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Lime mud, a kind of industrial waste that produced in paper mill, was proposed as CO2 sorbent in calcium looping process. The carbonation performance of the lime mud was investigated in a dual‐fixed bed reactor (DFR) and a thermogravimetric analyzer (TGA). The carbonation kinetics of the lime mud in the chemical reaction controlled stage was analyzed by a surface reaction‐controlled kinetic model. The results show that the lime mud presents much poorer carbonation performance during the chemical reaction controlled stage compared with the limestone, mainly due to the high content of chlorine in the lime mud. A prewash treatment process was used to decrease the chlorine content to mitigate the sintering of the lime mud when calcined at high temperature. After prewash treatment, the prewashed lime mud shows much higher CO2 capture capacity during the chemical reaction controlled stage compared with the lime mud. A prolonged carbonation process successfully further enhances the microstructure and improves the carbonation performance of the prewashed lime mud in the chemical reaction controlled stage. The lime mud can be effectively used as CO2 sorbent in calcium looping process after prewash treatment and the following prolonged carbonation treatment. [ABSTRACT FROM AUTHOR]

Supercritical carbon dioxide fracturing is an environmentally friendly anhydrous method. To study the propagation process during supercritical carbon dioxide fracturing, a full three‐dimensional model, coupled rock deformation, fluid transport, heat conduction, dynamic changes of carbon dioxide physical parameters, to investigate the process of fracture propagation during supercritical carbon dioxide fracturing, is established by the three‐dimensional boundary element method, the finite volume method, and finite difference method. And to solve the multiple physics coupling problems, a fully implicit solution and Newton‐Raphson iteration method are used. On the basis of this model established in this paper, the influential factors of supercritical carbon dioxide fracturing are analyzed. The results show that both of the reservoir temperature and the original in situ stress are important for carbon dioxide fracturing; The higher the reservoir temperature and the lower the initial in situ stress is, the longer and wider the fracture will be. The temperature of carbon dioxide at bottom is of no significance to the fracture length, fracture width, and the bottom hole pressure. A growing injection rate will lead to the increase of the fracture length and fracture width. This study would provide a reference for the fluid phase control of supercritical carbon dioxide fracturing technology. [ABSTRACT FROM AUTHOR]

Coal seam with low permeability is widely distributed in China. Injection of flue gas (N2:CO2 = 0.85:0.15) is an effective approach to improve coal seam gas drainage efficiency. This process relates complex responses among ternary gases (CH4, CO2, and N2) competitive sorption on coals, gas diffusion, gas‐water migration by means of two‐phase flow, and coal deformation. In this paper, an improved hydraulic‐mechanical model coupling above interactions is established for flue gas injection enhanced gas drainage. This model is used to simulate flue gas enhanced drainage by finite element method. The sensitivity analyses of key factors are made to recovery a better understanding on the processes controlling flue gas enhanced drainage. Results show that the flue gas enhanced drainage can indeed improve the efficiency of gas extraction and reduce the gas pressure to the required value in a shorter duration. Due to the competitive adsorption and gas sweeping effect of injected flue gas, CH4 is driven toward drainage borehole, and CH4 pressure and content near the injection borehole decrease faster than that near the drainage borehole. The peak CH4 pressure laterally moves from the injection borehole to the drainage borehole. Higher injection pressure, initial permeability, and smaller sorption affinity ratios may lead to greater CH4 production rate at early drainage stage, but smaller CH4 production rate at late stage. The factors controlling the behavior of flue gas enhanced drainage are initial permeability, injection pressure, and sorption affinity ratios in order. This work offers useful framework to investigate important technical challenges associated with enhanced mine gas drainage, as well as unconventional gas development. [ABSTRACT FROM AUTHOR]

The global warming is directly related to the increased greenhouse gas emissions from both natural and anthropogenic origins. There has been a drastic rise in the concentration of CO2 and other greenhouse gases since the industrial revolution primarily due to the intensifying consumption of fossil fuels. With the need to reduce carbon emissions and mitigate global warming certain strategies relating to carbon capturing and sequestration are indispensable. This paper comprehensively describes several physicochemical, biological and geological routes for carbon capture and sequestration. The trend of the increase in greenhouse gases over the years is illustrated along with the global statistics for fossil fuels usage and biofuels production. The physicochemical carbon capturing technologies discussed include absorption, adsorption, membrane separation and cryogenic distillation. The algal and bacterial systems, dedicated energy crops and coalbed methanogenesis have been vividly explained as the biological routes for carbon sequestration. The geological carbon sequestering route centers on biochar application and oceanic carbon storage. A systematic survey has been made on the origin and impact of greenhouse gases along with the potential for sequestration based on some fast-track and long-term sequestration technologies. [ABSTRACT FROM AUTHOR]

The performance of a multistage centrifugal compressor is highly influenced by the ambient conditions, especially during the summer seasons; their capacity shrinks and thus the power requirement for compression will increase. The prime cause of these constraints is the interstage cooling limitations. This study simulates various suction conditions of a multistage compressor on Aspen HYSYS® and suggests its debottlenecking by making the suction temperatures comparable to winter seasons. This is achieved by installing an additional exchanger at the downstream of each interstage cooler, cooling down the gas further by using absorption refrigeration chillers. These chillers are powered up by the waste heat recovered from the exhaust steam coming from the prime mover, steam turbine, of the same compressor. This modification will save a considerable amount of power (663 kW), net savings (Gross Savings – OPEX: 72 289 $/y), and reduce the carbon footprint (954 ton/y) of the overall process. [ABSTRACT FROM AUTHOR]

Global warming caused by the rapid increase in atmospheric CO2 concentration is regarded as one of the most serious problems faced by human being. Electrochemical CO2 reduction (ECR) is one promising strategy that can fix CO2 in a mild and clean manner combined with sustainable energies. However, the ECR performance is highly dependent on the catalysis system because of the difficulty in CO2 activation, low mass transfer, poor product selectivity, and competitive hydrogen evolution reaction (HER). The binding strength of electrocatalysts toward carbon intermediates is the crucial factor for ECR performance. Furthermore, the reaction conditions and the configurations of devices are also of significance for ECR efficiencies. Here, we briefly reviewed the effects of electrocatalyst materials, as well as the reaction conditions, coupled anodic reactions, and devices on the ECR. Moreover, challenges and some perspectives for large‐scale applications are included. [ABSTRACT FROM AUTHOR]

The booming progress of biomass fuels in the enhancement of energy sustainability has been witnessed over the past few decades. Drying or moisture content reduction is a critical pretreatment step for the efficient utilization of wet biomass fuels whose improvement requires this study to focus on the effect of the transportation behavior of biomass fuels inside drying facilities. Experiments were performed under a variety of operating conditions in order to determine the residence time distribution (RTD) and flow characteristics of s‐liked biomass fuels in the process of transportation. A series of experiments are carried out in a rotary drum with different baffle structures, a length of 1850 mm and a diameter of 770 mm. Meanwhile, s‐liked and CO2 expanded biomass particles were taken as standard and tracer materials. RTD and scattering and fallout angles are measured and studied under the conditions of different baffle heights (64‐184 mm), numbers (2‐8), installation slopes (70°‐110°), rectangular bend heights (24.8‐62.5 mm), and bend slopes (90°‐150°). The Taylor model can appropriately estimate the mean residence time (MRT) of particles in a rotating drum with variety of baffle structures, such as baffle height, number, and bend slope. [ABSTRACT FROM AUTHOR]

Storing CO2 in geological formations can reduce the amount of greenhouse gases in the atmosphere. In order to explore the fracture behavior of caprock during CO2 geological storage, three caprock adsorption experiments for supercritical, liquid, and gaseous CO2 were designed. The fracture toughness of mode I, mode II, and mixed‐mode I/II of sandstone before and after the experiment was tested, and X‐ray diffraction (XRD), X‐ray fluorescence (XRF), and scanning electron microscopy (SEM) were used to examine the fracture mechanical characteristics of sandstone. Results showed that the pure mode I fracture toughness of sandstone immersed in supercritical CO2 (ScCO2), liquid CO2, and gaseous CO2 for 30 days decreased by 27.89%, 11.01%, and 17.43%, respectively, compared to nonimmersed sandstone. Pure mode I fracture toughness was more sensitive than mixed‐mode I/II and pure mode II fracture toughness to the various CO2 phase states. Furthermore, the ability of sandstone to resist fracture and failure was significantly reduced by the adsorption of CO2 in different phases. The effects of the different phases were in the following order: ScCO2 > gaseous CO2 > liquid CO2. The decreased ability of sandstone to resist fracture was primarily due to the geophysical and chemical reactions between CO2 and minerals, the alteration of minerals, or the formation of new substances. SEM observations showed that liquid CO2 adsorption caused the sandstone to undergo intergranular fracture, and the adsorption of gaseous CO2 promoted the occurrence of transgranular fractures. In particular, due to the ScCO2 adsorption, various fracture forms such as intergranular fractures, transgranular fractures, and mutual coupling fractures existed simultaneously. Sandstone exhibited numerous fractures and pores, and fracture resistance was weakened. Results of this study have important significance for evaluating the stability and safety of CO2 geological storage. [ABSTRACT FROM AUTHOR]

The fracture system is a vital component of fractured low‐permeability reservoirs. The presence of fractures can improve reservoir flow capacity and injected carbon dioxide (CO2) utilization, thus leading to higher oil recovery. In this study, the effects of the presence of fracture, fracture morphology, soaking time, and CO2 injection volume on CO2 huff and puff were investigated through 11 low‐permeability cores with different properties. The experimental results indicated that the presence of fractures enhanced cyclic oil recovery and increased the effective cycle numbers during CO2 huff and puff in low‐permeability cores. Moreover, compared with low‐permeability cores without fractures, ultimate oil recovery of CO2 huff and puff was risen up by ~11% in fractured cores. Longer soaking time was conducive to enhancing ultimate oil recovery of CO2 huff and puff in fractured low‐permeability cores, but the excessive soaking time had little effect on ultimate oil recovery. Meanwhile, excessive CO2 injection volume did not significantly improve the performance of CO2 huff and puff, but it did reduce the CO2 utilization. Moreover, gravity caused the produced oil to deposit on the bottom surface of the blowout end of the fracture, which made oil recovery of the core with a horizontal fracture slightly higher (~7%) than that of the core with a vertical fracture. In addition, variation in the intersection angle of fractures had little effect on ultimate oil recovery of CO2 huff and puff in fractured low‐permeability cores. It, however, did change the conductivity of the entire core, thus affecting oil recovery during the first two cycles remarkably. [ABSTRACT FROM AUTHOR]

Mankind is constantly pursuing economic growth and social development, and while these bring convenience to people, they involve large amounts of greenhouse gas emissions under the heavy use of energy, which produces quite serious air pollution, which not only affects people's health but also leads to ecological environmental damage. Nowadays, the impact of the environment and the negative impacts of the world's economies while promoting economic growth are the most important issues for economies to achieve balanced development. This study uses the dynamic slack‐based data envelopment analysis (DEA) model to assess the environmental energy efficiency of high‐income economies (including China) and explore the negative impacts on the environment, to obtain a basis for energy‐saving emission reduction methods or configurations by using 48 high‐income economies (including China) from 2010 to 2014. The interperiod (carryover) variable is gross domestic product (GDP). The empirical results show that economies with high energy efficiency have a large consumption of energy and are unable to reduce carbon dioxide emissions. We also find that there exists a difference in the results depending on whether GDP is considered as the carryover variable. European economies are more efficient in energy consumption than others, and Asian economies are the most inefficient. In order to pursue GDP growth, economies need to consider reducing their energy consumption and CO2 emissions and improve their energy usage efficiency, further implementing sustainability. [ABSTRACT FROM AUTHOR]

CO2 reservoirs and high CO2 content gas reservoirs in marine sediments generally have complex pressure system, which usually encounters supercritical CO2(SC‐CO2) invasion into the wellbore during drilling process. The wellbore transient flow and phase transition along the wellbore during the drilling process has not been thoroughly investigated, because the CO2 physical properties and the reservoirs petrophysical properties could affect the transient flow of mixed fluid and phase transition of CO2 along the well. A numerical model is presented in this research to analyze the transient flow in wellbores and to predict phase transition of CO2 during formation SC‐CO2 invasion in the drilling process. The main considerations were the following: multiphase transient flow in wellbores was coupled with the non‐Darcy flow through the formation; wellbore temperature, pressure and the mixture of drilling fluid and SC‐CO2 were calculated in the method of coupling; the invaded SC‐CO2 could affect the mixed fluid physical properties in the annulus; the change of physical properties of CO2 (eg, solubility, phase transition) was considered and integrated. The research results indicate that as the mixture of drilling fluid and SC‐CO2 flows from the bottom to the surface, the invaded CO2 is difficult to be detected at the early invasion stage because of high CO2 density and solubility; the CO2 would change from supercritical to gas phase and the dissolved quantity and density of CO2 rapidly decrease near the wellhead, and further cause well‐control issues. Furthermore, the bottom‐hole pressure (BHP) would decrease and could not provide sufficient balance to the formation pressure, which could significantly increase the risk of well blowout. Sensitivity analysis was utilized to evaluate the effects of the choke pressure, drilling fluid pumping rate, initial pressure difference, reservoir permeability, and drilled reservoir thickness on the BHP and the depth of phase transition of CO2. A numerical model coupling the flow‐temperature distribution in wellbores with the non‐Darcy seepage through formation media was formulated to study the transient multiple‐phase flow during SC‐CO2 invasion. With proposed numerical method and field data, the characteristics of gas‐liquid two‐phase transient flow and phase transition of CO2 were further investigated. The mechanisms for well blowout triggered by solubility variation and phase transition of CO2 were studied. [ABSTRACT FROM AUTHOR]

A thermal dissociation process (ideally, 100% atom utilization) to regenerate the amine extractant and to produce gaseous HCl which is the key to realizing the CO2 mineralization with metal chloride waste liquids was investigated. Solvent effects on the thermal dissociation of tri‐n‐octylamine hydrochloride (TOAHCl) were predicted to be prominent via analyzing structure parameters, charge distribution, solvation free energy, apparent basicity, and N‐H frequency with the help of molecular simulation and experiments. Inert solvents with low polarity such as decalin, dodecane were favorable in thermal dissociation experiments. In particular, decalin enhanced the dissociation most effectively which is in agreement with the prediction. In dilute solutions, the thermal dissociation kinetics was shown to be first order. The apparent reaction rate (3.0 × 10−4−1.5 × 10−2 min−1) and activation energy (58.219‐121.827 kJ/mol) differ a lot at 180‐190°C in various solvents, confirming a strong solvent effect. A two‐stage reaction scheme in dilute solutions has been proposed from the experimental study. The overall process is entropically driven, with the removal of HCl into gas phase from the solvated state. The work could offer a fundamental direction for the further actual process. The solvent effect of thermal dissociation of tri‐octylamine hydrochloride was investigated systematically with both experimental and molecular simulation approaches. Decalin was selected as the best solvent. [ABSTRACT FROM AUTHOR]