Javier Royo

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.

Optimization of Biomass-Fuelled Combined Cooling, Heating and Power (CCHP) Systems Integrated with Subcritical or Transcritical Organic Rankine Cycles (ORCs)

This work is focused on the thermodynamic optimization of Organic Rankine Cycles (ORCs), coupled with absorption or adsorption cooling units, for combined cooling heating and power (CCHP) generation from biomass combustion. Results were obtained by modelling with the main aim of providing optimization guidelines for the operating conditions of these types of systems, specifically the subcritical or transcritical ORC, when integrated in a CCHP system to supply typical heating and cooling demands in the tertiary sector. The thermodynamic approach was complemented, to avoid its possible limitations, by the technological constraints of the expander, the heat exchangers and the pump of the ORC. The working fluids considered are: n-pentane, n-heptane, octamethyltrisiloxane, toluene and dodecamethylcyclohexasiloxane. In addition, the energy and environmental performance of the different optimal CCHP plants was investigated. The optimal plant from the energy and environmental point of view is the one integrated by a toluene recuperative ORC, although it is limited to a development with a turbine type expander. Also, the trigeneration plant could be developed in an energy and environmental efficient way with an n-pentane recuperative ORC and a volumetric type expander.

The dissipation temperature : A tool for the analysis of malfunctions in thermomechanical systems

The aim of this paper is to define and characterize a new parameter, the dissipation temperature. When a thermal plant component displays an internal deterioration (intrinsic malfunction), its performance gets worse. This fact is reflected in a variation of the internal parameters that describe its behavior (isentropic efficiency, effectiveness, pressure and/or temperature ratios, parameter θ [1]). On the other hand, the remaining components of the plant may be affected (by induced malfunctions) because they are working under different operating conditions with respect to the rated ones. The knowledge of variations of the internal parameters in each component of a thermal plant does not suffice to determine their performance state under these new conditions. Additional information is needed. The dissipation temperature, defined as dh/ds when a malfunction occurs, can supply it as is explained in this paper. Moreover, three interesting applications of the dissipation temperature are shown: description of an energy system when a malfunction occurs; assessment of the importance of an intrinsic malfunction in a component; and the analysis of the influence of a malfunction on the exergetic efficiency of a component.

Combustion Behavior of Novel Energy Crops in Domestic Boilers: Poplar and Brassica Experiences

In the Mediterranean countries, several reasons promote cultivation of energy crops with respect to other kind of biomass. Specifically, they are expected to enhance the biomass heating opportunities in the energy market. Focused on that goal, Spanish research efforts have involved the evaluation of all the bioenergy chain steps, from fuel production to its transformation into energy in the conversion system. In this work, special emphasis have been placed on the assessment of two crops (Brassica carinata and Populus sp.) combustion requirements and adaptability level of a novel 250 kWth Spanish grate fired technology to cope with their conversion according acceptable level of gaseous emissions and efficiency. Finally, further research steps, needed to improve the novel fuel conversion system performance, have been presented seeking for a more definite introduction of this heating system in the Spanish bioenergy market.