Reciprocating Air (Gas) Compressor

ByShridevi Bhat13/02/2016

Introduction

• An air compressor is a device that converts power (using an electric motor, diesel or gasoline engine, etc.) into potential energy stored in pressurized air.

• Work required for increasing pressure of air is available from the prime mover driving the compressor.

• Generally, electric motor, internal combustion engine or steam engine, turbine etc. are used as prime movers.

• In industry, reciprocating compressors are the most widely used type for both air and refrigerant compression.

The US Department of Energy (2003) reports that 70 to 90 % of compressed air is lost in the form of unusable heat, friction, misuse and noise. For this reason, compressors and compressed air systems are important areas to improve energy efficiency at industrial plants.

History

Human lungs – the earliest air

compressor

Water organ – 3rd century B.C. –

Ctesibius & Hero of Alexandria

Bellows – 1500 B.C. – The first mechanical

air compressors

Water wheel driven blowing cylinder –

1762 – John Smeaton of England

 It was replaced in turn by the blasting machine invented by John

Wilkinson in 1776. Wilkinson’s blasting machine became the

archetype for later mechanical air compressors.

Classification

Based on principles of operation

Reciprocating air compressor is a positive displacement compressor

In positive displacement compressors the compression is realized by displacement of solid boundary and preventing fluid by solid boundary from flowing back in the direction of pressure gradient. Due to solid wall displacement these are capable of providing quite large pressure ratios.Non-positive displacement compressors also called as steady flow compressors use dynamic action of solid boundary for realizing pressure rise. Here fluid is not contained in definite volume and subsequent volume reduction does not occur as in case of positive displacement compressors.

Reciprocating compressors generally, employ piston-cylinder arrangement where displacement of piston in cylinder causes rise in pressure.

How it works?

Single acting and double acting compressors

The reciprocating air compressor is considered single acting when the compressing is accomplished using only one side of the piston, i.e., has one discharge per revolution of crankshaft. A compressor using both sides of the piston is considered double acting, i.e., completes two discharge strokes per revolutions of crankshaft.

Configurations

Reciprocating compressors are available in many configurations, the four most widely used are horizontal, vertical, horizontal balance-opposed and tandem. Vertical type reciprocating compressors are used in the capacity range of 50 – 150 cfm. Horizontal balance opposed compressors are used in the capacity range of 200 – 5000 cfm in multi-stage design and up to 10,000 cfm in single stage designs.

Reciprocating air compressors are available either as air-cooled or water-cooled in lubricated and non- lubricated configurations, may be packaged, and provide a wide range of pressure and capacity selections.

A compressor is considered to be single stage when the entire compression is accomplished with a single cylinder or a group of cylinders in parallel.

Single stage and multistage compressors

Two stage machines areused for high pressures and are characterized by lower discharge temperature (140 to 160oC) compared to single-stage machines (205 to 240oC).

Applications

• The majority of applications for reciprocating compressors are in the oil and gas industries.

• Oil refineries use these compressors for processes that require high pressure delivery of essential gases.

• The natural gas industry also utilizes reciprocating compressors to transport gas via cross country pipelines.

• These compressors can also be found in chemical plants, refrigeration plants, or air compressors for tooling.

References

• http://elearning.vtu.ac.in/10/enotes/06ME43/Unit5-GP.pdf

• http://www.tech.plym.ac.uk/sme/THER205-web/recips.pdf