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In this paper an approach for analysing the potential for implementation of different technology pathways for the European pulp and paper industry (PPI) is presented. The approach is based on detailed technical research and aggregates the knowledge from previous studies to incorporate the whole European PPI. Thus, the potential for different technology pathways can be estimated on a European level whilst still considering important characteristics of individual mills. The usefulness of the approach was exemplified by applying it to a case study of the potential for introduction of carbon capture and storage (CCS) within the European PPI. The results from the case study show that for the European PPI, CCS has an up-hill road in order to be a viable, large scale alternative for reduction of CO2 emissions. If CCS is to be introduced in large scale within the European PPI, large biomass-based point sources of CO2 emissions need to be included when planning for CCS infrastructure and also the infrastructure needs to be built out for clusters emitting <20 MtCO2/yr. [ABSTRACT FROM AUTHOR]

This study focuses on waste paper gasification in carbon dioxide atmosphere with molten alkali carbonates including potassium, sodium, lithium carbonate or their intermixtures as catalyst. The molten catalysts is capable of facilitating a desired reaction (C+CO2→2CO), which was hardly feasible even at a high temperature of 973K if catalyst absences. It is that the catalysts which provides a gas–liquid interface between carbon and carbon dioxide, replacing original gas–solid, then allows the two reactants contact each other effectively. Further experimental results demonstrate that the intermixture carbonates exhibit strongly enhancement on catalytic activity than any carbonate salts in the form of single. The reaction rate depends on temperature evaluating manners, a rapid heating processes is favorable to the aimed reaction. With respect to recycling of carbon dioxide, the process provides a conversion in 30%. [Copyright &y& Elsevier]

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]

The gas adsorption/desorption-induced coal deformation effect is a significant factor governing the evolution of coalbed permeability. Current theoretical investigations typically coal bulk and fracture deformation induced by gas are equivalent, neglecting the matrix-fracture interactions. Based on internal adsorption stress, this paper proposes Internal Differential Strain Coefficient (IDSC) to quantitatively characterize the relationship between coal bulk and fracture strain under equilibrium conditions. Coupling this coefficient constructs a binary gas permeability evolution model considering matrix-fracture interactions. Through numerical simulations of CO 2 -ECBM processes under various internal differential strain circumstances using this model, dynamic evolution patterns of diverse parameters are obtained. The research findings indicate that along the direction of CO 2 injection, matrix-fracture interactions exhibit a complex trend of initially increasing, then decreasing and then increasing, and the increase in internal differential strain levels results in a downward trend in permeability peak. Additionally, the evolutionary characteristics of CH 4 recovery and cumulative CO 2 storage rising with increasing internal differential strain levels were obtained on time scales using a fixed-point monitoring methodology. Inspired by the aforementioned laws, this paper discusses the macroscopic influence of burial depth on the effects of internal differential strain, providing new theoretical support for CO 2 sequestration injection methods in deep coal seams. • A coefficient capable of quantitatively analyzing the internal differential strain in the CO 2 -ECBM process is proposed. • Based on IDSC, a model describing the evolution of coal seam permeability in CO 2 -ECBM process is established. • Analyzed the influence of internal differential strain on the permeability of coal beds in the CO 2 -ECBM process. • Analyzed the influence of internal differential strain characteristics on CO 2 injection capacity. [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]

Abstract In this paper, a method for improving the efficiency of the cascade mechanical compression–ejector cooling cycle is described. The considered cooling cycle is the combination of the electrically driven carbon dioxide (CO 2) subcritical mechanical compression cooling cycle as a bottoming cycle, and the heat driven ejector cooling cycle as a topping cycle. This cooling cycle is proposed to use superheated CO 2 vapor to preheat the working fluid supplied to the vapor generator, thus improving the whole system's efficiency. This paper provides thermodynamic analysis results for the cascade cooling system in a wide range of evaporating temperatures. Refrigerants R245ca, R600, and R601b were investigated as the working fluids for the ejector cooling cycle, and the results show that the proposed cooling cycle is the most effective at low evaporating temperatures. Highlights • A cascade CO 2 mechanical compression–ejector cooling cycle is studied. • Refrigerants R245ca, R600 and R601b are used for the ejector cooling cycle. • Performance improvement regarding COP, COP THERM and exergy efficiency is evaluated. • The refrigerant preheating has considerable influences on the cascade cycle performance. • The proposed cascade cooling cycle is compared with conventional cycle. [ABSTRACT FROM AUTHOR]

Human activities have led to increase in carbon dioxide emissions, and carbon tax is one of the main policy tools for reducing global emissions. This paper constructs nine scenarios considering different carbon tax rates and the different taxable industries to analyze the impact of Carbon Tax System (CTS) on energy, environment and the economy. We find that the negative impact of CTS on GDP is acceptable, and the maximum scenario will not exceed 0.5%. If carbon taxes are levied on energy-intensive enterprises, the impact on carbon emissions is also relatively small, even if the carbon tax rate is relatively high. Higher carbon tax rate will result in higher CO 2 emission reduction and higher marginal CO 2 emission reduction of CTS. The carbon tax rate follows the "law of increasing marginal emission reduction". We also argue that the focus of taxation should be on energy enterprises. It is only in this way that the efficiency of the energy market can be fully implemented to conserve energy and reduce emissions. This paper suggests that China should adopt CTS that simultaneously imposes a higher tax on energy companies and energy-intensive enterprises. This will maximize emissions reductions and have only a small impact on GDP. [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]

CO 2 injection into unconventional gas reservoir has been recognized as a promising approach to enhance unconventional gas recovery (CO 2 -EUGR) and sequester CO 2 geologically. The CO 2 -EUGR is a complex multi-physics coupling process. To accurately assess the effectiveness of different injection strategies, this paper firstly presents a non-isothermal compositional two-phase flow model coupling with geomechanics, in which a multicomponent adsorption kinetics is incorporated to separate free phase and adsorbed phase. A hybrid numerical approach combining EbFVM and GFEM is used for numerical solutions. The performance of different injection strategies for CO 2 -EUGR is evaluated. The results indicate that CO 2 injection is able to improve CH 4 recovery significantly, over 90 % of injected CO 2 can be adsorbed in reservoirs, The performance of CO 2 -EUGR is permeability dependent, the displacement effect occurs earlier when reservoir permeability is higher; Increase in temperature of injected gas and mixed CO 2 /N 2 injection can further improve CH 4 recovery, especially for low permeability gas reservoirs; Mixed gas injection also enables displacement effect to occur earlier; Cyclic injection can hardly lead to increase in CH 4 production, especially when reservoir permeability is higher, while it can cause an increase in amount of adsorbed CO 2 during injection period. Based on these findings, a geothermal-assisted CO 2 -EUGR method is proposed. • An efficient non-isothermal compositional model coupling with geomechanics is developed for CO 2 -EUGR. • The performance of different CO 2 injection strategies is evaluated quantitatively. • The occurring of displacement effect and performance of CO 2 -EUGR depend on reservoir permeability. • Increasing temperature of injected gas and mixed CO 2 /N 2 injection can further improve CH 4 recovery. [ABSTRACT FROM AUTHOR]

Subsurface reservoirs play an important role in decarbonizing the energy sector, be it through geothermal energy production or carbon capture and storage. In recent years, there has been an increasing interest in CO 2 -Plume Geothermal systems, which combine carbon sequestration with geothermal, using CO 2 instead of water as a subsurface heat and pressure energy carrier. Since CO 2 -Plume Geothermal systems are added to full-scale CO 2 Capture and Sequestration operations, all of the initially injected CO 2 is ultimately stored. CO 2 -Plume Geothermal, therefore constitutes of both CO 2 Capture Utilization as well as Storage. This paper assesses the huge technical potential of this technology, identifying a potentially highly relevant market for CO 2 equipment manufacturers and discusses the current research demand, based on the current state of the art of CO 2 equipment. Both temperature and pressure levels are significantly lower than CO 2 turbine designs investigated and proposed so far for other applications, such as waste heat recovery. For a depth of 5 km, a typical one-stage radial turbine design might have a rotational speed of 23'000 rpm to 42'000 rpm and an impeller diameter between 96 mm to 155 mm. Together with technology-specific requirements, due to produced fluid impurities, it becomes evident that significant further development efforts are still necessary. • CO 2 -Plume Geothermal (CPG) systems can combine CCS and geothermal energy. • In-depth evaluation of the turbine and compressor operational characteristics. • Assessment of the research demand for CPG-specific surface equipment. [ABSTRACT FROM AUTHOR]

Low-temperature seawater is far away from CO 2 critical temperature, which has significant impacts on the performance of CO 2 closed cycle in the marine environment. The temperature adaptability of CO 2 closed cycle to the marine environment and its performance remain open issues. In this paper, we compare performance advantages of transcritical/supercritical CO 2 cycle based on thermodynamic and dynamic models. Compared with supercritical CO 2 Brayton cycle, transcritical gas-phase CO 2 Brayton cycle exhibits higher thermal efficiency and specific power at low cycle maximum pressure, and its reduced heat load and thermal inertia of regenerator facilitate cycle rapid response. However, transcritical liquid-phase CO 2 Brayton cycle and transcritical CO 2 Rankine cycle demonstrate higher thermal efficiency and specific power at high cycle maximum pressure. Lower compressor inlet temperature causes CO 2 pseudo-critical point to migrate into regenerator, and the intersection point of c p curves of CO 2 on both sides is located within regenerator. This can lead to pinch point and non-physical design within regenerator that inhibits cycle response. It can be avoided by adjusting cycle matching parameters so that the temperature corresponding to intersection point is lower than regenerator hot side outlet temperature. This study provides insights into performance advantages of transcritical CO 2 cycles in marine environments. [Display omitted] • Compare the performance of trans/supercritical CO 2 cycles in marine environments. • Performance analysis based on the cycle thermodynamic and dynamic simulation model. • Transcritical CO 2 cycle performance is more advantageous in marine environments. • Migration of pseudo-critical point to regenerator can inhibit the cycle response. • Avoid pseudo-critical point migration by adjusting cycle matching parameters. [ABSTRACT FROM AUTHOR]

Plastics have become an integral part of our daily lives owing to their exceptional physicochemical properties, such as durability, low density, and cost-effectiveness, compared to traditional materials. However, the escalating production of plastics has resulted in a proportional increase in waste generation. This paper proposes environmentally benign valorization/disposal methods for plastic waste, with a particular focus on adopting a pyrolysis process that utilizes CO 2 as a strategic reaction medium. As a case study, polyoxymethylene (POM), a widely used engineering plastic, was valorized through CO 2 -mediated pyrolysis. This study experimentally demonstrates the mechanistic effectiveness of CO 2 in expediting the reaction kinetics of the thermal decomposition, specifically dehydrogenation and deoxygenation, of volatile matter derived from POM. The results revealed that employing CO 2 as a reactant in the two-stage pyrolysis at 500 °C produced 30.47 mmol more syngas than under inert conditions. In conclusion, the strategic utilization of a two-stage pyrolysis process at 500 °C with CO 2 as the reactant has emerged as an effective approach to the valorization of POM. This study contributes to developing sustainable methods for managing plastic waste by addressing environmental concerns and the need for efficient material recovery. [Display omitted] • Conversion of polyoxymethylene (POM) to syngas was tested using CO 2 a reactive gas. • CO 2 reacted with the volatile matters derived from pyrolysis POM to boost syngas. • Functionality of CO 2 was promoted when exerting additional heating element (500 °C). • CO 2 -assisted pyrolysis offers a strategic means for efficient material recovery. [ABSTRACT FROM AUTHOR]

The significant increase in renewable energy generation will lead to the unstable operation of the power system. Compressed carbon dioxide energy storage (CCES) is a promising energy storage technology, which can smooth the output of renewable energy. However, one of the disadvantages of conventional CCES is the need to store compression heat, which leads to the complex structure of heat storage units. In this paper, an isothermal CCES system integrated with solar thermal storage is proposed and modeled. The parameter variations of work fluids in the pressure vessels with time and the thermodynamic properties and economics of the system are analyzed. The results show that the round-trip efficiency is 107.14 %, the energy storage density is 5.174 MJ/m3, and the levelized cost of electricity is 0.142 $/kWh. The component with the highest exergy destruction is the regenerator, followed by the LP units. The combination of liquid spray technology can decrease the highest temperature of carbon dioxide in the pressure vessel from 358.80 K to 309.39 K and increase the isothermal compression efficiency from 78.72 % to 92.26 %. Increasing the liquid spray flow rate and decreasing the hydraulic pump flow rate can both make the actual compression process closer to the isothermal process. • The heat transfer properties of liquid piston and liquid spray are studied. • The thermodynamic and economic performance of the system is analyzed. • The variation of system performance at different operation states is analyzed. • The roundtrip efficiency and energy storage density are 107.14 % and 5.174 MJ/m3. [ABSTRACT FROM AUTHOR]

To advance renewable energy development, it is crucial to increase the operational flexibility of power plants to consume renewable energy. Supercritical compressed carbon dioxide energy storage (S C-CCES) system is considered as a promising solution. This paper develops thermodynamic and off-design models for system components to formulate the system off-design model. The round-trip efficiency (RTE), system power efficiency (SPE), total exergy efficiency (TEE), and energy storage density (ESD) are defined to analyze the off-design performance of the system under two operation strategies. The results indicate that the system achieves the RTE of 32.44 %, SPE of 67.58 %, TEE of 43.26 %, and ESD of 1.73 kWh/m3 under the rated operating condition. The input power, output power, heat transfer rate, and mass flow rate during the charging and discharging process are proportional to the load level for both operation strategies. The RTE and TEE of the system vary inversely with the charging load level and directly with the discharging load level. The ESD is independent of the charging load level and increases with the discharging load level. The speed regulation-throttling regulation (SR-TR) operation strategy demonstrates superior system performance and a broader range of operating conditions. • An off-design model of supercritical compressed CO 2 energy storge system is proposed. • The component parameters are designed based on the design parameters of the system. • Off-design system performances are studied under different charging and discharging load levels. • Two operational strategies are proposed to examine the performance and determine the optimal strategy. • The SR-TR strategy resulted in 3.29 % and 0.09 kwh/m3 improvement in SPE and ESD at 80%–80 % operating condition. [ABSTRACT FROM AUTHOR]

Gas turbine (GT) can play a significant role in the new power system with high renewable energy penetration. This paper develops the supercritical CO 2 power cycle (CPC) to improve its efficiency through waste heat recovery (WHR), and the integrated system is designed for large ship propulsion. An ideal WHR cycle perspective is drawn to guide the evolution of the CPC configuration, and the techno-economic model of these CPCs are established. Then, a system and component two-level evaluation framework with corresponding criteria is formed: through thermodynamic and multi-objective optimization and comparison, the layout with optimal comprehensive performance was identified; the conventional and advanced exergy analyses, as well as their comparison, were carried out to obtain the components' information. Results show that both the recuperative and the split-flow can substantially enhance the CPC's WHR capability, while the over-expansion has minimal effect. By integrating the CPC, the GT's efficiency can be improved by approximately 33 %. Multi-objective optimization reveals that the partial heating layout outperforms the recuperated layout in terms of overall performance. Specifically, despite having a similar levelized cost of electricity of 4.73 cents/kWh, its total heat recovery efficiency (THRE , 17.6 %) exceeds that of the latter by a margin of 14.2 %. The heater has the most considerable exergy destruction in the optimal layout, accounting for 19.3 %. With the current technology, the THRE can be increased to 25.5 % through component refinement. Conversely, the advanced exergy analysis indicates that the heater has a minimum improvement potential of 1.52 %. The turbine has the highest endogenous avoidable exergy destruction ratio of 31.8 %, which deserves focused development and investment. [Display omitted] • The GT-CPC is proposed for a large liquified gas carrier electric propulsion system. • An ideal cycle perspective is drawn to guide the evolution of the cycle layout. • A two-level evaluation framework with corresponding performance criteria is formed. • The partial heating cycle has superior overall performance to the recuperated cycle. • The turbine has the highest endogenous avoidable exergy destruction ratio. [ABSTRACT FROM AUTHOR]

This paper presents an arrangement of super hydrophobic lateral venting micro channels, which is fabricated around the anode gas diffusion electrode of micro direct methanol fuel cell (μDMFC). Work in this paper is aimed to prove the validity of the lateral venting design. Three types of DMFCs with lateral venting design is tested by contrast with control groups respectively. With the lateral venting configuration, CO 2 gas can release directly from the anode diffusion layer of membrane electrode assembly (MEA), which prevents CO 2 gas accumulating on the anode and decreasing the anode mass transportation. Results show that the novel structure can prevent the formation of CO 2 gas barrier to a great extent, which not only avoids the anode concentration loss but also improves the discharging stability, providing a new way of design and optimization on the DMFC. [ABSTRACT FROM AUTHOR]

Aircraft performance degradation causes higher fuel consumption. This results in higher emission and it is an important factor when the complete life cycle is analyzed. Current research in the field doesn’t quantify degradation emissions in the life cycle of an aircraft. The objective of this paper is to suggest a methodology for determining carbon dioxide emission during the life cycle of turbofan aircraft. Special attention is given to degradation and the importance of proper and timely maintenance as a way of controlling these emissions. Degradation plays a significant role in the carbon dioxide emission of turbo fan aircraft. The life cycle was modeled by eight sequences. In this paper a new mathematical interpretation is suggested for following life sequences: use and repair. In the use cycle, emission caused by aerodynamic structure degradation and engine degradation is calculated separately. The proposed methodology was implemented on four and tested on eight turbofan aircraft. Results show that more than 99% of carbon dioxide emission occurs in the use sequence. The emission caused by degradation (aerodynamic structure and engine) makes up between 3.6% and 6.4% of total carbon dioxide emission. A novel methodology for reducing emission caused by degradation is proposed by the authors. [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]

The decoupling analysis is a useful method to study the relationship between economic growth (GDP) and energy consumption or environment issue. However, no paper has paid attention to why does decoupling indicator changes over time? Based on the Log-Mean Divisia Index (LMDI), this paper provides a new way to study the changes of C-G (CO 2 emission-GDP) decoupling indicator in China. The changes of C-G decoupling indicator are decomposed into C-EF (CO 2 emission-Fossil energy consumption) decoupling indicator effect, EF-E (Fossil energy consumption-Total energy consumption) decoupling indicator effect, E-G (Total energy consumption-GDP) decoupling indicator effect. The main results as follows: (1) In China, energy-related CO 2 emission increased to 8858.47 Mt in 2013. (2) During the study period, coal accounted for more than 67% of total primary energy consumption. (3) The curve of energy intensity has the same trend as the CO 2 emission coefficient. (4) Over the study period, only three decoupling statuses occurred in the C-G decoupling. (5) During the study period, the E-G decoupling effect played an important role in the change of C-G decoupling indicator. However, the C-EF decoupling effect played a minor role in the change of C-G decoupling indicator over 1996–2013. [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]

Effects of three diluents on cycle-by-cycle variations of a spark ignition engine fueled with methanol were studied in this paper. Peak in-cylinder pressure, maximum rate of pressure rise and indicated mean effective pressure were investigated experimentally to assess these influences. The results showed that when addition ratios of carbon dioxide and nitrogen increased, the fluctuations of peak pressure and maximum rate of pressure rise increased first and then decrease, the dispersion of indicated mean effective pressure was enlarged, the mean values of these parameters all decreased gradually while carbon dioxide dropped faster. These three parameters did not present clear changes in fluctuation for Argon, only that their mean values showed a slight difference. Linearities between peak pressure and maximum rate of pressure rise corresponding to their crank angles were observed at low addition ratio of carbon dioxide and nitrogen, while it would disappear if the mixture was further diluted. Cycle-by-cycle variations of tested engine would be deteriorated by carbon dioxide and nitrogen, while it kept unchanged and indicated mean effective pressure was increased for argon dilution. The diluent tolerance of this methanol engine is higher than that of gasoline engine. • Cycle-by-cycle variations of a spark ignition methanol engine were examined. • Carbon dioxide dilution deteriorates methanol engine's cyclic variations mostly. • Argon dilution enhances Indicated mean effective pressure of methanol engine. • Cyclic variations of methanol engine changed slightly with argon dilution. • Methanol engine's diluent tolerance is higher than gasoline direct injection engine. [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]