Pipeline Project

In tardera with this project, a pipeline was proposed to transport medium and heavy crude oils 125 km from an existing oil export terminal to a new oil export terminal in Venezuela.

The proposed pipeline was designed to transport three types of crude oil with physical properties shown in Table 1.

The crude oils enter the pipeline in batches at a cycle of 2-6 days. The batch size ranges from less than 100, 000 to more than 700, 000 bbl, depending on storage availability, interface contamination, throughput requirements, and batching schemes.

Depending on the size of the pipeline ultimately selected, as many as six batches can flow simultaneously in the pipeline. To simplify the operation, spheres were not required to isolate oil batches.

Design capacity of this pipeline was 500^00 b/d initially and could be expandeato more than 750, 000 b/d with a mid-point booster station. Only heavy crude had to be heated at the beginning of the pipeline.

Table 2 shows throughput requirements for the various crude oils to be transported. The proposed route was fairly flat, traversing relatively flat and shallow bodies or water, including rivers, bays, and gulf, for a total distance of 125 km. The pipeline is designed to operate at a maximum allowable operating pressure (MAOP) of 1, 461 psig. This pressure limit is based on OD/WT (or. D/r) ratio criterion for offshore pipeline installation. In this case a ratio of 64 was found to be adequate. Based on API-5L Grade X-65 pipe, the 36-in. pipeline will have a 0.562 in. W.T. Based on preliminary information on-bottom current condiyions, Table 3 shows the concrete weight coating thicknesses.

Flow regime for any petroleum liquid is a function of the Reynolds number, which strongly affects thermal and fluid dynamics of crude oils. Light and medium crude oil pipelines are frequently operated at fully turbulent regions, in which temperature and pressure differentials are governed by the traditional turbulent-flow theory. The most commonly used formula for calculating pressure drops in turbulent flow is the Darcy Waisbach equation.

Heat transfer between pipe wall and crude oil for the turbulent flow regime is related to the Reynolds and Prandtl number. Heat transfer in this regime is much more efficient than heat conduction across pipe walls and surrounding environment and, for practical reasons, is often taken as infinity.

As the result, the crude oil temperature can be conveniently assumed to be equal to that of the pipe wall. Temperature and pressure differentials can be readily calculated for a given pipe size, pipe WT. coatings, flow rate, and surroundings.

When the Reynolds number is small, such as less than 2, 100, laminar flow theory generally applies for determining temperature and pressure drops. In this regime, heat transfer and friction coefficients are a simple function of the Nusselt and Reynolds number. A heavy crude oil pipeline is often operated in this region because of its high viscosity.

As will be shown presently, operating the pipeline at near the laminar flow regime could reduce internal heat-transfer coefficient and may prevent heat loss to occur from the pipeline that could, in some cases, increase throughput. As the Reynolds number is further reduced with lower operating temperature, laminar frictional effect begins to play a more dominant role that ultimately diminishes throughput.

Questions:

1 What was designed to transport three types of crude oil?

2 What is a function of the Reynolds number?

3 Are light and medium crude oil pipelines frequently operated at fully turbulent regions?

4 What is the Darcy Weisbach equation?

5 Can temperature and pressure differentials be readily calculated for a given pipe size, coatings, flow rate and surroundings?

6 What does laminar flow theory for?

7 What is related to the Reynolds and Prandtl number?

12.1 What is the main idea of the article?