甲烷-水合物两相平衡体系气相水含量研究

Study on gas-phase water content in methane-hydrate phase equilibrium

天然气中的微量气态水在天然气开采、集输过程中可能与气体小分子形成水合物,造成管路堵塞,因此需要对天然气进行脱水处理。为了合理设计天然气最大容许水含量参数,准确测量和计算天然气-水合物相平衡时的气相水含量具有重要意义。在压力为3.44~6.00 MPa、温度为270.00~274.00 K的条件下,通过实验测量和模型预测研究了甲烷-水合物相平衡时的气相水含量。结果表明,相比于压力露点,常压露点和气相水含量体积比随温度和压力的变化都具有规律性,气相水含量随温度的降低和压力的升高而减小。在实验的基础上,基于热力学相平衡理论建立了甲烷-水合物相平衡时的气相水含量热力学模型,气相水含量体积比的模型预测值与实验值的平均相对偏差为2.33%。该实验方法实现了甲烷-水合物相平衡体系气相水含量的原位测量,建立的热力学模型相比于通过查图获得的甲烷-液态水相平衡时的饱和水含量再外推至水合物区的方法更快速和准确。

In the process of natural gas extraction and transportation,the presence of trace amounts of gaseous water may lead to hydrate formation with small gas molecules,resulting in pipeline blockages,so it is necessary to remove water from natural gas through dehydration.To establish appropriate parameters for the maximum permissible water content in natural gas,it is crucial to measure and calculate the gas-phase water content in gas-hydrate phase equilibrium accurately.Under the conditions of pressure from 3.44 MPa to 6.00 MPa and temperature from 270.00 K to 274.00 K,the gas-phase water content of methane-hydrate phase equilibrium was studied by experimental measurements and model predictions.The results show that compared with pressure dew point,atmospheric dew point and gas-phase water content volume ratio change regularly with temperature and pressure.Gas-phase water content decreases with the decrease of temperature and the increase of pressure.On the basis of experiments,a thermodynamic model of gas-phase water content in methane-hydrate phase equilibrium was established based on thermodynamic phase equilibrium theory.The average relative deviation between the predicted values and experimental values is 2.33%.This method achieves in situ measurement of gas-phase water content in methane-hydrate phase equilibrium system,and the established model is faster and more accurate than the method of obtaining the saturated water content in methane-liquid water phase equilibrium by looking up the diagram and extrapolating to the hydrate zone.