We have conducted comprehensive exergy analyses of three integrated gasification combined cycle with carbon capture and storage (IGCC-CCS) power plant configurations: (1) a baseline model using Selexol™ for H₂S/CO₂ removal; (2) a modified version that adds a H₂-selective membrane before the Selexol™ acid gas removal system; and (3) a modified baseline version that uses a CO₂-selective membrane before the Selexol™ acid gas removal system. While holding the coal input flow rate and the CO₂ captured flow rates constant, it was determined that the H₂-selective membrane case had a higher net power output (584 MW) compared to the baseline (564 MW) and compared to the CO₂-selective membrane case (550 MW). Interestingly, the CO₂-selective membrane case destroyed the least amount of exergy within the power plant (967 MW), compared with the Baseline case (999 MW) and the H₂-membrane case (972 MW). The main problem with the CO₂-selective membrane case was the large amount of H₂ (48 MW worth of H₂ chemical exergy) remaining within the supercritical CO₂ that exits the power plant. Regardless of the CO₂ capture process used, the majority of the exergy destruction occurred in the gasifier (305 MW) and gas turbine (~380 MW) subsystems, suggesting that these two areas should be key areas of focus of future improvements. Full article

The paper presents a comparison of various CHP system configurations, such as Vapour Turbine, Gas Turbine, Internal Combustion Engine, External Combustion Engine (Stirling, Ericsson), when different thermodynamic criteria are considered, namely the first law efficiency and exergy efficiency. Thermodynamic optimization of these systems is performed intending to maximize the exergy, when various practical related constraints (imposed mechanical useful energy, imposed heat demand, imposed heat to power ratio) or main physical limitations (limited heat availability, maximum system temperature allowed, thermo-mechanical constraints) are taken into account. A sensitivity analysis to model parameters is given. The results have shown that the various added constraints were useful for the design allowing to precise the influence of the model main parameters on the system design. Future perspective of the work and recommendations are stated. Full article

Ground heat is a renewable resource that is readily available for buildings in cool climates, but its relatively low temperature requires the use of a heat pump to extract it for heating. We developed a system that uses low temperature ground heat directly in a building wall to reduce transmission heat losses. The Active Low Exergy Geothermal Insulation Systems (ALEGIS) minimizes exergy demand and maximizes the use of renewable geothermal heat from the ground. A fluid is pumped into a small pipe network in an external layer of a wall construction that is linked to a ground heat source. This decouples the building from the outside temperature, therefore eliminating large peak demands and reducing the primary energy demand. Our steady-state analysis shows that at a design temperature of −10 °C the 6 cm thick active insulation system has equivalent performance to 11 cm of passive insulation. Our comparison of heating performance of a building with our active insulation system versus a building with static insulation of the same thickness shows a 15% reduction in annual electricity demand, and thus exergy input. We present an overview of the operation and analysis of our low exergy concept and its modeled performance. Full article

Gas turbine power can be augmented by overspray process which consists of inlet fogging and wet compression. In this study exergy analysis of the overspray process in gas turbine system is carried out with a non-equilibrium analytical modeling based on droplet evaporation and the second law of thermodynamics. This work focuses on the effects of system parameters such as pressure ratio, water injection ratio, and initial droplet diameter on exergetical performances including irreversibility and exergy efficiency of the process. The process performances are also estimated under the condition of saturated water injection ratio above which complete evaporation of injected water droplets within a compressor is not possible. The results show that the irreversibility increases but the saturated irreversibility decreases with increasing initial droplet diameter for a specified pressure ratio. Full article

Small-scale bio-energy projects have been launched in rural areas of China and are considered as alternatives to fossil-fuel energy. However, energetic and environmental evaluation of these projects has rarely been carried out, though it is necessary for their long-term development. A village-level biomass gasification project provides an example. A hybrid life-cycle assessment (LCA) of its total nonrenewable energy (NE) cost and associated greenhouse gas (GHG) emissions is presented in this paper. The results show that the total energy cost for one joule of biomass gas output from the project is 2.93 J, of which 0.89 J is from nonrenewable energy, and the related GHG emission cost is 1.17 × 10⁻⁴ g CO₂-eq over its designed life cycle of 20 years. To provide equivalent effective calorific value for cooking work, the utilization of one joule of biomass gas will lead to more life cycle NE cost by 0.07 J and more GHG emissions by 8.92 × 10⁻⁵ g CO₂-eq compared to natural gas taking into consideration of the difference in combustion efficiency and calorific value. The small-scale bio-energy project has fallen into dilemma, i.e., struggling for survival, and for a more successful future development of village-level gasification projects, much effort is needed to tide over the plight of its development, such as high cost and low efficiency caused by decentralized construction, technical shortcomings and low utilization rate of by-products. Full article

In the energy realm there is a pressing need to make decisions in a complex world characterized by biophysical limits. Exergy has been promoted as a preferred means of characterizing the impacts of resource consumption and waste production for the purpose of improving decision-making. This paper provides a unique and critical analysis of universal and comprehensive formulations of the chemical exergy reference environment, for the purpose of better understanding how exergy can inform decision-making. Four related insights emerged from the analysis, notably: (1) standard and universal chemical exergy reference environments necessarily encounter internal inconsistencies and even contradictions in their very formulations; (2) these inconsistencies are a result of incompatibility between the exergy reference environment and natural environment, and the desire to model the exergy reference environment after the natural environment so as to maintain analytical relevance; (3) the topics for which exergy is most appropriate as an analytical tool are not well served by comprehensive reference environments, and (4) the inconsistencies point to a need for deeper reflection of whether it is appropriate to adopt a thermodynamic frame of analysis for situations whose relevant characteristics are non-thermodynamic (e.g., to characterize scarcity). The use of comprehensive reference environments may lead to incorrect recommendations and ultimately reduce its appeal for informing decision-making. Exergy may better inform decision-making by returning to process dependent reference states that model specific processes and situations for the purpose of engineering optimization. Full article

A conventional exergy analysis can highlight the main components having high thermodynamic inefficiencies, but cannot consider the interactions among components or the true potential for the improvement of each component. By splitting the exergy destruction into endogenous/exogenous and avoidable/unavoidable parts, the advanced exergy analysis is capable of providing additional information to conventional exergy analysis for improving the design and operation of energy conversion systems. This paper presents the application of both a conventional and an advanced exergy analysis to a supercritical coal-fired power plant. The results show that the ratio of exogenous exergy destruction differs quite a lot from component to component. In general, almost 90% of the total exergy destruction within turbines comes from their endogenous parts, while that of feedwater preheaters contributes more or less 70% to their total exergy destruction. Moreover, the boiler subsystem is proven to have a large amount of exergy destruction caused by the irreversibilities within the remaining components of the overall system. It is also found that the boiler subsystem still has the largest avoidable exergy destruction; however, the enhancement efforts should focus not only on its inherent irreversibilities but also on the inefficiencies within the remaining components. A large part of the avoidable exergy destruction within feedwater preheaters is exogenous; while that of the remaining components is mostly endogenous indicating that the improvements mainly depend on advances in design and operation of the component itself. Full article

The present study aims to develop a thermoeconomic-based approach for optimization of steam levels in a steam production and distribution system by use of the specific exergy costing (SPECO) method for determining optimum steam levels to minimize the cost caused by exergy destruction. In the field of total site optimization, incremental cost of the utility system caused by exergy destruction has been selected as an objective function and the result is compared with the case that energy minimization has been selected as the prime objective. The steam levels are optimized considering steam demand at each level, output power generated by turbines, boiler duty, fuel and cold utility requirements as well as capital cost of equipments. The analysis showed that thermoeconomic (exergoeconomic) approach in optimization not only can change the optimum structure of steam levels but also may reduce the total cost of utility system up to 8%. Full article