Evacuation of a residual oil pipeline by inert gas displacement.

An analysis was developed to model inert gas displacement process for evacuating a high pour point oil from a long pipeline. The governing equations were derived from the basic conservation equations for mass, momentum and energy. The resulting computer program accounts for effects such as pipeline elevation changes, laminar and turbulent oil flow, temperature dependent oil viscosity and heat loss from the oil to the ground. Results of computations for an 84 mile long residual oil pipeline operated by the Pennsylvania Power and Light Company are presented and compared with pressure measurements obtained during a trial purge of the system. The calculations show that the minimum nitrogen volume required for a successful pipeline evacuation increases considerably with increased delay time. In addition, the theoretical results indicate that for the PP&L case, the pipeline purge operation must begin within 20 hours of a shutdown to avoid evacuation difficulties. (A)