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Cursul 5
Bazele integr ării termice(cont)
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THE MINIMUM NUMBER OF UNITS
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Sa presupunem ca am realizat analiza de integrare, am determinat tintele si amsintetizat reteaua de schimbatoare de caldura in diagrama grid, dupa care am sintetizat
rocesul care arata ca in fi ura de fata
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Problema care se pune este cum sa sintetizam
o retea de unitati de transfer termic care sa
permita atingerea tintelor de import de utilitati,
dar, in acelasi timp trbuie sa contina si unnumar minim de unitati de transfer.
Asadar, cum identificam care este numarulminim de unitati de transfer si cum ne
raportam la el in timpul sintezei retelei de
schimbatoare ?
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Euler a tratat si rezolvat pentru prima data o problema de acest tip, legat de modul in
care se poate realiza transportul optim intre mai multe orase, situate la diverse distante
de un oras sursa (problema “traseului spatio-temporal”).
?
ROAD MAP ANALOGY
How many roads do we need to have ar least one connection from every cite to ever other city?
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SF
LA
CH
NO
NY SF
LA
CH
NO
NY
SF
LA
CH
NO
NY SF
LA
CH
NO
NY
Interstate network
4 roads 4 roads
4 roads4 roads
etc
4 roads seems to be the minimum
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Rule (by inspection):
We need at least N-1 lines (roads) to fullyconnect N nodes (cities)
Euler conclusion:
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Definitive case study conclusion:
FOUR ROADS IS THE MINIMUM
SF
LA
CH
NY
NO
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Back to Heat Exchangers Network
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Are six heat heat transfer units necessary?
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Exemplu cu o colectie de curenti, neseparati de Pinch (care nu are legatura cu
reprezentarea din slide-ul anterior) :
We need steam
E
F
P
R
St E
F P R
Set targets
Draw “Euler Diagram (Graph)”
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Some definitions:
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I II
I I I
IV
Asadar, pentru cazul in discutie:
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R e a c
t o r Recycle (R)
Feed (F)Product (P)
Design with four units!
S t e a
m
Remember? St E
F P REffluent
(E)
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1. Concluzie:
pentru cazul in care nu tinem seama de existenta Pinch-ului,numarul minim de aparatede schimb de caldura este egal cu:
Numarul curentilor de proces si util itari minus unu
(N -1)
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Ce se intampla insa, daca vrem sa stim numarul minim de unitatide transfer atunci cand reteaua construita vrem sa aiba si
caracteristica de asigurare a MER-ului (Cazul unei RSC construita
deoparte si de alta a zonei Pinch)?
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Above Below
2. Concluzie in cazul RSC pentru MER
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Exemplu:
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Practic, RSC-urile pentru MER sunt 2 in acest caz:
C ibil bti RSC MER i U i ?
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a bifa
Cum e posibil sa obtinem RSC cu MER, si Umin?
R e p r e z
e n t a n d e t a p e l e d e
c o n s t r u c t i e
R S C d
e a s u p r a P i n c h
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Maximising matches duties = many ticking-off streams
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= 5
= 4 + 3 = 7
I
II
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A preliminary advantage:
But, by design we can understand two main situations:
- grassroot design – new plant;
- retrofitting design ( i.e. HEN synthesized for MER, or an
existing HEN)
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I
II
Important case:
Identifying minimum of units in case of
HENs constructed for MER:
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See also slide 13
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Ne w road
see also slide 7…
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III
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S= numar maxim de sisteme create dupa realizarea oricarei taieri a unei legaturi intre curenti.
E l
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Examples:
So case Umin = N 1 is valid for targeting of number of units from HEN without loops
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So, case Umin = N – 1, is valid for targeting of number of units from HEN without loops
See slide 21
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See slide 21
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Summary
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Summary
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Reducing the number
of UNITS (heat transfer units)
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See slide 45 for data
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HU
CU
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Couple below pinch
Couple above pinch
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a path (betweenHU and CU)
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III
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