节流阀内天然气组分凝结规律研究

节流制冷低温分离工艺是天然气集输过程中常见的脱水脱烃技术,节流凝结过程是天然气露点温度能否达标、工艺系统能否优化运行的关键。基于天然气在节流阀内的凝结过程,建立均质凝结和异质凝结统一的数值模型,研究天然气中易发生凝结的四种烷烃(正戊烷、正己烷、正庚烷、正辛烷)组分的凝结规律,分析背压比和总温等因素对凝结性质的影响。结果表明:节流阀内部流场非常复杂,呈现强湍流特性,节流孔内达到极低的温度使烃类组分的凝结在节流孔出口前基本完成。背压比和总温增加会减弱节流温降,使各组分的凝结量和液滴尺寸同时减小。节流过程中各组分的凝结性质存在较大差异。分子量较小的轻烃类组分,节流孔出口凝结量大,且凝结量和液滴尺寸受背压比和总温的影响大。

Component Condensation of Natural Gas in Throttling Flow

In natural gas gathering and transportation process,the throttling expansion refrigeration and low temperature separation method is one of the most common technology.The condensation is a key issue during the throttling flow,as the temperature after throttle is the main influence factors of dew point.With the field data of throttling separation technology,uniform model for homogeneous and heterogeneous condensation is established to study the natural gas throttling condensation process.Four hydrocarbon components(n-pentane,n-hexane,n-heptane,n-butane) are chosen as the objects of study.The effects of back pressure ratio and inlet total temperature on the condensation properties of different hydrocarbon components are analyzed.It is shown that,the flow field in the throttle is extremely complex,and intense turbulent flow characteristics are presented.In the natural gas throttling process,extremely low temperature is obtained which provides the suitable condition for condensation of the hydrocarbons.With increase of back pressure ratio and total temperature,the condensation mass fraction and droplet size of each condensable component decrease.Great differences of condensation parameters are found among each component.For the lighter hydrocarbon components,the condensation mass fraction is greater,and the condensation mass fraction and droplet radius of which are much more affected by the back pressure ratio and inlet total temperature.