原油输送减阻技术与减阻效率

原油在管道中输送时,加入少量ppm的减阻剂,增输量可达到10%以上。用作减阻剂的油溶性聚合物,分子量一般高达几百万到上千万。按分子数计算,减阻剂在原油中占的比例微小,因此不会改变原油的粘度。减阻效率决定于聚合物在溶液中的形态,空间尺寸,聚合物的溶解性能以及使用减阻剂的技术。实验表明(1)减阻效率随减阻剂添加量而增加,但减阻剂浓度达到一定值后,减阻率提高缓慢;(2)流体的流速增加,使减阻效率显著增加,但对不同的聚合物影响结果不一样;(3)在管径相同的条件下,流体的雷诺数增加,减阻效率增加;(4)在一定范围内壁剪切应力增加,减阻率也随之增加,但过大的剪切力会使高聚物降解,分子量降低,减阻率下降;(5)原油中含微量水份会影响减阻率。当含水量超过一定值时,因聚合物溶解性不好,反而导致减阻剂失效。目前工业上使用的减阻剂品种主要是超高分子量的聚α—烯烃,在油中的添加量为φn×10ppm以内,使减阻率在20%左右,增输15%左右,可以明显增加经济效益。

DRAG REDUCTION TECHNOLOGY AND ITS EFFICIENCY IN PIPELINE TRANSPORTATION

Drag reducing agents are oil-soluble polymers with molecular weights ranged from several to ten million.With regard to the number of molecules,the amount of polymer contained in the oil is negligible,and has little effect on the viscosity of the oil.The drag reducing efficiency depends upon the configuration and size of the polymer molecule,and its solubility in the oil.Moreover,the efficiency also depends upon the drag reduction technology used.Experiments showed that the efficiency was increased with the amount of the drag reducing agent added within a certain limit,while the increase became less pronounced beyond that limit.The efficiency was also increased markedly with flow velocity.But its effect was not the same for different polymers.For the same pipe diameter,the efficiency was increased with increasing Reynold's number.The drag reduction efficiency was increased with increasing wall shear stress within a certain limit,but too high shear stress led to a degradation of the polymer and in turn decreased efficiency.A high water content resulted in lower solubility of polymer and lower efficiency.The drag reducing agents used in industry are polyolefins with ultra-high molecular weight at the dosage of tens ppm to give a 20% drag reduction efficiency and 15% increase in oil transported.