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This paper presents the energy and exergy analyses for a delayed coking unit in a Chinese refinery using the three-link energy structural model. According to the results of energy-use analysis and evaluation, the potentials of energy-use and improvements for energy-savings as well as detail procedures are suggested. The proposed improvements are expected to remarkably lower the energy consumption...
Hydrogen, a promising and clean energy carrier, could potentially replace the use of fossil fuels in the transportation sector. Currently, no environmentally attractive, large-scale, low-cost and high-efficiency hydrogen production process is available for commercialization. Solar-driven water-splitting thermochemical cycles may constitute one of the ultimate options for CO 2 -free production...
This paper presents a theoretical analysis based on the second law of thermodynamics to estimate the minimum work required for the air conditioning process. The air conditioning process for hot and humid climates involves reducing air temperature and humidity. In the present analysis the inlet state is the state of the environment which has also been chosen as the dead state. The final state is the...
A separation process of carbon isotopes, 12 C (98.9%), 13 C (1.1%) and 14 C (trace), by the chemical exchange reactions between CO 2 and amine carbamate was designed by the exergy analysis technique and the applicability of the exergy analysis to the design of isotope-separation process is discussed. The exergy loss (EXL) for the single-column process was increased...
Fuel cells have great application potential as stationary power plants, as power sources in transportation, and as portable power generators for electronic devices. Most fuel cells currently being developed for use in vehicles and as portable power generators require hydrogen as a fuel. Chemical storage of hydrogen in liquid fuels is considered to be one of the most advantageous options for supplying...
The optimization of the heat recovery steam generator (HRSG) is one of the key elements for increasing the efficiency of combined plants. According to the current technical practice, it can be organized at different levels of complexity with objectives sequentially defined: operating parameters, geometrical details and technological elements.According to this point of view, in the paper a complete...
The performance of the Dutch Energy Sector is analyzed using the Standard Exergy Analysis as well as Extended Exergy Accounting (EEA) method. Performance indicators based on energy, exergy and cumulative exergy consumption (CExC) are evaluated for three subsectors: exploitation, transformation, and distribution of energy. It is shown that performance indicators based on CExC are much lower than those...
The paper brings new evidence on the impact of separate mechanical ventilation system on the annual energy and exergy performance of several design alternatives of residential heating systems, when they are designed for a house in Montreal. Mathematical models of residential heating, ventilation and domestic hot water (HVAC–DHW) systems, which are needed for this purpose, are developed and furthermore...
Biomass has great potential as a clean, renewable feedstock for producing modern energy carriers. This paper focuses on the process of biomass gasification, where the synthesis gas may subsequently be used for the production of electricity, fuels and chemicals. The gasifier is one of the least-efficient unit operations in the whole biomass-to-energy technology chain and an analysis of the efficiency...
The gasification technology has been object of study of many researchers, especially those involved in promoting large-scale electricity generation in sugarcane mills. This paper presents a simplified model for the gasification process based on chemical equilibrium considerations. The model consists in the minimization of the Gibbs free energy of the produced gas, constrained by mass and energy balances...
The aim of this work is to perform a retrofit study of an ammonia plant, in purpose of improving energy efficiency. As a common practice, one can divide an ammonia plant into two parts: the hot-end and the cold-end. In the hot section, two different options are investigated that both lead to a threshold condition and achieve maximum energy saving. The first option covers only process-to-process energy...
An exergy analysis of an advanced hypersonic vehicle, a scramjet, is presented and discussed with a twofold scope. First, to perfect the exergy approach to the design and optimization of aerospace propulsion systems: the exergy flow diagram can provide aircraft engineers and system designers with additional insight on the avoidable and unavoidable systemic losses, thus allowing for effective design...
This paper presents the exergoeconomic analysis of a novel process generating electric energy and hydrogen. Coal and high-temperature heat are used as input energy to the process. The process is a true “zero-emission process” because (a) no NO X is formed during coal combustion with sulfuric acid, and (b) the combustion products CO 2 and SO 2 are removed separately as compressed...
A new kind of natural gas-based polygeneration system for methanol and power production is proposed in this paper. With the sequential connection between chemical production and power generation, the new system adopts innovative integration of partial-reforming and partial-recycle scheme in methanol synthesis subsystem. To reveal the characteristics of the new system, exegetic comparisons between...
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...
The present study provides a descriptive mathematical model for energy and exergy analysis for a cocurrent gas spray cooling system. Conservation laws of mass, energy and momentum are used to predict the variation of temperature and enthalpy of gas and liquid streams along the tower length. The same procedure is also used to calculate the energy and exergy efficiencies. The validity of the model for...
The irreversibilities (exergy destruction) within a component of an energy conversion system can be represented by two parts. The first part depends on the inefficiencies of the considered component while the second part depends on the system structure and the inefficiencies of the other components of the overall system. Thus, the exergy destruction occurring within a component can be split into two...
Sugarcane is one of the most important industries of the Brazilian economy, and its main products are sugar and ethanol. Most of the industrial plants produce both products in an integrated process, in which the sugarcane bagasse is a by-product that can be used as a fuel in the cogeneration system. The bagasse is used as the only fuel of the plant, supplying all energy required for the process, and...
In the present study, exergetic analyses and optimization of S-CO 2 recompression cycle have been performed to study the effect of operating parameters on the optimum pressure ratio, energetic and exergetic efficiencies and component irreversibilities. Effect of isentropic efficiency, recuperator effectiveness and component pressure drop on the second law efficiency is presented as well. Results...
Extended-exergy analysis (EEA) for Chinese society was carried out in this paper to present a benchmarking case for future comparative studies in social systems ecology based on exergetic biophysics. For the EEA as an extension of labor theory of value and a possible sustainability metric, exergetic values were assigned to the production factors including labor, capital and environmental remediation...
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