The Problems Facing Refining
Profitable operation of a refinery can be maximized by determining the best crude oils to purchase, optimizing the process unit conditions and determining which products to produce and at what volumes. Most crude oils offer considerable flexibility in cut points.
The optimization of the stream flows is constrained by the capacities of the refinery equipment and by the desired specifications of the refinery products. Exploiting such flexibility in operation provides an enormous potential to improve profitability. Even greater improvements can be achieved by strategic investment to overcome bottlenecks.
Having identified such bottlenecks, an investment strategy is required to overcome the bottlenecks and increase profitability further. The investment strategy should take account of forward projections for changes in raw material and product prices and volumes as well as maintenance schedules. How can refiners squeeze margins beyond the capabilities of current optimization practice?
The State-of-Art Approaches
At present, the methods used to address this problem use a combination of detailed simulation of individual units in isolation and linear programming of the overall refinery. However, linear programming can only give an indication of how to improve a refinery, because highly simplified assumptions are used. Moreover, the basis of such calculations is bulk properties of the refinery streams. Yet, increasingly the molecular as well as bulk property information is needed (e.g. maximum sulfur, maximum aromatics).
It is now possible to relate molecular and bulk properties to allow greater reliability in the simulation and optimization. In addition, more sophisticated optimization using non-linear optimization allows the optimization of individual units and optimization of the overall refinery flows simultaneously. This involves breaking the optimization problem down into two levels: the individual units and the site material flows. Feedback mechanisms then allow the optimization of the individual units and the material flows to be integrated. Not only does the approach allows improved optimization, but allows the bottlenecks in operations to be identified more clearly.
Process Integration Ltd helps refiners to meet the challenges to the petroleum refining business resulting from changes in environmental legislation, the quality of crude oil supply and the market for refinery products.