天然气—水/盐水体系相平衡计算

Phase equilibrium calculation of a natural gas-water/brine system

准确模拟天然气—水系统的相平衡对于消除油气安全输送隐患具有重要的意义。为此,基于气—水二元体系相平衡的研究成果,给出了3种简单实用的多元气—水体系相平衡求解方法:VPT状态方程法——采用状态方程计算气液相组分逸度;PR状态方程法——采用由实验数据回归拟合得到两套二元交互系数和新型Alpha函数,再分别计算气、液相组分逸度;PR-Henry法——采用状态方程、活度模型和Henry定律计算气液相组分逸度。此外,对于多元气—盐水体系的相平衡,采用Pizter模型计算了溶解盐的影响。数值计算结果表明:3种方法均能够较准确地预测气相含水量和气体在水/盐水中的溶解度,且计算精度能够满足工程要求,但其中以VPT状态方程法的精度为最佳。

Accurate simulation of natural gas-water phase equilibrium is of great significance to eliminating hazards in oil and gas transportation, such as pipeline corrosion, hydrate blockage, etc. In view of this, based on the research results of gaswater equilibrium, this paper introduces three simple and practical calculation methods for the multicomponentgas-water equilibrium. First, the Valderrama modification of the PatelTeja （VPT） equation of state is used to calculate the compositional fugacity in a gasliquid system. Second, the PR equation of state adopts two sets of binary interaction coefficients from the regression and fitting of the experimental data along with a new type of Alpha functions to calculate the compositional fugacity of gas and liquid respectively. Third, the PRHenry method employs the equation of state, the activity model, and the Henry’s Law to calculate the compositional fugacity of gas and liquid respectively. Meanwhile, taking into account the effect of dissolving salt, the phase equilibrium of the multicomponent-gas-brine water system is calculated with the Pizter model. The numerical calculations indicate that the above three methods can accurately predict water content of gas and gas solubility in water/brine but comparatively the VPT equation of state is the best among them.