Liquefied Natural Gas Composition Research Articles

A multi-zone thermodynamic model for predicting LNG ageing in large cryogenic tanks

During the storage and transportation of liquefied natural gas (LNG), generation of boiloff gas (BOG) and change in the LNG composition, also known as LNG aging, are inevitable. Thus, a thermodynamic model that can accurately predict LNG aging during long-term operation is critical. This study presents a novel aging model, in which the LNG tank is divided into five zones: the vapor phase region, thermal stratification, bulk liquid region, boundary layer, and surrounding thermal insulation region. The heat and mass transport into different regions were calculated separately, and the thermal conductivity of the solid walls was considered as a function of temperature. Following model validation, simulations were performed for various thermal insulation conditions, ambient temperatures, and initial liquid compositions. From the results, the errors of the pressure, BOG rate and total heat flux could be approximated to 17, 7, and 14% respectively, for the previous models omitting the variation of thermal conductivity with temperature. As the initial methane fraction increased (i.e., N fraction decreases), the BOG rate decreased at the initial stage, while the BOG rate became less sensitive with the initial LNG composition as evaporation proceeded. Such an effect is determined by the variation in the latent heat of vaporization and total heat loss. This study can provide guidance for the design and operation of LNG storage tanks.

Влияние состава сжиженного природного газа на концентрационные пределы распространения пламени

PURPOSE. The growth in the production of liquefied natural gas (LNG) in the Russian Federation sets the tasks of increasing safety level in this segment of the economy. The key parameter of the object of study under consideration is the concentration limits of flame propagation, which are determined by methane for LNG. However, the composition of LNG varies depending on its brand, storage process, transportation and loading and unloading operations. This fact requires a detailed analysis of the concentration limits of flame propagation for various LNG compositions. METHODS. The analysis of changes in the lower concentration limits of flame propagation (LFL) of methane, ethane, propane and butane presented in various reference data was carried out. The calculation method was used to establish LFL for the model composition of LNG vapors, and to determine the error between calculation and experiment. FINDINGS. The analysis of regulatory documents showed that the LFL value of 4.4 % for liquefied gas is the special case and requires clarification based on the LNG brand, storage process, transportation, and loading and unloading operations. The experimental data demonstrate the decrease in LFL of the model composition of LNG for class B compared to the calculated ones, the relative error does not exceed 14 %. RESEARCH APPLICATION FIELD. The results obtained will make it possible to differentiate the approach for determining fire and explosion hazard of LNG based on brand and life cycles of liquefied natural gas, which will allow applying a differentiated approach to the requirements for fire and explosion safety of LNG based on its composition. CONCLUSIONS. The concentration limits of flame propagation for LNG model compositions were calculated. Further directions of work on improving the methodology for calculating the parameters of liquefied natural gas explosion were determined, and the discrepancy between the normatively fixed LFL parameter of LNG vapors and experimental data was shown. It is proposed to take into account the brands and aging processes of LNG to predict the concentration limits of flame propagation.

Transient performance study of high pressure fuel gas supply system for LNG fueled ships

The transient performance of the fuel system is a critical issue for the operation of liquefied natural gas (LNG) fueled ships. In this paper, experiments and simulations of a high pressure fuel gas supply system (HP-FGSS) were conducted to investigate the system transient responses during load variations and environmental disturbances. A prototype of the HP-FGSS was tested at different running loads from 0% to 110% in combination with a MAN high pressure two-stroke dual fuel engine. A dynamic model of the HP-FGSS was developed and validated by the test data. The effects of the operating parameters and equipment sizes on the system performances were simulated and analyzed. The results show that during the load variations from 75% to 100% the fuel gas pressure fluctuation is nearly 10 bar and lasts for 5 min. The HP-FGSS control system has a high robustness to the LNG composition, but the pressure overshoot increases as the methane content decreases. The LNG composition will also affect the steady state value of the gas temperature. The buffer tank volume has a significant impact on the pressure response. The pressure disturbance in the LNG tank induced by violent sloshing will be transmitted to the suction port of the high pressure pump, causing a cavitation risk.

Numerical computation of Boil off Rate (BoR) in shipboard LNG tanks

Natural gas is an environment-friendly fuel and a raw material for many chemicals. Its offshore transport is economical when the gas is transported in liquefied form as Liquefied Natural Gas (LNG) over distances (exceeding 2000 kilometers) by sea. LNG is stored at near-atmospheric pressure and about 112 K in these tanks. Heat inleak from the ambient into the stored LNG causes considerable boil-off of the LNG due to low latent heat of vaporization of LNG. Boil off Gas (BoG) generation should be reduced to minimize the loss of LNG as well as environmental pollution. Determination of the boil-off rate (BoR) poses a challenge because it involves interplay of multitude of phenomena and considerations, like liquid sloshing that is likely to generate heat and increases the interfacial area between the liquid and the ullage, variation in LNG composition due to BoG generation, and thermal stratification. In this paper we present a numerical analysis of the BoG generation, including some of the effects just mentioned. A model including transport phenomena based-equations and thermodynamic phase relations has been developed for this purpose.The simulation results would help in carrying out more in depth study of BoG generation that is useful in the design and operation of the prismatic membrane tanks.

Advanced boil-off gas studies of liquefied natural gas used for the space and energy industries

Growing interest in liquefied natural gas (LNG) as a rocket fuel demands reliable prediction and an improved understanding of the changes in its composition arising from the preferential boil-off of lighter components during long duration storage. Unfortunately, current methods of predicting boil-off gas (BOG) evolution from cryogenic liquids are based on limited experimental data. This work reports a series of new experiments which measure the temporal change in BOG production, composition, and pressure at industrially relevant conditions for both ternary mixtures of methane, ethane, and nitrogen and an LNG mixture used as rocket fuel. Faster pressure build-up rates are consistently observed with decreasing initial liquid volume fraction, whilst a decline of 8% in the LNG higher heating value was observed after thirty-three days of weathering. The data is compared with a robust and efficient superheated vapor (SHV) model, implemented in the software package BoilFAST, which allows for reliable calculations of self-pressurisation and boil-off losses for different tank geometries and thermal insulation systems. The model exhibits good agreement with the experimental data across all conditions explored. Finally, the potential effect of LNG composition and heating value changes on rocket engine performance was assessed by examining changes in the adiabatic flame temperature and burnt gas volume ratio. While our data suggest that the rocket engine performance would improve as a result of weathering, the effectiveness of the weathered LNG as a coolant in a regeneratively cooled rocket engine decreases.

Development of the chemical kinetic mechanism and modeling study on the ignition delay of liquefied natural gas (LNG) at intermediate to high temperatures and high pressures

In the past decade, liquefied natural gas (LNG) has attracted attention as a sustainable energy resource. The composition of LNG is one of the primary factors that has an influence on the engine knock and determines the fuel reactivity and the heat release in the combustion processes due to the presence of C1-C5 alkanes. The knocking behavior of LNG in gas engines is derived by the methane number (MN) which is directly related to the composition of the mixtures and the operating conditions. The determination of the methane number therefore demands a comprehensive characterization of a fuel mixture towards its auto-ignition properties such as ignition delay time (IDT) based on chemical kinetics of the fuel oxidation.In this study, a detailed chemical kinetic mechanism was developed to discover a correlation between the MNs and IDTs. The comparison of the modeling and experiments results of the ignition of different LNG mixtures containing C1-C5 alkanes and N2, and reference mixtures containing only CH4 and H2 with known MN were carried out in the temperature range 850–1550 K, at pressures of 10, 20 and 40 bar, and equivalence ratios (ϕ) of 0.4 and 1.2. The newly developed model demonstrates very good performance in simulating the IDT of various LNG mixtures, while the improvement in reduction of the maximal discrepancies between model and experiments is from factor 7–10 to 1–2. Moreover, the modeling studies provided a deeper understanding of the oxidation chemistry of the investigated mixtures.

Investigation of measurement uncertainties in LNG density and energy for custody transfer

In the custody transfer of fuels such as liquefied natural gas (LNG), energy measurement accuracy is critical. The important elements in calculating transferred energy are the volume, the density and the superior calorific value (SCV). In this paper we have used a new approach to carefully study the various uncertainty factors contributing to two of these elements: the density and the SCV. For density, six methods were evaluated, namely the method of extended corresponding states, the Hiza method, the revised Klosek–McKinley method, the Groupe Européen de Recherche Gazière (GERG-2004) method, the GERG-2008 method, and the equation of state–LNG method, to estimate the modelling error in the density calculation. Other factors affecting LNG density estimation (LNG composition, reference densimeter, temperature and pressure) have also been investigated to derive the total uncertainty in LNG density estimation. For the SCV, the uncertainty has been analysed with consideration given to uncertainties in the composition and the SCV of LNG components. The expanded uncertainty in LNG energy during custody transfer is estimated to be 0.58% (k = 2) after considering the uncertainties due to the membrane-type tank’s unloaded LNG volume, SCV, density and their correlation effect.

Impact of Liquefied Natural Gas Composition Changes on Methane Number as a Fuel Quality Requirement

The one of main quality requirements of natural gas as an engine fuel is the methane number (MN). This parameter indicates the fuel’s capability to avoid knocking in the engine. A higher MN value indicates a better natural gas quality for gas engines. Natural gas with higher methane content tends to have higher MN value. This study presents analysis of deviation of liquefied natural gas (LNG) composition and its impact on LNG quality as an engine fuel. The analysis of higher hydrocarbons and nitrogen content impact on LNG parameters was considered for several samples of LNG compositions. Most engine manufacturers want to set a new, lower limit value for methane number at 80. This fact causes significant restrictions on the range of variability in the composition of liquefied natural gas. The goal of this study was to determine the combination of the limit content of individual components in liquefied natural gas to achieve the strict methane number criterion (MN > 80). To fulfill this criterion, the methane content in LNG would have to exceed 93.7%mol, and a significant part of the LNG available on the market does not meet these requirements. The analysis also indicated that the methane number cannot be the only qualitative criterion, as its variability depends strongly on the LNG composition. To determine the applicability of LNG as an engine fuel, the simultaneous application of the methane number and Wobbe index criteria was proposed.

Mathematical model of liquefied natural gas evaporation and analysis of original composition effect on evaporation speed

Subject of Research. The paper proposes a model for predicting evaporation of liquefied natural gas (LNG) stored in tanks of regasification terminals. The model is a combination of the strict thermodynamic LNG vapor-liquid equilibrium and heat transfer realistic models. Analysis of the initial composition effect and the stock of LNG, the initial content of nitrogen and the value of the outside air temperature on the LNG evaporation rate is carried out. Method. A numerical experiment using a mathematical model of the LNG evaporation process was based on the LNG composition data and its storage time in aboveground tanks. The proposed method provided a number of advantages compared to previously developed models: the heat input to the low-temperature part of the LNG storage tank was calculated taking into account the outdoor temperature and the LNG composition; the evaporation coefficient was not an input parameter, but was calculated as part of the simulation; the LNG density was calculated by experimental correlation. Main Results. An important parameter in assessing the LNG loss from its evaporation is the nitrogen content in the liquid, which evaporates at a higher rate than methane, the main LNG component. Analysis of the initial composition effect on the LNG evaporation rate has shown that the growth of the nitrogen content in the initial mixture causes noticeable decrease in the evaporation rate due to the nitrogen priority evaporation and, as a consequence, the growth of latent mixture heat vaporization. Analysis of the initial LNG supply value at the evaporation rate has shown that a large degree of the tank filling causes an outstripping reduction in losses from evaporation. The result is an earlier reduction in the amount of boil-off gas (BOG, stripping gas) for more filled tank. Analysis of the outdoor temperature effect on the rate of LNG evaporation has shown that the ambient temperature change of 1 °C leads to the decrease in the BOG amount by 0.2 %. Practical Relevance. The proposed mathematical model of the LNG evaporation process reduces BOG formation during long-term storage, maintain the original LNG quality, optimizes the operational parameters of regasification terminals, and provides the consumers with reliable supply of high-quality natural gas.

Mathematical Model for Determination of Liquefied Natural Gas Density by Its Parameters and Composition

Liquefied natural gas (LNG) production and export are becoming one of the most strategically important segments in the Russian gas industry, and therefore the maintenance of LNG production and transporting infrastructure is deemed a critical problem. The commercial accounting of LNG is carried out in the tankers of LNG marine vessels using the static method. The shifting to the indirect dynamic method used in commercial accounting for other liquid hydrocarbons is hindered by the lack of a change measurement chain for flow and density transmitters. The regulatory documents recommend defining the density through calculations using the modified Klosek-McKinley method applied to the LNG composition, which leads to certain difficulties. This article offers a mathematical model for the calculation of density using the compositional analysis and the state parameters of LNG. The adequacy of the model was tested on five LNG mixtures with different compositions (from 72% up to 90% methane), temperatures (from 110 K up to 130 К), and pressure (from 0.08 MPa up to 0.4 MPa). In all cases, the calculation error did not exceed 0.15%. Using this model will help to shift to the dynamic method of LNG commercial accounting. It can also be used for forecasting density values based on changing LNG parameters, which can be useful during overseas transporting and reservoir filling in order to increase the safety of these processes.

Dynamic simulation of fuel tank aging for LNG‐fueled ship apparatus in an X‐DF Otto cycle engine

AbstractThe increased density in a liquefied natural gas (LNG) tank caused by boil‐off gas (BOG) is a key factor to consider for LNG‐fueled ships with Otto cycle engines. This study conducted dynamic simulation using Aspen HYSYS to solve LNG aging in the fuel gas supply system (FGSS) of an extra‐long stroke dual fuel (X‐DF) engine. The aging phenomenon is severe in the Otto cycle internal combustion engine because heavy hydrocarbon (HHC) components must be removed during the process to satisfy the methane number (MN) requirement. HHC components such as ethane, propane, butane are separated in the HHC removal process so that HHC can be returned to the LNG storage or fuel tank without increased risk of equipment failure relative to steady‐state design conditions. Dynamic process simulations for four cases were conducted to verify the behavior of LNG aging for two fuel compositions and two fuel tank capacities. The results indicate that the different composition of LNG affects the pump duty, the duty of heat exchanger and BOG compressor in steady‐state simulation. Additionally, based on the analysis results, solutions to the problem caused by LNG aging for the FGSS in an X‐DF engine were provided.

Analysis of boil-off rate problem in Liquefied Natural Gas (LNG) receiving terminals.

Liquefied natural gas (LNG) has an increasingly important role in the global natural gas market. Global demand for natural gas will grow over the coming years. LNG is transported by ships to unloading points at the storage terminals. During the LNG storage processes some part of LNG evaporates into gas phase. Evaporated LNG is called Boil-off gas (BOG). LNG is stored at cryogenic temperatures. Heat flow has an impact on evaporation process. It indicates there is continuous boil-off of small fraction or portion of LNG due to warming during storage process. This boil-off gas is generated primarily due to heat flow from the ambient air through tank insulation, unloading and recirculation-line insulation. Vaporization process causes changes in the composition of stored Liquefied Natural Gas. Increased vaporization process may negatively affect the stability and safety of the LNG storage process. Rate of vaporization (boil off rate) should be precisely determined. For these reasons different calculation models to determine the LNG boil-off rate are shown in this paper, also there are presented some boil off rate calculation results for different Liquefied Natural Gas compositions. Obtained results show that Boil-off rate is higher for LNG composition which contains nitrogen. Due to lower bubble temperature nitrogen evaporates first from the LNG, it causes significant LNG density drop in surface layer in storage tank. Difference of densities in surface and bottom layer of stored LNG may cause the stratification process and consequently affect the stability of storage process (possibility of roll-over phenomenon).

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

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.

The influence of chemical composition of LNG on the supercritical heat transfer in an intermediate fluid vaporizer

A three-dimensional transient computational fluid dynamics (CFD) model has been established for the simulations of supercritical heat transfer of real liquefied natural gas (LNG) mixture in a single tube and a tube bundle of an intermediate fluid vaporizer (IFV). The influence of chemical composition of LNG on the thermal performance has been analyzed. The results have also been compared with those obtained from the one-dimensional steady-state calculations using the distributed parameter model (DPM). It is found that the current DPM approach can give reasonable prediction accuracy for the thermal performance in the tube bundle but unsatisfactory prediction accuracy for that in a single tube as compared with the corresponding CFD data. As benchmarked against pure methane, the vaporization of an LNG containing about 90% (mole fraction) of methane would lead to an absolute deviation of 5.5 K in the outlet NG temperature and a maximum relative deviation of 11.4% in the tube side HTC in a bundle of about 816 U tubes at the inlet pressure of 12 MPa and mass flux of 200 kg·m−2·s−1. It is concluded that the influence of LNG composition on the thermal performance should be taken into consideration in order to obtain an economic and reliable design of an IFV.

Variations of fuel composition during storage at Liquefied Natural Gas refuelling stations

Liquefied Natural Gas (LNG) and Liquefied Biogas (LBG) utilization within the heavy duty transport sector is today a sustainable alternative to the use of oil.However, in spite of the high degree of insulation in the storage tank walls, it is impossible to fully avoid any net heat input from the surroundings. Due to some degree of vaporization this results in variation in gas composition during storage at refuelling stations, potentially leading to engine failures.Within this study, a vaporizer/sampler has been built and tested at a station delivering liquefied biomethane (LBG) and occasionally; such in this case, LNG to heavy and medium duty trucks. The vaporizer/sampler has then been used to study the variation of the LNG composition in the storage tank during a two weeks period. The results clearly underline a correlation between the gas phase and the liquid phase as the concentration changes follow the same trend in both phases. Two opposite effects are assumed to influence the concentration of methane, ethane and propane in the liquid and in the gas phase. On one hand, because of the probable presence of not fully mixed layers in the storage tank and due to vehicles being refuelled, both liquid and gas phases are enriched in methane at the expense of ethane and propane. On the other hand, due to boil-off effect towards the end of the storage period, both liquid and gas phases are enriched in ethane and propane at the expense of methane.

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

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 0.7MN 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.

Weathering prediction model for stored liquefied natural gas (LNG)

A model is proposed to predict the weathering of LNG stored in containment tanks, typically used in regasification terminals, due to the effects of heat ingress and Boil-off-Gas (BOG) release. The model integrates a rigorous thermodynamic model of LNG vapour–liquid equilibrium and a realistic heat transfer model. It provides a number of advances on previously developed models, in so far as: (i) heat ingress is calculated based on the outside temperature and LNG composition, that allows for daily or seasonal variation; (ii) Boil-off-Ratio is not an input parameter, but is calculated as part of the simulations and (iii) the LNG density is estimated using an accurate experimentally based correlation.The model was validated using real industry data and the agreement obtained in predicting the overall composition of weathered LNG, its density and the amount vaporized was within current industry requirements. The model was run in the predictive mode to explore the sensitivity of BOG to different scenarios. In the initial stages of weathering the nitrogen content of LNG will have a marked effect on BOG generation. Even the presence of 0.5% of nitrogen will lead to nearly a 7% decrease in BOG, making the initial BOG unmarketable. The high sensitivity is a result of preferential evaporation of nitrogen and increase in the direct differential molar latent heat. In the final stages of weathering the heavier hydrocarbons govern the dynamics of BOG which becomes a strong function of the initial composition and the level of LNG remaining in the storage tank.The change in ambient temperature of 1 °C will lead to a change in BOG of 0.2%, irrespective of the size of the tank and initial LNG composition.

LNG energy transfer uncertainty–sensitivity to composition and temperature changes

Determining and reducing the measurement uncertainty of LNG energy transfer in custody transfer operations is considered extremely important and challenging for industry. The European Metrology Research Programme (EMRP) for Liquefied Natural Gas (LNG) has been focused on reducing the uncertainty in the evaluation of LNG energy transfers by improving existing measurement methods, validating new measurement methods and development of new traceable calibration systems. Part of this project was to produce realistic measurement uncertainty budgets and to determine the sensitivity of the overall LNG energy transfer uncertainty to changes in the composition and temperature of different LNG cargoes.This paper provides details on the development of an uncertainty budget and the results from the sensitivity study. It was found that the uncertainty in the LNG energy transfer ranged from 0.56% to 0.77% when using the uncertainty budget for 461 LNG cargoes. The variation was mainly due to the difference in the LNG composition and its associated uncertainty.

Final report on EURAMET.QM-S6/1195: Bilateral comparison of liquefied hydrocarbon mixtures in constant pressure (piston) cylinders

Traceable liquid hydrocarbon mixtures are required in order to underpin measurements of the composition and other physical properties of LPG (liquefied petroleum gas) and LNG (liquefied natural gas), thus meeting the needs of an increasingly large European industrial market.The development of traceable liquid hydrocarbon standards by National Measurement Institutes (NMIs) was still at a relatively early stage at the time this comparison was proposed in 2011. NPL and VSL, who were the only NMIs active in this area, had developed methods for the preparation and analysis of such standards in constant pressure (piston) cylinders, but neither laboratory had Calibration and Measurement Capabilities (CMCs) for these mixtures.This report presents the results of EURAMET 1195, the first comparison of liquid hydrocarbon mixtures between NMIs, which assessed the preparation and analytical capabilities of NPL and VSL for these mixtures. The comparison operated between August 2011 and January 2012. Each laboratory prepared a liquid hydrocarbon standard with nominally the same composition and these standards were exchanged for analysis.The results of the comparison show a good agreement between the laboratories' results and the comparison reference values for the six components with amount fractions greater than 1.0 cmol/mol (propane, propene, iso-butene, n-butane, iso-butane and 1-butene). Measurement of the three components with lower amount fractions (1,3-butadiene, iso-pentane and n-pentane) proved more challenging. In all but one case, the differences from the comparison reference values for these three components were greater than the expanded measurement uncertainty.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by EURAMET, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Calculation models for prediction of Liquefied Natural Gas (LNG) ageing during ship transportation

Abstract A group of European gas transportation companies within the European Gas Research Group launched in 2007 the ‘MOLAS’ Project to provide a software program for the analysis of the Liquefied Natural Gas (LNG) ageing process during ship transportation. This program contains two different modeling approaches: a physical algorithm and an ‘intelligent’ model. Both models are fed with the same input data, which is composed of the ship characteristics (BOR and capacity), voyage duration, LNG composition, temperature, pressure, and volume occupied by liquid phase at the port of origin, together with pressure at the port of destination. The results obtained are the LNG composition, temperature and liquid volume at the port of destination. Furthermore, the physical model obtains the evolution over time of such variables en route as it is based on unsteady mass balances over the system, while the i-model applies neural networks to obtain regression coefficients from historical data composed only of origin and destination measurements. This paper describes both models and validates them from previous published models and experimental data measured in ENAGAS LNG regasification plants.