Cogeneración

Pergamon

Energy Vol. I’). No. 3, pp. 27Y-286. IVY4 Copyright 0 1994 Elsevier Science Ltd Printed in Great Britain. All rights reserved 03hO-5442194 $6.00+0.0l1

CGAM PROBLEM:

DEFINITION AND CONVENTIONAL SOLUTION

ANTONIO VALERO, MIGUEL A. LOZANO and LUIS SERRA Department of Mechanical Engineering, University of Zaragoza, ETSH, 50015 Zaragoza, Spain GEORGE TSATSARONIS+ and JAVIER PISACenter for Electric Power, Tennessee Technological University, P. 0. Box 5032, Cookeville, TN 38505, U.S.A. CHRISTOS FRANGOPOULOS Department of Naval Architecture and Marine Engineering, National Technical University of Athens, P. 0. Box 64070, 15710 Zografou, Greece MICHAEL R. VON SPAKOVSKY LENI, Ecole Polytechnique Federale de Lausanne, CH-1015 Lausanne, Switzerland (Received 18 May 1993) 1.FOREWORD Developing techniques for designing efficient and cost-effective energy systems is one of the foremost challenges energy engineers face. In a world with finite natural resources and increasing energy demand by developing countries, it becomes increasingly important to understand the mechanisms which degrade energy and resources and to develop systematic approaches for improving the design ofenergy systems and reducing the impact on the environment. The second law of thermodynamics combined with economics represents a very powerful tool for the systematic study and optimization of energy systems. This combination forms the basis of the relatively new field of thermoeconomics (exergoeconomics). During the sixties, R. B. Evans, Y. M. El-Sayed, R. A. Gaggioli, and M. Tribus among othersconducted pioneering work in this field. However, the comprehensive effort to apply thermoeconomics systematically to the analysis, optimization and design of energy systems did not start until the eighties. New methodologies have flourished, giving rise to new concepts with their own nomenclature, definitions and applications. In 1990, a group of concerned specialists in the field (C.Frangopoulos, G. Tsatsaronis, A. Valero, and M. von Spakovsky) decided to compare their methodologies by solving a predefined and simple problem of optimization: the CGAM problem, which was named after +Author for correspondence.
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the first initials of the participating investigators. The objective of the CGAM problem is to show how the methodologies are applied, whatconcepts are used and what numbers are obtained in a simple and specific problem. In the final analysis, the aim of the CGAM problem is the unification of thermoeconomic methodologies. This comparison is not a competition among methodologies. Each methodology has specific fields of applications for which it provides proven and efficient solutions.

At the International Symposium on “Efficiency,Costs, Optimization, and Simulation of Energy Systems (ECOS ‘92)” held in Zaragoza, Spain, June 15-18, 1992, a special session was devoted to the CGAM problem. This paper describes and defines the CGAM problem and presents a conventional solution to the optimization problem. The following four papers discuss the application of four different methodologies to the same problem. We hope that this effortwill contribute to the understanding of thermoeconomics and to the unification of nomenclature and methodology.

2. INTRODUCTION For optimization purposes, it is necessary to specify the physical and cost models of the installation as well as the objective function to be minimized. The latter consists of the total costs of operation at a fixed demand. The models used in the CGAM problem arerealistic but incomplete from an engineering point of view since the object of this study is to present distinct models of thermoeconomic optimization. Therefore, it would be unreasonable to use an excessively complicated mathematical model to describe the performance of the plant. The CGAM problem refers to a cogeneration plant which delivers 30 MW of electricity and 14 kg/s of saturated steam at...