CO_2甲烷化制替代天然气热力学计算与分析

Thermodynamic analysis of CO_2 methanation for substitute natural gas

利用模拟软件ASPEN PLUS(V7.3),基于Gibbs自由能最小法,建立了CO_2甲烷化制替代天然气反应体系的热力学计算模型,获得了甲烷化过程中各组分的平衡组成和主要反应的标准平衡常数。计算结果表明,CO_2转化率随压力升高而增加,随温度升高先降低后逐渐升高。温度低于400℃、压力3.0 MPa有利于CO_2甲烷化反应。CO含量较高时,CO甲烷化反应速率大于CO_2甲烷化反应速率。在0.1 MPa下,温度低于625℃时,CO优先发生甲烷化反应。当温度高于625℃后,CO_2转化率高于CO转化率。当体系中CO含量不高于2.00%(x)时,CO_2甲烷化反应无积碳现象发生;当CO含量超过2.00%(x)、温度低于600℃时,反应出现明显积碳。

A thermodynamic model for CO2 methanation was established based on the Gibbs free energy minimization method by means of the ASPEN PLUS（V7.3） software, and the equilibrium composition and the standard equilibrium constants were obtained. It was indicated that, the CO2 conversion increased remarkably with increasing pressure, and firstly decreased and then gradually increased with temperature rise. Lower temperature than 400℃and high pressure were beneficial to the CO2 methanation. The reaction rate of the CO methanation was significantly higher than that of the CO2 methanation at high CO content. The CO methanation was prior to the CO2 methanation in the coexistence system under the conditions of lower while the CO2 conversion was higher than the CO temperature than 625 ℃ and pressure 0.1 MPa, conversion at higher temperature than 625 ℃. No carbon deposition was found when the CO content in feed gas was less than 2.00%（x）, while carbon deposition appeared significantly when the CO content was more than 2.00%（x） at lower temperature than 600 ℃.