Heavy Crude Oil Transfer Using Twin-Screw Pumps - Applications in Sudan and South America
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Dietrich Müller-Link
Dietrich Müller-Link
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It is not only since the Canadian heavy oil resources have been declared economical that in many other countries around the world this kind of hydrocarbons have been produced for a long time. Among these are Argentina and Venezuela. Heavy oil has been defined to have a dynamic viscosity of more than 10 cP or less than 22.3 ° API, and a high specific gravity. In addition there is ultra heavy oil (or bitumen) with a very high viscosity or less than 10° API respectively. In addition to these unfavourable characteristics for pumping, there may not only be a considerable content of paraffin and wax, but also solids and some gas. This all requires certain additional measures in regard to pumping process and pump selection.

For several decades positive displacement pumps have a proven and excellent track record in such services with those using the twin-screw working principle being at the forefront of them. Their high efficiency especially with viscous media, but moreover the insensivity against free or entrained gas as well as some solids make them well suitable for such a service.

While transport distances of about 50 km can easily be achieved with a single pumping station, longer pipelines require intermediate ones, depending on their diameter, landscape profile as well as capacity necessary.

The Fula pipeline leads from Baleela over 700 km to the North-East, to the Khartoum refinery. Final products are then pumped for export to Port Sudan at the Red Sea. At its final expansion stage the Fula pipeline will have 4 intermediate pumping stations, each one equipped with 3 diesel engine driven high pressure twin-screw pumps for a differential pressure of close to 100 bar. While the product viscosity ranges between 500 to 1500 cSt, the high wax content of the crude oil together with a pour point around 42 deg. C forms an additional challenge.

Another example is the pipeline from the oil fields in the Melut basin via Khartoum to Port Sudan. It has a total length of 1500 km with a 32” diameter. The final expansion state will see 500 MBPD. While the crude is normally moved with multistage centrifugal pumps, the pipeline can only be started after a shut down using twin-screw pumps. This is due to a “frozen” pipeline content because of the relatively low pour point of the crude.

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