Analysis of the main parameters of crude oil pipeline transport

Abstract

The paper presents results of experimental research and simulation of the main parameters of crude oil pipeline transport. In Serbia, 70 % of the produced oil belongs to a paraffin type, of which over 25 % has a high content of paraffin. High-content paraffin oil usually has a high pour point. The paraffin content in crude oil from Vojvodina, Serbia, is in the range 7.5 to 26 %, and the oil pour temperature varies from 18 to 36?C. The imported crude oil has a flow point max. 8?C. Homogenization, i.e. mixing of domestic and imported crude oil, improves the transport properties and decreases the pour point. After homogenization, the crude oil is pre-heated, and then transported by a pipeline to the refinery for further processing. Heating induces modification of crude oil physical properties, especially flow properties so to prevent wax formation within the oil pipeline. The aim of this paper was to determine operating parameters and flow characteristics for a particular oil pipeline (428 mm inner diameter, 91,000 m length) under real operating conditions. By heating in the range of 20 - 50?C, the viscosity of crude oil was reduced, approaching the viscosity of water. The pipeline is isolated (100 mm thick isolation) and buried into in the ground (1 m depth). It is found that the heat transfer coefficient has a dominant influence on the cooling rate of the oil in the pipeline. The heat transfer coefficient is mainly determined by the isolation thickness so that it was determined as 0.60 W m-2 K-1 for + 100 mm thickness, while it was 2.20 W m-2 K-1 for the non-isolated pipeline. Heat losses through the main pipeline ranged from 36 - 110 kJ m-1 h-1 (10 - 30 W m-1). The difference between the starting and the ending temperature of crude oil ranged from 10 to 12?C. Such a decrease of ?t = 10 oC and, consequently, the increase in viscosity induced a noti-ceable increase in the pressure drop and pump power by 3 to 4 %, at the maximum flowrate of 0.194 m3 s-1 (700 m3 h-1). The cooling rate during transportation under stationary thermal and hydraulic conditions is in the range 0.52 ? 0.5 oC h-1. In the case of domestic oil (Vojvodina, Serbia) transport, the downtime should not exceed 24 h, since stopping and cooling of the oil would result in formation of solid paraffin particles followed by oil gelation.