Results 1 - 10 of 1279
Results 1 - 10 of 1279. Search took: 0.022 seconds
|Sort by: date | relevance|
[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] An ecosystem is a complex system in which biotic and abiotic factors interact and influence each other both directly and indirectly. Each of these factors has to comply with a specific function in the different processes that occur inside the ecosystem, whether transporting or transforming energy or both. When anthropogenic emissions are produced, part of the useful energy of the ecosystem is used to assimilate or absorb those emissions, and the energy spent, loses its function and becomes lost work in accordance with the Gouy-Stodola theorem. Thus, the work that an ecosystem can carry out varies as a function of the lost work produced by anthropogenic sources. The permanency or loss of the ecosystem depends on how many irreversibilities it can support. The second law of thermodynamics through a systematic use of the exergy and lost work is the basis of this paper where a general environmental impact index, based on exergy, is proposed. For the purpose of this work, the ecosystem is divided in subsystems--water, soil, atmosphere, organisms and society- -all of them inter-related. The ideal work variation can be obtained from each subsystem within the selected ecosystem, and a global index can be determined by adding the partial lost work of each subsystem. This global index is then used to determine the trend followed by the ecosystem from its pristine, original or environmental line base state. This environmental impact index applicability is presented for a simple combustion example
[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] In this study an energy and exergy analysis of a Ceiling-type residential air conditioning (CTRAC) system operating under different climatic conditions have been investigated for provinces within the different geographic regions of Turkey. Primarily, the hourly cooling load capacities of a sample building (Q_e_v_a_p) during the months of April, May, June, July, August and September were determined. The hourly total heat gain of the sample building was determined using the Hourly analysis program (HAP). The Coefficient of performance (COP), exergy efficiency (η) and exergy destruction (Ex_d_e_s_t) values for the whole system and for each component were obtained. The results showed that lower atmospheric temperature (T_a_t_m) influenced the performance of the system and each of its components
[en] The concept of sustainability was developed from thermodynamic properties applied to complex adaptive systems. The origins of the perception about sustainable development and limitation in its application to analyze the interaction between a system and its surroundings were described. The properties of a complex adaptive system were taken as basis to determine how a system can to be affected by the resources restriction and irreversibility of the processes. The complex adaptive system was understood using the first and second law of thermodynamics, generating a conceptual framework to define the sustainability of a system. The contributions developed by exergy were shown to analyze the sustainability of systems in an economic, social and environmental context
[es]El concepto de sustentabilidad fue desarrollado a partir de propiedades termodinamicas aplicadas a sistemas adaptativos complejos. Los origenes de la percepcion sobre el desarrollo sustentable y la limitacion en su aplicacion para analizar la interaccion entre un sistema y su entorno fueron descritas. Las propiedades de un sistema adaptativo complejo fueron tomadas como base para determinar como un sistema puede ser afectado por la restriccion de recursos e irreversibilidad de los procesos. El sistema adaptativo complejo fue comprendido utilizando la primera y segunda ley de la termodinamica, generando un marco conceptual para definir la sustentabilidad de un sistema. Los aportes desarrollados por la exergia fueron mostrados para analizar la sustentabilidad de sistemas en un contexto economico, social y ambiental
[en] Highlights: • The overall energy and exergy efficiencies of the plant is found to be 59.37% and 38.99% respectively. • Performance assessment of a cement plant indicates that the calcination process involves the highest portion of energy losses. • The specific exergetic cost cement produced by the cement plant is calculated to be 180.5 USD/GJ. • The specific cement manufacturing cost is found to be 41.84 USD/ton. - Abstract: This paper is Part 2 of the study on the thermodynamic and exergoeconomic analysis of a cement plant. In Part 1, thermodynamic and exergoeconomic formulations and procedure for such a comprehensive analysis are provided while this paper provides an application of the developed formulation that considers an actual cement plant located in Gaziantep, Turkey. The overall energy and exergy efficiencies of the plant is found to be 59.37% and 38.99% respectively. The exergy destructions, exergetic cost allocations, and various exergoeconomic performance parameters are determined by using the exergoeconomic analysis based on specific exergy costing method (SPECO) for the entire plant and its components. The specific unit exergetic cost of the farine, clinker and cement produced by the cement plant are calculated to be 43.77 USD/GJ, 133.72 USD/GJ and 180.5 USD/GJ respectively. The specific manufacturing costs of farine, clinker and cement are found to be 3.8 USD/ton, 33.11 USD/ton and 41.84 USD/ton respectively
[en] Exergy analysis is a powerful tool for developing, evaluating and improving an energy conversion system. However, the lack of a formal procedure in using the results obtained by an exergy analysis is one of the reasons for exergy analysis not being very popular among energy practitioners. Such a formal procedure cannot be developed as long as the interactions among components of the overall system are not being taken properly into account. Splitting the exergy destruction into unavoidable and avoidable parts in a component provides a realistic measure of the potential for improving the thermodynamic efficiency of this component. Alternatively splitting the exergy destruction into endogenous and exogenous parts provides information on the interactions among system components. Distinctions between avoidable and unavoidable exergy destruction on one side and endogenous and exogenous exergy destruction on the other side allow the engineer to focus on the thermodynamic inefficiencies that can be avoided and to consider the interactions among system components. The avoidable endogenous and the avoidable exogenous exergy destruction provide the best guidance for improving the thermodynamic performance of energy conversion systems.
[en] Solar thermal is a promising renewable energy supplying technology that is being introduced slowly in industrial activities. Integration of solar thermal energy in a complex process, in combination with other energy provision devices, must be evaluated carefully, in order to obtain its maximum capacity and performance. This study tackles the integration of the thermosolar technology in a dairy process, sited in a climatic zone where diffuse irradiation is the meaningful one, based on two well developed thermodynamic tools: pinch and exergy analysis. Both tools have been utilized in the context of a low and middle temperature for the production of hot water for the steps of the dairy process. A combined implementation of both methodologies, helped by economical estimation, provides a powerful tool that allows finding the best integration of thermosolar and, by this, taking substantial design decisions. - Highlights: ► Integration of solar thermal energy in an industrial process was assessed. ► Pinch and exergy analysis were used to determine the optimal energy supply configuration. ► Solar thermal energy reduces the fossil energy demand with a moderate investment.
[en] To integrate measurements of eco-efficiency with control loop configuration has become an important topic since all industrial processes/plants are requested to increase their eco-efficiency. The exergy eco-efficiency factor, a new measure of eco-efficiency for control loop configuration, has been developed recently. The exergy eco-efficiency factor is based on the thermodynamic concept of exergy, which can be used to analyze a process in terms of its efficiency. The combination of the relative gain array (RGA), NI, CN, dynamic RGA, and the exergy eco-efficiency factor will help guide the process designer to find the optimal control design with low operating cost/eco-efficiency. In this paper, we validate the proposed exergy eco-efficiency factor for processes with recycles which are very common industrially
[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