ABSTRACT: The present paper attempts to provide a critical review of various parameters that should be considered while designing a pipeline system for transporting waxy crude (high paraffin content). In designing such a system both steady state and transient state have to be considered as the former is relevant during normal operation of the pipeline while the later is relevant for the start-up up operation after shut-down. Considerations regarding heat transfer coefficient and thermal conductivity variations of the wax deposition over a period of time are essentially required for simulating near pour point conditions in the pipeline. These considerations also play an important role in determining optimum shut-down periods after which the pour point zone is likely to be reached resulting in wax deposition in a large scale. The simulated pipeline temperature profile along with the rate of cooling down to the pour point zone are also presented which in turn determine the optimum shut-down period of the pipeline. A method for quick calculation of restart pressure has been put forward. The results of the case study are presented with critical analysis.
INTRODUCTION Waxy crude oil transportation, particularly through long distance pipelines requires critical attention by pipeline designers and operating personnel as the transportation process can create potential operational problems. The prime mover (i.e. pumps) availability in this regard plays an important role as sudden reduction 1n flow may cause gelling of wax inside the pipeline requiring higher start-up pressures. Evaluation of paraffin inhibition requirement in pipelines also requires to be dealt with care as often these inhibitors are very costly. Thus before recommending the optimum operational modes, a designer has to consider several aspects and in most cases has to recommend a number of options in order or their priorities.