10.2 DESCRIPTION:

The Expansion Engine is a vertical single - acting reciprocating type engine. This produces the cold required for operating the Plant. The 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 out side. The electric motor is used initially to start the machine. Thereafter the engine is moved by the air pressure itself and during which time, the engine motor retains the flywheel it loses its heat content (enthalpy). Thus the air gets cooled. This cooling is more than that of an expansion in and expansion valve.

An elementary factor for function of Expansion Engine is to use dry and Carbon Die-oxide free air, as otherwise, ice and dry ice will form or valve seats, causing mal-function.

The approximate temperature drop across Expansion Engine is 50 to 70 Deg.C. Depending upon inlet air pressure, temperature and inlet cam position.

The Expansion Engine can be considered as three major units:

The drive unit, the cylinder unit for air expansion; and the hydraulic system for operating the valves.

The drive unit is similar to any reciprocating machine with usual parts, such as, crank case, crank shaft, connecting rod, crosshead etc. The Expansion Engine has an extended crankshaft to enable to accommodate the cams for valve lifting and is housed by a cam box. The moving parts are lubricated through a hole in crank shaft. Oil scrapper rings are provided to prevent oil escape to cylinder unit.

The cylinder unit handling process air consists of cylinder, piston, inlet and outlet isolation valves. Pressure gauges and the ball valve assemblies. The ball valves are actuated mechanically by a push rod as per the timing transmitted by the came. The push rods are housed in a stuffing box to avoid air leakage and are outdated by the hydraulic system.

The hydraulic system is the control system. As per schematic sketch enclosed the hydraulic oil is fed by a pump to (a) pressurized oil container for valve actuation (b) to lubricate crankshaft and drive unit parts and (c) to lubricate the rolled holders. Oil pressure at P-15 should be 1.5 to 2 Kgs. /cm2 and can be adjusted by a value mounted on the pump. The oil specification should be viscosity 6.5 Deg.C. Angler at +50 Deg.C. And specific gravity 0.91 kgs. /cm2. Flash point of at least +175 Deg.C.. Solidifying point of at least -5 Deg.C. This requires an addition of Silicon Deforming agent of 1 - 2 drops per liter of oil.

Oil from pressurized oil container is fed to two control oil push pumps for inlet and outlet. The outlet valve cam rigid with one cam position creates a to-and-fro motion on the roller holder of the push pump. This motion is received by the pistons of the push pump and develops an oil pressure pulsation. This pulsation is transmitted to valve piston through a piping. This piston in valve pestle again transmits the pressure pulsation into a mechanical to and fro suction. As the piston of valve pestle is in line with the push rod, the ball valves are operated. Similarly, the inlet valve push pump operates the inlet ball valve as per the cam setting. The inlet valve cam has 8 different cam settings and the required cam setting is set by the selector arrangement. To change cam position : (a) release locking device of cam setting; (b) unload Expansion Engine by unloader valve; (c) change cm position by turning cam selector wheel; (d) check cam position by noting the pointer on cam number; (e) load Expansion Engine and (f) lock cam setting device by tightening lock handle on cam selector. The effects of different cam settings mentioned in the Plant start up procedure.

The Expansion Engine inlet ball valve is brought to close position by bypassing oil pressure pulsation/displacement from inlet push pump to pressurized oil container by an unloaded ball valve provided in the Top Box.

There are air release valve at each valve pestle. During initial start up, air should be released; (a) at air release plug of oil pressure container;

There should be no leaks in hydraulic system for best performance of engine. The oil pressure of 1.5 hz/cm2 should be maintained.

10.3 SAFETY:

In case of the power failure to the engine its braking mechanism will fail and this accelerating speed of the machine. To prevent this air supply to the engine should be cut - off.

a. A leaver load/unload valve is provided in the expansion engine, which can be operated by hand. This too will close the air inlet o the engine and can be operated by the operator when required.

A safety valve (bursting disc) is provided in the air outlet line before air out isolation Valve A-14. This safety is set to blow at 8 Kgs. /cm2.

Nitrogen purge is provided in distance piece below cylinder and in valve pestle housing to prevent atmospheric moist air to form frost on colder parts.

10.4 OPERATION:

10.5 START UP:

» Check oil level in crank case, cam case and pressure oil container.
» Open air outlet valve, Nitrogen purge valve and oil feed valve to control push pump.
» Start the motor and check direction of rotation.
» Observe oil pressure and release air locks.
» Check outlet valve lifting and inlet valve lifting by changing lever of ball valve.
» Open air inlet isolation valve slowly.

10.6 NORMAL RUN:

Check for oil levels, oil pressure, oil leaks, air lock in oil system and multifunction of hydraulic system and set right.

Check if valve lifting is normal.
If stuffing box of valve push rods is leaking, the Engine is to be stopped and attended to.
Avoid temperature less than -165 Deg.C.
Check that the cooling is proper by seeing temperatures T1 & T2.
Change inlet valve cam position, if necessary, as detailed in plant start up.

10.7 SHUT DOWN:

Unload inlet valve pestle by operating load/unload valve in hydraulic system.

10.8 Stop Motor:

Close air inlet valve.

10.9 Maintenance:

10.10 Change of Piston Rings:

Normally the Expansion Engine Piston rings wear out in about 4/6 months time but during the first year it is advisable to change earlier due to running in other cylinders lines. They have to be changed. The rings wearing out can be noticed by excessive air leak, at the bottom of the engine cylinder. If the cover plate of the distance piece is removed the leak can be felt.

Isolate Engine by closing the main inlet and outlet isolation valves (A-13 & A-14). Open the cylinder head on top of the Engine. Remove the oil scraper rings. Its housing is to be dismantled from the crank case, and is to be kept lifted up. Rotate the flywheel to attain top dead center. Remove the stud nuts of the piston rod bottom mounting flange. Hold the piston in position by lever and rotate the flywheel, so that the cross head gets disconnected from piston rod. Unscrew the piston rod mounting flange from piston and also remove the oil scraper housing. Now, the piston can be lifted from the top using eye-bolt threaded to the top of the piston. The piston rings and the guide rings are to be changed if worn out. While placing the new rings, take care that the play between bud joints of a ring is about 0.4 to 0.5 mm. The ring gaps are to be staggered at a degree of 120. Tension rings are provided on the inner for proper working of the rings. Now the piston with piston rings should be inserted in a liner provided for the purpose of maintenance. This liner with piston ring assembly inside is to be placed on top of cylinder, such that, the liner is in line with the cylinder. Now push the piston rod along with the rings, so that, the rings slide from the liner to main cylinder without distortion or expansion. After the piston has been pushed completely inside the main cylinder, the liner provided for the purpose of ring insertion is to be removed.

Insert the scraper ring housing inside the piston rod and then thread in the mounting flange on the piston. Tight the flange with stud bolts of the cross head. Fix the oil scrapper ring housing and oil scrapper rings.

Rotate the flywheel and check for free rotation. Place the small piece of lead on top of the piston and fix the cylinder head. Now rotate the flywheel for at least two rotations. Remove the cylinder head; check the thickness of lead which indicates the head end clearance. This should be above 1 mm. and less than 2 mm.

10.11 Valve Maintenance:

The inlet and outlet ball valve should be maintained properly for efficient performance of the Expansion Engine. The valves can be opened by opening the cap nut of the press screw. Then loosen the press screw. Remove the valve top block by unscrewing. The ball valve assembly can now be taken out by using a small eye-bolt. The ball valve assembly is to be dismantled. Check for spring tension, for no scratches either on the ball or on the ball seat. Reassemble the valve after cleaning with C.T.C. The whole assembly can be assembled as it was opened.

The clearance between the valve hydraulic pestle and the push rod of the ball valve should be such that it has around 0.4 mm. in inlet and 0.3 mm. in outlet or as per plant engineer. To check the same, remove the spring in the ball valve assembly and fix a solid wooden piece and tighten the valve assembly. Also tighten the valve top block. Using a lever, lift the push rod and the piston of the hydraulic valve pestle, using a feeler gauge. To vary the clearance, the check nut of the screw on top of the piston of the hydraulic valve pestle is to be loosened. Then either by tightening the screw or loosening the screw, the clearance can be varied. After setting the clearance, the check nut of the screw is to be tightened. After every maintenance of the ball valve, it is better to check the clearance of the push rod.