Area Target

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Area Target. T. Hot Streams. Cold Streams. Section Stream Population. j. k. H. Q j. enthalpy interval. Townsend, D. W. and B. Linnhoff, “Surface Area Targets for Heat Exchanger Networks”, IChemE Annual Research Meeting, Bath, England (April, 1984). T=100 . T=90 . CP = 0.5.
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Area TargetTHot StreamsCold StreamsSection StreamPopulationjkHQjenthalpy intervalTownsend, D. W. and B. Linnhoff, “Surface Area Targets for Heat Exchanger Networks”, IChemE Annual Research Meeting, Bath, England (April, 1984)T=100T=90CP = 0.5CP = 2.5CP = 1TCP = 1SteamCP = 6T=80T=75CPH=7T=100T=90T=80T=75CPC=14CWHFigure 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 8.1-1Approach temperature = 10250240230220210200190180170160150140130120110100 90HotutilityTemperature, F12+176++21+j+++22+Number of cold streamsin this interval111+Coldutility++0 200 400 600Enthalpy, 1000 Btu/hr = Hot + = ColdFIGURE 8.3-1Tempreature-enthalpy diagram.Hot composite Curve T (F) H (BTU/hr)103 100 0 120 80 140 180 160 280 200 480 250 530Cold composite Curve T (F) H (103 BTU/hr) 90 60 130 180 150 360 190 600MINIMUM HEAT TRANSFER AREA IN INTERVAL jStream No. CP  103 qk,j  103TS TTand Type(BTU/hr.F)(BTU/hr)(F) (F)1. Hot 1 36 176 1402. Hot 4 144 176 140 3. Cold 3 - 60 130 150 4. Cold 6 - 120 130 150Stream No. CP  103 qk,j  103TS TTand Type(BTU/hr.F)(BTU/hr)(F) (F)1. Hot 1 36 176 1402. Hot 2/3 24 176 140 31/3 120 176 140 3. Cold 1.8 - 36 130 150 1.2 - 24 130 150 4. Cold 6 - 120 130 150123MINIMUM HEAT TRANSFER AREA IN INTERVAL jMINwhere Nj = total number of process streams in interval jMINThot-cold(a)PINCHTcoldA Screening Procedure For Detection of “Bad” MatchesTA Good Match(b)TcoldA Screening Procedure For Detection of “Bad” MatchesTTwo Bad Matches(c)TcoldA Screening Procedure For Detection of “Bad” Matches (a) Temperature1-1 Exchanger (b) Temperature1-2 ExchangerTH1TH1TC2TC2TH2TH2TC1TC1LengthLengthTH1partial cuntercurrentpartial cocurrentcountercurrentTC1TC2TC2TH1TC1TH2TH2Q = UATLMQ =(UATLM)  FT FT = f (R,P)Figure 7.7 1-1 shells approach pure countercurrent flow, whereas 1-2 shells exhibitpartial countercurrent and partial cocurrent flow.R=1Figure 7.8Figure 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 largeP 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.)temperature crosses smallerAB(b) Putting shells in series reduces the temperature cross in individual exchangers.AFigure 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
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