The expansion engine is a vertical single acting, reciprocating type of engine which plays the most important role in cooling. The air enters the Expansion Engine, where it is expanded from 40 kg/cm2 to 5 kg/cm2. When the air expands rapidly the temperature drops to –1500C.
The Expansion Engine consists of three major units.
The drive unit is similar to any reciprocating machine with usual parts, such as, crank case, crankshaft, connecting rod, crosshead, etc. The Expansion Engine has an extended crankshaft enabling the accommodation of the cam box. The moving parts are lubricated through a hole in crankshaft. Oil scrapper rings are provided to prevent oil escape to cylinder unit.
Cylinder Unit for Air Expansion
The cylinder unit that handles the process air, consists of cylinder, piston, inlet and outlet isolation valve assemblies. The ball valves are actuated mechanically by a push rod as per the timing transmitted by the cam. The push rods are housed in a stuffing box to avoid air leakage and are actuated by the hydraulic system.
The hydraulic system is the control system. The hydraulic oil is fed by a pump to:
Pressurized oil container for valve actuation
Lubricate crankshaft and drive and drive unit parts