• Energy Research

This study explored underground biomethanation as a means to achieve carbon neutrality and promote carbon circular utilization by methanating CO2 and hydrogen-rich industrial waste gas in depleted natural gas reservoirs (MECHIG). This approach not only aids the development of carbon capture, utilization, and storage (CCUS) technologies, but also effectively processes industrial waste gas, thereby reducing pollutant emissions. In order to verify the feasibility of the MECHIG concept, this study builds upon the analysis of the MECHIG process overview and employs the net present value (NPV) analysis method to investigate its economic viability. Additionally, the study conducts a sensitivity analysis on six factors, namely methanation efficiency, facility site investment, hydrogen content in waste gas, natural gas prices, operation and maintenance (O&M) investment, and CO2 capture and injection prices. The results indicate the following: (1) Under the baseline scenario, the NPV of the MECHIG concept is approximately CNY 5,035,100, which suggests that the concept may be economically viable. (2) The fluctuation in natural gas prices has the most significant impact on NPV, followed by facility site investment and methanation efficiency. In contrast, the variations in hydrogen content in waste gas, O&M investment, and CO2 capture and injection prices have relatively smaller effects on NPV. (3) To ensure the economic feasibility of the concept, the acceptable fluctuation ranges for the factors of methanation efficiency, facility site investment, hydrogen content in waste gas, natural gas prices, O&M investment, and CO2 capture and injection prices are −16.78%, 5.44%, −32.14%, −4.70%, 14.86%, and 18.56%, respectively.

The global energy transition is a widespread phenomenon that requires international exchange of experiences and mutual learning. Germany’s success in its first phase of energy transition can be attributed to its adoption of smart energy technology and implementation of electricity futures and spot marketization, which enabled the achievement of multiple energy spatial–temporal complementarities and overall grid balance through energy conversion and reconversion technologies. While China can draw from Germany’s experience to inform its own energy transition efforts, its 11-fold higher annual electricity consumption requires a distinct approach. We recommend a clean energy system based on smart sector coupling (ENSYSCO) as a suitable pathway for achieving sustainable energy in China, given that renewable energy is expected to guarantee 85% of China’s energy production by 2060, requiring significant future electricity storage capacity. Nonetheless, renewable energy storage remains a significant challenge. We propose four large-scale underground energy storage methods based on ENSYSCO to address this challenge, while considering China’s national conditions. These proposals have culminated in pilot projects for large-scale underground energy storage in China, which we believe is a necessary choice for achieving carbon neutrality in China and enabling efficient and safe grid integration of renewable energy within the framework of ENSYSCO.

In a global context where sustainable growth is imperative, understanding carbon emissions in significant regions is essential. Henan Province, being a vital region in China for population, agriculture, industry, and energy consumption, plays a crucial role in this understanding. This study, rooted in the need to identify strategies that not only meet China’s broader carbon neutrality objectives but also offer insights regarding global sustainability models, utilizes the STIRPAT model combined with scenario analysis. The aim was to forecast carbon emission trajectories from 2020 to 2060 across the key industries—electricity, steel, cement, transportation, coal, and chemical—that are responsible for over 80% of the total emissions in Henan. The findings suggest a varied carbon peak timeline: the steel and cement industries might achieve their peak before 2025, and the transportation, coal, and chemical sectors might achieve theirs around 2030, whereas that of the power industry could be delayed until 2033. Significantly, by 2060—a landmark year for Chinese carbon neutrality ambitions—only the electricity sector in Henan shows potential for zero emissions under an extreme scenario. This study’s results underscore the importance of region-specific strategies for achieving global carbon neutrality and offer a blueprint for other populous, industrialized regions worldwide.

CO2 sequestration in deep saline formations has been proved to be an effective method for reducing greenhouse emissions into the atmosphere. However, pure sequestration of CO2 will add to the costs incurred by both industries and governments. A win–win method of CO2 injection and hot brine (water) extraction can become attractive to the investors, as it will not only increase the storage capacity of the injected CO2, but also offset the costs by selling and using the produced hot water for industrial, agricultural or household purposes. For instance, water from very hot geothermal reservoirs (T ≥ 150 °C) can be used for electricity generation in power plants and water from low-medium temperature reservoirs, the most predominant in natural systems, are more popular for direct use, e.g., in heating systems, household hot water, baths, aquaculture, etc. In this paper, low-medium geothermal reservoirs widely distributed in China, especially those in the Ordos Basin, were selected for the numerical case studies using TOUGH2MP with the ECO2N module for the simulations. Generally, simulation parameters were taken from the Ordos Basin, where the first full-integration CO2 sequestration project had been operated since 2010. The simulations in the base case study lasted 35 years, based on the lifespan of a normal geothermal project. Shallow re-injection systems were also considered to investigate the influence of thermal breakthrough, pressure perturbation, etc. Results show that injection of cold CO2 causes sharp decrease in temperature in the reservoir region near the injection well, which is enlarged with continuous injection. The region near the production well is dominated by different fluid phases during the CO2 driven process, including a single water phase, a two-phase fluid (water and CO2) and a phase of almost pure CO2. Results also show that the CO2 breakthrough lags far behind the pressure response in the geothermal production system. Before breakthrough, the injected CO2 pressurizes the reservoir, improving the overall performance of the geothermal reservoir. Furthermore, the heat extraction efficiency of CO2-based system is obviously higher than H2O-based system.

AbstractLarge‐scale underground hydrogen storage (UHS) provides a promising method for increasing the role of hydrogen in the process of carbon neutrality and energy transition. Of all the existing storage deposits, salt caverns are recognized as ideal sites for pure hydrogen storage. Evaluation and optimization of site selection for hydrogen storage facilities in salt caverns have become significant issues. In this article, the software CiteSpace is used to analyze and filter hot topics in published research. Based on a detailed classification and analysis, a “four‐factor” model for the site selection of salt cavern hydrogen storage is proposed, encompassing the dynamic demands of hydrogen energy, geological, hydrological, and ground factors of salt mines. Subsequently, 20 basic indicators for comprehensive suitability grading of the target site were screened using the analytic hierarchy process and expert survey methods were adopted, which provided a preliminary site selection system for salt cavern hydrogen storage. Ultimately, the developed system was applied for the evaluation of salt cavern hydrogen storage sites in the salt mines of Pingdingshan City, Henan Province, thereby confirming its rationality and effectiveness. This research provides a feasible method and theoretical basis for the site selection of UHS in salt caverns in China.

In the context of carbon neutrality, the phase-out of coal from the energy structure has resulted in numerous old coal mines that possess abundant underground space resources suitable for underground pumped hydroelectric energy storage (UPHES). Site selection and estimation of potential are critical to the planning and implementation of UPHES in old coal mines. This paper introduces a two-step site selection concept, including a screening assessment followed by a comprehensive assessment, to determine suitable locations for UPHES. The screening indicators in the screening assessment comprise geological features, mine water disasters, and minimum installed capacity, while the analytic hierarchy process (AHP) is applied in the comprehensive assessment. Additionally, coal mines in Henan Province are preliminarily screened through the screening assessment and the potential for UPHES is thoroughly investigated. The estimated volume of the drifts and shafts in old coal mines is approximately 1.35 × 107 m3, while in producing coal mines, it is around 2.96 × 107 m3. Furthermore, the corresponding annual potential for UPHES is 1468.9 GWh and 3226.3 GWh, respectively. By consuming surplus wind and solar power, UPHES is able to reduce 4.68 × 105 tonnes of carbon dioxide (CO2) emissions. The study provides preliminary guidance for policy-makers in developing UPHES in old coal mines.

Carbon Capture, Utilization, and Storage (CCUS) technology is essential for mitigating climate change as it captures CO2 and either utilizes it for chemical applications or stores it in geological formations [...]

This study employs DMSP-OLS and NPP-VIIS nighttime light remote sensing data to develop a carbon emission regression model based on energy consumption, analyzing the spatiotemporal evolution of carbon emissions in 57 cities within the Yellow River Basin from 2012 to 2021. The analysis uses a quantile regression model to identify factors affecting carbon emissions, aiming to enhance the basin’s emission mechanism and foster low-carbon development. Key findings include: 1) Carbon emissions from energy consumption increased in this period, with a decreasing growth rate. 2) Emissions were concentrated along the Yellow River and its tributaries, forming high-density carbon emission centers. 3) The Yellow River Basin has mainly formed a “high-high” agglomeration area centered on resource-based cities such as Shanxi and Inner Mongolia’s coal, and a “low-low” agglomeration area centered on Gansu and Ningxia. The standard deviation ellipse of carbon emissions in the Yellow River Basin generally extends from east to west, and its center of gravity tends to move northward during the study period. 4) Technological innovation, economic development, and population agglomeration suppressed emissions, with digital economy and foreign investment increasing them in certain cities. Urbanization correlated positively with emissions, but adjusting a single industrial structure showed insignificant impact.