LNG Cold Energy Research Articles

Optimum design point exploration and performance analysis of a novel CO2 power generation system for LNG cold energy recovery: Considering the temperature fluctuation of heat source

Optimum design point exploration and performance analysis of a novel CO2 power generation system for LNG cold energy recovery: Considering the temperature fluctuation of heat source

Design and optimization of a zero carbon emission system integrated with the utilization of marine engine waste heat and LNG cold energy for LNG-powered ships

Aiming at promoting LNG-powered ships to achieve zero carbon emission, this paper presents an efficient energy utilization system, which can fully recover the marine engine waste heat and LNG cold energy while realizing zero carbon emission. A combination of transcritical CO2 and organic Rankine cycles is adopted to replace the original ship's waste heat generation system. Based on balancing the ship's application constraints and energy efficiency indicators, the existing land air separation system is modified to recycle the products' cold energy and the oxygen-enriched combustion of the main engine is constructed. Then, through a sensible energy gradient design and adjusting the circulating flue gas parameters, the design goals are achieved while meeting the host power. The feasibility of the system's application is assessed through thermodynamic and economic analysis, and the optimal technical parameters are determined after working fluids matching and optimization of sensitive parameters based on the genetic algorithm. The results indicate that the system's CO2 capturing purity, exergy efficiency, net output power and annual net profit are 97.09%, 51.78%, 318.36 kW, US$485,165, respectively, demonstrating significant features such as high effective energy conservation and zero carbon emission.

Development of an integrated membrane condenser system with LNG cold energy for water recovery from humid flue gases in power plants

This paper investigates a detailed thermodynamic analysis of a modular-type membrane condenser system where a cooler or condenser is connected in series upstream of the membrane condenser module. A coolant circulates inside the cooler/condenser to cool down the industrial flue gas up to saturation conditions. The analysis covers water recovery rate and energy requirement for different combinations of flue gas humidity, flow rate, and temperature. Additionally, a case study is included which considers a practical industrial exhaust flue gas where the constituents of the flue gas with volumetric ratio and the feed parameters are referred from the literature. The case study investigated the utilization of cold energy obtained by LNG regasification facility as a cooling power source for the water vapor recovery process. A detailed heat transfer analysis based on the heat exchanger model is performed to determine the required mass flow rate of cooling water and natural gas. It is concluded that, the water self-sufficiency of a power plant can be achieved if the mass flow rate of the −50 °C natural gas which is entering the membrane condenser is kept around 0.3 kg s−1 for every 1 kg s−1 flow rate of the 168 °C flue gas.

System design and analysis of refrigerated containers utilizing LNG cold energy

In order to solve the problems of excess cold energy of the fuel and large power load required for refrigeration of refrigerated containers on LNG powered container ships, this study proposes a scheme to use the fuel cold energy of LNG powered container ships for refrigerated containers, the process simulation software Aspen HYSYS is used to simulate the cold energy utilization scheme, with the help of MATLAB, the multivariable optimization research on the cold energy utilization scheme of LNG powered container ship is carried out, taking the cold energy utilization rate of LNG cold energy scheme as the objective function, the LNG cold energy utilization scheme is optimized.

Research on a Novel Combined Cooling and Power Scheme for LNG-Powered Ship

Cold energy recovery in LNG-powered vessels can not only improve the utilization efficiency of energy, but also benefit environmental protection. This paper put forward a new cascade scheme for utilizing flue gas waste heat and LNG cold energy comprehensively. The scheme was integrated by a dual organic Rankine circulation system (ORC), a high- and low-temperature cold storage system (TCS), an air conditioning system (ACS) and a seawater desalination system (SDS). The working medium of the dual ORC system was firstly determined by considering exergy efficiency and economic index simultaneously. On this basis, the adaptive weighted particle swarm optimization algorithm was employed to enhance thermodynamic performance of the scheme with the net output power as the optimization objective. The maximum net power and annual net interest rate can reach 725.78 kW and $115,300, respectively. Furthermore, the economic benefit of the scheme was analyzed by referring to the running track and the operation condition of the target ship. The results showed that the proposed scheme is a potential large-scale cryogenic technology and can bring considerable economic benefits to ship navigation.

Design and analysis of a cascade energy storage system based on LNG-LAES

Faced with increasingly serious energy and environmental problems, LNG and renewable energy have gradually entered the public eye and become the key to solving these problems. However, if the large amount of cold energy contained in LNG and the energy storage technology that regulates the volatility of renewable energy are not properly utilized, energy loss will result. In this study, by combining LNG cold energy cascade utilization and liquid air energy storage technology, a cascade energy storage system based on LNG-LAES is proposed. According to the different electricity demand of end users at different times, the system is divided into three operation modes and respectively The heat transfer, energy, exergy and other aspects were analyzed. The analysis results show that the LNG-LAES cascade energy storage system designed in this research has certain advantages in terms of energy efficiency, exergy efficiency and practical economy.

基于HYSYS的LNG冷能利用方案设计与优化

基于HYSYS的LNG冷能利用方案设计与优化

Energy and exergy assessment and a competitive study of a two-stage ORC for recovering SFGC waste heat and LNG cold energy

In this paper, three functional modes of a new designed geothermal power plant are investigated, simulated, and analyzed. The single flash geothermal cycle (SFGC) is the first mode. The second mode is a SFGC with two-stage ORC recovery, and the third mode is an SFGC with two-stage ORC recovery and LNG cryogenic energy. Adding a two-stage ORC recovery and LNG refrigeration exergy cycle aims to improve the thermal efficiency and exergy efficiency of the basic SFGC system as well as use LNG's cold energy prior to entering urban consumption networks. For the two-stage recovery cycle, the ORC's working fluids also included R227ea/R116 and R124/R125. In order to analyze the proposed system, the equations of the first law and the second law of thermodynamics are used. Assuming a two-stage ORC and LNG recovery mode, the energy efficiency of the SFGC will increase from 0.2023 to 0.3863 when using R227ea and R116 working fluids, and from 0.4016 to 0.4066 when using R124 and R125 working fluids.

Appropriate number of stages of an ORC driven by LNG cold energy to produce acceptable power with reasonable surface area of heat exchangers

Cold energy of LNG can generate power through Organic Rankine cycle (ORC). Although power output increases with number of stages, they become complex, expensive, maintenance-intensive and prone to failure due to the presence of increased number of components. In this paper, a cascaded three-stage ORC system has been progressively truncated finally to a single-stage system to arrive at the appropriate trade-off between the plant complexity and generation of power. Sea-water is used as the heat source and with ethene, ethane and propane as the working fluids, the generation of power is maximised for a given total surface area of heat exchangers. Calculation has been done initially with 5 K temperature approach in all the heat exchangers. However, an appropriate distribution of total surface area times overall heat transfer (UA) resulting in an unequal temperature approaches in the heat exchangers generated much higher output of power. The simulation shows that though cascaded three-stages delivers the highest power. A two-stage system with only the first stage cascaded reduces power generation by 8.6% compared to that in a three-stage system. However, the former gains enormously in simplicity of configuration and operation. The corresponding reduction in surface area of the heat exchanger is 20%.

Research on the utilization of fuel cold energy for LNG powered container ships

Aiming at the problems that the fuel releases a lot of cold energy and the refrigerated containers consume a lot of electricity on large LNG powered container ships, a set of cold energy cascade utilization scheme that mainly uses LNG cold energy for refrigerated containers is designed. The simulation software Aspen HYSYS is used to establish and simulate the process of the ship’s cold energy cascade utilization system under five different working conditions, and the main parameters of the key nodes are obtained, according to the established exergy efficiency model, the exergy efficiency of the main equipment and the whole system is solved. Under the five working conditions, the maximum exergy efficiency of the refrigerated container system before optimization is 24.54%, at this time, the exergy efficiency of the entire cold energy utilization system is 24.86%. With the goal of improving the exergy efficiency of the entire system, using a hierarchical optimization method, the key parameters affecting the exergy efficiency of each cold energy utilization module are analyzed and optimized respectively, and the optimal operating parameters of different cold energy utilization module were determined. So as to realize the optimization of the whole cold energy cascade utilization system. The results show that the exergy efficiency of the optimized LNG cold energy cascade utilization system for ships under five working conditions is improved, under the 65% working condition, the exergy efficiency of the optimized refrigerated container system is 27.69%, and the exergy efficiency of the whole cold energy utilization system is 28.04%, which are increased by 3.15% and 3.18% respectively. Which proves that the LNG cold energy cascade utilization system can realize the effective utilization of LNG cold energy.

Modeling and optimization of a novel Oxy-fuel/Solar/Wind/Battery power generation system

• The optimized combined system can perfectly meet the needs of electricity grid. • The cold energy of LNG is used to condense CO 2 and nearly zero CO 2 emissions is achieved. • The optimal model is obtained by considering various wind-solar ratios and scales of battery storage capacity. • The LCOE of the combined system is reduced by 3% to 6% with the employment of solar-wind energy. It is proposed and built a novel oxy-fuel/solar/wind/battery power generation system. It consists of a solar-wind renewable system (SWRS) with battery bank and a liquefied natural gas-fueled oxy-fuel combined cycle (OFCC). The work is unique in that it uses SWRS to power OFCC’s main energy-consuming equipment, such as the recycled CO 2 compressor (RCC) and air separation unit (ASU). SWRS power is consumed locally, avoiding the negative effects of SWRS intermittency and variability on the electricity grid. CO 2 is compressed, cooled and then condensed by evaporating the cold LNG. MATLAB/Simulink and Aspen Plus were used to create the SWRS and OFCC, respectively. In order to find the optimal model of the combined system in terms of economic factors, various wind-solar ratios, scales of SWRS and OFCC, and battery storage capacity have been considered and combined. The results show that the optimized combined system can perfectly meet the needs of the electricity grid while having a high renewable energy utilization efficiency, no negative impact on power grid stability, low power generation costs, and low CO 2 emissions. This work will serve as a guide for the combined power system’s power supply planning.

Optimal design of dual-stage combined cycles to recover LNG cold energy and low-temperature waste thermal energy for sustainable power generation

To overcome the shortcomings of the low net power output of a single power generation cycle for LNG cold energy recovery, investigating dual-stage combined cycles with different cycle configurations under the same heat and cold source conditions is mandatory. Hence, this study proposes 12 dual-stage combined power generation cycles to utilize LNG cold energy and low-temperature (below 200 °C ) waste thermal energy. The developed method adopts an organic Rankine cycle and Brayton cycle as the bottoming cycle and the organic Rankine cycle, Brayton cycle, and supercritical carbon dioxide power cycle as the topping cycle with parallel and serial configurations. The optimization results show that the thermodynamic and economic performance are compared quantitatively. The optimally combined cycle is a dual-stage serial organic Rankine cycle with the highest specific net power output of 202.15 kJ/kg and lowest levelized cost of electricity of 0.11 $/kWh. Regarding the parallel configuration, it can enhance thermal and exergy efficiency via its internal heat integration. Moreover, the evaporation and condensation pressure of the bottoming cycle has a more significant influence on the optimally combined cycle than the topping cycle. Overall, this study paves the way to design economics-efficient dual-stage combined cycles for sustainable power generation by utilizing LNG cold energy and low-temperature waste thermal energy.

Design and analysis of LNG cold energy cascade utilization system integrating light hydrocarbon separation, organic Rankine cycle and direct cooling

• A novel LNG-LHS-ORC-DC system for cascade utilization of LNG cold energy is proposed. • Multi-objective optimization based on NSGA-II is performed. • The utilization of LNG cold energy by each subsystem is investigated. • Exergy destructions of all components are analyzed to find system improvement scheme. • Economic feasibility of the proposed system is studied based on net present value. To effectively recover the cold energy released in the liquefied natural gas (LNG) regasification process, this paper constructs a novel LNG cold energy cascade integrated utilization system. In the system, the LNG cold energy in low temperature zone is used for light hydrocarbon separation (LHS), and the remaining cold energy is divided into two parts. One part is used for organic Rankine cycle (ORC) as well as data center cooling (DCC), and the other part is used for cold warehouse cooling (CWC). The thermodynamic and economic analysis of the system is carried out in detail, and the multi-objective optimization based on NSGA-II is implemented to investigate the optimal performance. The results show that the net power output of the system is 4259.72 kW, much larger than that of the LNG cold energy single utilization system for LHS in reference, and the cold energy for data center and cold warehouse is equivalent to saving 12685.87 kW electric energy. Furthermore, the revenue of the system in 20 years is 2.9982 × 10 9 $, more than that of the reference system. Through the net present value analysis, it is found that the system is more sensitive to the ethane price than to electric price.

Safe design of liquid oxygen plant that absorbs LNG cold energy and offsets supply disruption by injecting liquid nitrogen

Cold thermal energy of LNG that is usually rejected into sea-water can be effectively utilized in an air separation unit (ASU) to reduce power consumption and carbon footprint. ASU producing liquid oxygen, which is the most saleable of its products, consumes 47.9% lower power with the utilization of LNG cold energy. However, it poses a finite fire safety concern for flammable hydrocarbon such as LNG in presence of oxygen in the same heat exchanger. An ASU becomes safer if LNG cold energy is extracted by nitrogen in a separate heat exchanger though it consumes 4.4% higher specific power. A further step towards a more reliable plant is taken by producing and storing a small quantity of liquid nitrogen that is used to keep the plant cold when the LNG supply is disrupted. The proposed modified ASU, that is simpler in design, more reliable in operation, has a lower power consumption and capital investment, is safer and can withstand LNG supply shut down for sufficient duration, and environment-friendly, meets the major criteria of sustainable energy planning. With the use LNG cold energy, the plant requires between 15% and 17% lower investments compared to the one without LNG cold utilization.

Improvement of Regasification Process Efficiency for Floating Storage Regasification Unit

Natural gas plays a vital role in the economically and environmentally sustainable future of energy. Its reliable deliveries are required, especially nowadays, when the energy market is so volatile and unstable. The conversion of natural gas to its liquefied form (LNG) allows its transport in greater quantities. Affordability and reliability of clean energy is a key issue even for developed markets. Therefore, natural gas usage enables to implement green solutions into countries’ economies. However, the LNG-production process consumes a considerable amount of energy. This energy is stored in LNG as cold energy. After LNG unloading into storage tanks at receiving terminals, it is vaporised and compressed for transmission to a natural gas pipeline system. During the regasification process, the large part of the energy stored in LNG may be recovered and used for electricity generation, seawater desalination, cryogenic air separation, hydrogen liquefaction, material freezing, carbon dioxide capture, as well as for combined LNG cold energy utilization systems. Moreover, increased efficiency of LNG terminals may attract potential clients. In the presented paper, a mathematical model is performed to determine the influence of LNG composition and regasification process parameters on the quantity of released LNG cold energy in a large-scale floating storage and regasification units (FSRU)-type terminal “Independence” (Lithuania). Flow rate of LNG regasification, pressure, and boil-off gas recondensation have been considered. Possibilities to reduce the energy losses were investigated to find the ways to improve the regasification process efficiency for real FSRU. The results analysis revealed that potential of LNG cold energy at FSRU could vary from 20 to 25 MW. A utilisation of industrial and urban waste heat for the heat sink FSRU is recommended to increase the energy efficiency of the whole regasification process.

Energy, exergy and economic benefits deriving from LNG-fired power plant: Cold energy power generation combined with carbon dioxide capture

According to The Paris Agreement, countries need to strictly control carbon emissions before global warming causes great damage to the environment. Therefore, how to reduce carbon emissions to restore carbon neutrality has become an inevitable life-and-death matter for all countries from a long-term perspective. In view of the ever-increasing LNG-fired power plants and the wasted LNG cold energy in vaporization process, a new environment-friendly cold energy utilization method is proposed to meet energy conservation and pollution reduction targets in this paper, integrating the organic Rankine cycle and the carbon dioxide capture cycle. Moreover, a full and deliberate comparison of pure and binary fluids is made to determine the optimal fluids of organic Rankine cycle (R600a) and carbon dioxide capture cycle (NH3+R125), respectively. After being optimized by genetic algorithm, the thermal efficiency is 33.7% and exergy efficiency reaches 47.2%. Meanwhile, the net specific work and total carbon dioxide capture generated by the system are 110.1 kWh/tLNG and 0.78 t/tLNG. In terms of economic benefit, this cold energy utilization system can recover the total investment cost in 1.85 years. Thus, the practical application of this proposed method is completely feasible and economical, and it can recover capital in a short time.

A comparative study of two liquid air energy storage systems with LNG cold energy recovery

Due to the nature of fluctuation and intermittency, the increasing penetration of wind and solar power will bring a huge impact to the power grid management. Therefore the concept of liquid air energy storage system was proposed. Compared to compressed air energy storage, liquid air energy storage has a larger storage capacity and no geographic constraints owing to the high density of liquid air. In order to obtain the optimum system design, two different liquid air energy storage systems with LNG cold energy recovery were studied. For one system, the LNG cold energy was used to precool the compressor inlet air to decrease the compression work. For another one, the LNG cold energy was applied to supplement the cold energy needed to liquefy the air and realize the decoupling between the energy storage and release processes. Thermodynamic analysis based on steady-state mathematical model was employed to evaluate the system performance difference.

Integrated design and optimization research of LNG cold energy and main engine exhaust heat utilization for LNG powered ships

This paper aims at the high-efficiency utilization of LNG cold energy and main engine exhaust heat of ten-thousand-box LNG-powered container ship, and takes the 9200TEU LNG powered ship as the target ship. The two-level parallel Rankine cycle system is used to replace the original exhaust heat boiler utilization system, and the LNG horizontal three-level nested Rankine cycle is added on the basis of the two-level parallel Rankine cycle, realizing the efficient integrated utilization of the LNG vaporization cold energy and the exhaust heat of the main engine. Aspen HYSYS is used to simulate the scheme, and the genetic algorithm is further used to optimize the parameter matching of the system. Finally, the economic analysis of the cost saved by the optimization scheme and the initial investment cost is carried out. The results show that the system exergy efficiency in summer conditions reaches 58.20%, and the system exergy efficiency in spring, autumn and winter conditions reaches 58.73%; the initial system equipment cost is US$34.41 million, the power production cost of the system is 0.129 US$/kWh, and the payback period PBP is 7.37 years.

Thermodynamic Optimization of a Composition-Tunable Zeotropic ORC Using LNG Cold Energy as a Heat Sink

Thermodynamic Optimization of a Composition-Tunable Zeotropic ORC Using LNG Cold Energy as a Heat Sink

Effect of environmental factors on a vaporizer with thermoelectric modules for LNG cold energy utilization

The new vaporizer with thermoelectric modules (VTEG) can convert LNG cold energy into electric energy. This study discussed the influence of environmental factors on the thermoelectric performance of VTEG. The results showed that increasing the heat transfer coefficient outside the tube not only increased the maximum power output significantly but also reduced the optimal tube length, thus improving the economics of VTEG. The LNG undergoes three different heat transfer processes in VTEG, with the most significant system efficiency when it is in the liquid-phase and two-phase regions. As the ambient temperature increases, the maximum power output increases almost linearly, and a 30 K increase in ambient temperature resulted in a 26.1% rise in generating efficiency. Overall, environmental factors have a significant impact on the generation performance of VTEG and must be considered in VTEG optimization design.