A Linde cycle with prerefrigeration processes atmospheric air at 27C and 1 atm. It compresses up to 200 atm. It is expanded to 1 atm and the nonliquefied fraction exits at 24C. The heat losses in the system are 3 kcal/kg. Three different refrigerants are available. The aim is to obtain a liquid fraction of 0.15 kg per kg of initial air (at least). Each refrigerant has a cost and generates a certain environmental burden. The emission cost for the facility is 50 h/t of CO2. Select the most appropriate refrigerant (Table P3.11).

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Table P3.11 Process Data I III Q (kcal/kg initial air) 15 20 25 Coste (e/kcal refrigerant) 4 5 6 Impact (kg CO produced/kcal refrigerant) 45 40 20