03 Compression Fundamentals

7/30/2019 03 Compression Fundamentals

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1COMPRESSION SYSTEMS


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Discussion Points

Basic Terminology

Rod (Pin) Load

Rod (Pin) Reversal

Area Classifications

NEMA Enclosures

Wire Separation

Intro to PV Card


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TERMINOLOGYTERMINOLOGY(Jargon)Gas Compressor Industry Language

Compression = The act of pressing or compacting into a smaller space.

Compressor = A machine which converts gas from low pressure to a higher

pressure.


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Packaged Compressor UnitPackaged Compressor Unit

This is a complete unit mounted on a skid or

skids which includes the prime mover,

compressor, necessary cooling facilities,

scrubbers, moisture traps, safety controls andpiping. In other words, a complete unit ready

to be connected to the suction and discharge

lines.


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The System


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TerminologyTerminology

Ratio of Compression (RC)

RC = Discharge Pressure(Pd)psig + 14.7 = ??? psia

Suction Pressure (Ps)psig + 14.7 = ??? psia

Note: Elevation or Barometric pressure must be taken

into account when figuring Rc.


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Finding Ratio of Compression (RC)Example 1: Ps = 200 psig, Pd = 600 psig

Rc = 600 psig + 14.7 = 614.7 psia = 2.863

200 psig + 14.7 = 214.7 psia

Example 2: Ps = 20 psig, Pd = 600 psig

Rc = 600psig + 14.7 = 614.7psia = 17.7

20psig + 14.7 = 34.7psia

Note: If we had not converted to psia the ratio

would have been 30:1.


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Finding Approximate HP Requirement:

To find the HP required for a single

stage unit (example 1):

Approximating HP Formula using

Example #1

HP = 21 x Rc x S x Q

Where:HP = Horse Power

21 = Standard (Constant)

Rc = Ratio Of Compression

S = # of Stages

Q = Quantity in MMCFD

HP = 21 x 2.86 x 1 x 2 = 120.12 or 121


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SA = Single Acting - The act of compressing

on one end of the compressor cylinder.

DA = Double Acting - The act of compressingon both ends of the compressor

cylinder.

Tandem = Two compressor cylinders either bolted

together or cast as one casting, using acommon piston rod with two piston

sizes.


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Single Acting TandemSingle Acting Tandem 2 Stage2 Stage


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Double ActingDouble Acting Single StageSingle Stage


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Typical Separators / ScrubbersTypical Separators / Scrubbers


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SCRUBBERRELIEF

VALVE

OUTLET

CONNECTION

MESH

FILTER

FLOATS

CONTROL

PRESSURE

SIGNAL TO

DUMPVALVE

AUTOMATICDRAIN

CUSTOMER

DRAIN

CONNECTIONMANUALDRAIN

GASINLET

CONNECTION

SIGHT

GAUGE

GAS

DEFLECTOR

HIGHLIQUID LEVEL

SHUTDOWNSWITCH

LIQUID


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Capacity = (or flow rate) Volume of gas compressed

and delivered at specified conditions of

temperature & pressure measured at the

compressor inlet. Usually expressed as

volume/unit of time - cubic feet per minute

or cubic feet per day.

Approach = Refers to the heat exchanger design

30F approach means the cooler will

cool the gas to 130

when ambienttemperature is 100F.


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Swept Volume= The volume swept by the piston during the forward and/or

backward stroke.

= Compressor speed is not a factor.

= Normally expressed in cubic inches and calculated as follows:

Swept Volume HE = Area of Piston X Stroke in Inches

Swept Volume CE = (Area of Piston - Area of Rod) X Stroke in Inches

Total Swept Volume = (2 X Area of Piston - Area of Rod) X Stroke In Inches


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Total Swept Volume Example (DA):

6 Diameter x 7 Stroke

2.5 Piston Rod Diameter

Total Swept Volume = (2 X 28.274 - 4.909) X 7

= (56.548 - 4.909) X 7

= 51.639 X 7= 361.473 cu. In.


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Units of Measure:

PSI = pounds per square inch

PSIG = pounds per square inch gauge

PSIA = pounds per square inch absolute= gauge + atmospheric pressure

MMCFD = million cubic feet per day

MMSCFD = million cubic feet per day @ the

standard conditions of 14.65psia & 60F


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Temperature Scales:

Degrees Centigrade or Celsius (C) =

A scale used worldwide which relates to the

metric system. At sea level, the freezing point of

pure water is 0 & the boiling point is 100. The

distance between these two points is 100.


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Temperature Conversion: Convert.exe


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Separable Engine

VConfiguration

InlineConfiguration

Horizontal OpposedConfiguration


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InIn--Line 4Line 4


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VV -- SixSix


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Horizontal 4Horizontal 4


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SeparableSeparable

Compressor FrameCompressor Frame

ClickClick

HereHere


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Compressor

Engine

Coupled Separables


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INTEGRAL ENGINE-COMPRESSORS

Left Bank Right Bank

RH

LH

1

2

Flywheel

Sheave

3

Flywheel

2L

1L

3L

4L

5L

1R

2R

3R

4R

5R


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Rod (Pin) Load DefinitionsRod (Pin) Load Definitions

External Rod Load The external rod load of a reciprocating compressor is a calculation considering

the unit in a static state. The calculation for deriving the ERL is:

ERL = PD(HA) - PS(CA) where:

PD = Discharge Pressure at the cylinder flange

PS = Suction Pressure at the cylinder flange

HA = Head End surface area of the piston

CA = Crank End surface area of the piston

Internal Rod Load

The internal rod load is often noted as the internal gas rod load of a reciprocating

compressor and the terms are synonymous. The IRL is a dynamic rod load

calculation based upon the internal gas pressures within the cylinder bore.

These gas pressures take into account the dynamic pressure drop characteristics

found across the valves and gas passages. The IRL is calculated through 360rotation of the crankshaft with the highest values being used.

Net Rod Load The net rod load is considered a dynamic rod load rating. The NRL is the sum of

the IRL calculation and the inertia loads of the reciprocating weights. The NRL is

calculated through 360 rotation of the crankshaft with the highest values beingused.


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2.5

ERL CompressionERL Compression

Pd=814.7 PSIA Ps=214.7 PSIA

Area of piston in square inches times discharge

pressure, minus area of piston, minus area of rodtimes suction pressure.

6

= 28.274 x 814.7 - (28.274 - 4.909) x 214.7= 23,035 - (23.365 x 214.7)

= 23.035 - 5016

= 18,019 #


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2.5

ERL TensionERL Tension

Pd=814.7 PSIAPs=214.7 PSIA

Area of piston in square inches, minus area of rod

times discharge pressure, minus area of the pistontimes suction pressure.

6

= (28.274 - 4.909) x 814.7 - (28.274 x 214.7)= 23.365 x 814.7 - (28.274 x 214.7)

= 19,035 - 6070

= 12,965 #


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Piston Rods Exceeding Rod LoadPiston Rods Exceeding Rod Load


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Rod (Pin) ReversalRod (Pin) Reversal

Crank PinCrosshead Pin

Connecting Rod

Piston Rod

Crosshead

Oil

Oil


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Data needed for Compressor

Sizing

Operating Conditions

Gas properties

Approximate HP per application

Suction Pressure (PS)

Discharge Pressure (Pd)

Quantity of gas in MMCFD

Conditions Assumed:

Suction Temp (TS) = 80F Ambient Temp (Ta) = 100F Discharge Temp (Td) required

approach = 20F Altitude = < 1500

Atmospheric Pressure = 14psi

Specific Gravity = 0.64

N value = 1.26

Sweet Gas


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Area Classification

Class I: Flammable gases and vapors Within this class are fourgroups in order of explosive potential This is where most gascompression will be found.

Group A: Acetylene

Group B: Hydrogen and other gases

Group C: Ethylene and other gases Group D: Acetone, Butane, Ethane, Methane, and other gases

Class II: Combustible dusts

Group E: Metallic dusts

Group F: Carbonaceous dusts (e.g.coal)

Group G: Agricultural, Chemical, and Plastic dusts

Class III: Combustible filings and fibers


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Area Classification

The NEC(National Electric Code) and CEC(Canadian Electric Code) recognizetwo further divisions distinguished by the likelihood of the material being

Present

Division 1: Areas where hazardous materials may be present undernormal operating conditions.

Intrinsically Safe: A system comprising of equipment and

interconnecting wiring in which any spark or thermal effect in any part ofthe system intended for use in the hazardous location is incapableunder prescribed conditions of causing ignition of the test gas mixture.

Division 2: Areas where hazards arise only as the resultof leaks,ventilation, or other unexpected breakdowns. As a rule of thumb theprobability of the presence of explosive materials must be less than 1% for

an area to be assigned to Division 2. Non-incendive Circuit: A circuit in which any spark or thermal effect,

that may occur in normal use, is incapable of causing an ignition of thetest gas mixture.


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NEMA Enclosure Standards

NEMA 12 enclosures are intended for indoor use primarily to provide adegree of protection against dust, falling dirt and dripping non-corrosiveliquids. They are not intended to provide protection against conditionssuch as internal condensation.

NEMA 3 enclosures are intended for outdoor use primarily to provide adegree of protection against windblown dust, rain, sleet, and externalice formation. They are not intended to provide protection againstconditions such as internal condensation or internal icing.

NEMA 3R enclosures are intended for outdoor use primarily to providea degree of protection against falling rain; and to be undamaged by the

formation of ice on the enclosure. They shall meet rain entry, externalicing, and rust-resistance design tests. They are not intended toprovide protection against conditions such as dust, internalcondensation, or internal icing.


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NEMA 4 enclosures are intended for indoor or outdoor use primarily to

provide a degree of protection against windblown dust and rain,

splashing water, and hose-directed water. They are not intended to

provide protection against conditions such as internal condensation or

internal icing.

NEMA 4X enclosures are intended for indoor or outdoor use primarily

to provide a degree of protection against corrosion, windblown dust and

rain, splashing water, and hose-directed water. They are not intended

to provide protection against conditions such as internal condensation

or internal icing. (Must specify 304 or 316 material, 304 will be

standard)


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NEMA 7 enclosures are for indoor use in locations classified as Class I,

Groups A, B, C, or D, as defined in the National Electrical Code. NEMA

7 enclosures shall be capable of withstanding the pressures resulting

from an internal explosion of specified gases, and contain such an

explosion sufficiently that an explosive gas-air mixture existing in the

atmosphere surrounding the enclosure will not be ignited. Enclosedheat generating devices shall not cause external surfaces to reach

temperature capable of igniting explosive gas-air mixture in the

surrounding atmosphere. Enclosures shall meet explosion, hydrostatic,

and temperature design tests. Note: If the NEMA 7 enclosure will be

used in an outdoor environment a NEMA 7, 4 enclosure can be

specified for weather proof.


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Wire Separation


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The

Pressure-Volume Card


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What is the P-V Card?

It is a primary tool for determining the reciprocating compressor

performance.

It describes the relationship of the internal pressures and volumes of a

particular end of the compressor cylinder during the compression cycle.


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Ideal Processes

in a Compressor

No losses. Perfect gas.

Isentropic Process.

No piping effects.

Real Processes

in a Compressor

Losses. Real gas.

Polytropic Process.

Piping effects.


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SUCTION INTAKE

VOLUME

DISCHARGE

VOLUME

COMPRESSIONRE-EXPANSION

STROKE OR VOLUME

PRESSURE

DISCHARGE

VALVE OPENSDISCHARGE

VALVE CLOSES

SUCTION

VALVE CLOSES

SUCTION

VALVE OPENS

MAXIMUM CYLINDER

VOLUMEMINIMUM CYLINDER

VOLUME

OUTBOARD

DEAD CENTER

INBOARD

DEAD CENTER

HEADEND

CRANKEND


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LOSS DUE TO

DISCHARGE VALVE

Typical Single Acting P-V Card

LOSS DUE TO

SUCTION VALVE

USEFUL

WORK


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Pressure

Volume

100

300

Valve Losses

Valve Losses

Typical Double Acting PV Card


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Analyzer Analysis Real Cards

200

250

300

350

400

450

500

550

0 25 50 75 100

JC1C cylinder 8 6/30/2000 11:43:05 AM HE Period 10, CE Period 10

Pressure(psig)

Percent swept volume

Poor Pv Trace

Acceptable Pv Trace

100

125

150

175

200

225

250

0 25 50 75 100

JC1C cylinder 2 6/30/2000 11:43:05 AM HE Period 4, CE Period 6

Pressure

(psig)

Percent swept volume


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PV Card

AnyQuestions?

03 Compression Fundamentals

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