基于水合物分离法提纯高浓度CO2瓦斯的相平衡研究

Study on phase equilibrium of separation and purification for gas with high CO2 concentration based on hydrate method

高浓度CO2瓦斯水合物相平衡的确定是基于瓦斯水合物分离法的瓦斯抽采利用关键问题。利用可视化瓦斯水合物相平衡装置,结合恒容温度搜索法和观察法,首先测定了不同温度、压力下3种高浓度CO2瓦斯气样的相平衡条件,在试验基础上提出了高浓度CO2瓦斯水合物相平衡温度与压力关系式,此外,对比分析了高浓度CO2瓦斯气样与纯CO2、纯CH4气样水合物相平衡的差异。结果表明:高浓度CO2瓦斯水合物形成条件较温和,0.44℃下相平衡压力最低,为1.58 MPa;高浓度CO2瓦斯水合物相平衡温度与压力呈二项式关系;高浓度CO2瓦斯水合物相平衡曲线位于纯CH4和纯CO2水合物相平衡曲线之间,且更为接近纯CO2相平衡曲线;较低温度、压力(0.44~4.94℃,1.58~2.80MPa)下,气样中CO2浓度上升能降低高浓度CO2瓦斯水合物相平衡压力,改善其相平衡条件,而较高温度、压力(4.94~7.80℃,2.80~4.02 MPa)下,气样中CO2浓度变化对水合物相平衡条件影响较小;高浓度CO2瓦斯水合物相平衡温度与压力关系式得到的压力计算值与实测值之间差值较小,平均相对误差为2.33%,能较准确地预测高浓度CO2瓦斯水合物相平衡条件。高浓度CO2瓦斯相平衡测定结果可为瓦斯水合分离技术中温度和压力选取,基于水合物分离法的CO2捕集与封存技术提供试验参考和理论基础。

The determination of the phase equilibrium of high-concentration CO2 gas hydrate is a key issue in the utilization of gas drainage based on gas hydration separation technology.Using the visual gas hydrate phase equilibrium device,combined with the constant volume temperature search method and the observation method,the phase equilibrium conditions of three high-concentration CO2 gas samples at different temperatures and pressures were first measured,and the high-concentration CO2 gas was proposed on the basis of the experiment.Then,a mathematical formula was fitted to describe the relation of phase equilibrium temperature and pressure.In addition,the difference in hydrate phase equilibrium between high-concentration CO2 gas samples and pure CO2 and pure CH4 gas samples is compared.The results show that the conditions for the formation of high-concentration CO2 gas hydrates are relatively mild.Specifically,the phase equilibrium pressure in this test range is the lowest at a temperature of 0.44℃,which is 1.58 MPa;the phase equilibrium temperature and pressure of high-concentration CO2 gas hydrates are in a binomial relationship;the phase equilibrium curve of CO2 gas hydrate lies between the phase equilibrium curve of pure CH4 and pure CO2 hydrate,and is closer to the phase equilibrium curve of pure CO2;at lower temperature and pressure(0.44~4.94℃,1.58~2.80 MPa),the gas increasing CO2 concentration in the sample can reduce the phase equilibrium pressure of high-concentration CO2 gas hydrate and improve its phase equilibrium conditions.At higher temperature and pressure(4.94~7.80℃,2.80~4.02 MPa),the change of CO2 concentration in the gas sample has an effect on hydration.The phase equilibrium conditions have little effect;the difference between the calculated value of the pressure obtained from the relationship between the phase equilibrium temperature and pressure of high-concentration CO2 gas hydrate and the actual measured value is small,and the average relative error is 2.33%,which can accurately predict high concentrations CO2 gas hydrate phase equilibrium conditions.Phase equilibrium measurement results of coal mine gas with high CO2 concentration provide experimental reference and theoretical basis for the selection of temperature and pressure in the gas separation and CO2 capture and sequestration technology based on the hydrate method.