General Information about Compressors

Written by Matt Milbury. Posted in Compressor

A compressor is a device that forces air or gas into a smaller area increasing the volume and creating a usable force of energy. Compressors come in many configurations and flow rates and can be found in every industry from refrigerating to welding, even your home. Compressors are split into two categories: positive displacement and dynamic.

Dynamic Compressors

Axial Compressor

Axial compressors are used where continuous flow and large amount of air is required. There are a series of blades on a shaft, the shaft having a number rows. The number of rows is referenced as a 10 stage, 15 stage and so on. The shaft is inside a tapered housing which compresses the air as it flows through. As the blades turn the air is pulled in the front, being compressed tighter as it exits.

Centrifugal Compressor

Centrifugal compressors are often used offshore for field gas compression and are often used in gas plant applications. These are used when there is limited space available, when vibrations could be a problem (offshore) or a low weight to horsepower ratio is required.

Positive Displacement

Reciprocating Compressor

Reciprocating compressors are primarily used in field gas compression and have a very large range of capacity and horsepower characteristics. The ranges for horsepower can be as low as 5HP and be as high as 2,000 HP.

Types of Reciprocating Compressors are:

  • Single Acting
  • Double Acting
  • Diaphragm - Much the same as a diaphragm pump, a Diaphragm compressor, is a positive displacement pump that uses a combination of the reciprocating action of a diaphragm and a series of check valves to pump a fluid. They are useful in processes where leaks through packing cannot be tolerated.

Rotary Compressor

  • Liquid Ring
  • Lobe
  • Screw
  • Scroll - A scroll compressor uses two interleaved spiral-like vanes to pump or compress the gas. One of the scrolls is fixed, while the other orbits eccentrically without rotating, thereby trapping and pumping or compressing pockets of gas between the scrolls. They operate more smoothly, quietly, and reliably than other types of compressors. These compressors are usually operated in the lower volume range
  • Vane - Sliding vane / rotary compressors are often used in tank vapor recovery (TVR) operations. These units take gas at very low suction pressures and raise them to pressures required for gas sales. If they cannot get them to the high pressures, they will often discharge into another compressor that can.

Supporting Equipment

A gas compressor does not run by itself. It needs quite a bit of equipment to keep it functioning properly. Examples of this equipment are:

Drivers

  • Internal Combustion Engine
  • Electric Motors may be attached to a gear set and / or a Variable Frequency Drive
  • Gas Turbines

Accessories

  • Lube Oil
  • Gas Cooler, typically an Air Cooled Heat Exchanger (as gas is compressed, heat is added and is usually removed)
  • Gas Scrubber for removing liquids before the gas enters the compression chamber.
  • Water Jacket Cooling for keeping the compressor, proper, cool.
  • Fuel system for driver
  • Control Panel
  • Starters

Installation

Foundations

Foundations are very important to the installation of a compressor. This is because compressors produce a huge amount of vibration and the foundation acts as a mass dampener. The cement foundation is usually very large and very well reinforced.

Grouting

Grouting ensures that the entire compressor skid is equally supported at all points. Grout is usually epoxy grout or cement based grout.

Alignment

Setting the unit on the foundation is very critical. If this is done hap-hazardously, the skid or piping can become deformed and not affect the operation of the equipment. Alignment of the compressor with respect to the driver absolutely must be done before grouting the unit. This should be completed by an expert and should be verified after the unit has been running for a given length of tme.

abbreviation

  • COMP - compressor

Standards

  • ISO Standards
    • ISO 5388 - Stationary air compressors -- Safety rules and code of practice