The components of quality
Quality is paramount when it comes to fuel, and mistakenly supplying sub-standard product can be costly. Rather than risking this, terminals are willing to invest in premium blending equipment
Although a significant amount of blending is carried out at the refinery, it is often necessary to blend or add extra fuel components after products reach the terminal. Fuels need to be altered depending on the climate and season in which they are used, and increasingly nowadays a percentage of bioethanol or biodiesel must be added to meet stringent environmental legislation.
Blending options
There are three distinct types of blending for oil products. The first is in-tank blending, which involves a number of products sequentially measured and mixed in the tank. ‘This type of blending works well when the properties of interest are predictable,’ Jon Moreau, sales and marketing director at UK-based sampling, blending and measurement company Jiskoot, says. However properties such as viscosity are difficult to predict and where blending occurs using products from tanks that are layered, the quality of the final product is affected. ‘The operator also needs to have an available tank, and will have to preblend the final stock before it is used, and made ready for shipment,’ Moreau adds. ‘In terms of inventory, flexibility of planning and cost optimisation and capital cost of plant – in-tank blending is archaic.’
With simultaneous metering blending, products are simultaneously measured into a vessel. ‘The system does not guarantee it is homogenous, and does not solve problems of variation in quality and feedstock segregation, meaning there will be no guarantee it is onspec unless the feedstocks are homogeneous and consistent,’ Moreau explains. Inline blending is the controlled, continuous mixing of a number of components into a tank to produce a finished product of closely defined quality. This comes in two types, one of which is ratio control, which forms a product that is blended to very high accuracy, with a certain percentage of different products in the final blend. The blender operates on a fixed volumetric, or mass ratio. This ratio is maintained by the closed loop between the flow signals from the field equipment and the control signals from the controller back to the field equipment.
