BaiGiang-truyenKhoi -DHLH

- 1 -

B GIO DC V O TO CNG HA X HI CH NGHA VIT NAM TRNG H LC HNG c lp T do Hnh phc

CHNG TRNH O TO TRNH I HC BI GING

MN HC: TRUYN KHI

CHNG 1: CC KHI NIM C BN

MC CH: Ni dung bi ging ny gip sinh vin nm c cc khi nim ban u v bn cht ca cc qu trnh truyn khi, phn loi c cc qu trnh, to nn tng khi nim cho nhng ni dung trong qu trnh hc tip theo.

S TIT: 8 BNG PHN CHIA THI LNG

STT NI DUNG S TIT

1 Khi nim v phn loi cc qu trnh truyn khi. 0.5

2 Biu din thnh phn pha. 0.5

3 Cn bng pha. 0.5

4 Qu trnh khuch tn. 0.75

5 Cn bng vt cht v phng trnh truyn khi. 1

6 Phng php tnh thit b truyn khi. 0.75

7 Bi tp v tho lun. 4

Tng 8 Bi tp v tho lun s c phn phi vo tng mc nh ca chng

TRNG TM BI GING - Tp trung khi qut ha cc khi nim c bn ca mn hc truyn khi. - Nm bt cc k hiu, nguyn tc chung.

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NI DUNG 1. Khi nim v phn loi cc qu trnh truyn khi ([1] trang 5, [5] trang 9)

Qu trnh di chuyn vt cht t pha ny sang pha khc khi hai pha tip xc trc tip vi nhau gi l qu trnh truyn khi hay l qu trnh khuch tn, qu trnh ny ng vai tr quan trng trong cng nghip ha hc, thc phm v cc ngnh cng nghip khc.

2. Biu din thnh phn pha: ([1] trang 6, [5] trang 14)

Pha lng Pha hi (kh)

1. Phn khi lng iiL

xL

= i

iGyG

=

2. Phn mol iiL

xL

= i

iGyG

=

3. T s khi lng iii

LXL L

=

ii

i

GYG G

=

4. T s mol iii

LXL L

=

ii

i

GYG G

=

Trong : L,G: sut lng mol pha lng, pha hi, kmol/h

GL, : sut lng khi lng pha lng, pha hi, kg/h

i: cu t bt k ca hn hp

VD1.1. Mt hn hp ru ethanol v nc c thnh phn khi lng ethanol l 30%. Xc nh thnh phn mol v t s mol ca hn hp

Gii: Thnh phn khi lng ca ethanol ca hn hp ethanol nc l 30% nn ta c

0,3ex = . p dng cng thc ta c thnh phn mol ca ethanol l

0,346 0,1440,3 1 0,3

46 46

e

ee

e n

e n

x

Mx

x x

M M

= = =

++

V t s mol ca ethanol s l

0,144 0,1681 1 0,144

ee

e

xXx

= = =

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VD1.2. Xc nh phn khi lng v t s khi lng ca hn hp benzen toluen, bit t l mol benzen trong hn hp l 0,4.

Gii: Theo u bi ta c 0,4bX = , p dng cng thc 0,41b

bb

xXx

= =

ta suy ra thnh

phn mol ca benzen trong hn hp l 0,4 0,2861 1 0,4

bb

b

Xx

X= = =

+ +

Khi ta tnh c thnh phn khi lng ca benzen trong hn hp l

. 0,286.78 0,253. . 0,286.78 (1 0,286).92

b bb

b b t t

x Mx

x M x M= = =

+ +

T s khi lng ca benzen l

0,253 0,3391 0,2531

bb

b

xXx

= = =

3. Cn bng pha: ([1] trang 10, [5] trang 71) 3.1. Khi nim v cn bng pha:

Mt h t trng thi cn bng pha th tha mn nhng nguyn tc sau: - Ti mi iu kin nhit v p sut xc nh, tn ti mt mi quan h cn bng gia

nng ca dung cht trong hai pha v c biu din bng ng cn bng. - Khi h t trng thi cn bng th khng c khuch tn tng cng gia hai pha. - Khi h cha t cn bng, qu trnh khuch tn ca dung cht gia hai pha s din ra nh

th no a h n iu kin cn bng.

3.2. Quy tc pha Gibbs: Bc t do C ca mt h l s thng s nhit ng c lp xc nh h trng thi cn

bng. tm c bc t do, ta s dng quy tc pha Gibbs, cng thc nh sau: C = k - f + n

Trong : f : s pha trong h k : s cu t c lp ca h n : s yu t bn ngoi nh hng ln cn bng ca h

3.3. Cc nh lut v cn bng pha: 3.3.1. nh lut Henry:

i vi dung dch l tng p sut ring phn p ca kh trn cht lng t l vi phn mol x ca n trong dung dch

pi = H.xi

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Suy ra: *. .i iH x y P= hay *

.i i iPy x mxH

= =

Vi P - p sut tng cng, iP p=

m - h s phn phi hay hng s cn bng H - hng s Henry

3.3.2. nh lut Raoult: p sut ring phn ca mt cu t trn dung dch bng p sut hi bo ha ca cu t (

cng nhit ) nhn vi nng phn mol ca cu t trong dung dch .

o

i i ip P x=

Trong :

pi : p sut hi ring phn ca cu t i trong hn hp hi. o

iP : p sut hi bo ha ca cu t i cng nhit .

xi : phn mol x ca cu t i trong dung dch

4. Qu trnh khuch tn: ([1] trang 15, [5] trang 15) 4.1. nh ngha:

Khi hai pha chuyn ng tip xc vi nhau do s cn tr ca pha ny i vi pha kia, ngha l trn b mt phn chia pha to thnh hai lp mng. Trong mng l chuyn ng dng v th gi l khuch tn phn t cn nhn chuyn ng xay v gi l khuch tn i lu. Khuch tn trong

mng rt chm so vi trong nhn nn n quyt nh n qu trnh khuch tn.

4.2. ng lc qu trnh: Qu trnh truyn khi gia cc pha xy ra mt cch t nhin khi nng lm vic v nng

cn bng ca cc cu t phn b trong mi pha khc nhau.

Hnh 1.1. S biu din qu trnh truyn khi

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Hiu s gia nng lm vic v nng cn bng gi l ng lc khuch tn hay ng lc truyn khi, c th biu din bng th (Hnh 1.1)

Nu tnh theo pha y ta c ng lc: yyy cb = hay l cbyyy =

Nu tnh theo pha x ta c ng lc: xxx cb = hay l cbxxx =

4.3. Khuch tn phn t ([1] trang 16, [5] trang 16) 4.3.1. Vn tc khuch tn

L lng vt cht khuch tn qua mt dn v din tch mng trong mt n v thi gian

.

dG dcv D

F d dx= =

Trong

F : din tch b mt, vung gc vi hng khuch tn

: thi gian khuch tn

G : lng vt cht khuch tn

D : h s khuch tn

4.3.2. Cng thc tnh h s khuch tn 4.3.2.1. Khuch tn trong pha kh

H s khuch tn gia hai kh A v B nhit T v p sut P c xc nh theo

cng thc 33 2

1 1 23 3

4,3.10 . 1 1.

.( )k A BA BTD

M MP V V

= ++

, m2/s

Trong

T : nhit tuyt i, K

P : p sut tuyt i, atm

MA, MB : khi lng mol ca kh A v kh B, g/mol VA, VB : th tch mol ca kh A v kh B

4.3.2.2. Khuch tn trong pha lng H s khuch tn gia lng A v lng B nhit T v p sut P c xc nh theo

cng thc 6

1 1 23 3

10 1 1.

. . .( )l A BA BD

M MA B V V

= ++

, m2/s

Trong

MA, MB : khi lng mol ca kh A v kh B, g/mol

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VA, VB : th tch mol ca kh A v kh B

: nht ca pha lng, mPa.s A, B : h s ph thuc theo tnh cht ca cht tan v dung mi

VD1.3. Tnh h s khuch tn ca kh A vo kh B 200C, p sut tuyt i 2 atm. Bit khi lng mol ca A v B ln lt l 16 v 18; th tch mol ca A v B ln lt l 24,2 v 14,8.

Gii: p dng cng thc tnh h s khuch tn gia hai pha kh 33 2

1 1 23 3

4,3.10 . 1 1.

.( )k A BA BTD

M MP V V

= ++

Th s liu ta c

33 2

1 1 23 3

4,3.10 .(20 273) 1 1.

16 182.(24,2 14,8 )kD

+= +

+

= 0,693 m2/s

VD1.4. Tnh h s khuch tn ca kh sulfur hidrogen trong nc 200C. Cho bit

Vi sulfur hidro Vi nc

A = 1

VA = 33

B = 4,7

VB = 14,8

= 1 mPa.s

Gii: Kh sulfur hidrogen khuch tn trong nc l qu trnh khuch tn pha kh vo pha lng nn h s khuch tn ca qu trnh ny c tnh theo cng thc:

6

1 1 23 3

10 1 1.

. . .( )l A BA BD

M MA B V V

= ++

Trong A l kh sulfur hidrogen c MA = 34 v B l nc, MB = 18 Th cc gi tr vo cng thc ta c

6

1 1 23 3

10 1 1.

34 181.4,7. 1.(33 14,8 )lD

= ++

= 1,93.10-9 m2/s

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4.4. Khuch tn i lu ([1] trang 20, [5] trang 39) Trong dng chy ri cc dng xoy chuyn ng s truyn vn vt cht t v tr ny

n v tr khc nh trong trng hp truyn vn moment v nhit lng, phng trnh

truyn khi c dng sau:

.Ndc

vdx

=

Vi l h s khuch tn dng xoy

5. Cn bng vt cht v phng trnh truyn khi ([1] trang 23, [5] trang 83) 5.1. Cn bng vt cht trong thit b truyn khi Xt qu trnh truyn khi nghch dng nh hnh 1.2

Hnh 1.2. Qu trnh truyn khi nghch chiu Gi:

G1, G2 : sut lng mol tng cng ca pha kh vo v ra khi thit b L1, L2 : sut lng mol tng cng ca pha lng ra v vo thit b Ltr, Gtr : sut lng mol ca cu t khng khuch tn (tr) trong pha lng v pha kh x1, x2 : phn mol ca dung cht trong pha lng ra v vo thit b y1, y2 : phn mol ca dung cht trong pha kh vo v ra khi thit b X1, X2 : t s mol ca dung cht trong pha lng ra v vo thit b Y1, Y2 : t s mol ca dung cht trong pha kh vo v ra khi thit b

L2 x2

Ltr x2

G2 Gtr

y2 y2

L x

Ltr x

L2 x1

Ltr x1

G1 y1

Gtr x1

G y

Gtr y

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Phng trnh cn bng vt liu i vi khong th tch thit b k t mt tit din bt k no vi phn trn ca thit b:

1 1( ) ( )tr trG Y Y L X X = T y ta rt ra:

1 1tr tr

tr tr

L LY X Y XG G

= +

5.2. H s truyn khi tng qut: ([1] trang 27, [5] trang 42) Gi Ky v Kx ln lt l h s truyn khi tng qut biu din ca qu trnh truyn khi

gia hai pha tnh theo pha kh v pha lng. Ta c

1 1y y x

m

K k k= +

V

1 1 1'x y xK m k k

= +

y ky, kx l h s truyn khi ring trong pha kh v pha lng

VD1.5. Tnh h s truyn khi tng qut v so snh tr lc pha khi h s truyn khi trong mi pha ln lt l ky = 8,7 kmol/m2.h (y = 1) v kx = 0,2 kmol/m2.h (x =1). Thnh phn cn bng ca pha lng v pha kh tun theo nh lut Henry nh sau: p* = 1,6.104x (mmHg). Bit thit b truyn khi hot ng p sut thng. Da vo t s tr lc hy bin lun xem ta nn chn thit bt ruyn khi loi no cho hiu qu.

Gii: Trc tin ta cn phi i phng trnh ra dng y* = mx Do thit b lm vic p sut thng v thnh phn cn bng ca pha kh v pha lng tun theo nh lut Henry nn ta c

* 4* 1,6.10

. 21,8735

py x x xP

= = =

H s truyn khi tng qut i vi pha kh

1 1 1 21,88,7 0,2y y x

m

K k k= + = +

Ta tnh c: Ky = 9,2.10-3 kmol/m2.h(y = 1) i vi pha lng

1 1 1 1 1. 21,8.8,7 0, 2x y xK m k k

= + = +

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Ta tnh c: Kx = 0,2 kmol/m2.h(x = 1) T s tr lc khuch tn gia pha kh v pha lng tnh theo pha kh l

10,2

. 21,8.8,7y x

y

x

k km m kk

= = = 0,001

Ta thy tr lc trong pha kh rt nh so vi tr lc trong pha lng nn c th xem qu trnh

khuch tn trong pha kh khng nh hng n qu trnh truyn khi. Tr lc tp trung trong

pha lng nn thit b truyn khi thch hp ta cn chn l thp sc kh.

VD1.6. Trong mt thit b truyn khi, t s tr lc truyn khi gia pha kh v pha lng tnh theo pha lng l 2. H s truyn khi tng qut trong pha lng l Kx = 1,62 kmol/h.m2.(y =1). Hy xc nh h s truyn khi trong mi pha v h s truyn khi tng qut trong pha kh. Bit phng trnh cn bng kh lng c dng y* = 1,22x

Gii: T s tr lc ca pha kh v pha lng tnh theo pha lng l 2 nn ta c

1.

21.

y x

y

x

m k km k

k

= = (1)

H s truyn khi tng qut trong pha lng l

1 1,621 1.

x

y x

K

m k k

= =

+

Suy ra 1 1 1 0,617. 1,62y xm k k

+ = = (2)

T (1) v (2) ta c h phng trnh

2.

1 1 0,617.

x

y

y x

km k

m k k

=

+ =

Gii h phng trnh trn ta tm c

2, 43. 4,86

x

y

km k

=

=

- 10 -

T phng trnh cn bng kh lng ca h y* = 1,22x, ta suy ra m = 1,22

H s truyn khi trong pha lng kx = 2,43 kmol/m2.h

H s truyn khi trong pha kh ky = 4,861,22

= 3,98 kmol/m2.h

H s truyn khi tng qut trong pha kh

1 11 1 1,22

3,98 2, 43

y

y x

Km

k k

= =

+ + = 1,22 kmol/m2.h

5.3. Phng trnh truyn khi v ng lc trung bnh: ([1] trang 26) Vn tc ca qu trnh no cng t l thun vi ng lc v t l nghch vi tr lc. Phng

trnh truyn khi c th biu din nh sau:

G = ky..F.ytb = kx..F.xtb Trong :

ky , kx : h s truyn khi tnh theo nng pha y v x

ytb , xtb : ng lc trung bnh ca qu trnh. F : din tch b mt tip xc pha.

: thi gian truyn khi.

Khi ng cn bng l ng thng th ng lc trung bnh theo lgarit theo pha y v x

nh sau:

2

1

21

lnyy

yyytb

=

2

1

21

lnx

x

xxxtb

=

y1, y2, x1, x2 l ng lc cui v u theo pha y v x

6. Phng php tnh thit b truyn khi: ([1] trang 33, [5] trang 101) 6.1. Tnh ng knh thit b

0785,0 VD =

Trong :

V : lu lng pha y , m3/s

0 : vn tc pha y i qua ton b tit din thit b, m/s

6.2. Tnh chiu cao thit b - Theo phng trnh chuyn khi:

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Mun tnh theo phng trnh truyn khi trc ht phi xc nh h s truyn khi ky, kx v ng lc trung bnh sau tnh b mt tip xc pha

tby ykGF

= Hay tbx xk

GF

=

T tnh chiu cao thit b H. Nu l thp m th:

F = V , m2 Hay l F = Hf , m2

T rt ra: fykGHtby ..

= , m fxkGHtbx ..

= , m

Trong : V - th tch lm vic ca thit b, m3

- b mt ring ca m, m2/m3

f tit din ngang ca thit b, m2 - Theo s bc thay i nng :

Hnh 1.3. th m t s bc thay i nng Trc ht phi xc nh c ng cn bng v ng lm vic. T chng ta xc nh

s bc l thuyt trn th Nlt (c biu din trn th Hnh 1.3) sau xc nh s mm thc t Ntt

lttt

NN

= - h s hiu chnh (hiu sut ngn) ly t 0,2 0,9

Chiu cao thit b c xc nh nh sau:

- i vi thp mm (a): ( 1)ttH h N= ,m h khong cch gia hai ngn, m

- i vi thp m (chm): 0 ttH h N= ,m h0 chiu cao tng ng mt bc thay i nng .

- 12 -

VD1.7. Thit k thp mm chp chng ct vi khong cch mm l 300 mm. Lu lng hi qua thp l 3200 m3/h v khi lng ring ca pha hi l 1,25 kg/m3 (ly iu kin chun), khi lng ring ca pha lng l 430 kg/m3. Xc nh ng knh ca thp nu p sut tuyt i trong thp l 1,2 at, nhit trung bnh 400C.

Gii: xc nh c ng knh ca thit b, trc tin ta phi xc nh vn tc lm vic cho php i trong thit b Khi lng ring ca pha hi iu kin lm vic l

1, 25.273.1, 2. (40 273).1

o oH

o

T PT P

= =+

= 1,31 kg/m3

Vn tc hi i trong thit b c tnh theo cng thc

430. 0,0315.

1,31L

H

v C

= = = 0,57 m/s

y C = 0,0315 c ta t gin H.2.2 trang 42 ti liu [2] Lu lng hi i qua thp iu kin lm vic

3200.(40 273).13600. 3600.273.1, 2

o oH

o

Q TPQT P

+= = = 0,85 m3/s

ng knh thit b c tnh

0,850,785. 0,785.0,57

HQDv

= = = 1,38 m

d dng trong thit k, ta chn quy chun ng knh l D = 1,4 m

- 13 -

CHNG 2: HP TH MC CH: Ni dung bi ging ny gip sinh vin nm c cc khi nim, kin thc c bn v qu trnh hp th, phn loi v ng dng cng nh xc nh cc thng s c bn ca qu trnh v tnh ton thit k thit b hp th.


STT NI DUNG S TIT

1 nh ngha. 0.25

2 Yu cu la chn dung mi. 0.5

3 ha tan cn bng ca cht kh trong cht lng. 0.5

4 Cn bng vt cht qu trnh hp th. 0.5

5 nh hng ca nhit v p sut ln qu trnh hp th. 0.5

6 Cc yu t nh hng n kch thc thit b 0.25

7 Thit b hp th. 0.5

8 Bi tp v tho lun 4

Tng 7

Bi tp v tho lun s c phn phi vo tng mc nh ca chng

TRNG TM BI GING - Nguyn l ca qu trnh hp th - Quy trnh, thit b hp th

NI DUNG 1. nh ngha: ([1] trang 152, [5] trang 136)

Hp th l qu trnh ha tan chn lc mt hay nhiu cu t trong hn hp kh vo trong

cht lng, cc cu t kh c ha tan gi l cht b hp th, cht lng dng ha tan gi l dung mi (hay cht hp th), kh khng b hp th gi l kh tr.

Qu trnh hp th ng mt vai tr quan trng trong sn xut ha hc, n c ng dng :

- Thu hi cc cu t qu - Lm sch kh

- 14 -

- Tch hn hp kh thnh cc cu t ring bit - To thnh mt dung dch sn phm mong mun.

2. Yu cu la chn dung mi: ([5] trang 137) Nu mc ch ca qu trnh hp th l to nn mt dung dch sn phm xc nh th

dung mi c xc nh bi bn cht ca sn phm. Nu mc ch ca qu trnh hp th l tch cc cu t ca hn hp kh th khi la chon

dung mi ta ch trng cc tnh cht sau: - C tnh cht ha tan chn lc: ngha l ch ha tan tt cu t cn tch ra v khng ha

tan cc cu t cn li hoc ch ha tan khng ng k. y l tnh cht ch yu ca

dung mi. - bay hi tng i thp nhm trnh mt mt - Tnh n mn ca dung mi thp d dng trong vic ch to thit b - Chi ph thp, dung mi d tm, gi thnh r - nht dung mi b: gip tng tc hp th, trnh ngp lt, truyn nhit tt - Nhit dung ring b t tn nhit khi hon nguyn dung mi - Nhit si khc xa vi nhit si ca cht ha tan nh vy s d tch cu t ra khi

dung mi. - Nhit ng rn thp trnh c hin tng ng rn lm tc thit b - Khng to thnh kt ta, khi ha tan trnh c tc thit b, v thu hi cu t n gin

hn

- Khng c i vi ngi v mi trng

Trong thc t, khi chn ta phi da vo nhng iu kin c th ca sn xut. Nhng d sao i na th iu kin th nht cng khng th thiu c trong bt c trng hp no.

3. ha tan cn bng ca cht kh trong cht lng ([1] trang 152, [5] trang 138) S ph thuc c th biu th bng nh lut Henry - Dalton nh sau: ycb = mx Khi tnh ton hp th, ngi ta thng dng nng phn mol tng i trong trng hp

ny ta c :

y = Y

Y+1

v x = X

X+1

Thay gi tr ca y v x vo phng trnh ta c :

Y =Xm

mX)1(1 +

- 15 -

4. Cn bng vt cht qu trnh hp th ([1] trang 154, [5] trang 141) Khi tnh ton hp th thng ngi ta cho bit lng hn hp kh nng u v nng

cui ca kh b hp th trong hn hp kh v trong dung mi. Xt qu trnh hp th nghch dng nh hnh 2.1

Gi:

G1, G2 : sut lng mol tng cng ca pha kh vo v ra khi thit b L1, L2 : sut lng mol tng cng ca pha lng ra v vo thit b Ltr, Gtr : sut lng mol ca cu t khng khuch tn (tr) trong pha lng v pha kh x1, x2 : phn mol ca dung cht trong pha lng ra v vo thit b y1, y2 : phn mol ca dung cht trong pha kh vo v ra khi thit b X1, X2 : t s mol ca dung cht trong pha lng ra v vo thit b Y1, Y2 : t s mol ca dung cht trong pha kh vo v ra khi thit b

Hnh 2.1. Qu trnh truyn khi trong thit b hp th Lng kh tr c xc nh theo cng thc sau y:

11

(1 )1tr y

GG G yY

= =

+

V phng trnh cn bng vt liu l :

1 2 1 2( ) ( )tr trG Y Y L X X = T y ta xc nh lng dung mi cn thit

L2 x2

Ltr x2

G2 Gtr

y2 y2

L x

Ltr x

L2 x1

Ltr x1

G1 y1

Gtr x1

G y

Gtr y

- 16 -

1 2

1 2

( )( )

trtr

G Y YLX X

=

Lng dung mi ti thiu hp th c xc nh khi nng cui ca dung mi t n nng cn bng, nh vy ta c:

min

max

1 2

1 2tr tr

Y YL GX X

=

Trong X1max l nng ra ca pha lng cc i ng vi lng dung mi ti thiu hay nng ra ca pha lng cn bng vi nng vo ca pha kh Lng dung mi tiu hao ring l:

1 2

1 2

tr

tr

L Y YlG X X

= =

Nu ta vit phng trnh cn bng vt liu i vi khong th tch thit b k t mt tit din bt k no vi phn trn ca thit b. Ta c:

1 1( ) ( )tr trG Y Y L X X = VD2.1. Xc nh lng acid sunfuric tiu hao lm kh khi khng kh c nng sut

500m3/h khng kh kh iu kin chun. Hm lng m ban u l 0,016 kg/kg khng kh kh, hm lng m cui l 0,006 kg/kg khng kh kh. Hm lng nc ban u trong acid l 0,6 kg/kg acid, hm lng cui l 1,4 kg/kg acid, khng kh c lm kh iu kin p sut kh quyn.

Gii: Tm tt u bi ta c: Khng kh vo thp vi sut lng F = 500m3/h

Nng m (nc) trong khng kh trc v sau khi ra khi thit b ln lt l 0,016VY = v

0,006RY =

i vi acid sunfuric, nng nc trong acid lc vo v ra khi thit b ln lt l 0,6VX = v

1, 4RX =

Khi lng ring ca khng kh iu kin chun l 1,293 kg/m3 nn sut lng ca dng kh l

G = F. = 500.1,293 = 646,5 kg/h p dng cng thc ta tnh c sut lng ca dng acid l:

( ) 0,016 0,006646,5.1,4 0,6( )

tr V Rtr

R V

G Y YLX X

= =

= 8,08 kg/h

- 17 -

VD2.2. Mt thp dng hp th hi aceton t khng kh bng dung mi l nc vi sut lng 3000 kg nc/h. Nng u ca aceton trong khng kh l 0,05 kg/kg khng kh kh, nng cui mong mun l 0,005 kg/kg khng kh kh. Hy xc nh nng sut thit b tnh theo lng kh cha aceton ban u. Bit nng aceton trong nc lc trc ra khi thit b l 0,03 kg/kg nc.

Gii: Tm tt u bi ta c Lng nc vo thp vi sut lng L = 500 kg/h

Nng aceton trong nc trc v sau khi ra khi thit b hp th ln lt l 0VX = v

0,03RX =

i vi khng kh cha aceton, nng aceton trong khng kh lc vo v ra khi thit b ln lt

l 0,05VY = v 0,005RY =

Cn bng vt cht trong thit b hp th ny cho dung cht l aceton ta c

( ) ( )tr R V tr V RL X X G Y Y = T phng trnh cn bng vt cht trn ta c th tnh c sut lng kh tr i vo thit b l

( ) (0,03 0)3000 (0,05 0,005)( )tr R V

tr

V R

L X XGY Y

= =

= 2000 kg/h

Sut lng pha kh vo thit b s l

(1 )tr VG G Y= + = 2000.(1 + 0,05) = 2100 kg/h Vy nng sut thit b l 2100 kg khng kh/h

VD2.3. Dng kh thi cha 0,06 kg NH3/ kg khng kh kh c cho qua thit b hp th bng nc hp th lng NH3. Nng sut nhp liu ca dng kh 50m3/ph nhit 250C, p sut thng. Lu lng nc cho vo thit b hp th l 8 m3/ph. Nng NH3 trong nc sau khi ra khi thit b l 0,015 kg/kg nc. Hy xc nh xem thit b c p ng c yu cu x l kh thi khng nu nng NH3 trong dng kh c php thi ra mi trng khng c vt qu 0,03 kg NH3/kg khng kh kh.

Gii: Tm tt u bi ta c i vi dung mi l nc: Lng nc vo thp vi sut lng F1 = 8 m3/h

Nng NH3 trong nc trc v sau khi ra khi thit b hp th ln lt l 0VX = v

0,015RX =

- 18 -

i vi kh thi cha NH3: Sut lng nhp liu ca dng kh l F2 = 50 m3/ph

Nng NH3 trong kh thi lc vo v ra khi thit b ln lt l 0,06VY = v ?RY =

250C v p sut thng ta c khi lng ring ca khng kh v nc ln lt l:

k = 1,293 kg/m3 v n = 1000 kg/m3. Sut lng ca dng kh G = F2.k = 50.1,293 = 64,65 kg/ph = 3879 kg/h

Sut lng kh tr nhp liu 38791 1 0,06tr V

GGY

= = =

+ +3659,4 kg/h

Sut lng ca dng nc L = Ltr = F1.n = 8.1000 = 8000 kg/h Cn bng vt cht trong thit b hp th ny cho dung cht l NH3 ta c

( ) ( )tr R V tr V RL X X G Y Y = Suy ra nng NH3 trong dng kh sau khi ra khi thit b hp th

8000.( ) 0,06 (0,015 0)

3659,4tr

R V R Vtr

LY Y X XG

= =

= 0,027 kg/kg khng kh kh Ta thy nng trn nh hn nng cho php ca NH3 trong kh thi nn thit b hp th

ny p ng yu cu.

5. nh hng ca nhit v p sut ln qu trnh hp th ([1] trang 157, [5] trang 146) Nhit v p sut l nhng yu t c nh hng quan trng ln qu trnh hp th, chng nh

hng trc tip ln trng thi cn bng v ng lc ca qu trnh. Nu nhit tng th ng lc truyn khi s gim, khi nhit nhit tng n mt im gii

hn no th qu trnh khng cn xy ra c na.

Tuy nhin, nhit cao cng c nh hng tt v nht ca dung mi gim rt c li trong trng hp tr lc khuch tn nm trong pha lng.

Nu tng p sut th th ng lc qu trnh truyn khi s tng.

Tuy nhin khi ta tng p sut th nhit cng tng theo v khi p sut cao s gy kh khn khi

ta thit k ch to thit b hp th.

6. Cc yu t nh hng n kch thc thit b trong qu trnh hp th ([1] trang 157, [5] trang 146)

Khi chn lng dung mi s dng v cc thng s vn hnh thit b, ta phi chn sao cho thch hp nht theo cc ch tiu k thut cng nh kinh t.

- 19 -

7. Thit b hp th ([1] trang 160, [5] trang 147) 7.1. Thp m

Ch lm vic ca thp m.

Trong thp m cht lng chy t trn xung theo

b mt m v kh i t di ln phn tn u trong cht lng .

Thp m c nhng u im sau:

- Hiu sut cao v b mt tip xc kh ln - Cu to n gin

- Tr lc trong thp khng ln lm

- Gii hn lm vic tng i rng

Nhng thp m c nhc im quan trng l kh

lm t nhiu m.

Nu thp cao qu th phn phi cht lng khng

u. khc phc nhc im , nu thp cao qu th

ngi ta chia m ra nhiu tng v c t thm b phn phn phi cht lng i vi mi tng m.

7.2. Thp a (thp mm) Thp a c ng dng rt nhiu trong k thut ha

hc. Trong thp a kh hi phn tn qua cc lp cht lng

chuyn ng chm t trn xung di, s tip xc pha ring bit trn cc a. So vi thp m th thp a phc tp hn do kh lm hn v tn kim lai hn.

Chia thp a (mm) ra lm hai lai c ng chy chuyn, kh v lng chuyn ng ring bit t a n sang a kia v khng c ng chy chuyn, kh v lng chuyn ng

t a n sang a kia theo cng mt l hay rnh. Trong thp

a c th phn ra nh sau thp chp, thp a li...

Hnh 2.3. Cu to thp a

Hnh 2.2. Cu to thp m

- 20 -

CHNG 3: CHNG CT

MC CH: Ni dung bi ging ny gip sinh vin nm c cc khi nim, kin thc c bn v qu trnh chng ct, phn loi v ng dng cng nh xc nh cc thng s c bn ca qu trnh v tnh ton thit k thit b chng ct.


STT NI DUNG S TIT

1 nh ngha v phn loi. 0.5

2 Cn bng pha qu trnh chng ct. 1

3 Chng n gin. 0.75

4 Chng ct lin tc. 0.5

5 Thit b chng ct. 0.25

6 Bi tp v tho lun 5


TRNG TM BI GING - Nguyn l ca qu trnh chng ct - xut quy trnh, tnh ton thit k h thng thit b chng ct.

NI DUNG

1. nh ngha v phn loi ([1] trang 49, [5] trang 167) Chng l phng php dng tch cc hn hp cht lng cng nh cc hn hp kh lng

thnh cc cu t ring bit da vo bay hi khc nhau ca cc cu t trong hn hp (ngha l khi cng mt nhit , p sut hi ca cc cu t khc nhau).

Trong sn xut ta thng gp cc phng php chng sau y:

- Chng n gin: Dng tch cc hn hp gm c cc cu t c bay hi rt khc nhau. Phng php ny thng dng tch s b v lm sch cc cu t khi tp cht.

- 21 -

- Chng bng hi nc trc tip: Dng tch cc hn hp gm cc cht kh bay hi v tp cht khng bay hi, thng c ng dng trong trng hp cht c tch khng tan vo nc.

- Chng chn khng: Dng trong trng hp cn h thp nhit si ca cu t, nh trng hp cc cu t trong hn hp d b phn hy nhit cao hay trng hp cc cu t c nhit si qu cao.

- Chng ct: Chng ct l phng php ph bin nht dng tch hon ton hn hp cc cu t d bay hi c tnh cht ha tan mt phn hoc ha tan hon ton vo nhau.

2. Cn bng pha qu trnh chng ct: ([1] trang 52, [5] trang 168) Trng hp cht lng ha tan vo nhau theo bt c t l no th p sut hi ca mi cu t

s gim i v p sut chung ca hn hp, nhit si ca hn hp cng nh thnh phn ca cu t

trong hi khng phi l mt hng s m thay i theo thnh phn ca cu t trong dung dch.

Hnh 3.1. th nhit - thnh phn ng cong OMD l ng ni lin cc im biu din cho thnh phn hi cn bng vi x.

ng ny gi l ng ngng t hay ng hi bo ha. ng cong OND l ng ni lin cc im ng vi thnh phn x, ng ny gi l ng cong si hay ng lng bo ha.

Khu vc pha trn ng OMD l khu vc hi, khu vc di ng cong OND l khu vc lng, khu vc gia hai ng cong l khu vc hn hp hi lng.

3. Chng n gin ([1] trang 69, [5] trang 210) 3.1. Nguyn tc

Chng ct n gin l qu trnh c 1 giai on trong pha lng c cho bc hi , pha hi to nn lun lun trng thi cn bng vi pha lng cn li trong thit b.

- 22 -

Dung dch c cho vo ni chng. Hi to thnh vo thit b ngng t. Sau khi ngng t v lm lnh n nhit cn thit cht lng i vo cc thng cha. Thnh phn cht lng ngng lun

lun thay i. Sau khi t c yu cu chng, cht lng cn li trong ni c tho ra. Chng

n gin c ng dng cho nhng trng hp sau: - Khi nhit si ca hai cu t khc nhau xa

- Khi khng i hi sn phm c tinh khit cao

- Tch hn hp lng ra khi tp cht khng bay hi - Tch s b hn hp nhiu cu t

3.2. S

Hnh 3.2. S qu trnh chng n gin 4. Chng ct lin tc ([1] trang 71, [5] trang 182)

4.1. S h thng v nguyn tc qu trnh chng luyn:

Hi i di ln qua cc l ca a, cht lng chy t trn xung di theo cc ng chy chuyn. Nng cc cu t thay i theo chiu cao ca thp, nhit si cng thay i tng ng

vi s thay i nng .

Trn mi a xy ra qu trnh chuyn khi gia pha lng v pha hi. Cui cng trn nh

thp ta thu c hn hp cha nhiu cu t d bay hi v y thp ta thu c hn hp cha nhiu cu t kh bay hi.

Mi a ca thp c xem l mt bc thay i nng hay bc l thuyt 4.2. Cn bng vt cht ([1] trang 71, [5] trang 182)

Phng trnh cn bng cho ton thp. F = W + D

FxF = WxW + DxD

F

W

P

- 23 -

Trong :

F, W, D - sut lng nhp liu, sn phm y v nh, kmol/h xF , xW , xD - phn mol ca cu t d bay hi trong nhp liu, sn phm y v nh.

- Phng trnh ng nng lm vic ca on ct.

11 ++

+=

Rx

xR

Ry D

Vi oLRD

= - l ch s hi lu ca thp

Lo - lng lng c hi lu, kmol/h

- Phng trnh ng nng lm vic ca on chng. 1

1 1 WR f fy x xR R

+ =

+ +

FfD

= - lng hn hp nhp liu so vi sn phm nh

4.3. Xc nh ch s hi lu v s a l thuyt - Ch s hi lu ti thiu

T s hi lu ti thiu vi s mm l v cc cho mt qu trnh chng ct xc nh trc

v tng ng l nhit ti ca thit b ngng t v ni un l ti thiu.

Hnh 3.3. th xc nh Rmin T s hi lu ti thiu c tnh da theo th xy:

* *

min

min 1D F D F

D F D F

R y y x yA tgR x x x x

= = = =+

- 24 -

Suy ra *

min *D F

F F

x yRy x

=

- Ch s hi lu lm vic Vn l chng ta xc nh lng R sao cho thch hp vi iu kin kinh t v k thut,

nu lng R qu b th thp v cng cao, iu ny kh thc hin, nu lng hi lu ln th thit b c thp i nhng ng knh li to v sn phm nh thu chng bao nhiu.

Nu gi Rx l ch s hi lu lm vic, ta c : Rx = .Rmin Vi l h s hi lu d. Trong thc t, t s hi lu lm vic c th tnh n gin nh sau:

Rx = 1,3.Rmin + 0,3

- S a l thuyt - Xc nh ch s hi lu thch hp

- V ng cn bng v cc ng lm vic. - Xc nh s mm l thuyt

VD3.1. Xc nh s mm thc ca thp chng ct dng phn tch hn hp ru metylic v nc p sut thng. Nhp liu vo thp cha 31,5% mol ru. Thnh phn ca sn phm nh cha 97,5% mol ru, sn phm y cha 1,1% mol ru. H s hon lu d = 1,77. S mm tng ng vi bc thay i nng l 1,7. Thp c gia nhit gin on bng hi nc. Cho bng cn bng lng hi ca hn hp methanol nc 1 atm nh bng bn di

x 0 5 10 20 30 40 50 60 70 80 90 100

y 0 26,8 41,8 57,9 66,5 72,9 77,9 82,5 87 91,5 95,8 100 Gii:

T s liu trong bng cn bng lng hi ca hn hp methanol nc 1 atm bi, ta xy dng ng cn bng x y ca h nh hnh 3.4

Theo u bi ta c xF = 0,315, t th cn bng pha bn trn ta xc nh c * 0,675Fy =

p dng cng thc ta xc nh c t s hon lu ti thiu Rmin nh sau:

*

min *D F

F F

x yRy x

=

Vi: xD = 0,975 v xW = 0,011 Ta tnh c

min0,975 0,6750,675 0,315

R = =

0,833

- 25 -

Hnh 3.4. th x y ca h methanol nc

T s hon lu lm vic l

min 1,77.0,833R R= = = 1,475

Phng trnh lm vic cho phn ct ca thp l:

1,475 0,9751 1 1,475 1 1, 475 1

DxRy x xR R

= + = ++ + + +

Hay y = 0,596x + 0,394 T phng trnh trn ta xy dng ng lm vic phn ct trn th. Ch rng ng lm vic phn ct lun i qua im c ton (xD, yD), ng lm vic phn chng lun i qua im (xW, yW). xy dng ng lm vic phn ct ln th th ta phi xc nh t nht 2 im, nh i vi bi ton ny, ta d dng nhn thy n s i qua 2 im (0; 0,349) v (0,975; 0,975) xy dng ng lm vic phn chng, ta phi xc nh thm 1 im na ngoi im (0,011; 0,011) c th ni thnh ng thng. Ch rng ng lm vic phn ct, ng lm

- 26 -

vic phn chng v ng nng xF nhp liu c chung 1 giao im. Ch cn ta xc nh c giao im ny th s c th xy dng c ng lm vic phn chng. Giao im chung ny c xc nh trn gin hay ta cng c th gii trc tip bng h phng trnh, nh trong bi ny ta phi gii h

0,3150,596 0,394

x

y x=

= +

Gii h phng trnh trn ta suy ra ta giao im chung l (0,315; 0,582). T y ta s xc nh c ng lm vic phn chng.

Ta bt u xc nh s a l thuyt trn th

Hnh 3.5. th xc nh s i l thuyt ca h methanol nc T th trn ta d dng nhn thy s bc thay i nng ca thp l 11, trong phn ct

l 7 v ca phn chng l 4.

Vy s mm thc cn thit cho thp chng hot ng l n = 11.1,7 = 18,7 = 19 mm, trong s mm ca on chng l nchng = 4.1,7 = 6,8 = 7 mm v s mm on ct nct = 7.1,7 = 11,9 = 12 mm

VD3.2. tch mt hn hp gm 40% khi lng benzen v phn cn li l toluen ngi ta s dng mt ct ct lin tc vi tc 4kg/s, cho sn phm u ct cha 97% khi

- 27 -

lng benzen v sn phm cui ct cha 98% khi lng toluen. Nguyn liu c np vo trng thi lng ti im si ca n.

D liu cn bn lng hi ca h benzen toluen:

X 0,10 0,20 0,30 0,40 0,50 0,60 0,70 0,80 0,90 Y 0,22 0,38 0,51 0,63 0,70 0,78 0,85 0,91 0,96

Hy:

a. Tnh nng sut sn phm u ct v cui ct (theo n v khi lng) b. Nu t s hi lu l 3,5 th ct ct ny cn c bao nhiu a p ng

c yu cu tch trn c. Tm s a thc nu hiu dng ca a l 60%

Gii: a. p dng phng trnh cn bng vt cht cho thp chng i vi dung cht l benzen ta c

F D W

F D W

F x Dx W x

= +

= +

Th s liu u bi vo phng trnh ta c

40,97 0,02 4.0, 4 1,6D W

D W+ =

+ = =

Suy ra

1,6 /W 2,4 /D kg s

kg s=

=

Vy lng sn phm nh ct l D = 1,6 kg/s v lng sn phm y thp l W = 2,4 kg/s b. Do cc nng benzen u bi u l nng khi lng nn ta cn chuyn chng v nng mol. Ta c

0, 478 0, 4400, 4 1 0, 4

78 92

F

BF

F F

B T

x

Mx

x x

M M

= = =

++

Tng t

0,9778 0,9740,97 1 0,97

78 92

D

BD

D D

B T

x

Mx

x x

M M

= = =

++

- 28 -

V

0,0278 0,0240,02 1 0,02

78 92

W

BW

W D

B T

x

Mx

x x

M M

= = =

++

Vi t s hi lu l R = 3,5 ta xc nh c phng trnh on ct nh sau:

3,5 0,9741 1 3,5 1 3,5 1

DxRy x xR R

= + = ++ + + +

Hay y = 0,778x + 0,216 Tnh ton tng t VD3.1 ta tm c ta giao im chung l (0,440; 0,558)

T bng s liu cn bng vt cht trn bi ta xy dng gin x y v xc nh s a l thuyt

Hnh 3.6. th xc nh s i l thuyt ca h benzen - toluen Qua gin trn ta d dng xc nh c s a l thuyt l 12, trong s a l thuyt

cho on chng l 6 v s a l thuyt cho on ct l 6. c. Vi hiu sut a E = 60% ta xc nh c s a thc theo cng thc

lt

tt

nEn

= suy ra 12 200,6

lttt

nn

E= = = mm.

- 29 -

4.4. Cn bng nng lng ([1] trang 74, [5] trang 183) 4.4.1. Cn bng nhit lng ca thit b un nng.

Ta c: 1

'

D f f mQ Q Q Q+ = = .

1DQ - nhit lng do hi t mang vo.

rDQD 11 = . D1 - lng hi t, kg/s.

r - n nhit ho hi ca hi t, J/kg,.

Qf - nhit lng do dung dich u mang vo, w; Qf = Fcf .tf ,W

Trong :

F - lng hn hp u,kg/s;

Cf - nhit dung ring ca hn hp u, J/kg;

tf - nhit u ca hn hp, 0C '

fQ - nhit lng do hn hp mang ra khi thit b v i vo thp chng. W.

' ' '

f f fQ FC t= ,W Trong :

'

fC - nhit dung ring ca hn hp, J/kg.

'

ft - nhit ca dung dch,0C.

Qm - nhit mt ra khi mi trng xunh quanh.W Ta c th ly Qm bng 5o/o

QD1 - nhit lng do hi t mang vo. Thay cc gi tr tnh vo ta c

D1 = ' '( )0,95f f f fF C t C t

r

,kg/s

4.4.2. Cn bng nhit ca thp.

2

'

f D x n w mQ Q Q Q Q Q+ + = + +

D2 = '

n w m f xQ Q Q Q Qr

+ + ,kg/s

Trong :

Qn : nhit do hi mang ra,W. Qn = D(1+Rx) ,W

- 30 -

D - lng sn phm nh, kg/s.

Rx - ch s hi lu thch hp.

- nhit lng ring ca hn hp, 1 1 2 2a a = + ,J/kg

1, 2 - nhit lng ring ca cc cu t trong hn hp, J/kg. a1,a2 - nng cc cu t trong hn hp, %khi lng.

Qw : nhit do sn phm y mang ra,W. Qw = twCwW

W - lng sn phm y, kg/s

Cw - nhit dung ring ca sn phm y , J/kg tw - nhit sn phm y,0C

Qm : nhit mt mt ra mi trng xunh quanh, ly bng 5% QD2 Qx : nhit lng do mi trng bn ngoi mang vo, W

Qx = RxDCxtx Cx - nhit dung ring ca cht lng hi lu.J/kg

Tx - nhit ca cht lng hi lu,0C '

fQ : nhit lng do hn hp mang ra khi thit b v i vo thp chng, W

' ' '

f f fQ FC t= ,W 4.4.3. Cn bng nhit lng ca thit b ngng t.

- Nu ch ngng t hi lu

DRxr = G1C1(t2t1) T y ta c lng nc lnh tiu tn l :

G1=1 2 1( )

xDR rC t t

,kg/s

C1 - nhit dung ring ca nc nhit trung bnh ttb = 0,5(t1 + t2) r - n nhit ho hi J/kg

t1,t2 - nht vo v ra ca nc, 0C

- Nu ngng t hon ton ta c :

D(1+Rx)r = G2C1(t2-t1) Do lng nc tiu tn l

G =1 2 1

(1 )( )

xD R rC t t

+

, kg/s

- 31 -

4.4.4. Cn bng nhit lng ca thit b lm lnh. Xt trng hp ngng t v lm lnh hon ton ta c

' '

1 2 2 1 2 1.( ). ( )pD t t C G C t t = Trong

'

1t , '

2t - nhit u vo v u ra ca sn phm nh

Cp - nhit dung ring ca sn phm nh nhit trung bnh 'tbt = 0,5( '1t + '2t ) G2 - lng nc lnh tiu tn cho qu trnh lm ngui sn phm nh

C1 - nhit dung ring ca nc nhit trung bnh ttb = 0,5(t1 + t2) t1,t2 - nht vo v ra ca nc, 0C

VD3.3. Thp chng ct hn hp methanol - nc. Nhp liu l 5000 kg/h nng 25% mol methanol nhit si. Sn phm nh thu c cha 95% mol methanol. Sn phm y cha 2,5% mol methanol. p sut trong thp l p sut thng. Xc nh:

a. Sut lng cc dng sn phm nh v y (kmol/h). b. Lng nc cn s dng ngng t sn phm nh, bit nhit nc lnh

vo v ra khi thit b ln lt l 20 v 300C. Cho bit n nhit ngng t ca ru v nc nh thp ln lt l 1125 kJ/kg v 2340 kJ/kg. Nhit dung ring trung bnh ca nc lnh l 4178 J/kgK

Gii: a. p dng phng trnh cn bng vt cht cho thp chng i vi dung cht l

methanol ta c

F D W

F D WFx Dx Wx

= +

= +

Trong xF = 0,25 xW = 0,025 xD = 0,95 V F c tnh nh sau:

5000 195,325,6F

GFM

= = = kmol/h

vi . (1 ). 0,25.32 (1 0,25).18 25,6F F me F nM x M x M= + = + = kg/kmol Th s liu vo h phng trnh ta c

195,30,95 0,025 195,3.0, 25 48,8D W

D W+ =

+ = =

- 32 -

Suy ra

47,5W 147,8D =

= ; kmol/h

Vy sut lng sn phm nh thp l D = 47,5kmol/h v sut lng sn phm y thp l W = 147,8kmol/h

b. Nhit ngng t ca hn hp hi nh thp

. (1 ) 0,95.1125 (1 0,95).2340 1185,8D me D nr x r x r= + = + = kJ/kg Cn bng nhit cho thit b ngng t ta c

. . .n

D r G C t=

Trong D = 47,5.(0,95.32+0,05.18) = 1486,8 kg/h Suy ra

3. 1486,8.1185,8 42198,4

4178.10 .(30 20).nD rG

C t = = =

kg/h

5. Thit b chng ct Xem li phn thp a (mm) v thp chm chng hp th

- 33 -

CHNG 4: TRCH LY CHT LNG

MC CH: Ni dung bi ging ny gip sinh vin nm c cc khi nim, kin thc c bn v qu

trnh trch ly cht lng, phn loi v ng dng cng nh xc nh cc thng s c bn ca qu trnh v tnh ton thit k thit b trch ly cht lng.


STT NI DUNG S TIT

1 Khi nim chung v trch ly. 0.5

2 S trch ly. 0.75

3 Cn bng pha trong h lng lng. 0.5

4 Cc phng php trch ly. 0.5

5 Thit b trch ly. 0.75


Tng 7


TRNG TM BI GING - Nguyn l ca qu trnh trch ly cht lng. - xut quy trnh, tnh ton thit k h thng thit b trch ly cht lng.

NI DUNG

1. Khi nim chung v trch ly ([1] trang 195, [5] trang 224) 1.1. Khi nim Qu trnh trch ly cht lng l qu trnh tch cht ha tan bng mt cht lng (dung mi)

khc khng ha tan.

Qu trnh trch ly c ng dng rng ri trong cng nghip ha hc, thc phm cng nh trong ngnh dc. V d tch axit acetic, du thc, ng vt

1.2. La chn dung mi Dung mi thch hp cho qu trnh trch ly cn p ng cc tnh cht:

- 34 -

- Tnh cht cn bn khng th thiu c l tnh ha tan c chn lc ngha l dung mi phi ha tan tt cht cn tch m khng ha tan hoc ha tan rt t cc cu t khc.

- Khi lng ring ca n phi khc xa vi khi lng ring ca dung dch.

- Khi trch ly thu c cu t nguyn cht ta cn tch dung mi ra, thng ta tch bng phng php chng ct, v th t c yu cu tit kim nhit lng trong khi hon

nguyn ta cn chn dung mi c nhit dung b. - Ngoi ra cn phi c tnh cht thng thng khc nh: khng c, khng n mn thit

b, khng c tc dng ha hc vi cc cu t trong hn hp, r tin, d kim 2. S trch ly ([1] trang 196, [5] trang 258) S nguyn tc ca qu trnh trch ly c th biu th hnh 4.1

Hnh 4.1. S qu trnh trch ly cht lng Qu trnh trch ly c tin hnh qua ba giai on sau:

- Giai on 1: Giai on trn ln, phn phi hai pha vo vi nhau to s tip xc pha tt

cho dung cht truyn t hn hp u vo dung mi. Nu thi gian tip xc pha th qu tnh

truyn vt cht xy ra cho n khi t cn bng gia hai pha.

- 35 -

- Giai on 2: Giai on tch pha, hai pha ny phn lp v tch ra d dng hay khng ph thuc vo chnh lch khi lng ring ca chng. Mt pha gi l pha trch gm dung mi v cu t phn b, mt pha gi l raphinat gm phn cn li ca dung dch

- Giai on 3: Giai on hon nguyn dung mi, tch cu t phn b ra khi dung mi.

3. Cn bng pha trong h lng lng ([1] trang 197, [5] trang 225) 3.1. Phn b

y* = m.x

Trong :

y* : nng cn bng trong pha trch

x : nng pha raphinat

m : h s phn b nng

3.2. th tam gic y l dng th c s dng nhiu m t thnh phn ca hn hp 3 cu t. Trong

khong cch t nh ca tam gic n 3 cnh biu din thnh phn ca 3 cu t. Mi nh tam gic biu din mt cu t nguyn cht theo k hiu.

Hnh 4.2. th tam gic c bn Khong cch t mt im bt k K trong tam gic xung cnh AB biu din thnh phn ca C

trong hn hp K. Mt im bt k trn cnh tam gic biu din thnh phn hn hp 2 cu t . Nu R (kg) hn hp ti R c trn vi E (kg) hn hp ti E, hn hp mi c to thnh ti M nm trn on RE v c xc nh theo h thc:

E M

M R

x xR MEE MR x x

= =

- 36 -

Xt h ba cu t A, B v C m trong cu t C ha tan hon ton trong A v B, nhng A v B ch ha tan trong gii hn c biu din bi im K (nhiu B) v im L (nhiu A) nh hnh bn di

Hnh 4.3. th tam gic ca h 3 pha s dng trong trch ly Xt im M bn di ng cong s to nn 2 pha lng bo ha c thn phn biu din bi

im R (nhiu A) v im S (nhiu B). ng ni thnh phn 2 pha cn bng gi l i tuyn v nht thit phi i qua M. C v

s i tuyn trong vng 2 pha, cc i tuyn t khi song song nhau, chng thay i dc chm v c th dng hay m ty h ba cu t. Cc im R v S tng dn ln v trng nhau ti im P gi

l im ti hn.

4. Cc phng php trch ly ([1] trang 204, [5] trang 233) 4.1. Trch ly mt bc

Hn hp ban u v dung mi c trn ln vi nhau to nn hn hp M, qu trnh

truyn khi gia hai pha c tin hnh cho n khi h t cn bng, sau hn hp M c lng tch ra thnh hai pha R v E.

t F l lng nhp liu ban u cha A v C vi phn khi lng C l xF c tip xc vi S cha ch yu l B vi

phn khi lng C l yS, sau hn hp tch ra lm 2 pha cn

bng R1 v E1 c ni vi nhau bng i tuyn R1E1. Ta c cn bng vt cht tng cng

F + S = M1 = E1 + R1

Hnh 4.4. Trch ly mt bc

- 37 -

V im M c xc nh trn on FS theo quy tc n by hoc tnh nng C trong M1 theo cn bng ca dung cht nh sau:

F.xF + S.yS = M1xM1

T tnh c xM1

Lng pha trch v pha raphinat c tnh theo cn bng vt cht cho C:

E1y1 + R1x1 = M1xM1

1 1 11

1 1

( )MM x xEy x

=

Tnh c E1 ta s tnh c R1.

VD4.1. Hy xc nh lng pha raphinat v pha trch thu c khi tin hnh trch ly mt bc 200kg acid axetic (chim 20% khi lng) ra khi hn hp nc v acid axetic bng isopropyl ete 200C. Dung dch trch sau khi tch dung mi cha 75% khi lng acid axetic, raphinat cha 1% khi lng. Bit t l dung mi/dung dch u bng 1.

Gii: Lng dung dch nc acid axetic ban u trc khi trch l

200 10000, 2

a

F

GFx

= = = kg

Do t l dung mi/ dung dch u bng 1 n lng dung mi c s dng l:

S = F = 1000 kg

p dng cn bng vt cht cho thit b trch ly 1 bc ny ta c

. . . E.xF S R E

R E F SF x S x R x

+ = +

+ = +

Trong E v R l lng pha trch v pha raphinat sau khi trch

Th s liu vo h phng trnh trn ta c

1000 1000 20001000.0,2 0 .0,01 E.0,75R E

R+ = + =

+ = +

hay 2000

0,01 0,75E 200R E

R+ =

+ =

Gii h phng trnh trn ta tm c

243, 21756,8

E kgR kg

=

=

Vy lng pha trch v pha raphinat sau khi trch ln lt l 243,2 kg v 1756,8 kg.

- 38 -

4.2. Trch ly nhiu bc cho dng

y l s ko di ca qu trnh trch ly 1 on trong pha raphinat lin tc i qua mi on tip xc vi dung mi mi, qu trnh c thc hin lin tc hay gin on

Cn bng vt cht tng cng cho on th n bt k Rn-1 + Sn = Mn = En + Rn

Cn bng cho C Rn-1xn-1 + SnyS = MnxMn = Enyn + Rnxn

Hnh 4.5. Trch ly nhiu bc cho chiu Lng dung mi s dng trong mi on c th khng bng nhau. Vi nng pha

raphinat cui cng c xc nh trc tng lng dung mi s dng, s t hn vi s on nhiu

hn.

VD4.2. Cho dung dch nc cha 30% (kh.l) aceton chuyn ng theo s cho dng trch ly aceton bng clorua benzen 250C, 1 atm. Hy xc nh:

a. S bc cn tin hnh cn st 2 % axeton trong nc ci R? b. Lng dung mi cn dng trch ly 300 kg dung dch u? c. Lng cht chit c?

Bit: T l dung mi/dung dch u trn mi bc u bng 1 Gii: d dng hn ta t li tn h 3 pha ny l N-A-C tng ng vi N v nc, A l aceton v

C l clorobenzen.

- 39 -

T bng s liu cn bng pha ca h 3 cu t nc aceton clorobenzen trn ta xy dng th tam gic.

Hnh 4.6. th cn bng pha ca h 3 cu t nc aceton clorobenzen a. Xc nh s bc trch ly: ` T th tam gic, trn cnh NA ta ly im F c trng cho nguyn liu ban u cha 30% aceton. p dng quy tc n by ta tm c im F ny nm bn pha N. Ni F vi C, trn on FC ny ta xc nh im M1 l hn hp ca nguyn liu u F v dung mi chit

nguyn cht C. Do bi cho t l dung mi/dung dch u trn mi bc u bng 1 nn M1 chnh l trung im ca on FC

T M1 theo cc ng ni suy m ta xy dng th tam gic lc u, ta xc nh c v tr pha trch E1 v pha raphinat R1. Ta thy nng pha raphinat ti im R1 cn ln hn 2%

Nc - Aceton - Clorobenzen Pha nhiu nc Pha nhiu Clorobenzen

Nc Aceton Clorobenzen Nc Aceton Clorobenzen 99.89 0.00 0.11 0.18 0.00 99.82 89.79 10.00 0.21 0.49 10.79 88.72 79.69 20.00 0.31 0.79 22.23 76.98 69.42 30.00 0.58 1.72 37.48 60.80 58.64 40.00 1.36 3.05 49.44 47.51 46.28 50.00 3.72 7.24 59.19 33.57 27.41 60.00 12.59 22.85 61.07 15.08 25.66 60.58 13.76 25.66 60.58 13.76

A

N C

- 40 -

nn ta tnh hnh trch thm bc na. Do bi yu cu trch ly cho chiu nn s b sung thm mt lng dung mi trch C mi, nn ta ni R1 vi C thnh on R1C. Tng t trn do t l dung mi/dung dch u trn mi bc u bng 1 nn v tr M2 c trng cho hn hp raphinat

1 v dung mi chnh l trung im ca R1M. T M2 theo cc ng ni suy m ta xy dng th tam gic lc u, ta xc nh c v

tr pha trch E2 v pha raphinat R2. Ta thy nng pha raphinat ti im R2 vn cn ln hn

2% nn ta tnh tc lp li qu trnh xy dng nh trn n khi nng aceton trong pha

raphinat cui cng nh hn hoc bng 2%.

Hnh 4.7. Xc nh s bc trch ly Cui cng, sau khi xy dng xong ta xc nh c s bc trch ly cho qu trnh ny l n = 3.

b. Xc nh lng dung mi cn thit Nh ta tin hnh xy dng th trch ly cho dng cho qu trnh trch ly trn v xc

nh c s bc trch ly l 3 nn lng dung mi thm vo trong mi bc trch ln lt c k hiu l S1, S2 v S3.

- i vi bc 1 Nh ta bit S1 = F = 300 kg

Suy ra M1 = F + S1 = 300 + 300 = 600 kg

A

C

R1

F

R2

N

M1

M2

M3

E1

E3 E2

R3

- 41 -

Cn bng vt cht cho bc th 1 ny ta c M1 = E1 + R1 (1) Mt khc, khi p dng quy tc n by cho on R1E1 ta thu c:

1 1 1

1 1 1

E R MR M E

= (2)

T th ta xc nh c rng 1 1 50,5R M = v 1 1 34,0M E = (3) Ta gii h phng trnh (1), (2) v (3) thu c kt qu nh sau

1

1

241,4358,6

R kgE kg

=

=

- Tng t cho bc th 2 ta c: M2 = R1 + S2

Do S2 = R1 = 241,4 kg suy ra M2 = 2.241,4 = 482,8 kg

p dng cn bng vt cht v quy tc cho n by cho bc th 2 ny ta c

2 2 2

2 2 2

2 2 2

482,850,042,7

E R M

E R MR M E

+ = =

= =

Suy ra 22

260,5222,4

E kgR kg

=

=

- Tng t cho bc th 3 ta c: M3 = R2 + S3

Do S3 = R2 = 222,4 kg suy ra M2 = 2.222,4 = 444,8 kg p dng cn bng vt cht v quy tc cho n by cho bc th 2 ny ta c

3 3 3

3 3 3

3 3 3

444,8

49,9646,25

E R M

E R MR M E

+ = =

= =

Suy ra 33

231,0213,8

E kgR kg

=

=

Vy lng dung mi cn s dng l S = S1 + S2 + S3 = 300 + 241,4 + 222,4 = 763,8 kg

c. Lng cht chit c: Lng pha trch thu c E = E1 + E2 + E3 = 358,6 + 260,5 + 213,8 = 832,9 kg Nng aceton trong tng pha trch c xc nh trn th ln lt l:

Bc 1: 84,2 % Bc 2: 93,2 % Bc 3: 96,7 % Vy lng cht chit c l:

- 42 -

GA = 358,6.0,842 + 260,5.0,932 + 213,8.0,967 = 751,5 kg Nng trung bnh ca dch chit l:

751,5 90,2832,9

AA

Gx

E= = = %

4.4. Trch ly nhiu bc ngc chiu

Dung dch ban u i vo u ny, dung mi i vo u kia, hai pha raphinat v pha trch lin tc i ngc chiu nhau qua mi on, cui cng c hai dng sn phm RN v E1.

Cn bng vt cht tng cng F + S = E1 + RN = M

Cn bng cho dung cht C: FxF + SxS = E1y1 + RNxN = MxM

VD4.3. Aceton c trch ly t dung dch aceton nc cha 30% khi lng aceton bng dung dch clobenzen. Pha raphinat cn li cha khng qu 2% khi lng aceton. Lng hn hp ban u c khi lng 500kg, nhit 200C. Qu trnh trch ly ngc chiu. Hy xc nh:

a. S bc trch ly b. Lng dung mi cn thit c. Lng pha trch thu c Bit t l dung mi/dung dch u bng 1

Gii: a. Xc nh s bc trch ly: T th tam gic, trn cnh NA ta ly im F c trng cho nguyn liu ban u cha

30% aceton. p dng quy tc n by ta tm c im F ny nm bn pha N. Ni F vi C, trn on FC ny ta xc nh im M l hn hp ca nguyn liu u F v dung mi chit nguyn cht C. Do bi cho t l dung mi/dung dch u trn mi bc u bng 1 nn M chnh l trung im ca on FC

T nng pha raphinat cui ti im R l 2%, ta ni RM ct ng cn bng ti E. Ko di FE v RC, chng s ct nhau ti mt im chung gi l im cc P. im P chnh l giao im chung ca tt c cc tia i qua nhng im c trng cho thnh phn cht tinh khit trn bc bt k v thnh phn trch ly trn bc tip theo.

T ng ni suy, ti E ta ni suy ra c ng ER1, ni P vi R1 ta c bc rch ly th 2. Tng t n khi nng v n v tr R. Cui cng, sau khi xy dng xong ta xc nh c s bc trch ly cho qu trnh ny l n = 3.

- 43 -

c. Xc nh lng dung mi cn thit Do c trng ca qu trnh trch ly ngc chiu l lng dung mi trch ban u

thc hin xuyn sut qu trnh m khng thm vo na nh qu trnh trch ly cho dng. Mt khc theo bi th t l dung mi/ dung dch u bng 1 nn S = F = 1000 kg

c. Lng cht chit c: Lng pha trch c tnh theo cng thc

E E

M F S

G G RMG G G RE

= =

+

Suy ra:

(1000 1000).57,3 1295,088,5E

G += = kg

5. Thit b trch ly ([1] trang 215, [5] trang 259) 5.1. Thp phun

Hnh 4.8. Cu to thp phun y l dng n gin nht trong qu trnh tip xc pha lin tc, ch c mt thp rng c b

phn phn phi cht lng v tho cht lng ra. Pha lin tc chim ton b th tch thp v i t di ln hoc t trn xung. Pha phn tn nh b phn phun to thnh ht nh v xuyn qua, phn tn vo pha lin tc

u im ca thit b ny l chi ph ch to khng ln, d vn hnh, v sinh c nng sut cao. Tuy nhin thp c hiu sut km nn t s dng trong thc t sn xut

- 44 -

5.2. Thp m (thp chm), thp a (thp mm) Xem li cu to v nguyn l hot ng cc chng trc 5.3. Thp trch nghch dng c cnh khuy, a quay

Hnh 4.9. Cu to thp trch nghch dng v thp c gy chn ng 5.4. Thp c gy chn ng

Xem hnh 4.9

- 45 -

CHNG 5: SY

MC CH: Ni dung bi ging ny gip sinh vin nm c cc khi nim, kin thc c bn v qu trnh sy, phn loi v ng dng cng nh xc nh cc thng s c bn ca qu trnh v tnh ton thit k thit b sy.


STT NI DUNG S TIT

1 nh ngha v phn loi. 0.25

2 Hn hp khng kh m. 0.25

3 Gin H-Y ca hn hp khng kh m. 0.25

4 S nguyn l lm vic ca my sy bng khng kh. 0.5

5 Cc phng thc sy. 0.5

6 ng hc qu trnh sy. 0.75

7 Thit b sy. 0.5

8 Bi tp v tho lun 5


TRNG TM BI GING - Nguyn l ca qu trnh sy. - xut quy trnh, tnh ton thit k h thng thit b sy.

NI DUNG

1. nh ngha v phn loi ([1] trang 269, [5] trang 268) Sy l qu trnh lm thot hi nc ra khi vt liu m bng nhit gi l sy. Ngi ta phn bit ra sy t nhin v sy nhn to. Sy t nhin tin hnh ngoi tri, dng

nng lng mt tri lm bay hi nc trong vt liu. Mc ch ca qu trnh sy l lm gim khi lng ca vt liu (gim cng chuyn ch); lm

tng bn (cc vt liu gm s, g); bo qun c tt.

- 46 -

2. Hn hp khng kh m ([1] trang 271, [5] trang 269) 2.1. Khi nim v hn hp khng kh m

Hn hp khng kh v hi nc cn gi l hn hp khng kh m

2.2. m tuyt i ca khng kh (Hm m). m tuyt i ca khng kh l lng hi nc cha trong 1 kg khng kh kh,

k hiu l Y (kg hi nc/ kg khng kh kh) 2.3. m tng i ca khng kh. m tng i ca khng kh hay cn gi l bo ha hi nc c nh

ngha bng pA/PA trong pA l p sut ring phn ca hi nc trong hn hp khng kh m v PA

l p sut hi bo ha ca nc cng nhit bu kh. m tng i k hiu l Khi pA = PA th m tng i t cc i = 1 = max 2.4. im sng Nhit tng ng vi trng thi bo ha gi l nhit im sng, k hiu l ts.

im sng l nhit gii hn ca qu trnh lm lnh khng kh m vi hm m khng i

2.5. Nhit bu kh L nhit hn hp kh c xc nh bng nhit k thng thng, k hiu l tk. 2.6. Nhit bu t L nhit n nh t c khi mt lng nh nc bc hi vo hn hp kh cha

bo ha hi iu kin on nhit, k hiu l t Nhit bu t thng c o bng nhit k thng thng c bc vi t bu.

2.7. Th tch hn hp khng kh m L th tch ca hn hp khng kh m tnh cho 1kg khng kh kh (kkk) nhit

v p sut nh

HA

RTv

P P=

, m3/kg kkk

Vi: R - hng s kh l tng, R = 287 J/kg.K T - nhit tuyt i ca khng kh, K

P - p sut tng ca hn hp khng kh m, N/m2

2.8. Enthalpy ca hn hp khng kh m L tng s enthalpy ca khng kh v hi nc c trong hn hp. Vy enthalpy ca

hn hp khng kh m trong cha 1kg khng kh kh l

.k AH C t YH= + hay 3 3(1000 1,97.10 . ) 2493.10 .H Y t Y= + + , J/kg kkk

- 47 -

3. Gin H-Y ca hn hp khng kh m ([1] trang 276, [5] trang 271) 3.1. Tng quan

Hm m Y ghi trn trc honh, cc ng thng Y song song vi trc tung trn th ch

v cc ng thng Y cn trc Y thng khng v. Enthalpy ca hn hp H ghi trn trc tung, cc

ng thng H khng vung gc vi trc Y .

Ngoi hai trc chnh trn, trn th cn thm cc ng ng nhit (t = const), ng m tng i khng i ( = const) v ng p sut hi nc ring phn Ph

3.2. Cch s dng

Hnh 5.1. Gin trng thi hn hp khng kh m

- 48 -

3.2.1. Xc nh trng thi hn hp hi Trng thi ca hn hp khng kh m c c trng bng giao tuyn ca bn

ng trn gin H Y : ng t, H, Y , khng i. Do mun xc nh trng thi ca hn hp khng kh m ta ch cn bit 2 trong 4

thng s (t, H, Y , ) ri t xc nh cc thng s cn li ca hn hp khng kh m. 3.2.2. Xc nh nhit im sng

Y = const, t gim dn n khi chm ng =1

Hnh 5.2. Cch xc nh im sng 3.2.3. Xc nh nhit bu t

H = const, t gim dn n chm ng =1

Hnh 5.3. Cch xc nh nhit bu t

VD5.1. Tm im sng ca khng kh c nhit t = 400C v m =0,8. S: ts = 350C

VD5.2. Tm nhit bu t ca khng kh c m =0,6 v enthalpy H = 150 kJ/kg S: t = 370C

Y

H

=1

t

ts

=1

t

H

Y

- 49 -

4. S nguyn l lm vic ca my sy bng khng kh ([1] trang 284) S nguyn l lm vic ca my sy bng khng kh c m t trn hnh 5.4

Hnh 5.4. S nguyn l lm vic ca my sy bng khng kh Vt liu sy ban u c m cao c a vo thit b sy, c sy khng trong phng

sy ri ra ngoi. Khng kh bn ngoi c a qua b phn t nng gia nhit ln n nhit sy cn thit, sau vo phng sy tip xc pha vi vt liu sy, cp nhit cho nc trong vt

liu bc hi. Trong qu trnh sy c th cho thm b phn t nng b sung trong phng sy nu cn thit.

4.1. Cn bng vt cht trong thit b sy bng khng kh ([1] trang 284, [5] trang 276) Gi: Gd,Gc - lng vt liu trc khi vo v sau khi ra khi my sy, kg/s;

Gk - lng vt liu kh tuyt i i qua my sy, kg/s;

cd xx , - m vt liu trc v sau khi sy, tnh theo % khi lng vt liu t

cd XX , - m vt liu trc, sau khi sy, tnh theo % khi lng vt liu kh tuyt i

W - lng m c tch ra khi vt liu khi qua my sy, kg/s

L - lng khng kh kh tuyt i i qua my sy, kgkkk/s

oY

- hm m khng kh trc khi vo caloriphe si kg/kg kkk

1Y , 2Y - hm m ca khng kh trc khi vo my sy (sau khi qua caloriphe si) v sau khi ra khi my sy kg/kg kkk;

Khng kh Gk, Ho, to, o, Yo

Khng kh thi Gk, H2, t2, 2, Y2

Vt liu ban u Phng sy

Vt liu sau khi

sy

B phn t nng B phn t

nng b sung

- 50 -

Trong qu trnh sy, ta xem nh khng c hin tng mt mt vt liu, do lng vt liu kh tuyt i coi nh khng b bin i trong sut qu trnh. Vy lng vt liu kh tuyt i i qua my sy:

100100

100100 c

c

ddk

xGxGG ==

T rt ra:

d

c

cdx

xGG

=

100100

v c

ddc

x

xGG

=

100100

Lng m tch ra khi vt liu trong qu trnh sy tnh theo cng thc:

W = Gd Gc

VD5.3. em sy 1kg vt liu m, trong cng iu kin nh nhau: a. Sy t m 50% n 25% theo vt liu t b. Sy t m 2% n 1% theo vt liu t.

Hi lng m c tch trong trng hp (a) ln hn (b) bao nhiu ln ? Gii: p dng cng thc tnh lng m tch ra nh sau

100d c

dc

x xW Gx

=

Xt vi trng hp (a) ta c 50%dx = v 25%cx = nn lng m tch ra khi vt liu l

150 251. 0,333

100 25W = =

kg

Xt vi trng hp (b) ta c 2%dx = v 1%cx = nn lng m tch ra khi vt liu l

22 11. 0,0101

100 1W = =

kg

Vy lng m tch ra trong giai on 1 ln hn trong giai on 2 l 0,333 330,0101

= ln

4.2. Lng khng kh kh i qua my sy: Cn bng m trong qu trnh sy:

L 1Y + W = L 2Y

2 1

WLY Y

=

, kg/s

i lng L l lng khng kh kh cn nhit l bc hi W kg m trong vt liu

- 51 -

4.3. Cn bng nhit lng trong my sy bng khng kh Ta k hiu:

Q - nhit lng tiu hao chung cho my sy, W Qs - nhit lng si nng khng kh caloriphe chnh, W Qb - nhit lng b sung trong phng sy, W Qm - nhit lng tn tht ca my sy, W

Ta c cn bng nhit lng cho thit b nh sau Q = Qs + Qb + Qm = L(H2 H0) + Qm , W

Khi Qm = 0 ta c qu trnh sy l thuyt vi phng trnh cn bng nh sau Q = L(H2 H0)

Khi Qm 0 ta gi qu trnh sy ny l sy thc t VD5.4. Dng thit b sy i lu c tun hon khng kh thi, sy mt loi vt liu t

m ban u 47% n m cui 5% (theo vt liu t). Nng sut thit b sy theo nhp liu l 1500 kg/h. Khng kh sy c enthalpy 50 kJ/kg v m tng i 70%. Khng kh thi c enthalpy 260 kJ/kg v m 80%. Hy

a. Xc nh lng khng kh cn cho qu trnh sy trong 1 gi b. Lng nhit cn cung cp trong 1 gi. Xem qu trnh sy trong thit b ny l

qu trnh sy l tng Gii

a. p dng cng thc tnh lng m tch ra khi vt liu nh sau

100d c

dc

x xW Gx

=

Trong 1500dG = kg/h ; 47%dx = v 5%cx =

Ta tnh c

47 51500 663,16100 5

W = =

kg/h

T gin ta xc nh c hm m ca khng kh vo v ra khi thit b sy ln lt l

1 0,011Y = kg m/ kg kkk v 2 0,078Y = m/ kg kkk

p dng cng thc, ta tnh c lng khng kh cn s dng cho qu trnh sy l

2 1

663,16 9897,90,078 0,011

WLY Y

= = =

kg/h

b. V l qu trnh sy l tng nn s khng c nhit tn tht v lng nhit cn cung cp c tnh nh sau

- 52 -

Q = L(H2 H0) = 9897,9.(260 50) = 2078555 W

5. Cc phng thc sy ([1] trang 297, [5] trang 283) 5.1. Sy c b sung nhit trong phng sy

Trong phng thc sy ny, lng nhit cn thit cho ton b qu trnh sy khng nhng c cung cp b phn t nng m cn c b sung ngay trong phng sy. Khi trng thi u v trng thi cui ca khng kh c xc nh th lng nhit

cn thit chung cho qu trnh l mt i lng khng i. Do , nu cn nhit thp th phi

gim lng nhit cung cp cho b phn t nng v tng nhit lng b sung trong phng sy.

Hnh 5.5. Qu trnh sy c b sung nhit Phng thc sy ny dng trong trng hp vt liu sy khng chu c nhit cao

5.2. Sy t nng khng kh gia cc bung sy Phng thc sy ny nhm gim nhit ca khng kh sy, ta chia phng sy ra

lm nhiu khu vc sy v trc mi khu vc c b tr mt b phn t nng.

Hnh 5.6. S sy t nng khng kh gia cc bung

H

HB2

HB3

=1

C

t1

B2

B3

H

Y

B1

t2

Khng kh

Gk, Ho, to, o, Yo Khng kh

Gk, Ho, to, o, Yo SY 1 SY 2 SY 3

t nng

1

t nng

2

t nng

3

- 53 -

Hnh 5.7. Qu trnh sy t nng khng kh gia cc bung Khi sy c t nng gia chng, nhit ti a c th nh hn rt nhiu ty thuc

vo s giai on t nng gia chng.

Phng thc sy ny thch hp sy cc vt liu sy khng chu c nhit cao

5.3. Sy tun hon mt phn kh thi Trong qu trnh sy ny, khng kh sau khi sy xong ch thi ra bn ngoi mt phn,

phn cn li th cho tun hon tr li trn ln vo khng kh mi b sung vo Phng thc sy tun hon kh thi c nhng u im sau:

- C th iu chnh m ca khng kh do c th ng dng sy cc vt liu khng chu c iu kin m khng kh nh v nhit cao, v d nh g

- Tc khng kh i qua phng sy ln.

5.4. Sy bng khi l trc tip Kh l c to thnh khi t nhin liu c thi trc tip vo bung sy sy

vt liu.

u im ca phng php ny l n gin, t mt mt nhit lng, sy tt. Tuy

nhin phng php sy ny ch thch hp sy vt liu chu c nhit cao v khng yu cu

phm cht sn phm sau khi sy.

6. ng hc qu trnh sy ([1] trang 307, [5] trang 289) 6.1. Trng thi lin kt m trong vt liu.

m v vt liu trong vt liu m tn ti tn ti nhiu lin kt:

- Lin kt hp th n phn t

H B1

B3

C2 C1 C

A

to

= 1

Y

B3

- 54 -

- Lin kt hp ph a phn t (cn gi l hp ph ha l - Lin kt mao qun

- Lin kt kt dnh 6.2. Tc sy ([1] trang 307, [5] trang 291)

6.2.1. Khi nim Tc sy c biu din bng hm lng m (kg) bay hi trn 1m2 b mt vt liu sy

trong mt n v thi gian (h) v c vit di dng sau:

.

dWNS d

= , kg m/ m2.h

Vi: W - lng m bay hi trong qu trnh sy, kg S - din tch b mt vt liu sy, m2

- thi gian sy, h Tc sy N bin i theo thi gian, gim dn theo mc gim hm m trong vt liu sy c th hin trong ng cong sy v ng cong tc sy

6.2.2. ng cong sy v ng cong tc sy:

Hnh 5.8. ng cong sy - on AB: giai on t nng vt liu, nhit vt liu tng ln n nhit bu t tng

ng vi trng thi khng kh lc sy, m vt liu thay i khng ng k, tc sy tng nhanh

n tc cc i.

A

A

D

C

B

E

X =

kg

m

/kg

vt

li

u kh

t = thi gian, h

X*

- 55 -

- on BC: giai on tc sy khng i (ng tc), m vt liu gim nhanh v u n theo mt ng thng (on BC trn ng cong sy), nhit vt liu khng i v vn bng nhit bu t.

- on CD: giai on tc sy gim dn nhng u (ng chm l ng l thuyt), nhit ca vt liu tng ln dn, m gim dn n m cn bng nhng mc gim chm hn giai on trn. im E tng ng vi m cn bng khi t m cn bng th nhit ca vt liu bng vi nhit ca tc nhn sy.

T nhng nhn xt trn, ta thy qu trnh sy c 2 giai on

a. Giai on tc sy khng i giai on sy ng tc Lc bt u sy, trong vt liu c nhiu nc, tc khuch tn ca nc bn trong

vt liu ln hn tc bay hi trn b mt vt liu. V th tc sy trong giai on ny ph thuc ch yu vo cc yu t bn ngoi, khng ph thuc vo cc yu t bn trong vt liu. Khi cc yu t bn ngoi khng i th tc sy cng khng i

b. Giai on tc sy gim dn giai on sy gim tc Lc ny vt liu tng i kh, lng nc trong vt liu cn t nn tc khuch

tn ca nc trong vt liu gim xung nh hn tc bc hi ca nc trn b mt vt liu. Lng m khuch tn gim dn nn lng m bay hi cng gim do tc sy gim

6.2.3. Cc yu t nh hng n tc sy Tc sy ph thuc vo mt s yu t ch yu sau:

- Bn cht vt liu sy nh cu trc, thnh phn ha hc, c tnh lin kt m .

- Hnh dng vt liu sy: kch thc mu sy, b dy lp vt liu Din tch b mt ring ca vt liu cng ln th tc sy cng cao

- m u, m cui v m ti hn ca vt liu

- m, nhit v vn tc ca khng kh

- Chnh lch gia nhit u v nhit cui ca khng kh sy

- Cu to thit b sy, phng thc v ch sy. 6.3. Thi gian sy ([1] trang 313) a. Giai on tc khng i

( )1 11

1thX XN

=

Trong :

1 : thi gian sy ng tc

N1 : tc sy ng tc

- 56 -

1X : hm m ban u ca vt liu

thX : hm m ti hn ca vt liu

b. Giai on tc gim dn * *

2*

1 2

lnth thX X X XN X X

=

Trong

2 : thi gian sy gim tc

N1 : tc sy ng tc

*X : hm m cn bng ca vt liu

2X : hm m cui ca vt liu

thX : hm m ti hn ca vt liu

Thi gian sy chung ca qu trnh sy l:

1 2 = +

( ) * *1*

1 1 2

1 lnth ththX X X XX X

N N X X

= +

VD5.5. Mt loi vt liu c m ban u l 33%, m ti hn 17% v m cn bng 2% (tnh theo vt liu kh tuyt i), c em sy trong thit b sy 8 gi theo iu kin khng i ca tc nhn th m ca vt liu t 9% (theo vt liu kh tuyt i). Nu tip tc sy vi iu kin nh trn th cn bao nhiu thi gian m vt liu t 3%.

Gii: Xt trong trng hp sy th nht, vt liu t m 2 9%X = theo vt liu kh tuyt

i th thi gian sy s l

( ) * *1 1*

1 1 2


N N X X

= +

Vi thi gian c cho l 8 gi, t cng thc trn ta tnh c tc sy gim tc nh sau:

( ) * *1 1*

1 1 2

1 lnth ththX X X XN X X

X X

= +

= ( )1 0,17 0,02 0,17 0,020,33 0,17 ln8 8 0,09 0,02

+

= 0,0343 kg/h

- 57 -

vt liu t m '2 3%X = cng iu kin sy trn ngha l cng gi tr tc sy

ng tc th thi gian sy cn thit l

( ) * *2 1' *

1 1 2


N N X X

= +

= ( )1 0,17 0,02 0,17 0,020,33 0,17 ln0,0343 0,0343 0,03 0,02

+

= 16,5 h Vy thi gian sy cn thit l 16,5 gi

VD5.6. Mt vt liu c sy gin on, ban u vt liu c m 25%, m cui cn 6% trn cn bn vt liu t. Hy xc nh thi gian sy cn thit. Bit vn tc sy trong giai on ng tc kho st c l N = 0,3 kg/h, m ti hn v m cn bng ca vt liu ln lt l 12% v 2% tnh theo vt liu t. Gii: Do cc m u bi c cho di dng tnh theo vt liu t nn ta cn i cc s liu ny v vt liu kh mi c th p dng c cng thc tnh thi gian sy trong bi. Ta c

10, 25 0,333

1 0,25X = =

kg/ kg kkk

20,06 0,064

1 0,06X = =

kg/ kg kkk

0,12 0,1361 0,12th

X = =

kg/ kg kkk

* 0,02 0,0204100 0,02

X = =

kg/ kg kkk

Th vo cng thc, ta tnh c thi gian sy cn thit l

( ) * *1*

1 1 2


N N X X

= +

( )1 0,136 0,0204 0,136 0,02040,333 0,136 ln0,3 0,3 0,064 0,0204

= +

= 1,032 h

Vy thi gian sy cn thit l 1,032 gi hay 62 pht.

- 58 -

7. Thit b sy ([1] trang 315, [5] trang 300) 7.1. Phng sy

Trong phng sy vt liu c sy gin on p sut kh quyn, vt liu c xp

trn nhng khay hoc khe y. Vic np liu v tho liu c thc hin ngoi phng sy.

Hnh 5.9. Cu to phng sy Nhc im ca thit b l thi gian sy di do vt liu khng c o trn, sy

khng u, khi np v tho liu b mt mt nhit qua ca, kh kim tra qu trnh sy.

7.2. Hm sy Hm sy lm vic p sut kh quyn v dng tc nhn sy l khng kh hoc khi l. Vt liu c xp trn cc khay t trn xe goong di chuyn dc theo chiu di hm. Hm sy c nhc im l sy khng u do s phn lp khng kh nng v lnh theo chiu cao ca hm

7.3. Thit b sy thng quay y l loi thit b quan trng c s dng rng ri trong cng nghip ha cht, thc phm sy cc loi ha cht, phn m, ng cc, bt ng Thit b lm vic p sut kh quyn, tc nhn sy c th l khng kh hoc khi l. Thit b gm mt thng hnh tr t hi dc so vi mt nm ngang, c 2 vnh ai khi thng quay th trt ln cc con ln ta.

- 59 -

Hnh 5.10. Cu to thit b sy thng quay u im ca thit v ny l qu trnh sy u n v mnh lit nh tip xc pha tt,

cng sy tnh theo lng m cao. Tuy nhin do xo trn nhiu nn sn phm d b gy vn xin ra bi, gim phm cht sn phm

7.4. Thit b sy phun Thit b ny dng sy cc vt liu dng lng nh sa, trng, dung dch u nnh Dung dch lng c phun di dng sng vo bung sy, qu trnh sy din ra rt nhanh. Sn phm thu c dng bt mn u im ca thit b sy phun l sy nhanh, sn phm thu

c dng bt mn.

Tuy nhin nhc im l phng sy phi ln m vn tc tc nhn sy phi nh nn cng

sy nh, tiu tn nhiu nng lng, c cu phun phc tp

Hnh 5.11. H thng sy phun

- 60 -

7.5. Thit b sy tip xc Trong thit b sy tip xc, nhit lng c truyn n vt liu bng cch cho vt liu tip xc trc tip vi b mt c t nng. Loi thit b ny c cng sy tnh trn mt n v din tch b mt t nng trung bnh vo khong 1 2 kg kg nc bc hi/h.m2

Hnh 5.12. Cu to thit b sy tip xc u im ca thit b ny l c cu to n gin, c th sy nhiu loi vt liu khc nhau nhng nhc im l nng sut thp, vt liu sy trng thi tnh, truyn nhit km

- 61 -

CHNG 6: HP PH

MC CH: Ni dung bi ging ny gip sinh vin nm c cc khi nim, kin thc c bn v qu trnh hp ph, phn loi v ng dng cng nh xc nh cc thng s c bn ca qu trnh v tnh ton thit k thit b hp ph.


STT NI DUNG S TIT

1 Khi nim hp ph. 0.5

2 Bn cht ca qu trnh hp ph. 0.5

3 ng dng ca qu trnh hp ph. 0.25

4 Cht hp ph. 0.25

5 Cc thuyt hp ph. 0.5

6 Cn bng vt cht trong qu trnh hp ph. 0.5

7 Thit b hp ph. 0.5


Tng 7


TRNG TM BI GING - Nguyn l ca qu trnh hp ph. - xut quy trnh, tnh ton thit k h thng thit b hp ph

NI DUNG

1. Khi nim hp ph ([1] trang 238, [5] trang 311) Hp ph l qu trnh ht la chn cc cu t trong pha kh hay pha lng ln b mt cht

rn. Cu t pha kh hay pha lng b ht c gi l cht b hp ph hay dung cht, cht rn dng ht dung cht gi l cht hp ph v nhng cu t khng b hp ph gi l cht tr.

2. Bn cht ca qu trnh hp ph ([1] trang 238, [5] trang 311) Ty theo c trng ca qu trnh m chng ta phn bit cc loi hp ph sau y:

- 62 -

- Hp ph vt l: hay hp ph Van der Walls l hin tng hp ph thun nghch, hin tng ny km theo phn ng ta nhit, lng nhit ta ra lun ln hi n nhit ha hi v gn

bng nhit thng hoa ca cht kh. - Hp ph ha hc: l hp ph c km theo phn ng ho hc gia cht hp ph v cht b

hp ph. Trong phm vi gio trnh ny chng ta khng xt n hp ph ho hc.

Ch rng trong thc t tt c cc loi hp ph trn u c th xy ra ng thi, nhng ty iu kin thc t m loi ny hay loi khc chim u th hn.

3. ng dng ca qu trnh hp ph ([1] trang 238, [5] trang 311) Qu trnh hp ph c ng dng :

- Lm sch v sy kh. Khi lm sch v sy kh thng cht b hp ph thng khng c gi tr. V d lm sch amoniac trc khi oxy ho, lm sch H2 trc khi hyr ho, lm sch khng kh trong b phn chng kh c, lm sch khng kh kh mi.

- Tch nhng hn hp kh hay hi thnh nhng cu t. Khi tch cc hn hp th cht b hp ph thng l cht qu. Mun thu c cc kh th sau khi hp ph ta phi tin hnh qa trnh nh v tip theo l ngng t. V d nh thu hi dung mi d bay hi, ly hn xng ra khi kh t nhin, tch hn hp cacbuahyr t cc cht ring bit.

- Tin hnh qu trnh xc tc khng ng th trn b mt phn chia pha. Trong trng hp ny cht hp ph l cht xc tc. V d qu trnh oxy ha NH3 thnh oxytnit trn b mt bch kim, oxy ha SO2 thnh SO3 trn b mt bch kim hay oxyt vanaium.

Nh vy, ta thy rng tr mc ch th 3, hai mc ch u ging nh mc ch ca hp th nhng phm vi s dng hai phng php hp th v hp ph khc nhau.

4. Cht hp ph ([1] trang 239) Yu cu cn bn ca cht hp ph l b mt ring phi ln. Hin ti ngi ta hay dng than

hot tnh v silicagel lm cht hp ph.

4.1. Than hot tnh. Than hot tnh l mt cht hp ph rt tt, n c ng dng ch yu trong thu hi dung mi

hu c v lm sch kh.

Nhc im ca than hot tnh l d chy nhit cao, thng khng dng than hot tnh nhit ln hn 2000C. khc phc nhc im ngi ta trn silicaghen vi than hot tnh

ca than.

4.2. Silicaghen: Silicaghen l axit silic kt ta khi cho tc dng H2SO4, hay HCl hay l mui ca chng vi

silicat natri kt ta em ra sch v sy nhit 115 1300C n m 5 7%. Silicaghen

- 63 -

c ng dng dng ht kch thc t 0,2 7mm. B mt ring t n 600m2/g. ng dng ch

yu ca silicaghen l sy kh (ht hi nc trong hn hp kh). 4.3. Zeolit:

Zeolit l dng khong t aluminosilicat, lc u ch l khong t nhin, sau c tng hp pht trin cc c tnh qu gi ca n. Zeolit c gi l sng phn t.

5. Cc thuyt hp ph ([1] trang 244, [5] trang 316) 5.1. Thuyt hp ph Langmuir

Trn b mt hp ph cha cc tm hp ph, lc hp ph ny ch to ra mt lp, cc phn t b hp ph khng tng tc vi nhau.

.

1mKC

a aKC

=

+

Trong :

a : hot

am : kh nng hp ph b mt hot ng. C : nng cht hp ph trong dung dch trng thi cn bng. K : hng s c trng

i vi qu trnh hp ph cht kh th ta c cng thc

'

'.

1mK P

a aK P

=

+

Trong P l p sut ring phn ca cht hp ph trong pha kh khi cn bng.

5.2. Thuyt hp ph Freundlich Trong mt khong nng nh v c bit vi dung dch long, ng ng nhit cho qu

trnh hp ph c th c miu t theo biu thc thc nghim Freundlich: a = K.Cn

Vi:

a : hot

C : nng cht hp ph trong dung dch trng thi cn bng. K, n : cc hng s c trng.

i vi qu trnh hp ph cht kh th ta c cng thc

a = K.Pn

Trong P l p sut ring phn ca cht hp ph trong pha kh khi cn bng.

- 64 -

5.3. Thuyt hp ph BET Cc phn t b hp ph khng chuyn ng t do trn b mt v khng tng tc vi nhau. nhng phn t khc nhau trn b mt c th hnh thnh hp ph nhiu lp vi s lp khc nhau

*

0 0* *

0

1. .

. .m m

P PP C PV P P V C V C

= +

Trong

P : p sut ring phn ca kh khi cn bng P0 : p sut hi bo ha ca kh

V : Th tch kh b hp ph cn bng p sut P Vm : Th tch kh hp ph bo ha trong lp n phn t C* : Tha s nng lng.

VD6.1. hp ph A trong dung dch ln b mt than hot tnh 250C ph thuc nng acid cn bng nh sau:

C, mol/l 0,12 0,54 1,08 1,6

a, g/1 g than 0,07 0,125 0,165 0,21

Hy xc nh xem phng trnh hp ph ng nhit ca qu trnh l Langmuir hay Freundlich. Tm cc h s c trng ca phng trnh ph hp.

Gii: - Gi s qu trnh hp ph trn c dng phng trnh hp ph ng nhit Langmuir. Da

theo VD6.1 ta c dng phng trnh tuyn tnh l 1. m m

C Ca B a a

= + , trong C l nng ca A b

hp ph, a l hot hp ph ca than v B l hng s c trng ca qu trnh hp ph.

Lp bng tnh ton:

C 0,97 1,90 4,05 7,05

C/a 1,71 4,32 6.55 7,62

Dng phng php bnh phng cc tiu ta tnh c R2 = 0,853. - Gi s qu trnh trn tun theo thuyt hp ph Freundlich, tng t nh VD6.2 phng trnh tuyn tnh biu din qu trnh nh sau

lna = lnK + n.lnC Ta lp bng tnh ton:

lnC -2.66 -2.08 -1.80 -1.56

lna -2.12 -0.62 0.08 0.47

- 65 -

Dng phng php bnh phng cc tiu ta tnh c R2 = 0,997. Ta thy r rng rng thuyt hp ph Freundlich cho kt qu tng thch hn rt nhiu nn ta

c th kt lun rng qu trnh hp ph A bng than hot tnh 250C tun theo thuyt hp ph ng nhit Freundlich. Dng phng php bnh phng cc tiu ta tm c:

ln 2, 4054,324

Kn

=

= hay

11,14,324

Kn

=

=

Vy phng trnh hp ph ng nhit Freundlich ca qu trnh ph A trong dung dch ln b mt than hot tnh 250C l: a = 11,1C4,324

VD6.2. Th tch kh N2 c hp ph trn 1g TiO2 75K thay i theo p sut nh sau:

P, mmHg 14 87,5 164,4 204,7

V, cm3 720 935 1146 1254

Hy xc nh phng trnh BET m t s hp ph trn, bit p sut hi bo ha ca N2 75K l 570 mmHg. Gii: Ta bit dng thuyt tnh ca phng trnh BET nh sau

*

0 0* *

0

1. .

. .m m

P PP C PV P P V C V C

= +

Trong d dng nhn thy cc i lng Po, Vm v C* l cc hng s nn phng trnh

trn c dng tuyn tnh Y = B + AX trong 00

.

PPYV P P

=

v X P= cng cc h s i km

tng ng.

T bng s liu ban u, ta lp bng tnh ton cho cc gi tr X, Y ny nh sau:

X = P 14,0 87,5 164,4 204,7

0

0

.

PPYV P P

=

0,020 0,111 0,202 0,255

Dng phng php bnh phng cc tiu ta tm c cc h s trong phng trnh nh sau:

30*

*

3*

2,95.10.

1 1, 22.10.

m

m

PV CCV C

=

=

Hay 3

*

816,3236,7

mV cmC =

=

- 66 -

Vy phng trnh BET m t qu trnh hp ph N2 trn TiO2 75K c dng nh sau :

3570.10. 2,95 1, 22570

P PV P

= +

6. Cn bng vt cht trong qu trnh hp ph ([1] trang 253, [5] trang 316) 6.1. Qu trnh mt bc

S biu din nh hnh 6.1, qu trnh c th hot ng gin on hoc lin tc. V lng cht hp ph s dng thng rt nh so vi lng dung dch c x l, v ch c dung cht l b hp ph mnh nn b qua qu trnh hp ph cc cu t khc.

Gi: Ltr, Gtr : sut lng mol ca cht hp ph v dung dch Xo, X1 : t s mol ca dung cht trong cht hp ph trc

v sau khi hp ph.

Y0, Y1 : t s mol ca dung cht trong dung dch trc v sau khi hp ph.

Cn bng cho dung cht l: Gtr(Y0 Y1) = Ltr(X1 X0)

6.2. Qu trnh nhiu bc giao chiu S ca qu trnh 2 bc giao chiu c trnh by nh hnh 6.2

Hnh 6.2. Hp ph hai bc giao chiu Lng dung dch khng i khi i qua mi bc vi cht hp ph x l trong mi bc ln lt l Ltr1 v Ltr2 , nng ca dung cht trong dung dch gim t Y0 n Y2. Ta c cn bng vt cht nh sau:

Cho bc 1: Gtr(Y0 Y1) = Ltr1(X1 X0) Cho bc 2: Gtr(Y1 Y2) = Ltr2(X2 X0)

Hnh 6.1. Hp ph mt bc

- 67 -

6.3. Qu trnh nhiu bc nghch chiu Cn bng vt cht cho qu trnh N bc l:

Gtr(Y0 YN) = Ltr(X1 XN+1)

Hnh 6.3. Hp ph nhiu bc ngc chiu Vi qu trnh 2 bc nh bn di:

Hnh 6.4. Hp ph hai bc ngc chiu Cn bng vt cht cho dung cht trong ton qu trnh s l:

Gtr(Yo Y2) = Ltr(X1 X0) VD6.3. Hy xc nh lng than hot tnh, ng knh thit b hp ph v thi gian hp

ph mt m 180m3 hi octan tch t hn hp khng kh vi cc d liu sau: nng ban u ca hi octan Co = 0,012 kg/m3; hot tnh ca than theo octan l 7%, khi lng ring ca than hot tnh pb = 350 kg/m3; chiu cao lp than trong thit b hp ph H = 1,0 m. Gii: Lng hi octan trong hn kh ban u l F.Co Lng hi octan hp ph trn than hot tnh l G.a*

Trong F l lng hn hp kh ban u F = 180m3, Co l nng ban u ca octan trong hn hp Co = 0,012 kg/m3, a l hot tnh ca than theo octan a* = 0,07. Cn bng vt cht cho qu trnh hp ph ny ta c:

F.Co = G.a*

Suy ra lng than hot tnh cn dng trong qu trnh hp ph ny l

*

. 180.0,012 30,860,07

oF CGa

= = = kg

Th tch than hot tnh cn dng

30,86 0,0882350

GV

= = = m3

- 68 -

ng knh thit b hp ph c tnh nh sau

Ta c 2

.

4DV Hpi=

Suy ra

4 4.0,0882 0,335.1

VDHpi pi

= = = m

Ly theo chun ta chn ng knh thit b l 0,4 m hay 400 mm

VD6.4. Hn hp khng kh ln NO2 c cho tip xc lin tc nghch dng vi silicagel hp ph NO2. Dng kh i vo thit b hp ph vi sut lng 500kg/h c nng l 1,62% NO2 theo th tch v 91,6% NO2 trong pha kh c hp ph. Qu trnh c thc hin 250C, 1atm. Silicagel i vo thp l nguyn cht. Hy tnh sut lng ti thiu mi gi ca silicagel. S liu cn bng hp ph ng nhit 250C c cho nh bng sau:

p sut ring phn ca NO2, mmHg 0 2 4 6 8 10 12

NO2 , g/g silicagel 0 0,62 1,32 2,02 2,78 3,47 4,22

Gii: Gi s qu trnh trn tun theo thuyt hp ph Freundlich, tng t nh VD6.2 phng trnh tuyn tnh biu din qu trnh nh sau

lna = lnK + n.lnC

Ta lp bng tnh ton:

lnC 0.693 1.386 1.792 2.079 2.303 2.485 lna

-0.478 0.278 0.703 1.022 1.244 1.440 Dng phng php bnh phng cc tiu ta tnh c R2 = 0,999. Ta thy r rng rng thuyt hp ph Freundlich cho kt qu rt tng thch. Nn qu trnh

hp ph NO2 bng Silicagel 250C tun theo thuyt hp ph ng nhit Freundlich. Cc hng s c trng tm c khi ta dng phng php bnh phng cc tiu l

ln 1,2131,07

Kn

=

= hay

0, 2971,07

Kn

=

=

Vy qu trnh hp ph NO2 bng Silicagel 250C trong thit b hp ph ny c phng trnh ng nhit dng a = 0,297.P1,07

Do NO2 trong hn hp kh chim 1,62% th tch nn p sut ring phn ca NO2 trong thit

b l: 2

1,62.760 12,31

100NOP = = mmHg

- 69 -

Th gi tr p sut trn vo phng trnh hp ph ta tm c hot hp ph cn bng trong thit b nhit 250C v p sut 1 atm l a

* = 0,297.12,311,07 = 4,36 g NO2/g silicagel

Cn bng vt cht cho qu trnh hp ph trong thp ta c: F.(Co C) = G.(a* ao) Suy ra sut lng ti thiu ca silicagel cn dng trong qu trnh hp ph ny l

[ ]*

500. 1,62 1,62.(1 0,916).( ) 170,24,36 0

o

o

F C CGa a

= = =

kg/h

Vy sut lng ti thiu ca silicagel cn dng trong thit b hp ph l 170 kg/h.

VD6.5. Hy xc nh lng than hot tnh cn thit, ng knh thit b hp ph v chiu cao lp hp ph dng hp ph hi xng hn hp vi khng kh. Lu lng hn hp kh l 3650m3/h. Nng ban u ca xng l Co = 0,02 kg/m3; Tc ca hn hp kh hi l w = 25 m/ph tnh theo tit din ngang ton phn ca thit b; hot tnh ng lc hc ca than i vi xng l 7% (khi lng), khi lng ring ca than hot tnh b = 500 kg/m3. Thi gian nh, sy v lm ngui cht hp ph l 1,45 gi. Gii: Lng hi xng trong hn kh ban u l F.Co Lng hi xng hp ph trn than hot tnh l G.a*

Trong F l lng hn hp kh ban u F = 3650m3/h, Co l nng ban u ca xng trong hn hp Co = 0,02 kg/m3, a* l hot tnh ca than theo xng a* = 0,07. Cn bng vt cht cho qu trnh hp ph ny ta c:

F.Co = G.a*

Suy ra sut lng than hot tnh cn dng trong qu trnh hp ph ny l

*

. 3650.0,02 10430,07

oF CGa

= = = kg/h

Do thi gian nh, sy v lm ngui cht hp ph l 1,45 gi nn lng than hot tnh cn dng l: Gt = G.t = 1043.1,45 = 1512,4 kg ng knh thit b hp ph c tnh theo cng thc chung nh sau

3650 1,760,785. 0,785.25.60

FDv

= = = m

Ly theo chun ta chn ng knh thit b l 1,8 m hay 1800 mm Chiu cao lp than hot tnh dng hp ph l

2 24 4.1512, 4 1,2

. . .500.1,8t

b

GHDpi pi

= = = m

- 70 -

7. Thit b hp ph ([1] trang 257) 7.1. Hp ph gin on. Hp ph gin c th tin hnh theo 3 phng thc sau:

Phng php 4 giai on: Hp ph - Nh bng hi nc - Sy cht hp ph bng khng kh nng - Lm lnh cht hp ph bng khng kh lnh .

Phng php 3 giai on: Hp ph - Nh bng cch t nng than bng kh tr (kh b hp th i vo thit b ngng t) sau cho hi nc i qua - Lm lnh cht hp ph bng khng kh lnh.

Hnh 6.5. Cu to thit b hp ph gin on Phng php 2 giai an: Cho hn hp v khng kh nng i qua cht hp ph m v nng,

qu trnh hp ph vi qu trnh sy ng thi tin hnh, sau l nh hp ph. Phng php ny

nng lng tiu tn t v nng sut cao.

7.2. Thit b tng si Trong thi gian gn y tng si c p dng trong hp ph so vi hp ph c lp cht

hp ph ng yn th hp ph tng si c u im.

V chuyn ng mnh v trn ln nn khng c s phn lp cht hp ph gia cc ht lm

vic v cc ht cha lm vic ngha l khng c khu vc cht, trnh hin tng qu nhit, nng

sut cao nhng ht chng mn, i hi bn c hc cao

- 71 -

TI LIU THAM KHO

[1] GS.TSKH. Nguyn Bin Cc qu trnh, thit b trong cng ngh ha cht v thc phm Tp 4 Phn ring di tc dng nhit Nh xut bn Khoa hc v K thut H Ni 2005.

[2] Trnh Vn Dng Qu trnh v Thit b cng ngh Ha hc & Thc phm, Bi tp truyn khi Nh xut bn i hc Quc gia Tp.HCM 2006.

[3] TS. Trn Xoa, TS. Nguyn Trng Khung, TS Phm Xun Ton S tay Qu trnh v thit b Cng ngh Ha hc Tp 1 Nh xut bn Khoa hc v K thut H Ni 2004.

[4] TS. Trn Xoa, TS. Nguyn Trng Khung, TS Phm Xun Ton S tay Qu trnh v thit b Cng ngh Ha hc Tp 2 Nh xut bn Khoa hc v K thut H Ni 2004.

[5] V Vn Bang, V B Minh Qu trnh v Thit b cng ngh Ha hc & Thc phm, Tp 3 Truyn khi Nh xut bn i hc Quc gia Tp.HCM 2007.

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