giao trinh san pham dau mo thuong pham
DESCRIPTION
các sản phẩm dầu mỏ_hóa dầu.TRANSCRIPT
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Sn Phm Du M Thng Phm
Chng I NHIN LIU CHO NG C XNG
1.1. Gii thiu chung v nhin liu cho ng c xng
Nhin liu dng cho ng c xng c gi l xng, y l mt hn hp cha
nhiu cc hp cht khc nhau. Khi nghin cu v thnh phn ho hc ca du m,
phn on du m ni chung hay ca xng thng phm ni ring ngi ta thng
chia thnh phn ca n thnh hai nhm cht ch yu l cc hp cht hydrocacbon
v cc hp cht phi hydrocacbon.
Nhin liu cho ng c xng l mt sn phm quan trng ca nh my lc du,
n tr thnh mt mt hng quen thuc trong i sng sinh hot hng ngy ca con
ngi cng nh hot ng sn xut trong cng nghip.
ng c xng ra i sm hn ng c Diesel (c pht minh ra ng thi
Php v c vo khong 1860), n pht trin mnh m t sau nhng nm 50 ca
th k trc. Vi nn cng nghip ch to t hin i nh ngy nay cho ra i
nhiu chng loi vi cng sut khc nhau v c p dng trong nhiu lnh vc ca
i sng sn xut v sinh hot ca con ngi.
Cng vi s gia tng v s lng ng c xng, nhu cu v xng nhin liu
ngy cng tng nhanh, iu ny mang n cho cc nh sn xut nhin liu nhng c
hi v c nhng thch thc mi, bi trong thc t, bn cnh nhng li ch m ng c
ny mang li cho con ngi th ng thi n cng thi ra mi trng mt lng ln
cc cht c hi lm nh hng n sc kho v c mi trng sinh thi.
V vy xng thng phm bt buc phi bo m c cc yu cu khng
nhng lin quan n qu trnh chy trong ng c, hiu sut nhit m cn phi bo
m cc yu cu v bo v mi trng.
Thng thng xng thng phm cn t c cc yu cu c bn nh sau:
Khi ng tt khi ang nhit thp. ng c hot ng khng b kch n.
ThS. Trng Hu Tr Trang 1
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Sn Phm Du M Thng Phm
Khng kt ta, to bng trong bnh cha v c trong b ch ho kh. Khng to nt hi trong h thng cung cp nhin liu. Du bi trn b pha long bi xng l t nht. Tr s octan t b thay i khi thay i tc ng c. Cc cht c hi thi ra mi trng cng t cng tt. Xng nhin liu thu nhn c trong cc nh my lc du, ban u ch t phn
xng chng ct kh quyn, tuy nhin hiu sut thu xng t qu trnh ny rt thp ch
vo khong 15% khi lng du th ban u.
Khi nhu cu v xng tng ln th phn on ny khng cung cp cho cc nhu
cu thc t, v vy bt buc con ngi phi ch bin cc phn thu khc nhm thu hi
xng vi hiu sut cao hn, iu ny lm xut hin cc phn xng khc nh phn
xng crckinh, alkyl ho . . .
Ngoi l do va nu trn th do yu cu v hiu sut ca ng c ngy cng tng
v cht lng xng ngy cng cao nn cc nh sn xut nhin liu phi a ra nhiu
qu trnh sn xut khc nhm m bo cc yu cu ca xng thng phm.
Thc t trong cc nh my lc du hin nay xng thng phm c phi trn t
nhng ngun sau:
Xng ca qu trnh FCC Reformat Xng chng ct trc tip Xng ca qu trnh isomer ho Alkylat Xng ca qu trnh gim nht, cc ho, cc qu trnh x l bng hydro Xng thu c t cc qu trnh tng hp nh Methanol, Ethanol, MBTE.
Ni chung hai loi u tin l cc ngun chnh phi trn, phn cn li ph
thuc vo yu cu v cht lng ca xng v yu cu ca tng Quc gia m ngun
nguyn liu v hm lng ca n c chn khc nhau.
ThS. Trng Hu Tr Trang 2
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Sn Phm Du M Thng Phm
V d:
- T l ca cc ngun phi trn xng thng phm M (trc nm 2000)
34,7
4
4,7131,8
5,6
36,2ReformatNaphta nh?IsomerisatAlkylat/PolymerisatEtherButanXng FCC
- T l ca cc ngun phi trn xng thng phm Ty u (trc nm 2000)
49,6
7,655,9
1,8
5,7
27,1ReformatNaphta nh?IsomerisatAlkylat/PolymerisatEtherButanXng FCC
- T l phi trn Php t nm 2000
Reformat 35% < < 45% Butan 5% Xng FCC 15% < < 25% Xng isomer ho 0% < < 15% Alkylat 0% < < 20% MTBE 0% < < 5% (trng hp c bit
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Sn Phm Du M Thng Phm
1.2. Thnh phn ho hc ca nhin liu xng
1.2.1. Gii thiu chung v thnh phn ho hc ca xng
Nh phn trn va nu, xng thng phm khng phi l sn phm ca mt qu
trnh no trong nh my lc du m n l mt hn hp c phi trn cn thn t
mt s ngun khc nhau, kt hp vi mt s ph gia nhm m bo cc yu cu hot
ng ca ng c trong nhng iu kin vn hnh thc t v c trong cc iu kin
vn chuyn, tn cha v bo qun khc nhau.
Thnh phn ho hc chnh ca xng l cc hydrocacbon c s nguyn t t C4 C10 thm ch c c cc hydrocacbon nng hn nh C11, C12 v c C13. Ngoi ra trong
thnh phn ho hc ca xng cn cha mt hm lng nh cc hp cht phi
hydrocacbon ca lu hunh, nit v oxy.
Vi s nguyn t cacbon nh trn, trong thnh phn ca xng cha y c
ba h hydrocacbon v hu nh cc cht i din cho cc h ny u tm thy trong
xng.
Mc d trong thnh phn ca du m ban u khng c cc hp cht khng no
nh lfin nhng trong qu trnh ch bin xy ra qu trnh ct mch hnh thnh nn
cc hp cht i ny, do trong thnh phn ho hc ca xng thng phm cn c
mt cc hp cht i.
ThS. Trng Hu Tr Trang 4
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Sn Phm Du M Thng Phm
S phn b cc cu t theo s nguyn t cacbon v theo h hydrocacbon ca
mt loi xng super thng phm.
Thnh phn tnh theo khi lng S nguyn
t cacbon Parafin % Naphten% Olefin% Diolefin% Aromatic% Tng %
4 1.46 0 0.59 0. 0 2.05
5 11.64 0.18 3.16 0.06 0 15.04
6 12.27 1.03 2.09 0.06 2.22 17.67
7 11.52 1.41 1.40 0 12.84 27.17
8 4.26 0.05 0.12 0 16.70 21.13
9 0.65 0 0 0 10.76 11.41
10 0 0 0 0 3.08 3.08
11 0 0 0 0 0.19 0.19
Tng 41.8.0 2.67 7.36 0.12 45.79 97.74
Cc cu t khng xc nh chim 2.26%
Cc gi tr c cung cp bi IFP
ThS. Trng Hu Tr Trang 5
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Sn Phm Du M Thng Phm
S phn b cc cu t theo s nguyn t cacbon v theo h hydrocacbon ca
mt loi xng thng thng phm.
Thnh phn tnh theo khi lng S
nguyn t
cacbon N-parafin
%
Isoparafin
%
Naphten
%
Olefin
%
Aromatic
%
Hp cht
cha oxy %
Tng
%
4 5.14 0.3 0 1.49 0 0 6.93
5 1.26 7.84 0 10.11 0 0.5 19.71
6 0.64 6.34 1.19 5.07 1.23 3 17.47
7 0.65 3.22 1.05 1.56 8.11 0 14.59
8 0.48 11.47 0.43 0.34 13.61 0 26.33
9 0.11 1.12 0.16 0.07 9.49 0 10.95
10 0.01 0.09 0.09 0.02 2.80 0 3.01
11 0 0.1 0 0 0.25 0 0.35
12 0 0.61 0 0 0 0 0.61
13 0 0.01 0 0 0 0 0.01
Tng 8.29 31.1 2.92 35.49 18.66 3.5 99.96
Cc cu t khng xc nh chim 0.4%
Cc gi tr c cung cp bi IFP
ThS. Trng Hu Tr Trang 6
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Sn Phm Du M Thng Phm
1.2.2. Thnh phn ho hc ca xng
Khi nghin cu v thnh phn ho hc ca du m cng nh cc phn on hay
sn phm ca n th ngi ta thng chia thnh phn chng ra lm hai phn chnh l
hydrocacbon v phi hydrocacbon.
1.2.2.1. Thnh phn hydrocacbon ca xng
H parafinic
Cng thc ha hc chung l CnH2n+2, bao gm cc cht c s nguyn t nh
nu trn, chng tn ti di 2 dng: mch thng (n-parafin) v mch phn nhnh (i-
parafin), vi cc isoparaffin th mch chnh di, mch nhnh ngn, ch yu l gc
metyl.
Olefin
Cc hydrocacbon olefine c cng thc chung l CnH2n, c to thnh t cc
qu trnh chuyn ha, c bit l qu trnh cracking, gim nht, cc ho . . . Cc
olefine ny cng bao gmhai loi n-parafin v iso-parafin.
H naphtenic
Hydrocacbon naphtenic l cc hydrocacbon mch vng no vi cng thc chung
l: CnH2n v cc vng ny thng 5 hoc 6 cnh, cc vng c th c nhnh hoc khng
c nhnh, hm lng ca h ny chim mt s lng tng i ln, trong cc hp
cht ng u dy thng t hn cc ng ng ca n, nhng ng phn ny thng
c nhiu nhnh v nhnh li rt ngn ch yu l gc metyl (-CH3)
H aromatic
Cc hp cht ny trong xng thng chim mt hm lng nh nht trong ba
h v cc hp cht u dy cng t hn cc hp cht ng ng ca n.
1.2.2.2. Thnh phn phi hydrocacbon ca xng
Trong xng, ngoi cc hp cht hydrocacbon k trn cn c cc hp cht phi
hydrocacbon nh cc hp cht ca O2, N2, S. Trong cc hp cht ny th ngi ta
quan tm nhiu n cc hp cht ca lu hunh v tnh n mn v nhim mi trng.
ThS. Trng Hu Tr Trang 7
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Sn Phm Du M Thng Phm
Trong xng, S ch yu tn ti ch yu dng mercaptan (RSH), hm lng ca
n ph thuc vo ngun gc ca du th c cha t hay nhiu lu hunh v hiu qu
qu trnh x l HDS.
Cc hp cht ca cc nguyn t khc c hm lng ch yu dng vt, trong
nit tn ti ch yu dng pyridin cn cc hp cht ca oxy th rt t v chng
thng dng phenol v ng ng.
1.3. c im ca cc ngun dng phi trn xng
1.3.1. Xng ca qu trnh reforminh xc tc.
Xng thu c ca qu trnh reforming xc tc c gi l reformat. y l
ngun nguyn liu chnh phi trn to xng c cht lng cao, chng c cha mt
hm lng cc hp cht aromatic cao nn ch s octan ca no cao (RON = 95- 102).
1.3.2. Xng cracking xc tc:
y l ngun cho xng ln nht trong nh my lc du. Tr s octane ca xng
ny khong 87- 92 tu theo iu kin cng ngh. Thnh phn ha hc cha ti 9- 13%
hydrocacbon olefine. S c mt ca ca cc olefine ny chnh l nguyn nhn lm mt
tnh n nh ca xng.
1.3.3. Xng chng ct trc tip:
Phn xng chng ct p sut kh quyn l mt phn xng quan trng nht
trong nh my lc du c nhim v phn chia du th thnh nhiu phn on khc
nhau. Phn hi thu c nh sau khi n nh ta s thu c xng. Loi xng chng
ct trc tip ny c ch s octan thp khong 54- 65 nn ch dng mt lng t phi
trn cn phn chnh c phn chia thnh xng nh (ch yu C5 v C6) v xng nng.
Phn xng nh thng lm nguyn liu cho qu trnh isomer ho cn phn xng nng
lm nguyn liu cho qu trnh reforming xc tc.
1.3.4. Alkylat
Trong cng ngh lc ha du ngi ta s dng qu trnh alkyl ha sn sut
xng c tr s octane cao. Ngy nay qu trnh alkyl ha c s dng ph bin cc
nc trn th gii. Vi qu trnh ny, ngi ta to ra mt ngun phi liu c tr s
ThS. Trng Hu Tr Trang 8
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Sn Phm Du M Thng Phm
octane cao hu nh khng c tp cht v cc hp cht aromatic p ng yu cu sn
sut xng sch bo m cc yu cu v ng c v mi trng.
1.3.5. Cc ngun phi liu khc
Ngoi cc ngun chnh trn th xng cn c phi liu t cc ngun khc nh:
xng gim nht, xng cc ha ... y l cc sn phm ph ca cc qu trnh.
c im ca xng ny l hm lng cc hp cht phi hydrocacbon ln, xng
km n nh v cha lng ln cc hp cht khng no.
Cng cc loi xng trn th ngy nay khi yu cu v vic gim cc cht gy
nhim mi trng trong khi thi ca ng c cng kht khe th vic dng cc cu t
c tng hp t cc phn ng ho hc c tr s octane cao nh: MTBE, TAME,
methanol, ethanol.. phi trn xng thng phm cng ang c p dng rng ri.
ThS. Trng Hu Tr Trang 9
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Sn Phm Du M Thng Phm
1.4. Nguyn tc hot ng v c im ca ng c xng
1.4.1. Nguyn tc hot ng ca ng c xng
ThS. Trng Hu Tr Trang 10
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Sn Phm Du M Thng Phm
ng c xng l mt ng c nhit dng bin nng lng ho hc ca nhin
liu khi b t chy thnh nng lng c hc di dng chuyn ng quay. ng c
ny lm vic theo nguyn tc mt chu trnh gm bn giai on: np, nn, chy n v
gin n sinh cng, thi kh chy ra ngoi. S nguyn l nh sau:
Hnh trnh 1-K np.
Piston i t im cht trn (CT) xung im cht di (CD), xupap np m,
xupap thi ng, trc khuu quay t v tr 0 = 0 n 1800. Trong k np tiu tn cng ko piston xung, th tch xi lanh tng ln, p sut trong xi lanh gim xung to s
chnh lch p sut, do xng v khng kh t b ch ho kh c ht vo trong xi
lanh. tng lng kk np trong mi chu k th khi piston i t CT xung, xupap
np c m sm trc CT mt gc 1= 10450 v ng mun sau CD mt gc 2 = 40-800. V vy, qu trnh np trn th cng l: I-a-II, c tin hnh trong phm vi gc quay trc khuu l 1 + 1800 + 2.
ThS. Trng Hu Tr Trang 11
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Sn Phm Du M Thng Phm
th cng v th phi kh
Hnh trnh 2-K nn
Piston i t CD n CT, c hai xupap np v thi u ng, trc khuu quay
t v tr 1800 3600. Trong k nn tiu tn cng piston i ln nn hn hp, th tch xi lanh gim trong iu kin hai van ng nn p sut hn hp nhin liu trong xi lanh
tng ln. chun b cho qu trnh chy c tt th gn cui qu trnh nn Bugi bt
tia la in sm trc CT, ti im c'. Do vy, qu trnh nn trn th cng l t
im II - c'.
Hnh trnh 3 - chy - gin n (k cng tc)
Piston i t CT n CD, c hai xupap u ng, trc khuu i t v tr = 3600 n 5400. Trong hnh trnh ny, nh qu trnh chy lm tng p lc trong bung
chy v p lc ny y piston i xung v sinh cng, n bao gm hai qu trnh: chy
v gin n. Qu trnh chy bt u ti im c' trc CT mt gc nh la sm = 1 = 10-300 v kt thc ti im d sau CT, cn qu trnh gin n bt u t im d v
kt thc ti III.
Hnh trnh 4 - thi kh chy ra ngoi
ThS. Trng Hu Tr Trang 12
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Sn Phm Du M Thng Phm
Piston i t CD n CT, xupap thi m, xupap np ng, trc khuu quay t
v tr = 5400 n 7200. Trong k thi tiu tn cng a piston i ln v y sn vt chy ra ngoi. Xupap thi c m sm ti im III trc CD mt gc 3, nu 3 qu ln s tng tn tht cng gin n k chy. qu trnh thi trit cc sn vt
chy ra ngoi, xupap thi ng mun sau CT mt gc 4, ti im IV. Qu trnh thi c biu din trn th cng l III-b-IV, c tin hnh trong phm vi gc quay
trc khuu l 3+1800+ 4, cn on I-r-IV gi l on trng ip, tc c hai van np v thi u m.
Nh vy, ton b chu trnh cng tc c thc hin theo bn hnh trnh trong
hai vng quay ca trc khuu, trong bn hnh trnh ny ch c mt hnh trnh chy v
gin n l sinh cng, cn ba hnh trnh khc th phi tiu tn cng.
1.4.2. c im ca qu trnh hot ng trong ng c xng
T vic phn tch hot ng ca ng c xng trn ta rt ra c nhng c
im ca ng c ny nh sau:
Nhin liu trc khi np vo xylanh n c phi trn vi khng kh to hn hp chy, nh vy bay hi ca xng trong bung chy khng phi l vn
ln nh hng n cht lng ca qu trnh chy.
Qu trnh chy ca nhin liu ch c thc hin khi bugie bt la hoc khi mng la lan truyn n.
Khi bugie bt la th qu trnh chy bt u, lc ny hn hp trong bung chy c chia thnh hai phn: Phn th nht l kh chy, phn th hai l hn hp
ca khng kh v nhin liu cha chy (hn hp cng tc), trong iu kin nhit
v p sut cao vi s c mt ca oxy khng kh th cc hydrocacbon ca
nhin liu s b bin i mt cch su sc, c th l chng s b oxy ho to
thnh cc hp cht c kh nng t bc chy khi mt la cha lan truyn n.
Trong trng hp ny, nu nh phn nhin liu t bc chy nhiu th n s lm
tng p sut trong bung chy mt cch t ngt v gy ra nhng sng xung
kch va p vo piston, xylanh to ra nhng ting g kim loi. Hin tng ny
c gi l hin tng chy kch n.
ThS. Trng Hu Tr Trang 13
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Sn Phm Du M Thng Phm
1.5. Ch tiu cht lng ca xng
Ngy nay ng c tr thnh mt b phn quan trng trong i sng sn xut
v sinh hot ca con ngi. Bn cnh nhng li ch to ln m chng mang li th ng
c cng ng thi thi mt lng rt ln cht c hi ra mi trng gy nh hng
n sc kho con ngi v nh hng xu n mi trng sinh thi. V vy, cn thit
phi t ra nhng quy nh nhm hn ch vic thi cc c hi v thc hin cc quy
nh ny mt cch nghim tc.
gc ca nhin liu th cn phi t ra cho xng thng phm nhng ch
tiu nhm bo m c cht lng i vi ngi s dng v hn ch c lng cht
c hi trong khi thi.
1.5.1. Hin tng kch n v ch s octan
1.5.1.1. Hin tng kch n
Nh va nu trong phn trc, khi bugie bt la th qu trnh chy ca nhin
liu trong bung chy mi c bt u ti bugie cn phn nhin liu nm v tr
khc ch c chy khi mng la lan truyn n. Tuy nhin trong thc t c mt phn
nhin liu trong bung chy b oxy ho dn n qu trnh t bt chy kh mng la
cha lan truyn n. Nu nh phn nhin liu t bt chy ny ln lm tng nhit
v p sut trong bung chy mt cch t ngt v to ra nhng sng xung kch va
p vo piston, xylanh to ra nhng ting g kim loi th qu trnh chy ny c gi
l chy kch n.
Nh vy, trong bung chy lun tn ti mt s cnh tranh gia qu trnh chy
do mng la lan n (chy cng bc) v qu trnh t bc chy, qu trnh chy no
chim u th l ph thuc vo nhiu yu t khc nhau.
Bng thc nghim ngi ta xc nh c thi gian ca qu trnh t bc
chy theo cng thc sau:
D = A P-nEXP(B/T)
Trong : A,B l cc hng s thc nghim.
ThS. Trng Hu Tr Trang 14
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Sn Phm Du M Thng Phm
Cc thng s nh hng ln thi gian t bc chy bao gm:
T s nn H s y Gc nh la sm Nhit v p sut vo bung chy giu Nhin liu Nhin liu nh hng ln qu trnh chy kch n ny c th hin thng qua mt
khi nim gi l ch s octan
1.5.1.2. Bn cht ca hin tng chy kch n trong ng c xng
Qua phn tch trn cho thy qu trnh chy trong ng c xng c th l bnh
thng, c th l kch n chng ph thuc vo bn cht ca nhin liu, kt cu v iu
kin vn hnh ca ng c.
Qu trnh chy c gi l bnh thng khi mt la lan truyn u n vi vn
tc trong khong 15 40 m/s. Cn khi vn tc lan truyn ca mt la qu ln khong 300 m/s th qu trnh chy trong xylanh xy ra gn nh tc thi km theo nhng ting
g kim loi nh va nu trn th c gi l chy kch n.
Bn cht ca hin tng kch n rt phc tp, c nhiu quan im gii thch
khc nhau song bn cht ca n l do cc hp cht hydrocacbon trong nhin liu nm
trc mt la chu mt in kin rt khc nghit nn chng b bin i ho hc mt
cch su sc to ra nhng hp cht mi c kh nng t bng chy. C th trong
iu kin nhit v p sut cao ca bung chy th cc hydrocacbon km bn oxy
ho nh paraffin d dng b oxy ho to ra cc hp cht cha oxy nh peroxyt,
hydroperoxyt, ru, xeton, axt . . . trong s cc hp cht ny th ng ch nht l
cc hp cht peroxyt, hydroperoxyt y l nhng hp cht km bn d b phn hu to
ra cc gc t do sinh ra cc phn ng chui dn n s t bc chy.
Khi nghin cu v hin ny ngi ta i n kt lun v kh nng chng li
s t bc chy ca cc hydrocacbon tng dn nh sau:
ThS. Trng Hu Tr Trang 15
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Sn Phm Du M Thng Phm
Parafin mch thng < naphten < olefin mch thng < naphten mch nhnh khng no < parafin mch nhnh < aromatic. 1.5.1.3. nh hng ca hin tng kch n ln ng c
Hng join lt gia np v thn my Lm xi mn piston v np Lm v cordons ca piston v xecmng Lm nng chy cc b piston v xupap Ngoi nhng nh hng k trn th qu trnh chy kch n thng km theo vic
thi nhiu cht c hi ra mi trng, lm nng my nhanh chng nn lm gim nhanh
tui th ca ng c.
1.5.1.4. Ch s octan
Ch s octan l mt i lng quy c c trng cho kh nng chng li s
kch n ca xng, gi tr ca n c tnh bng phn trm th tch ca iso-octan
(2,2,4-trimetylpentan) trong hn hp ca n vi n-heptan khi m hn hp ny c kh
nng chng kch n tng ng vi kh nng chng kch n ca xng ang kho st.
Trong hn hp ny th iso-octan c kh nng chng kch n tt, c quy c bng
100, ngc li n-heptan c kh nng chng kch n km v c quy c bng 0.
Trong trng hp tr s octan ln hn 100 th xc nh tr s octan ngi ta
cho thm vo xng mt hm lng Tetraetyl ch ri tin hnh o. Tr s octan c
tnh theo cng thc sau:
IO = 100 + ( ) 2/12435216.0472.11736.01 28.28 TTT T+++ Trong T l hm lng Tetraetyl ch ml
Cc yu t lin quan n ng c nh hng n ch s octan bao gm:
T s nn H s y Gc nh la sm
ThS. Trng Hu Tr Trang 16
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Sn Phm Du M Thng Phm
Nhit v p sut vo giu
1.5.1.5. ngha ca ch s octan
Tr s octan l mt ch tiu rt quan trng ca xng khi dng xng c tr s
octan thp hn so vi quy nh ca nh ch to th s gy ra hin tng kch n lm
gim cng sut ca ng c, nng my, gy mi mn cc chi tit my, to khi en
gy nhim mi trng. Ngc li nu dng xng c tr s octan cao qu s gy lng
ph. iu quan trng l phi dng xng ng theo yu cu ca nh ch to, c th l
theo ng t s nn ca ng c, khi t s nn ln th yu cu tr s octan ln v
ngc li.
1.5.1.6. Cc phng php o ch s octan
Thng thng th ch s octan c o theo hai phng php nh sau:
Phng php nghin cu (RON) o theo tiu chun ASTM D 2700 Phng php m t (MON) o theo tiu chun ASTM D 2699
C hai phng php ny u c o trn cng mt ng c CFR (Cooperative Fuel Research). y l ng c c mt xylanh c cc thng s nh sau:
ng knh xylanh: 82.55 mm Khong chy piston: 114.30 mm Th tch xylanh: 661 cm3
T s nn: 4 18 Vn tc quay khi th nghim l c nh giu iu chnh c
pht hin ra hin tng kch n c th dng cc thit b sau:
+ Capteur t
+ Theo tnh hiu
+ Theo cng m thanh.
ThS. Trng Hu Tr Trang 17
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Sn Phm Du M Thng Phm
iu kin o ca hai phng php ny nh sau:
Cc thng s lm vic RON MON
Tc quay Gc nh la sm trc khuu Nhit ca khng kh ht vo oC Nhit ca hn hp nhin liu oc
600 13 48 -
900
14 16 38 149
Cng mt loi nhin liu th RON thng ln hn MON, chnh lch ca hai
phng php ny c gi l nhy ca xng, nhy cng thp cng tt. Paraffin
c nhy thp cn aromatic c nhy cao. Gi tr ca MON cho php d on kh
nng chng kch n ch vng quay ln cn RON th cho php d on ch
vng quay nh.
Trong hai phng php o trn th tc vng quay khng i v ng c ch
c mt xylanh, nhng cc ng c trong thc t lun c s xylanh ln hn mt v khi
ng c chy trn ng th vn tc ca n lun thay i tc l ch vng quay thay
i. Do RON v MON thng khng nh gi ng kh nng chng kch n thc
ca xng khi ng c hot ng.
C hai phng php trn u cho ch s octan vi mt tc ng c nht nh,
tuy nhin trong thc t th ng c lun hot ng vi nhng tc khc nhau, do
RON v MON khng nh gi ht c kh nng chng kch n ca xng trong thc
t.
chnh xc hn ngi ta cn dng khi nim ch s octan trn ng, k hiu
IOR. Ch s octan ny cng c o trn ng c nu trn nhng iu kin o khc
v iu ng ch l vn tc quay ca trc khuu s thay i theo qu trnh o. Gi tr
ca IOR c th cao hn hoc thp hn RON.
Tr s octan trn ng c xc nh theo cng thc
IOR = RON S2/a
Trong : S nhy, S = RON MON
:a h s t 4.6 6.2 ph thuc vo t s nn ca ng c
ThS. Trng Hu Tr Trang 18
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Sn Phm Du M Thng Phm
Mt khc do xng cha nhiu thnh phn c s khc bit kh ln v kh nng
chng kch n. Thng thng th phn c nhit si thp (ngoi tr izo pentan,
benzen) c ch s octan thp, do trong mt s ch lm vic ca ng c c th
xy ra s chia tch xng trong ng c, dn n trong mt thi im nht nh no
lng nhin liu c np vo xylanh cha nhiu thnh phn nh, bc hi nhanh
nhng ch s octan li thp do d dn n qu trnh chy kch n trong mt s chu
k nht nh. V vy, ngoi ba loi trn th ngi ta cn o ch s octan ca phn ct
c nhit si n 100oC v c k hiu R-100, gi tr ca n lun nh hn RON v
chnh lch ny c gi l RON 1.5.1.7. Cc bin php lm tng ch s octan
Nh trong phn trc ta thy ch s octan ca xng chng ct trc tip rt
thp, s lng t khng m bo c v cht lng cng nh s lng. V vy ngi
ta cn c cc phng php nhm tng s lng v cht lng ca xng. Cc phng
php ny c phn thnh ba loi nh sau:
Phng php ho hc
Thc hin cc phn ng ho hc bin i cu trc ca nguyn liu xng ban
u nh RC, FCC, Alkyl ho, Isomer ho . . . phng php ny c dng rng ri v
chim i b phn xng thng phm.
Dng ph gia
Phng php ny dng ho cht lm tng ch s octan nh nc ch. Phng
php ny ngy nay gn nh b cm bi s c hi do ch gy ra.
Phng php dng cc cu t c ch s octan cao
Phng php ny dng cc cu t c ch s octan cao pha trn vo xng nh
MBTE, EBTE, Methanol, Ethanol . . . phng php ny ngy nay c khuyn khch
dng nhiu bi nhng u im v mt bo v mi trng.
ThS. Trng Hu Tr Trang 19
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Sn Phm Du M Thng Phm
1.5.2. T trng
T trng ca mt cht lng l t s gia khi lng ring cht so vi khi
lng ring ca nc c o trong nhng iu kin nhit xc nh. Nh vy t
trng l mt i lng khng c th nguyn.
Ngi ta thng k hiu l t1t2, trong t1 l nhit m ti ngi ta xc nh khi lng ring ca nc, tng t nh vy t2 l nhit m ti ngi ta o
khi lng ring ca cht cn o.
Trong thc t ta thng gp 420, 415, 15.615.6, i vi du m v cc sn phm ca n th trong tnh ton ngi ta thng dng t trng chun 15.615.6.
M v mt s nc khc ngi ta cn biu th t trong thng qua mt i
lng khc gi l API v gi tr ca n c xc nh thn qua t trng chun nh
sau:
oAPI = 6.156.15
5.141 - 131.5
C nhiu phng php xc nh t trng, nhng thng thng n c xc
nh theo 3 phng php sau:
Phng php dng picnomet Phng php dng ph k Phng php dng cn thu tnh. Theo tiu chun ca chu u th gi tr ny nm trong khong 720 n 775 kg/m3.
i vi xng th vic xc nh t trng khng c nhiu ngha nh i vi du th
hay Diesel hoc mt sn phm khc, tuy nhin n cng c nhng ngha nht nh
trong vic iu khin giu khi bt u khi ng ng c, nh hng trc tip ln
nhit chy th tch do nh hng ln s tiu th ring ca nhin liu, c th khi t
trng tng ln th sut tiu th ring gim xung.
1.5.3. Cc ch tiu ln quan n bay hi
Nh chng ta u bit xng thng phm l mt hn hp ca nhiu cc hp
cht hydrocacbon c nhit si thay i trong khong rng. Thc t, trong khong
ThS. Trng Hu Tr Trang 20
-
Sn Phm Du M Thng Phm
phn on ca n th nhit no cng c nhng hydrocacbon bay hi, nhng mt
nhit nht nh th cng bay hi ca cc cu khc nhau l khng ging nhau.
Tnh cht bay hi ca xng c ngha rt ln trong qu trnh bo qun, vn chuyn
cng nh trong qu trnh s dng. V vy bay hi ca xng l mt tnh cht ht sc
quan trng. Tnh bay hi ny c c trng bng nhng tnh cht nh: Thnh phn
ct, p sut hi bo ho, im cht chy. Nh n m ta c th nh gi s b v thnh
phn, s phn b ca cc cu t trong xng, kh nng bay hi gy mt mt v mc
an ton trong qu trnh vn chuyn cng nh bo qun v s dng.
1.5.3.1. Thnh phn ct
Nhng khi nim c bn
Thnh phn ct l khi nim dng biu din phn trm bay hi theo nhit
hoc ngc li nhit theo phn trm thu c khi tin hnh chng ct mu trong
thit b chun theo nhng iu kin xc nh. y ta c nhng khi nim sau.
Nhit si u:
L nhit c c trn nhit k vo lc git cht lng ngng t u tin chy
ra t cui ng ngng t.
Nhit si cui:
L nhit cao nht t c trong qa trnh chng ct.
Nhit phn hy:
L nhit c c trn nhit k khi xut hin cc du hiu u tin ca s
nhit phn nh xut hin hi trng
Nhit si 10% (t10%), t50%, t90%, t95%, . . :
L nhit c trn nhit k tng ng khi thu c 10%, 50%, 90%, 95% . . .
cht lng ngng t trong ng thu.
Phn trm thu hi c l s ml cht lng ngng t thu c trong ng ong c
chia tng ng lc c nhit .
ThS. Trng Hu Tr Trang 21
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Sn Phm Du M Thng Phm
ngha ca vic xc nh thnh phn ct
Ngoi vic nh gi thnh phn ho hc ca xng th thnh phn ct cn c
ngha rt quan trng i vi xng nhin liu bi cc gi tr ca n nh hng trc tip
ln kh nng khi ng, kh nng tng tc v c kh nng chy ho ton trong bung
chy.
nh hng n kh nng khi ng
Xng cho ng c phi c mt bay hi nht nh cho ng c c th khi
ng c nhit thp. Qua nghin cu thc t cho thy kh nng khi ng ca
ng c nhit thp ph thuc vo nhit si u, nhit si 10%, 20%, 30%.
Khi nhng gi tr ny cng thp th ng c cng d khi ng, nhng nu chng thp
qu th xng bay hi qu nhiu do d gy ra hin tng nt hi lm thay i thnh
phn ca xng c np vo xylanh mt s chu k no gy ra hin tng thiu
ht xng cung cp cho ng c, iu ny thng dn n qu trnh chy khng hon
ton v to ra nhiu cht c hi trong khi thi lm nhim mi trng. Ngoi ra qu
trnh bay hi ln s gy mt mt vt cht v cng gy nhim. Ngc li khi nhng
gi tr qu ln ngha l xng kh bay hi th ng c rt kh khi ng khi ang
nhit thp.
nh hng ln kh nng tng tc
Khi chuyn t ch chm sang ch nhanh, ng c i hi lng xng np
vo phi ln v bay hi nhanh bo m cho qu trnh chy cung cp nhit.
bay hi ny ph thuc vo nhit si u n nhit si t50%, t60%,
Cng tng t nh trn, khi nhng nhit si ny cng nh th bay hi
cng tt to iu kin tt cho qu trnh chy tt. Ngc li khi nhng gi tr ny ln
th qu trnh ho hi khng tt do d dn n qu trnh chy khng hon ton to ra
nhiu cht c hi trong khi thi gy nhim mi trng.
nh hng n kh nng chy ht
Nhit si cui v nhng nhit si 90%, 95% ca xng phi c gii hn
nht nh bo m qu trnh chy tt. Nu nhng gi tr ny ln qu th qu trnh
chy s khng hon ton.
ThS. Trng Hu Tr Trang 22
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Sn Phm Du M Thng Phm
Phn nhin liu khng chy ht c th b phn hu trong iu kin nhit cao
lm tng nng cht c hi trong khi thi hoc chng tn ti trng thi lng v
ng li trn thnh xy lanh lm long mng du bi trn gy ra hin tng mi mn,
sau chng c xecmng a xung carter cha du v lm bn du bi trn.
1.5.3.2. p sut hi bo ho
p sut hi l mt i lng vt l c trng cho tnh cht cc phn t trong
pha lng c xu hng thot khi b mt ca n chuyn sang pha hi nhit no
. Nh vy p sut hi bo ho chnh l p sut hi m ti th hoi cn bng vi
th lng.
p sut hi l mt hm s ca nhit v ca c tnh pha lng. S si ca mt
hydrocacbon no , hay ca mt phn on du m ch xy ra khi p sut hi ca n
bng vi p sut hi ca h. V vy, khi p sut h tng ln, nhit si ca phn on
s tng theo nhm to ra mt p sut hi bng p sut ca h. Ngc li, khi p sut
ca h gim thp, nhit si ca phn on s gim i tng ng.
i vi cc hydrocacbon ring l, p sut hi ca n ch ph thuc vo nhit
, v vy mt p sut nht nh ch c mt nhit si tng ng.
i vi mt phn on du m trong bao gm nhiu hydrocacbon ring l
th p sut hi ca phn on, ngoi s ph thuc vo nhit , cn ph thuc vo
thnh phn cc hydrocacbon c p sut ring phn khc nhau, ngha l p sut hi ca
phn an mang tnh cht cng tnh ca cc thnh phn trong v tun theo nh lut
Raoult: P = iixP(Pi, xi l p sut ring phn v nng phn mol ca cu t i trong phn an).
p sut hi bo ho c th c biu din theo 3 phng php khc nhau: Phng php ca Reid (PVR). Phng php ca Grabner Phng php xc nh t l lng - hi (V/L). Trong ba phng php trn th phng php ca Reid thng c dng nhiu
nht. p sut thu c l p sut tut i. p sut ny c o 100oF (37,8oC).
ThS. Trng Hu Tr Trang 23
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Sn Phm Du M Thng Phm
Cng tng t nh thnh phn ct, p sut hi bo ho c trng cho kh nng
khi ng ca ng c nhit thp. Khi gi tr ny ln th ng c d khi ng
nhng nu gi tr ny ln qu s gy ra hin tng nt hi, thiu nhin liu khi cung
cp cho ng c v gy mt mt, nhng nu nh qu th ng c kh khi ng.
1.5.3.3. Nhit cht chy
Nhit cht chy l nhit thp nht m ti nhin liu bay hi to vi
khng kh mt hn hp c th pht chy ri tt ngay nh mt tia chp khi a ngn
la n gn.
Nhit chp chy c xc nh trong hai loi thit b cc kn v cc h khc
nhau nn tng ng ta cng c hai loi nhit cht chy cc kn v cc h. loi cc
kn thng dng cho cc loi sn phm c bay hi ln cn loi cc h thng dng
cho cc phn on nng.
Nhit chp chy c trng cho cc phn nh d bay hi trong nhin liu, khi
phn nh cng nhiu th kh nng bay hi cng ln iu ny s gy ra mt mt vt cht
v iu quan trng hn c l n c th to ra hn hp n trong qu trnh bo qun v
vn chuyn. V vy ch tiu ny c trng cho mc ho hon ca xng. i vi
xng th iu kin thng bay hi ca n ln nn to hn hp vi khng kh nm
ngoi gii hn n.
Quy nh v bay hi ca xng khng chi chu u
Tnh cht n v Gi tr gii hn ca cc loi khc nhau 1 2 3 4 5 6 7 8 p sut hi
KPa nim KPa max
35 70
35 70
45 80
45 80
55 90
55 90
60 95
65 100
E70 % nim %max
15 45
15 45
15 45
15 45
15 47
15 47
15 47
20 50
FVI max 900 950 1000 1050 1100 1150 1200 1250 E100 % nim
%max 40 65
40 65
40 65
40 65
43 70
43 70
40 70
43 70
E180 % nim 85 85 85 85 85 85 85 85 PF oC max 215 215 215 215 215 215 215 215 Cn %max 2 2 2 2 2 2 2 2 FVI =PVR (mbar) +7E70
ThS. Trng Hu Tr Trang 24
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Sn Phm Du M Thng Phm
1.5.4. n nh oxy ho Trong qu trnh vn chuyn v bo qun du th cng nh sn phm ca n
thng tip xc vi khng kh nn cc hydrocacbon d b oxy ho to thnh cc sn
phm nng hn v thng gi l nha, cc hp cht ny thng gy ra nhiu nh
hng xu n qu trnh hot ng ca ng c nh: Lm tt nghn li lc trong
bm np liu, gicluer, to cn trong cc rnh ca piston v trn xecmng.
c trng cho kh nng chng li qu trnh oxy ho ngi ta dng khi nim
n nh oxy ho, n c th c xc nh theo nhiu phng php khc nhau.
n nh oxy ho ph thuc vo thnh phn ho hc ca cc h hydrocacbon.
Trong du th cng nh cc sn phm ca n th cc hydrocacbon c n inh ho
hc khc nhau, cc hp cht Aromatic c n nh km nht cn cc hp cht
Parafinic c n nh cao nht, tuy nhin iu kin nhit thng th tc oxy
ho ca cc h hydrocacbon ny khng ln.
Trong du th khng c cc hp cht olefin, nhng trong qu trnh ch bin,
di tc dng ca nhit cc hydrocacbon km bn nhit s b ct mch to thnh
cc sn phm nh hn trong c cc hp cht khng no nh olefin, phn trn
chng ta thy xng thng phm c phi trn t rt nhiu khc nhau trong
ch yu l cc sn phm ca cc qu trnh ch bin su, trong cc sn phm ny
thng cha cc hp cht khng no. V vy trong thnh phn ca xng lun cha cc
hp cht olefin, y l hp cht km bn d b oxy ho to nha v cc hp cht c hi
khc cho xng, chnh v l do ny m ngoi ch tiu v n nh oxy ho th cn phi
khng ch hm lng ca lefin trong xng.
1.5.5. Hm lng lu hunh
Trong phn on xng thu c t qu trnh chng ct kh quyn hay trong
xng thng phm th hm lng lu hunh khng nhiu, chng c th tn ti di
nhiu dng khc nhau tu theo ngun gc phi trn. Trong cc dng tn ti ny th
ngi ta quan tm nhiu nht n hp cht mercaptan (c trong phn on xng chng
ct trc tip) v y l hp cht c kh nng gy n mn trc tip cc thit b trong tn
cha bo qun, vn chuyn cng nh s dng trong ng c.
ThS. Trng Hu Tr Trang 25
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Sn Phm Du M Thng Phm
Mc d hm lng cc hp cht ny khng ln trong thnh phn ca xng
nhng n gy ra nhiu nh hng xu n cht lng ca xng nh va nu trn.
Khi chy trong ng c chng to ra khi SO2, kh ny sau c th chuyn mt phn
thnh SO3, cc cht kh ny s to thnh cc axit tng ng khi nhit xung thp,
y l cc cht gy n mn rt mnh. Ngoi ra khi theo khi thi ra ngoi cc cht kh
ny s lm nhim c xc tc trong b h thng x l kh thi v gy nhim mi
trng khi thi ra khi quyn.
1.5.6. Hm lng benzen
Nh chng ta bit benzen l mt cht c n c th gy cht ngi khi
trong mi trng c hm lng benzen cao, vi nng thp th benzen c th gy ra
cn bnh ung th cho con ngi.
Qu trnh chy trong ng c thng khng hon ton bi iu kin chy trong
ng c kh c bit. Trong kh thi ca ng c ngoi cc kh CO2, H2O, N2 cn c
thm mt s cc cht khc nh CO, NOx, SOx, cc hydrocacbon cha chy, b hng .
. . hydrocacbon cha chy thc cht l mt hn hp cc hp cht hu c nh benzen,
butadien, fornaldehyt, acetaldehyt ... cc hp cht ny khi thi ra mi trng u c
hi cho con ngi v mi trng sinh thi, iu ny bt buc con ngi phi x l n.
C nhiu phng php nhm hn ch cc cht nhim ny nh ci tin cu trc
ca ng c, khng ch iu kin lm vic ti u hay ci thin cht lng ca nhin
liu. Trong cc gii php ny th hai gii php u tin rt kh lm gim hm lng
benzen trong kh thi v benzen l mt cht kh chy nht trong cc hp cht ny. V
nhng l do ny m ngi ta bt buc phi khng ch hm lng benzen v c hm
lng cc hp cht aromatic trong nhin liu.
Benzen trong kh thi ng c xng ph thuc vo hm lng aromatic
Hm lng benzen trong kh cha chy trong kh x (%) Hm lng aromatic trong nhin liu (%)
1% benzen trong nhin liu 3% benzen trong nhin liu
20 1.5 2.25
35 2 2.9
50 2.5 3.5
ThS. Trng Hu Tr Trang 26
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Sn Phm Du M Thng Phm
Ngoi nhng tiu chun quan trng nu trn th mt loi xng thng phm cn
phi t nhiu tnh cht khc nh: hm lng nha, cn, tro, tiu chun v mu sc
cc ch tiu v kim, axxit . . .
Ngy nay, trong thnh phn ca xng thng phm ngoi ph gia nhm nng
cao ch s octan th ngi ta cn dng mt s ph gia khc nh ph gia chng oxy
ho, ph gia ty ra . . .
TIU CHUN VIT NAM V XNG T KHNG CH (TCVN 6776 : 2000)
Xng khngch
Cc ch tiu cht lng
Phng php th
90 92 95 1.Tr s octan - Theo phng php nghin cu (RON)
min ASTM D2699 90 92 95
2. Thnh Phn Ct, 0C im si u 10% Th tch 50% Th tch 90% Th tch im si cui Cn cui
max max max max max
ASTM D 86
Bo co 70 120 190 215 2.0
3. n mn tm ng 500C/3h max TCVN 2694:2000 (ASTMD130)
1
4. Hm lng nha thc t, mg/100ml
max TCVN 6593:2000 (ASTMD381)
5
5. n nh oxy ho, pht min TCVN 6778:2000(ASTMD525)
240
6. Hm lng lu hunh tng, % KL
max ASTM D1266 0.15
7. Hm lng ch, g/l max TCVN 6704:2000 (ASTMD5059)/ASTM D3237
0.013
8. p sut hi bo ho Ried, kPa
TCVN 5731:2000 (ASTMD323)/ASTM D4953
43 - 80
9. Hm lng benzen, % th tch
max TCVN6703:2000 (ASTMD3606)
5
10. Khi lng ring (150C), kg/m3
TCVN 6594:2000 Bo co
11. Ngoi quan Kim tra bng mt thng
Trong sut,khng c tpcht l lng
ThS. Trng Hu Tr Trang 27
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Sn Phm Du M Thng Phm
Chng II NHIN LIU CHO NG C DIESEL
2.1. Gii thiu chung v nhin liu diesel
Nhin liu Diesel l mt loi nhin liu lng, nng hn du ha v xng, s
dng cho ng c Diesel (ng b, ng st, ng thy) v mt phn c s
dng cho cc loi my mc cng nghip nh tuabin kh, my pht in, my mc xy
dng . . .
Ngy nay ng c Diesel pht trin mnh m, a dng ho v chng loi
cng nh kch thc v c p dng trong nhiu lnh vc khc nhau ca i sng sn
xut v sinh hot ca con ngi bi tnh u vit ca n so vi ng c xng. Do vy,
nhu cu v nhin liu Diesel ngy cng tng, iu ny t ra cho cc nh sn xut
nhin liu nhng thch thc mi, v iu ny cng kh khn hn bi nhng yu cu
ngy cng kht khe ca lut bo v mi trng.
Trong nh my lc du th nhin liu Diesel c ly ch yu t phn on
gasoil ca qu trnh chng ct du m. y chnh l phn on thch hp nht sn
xut nhin liu Diesel m khng cn phi p dng nhng qu trnh bin i ha hc.
Tuy nhin, m bo v s lng ngy cng tng ca nhin liu Diesel v vic s
dng mt cch c hiu qu cc sn phm trong nh my lc du th thc t nhin liu
Diesel lun c phi liu t cc ngun khc nh : Phn on gasoil ca qu trnh
hydrocracacking, phn on gasoil t qu trnh FCC, cc sn phm ca qu trnh
oligome ha, dime ha, trime ha, gim nht, HDS...
2.2. Thnh phn ho hc ca nhin liu Diesel
Nh nu trong phn trc, nhin liu Diesel thng phm c phi trn t
nhiu ngun khc nhau trong nh my lc du. Thnh phn ho hc ca cc ngun ny
thay i rt nhiu ngay c khi cng mt ngun gc du th. xem xt, trc ht ta
xem xt cc ngun dng phi trn nhin liu Diesel.
Trong nh my lc du th Diesel thng thu nhn theo cc qu trnh nh s sau:
ThS. Trng Hu Tr Trang 28
Xng
GPL
RC
-
Sn Phm Du M Thng Phm
Theo s ny, nhin liu Diesel nhn c t cc ngun nh sau:
ThS. Trng Hu Tr Trang 29
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Sn Phm Du M Thng Phm
Phn on Gasoil ca thp chng ct kh quyn (phn on chnh phi trn) T phn xng crackinh xc tc T phn xng hydrocrackinh T phn xng gim nht T phn xng cc ho T phn xng tch loi lu hunh km theo qu trnh chuyn ho T cc qu trnh tng hp nh oligome ho
2.2.1. Thnh phn ho hc ca ca phn on gassoil
y l thnh phn chnh phi trn nhin liu Diesel. Trc y phn on
ny c ly t thp chng ct kh quyn c khong nhit si l 250oC 350oC, vi khong nhit si ny th thnh phn ho hc ca gasoil bao gm cc
hydrocacbon c s nguyn t cacbon t C16 C20, hu ht cc nhm cht c mt trong du th u tm thy trong phn on ny. Cng nh khi nghin cu du m hay cc
sn phm du m khc, thnh phn ho hc ca gasoil c chia thnh hai nhm cht
chnh nh sau:
2.2.1.1. Nhm hp cht hydrocacbon
Nhm cht ny bao gm cc h nh sau: Paraffin, Naphten, Aromatic
H Parfinic
c im chung v cc hydrocacbon parafinic trong phn on ny l s phn
b gia cu trc thng v cu trc nhnh y c khc: hu ht l cu trc mch thng
(n-parafin), dng cu trc nhnh ng phn ca chng th rt t v nhnh ch yu l
gc mtyl.
ng ch l v cui phn on gasoil, bt u c mt nhng hydrocacbon n-
parafinic c nhit kt tinh cao nh: C16 c nhit kt tinh 18,1oC, C20 c nhit
kt tinh 36,7oC. Khi nhng parafin ny kt tinh, chng s to ra mt b khung
phn t, nhng hydrocacbon khc cn li dng lng s nm trong , nu cc n-
ThS. Trng Hu Tr Trang 30
-
Sn Phm Du M Thng Phm
parafin rn ny c nhiu, chng s lm cho c nhin liu mt tnh linh ng thm ch
c th lm ng c li nhng nhit thp.
H Naphten v Aromatic
Nhng hydrocacbon loi naphten v aromatic trong phn on ny bn cnh
nhng loi c cu trc mt vng c nhiu nhnh ph nh xung quanh cn c mt cc
hp cht 2 hoc 3 vng.
Ngoi ra trong gasoil c mt cc hp cht hydrocacbon c cu trc hn hp
gia vng naphten v aromatic nh ttralin v cc ng ng ca chng.
Ngoi ba h trn th trong thnh phn ca nhin liu Diesel lun cha mt hm
lng ng k cc hp cht khng no nh olefin (phn ch yu), dien ...cc hp cht
khng no ny n t cc qu trnh ch bin su nh FCC, gim nht . . .
2.2.1.2. Nhm hp cht phi hydrocacbon
Trong Diesel thng phm th cc cht phi hydrocacbon tn ti di nhiu dng
khc nhau.
Hp cht ca lu hunh
Nu nh trong xng, lu hunh dng mercaptan chim phn ch yu trong s
cc hp cht lu hunh , th trong phn on gosoil loi lu hunh mercapten hu
nh khng cn mercaptan na. Thay th vo l lu hunh dng sunfua v disunfua,
cng nh lu hunh trong cc mch d vng. Trong s ny, cc sunfua vng no (d
vng) l loi c ch yu.
Hp cht ca oxy
Cc hp cht cha oxy trong phn on gasoil cng tng dn ln. c bit
phn on ny, cc hp cht cha oxy di dng axit, ch yu l axit naphtenic c rt
nhiu v t n cc i trong phn on gasoil.
Ngoi cc axit, cc hp cht cha oxy trong phn on gasoil cn c cc
phenol v ng ng ca chng nh crezol, dimetyl phenol.
ThS. Trng Hu Tr Trang 31
-
Sn Phm Du M Thng Phm
Hp cht ca nit
Cc hp cht ca nit trong phn on ny cng c t nhng chng c th nm
di dng cc Quinolin v ng ng, hoc cc hp cht cha nit khng mang tnh
baz nh Pirol, Indol v cc ng ng ca n.
Ngoi nhng hp cht cha thun tu N2, O2, S th trong phn on gasoil c
mt cc cht nha, trng lng phn t ca nha vo khong (300-400). Ni chng
cc cht nha ca du m thng tp trung ch yu vo cc phn on sau gasoil, cn
trong phn on ny s lng chng rt t.
2.2.2. Thnh phn ho hc cc ngun ngoi phn on gasoil sn xut Diesel
Trong cc ngun ny th thnh phn ho hc ca n thay i rt nhiu. Chng
khng ch ph thuc vo loi du th m cn ph thuc vo qu trnh s dng v iu
kin cng ngh. Cc ngun ny c th chia lm hai nhm nh:
Nhm th nht:
Nhm ny bao gm cc loi gasoil nhn c t cc qu trnh sau:
Crackinh nhit, xc tc Gim nht Cc ho
Gasoil thu c t cc qu trnh ny thng c cht lng rt xu (ch s cetan
thp, hm lng lu hunh cao, cc cht km n nh nhiu, hm lng aromatic v
hp cht nha nhiu). Khi phi trn trc tip th nhm gasoil ny ch chim mt lng
nh, nhng thng thng th chng phi qua qu trnh x l (HDS) ri mi em phi
trn.
Nhm th hai:
Nhm ny bao gm cc loi gasoil thu c t cc qu trnh x l bng hydro
nh: HDS, Hydrocrackinh, cc qu trnh tng hp . . .
c im ni bt ca gasoil nhm ny l cht lng rt tt c ngha l ch s
cetan cao, hm lng cc hp cht phi hydrocacbon nh lu hunh, nit gim xung
rt nhiu, hm lng aromatic v cc cht khng no cng gim i nhiu ln.
ThS. Trng Hu Tr Trang 32
-
Sn Phm Du M Thng Phm
Sau y ta s xem xt mt s v d v thnh phn ca cc loi gasoil v s bin
i ca n theo cc qu trnh x l.
Thnh phn ho hc ca gasoil thu c t cc qu trnh chuyn ho
Dng sn phm
Tnh cht
LCO (HTS)
LCO (BTS)
VB1 VB2 HCK CK
- Khi lng ring 15oC (kg/lit) - nht (cSt) - Lu hunh(%) - Nit ppm - Ch s brm -Thnh phn ct (oC) PI PF - Ch s cetan - Thnh phn ho hc (% kl) Paraffin Naphten Mono aromatic Di aromatic Tri aromatic Benzothiophen Dibenzothiophen
0.942 4.6 2.76 630 14.9 218 359 21.3 13.7 8.8 17.1 35.8 4.1 15.6 4.0
0.924 3.1 0.68 110 7.3 199 296 18.3 21.3 8.9 20.1 44.7 0.5 4.3 0.3
0.866 5.5 2.2 27 229 348 45.5 23 33.4 17.7 10.4 1.4 12.2 1.8
0.821 2 1.46 247 45.5 156 293 39.2 22.4 53.3 17.4 2.8 0.1 4.1 0.0
0.803 2.94 0.006 6 179 333 54.2 39.8 58.5 1.5 0.2 0.0 0.0 0.0
0.936 3.8 1000 21 308 360 27 4 31 65
Nhn xt:
Gasoil thu c t qu trnh hydrocrackinh c cht lng rt tt tc l hm
lng cc hp cht phi hydrocacbon, hm lng cht thm rt thp, ch s cetan cao.
ThS. Trng Hu Tr Trang 33
-
Sn Phm Du M Thng Phm
So snh tnh cht ca gasoil trc v sau khi kh lu hunh su
(p sut chung 27 bar, V.V.H 3)
Tnh cht Nguyn liu (RA)
Sn phm
- Khi lng ring 15oC (kg/lit) - nht (cSt) 20oC
50oC
- Lu hunh(%) - Nit ppm - Thnh phn ct(oC) PI 50% 90% PF - Ch s cetan - Thnh phn ho hc (% kl) Paraffin Naphten Mono aromatic Di aromatic Tri aromatic Benzothiophen Dibenzothiophen
0.846 6.14 2.99 1.31 65 217 294 341 358 54.8 40.7 32.6 11 7.4 1.0 5.4 1.9
0.834 5.58 2.81 0.07 221 285 329 350 56.4 43.2 31.1 18.2 5.9 0.5 0.5 0.6
0.833 5.52 2.79 0.015 54 221 285 329 349 57.6 44.0 30.9 17.6 6.5 0.4 0.4 0.2
(Ct sau l kt qu thu c trong trng hp nghim ngt cao hn)
Nhn xt:
Sn phm thu c sau qu trnh HDS c hm lng cc hp cht phi
hydrocacbon v hp cht aromatic mt hay nhiu vng gim i rt nhiu, paraffin
tng ln, ch s cetan tng ln, nhit si u tng ln cht t nhng nhit si
50%, 90%, nhit si cui gim iu ny cho nhin liu c kh chy tt ngha l qu
trnh ny cho cht lng gasoil tt hn.
Khi nghim ngt tng ln th cht lng ca gasoil cng tng ln.
ThS. Trng Hu Tr Trang 34
-
Sn Phm Du M Thng Phm
So snh tnh cht ca gasoil trc v sau khi kh lu hunh su
(p sut chung 27 bar, V.V.H 3)
Tnh cht Nguyn liu: 80% RA+20%LCO
Sn phm
- Khi lng ring 15oC (kg/lit) - nht (cSt) 20oC 50oC - Lu hunh(%) - Nit ppm - Thnh phn ct(oC) PI 50% 90% PF - Ch s cetan - Thnh phn ho hc (% kl) Paraffin Naphten Mono aromatic Di aromatic Tri aromatic Benzothiophen Dibenzothiophen
0.862 5.55 2.76 1.16 216 214 288 332 353 49 36.5 24.3 14.2 15.4 1.8 5.4 2.4
0.85 5.34 2.7 0.064 150 224 283 329 350 50.4 36.2 24.3 23 12 10.0 1.5 0.9
0.833 5.52 2.79 0.015 54 221 285 329 349 49 36.7 26.5 21.9 12.6 0.9 1.0 0.4
(Ct sau l kt qu thu c trong trng hp nghim ngt cao hn)
Kt qu thu c y hon ton ging nh trn.
ThS. Trng Hu Tr Trang 35
-
Sn Phm Du M Thng Phm
So snh tnh cht ca gasoil trc v sau khi x l bng hydrocacbon
Sn phm Tnh cht Nguyn liu (RA)
P 50 bar VVH 1
P 75bar VVH 0.5
- Khi lng ring 15oC (kg/lit) - nht (cSt) 20oC 50oC - Lu hunh(%) - Thnh phn ct(oC) PI 50% 90% PF - Ch s cetan - Thnh phn ho hc (% kl) Paraffin Naphten Mono aromatic Di aromatic Tri aromatic Benzothiophen Dibenzothiophen
0.846 6.14 2.99 1.31 217 294 341 358 54.8 40.7 32.6 11 7.4 1.0 5.4 1.9
0.825 5.3 2.71 218 282 326 347 60.2 43.7 38.1 13.7 2.8 0.3 0.2 0.3
0.818 5.27 2.6 203 280 326 346 65.4 45.7 50.3 3.4 0.6 0 0 0
Kt qu hon ton ging nh qu trnh HDS
ThS. Trng Hu Tr Trang 36
-
Sn Phm Du M Thng Phm
So snh tnh cht ca gasoil trc v sau khi kh lu hunh su
Sn phm Tnh cht
Nguyn liu: 80% RA+20%LCO
P 50 bar VVH 1
P 75 bar VVH 0.5
- Khi lng ring 15oC (kg/lit) - nht (cSt) 20oC 50oC - Lu hunh(%) - Thnh phn ct(oC) PI 50% 90% PF - Ch s cetan - Thnh phn ho hc (% kl) Paraffin Naphten Mono aromatic Di aromatic Tri aromatic Benzothiophen Dibenzothiophen
0.862 5.55 2.76 1.16 214 288 332 353 49 36.5 24.3 14.2 15.4 1.8 5.4 2.4
0.838 5.12 2.63 0.0022 213 278 324 346 53.9 36.9 37.7 20.2 4.5 0.4 0.3 0.0
0.827 4.9 2.54 0.0004 212 275 324 347 60.2 41.5 51.8 6 0.7 0.0 0.0 0.0
ThS. Trng Hu Tr Trang 37
-
Sn Phm Du M Thng Phm
Cc ngun dng phi trn gasoil
Ngun
nguyn liu
Du th paraffin Du th
naphten
Phn ct ca
DSV
Phn cn ca RSV
Qu trnh x
l
DA DA FCC HCK VB CK HCK
Hiu sut (%
kl)
30.3 32.8 36.7 29.2 47.2 1015 -- 515 35 --
d15
4(kg/l) 0.835 0.825 0.843 0.827 0.856 0.93 0.835 0.845 0.900 0.855
Thnh phn
ct
PI
PF
170
370
180
375
170
400
180
350
170
370
170
370
200
358
170
370
170
370
196
343
im vn c
(oC)
-5 -2 +1 -10 -20 -5 -14 -4 -8 -15
im chy
(oC)
-12 -9 -6 -18 -33 -14 -25 -18 -20 -26
Ch s cetan 50 51 54 54 43 24 58 40 28 50
Hm lng
lu hunh
(% kl)
0.12 0.04 0.83 0.80 0.09 2.8 0.02 2.33 2.10
ThS. Trng Hu Tr Trang 38
-
Sn Phm Du M Thng Phm
2.3. Nguyn tc hot ng v c im qu trnh chy trong ng c Diesel
kho st thnh phn v tnh cht nhin liu Diesel nh hng n qu trnh
hot ng ca ng c v vn nhim mi trng, trc ht ta xt s lc v hot
ng v c im qu trnh chy ca nhin liu trong ng c Diesel.
2.3.1. Vi nt lch s ng c Diesel
ng c Diesel mang tn ca nh pht minh ni ting Rudolf Diesel. R.Diesel
sinh nm 1858 l k s ngi c nhng phn ln hot ng nghin cu my mc
ca ng thc hin Paris (Php). Nm 1892 ti Berlin R.Diesel c cp bng pht
minh nghin cu v s hot ng ca mt loi ng c vi nhin liu l dng hi
sng cc ht hydrocacbon. Tuy nhin, ti ny ch mang tnh phc ho, sau n
nm 1897 ngun nhin liu ca ng c c thay th bng ngun nhin liu c ngun
gc t du m (phn on gasoil) v ng c em li mt hiu sut ng k (247
g/ch.h), xylanh ca ng c Diesel u tin ny c th tch 19,6 lt, cho mt cng sut
14,7 KW, vi tc quay trc khuu l 172 vng/pht. Sau , loi ng c ny
c pht trin mnh m vi nhiu chng loi khc nhau v c ng dng rng ri
nht l sau chin tranh th gii nht trn cc loi xe ti nhng nm 1930-1939.
Chic xe du lch u tin trang b ng c Diesel c gii thiu bi hng
Mercedes nm 1936 (206D) nhng thnh cng hn l chic xe ca hng Peugoet
(Diesel 402) xut xng nm 1938 (c 1000 khun mu).
Sau nm 1945, ng c Diesel tr nn ph bin trong cc loi phng tin
giao thng dn dng nhng n ch tn ti trong mt s gii hn cu trc, mu m ca
cc hng sn xut t ln nh Mercedes, Peugeot.
n nhng nm 1970, ng c Diesel c s pht trin vt bc. Cc phng
tin vn ti c trang b ng c Diesel vi bung t kiu phun trc tip, cc loi xe
du lch vi bung t kiu phun gin tip. n u nm 1980, th trng cc ng c
Diesel cho cc loi phng tin vn ti bng n trn ton th gii.
ThS. Trng Hu Tr Trang 39
-
Sn Phm Du M Thng Phm
2.3.2. Nguyn l hot ng ca ng c Diesel
ng c Diesel l mt ng c nhit dng bin nng lng ho hc ca
nhin liu khi chy thnh nng lng c hc di dng chuyn ng quay. ng c
ny lm vic theo nguyn tc mt chu trnh gm k: np, nn, chy n v gin n sinh
cng, thi kh chy ra ngoi. S nguyn l nh sau:
1.Trc khuu
2. Thanh truyn
3. Piston
4. Xylanh
5. Kim phun
Xupap nap Xupap
1 G C
5
4
2
3
C
S ng c Diesel 4 k
Trong qu trnh vn hnh ca ng c, trc khuu quay theo chiu mi tn,
piston i ng ln xung trong xylanh, thanh truyn truyn vn ng tnh tin ca
piston cho trc khuu quay trn. y ta c khi nim im cht trn v im cht
di l cc im tng ng vi v tr cao nht v thp nht ca piston trong xylanh.
Chu trnh cng tc ca ng c Diesel c tin hnh nh sau :
K 1 Hnh trnh np
Khi piston i t im cht trn xung im cht di xupap x ng li xupap
np m ra khng kh c ht qua xupap np vo trong xylanh.
K 2 Hnh trnh nn
Sau khi n im cht di piston s i ngc ln pha trn, lc ny c hai
xupap u ng li khng kh trong xylanh c nn n nhit cao khong
450500oC tu thuc vo t s nn ca ng c.
ThS. Trng Hu Tr Trang 40
-
Sn Phm Du M Thng Phm
K 3 Hnh trnh Phun nhin liu chyv gin n sinh cng
Khi piston gn n im cht trn th nhin liu c bm cao p phun vo
di dng cc sng (cc ht c kch thc rt nh), t cc ht sng ny nhin liu
s bay hi to vi khng khi mt hn hp t bc chy. Nh vo kt qu ca qu trnh
chy, nhit v p sut trong xylanh tng cao nn chng y piston chy t im
cht trn xung im cht di v ng thi thc hin qu trnh gin n sinh cng.
K 4 Hnh trnh thi
Khi piston b y xung im cht di theo lc qun tnh n ngc ln pha
trn, lc ny xupap x m ra y kh chy ra ngoi v kt thc mt chu trnh. Sau
chu trnh ny piston li i xung pha di thc hin chu trnh tip theo.
Trong thc t th cc xupap ng m cng nh thi im phun nhin liu khng trng
vi im cht trn v im cht di. Thng np c nhiu khng kh vo
xylanh ngi ta cho cc xupap c m sm nhng ng mun, cn nhin liu s
c phun vo trc khi piston n im cht trn khong ln hn khong 10 theo
gc quay ca trc khuu.
Nh vy, ton b chu trnh cng tc c thc hin theo bn hnh trnh trong
hai vng quay ca trc khuu, trong bn hnh trnh ny ch mt hnh trnh chy v
gin n duy nht sinh cng, cn ba hnh trnh khc khng sinh cng.
2.3.3. c im ca qu trnh chy ca nhin liu trong ng c Diesel
T vic phn tch hot ng ca ng c Diesel trn ta rt ra c nhng c
im ca qu trnh chy trong ng c ny nh sau:
Khc vi ng c xng nhin liu c phi trn trc trong b ch ho kh th
ng c Diesel nhin liu khng c phi trn trc m ch c phun vo xylanh
khi khng kh c nn t nhit v p sut cao, trong iu kin ny th
nhin liu bay hi ri to hn hp t bc chy m khng cn n s nh la ca bugi.
Trong ng c xng th qu trnh chy phi c bt u t bugi sau lan
truyn i theo cc mt cu v nhin liu ch c php chy khi mng la lan trn n
cn trong ng c Diesel th qu trnh bt chy c th bt k ch no trong xylanh m
nhin liu c phi trn tt vi khng kh c th t bc chy.
ThS. Trng Hu Tr Trang 41
-
Sn Phm Du M Thng Phm
Nu nh trong ng c xng vic tng cng sut bng cch tng t s nn s
vp phi hin tng nhin liu chu nhit v p sut cao s t bc chy kh mt la
cha lan truyn n th trong ng c Diesel bt buc phi c t s nn cao bo
m cho nhin liu c th t bay hi v bc chy. Do cng sut ca ng c Diesel
lun ln hn cng sut ca ng c xng khi cng mc tiu th nhin liu.
Nhin liu sau khi phun vo bung chy n khng chy ngay m cn c mt
thi gian nht nh chun b, thi gian ny c gi l thi gian chy tr hay thi
gian cm ng. Thi gian ny di hay ngn ph thuc hon ton vo bn cht ca nhin
liu v cu trc ca ng c, n thng c chia thnh hai loi l thi gian cm
ng vt l v thi gian cm ng ho hc, thi gian cm ng ho hc ny c xc
nh theo cng thc thc nghim sau:
D = A P-nEXP(B/T)
Trong : A,B l cc hng s thc nghim.
So snh li ch ca ng c Diesel v ng c xng Khi so snh v li ch ca ng c Diesel so vi ng c xng ngi ta nhn
thy ng c Diesel c nhiu li ch hn theo nhiu g
Xt v gc nhit tr:
Nhit tr khi lng ca Diesel ln hn nhit tr khi lng ca xng khong
10% do khi xem xt 2 ng c c cng hiu sut th ng c Diesel tiu th nhin
liu t hn khong 10%.
Xt v hiu sut s dng nhit:
Hiu sut s dng nhit ca ng c Diesel lun ln hn ng c xng v n
khng c l trp to ra m p trong giai on ht do trn th P-V din tch
ca vng p sut thp nh hn so vi ng c xng. Tuy nhin hiu sut ca ng c
Diesel gim nhanh khi tc tng ln do tn thp p sut do ma st tng nhanh v qu
trnh chy trong thi gian ngn kho khn hn so vi ng c xng.
ThS. Trng Hu Tr Trang 42
-
Sn Phm Du M Thng Phm
Xt v gc nhin liu:
Gi thnh ca Diesel r hn xng, theo tnh ton nh my lc du th nng
lng tiu th sn xut Diesel nh hn sn xut xng khng 6% (13% so vi 19%)
So snh mc tiu th nhin liu ca ng c Diesel v Xng theo cc iu kin vn
hnh khc nhau:
100 100 100 100 100116 115 120 113
124
020406080
100120140
D10,9;V
33,9
D17,9;V
34,3
D 19;V29,1
D5,8;V41,2
D2,5;V11,5
Quang uong i va van toc
Muc
tieu
hoa
nhi
en li
eu (k
g/10
0 km
)
C Diesel C Xng
V nhng u im ca ng c Diesel m chung c s dng ngy cng rng
ri. Chung ta c th thy r iu ny qua s lng nhin liu tiu th ti th trng
Php.
0
5000
10000
15000
20000
25000
30000
1980 1997 1998 1999
Muc
tieu
thu
(Trie
u ta
n)
XngDieselFODD?u n?ng
ThS. Trng Hu Tr Trang 43
-
Sn Phm Du M Thng Phm
2.4. Cc ch tiu cht lng ca nhin liu Diesel.
Nh va thy trong phn trc, qu trnh chy trong ng c khng phi l qu
trnh chy l tng nn n s lm gim cng sut ca ng c, nhng iu quan trng
hn c l qu trnh chy khng hon ton ny s to ra cc cht c c hi cho con
ngi v mi trng. Do vic nghin cu nhm lm gim cc cht c ny l iu
bt buc i vi cc nh sn xut ng c v nhin liu.
i vi nhin liu Diesel thng phm n phi m bo c cc tnh cht sau:
2.4.1. Ch s xtan IC (Indice de Ctane)
2.4.1.1. nh ngha
Ch s xtan l mt i lng qui c c trng cho kh nng t bc chy ca
nhin liu Diesel v c tnh bng % th tch ca n-xtan trong hn hp ca n vi -mtylnaphtalen khi hn hp ny c kh nng t bc chy tng ng vi nhin liu
Diesel ang kho st. Trong hn hp ny th n-xtan c kh nng t bc chy tt nn
tr s ca n c qui c bng 100, cn -mtlnaphtalen c kh nng t bc chy km c qui c bng 0.
Trong thc t mt vi phng th nghim ngi ta dng hephtametylnonan
(HMN) thay cho -mltnaphtalen, trong HMN c IC = 15. 2.4.1.2. Phng php xc nh ch s xtan
Ch s xtan c th xc nh theo nhiu phng php khc nhau nh do trc
tip trn ng c hay xc nh t cc tnh cht ca n.
Vic xc nh trc tip IC c thc hin trn ng c CFR (Coferation Fuel
Reseach) nh trong ng c xng vi gc phun sm nhin liu l 13 theo gc quay
ca trc khuu. Phng php ny trong thc t t c s dng v n phc tp v tn
km.
Ch s IC c th c cc nh t cc tnh cht ca nhin liu Diesel, ch s thu
c gi l ch s IC tnh ton. Theo cch ny th trong thc t cng tn ti nhiu cng
thc khc nhau xc nh IC.
ThS. Trng Hu Tr Trang 44
-
Sn Phm Du M Thng Phm
- T nhit si ng vi 50% chng ct v t trng ta c th xc nh c IC
theo cng thc sau:
CCI = 454,74-1641,41d+774d2 -0,554T50 +97,083(lgT50)2
T cng thc ny ngi ta xy dng c th xc nh nh sau.
Xc nh CI bng phng php th
V ng thng qua 2 im : T50 v 0API (hoc d415) ng thng ny ct vch
thang chia IC ti CCI cn tm.
V d :
Nhin liu c d415=0,84 (khi lng ring tiu chun) v T50=2800C (ASTM-
D86) ta tm c CCI =56.
Trong phm vi IC=4055 sai lch gia CCI v IC o c l tng i nh nu nhin liu khng s dng ph gia ci thin IC.
Trn y l phng php c s dng nhiu trong thc t. Ngoi phng php
ny th ch s IC cong c th c xc inh t nhit si 10%, 50% v 90%; t im
anline hay t vic phn tch sc k, khi ph thnh phn ho hc ca nhin liu Diesel.
ThS. Trng Hu Tr Trang 45
-
Sn Phm Du M Thng Phm
2.4.1.3. Ci thin IC bng ph gia
Nh trong phn u chng ta thy nhin liu Diesel thng phm c phi
trn t rt nhiu ngun vi cht lng rt khc nhau, chng hn nh ngun LCO ca
qu trnh FFC hay gasoil ca cc qu trnh cc ho, gim nht ... ch s IC rt thp.
Khi nu cn nng cao ch s ny th ngi ta c th dng cc ph gia. Ph gia nhm
nng cao ch s IC c nhiu loi khc nhau nhng c th chia thnh hai nhm nh sau:
Nhm th nht bao gm cc hp cht peroxyt Nhm th hai bao gm cc hp cht nitrat alkyl
Cc hp cht peroxyt c bit n t lu nhng chung t c ng dng v
y l cc hp cht rt km bn v vn gi c. Trong nhm th hai th hp cht 2-
Etylhecxyl nitrat c s dng nhiu nht.
H H H H H H
C C C C C C
H C2H5 H H H H
HNO3
2.4.1.4. nh hng ca ch s IC ln hot ng ca ng c
Trong thc t ngy nay cc ng c Diesel c yu cu v ch s IC vo khong
4060 tu theo tc ca ng c, vi khong yu cu ny th ngi ta d dng t c trong cc nh my lc du. Tuy nhin iu quan trng l phi s dng loi nhin
liu hp vi ng c theo qui nh ca nh ch to v ch s ny lin quan trc tip n
thi gian cm ng.
Khi ch s IC gim xung th thi gian cm ng s tng ln iu ny s nh
hng trc tip n qu trnh chy trong ng c, c th l khi nhin liu phun vo c
ch s IC nh s c thi gian cm ng ln do khi n c th t bt chy th khi
lng nhin liu trong bung chy ln nn qu trnh chy c th xy ra vi tc ln
lm cho p sut trong bung chy tng cao mt cch t ngt, iu ny s to ra nhng
ting g kim loi, gy nng my v lm gim tui th ca ng c, ngoi ra khi tc
ThS. Trng Hu Tr Trang 46
-
Sn Phm Du M Thng Phm
chy qu ln th mt phn nhin liu c th khng chy kp m b phn hu do lm
gim cng sut v thi ra nhiu cht gy nhim mi trng. Tuy nhin s nh hng
ny s t hn trong ng c bung chy trc so vi ng c c bung chy trc tip.
Ngc li, khi ch s IC qu cao th thi gian cm ng s qu nh iu ny c
th dn n qu trnh t bt chy qu sm nn phn nhin liu phun vo sau c th b
phun vo trong kh chy c nhit qu cao nn nhin liu khng thi gian bay
hi th nhn c mt lng nhit qu ln nn n b phn hu trc khi chy, trong
trng ny cng sut ca ng c cng b gim v khi thi ra nhiu cht c hi cho
con ngi v mi trng.
2.4.2. T trng
Theo tiu chun ca Vit Nam: 860 kg/m3
Theo tiu chun ca chu u trc 01/01/2000 : 820 15.515.5 860 kg/m3
Theo tiu chun ca chu u t 01/01/2000 : 820 15.515.5 845 kg/m3
C nhiu phng php xc nh t trng, nhng thng thng n c xc
nh theo 3 phng php sau:
Phng php dng picnomet, Phng php dng ph k, Phng php dng cn thu tnh. Trong cc phng php trn th phng php dng picnomet l phng php cn
n t mu nht v cho chnh xc cao nht. Nh vy phng php ny c ngha
ln khi c t mu v i hi chnh xc cao. Phng php ny c th p dng cho
cc loi mu khc nhau. Nhc im duy nht ca phng php ny cn nhiu thi
gian.
T nguyn tc hot ng ca ng c Diesel ta nhn thy nhin liu trc khi chy
chng phi tri qua mt qu trnh bin i t vic b phn chia thnh cc ht sng sau
khi qua kim phun cao p, ho hi trn ln vi khng kh v bin i t bc chy,
cc qu trnh ny u lin quan trc tip n t trng ca Diesel.
ThS. Trng Hu Tr Trang 47
-
Sn Phm Du M Thng Phm
Khi khi lng ring ln th ng nng ca dng nhin liu ln, nhin liu b phun
i xa hn khi khng gian trn ln ca nhin liu vi khng kh ln. Tuy nhin, khi
nhin liu c khi lng ring ln th thng nht ca nhin liu cng ln nn kh
nng bay hi to vi khng kh hn hp t bc chy thp iu ny lm cho qu trnh
chy ca nhin liu km.
Nu nh khi lng ring ln qu th khi phun nhin liu c th va p vo thnh
ca bung chy, iu ny s lm long mng du bi trn trn thnh ca bung chy
gy ra hin tng mi mn.
Ngoi ra khi b phun vo mng du bi trn thnh xylanh th nhin liu s b hp
th trong mng du ny, sau trong giai on thi kh chy chng c th bay hi theo
kh chy v c y ra ngoi lm tng hm lng cc cht c hi trong kh thi.
Khi hai loi nhin liu c cng gii hn si th nhin liu no c khi lng ring
cao hn th s c hm lng cc hydrocacbon thm v naphtenic cao hn, nhin liu
c khi lng ring thp s cha nhiu parafin. Tuy nhin, vic khng ch gi tr ti
a ca khi lng ring trnh a vo nhin liu cc phn nng gy kh khn cho
qu trnh t bc chy, tng giu ca nhin liu lm tng thi ra khi en, b hng.
Qua phn tch trn cho thy khi lng ring ca nhin liu s c nhng nh
hng n qu trnh s dng nhin liu Diesel qua cc thng s sau:
Cng sut ca ng c Tiu th ring Hm lng CO, HC, Particules trong khi thi.
2.4.3. Thnh phn ct
Cng tng t nh nhin liu xng, nhin liu Diesel l mt hn hp ca rt
nhiu cc hp cht khc nhau c nhit si thay i trong khong rng. Thc t,
trong khong phn on ca n th nhit no cng c cc hydrocacbon tng ng
bay hi, nhng iu cn quan tm y l mt nhit nht nh th cng bay
hi ca cc cu t khc nhau l khng ging nhau. V vy c trng cho bay hi
ca nhin liu Diesel th ngi ta dng hai khi nim l Thnh phn ct. Nh khi
ThS. Trng Hu Tr Trang 48
-
Sn Phm Du M Thng Phm
nim ny m ta c th bit c s phn b ca cc hydrocacbon trong nhin liu
Diesel.
Nhng khi nim v nh ngha c dng y cng nh nu trong phn
nhin liu cho ng c xng.
Thnh ct c xc nh theo phng php th ASTM-D86.
Cng tng t nh xng, nhin liu diesel cng cn phi c thnh phn ct theo
quy nh bo m cho qu trnh hot ng ca ng c bi bay hi ca nhin
liu s nh hng trc tip qu trnh chy ca n trong bung chy, nhng iu cn
phi ch nhin liu Diesel l nhit u v nhit cui thay i trong khong
rng (do nhin liu Diesel c phi trn t nhiu ngun c khong nhit rt khc
nhau nh nu trn v cng tu theo yu cu v cht lng ca n) nn ngi ta
thng khng quan tm nhiu nh trong ng c xng, thng i vi nhin liu
Diesel th ngi ta quan tm n phn trm chng ct mt s nhit nht nh.
Theo tiu chun Vit Nam th c hai gi tr nh sau:
im ct 50% th tch l 290 oC (E50) im ct 90% th tch l 350 oC (E90)
Theo tiu chun Chu u th c ba gi tr sau c quan tm:
250oC thnh phn ct thu c phi nh hn 65% 350oC thnh phn ct thu c phi ln hn 85% 370oC thnh phn ct thu c phi ln hn 95%
Hoa K th ngi ta phn bit hai loi gasoil l gasoil dng cho phng
tin giao thng vn ti v gasoil dng cho cc my mc cng nghip, trong loi th
nht th nhit 90% chng ct phi nh hn 288oC, cn loi th hai nhit ny
mn trong khong 282 oC 338 oC. Tuy nhin, nhng gi tr ca nhit si u cng khng c qu thp v
nhit cui khng c qu cao v iu ny s nh hng xu n vic s dng
trong ng c. Nu nhit cui cao qu tc l trong thnh phn ca n cha nhiu
cu t nng lm cho qu trnh bay hi to hn hp t bc chy km lm tng qu
ThS. Trng Hu Tr Trang 49
-
Sn Phm Du M Thng Phm
trnh chy khng hon lm gim cng sut ca ng c (thc nghim cho thy cng
sut ca ng c s gim i khong 1 5%), to nhiu cht gy nhim mi trng, lm long mng du bi trn trong bung chy hay lm gim nht ca du trong
carter nh nu i vi ng c xng. Ngc li, khi nhit si u nh n khng
nh hng trc tip cng sut ca ng c, nhng nu nh nhit u qu nh th
lm tng bay hi gy mt mt trong qu trnh vn chuyn hay bo qun hay lm
gim nht ca nhin liu c th gy mi mn kim phun.
2.4.4. im cht chy
Nhng khi nim v nh ngha c nu trong phn nhin liu xng.
Cng tng t nh trong phn trc, tiu chun ny c trng cho cc phn nh
d bay hi trong nhin liu, khi phn nh cng nhiu th kh nng bay hi cng ln
iu ny s gy ra mt mt vt cht v iu quan trng hn c l n c th to ra hn
hp n trong qu trnh bo qun v vn chuyn. V vy ch tiu ny c trng cho mc
an ton ca nhin liu Diesel.
Nu nh i vi xng th iu kin thng bay hi ca n ln nn to hn
hp vi khng kh nm trn gii hn n th ngc li y nhin liu Diesel c bay
hi km, iu kin thng th n ch to c hn hp nm di gii hn di ca
hn hp n. Tuy nhin khi nhin liu Diesel c ln nhng phn nh th n c th to ra
nhng hn hp n.
2.4.5. nht (). nht ca nhin liu l mt i lng vt l c trng cho tr lc do ma st
ni ti sinh ra ngay trong lng cht lng khi c s chuyn ng tng i ca cc phn
t vi nhau.
nht c th c biu din di ba dng chnh nh sau: nht ng lc
(cP), nht ng hc (cSt) v nht quy c.
nht ng lc hay nht tuyt i l i lng biu din lc ma st ni ti
thc sinh ra khi cc phn t chuyn ng tng i vi nhau, hai loi nht cn li
l nhng i lng ch cho bit gi tr tng i hay gin tip.
ThS. Trng Hu Tr Trang 50
-
Sn Phm Du M Thng Phm
nht ng lc c rt ra t phng trnh ca Newton v cht lng chy
trong dng ch chy dng (phn ln cc cht lng u c th p dng c
phng trnh ny).
Phng trnh ca Newton c pht biu nh sau: Lc ma st ni ti sinh ra
gia hai lp cht lng c s chuyn ng tng i vi nhau s t l vi din tch b
mt ca hai lp cht lng, vi tc bin dng (khng phi l gradient vn tc).
Phng trnh c biu din nh sau:
dzdvSF ..=
Trong :
F l lc tc dng t bn ngoi lm hai lp cht lng chuyn ng tng i vi nhau v chnh bng lc ma st sinh ra gia hai b mt.
S l din tch ca hai b mt. V l vn tc tng i gia hai lp cht lng. Z l khong cch gia hai lp
l nht ng hc. nht ng hc c th biu theo nhiu n v khc nhau tu theo h thng
n v s dng, nhng thng thng th trong lnh vc du kh n thng c o
trong h CGS, trong h thng ny thn v ca n l Poise (P), thc t th hay dng
i lng c s ca n l centipoise (cP).
Cng tng t nh thnh phn ct hay t trng, nht cng c nhng nh
hng trc tip n hot ng ca ng c. Thc t khi nht qu ln s lm tng
tn tht p sut trong bm v trong kim phun, lm tng kch thc ca cc ht sng
nhin liu do cc tia nhin liu s bay xa nn n c th v p vo thnh ca bung
chy gy ra nhng tc hi nh nu trong phn trn.
Ngc li, khi nhin liu c nht qu thp s lm tng lu lng thot ra
bm np liu, nh vy s lm gim lu lng th tch thc thot ra kim phun (bm
cao p). Trong trng hp ny th kim phun c nng ln chm hn iu ny s lm
ThS. Trng Hu Tr Trang 51
-
Sn Phm Du M Thng Phm
gim nhin liu cung cp cho ng c. Vi nhin liu Diesel c nht nh qu th
khi phun vo xylanh n s to thnh cc ht qu mn, khng th ti c cc vng xa
kim phun c ngha l khng gian trn ln gia nhin liu - khng kh nh, iu ny
lm cho qu trnh to hn hp t bc chy khng tt ng thi phn c phun vo
u c th t bt chy qu sm nn phn phun vo sau c th b phun vo trong kh
chy c nhit qu cao nn nhin liu Diesel khng thi gian bay hi th
nhn c mt lng nhit qu ln nn b phn hu trc khi chy. Nh vy, trong
trng ny cng sut ca ng c cng b gim. Ngoi ra, nhin liu Diesel cn c tc
dng bi trn cho bm cao p v cc l xo trong b phn bm nn khi nht qu
nh d gy ra s rt lm mi mn h thng ny.
2.4.5. Cc ch tiu lin quan n iu kin lm vic nhit thp
Nh chng ta bit nhin liu Diesel thng phm c phi trn t rt nhiu
ngun khc vi thnh phn ho hc ca n c th cha cc hydrocacbon c s nguyn
t cacbon t 10 35. Mun m bo kh nng bay hi to hn hp t bc chy trong bung chy th thnh phn ho hc ca nhin liu Diesel phi cha mt hm lng
nht nh cc hydrocacbon Paraffin, nhng chnh cc hp cht s gy ra cho nhin liu
Diesel nhng kh khn khi nhit ca mi trng xung thp.
Khi nhit xung thp cc hydrocacbon n-paraffin c mch di s kt tinh,
cc tinh th ny c dng hnh kim chng d to ra cc khung tinh th cha nhng
phn cn li, iu ny s lm gim linh ng ca nhin liu. Khi np liu cho ng
c th nhin liu Diesel phi i qua mt h thng lc c mt li lc vi kch thc
khong vi micromet. Trong trng hp ny cc tinh th paraffin c th lm bt cc l
ca li lc dn n sai lch v lng nhin liu cung cp cho ng c ng thi cc
tinh th paraffin ny cn c th gy nhng nh hng xu cho bm nhin liu.
Qua nhng phn tch trn cho thy vic cn thit phi c nhng tiu chun
m bo cho nhin liu Diesel c kh nng lm vic c nhit thp.
Trong thc t, c trng cho kh nng lm vic ca nhin liu Diesel nhit
thp ngi ta dng ba khi nim khc nhau, l: Nhit vn c, im ng
c (im chy), Nhit lc ti hn.
ThS. Trng Hu Tr Trang 52
-
Sn Phm Du M Thng Phm
Gi tr quy nh cho cc tiu chun ny ph thuc vo tng Quc gia, tng chu
lc v tu thuc theo ma khc nhau v cui cng l tu theo loi nhin liu Diesel.
2.4.5.1. im vn c
im vn c l nhit m bt u xut hin s kt tinh ca cc phn t
paraffin trong hn hp ca n iu kin th nghim.
Vic xc nh in vn c c tin hnh theo cc tiu chun ISO 3015 hoc
ASTM D2500, trc y cc kt qu quan st bng mt, ngy ny nhiu phng th
nghim trang b cc thit b bn t ng v kt qu khng cn quan st bng mt
na m n c c nh hai si cp quang.
Gi tr ca im vn c thay i tu theo Quc gia hoc khu vc nhng thng
thng n nm trong khong 0 n -15oC n cng c th ln n 14oC cc nc
nng nhng cng c th xung - 40oC cc nc qu lnh.
2.4.5.2. im ng c hay im chy
im ng c l im m gi tr ca n chnh bng gi tr ca nhit cao
nht m nhin liu Diesel cn c th chy lng.
Gi tr ca im ng c thay i tu theo Quc gia hoc khu vc, khong
giao ng ca n rt rng t + 4oC n -39oC, nhng thng thng n nm trong
khong t - 18oC n - 30oC.
Vic xc nh in ng c c tin hnh theo cc tiu chun ISO 3016 hoc
ASTM D97.
Trong thc t th vic xc nh im ng c cng tng t nh im vn c,
y ngi ta cho 40 ml nhin liu Diesel vo trong ng thu tinh y np kn c gn
nhit k, trc ht un nng hn hp n 45oC sau lm lnh vi tc xc nh
cho n nhit ln hn khong 9oC so vi nhit im chy d on th ta bt u
th nghim tc l t ng nghim sang trang thi nm ngang, nu nhin liu Diesel
trong ng nghim b chy th tip tc lm lnh xung thm 3oC na ri lp li thao tc
trn cho n khi nhin liu Diesel trong ng nghim khng chy khi t ng nghim
nm ngang trong vng 5 giy th ta dng th nghim. im ng c bng gi tr ca
nhit khi dng th nghim cng thm 3.
ThS. Trng Hu Tr Trang 53
-
Sn Phm Du M Thng Phm
2.4.5.3. Nhit lc ti hn
Hai tiu chun va nu trn nhm nh gi linh ng ca nhin liu Diesel
khi c s kt tinh vi mt lng ng k tc l lng tinh th paraffin c th
bt phim lc lm tt qu trnh np liu cho ng c. Tuy nhin trong thc t khi nhit
gim mt mc no m cc tinh th paraffin cha xut hin hoc xut hin
cha nhiu nhng nht ca nhin liu Diesel tng ln mt cch ng k, khi
n s lm gim tnh linh ng ca nhin liu nn n c th lm gim lu lng ca
nhin liu cung cp cho ng c, iu ny s c nhng nh hng xu n qu trnh
hot ng ca n. V vy m bo cho ng c Diesel lm vic tt trong iu kin
ny th ngi ta a ra tiu chun nhit lc ti hn. (TLF)
Nhit lc ti hn l nhit cao nht m mt th tch xc inh ca
nhin liu Diesel (20ml) khng chy qua c mt h thng lc c kch thc xc
nh trong khong thi gian xc nh (60 giy) iu kin th nghim ( chn khng
20mbar).
2.4.6. Hm lng lu hunh
Nh chng ta bit lu hunh trong du th cng nh trong cc sn phm ca
n tn ti di nhiu dng khc nhau nh: Lu hunh dng nguyn t, H2S,
mercaptan, sulfua, disulfua, d vng . . . tu theo dng tn ti ca n m n c th gy
n mn trc tip hay gin tip.
Nu nh trong nhin liu xng lu hunh tn ti ch yu di dng mercaptan
gy ng mn trc tip th trong nhin liu Diesel dng tn ti ny hu nh khng cn
na m ch yu di dng sulfua, disulfua hay d vng khng c kh nng n mn
trc tip m chng ch gy n mn khi b chy trong ng c to ra SO2 sau n
c th chuyn mt phn thnh SO3.
Phn ln lng kh ny thot ra ngoi cng kh chy, nhng c th mt phn
nh lt qua cc xecmng vo trong carter cha du v khi nhit trong carter ny
xung thp th chng kt hp vi hi nc to ra cc axit tng ng gy n mn
cc b mt chi tit khi du c bm tr li cc b mt bi trn.
ThS. Trng Hu Tr Trang 54
-
Sn Phm Du M Thng Phm
Trong cc ng c hin i ngy nay, nhm lm gim hm lng cc cht gy
nhim cho mi trng trong khi thi th ng c c trang b b xc tc chuyn
cc cht c hi thnh cc cht khng hoc km c hi hn. Khi c mt cc kh SOx
trong dng kh thi n s lm gim hot tnh, ng c xc tc v nh hng n nhit
lm vic ca b xc tc. S nh hng ny c th hin trn th sau:
240
% HC c chuyn ho
(0C)
20
40
60
200
220 = 25oC
180
160
0 %S
0,05%S
0,15%S
Nhit kh vo b xc tc
Ngoi ra, khi hm lng lu hunh tng th n s lm gim nhit chy ca
nhin liu Diesel v vy n s lm tng hm lng cc hydrocacbon cha chy, b
hng, mui than trong sn vt chy do cng lm mi mn my mc. Thc nghim
cho thy :
-Hm lng lu hunh khong 0,06% khi lng nhin liu th lng mui
than sinh ra trn secmng v piston l 2,1%.
-Hm lng lu hunh khong 0,85% khi lng nhin liu th lng mui
than sinh ra trn secmng v piston l 5,8%.
-Hm lng lu hunh khong 2,9% khi lng nhin liu th lng mui than
sinh ra trn secmng v piston l 12,2%.
ThS. Trng Hu Tr Trang 55
-
Sn Phm Du M Thng Phm
2.4.7. n nh oxy ho Nhin liu Diesel thng phm c phi trn t nhiu ngun khc nhau trong
c nhiu ngun thu c t cc qu trnh ch bin su m trong thnh phn ca n
c cha nhiu hp cht km bn nh olefin, diolefin, aromatic . . .
Trong qu trnh ch bin, vn chuyn, bo qun cng nh trong qu trnh np
liu cho ng c th nhin liu lun tip xc vi cc tc nhn gy oxy ho nh oxy,
nhit v c s c mt ca xc tc th nhin liu s b bin i to ra cc hp cht
nh nha, cn . . . y l cc hp cht c hi ca nhin liu v n c th gy n mn,
gy tt nghn phim lc . . . v vy cn thit nhin liu Diesel phi m bo c tiu
chun ny.
2.4.8. n mn tm ng Mc d phn ln cc thnh phn cha lu hunh c loi ra khi nhin liu
trong qu trnh ch bin nhng vic loi ra ton b l khng kh thc hin v mt cng
ngh v khng kinh t. Mc d phn cn li trong sn phm l khng nhiu nhng s
tn ti ca n cng vi s tn ti ca cc hp cht hu c cha oxy cng c th gy ra
s n mn mnh i vi cc b phn ca ng c. V vy, hm lng ca cc hp cht
ny trong nhin liu Diesel cng cn phi nm trong mt gii hn nht nh. Gii hn
ny c biu din qua php th tnh cht n mn tm ng.
Tiu chun vit Nam v n mn tm ng i vi nhin liu Diesel theo
phng php th ASTM-D130 ti a l mc N1.
2.4.9. Hm lng nc Nc trong nhin liu cng rt nguy him cho ng c v chng gy n mn
mnh v r, gy tr ngi cho qu trnh chy. Trong qu trnh chng ct kh quyn, phn
on gasoil trc khi c ly ra lun phi qua qu trnh tripping bng hi nc, sau
nc c tch loi nhng n vn cn mt gii hn nht nh. Hn na, trong
qu trnh bo qun do s th ca cc b cha nn mt lng nc t hi m ca
khng kh s i vo trong nhin liu Diesel.
Hm lng nc trong nhin liu Diesel c xc nh theo phng php o
ASTM-D95.
ThS. Trng Hu Tr Trang 56
-
Sn Phm Du M Thng Phm
Chng III
NHIN LIU CHO NG PHN LC
3.1. Gii thiu chung v ng c phn lc v nhin liu ca n
3.1.1. S lc v lch s pht trin ca ng c phn lc v nhin liu ca n
Nhin liu cho ng c phn lc l mt loi nhin liu c s dng cho cc
ng c trn my bay phn lc, loi ng c ny lm vic trong iu kin rt c bit
(nhit v p sut mi trng thp, cao ln). V vy nhin liu cho n i hi
mt s kht khe nht trong tt c cc loi phng tin giao thng.
Lch s chic my bay c th tnh bt u vo ngy 09/09/1890 khi Clement
Ader cho th nghim thnh cng loi thit b c th bay trn mt t, chiu di mi
chuyn bay khong 50 m. Clement Ader t tn cho n l "my bay".
Ngy 17 thng 12 nm 1903 ngi ta sn xut c loi my bay trang b
ng c piston vi cng sut 16 sc nga c hai cnh qut, nhng bc ngoc trong
ngnh hng khng phi i n ngy 15 thng 9 nm 1904 v ngy 20 thng 9 nm
1904 ngi ta mi thc hin c mt hnh trnh trn vn.
ng c piston cho ngnh hnh khng pht trin mnh m t nm 1910 n
1930 v t c nhng thnh cng nht nh di gc hiu sut, nhng n b
hin tng kch n ca nhin liu khng ch do y ngi ta cng s dng khi
nim ch s octan nh trong nhin liu ca ng c xng.
Nm 1911 mt k s ngi Php tn la Ren Lorin thit k ng c phn
lc u tin nhng trn ho tin sau n c pht trin bi Ren Leduc nm
1937, nhng thnh cng trong lnh vc ny cho php ch to c loi ng c
phn lc thng v chuyn bay u tin ca n c thc hin vo ngy 21/04/1949
Php. Sau nhng thnh cng ny ngi ta ch to c cc loi ng c phn lc
kiu turbine. S thnh cng ca loi ny din ra trong thi chin tranh th gii th hai
t nm 1939 n 1944 vi vn tc cc i t c tri qua t 300 km/h n 700
km/h.
ThS. Trng Hu Tr Trang 58
-
Sn Phm Du M Thng Phm
Ngy 2 thng 5 nm 1952 ngi Anh thc hin c chuyn bay dn dng
u tin bng my bay phn lc nh du mt k nguyn mi cho loi ng c ny
ng thi loi b hon ton loi my bay trang b ng c piston.
Nhng thnh cng trong lnh vc ny tip tc c pht trin, nng cao v c
p dng rng ri cho n nhng nm 1970 v c nh du bng s ra i ca chic
my bay dn dng Concorde do ngi Anh v Php hp tc sn xut.
Ngy nay vi hn khong 15000 chic my bay dn dng tn ti trn ton th
gii n tiu th khong 700 000 tn nhin liu.
Nh vy th h u tin ca my bay l loi trang b ng c piston nhin liu
dng cho n c gi l xng my bay. Nhng th h my bay tip theo c trang b
ng c phn lc nh ng c phn lc kiu thng, cnh qut, turbine. Ngy nay hai
loi cui cng ny dc s dng ph bin nht.
trong phn ny ta ch nghin cu nhin liu dng cho hai loi cui cng ny,
loi ny dc gi chung l nhin liu cho ng c phn lc.
3.1.2. Phn loi nhin liu dng cho ng c phn lc
ng c phn lc tri qua nhiu th h khc nhau t khi xut hin, do
nhin liu ca n cng phi thay i theo p ng c cc yu cu mi. Hn na
s khc nhau ny cn ph thuc vo mc ch s dng l qun s hay dn dng m
yu cu v nhin liu cng c nhng khc nhau nht nh. Trong thc t th nhin liu
dng cho ng c phn lc gn nh ging nhau nhng chng c k hiu khc nhau
Hoa K v cc vng cn li.
ThS. Trng Hu Tr Trang 59
-
Sn Phm Du M Thng Phm
S phn loi ca khi OTAN
Dng nhin liu Ph gia
chng ng
K hiu
ca
OTAN
S dng
cho dn
dng theo
tiu chun
ASTM
D1655
S dng cho mc
dch qun s
Kerosen
Kerosen c im cht
chy cao
Loi phn on rng
Loi c n nh
nhit cao
C
Khng
C
Khng
C
Khng
C
F-34
F-35
F-44
F-43
F-40
F-45
Jet A1
Jet B
TRO, JP-8,
AVTUR (TRO/ni*,
AVTUR)
TR5, JP-5
(TR5/ni*)
TR4, JP-4
(TR4/ni*)
TS, JP-7
Loi c nhit nng th
tch cao
C
Khng
RJ-6, JP-9, JP-10
RJ-4, RJ-5
3.1.3. Nhin liu cho ng c phn lc
Nh cch phn loi trn th nhin liu cho ng c phn lc c th c chia
thnh ba dng chnh: Dng Kerosen, dng Kerosen vi im cht chy cao v dng
phn on rng.
ThS. Trng Hu Tr Trang 60
-
Sn Phm Du M Thng Phm
Loi nhin liu c dng cho cc my bay dn dng trn th gii l dng
kerosen Jet A1 tng ng F-35 ca khi OTAN, Hoa K th dng cho my bay dn
dng ny l loi Jet A tng t nh loi Jet A1 trn nhng im chy ca n cao hn
(-40oC thay v -47oC).
i vi dng th hai cho php tn cha rt an ton trong nhng khoang cha
ca my bay. Cn loi th ba th c nhit si u rt thp khong 70oC, thc cht
y l sn phm thu c t vic phi trn ca phn on naphta nh vi Kerosen.
Ngoi ra nhin liu phn lc cn c nhiu dng khc nhau phc v cho nhng
mc ch khc nhau nh loi nhin liu co nhit nng cao dng cho ho tin.
3.2. Nguyn tc hot ng ca ng c phn lc
Qu trnh hot ng ca ng c phn lc c th c chia thnh ba giai on
lin tip nh sau: Ht v nn kh, chy ng p v gin n sinh cng. Qu trnh
chy xy ra lin tc trong mt dng kh c tc ln. im khc nhau ca ng c
phn lc turbine v ng c phn lc cnh qut l phng thc chuyn ng nng
ca dng kh chy thnh lc lm chuyn ng my bay.
ng c phn lc turbine th ch dng mt phn ng nng ca dng khi thi
do nhin liu b t chy trong bung chy to ra lm quay burtine - my nn
phn ng nng ch yu cn li cho gin n qua tuye ra ngoi vi vn tc ln to
nn mt phn lc tc ng ln ng c lm cho ng c chuyn ng v pha trc.
ng c phn lc cnh qut th ton b ng nng ca dng kh chy c gin n qua
turbine nhm lm quay my nn v cnh qut cng cc thit b ph bn ngoi.
S nguyn l ca ng c phn lc nh sau:
ThS. Trng Hu Tr Trang 61
-
Sn Phm Du M Thng Phm
Khng kh i vo ng c qua ca ht sau qua thit b phn phi. phn t
chy c a vo my nn nn n mt p sut nht nh sau dng kh c gim
vn tc n gi tr thch hp trc khi vo bung chy, y khng kh s trn ln vi
nhin liu do bm nhin liu a vo qua kim phun. khi ng ng c, bugie
nh la v hn hp s bt chy, kh chy sinh ra c cho qua turbine tt c hay ch
mt phn nh va nu trn. iu cn ch y l bugie ch nh la mt ln trong
khong thi gian khng qu 30 giy cho mi chuyn bay.
Qua phn tch nguyn tc hot ng ca ng c cho thy mun tng tc ca
ng c th cn tng ng nng ca dng kh thi. Khi mun tng vn tc ca dng kh
thi bng cch tng p sut nn th s lm cho nhit ca kh thi ln, iu ny c
th vt qua gii hn chu nhit ca vt liu lm bung chy . . . trong thc t c hai
phng php lm tng vn tc dng kh thi nh sau:
ng c phn lc c hai dng kh np (Le Turborarteur double flux) ng c phn lc c hai vng t chy nhin liu.
3.3. Cc ch tiu v cht lng ca nhin liu cho ng c phn lc
Trc khi nu v phn tch cc ch tiu ca nhin liu nh hng n hot ng
ca ng c phn lc ta c nhng nhn xt ban u v c im hot ng ca ng
c phn lc nh sau:
Qu trnh chy trong ng c phn lc l mt qu trnh chy c bit trong
dng kh xoy c tc ln v ng c lm vic trong iu kin nhit v p sut
mi trng thp. V vy m bo cho hot ng ca ng c c n nh th nhin
liu phi t c nhng tnh cht sau:
Nhng tnh cht lin quan n qu trnh chy Nhng tnh cht lin quan n iu kin lm vic cao ln Nhng tnh cht lin quan n qu trnh bao qun v phn phi cho ng c.
C th nhin liu phi m bo cc yu cu chnh sau y:
C kh nng bt chy tt v khng b tt trong dng kh chy Tc chy ln, chy iu ho
ThS. Trng Hu Tr Trang 62
-
Sn Phm Du M Thng Phm
Chy hon ton v t to cn Nhit chy ln (trn 10200 kcal/kg) Nhit ng t thp
3.3.1. Nhng ch tiu lin quan n qu trnh chy Trong ng c phn lc th qu trnh chy din ra trong mt h m nn trnh
c nhng hin tng kch n. V vy, gc ny th nhng tnh cht lin quan
n s bt chy ca nhin liu s khng nh hng ln nh trong nhin liu xng v
Diesel. Tuy nhin thnh phn ho hc ca nhin liu cng c nhng nh hng nht
nh n tc chy ca nhin liu do s nh hng n cht lng ca qu trnh
chy.
Cc tnh cht lin quan n qu trnh chy ny c th phn thnh hai nhm:
Cc tnh cht vt l ca nhin liu Cc tnh cht v nhit ho hc
3.3.2. Cc tnh cht vt l ca nhin liu Nh ni trong phn trc, trong ng c phn lc th nhin liu c phun
vo trong mt dng kh c tc ln sau mt khong thi gian nht nh mi b t
chy, thi gian ny cn thit cho nhin liu bay hi v to hn hp vi khng kh.
Cht lng ca qu trnh chy ph thuc nhiu vo cu trc hnh hc ca bung chy
v thit b phun nhin liu. Tuy nhin, cc tnh cht nh bay hi, sc cng b mt
nht ca nhin liu s c nhng nh hng ln n s phun nhin liu v s khut
tn ca n vo trong khng kh.
Nu nh bay hi ln th kh nng bay hi to hn hp vi khng kh d
dng cho qu trnh chy c tt. Nhng khi qu trnh bay hi qu ln th d to ra
hin tng nt hi nh hng xu n qu trnh np liu cng nh cc tnh cht v an
ton, mt mt vt cht.
Nhin liu c phun vo bung chy di dng cc ht sng, y n s tip
xc vi dng khng kh c nn n nhit v p sut nht nh, khi nhin
liu s nhn nhit t khng kh bay hi. Nu nh sc cng b mt nh th kh nng
ho hi ca cc ht sng ny tt do nhin liu cng d ho trn vi khng kh
ThS. Trng Hu Tr Trang 63
-
Sn Phm Du M Thng Phm
to hn hp chy tt. Ngc li, khi sc cng b mt ln th kh nng bay hi to hn
hp chy s km nn qu trnh chy s km.
Nhin liu c phun vo bung chy di dng cc ht sng, kch thc ca
cc ht sng ny cng vi khng gian trong bung chy do cc ht sng ny chim
ch ngoi vic ph thuc vo cu to v p lc ca kim phun th nht ca nhin
liu cng c nhng nh hng n qu trnh ny. Khi nht ln th cc tia nhin
liu phun ra cng di, ngha l khng gian chim ch ca nhin liu cng ln, y l
iu c li cho qu trnh bay hi, nhng ngc li khi nht ln th kch thc ca
cc ht sng ln lm cho qu trnh bay hi s km. Ngoi ra khi nht ln th tr
lc trong h thng np liu cng ln. Ngc li, khi nht qu nh th nguy c gy
mi mn h thng np liu cng ln.
3.3.3. Cc tnh cht v nhit ho hc bo m cho hiu sut s dng nhit cao v ko di tui th ca cc vt liu
trong bung chy, turbine v tuye th yu cu t ra l nhin liu khi chy phi c
ngn la sng mu, hn ch thp nht s bc x nh