thiet ke phan xuong cracking xuc tac
TRANSCRIPT
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7/31/2019 Thiet Ke Phan Xuong Cracking Xuc Tac
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n tt nghip Thit k phn xng Cracking xc tc
Nguyn Vit Hun Ho Du K44-QN HBK HN1http://www.ebook.edu.vn
M u
Hin nay, trn th gii, mt hng xng du l mt mt hng quan trng
v c bit quan trng .N chnh l mu huyt ca nn kinh t quc dn vquc phng cho bt k mt quc gia no.
V Vit Nam ,nhu cu tiu th sn phm du kh ang tng ln cng
vi s tng trng ca nn kinh t quc dn v quc phng.Tuy nhin sn
phm xng Vit Nam hin nay u c nhp khu t nc ngoi.Phn ln
t Singapore vi ba u ni tip nhn l H Ch Minh, Nng v Qung
Ninh. V t ba u ni tip nhn ny ,sn phm c phn phi ti cc kho
trung chuyn trn ton quc. Trong tng lai vic nhp sn phm xng du l
diu khng c li cho nn kinh t ca c nc. V vy m c th p ng
nhu cu xng cho ngi tiu dng th nht thit phi c nh my lc v ch
bin ,trong quan trng hn c l phi c phn xng sn xut xng du [8].
Ngi ta c th sn xut xng bng nhiu cc qu trnh ch bin khc
nhau nh l cracking xc tc, Reforming xc tc, izome ha ...V..V...trong
cracking xc tc l qu trnh ch yu sn xut xng . Tiu chun quan
trng ca nhin liu dng cho ng c xng l ch s octan . Ch s ny cng
cao th kh nng chng kch n cng cao. Thot tin th ngi ta thc hin
cracking phn on du m c nhit si trong khong 490 800 K bng
nhit , nhng vi phng php ny th hiu qu rt thp v sn phm cha
nhiu hydrocacbon phn t thp . n khong nhng nm 1930 , qu trnh
cracking nhit c thay th bng cracking xc tc , vi cht xc tc l
Aluminosilicat t nhin. V u tin ngi ta s dng lp xc tc tnh nhng
m n cng cha mang li hiu sut v cht lng xng cao nh mong mun ,
n li c qa nhiu nhc im chnh v nhng l do nh vy cho nn ngi ta
thay th n bng qu trnh Cracking c lp xc tc chuyn ng .
C rt nhiu cng ngh khc nhau cho qu trnh Cracking c lp xc tc
chuyn ng. Nhng ngy nay ngi ta dng ph bin l cng ngh ca FCC.
Vi cng ngh ny cho ngi ta thu c nhiu xng v cht lng cng tt
hn rt nhiu , phn no cng p ng
c nhu cu xng du hin nay.
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n tt nghip Thit k phn xng Cracking xc tc
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Phn ITng quan l thuyt qu trnh
cracking xc tc
Trong cng ngh ch bin du m cc qu trnh chuyn ha ha hc
di tc dng ca cht xc tc chim mt t l rt ln v ng vai tr v cng
quan trng . Cht xc tc trong qu trnh chuyn c kh nng lm gim nng
lng hot ha ca phn ng v vy m tng tc phn ng ln rt nhiu .
Mc khc , khi c mt cht xc tc th phn ng c kh nng tin hnh nhit
thp hn iu ny rt quan trng i vi nhng phn ng c hiu ngdung nhphn ng hydro ha , alkyl ha , polime ha v.v...
S c mt cht xc tc va thc y nhanh qu trnh chuyn ha ha
hc , va c kh nng to ra nhng nng cn bng cao nht , c ngha l
tng hiu sut ca qu trnh .iu quan trng nht l cht xc tc c kh nng
tng nhanh khng ng u gia cc loi phn ng m v phng din nhit
ng l chng xy ra cng lc trong qu trnh , trong iu kin nh nhau ,
ngi ta gi y l tnh cht chn la ca xc tc. Ngi ta nghin cu rt
nhiu loi cht xc tc v ngi ta cng li dng tnh cht chn la ca n m
hng phn ng ca qu trnh ch bin theo chiu c li nhm thu c
nhng sn phm chnh t hiu sut v cht lng tt nh mong mun.
Chnh v l do cho nn p ng ngy cng nhiu nhu cu dng
xng du th ngi ta nghin cu v ci tin dn qu trnh cracking xc tc
. Qu trnh cracking xc tc vi dy chuyn cng ngh FCC l u im hnc.
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n tt nghip Thit k phn xng Cracking xc tc
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Chng IMc ch v ngha Bn Cht Ha Hc
vc ch phn ng
I. Mc ch v ngha ca qu trnh cracking xc tc
Cracking xc tc chim mt v tr c bit quan trng trong cng
nghip ch bin du m . Lng du m dng ch bin bng cracking xc
tc l tng i ln.V d nh : vo thng mt nm 1965 tng lng du m
n
c m ch bin l 1500 tn/ngy trong c 800 tn/ngy (tc khong53%) c ch bin bng cracking xc tc[3-trang62]
Qu trnh cracking xc tc l mt qu trnh ch yu sn xut xng
cho t v mt t cho xng my bay.Chnh v vy m khng c nh my lc
du no li thiu phn xng cracking xc tc.
Mc ch qu trnh cracking xc tc [1,2,3] l bin i phn on du
m c nhit si cao thnh cc cu t xng c cht lng cao, ngoi ra cn
thu thm mt s sn phm ph khc nh gasoil nng , gasoil nh, kh,...Qu
trnh cracking xc tc thc cht l qu trnh cho tip xc nguyn liu vi cht
xc tc trong iu kin qui nh v ch cng ngh ,cc phn ng c li xy
ra nhm thu dc sn phm c cht lng tt v hiu sut ln, ng thi cc
phn ng ph c hi cng xy ra nh phn ng to cc bm trn b mt cht
xc tc lm cho xc tc gim hot tnh.Do vy m cn phi tin hnh ti sinh
xc tc.II. C ch phn ng : [1,2,3,4,5,6,7]
Trong iu kin m chng ta tin hnh qu trnh cracking xc tc, mt
s lng ln cc phn ng ha hc xy ra v chng quyt nh cht lng hiu
sut ca qu trnh. l cc phn ng sau:
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n tt nghip Thit k phn xng Cracking xc tc
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1. Phn ng phn hu cc mch C C, phn ng crackingL phn ng phn hu b gy mch nhng phn t c kch thc ln
(trng lng phn t ln) thnh nhng phn t c kch thc nh hn (trng
lng phn t nh hn). y l phn ng chnh ca qu trnh.
+ Phn hu parafin to olefin v parafin c trng lng phn t nh hn
CnH2n+2 CmH2m + CpH2p+2 (n = m + p)
+ B gy mch olefin to olefin nh hn
CnH2n CmH2m + CpH2p (n = m + p)
+ Hydrocacbon thm c nhnh bn b b gy to thnh parafin v
hydrocacbon thm c nhnh nh hn
ArCnH2n+1 ArCmH2m+1 + CpH2p (n = m + p)
+ Naphten b b gy m vng to cc olefin (tr vng hexan)
CnH2n CmH2m + CpH2p (n = m + p)
naphten olefin olefin
CnH2n C6H12 + CmH2m + CpH2p (n = m + p+ 6)
naphten xyclohexan olefin olefin
2. Phn ng ng phn ho (izome ho)L phn ng to ra nhng hydrocacbon c cu trc mch nhnh (cu t
lm tr s octan tng ln).
n-olefin izo-olefin
n-parafin izo-parafin
3. Phn ng chuyn di hydro di tc dng ca xc tcNh c xc tc m c s phn b li hydro cho nn lm no c mt
s hydrocacbon i (sn phm phn hu), v vy lm tng c tnh n nh
ho hc ca sn phm thu.
Naphten + olefin hydrocacbon thm + parafin
4. Phn ng trng hp
Ch yu xy ra vi hydrocacbon i.
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n tt nghip Thit k phn xng Cracking xc tc
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CnH2n + CmH2m CpH2p (n + m = p)
5. Phn ng alkyl ho v kh alkyl hoPhn ng alkyl ho xy ra nhit thp, lm gim hiu sut kh.
ArH + CnH2n Aromat CnH2n+1
Hydrocacbon thm olefin alkyl thm
Phn ng kh alkyl ho ngc vi phn ng alkyl ho, xy ra nhit
cao v to nhiu kh.
6. Phn ng ng
ng t to ccPhn ng ny ch yu xy ra i vi cc hydrocacbon thm a vng, xy
ra khi nhit cao.
S to cc trong qu trnh cracking xc tc l khng mong mun, v cc
to thnh thng bm trn b mt xc tc, gim hot tnh b mt xc tc,
gim thi gian lm vic ca xc tc.
Hiu ng nhit ca cc phn ng trn khc nhau v du cng nh v gi
tr. a s cc phn ng phn hu l phn ng thu nhit mnh, cn cc phn
ng nh phn ng ng phn ho, chuyn v hydro, polyme ho v phn ng
ngng t l cc phn ng to nhit yu. Hiu ng nhit tng cng ca qu
trnh cracking xc tc l thu nhit, vi gi tr thay i t 100 n 400 kJ/kg
nguyn liu, tu theo bn cht ca nguyn liu c s dng trong qu trnh.
Hin nay, vn cha c s nht tr hon ton trong vic gii thch c ch xc
tc qu trnh cracking.Nhng nhn chung th ph bin hn l gii htch theo c
ch ioncacbonic.Cc ioncacbonic ny c to ra khi m cc phn t
2H2 H22
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n tt nghip Thit k phn xng Cracking xc tc
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hydrocacbon ca nguyn liu tc dng vi tm axit ca xc tc.Theo thuyt
ny th qu trnh cracking xc tc xy ra theo 3 giai on chnh sau y:
a. To ioncacboni
- Paraffin : Cc hydrocacbon paraffin, trong qu trnh tin hnhcracking xc tc, n s b hp th trn trung tm axit Lewis ca cht xc tc
to ra ion cacboni :
V d : Cracking n-hexan ( 2 -trang 109 )
CH3-CH+-CH2-CH2-CH2-CH3
CH3-CH2-CH2-CH2-CH2-CH3 +H2
CH3-CH2-CH2-CH2-CH2-CH3in tch dng khng bao gi nhn c cacbon bc mt.
Tng qut c th vit :
A (H + )
CnH2n+2 CnH2n+1 + H2
Ngoi ra , Parafin cng c th b hp th trn nhng tm axit Bronsted :
CnH2n+1 +H2
CnH2n+2 + H+ CnH2n+3
CmH2m+1 + CpH2p
- Olefin: y l thnh phn khng c trong nguyn liu ban u ca qu
trnh m n c to ra do s phn hy cc hydroccbon thm ,Parafin ,
naphten ,...Olefin l hp cht rt hot ng ,nh vy m n tham gia vo phn
ng to Ion cacboni do s tc dng ca olefin vi tm axit Bronsted ca xctc:
Ion cacboni to thnh do s tc dng ca olefin vi tm axit Lewis ca
xc tc:
+ H+ (xt)+
R1 CH C R2 + (xt)
H
R1 CH C R2
H H
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n tt nghip Thit k phn xng Cracking xc tc
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hoc l
CnH2n + H+ Cn
+H2n+1
CnH2n + L C+
nH2n+1 + LH
Ion cacboni to thnh trong cc phn ng tun theo quy tc nht nh.
Nh khi olefin tc dng vi H+(xt) th xc sut to alkyl bc 2 ln hn alkyl
bc mt.
Khi olefin c lin kt i cacbon bc 3 th ion cacboni bc 3 d to
thnh hn cacbon bc 2.
T hydrocacbon naphten:
Khi hydrocacbon naphten tc dng vi tm axit ca xc tc hay cc ion
cacboni khc s to ra cc ion cacboni mi tng t nh qu trnh xy ra vi
parafin.
T hydrocacbon thm :ngi ta quan st thy s to thnh ion
cacbonil s kt hp trc tip ca H+ vo nhn thm
Cc hydrocacbon thm c mch bn di th s to thnh ion cacboni
cng ging nh trng hp parafin.
RH + R+
H Al O Si
O
Oolefin
Al O Si
O
O
CH3 CH2 CH CH2+
CH3 CH2 CH2 CH2+
d to thnh hnCH3 CH2 CH CH2 H+
(xt)+
d to thnh hnH+
(xt)+CH3 CH C CH3
CH3
CH3
CH3 CH2 C CH3+
CH3CH3 CH CH CH3
+
H+CH2 CH3
+
CH2 CH3H+
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n tt nghip Thit k phn xng Cracking xc tc
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Thi gian sng ca cc ion cacboni c to ra dao ng t phn triu
giy n hng pht. Cc ion cacboni ny to ra nm trong lp cc phn t hp
ph, chng l nhng hp cht trung gian rt hot ng i vi nhiu phn ng
xy ra khi cracking.
b. Giai on bin i ion cacboni
Cc ion cacboni l nhng hp cht rt hot ng ,chnh v vy khi c
to ra t giai on trn li nhanh chng tham gia vo cc phn ng bin i
khc nhau nh :
Phn ng ng phn ho, chuyn di ion hydro, nhm metyl to cu
trc nhnh.
RCCCC CCCCR
n nh ca ion cacboni theo bc l gim dn nh sau :
C3+ (bc 3) > C2+ (bc 2) > C3+ (bc 1)
- Ion cacboni tc dng vi phn t trung ho to thnh ion cacboni mi
v phn t mi (hydrocacbon no hay i) theo phn ng vn chuyn ion
hydrit.
C+nH2n+1 + CmH2m CnH2n + C+
mH2m+1
C+nH2n+1 + CmH2m+2 CnH2n+2 + C+
mH2m+1
Phn ng cracking: Cc ion cacboni c s nguyn t cacbon ln xy ra
s phn hu v t mch v tr so vi nguyn t cacbon tch in. Sn
phm phn hu l mt phn t hydrocacbon trung ho v ion cacboni mi c
s nguyn t cacbon nh hn
R CH2 CH CH3+
CH3
R C CH2+
CH3
R CH CH2+
++
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.
Nu ba lin kt CC v tr th lin kt CC v tr [A] l c xc sut
t mch ln nht, sau n v tr [B] v cui cng n v tr [C].
Vi ion cacboni mch thng:
i vi ion cacboni l ng ng ca benzen, v d nu p dng quy tc
v tr bnh thng th v tr rt bn vng. Chnh v vy m ngi ta cho
rng proton phi c kt hp vi mt trong nhng lin kt CC trong nhn
thm to thnh nhng hp cht trung gian, sau mi phn hu theo quy tc
nu trn. Khi phn hu, in tch ion cacboni s dch chuyn theo s sau:
Nh vy trong hydrocacbon thm hiu ng tch in nhn thm l
nguyn nhn quan trng hn so vi nguyn nhn l s bin i ion cacboni
bc hai thnh bc ba.
Cc ioncacboni l ng ng ca Benzen m c mch nhnh cng di th
tc xy ra cng lnv cng d. V d nh ioncacboni izobutyl-benzen c
tc ln hn 10 ln so vi ioncacboni izopropyl-benzen .
Cc nhm metyl , etyl , rt kh b t ra khi nhn Benzen ( v l nng
lng lin kt ln ) v do kh to c ion CH3+ v C2H5
+. iu ny gii
thch c v sao trong xng cracking xc tc li c hm lng hydrocacbon
c mch nhnh bn ngn l ln v cng gii thch c l v sao trong sn
phm kh ca qu trnh cracking li nhiu hydrocacbon mch nhnh.
R C C C C C C+
C
C
[A] [B]
[C]
+
CH3 CH CH2 R+
RCH3 CH CH2+
C
C C+
C
CH C+
+C
C C
C+
H
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n tt nghip Thit k phn xng Cracking xc tc
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c. Giai on dng phn ng
Giai on ny xy ra khi cc ion cacboni kt hp vi nhau hoc chng
nhng hay nhn nguyn t hydro ca xc tc to thnh cc phn t trung
ho. Nhn chung , nhng phn ng ha hc xy ra trong qu trnh cracking
xc tc l rt phc tp.
III. ng hc cho qu trnh cracking xc tc.[4,5,6,7,14]
V ng hc, cracking xc tc l mt th d in hnh v xc tc d th.
Qu trnh cracking xc tc c th xy ra cc giai on sau:
1- Qu trnh khuch tn nguyn liu n b mt xc tc (khuch tn
ngoi).2- Khuch tn hi nguyn liu n cc tm hot tnh trong l xp ca
xc tc (khuch tn trong).
3- Hp ph nguyn liu trn tm hot hot tnh xc tc.
4- Cc phn ng ha hc trn b mt xc tc.
5- Kh hp ph cc sn phm cracking v nguyn liu cha tham gia
phn ng ra khi b mt v ra khi l xp ca xc tc.6- Tch cc sn phm cracking v nguyn liu cha tham gia phn ng
ra khi vng phn ng.
Tc chung ca qu trnh nh vy s c quyt nh bi giai on no
chm nht. Phn ng xy ra trong vng ng hc hay vng khuch tn hon
ton ph thuc vo bn cht ca xc tc c s dng, ph thuc vo bn cht
ca nguyn liu v vo ch cng ngh ca qu trnh. Cc nghin cu cho thy, nu qu trnh cracking xc tc nguyn liu l gazoil nh (nguyn
liu mu) trn xc tc dng cu khi kch thc ht xc tc t 3 5 mm v
nhit l 450 5000C th phn ng xy ra vng trung gian gia ng hc
v khuch tn. Cn khi cracking lp si (FCC) ca xc tc nhit 480
5300C th phn ng xy ra vng ng hc.
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n tt nghip Thit k phn xng Cracking xc tc
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Tc ca phn ng cracking xc tc, trong a s cc trng hp c
miu t bng phng trnh bc mt c dng:
k = v0.n.ln(1 x) (n 1)x
y: k: tc ca phn ng (mol/g.h)
v0 : tc truyn nguyn liu (mol/h)
n: s mol sn phm c to thnh t 1 mol nguyn liu
x: mc chuyn ha (phn mol).
i vi phn on du trn xc tc zeolit, phng trnh bc 1 li c dng
sau:
k=vo/(1-x)
y v0 l tc th tch khng gian truyn nguyn liu (m3/m3.h).
IV. Cracking xc tc cc hp cht hydrocacbon ring
l.[1,2,3,4,5,6,7]
1. S bin i cc hydrocacbon parafinCc hp cht parafin l cu t quan trng ca phn on gazoil. Cc
nghin cu qu trnh cracking xc tc parafin s gip cho php tin hnh mhnh ha cc hin tng ca qu trnh.
Ging nh qu trnh cracking nhit, qu trnh cracking xc tc, cc
hydrocacbon parafin cng b phn hy to thnh phn t olefin v parafin c
trng lng phn t b hn.
Phng trnh tng qut:
CnH2n+2 CmH2m+2 + CpH2p (p, m < n)Nu mch parafin cng di th s phn hy xy ra ng thi mt s ch
trong mch ch khng phi ch xy ra hai u mt ca mch nh qu trnh
cracking nhit. Cc hydrocacbon parafin c trng lng phn t thp th kh
nng phn hu km.
+
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V d: i vi butan C4H10 nhit 5000C; v0 = 1 h
1 ch c 1 % trng
lng b phn hy. Tuy nhin tc phn hy ca n vn ln hn gp 6 ln so
vi khi phn hu n thun di tc dng ca nhit.
Ngoi ra cn b kh hydro nhng mc nh.
Khi trng lng phn t ca parafin tng ln th kh nng phn hy v
tc phn hy cng tng ln. Tc phn hy ca parafin di tc dng ca
xc tc ln hn nhiu so vi khi phn hu iu kin cracking nhit. Tnh hp
ph chn lc ca xc tc trc tin v cao nht l i vi hydrocacbon olefin.
V vy parafin khng nm trong lp hp ph ha hc m nm ngoi gii hn
ca lp ny. Song nng lng b mt xc tc vn c tc ng n parafin cho
nn to ra nhng khu vc c nng cc phn t hydrocacbon cao m c lin
kt CC yu. Nh vy lm gim nng lng hot ha khi phn hu.Nng lng hot ha ca phn ng cracking parafin gim dn nu chiu
di mch hydrocacbon parafin tng.
Bng 1 : Nng lng hot ha ca cc n-parafin in hnh
Hydrocacbon nC6H14 nC7H16 n-C8H18
E kcal/mol 36 29 24
V vy khi cracking, mch hydrocacbon parafin cng di, cng d b b
gy. V d khi cracking xc tc cc parafin nhit 5500C nh sau:
C4H10 C2H6 C2H4+ (30%)
C4H6 H2+ (10%)
t C, xc t co
(60%)CH4 C3H6+
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Bng 2:
Hydrocacbon n-C5H12 n-C7H16 n-C12H26 n-C12H26
% cracking 1 3 18 42
Cho nn cc parafin c trng lng phn t ln khi phn hu to thnh
parafin c trng lng phn t nh hn v c th b phn hu tip tc:
Cc parafin c cu trc mch nhnh tham gia phn ng phn hy vi tc
ln hn cc parafin mch thng:
S phn nhnh v s lng nhnh ca parafin c vai tr rt quan trng
trong qu trnh cracking. N c lin quan n kh nng to ion cacboni v do
n s quyt nh c tc to thnh sn phm. iu ny c chng
minh t cc s liu % chuyn ha parafin C6 khi cracking trn xc tc
aluminosilicat nh di y:
t C, xc t co
C9H20 C5H10+CH3 (CH2)12 CH3
t C, xc t co
C5H12 C4H8+C9H20
(phn hu 42%)t C, xc t c
o
C4H8 C4H10+C8H18n-
(phn hu 49%)izo- izo-C4H10 C4H8+C8H18t C, xc tc
o
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Bng 3:
C6 % chuyn ho
CCCCCC 14CCCCC
C
25
CCCCC
C
25
CCCC
C C
12
C
CCCC
C
10
Khi cracking n-hexan nhit 5500C trn xc tc axit, s phn b cc
sn phm xy ra nh sau:
Bng 4:
Hydrocacbon H2 CH4 C2 C3 C4 C5
%V 9 12 19 49 8,5 1,6
S phn b ny khng i xng nhau qua C3. S c mt mt lng ln H2
v metan cho thy rng cng mt lc xy ra nhiu phn ng, c th c c phn
ng cracking nhit cng vi cc phn ng ca ion cacboni nh nu trn.
Phn ng chnh to sn phm s ph thuc vo tng quan gia cc phn ng
cracking (theo quy tc ) v phn ng vn chuyn hydro ca ion cacboni.
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Do cracking xc tc m lm gim kch thc ca ion cacboni R+ cc ion
c kch thc nh nh+CH3 hay+C2H5 s kh to ra (do ct mch v tr so
vi cacbon mang in tch). V th trong sn phm u tin to ra C3 hay C4
nhiu hn C1 v C2 so vi qu trnh cracking nhit.
Ngoi ra cc parafin cn tham gia phn ng ng phn ha, chuyn di
hydro v nhm metyl, nguyn t cacbon tch in:
2. S bin i ca hydrocacbon olefin (1,2,3)Nh ni trn , Olefin khng c mt trong thnh phn nguyn liu m
n c to ra do cc phn ng ca qu trnh v tnh hp ph chn lc cao
nht ca xc tc l hydrocacbon olefin trong qu trnh cracking xc tc, chonn iu kin cracking xc tc cc hydrocacbon olefin chuyn ha vi tc
nhanh hn hng nghn n hng chc nghn ln so vi khi cracking nhit.
Hydrocacbon olefin c mt trong hn hp phn ng l do phn ng
cracking parafin, naphten hay alkyl thm. Hydrocacbon olefin l nhng hp
cht hot ng hn, trong giai on u tin ca qu trnh, chng tham gia
phn ng to ion cacboni bi qu trnh hp th mt proton vo lin kt i.
Ion cacboni va to ra s b cracking theo quy tc , khi to thnh mt
olefin nh hn v mt ion cacboni bc mt m ion ny c th li proton
trn b mt ca xc tc hay c th ng phn ha thnh ion cacboni bc hai.
V d: RCH=CHCH2CH2R1 + H+
RCH2CHCH2CH2R1 RCH2CH=CH2 + CH2CH2R1
CH3CH2R1 R1CH=CH2 + H2
n- izo-C5H11C5H11+ +
izo-C5H12+
izo-C5H11+
C4H10+ C4H9++
RRH R1+
+
+ R1H+
R2 olefin++
+ +
+
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Cc hp cht olefin nh C2 C5 va to thnh t tham gia vo cc phn
ng cracking, m chng thng tham gia vo cc phn ng vn chuyn hydro
v phn ng a t, kt qu l dn n to ra parafin v cc. Khi cracking cc
olefin t C5 tr ln, ngoi phn ng ct mch theo qui tc , ngi ta cn quan
st thy c xy ra phn ng dime ha. V d khi cracking penten quan st
thy cc phn ng sau:
H+ + C=CCCC CH3CHCH2CH2CH3
CH3CH=CH2 + CH2CH3
2C5 C10 C3 + C7
C7 C3 + C4
Chnh v xy ra cc phn ng trn m trong sn phm c t l C3/C4 bng
2. Phn ng cracking penten l phn ng lng phn t, trong khi phn ng
cracking hepten li l phn ng n phn t, ngha l khng c s cnh tranh
ca phn ng dime ha:
C7 C3 + C4 (vi C3/C4 = 1)
Cn i vi hexen, tc ca qu trnh n phn t khng nhanh hn so
vi qu trnh lng phn t. T l gia tc phn ng n phn t vi phn
ng a phn t, i vi penten, hexen, hepten tng ng bng 0 : 0,2 : 7. Gi
tr ny cho thy tc cracking olefin C7 ln hn nhiu ln so vi tc
cracking n-heptan (l parafin). So vi qu trnh cracking nhit, tc phn
ng ca olefin trong cracking xc tc ln hn rt nhiu.
Ngoi phn ng ct mch, cc hydrocacbon olefin cn tham gia phn ng
ng phn ha:
CH3 C CH2
CH3
CH3 CH CH CH3
CH2 CH CH2 CH3
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Tc phn ng ng phn ha tng khi trng lng phn t ca olefin
tng. Cc olefin cn tham gia phn ng trng hp to ra phn t c trng
lng ln hn.
Cc olefin cn phn ng vi hydro to thnh parafin:
Cc olefin trong qu trnh cracking xc tc cn tham gia phn ng ngng
t, ng vng to hydrocacbon thm a vng v vng thm a t l cc:
3. S bin i cc hydrocacbon naphtenic:Cc hydrocacbon naphtenic tham gia phn ng trong qu trnh cracking
xc tc vi tc ln hn 500 4000 ln so vi khi cracking nhit. Trong
iu kin cracking xc tc naphtenic tham gia phn ng alkyl, kh hydro v
phn b li hydro to hydrocacbon thm, parafin v hydro.
V d:
Phn ng phn hy vng naphten to izo-parafin:
CH3 CH2 CH CH22 CH3(CH2)5 CH CH2
CH2 CH CH2 CH3
CH2 CH CH CH2CH2 CH2CH2 CH2 +
+R CH2 CH2 H2 R CH2 CH3
CH2 CH2 CH2 CH2 CH2 CH2 H2+ + + 3
CH2 CH CH2 CH2 CH2 CH3H2 H2 H2
H2+ 2CH2 CH2 CH3
C3H8 +
+ H23
CH3 CH3 CH2 CH2 CH2 CH CH3
CH3
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* Phn ng ng phn ha vng naphten
Phn ng chuyn v cc nhm bn:
Sn phm khi cracking naphten c tnh cht no nhiu hn so vi cracking
parafin. Trong cc phn ng phn hu, cc phn t c to thnh a s c s
cacbon nhiu hn C3. Cracking xc tc naphten cho hiu sut sn phm lng
cao, ngha l hiu sut s cao hn, cho nn naphten l thnh phn l tng
nht trong nguyn liu cracking xc tc.
4. S bin i ca hydrocacbon thm (1,2,3)Cc hydrocacbon thm m c gc alkyl nh bn th rt kh b cracking
ngay c khi c mt ca cht xc tc , v vng benzen c bn cao .V vy
m trong qu trnh cracking xc tc, cc hp cht alkyl thm do vng thm c bn cao hn nn trc tin s xy ra qu trnh ct nhnh alkyl (3-trang92 )
. Nhng toluen c bn rt ln, v th khng th tch nhm metyl hay etyl
trong iu kin cracking. Mch alkyl cng di th cng d b b gy v nu
mch alkyl li c nhnh th tc ct nhnh cn ln hn nhiu. iu ny d
dng gii thch khi xem xt nng lng hot ha ca hydrocacbon thm. (1-
trang 112, 2-trang 114, 3-trang 92,93 )
CH3
CH2 CH3
CH3
CH3
CH3
CH3
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Bng 5:
Loi hydrocacbon thm Nng lng hot ho (kcal/mol)
C6H5C2H5 50
C6H5C4H9 34
C6H5CHCH2CH3
CH3
19
C6H5CHCH3CH3
17,5
V d: Khi cracking xc tc propyl benzen, phn ng xy ra nh sau:
C6H5CH2CH2CH3 C6H6 + CH3CH=CH2
Cn khi cracking nhit li xy ra theo hng khc:
C6H5CH2CH2CH3 C6H5CH3 + CH2=CH2
Cc phn ng khc li xy ra trong qu trnh
cracking xc tc hydrocacbon thm l:
Phn ng ng phn ho: Cc hydrocacbon thm cha nhiu gc metyl
d tham gia phn ng ng phn ho do s chuyn v cc nhm metyl theo
vng benzen.
V d:CH3
CH3
t C, xc t co
CH3
CH3
CH3CH3t C, xc t co
para-xylen meta-xylen octo-xylen
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Hydrocacbon thm cn tham gia phn ng chuyn v nhm metyl
ngoi phn t: (1,2,3)
Hydrocacbon thm c nhnh alkyl di c th khp vng to
hydrocacbon thm d vng:
Cc hydrocacbon thm a vng xy ra phn ng ngng t v to cc:
hay
Cc hydrocacbon thm a vng ngng t cao to cc d hp ph trn b
mt xc tc. V vy chng km hm qu trnh lm nh hng n qu trnh
cracking cc loi hydrocacbon khc.
Trong iu kin ca cracking xc tc, cc bin i ca hydrocacbon
ring l c th tm tt nh sau:
2t C, xc t c
o
CH3
CH3
CH3
+
CH3
CH3CH3
t C, xc tco
CH2 CH2 CH2 CH3
CH2 CH2 CH2 CH3
H25+
2 + CH2 CH2
2H2 H22
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Olefin v parafin
Parafin Olefin v hydro
izo-parafin
Cc hp cht olefin c trng lng thp
Parafin v dien
Olefin Parafin hay naphten v hydrocacbon thm
Polyme, cc
Olefin v parafin
Naphten Xyclohexan v olefin
Hydrocacbon thm
Olefin
Parafin v alkyl thm c mch bn ngn
Hydrocacbon thm ng phn ho, chuyn v nhm alkyl
(alkyl thm) Sn phm ngng t, cc
Ngoi ra cn xy ra cc phn ng bc 2 nh:
Naphten + Olefin Hydrocacbon thm v parafin
Hydrocacbon thm + Olefin Sn phm ngng t, cc
V. Cracking phn on du m (1,11,12)
cracking xc tc phn on du m, do qu trnh rt phc tp, nn
thc t khng th miu t tt c cc phn ng ho hc xy ra trong qu trnh.
Do ngi ta thng a ra s kho st cc hng phn ng chnh trongqu trnh cracking xc tc. V d khi nguyn liu l phn gazoil chng ct
chn khng, ta c th dng s sau:
LCO - phn on du nh ca cracking xc tc
HCO - phn on du nng ca cracking xc
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chng IIxc tc ca qu trnh Cracking
Xc tc l mt trong nhng lnh vc khoa hc k thut lun c nhiu
ngi quan tm v nghin cu, c bit l xc tc dng cho cng nghip ha
du , trong c qu trnh cracking . Nh vo kh nng lm gim nng lng
hot ha ,nh vo tnh xht chn lc phn ng , ...m hiu sut cng nh cht
lng ngy cng tng ln .
S pht trin v ci tin qu trnh cracking xc tc trong cng nghip
ch bin du m, ngoi vic ci thin v nguyn liu, h thng thit b, ch cng ngh v.v..., th ta thy rng ci chnh l do s ci tin trong vic s dng
cc cht xc tc. Phn ng cracking xc tc ch yu xy ra trn b mt xc
tc, chiu hng ca phn ng ph thuc rt nhiu vo bn cht ca xc tc.
Xc tc c dng trong qu trnh cracking thng l xc tc rn, xp, c
ngun gc thin nhin hay tng hp, vi b mt ring ln. Xc tc cracking
u tin c dng l t st thin nhin c tnh axit (v d loi
montmorillonit).
V d: Lin X vo nhng nm 1919 - 1920 dng xc tc AlCl 3
trong h thng cracking sn xut xng.
Xc tc AlCl3 tin hnh nhit thp 200 3000C. Nhng trong qu
trnh s dng ngi ta thy c nhiu nhc im sau: Xc tc b mt mt
nhiu do to phc vi cc hydrocacbon ca nguyn liu, iu kin tip xc
gia xc tc v nguyn liu khng tt, cho hiu sut v cht lng xng thp.
V sau ngi ta nghin cu s dng aluminosilicat v nh hnh m u
tin l t st bentonit. Vo nm 1936 Lin X s dng xc tc
aluminosilicat quy m cng nghip. Ngi ta tin hnh tng hp
aluminosilicat trong cc nh my ch to xc tc. Sau trong cng nghip
ch bin du m ngi ta dng ph bin xc tc aluminosilicat tng hp v
n c hot tnh v chn lc tng i cao. Xc tc ny tng c s
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dng trong cng nghip cracking sut 30 nm. Tuy vy, hin nay vic ci
thin xc tc vn khng ngng pht trin v n cui thp nin 60 ca th k
20, ngi ta chuyn sang ch yu dng xc tc cha zeolit.
M vo nm 1972 s dng khong 80% cht xc tc cha zeolit cho
qu trnh cracking xc tc. Hng nm M tiu th 130 nghn tn xc tc,
trong ch c 14 nghn tn l khng cha zeolit.
I. Vai tr ca xc tc trong qu trnh cracking (1,2,3,12,14)
Xc tc trong qu trnh cracking c tm quan trng rt ln. N c kh
nng lm gim nng lng hot ha ca phn ng, do vy m tng mc
phn ng ln rt nhiu. Dng xc tc cho php qu trnh tin hnh iu kinmm hn. V xc tc c tnh chn lc nn hng qu trnh ch bin theo
nhng phn ng c li nhm thu c sn phm phn ng c cht lng v
hiu sut cao.
II. Nhng yu cu cn thit i vi xc tc
Xc tc cho qu trnh cracking i hi nhng yu cu sau:
1. Hot tnh xc tc phi cao: [1-trang120]Hot tnh xc tc l yu cu quan trng nht i vi xc tc dng trong
qu trnh cracking.
V mc ch ca cracking l nhn xng, nn phng php dng hiu sut
xng thu c nh gi hot ng ca xc tc s n gin hn, hot tnh
ca xc tc cng cao s cho hiu sut xng cng ln. Do vy, hot tnh ca
xc tc thng c biu din thng qua ch s hot tnh. l gi tr ca
hiu sut xng (%KL) khi cracking nguyn liu mu trong iu kin phng th
nghim.
Hot tnh xc tc ph thuc vo tnh cht vt l - ha hc ca xc tc,
m trc ht l ph thuc vo thnh phn ha hc ca xc tc cng nh ph
thuc vo iu kin cng ngh ca qu trnh. Trong thc t sn xut, da vo
hot tnh ca xc tc, ngi ta phn xc tc thnh cc loi nh sau:
+ Xc tc c hot tnh cao, hiu sut xng > 45%
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+ Xc tc c hot tnh trung bnh, hiu sut xng t 30 n 40%
+ Xc tc c hot tnh thp, hiu sut xng < 30%.
Bng 6: Tnh cht ca xc tc FCC
Thnh phn ho hc, %
Oxyt nhm 13
Oxyt silic 87
Oxyt cc nguyn t t him 2 4
Oxyt natri 0,02 0,2
Trng lng rt, g/cm3 0,8 0,9
hot tnh n nh 55 60
hot tnh theo ASTM 75 80
bn do mi mn, % 94 96
Thnh phn c ht, %
n 20 m
n 40 m
n 100 m
< 2 3
15 25
96 98
B mt ring, m2/g 400 450
2. chn lc xc tc phi caoXc tc cn c chn lc cao cho ta xng c cht lng cao v hiu
sut ln, v trong kh cracking c nng ln cc hydrocacbon c cu trc
nhnh.
Trc tin cht xc tc lm tng tc ca cc phn ng c li trong
nhng iu kin nhit v p sut nht nh, sau c tc dng lm gim
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tc cc phn ng ph ,nht l nhng phn ng gy ng c xc tc nh
phn ng to cc (6 - trang 104)
Trong qu trnh cracking, chn lc ca xc tc quyt nh kh nng
to cc sn phm c gi tr ca n, l cc cu t xng c tr s octan cao.
Ngi ta c th nh gi chn lc bng cch xc nh t l gia hiu sut
xng v cc (hay kh) cng mt su bin i. Xc tc thng c nh
gi ng thi hot tnh v chn lc ca n so vi xc tc mu khi tin
hnh trong cng mt iu kin cracking. T s gia hiu sut xng v cc
(hay kh) cng ln th chn lc xc tc cng cao. Sau mt thi gian lm
vic c hot tnh v chn lc ca xc tc u b gim do c nhng thayi v tnh cht ca xc tc trong iu kin lm vic.
3. n nh phi ln: (1,2,3,14)Xc tc ch to ra cn phi gi c nhng c tnh ch yu (hot tnh,
chn lc) sau mt thi gian lm vic lu di. Cht xc tc c thi gian lm
vic lu di th gi thnh chi cho cht xc tc cng thp ( cho d tin mua xc
tc c t ) hn so vi khi mua xc tc r m thi gian lm vic ngn.
n nh xc tc c trng cho kh nng khng thay i cc tnh cht
trong qu trnh lm vic. Xc tc c n nh cng cao cng tt trong qu
trnh s dng.
4. m bo bn c v bn nhit: [3]Trong qu trnh lm vic, xc tc c xt vi nhau v c xt vi thnh
thit b lm cho xc tc d b v, do lm tn tht p sut qua lp xc tc
tng ln, lm mt mt xc tc ln. V vy m xc tc phi m bo bn c.
Khi lm vic nhit c th thay i, khi nhit cao qu m nu xc
tc khng c bn nhit th c th b bin i cu trc dn n lm gim cc
tnh cht ca xc tc.
6. Xc tc phi m bo thun nht caoXc tc cn ng nht v thnh phn, v cu trc, v hnh dng, v kch
thc. Khi kch thc khng ng u s to ra nhng vng phn lp v c tr
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lc khc nhau v do s phn lp theo kch thc nn s ph v ch lm
vic bnh thng ca thit b. Mt khc khi kch thc khng ng u lm
tng kh nng v vn dn n mt mt xc tc. Cu trc l xp khng ng
u s lm gim b mt tip xc dn n lm gim hot tnh xc tc.
7. Xc tc phi bn vi cc cht lm ng c xc tcXc tc phi chng li c hiu qu tc dng gy ng c ca nhng hp
cht ca nit, lu hunh, cc kim loi nng ko di thi gian lm vic ca
xc tc.
8. Xc tc phi c kh nng ti sinh
y l yu cu quan trng trong qu trnh s dng xc tc. Xc tc ckh nng ti sinh tt s nng cao c hiu qu v nng sut ca qu trnh,
lng tiu hao xc tc cng gim xung.
9. Xc tc phi d sn xut v r tin:y cng l yu t quan trng gp phn nh hng cho cc nh nghin
cu v sn xut.
III. zeolit v xc tc cha Zeolit
1. Xc tc Zeolit [1,2,3,12,13,14]Zeolit l hp cht ca alumino - silic, l cht tinh th c cu trc c bit.
Trong htin nhin c khong 40 loi Zeolit c pht hin . Song cc ng
dng quan trng trong lp hp ph , tch lc xc tc ...ch yu l nh vo
Zeolit nhn to . Ngy nay , ngi ta tng hp c khong 200 loi Zeolit ,
tuy nhin trong ch c mt s t c s dng trong cng nghip ( 14-trang
122).
1.1 Thnh phn ha hc ca Zeolit :
Cu trc ca chng c c trng bng mng cc l rng, rnh, rt nh
thng vi nhau. Cc cht zeolit c ch to cng vi cc xc tc
aluminosilicat hay vi t st thin nhin, ri sau c x l bng phng
php c bit hp thnh xc tc cha zeolit. Xc tc cha zeolit ny c hot
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tnh cao, c chn lc tt v li c gi thnh va phi, v th ngy nay chng
c s dng rt rng ri.
V thnh phn ha hc ca zeolit, ngi ta c th biu din bng cng
thc phn t nh sau:
(Me+)x[(Al2O3)x.(SiO2)y]z.2H2O
Trong : Me - l cation bi tr in tch
x,y - l cc h s tng ng
z - s phn t nc kt tinh trong Z ( 2-trang 193, 6-trang 123)
n v cu trc c bn ca Zeolit l t din TO4, l mt cation T c
bao quanh bi 4 ion O-2. Nu T l Si th SiO4 l t din trung ha in tch ,
nu l nhm Al (+3) th t din AlO-4 mang mt in tch m:
O2-
O2- O2-
Si4+
O2-
Hnh 2: T din SiO4
O2-
O2- O2-
Al3+
O2-
Hnh 3 : T din AlO-4
S thay th Si+4 bng nhm Al+3 lm xut hin mt in tch m trong
mng tinh th v n c b tr bi cation b tr in tch hay cation i.
Tnh cht ca Zeolit c thay th bi cc cu trc v hnh thi ca
chng ,tc l s sp xp trt t ca t din , phn th tch rng , s tn ti cc
mao qun v cc l ,kch thc ca cc mao qun v cc l. Ngoi ra tnh cht
ca Zeolit cn ph thuc vo t l Si/Al v cation b tr in tch (K+ , Na +...)
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Quy tc Lowenstion xc nh rng : 2 nguyn t nhm khng th tn ti
ln cn nhau , ngha l trong cu trc Zeolit khng th tn ti cc lin kt Si-
O-Si v Si-O-Al . V vy m t l Si/Al lun lun ln hn hoc bng 1.
1.2 cu trc ca Zeolit:
V cu to, zeolit c to thnh t cc n v cu trc c bn gi l n
v cu trc Sodalit (hnh 4). Nu cc n v ny ni vi nhau theo cc mt 4
cnh, ta c zeolit loi A. Nu ni vi nhau theo mt 6 cnh, ta c zeolit loi X
hay Y c cu trc tng t nh faurazit (hnh 5).
Hnh 4. n v c bn ca zeolit
Zeolit A Zeolit X
Hnh 5. Cu trc ca zeolit A v X, Y
Si4+O
2
O2
Al3+
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Ngy nay ngi ta ch to c hng trm loi zeolit, chng c c
trng bi kch thc cc ca s khc nhau [1-trang 117].
V d c trng ca mt s loi zeolit c dng ph bin trong cracking
xc tc c dn ra bng sau:
Bng 7 : c trng c bn ca mt vi loi zeolit
Zeolit Thnh phn ho hc ng knh l trung bnh,
A Na2O.Al2O3.2SiO2.4,5H2O 3,6 3,9
X Na2O.Al
2O
3.2,5SiO
2.6H
2O 7,4
Y Na2O.Al2O3.4,8SiO2.8,9H2O 7,4
Mordenit Na8O(Al2O3)8(SiO2)40.24H2O 6,7 7,0 (2,9 5,7)
ZSM-5 v 11 5,4 5,6
2. Zeolit v xc tc cha Zeolit dng cho qu trnh cracking [1-trang
118,119]Khi ch to xc tc cracking, hm lng natri (Na) cn phi gim ti cc
tiu bi v s c mt ca Na nhit cao v c mt hi nc, n lm gim i
ng k hot tnh cng nh chn lc ca xc tc cracking.
Khi thay th Na bng cc cation kim loi ha tr ln hn 2 hay bng 2,
th d nh canxi (Ca), reni (Re) hay cc nguyn t t him, s lm thay i
c trng cu trc ca zeolit. Kch thc l tng ln, ng thi khi li to
ra cc tm axit lm hoi tnh ca xc tng ln.
Ngi ta cho thy rng, zeolit cha oxyt silic cng nhiu, lng oxyt
nhm cng t th axit ca n cng tng. ng nhin khi tng t s oxyt
silic/oxyt nhm, khng c dn n ph hy cu trc ca zeolit. Hay ni
cch khc l t s ny cng ch tng n mt gii hn nht nh.
Qu trnh cracking xc tc thng dng zeolit loi X, Y c cha cc
nguyn t t him hay dng trao i ion v c x l bng cc phng
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php c bit, ng thi kt hp vi cc hp phn lm tng bn c, bn
nhit hay iu chnh kch thc l xp. Zeolit c hot tnh cracking ln, v th
ngi ta thng dng n dng hn hp vi xc tc v nh hnh hay
aluminosilicat tinh th v c gi l xc tc cha zeolit. Trong sn xut xc
tc, ngi ta trn 10 n 20% (KL) zeolit v vi hp phn nh vy, xc tc
cng rt hot ng, hn hn xc tc aluminosilicat thng thng. Hn na
cc ch tiu kinh t cng t tt hn.
Trong cng nghip, ngi ta ch to xc tc cha zeolit hai dng chnh.
Xc tc dng cu v xc tc dng bt. Xc tc dng bt v sau ci tin
thnh xc tc vi cu th
ng
c p dng cho qu trnh cracking lp si(FCC), cn xc tc dng cu vi kch thc ht t 3 n 5 mm thng c
dng cho qu trnh cracking xc tc chuyn ng (TCC).
Zeolit c hai loi kch thc l xp: kch thc ca s v kch thc l
ln, khi a chng vo trn ln vi aluminosilicat, chng ta s iu chnh
c cu trc l ca chng nhn c kch thc l trong gii hn thch
hp nht, nhm tng chn lc ca xc tc. V d, trong xc tc cha zeolit
loi A, kch thc l ca n khng vt qu 4 n 5 . Trong cc l nh vy
propylen c th chuyn qua t do, nhng iu li khng xy ra i vi izo-
butylen. Do trn xc tc nh vy c th tin hnh qu trnh polyme ho
chn lc propylen c trong hn hp vi izo-butylen m khng phi phn tch
chng. Hay t zeolit vi kch thc 5 c th dng lm xc tc cracking
chn lc n-parafin c trong hn hp vi izo-parafin, v trong iu kin , izo-
parafin b cracking khng ng k.
Xc tc cha zeolit X v Y c kch thc l khong 8 n 10 c
dng cracking nguyn liu c thnh phn phn on rng (v d gazoil).
Khi cc phn t ln ca nguyn liu vn c th d dng ti b mt ca xc
tc, cn cc phn t nh hn c th tip xc vi cc tm hot tnh b mt
trong ca xc tc. V cc l hp cht cao phn t nn chng thng tp trung
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b mt ngoi ca xc tc v do vy to iu kin thun li cho qu trnh t
chy cc khi ti sinh xc tc.
Zeolit loi X, Y, ZSM-5 (11) l loi c cc tnh cht thch hp nht cho
qu trnh cracking xc tc. Kch thc l ln ca chng xp x 10 s cho
php khuch tn d dng cc phn t ca nguyn liu vo b mt l xp ca
chng cng nh khuch tn sn phm ra ngoi. V vy chng c s dng
ch to xc tc cracking cng nghip. Thng thng cc zeolit ny l loi
trao i cation (H+, NH4+ hay cation a ha tr) kt hp vi cc phng php
x l thch hp v phi trn vi aluminosilicat v nh hnh. Loi xc tc ny
c hot tnh cao hn hng trm ln v c chn lc cao hn so vi xctc aluminosilicat thun khit. Hiu sut xng tng ln t nht l 20%, trong
khi hiu sut cc v kh li gim khi tin hnh cng mt iu kin.
th gii cc cht xc tc cracking c nhiu hng sn xut, l:
Grace, Engel Grard, Mobil, Fihtrol, AK20, Crosfiel, Catalystics.
Cc c trng c bn ca xc tc cracking l: thnh phn, trng lng
rt, cu trc xp, hot tnh, thnh phn c ht v bn.Ngoi nhng u im trn xc tc cha zeolit vn cn mt s nhc
im nh sau:
+ Gi thnh sn xut chng cao
+ Nu s dng xc tc zeolit nguyn cht th tc trao i cht ca qu
trnh phc hi v trao i nhit b hn tc chnh bn thn phn ng xc
tc. V vy m ta dng xc tc cha zeolit (zeolit tm trn cht mang, 2 20%
trn aluminosilicat tng hp).
Ni tm li, xc tc cha zeolit cho qu trnh cracking c nhiu u im
hn hn cc xc tc khc, nn hin gi y cc nc cng nghip ch bin
du m v kh tin tin, ngi ta ln lt thay th xc tc cha zeolit cho
aluminosilicat tng hp. Hin nay ngi ta ang s dng xc tc zeolit siu
bn, n p ng c mi yu cu ca xc tc trong qu trnh cracking.
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III. Nhng thay i tnh cht ca xc tc khi lm vic [1,3,12,13]
[1-trang122]
Xc tc cracking trong qu trnh lm vic b gim hot tnh v chn
lc. Hin tng ny ngi ta gi l qu trnh tr ho xc tc. Qu trnh tr ho
xc tc cng nhanh nu ta tin hnh qu trnh iu kin cng ngh kh
khn, kht khe tng (v d nhit qu cao, thi gian tip xc qu di,
nguyn liu xu). Ngoi ra cn xy ra cc qu trnh khc lm tng tc tr
ho. Chng ta c th phn qu trnh tr ho xc tc lm hai qu trnh chnh,
l s tr ho do tc dng ca cc cht lm ng c xc tc v s tr ho do
tc dng lm thay i cc tnh cht l - ho ca xc tc.
Nguyn nhn ca s tr ho xc tc c th l do:
Tc dng ca cc c t nh NH3, CO2 ca cc hp cht luhunh m c bit l H2S nhit cao.
S tch t cc kim loi nng di dng cc oxyt lm thay i chcnng ca xc tc.
S tc ng ca nhit cao v hi nc.Cc hp cht kh tc dng vi xc tc c th chia lm 3 nhm:
- Nhm khng tc dng vi xc tc nhit thp hn 6200Cnh CO, CO2 v NH3.
- Nhm lm gim hot tnh ca xc tc nhng khng lm gim chn lc nh hi nc.
- Nhm lm gim chn lc ca xc tc (H2S nhit trn4250C v NH3 , SO2, SO3 nhit trn 620
0C).
T kinh nghim thao tc cng ngh cracking cho thy, hot tnh ca xc
tc c th c duy tr nu ta thm hi nc vo nguyn liu, hay vic x l
trc v sau khi ti sinh xc tc. Thm hi nc khi ch bin nguyn liu c
lu hunh s c tc dng m v khi li lm tng qu trnh n mn thit b
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v sn phm ca qu trnh n mn li lm nhim bn xc tc, dn ti lm
gim hot tnh, chn lc ca xc tc.
Tc dng ng thi ca nhit cao v ca hi nc lm gim hot tnh
tng cng ca xc tc. Khi p dng lp si (FCC), do cn phi duy tr iu
kin cc t lng ng trn xc tc v xc tc khng b qu nhit khi ti
sinh, ngi ta phi a vo mt lng nh hi nc. Hn na, cng cn phi
trnh s to cc qu t, v iu dn ti ph v cn bng nhit ca h l phn
ng v ti sinh, do nhit to ra trong qu trnh ti sinh khng b nhit
thu vo ca cc phn ng cracking trong l phn ng.
Hm lng cc trn xc tc khi ra khi l phn ng ph thuc vo lngxc tc tun hon trong h thng. i vi a s cc qu trnh FCC, khi dng
xc tc zeolit, lng cc to ra thng chim vo khong 1,3 n 1,8% KL
xc tc, cn sau khi ti sinh l 0,1 n 0,05% KL.
Cc hp cht c kim v cc hp cht cha nit trong nguyn liu u l
cc phn t lm gi ho nhanh xc tc. Nhiu nghin cu ch ra rng, s c
mt ca cc hp cht nit trong nguyn liu lm gim hiu sut xng v cc
sn phm trng. V d, hm lng nit tng t 0,1 n 0,4% KL, hiu sut
xng b gim i ti 2 ln, cn hiu sut gazoil nh cng b gim, ng thi
lm tng hiu sut cn nng v gazoil nng. Khi tng nhit , tc dng c hi
ca cc hp cht nit s gim.
S u c xc tc bi cc kim loi cng c nhiu nghin cu
cp ti v ch r c ch tc dng ca chng n hot tnh ca xc tc. Khi
lng ng cc oxyt kim loi nng trn xc tc s dn ti lm gim su
cracking v gim hiu sut xng do tng qu trnh to cc.
Khi hm lng cc hp cht lu hunh trong nguyn liu tng th hm
lng cc kim loi nng nh niken v vanadi cng tng theo, v a phn chng
u tp trung phn cn nng v phn on nha - asphan. V d, trong du
m c lu hunh th c ti 90% phc cht porphirin cha vanadi, cn trong
du cha t lu hunh th l phc vi niken.
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V. Ti sinh xc tc [1,2,3]
Xc tc trong qu trnh cracking lm vic c mt thi gian s c mt
lng cc to ra do mt s phn ng c hi, cc s bm ln b mt xc tc
lm che ph cc tm hot ng ca xc tc. iu dn n gim hot tnh
ca xc tc v vy hiu qu qu trnh cracking xc tc b gim. xc tc lm
vic bnh thng (cc tnh cht ca xc tc khng b thay i) th ngi ta
phi tin hnh ti sinh xc tc. ti sinh xc tc ngi ta cn phi tin hnh
t cc bng khng kh nng trong l ti sinh. Kt qu ca qu trnh t chy
cc s sinh ra CO v CO2. Cc phn ng ny to nhiu nhit. Ngoi ra cn c
phn ng kh cc hp cht l
u hunh. Cc phn ng xy ra khi ti sinh c thmiu t nh sau:
C + O2 CO2 Q = 33,927 34,069 MJ/kg
C + O2 CO Q = 10,629 10,314 MJ/kg
CO + O2 CO2 Q = 23,650 23,755 MJ/kg
H2 + O2 H2O Q = 1210,043 1210,252 MJ/kg
S + O2 SO2 Q = 9,132 9,222 MJ/kg
SO2 + O2 SO3
MeO + SO3 MeSO4
MeSO4 + 4H2 MeO + H2S + 3H2
Nhit lng to ra c dng cp nhit cho xc tc mang vo l phn
ng, ngoi ra cn tn dng sn xut hi nc dng trong nh my.
Kh nng ti sinh c th nh gi bng cng chy cc, cng
chy cc cng cao, qu trnh ti sinh cng nhanh, th tch thit b ti sinh yu
cu cng nh. Cng chy cc ph thuc vo nhiu yu t: nhit , p
sut ring phn ca oxy, hm lng cc bm trn xc tc, cht xc tc v.v...
Yu t nhit nh hng ln cng chy cc: Qua nghin cu ta
thy nhit khong 540 6300C tin hnh ti sinh xc tc l tt nht.
Nhit ti sinh ph thuc nhiu vo cht xc tc c dng v loi l
12
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ti sinh. Mc ti sinh cn phi khng ch cht ch khng ch bo m
hot tnh ca xc tc m cn m bo vn v sinh mi trng, v th khng
nn c mt CO trong kh khi thi. Hn na, qu trnh chy cng khng
xy ra nhit qu cao hay tch nhit cc b dn ti ph hu xc tc. Cn
nu nhit qu thp th tc ti sinh s chm, cc bm trn xc tc chy
khng trit . Sau khi ti sinh, hm lng cc cn li trn xc tc phi l cc
tiu (lng cc cn cn li t 0,1 n 0,3% KL xc tc) khi phc ti a
hot tnh ca xc tc.
Tc ti sinh c th biu din theo phng trnh:
RT
En
OHO CPKPV
+= )1(K22 21
Trong :
V - tc ti sinh
PO2, PH2O - p sut ring phn ca oxy v hi nc
C - hm lng cc bm trn xc tc
n - bc phn ng theo cacbon
K1, K2 - hng s.
Vy tng tc ti sinh th ta phi tng nhit ti sinh (hiu qu
nht vng ng hc), tng p sut ring phn ca oxy trong khng kh, gim
ng knh cc ht xc tc.
Xc tc c ng knh l xp cng ln v ng u th qu trnh ti sinh
cng nhanh v oxy d khuch tn. Tuy vy iu ny b gii hn bi bn ca
xc tc v mt s tnh cht khc ca n.
Qu trnh ti sinh xc tc bng phng php t cc cha gii quyt
c vic kh cc kim loi nng hp ph trn xc tc. V vy hon thin
qu trnh ti sinh ngi ta tin hnh thm qu trnh trao i ion kh cc
kim loi nng, iu ny gii quyt c s nng cao c hiu qu ca qu
trnh ti sinh xc tc.
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VI. Cc dng hnh hc ca xc tc [1,2,3]
Xc tc dng bi:
Xc tc dng bi c kch thc t 1 n 150 m. Phn ln l cc phn
xc tc c kch thc 40 80 m.
Xc tc dng vi cu:
C kch thc ht t 10 n 150 m. So vi xc tc dng bi, xc tc
dng vi cu trong qu trnh lm vic b mi mn t hn v mt mt xc tc t
hn. Xc tc dng bi v dng vi cu thng c dng trong h thng
cracking xc tc vi lp xc tc gi si.
Xc tc ht cu ht ln:
ng knh cc ht xc tc t 3 n 6 mm. bn c ca loi ny tt,
trong qu trnh lm vic t b mi mn v t b v vn. Xc tc dng ny c
s dng trong h thng vi lp xc tc chuyn ng.
Xc tc dng tr:
C
ng knh t 3 n 4 mm, chiu cao t 3 n 5 mm. bn c km.Trong qu trnh s dng xc tc d b v vn, lm tiu hao xc tc ln. Xc
tc loi ny ch dng trong h thng cracking vi lp xc tc tnh.
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CHng IIINGuyn Liu V Sn PHm
Ca QuTRnh Cracking Xc Tc
I. Nguyn liu ca qu trnh cracking xc tc: [1,2,3,4,5,6,7]
Nguyn liu c bn cho qu trnh cracking xc tc l phn ct chn
khng ca cn du th khi chng ct kh quyn. Chng thng cha 5 10%
phn on si n 3500C v c nhit si cui ti 520 5400C. Trong nhiu
trng hp, ngi ta cng c th dng c phn on nh ca chng ct kh
quyn, phn on kerosen-gazoil ca cracking nhit hay cc ho v c th cphn rafinat ca qu trnh kh asphan mazut v gudron trong sn xut du
nhn hoc l phn on mazut ca du t kim loi. Cc c trng quan trng
nht ca nguyn liu c nh hng quyt nh n cc ch tiu ca qu trnh
cracking l thnh phn phn on, hng s c trng K, thnh phn nhm
hydrocacbon, hm lng nha - asphan, hm lng cc tp cht nit, lu
hunh, kim loi v cc ho.
Khi cracking trn xc tc cha zeolit, do c hot tnh cao m nh hng
ca thnh phn phn on ca nguyn liu khng phi l yu t quan trng.
Quy lut thng thng l khi tng phn nh (hay cn gi l nh) ca
nguyn liu, hiu sut hydrocacbon loi C3, C4 v xng u tng ln, cn hiu
sut H2 v cc gim xung. Nu nguyn liu l phn ct chn khng c t
phn on nng (
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cht lng sn phm. V d s phn b ca hp cht lu hunh vo sn phm
cracking nh sau (% KL so vi nguyn liu): H2S: 20 n 30; xng: 2 n 5;
phn on si trn 1950C: 30 n 60; cc: 5 n 10.
Trong nguyn liu cracking xc tc khng nn c mt cc phn on nh
c nhit si < 2000C v khi phn hu s to nhiu kh lm gim hiu sut
xng v gim c tr s octan ca xng. Nguyn liu khng cho php cha hm
lng ln hydrocacbon thm a vng (v trong qu trnh d ngng t to cc
bm trn b mt xc tc), asphan v cc tp cht cha N v S.
Nguyn liu cng nng cng cha nhiu asphan v kim loi, khi cracking
cn phi qua x l bng hydro ho lm sch nhn c nguyn liu c chtlng cao cho qu trnh cracking xc tc.
Ni tm li, trc khi a nguyn liu vo qu trnh cracking xc tc,
chng ta phi nghin cu k cht lng ca nguyn liu, loi xc tc dng v
tu theo iu kin k thut, hiu qu ca cc phng php lm sch nguyn
liu yu cu nguyn liu dng m ngi ta quyt nh phng php lm sch
nguyn liu cho thch hp.
Trong cng nghip cracking xc tc, ngi ta c th s dng mt trong
cc nhm nguyn liu sau:
Nhm 1: l nhm nguyn liu nh c tn l phn on kerosen - sola
nhn c t qu trnh chng ct trc tip v c gii hn si t 210 n 3600C.
Chng c t trng trung bnh t 0,860 n 0,830. Trong lng phn t trung
bnh vo khong 190 200. y l nhm nguyn liu tt nht dng sn
xut xng t v xng my bay.
Nhm 2: l nhm nguyn liu ly t phn on gazoil chng ct chn
khng c nhit si t 300 n 5000C (hay 5500C). Nhm ny c cc c
trng l t trng trung bnh t 0,880 n 0,920, trng lng phn t trung bnh
t 280 n 330.
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Nhm 3: l nhm nguyn liu c thnh phn rt rng, c gii hn si
t 210 5000C.
Nhm 4: l nhm nguyn liu c nhit si t 300 4500C.
[1-trang 125]
Bng 8:c tnh 4 nhm nguyn liu ca qu trnh cracking xc tc
Ch tiu Nhm 1 Nhm 2 Nhm 3 Nhm 4
T trng 0,8300,870 0,8300,920 0,8700,885 0,8700,875
Thnh phn
phn ont0 si u (0C) 200 215 300 315 225 235 n 250
t0 si 10% (V) 225 240 335 355 290 305 275 300
t0 si 50% 260 270 420 445 390 400 335 375
t0 si 80% 490 500 385 450
t0 si 90% 290 320 520 540
t0 si cui 315 360 540 550
(95%)
515 520
(95%)
420 490
(95%)
Hm lng S
(%) TL 0,2 0,6 0,6 1,8 0,35 0,75 0,5 1,4
cc % TL 0,2 0,9 0,2 0,3 0,05 0,2
Trong s cc nhm nguyn liu k trn th nhm gazoil chn khng l
ph bin nht trong qu trnh cracking xc tc. Trong nhng nm gn y, khi
nguyn liu tt ngy mt cn dn v nht l khi ch to c xc tc cracking
mi v cng ngh mi c hiu qu hn, ngi ta tin ti s dng nguyn liu
ngy cng nng hn, cht lng xu hn m vn cho php nhn c xng vi
nng sut cao v cht lng tt. l xu hng ci tin qu trnh cracking
xc tc trong hin i v trong tng lai.
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II. Cc sn phm ca qu trnh cracking xc tc [1,2,3]
Cht lng ca sn phm cracking xc tc thay i trong mt khong rt
rng v ph thuc vo nhiu yu t nguyn liu, loi xc tc v cc thng s
cng ngh ca qu trnh. Trong thc t qu trnh cracking xc tc thng nhn
c cc sn phm sau:
1. Sn phm kh
Hiu sut kh cracking chim khong 10 25% lng nguyn liu em
cracking. Hiu sut ny ph thuc vo iu kin cracking. Thnh phn ca kh
cracking ph thuc vo bn cht ca nguyn liu v bn cht ca xc tc.
Bng 9:Kh hydrocacbon % khi lng
C1 C2
C3
C4
C5
10 25
25 30
30 50
10 20
Sn phm kh c a n b phn tch kh. Sau khi phn on, kh khc s dng lm nhin liu kh.
Cn phn on propan propylen v butan butylen c dng lm nguyn
liu cho qu trnh alkyl ho hay nguyn liu tng hp ho du v ho hc. Phn
on C5 c pha vo xng. Trong phn on C3, hm lng propylen c th t
ti 70 80%. Trong phn on C4, hm lng buten l 45 55%, hm lng izo-
butan l 40 60% v hm lng n-butan nh, ch vo khong 10 20%.
2. Xng cracking xc tcXng l sn phm chnh ca qu trnh, hiu sut xng cracking xc tc thng
thu c t 30 55% lng nguyn liu em cracking. Hiu sut xng v cht
lng xng ph thuc vo cht lng nguyn liu, xc tc v ch cng ngh.
Nu nguyn liu c hm lng hydrocacbon naphten th cho hiu sut v
cht l
ng xng cao. Nu nguyn liu c hm l
ng ln parafin th nhn
c
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xng c tr s octan thp. Trong nguyn liu c hm lng lu hunh cao th
xng nhn c c hm lng lu hunh ln, thng chim khong 15%
trng lng lu hunh cha trong nguyn liu.
Xng nhn c t qu trnh c t trng khong 0,72 0,77. Tr s octan
theo phng php nghin cu (RON) khong 87 91.
Thnh phn ho hc ca xng cracking xc tc khc hn vi xng
cracking nhit v xng chng ct trc tip. Xng cracking xc tc c tr s
octan cao hn, c cha 9 10% trng lng hydrocacbon thm. Ni chung
xng cracking xc tc l cu t c bn ch to xng thng phm.
Phn on xng cc dy chuyn cng ngh Lin bang Nga thng c
nhit si cui l 1950C, cn cc nc khc thay i c th l 204 hay
2200C. Chng c tnh cht c trng c trnh by bng sau:[1-trang 126]
Bng 10 : c trng ca xng Cracking xc tc
204d
Hm lng S (% KL)
Tr s octan (sch)RON
MON
Thnh phn hydrocacbon (%)
Hydrocacbon thm
OlefHin
Naphten
Parafin
0,72 0,77
0,01 0,20
87 95
78 85
25 40
15 30
2 10
35 60(izo-parafin chim phn chnh)
3. Phn on si cao hn 1950CPhn on ny c chia thnh:
Phn on 195 3500C v phn cn c nhit cao hn 3500CPhn on 195 270
0
C dng ch to nhin liu kerosen
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dng lm cu t pha cho nhin liu diezen, c th lm nguyn liu sn xut b
hng hay lm cu t pha long mazut.
Gazoil nh c c tnh sau:
T trng 204d = 0,83 0,940
Thnh phn ho hc gm:
Lu hunh 1,7 2,4% trng lng
Hydrocacbon olefin 6%
Hydrocacbon thm 30 50%
Cn li l hydrocacbon parafin v naphten.* Gazoil nng:
L sn phm cn ca qu trnh. Cht lng ca n ph thuc ch cng
ngh, ngun nguyn liu v cht lng gazoil nh.
Gazoil nng c nhit si > 3500C, c t trng 204d = 0,89 0,99, n
cha mt lng ln tp cht c hc. Hm lng lu hunh trong cao hn
khong 1,5 ln so vi nguyn liu ban u.Dng lm nguyn liu cho cracking nhit v cc ho hoc lm nhin liu
t l. Ngy nay ngi ta cn dng n lm nguyn liu sn xut b hng.
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Phn IITnh Ton V Thit K Dy ChuynCng Ngh CrackingXc Tc
Chng I. Cc yu t nh hng nqu trnh cracking xc tc
nh hng n cc ch tiu lm vic ca qu trnh cracking xc tc
khng ch l nguyn liu v cht xc tc m cn c cc thng s cng ngh
ca qu trnh. Cc thng s cng ngh bao gm: nhit , p sut, tc np
liu khng gian th tch hay trng lng (cn gi l tc np liu ring), bi
s tun hon xc tc v mc bin i hay su chuyn ho.
I. Nhit [1,2,3,4,5,6,7]
Qu trnh cracking xc tc thng tin hnh nhit 480 5500C. Khi
tin hnh tng nhit , lc u hiu sut xng tng v sau t n cc i
ri gim xung. iu ny l do qu trnh phn hu tng, lm phn hu c cc
cu t xng va c to thnh.
Khi tng nhit , phn ng phn hu tng nhng ng thi cc phn
ng bc 2 nh dehydro cng tng, lm tng hiu sut hydrocacbon thm v
olefin. Khi trong sn phm kh hm lng C1 C3 tng, cn C4 gim, t
trng v tr s octan tng ln.
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Hnh 6
Bng 12. nh hng ca hydrocacbon n hiu sut v cht lng ca sn
phm vi nguyn liu l phn on xola (du m Lin X)
Cc thng sNhit trung bnh trong TBP
415 452 480 513
Hiu sut cc sn phm (%TL)
Kh kh 2,31
Kh bo 5,00 5,13 8,34 18,80
Xng 30,29 7,49 9,41 9,45
Gazoil nh 59,20 30,72 32,45 37,42
Gazoil nng 53,30 46,30 28,10
Cc 3,20 3,30 3,50 6,60
Tng cng 100,00 100,00 100,00 100,00
su chuyn ho (%TL) 40,80 46,70 53,70 71,90
Tr s octan ca xng (RON)
khng c pha ch 84,10 91,70 93,70 94,40
c pha 0,8 ml TEP/ 1lt xng 93,00 98,20 98,20 98,50
T trng ca xng 15
15d 0,748 0,748 0,757
390 420 450 480 510 540 425 450 475 500 5250C
30
20
10
0
4
6
810
Hiusutxngv
kh,
Hiusutcc,%TL
NC(sch),%
95
100
90
85
80 40
50
60
70
80
%V
Nhit cracking, 0C
Ch s octan
chuyn ho
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II. p sut [1,2,3,4,5,6,7]
Qu trnh cracking xc tc thng tin hnh p sut d 1,4 1,8 at.
iu kin ny phn ng xy ra pha hi.
Khi tng p sut, hiu sut xng tng ln, hiu sut kh C1 C3 gim,
hm lng olefin v hydrocacbon thm gim, hm lng hydro-cacbon no
tng v do vy cht lng xng gim (tr s octan NO gim).
Vy khi tng p sut s tng hiu sut xng, cn hiu sut kh gim,
nhng qu trnh to cc tng. Vic tng p sut ca qu trnh cracking xc tc
khng c hiu qu kinh t cao. V vy ch tin hnh p sut thng.
Bng 13. chuyn ho C, hiu sut sn phm v thnh phn
RH ca xng ph thuc vo nhit phn ng [1-trang130]
Nhit,
0C
C,
%KILN
SP
tng,
%KL
Xng,
%KILN
Kh,%KL
Cc,
%KL
Cn,
%KL
M
tmt,%KL
RHno,
%V
RHO,
%V
RH
a,
%V
400 64,5 81,5 49,2 11,6 3,7 32,3 3,2 66,8 7,7 25,3
420 70,2 76,7 49,7 16,0 4,5 27,0 2,8 61,9 8,5 29,6
435 72,1 74,4 49,1 18,2 4,8 25,3 2,6 56,5 9,6 33,9
450 75,5 69,9 47,5 22,2 5,8 22,4 2,1 50,8 10,8 38,4
470 74,4 61,9 38,6 29,5 6,5 22,5 2,9 39,6 13,9 46,5
485 74,9 59,7 33,2 32,6 7,8 24,7 2,4 28,6 15,0 56,4
500 73,8 52,5 31,3 37,2 7,2 21,0 3,2 28,6 14,8 56,4
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Hnh 7: nh hng p sut n hiu sut v cht lng xng
III. Mc chuyn ho Ci vi hydrocacbon tinh khit, khi tham gia phn ng, mc chuyn
ho c o bng lng sn phm to thnh theo thi gian. Nhng i vi
phn on phc tp nh phn on du m, trong cracking xc tc ngi ta li
o lng xng l sn phm chnh v sn phm nh kh v cc. Nu gi y l %
th tch ca sn phm vi im si cui cao hn im si cui ca xng, th
chuyn ho C
c tnh theo biu thc:C = 100 y
ng nhin cch xc nh nh vy cha st vi thc t. hiu chnh
theo s bin i ho l trong qu trnh to xng v kh, ngi ta xc nh mc
bin i theo cng thc sau:
C = 100 y(100 z)
y z l % xng c trong nguyn liu.IV. Tc np liu ring [1]
Tc np liu ring (hay tc khng gian np liu) l t l gia lng
nguyn liu c np trong mt n v thi gian trn lng xc tc trong
reactor (hay t l v th tch ca chng) v c k hiu bng M/H/M hay
V/H/V (V/V/H).
0,5 1,0 1,5 2,0 2,5 3,0 3,5 kG/cm2
50
40
30
20
85
90
95
O%V
80
% xng
% NO
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Nu P l p sut trong reactor v c tnh bng (at) th chuyn ho C
c lin quan vi M/H/M theo biu thc:
M/H/M
P.K
C100
C=
Phng trnh biu din p dng rt ng vi trng hp xc tc c nh,
y khng xy ra s chuyn ng ri hay s xo trn ca hi nguyn liu v
sn phm. Trong trng hp cracking xc tc vi lp si ca xc tc (FCC),
chuyn ho C l ph hp vi cng thc sau:
M/H/M
P.K
100C1100
C2=
K l hng s tc tng cng ca qu trnh.
Ta thy rng khi tng tc np liu ring, s lm gim chuyn ho.
Cn khi gim tc np liu ring th chuyn ho tng, v rng tc np
liu l i lng ngc vi thi gian phn ng. Khi s dng xc tc c hot
tnh cao, ta c th tng tc np liu v nh
vy s tng
c nng sut cathit b.
Hnh 8.
M/H/M0,2 1,0 2,0 3,0
70
50
30
10
6
10
%KL%V
2
% xn% xng
Cc
2 4 6 8 10
chu n chu n ho
Cc
80
60
40
20
6
10
2
%KL%V
X/RH
nh hng ca tc np liu ring nh hng ca t l X/RH
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Trong thc t, nu dng xc tc aluminosilicat v nh hnh, tc np
liu th tch ch t t 4 5 h1. Nhng nu dng xc tc cha zeolit, tc
np liu th tch l 80 120 h1 khi tnh trong ng ng ca reactor v t 20
30 h1 khi tnh trong lp si ca reactor.
Khi tng tc np liu, nu ta tng nhit phn ng, s tng tr s
octan ca xng v tng hiu sut olefin trong kh. l phng php chnh
iu khin ch sn phm propylen v buten trong qu trnh cracking xc
tc.
V. T l lng xc tc/nguyn liu (X/RH) hay bi s tun hon
xc tc [1,3]
Khi dng xc tc cha zeolit, cho php gim t l X/RH xung cn 10/1
so vi xc tc v nh hnh l 20/1. Nu khi dng cng ngh xc tc chuyn
ng vi kch thc ht xc tc t 3 5 mm, t l X/RH cn thp hn na, ch
khong 2/1 5/1.
Khi thay i t l X/RH s lm thay i nhit ca reactor, thay i
thi gian lu ca xc tc trong reactor v l ti sinh, ng thi cng lm thay
i c lng cc bm trn xc tc trong mt chu trnh.
Nu ch n nh, tng t l X/RH s lm tng chuyn ho, tng
hiu sut cc/nguyn liu, nhng hm lng cc bm trn xc tc li gim
xung. iu ny c gii thch l do lng cc c dn ra mt lng
xc tc ln hn. Khi gi tc np liu M/H/M l khng i, nu tng t l
X/RH th thi gian tip xc gia xc tc v nguyn liu gim, v nh vy hot tnh trung bnh ca xc tc tng ln. l l do t hiu qu cao ca qu
trnh vi xc tc lp si (FCC). Nh t hiu qu cao m cho php gim kch
thc ca thit b. Nhng d dng nhn thy rng, nu tng cao qu mc
tun hon xc tc s lm nh hng n qu trnh tch hi bm trn xc tc v
lm nh hng n qu trnh ti sinh l ti sinh v cc trang thit b km
theo.
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Ni chung thng s bi s tun hon xc tc rt quan trng trong qu
trnh cracking xc tc, n nh hng khng nhng ln hiu sut v cht lng
sn phm n cc thng s khc m cn nh hng n vic xc nh kch
thc cc thit b chnh ca qu trnh. V vy ta phi chn c thng s ny
mt cch ti u.
VI. Hiu ng nhit
Hiu ng nhit ca qu trnh bng tng hiu ng nhit ca cc phn ng
ring bit ca qu trnh, hiu ng nhit ph thuc vo su chuyn ho.
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Chng II
I. Lch s pht trin cng ngh cracking xc tc [1,2,3]
Qu trnh cracking xc tc c nghin cu t cui th k 19, nhng
mi n nm 1923, mt k s ngi Php tn l Houdry mi ngh a qu
trnh p dng vo cng nghip. V n nm 1936 nh my cracking xc tc
u tin ca Cng ty Houdry Praess Corporahon c xy dng M. Dy
chuyn cracking xc tc u tin ny c a vo cng ngh ch bin du,
l h thng cracking xc tc trong lp xc tc tnh, h thng lm vic gin
on. V sau ny, h thng loi trn i vo lch s v n c nhng nh
cim sau:
+ Qu trnh lm vic gin on nn nng sut thit b thp
+ Ch lm vic ca h thng khng n nh v vic iu chnh cc
thng s k thut ca h thng kh khn, phc tp trong vn hnh
+ Trong qu trnh lm vic hot tnh ca xc tc thay i lin tc lm
nh hng n cht lng sn phm v cn bng vt cht ca h thng.
Nm 1941, xut hin qu trnh cracking vi lp xc tc chuyn ng
thay th cho qu trnh Houdry. Vic tin hnh cracking v ti sinh xc tc
c thc hin cc thit b ring bit.
+ Thit b phn ng (reactor)
+ Thit b ti sinh (regenerator)
Xc tc t thit b phn ng vo thit b ti sinh v ngc li hoc bng
t chy, hoc bng cng bc. Xc tc lm vic c cha cc chuyn ng
vo l ti sinh, cn xc tc ti sinh vo l phn ng to thnh mt chu trnh
lin tc. Dy chuyn loi ny Nga c tn gi l loi 43-1 v 43-102, cn
nc khc c tn l Thermofor (TCC) hay Houdry Flow. Tuy nhin cc dy
chuyn ny cng v sau cng lin tc c ci tin so vi dy chuyn ban u
khu vn chuyn xc tc ( dng vn chuyn bng hi thay cho vn chuyn
bng c hc).
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Nm 1942, dy chuyn cracking xc tc lp si (FCC) u tin c
a vo hot ng vi cng sut 12.000 thng nguyn liu/ngy. Loi dy
chuyn ny c tn l Up Flow (model I). Trong dy chuyn ny, xc tc c
a ra t nh l phn ng v l ti sinh.
Sau , vo nm 1944 ngi ta tng ng knh ca cc thit b phn
ng v ti sinh, qu trnh tch hi sn phm c thc hin ngay trong thit b
phn ng, ti sinh xc tc dng tng si v qu trnh thi cng ngy cng
c ci tin cho xc tc chuyn ng t pha di v ly ra ngoi y
thit b. Dy chuyn c thit b hot ng nh vy mang tn l Dow Flow
model II, v l dng nguyn thu ca thit b phn ng v ti sinh lp sihin i ngy nay. Tip theo, ngi ta cng ci tin c hnh dng ca xc tc.
Xc tc ph bin l loi c dng hnh vi cu, nn gim c s mt mt xc
tc hay s mi mn thit b, nng cao hiu qu tch ca cc xyclon.
Trong dy chuyn model I, t l xc tc/nguyn liu u (X/RH) ch t
gii hn cc i l 3, nhng model II t l X/RH c th tng ln t 3 10.
n nm 1946, model III l loi cn bng p sut c thit k bi hng
M. W. Kellogg.
Nm 1947, hng UOP thit k loi FCC trong thit b phn ng v
thit b ti sinh chng ln nhau trn cng mt trc. n nm 1951, loi Orthor
Flow u tin ca M. W. Kellogg xut hin. Sau hng Standard Oil thit
k mt loi FCC mi gi l model IV, l ci tin ca model III v dy
chuyn cng ngh model IV u tin p dng trong cng nghip vo nm
1952.
Cng vi thi gian, FCC ngy cng c ci tin c c hiu sut,
cht lng xng cao hn v c th dng nguyn liu ngy cng nng hn, vi
cht lng nguyn liu ngy cng xu hn. [1-trang 132].
II. La chn cng ngh cracking xc tc
Qua lch s pht trin ca qu trnh cracking xc tc, ng thi qua phn
tch nh gi cc yu cu khc nh ch lm vic, nguyn liu xc tc... ta
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thy qu trnh FCC c rt nhiu u im v thun li, h thng ny c s
dng ngy cng ph bin trong cng nghip du m, n c cc hng cng
nghip hng u trong lnh vc ny nh UOP, Kellogg, Shell, IFP, Exxon...
nghin cu hon thin hn nhm mc ich t nng sut hiu qu cao nht,
s dng nguyn liu nng hn, tit kim c xc tc... v phi l kinh t
nht.
Qua thc t dng h thng cracking xc tc lp si s dng xc tc dng
bi hay vi cu, ngi ta thy n c nhiu u im hn h thng cracking xc
tc trong lp xc tc chuyn ng. Nhng u im l:
+ Cc thit b chnh ca qu trnh l thit b phn ng v thit b ti sinhu c cu to rt n gin, so vi cc dng thit b khc ca qu trnh
cracking thc t chng l hnh rng.
+ S tun hon xc tc t thit b phn ng n thit b ti sinh v ngc
li l nh s vn chuyn lin tc ca hi v kh trong mt gii hn rng.
+ Do s khuy trn mnh m ca xc tc v hi nguyn liu dn n s
ng nht v nhit trong ton b th tch lp xc tc thit b phn ng
cng nh thit b ti sinh, khc phc c hin tng qu nhit cc b.
+ H thng ny c kh nng ch bin cc dng nguyn liu khc nhau,
nh t nguyn liu l phn on kerosen n nguyn liu nng l mazut, lm
tng tnh vn nng ca h thng.
+ H thng ny c cng sut lm vic ln v c thi gian tip xc ngn
(thi gian tip xc gia nguyn liu v xc tc l cc tiu) dn n vic t
c hiu sut xng cc i v olefin nh khng xy ra phn ng ngng t bc
hai m to xng. ng dng phng php ti sinh (chy hon ton CO trong
thit b ti sinh) dn n t hm lng ct cn rt thp trong xc tc.[1v 3]
Qua cc u im ta chn s cng ngh xc tc lp si FCC vi
thi gian tip xc ngn cho qu trnh cracking xc tc.
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III. Dy chuyn FCC vi thi gian tip xc ngn
Trc ht nguyn l ca qu trnh cracking xc tc c th miu t bng
s sau:
Qu trnh cracking xc tc thng c tin hnh iu kin cng ngh
sau:
Nhit 470 5500C
p sut trong vng lng ca l phn ng 0,27 MPa
Tc khng gian th tch truyn nguyn liu tu theo dy chuyn
cng ngh c th t 1 120m3/m3.h
Xc tc l zeolit mang tnh axit.
1. S dy chuyn FCC thi gian tip xc ngn:Dy chuyn cng ngh FCC gm ba b phn chnh:
Reactor Ti sinh v vn dng nhit ca kh khi
Phn on phn chia sn phm.
Nguynliu
Chun bx l
Lphn ng
Sn phmqua chng tch
Xc tc lm vic
Xc tc ti sinh
L ti sinhxc tc
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a) Thuyt minh dy chuyn cng ngh1. B cha nguyn liu u 15. Thit b gia nhit2. Bm 16. ng dn hi sn phm3. Van tit lu 17. Thit b phn ng FCC4. L t 18. Thp ti bay hi5. Thit b phn ly tch cn bn 19. B phn ng ng6. B cha sn phm 20. Xyclon 2 cp7. Thit b trao i nhit 21. Thit b ti sinh xc tc8. Thit b lm mt bng khng kh 22. Van l9. Thit b lm lnh bng nc 23. Bung lng tch10. Thp chng tch sn phm 24. Ni hi tn dng nhit11. B lng tch 25. Thit b tn dng nhit12. Thp tch kh 26. My nn kh13. Thp n nh14. Thit b phn dng
2. Nguyn l hot ng:+ B phn Reactor - ng ng:
Nguyn liu mi t b cha nguyn liu (1) c cho qua thit b trao
i nhit ng chm, nguyn liu mi c th c trn vi phn tun hon
(HCO) (6),(l phn on du nng ca qu trnh cracking xc tc ) v cn y
thit b (5), sau cho qua l t nng nguyn liu cracking Nguyn liu
cracking c tip xc vi xc tc nng ti sinh i vo y ca ng
ng(19), khi nguyn liu bay hi cng vi hn hp ca hi nng v xc
tc c i ln pha trn ti nh ca ng ng, ng thi xy ra cc phn ng
cracking xc tc. Hu ht nguyn liu u tham gia phn ng v chuyn ho
trong ng ng, cn reactor c dng nh mt thit b tch xc tc v hi
hydrocacbon.
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Mt b phn c thit k c bit, b tr gn van chn, dng hi nc
thi xc tc v du, lm nh vy s hn ch n mc ti a hin tng trn
quay tr li ca xc tc v hi kh lm vic. Vng ng ng v b phn
tch hi ca reactor c thit k cho qu trnh FCC vi thi gian tip xc
ngn gia xc tc v du. Sau khi tch khi xc tc, hi sn phm nng (16)
c chuyn ti ct phn on. Xc tc lm vic (10) c cho qua vng
tch hi (cn gi l b phn ra xc tc) bng cch thi hi nc vo. B phn
ra khng ch lm nhim v ui ht hydrocacbon hp ph trn xc tc m
cn lm ti cc ht xc tc chng khng dnh vo nhau trc khi sang l
ti sinh. Cn iu chnh mt tc hi thch hp cho nhim v ny. Cn thitphi kim tra cht ch thi gian lu ca xc tc trong b phn ra trnh
phi dng qu nhiu khng kh trong l ti sinh. p sut trong reactor c
khng ch bng b phn iu chnh p sut ca ct phn on.
+ L ti sinh v khi tn dng nhit ca khi l:
Xc tc c cha cc (cc bm trn xc tc) c chuyn qua van iu
khin (23) v khng ch bi b kim tra mc xc tc trong l phn ng, sau
i vo l ti sinh. Xc tc vo l ti sinh theo hng tip tuyn vi thnh
l. Mc ch chnh ca ti sinh l t chy cc bm trn xc tc lm vic
bng oxy ca khng kh, khi to thnh CO, CO2, hi nc, nh vy m
tr li b mt hot tnh cho xc tc. Sau khi nn, khng kh t c cho
vo y l ti sinh, qua li phn phi trn c hiu qu khng kh v xc
tc. S chy cng xy ra trong lp si v t c iu , tc ca
khng kh phi t ln hn 1 m/s. Xc tc ti sinh c chuyn vo ngng sau khi ui c sch kh qua mt van l m s hot ng van ny
c khng ch, iu khin t ng nh b phn iu chnh nhit ca
reactor, ri sau xc tc c trn vi nguyn liu cracking v hon thnh
mt chu trnh. ng thi ngi ta tho xc tc bn gi ho ra, b sung xc
tc mi m bo hot tnh n nh ca xc tc theo thi gian lm vic.
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Kh ca qu trnh chy cc v cc ht xc tc chuyn ng t pha c
vo pha long nh l ti sinh, qua hai cp xyclon gi li cc ht xc tc
v tch kh. Sau , kh khi c qua bung lng (23) tch tip bi xc
tc, ri qua b phn tn dng nhit( 24), tip theo kh khi c lm sch bi
xc tc bng lc in(26) ri i ra ngoi theo ng khi.
+ B phn phn chia sn phm:
Hi sn phm (16) c np vo ct phn on chnh chia thnh cc
sn phm khc nhau, xng v phn nh hn c cho qua b phn ngng t
ri vo thit b tch kh. Sau khi tch kh, ta nhn c phn on C1,C2( I ),
cc sn phm ny c th c dng lm kh nguyn liu cho dy chuyn.Phn on C3,C4(II) cha nhiu propylen v buten c dng lm nguyn liu
cho dy chuyn alkyl ho v sn phm tip theo l xng kh butan
T ct phn on chnh, ta cn nhn c cc phn on sn phm nh
naphta nng, LCO v HCO. Phn HCO c th cho tun hon li mt phn , v
cui cng l phn du cn c lm sch khi bn xc tc (5). Mt phn
sn phm nh ca thit b tch bn xc tc cng c cho tun hon cng vi
HCO.
IV. Hng pht trin v ci tin
ca FFC trong lc du
T thp nin 90 tr li y, qu trnh
FFC vn khng ngng c ci tin c v
cng ngh v xc tc to cho FFC trong
tng lai ph hp vi yu cu ca cng
ngh lc - ho du, ng thi cho php s
dng c nguyn liu nng hn, nhim
bn hn, ngha l vi cht lng nguyn
liu ngy cng xu hn. T mc tiu ,
cc nh thit k v cng ngh t ra cc nhim v chnh sau:
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1- Ci tin v cng ngh thch ng vi nguyn liu c cht lng xu
m hiu sut xng hay phn ct vn t cc i, gim lng cc, nng cao
cht lng ca xng.
2- Ch to v ci tin cht xc tc c bn nhit, bn c cao, bn vi
cc c t, c hot tnh cao v n nh, d ti sinh v c thi gian lm vic lu
di hn.
3- Chn la cc thng s lm vic ti u bng cc cng ngh iu khin
v kim tra tin tin, hin i.
4- Ci tin cc trang thit b cng vi cng ngh khng nhng nng
cao cht lng sn phm m cn cho php kt hp sn xut cc nguyn liucho tng hp ho du v ho hc. V d nh nhn etylen, propylen, buten...
Ch trong vng vi chc nm tr li y, ngoi vic nng cao, ci tin v
p dng xc tc mi c hiu qu, ngi ta thit k cc dy chuyn FCC
hin i sn xut c khng nhng nhiu xng vi cht lng cao hn m
cn cho php nhn cc nguyn liu cho tng hp ho du. Thnh cng ,
trc ht phi k n qu trnh FCC vi thi gian cracking ngn v siu ngn
(MSCC), hay qu trnh cracking su (DCC).
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Tnh Ton thit b chnh
I. S liu ban u
+ Nng sut : 2400.000 kg/m3
Bng 1: T trng v hiu sut ca sn phm
Sn phm Hiu sut (%TL) T trngkg/m3
Kh 17 1.22
Xng 48 0.764Gazoil nh 17 0.933
Gazoil nng 13 0.942
Cc 5
+thnh phn ha hc ca cc l : C =87%(TL) ;H2=9%(%TL) ;
S=4(%TL)
Khi chy th 90% cacbon bin thnh CO2 v 10% bin thnh CO
+ Nhit lp si ca xc tc trong l phn ng 485 0C
+ Nhit lp si ca xc tc trong l ti sinh 600 0C
+ Nhit cc sn phm crackinh khi i ra t l phn ng 450 0C
+ Nhit phn ng crackinh xc tc 105 kcal/1 kg xng
+ Ti ng vn chuyn ca l phn ng v ti vng kh lp hp ph c
a vo 5% v 3% hi nc (so vi nguyn liu)
+ Hi nc qu nhit a vo l phn ng c nhit l 450 0C
+ p sut lp si trn xc t c 1050 mmHg
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II. Cn bng vt cht
- S ngy lm vic l 350 ngy
- S ngy ngh sa cha l 15 ngy
*nng sut thit b theo nguyn liu l
Gnl=24350
1000000.2400
=285714,286 kg/h
- Lng kh crackinh l
Gk=Gnl 17.0 = 2857140,286 17.0 = 48571.429 kg/h
- Lng xng l
Gx=Gnl 48.0 =285714,286 48.0 =137142,857 kg/h
- Lng gazoil nh l
Gg= Gnl 17.0 =285714,286 17.0 =48571,429 kg/h
- Lng gazoil nng l
Gn= Gnl 13.0 =28571 4,286 13.0 =37142,857 kg/h
- Lng cc l
Gc=Gnl 05.0 =285714,286 05.0 =14285,286 kg/h
Vy tng sn phm lGk + Gx + Gg + Gn +Gc = 48571,429 +137142,857 +48571,429
+37142,857 + 14285,714 =285714,286 kg/h
* tng hiu sut xng ca qu trnh th ngi ta cho tun hon mt phn
Gazoil nngv h s tun hon khong 0,3 .Vy lng Gazoil tun han li
l :
Gth = Gn 03.0 =37142,857 03.0 =11142,857 kg/h
- Tiu hao hi nc l
Gn =Gnl ( 0.03 + 0.05) =285714,286 08.0 =22857,143 kg/h
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* Bng 2 : Cn bng vt cht
Sn phm S lng (kg/h)
*Dng nguyn liu vo
+Nguyn liu 285714,286
+Gazoil tun hon 11142,857
* Tng vo 296857,143
*Dng sn phm ra
+kh 48571,429
+xng 137142,857
+Gazoil nh 48571,429
+Gazoil nng 37142,857
+ Cc 14285,714
+Gazoil tun hon 11142,857
* Tng ra 296857,143
III: Cn Bng Nhit Lng
1. Xc nh nhit chy ca ccq = a1. qCO2 + a2.qCO + a3.qH2O kcal/kg
Trong :
a1 :l phn cacbon trong cc c t chy thnh CO2
a 2 : l phn cacbon trong cc
c t chy thnh COa 3 : hm lng hydro trong cc
qCO2 : lng nhit ta ra khi t chy 1kg cc thnh CO2
qCO2=6137 kcal/kg
qCO2 :lng nhit ta ra khi t chy 1kg cc thnh CO
qCO=2450 kcal/kg
qH2o :lng nhit ta ra khi t chy 1kg cc thnh nc
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qH2O = 28905 kcal/kg
_ Theo ti liu thc nghim ta c :
a1 = 0.85 9.0 ; a2= 0.05 01.0 ; a3= 0.046 056.0
+ suy ra:
q =0.86 8137 + 0.1 2450 +0.045 28905 =8543,545 kcal/kg
Nhit lng mang rakhi l phn ng gma) do sn phm crackinh v hi nc
Q/1 = Gk.Ck.485 + Gx.qx
485 + Gg.qg485 + Gn.q
n485 + Gth.q
th485 + Gn .q
n485
_ Hm nhit ca hi xng ,gazoil nh , gazoil nng v phn hi l
u
ctnh theo cng thc sau :
qdt=
1(0,403t + 0,000405 t2)
Trong :
: t trng ca cc sn phm lng
t : nhit oc
Suy ra :
qx485 =764,0
1(0,043 .485 + 0,000405 .4852)
=322,633 kcal/kg
qg
485= 933,0
1
(0,043.485 + 0,000405 4852
)
= 301 kcal/kg
qn485 =942,0
1(0,403 .485 + 0,000405 .4852)
=299,4 kcal/kg
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qth485=934,0
1( 0,403 .485 + 0,000405 .4852)
=300,83 kcal/kg
Hm nhit ca hi nc qu nhit 485 0 C l ;:
q H2O485 =833,6 kcal/kg
t nhit ca kh crackinh l Ck=0,38 kcal/kg0 C
Vy :
Q/1 = 48571,429 . 0,38 . 485 +137142,857 . 332,633
+48571,429 .301 +37142,857 .299,4 + 11142,857 .300,83
+285714,286 .833,6 = 321834060,3 kcal/kg
b) do xc tc lm vic v cc mang ra :Q/2 = (Gxt.C1 +Gc .C2)t
Trong :
C1 : l t nhit ca xc tc C1 = 0,27 kcal/kg0 C
C2 : l tt nhit ca cc C2 = 0,6 kcal/kg0
CGxt : l khi lng xc tc tun hon gia l phn ng v l ti sinh
Ta c: Gxt = n. Gnl kg/h
Vi n l bi s tun hon
Gxt = 5. 2875714,286 = 1428571,43 kg/h
Vy :
Q/
2 = (2785. 0,27 + 14285,714 .0,6)485=4521838,524 kcal/h
c) do tiu hao cho phn ng crackinh xc tc :
Q/3 =Gx .i kcal/h
Trong :
i : l nhit ca phn ng crackinh xc tc i = 105 kcal/1 kg xng
Gx : lng xng to thnh
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Suy ra :
Q/3 = 137142,857 .105 =14399999,99 kcal/h
d) Nhit mt mt vo mi trng ly bng 5% lng nhit cn bngQ/4 = ( Q
/1 + Q
/2 + Q
/3 ) 05,0 =2673131,59 kcal/h
* Nhit mang vo phn ng gm c
a) Do nguyn liu nng : Q1= Gnl . qnl kcal/h
trong :
Gnl : lng nguyn liu ban u kg/h
Qnl: hm nhit ca nguyn lu
b) Do xc tc ti sinh
Q2 = Gnl .n .C1.t2 kcal /h
Trong :
Gnl : lng nguyu n liu ban u kg/h
n :bi s tun hon
C1
: t nhit ca xc tc C1
= 0,27 kcal/kg o C
T2 : nhit trong l phn ng t2 = 5800 C
Suy ra :
Q2 = 285714,286 .5 .0,27 .580 = 226063285,9 kcal/h
c) do hi nc :Q3= Gn .q
n485 = 22857,143 .833,6 = 19053714,4 kcal/h
e) do gazoil tun hon vo thit b l :Q4 = Gth .. q
th290 kcal/h
Trong :
Gth : lng Gazoil tun hon li kg/h
q th290 : hm nhit ca xc tc tun hon li
qth290 =
1(0,043t2 + 0,000405 t
22)
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=934,0
1(0,043 .290 + 0,000405 . 2902)
=156,172 kcal/kg
trong :
t2 : nhit ca xc tc tun hon li
suy ra :
Q4 = 11142,857 .156,172 =1740202,263 kcal/h
Vy lng nhit mang vo l phn ng l
Q1 + Q2 + Q3 +Q4=Q1 + 246857202,6 kcal/h
T phng trnh cn bng nhit lng ca l phn ng ta c
Q1 +Q2 + Q3 + Q4 = Q/
1 + Q/
2 + Q/
3 + Q/
4
Q1 = (Q/
1 + Q/
2 + Q/
3 + Q/
4) - ( Q2 + Q3 +Q4)
=553835763,4 246857202,6 = 306978560,8 kcal/h
vy hm nhit ca nguyn liu l :
qnl = Qnl1Q = 268,285714 8,306978560 = 1074,425 kcal/kg
III. Tnh ng knh l phn ng
1. Xc nh ng knh l phn ng theo cnh thc sau :
D = 1,128 s (m)
Trong :
S : l din tch tit din ngang ca l phn ng (m
2
)
S =.3600
V(m2)
V : th tch hi i qua tit din t do ca l phn ng (m3/h)
: tc cho php ca hi trong tit din t do ca l phn ng
(m/s) , theo ti liu : = 0,60 (m/s)
*Xc nh i l
ng V theo cng thc sau :
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V =p273
)t273(Mi
Gi4,22
p +
MiGi :Lu lng hi trong l phn ng.
tp :Tc trong l phn ng.
P: p sut tut i bn trn lp gi si ca l phn ng ly bng 0,2at
tnh i lngMi
Gita phi xc nh dc trng lng phn t
trung bnh ca kh Cracking:
Mtb =1460
429,48571= 33,27
Suy ra: Mi
Gi=
27,33
429,48571+
105
137142+
200
429,48571+
340
857,37142
+18
143,22857 +248
857,11142 = 4432,91 Kcal / h
Vy V =2x273
)485273(91,4432x4,22 += 137852,13 m3/ h
Gi tr ca i lng V va tnh c l ln nht v th tch tng cng
ca tt c cc sn phm Cracking s ln hn th tch ca nguyn liu
Suy ra: S = 6,0x3600 13,137852 = 63,8 m2
Vy ng knh l phn ng:
D = 1,128 S = 1,128 8,63 = 9,0 m
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2. Chiu cao l phn ng:
Xc nh chiu cao ton b l phn ng theo cng thc:
Hn = h + h1 + h2 + h3 + h4 + h5 , m
h: chiu cao lp gi si.
h1: chiu cao ca vng chuyn tip t lp gi si n vng tch
h2: chiu cao vng tch; h2 = 6m
h3: chiu cao vng phn ly; h3 = 6m
h4: chiu cao vng t Xyclon; h4 = 6m
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h5: chiu cao nh l phn ng, nh l phn ng c dng bn cu nn
thng ly n bng 0,5D
h5 =