Adaptation of the ascendency theory to industrial systems

Abstract

Growth and development of ecosystems are subject to restrictions. Besides exergy, other properties, such as ascendency, have been described as goal functions that can inform about the health of ecosystems and synthesize information about the energy and matter flows in relation to an ideal theoretical state. Ascendency is an index that quantifies both the growth and the degree of organization in an ecosystem, in which several subsystems interact with mass and energy flows. Ascendency is quantified in terms of mass and energy exchanges among different subsystems constituting an ecosystem. Its value increases when the activity of the ecosystem increases (amount of mass and energy exchanges increase) and when the ecosystem evolves to a higher complexity of its structure (level of integration of the subsystems). Exergy provides information about the quality of energy and is therefore very appropriate for evaluating the thermodynamic efficiency of energy conversion processes. Growing concerns about energy efficiency have stimulated the development of techniques for the analysis, design, and diagnosis of complex energy systems based on the second law of thermodynamics. In this context, the set of methodologies called thermoeconomics was created, aimed at cost allocation (economic, thermodynamic, or environmental) and optimization of thermal systems based on thermodynamic concepts of system operation, which very often use exergy. Thermoeconomic analysis provides information on the interaction among the different components of energy systems and how energy resources are distributed throughout the internal mass and energy flows of the system. Herein the formulation of ascendency was adapted to industrial systems using exergy flows as the quantity of interest, employing the productive structure obtained from thermoeconomic analysis techniques to describe the production process of the system. Ascendency was then applied to a set of simple thermodynamic power systems based on the Rankine cycle to study the connection between energy (thermodynamic) efficiency and the “growth” and “development” of the power system. Four configurations with different interconnection levels between the equipment were studied, maintaining the final product of the power systems (net power) and the energy efficiency of the entire cycle constant, for comparison purposes. Moreover, different turbine efficiencies were also analyzed, maintaining a fixed system structure and constant net power produced, to obtain comparable results. It was verified that in the case of steam power plants based on the Rankine cycle, an increase in system complexity, maintaining the total plant production constant, increases ascendency as well as its potential for energy efficiency improvement. When different cases with the same interconnection level between equipment (same system structure), same net power production and different efficiencies are compared, the configuration with the highest ascendency value also presents a better potential for optimization.