A HARD-SPHERE VOLUME-TRANSLATED VAN-DER-WAALS-EQUATION OF STATE FOR SUPERCRITICAL PROCESS MODELING .1. PURE COMPONENTS

An equation of state (EOS) has been developed to model thermodynamic p roperties of pure species and mixtures from ambient to supercritical c onditions. It has been developed for use in modeling supercritical wat er oxidation (SCWO) of liquid and slurried organic wastes. Kinetic and flow simulations of the SCWO process require accurate predictions of densities (errors +/- 10% or less) and other thermodynamic properties from ambient to supercritical conditions of water (25 degrees C < T le ss than or equal to 600 degrees C; 1 bar < P less than or equal to 300 bar). Over these temperature and pressure ranges, EOSs proposed by ot her investigators have been unsuccessful in estimating accurate proper ties such as fluid densities, vapor pressures, residual enthalpies and residual entropies for water and aqueous mixtures containing carbon d ioxide, nitrogen, organics and oxygen. Some improvement has been achie ved using volume translation methods with cubic equations of state, bu t even these EOSs have limited accuracy for predicting densities. The proposed pure-component EOS couples a volume translation to a pressure -explicit equation in volume and temperature that combines a Carnahan- Starling hard-sphere repulsive term b and a simple van der Waals attra ction term a. The translation constant t is determined by a fit to liq uid and vapor coexistence density data while a and b are determined fr om critical point data. The focus of this paper is on the analysis of pure components for which the proposed EOS is shown to fit a number of important thermodynamic properties to within average deviations of 1- 30% over a wide range of conditions for ammonia, carbon dioxide, ethyl ene, methane, nitrogen, oxygen and water.