Integrated Refinery Gasoline, Gas oil and fuel blending

The operational benefits resulting from the implementation of an integrated gasoline blending operation are generated in the areas of off-line blend planning and scheduling, together with the on-line optimization control up to the final product certification. The savings achieved by implementing such a system are quantifiable, and as the technology applied is readily available, can be captured by all refineries.

Interaction planning / scheduling and online optimization

Refineries use an LP based monthly planning system to balance crude supply and product demand on a monthly basis. Imbalances remaining after crude optimization are compensated for by the purchase of additional gasoline products or gasoline components. These components are known as the marginal gasoline components, as they are commercially available and therefore have a market value. These component prices, together with the final product values, are important drivers for optimization.

The offline Blend Optimization and Supervisory Software (BOSS) is using the product deliveries (blend schedule) as input. Based on this schedule, the current component inventories / production, equipment constraints, and quality projections, the offline BOSS defines the optimum scenario for production of the refinery product (gasoline) blends.

Application and advantages of on-line blend optimization

The on-line part of BOSS uses real-time multi variable (N)LP based profit optimization techniques to maximize the value of the blended product. It calculates and sets the optimum component ratios every 3-6 min. It ensures the maximum economic use of the given components, within the given component availability, quality, equipment, and process constraints.

Using this control approach, the blending process is directed into an operational environment where it hits the operational constraints that are economically attractive.

The number of components used also defines the control degrees of freedom. More constraints can be hit with BOSS as shown in the RVP give-away figure where the give-away is shown before and after implementation of BOSS

A traditional multi-variable controller will not be able to achieve these results, as the model error would prevent it from getting close enough to the quality constraint.

For certain refineries, the light and middle distillate blending operation (gasolines, naphthas) has more than one blender. In these situations, BOSS is applied in the pool-blending mode. Online, the component allocation is optimized between the two (or more) active blends. This application will provide additional degrees of optimization, resulting in additional savings. This strategy has been implemented at two refineries.

Besides the requirement to apply the aforementioned optimization and control strategy, it is the refineries experience that the operator (user) friendliness is essential for successful acceptance of the application. Because of the user friendliness of the BOSS package, operator acceptance is high, and the package is efficiently used.

Blend header analyzer and its application for certification

In order to demonstrate the reliability of the online analyzers, Invensys has developed a software tool that supports the calibration of the blend header analyzers. This tool, called Analyzer Maintenance And Data Acquisition Software (AMADAS), automatically generates analyzer control charts, and forms the bases for the analyzer based certification of the blended product, In the case of a 200,000 bpd refinery, the margin improvement resulting from analyzer-based certification can be up to US$ 2 million/yr.

Conclusions

With more then 50 gasoline & gas oil blending systems operational at refineries, Invensys has proved that the savings of more than US$ 4 million/yr can be achieved by implementing the integrated gasoline or gas oil blending system for a 200 kbd refinery.

The Invensys blending solution is a low risk capital investment with high return on the capital employed.