Abstract

Achieving net-zero emissions and curbing the long-term increase in global warming requires large-scale carbon dioxide (CO2) sequestration through various techniques. Among the plethora of options for large-scale CO2 storage, geological storage stands out as the most promising, given its expansive storage capacity and minimal environmental impact. Deep saline aquifers, in particular, have emerged as frontrunners due to their vast storage potential and broad global availability. In saline aquifers, various trapping mechanisms, including structural and stratigraphic trapping, residual or capillary trapping, solubility trapping, and mineral trapping, work synergistically to store CO2. The displacement dynamics of CO2-brine two-phase flow in pore-scale dictates the structural and residual trapping of CO2 in subsurface formations. In this regard, a highly heterogeneous porous microchannel was used to investigate the impact of salinity and porous heterogeneity on CO2-brine displacement dynamics. A computational fluid dynamics (CFD) simulation based on the volume-of-fluid (VOF) method was used to study the immiscible two-phase flow dynamics under deep reservoir extreme temperature and pressure conditions. Microfluidic experiments, conducted under a high-resolution digital microscope with different brine salinities, provide pore-scale flow visualization and quantification of trapped CO2. Meanwhile, CFD simulations on the same porous media consider thermophysical property changes for CO2 and brine under high-pressure and high-temperature conditions, elucidating their impact on CO2 trapping or storage. The observed unstable finger-like displacement pattern in the microchannel, attributed to very low capillary number (Ca) and viscosity ratio (M) values, results in CO2 channeling with limited water displacement, thus restricting CO2 saturation at around 50 %. Along with viscous fingering, small pore-throats pronounce the snap-off effects at the micro-scale, which increase the residual trapping of CO2 in the porous media. An increase in brine salinity increases viscosity, interfacial tension, and contact angle, leading to a more vertical sweep of water and increasing the CO2 storage capacity of a saline aquifer. Under reservoir conditions, the comparatively higher density of CO2 and increase in contact angle resulting from the adsorption of CO2 increases CO2 trapping in porous channels. This combined approach of microfluidic experiments and CFD simulations provided valuable visualization and insights into CO2-brine dynamics at the pore-scale, which would contribute significantly towards efficient, enhanced, and secure storage of CO2.

Abstract

The supercritical carbon dioxide (s-CO2) Brayton cycle is one of the recommended power cycles for next generation high efficiency power plants. An additional benefit of using this working fluid is the miniaturised moving parts when compared to conventional Rankine or Brayton cycle. However, one of the challenges is the
miniaturised design of heat exchangers used in gas cooler, gas heater and regenerators. This can be achieved by reducing the hydraulic diameter of fluid flow channel. However, heat transfer coefficients for supercritical CO2 flow through such miniaturised channels are yet to be studied. In any heat exchanger, the decrease in hydraulic diameter of the channel leads to a higher heat transfer coefficient at the expense of higher pumping power. This study deals with the comparison of a large-diameter single-channel type (SCT) heat exchanger and a small hydraulic diameter multichannel type (MCT) heat exchanger using s-CO2. A numerical investigation is done on a tube-in-tube type heat exchanger, and the effect of mass flow rate and channel diameter at the given inlet temperature and pressure is depicted. At 3 different mass flow rates, such as 1 kg/hr, 3 kg/hr, and 4 kg/hr, the percentage enhancement in the rate of heat transfer for MCT is found to be higher w.r.t. SCT, by 33.4%, 30.34%, and 25%, respectively.

Abstract

Catering to variable load has been a big challenge for large chillers for air-conditioning and process cooling applications. Traditionally chillers were designed for catering to peak capacity with hot-gas bypass being the most common technique for capacity control in fixed speed operation. In more recent applications variable speed compressors have been the preferred choice. In this study we propose a novel hybrid system which combines the mechanical and thermal compression techniques for producing chilled water. The mechanical compression caters to steady load whereas the adsorption based thermal compression caters to variable load. The refrigerant used in this study is R134a with coconut shell based activated carbon as the adsorbent. The adsorber connects to evaporator under peak load operation whereas it regenerates during low load condition thereby keeping the chilled water outlet temperature nearly constant. Experiments are conducted on a lab-scale 1 RTon system. The proposed operational strategy has the potential to handle up to a 26% variation in refrigeration load on the evaporator for maximum regeneration temperature of 850C for the adsorbent.

Abstract

During load cycling processes of coal-fired power plants, the MPS pulverizers system’s response time dominates the power unit’s operation flexibility. Reducing the effect of the delay and inertia of the pulverizing system is urgent. This study established and validated a complete pulverizing system model, which included six coal mills, coupling with an established coal-fired power plant model. A revised fuel demands control strategy based on the main-auxiliary coordination was proposed. The results show that by implementing the revised control strategy, the absolute pulverized coal output deviation was reduced by up to 216 kg, 126kg, and 116kg, respectively, with three operating modes. When four coal mills were operational, the reduction constituted 0.09% of the pulverizing system’s output during the load transition. The new control strategy enhanced the matching of the main and auxiliary systems in coal-fired power units.

Abstract

In this study, methanol has been produced from biomass feedstocks using Aspen Plus simulation tool. The proposed system is a combination of gasification plant, syngas cleaning facility and methanol generation plant. Hydrogen rich syngas was generated using steam biomass gasification facility. After extensive gas cleaning the syngas was fed to the methanol generator system. Five different biomass feedstocks, viz. wheat, barley, rice husk, food waste and date pits were used for the analysis. Among all the feedstocks, date pits yielded the highest amounts of hydrogen (52.52%) and carbon monoxide (34.29%). It was observed that the methanol yield for date pits was the highest (0.82 kg/kg of biomass).

Abstract

In this research, a solar/wind hybrid energy system assisted with battery storage was proposed to study Japan’s strategies for domestic green hydrogen production in the 2030s. A LP optimization model of the proposed system was developed, and calculations were done using ERA5 meteorological data. A comprehensive sensitivity analysis and a comparison with overseas production in western Australia were also conducted.

Abstract

Cold seep can generate dissolved inorganic carbon (DIC) through various processes, such as anaerobic oxidation of methane. The DIC can be emitted into the sea surface via vertical movement of the water column. This part of DIC can bare the possibility of being released to the atmosphere through air-sea exchange. In this way, cold seep can be a carbon source. Yet the contribution in terms of DIC of cold seep has not been considered hitherto. The present study collected samples from four stations in the Haima cold seep from the South China Sea and measured the carbon content and isotope. The results show that cold seep is not a carbon source because of ocean fertilization by methane. Also, cold seep is not the only contribution of DIC. This part of the contribution demands more study to differentiate.

Abstract

Integrated solar energy storage and charging power station is gradually being promoted and applied because of their energy-saving, environmental protection, and excellent economic characteristics. In this paper, the cost-benefit modeling of integrated solar energy storage and charging power station is carried out considering the multiple benefits of energy storage. The model takes five factors into account, e.g., power station charging service, electricity charge, capacity charge, energy storage cycle cost and network loss cost. Its goal is to improve the economy of the power station by comprehensively considering reducing the cost of electricity, extending the life of energy storage equipment, and reducing the loss of electric energy. The effectiveness of the proposed method is proved by an example analysis, and it is found that the capacity benefit and electricity benefit can be balanced by reasonable optimal scheduling.

Abstract

Under the background of “carbon neutral”, the new energy storage represented by electrochemical energy storage is developing rapidly. Shenzhen, as an electrochemical advantageous industrial city of China, has a strong industrial foundation and technical independence. This paper takes Shenzhen as an example, through technical analysis, policy analysis and patent analysis, the status quo and challenges and opportunities of Shenzhen energy storage systems are deeply analyzed to provide a reference for the future development of new energy storage system in China.

Abstract

This study developed a hybrid louver lighting system that combines daylighting using solar energy and LED to solve the problems of high electric consumption and heat load of LED used in vertical farm. This system can control the LED lamp according to the intensity of daylighting that changes in real time to meet the set target PPFD. The louver is composed of transparent vacuum glass and diffuser, and multiple horizontal slats installed air cavity in louver effectively transmit the daylighting to the indoor and distribute the required PPFD. The vent applied to the upper and lower of the louver discharges unnecessary heat generated from the LED lamp to the outdoor in summer and utilizes the required heat indoor in winter. The electric consumption of the hybrid louver lighting system and the indoor temperature due to the heat load were evaluated using a full scale mock-up facility.