Gas compressors and gas compressor systems pressurize and circulate gas through a process, enhance conditions for chemical reactions, provide inert gas for safety or control systems, recover and recompress process gas, and maintain correct pressure levels by either adding or removing gas or vapors from a process system.

Types of Gas Compressors and Gas Compressor Systems

Gas compression can be accomplished by many different techniques. Positive displacement compressors include reciprocating compressors and rotary compressors. Reciprocating compressors utilize the thrust of a crankshaft-driven piston moving within a cylinder to create the motive pressure. Rotary compressors move gas through the system by the motion of rotating lobes, screws, or vanes. Dynamic compressors, including axial and centrifugal systems, are another type of compressor.

Gas compressors use a variety of technologies to compress gas.

• Axial: Multiple-blade rotor imparts axial velocity that is converted to pressure; with very high flow rates.
• Blower: Dynamic head is imparted to the gas by means of high-speed impellers rotating in a confining case. Blowers are available in axial flow, radial, or centrifugal configurations.
• Centrifugal: High-speed impeller produces radial airflow; velocity converted to pressure energy.
• Diaphragm: Diaphragm oscillation driven by rod; no sliding seals or parts.
• Linear: Linear compressors have no sliding parts; compression is generated with electromagnetic oscillation. This type of compressor is clean and quiet.
• Reciprocating piston: Piston mechanically reduces air volume inside cylinder.
• Rotary lobe: Gas is moved by the positive displacement of two rotating lobes confined in an eccentric cylinder.
• Rotary screw: Rotating helical screw compresses air prior to discharge; provides even flow at relatively low pressures. Wet or dry screw types are utilized.

Video credit: BlackmerGlobal

Gas Types

Gas compressors are capable of handling a wide range of gases, including:

• Compressed air for plant use, purified air for breathing applications, a combustion process or for feeding a gas separation unit for the generation of nitrogen or oxygen.
• Ammonia (NH4) gas is used as a refrigerant gas or dissociated into hydrogen and nitrogen gases for metallurgical or chemical process applications.
• Argon is an inert gas that is heavier than air. The high density and inert nature allows argon to displace air which is important is shielding applications. Shielding or protective atmosphere gases prevent the oxidation or contamination of metal during welding or furnace processing.
• Corrosive gases include sour gas, acid gas, halogen gases (chlorine or fluorine), and halide gases (e.g. hydrogen chloride, hydrogen fluoride). Sour gas is laden with traces of H2S.
• Carbon dioxide (CO2) is a heavy gas consisting of a molecule of carbon and oxygen.
• Helium is an inert gas that is lighter than air.
• Hydrocarbon gas including acetylene, propane, ethane, methane, natural gas or other hydrocarbons available in a gaseous state at room temperature.
• Natural gas is a gas mixture containing hydrocarbons with some impurities. It is comprised mostly of methane (CH4), an abundant organic compound readily used as a fuel and chemical feedstock.
• Nitrogen (N2) gas makes up 78.1% of the Earth’s air, by volume.
• Oxygen (O2) is a gaseous element, forming 21% of the atmosphere by volume and is obtained by liquefaction and fractional distillation. It is highly flammable.
• Propane is a heavy flammable gaseous alkane C3H8 found in crude petroleum and natural gas and used especially as fuel and in chemical synthesis.
• Refrigerant gases are used in refrigeration processes such as ammonia, chlorofluorocarbon gases, R11 (CFC-11 or trichlorofluoromethane), R22 (HCFC-22 or chlorodifluoromethane), R12 (CFC-12 or dichlorodifluoromethane), R502, R134a, R113, R123, R717, R500, R408A, R409A or R404A.

Applications

Gas Boosting

Gas boosting increases the pressure in a system by introducing a gas to induce or maintain flow of a liquid in a storage tank, tank cars, or vessel. It can also be used to maintain the pressure in a system to prevent influx of contaminants, or to maintain a fuel gas at a pressure suitable for combustion in a gas turbine. Gas boosting is also used to increase the pressure of gas gathered from the wellhead to transmission pressure levels.

Gas Transmission/Delivery

Systems used to move or pump gas through gas transmission pipelines or plant delivery lines.

Fuel Gas / Power Generation

A unit or system that is suitable for fuel gas compression in gas turbine applications. The compressor system increases the pressure of the fuel gas, such as waste or landfill gas, to a level suitable for efficient combustion in a gas turbine or other combustion engine.

Gas Generation/PSA

Systems used in gas separation, generation, or purification operations to produce oxygen, nitrogen, or other gases from a compressed air or other feed. For example, systems for processing tail or feed gas from the molecular sieve portion of a pressure or vacuum swing adsorption process unit.

Oil Refining / Chemical Processing

Cracking, distillation, hydrotreating, and other refining processes require gases to convert crude oil into gasoline, fuel oil, and petroleum by-products. Compressor systems supply front-end, recycled, and make-up gases for the oil refining equipment.

Oil/Vapor Recovery

Systems used to recover oil or vapor from a well or field site. Environmental regulations may restrict the flaring or venting of by-product vapors at the oil well. Gas injection or lifting inserts compressed gas to the wellhead to aerate or displace the produced fluids, reducing the pressure at the bottom of the well bore and increasing or sustaining the well's flow rate.

Process Gas Feeding/Injection

This includes chemical, metallurgical, or other process gas application, such as feeding gas into or out of a reactor or furnace. Hydrogen, carbon dioxide, nitrogen, hydrocarbons, or other gases are commonly fed into a reactor or process unit for:

• Hydrogenation
• Protective blanketing
• Injection or sparging of a gas into a liquid to remove contaminants or dissolve a gas
• Recovery of solvents
• Polymerization or to initiate other chemical reactions

Refrigeration/Gas Drying

Gas plant glycol dehydration, gas chiller, and refrigeration skids are examples of refrigeration packages for industrial plants.

Vessel/Cylinder Filling

Gas compressor systems designed for filling vessels, cylinders, or bottles with high-pressure gas.

Features 

• Integral Cooler: Intercoolers cool gas between stages; aftercoolers cool gas exiting a compressor or system.
• Integral Dryer: A dryer removes entrained liquid particles from the compressed gas.
• Explosion Proof: An explosion proof motor for use with highly flammable gases.
• Integral Filter: A filter to remove any entrained particulate from the air.
• Multistage: A unit or system consisting of multiple stages in which the gas pressure is sequentially increased above the previous stage.

Standards

API STD 617--Axial and centrifugal compressors and expander-compressors for petroleum, chemical, and gas industry services

ISO 13707--Petroleum and natural gas industries - reciprocating compressors

SAE AS26805--Compressor units, air/gas, general requirements

Image credits:

Aerzen USA Corp. | Haskel International