Evaluation on heating energy saving of double crude oil pipelines laid in one trench

Laying two hot pipelines in one trench is probably an effective way not only to minimize environmental damage but also to bring tremendous economic and social benefits. In this paper heating energy saving evaluations of operation on two hot crude oil pipelines laid in one trench as compared to single pipeline system are performed. In the calculations a Delaunay triangulation method is used to generate the grids of the soil domain automatically with denser meshes near the pipelines. A structural grid generation in polar coordinates is applied to the steel pipe wall and corrosion protective covering. A finite volume method combined with a finite difference scheme is used to discretize the governing equations. The discretized equations are solved by a Gauss-Seidel method. The thermal impact between two hot crude oil pipelines laid in one trench under four operating conditions are numerically analyzed. Through numerical simulations the outlet temperatures for safe pipelining hot crude oils of double pipelines can be obtained as well as heating energy consumption. Comparison between double-pipeline system and single pipeline system is made to evaluate the economy of different operating schemes. It is found that applying the prospective new technology can dramatically lower the outlet temperatures of the two pipelines and it would save a lot of heating energy.