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Abstract: RPC detectors require to be flushed with small but continuous flow of gas mixture. Dealing with large number of detectors, gas consumption to very large volumes. Gas flow is a running expense and constituent gases are too expensive to be treated as consumables. Exhaust gas mixture from detectors is a potential environmental hazard if discharged directly into the atmosphere. Storage of gases on a large scale also leads to inventory- and safety-related problems. A solution to these problems is the recovery and reuse of exhaust gas mixture from RPC detectors. Close loop method employs recirculation of exhausted gas mixture after purification, analysis and addition of top-up quantities. In open loop method, under consideration here, individual component gases are separated from gas mixture and reused as source. During open loop process, gases liquefiable at low pressures are separated from ones liquefiable at high pressure. The gas phase components within each group are successively separated by either fractional condensation or gravity separation. Gas mixture coming from RPC exhaust is first desiccated by passage through molecular sieve adsorbent type (3A+4A). Subsequent scrubbing over basic activated alumina removes toxic and acidic contaminants such as S2F10 produced during corona (arcing) discharge. In the first stage of separation isobutane and freon are concentrated by diffusion and liquefied by fractional condensation by cooling upto −30°C. Liquefied gases are returned to source tanks. In the second stage of separation, argon and sulphur hexafluoride, the residual gases, are concentrated by settling due to density difference. SF6 is stored for recovery by condensation at high pressure while argon is further purified by thermal cracking of crossover impurities at 1000°C followed by wet scrubbing. [Copyright &y& Elsevier]

Abstract: The efficiency of recovery achieved by open or closed loop extraction of RPC exhaust gases is in the range of 90–95% under optimum conditions. For a large detector setup operating on one volume change per day basis, a 5% loss amounts to discharging 50kg of R134a and 0.5kg of SF6 into atmosphere every day. The emissions are equivalent to create nearly 50000m3 of carbon dioxide daily. The gas emissions need to be completely converted to safer compounds. The gases such as R134a and SF6 are stable compounds. In order to decompose these, the mixture is first activated by adding of 50% oxygen and 2% argon and under typical RF plasma conditions of 13.56MHz, 1Torr pressure and 0.2W/cm2 power density. The chemical reaction takes place on the surface of a silicon electrode. The product of the reaction is mainly SiF4 (gas), which is further hydrolyzed to form HF solution and silicon hydroxide sludge. More than 90% of the effluent gas mixture can be effectively removed by this method. [Copyright &y& Elsevier]

Abstract: In this presentation, we describe a mass-flow controller based on-line gas mixing unit with the multi-channel distribution system. We highlight different aspects such as requirement, design, calibration, control and operation of this system. This unit has the capability to mix up to four different input gases and distribute over 16 output channels. Output in individual channels is controlled accurately by using capillary-based system. At present, we are using this gas mixing unit for prototype of iron calorimeter (ICAL) detector of India-based Neutrino Observatory (INO). [Copyright &y& Elsevier]