1,3 Dioxolane versus tetrahydrofuran as promoters for CO 2 -hydrate formation: Thermodynamics properties, and kinetics in presence of sodium dodecyl sulfate

This paper makes a comparison between tetrahydrofuran (THF) and 1,3 dioxolane (DIOX) in terms of their respective performances as promoters for the formation of clathrate hydrates with CO2. The aim is to find products that can be substituted for THF, which is known to be harmful and difficult to handle. Drawing on a review of the chemical and physical properties of these two organic compounds, experiments were performed using high-pressure differential scanning calorimetry (DSC) and a batch reactor. Details of the thermodynamic equilibria of mixed THF+CO2 and DIOX+CO2 hydrates obtained with various additive concentrations are provided, along with hydrate kinetics data relating to the hydrate formation. The effect of the presence of an anionic surfactant, SDS (sodium dodecyl sulfate), on hydrate formation kinetics was also evaluated, showing that a combination of THF or DIOX and SDS is a very advantageous solution for accelerating hydrate formation. THF has been found to outperform DIOX as a hydrate promoter from both a thermodynamic, and a kinetic standpoint in presence of SDS. However, DIOX remains an interesting practical solution, due to the benefits offered as the least toxic and aggressive of these two organic compounds

Storage by phase change materials of the thermal energy released by the industry at low temperature

Une grande quantité d’énergie est rejetée par l’industrie à bas niveau de température, en dessous de 200 °C. Afin d’améliorer le rendement énergétique global des procédés utilisés, il est envisageable de valoriser cette chaleur perdue appelée chaleur fatale. Cependant cette valorisation est souvent rendue difficile par la présence d’un décalage temporel entre le moment où l’énergie est rejetée et le moment auquel cette énergie pourrait être de nouveau utilisée. Associant de fortes capacités de stockage ainsi qu’une possible restitution d’énergie à température constante, la solution du stockage de l’énergie thermique par des Matériaux à Changement de Phase, appelés MCP, apparaît comme particulièrement attractive. Cependant, la mise en œuvre de ces systèmes de stockage se heurte à des verrous scientifiques et technologiques tant au niveau du matériau de stockage que du système mais également de son contrôle commande et de son insertion dans les procédés industriels.L’objectif de la thèse est de mettre au point un système de stockage par MCP solide-liquide dans deux gammes de température : 70-85 °C et 120-155 °C. La première correspond aux températures des réseaux de chaleurs ou des chauffages domestiques alors que la deuxième s’applique au préchauffage des procédés industriels déjà existants. La thèse vise à démontrer la faisabilité technique du système de stockage. Le travail s’articule autour de différentes tâches allant de la sélection et la caractérisation des MCP jusqu’à leur mise en œuvre dans un organe de stockage et la simulation numérique de la solution de stockage.Les MCP recensés dans la bibliographie à ces niveaux de températures ont été caractérisés finement par calorimétrie (DSC) afin de déterminer leurs propriétés thermo-physiques sur des échantillons de grade laboratoire. L’acide stéarique pour la gamme 70-85 °C et l’acide sébacique pour la gamme 120-155 °C ont été sélectionnés. Des analyses calorimétriques plus poussées sur le grade industriel de ces matériaux ont été réalisées avec notamment des analyses de vieillissement et de compatibilité avec leur encapsulation respective au sein d’un banc expérimental. Le prototype expérimental de stockage thermique a été dimensionné et conçu pour répondre aux sollicitations simulant les rejets et les demandes d’un procédé industriel. Ce banc d’essais est composé principalement de deux organes de stockage que sont une cuve cylindrique et un échangeur multitubulaire et d’un thermorégulateur servant à simuler le fonctionnement du procédé industriel. Dans l’échangeur multitubulaire, le MCP occupe toute le volume de la calandre tandis que le fluide caloporteur circule dans les tubes. La cuve, quant à elle, contient des capsules sphériques en polyoléfines dans lesquelles le MCP est confiné. Elle est traversée par le fluide caloporteur procédant aux échanges thermiques. Ces capsules sphériques appelées nodules ne peuvent supporter plus de 100 °C et sont exclusivement réservées pour la gamme basse température. Ainsi, l’acide stéarique a été confiné dans les nodules afin de remplir la cuve de stockage. L’acide sébacique a lui été intégré dans la calandre de l’échangeur multitubulaire. Les campagnes expérimentales réalisées ont montré la faisabilité de ces types de stockage. Enfin, un modèle numérique simulant les performances du module de stockage utilisant les MCP encapsulés a été réalisé. Il constitue la première étape d’un outil de simulation complet intégrant les briques technologiques du stockage latent.A large amount of energy is rejected by the industry at low temperature level, below a temperature of 200 °C. In order to improve the overall energy efficiency of industrial processes, it is possible to re-use this waste heat. However, this energy recovery is often made difficult because of the time difference between the process step at which the energy is lost and the process step at which this energy could be reused. Combining high energy storage capabilities and a possible energy recovery at constant temperature, thermal storage solution by phase change materials (PCM) is particularly attractive. However, this storage systems implementation faces scientific and technologic obstacles concerning both the storage material and system but also its command system and its integration into industrial processes.This thesis aims to develop a thermal energy storage system using a solid-liquid PCM technology in two temperature ranges: 70-85 °C and 120-155 °C. The first one corresponds to temperatures of heating networks or domestic heating systems, while the second one could directly preheat existing industrial processes. The thesis aims to demonstrate the technical feasibility of the storage system. The purpose is divided into different tasks such as PCMs selection and characterization, PCM implementation in a storage system but also numerical simulation of the storage solution.PCM documented in the literature at those temperature ranges were characterized by Differential Scanning Calorimetry (DSC) in order to determine thermo physical properties on laboratory grade samples. Stearic acid for the 70-85 °C temperature range and sebacic acid for the 120-155 °C temperature range were selected. Deeper differential scanning calorimetry analyses were carried out on those industrial grade materials including material ageing process analyses and their compliance with their respective encapsulation within an experimental test bench.Thermal storage experimental prototype was designed in order to meet the demands simulating the rejects and needs of industrial processes. The test bench is mainly composed of two storage systems : a cylindrical tank, a multitubular exchanger and a thermoregulator used to simulate industrial process functioning. The PCM, while in the multitubular exchanger, fills up the whole volume of the shell whereas the heat transfer fluid flows in tubes. The tank, for its part, contains polyolefin spherical capsules in which the PCM is contained. The tank is crossed by the heat transfer fluid conducting heat exchanges. Those spherical capsules called nodules cannot be exposed to temperatures exceeding 100 °C and are exclusively reserved for the low temperatures range. Thus, stearic acid was confined in nodules so as to fill the storage tank. The sebacic acid was incorporated in the multitubular exchanger shell. Experimental campaigns carried out have demonstrated the feasibility of those storage types

Latent Thermal Energy Storage System for Heat Recovery between 120 and 150 °C: Material Stability and Corrosion

Thermal energy represents more than half of the energy needs of European industry, but is still misspent in processes as waste heat, mostly between 100 and 200 °C. Waste heat recovery and reuse provide carbon-free heat and reduce production costs. The industrial sector is seeking affordable and rugged solutions that should adapt the heat recovery to heat demand. This study aims to identify suitable latent heat materials to reach that objective: the selected candidates should show good thermal performance that remains stable after aging and, in addition, be at a reasonable price. This paper details the selection process and aging results for two promising phase change materials (PCMs): adipic and sebacic acid. They showed, respectively, melting temperatures around 150 °C and 130 °C, degradation temperatures (mass lost higher than 1%) above 180 °C, and volumetric enthalpy of 95 and 75 kWh·m−3. They are both compatible with the stainless steel 316L while their operating temperature does not exceed 15 °C above the melting temperature, but they do not comply with the industrial recommendation for long-term use in contact with the steel P265GH (corrosion speed > 0.2 mm·year−1)

Gas hydrate promoters for CO2 hydrate formation: thermodynamic and kinetic studies with cyclic ethers and surfactant

Gas hydrates are solid crystalline compounds consisting of a lattice structure formed by a network of water molecules which can encage small guest molecules such as CO2 1. These compounds are of interest in many practical applications (flow assurance, separation processes, storage of gases, etc…) where thermodynamic and kinetic properties are of importance. For some applications, it is necessary to accelerate hydrate formation, and for this purpose, the addition of additives is of common use. Among the various chemical compounds able to act as thermodynamical hydrate promoters, Tetrahydrofuran (THF), a cyclic ether with the formula C4H8O, is very popular 2. However, this compound is harmful and may cause technical damages in the process installations. This study propose to investigate how another cyclic ether, the 1,3 dioxolane (DIOX) could be used as a substitution product than THF, as DIOX is less harmful and more easy to use than THF 3. In this respect, this studies proposes: (i) to study using high pressure calorimetry the thermodynamical effect of these two additives on hydrate phase equilibria with CO2 gas; (ii) to study using a batch reactor the hydrate formation kinetics obtained by using THF or DIOX with/or without surfactant (SDS). On a thermodynamical point of view, our results demonstrate clearly that THF is a better thermodynamic promoter than DIOX. On a kinetic point of view, it was shown that the combination of the thermodynamic promoter (THF or DIOX) with the surfactant (SDS) was a very interesting solution to accelerate hydrate formation. Finally, it can be concluded that the combination THF+SDS, both thermodynamically and kinetically, remains the more efficient solution to enhance hydrate formation in the scope of this work

Latent thermal energy storage system for heat recovery: numerical study

International audienceThe continuous increase in the level of greenhouse gas emissions and the rise in fuel prices are the main driving forces to encourage all stakeholders in the energy sector to improve the efficiency of the systems. A large amount of energy is rejected by the industry at low temperature level (between 0 and 150 °C). Indeed, considering all the industrial processes in France, the amount of energy lost in this temperature range is estimated at 75 TWh/year. Storage of heat is one of the major issues to bridge the gap between energy supply and demand. The thermal energy storage (TES) technology including phase change materials (PCM) appears particularly attractive in this specific application. This solution is attractive since it provides a high energy storage density and has the capacity to store heat as latent heat of fusion at a constant temperature corresponding to the phase change transition temperature of the PCM (in the case of pure substances). These parameters are especially suitable for heat recovery in industrial processes in which there is a delay between the process step at which the energy is lost and the process step at which this energy could be recovered. The general objective of our work is to propose a design of a TES system dedicated to the kind of applications detailed above. This paper describes a numerical study on a future experimental pilot composed of a cylindrical tank filled with encapsulated PCM. This model investigates the influence of various parameters on the charge mode. Among the studied parameters, the thermal conductivity of the PCM and the diameter of the capsule are significant parameters on the storage mode. An increase in the PCM thermal conductivity and a decrease in the capsule diameter increase the storage power

Latent thermal energy storage system devoted to batch processes heat recovery

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Projet STEEP : Stockage thermique pour l’éco-efficacité des procédés

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Analyse calorimétrique de matériau de stockage thermique pour valorisation de chaleur fatale industrielle,

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Stockage de l’énergie thermique par matériaux à changement de phase adapté à la valorisation de chaleur fatale : études expérimentales et numériques

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Analyse calorimétrique de matériau de stockage thermique pour valorisation de chaleur fatale industrielle,

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