Optimization of working conditions of CMS's R134a recovery system for Resistive Plate Chambers

<!--HTML-->R134a is an important gas for the gaseous mixture used to feed the Resistive Plate Chamber (RPC) in CERN’s experiment Compact Muon Solenoid (CMS). The mixture has also other components such as water, SF6, nitrogen and isobutane. This last component forms a minimum azeotrope with the R134a (65/35 R134a/isobutane) which makes the R134a’s separation and purification particularly difficult. R134a is a Green House Gases (GHG) with a high Global Warming Potential (GWP), its cost is very high not only because of the big volume needed to use the CMS revelator, but also because the European political choice discourages the use of GHG with their taxation. A system to recycle as much as possible R134a is not only an economical choice but also an ethical one. The main component of gas detectors is the gas mixture that must be correct and stable for the proper system’s working; the use of expensive and greenhouse gases cannot be avoided because of physical requirements that impose certain choices on the gas mixture composition.<br>The aim of this thesis consists of a study of the R134a recuperation system working on CMS, with the goals to find the key variables that allow the separation, to optimize them, and finding out if the system can work in continuous or semi-continuous to manage all the gas needed for the CMS working. The separation is based on a distillation process because the composition of the mixture is possible to do a standard distillation eliminating the azeotrope (65/35 R134a/isobutane) in the vapor phase. Part of the R134a is wasted to allow the formation of the azeotrope and so the purification, but the recuperation efficiency after the purification is around 80%.<br>The performances of the distillation process were studied and optimized in the light of gas chromatography measurements. The effects of experimental parameters affecting the performance have been investigated.<br>Considering the experimental evidence reported in this Thesis, the system’s semi-continuous operating mode is available and well-tested, and it can trait the needed volume of gas with 80% efficiency and 99.9% of R134a purity. The continuous mode also has been tested, but only superficially and encouraging results were obtained.