presentation_compressed air system

8/13/2019 Presentation_compressed Air System

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INTRODUCTION

Compressed air system is required in

various industries to supply process air

requirements, to operate pneumatic tools

and equipments and to meet

instrumentation need for moisture free

compressed air.


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COMPONENTS

Main components of compressed air

systems are

Compressor

Air receiver

Air dryer


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COMPRESSOR

The compressor is the mechanical device used

to increase the pressure of a compressible fluid.

The fluid can be any compressible fluid, either

gas or vapour, and can have a wide molecularweight range.The inlet pressure level can be any

value from a deep vacuum to a positive

pressure. The discharge pressure can range

from sub atmospheric level to high values ofabout 700 bar. The prime mover powers the

compressor.


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COMPRESSOR

Detail classification of compressor :


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Positive Displacement Compressors

Reciprocat ing Compressors

Reciprocating compressor is the most widely used of all compressors. It consists of amechanical arrangement in which reciprocating motion is transmitted to piston that isfree to move in a cylinder. The displacing action of the piston, together with the inletvalve or valves, causes a quantity of gas to enter the cylinder where it is in turncompressed and discharged.

Reciprocating compressor can be single acting or double acting based on

compression on one side of the piston or both side of the piston respectively.

Compressor can be single cylinder or multiple cylinder configuration. Multiple cylindercan be arranged in parallel or series which are referred as single or multistagecompressor.

The reciprocating compressor is generally in the lower flow end of the compressor

spectrum. It is particularly well suited for higher pressure services.

They are characterized by a flow output that remains nearly constant over a range ofdischarge pressures. Also, the compressor capacity is directly proportional to thespeed. The output, however, is a pulsating one.


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Reciprocat ing Compressors

In the case of lubricated machines, oil has to be separated from thedischarge air. Non-lubricated compressors are especially useful forproviding air for instrumentation and for processes which require oil freedischarge. However non-lubricated machines have higher specific powerconsumption (kW/cfm) as compared to lubricated types.

Single cylinder machines are generally air-cooled, while multi-cylinder

machines are generally water cooled, although multi-stage air-cooled typesare available for machines up to 100 kW. Water-cooled systems are moreenergy efficient than air-cooled systems.Two stage machines are used forhigh pressures and are characterized by lower discharge temperature (140to 160C) compared to single-stage machines (205 to 240C). In somecases, multi-stage machines may have a lower specific power consumptioncompared to single stage machines operating over the same total pressuredifferential. Multi-stage machines generally have higher investment costs,

particularly for applications with high discharge pressure (above 7 bar) andlow capacities (less than 25 cfm). Multi staging has other benefits, such asreduced pressure differential across cylinders, which reduces the load andstress on compressor components such as valves and piston rings.


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Rotary Compressors

Rotary compressors have rotors in place of pistons and give a continuous, pulsation freedischarge air.They are directly coupled to the prime mover and require lower starting torque ascompared to reciprocating machine. They operate at high speed and generally provide higherthroughput than reciprocating compressors. Also they require smaller foundations,vibrate less,and have a lower number of parts - which means less failure rate.

Among rotary compressor, the Roots blower (also called as lobe compressor) and screwcompressors are among the most widely used. The roots blower is essentially a low-pressureblower and is limited to a discharge pressure of 1 bar in single-stage design and up to 2.2 bar intwo stage design.

The most common rotary air compressor is the single stage helical or spiral lube oil flooded screwair compressor. These compressors consist of two rotors, within a casing where the rotorscompress the air internally. There are no valves. These units are basically oil cooled (with aircooled or water cooled oil coolers) where the oil seals the internal clearances. Since the coolingtakes place right inside the compressor, the working parts never experience extreme operatingtemperatures. The oil has to be separated from discharge air. Because of the simple design andfew wearing parts, rotary screw air compressors are easy to maintain, to operate and install.

The oil free rotary screw air compressor uses specially designed air ends to compress air without

oil in the compression chamber producing true oil free air. These compressors are available asaircooled or water cooled types and provide the same flexibility as oil flooded rotary compressors.There is a wide range of availability in configuration and in pressure and capacity. Dry typesdeliver oil-free air and are available in sizes up to 20,000 cfm and pressure upto 15 bar.Lubricated types are available in sizes ranging from 100 to 1000 cfm, with discharge pressure upto 10 bar.


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RECIPROCATING COMPRESSOR

Reciprocating air compressors are positive displacement compressors. Thismeans they are taking in successive volumes of air which is confined withina closed space and elevating this air to a higher pressure. The reciprocatingair compressor accomplishes this by using a piston within a cylinder as thecompressing and displacing element.

The reciprocating air compressor is considered single acting when thecompressing is accomplished using only one side of the piston.

A compressor using both sides of the piston is considered double acting.

The reciprocating air compressor uses a number of automatic spring loadedvalves in each cylinder that open only when the proper differential pressureexists across the valve. Inlet valves open when the pressure in the cylinderis slightly below the intake pressure. Discharge valves open when thepressure in the cylinder is slightly above the discharge pressure.


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presentation_compressed air system

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