凝析气管道的混相输送

MIXED PHASE TRANSPORTATION IN CONDENSATE GAS PIPELINE

凝析气是多元组分的气体混合物 ,以饱和烃组分为主 ,在输送过程中由于沿线温度、压力的变化引起的凝析和反凝析现象显著 ,这使凝析气的管道输送不同于气体或液体的单相输送 ,其管输方式可分为气液混输、气液分输。气液两相混输投资少、工期短 ,但要解决因凝析液的积聚而降低输送能力及液塞处置等技术问题 ;气液分输是先将凝析气分离 ,然后将天然气和凝析液分别输送 ,管内流体均为单相流动 ,气液分输又可分为双管输送和顺序输送。凝析气的气液混相输送是多相流输送的一种特例。针对东海平湖油气田海底输气管道采用多相流技术输送凝析气的实例 ,分析了凝析气混相输送管道压降、输量和持液率的关系 ,并指出了预测管路温度下降值是管路安全运行的必要条件。通过对平湖凝析气管道的运行分析 ,强调工艺配套是多相流技术成功应用的重要条件。

Condensate gas is a multicomponent gas mixture and mainly composed of saturated hydrocarbons. The condensation and retrograde condensation phenomena caused by the change in temperature and pressure along pipeline are obvious in the process transportation, which makes the mixed phase transportation in condensate gas pipeline being different from the single phase transportation in gas or liquid pipeline. The pipeline transportation methods may be divided into gas-liquid mixed flow and gas-liquid separated flow. The former has many advantages as less investment and shorter time-limit, it is necessary, however, to solve some technical problems, as the decrease in pipeline transmission capacity and the slug treatment, caused by the accumulation of condensed liquid; and the latter is to separate condensate gas first, then to transport natural gas and condensed liquid respectively, the fluid in pipeline being a single-phase flow. The gas-liquid separated flow may be subdivided into dual pipeline transportation and batch transportation and the gas-liquid mixed flow is a special case of multiphase flow transportation. By taking the Pinghu oil and gas field, where the multiphase flow technology has been adopted for transporting condensate gas in the submarine gas pipelines, as an example, the relation among pressure drop, throughput rate and liquid holdup in condensate gas multiphase transportation pipline is analyzed in the paper, and it is pointed out that to predict the pipeline temperature dropping value is a necessary condition of safety in operation. Through analyzing the running circumstances of the condensate gas pipelines in Pinghu oil and gas field, it is emphasized that to form a complete technological system is an important condition of applying the multiphase flow techniques successfully.