A Computer Program to Calculate the Stream Exergy using the Visual Basic Graphical Interface

Abstract

The thermodynamic concept of exergy unequivocally indicates what is wasted in terms of energy. Exergy is the component of energy which is available for useful work. This concept can be used to appraise the eco-efficiency of a process. A process is highly eco-efficient if products of that process have exergy values close to those of its raw materials. All systems including chemical, biological and material processes feed on energy and convert some part of it into useful work and the remaining portion is disposed to the environment as entropy. This paper presents a new calculation method for the exergy of multi-component two phase process streams which allows the calculation of exergy gains of material streams for the calculation of the Relative Exergy Array (REA) (Montelongo-Luna et al., 2010). The total exergy calculation method developed in this work differs from most other authors by dividing total exergy into its constitutive components of chemical exergy, physical exergy and the exergy change due to mixing. The exergy calculation method developed has been incorporated within a commercial process simulator as an additional property of a material stream along with other orthodox calculations like mass and energy balances. Some external data in the form of standard chemical exergies is required. Exergy loss is determined by comparing exergy in and exergy out from a process after exergy analysis. An example calculation of the total exergy of a material stream is presented. The resulting calculated exergy values can then be used as a tool for energy efficient process design, energy efficient process control and optimization.