Measurement Library

PRCI Publications (2009)

PRCI

L52315 Testing of Environmentally-Friendly Gas Sampling Methods
Author(s): Darin George
Abstract/Introduction:
Recent environmental concerns have led to calls for reduced hydrocarbon emissions to the atmosphere from a variety of sources. One source of emissions being examined in this regard is natural gas spot sampling methods that vent pipeline gases to the atmosphere. Some sampling techniques and equipment have been developed that do not emit greenhouse gases, but the need exists to test these methods for their ability to collect accurate, representative samples. Another related concern is the accuracy of samples drawn from streams near their hydrocarbon dew point (HDP). While the spot sampling methods recommended by current industry standards perform well on streams far above their HDP, little data are available on their performance near or at the HDP, where poor sampling methods can cause heavy hydrocarbons to condense from the sample and distort the analysis. This project evaluated the ability of four natural gas spot sampling methods, including two zero emissions sampling methods, to capture accurate, representative samples of gas streams at or near their hydrocarbon dew point (HDP). Two of the sampling methods tested were variations on the GPA fill-and-empty method, with additional steps intended to heat the sampling equipment above the HDP or clear condensed hydrocarbon liquids from the sample line. The other two sampling methods, which use the A+ Q2 sample cylinder and a constant-pressure floating-piston sample cylinder, were developed to prevent condensation of heavy hydrocarbons during the sampling process.
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PR-015-07605-R01 Lower-Cost Liquid Meter Prover Calibration Method
Author(s): Grimley
Abstract/Introduction:
To maintain measurement accuracy, stationary volume provers must be re-proved periodically. The most direct method of determining a provers volume is through a process known as water drawing where water is circulated through the prover and swept into certified measurement volumes. Since the can volumes can be directly calibrated by national metrology agencies, the traceability chain is short. However, proving with water requires that the prover be first cleaned of any hydrocarbon product that may alter the working volume of the prover and create waste products that must be handled properly. The master meter method uses the flowing product instead of water for the prover calibration and, therefore, eliminates substantial on-site waste handling issues. A master meter system consists of a portable volume prover and a turbine or positive displacement meter that is plumbed in series with the stationary prover to provide the calibration. The increased uncertainty associated with the two-step process of proving with a master meter is specifically mentioned in the API references concerning liquid meter proving however, there has not been significant published testing to assess the differences in the methods. The objective of this project was to provide a comparison between the volume determined via the water draw method and that determined via the master eter method. A new stationary prover was used as the target device for the prover trials. Two water draw calibrations were performed and compared to the factory-provided water draw volume. The water draw results showed that with consistent measurement techniques, the results from three independent sources were within 0.02%. It is important to note that one data set had to be adjusted (based on tests) to provide this level of agreement.
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PR-015-08605-R01 Assessment of Orifice Meter Flow Measurements with Low Differential Pressures - Unblinded
Author(s): George, Jowers, Grimley
Abstract/Introduction:
Measurement of natural gas flow with an orifice meter is a well-established methodology however, orifice measurement accuracy is of concern when flow rates are low and the differential pressure (DP) across the orifice is at the extreme low end of common DP transmitter ranges. This research evaluated the performance of multiple types of transmitters in 10-inch and 4-inch orifice meter runs at differential pressures approaching 1 inch of water column (1 H2O), simulating low flow transmission meter stations and depleted production well stations. The results were analyzed to characterize and better understand the uncertainties and measurement errors associated with orifice meters operating with small bore diameters and low DPs. Transmitters tested included typical DP transmitters with stated accuracies of 0.1% of full scale, DP transmitters with stated accuracies as a percent of reading and high-frequency-response DP transmitters. Data acquisition methods, transmitter technologies, and various calibrated measurement spans were studied for their potential to improve orifice meter accuracy at low DP conditions. This is an un-blinded report.
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PR-015-08606-R01 Assessment of Dirty Meter Performance
Author(s): Grimley
Abstract/Introduction:
Like most metering technologies, ultrasonic meters are known to be affected by the buildup of material inside the meter and surrounding pipe due to common pipeline contaminants. The buildup affects the metering accuracy by reducing the flow area sampled by the ultrasonic transducers and by changing the shape of the velocity profile through the creation of additional roughness elements on the pipe wall. The goal of this project was to relate the contamination level to the measurement error. The approach was to evaluate the flow measurement performance of two commercially-available ultrasonic flow meters under conditions in which there were various levels of coating on the pipe upstream of the test meter. The tests were performed under controlled conditions in the SwRI Metering Research Facility (MRF) High Pressure Loop and were designed to compare the baseline (clean pipe) flow measurement performance of each meter to the performance attained with various levels of coating on the upstream pipe.
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PR-343-06604-R02 Smart USM Diagnostics - Phase 2
Author(s): Zanker
Abstract/Introduction:
It has long been known that all ultrasonic flow meters, especially those that exploit multiple paths to achieve higher accuracies, are capable of extensive self-diagnosis. However, each manufacturer of the technology has tended to develop diagnostic tools peculiar to his particular device. This has led to a confusing mix of offerings that are not transportable between meters, and whose interpretations are not always consistent. This report addresses: Verification of the Phase 1 models against available field data Implementation of field-tested methods offered by PRCI users Trending the diagnostics with time to detect changes Establishing the significance of the changes (magnitude of error) Deciding if the changes require intervention (maintenance, re-calibration) Tuning of the Phase 1 models based on this experience Verification of the models using experimental testing.
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PR-343-06605-R02 USM Recalibration Frequency
Author(s): Hall, Zanker Kelner
Abstract/Introduction:
This program is intended to improve the understanding of the stability over time of gas multi-path ultrasonic flow meters (USMs). Within the Natural Gas Industry, there are currently on universal standards requiring periodic recalibration of USMs. Removing these flow meters from serviced for recalibration is costly and inconvenient. However, the primary reason that a recalibration standard does not exist is the lack of definitive data regarding the long-term stability of installed USMs. In order to address this situation, collection and analysis of data was performed to help formulate a recalibration guideline. Specific tasks include: (1) review and utilization of existing published technical papers, (2) working with certified flow calibration facilities to obtain data, (3) obtaining data from USM manufactures on changing of electronics and/or transducers, (4) obtaining historical recalibration data, and (5) participation in selected recalibrations by PRCI member companies.
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PR-365-08608-R02 MEMS Technology for Natural Gas-Liquid Quality Measurement (Phase II)
Author(s): Field, Gunther
Abstract/Introduction:
This report summarizes a follow-on task to the project in which SmallTech Consulting was asked by PRCI to undertake an evaluation of MEMS1 Technology for Natural Gas/Liquid Quality Measurement. SmallTech examined the feasibility of using MEMS-based sensors to determine chemical composition measurands of interest within a natural gas pipeline, at or near real-time. This update includes information on timing and estimated costs for collaboration with the most promising of the front-runner candidates as potential vendors or development partners for PRCI.
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