液态CO_(2)管道输送注入端相变特性试验研究

Study on liquid CO_(2) phase-transition characteristics at the injection port in the pipeline

液态CO_(2)输送过程具有不稳定性,尤其是管道注入端易受外界环境影响发生相变而造成管路堵塞。因此,研究注入端液态CO_(2)相变特性对非稳态输送具有重要意义。通过自主搭建的耐高压管道式CO_(2)相变特性测试系统研究了不同初始压力下注入端压力及温度的变化情况,分析了注入端相态变化及传热特性。结果表明:液态CO_(2)注入平均质量流量一定时输入管道后发生热交换,瞬时相变导致注入端压力先上升后逐渐降低,温度在短时间内保持不变后快速下降,最终压力和温度趋于稳定;不同平均质量流量下,注入端压力/温度变化趋势一致,平均质量流量越大,气化过程越缓慢,所需时间越长;管道初始压力为1 MPa时,注入端CO_(2)介质由气态变为气液两态最终变为过热液体,通过温度-压力特性曲线得出,注入端压力和温度变化较小,前后压力差为0.099 MPa;管道内预先充入一定量CO_(2)气体,可防止温度和压力大幅度变化而产生干冰堵塞管道。

To study the phase-transition characteristics of liquid CO_(2)(LCO_(2))injection port of pipeline transportation,a LCO_(2)phase-transition characteristics experimental system was built with a high-pressure pipeline independently.The system mainly consists of LCO_(2)injection pump,high-pressure transmission device,phase-transition test pipeline,data acquisition,analysis system,and tail gas recovery unit,etc.The pressure and temperature changes of the injection port under different initial pressures were investigated,and the phase-transition and heat-transformation characteristics of the injection port were analyzed,respectively.The influence of the average mass flow rate on the pressure and temperature at the injection port was discussed.The results indicated that heat-transformation occurs after the average mass flow of LCO_(2)injected into the pipeline.There is a pressure difference between the injection pressure and the initial pressure of the pipeline.The instantaneous phase-transition results in the pressure of the injection port increasing rapidly at first and then decreasing gradually.Furthermore,the temperature remains for a short period and then decreases instantaneously.Finally,the pressure and temperature tend to be stable.Under different average mass flow rate conditions,the pressure and temperature variation trend of LCO_(2)injection port are consistent.A larger average mass flow rate means a slower vaporization process and longer time required.When the initial pressure of the pipeline is 0,CO_(2)medium at the injection port may eventually drop to nearly the three-phase point.When the initial pressure of the pipeline is 1 MPa,CO_(2)medium at the injection port changes from a gas phase to a gas-liquid phase and finally becomes superheated liquid.According to the temperature-pressure curves by LCO_(2)injection,the pressure and temperature at the injection port change slightly,and the pressure difference is above 0.099 MPa.Prefilling a certain amount of CO_(2)gas in the pipeline can prevent the pipeline from blocking by dry ice due to the significant change of temperature and pressure.