sau:

- S tn p khi xuyn qua cc l c tit din nh trn mm

- Mt phn pha kh b gi li trong dng cht lng

- S hnh thnh v ph v cc bt kh do sc cng b mt gia 2 pha kh lng

gim p v chiu cao thp mm c mi lin h cht ch vi nhau bi v nu p sut

pha kh gim qu nhiu s dn n hin tng lung kh khng ln c ti nh

thp v lm suy gim hiu qu truyn khi ca thit b. Trung bnh vi thp mm,

st p cho mi mm t 0.35 1.03 kPa.

Chiu cao thp mm thng tnh bng khong cch gia cc mm x (s mm-1) v b

sung thm 10ft (3m) di y thp v 4ft nh thp. Khong cch gia cc mm dao

ng t 0.15 1m v cng ph thuc vo ng knh mm. Nu ng knh mm >

1m, khong cch gia cc mm ti u l 0.5m.

2.3. Thp m/ct chm

Bng 2.3. So snh cc pp sp xp vt chm

2.3.1. Tnh ton chiu cao thp m

p dng thuyt 2 lp film (chng 1)

;*111

xx

yy

kkK I

I

xayaya

I

I

yaxaxa yy

xx

kkK

*111

Chiu cao thp m tnh theo cng thc sau: OGOGT NHl .

Chiu cao 1 n v truyn khi trong thp:

AHHH

SyK

VH

SK

VH

LGOG

LMya

OG

ya

OG

/

.)1(

.

'

Dd long

S n v truyn khi trong thp quy i:

in

out

y

y

inoutininOG

AA

AxKyxKyAA

yy

dyN

/)1(

)}/1(././)1ln

*

Vi A l h s hp ph: A= L/(K.V)

Bng 2.3. Cc cng thc tnh chiu cao v s n v truyn khi trong thp m

2.3.2. S ngp lt, ng knh thp v gim p sut trong thit b

gii quyt cc vn trn, ta s dng thuyt GPDC ca Leva xoay quanh gim p

ca thit b. Tng t thp mm, lung kh trong thp c thit k mc f=0.5-0.7

vn tc ngp lt. Tuy nhin khc vi thp mm, khi xem xt vn gim p ca thp

m ta phi lu cht ca thp (m3/m3) v h s tit din ngoi ca vt chm a

(m2/m3)

H s sp xp vt chm trong thp m : Fp = (a/)^3

Tc ngp lt trong thp m tnh da vo th gii tch ca FLV

ng knh thp m: 5.0

...

..4

Vvf

V

uf

MVD

(2.11)

(2.12)

Hnh 2.2. th

GPDC ca Leva

2.1. Trong ngnh cng nghip ma ng, mt r c th dng ln men v sn xut ru

(ethyl alcohol). Mt phn ethyl alcohol b li cun bi CO2 sinh ra trong qu trnh ln men.

Mt thp mm c thit k tch ethyl alcohol ra khi hn hp kh.

- Dng kh vo thp: 180 kmol/h (98% CO2 v 2% ethyl alcohol); 30C; 110 kPa

- Cht lng hp th : nc 30C ; 110 kPa

Cho hp thu l 97% v h s K ca ethyl alcohol l 0.57.

a/ Hy c tnh s mm l thuyt ca thp.

b/ Cho khong cch gia cc mm l 24 inch (0.61m), h s foam FF = 0.90, sc cng

b mt cht lng =70 dynes/cm, hy tnh vn tc ngp lt trong thp.

c/ Thp c thit k vn hnh tc kh bng 80% tc ngp lt. Hy c

tnh ng knh ca thp.

2.2. Thay thp mm trong bi tp 2.1 bng thp m s dng m metal Pall ring 1.5

inch. Nu lu lng dng cht hp th l 151.5 kmol/h v chiu cao 1 n v truyn khi

HOG = 2.0 ft (0.61m), hy tnh s n v truyn khi NOG.

2.3. Lung khng kh cha 1.6% SO2 c x l trong mt thp m cao 3.5m v c

tit din 1.5m2. Lu lng dng kh v dng lng ln lt l 0.062 v 2.2 kmol/s. Cho

nng phn mol ca SO2 u ra ca thp l 0.004 v h s K(SO2) = 40. Hy c

tnh:

a/ S n v truyn khi v chiu cao mi n v

b/ H s Kya ca SO2

2.4. Cho dng khng kh c ln NH3 (5% mol) i vo thp m vi lu lng 40 kmol/h

(20C, 1 atm). Sau khi x l, 90% amoniac s c hp th bi dng nc c lu lng

3000 kg/h. Thp s dng m ceramic Raschig 1 inch (25mm); vn tc dng kh thit

k bng 70% vn tc ngp lt. Hy tnh:

a/ Vn tc ngp lt trong thp

b/ ng knh thp

c/ gim p sut trong thp