Liquid Air Storage Research Articles

Power generation system utilizing cold energy from liquid hydrogen: Integration with a liquid air storage system for peak load shaving

Liquid hydrogen (LH2) can serve as a carrier for hydrogen and renewable energy by recovering the cold energy during LH2 regasification to generate electricity. However, the fluctuating nature of power demand throughout the day often does not align with hydrogen demand. To address this challenge, this study focuses on integrating liquid air energy storage with a power generation system based on LH2 regasification. Three configurations are proposed and compared: no-storage, partial-storage, and full-storage. In the no-storage system, power is generated using recuperated Brayton cycle and two organic Rankine cycles without energy storage. In contrast, the partial-storage system offers flexible operational modes. During peak times, cold energy is utilized for power generation, while it is diverted to store liquid air during off-peak times. In the full-storage system, produced energy is partially reserved throughout the day. Thus, compared to the partial-storage system, the full-storage system boasts a simplified configuration, eliminating the need for operational mode transitions. Furthermore, its larger liquid air storage capacity maximizes the difference in power production up to 4.53 MW between on- and off-peak times. Consequently, despite its higher capital costs, the full-storage system demonstrates greater economic viability, especially when considering government subsidies.

Utmost substance recovery and utilization for integrated technology of air separation unit and liquid air energy storage and its saving benefits

The integration of air separation units (ASUs) and liquid air energy storage (LAES) (ASU-LAES) can bring very good economic benefits based on their resource complementarity at the same low-temperature energy level. Two types of novel process flows are proposed in this paper for ASU-LAES. These flows can use the ASU to recover the maximum amount of refrigerated air from energy storage process to the front or back of the air compressor (i.e., pre- or post-machine recovery), so as to improve the energy efficiency and economic benefits. The pre-machine recovery process flow can achieve an electrical roundtrip efficiency of up to 76.38%. Although a lower refrigeration expansion ratio is used in the post-machine recovery process flow, it can form an air refrigeration cycle without passing through air compressor. Its exergy loss from expansion and compression is smaller, which maximizes liquid air storage. The electrical round-trip efficiency can reach up to 72.9%, and the larger storage scale increases its economic benefit compared to the pre-machine recovery. Based on the peak-to-valley price ratio of 3.4:1, the post-machine recovery process flow can save up to 13.23% of electricity cost compared to the conventional ASU. The dynamic payback period of the LAES is 2.27 years. Compared to ASU-LAES without recovery of refrigeration air, the electricity cost-saving ratio is improved by 134.9%, and the dynamic payback period of the LAES is shorten by 41.8%.

Molecular dynamics simulation of temperature and concentration distribution at liquid-gas interface during liquid air storage process

To address global challenge of climate changes, renewable energy has been fully developed in recent years. However, renewable energy is usually intermittent which makes it challenging for application. Liquid air energy storage can effectively store intermittent energy with promising prospects. Liquid air is a mixture composed of N2, O2 and Ar with different evaporation temperatures. It is assumed to form temperature and concentration stratification during storage and thus causes safety challenge. To address this issue, molecular dynamics (MD) simulation method is used to study the temperature and concentration distribution characteristics in liquid air. The results show that the system temperature remains constant at 94 K with no temperature stratification during storage. However, the concentration of liquid air changes along vertical direction (z axis): the oxygen concentration remains stable around 21% as z is 0-60 Å, rises to 22.1% as z is from 60-70 Å and drops to 0% as z is above 80 Å. The thin and short stratification phenomenon occurs at the gas-liquid interface region. In addition, a higher heat flux leads to a higher evaporation rate and a larger oxygen concentration. As the heat flux increases from 0.0 to 2.4 W/m2, evaporation rate rises from 0.13 to 0.2% and the oxygen concentration at the liquid-gas interface reaches 22.3%. Thus, concentration stratification exists during liquid air storage and should be treated carefully. This paper provides an insight into the temperature and concentration distribution of liquid air during storage and is significant for safety improvement and development of liquid air energy storage.

The effect of insulation on boil-off gas in liquid air storage tank

Increasing renewable energy is posing a challenge to the stability of electricity grid, and the importance of an energy storage system (ESS) is becoming clearer. A Liquid Air Energy Storage System (LAES) is proposed as one of the promising ESS technologies. LAES converts electricity to liquid air efficiently and economically. However, since the storage temperature of liquid air is −196 °C, loss of liquid air is inevitable due to evaporation, i.e., boil-off gas (BOG). A loss of liquid air has negative effect on the round-trip efficiency of LAES; therefore, the BOG rate must be minimized. In this research, the insulation performance of liquid air tank is evaluated. To calculate the heat ingress and BOG rate, a partial equilibrium model is developed. The insulation performance is evaluated with varying insulation thickness, emissivity, aspect ratio and materials. The results show that the BOG rate of vacuum insulation can reach 1.8 %/day. For foam glass insulation, the BOG rate can become 2.25 %/day. With optimal geometry, 0.7 %/day for vacuum insulation and 1 %/day for foam glass insulation can be achieved. The vacuum insulation generally shows better insulation performance, however, there is area where the foam glass insulation shows better performance depending on the insulation thickness and emissivity.

Green hydrogen production and liquefaction using offshore wind power, liquid air, and LNG cold energy

Coastal regions have abundant off-shore wind energy resources, and surrounding areas have large-scale liquefied natural gas (LNG) receiving stations. From the engineering perspectives, there are limitations in unstable off-shore wind energy and fluctuating LNG loads. This article offers a new energy scheme to combine these 2 energy units, which uses surplus wind energy to produce hydrogen, and use LNG cold energy to liquefy and store hydrogen. In addition, in order to improve the efficiency of utilizing LNG cold energy, and reduce electricity consumption for liquid hydrogen (LH2) production at coastal regions, this article introduces the liquid air energy storage (LAES) technology as the intermediate stage, which can stably store the cold energy from LNG gasification. A new scheme for LNG-LAES-LH2 hybrid LH2 production is built. The case study is based on a real LNG receiving station at Hainan province, China, and this article presents the design of hydrogen production/liquefaction process, and carries out the optimizations at key nodes, and proves the feasibility using specific energy consumption and exergy analysis. In a 100 MW system, the liquid air storage round-trip efficiency is 71.0% and the specific energy consumption is 0.189 kWh/kg, and the liquid hydrogen specific energy consumption is 7.87 kWh/kg and the exergy efficiency is 46.44%. Meanwhile, the corresponding techno-economic model is built, and for a LNG-LAES-LH2 system with LH2 daily production 140.4 tons, the shortest dynamic payback period is 9.56 years. Overall, this novel hybrid energy scheme can produce green hydrogen using a more efficient and economical method, and also can make full use of surplus off-shore wind energy and coastal LNG cold energy.

A Novel Analysis of Energy Density Considerations and Its Impacts on the Cost of Electrical Energy Storage (EES) Plants

Geological restrictions and the low energy density of compressed air energy storage (CAES) plants constitute a technical and economic barrier to the enablement of variable and intermittent sustainable sources of energy production. Liquid air energy storage (LAES) and pumped thermal energy storage (PTES) systems offer a promising pathway for increasing the share of renewable energy in the supply mix. PTES remains under development while LAES suffers from low liquefaction unit efficiency, although it is at a higher technology readiness level (TRL) than PTES. The most significant element of large-scale EES is related to the discharge features of the power plants, especially the energy storage unit. Here, a novel multi-aspect equation, based on established codes and thermodynamic principles, is developed to quantify the required storage capacity to meet demand consistent with the design parameters and operational limitations of the system. An important conclusion of the application of the multi-aspect equation shows that liquid air storage systems instead of compressed air would reduce the space required for storage by 35 times. Finally, a cost equation was introduced as a function of the required storage volume. Calculations have demonstrated that the use of the novel cost equation, in lieu of the old one-aspect cost equation, for an LAES power plant with a production capacity of about 50 MW makes the costs of installing liquid air storage tanks against the total expenditure of the power plant about six times higher than what was reported in earlier research.

Techno-economic analysis of solar aided liquid air energy storage system with a new air compression heat utilization method

Solar aided liquid air energy storage (SA-LAES) system is a clean and efficient large-scale energy storage system. Traditional SA-LAES system requires the storage equipment for air compression heat, which results in a high economic cost and low energy storage density. And the air compression heat cannot be completely utilized. To solve these problems, this study proposes a novel solar aided liquid air storage system (SA-LAES) with a new cascade air compression heat utilization method in the charging process. The results show that the round trip efficiency (RTE) of the new system (Case 2) is 110.29%, 2.97% higher than that of the reference system (Case 1). The energy storage density of the Case 2 is 35.38 kWh/m3, 75.67% higher than that of the Case 1. The payback period of Case 2 is 5.25 years, 41.79% lower than that of Case 1. The levelized cost of energy (LCOE) is 0.07 $/kWh, 20.73% lower than that of Case 1. At the same time, Case 2 can effectively avoid the heat accumulation phenomenon of Case 1. These results show that the proposed SA-LAES system (Case 2) is efficient and economical and can be a promising candidate for advanced energy storage technology in engineering applications.

Thermodynamic, exergoeconomic, and economic analyses with multi-objective optimization of a novel liquid air energy storage coupled with an off-shore wind farm

The liquid air energy storage is a cutting-edge technology that covers the geographical drawbacks of other utility-scale energy storage alternatives. The coupling the liquid air storage system with renewable energies and heat recovery units can compensate the grid unstability and lack of their round trip efficiency, respectively. In the present paper, an off-shore wind farm including different wind turbines is assessed from technical, availability, and economic viewpoints to be combined with a liquid air energy storage unit, expolits a Kalina cycle for waste heat recovery. First, a comprehensive energy, exergy, and economic analyses are conducted for the integrated system; then, a coupling of artificial neural network and multi-objective genetic algorithm optimization method are carried out to find the optimum design condition. The findings show that around 93 MWh of the generated power in the wind site during off-peak period can be utilized to charge the system. Then, in addition to power generation in the wind farm, the reference system generates 76.4 MWh of extra power and 585 tons of domestic hot water during peak hours for peak shaving. Based on the optimization results, the round trip efficiency and total cost rate are 44.7% and 476 $/hr, repectively. The result of economic analysis demonstrated that the Enercon E-126 EP4 is the most cost-effective wind turbine for the proposed system, resulting in a period of 5.5 years. It has been also resulted that the existence of the LAES-KC system can half the paybacks.

TECHNOLOGIES OF CRYOGENIC STORAGE OF ELECTRICITY FROM RENEWABLE SOURCES

The peculiarities of storing electricity produced by traditional systems of its production and using renewable energy sources are considered, the state of the problem is discussed. Examples of industrial application of electricity storage systems using compressed and liquefied air are given. Liquid air storage systems have been shown to be the most efficient. A scheme for the accumulation of electricity and its production with the use of turbo-expander power generator units with the use of liquefied air is proposed. Taking into account the situation that has developed in Ukraine in connection with the spread of the COVID-19 virus, a scheme for obtaining liquid medical oxygen by the cryogenic method on low-tonnage transportable equipment is proposed. Bibl. 10, Fig. 2.

Experimental investigation of tank stratification in liquid air energy storage (LAES) system

Liquid air energy storage technology is a technology that stores liquid air in case of excess power supply and evaporates the stored liquid air to start a power generation cycle when there is an electric power demand. When liquid air is stored for a long-time during operation, safety and performance degradation can be caused or mitigated by the tank stratification. To investigate the tank stratification phenomenon and associated issues, an experimental facility is constructed. The heat ingress is controlled with respect to changing vacuum level in the experiment. Furthermore, the conditions under which stratification occurs are defined in terms of temperature and concentration, and based on this, the stratification stability ratio and the stability map are defined and evaluated experimentally. The results show that the time required for destratification is 8–29% shorter for liquid air mixture cases than for liquid nitrogen. Moreover, the time required for destratification is 2.4 times longer for the high tank pressure cases, and it is 39% shorter for the case of high heat ingress. From experimental observations, an operation strategy utilizing stratification inside the liquid air storage tank is newly suggested that can minimize the boil-off gas of liquid air in the tank.

Thermodynamic analysis and efficiency assessment of a novel multi-generation liquid air energy storage system

In order to get the utmost out of the thermal energy stored in the general liquid air energy storage (LAES) system and improve the cycle efficiency of the energy storage system, this paper proposes a novel multi-generation LAES system. The thermodynamic model and economic model of the novel multi-generation LAES system are constructed. The thermodynamic performance and economy of the novel multi-generation system are analyzed, the cycle efficiency and economic indexes are used as evaluation indicators to compare with the general LAES system. The results show that the novel multi-generation LAES system can provides 325.02 kW of thermal energy, 177.43 kW of cold energy and 3.01 m3/s of fresh air except meets the requirements of 1.5 MW power output. Compared with the general LAES system of 56.48% cycle efficiency, the cycle efficiency of the novel multi-generation LAES system can reach 75.40%. The leveled cost of electricity (LCOE) of the multi-generation LAES system in Beijing is 0.79 ¥/kWh, the rate of return on investment is 20.5%, and the internal rate of return is 27%. The air liquefaction rate reaches 84.52% and the volume of liquid air storage tank is only 121.91 m3. Therefore, the novel multi-generation LAES system with high energy storage density can play a better role in the energy storage scenarios, and not restricted by the geographical environment. In addition, the influence rules of the key parameters, such as unit stages, temperature, pressure and adiabatic efficiency, on the thermodynamic characteristic of the system are also obtained. The novel multi-generation LAES system and related analysis results proposed in this study can provide references for the user side energy storage.

A novel air separation unit with energy storage and generation and its energy efficiency and economy analysis

Air separation units (ASUs), as a single industrial equipment item, accounted for a considerable proportion (4.97%) of China’s national total power consumed. Therefore, combining with energy storage technology and implementing demand side management on ASUs can balance the demand on a power grid and bring economic benefits to various enterprises. Air liquefaction is a facet of air separation technology, however, stand-alone liquid air energy storage (LAES) has still issues such as the need for signification investment and a long payback period. To address these issues, we propose a novel air separation unit with energy storage and generation (ASU-ESG) which integrates an ASU, a liquid air storage unit, and an energy release and generation unit. It not only meets the product purity and yield requirements for ASUs, but also realizes the large-scale storage with only one type of device, using a single technology. To assess the performance of ASU-ESG, energy efficiency and economic analyses are conducted, and its effects on power grid balancing are discussed. When no external energy used in ASU-ESG, its electrical round-trip efficiency reaches 53.18%, the electricity cost saves 4.58~6.84% compared with the conventional internal compression ASUs, and the payback period for the LAES system is 2.8~4.2 years. If the ASU-ESG is implemented in China’s ASUs, the annual reduction in the average peak-valley ratio (25.98%) in China is 6.4~7.3%. Considering the widespread application of such ASUs’, for any country and region, its implementation will be of great practical significance to improving the economic benefits of ASUs and balancing the power demand.

Advanced integration of LNG regasification power plant with liquid air energy storage: Enhancements in flexibility, safety, and power generation

Power plants for regasification of liquefied natural gas (LNG), integrated with liquid air energy storage (LAES), have benefits in terms of power generation flexibility to match the electricity demand profiles and increased operating profits from electricity arbitrage. However, issues with the flexibility and safety of this integration still remain. In addition, further improvements in power generation were identified from the use of high-grade LNG cold energy in LAES. Thus, this paper proposes a novel and advanced integration (denoted as LNG-LAES) for enhancements in flexibility, safety, and power generation. LNG is re-gasified in two different manners: it flows into a parallel two-stage regenerative Rankine cycle for conventional power generation during peak times or transfers high-grade cold energy to LAES for energy storage during off-peak times. Pressures of LNG vaporization and liquid air storage are minimized to 7 and 0.15 MPa to achieve an inherently safer design. The process assessment is performed considering possible demand and marketing scenarios, in which the LNG-LAES process exhibits the best performance in terms of power generation and economic benefits. In the base-case, the specific daily net power output increases up to 94.8 kJ/kgLNG and the electrical round trip efficiency of LAES achieves 129.2%. Moreover, the LNG-LAES process has design flexibility that the amount of LNG cold energy utilized in LAES can be varied at the design stage to maximize the operating profit corresponding to a specific electricity market scenario. The analyzes demonstrate that the proposed LNG-LAES process is both technically feasible and economically preferable for industrial applications.

Energy and economic performance assessment of the novel integration of an advanced configuration of liquid air energy storage plant with an existing large-scale natural gas combined cycle

This article proposes the novel integration of an advanced configuration of Liquid Air Energy Storage (LAES) plant and an additional gas turbine cycle with an existing large-scale Natural Gas Combined Cycle (NGCC). A novel mode of exploiting the electric energy stored within the LAES plant and additional gas turbine cycle in combination with the existing NGCC is aimed at increasing its revenues in the electricity market. The energy performance analysis of the integrated plant at off-design conditions is carried out in presence of simultaneous changes of the pressure in the liquid air storage site (p3) and of the pressure at the outlet of the cryogenic pump in the discharging circuit (p25). The maximum storage efficiency is 2.173. The uncertainty economic analysis is performed in three alternative economic scenarios - expected, pessimistic and optimistic - in order to assess the profitability of the installation and operability of the integrated plant compared with the stand-alone NGCC. In the expected scenario, the integrated plant leads to profitability in the whole range of each p3 and p25, with the exception of the minimum value of p25. With varying p3 and p25, the profitability is always absent in the pessimistic scenario, whereas it is always present in the optimistic one. The proposed approach can be extended to the integration of an LAES plant with a generic existing large-scale thermal power plant in order to increase its revenues in the electricity market.

Thermodynamic analysis of the cascaded packed bed cryogenic storage based supercritical air energy storage system

This paper presents a thermodynamic analysis of a novel stand-alone supercritical air energy storage (SAES) system, based on cascaded packed bed cryogenic storage. This system has the advantages of low cost, high efficiency and safety thanks to the different grade cryogenic energy be transferred and stored in two cascaded packed beds. Thermodynamic analysis results show that the discharge pressure and roundtrip efficiency are influenced by component efficiencies, charge pressure and middle temperature, and the optimized charge pressure and middle temperature are 120.0 bar and -70°C, respectively, no matter how component efficiencies changes. The increasing liquid air storage pressure reduces the exergy loss in evaporator and condenser and improves the round trip efficiency. Results show that a high round trip efficiency, which is up to 65% could be obtained in this novel supercritical air energy storage system.

P11-06 液体空気利用によるガスタービン吸気冷却/出力向上技術

P11-06 液体空気利用によるガスタービン吸気冷却/出力向上技術