Modelling of CO2 capture and separation from different gas mixtures using semiclathrate hydrates

In this work we present a model for predicting hydrate formation condition to separate carbon dioxide (CO₂) from different gas mixtures such as fuel gas (H₂+CO₂), flue gas (N₂+CO₂), and biogas gas (CH₄+CO₂) in the presence of different promoters such as tetra-n-butylammonium bromide (TBAB), tetra-n-butylammonium chloride (TBAC), tetra-n-butylammonium fluoride (TBAF), tetra-n-butyl ammonium nitrate (TBANO₃), and tetra-n-butylphosphonium bromide (TBPB). The proposed method was optimized by genetic algorithm. In the proposed model, hydrate formation pressure is a function of temperature and a new variable in term of Z, which used to cover different concentrations of studied systems. The study shows experimental data and predicted values are in acceptable agreement.     

Prediction of hydrate formation conditions to separate carbon dioxide from fuel gas mixture in the presence of various promoters

In this study estimation of hydrate formation conditions to separate carbon dioxide (CO₂) from fuel gas mixture (CO₂+H₂) was investigated in the presence of promoters such as tetra-n-butylammonium bromide (TBAB), tetra-n-butylammonium fluoride (TBAF), and tetra-n-butyl ammonium nitrate (TBANO₃). The emission of CO₂ from the combustion of fuels has been considered as the dominant contributor to global warming and environmental problems. Separation of CO₂ from fuel gas can be an effective factor to prevent many of environmental impacts. Gas hydrate process is a novel method to separate and storage some gasses. In this communication, a feed-forward artificial neural network algorithm has been developed. To develop this algorithm, the experimental data reported in the literature for hydrate formation conditions in the fuel gas system with different concentrations of promoters in aqueous phase have been used. Finally, experimental data compared with estimated data and with calculation of efficiency coefficient, mean squared error, and mean absolute error show that the experimental data and predicted data are in acceptable agreement which demonstrate the reliability of this algorithm as a predictive tool.     

含杂质CO2管道输送水合物形成规律研究

在延长油田产生的CO₂气体输送过程中,管线会发生水合物冰堵,影响气体输送流量,为了探究CO₂水合物在管道输送过程中的形成规律,利用PVTSIM软件生成了CO₂水合物的相平衡曲线,并通过OLGA软件对水平管和弯管输送的水合物形成规律进行了模拟分析。结果表明:在低温高压条件下,水平管和弯管输送过程中均会有水合物形成,其生成过程是一种类似于盐类的结晶过程,通常包括成核和生长两个阶段,然后依靠流体颗粒之间的黏附力致使水合物聚集,与直管段相比,弯管段更容易产生水合物;水合物生成速率均由小到大,然后快速进入稳定阶段,最后趋于0。现场管线的水合物也多发生在弯管处,从而进一步验证了CO₂水合物的形成规律。因此,在管道输送过程中应避免高压出口和低温入口条件,保证管道安全运营。      

Influence of hydrogen sulfide on the efficiency of xenon recovery from natural gas by gas hydrate crystallisation

A mathematical simulation of the gas hydrate formation based on a gas mixture approximated to natural gas composition – CH₄+H₂S?+?CO₂+Xe at a normalized increase in hydrogen sulfide (H₂S) concentration in gas mixture from 3.08·10^?4?vol.% to 4.88?vol.%, at changes in the gas hydrate formation temperatures from 273.15?K to 283.15?K. It is shown that xenon (Xe) distribution coefficient decreases from 12.37 to 5.90, and is more dependent on the change in H₂S concentration than on the change in the gas hydrate formation temperature. Effective Xe recovery from natural gas at the gas hydrate formation temperature is 273.15?K, and at a minimum impurity concentration with a dissociation pressure close to Xe.     

Gas–liquid membrane contactors for carbon dioxide capture from gaseous streams

Membrane technology is characterized by high efficiency, compatibility and flexibility of various membrane processes in integrated systems, low power consumption, high stability and environmental safety of processes, comparative ease and simplicity of controlling and scaling-up, as well as a unique functional flexibility of the membrane processes. This is why the membrane technology is considered as a promising way to reduce anthropogenic emissions of carbon dioxide into the atmosphere. Gas–liquid membrane contactors are a prime example of high-performance hybrid processes using membrane technologies. Integrating several separation methods in one device (membrane contactor) makes it possible to retain benefits of membrane technology, such as small size and flexibility, complementing them with high separation selectivity typical of CO₂ absorption. This review presents the basic principles of operation and design of membrane contactors, and a wide range of materials, membranes, and liquid absorbents for membrane CO₂ absorption/stripping are considered. Particular attention has been paid to current studies on CO₂ removal from thermal power plant flue gas, natural gas, biogas, and syngas. The examples of pilot-scale and semi-commercial implementation of CO₂ absorption/stripping in membrane contactors have been given.     

The Induction Time of Hydrate Formation From a Carbon Dioxide-Methane Gas Mixture

Kinetics of hydrate formation from CO₂?CH₄ gas mixture has been investigated. Eight experiments in various pressures, gas compositions, and load factors (volume of injected water/volume of reactor) were performed in a 460 CC vessel. For each gas mixture, the induction time of hydrate formation has been measured and the pressure-temperature-time diagram has been plotted. The results of the experiments show that by increasing the composition of carbon dioxide in the gas, the induction time of hydrate formation decreased and by increasing the load factor, the hydrate formation rate increased.     

Kinetics of (TBAF + CO2) semi-clathrate hydrate formation in the presence and absence of SDS

In this communication, the impacts of adding SDS (sodium dodecyl sulfate), TBAF (tetra-n-butylammonium fluoride) and the mixture of SDS + TBAF on the main kinetic parameters of CO₂ hydrate formation (induction time, the quantity and rate of gas uptake, and storage capacity) were investigated. The tests were performed under stirring conditions at T = 5 ℃ and P = 3.8 MPa in a 169 cm³ batch reactor. The results show that adding SDS with a concentration of 400 ppm, TBAF with a concentration of 1–5 wt%, and the mixture of SDS + TBAF, would increase the storage capacity of CO₂ hydrate and the quantity of gas uptake, and decrease the induction time of hydrate formation process. The addition of 5 wt% of TBAF and 400 ppm of SDS would increase the CO₂ hydrate storage capacity by 86.1% and 81.6%, respectively, compared to pure water. Investigation of the impact of SDS, TBAF and their mixture on the rate of gas uptake indicates that the mixture of SDS + TBAF does not have a significant effect on the rate of gas uptake during hydrate formation process.     

Phase equilibrium modeling of semi-clathrate hydrates of the CO2+H2/CH4/N2+TBAB aqueous solution system

In this study, the semi-clathrate hydrate dissociation pressure for the CO₂+N₂, CO₂+H₂, CO₂+CH₄, and pure CO₂ systems in the presence of different concentrations of TBAB aqueous solutions is predicted using a strong machine learning technique of multi-layer perceptron neural network (MLP-NN). The developed model, with an overall correlation coefficient (R²) of 0.9961 and mean square error (MSE) of 5.96E?02, presented an excellent accuracy in prognosticating experimental data. A complete statistical evaluation performed to promise the strength and generality of the multi-layer perceptron artificial neural network (MLP-ANN). In addition, the applicability of the proposed network and quality of experimental data was assessed through the Leverage approach.     

Experimental study of separation of ammonia synthesis vent gas by hydrate formation

Termodynamic data on methane hydrate formation in the presence of ammonia are very important for upgrading of ammonia synthesis vent gas using hydrate formation. This paper is focused on the formation conditions of methane hydrate in the presence of ammonia and the effects of gas-liquid ratio and temperature on the separation of vent gas by hydrate formation. Equilibrium data for methane hydrate within an ammonia mole concentration range from 1% to 5 % were obtained. The experimental results indicated that ammonia has an inhibitive effect on hydrate formation. The higher the ammonia concentration, the higher is the pressure reguired for methane hydrate formation would be. The primary experimental results showed that when volume ratio of gas to liquid was 80：1 and temperature was 283.15 K, total mole fraction of （H2＋N2） in gas phase could reach 96.9 %.     

Thermodynamic modeling of equilibrium conditions of CH4/CO2/N2 clathrate hydrate in presence of aqueous solution of sodium chloride inhibitor

In this work, the effect of sodium chloride (NaCl) on thermodynamic properties of CH₄+CO₂+N₂ hydrate formation and equilibrium condition has been studied. The three-phase (hydrate–liquid–gas) equilibrium calculation has been carried out using the Peng–Robinson equation of state (PR EoS) and Universal Quasi Chemical (UNIQUAC) activity coefficient models. The PR EoS coupled with classic mixing rule is applied for the vapor phase. The calculations of the gas hydrate formation pressures are performed in the absence and presence of sodium chloride inhibitor for the gas hydrate systems. The Chen–Guo model has been used for the hydrate phase and the UNIQUAC activity coefficient is applied for non-ideality of the liquid phase. To obtain higher accuracy, the solubility of the gases in the aqueous phase is also taken into account using pressure corrected Henry's law. Finally, the stepwise procedure has been followed to obtain the results and compared with the experimental results. The addition of 2% (by volume) sodium chloride to water results in large shifts in phase equilibrium boundary to increase pressure for the same temperature condition.     

水合物法天然气脱酸的影响因素

为了促进水合物法分离CO₂在天然气脱酸工艺中的应用,以CH₄+CO₂混合气为例,采用CO₂分离率、CH₄损失率及分离因子作为水合物法脱酸的评价指标,利用自主设计的水合物法气体分离实验装置考察了初始压力、操作温度、四氢呋喃（THF）及实验用水量对水合物法分离CH₄+CO₂混合气的影响。结果表明,随初始压力增大和操作温度降低,平衡时气相CO₂浓度降低,CO₂分离率和CH₄损失率同时增大,分离因子小幅减小;随THF浓度增大,平衡时气相CO₂浓度增加,在THF摩尔分数为1.0%时,体系具有较大的CO₂分离率和分离因子,较低的CH₄损失率;随实验用水量增加,平衡时气相CO₂浓度降低,CO₂分离率增大,CH₄损失率减小,分离因子增大。综合分析,可通过提高初始压力、降低操作温度、增加实验用水量,并添加摩尔分数1.0%THF来促进水合物生成,提高分离效率。     

Prediction of the conditions for sour gas hydrate formation in the presence of methanol inhibitor

In this work a new thermodynamic model for accurate prediction of H₂S and CO₂ containing sour gas hydrate equilibrium dissociation temperatures in the presence of a gas hydrate thermodynamic inhibitor (methanol) is presented. The average absolute deviation between the predicted and measured sour gas hydrates dissociation temperatures (AADT%) considering pure and mixed acid gases in the presence of methanol inhibitor is about 0.274% which is much lower than those obtained by the other available thermodynamic models. The proposed approach is quite reliable over wide ranges of methanol and acid gases concentrations and can be used for performance evaluation of other gas hydrate inhibitors regarding the design of sour natural gas flow assurance systems in oil and gas industries.     

基于吸收式热泵的锅炉烟气余热回收工艺系统性能研究

为提高锅炉烟气余热综合利用效率,降低锅炉热损失,基于溴化锂吸收式热泵原理,开发了锅炉烟气余热回收工艺系统;采用理论分析方法,分析了系统的性能及其动态特性。分析结果表明:具有良好的制热效率并能有效节省锅炉燃煤量,减少CO_2的排放;年节省标准煤量为5.13×10~5 kg,年减少CO_2排放量4.04×10~5 m~3;制热系数随蒸发温度增加略有减小,但变化趋势基本保持不变;热能转换率随循环水温差增大而逐渐升高;回收量标准煤与循环水温差紧密相关,受其他因素影响较小;热能转换率与减少CO_2排放量呈正线性关系。以上结论为锅炉余热回收系统分析计算提供了理论依据。     

Computation of equilibrium hydrate formation temperature for CO2 and hydrocarbon gases containing CO2 in the presence of an alcohol, electrolytes and their mixtures

This work presents the applicability of a unified model to predict the CO₂-rich gas and pure CO₂ hydrate formation conditions in aqueous solutions containing glycerol, methanol, ethylene glycol, electrolytes and their mixtures. A water activity model is introduced that combines the effect of the soluble gases, an alcohol and electrolytes. Then this model is used together with the model of Holder et al. [Holder, G.D., Corbin, G., Papadopoulos, K.D., 1980. Thermodynamic and molecular properties of gas hydrates from mixtures containing methane, argon and krypton. Ind. Eng. Chem. Fundam. 19 (3) 282] to predict CO₂-rich gas and CO₂ hydrate formation conditions. The predictions are in excellent agreement with experimental data.     

Nanofluid-assisted gas to hydrate (GTH) energy conversion for promoting CO2 recovery and sequestration processes in the petroleum industry

In this work the enhancement of gas to hydrate conversion employing the nanographene oxide (NGO)–based nanofluid regarding CO₂ capture and sequestration recovery is investigated. A new series of experiments are carried out at different pressures, temperatures, agitation intensities and NGO promoter concentrations by using a newly developed fully automated GTH (gas to hydrate) energy converter. According to the presented results at the 3 MPa and 275.15 K and in the presence of 30 ppm NGO, it is possible to reach a CO₂ gas to hydrate conversion of 95% at a low impeller speed in less than 2.5 h, which is quite interesting from an energy consumption standpoint. The presented approach can have potential application for development of low cost hydrate-based carbon dioxide recovery plants in petroleum industry.     

Optimal activated carbon for separation of CO2 from (H2 + CO2) gas mixture

Seven types of activated carbon were used to investigate the effect of their structure on separation of CO₂ from (H₂ + CO₂) gas mixture by the adsorption method at ambient temperature and higher pressures. The results showed that the limiting factors for separation of CO₂ from 53.6 mol% H₂ + 46.4 mol% CO₂ mixture and from 85.1 mol% H₂ + 14.9 mol% CO₂ mixture were different at 20 C and about 2 MPa. The best separation result could be achieved when the pore diameter of the activated carbon ranged from 0.77 to 1.20 nm, and the median particle size was about 2.07 lm for 53.6 mol% H₂ ? 46.4 mol% CO₂ mixture and 1.41 lm for 85.1 mol% H₂ + 14.9 mol% CO₂ mixture. The effect of specific area and pore diameter of activated carbon on separation CO₂ from 53.6 mol% H₂ ? 46.4 mol% CO₂ mixture was more significant than that from 85.1 mol% H₂ ? 14.9 mol% CO₂ mixture. CO₂ in the gas phase can be decreased from 46.4 mol% to 2.3 mol%–4.3 mol% with a two-stage separation process.     

H2S废气反应炉燃烧数值模拟

针对某炼油化工厂H_2S反应炉设计的不同结构的燃烧器进行三维数值模拟,研究了不同燃烧器结构参数、燃料气成分与分配比例、反应炉花墙结构等因素对炉内流动与燃烧的影响,并确定了合理的燃烧器结构。结果表明:原始燃烧器结构下,单烧酸性气工况时,降低内圈酸性气比例有利于H_2S的完全燃烧,炉膛出口烟温有所提高;优化后的燃烧器结构较原始结构下,增强了内圈酸性气与空气的混合,更有利于H_2S气体的燃烧;反应炉内花墙结构能造成炉膛内烟气回流,提高了烟气的停留时间,有利于H_2S气体的燃烧完全;掺烧天然气工况较单烧酸性气工况,炉内燃烧变差。     

Origin, migration, and accumulation of carbon dioxide in the East Changde Gas Field, Songliao Basin, northeastern China

CO₂ reservoirs are widely distributed within the Yingcheng Formation in the Songliao Basin, but the extreme horizontal heterogeneity of CO₂ content causes difficulties in the exploration and exploitation of methane. Former studies have fully covered the lithology, structure, and distribution of the reservoirs high in CO₂ content, but few are reported about migration and accumulation of CO₂. Using the East Changde Gas Field as an example, we studied the accumulation mechanisms of CO₂ gas. Two original types of accumulation model are proposed in this study. The fault-controlled accumulation model refers to gas accumulation in the reservoir body that is cut by a basement fault (the West Xu Fault), allowing the hydrocarbon gas generated in the lower formation to migrate into the reservoir body through the fault, which results in a relatively lower CO₂ content. The volcanic conduit-controlled accumulation model refers to a reservoir body that is not cut by the basement fault, which prevents the hydrocarbon gas from being mixed in and leads to higher CO₂ contents. This conclusion provides useful theories for prediction of CO₂ distribution in similar basins and reservoirs.     

液态CO2原位置换整形天然气水合物的形态研究

CO_2置换法在开采天然气(CH_4)水合物资源的同时,能将温室气体(CO_2)以稳定的水合物形式永久封存并保持海底地质结构的稳定。探究液态CO_2原位置换整形天然气水合物的过程形态,验证水合物的形态结构是否会破坏,对实际开采技术的研发具有关键意义。利用自行设计的可视化反应釜对液态CO_2置换整形天然气水合物进行实验观测研究。结果表明:①在置换过程中,原位CH_4水合物分解的同时生成CO_2水合物,并保持过程中水合物的整形结构稳定的第二类原位置换过程是可以实现的;②在实际工程应用中,采用液态CO_2在相应的相平衡压力条件下,对大规模的天然气水合物藏进行第二类原位置换,可望获得较高的水合物藏置换开采效率。实验结果为进一步研究液态CO_2置换天然气水合物开采工艺提供了直观的过程现象。