Supercritical water oxidation process under energetically self-sufficient operation

In this paper, an energetic study of the supercritical water oxidation (SCWO) process for diluted wastewater is presented. An empirical correlation for the calculation of reaction heat is proposed, in terms of C, H and 0 content in the waste, in order to determine the energy released in the oxidation reaction and to propose a suitable energy integration of the plant. The energy study of the process has been performed using the chemical plant simulation software ASPEN PLUS. This simulation has been carried out for a plant with a treatment capacity of 2 m(3)/h of diluted wastewater. This study has revealed that the minimum heating value required in the feedstream for energy self-sufficient operation is 930 kJ/kg. This value is equivalent, for instance, to a water stream containing 2% w/w n-hexane, 2.4% w/w 1-hexanol or 3.2% w/w hexanoic acid, depending on the oxidation degree of the compound. Operational variables used in the simulation, such as reaction temperature, pressure and oxidant excess, have been fixed in terms of experimental results obtained in the pilot plant of the Chemical Engineering Department at the University of Valladolid (Spain). From these results, removal efficiencies greater of 99.95% are reached for reaction temperature above 650 degreesC, P = 23.0 MPa, residence time lower than 50 s and oxygen excess slightly greater than the stoichiometric value. (C) 2002 Elsevier Science B.V. All rights reserved.