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Sampling Method GPA 2166
Prepared by :
Candra Aditya Wiguna 6512010005
Magda Dwi Apriani 6512010014
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Agenda
Scope
Important Note
Definition
Principles of Sampling
Safety
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Scope of GPA 2166
Purpose
To recommend procedures for obtaining representative samples from flowing natural gas stream
Not Included
Two-phase sample
Composite gas sample
Vacuum sources
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Note of GPA 2166
Hydrogen Sulfide
Should be analyzed on site
Moisture
Should be analyzed on site or using moisture saturation calculation
Dew Point
Determine the dew point using chilled mirror test (the gas portion at two-phase system is at hydrocarbon dewpoint)
Temperature setting
Temperature of the line must 30F (17C) above the calculated hydrocarbon dewpoint
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Note of GPA 2166
Equipment
All equipment between sample valve and sample cylinder must be maintained above hydrocarbon dewpoint
Sample conditioning downstream and sample purging must be maintained above hydrocarbon dewpoint
Regulator must be heated due to temperature decrease because of the JT process
Flow control must be located at the outlet of sample container
Flow control must be located at the end of an extension tube (pigtail) to thermally isolate the cooling effect caused by JT process
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Definitions
Absorption
Natural gas constituents are dissolved into a liquid or solid that is not considered to be part of the mixtures liquid phase
Adsorption
A thin film of molecules adheres to aliquid or solid surface
Chilled mirror test
Used to determine dew points (water and/or hydrocarbon) by passing the natural gas over amirror while gradually reducing the temperature of the mirror until condensation forms in the surface of the mirror
De-sorption
Adsorbed or absorbed molecules are release from a liquid or solid surface
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Definitions
Floating Piston Cylinder
A sample container which has moving piston that has sample pressure on one side of the piston, balanced by a pre-charge pressure on the other side of the piston
Flow-Proportional Composite Sampling
The process of collecting gas over a period of time at a rate that is proportional to the pipeline flow rate
Gas Sampling Separator
A device in the sampling system used to remove contaminant liquids from the natural gas sample
Multi Phase Flow
Two or more phase such as vapor and liquid in the sample stream
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Representative Gas Sample
A gas sample that is compositionally identical, or as near to identical, as possible to the sample source stream
Sample Container
Any container used to hold a natural gas sample
Sample Probe
A device extending through the meter tube or piping into the stream to be sampled
Single-Phase Flow
For natural gas, natural gas flowing at the temperature above the Hydrocarbon Dew Point and free of compressor oil, water, or other liquid or solid contaminants in the flow stream
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Principles of Sampling
Purging Fill and Empty Method
Purging Controlled Rate Method
Evacuated Container Method
Reduced Pressure Method
Helium Pop Method
Glycol or Water Displacement Method
Floating Piston Cylinder Method
Portable or On-Line Gas Chromatograph
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Aparatus
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Aparatus
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Aparatus
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Aparatus
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Principles of Sampling Fill and Empty Purge Cycles
Method
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Principles of Sampling
Maximum gas pressure in container, psig (kPa gauge)
Number of fill and empty cycles
15-29 (100-200) 13
30-59 (200-405) 8
60-89 (405-615) 6
90-149 (615-1025) 5
150-500 (1025-3450) 4
>500 (>3450) 3
Fill and Empty Purge Cycles Method
Number of Purge Cycles = log(X)Y X = atmospheric pressure + fill pressure (psia) Y = maximum allowable mole fraction of contaminants
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Principles of Sampling
Purge Rate Controlling Method
Hig
her
Volu
me
Longer Purging
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Reducing Pressure Method
Reducing pressure from high pressure line to sample line system
Sample not allowable to cross the two phase area
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Helium Pop Method
He
5 psig Desired pressure
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Water and Glycol Displacement Method
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Water and Glycol Displacement Method
Water and Glycol can cause absorbtion and desorbtion
Use Glycol as displacement medium
When temperature
is below 32F (0C)
Use Water and Glycol as displacement medium
When temperature
is above 32F (0C)
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Seals or Lubricant can absorb sample component
Seal or Lubricant must be inert
Floating Piston Cylinder Method
Open sample valve
Open purge valve
Close purge valve
Open sample inlet valve
Adjust pressure
Adjust pressure
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Portable Gas Chromatography
Must using a regulator
Must heating the sample tubing and regulator
Use stainless steel and nylon 11 tubing
Separator in downstream sample conditioning must be heated and cleaned regulary
On-line Gas Chromatography
Must reduce pressure at or close to the sample probe to reduce
transfer sample lag time
Sampling system must be heated
Using bypass to get the current sample
Using membrane filter to protect GC from the
unwanted liquid
Portable and On-line GC Method
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Handling
Sample container should be stored on shelves or racks
If sample container is known to have leaked, secure another sample. If another sample is unavailable, follow company procedure
Sample container should be heated to a minimum of 20OF (11oC) above sample source temperature. Sample Containers should be held at temperature for at least 2 hours prior to sample analysis
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Safety
No. Activity Hazard Consequences Control
1 Sampling Natural Gas
Hydrocarbon vapors
Can cause fire Can cause
explosion
Technician should be trained properly
Dangerous component (H2S)
Can cause health hazards
Replacing breathing air
Technician should be trained properly
Auto-ignition and air mixture
Explosion Dont open valve rapidly
High Pressure Can injure the technician
Technician should be trained properly
2 Transportation Pressure Can cause leakage of the sample
Containers should meet appropriate pressure and pressure relief requirements
Those who transport or ship sample containers must be trained
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Safety Hazard Preventive Hydrocarbon vapors are flammable and can be explosive
Technician should be trained properly in the safe handling of natural gas
Natural gas samples may contain component that cause health hazards (H2S) or replacing breathing air
Heating in laboratory analysis Ensure that any heating device meets the requirements
Transportation Containers should meet appropriate pressure and pressure relief requirements. Those who transport or ship sample containers must be trained in the current regulations.
Auto-ignition of natural gas and air mixtures in gaas sample cylinders
Dont open valves rapidly
High pressures Technician must be properly trained to work with compressed gasses. Sampling equipment shoul be rated equal to or higher than the highest expected pressure.pressure reduction from pipeline must be carried out with appropriately designed pressure regulators. Pressure relief devices should be used to protect from over pressure conditions
No. Activity Hazard Consequences Control
3 Analysis Heat Injured the analyst
Ensure that any heating device meets the requirements