水合物法捕集烟气中CO_2的新拟合热力学模型

水合物法捕集烟气中的CO_2具有能耗低、操作简便和有利于后续CO_2储存利用的优点,为了降低多级水合反应累计的总误差,建立准确的热力学模型就显得尤为重要。为此,基于vdW-P+CPA模型,考虑了CO_2与H_2O之间的相互缔合作用,重新拟合了热力学模型中的参数。首先将H_2O与CO_2的能量参数α~(0.5)分别拟合为[1-(T/Tc)~(0.5)]的三次函数与一次函数,然后基于与温度相关的二元交互作用参数(k_(ij)),将vdW-P模型中Langmuir吸收系数的计算参数重新拟合。研究结果表明:①新拟合的热力学模型在预测饱和液相密度时,H_2O与CO_2的平均绝对误差分别由1.84%降至0.08%、由4.06%降至2.09%;②在预测纯CO_2与纯N_2生成水合物的相平衡压力时,平均绝对误差分别为0.86%与0.82%;③在计算不同组成烟气生成水合物的相平衡条件时,平均绝对误差由15.16%降至5.02%。结论认为,新拟合的热力学模型准确度较高,一定程度上降低了多级水合反应的总累计误差,为水合物法捕集烟气中CO_2的实际应用提供了参考。

A newly fitted thermodynamic model for the capture of CO2 from flue gas by the hydrate method

The hydrate-based gas separation for capturing CO2 from flue gas has the characteristics of low energy consumption, simple operation and convenience for subsequent CO2 storage and utilization. In order to reduce the total cumulative deviation of multi-stage hydration reaction, it is of great importance to establish an accurate thermodynamic model. Based on the vdW-P+CPA model, therefore, we refitted the parameters of the thermodynamic model considering the association between CO2 and H2O. Firstly, the energy parameter α0.5 of H2O and CO2 were developed as the cubic function and the liner function of [1－(T/Tc)0.5], respectively. Then, the calculation parameters of Langmuir absorption coefficient of vdW-P model was refitted based on the temperature dependent binary interaction parameters kij. And the following research results were obtained. First, when the newly fitted thermodynamic model is used to predict the density of saturated fluid, the average absolute deviation (AAD) of H2O drops from 1.84% to 0.08% and that of CO2 drops from 4.06% to 2.09%. Second, when it is used to predict the phase equilibrium pressure of the hydrate generated from pure CO2 and pure N2, the AAD is 0.86% and 0.82%, respectively. Third, when it is used to calculate the phase equilibrium condition of hydrate generated from flue gas with different compositions, the AAD is decreased from 15.16% to 5.02%. In conclusion, this newly fitted thermodynamic model is of higher accuracy and it, to some extent, can decrease the total accumulative deviation of multi-stage hydration reaction. The research results provide reference for the actual application of the hydrate-based gas separation for capturing CO2 from flue gas.