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Training gas chromotograph
 

Training gas chromotograph

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    Training gas chromotograph Training gas chromotograph Presentation Transcript

    • Training Seminar: REV. 10/16/02REV. 10/16/02 Sample Conditioning of Natural Gas for “On-Stream” BTU Analysis“On-Stream” BTU Analysis Presented By:
    • Analyzer Natural Gas Sample Source •The analyzer can not tolerate the natural gas sample when delivered under the pipeline conditions. •The sample gas must be extracted, transported, and conditioned so that it is compatible with the analyzer – including: - Pressure control - Flow control - Particulate removal - Liquid removal 2
    • 3 The sample system also includes other functions such as: •Stream multiplexing (switching) •Calibration gas control A sample (conditioning) system is utilized for extracting,Conditioning, and transporting the sample gas to an analyzer
    • The sample needs to be made compatible with the analyzer,therefore we must first understand the analyzer before designing a sample system for one. 4 During the sample conditioning process the sample composition must be preserved.
    • In this case, the analyzer is a Gas Chromatograph (GC) The objective is to determine the composition of the natural gas in order to compute: -The heating value (BTU determination) -The physical properties used to correct the flow (volume) of the natural gas stream ( compressibility, viscosity, specific gravity, etc.) This is very important since it has a direct impact on profitability. 5
    • -Sample flows thru the inject valve sample loop. (PURGE MODE) -Sample injected previously is being analyzed . (SEPARATED AND DETECTED) 6 Protection of “on line” Gas chromatographs (GC) for gas stream analysisProtection of “on line” Gas chromatographs (GC) for gas stream analysis INDEXINDEX
    • -Sample flows is shut off by SSO valve. -Sample loop is referenced to atmospheric pressure. 7 Protection of “on line” Gas chromatographs (GC) for gas stream analysisProtection of “on line” Gas chromatographs (GC) for gas stream analysis INDEXINDEX
    • -Sample is injected into the carrier gas stream where it will become separated into its individual components and detected. (INJECTED MODE) -Sample gas flows into and out of inject valve but does not flow thru the sample loop. 8 Protection of “on line” Gas chromatographs (GC) for gas stream analysisProtection of “on line” Gas chromatographs (GC) for gas stream analysis INDEXINDEX
    • -Sample flows thru the inject valve sample loop. (PURGE MODE) -Sample injected previously is being analyzed . (SEPARATED AND DETECTED) 9 Protection of “on line” Gas chromatographs (GC) for gas stream analysisProtection of “on line” Gas chromatographs (GC) for gas stream analysis INDEXINDEX
    • Protection of “on line” Gas chromatographs (GC) for gas stream analysisProtection of “on line” Gas chromatographs (GC) for gas stream analysis
    • Protection of “on line” Gas chromatographs (GC) for gas stream analysisProtection of “on line” Gas chromatographs (GC) for gas stream analysis
    • Protection of “on line” Gas chromatographs (GC) for gas stream analysisProtection of “on line” Gas chromatographs (GC) for gas stream analysis
    • Protection of “on line” Gas chromatographs (GC) for gas stream analysisProtection of “on line” Gas chromatographs (GC) for gas stream analysis
    • Protection of “on line” Gas chromatographs (GC) for gas stream analysisProtection of “on line” Gas chromatographs (GC) for gas stream analysis Multiple StreamMultiple Stream
    • Protection of “on line” Gas chromatographs (GC) for gas stream analysisProtection of “on line” Gas chromatographs (GC) for gas stream analysis Multiple StreamMultiple Stream Double Block and BleedDouble Block and Bleed Why use a Genie on each stream? *not contaminate common line. *block all streams because of one bad line. Why have multiple streams to one analyzer?
    • Double Block and Bleed conceptDouble Block and Bleed concept Block valves “opened” Bleed valve “closed” Block valves “closed” Bleed valve “opened” 16
    • •A keen understanding of the physical relationship between liquids, gases, and surfaces which contain them is a must for anyone involved with sample conditioning. •The following slides are designed to help you understand these physical relationships. 17 Basic Physics and Chemistry Involved in Sample Conditioning
    • Definition of terms commonly used in sample conditioning for “on-stream” BTU analysis. Absorption- the act of taking up or assimilating Adsorption- attraction of a thin layer of gas or liquid molecules to a surface Aerosol- a microscopic droplet of liquid suspended in a gas BTU- British thermal unit. A unit for measuring the heating value of natural gas Coalescing- bringing together small (aerosol) droplets of liquid to form large drops or a film 18
    • Condensed liquid- liquid originating from the condensation of a vapor or gas Desorption- to release from a condition of being absorbed or adsorbed Droplet- small drop of liquid Entrained liquid- liquid in any form carried along or suspended in a stream of natural gas 19 Condense- to change from a gas or vapor to a liquid Equilibrium-a dynamic state of balance where the Population of molecules per unit volume in the vapor Space remains constant
    • Gas – any substance that has no shape or size of its own and can expand without limit Gas phase- a phase consisting exclusively of gas and/ or vapor. Liquid in any form,even though it may be suspended in a gas is not a part of the “gas phase”. Hydrocarbon dew point- the temperature, at any given pressure, at which hydrocarbon liquid initially condenses from a natural gas mixture 20 Free liquid- liquid in any form – A microscopic aerosol droplet exhibits the same characteristics as a large pool of liquid Fluid- anything that flows in any way, either a liquid or a gas
    • Latent heat- the heat required to change a liquid to a gas or vapor, without a change of temperature. It is also the heat released in the reverse process. Lean gas- gas containing a relatively small quantity of heavy hydrocarbon vapor and having an average or low BTU value Liquid- a liquid is composed of molecules that move freely over each other so that it has the shape of its container , like a gas, but, unlike a gas it has a definite volume 21 Joule-Thomson effect – the cooling that occurs when a highly compressed gas is allowed to expand in such a way that no external work is done.
    • Natural gas- a naturally occurring mixture of hydrocarbon and nonhydrocarbon gases found in porous geological formations. Its main constituent is methane. Phase- a state of matter such as solid, liquid, gas or vapor 22 Liquid vapor- see vapor Membrane- a thin sheet of semi-permeable synthetic or natural material Liquid forms- the geometric shape that liquid may be found in natural gas such as film, droplet or aerosols and pools
    • 23 Rich gas- natural gas containing a large amount of heavy hydrocarbon vapor and having an elevated BTU value Sample train- see sample system Sample transport system- all associated pipe, tube, fittings and hardware such as filters, rotameters, etc. which transport a gas sample from its source to an intended destination such as an analyzer or sample Phase-separating membrane- a membrane adapted for separating entrained liquid in any form from gases. Gas passes readily through membrane leaving behind any liquid that may have been entrained
    • Vapor-a substance, which is normally liquid at ambient temperature and atmospheric pressure but becomes a gas at elevated temperature or lower pressures Wet gas- a gas which contains a high concentration of water vapor Volatility- The ease at which a liquid vaporizes. 24 Sample system- all components associated with extracting,transporting, and conditioning of a natural gas sample
    • Joule-Thomson effect Reduction of pressure cools a gas due to a phenomenon known as the Joule-Thomson effect. The cooling effect may lower the gas temperature below its dew point. When the temperature of a gas drops below its dew point condensation occurs. This in turn causes changes in the gas phase composition. Restriction High Pressure Lower Pressure 25
    • Demonstration of “Joule-Thomson effect” Atmospheric Pressure PROPANE VAPOR 125-150 PSI Temperature of gas, after pressure drop, is slightly lowered by the J.T. effect. LIQUID PROPANE 26
    • Demonstration of “Latent Heat of Vaporization” Atmospheric Pressure 27 PROPANE VAPOR LIQUID PROPANE 125 - 150 PSI Temperature of gas, after liquid vaporizes, is substantially lower
    • Nearly 1000 BTUs required to vaporize 1lb of H2O One BTU = heat to change 1lb of H2O 1 o F Latent Heat of Vaporization Latent heat of vaporization is the most frequent of valve/regulator “freeze ups” in sample systems. “Freeze ups” indicate liquid is present, composition errors are likely to occur. 28 Conclusion:
    • A pure liquid and its vapor – No other gases presentA pure liquid and its vapor – No other gases present •Equilibrium is a dynamic state of balance where the population of molecules per unit volume in the vapor space remains constant. •The rate at which molecules pass from the liquid to the gas phase is dependent on the temperature •Increasing the temperature increases the rate and conversely, lowering the temperature decreases the rate. •The pressure caused by the gas phase molecules striking the containment vessel surface is the vapor pressure. Liquid Phase Gas/Vapor PhaseGas/Vapor Phase Gas Molecules Leaving and Returning to the Liquid 29
    • A pure liquid and its vapor – Other gases presentA pure liquid and its vapor – Other gases present •Number of vapor molecules in the Gas/Vapor Phase depends on the liquid’s vapor pressure. •Vapor pressure depends on temperature. •Concentration of vapor depends on system pressure. Liquid Phase Gas/Vapor Phase Interface 30
    • Pressure and temperature changes in a gas containing a mixture of liquids alter the gas phase composition 31 Gas / Vapor Phase Liquid Phase HC liquid #1 HC liquid #2 HC liquid #3
    • ““PressurePressure Decreases”Decreases” Pressure and temperature changes in a gas containing a mixture of liquids alter the gas phase composition 32 Gas/Vapor Increases Gas / Vapor Phase Liquid Phase HC liquid #1 HC liquid #2 HC liquid #3
    • Pressure and temperature changes in a gas containing a mixture of liquids alter the gas phase composition 33 Gas / Vapor Phase Liquid Phase HC liquid #1 HC liquid #2 HC liquid #3
    • ““TemperatureTemperature Increases”Increases” Pressure and temperature changes in a gas containing a mixture of liquids alter the gas phase composition 34 Gas/Vapor Increases Gas / Vapor Phase Liquid Phase HC liquid #1 HC liquid #2 HC liquid #3
    • Pressure and temperature changes in a gas containing a mixture of liquids alter the gas phase composition 35 Gas / Vapor Phase Liquid Phase HC liquid #1 HC liquid #2 HC liquid #3
    • Pressure and temperature changes in a gas containing a mixture of liquids alter the gas phase composition 36 Gas / Vapor Phase Liquid Phase HC liquid #1 HC liquid #2 HC liquid #3 ““PressurePressure Increases”Increases” Gas/Vapor Decreases
    • Pressure and temperature changes in a gas containing a mixture of liquids alter the gas phase composition 37 Gas / Vapor Phase Liquid Phase HC liquid #1 HC liquid #2 HC liquid #3
    • Pressure and temperature changes in a gas containing a mixture of liquids alter the gas phase composition 38 Gas / Vapor Phase Liquid Phase HC liquid #1 HC liquid #2 HC liquid #3 ““TemperatureTemperature Decreases”Decreases” Gas/Vapor Decreases
    • DesaturationDesaturation – Very important technique A mixture of liquids, their vapor, and other gases presentA mixture of liquids, their vapor, and other gases present Condensation Evaporation Liquid Phase Saturated and at Dew point Temperature •Saturated and at Dew point Temperature. •Lower temperature or increase pressure – condensation occurs. •Increase temperature or reduce pressure – will Desaturate. 39
    • What happens when liquid is carried over into the sample system and sample “pressure” is decreased? External Pressure Regulator Aerosol droplets •Aerosol droplets enter probe •Pressure drop across regulator (or valve) causes liquids to flash (vaporize) •Gas phase composition changes •BTU value is altered •Flow rate calculations are impacted 40
    • What happens when liquid is carried over into the sample system and sample “pressure” is decreased? Insertion Regulator •Aerosol droplets enter probe •Pressure drop across regulator (or valve) causes liquids to flash (vaporize) •Gas phase composition changes •BTU value is altered •Flow rate calculations are impacted 41
    • Forms of Liquid Existing In A Pipeline Film Pool Aerosol Droplet All Forms of Liquid Exhibit the Same Properties 42
    • Liquid in the pipeline is constantly changing forms Aerosol generated from “wave” in surface film Aerosols impinge on a surface and create large drops High gas velocity with liquid flowing across a sharp object, such as an orifice plate, generates aerosols Liquid Pools 43
    • Conclusion: •Insertion (Probe) Regulators were designed to prevent condensation during pressure reduction. •When liquid is entrained (present) in the sample source, they cause composition errors. 44
    • What happens when liquid is carried over into the sample system and sample “temperature” is increased? Heat Tracing •Aerosol droplets enter probe •Heat Tracing vaporizes the liquid •Gas phase composition changes •BTU value is altered •Flow rate calculations are impacted 45
    • Conclusion: •Heat tracing is designed to prevent condensation. •However, it will cause composition errors when liquid is entrained in the sample source 46
    • What happens when liquid is carried over into the sample system and sample “temperature” is decreased? Ambient temperature is lower than the flowing gas temperature •Aerosol droplets enter probe – this means that the gas phase is saturated •Cooling of the saturated gas phase results in “condensation” of some gas components •Condensation causes composition changes in the gas phase •BTU value is altered •Flow rate calculations are impacted 47
    • Conclusion •Hardware designed to prevent condensation can change the sample gas composition when liquid is present •When liquid is present in the source gas changes in either the temperature or pressure will change the gas phase composition, BTU value, and physical properties used in calculating flow rate. 48
    • -Small amount of liquid is equivalent to large volume gas •Liquid has major impact on BTU 49
    • 800 PSIG Temp F 500 F 00 F -250 F -500 F -750 F Mole% N2 2.5 2.501 2.501 2.502 2.505 CO2 1.2 1.2 1.2 1.199 1.197 C1 93.75 93.769 93.786 93.808 93.847 C2 2 1.999 1.998 1.995 1.985 C3 0.352 0.351 0.35 0.347 0.339 iC4 0.042 0.042 0.041 0.041 0.038 nC4 0.064 0.064 0.063 0.06 0.055 iC5 0.014 0.014 0.013 0.012 0.01 nC5 0.026 0.025 0.024 0.021 0.016 C6 0.021 0.019 0.017 0.012 0.007 C7 0.015 0.01 0.005 0.002 0.001 C8 0.011 0.005 0.002 0.001 0 C9 0.005 0.001 0 0 0 Liquid g 0 0.0349 0.0691 0.122 0.247 100%Vapour 1000 BTU Natural Gas 500 cc vessel 50 Removal of 0.247g of liquid resulted in a loss of 3 BTU
    • Component Methane Ethane Propane Iso-butane Normal-butane Iso-pentane Normal-pentane Normal-hexane Normal-heptane Normal-octane Normal-nonane Normal-decane Nitrogen Carbon Dioxide Total Mole Percent 64.107 10.33 7.128 2.174 6.386 1.874 2.307 0.538 0.187 0.086 0.023 0.016 3.939 0.906 100.001 1500 BTU Mix Dew point of mixture is 91ºF Heating value is 1500 BTU Reducing the temperature to 41ºF (50ºF temperature drop) •Removes 5.9 grams of liquid •Heating value is lowered from 1500 to 1430 (70 BTU loss)
    • No technology available for extracting a gas sample containing a representative amount of entrained liquid. 52 www.geniefilters.com
    • -Liquids entrained in Natural gas has caused many problems -No distinction made between “entrained” and “condensed” liquid •Impact often overlooked *Analyzer damage is usually first concern 53 -Proper treatment depends on the origin of the liquid www.geniefilters.com
    • -Entrained liquid not always easy to detect •Erratic on-line gas analysis •Spot, composite, on-line analyzer don’t agree •Valve or Pressure Regulator freeze ups 54 Some indicators that liquid may be present are: www.geniefilters.com
    • Sources of Sampling Problems •Entrained Liquid •Condensed Liquid •Construction Material for Sample Conditioning Components •Contaminates •Improper Selection of Sample Conditioning Components •Ambient Temperature •Cooling of Sample Gas Resulting From Pressure Drops 55
    • Sample Conditioning System Tasks •Extraction •Removal of Unwanted Liquids and Solids •Pressure Regulation •Transportation •Preservation of Sample Composition •Flow Control •Stream Multiplexing and Cal Gas Switching 56
    • Sample Conditioning System Tasks Extraction Removal of Unwanted Liquids and Solids Pressure Regulation Transportation Preservation of Sample Composition Flow Control Stream Multiplexing and Cal Gas Switching Probe Purpose – Exclusion of unwanted liquid and particles Natural Gas Pipeline 57
    • Sample Conditioning System Tasks Extraction •Probe Purpose – Exclusion of unwanted liquid and particles Issues Location On Line •Area with minimum probability of liquid present •Not directly downstream of a pressure reducing device Position of Line– Horizontal is Preferred •Depth of Probe •Away from pipe wall •Current center 1/3 depth recommended by GPA and API is not a bad practice but is not supported by test. •No evidence to support a specific depth when the gas source is liquid free. •Center 1/3 depth of large diameter pipe could result in vibration damage to probe. 58
    • Sample Conditioning System Tasks Extraction Purpose – Exclusion of unwanted liquid and particles •Probe Issues – Continued Opening •Square Cut – Probably best for all applications •Angle Cut – Not necessary and if installed incorrectly could increase liquid intake. Types of Probes •Straight Probe •Pitot Tube •Probe with Integral Regulator •Probe with Membrane Liquid Separator and Integral Regulator 59
    • Extraction Purpose – Exclusion of unwanted liquid and particles •Probe Issues – Continued Types of Probes •Straight Probe Positive – Helps prevent wall film from entering sample system Negative – Does not prevent entrained aerosols from entering sample systems. Aerosols are almost always present whenever liquid is present in any form. 60
    • 61 Straight Probe
    • Positive – Helps prevent wall film from entering sample system Provides external circulation of sample gas Negative – Does not prevent entrained aerosols from entering sample systems. Aerosols are almost always present whenever liquid is present in any form. 62 Extraction Purpose – Exclusion of unwanted liquid and particles •Probe Issues – Continued Types of Probes •Pitot Tube
    • 63 FLOW TO ANALYZER OR COMPOSITE SAMPLER ½“ NPT, ¾” NPT or 1” NPT ¼“ NPT Full Opening S.S. Plug Valve (Optional) Product Return Product Out CL of Pipeline Low Pressure Return Pitot Tube
    • Insertion Regulator •Aerosol droplets enter probe •Pressure drop across regulator (or valve) causes liquids to flash (vaporize) •Gas phase composition changes •BTU value is altered •Flow rate calculations are impacted 64 •Probe with Integral Regulator Types of Probes Negative Positive •Helps prevent condensation due to Joule-Thomson Cooling
    • AdvantagesAdvantages -Liquid is removed before pressure reduction -Vapor phase composition changes are avoided Types of ProbesTypes of Probes Probe with Integral Membrane & Regulator 65
    • Membrane Foot Valve Gas Flow Coalesced Liquid Genie Probe Regulator 66
    • Genie ModelGenie Model 130 HPM130 HPM 67 External means for removing liquid from Sample Gas at line pressure Gas & Entrained Liquid Gas Only Entrained Liquid (shed by the membrane) is returned to the sample source.
    • Handling LiquidsHandling Liquids -Remove at line pressure & temperature conditions. -Prevents changes in gas composition -Prevent condensation -Heat and/or insulate -Lower pressure at source to lower Dew point -Protect analyzer -Provide liquid “safety net” at analyzer 68
    • Sample Conditioning System Tasks Recap Extraction Removal of Unwanted Liquids and Solids Pressure Regulation Transportation Preservation of Sample Composition Flow Control Stream Multiplexing and Cal Gas Switching Prevent adsorption and /or condensation Otherwise loss of “heavies” will occur and BTU value is diminished and/or erratic GC Heated or Insulated 69
    • Transporting Sample LinesTransporting Sample Lines -Diameter-Diameter -Length -Slope -Heating/Insulation -Temperature Differences DiameterDiameter 1/8” diameter for lines under 25’ long ¼”diameter for lines longer than 25’ 70
    • -Diameter -Length-Length -Slope -Heating/Insulation -Temperature Differences LengthLength Minimize length –reduce pressure drop –reduce lag time –reduce exposed surface area Transporting Sample LinesTransporting Sample Lines 71
    • -Diameter -Length -Slope-Slope -Heating/Insulation -Temperature Differences SlopeSlope To Prevent accumulation of liquid pools Transporting Sample LinesTransporting Sample Lines 72
    • -Diameter -Length -Slope -Heating/Insulation-Heating/Insulation -Temperature Differences -Prevent sample gas from approaching dew point. Heating/InsulationHeating/Insulation -Prevent condensation. Transporting Sample LinesTransporting Sample Lines 73
    • Heat TracingHeat Tracing •Heat trace when ambient conditions could cause sample wetted components temperature to fall within 25°F of the expected hydrocarbon dew point. •Heat trace all exposed components. •When electrical heat tracing is used make sure that: (a) The heat tracing tape meets electrical codes for the intended service (b) The heat tracing tape is self-limiting to prevent over-heating (over-heated electrical components could cause injury or an explosion) •A catalytic heater can be used for some applications. •Insulate all heat traced components to prevent heat loss. 74
    • Heated Box Heat Traced Bundle Heat TracingHeat Tracing
    • -Diameter -Length -Slope -Heating/Insulation -Temperature Differences-Temperature Differences -Do not allow sample to cool below the the liquid removal temp. (Dew point) -Temperature Differences-Temperature Differences -Ambient and analyzer house temp. conditions reversed between winter/ summer Transporting Sample LinesTransporting Sample Lines 76
    • ““Lag Time”/Flow rateLag Time”/Flow rate -Too much emphasis given to “Lag Time” -Excessive bypass is not cheap -Balance sample conditioning needs with “Lag Time” requirements 77
    • Extraction Removal of Unwanted Liquids and Solids Pressure Regulation Transportation Preservation of Sample Composition Flow Control Stream Multiplexing and Cal Gas Switching Sample Conditioning System Tasks Recap •Remove unwanted components without changing gas composition. •Prevent condensation or adsorption phase of components. 78
    • Diagram for a Typical Single Stream Gas Chromatograph Installation with GPR and Genie Model 101
    • Purpose of Genie Probe Regulator (GPR) is to precondition the gas sample by: -removal of liquid (if present) at pipeline conditions of pressure and temperature. -pressure regulation (after liquid removal) -compensation for Joule-Thomson cooling effect during pressure regulation -removal of all solid particles Benefit: Prevent sample composition changes. 80
    • Purpose of a Genie Model 101 is to provide a safety net for the Gas Chromatograph by: -removal of all liquid or solid particles which may be present due to unusual conditions or equipment failure. Benefit: Protecting the Gas Chromatograph reduces maintenance expenditures and increases reliability. 81
    • Surface AdsorptionSurface Adsorption Surfaces attract gas molecules -high affinity for some molecules For a given surface/gas composition -increased temperature/decreased pressure decreases adsorption -decreased temperature/increased pressure increases adsorption -heating sample wetted surfaces minimizes surface adsorption -concentration in gas phase impacts adsorption 82
    • Surface AdsorptionSurface Adsorption Surface adsorption is undesirable -stores molecules in sample system -temperature/pressure sensitivity -night/day temperature cycles causes composition changes in sample gas 83 -maintain sample wetted surfaces at least 25º F above the sample dew point
    • Calibration gas issueCalibration gas issue Dew point -know what the calibration gas Dew point is. -maintain the temperature at least 25º F above the dew point at all times when calibration gas is in service. -removing gas when below Dew point will distort the calibration gas composition 84
    • Composition Storage -stratification does not occur -heat or insulate to prevent temperature differences in cylinder. (Recommend heating at least 25°(Recommend heating at least 25°FF above theabove the calibration gas Dew point, but not exceeding 140°calibration gas Dew point, but not exceeding 140°F).F). Calibration gas issueCalibration gas issue -place cylinder on an insulating medium to prevent a cold floor contacting cylinder bottom -look for increases of the heavy molecules as the cylinder pressure lowers. 85
    • G.C.G.C. Liquefied Petroleum Gas (LPG) AnalyzersLiquefied Petroleum Gas (LPG) Analyzers Genie Model 205 HP LPG & Immiscible Liquids (VPC) Vaporizing Pressure Regulator LGP Vapor Genie Model 101 Bypass LPG & All Immiscible Liquids Vent
    • Referenced PublicationsReferenced Publications API Chapter 14.1 “Collecting and Handling of Natural Gas Sample for Custody Transfer” Topical Report – Prepared by K.A. Behring II Of Southwest Research Institute Technical Memorandum – GPRi report number GPRi - 98/0034 Prepared by K.A. Behring II Handbook of Chemistry and Physics Published by Chemical Rubber Publishing Co. 40th Edition Perry’s Chemical Engineering Handbook 6th Edition Mark’s Standard Handbook for Mechanical Engineers 6th Edition 87