A Study on the Restart Pressure of Long-Distance Trunkline

Reducing transfer temperature and/or operation without successive heating in a certain pipeline can substantially reduce the energy consumption. However, the low transfer temperature will probably cause the restart problem, and the restartability will be the focus at the low temperature. By investigating the restart process of liquid pipeline and the thixotropy of non-Newtonian fluid as well as the relationship between them, this paper puts forward an approach to calculating the restart pressure of both Newtonian and non-Newtonian fluid pipeline, and reveals the relationship between restart pressure and flow rate. The paper also points out that the restart pressure consists of three kinds of forces: the inertia force to accelerate fluid to a certain velocity; the friction force between the pipe wall and fluid transported; and the extra stress to break down the structure of thixotropical fluid. The computation results demonstrate that the conventional method, in which yield stress serves as the decisive parameter to calculate the restart pressure of the pipeline with pseudoplastic fluid transported, is too conservative to obtain reasonable restart pressure. By employing the new approach recommended in this paper, the much more accurate restart pressure have been obtained, moreover, the longer the pipeline is, the more the accurate results are.