Reciprocating Compressor Trips and Safety Aspects

Reciprocating compressor Trips

High Suction Temperature

Due to cooling water failure to inter coolers, valve passing problems, Fouling and Leak in inter coolers

suction temperature of the gas will rise. Reciprocating compressor trip is provided for High suction

temperature as this will result in damage of the compressor parts.

Low Suction Pressure Trip

In reciprocating compressor handling Hazardous flammable gases like Hydrogen, trip has been provided

for low suction pressure. This is to avoid the atmospheric air ingression into the system through leaky

flanges or valves which may cause explosion/fire in the discharge of the compressor where the

temperature is high. In air compressors this trip is normally not necessary as it takes air from atmosphere.

High Discharge Temperature

High discharge temperature causes polymerization in some applications (like in Polyethylene) which will

plug the flow and causes rupture in pipelines. In air compressors ignition of oil will take place at High

discharge temperatures.

High Discharge Pressure

High discharge pressure in Reciprocating compressor may result in damage to pipes and machinery. It

may also cause personal injury. Reasons for High discharge pressure include control valve malfunctions

in consumption or in vent side, valve plate failures due to accumulation of foreign materials etc.

High Separator Level

Liquids are incompressible fluids which occupies space inside the compressor which reduces the mass

flow rate of the compressor. Liquid slugging causes stresses which damages compressor connecting

rods, piston, crank shaft etc. Therefore trip of the unit has to be provided for High levels in separators in

all stages.

High Bearing temperature or High Lube oil Temperature

At High temperatures Lube oil will get deteriorated and increase in viscosity does not form oil film. This

results in poor lubrication and causes failure of bearings. So trip for High Lube Oil/ Bearing temperature is

provided.

High Vibration

Reciprocating compressors produce pulsations due to intermittent flow. Double acting machines and

Pulsation dampeners will reduce the impact due to pulsation. During prolonged operation vibration of the

equipment is prone to go high due to damage in internals, change in operating conditions etc. Therefore

trip is provided for High Vibration in the reciprocating compressor.

Low Lube Oil Pressure

Adequate Lubrication is necessary for compressor moving parts. Therefore trip of the reciprocating

compressor is provided for low lube oil pressure. Starting Interlock bypass timer is provided to bypass the

trip during initial startup of the compressor. This time delay will allow the compressor to develop enough

lube oil pressure during start of the machine. During normal operation the compressor trips as soon as

low pressure is detected.

Cooling Water Failure

Cooling water is supplied to Inter coolers, Lube oil Coolers and Jacketing water coolers. Upsets in water

flow will result in any one of the trips discussed here. Any way cooling water failure trip is also provided.

Safety Aspects in Reciprocating Compressor

Discharge Vent

Since Reciprocating compressors are constant volume compressors they keep on delivering the gas at

the discharge. Therefore it is necessary to provide the vent in the discharge to avoid over pressurization

and other impacts.

Inter stage Relief Valves

Relief valves in inter stage separators are to be installed to prevent over pressurization due to Valve plate

failures and inter cooler fouling.

Motor Protections

Excitation of Torsional critical speed in reciprocating compressors does not allow variable speed

operations. Torsional critical speed is associated with angular or torsional deflection. Therefore in most of

the cases driver is electric motor. Normal motor protections like Over Current, Under Voltage, Under

Frequency trips are to be incorporated and executed with the help of relays.

Insulation

Thermal insulation has to be provided in the suction and discharge pipelines depending on the

temperature. Cold insulation in Refrigeration systems protect the pipelines from corrosion and heat

ingression into the system. Discharge pipelines contain gas at high temperature which is prone to cause

burns and has to be properly insulated.

Packing Gas Vent

Packing gas vent to safe atmosphere has to be provided to avoid gas contamination with oil in crankcase

and Fugitive emission.

SOURCE: http://www.chemicalengineeringsite.com/reciprocating-compressor-

trips-safety-aspects/310