Exergy And Energy Analysis Of Waste Heat Recovery Options For Cooling Capacity Production

Electricity production in Lebanon stands at around 1.5 GW while the demand exceeds 2.5 GW at peak times and peak cooling demands, resulting in rationing cuts from between 3 to 20 hours a day which is the worst performance in the Middle East. Due to the country energy shortfall, a large number of small-scale backup generators is installed to address the electric and cooling needs. The proliferation of use of these backup generators presents an interesting potential for waste heat recovery in order to achieve additional power generation and cooling capacity production. This paper investigates two possible configurations for waste heat recovery: A first configuration studies the potential of combining an Organic Rankine Cycle (ORC) with a conventional vapor compression refrigeration cycle (VCRC) to meet the required cooling load. A second option evaluates the possibility of using a dessicant cooling system (DCS) to handle the latent part of the cooling load, in tandem with a conventional vapor compression refrigeration cycle handling the sensible part. The investigations are based on exergy and energy analysis carried out for both configurations to compare their performance and assess their economical and environmental impacts

High-global warming potential F-gas emissions in California: comparison of ambient-based versus inventory-based emission estimates, and implications of refined estimates.

To provide information for greenhouse gas reduction policies, the California Air Resources Board (CARB) inventories annual emissions of high-global-warming potential (GWP) fluorinated gases, the fastest growing sector of greenhouse gas (GHG) emissions globally. Baseline 2008 F-gas emissions estimates for selected chlorofluorocarbons (CFC-12), hydrochlorofluorocarbons (HCFC-22), and hydrofluorocarbons (HFC-134a) made with an inventory-based methodology were compared to emissions estimates made by ambient-based measurements. Significant discrepancies were found, with the inventory-based emissions methodology resulting in a systematic 42% under-estimation of CFC-12 emissions from older refrigeration equipment and older vehicles, and a systematic 114% overestimation of emissions for HFC-134a, a refrigerant substitute for phased-out CFCs. Initial, inventory-based estimates for all F-gas emissions had assumed that equipment is no longer in service once it reaches its average lifetime of use. Revised emission estimates using improved models for equipment age at end-of-life, inventories, and leak rates specific to California resulted in F-gas emissions estimates in closer agreement to ambient-based measurements. The discrepancies between inventory-based estimates and ambient-based measurements were reduced from -42% to -6% for CFC-12, and from +114% to +9% for HFC-134a

Hydrostatic and osmotic pressure study of the RNA hydration

The tertiary structure of nucleic acids results from an equilibrium between electrostatic interactions of phosphates, stacking interactions of bases, hydrogen bonds between polar atoms and water molecules. Water interactions with ribonucleic acid play a key role in its structure formation, stabilization and dynamics. We used high hydrostatic pressure and osmotic pressure to analyze changes in RNA hydration. We analyzed the lead catalyzed hydrolysis of tRNAPhe from S. cerevisiae as well as hydrolytic activity of leadzyme. Pb(II) induced hydrolysis of the single phosphodiester bond in tRNAPhe is accompanied by release of 98 water molecules, while other molecule, leadzyme releases 86

Étude et conception d'un procédé de séchage combiné de boues de stations d'épuration par énergie solaire et pompe à chaleur

Wastewater sludge management raises a serious challenge due to ever increasing environmental pollution and energy consumption. The aim of this work is to study the drying of wastewater sludge using solar energy combined with heat pumps and to investigate possible ways of providing supplemental energy to sludge drying when needed. A laboratory-scale drying test bench was set up to study the conductive drying of sludge and evaluate its drying characteristics. An analytical method was developed to evaluate water vapor diffusivity within urban sludge, modelled as coarse aggregated porous medium where only aggregates external porosity is accounted for. This method, which is based on the analytical solution of a fickian diffusive model, allows the evaluation of the impedance to which vapor diffusion is subjected throughout drying, as a function of the sludge dry solid content. Experiments highlighted the effect of mixing frequency on drying enhancement. Convective heat and mass transfers, occurring between air and sludge, were experimentally characterized. Experiments have shown the effect of increased surface air velocities on the enhancement of the drying mechanism. A correlation giving the deviation from the Lewis' predicted mass transfer coefficients was established as a function of the sludge dry solid content. The concept of blowing air by means of linear slits along the greenhouse width was proposed as a way of improving air distribution inside the greenhouse. A mathematical model has been developed to simulate this new drying system and evaluate its performances and energy consumptions. Weather data were incorporated in order to evaluate system seasonal performances. The system analysis focused on the influence of climatic conditions on heat pumps operating conditions and allowed the definition of an optimal regulation based on the minimisation of the marginal energy consumption. Furthermore, simulations showed improvement on the combined drying system performances with reduced sludge thickness.La gestion des boues représente un véritable défi dû à sa consommation d'énergie et la pollution environnementale associée. L'objectif de ce mémoire est de concevoir et d'étudier un procédé de séchage de boues par énergie solaire et pompes à chaleur, et d'explorer les options techniques pour fournir l'appoint d'énergie aux boues. Un dispositif de séchage expérimental a été réalisé afin d'étudier le séchage conductif des boues et d'évaluer leurs caractéristiques. Une méthode analytique a été proposée pour évaluer la diffusivité de la vapeur d'eau dans les boues, modélisées en tant qu'ensemble d'agrégats poreux. Cette méthode, basée sur un modèle diffusif fickian, a permis de suivre l'évolution de facteur d'impédance de diffusion au cours d'un cycle de séchage. Les expériences ont souligné l'effet de la fréquence de retournements sur l'intensification du séchage. Les transferts de chaleur et de masse convectifs intervenant à l'interface de séchage air-boues ont été caractérisés expérimentalement. L'intensification de l'évaporation due à l'augmentation des vitesses d'air superficielles a été mise en évidence. Une corrélation a été établie pour rendre compte de l'écart entre les conductances latentes expérimentales et les conductances prévues par la théorie de Lewis, en fonction des siccités des boues. Le concept de soufflage d'air par fentes linéaires sur la largeur de la serre a été proposé comme moyen d'amélioration des conditions aérauliques dans une serre de séchage. A partir de ces développements, un modèle mathématique du procédé de séchage combiné a été établi afin d'évaluer ses performances et ses consommations énergétiques. Les données climatiques ont été intégrées afin d'évaluer les performances saisonnières du procédé et d'étudier l'influence des conditions climatiques sur les modes opératoires des pompes à chaleur. Les simulations ont permis de définir une logique de régulation optimale en termes de minimisation des consommations énergétiques marginales. En outre, le modèle a mis en évidence l'amélioration apportée par la réduction de l'épaisseur du lit de boues au cours d'un séchage combiné

Modélisation et conception d une serre solaire assistée par pompes à chaleur pour le séchage des boues de station d épuration

PARIS-MINES ParisTech (751062310) / SudocSudocFranceF

Sludge drying in greenhouse assised by a heat pump.

ISBN 13 978-2-913149-59-5International audienc

Modeling of a solar and heat pump sludge drying system

International audienceA slipping quasistatic model has been developed to evaluate the performance of a greenhouse sludge drying system assisted by a heat pump called "Solar and Heat Pump Sludge Drying System" (S&HPSDS). The model is derived entirely from the conservation laws of mass, energy, momentum and equations of state as well as correlations of heat transfer. Weather data are incorporated in order to evaluate the seasonal performance of the system. The model can be used for many different purposes; this paper focuses on the evaluation of the heating temperature leading to an annual thermo-economic optimum in terms of energy consumption

Characterization of Sewage Sludge Water Vapor Diffusivity in Low-Temperature Conductive Drying

International audienceIn order to study the low-temperature conductive drying of urban sewage sludge and evaluate its essential characteristics, a laboratory-scale drying device was set up. Sludge is modelled as a coarse aggregated, porous medium, and experiments are conducted to study its rheological behavior throughout a drying cycle and aggregation effects on diffusion. Investigations are based on a macroscopic model of sludge aggregates where only external porosity is accounted for This paper presents a method to evaluate water vapor diffusivity within urban sludge based on an analytical solution of a Fickian diffusive model which enables diffusivity determination by simple exponential regression over experimental data. Experiments are carried out with three levels of heating fluxes, 300, 525 and 700 W/m(2), without any remarkable effect of flux density on water vapor diffusivity over the tested range. Further experiments are conducted to underline the effect of mixing frequency. Predictive correlations for water vapor diffusivity as a function of sludge dry solid content and mixing frequency are reported in this work

High-Global Warming Potential F‑gas Emissions in California: Comparison of Ambient-Based versus Inventory-Based Emission Estimates, and Implications of Refined Estimates

To provide information for greenhouse gas reduction policies, the California Air Resources Board (CARB) inventories annual emissions of high-global-warming potential (GWP) fluorinated gases, the fastest growing sector of greenhouse gas (GHG) emissions globally. Baseline 2008 F-gas emissions estimates for selected chlorofluorocarbons (CFC-12), hydrochlorofluorocarbons (HCFC-22), and hydrofluorocarbons (HFC-134a) made with an inventory-based methodology were compared to emissions estimates made by ambient-based measurements. Significant discrepancies were found, with the inventory-based emissions methodology resulting in a systematic 42% under-estimation of CFC-12 emissions from older refrigeration equipment and older vehicles, and a systematic 114% overestimation of emissions for HFC-134a, a refrigerant substitute for phased-out CFCs. Initial, inventory-based estimates for all F-gas emissions had assumed that equipment is no longer in service once it reaches its average lifetime of use. Revised emission estimates using improved models for equipment age at end-of-life, inventories, and leak rates specific to California resulted in F-gas emissions estimates in closer agreement to ambient-based measurements. The discrepancies between inventory-based estimates and ambient-based measurements were reduced from −42% to −6% for CFC-12, and from +114% to +9% for HFC-134a