Comprehensive Guide to Ammonia (R-717) and Refrigeration Systems
Chemical and Physical Properties of Ammonia (R-717)
Ammonia, identified by the refrigerant designation R-717, is a chemical compound consisting of one nitrogen atom and three hydrogen atoms, represented by the chemical formula . It is primarily categorized as an inorganic compound; however, the transcript also notes its description as an organic based refrigerant. In practice, ammonia is lighter than air and possesses a boiling point of at atmospheric pressure. The substance is colorless and highly water-soluble, distinguished by a strong, pungent odor that facilitates easy detection of leaks. Because of its safety profile, which includes toxicity and slight flammability, ammonia is classified under Group 2, category B2(L). Ammonia is frequently selected for industrial use due to the fact that it is very cheap and provides a high refrigeration effect.
Industrial Application and Safety Classification
Ammonia systems are strictly not used for human comfort. Instead, they are utilized in specialized industrial settings such as frozen food plants, cold storage warehouses, skating rinks, and other similar scenarios. These systems are normally located in designated Class T Machinery Rooms to ensure safety and compliance. When stored, ammonia refrigerant tanks are color-coded silver for identification. Ammonia is compatible with various metering devices, including Thermostatic Expansion Valves (TEV), Automatic Expansion Valves (AEV), and Low/High Side Floats.
Component Specifications and Mechanical Standards
In terms of materials and construction, ammonia systems have specific requirements and exclusions. Ammonia can NOT be used with copper, as it causes corrosion, but it is compatible with aluminum. Condenser tubes in ammonia plants should be composed of steel, and the systems generally utilize vertical shell and tube type condensers. The liquid line piping is specified as schedule 80, while the suction line piping is schedule 60. Reciprocating compressors are generally the equipment of choice for these systems. Within the oil pump of an ammonia force-fed system, spring pressure is used as the mechanism to determine or adjust the oil pressure.
Specific Definitions and Prohibitions
Anhydroid is the term used to describe dry ammonia. Regarding system maintenance and moisture control, anhydrous calcium sulfate can NOT be used as a drier in ammonia systems. The transcript also mentions "acerace and voltage drop in an" at the beginning, though the context provided focuses on the metabolic and physical properties of the ammonia refrigerant itself.
Deep Dive into Centrifugal Compressor Engineering
Centrifugal compressors are high-speed machines capable of running at speeds of up to . They are most suitable for handling large quantities of refrigerant vapor. The mechanical operation involves an impeller that imparts high velocity to the gas; this high-velocity gas is then transformed into static pressure by a stationary diffuser. Stationary diffuser vanes are necessary components in this process to convert velocity energy into pressure. The capacity of a centrifugal compressor is primarily governed by its condenser pressure, and the unit can operate at a lowest capacity of of its full capacity. For capacity control, the preferable method is using suction line throttling dampers, although peroration guide vanes can also be used. The shaft seal in these compressors is an oil seal that functions with pressure applied from the outside of the seal.