Re-liquefaction System Research Articles

Fault Simulating Test Bed for Developing Diagnostic Algorithm of the Geared Rotating Machinery of Ships

To prevent critical failure of the functional machinery of a ship, condition monitoring technologies have been much studied in recent times. In this respect, securing a fault database is a top priority in technology development. In this paper, we developed a test bed that simulates the LNG (liquefied natural gas) re-liquefaction system installed on LNG carriers to obtain data in various types of faults of ship machinery. To maintain rotor-dynamics characteristics, the structure was scaled based on the critical speed margin of the dynamic system. The developed test bed includes a gearbox and multiple shafts. It can simulate mass imbalance, misalignment, bearing fault, gear fault and impeller fault. To verify the validity of the vibration data obtained from the developed test bed, experiments were conducted on three fault modes: main shaft imbalance, pinion shaft imbalance, and gear fault. The time series data and FFT results were analyzed, and time domain features were extracted and statistically validated. Additionally, a simple diagnosis model was developed using the acquired data to evaluate its performance. The test data show distinct data with respect to fault conditions, and we can expect that the diagnosis algorithm can be developed using the test data. The developed test bed can provide not only for the fault data of a single component of the rotating machine but also for the combined fault data of the total system. In addition, we expect that it will solve the problem of securing fault data in the development of condition diagnosis technology if reliability is verified by identifying correlations by comparing data from the real system and data from the scaled test bed.

Techno-Economic Evaluation of Direct Low-Pressure Selective Catalytic Reduction for Boil-Off Gas Treatment Systems of NH3-Fueled Ships

This study proposes a feasible solution for boil-off gas (BOG) treatment to facilitate NH3 fuel use by ocean-going ships, which is currently considered an alternative fuel for ships. Two systems were designed and analyzed for BOG in IMO Type-A NH3 fuel storage tanks for 14,000 TEU container ships. First, BOG lost inside the storage tank minimized economic losses through the onboard re-liquefaction system. The total energy consumed by the system to process NH3 gas generated in the fuel tank at 232.4 kg/h was 51.9 kW, and the specific energy consumption (SEC) was 0.223 kWh/kg. Second, NH3 was supplied to the direct Low-Pressure Selective Catalytic Reduction (LP-SCR) system to treat marine pollutants generated by combustion engines. The feasible design point was determined by calculating the NH3 feed flow rate using three methodologies. The energy consumed by the direct LP-SCR system was 3.89 and 2.39 kW, and the SEC was 0.0144 at 0.0167 kWh/kg at 100% and 25% load, respectively. The feasibility was indicated via economic analysis. Depending on the life cycle cost, the competitiveness of the re-liquefaction system depends on the price of NH3, where a higher price yields a more economical solution. In conclusion, the direct LP-SCR system has a low overall cost because of its low energy consumption when supplying NH3 and its reduced amount of core equipment.

Advanced process design of subcooling re-liquefaction system considering storage pressure for a liquefied CO2 carrier

Because carbon capture and storage methods are considered greenhouse gas reduction technologies, demand for a large liquefied CO2 (LCO2) carrier to transport captured CO2 to storage sites has arisen. To prevent the emission of boil-off CO2 gas during transport, a CO2 re-liquefaction system would be required. This study suggests a new type of LCO2 subcooling re-liquefaction system for an LCO2 carrier and demonstrates its effectiveness by comparing its performance with that of conventional re-liquefaction systems considering LCO2 storage pressure. The results show that the suggested LCO2 subcooling system has lower specific energy consumption than that of conventional LCO2 re-liquefaction systems, even with a simpler configuration. At 15 bar of storage pressure, the LCO2 subcooling system has a lower specific energy consumption of 176.91 kJ/kgCO2, which is 18.2 and 5.3 % lower than that of the Linde–Hampson cycle and vapor-compression refrigeration cycle using NH3 as a refrigerant, respectively. Additionally, economic benefits can be obtained because the boil-off CO2 compressor is not required in an LCO2 subcooling system. Finally, considering CO2 re-liquefaction performance and the design constraints of the LCO2 carrier, 15 bar LCO2 storage conditions with a subcooling system are considered the most economical LCO2 carrier design.

Design and optimization of liquid nitrogen precooling BOG re-liquefaction process for LNG ships

BOG re-liquefaction process is a necessary part for the safety of LNG cargo ships, and it is also the most common way to deal with evaporated gas (BOG) in LNG ships. Therefore, how to optimize the re-liquefaction process and save energy consumption is a problem that cannot be ignored in BOG re-liquefaction system. In this paper, based on the traditional BOG re-liquefaction process, a liquid nitrogen precooling circulation system is added and linked with the nitrogen purging system. Aspen HYSYS software was used to simulate and analyze the exergy efficiency, specific power consumption, exergy efficiency in the proposed liquefaction process. In addition, we introduced a bacterial foraging algorithm to optimize the process parameters. According to the operation results, the optimized process has a specific power consumption of 1.028 kWh/kgLNG, which is 21.53 % lower than that of the original NH3 and CO2 precooling system. Changing the traditional precooling system to liquid nitrogen tank reduces the complexity of the liquefaction system and improves the reliability of the system. Because liquid nitrogen has excellent cryogenic energy, small size, cheap price, safety in the actual use process and the linkage with the purge device on board, it shows excellent performance in the process of BOG pre-cooling liquefaction.

Application of Fuel Cold Energy in CO2 Bog Reliquefaction System on Ammonia-Powered CO2 Carrier

Abstract A CO2 boiled off gas (CO2 BOG) reliquefaction system using liquid ammonia cold energy is designed to solve the problems of fuel cold energy waste and the large power consumption of the compressor in the process of CO2 BOG reliquefaction on an ammonia-powered CO2 carrier. Aspen HYSYS is used to simulate the calculation, and it is found that the system has lower power consumption than the existing reliquefaction method. The temperature of the heat exchanger heater-1 heat flow outlet node (node C-4) is optimised, and it is found that, with the increase of the node C-4 temperature, the power consumption of the compressor gradually increases, and the liquefaction fraction of CO2 BOG gradually decreases. Under 85% conditions, when the ambient temperature is 0°C and the temperature of node C-4 is -9°C, the liquid fraction of CO2 BOG reaches the maximum, which is 74.46%, and the power of Compressor-1 is the minimum, which is 40.90 kW. According to this, the optimum temperature of node C-4 under various working conditions is determined. The exergy efficiency model is established, in an 85% ship working condition with the ambient temperature of 40°C, and the exergy efficiency of the system is the maximum, reaching 59.58%. Therefore, the CO2 BOG reliquefaction system proposed in this study could realise effective utilisation of liquid ammonia cold energy.

A feasibility study of HFO refrigerants for onboard BOG liquefaction processes

As the global demand for natural gas continues to increase, the production of liquefied natural gas (LNG) and the demand for LNG carriers are also on the rise. Following the advent of LNG propulsion engines, there has been widespread adoption of systems that use LNG or boil-off gas (BOG) as fuel, and subsequently re-liquefy remaining gas thorough the re-liquefaction system. In this study, we investigated the feasibility of hydrofluro-olefins (HFO) refrigerants, the newly developed refrigerants having low flammability and low global warming potential (GWP), in BOG re-liquefaction systems for liquefied natural gas carriers. Simulations of BOG re-liquefaction process were conducted and optimized to minimize energy consumption. Then, the explosion risk and global warming potential during the lifespan of the re-liquefaction processes are also analyzed. The optimization results indicate that using HFO refrigerants in the re-liquefaction process yields comparable energy consumption to the conventional hydrocarbon refrigerants. Additionally, the use of HFO refrigerants can contribute to reducing explosion risk of liquefaction process. However, despite HFO refrigerants being considered an environmentally friendly refrigerant, it is important to note that global warming impact has not decreased as significantly as expected. This is primarily due to the fact that the GWP of the system is heavily influenced by energy consumption.

Ship power plant with re-liquefaction installation for tankers transporting hydrogen

The use of hydrogen as a fuel for tankers carrying liquefied hydrogen is discussed in the paper. As a solution to the problem of the world industry decarbonization, the possibility of competitive use of hydrogen as a fuel on sea tankers transporting liquefied hydrogen over long distances is discussed. The main reasons that encourage countries with sea and river vessels to develop in the direction of improving the ship power plants, in anticipation of tightening the national and international requirements for environmental pollution prevention, are indicated. A brief overview of the development of hydrogen energy is given on the example of leading projects in Europe and Asia, the most successful of which should include the transportation of compressed hydrogen by an experienced tanker of the Japanese company Kawasaki “Suiso Frontier” from Australia to Japan. A strategy for choosing the optimal propulsion unit for a liquefied hydrogen tanker is given. As research methods, the analysis of data obtained in similar studies, as well as the analysis of thermodynamic characteristics of promising systems, is used. Integrated power system designs and re-liquefaction systems for ocean tankers transporting hydrogen are proposed. Data on existing projects with low and high pressure gas engines, solid oxide fuel cells are given. Five prospective energy systems and a re-liquefaction system with a Claude cycle, using hydrogen and liquid natural gas as fuel and refrigerant, are suggested. Their technological feasibility and environmental impact are evaluated. The re-liquefaction systems’ exergy efficiency and specific energy consumption ranges are 26.79–46.27 % and 3–7.45 kWh/kg, respectively. A system with a low pressure engine, solid oxide fuel cells and a re-liquefaction system is determined to be optimal.

Optimization of Reliquefaction System on Gas Carrier to Maintain The Condition and Temperature of Cargo Tank

Transport of liquefied hydrocarbon gases and their derivatives (methane, ethane, propane, butane, ethylene, propylene and other liquefied gases) is done using gas carrier tankers. Large gas carriers are equipped with re-liquefaction system to handle cargo during the process of loading, voyaging, and unloading. A reliquefaction system is installed on gas carriers to handle the Boil off-gas (BOG) problem. Operation constraints Reliquefaction system operating the reliquefaction system include the compound characteristics, liquefaction unit operating conditions, and system performance. These issues also hinder the BOG liquefaction process. This research sought to investigate the whole operation process of the system. This case study was conducted by observing the objects directly on the MT. Chinagas Legend vessel whose main cargoes are LPG. In case studies, research is carried out by studying the phenomenon of case problems that occur directly on the object. The identified problems and its resolutions could add valueable information to science. The research results revealed that MT. Chinagas Legend had a reliquefaction system with 2-stage or 3-stage options. The former type was used for butane (C4H10) cargoes and the latter was used for propane (C3H8) cargoes. The common problem in the process of reliquefaction systems was the presence of contaminants carried with seawater and clogging the filters. A leak in the intake or discharge valve slowed down the reliquefaction process and rendered it ineffective. The problems can be overcome through periodic routine inspections on components that are directly in contact with sea water, such as sea water filters.

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.

Process design of advanced LNG subcooling system combined with a mixed refrigerant cycle

LNG subcooling system is a conventional system to keep the pressure of an LNG storage tank for LNG carriers, but has a weak point of the low efficiency resulting in a new BOG reliquefaction system. This study suggests a new LNG subcooling system combined with mixed refrigerant cycle (MR-SLNG), which can increase efficiency significantly. The results show the coefficient of performance (COP) of the system becomes 2.5 times higher than that of the conventional LNG subcooling system based on a reverse Brayton cycle (RBC-SLNG). Additionally, MR-SLNG can be a compact system because the volumetric flowrate of the refrigerant compressor decreased to 8.9%, which brings additional benefits to the ship design.

A new optimization method of energy consumption for dynamic boil-off gas

Related research on refrigerant optimization based on the dynamic BOG has yet to be proposed. This study offers a new dynamic optimization method for boil-off gas (BOG) re-liquefaction system to improve the system's energy efficiency. The performance of C3MR (the propane precooling mixed refrigerant cycle) is analyzed based on the steady state model of leading liquefaction equipment in the process simulation in Aspen HYSYS software. And the principle of the energy consumption variation law of propane precooled compressor and mixed refrigerant compressor, based on the actual possible disturbance range obtained in the natural gas liquefaction process, is applied to construct the multi-objective optimization model with minimum energy consumption and maximum heat exchanger efficiency. Finally, the dynamic responses of disturbances were achieved and discussed with the aid of GA (Genetic Algorithm) and PSO (particle swarm optimization). The optimized performance of the dynamic liquefaction cycle is 34.8% better than the steady condition system in terms of energy efficiency, and the maximum energy consumption can be reduced by 50.60%. The advantage of the proposed optimization framework is its adaptability to other dynamic liquefaction processes. It has practical reference significance for the cost control of the BOG re-liquefaction recovery project.

EN Thermodynamic analysis of the ethylene reliquefaction system on LEG carriers when replacing throttle devices with ejectors

LEG carriers’ energy efficiency can be increased by improving the boil-off gas (BOG) reliquefaction installation processes in its components. In this study, it is proposed to replace the conventional reliquefaction process (CRP) of a LEG carrier “ANTIKITIRA” actual installation equipped throttle devices with an ejector reliquefaction process (ERP) having two-phase ejectors as expansion devices to increase the energy efficiency of the installation. Expansion devices EV2E and EV2R were replaced with two-phase ejectors in the proposed system. The ejector efficiencies are ensured by additional components (separators and the precooler in the bottoming stage of the cascade). Separators maintain a constant pressure at the compressor inlets, and the precooler reduces the load on the condenser-evaporator. An ejector model has been developed to analyze the proposed system. The design pressure at the ejector nozzle outlet is determined based on multivariate calculations. Energy and exergy analyses of ERP and CRP systems were carried out. According to the exergy analysis results, each component's influence on the energy efficiency of the CRP and ERP systems is estimated. The exergy losses in each ERP component are lower than the corresponding values in the CRP components. The exergy losses in the condenser and precooler of the CRP system are lower than in the ERP system. The total power consumption is the same in both cycles, and the cooling capacity of the ERP cycle has increased by 29.1 kW. Replacement of throttle devices led to a decrease in absolute exergy loss from 9.75 to 4.95 kW. The energy efficiency of the ERP cycle increased by 24%, and the exergy efficiency increased by 16%. The most significant exergy losses in both cycles are observed during compression in a two-stage cargo compressor of the bottoming stage of the cascade (29.0-34.1%). It is concluded that the proposed ERP cycle meets IMO requirements for vessel energy efficiency but requires additional capital investments

Energy, Exergy, and Economic (3E) Analysis of Boil-Off Gas Re-Liquefaction Systems Using LNG Cold Energy for LNG-Fueled Ships

Liquefied natural gas (LNG)-fueled ships have the effect of reducing most pollutants, which is advantageous for responding to strict regulations. Because boil-off gas (BOG) is generated in the LNG storage tank of an LNG-fueled ship, a BOG re-liquefaction system is required. The representative systems for LNG-fueled ships were proposed by Kwak and Shen, but their exergy efficiencies were only 19.6% and 24.9%, respectively. To improve the system, this paper proposes novel BOG re-liquefaction systems combined with the fuel gas supply system. The systems utilize LNG cold energy in the BOG stream and N2 reverse Brayton cycle, respectively. The proposed systems were simulated using a commercial program and were optimized using a genetic algorithm. The results of energy, exergy, and economic (3E) analyses performed for comprehensive evaluation of the proposed system show that the system in which LNG cold energy is applied to the BOG stream has the best performance. Specific energy consumption, exergy efficiency, and total annual costs of this system were improved by up to 78.6%, 69.2%, and 68.2%, respectively, compared to those of the existing systems. The overwhelmingly superior system is expected to greatly contribute to the improvement of the BOG re-liquefaction system for LNG-fueled ships.

A New Re-Liquefaction System for Dynamic Boil-Off Recovery Based on Single Mixed Refrigerant

A New Re-Liquefaction System for Dynamic Boil-Off Recovery Based on Single Mixed Refrigerant

Thermodynamic Analysis of an Ethylene Reliquefaction System Using the Entropy-Cycle Method

In this study, a boil-off gas reliquefaction system that is a part of liquid ethylene gas (LEG) carriers is evaluated. The reliquefaction system is formed by two thermally interconnected two-stage refrigeration cycles. The working fluid of the bottoming cycle is ethylene; the working fluid of the topping cycle is propylene. The research is based on determining the irreversibilities in the reliquefaction system cycles using the entropy-cycle method of thermodynamic analysis. The impact of the process performance in the main components on the reliquefaction system energy efficiency has been evaluated by the entropy-cycle method. The greatest thermodynamic irreversibility is observed in the two-stage compression process of the bottoming cycle (9%), total throttling irreversibility in the reliquefaction system (8.5%), and vapor superheating at the suction into the low stage of the two-stage compressor of the bottoming cycle (8%). The results of the study showed that it is necessary to improve the design of expansion devices using the replacement of throttle devices with ejectors when designing cascade ethylene reliquefaction plants. In addition, when operating such systems much attention should be paid to the condition of the insulation of cargo pipelines and the parameters of the cooling system of the cargo compressor.

Analysis of Energy Consumption of Novel Re-Liquefaction System Integrated with Fuel Supply System (FSS) for LPG-Fuelled LPG Carrier to Conventional Systems

This study analysed a novel re-liquefaction system integrated with a fuel supply system (FSS) for an LPG carrier to conventional systems. The re-liquefaction system and FSS were installed independently in a conventional LPG carrier, while those systems were combined in the novel system. The condensed LPG in the re-liquefaction system was directly transferred to the FSS without the cooling and expansion process in the novel system. 84,000 m3 LPG carrier equipped with a 10 MW engine at normal continuous rating (NCR) was selected as a target ship. Aspen HYSYS ver.12.1 was employed for process simulation. The results showed that the energy consumption for the novel system was reduced by 38%. The energy for re-liquefaction was decreased because the flow rate recirculated was decreased, and the energy for FSS was reduced as the temperature of the stream supplied to the FSS was relatively high in the novel system. A sensitivity analysis was conducted to investigate the effect of the parameters on the results. The investigated parameters were LPG compositions, seawater temperature, compressor efficiency, and pump efficiency. The energy consumption for the system was significantly different depending on the LPG composition, and the energy consumption was changed by 2.5% for conventional systems and 0.9% for the novel systems with the variation of 4 °C seawater temperature. The energy for the novel system was reduced by 2.8% for conventional systems and 2.3% for the novel systems with the 5% increment of compressor efficiency, whereas pump efficiency had little effect on the results.

Techno-Economic Analysis of NH3 Fuel Supply and Onboard Re-Liquefaction System for an NH3-Fueled Ocean-Going Large Container Ship

This study proposed the integrated design of an NH3 fuel supply system and a re-liquefaction system for an ocean-going NH3-fueled ship. The target ship was a 14,000 TEU large container ship traveling from Asia to Europe. The NH3 fuel supply system was developed to feed the liquid fuel at 40 °C and 80 bar and cope with the re-circulated fuel with the sealing oil. Its power consumptions and SECs ranged from 56.4 to 157.5 kW and from 0.0063 to 0.009 kWh/kg, respectively. An onboard re-liquefaction system with a vapor compression refrigeration cycle was also designed to liquefy the BOG from the fuel tank. The re-liquefaction system’s exergy efficiency and SEC were 34.71% and 0.224 kWh/kg, respectively. The equipment with the most exergy destruction was the heat exchangers, accounting for 60% of the total exergy destruction. NPV analysis found that it is recommended to introduce the re-liquefaction system to the target ship. At the NH3 price of USD 250/ton, the reasonable cost of the re-liquefaction system is less than USD 1 million. According to LCC, NH3 fuel is economically feasible if the carbon tax is more than USD 80/ton and the NH3 price is around USD 250/ton.

Comparative safety assessment of LNG re-liquefaction systems applied on LNG carriers

ABSTRACT This research was aimed to evaluate the safety of the LNG cargo compressor room against unwanted gas leakage from two different re-liquefaction systems applicable for an LNG carrier: 1) the Partial (Full) Re-liquefaction System (P(F)RS) and 2) the combination of Partial Re-liquefaction System and Mixed Refrigerant Re-liquefaction system (PRS+MRS). To achieve this goal, quantitative risk assessment was carried out with the integration of system hierarchical modelling, statistical analysis, and CFD simulation. The frequency of initial leakages, occurring to each component of the re-liquefaction systems, was analysed, whereas for the consequence analysis, a CFD program of PyroSim was employed to simulate the gas dispersion in the confined room fitted with mechanical ventilation systems. In addition, various ventilation capacities were investigated with changes in their allocations in the room in order to determine these parametric influences on the results. The risk level of re-liquefaction systems was determined in a quantitative way. Research results clearly presented the importance of the proper arrangement of the ventilation systems. The risk levels were estimated at 5.6 E-3/year for P(F)RS whereas about 9.6 E-3/year for the PRS+MRS in consideration of current regulations. However, the increase in the ventilation capacity was found to reduce the risk levels. The research findings are highly believed to offer meaningful guidance into future safety regulatory frameworks.

A novel boil-off gas reliquefaction system using liquid air for intercontinental liquefied natural gas transportation

The boil-off gas (BOG) reliquefaction of cryogenic liquefied natural gas (LNG) for its intercontinental transport is challenging. This paper proposes a novel BOG reliquefaction system using liquid air and two different process designs: (i) low-pressure liquid air (LPLA) and (ii) high-pressure liquid air (HPLA). In the proposed system, an open refrigeration system using liquid air reliquefies BOG, thereby replacing the current commercial closed refrigeration cycle. As the temperature of liquid air is in the cryogenic range, the energy consumption to reliquefy BOG onboard approaches zero. However, the additional total weight of the ship is required to store liquid air, thus necessitating increased propulsion energy. Nevertheless, the reduction in energy needed for BOG reliquefaction exceeds the energy requirement for the added engine load. Thus, the LPLA shows a massive energy reduction from 4,913.07 to 642.67 kW compared to the commercial BOG reliquefaction process involving the nitrogen expander cycle. The HPLA process shows further improved results of 436.34 kW by expanding the vaporized high-pressure air. In addition, the proposed HPLA design exhibits an exergy efficiency of 77.4 %, which is 37.6 % higher than that of the commercial nitrogen expander process. A techno-economic analysis, including the purchase and transport cost of liquid air, is conducted to reflect an effort on on-shore liquid air production and transportation. Despite the additional liquid air tanks, the overall process configuration is much simpler than that of the current commercial BOG reliquefaction system. Thus, the proposed HPLA process is more economical than commercial processes for all representative voyage duration scenarios (8, 13, and 21 days).

Numerical Simulation and Comparative Analysis of Three Boil-Off Gas Reliquefaction Systems

Abstract In view of the problem that the boil-off gas (BOG) generated by small liquefied natural gas (LNG) ships affects the transportation safety, three BOG reliquefaction systems are improved, which are as follows: case 1: serial nitrogen expansion reliquefaction system (N2-BOG); case 2: single mixed refrigerant reliquefaction system (SMR-BOG); and case 3: propane precooled mixed refrigerant reliquefaction system (C3MR-BOG). The basic process is simulated in aspen plus and combined with the mathematical model built up in matlab where the three cycles are optimized with the specific power consumption (SPC) as the objective function. The results show that the SPC of three cases are 0.8021 kWh/kg (LNG), 0.4150 kWh/kg (LNG), and 0.5063 kWh/kg (LNG); the coefficient of performance (COP) of cases 1, 2, and 3 are 0.20, 0.39, and 0.30; the exergy efficiency of 36.56%, 70.66%, and 57.93% along with the total product cost of 89.00 $/h, 55.73 $/h, and 77.54 $/h are achieved in Cases 1–3, respectively. In addition, the overall exergy destruction of the cycles and each equipment are discussed, and the matching of the cold and heat sources of the multistream heat exchanger in the three systems is analyzed. In conclusion, under the condition that the BOG mass flowrate is 350 kg/h, the improved SMR-BOG has advantages on thermodynamic performance and economic analysis, which makes it a better choice.