The Expansion Engine is vertical, single
acting, reciprocating type. This produces the cold required for the plant.
High- pressure air enters through inlet valve at the start of downward
stroke of the piston. On further downward motion, the inlet valve closes and
entrapped Air expands. During upward stroke, outlet valve remains open and
inlet valve remains closed.
Therefore, in downward stroke Air enters the cylinder and expands. In the
upward stroke the expanded air is pushed outside. The electric Motor is used
to start the machine. Thereafter the Engine is moved by the Air pressure
itself and during which time, the Engine motor retains the speed by acting
as a brake. Since work is done by Air in rotating the flywheel, it loses its
heat content (enthalpy), thus the Air gets cooled. This cooling is more than
that of an expansion in an Expansion Valve.
An elementary factor for the function of an Expansion Engine is to use dry
and carbon Dioxide free Air, as otherwise, ice and dry ice will form on
valve seats, causing mal-function. The approx. temperature drop across
Expansion Engine is 50 to 70°C, depending on inlet air pressure,
temperature and inlet cam position.
The Expansion Engine consists of three major units.
- The drive unit
- The cylinder unit for Air expansion
- The Hydraulic system for operating the valves
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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
The cylinder unit handling 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.
