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[en] Prediction models, based on ultimate analysis of biomass on dry basis (db) which is leveraged to predict chemical exergy, were proposed in this study. A new concept — chemical exergy per equivalent of available electrons transferred to oxygen (reductance degree) of model 1 was established. The result shows that chemical exergy per reductance degree of model 1 is relatively constant for the values of most biomass (db) beyond the±1% relative error range. A modified reductance degree of biomass was presented, whereas oxygen (O) content was neglected due to its inaccurate value and the high p-value for the coefficient of O variable. Chemical exergy per modified reductance degree of models 2 and 3 was approximated to be nearly a constant. Thus, two theoretical prediction models (model 2 and model 3) for the biomass (db) with and without sulfate (920.08(C/3 + H + S/8), 920.72(C/3 + H)) were established, respectively. The coefficients of the two models are of almost the same value, which indicates that the S content has also a negligible effect on chemical exergy. Model 3 (920.72(C/3 + H)) is also herein proposed for prediction of exergy of biomass. The average relative errors of model 1, model 2 and model 3 are 2.882%, 0.643% and 0.634%, respectively. - Highlights: • A new concept — chemical exergy per (modified) reductance degree is established. • Chemical exergy per modified reductance degree is approximately constant. • Estimation model of chemical exergy based on new concept provides higher accuracy. • Chemical exergy of biomass (db) can be easily estimated by simply using C and H.
[en] A new approach for the calculation of the interactions among the components of a thermal system for application to the concept of advanced exergy-based analysis is presented. The approach can be used to determine the thermodynamic interactions of system components, and to evaluate alternative designs. The new approach puts the calculation of endogenous and exogenous exergy destruction on a proper thermodynamic basis and introduces a straightforward and time-saving calculation procedure in contrast to various approaches used in the past. When employed to the analysis of the CGAM-problem, the new approach complies with qualitative reasoning, resolves the shortcomings and shows comparable results with previous approaches. The top-down hierarchical approach assists in achieving the best system design possible by identifying the effects of design decisions and by stimulating the engineer's creativity in terms of design alternatives and optimization options. Furthermore, the generalization of the approach allows for any level of aggregation, thus, making the determination of improvement potentials easier. By providing profound thermodynamic understanding for processes, the advanced exergy-based analysis is a promising tool for designing, analyzing and optimizing processes for higher efficiencies and lower costs. - Highlights: • A new concept for the application in advanced exergy-based analysis is introduced and verified. • Problems with previous approaches for advanced exergy analysis are solved. • The concept easily integrates into existing process design methodologies. • Thermodynamic interactions among components are straightforwardly determined.
[en] A phenomenological equation of exergy transfer, which indicates the relation between exergy flux, exergy resistance and exergy driving forces, is derived by applying non-equilibrium thermodynamics to second law analysis, and simultaneously the expressions of the coefficients of exergy transfer are obtained. The results show that exergy transfers in different forms interact on each other. This study also proposes a simplified expression of exergy transfer coefficients by neglecting some minor engineering couplings in exergy transfers. Furthermore, a mixture consisting of two components is discussed. As an application of this result, thermal exergy transfer within a flat plate is studied
[en] The concept 'environment' is of considerable importance in present-day engineering thermodynamics. Introduction of this concept in operation brings not only simplification of the methods of solving classical thermodynamic problems, but also gives the exergy method which forms the major new part of thermodynamics, including some parts of biology, economics and other fields of science. But practice shows that it is necessary to define the concept 'environment' more precisely in some cases
[en] Splitting the exergy destruction into endogenous/exogenous and unavoidable/avoidable parts represents a new development in the exergy analysis of energy conversion systems. This splitting improves the accuracy of exergy analysis, improves our understanding of the thermodynamic inefficiencies and facilitates the improvement of a system. An absorption refrigeration machine is used here as an application example. This refrigeration machine represents the most complex type of a refrigeration machine, in which the sum of physical and chemical exergy is used for each material stream
[en] This paper introduces a two-level idealization concept and decomposes the exergy losses of processing operations into the intrinsic part and the extrinsic part. The first level idealization is the reversible operation and the second level idealization is the thermodynamic equilibrium operation. The exergy losses arising from the deviations from the first level idealization only, caused by configuration constraints, are defined as the intrinsic exergy losses. The extra exergy losses which arise from further deviations from the second level idealization, caused by transport rate limitations, are defined as the extrinsic exergy losses. Demonstrated by several example cases of different complex levels, the analysis results can pinpoint what and where to focus on for improvements: (1) design configurations or transport rate limitations, and (2) the specific locations within the operations or processes. As an example, for a de-ethanizer, the improvement measures on configuration-related and transport rate-related design conditions result in a 11.42% reduction of overall column intrinsic exergy loss and a 81.74% reduction of total individual stage extrinsic exergy loss
[en] The integration of a turbine expander into different types of high pressure, exothermic chemical synthesis processes is considered. In conventional systems, the reaction heat is often transferred to generate steam to drive steam turbines or used for heat integration. The heat is reduced in quality due to the temperature driving forces in the heat exchange equipment. Reaction heat can be utilised at the maximum possible temperature by placing a turbine expander directly after the reactor. The power generated from such combined power and chemical systems can either be exported or used to satisfy the process compressor requirements. A methodology is presented to lend structure to the development and analysis of the flow sheets for the mentioned systems. The methodology involves the consideration of various factors that were identified to impact on the flow sheet development. These factors are discussed and a brief overview of the flow sheet development for four different case studies is given. Process data generated from simulations are used
[en] This work investigates the techniques used in evaluating distillation structures from lean manufacturing point of view. Oil and gas industry has already started adopting lean manufacturing principles in different types of processes from information flow to processing technologies. Generally, energy costs are the most important factors in processing hydrocarbons. Introducing flexibility desired by lean principles to the system may conflict energy efficiency of the system. However, this does not mean that the economic optimum is the energetic optimum. Therefore all possible changes due to temporarily stopped or not fully utilised plants have to be investigated, resulting in a large amount of cases that have to be evaluated. For evaluation exergy analysis can be used as it involves all energy types, and evaluation is straightforward. In this paper plain distillation structures are investigated, and the boundaries of the systems are set up according to the status of the site. Four component case studies are presented that show that the very same distillation structure can be more or less efficient depending on the status of the industrial site. It is also shown that exergy analysis used with different boundaries on the same system can show flexibility of the system and reveals potentials. - Highlights: • The article focuses on the flexibility aspect of lean manufacturing. • Exergy analysis of distillation scheme alternatives, energy efficiency. • Different boundaries define different scenarios of the same system is investigated. • The energy efficiency of distillation schemes also depends on their operating mode. • The exergy reserves of a distillation system can be revealed with exergy analysis
[en] This paper presents an energy and exergy analysis of a domestic refrigeration system using R1234yf as a drop-in replacement for R134a. We base our analysis on a series of independent tests using two refrigerants, namely R1234yf and R134a. The test equipment consists of a fully instrumented domestic refrigeration system. A computational model is developed to work out the thermodynamic parameters such as coefficient of performance, exergy destruction ratio, exergy-based rational efficiency, component efficiency defect as well as the dimensionless exergy balance for both refrigerants. The parameters varied in the analysis were the evaporator and condenser temperatures as well as the amount of refrigerant used in the system. The results indicate that irreversibilities are mainly concentrated in the compressor, this is the case both for R1234yf and R134a. This exergy analysis proposed for evaluation of refrigerants in domestic refrigerators permitted to determine that R1234yf may not be a likely alternative to R134a. - Highlights: • An energy and exergy study of R1234yf as a drop-in replacement for R134a is presented. • A domestic refrigerator was fully instrumented. • The analysis takes into account the variation of charge of R1234yf compared with R134a. • The condenser temperature has a greater effect on the performance of refrigerator. • R1234yf is not a better alternative to R134a under the conditions assumed in this work.
[en] According to some published suggestions, taxes should not be a kind of penalty for positive effects of human activity (productivity, invention) but should burden negative effects, like the depletion of natural resources, and deleterious impacts on the environment. The consumption of non-renewable resources of exergy has been proposed in the present paper as a measure of the negative effects of human activity and a basis for a pro-ecological tax. A proposed course for determining this tax has been formulated. The method presented takes into account also the deleterious impact of waste products on the natural environment, the wear of machines and installations and the import of foreign products. (author)