Wax Deposition In Athy Line And Pigging Scheme

With the exploitation of new block in Er-Lian area, the composition of crude oil transported by Ar-Sai pipeline becomes complex and diverse, the wax precipitation along the pipeline is severe and the pigging operation becomes difficult increasingly. According to this problem, countermeasures of Ar-Sai pipeline currently is to make the inlet temperature raise of10～15℃. This method not only causes economic loses and security risks but also can not solve the pigging problem radically. Hence, it is necessary to study the wax deposition law and pigging project of Ar-Sai pipeline in-depth which will provide realistic guidance to the security assurance of pipeline’s operation and pigging.This article uses a combined method of theoretical analysis, experimental study and computer programming. Regarding crude oil from Ar-Sai pipeline stations and sources and diesel-wax simulated oil as research subjects, the composition and property parameter of each oil and the condition of wax precipitation and deposition during the oil’s fluxion were measured in laboratory by using experimental equipments such as group component analyzer, microscopic image analysis system, rheometer and loop simulated facility. The internal cause and the major external cause influencing Ar-Sai pipeline’s wax deposition were analyzed and the wax deposition law of Ar-Sai pipeline was dissected. The pipe between4#and5#is confirmed as the most dangerous one during Ar-Sai pipeline transportation. the temperature drop along this pipe in the coldest month was simulated, the allowed minimum throughput of this pipe was calculated, and the deposition thickness of this objective pipe was predicted. The pigging condition of Ar-Sai pipeline and other domestic hot oil pipelines was analyzed, the essence of Ar-Sai pipeline’s abnormal pigging behavior was dissected and a reasonable pigging project was proposed.The research results show that the carbon number distribution and group component of Ar-Sai crude oil are internal causes influencing wax deposition. The oil temperature, wall temperature, flowrate. operation hours and pipe wall material are external factors effecting the deposition. Since Ar-Sai oil’s temperature drop below its wax appearance temperature during the oil flow between stations, the deposition condition exhibits a tendency of increasing significantly at first and then reducing gradually, and there is almost no sediment approaching the inlet of the next station. Therefore, oil temperature is the major external cause influencing Ar-Sai pipeline’s deposition, and molecular diffusion is the origin of wax deposition. The regular pattern of temperature drop along Ar-Sai pipe between4#and5#is almost identical under different pipe outlet temperature, and the higher of the outlet temperature, the faster of the temperature drop along this pipe. The allowed minimum throughput of pipeline feature of this pipe in February is the allowed minimum throughput of Ar-Sai pipeline during its operation. When the outlet temperature is65,70,75℃, the pipeline throughput should not be under120,105,95m3/h. The hypothesis of wax deposition differential pressure analysis exaggerates the severity of4#-5#pipe’s wax precipitation, and the result basing on inhomogeneity of the precipitation along this pipe can predict wax precipitation in pipe exactly. The largest wax deposition thickness of this pipe in the coldest month is4.41mm. The essence of Ar-Sai pipeline’s abnormal pigging is its pigging project using presently is unreasonable. By sending the groove type foam pig with diameter of255mm and cup panel mechanical pig (bypass percent by area is0.50%) with the diameter of260mm and265mm continuously can achieve an ideal pigging effect and the pigging frequency can be extended to33days.