Resistive Plate Chambers (RPC), working at the Large Hadron Collider (LHC) at CERN, are used with a mixture containing C2H2F4 (R134a) and SF6. In particular for the Compact Muon Solenoid the working mixture has the following composition: R134a 95.2%, iC4H10 4.5% e SF6 0.3%. The CMS Experiment is only one of the four big Experiments displaced long the LHC with ALICE, ATLAS and LHCb. Muons represent a very clean probe for the detection and characterisation of the collision occurring in LHC Experiments. The specific composition of the mixtures allows to have the best performance from the detectors themselves. Although these gases are necessary for the optimization of the detectors’ performances, they present some related problematics. There are two main problems for the RPC mixture: 1. R134a are SF6 Green-House Gases (GHG) with high Global Warming Potential (GWP) values, 1430 and 22800 respectively. 2. R134a and iC4H10 form a minimum boiling azeotrope with composition 65/35 which is impossible to separate through simple distillation. Some gases with high GWP values have been regulated in recent year from the EU. In order to reduce emissions from these gases, the EP-DT Gas Team at CERN consider different approaches. One of the possible ways is the one discussed in this thesis which is the separation of R134a from the RPC mixture. To reach this goal, a system for the separation of R134a from other components of the RPC mixture was built. Final purpose of the process is the recuperation and storage of the R134a to be re-used in the detection system. At the beginning it seemed hard to reach high efficiency in term of recuperated gas since a better understanding of the phenomena occurring in the system was necessary. Because of its difficult treatise, the “azeotrope issue” was investigated through the possible way to separate the gaseous azeotrope itself. By the moment that the injected mixture is 95/5 in R134a/iC4H10, a distant point from the azeotrope composition point (65/35), it was possible to achieve the R134a separation via simple distillation. The outcome vapour from buffer was enriched with the azeotropic mixture, while the outcome liquid (almost) pure R134a. In this thesis modifications to parameters and to the system itself were followed by test aimed to the verification of the separation results through gas-chromatographic and mass spectrometry analyses. Starting with the injected mixture with composition stated above (and with different inject flow tested), it was possible to achieve after several tests – aimed to improve the efficiency and data consistency of the recuperation process – pure R134a with no SF6 and iC4H10 in the recuperated gas with only few ppm of air. Moreover, the efficiency of the performed tests were stabilized between 80 and 90% in term of recuperated R134a.
I rivelatori Resistive Plate Chamber (RPC), in uso al Large Hadron Collider (LHC) del CERN, sono utilizzati con una miscela contenente C2H2F4 (R134a) ed SF6. Nello specifico dell’Esperimento CMS (Compact Muon Solenoid) è utilizzata una miscela con la seguente composizione: R134a 95.2%, iC4H10 4.5% e SF6 0.3%. L’esperimento CMS è uno dei quattro grandi Esperimenti dislocati lungo il percorso del LHC insieme ad ALICE, ATLAS e LHCb. I muoni rappresentano l’evidenza necessaria per la rilevazione e caratterizzazione delle collisioni che si verificano nel LHC. Le specifiche composizioni delle miscele permettono le migliori performance possibili per i detector stessi. Nonostante questi gas siano necessari per l’ottimizzazione delle performance del detector, essi presentano alcune problematiche. Nello specifico, i problemi derivanti dall’utilizzo della miscela RPC sono principalmente due: 1. R134a e SF6 sono gas serra (GreenHouse Gases – GHG) e hanno un valore di potenziale di riscaldamento globale (Global Warming Potential – GWP) rispettivamente di 1430 e 22800. 2. R134a e iC4H10 formano un azeotropo di minima alla composizione percentuale 65/35 impossibile da separare tramite processi di distillazione semplice. Alcuni gas serra con alto valore di GWP sono stati nei recenti anni regolamentati dall’Unione Europea. Per ridurre le emissioni derivanti da questi gas, il gruppo EP-DT Gas Team del CERN ha optato per diversi approcci. Uno di questi è stato quello preso in esame in questa tesi, ossia la separazione dalla miscela utilizzata negli RPC dell’R134a. Per raggiungere questo obiettivo è stato costruito un sistema volto alla separazione dell’R134a dalle altre componenti della miscela. Obiettivo finale del processo, il recupero e stoccaggio dell’R134a da riutilizzare nel sistema del rivelatore. Inizialmente i risultati non avevano portato ad una buona efficienza separativa non conoscendo appieno i fenomeni alla base delle interazioni tra le molecole della miscela. Il problema azeotropo è stata una sfida impegnativa, dal momento della sua difficile trattazione. Dopo un’indagine sui diversi metodi per la separazione degli azeotropi, dal momento che la composizione R134a/iC4H10 nella miscela in esame è circa di 95/5, è stata sfruttata una distillazione semplice per la separazione. Infatti, il vapore uscente dai buffer era ricco di miscela azeotropica, mentre il liquido di R134a. Nel lavoro di tesi, le modifiche ai parametri del sistema e al sistema stesso sono state seguite da test volti alla verifica dei risultati del processo tramite analisi di gascromatografia e di spettrometria di massa. Dalla miscela immessa nel sistema (a diversi flussi in entrata che sono stati testati) si è riusciti ad ottenere, dopo molti test volti a migliorare efficienza e consistenza dei dati, R134a sostanzialmente puro, senza SF6 e isobutano, e con pochi ppm di aria. Inoltre, l’efficienza dei test effettuati si attesta tra l’80 e il 90% in termini di recupero.
Separazione e recupero dell’R134a dalla miscela gassosa utilizzata nei detector Resistive Plate Chamber presso l’Esperimento CMS
CAMBIÈ, FEDERICO
2020/2021
Abstract
Resistive Plate Chambers (RPC), working at the Large Hadron Collider (LHC) at CERN, are used with a mixture containing C2H2F4 (R134a) and SF6. In particular for the Compact Muon Solenoid the working mixture has the following composition: R134a 95.2%, iC4H10 4.5% e SF6 0.3%. The CMS Experiment is only one of the four big Experiments displaced long the LHC with ALICE, ATLAS and LHCb. Muons represent a very clean probe for the detection and characterisation of the collision occurring in LHC Experiments. The specific composition of the mixtures allows to have the best performance from the detectors themselves. Although these gases are necessary for the optimization of the detectors’ performances, they present some related problematics. There are two main problems for the RPC mixture: 1. R134a are SF6 Green-House Gases (GHG) with high Global Warming Potential (GWP) values, 1430 and 22800 respectively. 2. R134a and iC4H10 form a minimum boiling azeotrope with composition 65/35 which is impossible to separate through simple distillation. Some gases with high GWP values have been regulated in recent year from the EU. In order to reduce emissions from these gases, the EP-DT Gas Team at CERN consider different approaches. One of the possible ways is the one discussed in this thesis which is the separation of R134a from the RPC mixture. To reach this goal, a system for the separation of R134a from other components of the RPC mixture was built. Final purpose of the process is the recuperation and storage of the R134a to be re-used in the detection system. At the beginning it seemed hard to reach high efficiency in term of recuperated gas since a better understanding of the phenomena occurring in the system was necessary. Because of its difficult treatise, the “azeotrope issue” was investigated through the possible way to separate the gaseous azeotrope itself. By the moment that the injected mixture is 95/5 in R134a/iC4H10, a distant point from the azeotrope composition point (65/35), it was possible to achieve the R134a separation via simple distillation. The outcome vapour from buffer was enriched with the azeotropic mixture, while the outcome liquid (almost) pure R134a. In this thesis modifications to parameters and to the system itself were followed by test aimed to the verification of the separation results through gas-chromatographic and mass spectrometry analyses. Starting with the injected mixture with composition stated above (and with different inject flow tested), it was possible to achieve after several tests – aimed to improve the efficiency and data consistency of the recuperation process – pure R134a with no SF6 and iC4H10 in the recuperated gas with only few ppm of air. Moreover, the efficiency of the performed tests were stabilized between 80 and 90% in term of recuperated R134a.È consentito all'utente scaricare e condividere i documenti disponibili a testo pieno in UNITESI UNIPV nel rispetto della licenza Creative Commons del tipo CC BY NC ND.
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https://hdl.handle.net/20.500.14239/14033