NH3- / CO2-Cascade refrigeration system for nitrogen cooling
Air separation plants use a technical method for gas separation, which enables the liquefaction of gas mixtures (e.g. air) and individual atmospheric gases (e.g. oxygen, nitrogen, noble gases) in large quantities.
In this case, the ARCTOS refrigeration system cools 28,000 Nm3/h of nitrogen from +30° C to -41° C.
The cooling is achieved with two refrigerant circuits connected in a cascade. Each circuit contains a natural refrigerant optimized for the operating conditions, making the task particularly energy-efficient and environmentally friendly.
The ammonia refrigerant circuit is responsible for pre-cooling the nitrogen at an evaporation temperature of -14° C. The deep cooling is then achieved through the CO2 circuit at an evaporation temperature of -47° C.
The energy efficiency of the NH3 cooling process is significantly improved by the use of an open economizer compared to a simple cooling process.
Additionally, compressors equipped with frequency inverters improve the part-load characteristics and ensure a smooth and energy-saving operation of the machines.
| Refrigerant | NH3 | R717 CO2 R744 |
|---|---|---|
| Charge Amount | 1,300 kg | 1,400 kg |
| Maximum Operating Pressure (ND/MD/HD) | 16 / 18 / 20.5 bar | 25 / - / 40 bar |
| Evaporation Temperature | -14° C | -47° C |
| Condensation Temperature | +33° C | -10° C |
| Cooling Capacity | 1,103 kW (at -14° C) | 412 kW (at -47° C) |
| Compressor Manufacturer | Sabroe | Sabroe |
| Compressor Type | Scroll Compressor SAB 233SR | Piston Compressor HPC 106SV |
| Motor Drive Power | 293 kW | 108 kW |
| COP Value | 3.76 | 3.81 |
CONTROL SYSTEM
The compressor control programmed by ARCTOS allows the operation mode to be flexibly adjusted to customer requirements. In this case, the control ensures an optimized coordination between the NH3 and CO2 compressors.
COMPRESSOR TYPES
For the ammonia circuit, a screw compressor from the SABROE SABTM 233SR series is used. This provides a maximum cooling capacity of 1,103 kW.
The CO2 circuit is equipped with a SABROE reciprocating compressor from the HPCTM 106SV series, reaching a cooling capacity of 412 kW at the operating point.
