Measurement Library

Natural Gas Sampling Technology Conference Publications (2008)

Sample Conditioning And Sampling Systems For Portable Gas Chromatograph Systems
Author(s): Joe Landes
Abstract/Introduction:
Portable micro gas chromatographs have been in use for over 20 years. The technology was originally developed for NASA and the space program. NASA still uses micro GCs and other industry sectors have adopted the technology for various applications. The early instruments had some design flaws that caused problems for hydrocarbon analysis. The instrument design has evolved and manufacturers have addressed these initial problems. Modern portable GCs are widely used for the analysis of Natural Gas. As the use of these instruments increased, it became important that industry standards consider applications and methods for them. Seven years ago, the GPA Technical Section B committee formed two workgroups to determine if existing methods could be used or modified to include portables, or if new methods would have to be developed to address portable GCs. One workgroup was to evaluate performance for the instrument under GPA 2261. The other workgroup was to evaluate sampling systems.
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Document ID: F8DF8C2D

The Impact Of Sample Conditioning On Gas Chromatographs
Author(s): Shane Hale
Abstract/Introduction:
Gas Chromatography is the industry accepted method of analyzing Natural Gas to determine the gas quality and physical properties used in the fiscal transfer. The values obtained from the Gas Chromatograph (GC) are used to calculate the corrected volumetric flow, and the total energy of the Natural Gas passing through the custody transfer station. Inaccuracies in the analysis of the gas directly impacts the users financially to a much larger degree than the cost to minimize these inaccuracies. One of the most common cause of inaccurate analysis is the improper sample handling practices which result in the composition of the gas changing between the sample point and the GC sample injection. Much has been written regarding the recommended practices for sample handling for gas chromatographs. This paper will present two real world examples of the impact of incorrect sample handling on the analysis, and thus the financial performance of the custody metering station.
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Document ID: 977B814C

Sample Conditioning For Natural Gas Pipeline Analyzers
Author(s): Colin B. Blakemore
Abstract/Introduction:
The single most difficult task in applying a well designed analyzer to a natural gas pipeline is the process of designing and installing the sample system. Creativity and attention to detail are essential. This paper does not address clean, very dry cryogenic applications. The main issue is straight forward, getting a sample of high pressure natural gas from a typically dirty pipeline to a low pressure analyzer, with the component(s) of interest unchanged and in a form acceptable to the analyzer. However, the reality is not so straight forward.1 For more than forty years, I have been an application specialist for first DuPont Instruments and now AMETEK PAI. My responsibility is to get involved when one of our instruments does not work as expected even though our service group says it is working electrically and mechanically. The problem turns out, almost always, to be either something we do not understand about the customers process, or most likely a poorly designed and/or executed sample system.
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Document ID: AFA7ED96

Analytically Correct Components And Systems And Why They Are Important
Author(s): Donald P. Mayeaux
Abstract/Introduction:
Most of the basic components of modern day sample conditioning systems were originally designed for application in pneumatic and hydraulic controls systems. As analyzers began their migration from laboratory settings to field locations sample conditioning became necessary. Early sample conditioning systems were primitive in their design, fabrication, and operation. At that time analyzers were utilized primarily for rough process control. Highly accurate compositional analysis was not expected nor obtained. In order to obtain the desired level of accuracy required by modern day analytical applications sample conditional systems (SCS) must become as efficient as their analyzer counterpart. For that to occur system component design and construction must be analytically correct. Additionally the system itself must be fabricated and operated in an analytically correct manner. Analytically correctness, as referenced in this presentation, means a manner of designing, constructing, and operating a sample conditioning system such that sample fluid compositions will not be altered in their passage through the system. Other characteristics of an analytically correct system are (a) low internal volume, (b) essentially no dead volume in the flow path of sample which will be analyzed, and (c) rapid fluid composition equilibrium.
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Document ID: 7AE98BC0

Research Results Of Cylinder Temperature Changes Which Occur During Spot Sampling
Author(s): Jay St. Amant
Abstract/Introduction:
You may recall from the NGS Tech 2007 conference we discussed research results of cylinder temperature changes that occur during spot sampling. This presentation will re-cap the 2007 results and disclose new research.
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Document ID: E98F9146

Benefits Of Training Natural Gas Measurement Technicians On The Science Of Sample Conditioning Or If You Always Do What You Always Did, You Always Get What You Always Got Poor Results
Author(s): Phil Rutledge
Abstract/Introduction:
Many people will state the sampling of natural gas is half-science and half-mystery, but I disagree. If we do not follow good scientific methods each and every time we sample a gas stream, our results can, and will, vary. When the gas analysis results vary, people say, Oh, it was the temperature or Oh, the flow was different, or the best reason They must be in a different producing zone. If that is the case, guess what, we might need a different contract. Are all of these different ideas a mystery? Are people being taught the correct methods of gas sampling? I think poor training and incorrect procedures cause all of these reasons. Many measurement technicians have worked for years in the industry and no one has ever questioned their results. It is time to change these practices and we, as and industry, are responsible to improve and change these practices.
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Document ID: 3A3180FA

Challenges In Updating Company Procedures To Conform To Changes In Industry Standards
Author(s): Mark Scripsick
Abstract/Introduction:
Improvements in technology and research data that offer or demonstrate more accurate methods to perform sampling operations are introduced to the industry continuously. Since the goals of industry sampling standards are to provide procedures to the industry to utilize these improvements, the standards must also change constantly. This creates a challenge for the users of these standards (our companies) to manage our systems and assure we keep abreast of these changes. Several of these challenges will be addressed with some suggestions to meet these challenges in this presentation.
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Document ID: 703CA86F

Writing Comprehensive Sampling Procedure Acceptable To A Companys Legal Department
Author(s): David Bromley
Abstract/Introduction:
We live in a litigious environment therefore, there is more focus on gas sampling today then there ever has been in this industry. With this increased focus comes additional interest from the company legal department. Currently, there is legislation in Washington regarding sampling, states are adopting rules governing measurement of natural gas, ongoing court cases, and the Bureau of Land Management is expressing an interest in gas sampling procedures. The winter of 2001 brought on new challenges to the natural gas sampling industry. Relative to liquid gas, prices for natural gas increased to a level where the heavier components held more value if kept in the form of natural gas. Operating companies ran economics, and made decisions to by-pass processing plants, in order to optimize the value of their product. Pipeline and distribution companies were then faced with issues related to liquid fallout in their systems. Pipeline companies started to lower their tariff levels on cricondentherm, which forced regulatory groups within the operating companies to get involved in hearings before FERC. The API and GPA standards were modified to include much more emphasis on heating and to assure that a more accurate representative sample was being obtained. As a result, many in the industry were introduced to new terms, such as, hydrocarbon dew point and cricondentherm. There were, and still are, issues regarding how to accurately determine the cricondentherm of a flowing gas stream. Many calculate the cricondentherm based upon the analysis of a gas sample. The slightest error in sampling can change the calculated cricondentherm 20 F therefore, obtaining an accurate representative sample is critical in todays environment and makes the sampling procedure process that much more important.
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Document ID: 0E291145

How Company Tariffs Impact Sampling Procedures
Author(s): Brad Massey
Abstract/Introduction:
A tariff places limits on gas quality specifications for a specific company. The management of various gas quality parameters in the pipeline industry requires monitoring to insure the integrity of the pipeline and the merchantability of the gas are not compromised. The awareness of the importance of this monitoring is becoming increasingly apparent throughout the industry. Review and further development of tariffs in order to maintain pipeline integrity without limiting supply options has become a challenge for a good number of pipeline operators. Often times, tariffs are written by people that dont fully consider operating conditions or sampling practices. A key consideration is how the impact of gas quality on operations has become increasingly important due to variations in the gas supply quality. Depending on how a tariff was submitted it can be quite restrictive on how gas quality specifications can be enforced or in some cases the manner in which the gas quality determination can be made. Conversely the tariff may not be restrictive enough to insure control limits are adequate. Depending on how a tariff is written, may influence how a company obtains gas samples. By not fully considering the influence of all constituents, existing conditions or by excluding specific methods of determination the outcome of the analysis may not provide the most accurate results. Careful consideration should be given when writing or re-writing gas quality limits as well as specifying sampling methods or determination procedures within a gas tariff.
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Document ID: 6F20DDC6

Results Of Research On Minimizing The Impact Of Ambient Temperature On Extraction Of Natural Gas Samples From A Pipeline.
Author(s): Justin Harvey
Abstract/Introduction:
During the extraction and transportation of a natural gas sample, it is very important to maintain a temperature which is equal to or greater than the samples hydrocarbon dew point. In fact, API 14.1 and GPA 2166 recommend maintaining a temperature of thirty degrees above the natural gas hydrocarbon dew point to avoid condensation. Most sample conditioning components can be easily housed in enclosures and heated, transport lines can be heated using heat tracing, and probe regulators can be heated by wrapping heat trace around them. To maintain the heat from the heat tracing, various companies have produced jacket products to cover the probe regulators. These jackets vary in composition and structure but they are usually designed to allow for easy removal to service the regulator or membrane. One area in need of insulation that has been largely ignored is the intersection of the probe and pipe wall. This paper will discuss the techniques and materials that can be used to prevent cooling at the pipe wall junction and various jacket designs and materials that can be used to achieve these means.
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Document ID: 1F86D5DF

The Stability Of Ppm Moisture Standards In Methane After Exposure To Temperatures Below The Calculated Dew Point
Author(s): Susan J. Brandon
Abstract/Introduction:
The experiments conducted in Pasadena, TX at Scott Specialty Gases and in Pueblo, Colorado at an independent customer site were designed to determine the percent recovery of Water in Methane calibration standards that had been exposed to temperatures below their calculated dew points. Pending the successful recovery of the standards, additional tests were constructed to determine the stability of the standards over the entire cylinder pressure range, the optimal operating temperatures for the use of the calibration standards and the optimal sampling regulators for the direct measurement of water using a SpectraSensors Moisture analyzer. Six cylinders were gravimetrically prepared at Scott Specialty Gases (SSG) in Pasadena, Texas. Three of the cylinders were manufactured at 10 pounds per million (200 ppmv) and three were manufactured at 7 pounds per million (140 ppmv). The calculated dew point of the 200 ppmv cylinder is 73 degrees F at 2000 psia, and the 140 ppmv is 62.9 degrees F at 2000 psia. The six cylinders were analyzed at SSG using a SpectraSensors Moisture analyzer and a Meeco Waterboy LP2. All six cylinders confirmed their calculated NIST traceable gravimetric values to within +/- 5% using the SpectraSensors analyzer, and within +/- 6% using the Waterboy LP2.
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Document ID: B173386D

Beyond The Ordinary: Sample System Best Practices For Cryogenic Moisture And Hydrocarbon Dew Point Applications
Author(s): Daniel R. Potter, Colin Blakemore, Randy Hauer
Abstract/Introduction:
Sampling techniques for BTU and moisture measurements are well understood but applications beyond the routine requires additional attention to detail. Two such applications are the subject of this paper. The first is the measurement of low level moisture (1 - 1,000 ppbv) for cryogenic processes. Measuring moisture below 1 ppm is an entirely different world from the traditional pipeline application because of the highly polar nature of the water molecule, as it tenaciously adheres to all surfaces in the sample system. Without consideration of these surface effects, sample transport and subsequent analyzer response is compromised. The second is measurement of the hydrocarbon dew point using a continuous device, a physical property rather than a quantitative method. The challenge is to sample the gas at pressure (or alternatively at a fixed inlet pressure), while separating oil, grease and liquid hydrocarbon without affecting the integrity of the sample gas.
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Document ID: 73387C11

Using Equations Of State In Sample QA/QC
Author(s): David Bergman
Abstract/Introduction:
Equations of State (EOS) can play an important roll in understanding the quality of both sampling methods and laboratory analyses. This is most evident in the calculation of phase envelopes, the bubble point and dew point curves. This work is aimed at showing the sensitivities of calculations to sampling and analysis and to provide clues as to how some sampling issues can be detected and corrected.
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Document ID: D82AB506

The Physics And Chemistry Of Natural Gas Sampling And Conditioning
Author(s): Darin L. George
Abstract/Introduction:
Recent research has led to changes in industry standards for natural gas sampling, such as the API Manual of Petroleum Measurement Standards Chapter 14.1 and GPA 2166. To best apply these standards, users should understand the physical phenomena that can lead to inaccurate samples. This presentation will review the physics of natural gas sampling, including phenomena such as adsorption and desorption, vapor-liquid equilibrium, and Joule-Thomson cooling the use of the phase diagram as a sampling tool and results of research on the physics of natural gas sampling that have led to new industry standards.
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Document ID: F0DB97A8

Review Of Sample Conditioning Components Available To Meet The Intent Of API 14.1 And Their Proper Installation
Author(s): Ken Thompson
Abstract/Introduction:
The following will cover a review of sample conditioning components available in todays market that will meet the intent of the American Petroleum Institutes Manual of Petroleum Measurement Standards, Chapter 14, Section 1 and GPA 2166-05 standard. This will be discussed in several segments removing a gas sample from a pipeline, preparing that sample and reducing the pressure in preparation for delivery to an analyzer for analysis of heating value, moisture content, H2S content, hydrocarbon dew point, etc. During this discussion various methods will be reviewed of how not to treat a gas sample and methods of how to prepare a gas sample, thereby ensuring the analytical device will provide a true reading of the gas in the pipeline. Please remember once a gas sample has been removed from a pipeline incorrectly, (due to an improperly designed and/or installed sample system) the gas composition once altered will not correct itself during transportation to the analytical device. A bad sample ends as a bad analysis.
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Document ID: D8C1AE23

Update On Research Projects Related To Gas Sample Conditioning
Author(s): Jim Witte
Abstract/Introduction:
This paper describes a limited review by the author of research efforts related to gas sampling system improvements. It will also offer some of the authors own reflections on what has been accomplished in previous research as well as current plans of the Pipeline Research Group International (PRCI).
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Document ID: A18B9E9A

Uncertainties In Natural Gas Properties Determined By Gas Chromatography
Author(s): Darin L. George
Abstract/Introduction:
Natural gas is bought and sold based on the energy flow rate through the gas pipeline, typically in millions of BTUs per day. The energy flow rate is determined from two quantities, the standard volumetric flow rate of the gas and the energy content of the gas stream. Volumetric flow rates are measured by ultrasonic meters, orifice meters, or turbine meters, while the energy content of natural gas is commonly determined through an analysis of the gas stream by a gas chromatograph (GC) located in the field, or perhaps a laboratory GC analysis of a gas sample taken from the pipeline. Natural gas transmission companies are continually working to accurately measure volume flow rates and reduce lost-and-unaccounted-for gas volumes that can impact custody transfer. Correct GC analyses are also crucial to accurate custody transfer and sales of natural gas. However, GC users may not understand how errors in calibration, sample mishandling, or fluctuations in GC performance can affect the energy flow rate determined for the gas in the pipeline. This paper will discuss several sources of uncertainty in GC analyses, including uncertainties in gravimetric calibration standards, chromatograph repeatability, and effects of sample distortion. The paper will then give examples of how these uncertainties can propagate into computed gas properties used in custody transfer, particularly heating values and energy flow rates. Identifying these sources of uncertainty and quantifying their impact can allow natural gas companies to find and minimize the largest contributions to error, improve the confidence in custody transfer by all parties involved, and avoid disputes between those involved in natural gas transportation and sales.
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Document ID: B22521FC

A Compilation Of Sample Conditioning Issues Which Need To Be Addressed
Author(s): Donald P. Mayeaux
Abstract/Introduction:
It is generally agreed that the weak link in any natural gas analytical system is the sample conditioning system. In recent years the combined efforts of the Natural Gas Industry and its suppliers has produced significant improvements in the science of sampling Natural Gas. However, there remain several issues which need to be addressed.
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Document ID: 9B47819B

Sample Conditioning Natural Gas For On-Line Analysis Of H2S
Author(s): Thomas Y. Tramel
Abstract/Introduction:
When sampling for on-line H2S analysis it is critical that the gas sample containing a representative concentration of H2S reach the analyzer in the shortest period of time possible. The response time of most analyzers is typically many times faster than the delivery time of the gas sample from the sample tap to the analyzer. This presentation addresses the issues involved in presenting a quality H2S sample to the analyzer in a timely manner.
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Document ID: 333BA5BF

Sample Conditioning Natural Gas For On Line Hydrocarbon Dew Point Determination
Author(s): Andy Benton
Abstract/Introduction:
Sampling and sample conditioning for successful on-line measurement of hydrocarbon dew point requires full attention to the unusual requirements specific to this parameter. Aspects covered in this paper include: Correct sample gas extraction to ensure that composition is representative of majority pipeline flow, Sample line handling at pipeline process conditions to maintain sample integrity, Consideration to filtration to ensure that the analyzer is protected from contamination, by entrained liquids or pipeline slugs, whilst ensuring that the full magnitude of any high excursions in process gas hydrocarbon dew point are registered, Consideration to phase envelope characteristics to ensure that sufficiently high temperature is maintained when reducing sample pressure to intermediate levels (cricondentherm condition) required for analysis of this parameter according to gas quality tariff specifications, Thought is also applied to the extreme scenario of a gas pipeline carrying liquid condensates as well as the optimum system configuration for the most commonplace application to confirm conformance to transmission pipeline gas quality tariff specifications.
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Document ID: 722830B6

Sample Conditioning Natural Gas For On-Line Analysis Of Moisture
Author(s): Charlie Cook
Abstract/Introduction:
Sample conditioning for moisture analysis is not a favorite topic in industry or among friends. The proof is that there is no standard currently in place to suggest and advise the user by with standards and practices that were empirically if not painstakingly acquired. What is at stake? Safety, overall measurement uncertainty, loss of production and staff productivity are all at stake. Moisture concentrations are generally limited to 7 pounds /MM SCF by common carriers, but it is a matter of opinion as to how to extract a sample and also calculate its state. Generally, specification of moisture analyzers is left either to engineering or field personnel. Often they will choose the same equipment and the same location criteria that are used for BTU custody measurement. Conversely, some feel that since it isnt as important and sometime visible, shortcuts are acceptable. Not surprisingly, under certain circumstances, they can attain desirable results. Under other circumstances, more discomfort remains following moisture analysis than ever.
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Document ID: A9DFFCCE


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