Expander

The principle of using the principle of reducing the temperature of the gas when the compressed gas expands and decompresses and outputs the mechanical work to the outside to obtain a cold machine. Expanders are commonly used in cryogenic equipment. Expanders are divided into piston expanders and turbo expanders according to the movement form and structure. The piston expander is mainly applicable to medium and small high and medium pressure deep cryogenic equipment with high pressure ratio and small flow. Compared with the piston expander, the turbo expander has characteristics of large flow, simple structure, small volume, high efficiency and long operation period, and is suitable for large and medium-sized deep cryogenic equipment.

Piston expander - An expander that expands the gas in a variable volume and outputs external power (usually the motor brakes the external work). This type of expander is divided into two types, vertical and horizontal. More vertical structures are used. Crankshafts, connecting rods, crossheads, pistons, intake valves, and exhaust valves are moving parts that are mounted in the fuselage, the cylinder, and the intermediate seat, respectively. The effect is similar to that of the reciprocating piston. Machine, but its inlet and exhaust valves are used to open and close the intake and exhaust cams. Due to the presence of intake and exhaust valve flow resistance, incomplete expansion, frictional heat, external heat and internal heat exchange, etc., the piston expansion machine generally suffers from loss of cooling capacity. The general adiabatic efficiency is: high pressure expander 65 to 85%, medium pressure expander 60 to 70%. In the 1950s, valveless and single-valve expanders without cam transmission mechanism were successively developed, which reduced the moving parts of expanders and improved the reliability of machine operation. They have been widely used in small cryogenic equipment. In the 1960s, PTFE-filled sealing elements were used instead of oil-lubricated metal sealing elements to prevent lubricating oil from being carried into deep cryogenic rectification or liquefaction zones to ensure safety.

Turbo expander - An expander that transfers energy as the gas expands. This type of expander is divided into single-stage and double-stage, vertical and horizontal, impulse and reaction-type. Single-stage centripetal runoff reaction is generally used, and the external power transmitted is absorbed by the generator, blower or oil brake. It is similar to a single-stage centrifugal compressor but has a (adjustable blade) deflector for adjusting the amount of intake air. The low speed bearing oil is forcibly lubricated and the high speed gas bearing is used. Turbine expander due to nozzle loss, impeller loss, loss of speed, loss of wheel friction, leakage loss, turbulence loss and intrusion of external heat loss, the general adiabatic efficiency: medium pressure expander 65 ~ 75%, low pressure expander 75 to 85%. In the 60's, it was made into a liquid expander, mostly used for natural gas separation equipment.