Compressed air is essential in most manufacturing plants, and the cost to produce it is much higher than most people realize.
Natural gas engine-driven air compressors greatly reduce power demand and energy consumption costs. Advances in engine control technologies and availability of standardized packages have further reduced equipment and operating costs of these air compressors.
Natural gas is highly pressurized as it travels through an interstate pipeline. To ensure that the natural gas flowing through any one pipeline remains pressurized, compression of this natural gas is required periodically along the pipe. The natural gas enters the compressor station, where it is compressed by either a turbine, motor, or engine.
CNG is a compressed natural gas that is a pressurized gas stored in cylinder tanks at pressure upto 36oo pounds per square inch. It is a pipeline gas that is compressed at a refuling station and dried.
Compressors can be classified into two basic categories, reciprocating and rotary. Reciprocating compressors are used for compressing natural gases and other process gases when desired pressures are high and gas flow rates are relatively low. They are also used for compressing air.
Types of CNG Compressors
Reciprocating compressors compress gas by physically reducing the volume of gas contained in a cylinder using a piston. As the gas volume is decreased, there is a corresponding increase in pressure. This type of compressor is referred to as a positive displacement type. Reciprocating compressors are typically a once-through process in which gas compression and lubricant separation occur in a single pass.
Reciprocating compressors can be single acting compressors where the gas is compressed on one side and can be double acting, where the gas is compressed on both the sides.
Rotary Compressors - Rotary compressors are classified as:
A positive displacement compressor utilizes gas volume reduction to increase gas pressure. Examples of this type of compressor include :
- Rotary Screw - Consists of two intermeshing
screws or rotors which trap gas between the rotors and the
- Lobe Compressor - In the compressor as the lobe
impellers rotate, gas is trapped between the lobe impellers and the
compressor case where the gas is pressurized through the rotation of
lobes and then discharged. The bearings and timing gears are
lubricated using a pressurized lubricating system or sump.
- Vane Compressors - Rotary vane compressors consist of a rotor with multiple sliding vanes that are mounted eccentrically in a casing.
Compressors in which air or gas is compressed by the mechanical action of rotating impellers imparting velocity and pressure to a continuously flowing medium. Dynamic compressors have a few key components that require a coolant/lubricant: gears, bearings and seals.
The choice of a compressor lubricant depends on:
- The type and construction of the compressor
- The gas being compressed
- The degree of compression
- The final outlet temperature.