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.     

CO2 hydrate: Modeling of incipient stability conditions and dissociation enthalpy

In this study, CO₂ hydrate incipient stability zone in pure water is modelled employing an empirical tool, classification and regression tree, least squares support vector machine, and adaptive neuro-fuzzy inference system. Furthermore, a new semi-theoretical model is developed to estimate CO₂ hydrate dissociation enthalpy. Moreover, the quality of CO₂ hydrate's experimental data is assessed through a thermodynamic-based and Leverage approaches. Results revealed that: (1) the proposed models provide satisfactory predictions; (2) there are some doubtful data in the database; (3) outcomes of the developed semi-theoretical model for estimating the CO₂ hydrate dissociation enthalpy are in good agreement with previous works.     

水合物法分离回收烟气二氧化碳研究进展

CO2的大量排放导致温室效应日趋严重。如何有效分离回收CO2资源,使之变废为宝,成为世界各国研究人员共同关注的问题。现有的分离技术普遍存在能耗大,投入高的缺点。水合物法分离回收CO2技术是一种新型的分离技术,该技术以其独特的优点成为近年来的研究热点。阐述了其基本分离原理、国内外研究现状和亟待解决的问题。     

复合添加剂对二氧化碳水合物生成条件影响的实验研究及动力学模型建立

基于水合物法储存分离二氧化碳具有较广阔的应用前景,通过实验研究了复合添加剂对二氧化碳水合物生成条件的影响,选用十二烷基硫酸钠(SDS)和十二烷基苯磺酸钠(SDBS)以及两者的混合溶液作为实验用溶液,研究发现当采用浓度为265mg/L的SDS和SDBS质量比为1:1的复合添加剂溶液时,二氧化碳水合物的相平衡点最低,最易生成,此时的溶液体系能很好的促进水合物生成,而且比单一的SDS溶液或者SDBS溶液体系下水合物的生成条件都有所降低。建立了考虑复合添加剂促进作用的新型水合物生成动力学模型。     

Phase equilibrium modelling of natural gas hydrate formation conditions using LSSVM approach

The formation of gas hydrates in industries and chemical plants, especially in natural gas production and transmission, is an important factor that can lead to operational and economic risks. Hence, if the hydrate conditions are well addressed, it is possible overcome hydrate-related problems. To that end, evolving an accurate and simple-to-apply approach for estimating gas hydrate formation is vitally important. In this contribution, the least square support vector machine (LSSVM) approach has been developed based on Katz chart data points to estimate natural gas hydrate formation temperature as function of the pressure and gas gravity. In addition, a genetic algorithm has been employed to optimize hyper parameters of the LSSVM. Moreover, the present model has been compared with five popular correlations and was concluded that the LSSVM approach has fewer deviations than these correlations so to estimate hydrate formation temperature. According to statistical analyses, the obtained values of MSE and R² were 0.278634 and 0.9973, respectively. This predictive tool is simple to apply and has great potential for estimating natural gas hydrate formation temperature and can be of immense value for engineers who deal with the natural gas utilities.     

管输流动体系下CO2水合物生成特性的研究

在高压水合物环路装置上进行CO2水合物生成特性实验,探究其耗气量与初始实验压力、流量等因素的关系.研究发现:在初始实验压力4.5 MPa、反应温度3℃,流量1375 kg/h、管路含水5 L的条件下,管输流动体系下诱导时间在1500～1600 s之间;CO2水合物生长速率与耗气量随着初始实验压力的升高、反应温度的降低而...     

静态超重力水合反应器中二氧化碳水合物生成过程热量分析

通过对二氧化碳水合物在静态超重力反应器中生成过程分析发现,其生成过程可以分为成核诱导生成和稳定快速生成两个阶段。第一个阶段内生成量很少,同时存在着气体积累过程。第二个阶段内水合物的生成与冰粒的融化和气体积累过程逐渐达到平衡,二氧化碳水合物的生成速率为249.8mol/h。同时对该生成过程的热量进行了分析,结果表明实验范围内水合反应器热量利用效率与超重力因子成线性增长关系,其最大值为87.39%。     

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.     

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.     

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.     

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.     

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。     

Prediction of hydrate formation temperature based on an improved empirical correlation by imperialist competitive algorithm

Formation of gas hydrates is an important problem in production and transmission of natural gases. Hence, it is a particular interest and also vital to estimate the hydrate formation conditions. To do so, the Katz gas gravity method can be used as one of the simplest techniques. Numerous correlations have been presented so far, among which one of the most popular one with very good accuracy is the so called Ghiasi model. In this study, the imperialist competitive algorithm is applied to improve the Ghiasi correlation by using the Katz data. Error analysis of the results demonstrated that the improved equation had the highest precision in comparison with the Ghiasi correlation and also the other models reported by researchers.     

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.     

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。     

CryoCell低温CO_2捕集技术在高含CO_2天然气处理中的应用

当天然气中CO2含量较高时,需要对CO2采取地下封存措施。传统的CO2脱除技术是在低压下脱除气态的CO2,CO2封存过程能耗较高,CryoCell低温CO2捕集技术则是在低温下以液体的形式把CO2从天然气中脱除出来,然后将液态CO2用泵加压到地下封存所需要的压力储存起来,大大降低了CO2封存过程所需的能耗。文中分析了传统技术在处理高含CO2天然气时的局限性及CryoCell技术存在的优势,重点描述了CryoCell技术的工艺流程。CryoCell技术避开了传统酸性气体处理过程中的缺点,避免了水的消耗、化学药剂的使用和与腐蚀相关的一些问题,能耗和减排成本大大降低,可用于高含CO2气田。     

Experimental and Zero-dimensional Analysis of CO2-N2 Gas Cyclic Injection Processes

Abstract

This study investigates the influence of dominant mechanisms in the cyclic injection of a CO₂ and N₂ process through laboratory experiments. A PVT cell was used to perform six cycles of injection at typical conditions found in shallow depleted oil reservoirs (150 psig and 70°F)—the prime reservoir candidates for gas cyclic injection. These conditions are kept for five different injected mixtures, said 100%–0%, 80%–20%, 53%–47%, 20%–80%, and 0%–100% of CO₂ and N₂ respectively. Experimental results are presented to reveal the mechanisms taking place during this process. A zero-dimensional model, based on a tuned cubic EOS, is proposed to successfully predict a component's trend through all cycles and observed experimental compositions in both phases.     

“自保护”态CO2水合物分解动力及影响因素

水合物"自保护"效应对利用水合物法进行天然气运输以及二氧化碳运输、封存具有重要应用价值,但目前此现象的成因尚未被彻底阐释。采用恒压、降温的方法在不同温度条件下于超纯水、十二烷基硫酸钠(SDS)溶液中形成不同含气量的CO2水合物并迅速冻结,使其进入"自保护"状态。随后通过均匀升温法分解不同条件下"自保护"态的水合物,并测量气体释放速率及起始分解温度。将气体释放速率对累积释放气体量一次求导,以表征分解过程中水合物释放气体能力。结果发现,阐释水合物"自保护"效应成因的"冰壳"理论不能完全解释实验结果,"自保护"效应更倾向于由"过冷水"理论主控。结合有关学者在水合物分解时溶液中形成的微型(微米、纳米级)气泡方面的研究结果,提出:CO2水合物"自保护"效应更倾向于由"自保护"状态下水合物周围存在的过冷液态水,以及水合物初步分解时液态水内溶解的微型(微米、纳米级)气泡控制。