Antonio Valero

Theory of the exergetic cost

The theoretical basis and several applications of the theory of exergetic cost, a major approach to the field of thermoeconomics, are presented in this paper. The fundamentals and criteria that enable the description of the cost formation process and the assessment of the efficiency in energy systems are formulated. The use of the second law of thermodynamics through a systematic use of the exergy concept, the fuel-product concept based on the productive purpose of a component within an energy system, and the mathematical formalization provided by systems theory are the cornerstones of the theory. The methodology presented here is a powerful tool in the analysis of energy systems. The following applications are presented: (i) assessment of alternatives for energy savings, (ii) cost allocation, (iii) operation optimization, (iv) local optimization of subsystems, (v) energy audits and assessment of fuel impact of malfunctions.

CGAM Problem: Definition and Conventional Solution

Note: (idem 93.31). Reference LENI-ARTICLE-1994-026 Record created on 2005-08-08, modified on 2017-05-10

Application of the exergetic cost theory to the CGAM problem

An optimization strategy for complex thermal systems is presented. The strategy is based on conventional techniques and incorporates assumptions and consequences of the exergetic cost theory (ECT) and of symbolic exergoeconomics. In addition to the results obtained by consventional techniques, this method provides valuable information about the interaction of components.

Structural theory as standard for thermoeconomics

In this paper the Structural Theory of Thermoeconomics is proposed as a standard and common mathematical formulation for all thermoeconomic methodologies employing thermoeconomic models that can be expressed by linear equations. In previous works it has been demonstrated that the Exergy Cost Theory (ECT), the AVCO approach and the Thermoeconomic Functional Analysis (TFA) can be dealt with the Structural Theory. In this paper, it is demonstrated that the Last-in-First-Out (LIFO) approach, a thermoeconomic cost accounting method, can also be reproduced with the Structural Theory. The LIFO and the Structural Theory are both applied to a combined cycle plant and it is shown that the equation systems obtained from both methods are the same. Moreover, a procedure to develop the productive structure representing the thermoeconomic model of LIFO (i.e. from which the same costing equations are obtained as with the LIFO approach) is explained in detail, which provides the tools to reproduce the costs obtained from LIFO with the Structural Theory for complex energy systems. This paper concludes a series of research works where it has been demonstrated that the most developed thermoeconomic optimization and cost accounting methodologies, as all of them employ thermoeconomic models that can easily be linearized, can be dealt with by the mathematical formalism of the Structural Theory.

Structural theory and thermoeconomic diagnosis: Part I. On malfunction and dysfunction analysis

Thermoeconomic diagnosis of complex energy systems is probably the most developed application of thermoeconomic analysis [NATO ASI on thermodynamics and optimization of complex energy systems, 1999, p. 117]. It is applied to diagnose the causes of the additional fuel consumption of a steadily operating plant, due to the inefficiencies of its components. In this paper, a new method based on the structural theory and symbolic thermoeconomics [Energy 19 (13) (1994) 365] is introduced. It integrates the thermoeconomic methodologies developed until now, such as fuel impact and technical exergy saving [Flowers 94, Florence World Energy Research Symposium, Florence, Italy, 1994, p. 149] and let us to compute the additional fuel consumption as the sum of both the irreversibilities and the malfunction costs of the plant components. Furthermore, it will be able to quantify the effect of a component malfunction in the other components of the plant. As result, new concepts are included in the diagnosis analysis: intrinsic malfunction, induced malfunction and dysfunction. The key of the proposed method is the construction of the malfunction/dysfunction table which contains, in a very compact form, the information related with the plant inefficiencies and their effects on each component and on the whole plant. This methodology is not only a theoretical advance but also it enhances the thermoeconomic diagnosis applications, based on performance tests or simulation models. Some of them are presented in this paper using a simple example. The application of the methodology is shown in the second part of the paper.

Structural theory and thermoeconomic diagnosis: Part II: Application to an actual power plant

In this second part of the paper, the new advances on thermoeconomic diagnosis presented in the part I are applied to the Escucha power plant, which is a 160 MW conventional coal fired power plant sited in Aragon (Spain). As a result the validity of the methodology is proved and quantified. The methodology is validated using a specific simulator of the Escucha power plant cycle, mainly based on [ASME Power Division, Paper no. 62-WA-209, 1974] method. This simulator reproduces with high accuracy the cycle behavior for different operating conditions, either in design and in off design conditions. The error is lower than 1% in most of cases. The simulated results, i.e. temperatures, pressures, mass flow rates, power and so on, are considered as plant measured and validated values. In this way all measurement uncertainties are avoided. A complete thermoeconomic diagnosis is presented applying the Structural Theory of Thermoeconomics. The impact of the component inefficiencies on the fuel plant consumption, and the effect of a component inefficiency (intrinsic malfunction) on the rest of the plant components (induced malfunctions and dysfunctions), are analyzed and quantified. The methodology is validated quantifying its accuracy.

Thermoeconomic optimization of a dual-purpose power and desalination plant

Abstract The thermoeconomic optimization of an actual steam power plant coupled with a MSF desalination unit is reported. A global optimization of the whole system is performed based on separated local optimizations of different plant units. The local optimization procedure described herein requires fewer computing resources and deals with simpler mathematical problems than conventional optimization methods. On the other hand, the local optimization method requires a thermoeconomic model providing the exery and economic costs of all mass and energy flows of a plant, including those corresponding to fresh and electricity produced. This application can be very useful, either for the plant management in order to achieve a cost-effective operation, and for a better plant design. In the example given, approximately 11% of the total cost was saved according to the optimization results in the nominal operating conditions of the plant.

Towards a unified measure of renewable resources availability: the exergy method applied to the water of a river

Abstract This paper applies the exergetic method to a renewable resource: the water of a river . Its application can be used to compare, diagnose and evaluate the river water along its different stages, while the river flows from its source to its mouth. River water availability (defined as the sum of the exergy components) will help to characterize the physical and chemical properties of the river. The different stages of the river can be characterized by its mass flow and the measure of five parameters: pressure, temperature, altitude, velocity and composition . As is well known, the exergy method can associate each parameter with its exergetic component: mechanical, thermal, potential, kinetic and chemical, respectively. These components will help to quantify some quality and quantity aspects of the river. The information provided by the exergy method will allow to understand concepts related to the water river availability . Furthermore, by comparing these availabilities at different stages, it will be possible to obtain a broad understanding of the degradation process that the river undergoes. An example of application has been developed to a particular river: the Ebro, the most abundant Spanish river. From eight sampling stations [1] , which are ordered following the going down of the river (stages), it is possible to obtain field data measurement needed to calculate the exergy components. The information provided will help to describe and compare the degradation process of the Ebro, from its source to its mouth: stage by stage, and during the year. The exergetic approach fulfils these aims by unifying in the same exergy units. An interpretation of the results has been made in terms of the geographic and hydrologic aspects.

Application of Thermoeconomics to Industrial Ecology

Industrial Ecology involves the transformation of industrial processes from linear to closed loop systems: matter and energy flows which were initially considered as wastes become now resources for existing or new processes. In this paper, Thermoeconomics, commonly used for the optimization and diagnosis of energy systems, is proposed as a tool for the characterization of Industrial Ecology. Thermoeconomics is based on the exergy analysis (Thermodynamics) but goes further by introducing the concepts of purpose and cost (Economics). It is presented in this study as a systematic and general approach for the analysis of waste flow integration. The formulation is based on extending the thermoeconomic process of the cost formation of wastes in order to consider their use as input for other processes. Consequently, it can be applied to important Industrial Ecology issues such as identification of integration possibilities and efficiency improvement, quantification of benefits obtained by integration, or determination of fair prices based on physical roots. The capability of the methodology is demonstrated by means of a case study based on the integration of a power plant, a cement kiln and a gas-fired boiler.

From Grave to Cradle

Life cycle assessment (LCA) is a promising tool in the pursuit of sustainable mining. However, the accounting methodologies used in LCA for abiotic resource depletion still have some shortcomings and need to be improved. In this article a new thermodynamic approach is presented for the evaluation of the depletion of nonfuel minerals. The method is based on quantifying the exergy costs required to replace the extracted minerals with current available technologies, from a completely degraded state in what we term “Thanatia�? to the conditions currently found in nature. Thanatia is an estimated reference model of a commercial end of the planet, where all resources have been extracted and dispersed, and all fossil fuels have been burned. Mineral deposits constitute an exergy bonus that nature gives us for free by providing minerals in a concentrated state and not dispersed in the crust. The exergy replacement costs provide a measure of the bonus lost through extraction. This approach allows performing an LCA by including a new stage in the analysis: namely the grave to cradle path. The methodology is explained through the case study of nickel depletion.