UCLA

This work identifies the global optimum for an infinite number of instances of the Total Annualized Cost (TAC) problem for compressor-intercooler sequences of constant compressibility factor gases with variable heat capacity. The prior state of the art involved the identification of the global optimum for an infinite number of instances of the TAC problem for compressor-intercooler sequences of constant compressibility factor gases with constant heat capacity. The resulting mathematical formulation of the TAC problem involves functions whose evaluation requires integral calculations. The necessary conditions of optimality for the TAC problem are then used to establish a number of mathematical properties, which are then used to establish the foundation of the proposed global optimization procedure. An illustrative case study on methane compression is then presented. Its results suggest that the use of an average (constant) heat capacity over the allowable operating temperature range is a reasonable approximation that yields a global TAC minimum that is within 1% of the true global TAC minimum.