In a context where refining margins are squeezed by overcapacity, cost-competitive access to crude oil can significantly boost a refinery’s margin.

Crudes present high variability in terms of quality, yield structure, and product qualities. Correlatively, the price differential between good crudes and low-quality crudes can exceed 10 $/bbl: this reflects the difficulty of processing low-quality crudes.

Through this simple realization, it is evident that adequate crude blending may yield significant profits. What is meant by adequate crude blending is the ability to compensate for the bad characteristics of one crude by the good characteristic of another. The idea is to benefit from the low prices of certain difficult crudes – but to dilute their otherwise negative effects by mixing them with just the right proportions of higher-quality crudes.

However, things are a little more complex in real-life operations, and optimal crude blending is a very challenging problem. This is due both to a large number of constraints and to a large number of possible combinations (degrees of freedom) in blending and sequencing.

Types of Blending Processes:

• In-tank Blending – all component is fed into a mixing tank and stirred until a homogeneous blend is achieved.
• In-Line blending – all components are continuously and simultaneously passed in the correct ratio through a static mixer, directly providing a final blend of the required quality.

The benefit of in-line blending over in-tank blending:

• Instantaneous production of the blend
• Material in-spec throughout the entire blending process
• Rapid availability of the product
• Storage of minimized small stocks of the product in a plant
• Less capital investment in mixing tanks and stored products
• No large occupation of mixing tanks, leading to low space requirements
• All tanks designated to final products
• Rapidly reacting to changes in production planning
• Rapidly reacting to fluctuations in raw materials
• Reduction of costly giveaways
• High production capacity – no lack time due to time-consuming laboratory analyses

A large number of degrees of freedom

The first source of complexity for the crude blending problem comes from the possibility of mixing crudes at each layer of the system:

• in reception tanks
• in feed tanks
• in the feed to each crude unit

Moreover, the fact that the timing of each event can be chosen independently creates a multitude of asynchronous dynamics in the system. Therefore, the crude blending problem is about orchestrating the various crude movements Crude blending optimization…at the successive layers so that the right crude blends are successively brought to the crude unit at the right moments.