PAGE 102 2001 PROCEEDINGSAMERICAN SCHOOL OF GAS MEASUREMENT TECHNOLOGY

FUNDAMENTALS OF GAS CHROMATOGRAPHY,GAS QUALITY & TROUBLESHOOTING

Larry EwingChandler Engineering Company LLC

2001 N. Indianwood Avenue, Broken Arrow, OK 74012

INTRODUCTION

Measurement of the quality of natural gas requires avariety of instrumentation, only one of which is the gaschromatograph. Contractual requirements frequentlydefine the energy content, relative density, and moisturecontent of the gas being sold. The sale of natural gas isperformed on the basis of the heating value per unitvolume of the gas. For these reasons, the industry usesinstruments to monitor the quality of the gas at the pointof sale or at strategic locations along a pipeline. Thefollowing instruments are commonly found in the fieldand in the laboratory:

• Gas Chromatographs• Moisture Analyzers• Gravitometers• Hydrogen Sulfide Monitors• Others

Many of the instruments listed above are portable andmany are installed as online instruments at custodytransfer points. In many cases, sample cylinders are usedto take a sample of the gas to a lab chromatograph foranalysis. If the method used to capture a gaseous samplein the cylinder is not optimal, an inaccurate sample couldbe obtained. For this reason, the need for propersampling systems and portable or online instrumentationhas increased. With modern instrumentation, the analysisof the gas is taking place in the field without transferringthe sample to a laboratory.

In this article we will restrict our discussions to gaschromatography (Refs. 2,6,8) used to measure thecomposition and heating value of the natural gas.

WHAT IS GAS CHROMATOGRAPHY?

Gas chromatography, “color writing”, is a technique usedto separate the components of a gas sample for analysis.After separation, the quantity, or mole %, of eachcomponent is accurately measured. Once the gascomposition has been determined, the heating value,relative density, and other characteristics of the sampleare calculated. Typical natural gas components arenitrogen, carbon dioxide, methane, ethane, propane, isoand n-butane, neo, iso, and n-pentane, and C6+.

The industry requirement for chromatograph repeatabilityis ±0.05%, commonly expressed as ±0.50 BTU per 1000Scf of gas. The accuracy of any instrument does not

exceed the accuracy of the associated calibrationstandard. For this reason, the accuracy of thechromatograph relies on the accuracy of the calibrationgas blend.

All chromatographs include the following majorcomponents:

• Sampling System• Column Oven• Packed or Capillary Columns• Sample Loop• Column Switching Valve(s)• Detector and associated electronics• Carrier Gas• Computer used for data acquisition, calibration,

communication

The specific details and instrument performance varywith manufacturer but the overall operational conceptsare nearly identical.

Sampling System

The chromatograph sampling system is the mostimportant part of the instrument. The sampling systemmust extract a representative gaseous sample from thepipeline, reduce the pressure, filter the sample, preventsample condensation, and efficiently deliver the sampleto the chromatograph. More measurement inaccuraciesoccur due to improper sampling systems than any otherreason. To prevent sampling errors one must study thephase behavior of the gas to determine the temperaturesand pressures at which condensation may occur anddesign accordingly.

Oven

The chromatograph oven usually contains the columns,the column switching valve(s), the sample loop, and thedetector. The temperature of the oven is preciselycontrolled since the performance of the columns anddetector is affected by changes in temperature.

Columns

The packed columns are usually 1-10 meter lengths of 4or 8 mm stainless steel tubing that is filled with coatedsolid material. The choice of the column packing materialdepends on the sample being analyzed and the desiredcomponent separations. After sample injection, the time

2001 PROCEEDINGS PAGE 103AMERICAN SCHOOL OF GAS MEASUREMENT TECHNOLOGY

required for each component to emerge, or “elute”, fromthe columns is proportional to the molecular weight andboiling point of the component. Capillary columns arealso used in lab chromatographs. The advantage ofcapillary columns is speed of component separation; thedisadvantages are column fragility, maintenance, andcost. The difference in the individual component transferrates through the columns causes the componentseparation and allows individual component detection.

BASIC GAS CHROMATOGRAPH

Valves

The sample valve introduces a fixed volume of the gassample into the chromatograph columns. For reliableoperation, the valve must inject a reproducible sampleas rapidly as possible. The sample volume varies withinstrument but is usually less than 0.50 mL at lowpressure. Refer to Figure 1.

FIGURE 1. Typical chromatography valve

For the determination of the gas heating value, there aretwo chromatographic techniques used to separate thecomponents, the “backflush” (BF) and “extendedanalysis” (EA) methods. The BF method is commonlyused to reduce the total analysis time by “backflushing”the heavier components (C6, C7, C8, etc..) to the detector.Since these components would pass through the longmeasuring column slowly, the backflushing techniquereduces the analysis time without sacrificing accuracy.In this way, the C6, C7, and C8 components are combinedand treated as a composite, the C6+ component. Referto Figure 1. The EA method provides the sameinformation as the BF method except that the C6+composite is separated into the individual components.The EA method, when using packed columns, usuallycauses long sample analysis times. When capillarycolumns are used, the EA method can be used effectivelywith great speed. There are advantages to bothchromatographic methods. In most cases, the relativecomposition of the C6+ components does not varysufficiently at a specific location to require the longeranalysis times or the expense of a capillary columnchromatograph.

Although one could assume that an extended analysisof the gas yields more reproducible or accurate results,this is frequently not the case. The technique ofmeasuring a composite C6+ component instead ofseparating C6+ into the myriad of sub-components hasmerit. Not only does backflushing the sample reducethe analysis time and simplify the design of theinstrument, but it provides excellent results. Thefoundation for this observation is that an extendedanalysis of C6+ usually produces over 50 components,all of which have associated measurement inaccuracies.The cumulative error in terms of BTU/Scf usually rivalsthe results from a chromatograph that uses the backflushtechnique. One of the uses of the extended analysis resultat a given location is to allow refinement of the value forthe C6+ mole% heating value.

Carrier Gas

A carrier gas, typically helium, is used to transport thegas sample through the columns. The carrier gas mustbe pure (99.995%) or a degradation of the sensitivity ofthe detector will occur.

Computer

An internal computer provides all of the instrumentcontrol and the integration of the chromatogram peakareas. Once the compositional analysis of the sample iscompleted, the computer calculates the heating value,relative density, and other parameters of the gas usingASTM, GPA, AGA, and ISO methods and componentheating value data (Refs. 1,3,5,9). The computer alsohandles the data communication and storage needs thatare frequently used as a part of SCADA systems.

PAGE 104 2001 PROCEEDINGSAMERICAN SCHOOL OF GAS MEASUREMENT TECHNOLOGY

A PORTABLE INSTRUMENT

FIGURE 2.

A portable chromatograph, also referred to as a “BTUAnalyzer”, is a light-weight, rugged, chromatograph(Figure 2) that is used to analyze a natural gas sampleonsite and determine the gas composition and heatingvalue.

Portable chromatographs have internal sampling systemcomponents that allow the chromatograph to beconnected directly to the gas pipeline sample probe. Inall other respects, a portable chromatograph providesall of the measurement features available in a singlestream online instrument. The analysis results aredisplayed using a digital display and stored in memoryuntil they can be printed at a later time (see report at theend of this article).

WHAT IS AN ONLINE CHROMATOGRAPH?

An online chromatograph is basically the same as aportable chromatograph with the main differences listedas follows (Refer to Figure 3.):

FIGURE 3. Typical Online Chromatograph System

• Automatic analysis cycling• Automatic calibration• Automatic sample selection• Remote control and data communication features• Current loop (4-20 mA) outputs• Parameter alarm features

These instruments and related sample switching systemsare packaged in environmental resistant enclosures(NEMA 4X or equivalent) to allow placement of theinstrument at pipeline locations. Many times theinstrument is located outdoors. The analysis results maybe printed locally and the data is automatically transferredto a central computer system using a data acquisitionsystem known as a SCADA system.

Advanced systems provide features that allow full remotecontrol and diagnostics for the chromatograph. In mostcases, the portable or online chromatograph and relatedequipment are located in Class I, Division 2, Group C &D hazardous environments. For this reason, all equipmentshould be approved for use in these environments by astandards organization such as Factory Mutual Research(FMRC), Canadian Standards Association (CSA),Underwriters Laboratory (UL), or equivalent EuropeanCommunity recognized laboratories (CENELEC).

SAMPLING SYSTEMS

As stated previously, the importance of an efficient andmaintained sampling system can not beoveremphasized. The sampling system for thechromatograph must perform the following functions:

• Extract the sample from the pipeline• Resist the corrosive nature of the gas• Reduce the pressure of the sample without liquid

condensation• Filter the sample• Transport the sample to the chromatograph• Control the sample flow rate and provide

appropriate sample venting

The sample probe must not be located near flowdisruptions (orifice plate, elbow, etc.) that will induce flowturbulence and cause inaccurate samples to becollected. The end of the sample probe must be locatedin the center 1/3 of the pipeline. All components of thesampling system must be made from 300 series stainlesssteel to resist possible corrosive attack from H2S, CO2,and water. The sample pressure must be reduced usinga heated sample regulator or an insertion probe/regulatorif the phase behavior of the gas indicates condensationof liquids due to the Joule-Thomson effect or low ambienttemperatures. Normally, a coalescing or membrane filteris used to remove particulates and entrained liquids fromthe sample. For this reason, the sampling system andrelated lines may require heating to prevent liquidcondensation problems. If the ambient temperatureapproaches the gas hydrocarbon dew-pointtemperature, the sampling system must be heated orburied. The sampling system design should provide ashut-in valve, a sample flow control valve, bypass loops,and venting. The specific requirements will vary with thechoice of components and the chromatographrequirements. Refer to Figure 4.

2001 PROCEEDINGS PAGE 105AMERICAN SCHOOL OF GAS MEASUREMENT TECHNOLOGY

MEMBRANEFILTER

GLYSORBFILTER

TOANALYZER

TO SAFEAREA VENT

PROBE/REGULATOR

FIGURE 4. Typical Sampling System

SAMPLE SWITCHING

An online chromatograph is used to analyze samplesfrom different pipelines using a sample switching system.Each pipeline must have a sample probe, regulator, filter,and related hardware. The design of the sample switchingsystem varies with manufacturer but the principle ofoperation does not change. The sample switchingsystem must provide a sample from each pipeline sampleprobe to the chromatograph without any mixing or “carry-over” from the previous sample. The sample switchingsystem must also provide a connection for thechromatograph calibration gas and a connection for asample cylinder if required. The computer in thechromatograph can be programmed to sequence thesample solenoid valves as required.

Typical components used in a sample switching systemare intrinsically safe 3-way solenoid valves. Thesesolenoid valves may be used in the “double block andbleed” (DBB) configuration. The DBB method preventssample mixing due to the possibility of an internallyleaking solenoid valve.

CALIBRATION

The accuracy of the results from a chromatograph istotally dependent on the accuracy of a certified blend ofgases known as “calibration gas”. A calibration gas blendmay be obtained from equipment suppliers or sourceswith NIST traceable gravimetric gas mixing equipment.A certified analysis report is included with each bottle ofcalibration gas. Most analysis reports will also include astatement of heating value and relative density atstandard temperature and pressure. Ideally, thesesources should provide proof of traceability to a primarystandard. The concentration of each component in thecalibration gas should be similar to the pipeline gas beingmeasured. If the temperature of the calibration gas blenddrops below the hydrocarbon dew-point, condensationof the heavier components in the calibration gas willoccur. Although the actual minimum temperature willdepend on the composition and pressure of the blend,as a general rule, the temperature of the gas should neverbe allowed to drop below 50˚F. In some areas, with certainblends, the bottle may require a heater.

A chromatograph is calibrated by analyzing thecalibration gas and relating the individual component

peak areas to the known component concentration inthe calibration gas. A constant, or “response factor” (RF),is determined for each component in the calibration gas.The following equation describes the response factorcalculation:

Comp. ConcentrationRF =Peak area

Once the chromatograph has been calibrated, theindividual response factors are used to determineunknown component concentrations from measuredpeak areas. The frequency of calibration of achromatograph will depend on manufacturerrecommendations. Advanced online chromatographs areprogrammed to automatically recalibrate atpredetermined time intervals. In many cases, custodytransfer contracts require chromatograph recalibrationevery 24 hours although most chromatographs do notrequire this frequency of calibration. In many cases,calibration every 30 days is adequate.

HEATING VALUE CALCULATION

Once the chromatograph has determined the pipelinegas composition, the heating value, relative density, andcompressibility values are calculated using the internalcomputer. Each pure component in the natural gas hasa known heating value and density. These heating valuesare obtained from tables published in current GPA, AGA,or ISO standards.

The heating value may be determined from the gascompositional analysis using the following equations:

HidealHeating Value =Z

n

Hideal = ∑ xiHii+l

where,Hideal = Ideal heating valuexi = Component concentrationHi = Component heating value/unit volumeZ = Compressibility of sample

Similarly, the relative density may be determined fromthe gas compositional analysis using the followingequations:

Hideal

Heating Value =Z

n

Gideal = ∑ xiGii=l

PAGE 106 2001 PROCEEDINGSAMERICAN SCHOOL OF GAS MEASUREMENT TECHNOLOGY

where,

Gideal = Ideal relative densityxi = Component concentrationGi = Component relative densityZa = Compressibility of airZ = Compressibility of sample

The compressibility of the gas may be determined usingan older method defined as NX-19 or using the morerecent AGA 8 method (Ref. 5). The AGA 8 method usesthe composition of the gas in the determination of gascompressibility. Due to the complexity of the calculation,a relatively powerful computer is required to use thecurrent AGA 8 method.

Since the heating value is expressed as kJ/m3 or BTU/Scf, the volume of the gas must be considered.Unfortunately, there is not wide agreement for the valuesof standard pressure and temperature. In the U.S.A., thestandard or “base” pressure standard may vary from14.65 to 14.73 Psia depending on location. In Europe,the standard temperature standard varies. Mostchromatograph computers are configurable for differentstandard temperatures and pressures. For this reason,before comparing heating value results from differentchromatograph systems, verify that the standardconditions at which the gas volume is calculated are thesame.

The heating value of natural gas is reported as “gross”,or “net” values:

Gross heating values

The “gross” gas heating values are reported as “dry” or“saturated” values. The “dry” result assumes that thegas contained no water prior to combustion. The“saturated” result assumes the gas is saturated withmoisture at standard temperature and pressure prior tocombustion. The saturated result accounts for thedifference in energy released during a complete and idealcombustion of the gas that includes the heating value(enthalpy of condensation) of water. All water formed bythe reaction condenses to a liquid (Ref. 7). Refer to thesample analysis report at the end of this article for acomparison of the gross “dry” and “saturated” results.

Net heating value

The “net” heating value represents the energy releasedfrom the total, ideal combustion of the gas at standardtemperature and pressure where all the water formed bythe reaction remains in the vapor state. The condensationof excess water vapor does not contribute to the heatingvalue (Ref. 7).

In both cases, gross or net values, the difference betweenthe “ideal” and “corrected” values referenced on typicalchromatograph reports is due to the effect ofcompressibility of the gas.

DATA COMMUNICATION

Online chromatographs must be able to transmit theanalysis data to a host computer, flow computer, or otherprocess using serial (Modbus) and current loop (4-20 mA)interfaces. Advanced chromatographs may be remotelycontrolled and data acquired using serial (RS232 orRS485) communication and appropriate software (Figure5). The current loop (4-20 mA) outputs from the onlinechromatograph may also be used to transmit defineddata values to a host computer, flow computer, controlroom, process, or SCADA system. The data gatheringsystem design will vary with installation and instrumentcapabilities.

TROUBLESHOOTING

The following items must be considered as a part ofoperating and maintaining a chromatograph.

Carrier Gas: Poor quality carrier gas or leaks in the carriergas system are responsible for more chromatographproblems than any other cause. Most chromatographsused for natural gas analysis require “zero-grade”(99.995%) helium as a carrier gas. Problems with achromatograph may occur when a depleted carrier gasbottle is replaced. The problems may be the result of acarrier gas leak that entrains air, low purity helium,contaminants, or air trapped in the carrier gas tubingand regulator. Air in the carrier gas will change thechromatogram baseline and may oxidize the filamentsin the detector, causing premature detector failure or lossof sensitivity and stability.

2001 PROCEEDINGS PAGE 107AMERICAN SCHOOL OF GAS MEASUREMENT TECHNOLOGY

Temperature: All chromatographs have an internal oventhat is maintained at a very constant temperature. Forthis reason, optimum accuracy will be achieved if widevariations in ambient temperatures are avoided. As ageneral rule, a temperature controlled environment(±20˚F) will improve the reliability and longevity of theinstrument.

Sampling System: If the sampling system is deficient,the analysis results will be unpredictable and thechromatograph may be contaminated by samples thatcontain liquids (heavy hydrocarbons, water, glycol, etc.).In most instances, to repair the chromatograph involvesdisassembly and a thorough cleaning. Thechromatograph columns may also require replacementif they are contaminated.

Vents: All chromatographs have vent ports for the carriergas and sample. Some chromatographs require aconstant flow of the sample through the sample loop.Other chromatographs require brief sample flow times.In any case, proper venting of the sample to a safe areais important. Major variations in the backpressure of theventing system may cause operational problems withthe chromatograph since the sample loop volume usedby the chromatograph is dependent on the samplepressure. The sample loop pressure will be affected bychanges in vent backpressure, atmospheric pressure,or a change in the flow rate of the sample through thesample loop. Minor changes in the sample volume donot cause analysis inaccuracy since the effect of samplevolume is removed by “normalizing” the data.

Flow Adjustments: The carrier gas flow rates mayrequire periodic adjustments. Typically, these flow ratesmeasure less than 20 mL/min and adjustments requirethe use of a low flow measurement instrument.

Usually, there are two adjustments of the carrier gas flowrates, the “measuring” and “reference” adjustments.Although the specific requirements will vary withequipment, the measuring and reference flow rates areadjusted to be equal. Changes in these flow rates maycause misidentification of components, changes insample analysis time, valve timing shifts, and calibrationchanges. Once a chromatograph has been installed andcalibrated, changes in the carrier gas flow rates shouldbe avoided.

Valve Timing and Integrator Gates: Somechromatographs require valve timing and integrator gateadjustments. These instruments can be more difficult tomaintain due to the critical nature of these adjustmentsand the multiple valves. The valve timing adjustmentsdefine the time intervals for the column valve(s) switching.The integrator gates enable or inhibit the integrator atthe anticipated start or end of a peak. These adjustmentsmust be made after the carrier gas flow rate and oventemperature is set. More recent chromatograph designsprovide a single valve time adjustment and the integratorgates are assigned automatically during calibration.

During the troubleshooting of a chromatograph, a stripchart recorder or a diagnostic report containing peakdata is commonly used. The shape of the peaks andrelative component elution times and valve switches areused to diagnose problems and make adjustments.

Comparing the reports with past records usually providesinsights into problems. Analyzing a known gas blendsuch as calibration gas is useful when evaluating theperformance and accuracy of the instrument.

CONCLUSION

Gas chromatography is in common use for the directmeasurement of the heating value of natural gas. Theadvantages of gas chromatography include improvedrepeatability and accuracy, and the ability to measurethe gas composition directly. Once the gas compositionis known, the gas heating values, relative density,compressibility, and liquid volumes may be determined.

Online or portable chromatographs may be used in theClass I, Division 2, Group C and D environments that arefound near gas pipeline installations. Chromatographdesigns that have been approved by FMRC, CSA, UL,or CENELEC are usually the best choice.

Gas chromatographs are available as portable or onlineinstruments. The portable version of the instrument isused to make onsite gas composition measurements,eliminating the need for sample cylinders and possiblesampling problems. The analysis results are storedinternally and communicate with SCADA systems usingthe industry standard Modbus protocol or printed usingcommon printers. Portable chromatographs must beeasy to use, reliable, and designed to withstand roughtreatment.

Potential problems with gas chromatography may beavoided through adequate attention to the samplingsystem design.

Advanced systems have state-of-the-art software anddata communication features. It is not unusual to havecomplete control of a remote online chromatograph byusing a computer, modems, and communicationsoftware.

The methods and heating values associated with gaschromatography governed by AGA, GPA, ASTM, and ISOare very similar with the principal differences being thevalues of standard temperature and pressure (Refs.1,3,5,9). Periodically, updated heating values arepublished causing a need to adjustments to theconstants used in the chromatographs.

The choice of a specific online or portable chromatographmust be made on the basis of performance, reliability,manufacturer support, ease of use, and cost. Theperformance issue usually involves a decision onrepeatability, C6+ backflush analysis, extended analysis,

PAGE 108 2001 PROCEEDINGSAMERICAN SCHOOL OF GAS MEASUREMENT TECHNOLOGY

and analysis cycle time. The reliability issue is paramountsince the instrument may be used continuously 24 hoursper day for years and downtime and repairs areexpensive. The ease of use of the instrument is importantsince it reduces the amount of operator training requiredto use the instrument efficiently and reduces the chanceof operator error. Ideally, the gas chromatograph (BTUAnalyzer) operator will not require extensive training inchromatography. The cost of the chromatograph systemsvaries with product complexity.

GLOSSARY

• Gas composition: The chemical content of thenatural gas. A natural gas will contain varyingamounts of methane, ethane, propane, nitrogen,carbon dioxide and other components.

• Heating value: The energy content of the naturalgas. The units are BTU/Scf or kJ/m3 and arereported as Net, Dry, or Saturated valuesdepending on the natural gas moisture content.

• Relative density (Specific gravity): The ratio ofthe density of the gas to the density of dry air,with normal CO2 content, at the sametemperature and pressure.

• BTU (British Thermal Unit): A measure of energy.A BTU is the defined International Tables Britishthermal unit. The term is defined as the quantityof heat required to raise the temperature of onepound of water at, or near its point of maximumdensity.

1 Btu/lbm = 2.326 J/g1 lbm = 453.59237 g

• Standard temperature and pressure (STP): Thestandard (reference) temperature and pressureat which gas volumes are calculated. In theU.S.A., the base temperature is 60?F and thebase pressure will vary (14.65, 14.696, 14.73Psia) depending on local standards. Whencomparing gas volumes, verify that the baseconditions are the same.

• Joule-Thomson Effect: The cooling that occurswhen a natural gas at high pressure is throttledthrough an orifice to a lower pressure. Thecooling, in many cases, will cause condensationof liquids (water and liquid hydrocarbons).

• Dew-point: The dew-point represents thetemperature and pressure at which liquid wateror hydrocarbons condense from a gas. The dew-points for water and hydrocarbons in natural gasexist at different temperatures and pressures.The relationship between dew-point (water) andmoisture content may be obtained from ASTMMethod D1142.

REFERENCES

1. GPA 2145 - “Table of Physical Constants of ParaffinHydrocarbons and Other Components of NaturalGas”.

2. GPA 2261 - “Analysis for Natural Gas and SimilarGaseous Mixtures by Gas Chromatography”.

3. GPA 2172 - “Calculation of Gross Heating Value,Relative Density and Compressibility Factor forNatural Gas Mixtures from Compositional Analysis”(except AGA 8 is used for supercompressibility).

4. GPA 8173 - “Method for Converting Mass of NaturalGas Liquids and Vapors to Equivalent LiquidVolumes”

5. AGA Transmission Measurement Committee ReportNo.8 “Compressibility and Supercompressibility forNatural Gas and Other Hydrocarbon Gases”.

6. ASTM D-1945 (Volume 5.05, Gaseous Fuels; Coaland Coke, 1990) - “Standard Method for Analysis ofNatural Gas by Gas Chromatography”.

7. ASTM D-3588-91 (Volume 5.05, Gaseous Fuels; Coaland Coke, 1992) - “Standard Practice for CalculatingHeat Value, Compressibility Factor, and RelativeDensity (Specific Gravity) of Gaseous Fuels”

8. ISO 6568, Natural gas - Simple analysis by gaschromatography, 1981

9. ISO 6976, Natural gas - Calculation of calorific value,density and relative density, 1983

TYPICAL ANALYSIS REPORT

The following report is representative of the informationthat is typically provided by an online chromatographused to determine the composition, heating value, andrelative density of a natural gas sample.

BTU AnalyzerTest time: Mar.10 99 18:11 Calibration #: 3Test #:165 Stream#:1 Location No. 990308

Standard/Dry Analysis Saturated /Wet AnalysisMole% BTU* R.Den.* GPM** Mole% BTU* R.Den.*

Methane 95.027 962.02 0.5264 — 93.373 945.28 0.5172Ethane 2.420 42.92 0.0251 0.6471 2.378 42.17 0.0247Propane 0.667 16.83 0.0102 0.1839 0.656 16.53 0.0100i-Butane 0.160 5.21 0.0032 0.0523 0.157 5.12 0.0032n-Butane 0.134 4.37 0.0027 0.0421 0.131 4.29 0.0026i-Pentane 0.051 2.03 0.0013 0.0185 0.050 1.99 0.0012n-Pentane 0.023 0.93 0.0006 0.0084 0.023 0.91 0.0006 (C6+) 0.079 3.99 0.0025 0.0339 0.077 3.92 0.0025Moisture 0.000 0.00 0.0000 — 1.740 0.88 0.0108Nitrogen 0.371 0.00 0.0036 — 0.365 0.00 0.0035 (CO2) 1.070 0.00 0.0163 — 1.051 0.00 0.0160Total 100.00 1038.3 0.5917 0.9861 100.0 1021.1 0.5922*Uncorrected for compressibility at 60˚F & 14.730PSIA**Liquid volume reported at 60˚F

Standard/Dry Analysis Saturated/Wet AnalysisMolar Mass = 17.138 17.153Relative Density = 0.5928 0.5934Compressibility Factor = 0.9978 0.9977Heating Value = 22938 Btu/lb 22538 Btu/lbHeating Value = 1040.6 Btu/CF 1023.5 Btu/CFAbsolute Gas Density = 45.3666 lbm/1000CF 45.4117 lbm/1000CFUnnormalized Total: 100.038Last Calibrated with Calgas of 1050.3 Btu/CF Jan.10 99 16:31C6+ Last Update: Mar.02 98 14:11C6+ BTU/CF 5065.8, C6+ lbm/Gal 5.6425, and C6+ Mol.Wt. 92.00