作为CO2捕集与封存的中间过程,管道输送是目前比较经济有效的CO2输送方式。捕集到的CO2通常含有氮气、氧气、甲烷、氩气、水蒸气等杂质,其对CO2性质有不同程度的影响,进而影响CO2的管输特性。采用Matlab 编程计算,利用Span Wag-ner 状态方程计算和分析了纯CO2的物性参数(密度、黏度、比热等),对比了PR、SRK、BWRS 状态方程应用于CO2物性计算的平均偏差,并以精度最高的PR 状态方程为基础,建立了一维可压缩流体管道模型,对含杂质CO2管道在不同输送状态(超临界、密相、液态、气态)、不同杂质类型与含量、不同管道参数等条件下的管道稳态特性进行了研究。研究结果表明,PR 状态方程对于含杂质CO2物性参数计算的偏差较小,在临界点附近也能有较高的精确度,可用于含杂质CO2物性参数的计算;在相同输送条件下,CO2管道密相输送的压降值最小、超临界状态输送的压降值次之、气态输送的压降值最大;杂质的存在使气液两相区的范围扩大,更容易出现两相流,增大摩阻。通过流动仿真,并与天然气管道对比,揭示了含杂质CO2管道在多种稳态流动条件下的管道沿线参数变化规律。
Pipeline transportation is regarded as an economical and effective way to transport CO2. The captured CO2 generally contains such impurities as N2, O2, CH4, Ar, and H2O. The type and content of impurities will impact the properties of CO2-rich mixture and subsequently the flow characteristics. The physical properties of pure CO2 were calculated and analyzed using Matlab based on Span Wagner EOS. Then the uniformly most accurate EOS for CO2-rich mixture was selected by comparing the calculation accuracy of the BWRS, SRK and PR EOS. Based on PR EOS, which has been proved to be the most proper EOS for CO2-rich mixture, a one-dimensional compressible flow model was developed to describe the steady and transient flow characteristics of CO2-rich mixture in the pipeline. Finally, the steady simulation under different flow states (supercritical state, dense phase, liquid state, gaseous state), impurities (type and content), and pipe parameters was conducted. The results show that PR EOS is the most proper EOS for CO2-rich mixture. Compared with gas transportation of CO2 pipeline, the pressure drop of dense phase and supercritical state transportation is relatively small, while the pressure drop of dense phase transportation is the least. Different types of impurities have different effects on broadening the gas-liquid two-phase region of CO2-rich mixture. Compared with that of natural gas pipeline, laws of steady flow of CO2-rich mixture pipeline are revealed, which may provide theoretical guidance for efficient operation and safe control of CO2 pipeline.
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