Luis M. Serra

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.

Comparison of heat transfer coefficient correlations for thermal desalination units

This paper presents several simulator models allowing studying the behavior of different types of thermal desalination plants [1]. Three types of evaporators have been distinguished in thermal desalination plants: horizontal falling film evaporators (HFF), vertical falling film evaporators (VFF) and vertical rising film evaporators (VRF). An in depth study of the correlations adopted to calculate the heat transfer coefficients (HTC) of the selected evaporator/condenser has been made, in order to predict the plant performance of dual-purpose plants. Once the sensitivity analysis of the possible HTC has been done, the selected HTC has been implemented in a complex simulation model of MSF and MED/VC/TVC desalination units. Validation (if possible) of the calculated HTC was also done with the real data encountered in the literature.

Hybrid desalting systems for avoiding water shortage in Spain

This paper presents the economic analysis of the Ebro River transfer (a total amount of 1.050 hm 3 /y) presented for the Spanish Government in his project for the National Hydrologic Plan and its alternative: drinking water obtained from desalination plants. In this paper is proved that the cost of the desalted water is similar to the transferred one, by using conventional reverse osmosis (RO) methods or hybrid methods combining thermal and membrane desalination processes. The sensitivity analysis of the desalting alternative is mainly restricted to the plant size and the energy prices (natural gas or electricity). The new concepts of the global cycle of non-conventional water resources (desalt, use and recycle) is also introduced in order to decrease the water cost for urban supply.

Software for the analysis of water and energy systems

Water and energy are crucial aspects strongly connected when dealing with the problem of augmenting fresh water resources. Surprisingly, in the scientific and technological community there is a marked lack of attention to the combined research of water and energy issues. The present paper outlines a development-oriented object program in the said direction, oriented to the integrated analysis of power and desalination plants, which would hopefully fill the gap in having user-friendly software in the form of building blocks as an appropriate framework for the analysis, synthesis and design of either individual or integrated systems for energy and water. Such an approach would transcend other traditional approaches for process integration and obviously prove of great help not only to designers but also to researchers, educators and students. For illustrative purposes, in order to show the scope of the software being developed, an example is presented in which two different operation conditions of a dual-purpose power and desalination plant are compared. In particular, the effect of the throttling part of the steam extracted to the desalination unit is analyzed, which significantly increases the cost of water and electricity produced.

Fundamentals of Exergy Cost Accounting and Thermoeconomics Part II: Applications

Part II of this paper develops the mathematical formulations of three applications of the thermoeconomic analysis methodology described in Part I of the paper: the operation diagnosis study, including new concepts that helps to separate different contributions to those inefficiencies; the local optimization process in case of special conditions for the whole plant, and the benefit maximization (a direct application of the exergy costs accounting analysis). The operation diagnosis, which is the most complex and sophisticated application, is presented with the help of an example: the co-generation plant, as it was described in Part I.