03-Gas Compression Fundamentals
Transcript of 03-Gas Compression Fundamentals
Gas Gas CompressionCompression
FundamentalsFundamentals
2
TERMINOLOGYTERMINOLOGY(Jargon)
Gas Compressor Industry Language
Compression = The act of pressing or compacting into a smaller space.
3
TerminologyTerminologyR/Rc = ratio of compression
Ps/P1 = suction pressure
Pd/P2 = discharge pressure
Ts/T1 = suction temperature
Td/T2 = discharge temperature
Ta = ambient temperature
Hp = horse power
HE = head end
CE = crank end
VE = volumetric efficiency
K = ratio of specific heats of a particular natural gas - a thermal dynamic value
4
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.
5
TerminologyTerminologyFinding 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.
6
TerminologyTerminologyFinding 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
7
TerminologyTerminologyFinding Approximate HP Requirement:
To find the HP required for a two
stage unit (example 2):
Take the square root of the ratio found earlier:
Rc = 17.71 = 4.20
HP = 21 x Rc x S x Q
HP = 21 X 4.2 X 2 X 1
HP = 176.4
8
TerminologyTerminology
SA = Single Acting - The act of compressing on one end of
the compressor cylinder.
DA = Double Acting - The act of compressing on both ends of
the compressor cylinder.
9
Terminology
Clearance Volume = The volume remaining in the compressor cylinder at the end of the discharge stroke. Normally expressed as a % of piston displacement.
Displacement = Area of piston X length of stroke X # of strokes per minute. For DA
compressors, the displacement on the CE is less than the HE due to the rod area. Normally expressed in cubic feet per minute or CFM.
10
Terminology
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 = 30°F approach means the cooler will cool the gas to 130° when ambient
temperature is 100°F.
11
TerminologySwept 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
12
TerminologyTerminology
Total Swept Volume Example (DA):
6” Diameter x 7” Stroke2.5” 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.
13
TerminologyTerminologyUnits 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 & 60°F
14
TerminologyTerminology
In-Hg = inches of mercury pressure
= can be a manometer or mercury filled gauge, used where pressures are low
& extreme accuracy is desired
= 1” Hg = .491 PSI
In-H2O = inches of water pressure
= usually a manometer filled with water
= used for measuring very low pressure
= 1/13.6 as heavy as mercury
13.6” of H2O = 1” of Hg = .491 PSI
15
TerminologyTerminology
Temperature:
Temperature =
A measure of molecular energy…the higher the temperature the more molecular energy.
Degrees Fahrenheit (°F) =
Temperature scale where, at sea level, the freezing
point of water is 32° & the boiling point is 212°. The
distance between these two points is 180°.
16
Terminology
Temperature:
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°.
Temperature range:
Centigrade = 100° = 5
Fahrenheit = 180° = 9
17
TerminologyTerminologyTemperature:
Converting from ° F to ° C expressed as follows:
° C = 5/9 X (° F - 32)
Example: Convert 100° F to ° C
° C = 5/9 X (100 - 32)
= 5/9 X 68
= 37.8° C
18Separable Engine
VConfiguration
InlineConfiguration Horizontal Opposed
Configuration
TerminologyTerminology
19
Separable Compressor Frame
ClickHere
TerminologyTerminology
20
Compressor
Engine
Separables Coupled
TerminologyTerminology
21
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
22
Rod Load DefinitionsRod 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 360° rotation 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 being used.
23
2.5”
ERL CompressionERL Compression
Pd=814.7 PSIA Ps=214.7 PSIA
Area of piston in square inches times dischargepressure, 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 #
24
2.5”
ERL TensionERL Tension
Pd=814.7 PSIAPs=214.7 PSIA
Area of piston in square inches, minus area of rodtimes 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 #
25
Piston Rods Exceeding Rod LoadPiston Rods Exceeding Rod Load
26
Rod ReversalRod Reversal
Crank PinCrosshead Pin
Connecting Rod
Piston Rod
Crosshead
Oil
Oil
27
• 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) = 80°F– Ambient Temp (Ta) = 100°F– Discharge Temp (Td) required
approach = 20°F– Altitude = < 1500’– Atmospheric Pressure = 14psi– Specific Gravity = 0.64– “N” value = 1.26– Sweet Gas
28
AnyQuestions?