Design of a Separation System to Recover N-decafluorobutane from a Gas Mixture

In recent years, CERN has faced a significant environmental and economic challenge due to the extensive use of gas mixtures with a high Global Warming Potential. Approximately 70% of CERN's emissions are attributed to the use of fluorinated gases in various gas detectors. Specifically, the LHCb experiment utilizes a mixture of carbon dioxide and n-decafluorobutane. Not only does C4F10 have a high environmental impact (9200 kg of CO2), but it has also seen a reduction in production due to EU regulations, leading to increased costs. This thesis aims to tackle this challenge by implementing a new strategy for the separation of the mixture. The recovery of these two molecules can significantly reduce pollution and allow for the replenishment of a fresh mixture in the LHCb detector. This thesis offers a comprehensive exploration of the principles, technologies, and strategies for the development of an advanced fluorinated gas recovery plant. The development of a standardized approach to one of the gas mixtures could serve as a foundation to recover and reuse high-polluting gases. The first chapter introduces CERN and the LHCb experiment, which investigates the decay of b-quarks and provides insights into matter-antimatter asymmetries. The use of C4F10 in the RICH-1 detector is explained, followed by an overview of the current methods to supply, distribute, and manage exhaust and recovery modules. The second chapter discusses the different phases of LHCb experiments (Filling, Cleaning, and Emptying) and the challenges faced while defining the project’s goals. The existing recovery system, which includes a partial condenser, is analyzed, highlighting its inability to guarantee the required purity due to variable composition and flow rates of the incoming feed and the lack of a control system to control process variables. The third chapter delves into the nature of the binary mixture. It defines metrics for measuring system performance and objectives and reviews the vapor-liquid equilibria. Thermodynamic models based on equations of state and predictive models are examined to select the most suitable physicochemical model. The choice is made based on minimizing errors between experimental evidence and model predictions. The fourth chapter focuses on the design phase. It begins with assessing the performance of the current recovery system, and revealing its inefficiency. The design choices are explained, highlighting the need to equalize the incoming stream and design a control system for managing disturbances. The plant consists of three subsystems: an Accumulation Tank and Pumping Station (ATPS) and two Separation Systems. The ATPS, which is responsible for accumulating the gas exiting the detector is explained. The first recovery system (DSE), consisting of two buffers, is then discussed. The influence of pressure and operating temperatures on purity, recovery, and recirculation flow rate are studied in-depth. The fourth chapter ends with the design of the second recovery system, a packed-bed distillation column (DC). The work includes defining specifications, degrees of freedom, and optimizing key variables to achieve the desired outcomes. The column's design, condenser, and reboiler are discussed, as well as the control loop. The conclusion and various appendices provide information on the current status of the plant, potential issues, and a timeline for future needs and developments.