The use of natural refrigerants is gradually spreading. Here are two examples of their use in the marine sector: - Environmentally-friendly fish transport American Freedom is one of the world's largest refrigerated ships and can hold up to 400 tonnes of sea fish. Atlantic Pelagic Seafood gave Grenco B.V. Marine the task of equipping it with a sustainable and efficient refrigeration system. It was put into service in late 2006 and operates in the Atlantic as a floating fishery fed by smaller herring and mackerel fishing boats. An ammonia and CO2 cascade refrigeration system operates on board. On the high-pressure side there are 4 ammonia screw compressors with an overall capacity of 4500 kW. This circuit contains 1500 kg ammonia, with an evaporation temperature of -6°C and a condensation temperature of 36°C. The low-pressure side comprises 4 CO2 screw compressors providing a refrigeration capacity of 2000 kW, with a -50°C evaporation temperature and a -2°C condensation temperature. The fish is first quick-frozen in 36 vertically mounted plate freezers and then stored in cold chambers cooled by CO2 air coolers. Defrosting is provided by the heated CO2, a more energy-saving option than a classic defrosting system. And the ammonia-using circuit is not only part and parcel of the cascade, it also supplies 2 sea-water cooling plants, which represents an innovative combination in the marine sector. - Cooling propane with propane Axima Réfrigération France has provided a refrigeration installation using propane, to a Phillips Petroleum Co. FPSO (Floating Production, Storage and Offloading) ship. FPSO ships are loaded with the petroleum and natural gas extracted by an offshore platform, and then process and store it until it is pumped into a tanker or a pipeline. The ship sails the Timor Sea between Australia and East Timor and is equipped with tanks for intermediate propane and butane storage. However, propane needs to be stored at -39°C and butane at -7°C, in outdoor temperatures of up to 30°C. For this purpose, 4 refrigerating plants with an overall capacity of 5 MW are used. At the heart of each plant is an oil-lubricated screw compressor with an 8000 m3/h flow rate. Propane refrigerant is cooled by a two-stage cascade system. The heat produced by the liquefaction process is rejected into the sea.