LNG analysis and LNG sampling systems, options and solutions
LNG analysis and LNG sampling equipment
LNG analysis with Natural Gas Chromatograph NGC8206
- Relative density
- Heating value
- VOS (velocity of sound)
- GPM (gallons of liquid per thousand cubic feet)
- Wobbe index
- HCDP (hydrocarbon dew point)
- API 21.1 EFM capability
- AGA8 compressibility calculations
- H2S measurement
The NGC8206 enables you to remotely analyze natural gas composition from N2 to C6+ (optional H2S separation), and format this information for output to most third-party software systems.The unit’s integrated, 32-bit Windows® CE controller seamlessly processes all chromatograms, performs all needed calculations, and reports results in real time, for accurate and timely information on the product in process. The NGC8206 retains this as historical data, to be referred to later for custody transfer, or to verify transmitter operation performance.
The NGC8206 requires not only very little space (a mere 1.1 cubic feet) but also very little power (less than 7 watts), so it can be left continuously running.
The NGC8206 — one simple-to-operate device providing total energy measurement at every point along the natural gas supply chain, from the wellhead to the distribution market and everywhere in between.
LNG analysis Natural Gas Quality, C1-nC6 Hydrocarbon Composition, and BTU/Wobbe Monitoring
The MKS Precisive® product platform of innovative optical analyzers based on Tunable Filter Spectroscopy (TFS™) provides real-time gas analysis in the natural gas and hydrocarbon processing industries, including refineries, hydrocarbon processing plants, gas-to-power machines, biogas processes and fuel gas transportation and metering, while delivering customers a substantially lower total cost of ownership. Analytical Solutions and Products B.V. includes the Precisive® TFS™ in LNG analysis and LNG sampling systems.
Precisive® TFS™ can be utilized from UV (Ultra-Violet) through IR (Infra-Red) spectral regions. The Precisive® TFS™ sensor platform has been on the market since 2008 with more than 2500 systems deployed.
Precisive® optical sensors are the first widely deployed hydrocarbon composition monitors to feature real-time unattended analytics with hydrocarbon speciation capability equivalent to traditional Gas Chromatography (GC) instruments yet, with much lower cost of ownership.
Now a part of MKS Instruments, the Precisive® TFS™ sensor platform will be further developed for trace/ppm through bulk/% applications where a multi-component, low-maintenance, stable analytical sensor-transmitter is required that is well positioned between traditional NDIR (Non-Dispersive Infrared) and laboratory-grade FTIR (Fourier Transform Infrared).
LNG analysis with the GasPT natural Gas Properties Transmitter
GasPT is an online transducer that provides information regarding the physical properties of natural gas – hence the name natural Gas Properties Transmitter. GasPT provides the industry critical information about the physical properties of natural gas:
- Calorific Value (CV) / British Thermal Unit (BTU)
- Wobbe Index (WI)
- Relative Density (RD)
- Compression Factor (Z)
- Methane Number (MN)
- Total Air Requirement (TAR)
- Plus others
The GasPT measures a number of easily monitored physical properties of a sample of gas from which it infers a composition. From the inferred composition GasPT uses ISO 6976 to calculate Calorific Value, Density, Relative Density and Wobbe index. Analytical Solutions and Products B.V. includes the GasPT in LNG analysis and LNG sampling systems.
The uncertainty of information of the physical properties calculated by GasPT is equal to the uncertainty when using gas chromatography. However, the speed of response will reduce the overall uncertainty. When integrated with our VE Technology® sampling system (GasPTi), the total uncertainty can be reduced to 50% of that typically available with chromatography.
GasPT is straightforward to install, similar to a pressure or temperature transmitter. With our VE Technology sampling system it can be installed directly on the pipeline. The electrical/data connection is provided through a safety interface, which is supplied as standard, providing certification for Zone 1 hazardous areas and for certain applications Zone 0.
LNG transfer time at FSRU ‘s
Time is money! Every hour an LNG carrier can sail away earlier from a FSRU, will have a significant positive financial impact. So it is important that an LNG FSRU can always operate at its maximum flow rate to minimize transfer time. Consequently the LNG sampling pressure at the cross-over manifold at the FSRU ‘s will be at its minimum, in practice it can be lower than 1 BarG.
The LNG sampling for custody transfer is done by means of an analytical vaporizer connected to a sample container and on-line analyzer. The location of the LNG sampling point(s) is at the cross-over manifold. Nearly all analytical sampling systems until now operated at pressures above 2,5 BarG.
The Catch-22 is: lose money on waiting time of the LNG carrier (increase the pressure by squeezing flow), or lose money on inaccurate LNG analysis?
The ASaP Phazer, cryogenic LNG probe-vaporizer is a combined probe/vaporizer, for direct mounting on the LNG transfer line. The Phazer operates at any LNG pressure and vaporized samples allowing LNG analysis with the lowest uncertainty.
LNG probe-vaporizer for LNG sampling
The Phazer has proven its outstanding performance at LNG pressures of 0,8 BarG at tests and during Ship-to-Ship transfers. The total measurement (vaporizer, LNG sampling system and analyzer) standard deviation during the StS was just 0,0019 MJ/Nm3!
The Phazer conforms to ISO 8943 and is tested against EN 12838. Your LNG measurement is only as accurate as your provided sample… The Phazer is the only cryogenic LNG probe-vaporizer that provides verifiably accurate and representative LNG samples at 0,8 BarG.
Field study of LNG probe-vaporizers
Field study abstract
For comparison of two probe-vaporizer systems for LNG sampling first the main causes of bad sampling are discussed. Pre- and partial vaporization is a heat related issue that will cause part of the liquid sample to boil creating a two phase flow. Due to the different vapor pressures of the components a two phase flow can create concentration differences. The expected influence on the sample is the loss of homogeneity and compositional integrity, both important sample properties.
The experimental details are discussed, the used equipment and the gathering of data. Both tested systems are commercially available, as is the accumulator and online GC setup. Only the data from the online GC is gathered for the datasets.
Statistical analysis of the data is done with a Lilliefors, Wilcoxon, and Levene’s test. These are robust methods to determine if the data is normal, if measured means are equal, and if the variances are equal, respectively. System 1 produces a more stable trend with a higher precision. System 2 measures significantly higher concentrations on lighter components and lower concentrations on heavier components, indicating partial vaporization might be an issue.
Lastly, the experimental setup is discussed from a research perspective. Increased randomization or a matched pair comparison would be ideal if possible in a field test. To overcome the assumption of a stable process the comparison needs to be done at a test facility with specialized equipment. Such a testing facility is currently under construction for use in further studies.
Field study introduction
For the trade of Liquefied Natural Gas (LNG) the price is based upon the energy content in the LNG. The accuracy of the energy content determination is therefore of the utmost importance. Small differences in the measured concentrations are multiplied by the volume of the transfer and could be of significant value. In this article we will discuss the common pitfalls in LNG sampling for analysis as introduction in the subject. The field study of LNG probe-vaporizers is based upon the experimental comparison of two vaporizing probes in a true field situation.
LNG sampling challenges
Sampling LNG has more than a few challenges, among the most important are pre-vaporization and partial vaporization. Both of these challenges are closely connected to the cryogenic nature of the sample. Described in ISO 8943:2007, the sampled LNG needs to be in a liquid sub-cooled state, that is at a lower temperature than the boiling point at that pressure. The risk is that due to the very low boiling point of the LNG any heat transfer into the system can readily cause vaporization.
LNG is a mixture of components therefore we do not have a precise boiling point. Figure 1 depicts a schematic representation of a bubble point curve for a two components mixture. The bubble point curve of a mixture shows the temperature at which the liquid starts to boil. Consequently the components vapor pressures determine the concentration ratios in the gas relative to the liquid. Based upon this principle is fractional distillation. In the field this could happen in case a sample line is poorly isolated and the liquid is heated to the bubble point curve and vaporized. This temperature is also represented on the dew point curve, which means the vapor could condense in a different composition depending on the vapor pressures. For LNG we would expect higher methane readings in the gas than in the liquid, for the vapor pressure of methane>ethane>propane4–6.
The heat causing the LNG to pre-vaporize could come from the vaporizer upstream that heats up the tubing, poor isolation, or excess ambient heat. The heat influx is not necessarily enough to fully vaporize the LNG, which would result in any variation of two phase flow7–9 and an inhomogeneous sample. In my experience heat influx is mainly caused by bad isolation on a sample line, easily recognized by ice formation10. This phenomena influences both the composition and the homogeneity of the sample. One of the solutions provided to address this problem is the probe-vaporizer setup. These kind of vaporizers are directly connected to the probe which is installed in the sub-cooled process liquid. An example is shown in Figure 2, noticeably there is no sample line for the liquid reducing the opportunity for pre-vaporization.
ASaP introduces their revolutionary LNG probe-vaporizer
The Phazer conforms to ISO 8943 and is tested against EN 12838. Your LNG analysis is only as accurate as your provided sample… The Phazer is the only cryogenic LNG probe-vaporizer that provides verifiably accurate and representative LNG samples at 0,9 barg.
Phazer design criteria for LNG sampling
- Prevent pre- & partial vaporization => Secure LNG measurements and revenues!
- Full compliance with ISO 8943; 2007
- Tested against EN 12838
- Sampling at 0,9 barg => Fast LNG transfer!
- Insulation: special preservation for high-vacuum lifetime stability
- Operation of primary shut-off and boil-off control valve without breaking high-vacuum
- Safety; meets all requirements for hazardous area classifications
- Power supply is the only utility needed
- Extremely small footprint and weight
- Install in any orientation
- No moving parts
- Practically maintenance-free
- Flash vaporization
- Proper operation at low LNG line pressure
- Integrated Zero Dead Volume™ accumulator
- Simple installation
Our LNG probe-vaporizer is robust, compact, flexible and simple to install
- Small footprint; 70 x 25 cm ( 28” x 10” ) approximately 29 kg ( 64 lb.
- Low to High pressure
- Any orientation
- Power supply only
LNG sample quality, guaranteed results!
It eliminates any uncertainty of your LNG sample quality. It is the most accurate, reliable and flexible LNG probe-vaporizer available.
We build the Phazer with the highest quality materials and include certificates such as ATEX and DNV. ASaP is a reputable provider of analytical solutions; We can provide you with a full service
package including analyzers, system integration etc. You are kindly invited to consult us on any analytical challenge! The Phazer is manufactured by ASaP, an ISO 9001:2008 certified company in the Netherlands.
If you have questions about the LNG analysis and sampling, don’t hesitate to call or send an e-mail to our LNG expert Mr Hans-Peter Visser.