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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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