分子动力学模拟预测天然气密度和黏度的可行性研究

doi:10.11949/0438-1157.20231028

摘要/Abstract

摘要：

天然气作为相对清洁、低碳的能源，在我国的一次能源消费占比持续增长，其物性的精准预测对天然气集输利用过程分析至关重要。通过收集文献中天然气在不同温度和压力下的物性实测数据，对比分析了分子动力学模拟和常用经验模型计算天然气密度和黏度的预测精度，明确了不同组成天然气适用的最佳物性预测模型。结果表明，分子动力学模拟在预测天然气黏度方面具有较强的适用性，尤其是在高温高压条件下，当温度为444.4 K时，平均相对误差小于5%；天然气密度则采用现有相对成熟的经验模型更合适，而采用分子动力学模拟方法的几种力场模型预测其精度均不高；天然气密度和黏度预测模型的预测精度，不仅受温度和压力范围的影响，还与天然气组成有关。

关键词: 天然气, 混合物, 密度, 黏度, 分子模拟

Abstract:

Natural gas is a kind of relatively clean and low-carbon energy, the proportion of primary energy consumption in China continues to increase, and its accurate physical property prediction plays an important role in the process of natural gas gathering, transportation and utilization. By collecting the measured data of natural gas properties at different temperature and pressure in literature, we compared and analyzed the prediction accuracy of molecular dynamics simulations and commonly used empirical models to calculate the density and viscosity of natural gas, and clarified the best physical property prediction models suitable for natural gas with different compositions. The results show that molecular dynamics simulation has strong applicability in predicting the viscosity of natural gas, especially at high temperature and pressure, when the temperature is 444.4 K, the average absolute error is less than 5%. For natural gas density, it is more suitable to use the relatively mature empirical model, while several force field models using molecular dynamics simulation methods are not accurate in predicting it. In addition, the accuracy of the prediction model of natural gas density and viscosity is not only affected by the temperature and pressure range, but also by the composition of natural gas.

Key words: natural gas, mixtures, density, viscosity, molecular simulation

中图分类号:

TE 642

吴凡, 彭旭东, 江锦波, 孟祥铠, 梁杨杨. 分子动力学模拟预测天然气密度和黏度的可行性研究[J]. 化工学报, 2024, 75(2): 450-462.

Fan WU, Xudong PENG, Jinbo JIANG, Xiangkai MENG, Yangyang LIANG. Study on adaptability of molecular dynamics in predicting density and viscosity of natural gas[J]. CIESC Journal, 2024, 75(2): 450-462.

图/表 16

图1 MD模拟周期性边界条件分析模型[26]

Fig.1 Periodic boundary condition analysis model of MD simulation[26]

图2 模拟盒

Fig.2 Simulation box

图3 模拟过程中能量、温度随时间的变化（1 cal=4.184 J）

Fig.3 The change of energy and temperature with time in the simulation process

图4 不同力场下的CH4密度和黏度值

Fig.4 Density and viscosity of CH4 with different force fields

图5 密度无关性验证

Fig.5 Independence verification of density

图6 黏度无关性验证

Fig.6 Independence verification of viscosity

表1 天然气组成

Table 1 Composition of natural gas

组分	含量/%
N₂	0.3
CO₂	0.6
CH₄	96.5
C₂H₆	1.8
C₃H₈	0.45
C₄H₁₀	0.2
C₅H₁₂	0.08
C₆H₁₄	0.07

图7 缺省样品下不同压力和温度时两种MD力场密度预测值对比

Fig.7 Comparison of two MD force field density prediction values at different pressure and temperature with default sample

图8 缺省样品下不同压力和温度时MD及经验公式密度预测相对误差

Fig.8 The relative error of MD and empirical formula predicting density at different pressure and temperature with default sample

图9 4种不同天然气的CH4及重烃和非烃组分比

Fig.9 CH4, heavy hydrocarbon and non-hydrocarbon component ratio of different kinds of natural gas

图10 不同组分比、压力和温度条件下的天然气密度相对误差

Fig.10 Relative error of natural gas density at pressure and temperature with different composition

表2 天然气组成

Table 2 Composition of natural gas

含量/

含量/

含量/

含量/

N₂

CH₄

C₂H₆

C₃H₈

C₄H₁₀

i-C₅H₁₂

n-C₅H₁₂

C₆H₁₄

C₇H₁₆

C₁₀H₂₂

图11 缺省样品下不同压力时MD力场黏度预测值对比

Fig.11 Comparison of MD force field viscosity prediction values at different pressure with default sample

图12 缺省样品下不同压力时MD及经验公式黏度预测相对误差

Fig.12 Relative error of MD and empirical formula predicting viscosity at different pressure with default sample

图13 高非烃样品在不同压力和温度时MD及经验公式黏度预测相对误差

Fig.13 The relative error of MD and empirical formula predicting viscosity at different pressure and temperature with high non-hydrocarbon sample

表3 高非烃样品组成

Table 3 Composition of high non-hydrocarbon sample

含量/

含量/

含量/

含量/

N₂

CO₂

CH₄

C₂H₆

C₃H₈

n-C₄H₁₀

i-C₄H₁₀

n-C₅H₁₂

i-C₅H₁₂

H₂S

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