Liquefaction Capacity Research Articles

Influence of physical properties and shear rate on static liquefaction of saturated loess

Flow sliding instability of saturated loess slopes is a common geological hazard in loess areas of China. Previous studies have found that the occurrence of flow-slip loess landslides is closely related to static liquefaction and is controlled by physical characteristics and load conditions. In this work, we comprehensively study these influences of physical properties (i.e. initial pore structure, gradation, dry density) and shear rate on the static liquefaction of saturated loess through a series of consolidated undrained triaxial tests, and the effect mechanism of these related factors on the static liquefaction of saturated loess are also discussed. The results present that: (1) The peak deviator stress and the maximum pore pressure of the undisturbed loess are much greater than these of the remodeled one under each level of confining pressure (except 450 kPa). Further, the calculated liquefaction potential index (LPI) of undisturbed loess is much greater, indicating that undisturbed loess is more prone to static liquefaction due to the initial pore structure. (2) The lower the relative clay/silt content ratio of the saturated remodeled loess, the stronger the potential liquefaction ability. With the increase of the relative content of clay from 0.125 to 0.698, the stress-strain curve gradually transitions from strain softening to hardening. (3) The remodeled loess show the steady-state strength tends to continuously increase with the increase of dry density from 1.38 g/cm3 to 1.56 g/cm3, while the LPI increases first and then decreases, and the largest value appears when the dry density reaches to 1.44 g/cm3. The reason is that the value of 1.44 g/cm3 is the normal consolidated condition, which essentially reflects the potential liquefaction change during the transformation from under consolidated to over consolidated state.(4) The effect of shear rate on the stress-strain curve of remolded loess is not significant, but the peak strength and ultimate pore pressure show a trend of increasing and then decreasing with the increase of shear rate. There exists a “critical shear rate “of 0.1 mm/min reflecting the liquefaction of loess is more likely to occur when reaches to this critical value. (5) Based on the comparison of static liquefaction tests, the influencing factors of static liquefaction of saturated loess are: initial pore structure> gradation > dry density > shear rate. This study can provide a systematic evaluation for understanding the influencing factors of static liquefaction capacity of saturated loess (especially remolded one), and also has a reference for explaining the loess flow-sliding failure mechanism under disturbance conditions.

The design and research of two-stage series-connected helium turbine expanders for hydrogen liquefaction system

The helium turbine expander, is a crucial part of hydrogen liquefaction systems, that determines the overall efficiency of the system. In this paper, a two-stage series-connected helium turbine expanders is designed to achieve a hydrogen liquefaction capacity of 1.7 tonnes per day (TPD). The proposed expander is based on the reverse Brayton cycle and realizes a high pressure ratio of 8.32 to meet the design objective. A dynamic design process in the expansion end is developed and numerically simulated based on the turbine expander design methodology. The off-rated condition performance of the turbine expander is predicted by adjusting the rotational speed and flow rate. The results show that the reasonable rotational speed range of the turbine expander is 46000–54000 RPM, and the reasonable flow coefficient range is 0.6–1.2, which can maintain a high level of efficiency. The internal flow characteristics of the turbine expander are analysed through numerical simulation. The results show that the outlet temperature is suitable for hydrogen liquefaction, and flow loss mainly occurs in the upper-middle part of the impeller and near the tip clearance, followed by the throat of the nozzle. In the prototype tests to verify the rationality of the design of the turbine expanders, the experimental results show that the two turbine expanders can achieve a temperature drop of 31 K, and isentropic efficiencies of 76.8 % and 80.5 %, respectively, which are higher than the design requirements of 75 %. The actual outlet temperature and isentropic efficiency are compared with the numerical simulation results. The errors are less than 4 % and 10 %, respectively, which means that the prototype manufacturing precision meets the system requirements perfectly. Thus, the design of the two-stage series-connected turbine expanders can satisfy the performance design requirements.

Exergy analysis and improvement of helium internal purifier

Exergy analysis was applied to the evaluation of helium internal purifier in this paper. The important operating parameters has been given to determine the exergy destructions in components as well as in the entire cycle of internal purifier. The analysis results show that the recovery of liquefied air energy can improve the performance of purifier and the exergy destruction of different heat exchanger is different. Results from the analysis helped evolving guidelines for designing appropriate technological process for practical helium internal purifier. An internal purifier with an optimized structure was designed to remove air impurities up to 10 mol%, beyond previous maximum impurity content. The impact on liquefaction capacity is minimized because of the small consumption of cold flow. The achievable performance was also provided in this paper. The purifier could remove air impurities up to 8 mol%.

Assessment of liquefaction potential based on shear wave velocity: Strain energy approach

Liquefaction assessment based on strain energy is significantly superior to conventional stress-based methods. The main purpose of the present study is to investigate the correlation between shear wave velocity and strain energy capacity of silty sands. The dissipated energy until liquefaction occurs was calculated by analyzing the results of three series of comprehensive cyclic direct simple shear and triaxial tests on Ottawa F65, Nevada, and Firoozkuh sands with varying silt content by weight and relative densities. Additionally, the shear wave velocity of each series was obtained using bender element or resonant column tests. Consequently, for the first time, a liquefaction triggering criterion, relating to effective overburden normalized liquefaction capacity energy (WL/σc’) to effective overburden stress-corrected shear wave velocity (Vs1) has been introduced. The accuracy of the proposed criteria was evaluated using in situ data. The results confirm the ability of shear wave velocity as a distinguishing parameter for separating liquefied and non-liquefied soils when it is calculated against liquefaction capacity energy (WL/σc’). However, the proposed WL/σc’-Vs1 curve, similar to previously proposed cyclic resistance ratio (CRR)-Vs1 relationships, should be used conservatively for fields vulnerable to liquefaction-induced lateral spreading.

Big Players Pivot in Response to Regulatory Pressures

_ Early January brought with it significant changes in the environmental side of the oil and gas industry. ExxonMobil and Chevron, the two largest US oil producers, announced they will exit California, and the Biden administration froze LNG export approvals. After 50 years of producing oil in California, ExxonMobil will take a $2.5 billion writedown of the value of some of its California properties to be recorded in its fourth-quarter earnings. The company said the decision is primarily related to its Santa Ynez operations off the coast of Santa Barbara. Its US Securities and Exchange Commission (SEC) filing said, “While the Corporation is progressing efforts to enable a restart of production, continuing challenges in the state regulatory environment have impeded progress in restoring operations.” After the Refugio oil spill in May 2015 (approximately 100,000 gal), resulting from a leak from a pipeline owned by Plains All American Pipeline, ExxonMobil acquired the damaged asset in October 2015. Just a few months before the purchase, the Santa Barbara County Board denied ExxonMobil’s request to truck its oil produced off the coast of Gaviota to its Las Flores Canyon processing facility and on to refiners located in Pentland, California. Seeking an alternative, ExxonMobil planned to replace two stretches of the 112-mile corroded pipeline for transit of its oil. Met with opposition to replace the damaged pipeline and denied permission to repair and restart production at the site (halted since 2015), ExxonMobil is now selling the Santa Ynez operation to Sable Offshore, a blank-check company created in 2020. The company will loan Sable the money for the purchase of its three offshore production platforms, pipeline, and onshore processing facility. Sable’s agreement with ExxonMobil requires production to be started by early 2026 or the assets and liabilities revert to ExxonMobil. Chevron, headquartered in San Ramon, California, will write down $3.5 billion to $4 billion in assets, citing its home state’s regulations that “have resulted in lower anticipated future investment levels.” The company intends to continue operating its oil fields and related assets. In the SEC filing, Chevron wrote it also will incur fourth-quarter charges related to decommissioning of US Gulf of Mexico assets that have reached the end of their productive lives. The company sold some of those assets, but US law stipulates that previous owners may be responsible for those costs if the current owner declares bankruptcy. Chevron wrote it’s “probable” that it may see such costs. January closed with another unexpected announcement on 26 January. The Biden administration paused decisions on permits to export LNG to non-free trade agreement countries to review current projects seeking approvals. US Energy Secretary Jennifer Granholm stated, “We must review export applications using the most comprehensive, up-to-date analysis of the economic, environmental, and national security considerations.” She added that this was not a ban on exports and would not affect already authorized exports, which when combined with existing plants, total 48 Bcf/D. “Within this decade another 12 Bcf/D of US export capacity already authorized and under construction will come online,” Granholm said. While environmental impact (greenhouse gas emissions including CO2 and methane) was one of the reasons for the decision, along with market, economic, national security, and energy security, Granholm pointed out that facilities totaling 22 Bcf/D of capacity have been approved but have not yet started construction. This capacity, combined with existing infrastructure, is “more than enough to make the US a ‘behemoth’ in the LNG field,” according to Holland & Knight in an analysis dated 29 January. The international law firm said this raises the question of whether further development of LNG facilities could hurt US citizens as higher percentages of produced gas are exported. “This line of thinking follows the historical rhetoric on this issue as domestic users of natural gas want to ensure their feedstock price is stable. To support those claims, recent studies have concluded that ‘higher LNG exports create a tighter domestic natural gas market (all else held equal), increasing domestic natural gas prices.’” Could unintended consequences of these recent announcements rear up in the future? And could they be a behemoth for the US or global markets? For Further Reading Growth in 2022 US LNG Liquefaction Capacity Hits Top of the Charts by Pat Davis Szymczak, SPE Oil and Gas Facilities.

Thermodynamic and economic analysis of new coupling processes with large-scale hydrogen liquefaction process and liquid air energy storage

Liquid hydrogen serves as an environmentally friendly energy carrier, playing a crucial role in alleviating greenhouse effects. In order to tackle the challenges concerning energy consumption and economic costs, it becomes imperative to develop an efficient and cost-effective large-scale hydrogen liquefaction process (LHLS). This study integrates of LHLS with liquefied air energy storage (LAES) and introduces three liquefaction processes to reduce the economic cost associated with hydrogen liquefaction. By coupling LAES, electricity generated during off-peak hours can be stored and subsequently utilized in LHLS operations during peak hours, leading to a reduction in electricity costs. Furthermore, utilizing the surplus cooling capacity of LAES can enhance the efficiency of LHLS. A genetic algorithm is used to optimize the coupling processes. The calculated total annual cost (TAC) of the most economically viable coupling process amounts to 12271.8 k$/year, representing in a 20.91 % reduction compared to the independent LHLS. This indicate a clear economic advantage with the coupling process. The levelized cost of hydrogen (LCOH) and the payback period (PBP) for this particular coupling process are 2.523 $/kg and 4.56 years, respectively. A sensitivity analysis reveals that the economic benefits of the coupling processes escalate with higher electricity prices and greater liquefaction capacity.

Relevance and potential of the Arctic Sea Routes on the LNG trade

The retreat of the ice around the freezing waters of the Arctic Ocean is opening new waterways where shipping activity could transport commodities between continents. One of the essential products is natural gas - LNG, which is transported in large tankers from exporters to importers. This study aims to explore the dynamics of the LNG trade by using these new tentative routes with conventional sea lanes and estimating the changes in the LNG trade. We utilize Agent-Based Modeling to develop a global LNG model with interactive GIS features, where the agents are the players in the LNG market. The results demonstrate the preponderance of the North-East Passage (NEP, Eurasian Arctic waters) over the North-Western Passage (NWP, the Canadian Arctic) in providing a shortcut connecting Europe with Asia. This passage favors a growing exporter like Russia with exporting facilities in Siberia and future strategic projects to increase liquefaction capacity. The NEP becomes crucial when considering scenarios of a European ban on Russian imports, as European countries are planning due to the crisis with Russia. On the importing side, the Asian Pacific and South Asian importers are the winners with a diverse and shorter LNG supply source. Future Canadian projects may also benefit from these new highways. However, there are also substantial challenges to providing the NEP with the proper infrastructure and systems to make the Polar LNG journeys safe and sound shortly. Beyond that, the Arctic sea corridors may alleviate the high LNG transit through the conventional routes and their chokepoints, but they are not a replacement for the conventional ones, not even with the most favorable conditions.

Techno-economic analysis on nitrogen reverse Brayton cycles for efficient coalbed methane liquefaction process

Recovery of coalbed methane (CBM) is of great significance for environmental protection, safe production of coal mines, and clean energy supply. To reveal the efficiency difference of different nitrogen reverse Brayton cycles (N2-RBC) for recovering CBM and identify the most efficient N2-RBC in terms of energy consumption and economy, four typical N2-RBCs were studied numerically. Each process was optimized globally by performing genetic algorithm (GA) procedure, using specific power consumption (SPC) per unit product as the objective function. Pinch analysis approach was used to improve N2-RBC. All proposed processes were assessed comprehensively concerning efficiency, exergy loss, and economy. It is found that the slope of the hot/cold composite curve is greatly influenced by the material streams’ mass flow rate while slightly affected by the specific heat except for the region near critical parameters. The parallel arrangement of expanders reaches a better match between hot and cold composite curves than the series. For the liquefaction capacity of 10 tons per day, the liquefaction process using parallel N2-RBC achieves the lowest SPC of 0.72 kWh·kg−1 and the highest figure of merit of 31.11%. It also has the lowest exergy loss of 180.1 kW and a total investment of 4047.76 k$, respectively.

Optimization and control strategy of BOG re-liquefaction process for LNG vessels

The re-liquefaction of BOG is a necessary part of the safety and security of LNG cargo ships. And the volatility of BOG will fluctuate with the sea conditions of ship transportation, so how to deal with the fluctuation of the re-liquefaction system and improve the liquefaction capacity is a problem that cannot be ignored in the operation of the liquefaction system; In this paper, a BOG buffer tank is added to the Reverse Brayton Process. Moreover, a control strategy is proposed to optimize the liquefaction process. The proposed four possible operating conditions' efficiency,the specific energy consumption (SEC), liquefaction rate and main heat exchanger parameters were simulated and analyzed by using Aspen HYSYS software. According to the results, the specific energy consumption of the basic re-liquefaction process is 1.329 kWh/kgLNG, which is 5.7% less than that of the reference process; In the study of flow fluctuation, after adopting the control strategy, the specific energy consumption of the whole process is 1.29 kWh/kgLNG, with 15.6% efficiency and 99.5% liquefaction rate. The whole system can be maintained at a low specific energy consumption level when the feed gas volume is fluctuating. The analyses of various BOG composition and the parameters of the main heat exchanger show that the regulation of the inlet gas volume can make the primary re-liquefaction process flexible and maintain the heat exchanger in a good working condition; Even if the system is in a worse working condition, the inlet gas volume can be improved by 12.2% compared with the reference process.

Development of Advanced Hydrogen Liquefaction System by using Magnetic Refrigeration Technology for JST-MIRAI Large-scale Project

For the supply chain of hydrogen, as the liquefaction cost may occupy 1/3 of the total supply price, developing a highly efficient hydrogen liquefier is one of the most important technology issues for hydrogen society. Magnetic refrigeration using the magnetocaloric effect has the potential to realize liquefaction efficiency higher than 50 %, and also to be environmentally friendly and cost effective. A hybrid refrigeration cycle consisting of the precooling cycle and magnetic active regenerator cycle has been proposed and is estimated to achieve a liquefaction capacity of >100 kg/day with liquefaction efficiency of >50 %.

Study on Performance Comparison of Two Hydrogen Liquefaction Processes Based on the Claude Cycle and the Brayton Refrigeration Cycle

Hydrogen liquefaction is an essential section for efficient storage and transportation of hydrogen energy. Both the Claude cycle and Brayton refrigeration cycle are available for large-scale hydrogen liquefaction systems. Two large-scale hydrogen liquefiers with the liquefaction capacity of 120 t/d based on the Brayton refrigeration cycle and the Claude cycle, respectively, are analyzed and compared in this study. Sensitivity analysis is used to optimize the parameters of two liquefaction systems in HYSYS. According to the results, the exergy loss and specific energy consumption of the Claude liquefier are 18.98 MW and 5.62 kWh/kgLH, which are 6.6% and 4.4% less than those of the Brayton liquefier, respectively. Exergy analysis reveals the exergy loss of compression and expansion systems in the Claude liquefier is less than that of the Brayton liquefier, while the exergy loss of the throttle valve in the Claude liquefier is more notable. In addition, the molar flow rate of hydrogen used as refrigerant in the Claude liquefier is 10.6% less than that of refrigerant in the Brayton liquefier. Owing to the smaller size requirements of equipment and the lower specific energy consumption, the Claude cycle is more suitable for large-scale hydrogen liquefaction processes.

Liquefaction Evaluation of Microbial Induced Calcium Carbonate Precipitation (MICP) Treated Sands; A Strain Energy Approach

ABSTRACT The present research investigates liquefaction behavior of microbial induced calcium carbonate precipitation (MICP)-treated Nevada sand with different silt content, for the first time in terms of dissipated strain energy. The obtained results indicated that normalized liquefaction capacity energy for MICP-treated soil was dependent on the CSR and NL. Moreover, acceptable relationships between the excess pore water pressure ratio and dissipated energy were found for both MICP-treated and untreated samples. Furthermore, Bender element tests results proved that shear wave velocities had a stronger relationship with rather than CSR, while, MICP treatment changed the relationship between and liquefaction resistance.

Title Supersonic Condensation and Separation Characteristics of CO2-Rich Natural Gas under Different Pressures

Supersonic separation technology is a new natural gas sweetening method for the treatment of natural gas with high CO2 (carbon dioxide) content. The structures of the Laval nozzle and the supersonic separator were designed, and the mathematical models of supersonic condensation and swirling separation for CO2-CH4 mixture gas were established. The supersonic condensation characteristics of CO2 in natural gas and the separation characteristics of condensed droplets under different inlet pressures were studied. The results show that higher inlet pressure results in a larger droplet radius and higher liquid phase mass fraction; additionally, the influence of centrifugal force is more pronounced, and the separation efficiency and removal efficiency of CO2 are higher. When the inlet pressure is 6 and 9 MPa, the liquefaction efficiency at the Laval nozzle outlet increases from 56.90% to 79.97%, and the outlet droplet radius increases from 0.39 to 0.72 μm, and the removal efficiency is 31.25% and 54.52%, respectively. The effects of inlet pressures on the removal efficiency of the supersonic separator are complicated and are controlled by the combined effects of liquefaction capacity of the nozzle and centrifugal separation capacity of the swirl vane.

Numerical simulation of carbon separation with shock waves and phase change in supersonic separators

The current study evaluated a potential carbon separation method. Based on engineering thermodynamics, heat transfer and phase transition dynamics, a mathematical model is proposed to predict the phase change in high pressure supersonic flow, and a flue gas model after dehydration, desulfurization and denitration is established. The flow features with shock waves and spontaneous condensation in the supersonic separator are clarified, the influence of flow model on shock waves and flow features is quantified, and the energy recovery process with phase change is studied. The results show that flue gas enters the supercooled state near the throat, reaches Wilson point at x = 0.077 m, and the nucleation rate surges from 0 to 4.46 × 1020 m−3 s−1. When vapor molecules reach the surface of droplets, droplets grow, and latent heat is transferred from droplets to the vapor phase, resulting in condensation wave. A shock wave is generated at the diffuser inlet, and the flow and liquid phase parameters change abruptly after the shock wave. The single-phase model incorrectly predicted the separator refrigeration capacity, flue gas expansion capacity, location and intensity of the shock wave, and the maximum deviation is up to 65.5%. Excessive improvement of pressure recovery efficiency results in reducing the liquefaction capacity of the separator.

The Design and Optimization of Natural Gas Liquefaction Processes: A Review

As the energy crisis intensifies, the global demand for natural gas is growing rapidly. Liquefied natural gas (LNG) technology is among the delivery solutions with flexible and reliable application prospects and is already a significant field of research in energy utilization. The performance of natural gas liquefaction process has a major influence on the production capacity, energy consumption, economics, and safety of the entire supply chain. Many scholars have conducted numerous studies on various LNG processes and designed many classical processes. This paper summarizes and discusses current research status and development level in the design and optimization of natural gas liquefaction processes in recent years, mainly focusing on cascade liquefaction process, expansion liquefaction process, and mixed refrigerant liquefaction process. The advantages and disadvantages of various liquefaction processes are compared and analyzed in terms of liquefaction capacity, energy consumption, economy, safety, and adaptability. In addition, the rapid development of pressurized liquefaction technology in recent years and its application outlooks are also introduced in detail. Finally, the present situation and industrial demand of LNG process are analyzed, and reasonable suggestions and future research prospects are put forward.

Sustainable design and analysis for helium extraction from sale gas in liquefied natural gas production

Currently, natural gas (NG) is an economically proven source of helium with up to 8 mol% concentration. Helium extraction at earlier stages in the natural gas liquefaction plant shows a motivating initiative to improve the economics and environmental aspects. Cryogenic fractionation is the most industrially used technology to recover helium from natural gas compared to other available technologies such as adsorption and membrane. In this work, three cryogenic-based fractionation processes, namely cold box, single column, and double columns, are assessed from technical, economic, and environmental perspectives. Aspen HYSYS simulation package is utilized to develop 1400 MMSCFD NG liquefaction capacity models for different helium concentrations. Cold box technology indicates the highest net profit per kg of helium recovery approximated at $260 for the case of a 10% ratio of sales gas vs. 90% LNG with a 1% initial helium concentration scenario. However, single column and double column technologies report the highest reduction in energy and emissions when integrating helium recovery and NG liquefaction with a 86% reduction for the same scenario.

Cascade JT systems with single-component refrigerants for hydrogen liquefaction

A thermodynamic study is carried out for hydrogen liquefaction with cascade Joule-Thomson (JT) systems, which do not require any expansion machines. Since there is no moving part at cryogenic temperatures, the cascade JT systems have a potential advantage of high reliability and easy scale-up of liquefaction capacity, as demonstrated in the full-scale LNG plants under operation. A variety of combinations for pre-cooling JT cycles with single-component refrigerants (including neon, nitrogen, argon, oxygen, hydrocarbons, and ammonia) are investigated to estimate the figure of merit (FOM) as a performance index of liquefaction. In every JT cycle, the pressure levels are optimized to maximize the FOM with a process simulator (Aspen HYSYS) and real properties of working fluids (NIST REFPROP). It is rigorously shown that the cascade JT systems can achieve a reasonably high FOM, if the irreversibility below 77 K is effectively reduced. A few suitable cascade systems for large-capacity hydrogen liquefaction are identified, and the details of optimized cycles are presented.

Experimental investigations on high pressure ratio cryogenic turboexpanders for helium liquefier

Experimental investigations of two variants of a high pressure ratio cryogenic turboexpander, from a new series of turboexpanders for Bhabha Atomic Research Centre (BARC), are presented in the article. Both the variants are designed based on an earlier reported enhanced midstream method. The new turboexpanders are designed with larger turbine impeller-diffuser radial clearances and smaller turbine impeller L/D ratio as compared to previous series of BARC turboexpanders. The experimental investigations are carried out in BARC developed helium refrigerator CP1000 and helium liquefier LHP50. Different aspects of turboexpander performance, as defined by isentropic efficiency, pressure ratio and power developed in response to variation in parameters such as turboexpander flow and operational specific speeds, are presented in detail. The idea of using process turboexpanders for the mass flow measurements is also briefly studied using the results of the experiments. Experiment is also devised to compute heat-in-leak from turboexpander mountings and the results are used to critically analyse and provide corrections to the thermodynamic performance of the turboexpanders achieved during other experiments. From the two new variants of the turboexpanders investigated here, the better performing one is selected and mounted on LHP50 as TEX-2 for determining the maximum helium liquefaction capacity. LHP50 plant performance is then compared to the earlier reported liquefaction capacities with previous versions of BARC turboexpanders.

Application of Feedforward Neural Network and SPT Results in the Estimation of Seismic Soil Liquefaction Triggering.

Soil liquefaction is a dangerous phenomenon for structures that lose their shear strength and soil resistance, occurring during seismic shocks such as earthquakes or sudden stress conditions. Determining the liquefaction and nonliquefaction capacity of soil is a difficult but necessary job when constructing structures in earthquake zones. Usually, the possibility of soil liquefaction is determined by laboratory tests on soil samples subjected to dynamic loads, and this is time-consuming and costly. Therefore, this study focuses on the development of a machine learning model called a Forward Neural Network (FNN) to estimate the activation of soil liquefaction under seismic condition. The database is collected from the published literature, including 270 liquefaction cases and 216 nonliquefaction case histories under different geological conditions and earthquakes used for construction and confirming the model. The model is built and optimized for hyperparameters based on a technique known as random search (RS). Then, the L2 regularization technique is used to solve the overfitting problem of the model. The analysis results are compared with a series of empirical formulas as well as some popular machine learning (ML) models. The results show that the RS-L2-FNN model successfully predicts soil liquefaction with an accuracy of 90.33% on the entire dataset and an average accuracy of 88.4% after 300 simulations which takes into account the random split of the datasets. Compared with the empirical formulas as well as other machine learning models, the RS-L2-FNN model shows superior performance and solves the overfitting problem of the model. In addition, the global sensitivity analysis technique is used to detect the most important input characteristics affecting the activation prediction of liquefied soils. The results show that the corrected SPT resistance (N1)60 is the most important input variable, affecting the determination of the liquefaction capacity of the soil. This study provides a powerful tool that allows rapid and accurate prediction of liquefaction based on several basic soil properties.

Weed colonization‐based performance improvement opportunities in dual‐mixed refrigerant natural gas liquefaction process

AbstractDual‐mixed refrigerant (DMR) process is a promising candidate for liquefying the natural gas (LNG) at onshore as well as offshore sites, thanks to its higher liquefaction capacity and flexibility in using full gas turbines. DMR involves two mixed refrigerant cycles to perform precooling and subcooling of natural gas (NG), and these refrigerant compositions need constant tweaking to match the ever‐changing NG cooling curve, as it is obtained from different gas fields. Mismatching of cooling curves often results in suboptimal operation, which ultimately leads to an increase in the overall energy consumption. Thus, this study is aimed at making DMR liquefaction operation close to optimal using the invasive‐weed paradigm. At first, the decision variables for performance improvement were determined using degrees of freedom analysis then through invasive‐weed paradigm the best set of parameters that results in minimal overall energy consumption were obtained. For the given set of conditions, it was found that after optimization, the DMR process can produce LNG using 16.2% less compression power compared to the published optimized DMR process. Taking into account the higher sensitivity of the DMR process against NG feed conditions, the IWO approach was also examined to find the multiple optimal solutions corresponding to different sets of feed conditions. The thermodynamic evaluation revealed that the mixed refrigerant involves in NG subcooling and interstage coolers have the highest level of exergy destruction. After successful performance improvement of the DMR process, it is also found that still, 62% improvement potential (based on avoidable/unavoidable exergy destruction analysis) is available in the DMR process that can be attained through either sole optimization or optimal retrofitting/revamping.