Why does CO2 hydrate disposed of in the ocean in the hydrate-formation region dissolve in seawater?

The fate of CO₂ hydrate disposed of in the ocean is analyzed based on thermodynamic theory. It is found that CO₂ hydrate and seawater form a stable system only when (a) the system pressure p and temperature T fall within the hydrate-formation region in the ocean (i.e. p > 4.5MPa and T < 283 K) and (b) seawater is saturated or supersaturated with respect to CO₂. At ocean depths below 440 m, the pressure and temperature required for system stability are satisfied. However, since seawater is highly unsaturated with respect to CO₂, the requirement for full thermodynamic stability cannot be met because the hydrate and seawater are not in chemical equilibrium and the chemical potential for CO₂ in the hydrate is larger than that in seawater. Therefore, the hydrate is unstable and dissolves in seawater. Thus, CO₂ hydrate disposed of in the ocean may not be a long-lived entity in the ocean as was predicted previously by many investigators. The results of our study have been confirmed by laboratory simulations.     

二氧化碳在深部盐水层中溶解封存规律的研究进展

将二氧化碳埋存到深部盐水层中是目前缓解温室效应的可行性对策之一,在评价储层理论埋存量时,溶解封存量在总埋存量中占有很大的比例。本文通过对相关文献的调研,计算对比了Duan&Sun模型模拟数据与前人实验数据的误差,根据前人实验与本文模拟数据分析了二氧化碳在盐水层中溶解的动力过程和热力过程,二氧化碳通过扩散作用溶解到盐水中,引起盐水层密度的变化,计算系统瑞利数满足对流运动发生的基本条件后,系统产生对流,这有利于二氧化碳的溶解。分析了温度、压力和矿化度对二氧化碳溶解的影响。在前几百年内溶解缓慢易导致泄漏,低温高压、低矿化度下二氧化碳溶解度较高,小二氧化碳水滴更有利于二氧化碳封存。     

Sequestration of CO2 in geological media in response to climate change: capacity of deep saline aquifers to sequester CO2 in solution

Geological sequestration is a means of reducing anthropogenic atmospheric emissions of CO₂ that is immediately available and technologically feasible. Among various options, CO₂ can be sequestered in deep aquifers by dissolution in the formation water. The ultimate CO₂ sequestration capacity in solution (UCSCS) of an aquifer is the difference between the total capacity for CO₂ at saturation and the total inorganic carbon currently in solution in that aquifer, and depends on the pressure, temperature and salinity of the formation water. Assuming non-reactive aquifer conditions, the current carbon content is calculated using standard chemical analyses of the formation waters collected by the energy industry on the basis of the concentration of carbonate and bicarbonate ions. Formation water analyses performed at laboratory conditions are brought to in situ conditions using a geochemical speciation model to account for dissolved gasses that are lost from the water sample. To account for the decrease in CO₂ solubility with increasing water salinity, the maximum CO₂ content in formation water is calculated by applying an empirical correction to the CO₂ content at saturation in pure water. The UCSCS in an aquifer is calculated by considering the effect of dissolved CO₂ on the formation water density, the aquifer thickness and porosity to account for the volume of water in the aquifer pore space and for the mass of CO₂ dissolved in the water currently and at saturation. The methodology developed for estimating the ultimate CO₂ sequestration capacity in solution in aquifers has been applied to the Viking aquifer in the Alberta basin in western Canada. Considering only the region where the injected CO₂ would be a dense fluid, the capacity of the Viking aquifer to sequester CO₂ in solution in the formation water is calculated to be 100 Gt. Simple estimates then indicate that the capacity of the Alberta basin to sequester CO₂ dissolved in the formation waters at depths greater than 1000 m is on the order of 4000 Gt CO₂. The results also show that using geochemical models to bring the analyses of the formation waters to in situ conditions is not warranted when the current total inorganic carbon (TIC) in the aquifer water is very small by comparison with the CO₂ solubility at saturation. Furthermore, in such cases, the current TIC may even be neglected.     

Spray characteristics and controlling mechanism of fuel containing CO2

This paper presents studies of spray characteristics and controlling mechanism of fuel containing CO₂. Using diesel fuel containing CO₂ gas, experiments were conducted on diesel hole-type nozzles and simple nozzles. The steady spray and transient spray characteristics were observed and measured by instantaneous shadowgraphy, high-speed photography, phase Doppler anemometry (PDA) and LDSA respectively. The effects of CO₂ concentration in the fuel, the injection pressure, the nozzle L/D ratio, surrounding gas pressure and temperature on the atomization behavior and spray pattern were evaluated. The results show that the injection of fuel containing CO₂ can greatly improve the atomization and produce a parabolic-shaped spray; and the CO₂ gas concentration, surrounding gas pressure, temperature and nozzle configuration have dominant influences on spray characteristics of the fuel containing CO₂. New insight into the controlling mechanism of atomization of the fuel containing CO₂ was provided.     

Effect of CO2 diffusion on wettability for hydrocarbon-water-CO2 systems in capillaries

The importance of wettability in enhanced oil recovery with high pressure CO₂ has been demonstrated by some authors. When CO₂ diffuse in hydrocarbons, it promotes swelling and reduction in contact angle and surface tension, these changes improve the tendency to fill the corners of solid surfaces, therefore filaments arise in corners. In this work, hydrocarbon-water-CO₂ behavior was studied in cylindrical and square capillaries. Square capillaries were used in order to observe the wetting in corners. Cylindrical capillaries were used to determine if there is swelling in hydrocarbons due to the CO₂ mass transfer, first through the water and then through the hydrocarbon. Contact angle and interfacial tension were measured in an attemp to explain the results. It was demonstrated that the CO₂ diffusion occurs first through water and then through hydrocarbons. The CO₂ diffusion is evident due to the contact angle diminution and the displacement of water-hydrocarbon interfaces. In addition, it was found that the behavior of water-hydrocarbon interphase depends on contact angle and surface tension. Finally, when interfacial tension is lower, the displacement is different and contact angle increasing is higher, as it was concluded by Campbell and Orr [1].     

深井CO2爆破致裂干热岩系统综合效应预评价

CO₂爆破致裂工艺为建造商业化EGS储层提供了新方案,有望突破深层地热能行业发展的技术瓶颈,但目前未见CO₂致裂技术用于干热岩系统的综合性能评价研究。基于此研究不足,借助数学建模定量科学评价其综合性能,解决此技术效果的不确定性和模糊性,填补深井地热系统综合评价体系的空白。考虑到深井CO₂爆破干热岩系统是一个多变、模糊、复杂的非线性系统,该文选取AHP-FCE优化数学模型,AHP对深井爆破干热岩系统复杂问题分层,构建递阶层次结构,通过Matlab将专家的定性判断定量化,进而确定FCE中各层评价指标权重大小,再通过FCE模糊关系合成原理,对多因素影响下的深井CO₂爆破致裂干热岩系统综合评分为83.36,预评价结果为较好,可考虑将CO₂爆破致裂器用于干热岩开采。评定结果可作为深井CO₂爆破致裂干热岩建设过程中的数据支撑,为地热开采工程提供一定的理论依据。     

CO2单井增强地热系统取热性能研究

为提高闭式单井系统取热性能,提出一种CO2单井增强地热系统（CO2-SEGS）。建立井筒流动换热和储层热-流-固耦合的数学模型,考虑CO2可压缩性以及井纵向压力传递特性,对比分析了水和CO2在SEGS中的取热性能,研究系统取热性能与封隔间距、井筒保温的关系。结果表明：（1）额定循环流量下,井口生产温度从134.09℃降低至116.06℃;CO2在采出过程中降压膨胀做功,产生明显的温降效应,中心管井口温度比底部低约57℃。（2）井筒不同位置处CO2的密度、热容差异很大,当循环流量小于50 kg/s时,依靠浮升力作用,SEGS可实现自主循环运行,无需额外泵功。（3）当水和CO2的流量分别为15 kg/s和40 kg/s时,两者年均取热速率近似相等,CO2的采出温度比水低约40℃,而压力损耗远小于水。（4）SEGS取热性能与封隔间距以及中心管保温性能呈正相关。研究结果可为SEGS系统的开发提供参考。     

Ni-Co双金属催化剂上沼气重整制氢宏观动力学

用传统湿式浸渍法制备La2O3掺杂的商业γ-Al2O3负载的沼气重整催化剂Ni-Co/La2O3-γ-Al2O3,通过对NiCo双金属催化剂上沼气重整制氢在常压下的宏观动力学分析,得出该催化剂上CH4与CO2消耗、H2与CO生成时的表观反应速率方程.通过改变进料中CH4与CO2的分压,求出各物质的反应分级数,确定总反应...     

Global warming and electric power generation: What is theconnection?

The greenhouse effect is explained, followed by a discussion of the US fossil fuel use and its contribution of greenhouse gases. US electric utilities' share of CO₂ and other emissions is quantified, including the effects of using various fuels. The possible recovery and disposal of CO₂ from power-plant flue gases is also discussed. The information presented should help prepare electric utilities to address future public concerns and the related regulatory pressures regarding the utility's role in carbon-dioxide proliferation and global warming     

CO2 emissions per individual based on a survey of university students

The amount of CO₂ produced by the daily activities of university students is estimated on the basis of statistical, questionnaire, and measurement data. The results reveal that a large proportion of CO₂ emissions occurs during energy consumption, food preparation and transport, and that the CO₂ emissions of dormitory residents are lower than those of students living in other situations. Practical methods for reducing student CO₂ emissions are also examined.     

CO2 recovery in molten carbonate fuel cell system bypressure swing adsorption

Carbon dioxide (CO₂) recycle configuration using pressure swing adsorption (PSA) is examined in the indirect internal reforming molten carbonate fuel cell (IIR-MCFC) system. It is shown that the CO₂ PSA makes the system efficiency higher than in an ordinary combustion process. A test plant was fabricated in order to evaluate the PSA performance in the IIR-MCFC system. The experimental results with respect to CO₂ recovery ratio, purity, and pressure fluctuations in both electrode chambers are acceptable     

On production behavior of enhanced geothermal systems with CO2 as working fluid

Numerical simulation is used to evaluate the mass flow and heat extraction rates from enhanced geothermal injection–production systems that are operated using either CO₂ or water as heat transmission fluid. For a model system patterned after the European hot dry rock experiment at Soultz, we find significantly greater heat extraction rates for CO₂ as compared to water. The strong dependence of CO₂ mobility (=density/viscosity) upon temperature and pressure may lead to unusual production behavior, where heat extraction rates can actually increase for a time, even as the reservoir is subject to thermal depletion. We present the first ever, three-dimensional simulations of CO₂ injection–production systems. These show strong effects of gravity on the mass flow and heat extraction due to the large contrast of CO₂ density between cold injection and hot production conditions. The tendency for preferential flow of cold, dense CO₂ along the reservoir bottom can lead to premature thermal breakthrough. The problem can be avoided by producing from only a limited depth interval at the top of the reservoir.     

The marginal cost of CO2 emissions

Haraden's model for estimating the economic cost of global warming is analysed. We change his method of discounting and some of his input parameters in a manner consistent with physical and economic theory as well as empirical data. We then find much higher costs than Haraden found. These costs are compared to the cost of reducing CO₂ emissions and we find that deep cuts of the emissions of CO₂ are preferable. A check of the sensitivity of our results with respect to some crucial parameter values does not alter that conclusion.     

Prediction of cost and emission from Indian coal-fired power plants with CO2 capture and storage using artificial intelligence techniques

Coal-fired power plants are one of the most important targets with respect to reduction of CO₂ emissions. The reasons for this are that coal-fired power plants offer localized large point sources (LPS) of CO₂ and that the Indian power sector contributes to roughly half of all-India CO₂ emissions. CO₂ capture and storage (CCS) can be implemented in these power plants for long-term decarbonisation of the Indian economy. In this paper, two artificial intelligence (AI) techniques—adaptive network based fuzzy inference system (ANFIS) and multi gene genetic programming (MGGP) are used to model Indian coal-fired power plants with CO₂ capture. The data set of 75 power plants take the plant size, the capture type, the load and the CO₂ emission as the input and the COE and annual CO₂ emissions as the output. It is found that MGGP is more suited to these applications with an R² value of more than 99% between the predicted and actual values, as against the ~96% correlation for the ANFIS approach. MGGP also gives the traditionally expected results in sensitivity analysis, which ANFIS fails to give. Several other parameters in the base plant and CO₂ capture unit may be included in similar studies to give a more accurate result. This is because MGGP gives a better perspective toward qualitative data, such as capture type, as compared to ANFIS.     

Pilot scale autothermal gasification of coconut shell with CO2-O2 mixture

This paper explored the feasibility and benefit of CO₂ utilization as gasifying agent in the autothermal gasification process. The effects of CO₂ injection on reaction temperature and producer gas composition were examined in a pilot scale downdraft gasifier by varying the CO₂/C ratio from 0.6 to 1.6. O₂ was injected at an equivalence ratio of approximately 0.33–0.38 for supplying heat through partial combustion. The results were also compared with those of air gasification. In general, the increase in CO₂ injection resulted in the shift of combustion zone to the downstream of the gasifier. However, compared with that of air gasification, the long and distributed high temperature zones were obtained in CO₂-O₂ gasification with a CO₂/C ratio of 0.6–1.2. The progress of the expected CO₂ to CO conversion can be implied from the relatively insignificant decrease in CO fraction as the CO₂/C ratio increased. The producer gas heating value of CO₂-O₂ gasification was consistently higher than that of air gasification. These results show the potential of CO₂-O₂ gasification for producing high quality producer gas in an efficient manner, and the necessity for more work to deeply imply the observation.     

下吸式固定床的生物质O2/CO2分段气化流程模拟

建立干桦木屑在下吸式固定床气化炉中的Aspen Plus气化模型,该模型预测煤气组成和煤气热值,与文献试验结果吻合良好。利用灵敏度分析模块模拟了氧碳比、CO₂/C对气化结果的影响,并提出O₂/CO₂分段气化流程,对比常规的CO₂气化特征,分析了CO₂/C对气化结果的影响。结果表明,纯氧气化时可获得高H₂和CO浓度的气化气,但其净CO₂排放量较高,氧碳比增加使碳转化率逐渐增加、冷煤气效率先增加后降低;CO₂作为气化剂时,随着CO₂/C的增加,净CO₂排放量逐渐减少,但碳转化率及冷煤气效率大幅降低;与常规CO₂气化相比,O₂/CO₂分段气化在保持低CO₂排放量的同时,可有效增加气化过程中的碳转化率及冷煤气效率。     

水合物法分离CO2工艺研究进展

随着温室效应加剧,CO₂减排行动已迫在眉睫。水合物法分离CO₂工艺作为一种发展前景广阔的新型CO₂分离技术,为CO₂减排提供了一种解决思路。水合物法分离CO₂工艺相比于化学吸收、物理吸附、深冷分离和膜分离等技术具有分离效率高、过程简单无副产物、条件温和的优势,为减缓CO₂排放增加对环境造成的影响提供了一个中短期解决方案,以此为前提将允许人类继续使用化石燃料直至可再生能源技术广泛应用。本文综合分析了国内外的相关文献,介绍了水合物法分离CO₂工艺的基本原理,并比较了水合物法分离CO₂不同工艺的优劣之处,为进一步优化水合物法分离CO₂工艺提供指导。     

Thermo-economic analysis of a direct supercritical CO2 electric power generation system using geothermal heat

A comprehensive thermo-economic model combining a geothermal heat mining system and a direct supercritical CO₂ turbine expansion electric power generation system was proposed in this paper. Assisted by this integrated model, thermo-economic and optimization analyses for the key design parameters of the whole system including the geothermal well pattern and operational conditions were performed to obtain a minimal levelized cost of electricity (LCOE). Specifically, in geothermal heat extraction simulation, an integrated wellbore-reservoir system model (T2Well/ECO2N) was used to generate a database for creating a fast, predictive, and compatible geothermal heat mining model by employing a response surface methodology. A parametric study was conducted to demonstrate the impact of turbine discharge pressure, injection and production well distance, CO₂ injection flowrate, CO₂ injection temperature, and monitored production well bottom pressure on LCOE, system thermal efficiency, and capital cost. It was found that for a 100 MW_e power plant, a minimal LCOE of $0.177/kWh was achieved for a 20-year steady operation without considering CO₂ sequestration credit. In addition, when CO₂ sequestration credit is $1.00/t, an LCOE breakeven point compared to a conventional geothermal power plant is achieved and a breakpoint for generating electric power generation at no cost was achieved for a sequestration credit of $2.05/t.     

CO2 utilization options, part II: Assessment of dimethyl carbonate production

In this paper, the potential to reduce CO₂ emissions from dimethyl carbonate production by switching from the traditional phosgene-based production to a urea-based CO₂ utilization process is assessed. The total CO₂ emission for each process is estimated, including emissions related to the carbon content of the products, energy consumption in the production process, and energy consumption in the production processes of the required reactants. Implementation of the CO₂ utilization process probably will reduce total CO₂ emissions. However, in order to achieve substantially reduced CO₂ emissions, serious consideration must be given to the optimization and design of the CO₂ utilization process. Furthermore, the fuel-mix employed is one of the factors that influences the total CO₂ emission the most.     

纤维素温和条件下一步水热法制备甲烷的研究

生物质发酵法制备甲烷存在甲烷收率低、CO₂含量高等问题。本研究以纤维素为原料,在温和条件下采用水热催化转化的方法制备甲烷。对一系列催化剂进行了考察,发现Ru/C对该反应的催化活性最高。采用Ru/C催化剂进一步考察了一系列反应条件,结果表明,升高反应温度、延长反应时间、增加催化剂用量以及提高氢气初始压力对甲烷的生成具有促进作用。在1 MPa H₂、220℃、12 h反应条件下,甲烷碳摩尔收率最高,达88%,反应过程中无CO₂产生。采用TEM、BET、XRD和FT-IR等对催化剂进行了表征,结果表明,Ru/C催化剂的高催化活性可能与催化剂本身比表面积大、钌粒子颗粒小且分散均匀的特性有关。本研究采用的催化转化方法具有甲烷收率高、CO₂排放量小（<5%）、反应条件更为温和等特点。