Expander is a kind of mechanical equipment that uses compressed gas to expand and depressurize, so that the gas temperature can be reduced to obtain the cooling capacity. In the air separation unit, the expander is an important equipment to provide cooling capacity for the air separation unit, and its cooling capacity accounts for 80% - 90% of the cooling capacity of the air separation unit.
The main structural forms of expander are piston type and turbine type.
The piston expander is suitable for air separation process with large pressure drop and small flow rate because of its convenient manufacture and low speed.
Turbine type has the characteristics of large gas flow, high efficiency, stable and reliable operation and no friction parts. Due to the low pressure air separation process used in large air separation units, the pressure drop and unit cooling capacity are very small, and because the expansion air is sent to the upper column for rectification, the expander is required to have higher efficiency to reduce the influence of expansion on distillation. Turbo expander is widely used in large-scale air separation unit because of its high efficiency up to 80% and sufficient performance to meet the full low pressure air separation process.
