Post on 14-Apr-2018
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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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TerminologyTerminology
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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TerminologyTerminology
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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TerminologyTerminology
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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TerminologyTerminology
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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TerminologyTerminology
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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TerminologyTerminology
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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TerminologyTerminology
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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TerminologyTerminology
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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TerminologyTerminology
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 Enclosure Standards
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 Enclosure Standards
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?