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Comparison of properties of ammonia refrigerant (R717) and fluorine refrigerant (R22 and R404A) in cold storage
In terms of safety: the explosiveness and toxicity of ammonia greatly limit its application, and with the frequent news of ammonia refrigeration systems in recent years, people have a certain fear of ammonia refrigeration systems. The high safety of fluorine refrigerants is the main reason for the rapid development of fluorine refrigeration systems in recent years.
Environmental protection: ODP of ammonia is zero, and GWP is also zero. R404A is a more environmentally friendly refrigerant, and R22 refrigerant due to its poor environmental performance, developing countries will restrict its application before 2020. At present, people in the industry are actively looking for alternative refrigerants that are more environmentally friendly.
Material compatibility: When ammonia contains moisture, it is corrosive to copper. Therefore, copper and copper alloys cannot be used for the pipes and valves of the ammonia system. There are certain limitations in the selection of system equipment materials. The chemical stability and thermal stability of fluorine refrigerant are very high, and theoretically it is not corrosive to all metals.
Interaction with water: the allowable water content of ammonia is less than 0.2%. Because ammonia is easily soluble in water, even if there is a trace of water, it will not appear "ice plug" like Freon, so it will dry the ammonia refrigeration system to the pipeline system The requirements are not as stringent as Freon. Freon is difficult to dissolve in water, so if there is water in the system, it is easy to cause ice clogging. Usually we have a filter drier in the system.
Interaction with oil: At present, the lubricating oil of the ammonia refrigeration system is mineral oil and cannot be miscible with ammonia. Equipment such as oil separator and oil collector are usually installed to return the lubricating oil to the compressor through automatic or manual control.
Ammonia has a much larger refrigeration capacity per unit mass of fluorine, indicating that ammonia has a better refrigeration capacity. However, when the evaporation temperature reaches -33.33℃, the gauge pressure of ammonia is 0. In order to avoid the system working under negative pressure, ammonia is generally used For systems with evaporation temperature above -33.33℃.
Ammonia refrigeration is a pump-supply system. Because the mineral lubricating oil used in the ammonia refrigeration system is not miscible with ammonia, the ammonia system is indispensable for oil separators, oil collectors and other equipment to ensure the oil return of the system and reduce the system temperature, so that the ammonia system The oil system is very complicated. These make the ammonia system huge, many auxiliary machines, complicated pipelines, many valves, complicated construction, and long construction period.