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Optimal mixed refrigerant liquefaction of natural gas / Ait Ali, Mohand Ameziane

Public ISBD Titre : Optimal mixed refrigerant liquefaction of natural gas Type de document : texte imprimé Auteurs : Ait Ali, Mohand Ameziane, Auteur ; Douglass Wilde, Directeur de thèse Editeur : Californie : University of Stanford Année de publication : 1979 Importance : 102 f. Présentation : ill. Format : 28 cm. Note générale : Thèse de Doctorat : Génie Mécanique : Californie, University of Stanford : 1979 Annexe f. 103 - 166 . Bibliogr. f. 167 - 170 Langues : Anglais (eng) Mots-clés : Refrigeration  systems Natural  gas Liquefaction Cascade  cycles Heat  transfer Equation  of  state Index. décimale : D001279 Résumé : The design of optimal industrial refrigeration systems, which often require several stages, involves primarily trading off heat transfer area for compressor work. For specified flow conditions and surface geometries, this is obtained by varying the mean temperature difference and the amount of refrigeration in each stage. The problem is dynamic in the interstage temperatures. Since in natural gas liquefaction cycles the total work related cost, which includes compressor, heat exchanger and cycle work, represents about nine times that of the heat exchangers, a minimum work design is nearly optimal for any feasibly small temperature approach. Single stage cascade cycles with pure component refrigerants and azeotropic mixtures lead to large refrigeration work and small heat transfer areas. In multistage cascade cycles the minimum sun of the ideal Carnot cycle work and the irreversible work of heat transfer is achieved when the refrigerant interstage temperatures equal the generalized geometric mean of the specified refrigerant end temperatures as defined. On the other hand, evaporator heat transfer area is a flat convex function of the feed stream interstage temperatures. Its maximum occurs when these temperatures equal the generalized arithmetic mean of the specified feed stream end temperatures. These two results approximate the minimum cost design for multistage refrigeration cycles. Compressor work for a mixed refrigerant Carnot cycle with constant temperature approach is the limit for a cascade cycle with a number of stages approaching infinity. The work saving and heat transfer area increase for such a cycle are compared parametrically with single-stage cost. The break-even point as a function of heat-sink temperature and minimum temperature approach show that mixed refrigerant cycles are clearly advantageous for low temperature refrigeration (small Tf/Tw ratio), while single-component refrigerant cycles are economical for nearly ambient refrigeration (Tf/Tw near unity). Actual multistage mixed refrigerant cycles do not lend themselves to closed form optimization methods; however numerical methods are useful. A two-stage natural gas precooling cycle is optimized numerically for a ternary ethane/propane/n-butane refrigerant and an equation of state based on ideal solution assumptions and Raoult's law vaporliquid equilibria. Rigorous thermodynamic formulation and monotonicity analysis reduced the optimization problem to a two-dimensional search with evaporator temperature approach and interstage temperature as decision variables. Power requirement is found to increase linearly with both decision variables. However, near the feasible domain boundary, decreased temperature approach leads to higher interstage temperature and vice versa. Moreover, minimum feasible values of these variables decrease with heat-sink temperature, leading to lower minima. With 75°F cooling water the minimum power is 162000hp per billion standard cubic feet per day of liquefied natural gas, 10% lower than for a comparable industrial propane precooling cycle. Cooling water requirement is 50% lower. Minimum precooling cost evaluated with 1976 cost data, is achieved for the minimum power design, since compressor work costs dominate. Optimal mixed refrigerant liquefaction of natural gas [texte imprimé] / Ait Ali, Mohand Ameziane, Auteur ; Douglass Wilde, Directeur de thèse . - Californie : University of Stanford, 1979 . - 102 f. : ill. ; 28 cm. Thèse de Doctorat : Génie Mécanique : Californie, University of Stanford : 1979 Annexe f. 103 - 166 . Bibliogr. f. 167 - 170 Langues : Anglais (eng) Mots-clés : Refrigeration  systems Natural  gas Liquefaction Cascade  cycles Heat  transfer Equation  of  state Index. décimale : D001279 Résumé : The design of optimal industrial refrigeration systems, which often require several stages, involves primarily trading off heat transfer area for compressor work. For specified flow conditions and surface geometries, this is obtained by varying the mean temperature difference and the amount of refrigeration in each stage. The problem is dynamic in the interstage temperatures. Since in natural gas liquefaction cycles the total work related cost, which includes compressor, heat exchanger and cycle work, represents about nine times that of the heat exchangers, a minimum work design is nearly optimal for any feasibly small temperature approach. Single stage cascade cycles with pure component refrigerants and azeotropic mixtures lead to large refrigeration work and small heat transfer areas. In multistage cascade cycles the minimum sun of the ideal Carnot cycle work and the irreversible work of heat transfer is achieved when the refrigerant interstage temperatures equal the generalized geometric mean of the specified refrigerant end temperatures as defined. On the other hand, evaporator heat transfer area is a flat convex function of the feed stream interstage temperatures. Its maximum occurs when these temperatures equal the generalized arithmetic mean of the specified feed stream end temperatures. These two results approximate the minimum cost design for multistage refrigeration cycles. Compressor work for a mixed refrigerant Carnot cycle with constant temperature approach is the limit for a cascade cycle with a number of stages approaching infinity. The work saving and heat transfer area increase for such a cycle are compared parametrically with single-stage cost. The break-even point as a function of heat-sink temperature and minimum temperature approach show that mixed refrigerant cycles are clearly advantageous for low temperature refrigeration (small Tf/Tw ratio), while single-component refrigerant cycles are economical for nearly ambient refrigeration (Tf/Tw near unity). Actual multistage mixed refrigerant cycles do not lend themselves to closed form optimization methods; however numerical methods are useful. A two-stage natural gas precooling cycle is optimized numerically for a ternary ethane/propane/n-butane refrigerant and an equation of state based on ideal solution assumptions and Raoult's law vaporliquid equilibria. Rigorous thermodynamic formulation and monotonicity analysis reduced the optimization problem to a two-dimensional search with evaporator temperature approach and interstage temperature as decision variables. Power requirement is found to increase linearly with both decision variables. However, near the feasible domain boundary, decreased temperature approach leads to higher interstage temperature and vice versa. Moreover, minimum feasible values of these variables decrease with heat-sink temperature, leading to lower minima. With 75°F cooling water the minimum power is 162000hp per billion standard cubic feet per day of liquefied natural gas, 10% lower than for a comparable industrial propane precooling cycle. Cooling water requirement is 50% lower. Minimum precooling cost evaluated with 1976 cost data, is achieved for the minimum power design, since compressor work costs dominate.

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Code-barres	Cote	Support	Localisation	Section	Disponibilité	Spécialité	Etat_Exemplaire
D001279	D001279	Papier	Bibliothèque centrale	Thèse de Doctorat	Disponible	Genie_mecanique	Consultation sur place