Simulation and Optimization of NGE-MR Natural Gas Liquefaction Process

In this paper, an exergy analysis model is applied with respect to a new liquefaction process of natural gas named NGE-MR, which precools natural gas with the cold energy generated by pressure energy recovery of high pressure natural gas pipeline. In order to figure out the performance of all modules in the process, the exergy destruction and exergetic efficiency are calculated. Specific distribution of exergy destruction is obtained and the influences of mixed refrigerant composition concentration on the performance of the NGEMR liquefaction process are analyzed. The result shows that the exergy destruction in the system is mainly caused by expansion turbines and compressors. For a certain high pressure of the MRC under a fixed pressure ratio, there is a corresponding optimal certain mixed refrigerant composition, under which the minimum exergy destruction of the liquefaction process could be obtained.

Design optimization of single mixed refrigerant LNG process using a hybrid modified coordinate descent algorithm

Advanced natural gas liquefaction and regasification processes: Liquefied natural gas supply chain with cryogenic carbon capture and storage

Simulation and Optimization of an LNG Plant Cold Section

Liquefied natural gas (LNG) is an important energy source and occupies an important proportion in natural gas consumption, therefore, the selection of appropriate liquefaction processes and related optimization should be seen as subjects of great importance. Accordingly, in the present review, we provide a comparative and critical analysis of the current status of natural gas liquefaction technology through examination of the advantages and disadvantages associated with three natural gas liquefaction processes (namely, the cascade liquefaction cycle, the expander-based cycle and the mixed refrigerant cycle). It is shown that the energy consumption related to the cascade refrigeration cycle is the lowest. Compared with it, the mixed refrigerant cycle has the advantages of being a simpler process, with less units, low investment cost and low requirements in terms of refrigerant purity. The expander-based cycle can be started and stopped quickly and simply, but the power consumption is relatively high.

Exergy and energy analysis of a hybrid natural Gas/Hydrogen liquefaction cycle combined with methanol production plant

Many small scale capacity natural gas liquefaction plants are based on mixed refrigerant cycles with hydrocarbons as a working fluid. Replacing hydrocarbons with non-flammable gases as a refrigerant may significantly improve the safety of operation and reduce the cost of equipment. The objective is to compare liquefaction cycles on hydrocarbon and non-flammable refrigerant. Mathematical modelling of the natural gas liquefaction process on the basis of a single-stage cycle with a phase separator based on hydrocarbon and nonflammable mixed refrigerants is made. The analysis of efficiency of the investigated cycles is made. Description of setup and experimental procedure is given. The results obtained can serve as a first step to the creation of reliable tools for the analysis of processes based on mixtures of non-flammable refrigerants and the subsequent practical development of this technology.

Performance study on a single-screw compressor for a portable natural gas liquefaction process

The development and analysis of combined hydrogen and natural gas liquefaction process are reported. Two refrigeration cycles using mixed refrigerants (MRs) are employed. The developed process is capable of generating 290 tons hydrogen and 296 tons liquid natural gas on daily basis. The first refrigeration cycle of the introduced process liquefies 3.5 kg·s−1 normal gaseous hydrogen and 3.5 kg·s−1 normal natural gas at room temperature and 21 bar to −195°C with the consumed power of 0.643 kWh/kgLH2,kgLNG. The second refrigeration cycle cools down the hydrogen and natural gas to −253°C with the consumed power of 1.662 kWh/kgLH2,kgLNG, leading to a lower total consumed power than that of the identical liquefaction processes. The use of novel and appropriately mixed refrigerants based on the configuration, and the thermal design of expanders and heat exchangers fora wide range of temperatures are the innovations of the process. Additionally, the refrigerant compositions of refrigeration cycles are novel. The energy analysis indicated that the coefficient of performance (COP) for the developed process is 0.2442, which is notably high compared with the COP of other identical processes (typically less than 0.1797). The exergy analysis revealed that the overall exergy efficiency of the liquefaction process is 62.54%. Highlight edited A novel integrated hydrogen and natural gas liquefaction process is introduced. The process can generate 290 tons hydrogen and 296 tons liquid natural gas per day. Total power consumptions of the process are 4.165 kWh/kgLH2,kgLNG. Coefficient of performance (COP) for the developed process is 0.2442, which is notably high compared with the COP of other identical processes. Overall exergy efficiency of the liquefaction process is 62.54%.

Enhancement of single mixed refrigerant natural gas liquefaction process through process knowledge inspired optimization and modification

Simulation based Heuristics Approach for Plantwide Control of Propane Precooled Mixed Refrigerant in Natural Gas Liquefaction Process

• A novel NG liquefaction process by nitrogen single expander technology is proposed. • The new components are integrated for better thermal management and improved efficiencies. • The proposed system is optimized using Aspen HYSYS process simulation software. • Results showed 7% reduction in unit energy consumption from 9.90 to 9.216 kW·h·kmol −1 . • Exergy analysis revealed the reduction in exergy destruction from 17.32 kW to 15.711 kW. Natural gas releases 45–50% less CO 2 emissions as compared with coal and the liquefaction process is employed for storage and transport of liquefied natural gas that is an energy-intensive process. Numerous scientific efforts are being directed to reduce the energy consumption in the natural gas liquefaction process and to increase the process efficiency. Thus, this study proposes a uniquely modified and energetically enhanced small-scale natural gas liquefaction process by nitrogen single expander technology with CO 2 precooling. The novelty of the designed liquefaction process is that the designed configuration does not only reduces the energy consumption of the liquefaction process but also improves the process efficiency. The proposed system is simulated and optimized using ASPEN HYSYS by different design key parameters, and energy consumption has been considered as a key function for the optimization of this cycle. Detailed characterization shows the energy consumption of 9.216 kWh·kmol −1 at a liquefaction rate of 0.77. Furthermore, the effect of pressure output of the valve on unit energy consumption and liquefaction rate is also observed and discussed. It has been observed that by decreasing the valve output pressure, the liquefaction rate decreases and energy consumption increases. Besides, the versatility of this cycle under various pressures, temperatures and composition of methane and other components in the feed gas are considered and effects of these parameters variation on system performance have been observed. The exergy destruction of each equipment is evaluated and investigated in detail for the optimization of results. Results are compared and it shows a 6.90% and 9.0% decrease of unit energy consumption and exergy as compared to referenced base cycle. The performance of numerous relationships is derived from the proposed study and compared with simulated referenced published data. By using energy consumption and liquefaction rate of compared LNG cycles, the maximum error is +0.93 and the minimum error is −0.12. Due to safe and simple operation, compact device, proposed liquefaction process shows a suitable application for development of small-scale, especially for offshore reserves.

Natural gas (NG) from stranded regions, where they are produced is normally transported to far away regions where they are marketed and consumed. One key natural gas transportation route is based on liquefied natural gas (LNG) technology, where the natural gas is first turned into a liquid (through a liquefaction process) and then transported using large ocean-going vessels. In this paper, we present comparative results obtained from optimizing a natural gas liquefaction process. The analyses are in three steps: In the first step, we modelled a CO2-N2 single expander liquefaction process based on data published in the prestigious Journal of Natural Gas Sciences and Engineering. In the second step, the CO2-N2 single expander process is optimized by upgrading to a CO2-N2 dual expander process and results demonstrate that the CO2-N2 dual expander process consumed less power relative to a CO2-N2 single expander process, albeit with relatively high specific power values. A further optimization effort involving the substitution of the CO2 precooling fluid with a nitrogen precooling fluid revealed that the N2-N2 dual expander process provides a relatively more optimal solution when compared to the CO2-N2 dual expander process, in terms of heat duty, log-mean temperature difference, natural gas mass flow rate, production capacity and specific power. However, the N2-N2 process has a relatively higher power consumption values which can be attributed to the relatively higher compressor power requirements during the precooling process. Most of the modelling and simulation work are based on the proprietary software – Aspen Hysys 8.6.

Considering its clean and environmental characteristics, natural gas has gradually attracted attention from countries around the world. China’s coal-to-gas project has significantly increased the country’s demand for, and supply of, natural gas. Liquefied natural gas (LNG) has also been gradually promoted, owing to its advantages of easy storage and transportation. However, the natural gas liquefaction process includes multiple phases, and each phase generates substantial industrial pollutants, such as CO2, SO2, and NOx. Despite this, the resulting environmental impacts have not been quantitatively assessed. Therefore, based on the production process of a liquefaction plant in the Shanxi Province, China, in this study, the Life Cycle Assessment (LCA) model was used to analyze the pollutant discharge in the unit’s natural gas liquefaction production process. By collecting data on the production capacity and composition reports of the eight major LNG-producing provinces, such as Henan, Sichuan, Inner Mongolia, Shaanxi, Xinjiang, Shanxi, Ningxia, and Hebei, the total amount of pollutants discharged from the natural gas liquefaction process in China was estimated. Finally, the environmental impact of the natural gas liquefaction process was evaluated according to the results of the environmental impact of pollutants. Our study arrived at the following conclusions: (i) 93.60% of China’s natural gas liquefaction output is concentrated in eight provinces; (ii) in terms of the unit’s LNG production, the Global Warming Potential (GWP), Acidification Potential (AP), Eutrophication Potential (EP), Photochemical Ozone Creation Potential (POCP) and Dust Potential (DP) proportions of each province explained the gas composition of LNG production gas sources in each province; (iii) the environmental problems caused by natural gas liquefaction were different in each provinces. In addition, we suggested relevant policy recommendations. First, the formulation of LNG-related policies should consider environmental pollution produced during the liquefaction stage. Second, if the problem of pollutant discharge in the liquefaction of natural gas is properly solved, it will not only reduce environmental pollution, but also generate additional income. Third, different provinces should optimize production technology based on the different gas qualities.

Mixed refrigerant (MR) system is commonly used for a liquefaction process of liquid natural gas (LNG) plants due to its higher efficiency of heat transfer rate compared to pure refrigerants. The performance of MR system is highly dependent on the variable refrigerant composition, which is challenging to obtain in a practical LNG plant setting. To address this challenge, this study investigates a unique approach to improve the exergy efficiency of liquefaction cycle employing ammonia in the mixture while keeping the MR molar composition constant in dual mixed refrigerant (DMR) cycle. A control strategy is proposed to regulate the MR flowrate through flow control sensors and a series of Joule-Thomason (JT) valves to sustain the desired efficiency of the cycle under various plant’s operation conditions. The robustness and adaptability of two proposed MR compositions were examined under eight cases by varying natural gas (NG) feed pressure and methane concentration. Composite curve plots were utilized as a tool to control the minimum temperature approach (MTA) and to improve exergy efficiency of the cycle. Furthermore, findings revealed that mixtures which included ammonia yielded a reduction in the number of compressors, as well as a reduced the overall amount of compressors rate of shaft work required for the liquefaction cycle. The results emphasize that DMR is most efficient when NG methane concentration is at 75%. Furthermore, the compressor rate of shaft work reduced by 13.3%, while exergy efficiency of the cycle increased by 14.3%, when natural gas methane concentration reduced from 90% to 75%.