This preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full DocumentThis preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
Unformatted text preview: M4; am Gama(30M +0“
mmﬁm gu‘kto We»;
(2&3qu kWh1 ? MM‘H—u I. SCHSN) Q E acewtm 
& 4x‘JL3TIQB
' NE: 2¢+1 (MWB . .‘.N=Z‘+(o
WADE) \Wb '
. 6 Mb, '
W4 UM ins90¢qu «we ~1«EMWHfM’ 6:4.) kJ N L 4C+ 1'5) — EZwngCHA +— N‘ T 3 w... tmim
M = 7u+ zuc +2c+‘ (19.5w)
N‘s! ——_.._..._. chcr'n  200—13 SNi put+7. i102 N. .lvm.
N
thuJc‘imemLSCo‘g N
2W i L
(xicc3l I L.“ “
$414.“... T l. l
S
wFZQ'F
Mo. ml % #611... a cmétl“ Ha. m M
014.. Qan— . m
44.30 M . Equations ' Number of Equations . Pressure equality _ , 1 PVOUT _ PLOUT TVOUT = TLOUT
' Phase equilibrium relationships, C (yavom = K£(xi)LOUT Component material balances, C — 1
LIN(xi)Lm + VIN(yi).VN = LOUT(xE)LOUT + VOUT(yi)VOUT Total material balance, 1
LIN + VIN = Low + Vour Energy balance, 1
Q + hLmLIN + hVINVIN = hLOUTLOUT + hVOUTVOUT Mole fraction constraints in entering and exiting streams 4 C
e.g., (yahm = 19
" NE = 2C + 7 ND=(4C+13)—(2C+7)=2C+6 —Variable Speciﬁcation Number of Variables Component mole fractions, (x,)LIN  C — 1
Total ﬂow rate, LIN 1
Component mole fractions, (yaym C — 1
Total ﬂow rate, VIN 1
Temperature and pressure of LIN
Temperature and pressure of VIN
Stage pressure (PVOUT or PLOW)
Heat transfer rate, Q 1 . N922C+6 I—lNN Speciﬁcation of these (2C + 6) variables permits calculation of the unknown variables Low, VOUT, (xc)Lm, (ydvm, all (x;)LOUT, TOUT, and all (y,)V0UT, where C denotes the
missing mole fractions in the two entering streams. VIN LOUT Figure 5.17 An Nstage cascade. Variable Speciﬁcation Number of Variables
Heat transfer rate for each stage (or adiabaticity) N
Stage pressures N
Stream VIN variables C .+ 2
Stream LIN variables  C + 2
Number of stages 1
2N + 2C + 5 auubv (2N + C + 6) 1. Recovery of 1. Number of Partial light key com stages above
ponent feed stage
' ' ' ' “~wa 2. "Recovery of “2. NTiiiDaefot‘
(CHI) 2:; ’ F" 1". .3; heavy key com stages below
9 — Q .. M ponent I feed stage
‘ 1 “' 3. Reﬂux ratio 3. Reﬂux ratio
(> minimum) 4. Distillate ﬂow
4. Optimum feed rate
stageb ‘"Reboier Figure 5.18 Complex distillation unit. . Element or Unit (N 1;)‘ (NE),
Total condenser (2C + 7) (C + 3)
Reﬂux divider (3C + 10) _ _ _ __ _ __ _' (2C + 5)
_ (N 3'3) stages [7(N — S) + 2(N — S)C + 2C + 7] [SUV — S) + 2(N — .S')C + 2]
Sidestream stage (5C + 16) (3C + 9)
(S—1)—Fstages [7(S—lF)+2(S—1—F)C [5(S—1—F)+2(S—1F)C
+ 2C + 7] + 2]
Feed stage (5C + 16) (2C + 8)
(F— 1) — 1 stages [7(F — 2) + 2(F — 2)C + 2C + 7] [5(F — 2) + 2(F  2)C + 2]
Partial reboiler (3C + 10) (2C + 6) 2(NV), = 7N + ZNC + 18C + 59 ZONE): = SN + 2NC + 4C + 22 Subtracting (C + 3) redundant variables for 13 interconnecting streams, according to_ (568),
with NA = 0 (no unspeciﬁed repetitions), gives (Nam = 2 (NE), w 13(C + 3) = 7N + me + 5C + 20
Subtracting the corresponding 13 redundant molefraction constraints, according to (569),
(Nahm. = 2 (NE), a 13 = 5N + 2N0 + 4c + 9
Therefore, from (571),
ND=(7N+2NC+5C+20)—(5N+2NC+4C+9)=2N+C+11 A set of feasible design variable speciﬁcations is Variable Speciﬁcation Number of Variables 1. Pressure at each stage (including partial reboiler) N
Pressure at reﬂux divider outlet 1
Pressure at total condenser outlet 1
Heat transfer rate for each stage (excluding partial reboiler) (N — 1)
Heat transfer rate for divider Feed mole fractions and total feed rate Feed temperature Feed pressure Condensate temperature (e.g., saturated liquid)
Total number of stages, N 11. Feed stage location 12. Sidestream stage location 13. Sidestream total ﬂow rate, S 14. Total distillate ﬂow rate, D or DEF 15. Reﬂux ﬂow rate, LR, or reﬂux ratio, I.ng i—n
PEOP'JTJP‘E"PPP D—lr—lr—‘FdlIIiIilil—‘nb—K ND = (2N + c+11) In most separation operations, variables related to feed conditions, stage heat transfer rates.
and stage pressure are known or set. Remaining speciﬁcations have proxies, provided that the
variables are mathematically independent of each other and of those already known. Thus. in
the above list, the ﬁrst 9 entries are almost always known or speciﬁed. Variables 10 to 15,
however, have surrogates. Some of these are 16. Condenser heat duty, QC. 17. Reboiler heat duty, QR 18. Recovery or mole fraction of one component in bottoms
19. Recovery or mole fraction of one component in distillate ...
View
Full
Document
This note was uploaded on 01/13/2010 for the course CHEM 1 taught by Professor Pines during the Winter '08 term at Berkeley.
 Winter '08
 Pines

Click to edit the document details