An ammonia refrigeration cycle system is a large-scale industrial cooling installation that uses ammonia (NH₃) as the refrigerant; its core function is to achieve cooling through the continuous circulation of ammonia undergoing phase changes (heat-absorbing vaporization and heat-releasing condensation).
I. System Components
The ammonia refrigeration system primarily consists of the refrigerant circulation, lubricating oil circulation, cooling water circulation, and secondary coolant (heat transfer fluid) circulation systems. Key equipment includes: ammonia compressors (screw compressors), condensers, ammonia receivers, oil separators, throttling valves (expansion valves), and evaporators, as well as emergency ammonia dump tanks, oil collectors, various valves, pressure gauges, and high/low-pressure piping. The four core components are the compressor, condenser, expansion valve, and evaporator. The ammonia circulation loop comprises the evaporator, ammonia compressor, condenser, and throttling valve.
II. Working Principle (Four Basic Processes)
Ammonia completes a refrigeration cycle within the system through four basic processes: evaporation, compression, condensation, and throttling:
Evaporation (Heat absorption for cooling): Liquid ammonia absorbs heat from the substance being cooled within the evaporator and vaporizes into low-pressure, low-temperature ammonia gas; the evaporation temperature can drop to approximately -27°C, thereby achieving the cooling effect.
Compression (Pressurization and temperature rise): Low-pressure ammonia vapor is drawn into the ammonia compressor and compressed into high-pressure, high-temperature ammonia gas.
Condensation (Heat release and liquefaction): After passing through an oil separator to remove refrigeration oil carried over from the compressor, the high-pressure ammonia gas enters the condenser (or evaporative condenser). Here, it releases heat to the cooling medium and condenses into high-pressure liquid ammonia, which flows into the ammonia receiver for temporary storage.
Throttling (Pressure reduction): Liquid ammonia from the receiver passes through a throttling valve (expansion valve), where it is throttled into low-temperature, low-pressure ammonia liquid. It then enters the low-pressure circulation vessel; from there, it is pumped through a regulating station into the evaporator to absorb heat and vaporize, thereby restarting the cycle.
III. Key Features and Applications
System Classification: The system is divided into two main sections: the high-pressure system (comprising the compressor and condenser for compression and condensation) and the low-pressure system (supplying liquid ammonia to the evaporator via gravity feed or direct expansion).
Energy Efficiency Optimization: Subcooling the saturated liquid ammonia at the condenser outlet increases the cooling capacity per unit mass of liquid ammonia, thereby reducing both the required ammonia quantity and the power consumption of the ammonia compressor. For instance, in a coal-chemical project utilizing an economizer for subcooling, Aspen simulations indicated an 8.4% reduction in ammonia compressor power consumption compared to a system without subcooling.
Application Areas: Suitable for industrial sectors such as ice making, air conditioning, and food refrigeration; also frequently used to meet the cooling requirements of units such as the Low-Temperature Methanol Wash process.