Chaleur de récupération | EPFL Graph Search

La chaleur de récupération, ou chaleur fatale, est l'énergie thermique émise par un procédé dont elle n'est pas la finalité. Son exploitation demande le développement d'une technologie complémentaire. Il s'agit généralement d'améliorer à la fois l'efficacité énergétique et l'impact environnemental d'un système produisant, de manière annexe, de la chaleur. Définition La chaleur de récupération, ou chaleur fatale, est la (définition retenue en France par la Programmation pluriannuelle de l'énergie). La chaleur fatale peut être réutilisée directement, ou après concentration ou stockage, pour améliorer un processus (préchauffage de gaz par exemple), pour chauffer un lieu ou des objets, pour refroidir (au moyen d'un évaporateur ou d'un autre système) ou pour produire de l'électricité (par exemple au moyen d'une machine à cycle organique de Rankine). Enjeux La récupération de chaleur s'inscrit dans une logique d’économie circulaire : d'un « déchet » (chaleur nuisibl

Dynamic modeling and simulation of a pipeline used for transportation of a fluid near the saturation

Zeli Zhang

A new district energy network has been developed by using CO2 as a heat transfer fluid. Only two pipes are required by the network, thus allowing the recovery of waste heat from the cooling users to be valorized by the heating users. Understanding and predicting the dynamics as well as identifying control methods and strategies is one of the key issues for the development of such a CO2 network that would operate in a safe, reliable and energy efficient manner. To assess the technical feasibility and address the safety problems, a physical-based model was developed to describe the fluid dynamics of CO2 pipelines used for transportation of a fluid near the saturation. Dynamic simulations were carried out to investigate pressure and flow fluctuation during transient flow and under changes of external perturbations. It shows that the system was able to response all these perturbations although the corresponding pressure wave propagates along the pipe.

2013

THERMOECONOMIC ANALYSIS AND OPTIMISATION OF AIR-BASED BOTTOMING CYCLES FOR WATER-FREE HYBRID SOLAR GAS-TURBINE POWER PLANTS

Raphaël Michel Adrien Marie Sandoz

Among the plethora of alternatives available, concentrated solar power (CSP) appears as one of the most favourable options. The stability and dispatchability of production achievable by the integration of storage and fuel-solar hybridisation are amidst the major advantages of this technology. Nevertheless, conventional CSP plants are based on stream-turbine cycles which consume large amounts of water. In addition to the low thermodynamic efficiency of this type of cycle, the installation of such plants in water-scarce areas is complicated by their reliance on water resources. Thus, the study of new concepts that overcome these drawbacks is necessary for the future of this technology. The availability of high temperature solar receivers for solar tower systems opens the way for the use of gas-turbines in hybrid solar- natural gas configurations. In order to increase the efficiency of the cycle while keeping the water consumption as low as possible, a promising alternative to the recovery of the waste heat in steam-turbines is to use a low-temperature intercooled-recuperated gas-turbine cycle. This work focuses on the analysis and optimisation of the performance of an innovative hybrid solar gas-turbine power plant with an air-based bottoming cycle (ABHSGT). The evaluation considers thermodynamic performance, economic viability and environmental impact as interrelated concerns. With this in mind, detailed steady-state and dynamic models of the power plant have been developed and validated by comparison with existing components. A second model without bottoming cycle has been built for comparison. A multi-objective optimisation using an evolutionary algorithm has then been performed, optimising both capital cost and specific CO2 emissions and resulting in a Pareto-optimal set of possible designs. The analysis of the trade-off curves resulting from the optimisation reveals promising outcomes. The global minimum for the levelised cost of electricity, found at relatively high solar shares, proves the economic potential of the technology. The integration of the bottoming cycle decreases significantly the levelised cost of electricity and the CO2 emissions of the system compared to the reference plant, and higher efficiencies are achieved. The optimal design selected for an in-depth thermoeconomic and environmental analysis exhibits a levelised cost of electricity of 109 [USD/MWhe] for a solar share of 20% and an overall exergetic efficiency 38.5%. The specific CO2 emissions are reduced by 33% compared to those of a simple gas-fired power plant. The water consumption is kept at very low levels compared to other CSP plants, making the system suitable for the deployment in water-scarce areas. In addition, the environmental impact induced by the land use requirements is considerably lower than that of other renewable energy technologies. The sensitivity analysis performed to assess the consequence of changes in varying financial conditions on the levelised cost of electricity and the net present value reveals that the system studied represents a profitable investment in the presence of feed-in tariffs. In the light of the performance obtained in the three aspects considered (thermodynamic, economic and environmental), it can be concluded that the ABHSGT represents a promising alternative to other renewable energy technologies, especially in water-scarce areas.

2012

Enthalpy and exergy analysis in the framework of a district scale energy balance

Cédric Lambiel

This report presents a study of an enthalpy and exergy analysis in the framework of a district scale energy balance. Energy demand (heating, cooling and lighting) for buildings represents more than 30 % of the total worlds energy use. Main eﬀorts have been made on increasing performances of new building envelop and on the use of low temperature processes in order to increase the exergy eﬃciency. On a district scale, diﬀerent temperature and energy ﬂow levels are present, meaning a great potential to make use of synergetic eﬀects by rationally managing energy ﬂow interactions between buildings as synergies by enhanced energy management and the usability of waste heat source. An optimisation of exergy ﬂows for the heating systems allows to identify the temperatures levels according to the energy demand, which helps to implement the best choice of available technologies. A number of connection cases will be described and studied to show the potential gain in terms of thermal and economical performances, where the thermal performances are deﬁned by both the energy and the exergy eﬃciency. This study shows an improvement of the thermal performances of connection cases where in all scenarios the heat losses are lower than the waste heat recovery. These gains on thermal performances may increase further by the integration of appropriate technologies such as heat pumps. The use of primary resource like gas can also be decreased.

2012

THERMOECONOMIC ANALYSIS AND OPTIMISATION OF AIR-BASED BOTTOMING CYCLES FOR WATER-FREE HYBRID SOLAR GAS-TURBINE POWER PLANTS

Raphaël Michel Adrien Marie Sandoz

2012