In Tank Blending
In-tank blending is the most traditional method of blending a number of products. However, due to the complexity of recipe calculations and the variability of bunker residual feedstock, it has been found to have a number of shortfalls, in addition to being time consuming. The process involves sequentially or simultaneously adding measured volumes (normally using a flow meter or level gauge) of the components to be blended into a dedicated blending tank with mixing facilities. The components are then mechanically mixed to homogenise the contents of the tank. A sample is extracted and then analysed to verify the blend quality. Any adjustments required are then made to the blend by adding additional components after which it is re-mixed and re-analysed to validate the batch. This is clearly a time consuming process requiring the availability of blending tanks, and possibly pre-blended feedstock, as well as the capability to predict, plan demand and store blended products.
The fact is that any blend recipe for bunker fuels is an approximation and residual feedstock is often layered, meaning the quality changes during the batch. These are some of the reasons that in-tank blending is being replaced by in-line blending as it is able to resolve many of these issues and deliver significant returns on investment for bunker suppliers. For in-tank blending the accuracy of the blend is totally reliant on the accuracy to specification of both base oils, and the equipment performing the sequential metering. Batch blending, however, is still a viable method where market demand is small and / or intermittent.