NAPHTALI-SANDHOLM DISTILLATION CALCULATIONS FOR NGL MIXTURES NEAR THE CRITICAL REGION

Multicomponent distillation calcultions are carried out using a modification of the Naphtali-Sandholm column calcultaion procedure coupled with the Soave-Redlich-Kwong equation of state for generating K-values and enthalpies. The modified Naphtali-Sandholm procedure is applicable when the individual stage efficiencies are unity and the K-values are not strongly dependent on the vapour-phase composition. For a column with M components and N stages, N(M + 2) relationships are set up. The N(M + 2) equations are solved using Newton-Raphson iteration with imposed maximum allowable changes of the independent variables between iterations. Analytical derivatives of the K-values and enthalpies with respect to composition and temperature are employed in the Jacobian. The method has been used for the process development and design of distillation columns associated with the separation of natural gas liquids (NGL). Fast and safe convergence is obtained even near the critical region. © 1979.