Area Target Section Stream Population j k Cold Streams Hot Streams H T QjQj enthalpy interval

Townsend, D. W. and B. Linnhoff, “Surface Area Targets for Heat Exchanger Networks”, IChemE Annual Research Meeting, Bath, England (April, 1984)

H T Steam CW  CP C =14  CP H =7 T=100  T=80  T=90  T=75  T=100  T=80  T=90  T=75  CP = 0.5 CP = 2.5 CP = 1 CP = 6 Figure B.1 within each enthalpy interval it is possible to design a network in (S - 1) matches. (From Ahmad and Simth, IChemE, ChERD, 67: 481, 1989; reproduced by permission of the Institution of Chemical Engineers.)

Table Approach temperature = Enthalpy, 1000 Btu/hr = Hot + = Cold Temperature,  F FIGURE Tempreature-enthalpy diagram. 176 Hot utility Cold utility Number of cold streams in this interval j

Hot composite Curve T (  F) H (BTU/hr)  Cold composite Curve T (  F) H (  10 3 BTU/hr)

MINIMUM HEAT TRANSFER AREA IN INTERVAL j Stream No. CP  10 3 q k,j  10 3 T S T T and Type (BTU/hr.  F) (BTU/hr) (  F) (  F) 1. Hot Hot Cold Cold Stream No. CP  10 3 q k,j  10 3 T S T T and Type (BTU/hr.  F) (BTU/hr) (  F) (  F) 1. Hot Hot 2 / / Cold Cold

MINIMUM HEAT TRANSFER AREA IN INTERVAL j MIN where N j = total number of process streams in interval j MIN

 T hot-cold T cold PINCH (a) A Screening Procedure For Detection of “Bad” Matches

TT T cold (b) A Screening Procedure For Detection of “Bad” Matches A Good Match

TT T cold (c) A Screening Procedure For Detection of “Bad” Matches Two Bad Matches

1-1 Exchanger (a) Temperature Length countercurrent Figure shells approach pure countercurrent flow, whereas 1-2 shells exhibit partial countercurrent and partial cocurrent flow. Q = UA  T LM T H1 T H2 T C2 T C1 T H1 T C2 T H2 T C1 T C2 T H1 T H2 T C1 Q =(UA  T LM )  F T F T = f (R,P) 1-2 Exchanger (b) Temperature Length T C1 T C2 T H1 T H2 partial cuntercurrent partial cocurrent

R=1 Figure 7.8

Figure 7.8 Designs with a temperature approach or small temperature cross can be accommodated in a single 1-2 shell, whereas designs with a large temperature cross become infeasible. (From Ahmad, Linnhoff, and Smith, Trans. ASME, J. Heat Transfer, 110: 340, 1988; reproduced by permission of the American Society of Mechanical Engineers.)

temperature cross large P large (a) A single 1-2 shell is infeasible. Figure 7.10 A large overall temperature cross requires shells in series to reduce the cross in individual exchangers.(From Ahmad, Linnhoff, and Smith, Trans. ASME, J. Heat Transfer, 110: 340, 1988; reproduced by permission of the American Society of Mechanical Engineers.)

A B AB temperature crosses smaller Figure 7.10 A large overall temperature cross requires shells in series to reduce the cross in individual exchangers.(From Ahmad, Linnhoff, and Smith, Trans. ASME, J. Heat Transfer, 110: 340, 1988; reproduced by permission of the American Society of Mechanical Engineers.) (b) Putting shells in series reduces the temperature cross in individual exchangers.