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This paper presents the engineering design and theoretical exergetic analyses of the plant for combustion gas turbine based power generation systems. Exergy analysis is performed based on the first and second laws of thermodynamics for power generation systems. The results show the exergy analyses for a steam cycle system predict the plant efficiency more precisely. The plant efficiency for partial...
One of the proposals to increase the performance of the gas turbines is to improve chemical recuperated cycle. In this cycle, the heat in the turbine exhaust gases is used to heat and modify the chemical characteristics of the fuel. One mixture of natural gas and steam receives heat from the exhaust turbine gases; the mixture components react among themselves producing hot synthesis gas. In this work,...
This paper is a brief review of the method for analyzing the space and time dependent exergy and irreversibility fields in processes. It presents the basic equations, the method for their use, major literature sources, and three examples from the authors' work: flow desiccation, combustion of oil droplets, and combustion of pulverized coal. Conclusions from this Second Law analysis are used to attempt...
A systematic and general methodology for defining and calculating exergetic efficiencies and exergy related costs in thermal systems is proposed. The methodology is based on the Specific Exergy Costing (SPECO) approach, in which (a) the fuel and product of a component are defined by taking a systematic record of all exergy additions to and removals from all the exergy streams of the system, and (b)...
This paper analyzes the optimal Re for the steady, laminar, fully developed forced convection in a helical coiled tube with constant wall heat flux based on minimal entropy generation principle. Two working fluids, water and air, are considered. It is found that the entropy generation distributions are relatively insensitive to coil pitch, λ. Through the entropy generation analysis for cases of coil...
Exergy is used as a common currency to assess and compare the reservoirs of theoretically extractable work we call energy resources. Resources consist of matter or energy with properties different from the predominant conditions in the environment. These differences can be classified as physical, chemical, or nuclear exergy. This paper identifies the primary exergy reservoirs that supply exergy to...
This paper presents a simulation code for the thermal power plant AVV1, located in Copenhagen, Denmark, in response to the challenge launched at the ECOS 2003 congress. The simulation program was specially created for this contest, including the calculation of the thermodynamic properties of water, as based on IAPWS97. Every component of the plant is modeled through mass and energy balance equations,...
Cogeneration plants for simultaneous production of water and electricity are widely used in the Arabian Gulf region. They have proven to be more thermodynamically efficient and economically feasible than single purpose power generation and water production plants. Yet, there is no standard or universally applied methodology for determining unit cost of electric power generation and desalinated water...
The simulation and exergy analysis of a hybrid Solid Oxide Fuel Cell–Gas Turbine (SOFC–GT) power system are discussed in this paper. In the SOFC reactor model, it is assumed that only hydrogen participates in the electrochemical reaction and that the high temperature of the stack pushes the internal steam reforming reaction to completion; the unreacted gases are assumed to be fully oxidized in the...
Wood torrefaction is a mild pyrolysis process that improves the fuel properties of wood. At temperatures between 230 and 300°C, the hemicellulose fraction of the wood decomposes, so that torrefied wood and volatiles are formed. Mass and energy balances for torrefaction experiments at 250 and 300°C are presented. Advantages of torrefaction as a pre-treatment prior to gasification are demonstrated....
The consumption of primary energy is often used to compare energy systems from a sustainability viewpoint at regional, national or even world level. For such comparisons to be “fair” and meaningful, this implies, however, to define primary energies in a coherent way for all the various possible sources (coal, oil, gas, nuclear, renewables). This paper stems from the acknowledgement that the definitions...
In this paper, the optimization of a hybrid solid oxide fuel cell–gas turbine (SOFC–GT) power plant is presented. The plant layout is based on an internal reforming SOFC stack; it also consists of a radial gas turbine, centrifugal compressors and plate-fin heat exchangers. In the first part of the paper, the bulk-flow model used to simulate the plant is presented. In the second part, a thermoeconomic...
This paper presents the definitions of some terms used in exergy analysis and exergy costing, discusses options for the symbols to be used for exergy and some exergoeconomic variables, and presents the nomenclature for the remaining terms.
Performance criteria, such as efficiencies and coefficients of performance, for energy systems, are commonly used but often without sufficient understanding and consistence. The situation becomes particularly incoherent when simultaneous energy interactions of different types, such as work, heating and cooling, take place with a system. Also, the distinction between exergy and Second Law efficiencies...
The use of exergetic and thermoeconomic analysis for the diagnosis of efficiency reductions in energy systems has been widely discussed in literature. Several procedures, based on thermoeconomic analysis with the aim of locating and quantifying malfunctions, have been proposed and applied to operating plants.The correct location of anomalies is made difficult by the effects that the anomalies induce...
The depletion of non-renewable natural exergy resources (the thermo-ecological cost) has been accepted as the objective function for thermo-ecological optimization. Its general formulation has been cited. A detailed form of the objective function has been formulated for a solar collector producing hot water for household needs. The following design parameters have been accepted as the decision variables:...
This paper explores two linked theses related to the role energy in economic development, and potential sources of increased energy efficiency for continued growth with reduced greenhouse gas (GHG) emissions. The first thesis is that, while reduced GHG emissions are essential for long-term global sustainability, the usual policy recommendation of increasing energy costs by introducing a carbon tax...
The effect of fuel composition on the thermodynamic efficiency of gasifiers and gasification systems is studied. A chemical equilibrium model is used to describe the gasifier. It is shown that the equilibrium model presents the highest gasification efficiency that can be possibly attained for a given fuel. Gasification of fuels with varying composition of organic matter, in terms of O/C and H/C ratio...
This paper aims to clarify some aspects of the discussion between “emergists” and “exergists”. First, we address the problem of the differences between energy-based emergy and exergy-based emergy: we show that the two are proportional, having the exergetic equivalent of solar energy as scale factor. In the second part, we show that emergy and transformity can be written as a function of exergy alone,...
The concept of exergy has been introduced to establish a universal standard for quality and efficient use of energy. In this work, applications of this concept to compression, heat exchange, and separation processes, in addition to the computation of their irreversibility rate and thermodynamic efficiency, are considered. An industrial case study on the purification of 1,2-ethylenedichloride (EDC)...
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