Papers

Investigations on the Determination of the Service Methane Number of LNG

LNG is a fuel that is under increasing discussion for transport purposes. It differs from CNG because it often has a higher concentration of hydrocarbons > C4. This affects knocking in a negative way. The knocking properties of a gaseous fuel are characterized by the Methane Number (MN) which is defined as the methane content in a mixture of methane and hydrogen which has the same knocking properties as the gas under investigation. It was defined by AVL in the late 1960s. In contrast to the Octane or Cetane Number there is no standardized measurement procedure for the MN, because the equipment AVL used was unique and does not exist anymore. But AVL created a calculation methodology based on the large amount of data they had measured. There are several software implementations of this methodology. Further there are other algorithms which are not based on the AVL data. If an MN is measured on an arbitrary engine the result is called a Service Methane Number (SMN). It usually shows the same tendencies as the MN but different absolute values. For a set of LNGs the SMNs are measured on two single cylinder SI test engines of 200 and 600 cc swept volume. Different approaches to measure the SMN are investigated. Further, several calculation methods are compared with the measurements.

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Autoignition studies of Liquefied Natural Gas (LNG) in a shock tube and a rapid compression machine

Abstract:
Liquefied Natural Gas (LNG) has become an increasingly important world energy resource and is a part of the European Union clean fuel strategy launched in 2013. Therefore, there are currently several ongoing measurement strategies considering quality specification of LNG. In this context, for application in gas engines, it is essential to understand the combustion behavior of these natural gas mixtures. The methane number (MN) which represents a scale for the knocking propensity, is one of the main indicators for this combustion behavior. In this study, we investigated the influence of the LNG composition on the ignition delay time and thus the knocking behavior of prototypical LNG Mixtures. Several LNG typical mixtures containing CH4/C2H6/C3H8/n-C4H10/i-C4H10/n-C5H12/i-C5H12/N2 were studied in the temperature range 850–1450 K, with pressures of 20 and 40 bar and at equivalence ratios of 0.4 and 1.2. The use of a shock tube and a rapid compression machine facility allowed us to study the ignition behavior over a wide range of operating conditions relevant to gas engines. We report a detailed investigation of LNG autoignition with respect to temperature, pressure and equivalence ratio thereby providing crucial validation data for chemical kinetic models for real applications.

Cryogenic flow rate measurement with a laser Doppler velocimetry standard

Abstract:
A very promising alternative to the state-of-the-art static volume measurements for liquefied natural gas (LNG) custody transfer processes is the dynamic principle of flow metering. As the Designated Institute (DI) of the LNE (‘Laboratoire National de métrologie et d’Essais’, being the French National Metrology Institute) for high-pressure gas flow metering, Cesame–Exadebit is involved in various research and development programs. Within the framework of the first (2010–2013) and second (2014–2017) EURAMET Joint Research Project (JRP), named ‘Metrological support for LNG custody transfer and transport fuel applications’, Cesame–Exadebit explored a novel cryogenic flow metering technology using laser Doppler velocimetry (LDV) as an alternative to ultrasonic and Coriolis flow metering.

Cesame–Exadebit is trying to develop this technique as a primary standard for cryogenic flow meters. Currently, cryogenic flow meters are calibrated at ambient temperatures with water. Results are then extrapolated to be in the Reynolds number range of real applications. The LDV standard offers a unique capability to perform online calibration of cryogenic flow meters in real conditions (temperature, pressure, piping and real flow disturbances). The primary reference has been tested on an industrial process in a LNG terminal during truck refuelling. The reference can calibrate Coriolis flow meters being used daily with all the real environmental constraints, and its utilisation is transparent for LNG terminal operators.

The standard is traceable to Standard International units and the combined extended uncertainties have been determined and estimated to be lower than 0.6% (an ongoing improvement to reducing the correlation function uncertainty, which has a major impact in the uncertainty estimation).

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Density measurements of liquefied natural gas (LNG) over the temperature range from (105 to 135) K at pressures up to 8.9 MPa

Abstract:
The (p, ρ, T, x) behaviour of five different synthetic liquefied natural gas (LNG) mixtures was investigated over the temperature range from (105 to 135) K at pressures up to 8.9 MPa utilizing a single-sinker magnetic suspension densimeter for cryogenic liquid mixtures. Due to the supercritical liquefaction procedure and the integration of a special VLE-cell, it was possible to measure densities in the homogeneous liquid phase of LNG without changing the composition. The mixtures were prepared gravimetrically and then analysed by gas chromatography according to highest metrological standards. The relative combined expanded uncertainty (k = 2) in density considering all effects, including the uncertainty in composition, was approximately 0.044% for all measurements. Comparisons of the new experimental data to the GERG-2008 equation of state for natural gas mixtures revealed clear and systematic deviations up to 0.22%. The reported uncertainty for the GERG-2008 equation is (0.1 to 0.5)% for the conditions considered, thus, all measured densities are represented well within this uncertainty range. Comparisons to density calculation methods often used in LNG industry, such as the revised Klosek and McKinley method as well as the COSTALD correlation, revealed that the quality of the calculations clearly depends on the pressure range and on the composition of the LNG mixture.

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Enhancement of the revised Klosek and McKinley method for density calculations of liquefied natural gas (LNG) over the temperature range from (100 to 135) K at pressures up to 10 MPa

By Christopher Tietz, Markus Richter, Reiner Kleinrahm and Roland Span

Abstract:
The revised Klosek and McKinley (RKM) method is a well-established model for the calculation of saturated liquid densities within the field of liquefied natural gas (LNG) custody transfer. Due to pressures higher than the vapor pressure in pipes from tanks to transfer stations, the densities resulting from this easy-to-use approach often deviate from the true density of the compressed liquid phase. However, higher pressures are typical for pipe flows in receiving terminals. Therefore, the applicability of the RKM method was expanded with the most recent highly accurate (p, ρ, T, x) data sets for six compressed LNG mixtures measured with a special densimeter for cryogenic liquid mixtures. The newly developed enhanced RKM (ERKM) method now enables density calculations of LNG mixtures at pressures up to 10 MPa, and the temperature restriction of the RKMmethod (T b 115 K) was expanded to reach temperatures up to 135 K. The estimated expanded uncertainty (k = 2) of the newly developed equation is 0.10% for the temperature range from (100 to 115) K and 0.15% for temperatures between (115 and 135) K at pressures up to 10MPa. Further restrictions of the method are basically the same as for the RKM method and are specified in more detail within the present paper.

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Development of a special single-sinker densimeter for cryogenic liquid mixtures and first results for a liquefied natural gas (LNG)

By Marcus Richter, Reiner Kleinrahm, Rafael Lentner, Roland Span

Abstract:
A special densimeter has been developed for accurate density measurements of liquid mixtures at cryogenic temperatures, e.g., liquefied natural gas (LNG). It covers the density range from (10 to 1000) kg · m−3, thus enabling density measurements in the supercritical region, in the homogeneous liquid region, along the saturated liquid line as well as in the homogeneous gas region. The apparatus is designed for measurements over a temperature range from (90 to 300) K at pressures up to 12 MPa. The densimeter is based on the Archimedes (buoyancy) principle and is a single-sinker system incorporating a magnetic suspension coupling. The density can be obtained directly without the need for calibration fluids. The relative combined expanded uncertainty (k = 2) for density measurements in the homogeneous liquid region (including the contribution resulting from the uncertainty of the sample gas analysis) was estimated to be 0.044%. First results for a synthetic five-component LNG mixture were obtained at the temperatures T = (105, 115, 120, 125, and 135) K with pressures up to 8.1 MPa. The results were compared to the GERG-2008 reference equation of state for natural gases, which represents the experimental values within 0.06%.

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Novel algorithm for calculating the methane number of liquefied natural gas with defined uncertainty

By Bjørn Gieseking, Andrew S. Brown

Abstract:
Liquefied natural gas (LNG) is increasing in importance both as an energy carrier and as a transport fuel. While the developments for an improved infrastructure for LNG are significantly advanced, no commonly agreed method for the characterization of LNG mixtures in terms of the so-called methane number (MN) exist. In this work we present a novel, simple and robust algorithm for calculating the methane number from LNG composition. It combines the detailed experimental data used to develop the commonly used method by AVL (“Anstalt für Verbrennungsmotoren Prof. H. List”) with automated calculation and optimisation routines that guarantee for a high degree of repeatability and reproducibility. This is in accordance with other modern MN calculation tools. The algorithm shows good agreement with other popular methods for a set of exemplar LNG mixtures covering a broad MN range between 60 and 99. Our comparison indicates that the observed differences between the methods might stem from different approaches used for the higher hydrocarbon and inert gas corrections. For the first time to our knowledge the algorithm also determines the uncertainty associated with the calculated MN yielding expanded uncertainties that vary between 0.2 and 0.7 MN depending on the composition of the mixture. We believe that incorporating the uncertainty associated with the calculation of the MN is important for developing a legislation for LNG quality as it would significantly enhance the confidence provided by the results of the calculation tools. In this context the definition of reasonable uncertainty limits in addition to a lower MN limit is recommended.

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The NIST/CEESI Liquid Nitrogen Flow Facility

This paper presents the current status of a liquid nitrogen calibration facility. Previously located on the NIST Boulder campus, it has been moved to the CEESI facility. The paper begins with a brief history, typical applications and a description of the operation. The discussion continues with a summary of the uncertainty components. Finally, the analysis of some historical data is presented:

The NIST_CEESI Liquid Nitrogen Flow Facility

Metrological support for LNG custody transfer and transport

In the framework of the ongoing EMRP Joint Research Project (JRP) ENG 60 “Metrology for LNG” (2014-2017), co-funded by the European Union, a number of metrological challenges associated with custody transfer and transport of LNG will be faced. The project consists of four technical work packages (WP), whereby the main objective is to reduce the measurement uncertainty of LNG custody transfer by a factor two. The focus in WP1 is the design and development of a traceable mid-scale calibration standard for LNG mass and volume flow. The goal is to provide traceable mass and volume flow calibrations up to 400 m3/h (180000 kg/h). In WP2, the emphasis is on the development and validation of a LNG sampling and composition measurement reference standard, consisting of sampler, vaporizer, gas standards, and gas chromatography (GC), which will be used to test and calibrate commercially available LNG sampling and composition measurement systems. The priority in WP3 is given to the development and validation of a method for the determination of the methane number, including correlations based on the LNG composition and corrections for traces of nitrogen and higher hydrocarbons. Since physical properties and quantities play an important role in LNG custody transfer, WP4 comprises reference quality density measurements of LNG to validate and improve models for LNG density predictions, the uncertainty evaluation of enthalpy and calorific value calculations and the development of a novel cryogenic sensor for the simultaneous measurement of speed-of-sound and density. The present paper gives an overview of recently achieved objectives within the project and provides an outlook to future activities.

Read the paper here: FLOMEKO_Metrological support for LNG custody transfer and transport

World’s first LNG research and calibration facility

A Liquefied Natural Gas (LNG) flowmeter research and calibration facility is being built in Rotterdam by the Dutch metrology institute VSL. This cryogenic test loop will also be used to test and develop LNG analysers, new technologies and devices for measurement of LNG physical properties. The facility will consist of a Primary Standard Loop (PSL) that can measure the mass of LNG flows traceable to the International Kilogram standard in Paris. The primary standard is capable of flow measurements up to 25 m3/hr. A second Midscale Standard Loop (MSL) will measure volumetric flow rate of up to 200 m3/h, expandable to at least 400 m3/h in the future. The Midscale standard is traceable to the PSL and scales the flowrate up using bootstrapping techniques. This paper describes the combined PSL and MSL facility, its objectives, and accomplishments to date.

Read the paper here: FLOMEKO_World’s first LNG research and calibration facility

Development of a special single-sinker densimeter for cryogenic liquid mixtures and first results for a liquefied natural gas (LNG)

By Marcus Richter, Reiner Kleinrahm, Rafael Lentner, Roland Span

Abstract:
A special densimeter has been developed for accurate density measurements of liquid mixtures at cryogenic temperatures, e.g., liquefied natural gas (LNG). It covers the density range from (10 to 1000) kg · m−3, thus enabling density measurements in the supercritical region, in the homogeneous liquid region, along the saturated liquid line as well as in the homogeneous gas region. The apparatus is designed for measurements over a temperature range from (90 to 300) K at pressures up to 12 MPa. The densimeter is based on the Archimedes (buoyancy) principle and is a single-sinker system incorporating a magnetic suspension coupling. The density can be obtained directly without the need for calibration fluids. The relative combined expanded uncertainty (k = 2) for density measurements in the homogeneous liquid region (including the contribution resulting from the uncertainty of the sample gas analysis) was estimated to be 0.044%. First results for a synthetic five-component LNG mixture were obtained at the temperatures T = (105, 115, 120, 125, and 135) K with pressures up to 8.1 MPa. The results were compared to the GERG-2008 reference equation of state for natural gases, which represents the experimental values within 0.06%.

Article in peer reviewed journal