(LocHoaDau.org)Nhien Lieu Dau Khi 4722

8/6/2019 (LocHoaDau.org)Nhien Lieu Dau Khi 4722

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NXB i hc quc gia H Ni 2007. 120 tr.

T kho: nhin liu du kh, tnh cht ca nhin liu, chy hp thc, chy khng

hon ton, nng sut ta nhit, nhin liu, sn xut nhin liu, lc du, du m, than

, ct bitum, nham phin, du m, kh thin nhin, du madt, xng ng c, nhinliu kh, phn tch nhin liu, nhit tr, s chy, csvt l ca s chy, csha

hc ca s chy, ng hc ca s chy, t bc chy, s n, ngn la.

Ti liu trong Th vin in tH Khoa hc Tnhin c thc sdng cho

mc ch hc tp v nghin cu c nhn. Nghim cm mi hnh thc sao chp, in

n phc v cc mc ch khc nu khngc schp thun ca nh xut bn v

tc gi.

Mc lc

MU ............................................................................................................................................4Chng 1 NHNG TNH CHT CBN CA NHIN LIU............................................... 5

1.1 Nhit bc chy ca nhin liu..............................................................................51.2 Gii hn n ca nhin liu ........................................................................................7

1.3 Tc truyn la ......................................................................................................91.4 Nhit ngn la....................................................................................................111.5 S chy hp thc v s chy khng hon ton.......................................................12

1.5.1 S chy hp thc (S chy hon ton) .......................................................................121.5.2 S chy ca cc ankan ................................................................................................131.5.3 S chy khng hon ton............................................................................................15

1.6 Hiu ng phn ly trong ngn la............................................................................181.7 Nng sut ta nhit (NSTN hay nhit tr)...............................................................18

1.7.1 Nhit tr tinh v nhit tr th........................................................................................181.7.2 Tnh ton nhit tr........................................................................................................19

1.8 Cng nhit........................................................................................................20

Nhin liu du kh

Hoa Hu Thu


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Chng 2 SN XUT NHIN LIU.........................................................................................232.1 Sn xut nhin liu t du m.................................................................................232.2 Sn xut nhin liu t lc du.................................................................................272.3 Sn xut nhin liu t ct bitum (Bituminous Sands).............................................31

2.4 Sn xut nhin liu t du nham phin...................................................................322.5 Sn xut nhin liu t du than ..........................................................................33Chng 3 CC NHIN LIU TDU M, KH THIN NHIN....................................... 35

3.1 Nhin liu lng nng (FO) (du madt)..................................................................353.1.1 B tr cung cp du cho l t ....................................................................................353.1.2 Phun du v l t bng du.......................................................................................363.1.3 Yu cu kthut i vi du madt (FO)....................................................................37

3.2 Xng ng c..........................................................................................................373.2.1 Xng t nhin (natural gasoline - casing - head spirit) ...............................................383.2.2 Xng thu c bng cch ct trc tip t du th.......................................................393.2.3 Xng crackinh v xng refominh ................................................................................40

3.3 Nhin liu iezen (DO)...........................................................................................513.4 Nhin liu kh..........................................................................................................56Chng 4 PHN TCH NHIN LIU.......................................................................................64

4.1 Nhng vn chung...............................................................................................644.2 Xc nh nhit tr ....................................................................................................66

Chng 5 ..........................................................................................................................................71Csvt l v ha hc ca s chy..................................................................................................71

5.1 Vi nt khi qut v s chy...................................................................................715.2 Nhit ng hc v ng hc ca s chy ...............................................................74

5.2.1 Csnhit ng hc ca s chy...............................................................................745.2.2 Csng hc ca s chy........................................................................................78

5.3 S t bc chy. S n .............................................................................................835.3.1 Xc nh nhit t bc chy.....................................................................................865.3.2 Gii hn cho s t bc chy........................................................................................90

5.4 S pht quang ho hc v ion ho ha hc.............................................................945.4.1 S pht quang ha hc................................................................................................955.4.2 Ion ho ha hc...........................................................................................................97

Chng 6 NG DNG CA NGN LA..............................................................................1006.1 S to thnh cc ht cacbon trong ngn la .........................................................1006.2 Sn xut axit xianhiric bng st chy ............................................................1016.3 S to thnh nitoxit trong ngn la ...................................................................102

6.4 Sn xut nng lng .............................................................................................1046.4.1 t chy cng nghip v dn dng...........................................................................1046.4.2 Sn xut cng chc v y.....................................................................................1056.4.3 Vn an ton s chy .............................................................................................106

Chng 7 PH GIA NHIN LIU...........................................................................................1077.1 Phn loi cc loi ph gia nhin liu ....................................................................107

7.1.1 Cc ph gia ty ra v chng ng c ....................................................................1077.1.2 Cht ph gia tng cng chy rt ........................................................................1077.1.3 Cc ph gia km hm oxi ho, n mn v lo ha ....................................................1077.1.4 Ph gia khng ch pht thi, khi v gip s chy..............................................1087.1.5 Cc ph gia chng kch n ........................................................................................108


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7.1.6 Cc ph gia chng tch in, dit khun, mu v ph gia nh ho...........................1087.2 Ph gia cho xng...................................................................................................1087.3 Nhin liu sch......................................................................................................109PH LC 1....................................................................................................................112

PH LC 2....................................................................................................................114


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4

MU

Nhin liu l nhng vt liu c kh nng cung cp nhit lng. Cc vt liu ny c th

l cy, c trn lp v Tri t, nhin liu ho thch trong lp v Tri t hay c snxut ra t cc ngnh cng nghip khc nhau. Trc khi bc vo k nguyn cng nghip,nhin liu ch yu s dng cho cc mc ch dn dng nh: si m, th p sng, nunng. Khi nn cng nghip th gii pht trin, vic s dng nhin liu thay i honton mc d t l s dng cho cc mc ch dn dng vn cao v nhu cu v nhin liu chocng nghip ngy cng tng ln. Ngy nay, nng lng nguyn tc s dng rng ri,song vai tr ca cc nhin liu ni trn vn rt quan trng trong i sng nhn sinh vhot ng sn xut cng nghip. Trong t nhin, nhin liu tn ti ba trng thi: kh, lngv rn.

Nhin liu kh gm: kh thin nhin; kh c sn xut t cng nghip nh: kh than,kh cc, kh tng hp, kh than t, kh l, kh metan t bn ao v t sinh khi, kh halng (LPG).

Nhin liu lng gm: du m, cc phn on du c tinh luyn, xng ng ccc loi, nhin liu iezen (DO), du nhin liu (FO), cc phn on chng ct lng thuc t ct du, du,...

Nhin liu rn gm: thc vt ph thi, g v than g, than cc dng khc nhau nh:than bn, than nu, than bitum, than bn bitum, than antraxit, cc,...

Trong ti liu ny cp n cc nhin liu thu c t du m v kh thin nhin. l kh thin nhin, kh ho lng (LPG), nhin liu cho ng cxng, nhin liu cho my

bay cnh qut, nhin liu cho my bay phn lc, du ho, nhin liu cho ng ciezen

(DO), nhin liu cho t l (FO). y l nhng nhin liu khng th thiu trong i sngv hot ng sn xut ca t nc ang trn ng hin i ho.

Trong ti liu ny cng cp ti csvt l v ha hc ca s chy - mt tnh chtc trng ca nhin liu - y l mt lnh vc phc tp lin quan ti nhiu khoa hc khcnhau. V th, vic i su vo cc lnh vc ny vt ra khi khun kh ni dung ca ti liu.

Ngoi ra ti liu cng gii thiu mt sng dng ca ngn la trong cng nghip v ccph gia cho nhin liu. Tng hp ni dung ca ti liu nhm cung cp nhng kin thc cbn nht v nhin liu cho cc sinh vin trong chuyn ngnh ha hc du m.


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5

Chng 1

NHNG TNH CHT CBN CA NHINLIU

Trc khi nghin cu cc nhin liu du kh v cc tnh cht ca chng, chng ta hynghin cu nhng tnh cht cbn chung ca cc loi nhin liu. V mt kinh t, vic lachn nhin liu cho mt mc ch cng nghi p hay mt mc ch no ph thuc rtnhiu vo ngun nhin liu, hay s ph dng ca nhin liu khu vc pht trin cngnghip cng l mt yu t quyt nh.

1.1 Nhit bc chy ca nhin liu

Nhit ca nhin liu cn phi c nng ln n khi xy ra s chy c gi lnhit bc chy ca nhin liu. Nhit bc chy l c trng cho mi loi nhin liu.

Nhit bc chy ca cc nhin liu c th xc nh c nhng phi ht sc cn thn, vnhit bc chy ca nhin liu khng nhng ph thuc vo bn cht ca nhin liu mcn ph thuc vo mi trng trong tin hnh xc nh nhit bc chy ca nhinliu. Nhit bc chy ca cc nhin liu rn v lng rt kh xc nh c chnh xc vchng ph thuc vo cc iu kin trong nhin liu c t nng.

Vi cc nhin liu kh v hi, nhit bc chy ca chng cng l nhit t bcchy v ph thuc vo iu kin ca cc phng tin c s dng xc nh nhit

bc chy. D vy, cc gi tr nhit bc chy ny vn chnh xc hn nhiu so vi ccnhin liu rn. C bn phng php thng c s dng xc nh nhit bc chyca nhin liu lng v kh.

1. Nh mt git nhin liu lng vo mt chn nung c t nng c iu khin(phng php Moore - Holm).

2. Nn on nhit n bc chy (phng php Dixon - Tizard).

3. Phng php cho n trong mt bnh c t nng v ht chn khng (phngphp Mallard v Le Chatelier).

4. Phng php ng ng tm (phng php Dixon v Coward).

Dng cc phng php ny xc nh nhit bc chy ca hirocacbon th kt qukhc nhau ng k. Theo phng php 3, cc gi tr v nhit bc chy trong khng khkhi dng hn hp h p thc i vi metan l 600C, pentan l 510C, octan l 250C,

benzen l 700C, xiclohexan l 510C, propan l 493C. Trong quyn oxi cc gi tr thuc s thp hn. V d minh hoc cho trong bng 1.


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Bng 1.Nhit bc chy (C) ca mt s nhin liu v kh

Nhin liu Trong khng kh Trong quyn oxi

Metan 580 506

Etan 472 432

n-Pentan 218 208

Toluen 552 516

Xng (OC73) 300 290

Du iezen (chs xetan 60) 247 242

Hirosunfua 292 220

Hnh 1 trnh by mi lin quan gia p sut v nhit bc chy ca nhin liuhirocacbon. p sut thp hn p sut kh quyn, mt s kh c nhit t bc chy trong vng B. Nhng p sut cao hn p sut kh quyn, cc kh n gin nh: CH4,C2H4, ... c nhit t bc chy gim i khi p sut tng (ng C). Vi cc hirocacbonln hn C3 th tn ti mt vng nhit tng i thp (t 300C n 400C, vng A) mtrong vng ny s chy cho hin tng ngn la lnh. Nhng t trn 400C, s chy cth xy ra hon ton v nhit bc chy li bin i theo ng cong C.

Hnh 1.nh hng ca p sut ln nhit bc chy ca kh v hi

i vi cc nhin liu dng cho ng ciezen, vic xc nh nhit bc chy cachng c tin hnh trong cc ng cchun cc iu kin nhit v p sut nhtnh theo phng php ca Foord. Theo phng php ny, ngi ta c tho c chnhxc thi gian tr gia thi im tim nhin liu vo ng cv thi gian xy ra s chy.Thng thng, nhit tiu chun ban u c ly l nhit thp nht m nhinliu sau mt thi gian phn hy s bng chy, thi gian ny c th ti hng giy. Nh vythi gian tr chy l quan trng. ng nhin thi gian ny c th rt ngn bng cch nngnhit v s khng ln hn 1/5 2/5 giy i vi ng ciezen tc cao.


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T cc ng cong thc nghim, Foord rt ra thi gian phn hy v nhit bc chy(trong khng kh) ca mt s nhin liu nh sau:

Thi gian (giy) 3 2 1 1/2

Gazoin (ch yu l parafin) 340C 350C 375C 500C

Du iezen (ch yu l naphten) 390C 412C 450C 575C

Creosote 485C 505C 533C 620C

i vi cc nhin liu kh, nhit bc chy ca chng thay i theo nng nhngtrong cc khong t l hp thc, nhit bc chy ca chng thay i khng nhiu. Khixc nh nhit bc chy ca nhin liu kh, phng php th 4 c s dng thchhp vi dng hi nc t nng s b kh, khng kh hoc oxi. Cc gi tr v khongnhit bc chy ca mt s kh n gin c trnh by trong bng 2.

Bng 2.

Nhit bc chy (C) ca mt s nhin liu kh p sut thng

Kh Trong khng kh Trong kh quyn oxi

Hiro 580 - 590 580 - 590

CO 637 - 658 644 - 658

Metan 556 - 700 650 - 750

Etan 520 - 630 520 - 630

Etilen 500 - 519 542 - 547

Axetilen 400 - 440 406 - 440

Nh vy, i vi cc kh n gin nh hiro, CO s thay i nhit bc chy lnh; i vi cc hirocacbon kh nhit bc chy c th chnh lch n trn 100C.Hn na, vi mt s nhin liu, nhit bc chy trong oxi v trong khng kh ltng t nhau; trong khi vi mt s nhin liu khc gi tr ny li khc nhau rtnhiu.

1.2 Gii hn n ca nhin liu

Cc nhin liu kh hay hi c kh nng chy trong khng kh hay trong oxi ch trong

cc gii hn v nng hon ton xc nh. Cc iu kin cn thit m bo s chygm: (1) nhit phi c pht trin y nng nhit ca kh ln gn nhit chy,(2) nhit sinh ra t qu trnh chy ca kh phi tip tc nng nhit ca kh ln n nhit bc chy.

Hai gii hn v nng cao v nng thp ca nhin liu c gi l gii hn trnv gii hn di ca s chy. Gii hn thp hn l t l nh nht ca nhin liu c khnng truyn s chy tip tc. Gii hn trn l hn hp c cha mt lng ti thiu khngkh gii phng mt lng nhit t chy lin tc. Khong nng ny i khingi ta gi l khong n, khong ny rt quan trng v n lin quan n nhng s c tai


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nn do s r r ca kh d chy hay hi d chy trong khng kh. iu ny cng rt quantrng i vi vic s dng thc t cc hn hp nhin liu trong ng ct trong.

Cc yu tnh hng ti cc gii hn chy l: (1) nhit tr, (2) th tch tng iv nhit dung ring ca cc kh, (3) nhit bc chy. C hai gii hn ny cn bnhhng bi dng ca bnh cha kh, hng truyn, p sut v nhit . S truyn hngln trong mt ng c ng knh 7,5 cm cho nhng iu kin ti u nht. Cc gii hnca tnh d chy ca mt s nhin liu c trnh by trong bng 3.

Bng 3.Cc gii hn ca tnh d chy ca cc nhin liu kh v lng nhit v p sut kh quyn (theo % th tch) trong khng kh

Loi kh Gii hn thp Gii hn cao

Kh l 35 74

Kh than 5,3 31,5

Kh thin nhin 4,8 13,5

Kh t 6,0 55

Du m 1,4 6,0

Benzen 1,4 7,4

Cn etylic 3,6 18

nh hng ca s thay i ng knh ng v hng ca dng nhin liu c trnhby trong bng 4 (y L hng ln trn, X l hng xung di, N l hng nm ngangca dng).

Bng 4.nh hng ca s thay i ng knh ng v hng ca dng nhin liu trong qu trnh chy

ng knh ng (cm) 7,5 5 2,5

Hng dng nhin liu L N X L N X L N X

Gii hn thp 2,60 2,68 2,78 2,60 2,68 2,80 2,73 2,78 2,90

Gii hn cao > 80,5 78,5 71,0 78,0 68,5 63,5 70,0 59,5 65,5

Vi nhng hirocacbon ln hn C3 cc gii hn trnn phc tp do hin tng lalnh. Vng la bnh thng tp trung gn hn hp l thuyt cho s chy hon ton, cn

vng la lnh tp trung gn thnh phn hot ng nht trong s chy chm.Bng 5.nh hng ca nhit v p sut ln gii hn tnh d chy trongkhng kh ca mt s nhin liu v kh

Nhit (C) H2 CO CH4(HT ln)*CH4 (HTxung)*

17 9,4 - 71,5 16,3 - 70,0 6,3 - 1,9 6,0 - 13,4

100 8,8 - 73,5 14,8 - 71,5 6,0 - 13,7 5,4 - 13,5

200 7,9 - 76,0 13,5 - 73,0 5,5 - 1,6 5,0 - 13,8


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400 6,3 - 81,5 11,4 - 77,5 4,8 - 16,0 4,0 - 14,7

p sut (atm)

20 10,2 - 68,5 17,8 - 62,8 6,0 - 17,1

50 10,0 - 73,3 20,6 - 56,8 5,4 - 29,0

125 0,9 - 74,8 20,7 - 51,6 5,7 - 45,6

(* nh hng ca hng truyn xung ca metan c a vo so snh, HT ln - hngtruyn ln, HT xung - hng truyn xung)

S tng nhit s mrng vng la bnh thng mt cch ng k. Vic tng psut cng mrng vng la tr trng hp ca cacbon monoxit, vng la b hp li.

Nhng nh hng ny i vi hiro, metan v CO trong khng kh c minh ha bng5.

Trong nhng trng hp ny, p sut c nh hng r rng hn ln cc gii hn. nh

hng ca nhit v p sut ln cc gii hn l rt quan trng i vi ng ct trong,bi v nhin liu lun lun b nn thi im chy v cng bt nng bi thnh xilanhnng. Vi hn h p hirocacbon/khng kh, p sut lm tng gii hn di, u tin bgim ti 50 atm v sau li tng ln. Tuy nhin, nhng nh hng sau ny nh v nhhng tng cng l s mrng ng k cc gii hn.

Gii hn chy i vi mt hn hp cc nhin liu kh c th tnh ton c t quy tcca Le Chatelier. Quy tc ny c gi tr trong mt s qu trnh cng nghip m s ngy nguy him c thc gim thiu bng cch a vo cc thnh phn nhin liu khcc gii hn trn thp. Quy tc Le Chatelier nh sau:

L = a + b + c L a b c

X A B C= + +

y a, b, c l cc thnh phn ca cc cu t. A, B, C l gii hn tnh d bc chy cachng. Quy tc ny p dng ng hn cho cc gii hn thp.

1.3 Tc truyn la

Tc truyn la qua hn h p nhin liu kh/khng kh c mt vai tr quan trngtrong d n xy dng l t v khng gian chy. Tc qu cao c th gy nn s qunng ca l hay s qu nng cc b, nu tc thp s dn n tt la. Tc truyn la

bnh hng bi t l cc cu t v dng ca bung t.

Phng php thng thng xc nh tc truyn la l cho hn hp nhin liuqua mt ng vi mt tc sao cho ngn la bt u pha u ra ca ng b tt v bt langay tr li. Nhng iu kin nh th ti hin li s chy ca kh nhng khng ging schy xy ra trong ng ct trong. ng ct trong lun lun c chuyn ng ri cahn hp nhin liu v khng kh. Tr nhng trng hp hn hp c nng rt nh th schuyn ng ri lm tng tc truyn la rt ln. S tng tc truyn la ca cc hnhp c nng thp l ln hn so vi cc hn hp chy nhanh v tc cao nht khng

phi l ng t l l thuyt nhin liu v khng kh t chy hon ton m n nm gnnh gia cc gii hn trn v di ca s chy. nhng gii hn ny ngi ta thy rng


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i vi 5 hirocacbon u trong dy ankan c tc truyn la vo khong 6,1 m trong 1giy.

Khi s truyn la c nghin cu bng phng php ng nh trn, ngi ta thyrng tc truyn la gim i theo ng knh ng ti mt gi tr nht nh. Tc truynla trong ng ng knh 2,54 cm gim i mt na so vi trong ng 30,5 cm.

Khi nghin cu tc truyn la ca cc nhin liu, ngi ta thy rng phn trmkh thp th tc cng thp. Khi phn trm kh tng ln th tc truyn cng tng ln timt cc i v sau li gim i khi t ti gii hn trn ca tnh d bt la. Cc tc thp nht, tc ca cc hn hp gii hn l nh nhau i vi tt c cc kh, vo khong19,8 cm/s (xem hnh 2).

Hnh 2.Tc chuyn ng u ca ngn la cc nhin liu kh trong khng kh

Tc truyn la cng bnh hng bi s c mt ca hi nc. V d, i vi COtc truyn la gim i ng k khi c mt nc. Nhng gi tr thu c trong mt ng6,35 cm c trnh by trong bng 6 sau y.

Bng 6.Tc truyn la cc i ca hn hp nhin liu kh vi khng khtrong ng nm ngang

Tc (cm/s) vi ng knhngNhin liu kh

% nhin liukh trong hnhp

2,5 (cm) 5,0 (cm)

Hiro 35 490 -

Metan 9,5 66 91

Etan 6,5 86 130

Propan 4,6 80 120

Butan 3,7 83 113

Pentan 3,0 82 115


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Etilen 7,2 142 -

Axetilen 8,9 282 -

1.4 Nhit ngn laNhit ngn la rt quan trng trong st nng kh bi v nhit ngn la cng

cao th tc t nng cng nhanh v khi nhit ngn la cng cao th hiu qu nhitca qu trnh cng ln.

Nhit ngn la rt kh o v cc gi tr s dng bnh thng l cc gi tr canhit l thuyt, ngha l nhng gi tr ngn la c tnh ton nu coi nhit tchy cht nng sn phm chy. Bi vy, nhit ngn la l thuyt c th tnh ton tnhit t chy, nhit dung ring v th tch cc kh. Dnhin, nhng gi tr ny l caohn nhng gi tr thc t, nhng chng quan trng so snh v dng tnh ton cchiu ng t nng sb, lng d khng kh... Mt s nhit ngn la ca cc nhinliu kh c trnh by trong bng 7.

Bng 7

Nhit ngn la ca mt s nhin liu kh

Nhin liu kh Nhit tr (cal/l) Nhit ngn la (C)

Kh than 4983 2160

Kh t 2758 2300

Kh my pht 1139 1680

Kh l 818 1460

Kh hiro 2847 2045

Metan 8854 1880

CO 2830 1950

Trong vic tnh ton cc gi tr nhit ngn la, ngi ta s dng nhit t chy thpnht ca kh bi v n nhit khng c gi trnhit ln hn 100C.

Nhit ngn la ca cc kh c trn vi nhau c th tnh ton c t cc bnghay cc th cho sn, t cc lng nhit tng cng ca cc sn phm chy. Sn phmchy ch yu l CO2, N2, H2O. Cc nhit l thuyt l tnh cho kh lnh v lng khngkh lnh theo l thuyt. Cc gi tr ny b gim i bi lng d khng kh v tng ln bngcch t nng s b khng kh hoc nhin liu kh. Trong thc t, nhit ngn la l


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thuyt tnh ton c khng tht chnh xc v: 1 - Cc d kin, c bit nhit dung ringca kh chy, khng tht chnh xc; 2 - Xy ra s phn ly sn phm CO2 v H2O; 3 - La

bc x nhit ra ngoi t 5 - 20%; v 4 - Nhit b mt i do i lu, dn nhit v s chy kodi trong mt thi gian ng k.

Cc nguyn nhn mt nhit (3) v (4) ph thuc vo cc iu kin c bit. Nhngnguyn nhn (2) c thc tnh ton t cc d liu bit v cn c hiu chnh bngcch tri nhit phn ly t nhit t chy kh. V nhit b hp th khi phn ly sn phmchy, nn nhit c iu chnh l thp hn ng k so vi nhit khng c iuchnh. V di vi CO nhit b sai lch n 400C.

Trong thc t, nhit ngn la cao c tht c bng (1) chy nhanh, (2) gimlng d khng kh n ti thiu v (3) t nng sb nhin liu. Tng lng d khngkh t 0 100% s lm gim nhit ngn la ca kh chy ln khong 30%. Cng khny c t nng sbn 500C v t chy vi khng kh cng 500C (ngha l t nng sb hn hp nhin liu v khng kh) th nhit ngn la tng ln thm n ~

20%.

1.5 S chy hp thc v s chy khng hon ton

Theo quan im ho hc, s chy l do tc dng ho hc ca oxi trong khng kh vicc nguyn t ca nhin liu c kh nng phn ng vi n. Ni chung s chy c thchin p sut khng i, gn vi p sut kh quyn ngha l n thp hn hay cao hn mtcht tu theo tng thit b.

1.5.1 Schy hp thc (Schy hon ton)

S chy hp thc hay s chy l thuyt l s chy hon ton v khng d khng kh.Khi sinh ra t s chy ny l nhng cht sau: CO2, H2O, SO2 v N2, vi iu kin l nhit chy khng gy nn s phn ly ca cc phn t ny. Nhng kh khc ch tn ti didng vt.

Th tch oxi hay khng kh cn thit t chy mt khi lng cho ca nhin liucha: C% cacbon, H% hiro, O% oxi, S% lu hunh, tt c theo khi lng, cho CO2,H2O v SO2c xc nh theo cc biu thc sau:

- Th tch oxi: Voxi = 0,0224C H S O

12 4 32 32 + +

m3/ kg nhin liu

- Th tch khng kh: Vkhng kh = 1.067 C H S O12 4 32 32

+ + m3/ kg nhin liu

V d, t chy 1 kg metan th cn mt th tch l thuyt oxi l 2,80 m3 hay th tchkhng kh l 13,34 m3.

t chy hp thc mt nhin liu m thnh phn ca n c biu th theo phntrm khi lng l nh sau: 84,7%C; 11,2%H; 3,5%S; 0,6%N th phi cn mt th tch oxil thuyt l 2,23 m3/kg hay mt th tch khng kh l 10,64 m3/kg. Trong trng hp, nungi ta kn cc th tch kh c sinh ra bi s chy v th tch kh nitc ngun gc tnhin liu v khng kh th lng khi l 11,28 m3/kg. Th tch ca khi kh thu c bng


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cch bi th tch hi nc c hnh thnh s l 9,909 m3/kg, hm lng CO2 l 15,45%,hm lng SO2 l 0,25%.

Trong s gn ng u tin, hm lng CO2 ca khi hp thc c xc nh bng ts th tch CO2 vi th tch khi kh hp thc (o), quyt nh s chy. i vi ccnhin liu khc nhau, o c cc gi tr gn ng nh sau:

- Kh thin nhin v kh sn xut : 11 < o < 12

- Butan v propen thng mi : o 14

- Du FO (fuel oils) : 15 < o < 16

- Than : 18 < o < 20

Trong i a s cc ng dng cng nghip, s chy hon ton c thc hin vi mtlng d khng kh. S chy nh thc gi l s chy oxi ha, s chy khc thchin khi thiu khng kh v c s dng trong mt s qu trnh luyn kim hay gm s.

Vic d khng kh phi c gii hn n cc tiu cn thit cho s chy hon ton. Sd ny thay i t 5 10% i vi cc thit b cng nghip c cng sut ln dng kh haycc nhin liu lng v t 10 50% i vi cc thit b dng than.

Khi s chy l khng hon ton th nhng cht khng b chy dng kh s nm trongkh chy di dng CO v CH4. S chy khng hon ton cng to thnh nhng chtkhng b chy dng rn nh than bm vo thit b hoc b ko i cng vi khi. Ngi tanhn thy rng vic phn tch cc kh chy cho ta mt d kin quan trng iu chnh schy. Tht vy, c nhng mi quan h gia lng d khng kh v hm lng oxi trongkhi kh cng nh lng d khng kh v hm lng CO2. Ni chung, ngi ta thy lngd oxi trong khi kh tng ln ngha l lng d khng kh tng ln th lng CO2 trongkhi gim i gn nh tuyn tnh.

Hnh 3.S bin i thnh phn kh chy khi t nhin liu theo s thay ilng khng kh

1.5.2 Schy ca cc ankan


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S chy hp thc ca cc ankan xy ra theo phng trnh phn ng sau:

CnH2n+2 +3n 1

2

+O2 nCO2 + (n+1)H2O

Phn ng ny l pht nhit. N c s dng trong cc ng c, nh my nhit indng nhin liu du v kh thin nhin, cc ni t nng. Nhit to ra khi t chy ankanc xc nh theo cng thc chung sau y:

o298,15H (CnH2n+2) = (609n + 193) kJ. mol1

n l s nguyn t cacbon trong ankan

Trong trng hp n gin ca metan:

CH4 + 2O2 CO2 + 2H2O vi o298,15H = 802,3 kJ.mol1

Rt kh xc nh nhit chy hay nhit ngn la ngha l nhit cc i m cc

kh chy ta ra. Nhit ny cng cao th s chy cng hon ton. Trong trng hp chyhon ton, trng thi cui cng l hon ton xc nh v vic tnh ton nhit cui cngl n gin, nu nh ta chp nhn rng khng c bt k s trao i nhit no hay s traoi cng no c thc hin vi bn ngoi. Ngha l nhit sinh ra ch dng t nng cckh b chy (hay s chy trong chon nhit).

Vy ta c: Q = Ho

Vi nhin liu l kh CH4 ta c:

802303 = (2 oPC (H2O) +oPC (CO2)) (T 298)= (2 51,103 + 60,35) (T 298)

T = 5233 K = 4960CTnh ton ny c n gin ha rt nhiu. y ngi ta s dng cc gi tr

oPC 2000 K ca cc sn phm chy c cho l c lp vi nhit T, khng n s

pha long bi cc kh trv cc cht khng b chy c mt trong kh chy, nhng trcht l khng n hin tng phn ly sn phm chy nh CO2, H2O, ...

Tht vy, phn ng chy ca metan khng tnh n s phn ly nhit ca cc phn tny tham gia vo s chy, nhng i vi CO2, H2O thm ch ngay 2000 K c th xuthin s phn ly kiu:

CO2 CO +1

2

O2 ; o298,15H = 283 kJ.mol

1

H2O H + OH

S phn ly ny sinh ra nhng phn t CO v cc loi gc hay nguyn t nhOH, O,H. S phn ly ny khi trln ln s lm gim ng k nhit chy cui cng t c.nh hng ny c minh ha trong trng hp chy ca metan c trnh by di y(cc gi trc tnh ton t thnh phn ca kh b chy theo %).

H2O O2 H2 OH CO CO2 H O


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37,2 6,9 6,9 14,4 15,1 11,7 4,6 3,3

Ch c 49% nc v CO2c hnh thnh khi s chy khng b phn ly. T rt ra

s gim ng k nhit t c (khong 2750C) trong khi gi tr tnh ton c trnl 4960C.

Bi vy khi nim v nhit tr ca mt nhin liu gn lin vi entanpi phn ng khng xc nh nhit thc ca kh chy v bn vng ngn la. Cn phi ch nthnh phn thc ca kh chy v bn vng nhit ca chng. V d, xianogen (CN)2 ms chy ca n dn n nhng phn t rt bn vng CO v N2 theo t l 98% so vi ch 2%gc cho php t c nhit khong 4000C. y l mt trong nhng nhit cao nhtm ta c th thu c bng cch t chy.

Trong thc t, qua phn tch cc sn phm chy ngi ta lun lun pht hin thy COngha l s chy thc t rt kh t c s chy hp thc.

1.5.3 Schy khng hon ton

Vi nhin liu l cc sn phm du v kh, cng thc tng qut ca phn ng chy nhsau:

CnHmOr+ (n +m r

4 2 )O2 nCO2 +

m

2H2O

Nh ni s chy hp thc trong khng kh, khi gm c CO2, H2O, N2 v SO2; cns chy khng h p thc trong khi cn c thnh phn CO ngha l sn phm khi gmCO2, CO, H2O, N2 v SO2.

Nu coi cc phn ng ha hc xy ra trong qu trnh chy nhin liu nh l cc phnng ca cc thnh phn nguyn t ca nhin liu vi oxi th s to thnh CO c th vitnh sau:

CO2 + H2 cbK

CO + H2O (1)

Trong trng hp nhit cao c th xy ra qu trnh phn ly:

CO2 CO +1

2O2

v phn ng sinh ra nc: H2

+1

2O

2 H

2O

Nh vy s chy khng hon ton c quyt nh bi cn bng (1). T cn bng nyta c hng s cn bng:

Kcb = 22 2

[CO][H O]

[CO ][H ]= 2 2

2 2

CO H O

CO H

V V

V V

y:2CO CO

V ,V l th tch CO v CO2 trong mt n v th tch chung ca khi.


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t:2

[CO]

[CO ]= (2)

v Kcb c th vit:

Kcb = 2

2

H O

H

VV

2

2

H O

H

VV

= cbK

(3)

Nu gi CT l lng cacbon tng cng trong mt n v th tch khi, HT l lnghiro tng cng trong mt n v th tch khi, th:

CT =2CO CO

V V+

HT =2 2H H O

V V+

T (2) ta c:2CO CO

V V= hay2

COCO

VV =

Vy CT =2CO CO2

V V + 2CO

V =)1(

1

+CT (4)

v COV 1

=

+CT (5)

T (3) c th rt ra:2H

cb

V( K )

=

+HT

v 2cb

H Ocb

K

V ( K )= + HT (6)

Theo cn bng vt cht:

2OV cung cp =

2OV tiu tn cho s chy +

2OV d trong khi

= (0,52 2CO CO H O

V V 0,5V+ + ) + OT (7)

Nu gi h s d lng khng kh l v coi oxi chim 20% th tch khng kh th:

2OV cung cp = 0,2..A

A l th tch khng kh tng ng a vo t chy nhin liu mt cch hp thc,ngha l = 1 hay:

0,2..A =2( 1)

+

CT +1

( 1) +CT + ch

ch

K

2( K ) +HT + OT

0,2..A =2

2( 1)

+ +

CT + chch

K

2( K ) +HT + OT (8)

Ta bit rng s chy l thuyt ( = 1) th = 0, lc phng trnh (8) c dng:


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0,2..A = CT +1

2HT + OT (9)

Nu ly (9) (8) ta c:

0,2.A( 1) =2( 1)

+

CT +ch2( K )

+

HT

hay: 0,4.A( 1) = T Tch

C H+

( 1) ( K )

+ + (10)

Nu gi F l th tch khi kh ( loi b nc):

F =2 2 2CO CO H N

V + V + V + V

F = CT +ch( K )

+

HT + 0,8..A + NT (11)

trong : NT - nittrong nhin liu, 0,8..A - th tch nita vo t khng kh.

Nh ni trn, nu s chy l s chy hp thc th:

= 0 H. = 0 v = 1

Khi phng trnh (11) c dng: oF = CT + NT + 0,8.A (12)

S khc gia chy l thuyt v chy thc l:

F och

F( K )

=

+HT + 0,8 ( 1).A (13)

Mt khc t phng trnh (10), ta c th vit:

( 1).A = T Tch

C H+

0,4 ( 1) ( K )

+ +

Thay biu thc ny vo (13), ta c:

F Fo =ch( K )

+

HT T Tch

C H0,8.+

0,4 ( 1) ( K )

+ +

F =T T

och

2C HF +( 1) ( K )

+ + (14)

Vy thnh phn v th tch khi kh s l:

%CO2 = 2COV

F= T

C

( 1)F +

%CO = COV

F= T

C

( 1)F

+


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%H2 = 2HV

F= T

cb

H

( K )F

+

%N2 = 100 (%CO2 + %CO + %H2)

1.6 Hiu ng phn ly trong ngn la

nhit cao do s chy kh xy ra th cng xy ra s phn ly ca CO2 v hi nc.S phn ly ny c cng hiu ng v nu hiro, CO khng b chy hon ton th nhit ngn la t c phi thp hn ngn la l thuyt. Vic hiu chnh i vi cc hiu ngkhuch tn nhit l rt kh khn, v th s hiu chnh ny thng c n gin ha bng

phng php th. Cc d kin cn thit cho vic tnh ton l:

1. Thnh phn ca kh thi khng c s phn ly.

2. Nhit bt ngun t nhit t chy ca nhin liu v bt k nhit t nng sb

no dng (c biu din bng kcal/m3

kh thi 0C v 760 mmHg).Vic s dng th cho php c th tnh ton c nhit ngn la c hiu

chnh. i vi bc x ngn la, mt hiu chnh xa hn c thc tin hnh v cho phpbnh thng t sai lch 10%. nhit 2000C, CO2 phn ly khong 6% v hi nc1,9% p sut kh quyn.

1.7 Nng sut ta nhit (NSTN hay nhit tr)

Mt tnh cht cbn ca nhin liu l nng sut ta nhit (hay nhit tr) ca n. Cngvi cc tnh cht khc, nhit tr c tm quan trng trong vic ch to cc thit b nhit c

kh nng d dng chuyn ha nhin liu thnh cng c ch mt cch hiu qu.Nhit tr ca nhin liu l lng nhit c gii phng ra khi n chy hon ton vi

oxi v ngng t cc sn phm ti mt nhit xc nh. Cc gi tr c thc biu thbng cc n v nhit tiu chun (cal/g, J/g) i vi cc nhin liu rn v lng.

Nhit tr ca mt kh c biu th bng sn v nhit c gii phng khi t chymt n v th tch kh p sut khng i. n v nhit tiu chun l kcal/m3. Nhit trca mt kh c xc nh ti mt nhit chun, c khng kh v kh u c a v nhit chun, sn phm chy cng c lm lnh ti nhit ny, qu trnh chy phi xy rahon ton, ngha l sn phm ch c CO2, SO2, H2O v N2.

Nhit tr ca mt nhin liu rn hay lng c xc nh bnh thng th tch khng

i trong mt nhit lng k c kh nng chu c p lc tng ln. V cc sn phm clm lnh ti nhit ca nhit lng k nn gi tr thu c l gi tr th.

1.7.1 Nhit tr tinh v nhit tr th

Khi mt nhin liu c cha hiro bt chy, nc c sinh ra v nu lng ncny c ngng t, n s gii phng nhit n cng vi nhit gii phng khi lm lnh tnhit chy n nhit ca nhit lng k. Vy tng nhit tr (NSTN th) ca mtnhin liu l sn v nhit c gii phng ra khi mt n v trng lng ca nhin liu(hay mt n v th tch nu nhin liu l kh) bt chy v sn phm chy c a v


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15C. Trong trng hp ny, hi nc bn thn n b ngng t. Tuy nhin trong thc t,nhiu trng hp nhit ny c ti bi nc sinh ra khi H2 b chy hay nc c sn trongnhin liu khng chuyn thnh cng v n khng gp phn nng nhit ca ngn la hay

pht nng lng trong ng ckh. Khi loi tr tt c cc yu t trn th nhit tr thu c

gi l nhit tr tinh. Vy nhit tr tinh l sn v nhit c gii phng ra khi mt n vtrng lng ca nhin liu bt chy v sn phm chy c ngng t 15C v hinc khng b ngng t.

Khi phi so snh gia cc mu than hoc cc mu du khc nhau th nhit tr tinh cngkhng cho thm nhiu khc bit, v than cng loi hay du cng c trng thng c hmlng hiro rt tng t nhau nn s khc nhau khi so snh gia nhit tr tinh v khi sosnh gia nhit tr th gn nh khng ng k.

1.7.2 Tnh ton nhit tr

Ni chung, ngi ta hay dng nhit lng k xc nh nhit tr ca mt nhin liu.Trong vic tnh ton nhit tr ngi ta gi s rng:

Gi tr nhit ca cc nguyn t trong nhin liu bng gi tr nhit ca nguyn t trng thi t do.

Khng c nhit no khc ngoi gi tr nhit ny hay ni cch khc l nhit khngc s dng gii phng cc nguyn t trong khi chy vi oxi.

Khi cacbon b chy trong oxi vi s to thnh CO2 th lng vt cht tham gia vophn ng v nhit c gii phng c thc biu th bng phng trnh sau:

C + O2 CO2 + 97.644 cal

12g C 32g O2 44g CO2

Khi hiro b chy to thnh nc p sut khng i, ta c:

H2 + 21

O2

H2O + 69.000 cal

2g H2 16g O2 18g nc (dng lng)

18g nc (dng hi) + 58.100 cal

Vy 1 g cacbon cho 8137 cal (14646 BTU/pound) v 1 gam hiro cho 34500 cal(62100 BTU/pound) nu hi nc c lm lnh ti 0C. Nu hi nc c gi100C

th nhit sinh ra l 29050 cal (52290 BTU/pound).Vy nhit tr th cho bt k nhin liu no ch cha hai nguyn t ny sc tnh

theo phng trnh sau:

NSTNCH =%C 8137 %H 34500

100

+ (1)

Nu nhin liu c cha sn oxi, lng nh oxi ny s cung cp cho s chy ca nhinliu v ngi ta khng k lng nhit ny vo nhit tr ca nhin liu. Gi s rng lngoxi c mt trong nhin liu ch kt hp vi hiro. Chng ta bit rng trong nc c 8 phntrng lng oxi kt hp vi mt phn hiro th lng hiro s gim i 1/8 so vi lng oxi


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trong nhin liu v lng hiro ny c gi l lng hiro c gi tr, v cng thc tnhton trthnh dng:

Nhit tr (th) cho 1 gam =

O%C 8137 % H 34500

8100

+

(2)

Vi nhin liu l than, cng thc tnh nhit tr (NT) y l:

NTthan=2

O N 1%C 8137 % H 34500 S 2220 600 H O

8100

+ + + cal (3)

Nu nhin liu l hn hp cc kh th nhit tr ca nhin liu l tng cc nhit tr cacc kh thnh phn.

Khi nhin liu ch cha C v H m ta p dng cng thc (1) cho hn hp cc kh nh

CH4 v CHCH th thy rng trong trng hp ca metan, gi tr nhit tr tnh ton cli cao hn nhiu so vi cc gi tr o c bng nhit lng k, trong khi i viaxetilen th nhit tr ca n li thp hn nhiu. Nh vy c mt lng nhit cn thit phvmetan trong hn hp metan v axetilen trc khi chy, trong trng hp ny nhit ly t s chy axetilen. iu ny c thc gii thch da vo nhit hnh thnh ca haikh. Khi metan c hnh thnh t cc nguyn t C v H th nhit c gii phng v vth tch cc nguyn t ny ra khi metan chng c th tham gia vo phn ng vi oxitrong khi chy th cn nhiu nhit hn. Nh vy, nhng h p cht m chng gii phngnhit khi hnh thnh c gi l cc hp cht pht nhit (exothermic). Ngc li, axetilenhp th nhit khi hnh thnh, nhit ny c gii phng khi phn hy v cng vi nhitsinh ra do s chy ca cc nguyn t thnh phn ca n. Nhng hp cht m s hnh thnhca chng i hi cung cp nhit c gi l cc cht thu nhit. Do , v l thuyt, tt ccng thc tnh ton cc nhit tr l khng chnh xc tr khi nhit hnh thnh ca nhinliu l rt thp hay m. Cng thc tnh c th p dng rt tt cho hu ht cc loi than, ngin l v than l nhin liu thu nhit rt nh nhng v c trng thu nhit ca n tng lnvi lng oxi c mt. i vi cc nhin liu kh, do nhit hnh thnh ca chng t ccnguyn t c th l dng hay m rt ln nn cc kt qu tnh thng b sai lch. i vicc nhin liu kh th cc kt qu tnh ton c t cc gi tr ca cc kh thnh phn thtch khng i l ph hp tt vi vic xc nh bng phng php nhit lng k.

Mt iu quan trng cn thit phi bit rng nhit tr ca mt nhin liu l cao hn khin bt chy p sut khng i so vi khi n bt chy th tch khng i. V d sn

phm cui cng ca s chy chim mt th tch nh hn th tch ca cc kh ban u (v dnh hiro), y hi nc ch chim 2/3 th tch cc kh ban u v nc c th ngng ttip dn ti th tch khng ng k.

Vic xc nh nhit tr ca cc nhin liu rn v lng bng nhit lng k bom thuc cc kt qu khc nhau khng ng k, v d vi than ch vi cal/g.

1.8 Cng nhit


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Trong khi bt k mt nhin liu no cng c kh nng duy tr s chy, th c nhiuthit b nhit, nhit t c khi nhin liu chy ph thuc khng nhng ch vo nhittr m cn vo nhiu iu kin khc nh:

- Trng lng sn phm chy,

- Lng khng kh d,

- Nhit dung ring ca chng,

- Nhit b mt i.

Gi s rng ton b nhit c s dng, khng b mt i khi nng nhit ca snphm th ngi ta c th tnh ton c nhit cc i theo l thuyt c tht c.Vic bit chnh xc s thay i v nhit dung ring ca kh theo nhit l iu mongmun t lu. Ch trong nhng nm gn y cc d liu chnh xc v nhit dung ringca cc kh nhit cao l c gi tr. Trong thc t him khi ngi ta c tht c cci l thuyt v s mt nhit khng th trnh khi qua bc x nhit v hp th nhit ca sn

phm.

Tuy nhin mt s nghin cu thc t c tin hnh. Hnh nh mt nhin liu angchy di mt thit bun si nc v mt nhit n nh t c, l s sn xutnhit v s mt nhit t n mt cn bng nht nh. Vic tng tc chy bng cchtng gi s khng nng lng nhit pht ra m vic sinh nhit tng ln theo t l thp hnnhiu so vi lng nhit b mt i, kt qu l mt cng nhit yu hn t c. Li mtln na, vic s dng qu nhiu khng kh t chy s h thp nhit mt cch ng kdo mt nhit.

Hiu ng ny c thc minh ha gn ng bng st chy hiro. Khi t chyhiro bng mt th tch l thuyt oxi tinh khit th nhit c tht c theo l thuyt l6000C; nhng vi mt lng l thuyt khng kh th nhit t c l 2300C. Cnnu tng lng khng kh ln 2 ln th nhit t c ch l 1400C.

Trong cc l ti sinh, nhit thot ra t st chy kh c s dng t nngkhng kh cn thit cho st chy nhin liu. y l mt bin php rt quan trng tngcng nhit. V d nhit t chy l thuyt ca st chy CO bng 2 ln th tchkhng kh v c kh (CO + khng kh) c dng nhit thng s thp hn 1600C.

Nhng nu nhit ban u ca CO v khng kh l 500C (thng qua st nng sb)th nhit t c ca s chy c tht c trn 2000C theo l thuyt.

Trong k thut hi nc, sp xp gi tr nhit ca nhin liu theo nng sut ho hi

ca nc t nhit 100C thnh hi nc cng mt nhit ngi ta dng nng sutho hi bng nhit tr ca nhin liu chia cho nhit ho hi ca nc p sut kh quyn l539,3 cal/g hay gn bng 971 BTU/pound.

Nhit ho hi ca nc (hay nhit n ca s ho hi nc) gim i vi s tng nhit hay ni cch khc l p sut un si cao hn. Theo Regnault, cho ti 230C, th nhitha hi bng 606,5 - 0,695t, y t l nhit si. l tng ca nhit ho hi v nhitcn thit nng nhit ca nc tu vo ti nhit si ca n. Theo Regnault, nccung cp 0C (32F) th nhit phi cung cp nc t ti 230C l bng 606,5 +0,305t. T cc gi tr ny th nhit ca nc vo phi gim i.


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V d, mt my un si nc lm vic p sut tuyt i l 52 kg/cm2; nhit nca vo ni l 15,5C th p sut ny nc si 170C. Nhit tng cng bng 606,5 +(0,305 170) = 658 cal cho mt kg nc. Vy nhit cn thit chuyn 1 kg nc thnhhi nc trong cc iu kin ny s l 658 15,5 = 642,5 cal. Nu than c nhit tr l 7500

cal/g (13500 BTU/g) th cng sut ho hi l thuyt s l 7500 /642,5 = 11,8.


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Chng 2

SN XUT NHIN LIU

2.1 Sn xut nhin liu tdu m

u tin, du mc s dng lm nhin liu cbn sn xut hi nc hay tnng l. Nhin liu ny l phn cn li ca vic chng ct n gin sn xut xng vdu bi trn. Vic pht minh ra ng ct trong lm thay i nhin liu ny v xngng c trnn mt sn phm c nhu cu ln v tip l du nng hn cn thit chong ciezen. Phn cn l du nhin liu. Du nhin liu c nhiu u im hn than v

n thay th than trong vn ti ng bin v mt s ngnh cng nghip.Nhng u im ca nhin liu ny so vi than nh sau:

1 - Nhit tr ca n cao hn than, khng c tro.

2 - D lu kho hn.

3 - D khng ch s chy hn, tit kim nhn cng, cng chy cao.

4 - Sch s hn trong khi s dng v trong khi np liu ln tu.

Du th c tch thnh cc phn on bng cc phng php chng ct chn lctrong kh quyn v chn khng. Du th cung cp nguyn liu u cho cng nghip ho

du v cng nghip ho cht. Nhin liu c sn xut t du m theo trt t tng dn vnhit chng ct l: xng my bay, xng t, du ho, nhin liu ng cphn lc, duiezen (DO), du madt (FO). T l cc nhin liu ny thu c t du th ph thuc vo

bn cht ca du. Vic tinh luyn cng c th lm thay i ng k hiu sut v tnh chtca cc phn on. Nh chng ta bit, du m l ngun c cha mt t l caohirocacbon kh ho tan (t 40 200 th tch iu kin tiu chun trong mt th tch dulng) v kh ny cn phi c tch ra khi du m khng lm mt i cc cu t c imsi thp. Vic tch kh u tin c thc hin ngay t ging khai thc bng cch gim pu ging trong thit b hnh trng ln. Khi cc kh cn li c tch ht th du th trnn an ton cho cc qu trnh tip theo. Kh t c tch u tin u ging c xl bng hp th hay nn thu hi xng ging du. nhng ging ch c kh v xng thu

c theo kiu ny ngi ta gi l xng t nhin (natural gasoline).Thnh phn ho hc ca du m: Thnh phn nguyn t thay i trong phm vi rt

nh, v d:

Cacbon 74,5 87,1, trung bnh l 84,5 Lu hunh 0,1 3,5Hiro 11,5 14,5, trung bnh l 12,5 Nit, oxi 0,1 0,5

Cch gi tn du th: Tu thuc vo chng loi cc hirocacbon a s c trong thnhphn du th: parafin, naphten, aromat, ngi ta t tn cc du th tng ng l duparafin, du naphten khi nhng phn on nh ca du c nhng hirocacbon tng ngchim a s.


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Khi nhng phn nng nht ca du th c cha nhiu sn phm ging asphalt thngi ta gi loi du l du asphalt.

Bng 8.Thnh phn in hnh ca cc loi du th

Thnh phn ca cchirocacbon (%khi lng)

Du th parafin Du th naphten Du th asphalt

Parafin 40 12 5

Naphten 18 75 15

Aromat 10 10 20

Asphaltene (a vng) 2 3 60

Trong thc t, tt c cc du th u cha hirocacbon ca ba loi trn. Ngi ta thyrng nhng hirocacbon naphten l ph bin nht (nhng khng phi trong cc phn nh)v phn cn cc hirocacbon ny c cha cc mch nhnh parafin di hay ngn v chng

che lp tnh cht naphten ca phn t.

Bng 9.Thnh phn ca cc phn on ca mt s loi du th

Du Grosni parafin Du Oklahome Du CaliforniaPhn on (C)

A* N* P* A* N* P* A* N* P*

60 95 3 25 72 5 21 73 4 31 6595 122 5 30 65 7 28 65 6 48 46

122

150 9 35 56 12 23 55 11 64 25150 200 14 29 57 16 29 55 17 61 22200 250 18 23 59 17 31 52 25 45 30250 300 17 22 61 17 32 51 29 40 31

A*, N*, P* l cc chvit tt ca kiu hirocacbon tng ng: Aromat, Naphten,Parafin

Cch gi tn cc du th trn cng khng tuyt i v th tu theo thnh phn ca baloi hirocacbon ngi ta cn t tn cc du th l du trung gian. Bng 8 v 9 trnh bythnh phn phn trm ca cc loi du th in hnh.

Tuy nhin, s phn loi du th theo cu t giu nht trong du th nh trn cngkhng hon chnh. Lane v Garton a ra mt cch phn loi c s dng rng rinht trong thi gian gn y. Cch phn loi du th ca Lane v Garton da vo 2 phnon ca du th:

(a) phn on t 250C 275C p sut chng ct l 1 atm v

(b) phn on t 275C 300C p sut chng ct l 40 mmHg.

Phn on (a) c gi l phn on cha kha 1. Phn on (b) c gi l phn oncha kha 2. Mi mt phn on trn c phn loi theo kiu hirocacbon: parafin, trung


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gian hay naphten theo t trng ca chng v du th c phn loi theo bn cht ca phnon cha kha theo bng di y:


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Bng 10.Phn loi du th theo Lane v Garton

Loi du th

T trng 15,5/15,5Cca phnon chakha 1

T trng 15,5/15,5C caphn on chakha 2

Parafin 0,8251 0,8762Parafin Trung gian nt 0,934 0,8762Parafin Naphten nt 0,934Trung gian 0,8251 0,8602 0,934 0,8762Trung gian Parafin nt 0,8762Trung gian Naphten nt 0,934Naphten 0,8602 0,934

Naphten Parafin nt 0,8762Naphten Trung gian nt 0,934 0,8762

Theo cch phn loi ny, mt du th c gi l khng cha sp hay c cha sp tytheo im c ca phn on cha kha 2 thp hn hay cao hn 15C.

Theo cch phn loi du th nh trn, c khong 85% du th trn th gii ri vo 3loi n gin l parafin, trung gian v naphten. Cc du th parafin - naphten v trunggian - naphten khng thy tn ti.

Cch phn loi du th ca Lane v Garton l mt cch i mi v phn loi du ththeo 4 nhm m trong nhiu trng hp ngi ta thy rng mt kiu hirocacbon no

c th chim ch yu trong mt phn on ny v n cng c th chim ch yu trong mtphn on khc. V th nhng nghin cu chi tit cn c xc nh phn loi du thc chnh xc hn.

V du th c o bng th tch, nn h s dn nnhit ca chng rt quan trng. Gitr ca i lng ny bnh thng tng ln vi s gim khi lng ring ca du trn mtkhong t 0,0007 0,0010 khi nhit tng 1C. i vi cc phn on du th s thayi c rng hn nh sau:

Phn on duS thay i h s dn n nhit

/CXng khi lng ring < 0,740

(g/ml)

0,00086

khi lng ring > 0,740(g/ml)

0,00081

Du ho 0,00072

Du gazoin 0,00064

Nhin liu iezen 0,00063

nht ca du m thay i rt ln, thm ch vi cc du t cng mt khu vc khaithc. nht tng ln cng vi khi lng ring. C hai i lng nht v khi lngring cng cao nu cc parafin lng cng cao.

Bng 11.


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Gi tr nhit dung ring ca mt s du th ti cc a im khcnhau

a imKhi lng ring

g/cm3Nhit dung ring (cal/(C/g)

Pensylvania 0,810 0,500

California 0,960 0,398

Nga 0,908 0,435

Burna 0,924 0,406

Scottland 0,880 0,406

Ngi ta cng nhn thy rng: cc du c cng khi lng ring nhng nht thayi rt rng. S tng nhit gy nn s gim rt nhanh nht v khi tng mt vi thng thng gy nn du c th chy t do.

Nhit dung ring ca du l i lng rt quan trng v n cn thit t nng ccdu nhin liu trc khi s dng. Nhit dung ring gim i gn nh t l vi s tng khi

lng ring. Bng 11 trnh by cc gi tr ny i vi cc du th khc nhau.

2.2 Sn xut nhin liu tlc du

nng cao gi tr ca du th, thng thng du th phi tri qua mt s kiu chngct, cc qu trnh ch bin v lm sch lu hunh trc khi em bn ngoi th trng.

Bc u tin l chng ct scp du th sau khi loi ht cc cht bn, mui vnc thnh cc phn on u tin gm: xng, xng nh, xng nng, du gazoin v duiezen, ti p theo giai on ct chn khng ngi ta tch c du bi trn t phn dumadt. Khong gn ng ca cc phn on ny c trnh by trong hnh 4.

Bn thn du th sau khi loi b bn, ct, nc ln trong cng l mt loinhin liu. Nhng trong thc t t khi ngi ta dng ngay du th lm nhin liu mthng tch du th thnh cc phn on hay cc loi nhin liu tha mn cc yu cu kthut khc nhau. Hnh 4 trn l s tch du th thnh cc phn on nhin liu khcnhau m khng lm thay i bn cht sn c ca chng trong t nhin.

Vic tch phn on du th bng cch chng ct chn lc trn c th nng cao hiuqu ca nhin liu v tha mn cc yu cu phc tp ca cc nh cng nghip sn xut ccloi ng cxng, ng ciezen, ng cphn lc khc nhau...

Do c im ca cc loi du th khc nhau dn n cng ngh lc - ha du cngkhc nhau. Bng 12 trnh by nhng tnh cht rt khc bit gia du parafin v du asphalt.


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Hnh 4.S tch du th thnh cc phn on nhin liu khc nhau


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Bng 12.Cc c trng ca du th parafin v asphalt

Tnh cht v hiu sut Du th parafin Du th asphalt

Khi lng ring Thp Cao

Hiu sut xng Cao Thp

Hm lng lu hunh Thp Cao

T l hiro / cacbon Thp Cao

im khi ca phn on du ha Cao Thp

Ch s xetan ca du DO Cao Thp

im sng ca phn on FO Cao Thp

Hiu sut phn on du bi trn Cao Thp

Ch s nht ca du bi trn Cao Thp

Hiu sut phn sp Cao Thp

Hiu sut bitum Thp Cao

Mi Thm Kh chu

Mu Sng Ti

V th, vi mc ch tch cc phn on du lm nhin liu s chng ct cc loi duparafin v asphalt c thc trnh by nh sau:

- i vi du parafin (trong s ny ch vit tt: n.l. = nhin liu)

- i vi du asphalt

Du parafin

Kh(gas)

Sp (wax) Du bi trn(lubricating oil)

Du mazut, n.l. lngnng (c chng cttrong chn khng, fueloil)

Du ha(kerosine)

Du gazoin, n.l.iezen (gas oil,diezel fuel)

Sp v sn phm chng ct c chn lc (Wax and

distilate, filtered)

Cn A, n.l.(residue A. fuel)

Xng(gasoline)

Cc distilat(distilate)


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Hnh 5.S nh my lc du Nghi Sn - Thanh Ha

2.3 Sn xut nhin liu tct bitum (Bituminous Sands)Du m hay cc sn phm t nhin tng tc tm thy trong ct hay khong st

lp tng i gn ca v Tri t c gi l ct bitum. C ni ct bitum l thin gm duasphalt rt nht v nc trn vi ct, bn v st. T l du/nc = 1216 / 315 tnh theo

phn trm.

Vic tch du ra khi hn hp ct, bn v st rt kh khn nhng n nay ngi ta tm c phng php tch du ny. Tt c cc loi du tch c u l cc loi duasphalt. T trng ca chng thay i t 1,4 1,5 v nhit tr ca du vo khong 9990


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tch du ly t nham phin, ngi ta dng phng php chng ct vi hi nc.Lng hi nc c a vo ti 40%. Sau nham phin th c chng ct ti cctrong cc ni chng ng. Ni chng cc cui cng cho sn phm bo ho v bn vng hn.Php chng ct ny cho xng th, du khng cha sp, du c sp. Sp c thu hi bng

cch nn cho kt tinh 10C. Hai sn phm khng cha sp c tinh luyn bng cchx l vi kim hoc axit v ct ly du iezel. Du iezel gm hu ht cc parafin v ccht lng cao, ch s xetan cao, nhng li khng thch hp cho xng ng cv ch soctan thp (khong 58). Sp c tinh luyn, c ty trng v c ch to thnh nn vc dng nh mt nhin liu.

2.5 Sn xut nhin liu tdu than

Khi chng ct khan (khng c khng kh) than ta s thu c du than . T duthan th, bng cch chng ct tip tc ngi ta thu c cc nhin liu sau:

Xng ng cphn on cui ca du creosote thu c bng cch x l th cp vihiro.

Benzen ch thu c mt phn t nha than . Phn ln hn c th thu c bng

cch x l kh than vi hi nc. Nha than cha cc hirocacbon a nhn ho tantrong benzen.

Khng ging cc du c ngun gc t du m, du than c cha mt t l ln cch p cht cha oxi (di dng phenol), nit di dng cc bazhu c. Cc thnh phnnguyn t chnh ca du than t cng mt than nhng cch tch nhin liu khc nhaucng cho cc kt qu khc nhau (bng 13).

Cc du than nhit thp khc ng k du than nhit cao nh khi lngring thp hn, khng c naphten.


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Bng 13.Thnh phn nguyn t chnh ca du than theo iu kin chng

ct

Thnh phn nguynt (%)

Ni ct nmngang

Ni ct thngng

Ct nhit thp

Cacbon 85,9 85,7 83,5

Hiro 6,3 6,3 8,5

Lu hunh 1,2 1,6 0,8

Nit 2,0 1,0 1,0

Oxi 4,0 5,4 6,2

Nhng tnh cht khc ca du than l:

- Nhit tr thay i trong gii hn tng i nh;

- H s dn nthay i rt t;

- Nhit dung ring ca du than thay i t 0,30 0,4 cal/g.40C v nhitdung ring ca cc du v du than thay i t 0,3 0,38 15 40C.


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Chng 3

CC NHIN LIU TDU M, KH THINNHIN

3.1 Nhin liu lng nng (FO) (du madt)

Nh trn trnh by, du madt l phn on nng thu c khi chng ct du thparafin v asphalt p sut kh quyn v trong chn khng. Cc du FO c im si cao.Trong k thut i khi ngi ta cn chia thnh du FO nh v FO nng. V th, cc ctrng ho hc ca du madt c nhng thay i ng k nhng khng phi tt c cc c

trng ny nh hng ti vic s dng chng lm nhin liu v cc k thut s dng thiu qu cao.

Mt trong nhng tnh cht quan trng nht ca du madt l nhtc xc nh nhng nhit quy nh, v d20C v 50C. Ni chung cc t nng v nh c sdng m t cc nhin liu du madt c nht cao v thp tng ng. Nhng du cnc nht cao (> 7000 giy) thng thng phi tri qua bc crackinh nh ph vnhng phn t nng v do lm gim nht ca du. Qu trnh ny cng gy nn stht thot du di dng kh v qu trnh c gi l visbreaking.

Tnh cht quan trng th hai ca du madt l im chp chy. im chp chy cctiu ca tt c cc du l 65,5C (~ 150F).

Tnh cht quan trng th 3 ca du madt l hm lng nc. Bi v cc du nng ct trng gn bng t trng ca nc nn phi gi du khng tip xc vi nc trong qutrnh sn xut v bo qun v nu ln nc rt kh tch ra khi du. Tnh cht cui cng lcc du khng c cha cn sa lng bi v cc cn ny s tp trung dn dn y bcha.

V th, yu t c bn trong vic s dng cc du madt l khng ch s chy cachng v chn lc cp du cho mc ch s dng thch hp v mt kthut nh kch thc

bung t chy, bn cht ca thit b, kiu cch v kch thc thit bt, phng phpphun nhin liu. Dnhin, gi c cng l mt yu t bi v vic s dng cc du c nhtcao cn cung cp nhit cho cc ng t nng trong cc b cha, do cc trm tiu th sc gi thnh cao.

3.1.1 B tr cung cp du cho l t

Du cp cho l t trong cng nghip cn phi khan ngha l loi b ht cc ht ncphn tn trong du v cc ht rn trong . Nhng hu ht cc thit b cung cp khng thp ng c yu cu ny. Khi du c cp bng cch rt t cc b cha th thngthng phi s dng mt cp b. y, ta phi t nng bng hi nc tng cngvic tch nc v tng cng chy lng ca du. Sdngi ta phi dng k thut tnng v: nhit thng, vic tch cc ht nc trong du rt chm do s khc nhau v


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khi lng ring gia chng rt nh v vi nht cao ca du th cc ht llng ny vntn ti khng th loi ht c. Khi t nng du c hai thay i r rng xy ra: (1) nht ca du b gim i rt nhanh v (2) du dn nnhiu hn nc v v th s khc nhauv khi lng ring trnn ln. Nhng h s dn ntng i ca du nng v ca nc

tng ng l 0,00070 / v 0,000476 /, v th cn t nng tch c nc ra khidu.

Du c thc t nng sbn trn im chp chy nhng phi di p sutcao v cbn l phi t c mm du c th chy hay phun qua cc van. Nhit ca du phi ng u v p sut phi gi khng i.

Khi phun khng kh hay du th vic cp du c th thc hin t mt b cha nhin liuhay nhiu b cao to thnh dng chy cn thit. V cc du rt nht khng th

phun mt cch c hiu qu nn vic t nng l cn thit. Thng thng t nng ngita dng mt thit bt nng bng hi nc b tr ngay trn ng cp du.

Trong thc t nhit cn thit bm du l: 38 120C (100 250F) cn nhit cn thit phun du vo l t l: 65,5 150C (150 300F). V d, du c kh nng

bm c nhit 38C c nht khc nhau th nhit bm thay i nh sau:

nht, 38C (st) Nhit bm, C200 7,5

600 15,5

1500 27,0

Trong cc thit b phun bng p sut, cc thit b lc c trang b ging ht nhau chai pha ht v y ca my bm du. Li lc trong thit b lc ca pha ht c kchthc mt l ln hn so vi li pha phun. Thng thng cli ph thuc vo lngca du c s dng. Do kthut pht trin, ngy nay ngi ta dng cc thit b lc khchiu qu hn vic dng li lc nh thit b lc dng chy (streamline filter) hay thit blc Autoclean. Trong thit b lc Autoclean, du i t bn ngoi qua nhiu tm thpmng c khoan l vi khong hrt nh gia cc l. Gia cc tm thp c nhiu daobng thp mng c gi cnh. Khi du i qua thit b ny cc cn bn b gi li v rivo bn cha, sau b loi ra ngoi.

3.1.2 Phun du v l t bng du

du chy hon ton th du phi trn tht u vi khng kh. V mt l thuyt, iuny c th thc hin kh d dng i vi hi du, song rt kh thc hin c i vi ccdu nng. V ho hi du, phi tng nhit , m tng nhit s dn n ph vphnt du v to nn cn cc trong thit b ho hi v thit bt chy bng kim loi. Tuynhin, vn c th p dng c i vi cc du c nhit si thp nh du ho, du trunggian. Ngi ta c th thc hin c s ho hi bng cch cho mt lng khng kh thchhp vo thit b ho hi.

Vi cc du nng hn (nh du FO nng, nh) c th dng cc my phun khc nhau chuyn du thnh cc ht nh vi khng kh a vo l t. tng din tch tip xc


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du/khng kh ngi ta dng thit b phun c cc i t 1 1,5 nghn l trn mt cm2.Ngoi ra l t cn c nhim v:

- Nng nhin liu t mt mc thp hn ln mc cao hn.

- a vo mt phn hay tt c hn hp nhin liu/khng kh c trn u vimt tc sao cho ng lng ca n s ko theo mt lng khng kh phcn thit c c di ngn la mong mun.

- Gi tuyn la bn vng v ngn la thch hp vi hnh dng ca l.

- Hon chnh s chy ca nhng git du nh trc khi ngn la b lm lnh ti khikhi bc ln.

Nu l cho mt ngn la nghing mt gc hp, tc cao th khng kh chy b htvo ngn la do tc dng ca thit b phun.

3.1.3 Yu cu kthut i vi du madt (FO)

i vi cc du madt, yu t quan trng hng u l nhit tr cao, im chp chycao, khng c vt nc v cc ht rn. Ngoi nhng yu t ny ra, cn phi la chn ducho thch hp vi nhng iu kin c bit s dng v lu tr du. Nu vic tng trphi t nng khng c kh nng thc hin c th nn chn du c nht thp. Nuvic t nng c kh nng thc hin c th cc du nng hn v r hn c th s dngc, thm vo kiu l cng c ngha trong vic chn la.

V d, Anh nhng yu cu trn c chia thnh cc cp khc nhau v cc cp cng c th b thay i. Vi cc du madt dng cho ng ci bin ca Anh nh sau:

Cp E F G H

im chp chy (min), C 65 65 65 65

nht , Redwood I 380C, mm2 / s(max) 250 450 2500 7000

Hm lng nc (max), % 1 1 1,5 1,5

Nhit tr, kcal / kg (min) 10120 9990 9990 9990

Trong cc yu cu k thut i vi du madt th yu t nht l quan trng nht,bi v nht thay i rt nhiu theo nhit . Nu nhit thp, nht ln thkhng thiu khin c s chy ca du.

Hm lng lu hunh v tro khng quan trng lm trong nhiu ng dng, song nudng lm nhin liu luyn kim th hm lng lu hunh v tro c thnh hng ti vtliu bt nng, tc l cc sn phm luyn kim.

Mt yu t quan trng cui cng l phi xem xt xem du madt l du chngct hay du cn, bi v du cn c cha mt t l cao asphalt m du chng ct khng c.Nhng loi du ny c dng trong cc mc ch khc nhau khng nh hng ti vtliu chu t nng.

3.2 Xng ng c


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Trc khi nn cng nghip t pht trin, nhin liu thu c ch bng cch chng ctdu th. Phn on naphtha c chng ct li cho xng c khong nhit si trong mtvng nht nh. l sn phm cui a vo s dng. Vic tinh luyn bng cch ravi axit v kim nhm mc ch loi b nhng lng nh cc olefin v ci thin mu ca

xng. Vic chng ct trc tip du th l bc x l u tin du th v phn xng ng cc gi l xng trc tip (Straight run spirit). Xng ny l phn on tng i khng bbin i ca du th nguyn thu.

V nhu cu ca xng t, my bay ngy cng tng nn hiu sut xng, cht lng xngcn phi ngy cng c ci thin. V th, cng nghip lc du a vo cc qu trnhcrackinh cc phn on du nng, refominh phn on naphtha nng, polime ho cc olefinnh, ankyl ha isobutan bng cc olefin... Bng cc phng php ny sn lng xng ngcthu c t du m tng ln, v cht lng xng cng tng. V nhng bin i ho hck trn nn tn gi cc xng thu c t cng nghip lc ho du kh phc tp.

3.2.1 Xng tnhin (natural gasoline - casing - head spirit)Xng t nhin hay xng thu c t kh ging du. Kh ging du cha ch yu 5

hirocacbon parafin (t C1 n C5). Ngoi ra, cn c thm mt lng nh hirocacbonphn nhnh v vng c im si rt gn vi cc hirocacbon parafin trn (bng 14).

Bng 14.Nhng tnh cht ca cc hirocabon trong kh ging du

Nhit si(C)

Nhit ti hn(C)

p sut ti hn(at)

Metan 164 95,5 50

Etan 84 34 50

Propan 44 97 44

n-Butan + 0,3 - -

iso-Butan 17 - -

n-Pentan 36 197 33

iso-Pentan 30 194 33

n-hexan 69 250 30

V ngha thc t v kinh t: hai hirocacbon u tin khng th ngng t cn cchirocacbon khc cao hn u c th thu hi c. Thng thng ch nhng hirocacboncao hn propan to nn xng t nhin.

C ba phng php c s dng thu hi hirocacbon ngng t:

1 - Nn theo cc giai on v lm lnh.

2 - Hp th vo trong du sau gii hp th ly hirocacbon.

3 - Hp ph trn than hot ng.

Cc qu trnh (1) v (2) l ph bin nht. Qu trnh thu hi c iu khin mbo thu hi hon ton cc pentan v tt c cc hirocacbon cao hn. Trong qu trnh ,


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mt t lng k butan ho tan vo trong v nh vy sn phm c mt p sut hi cth l qu cao i vi xng t. Mt xng t nhin khng cha butan c p sut hi Reid l1,4 kg/cm238C; nhng nu xng cha 25% butan th p sut hi Reid s tng ln ti 2,3kg/cm2. Trong xng khng c butan th t l cc hirocacbon c to nn nh sau: cc

pentan ln gp hai ln hexan, hexan ln hn hai ln so vi heptan v octan bng heptan.Cng dng chnh ca xng t nhin l dng sn xut cc xng theo yu cu ca thtrng bng cch trn xng t nhin vi cc xng khc. V mc ch ny p sut hi caxng hn hp cng cao cng tt, v ngi ta thy rng p sut hi cng cao th ch s octancng cao.

3.2.2 Xng thu c bng cch ct trc tip tdu th

Thnh phn ho hc ca xng ct trc tip tinh luyn c nghin cu cn thn hnnhiu so vi bt k phn on no ca du m. Cc xng ny gm cc hirocacbon parafin, naphten v aromat. Chng khng cha cc olefin hay cc dn xut vng ca

propan, butan hay heptan. Cc dn xut vng c th l xiclopentan v xiclohexan, thm chc c benzen v toluen. T l cc loi hirocacbon thay i rt rng tu theo ngun du(xem bng 15).

Nh vy, cc naphten v parafin l cc cu t chnh. Xng ct trc tip t du parafinrt giu parafin (~70%); du trung gian c hm lng parafin ti 50%, cn du th asphaltc hm lng parafin khong 3% trong xng ct trc ti p. Cc xng giu naphten varomat khng ph bin. Du th Borneo cho xng ct trc tip giu hirocacbon aromat.

Bng 15.Thnh phn ca cc xng ct trc tip ph thuc vo ngun du

Thnh phn (%)Khi lng ring 15C (g/cm3) im kt thc(C)

Aromat Naphten Parafin

Pensylvania 0,732 207 7 18 75

Oklahoma 0,739 177 10 29 61

Texas 0,750 150 33 21 57

Mehico 0,727 200 10 35 55

Romania 0,736 150 12 30 54

Xng ct trc tip thng ly trong gii hn t 40C 200C. Trong khong nhit ny nhng hirocacbon cao cng bay hi to nn thnh phn ca xng (bng 16).

Bng 16. Cc hirocabon trong xng ct trc tip

+ Cc n-parafin

Cng thc Nhit si (C) Khi lng ring 20C (g/cm3)

Nhit dung ring(cal/g.C)

Nhit ho hi(cal/g)


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Pentan C5H12 37 0,63 - 85,5

Hexan C6H14 69 0,66 0,527 70,4

Heptan C7H16 98 0,68 0,507 76,5

Octan C8H18 125 0,78 0,505 71,0

Nonan C9H20 150 0,72 0,503 -

+ Cc naphten

Cng thcNhit si

(C)Khi lng ring 20C (g/cm3)

Nhit dung ring(cal/g.C)

Nhit ho hi(cal/g)

Xiclo-pentanC5H10

49,5 0,754 - -

Xiclo-hetan C6H12 81,4 0,779 0,506 87

Xiclo-heptanC7H14

118,0 0,811 - -

Xiclo-octan C8H16 150,6 0,839 - -

Xiclo-nonanC9H18

172,0 0,770 - -

Chng ta thy rng i vi mt xng, t l ca phn ct cng cao mt nhit thpth mc bay hi ca xng cng cao. Nhng xng ct trc tip theo kiu ny bn thn ncha th l xng thch hp cho ng ct v cc c trng s dng ca xng cha thamn.

3.2.3 Xng crackinh v xng refominh

3.2.3.1 Gii thiu chung

Nhngc trng cbn ca mt xng t l g ?

Nhng c trng ny gm hai loi:

1 - Nhng c trng gn lin vi ng cong chng ct (xem ph lc 2);

2 - Nhng c trng gn thnh phn ho hc ca cc hirocacbon c mt trong xng.

hiu r vn ny, chng ta theo di qu trnh ca xng t bnh cha ti khi rakhi ng ct trong.

Xng i ti b ch ho kh qua ng dn. Nu xng qu d bay hi, n s ho hi mtphn di tc dng ca nhit to ra tng cv hnh thnh trong ng dn nhng bt kh.Bt kh ny lm gin on dng xng chy vo b ch ho kh. Bi vy, cn thit phi iuchnh ngay ti nh my lc du p sut hi ca xng di mt gii hn thch hp m psut ny trong ma ng s cao hn ma h.

Xng tip tc i qua b ch ho kh to nn mt hn hp vi khng kh. Ngi ta ddng nhn thy rng dng ca ng cong chng ct xng c mt nh hng ng k trc


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ht ln s ch ho kh, sau ln cch m hn hp xng/khng kh (kk) s hot ngtrong ng c.

Khi khi ng ng c, hn hp nhin liu v khng kh cn phi tng i giu cth bc chy mc d xng b ngng t kh nhiu khi b tip xc vi cc ng lm lnh. Nichung, ngi ta chp nhn nhit si ca im 10% c trng cho khi ng my. Nhit si ny thng nm trong khong gia 50C v 60C i vi cc t v my bay.

S lm vic bnh thng ca ng cv c bit khi tng tc ph thuc vo s hohi hon ton ca ton b nhin liu, ngi ta chp nhn rng nhit si ca im trungbnh, im 50%, m bo hot ng ny. i vi cc xng thng thng, nhit nythng nm gia 90 v 110C.

im si cui cng, cn thit l xng khng cha cc phn t nng kh bay hi honton trong cc iu kin bnh thng, nu khng c th gy nn s ho long nhanh duca cacte. Mt khc, s c mt ca cc phn t nng c th gy nn nhng bt tin khc

i vi ng c khi ng c quay nhanh bi v s chy ca cc phn t nng khngnhanh bng cc phn t nh. Vi cc ng c4000 vng quay hay ln hn, ng csthi ra mui do xng chy khng hon ton.

Nhng php o chnh xc chng minh rng s phn b ca hn hp xng/khngkh cng bt thng trong xilanh khi nhit ca im 90% cng cao.

V tt c cc nguyn nhn ny, im cui cng ca ng cong chng ct ni chungc gidi 190C i vi cc xng cho t. Cn cc xng cho my bay, im cuicng ca ng cong chng ct l trc 170C.

Chng ta thy rng vic phn on cn thn ca xng l rt quan trng v cc nh mylc ho du quan tm n vn ny sut trong qu trnh sn xut.

Ngc li, ngi ta thy rng 2 xng c cng ng cong chng ct, cng mt nhittr nhng c th c s khc nhau rt ln v hiu sut trong mt ng c. Sdnh vy vc trng cho xng cn c kh nng chng kch n.

Nm 1927, Graham Edgar a ra thang octan. u cao l iso-octan (2,2,4-trimetylpentan) mt cht chm n nht trong s 18 ng phn ca octan. u thp l n-heptan mt cht d n nht trong 9 ng phn ca heptan v quy nh tng ng chonhng hirocacbon trn cc gi tr 100 v 0. l thang ch s octan.

xc nh ch s octan ca mt xng ngi ta s dng ng cCFR (Cooperative ofFuel Research). l ng cc 1 xilanh v t l nn c th thay i c. T l nn c

th thay i bng cch iu chnh sao cho thu c s n ca xng cn xc nh ch soctan. Nh vy, s n ca xng tu thuc vo ng c. cc php o c tnh lp li thcn phi gi cc iu kin o tht chnh xc, c bit l ch quay ca ng c, chny s quyt nh s ma st cng nh thi gian tip xc gia khng kh v hirocacbon.

Ty theo cch lm vic ca ng cngi ta c th thu c:

- Ch s octan nghin cu F1 (RON) hay phng php F1 vi ng c quay 600vng/pht.

- Ch s octan mt F2 (MON) hay phng php F2 vi ng c quay 900vng/pht.


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Ch s octan mt(MON) ca mt nhin liu ni chung thp hn ch s octan nghincu (RON). S khc nhau gia hai gi tr RON v MON cho ta bit nhy ca nhin liuc nghin cu. Thc t ngi ta thy nhng kt quo theo phng php mt(MON)l rt tha ng ngay ci vi xng c bn cht parafin. Cc gi tr MON c trng cho

tnh cht ca nhin liu khi xe i trn ng vn chuyn di tc cao. Cn ch s RONli c trng cho tnh cht ca nhin liu khi xe i trong thnh ph tc va phi vthng xuyn phi tng tc.

Vi xng my bay ngi ta dng phng php F3 vi ng c c s vng quay l1200 v/ph. Cn phng php F4c trng cho tnh cht nhin liu dng khi my bay ctcnh hay my bay chin u c xc nh vi ng cc s vng quay 1800 v/ph.

Nh vy, ch s octan quyt nh cht lng chy ca nhin liu v cc iu kin tiu c s dng, ch s octan gn lin vi khi nim v hiu sut s dng nhin liu.

Hiu sut nhit ng hc ca mt vng hot ng ca ng ct trong t hay mybay tng khi tng t l nn. Ngha l t s ca th tch xilanh (im cht thp) vi th tchca xilanh im cht cao cng ln. Nhng c mt gii hn trn cho s tng t s nn ny. trn gii hn ny, hiu sut s gim i v xut hin ting g lch cch ca kim loi.

Khi ng chot ng bnh thng (khng c ting g) s chy ca hn hp khngkh - nhin liu (kk - nl) (c bt u bng tia la t bugi) c truyn theo cc sngng tm vi tc truyn la khong vi mt/giy. Tuyn la trong khi truyn, nn phncn li ca kk - nl cha b chy lm tng nhit ca hn hp. Nhng iu kin nhit v p sut qu cao ny thun li cho s hnh thnh cc hp cht peoxit km bn vng.Khi nng ca chng trong hn hp t n mt gi tr thch hp th chng t phn hymt cch t ngt gy nn s n. S n ny c c trng bng mt tc rt ln struyn sng. Sng ny p vo n p xilanh v u ca pittong gy nn ting n mnh.

Vy ting g lch cch l kt qu ca sng chc v nhit gy ra.Sng c hc tc ng n ng c, song ngi ta c th ch to c cc ng c

khng bnh hng bi sng ny. Nhng hiu ng nhit li rt nguy him, cn thit philm lnh loi bt nhit to ra khi nhin liu chy. Nu khng ng cbt nng thunli cho qu trnh to peoxit, to mui cacbon bm trn u pittong. Mui ny b nng gy nn s t chy ca nhin liu m khng cn bugi nh la v ng c vn tip tcquay khi ta ngt tip xc. Nh vy, i vi mt nhin liu cho s n gn lin vi vicch to ng c, h s nn, ri ca dng kk - nl, dng ca np xilanh,... cht lng ca

bugi. i vi mt ng c cho, s n ph thuc vo thnh phn nhin liu. Cc yu ttrn dn ti vic phi s dng phng php phn loi cc nhin liu tu theo cht lng

khng n ca chng trong ng c. Nguyn tc ca vic phn loi cc nhin liu l so snhchng trn cng mt ng cchun tnh cht ca mu nghin cu vi tnh cht ca mthn hp hirocacbon tinh khit ly lm chun.

Bng 17.Cc c trng ca xng thng v xng cao cp Php

Quy nh Xng thng Xng cao cp

Hn hp cc hirocacbon c ngun gc t nhin hay tng hp


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Mu Vng sng

Khi lng ring (kg/l) 0,765 0,770

c trng chng ct:

% Th tch 70C 10%

% Th tch 140C 50%

% Th tch 195C 45%

Khong cch im 5% v im 90% > 60C

im cui cng 205C

Cn (% th tch) < 2,5 < 3

p sut hi 37,8C:

- T 15/10 n 30/4 (ma ng) 0,8 at- T 1/5 n 14/10 (ma h) 0,65 at

Hm lng lu hunh (% khi lng) < 0,20 < 0,15

n mn tm ng 1b cc i

Hm lng gm hin hnh 10 mg/cm3

RON 89 92 97 99

Hm lng ch 0,40 g/l

- ng cchun l ng cCFR ni trn

- Hirocacbon chun l:

n-C7H16 c OC = 0 v iso-C8H18 (2,2,4-trimetylpentan) c OC = 100.

Nh vy, mt nhin liu c ch s octan l X, nu trong ng cCFR n gy nn mtting g tng ng vi ting g quan st thy ca mt hn hp gm X phn trm thtch iso-octan v (100 x) phn trm th tch n-heptan.

Ngoi nhng cht lng v bay hi v ch s octan ni trn, mt nhin liu tkhng c cha cc hp cht ca lu hunh c mi hi, cc hp cht c tnh axit n mnthit b cha xng cng nhng c. Xng phi khng c cha gm, v gm c th gynn hiu qu bt nhanh cc l phun v supap. Bng 17 trnh by cc c trng ca xngthng v xng cao cp c s dng Php.

Trong thi gian gn y, quy nh ca xng cao cp b thay i v chp nhn s cmt ca nhng hp cht hu ccha oxi nh CH3OH, C2H5OH, C4H9OH hay cc ete nhMTBE. Ni chung, cc hp cht ny c ch s octan cao (>100) nhng chng c th gy nmn thit b hoc gy trngi cho s phi trn nhin liu nu chng c ln hi nc.

lm tng cht lng ca xng ngi ta c th dng xng crackinh v xngrefominh.

3.2.3.2 Xng crackinh


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Xng crackinh l xng thu c sau qu trnh crackinh mt phn on nht nh cadu th.

Nhng tnh cht ca xng crackinh:

Cc xng crackinh nhit c ch s octan c bit cao hn cc xng chng ct trc tip.Thng thng ch s octan RON ca xng crackinh nhit l 70 80.

Xng crackinh nhit khng bn vng, chng c khuynh hng cho gm pht trintng i mnh trong qu trnh bo qun ti kho vi s c mt ca khng kh. Tuy nhinngi ta tm ra cc phng php lm sch xng hay dng cht km hm to gm cho

php c th dng xng m khng c bt k mt bt tin no i vi t.

Nhng ngi ta khng th, ngay c bng cch tng cng cc bin php x l ho hcbng cc cht km hm, lm cho xng crackinh nhit c mt bn vng s dngchng lm xng my bay. Ngc li, crackinh xc tc cho cc kt qu tho mn hn nhiu,v thc t cc xng crackinh xc tc khng cha nhng hirocacbon ietilenic m chng l

nhng hirocacbon km bn vng nht.Ch s octan RON > 90 ca cc xng crackinh xc tc l do:

- Cc hirocacbon nh ca xng cha mt t l ln cc iso-parafin v iso-olefin.

- Cc hirocacbon nng ca xng c bit giu cc hirocacbon thm. Chng ta bitrng ch s octan ca ba loi hirocacbon ny ln hn nhiu so vi ch s octanca cc parafin mch thng.

Bng 18.Thnh phn ca phn on hexan (C6) thu c t xng ca cng du th nhng c sn xuttheo cc cch khc nhau

Cc parafin trong phn onC6 (%) Xng thu c tchng ct Xng crackinhnhit Xng crackinh xctc

2-metylpentan 32 18 48

3-metylpentan 16 16 27

2,3-imetylbutan 1 3 13

2,2-imetylbutan - - 3

Tng s iso-parafin 49 37 91

n-hexan 51 63 9

Tng 100 100 100

Bng 18 cho thy nhng hirocacbon parafin ca phn on hexan c tch ra t baxng c cng mt ngun gc du th nhng thu c theo ba phng php khc nhau.

Chng ta thy rng cc parafin ca xng crackinh xc tc b phn nhnh hn rt nhiuso vi cc xng khc.

Cn cc phn nng, chng ta s thy thnh phn ca chng trn cc th tronghnh 6 v 7 di y khi x l cng mt nguyn liu u.


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Hnh 6.

Thnh phn ca cc loi hirocacbon thu c trongcrackinh nhit

Hnh 7.Thnh phn ca cc loi hirocacbon thu c trongcrackinh xc tc

3.2.3.3 Xng refominh

nng cao cht lng xng, ngi ta c th dng xng refominh.

- Xng refominh nhitc ch s octan cao hn nhiu so vi xng ct trc tip t duth. Bng 19 di y trnh by cc c trng ca xng refominh nhit ca 2 phnon tng i khc nhau ca cng du th Irc.

Bng 19.c trng xng refominh nhit ca 2 phn on t cng ngun duth Irc

c trng Phn on 1 Phn on 2

im u (C) 90 125

im cui (C) 205 240


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RON ca nguyn liu u 40 32

RON ca phn refominh nh 78 72

RON ca phn refominh nng 71 65

Chng ta thy rng refomat nhit c ch s octan cao hn nhiu so vi ch s octan canguyn liu u.

- Xng refominh xc tc. Qu trnh refominh xc tc cc hirocacbon l mt qutrnh rt phc tp bao gm:

+ ehiro ho cc naphten thnh cc hirocacbon thm;

+ ehiro vng ho cc parafin thnh cc naphten;

+ ng phn ho cc parafin v naphten thnh isoparafin...

Cc qu trnh ny u dn ti cc loi hirocacbon c ch s octan cao. Chnh v th,

cc c trng ca xng refominh xc tc l rt tt cho cc ng ct v my bay. V d,ch s octan RON l 92,5, im chng ct 50% 111C.

3.2.3.4 Xng tng hp tkh

Trong cc nh my lc ho du c cc kh d:

- Loi parafin: CH4, C2H6, C3H8, C4H10 v iso-C4H10

- Loi etilenic: C3H4, C3H6, 1-buten, 2-buten v iso-buten.

y l ngun nguyn liu qu tng hp cc xng c ch s octan cao. Chng ta bitrng cc hirocacbon c tnh khng n cao l cc ng phn phn nhnh, ngha l trongcc phn t ny cha nguyn t cacbon bc ba. S phn nhnh cng nhiu th ch s octan

ca phn t cng cao. Hn na ngi ta cng nhn thy rng bn ca phn t vi s vachm tng ln khi phn t t tp trung li hay di tc dng ca hiu ng phn nhnh.V di vi hirocacbon parafin C7:

- n-heptan: CH3-(CH2)5-CH3 c ch s octan 0 (theo quy c).

- 2-metylhexan : CH3-CH(CH3)-CH2-CH2-CH2-CH3 c ch s octan 45.

- 3-metylhexan: CH3-CH2-CH(CH3)-CH2-CH2-CH3 c ch s octan 65.

Ch s octan tng ln khi cc nhnh tp trung v trung tm ca phn t:

- 3,3-imetylpentan: CH3-CH2-C(CH3)2-CH2-CH3 c ch s octan 94.

- 2,2,3-trimetylbutan (triptan): CH3-C(CH3)2-CH(CH3)-CH3 c ch s octan 105.Triptan c thc s dng trong mt m tm t l nn l khong 15/1.

Lut tng ch s octan ca cc hirocacbon parafin vi s tp trung ca phn t vopha tm ca n l rt tng qut v ta c th thy s thay i hon ton tng ti vi cchirocacbon C6, C8... v nn nhrng nhy hay hiu s gia RON v MON tng lnvi s tp trung ca phn t vo pha tm ca n.

Ni chung, ngi ta nhn thy rng nhng hirocacbon etilenic ring bit c ch soctan cao hn mt cht so vi cc parafin tng ng, trc ht l nhng hirocacbon C8.


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Mt khc, nhy v ch s octan ca hn hp cc hirocacbon etilenic l cao hn nhiuso vi nhy v ch s octan ca hn hp cc parafin c cng s nguyn t cacbon.

Ch s octan ca cc naphten cao hn mt cht so vi ch s octan ca cc parafintng ng nhng nhy ca chng khng cao hn.

Nhng hirocacbon aromat c ch s octan rt cao. nhy ca chng trong hn hpcng rt ln nh ch s octan khi nng ca chng trong hn hp nh. T nhng nhnxt trn y ta s thc hin chuyn ho cc kh thnh cc nhin liu c ch s octan cngcao cng tt. Cc phng php tng hp nh sau:

* Polime ho xc tc (oligome ho)

- Nguyn liu u l cc olefin ni trn.

- Xc tc: axit H3PO4, pyrophotphat ng, quartz tm H3PO4 lng.

- L phn ng c cha cht xc tc c th l mt thng ln hay l nhng ng phn

ng c ng knh tng i nh m ngi ta c th lm lnh chng bng nc.- Nhit phn ng thng thng l 150 220C v chuyn ho ca olefin c

tht ti 85 95% ch qua 1 vng phn ng.

- Tc cung cp olefin c th dng t 0,1 0,5 m3/h tu theo hot ng caxc tc v p sut c thi t 35 bar 70 bar.

trnh s phn hu ca xc tc, gi hot ng lu di ca chng, ngi ta thnga khong 5% nc vo nguyn liu u v lm lnh phn ng, gi nhit phn ng saocho khng vt qu 220C.

Vic polime ho chn lc nh ime ho isobuten hoc ng ime ho isobuten v

buten, tip theo l hiro ho cho ta nhng iso-octan c ch s octan F3 ~ 100. Cc phn ngime ho chn lc ny dn dn c thay th bng ankyl ho c tnh u vit hn.

* Ankyl ho hirocacbon phn nhnh bng olefin nh

Nhng hirocacbon bo ho c cha nguyn t cacbon bc 3 nh isobutan,isopentan... kt hp d dng vi cc hirocacbon etilenic khi c mt ca cc xc tc nhH2SO4, HF.

C2H4 + iso-C4H10 2,2-imetylbutan, RON = 92

C2H4 + iso-C4H10 2,3-imetylbutan, RON = 101

C2H4 + iso-C4H10 2,2,4-trimetylpentan, RON = 100Hai hirocacbon u tin, 2,2-imetylbutan v 2,3-imetylbutan c ch s octan RON

tng ng l 92 v 101, cn 2,2,4-trimetylpentan c RON = 100 theo nh ngha. Nuchng ta dng cc iso-olefin, ta sc cc sn phm sau y:

iso-C4H8 + iso-C4H10 iso-octan RON = 92 94

iso-C5H10 + iso-C4H10 iso-nonan RON = 90 92

C3H6 + iso-C4H10 iso-heptan RON = 89 91


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Trong cng nghip, nu dng H2SO4 lm xc tc cho cc phn ng trn, thng ngita phi quay vng phn ng nhiu ln i vi iso-butan sao cho gic trong l phn ngt l iso-C4H10/olefin = (6 8)/1. Sdphi gi t l ny v olefin b hp th bi axit H2SO4rt d dng. Nu t l ny cng ln th hiu sut s cng cao v vic tiu tn axit H2SO4/1

lt ankylat cng thp.Xc tc H2SO4 nng lc ban u l 98% sau c th kt hp dng H2SO4 s

dng c nng 90%. Thng thng ngi ta dng axit H2SO4 vi nng ban u 98%v vic tiu tn tng cng axit l t 1,5 kg 6,5 kg /1m3 alkylat.

Nu H2SO4 khng th ti sinh c th ngi ta c th dng chng vo mc ch khcnh tinh ch du bi trn. Ankyl ho vi s c mt ca axit H2SO4 l mt phng phpt tin do phi tiu tn nhiu axit.

Vi vic dng axit HF lm xc tc th ngi ta c th thu hi HF cui mi mt vngphn ng nn s tiu tn axit HF gim xung (t 0,8 2,3 kg/m3 ankylat).

3.2.3.5 Xng khng chNh chng ta bit, lm tng ch s octan ca xng, ngi ta dng cc ph gia

nh Pb(C2H5)4, Pb(CH3)4 hay hn hp Pb(C2H5)4 v Pb(CH3)4. Do s pht trin qu nhanhca nn cng nghip t nn vic tiu th xng cng tng rt nhanh. Mt dy c ttrn cc ng ph thi vo khng kh mt lng ch khng nh v gy nn nhimmi trng, gy hi cho sc kho con ngi. V th, vic dng xng khng ch ngy cng

ph bin. Cc nc cng nghip pht trin a ra nhiu lut t hn ch dng xng cch tin ti dng xng khng ch.

Bng 20.Th trng th gii v chu u v vic dng xng khng ch (tnhn thng 6 - 1990)

Cc loi nhin liu khng ch (%)

NcNhin liukhng ch

(%) Thng thng EurosuperSupermium

Nht 100 86 - 14

Canada 92 65 4 23

M 90 60 6 24

o 53 30 23 -

B 30 - 28 2

Phn Lan 50 - 50 -

Php 10,5 - 2 8,5

Italia 4 - 4 -

Luxembourg 21 - 19 2

H Lan 40 - 33 7

an Mch 45 - 45 -

Bo Nha 0,2 - 0,2 -


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Ty Ban Nha 0,5 - 0,5 -

Anh 25 - 21 4

Thy in 42 - 41,5 0,5

Xng khng ch dng chu u chia lm 3 loi:

1 - Mc bnh thng (Regular-grade) c dng ch yu c, c RON t 92 93 v MON t 82 83.

2 - Nhin liu ng cchun dng cho tt c cc nc trong khi cng ng chu uc RON cc tiu l 95, MON cc tiu l 85 (nhng nc khng thuc cng ng chu ucng dng l o, Phn Lan, an Mch, Thuin v Thy S, tnh n nm 1990).

3 - Nhin liu c ch s octan cao RON 98 v MON 88. Cc nc dng xng ny lPhp, H Lan.

Bng 20 gii thiu vic dng nhin liu ng cxng khng ch trn th gii.Ton b chu u dng xng khng pha ch khong 118 triu tn/nm chim khong

26% th trng nhin liu.

Nh trn trnh by, tu thuc vo gi tr RON v MON ngi ta chia xng tthnh cc cp khc nhau v nh th thnh phn ha hc ca chng cng khc nhau vngay xng cng cp (Eurosuper vi RON 95, MON 85) cng c hm lng olefin varomat khc nhau tu thuc vo tng quc gia chu u (bng 21). Bng 22 cho bit hmlng olefin v aromat trong cc xng c cp khc nhau chu u.

Bng 21.Hm lng olefin v aromat ca cc nhin liu khng ch chu u (cp

Eurosuper vi RON 95, MON 85)

Hm lng olefin(%V)

Hm lng aromat(%V)Quc gia

RON 95 MON 85 RON 95 MON 85

Ty c 7,7 22,4 38,9 45,5

Italia 5,9 13,8 35,3 43,4

B 7,4 14,4 36,0 45,0

Anh 6,4 9,0 35,8 43,6

an Mch, Thy in 9,1 18,2 42,1 45,6

Ph gia quan trng v ph bin nht thay th cho cc hp cht cch l MTBE (metyl-tec-butylete). Vic s dng MTBE trong xng khng ch chu u c trnh by trong

bng 23.


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Bng 22.S khc nhau ca cc loi xng khng ch chu u

Kiu xngHm lng olefin trung bnh

(%V)

Hm lng aromat trung bnh

(%V)

Regular (c) 12,1 31,8

Eurosuper (EEC) 7.3 37,6

Superpremium (Php) 5,4 50,1

Ta thy rng MTBE c dng trong tt c cc loi xng. Ngoi MTBE ngi ta cndng cc tc nhn lm tng ch s octan khc l:

- TAME, (Tec-amylmetyl ete).

- Metanol vi hm lng trung bnh ~ 1,2 %.- Tec-butanol hm lng trung bnh ~ 1,4 %.

Ngi ta cng c th kt hp cc ancol ny vi MTBE thm vo thnh phn ca xngkhng ch.

Bng 23.Vic s dng MTBE trong xng khng ch chu u

Hm lng MTBE quan st c (%trng lng)Nc Kiu xng

Phn nhin liucha MTBE

Cc tiu Trung bnh Cc iB Eurosuper 100 0,8 2,1 4,0

Superpremium 64 1,0 6,8 11,4

Eurosuper 42 0,7 1,1 1,6c

Regular 42 0,1 0,5 1,1

Anh Eurosuper 25 - 4,4 -

Italia Eurosuper 50 2,2 4,0 6,2

S c mt ca cc hp cht cha oxi dng nh khng c bt k nh hng g n hpxc tc x l kh thi. Tuy nhin, cc nh sn xut t khng mun c mt khong qurng v nng ca cc cu t cha oxi. Bi v h phi nghin cu nhng thnh phnphn cc c th cho nhin liu t thu c s chy tho mn trong tt c cc trnghp. V d, s khc nhau v t lng lng cc cu t ca xng do s thay i hmlng MTBE c th lm thay i s pht thi cc sn phm cha chy ht (CO v CH)trong giai on u khi hp xc tc cha hot ng.

Ni tm li, xng khng ch l mt t hp phc tp ca cc hirocacbon v cc ph gia.Ph gia tng ch s octan l cc hp cht cha oxi nh MTBE, CH3OH, C2H5OH, (CH3)3C-


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OH, tec-amylmetylete... Thnh phn xng ny c th c thay i nh tu thuc vo kh huv a hnh c th ca tng nc s dng xng.

Cc nh nghin cu cho rng ph gia C2H5OH cho xng c trin vng sng sa nht vC2H5OH khng c hi, v ngi ta c th sn xut c nhng lng rt ln t ngunnguyn liu nng nghip v du m.

3.3 Nhin liu iezen (DO)

Khi chng ct scp du th ta thu c phn on si gia 200C v 320C. Phnon ny c gi l gazoin hay du iezen. Du gazoin thu c t cc sn phmcrackinh nhit v crackinh xc tc rt khc vi gazoin thu c t chng ct trc tip duth do thnh phn ca chng b bin i. Hm lng parafin b gim i do s hnhthnh cc hirocacbon khng bo ho v hirocacbon thm, cht lng n v ch s xetanca du b gim i.

Tn gi du gazoin c ngun gc t vic dng du ny sn xut kh thp sng bngcrackinh v mc du ngy nay ngi ta khng cn dng na nhng tn phn on ny vnc gi nguyn v nhng lng ln du vn c dng sn xut kh t. V mc chny, du gazoin phi c c trng parafin khi crackinh nhit ngi ta thu c hiu sutcao kh c nhit tr ln. Bi vy, du gazoin phi l distillat ct trc tip t du m parafin.

Nhin liu iezen (Diezel fuel) c cng mt khong nhit chng ct (200 320C)nh du gazoin v dnhin chng l cng mt nhin liu nhng c s dng cho ng cnn - n (c gi l ng ciezen) v th chng c gi l nhin liu iezen. Cc ngciezen c rt nhiu dng v tc , s dng mt khong rt rng cc nhin liu t ccdistillat ca du th n cc phn on chng ct du than v cc du thc vt.

3.3.1. Du gazoinV l mt sn phm thu c t chng ct nn du gazoin thay i v thnh phn

tu theo bn cht ca du th nhng mt s tnh cht c trng phi c tho mn l im chp chy, khong nhit chng ct (t 200 320C). Bng di yminh ho mt s tnh cht ca du gazoin khc nhau ty theo khi lng ring cachng.

Bng 24. Thnh phn v tnh cht ca cc du gazoin

T trn 15,5 / 15,5C 0,84 0,88 0,86

im chp chy, C 200 186 186 nht Redwood 37,7C 35 33 37

Nhit khon si th nht, C 220 200 210

% chn ct ti 300C 65 34 47

Ch s xetan 62 34 47

Cn cacbon Conradson (% trng lng) 0,02 0,07 0,02

im rt, C 4 9 12


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Cng dng chnh ca du gazoin l dng sn xut kh t v tch benzen t khthan (coal gas), nhng du gazoin c thc dng lm nhin liu cho ng ciezen tuthuc vo ch s xetan ca n. Nu ch s xetan cao th n rt thch hp cho cc ng ciezen cnh v tc cao. Nu nht ca du gazoin cao th khng thch hp cho cc

ng ciezen chy ng bin, trong cng nghip c tc thp v vic bm nhin liukh khn.

3.3.2. Nhin liu iezen v ng ciezen

Nhng tnh cht ca nhin liu iezen c gii thch tt nht sau khi nghin cu ccc trng ca ng cnn-n - ng ciezen. Sng cnn-niezen c chotrn hnh 7.

Hnh 7Sng c nn-niezen

Nguyn l c bn ca ng c ny l da trn nhit nn lm bc chy nhin liu.Nhin liu c tim vo bung nn m khng kh c nn ti 1 p lc t 41,5 -45,5 kg/cm2 v t ti nhit t nht l 500C. Nhit ny lm bc chy nhinliu v kh dn nlm tng p lc ln ti trn 70 kg/cm2. p lc ny tc ng ln pittong

v lm ng cchuyn ng. Trong ng cnn-n 4 k bnh thng, 1 vng c th chiathnh 4 k:

1. Ht khng kh vo xilanh, sau van vo ng li.

2. Nn khng kh trong xilanh ti mt th tch xc nh (trong k nn ny p sut vnhit tng ln), khi nhin liu iezen c phun vo bung nn.

3. Nhin liu chy. Kh chy dn n trong khi tt c cc van ng, p lc tc ngln u pittong lm my chuyn ng.


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4. Van x mv kh chy c thi ra ngoi bung nn. K ny hon thnh 1 vngca ng cv vng tip theo c bt u vi vic ng van x. Nh vy c 1k sinh cng v 3 k khng ti cho hai chuyn ng ca tay quay.

Trong ng c2 k khng kh b nn nh trn, nhng ngay gn u k sinh cng, vanx m ra v xilanh c qut bng khng kh sch t 1 my bm sao cho k tr li nnkhng kh sch. Nn khng kh sch l cn thit t hiu qu ca tay quay v ng clm vic mnh hn v m hn so vi ng cbn k c cng cv tc .

Nhng thun li ch yu ca ng ciezen l s gn gng ca ng c, sch s vhiu qu nhit cao, c th k ra nh sau:

1. Vi mc ch hng hi, ng ciezen chim ch t hn so vi ng chi ncc cng cng sut nng lng.

2. N khng tiu tn nc v nc lm lnh c th quay vng.

3. Vi mc ch chy ng b, h thng tim nhin liu ca ng ciezen hiuqu hn ng cxng v tiu tn nhin liu ch vo khong mt na cho cngmt cung ng.

4. ng cc th xut pht trong iu kin lnh v c tht c cng sut hunh ngay thc thi, mt thun li rt ln so vi bt k ng chi nc no.

5. c kt hp vi vic sn xut in th ng ciezen hiu qu hn bt k ngcno khc cung cp nng lng cho vic s dng trung gian.

6. ng ciezen lm vic vi hiu sut nhit cao khong 30 35%.

Nh trn trnh by, trong chu trnh lm vic ca ng ciezen, nhin liu t bcchy trong iu kin nhit v p sut ti hn, khng cn mi la t bugi. V th tnhcht quan trng ca nhin liu iezen l cht lng chy ca n. u tin, nhin liu phic kh nng d dng chy nhit nn thp m bo s chy, thm ch khi xut

pht iu kin nhit thp. Th hai, thi gian gia khi tim nhin liu vo xilanh vchy phi khng c qu di hay qu nhiu du trong xilanh khi s chy xy ra v nhth p sut cao khng cn bng s sinh ra v ng chot ng khng tt.

Bi vy, cht lng chy ca nhin liu iezen phi c o bng nhit chy tcthi v bng cc php thng cc ch to c bit thu c cc gi tr si vis tr chy.

Nhit chy tc thi (SIT - Spontaneous Ignition Temperature) lin quan rt nhiun hm lng hiro ca du v ng thi n c xem nh php o s tin li ca vicdng nhin liu iezen. Mt phng php chun l im chp chy trong kh quyn oxic xc nh bng cch nh tng git du vo mt ci cc kim loi c t nng lintc.

Mt gi tr nhit thp ca s t bc chy trong oxi c xem l thun tin cho vicdng du . Php th ny ch l mt ch dn rt chung cho s tin li ca vic dng nhinliu iezen.

Gi tr SIT ca xng t (OC 75) l khong 500C, ca du iezen (ch s xetan 50) l260C v ca octan l 235C.


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Phng php tt nht nh gi cht lng nhin liu iezen l th trong ng c,nhng mt phng php th gn ng c th thu c l xc nh t l parafin trong nhinliu iezen.

Trong trng hp cc nhin liu i t du m th hm lng parafin cng cao th chtlng chy cng tt. iu ny khng phi lun ng vi cc nh

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