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.     

A new empirical correlation for prediction of carbon dioxide separation from different gas mixtures

Carbon dioxide (CO₂) emission from different systems such as fuel gas (H₂+CO₂), flue gas (N₂+CO₂), and biogas gas (CH₄+CO₂) is one of the main factors of global warming and environmental problems. So, CO₂ separation from different systems is essential. Low energy consumption, environmental friendliness, and low operational cost of hydrate-based gas separation (HBGS) process show the high potential of this approach in separation of some gases such as CO₂. Hydrate phase equilibrium data are required for designing the separation process. So far numerous models has been proposed for prediction of hydrate formation/dissociation conditions in various systems with/without promoters or inhibitors. This study attempts to present a simple and comprehensive model for fast prediction of hydrate formation conditions to separate CO₂ from biogas, fuel gas, and flue gas systems in the presence of promoters such as tetra-n-butylammonium bromide, tetra-n-butylammonium chloride, tetra-n-butylammonium fluoride, tetra-n-butyl ammonium nitrate, and tetra-n-butylphosphonium bromide. According to the error analysis results, this point can reach the new proposed correlation has better estimation capability in comparison with Sayyad Amin et al. model. On the other hand, hydrate formation temperature can be predicted in the presented correlation with high accuracy.     

表面活性剂促进CO_2水合物生成的实验及动力学模型

采用自行设计的水合物生成实验系统,在静态条件下,在十二烷基苯磺酸钠(SDBS)、十二烷基硫酸钠(SDS)体系中进行了CO2水合物生成的实验。考察了表面活性剂浓度对CO2水合物生成的影响;建立了CO2水合物生成动力学模型;分析了表面活性剂对CO2水合物生成促进作用机理。实验结果表明,SDBS和SDS均能缩短CO2水合物生成的诱导时间、提高生长速率和储气密度;SDBS比SDS具有更好的CO2水合物生成促进效果,两种添加剂的最佳用量分别为0.5,0.3 g/L;建立的CO2水合物生成动力学模型能对水合物生成过程进行准确预测。     

Model of transient CO2 gas hydrate particle size distribution at its equilibrium condition

Abstract

It is important to comprehend the relationship between temperature and pressure at which different sizes of hydrates with a particular distribution. When hydrate particles are formed at unsteady state condition, the moment and the spreadness of the distribution of the formation of the hydrate particles is changed with time. The change of distribution of hydrate particle is one of the important parameter for the secondary nucleation rate of gas hydrate. In this study, a model is developed and proposed to predict the particle size distribution of carbon dioxide gas hydrate at its equilibrium condition. The distribution model may be useful for further understanding of the nucleation mechanism and its rate of gas hydrate formation.     

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.     

The Equilibrium Data and Thermodynamic Modeling of Hydrate Formation for CO2 and Mixtures of CO2 and CH4 in the Presence of Methanol

Equilibrium data for the novel formation of hydrates of carbon dioxide and mixtures of carbon dioxide and methane in 20 wt% aqueous methanol solution were measured by the constant-volume method. For CO₂, these data were taken at the temperature and pressure ranges of 264.7–270.7 K and 1,470–3,160 kPa, respectively. For mixtures of carbon dioxide and methane, these data were taken at the temperature and pressure ranges of 262.9–273.7 K and 1,370–5,100 kPa, respectively. The data obtained for CO₂ in 20 wt% aqueous methanol solution were in disagreement with previously published data, but there was good agreement between our data and the predictions of thermodynamic models. The Peng-Robinson equation of state (PR EOS) coupled with the Wong-Sandler (WS) mixing rule was used to obtain the fugacities of the components in the gas and aqueous liquid phases. The PR EOS was then coupled with van der Waals-Platteeuw (vdW-P) hydrate model and applied to predict hydrate-formation conditions in the system containing methanol. The model predictions demonstrated good agreement with the experimental data.     

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.     

化学添加剂对水合物生成和储气的影响

为了研究促进剂对水合物生成的影响,采用自行设计的水合物反应系统,通过恒温定容实验,研究了四氢呋喃(THF)和十二烷基硫酸钠(SDS)对二氧化碳水合物生成的影响。并在实时测量水合物生成过程中系统的温度、压力的基础上,计算得出水合物的生成速率、储气量及表观水合数。结果表明,适宜浓度的SDS能促进气体在液相的溶解,提高水合物的生长速率和储气密度;单独添加THF对水合物生成过程促进效果并不明显;SDS和THF复合添加剂共同作用对水合物促进效果最显著。     

二氧化碳水合物生成驱动力的研究

选用摩尔吉布斯自由能的变化作为水合物生成的通用驱动力,推导CO2水合物的水合反应驱动力表达式。通过雾流强化水合反应系统装置,针对CO2水合物的生成驱动力进行实验研究,揭示CO2水合物生成过程动力学特性。结果表明,水合反应系统压力越高、温度越低,CO2水合物的生成驱动力数值的绝对值越大,越有利于CO2水合物的生成;在275.15K,随着压力的增加,驱动力增强,但不呈线性,而是从快到慢渐趋于平缓,驱动力数值的绝对值为0.1820kJ/mol~1.1903kJ/mol;CO2水合物的生成量随着实验条件生成驱动力的增加而增大。     

影响二氧化碳水合物生成特性的实验研究

在小型水合物反应装置上研究了纯水、四丁基溴化铵(TBAB)、四氢呋喃(THF)三种不同水合体系对二氧化碳水合物生成过程的诱导时间、气体消耗速率及反应最终压力等特性的影响。结果表明,设定温度在0℃～3℃范围内时四丁基溴化铵体系中生成水合物的诱导时间最长,受温度影响最大,而水合反应气体消耗速率最大;四氢呋喃体系中生成水合物的诱导时间最短,受温度影响最小,而水合反应气体消耗速率最小;四丁基溴化铵、四氢呋喃体系反应最终压力略高于纯水体系。较高温度范围内THF体系对水合物生成特性的影响明显优于其他两种。     

新型可回收烟道气二氧化碳的能源系统的概念探讨

通过天然气和烟气三重整反应的原理分析,提出了新型的可回收二氧化碳生产二甲醚的多联产能源系统的概念性流程,从而为解决回收电站烟道气中的二氧化碳提供了新的思路。该能源系统中需要解决的关键性问题是开发耐二氧化硫的催化剂、高温除尘、多联产系统流程分析等。     

Predicting the conditions for gas hydrate formation

Gas hydrate is a crystalline mixture obtained from gas molecules trapped in the cavity of hydrogen bonding water. To date, an essential step in the development of natural gas industry has been the acquisition of knowledge in the operation and handling of gas under high pressure without hydrate formation. Since there are several ways to predict hydrate formation, this study investigates predicting hydrate formation using the Katz method. In addition, several new models for accurate estimation of gas hydrate formation conditions will be provided. These models are based on artificial neural network (ANN) requirements. To create the model, predictive experimental data published in books and journals, as well as data extracted from Katz graph (Katz chart), estimate the formation conditions of gas hydrate. We validate the model created with the use of various statistical parameters such as mean squared error (MSE) and R²-value. The result of these parameters in models created to predict the formation of hydrates accurately and efficiently is evaluated. In this study, our goals are to use an artificial intelligence neural network to predict the formation of gas hydrates.     

热等离子体重整甲烷和二氧化碳制合成气的热力学研究

常压下利用4kW的直流电弧等离子体装置,进行了甲烷和二氧化碳在氮气等离子体射流作用下重整制备合成气的实验研究。利用氮气作为放电气体产生等离子射流,甲烷和二氧化碳作为反应气体垂直送入此高温射流中,考察了甲烷与二氧化碳配比、进气流量和输入功率对原料转化率、化学能效及热值产率的影响。结果表明:热等离子体重整甲烷和二氧化碳制合成气具有处理量大、甲烷和二氧化碳转化率高、化学能效和热值产率高的特点。     

CO_2乳化液强化置换水合物中CH_4的作用研究进展

综述了天然气水合物中甲烷的置换反应的研究进展,比较了传统置换法与CO2置换法的优缺点,论述了CO2置换法尤其是CO2乳化液法的优越性。CO2乳化液具有更高的反应温度以及更好的传导率和扩散性,在置换反应中起到了强化作用,增加了CH4从水合物中的释放,提高了置换的反应速率,同时乳化液的热可以使热源增强,从而使置换反应得到进一步强化。     

添加剂对CO2水合物生成的影响

以水合物的方式分离/储存CO₂气体是一项具有挑战性的新技术。为了提高水合物的生成速率和储气密度，在小型可视化的水合物反应装置上实验研究了不同种类的添加剂对CO₂水合物生成特性的影响。结果表明，实验用有机硅系列添加剂可以有效降低气-水界面的表面张力，提高水合物的生成速率。CO₂水合物的生成量随着添加剂浓度的增大而增大，但当浓度高于0.1%以后，其生成量增长非常缓慢。单组分添加剂Silwet L-77效果最好，而单组分添加剂THF对CO₂水合物的生成没有任何改善，但将浓度为4%的THF和1%的Silwet L-77混合后却对水合物的生成起到了显著的改善效果，12 h内的气体压降可达到0.27 MPa，是纯水体系的10倍之多，照片显示有大量的水合物生成。研究结果对寻找适合于CO₂水合物快速生成的添加剂，为其应用于高效分离储存CO₂气体技术等方面提供了指导。     

On Estimating the Water Content of CO2 in Equilibrium With Formation Brine

Abstract

Water content of carbon dioxide (CO₂) is an important parameter in engineering applications, such as CO₂ storage in deep saline aquifers and enhanced oil recovery processes. A large number of experimental data have been reported on solubility of CO₂ in brine. However, experimental data on water content of CO₂ in equilibrium with formation brine are not reported in the literature. Water content of natural gas is traditionally calculated by general water content charts; however, these charts are not available for CO₂ in equilibrium with formation brine. Using an accurate fugacity and activity model available in the literature, the authors developed an efficient and simple procedure to estimate the water content of CO₂ in equilibrium with formation brine. To validate the developed procedure, the predicted CO₂-rich phase water content is compared with the reported experimental data in the literature and other predictive models for CO₂-water system. A CO₂ water content chart is presented that can be simply used to predict the water content of CO₂ in equilibrium with formation brine. The procedure presented may be used for generating necessary input data for flow simulation of CO₂ storage in deep saline aquifers.     

Prediction of carbon dioxide separation from gas mixtures in petroleum industries using the Levenberg–Marquardt algorithm

In this study, two mathematical models for hydrate formation process to separate carbon dioxide by a combination of two different kinds of organic and surfactant promoters are presented. Promoters such as sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, and dodecyl trimethyl ammonium chloride as surfactant promoters; also, tetrahydrofuran, cyclopentane, 1,3-dioxolane, and 2-methyl tetrahydrofuran as organic promoters have been used in recent years. The results showed that a combination of 3000 ppm of surfactant promoters and 4 wt% organic promoters had the highest separation rate of carbon dioxide and; consequently, the investigated models were based on this optimum condition. As a matter of fact, by using these simulations the hydrate formation behavior was predicted with high accuracy; moreover, conducting consuming experiments is not essential anymore. To sum up, in the present research both Vandermonde matrix model and Levenberg-Marquardt algorithm were applied to predict the hydrate formation behavior; in addition, their results were precisely considered and validated with experimental data.     

MA水溶液吸收CO_2的实验研究

以MA水溶液作为吸收剂,在装填有三角螺旋填料的玻璃塔内进行CO2吸收实验,考察了MA浓度、吸收温度、吸收剂流量、气体流量等因素对CO2吸收速率的影响。实验结果表明:当MA的质量分数为40%、吸收温度为40℃、吸收剂流量为10 L/h、气体流量为80 L/h时,具有最佳的吸收效果,吸收速率达到0.01028mol.m-2.s-1,同时混合气体中的CO2体积分数从35%下降到0.1%以下。     

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.     

天然气中微量组分对吸附剂性能的影响

考察了天然气吸附剂LXC对天然气中微量组分C2H6,C3H8,CO2,N2的吸附和脱附特性及其对CH4吸附能力的影响。实验结果表明,天然气吸附剂LXC吸附CH4,C2H6,C3H8的吸附量依次增大,滞留比依次减小,不可逆吸附性增强;CO2在吸附剂上的吸附量和滞留量较大;N2的可逆吸附与脱附性能较好;天然气中C2H6,C3H8,CO2均能导致吸附剂LXC吸附CH4的能力降低。在20℃、充气压力3.5M Pa、放气压力0.1M Pa的条件下,吸附剂LXC对配制的混合气体经12次连续吸脱附后,其吸附能力下降27.5%。