LNG Cold Energy Research Articles

Comparative analysis of thermal economy of two SOFC-GT-ST triple hybrid power systems with carbon capture and LNG cold energy utilization

This paper studies the coupling of fuel cell power generation technology and conventional thermal power generation technology, constructs the thermodynamic model of combined cycle power generation of fuel cell, gas turbine and steam turbine, and analyzes the thermodynamic performance of the system from the important links such as compressor pressure ratio, steam carbon ratio, fuel utilization, fuel cell operating temperature and gas recirculation. Since natural gas as fuel will emit a lot of greenhouse gases, two new low-carbon power generation systems including composite power system, carbon capture and liquified natural gas cold energy utilization are proposed. In this paper, the post-combustion carbon capture which is more practical and conducive to the safe operation of the system is used. The adsorbents used in the two carbon capture methods are MDEA and CaO respectively. In the MDEA carbon capture process, flash tower and split flow process are added to reduce energy consumption. In the calcium looping carbon capture process, CO2 reflux process is set to optimize the calcination temperature, and two-stage waste heat boilers are set to recover a large amount of waste heat of CO2 and clean flue gas respectively. After that, to further save energy consumption, a method of cascade utilization of liquified natural gas cold energy is proposed. It can not only increase power output, but also provide natural gas at normal temperature and pressure for the system and the outside. The calculation results show that the efficiency of the optimized combined cycle system of fuel cell, gas turbine and steam turbine reaches 70.32%. In terms of energy saving, the system efficiency of MDEA carbon capture process is 1.81% higher than that of calcium looping carbon capture process, and calcium looping carbon capture process has more advantages in economic cost. In addition, the cascade utilization of liquified natural gas cold energy provides additional 410.86 kW, 382.64 kW electric energy and more directly usable natural gas for the two systems. The research results of this paper can provide meaningful guidance for the design of low-carbon and high-efficiency power generation system based on fuel cell.

Design of utilization cold energy and economic analysis on LNG carrier

Based on the principle of energy cascade utilization, this research uses 147000m3 LNG carrier as the research object. According to the principle of energy cascade utilization, LNG cold energy is applied to Rankine cycle power generation, ship desalination, ship low-temperature cold storage, ship high-temperature cold storage, ship air conditioning and nitrogen production, etc. Design a set of LNG cold energy comprehensive utilization system. Using Aspen HYSYS software for simulation, after analysis and calculation, the feasibility of the system design scheme was demonstrated. According to the route of the parent ship and the operating conditions of the cold energy utilization system, calculate the electricity and economic benefits saved by the LNG cold energy utilization system in each month. Through calculation, it can be known that 1.886×106 kW·h of electricity can be saved in one year, resulting in a benefit of more than 4 million yuan. The results show that the cold energy utilization system can bring good economic benefits and is worthy of promotion and application on ships.

Study on a near-zero emission SOFC-based multi-generation system combined with organic Rankine cycle and transcritical CO2 cycle for LNG cold energy recovery

This study proposes a near-zero emission SOFC based multi-generation system integrated with organic Rankine cycle and transcritical carbon dioxide cycle, and a LNG cold energy utilization system is also introduced in order to realize CO2 condensation and cryogenic capture. In the proposed system, the unreacted anode gas of SOFC is burned with pure oxygen instead of cathode gas by which it can provide the possibility for the follow-up CO2 capture at low energy consumption assisted by LNG cold energy utilization. The novel poly-generation system can realize the cooperative production of the energy (cooling, heating and power output), and the matter (condensate recovery and captured CO2). The energy and exergy analysis are performed to investigate the proposed system performance based on the established steady-state model. The results reveal that, under the design conditions, the thermal efficiency, net electrical efficiency and exergy efficiency of the proposed system achieve 90.99%, 55.01% and 53.07%, respectively. And the amount of CO2 captured, condensate recovery, and natural gas supply reach 5219.21 ton/year, 1324.83 ton/year and 4273.13 ton/year, respectively. Moreover, the exergy analysis shows that the exergy loss proportion of SOFC top cycle accounts for 47.3% of the total losses. Parameters analysis indicate that the electrical efficiency and the exergy efficiency are increased first and then decreased, and achieve the maximums at the SOFC inlet temperature of 554.4℃ and the operating pressure of 650 kPa, respectively. In addition, it is observed that the variation of steam-to-carbon ratio (STCR) has little effect on electrical efficiency and exergy efficiency, but has obvious effect on thermal efficiency. It is also found that the cooling, heating and power output are increased, but all the efficiencies are decreased as current density increases.

Thermo-Economic Analysis and Three-Objective Optimization of a Novel Solar-Based Power, Cooling, Hydrogen, and Freshwater Production System Using Trans-Critical Co2 Rankine Cycle, Lng Cold Energy, and Stirling Engine

Thermo-Economic Analysis and Three-Objective Optimization of a Novel Solar-Based Power, Cooling, Hydrogen, and Freshwater Production System Using Trans-Critical Co2 Rankine Cycle, Lng Cold Energy, and Stirling Engine

Novel Cryogenic Carbon Dioxide Capture and Storage Process Using Lng Cold Energy in a Natural Gas Combined Cycle Power Plant

Novel Cryogenic Carbon Dioxide Capture and Storage Process Using Lng Cold Energy in a Natural Gas Combined Cycle Power Plant

Integrated Design and Optimization Research of Lng Cold Energy and Main Engine Exhaust Heat Utilization for Lng Powered Ships

Integrated Design and Optimization Research of Lng Cold Energy and Main Engine Exhaust Heat Utilization for Lng Powered Ships

Research on the Application of Cold Energy of Largescale Lng-Powered Container Ships to Refrigerated Containers

Abstract With the aim of considering the problem of excess fuel cold energy and excessive power consumption of refrigerated containers on large LNG-powered container ships, a new utilisation method using LNG-fuelled cold energy to cool refrigerated containers in cargo holds is proposed in this study, and the main structure of the cold storage in the method is modelled in three dimensions. Then, combined with the different conditions, 15 different combination schemes of high temperature cold storage and low temperature cold storage are designed to utilise the cold energy of LNG fuel, the exergy efficiency and cold energy utilisation rate calculation model of the system is established. The simulation tool ‘Aspen HYSYS’ is used to simulate and calculate the exergy efficiency and cold energy utilisation rate of the system under 15 combinations, verifying the feasibility of the scheme. According to the characteristics of such a ship’s cross-seasonal navigation routes and the number of refrigerated containers loaded in different ports, the combination schemes of the number of low-temperature cold storage and high-temperature cold storage are selected. Thus, the average exergy efficiency and cold energy utilisation rate of the whole line is obtained, which proves that LNG-powered container ships could effectively utilise the cold energy of LNG. By calculating the total electric energy consumed by refrigerated containers on the whole sailing route, before and after the adoption of the LNG cold energy method, it is found that the adoption of this new method can promote the realisation of energy saving and emission reduction of ships.

Novel Steam Methane Reforming System with Amine-Based Carbon Dioxide Capture and Liquefaction Process Utilizing Lng Cold Energy

Novel Steam Methane Reforming System with Amine-Based Carbon Dioxide Capture and Liquefaction Process Utilizing Lng Cold Energy

Evaluating and optimizing the cold energy efficiency of power generation and wastewater treatment in LNG-fired power plant based on data-driven approach

Energy shortage, greenhouse effect and environmental pollution are the three major crises faced by mankind. How to solve these three problems effectively has become the focus of all countries. Therefore, this paper proposes an innovative LNG cold energy utilization method that can simultaneously alleviate these three problems. This method includes an improved structure of the organic Rankine cycle, CO2 capture cycle and supercritical CO2 extraction of wastewater. In addition, automated machine learning based on data-driven approach is effectively used for modeling the wastewater extraction. Then, after verifying the accuracy of the proposed model, some parameters have great influence on the system performance. For instance, the temperature of supercritical CO2 and working fluid water affect the local exergy efficiency and their regression coefficients are −0.29%/°C and 0.13%/°C, respectively. These parameters in wastewater extraction process are studied. Finally, under the optimization of genetic algorithm, the maximum wastewater treatment can reach 62.7 t/h increasing by 14.0%, and the LNG cold energy generation can reach 110.1 kWh/tLNG with an increase of 28.9%, while the exergy efficiency of the system is 50.4% increasing by 24.1%. Thus, organic Rankine cycle power generation, carbon capture and wastewater treatment play the roles of energy saving, emission reduction and environmental protection. At the same time, the results are compared with those of other scholars to verify the superiority of the proposed scheme.

An integrated design of LNG cold energy recovery for supply demand balance using energy storage devices

Due to the fluctuation of LNG supply, the profile of power generation has a mismatch with that of power demand, which causes power shortage at the demand peak time and power overcapacity at the valley time. To address this issue, a combined system containing standalone power generation subsystem and liquid air energy storage subsystem is proposed. The energy storage subsystem stores the surplus cold energy of LNG at the valley time, and it is released as power supplement at the peak time. As a stable heat source, geothermal energy is utilized to enhance the work output. Considering the uncertainties of power supply and power demand, Gaussian distribution model is introduced. Finally, the energy storage subsystem obtains 138 kW net work output of unit mass flow of LNG, achieving at least 29% improvement compared with previous works in the literature. The stored power can reach 148 MW/day and can meet the power shortage in the boundary condition of Gaussian distribution, which is a unique work in contrast to previous studies. The combined system achieves the net present value of 326.7 million dollars at the end of span life, and 3.6 dynamic payback years.

Conceptual design and assessment of a novel energy management system for LNG fueled ships with air separation

Medium and large ships always need to carry many different types of gas cylinders. Limited by the hull, their gas storage is small, restricting the ship's ocean voyage time. It is the most effective solution to use the air separation device and cabin air to prepare various purified gases on site. However, the traditional cryogenic air separation system has large energy consumption and low efficiency, which is not suitable for shipboard use. Therefore, this paper innovatively proposes the air separation systems for the cold energy utilization of onboard LNG-powered ships. According to the characteristics of ship engine power and pressure ratio change of LNG fuel supply system, LNG energy management systems (LNGEMSs) with high and low pressure matching cold energy utilization air separation unit processes are proposed and compared. The exergetic analysis model of the design was established using pinch point analysis, energy balance methods, and energy efficiency indexes. The applicability conclusion was determined through actual onshore process verification, comparison, and exergy analysis. The cryogenic air separation system on LNG fueled ships can adopt a different pressures heat exchange network solution to make full use of LNG cold energy to improve energy efficiency. The LNG cold exergy efficiency of the LNGEMSs can reach 83.2%, and the unit liquid product energy consumption is only 0.225 kWh·Nm−1. Due to the additional means of energy conversion and utilization, the ship design and operating indexes with the new system meet or exceed the current regulations and the current technical level. Additional oxygen obtained by air separation can further improve the combustion efficiency of marine gas turbines, which brings good prospects for marine air separation technology.

Effects of cooling and heating sources properties and working fluid selection on cryogenic organic Rankine cycle for LNG cold energy utilization

Cryogenic organic Rankine cycle (ORC) is considered as one of the most attractive solutions to utilize LNG cold energy for power generation. However, its thermodynamic performance is affected by cooling and heating sources and working fluid selection significantly. Thus, it is crucial to quantify the effects of these factors on cryogenic ORC performance. In this work, we proposed a single-stage cryogenic ORC system to utilize LNG cold energy for sustainable power generation. The effects of LNG vaporization pressure, seawater temperature, minimum temperature approach (MTA), and working fluid selection on cryogenic ORC performance were explored quantitatively. The proposed system adopting different single working fluids and binary working fluids was optimized by particle swarm optimization algorithm to maximize specific net power output (SNPO) with respective to different cooling and heating source properties. The results indicated that the LNG vaporization pressure had the most significant influence on ORC performance. Moreover, R1270 exhibited the highest SNPO (89.34 kJ/kg) and exergy efficiency (18.96%), while C2H6 showed the highest thermal efficiency (14.51%). The overall performance was improved significantly by using R1270 and C2H6 (30% and 70%) as binary mixture working fluid at 4000 kPa LNG vaporization pressure. However, performance intensification was marginal for a higher LNG vaporization pressure. These results revealed that binary working fluids were not always superior to single working fluids. Hence, this study provided valuable insights on choosing proper working fluids and optimizing design parameters for cryogenic ORC at different operation conditions.

Eco-efficient marine power system with cooled air ventilation by waste LNG cold energy for reefer holds in an ultra-large container ship

This study investigates dissipated heat removal from the internal cargo holds of an ultra-large container ship utilizing an LNG waste cold source. The reefer containers in the cargo hold dissipate heat to maintain certain freight conditions. While the extracted air from the atmosphere absorbs cold energy during LNG vaporization, it prevents a temperature increase inside the cargo holds by supplying cooled air. Herein, the marine power system is an electric propulsion type with a combined gas turbine electric and steam system. The cooled-airflow-ventilation system linked to the power system is evaluated regarding energy and exergy flows and greenhouse gas emissions. Cooled-airflow-ventilation performs efficiently as its coefficient-of-performance becomes twice that of atmospheric-airflow-ventilation when the reefer container box temperature is above zero and heat dissipation is high. Moreover, cooled-airflow-ventilation reduces the maximum-continuous-rating and improves the exergy efficiency. LNG waste cold source utilization benefits the response to the enforced regulation of ship greenhouse gas emissions. However, a high atmospheric temperature makes dissipated heat removal difficult. Consequently, cold energy cannot be provided to all cargo holds. The lower the box temperature is; the more cargo holds that can utilize cold energy.

An Integrated Design of Lng Cold Energy Recovery for Supply Demand Balance Using Energy Storage Devices

Conventionally, massive cold energy from the re-gasified process of liquefied natural gas (LNG) in the receiving station is harvested by power cycles. In addition, geothermal energy is widely used in LNG receiving station for its clean, sustainable and fast advantages, which is regarded as an effective way to improve the power cycle efficiency. However, the issue of mismatch between power generation and power demand has not been effectively solved yet. Therefore, a standalone power generation system (SAP) integrated with a liquid air energy storage system (LAES) is carried out. Firstly, the mathematical models are established based on thermodynamic equations, and the authority of simulation results are preliminarily verified. After introducing geothermal energy, the thermodynamic analysis results demonstrate that the net power output and round trip efficiency of the LAES subsystem reach 143 kW and 166%, respectively, showing outstanding competitiveness compared with previous literature. Significantly, the balance of power generation and demand has been achieved, owing to the LAES subsystem with 180 MWh/day efficient power storage and release. The economic analysis results indicate that the SAP-LAES subsystem and desalination subsystem have considerable economic benefits, with 3.8 and 2.8 dynamic payback years, respectively.

Energy assessment and external circulation design for LNG cold energy air separation process under four different pressure matching schemes

As an emerging energy conservation approach, the combination system of LNG regasification and air separation can not only recover the low-grade cold energy of LNG, but also reduce the power consumption of traditional air separation process. This paper proposes four external circulation design schemes for the energy conversion of LNG regasification and nitrogen cooling under different pressure matching conditions to realize the cascade energy utilization of LNG cold energy air separation process. The energy and exergy thermodynamic models are built for the four schemes based on the energy balance and pinch point analysis. The Linde cycle with LNG pre-cooling is used for the model testing, and the related performance indicators of the newly designed systems are compared with the traditional and existing systems. The results indicate that the four schemes proposed in this paper can greatly reduce the energy consumption per unit liquid product, the minimum consumption of which is only 0.189 kW·h·kg−1. In addition, with the increase of LNG pressure, the exergy loss of each scheme decreases. According to the comparison of different schemes, the external circulation with high-pressure LNG and low-pressure circulating nitrogen has the smallest LNG demand, minimum exergy loss and the largest exergy efficiency of 0.869, and the LNG volume required per unit liquid nitrogen production is 1.739 Nm3, achieving the best LNG cold energy utilization rate.

Cycle analysis and economic evaluation for seawater-LNG Organic Rankine Cycles

An Organic Rankine Cycle (ORC) has a variety of environmental and operating conditions, which result in different efficiency and net work of cycle. In this regard, it is important to determine the optimal operating conditions with the consideration of various operating variables since the outcomes of the low-grade waste heat recovery systems are low as well as highly dependent on the conditions. In this study, the ORC having seawater as a heat source and LNG cold energy as a heat sink is analyzed with cycle parameters as well as the environmental conditions such as seawater temperature. An ORC Economic evaluation Code (OEC) is developed to consider the effects of numerous parameters such as the pump outlet pressure, mass flow rate, pinch point, materials of the heat exchangers, the type of working fluid, cycle configuration, and seawater temperature simultaneously. Based on the analysis, an economic assessment is conducted, so we could find the optimal conditions for the designed ORC systems. Also, it is found that the seawater temperature variation could affect about 23.8% in terms of net work compared to fixed heat source temperature conditions.

Life cycle assessment (LCA) of a novel geothermal-based multigeneration system using LNG cold energy- integration of Kalina cycle, stirling engine, desalination unit and magnetic refrigeration system

A comprehensive and detailed investigation is conducted on a novel multigeneration system developed for Minab city (as a case study) in terms of thermodynamic, economic and environmental aspects. The system utilizes geothermal energy source to simultaneously generate four useful commodities: 36 ton/h pure water, 7774 kW net electricity, 354 ton/h hot water (at 77 °C), and 45 ton/h cold water (at 5 °C). The integrated system consists of four subsystems (Kalina cycle, Stirling engine, magnetic refrigeration system and desalination unit). The process simulation and exergetic evaluation are conducted by Aspen HYSYS V 11 and MATLAB software, respectively. The whole system is 42.95% efficient in terms of exergy and exergy destruction rate is 11382 kW. A sensitivity/3D analysis is also conducted to investigate the mutual interactions among exergy destruction, costs and environmental impact of each component. The exergoeconomic analysis and life cycle assessment conclude that heat exchanger HX-8 should be re-designed to improve the cost-affectivity and decline the negative environmental impact of the designed integrated energy conversion system. A comparison between the proposed multigeneration system and four other geothermal energy based systems consisting of LNG regasification sub-unit shows a significantly higher exergy efficiency and lower cost flow rate of product.

Energy, exergetic and economic analysis and multi-objective optimization of atmospheric and pressurized SOFC based trigeneration systems

In this study, the novel trigeneration systems based on the atmospheric and pressurized SOFC are proposed and investigated. The proposed systems include the SOFC based top cycles and an innovative bottom cycle which combines a transcritical CO2 cycle, a transcritical organic Rankine cycle, and a LNG cold energy utilization system. The mathematical model is developed, and the energetic, exergetic and economic analysis is conducted accordingly. Then, the effects of key parameters, such as current density, operating temperature, steam-to-carbon ratio (STCR) on system performance are evaluated. Under design conditions, the results show that the electrical efficiencies, the overall system efficiencies, the exergy efficiencies, and the total cost rate of the integrated systems can reach 57.14%, 59.56%, 55.12%, 16.73 $/h for the atmospheric system and 68.1%, 68.8%, 65.7%, 19.84 $/h for the pressurized system, respectively. Parameter study shows that the thermodynamic performance of pressurized system is significantly better than that of the atmospheric system, but economic cost is much higher. SOFC inlet temperature has a positive effect on the pressurized system performance, while this positive effect is found when the inlet temperature is less than 510 °C for atmospheric system. Besides, the multi-objective optimization by using genetic algorithm (NSGA-II) for the novel trigeneration systems has been performed. And the technique for order preference by similarity to an ideal solution (TOPSIS) based on entropy weight is performed to choose the final optimum design point of the combined systems. The multi-objective optimization results demonstrate that the exergy efficiency and the total cost rate achieve the values of 56.1%, 16.82 $/h and 66.83%, 12.02 $/h for atmospheric and pressurized system, respectively, at the optimal balance point selected by the TOPSIS method.

LNG 냉열과 폐열 회수를 위한 다단 열사이클 설계

In this study, a multi-stage thermal cycle was designed to recover the LNG cold energy and the waste heat from the LNG fuelled ship. In the low temperature cycle, the LNG cold energy was used as the heat sink and the jacket cooling water of the main engine was used as the heat source. And in the high temperature cycle, the LNG cold energy and the exhaust gas were used as the heat sink and the heat sources, respectively. Seven types of working fluids were used for constituting the multi-stage thermal cycle. The multi-stage thermal cycle was analyzed by calculating the net power, thermal efficiency, exergy efficiency, and cold thermal efficiency. It was found that the R152a-hexane combination had the highest net power of 626.3kW, thermal efficiency of 20.5%, exergy efficiency of 29.1% and cold thermal efficiency of 23.3%.

Study on LNG cold energy recovery using combined refrigeration and ORC system: LNG-fueled refrigerated cargo carriers

Study on LNG cold energy recovery using combined refrigeration and ORC system: LNG-fueled refrigerated cargo carriers