ABSTRACT

Use of Drag Reducing Agents (DRA) in a liquids pipelines can increase throughput and / or reduce operating costs, both of which can have a significant impact on the revenue and profit of the pipeline company. The decision to use DRA is often based on a short-term test in one segment of the pipeline. This fulfills the need to justify the use of DRA but does not provide the information required to model the DRA for detailed engineering studies, operator training, and computational pipeline monitoring. The information required to accurately model the effects of DRA use in a pipeline requires significantly more testing and data analysis. The hydraulic modelling software must be provided with a detailed description of the effectiveness of DRA in a pipeline and must be able to provide the solution capabilities that accurately simulate the behavior of DRA under all operating conditions. The effectiveness of DRA is measured in terms of the percentage reduction in the frictional losses in the pipeline. This effectiveness varies with the DRA concentration, viscosity of the solvent fluid, pipeline temperature, pipeline diameter, pipeline fluid velocity. Degradation of this effectiveness varies with the length of pipe sections and the amount of shear stress due to pipeline facilities such as valves and bends. Accurate DRA modelling requires that the actual effectiveness be determined for individual pipeline segments for all operating conditions. Measurements from process variables and the pipeline facilities layout are used to determine or infer effectiveness and degradation. Enbridge Pipelines Inc. has modeled DRA for two pipelines; a single fluid crude oil 16"/18"/20"/24"/26" looped pipeline that is 800 miles long, and a 18"/20"/24" multi-fluid (NGL, gasoline, diesel, synthetic crude) batched pipeline that is 1100 miles long. The Enbridge Pipelines Inc. experience with modelling DRA in these two pipelines is discussed. Details will be provided regarding the data gathered, analysis methods used, SCADA data (process variables) required, model configuration details, and modelling results.

INTRODUCTION

The use of DRA may be one of several options investigated to meet operational changes or to reduce operating costs of a pipeline. Operational changes may include new commodities or changes in commodity properties, increased or reduced throughput, or changes in the allowable operating pressures. A reduction in operating costs may be realized by replacing pumping power or by providing an incremental increase in capacity at a lower cost than could be provided with additional pumping power. Whatever the required objectives, DRA is one of several potential options to meet these objectives. If DRA is deemed a viable alternative to the other methods of achieving the stated objectives, a shortterm test is performed in one segment of the pipeline. The results from the test section provides feedback on the performance of the DRA in the real pipeline conditions. Decisions made based on expected performance made need to be reevaluated if the actual performance is significantly different from the expected performance.

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