• Energy Research

Abstract Liquid air energy storage (LAES) is regarded as one of the most promising large-scale energy storage technologies due to its unique advantages of high energy storage density, no geographical constraints and long life-span. The LAES mainly includes air liquefaction (charging cycle) at off-peak time and power generation (discharging cycle) at peak time. During air liquefaction, ambient air is first required to remove its compositions with high freezing points (H2O and CO2) before it is cooled down (denoted as air purification process), preventing pipeline blockage and guaranteeing safe operation. However, most of previous studies simply neglected the air purification process and assumed ambient air was already purified. This may cause overestimation of the LAES performance as the air purification process usually consumes thermal energy or electricity. To address this issue, this paper proposes a novel LAES system with energy-efficient air purification. Dynamic characteristics of the air purification process are investigated from molecular to systematic modeling for the first time. Simulation results show that the air purification process could be driven by exhaust air from the air turbine at peak time rather than thermal energy or electricity in the traditional methods. This could improve the electrical round trip efficiency by 2.3% compared with the traditional methods. In addition, the proposed LAES system shows a combined heat and power efficiency of 82.5-86.7%, an electrical round trip efficiency of 47.9-59.6% and an exergy efficiency of 58.4-68%. These findings will be helpful to understand the function of air purification in the LAES system, providing guidelines for practical applications.

Abstract Liquid air energy storage (LAES) is regarded as one of the most promising large-scale energy storage technologies due to its unique advantages of high energy storage density, no geographical constraints and long life-span. The LAES mainly includes air liquefaction (charging cycle) at off-peak time and power generation (discharging cycle) at peak time. During air liquefaction, ambient air is first required to remove its compositions with high freezing points (H2O and CO2) before it is cooled down (denoted as air purification process), preventing pipeline blockage and guaranteeing safe operation. However, most of previous studies simply neglected the air purification process and assumed ambient air was already purified. This may cause overestimation of the LAES performance as the air purification process usually consumes thermal energy or electricity. To address this issue, this paper proposes a novel LAES system with energy-efficient air purification. Dynamic characteristics of the air purification process are investigated from molecular to systematic modeling for the first time. Simulation results show that the air purification process could be driven by exhaust air from the air turbine at peak time rather than thermal energy or electricity in the traditional methods. This could improve the electrical round trip efficiency by 2.3% compared with the traditional methods. In addition, the proposed LAES system shows a combined heat and power efficiency of 82.5-86.7%, an electrical round trip efficiency of 47.9-59.6% and an exergy efficiency of 58.4-68%. These findings will be helpful to understand the function of air purification in the LAES system, providing guidelines for practical applications.

Abstract This work concerns with self-reinforced composite phase change materials (CPCMs) for thermal energy storage (TES) to deal with the mismatch between energy generation and demand under deep renewable energy penetration scenarios to combat climate change challenges. It focuses specifically on the cost-effective manufacturing of CPCMs at a large scale, aimed to promote the deployment of CPCMs. For this, a novel high-density-polyethylene (HDPE)/pentaerythritol/graphite CPCM is formulated and manufactured by using a continuous hot-melt extrusion method for the first time. A correlation between the manufacturing parameters and the CPCM structural properties is established. An optimal extrusion rate and the processing temperature are found for producing a dense and homogeneous structure. Thermal characterization of the fabricated CPCM shows a high energy density of 426.17 kJ/kg in a working temperature range between 100 °C and 200 °C. The CPCM also has an improved thermal conductivity of 0.42 w/(m·K), which is 26.02% higher compared with the pure HDPE. A good stability of the fabricated CPCM is observed through 100 times of thermal cycling, which shows a small change of the latent heat. The throughput of the formulated CPCM on a lab-based extruder can reach 2.09 kg/h, and an economic analysis of the produced CPCM indicates a great potential for commercialisation.

Abstract This work concerns with self-reinforced composite phase change materials (CPCMs) for thermal energy storage (TES) to deal with the mismatch between energy generation and demand under deep renewable energy penetration scenarios to combat climate change challenges. It focuses specifically on the cost-effective manufacturing of CPCMs at a large scale, aimed to promote the deployment of CPCMs. For this, a novel high-density-polyethylene (HDPE)/pentaerythritol/graphite CPCM is formulated and manufactured by using a continuous hot-melt extrusion method for the first time. A correlation between the manufacturing parameters and the CPCM structural properties is established. An optimal extrusion rate and the processing temperature are found for producing a dense and homogeneous structure. Thermal characterization of the fabricated CPCM shows a high energy density of 426.17 kJ/kg in a working temperature range between 100 °C and 200 °C. The CPCM also has an improved thermal conductivity of 0.42 w/(m·K), which is 26.02% higher compared with the pure HDPE. A good stability of the fabricated CPCM is observed through 100 times of thermal cycling, which shows a small change of the latent heat. The throughput of the formulated CPCM on a lab-based extruder can reach 2.09 kg/h, and an economic analysis of the produced CPCM indicates a great potential for commercialisation.

Abstract Liquid desiccant dehumidification is promising as it could be driven by renewable energy. In the present study, it newly investigated the dehumidification characteristics of KCOOH solution in an internally cooled dehumidifier. To select suitable concentration range, the vapor pressure of KCOOH solution with different solution concentration and temperature was measured with static method firstly. Then comparative experimental study was conducted to identify the dehumidification performance of KCOOH and LiCl solution under different solution and air flow rate, temperature and air humidity. Experimental results indicated that 70.3% KCOOH solution had almost the same vapor pressure as 35% LiCl solution. Under the same experimental conditions, the absolute moisture removal of 70.3% KCOOH solution was slightly higher than that of 35% LiCl solution as a result of the increased wetting area. It was found that the mass transfer coefficients of the two liquid desiccants were almost the same. An empirical correlation of S h number was obtained to predict the mass transfer coefficient of KCOOH solution for dehumidification with a mean absolute relative deviation of 7.81%.

Abstract Liquid desiccant dehumidification is promising as it could be driven by renewable energy. In the present study, it newly investigated the dehumidification characteristics of KCOOH solution in an internally cooled dehumidifier. To select suitable concentration range, the vapor pressure of KCOOH solution with different solution concentration and temperature was measured with static method firstly. Then comparative experimental study was conducted to identify the dehumidification performance of KCOOH and LiCl solution under different solution and air flow rate, temperature and air humidity. Experimental results indicated that 70.3% KCOOH solution had almost the same vapor pressure as 35% LiCl solution. Under the same experimental conditions, the absolute moisture removal of 70.3% KCOOH solution was slightly higher than that of 35% LiCl solution as a result of the increased wetting area. It was found that the mass transfer coefficients of the two liquid desiccants were almost the same. An empirical correlation of S h number was obtained to predict the mass transfer coefficient of KCOOH solution for dehumidification with a mean absolute relative deviation of 7.81%.