Gas Compressors - Types, Sizes And Functions

Gas Compressor: Types, Sizes and Functions

Types of Compressor:

As described, compressors fall into two separate and distinct categories:

• Dynamic  and
• Positive displacement.

Positive Displacement Compressors:

• In all positive displacement machines, a certain inlet volume of gas is confined din a given space and subsequently compressed by reducing this confined space or volume. At this elevated pressure, the gas is next expelled into the discharge piping or vessel system.

• Although positive displacement compressors include a wide spectrum of configurations and geometries, the most important process machines are piston compressors and helical screw rotating machines. Though there are a number of other, including diaphragm and sliding vane compressors, the overwhelming majority of significant process gas-positive displacement machines are clearly reciprocating piston and twin helical screw-rotating or rotary screw machines.

Reciprocating compressor

• Reciprocating or piston compressor is a positive displacement compressor that uses the movement of a piston within a cylinder to move gas from one pressure level to another (higher) pressure level.

Reciprocating compressors types include the following:

a) Simple Single-Cylinder: As single cylinder has one suction, compression and discharge area. Double acting cylinder designs have two suction, compression and discharge areas.

b) Multi-Cylinder: Some reciprocating compressors can have up to six cylinders. Pistons connected to crankshaft are utilized to compress the gas.

c) Multi-stage Design: Multi-stage compression stage take the vapour and compress it into

Rotary compressors:

• Screw compressor is a positive displacement machine and has a distinct working phases: suction, compression and discharge. Two counter rotating helical screw are arranged in a compressor casing; gas inlet and discharge nozzles are at opposite ends.

• Rotary screw compressors are very likely the equipment of choice for either oil-free or oil-wetted compression of air in mining, construction, industrial refrigeration or a host of other applications where their relative simplicity, general reliability and high availability are appreciated. Rotary screw compressors are equally suited to compress process gases.

Dynamic Compressors:

• Imparting velocity to a gas stream and then converting this velocity energy into pressure energy. These compressors are frequently called turbo compressors, and centrifugal machines comprise perhaps 80% or more of dynamic compressors. The remaining 20% or less is axial flow machines intended for higher-flow, lower-pressure applications.

Centrifugal Compressor:

• The centrifugal compressor is a dynamic machine that achieves compression by applying inertial forces to the gas (acceleration, deceleration and turning) by means of rotating impellers. The centrifugal compressor is made up

Axial Flow Compressor:

• Axial-flow  Compressors can handle large flow volumes in relatively small casings and with favourable power requirements. Pressure range for axial compressor is low to medium.

Turbo-Expander Compressor Assembly:

• A Turboexpander, also referred to as an expansion turbine, is a centrifugal or axial, flow turbine through which a high pressure gas is expanded to produce work that is used to drive a compressor.
• The term “Turboexpander”, as shown is normally used to define an Expander/Compressor machine as a single unit. It consists of two primary components; the Radial Inflow Expansion an a Centrifugal (Booster) Compressor combined as an assembly. Its wheels are connected on a single Shaft. The expansion turbine is the power unit and the Compressor is the driven unit.
• In a Gas Processing Plant, the purpose of Turbo-expander is to efficiently perform two distinctly different, but complimentary, functions in a single machine. The primary function is to efficiently generate refrigeration in the process gas stream. This is done at the expansion turbine end by efficiently extracting.