准确度更高的高含硫天然气压缩因子计算方法

目的考查国内外不同状态方程计算结果的准确性。 方法通过python3.6编写了GERG-2008状态方程的软件模块,与AGA8-92DC、PR、SRK、CPA、BWRS等状态方程的计算结果进行对比分析,评估了不同状态方程对不同组成高含硫天然气压缩因子计算的准确性。 结果①对标准中规定的组成较简单的管输天然气,GERG-2008方程与AGA8-92DC方程的计算准确度基本相当,在天然气管输温度、压力范围内,两个方程的计算准确度均在0.10%以内;②基于331组高含硫天然气压缩因子实验数据的计算结果,GERG-2008方程准确度最高,偏差范围为0.31%~1.14%,平均偏差为0.67%,相比于AGA8-92DC提升了14.9%;③H₂S摩尔分数在0%~27%范围内,对于研究的几种状态方程的压缩因子计算方法,其准确度排序依次为:GERG-2008、AGA8-92DC、CPA、BWRS、SRK、PR。由于实验数据有限,现有研究大多是针对某种工况下的计算分析,其在更广的范围内计算准确性需要进一步验证;④ISO 20765-2:2015 Natural gas—Calculation of thermodynamic properties—Part 2:Single-phase properties(gas,liquid,and dense fluid)for extended ranges of application是以GERG-2008方程为基础制订的适用于不同组成、不同相态天然气物性计算的国际标准。 结论GERG-2008方程对管输天然气压缩因子、高含硫气藏天然气压缩因子的计算都十分准确,建议天然气行业相关组织加快该国际标准及其后续标准的转化进程。      

一种预测超高压气藏压缩因子的新方法

天然气压缩因子的实验测定费用昂贵且耗时长,而应用经验关联式和状态方程求解又复杂且适用范围受限,计算精度和实用性难以确定。为此,根据Standing Katz天然气压缩因子图版,结合收集到的近1 000个实验数据点,采用最小二乘法拟合建立了高压天然气压缩因子的解析模型。与DPR、DAK、Brills、Ehsan等具有代表性的经验关联式和SRK状态方程的计算结果进行对比,所建模型计算得到的气藏压缩因子在高压及超高压条件下具有较高的精度,可满足工程计算的要求。     

应用状态方程预测液化天然气的热物理性质

状态方程是预测和关联流体热力学性质的主要工具。将Soave-Redlich-Kwong(SRK)、PengRobins on(PR)、Le e-Ke s le r-Plocke r(LKP)和Modifie d-Be ne dict-We bb-Rubin-Starling(MBWRS)四个适用于气相和液相的状态方程用于预测液化天然气(LNG)的密度、压缩因子、焓、熵和比热容等热物理性质。HYSYS软件预测结果表明,除了比热容之外,四个状态方程预测结果都比较精确。在液化天然气热物性计算中,当流体相超出MBWRS方程适用范围时(Tr≥0.3),MBWRS状态方程的预测结果与LKP、SRK、PR方程的计算结果相比,仍然较为精确,可以用于预测液化天然气热物理性质。     

通过研究得出计算酸气密度的最佳方法

准确计算CO2 、H2 S密度对注气方案设计至关重要。本文介绍了三个常用的计算酸气密度的状态方程 :SRK方程、PR方程、PT方程。运用Peneloux ,Mathias体积校正法对SRK方程和PR方程计算结果进行校正 ,并提出了误差计算公式。用SRK、SRK Peneloux、PR、PR Peneloux、PR Mathias和PR方程分别计算了CO2 、H2 S及其混合物的密度 ,同时还评估了绝对误差、平均误差、绝对平均误差和最大误差。研究表明 ,除SRK方程外其它 5个方程都满足工程需要     

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文章采用SRK和DPR理论计算模型并结合不同的校正模型，对四川罗家寨高含硫气田的罗7、罗9井，计算了80℃、103℃条件下压力在9.014～45.02 MPa范围内气体的偏差因子，并与实验测试的结果进行了对比分析。试验测试结果表明，酸性气体偏差因子变化规律与常规天然气相似；试验与计算结果对比表明，计算酸性气体的偏差因子时必须对其临界参数进行校正，否者计算结果偏小；SRK状态方程在计算酸性气体偏差因子时误差较大，DPR计算方法能够满足工程计算的要求；随着温度的升高，硫化氢和二氧化碳对于体系的压缩因子的影响越来越小。     

高压氢气压缩因子计算模型研究

目的针对目前高压氢气圧缩因子计算方法精度不足的问题,经比较后得出高压氢气压缩因子的精确计算模型。 方法讨论了几种计算高压氢气压缩因子的计算模型,包括直线方程、Virial(维里)方程、Van der Waals方程和Redlich and Kwong方程。对NIST提供的高压氢气密度数据换算为压缩因子数据,并对由模型计算的压缩因子与NIST数据作了比较。 结果在温度200~293 K、压力10~60 MPa范围内,Redlich and Kwong方程计算精度<1%。当p/T≥1 MPa/K时,NIST提供的高压氢气压缩因子数据可以拟合成一个直线方程,线性误差<0.55%。 结论采用Redlich and Kwong方程在较宽的温度、压力范围内计算高压氢气压缩因子可以获得较高的精确性。      

GERG-2008方程计算天然气压缩因子及烃露点

GERG-2008方程是国际标准ISO 20765-2推荐的天然气热物性参数计算方法,全面评估GERG-2008方程对不同组成、不同相态天然气的压缩因子、密度及天然气烃露点的计算准确性,对于合理选用天然气物性参数计算方法、提升天然气物性计算准确性及质量控制水平都具有重要的意义。为此,在收集大量实验数据的基础上,评估了用GERG-2008和AGA8-92DC方程计算气态天然气密度(压缩因子)的准确性,以及用GERG-2008方程计算高含硫天然气压缩因子、LNG密度及天然气烃露点的准确性。研究结果表明:(1)对标准规定的组成较简单的管输天然气,GERG-2008与AGA8-92DC方程的密度计算准确度相当,在管输温度、压力范围内,准确度均在±0.10%以内;(2)对重组分含量相对较高的天然气,当临界凝析温度接近计算温度时,在管输天然气压力下,上述两个方程的密度计算准确性均变差,GERG-2008、AGA8-92DC方程的相对平均绝对值偏差分别约为0.30%和0.50%,前者表现略优;(3) GERG-2008用于C_5~+摩尔分数低于0.20%的LNG的密度计算时,与测试值相对平均绝对值偏差小于0.10%;(4) GERG-2008可用于不含或含微量C_6~+同分异构体天然气的烃露点计算,其准确度优于PR或SRK类状态方程。结论认为,GERG-2008方程具有准确、全面的天然气物性计算能力,可在天然气工业多个环节得以广泛应用,建议天然气行业相关组织加快制订相关国家标准。     

碳氢燃料在亚临界及超临界状态下的状态方程研究

利用常用的状态方程VDW EOS、RK EOS、SRK EOS和PR EOS对甲烷、乙烯、甲醇和乙醇在亚临界及超临界状态下的比容进行了理论计算,从而计算出压缩因子。并将理论计算得到的压缩因子与试验结果进行了对比分析,得出了影响状态方程预测精度的几个重要因素。     

高含二氧化碳天然气压缩系数的计算方法比较

天然气工业工程实践中,在CO<,2>、H<,2>S等酸性气体含量不高的情况下,RK方程、SRK方程、PR方程与BWRS方程计算压缩系数精度高,得到了广泛使用;而在酸性气体含量较高的情况下,上述方程只在一定范围内适用.为确定RK方程、SRK方程、PR方程与BWRS方程用于计算高含CO<,2>天然气压缩系数时的适用范围,将方程的计算误差与实验数据进行对比,结果表明BwRs状态方程精度高,适用范围广.     

基于气体组成的天然气压缩因子计算方法

天然气压缩因子Z在天然气工程计算中是最重要的物性参数之一,其获取方法主要分为查Standing-Katz图法、实验法、状态方程计算法和经验公式法。前两种方法在使用上有很大的限制性,目前状态方程计算法和经验公式法的应用优势明显。对基于气体组成来求解压缩因子的AGA8-92DC、Piper-DAK、Piper-Mahmoud、Elsharkawy-DAK和Elsharkawy-Mahmoud方程进行了计算准确度评价。将这5个待评价的计算关系式写入Visual Basic 6.0,并使用113个酸性贫气压缩因子实测值对5个方程的计算值进行了对比分析。分析结果认为,对于低中压含碳贫气,AGA8-92DC方程的计算误差最小;对于低中压含硫含碳贫气,Piper-Mahmoud的计算误差较其他方程最小。此外还发现,当天然气温度升高时,5个方程的计算值误差较原来均有所减小。     

Thermodynamic modeling of ternary systems containing imidazolium-based ionic liquids and acid gases using SRK,Peng-Robinson,CPA and PC-SAFT equations of state

Abstract

In this study, the cubic and the associative equations of state are applied to model the VLE data of ternary systems containing ionic liquids. In the first section, the simultaneous solubility of CO₂ and H₂S in the ionic liquids [omim][Tf₂N], [omim][PF₆] and [bmim][PF₆] is modeled and the selective absorption of CO₂/H₂S is investigated at the temperatures T/K = (303.15 and 343.15) and the pressures P/MPa = (0.1 and 1). According to the obtained results, the percent deviations in pressure were varying between 6.0 and 10.8 for the SRK EoS, 6.0 and 10.6 for the PR EoS, 2.6 and 9.6 for the CPA EoS and 3.4 and 6.1 for the PC-SAFT EoS. Also, percent deviations in vapor phase composition were varying between 3.1 and 4.9 for the SRK EoS, 3.3 and 4.9 for the PR EoS, 3.1 and 7.0 for the CPA EoS and 3.8 and 4.9 for the PC-SAFT EoS. In the selectivity calculations, at high ionic liquid concentrations, the cubic models predict the selectivity drop; while the associative models present increasing trend. In the second section, the CO₂ solubility in ethanol and [emim][Tf₂N] as well as the mixture of ethanol and [emim][Tf₂N] is modeled and the experimental points were tested for thermodynamic consistency. According to the obtained results, the percent deviation in pressure of the ternary systems was 3.9 for the SRK EoS, 3.9 for the PR EoS, 3.8 and 4.0 for the CPA EoS and 3.1 and 3.2 for the PC-SAFT EoS. In the same temperature and pressure, the CO₂ solubility decrease when the concentration of ethanol increases, and the proposed models can describe this phase behavior.     

The CPA EoS application to model CO2 and H2S simultaneous solubility in ionic liquid [C2mim][PF6]

The CPA EoS was utilized for solubility modeling of pure CO₂ and H₂S and their mixture in [C₂MIM][PF₆]. The model is comprised of SRK EoS in addition to Wertheim's association term. Up to now, several associating models such as SAFT variants have been successfully applied to such systems. Considering the complexity and time consuming nature of SAFT EoSs, CPA can be a good alternative due to its accuracy and simplicity with respect to the SAFT.

The AAD % for binary systems including H₂S+ IL and CO₂+ IL are 11.78, 10.40 respectively. Moreover, the ternary system show AAD% equal to 16.51.     

Prediction of thermodynamic properties of natural gas mixtures using 10 equations of state including a new cubic two-constant equation of state

In this contribution, 10 equations of state (EoSs) are used to predict the thermo-physical properties of natural gas mixtures. One of the EoSs is proposed in this work. This EoS is obtained by matching the critical fugacity coefficient of the EoS to the critical fugacity coefficient of methane. Special attention is given to the supercritical behavior of methane as it is the major component of natural gas mixtures and almost always supercritical at reservoir and surface conditions. As a result, the proposed EoS accurately predicts the supercritical fugacity of methane for wide ranges of temperature and pressure. Using the van der Waals mixing rules with zero binary interaction parameters, the proposed EoS predicts the compressibility factors and speeds of sound data of natural gas mixtures with best accuracy among the other EoSs. The average absolute error was found to be 0.47% for predicting the compressibility factors and 0.70% for the speeds of sound data. The proposed EoS was also used to predict thermal and equilibrium properties. For predicting isobaric heat capacity, Joule–Thomson coefficient, dew points and flash yields of natural gas mixtures, the predictive accuracy of the EoS is comparable to the predictive accuracy of the Redlich–Kwong–Soave (RKS) EoS or one of its variants. For predicting saturated liquid density of LNG mixtures, however, the accuracy of predictions is between the RKS and Peng–Robinson (PR) EoSs.     

Modeling of acid gases solubility in ionic liquid [BMIM][MeSO4] using CPA EoS

This work follows the thermodynamically modeling procedure to correlate the solubility of pure CO₂ and H₂S in [BMIM][MeSO₄]. Moreover, solubility of acid gases mixture was predicted. The bubble point pressure calculation method was applied in which CPA EoS is responsible for fugacity coefficients calculation of the components. The CPA EoS combines SRK and Wertheim's association term to handle non-ideal behavior of the polar and associating components.

The AADs% of H₂S+IL and CO₂+IL binary subsystems were calculated as 18.4 and 17.36 respectively. Moreover, AADs% equal to 27.26 and 6.74 were obtained for predicted partial pressures of CO₂ and H₂S, respectively.     

Implementation of CPA EoS for simultaneous solubility modeling of CO2 and H2S in ionic liquid [OMIM][Tf2N]

In this study, solubility of pure CO₂ and H₂S and their mixture in [OMIM][Tf₂N] modeled applying CPA EoS. CPA combines the SRK equation with an advanced association term, which is similar to that of SAFT. From a practical point of view, the target in the CPA project was to develop a thermodynamic model capable of describing complex equilibria of mixtures containing polar/associating chemicals through a simple procedure with respect to the SAFT.

The AAD% for binary systems, including H₂S+ IL and CO₂+ IL are 6.81, 5.21 respectively. Moreover, AAD% equal to 13.89 was achieved for the ternary system.     

Application of reaction equilibrium thermodynamic model for correlation of H2S solubility in ionic liquids [emim][Ace] and [hmim][Ace] using CPA equation of state

Correlation of H₂S solubility in ionic liquids [emim][Ace] and [hmim][Ace] was performed using CPA EoS. For taking into account the effect of possible chemical reactions, the Reaction Equilibrium Thermodynamic Model (RETM) was used. This model assumes that an AB₂ type reaction mechanism between two IL molecules and one H₂S molecule is taken place. Both of H₂S and ILs was considered as association components following 4C and 2B association schemes, respectively. First, pure components parameters achieved using CPA EoS. Consequently, the binary systems were investigated applying RETM. The results show AAD% equal to 4.75 and 12.44 for [emim][Ace] and [hmim][Ace] respectively.     

The High-Pressure Physical Property of Gas With CO2 in the Changshen Gas Reservoir

The natural gas in Changshen gas reservoir has high CO₂ content. There are no conventional methods to calculate the physical parameters of natural gas. In view of this specificity, the physical parameters are determined and analyzed by PVT laboratory experiments. Experimental studies show that, below 20 MPa, the compressibility factor, volume factor, density, and isothermal compressibility have strong sensitivity to pressure, but the steam content contributes little and the absolute viscosity maintains strong pressure sensitivity. The compressibility factor, density, absolute viscosity, and steam content increase violently stronger than volume factor with the increase of CO₂, and the isothermal compressibility is not sensitive to CO₂. The variations of the high-pressure physical properties of Changshen gas reservoir depend on pressure and CO₂ content, which should be considered in the reservoir development.     

The solubility of acid gases in the ionic liquid [C8mim][PF6]

Mixtures containing associating compounds, represent highly non-ideal phase behavior, due to the presence of powerful hydrogen bonding interactions. Up to now, several associating models such as SAFT variants have been applied to such systems. The CPA EoS was introduced by Kontogeorgis and his coworkers in order to combine a cubic EoS, and the SAFT theory. At the present survey, acid gas mixtures solubilities in IL [C₈mim][PF₆] has been thermodynamically modeled using CPA EoS. The AAD % for binary systems, including H₂S+ IL and CO₂+ IL are 8.74, 2.14 respectively. Moreover, for ternary systems AAD % is equal to 17.43.