Heat of reaction of hydrothermal liquefaction reactions

Wet waste streams include a wide variety of products such as food processing residues, sewage sludge but also the organic fraction of municipal solid waste. Humidity typically varies from 50 to above 90 %. Dewatering and drying is possible for most feedstocks but at a significant cost. Hydrothermal liquefaction produces a biocrude that can be further upgraded into biofuels. The conversion takes place at temperatures between 250 and 400 °C and at pressures above the saturation pressure to ensure that water remains in the liquid phase, typically above 100 bar [1]. Even though the basic principles of hydrothermal liquefaction are well known, there are still some significant scientific questions and technical issues. One of the important questions that remain is the heat of reaction and the heat balance of the reaction. Please click Additional Files below to see the full abstract

Hydrothermal liquefaction process of food waste in batch and continuous lab scale reactors

Due to the energy burden that represents the drying step, wet biomass is often underexploited for energy purpose. Indeed, this step represents one of the most energy consuming step in a thermochemical process and is often economically prohibitive. During hydrothermal liquefaction, conversion of biomass takes place at temperatures between 250 and 374 °C and at pressures above the saturation pressure to ensure that water remains in the liquid phase, typically above 100 bars, avoiding enthalpy energy penalties [1]. To avoid competitive use of land for food supply and excessive cost of entrance biomass, blackcurrant pomace and brewery’s spent grains have been selected and tested on liquefaction as food residues. Experiments have been carried out in a 600 mL batch reactor (PARR), allowing maximum temperature of 320°C and maximum pressure of 130 bars. Effects of operating parameters such as temperature and holding time, biomass pretreatment and reactor configuration are investigated on mass yields, aqueous phase composition and energy balance. Results obtained in the batch reactor constitute the reference of this study, in the comprehension of the mechanism of the liquefaction of food residues. Also, these results form the basis for a model to scale up the process, and are confronted to the results on a continuous lab scale plant. Please click Additional Files below to see the full abstract

Des prêts-à-écrire au service de l’écriture et de la créativité des élèves de 8 à 11 ans

Nous proposons une analyse de 180 textes narratifs, du CE2 au CM2 (8-11 ans), de différentes classes et différents milieux. Il a été demandé aux élèves de produire un récit dont le début et la fin étaient donnés. Notre intérêt s’est porté sur les mots de la narration utilisés par les élèves. Nos analyses révèlent, premièrement, qu’une tension s’opère, lors de la production écrite, entre le recours à sa langue (la langue de tous les jours) et le recours à une langue plus élaborée. Deuxièmement, nous constatons que les élèves puisent des éléments lexicaux dans des scénarios de leur propre vie (en lien avec le sujet de production), tout en les combinant avec leurs connaissances linguistiques. Ils recourent à des segments plus élaborés issus de leur mémoire des textes lus ou entendus. Cette combinaison provoque soit des réussites, soit des distorsions de diverses natures : recherches lexicales ou télescopages entre différentes constructions disponibles en langue.Notre étude montre la variété des constructions que les élèves sont capables de mobiliser pour répondre à la situation d’écriture. Les choix des élèves, qui ne sont pas effectués au hasard, sont révélateurs de leur créativité.We propose an analysis of 180 narrative texts, from third to fifth grade (8-11 years old), from different classes and backgrounds. Students were asked to produce a narrative with a given beginning and ending. Our focus was on the narrative words used by the students.Our analyses reveal, first, that a tension arises in the written production between the use of one's own language (everyday language) and the use of a more elaborate language. Second, we find that students draw lexical elements from their own life scenarios (related to the production topic), while combining them with their linguistic knowledge. They resort to more elaborate segments taken from their memory of texts they have read or heard. This combination leads either to successes or to distortions of various kinds: lexical searches or telescoping between different constructions available in the language.Our study shows the variety of constructions that students are able to mobilize to respond to the writing situation. The students' choices, which are not made at random, reveal their creativity

Bibliothèque : faire société (La)

Rencontre organisée à l\u27enssib les 25 et 26 juin 2012 dans le cadre des Estivales. Thématiques du 25 juin : Bibliothèque, création et mémoire Thématiques du 26 juin : Bibliothèque, éducation et politique Comme l’école, après l’école, la bibliothèque peut être un instrument de connaissance du passé, d’analyse du présent et de construction de l’avenir. Qu’est-ce qui rend ce projet possible, légitime, nécessaire ? En quoi la bibliothèque et, plus généralement, les instances de partage du savoir et les institutions culturelles permettent d’être « parmi les hommes » ? Comment, inscrites dans l’épaisseur du temps, elles se nourrissent nécessairement de mémoire et d’histoire ? En quoi elles peuvent/doivent contribuer à la reconstruction d’un espace public, d’un débat public ? Quelle ambition politique, quel projet démocratique peuvent trouver un ancrage une assise, dans ces institutions et fonder leur raison d’être ? A travers ce colloque et ses intervenants, l’enssib a souhaité interroger quelques-unes de ses convictions et de ses exigences : la curiosité intellectuelle, la liberté de l’esprit, la mémoire partagée, la passion de la chose publique, le rôle politique de la bibliothèque. Une éthique de la bibliothèque

Rapport final BiogasMotor/ programme de recherche chaleur ambiante et rejets thermiques; installations chaleur-force.

The object of this work is to test the unscavenged prechamber ignition system on a 150 kW cogeneration engine feed with biogas. The engine performances in term of fuel conversion efficiency are observed and the reduction potential f the exhaust emissions below the Swiss limit are verified (NOx CO : 400 and 650 mg/Nm3, 5 % O2 and 0 % relative humidity) ; and the non-limited HC emissions too. The interesting variables are the air-fuel ratio, the fuel composition, the compression ratio and the spark-timing. The aim of this work is to reach at least 36 % in fuel conversion efficiency with exhaust gas emissions lower than the regulations limits without exhaust gas after-treatment. The engine used is a turbocharged spark ignited Liebherr G926 TI, 10 L, 6 cylinders in line engine fitted with combustion prechambers (with a volume of 3 % of the cylinder volume). As a first step, the engine fuel supply has been modified to allow the use of natural gas / CO2 mixtures to simulate biogas. Natural gas tests have been performed with direct ignition and prechamber ignition as references. The same experimental conditions have been applied for the simulated biogas tests. Different spark timing advances have been tested in the configuration with the initial compression ratio of 12,0. Afterwards new pistons have been developped to reach a compression ratio of 13,3. Two different CO2 proportions (20 % and 40 %) have been used to observe the influence of CO2 in fuel on the performances. With a compression ratio of 12,0, 40 % of CO2 inducee a CO reducion of 15 % and an HC reduction of 8 % for the same NOx emissions with a slight reduction of 1 % in fuel conversion efficiency, compared to pure natural gas. The results for the compression ratio of 13,3, a spark timing of 8 caBTDC, of 1,63 and 39,5 % CO2 are a fuel conversion efficiency of 38 % and NOx and CO emissions below the swiss limit. Those performances and emissions are compared to the ones obtained for the natural gas with a compression ratio of 12,0 and prechamber ignition. The use of a compression ratio of 13,3 instead of 12,0 allows to balance the loss in fuel conversion efficiency due to the 40 % of CO2 . If the percentage of CO2 is lower then the efficiency is higher but the CO and HC emissions too. Moreover, it seems better to use a higher compression ratio than a sooner spark timing (see fig. 29, 30, 31). Those tests demonstate that the CO2 does not modify the combustion process nor the prechamber ignition mode. This study shows that gas engines with unscavenged prechambers could allow a significant boost in energy conversion from biogas while keeping the emissions within the tough Swiss limits

Controlled Auto-Ignition (CAI) in Engine Combustion Prechamber

Unscavenged prechamber ignition has recently been developed at LENI-EPFL to reduce the emissions from cogeneration spark ignition gas engines (natural gas and biogas) within the Swiss Motor project supported by the Federal Office of Energy. Prechambers fitted with conventional spark plug allow a 40% reduction of the CO emissions and a reduction of the NOx emissions below the Swiss limits of the OPair law (Swiss emissions legislation), and a reduction of 55 % of the HC emissions. Unfortunately, spark plugs are weak components in therms of lifetime, reliability and maintenance. There consequently exists a strong motivation to develop new ignition systems which include: pilot injection of fuel, direct injection of fuel with a glow plug or hot gas jets from a prechamber where the comustion is initiated by auto-ignition, controlled mainly by pressure and temperature conditions. In this mode, the prechamber auto-ignition replaces the spark plug and the combustion mode is similar to a HCCI (Homogeneous charge compression ignition) one. The first step in the development of the system is the simulation of the auto-ignition in the prechamber in order to understand the phenomena and later to control them. As HCCI combustion is strongly dependent on chemical kinetics and fluid dynamics, a CFD code and a chemical reactions solver have to be numerically linked. First the 3D fluid flows in the prechamber and in the engine cylinder has been modelled with the well known KIVA 3-V code. Those results will be taken as reference for further calculations and initial conditions for the chemical reaction calculations. To elaborate and validate an auto-ignition reaction mechanism for natural gas, auto-ignition delays for various gas mixtures have been measured in the rapid compression machine of Lille [1[. The data identification will be performed using the GRI mechanism as a base for the auto-ignition delays simulation with Chemkin-II. The next step will be the development of an interface between the Chemkin-II solver and a CFD code NSMB (Navier Stokes Multi Block solver [2,3]). NSMB is an in-house code developed to deal with large meshes on parallel computers and to be coupled with other applications. It has been modified to support dynamic meshes. The coupling is under development

Les prêts-à-écrire au service de la compétence scripturale des élèves du projet ÉCRICOL

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