Introduction
The global storage terminals industry faces many challenges, some old, some new; this article will discuss two of them both concerning the merits of mixing in above-ground storage tanks.
We will discuss the challenge of handling a variety of different grades of fuel and the necessity to process them into a final specification in the shortest possible time. The other challenge is the necessity to keep tankage free from deposition – basic sediment and water. Failure to handle either of these challenges could spell disaster and huge revenue losses.
Effective tank mixing
Whether it is fuel oils, petrol/gasoline, diesel and biofuels, many terminals now blend on a regular basis. Each type of material comes with its own issues, and with tighter clean fuel specifications mandated (Euro V spec/tier 2 gasoline and 40 CFR 80 subpart I for diesel in the US) the blender/scheduler also has fuel quality and availability to contend with. The last thing needed is to find that a large batch of finished product is ‘off spec’ just as the barge is docking, rail car train is pulling in or ocean vessel is arriving at the dock. This leaves the blender/scheduler in a dilemma, do they delay shipment and incur demurrage charges or sell at a lower specification and at lower margins. Here again effective tank mixing can save the refinery thousands in any monetary currency.
As many refineries now specify their crude oil blend requirements to produce certain volumes of finished product as demanded by their fuels marketing group, and seasonal requirements, this brings additional headaches for the terminal blender/scheduler. The main reason for this is because refinery process units are fully automated to deliver the required finished products and volumes of intermediate or finished product. If the feed stock, in this case crude oil, is not fully uniform (gravity) the end results will not be achieved.
Computational fluid dynamics (CFD)
The use of computational fluid dynamics (CFD) provides the tank mixer vendor with a tool that can prove our selections before the equipment will even see the light of day. This will ensure the tank contents are thoroughly mixed so that when a fuel specification (gravity) sample is pulled from the top, middle and bottom it is equal to the 3rd or 4th decimal point. The 'key component' in achieving this is the propeller; the equipment must have a propeller capable of penetrating across the tank floor and creating a bottom to top to bottom rotation of the stored product.
Upgrading and additional tankage
When making upgrades to …
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