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In this paper, a novel combined heating and power (CHP) system is proposed to realize full-scale utilization of geothermal energy and efficient multi-generation, which not only performs preferable overall performance than previous homogeneous system, but also offers an effective energy cascade utilization approach for self-condensing transcritical CO 2 (TCO 2) Rankine cycle. Based on the established mathematical models, the performance comparison is conducted for proving the superiority of the novel CHP system. Then, an overall performance analysis is implemented to reveal the combined effects for six key parameters on system thermodynamic, exergoeconomic and exergoenvironmental performances. Furthermore, multi-objective optimization considering system overall performance is conducted. The results show that for the novel CHP system, the largest relative improvement rate of system exergy efficiency (η exg) and declining rate of total unit product exergy cost (c P , total ) versus the previous CHP system are 15.03 % and 18.89 %, respectively. The final optimization results of η exg , c P , total and total unit product exergy environmental impact (b P , total ) are determined as 51.10 %, 14.12 $/GJ and 9.00 mPts/GJ, respectively. This paper fulfills an elaborate performance analysis and optimization for the novel CHP system, which fills the research gap of efficient and promising CHP system based on self-condensing TCO 2 Rankine cycle. • A novel self-condensing transcritical CO 2 cycle based cogeneration system is proposed. • Full-scale utilization of geothermal energy is realized by the novel system. • Overall performance superiority of the novel system is proved by comparison study. • Combined effects of six key parameters on system overall performance are revealed. • Multi-objective optimization of system overall performance is performed. [ABSTRACT FROM AUTHOR]

By purchasing emission reduction equipment or reducing production scale, it is possible to effectively decrease CO 2. Therefore, understanding the marginal abatement cost (MAC) associated with these methods is crucial for making decisions. However, previous studies using the directional distance function (DDF) approach often mis-specified production functions and neglected data noise. They also assumed decision-making units (DMUs) to be on the production frontier and used proportional changes in inputs and outputs as abatement paths. This paper addresses these limitations by developing the convex quantile non-radial directional distance function (CQR-NDDF) method, which estimates the MAC of CO 2 and determines optimal abatement paths for DMUs without assuming a specific production function, employing linear programming techniques. Applying this method to 30 provinces in mainland China from 2011 to 2019, the study finds that China's CO 2 MAC increased from 182 to 247 yuan/ton. The lowest-cost abatement path varies by province and time. The club convergence and ordered probit model are employed to conclude that the second industry and urbanization increase the MAC of CO 2 , while factors such as foreign direct investment, openness level, and human capital decrease the MAC. Moreover, the CQR-NDDF method yields significantly lower MAC estimates than the NDDF method. In conclusion, this paper provides new insights into China's CO 2 MAC, emphasizing the importance of considering inefficiency and data noise in MAC estimation. We anticipate that utilizing CO 2 MAC as a benchmark for carbon trading market prices could lead to an increase in prices within China's carbon trading market. • A novel method for estimating CO 2 MAC has been developed. • Ignoring inefficiency will result in an overestimation of CO 2 MAC. • Three different emission reduction pathways are considered in the estimation. • The heterogeneity of the lowest cost abatement pathways has been identified. [ABSTRACT FROM AUTHOR]

This work describes the one-dimensional, thermo-hydraulic model of the sCO 2 cycle Sofia developed to investigate optimal control methods and the behaviour of the cycle during operation. This dynamic model includes all devices such as turbomachinery, heat exchangers, valves, and piping including heat loss, in line with concept of the 1 MWe sCO 2 cycle, to be realised in the site of a fossil power plant in the Czech Republic. The model assembly and calculations were conducted using the commercial Modelica-based library ClaRa + using the simulation environment Dymola and in combination with another Modelica-based library, UserInteraction; the real-time simulations, with some parameter changes during the calculation, are made and described in this paper. Nominal parameters were achieved during the steady-state simulation, except for the lower mass flow of sCO 2. Transient simulation of power turbine start-up from standby state and results are also presented in this paper. The nominal state is achieved with the semi-automatic procedure in approx. 3 h. The simulation results allow more detailed analyses of control methods and a better understanding of real device control and behaviour during start-up, shutdown, or other transients. Careful manipulation of turbine valves in coordination with the pressuriser operation was identified as crucial for optimal control of the system. Also, the initial amount of CO 2 in the pressuriser affects its behaviour during transients. • Models of the PCHE and BPHE heat exchangers were prepared, and turbomachines models determined by CFD simulations were used. • Control system of the electric heater, which is the largest facility in the Sofia cycle, was designed. • Real-time simulations were performed using ClaRa+ and UserInteraction Dymola libraries. • Careful trubine valves manipulation and corresponding pressuriser control were identified as key control interventions. • Initial amount of CO 2 in the pressuriser affects its behaviour during transients. [ABSTRACT FROM AUTHOR]

A dynamic model of a compressed gas energy storage system is constructed in this paper to discover the system's non-equilibrium nature. Meanwhile, the dynamic characteristics of the CO 2 binary mixture (i.e., CO 2 /propane, CO 2 /propylene, CO 2 /R161, CO 2 /R32, and CO 2 /DME) based system are first studied through energy and exergy analyses. Performance indicators are considered, including round trip efficiency, exergy efficiency, energy density, discharge time, and average power output. The effects of tank volume and ambient temperature on the system performance are analyzed. According to the results, although the round trip efficiency of the CO 2 mixture system is reduced by about 0.68%–11.97% compared to pure CO 2 , the compressor performance and the system pressure stability are improved. When the tank volume increases from 10,000 m3 to 15,000 m3, the system round trip efficiency increases by 0.16%–0.33%. A further improvement of round trip efficiency for the CO 2 mixture is found compared to pure CO 2 at higher ambient temperature. This paper demonstrates the dynamic operational characteristics of the compressed gas energy storage system when using different CO 2 binary mixtures, providing a reference for optimizing related systems. Potential scenarios and applications for the CO 2 binary mixture are discussed for future research. • A dynamic model of Compressed CO 2 binary mixture Energy Storage is constructed. • The effects of different CO 2 binary mixtures on dynamic performance are compared. • The effects of storage pressure and ambient temperature on performance are analyzed. • The RTE of CO 2 mixture system is reduced by 0.68%–11.97% compared to pure CO 2. • A 1 K increase in ambient temperature results in a 5% increase in storage density. [ABSTRACT FROM AUTHOR]

The pursuit of high amplitude and low onset temperature difference is one important topic in thermoacoustic engines. In this paper, a novel standing-wave thermoacoustic engine is constructed working with supercritical CO 2 , whose core components are integrated as a printed circuit heat exchanger (PCHE). Our experimental results confirm that at any location on the resonator, the pressure obeys a cosine law with time, and the whole pressure field exhibits a seesaw-like spatiotemporal behavior. Under a fixed charging mass, the amplitude of pressure oscillation increases with temperature difference, obeying a power law relation. The maximum amplitude achieved in this work is 0.419 MPa at a temperature difference of 151.0 ° C and a mean pressure of 9.621 MPa. Besides, the frequency with an average of 7.6 Hz shows weak variations. The onset temperature difference decreases as the critical pressure is approached, and the minimum value achieved is 14.8 ° C. Moreover, the cooling effect of oscillating CO 2 to the high-temperature portion of the stack is revealed, causing the strongly nonlinear temperature profile along the stack. This paper manifests that supercritical CO 2 and PCHE are highly prospective to be employed in thermoacoustic devices. [Display omitted] • A standing-wave thermoacoustic engine based on PCHE is constructed and tested. • CO 2 at supercritical pressures is employed as the working fluid. • The dimensionless pressure amplitude obeys a power law relation with temperature difference. • Low frequency (averagely 7.6 Hz) and high amplitude (maximum 0.419 MPa) are achieved. • The minimum onset temperature difference is 14.8 ° C. [ABSTRACT FROM AUTHOR]

CO 2 capture, utilization, and storage (CCUS) are critical technical measures to effectively mitigate the global climate change problem. However, most of the existing research has focused on the capture end and lacks in-depth analysis of subsequent processes such as compression, leading to limitations in the improvement of system economics. Therefore, a novel CCS system for a 300 MW coal-fired power plant was proposed in this paper with two strategies: (1) a CCS system integrating CO 2 refrigeration cycle (CFPP-CCS-CRC); and (2) a CCS co-generation plant integrating CO 2 refrigeration cycle (CHP-CCS-CRC). The proposed systems' performance was comparatively evaluated by applying energy, exergy, and economic (3E) analyses. The results demonstrated that at different CO 2 capture percentages (13.1 %∼72.9 %), the CHP-CCS-CRC system has improved energy utilization efficiency by 1.2 %∼5.6 % and exergy efficiency by 7.7 %∼25.8 %, compared to the conventional CCUS system (CFPP-CCS). In particular, at a percentage of 13.1 %, the combined energy consumption of the CHP-CCS-CRC system was 0.39 GJ/tCO 2 , a 79 % reduction compared to 1.87 GJ/tCO 2 of the CFPP-CCS system, which resulted in a static payback period of less than 2 years. In general, the newly proposed system features more adequate energy utilization, lower operating costs, and higher economic efficiency. [Display omitted] • A novel CCUS system coupled with CO 2 refrigeration were proposed. • The performance of the proposed systems is comparatively evaluated by 3E analysis. • The energy consumption of the proposed CCUS systems is reduced by 29.24 %–79 %. • The exergy efficiency of the proposed CCUS systems is reduced by 7.7 %–25.8 %. • The static payback period for the proposed systems is reduced to less than 2 years. [ABSTRACT FROM AUTHOR]

As main by-product in iron and steel industry, high value-added utilization of blast furnace slag had received extensive attention. In this paper, a novelty technology was proposed for using blast furnace slag as raw material to obtain excellent CO 2 adsorbent-layered double oxides. The characteristics of layered double hydroxides and layered double oxides were investigated in detailed. Most notably, the laminate structure of layered double hydroxides collapsed and the pore structure, particle size distribution and functional groups of the sample had been greatly changed. The layered double oxides were occupied by phases of CaO, Ca 12 Al 14 O 32 Cl 2 and MgO. The transformation mechanism of the layered double oxides preparation was obtained. In addition, CO 2 concentration and temperature influencing on CO 2 adsorption of layered double oxides were studied and established a suitable kinetic model. The optimal kinetic mechanism model of CO 2 adsorption by layered double oxides was PSO. The activation energy and pre-exponential factors were 56.88 kJ‧mol−1 and 12.26 min−1, respectively. Ultimately, CO 2 adsorption capacity comparison and preliminary economic evaluation were conducted to assess the industrial feasibility of this technology. This work achieved the goals between CO 2 reduction and high value-added utilization of solid waste in iron and steel industry. [Display omitted] • Blast furnace slag used for high value-added CO 2 capture technology. • Successful transformation of slag-derived hydroxides into effective CO 2 adsorbent. • Detailed investigation of changes in structure and characteristics of the adsorbent. • Achieved CO 2 reduction and waste utilization in the iron and steel industry. [ABSTRACT FROM AUTHOR]

Integrating renewable energies into district heating systems has a large potential to reduce CO 2 -emissions in the heating sector. As district heating systems offer the possibility of incorporating renewable energies into the heat supply, new systems have to be built and the existing networks must be maintained. This study investigates ways to optimize existing district heating systems in order to ensure economic sustainability in the long-term. Previous case studies have elaborated on a variety of optimization measures. However, to date, these measures have neither been collected nor consistently assessed for a wider application range. Therefore, in the study presented here a system for assessing the ecological and economic benefits of optimization measures was developed and applied. The assessment method utilized showed that optimization of district heating consumer substations and adding of a central buffer storage tank has a high optimization potential in comparison to intermittent operation strategy, which has a significantly lower optimization potential. From this information and the transferability data, a district heating operator can determine which optimization measure should be prioritized, which is shown at the end of the paper on an example case. • A method was developed to assess benefits of optimizing district heating systems. • A survey was conducted to assess the ecological and economic value. • Optimization measures for DH systems were compared using the new method. • A guideline is provided to offer operators a suggested approach to take. [ABSTRACT FROM AUTHOR]

CO 2 is assumed to be one of the most potential refrigerant alternatives for electric vehicles for its excellent properties. However, the charge determination of CO 2 in current studies remain controversial. In this study, a transcritical CO 2 air-conditioning heat pump system was established and experimentally tested to analyze the optimal charge amount. Based on two conflicting methods of charge determining proposed by the preceding research, this paper substantiated the existing controversy and subsequently proposed a more comprehensive method. The effects of different refrigerant charge on the system characteristics were investigated. The influence of the compressor speed on the optimal refrigerant charge and system characteristics was also analyzed. It was found that the optimal charge plateau occurred from refrigerant of 500 g–580 g at the compressor speed of 3000 r·min−1. However, the optimal charge declined with the increment of compressor speed from 3000 r·min−1 to 4500 r·min−1. Among three models, Hughmark's model was proved to be the most appropriate for the theoretical calculation of optimal charge within an error of 6.09%. Further study illustrates that refrigerant mass in high-pressure pipe and intermediate heat exchanger/accumulator (IHX/A) accounted for the main proportion about 52.6%–55.14%. • A novel principle to determine the optimal charge plateau is verified. • The optimal charge of the CO 2 ACHP system is tested under different compressor speeds. • Hughmark's model is the most accurate within the error of 6.09%. • High-pressure pipe accounts for the largest proportion of refrigerant mass. [ABSTRACT FROM AUTHOR]

This paper investigates the inhibitory effect of CO 2 on oxygen adsorption during the low-temperature oxidation of coal. Taking the example of Tingnan coal, the physical adsorption barriers of CO 2 during coal oxidation at different temperatures were analyzed in terms of competitive adsorption curves, adsorption capacity, adsorption selectivity and diffusion coefficients using a combination of indoor experiments and molecular simulations. It is proposed that the competitive adsorption advantage of CO 2 is significantly greater than that of O 2 , and it is negatively correlated with temperature. Additionally, the variations of aliphatic gas-phase products are evident during the pre-oxidation temperature stages. When the pre-oxidation temperature exceeds 70 °C, the amounts of CH 4 and C 2 H 4 released increase with the pre-oxidation temperature, and the inhibitory effect of injected CO 2 deteriorates. The simulation results validate the experimental conclusions and are in line with the actual situation, providing auxiliary optimization and guidance for coal mine fire prevention work. • The competitive adsorption law of O 2 and CO 2 under the dual effect of temperature and pressure was obtained. • CO 2 exhibits an inhibitory effect on the system activity in the coal pore model. • There were large differences in the inerting inhibition effects after CO 2 injection at different temperature stages. • The main reason for the difference in the effect of CO 2 oxygen barrier adsorption with increasing temperature was obtained. [ABSTRACT FROM AUTHOR]

This paper examines the long-term effects and related short-term movements of energy security (ENS), economic policy uncertainty (EPU), and government ecological expenditure (GEE) on China's carbon dioxide (CO 2) emissions by applying the quantile autoregressive distributed lag approach. The empirical findings demonstrate that ENS and EPU have prominent negative and positive impacts, respectively, on CO 2 emissions in the long term for the majority of quantiles, while their short-term influences are less obvious. In addition, the effect of GEE is short-term and concentrated in high quantiles. The following are the article's main contributions. This study builds special energy security indicators based on the actual situation in China, providing a basis for better understanding the interaction mechanism between ENS and CO 2. Considering that China is the largest oil importer and greenhouse gas emitter, this study explores for the first time the linkages between ENS and CO 2. Both short- and long-term impacts are observed, and long-run effects are dominant in the linkages among variables, suggesting that the level of CO 2 emissions is mainly driven by long-term shocks. In addition, to clarify the nexus between ENS and CO 2 , time- and quantile-varying analyses are used, which take into account not only varied CO 2 emission levels but also distinct time periods for events. The findings emphasize the importance of market participants to form a better understanding of how ENS, EPU, and GEE affect CO 2 under different emission levels. Some detailed policies, including optimizing the energy consumption structure, making prudent economic policy adjustments, and strengthening ecological protection expenditures, are provided to curb pollution. • Energy security and carbon neutralization are main targets for China. • Energy security negatively affects carbon dioxide in the long-term. • Time-varying and quantile-varying features are captured for Energy security. • The quantile autoregressive distributed lag model is utilized in this paper. [ABSTRACT FROM AUTHOR]

Injecting CO 2 into gas reservoirs can achieve CO 2 Storage with enhanced gas recovery (CSEGR). The development of liquid-CO 2 injection has the characteristics of high injectability, high mobility ratio, and low diffusion coefficient. Therefore, this paper established a wellbore-reservoir-thermo-hydro-mechanical-diffusion (WR-THMD) multi-physics fully coupled model of the wellbore-reservoir system, and verified the model based on field and experimental data. The mass transfer, heat transfer, and gas physical property changes in the wellbore and reservoir during the injection of liquid-CO 2 were studied. The impact of different engineering parameters on improving CH 4 recovery and CO 2 storage is also discussed. The results show that the impact of the wellbore on the physical properties and phase state of CO 2 is crucial. The injection of liquid-CO 2 is beneficial to the storage of CO 2 and the displacement of CH 4. Lowering the injection temperature will slightly improve the injectability of liquid-CO 2 and increase the CO 2 storage rate by 5.13%. Using a high injection mass flow rate will effectively raise CH 4 recovery rate by 15.60%, but it will weaken the injectability of CO 2 and cause CO 2 to break through in the production well prematurely. The research results provide important suggestions and theoretical support for the application of liquid-CO 2 injection on CSEGR. • 3D fully coupled wellbore-reservoir-thermo-hydro-mechanical-chemical (WR-THMD) model is established. • CO 2 physical properties and status in the wellbore are comprehensively analyzed. • Mass transfer, heat transfer and fluid physical properties in the reservoir are comprehensively analyzed. • Effects of injection parameters on CH 4 recovery, CO 2 injection and storage were studied. [ABSTRACT FROM AUTHOR]

With huge reserves and wide distribution, tight oil and gas resources are the focus and hotspot of unconventional oil and gas research in recent years. In this paper, firstly, the multi-scale model of CO 2 fracturing gas is established by considering the phase evolution characteristics of CO 2. Secondly, considering the hydrophilicity of the tight reservoir, a microscale seepage model of CO 2 under the adsorption condition of fracturing fluid is proposed. Again, considering the shrinkage effect of dense reservoir matrix, a dynamic coupling model of gas-liquid-solid under CO 2 fracturing conditions is established. The results show that: (a) When the volume of the adsorbed layer of CO 2 fracturing fluid accounts for 10% of the pore volume and the CO 2 concentration is 20%, the fluid transport in the tight reservoir shows significant separation characteristics. (b) More CO 2 enters the crude oil after considering the diffusion effect of CO 2 body. The influence of CO 2 diffusion mechanism on oil recovery should not be neglected. (c) Enhancement of elastic energy is one of the main mechanisms by which CO 2 improves oil driving efficiency in tight reservoirs. • A multi-scale model of CO 2 fracturing gas was established considering the phase evolution. • A CO 2 microscale percolation model under the adsorption conditions of fracturing fluid was proposed. • A gas-liquid-solid dynamic coupling model was established under CO 2 fracturing conditions. [ABSTRACT FROM AUTHOR]

In oil and gas fields, there are numerous abandoned wells that are distributed in a network pattern. The reuse of abandoned wells for CO 2 storage can reduce storage costs and pollution. Previous studies have been limited to single-well researches, neglecting the effect of CO 2 injection on different abandoned wells. This paper develops a numerical model with dual-well coupling the thermal-flow-multiphase field, simulating mechanisms of CO 2 storage and migration under the dual-well and comparing effects of injection parameters and heterogeneous reservoir parameters on CO 2 storage effect. The results indicate that the dual-well can alleviate the increase in reservoir pressure. The injection rate and injection time should be large to ensure desirable storage efficiency and migration range. Compared to the minimum well spacing, the maximum well spacing increases the storage capacity by 2.41 × 109 kg and extends the migration distance by approximately 800 m. The migration distance of the upper-injection and down-production mode is about 300 m less than that of the other two modes. Heterogeneity in reservoirs benefits storage and impedes migration. By selecting proper well positions, negative impacts of heterogeneity on CO 2 migration can be reduced. This work assists in providing supports for the CO 2 storage with abandoned wells. • Conducting CO 2 storage research using multiple abandoned wells. • Identify the influence of various parameters on CO 2 storage effect of the system. • Identify the impact of reservoir heterogeneity on storage effect through building a heterogeneous reservoir model. [ABSTRACT FROM AUTHOR]

Both environmental regulation (ER) and different pollutants emission are characterized by differentiation, but the nonlinear relationship between different intensities of ER and different levels of pollutants emission has not yet been elaborated. This paper examines the nonlinear effects of ER at different intensities on PM 2.5 and CO 2 at different states with the help of cutting-edge Quantile on Quantile Approach (QQA), comprehensively reveals the inner law of ER to promote pollutants synergistic reduction. This study found that, both PM 2.5 and CO 2 show obvious regional differences but are not polarized. ER can effectively help reduce PM 2.5 and CO 2 in average, and this reduction effect is more obvious for central-western cities. The effects of different intensities of ER on different states of PM 2.5 and CO 2 have obvious nonlinear spillover characteristics. The impact of ER on PM 2.5 shows wave-like changes. Increasing ER intensity has a stronger inhibitory effect on PM 2.5 of high scale, but when PM 2.5 is relatively low, moderate ER is needed to match it, and excessive intensity of ER will be detrimental to reduce PM 2.5. The negative impact of ER on CO 2 fluctuates relatively stable. ER at high quantiles have more obvious reduction effect on CO 2 of high levels, but excessive intensity of ER is not conducive to reduce CO 2. Achieve the synergistic reduction of PM 2.5 and CO 2 should not only consider the differences in ER between regions, but also to combine the scale differences of pollution and carbon emission. Our study suggests that the improvement of synergistic emission reduction system needs to consider the strength of ER and the level of pollutants emission according to local conditions, which will help to realize green development more efficiently. • Assessing the impacts of different intensities of ER on different levels of PM 2.5 and CO 2. • The use of QQ approach can obtain richer nonlinear information. • The effects of ER on PM 2.5 and CO 2 are asymmetric and heterogeneous. • Increasing ER intensity has a stronger inhibitory effect on PM 2.5 of high scale. • Nonlinear changes in the negative impact of ER on CO2 fluctuates relatively stable. [ABSTRACT FROM AUTHOR]

Carbon Capture, Utilization, and Storage (CCUS) is an indispensable technology to achieve carbon neutrality in China, but confined by technology and economy, the offshore CCUS in China is still in the planning stage and has not yet reached the desired scale. Offshore source-sink matching and cost analysis of CCUS is the premise and basis of offshore CCUS deployment. Thus, based on the CO 2 storage potential of offshore sedimentary basins in China, this paper conducts the offshore source-sink matching and cost analysis of CCUS in China under different constraints. The result showed that: ⅰ) the CO 2 storage capacity of China's offshore sedimentary basins is estimated to be 767.3 Gt, which is enough to meet approximately 200 years of coal power CO 2 emissions in China. ⅱ) the CO 2 storage potential could reach 721.9 Mt/a by source-sink matching under different constraints. ⅲ) early opportunities for offshore CCUS would be in the Bohai Bay and Pearl River Mouth Basin, considering the compensation effect of CO 2 -EOR. ⅳ) combined with the CCUS cost and emission reduction in China under different time nodes, it is inferred that deploying offshore CCUS in China between 2030 and 2040 commercially will be advantageous. • The CO 2 storage potential in China's offshore sedimentary basin was evaluated. • The cost of offshore CCUS was analyzed under different technology combinations. • Bohai Bay and Pearl River Mouth Basin would be early opportunities for offshore CCUS. • 2030–2040 would be the favorable time to deploy the large-scale offshore CCUS. [ABSTRACT FROM AUTHOR]

Agricultural greenhouses are still heavily dependent on fossil fuel-based products despite the abundant residual biomass at their disposal. This paper presents two novel decentralized systems that can convert biomass simultaneously into synthetic natural gas (SNG), electricity, useful heat, and a CO 2 -rich stream. To do so, the electricity and H 2 /O 2 production features of reversible solid oxide cells (RSOCs) are exploited. A steam dual fluidized bed (DFB) gasifier is used in the first proposed system, while the second one adopts a simpler oxygen/steam-blown downdraft gasification approach. Thermodynamic simulations using Aspen Plus software reveal that the total polygeneration process efficiency could reach 86.6%, with a CO 2 generation capacity exceeding 275g per kilogram of biomass input. If not used inside the greenhouse atmosphere to enhance crop growth, this high-purity CO 2 stream could be sequestered/liquefied to render the process carbon negative. The flexibility of the polygeneration systems is investigated through parametric analysis, where maximum SNG efficiencies that are on par with large-scale plants are obtained. The possibility of storing surplus electricity from intermittent sources as chemical energy in SNG is also highlighted. • Natural gas, electricity, heat, and high-purity CO 2 are produced at 86 % efficiency. • Thermodynamic modelling highlights the flexibility of the small-scale systems. • Maximum synthetic natural gas yield at 63 % is similar to large-scale systems. • Carbon capture and storage at a maximum recovery rate of 52 % is possible. [ABSTRACT FROM AUTHOR]

The transcritical CO 2 heat pump system experiences significant throttling losses in space heating operation due to the higher temperature of returning water. This paper presents an energy, exergy, and exergoeconomic analyses of an air source transcritical CO 2 heat pump integrating a tri-partite gas cooler, which is an effective method to match CO 2 temperature glide with water for simultaneous domestic hot water and space heating (DHW+SH) production. A pinch point-based numerical model is developed to find the optimal discharge pressure. This validated model is then utilized to investigate the impacts of water inlet temperature and ambient temperature. Two configurations are examined: one with only DHW supply and the other with DHW+SH supply. The results indicate that combining SH with DHW enhances COP by 7.5% with a 7.9% reduction in discharge pressure at 10 °C ambient temperature and 10 °C water inlet temperature. At a water temperature of 10 °C, exergy efficiency improves by 4%. The compressor accounts for 54%–60% of the total exergy loss. The DHW+SH system exhibits an average exergy destruction reduction of 7.6%. With each 5 °C rise in ambient temperature, the DHW+SH system's total exergy destruction cost rate decreases on average 7.7% compared to the DHW system. Furthermore, the combined exergy destruction cost rate of GC2 and GC3 in DHW+SH is significantly lower (by 48.2%) than only GC3 in DHW. The exergoeconomic factors of the compressor, gas cooler 2, and gas cooler 3 emphasize the need to decrease their costs to enhance cost-effectiveness. • Transcritical CO 2 heat pump with tri-partite gas cooler is studied for simultaneous domestic hot water and space heating (DHW+SH). • Energy, exergy, and exergoeconomic comparative analyses between only DHW supply and DHW+SH supply are investigated. • Combining SH with DHW improves COP by 7.5% with a 7.9% reduction in discharge pressure compared to DHW. • The exergy destruction of DHW+SH is lower due to the improvement in temperature matching. • DHW+SH system's total exergy destruction cost rate drops on average 7.7% per 5 °C ambient temperature increase compared to DHW. [ABSTRACT FROM AUTHOR]

Addressing environmental concerns and developing efficient systems pose significant challenges for researchers. This paper presents a groundbreaking multi-generation system designed to generate power, heating, cooling, freshwater, and methane. The system comprises a flash-binary power plant, a modified transcritical CO 2 cycle, a proton exchange membrane electrolyzer, and a methanation unit. Integration of the modified transcritical CO 2 cycle with the ejector refrigeration cycle, solar still desalination unit, and heating unit enhances its functionality. The proton exchange membrane electrolyzer supplies hydrogen to the methanation unit. The thermodynamic, economic, and environmental approaches are employed to analyze the system, and three scenarios are considered to assess the optimum state. Accordingly, the exergy efficiency, products' total cost, and exergoenvironmental impact rates are obtained at about 28.30%, 4.153 $/h, and 73.48 mPts/h, respectively. The gas heater unit has the highest exergy destruction rate and cost rate and exergoenvironmental impact rate by 37.6%, 36.4%, and 22.7% portions, respectively. The optimal state provides 33.25% exergy efficiency, 450.9 kW net power, 10.07 kg/h freshwater, and 2.149 kg/h methane. The cooling and heating production rates are attained 28.16 kW and 183.5 kW. The product's cost rate and exergoenvironmental impact rates are estimated at about 4.357 $/h and 76.64 mPts/h. • Novel multi-generation system proposed for power, heating, cooling, freshwater, and methane production. • Integration of flash-binary power plant, modified transcritical CO 2 cycle, electrolyzer, and methanation unit. • Thermodynamic, economic, and environmental analysis conducted for system evaluation. • Optimum state achieves 33.25% exergy efficiency, 450.9 kW net power, and 10.07 kg/h freshwater. [ABSTRACT FROM AUTHOR]

Coal-fired power plants with direct air-cooling condensers (DACC-CFPP) are water-saving, eco-friendly and thus widely installed in regions rich in coal but short of water. As such regions have better geological conditions for CO 2 storage, retrofitting these plants with carbon capture techniques provides a cost-efficient way to reduce carbon emissions and retain dispatchable power. However, the integration of carbon capture poses significant challenges for CFPP and DACC. Therefore, this paper develops a plant-wide model of the 660MWe DACC-CFPP integrated with post-combustion carbon capture (PCC). A connection system, including a steam extraction valve, water spray and condensate returning, is designed, added to the Steam turbine-Feedwater heaters-Condenser system and modeled to reflect dynamic interactions between the DACC-CFPP and PCC. This model is then used to evaluate the reliability, economics and flexibility of the DACC-CFPP-PCC over wide operating conditions. Results show that the integration of PCC causes changes in steam flowrate, pressure and temperature within the turbine, creating reliability risks; brings 5%–10% extra exergy loss to the DACC-CFPP, but not necessarily economic losses; reduces the minimum power load by 44MWe and improve the ramping speed by 3.75MWe/min. This paper provides in-depth insights for decision-makers, designers, and operators to manage the DACC-CFPP-PCC plant. • A plant-wide dynamic model of integrated DACC-CFPP-PCC system is developed. • Reliability, economy and flexibility of the DACC-CFPP-PCC are evaluated. • PCC itself brings 5%–10% additional exergy loss, but not necessarily economic losses. • Power ramping ability of CFPP can be improved if PCC is allowed to operate flexibly. • Turning off fan columns is needed to ensure safe operation in cold weather. [ABSTRACT FROM AUTHOR]

One of the primary objectives of the negative carbon dioxide gas power plant (nCO 2 PP) is to develop an innovative technology confirming the possibility of the use of sewage sludge to produce electricity while having a positive impact on the environment. In this paper, a mathematical model is presented to estimate thermodynamic parameters of the system in relation to the gasification process and changes in such parameters in the bleeds as well as temperature and pressure. The main novelty of this paper is the integration of the gas-steam turbine model with the gasification reactor model in such a way that the effect of the gasification products on the turbine output is established. In turn, parameters from the turbine bleed directly affect the gasification process and cause feedback for the system. Developed code allows determination of parameters such as efficiency of the proposed nCO 2 PP cycle, gas composition from the gasifier, temperature in the gas turbine bleed and other related information. The synergy between the CCS plant and the proposed utilization of sewage sludge (which is considered as a renewable energy source) enables the installation to achieve negative overall emissions of CO 2. • The bleed is extracted from the steam-gas turbine. • The bleed extraction is used as a converting agent for the gasification process. • The gasification model is integrated to the power plant with CO 2 capture model. • Pressure of the gasifying agent on the power plant efficiency is examined. • The bleed extraction as gasifying agent increases the efficiency of the power plant. [ABSTRACT FROM AUTHOR]

This paper presents an optimization method using Non-dominated Sorting Genetic Algorithm (NSGA) Ⅲ to drive support vector machine (SVM). In the NSGA Ⅲ algorithm, brake specific fuel consumption (BSFC), NOx and CO 2 are optimized by changing the engine control parameters including spark angle, VVT-I (intake), VVT-E (exhaust) and exhaust gas recirculation (EGR). The engine GT-Power physical model is used to generate training data for the SVM, and verify the accuracy of the results of NSGA Ⅲ algorithm during the optimization process. The SVM with fast calculation speed is used in the calculation of NSGA Ⅲ fitness evaluation. In addition, enhancing training is utilized to improve the accuracy of the SVM model in this research. When the optimization method is applied to the Atkinson cycle gasoline engine, its high efficiency has been presented. In the three plans obtained by GT-Power physical model with all four parameters optimized, the maximum reduction rates of BSFC, NOx, CO 2 and CO (g/kW·h) reached 7.07%, 35.90%, 6.62% and 5.50% respectively. The SVM model is compared with back-propagation algorithm, and the result proves that SVM is more suitable for such problems. Finally, based on the Pareto optimal solution obtained by the optimization method, it significantly promotes the solution of multi-objective optimization problems. Theoretically, the time cost of the optimization method in this paper can reach 1/23 of that for the optimization algorithm directly driving physical model. • High-accuracy simulation-optimization platform for the engine is developed. • NSGA Ⅲ and SVM are coupled, clarified and applied for the optimization of full engine MAPs. • Maximum reduction rates of BSFC, NOx, and CO (g/kW·h) reach 7.07%, 35.90%, and 5.50%. • Time cost of the optimization method of SVM model is 1/23 of that for the physical model. [ABSTRACT FROM AUTHOR]

Co-gasification of biomass and waste plastic to produce syngas and value-added products is an attractive technology for renewable energy utilization and waste disposal. CO 2 as a gasifying agent has received much attention as it can act as carbon source and oxidant in the reaction. In this paper, the feasibility and characteristics of CO 2 -assisted co-gasification of polyethylene and softwood lignin were explored. Simulation results showed that the lignin macromolecule began to decompose through C–O–C bond breaking and the PE chain gradually decomposed through C–C bond breaking. CO 2 -assisted co-gasification showed a negative synergistic effect on gas yield at the early stage, which delayed the reaction, but showed a positive synergistic effect at the late stage. The reaction between CO 2 and carbon-containing fragments greatly promoted CO production. The hydrogen and hydrocarbon radicals from PE were actively involved in H 2 and hydrocarbon gas production. Compared with O 2 -assisted co-gasification, the CO 2 -assisted and CO 2 /O 2 -assisted co-gasification yielded more CO, hydrocarbon gases and combustible gases and increased the lower heating value of gas product. This work sheds light on the underlying mechanisms of CO 2 -assisted co-gasification of polyethylene and softwood, and would be helpful for the development of this technology. • CO 2 -assisted co-gasification of softwood lignin and polyethylene is explored. • Synergistic effect at the late stage of co-gasification promotes gas production. • Polyethylene provides hydrogen and hydrocarbon radicals during co-gasification. • The addition of CO 2 increases the gas yield and the lower heating value of syngas. [ABSTRACT FROM AUTHOR]

In this paper, THM model and coal molecular model are established to study the gas adsorption and desorption behavior in coal seam at different injection pressures. The results show that, the total energy decreases during the adsorption process and increases in the desorption process. CO 2 has a stronger adsorption capacity which is in a dominant position in the competition adsorption process, while N 2 is in a weak position. The order of the diffusion coefficient is N 2 >CH 4 (CH 4 –N 2) > CH 4 (CH 4 –CO 2) > CO 2. The diffusion coefficient does not necessarily increase with the increase of injection pressure. At the same injection pressure, the relative concentration of CH 4 in the CH 4 –CO 2 system is greater than that in the CH 4 –N 2 system, and injection of CO 2 to promote CH 4 desorption is significantly better than the injection of N 2. With the increase of injection pressure, the average relative concentration of CH 4 /CO 2 /N 2 in the vacuum layer increased. The optimal injection pressure for N 2 injection to promote CH 4 desorption is 2 MPa, and the reasonable injection pressure for CO 2 injection is 1–3 MPa. • THM model and coal molecular model are established to study the gas adsorption and desorption at different injection pressures. • The total energy of the system decreases during the adsorption process and increases in the desorption process. • The diffusion coefficient does not necessarily increase with the increase of gas injection pressure. • Relative concentration of CO 2 in the vacuum layer is lower than N 2 , the adsorption performance of CO 2 is greater than N 2. [ABSTRACT FROM AUTHOR]

Utilizing fly ash (FA) directly to mineralize CO 2 and injecting carbon sequestration products into goafs of coal mines is a novel and promising technology. The impact mechanisms of CO 2 direct mineralization reactions on the characteristics of key groups, physical phases, surface micromorphology, particle size and pore structure of FA are discussed systematically in detail. The focus is imposed on the impacts of different reaction conditions (water-to-solid ratios and pressures of CO 2). Based on the FT-IR, XRD and ESEM-EDS analysis, CO 2 is transformed into carbonates of five vibrational models after mineralization and largely sequestered as calcite by portlandite, which forms a passivated layer on the FA surface. The particle size of carbonated FA particles gets smaller and less uniform, and the variation laws of the particle size at full scale are analyzed by particle size intervals. The variation process of the pore can be divided into the dissolution of FA for pore expansion, the low degree of CO 2 mineralization reaction for further expanding the pore and the high reaction degree for pore shrinkage. This paper provides theoretical bases for improving the direct CO 2 sequestration capacity and research directions for the subsequent application properties of carbon sequestration products. • CO2 is transformed into carbonates of five vibrational models after mineralization. • CO2 is sequestered as calcite by portlandite to form passivated layers on surface. • The full-scale particle size of fly ash is analyzed by proper interval division. • The particle size of carbonated fly ash overall shrinks and gets poorer uniform. • Dissolution and low reaction degree for pore expansion, high degree for shrinkage. [ABSTRACT FROM AUTHOR]

This paper presents a novel process for methanol production from blast furnace gas (BFG) and landfill gas (LFG). The process is evaluated using the energy, exergy, economic, and environmental (4E) analyses. The process consists of a power plant fueled by LFG, carbon dioxide (CO 2) chemisorption using 30% (wt.) solution of monoethanolamine, methanol synthesis and separation, and power and steam plants. Thermodynamic analysis shows that the total energy and exergy efficiencies for the proposed process are 59% and 63.2%, respectively. The carbon efficiency for this method is 42%. Environmental analysis shows that the total CO 2 emission is 2614.85 kg/h. Based on the simulation results, this process produces 18,200 kg/h methanol, which results in a CO 2 emission intensity of 0.144 kg CO 2 /kg MeOH. Economic evaluation determines that the proposed scheme has a capital cost of $100, 315, 128.9 with a payback period of 1.94 years. In addition, methanol production's annual profit is $4,798,088.309, and the minimum selling price of the produced methanol is $0.388/kg. The proposed process is a promising alternative for methanol production from BFG and LFG. It has high energy and exergy efficiencies, low CO 2 emission intensity, and a short payback period. The economic analysis shows that the process is profitable. • A novel methanol production system using blast furnace gas and landfill gas is proposed • The system is analyzed from energy, exergy, economic, and environmental viewpoints • The total energy and exergy efficiencies are obtained to be 59% and 63.2%, respectively • This plant produces 18,200 kg/h methanol, which results in CO 2 emission intensity of 0.144 k g C O 2 / k g M e O H . • The proposed plant has a capital cost of 100315128.9 USD with a payback period of 1.94 years. [ABSTRACT FROM AUTHOR]

The combined use of bio-fuels along with CO 2 capture techniques is the basis for the so-called negative emissions energy systems. In this paper, oxy-fuel combustion of two torrefied biomasses is experimentally investigated in a lab-scale entrained flow reactor. The torrefied biomasses are fired alone, and co-fired with coal (50%). Two oxygen concentrations (21% and 35%) and four steam concentrations are tested: 0% (dry recycle oxy-combustion), 10% (wet recycle oxy-combustion), 25% and 40% (towards the concept of oxy-steam combustion). The tests are designed to get the same mean residence time for all the fuels and conditions. Burnout degrees are significantly increased (up to 9 and 16 percentage points) when the share of torrefied biomass is raised, with a slightly better behavior of the torrefied pine in comparison to the torrefied agro-biomass. C-fuel conversion to CO 2 follows a similar trend to the observed for the burnout degrees. NO formation rates are reduced when oxy-firing torrefied biomass alone in comparison to the blends, with maximum diminutions of 16.9% (torrefied pine) and 8.5% (torrefied agro-biomass). As regards the effect of steam, the best results are found for the 25% H 2 O atmospheres in most of the cases, yielding maximum conversions along with minimum NO levels. • New oxy-combustion results for two torrefied biomasses (up to 35% O 2 and 40% H 2 O). • Replacements of coal by torrefied biomasses improve fuel conversion and reduce NO. • Torrefied pine wood shows better behaviour than torrefied agro-biomass. • Best results are detected in most cases when 25% CO 2 is replaced by H 2 O. • The extent of NO reduction caused by H 2 O significantly depends on the fuel rank. [ABSTRACT FROM AUTHOR]

One promising solution for developing low-emission power technologies is using gaseous fuel combustion in pure oxygen when the exhaust gas mixture is composed of H 2 O and CO 2 , and where CO 2 is separated after steam condensation. The paper presents the results of computational analyses providing to the Spray-Ejector Condenser (SEC) development, which is one of the crucial components of the negative CO 2 gas power plant (nCO 2 PP) cycle development. The proposed design of the ejector-condenser to ensure the high effectivity of vapor condensation and CO 2 compression with preparation to separation, ready for application in gas power cycle, is a novelty of this research. Different computational techniques leading to the development and better understating of ejector operation were applied. The main operating conditions in the characteristic connected with the developed nCO2pp cycle points were investigated to evaluate the impact of the operating conditions on SEC performances. The amount of motive water needed for the cooling purpose is susceptible to the inlet water pressure and temperature and strongly affects the generated pressure of the suction stream. The preliminary results confirm that the SEC's basic design and geometrical dimensions can be applied in the negative CO 2 power plant cycle. Results from CFD modeling give the possibility to investigate the turbulent flow of water/steam/CO 2 mixture together with the condensation process occurring at this same time. It is found that the average droplet diameter and motive water supplying method significantly effects the condensation intensity. The further direction of the presented computational research activities and results is to test various designs of Spray-Ejector Condensers that will enable the evaluation of the direct contact condensation process and develop the final geometrical design. • Spray-Ejector Condenser application in negative CO 2 gas power plant is presented • Performances of Ejector Condenser were calculated using developed model to provide guidelines for a detailed design process • The basic design of the Spray-Ejector Condenser in two variants was developed • CFD model for Direct Contact Condensation was developed, and the impact of water droplet size was studied [ABSTRACT FROM AUTHOR]

Multilateral wells offer promising opportunities for the commercial development of natural gas hydrates. The reservoir strength and stiffness weaken as hydrates decompose during the depressurization production process, potentially leading to formation subsidence, seabed inclination, and other associated geomechanical risks. Thus, understanding the geomechanical issues surrounding the wellbore is crucial for attaining safe and efficient hydrate development. This paper develops a three-dimensional numerical model to simulate the production capacity of hydrate reservoirs through CO2 injection in multilateral wells. The study compares the pressure and temperature response of the reservoir, the characteristics of gas and water production, the variation in hydrate and methane saturation, the productivity, and the geological subsidence patterns during the extraction process. Results indicate that hydrates generated through CO2 injection inhibit methane hydrate decomposition, with delayed injections resulting in higher cumulative yields. CO2 injection can restore reservoir pressure and mitigate formation subsidence. The combined depressurization method, which involves CO2 injection in multilateral wells, can increase hydrate production while preserving formation stability, offering a potential approach for commercial hydrate exploitation. This approach is anticipated to advance the industrialization of gas hydrate extraction and propose a new possibility for CO2 utilization to curb climate change. • Proposing a THMC-coupled model for exploiting hydrate reservoirs through a combination of CO 2 injection and depressurization in multilateral wells • Hydrates generated through CO 2 injection inhibit methane hydrate decomposition, with delayed injections resulting in higher cumulative yields • Increased hydrate production and formation stability can be achieved by depressurization combined with CO 2 injection in multilateral wells [ABSTRACT FROM AUTHOR]

The transportation of carbon dioxide (CO 2) from the capture point to the pooling site through distribution tubes is a crucial link in the carbon capture, utilization, and storage (CCUS) chain. Existing experiments have not been conducted to study the full-scale fracture of the CO 2 -distributed pipelines, the pressure and temperature evolution inside the pipe during crack initiation, fracture extension, and stopping have not been revealed. The rate of fracture extension velocities has not been quantitatively described, and the crack morphology has not been analyzed. This paper conducted the first supercritical CO 2 pipeline full-scale fracture experiment based on a novel experimental setup with a total length of 21.7 m and the inner diameter of 98.3 mm, 16.7 m of which is the main pipeline and 5 m is the sacrificial pipeline. After the sacrificial pipeline rupture, high-frequency transducers were used to measure the change in fluid pressure, and multilayer thermocouples monitored the temperature distribution in four cross-sections within the pipe. Moreover, the decompression wave propagation velocity of supercritical CO 2 and sacrificial pipeline fracture velocity has been obtained and calculated, respectively. The microscopic morphology of the cracks obtained by scanning electron microscopy revealed the failure mechanism of the sacrificial pipeline with prefabricated defects. This work establishes a reliable experience for industry-scale CO 2 pipelines and creates a pipeline design foundation for higher security transport in the future. [ABSTRACT FROM AUTHOR]

Direct air capture (DAC) for indoor CO 2 removal can not only effectively regulate air quality but also improve the capture efficiency to a certain extent, which is a highly feasible win-win solution to decarbonization and human health. This paper proposes a W-shaped packed adsorption bed for indoor direct capture which is optimized and compared with the conventional bed. Firstly, the pressure drop of different adsorption beds is simulated by Darcy-Fochheimer law. The results demonstrate that pressure drop of the W-shaped bed performs better than the conventional adsorption bed. Then temperature swing adsorption process is investigated using an amine functionalization material. It is indicated that energy consumption of the conventional packed bed and the W-shaped packed bed are 236.2 kJ mol−1 and 167.9 kJ mol−1 for CO 2 capture process, respectively. Because of the lower pressure drop of the W-shaped bed, energy consumption of fan could be greatly reduced from 88.7 kJ mol−1 to 15.1 kJ mol−1. Finally, a simple indoor CO 2 concentration condition model coupled with the reactor CFD model is established to verify the performance of CO 2 purification of the reactor, and it shows an excellent regulatory effect on indoor CO 2. The concept can provide some valuable insights for DAC in buildings and have the potential of coupling application with various carbon capture systems. • A structured packed adsorption bed is established for direct air capture. • Pressure drop performance of the W-shaped adsorption bed is studied. • Energy consumption of the W-shaped packed bed could be reduced by 29.3%. • The concept provides valuable insights for direct air capture in buildings. [ABSTRACT FROM AUTHOR]

For a micro-scale (< 10 kW) transcritical CO 2 waste heat recovery power system, the scroll-type expander is a potential candidate. However, the scroll expander suffers from leakage and pressure imbalance issues because of the high-pressure working conditions. The current study designs twelve different sealing cavities based on the reference of labyrinth seals and presents a transient CFD analysis to investigate the flow behaviors. The results show that the sealing cavity has a positive impact on the machinery performance, where the isentropic efficiency improves from 0.907 % to 0.952 % for the single group. Increasing the height and cavity number of single-group sealing can improve the performance while enlarging the cavity spacing shows the opposite. There is no significant difference between the three different shapes of RST, ITST and RTST. However, the improvement in the instantaneous leakage ratio is remarkable, the leakage reduces from 55.3 % to 70.2 %. For the multi-group sealing cavity, the isentropic efficiency slightly improves to 0.982 %, and the pressure imbalance gets partially optimized. The locations of the sealing cavity are important to solve the pressure imbalance between two symmetrical working chambers. The paper suggests designing the upstream sealing cavity for a lower-pressure working process and downstream for a higher-pressure working process, which can ideally achieve the maximum pressure balance. • A micro-scale CO 2 scroll expander model with flank clearance sealing cavity has been constructed. • The isentropic efficiency, leakage ratio, and flow structure of different sealing cavity designs are discussed in detail. • The pressure imbalance is more sensitive than isentropic efficiency with multi-group seal cavities. [ABSTRACT FROM AUTHOR]

The technological development of preparing bio-oil from low-temperature hydrothermal conversion of agricultural and forestry waste has positive significance for alleviating the shortage of oil energy supply and reducing environmental pollution. This paper selects typical oxides (Al 2 O 3 , CeO 2 , MgO, SiO 2 , TiO 2 , and ZnO) as catalysts to set up a low-temperature (220 °C) hydrothermal conversion process of cotton stalk containing pretreatment processes including chopping. For moderate amplification estimation, lab-scale experimental data is used as a benchmark for calculation, and the functional unit for this study is set to be a 1 kg bio-oil product. The results suggest that the cerium dioxide-involved process with the highest bio-oil yield and highest synthetic consumption, and the silica-involved process with the lowest bio-oil yield, caused the highest environmental impact, resulting in greenhouse gas (GHG) emissions of 67.729 kg CO 2 e/kg and 60.001 kg CO 2 e/kg, respectively. It indicates that catalysts need to consider the balance between synthetic consumption and catalytic performance. Magnifying lab-scale data to an industrial scale using scale-up frameworks introduces a low model uncertainty, as the practical value had little effect on the overall evaluation results. However, existing equipment data should be used to reduce the uncertainty of the model itself. The environmental sustainability of bio-oil production by low-temperature hydrothermal liquefaction still needs to be improved, especially by catalyst recovery and bio-oil yield improvement. • A low temperature hydrothermal bio-oil production process based on cotton stalks is developed. • Life cycle environmental and energy consumption models of low-temperature hydrothermal bio-oil are developed. • The environmental impact of six typical nanoscale oxide catalysts in bio-oil production is evaluated. • Catalyst synthesis plays an important role in the overall environmental contribution. • The uncertainty of the process and the practical framework for scaling up are discussed. [ABSTRACT FROM AUTHOR]

As a promising large-scale physical energy storage technology, the main challenge of compressed CO 2 energy storage currently is the issue of low-pressure CO 2 high-density storage. To address that issue, a novel trans -critical compressed CO 2 energy storage system based on 13X zeolite variable temperature adsorption (TSA-TC-CCES) is proposed in this paper. Based on the principle of 13X zeolite adsorption gas storage, combined with the temperature swing adsorption (TSA) method and contact heat exchange scheme, it realizes low-pressure CO 2 high-density storage and real-time internal circulation of heat. Under the design conditions, the adsorption tower volume, system round-trip efficiency, energy storage density, energy efficiency, and energy cycle efficiency are 360.55 m3, 89.19%, 6.29 kW ⋅ h/m3, 70.8%, and 93.53%, respectively. The sensitivity analysis results indicate that energy storage density and round-trip efficiency decrease with increasing adsorption temperature while growing with increasing desorption temperature. The increase in storage pressure positively affects energy storage density, while the increasing storage temperature harms energy storage density. The release pressure at the critical point causes abrupt changes in system performance. • A trans -critical compressed CO 2 energy storage system based on 13X zeolite temperature swing adsorption is proposed. • The contact heat exchange solution enables instant internal circulation of heat, eliminating the need for heat storage media. • This system utilizes temperature fronts to control the reheat temperature and compressor inlet temperature. [ABSTRACT FROM AUTHOR]

CO 2 hydrate is a potential cold thermal energy storage material with latent heat of 500 kJ/kg, however, the dissociation principle of CO 2 hydrate is different from that of solid-liquid phase change materials and therefore, exploring the dissociation mechanism of CO 2 hydrate is of great significance for efficient cold storage. In this paper, a new lattice Boltzmann model is proposed, considering dissociation kinetics, two phase flow, heat transfer, latent heat, surface reaction, thermal buoyancy and variable parameter depended with temperature. The necessity of the temperature consideration related with latent heat and buoyancy is clarified. For the combined effect of depressurization decomposition and thermal decomposition of CO 2 hydrate dissociation, depressurization decomposition diminishes as time increases and initial pressure increases and thermal decomposition enhances as hot wall temperature increases. The fully dissociated Fo is 0.544, 0.514, 0.604, 0.628, showing a first decreasing and then increasing trend while initial pressure increases from 0 to 0.002, 0.004, 0.006 lu. As hot wall temperature increases from 8, 10, 12–14 °C, the fully dissociated Fo is 0.566, 0.544, 0.473 and 0.419 respectively. This new lattice Boltzmann model is of significance in providing guidance for the future cold thermal energy storage system application by using CO 2 hydrate. • A lattice Boltzmann model with thermal buoyancy consideration is developed for the dissociation process of CO 2 hydrate. • The dissociation tendency of CO 2 hydrate is revealed when coupling depressurization and thermal decomposition. • Increasing initial environmental pressure reduces the dissociation rate, but prolongs the fully dissociated time. • Increasing hot wall temperature apparently accelerates the heat transfer and dissociation performance. [ABSTRACT FROM AUTHOR]

Waste heat recovery systems are a promising solution to reduce the overall energy consumption. These systems are capable of producing energy from both high grade and low-grade waste heat without producing any pollution. This paper proposes a novel waste heat recovery system installed on a ship that can produce power and cooling by supercritical/transcritical CO 2 waste heat recovery. For this purpose, supercritical and transcritical carbon dioxide cycles are integrated in a special configuration to recover the highest amount of energy in the ship. To analyze the system, 3E analyses (Energy, Exergy, and Economic) are utilized. Then, to achieve the best performance, the most important and influential parameters have been optimized with the aim of increasing energy, exergy efficiency, and reducing the capital cost. Based on the obtained results, energy, exergy efficiency, and capital cost of the plant reaches 69.6%, 42.3%, and 2.5 M$ respectively in the best condition. Finally, at design condition, the system produces a net power of 9.061 kW and 19.522 kW of cooling. [Display omitted] • New cascade supercritical/transcritical CO2 cycle by using exhaust gas of ship. • Genetic algorithm is employed for multi-objective optimization. • Eight effective variables have been optimized by using 3E criterion. • In optimal condition 9061 kW net power and 19,522 kW cooling produce. [ABSTRACT FROM AUTHOR]

Deep saline formations are considered potential sites for geological carbon storage. To better understand the CO 2 trapping mechanism in saline aquifers, it is necessary to develop robust tools to evaluate CO 2 trapping efficiency. This paper introduces the application of Gaussian process regression (GPR), support vector machine (SVM), and random forest (RF) to predict CO 2 trapping efficiency in saline formations. First, the uncertainty variables, including geologic parameters, petrophysical properties, and other physical characteristics data, were utilized to create a training dataset. In total, 101 reservoir simulations were then performed, and residual trapping, solubility trapping, and cumulative CO 2 injection were analyzed. The predicted results indicated that three machine learning (ML) models that evaluate performance from high to low (GPR, SVM, and RF) can be selected to predict the CO 2 trapping efficiency in deep saline formations. The GPR model had an excellent CO 2 trapping prediction efficiency with the highest correlation factor (R2 = 0.992) and the lowest root mean square error (RMSE = 0.00491). Also, the predictive models obtained good agreement between the simulated field and predicted trapping index. These findings indicate that the GPR ML models can support the numerical simulation as a robust predictive tool for estimating the performance of CO 2 trapping in the subsurface. [Display omitted] • This paper introduces three machine learning methods for predicting carbon storage in saline aquifers. • The prediction performance from high to low is Gaussian Process Regression, Support Vector Machine, and Random forest. • Gaussian Process Regression achieves a good agreement between the predicted results and field-scale simulation. • Blind testing is necessary for preventing overfitting in machine learning models. • Machine learning methods could support the numerical simulation as a fast predictive tool for carbon geological storage. [ABSTRACT FROM AUTHOR]

Based on the extended environmental input-output model and complex network theory, this paper reviews and evaluates the global energy transition based on the principle of shared responsibility, and identifies the key countries affecting the energy transition from the perspective of embodied energy. The results show that although the proportion of clean energy and renewable energy use remains low (only 34.6% and 8.8%), the global energy transition process has progressed rapidly in the past 20 years. From 2000 to 2016, global energy consumption decreased global warming potential (GWP) by 18.7%, acidification potential (AP) decreased by 33.37%, but eutrophication potential (EP) increased by 28.42%. The United States is the largest contributor to the global energy transition, with a total reduction of 1.52 × 10^5 Mt CO 2 -eq, 148.32 Mt SO 2 -eq and 12.4 Mt P O 4 3 − -eq through the energy transition. The energy-consumption emissions from China and other developing countries show an increasing trend (From 2000 to 2016, China increased its emissions by 1.49 × 10^5 Mt CO 2 -eq, 65.09 Mt SO 2 -eq and 76.64 Mt P O 4 3 − -eq). With the slowdown of economic growth and the promotion of energy transition, the growth rate of energy-consumption emissions gradually decreases. Considering embodied energy plays an important role in the scientific evaluation of global energy transition. Under the principle of shared responsibility, ignoring embodied energy is expected to overestimate China's GWP by 4.5%, AP by 3.7%, and EP by 7.4%, and underestimate America's GWP by 10.5%, AP by 7.48%, and EP by 12.5%. We, therefore, focus on the transfer of pollution due to embodied energy and find that China, Russia, India, and South Africa are important agents for the embodied pollution transfer between communities. • Consider the impact of embodied energy on energy transition assessments. • Identifying key countries affecting energy transition from embodied energy. • Calculated the energy transition process of each country. • Measure the energy transition process from multiple perspectives. [ABSTRACT FROM AUTHOR]

Zero tailpipe emission vehicles are seen as a promising route to reduce the carbon footprint of transport sector. Therefore, there is a global movement at customer, industry and administration levels to accelerate their adoption. This paper explores the effect of electric vehicles on the combined emissions reduction from passenger vehicles and power-generation in the island of Tenerife, representative of a small-to-medium isolated system. In order to understand the system response to mass adoption of plug-ins, a high level model of the island's power-generation system have been developed. Modeling results evidence that projections for future plug-ins selling shares together with current estimation of renewable energy penetration do not bring any benefit to reduce both CO 2 and fuel dependence in the short term with respect to measures focused on fleet fuel economy improvements. An additional exercise, exploring the effectiveness under a scenario where Government targets for renewable energy penetration are met, has been carried out. Simulation results show that optimized charging strategies and significantly larger power and storage capacities are required. Under these conditions, an electrification focus scenario provides a slightly larger overall CO 2 abatement, 4% higher than the scenarios focused on fuel efficiency improvement. • Evaluation of mass EVs adoption potential to reduce emissions and fuel dependence. • Current renewable energy projections are insufficient to cover the additional demand. • Measures based on fleet fuel savings provide better benefits in the short term. [ABSTRACT FROM AUTHOR]

In this paper, the effects of diluted gas (N 2 , CO 2) on the pressure and time parameters of hydrogen explosion are tested by experiments. The combustion heat loss and thermodynamic state parameters during combustion were also calculated. The results show that as the diluent gas content increases, the maximum hydrogen explosion pressure decreases, and the rapid hydrogen deflagration time increases. The effect of dilution gas on hydrogen explosion pressure parameters and explosion time parameters in the rich-combustion state is more significant than that in the lean-combustion state. When φ = 1.0 and 20% of N 2 and CO 2 are added, the heat loss per unit area increases approximately 3.23 times and 4.97 times, respectively. The thermal diffusivity did not change as the N 2 content increased under different equivalence ratios but decreased linearly as the CO 2 content increased. When the CO 2 content increases from 5% to 30% at φ = 0.6, α decreases by 14.1%. N 2 has no significant effect on the adiabatic flame temperature under the lean-combustion state. At different equivalence ratios, the adiabatic flame temperature decreases linearly as the CO 2 content increases, and the inhibition effect of CO 2 on the adiabatic flame temperature is significantly higher than that of N 2. • Diluent gas has a significant suppression effect on hydrogen explosion under rich burn conditions. • Dilution gas increases the rapid deflagration time and continuous combustion time. • The effect of CO 2 on thermal diffusivity is more significant. • The heat loss per unit area increases with the increase of the volume fraction of diluted gas. [ABSTRACT FROM AUTHOR]

Crop residue-based bioenergy (CRB) is a green replacement for fossil fuels and an effective way of utilizing crop residues. Understanding CRB's GHG reduction effects is critical for predicting its contributions to carbon neutrality. However, many studies have focused on single products or regional assessments, and results remain uncertain and lacking in systematic examination of the diversity in products, feedstock types and their supply. Therefore, this paper systematically investigates the GHG reduction efficiency, driving factors and abatement costs of principal CRB products using a database of 225 cases composed of 71 carbon trading projects and 154 projects analyzed in scientific publications. The results show that bio-power and/or heat (bio-P&H) is highly efficient (689 kg CO 2 e/t dry CR) and economical (269 $/t CO 2 e) in reducing GHG emissions, but liquid biofuels is not encouraged because of its inefficient performance. Plant size and feedstock collection radius significantly affected GHG reductions of bio-P&H and liquid biofuel. Recommended plant sizes and feedstock types for CRB production were identified from environmental and economic perspectives. Overall, these results clarify the patterns and driving factors of GHG reduction efficiency and abatement costs of various CRB products, providing a framework for optimizing CRB development to combat climate change. [Display omitted] • AsSessing GHG reduction patterns of various crop residue-based bioenergy products. • Comprehensive assessment of the environmental and economic performance. • Identifying the impacts of key factors influencing GHG reduction efficiency. • A meta-analysis based on both scientific publications and project datasets. • Bio-power & Heat shows good GHG reduction efficiency with lower abatement cost. [ABSTRACT FROM AUTHOR]

Industry decarbonization is a key a challenge towards the transition to climate neutrality. Indeed, there is a need to satisfy heat at temperatures higher than 150 °C in relevant industrial sectors by upgrading lower temperature heat flows, such as heat from renewable heat sources, ambient heat or industrial waste heat. High temperature heat pumps (HTHP) can upgrade such heat flows enabling great savings in carbon emissions. New refrigerants are needed to develop HTHPs achieving high performances at high temperatures. This paper proposes the use of a new zeotropic mixture composed of carbon dioxide and acetone as the refrigerant of HTHPs working in the temperature range of 150–220 °C. The new fluid is compared with existing pure refrigerants currently used. The thermodynamic characterization of the CO 2 /acetone mixtures shows temperature glides below 50 K for CO 2 mass fractions up to 10%. The best HTHP performance is shown for the mixture 5% CO 2 /95% acetone in mass fraction. For instance, such a mixture obtains a COP of 5.63 when the target outlet sink temperature is 200 °C and the temperature difference between the outlet heat sink and the inlet heat source is 70 K, showing an improvement of 46% compared to pure acetone. • Industry decarbonization at T > 150 °C is a key a challenge towards climate neutrality. • A new refrigerant for high temperature heat pumps is proposed for 150–220 °C. • The refrigerant is a zeotropic binary mixture composed by carbon dioxide and acetone. • The new fluid is compared with existing refrigerants in a common heat pump layout. • 5%CO2/95% acetone in mass fraction show the best coefficient of performance. [ABSTRACT FROM AUTHOR]

As an important component of biomass, lignin greatly affects the overall conversion efficiency of biomass. In this paper, the microscopic reaction mechanism for CO 2 gasification of softwood lignin was investigated by reactive force field molecular dynamics simulation. The whole process of CO 2 gasification of softwood lignin was divided into two stages, i.e., the pyrolysis of softwood lignin macromolecule, and the reaction of molecular fragments with CO 2. During the pyrolysis stage, the softwood lignin macromolecule first decomposed into fragments containing benzene rings by C–O–C bonds breaking. Then, the benzene rings opened to form carbon chains and broke down. During the gasification stage, CO 2 reacted with lignin fragments to produce CO, while H 2 O molecules provided H for the generation of H 2 and hydrocarbon gases. The proportion of products could be adjusted to meet specific industrial needs via changing the CO 2 /steam ratio. The activation energy of CO 2 /steam gasification was not much different from that of steam gasification, so it would not have a great impact on the occurrence of the reaction. This work provides a theoretical basis for the production of high-quality gasification products. [Display omitted] • CO 2 gasification mechanism of lignin is investigated by ReaxFF MD simulation. • Lignin macromolecules begin to decompose through C–O–C bonds breaking. • The reaction between CO 2 and lignin fragments promotes the generation of CO. • H 2 O promotes the formation of oxygen-containing compounds. [ABSTRACT FROM AUTHOR]

Recently, the incorporation of chemical looping combustion (CLC) and sCO 2 Brayton cycle has been regarded as a promising technology for clean and efficient power generation. The intrinsic characteristics of the CLC reactors (interconnected circulating fluidized bed or fixed bed) allow them to operate at different pressures, leading to different technological directions. Therefore, a pair of "CLC coupled sCO 2 cycle" systems was proposed, namely the atmosphere CLC (A-CLC-sCO 2) and pressurized CLC (P-CLC-sCO 2). The purpose of this paper is to determine which configuration holds more benefits from a combined exergetic and economic perspective. The operational boundary conditions for thermodynamic advantage of P-CLC-sCO 2 over the optimized A-CLC-sCO 2 was firstly investigated. Under respective optimal conditions, the exergy efficiency of P-CLC-sCO 2 (51.09%) was found to be 1.16% higher than that of A-CLC-sCO 2 (49.91%). Besides, the P-CLC-sCO 2 exhibited a lower levelized cost of electricity (79.59 $/MWh) than A-CLC-sCO 2 (81.31 $/MWh) when using a nickel-based oxygen carrier (OC), but the A-CLC-sCO 2 could further reduce LCOE to 78.93 $/MWh by adopting ilmenite-based OC. In addition, the exergy and exergoeconomic analysis of the main components was carried out to find the system improvement strategies. • The sCO 2 cycle was thermally coupled with CLC unit for power generation. • The boundary conditions for P -CLC-sCO 2 to be superior to A-CLC-sCO 2 were studied. • Cost reduction potential for A-CLC-sCO 2 system was revealed. • Comparative exergoeconomic analysis was exerted to find improvement strategies. [ABSTRACT FROM AUTHOR]

Carbon dioxide mineralization using alkaline earth metals rich waste, offers the opportunity of a combined utilization of captured carbon dioxide and valorization of burdensome waste. Most of the studies reported refer to the utilization of steel slags or combustion products of coal and petcoke blends, lignite, municipal waste or air pollution control system residues from conventional boilers. Indirect wet and direct dry carbonation methods under elevated pressure and/or temperature are mostly considered. Within this paper, the results of the experimental study on a dry, direct carbonation method with the use of bituminous coal derived fluidized bed fly ash and performed under ambient conditions are presented. The porous structure parameters of the process product, missing from the existing literature, are analyzed. Therefore, the study differs from the existing literature in terms of the carbonation method used, alkaline earth metals source, scale of the experiment, process conditions employed and product parameters studied. The efficiency of carbon dioxide uptake of 0.008–0.054 kgCO 2 /kg was proven to be comparable with reported for more energy- and cost-intensive methods. The development of porous structure of the process product was also demonstrated with up to several fold increase in the specific surface area and the total pore volume. • Bituminous coal fluidized bed fly ash as a valuable source of alkaline earth metals. • Valorization of bituminous coal fluidized bed fly ash combined with CO 2 utilization. • Beneficial modifications of porous structure of carbonated fluidized bed fly ash. • Efficiency comparable to more complex, energy- and cost-intensive carbonation methods. [ABSTRACT FROM AUTHOR]

This paper presents the results of tests conducted on the methanation reactor installation at the Silesian University of Technology. The reactor is a fixed-bed type and it consists of one tube filled up with the nickel powder and Ru/(Al 2 O 3) used as a catalyst. The results obtained before and after the modernization of the installation are described. The produced gases are analyzed in the VARIO Luxx of MRU air Emission Monitoring Systems gas analyzer. During the tests, the temperature in three zones of the reactor was measured continuously. The gauge pressure at the inlet and outlet of the reactor was also measured. In the performed tests, the effect of different volumetric flows of substrates (CO 2 and H 2 in stoichiometric ratio) and the effect of pressure on the produced gas composition were examined. Additionally, for the measurement series carried out on the laboratory stand, the estimated CO 2 to CH 4 conversion factors were calculated. For the operation of a methanation reactor under atmospheric conditions, the volumetric share of CH 4 in the produced Synthetic Natural Gas was between 71.0% and 74.5% for analyzed cases of Gas Hourly Space Velocity and for a reaction pressure of 5 bar, CH 4 content was between 88.6 and 89.5%. • Lab-scale methanation unit was developed at SUT and used for experimental research. • The influence of methanation process parameters on the gas composition was analyzed. • Content of CH 4 in SNG up to 89.5% for reaction pressure of 5 bar was obtained. [ABSTRACT FROM AUTHOR]

In many cases, inefficient economics and policies hinder renewable sources from being exploited. For the case of geothermal sources; however, using newer combined cycles has been proven to contribute to this issue. In this paper, ‏ a novel coupling of three geothermal cycles for power generation is studied and optimized for 8 parameters simultaneously. The optimization is interpreted through four scenarios to make the analysis a less complex task. C O 2 and C 5 H 12 are fed directly by the geothermal source, using LNG as the heat sink for power generation. The proposed cycle has a net output power of 1211 KW, an exergy destruction rate of 1593 KW, and f k of 16.2% that were later optimized to 271.6 KW, 1532 KW, 16.5%, respectively. The output pressure of the LNG is shown to equal that of city gas common pressure that is sold for 5 $/gallon in the US. The addition of the LNG stream to the system, added to the plant's investment costs; however, it needs to be taken into account that the configuration with the presence of the LNG showed greater energy efficiency and that the electricity generated can be sold or consumed by the system. • Addition of LNG added roughly 16 $/hr to the capital cost. • Addition of LNG stream added 633 KW to the produced power. • The optimization results were assessed in four scenarios to provide a more detailed viewpoint. • Exergy, energy and exergoeconomic analyses were performed. [ABSTRACT FROM AUTHOR]