report on gass compresor

8/2/2019 Report on Gass Compresor

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Gas compressor


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A gas compressor is a mechanical device thatincreases the pressure of a gas by reducing itsvolume.

Compressors are similar to pumps: bothincrease the pressure on a fluid and both cantransport the fluid through a pipe. As gases arecompressible, the compressor also reduces the

volume of a gas. Liquids are relativelyincompressible, so the main action of a pump isto pressurize and transport liquids.


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Often called a third utility (after electricity andnatural gas)

Almost every manufacturing plant has air

compressors that operate. Compressed air used for controls, to move

things around, to clean work areas, to liftthings, and hold things in place

Can be a significant part of electrical load


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Pressure usually measured in pounds persquare inch (psi)

Usually talk about gage pressure (psig), which is

pressure measured above atmospheric pressure Absolute pressure (psia) used for calculations,

pressure measured against vacuum

Absolute Pressure = Gage Pressure + 14.7 psia


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http://en.wikipedia.org/wiki/File:Compressor_Types.png


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Use pistons driven by acrankshaft

. They can beeither stationary orportable, can be single ormulti-staged, and can bedriven by electric motors

or internal combustionengines. Smallreciprocating compressorsfrom 5 to 30 horsepower(hp) are commonly seen inautomotive applications

and are typically forintermittent duty. Largerreciprocating compressorswell over 1,000 hp(750 kW) are commonlyfound in large industrialand petroleum

applications.
http://en.wikipedia.org/wiki/Pistonhttp://en.wikipedia.org/wiki/Horsepowerhttp://en.wikipedia.org/wiki/Horsepowerhttp://en.wikipedia.org/wiki/Horsepowerhttp://en.wikipedia.org/wiki/Piston


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Discharge pressures canrange from low pressure tovery high pressure (>18000

psi or 180 MPa). In certainapplications, such as aircompression, multi-stagedouble-acting compressorsare said to be the mostefficient compressors

available, and are typicallylarger, and more costly thancomparable rotary units.Another type ofreciprocating compressor is

the swash plate compressor,which uses pistons which aremoved by a swash platemounted on a shaft.


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1) Cylinder: In small compressors the cylinder is made by directly boring into the main

body of the compressor, which is usually made up of cast iron. In case of thelarge multi-cylinder compressors, the cylinder is made separately and it is fittedinto the main body of the compressor. This type of cylinder is also called as theliner or sleeve. In such compressors if any of the cylinders gets worn out ordamaged, it can be replaced easily by the new liner, without having to replacethe whole compressor.

2) Piston: The piston performs upwards and downwards motion inside the cylinder,

which is also called as the reciprocating motion. During its motion the pistonenables suction and compression of the refrigerant. The piston is made of castiron or aluminum. During its motion inside the cylinder the refrigerant shouldnot leak through the gap between the cylinder walls and the piston to thecrankcase, hence piston is covered with the piston rings. The piston rings arenot required in the smaller compressors. The gap between the piston and the

cylinder is also filled with the lubricating oil, which also prevents the leakage ofthe compressed refrigerant to the crankcase.

3) Piston rings: The piston rings are circled around the piston. When the piston performs

reciprocating motion inside the cylinder, it is the piston rings that come incontact with the walls of the cylinder. There is lots of friction between thecylinder walls and the piston rings, thus they have to be replaced from time-to-

time for proper functioning of the compressor. This helps increasing the life ofthe piston and prevents replacement of the complete piston.


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4) Crankshaft: The piston can perform reciprocating motion inside the cylinder

because of the rotary motion of the crankshaft. The crankshaft isthe main shaft of the compressor. On one side it is connected to the

electric motor directly by the coupling or by the belt and pulleyarrangement. The rotation of the motor shaft brings about therotation of the crankshaft. On the other side the crankshaft is alsoconnected to the connecting rod, which is then connected to thepiston at it other end. The rotary motion of the crankshaft isconverted into the reciprocating motion of the piston by

connecting rod. In case of the multi-cylinder compressors, thenumber of connecting rods connected to the crankshaft is same asthe number of cylinders.

5) Connecting Rod: The connecting rod is the connecting link between the piston and

the crankshaft. On one side the connecting rod is connected to the

piston by piston pin and on the other side it is connected to thecrankshaft by connecting rod cap. Both these connections of theconnecting rod enable converting the rotary motion of thecrankshaft into the reciprocating motion of the piston inside thecylinder. The connecting rod is usually made up of carbon steelforging.


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6) Suction Valve and Discharge Valve:

Through the suction valve the low pressure refrigerant issucked inside the cylinder and through the discharge valvethe compressed high pressure refrigerant is discharged to thedischarge line, from where the refrigerant goes to thecondenser. The operation of the suction valve is such that isopens when the piston moves downwards and closes whenthe refrigerant is being discharged. The discharge valve opensonly when piston reaches to certain level inside the cylinder

and refrigerant has reached to the desired level of pressure.When the refrigerant is delivered from the cylinder, thedischarge valve closes.

7) Suction and Discharge Pipelines:

Through the suction piping the low pressure refrigerant istaken inside the cylinder via suction valve. The high pressurecompressed refrigerant is delivered though the discharge line


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Single-Acting Compressors: These are usually

reciprocating compressors,which has piston working onair only in one direction. Theother end of the piston isoften free or open whichdoes not perform any work.The air is compressed onlyon the top part of the piston.The bottom of the piston is

open to crankcase and notutilized for the compressionof air.

Double-ActingCompressors:

These compressors are

having two sets ofsuction/intake and deliveryvalves on both sides of thepiston. As the piston movesup and down, both sides ofthe piston is utilized incompressing the


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Advantages

Good for smallapplication

Uses no / little powerwhen unloaded

Cheap and simple tooperate

Operates over a widerange of pressures

Disadvantages

Noisy

Maintenance can be an

issue Not good for larger

applications

Oil-free air units are

expensive


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The majority of applications for reciprocatingcompressors are in the oil and gas industries. Oilrefineries use these compressors for processes that

require high pressure delivery of essential gases.The natural gas industry also utilizesreciprocating compressors to transport gas viacross country pipelines. These compressors can

also be found in chemical plants, refrigerationplants, air compressors for tooling, etc.


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Very common inplants

Good mid-rangesize (25 hp 300 hp)

Models include oilflooded or oil free

Oil flooded unitsoffer best efficiency


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Rotary screw compressorsuse two meshed rotatingpositive-displacementhelical screws to force thegas into a smaller space.These are usually used forcontinuous operation incommercial and industrialapplications and may beeither stationary orportable. Their applicationcan be from 3 horsepower(2.2 kW) to over1,200 horsepower (890 kW)

and from low pressure tomoderately high pressure(>1200 psi or 8.3 MPa).
http://en.wikipedia.org/wiki/Helixhttp://en.wikipedia.org/wiki/Helixhttp://en.wikipedia.org/wiki/File:RotaryScrewCompressor.gifhttp://en.wikipedia.org/wiki/Helixhttp://en.wikipedia.org/wiki/Helixhttp://en.wikipedia.org/wiki/Helix


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Oil-free

In an oil-free compressor, the air is compressed entirelythrough the action of the screws, without the assistance

of an oil seal. They usually have lower maximumdischarge pressure capability as a result. However,multi-stage oil-free compressors, where the air iscompressed by several sets of screws, can achievepressures of over 150 psig, and output volume of over

2000 cubic feet per minute (measured at 60 C andatmospheric pressure).

Oil-free compressors are used in applications whereentrained oil carry-over is not acceptable, such asmedicial research and semiconductor manufacturing.

However, this does not preclude the need for filtrationas hydrocarbons and other contaminants ingested fromthe ambient air must also be removed prior to the point-of-use. Subsequently, air treatment comparable to anOil-flooded screw compressor is frequently stillrequired to ensure a given quality of compressed air.


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Oil-flooded

In an oil-flooded rotary screw compressor, oil is

injected into the compression cavities to aidsealing and provide cooling sink for the gascharge. The oil is separated from the dischargestream, then cooled, filtered and recycled. The oil

captures non-polar particulates from theincoming air, effectively reducing the particleloading of compressed air particulate filtration. Itis usual for some entrained compressor oil to

carry over into the compressed gas streamdownstream of the compressor.


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Advantages

Good efficiency for oilflooded models(continuous

intercooling) Low maintenance costs

Not usually noisy

Can run fully loaded for

extended periods oftime

Good for heat recoveryfor space heating

Disadvantages

Can use 40%-90% offull load power when

unloaded Not good for very

small or very largeloads


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1. Rotary screw compressors are used in a diverserange of applications. Typically, they are used tosupply compressed air for general industrialapplications. Trailer mounted diesel poweredunits are often seen at construction sites, and areused to power air operated constructionmachinery.


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Axial-flow compressors are

dynamic rotating compressors thatuse arrays of fan-like airfoils toprogressively compress the workingfluid. They are used where there is arequirement for a high flow rate or a

compact design.

The arrays of airfoils are set in rows,usually as pairs: one rotating andone stationary. The rotating airfoils,

also known as blades or rotors,accelerate the fluid. The stationaryairfoils, also known as stators orvanes, decelerate and redirect theflow direction of the fluid, preparing

it for the rotor blades of the nextstage


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Axial compressors canhave high efficiencies;around 90% polytropic

at their designconditions. However,they are relativelyexpensive, requiring alarge number of

components, tighttolerances and highquality materials. Axial-flow compressors can befound in medium to

large gas turbineengines, in natural gaspumping stations, andwithin certain chemicalplants.
http://en.wikipedia.org/wiki/Polytropichttp://en.wikipedia.org/wiki/Polytropichttp://en.wikipedia.org/wiki/Gas_turbinehttp://en.wikipedia.org/wiki/Gas_turbinehttp://en.wikipedia.org/wiki/File:Axial_compressor.gifhttp://en.wikipedia.org/wiki/Gas_turbinehttp://en.wikipedia.org/wiki/Polytropic


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http://upload.wikimedia.org/wikipedia/commons/e/e3/DH_Goblin_annotated_colour_cutaway.png


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Centrifugal compressors usea rotating disk or impeller ina shaped housing to force thegas to the rim of the impeller,increasing the velocity of thegas. A diffuser (divergentduct) section converts thevelocity energy to pressureenergy.Their application canbe from 100 horsepower(75 kW) to thousands ofhorsepower. With multiplestaging, they can achieveextremely high outputpressures greater than10,000 psi (69 MPa).


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1. In pipeline transport of natural gas to move the gasfrom the production site to the consumer.2. In oil refineries, natural gas processing plants,

petrochemical and chemical plants.3. In air separation plants to manufacture purified end

product gases.4. In refrigeration and air conditioner equipment

refrigerant .5. In industry and manufacturing to supply compressed

air for all types of pneumatic tools.

6. In gas turbines and auxiliary power units.7. In automotive engine and diesel engine turbochargers

and superchargers.8. In oil field re-injection of high pressure natural gas to

improve oil recovery.


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Advantages

Can be staged for highpressure applications

Typically used for loadsgreater than 200 hp

Can be 1,500 hp orlarger

Low maintenance Part load performance

is adequate (close offinlet)

Disadvantages

Intercooling must beprovided for higherpressures

Not as efficient asscrews


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Excessively low dischargepressure

Caused by: 1Low oil pressure or faults of

suction and discharge valve; 2Faults of pressure control

valve or oil compensatingpump; 3Damaged diaphragm(s); 4Leaking of gas-piping

system; 5Overmuch suction

resistance ; 6Gas-demand exceeds gas-

supply.

Solutions 1Adjust the oil pressure and

keep it in required range; 2Check and repair the

suction or discharge valve; 3Check and repair the

suction or discharge valve; 4Replace the damaged

diaphragm(s); 5Check and repair the

leaking point(s); 6Clean the gas inlet filter and

adjust suction pressure; 7Adjust the gas-demand and

gas supply to keep them inequilibrations.

Excessively high dischargepressure


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Excessively high discharge

pressure Caused by: 1The gas release valve is

closed or slightly open; 2Gas-supply exceeds gas-

demand or the suctionpressure is too high;

Solutions 1Check and adjust the gas

release valve; 2Adjust the suction

pressure and gas-demand.

Excessively high dischargepressure

Caused by: 1The gas release valve

is closed or slightly open; 2Gas-supply exceeds

gas-demand or the suctionpressure is too high;

Solutions 1Check and adjust the

gas release valve; 2Adjust the suctionpressure and gas-demand.


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Isothermal Compression/Expansion Processes If a compression or expansion takes place under constant

temperature conditions - the process is said to be isothermal.The isothermal process can with the Ideal Gas Law beexpressed as

p / = constant

where p = absolute pressure = density The isothermal process can also be expressed as pV = constant or p1V1 = p2V2 where V = gas volume (m3, ft3...) suffix

1

denotes initial conditions and suffix2

denotes final conditions


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Isentropic (or adiabatic) Compression/Expansion Processes

If a compression or expansion takes place under constantvolume conditions - the process is said to be isentropic. Theisentropic process can with the Ideal Gas Law be expressed as

p /k = constant

where k = cp / cv - the ratio of specific heats - the ratio of specific heat at

constant pressure- cp - to the specific heat at constant volume - cv

The isentropic or adiabatic process can also be expressed as

pVk= constant

or p1V1

k = p2V2k


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Polytropic Compression/Expansion Process An isothermal process must occur very slowly to keep

the temperature in the gas constant. The adiabaticprocess must occur very rapidly without any flow ofenergy in or out of the system. In practice most

expansion and compression processes are somewhere inbetween, or said to be polytropic.

The polytropic process can be expressed as

pVn= constant (3a)

or p1V1

n = p2V2n (3b)

where

n = polytropic index (ranging 1 to 1.4)


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1.An air compressor takes air at 100 KPa and dischargesto 600KPa. If the volume flow of discharge is 1.2m3/s,determine the capacity of the air compressor.

Given: air compressor

P1 = 100 KPa P2 = 600 KPa

V2 = 1.2 m3/s

Required: V1, capacity of the air compressor

Solution: n = 1.4 n = polytropic index P1V1

n = P2V2n

V1n = P2V2

n/P1 = 600KPa (1.2m3/s)1.4/100 KPa

V1 = 4.3152 m3/s, capacity of the air compressor


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A 355 mm x 381 mm air compressor has a pistondisplacement of 0.1885 m3/s. Determine the operatingspeed of the compressor.

Given: air compressor; D = 0.355m; L = 0.381m; VD =

0.1885m3/s

Required: N = ?, operating speed

Solution: VD = D2 LN /4 ->

0.1885 m3 /s = (0.355m)2 /4 x 0.381m x N

N = 0.1885 m3/s / 0.381 0.098979803m2

N = 5 rev/s 60s /m = 300 rpm, operatingspeed of the compressor


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www.turbocor.com/literature/renovation

www.compressorworld.com

en.wikipedia.org/wiki/Gas_compressor

Understanding Thermodynamics by H. C. VanNess

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