Optimisation conjointe mélange de travail / cycle innovant de thermotransformateur à absorption démixtion – Optidemix

1. Scientific background and objectives The technology of absorption heat pump proposes, through the heat transformer cycle, an interesting way to upgrade industrial waste heat. Unfortunately, the performances of these energy converters are moderate: the thermal yield (upgraded energy at high temperature / supplied waste energy) is around 40%; moreover some technical problems like corrosion (with LiBr solutions) have limited the industrial development of such machines. The use of mixtures exhibiting a miscibility gap at low temperature enabled to design and patent an innovative cycle called Absorption-Demixing Heat Transformer (ADHT)*. The separation step, usually done by rectification degrading a lot of energy, is then replaced by settling. Thus, the separation is performed without energy consumption (only the free potential energy is used), therefore the thermal yield of the operation is significantly increased. Moreover the investment cost is also reduced. The technical feasibility of this ADHT cycle was already demonstrated ** with the mixture DMF (DimethylFormamide) – n-heptane. But the low temperature lift obtained, about 8°C, limits the industrial application of such a cycle to upgrade residual heat. The objective of this project is to perform a simultaneous optimisation of this innovative cycle and of the working mixture in order to obtain high performances leading to industrial development of this process. It is therefore necessary to develop a methodology and numerical tools for a systematic research of the optimal association process-working mixture. Two simulation tools will be developed: the first one to predict the liquid-liquid and vapour-liquid equilibria for numerous mixtures ; the second one to calculate the thermal performances of the cycle as function of the operating conditions and of the properties of the working mixture. The suitable mixtures associated with the operating conditions leading to optimal performances will be experimentally tested. 2. Description of the project, methodology The first step of the project consists in developing a tool to simulate the innovative Absorption-Demixing Heat Transformer (ADHT) enabling to predict the performances of such a cycle as function of the operating conditions and of a reduced number of physical and chemical characteristic parameters of the working mixture. A sensitivity analysis will then allow the identification of the properties that are the most influential. It will then be possible to define the suitable properties for an optimal mixture for a given cycle. The development of a thermodynamic simulation tool to predict the liquid-liquid and vapour-liquid equilibria will enable to explore 'numerically' a large range of compounds in order to identify the mixture(s) with the suitable properties. The liquid-liquid and vapour-liquid equilibria will be experimentally measured in order to validate the simulation results. Finally, a pilot unit of ADHT will be designed and installed in LSGC in order to validate experimentally the proposed cycle with the chosen mixture(s) and to study the influence of the operating conditions. The results will be compared with the simulation results. This pilot unit will also be used to present this innovative cycle and its performances to industrials that may develop commercially this attractive technology. 3. Expected results • Design and development of a simulation tool to predict and optimize the performances of the innovative Absorption-Demixing Heat Transformer (ADHT) • Design and development of a thermodynamic tool to simulate liquid-liquid and liquid-vapour equilibria required to predict the ADHT performances • Design and optimization of experimental devices to measure accurately the liquid-liquid and liquid-vapour equilibria • Design, construction and operation of a pilot unit of ADHT supplying a thermal power of 5 to 10 kW. • Creation of a inter laboratory-team specialized in thermodynamics applied to energy conversion processes combining simulation competencies as well as experimental validation. The methodology developed through this project will then be applied to the optimisation of other energy conversion or separation processes.