Abstract

Hydrogen is an ideal and potential energy carrier due to its high energy efficiency and low pollution. An alternative and promising approach to hydrogen generation is the chemical looping steam methane reforming (CL-SMR) over iron-based oxygen carriers. However, the process faces challenges such as high reaction temperature (>850°C) and low methane conversion. We demonstrate that Ni-mixed Fe-based oxygen carrier particles have significantly improved the methane conversion and hydrogen production rate in the range of 450-600°C under atmospheric pressure. The effect on the reaction reactivity of oxygen carrier particles with different Ni-based particles mixed mass ratios has been determined in the continuous unit. More than 85% of methane conversion has been achieved at 600oC, and hydrogen can be produced in both reduction and oxidation steps. Moreover, the iron-based oxygen carrier particles exhibited good cyclic performance during 150 consecutive redox cycles at 600°C. The mid-temperature iron-based oxygen carrier particles, integrated with a moving-bed chemical looping system, might provide a powerful approach toward more efficient and scalable hydrogen production.

Abstract

The bivalves in cold seep ecosystem can assimilate dissolves inorganic carbon (DIC) into their shell through extrapallial fluid (EPF) and methane through endosymbionts on their gills. Therefore, the DIC and methane released from cold seep can be decreased by the biological metabolism process of the bivalves, which can reduce such carbon enter into the atmosphere. Yet the contribution of cold seep bivalves are not considered hitherto. We choose three common bivalves from cold seep of South China Sea, Bathymodiolus platifrons, Gigantidas haimaensis, Archivesica marissinica and measure the carbon content as well as wet weight and dry weight. Comparing to five shellfish species the cold seep bivalves can store more carbon into their tissue. Combining the fact they feed on methane-oxidizing bacteria and sulfide-oxidizing bacteria, they can reduce the methane possibly released to the air. The Archivesica marissinica bivalves have the best carbon sequestration capacity for higher tissue weight.

Abstract

The process of methane anaerobic oxidation coupled with sulfate reduction promotes alkaline conditions and the formation of carbonate minerals in cold seep environments. The existing studies on microbial communities inhabiting carbonate rock surfaces in cold seep environments primarily revolve around in situ investigations. In this study, high-pressure enrichment cultivation was conducted using methane as the sole carbon source, and periodic monitoring of community dynamics was performed. The results revealed a selective increase in the abundance of the ANME-2c group, which is a typical type of microorganism in methane utilization, anaerobic oxidation, and the synthesis of other nutrients. Additionally, temperature was identified as a crucial factor influencing microbial populations and carbonate processes. Higher temperatures stimulated microbial metabolism, resulting in the production of acidic substances and extracellular hydrolytic enzymes, potentially leading to carbonate dissolution. Conversely, lower temperatures had minimal impact. These findings reveal the significance of methane metabolism and temperature in microbial community dynamics and carbonate kinetics in deep-sea environment.

Abstract

The proper scheduling of residential demand-side flexible resources, such as static batteries and flexible loads, is crucial for mitigating the impacts of intermittent and fluctuating residential rooftop PV generation on utility grids. Previous studies have often overlooked the benefits of different stakeholders involved in the optimal scheduling process. To address these gaps, this study proposed a comprehensive framework for the many-objective optimal dispatch of residential PV-battery-flexible load systems, considering the interests of users, grid operators, and governments. Specifically, a day-ahead optimal dispatch model with six objective functions relevant to the three stakeholders’ benefits was developed. The effectiveness of the framework was validated through case studies, which demonstrated a significant improvement in system performance compared to the maximizing self-consumption strategy. The proposed framework can provide valuable guidance for the optimal scheduling of residential PV-battery-flexible load systems in practice.

Abstract

Renewable energy will be globally implemented through energy carriers in the low-carbon energy system. This paper first analyzes the chemical properties of methanol, methane, and ammonia, and then constructs detailed models of solid oxide fuel cells and homogeneous compression charge ignition engines. The lifecycle technical efficiency of methane, ammonia, and a combination of methane and ammonia is 30.8%, 30.7%, and 28.5%, respectively. The specific electric energy costs for methane, ammonia, and methanol are 1.64 CNY/kWh, 2.47 CNY/kWh, and 3.04 CNY/kWh, respectively. Currently, E-methane is more favorable compared to both ammonia and methanol, both in terms of efficiency and carbon emissions. In the future, the fuel costs for methanol, methane, and ammonia could be reduced to at least 1.02 CNY/kg, 2.47 CNY/kg, and 0.9 CNY/kg respectively. The electricity cost based on a hybrid SOFC-ICE system will be comparable to coal power generation.

Abstract

Demand response is an effective method for achieving energy flexibility. By utilizing the thermal properties of the building envelope, energy shifting can be achieved by preheating. In this study, a simulation-based method was used to quantify the energy flexibility of residential buildings in Kitakyushu City, Japan. A rule-based control method was used to control the heating systems, resulting in different heat energy reduction ratio after preheating at different start time during the day. Then, k-means clustering analysis was performed on the energy reduction of different buildings during January. The optimal number of clusters was determined to be two based on the Calinski-Harabasz and Davies-Bouldin indices. The results of the clustering analysis showed that the energy reduction was significantly affected by the thermal insulation properties of the building envelope compared to the thermal mass. In addition, weather conditions also had a significant impact on energy reduction, with higher solar radiation and lower humidity contributing to a significant enhancement of energy reduction effects.

Abstract

Geochemical characterization of seafloor sediment porewater as a rapid response to methane seepage and its biogeochemical processes to document methane seepage characteristics. In this study, methane seepage and geochemical indicators in porewater were investigated for five stations in “Haima” Cold Seep in the South China Sea. The results showed that the methane release in different stations was quite different, with the methane diffusion flux ranged from 0.3 to 168.3 μmol/(m²·a). However, there were some similarities in the geochemical indicators for every station. Correlation analysis indicated that methane seepage was positively correlated with depth and PO43-, and negatively correlated with TS, K+, Na+, Mg2+, Mn2+, Fe3+, and NO2-. The PCA cluster analysis results were similar to the classification of habitat characteristics observed during sampling. Therefore, it may be possible to provide an indication of methane leakage through habitat characteristics in future studies.

Abstract

China proposed a target to reach maximum CO2 emissions before 2030 and attain carbon neutrality by 2060 in 2020. As a system highly relying on fossil fuel, and at the same time, with the rapid growth of renewable energy, the power system in China has to face the challenges both from carbon emission reduction and stability of electric grid. It can be predicted that the future coal fired power plants has to frequently work in partial load conditions to contribute flexibility to the grid, and moreover, to recover its carbon emission through adopting CO2 capture technology. However, the partial load operation of power generation system will undoubtedly influence the CO2 capture unit, which may lead to the variation of CO2 capture ratio (CCR). Through investigating the interaction between power generation system and CO2 capture unit under partial load conditions, the aim of this paper is to evaluate the potential of CO2 emission reduction of a variable load power plant. The model of a coal-fired power plants with post-combustion CO2 capture had been setup via EBSILON and Aspen. The performance of MEA CO2 separation unit had been simulated. By quantitatively analyzing the performance of a typical coal fired power plants in partial load operation and further combining the CO2 capture unit with the power generation system, the operating characteristics of the CO2 capture unit in partial load operation are explored. The results indicate several factors including the pressure of extracted steam for reboiler, the CO2 concentration in the flue gas and the flow rate of flue gas, will impose the possible impact on CO2 capture unit. The extraction steam temperature and pressure of the power generation unit also decrease as the power load decreases. When the load depth falls below 50%, the pressure drops to a certain level that could not meet the requirements for the operation of the CO2 capture unit, the capture unit will cease operation. The opening of the steam extraction valves remains unchanged, and the operating parameters of the capture unit are not adjusted under power load variation conditions. As the power load decreases, the mass flow of flue gas decreases from 1148.72 kg/s at 100% load to 521.63 kg/s at 30% load, while the CO2 mass fraction in the flue gas decreases from 17.8% to 13.9%. These changes will undoubtedly affect the CO2 load in solvent. The three factors together reduced the CCR for treated gas from 90% at 100% load to 50.42% at 30% load. The practical CCR for a power generation unit in a period of real operation conditions is lower than design CCR for treated gas, which is 90% at 100% load. Conclusively, the factors influencing capture ratio on the power generation side, such as flue gas and steam parameters, are important factors in CCR changing.

Abstract

CO2 splitting driven by solar energy is a clean and promising approach for addressing the issue of CO2 emission and approaching the dual-carbon target. Here, a high-efficient solar CO2 electrolysis system containing photovoltaic (PV) cell, photon-enhanced thermionic emission cell (PETE), and solid oxide electrolysis cell (SOEC) is proposed. CO2 serves as cool fluid to decrease the temperature of PV cells for the enhancement of PV efficiency, and the heated CO2 by PV cells and PETE is fed into SOEC at a high temperature to decrease the Gibbs free energy utilized in electrolysis. The combination of PV cell and PETE can enlarge the temperature range for full solar spectrum utilization. Compared to H2O splitting in SOEC, CO2 splitting can convert more thermal energy with relatively low energy level into high-energy-level chemical energy. The system can reach the energy efficiency, exergy efficiency, and solar-to-fuel efficiency of 73.5%, 48.0%, and 33.3%, respectively. This research sheds light on high-efficient solar CO2 splitting system design with full solar spectrum utilization in a wide temperature range.

Abstract

Wind power is one of the fastest-growing renewable energy sources in the world because of its many advantages. Wind power also presents fundamental challenges in some regions of the world, which are being addressed through research and development projects. This study aims to design and analyze propeller wind turbine for low-speed regions especially in those frontier, outermost and least developed regions often referred to as 3T (terdepan, terluar, tertinggal) in Indonesia. An open-source numerical software tool for aerodynamic and structural analysis of wind turbines is used to design airfoils. Four different airfoil types are selected based on literature study which produced four turbine blades: S826 (Antasena 1.1), NACA 4412 (Antasena 1.2), NACA 4415 (Antasena 1.3), and SG6043 (Antasena 1.4). Through simulations and analysis, it is found that Antasena 1.4 (SG6043) is the most suitable airfoil for low wind speed conditions (3-5 m/s). The power output predictions for various wind speed classes indicate that Antasena 1.4 has the highest potential power output, meeting and even surpassing the target values in certain months. Numerical simulation of Antasena 1.4 shows best power coefficient (Cp) 0.5747. The results demonstrate the promising applicability of Antasena 1.4 as an airfoil profile for turbines operating under low wind speed conditions.