Search

International audience

International audience; District Heating (DH) technology is an efficient and cost-effective solution to provide heating services to the built environment. However, the existing DH technology may not be technically and economically effective to service buildings with low energy demands. Here, low-temperature based district heating (LTDH) can provide a better match between supply and demand in terms of energy quality and quantity. This paper deals with the energy and exergy analyses of a LTDH substation supplying a secondary LTDH network as a subnet of the existing DH system. In order to improve the temperature match, a mix of supply and return streams from the primary DH network are used to supply the substation. Based on modelling and simulation, an energy and exergy analysis is employed to compare the performance of two proposed substation configurations to that of a conventional DH substation operating at low temperatures. The results show that the proposed LTDH substation reduced the share of the yearly energy demand of the LTDH network that is covered by the primary DH supply flow by 20% to 25%; the rest being supplied by the primary DH return flow. Likewise, by using the flow from the main DH return pipe, the final exergy efficiency of the overall system increased by 5% on average. The exergy destruction occurring at the system components was also identified and compared: during high heat demand periods the substation heat exchanger is responsible for the largest share of exergy destruction, whereas for low heat demands, it is due to the pumping effort. Based on these results, the proposed system is seen as an effective approach to increase the quality and quantity match between the low-temperature network and the conventional supply.

International audience; Building sector is currently one of the major sources of CO 2 emissions. Considering that the largest proportion of energy in buildings in Europe is used for heating services, significant potential for emissions decrease could be exploited through heat demand reductions. The scope of this paper is to evaluate the impacts of changed climate and building renovation on heating related CO 2 emissions on a neighborhood level. A combination of existing tools (EnergyPLAN, ArcGIS, CCWorldWeatherGen) and a tool previously developed by the authors (resistance-capacitance analogy based heat demand model [1]) were used. Three weather scenarios for the future were considered (low, medium, high temperature increase), as well as four renovation paths (no renovation, shallow, intermediate, deep renovation path). Three heating system options were taken into the account: individual electric heaters in each dwelling, natural gas distribution network with individual boilers in each dwelling and district heating network with centralized heat production in natural gas fueled boiler. Generic neighborhood configuration for Portugal was created based on the district of Alvalade that is located in Lisbon. This particular district was chosen due to the fact that it possesses desirable urban morphology and it was built during several construction periods over the last century. The results showed that the changed climate, by itself, could decrease annual CO 2 emissions from 8% up to 34% in 2050 compared to 2010 (depending on the weather scenario and heating system considered) due to the changed weather parameters. Furthermore, building envelope renovation could enable additional 80-260ktCO 2 savings in cumulative emissions for the regarded period (2010-2050).

International audience

International audience

International audience; The application of catalytic membrane reactors (CMRs) is beneficial for the production of fuel cell grade hydrogen via reforming processes because of a higher hydrogen yield compared to traditional reactors as a result of the shift effect and simultaneous production of ultra pure hydrogen in the case of a Pd-Ag membrane. Regarding the catalytic conversion, noble metals have shown superior catalytic reactivity in terms of hydrogen production and carbon deposition prevention [1]. Apart from the experimental studies, energy and thermal evaluations are essential for the realization of optimization of the hydrogen production systems. In this work, first, ethanol steam reforming (ESR) experiments over Pd-Rh/CeO2 catalyst were performed in a CMR at different temperatures, pressures, and water/ethanol ratios. Then, the exergy efficiency and exergy destruction of the system were evaluated based on inlet and outlet streams using the experimental data. Exergy analysis can give a more detailed picture of the process [2]. The aim of this work is to propose and analyze a new CMR configuration with enhanced performance in terms of pure hydrogen production via ESR.

International audience; Ethanol steam reforming (ESR) experiments over Pd-Rh/CeO2 catalyst were performed in a catalytic membrane reactor (CMR) at different temperatures and pressures, using a mixture of ethanol and water at various S/C ratios to resemble bio-ethanol. The reactor was filled in by the catalyst so that the membrane was fully covered to achieve the maximum amount of hydrogen production and permeation. Hydrogen yield of 0.6 at 12 bar and 923 K was reached at S/C=3 and hydrogen recovery was 92%. 0.9 LN hydrogen/ml EtOH equal to 3.5 mole of pure hydrogen per mole of inlet EtOH was obtained at 12 bar. It was proved that reforming reactions are nearly complete when the system was running at 923 K and pressures greater than 6 bar. The experimental results were compared to a staged membrane reactor (SMR) configuration in which the same experimental conditions were applied and the same catalyst was used. The CMR system showed a superior performance and comparable results to what has been reported in the literature were obtained. Besides, a model based on the Arrhenius law was developed to simulate the reforming process and hydrogen permeation in the CMR aiming at simulating a pure hydrogen production system able to feed a PEM fuel cell online.

International audience; This paper describes a CFD study of the steam-reforming process (SRP) of methanol in a short pseudo-contact time reactor of fixed bed type, in axi-symmetric conditions. The SRP is important sake for hydrogen production, and the design /scale-up/control of the industrial processes in the future are supported by a reliable knowledge and prediction of the catalytic reaction. The difficulty of determining the reaction scheme and the associated constants is well-known, due to the necessity of identifying the reaction kinetics in purely chemical regime, meaning with a perfect homogeneity and flow independence. Practically these ideal conditions, albeit assumed, are not fulfilled so that the intrinsic chemical kinetics is not reached. For the case of SRP, we have attempted here to validate the Peppley’s model by a numerical modelling reproducing exactly the local conditions in the experimental duct, accounting for gradients in the cross section. The numerical results show the same trends than the experimental one, but with a slight shift of 20% as a consequence of the reactor heterogeneity. This result seems acceptable to validate the use of the Peepley’s model for further studies in other types of complex flow reactors.

International audience; The exergy efficiency and exergy destruction of a catalytic membrane reactor were evaluated based on inlet and outlet streams using experimental data. To calculate the exergy content of chemical species, three different parts i.e. physical exergy, chemical exergy, and exergy of mixing has been taken into account. For the system under study, ethanol steam reforming (ESR) experiments were performed over PdRh/CeO2 catalyst in a membrane reactor (MR) containing Pd-Ag membranes. Experiments were performed at T=873-923 K, P=4-12 bar, and fuel flow rates of 50 and 100 µl/min. The fuel was a mixture of ethanol and distilled water with steam to carbon ratio=1.6, 2, and 3. The exergy efficiency of the system was evaluated considering both an insulated reactor (without heat loss), and non-insulated reactor (with heat loss). The significant effect of pressure and temperature on the exergy efficiency was observed. Exergy efficiency up to around 50% was reached in the case of insulated reactor at 12 bar and 923 K. It was concluded that the highest amount of exergy was destructed by heat losses. The study showed that the exergy content of the retentate gas especially at lower pressures can provide the reactor with a fraction of its required heat at steady state conditions. This notably increased the exergy efficiency of the system. Thermal efficiency of the system was between 70-90% for insulated reactor system and decreased to between around 40-60% when the heat loss was considered.

International audience; Le recyclage matière est a priori considéré comme éco-favorable par rapport à l'exploitation de minerais provenant de mines, par nature en quantité finie et donc s'épuisant. Néanmoins, une vision holistique du recyclage requiert l'analyse de l'ensemble des ressources mobilisées pour effectuer cette opération. De plus, en suivant le déplacement/cheminement de la matière dans le temps, il devient alors nécessaire de connaître l'ensemble de l'historique de la matière considérée. Les auteurs établissent une équation théorique décrivant l'évolution à temps discret de l'émergie d'un produit : le pas d'échantillonnage est le temps du cycle. L'équation peut se réduire à une suite géométrique de raison, la fraction à recycler, sous certaines hypothèses. L'aluminium est ensuite proposé comme exemple d'application.

The development of district heating (DH) systems is facing the challenge of servicing areas with lower energy demands whose connection might not be either effective or profitable if the conventional DH technology is used. The purpose of this paper is to propose a complementary approach on how to effectively service low-energy building (LEB) areas using the existing DH networks. The proposed solution consists in supplying a secondary low-temperature (LT) network by means of a ‘low temperature’ substation that uses the return water from the main DH network as a substitute for the primary energy source, together with a minor portion of the main DH supply. Two types of LT substations are proposed and compared to a reference substation: First, a one-stage heat exchanger that uses a mixture of the main DH network return and supply flows as thermal energy source. Second, a two-stage heat exchanger that is fed by both the main DH return and supply flows. The system subject to this study consists on the LT substation with supply/return temperatures at 55/25 °C average. The system energetic performance is analysed though thermodynamic simulation. Outdoor ambient temperatures variations throughout the year are considered for two specific locations, assuming full and partial load operation. The results show that it is possible to supply 20-50% of the total annual heat demand of a LTDH network using the return flow from the main DH network. The solution presented in this paper is seen as being of potential interest to deliver thermal energy services to LEB areas. QC 20160616

The present invention relates to a method of determining at least one energy property of a gaseous mixture which consists in: 1. measuring, on said gaseous mixture, n physical properties phii at a temperature T and/or one physical property phii at n different temperatures; 2. determining, from said physical properties, the composition of a gas with n+1 components that is equivalent to said mixture; and 3. deducing the energy properties of said gaseous mixture from said composition of the equivalent gas.

International audience

cited By (since 1996)0; International audience; Blending H 2 with natural gas in spark ignition engines can increase for electric efficiency. In-situ H 2 production for spark ignition engines fuelled by natural gas has therefore been investigated recently, and reformed exhaust gas recirculation (RGR) has been identified a potentially advantageous approach: RGR uses the steam and O 2 contained in exhaust gases under lean combustion, for reforming natural gas and producing H 2, CO, and CO 2. In this paper, an alternative approach is introduced: air gas reforming circulation (AGRC). AGRC uses directly the O 2 contained in air, rendering the chemical pathway comparable to partial oxidation. Formulations based on palladium and platinum have been selected as potential catalysts. With AGRC, the concentrations of the constituents of the reformed gas are approximately 25% hydrogen, 10% carbon monoxide, 8% unconverted hydrocarbons and 55% nitrogen. Experimental results are presented for the electric efficiency and exhaust gas (CO and HC) composition of the overall system (SI engine equipped with AGRC). It is demonstrated that the electric efficiency can increase for specific ratios of air to natural gas over the catalyst. Although the electric efficiency gain with AGRC is modest at around 0.2%, AGRC can be cost effective because of its straightforward and inexpensive implementation. Misfiring and knock were both not observed in the tests reported here. Nevertheless, technical means of avoiding knock are described by adjusting the main flow of natural gas and the additional flow of AGRC. Copyright © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Simulation studies indicated that the start and end of combustion in an internal combustion engine could be determined from the points of minimum and maximum entropy in the cycle. This method was further used to predict the beginning and end of the combustion process from experimentally obtained pressure crank angle data from a natural gas operated, single cylinder, spark ignition engine. The end of combustion always matched well with the point of maximum entropy. The start of combustion could be determined easily from the rate of change of entropy, which showed a sharp change at ignition. Results closely agreed with those obtained from a heat release analysis.