Abstract
A robust algorithm for flash calculations that uses an equation of state (EOS) is presented. It first uses a special version of the successive substitution (SS) method and switches to Powell's method if poor convergence is observed. Criteria are established for an efficient switch from one method to the other. Experience shows that this method converges near the critical point and also detects the single-phase region without computing the saturation pressure. The Soave-Redlich-Kwong1 (SRK) and the Peng-Robinson2 (PR) EOS's are used in this work, but the method is general and applies to any EOS.